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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 249–253 249 Complexes of lithium tetrahydroaluminate with N,N,N9,N9-tetramethylethane- 1,2-diamine (tmen). Crystal structures of [{Li(tmen)- (AlH4)}2] and [Li(tmen)2][AlH4] and the use of the 6Li-{1H} nuclear Overhauser eVect to study LiAlH4 and LiBH4 in donor solvents Mbolatiana M. Andrianarison, Anthony G. Avent, Miles C. Ellerby, Ian B. Gorrell, Peter B. Hitchcock, J. David Smith * and David R. Stanley School of Chemistry, Physics and Environmental Science, University of Sussex, Falmer, Brighton, UK BN1 9QJ Two crystalline complexes (1 : 1 and 1 : 2) of LiAlH4 with N,N,N9,N9-tetramethylethane-1,2-diamine (tmen) have been isolated. A crystal structure determination of the 1 : 1 complex showed that it formed centrosymmetrical dimers in which [AlH4]2 anions and [Li(tmen)]1 cations are linked by m-hydrogen bridges.Bond lengths and angles within the non-planar eight-membered rings are Al]H 1.55(3), Li]H 1.99(3) Å, H]Li]H 131(1) and H]Al]H 112(1)8 and the exocyclic Al]H distance was 1.53(4) Å.Cryoscopic data indicated that the dimeric structure with Li]H]Al bridges was preserved in benzene solution and measurements of the 6Li-{1H} nuclear Overhauser effect (NOE) showed the presence of Li ? ? ?H]Al interactions. The 1 : 2 adduct [Li(tmen)2][AlH4] 2, which crystallised with an ionic NaCl structure, was converted into 1 by heating under vacuum at 120 8C. The NOE measurements on solutions of 2 in benzene showed the presence of Li ? ? ?H]Al interactions even when a large excess of tmen was present.Aluminium-bound hydrogen was shown to be near to lithium in solutions of LiAlH4 in diethyl ether, tetrahydrofuran, mono- and di-glyme [MeO(CH2)2O(CH2CH2O)nMe, n = 0 or 1]. The NOE measurements on solutions of LiBH4 in Et2O and NMR spectra of partially deuteriated species suggested the formation of contact ion pairs, with Li ? ? ?H4B interactions which were fluxional on the NMR time-scale.Lithium tetrahydroaluminate, LiAlH4, finds widespread use in both inorganic and organic chemistry as a reducing agent and as a hydride or hydroaluminate transfer reagent.1,2 It is usually added to a reaction mixture as a solution in diethyl ether (Et2O) or tetrahydrofuran (thf) and the species in solution have been studied by a variety of techniques, e.g. conductance and ebullioscopic measurements on both Et2O and thf solutions,3,4 vibrational spectroscopy on samples in Et2O, thf and monoglyme,5,6 27Al7–10 and 7Li NMR spectroscopy8,9 on Et2O, thf, mono-, di- and tri-glyme [MeO(CH2)2O(CH2CH2O)nMe (n = 0, 1 or 2)] solutions, and dielectrometry in Et2O.6 Results in Et2O have been interpreted as evidence for ion pairs in dilute solution with multiple-ion formation at higher concentrations. 3–5,8 It has not been established whether the ions within a pair are separated by solvent molecules or whether they are linked by hydrogen bridges as in [(Et2O)2Li(m-H)2AlH2].6 Solvent-separated ion pairs were thought to be the major species in thf 3–5,9 and glyme solvents.5,9,10 In this paper we describe the structural characterisation of N,N,N9,N9-tetramethylethane-1,2-diamine (tmen) complexes of LiAlH4 [{Li(tmen)(AlH4)}2] 1 and [Li(tmen)2][AlH4] 2, and the use of 6Li-{1H} heteronuclear Overhauser effect spectroscopy to study their solutions in benzene.This last technique, which relies on the low quadrupole moment of 6Li and the consequent domination of its relaxation by dipolar interaction with nearby protons, has been used previously in one-dimensional form to study, for example, lithium hydro- [tris(trimethylsilyl)methyl] compounds of boron, aluminium, gallium and indium 11 and in two-dimensional form to study organolithium compounds.12 We also describe 6Li-{1H} nuclear Overhauser effect (NOE) measurements on solutions of LiAlH4 in Et2O, thf, mono- and di-glyme and solutions of LiBH4 in Et2O and compare the conclusions with those derived previously by other methods.Results and Discussion LiAlH4–tmen complexes The reaction between LiAlH4 and 1 equivalent of tmen in thf gave, after recrystallisation from toluene, colourless, airsensitive crystals of the known13 adduct, Li(tmen)AlH4 in good yield. A crystallographic study showed the structure to consist of centrosymmetric dimers 1 (Fig. 1) based on eight-membered rings similar to those observed in the structures of Li[AlH3- {C(SiMe2Ph)3}]?2thf 3,14 Li[AlH3(C6H2Ph3-2,4,6)]?1.5Et2O 4, Li[AlH3(C6H2But 3-2,4,6)]?2thf 5, Li[AlH3{N(SiMe3)2}]?2Et2O 6 15 and LiAlH4?HN(But)CH(But)CH2N(But)H 7, and suggested for that of LiAlH4?HN(But)CH(But)CH]] NBut.16 Discussion of bond lengths and angles (Table 1) is inevitably tentative because of the high standard deviations associated with bonds to hydrogen.However, the average Al]H bond length within the Al2H4Li2 ring of compound 1, 1.55(3) Å, is at the short end of the range found in the related hydroaluminate derivatives 3–714–16 [cf. 1.62(4) in 3, 1.62(4) in 4, 1.57(4) in 5, Fig. 1 Molecular structure of compound 1250 J. Chem. Soc., Dalton Trans., 1998, Pages 249–253 1.62(4) in 6 and 1.56(4) Å in 7]. The average terminal Al]H bond length is 1.53(4) Å so that, as in 3–7, terminal and bridging Al]H bond lengths are similar. The Li]H bond length in 1 [1.99(3) Å] is long [cf. 1.77(4) in 4, 1.78(4) in 6, 1.85(5) in 7, 1.93(4) in 3 and 2.00(5) Å in 5] and the Li]N bond lengths are normal.The ring in 1 is puckered with the two aluminium atoms 0.9 Å above and below, and the two lithium atoms 0.1 Å above and below, the plane defined by the ring hydrogen atoms. Similar puckered rings are found in 3–5 and 7 but the ring in 6 is planar. The endocyclic H]Al]H angle in 1 is 112(2)8. Other H]Al]H angles differ somewhat from this value but the mean [109(2)8] is close to those for 3 [105(1)], 4 [106(2)] and 5 [107(3)8] and not significantly different from the tetrahedral value.The H]Li]H angles [131(1) in 1, 117(1) in 3, 126(2) in 4, 103(2) in 5, 107(2) in 6 and 91(2)8 in 7] show much wider variation. These data suggest that within the dimers the [AlH4]2 ions retain their integrity so that the species 1 is best described as comprising two [AlH4]2 anions and two [Li(tmen)]1 cations. The nonplanarity of the ring in 3 was attributed to the presence of the large alkyl group attached to aluminium 14 but this steric constraint cannot apply to 1.Here the puckering is probably associated with the narrow exocyclic N]Li]N angle imposed by the tmen ligand, which in turn affects the endocyclic H]Li]H angle. The structure of 1 differs from that of [{Li(tmen)- (BH4)}2] in which each [BH4]2 group bridges two lithium centres through three hydrogens (two m, one m3) so that the metal atoms are six- not four-co-ordinate as in 1.17 This difference in structure is probably related to the greater size of aluminium as illustrated by the mean Li ? ? ? B (2.464) and Li ? ? ? Al (2.972 Å) distances.The boron compound did not react with an excess of tmen but the reaction between LiAlH4 and an excess of tmen in thf gave LiAlH4?2tmen 2 in high yield. An X-ray study of the colourless, air-sensitive crystals showed that separate [Li- (tmen)2]1 cations and [AlH4]2 anions (Fig. 2) were packed in a structure of the sodium chloride type (mean Li ? ? ? Al 5.66 Å).Fig. 2 Molecular structure of compound 2 Table 1 Bond lengths (Å) and angles (8) for [{Li(tmen)(AlH4)}2] 1 Al]H(7) Al]H(8) Li]N(2) Li]H(8) H(7)]Al]H(9) H(9)]Al]H(8) H(9)]Al]H(10) N(2)]Li]N(1) N(1)]Li]H(8) N(2)]Li]H(109) 1.55(4) 1.52(3) 2.090(5) 2.04(3) 113(2) 117(2) 111(1) 88.2(2) 114.3(8) 109.3(8) Al]H(9) Al]H(10) Li]N(1) Li]H(109) H(7)]Al]H(8) H(7)]Al]H(10) H(8)]Al]H(10) N(2)]Li]H(8) N(1)]Li]H(109) H(8)]Li]H(109) 1.50(3) 1.59(3) 2.095(5) 1.94(3) 97(2) 106(2) 112(1) 100.7(9) 104.6(8) 131(1) Symmetry transformation: 9 2x, 2y, 2z.The tetrahydroaluminate anion has been structurally characterised previously as the [NEt4]118 and [AlH2L]119 salts (L = N,N,N9,N0,N0-pentamethyldiethylenetriamine or 1,4,8,11- tetramethyl-1,4,8,11-tetraazacyclotetradecane). The mean Al]H distance [1.52(7) Å] in 2 may be compared with values of 1.61(5) Å in [NEt4][AlH4] and 1.55(3) Å in LiAlH4.20 Compound 2 was converted into 1 when it was heated to 120 8C under vacuum.The dimeric structure of compound 1 in benzene was con- firmed by cryoscopic measurements. Fig. 3 shows the 1H NMR spectrum of a ca. 0.1 M solution in C6D6; the hydride resonance is exceedingly broad and even in spectra obtained from concentrated solutions only just visible above the baseline. The width of the 27Al-{1H} peak, 390 Hz, is somewhat broader than those found for LiAlH4 in donor solvents (ca. 180 Hz in diethyl ether and as low as 14 Hz in diglyme).8 The aluminium is thus in an environment similar to that in [AlH4]2, distorted enough from tetrahedral for 27Al relaxation to broaden the 1H signal but not enough to cause it to collapse to a single line.The 6Li-{1H} difference spectra show enhancements of ca. 50% on selective irradiation in the hydride region of the spectrum and ca. 38% in the NMe region but not elsewhere. They indicate that the lithium nuclei are close to hydrogen atoms of AlH4 and NMe fragments.The NMR and cryoscopic data taken together are in accord with the presence in solution of species which are cyclic as in solid 1. It is not possible to tell whether there is rapid exchange on the NMR time-scale of ionic fragments between rings. The NMR data for compound 2 were similar to those for 1 and the NOE was strong in both the Al]H and N]Me regions. The ions present in the crystals of 2 cannot therefore be fully separated in solution since if this were the case the NOE in the hydride region would disappear, leaving only a weak enhancement near the NMe signal.Similar results were obtained from solutions of 2 in Et2O. Since the concentration of solventseparated ion pairs would be expected to be increased by the addition of base, samples containing a 10-fold excess of tmen were examined. Unfortunately the Al]H and tmen signals now overlapped so that separate enhancements could not be observed but an NOE could still be observed over the whole hydride region.Hence although the solid that separated from solution was the ionic compound 2, significant Li ? ? ?H]Al interactions persisted in the supernatant solution. The ionic compound 2 must therefore either dissociate into 1 and free tmen or give other species in which [AlH4]2 competes successfully with tmen for a place in the co-ordination sphere of lithium. Problems associated with the study of the coordination of tmen in solution have been reviewed: it seems that bonds between lithium and tmen can be broken in a wide range of solvent systems.21 Fig. 3 Proton NMR spectrum of a 0.1 M solution of compound 1 in C6D6, and 6Li-{1H} difference spectra with signals placed at the positions of the selective irradiation in the 1H spectrumJ. Chem. Soc., Dalton Trans., 1998, Pages 249–253 251 Proton and 6Li-{1H} NOE spectra of LiAlH4 in ethers Diethyl ether. The relationship between solute concentration and 27Al NMR signal widths for solutions of LiAlH4 in Et2O has been studied previously.The peak width, which is ca. 1 kHz at a concentration of 1.0 M, decreases in more dilute solutions so that Al]H coupling may be observed.8 Conversely, signals from hydrogen atoms bound to aluminium are sharp at high concentrations but become broad upon dilution so that chemical shifts are difficult to determine. Data for a range of concentrations, wider than that reported previously, are given in Table 2. They show that in the more concentrated solutions the environment around aluminium is highly distorted from tetrahedral, the electric field gradient is large, and quadrupole relaxation is so fast that coupling to hydrogen is completely suppressed. At lower concentrations the aluminium environment is less distorted from tetrahedral and the 1H signals are broadened by Al]H coupling.Fig. 4(b) shows 6Li-{1H} NMR spectra of LiAlH4 in Et2O obtained with selective irradiation at various frequencies in the proton spectrum [Fig. 4(a)]. The largest NOE (180%) resulted from irradiation of the hydrogen atoms attached to aluminium and there was only a small effect near the methylene and the methyl protons of the diethyl ether. This implies that the hydrogens on aluminium spend a signifi- cant proportion of their time close to lithium. In previous work,8 the 7Li NMR spectra were recorded for solutions of LiAlH4 in Et2O in the concentration range 3.75–0.0075 M. The linewidths (0.55–2.8 Hz) were concentration dependent but as they changed only negligibly (typically <0.1 Hz) on broad-band decoupling it was deduced that persistent Li]H]Al bridges were absent.8 It is however notoriously difficult to observe Li]H coupling.15 Our results suggest that although Li ? ? ?H]Al interactions may not be stable over periods long enough for Li]H coupling constants to be measured they are sufficient to generate a significant NOE.The effect on ebullioscopic and conductimetric results has been described previously.3,4 Tetrahydrofuran.The 1H NMR spectra of a 0.5 M solution of LiAlH4 in thf [Fig. 4(c)] showed only solvent signals at d 1.7 Fig. 4 (a) The 1H NMR spectrum of a 1.0 M solution of LiAlH4 in diethyl ether, (b) 6Li-{1H} spectra placed at positions of selective irradiation in the proton spectrum, (c) the 1H spectrum of a 0.5 M solution of LiAlH4 in thf, and (d ) 6Li-{1H} spectra placed at positions of selective irradiation in the proton spectrum Table 2 Peak widths of 1H NMR resonances in concentrated solutions of LiAlH4 in diethyl ether Concentration/M 1.92 2.36 4.87 5.16 5.85 Dn2� 1 /Hz 20 9.9 9.1 8.2 6.3 and 3.7; the hydrogen atoms attached to aluminium could not be directly observed, suggesting that the signals were broadened as a result of coupling to nearby aluminium nuclei in nearly tetrahedral environments.The 6Li-{1H} spectra are shown in Fig. 4(d ). The largest NOE resulted from irradiation of the downfield a-methylene multiplet of thf.This showed that, in contrast to solutions of LiAlH4 in Et2O, the a-methylene protons of the solvent were close to the lithium. However, the NOE spectra also showed a large effect upon irradiation between the solvent signals in the region where Al]H resonances have been located.22 The results provide direct evidence for the proximity of lithium and hydroaluminate ions and a method for the determination of values of dH for hydrogens attached to aluminium in a system in which direct observation is difficult or heteronuclear decoupling of aluminium is not possible.Although earlier 7Li NMR studies9 indicated that Li]H scalar coupling was absent, the NOE results show that Li ? ? ?H]Al bridges are formed at least transiently in 0.5 M solution. When 1 mol equivalent of HCl was condensed into the thf solution at 278 8C the NOE near the a-protons of the solvent remained, and that over the hydride region was suppressed, showing that Li ? ? ?H]Al interactions were absent. The species in solution were probably solvent-separated ion pairs [Li(thf)4][AlClnH4 2 n] or chloride-bridged species, e.g.(thf)3LiClAlH3 in which electron-deficient Li]H]Al bridges have been replaced by stronger electron-precise Li]Cl]Al links. Mono- and di-glyme. The 1H NMR spectra of a 0.5 M solution of LiAlH4 in monoglyme showed a weak sextet [d 2.90, 1J(Al]H) 172.8 Hz], resulting from coupling of hydrogen to aluminium nuclei (I = 5 2 – ), partly obscured by intense solvent signals between d 3 and 4.In the 6Li-{1H} spectra the largest NOE arose from irradiation of the methylene protons of the solvent, but there was a slightly smaller effect from the hydrogens bound to aluminium with an approximate correlation with maxima at points expected if the signal were a sextet. As with solutions in thf, the NOE results showed that both the methylene protons of the solvent and the hydrogen atoms attached to aluminium were close to the lithium cations.The solutions in diglyme were similar [d 3.10, 1J(Al]H) = 173.5; lit.,10 d 3.08, 1J(Al]H) 173 Hz]. Hence the [AlH4]2 anion is able to compete successfully with the glyme for a place in the lithium coordination sphere even when the aluminium environment is sufficiently symmetrical to allow the sextet in t 1H spectrum to be observed. Hydrogen–deuterium exchange between LiBH4 and LiBD4 in Et2O Solutions of LiBH4 in Et2O have been investigated by ebullioscopic and conductance measurements,3 and by vibrational 6,23 and NMR24 spectroscopy.It has been suggested that the species in solution are either contact ion pairs and multiple ions or hydride-bridged molecular species. Multinuclear NMR and NOE measurements allow a distinction between these two possibilities to be made. The 1H spectra (see Fig. 5) from a 0.5 M solution of LiBH4 in Et2O show, besides solvent peaks, a sharp quartet due to hydrogens coupled to 11B [1J(11B]H) = 81.25 Hz] and a less intense septet from hydrogens coupled to 10B nuclei [1J(10B]H) = 26.6 Hz].The NOE spectra show that the largest effect results from irradiation of the components of the hydridic quartet and septet, and that a smaller effect is produced upon irradiation of the downfield resonance of the solvent. These results suggest (a) that LiBH4 in Et2O gives species in which the lithium and hydrogen atoms are close and (b) that the [BH4]2 anion is not significantly distorted from tetrahedral.Further evidence comes from the isotope shifts in partly deuteriated LiBH4. The 1H NMR spectrum of a 1 : 1 mixture of LiBH4 and LiBD4 in Et2O (Fig. 6) showed four major features252 J. Chem. Soc., Dalton Trans., 1998, Pages 249–253 which could be assigned to the statistical mixture of isotopomers [LiBH4 2 nDn]2 (n = 0–3) observed earlier.24 If there were specific interactions via (m-H)2 or (m-H)3 bridges between lithium and boron there would be a non-uniform equilibrium isotope shift as hydrogen was replaced by deuterium and this non-uniformity would be expected to increase when the sample was cooled.If however the interactions were non-specific and largely electrostatic, only small secondary isotope shifts would be expected. Fig. 6 shows that the second alternative is observed. The resonance centres were shifted only 0.01 ppm to lower frequency for each increase in the value of n and although resolution was lost at 230 8C the spectrum had a very similar envelope to that at 25 8C showing that the effect of changing temperature was small.There was also an isotope effect on the coupling constant 1J(11B]H), viz. LiBH4 81.3, LiBH3D 81.1, LiBH2D2 80.9 and LiBHD3 80.6 Hz, corresponding to a monatonic decrease in the value of 1J as n increased. The isotope effects on the coupling constant 2J(H]D) (1.56 Hz) were too small to be measured. Similar results have been obtained for NaBH4 2 nDn and KBH4 2 nDn in ether solvents.25 An attempt to make a similar assessment of the specificity of the hydride bridges in the LiAlH4–LiAlD4 system was inconclusive. The 1H-{27Al} NMR spectra of samples of LiAlH4 and LiAlH4–LiAlD4 (1 : 1) in Et2O gave singlets with Dn2� 1 7 Hz so that with reasonable estimates of the isotope shifts it was clear that the peaks were too broad for signals from individual isotopomers like those in the LiBH4–LiBD4 system to be observed.The asymmetry of the broad signals should however have been sufficient to show the presence of mixed species LiAlHnD4 2 n.We were surprised therefore to find that the 1H signal in the LiAlH4–LiAlD4 mixture was symmetrical indicating that under our conditions (in Et2O at 50 8C for 17 h) H–D exchange had not taken place. Hydrogen–deuterium exchange has been observed previously in strong donor solvents such as thf,26 diglyme9,26 or MeCN.26 Fig. 5 (a) The 1H NMR spectrum of a 0.5 M solution of LiBH4 in Et2O, (b) 6Li-{H} difference spectra with irradiation at various positions in the proton spectrum.The peak marked S is attributed to silicone grease Fig. 6 Proton NMR spectra of a 1 : 1 mixture of LiBH4 and LiBD4 in Et2O at (a) 243 and (b) 288 K Conclusion The solid obtained from a toluene solution containing LiAlH4 and an equivalent of tmen is the complex 1 in which Li and Al are joined by m-H bridges. The solid that separates from a toluene solution of LiAlH4 containing an excess of tmen is [Li(tmen)2][AlH4] 2.There are no specific bonds between the anion and cation in the solid 2 but 6Li-{1H} NOE measurements indicate that [AlH4]2 ions in solution are brought near to Li. Similar Li ? ? ?H]Al contacts are detected in solutions of LiAlH4 in ether solvents in the absence of amine donors. The Li ? ? ?H]Al interactions are stronger in diethyl ether or thf than in mono- or di-glyme and apparently determine the structure of the solvent-free solid which crystallises from diethyl ether.20 The NOE measurements in themselves are not sufficient to distinguish between hydride bridges between specific lithium and aluminiun atoms in well defined species such as 1 and less discriminate fluxional interactions within ion pairs.For LiBH4 in Et2O the interactions are of the second kind. For LiAlH4 in Et2O the nature of the interaction is still unclear. The NOE measurements appear to show that whereas the symmetry of the [AlH4]2 ions is significantly perturbed by the formation of hydrogen bridges, that of the [BH4]2 ion remains essentially tetrahedral.Although this observed difference between boron and aluminium may result from genuine differences in the nature of the hydride-bridged species, it may simply reflect the different sensitivities of the boron and aluminium nuclei to the symmetry of their environments. More work is required to resolve this problem. Interactions analogous to those described in this paper have been postulated in solutions of the complex [Li(hmpa)4][BF4] [hmpa = hexamethylphosphoramide, P(NMe2)3O] in aromatic solvents.27 Experimental All materials were manipulated by standard Schlenk techniques using a conventional vacuum manifold and argon as a blanket gas.Solvents were dried, by heating under reflux with LiAlH4 for ethers and with sodium for toluene, and subsequently distilled. The compound LiAlH4 (Aldrich) was used as received and tmen (Aldrich) was dried over CaH2 and then distilled.Solutions of LiAlH4 were made by heating 1 g under reflux in the relevant ether (20 cm3), filtering through Celite, determining the concentration by decomposing aliquots in 1 M sulfuric or hydrochloric acid, measuring the dihydrogen evolved with a Sprengel pump,28 and diluting to give the concentrations required. Melting points were measured on samples in sealed capillaries and IR spectra were recorded as Nujol mulls on a Perkin-Elmer 1720 FT spectrometer.For the H–D exchange reaction between LiBH4 and LiBD4 in Et2O a solution of LiBD4 (0.32 g, 12.5 mmol) and LiBH4 (0.27 g, 12.5 mmol) in Et2O (50 cm3) was heated under reflux for 30 min in an atmosphere of argon, allowed to cool to room temperature, and filtered through a medium-porosity glass frit. All NMR spectra were recorded on samples in sealed glass tubes or tubes with rotationally symmetrical poly(tetrafluoroethylene) valves.The 1H NMR spectra were recorded at 90, 250, 360 or 500 MHz using respectively Perkin-Elmer R32, Bruker AC 250, WM 360 or AMX 500 instruments. The 7Li NMR spectra were recorded on a Bruker WP 80 FT spectrometer at 31.14 MHz, a Bruker AC 250 instrument at 73.6 MHz, or a Bruker WM 360 spectrometer at 139.9 MHz; chemical shifts are relative to external aqueous LiNO3. The 6Li NMR spectra were recorded on a Bruker WM 360 spectrometer at 52.99 MHz or an AMX 500 spectrometer at 73.59 MHz.The 6Li NOE difference spectra were obtained by selectively irradiating a resonance in the 1H spectrum for 14 s before obtaining a 6Li spectrum using a 308 pulse and no decoupling during the 8.4 s acquisition period. The procedure was repeated with selective irradiation of an empty region of the 1H spectrum and the two 6Li spectra wereJ. Chem. Soc., Dalton Trans., 1998, Pages 249¡V253 253subtracted to give the difference spectrum. The value of theNOE enhancement cited was obtained by absolute integrationof the two 6Li spectra; the theoretical maximum enhancement is340%.The power level for the selective irradiation was the sameas that used in the more familiar 1H¡V1H NOE experiment. The27Al NMR spectra were recorded on a Bruker WM 360 spectrometerat 93.8 MHz; chemical shifts are relati to external[Al(H2O)6]31.PreparationsLiAlH4?tmen 1. A mixture of tmen (0.8 cm3, 5.3 mmol) andLiAlH4 (0.2 g, 5.27 mmol) was stirred in thf (25 cm3) for 24 h at20 8C.Filtration through Celite followed by removal of solventand crystallisation from toluene gave colourless crystals ofcompound 1 (0.57 g, 70%), m.p. 179 8C (Found: C, 46.7; H, 12.8;N, 17.7%; M = 310. C12H40Al2Li2N4 requires C, 46.7; H, 13.1; N,18.2%; M = 308). n& max/cm21 (Al]H) 1660s (br) and 1730 (sh);dH(C6D6) 1.73 (4 H, CH2) and 2.07 (12 H, CH3); dC(C6D6)46.0 (CH3) and 56.5 (CH2); dLi(C6D6) 0.47; dAl(C6D6) 103[qnt, J(Al]H) 172 Hz, Dn2 1(27Al-{1H}) 391 Hz].LiAlH4?2tmen 2.A mixture of tmen (2.0 cm3, 13.3 mmol) andLiAlH4 (0.2 g, 5.27 mmol) was stirred at 60 8C in thf (25 cm3)for 6 h. After cooling to 20 8C and filtration through Celite thesolvent was removed to give a white solid. Crystallisation fromtoluene gave colourless crystals of compound 2 (1.28 g, 90%)(Found: C, 52.5; H, 13.1; Al, 10.0; Li, 2.7; N, 20.8. C12H36-AlLiN4 requires C, 53.3; H, 13.4; Al, 10.0; Li, 2.6; N, 20.7%).n& max/cm21 (Al]H) 1651s (br); dH(C6D6) 2.0 (8 H, CH2) and 2.07(24 H, CH3); dC(C6D6) 46.0 (CH3) and 57.3 (CH2); dLi(C6D6)0.45; dAl(C6D6) 103 [qnt, J(Al]H) 171 Hz, Dn2 1(27Al-{1H}) = 365Hz].CrystallographyCrystal data.For 1, C12H40Al2Li2N4, M = 308.3, monoclinic,space group P21/n (no. 14), a = 7.839(2), b = 15.802(5), c =9.132(6) , b = 98.17(4)8, U = 1119.7(9) 3, Z = 2, Dc = 0.91Mg m23, F(000) = 344. Colourless, air-sensitive block 0.4 ¡Ñ0.3 ¡Ñ 0.3 mm, m(Mo-Ka) = 0.13 mm21, T = 173 K.Data collection and processing: CAD4 diffractometer, q¡V2qscan, Mo-Ka radiation, l = 0.710 73 , 2 < q < 258, 1967 uniquereflections giving 1400 with I > 2s(I), no absorption or decaycorrection.Structure analysis and refinement: direct methods(SHELXS 86),29 full-matrix least-squares refinement on all F2using SHELXL 93,30 all non-H atoms anisotropic, hydride Hatoms located on a difference map and freely refined with isotropicthermal parameters, ligand H atoms included in ridingmode with Uiso(H) = 1.2 Ueq(C) or 1.5 Ueq(C) for methylgroups.R1 = S( Fo| 2 |Fc )/S|Fo| = 0.049 [for I > 2s(I)], wR2 =[Sw(Fo2 2 Fc2)2/Sw(Fo2)2] = 0.138, S = 1.03 (for all data).For 2, C12H36AlLiN4, M = 270.4, orthorhombic, space groupPnma, a = 18.146(2), b = 11.616(5), c = 9.438(3) , U =1989.4(11) 3, Z = 4, Dc = 0.90 Mg m23, F(000) = 608, colourlessair-sensitive needle 1.0 ¡Ñ 0.4 ¡Ñ 0.15 mm (in a capillary),m(Mo-Ka) = 0.10 mm21, T = 293 K, 1833 reflections, for2 < q < 258, no absorption or decay correction.Refinement on F2 using SHELXL 93, non-H atoms anisotropic,hydride H atoms located on a difference map and positionsrefined, ligand H atoms in riding mode, R1 = 0.072 [for502 reflections with I > 2s(I) and 98 parameters], wR2 =0.367, S = 1.02 (for all data). Both the anion and cation lie on acrystallographic mirror plane, with consequent averaged positionsfor the disordered central CH2CH2 groups of the tmenligands.CCDC reference number 186/790.AcknowledgementsThe authors thank the EPSRC for financial support and ICI plcfor a CASE studentship for M.C. E.References1 See, for example, A. R. Barron and G. Wilkinson, Polyhedron, 1986,5, 1897; B. M. Bulychev, Polyhedron, 1990, 9, 387 and refs. therein.2 Comprehensive Organic Synthesis, eds. B. M. Trost and I. Fleming,Pergamon, Oxford, 1991, vol. 8.3 E. C. Ashby, F. R. Dobbs and H. P. Hopkins, J. Am. Chem. Soc.,1975, 97, 3158.4 E. C. Ashby, F. R. Dobbs and H. P. Hopkins, J. Am. Chem. Soc.,1973, 95, 2823.5 A.E. Shirk and D. F. Shriver, J. Am. Chem. Soc.,1973, 95, 5904.6 S. V. Sigalova, I. P. Romm, E. N. Gur¡¦yanova, R. R. Shifrina,E. S. Shcherbakova, L. N. Margolin, L. P. Ivanov and A. I.Gorbunov, J. Gen. Chem. USSR., 1989, 59, 301.7 S. Her£¾mnek, O. Kr£¾iz, J. Ples£¾ek and T. Hanslk, Chem. Ind.(London), 1975, 42.8 H. Nth, Z. Naturforsch., Teil B, 1980, 35, 119.9 H. Nth, R. Rurlnder and P. Wolfgardt, Z. Naturforsch., Teil B,1981, 36, 31.10 V. P. Tarasov, V. I.Privalov, A. A. Gorbik and S. I. Bakum, Sov. J.Coord. Chem. (Engl. Transl.), 1985, 11, 935.11 A. G. Avent, C. Eaborn, M. N. A. El-Kheli, M. E. Molla, J. D. Smithand A. C. Sullivan, J. Am. Chem. Soc., 1986, 108, 3854.12 See, for example, W. Bauer, in Lithium Chemistry A Theoretical andExperimental Overview, eds. A.-M. Sapse and P. von R. Schleyer,Wiley, New York, 1995, ch. 5; H. Balzer and S. Berger, Chem. Ber.,1992, 125, 733 and refs. therein.13 J. A. Dilts and E. C. Ashby, Inorg. Chem., 1970, 9, 855.14 C. Eaborn, I. B. Gorrell, P. B. Hitchcock, J. D. Smith andK. Tavakkoli, Organometallics, 1994, 13, 4143.15 A. Heine and D. Stalke, Angew. Chem., Int. Ed. Engl., 1992, 31, 854;R. J. Wehmschulte, J. J. Ellison, K. Ruhlandt-Senge and P. P. Power,Inorg. Chem., 1994, 33, 6300.16 M. G. Gardiner, S. M. Lawrence and C. L. Raston, Inorg. Chem.,1995, 34, 4652; 1996, 35, 1349.17 D. R. Armstrong, W. Clegg, H. M. Colquhoun, J. A. Daniels,R. E. Mulvey, I. R. Stephenson and K. Wade, J. Chem. Soc., Chem.Commun., 1987, 630.18 K. Semenenko, A. L. Dorosinskii and . B. Lobkovskii, J. Struct.Chem. (Engl. Transl.), 1973, 14, 700.19 J. L. Atwood, K. D. Robinson, C. Jones and C. L. Raston, J. Chem.Soc., Chem. Commun., 1991, 1697.20 N. Sklar and B. Post, Inorg. Chem., 1967, 6, 66921 D. B. Collum, Acc. Chem. Res., 1992, 25, 448.22 D. A. Horne, J. Am. Chem. Soc., 1980, 102, 6011.23 A. E. Shirk and D. F. Shriver, J. Am. Chem. Soc., 1973, 95, 5901.24 B. D. James, B. E. Smith and R. H. Newman, J. Chem. Soc., Chem.Commun., 1974, 294; B. E. Smith, B. D. James and R. M. Peachey,Inorg. Chem., 1977, 16, 2057.25 I. A. Oxton, A. G. McInnes and J. A. Walter, Can. J. Chem., 1979,57, 503.26 V. P. Tasarov, S. I. Bakum, V. I. Privalov and Yu. A. Buslaev, Dokl.Akad. Nauk SSSR, 1982, 266, 1423; V. P. Tasarov, S. I. Bakum,V. I. Privalov, Yu. A. Buslaev and A. M. Kuznetsov, Koord. Khim.,1983, 9, 822.27 D. Barr, K. B. Hutton, J. H. Morris, R. E. Mulvey, D. Reed andR. Snaith, J. Chem. Soc., Chem. Commun., 1986, 127.28 A. Weissberger (Editor), Techniques of Organic Chemistry, 2nd edn.,Interscience, London, 1957, vol. 3, Part II, p. 365.29 G. M. Sheldrick, SHELXS 86, University of Gttingen, 1986.30 G. M. Sheldrick, SHELXL 93, University of Gttingen, 1993.Received 15th August 1997; Paper 7/06003C

ISSN:1477-9226    

DOI:10.1039/a706003c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 251–257 251 Anion recognition and sensing by neutral and charged transition metal co-ordinated ferrocene phosphine amide receptors Justine E. Kingston,a Lynette Ashford,a Paul D. Beer *a and Michael G. B. Drewb a Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK OX1 3QR b Department of Chemistry, University of Reading, Whiteknights, Reading, UK RG6 2AD Received 6th October 1998, Accepted 16th November 1998 A new bis(phosphine) amide linked ferrocene ligand [Fe{h-C5H4CONH(CH2)3PPh2}2] and molybdenum, chromium, rhodium and ruthenium transition metal chelated receptors of it have been prepared.Proton NMR anion-binding investigations revealed that in general the combination of the Lewis acid transition metal centre and the ferrocene amide moiety enhances the strength of anion binding. Electrochemical studies showed all receptors can electrochemically sense halide, dihydrogenphosphate and hydrogensulfate anions via significant cathodic perturbations of the respective ferrocene and transition metal oxidation wave.Negatively charged species are known to play numerous fundamental roles in biological and chemical processes and consequently intense current interest is being shown in the design and syntheses of positively charged or neutral electron-deficient anion receptors.1 In addition, the importance of being able to detect and extract certain environmental anionic pollutants has only recently been recognised.2 As part of a research programme aimed at developing anion sensor technology we have shown that positively charged and neutral transition-metal organometallic and co-ordination receptor systems in combination with amide (CONH) hydrogen-bond donor groups can complex and sense via electrochemical and optical responses a variety of anions in organic and aqueous media.3 In particular a range of neutral ferrocenoyl amide receptors 4 have been shown electrochemically to recognise halide, dihydrogenphosphate, nitrate 4,5 and hydrogensulfate anions via cathodic perturbations of their respective ferrocene oxidation wave.The combination of additional Lewis acid transition metal centres with the redox-responsive ferrocenoyl amide moiety may lead to new acyclic and macrocyclic heteropolymetallic receptors that exhibit greater anion thermodynamical stability and new selectivity trends (Fig. 1).By co-ordinating a variety of Lewis acidic transition metal centres to a new ferrocene phosphine amide ligand we report here the syntheses, structures, anion coordination and electrochemical recognition properties of a new class of bimetallic redox-active macrocyclic anion receptor. Experimental Instrumentation Nuclear magnetic resonance spectra were obtained on a Bruker AM300 instrument using the solvent deuterium signal as internal reference, fast atom bombardment (FAB) mass spectra Fig. 1 Anion receptor design, combining a redox-active moiety with an additional Lewis acidic centre. at the EPSRC mass spectrometry service, University College, Swansea. Electrochemical measurements were carried out using an E. G. and G. Princeton Applied Research 362 scanning potentiostat. Elemental analyses were performed at the Inorganic Chemistry Laboratory, University of Oxford. Solvent and reagent pretreatment Where necessary, solvents were purified prior to use and stored under nitrogen.Acetonitrile was predried over class 4A molecular sieves (4–8 mesh) and then distilled from calcium hydride. Unless stated to the contrary, commercial grade chemicals were used without further purification. 1,19-Bis(chlorocarbonyl)- ferrocene 1 6 and 3-aminopropyldiphenylphosphine 7 were prepared according to literature procedures. Syntheses 1,19-Bis(3-diphenylphosphinopropylaminocarbonyl)ferrocene 2. A solution of 1,19-bis(chlorocarbonyl)ferrocene 1 (0.83 g, 266 mmol) in toluene (50 ml) was added dropwise under a nitrogen atmosphere to a solution of 3-aminopropyldiphenylphosphine (1.33 g, 5.32 mmol) and triethylamine (0.54 g, 5.32 mmol) in toluene (50 ml).Once addition was complete, the reaction was stirred for 2 h at room temperature during which time a fine precipitate formed. The solvent was removed in vacuo to give an orange oil which was redissolved in dichloromethane (100 ml) and washed with water (3 × 50 ml). The organic layer was dried over anhydrous magnesium sulfate and evaporated to dryness in vacuo.This residue was purified by column chromatography on alumina, using 99 : 1 dichloromethane–methanol as the eluent. After recrystallising from dichloromethane the product was obtained as orange microcrystals. Yield: 0.97 g, 47%. 1H NMR (CD2Cl2): d 1.75 (m, 4 H, CCH2C), 2.15 (m, 4 H, PCH2), 3.48 [dt (obs. q), J = 6.6, 4 H, NCH2], 4.32 [dd (obs. t), J = 1.9, 4 H, Cp H], 4.43 [dd (obs. t), J = 1.9, 4 H, Cp H], 6.85 (t, J = 5.8 Hz, 2 H, NH) and 7.31–7.47 (m, 20 H, aryl-H), 13C NMR (CD2Cl2): d 25.5 [d, J(P–C) = 12.2, CCH2C], 26.3 [d, J(P–C) = 13.8, PCH2], 40.7 [d, J(P–C) = 13.8, NCH2], 70.7 (Cp C–H), 70.8 (Cp C–H), 78.8 (Cp C–C), 128.5 [d, J(P–C) = 6.2, aryl C–H], 128.6 (aryl C–H), 132.7 [d, J(P–C) = 18.5, aryl C–H], 138.4 [d, J(P–C) = 12.3 Hz, aryl C–C] and 170.3 (C]] O). 31P NMR (CD2Cl2): d 219.4 (Found: C, 69.39; H, 5.78; N, 3.77. C42H42- FeN2O2P2 requires C, 69.62; H, 5.84; N, 3.87%).IR: n& max/cm21252 J. Chem. Soc., Dalton Trans., 1999, 251–257 3315 (N–H), 1622 (C]] O) and 1542 (C–H aryl). FAB MS: m/z 725, [M 1 H]1; 747, [M 1 Na]1. mp 145–147 8C. [1,19-Bis(3-diphenylphosphinopropylaminocarbonyl)ferrocene] tetracarbonylmolybdenum 3. A solution of compound 2 (240 mg, 0.33 mmol) in dichloromethane (50 ml) and a solution of [Mo(CO)4(nbd)] (100 mg, 0.33 mmol) in dichloromethane (50 ml) were added simultaneously and dropwise to dichloromethane (100 ml) whilst stirring at room temperature in a nitrogen atmosphere.After addition was complete the reaction mixture was stirred at room temperature for 12 h before the solvent was removed in vacuo. The pure product was obtained as a yellow solid following recrystallisation from chloroform. Yield: 160 mg, 53%. 1H NMR (CD2Cl2): d 1.67–1.73 (m, 4 H, CCH2C), 1.97–2.05 (m, 4 H, PCH2), 3.31 [dt (obs. q), J = 6.2, 4 H, NCH2], 4.39 [dd (obs. t), J = 1.9, 4 H, Cp H], 4.48 [dd (obs.t), J = 1.9 Hz, 4 H, Cp H], 6.56 (br s, 2 H, NH) and 7.36–7.51 (m, 20 H, aryl H). 31P NMR (CD2Cl2): d 21.6 (Found: C, 57.46; H, 4.41; N, 3.37. C46H42FeMoN2O6P2?H2O requires C, 58.10; H, 4.63; N, 2.94%). IR: n& max/cm21 3440 (H2O), 3270 (N–H), 2017 (Mo–C]] O), 1895 (br Mo–C]] O), 1634 (C]] Oamide) and 1532 (C–H, aryl). FAB MS: m/z 933, M1; 876/8, [M 2 (CO)2]1; 850, [M 2 (CO)3]1; and 820/2, [M 2 (CO)4]1. mp 76–78 8C. [1,19-Bis(3-diphenylphosphinopropylaminocarbonyl)ferrocene] tetracarbonylchromium 4.A solution of compound 2 (280 mg, 0.39 mmol) in dichloromethane (10 ml) and benzene (40 ml) and a solution of [Cr(CO)4(nbd)] (100 mg, 0.39 mmol) in benzene (50 ml) were added simultaneously and dropwise to refluxing benzene (50 ml) under a nitrogen atmosphere. The resultant mixture was stirred at reflux for 12 h before the benzene was removed in vacuo. The residue was recrystallised from methanol–acetonitrile (50 : 50) to yield the pure products as yellow crystals.Yield: 160 mg, 46%. 1H NMR (CD2Cl2): d 1.67– 1.72 (m, 4 H, CCH2C), 2.05–2.10 (m, 4 H, PCH2), 3.29 [dt (obs. q), J = 6.0, 4 H, NCH2], 4.40 [dd (obs. t), J = 1.7, 4 H, Cp H], 4.48 [dd (obs. t), J = 1.7 Hz, 4 H, Cp H], 6.65 (br s, 2 H, NH) and 7.3–7.5 (m, 20 H, aryl H). 31P NMR (CD2Cl2): d 40.2 (Found: C, 62.17; H, 4.76; N, 3.15. C46H42CrFeN2O6P2 requires C, 62.27; H, 5.02; N, 3.00%). IR: n& max/cm21 2005 (Cr–C]] O), 1880 (br Cr–C]] O), 1640 (C]] Oamide) and 1532 (C–H, aryl).FAB MS: m/z 889, [M 1 H]1; 776, [M 2 (CO)4]1. mp 186–189 8C. [1,19-Bis(3-diphenylphosphinopropylaminocarbonyl)ferrocene] carbonylchlororhodium 5. A solution of compound 2 (90 mg, 0.12 mmol) in dichloromethane (10 ml) and a solution of dirhodium dichloride tetracarbonyl (30 mg, 0.06 mmol) in dichloromethane (10 ml) were added dropwise and simultaneously to dichloromethane (80 ml) whilst stirring at room temperature under a nitrogen atmosphere. After addition was complete, the reaction mixture was stirred at room temperature for 12 h before the solvent was removed in vacuo.The residue was recrystallised from dichloromethane and hexane to yield the pure product. Yield: 50 mg, 45%. 1H NMR (CD2Cl2): d 1.97– 2.02 (m, 4 H, CCH2C), 2.63–2.67 (m, 4 H, PCH2), 3.48–3.52 (m, 4 H, NCH2), 4.35 [dd, (obs. t), J = 1.6, 4 H, Cp H], 4.67 [dd, (obs. t), J = 1.6 Hz, 4 H, Cp H], 6.97 (br s, 2 H, NH), 7.40–7.50 (m, 12 H, aryl H) and 7.65–7.72 (m, 8 H, aryl H). 31P NMR [(CD2Cl)2]: d 21.1 [J(P–Rh) = 122 Hz] (Found: C, 56.78; H, 4.71; N, 2.97. C43H42ClFeN2O3P2Rh?H2O requires C, 56.82; H, 4.85; N, 3.08%). IR: n& max/cm21 3500 (H2O), 3335 (N–H), 1970 (Rh–C]] O), 1635 (C]] Oamide) and 1539 (C–H, aryl). FAB MS m/z: 891 M1, 913 (M1Na)1, 855 (M 2 Cl)1. [Ï-1,19Bis(3-diphenylphosphinopropylaminocarbonyl)ferrocene]- bis[bis(2,29-bipyridyl)chlororuthenium] 6. cis-Bis(bipyridyl) ruthenium dichloride, cis-[Ru(bpy)2Cl2]?2H2O (72 mg, 0.14 mmol), and compound 2 (75 mg, 0.10 mmol) were dissolved in a mixture of ethanol (10 ml) and water (10 ml). The reaction mixture was deaerated with nitrogen for 15 min and then heated at reflux for 5 h under a nitrogen atmosphere.The ethanol was removed in vacuo and water (10 ml) added. The solution was filtered to remove unchanged ligand and a saturated aqueous solution of ammonium hexafluorophosphate was added to the filtrate. A red precipitate formed which was collected by filtration, washed with water and diethyl ether and dried.This product was recrystallised from acetone and diethyl ether. Yield: 85 mg, 64%. 1H NMR (CD2Cl2): d 1.23–1.29 (m, 4 H, CCH2C), 2.40–2.45 (m, 4 H, PCH2), 3.03–3.09 (m, 4 H, NCH2), 4.34 [dd (obs. t), J = 2.0, 4 H, Cp H], 4.38 [dd (obs. t), J = 2.0, 2 H, Cp H], 4.44 [dd (obs. t), J = 2.0, 2 H, Cp H], 6.74– 6.88 (m, 6 H, aryl H), 7.04 (t, J = 7.1, 4 H, aryl H), 7.15–7.29 (m, 12 H, aryl H), 7.38–7.56 (m, 10 H, aryl H, NH), 7.67–7.74 (m, 6 H, aryl H), 7.86–8.03 (m, 8 H, aryl H), 8.25 (dd, J = 8.3, 4 H, aryl H), 8.91 (d, J = 5.0 Hz, 2 H, aryl H) and 9.65 (t, 2 H, aryl H). 31P NMR (CD2Cl2): d 33.5 (Found: C, 49.34; H, 3.92; N, 6.85. C82H74Cl2F12FeN10O6P4Ru2?4H2O requires C, 49.60; H, 4.13; N, 7.06%). IR: n& max/cm21 3650 (H2O), 3430 (N–H), 1636 (C]] Oamide) and 1533 (C–H aryl). FAB MS: m/z 1912, M1; 1765/7, [M 2 (PF6)]1; and 1622/4, [M 2 (PF6)2]1. 3-Diphenylphosphinopropylaminocarbonylmethane. Acetyl chloride (0.48 g, 6.0 mmol) was dissolved in toluene (30 ml) and added dropwise to a solution of compound 2 (1.5 g, 6.0 mmol) and triethylamine (0.6 g, 6.0 mmol) in toluene (30 ml) whilst stirring under nitrogen.After addition was complete, the reaction mixture was stirred for 4 h before the solvent was removed in vacuo. The residue was dissolved in dichloromethane (50 ml) and washed with water (3 × 30 ml). The organic layer was dried over anhydrous magnesium sulfate and the solvent removed in vacuo to yield the product as a white solid.Yield : 1.21 g, 71%. 1H NMR (CDCl3): d 1.59–1.66 (m, 2 H, CCH2C), 1.94 (s, 3 H, CH3), 2.00–2.08 (m, 2 H, PCH2), 3.32 [dt (obs. q), J = 6.9 Hz, 2 H, NCH2], 5.56 (br s, 1 H, N–H) and 7.32–7.48 (m, 10 H, aryl, H). 13C NMR (CDCl3): d 23.3 (CH3), 25.4 [d, J(P–C) = 10.9, CCH2C], 26.1 [d, J(P–C) = 16.1, PCH2], 40.5 [d, J(P–C) = 12.4, NCH2], 128.5 (aryl C–H) 128.6 [d, J(P– C) = 12.4, aryl C–H], 130.7 (aryl C–H), 132.7 [d, J(P–C) = 18.3 Hz, aryl C–H], 138.4 (aryl C–C) and 170.0 (C]] O). 31P NMR (CD2Cl2): d 219.2 (Found: C, 71.16; H, 7,41; N, 4.79. C17H20- NOP requires C, 71.50; H, 7.06; N, 4.91%). IR: n& max/cm21 1636 (C]] O) and 1555 (C–H, aryl). mp 73–76 8C. Tetracarbonylbis(3-diphenylphosphinopropylaminocarbonylmethane) molybdenum 7. A solution of [Mo(CO)4(nbd)] (110 mg, 0.36 mmol) in dichloromethane (30 ml) was added dropwise to a solution of the above compound (200 mg, 0.70 mmol) in dichloromethane (30 ml) whilst stirring under a nitrogen atmosphere.The reaction was stirred for 12 h and filtered. The solvent was removed from the filtrate and the residue recrystallised from dichloromethane and hexane to yield the pure product as beige microcrystals. Yield: 100 mg, 37%. 1H NMR (CDCl3): d 1.28–1.38 (m, 4 H, CCH2C), 1.92 (s, 6 H, CH3), 1.97–2.02 (m, 4 H, PCH2), 3.13 [dt (obs. q), J = 6.7, 4 H, NCH2], 5.67 (t, J = 5.4 Hz, 2 H, NH) and 7.26–7.35 (m, 20 H, aryl H). 13C NMR (CDCl3): d 23.2 (CH3), 24.7 (CCH2C), 30.1 [d, J(P–C) = 10.8, PCH2], 40.1 (NCH2), 128.4 (aryl C–H), 129.5 (aryl C–H), 132.3 (aryl C–H), 136.7 [d, J(P–C) = 15.6 Hz, aryl C–C], 170.2 (C]] O) and 210.0 (Mo–C]] O). 31P NMR (CDCl3): d 22.7 (Found: C, 58.91; H, 5.29; N, 3.51. C38H40MoN2O6P2 requires C, 58.56; H, 5.14; N, 3.60%). IR: n& max/cm21 2016 (Mo– C]] O), 1903 (Mo–C]] O), 1874 (Mo–C]] O), 1646 (C]] Oamide) and 1554 (C–H, aryl). FAB MS: m/z 779, M1; 780, [M 1 H]1; 802, [M 1 Na]1; 723 [M 2 (CO)2]1; and 667, [M 2 (CO)4]1.mp 162–164 8C. Crystallography Crystal data for compounds 3 and 4 are given in Table 1, together with refinement details. Data for the two crystals wereJ. Chem. Soc., Dalton Trans., 1999, 251–257 253 collected with Mo-Ka radiation using the MARresearch Image Plate System. The crystals were positioned at 70 mm from the image plate. 95 Frames were measured at 28 intervals with a counting time of 2 min. Data analysis was carried out with the XDS program.8 The structure of 4 was solved using direct methods with the SHELXS 86 program9 and the structure of 3 was isomorphous.In both structures the non-hydrogen atoms were refined with anisotropic thermal parameters apart from those in solvent molecules which were refined isotropically and with reduced occupancies. The hydrogen atoms were included in geometric positions. Both structures were then refined on F2 using SHELXL.10 All calculations were carried out on a Silicon Graphics R4000 Workstation at the University of Reading.CCDC reference number 186/1256. 1H NMR titrations A solution of the receptor (500 ml) was prepared at a concentration typically of the order of 0.01 mol dm23 in deuteriated dichloromethane. The initial 1H NMR spectrum was recorded and aliquots of anion were added by gas-tight syringe from a solution made such that 1 mole equivalent was added in 20 ml. After each addition and mixing, the spectrum was recorded again and changes in the chemical shift of certain protons were noted.The result of the experiment was a plot of displacement in chemical shift as a function of the amount of added anion, which was subjected to analysis by curve-fitting since the shape is indicative of the stability constant for the complex. The computer program EQNMR11 was used which requires the concentration of each component and the observed chemical shift (or its displacement) for each data point.Typically these titration experiments were repeated three times with at least fifteen data points in each experiment. Results and discussion Synthesis of ferrocene phosphine ligand The new ferrocene appended phosphine amide ligand 2 was prepared via the condensation of 1,19-bis(chlorocarbonyl)- ferrocene 16 with 2 equivalents of 3-aminopropyldiphenylphosphine 7 in toluene in the presence of triethylamine (Scheme 1). The pure product was obtained after column chromatography and recrystallisation from dichloromethane as orange microcrystals in 47% yield. Synthesis of transition metal co-ordinated macrocycles of compound 2 Adapting the synthetic methodology used in the preparation of molybdenum carbonyl phosphine chelated metallocrown ether macrocycles,12 the high-dilution reaction of 1 equivalent of [Mo(CO)4(nbd)] with 1 equivalent of compound 2 in dichloromethane produced, after recrystallisation from dichloromethane, the macrocyclic receptor 3 in 53% yield (Scheme 2).An analogous synthetic procedure with [Cr(CO)4(nbd)] aVorded a crude product which was recrystallised from a 1: 1 mixture of methanol–acetonitrile to give 4 in 46% yield. The rhodium(I) containing receptor 5 was prepared by the high-dilution reaction of [Rh2Cl2(CO)4] with 0.5 equivalent of 2 in dichloromethane in 45% yield (Scheme 3). The reaction of Scheme 1 [Ru(bpy)2Cl2]?2H2O and 2 in refluxing aqueous ethanol gave on addition of an excess of NH4PF6 a red product which was characterised as being the bis(ruthenium) compound 6 (Scheme 4).Scheme 2 Scheme 3 Scheme 4254 J. Chem. Soc., Dalton Trans., 1999, 251–257 No trace of the expected chelated product was found and attempts to prepare this complex using high-dilution experimentation proved unsuccessful. All four transition metal–ferrocene receptors were characterised by 1H and 31P NMR, IR spectroscopy, elemental analysis and FAB mass spectrometry (see Experimental section).The 31P NMR data reveal a single resonance for all the complexes which suggests a single isomer has been produced in each case. This indicates the rhodium(I) compound 5 is square planar with the two phosphine ligands arranged in a trans conformation; the corresponding cis isomer would have given rise to two resonances. Synthesis of model phosphine ligand and its molybdenum complex In an eVort to elucidate the individual eVects the ferrocene redox active moiety and co-ordinated transition metal Lewis acid centre have on the anion binding properties of these receptor systems a model phosphine ligand and its molybdenum complex were prepared.Condensation of 3-aminopropyldiphenylphosphine with acetyl chloride in toluene in the presence of triethylamine gave the amide in 71% yield. Reaction of 2 equivalents of it with 1 of [Mo(CO)4(nbd)] in dichloromethane aVorded after recrystallisation from dichloromethane–hexane 7 as beige microcrystals in 37% yield (Scheme 5).X-Ray structural investigations of compounds 3 and 4 Crystals of compound 3 suitable for structural determination were grown from a 1: 1 acetronitrile–ethanol solvent mixture, and those of 4 from a dichloromethane–methanol–hexane solvent mixture. The two structures, 3 containing molybdenum and 4 containing chromium respectively, are isomorphous, though with some diVerences in the solvent. The Mo and Cr atoms are octahedral being bonded to four carbonyls and two mutually cis phosphorus atoms.The two phosphorus atoms form a chelate ring containing 10 atoms and additionally a ferrocene moiety. The structure of 4 is shown in Fig. 2 together with the common numbering scheme. The dimensions of the metal co-ordination spheres are as expected with those in the Mo longer by ca. 0.14 Å than those for Cr reflecting the diVerence in the metal radii. The two amide groups in the molecule have a diVerent orientation in that O(15) is directed out and N(14) directed in while O(25) is directed in and N(24) is directed out.This arrangement facilitates the formation of a hydrogen bond between N(24) and O(15) in a neighbouring molecule [2.96(2) in 4, 2.95(2) Å 3]. The ferrocene moieties have the expected dimensions with the eclipsed conformation as is apparent from Fig. 2. The remaining dimensions in the molecule are also as expected. Scheme 5 Anion co-ordination studies Proton NMR titrations. Proton NMR titration experiments were carried out in deuteriated dichloromethane with compound 2, the transition metal co-ordinated receptors and various tetrabutylammonium anion salts.Typically significant downfield shifts of the amide and cyclopentadienyl protons were observed following the addition of anions. The EQNMR11 analysis of the resulting titration curves (Fig. 3) gave stability constant values for 1 : 1 solution anion complexes shown in Table 2. A comparison of the stability constant data for chloride anion binding reveals several noteworthy features.As was hoped compared with 2, the presence of the phosphine co-ordinated transition metal increases the strength of anion binding. The largest increase in magnitude of binding occurs with the charged ruthenium(II) receptor 6 which highlights the importance of attractive electrostatic forces in the anion complexation process. The chloride anion stability constant values for the neutral molybdenum 3 and chromium 4 receptors are an order of magnitude larger than that of the parent ferrocene phosphine ligand 2 which suggests a macrocyclic eVect may be responsible.However, the similarity between stability constant values determined for the two molybdenum receptors 3 and 7 implies the interaction between the anion and the chelated Lewis acid metal may be the dominant favourable binding eVect. Regarding anion selectivity trends Table 2 shows with receptors 3, 4 and 7 the strength of anion binding decreases in the order Cl2 > Br2 > I2 which reflects the decrease in charge den- Fig. 2 Structure of compound 4 with the atomic numbering scheme. The structure of 3 is isomorphous. The ellipsoids are shown at 30% occupancy. Cr(1) to carbonyl 1.853(8), 1.856(8), 1.887(8), 1.899(8), Cr(1)–P(2) 2.422(2), Cr(1)–P(3) 2.448(2) Å. Dimensions in the isomorphous molybdenum compound are Mo(1) to carbonyl 2.013(8), 1.995(8), 2.042(7), 2.046(7) and Mo(1)–P(2) 2.546(2), 2.568(2) Å.Fig. 3 Proton NMR titration curves of compounds 2, 3 and 6 with Cl2 in CD2Cl2.J. Chem. Soc., Dalton Trans., 1999, 251–257 255 Table 1 Crystal data and structure refinement for compounds 3 and 4 Empirical formula Formula weight T/K l/Å Crystal system, space group a/Å b/Å c/Å b/8 V/Å3 Z, Dc/Mg m23 m/mm21 F(000) Crystal size mm q range for data collection/8 Index ranges Reflections collected/unique Data/restraints/parameters Final R1, wR2 [I > 2s(I)] (all data) Extinction coeYcient Largest diVerence peak and hole/e Å23 4 [CrL(CO)4]?0.5EtOH?MeOH C48.50H49CrFeN2O7P2 941.69 293 (2) 0.71073 Monoclinic, P21/c 14.093(11) 14.512(10) 26.82(2) 103.720(10) 5328 2, 1.174 0.581 1960 0.25 × 0.25 × 0.30 2.49 to 28.60 216 < h < 0, 217 < k < 17, 231 < l < 32 16458/9256 [R(int) = 0.0582] 9256/0/558 0.0998, 0.2887 0.1370, 0.3224 0.024(3) 0.821 and 20.844 3 [MoL(CO)4]?0.5MeCN?0.5EtOH C48H46.5FeMoN2.5O6.5P2 976.10 293 (2) 0.71073 Monoclinic, P21/c 14.050(13) 14.344(13) 26.88(2) 102.790(10) 5283 2, 1.227 0.617 2008 0.25 × 0.25 × 0.25 1.90 to 23.99 216 < h < 0, 216 < k < 16, 230 < l < 29 14791/7695 [R(int) = 0.0333] 7695/0/551 0.0653, 0.1697 0.0854, 0.1854 0.0061(6) 0.905, 20.547 sity of the anionic guest species.In contrast the ruthenium(II) receptor 6 displays a similar strength of binding for chloride and iodide whilst bromide forms the strongest complex. The binding of dihydrogenphosphate is generally weak for all receptors except 7.In the case of 3 and 4 this may be a consequence of their macrocyclic cavities being too small to accommodate this relatively large anionic guest. Similarly the small macrocyclic cavity size of the rhodium(I) receptor 5 may account for this receptor’s inability to complex the largest bromide, iodide and dihydrogenphosphate guest anions. Electrochemical investigations The electrochemical properties of the receptors were investigated by cyclic voltammetry in a 1 : 1 mixture of acetonitrile and dichloromethane with NBu4BF4 as supporting electrolyte (Table 3).The ferrocene phosphine ligand 2 displayed a single irreversible oxidation wave characteristic of an electrochemical step-chemical step (EC) mechanism. It is possible that the irreversible nature of this oxidation process arises from an interaction between the lone pairs of electrons of the phosphorus atoms and the positively charged ferrocenium unit.Interestingly in support of this the phosphine–transition metal co-ordinated receptors gave cyclic voltammograms of more reversible character (Fig. 4). Similar electrochemical findings have been reported with polyaza ferrocene ligands.13 The cyclic voltammograms of 3–6 all contain two oxidation waves which can be assigned to the oxidation of the ferrocene moiety and Table 2 Anion stability constant data Ka/dm3 mol21 Receptor 234567 Cl2 10 70 70 20 240 70 Br2 — 50 60 nb 320 40 I2 — 10 15 nb 250 20 H2PO4 2 10 20 20 nb ppt 50 a Determined in CD2Cl2, at 293 K, errors estimated to be £20%.nb = No binding; ppt = precipitate formed during titration, K could not therefore be calculated. the respective transition metal centre (Fig. 4) (Table 3). In the case of 3 thin layer coulometric experiments confirmed the two oxidation waves to be two one electron redox processes. Table 3 shows the ferrocene oxidation potentials for the transition metal containing receptors are anodically shifted compared to that of the ‘free’ ligand 2.This anodic shift can be ascribed to the presence of the closely bound Lewis acidic metal centre withdrawing electron density presumably via through space communication making the oxidation process less favourable. Surprisingly the largest magnitude of anodic per- Fig. 4 Cyclic voltammograms of compound 4 in 1 : 1 acetonitrile– dichloromethane at scan rates 50, 100 and 200 mV s21. Table 3 Electrochemical data Receptor 234567 Epa(Fc–Fc1) a/mV 440 460 485 470 460 — Epa(Metal) a/mV — 520 360 400 640 470 a Epa = anodic peak potential. Obtained in 1: 1 acetonitrile– dichloromethane solution containing 0.2 mol dm23 NBu4PF6 as supporting electrolyte.Solutions were ca. 1 × 1023 mol dm23 in receptor and potentials were obtained with reference to a Ag–Ag1 electrode at 293 K, scan rate = 100 mV s21.256 J. Chem. Soc., Dalton Trans., 1999, 251–257 Table 4 Electrochemical anion recognition data DEpa(Cl2) a/mV DEpa(Br2) a/mV DEpa(HSO4 2) a/mV Receptor 234567 Fc–Fc1 65 90 85 65 70 — Metal — 95 30 80 25 25 Fc–Fc1 30 30 30 — 35 — Metal — 30 55 —— b 25 Fc–Fc1 70 35 35 60 45 — Metal — 50 30 30 45 25 a Cathodic shift in oxidation potential produced by presence of 5 equivalents of anion added as its tetrabutylammonium salt.Solvent 1 : 1 acetonitrile–dichloromethane, 293 K. b Could not be investigated as oxidation potential is greater than oxidation potential of anion.turbation occurs with the neutral chromium receptor 4 and not the positively charged ruthenium(II) receptor 6. The eVect of anion binding on the electrochemical properties of compounds 2–6 and 7 was also investigated. Following the addition of chloride, bromide and hydrogensulfate anions, significant cathodic shifts were observed in the ferrocene and metal centre oxidation potentials (Table 4). The bound anion eVectively stabilises the positively charged ferrocenium or oxidised transition metal facilitating the oxidation redox process.Interestingly Table 4 shows chloride causes larger cathodic perturbations than bromide, which reflects its higher charge : radius ratio. Chloride also causes larger perturbations than hydrogensulfate for the three macrocyclic receptors 3–5 which may be ascribed to a size selective eVect; the chloride ion is of complementary size to the respective macrocyclic cavity whereas the larger tetrahedral hydrogensulfate anion is not.The eVects of dihydrogenphosphate anions on the electrochemical properties of compounds 2–4 and 6 were intriguing. For example the cyclic voltammograms obtained for the chromium receptor 4 in the presence of increasing amounts of H2PO4 2 are shown in Fig. 5. As the anion was added the chromium oxidation wave decayed and the ferrocene oxidation was significantly shifted to lower potential (Table 5). Similar observations were noted in the cyclic voltammograms of compounds 2, 3 and 6 and Table 5 reports the relatively large Fig. 5 Cyclic voltammograms of compound 4 in the presence of (a) increasing amounts of H2PO4 2 and (b) 5 equivalents of H2PO4 2 in 1 : 1 acetonitrile–dichloromethane. Scan rates in (b) are 50, 100, 200, 400 and 800 mV s21.H2PO4 2 induced cathodic shifts of their respective ferrocene oxidation potentials. The shape of the cyclic voltammogram following the addition of 5 equivalents of H2PO4 2 was characteristic of an EC mechanism.Fig. 5(b) shows with compound 4 that as the scan rate is increased the reduction peak becomes increasingly apparent. The sharp, symmetrical shape of the reverse peak is characteristic of electron transfer to a surface confined species suggesting the product of the chemical reaction is adsorbed onto the electrode surface. Conclusion The syntheses of a new bis(phosphine) amide linked ferrocene ligand and molybdenum, chromium, rhodium and ruthenium transition metal chelated receptors have been achieved. Singlecrystal X-ray structural investigations of the molybdenum and chromium receptors reveal monomeric transition metal phosphine chelation with cis-co-ordination geometry at the metal centre.Proton NMR anion co-ordination investigations enabled stability constants to be determined for 1 : 1 stoichiometric receptor : anion complexes. A comparison of stability constant values suggests the combination of the transition Lewis acid metal centre and the ferrocene amide moiety enhances the strength of anion binding.It is noteworthy that the strength of anion binding was greatest with the positively charged ruthenium receptor 6 which indicates that attractive electrostatic forces are of significant importance to the anion recognition process. Electrochemical investigations show all receptors can electrochemically sense various anions via signifi- cant cathodic perturbations of the respective ferrocene and transition metal oxidation wave.Acknowledgements We thank the EPSRC for a studentship (to J. E. K.) and for use of the mass spectrometry service at University College Swansea. The University of Reading and the EPSRC are gratefully acknowledged for funding towards the crystallographic image plate system. References 1 P. D. Beer and D. K. Smith, Prog. Inorg. Chem., 1997, 46, 1; F. P. Schmidtchen and M. Berger, Chem. Rev., 1997, 97, 1609; J. L. Atwood, K. T. Holman and J. W. Steed, Chem. Commun., 1996, 1401. Table 5 Dihydrogenphosphate induced cathodic shifts of ferrocene– ferrocenium oxidation potential of receptors Receptor DEpa a /mV 2 135 3 135 4 185 6 180 a Cathodic shift in ferrocene–ferrocenium oxidation potential produced by presence of 5 equivalents of tetrabutylammonium dihydrogenphosphate in 1 : 1 acetonitrile–dichloromethane.J. Chem. Soc., Dalton Trans., 1999, 251–257 257 2 P. D. Beer, Chem. Commun., 1996, 689; M. M. G. Antonisse and D. N. Reinhoudt, Chem. Commun., 1998, 443. 3 P. D. Beer, Acc. Chem. Res., 1998, 31, 71; P. D. Beer, P. A. Gale and Z. Chen, Adv. Phys. Org. Chem., 1998, 31, 1. 4 P. D. Beer, A. R. Graydon, A. O. M. Johnson and D. K. Smith, Inorg. Chem., 1997, 36, 2112; P. A. Gale, Z. Chen, M. G. B. Drew, J. A. Heath and P. D. Beer, Polyhedron, 1998, 17, 405. 5 P. D. Beer, M. G. B. Drew and R. Jagessar, J. Chem. Soc., Dalton Trans., 1997, 881. 6 H. J. Lorkowski, R. Pannier and A. Wende, J. Prakt. Chem., 1967, 35, 149. 7 D. A. Blinn, R. S. Button, V. Farazi, M. K. Need, C. L. Tapley, T. E. Trehearne, S. D. West, T. L. Kruger and B. N. StorhoV, J. Organomet. Chem., 1990, 393, 143. 8 W. Kabsch, J. Appl. Crystallogr., 1998, 21, 1916. 9 SHELXS 86, G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. 10 SHELXL, G. M. Sheldrick, program for crystal structure refinement, University of Göttingen, 1993. 11 M. J. Hynes, J. Chem. Soc., Dalton Trans., 1993, 311. 12 J. Powell, M. R. Gregg, A. Kuksis, C. J. May and S. J. Smith, Organometallics, 1989, 8, 2918. 13 P. D. Beer, Z. Chen, M. G. B. Drew, A. O. M. Johnson, D. K. Smith and P. Spencer, Inorg. Chim. Acta, 1996, 246, 143. Paper 8/07763K © Copyright 1999 by the Royal Society of Chemistry

ISSN:1477-9226    

DOI:10.1039/a807763k

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 255–262 255 Synthesis of new adducts and co-ordination complexes of zirconium and titanium containing ‚-aminoketone ligands. Crystal structures of isostructural adducts MCl4?2PriHNCMe] CHCMe] O (M 5 Ti or Zr) and the complex [Zr(PhNCMe] CHCMe] O)2Cl2] David Jones,a Andrew Roberts,a Kingsley Cavell,*,a Wilhelm Keim,b Ulli Englert,c Brian W. Skelton d and Allan H. White d a Chemistry Department, University of Tasmania, PO Box 252-75, Hobart 7001, Australia b Institut für Technische und Petrol Chemie der RWTH Aachen, Worringer Weg 1, D-52056, Aachen, Germany c Institut für Anorganische Chemie der RWTH, Aachen, Templergraben 55, D-52056, Aachen, Germany d Department of Chemistry, University of Western Australia, Nedlands 6907, Australia The reaction of MCl4 (M = Zr or Ti) with b-aminoketones HL (R1HNCR2]] CHCR3]] O; R2 = R3 = Me; R2 = Me, R3 = CF3) yielded the bis(ligand) adducts MCl4?2HL (M = Zr, R1 = Pri or Ph; R2 = R3 = Me; or R1 = Pri, R2 = Me, R3 = CF3; M = Ti, R1 = Pri or CH2CH]] CH2, R2 = R3 = Me).Reaction of MCl4 with the alkali-metal salts of the b-aminoketone ligands yielded the bis(ligand) complexes [M(R1NCMe]] CHCMe]] O)2Cl2] (M = Zr, R1 = Ph, p-ClC6H4, p-MeOC6H4 or Pri; M = Ti, R1 = Ph or p-MeOC6H4). Crystal structure determinations of the isostructural compounds ZrCl4?2PriHNCMe]] CHCMe]] O and TiCl4?2PriHNCMe]] CHCMe]] O indicated an octahedral co-ordination environment around the metal with the trans monodentate N]O ligands bound through the oxygen only.Strong intramolecular hydrogen bonding of the hydrogen on the nitrogen with the ligand oxygen is consistent with a ligand immonium enolate structure. An X-ray study of the octahedral complex [Zr(PhNCMe]] CHCMe]] O)2Cl2] indicated that the oxygens of the chelating N]O ligands are trans to each other and the chloride ligands are in a cis arrangement. The plane of one N]O chelate is in the equatorial plane of the complex and the plane of the second N]O ligand is at right angles to the first.The ligand forms a predominantly delocalised chelate ring but some ene–imine structure is apparent. Although the chemistry of organo-titanium, -zirconium and -hafnium complexes has been extensively studied, particularly in relation to their application as polymerisation catalysts, the co-ordination chemistry of these oxophilic metals has concentrated on the use of oxygen donors.1 A relatively small number of articles have reported complexes with ligands containing nitrogen, phosphorus and sulfur donors.1 Several reports have appeared describing Group 4 metal complexes containing mixed donor chelating ligand systems, e.g.complexes of monothio-b-diketonates and N]O Schiff bases; tetradentate o-phenylenebis(salicylideneiminate) (salphen) complexes of zirconium1–9 have been reported and a single bis(ligand) ZrL2Cl2 complex (L = msal = N-methylsalicylideneiminate) has been described.2 These mixed donor ligand systems offer opportunities for synthesizing complexes with potentially valuable reaction chemistry.Ligands of the type O]Y (where Y is for example N or S) are particularly interesting; the oxygen provides a site for strong co-ordination whereas the donor, Y, is likely to be less strongly bound and hence may lead to ligand hemilability and subsequently to interesting catalytic behaviour. We have found that efficient catalyst systems for the conversion of ethylene into linear a-olefins are generated by in situ reaction of ZrCl4 with an appropriate alkylaluminium cocatalyst in the presence of b-aminoketones.10,11 To gain a better understanding of the nature of the catalyst system and to investigate factors which affect Group 4 metal-catalysed 1- olefin oligomerisation/polymerisation it was desirable to synthesize possible catalyst precursors formed from the reaction of b-aminoketones with the metal halide.Furthermore, complexes of the type ML2Cl2 (where M = Zr or Ti, and L = mixed donor, chelate ligand) are of interest; mixed-ligand complexes have been shown to be very effective catalysts in, for example, nickelbased systems.12–14 In particular, b-aminoketones are an interesting class of bidentate ligand for Group 4 elements as amine/ imine nitrogens co-ordinate relatively weakly to these metals. Although extensively studied for the late transition metals,15–17 very few Group 4 metal complexes containing such ligands have been reported.18 Several complexes containing analogous tetradentate b-aminoketones have been reported.2–7 None of the published complexes has the form ML2Cl2.We describe here the reaction of a variety of free b-aminoketones and b-aminoketonate anions with MCl4 (M = Zr or Ti) to produce a number of unusual bis(b-aminoketone) adducts MCl4?2HL (HL = R1HNCR2]] CHCR3]] O or R1MeNCR2]] CHCR3]] O) (M = Zr, R1 = Pri or Ph, R2 = R3 = Me; or R1 = Pri, R2 = Me, R3 = CF3; M = Ti, R1 = Pri or CH2CH]] CH2, R2 = R3 = Me) and complexes of the type [ML2Cl2] (L = R1HNCMe]] CHCMe]] O) (M = Zr, R1 = Ph, p-ClC6H4, p-MeOC6H4 or Pri; M = Ti, R1 = Ph or p-MeOC6H4).An X-ray crystallographic study of the isomorphous compounds MCl4?2PriHNCMe]] CHCMe]] O (M = Zr or Ti) and the complex [ZrCl2(PhNCMe]] CHCMe]] O)2] has provided detailed structural information. Experimental All reactions were carried out under purified nitrogen using normal Schlenk techniques.Solvents were dried and purified N H O R2 R3 R1256 J. Chem. Soc., Dalton Trans., 1998, Pages 255–262 using standard techniques. The ligands were prepared by known methods either in the presence of a drying agent,17 in refluxing toluene using a Dean–Stark apparatus,19 or where reaction rates were slow or the b-diketone acidity was too high (leading to formation of the b-diketonate ammonium salt) by reaction with the trimethylsilyl ether of the appropriate bdiketone. 20 Infrared spectra were recorded on a Hitachi 270-30 spectrometer, 1H and 13C NMR spectra with a Varian EM390, Bruker CXP 200 or Bruker AM300 spectrometer. The highly moisture-sensitive potassium or sodium alkyl- or aryl-b-aminoketonates have been isolated for the first time by a modified literature reaction.16 Synthesis of R1KNCMe]] CHCMe]] O (R1 5 p-ClC6H4, p-MeOC6H4, Ph or Pri) A typical procedure for the formation of these salts is described using p-MeOC6H4KNCMe]] CHCMe]] O as an example.In a Schlenk flask (250 cm3), KOBut (1.6 g, 14.25 mmol) was suspended in a mix of toluene (20 cm3) and tetrahydrofuran (50 cm3). A solution of (p-MeOPh)HNCMe]] CHCMe]] O [3.22 g, 15.68 mmol (10% excess)] in thf (20 cm3) was added and the flask heated to 60 8C with stirring for 4 h. The solution went yellow-orange as the KOBut reacted. After 4 h the solution was cooled to room temperature and the thf was removed under vacuum (a voluminous precipitate formed).Enough toluene (20–30 cm3) was added to slurry the precipitate and the product was filtered off. Excess of aminoketone and impurities were removed by washing with toluene (2 × 20 cm3) then with hexane (2 × 20 cm3). The product was dried under vacuum and did not need recrystallising. Sodium salts of the ligands could also be isolated following the above procedure using sodium hydride instead of KOBut. In CD3OD the salts appear to be partially deuteriated.† In non-protic solvents (i.e.[2H8]toluene) the 1H NMR spectrum is ‘normal’ showing a ketoenamine structure. p-MeOC6H4KNCMe]] CHCMe]] O: yield 86.0%; dH(CD3OD, 300 MHz) 2.14 (m, 2 H, CH2), 2.227 (s, 3 H, Me), 3.982 (s, 3 H, OMe), 5.301 (s, 2 H, CH2), 7.127 (d, 2 H, JHH 8.3, m-H of Ph) and 7.262 (d, 2 H, JHH 8.3 Hz, o-H of Ph). PhKNCMe]] CHCMe]] O: yield 92.0%; dH(CD3OD, 300 MHz) 2.085 (m, 2 H, CH2), 2.101 (s, 3 H, Me), 4.974 (s, 2 H, CH2), 7.284 (m, 1 H, p-H of Ph), 7.365 (m, 2 H, JHH 8.4, o-H of Ph) and 7.414 (t, 2 H, JHH 8.1 Hz, m-H of Ph). An identical spectrum is obtained when NaOMe is added to the aminoketone in CD3OD in a 1 : 1 ratio.In both cases when water is added the spectrum of the free aminoketone is seen. PhNaNCMe]] CHCMe]] O: yield 96.0%; dH([2H8]toluene, 300 MHz) 1.507 (br s, 3 H, Me), 1.975 (br s, 3 H, Me), 4.575 (br s, 1 H, CH), 6.369 (br s, 2 H, m-H of Ph), 6.759 (m, 1 H, p-H of Ph) and 6.994 (m, 2 H, o-H of Ph).p-ClC6H4KNCMe]] CHCMe]] O: yield 92.7%; dH(CD3OD, 300 MHz) 2.08 (m, 2 H, CH2), 2.099 (s, 3 H, Me), 5.054 (s, 2 H, CH2), 7.204 (d, 2 H, JHH 6.6, C6H4Cl) and 7.421 (d, 2 H, JHH 6.6 Hz, C6H4Cl). Other salts were synthesized and used as required without characterisation. Synthesis of the adducts MCl4?2R1HNCR2]] CHCR3]] O (M 5 Zr or Ti, R1 5 Pri, Ph, R2 5 R3 5 Me; M 5 Zr; R1 5 p-MeOC6H4, R2 5 Me, R3 5 CF3) and MCl4?2R1R19NCMe]] CHCMe]] O (M 5 Zr, R1 5 R19 5 Et or Ph; M 5 Ti, R1 5 p-MeOC6H4, R19 5 Me) A similar method to that reported for the preparation of the thf adduct of ZrCl4 was used.21 A typical synthesis is described for † The splitting pattern tends to indicate partial deuteriation. However, extensive exchange of the methyl and methine protons is not observed. Rapid quenching with water followed by hexane extraction led to isolation of the fully protonated free aminoketone.In non-protic solvents metal chelate formation is observed with the expected methine signal.the adduct ZrCl4?2PriHNCMe]] CHCMe]] O. In a Schlenk flask (250 cm3), ZrCl4 (11.83 g, 50.8 mmol) was suspended in CH2Cl2 (150 cm3) at 0 8C. To this was added a solution of PriHNCMe]] CHCMe]] O [16 g, 115 mmol (10% excess)] in CH2Cl2 (20 cm3). The solution initially went clear before a white solid precipitated. The slurry was stirred for 60 min at room temperature and the solids filtered off, washed twice with CH2Cl2 (20 cm3) and dried under vacuum.The product could be purified by continuous extraction with refluxing CH2Cl2. Crystals suitable for structure determination were obtained by slow cooling of a saturated CH2Cl2 solution. For the zirconium complexes the synthesis can be performed in the presence of an excess of ligand, or in the presence of Et3N as base; in each case only the adduct is formed. ZrCl4?2PriHNCMe]] CHCMe]] O 1: white crystalline solid (yield 74.8%) (Found: C, 37.21; H, 5.90; N, 5.46. C16H30- Cl4N2O2Zr requires C, 37.28; H, 5.87; N, 5.43%); dH(CDCl3, 300 MHz) 1.43 [d, 6 H, JHH 6.5, CH(CH3)2], 2.10 (s, 3 H, Me), 2.44 (s, 3 H, Me), 3.90 [d of spt, 1 H, 2JHH 9.2, JHH 6.5 Hz, CH(CH3)2], 5.07 (s, 1 H, CH) and 10.50 (br s, 1 H, NH).ZrCl4?2PhHNCMe]] CHCMe]] O 2: pale yellow crystalline solid (yield 76.2%) (Found: C, 44.98; H, 4.61; N, 4.79. C22H26- Cl4N2O2Zr requires C, 45.29; H, 4.49; N, 4.80%); dH(CDCl3, 300 MHz) 2.136 (s, 3 H, Me), 2.537 (s, 3 H, Me), 5.397 (s, 1 H, CH), 7.3–7.4 (br m, 5 H, Ph) and 12.1 (s, 1 H, NH).ZrCl4?2(p-MeOC6H4)HNCMe]] CHCCF3]] O 3: pale yellow crystalline solid (yield 86.4%) (Found: C, 37.93; H, 3.25; N, 3.60. C24H24Cl4F6N2O4Zr requires C, 38.36; H, 3.22; N, 3.73%); insoluble in CD2Cl2, CDCl3 and ligand is displaced by C4D8O solvent. ZrCl4?2Ph2NCMe]] CHCMe]] O 4: yellow crystalline solid (yield 60.6%) (Found: C, 55.42; H, 4.91; N, 3.84. C34H34- Cl4N2O2Zr requires C, 55.51; H, 4.66; N, 3.81%); dH(CDCl3, 300 MHz) 2.464 (s, 3 H, Me), 2.983 (s, 3 H, Me), 5.335 (s, 1 H, CH) and 7.1–7.5 (br m, 10 H, Ph).ZrCl4?2Et2NCMe]] CHCMe]] O 5: yellow crystalline solid (yield 82.3%) (Found: C, 39.55; H, 6.09; N, 5.04. C18H34- Cl4N2O2Zr requires C, 39.78; H, 6.31; N, 5.15%); dH(CDCl3, 300 MHz) 1.27 (t, 3 H, JHH 7.2, CH2CH3), 1.30 (t, 3 H, JHH 7.2, CH2CH3), 2.539 (s, 3 H, Me), 2.983 (s, 3 H, Me), 3.532 (q, 2 H, JHH 7.2, CH2CH3), 3.540 (q, 2 H, JHH 7.2 Hz, CH2CH3) and 5.309 (s, 1 H, CH). TiCl4?2PriHNCMe]] CHCMe]] O 6: dark red crystalline solid (yield 96.0%) (Found: C, 40.67; H, 6.49; N, 6.14.C16H30- Cl4N2O2Ti requires C, 40.70; H, 6.40; N, 5.93%); dH(CDCl3, 300 MHz) 11.02 (br s, 1 H, NH), 5.122 (s, 1 H, CH), 3.972 [d of spt, 1 H, 2JHH 9.3, JHH 6.6, NCH(CH3)2], 2.678 (s, 3 H, Me), 2.173 (s, 3 H, Me) and 1.486 [d, 6 H, JHH 6.6 Hz, NCH(CH3)2]; dC(CDCl3, 75.5 MHz) 189.1 (CO), 168.9 (CN), 98.0 (CH), 49.1 [NCH(CH3)2], 25.9 and 20.1 (Me) and 21.8 [NCH(CH3)2]. TiCl4?2(p-MeOC6H4)MeNCMe]] CHCMe]] O 7: dark maroon crystalline solid (yield 75.1%) (Found: C, 49.77; H, 5.52; N, 4.39.C26H34Cl4N2O4Ti requires C, 49.71; H, 5.45; N, 4.46%); two ligand environments, dH(CD2Cl2, 300 MHz) 5.623 (s, 1 H, CH), 5.040 (s, 1 H, CH), 3.839 (m, 6 H, p-MeOC6H4), 3.550 [s, 6 H, NMe(p-MeOC6H4)], 3.226 (narrow m, 2 H, part Me), 2.990 (s, 1 H, part Me), 2.820 (s, 3 H, Me), 2.768 (s, 3 H, Me), 2.635 (s, 1 H, part Me), 2.466 (s, 2 H, part Me) and 6.92–7.19 (m, 8 H, p-MeOC6H4); dC(CD2Cl2, 75.5 MHz, referenced to CD2Cl2 at d 53.80) 193.8 and 191.9 (CO), 176.5 and 175.1 (CN), 160.2 (p-C of Ph), 136.9 (i-C of Ph), 126.9, 126.6 and 124.2 (m-C of Ph), 115.8, 115.7, 115.5 and 115.3 (o-C of Ph), 98.61 and 96.87 (CH), 55.9 (MeO), 44.2 and 43.6 (NMe), 28.26, 27.87, 22.96 and 20.63 (Me).TiCl4?2(CH2]] CHCH2)HNCMe]] CHCMe]] O 8: maroon microcrystalline solid (yield 97%) (Found: C, 40.97; H, 5.57; N, 5.95. C16H26Cl4N2O4Ti requires C, 41.05; H, 5.60; N, 5.98%); dH(CDCl3, 300 MHz) 11.58 (br s, 1 H, NH), 5.937 (ddt, 1 H, JXH 5.5, JAX 17.2, JBX 10.3 Hz, ]] CH), 5.34–5.24 [br m(ddt’s), 2J.Chem. Soc., Dalton Trans., 1998, Pages 255–262 257 H, CH2]] ], 5.234 (s, 1 H, CH), 4.170 [br m(dddd), 2 H, CH2], 2.644 (s, 3 H, Me) and 2.160 (s, 3 H, Me); resolution inadequate to determine finer coupling constants; dC(CD2Cl2, 58.9 MHz) 186.9 (CO), 172.7 (CN), 131.1 (]] CH), 118.7 (CH2]] ), 98.9 (CH), 48.5 (CH2), 25.5 and 20.3 (Me). Synthesis of the complexes [Zr(R1NCR2]] CHCR3]] O)2Cl2] (R1 5 Pri, Ph, p-C6H4 or p-MeOC6H4, R2 5 R3 5 Me) The bis(ligand) complexes can be synthesized by the reaction of ZrCl4 with the isolated ligand salt, by in situ generation of the ligand salt, or from the bis(ligand) adduct and LiBun.Typical procedures are described below. Method A. In a Schlenk flask (100 cm3), ZrCl4 (1.26 g, 5.39 mmol) was suspended at 220 8C in CH2Cl2 (20 cm3). To this was slowly added a cold (220 8C) solution of p-ClC6H4- KNCMe]] CHCMe]] O (2.67 g, 10.8 mmol) in CH2Cl2 (20 cm3).The solution, which went pale yellow with some suspended solids, was stirred for 1 h and then filtered, keeping the solution below 0 8C. Hexane (30 cm3) was added to the filtrate and the volume reduced under vacuum to approximately 40 cm3. The flask was placed in a freezer overnight yielding a crop of pale yellow crystals. The complex was recrystallised from CH2Cl2 and hexane at 0 8C. [Zr(p-ClC6H4NCMe]] CHCMe]] O)2Cl2]?CH2Cl2 9: yield 56.1% [Found: C, 40.99; H, 3.68; N, 4.11.Calc. for C23H24- Cl6N2O2Zr: C, 41.58; H, 3.64; N, 4.22% (non-stoichiometric solvent ratio of approximately 1 : 1)]; dH(CD2Cl2, 200 MHz, 220 8C) 1.327 (s, 3 H, Me), 1.690 (s, 3 H, Me), 5.300 (s, ª2 H, CH2Cl2), 5.341 (s, 1 H, CH), 6.566 (dd, 1 H, JHH 8.4, 2.4, o-H of Ph), 7.260 (dd, 1 H, JHH 8.4, 2.4, o-H of Ph), 7.157 (dd, 1 H, JHH 8.4, 2.4, m-H of Ph) and 7.348 (dd, 1 H, JHH 8.4, 2.4 Hz, m-H of Ph); see Discussion for interpretation; dC(CD2Cl2, 75.5 MHz, 220 8C) 175.2 or 174.6 (CO), 175.2 or 174.6 (CN), 147.0 (i-C of Ph), 131.6 (p-C of Ph), 127.3 and 125.0 (o-C of Ph), 129.4 (m-C of Ph), 107.2 (CH), 25.3 and 23.1 (Me). [Zr(p-MeC6H4NCMe]] CHCMe]] O)2Cl2] 10: yield 57.2% (Found: C, 50.56; H, 5.07; N, 4.87.Calc. for C24H28Cl2N2O4Zr: C, 50.52; H, 4.95; N, 4.91%); dH(CD2Cl2, 200 MHz, 220 8C) 1.359 (s, 3 H, Me), 1.687 (s, 3 H, Me), 3.755 (s, 3 H, C6H4OMe), 5.305 (s, 1 H, CH), 6.566 (d, 1 H, JHH 8.5, o-H of Ph), 6.796 (d, 1 H, JHH 8.5, m-H of Ph), 6.876 (d, 1 H, JHH 8.5, m-H of Ph) and 7.098 (d, 1 H, JHH 8.5 Hz, o-H of Ph); see the Discussion section for interpretation; dC(CD2Cl2, 75.5 MHz, 220 8C) 174.7 (CO), 174.7 (CN), 157.6 (p-C of Ph), 140.9 (i-C of Ph), 126.4 and 124.5 (o-C of Ph), 114.7 and 113.5 (m-C of Ph), 107.2 (CH), 55.8 (C6H4OMe), 25.0 and 23.2 (Me); dH(CDCl3, 200 MHz, 20 8C), 1.433 (s, 3 H, Me), 1.721 (s, 3 H, Me), 3.811 (s, 3 H, C6H4OMe), 5.271 (s, 1 H, CH) and 6.5–7.3 (br m, 4 H, C6H4OMe); see Discussion for interpretation.Method B. To a Schlenk flask (100 cm3) containing NaH (1 g, 80% in mineral oil, 15% excess) suspended in thf (20 cm3) at 0 8C was slowly added a solution of PhHNCMe]] CHCMe]] O (5.00 g, 28.5 mmol) in thf (20 cm3). A vigorous reaction occurred. The solution was stirred at room temperature for 1 h and then filtered through dry Celite. The solution volume was reduced by about 10 cm3 under vacuum to ensure all hydrogen was removed.This thf solution of PhNaNCMe]] CHCMe]] O was slowly added to a suspension of ZrCl4 (3.30 g, 14.16 mmol) in toluene (30 cm3) at 0 8C (the initial addition must be very slow). The ZrCl4 dissolved during the addition and the solution went a cloudy pale yellow. It was stirred for 1 h at room temperature, filtered through dry Celite to remove the NaCl and the volume reduced to about half. The product precipitated on adding hexane (40 cm3). It was recrystallised from CH2Cl2 with hexane (the complex can also be recrystallised from thf with hexane at 0 8C).Crystals of [Zr(PhNCMe]] CHCMe]] O)2Cl2] suitable for structure determination were obtained by slow cooling of a saturated toluene–CH2Cl2 solution. [Zr(PhNCMe]] CHCMe]] O)2Cl2] 11: yield 65.6% (Found: C, 51.56; H, 4.72; N, 5.30. Calc. for C22H24Cl2N2O2Zr: C, 51.75; H, 4.74; N, 5.49%); dH(CDCl3, 200 MHz, 20 8C), 1.327 (s, 3 H, Me), 1.701 (s, 3 H, Me), 5.247 (s, 1 H, CH) and 6.5–7.4 (br m, 5 H, o-, m-, p-H of Ph); see Discussion for interpretation; dH(CD2Cl2, 200 MHz, 220 8C) 1.248 (s, 3 H, Me), 1.681 (s, 3 H, Me), 5.309 (s, 1 H, CH), 6.662 (d, 1 H, JHH 7.6, o-H of Ph), 7.189 (t, 1 H, JHH 6.33, p-H of Ph overlapping with o-H), 7.201 (d, 1 H, JHH 7.6, o-H of Ph), 7.295 (t, 1 H, JHH 7.0, m-H of Ph) and 7.373 (d, 1 H, JHH 7.0 Hz, m-H of Ph); see Discussion for interpretation; dC(CD2Cl2, 75.5 MHz, 220 8C) 174.6 or 174.0 (CO), 174.6 or 174.0 (CN), 148.3 (i-C of Ph), 129.3 and 129.1 (m-C of Ph), 126.1 and 123.3 (o-C of Ph), 125.2 (p-C of Ph), 107.1 (CH), 25.1 and 22.9 (Me).[Zr(p-MeOC6H4NCMe]] CHCCF3]] O)2Cl2] 12: yield 3.2% (microanalytical data for the fluorine-containing complexes were unreliable, consistently falling outside the accepted range, hence the data are not reported); dH(CDCl3, 200 MHz, 20 8C) 1.912 (s, 3 H, Me), 3.788 (s, 3 H, OMe), 5.807 (s, 1 H, CH) and 6.9 (br m, 4 H, o-, m-H of Ph); see Discussion for interpretation; dC(CD2Cl2, 75.5 MHz, 20 8C) 177.8 (CN), 159.6 (p-C of Ph), 156.1 (q, JCF 34.7, CO), 138.7 (i-C of Ph), 125 (br s, o-C of Ph), 119.3 (q, JCF 281 Hz, CF3), 115.7 (m-C of Ph), 105.2 (CH) and 25.5 (Me).Method C. In a Schlenk flask (250 cm3) the adduct ZrCl4? 2PriHNCMe]] CHCMe]] O (1.21 g, 2.33 mmol) was suspended in thf (30 cm3) at 270 8C. To this was slowly added LiBun (6.98 cm3, 0.671 M, 4.668 mmol) in pentane (20 cm3) leaving a pale yellow solution with some suspended solids.The solution was stirred and allowed to warm to 0 8C. It was then filtered and the volume reduced to 30 cm3. Pentane (40 cm3) was added to precipitate a pale yellow solid. The complex may be recrystallised from thf and hexane. [Zr(PriNCMe]] CHCMe]] O)2Cl2] 13: yield 65.6% (Found: C, 43.61; H, 6.44; N, 6.28. Calc. for C16H28Cl2N2O2Zr: C, 43.43; H, 6.38; N, 6.33%); dH(CDCl3, 300 MHz) 1.450 [d, 6 H, JHH 6.8, CH(CH3)2], 1.918 (s, 3 H, Me), 2.159 (s, 3 H, Me), 4.539 [spt, 1 H, JHH 6.8 Hz, CH(CH3)2] and 5.382 (s, 1 H, CH); dH(CD2Cl2, 300 MHz, 0 8C), 1.392 [d, 6 H, JHH 6.8, CH(CH3)2], 1.909 (s, 3 H, Me), 2.154 (s, 3 H, Me), 4.497 [spt, 1 H, JHH 6.8 Hz, CH(CH3)2] and 5.398 (s, 1 H, CH); dC(75.5 MHz, CD2Cl2, 0 8C) 173.9 and 172.6 (CO and CN), 109.0 (CH), 52.6 [CH(CH3)2], 25.0 and 24.1 (Me), 22.2 [CH(CH3)2].Synthesis of the complexes [Ti(R1NCR2]] CHCR3]] O)2Cl2] (R1 5 p-MeOC6H4, Ph or allyl, R2 5 R3 5 Me) The bis(ligand) complexes can be synthesized by the reaction of TiCl4 with the isolated ligand salt (Method A, above), also by reaction of TiCl4?2L with an excess of triethylamine (Method D, below). [Ti(p-MeOC6H4NCMe]] CHCMe]] O)2Cl2] 14: very dark red-black crystals (yield 75.0%) (Found: C, 54.76; H, 5.29; N, 5.22.C24H28Cl2N2O4Ti requires C, 54.67; H, 5.35; N, 5.31%); dH(CD2Cl2, 300 MHz) 1.407 (s, 3 H, Me), 1.694 (s, 3 H, Me), 3.801 (s, 3 H, MeO), 5.412 (s, 1 H, CH), 6.582 (dd, 1 H, JHH 2.4, 8.7, o-H of Ph), 6.826 (dd, 1 H, JHH 3.0, 8.7, o-H of Ph), 6.945 (dd, 1 H, JHH 2.7, 9.0, m-H of Ph) and 7.181 (dd, 1 H, JHH 2.4, 8.7 Hz, m-H of Ph); dC(CD2Cl2, 75.5 MHz) 175.5 (CO), 170.9 (CN), 157.7 (p-C of Ph), 144.75 (i-C of Ph), 126.8 and 123.5 (o-C of Ph), 113.9 (m-C of Ph), 110.0 (CH), 55.8 (MeO), 24.6 and 22.3 (Me). [Ti(PhNCMe]] CHCMe]] O)2Cl2] 15: dark maroon leaflet crystals (yield 47.5%) (Found: C, 56.32; H, 5.11; N, 5.90.C22H24Cl2N2O2Ti requires C, 56.55; H, 5.18; N, 5.99%); dH(CDCl3, 300 MHz) 1.328 (s, 3 H, Me), 1.694 (s, 3 H, Me), 5.364 (s, 1 H, CH), 6.667 (dd, 1 H, JHH 1.6, 8.2, o-H of Ph), 7.186 (dt, 1 H, JHH 1.2, 7.1 Hz, p-H of Ph) and 7.26–7.38 (m, 3 H, m-, o-H of Ph); dC(CDCl3, 75.5 MHz) 175.5 (CO), 169.7258 J.Chem. Soc., Dalton Trans., 1998, Pages 255–262 (CN), 151.2 (i-C of Ph), 128.7 and 128.2 (m-C of Ph), 125.8 and 125.6 (p-, o-C of Ph), 122.0 (o-C of Ph), 109.5 (CH), 24.4 and 22.0 (Me). Method D. To a stirred suspension of TiCl4?2(CH2]] CHCH2)HNCMe]] CHCMe]] O (0.53 g, 1.13 mmol) in CH2Cl2 (12 cm3) at 0 8C was added NEt3 (0.80 g, 7.90 mmol) dropwise, giving a dark solution.Stirring was continued for 1.5 h at 0 8C before concentrating the solution under vacuum (to 4 cm3). Hexane (30 cm3) was added, precipitating an impure solid. This was collected and vacuum dried before extracting with toluene (4 × 25 cm3) and filtering through Celite to give a dark solution. Removal of toluene followed by redissolution in CH2Cl2 (4 cm3), then layering with hexane (30 cm3) and storage in a freezer overnight gave a crop of very dark red block-shaped crystals.[Ti{(CH2]] CHCH2)NCMe]] CHCMe]] O}2Cl2] 16: yield 58% (Found: C, 48.57; H, 6.32; N, 7.08. C16H24Cl2N2O4Ti requires C, 48.63; H, 6.12; N, 7.09%); two ligand environments with labile N-alkyl substituents labelled NCHAHBCHCH2 and NCH2- CHCH2; dH(CDCl3, 300 MHz) 5.771 (s, 1 H, CH), 1.954, 2.030, 2.041, 2.136 (s, 12 H, Me), 4.427 (br m, 1 H, CHB), 4.601 (br m, 3 H, CH2 overlapping CHA), 5.098 (br m, 4 H, CH2]] ), 5.615 (s, 1 H, CH) and 5.771 (s, 1 H, CH); dH(C6D5CD3, 200 MHz) 1.416 and 1.511 (s, 6 H, MeCN), 1.730 (s, 6 H, MeCO), 4.2–4.4 (vbr s, ca. 0.5 H, CH2N), 4.511 (br s, ca. 3.5 H, CH2N) and 5.146 (s, 2 H, CH); dC(CDCl3, 75.5 MHz) 177.8, 174.8, 173.4 and 173.0 (CO, CN), 133.5 and 133.29 (]] CH), 116.4 and 116.1 (CH2]] ), 111.4 and 110.9 (CH), 57.2 and 55.3 (CH2), 23.5, 23.1, 22.2 and 21.5 (Me); dC(CD2Cl2, 75.5 MHz) 174.9 (both CO), 173.5 and 173.1(CN), 134.2 and 133.9 (]] CH), 116.6 and 116.4 (CH2]] ), 111.5 and 111.1 (CH), 57.3 and 55.7 (CH2), 23.5, 23.2, 22.5 and 21.8 (Me).Crystallography Unique room-temperature diffractometer data sets (2q–q scan mode; monochromatic Mo-Ka radiation, l = 0.710 73 Å; T ª 295 K) were measured yielding N independent reflections, No with I > 3s(I) being considered ‘observed’ [I > s(I) for compound 1] and used in the full-matrix least-squares refinement after absorption correction.Anisotropic displacement parameters were refined for the non-hydrogen atoms; (x,y,z, Uiso)H were included constrained at estimated values for 11 and refined for 1 and 6. Conventional residuals R, R9 on |F| are quoted (statistical weights). Neutral atom complex scattering factors were employed. Pertinent results are given in the figures and tables. Crystal/refinement data. ZrCl4?2PriHNCMe]] CHCMe]] O 1, C16H30Cl4N2O2Zr, M = 515.5, triclinic, space group P1� (no. 2), a = 8.636(4), b = 9.090(6), c = 9.117(6) Å, a = 119.58(4), b = 91.07(5), g = 107.25(5)8, U = 582.6 Å3, Dc(Z = 1) = 1.469 g cm23, Scheme 1 MCl4 + 2HL M = Zr or Ti M O Cl O Cl Cl Cl N R1 H N H MCl4•2PriHNCMe CHCMe O M = Zr 1; Ti 6 CHCMe O L = R1NCM ZrCl4•2PhHNCMe CHCMe O 2 ZrCl4•2( p-MeOC6H4)NCMe CHCMe O 3 ZrCl4•2Ph2NCMe CHCMe O 4 ZrCl4•2Et2NCMe CHCMe O 5 TiCl4•2( p-MeOC6H4)MeNCMe CHCMe O 7 CHCH2)HNCMe CHCMe O 8 TiCl4•2(CH2 F(000) = 264, mMo = 9.4 cm21, specimen 0.20 × 0.20 × 0.20 mm, A*min,max = 0.9721, 0.999, 2qmax = 708, N = 5112, N0 = 4010, R = 0.053, R9 = 0.058.TiCl4?2PriHNCMe]] CHCMe]] O 6, C16H30Cl4N2O2Ti, M = 472.14, triclinic, space group P1� , a = 8.834(4), b = 8.974(4), c = 9.028(4) Å, a = 120.18(3), b = 90.10(3)= 107.62(3)8, U = 579.3 Å3, Dc(Z = 1) = 1.353 g cm23, F(000) = 246, mMo = 8.6 cm21, specimen 0.20 × 0.16 × 0.60 mm, A*min,max = 1.13, 1.35, 2qmax = 508, N = 3297, N0 = 2624, R = 0.037, R9 = 0.044. [Zr(PhNCMe]] CHCMe]] O)2Cl2] 11, C22H24Cl2N2O2Zr, M = 510.6, orthorhombic, space group Pbca (no. 61), a = 17.221(3), b = 16.448(12), c = 16.584(4) Å, U = 4697 Å3, Dc(Z = 8) = 1.449 g cm23, F(000) = 2080, mMo = 7.1 cm21, specimen 0.28 × 0.65 × 0.36 mm, A*min,max = 1.20, 1.27, 2qmax = 508, N = 4141, N0 = 2619, R = 0.037, R9 = 0.037. CCDC reference number 186/784. See http://www.rsc.org/suppdata/dt/1998/255/ for crystallographic files in .cif format. Results and Discussion In situ addition of a Lewis acid cocatalyst to a solution of MCl4 and a b-aminoketonate gives rise to active catalyst systems for the oligomerisation and polymerisation of ethylene.11 To study the nature of the catalyst and hence selectively moderate catalyst behaviour it was considered important to investigate possible compounds formed from the treatment of Group 4 metal salts with N]O ligand species.The reaction of baminoketonate ligands with MCl4 (M = Zr or Ti) under various reaction conditions generated several isolable complex types (adducts and complexes) which may be formed in the in situ catalysis.Consistent with the concept that these new compounds may be the catalyst precursors, treatment of bis(ligand) adducts and complexes with an alkylaluminium cocatalyst generated active ethylene oligomerisation catalysts, even under very mild conditions. Furthermore, the adducts gave rise to catalysts with very similar catalytic behaviour to that observed for the in situ generated catalyst systems.Owing to complicated ligand–cocatalyst interactions the complexes and adducts have significantly different activities and product distributions.11 On reaction of >2 equivalents of free b-aminoketone with MCl4 in CH2Cl2 the low acidity of the ligand leads to formation of the bis(ligand) adducts (Scheme 1). In the case of the zirconium adducts there is no further reaction (deprotonation of the ligand) even in the presence of triethylamine or under forcing conditions, such as refluxing toluene. It has been previously observed that the more acidic salicylaldimines often deprotonate in refluxing toluene.1 Interestingly, unlike the analogous zirconium compounds, the titanium adduct 8 smoothly deprotonates in the presence of triethylamine to give the relevant complex (TiL2Cl2) in reasonable yield and high purity.In fact this approach proved to be the best method for the synthesis of 16. Synthesis of 16 via the sodium salt of the ligand resulted in the production of a large quantity of unidentified solid, giving a much lower yield for the desired complex.The ease with which the titanium adduct 8 was deprotonated possibly indicates an interaction in solution between the nitrogen of the bound ligand and the more Lewis-acidic and smaller titanium centre, leading to labilisation of the nitrogen proton. The treatment with triethylamine may be a general and very effective method for conversion of titanium adducts into complexes, and work is continuing in this area.The bis(ligand) adducts show limited solubility in most nonprotic polar solvents of lower donor ability than that of the ligand. They can be purified by extraction with CH2Cl2 which also allows spectroscopic characterisation by proton NMR spectroscopy. Ligand peaks for the adducts 1, 6 and 2 are shifted slightly downfield compared to those of the free aminoketone, Table 1, and are somewhat broadened. For 1 andJ. Chem.Soc., Dalton Trans., 1998, Pages 255–262 259 Table 1 Selected NMR data for the ligands R1HNCMe]] CHCMe]] O (R = Ph or Pri), and bis(ligand) adducts 1, 6 and 2 Compound PriHNCMe]] CHCMe]] O 1 6 PhHNCMe]] CHCMe]] O 2 R2 = R3 = Me 1.96, 1.92 2.44, 2.10 2.68, 2.17 2.05, 1.98 2.54, 2.14 Methine 4.88 5.07 5.12 5.19 5.40 NH 10.80 10.50 11.02 12.50 12.10 R1 1.20 (d, 6 H, Me), 3.68 (m, 1 H, CH) 1.43 (d, 6 H, Me), 3.90 (m, 1 H, CH) 1.49 (d, 6 H, Me), 3.97 (m, 1 H, CH) 7.14 (m, 2 H), 7.17 (m, 1 H), 7.33 (m, 2 H) 7.32–7.42 (m, 5 H) Table 2 Selected 1H and 13C NMR data for the ligand PhHNCMe]] CHCMe]] O and complexes 11 and 15 Ligand backbone Amine substituent (C, H of Ph) dH dC PhHNCMe]] CHCMe]] O 11 15 PhHNCMe]] CHCMe]] O 11 15 Me 1.978, 2.050 1.698, 1.322 1.690, 1.335 20.35, 29.62 23.38, 25.17 22.0, 24.5 CH 5.191 5.294 5.354 98.19 107.2 109.5 CO 196.5 175.5 175.6 CN 160.6 174.3 169.7 i 139.6 149.3 151.2 o 7.135 6.689, 7.114 6.65, 7.26 125.2 121.3, 126.6 125.9, 122.0 m 7.335 7.336 7.32 129.8 129.6 128.8, 128.2 p 7.174 7.192 7.160 126.0 126.6 125.6 Shifts (ppm) in CD2Cl2 at room temperature. 6 the isopropyl a-proton signal is split indicating coupling with a proton on the amine nitrogen, providing evidence that the ligand is still protonated with the proton on the nitrogen. The IR spectra of the free aminoketones show a strong band at approximately 1620 cm21 [n(C]] O)] which shifts to lower wavenumbers [to overlap with a strong band at 1560 cm21 (C]] C stretch)] for the adduct 1.The appearance of a sharp peak at 3280 cm21 on adduct formation has been assigned to an N]H stretching band with diminution of strong hydrogen bonding.18 These data clearly demonstrate that co-ordination of the N]O ligand to the metal is via the ligand oxygen. A subsequent X-ray study (see later) indicates that the solid-state structure is consistent with these proposals. Reaction of ZrCl4 with either a potassium b-aminoketonate (isolated by reaction of the free aminoketone with KOBut in thf–toluene) or a sodium b-aminoketonate (formed in situ) in a 1 : 2 ratio or greater leads to the formation of the bis(ligand) complexes [Zr(R1NCR2]] CHCR3]] O)2Cl2] (Scheme 2).The pale yellow, moisture-sensitive zirconium complexes 9–13 are generally stable at room temperature or below and soluble in polar, non-protic organic solvents. N-Alkyl-substituted complexes are significantly less stable in solution than the N-aryl-substituted complexes with 10–15% decomposition of 13 in CD2Cl2 at room temperature in 24 h.No change was seen for a solution of 11 over a similar time-frame. Variable-temperature 1H and 13C NMR studies indicate that the b-aminoketonate ligands in bis(ligand) complexes are bonded through nitrogen and oxygen with no line broadening apparent for the backbone methyl groups up to 40 8C in CD2Cl2, indicating no observable ligand hemilability at these temperatures (Table 2).The complexes contain a delocalised chelate ring as indicated by the similar shifts of the amino and carbonyl carbons (dC 175.5 and 174.3), which are widely separated for the free aminoketones. The aminophenyl group in 11 displays restricted movement, with Scheme 2 M = Zr or Ti M O N O Cl N Cl R1 R1 MCl4 + 2KL – 2KCl [M( p-MeOC6H4NCMe CHCMe O)2Cl2 M = Zr 10; Ti 14 CHCR3 L = R1NCR2 O [Zr( p-MeOC6H4NCMe CHCMe O)2Cl2] 9 [M(PhNCMe CHCMe O)2Cl2 M = Zr 11; Ti 15 [Zr( p-MeOC6H4NCMe CHCCF3 O)2Cl2] 12 [Zr(PriNCMe CHCMe O)2Cl2] 13 CHCH2)CMe CHCMe O}2Cl2] 16 [Ti{(CH2 a broad resonance for the m-proton (dH 7.34) and split broad resonances for the o-protons (dH 6.66 and 7.20).The peaks resolve and sharpen with decreasing temperature [Fig. 1(a)]. The variable-temperature 13C NMR spectra show similar changes [Fig. 1(b)]. All bis(ligand) complexes isolated to date show similar restricted movement of the aminohydrocarbyl unit. The NMR spectra display temperature-dependent splitting of phenyl resonances or separate environments for alkylsubstituted b-aminoketones.The underlying cause of the NMR splitting is thought to be due to the preferred cis-nitrogen/transoxygen configuration of the complexes as will be discussed in the next section. The dark red, moisture-sensitive bis(ligand) titanium complexes 14–16 are in general less stable than their zirconium analogues. The Pri-substituted complex could not be isolated. Although these titanium complexes also show temperaturedependent NMR spectra the variation is significantly less than for the analogous zirconium complexes 9–13 with little evidence for peak coalescence on warming to room temperature.This can be explained by the smaller titanium atom effectively limiting the free rotation of the ligand substituents, even at higher temperatures. The NMR data indicate that the titanium complexes have similar structures to those of the zirconium complexes.Solid-state structures of ZrCl4?2PriHNCMe]] CHCMe]] O, TiCl4?2PriHNCMe]] CHCMe]] O and [Zr(PhNCMe]] CHCMe]] O)2Cl2] The unusual nature of the adducts formed from the direct Fig. 1 Variable-temperature 1H (a) and 13C (b) NMR spectra of complex 11260 J. Chem. Soc., Dalton Trans., 1998, Pages 255–262 Table 3 Selected ligand bond lengths for 1, 6 and 11 and related complexes Complex 1 6 11 [Zr(acen)Cl2] [Zr(msal)2Cl2] [Ti(h-C5H5)3L]1a [Pd(h-C3H4Me)- (PhCH2CH2NCMe]] CHCMe]] O)]2 b O]C(1) 1.303(2) 1.318(3) 1.323(6), 1.320(6) 1.318(5), 1.329(6) 1.349(8) 1.266(13) 1.34(2) C(1)]C(2) 1.363(3) 1.357(3) 1.337(7), 1.348(7) 1.359(7), 1.334(9) 1.38(1) 1.342(17) 1.38(2) C(2)]C(3) 1.418(3) 1.449(3) 1.430(7), 1.412(7) 1.429(7), 1.421(8) 1.468(10) 1.431(18) 1.51(3) C(3)]N 1.310(3) 1.323(3) 1.321(5), 1.331(6) 1.319(6), 1.317(7) 1.305(9) 1.271(15) 1.28(3) a L = 2,4,6-Me3C6H2NCMe]] CHCMe]] O.18 b Ref. 22. Table 4 Selected geometries (distances in Å, angles in 8) for complexes 1 and 6.The two values in each entry are for M = Zr, Ti respectively M]Cl(1) M]Cl(2) M]O O]C(1) C(1)]C(2) C(2)]C(3) C(3)]N N]H H? ? ? O 2.468(1), 2.3726(9) 2.464(1), 2.378(1) 2.052(1), 1.916(2) 1.303(2), 1.318(3) 1.363(3), 1.357(3) 1.418(3), 1.449(3) 1.310(3), 1.323(3) 0.84(3), 0.77(3) 2.05(4), 2.19(2) Cl(1)]M]Cl(2) Cl(1)]M]O Cl(2)]M]O M]O]C(1) O]C(1)]C(2) C(1)]C(2)]C(3) C(2)]C(3)]N C(3)]N]H N]H? ? ? O 90.20(2), 91.10(4) 87.98(4), 88.77(6) 92.02(5), 90.87(6) 154.72(13), 153.4(1) 122.2(2), 120.9(2) 126.8(2), 127.0(2) 122.9(2), 123.5(2) 111(2), 117(2) 141(3), 133(3) reaction of MCl4 (M = Zr or Ti) with b-aminoketones led us to investigate in detail the structures of these compounds. Crystals of the isostructural complexes 1 and 6 suitable for structure determination were grown by slow cooling of a saturated CH2Cl2 solution or from a CH2Cl2 solution layered with hexane, respectively.Selected bond distances and angles are presented in Tables 3 and 4 and the structure of the zirconium complex 1 is shown in Fig. 2. The structure shows the oxygen donors of the N]O ligands co-ordinated in trans positions. A significant rearrangement of electron density in the ligand is apparent to give what could be called an immonium enolate structure in the solid state. The N]C(3) bond lengths in 1 and 6 (Table 4) approach that of a C]N double bond (ca. 1.30 Å). The C(1)]C(2) bonds are notably shorter than a normal C]C single bond (ca. 1.53 Å) and therefore can be considered to have appreciable olefinic character, whereas the O]C(1) bonds are considerably longer than expected for a C]O double bond (ca. 1.19 Å). The ligand amine hydrogens for 1 and 6 have been refined isotropically and are clearly associated with the nitrogen atom. They form intramolecular hydrogen bonds to the ligand oxygens with the following geometries: 1, N]H 0.84(3), O ? ? ?H 2.05(4) Å, N]H? ? ? O 141(3)8; 6, N]H 0.77(3), O ? ? ? H 2.19(2) Fig. 2 A PLATON plot23 of complex 1 with 30% probability ellipsoids; the carbon-bonded hydrogens have been omitted for clarity. Primed atoms are related to unprimed ones by the symmetry operation 2x, 2y, 2z Å, N]H? ? ? O 133(3)8. A less intimate association is found with Cl(1). This structure is maintained in solution as indicated by the splitting pattern of the NPri methine in the 1H NMR spectrum (doublet of septets). The strength of the N]H? ? ?O intramolecular hydrogen bond and hence the ease or difficulty of deprotonation in adducts of type 1 appears to be an important feature of the catalytic behaviour of these compounds. It is apparent that the catalyst species formed during activation (and hence the product distribution obtained) depends on whether deprotonation occurs or not.The behaviour of catalyst systems generated from these compounds will be discussed in detail in a later publication. Crystals of complex 11, suitable for structural analysis, were obtained by slow cooling of a saturated toluene–CH2Cl2 solution.The structure is shown in Fig. 3 with relevant crystallographic data collected in Tables 3 and 5. The monomeric complex contains zirconium in a slightly distorted octahedral Fig. 3 Projection of a molecule of complex 11; 20% thermal ellipsoids are shown for the non-hydrogen atoms, hydrogen atoms having arbitrary radii of 0.1 ÅJ. Chem. Soc., Dalton Trans., 1998, Pages 255–262 261 Table 5 Selected bond lengths (Å) and angles (8) for complex 11. Where two entries are given they are for segments n = 1, 2 respectively.Primed atoms lie in the alternate segment Zr]Cl(n) Zr]N(n) Zr]O(n) N(1)]Zr]N(2) O(1)]Zr]O(2) Cl(1)]Zr]Cl(2) Cl(n)]Zr]N(n) Cl(n)]Zr]O(n) N(n)]Zr]O(n) Cl(n)]Zr]N(n9) 2.432(2), 2.421(2) 2.312(3), 2.299(3) 2.007(3), 2.012(3) 86.0(1) 165.1(1) 95.58(6) 89.6(1), 90.5(1) 97.41(9), 97.64(9) 77.1(1), 77.6(1) 168.87(9), 169.04(9) O(n1)]C(n1) C(n1)]C(n2) C(n2)]C(n3) C(n3)]N(n) Cl(n)]Zr]O(n9) N(n)]Zr]O(n9) Zr]O(n)]C(n1) O(n)]C(n1)]C(n2) C(n1)]C(n2)]C(n3) C(n2)]C(n3)]N(n) C(n3)]N(n)]Zr 1.323(6), 1.320(6) 1.337(7), 1.348(6) 1.430(7), 1.412(7) 1.321(5), 1.331(6) 92.34(9), 92.6(1) 91.7(1), 91.6(1) 142.3(3), 141.6(3) 122.4(4), 122.3(4) 125.2(4), 125.5(4) 123.1(4), 123.3(4) 129.8(3), 129.4(3) environment in which the oxygen atoms are trans to each other while the nitrogen atoms are cis, presumably due to unfavourable steric interactions between the amino-substituent and the carbonyl methyl of the second ligand if the nitrogen atoms were trans.In this orientation the aminophenyl substituent can align approximately parallel with the chelate ring formed by the second ligand, but being offset (interplanar dihedral angles are shown in Table 6), thereby bringing one o-carbon in line with the centre of the chelate ring (H ? ? ? chelate plane distance ª2.8, H? ? ? O ª3.4 and H ? ? ? N ª3.2 Å; see Fig. 4) while the other approaches one of the chlorides leading to significantly different environments for the two ortho protons.The variabletemperature NMR data indicate that this structure is maintained in solution although the degree of association is unknown. Deprotonation of the b-aminoketone in adducts of type 1 to form the ligand chelate in complexes such as 11 is accompanied by an electronic redistribution. The C]N and C]O bond lengths increase slightly for 11 compared with 1 and the C(1)]C(2) carbon double bond is shortened but an ene–imine structure is assigned (Table 3).As expected the M]Cl and M]O distances are shorter in 11 than in 1. In the similar cationic titanium complex the C]O and C]N distances are considerably shorter, presumably due to the higher Lewis acidity of the cationic titanium centre. This may be compared with the palladium complex [Pd(h-C3H4Me)(PhCH2CH2- NCMe]] CHCMe]] O)] in which an ene–imine structure is an appropriate description.22 Related acen (2OCMe]] CHCMe]] NCH2CH2N]] CMeCH]] CMeO2) zirconium complexes have shorter M]N bond lengths than those of 11 (presumably due to constraints imposed by the Fig. 4 Positioning of the o-proton of the phenyl ring attached to the nitrogen of one b-aminoketone ligand in relation to the plane of the second ligand Zr O(2) N(2) a = 3.4 Å N(1) H b = 3.2 Å a b Table 6 Interplanar dihedral angles (8) for complex 11 where L1, P1 and L2, P2 are the planes formed by the ligand chelate ring and phenyl ring for ligands 1 and 2 respectively L2 P1 P2 L1 83.0(1) 88.3(2) 27.6(2) L2 24.3(1) 88.6(2) P1 85.8(2) acen ligand) while the M]O distances are roughly equivalent (Table 4), and the M]Cl bonds are even longer than those in 1.The M]N and M]O bond lengths in 11 are closer to those for [Zr(msal)2Cl2] indicating a closer affinity with the ene–imine structure in the solid state.2 Conclusion In situ mixtures of Group 4 metal chlorides (TiCl4 and ZrCl4), b-aminoketones and an alkylaluminium cocatalyst generate exciting new catalysts for the oligomerisation of ethylene.To furnish information about the possible nature of the active species we have synthesized likely catalyst precursers formed by the addition of b-aminoketones to MCl4. The adduct compounds formed initially (1–8) are unusual species involving monodentate co-ordination through the ligand oxygen atom with the oxygens in trans positions. Reaction of MCl4 with the b-aminoketonate anion leads to formation of bis(ligand) complexes [M(N]O)2Cl2 9–16] in which the b-aminoketonate is now chelating through the oxygen and nitrogen atoms.Deprotonation of b-aminoketones may be achieved with strong bases, or in some instances under catalytic conditions at higher temperatures. In the complexes the (N]O)2 ligands are so arranged that the remaining chloride ligands on the metal centre are in cis positions, ideally placed for activation of the complexes for catalysis. It has been found that the bis(ligand) complexes give rise to very active oligomerisation catalysts on treatment with suitable cocatalysts.Details of the catalytic behaviour of the various systems will be reported in a forthcoming publication. Acknowledgements We would like to thank ICI (Australia) and the Australian Research Council for their support and for Australian Postgraduate Research Awards (Industry) for D. J. and A. R. The financial support provided by the Australian Department of Industry, Science and Tourism (DIST, formerly DITAC) is acknowledged. Staff of the Central Science Laboratory of Tasmania are also gratefully acknowledged for their assistance in obtaining and interpreting spectroscopic data. References 1 R. C. Fay, in Comprehensive Coordination Chemistry, The Synthesis, Reactions, Properties and Applications of Coordination Compounds, eds. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon, Exeter, 1st edn., 1987, vol. 3, pp. 32, 363–451. 2 F. Corazza, E. Solari, C. Floriani, A. Chiesi-Villa and C. Guastini, J. Chem. Soc., Dalton Trans., 1990, 1335. 3 E. B. Tjaden, D. C. Swenson, R. F. Jordan and J. L. Petersen, Organometallics, 1995, 14, 371. 4 C. Floriani, Polyhedron, 1989, 8, 1717. 5 M. Mazzanti, J. M. Rosset, C. Floriani, A. Chiesi-Villa and C. Guastini, J. Chem. Soc., Dalton Trans., 1989, 953. 6 J. M. Rosset, C. Floriani, M. Mazzanti, A. Chiesi-Villa and C. Guastini, Inorg. Chem., 1990, 29, 3991.262 J. Chem. Soc., Dalton Trans., 1998, Pages 255–262 7 D. G. Black, D. C. Swenson, R. F. Jordan and R. D. Rogers, Organometallics, 1995, 14, 3539. 8 G. Dellamico, F. Marchetti and C. Floriani, J. Chem. Soc., Dalton Trans., 1982, 2197. 9 E. Solari, C. Floriani, A. Chiesi-Villa and C. Rizzoli, J. Chem. Soc., Dalton Trans., 1992, 367. 10 D. J. Jones, K. J. Cavell and W. Keim, unpublished work. 11 D. J. Jones, K. J. Cavell and W. Keim, Aust. Prov. Pat., PO 4397, 1996. 12 M. Peukert and W. Keim, Organometallics, 1983, 2, 594. 13 B. Reuben and H. Wittcoff, J. Chem. Educ., 1988, 65, 605. 14 A. Behr and W. Keim, Arab. J. Sci. Eng., 1985, 10, 377. 15 K. Robards, E. Patsalides and S. Dilli, J. Chromatogr., 1987, 411, 1. 16 G. W. Everett, jun. and R. H. Holm, J. Am. Chem. Soc., 1965, 87, 2117. 17 G. O. Dudek and R. H. Holm, J. Am. Chem. Soc., 1962, 84, 2961. 18 P. Veya, C. Floriani, A. Chiesi-Villa and C. Rizzoli, Organometallics, 1993, 12, 4892. 19 D. F. Martin, G. A. Janusonis and B. B. Martin, J. Am. Chem. Soc., 1961, 83, 73. 20 H. K. Shin, M. J. Hampden-Smith, T. T. Kodas and A. L. Rheingold, J. Chem. Soc., Chem. Commun., 1992, 217. 21 L. E. Manzer, Inorg. Synth., 1982, 21, 135. 22 R. Claverini, P. Ganis and C. Pedone, J. Organomet. Chem., 1973, 50, 327. 23 A. L. P.-Ù. Spek, PLATON, University of Utrecht, 1994. Received 14th October 1997; Paper 7/07422K

ISSN:1477-9226    

DOI:10.1039/a707422k

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 257–261 257 Carbonyl dibromide: a novel reagent for the synthesis of metal bromides and bromide oxides † Michael J. Parkington,a T. Anthony Ryan b and Kenneth R. Seddon *,c a School of Chemistry and Molecular Sciences, University of Sussex, Falmer, Brighton BN1 9QJ, UK b ICI Chemicals and Polymers Ltd., The Heath, Runcorn, Cheshire WA7 4QD, UK c School of Chemistry, The Queen’s University of Belfast, Stranmillis Road, Belfast BT9 5AG, UK Carbonyl dibromide reacted with a wide selection of d- and f-block transition-metal oxides to form either the metal bromide or bromide oxide; the reactions are driven by the elimination of carbon dioxide.In a typical reaction the metal oxide was treated with an eight-fold excess of COBr2 in a sealed Carius tube at 125 8C for 10 d (to ensure complete reaction of the metal oxide). As COBr2 and the reaction by-products (CO2, CO and Br2) are all volatile, the desired products were obtained in essentially quantitative yield and a high degree of purity.Under these conditions V2O5, MoO2, Re2O7, Sm2O3 and UO3 were converted into VOBr2, MoO2Br2, ReOBr4, SmBr3 and UOBr3, respectively. This route offers great potential for the preparation of many known bromide derivatives of the transition metals, lanthanides and actinides, in a very convenient manner, and also for the synthesis of new materials. A modified synthesis of carbonyl dibromide was elaborated, and its 17O NMR and electron impact mass spectra are reported for the first time.Although the routes to pure anhydrous metal chlorides are well established, versatile, and generally convenient,1–3 the analogous routes to metal bromides and bromide oxides are poorly explored.1–3 When appropriate, they can best be prepared by reaction of the element with either dibromine, e.g. equation (1),4 2V + 3Br2 400 8C 2VBr3 (1) or hydrogen bromide, equation (2),5 by bromination of the Cr + 2HBr 750 8C CrBr2 + H2 (2) metal oxide with Br2,6,7 BBr3,8 AlBr3,9 CBr4,10,11 or SOBr2,12 or by halide exchange with HBr13 or BBr3.14 In addition, less general routes include the reduction of high-oxidation-state bromides with the appropriate metal (aluminium or dihydrogen are alternative reductants in some cases),1,2 e.g.equation (3),15 or by 3HfBr4 + Hf 500 8C 4HfBr3 (3) thermal disproportionation, equation (4),15,16 or thermal 2ZrBr3 350 8C ZrBr4 + ZrBr2 (4) decomposition, equation (5),17 of a higher-oxidation-state 2OsBr4 350 8C 2OsBr3 + Br2 (5) binary bromide.Metal-vapour synthesis has also been used to synthesize metal bromides:18 thus co-condensation of rhenium atoms with 1,2-dibromoethane (followed by extraction with tetrahydrofuran, thf) gave [Re3Br9(thf)3]. As is apparent, there is no satisfactory general route to metal bromides and bromide oxides. The two main problems appear to be: (a) many of the synthetic routes require severe experi- * E-Mail: k.seddon@qub.ac.uk WWW: http://www.ch.qub.ac.uk/krs/ krs.html † Non-SI unit employed: mB ª 9.27 × 10224 J T21.mental conditions, and (b) alternative syntheses, performed under milder conditions, frequently lead to product contamination, the contaminant often being extremely difficult to remove (see below). Metal chlorides have long been prepared by treating metal oxides with phosgene, COCl2, equation (6).19 These syntheses MxOy + yCOCl2 æÆ xMCl2y/x + yCO2 (6) are not only clean, high yielding, and performed under mild conditions, but also provide the basis of many patents (e.g.for dealuminating zeolites).20,21 It was somewhat surprising, therefore, that the analogous routes to metal bromides using carbonyl dibromide had not been investigated. The only report in the literature of a reaction between a metal oxide and COBr2 is by Prigent,22 who proposed that heating UO3 with COBr2 in a sealed tube for 2 h at 126 8C produced uranium(V) bromide.In our hands, and those of others,23 however, these observations were unrepeatable. Indeed, as uranium(V) bromide decomposes above 80 8C24 it would have been a very surprising result. We report here on the reaction between a wide range of metal oxides with carbonyl dibromide, which offers great potential for the preparation of many known bromide derivatives of the transition metals, lanthanides and actinides, in a very convenient manner, and for the synthesis of new materials.Preliminary observations on this system have been reported previously in a communication 25 and patent applications.26,27 Experimental CAUTION: The physiological effects of carbonyl dibromide were judged (as a result of some rather amateur experiments on white mice) similar to those of phosgene,28 but clearly a modern detailed evaluation is required if COBr2 is to be used more widely. The following safety precautions were adopted on the assumption that its toxicity is similar to that of phosgene.Handling carbonyl dibromide Phosgene is a toxic gas, with a permissable UK Occupational Exposure Limit (OEL) of 0.08 mg m23 of air (0.02 ppm v/v).29 In the event of exposure, the victim may experience chest pain,258 J. Chem. Soc., Dalton Trans., 1997, Pages 257–261 coughing and rapid breathing associated with pulmonary œdema, and it may take over 24 h for symptoms to appear. There is no antidote to phosgene poisoning,19 and hence treatment is usually directed to the main symptom, toxic pulmonary œdema.30 Hence, all manipulations involving carbonyl dibromide were carried out in a well ventilated fume cupboard with a face velocity of >0.75 m s21, and in the presence of at least one other experienced research worker.The vacuum line was constructed within the fume cupboard. The atmosphere both inside and outside the fume cupboard was constantly checked using Dräger tubes 31 and detector tape (Rimon Laboratories Ltd.).All glassware used greaseless taps, and joints were lubricated with Teflon sleeves. After use, carbonyl dibromide was destroyed by passage through a column containing moist activated charcoal. The fume cupboard was fitted with an alarm system, which was activated automatically if the extractor mechanism failed, or manually in the event of an accident. After use all equipment was washed with an aqueous solution of sodium hydroxide before removal from the fume cupboard.Spectroscopic measurements Carbon-13 and 17O NMR spectra were recorded on a Bruker WM360 spectrometer operating at 90.55 and 48.82 MHz, respectively. The 13C and 17O chemical shifts were measured with respect to external tetramethylsilane and water, respectively. Mass spectra were recorded on a Kratos MS80RF spectrometer, and infrared spectra on a Perkin-Elmer 598 spectrometer. Gas-phase infrared spectra were recorded using a 10 cm gas cell fitted with CsI windows, those of solids were recorded as Nujol mulls, using CsI plates.All spectra were calibrated using polystyrene (1601 and 907 cm21) and indene (551.7 and 420.5 cm21). Magnetic susceptibilities were measured at room temperature on a Johnson Matthey magnetic susceptibility balance. Preparation of carbonyl dibromide Concentrated sulfuric acid (20 cm3) was slowly added to molten tetrabromomethane (20 g, 60 mmol) at ca. 90 8C. The reaction vessel, which was connected to a conventional distillation unit, fitted with a high-surface-area trap, was then heated to 150–170 8C for 2 h.The products were collected, as the reaction proceeded, in a 210 8C trap. The deep red impure distillate was then transferred quickly to a vacuum line, held at 295 8C and continuously evacuated for 1 h to remove the small amounts of SO2 present. To remove the considerable quantities of free dibromine, the product was condensed into an ampoule (fitted with a greaseless tap) containing mercury, and allowed to warm to room temperature.The ampoule was then closed, removed from the vacuum line, and vigorously (but carefully) agitated within the fume cupboard for 5 min. It was then reconnected to the vacuum line, and the liquid was distilled into a storage bulb. The colourless liquid was redistilled into an ampoule fitted with a greaseless tap, and then stored at room temperature in the absence of light. The purity of the product was checked by gasphase infrared,13C and 17O NMR and mass spectrometry.Yield (based on CBr4): 5.8 g (51%). Preparations of metal bromides and metal bromide oxides The procedure for performing the reaction of UO3 with COBr2, and the subsequent isolation of the product, UOBr3, is described in detail. Exactly the same experimental procedures were followed for the other reactions. All reactions were performed at 125 8C for 10 d and in all cases free dibromine was observed during them. Uranium(V) tribromide oxide.Carbonyl dibromide (0.9 g, 4.84 mmol) was condensed into a Carius tube containing uranium( VI) oxide (0.18 g, 0.63 mmol), which was then sealed in vacuo and heated at 125 8C for 10 d. After this time the Carius tube was cooled to 295 8C, and the top (which had been carefully scored with a glass knife) fitted with Portex tubing (which was attached to a ground-glass joint). The Carius tube was then connected to a high-vacuum line, opened carefully and, after removal of the excess of COBr2 and gaseous reaction products, isolated, removed from the high-vacuum line, and taken into an inert-atmosphere dry-box where the contents were transferred into a Schlenk tube.The black powder was subsequently identified as uranium(V) tribromide oxide by bromide analysis (Found: Br, 50.05. Calc. for Br3OU: Br, 48.9%), magnetic measurements [cg = 4.07 × 1028 m3 kg21, meff (296 K) = 2.04 mB], and infrared spectroscopy [960m (br), 812m, 607w, 473m (br), 339s (br) and 281m cm21].Yield (based on UO3): 0.28 g (90%). Samarium(III) bromide. Reaction of carbonyl dibromide (0.95 g, 5.05 mmol) and samarium(III) oxide (0.23 g, 0.66 mmol) at 125 8C for 10 d gave a pale yellow powder which was shown to be samarium(III) bromide by bromide analysis (Found: Br, 61.1. Calc. for Br3Sm: Br, 61.45%), magnetic measurements [cg = 3.29 × 1028 m3 kg21, meff (294 K) = 1.64 mB] and infrared spectroscopy. Yield (based on Sm2O3): 0.47 g (92%). Rhenium(VI) tetrabromide oxide.Reaction of carbonyl dibromide (0.91, 4.84 mmol) and rhenium(VII) oxide (0.31 g, 0.65 mmol) at 125 8C for 10 d gave a deep blue-black solid which was shown to be rhenium(VI) tetrabromide oxide by bromide analysis (Found: Br, 60.3. Calc. for Br4ORe: Br, 61.25%), magnetic measurements [cg = 2.58 × 1028 m3 kg21, meff (296 K) = 1.71 mB], infrared spectroscopy (1003s and 239s cm21), and mass spectrometry {m/z 522 ([ReOBr4]+, 46), 314 ([ReO3Br]+, 64), 283 ([ReOBr]+, 37), 235 ([ReO3]+, 40), 187 (Re+, 58), 160 (Br2 +, 100) and 81 (Br+, 64%)}.Yield (based on Re2O7): 0.59 g (88%). Molybdenum(VI) dibromide dioxide. Reaction of carbonyl dibromide (1.03 g, 5.48 mmol) and molybdenum(IV) oxide (0.09 g, 0.70 mmol) at 125 8C for 10 d gave purple-brown crystals which were shown to be molybdenum(VI) dibromide dioxide by bromide analysis (Found: Br, 56.4. Calc. for Br2MoO2: Br, 55.5%), magnetic measurements (cg = 23.90 × 1028 m3 kg21), infrared spectroscopy [846s (br), 759s (br), 391w, 366w, 340m, 325m, 298m and 261w cm21], and mass spectrometry {m/z: 209 ([MoO2Br]+, 82), 193 ([MoOBr]+, 46), 177 ([MoBr]+, 30), 160 (Br2 +, 15), 130 ([MoO2]+, 12), 114 ([MoO]+, 22), 98 (Mo+, 36) and 79 (Br+, 100%)}. Yield (based on MoO2): 0.18 g (87%).Vanadium(IV) dibromide oxide. Reaction of carbonyl dibromide (0.98 g, 5.21 mmol) and vanadium(V) oxide (0.13 g, 0.71 mmol) at 125 8C for 10 d gave olive-brown leaflets which were shown to be vanadium(IV) dibromide oxide by bromide analysis (Found: Br, 69.7.Calc. for Br2OV: Br, 70.5%), magnetic measurements [cg = 5.34 × 1028 m3 kg21, meff (293 K) = 1.57 mB], and infrared spectroscopy [881s (br), 361m, 290s and 238s cm21]. Yield (based on V2O5): 0.30 g (92%). Results and Discussion Carbonyl dibromide The early attempts 32–37 to prepare COBr2, and the claims and counterclaims of success and failure, are summarized elsewhere. 19 By 1906, von Bartal 34 had demonstrated that COBr2 could be prepared in 50–60% yield by the oxidation of CBr4 with concentrated sulfuric acid at 150–170 8C, equations (7) and (8), although oleum is too vigorous a reagent, oxidizing the CBr4 + H2SO4 150–170 8C COBr2 + 2HBr + SO3 (7) 2HBr + SO3 æÆ SO2 + H2O + Br2 (8)J.Chem. Soc., Dalton Trans., 1997, Pages 257–261 259 CBr4 through to CO2 and Br2. By the nature of all the known synthetic routes, COBr2 is always produced contaminated with elemental bromine, and von Bartal 34 proposed a two-step puri- fication technique. Crude COBr2 is initially shaken with mercury at 0 8C, and then distilled, collecting the 62–65 8C fraction.This distillate is then treated with powdered antimony, and redistilled to yield colourless COBr2. If the first stage of the reaction with mercury is omitted the reaction with antimony is too vigorous, and some COBr2 is lost through decomposition. Slight modifications of this procedure were later published by Schumacher and Lenher,28 and this has become the most commonly used procedure.38 The procedures used here are derived from von Bartal’s preparation,34 followed by Schumacher and Lenher’s purification, 28 but they differ in some significant details (especially in the procedure for the removal of Br2).The antimony step has been eliminated, as the heat generated was observed to cause decomposition of the carbonyl dibromide. The infrared spectrum of gaseous COBr2 did not differ significantly from that reported elsewhere,38 and showed no detectable traces of CO2, CO, COCl2 or COBrCl. The 13C and 17O NMR spectra (in CD2Cl2 at 250 8C) of COBr2 gave chemical shifts at d 106.9 and 549.2, respectively [cf.d(C) 103.4 in CCl3F],39,40 and its mass spectrum (Table 1) is discussed in the preceding paper.41 These data highlight the purity of the product produced. The pure COBr2 was stored in the dark, since it was found that, in the presence of light, the colourless liquid became straw-coloured within 1 d due to decomposition to carbon monoxide and dibromine, equation (9).Over a prolonged COBr2 CO + Br2 (9) period this would result in a hazardous build-up of pressure in the storage vessel. Reactions of carbonyl dibromide with metal oxides The yields of the metal-containing products from the reactions of UO3, Sm2O3, Re2O7, MoO2, or V2O5 with COBr2 at 125 8C were all greater than 87%, and it can be assumed that, neglecting manipulative losses, conversion of the oxide was essentially quantitative.Attempted reactions with WO3, PbO2, Al2O3 and CaO led to incomplete reaction, products being heavily contaminated with unreacted metal oxide; as convenient syntheses of the desired products already existed, the use of alternative reaction conditions was not explored, although the reaction with WO3 had clearly produced significant amounts of WO2Br2. Although free Br2 was observed in all the reactions, its presence can give no information concerning the stoichiometry of the reactions, since pure COBr2, if heated to 125 8C, undergoes some dissociation to CO and Br2, equation (9).28 The presence of Br2 raises the possibility of the formation of [Br3]2; however, the satisfactory bromide analyses together with the appropriate magnetic moments mean that [Br3]2 contamination of the product can be safely discounted.Uranium(V) tribromide oxide. The reaction of UO3 and COBr2 at 125 8C gave UOBr3, as a black powder, presumably Table 1 Mass spectral data for COBr2 m/z Relative intensity Assignment 190, 188, 186 162, 160, 158 109, 107 93, 91 81, 79 28 — 37 100 12 86 4 M+ [Br2]+ [COBr] + [CBr] + Br + [CO] + according to equation (10).Unfortunately, the colour of UOBr3 2UO3 + 4COBr2 125 8C 2UOBr3 + 4CO2 + Br2 (10) is not reported in the literature, nor are there any reports of its magnetic moment or infrared spectrum. The effective magnetic moment of 2.04 mB (at 296 K) reported here is similar to values obtained for other uranium(V) compounds, e.g.UO2Cl [meff (295 K) = 1.86 mB]42 and UCl5 [meff (300 K) = 2.00 mB].43 The infrared spectrum of UOCl3 has been reported twice (1000–450 cm21 only),44,45 with the bands at 965, 845, 615 and 450 cm21 analogous to the bands at 960, 812, 607 and 473 cm21 for UOBr3. Attempts to record the electron impact (EI) mass spectrum of UOBr3 were unsuccessful due to its involatility, and the positive-ion fast-atom bombardment (FAB) technique failed to give a spectrum due to reaction of the UOBr3 with the matrix.Interestingly, the proposal by Russian workers 46 that UOBr3 slowly evolved Br2 at room temperature was not vindicated. The only reproducible synthesis of UOBr3 in the literature is by Prigent,10 who heated UO3 in a stream of N2 and CBr4 vapour at 110 8C. It has been reported, also by Prigent,22,47 that reaction of UO3 and COBr2 in a sealed tube at 126 8C (i.e. the same conditions as used here) gave UBr5, although attempts to repeat this by other workers have been unsuccessful.23 Furthermore, work by Blair and Ihle 24 has shown that UBr5 readily decomposes at >80 8C, and hence Prigent’s claim 22,47 to have prepared UBr5 must be regarded as incorrect.It was hoped that performing the reaction of UO3 and COBr2 at a lower temperature, viz. 70 8C, might give a different product (perhaps even UBr5); unfortunately, under these milder conditions, no reaction occurred.Samarium(III) bromide. The reaction of Sm2O3 and COBr2 at 125 8C gave SmBr3, as a pale yellow powder (the same colour as reported in the literature),3 presumably according to equation (11). The effective magnetic moment of 1.64 mB (at 294 K) was in Sm2O3 + 3COBr2 125 8C 2SmBr3 + 3CO2 (11) reasonable agreement with the 1.51 mB (at 293 K) obtained by Selwood.48 The infrared spectrum showed no bands in the range 1000–200 cm21, indicating the absence of Sm2O3 and SmOBr.The existing syntheses of anhydrous SmBr3 involve either dehydration of SmBr3?6H2O in the presence of HBr at high temperature (>640 8C),49 or reaction of Sm2O3 and NH4Br, again at high temperature.50–52 The synthesis reported here required less severe conditions, and more importantly did not produce unwanted SmBr2 and SmOBr, the latter being a frequent contaminant when synthesizing SmBr3 from SmBr3? 6H2O.3,53 Rhenium(VI) tetrabromide oxide. The reaction of Re2O7 and COBr2 at 125 8C gave ReOBr4, as a deep blue-black solid (the same colour as reported in the literature 54,55), presumably according to equation (12).The effective magnetic moment of Re2O7 + 5COBr2 125 8C 2ReOBr4 + 5CO2 + Br2 (12) 1.71 mB (at 296 K) and infrared spectral bands at 1003s and 239s cm21 were in reasonable agreement with those reported by Edwards and Ward [meff = 1.80 ± 0.1 mB (at 294 K), infrared bands at 1005s, 364m and 242s cm21],55 although they report a band at 364 cm21 in their infrared spectrum which was not observed here.The previously unrecorded mass spectrum of ReOBr4 shows a strong molecular ion. The most recent synthesis of ReOBr4 was by the reaction of rhenium metal, Br2 and SO2 in a sealed tube at 400 8C:55 the preparation reported here was performed under far milder conditions.260 J. Chem. Soc., Dalton Trans., 1997, Pages 257–261 Molybdenum(VI) dibromide dioxide. The reaction of MoO2 and COBr2 at 125 8C gave MoO2Br2, as purple-brown crystals (the same colour as reported in the literature),2 presumably according to equation (13).The diamagnetism of the product is MoO2 + COBr2 125 8C MoO2Br2 + CO (13) consistent with a d0 molybdenum(VI) compound. The infrared and mass spectra were in good agreement with those reported by Barraclough and Stals,56 the only significant difference being the absence of the molecular ion in the mass spectrum reported here. This compound is usually prepared by passing a mixture of O2 and Br2, diluted with N2, over the metal at 300 8C.57 The method reported here was performed under milder conditions, and may be considered a more accessible synthesis.Vanadium(IV) dibromide oxide. The reaction of V2O5 and COBr2 at 125 8C gave VOBr2, as olive-brown leaflets (the same colour as reported in the literature),6,58 presumably according to equation (14). The magnetic moment of 1.57 mB (at 293 K) was V2O5 + 3COBr2 125 8C 2VOBr2 + 3CO2 + Br2 (14) reasonable for a d1 halide oxide with an extended lattice.The infrared spectrum was in very good agreement with that reported by Dehnicke 6 [bands at 871s (br), 360m and 293m cm21], although he did not report the spectrum below 250 cm21 and thus did not observe the band at 238 cm21. There are several syntheses of VOBr2 reported in the literature, 1,58 the two most widely used being bromination of V2O3 at 600 8C in a flow system 6 and thermal decomposition of VOBr3 at 180 8C.59 The synthesis employed here has an obvious advantage over the bromination reaction, and is also preferable to the alternative method, since synthesis of VOBr3 is itself not trivial.1,58 Thermodynamic comparison of brominating agents The thermodynamics of the reactions of EBr3 (E = B or Al), CBr4 and EOBr2 (E = S or C) with metal oxides [equations (15)–(17)], derived from the JANAF Thermochemical Tables 60 3M2On + 2(n22)EBr3 æÆ 6MOBrn22 + (n22)E2O3 (15) M2On + (n 2 2)CBr4 æÆ 2MOBrn22 + (n22)COBr2 (16) M2On + (n22)EOBr2 æÆ 2MOBrn22 + (n22)EO2 (17) and the NBS Tables,61 are compared in Table 2.As the metal oxide, M2On, and metal-containing product, MOBrn22, are assumed to be the same in each case, only the differences in free energy of formation, DGdiff (and enthalpy of formation, DHdiff) of the brominating agent and the product derived from the brominating agent are listed, expressed per mol of MOBrn22 formed. Dibromine was not included in this table since no thermodynamic data were available for Br2O (the ‘expected’ byproduct of the reaction of Br2 with metal oxides).However, as Br2O is unstable above 240 8C62 it is unlikely to provide a significant thermodynamic driving force, and this is reflected in the observation that conversion of metal oxides into metal bromide oxides using Br2 often requires the use of very high temperatures and/or the presence of reducing agents.1–3 Thermodynamically, SOBr2 (which decomposes above 80 8C)12 and CBr4 are the poorest brominating agents listed in Table 2 and, not surprisingly, are rarely used in this way (cf.CCl4, which is a significantly better halogenating agent, and is commonly used in the synthesis of metal chlorides and chloride oxides 1–3). The remaining brominating agents listed in Table 2, BBr3, AlBr3 and COBr2, are all thermodynamically excellent, with COBr2 being the best. The driving force for the first two reactions is the large enthalpy of formation of the extended solids B2O3 and Al2O3, respectively, whilst for COBr2 both the enthalpy of formation of CO2 and the concomitant favourable increase in entropy provides a significant part of the driving force.However, although BBr3 and AlBr3 are thermodynamically excellent brominating agents, the generation of E2O3 (E = B or Al) as by-products often causes experimental difficulties, viz. separation of the E2O3 from the metal bromide or bromide oxide. Sublimation (providing, of course, the product is volatile) often leads to decomposition (e.g.FeBr3 and TaOBr3),63 while other separation techniques, such as dissolution in methanol (often used to remove B2O3),8,63 are often unsuitable since many metal bromides and bromide oxides react with donor solvents (e.g. UOBr3 10,64,65 and TiBr4 58) giving both solvation and solvolysis products. Alternative syntheses of metal bromides and bromide oxides usually involve the use of high temperatures and pressures, one of the few exceptions being the halogen-exchange reaction with BBr3.14 The advantage of this halogen-exchange method is that the reaction can be carried out under mild conditions, and, more importantly, since the by-products are volatile puri- fication is straightforward.The only problem with it is the possibility of mixed-halide formation (e.g. WOCl3Br and WCl3Br2 are well known,66 and are possible products of the reaction of BBr3 with WOCl4 and WCl5, respectively).In the light of this discussion, it is apparent that existing syntheses of metal bromides and bromide oxides are, on the whole, performed under very forcing conditions, and in many cases yield impure products. The use of COBr2 offers a new synthetic route under mild conditions. The synthesis of a pure 3d, 4d, 5d and 5f bromide oxide, together with a pure 4f bromide illustrates the widespread applicability of COBr2 as a brominating agent. There is a strong thermodynamic driving force (viz.formation of CO2) and, more importantly, puri- fication of the metal-containing product is trivial providing reaction has gone to completion. Given the efficacy of COBr2 in synthesizing metal bromides and bromide oxides, its toxicity is not of major significance. Indeed, current synthetic routes frequently involve the use of toxic (but less emotive) compounds, and COBr2 appears to be no more toxic that O3, and is considerably less toxic than [Ni(CO)4].Acknowledgements We are grateful to the EPSRC and ICI plc for the award of a Table 2 Thermodynamic comparison of some brominating agents, at 600 Ka Brominating agent Product derived from the brominating agent DHdiff b/kJ mol 2 1 DGdiff b/kJ mol 2 1 BBr3 (g) Al2Br6 (g) CBr4 (g) SOBr2 (g) COBr2 (g) B2O3 (s) a-Al2O3 (s) COBr2 (g) SO2 (g) CO2 (g) 2 128c 2 108c 2 53d 2 91e 2 140e 2 112c 2 101c 2 79d 2 75f 2 154e a Enthalpies and free energies of formation of the brominating agents and the products derived from the brominating agent were obtained from the JANAF Thermochemical Tables,60 except for COBr2 19 and SOBr2 61.b DHdiff is the difference in enthalpy of formation (DHf) of the product derived from the brominating agent and the brominating agent itself, expressed per mol of MOBrn 2 2 formed. Thus, for COBr2, DHdiff = ��� [DHf (CO2) 2 DHf (COBr2)]. DGdiff is the analogous freeenergy difference. c Calculated for a general reaction (15). d Calculated for a general reaction (16).e Calculated for a general reaction (17). f The free energy of formation of SOBr2 was estimated assuming that DHf (SOBr2) is independent of temperature.J. Chem. Soc., Dalton Trans., 1997, Pages 257–261 261 CASE studentship (to M. J. P.), to the EPSRC and Royal Academy of Engineering for the award of a Clean Technology Fellowship (to K. R. S.), and to Drs. A. K. Abdul-Sada and A. G. Avent for spectroscopic assistance. References 1 R.Colton and J. H. Canterford, Halides of the First Row Transition Metals, Wiley, London, 1969. 2 J. H. Canterford and R. Colton, Halides of the Second and Third Row Transition Metals, Wiley, London, 1968. 3 D. Brown, Halides of the Lanthanides and Actinides, Wiley, London, 1968. 4 R. E. McCarley and J. W. Roddy, Inorg. Chem., 1964, 3, 60. 5 R. J. Sime and N. W. Gregory, J. Am. Chem. Soc., 1960, 82, 800. 6 K. Dehnicke, Chem. Ber., 1965, 98, 290. 7 S. A. Shchukarev and G. A.Kokovin, Russ. J. Inorg. Chem., 1964, 9, 849. 8 P. M. Druce and M. F. Lappert, J. Chem. Soc. A, 1971, 3595. 9 M. Chaigneau, Compt. Rend., 1956, 243, 957. 10 J. Prigent, Ann. Chim. (Paris), 1960, 5, 65. 11 S. A. Shchukarev, E. K. Smirnova, I. V. Vasil’kova and N. I. Borovkova, Russ. J. Inorg. Chem., 1962, 7, 625. 12 R. C. Paul, M. Singh and S. K. Vasisht, J. Indian Chem. Soc., 1970, 47, 3. 13 A. Anagnostopoulos, D. Nicholls and M. E. Pettifer, J. Chem. Soc., Dalton Trans., 1974, 569. 14 P. M. Druce, M. F. Lappert and P. N. K. Riley, Chem. Commun., 1967, 486. 15 E. M. Larson and J. J. Leddy, J. Am. Chem. Soc., 1956, 78, 5983. 16 R. C. Young, J. Am. Chem. Soc., 1931, 53, 2148. 17 I. N. Semenov and N. I. Kolbin, Russ. J. Inorg. Chem., 1962, 7, 111. 18 P. R. Brown, F. G. N. Cloke, M. L. H. Green and R. C. Tovey, J. Chem. Soc., Chem. Commun., 1982, 519. 19 T. A. Ryan, C. Ryan, E. A. Seddon and K. R. Seddon, Phosgene and Related Carbonyl Halides, Elsevier, Amsterdam, 1996. 20 B. Fahlke, G. Blumenthal, W. Wieker, G. Wegner, K. Kintscher, W. Roscher and P. Knop, Ger. (East) Pat., DD 222 271, 1985. 21 D. Parris, Can. Pat., CA 1 209 976, 1986. 22 J. Prigent, C. R. Acad. Sci., 1954, 239, 424. 23 F. Lux, G. Wirth and K. W. Bagnall, Chem. Ber., 1970, 103, 2807. 24 A. Blair and H. Ihle, J. Inorg. Nucl. Chem., 1973, 35, 3795. 25 M. J. Parkington, K. R. Seddon and T. A. Ryan, J. Chem. Soc., Chem. Commun., 1989, 1823. 26 M. J. Parkington, T. A. Ryan and K.R. Seddon, UK Pat., GB 8 728 883, 1988. 27 M. J. Parkington, T. A. Ryan and K. R. Seddon, Eur. Pat., 320 161, 1988. 28 H.-J. Schumacher and S. Lenher, Ber. Dtsch. Chem. Ges., B, 1928, 61, 1671. 29 Occupational Exposure Limits 1995, Guidance Note EH40, Health and Safety Executive, 1995. 30 W. F. Diller, Toxicol. Ind. Health, 1985, 1, 93. 31 K. Leichnitz, Dräger Detector Tube Handbook, Drägerwerk, Lubeck, 1979. 32 J. Schiel, Liebig’s Ann. Chem. Pharm., Suppl., 1863, 2, 311. 33 A.Emmerling, Ber. Dtsch. Chem. Ges., 1880, 13, 873. 34 A. von Bartal, Liebigs Ann. Chem., 1906, 345, 334. 35 A. Besson, Compt. Rend., 1895, 120, 190. 36 A. Besson, Compt. Rend., 1896, 122, 140. 37 A. Brochet, Bull. Soc. Chim., 1897, 13, 221. 38 J. Overend and J. C. Evans, Trans. Faraday Soc., 1959, 55, 1817. 39 W. Gombler, Z. Naturforsch., Teil B, 1981, 36, 1561. 40 W. Gombler, Spectrochim. Acta, Part A, 1981, 37, 57. 41 M. P. Parkington, T. A. Ryan and K. R. Seddon, preceding paper. 42 J. C. Levet, Compt. Rend., 1969, 268, 703. 43 P. Handler and C. A. Hutchinson, J. Chem. Phys., 1956, 25, 1210. 44 I. A. Glukhov, S. S. Eliseev and E. E. Vozhdaeva, Russ. J. Inorg. Chem., 1969, 13, 483. 45 S. Sostero, O. Traverso, C. Bartocci, P. DiBernado, L. Magon and V. Carassiti, Inorg. Chim. Acta, 1976, 19, 229. 46 S. A. Shchukarev, I. V. Vasil’kova and V. M. Drozdova, Russ. J. Inorg. Chem., 1958, 3, 75. 47 J. Prigent, Compt. 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Data, 1985, 14 (suppl. 1), 1. 61 D. D. Wagman, W. H. Evans, V. B. Parker, R. H. Schumm, I. Halow, S. M. Bailey, K. L. Churney and R. L. Nuttall, The NBS Tables of Chemical Thermodynamic Properties, J. Phys. Chem. Ref. Data, 1982, 11 (suppl. 2), 1. 62 C. Campbell, J. P. M. Jones and J. J. Turner, Chem. Commun., 1968, 888. 63 P. M. Druce, D. Phil Thesis, University of Sussex, 1968. 64 G. Kaufmann and R. Rohmer, Bull. Soc. Chim. Fr., 1961, 1969. 65 G. Kaufmann, Rev. Chim. Miner., 1964, 1, 129. 66 P. M. Boorman, N. N. Greenwood and H. J. Whitsfield, J. Chem. Soc. A, 1968, 2256. Received 6th June 1996; Paper 6/

ISSN:1477-9226    

DOI:10.1039/a603977d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 263–270 263 New mono- and di-nuclear complexes of PdII, PtII and NiII of PNNP ligands with a 2,29-biaryl bridging unit Alette G. J. Ligtenbarg,a Esther K. van den Beuken,a Auke Meetsma,a Nora Veldman,b Wilberth J. J. Smeets,b Anthony L. Spek b and Ben L. Feringa *,a a Department of Organic and Molecular Inorganic Chemistry, Groningen Center for Catalysis and Synthesis, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands b Crystal and Structural Chemistry, Bijvoet Center for Biomolecular Research, University of Utrecht, Padualaan 8, 3584 CH Utrecht, The Netherlands The Schiff bases 2,29-bis{N-[(2-diphenylphosphino)phenyl]formimidoyl}biphenyl (L1) and 2,29-bis{[(2-diphenylphosphino) benzylidene]amino}biphenyl (L2) were synthesized from the appropriate amine and aldehyde. Their co-ordination behaviour towards PdII, PtII and NiII has been studied. Dinuclear complexes were formed when treating L1 with 2 equivalents of [PdCl(Me)(cod)] (cod = cycloocta-1,5-diene) and Pd(O2CMe)2.In the case of the reaction of L1 with Pd(O2CMe)2 an unexpected double cyclopalladated complex was formed. However, treatment of L1 with 2 equivalents of [PtCl2(MeCN)2] resulted in hydrolysis of the ligand and a mononuclear complex of (2-diphenylphosphino)benzenamine was obtained. The structure of [Pd2L1Cl2Me2] 1 has been established by an X-ray diffraction study. The dihedral angle between the biphenyl rings is 49.2(8)8 and the intramolecular Pd ? ? ? Pd distance is 7.165(3) Å.The biphenyl bridging moiety shows a remarkable bending of 169.2(8)8. Treatment of 1 with carbon monoxide resulted in a double CO insertion, yielding the bis(acetyl)palladium compound [Pd2L1Cl2- {C(O)Me}2] 2. The structure of [Pd2L1(O2CMe)2]?4CH2Cl2 3 was also determined by X-ray diffraction. The dihedral angle between the biphenyl rings is 75.9(14)8 while the intramolecular Pd ? ? ? Pd distance is 8.655(2) Å.The reaction of L2 with 2 equivalents of anhydrous [PdCl2(MeCN)2] or NiCl2 afforded mononuclear complexes. The crystal and molecular structure of [PdL2]Cl2?3.5CH2Cl2 was determined. The compound has an approximately square-planar P2N2 geometry. The chemistry of dinuclear transition-metal complexes has attracted considerable interest in recent years.1 In particular dinuclear models of metalloproteins 2 have received great attention 3 and a variety of new homo-4 and hetero-dinuclear 5 complexes has been synthesized.In the design of these types of compounds the choice of the ligand system is of prime importance. 6 When the two metal centres are incorporated in close proximity the complexes have the potential of catalysing reactions either more efficiently, or with different chemo-, regio- or stereo-selectivity than those of corresponding mononuclear ones, due to co-operation of the two metals in the transition state of the catalytic reaction.7 An excellent example of a dinuclear catalyst which exhibits higher regioselectivity and reactivity than those of the related mononuclear system by bimetallic co-operation is the dirhodium system reported by Stanley and co-workers 8 for the hydroformylation of a-olefins.In our group oxygen activation on dinuclear copper complexes contain a meta-arene-bridged ligand system was investigated.9 Recently dinuclear rhodium phosphite complexes based on a tetranaphthol skeleton were studied as catalysts in hydroformylation reactions.10 In the systems studied so far ligands are often either highly flexible or rigid; in the second case the two metal centres are in a fixed orientation towards each other.It was envisaged that when the distance between the two metal ions is flexible this might result in optimum co-operation of the metal centres in the transition state of a catalytic reaction. A building block for this approach is a biphenyl unit, which can act as a bridging moiety between two ligating groups.Réglier et al.11 have reported a dinuclear complex of a bis(pyridyl)- substituted biphenyl ligand which acts as a functional mimic of tyrosinase, a copper-containing monooxygenase. However, in most cases where a biaryl backbone is used, mononuclear complexes are obtained e.g. with NiII, CuII, CoII, ZnII and PdII.12,13 In the approach described here a biphenyl ligand system is developed consisting of two fairly rigid arms connected to the backbone which has flexibility at point a.Owing to the bulky 2,29 substituents, however, hindered rotation is expected around the biaryl bond (atropisomerism), which might result in stereoisomers of these ligands or complexes. As donor sets phosphorus and imino-nitrogen atoms were chosen, and the co-ordination behaviour of these ligands with metals of Group VIII, e.g. PdII, PtII and NiII, was studied. The co-ordination geometry of the metals will largely be determined by the angle between the two phenyl rings in the biphenyl moiety (a) and by rotation around the single bonds connecting the side-arms to this unit (b).Results Synthesis of 2,29-bis{N-[(2-diphenylphosphino)phenyl]- formimidoyl}biphenyl (L1) The tetradentate diimine ligand 2,29-bis{N-[(2-diphenylphosphino) phenyl]formimidoyl}biphenyl (L1) was synthesized by the Schiff-base formation of 2 equivalents of biphenyl-2,29- dicarbaldehyde with (2-diphenylphosphino)benzenamine14 (Scheme 1).The synthesis of biphenyl-2,29-dicarbaldehyde by phenanthrene ozonolysis is a known literature procedure 15 but the yields are often low. Therefore we developed a more convenient route towards this compound starting from diphenic acid ([1,19-biphenyl]-2,29-dicarboxylic acid).16 In a first step the dimethyl ester I was formed in 80% yield. Subsequently reduction with lithium aluminium hydride gave the corresponding N N P P b b a264 J.Chem. Soc., Dalton Trans., 1998, Pages 263–270 diol II in 90% yield. Next, a mild Swern oxidation was performed, affording the dialdehyde III in high yield (90%). The synthesis of L1 was carried out under a nitrogen atmosphere in dry benzene. The reaction was followed by 31P NMR spectroscopy, which revealed that imine formation was rather slow and was complete after 24 h. Besides a Dean–Stark trap, addition of molecular sieves was necessary in order to remove all the water produced during the reaction and to drive it to completion. Even small amounts of water in the reaction mixture caused oxidation of the product.The compound L1 was purified by crystallisation from a dichloromethane–pentane solvent mixture. It showed in the 31P NMR spectrum an absorption at d 214.9 and is air-stable in the solid state. Furthermore, the ligand was characterised by 1H NMR spectroscopy, elemental analysis and mass spectrometry (see Experimental section). Synthesis of 2,29-bis{[2-(diphenylphosphino)benzylidene]amino}- biphenyl (L2) A related tetradentate Schiff-base ligand (L2) with phosphorus and imino-nitrogen donor sets was also synthesized.In L2 the imino nitrogen atom is attached to the biphenyl moiety, instead of the imino carbon atom in L1. We expected this ligand to be more stable towards oxidation and more easily synthesized. Furthermore, upon co-ordination of the phosphorus and nitrogen atoms to a metal ion, a six-membered chelate ring will be formed instead of a five-membered ring in the case of L1.Ligand L2 was synthesized by a Schiff-base reaction of 2,29- diaminobiphenyl 17 and 2-(diphenylphosphino)benzaldehyde (Scheme 2).18 After 4 h reflux in benzene under Dean–Stark conditions with a catalytic amount of toluene-p-sulfonic acid L2 was obtained in 92% yield. It showed an absorption at d Scheme 1 (i) MeOH, H2SO4, reflux, 16 h, yield 80%; (ii) LiAlH4, tetrahydrofuran (thf), reflux, 17 h, 90%; (iii) ClCOCOCl, dimethyl sulfoxide (dmso), 260 8C, 45 min; (iv) NEt3, 90%; (v) (2-diphenylphosphino) benzenamine, toluene-p-sulfonic acid, benzene, molecular sieves (4 Å), Dean–Stark, reflux, 24 h, 65% CO2H CO2H CO2Me CO2Me ( iii), ( iv) ( i) ( ii) CHO CHO N N PPh2 PPh2 OH OH ( v) I II III L1 Scheme 2 (i) NaN3, H2SO4, 30–40 8C, 95 min, yield 65%; (ii) 2- (diphenylphosphino)benzaldehyde, toluene-p-sulfonic acid, benzene, Dean–Stark, reflux, 4 h, 92% CO2H CO2H NH2 NH2 N N PPh2 PPh2 ( i) (ii) L2 215.2 in the 31P NMR spectrum.The product was also characterised as for L1. Compound L2 was air-stable in the solid state as well as in solution. The Schiff-base reaction yielding it was much faster than the imine formation affording L1 as only 4 h for complete conversion for L2 and 24 h for L1 were required. In addition, a larger overall yield for L2 compared to L1 (60 and 45%, respectively) was found. Palladium and platinum complexes based on L1 Ligand L1 was allowed to react with 2 equivalents of [PdCl(Me)(cod)]19 (cod = cycloocta-1,5-diene) in tetrahydrofuran for 16 h at room temperature yielding a precipitate, which was crystallised from dichloromethane–pentane as pale yellow crystals in 65% yield.The cod group of the starting material was replaced by L1, giving rise to dinuclear complex 1 (Scheme 3). The 31P NMR spectrum shows a singlet at d 35.4 (CDCl3), which indicates that the two phosphorus atoms are identical.Compared with the free biphenyl (d 214.9, CDCl3) a strong downfield shift is observed. The 1H NMR spectrum of 1 revealed that the methyl groups on the metal ions are equivalent giving a sharp doublet at d 0.86 due to phosphorus proton coupling [J(P]H) = 2.93 Hz]. The magnitude of this coupling indicates a cis relationship 20 between two groups having a large trans influence,21 i.e. the phosphorus atom and the methyl group. The crystal structure of [Pd2L1Cl2Me2] 1 was established by an X-ray diffraction study (Fig. 1). Selected bond lengths, angles and torsion angles are listed in Table 1. The notion that the ligand has imposed C2 symmetry on the palladium complex was confirmed by the X-ray diffraction analysis showing a two-fold axis dividing the C(25)]C(25a) Scheme 3 (i) thf, room temperature (r.t.), 16 h, yield 65%; (ii) CDCl3, r.t., 15 min; (iii) CH2Cl2, r.t.; (iv) CH2Cl2, r.t., 1 h N N Pd Ph2P Cl Me Pd PPh2 Cl Me N Pd Ph2 P MeCO2 N Pd P Ph2 O2CMe P Ph2 H2 N Pt Ph2 P NH2 1 L1 + 2[PdCl(Me)(cod)] L1 + 2Pd(O2CMe)2 3 2+ 2 Cl– 1 + 2CO N N Pd Ph2P Cl MeC Pd PPh2 Cl CMe L1 + 2[PtCl2(MeCN)2] 4 2 O O ( iv) ( iii) ( ii) ( i)J.Chem. Soc., Dalton Trans., 1998, Pages 263–270 265 bond. The metals adopt a distorted square-planar coordination geometry. The P]Pd]N angle of 79.70(11)8 is signifi- cantly smaller than the ideal 908 angle, whereas the Cl]Pd]N angle of 98.57(11)8 is significantly larger than 908. The distances between palladium and the donor atoms are within the normal range;20b,23,24a Pd]N and Pd]P distances are 2.237(4) and 2.1963(16) Å, respectively whereas Pd]Cl and Pd]CH3 are 2.3625(15) and 2.020(6) Å, respectively.The Pd ? ? ? Pd distance is 7.165(3) Å and the metal ions are directed to the outside (anti-folding, see Scheme 5, structure A). The two phenyl rings of the biphenyl are twisted with respect to each other resulting in a dihedral angle of 49.2(8)8 for C(20)]C(25)]C(25a)]C(20a).A remarkable feature of the biphenyl moiety is the significant non-linearity as shown by the orientation of the atoms C(22), C(25), C(25a) and C(22a). The angle C(22)]C(25)]C(22a) is 169.2(8)8 instead of the ideal 1808. The carbon atoms of the phenyl ring of C(20) to C(25) deviate 0.022 Å from the mean plane. Carbon atom C(22a) is 0.366(6) Å and C(25a) 0.123(5) Å out of that plane. Complexes containing a metal–carbon s bond can undergo insertion reactions with e.g. carbon monoxide 24 and isocyanides. 25 Treatment of a solution of 1 with carbon monoxide in CDCl3 at room temperature for 15 min resulted smoothly and nearly quantitatively in double CO insertion leading to the formation of the dinuclear acetylpalladium compound [Pd2L1Cl2{C(O)Me}2] 2 which was characterised by IR and NMR spectroscopy. The CO stretching vibration at 1697 cm21 indicates inserted carbon monoxide.24a In the 1H NMR spectrum the methyl absorption is shifted to d 2.25 compared with d 0.86 in 1 and the coupling pattern has disappeared. The 13C NMR spectrum shows an additional carbonyl absorption at d 210.8 and an acetyl methyl signal at d 10.93 whereas the methyl resonance in 1 was located at d 21.42.The 31P resonance has shifted upfield to d 14.29. Reaction of 1 with tert-butyl Fig. 1 An ORTEP22 plot of complex 1 (50% probability level) Table 1 Selected bond distances (Å) and angles (8) and torsion angles (8) of complex 1 with estimated standard deviations (e.s.d.s) in parentheses Pd]N Pd]Cl Pd]P Cl]Pd]N P]Pd]N P]Pd]C(26) Cl]Pd]C(26) 2.237(4) 2.3625(15) 2.1963(16) 98.57(11) 79.70(11) 92.0(2) 89.8(2) Pd]C(26) C(25)]C(25a) Pd(1) ? ? ? Pd(1a) Cl]Pd]P N]Pd]C(26) C(20)]C(25)]C(25a) C(24)]C(25)]C(25a) 2.020(6) 1.486(6) 7.165(3) 178.21(5) 169.6(2) 126.0(4) 116.5(4) C(20)]C(25)]C(25a)]C(20a) 49.2(8) isocyanate resulted in the formation of some palladium(0) and a complex reaction mixture, according to NMR spectroscopy, which was not further identified.Reaction of 2 equivalents of Pd(O2CMe)2 with L1 was carried out in dichloromethane at room temperature under a nitrogen atmosphere for 1.5 h. Subsequently, the solvent was removed in vacuo and the resulting dark yellow-brown oil was crystallised from dichloromethane–pentane. Dark red crystals of the cyclopalladated complex 3 were obtained after a few weeks and its structure confirmed by X-ray crystallography (Fig. 2). The 31P NMR spectrum shows a singlet at d 44.9 (CDCl3), which indicates that the two phosphorus atoms are identical.The complex has C2 symmetry with a two-fold axis dividing the C(25)]C(25a) bond. The two phenyl rings of the biphenyl moiety are twisted with respect to each other with a dihedral angle of 75.9(14)8 for C(20)]C(25)]C(25a)]C(20a). Atoms C(22), C(25) and C(25a), C(22a) show a nearly linear arrangement. For example the angle between C(22), C(25) and C(25a) is 179.1(9)8. The distances between palladium and the coordinated donor atoms in complex 3 are in the normal range, Pd]N and Pd]P are 2.000(7) and 2.319(2) Å, respectively and Pd]O and Pd]C are respectively 2.051(7) and 1.978(10) Å.26 The intramolecular metal–metal distance is 8.655(2) Å.The metal adopts a distorted square-planar co-ordination geometry: the angles P(1)]Pd(1)]N(1) [84.5(2)8] and N(1)]Pd(1)] C(21) [82.0(3)8] are significantly less than the ideal 908. The angles P(1)]Pd(1)]O(1) and O(1)]Pd(1)]C(21) are respectively 100.0(2) and 93.4(3)8.Selected bond lengths and angles are listed in Table 2. From 31P and 1H NMR studies it can be concluded that cyclometallation of L1 with Pd(O2CMe)2 in dichloromethane is a very slow process. Initially, upon addition of Pd(O2CMe)2, a mixture of products is formed. These products eventually rearrange to give the more stable cyclopalladated compound together with acetic acid. The formation of [Pd2(O2CMe)2L1] is irreversible. The binding of L1 to PtII was briefly examined by treating a solution of L1 in dichloromethane with 2 equivalents of bis- (acetonitrile)platinum(II) chloride. After 1 h at room temperature 31P NMR spectroscopy showed the presence of various compounds.After 1 night this composition had not changed. Attempts to isolate either a mono- or a di-nuclear complex of L1 failed. The only complex that was isolated according to 1H, 13C NMR spectroscopy and elemental analysis was the platinum complex 4 of (2-diphenylphosphino)benzenamine IV.Obviously, the complexes formed initially are highly water sensitive. During work-up by filtering the solution in the presence of air the ligand was hydrolysed, followed by complexation of Pt to form 4. Palladium and nickel complexes based on L2 To study the co-ordination behaviour of L2, 2 equivalents of [PdCl2(MeCN)2] were added to a solution of L2 in dichloromethane at room temperature. Remarkably, in this case no Table 2 Selected bond distances (Å) and angles (8) and torsion angles (8) of complex 3 with e.s.d.s in parentheses Pd(1)]N(1) Pd(1)]O(1) Pd(1)]P(1) P(1)]Pd(1)]O(1) P(1)]Pd(1)]N(1) O(1)]Pd(1)]C(21) N(1)]Pd(1)]C(21) 2.000(7) 2.051(7) 2.319(2) 100.0(2) 84.5(2) 93.4(2) 82.0(3) Pd(1)]C(21) C(25)]C(25a) Pd(1) ? ? ? Pd(1a) O(1)]Pd(1)]N(1) P(1)]Pd(1)]C(21) C(20)]C(25)]C(25a) C(24)]C(25)]C(25a) 1.978(10) 1.508(14) 8.655(2) 172.7(3) 166.6(3) 122.5(8) 119.8(9) C(20)]C(25)]C(25a)]C(20a) 75.9(14)266 J.Chem.Soc., Dalton Trans., 1998, Pages 263–270 Fig. 2 An ORTEP plot of complex 3 (50% probability level) formation of a dinuclear species was observed. According to 31P NMR spectroscopy, mononuclear complex 5 (Scheme 4) was formed quantitatively, giving rise to a 31P NMR absorption at d 31.1 (free biphenyl d 215.2). Crystallisation from dichloromethane–pentane afforded orange crystals suitable for X-ray analysis. The crystal structure of 5 is shown in Fig. 3. Selected bond lengths, angles and torsion angles are listed in Table 3.Complex 5 exists in two forms in the unit cell which slightly differ from one another, together with seven solvent molecules Scheme 4 (i) CH2Cl2, r.t., 1.5 h, yield 66%; (ii) absolute EtOH, reflux, 3 h; (iii) CH2Cl2, 4 NaBF4, r.t., 2 h, 53% N N P Ph2 P Ph2 Pd L2 + [PdCl2(MeCN)2] 5 N N P Ph2 P Ph2 L2 + NiCl2 Ni 6 2+ 2+ 2BF4 – 2Cl– ( i) ( ii), ( iii) Table 3 Selected bond distances (Å) and angles (8) and torsion angles (8) of complex 5 * with e.s.d.s in parentheses Pd(1)]N(1) Pd(1)]N(2) Pd(1)]P(1) P(1)]Pd(1)]N(2) P(1)]Pd(1)]P(2) N(1)]Pd(1)]N(2) P(2)]Pd(1)]N(1) 2.086(6) 2.164(6) 2.243(2) 85.08(18) 96.56(8) 90.0(2) 88.29(17) Pd(1)]P(2) Pd(1) ? ? ? Cl(1) C(251)]C(261) P(1)]Pd(1)]N(1) P(2)]Pd(1)]N(2) C(201)]C(251)]C(261) C(241)]C(251)]C(261) 2.262(2) 2.8025(19) 1.470(11) 175.08(17) 161.98(16) 122.6(7) 119.5(7) C(241)]C(251)]C(261)]C(271) 51.4(11) * Values for only one crystallographically independent molecule are given.The dimensions of the second are very similar. (dichloromethane). In both structures the chlorides are nonco- ordinating. The palladium ion adopts a slightly distorted square-planar geometry. The twist in the biphenyl moiety is 51.4(11)8 for C(241)]C(251)]C(261)]C(271) and 51.5(11)8 for the corresponding carbon atoms in the second structure. The distances between palladium and the donor atoms are within the normal range.23 The distances between Pd(1) and P(1) and P(2) are 2.243(2) and 2.262(2) Å, respectively. The Pd]N distances are 2.086(6) Å for Pd(1)]N(1) and 2.164(6) Å for Pd(1)]N(2).Also in this compound the atoms C(221)]C(251)] C(261)]C(291) show a non-linear arrangement, but the bending in the biaryl unit is significantly less than in complex 1 (see above). The angle between C(251), C(261) and C(291) is 175.5(6)8 and for the corresponding atoms in the second structure 175.2(6)8. For a related mononuclear rhodium(I) complex of an asymmetric 6,69-dimethyl-2,29-bis{[2-diphenylphosphino) benzylidene]amino}biphenyl ligand 27 no bend in the biphenyl moiety was reported, whereas the dihedral angle between the rings was larger (698).Upon reaction of L2 with anhydrous nickel(II) chloride mononuclear complex 6 was formed which was characterised by 31P and 1H NMR spectroscopy, elemental analysis and mass spectrometry (see Experimental section). The complex shows an absorption in the 31P NMR spectrum at d 31.3.Fig. 3 An ORTEP plot of one of the two independent molecules in the crystals of complex 5 (50% probability level)J. Chem. Soc., Dalton Trans., 1998, Pages 263–270 267 Discussion From these results it can be concluded that L1 is an excellent dinucleating ligand for palladium. When [PdCl(Me)(cod)] is added to L1 a geometry is adopted in which the ligating groups at each phenyl ring point to the ‘inside’ and the two metal centres are directed to the ‘outside’ as illustrated in Scheme 5, structure A.Probably steric interactions between the two sidearms disfavour the formation of a syn-folded geometry as indicated in structure B, although it must be emphasised that in solution rotation around the single bonds connecting the sidearms to the backbone is still possible. In geometry B the two metals are in closer proximity, yielding a complex in which they might be able to co-operate in a catalytic reaction. However, in the double cyclometallated complex 3 (Fig. 2), despite the biaryl rotation, the formation of a syn-folded geometry is not possible because the palladium ions are directly attached to the biphenyl backbone via C(21)]Pd(1) [C(21a)]Pd(1a)] aryl–metal bonds. In the case of L2 only mononuclear complexes were formed with the general structure as shown in Scheme 5, C. In spite of the possibility of adopting a conformation able to accommodate two metal ions simultaneously, by rotation around the single bond in the biphenyl backbone, only mononuclear complexes are formed.Apparently, these are very stable. Once a metal ion is complexed between the four donor atoms in the ligand, the binding of a second metal ion is disfavoured. Conclusion Two new ligand systems, L1 and L2, were developed containing a PNNP donor-atom sequence and a biphenyl backbone. We have shown that L1 can readily accommodate two palladium ions. Furthermore, a mild double cyclometallation reaction was observed with Pd(O2CMe)2 although the process is rather slow.In contrast, L2 only affords mononuclear complexes of palladium and nickel. Notably, the crystal structures of [Pd2- L1Cl2Me2] 1 and [Pd2L2]Cl2 5 obtained by X-ray analyses showed that the biphenyl moiety is twisted to approximately the same degree (about 508) for both complexes. However, the twist in the biphenyl moiety of [Pd2L1(O2CMe)2] 3 is much larger (75.98). Another remarkable feature of these compounds is the significant non-linearity in the biphenyl entity leading to significant biphenyl bending.Finally with complex 1 a successful double-insertion reaction was performed with carbon monoxide yielding [Pd2L1Cl2{C(O)Me}2] 2. Experimental Melting points (uncorrected) were determined on a Mettler FP- 2 apparatus equipped with a FP-21 microscope and are uncorrected. Proton NMR spectra were recorded on a Varian Gemini-200 (at 200 MHz), on a VXR-300 (at 300 MHz) or on a Unity 500 spectrometer (at 500 MHz).Chemical shifts are reported in d units (ppm) relative to the solvent and converted into the SiMe4 scale (d 0) using d (CHCl3) 7.26. Carbon-13 NMR spectra were recorded on a Varian Gemini-200 (at 50.3 MHz), on a VXR-300 (at 75.4 MHz) or on a Unity 500 spectrometer (at 125 MHz), 31P NMR spectra on a Varian Gemini- Scheme 5 Representation of the geometries of mono- and di-nuclear complexes based on PNNP ligands N N M N M P P P N N P P M M N P M A B C 200 spectrometer (at 80.95 MHz) with triphenyl phosphate as an external reference (d 218).High-resolution mass spectra were obtained on an AEI MS-902 spectrometer by electron impact (EI), electron spray (ES) mass spectra on a NERMAG mass spectrometer. Infrared spectra were recorded on a Perkin- Elmer 841 spectrometer. Elemental analyses were performed in the Microanalytical Department of our laboratory. All manipulations were carried out under an atmosphere of dry dinitrogen except for the synthesis of compound I.Dichloromethane, pentane and hexane were distilled from phosphorus pentaoxide, methanol from magnesium, benzene from sodium wire and tetrahydrofuran from sodium– benzophenone. Dimethyl sulfoxide was dried by stirring over barium oxide during 18 h before use. (2-Diphenylphosphino)- benzenamine,14 2,29-diaminobiphenyl,17 2-(diphenylphosphino) benzaldehyde 18 and [PdCl(Me)(cod)]19 were synthesized using literature procedures. Diphenic acid, 2-bromobenzaldehyde and chlorodiphenylphosphine obtained from Aldrich were used without further purification.Preparations Biphenyl-2,29-dicarboxylic acid dimethyl ester I. To biphenyl- 2,29-dicarboxylic acid (25.0 g, 103 mmol) in methanol (250 cm3) was added sulfuric acid (4 cm3) and the solution was heated under reflux for 16 h. The resulting dark brown reaction mixture was poured into a water–ice mixture (300 cm3) and subsequently ethyl acetate (300 cm3) was added. Evaporation of most of the methanol yielded a two-phase system.The dark green aqueous layer was extracted with ethyl acetate (2 × 75 cm3) and the combined organic layers were subsequently washed with saturated sodium hydrogencarbonate solution (2 × 75 cm3), water (1 × 75 cm3) and brine (1 × 50 cm3). Drying (MgSO4) and evaporation of the solvent yielded a pale brown solid which was crystallised from ethyl acetate (10 cm3). Yield: 22.6 g as white crystals (80%). M.p. 76.7–77.7 8C; 1H NMR (CDCl3) d 8.05–8.00 (m, 2 H), 7.60–7.40 (m, 4 H), 7.24–7.20 (m, 2 H) and 3.63 (s, 6 H); 13C NMR (CDCl3) d 167.4 (C), 143.3 (C), 131.4 (CH), 130.2 (CH), 129.8 (CH), 129.3 (C), 127.2 (CH) and 51.8 (CH3). 2,29-Di(hydroxymethyl)biphenyl II.Dimethyl ester I (7.0 g, 25.9 mmol) in thf (100 cm3) was added slowly to a suspension of LiAlH4 (2.0 g, 0.21 mol) in thf (150 cm3) at 0 8C. The reaction mixture was refluxed for 17 h. After cooling to 0 8C, aqueous 1.4 M KOH (20 cm3) was added carefully. After refluxing for 1 h, filtering, drying (MgSO4) and evaporation of the solvent, II was obtained in 94% yield as a white solid which was recrystallised from ethyl acetate (10 cm3).Yield: 5.0 g as white needles (90%). M.p. 112.4–113.5 8C; 1H NMR (CDCl3) d 7.36 (m, 6 H), 7.13 (dd, J = 0.9, J = 3.6 Hz, 2 H), 4.27 (s, 4 H) and 3.66 (s, OH, 2 H); 13C NMR (CDCl3) d 140.0 (C), 138.6 (C), 129.61 (CH), 129.55 (CH), 128.0 (CH), 127.6 (CH) and 62.7 (CH2). Biphenyl-2,29-dicarbaldehyde III. A solution of oxalyl chloride (2.75 cm3, 0.032 mol, 2.7 equivalents) in dichloromethane (50 cm3) was cooled to 260 8C and a mixture of dmso (3 cm3, 0.042 mol, 3.5 equivalents) and dichloromethane (10 cm3) was added carefully.After stirring for 5 min, II (2.6 g, 0.012 mol) in dmso (1 cm3) and dichloromethane (50 cm3) was added in less than 5 min. The resulting white solution was stirred for 45 min at 260 8C. Next a large excess of triethylamine (10 cm3, 0.072 mol, 6.0 equivalents) was added carefully.The mixture was allowed to warm to room temperature and subsequently washed with 5% HCl solution (30 cm3), aqueous NaHCO3 (saturated, 30 cm3) and brine (30 cm3). Drying (MgSO4) and evaporation of the solvent gave dialdehyde III as a pale yellow oil that solidified upon standing. Yield: 2.3 g as a yellow solid (90%). M.p. 63.2–64.3 8C (lit.,15 62.5–63.5 8C); 1H NMR268 J. Chem. Soc., Dalton Trans., 1998, Pages 263–270 (CDCl3) d 9.80 (s, CHO, 2 H), 8.02 (d, J = 4, 2 H), 7.70–7.57 (m, 4 H) and 7.33 (d, J = 3 Hz, 2 H); 13C NMR (CDCl3) d 191.0 (CH), 141.2 (C), 134.5 (C), 133.4 (CH), 131.7 (CH), 128.8 (CH) and 128.5 (CH). 2,29-Bis{N-[(2-diphenylphosphino)phenyl]formimidoyl}- biphenyl L1. To a mixture of biphenyl-2,29dicarbaldehyde III (0.31 g, 1.49 mmol), (2-diphenylphosphino)benzenamine IV (0.83 g, 2.98 mmol, 2.0 equivalents) and a catalytic amount of toluene-p-sulfonic acid in dry benzene (40 cm3) were added molecular sieves (4 Å).The reaction mixture was refluxed under Dean–Stark conditions for 16 h. After 90% completion of the reaction according to 31P NMR spectroscopy (16 h), the mixture was filtered over Celite and the yellow solution refluxed for 6 h. Evaporation of the solvent yielded a pale yellow foam. Pure L1 was obtained upon crystallisation from dichloromethane– pentane (1 : 2). Yield: 0.76 g as a pale yellow powder (65%). M.p. 183.3–185.3 8C; 1H NMR (CDCl3, 200 MHz) d 8.10–8.05 (m, 2 H), 7.87 (s, 2 H), 7.41–7.32 (m, 4 H), 7.31–7.20 (m, 22 H), 7.08 (t, J = 7.5, 2 H), 7.00–6.95 (m, 2 H), 6.79 (d, J = 1.2, 1 H), 6.77 (d, J = 1.5, 1 H), 6.74 (d, J = 4.4, 1 H), 6.71 (d, J = 1.0, 2 H) and 6.69 (d, J = 1.2 Hz, 1 H); 13C NMR (CDCl3, 50.3 MHz) d 157.9 (CH, 4JPC = 1.5), 154.0 (C, 1JPC = 17.9), 140.3 (C), 136.8 (C, 2JPC = 10.7), 134.4 (C), 134.0 (CH, 2JPC = 20.6), 132.6 (C, 1JPC = 11.4), 132.3 (CH), 130.7, 130.2 (CH), 129.7 (CH), 128.4 (CH), 128.2 (CH, 3JPC = 7.3 Hz), 128.0 (CH), 127.2 (CH), 125.8 (CH) and 117.0 (CH); 31P NMR (CDCl3, 80.95 MHz) d 214.9. High-resolution mass spectrum: m/z 728.251 (calc.for C50H38N2P2: 728.251) (Found: C, 82.04; H, 5.47; N, 3.75; P, 8.29. Calc. for C25H19NP: C, 82.40; H, 5.26; N, 3.84; P, 8.50%). 2,29-Bis{[2-(diphenylphosphino)benzylidene]amino}biphenyl L2. A mixture of 2-(diphenylphosphino)benzaldehyde (1.01 g, 3.44 mmol), 2,29-diaminobiphenyl (0.322 g, 1.72 mmol) and a catalytic amount of toluene-p-sulfonic acid in benzene (40 cm3) was refluxed for 4 h under Dean–Stark conditions. The solvent was evaporated and the product crystallised from absolute ethanol (15 cm3).Yield: 1.15 g as a pale yellow powder (92%). M.p. 170.8–171.2 8C; 1H NMR (CDCl3, 200 MHz) d 8.98 (d, J = 5.6 Hz, 2 H), 7.86–7.79 (m, 2 H), 7.38–7.15 (m, 30 H), 6.85– 6.78 (m, 2 H) and 6.39 (m, 2 H); 13C NMR (CDCl3, 50.3 MHz) d 158.4 (CH, 3JPC = 25.2), 150.6 (C), 139.4 (C, 1JPC = 17.2), 138.0 (C, 1JPC = 19.5), 136.2 (C, 2JPC = 10.7), 134.0 (CH, 2JPC = 20.2), 133.7 (C), 132.7 (CH), 131.0 (CH), 130.4 (CH), 129.0 (CH), 128.7 (CH), 128.5 (CH, 3JPC = 7.3), 128.1 (CH), 127.4 (CH, 2JPC = 4.2 Hz), 124.9 (CH) and 118.2 (CH); 31P NMR (CDCl3, 80.95) d 215.2.High-resolution mass spectrum: m/z 728.251 (calc. for C50H38N2P2: 728.251) (Found: C, 82.08; H, 5.43; N, 3.82; P, 8.35. Calc. for C25H19NP: C, 82.40; H, 5.26; N, 3.84; P, 8.50%). [Pd2L1Cl2Me2] 1. To L1 (100 mg, 0.14 mmol) in thf (1.5 cm3) was added [PdCl(Me)(cod) (72.7 mg, 0.28 mmol, 2.0 equivalents).After stirring for 16 h at r.t., the yellow solution was concentrated under reduced pressure until a white precipitate was formed. Filtration and crystallisation from dichloromethane –pentane yielded pale yellow crystals, 95 mg (65%). 31P NMR (CDCl3): d 35.4. 1H NMR (CDCl3, 200 MHz): d 9.16 (d, J = 5.1, 2 H), 8.86 (s, 2 H), 7.65–7.34 (m, 30 H), 7.21–7.15 (m, 2 H), 7.05–7.00 (m, 2 H) and 0.86 (d, J = 2.9 Hz, 6 H). 13C NMR (CDCl3, 75.4 MHz): d 167.43 (CH), 155.89 (d, C, 2JPC = 15.9), 140.90 (C), 134.32 (s, CH), 133.56 (d, CH, 2JPC = 13.4), 133.40 (d, CH, 2JPC = 11.0), 133.51 (C), 132.39 (CH), 131.97 (CH), 131.32 (CH), 131.06 (CH), 131.03 (CH), 130.45 (CH), 130.14 (CH), 129.53 (d, C, 1JPC = 40.3 Hz), 129.01 (d, CH, 3JPC = 11.0), 128.85 (d, CH, 3JPC = 11.0), 128.81 (d, C, 1JPC = 37.9), 128.35 (d, CH, 2JPC = 6.1), 128.07 (C), 120.51 (d, CH, 2JPC = 7.3 Hz) and 21.42 (CH3). ES mass spectrum: m/z 1007 (M 2 Cl), 1039 (M 2 Cl 1 MeOH) and 486 (M 2 2Cl) (Found: C, 59.29; H, 4.26; N, 2.64.Calc. for C26H22ClNPPd: C, 59.90; H, 4.25; N, 2.69%). [Pd2L1Cl2{C(O)Me}2] 2. The complex [Pd2L1Cl2Me2] (25 mg, 0.02 mmol) in CDCl3 was stirred for 15 min under 1 bar (105 Pa) CO at r.t. According to NMR data the conversion was nearly quantitative. IR (CDCl3); nCO 1687 cm21. 31P NMR (CDCl3): d 14.3. 1H NMR (CDCl3, 200 MHz): d 9.35 (d, J = 7.8 Hz, 2 H), 8.57 (s, 2 H), 7.76–7.42 (m, 30 H), 7.36–7.26 (m, 2 H), 7.22–7.09 (m, 2 H) and 2.25 (s, 6 H). 13C NMR (CDCl3, 75.4 MHz): d 223.39 (d, C, 2JPC = 7.3), 167.10 (CH), 155.03 (d, C, 2JPC = 15.9), 140.83 (C), 134.37 (CH), 133.57 (d, CH, 2JPC = 13.4), 133.17 (C), 133.11 (d, C, 2JPC = 13.4), 132.60 (CH), 132.15 (CH), 131.31 (CH), 131.00 (CH), 130.39 (CH), 129.98 (CH), 129.66 (CH), 129.15 (d, CH, 3JPC = 11.0), 129.01 (C), 128.91 (d, CH, 3JPC = 9.8), 128.41 (CH), 128.36 (CH), 120.50 (d, CH, 2JPC = 7.3) and 37.43 (d, CH3, 3JPC = 21.8 Hz); one Cq was not resolved.[Pd2L1(O2CMe)2] 3. To L1 (100 mg, 0.14 mmol) in CH2Cl2 (4 cm3) was added Pd(O2CMe)2 (62 mg, 0.28 mmol, 2.0 equivalents) and the resulting clear dark red solution was stirred for 1.5 h at r.t. The product was precipitated as a yellow powder by adding the solution dropwise to pentane while stirring vigorously. The pentane was decanted and the powder crystallised from dichloromethane–pentane to yield orange-red crystals suitable for X-ray analysis. 31P NMR (CDCl3): d 44.9. 1H NMR (CDCl3, 200 MHz): d 8.14–7.98 (m, 4 H), 7.90–7.76 (m, 6 H), 7.60–7.21 (m, 24 H), 7.20–7.00 (m, 4 H) and 1.92 (s, 6 H). [Pt(H2NC6H4PPh2-2)2]Cl2 4. To L1 (100 mg, 0.14 mmol) in CH2Cl2 (1 cm3) was added [PtCl2(MeCN)2] (49 mg, 0.14 mmol, 2.0 equivalents). The resulting yellow solution was stirred for 1 h at r.t. The solution was quickly filtered in the presence of air to remove undissolved material. Evaporation of the solvent and crystallisation from dichloromethane–pentane yielded pale yellow crystals. 31P NMR (CDCl3): d 25.8 (s), 25.8 (d, JPPt = 3334 Hz). 1H NMR (CDCl3, 200 MHz): d 7.79 (dd, J = 3.4 Hz, 2 H), 7.46 (m, 2 H), 7.40–7.30 (m, 14 H) and 7.26–7.11 (m, 14 H). 13C NMR (CDCl3, 50.3 MHz): d 147.30 (C), 134.12 (CH), 133.13 (t, CH, 2JPC = 11.8), 132.16 (CH), 132.06 (CH), 103.19 (d, C, 1JPC = 64.9), 128.95 (t, CH, 3JPC = 11.8), 128.34 (t, CH, 3JPC = 7.6), 127.01 (t, CH, 3JPC = 14.1) and 125.84 (d, C, 1JPC = 67.1 Hz) (Found: C, 51.26; H, 4.02; N, 3.34.Calc. for C36H32Cl2N2P2Pt?1.5CH2Cl2: C, 51.35; H, 3.85; N, 3.31%). [PdL2]Cl2 5. To L2 (100 mg, 0.14 mmol) in CH2Cl2 (2 cm3) was added [PdCl2(MeCN)2] (35.6 mg, 0.14 mmol, 1.0 equivalent) and the clear red solution was stirred for 1.5 h at r.t. Crystallisation from dichloromethane–pentane afforded large red crystals suitable for X-ray analysis. Filtration and drying of the crystals in vacuo gave 82 mg of analytically pure [PdL2]Cl2 as an orange-red powder (66%). 31P NMR (CDCl3): d 31.3. 1H NMR (CDCl3, 500 MHz): d 8.17 (d, J = 11.5, 2 H), 8.02 (br, 4 H), 7.76 (m, 2 H), 7.67 (t, J = 7.6, 4 H), 7.60–7.55 (m, 8 H), 7.45 (t, J = 7.6, 2 H), 7.35 (m, 2 H), 7.30 (m, 6 H), 6.94 (br, 2 H), 6.88 (m, 4 H) and 6.58 (d, J = 7.7 Hz, 2 H). 13C NMR (CDCl3, 125 MHz): d 168.96 (CH), 148.45 (C), 138.77 (CH), 135.60 (CH), 134.80 (CH), 133.63 (t, C, 2JPC = 26.1), 133.48 (CH), 132.89 (C), 131.87 (CH), 131.68 (CH), 131.34 (C), 131.07 (CH), 129.56 (CH), 129.45 (CH), 129.37 (t, C, 2JPC = 11.8), 129.12 (t, CH), 126.3 (d, CH, 1JPC = 52.5), 124.52 (d, C, 1JPC = 53.6), 123.66 (CH) and 123.30 (d, CH, 1JPC = 65.5); one CH was not resolved due to overlap.ES mass spectrum: m/z 869 (M 2 Cl) and 417 (M 2 2Cl). [NiL2][BF4]2 6. To a suspension of L2 (100 mg, 0.14 mmol) in absolute EtOH (2 cm3) was added dry NiCl2 (15 mg, 0.14 mmol, 1.0 equivalent) and the resulting clear dark brown solution was warmed to reflux for 3 h. After evaporation of theJ.Chem. Soc., Dalton Trans., 1998, Pages 263–270 269 EtOH, CH2Cl2 (2 cm3) was added. To the resulting pale brown suspension was added NaBF4 (60 mg, 0.55 mmol, 4 equivalents). After stirring for an additional 2 h at r.t., the reaction mixture was filtered over Celite to remove the excess of NaBF4 and evaporation of the solvent gave a dark brown solid that was crystallised from dichloromethane–pentane to afford complex 6 as dark brown crystals: 63 mg (53%). 31P NMR (CDCl3): d 31.3. 1H NMR (CDCl3, 200 MHz): d 8.2–8.0 (br, 2 H), 7.9–7.3 (m, 28 H), 7.3–7.0 (br, 6 H) and 7.0–6.8 (br, 2 H). ES mass spectrum: m/z 873 (M 2 BF4) and 394 (M 2 2BF4) (Found: C, 62.50; H, 4.28; N, 3.12. Calc. for C50H38B2F8N2NiP2: C, 62.48; H, 3.99; N, 2.91%). Crystallography X-Ray data for compound 1 were collected at 130 K on an Enraf-Nonius CAD-4F2 diffractometer with Mo-Ka radiation (l = 0.710 73 Å). The orange crystal was quickly removed from the wall of the vessel and mounted on top of a glass fibre.The structure was solved by Patterson methods and extension of the model was accomplished by direct methods applied to difference structure factors using the program DIRDIF.28 The positional and anisotropic thermal displacement parameters for the non-hydrogen atoms were refined on F 2 with full-matrix least-squares procedures minimising the Q = Sh[w(|Fo)2 2 k(Fc)2|2], where w = 1/[s2(Fo)2 1 (aP)2 1 bP], P = [max(Fo,02) 1 2Fc 2]/3. Reflections were stated observed if satisfying the F 2 > 0 criterion of observability. A subsequent Fourier-difference synthesis resulted in the location of all hydrogen atoms, the coordinates and isotropic thermal displacement parameters of which were refined.Final refinement on F 2 carried out by fullmatrix least-squares techniques converged at wR(F 2) = 0.1298 for 4269 reflections with F 2 > 0 and R(F ) = 0.0471 for 3921 reflections with F > 4.0s(F ) and 359 parameters. A final Fourier-difference map showed residual densities between 21.14 and 11.22(13) e Å23 and one peak of 3.13 e Å23 located near (1.86 Å) the Pd atom.No other significant peaks having chemical meaning were observed in the final Fourier-difference syntheses. Geometrical calculations were done with PLATON.29 X-Ray data for compounds 3 and 5 were collected at 150 K on an Enraf-Nonius CAD4T diffractometer with rotating anode and graphite monochromated Mo-Ka radiation. Orange crystals were cut to size and covered by inert oil to avoid deterioration due to loss of solvent.A total of 12 388 reflections for 3 and 19 488 for 5 were scanned to qmax of 26.0 and Table 4 Summary of crystal data for compounds 1, 3 and 5 Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Dc/g cm23 Z F(000) Crystal size/mm m(Mo-Ka)/cm21 Ra wR2 b S 1 (C26H22- ClNPPd)2 1042.6 Monoclinic C2/c 17.789(5) 14.170(4) 19.423(7) 113.02(2) 4506(3) 1.537 4 2104 0.19 × 0.44 × 0.50 10.26 0.0471 0.1298 1.083 3?4CH2Cl2 (C27H21NO2- PPd)2 1397.45 Trigonal P3121 13.009(2) 13.009(2) 29.706(6) 4353.7(13) 1.599 3 2106 0.40 × 0.50 × 0.50 10.9 0.0653 0.156 0.988 5?3.5CH2Cl2 C50H38Cl2N2- P2Pd 906.1 Triclinic P1� 15.1653(18) 19.369(2) 20.3003(17) 100.755(10) 99.828(8) 111.470(10) 5262.1(10) 1.519 4 2436 0.45 × 0.70 × 0.70 9.1 0.0673 0.174 1.008 a R = S(|Fo| 2 |Fc|)/S|Fo|.b wR2 = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� . 25.48 respectively. Intensity data for 3 were corrected for absorption PLATON/DIFABS.29 The structures of 3 and 5 were solved by Patterson methods (DIRDIF) 28 and direct methods (SHELXS 8630), respectively.Least-squares refinement of F 2 was done with SHELXL 96.31 Hydrogen atoms were taken into account at calculated positions riding on their carrier atoms. Convergence was reached at wR2 = 0.1560 [5513 reflections, R1 = 0.0653 for 3793 reflections with I > 2s(I)] and 0.1735 [18 889 reflections, R1 = 0.0673 for 11 771 reflections with I > 2s(I)].The final difference map did not show any significant residual features. Geometrical calculations and the ORTEP illustrations were done with PLATON.29 The final results were checked for missed symmetry with the PLATON/ MISSYM option and solvent-accessible voids with the PLATON/SOLV option. CCDC reference number 186/754. See http://www.rsc.org/suppdata/dt/1998/263/ for crystallographic files in .cif format. Acknowledgements This work was supported in part (A.L. 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ISSN:1477-9226    

DOI:10.1039/a704170e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 269–272 269 Bis[hydrazido(22)] and related complexes of molybdenum(VI): towards alkene-metathesis catalysts based on hydrazido(22) ligation Jonathan R. Dilworth,*,a Vernon C. Gibson,*,b Canzhong Lu,a John R. Miller,a Carl Redshawb and Yifan Zheng a a Department of Biological and Chemical Sciences, University of Essex, Wivenhoe Park, Colchester CO4 3SQ, UK b Department of Chemistry, Imperial College, London SW7 2AY, UK The complex [Mo(NBut)2Cl2(dme)] (dme = 1,2-dimethoxyethane) underwent an imide-ligand exchange reaction with an excess of 1,1-diphenylhydrazine hydrochloride in refluxing dme to give the bis[hydrazido(22)] complex [MoCl2(NNPh2)2(dme)] 1.Reaction of 1 with an excess of PMe3 in CH2Cl2 gave [MoCl2(NNPh2)2(PMe3)2] 2. Treatment of Na2[MoO4] with 2 molar equivalents of Ph2NNH2?HCl in the presence of NEt3 and SiMe3Cl in refluxing dme afforded the salt [NHEt3][MoCl4(NNPh2)(NHNPh2)] 3. The crystal structures of 1–3 have been determined; all possess octahedral geometries with unidentate hydrazido groups.The hydrazido(22) Mo]N bond distances vary from 1.749(2) and 1.771(2) Å in 1, to 1.793(3) in 2 and 1.748(2) Å in 3, with no simple correlation with the Mo]Na]Nb angle. The anionic component of 3 contains a bent hydrazide(12) ligand (Mo]N]N 136.08) and a linear hydrazido(22) group (Mo]N]N 174.48). Imide ligands play a central role in the stabilization of welldefined metathesis catalysts of molybdenum,1 tungsten 2 and rhenium.3 The four-co-ordinate molybdenum complexes [Mo(NC6H3Pri 2-2,6)(CHCMe2Ph)(OR)2] [R = CMe3, CMe2- (CF3) or CMe(CF3)2] in particular have found widespread application in the controlled synthesis of polymers via ringopening metathesis polymerization.4 In view of the close isoelectronic relationship between the hydrazide(22) ligand and the imido (NR) group, we have embarked upon a programme of study aimed at exploring the potential of hydrazide ligands for stabilizing a new family of well defined metathesis catalysts.Here, we report the synthesis, characterization and crystal structures of several important precursors. Results and Discussion We have recently shown that the complex [MoCl2(NBut)2(dme)] (dme = 1,2-dimethoxyethane) undergoes imide ligand exchange upon treatment with anilines in dme at 70 8C.5 This synthetic procedure is quite general and we show here that it can be extended to the synthesis of hydrazido(22) complexes by treatment of bis(imido)molybdenum precursors with the hydrochloride salt of diphenylhydrazine.The reaction of [MoCl2(NBut)2(dme)] with Ph2NNH2?HCl (2 equivalents) in refluxing dme (ca. 2 h) readily gives multigram quantities of [MoCl2(NNPh2)2(dme)] 1 as an orange solid. Complex 1 shows a single nNN stretch at 1586 cm21. Crystals suitable for an X-ray analysis were grown from dme at 220 8C; the molecular structure is shown in Fig. 1. Bond lengths and angles are collected in Table 1 and crystal data are given in Table 4.The molecular geometry is distorted octahedral with trans chloride and cis hydrazido(22) groups. The N(1)]Mo]N(3) angle is 105.56(10)8, the cis O(1)]Mo]Cl(2) and trans Cl(2)]Mo]Cl(1) angles are 85.99(5)8 and 162.14(3)8 respectively. The two hydrazide(22) ligands are somewhat different: the Mo]N distances are short [Mo]N(1) 1.749(2), Mo]N(3) 1.771(2) Å], the former is the shortest reported to date for the cis-{M(NNR2)2} core.6 The corresponding Mo]N]N angles are 173.4(2) and 154.6(2)8.By comparison with analogous bis(imido)molybdenum complexes, the latter is likely to be at the lower limit for a linear hydrazido(22) group. Treatment of complex 1 with 1 equivalent of magnesium in thf in the presence of an excess of trimethylphosphine afforded orange crystalline [MoCl2(NNPh2)2(PMe3)2] 2. Roomtemperature NMR data reveal a virtually coupled triplet centred at d 1.55 in the 1H NMR spectrum and a singlet in the 31P NMR spectrum (d 5.92) consistent with a structure in which the two phosphines are equivalent.Crystals of 2 suitable for a structure determination were grown by diffusion of heptane into a saturated CH2Cl2 solution. Fig. 2 shows the cis chloride, trans phosphine pseudo-octahedral geometry of 2. The crystal data are given in Table 4 and selected bond lengths and angles are in Table 2. The molecules lie on crystallographic two-fold axes.The Mo]N separation of 1.793(3) Å and the associated Mo]N(1)]N(2) angle of 175.2(2)8 are consistent with linear hydrazido(22) units. Attempts to isolate complex 1 by interaction of Na2[MoO4] with Ph2NNH2?HCl in the presence of NEt3 and SiMe3Cl in refluxing dme led, after work-up, to a diamagnetic purple crystalline solid. Infrared data showed a N]H stretch at 3208 cm21 and a strong nNN stretch at 1585 cm21, while the 1H NMR spectrum contained resonances at d ca. 8.2 (br) and ca. 12.9 (sharp) due to two different nitrogen-bound hydrogens. Analytical data Fig. 1 Molecular structure of complex 1, without H atoms and with key atoms labelled270 J. Chem. Soc., Dalton Trans., 1997, Pages 269–272 were consistent with the stoichiometry [NHEt3][MoCl4- (NNPh2)(NHNPh2)] 3. The structure was determined by X-ray diffraction and a view of the ion pair is shown in Fig. 3. Selected bond lengths and angles and crystal data are given in Tables 3 and 4 respectively.The structure contains a pseudooctahedral anionic molybdenum fragment with cis NNPh2 units bound in two different ways. One has the linear Mo]N]N arrangement, with short M]N and N]N bonds and a trigonalplanar arrangement of the N(2) atom, and may be described as a ‘hydrazide(22)’ ligand, or better related to its geometry, as an ‘isodiazene’.7 The other ligand is notably different, with a Mo]N]N angle of 136.0(2)8, a Mo]N distance of 1.958(2) Å and a N]N distance of 1.358(3) Å.Atom N(4) has a trigonal- Fig. 2 Molecular structure of complex 2, without H atoms and with key atoms labelled Table 1 Selected bond lengths (Å) and angles (8) for complex 1 Mo]N(1) Mo]O(1) Mo]Cl(2) N(1)]N(2) N(2)]C(21) N(4)]C(31) 1.749(2) 2.322(2) 2.4380(9) 1.324(3) 1.435(3) 1.421(3) Mo]N(3) Mo]O(2) Mo]Cl(1) N(2)]C(11) N(3)]N(4) N(4)]C(41) 1.771(2) 2.331(2) 2.4451(9) 1.430(3) 1.326(3) 1.440(3) N(1)]Mo]N(3) N(3)]Mo]O(1) N(3)]Mo]O(2) N(1)]Mo]Cl(2) O(1)]Mo]Cl(2) N(1)]Mo]Cl(1) O(1)]Mo]Cl(1) Cl(2)]Mo]Cl(1) N(1)]N(2)]C(11) C(11)]N(2)]C(21) N(3)]N(4)]C(31) C(31)]N(4)]C(41) 105.56(10) 89.75(9) 159.68(9) 97.19(7) 85.99(5) 94.23(7) 79.40(5) 162.14(3) 120.0(2) 122.2(2) 118.3(2) 122.6(2) N(1)]Mo]O(1) N(1)]Mo]O(2) O(1)]Mo]O(2) N(3)]Mo]Cl(2) O(2)]Mo]Cl(2) N(3)]Mo]Cl(1) O(2)]Mo]Cl(1) N(2)]N(1)]Mo N(1)]N(2)]C(21) N(4)]N(3)]Mo N(3)]N(4)]C(41) 164.13(8) 94.46(9) 70.60(7) 92.88(8) 80.98(6) 97.23(8) 84.49(5) 173.4(2) 116.3(2) 154.6(2) 118.6(2) Table 2 Selected bond lengths (Å) and angles (8) for complex 2 Mo]N(1) Mo]P Mo]Cl P]C(2) P]C(1) 1.793(3) 2.5141(12) 2.5625(11) 1.805(5) 1.810(4) P]C(3) N(1)]N(2) N(2)]C(11) N(2)]C(21) 1.811(4) 1.306(4) 1.432(4) 1.450(4) N(1)]Mo]N(1I) N(1)]Mo]P N(1)]Mo]PI P]Mo]PI N(1)]Mo]ClI P]Mo]ClI N(1)]Mo]Cl 103.6(2) 92.59(9) 93.02(9) 170.92(5) 165.80(9) 82.45(4) 90.03(9) P]Mo]Cl ClI]Mo]Cl N(2)]N(1)]Mo N(1)]N(2)]C(11) N(1)]N(2)]C(21) C(11)]N(2)]C(21) 90.42(4) 76.76(5) 175.2(2) 121.4(3) 119.7(3) 118.8(3) Symmetry relation: I 2x, y, 2z + ��� .planar environment. The atoms Mo, Cl(2), N(1), N(2), N(3) and N(4) are virtually coplanar [maximum deviation through the best plane 0.026 Å for N(3)], and the Mo]N(3)]N(4) unit bends towards the Mo]N(1)]N(2) fragment most likely in order to accommodate a bond to a hydrogen atom (see below). In order to account for the diamagnetism of the compound and the presence of N]H stretching frequencies in the infrared spectrum, the anion has to contain a hydrogen atom not detected by the X-rays but attached to a nitrogen atom; we have placed this hydrogen atom on the first N atom, N(3), of the bent NNPh2 ligand, which would normally imply its description as a ‘N,N-diphenylhydrazido(12)’ group; the internal geometry, particularly the coplanarity of N(4) with N(3), C(31) and C(41), suggests however that it could also be described as a prot diphenylisodiazene. The calculated position of H(1) places it 2.57 Å from Cl(2), consistent with an internal hydrogen bond.The C and N atoms of the triethylammonium cation are very well defined in the structure determination and the Nbound hydrogen atom was placed in a calculated position 0.9 Å from the N atom. This position indicates that it is hydrogen bonded to Cl(3) and Cl(4), with H? ? ? Cl distances of 2.58 and 2.72 Å respectively; thus in the solid state 3 is an ion pair. The internal geometry of the NaNbPh2 units in complexes 1– 3 and in many other complexes of this type, supports the suggestion 7 that these ligands are described more accurately as ‘isodiazene’ than as ‘hydrazido(22)’.The coplanarity of the three bonds to Nb is a constant theme, pointing to Nb being conjugated. The Na]Nb bond distances are intermediate between those for single and double bonds8 (single bond, 1.40– 1.46; double bond, 1.22–1.26 Å). Even in the protonated ligand of 3, Nb is trigonal planar and the N]N distance is only 1.358(3) Å . Isoelectronic with ketones, isodiazenes would be Fig. 3 Molecular structure of complex 3, without H atoms and with key atoms labelled Table 3 Selected bond lengths (Å) and angles (8) for complex 3 Mo]Cl(1) Mo]Cl(3) Mo]N(1) N(1)]N(2) H]Cl(3) 2.4448(7) 2.4213(7) 1.748(2) 1.304(3) 2.579(1) Mo]Cl(2) Mo]Cl(4) Mo]N(3) N(3)]N(4) H(1)]Cl(2) 2.4788(7) 2.4641(7) 1.958(2) 1.358(3) 2.573(1) Cl(1)]Mo]Cl(2) Cl(1)]Mo]Cl(4) Cl(1)]Mo]N(3) Cl(2)]Mo]Cl(4) Cl(2)]Mo]N(3) Cl(3)]Mo]N(1) Cl(4)]Mo]N(1) N(1)]Mo]N(3) N(1)]N(2)]C(11) C(11)]N(2)]C(21) N(3)]N(4)]C(31) C(31)]N(4)]C(41) 84.51(3) 85.73(3) 86.43(7) 87.70(3) 82.97(6) 94.58(7) 92.10(7) 97.15(9) 119.8(2) 121.3(2) 118.5(2) 120.7(2) C(1)]Mo]Cl(3) Cl(1)]Mo]N(1) Cl(2)]Mo]Cl(3) Cl(2)]Mo]N(1) Cl(3)]Mo]Cl(4) Cl(3)]Mo]N(3) Cl(4)]Mo]N(3) Mo]N(1)]N(2) N(1)]N(2)]C(21) Mo]N(3)]N(4) N(3)]N(4)]C(41) 169.31(3) 94.82(7) 86.07(3) 179.32(7) 88.85(3) 97.43(7) 168.34(7) 174.4(2) 118.8(2) 136.0(2) 119.0(2)J. Chem.Soc., Dalton Trans., 1997, Pages 269–272 271 Table 4 Crystal structure determinations for complexes 1–3 1 2 3 Empirical formula M Crystal size/mm Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 m(Mo-Ka)/mm21 F(000) T/K 2q Range/8 hkl Range Reflections collected Independent reflections (Rint) Reflections observed Absorption correction Tmax, Tmin Weighting scheme, w Data, restraints, parameters R1, wR2 a Sc C28H30Cl2MoN4O2 621.40 0.25 × 0.5 × 0.56 Monoclinic P21/n 15.981(5) 9.984(2) 17.688(5) 97.78(2) 2796.1(13) 4 1.476 0.692 1272 291 1.61–25.02 0–18, 0–11, 221 to 20 5096 4910 (0.0121) 4004 [I > 2 s (I)] 1.00, 0.92 1/[s2(Fo 2) + (0.0299P)2 + 1.4945P], P = (Fo 2 + 2Fc 2)/3 4910, 0, 454 0.0267, 0.0678 1.193 C15H19ClMo0.5N2P 341.71 0.39 × 0.72 × 0.83 Orthorhombic Pbcn 9.278(3) 21.692(7) 16.097(9) 3240(2) 8 1.401 0.694 1408 291 1.88–24.98 0–11, 225 to 19, 0–19 5419 2827 (0.0414) 2240 [I > 2 s (I)] 1.00, 0.857 1/[s2(Fo 2) + (0.0475P)2 + 0.9756P], P = (Fo 2 + 2Fc 2)/3 2827, 0, 177 0.0475, 0.1033 1.251 C30H37Cl4MoN5 705.4 0.2 × 0.3 × 0.7 Monoclinic P21/n 12.1775(36) 10.6011(9) 26.4756(97) 99.44(2) 3371.5(1.6) 4 1.390 0.725 1448 291 1.5–25.0 0–14, 212–0, 231 to 31 6620 6305 (0.013) 5016 [I > 1.5 s (I)] 1.00, 0.93 1/[s2(Fo) + (0.02Fo)2] 5016, 0, 361 0.034, 0.046 b 1.80 d a R1 = S |Fo 2Fc|/S|Fo|, wR2 = {[Sw(Fo)2 2 (Fc)2]2/Sw(Fo)2}��� .b wR = [Sw(Fo 2Fc)2/SwFo 2]��� . c [Sw(Fo)2 2 (Fc)2]2/(n 2 p)]��� where n = number of reflections and p = total number of parameters.d [Sw(Fo 2 Fc)2/(n2p)] � �� . expected to have two Na lone pairs in the NaNbC2 plane (alternatively regarded as a combination of a s lone pair on the NN vector and a p pair in the NNC2 plane); Na would be expected to be more basic, and therefore a better donor, than the O atom of a ketone as it carries an effective negative charge. We suggest that the difference between the isodiazene and hydrazido(22) descriptions is real because hydrazido(22) complexes should have pyramidally bound Nb atoms and distinctly longer N]N distances.Assignment of the ligands as electronically neutral isodiazenes implies that they are derived from hydrazines by oxidation rather than via reductive deprotonation. The Mo]N distances in all the complexes suggest multiplebond character except for the protonated ligand of 3, where the distance of 1.958(2) Å is readily assigned to a single bond; this is also consistent with the Mo]Na]Nb angle of 136.0(2)8, i.e.one of the Na lone pairs co-ordinates to Mo, the other to H+. Among the unprotonated ligands there is no correlation between bond distances and the Mo]Na]Nb angle. The derivative chemistry of these hydrazido(22) complexes is under development and will be reported at a future date. Experimental General All manipulations were carried out under an atmosphere of nitrogen using standard Schlenk and cannula techniques or in a conventional nitrogen-filled glove-box. Solvents were refluxed over an appropriate drying agent, and distilled and degassed prior to use.Elemental analyses were performed by the microanalytical services of the Department of Chemistry at Durham and Medac Ltd. The NMR spectra were recorded on a Varian VXR 400 S spectrometer at 400.0 (1H) and 162.0 MHz (31P, referenced to dilute aqueous H3PO4, d 0) and a Bruker DRX 300 machine at 75.0 MHz (13C); chemical shifts are referenced to the residual protio impurity of the deuteriated solvent. The IR spectra (Nujol mulls, CsI or KBr windows) were recorded on Perkin-Elmer 577 and 457 grating spectrophotometers.The complex [Mo(NBut)2Cl2]?dme9 was prepared by the literature method. All other chemicals were obtained commercially and used as received unless stated otherwise. Syntheses [MoCl2(NNPh2)2(dme)] 1. The complex [MoCl2(NBut)2(dme)] (1.0 g, 2.5 mmol) and Ph2NNH2?HCl (1.1 g, 5.0 mmol) in dme (30 cm3) were refluxed for 12 h. After filtration and concentration (to ca. 20 cm3) deep orange prisms of the product were deposited on standing at room temperature. Yield 0.48 g, 31%. Further crops can be obtained from the mother-liquor; overall yield 70% (Found: C, 54.1; H, 4.9; N, 9.1. C28H30Cl2MoN4O2 requires C, 54.1; H, 4.9; N, 9.0%). IR: 2711w, 2600w, 2500w, 2078w, 1586s, 1511w, 1328w, 1298m, 1262s, 1158s, 1087 (br) bs, 1043s, 922w, 862s, 848m, 801s, 760s, 692s, 654w, 634m, 530w and 494m cm21. NMR (CDCl3): 1H (400 MHz), d 7.31 (m, 8 H, o-H), 7.13 (m, 8 H, m-H), 6.94 (m, 4 H, p-H), 3.96 (s, 4 H, CH2) and 3.52 (s, 6 H, CH3); 13C-{1H} (75 MHz), d 142.77, 128.39, 125.58, 120.87, 71.01 (s, CH2 of dme) and 63.86 (s, CH3 of dme).[MoCl2(NNPh2)2(PMe3)2] 2. Trimethylphosphine (0.21 cm3, 2.0 mmol) was added to [MoCl2(NNPh2)2(dme)] (0.5 g, 0.8 mmol) and Mg (0.02 g, 0.83 mmol) in thf (30 cm3). After stirring for 12 h, the volatiles were removed under reduced pressure and the residue was taken up in CH2Cl2 (20 cm3).Diffusion of heptane into CH2Cl2 gave orange prisms. Yield 0.4 g, 82% (Found: C, 52.5; H, 5.7; N, 8.0. C30H38MoN4P2?CH2Cl2 requires C, 53.3; H, 5.8; N, 8.0%). IR: 1587w, 1338w, 1294m, 1250w, 1163w, 948m, 755w, 692w, 497w, 476w, 358w 330w, 314w, 294m and 251vs cm21. NMR (CDCl3): 1H (400 MHz), d 7.19 (m, 16 H, o,m-H), 7.06 (tt, 4 H, J = 6.8, J9 = 1.6, p-H) and 1.55 (t, 18 H, J = 4.0 Hz, PMe3); 13C-{1H} (75 MHz), d 146.39, 131.64, 128.66, 124.29, 17.72 (t, J = 13.0 Hz, PMe3); 31P (162 MHz), d 5.92 (s).[NHEt3][MoCl4(NNPh2)(NHNPh2)] 3. Triethylamine (13.6 cm3, 97.6 mmol) and SiMe3Cl (24.5 cm3, 193.0 mmol) were added to Na2[MoO4] (5.0 g, 24.3 mmol) and Ph2NNH2?HCl (10.72 g, 48.5 mmol) in dme (ca. 20 cm3). After refluxing for 12 h the suspension was filtered whilst hot. Purple lustrous crystals of complex 3 were deposited on standing at room temperature (2.81 g, 16.4% isolated yield) (Found: C, 51.2; H, 5.3; N, 9.8.272 J. Chem. Soc., Dalton Trans., 1997, Pages 269–272 C30H37Cl4MoN5 requires C, 51.0; H, 5.3; N, 9.9%).IR: 3208w, 1585m, 1460s, 1377s, 1261s, 1154m, 806m, 758s, 734m, 693s, 654s, 610m, 522w and 1H (400 MHz), d 12.94 (s, 1 H, NHNPh2), 8.29 (br s, 1 H, Et3NH), 7.17– 7.05 (m, 18 H, o,m-H), 6.89 (t, 2 H, J = 7.4, p-H), 3.21 (m, 6 H, CH2CH3) and 1.31 (t, 9 H, J = 7.2 Hz, CH2CH3); 13C-{1H} (75 MHz), d 144.48, 137.98, 129.49, 128.96, 127.89, 127.36, 124.02, 122.57, 47.12 and 9.13. X-Ray crystallography Numerical data are summarised in Table 4.Data collection. Intensity data were collected on an Enraf- Nonius diffractometer with monochromated Mo-Ka radiation (l = 0.710 73 Å). Cell constants were obtained from least-squares refinement of the setting angles of 25 centred reflections in the range 20 < q < 258 for complex 1, 20 < q < 228 for 2 and 22 < q < 258 for 3. The data were collected in the w–2q scan mode and three standard reflections were measured every 3 h of exposure; 4.5 (for 1), 0 (2) and 6.0% (3) loss of intensity was observed which was linearly corrected during processing.Three standard reflections were measured every 200 to check the crystal orientation. The data were corrected for Lorentzpolarization factors and an absorption correction was applied using y scans of nine reflections. Structure analysis and refinement. Structures 1 and 2 were solved via direct methods (core atoms) 10 and refined on Fo 2 by full-matrix least squares.11 All non-hydrogen atoms were anisotropic. The hydrogen atoms were revealed by Fourier-difference synthesis and isotropically refined.The weighting scheme gave satisfactory agreement. Final R indices [I > 2s (I)]: for 1, R1 (on F) 0.0267, wR2 (on F2) 0.0678; for 2, 0.0475, 0.1033. Largest difference peak and hole: for 1, 0.0245 and 20.447; for 2, 0.679 and 20.429 e Å23. Maximum shift/e.s.d. was 20.212 (for 1) and 20.001 (for 2). Sources of scattering factors were as in ref. 11. Structure 3 was solved by the Patterson heavy-atom method and refined on Fo by full-matrix least squares.12 All nonhydrogen atoms were anisotropic. The hydrogen atoms were included in calculated positions. Final R indices [Fo > 3 s (Fo)]: R1 (on F) 0.034, R9 (on F) 0.046. Largest difference peak and hole: 0.710 and 20.229 e Å23. The maximum shift/e.s.d. was < 0.01. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1977, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/293. Acknowledgements The EPSRC is gratefully acknowledged for a grant to J. R. D. and V. C. G. References 1 R. R. Schrock, J. S. Murdzek, C. G. Bazan, J. Robbins, M. DiMare and M. O’Regan, J. Am. Chem. Soc., 1990, 112, 3875; H. H. Fox, K. B. Yap, J. Robbins, S. Cai and R. R. Schrock, Inorg Chem., 1992, 31, 2287; H. H. Fox, J.-K. Lee, L. Y. Park and R. R. Schrock, Organometallics, 1993, 12, 759. 2 R. R. Schrock, R. T. Depue, J. Feldman, K. B. Yap, D. C. Yang, W. M. Davies, L. Y. Park, M. DiMare, M. Schofield, J. Anhaus, E. Walborsky, E. Evitt, C. Kruger and P. Betz, Organometallics, 1990, 9, 2262; R. R. Schrock, R. T. Depue, J. Feldman, C. J. Schaverian, J. C. Dewan and A. H. Liu, J. Am. Chem. Soc., 1988, 110, 1423. 3 R. Toreki and R. R. Schrock, J. Am. Chem. Soc., 1990, 112, 2448; R. Toreki, R. R. Schrock and W. M. Davies, J. Am. Chem. Soc., 1992, 114, 3367. 4 See V. C. Gibson, Adv. Mater., 1994, 6, 37 and refs. therein. 5 A. Bell, W. Clegg, P. W. Dyer, M. R. J. Elsegood, V. C. Gibson and E. L. Marshall, J. Chem. Soc., Chem. Commun., 1994, 2547. 6 P. B. Kettler, Y. D. Chang and J. Zubieta, Inorg Chem., 1994, 33, 5870. 7 A. A. Danopoulos, G. Wilkinson and D. J. Williams, J. Chem. Soc., Dalton Trans., 1994, 907. 8 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer and A. G. Orpen, J. Chem. Soc., Perkin Trans. 2, 1987, S1. 9 P. W. Dyer, V. C. Gibson, J. A. K. Howard, B. Whittle and C. Wilson, Polyhedron, 1995, 14, 103. 10 G. M. Sheldrick, SHELXS 86, University of Göttingen, 1986 11 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 12 MOLEN, An Interactive Structure Solution Procedure, Enraf- Nonius, Delft, 1990. Received 24th September 1996; Paper 6/06575I

ISSN:1477-9226    

DOI:10.1039/a606575i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 271–277 271 Generation of (Á2-benzyne)bis(triphenylphosphine)platinum(0): orthometallation of the Pt(PPh3)2 complexes of benzyne (C6H4 ) and cyclohexyne (C6H8) Martin A. Bennett,* Thomas Dirnberger, David C. R. Hockless, Eric Wenger and Anthony C. Willis Research School of Chemistry, Australian National University, GPO Box 414, Canberra, A.C.T. 2601, Australia The benzyne–platinum(0) complex [Pt(PPh3)2(h2-C6H4)] has been generated by treatment of a mixture of [Pt(PPh3)2(h2-C2H4)] and chlorobenzene with 2,2,6,6-tetramethylpiperid-1-yllithium at 0 8C and identified by comparison of its 31P NMR parameters with those of the cyclohexyne analogue, [Pt(PPh3)2(h2-C6H8)].The compounds isolated from the reaction and identified by NMR spectroscopy and X-ray crystallography are the (2,29-biphenyldiyl)platinum(II) complex [Pt(h1 :h1-C6H4C6H4)(PPh3)2], formed by reaction of [Pt(PPh3)2- (h2-C6H4)] with free benzyne, and the orthometallated (h1-phenyl)platinum(II) complex [Pt{C6H4(PPh2)-2}(C6H5)- (PPh3)], formed by internal hydrogen-atom migration in [Pt(PPh3)2(h2-C6H4)].The complex [Pt(PPh3)2(h2-C6H8)] undergoes a similar isomerization on heating in benzene to give the (h1-cyclohexen-1-yl)platinum(II) complex [Pt{C6H4(PPh2)-2}(C6H9)(PPh3)], whose structure has also been determined by X-ray crystallography. Short-lived cyclic alkynes, such as cycloheptyne (C7H10), cyclohexyne (C6H8) and benzyne (C6H4) can be stabilized by complex formation with a variety of transition-metal fragments,1–3 including those of the zerovalent d10 metals ML2 (M = Ni, Pd or Pt; L = various tertiary phosphines).A key compound in this work is the cyclohexyne complex [Pt(PPh3)2- (h2-C6H8)] 1, which was first prepared in high yield by the reduction of 1,2-dibromocyclohexene with 1% sodium amalgam in the presence of [Pt(PPh3)3] or [Pt(PPh3)2(h2-C2H4)].4,5 This reaction is believed to proceed via an undetected intermediate platinum(0) complex of 1,2-dibromocyclohexene (Scheme 1).3,6 More recently, Jones and co-workers 7 have made complex 1 by an alternative method in which a mixture of 1-bromocyclohexene and [Pt(PPh3)3] is treated at room temperature with lithium diisopropylamide, LiNPri 2; a likely intermediate is a platinum(0) complex of 1-bromocyclohexene, which would probably undergo rapid dehydrohalogenation in the presence of LiNPri 2 (Scheme 1).This procedure has been extended to generate the Pt(PPh3)2 complexes of the tropylium analogue of benzyne (tropyne, C7H5), [Pt(PPh3)2(h2-C7H5)]1,8 and the Pt(PPh3)2 complexes of other cyclic alkynes.9 Platinum(0)–benzyne complexes [PtL2(h2-C6H4)] [L2 = dcpe, 2P(C6H11)3, 2PEt3, 2PPri 3; dcpe = 1,2-bis(dicyclohexylphosphino) ethane, (C6H11)2PCH2CH2P(C6H11)2] have been made by reduction of the appropriate (o-halogenoaryl)platinum(II) precursors with 43% sodium amalgam (Scheme 2); 10 the weaker reducing agents 1% sodium amalgam or lithium, which are effective in forming nickel(0) complexes of benzyne and of 2,3-didehydronaphthalene from the corresponding nickel(II) precursors,11–13 do not work.However, all attempts to make the benzyne analogue of complex 1, [Pt(PPh3)2(h2-C6H4)] 2, by this procedure have failed, possibly because of preferential reductive cleavage of the P]Ph bond. Complex 2 also could not be obtained from the reaction of cis-[PtCl2(PPh3)2] with o-Li2- C6H4.14 Early attempts to trap benzyne,15,16 generated by thermal decomposition of benzenediazonium carboxylate or benzo- 1,2,3-thiadiazole-1,1-dioxide, with [Pt(PPh3)4] or [Pt(PPh3)2- (h2-C2H4)] were equally unsuccessful owing to the formation of chelate heterocyclic derivatives of platinum(II), such as compounds 3 and 4, which did not fragment to give complex 2; however, the formation of triphenylene in some of these reactions was believed to indicate the possibility of organoplatinum intermediates.The work described here resulted from attempts to generate [Pt(PPh3)2(h2-C6H4)] 2 by a modification of Jones’s procedure, i.e. by treatment of a mixture of [Pt(PPh3)2(h2-C2H4)] and chlorobenzene with the nonnucleophilic base 2,2,6,6-tetramethylpiperid-1-yllithium, Li[NCMe2CH2CH2CH2CMe2] (LiTMP). This reagent was chosen in the light of its reported reaction with chlorobenzene Scheme 1 (i) [Pt(PPh3)3] or [Pt(PPh3)2 (h2-C2H4)]; (ii) 1% Na–Hg; (iii) LiNPri 2; (iv) [Pt(PPh3)3] Pt Br Br Br Br PPh3 PPh3 Pt PPh3 PPh3 Pt Br Br PPh3 PPh3 ( iv ) possible intermediate possible intermediate 1 ( i ) ( ii ) ( iii ) Pt O Pt O S O O PPh3 PPh3 PPh3 PPh3 3 4272 J.Chem. Soc., Dalton Trans., 1998, Pages 271–277 to generate benzyne, which could be trapped in moderate to good yield in the form of its Diels–Alder adducts with 1,3- diphenylisobenzofuran, 2,5-dimethylfuran, pyrrole, or Nmethylisoindole. 17 This approach has also been used to synthesize a dinickel(0) complex of 1,2,4,5-tetradehydrobenzene (benz-1,4-diyne), [Ni2(dcpe)2(m-1,2-h2 : 4,5-h2-C6H2)] by LiTMP-promoted dehydrohalogenation of the 4-fluorobenzyne –nickel(0) complex [Ni(dcpe)(h2-C6H3F-4)] in the presence of [Ni(dcpe)(h2-C2H4)].18 Results A mixture of [Pt(PPh3)2(h2-C2H4)] and chlorobenzene was treated dropwise with approximately 4 equivalents of LiTMP at 0 8C.Monitoring by 31P NMR spectroscopy showed that only ca. 10% of [Pt(PPh3)2(h2-C2H4)] had undergone reaction.After the remaining LiTMP had been added, the 31P NMR spectrum showed, in addition to the singlet at dP 34.5 [1J(PtP) 3741 Hz] due to unchanged [Pt(PPh3)2(h2-C2H4)], a new singlet at dP 28.2 [1J(PtP) 3325 Hz] together with a small singlet at dP 29.0. The similarity of the 31P NMR parameters of the first formed species to those of the cyclohexyne complex [Pt(PPh3)2- (h2-C6H8)] 1 [ dP 28.3; 1J(PtP) 3406 Hz] 19 suggested that they could arise from the desired benzyne complex [Pt(PPh3)2- (h2-C6H4)] 2.Unfortunately, this species was not stable under the reaction conditions and attempts to isolate it failed; it decomposed to give two compounds whose relative amounts depended on temperature, and, more difficult to control, the amount of base in solution. In one experiment, a solution containing 2 was stored at 278 8C, but after 16 h the main species present was characterized by a singlet in the 31P NMR spectrum at d 29.0 [1J(PtP) 2003 Hz].This compound was isolated in a pure state by preparative thin-layer chromatography and was shown by X-ray structural analysis (see below) to be the (2,29- biphenyldiyl)platinum(II) complex, cis-[Pt(h1 :h1-C6H4C6H4)- (PPh3)2] 5. It showed a parent-ion peak in its electron impact (EI)-mass spectrum. The magnitude of 1J(PtP) is ca. 300 Hz greater than generally observed for neutral bis(tertiary arylphosphine) –h1-aryl complexes of the type cis-[PtX(R)L2],20 e.g.for X = R = C6H5, L = PPh3, values of 1J(PtP) in C6D6 of 1763 Hz20 and 1730 Hz21 have been reported. Compound 5 is believed to arise by reaction of the benzyne complex 2 with free benzyne at 278 8C (see Discussion) and can be isolated in 72% yield from reaction of a mixture of [Pt(PPh3)2(h2-C2H4)] and chlorobenzene with a large excess of LiTMP. At room temperature, a solution containing mainly 2 (and some 5) was stable for at least 1 h, but after heating to 50 8C or, alternatively, after evaporation of the solvent at room temperature, the main species present, 6, showed in its 31P NMR spectrum a pair of doublets at d 255.0 and 21.2 [2J(PP) 10.9 Hz] assignable to inequivalent, mutually cis phosphorus atoms, P(1) and P(2), in a planar platinum(II) complex.22 The shielding of P(1) suggests that this phosphorus atom is part of a fourmembered metallacycle,23 cf.[Pt{C6H4(PPh2)-2}2] (dP 252.3) 24 Scheme 2 (i) 43% Na–Hg Pt L L Br Pt Br L L Br P(C6H11)2 Pt (C6H11)2P Br L = PEt3, PPri 3 or P(C6H11)3 L = PEt3, PPri 3 or P(C6H11)3 2L = dcpe ( i ) and [Pt{C6H4(PPh2)-2}(PPh3)2][CF3SO3] (dP 268.3),25 and the remarkably low value of 1J(PtP1), 1021 Hz, indicates that P(1) is trans to a ligand of high trans influence, presumably s-bonded carbon, cf.[Pt{C6H4(PPh2)-2}2], 1352 Hz.24 It should be noted, however, that 1J(PtP) for the phosphorus atom trans to the s-bonded carbon atom of the cycloplatinated ring in [Pt{C6H4(PPh2)-2}(PPh3)2][CF3SO3] is 2006 Hz,25 so these coupling constants can clearly span a wide range.The magnitude of 1J(PtP2) in complex 6 is 2047 Hz, which allows P(2) to be assigned tentatively to PPh3 trans to a s-bonded carbon atom. The 31P NMR data, therefore, suggest the formulation of 6 as cis-[Pt{C6H4(PPh2)-2}(h1-C6H5)(PPh3)]. This compound was also obtained in a pure state by thin-layer chromatography and its structure was confirmed by X-ray crystallography (see below). It is clearly an isomer of the benzyne complex 2 derived by migration of a hydrogen atom from triphenylphosphine to co-ordinated benzyne.The sequence of reactions occurring on treatment of [Pt(PPh3)2(h2-C2H4)] and chlorobenzene with LiTMP is summarized in Scheme 3. The suggested origin of complex 6 receives additional support from the observation that the cyclohexyne complex [Pt(PPh3)2(h2-C6H8)] 1 undergoes a similar, though much slower, isomerization to the (h1-cyclohexen-1-yl)platinum(II) complex [Pt{C6H4(PPh2)-2}(h1-C6H9)(PPh3)] 7 (Scheme 4).This compound was isolated in good yield as a yellow solid when complex 1 was heated in benzene under reflux for 18 d and its identity was confirmed by X-ray crystallography (see below). Use of unrecrystallized samples of complex 1 also gave small amounts of trans-[PtBr(h1-C6H9)(PPh3)2], presumably derived from NaBr impurity in the original preparation.4,5 The 31P NMR spectrum of complex 7 is similar to that of 6, consisting of a doublet at d 252.8 [2J(PP) 10.9, 1J(PtP) 861 Hz] due to the phosphorus atom P(1) in the cyclometallated fourmembered ring and a doublet at d 20.8 [2J(PP) 10.9, 1J(PtP) Scheme 3 (i) [Pt(PPh3)2(h2-C2H4)], LiTMP, 0 8C; (ii) room temperature Pt Cl Pt PPh3 PPh3 Ph2P Pt P2Ph3 PPh3 PPh3 2 5 6 1 ( i ) ( ii ) Scheme 4 (i) C6H6, reflux Pt PPh3 PPh3 Ph2P Pt C3 P2Ph3 C1 C2 1 7 ( i ) 1J.Chem. Soc., Dalton Trans., 1998, Pages 271–277 273 2144 Hz] due to the phosphorus atom P(2) cis to the cyclohexenyl group.The Pt]P couplings are reproduced in the 195Pt NMR spectrum, which shows the expected doublet of doublets at d 23981 (relative to K2PtCl6). The vinylic proton of the h1- cyclohexen-1-yl group appears as a doublet of multiplets at d 5.26 [J(PH) 11.2, J(PtH) 84 Hz], the chemical shift and coupling constants being similar to those of other (h1-cyclohexen- 1-yl)platinum(II) complexes 5,19 and of [Pt{C6H4(PPh2)-2}{h1- C(CO2Me)]] CHCO2Me}(PPh3)].26 In the 13C NMR spectrum of 7, signals due to the quaternary carbon atoms (numbered as in Scheme 4) were located: a doublet of doublets at d 149.70 [J(PC) 107.4, 9.4, 1J(PtC) 905 Hz] due to a carbon atom s bonded to the metal, either that of the cycloplatinated ring (C1) or of the h1-cyclohexen-1-yl group (C3), a broad doublet at d 153.20 [J(PC) 53.0, 2J(PtC) 32 Hz] due to the remaining carbon atom (C2) of the four-membered ring, and a broad doublet at d 154.51 [J(PC) 117.1, 1J(PtC) 844 Hz] due to C3 or C1.The chemical shifts and coupling constants are similar to those of the cycloplatinated ring in [Pt{C6H4(PPh2)-2}(PPh3)3]- [CF3SO3].25 The magnitudes of 1J(PtP) trans to C6H9 in complex 7 (861 Hz), which is one of the smallest 1J(PtP) values reported for a phosphorus trans to a carbon atom, and of 1J(PtP) trans to C6H5 in complex 6 (1021 Hz) follow the same trend as observed for 1J(PtP) trans to the carbon s-donor in [PtCl(R9)(Ph2PCH2CH2PPh2)] [R9 = C6H9, 1J(PtP) = 1558 Hz; R9 = C6H5, 1J(PtP) = 1613 Hz],27 and indicate that cyclohexen- 1-yl has a slightly higher NMR trans influence than phenyl.However, the difference is too small to be reflected in the Pt]P bond lengths (see below). Complex 7 was also formed when 1 was heated at 80 8C in [2H8]toluene, but prolonged reaction in the refluxing solvent generated two more compounds, 8 and 9, whose 31P and 195Pt NMR parameters were closely similar to, but clearly distinct from, those of 7 (see Experimental section); these compounds clearly contain the cycloplatinated unit Pt[C6H4(PPh2)-2].The final solutions contained approximately equal amounts of compounds 7 and 8 and only minor amounts (5–10%) of 9. Similar changes occurred when 1 was heated over several days in refluxing methylcyclohexane, thus eliminating the obvious possibility that the new compounds were isomeric tolyl complexes resulting from the oxidative addition of toluene to complex 7 and subsequent reductive elimination of cyclohexene.The compounds may be cyclohexen-2-yl or cyclohexen- 3-yl isomers of complex 7 resulting from a metal-catalysed migration of the double bond in the six-membered ring. Unfortunately the compounds could not be separated by fractional crystallization or column chromatography, and attempts to promote a double-bond shift in complex 7 by heating it in the presence of a base (NEt3) were unsuccessful. Molecular structures of [Pt(Á1 :Á1-C6H4C6H4)(PPh3)2] 5, cis- [Pt{C6H4(PPh2)-2}(Á1-C6H5)(PPh3)] 6 and cis-[Pt{C6H4(PPh2)- 2}(Á1-C6H9)(PPh3)] 7 The molecular geometry of complex 5 is shown in Fig. 1 together with atom numbering. Selected interatomic distances and angles are listed in Table 1. The molecule occupies a general position in the unit cell. The metal atom Pt(1) is in a distorted square-planar co-ordination environment, carbon atoms C(1) and C(19) being, respectively, 0.422 Å above and 0.293 Å below the plane defined by Pt(1) and the mutually cis phosphorus atoms.The aromatic rings of the biphenyldiyl ligand are planar, with a dihedral angle of 14.88. The two Pt]C bond lengths [Pt(1)]C(1) 2.068(5), Pt(1)]C(19) 2.092(5) Å] are slightly but significantly different, this difference probably arising from crystal packing. The aromatic C]C bonds in the platinacycle [C(1)]C(2) 1.421(6), C(19)]C(29) 1.427(6) Å] are longer than the remaining C]C bonds in the phenyl rings, which are in the usual range (1.366–1.393 Å).The separation between the linked carbon atoms of the two phenyl rings [C(2)]C(29) = 1.466(7) Å] is similar to those reported for other (2,29-biphenyldiyl)- platinum(II) complexes, i.e. [PtL(PPh3)2] [1.461(11) Å],29 [PtL9- (cod)] [1.486(10) Å],29 and [PtL9(bipy)] [1.493(14) Å] 30 [L = 5,59-bis(trifluoromethyl)-2,29-biphenyldiyl; L9 = 5,59-bis- (tert-butyl)-2,29-biphenyldiyl; cod = cycloocta-1,5-diene; bipy = 2,29-bipyridyl]. The Pt]C and Pt]P distances [Pt(1)]C(1) 2.068(5), Pt(1)]C(19) 2.092(5); Pt(1)]P(1) 2.333(1), Pt(1)]P(2) 2.345(1) Å] are also similar to those found in the 5,59- bis(trifluoromethyl) derivative [Pt]C 2.058(7), 2.065(7); Pt]P 2.328(2), 2.346(2) Å].29 Other bond lengths in complex 5 are unexceptional.The molecular geometries of complexes 6 and 7 are very similar, and are shown in Figs. 2 and 3 together with the atom numbering. Selected interatomic distances and angles are given in Tables 2 and 3, respectively.In both compounds the metal atom lies almost in the co-ordination plane defined by the two mutually cis phosphorus atoms and the s-bonded carbon atoms; the distances from the plane P(1), P(2), C(1) and C(8) Fig. 1 An ORTEP28 diagram of [Pt(h1 :h1-C6H4C6H4)(PPh3)2] 5 with atom labelling and 20% probability ellipsoids Table 1 Selected bond distances (Å) and angles (8) for [Pt(h1 :h1- C6H4C6H4)(PPh3)2] 5 Pt(1)]P(1) Pt(1)]C(1) C(1)]C(2) C(2)]C(29) C(19)]C(69) P(1)]Pt(1)]P(2) P(1)]Pt(1)]C(1) P(2)]Pt(1)]C(1) Pt(1)]C(1)]C(2) 2.333(1) 2.068(5) 1.421(6) 1.466(7) 1.388(6) 94.19(5) 95.1(1) 165.0(1) 115.7(4) Pt(1)]P(2) Pt(1)]C(19) C(19)]C(29) C(1)]C(6) C(1)]Pt(1)]C(19) P(1)]Pt(1)]C(19) P(2)]Pt(1)]C(19) Pt(1)]C(19)]C(29) 2.345(1) 2.092(5) 1.427(6) 1.388(7) 79.7(2) 169.3(1) 92.9(1) 113.4(4) Table 2 Selected bond distances (Å) and angles (8) for cis- [Pt{C6H4(PPh2)-2}(h1-C6H5)(PPh3)] 6 Pt(1)]P(1) Pt(1)]C(1) P(1)]C(7) C(1)]C(2) P(1)]Pt(1)]P(2) P(1)]Pt(1)]C(8) P(2)]Pt(1)]C(8) Pt(1)]P(1)]C(7) C(7)]C(8)]C(9) Pt(1)]C(8)]C(9) 2.330(2) 2.052(7) 1.806(7) 1.40(1) 104.18(7) 68.7(2) 171.1(2) 84.3(3) 117.2(6) 136.3(6) Pt(1)]P(2) Pt(1)]C(8) C(7)]C(8) C(1)]C(6) P(1)]Pt(1)]C(1) P(2)]Pt(1)]C(1) C(1)]Pt(1)]C(8) P(1)]C(7)]C(8) Pt(1)]C(8)]C(7) C(8)]C(7)]C(12) 2.309(2) 2.057(6) 1.41(1) 1.41(1) 159.3(2) 95.9(2) 90.8(3) 100.6(5) 106.5(5) 123.8(6)274 J.Chem. Soc., Dalton Trans., 1998, Pages 271–277 are only 0.092 Å and 0.069 Å, respectively, and the bound carbon atoms C(1) and C(8) in both complexes are less than 0.2 Å below the plane defined by Pt(1), P(1) and P(2).The angle subtended at the metal atom in the orthometallated ring in both compounds is 698 (cf. 698 in [Pt{C6H4(PPh2)-2}2]); 24 there are corresponding increases from the ideal value of 908 in the valence angles P(1)]Pt(1)]P(2) [104 (6), 1078 (7)]. The Pt]P distances in both four-membered rings [Pt(1)]P(1) 2.330(2) (6), 2.336(1) Å (7)] are comparable both to those in the cycloplatinated complexes [Pt{C6H4(PPh2)-2}2] ][2.297(1) Å] 24 and [Pt{C6H4(PPh2)-2}{h1-C(CO2Me)]] CH(CO2Me)}(PPh3)] [2.329(2) Å],31 and to the Pt]P bond length to the unmetallated PPh3 ligand [Pt(1)]P(2) = 2.309(2) (6), 2.296(1) Å (7)].The Pt]C distances in the four-membered ring of all four platinacycles discussed above fall in the narrow range 2.056–2.063 Å, and are similar to the Pt]C6H5 bond length in 6 [Pt(1)]C(1) 2.052(7) Å] and to the Pt]C6H9 bond length in 7 [Pt(1)]C(1) 2.054(5) Å].Discussion Although the benzyne complex [Pt(PPh3)2(h2-C6H4)] 2 is generated by treatment of a mixture of chlorobenzene and [Pt(PPh3)2(h2-C2H4)] with LiTMP, the procedure is evidently not as successful as that used by Jones and co-workers 7 to prepare the cyclohexyne complex [Pt(PPh3)2(h2-C6H8)] 1 (Scheme 1). In principle, there are two possible routes by which complex 2 could have been formed: (i) deprotonation of a transient intermediate dihapto chlorobenzene complex [Pt(PPh3)2(h2- C6H5Cl)], analogous to the intermediate 1-bromocycloheptene complex [Pt(PPh3)2(h2-C7H11Br)] detected by Jones and co- Fig. 2 An ORTEP diagram of cis-[Pt{C6H4(PPh2)-2}(h1-C6H5)(PPh3)] 6 with atom labelling and 20% probability ellipsoids Table 3 Selected bond distances (Å) and angles (8) for cis- [Pt{C6H4(PPh2)-2}(h1-C6H9)(PPh3)] 7 Pt(1)]P(1) Pt(1)]C(1) P(1)]C(7) C(1)]C(2) P(1)]Pt(1)]P(2) P(1)]Pt(1)]C(8) P(2)]Pt(1)]C(8) Pt(1)]P(1)]C(7) C(7)]C(8)]C(9) Pt(1)]C(8)]C(9) 2.336(1) 2.054(5) 1.799(5) 1.361(8) 106.95(4) 68.6(1) 174.5(1) 84.1(2) 117.2(5) 136.6(4) Pt(1)]P(2) Pt(1)]C(8) C(7)]C(8) C(1)]C(6) P(1)]Pt(1)]C(1) P(2)]Pt(1)]C(1) C(1)]Pt(1)]C(8) P(1)]C(7)]C(8) Pt(1)]C(8)]C(9) C(8)]C(7)]C(12) 2.296(1) 2.057(5) 1.409(7) 1.466(8) 159.7(2) 92.8(2) 91.3(2) 101.0(4) 106.2(3) 122.5(5) workers 7 in the preparation of the cycloheptyne complex [Pt(PPh3)2(h2-C7H10)]; (ii) deprotonation of chlorobenzene to give free benzyne, which is trapped by [Pt(PPh3)2(h2-C2H4)].It is plausible that the vinylic halides 1-bromocyclohexene and 1-bromocycloheptene form much stronger p complexes than the aromatic halide chlorobenzene with platinum(0); hence free cyclohexyne or cycloheptyne are not formed whereas under similar reaction conditions free benzyne is readily generated. By whatever route complex 2 is formed, it is clearly capable of reacting rapidly with the highly reactive alkyne benzyne to give [ Pt(h1 :h1-C6H4C6H4)(PPh3)2] 5.This insertion is analogous to the first step, forming a benzonickelacyclopentadiene, of the double insertion of alkynes into nickel(0)–benzyne and nickel(0)–2,3-h-didehydronaphthalene bonds to give, respectively, substituted naphthalenes and anthracenes after reductive elimination of the nickel(0) fragment.3,11–13,32 Fewer reactions of this type are known with platinum(0) complexes: complex 1 is inert towards alkynes, although its derivatives [Pt(R02- PCH2CH2PR02)(h2-C6H8)] (R0 = Me, Et or C6H11) undergo monoinsertion with dimethyl acetylenedicarboxylate to give [Pt{C6H8C(CO2Me)]] C(CO2Me)}(R02PCH2CH2PR02)].33 Benzyne has been reported to insert into the Ni]CH2 bond of the metallacycle [Ni{C6H4(CMe2CH2)-2}(PMe3)2] to give, after reductive elimination, 9,9-dimethyl-9,10-dihydrophenanthrene. 34 It also inserts into the metal–phenylacetylide bond of the trichlorovinylnickel(II) complex trans-[Ni(C2Ph)(C2Cl3)- (PEt3)2] to give trans-[Ni(C6H4C2Ph-2)(C2Cl3)(PEt3)2], together with the product of reductive elimination, C6H4(C2Ph)-1- (C2Cl3)-2.35 A second reason for the failure to isolate the benzyne complex 2 is that it readily isomerizes at or just above room temperature to the orthometallated complex cis-[Pt{C6H4(PPh2)- 2}(h1-C6H5)(PPh3)] 6.The mechanism by which the hydrogen atom is transferred from PPh3 to the unsaturated fragment is not known, but the process is clearly faster than the corresponding isomerizations of the cyclohexyne complex 1 to the cyclohexen-1-yl complex 7 and of the dimethyl acetylenedicarboxylate complex [Pt(PPh3)2(h2-MeO2CC2CO2Me)] to the cis-1,2-bis(methoxycarbonyl)vinyl complex [Pt(C6H4PPh2-2)- {h1-C(CO2Me)]] CH(CO2Me)}(PPh3)],26,31 which require long reaction times at elevated temperatures.The difference may reflect the relatively greater strain and weaker binding of benzyne to the platinum(0) centre. Other orthometallations of platinum(0)–triphenylphosphine complexes also generally require forcing conditions, e.g.irradiation at 254 nm for the Fig. 3 An ORTEP diagram of cis-[Pt{C6H4(PPh2)-2}(h1-C6H9)(PPh3)] 7 with atom labelling and 20% probability ellipsoidsJ. Chem. Soc., Dalton Trans., 1998, Pages 271–277 275 isomerization of [Pt(PPh3)2(h2-C2H4)] to [Pt{C6H4(PPh2)-2}- (C2H5)(PPh3)] 36 and elevated temperatures for the formation of dinuclear or polynuclear cycloplatinated complexes from [Pt(PPh3)n] (n = 2–4).37–41 Experimental General procedures All experiments were performed under an inert atmosphere with use of standard Schlenk techniques, and all solvents were dried and degassed prior to use.All reactions involving benzyne complexes were carried out under argon. The NMR spectra were recorded on the following spectrometers: Varian XL-200E (1H at 200 MHz, 13C at 50.3 MHz, 31P at 80.96 MHz and 195Pt at 42.83 MHz), Varian Gemini-300 BB (1H at 300 MHz, 13C at 75.4 MHz and 31P at 121.4 MHz), Varian VXR-300 (1H at 300 MHz and 13C at 75.4 MHz) and Varian VXR-500 (1H at 500 MHz).The chemical shifts (d) for 1H and 13C are given in ppm relative to residual signals of the solvent, to external 85% H3PO4 for 31P and to external K2PtCl6 for 195Pt. The spectra of all nuclei (except 1H) were 1H decoupled. The coupling constants (J) are given in Hz. Infrared spectra were measured in solid KBr or in solution (KBr cells) on Perkin-Elmer 683 or 1800 FT-IR spectrometers.Mass spectra were obtained by the electron impact (EI) method on a VG Micromass 7070F or a Fisons Instruments VG AutoSpec spectrometer. Starting materials The ethene complex [Pt(PPh3)2(h2-C2H4)] was prepared as described by Nagel.42 The cyclohexyne complex [Pt(PPh3)2- (h2-C6H8)] 1, obtained by a published procedure,5 was washed thoroughly with air-free water and recrystallized from toluene– hexane (1 : 6) before use. Reaction of LiTMP with chlorobenzene in the presence of [Pt(PPh3)2(Á2-C2H4)] In a typical experiment, a solution of LiTMP in tetrahydrofuran (thf) (10 cm3), prepared from 2,2,6,6-tetramethylpiperidine (0.23 cm3, 1.35 mmol) and LiBun (0.79 cm3 of 1.37 M solution in hexane, 1.08 mmol), was added over 1.5 h to a thf solution (10 cm3) at 0 8C containing [Pt(PPh3)2(h2-C2H4)] (200 mg, 0.27 mmol) and chlorobenzene (0.29 cm3, 2.7 mmol).After addition of 1 equivalent of base, monitoring by 31P NMR spectroscopy showed that only 10% of [Pt(PPh3)2(h2-C2H4)] had reacted to form [Pt(PPh3)2(h2-C6H4)] 2.After complete addition of the base and further stirring for 2 h at room temperature, the solution contained a mixture of [Pt(PPh3)2- (h2-C2H4)] [dP 34.5, J(PtP) 3741], [Pt(h1 :h1-C6H4C6H4)(PPh3)2] 5 and 2 in a ratio of 2.1:1:3.9. Attempts to isolate the benzyne complex were unsuccessful. For example, after removal of most of the toluene in vacuo and addition of hexane (20 cm3), the solution was left for 16 h at 278 8C but no crystallization occurred.After evaporation of the solvent, the 31P NMR spectrum of the residue showed the presence of a 3 : 1 mixture of compounds 5 and 2, indicating that further reaction of 2 with free benzyne to give 5 had occurred. In another work-up, the reaction mixture was left at room temperature and the solvent was evaporated. The 31P NMR spectrum of the residue showed the presence of a 1.8:1:2.4 mixture of compounds 5, 2 and 6 with only a trace of [Pt(PPh3)2(h2-C2H4)]; rearrangement of 2 into the cyclometallated product 6 had occurred. Several fractions were combined and complexes 5 and 6 were separated by preparative TLC (silica gel, hexane–diethyl ether 5 : 1); 6 migrated faster than 5.Yellow crystals of 5 and colourless crystals of 6 suitable for X-ray analysis were obtained from toluene–hexane and chlorobenzene–hexane, respectively. The amount of 6 was, however, insufficient for microanalysis. In another experiment, the biphenyldiyl complex 5 was prepared by adding chlorobenzene (0.72 cm3, 6.7 mmol) and a solution of [Pt(PPh3)2(h2-C2H4)] (500 mg, 0.67 mmol) in thf (15 cm3) to a solution of LiTMP (2.68 mmol) in thf (20 cm3) at 260 8C.The solution was stirred for 2.5 h at 0 8C and 2 h at room temperature. As the 31P NMR spectrum of the solution showed that some 2 was still present, further LiBun (1 cm3 of 1.37 M solution in hexane) was added dropwise and the mixture was stirred for 16 h at room temperature.After evaporation of the solvent, the crude product was dissolved in diethyl ether and the solution was filtered through a silica gel column. Removal of the solvent afforded pure 5 (421 mg, 72%). Complex 2: dP(80.96 MHz, C6D6) 28.2 [J(PtP) 3325]. Complex 5: (Found: C, 65.6; H, 4.1. C48H38P2Pt requires C, 66.1; H, 4.4%); dH(300 MHz, CD2Cl2) 7.00–7.70 (m, 34 H); dC(75.43 MHz, CD2Cl2) 127.9–128.4 (m), 128.75, 129.90, 129.99, 132.19, 132.32, 134.2– 135.5 (m); dP(80.96 MHz, C6D6) 29.0 [J(PtP) 2003]; m/z (C48H38P2Pt) 871 (M1, 5%), 262 (100), 228 (66), 183 (44), 154 (44), correct isotopic patterns.Complex 6: dH(500 MHz, CD2Cl2) 6.75–7.40 (m, 34 H); dC(75.43 MHz, CD2Cl2) 126.27, 127.57, 127.69, 128.02, 128.15, 128.24, 129.44 [d, J(PC) 2.2], 129.52, 129.60 [d, J(PC) 2.7], 132.71, 132.86, 133.87, 134.03, 137.58 [J(PtC) 38.5, CH]; dP(121.4 MHz, C6D6) 255.0 [d, J(PP) 10.9, J(PtP) 1021, P(1)], 21.2 [d, J(PP) 10.9, J(PtP) 2047, P(2)]; m/z (C42H34P2Pt) 795 (M1, 38%), 718 (5), 455 (5), 377 (6), 262 (100), 228 (24), 183 (62), 154 (35), correct isotopic patterns.Preparation of cis-[Pt{C6H4(PPh2)-2}(Á1-C6H9)(PPh3)] 7 A solution of [Pt(PPh3)2(h2-C6H8)] 1 (0.16 g, 0.2 mmol) in benzene (5 cm3) was stirred under reflux for 18 d and the solvent was removed by evaporation under reduced pressure. The yellow residue was recrystallized from CH2Cl2–hexane to give 7 as a pale yellow crystalline solid (96 mg, 75%) (Found; C, 63.5; H, 5.1.C42H38P2Pt requires C, 63.1; H, 4.8%); m.p. 234 8C (decomp.); n& max/cm21 (KBr) 3040w, 2980w, 2920m, 2859w, 2810m, 1600w, 1588w, 1560m, 1480s, 1430s, 1308m, 1275m, 1095s, 1035m, 998m, 745s, 735s, 720s, 690s, 530s, 510s, 450m, 440m; dH(200 MHz, CD2Cl2) 0.35–0.55 (br, 4 H, CH2), 1.80– 2.00 (br, 2 H, CH2), 2.05–2.25 (br, 2 H, CH2), 5.26 [dm, 1 H, J(PH) 11.2, J(PtH) 84, ]] CH], 7.00–7.65 (m, 29 H, Harom), 7.65– 7.75 [m, 1 H, J(PtH) 57, PtC]] CHortho]; dC(50.3 MHz, CD2Cl2) 24.39 [C(4)]H2], 26.36 [d, J(PC) 5.7, J(PtC) 59.6, C(5)]H2], 29.55 [d, J(PC) 9.6, J(PtC), 86.4, C(6)]H2], 38.44 [d, J(PC) 4.5, J(PtC) 57.2, C(3)]H2], 125.00 [m, J(PtC) 20, CH], 127.70 (m, CH), 128.15 [d, J(PC) 9.7, CH], 128.26 [d, J(PC) 9.7, CH], 128.62 [d, J(PC) 9.5, CH], 128.75 [d, J(PC) 9.5, CH], 129.97 (br s, CH), 130.25 (CH), 131.45 [d, J(PC) 32, C], 131.70 (m, CH), 133.30 [d, J(PC) 10.7, CH], 133.43 [d, J(PC) 10.7, CH], 134.0– 134.6 (m, C), 134.58 [d, J(PC) 11.7, CH], 134.72 [d, J(PC) 11.7, CH], 138.25 [m, J(PtC) 39, CH], 149.70 [dd, J(PC) 107.4, 9.4, J(PtC) 905, C(112) or C(31)], 153.20 [br d, J(PC) 53.0, J(PtC) 32, C(111)], 154.51 [br d, J(PC) 117.1, J(PtC) 844, C(31) or C(112)]; dP(80.96 MHz, CD2Cl2) 252.8 [d, J(PP) 10.9, J(PtP) 861, P(1)], 20.8 [d, J(PP) 10.9, J(PtP) 2144, P(2)]; dPt(42.83 MHz, CD2Cl2) 23981 [dd, J(PtP) 2144, 861].Under the same conditions, samples of compound 1 that had not been freed from NaBr gave a ca. 4 : 1 mixture of complex 7 and trans-[PtBr(h1-C6H9)(PPh3)2], which could be almost completely separated by fractional crystallization from CH2Cl2– hexane. The latter compound was identified by comparison of its spectroscopic parameters with those of a sample prepared by treatment of complex 1 first with the calculated quantity of 0.1 M HCl in thf to give a mixture of cis- and trans-[PtCl- (h1-C6H9)(PPh3)2] and then with NaBr to give the required product as the colourless trans isomer (Found: C, 56.3; H, 4.5.C42H39BrP2Pt?0.25CD2Cl2 requires C, 55.3; H, 4.5%); m.p. 213 8C (decomp.); n& max/cm21 (KBr) 3070w, 3050w, 2920m, 2850m, 2820m, 1615w, 1585w, 1570w, 1480s, 1430s, 1095s, 740s, 690s, 520s, 510s, 495s; dH(200 MHz, CD2Cl2) 0.25–0.35 (br m, 2 H, CH2), 0.40–0.55 (br m, 2 H, CH2), 1.20–1.30 (br m, 2 H,276 J. Chem. Soc., Dalton Trans., 1998, Pages 271–277 Table 4 Crystal and structure refinement data for [Pt(h1 :h1-C6H4C6H4)(PPh3)2] 5, cis-[Pt(C6H4PPh2-2)(h1-C6H5)(PPh3)] 6 and cis-[Pt(C6H4PPh2-2)- (h1-C6H9)(PPh3)] 7 Compound Chemical formula M Crystal system a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Space group Dc/g cm23 Z T/K F(000) Colour, habit Crystal size/mm m/cm21 Diffractometer X-Radiation Scan mode w Scan width 2q limits/8 h, k, l Ranges Total reflections Unique reflections Used reflections Corrections (transmission factors) Structure solution Refinement No.of parameters g in Weighting scheme d R (used reflections) R9 (used reflections) Goodness of fit rmax, rmin/e Å23 5 C48H38P2Pt 964.01 Triclinic 12.910(4) 13.077(3) 4.724(3) 74.05(2) 79.12(2) 65.70(2) 2170(1) P1� (no. 2) 1.475 2 293 968 Yellow, irregular 0.32 × 0.24 × 0.16 33.31 Rigaku AFC6S Mo-Ka (graphite monochromated) w–2q 0.80 1 0.34 tan q 50.1 (0, 216, 218) to (15, 16, 18) 8057 7681 (Rint = 0.021) 6137 [I > 3s(I)] Azimuthal scans (0.8806–1.0000) Direct methods a (SHELXS 86,48 DIRDIF 9449) Full-matrix least squares 523 0.002 0.030 0.024 1.59 0.83, 20.79 6 C42H34P2Pt?1.22C6H5Cl?0.28C6H14 795.78 1 162.38 Monoclinic 10.910(3) 22.913(4) 16.877(4) 100.28(2) 4151.0(17) P21/n (no.14) 1.533 4 298 1915 Colourless, trapezoidal 0.06 × 0.09 × 0.12 80.3 Rigaku AFC6R Cu-Ka (graphite monochromated) w–2q 1.21 1 0.30 tan q 120 (0, 0, 218) to (12, 25, 18) 6368 6176 (Rint = 0.015) 4454 [I > 2s(I)] Analytical (0.519–0.706) Direct methods b (SIR 92) 53 Full-matrix least squares with conditions 55 455 0.015 0.035 0.047 1.05 0.91, 20.75 7 C42H38P2Pt 799.79 Monoclinic 11.178(1) 14.892(1) 21.156(1) 98.20(1) 3485.7(4) P21/c (no. 14) 1.524 4 293 1592 Colourless, block 0.24 × 0.15 × 0.26 86.89 Philips PW1100/20 Cu-Ka (graphite monochromated) w–2q 1.2 1 0.142 tan q 128 (213, 0, 0) to (12, 17, 24) 6228 5798 5249 [I > 3s(I)] Analytical (0.155–0.386) Patterson method c (SHELXS 86)48 Full-matrix least squares 406 0.01 0.028 0.046 1.827 0.4, 21.2 a All calculations were performed by use of TEXSAN43 with neutral atom scattering factors from Cromer and Waber,44 Df and Df9 values from ref. 45 and mass attenuation coefficients from ref. 46. Anomalous dispersion effects were included in Fc.47 b Structure solved with TEXSAN,50 data reduction and refinement were performed using XTAL 3.4,51 with neutral atom scattering factors, Df and Df9 values from ref. 52. c Structure solved with SHELXS 86,48 data reduction and refinement were performed using XTAL 3.0,54 with neutral atom scattering factors, Df and Df9 values from ref. 52. d w = 4Fo 2/[s2(Fo 2) 1 (gFo 2)2]. CH2), 1.45–1.55 (br m, 2 H, CH2), 5.21 [br s, 1 H, J(PtH) 69.0, ]] CH], 7.43 (br s, 18 H, Harom), 7.70–7.85 (m, 12 H, Harom); dC(50.3 MHz, CD2Cl2) 22.41 [C(4)]H2], 24.60 [s, J(PtC) 54.2, C(5)]H2], 28.97 [s, J(PtC) 81.0, C(6)]H2], 37.14 [s, J(PtC) 40.1, C(3)]H2], 126.20 [t, J(PC) 4.2, C(2)]H], 127.98 [t, J(PC) 5.2, CH], 130.47 (CH), 131.80 [t, J(PC) 27.7, J(PtC) 21.3, Carom], 135.71 [t, J(PC) 5.8, CH], 138.10 [t, PC) 8.3, PtC(1)], J(PtC) not resolved for C(1) and C(2); dP(80.96 MHz, CD2Cl2) 24.8 [s, J(PtP) 3322]; dPt(42.83 MHz, CD2Cl2) 24448 [t, J(PtP) 3323]; m/z (C42H39BrP2Pt) 880 (M1, 5%), 846 (8), 800 (56), 719 (71), 307 (100), correct isotopic patterns.Isomerization of complex 7. Qualitative NMR experiments showed that when complex 1 (40 mg) was heated in [2H8]toluene (1.5 cm3) at various temperatures for 4 d, the formation of 7 was accompanied by an increasing amount of an isomer 8 and small amounts of a second isomer 9.The proportions as determined by 31P NMR spectroscopy were 1.00 : 0.10 : 0.05 (80 8C), 1.00 : 1.00 : 0.15 (120 8C) and 1.00 : 1.60 : 0.05 (132 8C), respectively. Traces of other unidentified complexes were also observed. Complex 8: dP(80.96 MHz, CD2Cl2) 255.4 [d, J(PP) 11.5, J(PtP) 1052.9, P(1)], 20.3 [d, J(PP) 11.5, J(PtP) 2061.4, P(2)]; dPt(42.83 MHz, CD2Cl2) 23929 [dd, J(PtP) 2061, 1055]. Complex 9: dP(80.96 MHz, CD2Cl2) 253.6 [d, J(PP) 11.0, J(PtP) 849, P(1)], 24.8 [d, J(PP) 11.0, J(PtP) 2154, P(2)]; dPt(42.83 MHz, CD2Cl2) 23985 [dd, J(PtP) 2155, 851].X-Ray crystallography of [Pt(Á1 :Á1-C6H4C6H4)(PPh3)2] 5, cis- [Pt{C6H4(PPh2)-2}(Á1-C6H5)(PPh3)] 6 and cis-[Pt{C6H4(PPh2)- 2}(Á1-C6H9)(PPh3)] 7 Selected crystal data, details of data collection, data processing, structure analysis and structure refinement are in Table 4. The structure of complex 5 was solved by direct methods (SHELXS 86)48 and was expanded using Fourier techniques (DIRDIF 94).49 The calculations were performed using TEXSAN (version 1.6c).43 The structure of 6 was solved by direct methods (SIR 92) 53 using TEXSAN (version 1.7).50 One solvation molecule of chlorobenzene was identified in a general crystallographic position, plus further molecules of solvation about the centre of symmetry ��� , 0, 1 corresponding to disordered chlorobenzene and hexane molecules.The data reduction and refinement computations were performed with XTAL 3.4.51 The structure of 7 was solved by Patterson and Fourierdifference techniques (SHELXS 86).48 Data reduction and refinement computations were performed with XTAL 3.0.54 All non-hydrogen atoms were refined anisotropically by full-matrix least squares, except for the C atoms of the disordered solvation molecules in 6 which were restrained.55 Hydrogen atomsJ.Chem. Soc., Dalton Trans., 1998, Pages 271–277 277 were included at calculated positions (C]H 0.95 Å) and held fixed.CCDC reference number 186/799. See http://www.rsc.org/suppdata/dt/1998/271/ for crystallographic files in .cif format. Acknowledgements We thank the Alexander von Humboldt Foundation for the award of a Feodor von Lynen Fellowship (to Thomas Dirnberger). References 1 M. A. Bennett and H. P. Schwemlein, Angew. Chem., 1989, 101, 1349; Angew. Chem., Int. Ed. Engl., 1989, 28, 1296. 2 S. L. Buchwald and R. B. Nielsen, Chem. Rev., 1988, 88, 1047. 3 M. A. Bennett and E.Wenger, Chem. Ber., 1997, 130, 1029. 4 M. A. Bennett, G. B. Robertson, P. O. Whimp and T. Yoshida, J. Am. Chem. Soc., 1971, 93, 3797. 5 M. A. Bennett and T. Yoshida, J. Am. Chem. Soc., 1978, 100, 1750. 6 M. A. Bennett, Pure Appl. Chem., 1989, 61, 1695. 7 Z. Lu, K. A. Abboud and W. M. Jones, Organometallics, 1993, 12, 1471. 8 Z. Lu, K. A. Abboud and W. M. Jones, J. Am. Chem. Soc., 1992, 114, 10 991. 9 J. Klosin, K. A. Abboud and W. M. Jones, Organometallics, 1995, 14, 2892. 10 M.A. Bennett, J. S. Drage, T. Okano, N. K. Roberts and H.-P. Schwemlein, unpublished work, cited in ref. 1. 11 M. A. Bennett, T. W. Hambley, N. K. Roberts and G. B. Robertson, Organometallics, 1985, 4, 1992. 12 M. A. Bennett and E. Wenger, Organometallics, 1995, 14, 1267. 13 M. A. Bennett, D. C. R. Hockless and E. Wenger, Organometallics, 1995, 14, 2091. 14 H. J. S. Winkler and G. Wittig, J. Org. Chem., 1963, 28, 1733. 15 T. L. Gilchrist, F. J. Graveling and C.W. Rees, Chem. Commun., 1968, 821; J. Chem. Soc. C, 1971, 977. 16 C. D. Cook and G. S. Jauhal, J. Am. Chem. Soc., 1968, 90, 1464. 17 K. L. Shepard, Tetrahedron Lett., 1975, 3371. 18 M. A. Bennett, J. S. Drage, K. D. Griffiths, N. K. Roberts, G. B. Robertson and W. A. Wickramasinghe, Angew. Chem., 1988, 100, 1002; Angew. Chem., Int. Ed. Engl., 1988, 27, 941. 19 M. A. Bennett and A. Rokicki, Aust. J. Chem., 1985, 38, 1307. 20 C. Eaborn, K. J. Odell and A. Pidcock, J. Chem. Soc., Dalton Trans., 1978, 357. 21 V. V. Grushin, I. S. Akhrem and M. E. Vol’pin, J. Organomet. Chem., 1989, 371, 403. 22 P. S. Pregosin and R. W. Kunz, 31P- and 13C-NMR of Transition Metal Phosphine Complexes, Springer Verlag, Berlin, 1979, p. 92. 23 P. E. Garrou, Chem. Rev., 1981, 81, 229. 24 M. A. Bennett, D. E. Berry, S. K. Bhargava, E. J. Ditzel, G. B. Robertson and A. C. Willis, J. Chem. Soc., Chem. Commun., 1987, 1613. 25 C. Scheffknecht, A. Rhomberg, E. P. Müller and P. Peringer, J.Organomet. Chem., 1993, 463, 245. 26 H. C. Clark and K. E. Hine, J. Organomet. Chem., 1976, 105, C32. 27 T. G. Appleton and M. A. Bennett, Inorg. Chem., 1978, 17, 738. 28 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 29 T. Debaerdemaeker, R. Hohenadel and H.-A. Brune, J. Organomet. Chem., 1991, 410, 265. 30 T. Debaerdemaeker, R. Hohenadel and H.-A. Brune, J. Organomet. Chem., 1988, 350, 109. 31 N. C. Rice and J. D. Oliver, J.Organomet. Chem., 1978, 145, 121. 32 M. A. Bennett and E. Wenger, Organometallics, 1996, 15, 5536. 33 J. A. Johnson, Ph.D. Thesis, Australian National University, 1991. 34 J. Cámpora, A. Llebaria, J. M. Moretó, M. L. Poveda and E. Carmona, Organometallics, 1993, 12, 4032. 35 R. G. Miller and D. P. Kuhlman, J. Organomet. Chem., 1971, 26, 401. 36 S. Sostero, O. Traverso, M. Lenarda and M. Graziani, J. Organomet. Chem., 1977, 134, 259. 37 D. M. Blake and C. J. Nyman, Chem. Commun., 1969, 483. 38 R. Ugo, G. La Monica, F. Cariati, S. Cenini and F. Conti, Inorg. Chim. Acta, 1970, 4, 390. 39 R. Ugo, S. Cenini, M. F. Pilbrow, B. Deibl and G. Schneider, Inorg. Chim. Acta, 1976, 18, 113. 40 S. Sostero, O. Traverso, R. Ros and R. A. Michelin, J. Organomet. Chem., 1983, 246, 325. 41 N. A. Grabowski, R. P. Hughes, B. S. Jaynes and A. L. Rheingold, J. Chem. Soc., Chem. Commun., 1986, 1694. 42 U. Nagel, Chem. Ber., 1982, 115, 1998. 43 TEXSAN, Single Crystal Structure Analysis Software, version 1.6c, Molecular Structure Corporation, The Woodlands, TX, 1993. 44 D. T. Cromer and J. T. Waber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, p. 72. 45 D. C. Creagh and W. J. McAuley, International Tables for X-Ray Crystallography, Kluwer Academic, Boston, MA, 1992, vol. C, p. 219. 46 D. C. Creagh and J. H. Hubbell, International Tables for X-Ray Crystallography, Kluwer Academic, Boston, MA, 1992, vol. C, p. 200. 47 J. A. Ibers and W. C. Hamilton, Acta Crystallogr., 1964, 17, 781. 48 G. M. Sheldrick, in Crystallographic Computing 3, eds. G. M. Sheldrick, C. Krüger and R. Goddard, Oxford University Press, 1985, p. 175. 49 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, R. de Gelder, R. Israel and J. M. M. Smits, The DIRDIF 94 Program System, Technical Report of the Crystallographic Laboratory, University of Nijmegen, Nijmegen, 1994. 50 TEXSAN, Single Crystal Structure Analysis Software, version 1.7, Molecular Structure Corporation, The Woodlands, TX, 1995. 51 XTAL 3.4 Reference Manual, eds. S. R. Hall, G. S. D. King and J. M. Steward, University of Western Australia, 1995. 52 International Tables for X-ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, pp. 99–101 and 149–150. 53 A. Altomare, M. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl. Crystallogr., 1993, 26, 343. 54 XTAL 3.0 Reference Manual, eds. S. R. Hall and J. M. Steward, Universities of Western Australia and Maryland, 1990. 55 J. Waser, Acta Crystallogr., 1963, 16, 1091. Received 1st October 1997; Paper 7/

ISSN:1477-9226    

DOI:10.1039/a707089f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 273–276 273 Co-ordination ability of amino acid oximes. Potentiometric, spectroscopic and structural studies of complexes of 2-cyano-2- (hydroxyimino)acetamide Tatiana Yu. Sliva,*,a Anna M. Duda,b Tadeusz G�owiak,b Igor O. Fritsky,a Vladimir M. Amirkhanov, a Andrei A. Mokhir a and Henryk Koz�owski*,b a Department of Chemistry, Shevchenko University, 252017 Kiev, Ukraine b Faculty of Chemistry, University of Wroc�aw, F. Joliot-Curie 14, 50383 Wroc�aw, Poland X-Ray crystallographic and solution studies have revealed the first examples of complexes of Cu2+ and Ni2+ with an oxime derivative in which completely deprotonated ligand molecules bind in trans position because of the lack of a hydrogen bond between the hydroxyl oxygens which usually stabilises the cis positioning.Oximes of amino acids and peptides were shown to be specific and efficient ligands for Cu2+ and Ni2+ ions.1,2 The complexes formed are stable and soluble and extensive dimer formation for Cu2+-containing systems is observed at pH >5.The binuclear complex formation results from the two alternative donor centres at the oxime (]] N]OH) group (N and O) in the ligands which both have a high affinity for M2+ and cannot both coordinate to the same metal ion. The co-ordination properties of oxime analogues of amides or peptides are, to a large extent, governed by the presence of a planar RC(]] NOH)CONH framework which may allow the formation of different chelate rings with virtually no change in conformation.The formation of bis complexes of the MH21L2 type having cis ligand coordination stabilised by hydrogen bonding between the oxime oxygens is the most characteristic feature of complexes with amino acid or amide analogues. The deprotonation of the first proton of the bis complex of Ni2+ has a critical impact on binding ability of the neighbouring nitrogen. In the case of 2- (hydroxyimino)propanamide complexes the NiL2 species having both oxime hydroxyl groups protonated is octahedral, while its deprotonated product NiH21L2 is square-planar.There is no change of binding groups during this deprotonation process. The only change possible is the distinct shift of electron density from the deprotonated hydroxyl group of the oxime moiety towards the neighbouring oxime nitrogen. The exceptional stability of the NiH21L2 complex with the amide ligand is also seen in the log K value (7.64) of the deprotonation reaction NiL2 aA NiH21L2 when compared to that for deprotonation of free amide (9.87) or removal of the proton from the NiH21L2 species (10.54).The same behaviour is observed for the acidic form of the oxime ligand. In this work the binding ability of a compound having a strongly electron-withdrawing cyano group at the a-carbon of an amide oxime is studied. This modification may have a critical impact on the role of hydrogen bonding in coordination of oxime by affecting the basicity of the oxime hydroxyl group.Experimental Synthesis of 2-cyano-2-(hydroxyimino)acetamide (H2chia) The oxime was synthesized by treating cyanocetamide (Fluka) with sodium nitrite in aqueous solution in the presence of acetic acid; the sodium salt formed was then treated with hydrochloric acid in order to obtain the free oxime as described elsewhere,3 the purity being checked by elemental analysis and NMR spectroscopy, [Found (Calc.for C3H3N3O2): C, 31.55: (31.85); H, 2.9 (2.65); N, 37.1 (37.15)%]. Potentiometry also showed the oxime to be near 100% pure and a very good fit was obtained between calculated and experimental titration curves with alkali over the whole pH range. Potentiometric studies Titrations involved an ionic background of 0.1 mol dm23 KNO3, a pro-ligand concentration of 3 × 1023 mol dm23 and metal-to-pro-ligand ratios of 1 : 1, 1 : 2, 1 : 3 and 1 : 5. Stability constants for the complexes of H+, Cu2+ and Ni2+ were calculated from titrations carried out using total volumes of 2 cm3.Alkali was added from a 0.100 cm3 micrometer syringe which had been calibrated by weight titrations and the titration of standard materials. The pH-metric titrations were performed at 25 8C using a MOLSPIN automatic titration system with a microcombined glass–calomel electrode calibrated in hydrogenion concentration using HNO3.4 Titrations were performed in triplicate and the SUPERQUAD computer program was used for stability constant calculations (bpqr = [MpHrLq]/ [M]p[H]r[L]q).5 Standard deviations quoted refer to random errors only.They are, however, a good indication of the importance of a particular species in the equilibrium. Spectroscopic studies Absorption spectra were recorded on a Beckman DU 650 spectrophotometer. The metal-ion concentrations were 2.5 × 1023 mol dm23 and the metal-to-pro-ligand molar ratios were 1 : 1, 1 : 2 and 1 : 5.The EPR spectra were recorded on a Brüker ESP 300E spectrometer at X-band (9.3 GHz) at 120 K, in ethane- 1,2-diol–water (1 : 2) as a solvent. Concentrations used in the spectroscopic measurements were similar to those given for potentiometric titrations. Syntheses of complexes Nickel(II). The compound NiCl2?6H2O (0.238 g, 1 mmol) was dissolved in acetonitrile (20 cm3) and added to a solution of the acetamide (0.226 g, 2 mmol) in acetonitrile (10 cm3). A 25% aqueous solution (1.44 cm3) of tetramethylammonium hydroxide was added dropwise.The dark brown solution was set aside274 J. Chem. Soc., Dalton Trans., 1997, Pages 273–276 for 48 h at room temperature. The crystalline precipitate of the anionic complex was filtered off, washed with acetonitrile and dried in a vacuum desiccator over CaCl2. Red-brown needleshaped single crystals suitable for X-ray analysis were obtained by recrystallisation from acetonitrile–water (3 : 1) upon slow evaporation in the air at room temperature.Yield 65% [Found (Calc. for C14H30N8O6): C, 36.2 (36.15); H, 6.45 (6.5); N, 24.1 (24.1); Ni, 12.8 (12.6)%]. Copper(II). A 25% aqueous solution (0.72 cm3, 2 mmol) of tetramethylammonium hydroxide was added to a suspension of [Cu(Hchia)]?0.5H2O6 (0.297 g, 1 mmol) in water (5 cm3). In 30 min red crystals were filtered off, washed with water and acetone and dried in vacuum. Single crystals suitable for X-ray analysis were grown by slow diffusion of methanol vapour into a 15% solution of the complex in acetonitrile.Yield 70% [Found (Calc. for C14H30CuN8O6): C, 35.55 (35.8); H, 6.55 (6.45); Cu, 13.75 (13.5); N, 23.7 (23.85)%]. Crystallography Crystal data and parameters for data collection and structure refinement are presented in Table 3, while selected distances and angles are collected in Tables 4 and 5, respectively. For X-ray Table 1 Protonation constants and complex-formation constants of 2-cyano-2-(hydroxyimino)acetamide at 25 8C and I = 0.1 mol dm23 KNO3 Species log b log b* HL 5.12(1) 9.87 Nickel(II) complexes NiL NiH21L2 NiH22L2 3.38(1) 21.88(1) 27.72(3) 4.82 — 28.97 Copper(II) complexes CuL Cu2H22L2 CuH22L2 3.74(1) 21.06(2) 26.64(2) 7.87 5.66 24.74 * Data for 2-(hydroxyimino)propanamide.1 Table 2 Spectral parameters (visible and EPR) for metal(II)–2-cyano- 2-(hydroxyimino)acetamide systems at 25 8C and I = 0.1 mol dm23 (KNO3).Pro-ligand concentration 2.5 × 1023 mol dm23 and metal-topro- ligand molar ratio 1 : 5 (for Ni2+) and 1 : 2 (for Cu2+) UV/VIS Species (binding mode) l/nm e/dm3 mol21 cm21 NiL (N, N2) NiH21L (N, N2) NiH22L2 (2 × N, N2) 395.0a 517.0b 645.0b 974.0b 395.0a 535.0b,c 986.0b 398.0a 539.0c 79 2 0.8 1.2 355 17 3 708 100 CuL (N, N2) Cu2H22L2 (N, N2, O2) CuH22L2 (2 × N, N2) 710.0 662.0 607.0 47d 64 155e a Intraligand transition.b d–d Transition of Oh nickel(II) complex. c d–d Transition of square-planar nickel(II) complex. d A|| 156 G, g|| 2.260.e A|| 188, g|| 2.222. analysis a needle-shaped single crystal was chosen and sealed in a glass capillary to avoid crystal powdering. Data collection and processing. Intensity data were collected at 293(2) K with a KM4 computer-controlled four-circle diffractometer. 7 The structure was solved by direct methods and refined by full-matrix least sqsing SHELXL 93 8 with anisotropic thermal parameters for non-hydrogen atoms. All H atoms were located from the successive Fourier-difference maps and only their displacement parameters included in the refinement.Correction for extinction was taken into account in the course of refinement. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to CCDC for this material should quote the full literature citation and the reference number 186/279.Results and Discussion Solution studies 2-Cyano-2-(hydroxyimino)acetamide (H2chia) exhibits one measurable protonation constant corresponding to protonation of the hydroxyimino group C]] NO2. Its value, log K = 5.12, is more than six orders of magnitude lower than that of 2- (hydroxyimino)propanoic acid (log K = 11.6 1) and more than four and half orders of magnitude lower than that of 2- (hydroxyimino)propanamide (log K = 9.87 1). This very acidic behaviour of the oxime hydroxyl group derives from the strong electron-withdrawing effect of the 2-cyano substituent.Complexes with 2-cyano-2-(hydroxyimino)acetamide The complex species evaluated from the potentiometric calculations for Cu2+ and Ni2+ are collected in Table 1. Results Fig. 1 Species distribution curves for the complexes formed in the Cu2+–H2chia (a) and Ni2+–H2chia (b) systems as a function of pH. Pro-ligand concentration 0.003 mol dm23, and metal-to-ligand molar ratios 1 : 5 (for nickel) and 1 : 3 (for copper)J. Chem.Soc., Dalton Trans., 1997, Pages 273–276 275 Table 3 Crystal data and structure refinement for the 2-cyano-2-(hydroxyimino)acetamide complexes * Empirical formula M (Cu-Ka)/Å a/Å b/Å c/Å a/8 b/8 „/8 U/Å3 Dc/Mg m23 m/cm21 F(000) Crystal size/mm q Range for data collection/8 hhl Ranges Reflections collected Independent reflections Data, parameters Goodness of fit on F2 R1, wR2 Final indices [I > 3s(I)] Weighting scheme, w Extinction coefficient Largest difference peak and hole/e Å23 C14H30N8NiO6 465.18 1.541 80 7.905(2) 8.589(2) 9.017(2) 107.11(3) 97.69(3) 101.36(3) 561.5(2) 1.376 16.47 246 0.15 × 0.18 × 0.18 5.24–80.35 0–10, 210 to 10, 211 to 11 2302 2302 2143, 146 1.073 0.0356, 0.1092 1/[s2 (Fo 2) + (0.0722P)2 + 0.1537P] where P = (Fo 2 + 2Fc 2)/3 0.0058(14) 0.269, 20.263 C14H30CuN8O6 470.00 1.541 78 7.683(2) 8.754(2) 9.059(2) 108.42(3) 97.46(3) 98.44(3) 561.6(2) 1.390 1.773 247 0.4 × 0.4 × 0.2 5.24–58.05 21 to 8, 29 to 9, 29 to 9 1704 1553 [Rint = 0.0137] 1553, 137 0.892 0.0330, 0.0860 0.0126(13) 0.269, 20.263 * Details in common: triclinic, space group P1� ; Z = 1; full-matrix least-squares refinement on F2.obtained earlier for 2-(hydroxyimino)propanamide1 are also shown for comparison. Copper(II) forms three major complexes: two monomeric, CuL and CuH22L2, and the dinuclear species Cu2H22L2 (Fig. 1). The latter is EPR silent in the region pH 5.5–6.5.The same three species were also observed, among others, in the case of 2-(hydroxyimino)propanamide. The strongly acidic character of the present oxime donor results in much less stable complexes when compared to those of 2- (hydroxyimino)propanamide. The stability constant for the dimeric species differs by more than six orders of magnitude (Table 1). The EPR and absorption spectral data collected in Table 2 indicate the involvement of two or four nitrogen atoms.1,2 In the dinuclear species the involvement of deprotonated hydroxyimino oxygen is most likely, as was found earlier in similar oxime systems in the analogous pH regions.1 Unfortunately, the strong intraligand transitions observed in the range 400–200 nm do not allow one to observe O2 oximeÆCu2+ charge-transfer band to support this binding mode (see ref. 1). In the case of Ni2+-containing solutions the three major complexes formed are monomeric NiL, NiH21L and NiH22L2 species (Fig. 1).According to the absorption spectra (Table 2) the latter bis complex is square planar, while the first two are both octahedral. The binding mode is likely to be the same as that observed for Cu2+, i.e. involving the nitrogen donors of the ligand (see below). The interesting feature of the nickel system is the much lower difference in stabilities between the complexes of the present derivative and that of 2-(hydroxyimino) propanamide (Table 1). Table 4 Selected bond lengths (Å) and angles (8) for the nickel(II)–2- cyano-2-(hydroxyimino)acetamide complex Ni]N(2i) Ni]N(2) 1.858(2) 1.858(2) Ni]N(1) Ni]N(1i) 1.899(2) 1.899(2) N(2i)]Ni]N(2) N(2i)]Ni]N(1) N(2)]Ni]N(1) 180.0 96.38(7) 83.62(7) N(2i)]Ni]N(1i) N(2)]Ni]N(1i) N(1)]Ni]N(1i) 83.62(7) 96.38(7) 180.0 Symmetry transformation used to generate equivalent atoms: i 2x, 2y, 2z.Crystal structures of the complexes [NMe4]2[M{N(O)C(CN)C- (O)N}2]?2H2O (M = Ni or Cu) Both copper and nickel ions give the same molecular structure for the MH22L2 complex, consisting of tetramethylammonium cations, complex anions MH22L2, and water molecules.In the crystal packing (Fig. 2) the complex anions are linked by hydrogen bonds into chains spread along the z direction. The Fig. 2 Packing of molecules of the copper(II)–2-cyano-2-(hydroxyimino) acetamide complex Table 5 Selected bond lengths (Å) and angles (8) for the copper(II)–2- cyano-2-(hydroxyimino)acetamide complex Cu]N(2) 1.895(2) Cu]N(1) 2.056(2) N(2)]Cu]N(2i) N(2)]Cu]N(1) 180.0 81.60(8) N(2i)]Cu]N(1) N(1)]Cu]N(1i) 98.40(8) 180.0 Symmetry transformation as in Table 4.276 J.Chem. Soc., Dalton Trans., 1997, Pages 273–276 hydrogen bonds are formed between the amide and oxime oxygen atoms and the proton of the amide group and water. The NMe4 + cations form columns along the z axis of the crystal, occupying empty spaces between the translational chains of the complex anions. In complex anion (Fig. 3, for Ni2+) the metal atom occupies a partial position at the centre of symmetry.The distorted square-planar co-ordination sphere consists of four nitrogen atoms belonging to the deprotonated hydroxyimino and amide groups. The two dianions of 2-cyano-2- (hydroxyimino)acetamide are situated in trans position with respect to each other. The Cu]Noxime and Cu]Namide distances are 2.056 and 1.895 A respectively, noticeably different, while e.g. in the complex of Cu2+ with 2-(hydroxyimino)- propanamide9 these distances are in the ranges 1.91–1.94 and 1.92–1.95 A, respectively, i.e.close to each other. The elongation of the Cu–Noxime bond in the present complex clearly indicates the strong electron-withdrawing effect of the 2-cyano substituent (see above). In the nickel(II) complex with 2-cyano-2-(hydroxyimino)- acetamide the Ni]Noxime and Ni]Namide distances are 1.899 and 1.858 A, respectively, relatively close to each other, although the bond distance with oxime nitrogen is also the longer as also found in the copper complex.Both distances are very close to those observed for the nickel complex with 2-(hydroxyimino)- propanamide in which the Ni]Noxime and Ni]Namide bond lengths are 1.872 and 1.853 A, respectively.2 The geometrical parameters of the present ligand are similar to those observed for other ligands having deprotonated oxime and amide groups. The distances N(1)-O(1) of 1.289 and 1.281 A and N(1)-C(1) of 1.302 and 1.314 A for copper and nickel respectively, are close to those reported for the N-co-ordinated deprotonated oxime group.10 This indicates that the CNO2 moiety exists in the nitroso-form.11 Fig. 3 Crystal structure of the nickel(II)–2-cyano-2-(hydroxyimino)- acetamide complex Conclusion The high acidity of the oxime hydroxyl group in 2-cyano-2- (hydroxyimino)acetamide changes considerably the coordination mode of the oxime ligand with Cu2+ and Ni2+ ions. Although the donor atoms bound to the metal ions are the same as with 2-(hydroxyimino)propanamide, two molecules of the propanamide ligand are bound in cis position, while in the case of the 2-cyano derivative the ligands are trans to each other.The mor factor deciding the cis positions of the ligand molecules in the major complex, MH21L2, formed with oxime analogues of amino acids is the hydrogen bond between the two hydroxyl oxygens. This hydrogen bond is not present in the corresponding complex of the 2-cyano derivative, MH22L2, due to the very acidic oxime hydroxyl group.The MH21L2 species is not observed in the present case. Acknowledgements This work was supported by the Polish State Committee for Scientific Research (KBN 3T09A06908). T. Yu. Sliva thanks Kasa J. Mianowskiego for financial support. References 1 Ch. O. Onindo, T. Yu. Sliva, T. Kowalik-Jankowska, I. O. Fritsky, P. Buglyo, L. D. Pettit, H. Kozlowski and T. Kiss, J. Chem. Soc., Dalton Trans., 1995, 3911. 2 T. Yu. Sliva, T. Kowalik-Jankowska, V. M. Amirkhanov, T. Glowiak, L. D. Pettit, I. O. Fristky and H. Kozlowski, J. Inorg. Biochem., in the press. 3 C. A. Schultze, Berichte, 1909, 42, 735. 4 H. M. Irving, M. H. Miles and L. D. Pettit, Anal. Chim. Acta, 1967, 68, 475. 5 P. Gans, A. Sabatini and A. Vacca, J. Chem. Soc., Dalton Trans., 1985, 1195. 6 V. V. Skopenko, R. D. Lampeka and Yu. L. Zub, Zh. Neorg. Khim., 1981, 26, 142. 7 KUMA M4 Software User Guide, Version 3.1, Kuma Diffraction, Wroc�aw, 1986. 8 G. M. Sheldrick, SHELXL 93, Program for refinement of crystal structures, University of Göttingen, 1993. 9 Yu. A. Simonov, V. Kh. Kravtsov, I. O. Fritsky, E. E. Gubina, R. D. Lampeka, T. S. Iskenderov and A. Zh. Zhumabaev, Koord. Khim., 1995, 21, 407. 10 I. O. Fritsky, R. D. Lampeka, V. V. Skopenko, Yu. A. Simonov, A. A. Dvorkin and T. I. Malinovsky, Z. Naturforsch., Teil B., 1993, 48, 270. 11 K. V. Domasevich, A. N. Chernega, S. V. Lindeman and Yu. T. Struchkov, Zh. Neorg. Khim., 1995, 40, 426. Received 23rd July 1996; Paper 6/0512

ISSN:1477-9226    

DOI:10.1039/a605125a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 277–281 277 Crystal structure of bis(tetraethylammonium) bis[4,5-disulfanyl-1,3- dithiol-2-onato(22)]nickelate(II) and spectroscopic and electrical properties of related oxidized complexes‡ Shuging Q. Sun, Bin Zhang, Peiji J. Wu and Daoben B. Zhu*,† Institute of Chemistry, Chinese Academy of Sciences, Beijing, 100080, P.R.China Bis(4,5-disulfanyl-1,3-dithiol-2-onato)nickelate anion complexes [Ni(C3S4O)2]22 were prepared. A singlecrystal structure analysis has been performed for the bis(tetraethylammonium) salt 1: orthorhombic, space group I4(1)acd, Z = 8, a = b = 19.605(3), c = 16.217(5) Å.Full-matrix least-squares refinement based on 744 independent reflections with I > 2s(I) yielded an R factor of 0.0651. The geometry around the nickel atom is greatly distorted from square planar, with a dihedral angle of 17.48 between the dithiolate ligand planes. Although it is essentially an insulator, with an electrical conductivity of 1.4 × 1028 S cm21 measured for a single crystal at room temperature, some partially and completely oxidized nickel complexes as well as iodine-doped single crystals exhibit increased conductivities of 1023–1022 S cm21.Electronic, IR, ESR and X-ray photoelectron spectra of these complexes are discussed. Many electrically conducting materials derived from bis- [4,5-disulfanyl-1,3-dithiole-2-thionate(22)]metal complexes [M(C3S5)2]n2(M = Ni, Pd or Pt) have been investigated.1 Up to now, six of them2 have been found to undergo a superconducting transition under pressure. In addition, [ettf][Ni- (C3S5)2] [ettf = ethylenedithiotetrathiafulvalene, i.e. 2-(1,3- dithiol-2-ylidene)-4,5-ethylenedithio-1,3-dithiole] has been found to be a superconductor at ambient pressure.3 It was thus interesting to extend such investigations to other similar polysulfur-ligand complexes. 4,5-Disulfanyl-1,3-dithiol-2- onate (C3S4O) has been synthesized 4 but fewer studies have been carried out on either the synthesis or the electrical properties of [M(C3S4O)2] complexes.5 Recently the bistable electrical switching properties in electrodeposited thin films based on [Ni(C3- S4O)2]x2 anion complexes were discovered in our laboratory.6 This encouraged us to investigate further the changing of the intra- and inter-molecular interaction due to the replacement of S by O.This paper reports the crystal structure of [NEt4]2[Ni(C3S4O)2] as well as the spectral and electrical properties of its analogues and oxidized complexes.As far as we know, this is the first report of the crystal structure of a [M(C3S4O)2]22 complex. Experimental Preparation of the complexes [NEt4]2[Ni(C3S4O)2] 1, [NMe4]2[Ni(C3S4O)2] 2 and [NEt4]2- [Cu(C3S4O)2] 3. To 4,5-bis(thiobenzoyl)-1,3-dithiol-2-one (500 mg, 1.28 mmol) in dry degassed methanol (20 cm3) under an argon atmosphere, was added an excess of sodium methoxide in dry degassed methanol [70 mg (3 mmol) sodium in 5 cm3 methanol] and the mixture was stirred under argon for 0.5 h to give a dark red solution.The compound NiCl2?6H2O (150 mg, 0.63 mmol) was added followed by tetraethylammonium bromide (270 mg, 1.28 mmol) dissolved in dry degassed methanol (10 cm3). The mixture was stirred for 30 min to precipitate brown microcrystals of [NEt4]2[Ni(C3S4O)2] 1, which were filtered off, washed with anhydrous methanol then with anhydrous diethyl ether, and air dried (yield 61%).Recrystal- † E-Mail: zhudb@infoc3.icas.ac.cn ‡ Non-S1 unit employed: eV ª 1.60 × 10219 J. lization of this complex from acetonitrile under argon afforded dark green crystals, which were used for structure analysis and electrical measurement. Similarly, brown microcrystals of [NMe4]2[Ni(C3S4O)2] 2 (68%) and [NEt4]2[Cu(C3S4O)2] 3 (64%) were obtained by using NMe4Br or NEt4Br and NiCl2? 6H2O or CuCl2?2H2O. Oxidized [Ni(C3S4O)2]x2 complexes. An acetonitrile–acetone (1:1) solution (15 cm3) of iodine (100 mg, 0.39 mmol) was added to complex 1 (100 mg, 0.15 mmol) dissolved in the same solvent (40 cm3).The mixture was stirred for 30 min to give a black precipitate of [Ni(C3S4O)2] 4 which was filtered off, washed with acetonitrile and diethyl ether, then dried in air (87% yield based on 1). Finely powdered complex 1 (100 mg, 0.15 mmol) was suspended in a solution of iodine (200 mg, 0.78 mmol) in diethyl ether (30 cm3). The suspension was stirred for 1 d at room temperature under an argon atmosphere.The resulting solid [NEt4]2[Ni(C3S4O)2]I7.8 5 was filtered off and dried in air. The complex [NEt4]2[Ni(C3S4O)2]I2.3 6 was obtained when 5 was washed extensively with diethyl ether. The salt [NEt4]0.17- [Ni(C3S4O)2] 7 was obtained by galvanostatic anode oxidation of 1 (1023 mol dm23) in acetonitrile containing [NBun 4][ClO4] (5 × 1022 mol dm23) as supporting electrolyte. A twocompartment cell where the anode and the cathode are separated by a medium-porosity frit was used with platinum electrodes (diameter 1 mm).The current was held constant at 1 mA. After 2 weeks the polycrystalline powders adhering to the anode electrode were collected, washed with acetone and dried in air. Iodine-doped single crystals of complexes 1 and 2. These experiments were carried out using a capsuled bottle filled with iodine vapour. The typical size of the crystal was 1 × 0.3 × 0.2 mm. Two gold-wire electrodes were glued to the crystal by gold-conducting paste.Elemental analysis for the complexes obtained are listed in Table 1. Physical measurements Electronic absorption spectra were recorded on a Sigmazu UV- 3100 spectrophotometer, electronic powder reflectance spectra278 J. Chem. Soc., Dalton Trans., 1997, Pages 277–281 Table 1 Elemental analyses * for the complexes obtained Analysis (%) Complex C H N S Ni I 1 [NEt4]2[Ni(C3S4O)2] 2 [NMe4]2[Ni(C3S4O)2] 3 [NEt4]2[Cu(C3S4O)2] 4 [ Ni(C3S4O)2] 5 [NEt4]2[Ni(C3S4O)2]I7.8 6 [NEt4]2[Ni(C3S4O)2]I2.3 7 [NEt4]0.17[Ni(C3S4O)2] 38.9 (38.9) 29.7 (29.6) 38.5 (38.6) 17.9 (17.2) 15.7 (15.8) 27.1 (27.2) 19.9 (20.0) 5.9 (5.9) 4.2 (4.2) 5.8 (5.85) <0.3 (0) 2.5 (2.4) 4.3 (4.1) 0.9 (0.8) 4.0 (4.1) 5.0 (4.9) 4.0 (4.1) 0 (0) 1.5 (1.7) 2.6 (2.9) 0.6 (0.5) 37.6 (37.7) 45.0 (45.7) 61.0 (61.1) 15.9 (15.3) 27.2 (26.4) 57.0 (58.1) 3.6 (3.5) 6.1 (6.05) 13.4 (13.3) 58.8 (59.3) 29.9 (30.1) * Calculated values in parentheses.with a Sigmazu integrating sphere unit, IR spectra on a Bruker IFS-113 spectrophotometer using KBr pellets over the range 4000–400 cm21, ESR spectra on a Bruker ESP-300 spectrometer, X-ray photoelectron spectra on a Kratos ES-300 spectrophotometer and Raman spectra on a Nicolet FT-Raman 910 spectrometer. Cyclic voltammograms were measured in acetonitrile containing [NBu4][ClO4] as supporting electrolyte, using a conventional cell consisting of a glass–carbon and a platinum plate as working and counter electrode and a saturated calomel electrode (SCE) as reference.The resistivities of compacted pellets as well as single crystals were measured by using the conventional two-probe technique.7 Crystallography Crystal data and data collection parameters for complex 1. C22H40N2NiO2S8, M = 679.75, orthorhombic, space group I4(1)/acd (no. 142), a = b = 19.605(3), c = 16.217(5) Å, U = 6233(2) Å3 (by least-squares refinement on diffractometer angles from 33 centred reflections, 10 < 2q < 248), T = 293 K, graphite-monochromated Mo-Ka radiation, l = 0.710 73 Å, Z = 8, Dc = 1.449 g cm23, F(000) = 2864, black plate with dimensions 0.8 × 0.4 × 0.1 mm, transmission factors 20.304 to 0.432.Siemens P4 diffractometer, w–2q scan mode with left and right scan widths of 0.7, data collection range 2.08 < q < 258, h 21 to 23, l 21 to 23, k 21 to 19. Three standard reflections were monitored per 97 and showed no significant variation in intensity. 3288 Reflections measured, 1328 unique (Rint = 0.0712) and 774 [I > 2s(Io)] were used in all calculations.Scattering factors were taken from ref. 8 and Lorentz-polarisation absorption was applied. Structure solution and refinement. The structure was solved by the heavy-atom method, and subsequent Fourier-difference techniques, and refined anisotropically by full-matrix least squares on F2 with SHELXL 93.9 Hydrogen atoms were placed in calculated positions and not refined.The weighting scheme was w = 1/[s2(Fo 2) + (0.0877P)2], where the P = (Fo 2 + 2Fc 2)/3. The final R = 0.0651, R9 = 0.1498, for 101 parameters and no restraint, goodness of fit = 1.215, maximum D/s = 0.00, Dr = 20.023 e Å23, without any chemical meaning. During the structural refinement the carbon atoms bonded to N(1) and the terminal carbon atoms C(1), C(2) were disordered in two positions C(3), C(4) and C(5), C(6), having equal occupancy in the last refinement.Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/268. Results and Discussion Crystal structure of [NEt4]2[Ni(C3S4O)2] 1 The crystal structure of complex 1 consists of 16 NEt4 moieties and 8 [Ni(C3S4O)2] anions in the unit cell.Fig. 1 shows the molecular geometry together with the atom labelling scheme and a stereoscopic view is given in Fig. 2. Selected bond distances and angles are summarized in Table 2. The atoms in the [NEt4]+ cation show considerable thermal motion and the standard deviations of the bond distances are therefore high. The nickel(II) ion is co-ordinated by four sulfur atoms. The nickel–sulfur distance [2.194(2) Å] is in better agreement with those in doubly negatively charged nickel dithiolene complexes, Fig. 1 Molecular geometry of [NEt4]2[Ni(C3S4O)2] 1 together with the atom-labelling scheme Fig. 2 Stereoscopic view of [NEt4]2[Ni(C3S4O)2] 1J. Chem. Soc., Dalton Trans., 1997, Pages 277–281 279 i.e. 2.216(6) Å for [{Ni(C3S5)2}2] 10 and 2.166(6) Å for [{Ni(mnt)2}2] (mnt = maleonitriledithiolate).11 The carbon– sulfur distances 1.733(6), 1.760(6) and 1.763(5) Å have values intermediate between single (1.81) and double (1.71 Å) bonds, indicating a high degree of electron delocalization.Both of the carbon–carbon [1.339(13) Å] and carbon–oxygen [1.214(9) Å] distances are close to double-bond values (1.39 Å for C]] C and 1.20 Å for C ]] O). The geometry around nickel is greatly distorted from planar, with a dihedral angle of 17.48 between the two C3S4O planes. This behaviour resembles that of [NBu4]- [Ni(C3S5)2] and [epy]2[Cu(C3S5)2] (epy = N-ethylpyridinium) for which the dihedral angles between the two ligand planes are 6.1 (ref. 12) and 57.38.13 Non-planarity around metal ions observed in C3S5 metal complexes, such as [ttf][Pt(C3S5)2]3,14 is caused by a direct metal–metal interaction which induces the formation of [{Pt(C3S5)2}2] dimers and thus folding of the normally planar Pt(C3S5)2 unit (dihedral angle 11.28). In the case of complex 1 there is no such evident theoretical reason for such a distortion. We can only assume that the distorted geometry may result from the packing effect of the anions or the negatively charged sulfur or oxygen of the ligand.No interaction between [Ni(C3S4O)2]22 ions is observed, which results in the low conductivity of the complex. Electronic and ESR spectra of the complexes Fig. 3 shows the electronic absorption and powder reflectance spectra of complex 1, together with the reflectance spectrum of neutral complex 4. In spectrum (a) the absorption bands at 219, 262 and 310 nm are ascribed to local excitation of the C3S4O ligand and correspond to the bands at 224, 280 and 330 nm of [NEt4]2[Zn(C3S4O)2].Another p æÆ p* transition is observed at 605 nm, which also corresponds to the band at 486 nm observed for [NEt4]2[Zn(C3S4O)2]. The band at 410 nm observed in (a) is reasonably assigned to a Ni�S chargetransfer (c.t.) transition. These bands are similar to those of Fig. 3 Electronic absorption spectrum of complex 1 in acetonitrile (1.0 × 1024 mol dm23) [newly resolved (a) and on standing for 1 d in air (b)] and powder reflectance spectra of 1 (c) and 4 (d) Table 2 Selected bond distances (Å) and angles (8) with estimated standard deviations in parentheses for [NEt4]2[Ni(C3S4O)2] 1 Ni(1)]S(1) S(2)]C(19) O(1)]C(29) 2.194(2) 1.760(6) 1.214(9) S(1)]C(19) S(2)]C(29) C(19)]C(19B) 1.733(6) 1.763(5) 1.339(13) S(1)]Ni(1)]S(1A) S(1)]Ni(1)]S(1C) C(19)]S(2)]C(29) C(19A)]C(19)]S(2) S(1)]C(19)]S(2) 93.22(9) 167.04(10) 97.0(3) 116.8(2) 120.9(4) S(1)]Ni(1)]S(1B) C(19)]S(1)]Ni(1) C(19A)]C(19)]S(1) S(2)]C(29)]S(2A) O(1)]C(29)]S(2) 88.24(10) 101.1(2) 122.3(2) 112.3(5) 123.9(3) Symmetry transformations: A ��� + x, 2y, z; B ��4 2 x, ��4 2 y, ��4 2 z.[M(C3S5)2]22 complexes at around 224, 280, 310, 540 and 400 nm (due to local excitation of the C3S5 ligand and M�S charge-transfer transitions). The p æÆ p* transitions of [NEt4]2[Ni(C3S4O)2] occur at shorter wavelengths than those of [M(C3S5)2]22 anions. These differences obviously result from the different electron-withdrawing abilities of C]] O and C]] S.When the solution of complex 1 in acetonitrile was allowed to stand in air for some time all the bands were blue-shifted as illustrated in spectrum (b). That at 220 nm was shifted to lower wavelength and out of the spectrum; the bands at 262 and 310 nm were shifted to 248 and 306 nm with a slight decrease in intensity; and a Ni�S charge-transfer (c.t.) transition at 410 nm was also blue-shifted to 373 nm. Spectrum (b) is very similar to that of the [Ni(C3S4O)2]2 anions, indicating aerial oxidation from [Ni(C3S4O)2]22 to [Ni(C3S4O)2]2 had occurred.It should be noted that although a strong absorption band at 384 nm owing to conjugation of the carbonyl group with the ethylene double bond15 was observed for 4,5-bis(methylsulfanyl)-1,3-dithiol-2- one, the band at 373 nm for [Ni(C3S4O)2]2 could not be assigned to the same process. For [M(C3S4O)2]n2 (n = 1 or 2) the conjugation of the carbonyl group with the ethylene double bond was extended to the negatively charged sulfur atoms co-ordinated to the metal.This resulted in a red-shifted absorption band. The solid-state spectrum (c) of the present complex is essentially the same as the solution spectrum, indicating no significant electronic interaction among the complex ions in the solid state. In contrast, spectrum (d) exhibits a broad reflectance band around 760 nm, which may be due to an interaction among the neutral complex molecules.Fig. 4 illustrates the ESR spectra of powder (a) and acetonitrile solution (b) of complex 3 as well as that of an acetonitrile solution of [Ni(C3S4O)2]2 (c). Complex 3 exhibits an isotropic spectrum (g = 2.047) in the solid state, which can be compared with the isotropic spectrum found for [NMe4]2[Cu(C3Se5)2] (g = 2.074) (C3Se5 = 4,5-diselanyl-1,3- diselenol-2-selenate).16 A63/65Cu hyperfine structure is observed (g0 = 2.051, A0 = 67.4 × 1024 cm21) in the solution spectrum.The present A0 value is rather close to that of [epy]2- [Cu(C3S5)2] 13 (66.5 × 1024 cm21) and [mb]2[Cu(mnt)2]? Me2CO16 [mb = Methylene Blue cation; 3,7-bis- (dimethylamino)phenothiazin-5-ium] (68.4 × 1024 cm21) containing non-planar [Cu(C3S5)2]22 and [Cu(mnt)2]22, respectively, and is much lower than A0 = 80.0 × 1024 cm21 for the planar [Cu(mnt)2]22 anion.17 A drastic decrease in A0 values in CuS4 complexes was proposed to be caused by some distortion from a square-planar to a tetrahedral geometry around the copper atom.18 Thus, the present [Cu(C3S4O)2]22 complex seems to assume a geometry distorted from square planar in solution as [Ni(C3S4O)2]22 in the solid state as discussed above.As shown in spectrum (c), there is a sharp band of Fig. 4 The ESR spectra of [NEt4]2[Cu(C3S4O)2] 3 in the solid state (a) and in acetonitrile at room temperature (b), together with that of [NEt4][Ni(C3S4O)2] in acetonitrile (c). G = 1024 T280 J.Chem. Soc., Dalton Trans., 1997, Pages 277–281 Table 3 Infrared n(C]] C) and n(C]] O) bands as well as binding energies of Ni 2p��� and S 2p��� electrons of the [Ni(C3S4O)2] complexes Bind/cm21 n& (C]] O)/cm21 Ni 2p��� S 2p��� 145 1474 1273 1274 1641s, 1601s 1693vs, 1617w 1695vs, 1617w 854.5 855.3 855.3 165.2, 163.6, 162.1 165.3, 163.5, 162.2 165.1, 163.7, 162.3 w = Weak, v = very, s = strong. [Ni(C3S4O)2]2 in acetonitrile solution {obtained by aerial oxidation of [Ni(C3S4O)2]22 in acetonitrile}, with an isotropic signal at g0 = 2.049, which can be compared with that of [NBu- 4][Ni(C3S5)2] (g = 2.04) 19 and [NBu4][Ni(C3Se5)2] (g = 2.095).16 However the ESR signals of the further oxidized species, complexes 4 and 5, are very broad.This may be related to electron delocalization through the more effective conducting pathways of these complexes,19 which leads to high conductivities. Electrochemistry, IR and XPS study on complex 1 and its oxidized species Fig. 5 illustrates the cyclic voltammogram of complex 1 in acetonitrile, which shows two sets of redox peaks. The first peak is centred at E1 = 280 mV (vs. SCE) and assigned to the oneelectron reversible redox process between [Ni(C3S4O)2]22 and [Ni(C3S4O)2]2. This E1 value is less negative than that for the same redox process of [Ni(C3S5)2]22 (2170 mV, vs. SCE), due to the stronger electron-withdrawing ability of C]] O than that of C]] S.For the second redox couple the oxidation peak is not purely diffusion controlled but is also affected by modification of the electrode surface, for the backward peak is characteristic of a redissolution process, the intensity being proportional Fig. 5 Cyclic voltammogram of [NEt4]2[Ni(C3S4O)2] 1 (5 × 1024 mol dm23) in acetonitrile containing [NBun 4][ClO4] (0.1 mol dm23), scan rate 100 mV s21 Table 4 Room-temperature electrical conductivities of the complexes Complex s/S cm21 Complex s/S cm21 1 2 3 1.4 × 1028 (s) 1.6 × 1023 (sd) 8.5 × 1028 (s) 9.2 × 1024 (sd) 2.5 × 10210 (s) 4567 1.2 × 1023 (p) 3.1 × 1025 (p) 3.8 × 1025 (p) 1.8 × 1022 (p) s = Single crystal, d = after doping with iodine, p = compacted pellet.to the scan rate.20 This deposit probably comprises [Ni(C3S4O)2]20.17 7 which has been independently obtained by galvanostatic electrocrystallization. Therefore, the global scheme of the second oxidation step implies partial electron exchange according to [Ni(C3S4O)2]2 æÆ [Ni(C3S4O)2]x2 + (1 2 x)e, where x = 0.17.The small reduction peak at 20 mV (vs. SCE) may also result from redissolution of the deposited material. Finely powdered complex 1 suspended in diethyl ether reacted with an excess amount of iodine to give complex 5. This has a Raman peak at 175 cm21, which may be assigned to the symmetric stretching of I5 2 or I7 2 ion.21 When 5 was washed with diethyl ether extensively, 6 was obtained, and the Raman peak disappeared.X-Ray photoelectron spectroscopy (XPS) of this complex indicates only I2 exists as described later. Similar to the metal–C3S5 complexes, the C]] C stretching frequency of C3S4O–nickel complexes are very sensitive to the oxidation state. As shown in Table 3, the infrared band of complex 1 appears at 1474 cm21, whereas both 4 and 5 give a strong peak at ca. 1274 cm21, with a very weak peak at the original frequency of 1 for 5 but not for 4. The appearance of the band lowered by 200 cm21 suggests the presence of two electronoxidized C3S4O–nickel moieties, as evidenced by elemental analysis for complex 4. The XPS studies also indicate that there is no nitrogen in 4.In spite of the red-shift of the C]] C stretching band, on the other hand, the C]] O blue-shifted band is from 1641 and 1601 to about 1694 cm21 upon complete oxidation. The valence state of the nickel atoms of the complexes can be deduced from the binding energies of the 2p electrons as determined by XPS.As shown in Table 3, complexes 4 and 5 exhibit larger binding energies than that of 1 suggesting noticeable oxidation of the metal, similar to that of C3S5–metal complexes.22 In the case of 1 the ratio of the amounts of the two oxidation states of sulfur is nearly 1:1, however, in 4 and 5 the same two oxidation states are present, but the higher oxidation state is three times more populated than the lower. This indicates half of the sulfur co-ordinated to the metal is oxidized.It is interesting that the sulfur bound to the metal did not exist in the same oxidation state upon oxidation. Moreover, the I 3d5�2 binding energy of complex 6 is 619 eV, indicating the presence of I2 in the complex.23 The ratio of iodine and nickel estimated from relative intensities in the XPS spectra is about 2.1:1, consistent with the elemental analysis. Electrical conductivities The conductivity of the single crystal of complex 1 is somehow low, consistent with its crystal structure.However, the reflectance spectra of its oxidized complexes show broad bands at long wavelengths (see Fig. 3) which are not observed in the solution spectra. In accord with this the electrical conductivities of the oxidized complexes are significantly increased as described below. When the single crystal of complex 1 was exposed to iodine vapour the conductivity increased from 1028 to 1024 S cm21 within a few minutes; hours later the conductivity can be up to 1023 S cm21.Prolonging the doping time resulted in reduction of the conductivity, the final value being around 1024 S cm21, this may be due to complete oxidation of the complex. WhenJ. Chem. Soc., Dalton Trans., 1997, Pages 277–281 281 the conductivity had attained the maximum value, doping process was stopped, and the doped crystal ‘dried’ in vacuum (1025 mmHg, ca. 1.33 × 1023 Pa) for 1 d, the resistivity slightly increased from 40 to 48 kW, suggesting that a solid-state reaction occurred between I2 and complex 1 during doping, rather than adsorption of I2.The iodine doping of a single crystal of complex 2 leads to similar results. Table 4 summarizes the conductivity of the complexes, and it can be seen that the oxidized complexes exhibit higher conductivities. The highest conductor is the partially oxidized species. This is in accordance with the iodine doping of the single crystals. However, this process cannot be expected to occur inside the crystal, whereas the conductivity is estimated based on the total size; therefore, the conductivity of the compressed pellets is comparable with that of the doped crystal.Acknowledgements This work was supported by National 863 Program and Key Items of Chinese Academy of Sciences. Thanks are also due to Professor S. H. Liu for XPS discussion, and Professor S. Q. Zhou and Mrs. X. Y. Xu for their help with electrical conductivity and cyclic voltammogram measurements, respectively.References 1 P. Cassoux, L. Valade, H. Kobayashi, A. Kobayashi, R. A. Clar and A. E. Underhill, Coord. Chem. Rev., 1991, 110, 115. 2 L. Brossard, M. Ribault, L. Valade and P. Cassoux, Physica B (Amsterdam), 1986, 143, 378; Phys. Rev. B, 1990, 42, 3935; J. Phys. (Paris), 1989, 50, 1521; L. Brossard, H. Hurdequint, M. Ribault, L. Valade, J.-P. Legros and P. Cassoux, Synth. Met., 1988, 27, B157; A. Kobayashi, H. Kim, Y.Sasaki, R. Kato, H. Kobayashi, S. Moriyama, Y. Nishio, K. Kajita and W. Sasaki, Chem. Lett., 1987, 1819; K. Kajita, Y. Nishio, S. Moriyama, R. Kato, H. Kobayashi, W. Sasaki, A. Kobayashi, H. Kim and Y. Sasaki, Solid State Commun., 1988, 65, 361; A. Kobayashi, R. Kato, A. Miyamoto, T. Naito, H. Kobayashi, R. A. Clark and A. E. Underhill, Chem. Lett., 1991, 2163; H. Kobayashi, K. Bun, T. Naito, R. Kato and A. Kobayashi, Chem. Lett., 1992, 1909. 3 H. Tajima, M. Inokuchi, A. Kobayashi, T.Ohta, R. Kato, H. Kobayashi and H. Kuroda, Chem.Lett., 1993, 1235. 4 H. Poleschner, W. John, F. Hoppe and E. Fanghanel, J. Prakt. Chem., 1983, 325, 957. 5 I. Hawkins, R. A. Clark, C. E. Wainwright and A. E. Underhill, Mol. Cryst. Liq. Cryst., 1990, 181, 209; R. M. Olk, W. Dietzsch, K. Kohler, R. Kirmse, J. Reinhold, E. Hoyer, L. Golic and B. Olk, Z. Anorg. Allg. Chem., 1988, 567, 131; R. Vicente, J. Ribas, C. Faulmann, J.-P. Legros and P. Cassoux, C. R. Acad. Sci., 1987, 305, 1055; R.Vicente, J. Ribas, C. Zanchini, D. Gatteschi, J.-P. Legros, C. Faulmann and P. Cassoux, Z. Naturforsch., Teil B, 1988, 43,iu, P. J. Wu, Y. F. Li and D. B. Zhu, Phosphorus Sulfur Silicon Relat. Elem., 1994, 90, 219; S. G. Liu, Y. Q. Liu, S. H. Liu and D. B. Zhu, Synth. Met., 1995, 71, 137; J. X. Pan, Y. Q. Liu and D. B. Zhu, Chin. Chem. Lett., 1995, 6, 1077. 6 S. G. Liu, P. J. Wu, Y. Q. Liu and D. B. Zhu, Mol. Cryst. Liq. Cryst., 1996, 275, 211; S.G. Liu, Y. Q. Liu and D. B. Zhu, Mol. Cryst. Liq. Cryst., 1996, 281, 299. 7 S. Araki, H. Ishida and T. Tanaka, Bull. Chem. Soc. Jpn., 1978, 51, 407. 8 International Tables, Kluwer, Dordrecht, 1992, vol. C, Tables 4.2.6.8 and 6.1.1.4. 9 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. 10 O. Lindqvist, L. Sjölin, J. Sieler, G. Steimecke and E. Hoyer, Acta Chem. Scand., Ser. A, 1979, 33, 445. 11 R. Eisenberg and J. A. Ibers, Inorg. Chem., 1965, 4, 605. 12 O. Lindqvist, L. Anderson, J. Sieler. G. Steimecke and E. Hoyer, Acta Chem. Scand., Ser. A, 1982, 36, 855. 13 G. Matsubayashi, K. Takahashi and T. Tanaka, J. Chem. Soc., Dalton Trans., 1988, 967. 14 M. Bousseau, L. Valade, J.-P. Legros, P. Cassoux, M. Garbauskas and L. V. Interrante, J. Am. Chem. Soc., 1986, 108, 1908. 15 D. Y. Noh, M. Mizuno and J. H. Choy, Synth. Met., 1993, 55–57, 1705; Inorg. Chim. Acta, 1994, 216, 147. 16 G. Matsubayashi and A. Yokozawa, J. Chem. Soc., Dalton Trans., 1990, 3013. 17 D. Snaathorst, H. M. Doesburg, J. A. A. J. Perenboom and C. P. Keijizers, Inorg. Chem., 1981, 20, 2526. 18 U. Sakaguchi and A. W. Adisson, J. Am. Chem. Soc., 1977, 99, 5189. 19 Y. Sakamoto, G. Matsubayashi and T. Tanaka, Inorg. Chim. Acta, 1986, 113, 137. 20 A. J. Bard and L. R. Faulkner, Electrochemical Methods, Wiley, New York, 1980. 21 M. A. Cowie, A. Gleizes, G. W. Grynkewich, D. W. Kalina, M. S. McClure, R. P. Scaringe, R. C. Teitelbaum, S. L. Ruby, J. A. Ibers, C. R. Kannewurf and T. J. Marks, J. Am. Chem. Soc., 1979, 101, 2921; R. C. Teitelbaum, S. L. Ruby and T. J. Marks, J. Am. Chem. Soc., 1979, 101, 7568; 1980, 102, 332. 22 D. B. Zhu, M. X. Wang, P. Wang, D. H. Wang and S. H. Liu, Kexue Tongbao, 1986, 31, 382. 23 T. Ohta, M. Yamada and H. Kuroda, Bull. Chem. Soc. Jpn., 1974, 47, 1158. Received 25th June 1996; Paper 6/04434D

ISSN:1477-9226    

DOI:10.1039/a604434d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 279–284 279 Synthesis and characterisation of thioether crown hydrazones, and palladium(II) and platinum(II) complexes of 6-(2,4- dinitrophenylhydrazono)-1,4,8,11-tetrathiacyclotetradecane Liam R. Sutton, Alexander J. Blake, Wan-Sheung Li and Martin Schröder * Department of Chemistry, The University of Nottingham, University Park, Nottingham, UK NG7 2RD Reaction of the functionalised thioether crowns [14]aneS4-6-one (1,4,8,11-tetrathiacyclotetradecan-6-one, L1) and [10]aneS3-9-one (1,4,7-trithiacyclodecan-9-one, L2) with 2,4-dinitrophenylhydrazine in a protic solvent under acidic catalysis afforded the corresponding hydrazones L3 and L4, respectively, in high yield.Reaction of [14]aneS4-6-one with p-nitrophenylhydrazine under similar conditions affords the hydrazone L5. Reaction of L3 with [Pd(MeCN)4][BF4]2 in MeCN yielded the complex [Pd(L3)][BF4]2, while reaction of this ligand with [Pt(EtCN)4][CF3SO3]2 in MeCN afforded [Pt(L3)][CF3SO3]2. The single-crystal structures of L3–L5 and of [Pd(L3)][BF4]2 have been determined. In all cases, p–p stacking is observed, the free macrocycles crystallising as polymeric arrays of face-sharing hydrazone moieties.In [Pd(L3)]21, p–p interactions alternate with face sharing between planar [PdS4]21 units constructing a one-dimensional polymeric array. The hydrazone function forces distortions of the respective macrocyclic rings and imparts chirality to the [Pd(L3)]21 cation.The potential of these molecules as building blocks for macrocyclic liquid crystals and extended supramolecular arrays is discussed, as is the need to consider steric factors in rationalising the reactivity of keto-functionalised thioether crowns. Homoleptic sulfur-donor macrocycles bearing extended functionality are still rare and have only recently been applied to the synthesis of mesogenic materials, both as free macrocycles and as binding agents for the late transition-metal ions.1 The common feature of such materials is that the macrocycle bears a number of lengthy organic substituents which generate the anisotropy necessary to induce liquid-crystalline behaviour.2 Since derivatisation of a thioether crown must necessarily occur on the carbon backbone, work has been undertaken to build in precursor functionality which can be used subsequently for extended derivatisation.Macrocyclic thioether crowns have now been synthesized with hydroxyl,3 methine,4 hydroxymethyl 5 and ketone 6 functionalities. Most examples of further derivatisation have focused on hydroxyl derivatives.1,5,7 To date our own work in this area has concentrated on esterification of [14]- and [16]-aneS4-diols.1 Keto-functionalised thioether crowns, first synthesized independently by Setzer and Kellogg and their co-workers,6a,b have been treated with hydrazine by Kellogg and co-workers 8 to yield both inter- and intra-molecular azines, demonstrating that these carbonyl groups readily undergo sterically innocuous condensations.However, attempted Wittig and Grignard additions to these ketones were unsuccessful, the reason proposed being that they have a high tendency to enolise due to the sulfur atoms situated b to the carbonyl group.8 The tetradentate thioether crown [14]aneS4 (1,4,8,11-tetrathiacyclotetradecane) co-ordinates to an extensive range of metal atoms, most commonly as a platform for a square-planar S4 donor set.9 The d8 palladium(II) cation usually adopts square-planar co-ordination and this is observed in its complexes with both the parent ligand 10 and with several functionalised derivatives 11 where the hydrocarbon links form the sides of a shallow bowl with the PdS4 square as its base.We report herein the synthesis of phenylhydrazono derivatives of [14]- aneS4-6-one (1,4,8,11-tetrathiacyclotetradecan-6-one, L1) and [10]aneS3-9-one (1,4,7-trithiacyclodecan-9-one, L2) and complexes with PdII and PtII.Results and Discussion The ligands were synthesized from the appropriate ketonic starting material via condensation with aryl-substituted hydrazines to generate resonance-stabilised functionalised macrocycles incorporating an sp2-hybridised carbon atom. Interdependence of the conformation of each macrocycle and the nature of its substituent is evident by comparison of the single-crystal structures of the parent ketones, L1 and L2, their hydrazones L3–L5, and [Pd(L3)]21.Synthesis of L1 and L2 The ketones used for further derivatisation, L1 and L2, were prepared by literature methods developed primarily by Kellogg and co-workers 6a and by Setzer et al.6b Crystal structure determinations 6c,12 reveal that L1 and L2 adopt exodentate conformations similar to those exhibited by their unsubstituted parent macrocycles with little distortion due to the presence of the carbonyl oxygen. Synthesis and structural description of L3–L5 Compounds L3 and L4 were synthesized by the condensation 13 of 2,4-dinitrophenylhydrazine with L1 and L2 respectively (Scheme 1).The hydrazine was suspended in EtOH, then protonated by the careful addition of concentrated H2SO4, to yield a bright yellow solution. This was then added to a colourless solution of the ketone in boiling EtOH, generating instant orange cloudiness in the mixture. Cooling to room temperature afforded almost quantitative yields of hydrazone.Analogously, L5 was synthesized from L1 and p-nitrophenylhydrazine using glacial acetic acid to dissolve the hydrazine in EtOH. Crystallisation at 218 8C yielded a mixture of product and excess of hydrazinium salt. Recrystallisation from EtOH afforded a 63% yield of yellow hydrazone L5. Selected bond lengths and angles are listed in Table 1. Features of note are the hydrogen bonds in compounds L3 and L4 between the hydrazone protons and an oxygen atom of the nitro groups in the ortho positions of the phenyl groups. Furthermore, the solid-state conformations of the macrocyclic core change significantly on condensation with the hydrazones.The crystal structure of L3 [Fig. 1(a)] reveals a marked distortion of the macrocycle by comparison with the structure of L1, which displays a quite regular [3434] conformation.6a The280 J. Chem. Soc., Dalton Trans., 1998, Pages 279–284 irregular [2435] conformation adopted by the macrocycle in L3 is, we propose, the result of a minimisation of steric interaction between the hydrazone proton H(16) and S(1) (Table 2).The packing diagram (Fig. 2) illustrates the p–p stacking in the structure.15 Interplanar separations are 3.383 and 3.407 Å (cf. 3.354 Å in graphite),16 offset such that the centroid–centroid separations between phenyl rings are both 3.905 Å (Table 3). Fig. 3 shows the structure of a single molecule of compound L4. The hydrazone proton again induces a solid-state conformational change in the macrocycle relative to its parent ketone which has a [2323] conformation.12 Significantly, the structure of L4 shows 8 out of 10 torsion angles less than 908 (Table 2) thus reducing direct contact between H(12) and S(1) and reflecting severe distortions within the ring.Interaction between the p systems of the molecules allows them to stack as arrays of interlocking L shapes (Fig. 4), with interplanar distances of 3.270 and 3.359 Å.Scheme 1 Synthesis of hydrazones S S S S O S S O S L1 L2 H2NNH NO2 R Hot EtOH/Acid S S S S N L3: R = NO2 L5: R = H HN R NO2 S S S N HN R NO2 L4: R = NO2 Fig. 1 Structures of compounds L3 (a) and L5 (b) A similar disruption of the ring conformation occurs in compound L5, which shows a [23225] conformation [Fig. 1(b)], showing that the NH ? ? ?O2N hydrogen bond present in L3 and L4 is not the key factor in determining the conformation of the macrocycle. Rather, conjugation in the hydrazone forces the NH hydrogen to occupy the position occupied by S(1) in the ketonic macrocycles.By comparison, the structure of an azine-bridged (]] N]N]] ) dimer of [13]aneS2O2 (1,4-dioxa-7,11- dithiacyclotridecane) obtained by Kellogg and co-workers 8 displays little distortion of the rings from the expected structure of [13]aneS2O2-6-one, highlighting the importance of the hydrazone proton. The p–p stacking motif observed in L4 is repeated in L5, with interplanar separations of 3.360 and 3.507 Å.Fig. 2 Packing of compound L3. Hydrogen atoms omitted for clarity Fig. 3 Structure of compound L4 Fig. 4 Packing of compound L4. Hydrogen atoms omitted for clarityJ. Chem. Soc., Dalton Trans., 1998, Pages 279–284 281 In the stacking of compounds L3–L5, large lateral offsets of neighbouring phenyl rings occur. This is due in part to the extended p systems of the phenyl ring, nitro groups and the hydrazone function. The view of the packing in L5 in Fig. 5, perpendicular to the aromatic plane, shows the close aligning of phenyl rings in adjacent hydrazones. Synthesis of complexes of PdII and PtII The complex [Pd(L3)][BF4]2 was synthesized by the addition of a solution of [Pd(MeCN)4][BF4]2 in MeCN to an orange mixture of MeCN and the partially soluble L3. The mixture immediately cleared and darkened slightly, the yellow product being crystallised by layering with Et2O. Crystals of composition [Pd(L3)][BF4]2?1.5MeCN were analysed by X-ray crystallography and the structure of the Fig. 5 Packing of compound L5. Hydrogen atoms omitted for clarity Table 1 Selected bond lengths (Å) and angles (8) L3 C(13)]N(15) N(15)]N(16) C(12)]C(13)]C(14) N(15)]C(13)]C(12) N(15)]C(13)]C(14) C(13)]N(15)]N(16) 1.289(6) 1.380(6) 118.4(5) 115.6(3) 126.0(5) 116.3(4) N(16)]C(17) O(22A) ? ? ? H(16) C(17)]N(16)]N(15) N(16)]C(17)]C(18) N(16)]C(17)]C(22) 1.347(7) 1.98 120.0(4) 120.3(5) 123.6(5) L4 C(9)]N(11) N(11)]N(12) C(8)]C(9)]C(10) N(11)]C(9)]C(8) N(11)]C(9)]C(10) C(9)]N(11)]N(12) 1.266(7) 1.392(5) 115.1(5) 114.2(5) 130.3(5) 119.3(5) N(12)]C(13) O(18A) ? ? ? H(12) C(13)]N(12)]N(11) N(12)]C(13)]C(14) N(12)]C(13)]C(18) 1.351(7) 2.01 117.8(5) 120.0(5) 124.6(6) L5 C(13)]N(15) N(15)]N(16) C(14)]C(13)]C(12) N(15)]C(13)]C(12) N(15)]C(13)]C(14) C(13)]N(15)]N(16) 1.298(7) 1.375(6) 117.8(4) 114.1(5) 127.6(5) 117.2(4) N(16)]C(17) N(15)]N(16)]C(17) N(16)]C(17)]C(18) N(16)]C(17)]C(22) 1.382(7) 118.4(5) 121.8(5) 118.3(5) [Pd(L3)][BF4]2?1.5MeCN Pd]S(1) Pd]S(4) Pd]S(8) Pd]S(11) S(1)]Pd]S(4) S(8)]Pd]S(4) S(8)]Pd]S(11) S(1)]Pd]S(11) C(14)]C(13)]C(12) 2.295(4) 2.301(3) 2.294(4) 2.308(4) 87.9(2) 87.7(2) 87.8(2) 96.6(2) 120.8(13) C(13)]N(15) N(15)]N(16) N(16)]C(17) O(22A) ? ? ? H(16) N(15)]C(13)]C(12) N(15)]C(13)]C(14) N(15)]N(16)]C(17) C(18)]C(17)]N(16) C(22)]C(17)]N(16) 1.29(2) 1.27(2) 1.41(3) 1.96 116.7(14) 123(2) 119(2) 119(2) 122(2) cation is shown in Fig. 6. Disorder modelling of the cation, both anions and both solvate molecules was required to refine the structure, an important factor in the cation being rotation of 1808 about the C(13)]N(15) bond.The minor parts of the disorder are omitted for clarity. The Pd]S distances are similar to those in [Pd([14]aneS4)][PF6]2,10 with the sp2 hybridisation of C(13) leading to an increase in the S(11)]Pd]S(1) angle to 96.6(2)8 but with the other three angles lying in the narrow range 87.7(2)–87.9(2)8. Fig. 6 Structure of the cation in [Pd(L3)][BF4]2?1.5MeCN. Minor parts of disorder and most hydrogens omitted for clarity Table 2 Diagnostic torsion angles for compounds L1–L5 Compound S]C]C]X Angles a/8 L1 L3 L5 L2 L4 211.2(3) b 273.7(6) 250.7(7) 220.7, 219.5 c 246.6(8) 25.8(3) b 2104.5(5) 133.7(4) 137.9, 136.2 c 123.1(5) S(1)]C(2)]C(3)]S(4) C(2)]C(3)]S(4)]C(5) C(3)]S(4)]C(5)]C(6) S(4)]C(5)]C(6)]C(7) C(5)]C(6)]C(7)]S(8) C(6)]C(7)]S(8)]C(9) C(7)]S(8)]C(9)]C(10) S(8)]C(9)]C(10)]S(11) C(9)]C(10)]S(11)]C(12) C(10)]S(11)]C(12)]C(13) S(11)]C(12)]C(13)]C(14) C(12)]C(13)]C(14)]S(1) C(13)]C(14)]S(1)]C(2) C(14)]S(1)]C(2)]C(3) L3 160.9(3) 176.0(4) 70.4(5) 69.0(6) 2164.2(4) 77.3(4) 72.8(5) 2179.4(3) 102.7(4) 2140.4(4) 75.7(5) 106.2(5) 264.1(4) 273.4(4) L5 2167.3(3) 285.5(5) 74.7(5) 50.7(6) 172.4(4) 65.1(5) 72.6(5) 2174(3) 170.4(4) 279.8(5) 253.8(6) 137.9(4) 245.3(5) 2178.7(4) S(1)]C(2)]C(3)]S(4) C(2)]C(3)]S(4)]C(5) C(3)]S(4)]C(5)]C(6) S(4)]C(5)]C(6)]S(7) C(5)]C(6)]S(7)]C(8) C(6)]S(7)]C(8)]C(9) S(7)]C(8)]C(9)]C(10) C(8)]C(9)]C(10)]S(1) C(9)]C(10)]S(1)]C(2) C(10)]S(1)]C(2)]C(3) L4 158.6(3) 266.1(5) 283.5(5) 67.3(6) 72.6(6) 282.2(5) 263.9(6) 141.7(4) 242.1(5) 263.5(5) a X = O or N.b Ref. 6(c). c Taken from the Cambridge Structural Database. 12,14 Table 3 Phenyl ring separations in compounds L3–L5 and [Pd(L3)]- [BF4]2?1.5MeCN L3 L4 L5 [Pd(L3)]21 Centroid–centroid distance a/Å 3.905, 3.905 3.602, 3.700 4.262, 4.519 3.683, — Interplanar separation b/Å 3.383, 3.407 3.270, 3.359 3.360, 3.507 3.270, — a Distance between dummy atoms placed at geometric centroids of adjacent phenyl ring carbon atoms.b Perpendicular distance from dummy atom to mean plane of adjacent phenyl ring carbon atoms.282 J. Chem. Soc., Dalton Trans., 1998, Pages 279–284 Fig. 7 Linear polymeric array of cations in [Pd(L3)][BF4]2?1.5MeCN. Minor parts of disorder omitted for clarity. Phenyl centroid separation (– – – –) = 3.683 Å; S(4) ? ? ? S(4) 3.341 Å Compound L3 co-ordinates to PdII to produce a flattened cup-like structure, resulting in chirality since the hydrazone at the rim of the cup can point either clockwise or anticlockwise, generating distinct enantiomers.The sp2 linkage is rigid and the macrocycle is denied flexibility by the co-ordinated metal atom. In constructing linear polymers of cations (Fig. 7), the dicationic heads are held in close proximity with a shortest contact between neighbouring S(4) atoms of 3.341 Å.The tetrafluoroborate anions appear to exert considerable influence on the arrangement of the cations, with F atoms in close proximity to Pd, S(8) and S(11) and certain H atoms (Fig. 8). The aromatic groups show an interplanar separation of 3.270 Å. The linear polymers, formed from predominantly identical enantiomers, lie side by side to form sheets, with alternate sheets constructed from the alternate enantiomer to produce a racemic crystal. The complex [Pt(L3)][CF3SO3]2 was synthesized using a similar method to that for [Pd(L3)][BF4]2 but using [Pt(EtCN)4]- [CF3SO3]2 as starting material.The yellow suspension of L3 in MeCN cleared only slightly on addition of the [Pt(EtCN)4]- [CF3SO3]2 but no colour change was observed in this case. The cloudiness is presumably due to some hydrolysed platinum(II) starting material, which is relatively moisture-sensitive. The reaction mixture was filtered and the filtrate evaporated, then taken up in a small amount of MeCN and precipitated by layering with Et2O.Satisfactory characterisation data were obtained for all compounds using NMR, IR and mass spectrometry and elemental analysis. Conclusion Thioether crown ketones may be condensed with nitrophenylhydrazines to give new amphiphilic ligands for late transition metals. These ligands may be used in complex-forming reactions with PdII and PtII. The crystal structures highlight extensive p–p interaction while in the new palladium(II) complex sheets of parallel chains of chiral amphiphiles are formed.Furthermore, the crystal structures suggest an additional explanation for the failure of many reactions involving keto- Fig. 8 Influence of BF4 2 on cation packing in [Pd(L3)][BF4]2? 1.5MeCN functionalised thioether crowns. The marked distortion of the macrocycles due to a remote hydrogen atom implies that the steric interaction between the ring and the added substituent is critical. In our hands, attempted acid-catalysed imine formation using anilines in benzene under azeotropic distillation conditions resulted in C]S bond cleavage and decomposition, presumably via b-proton elimination.17a Comba et al.17b have recently investigated thermal C]S bond cleavage and ring contraction in 6-chloro- and 6,13-dichloro-[14]aneS4. We speculate that the thioether crown hydrazones exhibit intermediate stability compared with crown thioethers bearing small substituents like oxygen and CH2 and hypothetical examples bearing sterically demanding aromatic imines.The forcing conditions required to synthesize the imines thus cause decomposition. We also conclude that the failure of certain functionalisations of thioether crown ketones has a steric basis. We are currently attempting to extend the chains attached to the macrocycles using both covalent and non-covalent bonding so increasing the anisotropy of the products. Of particular interest is the nitro–iodo interaction between nitro- and iodobenzenes recently reviewed by Desiraju.18 These approaches should in due course lead to both thermotropic and lyotropic liquid crystals and extended arrays.Experimental Spectra were recorded on a Bruker DPX 300 (1H and 13C NMR) and a Perkin-Elmer 1600 spectrometer (FTIR, samples in KBr discs). Melting points were measured using a Gallenkamp apparatus and are uncorrected. Elemental analytical data were obtained by the Microanalytical Service (Perkin-Elmer 240B analyser) at the University of Nottingham and EI (electron impact) mass spectra were measured using a VG Autospec VG7070E spectrometer.Electrospray mass spectra were obtained by the EPSRC National Mass Spectrometry Service at the University of Swansea. The compounds [14]aneS4-6-one (L1), [10]aneS3-9-one (L2), [Pd(MeCN)4][BF4]2 and [Pt(EtCN)4][CF3SO3]2 were prepared according to literature methods.6,19 All starting materials, including anhydrous dimethylformamide, were obtained from Aldrich or Lancaster Synthesis and used without further purification.Syntheses 1,4,8,11-Tetrathiacyclotetradecane-6-one 2,4-dinitrophenylhydrazone (L3) and 1,4,7-trithiacyclodecane-9-one 2,4-dinitrophenylhydrazone (L4). 2,4-Dinitrophenylhydrazine (50 mg, 0.25 mmol) was suspended in EtOH (5 cm3) in an Erlenmeyer flask (25 cm3). To the stirred solution were added five drops of concentrated H2SO4 yielding a yellow solution. In another Erlenmeyer flask (25 cm3) compound L1 (42 mg, 0.15 mmol) or L2 (31 mg, 0.15 mmol) was dissolved in boiling EtOH (5 cm3) and stirred; the hydrazine solution was added to this colourless solution giving an orange suspension which on cooling to 4 8C yielded a yellow microcrystalline solid and an orange super-J.Chem. Soc., Dalton Trans., 1998, Pages 279–284 283 Table 4 Crystallographic data summarya Empirical formula M Colour, habit Crystal size/mm Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 T/K m/mm21 F(000) 2q Range/8 Independent reflections Observed reflections [|Fo| > 4s(|Fo|)] Absorption correction method Maximum, minimum transmission Decay correction (%) Number of parameters Weighting scheme a, b b Final R1 (wR2) c Maximum D/s Largest difference peak, hole/e Å23 L3 C16H22N4O4S4 462.62 Yellow plate 0.65 × 0.37 × 0.04 Monoclinic P21/c 7.7711(19) 19.458(9) 13.480(4) — 93.63(3) — 2034.3(10) 4 1.511 150 0.498 968 5–50 4402 2463 y Scans 0.880, 0.803 Random ±2 253 0, 6.41 0.0688 (0.1171) 0.001 0.38, 20.40 L4 C13H16N4O4S3 388.48 Yellow needle 0.35 × 0.10 × 0.06 Monoclinic P21/c 7.249(4) 10.786(4) 21.330(9) — 96.66(4) — 1656.5(10) 4 1.558 150 0.474 808 5–45 2148 1265 None — Random ±8.5 218 0.22, 0 0.0556 (0.1213) 0.001 0.30, 20.31 L5 C16H23N3O2S4 417.6 Yellow plate 0.47 × 0.22 × 0.12 Triclinic P1� 5.6363(11) 8.7733(15) 19.833(4) 93.28(2) 93.55(2) 105.54(2) 940.3(3) 2 1.475 150 0.521 440 5–45 2462 1866 None — 10 227 0.064, 2.54 0.0557 (0.0842) <0.001 0.34, 20.52 [Pd(L3)][BF4]2?1.5MeCN C19H26.5B2F8N5.5O4PdS4 804.22 Yellow column 0.33 × 0.20 × 0.19 Triclinic P1� 10.181(2) 12.569(3) 13.985(3) 96.16(2) 107.81(2) 96.02(2) 1676.1(4) 2 1.594 210 0.881 806 5–45 4402 3257 Numerical 0.898, 0.838 38.6 381 0.13, 39.0 0.1071 (0.1439) 0.009 1.68, 21.83 a Details in common: Stoë Stadi-4 four-circle diffractometer, Oxford Cryosystems open-flow cryostat,21 graphite-monochromated Mo-Ka radiation (l = 0.710 73 Å); w–q scans; refinement based on F 2.b In w21 = s2(Fo 2) 1 (aP)2 1 bP, where P = (Fo 2 1 2Fc 2)/3. c Defined in ref. 20. natant. The solid was separated by suction filtration, washed with cold EtOH (2 × 5 cm3) and dried in vacuo. Crystals of L3 suitable for X-ray diffraction were grown by diffusion of Et2O vapour into a CH2Cl2 solution at 4 8C. Compound L4 was crystallised by slow evaporation of a CH2Cl2 solution at room temperature. Compound L3: yield 64 mg (93%) (Found: C, 41.9; H, 4.8; N, 11.7.C16H22N4O4S4 requires C, 41.5; H, 4.8; N, 12.1%); m.p. 130 8C (decomp.); n& max/cm21 3311m, 1615vs, 1590s, and 1510s; dH(CDCl3) 9.16 [1 H, s, C(NO2)CHC(NO2)], 8.35 (1 H, m, aryl), 7.97 (1 H, m, aryl), 3.75 (2 H, s, Z-CH2C]] NNH), 3.63 (2 H, s, E-CH2C]] NNH), 3.05–2.90 (8 H, m, SCH2CH2S), 2.75 (4 H, m, CH2CH2CH2) and 1.95 (2 H, qnt, CH2CH2CH2); dC[CDCl3, H connectivity confirmed by DEPT (distortionless enhancement of polarisation transfer) 90 and DEPT 135] 151.72 (C]] N), 144.80, 138.71 and 130.24 (aryl CN), 129.95, 123.30 and 116.63 (aryl CH), 39.79 (Z-CH2C]] NNH) and 33.86, 33.65, 32.59, 32.24, 31.03, 30.70, 29.93 and 29.27 (other CH2); m/z (EI) 460 (M1 2 2 H) and 391 (M1 2 71).Compound L4: yield 50 mg (87%) (Found: C, 39.7; H, 4.3; N, 14.0. C13H16N4O4S3 requires C, 40.2; H, 4.15; N, 14.4%); m.p. 168 8C (decomp.); n& max/cm21 3157m, 3087w, 2914w, 2852w, 1613vs, 1590s, 1530m, 1513s and 1499s; dH(CDCl3) 9.15 [1 H, s, C(NO2)CHC(NO2)], 8.33 (1 H, m, aryl), 7.95 (1H, m, aryl), 3.75 (2 H, s, Z-CH2C]] NNH), 3.50 (2 H, s, E-CH2C]] NNH) and 3.24–2.83 (8 H, m, SCH2CH2S); dC(CDCl3, H connectivity con- firmed by DEPT 90 and DEPT 135) 151.38 (C]] N), 144.86, 138.59 and 130.42 (aryl CN), 129.77, 123.34 and 116.55 (aryl CH), 41.68, 35.12, 35.00, 34.16, 33.43 and 31.02 (CH2); m/z (EI) 327 (M1 2 71). 1,4,8,11-Tetrathiacyclotetradecane-6-one 4-nitrophenylhydrazone (L5). In a round-bottomed flask (25 cm3) equipped with a magnetic stirrer bar and a reflux condenser, compound L1 (50 mg, 0.18 mmol) was suspended in EtOH (5 cm3) and refluxed to give a colourless solution.In a second flask (25 cm3), p-nitrophenylhydrazine (50 mg, 0.33 mmol) was suspended in EtOH (5 cm3) and treated with glacial acetic acid (four drops). On heating, a dark brown solution formed which was mixed with the refluxing ketone solution. The mixture was refluxed for 1 h, then stoppered and stored at 218 8C for 18 h.The resulting precipitate was isolated by suction filtration and recrystallised from EtOH to yield a yellow powder. Crystals suitable for X-ray diffraction were grown by slow evaporation of a solution of L5 in CHCl3. Compound L5: yield 47 mg, 0.11 mmol (63%) (Found: C, 46.1; H, 5.7; N, 10.3. C16H23N3O2S4 requires C, 46.0; H, 5.6; N, 10.1%); m.p. 141–143 8C (decomp.); n& max/cm21 3273m, 2920m, 1595vs, 1523s, 1498s, 1481s, 1425w, 1324vs, 1264vs, 1110vs and 1080s; dH(CDCl3) 9.37 (1 H, s, NH), 8.18 (2 H, m) and 7.10 (2 H, m, aryl), 3.69 (2 H, s) and 3.50 (2 H, s, CH2C]] N), 2.98–2.86 (8 H, m, SCH2CH2S), 2.75–2.67 (4 H, m, CH2CH2CH2) and 1.90 (2 H, m, CH2CH2CH2); dC(CDCl3) 149.64 (C]] N), 142.83 and 140.68 (aryl CN), 125.99 and 112.11 (aryl CH), 40.39, 33.32, 32.69, 32.38, 32.06, 30.72, 30.38, 29.64 and 29.40 (CH2); m/z (EI) 417 (M1).[Pd(L3)][BF4]2. A Schlenk tube (50 cm3) was charged with compound L3 (20 mg, 0.04 mmol) and a magnetic stirrer bar and pump-filled with N2.A solution of [Pd(MeCN)4][BF4]2 (19 mg, 0.04 mmol) in degassed MeCN (10 cm3) was added via cannula, which was washed through with degassed MeCN (5 cm3). The yellow solution became orange as all of the hydrazone dissolved. The solution was stirred for 1 h but no further change was observed. The MeCN solution was then layered with diethyl ether (30 cm3) and left to stand for 24 h. Orange crystals formed which immediately became powder on suction filtration.[Pd(L3)][BF4]2?0.5MeCN: yield 28 mg, 0.038 mmol (94%) (Found: C, 26.5; H, 3.3; N, 7.9. C16H22B2F8N4O4PdS4? 0.5MeCN requires C, 26.8; H, 3.1; N, 8.25%); n& max/cm21 3432m, 2923w, 2211vs, 1615s, 1596s, 1503m, 1427w, 1340s and 1084s; dH(CD3CN) 11.12 (1 H, s, NH), 8.99 (1 H, m, CNCHCN), 8.44 (1 H, m) and 7.95 (1 H, m, CNCHCHCN), 4.43–4.37 (4 H, m,284 J. Chem. Soc., Dalton Trans., 1998, Pages 279–284 CH2C]] N) and 3.93–2.90 (16 H, m, other SCH2) (CH2CH2CH2 coincident with solvent peaks at 2.20–1.90); dC(CD3CN4.99, 141.33 and 132.78 (aryl CN), 131.35, 123.74 and 118.20 (aryl CH), 43.26, 42.61, 42.35, 39.18, 38.78, 36.14 (2 C), 32.25, 26.26 (CH2) (CH at 118.20 coincident with CD3CN, detected using DEPT 90 and 135; C]] N not detected but possibly coincident with one of the aryl CN peaks; H connectivity confirmed using DEPT); m/z (positive-ion electrospray, MeOH, 80 V) 567 (M1 2 2 BF4, 100%).Crystals suitable for X-ray analysis were grown by diffusion of Et2O vapour into an MeCN solution of the complex. They were found to be of composition [Pd(L3)][BF4]2?1.5MeCN.[Pt(L3)][CF3SO3]2. To a stirred suspension of L3 (11 mg, 0.024 mmol) in MeCN (5 cm3) in a round-bottomed flask (25 cm3) was added a solution of [Pt(EtCN)4][CF3SO3]2 (17 mg, 0.024 mmol) in MeCN (5 cm3). The flask was stoppered and the mixture stirred for 24 h at room temperature. After this time a faintly cloudy yellow solution had formed which was filtered by gravity.The filtrate was evaporated, the residue taken up in MeCN (2 cm3) and precipitated by layering with Et2O and storing at 4 8C for 16 h. A yellow powder was isolated by suction filtration, washed with Et2O (2 × 5 cm3) and dried in air. [Pt(L3)][CF3SO3]2: yield 17 mg, 0.018 mmol (75%) (Found: C, 25.3; H, 2.9; N, 6.0; Pt, 19.0. C18H22F6N4O10PtS6?Et2O requires C, 25.7; H, 3.1; N, 5.4; Pt, 18.9%); m.p. 155–160 8C (decomp.); n& max/cm21 3454m, 3295w, 2983w, 2926w, 1519s, 1596m, 1502s, 1421w, 1343vs, 1316m, 1261vs, 1165s, 1097w, 1030s, 638s and 518w; dH(CD3CN) 11.16 (1 H, s, NH), 9.00, 8.44, 7.97 (each 1 H, m, aryl), 4.63–4.40 (3 H, m), 3.96–2.85 (m, 13 H, SCH2) and 2.12 (H2O, conceals CH2CH2CH2); dC(CD3CN) 144.99, 141.39, 140.53, 132.60 (C]] N and aryl CN), 131.40, 123.80, 120.01 (aryl CH), 43.42, 43.17, 42.27, 41.23, 38.95, 38.47, 36.61, 32.75, 26.12 (other CH); m/z (positive-ion electrospray, MeCN) 958 (M1 1 2 H) and 657 (M1 2 2 CF3SO3 2 2 H) (both peak sets agree closely with theoretical distributions).Crystallography Table 4 summarises the crystal data, data collection, structuresolution and refinement parameters for ligands L3–L5 and the complex [Pd(L3)][BF4]2?1.5MeCN. All structures were solved using direct methods and all non-hydrogen atoms except for those in disordered groups were refined anisotropically. Hydrogen atoms were placed in calculated positions and refined using a riding model.The asymmetric unit of the complex was found to contain two MeCN sites, one of which was half-occupied: disorder of the full-occupancy MeCN was successfully modelled by an approximately equal distribution of two orientations. Disorder in one BF4 2 was modelled using two-fold rotation about the B(1)]F(1) vector, whilst the other was modelled as two tetrahedra with a common centre at B(2). Disorder in the cation was modelled by a 1808 rotation about the C(13)]N(15) vector with a 65 : 35 random distribution.The symmetry of the unit cell imparts the racemic nature of the crystal. The phenyl ring was restrained to be flat to within 0.02 Å with C]C distances of 1.40(2) Å. Structure solution and least-squares refinement for all crystals was carried out using Dell Dimension 133 MHz Pentium personal computers running SHELXTL PC software 20 except for the structure solution for L4 which was performed using SHELXS 86.22 CCDC reference number 186/773. Acknowledgements We thank the EPSRC for support and the EPSRC National Mass Spectrometry Service at the University of Swansea for electrospray mass spectra. We also thank Professors R.M. Kellogg and P. Comba for details of unpublished results. References 1 A. J. Blake, D. W. Bruce, I. A. Fallis, S. Parsons and M. Schröder, J. Chem. Soc., Chem. Commun., 1994, 2471; A. J. Blake, D. W. Bruce, I. A. Fallis, S. Parsons, H. Richtzenhain, S. A. Ross and M. Schröder, Philos.Trans. R. Soc. London, Ser. A, 1996, 354, 395. 2 F. Vögtle in Supramolecular Chemistry, Wiley, Chichester, 1991, pp. 231–290. 3 V. B. Pett, G. H. Leggett, T. H. Cooper, P. R. Reed, D. Situmeang, L. A. Ochrymowycz and D. B. Rorabacher, Inorg. 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Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 1, 31. 15 C. A. Hunter, Chem. Soc. Rev., 1994, 23, 101. 16 N. N. Greenwood and A. Earnshaw, Chemistry of the Elements, Pergamon, Oxford, 1984, p. 304. 17 (a) A. J. Blake, A. J. Holder, T. I. Hyde, H. J. Kuppers, M. Schröder, S. Stotzel and K. Wieghardt, J. Chem. Soc., Chem. Commun., 1989, 1600; (b) P. Comba, A. Fath, B. Nuber and A. Peters, J. Org. Chem. in the press. 18 G. R. Desiraju, Angew. Chem., Int. Ed. Engl., 1995, 34, 2311. 19 R. R. Thomas and A. Sen, Inorg. Synth., 1990, 28, 128; V. Y. Kukushkin, Å. Oskarsson and L. I. Elding, Zh. Obsch. Khim., 1994, 64, 881. 20 G. M. Sheldrick, SHELXTL PC, version 5.03, Siemens Analytical Instrumentation, Madison, WI, 1994. 21 J. Cosier and A. M. Glazer, J. Appl. Crystallogr., 1986, 19, 105. 22 G. M. Sheldrick, SHELXS 86, Acta Crystallogr., Sect. A, 1990, 46, 467. Received 15th August 1997; Paper 7/05996E

ISSN:1477-9226    

DOI:10.1039/a705996e

出版商:RSC    

年代:1998

数据来源: RSC