摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2163–2166 2163 Formation of an adduct between thiocyanate ion and nitrosyl thiocyanate Anne M. M. Doherty,a Michael S. Garley,b Neil Haine a,b and GeoVrey Stedman *,b a Science Department, Worcester College of Higher Education, Henwick Grove, Worcester WR2 6AJ, UK b Chemistry Department, University of Wales Swansea, Singleton Park, Swansea SA2 8PP, UK Nitrosyl thiocyanate reacted with sufficiently high concentrations of thiocyanate ion to form an adduct, [ON(SCN)2]2, which absorbs strongly in the UV region.This species has different properties to that species described in the literature as [NO(SCN)2]2 formed in pulse-radiolysis experiments involving (SCN)2 2 and NO. The difference probably arises from different structures, an S-nitroso as compared to an N-nitroso compound. Acidic solutions containing both nitrous acid and thiocyanate ions have a marked red colour, due to an absorption maximum at 460 nm.From the variation of A460 with [H1], [HNO2] and [SCN2] it has been established 1 that the red species is nitrosyl thiocyanate, ONSCN, formed as shown in equation (1). This H1 1 HNO2 1 SCN2 ONSCN 1 H2O (1) species has also been isolated at low temperatures 2 by the reaction of ONCl with AgSCN. From these absorbance measurements the formation constant of ONSCN has been calculated, and emax established as 100 dm3 mol21 cm21. These measurements used relatively low concentrations of thiocyanate ion, less than 0.1 mol dm23.Later measurements,3 using much higher values of [SCN2], several mol dm23, showed that although the colour appeared much the same to visual observation the shape of the spectrum changed. The absorbance minimum on the low-wavelength side of 460 nm disappeared and the spectrum was a smooth curve in which the absorbance rose steeply towards low wavelengths in the UV region. Changes on the high-wavelength side of 460 nm were much less marked.It was suggested that this might be due to the formation of a species [ON(SCN)2]2. Recently Czapski et al.4 used pulse radiolysis to study the reaction of NO with a number of radical anions including (SCN)2 2, and observed the formation of a species absorbing strongly in the UV region with e260 ª 7570 dm3 mol21 cm21 which they suggested was [NO(SCN)2]2. This was observed to decay by a process showing first-order kinetics with a rate constant 2 × 104 s21 that was independent of pH, [NO] and [SCN2] to yield a species with a much weaker UV absorption and which was suggested to be NOSCN, as shown in (2).[NO(SCN)2]2 NOSCN 1 SCN2 (2) There were a few measurements of the decay of NOSCN to form NO2 2 and SCN2, with kinetics that had a fractional order in [H1]. A comparison of the results of Czapski et al.4 with our observations indicated a number of points of disagreement and we have therefore extended our own work. Results and Discussion Nitrosyl thiocyanate is unstable in aqueous solution; the red colour fades over a period of 10–20 min with the evolution of bubbles of NO, and in the original work,1 which involved manual spectroscopy, this was allowed for by measuring the absorbance at a number of times and extrapolation to the time of mixing the reactants.This would not, however, detect a rapid initial reaction in the interval between mixing the solutions and measuring the first point. We have therefore used stopped-flow methods, mixing solutions of NaSCN 1 NaNO2 with HClO4, recording the initial absorbance after mixing.Fig. 1 shows a spectrum of ONSCN plotted for a series of repeat runs carried out at selected wavelengths, and the ONSCN peak at 460 nm can be clearly seen. Using the value of e460 = 100 dm3 mol21 cm21, the equilibrium constant K1 = [ONSCN]/[H1][HNO2]- [SCN2] is calculated as 44 dm6 mol22 for 2 mol dm23 ionic strength (NaClO4); this may be compared with earlier values of 21.0, 28.6 and 36.3 for ionic strengths of 0.42, 1.02 and 1.42 mol dm23 obtained by manual spectrometry1 with a Unicam SP500 spectrometer.The figure also shows a trace obtained at a much higher thiocyanate ion concentration, [SCN2] = 0.5 mol dm23, where it can be seen that the absorption on the low-wavelength side of 460 nm has increased markedly, with much smaller increases on the high-wavelength side. The value of A460 is significantly higher than that expected for K1 = 44 dm6 mol22 and [SCN2] = 0.5 mol dm23, confirming the presence of another species.Unfortunately the limitations of our stopped-flow apparatus made it impossible to extend these measurements into the UV region. Measurements by the stopped-flow method made at a single wavelength, 460 nm, and with varying [SCN2] are shown in Fig. 2. On the basis of K1 = 44 dm6 mol22 there ought to be 81% conversion of nitrite into ONSCN at [SCN2] = 1 mol dm23 and the absorbance vs. [SCN2] curve would be expected to be levelling off; instead the absorbance increases steadily, indicating the presence of another species.To extend our measurements to lower wavelengths we turned to conventional spectrophotometry. A spectrum of ONSCN Fig. 1 Visible spectra of ONSCN obtained by stopped-flow spectrophotometry at pH 1 and 25 8C: (m) [SCN2] = 0.02, [HNO2] = 0.02 mol dm23; (d) [SCN2] = 0.5, [HNO2] = 0.02 mol dm232164 J. Chem. Soc., Dalton Trans., 1997, Pages 2163–2166 obtained at low [SCN2] is shown in Fig. 3. The rate of decomposition of nitrosyl thiocyanate is a very sensitive function of concentration. To stabilise the solutions we reduced the nitrite concentration to 1024 mol dm23, and used 4 cm cells to obtain reasonable absorbances. Typical spectra are shown in Fig. 4, where it can be seen that as [SCN2] increases the UV absorption increases rapidly, filling the minimum below 460 nm, so that the peak characteristic of ONSCN disappears. Plots of A vs.[SCN2] show a linear increase in absorbance, typical values being included in Fig. 2. In making these measurements it was important to record the spectrum as soon as possible after mixing to avoid complications due to formation of the heterocycle iso-perthiocyanic acid (also known as xanthane hydride), 5-amino-1,2,4-dithiazole-3- thione (C2H2N2S3). The rate of formation of this yellow species is a very sensitive function of [SCN2], and Wilson and Hall 5 have shown that the rate of its formation is n = k[H1][SCN2]3.It has a very characteristic VIS/UV spectrum with fine structure peaks, and is readily identifiable. No trace of its spectrum was seen in our work, or in the published spectra of Czapski et al.4 However at our highest concentration of thiocyanate this compound precipitated on standing, and was identified by mass5 and infrared spectroscopy.6 We interpret our VIS/UV spectra as showing the formation of an additional species by the reaction of SCN2 with ONSCN.The increase in absorbance with [SCN2] is almost linear, suggesting that one thiocyanate ion is involved; as there is no sign of levelling off it seems likely that under our conditions only a small fraction of the ONSCN has been converted into the new species. We suggest the reaction is shown in equation (3), ONSCN 1 SCN2 [ON(SCN)2]2 (3) Fig. 2 Variation of absorbance with [SCN2] for solutions of H1 1 HNO2 1 SCN2 at 25 8C by stopped-flow (m) and UV spectrophotometry (d) (m): [H1] = 0.1, [HNO2] = 0.02 mol dm23; l = 2 mm; l = 460 nm; (d) [H1] = 0.1, [HNO2] = 0.0001 mol dm23; l = 4 cm; l = 320 nm Fig. 3 The UV/VIS spectrum of ONSCN at [H1] = 0.1, [HNO2] = 0.01, [SCN2] = 0.01, I = 2 mol dm23 and l = 4 cm without specifying a structure for [ON(SCN)2]2. If we assign formation constants K1 and K2 and absorption coefficients e1 and e2 to the species ONSCN and [ON(SCN)2]2 then the apparent absorption coefficient eobs is shown in equation (4), eobs = A/[nitrite]l = e1K1[H1][SCN2] 1 e2K1K2[H1][SCN2]2 1 1 K1[H1][SCN2] 1 K1K2[H1][SCN2]2 (4) where [nitrite] = [HNO2] 1 [ONSCN] 1 [ON(SCN)2 2] and l is the path length.Fitting data of the type shown in Fig. 2 by equation (4) has limitations because the measurements do not extend to concentrations where A begins to level off for substantial conversion into [ON(SCN)2]2, and this introduces large error limits on the constants deduced. In addition, although there is formal constant ionic strength, at concentrations of 2 mol dm23 the activity effects of NaClO4 and NaNCS will be different; thus the mean ion activity coefficients at a molality of 2 are 0.744 (NaNCS) and 0.609 (NaClO4).We assigned e1 = 100 dm3 mol21 cm21 as this is well established. Fitting the stopped-flow data at 460 nm by equation (4) we obtain 1023e2 = 1.74 ± 0.54 dm3 mol21 cm21, K1 = 33.4 ± 4.6 dm6 mol22 and 102K2 = 3.6 ± 1.3 dm3 mol21. The value of K1 is in fair agreement with earlier measurements and serves as a check on the curve fitting, but there are substantial errors associated with both K2 and e2.Such calculations are very sensitive to the values assigned to parameters in the equation. If, in addition to assigning e = 100 dm3 mol21 cm21 we also fix K1 as 44 dm6 mol22 then 1023e2 = 1.77 ± 0.71 dm3 mol21 cm21 and 102K2 = 1.32 ± 0.59 dm3 mol21. As the increase in absorbance with [SCN2] is almost linear we have only a small conversion into [ON(SCN)2]2 and we are virtually measuring K2e2 and there is not sufficient curvature to assign precise separate values to K2 and e2, though it is clear that K2 is small and e2 large (compared to K1 and e1 respectively).We now turn to a comparison of the present results with those of Czapski et al.4 Their evidence for the formation of a species with an intense UV spectrum by an encountercontrolled reaction between NO and (SCN)2 2 is very strong and [NO(SCN)2]2 seems a likely formulation.It must however be a different species to that formed by the reaction of SCN2 with ONSCN. The species [NO(SCN)2]2 decomposes with a firstorder rate constant of 2.1 × 104 s21 (t2� 1 = 3.3 × 1025 s), and would have completely decomposed long before our first measurements, even by stopped flow. Nevertheless the UV evidence for the presence of a species in our work is unmistakable and we suppose that they must be different compounds, possibly isomers. For this reason we write the formulae of the Czapski species in the same way as in their original paper, [NO(SCN)2]2 Fig. 4 The UV/VIS spectra at various [SCN2], [H1] = 0.1, [HNO2] = 0.0001, I = 4 mol dm23 and l = 4 cm. [SCN2] = 2.5 (A), 2.0 (B), 1.5 (C), 1.0 (D), 0.5 (E), 0.25 (F) and 0.1 (G) mol dm23. The spectra are shown in sequence A æÆ GJ. Chem. Soc., Dalton Trans., 1997, Pages 2163–2166 2165 Table 1 Variation of e420 with [thiourea] at 25 8C [(NH2)2CS]/mol dm23 e420 a/dm3 mol21 cm21 0.035 113 0.072 113 0.147 118 0.222 119 0.297 120 0.409 126 0.522 132 0.709 132 0.897 139 [(NMe2)2CS]/mol dm23 e420 b/dm3 mol21 cm21 0.02 192 0.06 196 0.10 199 0.14 204 0.18 208 a [H1] = 0.10, I = 0.3, [(NH2)2CSNO1] = 0.003 16 mol dm23.b [H1] = 0.49, I = 0.5, [(NMe2)2CSNO1] = 0.006 37 mol dm23. and NOSCN, whereas we write our species as [ON(SCN)2]2 and ONSCN emphasising that the nitroso group is bonded to sulfur. Czapski et al.4 suggested that [NO(SCN)2]2 decomposed to NOSCN 1 SCN2, and they show a spectrum for NOSCN that rises smoothly towards lower wavelengths in the UV region.Unfortunately their measurements do not extend above 340 nm, so it is not known whether the characteristic peak of ONSCN at 460 nm appears. The general shape of the UV spectrum is similar to our own observation on ONSCN, but the absorption coefficient at 320 nm is ª190 dm3 mol21 cm21, much lower than our own value of 924 dm3 mol21 cm21. Again it appears that they may be observing a different species.The hydrolysis reaction of the Czapski species NOSCN was found to obey pseudo-first-order kinetics, with a rate constant that decreased with increase of pH, 730 (pH 5.9), 458 (6.8), 126 (7.9) and 1.3 s21 (1.5). This was interpreted by the mechanism in equations (5) and (6) with k6 ª 800 s21 and k25/k6 ª 107. There NOSCN 1 H2O (HO]NOSCN)2 1 H1 (5) (HO]NOSCN)2 1 H1 HNO2 1 SCN2 (6) are some unusual features here. Reaction (6) is written as a bimolecular process, but k6 is quoted as a first-order rate constant.The value of 800 s21 looks to be a limiting value of the observed pseudo-first-order rate constant at high acidity. It can be compared with the value obtained by conventional methods for the hydrolysis of ONSCN. The rate constant for the forward reaction (1) is 7 11 700 dm6 mol22 s21, and this value is supported by an independently determined value 8 at 0 8C which, when corrected for temperature variation (E = 54 kJ mol21), gives 10 900 dm6 mol22 s21 at 25 8C.The equilibrium constant 1 for (1) is 32 dm6 mol22, giving the rate constant for the hydrolysis reaction of 365 s21. The difference between this figure and 800 s21 may be significant, but is not sufficiently large to be certain. The reasons for the differences between our results and those of Czapski et al.4 seem most likely to lie in different structures. Czapski did not, of course, on the basis of only UV evidence suggest a structure for [NO(SCN)2]2, but as we propose that we observe an isomer it is incumbent on us at least to make a suggestion.The structure of thiocyanogen (SCN)2 certainly involves a sulfur–sulfur bond, and it seems likely that (SCN)2 2 will be [NCS]SCN]2. An encounter-controlled reaction with NO? could lead to the formation of an N-nitroso species [NCS]SCN?NO]2. The sulfur–nitroso compounds (thionitrites) are characterised by red/yellow colours and absorption in the visible region, and nitrosyl thiocyanate clearly belongs in this class with an S]N]] O chromophore. We do not know the structure of our adduct, but if it is derived from ONSCN then it is likely that it will have an S]NO bond and hence be different from [NCS]SCN?NO]2 and have a different spectrum and different stability.The decomposition of [NCS]SCN?NO]2 with loss of SCN2 will presumably produce nitrosyl isothiocyanate SCNNO, which will differ from our species ONSCN. Detailed calculations have been published by Westwood and Pasinszki 9 of the stability of open-chain and ring isomers of composition CN2OS.They calculate that the gasphase species SCNNO is some 16–17 kJ mol21 less stable than ONSCN. Both are anti structures. These calculations indicate that the differences in stability of the N- and S-nitroso isomers is small enough that there is nothing unreasonable in postulating this as the structure of Czapski’s compound, thus accounting for the differences between his results and ours.In conclusion we cite some other evidence for the existence of other disulfide species with sulfur bonded to a nitroso group. Nitrous acid reacts with thiourea to form10 a yellow S-nitroso product, (NH2)2CSNO1, as shown in equation (7), with a (NH2)2CS 1 H1 1 HNO2 (NH2)2CSNO1 1 H2O (7) formation constant of ca. 5000 dm6 mol22. The stability of this species has been extensively examined11 by stopped-flow methods at 420 nm, and its chemistry as a nitrosating agent has been studied in detail by Dix and Williams,12 it shows a very similar reactivity pattern to that of ONSCN. The absorption coefficient at 420 nm of solutions of thiourea 1 nitrous acid in which there is essentially 100% conversion of nitrite into (NH2)2CSNO1 increases markedly and linearly with increase in [(NH2)2CS].Similar behaviour is observed for solutions of (NMe2)2CS 1 nitrous acid. Data are shown in Table 1. These observations parallel the effects observed in the HNO2–SCN2 system, but in this case there is kinetic evidence that is consistent with the presence of a species [(NH2)2CS]2- NO1, equation (8).The rate of decay of (NH2)2CSNO1 (NH2)2CSNO1 1 (NH2)2CS K3 [(NH2)2CS]2NO1 (8) has been measured,11 and in the presence of a large excess of thiourea the rate law (9) is observed. This was originally 2d[(NH2)2CSNO1]/dt = k2[(NH2)2CSNO1][(NH2)2CS] (9) interpreted as attack by thiourea on (NH2)2CSNO1 to form (NH2)2CSSC(NH2)2~1 1 NO?, the radical cation undergoing further oxidation to form the known product (NH2)2CSSC- (NH2)2 21.This does not account however for the increase in absorbance with [(NH2)2CS]. However if there is the formation of a small amount of a thiourea adduct which absorbs much more strongly than (NH2)2CSNO1 and which decomposes then precisely the same rate law would be observed, the difference ing that k2 would be K3k3, equations (8) and (10). [(NH2)2CS]2NO1 k3 (NH2)2CSSC(NH2)2~1 1 NO (10) The structure of the postulated adduct is not known, but as the end product of the decomposition of (NH2)2CSNO1 is (NH2)2CSSC(NH2)2 21 which is known from X-ray crystallography 13 to contain an S]S linkage it is reasonable to assume that this exists in the adduct also.We considered the possibility that the rate law (9) might be due to nitrosation of a dimer of thiourea, but investigation of the 13C NMR shift of aqueous solutions of thiourea showed no sign of any variation with [(NH2)2CS].Similarly we were unable to detect any deviation from the Beer–Lambert law for thiourea solutions, so we did not find any evidence for dimer formation.14 We conclude that sulfur–nitroso compounds can undergo addition reactions with other sulfur nucleophiles to form adducts in which a sulfur–sulfur bond is formed. It seems likely2166 J. Chem. Soc., Dalton Trans., 1997, Pages 2163–2166 that the species [NO(SCN)2]2 and NOSCN observed in pulse radiolysis are N-nitroso compounds, and that the compound described by Czapski et al.4 as NOSCN is different from the nitrosyl thiocyanate known as a nitrosating agent in aqueous solutions.Experimental Materials All chemicals were of AnalaR grade with the exception of tetramethylthiourea and were used without further purification. Spectrophotometric and kinetic measurements Stopped-flow measurements were made with a Hi Tech Canterbury SF-3A instrument, fitted with a data-collection system as described previously.11 Conventional VIS/UV spectra were measured on a Perkin-Elmer lambda nine spectrometer about 30 s after mixing.The spectrum of ONSCN, Fig. 1, was obtained from a solution of H1 1 HNO2 1 SCN2 at low [SCN2] in order to avoid complications due to formation of [ON(SCN)2]2. Under these conditions there is only partial conversion into nitrosyl thiocyanate and corrections for absorption due to HNO2 and SCN2 were subtracted. Absorption coefficients were calculated by taking the absorbance at 460 nm to be equivalent to e = 100 dm3 mol21 cm21. Acknowledgements We acknowledge financial support from Worcester College of Higher Education (to N. H.). References 1 G. Stedman and P. A. E. Whincup, J. Chem. Soc., 1965, 4813. 2 C. C. Addison and J. Lewis, Q. Rev. Chem. Soc., 1955, 9, 115. 3 C. G. Munkley, Ph.D. Thesis, University of Wales, 1990. 4 G. Czapski, J. Holcman and B. H. J. Bielski, J. Am. Chem. Soc., 1994, 116, 11 465. 5 I. R. Wilson and W. H. Hall, Aust. J. Chem., 1969, 22, 513. 6 H. J. Emeleus, A. Haas and N. Shepherd, J. Chem. Soc., 1963, 3165. 7 J. Fitzpatrick, T. A. Meyer, M. E. O’Neill and D. L. H. Williams, J. Chem. Soc., Perkin Trans. 2, 1984, 927. 8 G. Stedman, J. Chem. Soc., 1959, 2949. 9 N. P. C. Westwood and T. Pasinszki, J. Chem. Soc., Faraday Trans., 1996, 333. 10 K. Y. Al-Mallah, P. Collings and G. Stedman, J. Chem. Soc., Perkin Trans. 2, 1975, 1734. 11 P. Collings, M. S. Garley and G. Stedman, J. Chem. Soc., Dalton Trans., 1981, 331; M. S. Garley, G. Stedman and H. Miller, J. Chem. Soc., Dalton Trans., 1984, 1959. 12 L. R. Dix and D. L. H. Williams, J. Chem. Res., 1982, (S) 190. 13 O. Foss, J. Johnsen and O. Tvedten, Acta Chem. Scand., 1958, 12, 1782. 14 M. S. Garley, Ph.D. Thesis, University of Wales, 1982. Received 14th February 1997; Paper 7/01059A

ISSN:1477-9226    

DOI:10.1039/a701059a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2167–2169 2167 Formation of a diazadiphosphetidine from the reactions of a bis(aminosilyl) ether with PCl3: crystal structure of cis- [(ButNH)PNBut]2 N. Dastagiri Reddy,a Anil J. Elias *,a and Ashwani Vij b a Department of Chemistry, Indian Institute of Technology, Kanpur, 208 016, UP, India b Single Crystal Diffraction Laboratory, University of Idaho, Moscow, Idaho 83843, USA Reaction of O[SiMe2N(But)H]2 1 with PCl3 in 1 : 1 molar ratio in hexane in presence of NEt3 gave the cyclic fourmembered diazadiphosphetidine cis-[(ButNH)PNBut]2 2 instead of the expected six-membered silazoxyphosphine indicating cleavage of the Si]N bond.A crystal structure analysis of 2 showed that the NH hydrogens of the ButNH groups are in an endo-endo orientation above the (PN)2 ring which is in contrast to the exo-endo orientation for the known structure of its disulfide. Bis(aminosilyl) ethers of the type O[SiMe2N(R)H]2 (R = Me, Et or But) are excellent starting materials for the synthesis of novel inorganic heterocycles as well as metallacycles having Si, N, O and another heteroelement as part of the ring framework.Wannagat and co-workers carried out detailed reactions of O[SiMe2N(R)H]2 ( R = Me or Et ) with a variety of maingroup halides such as PPhCl2, PEtCl2,1 PMeCl2,2 SnCl4, GeCl4, AsCl3, SiMe(CH2]] CH)Cl2, SiCl4, SiBr4,3 and BeCl2 4 in the presence of NEt3 as HCl scavenger or after dilithiation using nbutyllithium.The reactions invariably led to the formation of six-membered heterocycles of the type LnMSi2N2O [LnM = PhP, EtP, MeP, Cl2Sn, Cl2Ge, ClAs, Me(CH2]] CH)Si, Cl2Si, Br2Si or Be]. Reactions with TiCl4 and ZrCl4 also gave similar metallacycles which were spirocyclic in nature.5 Recently Roesky and co-workers carried out reactions of O[SiMe2N(But)H]2 1 after dilithiation with main-group and transition metal halides in low oxidation states to synthesize novel six-membered silazoxy metallacycles with TeII, SnII and GeII 6 as the heteroelement as well as twelve-membered silazoxy metallacycles with ZnII, CoII,7 FeII, MnII, NiII or CrII 6 wherein the metals, were stabilized in low co-ordination and oxidation states. A variety of reactions have also been carried out on PIIISi2N2O ring compounds (Me and Ph substituents on P, Me on N) leading to oxidation of the phosphorus(III) site to PV while retaining the six-membered ring structure.2 Similar silazoxy heterocycles with PV as part of the ring framework were also prepared by reactions of phenoxy thiophosphoryl dihydrazide and phenoxy phosphoryl dihydrazide with tetraalkyl-1,3- dichlorodisiloxanes and structurally characterized.8 Reactions of O[SiMe2N(R)H]2 with PCl3 have been reported briefly as leading to only polymeric products which were not properly identified.1 In our attempts to make silazoxyphosphines with varying ring sizes and substituents on silicon, nitrogen and phosphorus, we observed for the first time that instead of cyclization to form a six-membered silazoxyphosphine, O[SiMe2N(But)H]2 cleaves at the Si]N bonds and forms the diazadiphosphetidine cis-[(ButNH)PNBut]2 2.We report herein the details of this unusual reaction as well as the crystal structure of 2. Experimental All manipulations were carried out using standard Schlenk techniques using a vacuum line in an atmosphere of dry nitrogen. The compound O[SiMe2N(But)H]2 1 was prepared according to the reported procedure,7 PCl3 (Aldrich) was distilled prior to use and hexane and triethylamine were distilled and dried by standard procedures.In a typical reaction 1 (1.22 g, 4.4 mmol) was first dissolved in hexane (30 cm3), the solution cooled to 0 8C and with vigorous stirring, PCl3 (0.62 g, 4.5 mmol) added slowly using a syringe. After adding triethylamine (1.50 cm3), the mixture was brought to room temperature over a period of 15 min and then refluxed for 36 h whereupon a white solid (identified as NEt3?HCl) was observed.This was filtered off using a frit under nitrogen and the filtrate concentrated in vacuo to yield a semisolid mass which was sensitive to air and moisture. On redissolving this in hexane and keeping it at 0 8C for 24 h, colourless crystals of cis-[(ButNH)PNBut]2 2 were obtained (0.43 g, 56%), m.p. 143 8C (from hexane) (Found: C, 55.1; H, 11.2. C16H38N4P2 requires C, 55.2; H, 10.9%); n& max/cm21 3320w, 2915s, 1460s, 1362s, 1220s, 1040m, 1030m, 998s, 915w, 870s, 820m, 790m and 735m (Nujol); dH(C6D6) 1.28 (18 H, s, CH3), 1.53 (18 H, s, CH3) and 2.60 (2 H, br s, NH); dP(C6D6) 89.1 (s).These data were found to agree with the reported values for 2.9–11 Crystallography Single crystals of cis-[(ButNH)PNBut]2 2 suitable for X-ray studies were obtained by slow crystallization under nitrogen from hexane at 0 8C. Crystal data and data collection parameters. C16H38N4P2, M = 348.44, monoclinic, space group Pc, a = 9.6654(5), b = 5.9212(3), c = 18.9757(9) Å, b = 100.68(10)8, U = 1067.18(9) Å3, T = 213 K, graphite-monochromated Mo-Ka radiation, l = 0.710 73 Å, Z = 2, Dc = 1.084 Mg m23, F(000) = 384, colourless crystals with dimensions 0.35 × 0.20 × 0.15 mm, m(Mo-Ka) = 0.207 mm21, SADABS absorption correction,12 maximum and minimum transmission 0.962 and 0.783, Siemens SMART diffractometer with a CCD detector at 254 8C, q range for data collection 2.14–25.008, limiting indices 212 < h < 12, 26 < k < 7, 225 < l < 24, reflections collected 10 309, independent reflections 3102 (Rint = 0.0297). The data were acquired using Siemens SMART software and processed on a SGI-Indy/Indigo 2 workstation by using the SAINT software.13 Structure solution and refinement.The structure was solved by direct methods using the SHELXS 90 14 program and refined by full-matrix least squares on F 2 using SHELXL 93, incorporated in SHELXTL-PC V 5.03.15 All non-hydrogen atoms were refined anisotropically. The hydrogen atoms were located from the difference electron-density maps and included in the refinement process in an isotropic manner.The final R indices were2168 J. Chem. Soc., Dalton Trans., 1997, Pages 2167–2169 [I>2s(I)]; R(F) = 0.047 and wR(F 2) = 0.113, parameters refined = 188, goodness of fit = 1.06. 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 186/494. Results and Discussion In our attempts to make PIII-containing silazoxy heterocycles by the reactions of compound 1 with PPhCl2 in presence of a tertiary amine or after lithiation we observed a general hesitancy for the reaction to proceed.A similar trend in reactivity was observed when transamination was attempted using P- (NR2)3 (R = Me or Et) with 1. However, a reaction of PCl3 with 1 in the presence of NEt3 was found to proceed slowly on refluxing in hexane. Instead of the expected silazoxy phosphine, the reaction gave exclusively a diazadiphosphetidine 2 (Scheme 1). All reactions reported so far of O[SiMe2N(R)H]2 and MeN- [SiMe2N(R)H]2 as such or after metallation, with main-group and transition-metal halides, have resulted in the formation of six- or twelve-membered heterocycles indicating the stability of the Si]N bond during such reactions.Reactions of phosphorus( III) dihalides like PRCl2 (R = Me, Et or Ph) with O[Si- Me2N(R)H]2 and MeN[SiMe2N(R)H]2 (R = Me or Et) are reported to give silazoxy and silaza phosphines which have been characterized by spectral and analytical techniques.1,2 The fact that O[SiMe2N(But)H]2 1 behaves differently may be related to a variety of factors. The bulkiness of the tertiary butyl group possibly prevents attack of the PCl2 moiety of the HN(But)- SiMe2OMe2Si(But)NPCl2 unit formed in the first step of the reaction on the other amino hydrogen.This may lead to the formation of ClSiMe2OMe2Si(But)NP(Cl)N(But)H which may further cleave at the Si]N bond leading to ButN]] PNHBut. Dimerization of the latter can lead to the diazadiphosphetidine 2. It is noteworthy that isolation of mono- and di-chloro analogues of the diazadiphosphetidines16–18 were not observed in this reaction.Reactions leading to cleavage of Si]N bonds with phosphorus chlorides are well documented.19 This being the first step followed by N]H cleavage to precipitate amine hydrochloride may also bring about the formation of 2. This is further assisted by the fact that the P]Cl bonds in PCl3 are comparatively weaker (326 kJ mol21) than a standard Si]Cl bond (381 kJ mol21).20 In addition, the inherent stability of the diazadiphosphetidine 2 over the sterically crowded silazoxy phosphine also might contribute to the reaction proceeding in this way, similar to the observation of Markovskii et al.10 where 2 is also formed in the reaction of (2,2,6,6-tetramethylpiperidino)- phosphorus dichloride with tert-butylamine. Structure of cis-[(ButNH)PNBut]2 The compound cis-[(ButNH)PNBut]2 2 was first prepared in 1963 by Holmes and Forstner 11 by the reaction of tertbutylamine with PCl3.Although initially the molecule was Scheme 1 P N P N But NBut But ButN H H N Si O Si N P But Me Me Me MeBut Cl 1/2 O[SiMe2N(But)H]2 + PCl3 Et3N thought to be ButN]] PNHBut, subsequent reports on the compound with a molecular weight determination and a single signal in the 31P NMR spectrum confirmed the molecule as a diazadiphosphetidine existing as a pure configurational isomer.9,10 While three different structural isomers are possible with respect to the orientation of the ButNH groups on the (PN)2 ring, namely the NH hydrogens in the exo-exo (a), exo-endo (b) and endo-endo (c) orientations, the crystal structure shows that the orientation (c) is preferred.It is noteworthy that this was the structure predicted by Norman and co-workers 9 in the solution phase based on 2JPNH values from 31P NMR data measured at various temperatures. Fig. 1 shows the molecular structure of compound 2 with the atom numbering scheme. Selected bond distances and angles are given in Table 1.In contrast, the crystal structure of the disulfide of the diazadiphosphetidine cis-[(ButNH)P(S)NBut]2 9 shows the exo-endo orientation (b). A similar orientation was observed for the phosphorus(III) diazadiphosphetidine [(PhNH)P2(NPh)2]2- NPh.21 The endo-endo orientation is similar to the orientation of the N(Me) groups observed in the case of cis- [(Ph2P)N(Me)PNBut]2.22 The crystal structure of 2 also provides data for an interesting comparison of the P]N ring bond distances of phosphorus-(III) and -(V) 1,3,2,4-diazadiphosphetidines.It is generally observed that these distances in phosphorous( III) diazadiphosphetidines are comparatively longer than those of phosphorous(V) diazadiphosphetidines.23–25 Muir16 Fig. 1 Molecular structure of cis-[(ButNH)PNBut]2 2 showing the atom numbering scheme P N P N N N But H But H P N P N N N H But But H P N P N N N H But H But ( a) (b) (c) Table 1 Selected bond lengths (Å) and angles (8) for compound 2 P(1)]N(3) P(1)]N(2) P(1)]N(1) P(1)]P(2) P(2)]N(2) P(2)]N(4) N(3)]P(1)]N(2) N(3)]P(1)]N(1) N(2)]P(1)]N(1) N(3)]P(1)]P(2) N(2)]P(1)]P(2) N(1)]P(1)]P(2) N(2)]P(2)]N(4) N(2)]P(2)]N(1) N(4)]P(2)]N(1) N(2)]P(2)]P(1) 1.619(6) 1.743(5) 1.763(6) 2.616(7) 1.702(6) 1.710(5) 105.3(3) 104.7(3) 79.6(2) 117.5(2) 40.0(2) 40.8(2) 105.0(3) 81.8(2) 105.0(3) 41.2(2) P(2)]N(1) N(1)]C(1) N(2)]C(5) N(3)]C(9) N(4)]C(13) N(4)]P(2)]P(1) N(1)]P(2)]P(1) C(1)]N(1)]P(2) C(1)]N(1)]P(1) P(2)]N(1)]P(1) C(5)]N(2)]P(2) C(5)]N(2)]P(1) P(2)]N(2)]P(1) C(9)]N(3)]P(1) C(13)]N(4)]P(2) 1.725(5) 1.463(9) 1.495(8) 1.493(8) 1.489(8) 118.2(2) 42.0(2) 126.9(5) 124.1(4) 97.2(3) 125.8(5) 122.4(4) 98.8(3) 129.7(5) 131.1(5)J.Chem. Soc., Dalton Trans., 1997, Pages 2167–2169 2169 while comparing the structures of (ButNPCl)2 (average ring P]N distance 1.689 Å) and [ButNP(O)Cl]2 (average ring P]N distance 1.661 Å) have proposed that a possible reason for this can be due to a lesser delocalization of the nitrogen lone pairs on to the phosphorus atoms in the phosphorous(III) heterocycles.On comparing the structure of 2 with that of cis- [(ButNH)P(S)NBut]2 9 we observe that the average ring P]N distance in the former is 1.733 Å while that of latter is 1.685 Å. A similar variation is observed in the cases of [(PhNH)PNPh]3 26 (average ring P]N distance 1.722 Å) and [(PhNH)P(S)NPh]2 27 (average ring P]N distance 1.698 Å). In conclusion, cleavage of O[SiMe2N(But)H]2 at the Si]N bond on reaction with PCl3 is observed instead of substitution of the NH hydrogen.The diazadiphosphetidine 2 formed is characterized by X-ray structural analysis to have the NH groups of the ButNH moiety in an endo-endo orientation above the (PN)2 ring as predicted from solution studies. The method offers a new synthetic route to a variety of diazadiphosphetidines and indicates the need for a relook into the reactions of silazoxy and silaza diamines with transition- and main-group metal halides. Further work in this regard is currently underway.Acknowledgements A. J. E. thanks the Department of Science and Technology, India, (DST) for financial assistance for this work under the SERC young scientist scheme (SR/OY/C-03/94 ). N. D. R. thanks University Grants Commission (UGC), India for a research fellowship. References 1 U. Wannagat, K. Giesen and F. Rabet, Z. Anorg. Allg. Chem., 1971, 382, 195. 2 U. Wannagat, K.-P. Giesen and H.-H.Falius, Monatsh. Chem., 1973, 104, 1444. 3 U. Wannagat and F. Rabet, Inorg. Nucl. Chem. Lett., 1970, 6, 155. 4 D. J. Brauer, H. Bürger, H. H. Moretto, U. Wannagat and K. Wiegel, J. Organomet. Chem., 1979, 170, 161. 5 H. Bürger and K. Wiegel, Z. Anorg. Allg. Chem., 1976, 419, 157; J. Organomet. Chem., 1977, 124, 279; Z. Anorg. Allg. Chem., 1976, 426, 301. 6 A. J. Elias, H. W. Roesky, W. T. Robinson and G. M. Sheldrick, J. Chem. Soc., Dalton Trans., 1993, 495. 7 A.J. Elias, H.-G. Schmidt, M. Noltemeyer and H. W. Roesky, Eur. J. Solid State Inorg. Chem., 1992, 29, 23. 8 U. Engelhardt and T. Bünger, Z. Naturforsch, Teil B, 1979, 34, 1107; Inorg. Nucl. Chem. Lett., 1978, 14, 21; U. Engelhardt, T. Bünger and B. Stromburg, Acta Crystallogr., Sect B, 1982, 38, 1173. 9 T. G. Hill, R. C. Haltiwanger, M. L. Thompson, S. A. Katz and A. D. Norman, Inorg. Chem., 1994, 33, 1770. 10 L. N. Markovskii, V. D. Romanenko, A. V. Ruba and L. A. Robenko, Zh. Obshch.Khim., 1980, 50, 337. 11 R. R. Holmes and J. A. Forstner, Inorg. Chem., 1963, 2, 380. 12 G. M. Sheldrick, SADABS, Siemens Analytical Instruments Division, Madison, WI, 1996. 13 SMART V 4.043 and SAINT V 4.035 softwares for CCD detector system, Siemens Analytical Instruments Division, Madison, WI, 1995. 14 G. M. Sheldrick, Acta Crystallogr., Sect A, 1990, 46, 467. 15 (a) G. M. Sheldrick, SHELXL 93, Program for the refinement of crystal structure, University of Göttingen, 1993; (b) SHELXTL 5.03 (PC Version), Program library for structure solution and molecular graphics, Siemens Analytical Instruments Division, Madison, WI, 1995. 16 K. W. Muir, J. Chem Soc., Dalton Trans., 1975, 259. 17 G. Bulloch and R. Keat, J. Chem Soc., Dalton Trans., 1974, 2010. 18 R. Jefferson, J. F. Nixon, T. M. Painter, R. Keat and L. Stobbs, J. Chem. Soc., Dalton Trans., 1973, 1414. 19 R. H. Nielson, in Encyclopedia of Inorganic Chemistry, ed. R. B. King, Wiley, Chichester, 1994, vol. 6, pp. 3181–3198; M. Shakir and H. W. Roesky, Phosphorus Sulfur Silicon Relat. Elem., 1994, 93, 13; R. A. Shaw, Phosphorus Sulfur Relat. Elem., 1978, 4, 101. 20 J. E. Huheey, E. A. Keiter and L. R. Keiter, Inorganic Chemistry, Harper Collins, New York, 4th edn., 1993, p. A 30. 21 M. L. Thompson, A. Tarassoli, R. C. Haltiwanger and A. D. Norman, Inorg. Chem., 1987, 26, 684. 22 D. A. Harvey, R. Keat, A. N. Keith, K. W. Muir and D. S. Rycroft, Inorg. Chim. Acta, 1979, 34, L201. 23 W. A. Kamil, M. R. Bond, R. D. Willet and J. M. Shreeve, Inorg. Chem., 1987, 26, 2879. 24 S. S. Kumaravel, S. S. Krishnamurthy, T. S. Cameron and A. Liden, Inorg. Chem., 1988, 27, 4546. 25 K. W. Muir, Acta Crystallogr., Sect B, 1977, 33, 3586. 26 A. Tarassoli, M. L. Thompson and A. D. Norman, Inorg. Chem., 1988, 27, 3382. 27 C.-C. Chang, R. C. Haltiwanger, M. L. Thompson, H.-J. Chen and A. D. Norman, Inorg. Chem., 1979, 18, 1899. Received 27th January 1997; Paper 7/00604G

ISSN:1477-9226    

DOI:10.1039/a700604g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2171–2175 2171 Self-assembly of a chiral phosphinegold(I) building block into a twodimensional netsheet based on a hydrogen bond between one Cl2 anion and three hydroxy groups, co-ordination and aurophilicity interactions† Ji-Cheng Shi,*,a Bei-Sheng Kang a,b and Thomas C. W. Makc a State Key Laboratory of Structural Chemistry and Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fijian, Fuzhou 350002, China b Department of Chemistry, Zhongshan University, Guangzhou, Guangdong 510275, China c Department of Chemistry, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong The trigold(I) complex [{Au(mbpa)}3S]Cl 2 [mbpa = methyl 4,6-O-benzylidene-3-deoxy-3-(diphenylphosphino)-a- D-altropyranoside] has been obtained from the compound [Au(mpba)Cl] 1 and L-cysteine.Complex 2 crystallizes in space group P66 with a = 15.165(2), c = 18.897(3) Å and Z = 2, R = 0.030, R9 = 0.050.The crystal structure shows that the Au3S core is a perfect trigonal pyramid with angles Au]S]Au and P]Au]S of 88.7 and 179.68, respectively, and that the chiral building blocks [{Au(mpba)}3S]1 assemble through triple hydrogen bonding between one hydrogen-bond acceptor, Cl2, and three hydrogen-bond donors [Cl ? ? ? O(2) 3.017(10) Å], and form infinite two-dimensional netsheets. The netsheets align in the same direction. A relativistic interaction of the d10 closed shell of gold(I) was revealed by NMR studies.Complex 2 displays a strong bright white emission at 495 nm when excited at 303 nm at room temperature, where the lowest-energy transition is of metal-to-ligand chargetransfer (AuÆS) type. Gold(I) complexes have an unusual structural chemistry based on non-classical intermolecular gold(I)–gold(I) contacts.2 Recently Schmidbaur and co-workers3 have found that the (phosphine)gold(I) cation can ligate to main-group elements such as carbon and nitrogen with co-ordination numbers as high as five and six and gives certain interesting structures.The novel bonding configurations are caused by the contraction of the 6s orbital of the gold(I). Theoretical descriptions of the gold(I)– gold(I) attraction which requires the inclusion of electron correlation and relativistic effects have been carried out.4 The photochemistry of gold(I) complexes has attracted a great deal of attention over the last few years.5 The relationship between the emission and the gold(I)–gold(I) interaction is an interesting subject of experimental 6 and theoretical studies.7 Recently, Fackler and co-workers6a and Bruce and co-workers 6b have concluded that luminescence in gold(I) complexes cannot be used as a diagnostic test for the presence of the interaction, but the interaction, in some cases, can shift the emission maximum to lower energies.It has been observed 8 that the strength of the interaction is influenced by the electronic and steric effects of the phosphine ligands in the trigold(I) cations [{Au(PR3)}3S]1.However, the photochemical consequences have not been seen so far.9 The control of molecular assembly by hydrogen bonding is a major tool in crystal engineering.10 A common feature in the work of Whitesides,11 Lehn,12 Hamilton,13 and Mingos14 and their co-workers is to use complementary hydrogen-bonding groups structurally related to those found in nucleic acid–base pairs, in order to persuade building blocks to aggregate in the desired manner.The use of F2 or Cl2 as hydrogen-bond acceptor to link to two or three hydrogen-bond donors through hydrogen-bonding interactions is much rarer in the supramolecular systems, although it has some merits: (a) to balance charge and to introduce a Coulomb attraction to increase pack- † Chiral phosphine ligands derived from sugars. Part 9.1 ing forces, (b) to avoid the problem14 of the poor solubility of starting materials encountered in the systems of complementary triple hydrogen bonds.The ionic type of aggregation will often be met in supramolecular systems containing transition-metal ions. It is very important to incorporate transition-metal ions into such systems to introduce the magnetic, optical and conductive properties characteristic of these ions into materials with potentials for non-linear optical, conducting, and ferromagnetic properties.10a The gold(I)–gold(I) interactions arising mainly from relativistic effects 2 are comparable to hydrogen bonds in bond energy.15 Accordingly, it is an intriguing approach16 to take advantage of ‘aurophilicity’ to associate appropriate gold(I) building blocks into cluster-like and/or polymeric structures.17 The compound methyl 4,6-O-benzylidene-3-deoxy-3-(diphenylphosphino)- a-D-altropyranoside (mbpa) has been prepared for asymmetric catalysis18 and its gold(I) complexes have attracted our interest because many of them possess high antitumour activity.19 In addition to the importance of thiolate ligands in the formation of gold drugs, binding of gold(I) to thiolate functions in proteins is expected to play a key role in the molecular pharmacology of gold.20 Herein we report the formation of a trigold(I) complex [{Au(mbpa)}3S]Cl 2 from the reaction of [Au(mbpa)Cl] 1 and L-cysteine, and the luminescence of these complexes at room temperature.Experimental Elemental analyses were performed by the Chemical Analysis Division of this Institute.Infrared spectra were measured on a O O O Ph PPh2 OH OMe 1 2 3 4 5 6 mbpa2172 J. Chem. Soc., Dalton Trans., 1997, Pages 2171–2175 Bio-Rad FTS-40 spectrometer (in KBr discs, 4000–200 cm21), Raman spectra on a Nicolet 910 Fourier-transform spectrometer using a Raman 1064 nm laser source at a resolution of 2 cm21 with 300 scans and NMR spectra on a Varian Unity-500 spectrometer operating at 499.98 MHz for 1H, 125.71 MHz for 13C and 202.36 MHz for 31P.Chemical shifts are expressed in parts per million (ppm) downfield from internal SiMe4 (1H and 13C) or external 85% H3PO4 (31P) standards as positive values. Emission and excitation spectra were measured at room temperature with a Shimadzu RF-540 spectrofluorometer using a xenon lamp. They were not corrected for instrumental response. Pseudo-potential ab initio calculations were performed on a VAX 11/785 computer using the GAUSSIAN 92 package.4b,21 The Au]S and Au]P distances and the Au]S]Au and P]Au]S angles were fixed at the values found from the crystal structure.L-Cysteine was used as received. Preparations The compound [Au(mbpa)Cl] 1 was prepared by the literature method.19 NMR (CDCl3): 1H, d 8.10–6.70 (m, 15 H, aryl H), 5.41 (s, 1 H, PhCH], 5.06 [m, 1 H, H(5)], 4.67 [m, 1 H, H(4)], 4.60 [s, 1 H, H(1)], 4.31 [dd, 1 H, H(6e)], 3.80 [t, 1 H, H(6a)], 3.77 [m, 1 H, H(3)], 3.73 [d, 1 H, H(2)] and 3.44 (s, 3 H, CH3); 13C, d 101.9 (PhCH)], 99.0 [C(1)], 75.4 [C(4)], 69.2 [C(6)], 69.1 [C(2)], 60.6 [C(5)], 54.1 (CH3) and 41.0 [C(3)]; 31P, d 28.3.IR (KBr): n(O]H) 3518m, 3453m; n(C]] C) 1450m; n(aryl]P) 1439s; n(alkyl]P) 1396m; n(C]O]C) 1327m, 1311w and 1292m; n(Au]P) 392m; n(Au]Cl) 316s cm21. [{Au(mbpa)}3S]Cl 2. To a solution of L-cysteine hydrochloride (17.5 mg, 0.1 mmol) in MeOH (10 cm3) containing NaOMe (10.8 mg, 0.2 mmol) was added a solution of compound 1 (68.2 mg, 0.1 mmol) in CH2Cl2 (10 cm3) and stirred for 10 h at room temperature under a nitrogen atmosphere.The solvent was removed under reduced pressure. The residue was taken up in hot dimethylformamide and filtered while hot. The filtrate was kept at room temperature for a few weeks to give colourless crystals of 2 (14.1 mg, yield 21.0% based on 1), m.p. 190 8C (decomp.). NMR [CDCl3–(CD3)2SO (1: 1, v/v)]: 1H, d 8.19–6.35 (m, 15 H, aryl H), 5.42 (s, 1 H, PhCH), 5.08 [m, 1 H, H(5)], 4.75 [m, 1 H, H(4)], 4.51 [s, 1 H, H(1)], 4.39 [dd, 1 H, H(3)], 4.31 [dd, 1 H, H(6e)], 3.92 [d, 1 H, H(2)] and 3.80 [t, 1 H, H(6a)]; 13C, d 100.8 (PhCH), 100.2 [C(1)], 75.1 [C(4)], 69.2 [C(6)], 68.1 [C(2)], 61.0 [C(5)], 53.8 (CH3) and 29.5 [C(3)]. 31P, d 26.9. IR (KBr): n(O]H) 3457m, 3224m; n(C]] C) 1452m; n(aryl]P) 1437s; n(alkyl]P) 1389m; n(C]O]C) 1324m, 1307m, 1289m; n(Au]P) 384m; n(Au]S) 314s cm21. Crystallography A single crystal of compound 2 suitable for X-ray diffraction was obtained directly from the reaction solution.Reflection data were collected at 294 K on a Rigaku AFC 7R diffractometer with Mo-Ka radiation (l 0.710 73 Å), using the w-scan technique (4.0 < 2q < 55.08) for a crystal with dimensions 0.20 × 0.25 × 0.50 mm, mounted on a glass fibre. Details of the crystal data are summarized in Table 1. Crystal and instrument stabilities were monitored with a set of three standard reflections measured every 100; in all cases no significant variations were found.The intensity data collected were corrected for Lorentz-polarization and absorption (empirically).The structure was solved by the Patterson method and refined on F by full-matrix least squares. All calculations were performed on an IBM PC/486 computer with the Siemens SHELXTL-PC program package.22 Of the 1746 reflections collected, 1312 with F > 4.0s(F) were used in the solution and refinement. Final refinements of all the non-hydrogen atoms except those of the phenyl rings are anisotropic, the carbon atoms of the phenyl rings were fixed as a rigid group with C]C bond distances of 1.395 Å, and hydrogen atoms (which were calculated geometrically) as fixed isotropic contributions.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 186/470.Results and Discussion Synthesis The reaction of equimolar quantities of [Au(mbpa)Cl] 1 in CH2Cl2 with L-HSCH2CH(NH2)CO2Na in MeOH gives a low yield (21.0%) of [{Au(mbpa)}3S]Cl 2, as a colourless crystalline product, which decomposes at 190 8C without melting. Analogues of complex 2 have been prepared through the reaction of [{Au(PR3)}3O]1 or [Au(PR3)]1 with bis(trimethylsilyl) sulfide8 or hydrogen sulfide.23 Jones et al.24 have reported that [Au(PPh3)Cl] abstracts a sulfur atom from Et4P2S2 to give m3- sulfido-tris[(triphenylphosphine)gold(I)] hexafluorophosphate [{Au(PPh3)}3S]PF6. Since attempts to isolate and identify the organic product of C]S bond cleavage were unsuccessful, the mechanism of [Au(mbpa)Cl] abstracting a sulfur atom from L-cysteine to form the trigold(I) complex remains unclear. Cleavage of the C]S bond of ethane-1,2-dithiolate (edt) with the late transition-metal ions (Ni21 or Co1) has been observed and afforded compounds [Ni(tpdt)(PPh3)]25a (tpdt = 3-thiapentane- 1,5-dithiolate) and [Co7S6(PPh3)6Br],25b respectively, in which the tpdt ligand arose from the condensation of two edt and loss of a sulfur atom.Isab and Sadler26 have found that ligands exchange between a medicine myocrisin and cysteine in vivo when the latter is injected. Crystal structure As can be seen from Fig. 1, each Cl2 anion links to three [{Au(mbpa)}3S]1 cations through hydrogen bonds between the Fig. 1 Packing of complex 2 in the lattice; in (b) all the phenyl rings are omitted for clarityJ. Chem. Soc., Dalton Trans., 1997, Pages 2171–2175 2173 OH group of the altropyranose ring [Cl ? ? ? O(2) 3.017(10) Å], to form an infinite two-dimensional net structure. This results in a novel two-dimensional netsheet. Each netsheet is in the same direction as shown in Fig. 1(b). All Au, S or Cl atoms in the same sheet are coplanar, and the distance of two planes composed of the same atoms in adjacent sheets is equal to c/2 (9.446 Å).The phenyl rings of the adjacent sheets interlock each other, although there are no p-stacking effects. The structure of the cation of complex 2 shown in Fig. 2 has a crystallographically imposed C3 axis which is perpendicular to the Au3 plane and passes through the m3-S atom. The Au3S core shows a perfect trigonal-pyramidal structure with the sulfur atom occupying the apical position.In comparison with those reported,8,24,27 the angle Au]S]Au is the nearest to 908 (deviation of 1.38), indicating that the sulfur atom uses its p orbital to form bonds with three Au atoms which are each linked to the phosphorus atom of the chiral phosphine of mbpa to make a linear two-co-ordinate geometry at gold(I) [179.6(1)8]. To our knowledge, the angle P]Au]S is also the nearest to 1808 among those reported.8,24,27 The Au]P [2.269(4) Å] and Au]S [2.325(3) Å] bond lengths (Table 2) are similar to those in [{Au(PPh3)}3S]1 (average 2.266 and 2.327 Å, respectively),24 but shorter than those in [{Au(PPh3)}3S]21 (average 2.270 and 2.399 Å, respectively)27 Fig. 2 Structure of the cation [{Au(mbpa)}3S]1 of complex 2. Hydrogen atoms are omitted for clarity. Fig. 3 Partial view of compound 2 with the atom labelling of the chiral phosphine ligand and longer than those in [Au(mbpa)(NC5H4S-2)] 3 (2.256 and 2.303 Å, respectively),19 as expected.Similar to those in free mbpa,28 the altropyranose ring and the 4,6-O-benzylidene ring in complex 2 adopt a distorted chair conformation. The average torsion angles are ±57 (altropyranose ring) and ±618 (4,6-O-benzylidene ring) and ±55 (altropyranose ring) and ±608 (4,6-O-benzylidene ring) for free mbpa.28 The torsion angles P]C(3)]C(2)]O(2) and O(2)]C(2)] C(1)]O(1) for 2 are 161 and 1718, respectively, indicating that the substituents PPh2, OH and OMe are in pseudo-axial positions. The torsion angles C(21)]P]C(3)]C(2) and C(15)]P]C(3)] C(4) (173 and 1478) are comparable to those of free mbpa (173 and 1528).Spectroscopic studies As can be seen from the 1H and 13C NMR data compiled in the Experimental section, the resonances of the altropyranose ring of compound 2 are very similar to those of 1, except for those of H(3) and C(3). The chemical shift of H(3) is d 4.39 for 2 and 3.77 for 1, and that of C(3) is d 29.5 for 2 and 41.0 for 1. This suggests that: (a) the conformation of the altropyranose ring of 2 is very similar to that of 1, and the formation of the Au3S core does not affect the conformation; (b) the Au3S core perturbs the electron distribution of the phosphinoaltrose ligand only locally at C(3), although significantly in comparison to that in 1, (c) the gold(I) in the Au3S core is electron rich, compared to that in AuCl, which may be in part from the interaction of the d10 closed shell of gold(I).The latter is also confirmed by the 31P-{1H} NMR data, which show a single peak at d 26.9 for three phosphorus atoms, shifted upfield by 1.4 and 2.4 ppm in comparison to the starting material 1 and the mononuclear P]Au]S compound [Au(mbpa)(NC5H4S-2)] 3,19 respectively.The n(Au]P) and n(Au]S) absorptions in the IR spectrum Table 1 Crystal data for [{Au(mbpa)}3S]Cl 2 Formula M Colour Crystal system Space group a/Å c/Å U/Å3 Z Dc/g cm23 F(000) h m/mm21 h, k, l Ranges Goodness of fit Ra R9 b (D/s)max Final difference peak, hole/e Å23 C78H81Au3ClO15P3S 2009.7 Colourless Hexagonal P63 (no. 173) 15.165(2) 18.897(3) 3760(2) 2 1.775 1968 21.00(7) 6.030 0–17, 0–19, 0–24 1.09 0.030 0.050 0.214 0.49, 20.50 a R = (S||Fo| 2 |Fc||)/S|Fo|. b R9 = [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� ; w21 = s2(F) 1 0.0002F2. Table 2 Selected atomic distances (Å) and angles (8) for [{Au(mbpa)} 3S]Cl 2 Au(1)]S Au(1)]Au(1a) P(1)]C(21) Cl ? ? ?O(2) 2.325(3) 3.251(1) 1.811(15) 3.017(10) Au(1)]P(1) P(1)]C(15) P(1)]C(3) 2.269(4) 1.835(17) 1.846(12) S]Au(1)]P(1) P(1)]Au(1)]Au(1a) Au(1)]Au(1a)]Au(1b) Au(1)]P(1)]C(15) Au(1)]P(1)]C(3) 179.6(1) 134.2(1) 60.0(1) 112.4(4) 118.8(5) S]Au(1)]Au(1a) P(1)]Au(1)]Au(1b) Au(1)]S]Au(1a) Au(1)]P(1)]C(21) 45.6(1) 134.8(1) 88.7(2) 112.8(5)2174 J.Chem. Soc., Dalton Trans., 1997, Pages 2171–2175 of compound 2 appear at 384m and 314m cm21, respectively, which are comparable to those assigned to compounds [Au(PR3)(SCN)] 29 (388–375 and 360–291 cm21, respectively) and [AuL(X)] (L = mbpa or its 2-PPh2 analogue, X = Cl, pyridine-2-thiolate or benzimidazole-2-thiolate) (395–368 and 3sh;322 cm21, respectively).19 The Raman spectrum of compound 2 is shown in Fig. 4(c). Compared to those of free mbpa [Fig. 4(a)] and 1 [Fig. 4(b)], the absorptions in the region 300–150 cm21 are similar to each other and may be ascribed to the d(P]C) mode.30 The band at ca. 315 cm21 of 2 is weaker than that of 1, attributed to the fact that the n(Au]Cl) mode is replaced by the n(Au]S) mode.The Au]P stretching frequency is only observed for 1 at 390 cm21. The peaks at 200 cm21 for 1 and 190 cm21 for 2 are not from n(Au]P), but from the splitting of the d(P]C) mode upon co-ordination of P to AuI. Of the three complexes 1–3, only 2 luminesces at room temperature in the solid state. It displays a strong bright white emission at 495 nm when excited at 303 nm (Fig. 5). The luminescence spectrum is very similar in bandshape, but the Stokes shift of 12 800 cm21 is nearly twice, to those reported,6b which are assigned to phosphorescence by lifetime measurements using time delays.A large Stokes shift with the present complex is indicative of a large distortion in the excited state compared to the ground state and implies that the emission is phosphorescence.6 For phosphinegold(I) complexes with arene- or alkanethiolate ligands it is generally accepted that the emission is due Fig. 4 Raman spectra of (a) free mbpa, (b) complex [Au(mbpa)Cl] 1 and (c) complex [{Au(mbpa)}3S]Cl 2 Fig. 5 Uncorrected solid-state excitation and emission spectra for the complex [{Au(mbpa)}3S]Cl 2 at room temperature to a metal-to-ligand charge transfer (m.l.c.t.) with the excitation from an orbital primarily associated with the sulfur to the metal-based orbital of the excited state.6 The excited transition of the present trigold(I) complex is also of the SÆAu c.t. type, since S22 can be seen as a reducing ligand compared to arene- or alkane-thiolates.This proposed assignment of the emission is confirmed by pseudo-potential ab initio calculations, which show that the highest occupied molecular orbital of [{Au- (3-mpba)}3S]Cl consists of large contribution from the sulfur 3s and 3p orbitals and the lowest unoccupied molecular orbital from the gold(I) 6p orbital. This structure is noteworthy because it represents a novel example of a chiral building block containing a cluster-like core assembled through the triple hydrogen bonding between one hydrogen-bond acceptor of the anion and three hydrogen-bond donors.Therefore, this work provides a new direction in the design of supramolecular systems containing transition-metal ions using the anionic type of hydrogen-bond acceptor such as F2, Cl2 and NO3 2. Further studies with mbpa in related systems are in progress. Acknowledgements This work was supported by the State Key Project for Fundamental Research, the National Natural Science Foundation of China, and the Hong Kong Research Grants Council Earmarked Grant No.CUHK 311/94P. The authors thank Dr. C. T. Chen and Dr. B. M. Wu for the X-ray data sets, Mr. D. X. Wu for recording the NMR spectra, and Dr. S. J. Zhong for the preliminary theoretical calculations. References 1 Part 8, J. C. Shi and H. Q. Wang, Chin. J. Struct. Chem., 1997, 16, 11. 2 H. Schmidbaur, Pure Appl. Chem., 1993, 65, 691; M. Jansen, Angew. Chem., Int.Ed. Engl., 1987, 26, 1098; E. J. Fernandez, M. C. Gimeno, P. G. Jones, A. Laguna, M. Laguna and J. M. Lopez-de-Luzuriaga, Angew. Chem., Int. Ed. Engl., 1994, 33, 87; D. L. Sunick, P. S. White and C. K. Schauer, Angew. Chem., Int. Ed. Engl., 1994, 33, 75. 3 F. Scherbaum, A. Grohmann, G. Müller and H. Schmidbaur, Angew. Chem., Int. Ed. Engl., 1989, 28, 463; F. Scherbaum, A. Grohmann, B. Huber, C. Krüger and H. Schmidbaur, Angew. Chem., Int. Ed. Engl., 1988, 27, 1544; A.Grohmann, J. Riede and H. Schmidbaur, J. Chem. Soc., Dalton Trans., 1991, 783. 4 (a) E. Zeller, H. Beruda, A. Kolb, P. Bissinger, J. Riede and H. Schmidbaur, Nature (London), 1991, 352, 141; (b) P. Pyykkö, K. Angermaier, B. Assmann and H. Schmidbaur, J. Chem. Soc., Chem. Commun., 1995, 1889. 5 D. M. Roundhill, Photochemistry and Photophysics of Metal Complexes, Plenum, New York, 1994; H. R. C. Jaw, M. M. Savas, R. D. Rodgers and W. R. Mason, Inorg. 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Angermaier and H. Schmidbaur, Chem. Ber., 1994, 127, 2387. 9 Z. Assefa, B. G. McBurnett, R. J. Staples, J. P. Fackler, jun., B. Assmann, K. Angermaier and H. Schmidbaur, unpublished work. 10 (a) A. D. Burrows, C.-W. Chan, M. M. Chowdhry, J. E. McGrady and D. M. P. Mingos, Chem. Soc. Rev., 1995, 24, 329; (b) G. M. Whitesides, E. E. Simanek, J. P. Mathias, C. T. Seto, D. N. Chin, M. Mammen and D. M. Gerdon, Acc. Chem. Res., 1995, 28, 37; (c) J.-M. Lehn, Angew. Chem., Int. Ed.Engl., 1988, 27, 89.J. Chem. Soc., Dalton Trans., 1997, Pages 2171–2175 2175 11 J. A. Zerkowski, C. T. Seto and G. M. Whitesides, J. Am. Chem. Soc., 1990, 112, 9025; C. T. Seto and G. M. Whitesides, J. Am. Chem. Soc., 1991, 113, 712; J. A. Zerkowski, C. T. Seto and G. M. Whitesides, J. Am. Chem. Soc., 1992, 114, 5473; C. T. Seto and G. M. Whitesides, J. Am. Chem. Soc., 1993, 115, 905; C. T. Seto, J. P. Mathias and G. M. Whitesides, J. Am. Chem. Soc., 1993, 115, 1321. 12 J.-M. Lehn, M. Mascal, A. DeCian and J. Fischer, J. Chem. Soc., Chem. Commun., 1990, 479; J. Chem. Soc., Perkin Trans. 2, 1992, 461. 13 S. K. Chang and A. D. Hamilton, J. Am. Chem. Soc., 1988, 110, 1318; S. J. Geib, S. C. Hirst, C.Vincent and A. D. Hamilton, J. Chem. Soc., Chem. Commun., 1991, 1238; F. Garcia-Tellado, S. J. Geib, S. Goswami and A. D. Hamilton, J. Am. Chem. Soc., 1991, 113, 9265; E. Fan, S. A. Van Arman, S. Kincaid and A. D. Hamilton, J. Am. Chem. Soc., 1993, 115, 369. 14 M. M. Chowdhry, D. M. P. Mingos, A. J. P. White and D. J. Williams, Chem. Commun., 1996, 899. 15 H. Schmidbaur, W. Graf and G. Müller, Angew. Chem. Int., Ed. Engl., 1988, 27, 417. 16 B.-C. Tzeng, K.-K. Cheung and C.-M. Che, Chem. Commun., 1996, 1681. 17 D. M. P. Mingos, J. Yau, S. Menzer and D. J. Williams, Angew. Chem., Int. Ed. Engl., 1995, 34, 1894. 18 J. C. Shi, M. C. Hong, D. X. Wu, Q. T. Liu and B. S. Kang, Chem. Lett., 1995, 685. 19 J. C. Shi, X. Y. Huang, D. X. Wu, Q.T. Liu and B. S. Kang, Inorg. Chem., 1996, 35, 2742. 20 A. A. Isab and P. J. Sadler, J. Chem. Soc., Dalton Trans., 1982, 135; R. M. Snyder, C. K. Mirabelli and S. T. Crooke, Biochem. Pharmacol., 1986, 35, 923; M. T. Coffer, C. F. Shaw, III, M. K. Eidsness, S. W. Watkins, II and R. C. Elder, Inorg. Chem., 1986, 25, 333; C. F. Shaw, III, M. T. Coffer, J. Klingbeil and C. K. Mirabelli, J. Am. Chem. Soc., 1988, 110, 729. 21 M. J. Frisch, G. W. Trucks, M. Head-Gordon, P. M. W. Gill, M. W. Wong, J. B. Foresman, B. G. Johnson, H. B. Schlegel, M. A. Robb, E. S. Replogle, R. Gomperts, J. L. Andres, K. Raghavachari, J. S. Binkley, C. Gonzaleg, R. L. Martin, D. J. Fox, D. J. Defrees, J. Baker, J. J. P. Stewart and J. A. Pople, GAUSSIAN 92, Revision A, Gaussian Inc., Pittsburgh, PA, 1992. 22 G. M. Sheldrick, SHELXTL-PC, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1990. 23 C. Kowala and J. M. Swan, Aust. J. Chem., 1966, 19, 547. 24 P. G. Jones, G. M. Sheldrick and E. Hadike, Acta Crystallogr., Sect. B, 1980, 36, 2777. 25 (a) R. Cao, M. C. Hong, F. L. Jiang, X. L. Xie and H. Q. Liu, J. Chem. Soc., Dalton Trans., 1994, 3459; (b) F. L. Jian, X. J. Lei, M. C. Hong, Z. Y. Huang, B. S. Kang and H. Q. Liu, J. Organomet. Chem., 1993, 443, 229. 26 A. A. Isab and P. J. Sadler, J. Chem. Soc., Dalton Trans., 1982, 135. 27 H. Schmidbaur, A. Kolb, E. Zeller, A. Schier and H. Beruda, Z. Anorg. Chem., 1993, 619, 1575; F. Canales, M. C. Gimeno, P. G. Jones and A. Laguna, Angew. Chem., Int. Ed. Engl., 1994, 33, 769. 28 J. C. Shi, Q. T. Liu, B. S. Kang and H. Q. Wang, Chin. J. Struct. Chem., 1997, 16, 6. 29 M. M. El-Etri and W. M. Scovell, Inorg. Chem., 1990, 29, 480. 30 B. Weissbart, L. J. Larson, M. M. Olmstead, C. P. Nash and D. S. Tinti, Inorg. Chem., 1995, 34, 393; R. J. H. Clark, C. O. Flint and A. J. Hempleman, Spectrochim. Acta, Part A, 1987, 43, 815. Received 28th February 1997; Paper 7/01434A

ISSN:1477-9226    

DOI:10.1039/a701434a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2177–2182 2177 Synthesis and structure of bimetallic complexes with Û,�-bridged monocarbene ligands ‡ Yvette M. Terblans and Simon Lotz *,† Department of Chemistry, University of Pretoria, Pretoria 0001, South Africa The Fischer method was employed to synthesize bimetallic monocarbene complexes from lithiated [Cr(SC4H4)(CO)3] and metal hexacarbonyls. In addition to the formation of [M{C[h5-C4H3SCr(CO)3]OEt}(CO)5] (M = Cr 1 or W 2) the complexes [M{C[h5-C4H3SCr(CO)3]O(CH2)4OEt}(CO)5] (M = Cr 3 or W 4), were also obtained.The formation of 3 and 4 is ascribed to the activation of tetrahydrofuran (thf) by a s,p-co-ordinated acyl metalate, which triggers the cleavage of the thf ring and leads to its inclusion into the alkoxy substituent of the resulting carbene moiety. In polar solvents the Cr(CO)3 fragments are displaced to give known pentacarbonyl- [ethoxy(thienyl)carbene] complexes and the new mononuclear carbene complexes [M{C(C4H3S)O(CH2)4OEt}- (CO)5] (M = Cr 5 or W 6).The analogous benzo[b]thienyl carbene complex [Cr{C[h6-C8H5SCr(CO)3]OEt}(CO)5] 7 was prepared similarly, but did not afford the thf-inserted product and the corresponding conversion into the mononuclear carbene complex [Cr{C(C8H5S)OEt}(CO)5] 8, was much slower. The activation of simple organic molecules by more than one transition-metal constitutes an area of research which has grown in importance over the last decade.2 Transition-metal complexes with bridging ligands and without metal–metal bonds can be conveniently divided into three classes based on the mode of co-ordination of the ligand.Attachments of ligands to metal centres may consist of (i) s,s, (ii) s,p or (iii) p,p bonds. Small bridging ligands place a second metal fragment in close proximity to the first one and if these ligands contain conjugated p systems electronic contact is established between the two metal centres.Our interest in this area deals with the activation of benzene 3 and thiophene 4 derivatives by more than one metal centre. We have recently shown that an interesting form of activation exists when thiophene is p bonded to Cr(CO)3 and s bonded to Mn(CO)5 in the 2 position. We discovered that the metal fragments irreversibly exchanged coordination sites, which indicated that different metal fragments exhibit preferences for specific co-ordination sites in s,pbimetallic complexes,1,4 Scheme 1.This novel conversion was the result of the metals being in direct electronic contact through the bridging thienyl ligand, the presence of a lowenergy pathway facilitating the conversion and the fact that the converted product is thermodynamically more stable than the precursor. Metal–metal communication is also possible via p-resonance effects when a second metal fragment is s bonded via a carbene unit to a p-co-ordinated thienyl ligand. This prompted us to investigate the effect of p co-ordination on the properties of such a carbene functionality.Examples of bimetallic monocarbene complexes with s,pbridging benzene and cyclopentadienyl ligands are scarce but have been documented, i.e. [(OC)5M{h1:h6-C6H5C(OEt)}- Cr(CO)3] (M = W, Mo or Cr),5 [(OC)5M{h1:h5-C5H3RC(OEt)}- M9(h5-C5H4R)] (M = W, Mo or Cr; M9 = Fe or Ru; R = H or Me),6 a series of ferrocenyl carbene complexes of chromium, tungsten and manganese, which were synthesized to study electronic effects of the ferrocenyl substituent on the carbene ligand, 7 and the modification of the cationic ferrocenyl carbyne complexes of manganese with thiolate, selenolate, tellurolate and [Co(CO)4]2 to afford the corresponding neutral carbene complexes.8 The addition of anionic carbene complexes [M{C(OMe)CH2}(CO)5]2 to cationic complexes with co- † E-Mail: slotz@scientia.up.ac.za ‡ p-Heteroarene complexes.Part 4.1 ordinated unsaturated hydrocarbons, e.g. ethene and tropylium, etc., also afforded bimetallic mononuclear carbene complexes with s,p-bridging ligands, but without p conjugation.9 In this paper we report results obtained from the reaction of [Cr(h5-SC4H3Li)(CO)3] and [M(CO)6] which after subsequent alkylation in dichloromethane with Et3OBF4 afforded, not only the expected bimetallic Fischer-type carbene complex 1 or 2, but a second modified carbene complex 3 or 4 (Scheme 2).The latter involved the incorporation of a cleaved tetrahydrofuran (thf ) molecule into the ethoxy substituent of the carbene ligand.The lability of the p-thienyl ligand is demonstrated by the displacement of the Cr(CO)3 fragment in polar solvents. Results and Discussion Synthesis The p-bonded heteroarene ring complex [Cr(SC4H4)(CO)3] can be used advantageously as a precursor in the synthesis of s,pbimetallic complexes. It was prepared for the first time in a low yield by Fischer and Öfele 10 in the thermal reaction of [Cr(CO)6] and thiophene. The synthesis was improved by a twostep procedure, in which the [Cr(CO)6] was converted into [Cr(CO)3(NH3)3] 11 and thereafter treated with an excess of thiophene and 3 equivalents of the Lewis acid, BF3, in diethyl ether.12 Metallation of [Cr(SC4H4)(CO)3] at low temperatures is readily achieved.13 Another p-bonded heterocycle which could be utilized with Scheme 1 (i) Acetone, 0 8C, 3 d R Mn(CO)5 X R Cr(CO)5 Mn(CO)3 X Cr(CO)3 (i) R = H, Me or Mn(CO)5; X = S or Se Scheme 2 (i) LiBu, thf, [M(CO)6]; (ii) Et3OBF4, CH2Cl2 S Cr(CO)3 S Cr(CO)3 S Cr(CO)3 C OEt C O O M(CO)5 M(CO)5 ( i), ( ii) 1,2 3,42178 J.Chem. Soc., Dalton Trans., 1997, Pages 2177–2182 success and has the advantage of being related to the thiophene system is the complex [Cr(SC8H6)(CO)3] (SC8H6 = benzo[b]- thiophene) which can be prepared in a direct procedure by heating the thiophene derivative and chromium hexacarbonyl in dibutyl ether.14 Complexes with a benzene instead of a p-coordinated thiophene ligand are less labile and exhibit greater stability against Cr(CO)3 displacement in polar solvents.The reaction of chromium and tungsten hexacarbonyl complexes with lithiated [Cr(SC4H4)(CO)3] followed by alkylation with Et3OBF4 in dichloromethane afforded, in addition to the desired s,p-monocarbene complexes [M{C[h1:h5-C4H3SCr- (CO)3]OEt}(CO)5] (M = Cr 1 or W 2), a second, more soluble in hexane, bimetallic monocarbene complex, [M{C[h1:h5- C4H3SCr(CO)3]O(CH2)4OEt}(CO)5] (M = Cr 3 or W 4). The compounds 3 and 4 were recrystallized from dichloromethane– hexane mixtures. Complexes 1 and 2 are stable under an inert atmosphere in the solid state, but decompose slowly in polar solution giving the known complexes [M{C(C4H3S)OEt}- (CO)5].15,16 Complexes 3 and 4 are more soluble in hexane than 1 and 2, respectively, but less stable owing to faster displacement of the Cr(CO)3 fragment in polar solvents to afford the mononuclear carbene complexes [M{C(C4H3S)O(CH2)4- OEt}(CO)5] (M = Cr 5 or W 6).The preparative yields of 3 and 4 were optimized by extending the reaction time at room temperature, but this unfortunately also leads to higher yields of 5 and 6, respectively. The synthesis of the analogous p-coordinated thienyl carbene complexes of [Mn(h5-C5H5)(CO)2] instead of [M(CO)5] was attempted, but without success. The formation of complexes 3 and 4 is very interesting as it represents the cleavage and inclusion of tetrahydrofuran into the ethoxy substituent of the bimetallic carbene complex. Christoffers and Dötz 17 have previously reported a similar insertion of thf into the allyloxy C]O bond of a carbene complex while utilizing a one-pot, Fischer-type nucleophilic/ electrophilic addition methodology using allyl triflate (trifluoromethane sulfonate) as alkylating reagent in thf.It was evident that the very strong allyl triflate interacts with the solvent thf whereby the cyclic O-allyloxonium ion is generated, which subsequently undergoes ring opening upon nucleophilic attack by the acyl chromate to form the {[(allyloxy)butyl]oxy}carbene side chain.By contrast, in our two-step synthesis the formation of the acyl metalate was achieved in thf, whereafter the solvent was completely removed and the residue washed several times with hexane, before the alkylation was performed in dichlomethane. Therefore, it seems unlikely that thf ring opening was only triggered during the alkylation step by [C4H8O?Et]1 and that it probably involves an earlier attack of the s,p-bonded acyl metalate on an activated thf molecule in a bimetallic intermediate species.If so, a different mechanism to that proposed by Christoffers and Dötz 17 involving bimetallic activation is operative. Efforts to isolate, purify and study intermediate acyl metalates spectroscopically were not successful and abandoned. Tetrahydrofuran has been successfully cleaved at low temperatures by reducing agents in the presence of Lewis acids.18 The reductive cleavage of free thf at 278 8C was easily achieved by using lithium powder or even lithium 4,49-di-tertbutylbiphenyl and BF3?OEt2 in the presence of a catalytic amount of arene, e.g.naphthalene, biphenyl, 4,49-di-tertbutylbiphenyl or anthracene. Scheme 3 presents a possible explanation for the formation of the products 1–6. In the first step, a carbonyl ligand of the parent acyl metalate, which leads to the formation of 1 or 2, is substituted by a thf solvent molecule.Under the prevailing reaction conditions the p-bonded thienyl is fairly labile and the gradual decomplexation of Cr(CO)3 can occur. This is also evident from the formation of the known thienyl carbene complexes [M{C(C4H3S)- OEt}(CO)5]15,16 during the reaction. Electron-withdrawing effects and steric implications of the p-co-ordinated Cr(CO)3 unit facilitates the co-ordination of a thf molecule at an appropriate position close to the acylate’s oxygen atom.Furthermore, the co-ordination of thf induces a formal positive charge on the oxygen atom, leading to greater polarization of the C]O bond. The higher electron density on the metal can be distributed effectively via stronger p-back bonding to its carbonyl ligands and will also affect the carbene carbon atom by stronger interaction with the metal, resulting in an enhanced nucleophilic character on the adjacent oxygen atom. Attack by the acylate oxygen atom on the a-carbon of co-ordinated thf in the second step induces cleavage of the thf ring.We propose as key intermediates either one where the metal centre accommodates the excess of negative charge and is part of an eightmembered ring or a second, rearranged formulation resulting from migration of the oxygen from the metal onto the carbene carbon atom giving an anionic seven-membered ring intermediate as is shown in I.In the final step the alkylation of the oxygen with Et3OBF4 leads to the final products 3 and 4. Important features are the favourable electronic situation and arrangement of ligands in the p-bonded thienyl acylate which promote and facilitate the attack on a cis co-ordinated thf molecule. By contrast, as these conditions did not prevail for Li(C4H3S),15,16 the p-bonded phenyl precursors [(Cr(h6-C6H5Li)- (CO)3]5 or [Cr(h6-SC8H5Li)(CO)3], when treated in the same way and under similar reaction conditions the insertion of thf was not observed.In spite of the fact that co-ordination of Cr(CO)3 is through the benzene ring in [Cr(h6-SC8H6)(CO)3] activation by coordination towards metallation is at the 2 position on the thiophene ring.19 As a result of its separation the Cr(CO)3 fragment is sterically less influenced by the substituents at the 2 position of the thiophene ring. The dark purple-blue ethoxycarbene Scheme 3 S Cr(CO)3 C O O M(CO)5 S S Cr(CO)3 Cr(CO)3 C M(CO)5 C M O O– S Cr(CO)3 C OEt M(CO)5 O– S Cr(CO)3 C O M O S C O O M(CO)5 3,4 (CO)4 (CO)4 1,2 thf CO Et+ Et+ CO 5,6 S C O O M(CO)5 Cr(CO)3 IJ.Chem. Soc., Dalton Trans., 1997, Pages 2177–2182 2179 complex [Cr{C[h6-C8H5SCr(CO)3]OEt}(CO)5] 7 was obtained in excellent yield and was purified by crystallization from dichloromethane–hexane. Although very stable in the solid state, the Cr(CO)3 fragment was lost very slowly to give [Cr{C(C8H5S)OEt}(CO)5] 8 in polar solvents.Spectroscopic properties of complexes Complexes 1–8 were fully characterized by elemental analyses, mass, infrared (Table 1), 1H and 13C-{H} NMR (Tables 2 and 3) spectroscopy. General features displayed in the infrared spectra are well resolved bands in hexane allowing assignments to the M(CO)5 and M(CO)3 fragments and the lifting of the degeneracy of the E band (A9, A0) of the Cr(CO)3 fragment for p-coordinated thienyl complexes. Two characteristic features of the s,p-bimetallic monocarbene complexes are the upfield shifts of the thienyl protons in the 1H NMR spectra of 1–4 by more than 1 ppm compared to those of free thiophene 20 and 5 or 6 and the duplication of the methylene resonances of the C(carbene)OCH2 unit.Localization of the p bonds by co-ordination to a transition-metal affects the proton resonances to such an extent that upfield Table 1 Infrared data * (n& CO/cm21) for the carbene complexes 1–8 M(CO)5 Cr(CO)3 Complex 12 3 4 5 678 A1 (1) 2062 2069 2067 2062 2061 2080 2069 2069 2059 2082 2060 2069 B 1978 — — — 1988 1972 —— 2009 E 1952 1947 1941 1951 1945 1953 1941 1948 1940 1942 1980 1987 A1 (2) 1963 1952 1941 1964 1945 1942 1941 1978 1940 1984 1980 1987 A1 1990 1989 1981 1989 1984 1935 1980 E(A9,A0) 1935, 1920 1947 1895 1947, 1919 1915, 1895 1941 1893 * The first set of values was recorded in hexane and the second in dichloromethane. In some instances bands of the M(CO)3 fragment were obscured by those of the M(CO)5 fragment.shifts are observed in the 1H NMR spectra.21 The 1H NMR data for 1–4 and in particular the methylene resonances of the alkoxy substituent are affected by the lack of a plane of symmetry imposed on the complexes by p co-ordination to the Cr(CO)3 fragment. The methylene protons C(carbene)OCH2R are prochiral and the chemical shifts are duplicated with resonances at d 4.99 and 4.88 for 1, 4.83 and 4.77 for 2, 4.97 and 4.96 for 3, and 4.80 and 4.77 for 4.Other resonances of the alkoxy substituents are broad. In addition, a second set of resonances having the same pattern as the above, but of lower intensity (the ratio based on peak integrations of the 1H NMR data is ca. 1 : 3 for 1–4), are observed indicating the existence of a second isomer in solution. The two components are believed to be diastereoisomers, which can formally be related by a simple rotation around the thienyl–carbon(carbene) bond. The presence of a second diastereoisomer is also indicated by an additional resonance in the 13C NMR spectra of 1–3 in the carbene region (not observed for 4). Restricted rotation around the carbene– thienyl carbon bond will sustain the two different orientations A and B for the W(CO)5 fragment and the alkoxy substituents. Restricted rotation originating from electronic features is not supported by comparison of the observed resonances of the thienyl protons.Support for steric effects is found in the structure determined for 2 which displays a very compact arrangement of W(CO)5 and (p-thienyl)Cr(CO)3 units.The bond distances (see below) in the solid state show very little multiple bond character in any of the bonds around the carbene carbon atom. However, once formed, the bulky metal carbonyl fragments may inhibit conversion of one diastereoisomer into the other. We observed no change in the diastereoisomeric ratios by recording the NMR spectrum at different temperatures.The corresponding methylene resonances for 5 and 6 reduce to single triplets on removing the chirality caused by the planar ring and the Cr(CO)3 fragment. Furthermore, the barrier to rotation has been lifted by removal of the Cr(CO)3 fragment and allowing free rotation around the C (thienyl)–C (carbene) bond. Support is found in the spectrum of the s,pbimetallic complex 7 where the metal carbonyl fragments are far apart and restricted rotation around the C (thienyl)–C (carbene) bond is lifted. In fact, the effect on the resonances of the carbene methylene protons due to planar chirality imposed by the Cr(CO)3 fragment on one side of the benzothiophene Table 2 Proton NMR data (d, J/Hz) in CDCl3 for the carbene complexes [M{C(R)OR9}(CO)5] 1–8 R R9 ———————————————————— Thienyl Other Alkoxy Other Complex 1 2 3 4 5 6 7 8 H3 5.81 (d) 3JHH 3.7 5.95 (d) 3JHH 3.8 5.81 (d) 5.89 (d) 7.67 (d) 7.79 (d) 8.14 (s) 8.47 (s) H4 5.79 (t) 3JHH 3.7 5.79 (t) 3JHH 3.8 5.75 (t) 5.75 (t) 7.21 (t) 7.20 (t) H5 6.54 (d) 3JHH 3.7 6.49 (d) 3JHH 3.7 6.54 (d) 6.48 (d) 8.24 (d) 8.14 (d) 6.29 (d), 6.07 (d), 5.24 (dt), 5.62 (dt) 7.97 (d), 7.78 (d), 7.47 (dt), 7.39 (dt) CH2 4.99 (q), 4.88 (q) 5.02 (q), 4.82 (q) 3JHH 7.2 4.83 (q), 4.77 (q) 4.89 (q), 4.72 (q) 3JHH 7.2 4.97 (t), 4.96 (t) 5.02 (t), 4.89 (t) 3JHH 6.3 4.80 (t), 4.77 (t) 4.83 (t), 4.74 (t) 5.13 (t) 4.95 (t) 5.20 (q) 5.24 (q) CH3 1.53 (t) 3JHH 7.1 1.51 (t) 3JHH 7.1 3.47 (t), 3.49 (q), 2.02–1.93 (m), 1.78–1.69 (m), 1.21 (t) 3.47 (q), 3.46 (t), 2.00–1.91 (m), 1.87–1.72 (m), 1.20 (t) 3.51 (t), 3.48 (q), 2.11 (q), 1.83 (q), 1.20 (t) 3.51 (t), 3.47 (q), 2.09 (q), 1.84 (q), 1.20 (t) 1.68 (t) 1.71 (t)2180 J.Chem. Soc., Dalton Trans., 1997, Pages 2177–2182 Table 3 Carbon-13 NMR dataa for complexes 1–4, 7 and 8 d Complex 1 2 3 4 7 8 M(CO)5 222.2 (trans) 215.8 (cis) 201.6 (trans) 196.4 (cis) 222.1 (trans) 216.9 (cis) 201.7 (trans) 196.6 (cis) 223.3 (trans) 216.5 (cis) 222.0 (trans) 216.9 (cis) M(CO)3 232 232.6 232.4 232.5 231.4 — Ccarb 312.3 268.8 311.2 285.7 312.8 303.5 312.0 — 318.1 320.1 Thienyl b 108.8, 93.5, 88.1, 6.8 111.8, 93.1, 88.4, 7.8 123.5, 93.0, 83.3, 6.5 113, 92.8, 88.1, 7.4 167.0, 138.0, 124.0, 106.0 176.0, 155.1, 139.0, 128.9 Other 76.6 15.1 78.2 14.9 83.2, 69.9 66.3, 29.4, 29.4, 15.4 82.1, 69.6 66.2, 26.2, 26.2, 15.1 92.3, 84.3 89.8, 88.9, 76.6, 15.1 126.7, 122.8 125.0, 123.5, 76.6, 15.1 a Recorded in CDCl3.b Thienyl carbons are given in the sequence C2 to C5. ring has been greatly reduced and the signal appears as a slightly broadened quartet. The Cr(CO)3, Cr(CO)5 and W(CO)5 chemical shifts in the 13C NMR spectra are insensitive to changes in substituents and compare well with those reported.22 As is the case for the 1H NMR chemical shifts, the 13C shifts of the thienyl carbons are downfield (ca. 40 ppm) for the p-coordinated thienyl complexes 1–4 compared to monocarbene thienyl complexes.15 Crystal structure The crystal structure of complex 2 was determined and selected bond distances and angles are given in Table 4.Fig. 1 displays the molecular structure with the atom labelling used. The molecular structure shows the typical three-legged piano-stool arrangement for the thienyl ring and Cr(CO)3 fragment linked via the carbene unit to an octahedrally co-ordinated tungsten centre. Although relatively crowded, the carbonyl ligands are orientated in their normal, electronically favoured positions.The Cr(CO)3 tripod is arranged with one of the carbonyl ligands trans to the thienyl sulfur 23 and three of the four ciscarbonyl ligands of the W(CO)5 fragment displaced marginally out of the plane, away from the carbene ligand. The thienyl ring is planar and the ring carbons are at approximately equal dis- S C M(CO)5 OR S C OR M(CO)5 Cr Cr Cr = Cr(CO)3; M = W or Cr A B Table 4 Selected bond lengths (Å) * and bond angles (8) for complex 2 W]C(5) (carbene) W]C (carbonyl) trans cis Cr]C (carbonyl) Cr]C(1) Cr]C(2) Cr]C(3) Cr]C(4) Cr]S C(1)]C(2) C(2)]C(3) C(3)]C(4) S]C(1) S]C(4) C(4)]C(5) C(5)]O(1) C(7)]O(1) 2.173(9) 2.011(15) 2.039(15) 1.858(13) 2.176(10) 2.205(10) 2.183(9) 2.152(9) 2.360(3) 1.420(15) 1.416(13) 1.404(13) 1.726(11) 1.780(9) 1.499(13) 1.311(11) 1.458(12) C(1)]S]C(4) S]C(4)]C(3) S]C(4)]C(5) C(1)]C(2)]C(3) C(2)]C(3)]C(4) S]C(1)]C(2) C(3)]C(4)]C(5) C(4)]C(5)]O(1) W]C(5)]C(4) W]C(5)]O(1) C(5)]O(1)]C(7) C(21)]Cr]C(31) C(11)]Cr]C(31) C(11)]Cr]C(21) C(5)]W]C(41) C(5)]W]C(61) C(5)]W]C(71) C(5)]W]C(81) 90.6(5) 111.8(7) 117.3(7) 112.7(9) 112.1(8) 112.4(7) 131.0(8) 104.2(7) 124.6(6) 131.2(6) 122.7(8) 91.8(5) 91.3(5) 90.9(6) 93.8(4) 92.5(4) 91.0(4) 89.6(4) * Carbonyl distances are averaged values.tances from the chromium with the ipso-carbon closest and the adjacent carbon furthest away from the chromium. The only sign of possible crowding is found in a relative long W]C (carbene) bond distance of 2.17 Å which is significantly longer than the corresponding distance of 2.05 Å in [W{C(OMe)Ph}- (CO)5],24 but shorter than the corresponding distance of 2.23 Å recorded for a similarly crowded s,p-bimetallic complex [(OC)5W{C(OEt)C5H4}Ru(C5H5)].25 The C (carbene)-O bond of 1.311(11) Å is significantly shorter than the O(1)–C(7) distance of 1.458(12) Å.The three C–C distances in the ring are the same, indicating delocalization of electron density in the ring.By contrast, free thiophene displays localized bonds with two exhibiting double-bond character (1.370 Å) and one singlebond character (1.424 Å).26 Experimental All reactions were performed under an inert atmosphere using standard Schlenk-tube techniques.27 Solvents were dried by the usual procedures and distilled under nitrogen prior to use. The starting materials, [Cr(CO)6], [W(CO)6], LiBu and benzo[b]thiophene, were used as obtained from Aldrich and thiophene was purified as described previously.28 The starting compounds were prepared according to literature methods, [Cr(NH3)3(CO)3],11 Fig. 1 Molecular structure of complex 2 with the atom numbering schemeJ. Chem.Soc., Dalton Trans., 1997, Pages 2177–2182 2181 [Cr(SC4H4)(CO)3],12 [Cr(SC8H6)(CO)3] 14 and triethyloxonium tetrafluoroborate.29 Column chromatography was performed on silica gel (0.063–0.200 mm) and the column cooled by recycling (220 8C) PriOH through the column jacket.The NMR spectra were recorded at 220 8C on a Bruker AC-300 spectrometer with reference to the deuterium signal of the solvent employed; 1H and 13C spectra were measured at 300.135 and 75.469 MHz, respectively, unless specified otherwise. The NMR solvents were degassed by several freeze–pump–thaw cycles, and NMR sample tubes sealed under nitrogen. Infrared spectra were recorded as liquid solutions on a Bomem Michelson-100 FT spectrophotometer, and wavenumbers (cm21) were assigned relative to a polystyrene standard.Mass spectra were recorded on a Perkin-Elmer RMU-6H instrument operating at 70 eV (ca. 1.12 × 10217 J). Elemental analyses were obtained from the Analytical Division (PCMT) of the Council for Scientific and Industrial Research, Pretoria, South Africa. Melting points were recorded in capillaries on a Gallenkamp hot-stage apparatus and are uncorrected. Preparations [Cr{C[Á5-C4H3SCr(CO)3]OEt}(CO)5] 1, [Cr{C[Á5-C4H3SCr- (CO)3]O(CH2)4OEt}(CO)5] 3 and [Cr{C(C4H3S)O(CH2)4OEt}- (CO)5] 5.The dropwise addition a 1.6 mol dm23 hexane solution (4–5 cm3) of LiBu (5.5 mmol) to a cooled (250 8C) thf solution (60 cm3) containing [Cr(SC4H4)(CO)3] (1.09 g, 5 mmol) afforded the lithiated thienyl complex in high yields after 30 min. Addition of [Cr(CO)6] (1.1 g, 5 mmol) in small portions over 10 min resulted in a gradual change from yellow to dark red-brown. After stirring for 30 min in the cold, the reaction mixture was warmed to room temperature and stripped of solvent under reduced pressure.The brown residue was washed several times with hexane, redissolved in dichloromethane, cooled to 230 8C and carefully treated with Et3OBF4 (0.91 g, 5.0 mmol) dissolved in dichloromethane (20 cm3). After stirring for 1 h and allowing the reaction mixture to warm to room temperature, the cerise pink solution was filtered through silica gel and evaporated to dryness in vacuo. The residue was chromatographed on silica gel (0.063–0.200 nm) and five bands separated.The first yellow product was the known mononuclear carbene complex [Cr{C(C4H3S)(OEt)}(CO)5] (0.1 g, 10.1%). The second product, yield 0.55 g (50.2%), was purple and was identified as the s,p-bimetallic carbene complex [Cr{C[h5- C4H3SCr(CO)3]OEt}(CO)5] 1. The third orange band gave unchanged starting complex (0.06 g, 5.2%), and the fourth orange product was identified as the modified mononuclear carbene complex [Cr{C(C4H3S)O(CH2)4OEt}(CO)5] 5 (0.1 g, 10.1%).The last blue band was characterized as the modi- fied s,p-carbene complex [Cr{C[h5-C4H3SCr(CO)3]O(CH2)4- OEt}(CO)5] 3 (0.2 g, 20.5%). The yield of 3 was increased to 30% by stirring the thf reaction mixture at room temperature for 2 h. Complex 1 (Found: C, 33.35; H, 2.70. C15H8Cr2O9S requires C, 33.95; H, 2.4%): mass spectrum m/z 468 (M1), 328 (M1 2 5CO) and 244 (M1 2 8CO). Complex 3 (Found: C, 33.35; H, 2.7. C19H16Cr2O10S requires C, 33.95; H, 2.4%): mass spectrum m/z 540 (M1), 400 (M1 2 5CO) and 316 (M1 2 8CO).Complex 5 (Found: C, 33.35; H, 2.7. C16H16Cr2O7S requires C, 33.95; H, 2.4%): mass spectrum m/z 407 (M1) and 267 (M1 2 5CO). [W{C[Á5-C4H3SCr(CO)3]OEt}(CO)5] 2, [W{C[Á5-C4H3SCr- (CO)3]O(CH2)4OEt}(CO)5] 4 and [W{C(C4H3S)O(CH2)4OEt}- (CO)5] 6. A 1.6 mol dm23 solution (8.4 cm3) of butyllithium (13.5 mmol) in hexane was added to a solution (30 cm3) of [Cr- (SC4H4)(CO)3] (2.70 g, 12.3 mmol) in thf.The reaction was effected in the same manner as for the chromium analogue with the addition of [W(CO)6] (4.32 g, 12.4 mmol) and the alkylation done with triethyloxonium tetrafluoroborate (2.26 g, 13.9 mmol). Five compounds analogous to the chromium products above were purified by column chromatography and fully characterized: known yellow mononuclear carbene complex [W{C(C4H3S)(OEt)}(CO)5], yield 0.46 g (10.7%), blue s,pcarbene complex [W{C[h5-C4H3SCr(CO)3]OEt}(CO)5] 2, yield 2.26 g (54.6%), unreacted starting material (0.2 g, 5.1%), the carbene complex [W{C(C4H3S)O(CH2)4OEt}(CO)5] 6, yield 0.4 g (10.2%), and the s,p-carbene complex [W{C[h5- C4H3SCr(CO)3]O(CH2)4OEt}(CO)5] 4, yield 0.8 g (18.6%).The yield of 4 was increased by stirring the thf reaction mixture at room temperature for 2 h. Complex 2 (Found: C, 33.35; H, 2.7. C15H8CrO9SW requires C, 33.95; H, 2.4%): mass spectrum m/z 599 (M1), 459 (M1 2 5CO) and 375 (M1 2 8CO). Complex 4 (Found: C, 33.35; H, 2.7.C19H16CrO10SW requires C, 33.95; H, 2.4%): mass spectrum m/z 671 (M1), 531 (M1 2 5CO) and 477 (M1 2 8CO). Complex 6 (Found: C, 33.35; H, 2.7. C16H16CrO7SW requires C, 33.95; H, 2.4%): mass spectrum m/z 535 (M1) and 395 (M1 2 5CO). [Cr{C[Á6-C8H5SCr(CO)3]OEt}(CO)5] 7 and [Cr{C(C8H5S)- OEt}(CO)5] 8. Benzo[b]thiophene (0.42 g, 2.2 mmol) was dissolved in thf, the solution cooled to 250 8C and butyllithium (1.4 cm3, 2.2 mmol) was added to the stirred solution. The mixture was stirred for 30 min after which it was cooled to 270 8C, and [Cr(CO)6] (0.48 g, 2.2 mmol) was added, upon which the solution changed to dark red. The temperature was allowed to rise to 250 8C and stirred at this temperature for 2 h.The solvent was removed under reduced pressure and the residue redissolved in dichloromethane. The stirred solution was cooled to 230 8C and triethyloxonium tetrafluoroborate (0.40 g, 2.2 mmol) dissolved in dichloromethane was added. The solution was stirred at room temperature for 30 min during which time it changed to a dark purple.It was filtered through silica gel and the solvent was removed under reduced pressure. An almost quantitative yield of 0.45 g (95.2%) of [Cr{C[h6-C8H5SCr- (CO)3]OEt}(CO)5] 7 and 0.013 g (3.1%) of an orange product, [Cr{C(C8H5S)OEt}(CO)5] 8. The yield of 8 could be increased by stirring a thf solution of 7 for 24 h at room temperature. Complex 7 (Found: C, 33.35; H, 2.7. C18H10Cr2O9S requires C, 33.95; H, 2.4%): mass spectrum m/z 468 (M1), 328 (M1 2 5CO) and 244 (M1 2 8CO).Complex 8 (Found: C, 33.35; H, 2.7. C15H16CrO10S requires C, 33.95; H, 2.4%): mass spectrum m/z 540 (M1), 400 (M1 2 5CO) and 316 (M1 2 8CO). Crystallography Purple crystals of complex 2, grown from dichloromethane– hexane mixtures, were suitable for single-crystal X-ray diffraction studies. A dark plate single crystal of approximate size 0.40 × 0.15 × 0.05 mm was mounted on a glass fibre.All geometric and intensity data were taken from this sample using an automated four-circle diffractometer (Nicolet R3mV) equipped with Mo-Ka radiation (l = 0.710 73 Å). Important crystallographic parameters are summarized in Table 5. The lattice vectors were identified by application of the automatic indexing routine of the diffractometer to the positions of 28 reflections taken from a rotation photograph and centred by the diffractometer. The w–2q technique was used to measure 3666 reflections (3313 unique) in the range 5 < 2q < 508.Three standard reflections (remeasured every 97 scans) showed no significant loss in intensity during data collection. The data were corrected for Lorentz-polarization effects, and empirically for absorption. The 2460 unique data with [I > 3.0s(I)] were used to solve and refine the structure in the triclinic space group P1� . The structure was solved by Patterson methods and developed by using alternating cycles of least-squares refinement and Fourier-difference synthesis.The non-hydrogen atoms were refined anisotropically while hydrogens were placed2182 J. Chem. Soc., Dalton Trans., 1997, Pages 2177–2182 in idealized positions (C]H 0.96 Å) and assigned a common isotropic thermal parameter (U = 0.08 Å2). The final cycle of least-squares refinement included 244 parameters for 2460 variables [weighting scheme applied: w21 = s2(F ) 1 0.000 961 F 2] and did not shift any parameter by more than 0.001 times its standard deviation.The final R = 0.0409 and R9 = 0.0435, and the final Fourier-difference map was featureless with no peaks greater than 0.60 e Å23. Structure solution used the SHELXTL PLUS program package 30 on a microVax II computer. 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 186/473. Acknowledgements We thank Dr. D. Tocher, University College of London, for collecting the crystal data and solving the structure, also Mr. E. Palmer for assistance during NMR experiments. We are thankful for financial assistance from the University of Pretoria and the Foundation of Research Development of South Africa. Table 5 Crystal and data-collection parameters for complex 2 Formula Crystal symmetry Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 ZF (000) Dc/g cm23 m(Mo-Ka)/cm21 no.Orientation reflections 2q Range/8 T/K Data measured Unique data No. unique with I > 3.0s(I) No. parameters Ra R9b Weighting scheme, w21 Largest shift/e.s.d. in final cycle Largest peak/e Å23 C15H8CrO9SW Triclinic P1� 6.938(2) 10.855(4) 12.847(3) 88.92(2) 82.39(2) 86.44(2) 957 2 568 2.08 68.2 28 14–248 293 3666 3313 2460 244 0.0409 0.0435 s2(F) 1 0.000 961F2 0.001 0.6 a R = S Fo| 2 Fc S|Fo|.b R9 = [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� . References 1 Part 3. T. A. Waldbach, R. van Eldik, P. H. van Rooyen and S. Lotz, Organometallics, submitted. 2 S. Lotz, P. H. van Rooyen and R. Meyer, Adv. Organomet. Chem., 1995, 37, 219; W. Beck, B. Niemer and M. Wieser, Angew. Chem., Int. Ed. Engl., 1993, 32, 923; J. Forniés and E. Lalinde, J. Chem. Soc., Dalton Trans., 1996, 2587. 3 S. Lotz, M. Schindehutte and P. H. van Rooyen, Organometallics, 1992, 11, 629; P.H. van Rooyen, M. Schindehutte and S. Lotz, Organometallics, 1992, 11, 1104; Inorg. Chim. Acta, 1993, 208, 207; R. Meyer, P. H. van Rooyen, M. Schindehutte and S. Lotz, Inorg. Chem., 1994, 33, 3605. 4 T. A. Waldbach, P. H. van Rooyen and S. Lotz, Angew. Chem., Int. Ed. Engl., 1993, 32, 710; Organometallics, 1993, 12, 4250. 5 E. O. Fischer, F. J. Gammel and D. Neugebauer, Chem. Ber., 1980, 113, 1010. 6 E. O. Fischer, F. J. Gammel, J. O. Besenhard, A.Frank and D. Neugebauer, J. Organomet. Chem., 1980, 191, 261. 7 J. A. Connor and J. P. Lloyd, J. Chem. Soc., Dalton Trans., 1972, 1470. 8 E. O. Fischer and J. K. R. Wanner, Chem. Ber., 1985, 118, 2489. 9 J. Breimair, T. Weidemann, B. Wagner and W. Beck, Chem. Ber., 1991, 124, 2429. 10 E. O. Fischer and K. Öfele, Chem. Ber., 1958, 91, 2385; K. Öfele, Chem. Ber., 1966, 91, 2385. 11 M. D. Rausch, G. A. Moser, E. Jd A. L. Lipman, J. Organomet. Chem., 1970, 23, 185. 12 M. Novi, G. Guanti and C. Dell9Erba, J. Heterocycl. Chem., 1975, 12, 1055. 13 M. N. Nefedova, V. N. Setkina and D. N. Kursanov, J. Organomet. Chem., 1983, 244, C21. 14 E. O. Fischer, H. A. Goodwin, C. G. Kreiter, H. D. Simmons, K. Sonogashira and S. B. Wild, J. Organomet. Chem., 1968, 14, 359. 15 J. A. Connor, E. M. Jones, E. W. Randall and E. Rosenberg, J. Chem. Soc., Dalton Trans., 1972, 2419; M. Y. Darensbourg and D. J. Darensbourg, Inorg. Chem., 1970, 9, 32. 16 S. Aoki, T. Fujimura and E. Nakamura, J. Am. Chem. Soc., 1992, 114, 2985. 17 J. Christoffers and K. H. Dötz, Organometallics, 1994, 13, 4189. 18 B. Mudryk and T. Cohen, J. Am. Chem. Soc., 1991, 113, 1866; D. J. Ramón and M. Yus, Tetrahedron, 1992, 48, 3585. 19 J. L. Davidson, H. Patel and P. N. Preston, J. Organomet. Chem., 1987, 336, C44. 20 S. Gronowitz, Adv. Heterocycl. Chem., 1963, 1, 1. 21 A. Mangini and F. Taddei, Inorg. Chim. Acta, 1968, 2, 12. 22 B. E. Mann, Adv. Organomet. Chem., 1974, 12, 135. 23 M. F. Bailey and L. F. Dahl, Inorg. Chem., 1965, 4, 1306. 24 O. S. Mills and A. D. Redhouse, Angew. Chem., Int. Ed. Engl., 1965, 4, 1082. 25 E. O. Fischer, F. J. Gammel, J. O. Besenhard, A. Frank and D. Neugebauer, J. Organomet. Chem., 1980, 191, 261. 26 W. R. Harshbarger and S. H. Bauer, Acta Crystallogr., Sect B, 1970, 26, 1010. 27 D. F. Schriver and M. A. Drezdzon, The Manipulation of Air-sensitive Compounds, 2nd edn. Wiley, New York, 1980. 28 G. H. Spies and R. J. Angelici, Organometallics, 1987, 6, 1897. 29 H. Meerwein, Org. Synth., 1966, 46, 113. 30 G. M. Sheldrick, SHELXTL PLUS, University of Göttingen, 1986. Received 9th January 1997; Paper 7/00229G

ISSN:1477-9226    

DOI:10.1039/a700229g

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 2183 Polyhetero-ferrocenes and -ruthenocenes derived from the 1,4,2- diphosphastibolyl ring anion [P2SbC2But 2]2† Steven J. Black, Matthew D. Francis and Cameron Jones * Department of Chemistry, University of Wales, Swansea, Singleton Park, Swansea, UK SA2 8PP The complex [RuCl2(PPh3)3] reacted with the 1,4,2-diphosphastibolyl ring anion [P2SbC2But 2]2 (containing ca. 25% of the 1,2,4-triphospholyl anion [P3C2But 2]2) to produce a cocrystallised mixture (crystal structure) of two isomers of [Ru(h5-P2SbC2But 2)2] with [Ru(h5-P2SbC2But 2)(h5-P3C2But 2)].Variable-temperature 31P-{1H} NMR studies on the mixture show one of the isomers and the last complex to be fluxional at room temperature. It is believed that an interring Sb ? ? ? Sb interaction in the other isomer restricts its fluxionality in solution. The reaction of [P2SbC2But 2]2 with FeCl2 yielded only one isomer of the heteroferrocene complex [Fe(h5-P2SbC2But 2)2] which is also non-fluxional in solution and has a similar oxidation potential to that of ferrocene itself.The heteroruthenocene complexes [Ru(h5-P2SbC2But 2)(h5-C5R5)] (R = H or Me) were prepared by treating [Ru(h5- C5R5)(MeCN)3][PF6] (R = H or Me) with [P2SbC2But 2]2. The analogous ferrocene complex [Fe(h5-P2SbC2But 2)- (h5-C5Me5)] (crystal structure) was synthesized by treating a 1 : 1 mixture of [P2SbC2But 2]2 and Li(C5Me5) with half an equivalent of FeCl2.Treatment of [M(h5-P2SbC2But 2)(h5-C5Me5)] (M = Ru or Fe) with [W(CO)5(thf )] (thf = tetrahydrofuran) formed the secondary co-ordination complexes [M(h5-P2SbC2But 2)(h5-C5Me5){W(CO)5}] (M = Ru or Fe) in which the W(CO)5 fragment is h1 ligated to the phosphorus centre adjacent to the ring antimony centre. A diphosphastibolyl-bridged cationic triple-decker complex [(h5-C5Me5)Ru(m-h5: h5- P2SbC2But 2)Ru(h5-C5Me5)][PF6] was the product of the reaction of [P2SbC2But 2]2 with 2 equivalents of [Ru(h5-C5Me5)(MeCN)3][PF6].The chemistry of phospha- and polyphospha-ferrocene and -ruthenocene sandwich complexes is now a well established area that is largely based on the use of monophospholyl anions as ligands. A range of complexes employing either 1,2- or 1,3- diphospholyl, or 1,2,4-triphospholyl ring anions have also been reported.1 Representative examples of the latter include [M(h5- P3C2But 2)2] (M = Fe 1 2 or Ru 23), [M(h5-P3C2But 2)(h5-P2C3- But 3)] (M = Fe 3 2 or Ru 43) and [M(h5-P3C2But 2)(h5-C5R5)] (R = H, M = Fe 5 4 or Ru 6;3 R = Me, M = Fe 7 5 or Ru 83).In addition, several ferrocenes and ruthenocenes have been prepared from the pentaphospholyl anion, [P5]2.1 A common feature of phosphorus-substituted ferrocenes is their ability to undergo secondary co-ordination through sterically available phosphorus lone pairs to neutral metal fragments; several examples of such complexes have been reported.1 Compared with the large volume of work dedicated to phospha-ferrocenes and -ruthenocenes relatively few studies have examined the chemistry of the arsenic, antimony and bismuth counterparts of these species.This can be attributed to the decreasing stability of unsaturated Group 15 element– carbon bonds with increasing molecular weight of the Group 15 element. Ashe and Al-Ahmed 6 have, however, produced at least one example of each of the ferrocenes, [Fe(h5-EC4R4)2] 9 and [Fe(h5-EC4R4)(h5-C5H5)] 10 (R = H or alkyl, E = As, Sb or Bi) which in the case of 9 (E = Sb or Bi, R = Me) show strong interring E ? ? ? E interactions similar to the well known intermolecular solid-state E ? ? ? E contacts in thermochromic distibanes and dibismuthanes.All crystallographically characterised examples of 9 and 10 show evidence of a high degree of aromatic delocalisation within the heterocyclic ligand which presumably accounts for the stability of these complexes.6 It is noteworthy that several sandwich complexes, e.g.[M(h5- As5)(h5-C5Me5)] 11 (M = Fe or Ru), have also been prepared from the pentaarsolyl anion, [As5]2.7 It is only recently that this area of chemistry has been extended to hetero-ferrocenes and -ruthenocenes derived from † Non-SI units employed: mmHg ª 133 Pa, eV ª 1.60 × 10219 J. heterocycles containing mixtures of Group 15 elements with the synthesis of [Fe(h5-PCHAsC2Et2)2] 12,8 [Fe(h5-P2AsC2But 2)(h5- C5H5)] 13 9 and [M(h5-P2AsC2But 2)(h5-C5Me5)] (M = Fe 14 or Ru 15).10 The diphosphaarsolyl rings in 13–15 were found to exist as inseparable mixtures of both the 1,2- and 2,4- diphospha isomers.Complex 13 has been used as a P-donor ligand in the preparation of the secondary co-ordination complex [Fe(h5-P2AsC2But 2)(h5-C5H5){W(CO)5}] 16,9 whilst 14 and 15 have been utilised in the synthesis of the novel cationic triple-decker complex [(h5-C5Me5)Ru(m-h5 :h5-P2- AsC2But 2)Ru(h5-C5Me5)][PF6] 17.10 We have become interested in broadening this field to include ferrocenes and ruthenocenes employing mixed P, Sb-heterocyclic ligand systems.This has become possible with our recent regiospecific synthesis of the 1,4,2-diphosphastibolyl ring anion, [P2SbC2But 2]2,11 which we have utilised in the preparation of the ruthenocene complexes [Ru(h5-P2SbC2But 2)(h5-C5R5)] (R = H 18 or Me 19).12 Herein we report the full extension of this preliminary report. Results and Discussion Treatment of [Li(tmen)2][P2SbC2But 2] (tmen = N,N,N9N9- tetramethylethane-1,2-diamine) with [RuCl2(PPh3)3] led to the formation of an orange, air-stable mixture of two isomers of [Ru(h5-P2SbC2But 2)2] 20 and 21 with the compound [Ru(h5- P2SbC2But 2)(h5-P3C2But 2)] 22 after chromatographic work-up (Kieselgel, hexane) (Scheme 1).The presence of 22 in the mixture is a result of the cosynthesis of the 1,2,4-triphospholyl ring anion [P3C2But 2]2 (ca. 25%) in the preparation of the diphosphastibolyl precursor (ca. 75%), the anions being inseparable.11 Rigorous attempts to separate 20–22 by fractional crystallisation or sublimation (150 8C, 0.04 mmHg) met with failure due to persistent cocrystallisation of these compounds (see below). By contrast, the reaction of [Li(tmen)2]- [P2SbC2But 2] with FeCl2 yielded only one isomer of the mildly air-sensitive, brown heteroferrocene, [Fe(h5-P2SbC2But 2)2] 23, and none of the iron analogue of 22, viz. [Fe(h5-P2Sb-2184 J. Chem.Soc., Dalton Trans., 1997, Pages 2183–2190 C2But 2)(h5-P3C2But 2)], after recrystallisation from hexane or sublimation (170 8C, 0.04 mmHg). A small amount of the triphospholyl impurity is, however, present in the crude reaction mixture but cannot be crystallised from it. The variable-temperature 31P-{1H} NMR spectra for the mixture of compounds 20–22 are displayed in Fig. 1. It is clear that whilst 20 is non-fluxional in solution, 21 and 22 are undergoing fluxional processes at room temperature which can be attributed to a rotation, or partial rotation, of the heterocyclic rings about their metal–ring centroid axes.Such processes are common for sandwich complexes containing even heavily substituted cyclopentadienyl ligands 13 and have been observed for the closely related complex 2.3 It is difficult to calculate the energy barrier for these processes in 21 and 22 as the complexity of the 1H NMR spectra of the mixture rules out the assignment of their coalesence temperatures. At 260 8C, however, the 31P- {1H} NMR spectra can be assigned as an [AB]2 spin system for 20, a superimposition of two [AX] systems for 21, and the superimposition of an [AX] and an [AMX] system for 22, the three high-field signals in the latter arising from the [AMX] system of the triphospholyl ring.There are no observed interring couplings for any of the compounds. These assignments were made by correlating mutual couplings, peak multiplicities and peak integrations to the structures of 20–22.In addition, the low-temperature spectra of all three compounds have been successfully simulated using the PANIC program.14 Unfortunately the complexity of both the 1H and 13C NMR spectra of the mixture of compounds did not allow their assignment although molecular-ion peaks displaying the correct isotopic distributions were observed for the isomers 20 and 21 and complex 22 in the mass spectrum of the mixture. The 31P-{1H} NMR spectrum of the heteroferrocene 23 shows it to be non-fluxional in solution at room temperature as is its ruthenium analogue 20.The spectrum has been assigned and successfully simulated as an [AA9BB9] spin system with characteristic two-bond intraring couplings (34 Hz) in addition to an interring coupling, 2J(PAPB9) = J(PA9PB) = 8 Hz [J(PAPA9) = J(PBPB9) = 0 Hz]. There is no observable change in the spec- Scheme 1 (i) [RuCl2(PPh3)3], 1,2-dimethoxyethane (dme), 18 h, 25 8C; (ii) FeCl2, dme, 18 h, 25 8C Ru Sb P P But But P Sb P P Sb P But But But But Ru P P Sb P Sb P But But But But Ru P Sb P P P P But But But But Fe P Sb P P Sb P But But But But P P P But But _ 20 21 22 23 ( i) + + ( ca. 75%) _ ( ca. 25%) + ( ii) trum over the temperature range 25 8 to 260 8C. A similar interring coupling has been reported for the related complex 1,2 which was attributed to a through-space phosphorus– phosphorus interaction. It can be postulated that such an interaction also gives rise to the interring coupling in the present system which could explain why no such couplings are observed for 20 in which the interring distance is presumably larger.The 1H and 13C NMR spectra of 23 are as expected in that they highlight two sets of inequivalent tertiary butyl groups. It is interesting that both compounds 20 and 23 appear to have ‘rigid’ structures in solution at room temperature while the isomeric form of 20, viz. 21, is fluxional even at 240 8C.It seems likely that this is due to strong Sb ? ? ? Sb interring contacts in 20 and 23 similar to that previously reported for some distibaferrocenes 9.6 It is of course possible that 20 and 23 could exist as their ‘equienergetic’ P]P eclipsed conformers in solution. This, however, seems unlikely as 20 occurs solely as the Sb]Sb eclipsed conformer in the solid state (see below). The presence of such an Sb ? ? ? Sb interaction in 21 is not plausible as this would necessitate the tertiary butyl groups from each ring being eclipsed by those on the opposing ring.Further evidence for the proposed Sb ? ? ? Sb contact in 20 can be gained from its crystal structure. The molecular structure of the cocrystallised mixture of compounds 20–22 is depicted in Fig. 2 (Table 1). The labelling scheme shown is for 20. During the structural refinement it was found that the sites labelled Sb(1), Sb(2) and P(1) are partially occupied by phosphorus (51), phosphorus (13) and antimony (17%) respectively, while those labelled P(2), P(3) and P(4) all have a 100% phosphorus occupancy.This site disorder is consistent with the cocrystallisation of 20 and 21 (53% total) with 22 (47%) and is in line with the NMR spectra of the product mixture. The fact that P(2) has a 100% phosphorus occupancy confirms that 20 exists solely as its Sb]Sb eclipsed conformer in the cocrystallised mixture. The structural similarities between 20 and 22 have, no doubt, led to their ability to cocrystallise.Unfortunately any discussion of the bond lengths within the heterocyclic rings is precluded by the observed disorder, though the values for the cocrystallised mixture are shown in Table 1. It is evident, however, that the rings are essentially planar, almost parallel (dihedral angle 5.58) and h5-ligated to the ruthenium centre (centroid]Ru]centroid 170.58, cf. 174.48 for 2).3 The distances of the two rings from the ruthenium centre are almost equivalent {1.825(2) [Sb(1) ring] and 1.812(2) Å [Sb(2) Fig. 1 Variable temperature 31P-{1H} NMR spectra for the cocrystallised mixture of compounds 20–22J. Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 2185 ring]} and similar to that observed in the related complex 2, 1.814 Å.3 It is clear from Fig. 2(b) that the rings are eclipsed and arranged in such a fashion as to minimise the interring interaction of the tertiary butyl groups. The crystal structures of the triphospholyl-ferrocene and -ruthenocene complexes 1 2 and 2 3 show an identical arrangement of ligands about the metal centre. Although it is not valid to comment on the lengths of the interring Sb ? ? ? Sb contacts in the structure of 20, it is obvious that it will be well within the sum of the van der Waals radii for two antimony centres (4.40 Å) 14 and that an interaction should exist as predicted from the 31P NMR studies.Considering the smaller covalent radius of iron (1.17 Å) over ruthenium (1.24 Å),15 it seems likely that any Sb ? ? ? Sb contacts in 23 should be stronger than in 20 which may explain the absence of any other isomers in its preparation.Since the heteroferrocene 23 could be obtained in a pure state its electrochemistry was examined by cyclic voltammetry. These studies determined that 23 undergoes a pseudo-reversible oneelectron oxidation with an E2� 1 value of 78 mV relative to ferrocene. Similar studies have been carried out on the heteroferrocenes [Fe(EC4R4)2] (E = P, As, Sb or Bi) with the conclusion that when R = H the diphospha- and diarsa-ferrocenes are harder to oxidise than ferrocene itself, the distibaferrocene is slightly easier to oxidise than ferrocene and the dibismaferrocene is considerably easier to oxidise.6 When the heteroferrocenes were substituted with alkyl groups their oxidation became increasingly facile, presumably due to the electrondonating ability of the alkyl groups.These results suggested to the authors that P and As have greater effective p electronegativities than that of C, the p electronegativity of Sb is close to Fig. 2 Molecular structure of the cocrystallised mixture of compounds 20–22 (atomic labels represent 20) that of C and Bi is considerably more p electropositive than is C. Interestingly, the present system, 23, is only marginally more difficult to oxidise than is ferrocene. It is possible that this is due to a balance of the electron-withdrawing abilities of the phosphorus centres and the electron-donating ability of the tertiary butyl groups relative to the unsubstituted carbon centres in ferrocene.From the previous studies it would be expected that the antimony centres should not affect this balance significantly. Obviously further electrochemical studies will need to be carried out on a range of related polyheteroferrocenes to confirm this hypothesis. As reported in a preliminary communication,12 treatment of [Li(tmen)2][P2SbC2But 2] with [Ru(C5R5)(MeCN)3][PF6] affords (Scheme 2) moderate yields of the ruthenocenes [Ru(h5- P2SbC2But 2)(h5-C5R5)] (R = H 18 or Me 19) which cocrystallise with small amounts (ca. 10%) of the known triphospholyl complexes 6 and 8, respectively, due to the aforementioned contamination of [P2SbC2But 2]2 with [P3C2But 2]2.Full synthetic details for 18 and 19 are reported herein. The ferrocene analogue of 19, [Fe(h5-P2SbC2But 2)(C5Me5)] 24, can also be prepared in good yield by the reaction of FeCl2 with a 1 : 1 mixture of [Li(tmen)2][P2SbC2But 2] and Li(C5Me5) in dme.This airstable, brown complex can be partially purified by crystallisation from hexane but the product always cocrystallises with small amounts (ca. 15%) of the known triphospholyl complex 7,5 which could not be separated despite repeated attempts at fractional recrystallisation. The triphospholyl contamination of 18, 19 and 24 has precedent in the synthesis of the closely related diphosphaarsolyl complexes 13–15 which all cocrystallise with their triphospholyl counterparts.9,10 Several attempts were made to prepare the iron counterpart of 18, viz.[Fe(h5- P2SbC2But 2)(C5H5)], by the reaction of FeCl2 with Li(C5H5) and [Li(tmen)2][P2SbC2But 2] in a 1 : 1 ratio however this only yielded [Fe(C5H5)2] and 23 after work-up. This situation presumably arises due to a higher reactivity of Li(C5H5) relative to [P2Sb- Table 1 Selected intramolecular distances (Å) and angles (8) for the cocrystallised mixture of compounds 20–22 with estimated standard devictions (e.s.d.s) in parentheses Sb(1)]C(1) Sb(1)]Ru Sb(2)]P(3) Ru]C(1) Ru]C(4) Ru]P(2) Ru]P(3) P(1)]C(2) P(2)]C(2) P(4)]C(4) C(1)]C(9) C(3)]C(13) C(1)]Sb(1)]P(1) C(3)]Ru]C(4) C(1)]Ru]P(2) C(3)]Ru]P(4) C(3)]Ru]P(3) P(4)]Ru]P) C(2)]Ru]P(1) C(1)]Ru]Sb(1) P(2)]Ru]Sb(1) C(3)]Ru]Sb(2) P(4)]Ru]Sb(2) Sb(1)]Ru]Sb(2) C(1)]P(2)]C(2) C(4)]P(4)]C(3) C(9)]C(1)]Sb(1) C(5)]C(2)]P(2) P(2)]C(2)]P(1) C(13)]C(3)]P(3) C(17)]C(4)]P(4) P(4)]C(4)]Sb(2) 2.045(6) 2.674(1) 2.420(2) 2.292(5) 2.312(5) 2.441(1) 2.488(2) 1.914(6) 1.774(6) 1.748(5) 1.549(8) 1.558(8) 92.8(2) 72.1(2) 43.39(13) 43.7(2) 43.20(14) 79.22(5) 45.43(14) 47.88(14) 81.72(4) 80.61(13) 82.05(4) 81.33(2) 101.1(3) 101.1(3) 117.0(4) 118.2(4) 123.2(3) 117.4(4) 117.8(4) 124.2(3) Sb(1)]P(1) Sb(2)]C(4) Sb(2)]Ru Ru]C(3) Ru]C(2) Ru]P(4) Ru]P(1) P(2)]C(1) P(3)]C(3) P(4)]C(3) C(2)]C(5) C(4)]C(17) C(4)]Sb(2)]P(3) C(1)]Ru]C(2) C(2)]Ru]P(2) C(4)]Ru]P(4) C(4)]Ru]P(3) C(1)]Ru]P(1) P(2)]Ru]P(1) C(2)]Ru]Sb(1) P(1)]Ru]Sb(1) C(4)]Ru]Sb(2) P(3)]Ru]Sb(2) C(2)]P(1)]Sb(1) C(3)]P(3)]Sb(2) C(9)]C(1)]P(2) P(2)]C(1)]Sb(1) C(5)]C(2)]P(1) C(13)]C(3)]P(4) P(4)]C(3)]P(3) C(17)]C(4)]Sb(2) 2.312(1) 2.096(5) 2.729(1) 2.298(6) 2.331(5) 2.442(2) 2.587(1) 1.755(6) 1.770(6) 1.768(6) 1.556(8) 1.559(7) 87.7(2) 72.2(2) 43.57(14) 43.04(13) 81.59(13) 80.5(2) 80.31(5) 80.01(14) 52.11(3) 48.28(12) 55.04(4) 99.2(2) 101.4(2) 118.7(4) 123.5(3) 118.1(4) 117.0(4) 125.3(3) 117.4(3)2186 J.Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 Scheme 2 (i), [Ru(C5R5)(MeCN)3][PF6] (R = H or Me), dme, 18 h, 25 8C; (ii) [W(CO)5(thf)], thf, 18 h, 25 8C; (iii) FeCl2, Li(C5Me5), dme, 18 h, 25 8C; (iv) [W(CO)5(thf )], thf, 18 h, 25 8C; (v) 2[Ru(C5Me5)(MeCN)3][PF6], dme, 18 h, 25 8C Ru Sb P P But But P Sb P But But R R R R R Fe P Sb P But But Me Me Me Me Me Ru P Sb P But But Me Me Me Me Me Ru Me Me Me Me Me Fe P Sb P But But Me Me Me Me Me Ru P Sb P But But Me Me Me Me Me (OC)5W (OC)5W 18 R = H 19 R = Me _ 24 26 29 25 PF6 ( i) ( ii) ( iv) ( iv) ( iii) C2But 2]2 which facilitates the preferential consumption of Li(C5H5), i.e.ferrocene formation, in the early stages of the reaction. The spectroscopic data for compounds 18 and 19 have been reported in the preliminary communication and support their proposed structures.12 The 31P-{1H} NMR spectrum of 24 is similar to its ruthenium analogue 19 in that it displays an [AX] pattern with characteristic 2J(PAPX) couplings (44 Hz).Interestingly, however, both signals are shifted downfield (ca. 20 ppm) with respect to those in the spectrum of 19. In addition, the low-field signal is significantly broadened which suggests it arises from the ring phosphorus atom adjacent to the quadrupolar antimony centre. Both the 1H and 13C NMR spectra of 24 also resemble those of 19. The molecular structure of compound 24 (Fig. 3, Table 2) is isomorphous to that of 19 which was also reported in the preliminary communication.12 During refinement it was found that the site labelled Sb is partially occupied by phosphorus (15%) while the sites P(1) and P(2) have 100% phosphorus occupancy. This observation is consistent with the solution NMR data and confirms that the known triphospholyl complex 7 (15%) cocrystallises with 24 (85%). Owing to this site disorder it is not valid to comment on the bond lengths and angles within the diphosphastibolyl ring.However, it is clear that both rings are planar, h5-ligated to the Fe and almost parallel [dihedral angle 2.1(1)8, cf. 28 in 19).12 The distance from the iron atom to the heterocycle centroid [1.661(2) Å] is significantly less than to the C5Me5 ring centroid [1.711(2) Å], the centroid]Fe]centroid angle being approximately linear at 1768 (cf. centroid]Ru]centroid 1778 in 19 12). As in the structure of 19, the unit cell of 24 contains two molecules which have a close intermolecular contact between centrosymmetrically related P(2) centres [3.515(3) Å, cf. 3.467(3) Å in 19 12] which is significantly less than the sum of the van der Waals radii for two phosphorus centres (3.8 Å).14 This generates a pseudo-dimeric structure binding both enantiomers of 24.In an attempt to utilise compounds 19 and 24 as ligands in the formation of secondary co-ordination complexes they were treated with tetrahydrofuran (thf ) solutions of [W(CO)5(thf )] at room temperature to afford the orange-yellow crystalline complexes [M(h5-P2SbC2But 2)(h5-C5Me5){W(CO)5}] (M = Ru 25 or Fe 26).Again 25 and 26 cocrystallise with small amounts (ca. 15–20%) of their triphospholyl counterparts [M(h5- P3C2But 2)(h5-C5Me5){W(CO)5}] (M = Ru 27 or Fe 29) respectively, which originate from the triphospholyl impurities, 7 and 8, in the starting materials, 19 and 24. A similar contamination has been reported for the h5: h1-diphosphaarsolyl complex 16 which also cocrystallises with its triphospholyl analogue [Fe(h5- P3C2But 2)(h5-C5H5){W(CO)5}].9 The contaminants 27 and 29 could not be separated from the major products despite repeated attempts at fractional recrystallisation. The spectroscopic data for the tungsten pentacarbonyl com-J.Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 2187 plexes 25 and 26 can be easily assigned despite the presence of the cocrystallised impurities 27 and 29. The 31P-{1H} NMR spectrum for each shows an [AX] pattern with characteristic 2J(PAPX) couplings.In addition, the signals corresponding to the phosphorus centres adjacent to the antimony centres display 183W satellites with couplings indicative of one-bond interactions. These signals are also shifted considerably upfield relative to the corresponding signals of the parent molecules 19 and 24. Therefore, it can be concluded that co-ordination to the tungsten pentacarbonyl fragments occurs solely through the phosphorus centres in the 1 positions of the rings which is not surprising considering the steric inaccessibility of the P in the 4 positions and the expected higher s character of the antimony lone pairs.The 1H and 13C NMR spectra for 25 and 26 are consistent with this assignment, the latter showing normal cisand trans- two-bond P]C couplings between the 1-phosphorus centres and the carbonyl carbons. Molecular ion peaks with the correct isotopic distributions were observed in the FAB mass spectra of both compounds.An examination of the use of [P2SbC2But 2]2 in the formation of a triple-decker complex analogous to the diphosphaarsolylbridged species 1710 was also undertaken. To this end [Ru- (C5Me5)(MeCN)3][PF6] was treated with half an equivalent of [P2SbC2But 2]2 to afford low yields of the orange crystalline compound [(h5-C5Me5)Ru(m-h5: h5-P2SbC2But 2)Ru(h5-C5Me5)]- [PF6] 29 after recrystallisation from CH2Cl2–hexane.The contamination of the ring precursor [P2SbC2But 2]2 with [P3C2But 2]2 resulted in a small amount (ca. 3%) of the known triphospholyl-bridged triple-decker complex [(h5-C5Me5)Ru(mh5: h5-P3C2But 2)Ru(h5-C5Me5)][PF6] 30 10 cocrystallising with 29. The 31P NMR spectrum of 29 displays an [AX] [2J(PAPX) = 32 Hz] pattern shifted ca. 80 ppm upfield from that of the parent complex 19, in addition to a septet for the PF6 counter anion. Three singlets that integrate in the ratio 30 : 9:9 are seen in the 1 H NMR spectrum of 29 and correspond to the Me groups of the two C5Me5 ligands and the two inequivalent tertiary butyl groups of the heterocyclic ligand respectively. The base peak for the positive-ion FAB mass spectrum corresponds to the triple-decker cation and exhibits the correct isotopic distribution.Conclusion A range of polyhetero-ferrocene and -ruthenocene complexes have been prepared from the 1,4,2-diphosphastibolyl ring anion [P2SbC2But 2]2.These complexes display similar properties to those of their counterparts derived from the 1,2,4-triphospholyl anion [P3C2But 2]2 with the exception of [Ru(h5-P2SbC2But 2)2] 20 which shows evidence for strong interring Sb ? ? ? Sb contacts both in solution and the solid state. We have also demonstrated the utility of the h5-co-ordinated diphosphastibolyl ring as an Fig. 3 Molecular structure of the cocrystallised mixture of compounds 24 and 7 (atomic labels represent 24) h1 ligand in the formation of two heterobimetallic, secondary co-ordination complexes. The remarkable stability of all the prepared complexes is presumably due to a high degree of aromaticity within the metal-co-ordinated diphosphastibolyl ring.This stability has prompted us to extend the current study to an examination of the co-ordination chemistry of the analogous 1,4,2-diphosphabismolyl ring anion [P2BiC2But 2]2 which we have recently synthesized.16 The results of these studies will be reported in forthcoming publications.Experimental General remarks All manipulations were carried out using standard Schlenk and glove-box techniques under an atmosphere of high-purity argon or dinitrogen. The solvents tetrahydrofuran, 1,2- dimethoxyethane and hexane were distilled over Na/K alloy then freeze/thaw degassed prior to use. Dichloromethane was distilled from CaH2 prior to use. The 1H, 13C and 31P NMR spectra were recorded on either a Bruker WM-250 or AM 400 spectrometer in C6D6, [2H8]toluene, CD2Cl2 or CDCl3 and were referenced to the residual 1H resonances of the solvent used (1H NMR), the 13C resonance of the deuteriated solvent (13C NMR) or to external 85% H3PO4, (d 0.0, 31P NMR) respectively.Mass spectra were recorded using VG 12-253 quad [70 eV, electron/ chemical ionisation (EI/CI)], or VG-autospec [Cs1 ions, 25 kV, 3-nitrobenzyl alcohol matrix (FAB)] instruments and conditions. Cyclic voltammetry was performed with electrochemical equipment from EG & G Princeton Applied Research and a model 273 potentiostat/galvanostat.The electrochemical cell was operated under an atmosphere of argon with platinum working and auxiliary electrodes and an Ag–AgCl reference electrode, in a MeCN–dme (1 : 1) solvent mixture (1 mmol dm23 solution of complex 23). A 0.1 mol dm23 solution of [NBu4]- [ClO4] was used as supporting electrolyte. Microanalyses were obtained from the University of Wales, Cardiff Microanalytical Table 2 Selected intramolecular distances (Å) and angles (8) for the cocrystallised mixture of compounds 24 and 7 with e.s.d.s in parentheses Sb]C(11) Sb]Fe Fe]C(2) Fe]C(1) Fe]C(12) Fe]P(1) P(1)]C(11) P(2)]C(12) C(1)]C(5) C(2)]C(3) C(3)]C(4) C(4)]C(5) C(5)]C(10) C(12)]C(17) C(11)]Sb]P(2) C(3)]Fe]C(4) C(3)]Fe]C(1) C(4)]Fe]C(1) C(2)]Fe]C(5) C(1)]Fe]C(5) C(12)]Fe]P(1) C(12)]Fe]P(2) P(1)]Fe]P(2) C(11)]Fe]Sb P(2)]Fe]Sb C(12)]P(2)]Sb C(1)]C(2)]C(3) C(3)]C(4)]C(5) C(13)]C(11)]P(1) C(1)]C(11)]Sb C(17)]C(12)]P(2) 2.088(5) 2.6415(8) 2.090(4) 2.109(4) 2.173(4) 2.3196(14) 1.754(5) 1.780(5) 1.435(7) 1.436(6) 1.418(7) 1.434(6) 1.487(7) 1.549(6) 88.28(13) 39.6(2) 67.1(2) 66.7(2) 67.0(2) 39.7(2) 46.06(12) 45.99(13) 84.52(5) 49.98(12) 57.36(3) 100.9(2) 107.7(4) 108.6(4) 116.1(3) 123.8(2) 116.9(3) Sb]P(2) Fe]C(3) Fe]C(4) Fe]C(5) Fe]C(11) Fe]P(2) P(1)]C(12) C(1)]C(2) C(1)]C(6) C(2)]C(7) C(3)]C(8) C(4)]C(9) C(11)]C(13) C(3)]Fe]C(2) C(2)]Fe]C(4) C(2)]Fe]C(1) C(3)]Fe]C(5) C(4)]Fe]C(5) C(12)]Fe]C(11) C(11)]Fe]P(1) C(11)]Fe]P(2) C(12)]Fe]Sb P(1)]Fe]Sb C(11)]P(1)]C(12) C(2)]C(1)]C(5) C(4)]C(3)]C(2) C(4)]C(5)]C(1) C(13)]C(11)]Sb C(17)]C(12)]P(1) P(1)]C(12)]P(2) 2.4135(13) 2.085(4) 2.100(5) 2.116(5) 2.216(4) 2.3611(14) 1.763(5) 1.433(6) 1.499(6) 1.500(7) 1.499(6) 1.505(7) 1.560(6) 40.2(2) 66.9(2) 39.9(2) 66.9(2) 39.8(2) 76.4(2) 45.42(12) 86.68(12) 84.59(13) 86.05(4) 101.1(2) 108.1(4) 108.1(4) 107.5(4) 118.9(3) 117.3(3) 125.4(3)2188 J.Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 Service. Melting points were determined in sealed glass capillaries under argon, and are uncorrected. Those for cocrystallised mixtures are included for the benefit of experimenters wishing to repeat the syntheses of these mixtures. Quoted approximate percentage yields for one component of a cocrystallised mixture were calculated by relating the integration of the 1H NMR spectrum of the mixture to the total weight yield on the basis of the transition-metal precursor. Quoted infrared data are for the most prominent absorbances for all components of the cocrystallised mixture if present.Microanalytical data could not be obtained for compounds that cocrystallised with triphospholyl impurities. The starting materials [Li(tmen)2][P2SbC2But 2],11 Li(C5Me5),17 [RuCl2(PPh3)3],18 [Ru(C5H5)(MeCN)3][PF6] 19 and [Ru(C5Me5)(MeCN)3][PF6]20 were prepared by published procedures.All other reagents were used as received. Syntheses [Ru(Á5-P2SbC2But 2)2] 20, 21 and [Ru(Á5-P2SbC2But 2)(Á5- P3C2But 2)] 22. The salt [Li(tmen)2][P2SbC2But 2] (0.86 g, 1.55 mmol) in dme (10 cm3) was added over 15 min to a suspension of [RuCl2(PPh3)3] (730 mg, 0.77 mmol) in dme (5 cm3) at 240 8C. The mixture was warmed to room temperature and stirred for 18 h. Volatiles were removed in vacuo and the residue was purified by column chromatography (60 mesh silica, hexane eluent) and subsequent crystallisation from hexane to afford a cocrystallised mixture of compounds 20–22, yield 110 mg, m.p. 154 8C. 31P-{1H} NMR (101.4 MHz, [2H8]toluene, 213 K): d 20, 80 (d, 2JPP = 32) and 85 (d, 2Jpp = 32); 21, d 29 (d, 2JPP = 37), 73 (d, 2JPP = 35), 83 (d, 2JPP = 37) and 92 (d, 2JPP = 35); 22 d 5 (dd, 1JPP = 413, 2JPP = 39), 56 (dd, 1JPP = 413, 2JPP = 39), 70 (virtual t, 2JPP = 39, 2JPP = 39), 71 (d, 2JPP = 36) and 98 (d, 2JPP = 36 Hz). EI mass spectrum for the mixture (70 kV): m/z 746 (20, 211, 3), 656 (221, 14), 69 (CBut1, 38) and 57 (But1, 100%).IR (for the mixture): n& /cm21 750m, 1230m, 1359m and 1378m. [Fe(Á5-P2SbC2But 2)2] 23. The salt [Li(tmen)2][P2SbC2But 2] (1.1 g, 1.98 mmol) in dme (10 cm3) was added over 15 min to a suspension of FeCl2 (130 mg, 1.03 mmol) in dme (5 cm3) at 240 8C. The mixture was warmed to room temperature and stirred for 18 h. Volatiles were removed in vacuo and the residue was extracted with hexane (30 cm3) and filtered.The filtrate was reduced in volume to ca. 5 cm3 and placed at 220 8C overnight to yield brown-black crystals of compound 23 (113 mg, 16%), m.p. 165–169 8C. NMR (C6D6, 298 K): 1H (400 MHz), d 1.31 (s, 9 H, But) and 1.86 (s, 9 H, But); 13C (100.6 MHz), d 36.9 [virtual t, C(CH3)3, 3JPC = 9], 37.2 [d, C(CH3)3, 3JPC = 9], 43.1 [virtual t, C(CH3)3, 2JPC = 19, 2JPC = 19 Hz], 43.3 [d, C(CH3)3, 2JPC = 18], 148.4 [d, SbCP, 1JPC = 82], 159.9 (dd, PCP, 1JPC = 82, 106); 31P- {1H} (101.4 MHz), d 76.3 (dd, 2JPP = 34, interring 2JPP = 8) and 95.9 (dd, 2JPP = 34, interring 2JPP = 8 Hz).EI mass spectrum (70 kV): m/z 700 (M1, 50), 562 (M1 2 2CBut, 19), 81 (C2But 2 1, 100), 69 (CBut, 68) and 57 (But1, 76%). IR: n& /cm21 720m, 1220w and 1480w (Found: C, 34.85; H, 6.1. Calc. for C20H36FeP4Sb2: C 34.3; H, 5.2%). [Ru(Á5-P2SbC2But 2)(Á5-C5H5)] 18. The salt [Li(tmen)2][P2Sb- C2But 2] (1.1 g, 1.98 mmol) in dme (10 cm3) was added over 15 min to a suspension of [Ru(C5H5)(MeCN)3][PF6] (880 mg, 2.02 mmol) in dme (10 cm3) at 240 8C.The mixture was warmed to room temperature and stirred for 18 h. Volatiles were removed in vacuo and the residue was extracted with hexane (30 cm3) and filtered. The filtrate was reduced in volume to ca. 5 cm3 and placed at 220 8C overnight to yield orange cocrystals of compounds 18 (ca. 90%) and 6 (ca. 10%) (363 mg, 38%), m.p. 86 8C. NMR (C6D6, 298 K) for 18: 1H (250 MHz), d 1.24 (s, 9 H, But), 1.44 (s, 9 H, But) and 4.65 (s, 5 H, C5H5); 13C (100.6 MHz), d 36.6 [d of d, C(CH3)3, 3JPC = 10.5 and 10.5] 38.6 [d, C(CH3)3, 3JPC = 10.6], 40.2 [d of d, C(CH3)3, 2JPC = 19.4 and 15.4], 40.9 [d, C(CH3)3, 2JPC = 16.9], 76.6 (s, C5H5), 140.7 (d of d, PCP, 1JPC = 86.2 and 110.7) and 149.6 (d, SbCP, 1JPC = 84.3); 31P-{1H} (101.4 MHz), d 27.8 (d, CPC, 2JPP = 35.6 Hz) and 64.7 (d, SbPC).EI mass spectrum (70 kV): m/z 488 (M1, 10), 350 (M1 2 2CBut, 48%) and 57 (But1, 100%). IR: n& /cm21 810s, 1220m, 1780w and 1690w.[Ru(Á5-P2SbC2But 2)(Á5-C5Me5)] 19. The salt [Li(tmen)2]- [P2SbC2But 2] (1.0 g, 1.8 mmol) in dme (10 cm3) was added over 15 min to a suspension of [Ru(C5Me5)(MeCN)3][PF6] (900 mg, 1.79 mmol) in dme (10 cm3) at 240 8C. The mixture was warmed to room temperature and stirred for 18 h. Volatiles were removed in vacuo and the residue was extracted with hexane (30 cm3) and filtered. The filtrate was reduced in volume to ca. 5 cm3 and placed at 220 8C overnight to yield orange cocrystals of compound 19 (ca. 90%) and 8 (ca. 10%) (385 mg, 37%), m.p. 123 8C. NMR (C6D6, 298 K) for 19: 1H (250 MHz), d 1.45 (s, 9 H, But), 1.60 (s, 9 H, But) and 1.83 (s, 15 H, C5Me5); 13C (100.6 MHz), d 13.9 [s, C5(CH3)5)], 36.8 [d of d, C(CH3)3, 3JPC = 10.7 and 10.7], 38.6 [d, C(CH3)3, 3JPC = 10.8], 41.2 [d of d, C(CH3)3, 2JPC = 19.1 and 15.7], 41.9 [d, C(CH3)3, 2JPC = 17.7], 93.1 (s, C5Me5), 142.1 (d of d, PCP, 1JPC = 83.5 and 108.2 Hz) and 152.9 (d, SbCP, 1JPC = 82.3); 31P-{1H} (101.4 MHz), d 30.1 (d, CPC, 2JPP = 41.4 Hz) and 80.0 (d, SbPC). EI mass spectrum (70 kV): m/z 558 (M1, 10), 420 (M1 2 2CBut, 12) and 57 (But1, 100%).IR: n& /cm21 720m, 1040w and 1210w. [Fe(Á5-P2SbC2But 2)(Á5-C5Me5)] 24. A mixture of [Li- (tmen)2][P2SbC2But 2] (1.0 g, 1.8 mmol) and Li(C5Me5) (0.25 g, 1.8 mmol) in dme (20 cm3) was added over 15 min to a suspension of FeCl2 (230mg, 1.8 mmol) in dme (10 cm3) at 240 8C. The mixture was warmed to room temperature and stirred for 18 h.Volatiles were removed in vacuo and the residue was extracted with hexane (20 cm3) and filtered. The filtrate was reduced to ca. 5 cm3 and placed at 220 8C overnight to yield brown crystals of compounds 24 (ca. 85%) and 7 (ca. 15%) (280 mg, 26%), m.p. 124 8C. NMR (C6D6, 298 K) for 24: 1H (250 MHz), d 1.64 (s, 9 H, But), 1.78 (s, 9 H, But) and 1.80 (s, 15 H, C5Me5); 13C (100.6 MHz), d 13.7 [s, C5(CH3)5], 36.8 [virtual t, C(CH3)3, 3JPC = 10 and 10], 39.0 [d, C(CH3)3, 3JPC = 11], 42.3 [d of d, C(CH3)3, 2JPC = 17 and 20], 43.1 [d, C(CH3)3, 2JPC = 18], 86.0 (s, C5Me5), 152.1 (d of d, PCP, 1JPC = 79 and 104) and 165.2 (d, SbCP, 1JPC = 79); 31P-{1H} (101.4 MHz), d 49.0 (d, CPC, 2JPP = 44) and 100.0 (d, SbPC, 2JPP = 44 Hz).EI mass spectrum (70 kV): m/z 513 (M1, 10), 457 (M1 2 But, 3), 375 (M1 2 2CBut, 19) and 57 (But1, 100%). IR: n& /cm21 700m and 1020m. [Ru(Á5-P2SbC2But 2)(Á5-C5Me5){W(CO)5}] 25. The compound [W(CO)6] (310 mg, 0.88 mmol) in thf (75 cm3) was irradiated (254 nm) for 6 h.Compound 19 (220 mg, 0.4 mmol) in thf (5 cm3) was added to the resulting yellow solution and the mixture stirred overnight. Volatiles were removed in vacuo and the residue purified by column chromatography (Kieselgel, hexane). The pale orange band was collected and concentrated to ca. 3 cm3 to yield orange cocrystals of compounds 25 (79%) and 27 (21%) (60 mg, 14%), m.p. 157 8C (decomp.). NMR (CD2Cl2, 298 K) for 25: 1H (250 MHz), d 1.39 (s, 9 H, But), 1.57 (s, 9 H, But) and 2.10 (s, 15 H, C5Me5); 13C (100.6 MHz), d 11.5 [s, C5(CH3)5], 34.4 [dd, C(CH3)3, 3JPC = 6 and 12], 36.0 [d, C(CH3)3, 3JPC = 12], 38.5 [d of d, C(CH3)3, 2JPC = 17 and 5], 40.2 [d, C(CH3)3, 2JPC = 18], 93.4 (s, C5Me5), 126.8 (d of d, PCP, 1JPC = 73 and 88), 152.4 (d, SbCP, 1JPC = 83), 196.0 [d, W(CO), 2JPC = 5, 1JWC = 127] and 198.5 (d, 2JPC = 28 Hz); 31P-{1H} (101.4 MHz), d 33.3 (d, SbPC, 2JPP = 52, 1JPW = 212) and 36.7 (d, CPC, 2JPP = 52 Hz).FAB mass spectrum (25 kV): m/z 882 (M1, 5), 828 (M1 2 2CO, 11), 772 (M1 2 4CO, 16), 742 (M1 2 5CO, 34) and 558 [M1 2 W(CO)5, 29%]. IR: n& /cm21 1941s (sh), 2066s. [Fe(Á5-P2SbC2But 2)(Á5-C5Me5){W(CO)5}] 26. The compound [W(CO)6] (157 mg, 0.45 mmol) in thf (40 cm3) was irradiatedJ. Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 2189 (254 nm) for 6 h. Compound 24 (88 mg, 0.2 mmol) in thf (5 cm3) was added to the resulting yellow solution and the mixture stirred overnight.Volatiles were removed in vacuo and the residue was purified by column chromatography (Kieselgel, hexane). The pale orange band was collected and concentrated to ca. 3 cm3 to yield orange cocrystals of compounds 26 (86%) and 28 (14%) (56 mg, 35%), m.p. 165 8C (decomp.). NMR (CDCl3, 298 K) for 26: 1H (250 MHz), d 1.45 (s, 9 H, But), 1.61 (s, 9 H, But) and 1.92 (s, 15 H, C5Me5); 13C (100.6 MHz), d 13.3 [s, C5(CH3)5], 36.4 [dd, C(CH3)3, 3JPC = 6 and 12], 38.2 [d, C(CH3)3, 3JPC = 11], 40.8 [d of d, C(CH3)3, 2JPC = 19 and 6], 43.0 [d, C(CH3)3, 2JPC = 18], 87.6 (s, C5Me5), 133.6 (d of d, PCP, 1JPC = 71 and 85), 165.3 (d, SbCP, 1JPC = 79), 197.2 [d, W(CO), 2JPC = 6, 1JWC = 127] and 200.0 (d, 2JPC = 28 Hz); 31P-{1H} (101.4 MHz), 46.0 (d, SbPC, 2JPP = 54, 1JPW = 214) and 47.8 (d, CPC, 2JPP = 52 Hz).FAB mass spectrum (25 kV): m/z 836 (M1, 15), 782 (M1 2 2CO, 8), 754 (M1 2 3CO, 13) and 512 [M1 2 W(CO)5, 61%].IR: n& /cm21 1940s, 1975s and 2067m. [(Á5-C5Me5)Ru(Ï-Á5:Á5-P2SbC2But 2)Ru(Á5-C5Me5)][PF6] 29. The salt [Li(tmen)2][P2SbCBut 2] (0.96 g, 1.7 mmol) in dme (10 cm3) was added over 15 min to a suspension of [Ru(C5Me5)- (MeCN)3][PF6] (1.60 g, 3.2 mmol) in dme (10 cm3) at 240 8C. The mixture was warmed to room temperature and stirred for 18 h. Volatiles were removed in vacuo and the residue was extracted with thf (20 cm3) and filtered through a 5 cm pad of neutral alumina. Volatiles were removed from the filtrate in vacuo and the residue was taken up in CH2Cl2 (0.5 cm3) and layered with hexane (5 cm3) to yield orange cocrystals of compounds 29 (97%) and 30 (3%) (30 mg, 2%), m.p. 225 8C (decomp.). NMR (CDCl3, 298 K) for 29: 1H (250 MHz), d 1.27 (s, 9 H, But), 1.54 (s, 9 H, But) and 1.74 (s, 30 H, C5Me5); 13C (100.6 MHz), d 12.2 [s, C5(CH3)5], 38.2 [d of d, C(CH3)3, 2JPC = 11 and 14], 39.1 [virtual t, C(CH3)3, 3JPC = 10 and 10], 39.2 [d, C(CH3)3, 2JPC = 15], 41.0 [d, C(CH3)3, 3JPC = 10], 93.2 (s, C5Me5) and 119.5 (d, SbCP, 1JPC = 108); 31P-{1H} (101.4 MHz), d 1.2 (d, 2JPP = 32), 249.7 (d, 2JPP = 32) and 2143.9 (spt, PF6, 1JPF = 713 Hz).FAB mass spectrum (25 kV): m/z 794 Table 3 Crystal data for the cocrystallised mixtures [Ru(h5- P2SbC2But 2)2] 20, 21, [Ru(h5-P2SbC2But 2)(h5-P3C2But 2)] 22 and [Fe(h5- P2SbC2But 2)(h5-C5Me5)] 24, [Fe(h5-P3C2But 2)(h5-C5Me5)] 7 Chemical formula M Space group Crystal system a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 m(Mo-Ka) cm21 Absorption correction, Tmax, Tmin F(000) Reflections collected No.unique reflections Crystal size/mm q Range/8 R a (on F) wRb (on F2 for all data) x in weighting schemec 20–22 C20H36P4.47RuSb1.53 702.27 P21/n Monoclinic 16.638(2) 9.9790(7) 17.341(2) 112.890(6) 2652.4(4) 4 1.759 23.91 1.18, 0.85 1380 7001 3652 0.28 × 0.24 × 0.18 2–25 0.0446 0.0937 0.0483 24, 7 C20H33FeP2.15Sb0.85 499.39 P1� Triclinic 8.578(1) 10.465(1) 13.889(1) 96.75(1) 106.51(2) 109.97(2) 1091.2(2) 2 1.520 18.79 1.21, 0.82 509 4392 3031 0.32 × 0.22 × 0.20 2–25 0.0380 0.0797 0.0314 a S(DF)/S(Fo).b [Sw(DF2)2/Sw(Fo 2)2]� �� . c w = 1/[s2(Fo 2) 1 (xP)2] where P = [max(Fo 2) 1 2(Fc 2)]/3. (M1 2 PF6, 100) and 420 (M1 2 PF6 2 2CBut, 42%). IR: n& /cm21 1680w (br). Crystallography Cocrystals of compounds 20–22 and 24 and 7 suitable for structure determination were grown from hexane and mounted in oil. Intensity data were measured on a FAST21 area-detector diffractometer at 150(2) K using Mo-Ka radiation (l 0.710 69 Å).Both structures were solved by heavy-atom methods (SHELXS 8622) and refined by least squares using the SHELXL 9323 program. The structures were refined on F2 using all data. Neutral-atom complex scattering factors were employed.24 Empirical absorption corrections were carried out by the DIFABS method.25 Crystal data, details of the data collections and refinement are given in Table 3. Anisotropic thermal parameters were refined for all non hydrogen atoms.The hydrogen atoms in both structures were included in calculated positions (riding model). During refinement of the structure of (20–22) a site disorder was found to exist in which the sites labelled Sb(1), Sb(2) and P(1) are partially occupied by phosphorus (51), phosphorus (13) and antimony (17%) respectively. A site disorder is also present in the structure of 24 and 7 in which the site labelled Sb is partially occupied by phosphorus (15%).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 186/497. Acknowledgements We gratefully acknowledge financial support from The Leverhulme Trust (to S. J. B.), The University of Wales, Swansea (studentship for M.D. F.), The Nuffield Foundation and Johnson Matthey for a loan of ruthenium salts. We also thank ProfeB. Hursthouse and Mr. D. E. Hibbs (EPSRC Crystallography Service, Cardiff ) for the X-ray data collection and many helpful discussions. References 1 F. Mathey, Coord. Chem. Rev., 1994, 137, 1, and refs. therein. 2 R. Bartsch, P. B. Hitchcock and J. F. Nixon, J. Chem. Soc., Chem. Commun., 1987, 1146. 3 P. B. Hitchcock, J. F. Nixon and R. M. M. Matos, J. Organomet. Chem., 1995, 490, 155. 4 R. Bartsch, P. B. Hitchcock and J. F. Nixon, J. Organomet. Chem., 1988, 340, C37. 5 C. Müller, R. Bartsch, A. Fischer and P. G. Jones, J. Organomet. Chem., 1993, 453, C16. 6 A. J. Ashe III and S. Al-Ahmad, Adv. Organomet. Chem., 1996, 39, 325 and refs. therein. 7 O. J. Scherer, C. Blath and G. Wolmershäuser, J. Organomet. Chem., 1990, 387, C21; B. Rink, O. J. Scherer and G. Wolmershäuser, Chem. Ber., 1995, 128, 71. 8 M. L. Sierra, C. Charrier, L. Richard and F. Mathey, Bull. Soc. Chim. Fr., 1993, 521. 9 S. S. Al-Juaid, P. B. Hitchcock, J. A. Johnson and J. F. Nixon, J. Organomet. Chem., 1994, 480, 45. 10 P. B. Hitchcock, J. A. Johnson and J. F. Nixon, Organometallics, 1995, 14, 4382. 11 M. D. Francis, D. E. Hibbs, M. B. Hursthouse, C. Jones and K. M. A. Malik, J. Organomet. Chem., 1997, 527, 291. 12 M. D. Francis, D. E. Hibbs, M. B. Hursthouse, C. Jones and K. M. A. Malik, Chem. Commun., 1996, 1591. 13 C. Janiak and H. Schumann, Adv. Organomet. Chem., 1991, 33, 291, and refs. therein. 14 Parameter Adjustment in NMR by Iteration Calculation, version 820601, Brüker spectrospin. 15 J. Emsley, The Elements, Oxford University Press, 2nd edn., 1991. 16 S. J. Black and C. Jones, unpublished work.2190 J. Chem. Soc., Dalton Trans., 1997, Pages 2183–2190 17 D. W. Macomber and M. D. Rausch, J. Am. Chem. Soc., 1983, 105, 5325. 18 P. S. Halliman, T. A. Stephenson and G. Wilkinson, Inorg. Synth., 1970, 12, 237. 19 T. P. Gill and K. R. Mann, Organometallics, 1982, 1, 485. 20 J. L Schrenk, A. M. McNair, F. B. McCormick and K. R. Mann, Inorg. Chem., 1986, 25, 3501. 21 J. A. Darr, S. A. Drake, M. B. Hursthouse and K. M. A. Malik, Inorg. Chem., 1993, 32, 5704. 22 G. M. Sheldrick, Acta Crystallogr., Sect. A, 1990, 46, 467. 23 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 24 International Tables for X-Ray Crystallography, eds. J. A. Ibers and W. C. Hamilton, Kynoch Press, Birmingham, 1974, vol. 4. 25 N. P. C. Walker and D. Stuart, Acta Crystallogr., Sect A, 1983, 39, 158; adapted for FAST geometry by A. I. Karavlov, University of Wales, Cardiff, 1991. Received 6th February 1997; Paper 7/00869D

ISSN:1477-9226    

DOI:10.1039/a700869d

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 2191 pH-Dependent competition between Í2N7,O(P) macrochelation and Ï-N1,N7 oligomer formation for (Á6-arene)RuII complexes of adenosine and guanosine 59-mono-, -di- and -tri-phosphates Sandra Korn and William S. Sheldrick * Lehrstuhl für Analytische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany The pH-dependent reaction of [Ru(h6-C6H6)(D2O)3]21 with adenosine and guanosine 59-mono-, -di- and -tri-phosphates has been studied by 1H and 31P-{1H} NMR spectroscopy.Diastereomeric m-1kN1:2k2N6, N7 co-ordinated cyclic trimers of the type [{Ru(59-AMP)(h6-C6H6)}3] predominate for adenosine 59-monophosphate (59-AMP22) in the range pH* 3.30–9.18. An X-ray structural analysis of the RuSRuSRuS diastereomer [{Ru- (59-AMP)(h6-p-MeC6H4Pri)}3]?7.5H2O 1b established a pronounced degree of conformational flexibility in the sugar and phosphate residues. In contrast to 59-AMP22, cyclic trimers cannot be observed in more strongly acid solution (pH* < 3.16) for the equilibrium system 59-ATP–(h6-C6H6)RuII (59-ATP42 = adenosine 59-triphosphate) and remain relatively minor species even at neutral or higher pH* values.As confirmed by pronounced low-field 31P-{1H} NMR shifts of up to 7.8 and 8.6 ppm for the b- and g-phosphorus atoms, k3N7, O(P b), O(Pg) macrochelates provide the dominant metal species in acid solution. Time-dependent NMR studies for 59-ADP– (h6-C6H6)RuII (59-ADP32 = adenosine 59-diphosphate) indicated that initial macrochelation of this nucleotide is followed by cleavage of the b-phosphate group and formation of cyclic trimers of 59-AMP22.Reaction of guanosine 59-monophosphate (59-GMP22) with [Ru(h6-C6H6)(D2O)3]21 afforded kN7-co-ordinated 1 : 1 and 2 : 1 complexes in the range pH* 3.69–8.38. In addition to analogous 1 : 1 and 2 : 1 species, k3N7, O(Pb), O(Pg) macrochelates are observed for the 59-GTP–(h6-C6H6)RuII equilibrium system (59-GTP42 = guanosine 59- triphosphate) in acid solution.Initial macrochelation in the 59-GDP–(h6-C6H6)RuII system (59-GDP32 = guanosine 59-diphosphate) again leads to rapid cleavage of the terminal b-phosphate function. The presence of metal ions such as Mg21 is generally a prerequisite for enzymatic reactions involving nucleotides. Both hard oxygen atoms in the phosphate and sugar moieties and borderline aromatic nitrogen atoms in the purine or pyrimidine residues are available as potential binding sites in these structurally flexible bioligands.1–3 Differences in the basicities of the endocyclic base nitrogen sites have been demonstrated to be of crucial importance for the selective recognition of metal ions by nucleic acids and their constituents.4 For instance, it is well known5 that the widely used antitumour agent cis-[PtCl2- (NH3)2] preferably binds to the guanine and not the adenine bases of DNA.For borderline metal ions such as Fe21, Cu21 or Zn21 with their rather pronounced affinity for aromatic nitrogen sites, significant binding to the phosphate oxygen atoms might also be expected. Such a simultaneous interaction with two component parts of a nucleotide could provide a further degree of fine tuning for the selective recognition of metal ions.The possibility of macrochelate formation by purine nucleotides through co-ordination of a metal centre by both the nucleic base and phosphate residues was first discussed by Szent-Györgyi 6 in 1956.Despite continuous interest in this suggestion, 30 years were to pass before definitive kinetic and spectroscopic confirmation of simultaneous direct metal binding to both the phosphate group and the purine N7 atom was presented.7–10 Mononuclear macrochelates of the type [MLx- {59-NMP-k2N7,O(Pa)}]n1 have now been established by NMR investigations for the cis-(CH3ND2)2PtII,7a,b Cl(dmso)2(H2O)- RuII (dmso = dimethyl sulfoxide),7c (H2O)(tren)RhII [tren = tris- (2-aminoethyl)amine] 7d and (cp)2MoIV (cp = h5-C5H5) 9 fragments with purine 59-nucleoside monophosphates (59- H2NMP).Fast atom bombardment mass spectrometric and kinetic studies for the product of the reaction between cis- [Pt(H2O)2(NH3)2]21 and 59-GMP22 or 59-(29-deoxy)GMP22 also indicate direct intramolecular co-ordination of both nucleotide residues.8 The increased stability of various 59-NMP22 complexes of divalent 3d ions in comparison to expected values for phosphate-only co-ordination demonstrates that macrochelated species must be present in appreciable concentration.3,4 Support for inner-sphere co-ordination of both the phosphate group and the purine N7 atom is provided by kinetic studies 11 and modelling considerations.12 Purine 59-nucleoside di- and tri-phosphates (59-NDP32, 59- NTP42) can form a, b- and a, b, g-phosphate-co-ordinated inner- and outer-sphere macrochelates of the types I and II (Scheme 1 for 59-ATP42) with divalent 3d ions in aqueous solution.Sigel 3 has estimated the extent of inner-sphere coordination by comparing stability constants determined by potentiometric and ultraviolet absorption techniques. The extent of formation of type I complexes is found to vary between ca. 10% for Mn21 and 67% for the softer Cu21 cation. Proton and 31P NMR evidence has been presented by Marzilli and co-workers 7b that cis-(CH3ND2)2PtII co-ordinates to purine 59-nucleoside triphosphates in dilute D2O solution in an intramolecular fashion to both N7 and a g-phosphate oxygen atom.These authors also observed the involvement of N1 in Pt binding at a Pt : 59-ATP42 ratio greater than one and postulated Scheme 1 N7 Inner- and outer-sphere macrochelates for the reaction between 59-ATP42 and divalent 3d ions2192 J. Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 the formation of m-N1,N7 bridged oligomers in competition with k2N7,O(Pg) macrochelation. Analogous oligomers have been reported for the interaction of the 59-monophosphates of adenosine, guanosine and inosine with (en)PdII (en = ethane- 1,2-diamine) 13 and Harada and co-workers 14 have proposed that the apposite 59-GMP22 complex is a cyclic tetramer.On binding to N7, PdII enhances the deprotonation of N1 in guanosine and inosine derivatives 15 with the result that kN7 coordinated 1 : 2 complexes such as [Pd(59-HGMP-kN7)2(en)] exhibit an increased tendency to disproportionate to m-N1,N7 bridged oligomers and unbound 59-GMP22 on raising the pH value.13b The recent characterisation of m-1kN7:2kN9 coordinated tetramers such as [{RuCl(m-HAde)(h6-C6H6)}4]Cl4 (HAde = adenine) 16a and m-1kN1:2k2N6,N7 co-ordinated trimers (Scheme 2) such as [{Ru(m-AdoH21)(h6-C6H6)}3][CF3SO3]3 (Ado = adenosine) 16b and [{Rh(h-C5Me5)(m-59-AMP)}3] 17 suggests that the formation of cyclic oligomers may well be typical for the reaction of potentially bi- and tri-dentate fragments of heavier Group 8–10 transition metals with purines and their nucleoside 59-phosphates.To our knowledge no systematic investigation of the competition between macrochelation and oligomer formation has previously been reported for the reaction of purine nucleoside 59-mono-, -di- and -tri-phosphates with borderline or soft metal cations. We now describe a pH-dependent 1H and 31P NMR study of the interaction of the (h6-arene)RuII fragment (h6-arene = C6H6 or p-cymene) with adenosine and guanosine nucleotides. X-Ray structural studies are presented where appropriate.Results and Discussion Selected 1H NMR spectra for the aqueous 59-AMP–(h6-C6H6)- RuII equilibrium system (molar ratio R59-AMP:Ru = 1.05) at pH* values (pH meter readings uncorrected for deuterium isotope effects) in the range 3.30–9.18 are presented in Fig. 1. A pronounced downfield shift of H8 accompanied by an opposite shift for H2 is characteristic for the m-1kN:2k2N6,N7 co-ordination mode of bridging adenine derivatives in cyclic trimers of the type [{Ru(m-AdoH21)(h6-C6H6)}3] 16b or [{Rh(h-C5Me5)- (m-59-AMP)}3].17 The signal pair 1,19 [pH* 3.30; d 7.64, 7.69 (H2), 8.88, 8.92 (H8)] may, therefore, be unambiguously assigned to the diastereomeric pair (RuSRuSRuS/RuRRuRRuR) of the trinuclear cation [{Ru(59-HAMP)(h6-C6H6)}3]31 at pH* values below 5.Following loss of the second nucleoside 59- phosphate acid protons in the range pH* 5–7, this signal pair will correspond to the neutral cyclic trimer [{Ru(59-AMP)- (h6-C6H6)}3] in alkaline solution [pH* 9.18; d 7.66, 7.71 (H2), 9.05, 9.08 (H8)].The presence of a diastereomeric pair in solution also causes a splitting of the benzene proton resonance at higher pH* values [pH* 9.18; d 6.00, 6.01 (h6-C6H6)]. Diastereomer 19 clearly dominates in the investigated pH* range. The apparent inversion of the concentration ratio at pH* 5.30 is caused by a partial crystallisation of the dominant isomer from weakly acidic equilibrium solutions (range pH* 4.13– Scheme 2 m-1kN1:2k2N6,N7 Bridging 16b in the cyclic trimer [{Ru(m- AdoH21)(h6-C6H6)}3]31 5.84) at the relatively high concentration (0.050 mol l21) employed for the NMR study.Signals 2 in Fig. 1 correspond to the H2 and H8 resonances of free 59-HAMP2/59-AMP22; signal 3 is only observed at higher pH values and belongs to the dinuclear cation [{Ru(h6-C6H6)}2(m-OH)3]1.18 At lower pH* values (3.30, 5.30) the 31P NMR spectra of the 59-AMP–(h6-C6H6)RuII equilibrium system (R = 1.05) contain several neighbouring resonances in the range (d 0.5–1.1) typical for the non-coordinated adenosine 59-monophosphate P atom.These signals shift to lower field (d 4.50–4.67 at pH* 9.18) in the range pH* 4.5–7.5 in accordance with a second deprotonation of the phosphate group at a typical pKs value of ca. 6.7c In contrast to NMR studies on the 59-AMP–(h5-C5Me5)RhIII equilibrium system, 17b which exhibits a number of 31P resonances (pH* 5.14) with 8–12 ppm downfield shifts reminiscent of N7/O(Pa) macrochelate formation,7–10 no evidence could be found for phosphate co-ordination of the (h6-C6H6)RuII cation even at a 2 : 1 excess of the organometallic fragment.The cyclic trimer [{Ru(59-HAMP)(h6-p-MeC6H4Pri)}3]- [CF3SO3]3 1a can be prepared by reaction of [Ru(h6-p- MeC6H4Pri)(Me2CO)3]21 with 59-H2AMP in acetone at room temperature. Confirmation of the trimeric structure is provided by the FAB mass spectrum of 1a, which contains a molecular ion [M 2 2CF3SO3]1 at m/z 1892.Slow evaporation of an aqueous solution of 1a provided crystals of [{Ru(59-AMP)- (h6-p-MeC6H4Pri)}3]?7.5H2O 1b suitable for an X-ray structural analysis (Fig. 2). The asymmetric unit of 1b can contain up to 7.5 water molecules distributed over 11 possible sites. As depicted in Fig. 3, the cyclic trimer of the 59-AMP22 dianion, which crystallises as the RuSRuSRuS diastereomer, exhibits a pronounced degree of conformational flexibility in its sugar and phosphate residues.Although all three ribose moieties display a basically C39-endo conformation, their extent of twist differs, as may be gauged from the respective pseudo-rotation angles 19 P of 7.0, 15.7 and 27.38. In contrast to the second nucleotide, whose torsion angle c [C4]N9]C19]O49 2 179.38] lies in the anti-range typical for free purine 59-nucleotides,19 both nucleotides 1 and 3 adopt a ‘high-anti’ conformation (c = 286.9, 290.98) at the glycosidic bond N9]C19.A further interesting conformational difference is provided by the gauche, Fig. 1 Selected pH*-dependent 1H NMR spectra for the aqueous equilibrium system 59-AMP–(h6-C6H6)RuII at molar ratio R59-AMP:Ru- = 1.05 (cRu = 0.050 mol l21). The signal assignment is as follows: 1,19, cyclic trimers [{Ru(59-AMP)(h6-C6H6)}3]; 2,2 59-AMP22; 3, [{Ru(h6-C6H6)}2(m-OH)3]1J. Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 2193 trans siting (torsion angles O59]C59]C49]O49, O59]C59]C49]C39 = g) of the phosphate backbone in nucleotide 1 (torsion angles P]O59]C59]C49 = b, C59]C49]C39]O39 = d).Both nucleotides 2 and 3 exhibit the gauche, gauche conformation required for macro- Fig. 2 Molecular structure of [{Ru(59-AMP)(h6-p-MeC6H4Pr)}3] 1b (p-cymene substituents have been omitted for clarity) Fig. 3 Conformations of the nucleotide ligands 59-AMP22 in compound 1b chelation. Compound 1b provides the first example of a purine 59-nucleotide cyclic oligomer to be structurally characterised by X-ray analysis.The interaction of [Ru(h6-C6H6)]21 (aq) with adenosine 59-triphosphate at a molar ratio R59-ATP:Ru of 1.0 was investigated by 1H and 31P-{1H} NMR spectroscopy at pH* values in the range 1.82–7.82. Selected NMR spectra are presented in Figs. 4 and 5. The pronounced downfield shift for H8 accompanied by an upfield shift for H2 allows an unequivocal assignment of the signal pair 3,39 to m-1kN1:2k2N6,N7 co-ordinated cyclic trimers of the type [{Ru(59-H2ATP)(h6-C6H6)}3] at pH* values of 5.77 and higher.In striking contrast to the analogous 59-AMP–(h6-C6H6)RuII equilibrium system, this diastereomeric pair (RuSRuSRuS, RuRRuRRuR) cannot be observed in more strongly acid solution (pH* < 3.16) and remains a relatively minor species even at neutral or higher pH* values. Com- Fig. 4 Selected pH*-dependent 1H NMR spectra for the aqueous equilibrium system 59-ATP–(h6-C6H6)RuII at the molar ratio R59-ATP:Ru = 1.0 (cRu = 0.050 mol l21).The signal assignment is as follows: 1,19, macrochelate [Ru{59-H2ATP-k3N7,O(Pb),O(Pg)}(h6-C6H6)] (pH* 3.16); 2, kN1 co-ordinated species; 3,39, cyclic trimers [{Ru(59-H2ATP)(h6- C6H6)}3] (pH* 7.78); 4,59-H2ATP22; signals 5 and 6 could not be assigned unequivocally Fig. 5 Selected pH*-dependent 31P-{1H} NMR spectra for the aqueous equilibrium system 59-ATP–(h6-C6H6)RuII at the molar ratio R59-ATP:Ru = 1.0 (cRu = 0.050 mol l21).The signal assignment is as for Fig. 42194 J. Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 parison of the 1H and 31P-{1H} NMR spectra presented in Figs. 4 and 5 indicates that resonances 1,19 may be assigned to k3N7,O(Pb), O(Pg) co-ordinated complexes, signals 4 to free adenosine 59-triphosphate. As may be followed in Fig. 6(a) and 6(b), the base protons of this nucleotide experience a characteristic shift to higher field in the range pH* 2–6 [pH* 1.82, d 8.37 (H2), 8.56 (H8); pH* 5.77, d 8.17 (H2), 8.45 (H8)] corresponding to deprotonation of the pyrimidine nitrogen N1 (pKa = 3.9 20).The pH dependence of the analogous H2 and H8 resonances for the species 1,19 provides clear evidence for an N7 co-ordination. Not only is the upfield shift more pronounced for these metal complexes, it also takes place in a solution more acid by ca. one pH unit [pH* 1.82, d 8.47, 8.47 (H2), 8.6, 8.69 (H8); pH* 5.21, d 8.25, 8.26 (H2), 8.35, 8.39 (H8)].An enhancement of N1 deprotonation by up to two pKs units is typical for N7 co-ordinated adenine derivatives 15,21 and has also been reported for N7/O(Pa) macrochelation of the (Cp)2MoIV fragment.9b The pronounced low-field shifts of respectively up to 7.8 and 8.6 ppm for the b- and g-phosphorus atoms of species 1,19 in the range pH* 1.82–7.78 depicted in Fig. 5 are characteristic for metal–phosphate binding.7–9 Confirmation of the presence of a b-, a-phosphate six-membered ring in 1,19 is provided by a P–P COSY (correlation spectroscopy) spectrum recorded at pH* 6.7.The low-field g-phosphorus atoms at d 21.19 and 21.04 are found to couple only with the low-field b-phosphorus atoms at d 214.13 and 213.88. Within the pH* range investigated, the resonances for the non-co-ordinated a-phosphorus atoms of complexes 1,19 experience only a gradual shift from d 211.06 (pH* 2.61) to 29.65 (pH* 7.78) and lie close to those of other species and the free nucleoside 59-triphosphate. As may be followed in Fig. 6(c), metal co-ordination of the g-phosphate group in 1,19 leads to a marked enhancement of the second deprotonation at this position as evidenced by the earlier low- field shift of the g-phosphorus resonance in comparison to adenosine 59-triphosphate itself (signal 4). An analogous reduc- Fig. 6 Chemical shifts of the (a) H8, (b) H2 and (c) phosphate Pg NMR resonances as a function of pH* for the 59-ATP–(h6-C6H6)RuII equilibrium system.The signal assignment is as for Fig. 4 tion in the second pKs value has been described for N7/O(Pa) and N7/O(Pg) macrochelates.7b,c,9 The above 1H and 31P-{1H} NMR pH-dependent titrations and, in particular, the absence of a-phosphate co-ordination for the equimolar equilibrium systems 59-AMP–(h6-C6H6)RuII, 59- ADP–(h6-C6H6)RuII (see below) and 59-ATP–(h6-C6H6)RuII provide very strong evidence for k3N7,O(Pb),O(Pg) macrochelation in complexes 1,19.Both the ruthenium and bphosphorus atoms are chiral in such macrochelates, meaning that four diastereomers (Figs. 7, 8) are possible, of which at least two give rise to the separate 1H and 31P-{1H} NMR resonances at pH* > 4.38. The appearance of additional signals in the H2/H8 region of 1,19 indicates that the presence of further diastereomers cannot be ruled out at lower pH values. As may be seen in Figs. 7 and 8, the adoption of opposing RuS or RuR chiralities requires strikingly different anti or syn conformations at the glycosidic bond N9]C19. The C59]O59 nucleoside bond exhibits a gauche, gauche orientation for the S-configurated metal centre in contrast to the trans, gauche orientation found in the DRuR and LRuR diastereomers.As the anti conformation is typically observed for metal complexes of purine 59- nucleotides,2,22 it is possible that species 1,19 will be the DRuS and LRuS isomers depicted in Fig. 7. The NMR signals for complex 2 in the 59-ATP–(h6- C6H6)RuII equilibrium system are only found at pH* > 4.38, i.e.at values for which the pyrimidine nitrogen N1 (pKa 3.9) is deprotonated in adenosine 59-triphosphate. The pronounced high-field shift of its H2/H8 resonances [pH* 4.38, d 8.18 (H8), 7.90 (H2); pH* 7.78, d 8.15 (H8), 7.87 (H2)] in comparison to the macrochelates 1,19 and the rapid increase in its concentration at Fig. 7 Structural models for k3N7,O(Pb),O(Pg) co-ordinated DRuS and LRuS diastereomersJ.Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 2195 higher pH values both indicate that species 2 must correspond to a kN1 co-ordinated complex. As the chemical shifts of its a-, b- and g-phosphorus atoms are recorded at ppm values similar to those of free adenosine 59-triphosphate, an inner-sphere phosphate co-ordination can be ruled out. The observation 23 of very similar H2/H8 resonance positions for [{Rh(h5-C5Me5)- (m-OH)(9-mhpx-kN1)}2] (9-Hmhpx = 9-methylhypoxanthine) suggests that the signals 2 in the 59-ATP–(h6-C6H6)RuII equilibrium system will correspond to an analogous hydroxobridged dimeric complex [{Ru(h6-C6H6)(m-OH)(59-H2ATPkN1)} 2]22. Signals 5 and 6, of which the latter belongs to a 1 : 2 species (pH 3.16), could not be assigned with certainty.Two inner-sphere macrochelates with respectively k3N7, O(Pa), O(Pb) and k2N7, O(Pb) co-ordination can be postulated for the reaction of adenosine 59-diphosphate with the (h6- C6H6)RuII fragment (Scheme 3).In fact, an equimolar reaction solution 59-ADP–(h6-C6H6)RuII in the range pH* 2.65–5.92 is Fig. 8 Structural models for k3N7,O(Pb),O(Pg) co-ordinated DRuR and LRuR diastereomers Scheme 3 Possible k3N7,O(Pa),O(Pb) and k2N7,O(Pb) macrochelates in the aqueous 59-ADP–(h6-C6H6)RuII system found to contain a complex 1 the 1H and 31P-{1H} NMR chemical shifts (Figs. 9 and 10) of which are in accordance with the former formulation. For instance its a- and b-phosphorus resonances are shifted by respectively ca. 5.5 and 8.5 ppm to lower field in comparison to the free nucleotide. However the remaining 31P-{1H} NMR signals are rather broad and a timedependent study demonstrates that O(Pa), O(Pb) co-ordination is presumably followed by cleavage of the terminal phosphate group. The dramatic change in the appearance of the 1H and 31P-{1H} NMR spectra of the 59-ADP–(h6-C6H6)RuII reaction system (initial pH* 5.61) over a period of 14 d is illustrated by the selected spectra presented in Figs. 9 and 10. Two major species 1 and 2 are present in the reaction solution after 1 h. As was discussed for the 59-ATP–(h6-C6H6)RuII system, the high- field resonances 2 may be assigned to an N1-co-ordinated complex without phosphate binding. An apparently metal-assisted phosphate cleavage then leads to total disappearance of both 1 and 2 within 14 d and the exclusive formation of a variety of m-1kN1:2k2N6, N7 co-ordinated cyclic trimers 3 with their typical pronounced opposite H2 and H8 chemical shifts (ca. 7.7, 9.0 ppm). The occurrence of more than two 1H resonances for each of these adenine protons and the observation of low-intensity a- and b-phosphorus signals in the 31P-{1H} NMR spectrum Fig. 9 Time dependence of the 1H NMR spectrum of the 1 : 1 59- ADP–(h6-C6H6)RuII system at pH* 5.61 (c = 0.050 mol l21) Fig. 10 Time dependence of the 31P{1H} NMR spectrum of the 1 : 1 59-ADP–(h6-C6H6)RuII system at pH* 5.61 (c = 0.050 mol l21)2196 J.Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 after 14 d indicates the presence of mixed 59-AMP–59-ADP cyclic trimers. Free H2PO4 2 provides the 31P-{1H} NMR singlet at ca. d 1.1. The promotion of phosphate cleavage by k2N7, O(P) macrochelation has been reported for other metals.24 In contrast to adenosine 59-diphosphate, a time-dependent study of the 59- ATP–(h6-C6H6)RuII reaction system offers no evidence for significant hydrolysis of the pyrophosphate residue over a similar period of time.This finding suggests that the marked reduction in strain for k3N7, O(Pb), O(Pg) in comparison to k3N7, O(Pa), O(Pb) co-ordination will lead to an increased thermodynamic and/or kinetic stability of adenosine 59-triphosphate macrochelates with respect to phosphate cleavage and reorganisation to m-1kN1:2k2N6, N7 cyclic trimers. Guanosine 59-nucleotides In striking contrast to the co-ordination behaviour of 59- AMP22, reaction of [Ru(h6-C6H6)(D2O)3]21 with guanosine 59-monophosphate leads solely to the formation of kN7-coordinated 1 : 1 (1) and 2 : 1 (2) complexes in the range pH* 3.69– 8.38 (Fig. 11). As cyclic trimer formation with m-1kN1:2kN7,O6 bridging has been reported 23 for the 9-ethylhypoxanthine–(h5- C5Me5)RhIII equilibrium system, it seems reasonable to assume that the steric requirements of the guanine 2-amino substituent adjacent to the required binding site N1 will prevent an analogous co-ordination mode for 59-GMP22.In comparison to the free 59-nucleotide (signal 3), the H8 protons in species 1 and 2 exhibit a low-field shift [pH* 5.56 d 8.50 (1); 8.55, 8.67 (2); 8.02 (3)] in a range 0.48–0.65 ppm characteristic for N7 co-ordination. The 2 : 1 complex [Ru- (59-HGMP)2(h6-C6H6)(D2O)] (2) dominates for pH* values above 4.65. Absence of phosphate co-ordination is confirmed by the registration of 31P-{1H} resonances at chemical shift values typical for the free nucleotide (pH* 3.69, d 0.77 (1); 1.03, 1.28 (2); pH* 8.38, d 4.55, 4.71 (2); 4.13 (3)].Loss of the second phosphate proton with its pKa value of ca. 6 generates a characteristic shift of both the H8 and a-phosphorus resonances to lower field over the range pH* 4.5–7.5. Model complex 2, prepared by reaction of [{RuCl2(h6-C6H6)}2] with 9-ethylguanine (9-egua) in methanol after addition of 2 equivalents of Ag- (O3SCF3), exhibits a co-ordination pattern similar to that of Fig. 11 Selected pH*-dependent 1H NMR spectra for the aqueous equilibrium system 59-GMP–(h6-C6H6)RuII at the molar ratio R59-GMP:Ru = 1.0 (cRu = 0.050 mol l21). The signal assignment at pH* 5.56 is as follows: 1, [Ru(59-HGMP)(h6-C6H6)(D2O)2]1; 2, [Ru(59- HGMP)2(h6-C6H6)(D2O)]; 3, 59-HGMP2 species 2 in the 59-GMP–(h6-C6H6)RuII equilibrium system. Atom N7 is bonded to ruthenium as has also been reported for cis-[RuCl(bipy)2(9-egua)]Cl (bipy = 2,29-bipyridine).25 As depicted in Fig. 12, the oxo atom O(16) of one of the egua ligands of 2 participates in an outer-sphere fashion in the pseudo-tetrahedral co-ordination sphere of the ruthenium atom Ru(1), through a relatively strong O ? ? ?H]O hydrogen bond of length 2.537 Å between O(16) and the co-ordinated water molecule. Despite the differing binding modes of the two egua ligands, complex 2 exhibits only one H8 resonance at d 8.57, in contrast to species 2 of the 59-GMP–(h6-C6H6)RuII system which generates two H8 singlets of equal intensity.Outer-sphere macrochelation involving a (P)O ? ? ?H]O interaction for one of the 59-GMP ligands may well be responsible for this observation and supporting evidence for this suggestion is provided by the presence of two 31P-{1H} resonances for the a-phosphorus atom of 2. Analogous kN7 co-ordinated 1 : 1 and 2 : 1 complexes 1 and 2 are also present at lower pH* values in the 59-GTP– (h6-C6H6)RuII equilibrium system, for which selected pH*- dependent 1H and 31P-{1H} NMR spectra are presented in Figs. 13 and 14. However, as for adenosine 59-triphosphate, the introduction of two additional phosphate groups leads to the competitive formation of k3N7, O(Pb), O(Pg) macrochelates (3,39), which suppress species 1 and 2 at pH* values above 5.75. In contrast, the 2 : 1 species is present as the major complex for the 59-GMP–(h6-C6H6)RuII system in the range pH* 5.56–8.38 (Fig. 11). Signal 4, in Figs. 13 and 14, belongs to free guanosine 59-triphosphate, signal 5 to a 1 : 2 complex that could not be assigned unambiguously.Two further uncharacterised species are represented by signals 6 and 7 at pH* values of 3.30 and 4.73. Typical 31P-{1H} NMR shifts of respectively ca. 6.6 and 6.0 ppm to lower field are exhibited by the b- and g-phosphorus atoms of guanosine 59-triphosphate in the macrochelates 3,39. The P]P COSY spectra at pH* values of 5.25 and 6.31 confirm that Pb, Pg coupling is solely between co-ordinated phosphate groups.No evidence was found for the presence of k2N7, O(Pb) or k2N7, O(Pg) macrochelates. As illustrated by the characteristic low-field shift for the g-phosphorus resonance, ruthenium co-ordination of the terminal phosphate group in 3,39 leads to a reduction in the pKa value by about 2 units for the second deprotonation at this position. The H8 resonances of the macrochelates 3,39 (pH* 5.35, d 7.72, 7.86) are shifted to higher field with respect to the free nucleotide 59-triphosphate (pH* 5.35, d 8.04).This observation is, at first sight, somewhat surprising, in view of the fact that the kN7-co-ordinated complexes 1 and 2 display a pronounced low-field shift [pH* 5.35, d 8.41 (1), 8.49, Fig. 12 Molecular structure of the cation of [Ru(h6-C6H6)(9-egua)2- (H2O)][CF3SO3]2 2. Protons have been omitted for clarityJ. Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 2197 8.52 (2)]. However, the k2N7, O(Pa) macrochelate formed by the reaction of the (cp)2MoIV fragment with 59-dGMP22 is known to exhibit an H8 resonance with a chemical shift 9 similar to that of 3,39.Furthermore, the known preference of guanine derivatives Fig. 13 Selected pH*-dependent 1H NMR spectra for the aqueous equilibrium system 59-GTP–(h6-C6H6)RuII at the molar ratio R59-GTP:Ru = 1.0 (cRu = 0.040 mol l21). The signal assignment is as follows: 1, [Ru(59-H3GTP)(C6H6)(D2O)2]1 (pH* 3.30); 2, [Ru(59- H3GTP)2(C6H6)(D2O)] (pH* 3.30); 3, [Ru{59-HGTP-k2N7,O(Pb),- O(Pg)}(h6-C6H6)]2 (pH* 5.75); 4, 59 H2GTP22.Signals 5–7 cold not be characterised unambiguously Fig. 14 Selected pH*-dependent 31P-{1H} NMR spectra for the aqueous equilibrium system 59-GTP–(h6-C6H6)RuII at the molar ratio R59-GTP:Ru = 1.0 (cRu = 0.040 mol l21). Signal assignment is as for Fig. 13 for N7 co-ordination in acid or neutral solution and the disappearance of signals for 3,39 in alkaline solution all indicate binding to the imidazole ring.Additional support for this assignment is provided by the broadness of the proton resonances for 3 and 39, which would be expected if more than two diastereomers are present in solution and/or if the sugar and triphosphate residues were to exhibit pronounced conformational flexibility. Inspection of Figs. 7 and 8 for the macrochelates of adenosine 59-triphosphate indicates that the C8]H8 bond must point towards the phosphate backbone in the k3N7, O(Pb), O(Pg) co-ordination mode.This may provide an explanation for the increased extent of shielding experienced by H8 in the species 3,39 of the 59-GTP–(h6-C6H6)RuII equilibrium system. No evidence for a significant extent of metal-assisted cleavage of the pyrophosphate backbone in guanosine 59- triphosphate could be obtained from a time-dependent NMR investigation. This behaviour is once again in striking contrast to that of the nucleoside 59-diphosphate. The 31P-{1H} NMR spectra at pH* 5.04 for the 59-GDP–(h6-C6H6)RuII system after 1 h contains both a broad resonance (d 0.1) for the b-phosphorus atoms of k2N7, O(Pb)-co-ordinated macrochelates and a number of adjacent (d 0.8–2.2) sharp signals belonging to kN7-co-ordinated 59-monophosphate complexes and free 59- HGMP2 and H2PO4 2.Phosphate cleavage proceeds more rapidly than for adenosine 59-diphosphate. Although the number and the broadness of the NMR signals prevent a detailed analysis of the system it is possible to assign the macrochelate resonances without difficulty.A low-field shift for the bphosphorus atom of ca. 8 ppm provides confirmation of phosphate co-ordination. In contrast to the macrochelates of the 59-GTP–(h6-C6H6)RuII equilibrium system, the H8 resonance is shifted by ca. 0.2 ppm to lower field, a value more typical for N7 co-ordination. The present study provides the first systematic analysis of competition between macrochelation and oligomer formation for purine 59-nucleotides.In fact, macrochelates are only formed with the (h6-C6H6)RuII fragment by nucleoside 59-diand -tri-phosphates and, in the former case, facilitate a slow metal-assisted phosphate cleavage. Steric requirements of the 2- amino substituent in guanosine 59-monophosphate prevent the formation of cyclic trimers, which, in contrast, are predominant for the analogous adenine nucleotide. This restricts the palette of 59-GMP complexes to 1 : 1 and 2 : 1 kN7 co-ordinated species. The organometallic moiety (h6-C6H6)RuII has been shown to provide a stable facially tridentate half-sandwich fragment well suitable for analytical bioco-ordination chemistry in aqueous solution.Experimental Solvents were dried and distilled before use. Proton and 31P NMR spectra were recorded on a Bruker AM-400 spectrometer, FAB mass spectra on a Fisons VG Autospec instrument using 3-nitrobenzyl alcohol as the matrix. Elemental analyses were performed on a Carlo Erba 1106 analyser.The starting materials [{RuCl2(h6-C6H6)}2] and [{RuCl2(h6-p- MeC6H4Pri)}2] were prepared according to literature procedures. 26,27 The purine 59-nucleotides were obtained from Sigma and used as received. Syntheses [{Ru(59-HAMP)(Á6-p-MeC6H4Pri)}3][CF3SO3]3 1a. The compound Ag(O3SCF3) (0.167 g, 0.653 mmol) was added to a solution of [{RuCl2(h6-p-MeC6H4Pri)}2] (0.100 g, 0.163 mmol) in acetone (5 cm3). After removal of AgCl by filtration, 59- H2AMP (0.145 g, 0.327 mmol) was added to the filtrate and the resulting suspension stirred for 3 d at room temperature to afford compound 1 as an orange precipitate in 56% yield (0.1202198 J.Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 g) (Found: C, 35.5; H, 4.5; N, 10.0. C63H81F9N15O30P3Ru3S3 requires C, 34.5; H, 3.7; N, 9.6%). FAB mass spectrum: m/z 1892 (1, [M 2 2CF3SO3]1), 1397 (1, [M 2 59-HAMP 2 3CF3- SO3]1), 1162 {1, [M 2 Ru(h6-p-MeC6H4Pri) 2 59-HAMP 2 3CF3SO3]1} and 370 {100%, [Ru(HAde)(h6-p-MeC6H4Pri)]1}. 1H NMR (D2O): d (selected) 7.67, 7.72 (2s, H2 of 1), 8.33 (s, H2 of 59-AMP22), 8.50 (s, H8 of 59-AMP22), 9.00, 9.01 (2s, H8 of 1). Suitable crystals of [{Ru(59-AMP)(h6-p-MeC6H4Pri)}3]. 7.5 H2O 1b for an X-ray structural analysis were grown by slow evaporation of an aqueous solution of 1a. [Ru(Á6-C6H6)(9-egua)2(H2O)][CF3SO3]2 2. The compound Ag(O3SCF3) (0.204 g, 0.8 mmol) was added to a suspension of [{RuCl2(h6-C6H6)}2] (0.100 g, 0.2 mmol) in MeOH (5 cm3).After removal of the resulting AgCl by filtration, 9-ethylguanine (0.143 g, 0.8 mmol) was added to the filtrate, which was stirred for 2 d. The resulting precipitate was filtered off and recrystallised from an MeOH–water–Et2O solution at 230 8C to afford crystals of compound 2 in 68% yield (Found: C, 30.0; H, 3.6; N, 16.3. C22H26F6N10O9RuS2?2H2O requires C, 29.7; H, 3.4; N, 15.7%). FAB mass spectrum: m/z 687 (1, [M 2 CF3SO3 2 H2O]1), 537 (96, [M 2 2CF3SO3 2 H2O]1) and 358 (100%, [M 2 2CF3SO3 2 9-egua 2 H2O]1). 1H NMR [D2O–(CD3)2- CO]: d 1.37 (6 H, t, CH3), 3.5 (2 H, s, H2O), 4.12 (4 H, q, CH2), 6.21 (6 H, s, C6H6) and 8.57 (2 H, s, H8). NMR Spectroscopy The 400 MHz 1H and 162 MHz 31P-{1H} NMR spectra were recorded at 293 K with respectively sodium 3-(trimethylsilyl) tetradeuteriopropionate as internal and 85% H3PO4 as external standard. Stock solutions of [Ru(h6-C6H6)(D2O)3]21 were prepared by stirring Ag(O3SCF3) (0.257 g, 1.0 mmol) with [{RuCl2(h6-C6H6)}2] (0.126 g, 0.25 mmol) in D2O (5 cm3) for 2 h.After removal of precipitated AgCl the volume was increased to 10 cm3 to provide a solution of concentration 0.050 mol l21. Solution pH values were measured on a Metrohm 691 pH meter using a Hamilton microcombination electrode (Minitrode 238 100) calibrated with Riedel-de Haen standard buffers (pH 4.00, 7.00). Readings for D2O solutions were recorded directly prior to NMR measurement in 5 mm tubes. These are designated as pH* values as corrections for deuterium isotope effects were not employed. Reaction solutions were allowed to stand for 2 d at room temperature prior to NMR studies to ensure equilibrium conditions.Adjustment to the required pH* value was achieved by addition of 1.5 mol dm23 NaOD. X-Ray crystallography Unit-cell constants were obtained by least-squares refinement on centred angles for 25 reflections (25 < 2q < 308) on a Siemens P4 diffractometer. Intensity data were collected at 293 K on the diffractometer in the w-scan mode with monochromated Mo-Ka radiation (l = 0.710 73 Å) at 293 K.In each case three control reflections were monitored after collection of 100 reflections; no significant alterations in their intensities were registered. Semiempirical absorption corrections were applied on the basis of y-scan data. The structures were solved by a combination of Patterson and Fourier-difference syntheses and refined by full-matrix least squares against F using the SHELXTL set of programs.28 Scattering factors and corrections for anomalous dispersion were taken from ref. 29; R9 is defined as [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� . Complex 1b. Crystal data. C60H78N15O21P3Ru3?7.5H2O, M = 1876.6, orthorhombic, space group P212121 (no. 19), a = 17.623(4), b = 19.288(4), c = 23.238(5) Å, U = 7899(3) Å3, Z = 4, Dc = 1.575 Mg m23, F(000) = 3840, orange prism with dimensions 0.39 × 0.42 × 0.58 mm, m(Mo-Ka) = 0.72 mm21, transmission factors 0.37–0.49, data collection range 4.0 < 2q < 45.08, 1h, 1k, 1l, 5748 independent reflections measured, 3939 with Fo 2 > 2s(Fo 2) were employed in the leastsquares refinement.Structure solution and refinement. Anisotropic thermal parameters were introduced for the Ru, P and, where possible, the nucleotide O, N and C atoms. The high Ueq values for some of the atoms of the sugar and phosphate moieties of the second and third 5-AMP22 ligands suggest the presence of static disorder, which could not, however, be successfully modelled.Inclusion of hydrogen atoms at calculated positions did not lead to a significant improvement in the reliability indices and these were, therefore, omitted from the final refinement. The terminal values of R and R9 were 0.084 and 0.079 for 731 parameters with weights given by w = 1/[s2(Fo)]; goodness of fit = 1.88, maximum D/s = 0.056, maximum, minimum Dr = 0.84, 20.77 e Å23. The absolute configuration was confirmed by an h refinement to 0.9(2).30 Complex 2?2H2O.Crystal data. C22H30F6N10O11RuS2, M = 889.7, monoclinic, space group C2/c (no. 15), a = 25.218(5), b = 24.264(5), c = 12.811(3) Å, U = 6971(3) Å3, Z = 8, Dc = 1.692 Mg m23, F(000) = 3584, yellow prism with dimensions 0.15 × 0.18 × 0.43 mm, m(Mo-Ka) = 0.67 mm21, transmission factors 0.80–0.87, data collection range 3.0 < 2q < 45.08, 1h, 1k, 1l; 4774 reflections measured of which 4520 (Rint = 0.018) were unique. 1920 Reflections with Fo 2 > 2s(Fo 2) were employed in the least-squares refinement.Structure solution and refinement. One of the CF3SO3 2 anions is disordered with its two possible S atom positions lying on a crystallographic C2 axis; the atoms O(21)–F(23) and O(219)– F(239) of the disordered anion exhibit site occupation factors of 0.5. The high group isotropic thermal parameters for these atoms (0.132–0.266 Å3) suggest a degree of secondary disorder, that could not be modelled in a satisfactory manner.Anisotropic thermal parameters were introduced for the nonhydrogen atoms of the cation, the S atoms of CF3SO3 2 and the water O atoms. Inclusion of calculated hydrogen-atom positions in the final least-squares refinement cycles did not lead to an improvement in R and R9 and on this ground these atoms were not considered. The final values of R and R9 were 0.095 and 0.100 for 409 parameters with weights given by w21 = s2(Fo) 1 0.0008Fo 2; goodness of fit = 1.87, maximum D/s = 0.033, maximum, minimum Dr = 1.27, 20.71 e Å23 with the highest peaks in the region of the disordered CF3SO3 2 anions.The high values of R and R9 reflect the failure fully to describe the CF3SO3 2 disorder. 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 186/479.References 1 H. Lönnberg, in Biocoordination Chemistry, ed. K. Bürger, Ellis Horwood, Chichester, 1990, p. 284. 2 A. Terrón, Comments Inorg. Chem., 1993, 14, 63. 3 H. Sigel, Chem. Soc. Rev., 1993, 255. 4 H. Sigel, S. S. Massoud and N. A. Corfu, J. Am. Chem. Soc., 1994, 116, 2958. 5 S. E. Sherman and S. J. Lippard, Chem. Rev., 1987, 87, 1153. 6 A. Szent-Györgyi, in Enzymes: Units of Biological, Structure and Function, ed.O. H. Gaebler, Academic Press, New York, 1956, p. 393. 7 (a) M. D. Reily and L. G. Marzilli, J. Am. Chem. Soc., 1986, 108, 8299; (b) M. D. Reily, T. W. Hambley and L. G. Marzilli, J. Am. Chem. Soc., 1988, 110, 2999; (c) E. Alessio, Y. Xu, S. Cauci, G. Mestroni, G. Quadrifoglio, P. Viglino and L. G. Marzilli, J. Am. Chem. Soc., 1989, 111, 7068; (d) L. M. Torres and L. G. Marzilli, J. Am. Chem. Soc., 1991, 113, 4678.J. Chem. Soc., Dalton Trans., 1997, Pages 2191–2199 2199 8 M.Green and J. M. Miller, J. Chem. Soc., Chem. Commun., 1987, 1864 (correction 1988, 404); D. J. Evans, M. Green and R. van Eldik, Inorg. Chim. Acta, 1987, 128, 27; D. M. Orton and M. J. Green, J. Chem. Soc., Chem. Commun., 1991, 1612. 9 (a) L. Y. Kuo, M. G. Kanatzidis and T. J. Marks, J. Am. Chem. Soc., 1987, 109, 7207; (b) L. Y. Kuo, M. G. Kanatzidis, M. Sabat, A. L. Tipton and T. J. Marks, J. Am. Chem. Soc., 1991, 113, 9027. 10 H. Sigel, S. S. Massoud and R. Tribolet, J. Am. Chem. Soc., 1988, 110, 6857. 11 R. S. Taylor and H. Diebler, Bioinorg. Chem., 1976, 6, 247; A. Peguy and H. Diebler, J. Phys. Chem., 1977, 81, 1355; H. Diebler, J. Mol. Catal., 1984, 23, 209. 12 H. Sigel and K. H. Scheller, Eur. J. Biochem., 1984, 138, 291. 13 (a) U. K. Häring and R. B. Martin, Inorg. Chim. Acta, 1983, 80, 1; (b) K. J. Barnham, C. J. Bauer, M. I. Djuran, M. A. Mazid, T. Rau and P. J. Sadler, Inorg. Chem., 1995, 34, 2826. 14 K. Uchida, A. Toyama, Y. Tamura, M. Sugimura, F. Mitsumori, Y. Furukawa, H. Takeuchi and I. Harada, Inorg. Chem., 1989, 28, 2067. 15 K. H. Scheller, V. Scheller-Krattiger and R. B. Martin, J. Am. Chem. Soc., 1981, 103, 6833. 16 (a) W. S. Sheldrick, H. S. Hagen-Eckhard and S. Heeb, Inorg. Chim. Acta, 1993, 206, 15; (b) S. Korn and W. S. Sheldrick, Inorg. Chim. Acta, 1997, 254, 85. 17 (a) D. P. Smith, E. Baralt, B. Morales, M. M. Olmstead, M. F. Maestre and R. H. Fish, J. Am. Chem. Soc., 1992, 114, 10 647; (b) D. P. Smith, E. Kohen, M. F. Maestre and R. H. Fish, Inorg. Chem., 1993, 32, 4119; (c) H. Chen, M. F. Mastre and R. H. Fish, J. Am. Chem. Soc., 1995, 117, 3631. 18 M. Stebler-Röthlisberger, W. Hummel, P.-A. Pittet, H.-B. Burgi, A. Ludi and A. E. Merbach, Inorg. Chem., 1988, 27, 1358. 19 W. Saenger, Principles of Nucleic Acid Structure, Springer, New York, 1984. 20 E.ica, D. Dewaele, T. Kiss and G. Micera, J. Chem. Soc., Dalton Trans., 1995, 425. 21 R. B. Martin, Acc. Chem. Res., 1985, 18, 32. 22 K. Aoki, in Metal Ions in Biological Systems, ed. H. Sigel, Marcel Dekker, New York, 1996, vol. 33. 23 H. Chen, M. M. Olmstead, D. P. Smith, M. F. Maestre and R. H. Fish, Angew. Chem., 1995, 107, 1590. 24 H. Sigel, Coord. Chem. Rev., 1990, 100, 45. 25 P. M. van Vliet, J. G. Haasnoot and J. Reedijk, Inorg. Chem., 1994, 33, 1934. 26 R. A. Zelonka and M. C. Baird, Can. J. Chem., 1972, 50, 3063. 27 M. A. Bennett, T. N. Huang, T. W. Matheson and K. A. Smith, Inorg. Synth., 1982, 21, 74. 28 G. M. Sheldrick, SHELXTL PLUS programs for use with Siemens X-ray systems, University of Göttingen, 1990. 29 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4. 30 D. Rogers, Acta Crystallogr., Sect. A, 1981, 37, 734. Received 11th February 1997; Paper 7/00976C

ISSN:1477-9226    

DOI:10.1039/a700976c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2201–2205 2201 Symmetry of the co-ordination sphere of di-n-butyltin(IV) in complexes with sulfanylcarboxylic acids Krisztina Gajda-Schrantz,a László Nagy,*,a Erno� Kuzmann,b Attila Vértes,b Jan Holec¡ek c and Antonín Lyc¡ka d a Department of Inorganic and Analytical Chemistry, A. József University, H-6701 Szeged, PO Box 440, Hungary b Department of Nuclear Chemistry, L. Eötvös University, Budapest, Hungary c Inorganic and General Chemistry Department, University of Pardubice, CZ-532 10 Pardubice, Czech Republic d Research Institute for Organic Syntheses, CZ-532 18 Pardubice-Rybitvi, Czech Republic Four di-n-butyltin(IV) complexes have been prepared with sulfanylacetic, 2-sulfanylpropionic, sulfanylsuccinic and 2,3-disulfanylsuccinic acid, using two different procedures.The compounds were characterised by elemental analysis, Fourier-transform, Raman, 119Sn Mössbauer, 1H, 13C and 119Sn NMR spectroscopy. The IR and Raman data indicate the presence of bidentate carboxylate groups, non-linear C]Sn]C bonds, and Sn]S bonds.The results of Mössbauer spectroscopic measurements, based on point-charge model calculations, have shown the general occurrence of trigonal-bipyramidal environments at tin(IV). The multinuclear NMR studies also suggested the {O,S} co-ordination of the di-n-butyltin(IV) fragment, within the cyclic oligomeric complexes. The investigation of the interactions between organotin(IV) mono- and di-cations and biologically active ligands (among them carboxylates and polyhydroxy compounds1,2) is of considerable importance due to the possible modification of the biological properties of the organotin(IV) group in the presence of these ligands.Therefore, efforts have been made to elaborate simple procedures for the preparation of complexes,3,4 as well as to understand the antitumour activity of the organotin(IV) cations.5 The importance of the organotin(IV) complexes is confirmed by their wide range of possible applications, particularly of those containing sulfur.Until now only few papers have been published on the structure of organotin(IV)–carboxylate compounds containing {O,S} donor sites.6–9 Continuing our work on the synthesis, equilibrium and structural characterisation of organotin(IV) complexes with carbohydrates,4,10–12 as well as carbohydrate derivatives of thiazolidine-4-carboxylic acids 13 and N-Dgluconylamino acids 14 containing {O,O} and {O,N} donors, respectively, we have synthesized four di-n-butyltin(IV) complexes with four different ligands containing {O,S} donor atoms.The symmetry of the co-ordination sphere of organotin(IV) was determined on the basis of Mössbauer spectroscopy and FTIR, Raman and 1H, 13C and 119Sn NMR measurements were performed to determine the possible binding sites. Experimental Materials Compounds L1 and L2 were from Aldrich, L3 from Sigma and L4 from Fluka.Di-n-butyltin(IV) oxide was from Fluka. Other reagents and solvents were from Reanal (Hungary). CO2H CH CH3 SH CO2H CH2 SH CO2H CH CH2 SH CO2H CO2H CH CH SH CO2H HS L3 L2 L1 L4 Preparation of the complexes Method a. The complexes were obtained by refluxing equimolar quantities of L1–L4 and di-n-butyltin(IV) oxide in methanol for 2 h [Scheme 1(a)]. Compound 1a precipitated from the mixture, while the others (2a, 3a, 4a) were obtained after removal of the solvent by rotary evaporation, then washed and/or recrystallised from methanol or chloroform.Method b. Di-n-butyltin(IV) oxide (1 g) was refluxed in methanol–n-propanol (4 :1, 250 cm3) for 5 h. The oxide reacted with n-propanol, giving di-n-butyltin(IV) propoxide and water [Scheme 1(b)]. From the solvent mixture the water distils off as an azeotrope. After its removal and cooling, an equimolar quantity of L1–L4, dissolved in methanol, was added to the solution of di-n-butyltin propoxide with vigorous stirring.Compound 1b precipitated during the stirring, 2b crystallised out,while 3b and 4b were obtained after evaporation of the solvent at room temperature and then washed or recrystallised from methanol or chloroform. Elemental analyses (C, H, S) were carried out by Ilse Beetz Microanalytical Laboratory, Kronach, Germany. The analytical data are presented in Table 1 together with other characteristic physical constants. Measurements The 119Sn Mössbauer spectra were recorded at 77 K on a conventional RANGER spectrometer in constant-acceleration mode with a source activity of 0.4 GBq.Computer evaluation was used to determine isomer shift (i.s.) and quadrupole splitting (q.s.) values. The spectra were analysed as Lorentzian lines by least-squares fitting. The reproducibility of the Mössbauer Scheme 1 m = 1 for L1–L3, 2 for L4. (i ) MeOH, 2 h reflux; (ii ) PrnOH– MeOH (1: 4), 5 h reflux; (iii ) HnL, 1 h stirring ( a ) mSnBu2O + H nL (Bu2Sn)mHn–2mL + mH2O ( b ) mSnBu2O SnBu2(OPr)2 (Bu2Sn)mHn–2mL ( i ) ( ii ) ( iii ) – mH2O – 2 mPrOH2202 J.Chem. Soc., Dalton Trans., 1997, Pages 2201–2205 parameters was found to be ±0.02 (i.s.) and 0.04 mm s21 (q.s.), respectively, in each measurement. The i.s. values are referred to that of CaSnO3. The Fourier-transform IR spectra of L1–L4 and the complexes as KBr pellets were measured on Bio-Rad Digilab Division FTS-40 and FTS-65A instruments. Liquid samples were examined as thin films on KBr plates in the range 4000–200 cm21.Fourier-transform Raman spectra were recorded using a Bio-Rad Digilab Division spectrometer from liquid and solid samples contained in glass cuvettes. Relevant vibration bands are reported in Table 2. The 119Sn (134.29), 13C (90.56) and 1H (360.13 MHz) NMR spectra of complexes containing {O,S} donor atoms were recorded on a Bruker AMX 360 spectrometer equipped with a 5 mm multinuclear tuneable probe and an X32 computer using UXNMR software.The compounds were measured in CDCl3 or (CD3)2SO in a standard manner. The 13C chemical shifts were referred to appropriate signals of the solvents and recalculated to the d scale {d(13C) 77.00 (CDCl3), 39.60 [(CD3)2SO]}. The 119Sn chemical shifts were referred to external neat SnMe4 (d 0.0) placed in a coaxial capillary. The 119Sn and 13C chemical shifts are collected in Table 4. Calculations For the determination of the steric arrangement around tin(IV) in these compounds, q.s.values were calculated on the basis of a simple but general molecular orbital model, according to the partial quadrupole splitting (p.q.s.) concept,15,16 for the possible symmetries of five-co-ordinated tin(IV) given in Fig. 3 involving binding by two butyl groups and negatively charged (deprotonated) sulfur and carboxylate oxygen atoms. It was also taken into account that the carboxylate group can co-ordinate either in a mono- or bi-dentate manner.Equations (1)–(3) were used in q.s.1 = (27Rtbe 1 4Atba 1 4Ctba 1 Btbe)/72� �� (1) q.s.2 = (22Rtba 2 5Rtbe 1 4Atbe 1 4Ctbe 2 2Btba)/132� �� (2) q.s.3 = 24Rtba 1 Atbe 1 Btbe 1 Ctbe (3) the calculation, for the general structures I–III shown in Scheme 2. The p.q.s. values of the different functional groups used in our calculations, and the calculated q.s. values for tin(IV) in different stereochemical arrangements, are given in Table 6 and Fig. 3, respectively. Results and Discussion The analytical data and the characteristic physical constants for the complexes are reported in Table 1.Results refer to the formation of compounds with 1 : 1 metal-to-ligand ratio, with the exception of di-n-butyltin(IV)–2,3-disulfanylsuccinic acid (4a, 4b) where a 2 : 1 metal-to-ligand ratio was found, reflecting the four accessible binding sites. All the complexes are soluble in Me2SO. Compounds 1a, 1b, 2a and 2b are soluble also in CHCl3, CCl4 and C6H6.Complexes 2b, 3a, 3b, 4a and 4b are soluble in methanol, too. Fourier-transform IR and Raman spectroscopy The vibration spectroscopic data (Table 2) suggest that the two kinds of preparation methods used resulted in complexes with the same structure. In the spectra of free L1–L4 a characteristband for S]H vibrations, between 2550 and 2575 Scheme 2 A C B R R R B R A C R R C A B I II III cm21, and for the CO2H group, between 1690 and 1715 cm21, are present. These bands cannot be found in the spectra of the complexes, indicating co-ordination of deprotonated thiol and carboxylate group(s) to the tin.Fig. 1 shows the IR and Raman spectra of 2,3-disulfanylsuccinic acid and its di-n-butyltin(IV) complex, as an example. It is clear that all of the four possible donor groups are deprotonated and co-ordinated in the complex, which is possible only in the case of a 2 : 1 metal-to-ligand ratio. In spite of this, in the case of 3a and 3b, one of the two carboxylate groups (probably that which is far from the thiol group) remains protonated (non-co-ordinated), as evidenced by the IR bands characteristic for the n(C]] O) stretching vibrations, slightly shifted to higher wavenumbers, compared to the free L.Thus only one extra donor group in the molecule cannot promote the formation of a higher metal-to-ligand ratio in the complex, as in the case of compounds 4a and 4b. The difference (Dn) between nasym(CO2 2) and nsym(CO2 2) compared with that for sodium salts of L1–L4 (Table 3), reflects the bridging bidentate co-ordination mode of the CO2 2 group.In the case of compounds 1a, 1b, 4a and 4b these bands are doublets due to the asymmetrical (different C]O bond lengths) co-ordination to the tin. The presence of an Sn]S absorption band in the 380– 400 cm21 region of the Raman spectra of the complexes pro- Fig. 1 Infrared and Raman spectra of 2,3-disulfanylsuccinic acid (a) and its di-n-butyltin(IV) complex (b) Table 1 Physical and analytic data for di-n-butyltin(IV) complexes of ligands containing {O,S} donor atoms Analysis (%)a Ligand Compound C H S Colour M.p./8C L1 L2 L3 L4 1ab 1bc 2ab 2bc 3ab 3bc 4ab 4bc 37.25 37.25 (37.2) 38.4 39.25 (39.20) 37.8 37.75 (37.85) 34.95 34.85 (34.9) 6.25 6.25 (6.25) 6.4 6.55 (6.6) 5.75 5.8 (5.8) 5.45 5.5 (5.35) 9.9 9.9 (9.95) 9.55 9.5 (9.5) 8.45 8.45 (8.4) 14.6 14.65 (15.5) White White Yellow White White White White White 178–181 179–182 — 99–102 111–113 110–114 250–252 247–250 a Calculated values in parentheses.b Prepared under reflux. c Propoxide method.J. Chem. Soc., Dalton Trans., 1997, Pages 2201–2205 2203 Table 2 Infrared and Raman spectral data (cm21) for free L1–L4 and their di-n-butyltin(IV) complexes IR Raman Compound n(C]] O) nasym(CO2) nsym(CO2) n(SH) n(Sn]S) nasym(Sn]C) nsym(Sn]C) L1 1a 1b L2 2a 2b L3 3a 3b L4 4a 4b 1713.1vs 1714.2vs 1697.0vs 1745.0w 1713.2m 1713.3s 1713.3 (sh) 1693.6s 1573.7s 1547.9s 1574.2s 1548.1s 1546.9s 1542.8s 1552.2s 1552.1s 1577.8 (sh) 1552.6vs 1561.4 (sh) 1553.2s 1409.0m 1393.5m 1409.3m 1394.5m 1408.0m 1409.7m 1416.7m 1417.2m 1415.7m 1389.3m 1410.9mw 1389.3mw 2576.2vs 2574.6vs 2565.2vs 2549.2m 2564.5s 2539.1ms 382.4vs 382.5vs 397.8ms 395.5ms 394.6s 394.5s 386.7vs 386.2s 598.4w 598.6w 597.3m 599.3m 596.8m 597.4m 597.3m 516.6w 548.0vs 516.0m 515.2m 516.3m 517.9m 517.8m vides support for co-ordination of sulfur to tin.The presence of two (asymmetric and symmetric) Sn]C absorption bands in the region 600–515 cm21 reveals that the R]Sn]R bond angle is less than 1808 in all compounds.Vibration bands (480–450 cm21) characteristic for Sn]O bonds also appeared. In the spectra of all complexes, bands characteristic for the n-butyl skeleton are present.17 NMR spectroscopic measurements The 119Sn and 13C NMR spectroscopic data are shown in Table 4. For compound 1b one set of chemical shifts was observed in each of the 1H and 13C NMR spectra.In the 1H NMR spectrum the SH signal and the coupling constant 3J(CH2]SH) (observed for the starting L) disappeared. These facts, a ca. 6 ppm change of d(13C) for the CH2 group with respect to the starting acid and 3J(119Sn]1H) 33.1 Hz support the formation of a Sn]S bond. The 13C NMR chemical shift of the CO2 2 group and the changed value with respect to the starting acid in CDCl3, i.e. a considerable downfield shift, indicates the bidentate character of this group.18 Taking the existence of a Sn]S bond into account, the existence of this bidentate character is only possible via co-ordination of the C]] O oxygen to another tin atom.The d(119Sn) value corresponds to a 4 1 1 type of coordination, 19 in a trigonal-bipyramidal arrangement. The value of the coupling constant 1J(119Sn]13C) corresponds to a C]Sn]C angle 20 of ca. 1308 (trigonal-bipyramidal co-ordination sphere of tin with two butyl groups in the equatorial plane).Since there is only one signal in the 119Sn NMR spectrum, five-coordination can be realised only by formation of a cyclic oligomer or a very long linear oligomer (short linear oligomers would require the existence of at least two signals for end and Table 3 The difference between nasym(CO2) and nsym(CO2) for the carboxylates and their complexes nasym(CO2) 2 nsym(CO2)/cm21 Compound Sodium salta b L1 L2 L3 L4 156.2, 181.3 190.7 198.7 203.3 138.9, 180.22 148.1 144.3 163.4 138.9, 180.8 148.3 144.1 169.9 a Complex prepared under reflux.b Complex prepared by the propoxide method. middle structural units, the relative integral intensity being dependent on the length of the chain). Meunier-Piret et al.21 published the crystal structure of di-n-butyl(thiosalicylato)- tin(IV), showing that this compound forms a centrosymmetric hexamer. This finding is in line with the above-mentioned existence of only one signal in the 119Sn NMR spectrum. The 119Sn NMR chemical shift and coupling constant of complex 1b in Me2SO have practically the same values as those in CDCl3, but the d(13C) of CO2 2 is different.This may be accounted for by the formation of a monomeric unit from a cyclic oligomer, one molecule of solvent being co-ordinated and retaining five-co-ordination of tin [Fig. 4(d )]. The asymmetric bidentate character of the CO2 group is changed to monodentate. Lockhard22 has observed such a type of monomerisation in an analogous 3-sulfanylpropionic acid derivative, based on molecular-weight determination.The solubility of product 1a is much lower than 1b in CDCl3. We cannot exclude the formation of a linear polymer under the reported experimental conditions. Compound 2b has the same character as 1b as is clear from a comparison of the data in Table 3. Two sets of 13C pairs having non-equivalent abundance have been observed in the 13C NMR spectrum for Sn]CH2 groups. The formation of a pair of signals is due to the presence of a chiral centre in the molecule (C]S carbon). Two sets of pairs can be explained by the existence of two different types of cyclic oligomers: (i ) two conformational isomers due to stereochemical reasons; (ii ) two isomers having different ring sizes.Compounds 3a, 3b, 4a and 4b are practically insoluble in CDCl3 and as a result they were measured in Me2SO. The ligand to tin ratio is 1 : 1 in 3a, 3b and 1 : 2 in 4a, 4b according to 1H NMR integrals.The interpretation of the 13C and 119Sn NMR data is the same as for 1b in Me2SO. Mössbauer measurements Mössbauer parameters determined by computer evaluation of the spectra measured at liquid-nitrogen temperature are presented in Table 5. All spectra exhibit i.s. and q.s. which clearly indicate the presence of tin(IV) species. The spectra, independently of the preparation mode (a) and (b), with ligands L1–L4, comprised only one, well developed doublet (the narrowness of the full width at half of the resonance peaks is average) (Fig. 2), which suggests the presence of completely equivalent tin environments in these compounds. For structural elucidation based on Mössbauer parameters,2204 J. Chem. Soc., Dalton Trans., 1997, Pages 2201–2205 Table 4 Tin-119 and 13C NMR data for the di-n-butyltin(IV) complexes in CDCl3 and (CD3)2SOa d(13C)[nJ(119Sn]13C)/Hz (n = 1–3)] Compound d(119Sn) C1 C2 C3 C4 CO2 2 Others L1 b 1b b 1b c L2 b 2b b L3 c 3a c L4 c 4a c — 245.0 249.8 — 263.3 — 275.0 — 265.9 — 22.65 (547.9) 21.97 (558.9) — 23.02 22.25 22.90 22.13 — 22.05 (558.9) — 22.20 (550.1) — 27.58 (23.4) 27.25 (33.9) — 27.66 — 27.31 (33.9) — 27.30 (30.2) — 26.57 (97.8) 25.94 (86.9) — 26.61 — 26.03 (86.9) — 26.13 (88.2) — 13.67 13.68 — 13.69 — 13.75 — 13.79 176.36 182.02 174.61 179.95 184.68 172.16 173.88 176.10 172.54 171.87 174.24 26.06 CH2 31.44 39.60 35.22 CH 20.33 CH3 41.37 CH 24.55 CH3 39.94 CH2 35.87 CH 42.90 42.62 44.42 CH 54.11 a Atoms C1–C4 are the carbon atoms of butyl residues in sequence from the tin atom.b In CDCl3. c In (CD3)2SO. the p.q.s. concept 15,23,24 was used. The p.q.s. values of the functional groups15,25,26 used in the calculations are listed in Table 6. All possible arrangements for five-co-ordinated tin(IV) (which was evidenced by the above IR and NMR measurements) are shown in Fig. 3. All of the structures with calculated q.s. values smaller than 2.32 mm s21 can immediately be eliminated because of the great differences from the measured values.Structures in which the R]C]R bond angle is 180 or 908 can also be eliminated on the basis of NMR measurements which had shown the presence of a ca. 1308 R]C]R bond angle. In this way three structures remained: 1, 6 and 11. According to the IR spectroscopic measurements, there is no monodentate carboxylate co-ordination so the only possible structure must be 1, with the two butyl and the thiol groups in equatorial and Fig. 2 Mössbauer spectrum of the dibutyltin(IV)–2-sulfanylpropionic acid complex Table 5 Experimental 119Sn Mössbauer parameters (mm s21) for the di-n-butyltin(IV) complexes; proposed structure TBPY Ligand Method i.s. q.s. Ref. L1 L2 L3 L4 abaababaab 1.49 1.49 1.42 1.43 1.48 1.43 1.60 1.33 1.47 1.43 3.28 3.28 3.23 3.18 3.25 3.18 3.49 3.20 3.24 3.27 This work This work 14 c This work This work This work This work 14 c This work This work a Prepared under reflux. b Propoxide.c Dimethyltin(IV) complex. the bridging bidentate carboxylic groups in axial positions (Fig. 4). However, in some cases the difference between the calculated and measured q.s. values is larger than the experimental error. This can be explained in that the calculated value is given Fig. 3 Calculated quadrupole splitting values for the tin(IV) coordination spheres in different stereochemical arrangements with trigonal-bipyramidal (TBPY) symmetry of the R2SIV cation.b = Bidentate, m = monodentate – O2Cb(m)* S – – O2Cb(m) R R R S – R b(m)CO2 – b(m)CO2 – R S – – O2Cb(m) R b(m)CO2 – TBPY 1(6) 2.98(2.46) TBPY 2(7) 1.71(1.54) TBPY 3(8) 3.52(3.28) – O2Cb(m) – O2Cb(m) S – R R R – O2Cb(m) S – R b(m)CO2 – TBPY 4(9) 2.32(1.96) TBPY 5(10) 3.07(2.55) – O2Cb S – – O2Cm R R R S – R bCO2 – mCO2 – R S – – O2Cm(b) R b(m)CO2 – TBPY 11 2.73 TBPY 12(13) 1.81(1.45) TBPY 14 3.51 – O2Cb(m) – O2Cm(b) S – R R R – O2Cm S – R bCO2 – TBPY 15(16) 2.23(2.05) TBPY 17 2.81 Table 6 Partial quadrupole splitting values (mm s21) of the functional groups used in the calculations p.q.s. (R) p.q.s.(S2) p.q.s. (CO2 2) 21.37 (t) 20.94 (tba) 21.13 (tbe) 21.03 (oc) 20.595 (tba) 20.6 (tbe) 20.56 (oc) 0.0 75 (tba)b 0.293 (tbe)b 20.1 (tba)m 0.06 (tbe)m t = Tetrahedral, oc = octahedral.J. Chem. Soc., Dalton Trans., 1997, Pages 2201–2205 2205 for the ideal structure with a 1208 C]Sn]C bond angle. On the basis of equation (3) in ref. 27 the deviation from the ideal structure can be estimated.A distortion of 5–108 results in a 0.2–0.41 mm21 greater measured q.s. value than is that calculated for the ideal structure. In case of our complexes this means a C]Sn]C angle between 125 and 1308 which agrees well with the values determined by NMR measurements. Conclusion Both synthetic procedures used resulted in the formation of complexes with 1 : 1 metal-to-ligand ratio, except for 4a and 4b where a 2 : 1 metal-to-ligand ratio was found, reflecting the four accessible binding sites.The IR, Raman and NMR spectral data for the prepared complexes indicate five-co-ordinate trigonal-bipyramidal moieties with equatorial thiol and two butyl groups and axial carboxylate groups, forming cyclic oligomers, in some cases of different sizes, or very long linear oligomers. In compounds 3a and 3b one carboxylate group is not involved in co-ordination to tin(IV). The Mössbauer measurements in combination with IR and NMR spectroscopy allowed us to determine the steric arrangement around the tin, among the seventeen theoretically possible structures.Acknowledgements This work was supported financially by the Hungarian Research Foundation (OTKA I/5 T007384) and the Grant Agency of the Czech Republic (Grant No. 203/94/0024). Fig. 4 Proposed structures for the SnBu2 complexes with (a) sulfanylacetic and 2-sulfanylpropionic acid, (b) sulfanylsuccinic acid, (c) 2,3- disulfanylsuccinic and (d ) supposing co-ordination of solvent O Sn O C O S C R H Bu Bu C O O Sn O C O S C CH H Bu Bu C O HO2C ( a ) (b ) O Sn O C O S Bu Bu C O ( c ) O Sn O C O S Bu Bu C O CH HC O S Me Me Sn O Bu S Bu C CHR O ( d ) References 1 E.R. T. Tiekink, Appl. Organomet. Chem., 1991, 5, 1. 2 A. Patel and C. Poller, Rev. Silicon, Germanium, Tin, Lead Compds., 1985, 8, 263. 3 J. D. Donaldson, S. M. Grimes, L. Pellerito, M. A. Girasolo, P. J. Smith, A. Cambria and M. Fama, Polyhedron, 1987, 6, 383. 4 L. Nagy, L. Korecz, I. Kitricsi, L. Zsikla and K. Burger, Struct. Chem., 1991, 2, 231. 5 R. Barbieri, Inorg. Chim. Acta, 1992, 191, 253; R. Barbieri, G. Ruisi, A. Silvestri, A. M. Giuliani, A. Barbieri, G. Spina, F. Pieralli and F. D. Giallo, J. Chem. Soc., Dalton Trans., 1995, 476; R. Barbieri, A. Silvestri, S. Filippeschi, M. Magistrelli and F. Huber, Inorg. Chim. Acta, 1990, 177, 141. 6 G. K. Sandhu and N. Sharma, Appl. Organomet. Chem., 1993, 7, 33. 7 A. G. Davies, D. C. Kleinschmidt, P.R. Palan and S. C. Vasistha, J. Chem. Soc., 1971, 3972. 8 C.-D. Hager, F. Huber, A. Silvestri, A. Barbieri and R. Barbieri, Gazz. Chim. Ital., 1993, 123, 583. 9 C. H. Stapfer and R. H. Herber, J. Organomet. Chem., 1973, 56, 175. 10 K. Burger, L. Nagy, N. Buzás, A. Vértes and H. Mehner, J. Chem. Soc., Dalton Trans., 1993, 2499. 11 N. Buzás, M. A. Pujar, L. Nagy, E. Kuzmann, A. Vértes and H. Mehner, J. Radioanal. Nucl. Chem. Lett., 1995, 189, 237. 12 L. Nagy, B. Gyurcsik, K. Burger, S. Yamashita, T. Yamaguchi, H. Wakita and M. Nomura, Inorg. Chim. Acta, 1995, 230, 105. 13 N. Buzás, B. Gyurcsik, L. Nagy, X.-Y. Zhang, L. Korecz and K. Burger, Inorg. Chim. Acta, 1994, 218, 65. 14 B. Gyurcsik, N. Buzás, T. Gajda, L. Nagy, E. Kuzmann, A. Vértes and K. Burger, Z. Naturforsch., Teil B, 1995, 5, 515. 15 G. M. Bancroft, V. G. Kumar Das, Ts. K. Sham and M. G. Clark, J. Chem. Soc., Dalton Trans., 1976, 643. 16 L. Korecz, A. A. Saghier, K. Burger, A. Tzschach and A. Jurkschat, Inorg. Chim. Acta, 1982, 58, 243. 17 H. Geissler and H. Kriegsmann, J. Organomet. Chem., 1968, 11, 85. 18 E. Kleinpeter and R. Borsdorf, 13C NMR Spektroskopie in der Organischem Chemie, Akademie-Verlag, Berlin, 1981, p. 115. 19 J. Holec¡ek, M. Nadvornik, K. Handlir and A. Lyc¡ka, J. Organomet. Chem., 1986, 315, 299. 20 J. Holec¡ek and A. Lyc¡ka, Inorg. Chim. Acta, 1986, 118, L15. 21 J. Meunier-Piret, M.Boualam, R. Willem and M. Gielen, Main Group Met. Chem., 1993, 16, 329. 22 T. P. Lockhart, Organometallics, 1988, 7, 1438. 23 G. Ruisi, M.T. Lo Giudice and L. Pellerito, Inorg. Chim. Acta, 1984, 93, 161. 24 G. M. Bancroft and R. H. Platt, Adv. Inorg. Chem. Radiochem., 1972, 15, 59 and refs. therein. 25 G. M. Bancroft and Ts. K. Sham, J. Chem. Soc., Dalton Trans., 1976, 467. 26 R. Barbieri, A. Silvestri, F. D. Bianca, E. Rivarola and R. Cefalu, Mössbauer Effect Refs. Data J., 1983, 6, 69. 27 R. V. Parish, in Mössbauer Spectroscopy Applied to Inorganic Chemistry, ed. G. J. Long, Plenum, New York and London, 1984. Received 2nd December 1996; Paper 6/08136C

ISSN:1477-9226    

DOI:10.1039/a608136c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2207 Synthesis, multinuclear magnetic resonance spectroscopic studies and crystal structures of mono- and di-selenoether complexes of tin(IV) halides Sandra E. Dann, Anthony R. J. Genge, William Levason and Gillian Reid Department of Chemistry, University of Southampton, Highfield, Southampton, UK SO17 1BJ Reaction of SnX4 (X = Cl or Br) with Me2Se or diselenoether ligands in dry CHCl3 produced white or yellow solids [SnX4L2] in high yield [X = Cl, L2 = MeSe(CH2)nSeMe, PhSe(CH2)nSePh (n = 2 or 3), C6H4(SeMe)2-o or 2Me2Se; X = Br, L2 = MeSe(CH2)nSeMe (n = 2 or 3), C6H4(SeMe)2-o or 2Me2Se].These compounds have been characterised by a combination of variable-temperature 1H, 119Sn-{1H} and 77Se-{1H} NMR, IR spectroscopy and microanalyses. Single-crystal X-ray diffraction studies on trans-[SnX4(SeMe2)2], [SnX4{C6H4(SeMe)2-o}] (X = Cl or Br) and [SnCl4{MeSe(CH2)3SeMe}] confirm distorted octahedral geometry at SnIV in each case, with the bidentate ligands chelating.The C6H4(SeMe)2-o complexes adopt the meso arrangement, while the ligand is in the DL form in [SnCl4{MeSe(CH2)3SeMe}]. The trends in d(Sn]X) and d(Sn]Se) reveal that the trans influence of halide is greater than that of selenium in these systems. In comparable systems d(Sn]Se) is longer in the bromo than in the chloro systems, consistent with the greater Lewis acidity of SnCl4. The NMR studies revealed that pyramidal-inversion and ligand-dissociation processes are facile.In the SeMe2 complexes both cis and trans isomers are present, while in the diselenoether systems the meso and DL forms are both apparent at low temperatures. The co-ordination shifts in the 77Se-{1H} NMR spectra are markedly dependent upon chelate-ring size; the first time this has been observed for complexes of a p-block metal. The co-ordination chemistry of d-block metals has been one of the most active areas of inorganic chemistry in the last fifty years.Although p-block metals also form co-ordination complexes, these lack the characteristic UV/VIS spectra and magnetic properties, which provided much of the early impetus in the d-block work. p-Block metal complexes are often hydrolytically unstable and very labile in solution, which made them difficult to study and less suited to some spectroscopic techniques. The net result is that our knowledge of them is still very limited, although recent applications as precursors for metal chemical vapour deposition (MCVD) synthesis of new electronic materials have stimulated new investigations.In the case of tin(IV), nitrogen- and oxygen-donor ligand complexes have long been known1 and phosphine complexes have recently been studied.2 We recently reported a detailed study of dithioether complexes of tin(IV) halides using 1H and 119Sn-{1H} NMR spectroscopy in solution and 119Sn magic angle spinning (MAS) NMR in the solid state in conjunction with single-crystal X-ray diffraction.3 Here we describe the first systematic study of the synthesis and properties of mono- and di-selenoether complexes of tin(IV) halides.The only prior reports of selenoether complexes are studies of [SnX4(R2Se)2] (X = Cl or Br, R = Me or Me3SiCH2) utilising 1H NMR and vibrational spectroscopy.4,5 Results and Discussion The reaction of SnX4 (X = Cl or Br) with 2 molar equivalents of Me2Se or 1 molar equivalent of diselenoether in dry CHCl3 produced white or yellow solids [SnX4L2] [X = Cl, L2 = MeSe(CH2)nSeMe, PhSe(CH2)nSePh (n = 2 or 3), C6H4(SeMe)2- o or 2Me2Se; X = Br, L2 = MeSe(CH2)nSeMe (n = 2 or 3), C6H4(SeMe)2-o or 2Me2Se]. Attempts to isolate complexes of PhSe(CH2)nSePh (n = 2 or 3) with SnBr4, or SnI4 complexes with any of these ligands, were unsuccessful, although NMR evidence for their formation in situ was obtained in some cases (see below). As we observed previously with dithioethers,3 no interaction between these selenoethers and a suspension of SnF4 in chlorocarbons was apparent.The solid complexes appear indefinitely stable in sealed tubes or in a dry-box, but decompose quickly in moist air, and are very easily hydrolysed by traces of water in solution. The complexes are more hydrolytically unstable than the dithioether analogues,3 and all samples were handled in Schlenk equipment or in a glove-box (water levels < 10 ppm). Samples for solution NMR measurements were made up in rigorously anhydrous solvents in the glove-box, since trace amounts of water lead to some displacement of the neutral ligand.The IR spectra (Experimental section) show the presence of the selenium ligands and for the [SnX4(diselenoether)] complexes show several strong vibrations assignable as n(SnX) (theory 2A1 1 B1 1 B2), and confirm the absence of water. The far-IR spectra of [SnX4- (Me2Se)2] show single strong bands at 312 (X = Cl) and 220 cm21 (X = Br) in agreement with the previous study4 and consistent with the major isomer in the solid state being the trans form.Prior to this study there were no reports of structural data on any tin(IV) selenoether complexes. Therefore, in order to enable comparisons with the thioether derivatives which we reported previously,3 and to establish any trends between the solution NMR behaviour (below) and the solid-state structures, singlecrystal structure analyses were undertaken on trans- [SnX4(Me2Se)2] and cis-[SnX4{C6H4(SeMe)2-o}] (X = Cl or Br).For [SnX4(Me2Se)2] the structures show (X = Cl, Fig. 1, Table 1; X = Br, Fig. 2, Table 2) the central SnIV occupies a crystallographic inversion centre, co-ordinated via four precisely planar X atoms, with two mutually trans SeMe2 ligands completing the slightly distorted octahedral geometry [X = Cl, Sn]X 2.413(2), 2.427(2), Sn]Se 2.7001(9); X = Br, Sn]X 2.576(2), 2.587(2), Sn]Se 2.731(2) Å].In both cases the angles around the central Sn atom are very close to the 90 and 1808 expected for a regular octahedron. The Sn]Se distances in the bromo derivative are significantly longer than in the chloro species, probably a consequence of SnBr4 being a poorer acceptor than SnCl4. McAuliffe and co-workers 6 have reported the structures of the thioether analogues trans- and cis-[SnBr4(SMe2)2]. While the Sn]Br distances in these are very similar to those in trans- [SnBr4(SeMe2)2], the Sn]Se distances in this selenoether species are ca. 0.1 Å longer than d(Sn]S) in trans-[SnBr4(SMe2)2], consistent with the larger radius of Se over S.2208 J.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 The compounds [SnX4{C6H4(SeMe)2-o}] (X = Cl or Br) both show distorted octahedral co-ordination at SnIV with the diselenoether chelating and adopting the meso arrangement (X = Cl, Fig. 3, Table 3; X = Br, Fig. 4, Table 4) [X = Cl, Sn]X (trans X) 2.389(3), 2.426(3), Sn]X (trans Se) 2.360(3), 2.364(3), Sn]Se 2.749(1), 2.787(2); X = Br, Sn]X (trans X) 2.512(1), 2.547(2), Sn]Br (trans Se) 2.600(2), Sn]Se 2.841(2) Å].The trends apparent in d(Sn]X) with trans ligand parallel those Fig. 1 View of the structure of trans-[SnCl4(Me2Se)2] with the numbering scheme adopted. Ellipsoids are shown at 40% probability and atoms marked with an asterisk are related by a crystallographic inversion centre Fig. 2 View of the structure of trans-[SnBr4(Me2Se)2] with the numbering scheme adopted.Details as in Fig. 1 observed for the thioether compounds,3 i.e. d(Sn]X) trans X are consistently longer than d(Sn]X) trans Se. This suggests that the X ligands exert a greater trans influence than the Se (or S) donors in compounds of this type involving hard tin(IV) centres. Further evidence for this conclusion comes from a comparison of d(Sn]Se) in trans-[SnX4(SeMe2)2] vs. d(Sn]Se) in [SnX4- {C6H4(SeMe)2-o}]. In the former the Se donor atoms are trans to each other, and d(Sn]Se) is noticeably shorter than in the latter where the greater trans influence of the X ligands leads to a significant elongation in d(Sn]Se).As in the Me2Se complexes discussed earlier, the Sn]Se distances in the bromo derivative are longer than in the chloro species, consistent with the relative acceptor strengths of the SnX4 fragments. The angles involved in the chelate ring in [SnX4{C6H4(SeMe)2-o}] are 76.08(4) for X = Cl and 71.60(6)8 for X = Br, reflecting the restricted bite angle of the Se- (o-C6H4)Se linkage. This results in much more distorted overall stereochemistries for the bidentate ligand complexes compared to the monodentate species.Data collection was also undertaken on a poorly diffracting crystal of [SnCl4{MeSe(CH2)3SeMe}] * in an effort to establish whether the diselenoether is chelating or not. While the overall data quality was poor and the residuals rather high, preventing satisfactory refinement, the analysis was sufficient to confirm unambiguously that this compound does contain a chelating diselenoether ligand in the DL arrangement (Fig. 5). While there is no requirement that this structure is retained in solution, the solution NMR parameters suggest that at low temperature the MeSe(CH2)3SeMe compounds are chelated (see below). While the high estimated standard deviations associated with the atomic positions and geometric parameters in this compound preclude any detailed comparisons with structural data on Table 1 Selected bond lengths (Å) and angles (8) for trans- [SnCl4(Me2Se)2] Sn]Se(1) Sn]Cl(1) Sn]Cl(2) Se(1)]Sn]Cl(2) Se(1)]Sn]Cl(1) Sn]Se(1)]C(2) 2.7001(9) 2.413(2) 2.427(2) 91.25(6) 89.40(6) 100.2(3) Se(1)]C(1) Se(1)]C(2) Cl(1)]Sn]Cl(2) Sn]Se(1)]C(1) C(1)]Se(1)]C(2) 1.957(10) 1.952(9) 89.54(8) 100.7(3) 97.3(4) Table 2 Selected bond lengths (Å) and angles (8) for trans- [SnBr4(Me2Se)2] Sn]Br(1) Sn]Br(2) Sn]Se(1) Br(1)]Sn]Br(2) Br(2)]Sn]Se(1) Sn]Se(1)]C(2) 2.576(2) 2.587(2) 2.731(2) 90.47(5) 88.46(5) 102.2(5) Se(1)]C(1) Se(1)]C(2) Br(1)]Sn]Se(1) Sn]Se(1)]C(1) C(1)]Se(1)]C(2) 1.96(2) 1.94(2) 90.63(5) 100.9(4) 96.9(7) * C5H12Cl4Se2Sn, M = 490.6, tetragonal I41/a, a = 10.062(6), c = 25.702(10) Å, U = 2602(3) Å3, Z = 8, Dc = 2.504 g cm23, T = 150 K, colourless prism, 0.25 × 0.24 × 0.15 mm, m = 83.32 cm21, F(000) = 1824; w–2q scans, 1187 unique reflections measured (2qmax = 508), 836 with I > 3s(I) used in all calculations. The structure was solved by Patterson methods7 and refined using iterative cycles of full-matrix least squares 8 which revealed one half [SnCl4{MeSe(CH2)3SeMe}] molecule (with the Sn atom lying on a two-fold axis) in the asymmetric unit. At isotropic convergence the data were corrected for absorption using DIFABS (maximum transmission factor 1.000, minimum 0.662),9 and the Sn, Se and Cl atoms were then refined anisotropically and H atoms were included in fixed, calculated positions.This model refined to R, R9 = 0.106, 0.159 respectively and S = 6.83 for 43 parameters. The final Fourier-difference map showed several residual electron-density peaks of up to 4.5 e Å23. Some of these occurred within 1 Å of the Sn or Se atoms, and attempts to refine the others as partially occupied O atoms (e.g. from H2O solvate molecules) were not successful.J. Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2209 related compounds, the trends in the bond lengths are similar to those already discussed.Also, it is not surprising that the sixmembered chelate ring in this species, which results in a Se]Sn]Se angle of 85.9(2)8, leads to a considerably less strained octahedral geometry than in the o-phenylene derivatives discussed above. The SnX4/Me2Se (X = Cl or Br) systems have previously been examined by Ruzicka and co-workers 4 via 1H NMR spec- Fig. 3 View of the structure of [SnCl4{C6H4(SeMe)2-o}] with the numbering scheme adopted. 40% Probability ellipsoids are shown Fig. 4 View of the structure of [SnBr4{C6H4(SeMe)2-o}] with the numbering scheme adopted. 40% Probability ellipsoids are shown. Atoms marked with an asterisk are related by a crystallographic mirror plane Table 3 Selected bond lengths (Å) and angles (8) for [SnCl4{C6H4(SeMe)2-o}] Sn]Se(1) Sn]Cl(1) Sn]Cl(3) Se(1)]C(1) Se(2)]C(7) C(2)]C(3) C(2)]C(7) C(3)]C(4) 2.749(1) 2.426(3) 2.360(3) 1.95(1) 1.93(1) 1.39(2) 1.41(2) 1.38(2) Sn]Se(2) Sn]Cl(2) Sn]Cl(4) Se(1)]C(2) Se(2)]C(8) C(4)]C(5) C(5)]C(6) C(6)]C(7) 2.787(2) 2.389(3) 2.364(3) 1.92(1) 1.93(1) 1.38(2) 1.39(2) 1.40(2) Se(1)]Sn]Se(2) Se(1)]Sn]Cl(2) Se(1)]Sn]Cl(4) Se(2)]Sn]Cl(2) Se(2)]Sn]Cl(4) Cl(1)]Sn]Cl(3) Cl(2)]Sn]Cl(3) Cl(3)]Sn]Cl(4) Sn]Se(1)]C(2) Sn]Se(2)]C(7) C(7)]Se(2)]C(8) Se(1)]C(2)]C(7) C(2)]C(3)]C(4) C(4)]C(5)]C(6) C(5)]C(6)]C(7) Se(2)]C(7)]C(6) 76.08(4) 91.27(9) 90.50(9) 87.40(9) 166.37(9) 91.4(1) 93.0(1) 101.7(1) 100.3(3) 98.6(4) 100.2(6) 121.7(9) 120(1) 120(1) 119(1) 119.4(9) Se(1)]Sn]Cl(1) Se(1)]Sn]Cl(3) Se(2)]Sn]Cl(1) Se(2)]Sn]Cl(3) Cl(1)]Sn]Cl(2) Cl(1)]Sn]Cl(4) Cl(2)]Sn]Cl(4) Sn]Se(1)]C(1) C(1)]Se(1)]C(2) Sn]Se(2)]C(8) Se(1)]C(2)]C(3) C(3)]C(2)]C(7) C(3)]C(4)]C(5) Se(2)]C(7)]C(2) C(2)]C(7)]C(6) 82.41(8) 166.60(9) 83.16(8) 91.41(9) 169.7(1) 92.9(1) 95.4(1) 104.2(4) 99.4(5) 103.3(4) 118.7(9) 119(1) 120(1) 120.9(9) 119(1) troscopy.At 300 K in CD2Cl2, [SnCl4(Me2Se)2] exhibits a single d(Me) resonance with no evidence of 119/117Sn satellites, but on cooling to 250 K the resonance splits and ill defined satellites appear.At 180 K two resonances are present (Table 5) in the ratio ca. 1.5 : 1 due to trans and cis isomers, with 119/117Sn couplings of ca. 50–60 Hz. The behaviour of [SnBr4(Me2Se)2] is similar, although the trans : cis ratio is ca. 3 : 1. The 1H NMR spectra of the [SnX4(diselenoether)] complexes are summarised in Table 5. As in our previous study of dithioether complexes,3 NMR studies of the diselenoether complexes were carried out in anhydrous CD2Cl2 solution.The complexes of MeSe(CH2)nSe- Me are poorly soluble in CD2Cl2, especially at low temperatures, resulting in relatively poor quality spectra. Solubilities are higher in tetrahydrofuran or acetone, but the spectra obtained were significantly different and it is probable that these oxygen donors provide alternative ligands for the tin, hence these studies were not pursued. At 180 K the complexes of MeSe(CH2)nSeMe each show two d(Me) resonances (Table 5) due to DL and meso invertomers, which coalesce on warming due to the onset of pyramidal inversion and reversible ligand dissociation.Owing to the very poor solubility, convincing tin satellites were not observable. Resonances due to both invertomers were present in the 1H NMR spectrum of [SnCl4{MeSe(CH2)2SeMe}] below ca. 250 K, and below ca. 225 K in the corresponding spectrum of the bromide. The resonances of the invertomers were observed at lower temperatures for complexes of MeSe(CH2)3SeMe, and for [SnCl4{PhSe(CH2)3SePh}] the expected second-order CH2 resonances were very broad even at 180 K.The complex Fig. 5 View of the structure of [SnCl4{MeSe(CH2)3SeMe}] with the numbering scheme adopted. 40% Probability ellipsoids are shown. Atoms marked with an asterisk are related by a crystallographic twofold operation. Sn]Cl(1) 2.385(9), Sn]Cl(2) 2.427(9), Sn]Se(1) 2.766(4) Å; Se(1)]Sn]Se(1*) 85.9(2)8 Table 4 Selected bond lengths (Å) and angles (8) for [SnBr4{C6H4(SeMe)2-o}] Sn]Br(1) Sn]Br(3) Se(2)]C(1) C(1)]C(1*) C(2)]C(3) 2.600(2) 2.512(1) 1.93(1) 1.36(2) 1.42(2) Sn]Br(2) Sn]Se(2) Se(2)]C(4) C(1)]C(2) C(3)]C(3*) 2.547(2) 2.841(2) 1.95(1) 1.40(2) 1.36(2) Br(1)]Sn]Br(2) Br(2)]Sn]Se(2) Br(3)]Sn]Se(2) Br(3)]Sn]Se(2*) Se(2)]Sn]Se(2*) Sn]Se(2)]C(4) Se(2)]C(1)]C(1*) C(1*)]C(1)]C(2) C(2)]C(3)]C(3*) 169.12(7) 83.38(5) 93.15(4) 164.74(5) 71.60(6) 100.9(4) 120.6(3) 120.0(7) 119.5(7) Br(1)]Sn]Br(3) Br(1)]Sn]Se(2) Br(2)]Sn]Br(3) Br(3)]Sn]Br(3*) Sn]Se(2)]C(1) C(1)]Se(2)]C(4) Se(2)]C(1)]C(2) C(1)]C(2)]C(3) 92.44(5) 87.81(5) 94.40(5) 102.08(7) 96.5(3) 99.8(5) 119.4(8) 120(1)2210 J.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 Table 5 Proton NMR data a d Complex 300 180 Kb [SnCl4(Me2Se)2] [SnBr4(Me2Se)2] [SnCl4{MeSe(CH2)2SeMe}] [SnBr4{MeSe(CH2)2SeMe}] [SnCl4{MeSe(CH2)3SeMe}] [SnBr4{MeSe(CH2)3SeMe}] [SnCl4{C6H4(SeMe)2-o}] [SnBr4{C6H4(SeMe)2-o}] [SnCl4{PhSe(CH2)2SePh}] [SnCl4{PhSe(CH2)3SePh}] 2.51 2.36 2.48 (3 H), 3.30 (2 H) 2.25 (3 H), 3.15 (2 H) 2.30 (1 H), 2.46 (3 H), 3.2 (2 H) 2.41 (1 H 1 3 H), 3.1 (2 H) 2.83 (3 H), 7.5, 7.65 (2 H) 2.45 (3 H), 7.25, 7.38 (2 H) 3.39 (2 H), 7.2–7.7 (5 H) 2.10 (1 H), 3.25 (2 H), 7.2–7.7 (5 H) 2.44, 2.54 (1 : 1.5) 2.26, 2.40 (1 : 3) 2.40, 2.46, 3.10, 3.40 (1 : 1) 2.21, 2.30, 3.10, 3.30 (2 : 1) 2.40, 2.45, 2.51, 3.11, 3.42 (1 : 5) 2.38, 2.44, 3.05, 3.25 (1 : 3) 2.99, 2.79, 7.55 (5 : 1) 2.76 [2.55 (sh)], 7.47 3.5, 3.8, 7.0–7.8 (1 : 1) Ill defined (see text) a In CD2Cl2 relative to internal SiMe4.b For Me2Se complexes the ratio refers to the relative abundances of the geometric isomers, whereas for the bidentate ligand, it shows the abundances of the invertomers (meso and DL) obtained from integrating Me or CH2 resonances. [SnCl4{C6H4(SeMe)2-o}] was more soluble in CD2Cl2 and at 180 K two sharp methyl resonances with clearly resolved 117/119Sn satellites (3J ca. 40 Hz) were observed, attributable to the expected invertomers, although the relative intensities were quite disparate (>5 : 1). On warming to ca. 210 K the lines coalesced, and above this temperature only a singlet d(Me) resonance was present with no satellites. The corresponding spectrum of [SnBr4{C6H4(SeMe)2-o}] at 180 K contained a broad line at d 2.76 with a weak shoulder at 2.55, suggesting that even at this temperature the low-temperature-limiting spectrum was not achieved.Although the poor spectral quality resulting from the low solubilities, and complications introduced by ligand dissociation, preclude a more detailed treatment of the inversion processes, it is clear that qualitatively inversion barriers decrease in the order Se > S for analogous ligands. The 77Se-{1H} and 119Sn-{1H} NMR spectra of [SnCl4(Me2- Se)2] in CH2Cl2 contained single resonances at 300 K due to fast exchange between the isomers, but on cooling to ca. 250 K separate resonances for the cis and trans isomers are resolved which sharpen on further cooling, and at 180 K clear 1J couplings appear (Table 6). [The g(119Sn) : g(117Sn) ratio is 0.956 : 1 and separate couplings to the two tin isotopes were not resolved.] In contrast, CH2Cl2 solutions of [SnBr4(Me2Se)2] show neither 77Se-{1H} nor 119Sn-{1H} resonances at room temperature, but single resonances appear at ca. 280 K and on further cooling resonances due to the cis and trans isomers are resolved. A solution of [SnCl4(Me2Se)2] containing an excess of Me2Se in CH2Cl2 at 180 K shows sharp 77Se-{1H} resonances for cis and trans isomers and free Me2Se (Fig. 6), showing exchange is slow on the NMR time-scale. On warming to ca. 230 K the resonance of the cis isomer broadens and then disappears, but that of the trans form broadens only near ambient temperatures. Corresponding changes occur in the 119Sn-{1H} spectra as a function of temperature.The NMR spectra of the system [SnBr4(Me2Se)2]–excess Me2Se in CH2Cl2 had generally similar behaviour, but with the onset of exchange at lower temperatures. The behaviour of these complexes is qualitatively similar to that observed in the [SnX4(Me2S)2]–Me2S systems by Knight and Merbach.11 None of the [SnX4(diselenoether)] complexes exhibited a 119Sn-{1H} NMR resonance at 300 K (probably due to reversible ring opening), and only [SnCl4{MeSe(CH2)2SeMe}] exhibited a 77Se-{1H} resonance and even this was very weak and broad.On cooling resonances from both nuclei were observed, initially as single broad peaks which sharpened on cooling and in most cases resolved into two signals by 180 K (Table 6), consistent with the presence of the meso and DL invertomers. Poor solubility of the diselenaalkane complexes (see above) at low temperatures resulted in spectra with relatively poor signal-to-noise ratios even after long accumulations, and prevented identification of satellites and the spectral data in Table 6 should be viewed with these qualifications in mind.Nonetheless the behaviour with X and ligand structure observed in the spectra from the different nuclei (1H, 77Se and 119Sn) are internally consistent. A solution of [SnCl4{C6H4(SeMe)2-o}] containing free C6H4(SeMe)2-o showed separate 77Se-{1H} NMR resonances for the free selenoether and meso and DL forms of the co- Fig. 6 (a) 77Se-{1H} and (b) 119Sn-{1H} NMR spectrum of [SnCl4- (Me2Se)2] containing an excess of Me2Se in CH2Cl2 at 180 KJ.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2211 Table 6 77Se-{1H} and 119Sn-{1H} NMR data at 180 K a Complex d(77Se-{1H})b d(119Sn-{1H})c [SnCl4(Me2Se)2] d [SnBr4(Me2Se)2] [SnCl4{MeSe(CH2)2SeMe}] e [SnBr4{MeSe(CH2)2SeMe}] [SnCl4{MeSe(CH2)3SeMe}] [SnBr4{MeSe(CH2)3SeMe}] [SnCl4{C6H4(SeMe)2-o}] [SnBr4{C6H4(SeMe)2-o}] [SnCl4{PhSe(CH2)2SePh}] 185 (460), 204 (490) [1:1] 204 (555), 219 (500) [2:1] 482, 487 [1:1] 493, 496 [2:1] 231, 232 [5:1] 261, 263 [1:2] 323, 338 [1:5] 355 436 2691 (468), 2695 (490) 21296 (500), 21319 (550) 2680, 2682 21283, 21288 2685, 2686.5 21305, 21308 2632, 2635? 21258 (br) — Free selenoether: d(77Se) Me2Se, O; MeSe(CH2)2SeMe, 121; MeSe(CH2)3SeMe, 74; PhSe(CH2)2SePh, 340; C6H4(SeMe)2-o, 202.10 a In anhydrous CH2Cl2–CD2Cl2 containing [Cr(acac)3] (acac = acetylacetonate).b Relative to external neat Me2Se, 1J(77Se]117/119Sn)/Hz in parentheses, approximate ratios in square brackets. c Relative to external neat SnMe4, 1J(77Se–119Sn).d d(77Se-{1H}) 176, d(119Sn-{1H}) 2695 at 300 K. e d(77Se-{1H}) 486 at 300 K. ordinated selenoether at 180 K. The signals were clearly broadened by 220 K and had disappeared by 235 K showing fast ligand exchange at this temperature. The [SnCl4{PhSe(CH2)n- SePh}] (n = 2 or 3) complexes failed to show 119Sn resonances even at 180 K, presumably due to exchange, and only the n = 2 complex exhibited a 77Se resonance at 180 K.A solution of SnI4 in CH2Cl2 containing a large excess of Me2Se exhibited a 77Se-{1H} NMR resonance at d 1 152 at 180 K. This disappeared on warming and was not present unless a large excess of Me2Se was used. It seems likely that this may indicate the formation of a weak adduct {possibly trans- [SnI4(Me2Se)2]} in solution at low temperatures. In contrast, a CH2Cl2 solution of SnI4 containing an excess of MeSe(CH2)2- SeMe showed no evidence for adduct formation over the temperature range 180–300 K.No evidence for complex formation was observed in Ph2Se–SnX4 systems. The SnBr4– PhSe(CH2)2SePh–CH2Cl2 mixtures showed both 119Sn and 77Se resonances at low temperatures indicative of complex formation, but the solid complex could not be isolated. Several consistent trends can be discerned in these data. The 119Sn-{1H} NMR resonances for the complexes show similar patterns of behaviour in cis/trans-[SnX4(Me2E)2] (E = S or Se) and in [SnX4(L]L)] for dithioether and diselenoether analogues with d shifted by 110–150 ppm to low frequency on changing S for Se.In the 77Se-{1H} NMR spectra of [SnX4- (Me2Se)2] large high-frequency co-ordination shifts D ( = dcomplex 2 dligand) are observed of approximately 1200 with the resonance of the cis isomer slightly to high frequency of the trans. For transition-metal complexes containing chelating diselenoether ligands the magnitude of the co-ordination shifts vary greatly with the chelate-ring size.12 Following the approach of Garrou13 first used for diphosphine complexes, one calculates first the co-ordination shift as above, and then the chelate-ring parameter (DR) defined as D(chelate complex) 2 D(equivalent monodentate complex).For our purposes for the complexes of MeSe(CH2)nSeMe, the ‘equivalent monodentate complexes’ are cis-[SnX4(Me2Se)2]. For free MeSe(CH2)2SeMe d 121,10 leading to D 365 for the tin chloride complex and 374 for the bromide and corresponding DR 161 (Cl) and 155 (Br), that is large positive DR values for the five-membered-ring species.In contrast, for MeSe(CH2)3SeMe d 74, D 158 (Cl) and 188 (Br) and DR 246 (Cl) and 231 (Br), i.e. negative DR values for the sixmembered- ring complexes. This is clear evidence for the presence of a chelate-ring-parameter effect in the selenium chemical shift values, and is the first time this has been observed in complexes of a main-group metal. The trends are similar to those established with d-block metal complexes.12 The origin of the chelate-ring effect is unclear even in the much studied diphosphine systems,14 but the observation of such an effect in the tin complexes here, where the metal is behaving as a simple s acceptor, supports the suggestion that it involves the strain in different size rings.10 Since we do not have data for complexes of PhMeSe which would be the ‘equivalent monodentate ligand’ for PhSe(CH2)2- SePh or C6H4(SeMe)2-o, similar calculations of DR cannot be carried out for complexes of these bidentate compounds, although for the latter the substantial co-ordination shifts in themselves strongly suggest that the chelate structures identified by X-ray crystallography for solid [SnX4{C6H4(SeMe)2-o}] are also retained in solution. Experimental Physical measurements were made as described previously.3 The 77Se-{1H} NMR spectra were obtained from anhydrous CH2Cl2–10% CD2Cl2 solutions as described.10 The selenium ligands were made by literature methods.10,15 Syntheses The complexes [SnX4L2] were all made by the same general method. The tin(IV) halides are moisture sensitive, therefore all of the reactions were carried out under an atmosphere of dry nitrogen, using standard Schlenk, vacuum-line and dry-box techniques.[SnCl4(Me2Se)2]. Tin(IV) chloride (0.26 g, 1 mmol) was added to a solution of Me2Se (0.22 g, 2 mmol) in chloroform (10 cm3). The complex formed immediately as a white precipitate which was filtered off and dried in vacuo.Yield 0.44 g, 92% (Found: C, 9.75; H, 2.7. Calc. for C4H12Cl4Se2Sn: C, 10.05; H, 2.5%); n& max/ cm21 (Sn]Cl) 312. [SnBr4(Me2Se)2]. A saturated solution of tin(IV) bromide (0.44 g, 1 mmol) in chloroform (5 cm3) was added dropwise to a solution of Me2Se (0.22 g, 2 mmol) in chloroform (5 cm3). On reducing the volume in vacuo the complex slowly formed as yellow crystals which were filtered off and dried in vacuo.Yield 0.54 g, 82% (Found: C, 7.4; H, 1.9. Calc. for C4H12Br4Se2Sn: C, 7.3; H, 1.85%); n& max/cm21 (Sn]Br) 220. The same general method was used for the synthesis of all of the complexes involving bidentate ligands, and this is detailed for one example of each of X = Cl and X = Br. [SnCl4{MeSe(CH2)2SeMe}]. Tin(IV) chloride (0.26 g, 1 mmol) was added to a solution of the selenoether (0.22 g, 1 mmol) in chloroform (10 cm3). The complex precipitated as a white powder which was filtered off and dried in vacuo.Yield 0.45 g, 72% (Found: C, 10.3; H, 2.5. Calc. for C4H10Cl4Se2Sn: C, 10.1; H, 2.1%); n& max/cm21 (Sn]Cl) 339, 331, 320 and 312. [SnCl4{MeSe(CH2)3SeMe}]. White precipitate. Yield 0.72 g, 93% (Found: C, 12.5; H, 2.6. Calc. for C5H12Cl4Se2Sn: C, 12.25; H, 2.45%); n& max/cm21 (Sn]Cl) 336, 331, 325 and 313. [SnCl4{PhSe(CH2)2SePh}]. Yellow crystalline precipitate. Yield 0.59 g, 81% (Found: C, 27.2; H, 2.5. Calc. for2212 J.Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 Table 7 Crystallographic data Formula M Colour, morphology Crystal dimensions/mm Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 ZF (000) Dc/g cm23 m(Mo-Ka)/cm21 Transmission factors (maximum, minimum) No. of unique observed reflections Rint (based on F2) Unique observed reflections with Io > 2.5s(Io) No. parameters Goodness of fit R(Fo) R9(Fo) Maximum residual peak, trough/e Å23 trans-[SnCl4(Me2Se)2] C4H12Cl4Se2Sn 478.56 Colourless block 0.25 × 0.10 × 0.10 Monoclinic P21/n 6.539(2) 12.610(3) 8.111(2) 107.67(2) 637.2(2) 2 444 2.494 85.04 1.000, 0.694 1189 0.031 925 52 2.29 0.036 0.043 1.19 21.66 trans-[SnBr4(Me2Se)2] C4H12Br4Se2Sn 656.36 Yellow, rhomb 0.45 × 0.40 × 0.20 Monoclinic P21/n 6.768(3) 13.000(3) 8.373(3) 108.47(3) 698.7(4) 2 588 3.119 184.63 1.000, 0.645 1289 0.132 1039 52 4.35 0.050 0.057 1.66 22.15 [SnCl4{C6H4(SeMe)2-o}] C8H10Cl4Se2Sn 524.59 Colourless, block 0.30 × 0.15 × 0.12 Triclinic P1� 8.419(2) 11.323(3) 8.251(1) 90.32(2) 98.17(2) 109.68(2) 731.8(3) 2 488 2.380 73.85 1.000, 0.717 2563 0.028 1763 136 1.97 0.045 0.052 1.33 22.10 [SnBr4{C6H4(SeMe)2-o}] C8H10Br4Se2Sn 702.39 Yellow, block 0.30 × 0.20 × 0.20 Monoclinic P21/m 6.826(3) 11.324(2) 9.936(2) 100.67(2) 754.7(3) 2 632 3.119 184.63 1.000, 0.645 1402 0.043 1143 50 3.49 0.049 0.062 2.49 22.91 R = S(|Fo|i 2 |Fc|i)/S|Fo|i, R9 = [Swi(|Fo|i 2 |Fc|i)2/Swi|Fo|i 2]� �� and w21 = s2(F ).Goodness of fit = [S(|Fo|i 2 |Fc|i 2 |Fc|)/si]/(n 2 m) ª 1 where n = no.of data, m = no. of parameters. C14H14Cl4Se2Sn: C, 28.0; H, 2.35%); n& max/cm21 (Sn]Cl) 330, 324, 319 and 313. [SnCl4{PhSe(CH2)3SePh}]. Orange crystalline precipitate. Yield 0.53 g, 86% (Found: C, 29.5; H, 2.7. Calc. for C15H16Cl4Se2Sn: C, 29.8; H, 2.65%); n& max/cm21 (Sn]Cl) 330, 324, 315 and 304. [SnCl4{C6H4(SeMe)2-o}]. White crystalline precipitate. Yield 0.49 g, 94% (Found: C, 18.35; H, 2.0.Calc. for C8H10Cl4Se2Sn: C, 18.3; H, 1.9%); n& max/cm21 (Sn]Cl) 338, 328, 323 and 317. [SnBr4{MeSe(CH2)2SeMe}]. A saturated solution of tin(IV) bromide (0.44 g, 1 mmol) in chloroform (5 cm3) was added dropwise to a solution of the selenoether (0.22 g, 1 mmol) in chloroform (5 cm3). A pale yellow precipitate formed immediately which was filtered off and dried in vacuo. Yield 0.50 g, 69% (Found: C, 7.5; H, 1.8. Calc. for C4H10Br4Se2Sn: C, 7.35; H, 1.55%); n& max/cm21 (Sn]Br) 220, 218, 216 and 214.[SnBr4{MeSe(CH2)3SeMe}]. Yellow precipitate. Yield 0.48 g, 81% (Found: C, 9.3; H, 1.9. Calc. for C5H12Br4Se2Sn: C, 9.0; H, 1.8%); n& max/cm21 (Sn]Br) 219, 214, 206 and 201. [SnBr4{C6H4(SeMe)2-o}]. Orange crystals. Yield 0.67 g, 86% (Found: C, 13.9; H, 1.7). Calc. for C8H10Br4Se2Sn: C, 13.65; H, 1.4%); n& max/cm21 (Sn]Br) 230, 228, 224 and 222. X-Ray crystallography Single crystals of [SnCl4(Me2Se)2], [SnBr4(Me2Se)2], [SnCl4{C6H4(SeMe)2-o}] and [SnBr4{C6H4(SeMe)2-o}] were obtained from a solution of the appropriate complex in CHCl3.The compounds were extremely sensitive to hydrolysis on exposure to moist air. Therefore, in each case the selected crystal was coated with mineral oil, mounted on a glass fibre using silicone grease as adhesive, and immediately placed in a stream of cold nitrogen gas and cooled to 150 K. Data collection used a Rigaku AFC7S four-circle diffractometer equipped with an Oxford Cryostreams low-temperature attachment, and graphitemonochromated Mo-Ka X-radiation (lmax = 0.710 73 Å); T = 150 K, w–2q scans.The intensities of three standard reflections were monitored every 150. No significant crystal decay or movement was observed. As there were no identifiable faces the raw data for the compounds [SnCl4(Me2Se)2] and [SnCl4{C6H4(SeMe)2-o}] were corrected for absorption using y-scans. The weighting scheme w21 = s2(F) gave satisfactory agreement analyses in each case. Crystallographic data are present in Table 7.All four structures were solved by direct methods,16 and then developed by iterative cycles of full-matrix least-squares refinement (based on F) and Fourier-difference syntheses which located all non-H atoms in the asymmetric unit.8 For [SnBr4(Me2Se)2] and [SnBr4{C6H4(SeMe)2-o}] an empirical absorption correction using DIFABS9 was applied to the raw data at isotropic convergence. All non-H atoms in the structures were refined anisotropically (with the exception of [SnBr4- {C6H4(SeMe)2-o}] for which the C atoms were refined isotropically), and H atoms were placed in fixed, calculated positions with d(C]H) = 0.96 Å.Atomic co-ordinates, 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 186/498. Acknowledgements We thank the University of Southampton and the EPSRC for support, and the latter for a grant to purchase the diffractometer. References 1 I. R. Beattie, Q. Rev. Chem. Soc., 1963, 17, 382. 2 N. C. Norman and N. L. Pickett, Coord. Chem. Rev., 1995, 145, 27.J. Chem. Soc., Dalton Trans., 1997, Pages 2207–2213 2213 3 S. E. Dann, A. R. J. Genge, W. Levason and G. Reid, J. Chem. Soc., Dalton Trans., 1996, 4471. 4 S. J. Ruzicka and A. E. Merbach, Inorg. Chim. Acta., 1976, 20, 221; 1977, 22, 191; S. J. Ruzicka, C. M. P. Favez and A. E. Merbrg. Chim. Acta, 1977, 23, 239. 5 E. W. Abel, S. K. Bhargava, K. G. Orrell and V. Sik, Inorg. Chim. Acta, 1981, 49, 25. 6 N. Bricklebank, S. M. Godfrey, C. A. McAuliffe and R. G. Pritchard, J. Chem. Soc., Chem. Commun., 1994, 695. 7 PATTY, The DIRDIF Program System, P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, S. Garcia-Granda, R. O. Gould, J. M. M. Smits and C. Smykalla, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1992. 8 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1992. 9 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158. 10 D. J. Gulliver, E. G. Hope, W. Levason, S. G. Murray, D. M. Potter and G. L. Marshall, J. Chem. Soc., Perkin Trans 2, 1984, 429. 11 C. T. G. Knight and A. E. Merbach, Inorg. Chem., 1985, 24, 576. 12 E. G. Hope and W. Levason, Coord. Chem. Rev., 1993, 122, 109. 13 P. E. Garrou, Chem. Rev., 1981, 81, 229. 14 J. G. Verkade and L. D. Quin (Editors), Phosphorus-31 NMR Spectroscopy in Stereochemical Analysis, VCH, Deerfield Beach, FL, 1987. 15 E. G. Hope, T. Kemmitt and W. Levason, J. Chem. Soc., Perkin Trans. 2, 1987, 487. 16 G. M. Sheldrick, SHELXS 86, program for crystal structure solution, Acta Crystallogr., Sect. A, 1990, 46, 467. Received 19th February 1997; Paper 7/01181D © Copyright 1997 by the Royal Society of Chemistry

ISSN:1477-9226    

DOI:10.1039/a701181d

出版商:RSC    

年代:1997

数据来源: RSC