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DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1601–1605 1601 The reactivity of [2.2.2]paracyclophane towards Cr(CO)6: experimental and theoretical considerations Paul J. Dyson, *,a David G. Humphrey,b John E. McGrady,c Priya Sumana and Derek Tocher b a Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London SW7 2AY, UK b Christopher Ingold Laboratories, University College London, 20 Gordon Street, London WC1H 0AJ, UK c Department of Chemistry, The Australian National University, Canberra, ACT 0200, Australia The reactivity of [2.2.2]paracyclophane (C24H24) towards hexacarbonylchromium has been examined and the rates of reaction for the formation of mono-, bis- and tris-complexes established.The structures of [Cr(CO)3(h-C24H24)] and [{Cr(CO)3}2(h-C24H24)] have been established by single crystal X-ray diffraction. These experimental observations have been interpreted using approximate density functional molecular orbital calculations.The synthesis and characterisation of cyclophane–metal complexes has attracted a great deal of attention, and this area has recently been reviewed.1 Interest in these complexes has been stimulated by the unique properties which cyclophanes add to the area of transition metal–arene chemistry and the ultimate goal in this area is to prepare a polymeric material comprising alternating cyclophane–metal units which may have interesting electrical and magnetic properties.2 Unlike other planar polyarenes, the p electron density on the rings of cyclophanes overlap so that a through-space electrontransfer mechanism is a dominant factor in influencing their chemistry.3 This is exemplified by reactivity studies with the transition metals.For example, the crystal structure of the [2.2]paracyclophane complex, [Cr(CO)3(h-C16H16)], reveals that the two arene rings move closer together upon complexation to the electron-withdrawing Cr(CO)3 group.4 It was also found that the second ring is deactivated towards further substitution and more aggressive conditions are required to form the bis- (tricarbonylchromium) complex.5 We recently compared the reactivity of [2.2]paracyclophane with the non-strained arene, p-xylene.6 The presence of two arenes rings lying parallel to each other at a distance considerably less than a typical van der Waals contact confers increased reactivity to [2.2]paracyclophane due to the p–p repulsions between the arene rings, which increase electron density on the outer faces of the ligand, thereby increasing its nucleophilicity relative to p-xylene. The thermodynamic stability of [2.2]- paracyclophane complexes is also larger than expected and arises from the reduction in these p–p repulsions in the coordinated complex, a consequence of the electron withdrawing nature of metal fragments.As a continuation of these studies we have conducted some related experiments on [2.2.2]paracyclophane which are described in this paper.Results and Discussion Arene–tricarbonylchromium complexes, i.e. [Cr(CO)3(harene)], are conveniently prepared in high yield from the direct reaction of [Cr(CO)6] and the appropriate arene in high boiling ethers, typically 1,4-dioxane.7 It is generally accepted that the substitution mechanism is first order with the rate determining step involving dissociation of the three carbonyl ligands.8,9 The mono-, bis- and tris-tricarbonylchromium complexes of [2.2.2]paracyclophane, [Cr(CO)3(h-C24H24)] 1, [{Cr(CO)3}2- (h-C24H24)] 2 and [{Cr(CO)3}3(h-C24H24)] 3, have previously been prepared and characterised.10 We have, however, determined the rate of formation for the sequential addition of {Cr(CO)3} to [2.2.2]paracyclophane, viz. 1–3 by monitoring the disappearance of [Cr(CO)6] [n(CO) 1980 cm21] with time (see Experimental section for details). The rate constants for the complexations were estimated at 1.75 × 1026, 0.88 × 1026 and 0.80 × 1026 s21 for the first, second and third complexation reactions, respectively. It is noteworthy that there is a large difference in the rate of reaction between the first complexation and the other two, and that the difference in rates between the second and third complexations is quite small.These effects are rationalised using density functional molecular orbital calculations (see below) using structural parameters obtained from the molecular structures of compounds 1 and 2.Structural characterisation of compounds 1 and 2 Single crystals of compound 1 were obtained from a solution of dichloromethane–hexane stored at 4 8C for 24 h while compound 2 was crystallised from dichloromethane–hexane by slow evaporation. The molecular structures of 1 and 2 are shown in Figs. 1 and 2, respectively, and relevant bond parameters are listed in Tables 1 and 2. The molecular structures of compounds 1 and 2 are closely related and will be discussed together.They differ in that in 2, two {Cr(CO)3} units are coordinated to the ligand as opposed to only one in the other complex. The chromium–ring carbon bond distances indicate that the ring is not totally planar as the distances involving the bridgehead carbon atoms are slightly longer than the remaining Fig. 1 Molecular structure of [Cr(CO)3(h-C24H24)] 1 in the solid state1602 J. Chem. Soc., Dalton Trans., 1997, Pages 1601–1605 four C]C bonds.The Cr]C (ring) distances average 2.29 and 2.24 Å in 1 and 2.24 and 2.21 Å for 2 with respect to the bridgehead and C]H carbon atoms, respectively. It is clear that the difference between these parameters in 2 are less than in 1 (D 0.05 in 1 and D 0.03 in 2, although this is near the limit of meaningful significance for 2). This indicates that as the number of electron withdrawing {Cr(CO)3} units increases the intramolecular repulsion between the rings decreases.This is in keeping with both the kinetic data and the results obtained from density functional molecular orbital calculations (see below). The dihedral angle formed between the ‘boat ends’ of the coordinated rings is 4.98 in 1 and 1.1 and 1.28 in 2. The corresponding dihedral angles for the unco-ordinated rings are 4.1 and 2.98 in 1 and 6.68 in 2. These values indicate that two {Cr(CO)3} fragments are required in order for significant distortions of the [2.2.2]paracyclophane to take place.The average C]C distances of co-ordinated rings are longer than the uncoordinated rings [mean 1.40 versus 1.38 Å in 1 and 1.41 and 1.40 versus 1.39 Å in 2]. Again, this is in keeping with the decrease in bond order associated with co-ordination of the {Cr(CO)3} units. The orientations of the tricarbonyl units with respect to the underlying C6 ring also differ. In 1 the carbonyls adopt a staggered conformation with respect to the C atoms of the ring while in 2 they more closely approach an eclipsed conform- Fig. 2 Molecular structure of [{Cr(CO)3}2(h-C24H24)] 2 in the solid state Table 1 Bond lengths (Å) for compound 1 Cr]C, ring Ring 3, C]C Cr]C(1) Cr]C(2) Cr]C(3) Cr]C(4) Cr]C(5) Cr]C(6) Ring 1, C]C C(1)]C(2) C(1)]C(6) C(2)]C(3) C(3)]C(4) C(4)]C(5) C(5)]C(6) Ring 2, C]C C(9)]C(10) C(9)]C(14) C(10)]C(11) C(11)]C(12) C(12)]C(13) C(13)]C(14) 2.288(5) 2.252(6) 2.250(5) 2.301(5) 2.240(5) 2.248(5) 1.400(7) 1.414(7) 1.407(7) 1.383(7) 1.412(7) 1.398(8) 1.375(9) 1.377(8) 1.368(8) 1.389(7) 1.380(8) 1.386(8) C(17)]C(18) C(17)]C(22) C(18)]C(19) C(19)]C(20) C(20)]C(21) C(21)]C(22) Aliphatic links, C– C(1)]C(7) C(7)]C(8) C(8)]C(9) C(12)]C(15) C(15)]C(16) C(16)]C(17) C(20)]C(23) C(23)]C(24) C(4)]C(24) Carbonyls Cr]C(30) C(30)]O(30) Cr]C(40) C(40)]O(40) Cr]C(50) C(50)]O(50) 1.380(7) 1.377(7) 1.392(8) 1.382(7) 1.385(7) 1.373(7) C 1.501(7) 1.50(1) 1.515(8) 1.506(8) 1.537(8) 1.506(8) 1.490(7) 1.548(7) 1.505(7) 1.851(6) 1.142(8) 1.836(6) 1.149(8) 1.839(5) 1.159(6) ation.However, the barrier to rotation in arene–tricarbonylchromium complexes is typically very low, and as such variations of the orientation of the carbonyls with respect to the C6 ring are commonly encountered. While the idealised [2.2.2]paracyclophane molecule can be imagined to have the centroids of the rings at the vertices of an equilateral triangle with the rings perpendicular to it (D3h symmetry), the planes of the three rings in 1 do not all point towards each other.This is quite unusual as the rings in [2.2.2]paracyclophane itself and 2 align so as to face the centre of the molecule. However, in 1 one of the rings is twisted by ca. 278 from the parallel with respect to the mean planes of the other rings. It is not fully understood why this is the case but it is probably due to intermolecular forces rather than intramolecular ones. Density functional molecular orbital calculations In our previous paper 6 we examined the origin of the enhanced nucleophilicity of [2.2]paracyclophane relative to p-xylene, and also the greater thermodynamic stability of the complex [Cr(CO)3(h-C16H16)], relative to [Cr(CO)3(h-C6H4Me2-1,4)]. Both phenomena were traced to the destabilising influence of the repulsions between the occupied p orbitals on the benzene ring (transforming as a1g and e1u in D6h symmetry).The p electron density is forced out of the transannular region, thereby making it more available to an approaching electrophile, increasing the rate of reaction.The electron-withdrawing metal fragment then reduces the p density at the co-ordinated ring, thereby reducing the p–p repulsions in [Cr(CO)3- (h-C16H16)], stabilising it relative to other simple monoarene complexes. In this paper we extend the analysis given in ref. 6 to include the successive addition of two or more {Cr(CO)3} fragments to both [2.2]- and [2.2.2]-paracyclophane. Throughout this work similar assumptions to those in the previous paper are made.Firstly, it is assumed that cyclophanes can be adequately modelled by simply placing idealised benzene rings at the appropriate points in space (i.e. it is assumed that Table 2 Bond lengths (Å) for compound 2 Cr]C, ring Ring 3, C–C Cr(1)]C(11) Cr(1)]C(12) Cr(1)]C(13) Cr(1)]C(14) Cr(1)]C(15) Cr(1)]C(16) Cr(2)]C(19) Cr(2)]C(20) Cr(2)]C(21) Cr(2)]C(22) Cr(2)]C(23) Cr(2)]C(24) Ring 1, C]C C(11)]C(12) C(11)]C(16) C(12)]C(13) C(13)]C(14) C(14)]C(15) C(15)]C(16) Ring 2, C]C C(19)]C(20) C(19)]C(24) C(20)]C(21) C(21)]C(22) C(22)]C(23) C(23)]C(24) 2.251(8) 2.209(9) 2.215(8) 2.234(8) 2.231(8) 2.195(8) 2.231(8) 2.223(8) 2.204(8) 2.230(9) 2.195(9) 2.221(9) 1.404(12) 1.395(12) 1.438(12) 1.385(12) 1.398(13) 1.433(12) 1.419(12) 1.382(13) 1.380(12) 1.418(13) 1.403(13) 1.418(13) C(27)]C(28) C(27)]C(32) C(28)]C(29) C(29)]C(30) C(30)]C(31) C(31)]C(32) Aliphatic links, C– C(11)]C(34) C(14)]C(17) C(17)]C(18) C(18)]C(19) C(22)]C(25) C(25)]C(26) C(26)]C(27) C(30)]C(33) C(33)]C(34) Carbonyls Cr(1)]C(1) O(1)]C(1) Cr(1)]C(2) O(2)]C(2) Cr(1)]C(3) O(3)]C(3) Cr(2)]C(4) O(4)]C(4) Cr(2)]C(5) O(5)]C(5) Cr(2)]C(6) O(6)]C(6) 1.390(14) 1.386(14) 1.40(2) 1.381(4) 1.408(14) 1.38(2) C 1.516(12) 1.511(12) 1.532(14) 1.510(11) 1.498(12) 1.55(2) 1.520(14) 1.503(14) 1.528(14) 1.833(10) 1.154(11) 1.835(10) 1.149(12) 1.846(11) 1.153(12) 1.838(10) 1.143(11) 1.821(11) 1.154(13) 1.837(11) 1.157(13)J. Chem.Soc., Dalton Trans., 1997, Pages 1601–1605 1603 the through-space p–p interactions are the dominant pathway for electronic communication).This assumption is least valid for [2.2]paracyclophane where there is a distinct distortion of the arene rings towards a bowl-shaped geometry, but even in this case the assumption of planar benzene rings reproduced the correct trends in reactivity and stability. Secondly, it is assumed that the dominant conformation in solution corresponds to the case where the faces of all the arene rings point inwards towards the centre of the molecule.The other computational details remain exactly as before. Thermodynamic cycles are constructed from successive metallation of [2.2]- and [2.2.2]-paracyclophane, relating successive association energies to differences in p–p repulsions in the various species.† The data summarised in Scheme 1 confirm that the association of {Cr(CO)3} with [2.2]paracyclophane is some 27 kJ mol21 more favourable than with benzene, due to the reduction in p–p repulsions by the tricarbonylchromium group.The addition of a second {Cr(CO)3} unit further reduces the repulsion between the arene rings, but this time only by 11 kJ mol21, and so the complexation of the second {Cr(CO)3} fragment is still favoured over that of benzene, but by less than half as much as the first. Once again the thermodynamically favourable association can be linked to the enhanced rate of reaction by noting that the residual p–p repulsions in [Cr(CO)3(h-C16H16)] will result in greater electron density on the outer face of the unco-ordinated ring, and hence to greater nucleophilicity. Therefore, on the basis of energetic arguments alone, we would anticipate the rate for the reaction of [Cr(CO)6] with [Cr(CO)3(h-C16H16)] to be intermediate between those for the corresponding reactions with free [2.2]paracyclophane and benzene.This is contrary to experimental observations, and the additional statistical preference for co-ordination of the Cr(CO)3 unit to [2.2]paracyclophane or benzene rather than to [Cr(CO)3(h-C16H16)] must also be considered. The partially metallated complex has only one arene face available for complexation, compared to two in both free [2.2]paracyclophane and benzene, which will further reduce the rate of reaction of [Cr(CO)6] with [Cr(CO)3(h-C16H16)] by a factor of two.Accordingly, the preparation of [{Cr(CO)3}2- (h-C16H16)] from [Cr(CO)3(h-C16H16)] and hexacarbonylchro- Scheme 1 The thermodynamic cycle relating successive association energies of {Cr(CO)3} (kJ mol21) to changes in p–p repulsion energies for the model system for [2.2]paracyclophane Cr(CO)3 2 + 2 DE = –238.2 DE = –238.2 DE = +53.4 DE = +26.1 DE = +15.2 DE = –265.5 DE = –249.1 Cr(CO)3 Cr(CO)3 Cr(CO)3 Cr(CO)3 † See Fig. 3 of ref. 6 for a detailed discussion of the methodology. mium occurs more slowly than the metallation of either pxylene or [2.2]paracyclophane, and high temperatures are required to drive the reaction.5 Furthermore, the yield of ca.<10% is low compared to complexation of the first {Cr(CO)3} unit, which takes place in near quantitative yields. The larger cyclophane, [2.2.2]paracyclophane, shows similar trends to [2.2]paracyclophane. Scheme 2 shows that the repulsion between the rings in free [2.2.2]paracyclophane is of similar magnitude to that in [2.2]paracyclophane, but now it results from three interactions rather than two.The net repulsion per benzene ring is therefore reduced from 27 kJ mol21 to 17 kJ mol21. Furthermore, the rings are no longer parallel and so van der Waals contacts between the hydrogen atoms may also contribute to the total repulsive energy, along with the familiar p–p repulsions. The hydrogen–hydrogen repulsions will remain approximately constant regardless of the degree of metallation, and so the differences in repulsion energies, and hence different reactivity of the complexes, will still be determined principally by changes in the p–p repulsions. Complexation of one {Cr(CO)3} fragment reduces the p–p repulsions in [2.2.2]paracyclophane, but only by 10 kJ mol21, indicating that the reactivity should be enhanced relative to Scheme 2 The thermodynamic cycle relating successive association energies of {Cr(CO)3} (kJ mol21) to changes in p–p repulsion energies for the model system for [2.2.2]paracyclophane Cr(CO)3 Cr(CO)3 Cr(CO)3 (OC)3Cr Cr(CO)3 Cr(CO)3 Cr(CO)3 Cr(CO)3 Cr(CO)3 3 2 3 + + 2 DE = –238.2 DE = –238.2 DE = +51.4 DE = +41.1 DE = +37.3 DE = +40.3 DE = –248.5 DE = –242.0 DE = –235.2 DE = –238.21604 J.Chem. Soc., Dalton Trans., 1997, Pages 1601–1605 benzene, but not to the same extent as that observed in [2.2]paracyclophane. This conclusion is again contrary to the experimental rate constants, which suggest that [2.2.2]paracyclophane is more reactive than the [2.2] species.The reason for the discrepancy between calculation and experiment may again lie in the neglect of statistical factors in the former. [2.2.2]Paracyclophane has three available co-ordination sites, as opposed to only two in [2.2]paracyclophane, and consequently even in the absence of a thermodynamic preference for co-ordination to one or the other, we would anticipate a 1.5 fold enhancement of the rate constant in the former. We therefore conclude that a combination of both energetic and statistical factors is responsible for the high rate constant observed for the reaction of [Cr(CO)6] with [2.2.2]paracyclophane.In contrast to the first metallation, complexation of a second and third {Cr(CO)3} fragment results in only very minor changes in p–p repulsions. Accordingly, the second and third arene faces behave essentially as isolated benzene rings, and the much reduced rates for the second and third metallations reflect this change. The high residual repulsive energy present even after three {Cr(CO)3} units have been co-ordinated is probably largely due to H ? ? ? H repulsions rather than p–p repulsions.The relative stabilities of {Cr(CO)3} complexes of both [2.2]paracyclophane and [2.2.2]paracyclophane are summarised in Fig. 3. The difference between the calculated association energy (DEass) and that on an isolated benzene ring (DEass benzene) is plotted as a function of the number of associated metal fragments.Several important conclusions emerge from this figure. First, the stabilities of the monometallated complexes of both [2.2]paracyclophane and [2.2.2]paracyclophane are significantly greater than the corresponding complex with benzene, due to the co-ordination-induced relief of p–p repulsions in the cyclophanes. In both cases, the addition of a single electron-withdrawing {Cr(CO)3} fragment is suf- ficient to remove the majority of these p–p repulsions and further metallation is favoured over the reaction with benzene only to a minor extent.The contrast between first and second metallations is more marked in the [2.2]paracyclophane complexes, where the two arene rings lie parallel and close to each other and hence p–p repulsions are most significant. In the larger [2.2.2]paracyclophane system, where the distance between the centroids of the arene rings is much greater, p–p repulsions are in general less significant, and hence the relative stabilities of the complexes are less dependent on the degree of metallation.Experimental All reactions were carried out under an atmosphere of nitrogen gas using dried and degassed solvents. The Strohmeier reflux method11 was used in all reactions in order to ensure that [Cr(CO)6] was not lost from the reaction mixture by sublimation. The apparatus consisted of two reflux condensers con- Fig. 3 Relative association energies (DEass 2 DEass benzene/kJ mol21) for successive metallation of [2.2]- and [2.2.2]-paracyclophane nected in series, the lower one without cooling water, the upper one with cooling water.Any [Cr(CO)6] which sublimes onto the lower condenser is then washed back into the reaction vessel by the solvent which condenses on the upper condenser. Hexacarbonylchromium was purchased from Aldrich Chemicals and was used without further purification, [2.2.2]paracyclophane (C24H24) was prepared according to the literature procedure.12 Solution infrared spectra (1.0 cm21 resolution) were recorded in a Specac solution cell (KBr windows, path length 0.1 mm) against a neat solvent background, using a dry-air purged Nicolet 750 FT spectrometer.Proton NMR spectra were recorded on a JEOL JNM-EX270 FTNMR spectrometer calibrated to internal SiMe4. Synthesis of [Cr(CO)3(Á-C24H24)] 1, [{Cr(CO)3}2(Á-C24H24)] 2 and [{Cr(CO)3}3(Á-C24H24)] 3 In a typical reaction, C24H24 (0.5 g, 1.6 mmol) and [Cr(CO)6] (0.35 g, 1.6 mmol for 1, 0.71 g, 3.2 mmol for 2 and 1.05 g, 4.8 mmol for 3) were dissolved in 1,4-dioxane. The reaction mixture was heated to reflux for 36 h for 1, 72 h for 2 and 120 h for 3.The solvent was removed in vacuo and the yellow solid redissolved in CH2Cl2–hexane (1 : 1, v/v). Single crystals of 1 were obtained after storing the solution at 4 8C for 24 h and single crystals of 2 were obtained from slow evaporation of the solvent over several days. Crystals of 3 were obtained, but these were not suitable for single-crystal X-ray diffraction analysis. All compounds were obtained in yields exceeding 90% prior to recrystallisation. Spectroscopic data for compound 1: IR (KBr) 1966s, 1857s cm21; 1H NMR (CDCl3), d 6.85 (d, J = 6.3, 4 H), 6.7 (d, J = 6.3, 4 H), 4.9 (s, 4 H), 3.1 (s, 4 H), 2.88 (d, J = 6.7, 4 H), 2.68 (d, J = 6.7 Hz, 4 H) [Found (Calc.): C, 72.3 (72.3); H, 5.4 (5.4)%].Spectroscopic data for compound 2: IR (KBr) 1958s, 1857s cm21; 1H NMR (CDCl3), d 6.90 (s, 4 H), 5.00 (d, J = 6.9, 4 H), 4.90 (d, J = 6.9, 4 H), 2.96 (d, J = 6.6, 4 H), 2.93 (d, J = 6.6 Hz, 4 H), 2.60 (s, 4 H) [Found (Calc.): C, 61.0 (61.6); H, 3.85 (4.1)%].Spectroscopic data for compound 3: IR (KBr) 1951s, 1882s cm21; 1H NMR (CDCl3), d 3.67 (s, 12 H), 2.18 (s, 12 H). The spectroscopic data for all the compounds are in good agreement with those previously reported.10 Kinetic studies Compounds [Cr(CO)6] (80 mg, 0.36 mmol), C24H24 (113 mg, 0.36 mmol) and 1,4-dioxane (50 cm3) were heated to reflux (solvent temperature ª 380 K).Aliquots (0.1 cm3) were periodically withdrawn from the reaction mixture and the infrared spectrum of the aliquot recorded immediately after sampling. On completion of the reaction the solvent was removed under reduced pressure and the product was used for the next kinetics measurements in the manner outlined above. The rate of reaction of [Cr(CO)6] with the arenes was determined by monitoring the disappearance of n(CO) from [Cr(CO)6] at 1980 cm21 (t1u) with time.The concentration of [Cr(CO)6] was determined from the absorbance at the analytical wavenumber, given that Beer’s law holds over the concentration range used. Plots of ln(At/A0) versus time (where At = absorbance at time t and A0 = initial absorbance) gave first-order rate constants. Reagent concentrations were not corrected to account for the loss of material contained in each sampled aliquot. Structural characterisation Crystal diffraction data were collected on a Nicolet R3mV automated four-circle diffractometer equipped with Mo-Ka radiation (l = 0.710 73 Å).Important crystallographic parameters are summarised in Table 3. The structures were solved by direct methods and developed by using alternating cycles of least-squares refinement on F and Fourier-difference synthesis. The non-hydrogen atoms were refined anisotropically whileJ. Chem. Soc., Dalton Trans., 1997, Pages 1601–1605 1605 Table 3 Crystallographic parameters for compounds 1 and 2 1 2 Formula T/K Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 ZF (000) Dc/g cm23 m/cm21 Crystal size/mm q range/8 h,k,l Index ranges Data measured Unique data No.unique data with [I > 2s(I)] No. parameters Ra R9 b Weighting scheme Largest shift/e.s.d. Largest peak/e Å23 C27H24CrO3 293 Monoclinic P21/n 6.246(1) 14.436(3) 24.120(5) 97.55(3) 2156(1) 4 936 1.38 5.6 0.25 × 0.15 × 0.10 2.5–27.5 0–8, 0–18, 229 to 28 5373 4756 2176 280 0.0455 0.0479 w21 = s2(F) 1 0.0009F2 0.002 0.40 C30H24Cr2O6 293 Monoclinic P21/n 9.878(3) 22.952(4) 12.429(4) 112.33(2) 2606(1) 4 1200 1.49 8.7 0.78 × 0.45 × 0.15 2.5–25 0–11, 0–27, 214 to 13 4692 4427 3276 343 0.0930 0.2776 w21 = s2(F) 1 0.014F2 0.001 1.7 Empirical absorption corrections using the y-scan method.a R = S[|Fo| 2 |Fc|]/S|Fo|. b R = Sw� �� [|Fo| 2 |Fc|]/Sw� �� |Fo|. hydrogens were placed in idealised positions [C]H 0.96 Å] and assigned a common isotropic thermal parameter (U = 0.08 Å2).Structure solution and refinement used the SHELXTL PLUS program.13 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 186/424. Computational cular orbital calculations.All calculations were based on approximate density functional theory using the Amsterdam Density Functional (ADF) package developed by Baerends and co-workers.14 The local density approximation was employed using the parameterisation of Vosko et al.15 for the exchangecorrelation potential. Gradient corrections to exchange (Becke 16) and correlation (Perdew17) functionals were included at each iteration of the self-consistent field procedure. The valence orbitals of Cr (3d, 4s and 4p) were represented by a triple-z Slater type orbital (STO) basis set.A double-z basis was employed for the 2s and 2p orbitals of C and O and the 1s orbital of H. For C and O this basis was augmented by a single 3d function, while for hydrogen a 2p orbital was used for polarisation. All electrons in lower shells were considered as core and treated according to the frozen-core approximation of Baerends et al.18 An auxiliary set of s, p, d, f and g STO functions, centred on all nuclei, was used to fit the molecular density.Idealised model geometries were based on the experimental structures of [Cr(CO)3(h-C16H16)] and [Cr(CO)3(h-C24H24)]. Within the {Cr(CO)3} fragments, the following bond lengths and angles were utilised: Cr]C 1.73, C]O 1.16 Å, O]C]Cr 180.0, C]Cr]C 90.08 and the chromium atom was placed 1.84 Å from the centroid of the co-ordinated ring. The centroids of the benzene rings were placed 3.02 Å and 4.36 Å apart to model [2.2]- and [2.2.2]-paracyclophane respectively.Acknowledgements P. J. D. acknowledges the Royal Society for a University Research Fellowship, D. G. H. thanks the Ramsay Memorial Fellowship Trust for a British Ramsay Fellowship and P. S. thanks the EPSRC for financial support. References 1 J. Schulz and F. Vögtle, Top. Curr. Chem., 1994, 172, 41. 2 E. D. Laganis, R. H. Voegeli, R. T. Swann, R. G. Finke, H. Hopf and V. Boekelheide, Organometallics, 1982, 11, 1415. 3 D. J. Cram and H. Steinberg, J. Am. Chem. Soc., 1951, 73, 5691; D. J. Cram and J. M. Cram, Acc. Chem. Res., 1971, 4, 204. 4 Y. Kai, N. Yasuoka and N. Kasai, Acta Crystallogr., Sect. B, 1978, 34, 2840. 5 H. Ohno, H. Horita, T. Otsubo, Y. Sakata and S. Misumi, Tetrahedron Lett., 1977, 265. 6 P. J. Dyson, D. G. Humphrey, J. E. McGrady, D. M. P. Mingos and D. J. Wilson, J. Chem. Soc., Dalton Trans., 1995, 4039. 7 M. Vemura, Adv. Met. Org. Chem., 1991, 2, 195. 8 E. O. Fischer, K. Ofele, H. Essler, W. Frohlich, J. P. Mortensen and W. Semmlinger, Chem. Ber., 1958, 91, 2763. 9 D. A. Brown, N. J. Gogan and H. Sloan, J. Chem. Soc., 1965, 6873. 10 C. Elschenbroich, J. Schneider, M. Wünsch, J.-L. Pierre, P. Baret and P. Chautemps, Chem. Ber., 1988, 121, 177. 11 W. Strohmeier, Chem. Ber., 1961, 94, 2490. 12 I. Tabushi, H. Yamada, Z. Yoshida and R. Oda, Tetrahedron, 1971, 27, 4845. 13 G. M. Sheldrick, SHELXTL PLUS, Program package for structure solution and refinement, version 4.2, Siemens Analytical X-Ray Instruments, Madison, WI, 1990. 14 P. M. Boerrigter, G. te Velde and E. J. Baerends, Int. J. Quantum Chem., Quantum Chem. Symp., 1988, 33, 307. 15 S. H. Vosko, L. Wilk and M. Nusair, Can. J. Phys., 1980, 58, 1200. 16 A. D. Becke, Phys. Rev. A, 1988, 38, 3098. 17 J. P. Perdew, Phys. Rev. B, 1986, 33, 8822. 18 E. J. Baerends, D. E. Ellis and P. Ros, Chem. Phys., 1973, 2, 41. Received 20th January 1997; Paper 7/00484B

ISSN:1477-9226    

DOI:10.1039/a700484b

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1607–1610 1607 Synthesis and crystal structure of the subvalent mercury cluster [triangulo-Hg3(Ï-dmpm)4][O3SCF3]4 (dmpm = Me2PCH2PMe2) Anna Mühlecker-Knoepfler,a Ernst Ellmerer-Müller,b Robert Konrat,b Karl-Hans Ongania,b Klaus Wurst a and Paul Peringer *,a a Institut für Allgemeine, Anorganische und Theoretische Chemie der Universität Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria b Institut für Organische Chemie der Universität Innsbruck, Innrain 52a, A-6020 Innsbruck, Austria The subvalent mercury cluster [triangulo-Hg3(m-dmpm)4][O3SCF3]4 [dmpm = bis(dimethylphosphino)methane], involving the 14/3 oxidation state of mercury, was formed by reaction of [Hg2]21 with 2 equivalents of dmpm or by reduction of a mixture of [Hg(Me2SO)6][O3SCF3]2 and dmpm in the molar ratio 2 : 4 with elemental Hg.The cation consists of a Hg3 triangle [Hg]Hg 276.68(14), 280.99(14) and 295.53(14) pm] in which two edges are bridged by one dmpm ligand and the third edge is doubly bridged by a pair of dmpm ligands.The three Hg atoms and the phosphorus atoms of the singly bridging dmpm ligands are nearly in a plane. The dihedral angles of the Hg3 triangle and the mean planes formed by the doubly bridged Hg atoms and the phosphorus atoms of the two bridging dmpm ligands respectively are 61 and 468. The complex is fluxional on the 31P NMR time-scale at 81 MHz at ambient temperature due to intramolecular exchange between the two different types of dmpm ligands.An interesting feature of the chemistry of mercury is the existence of subvalent cationic clusters.1,2 Mercury is unique in forming linear systems of directly bonded metal atoms. The simplest example is the mercury(I) ion [Hg]Hg]21 which can be regarded as a complex [HgL]21 with L = Hg0.2 Many salts and complexes of [Hg]Hg]21 are known.3 The formal co-ordination of one or two Hg0 atoms to [Hg]Hg]21 leads to [Hg]Hg] Hg]21 4–9 or [Hg]Hg]Hg]Hg]21.10–12 Infinite arrangements of Hg atoms are present in [Hg3–d]2 which contain either infinite linear chains 12–16 or planes 17 of Hg atoms.All the clusters mentioned above involve formal oxidation states <1. The cyclic system [Hg3]41, in which Hg has an oxidation number of 14/3, is the sole subvalent mercury cluster with a formal oxidation state >1. This can be formally regarded as an Hg0 atom donating to two mercury(II) ions resulting in threecentre two-electron bonding.In D3h symmetry the overlap of the s orbitals generates a bonding a19 molecular orbital and two degenerate weakly antibonding e9 orbitals. The a19 orbital is filled with two electrons, the e9 orbitals are empty.18 So far two examples containing the [Hg3]41 system are known: the mineral terlinguaite, Hg4Cl2O2, an insoluble co-ordination polymer,19–21 is composed of separate [Hg3]41 and Hg21 elements. The cluster [triangulo-Hg3(m-dppm)3][O3SCF3]4 1 [dppm = bis(diphenylphosphino) methane], the second example, is a molecular complex of [Hg3]41 entities and is soluble in common organic solvents.22 The existence of compound 1 indicates an important difference between subvalent clusters with formal oxidation states <1 and >1: most complexes of oxidation state <1 are co-ordinated by oxygen- or nitrogen-donor ligands or halides, but are unstable towards disproportionation into Hg0 and HgII in the presence of strong ligands, e.g.phosphines. It has been shown that PPh3 always causes disproportionation of [Hg]Hg]21, while weaker donors, e.g. PPh2(CF3) or PF3, cause disproportionation only if present in a ligand to [Hg]Hg]21 ratio of >1: 1 if at all.23,24 In contrast, each Hg atom of the [Hg3]41 cluster 1 is co-ordinated by two phosphorus atoms of the alkyldiarylphosphine dppm. This difference is now confirmed by the synthesis of the [Hg3]41 cluster [triangulo-Hg3(m-dmpm)4]41 2 [dmpm = bis(dimethylphosphino)methane]: the trialkylphosphine dmpm is strongly basic, and up to three P-donor atoms are coordinated per mercury.There is current interest in the luminescent properties of cluster chromophores. The photoluminescence of compound 1 18 as well as of heterometallic triangulo-clusters 25 has recently been investigated. The related cluster complexes [triangulo-Pt3(m-CO)- (m-dmpm)4]21 326 and [triangulo-Ni3(m3-CO)(m-dmpm)4]21 427 have been reported. Results and Discussion Synthesis Reaction of a mixture of [Hg(Me2SO)6][O3SCF3]2 and dmpm in the molar ratio 2 : 4 with elemental Hg at ambient temperature gives the cluster 2 [equation (1)].Alternatively, 2 was prepared 2[Hg(Me2SO)6][O3SCF3]2 1 4 dmpm 1 Hg [Hg3(m-dmpm)4][O3SCF3]4 1 12 Me2SO (1) by reaction of Hg2(O3SCF3)2 with dmpm according to equation (2). Crystals of 2 suitable for X-ray diffraction analysis were 2[Hg2][O3SCF3]2 1 4 dmpm [Hg3(m-dmpm)4][O3SCF3]4 1 Hg (2) obtained upon standing of a solution of [Hg(Me2SO)6]- [O3SCF3]2 and dmpm in the ratio 2 : 3 in MeOH–water.† In this reaction dmpm is thought to act as a reducing agent, since dmpm oxides were identified in the reaction mixture.Complex 2 is soluble in Me2SO and dimethylformamide (dmf) and has a very limited solubility in CH2Cl2, MeOH or acetone. Crystal structure The structure of complex 2 was determined by single-crystal X-ray analysis and is shown in Fig. 1. Crystal data are in Table 1, selected bond distances and angles in Table 2.The structure contains four CF3SO3 2 anions for each [Hg3(m-dmpm)4]41 cation confirming the 14/3 oxidation state of Hg. The cation consists † In a solution of this composition the manxane-type complex [Hg2- (m-dmpm)3][O3SCF3]4 is formed.281608 J. Chem. Soc., Dalton Trans., 1997, Pages 1607–1610 of a Hg3 triangle, two edges of which are spanned by one dmpm ligand whilst the third edge is doubly bridged by a pair of dmpm ligands. Correspondingly, the atoms Hg(1) and Hg(2) are surrounded by three phosphorus and two Hg atoms respectively.Atom Hg(3) is surrounded by two phosphorus, two Hg and one CF3SO3 oxygen atom. The three Hg atoms and the phosphorus atoms of the singly bridging dmpm ligands are nearly in a plane. The dihedral angles of the Hg3 triangle and the mean planes Hg(1)Hg(2)P(12)P(22) and Hg(1)Hg(2)- P(11)P(21), i.e. the planes formed by the doubly bridged Hg atoms and the phosphorus atoms of the two bridging dmpm ligands, are 61 and 468 respectively (Fig. 2). Both Hg(1)Hg(2)- P2C rings adopt envelope conformations with P]Hg]Hg]P torsion angles near zero. The co-ordination geometry of the doubly bridged Hg atoms makes a major difference to the related platinum and nickel complexes 3 26 and 4:27 both contain roughly planar M3(m-dmpm)3 groupings, whilst the fourth dmpm is co-ordinated roughly perpendicular to the M3(m-dmpm)3 planes (Fig. 2). Therefore, the two types of dmpm ligands have been termed latitudinal and longitudinal.The Hg]Hg distances in 2 are 276.68(14), 280.99(14) and 295.53(14) pm. The metal– metal distance in elemental mercury is 299 pm. All Hg]Hg separations are shorter than the P ? ? ? P bites of the corresponding dmpm ligands [P(11) ? ? ? P(21) 316.0(8), P(12) ? ? ? P(22) 312.2(8), P(13) ? ? ? P(31) 306.1(8), P(23) ? ? ? P(32) 306.3(8) pm]. The distance between the doubly bridged atoms Hg(1) Fig. 1 View of [triangulo-Hg3(m-dmpm)4]41 2 Fig. 2 View along the vector of the doubly bridged Hg atoms of [triangulo-Hg3(m-dmpm)4]41 2 and analogous projections of [triangulo- [Pt3(m-CO)(m-dmpm)4]21 3 and [triangulo-Ni3(m3-CO)(m-dmpm)4]21 4 showing the different co-ordination geometries of the doubly bridging dmpm ligands and Hg(2) is distinctly longer than the separations Hg(1)]Hg(3) and Hg(2)]Hg(3) involving the single bridges. The Hg]Hg distances in 1 22 are 276.4(1), 276.4(1) and 280.2(1) pm, a mean 277.7 pm, compared with 284.4 pm for 2.In contrast, there is Table 1 Crystal data and structure refinement for complex 2 Molecular formula C24H56F12Hg3O12P8S4 M 1742.46 Colour, habit Colourless prism Crystal size/mm 0.3 × 0.25 × 0.25 Crystal system Monoclinic Space group C2/m (no. 12) a/pm 2391.0(10) b/pm 1305.5(4) c/pm 3616.0(10) b/8 107.17(3) U/nm3 10.784(6) Z 8 T/K 173(2) Radiation (l/pm) Mo-Ka (71.073) Dc/Mg m23 2.146 m/mm21 9.000 F(000) 6624 q Range for data collection/8 3.02–24.28 hkl Ranges 215 to 23, 213 to 14, 239 to 38 Reflections collected 7691 Independent reflections (Rint) 6779 (0.0542) Reflections with I > 2s(I) 4408 Absorption correction y Scan Maximum and minimum transmission 1.00, 0.74 Data, restraints, parameters 6757, 9, 479 Goodness of fit on F2 1.072 Final R1, wR2 [I > 2s(I)] 0.0570, 0.1111 (all data) * 0.1098, 0.1488 Largest difference peak, hole/e nm23 1834, 21180 * Weighting scheme w = 1/[s2(Fo)2 1 (0.0211P)2 1 2.15P] where P = (Fo 2 1 2Fc 2)/3.Table 2 Selected bond lengths (pm) and angles (8) for complex 2 Hg(1)]P(11) 253.4(5) Hg(1)]P(13) 253.7(6) Hg(1)]P(12) 253.8(5) Hg(1)]Hg(3) 276.68(14) Hg(1)]Hg(2) 295.53(14) Hg(2)]P(23) 253.7(6) Hg(2)]P(21) 254.9(6) Hg(2)]P(22) 254.9(5) Hg(2)]Hg(3) 280.99(14) Hg(3)]P(32) 251.7(5) Hg(3)]P(31) 255.0(6) Hg(3)]O(1) 274(2) Hg(3) ? ? ? F(12I) 307(2) P(11)]C(21) 184(2) P(12)]C(12) 184(2) P(13)]C(13) 184(2) P(23)]C(23) 183(2) P(21)]C(21) 181(2) P(31)]C(13) 178(2) P(22)]C(12) 179(2) P(32)]C(23) 180(2) P(11)]Hg(1)]P(13) 104.1(2) P(11)]Hg(1)]P(12) 107.3(2) P(13)]Hg(1)]P(12) 108.7(2) P(11)]Hg(1)]Hg(3) 126.54(13) P(13)]Hg(1)]Hg(3) 90.46(13) P(12)]Hg(1)]Hg(3) 116.13(13) P(11)]Hg(1)]Hg(2) 91.52(13) P(13)]Hg(1)]Hg(2) 148.60(13) P(12)]Hg(1)]Hg(2) 91.83(13) Hg(3)]Hg(1)]Hg(2) 58.71(3) P(23)]Hg(2)]P(21) 105.9(2) P(23)]Hg(2)]P(22) 108.6(2) P(21)]Hg(2)]P(22) 105.7(2) P(23)]Hg(2)]Hg(3) 90.77(14) P(21)]Hg(2)]Hg(3) 127.83(13) P(22)]Hg(2)]Hg(3) 115.19(13) P(23)]Hg(2)]Hg(1) 147.55(14) P(21)]Hg(2)]Hg(1) 91.71(13) P(22)]Hg(2)]Hg(1) 91.91(14) Hg(3)]Hg(2)]Hg(1) 57.29(3) P(32)]Hg(3)]P(31) 106.6(2) P(32)]Hg(3)]Hg(1) 156.84(13) P(31)]Hg(3)]Hg(1) 96.16(14) P(31)]Hg(3)]Hg(2) 159.2(2) P(32)]Hg(3)]Hg(2) 93.78(13) Hg(1)]Hg(3)]Hg(2) 64.00(4) C(21)]P(11)]Hg(1) 110.8(6) C(21)]P(21)]Hg(2) 111.3(6) C(12)]P(12)]Hg(1) 111.2(6) C(13)]P(31)]Hg(3) 106.6(7) C(13)]P(13)]Hg(1) 110.9(7) P(21)]C(21)]P(11) 116.4(10) C(12)]P(22)]Hg(2) 111.6(6) P(32)]C(23)]P(23) 114.6(12) C(23)]P(23)]Hg(2) 113.6(8) C(23)]P(32)]Hg(3) 107.7(8) P(22)]C(12)]P(12) 118.3(10) P(31)]C(13)]P(13) 115.4(11) Symmetry transformation used to generate equivalent atoms: I 2x, y, 2z 1 ��� .J.Chem. Soc., Dalton Trans., 1997, Pages 1607–1610 1609 little variety in the Pt]Pt bond lengths of 3, the distance between the doubly bridged Pt atoms (264.8 pm) being very close to the distances between the singly bridged Pt atoms (262.8 and 262.0 pm). The mean Pt]Pt bond length of 3 (263.2 pm) is almost identical to the average value in [Pt3(m3-CO)(mdppm) 3]21 (263.4 pm).29 This has been interpreted to imply that the extra electrons in 3 do not occupy strongly antibonding orbitals.26 The Hg]P bond lengths cover a range of 251.7(5)– 255.0(6) pm and no obvious sensitivity to the environment can be observed.One oxygen atom of a CF3SO3 2 ion has a contact to Hg(3) at 274(3) pm. NMR spectroscopy The 31P-{1H} NMR spectrum of complex 2 in dmf at 297 K consists of three broad signals which sharpen upon cooling to 243 K.At 333 K there is only one slightly broadened resonance at the average value of the signals observed at 297 K; this is flanked by 199Hg satellites [J(HgP) 791 Hz] implying the presence of intramolecular exchange between the two different types of dmpm ligands present. The exchange on the 31P NMR time-scale (81 MHz) appears to be slow at 243 K and approaches the fast limit at 333 K. In contrast, the related platinum complex 3 is kinetically stable on the NMR time-scale at ambient temperature.26 The nickel complex 4 shows a rapid intramolecular rotation of the axial dmpm ligand about the Ni3 triangle.27 There is no interconversion of the dmpm ligands positioned in the Ni3 plane and the axial dmpm.Rotation about the M3 triangle thus occurs in both the complexes of Hg and Ni. However, all dmpm ligands in the mercury complex exchange only because of the equivalence of the two doubly bridging dmpm ligands.The signal at highest frequencies is attributed to atoms P(31) and P(32) (labelling as in Fig. 1) because the phosphorus-31 shift usually decreases as the co-ordination number of a d10 metal increases.30 The other two types of phosphorus atoms [P(11), P(12), P(21), P(22) and P(13), P(23) respectively] are readily assigned according to the intensity of the signals. The 31P-{1H} NMR spectrum of the isotopomer without 199Hg nuclei consists of a AA9XX9YY9Y9Y0Y90 spin system.The pattern is very complex and insufficiently resolved even at 11.744 T. Efforts to analyse the spectrum were unsuccessful. The patterns of the isotopomers containing 199Hg nuclei are broadened, presumably due to chemical shift anisotropy (CSA) relaxation processes. No 199Hg-{1H} NMR spectrum could be obtained. Mass spectrometry The use of gentle ionisation techniques has enabled the characterisation of ionic high-molecular-weight cluster complexes.The mass spectra of the related subvalent nickel complexes [triangulo-Ni3(m3-L)(m3-I)(m-dmpm)4]n1 and [{triangulo-Ni3- (m3-I)(m-dmpm)4}2(m3,m39-h1,h19-CN]R]NC)]21 [R = (CH2)6 or 1,4-C6H4] were recently measured by plasma desorption and fast atom bombardment (FAB) mass spectrometry.31 These clusters are neutral, mono- or di-cations. The mass spectrum of 2 was measured by FAB mass spectrometry. The molecular-ion signal enables the determination of the molecular weight. Experimental All reactions were carried out in Schlenk glassware by using standard inert-atmosphere techniques.The 31P NMR spectra were recorded on a Bruker AC 200 spectrometer at 81.015 MHz and are referenced against external H3PO4, mass spectra on a Finnigan MAT 95 instrument with the FAB technique. Microanalyses were by the Mikroanalytisches Laboratorium, Institut für Physikalische Chemie, Universität Wien. The complex [Hg- (Me2SO)6][O3SCF3]2 was prepared as described previously;32 dmpm was obtained from Strem Chemical Corp.Synthesis of [Hg3(Ï-dmpm)4][O3SCF3]4 2 (a) To a dmf (0.5 cm3) solution of [Hg(Me2SO)6][O3SCF3]2 (72.6 mg, 0.075 mmol) were added dmpm (0.0225 cm3, 0.15 mmol) and elemental Hg (0.1 cm3). After stirring for 12 h the dmf phase was separated and the solvent removed under reduced pressure. The residue was washed with MeOH (0.5 cm3) leaving the product as a white powder in almost quantitative yield, m.p. 268–270 8C (decomp.) (Found: C, 16.45; H, 2.9.C24H56F12Hg3O12P8S4 requires C, 16.55; H, 3.25%). 31P-{1H} NMR (243 K, [2H6] dmf): d 39.9 [m, P(31), J(HgP) ca. 1300], 12.9 [m, P(13), J(HgP) ca. 1500], 7.7 [m, P(11), J(HgP) ca. 1650 and 850 Hz], labelling as in Fig. 1. FAB mass spectrum: m/z 1747 (M1, 1.7), 1598 {[Hg3(dmpm)4(O3SCF3)3]1, 2.3}, 1462 {[Hg3(dmpm)3(O3SCF3)3]1, 5.0}, 1396 {[Hg2(dmpm)4(O3SCF3) 3]1, 3.1}, 1260 {[Hg2(dmpm)3(O3SCF3)3]1, 10.9}, 1124 {[Hg2(dmpm)2(O3SCF3)3]1, 28.6} and 1111 {[Hg2(dmpm)3(O3SCF3) 2]1, 2.0}.(b) To a MeOH (0.5 cm3) solution of [Hg(Me2SO)6][O3SCF3]2 (72.6 mg, 0.075 mmol) was added elemental Hg (0.1 cm3) and the mixture stirred for 10 min producing a solution of [Hg2]- [O3SCF3]2.31 The compound dmpm (0.0225 cm3, 0.15 mmol) was added and the mixture was stirred for 10 min. The MeOH phase was discarded and the residue was treated with dmf (0.5 cm3). The dmf phase was separated and processed as in (a). (c) Single crystals of complex 2 were obtained upon standing a solution of [Hg(Me2SO)6][O3SCF3]2 (48.4 mg, 0.05 mmol) and dmpm (0.011 cm3, 0.075 mmol) in water (0.6 cm3) and MeOH (0.4 cm3).Their identity with the products of methods (a) and (b) was checked by 31P NMR spectroscopy. Crystallography The crystallographic data were acquired on a Siemens P4 diffractometer. The structure was solved by direct methods (SHELXS 86) 33 and refined by a full-matrix least-squares procedure using F2 (SHELXL 93).34 All non-hydrogen atoms were refined with anisotropic displacement parameters.The hydrogen atoms were included in the refinement at calculated positions using a riding model. Three of the four CF3SO3 2 ions are located in general positions. The fourth is disordered in two positions with 50% occupancy. One of the disordered anions lies near the two-fold axis and could be refined without further difies. The other lies near an inversion centre with two or three possible directions of the S]C ion axis.An exact analysis of this disorder failed, because of different occupancy and overlying of the O, F and C atoms. Therefore only the two major orientations were refined with constrained S]C and C]F bond lengths. A crystal structure analysis of another crystal of complex 2 showed the same phenomenon. 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 186/418. Acknowledgements Financial support from the Fonds zur Förderung der Wissenschaftlichen Forschung. Project P 11842-PHY is gratefully acknowledged. References 1 L. H. Gade, Angew. Chem., Int. Ed. Engl., 1993, 32, 24. 2 P. A. W. Dean, in Comprehensive Coordination Chemistry, ed. G. Wilkinson, Pergamon, Oxford, 1987, vol. 2, p. 1. 3 K. Brodersen and H.-U. Hummel, in Comprehensive Coordination Chemistry, ed. G. Wilkinson, Pergamon, Oxford, 1987, vol. 5, p. 1049.1610 J. Chem. Soc., Dalton Trans., 1997, Pages 1607–1610 4 G. Torsi and G. Mamantov, Inorg. Nucl. Chem. Lett., 1970, 6, 843. 5 G. Torsi, K. W. Fung, G. M. Begun and G. Mamantov, Inorg. Chem., 1971, 10, 2285. 6 C. G. Davies, P. A. W. Dean, R. J. Gillespie and P. K. Ummat, Chem. Commun., 1971, 782. 7 R. J. Gillespie and P. K. Ummat, Chem.Commun., 1971, 1168. 8 R. D. Ellison, H. A. Levy and K. W. Fung, Inorg. Chem., 1972, 11, 833. 9 B. D. Cutforth, C. G. Davies, P. A. W. Dean, R. J. Gillespie, P. R. Ireland and K. Ummat, Inorg. Chem., 1973, 12, 1343. 10 B. D. Cutforth, R. J. Gillespie and P. R. Ireland, J. Chem. Soc., Chem. Commun., 1973, 723. 11 B. D. Cutforth, R. J. Gillespie, P. R. Ireland, J. F. Sawyer and P. K. Ummat, Inorg. Chem., 1983, 22, 1344. 12 I. D. Brown, R. J. Gillespie, K. R. Morgan, J. F. Sawyer, K.J. Schmidt, Z. Tun, P. K. Ummat and J. E. Vekris, Inorg. Chem., 1987, 26, 689. 13 I. D. Brown, B. D. Cutforth, C. G. Davies, R. J. Gillespie, P. R. Ireland and J. E. Vekris, Can. J. Chem., 1974, 52, 791. 14 N. D. Miro, A. G. MacDiarmid, A. J. Heeger, A. F. Garito and C. K. Chiang, J. Inorg. Nucl. Chem., 1978, 40, 1351. 15 Z. Tun and I. D. Brown, Acta Crystallogr., Sect. B, 1982, 38, 2321. 16 Z. Tun, I. D. Brown and P. K. Ummat, Acta Crystallogr., Sect. C, 1984, 40, 1301. 17 I. D. Brown, R. J. Gillespie, K. R. Morgan, Z. Tun and P. K. Ummat, Inorg. Chem., 1984, 23, 4506. 18 H. Kunkely and A. Vogler, Chem. Phys. Lett., 1993, 206, 467. 19 S. Scavnicar, Acta Crystallogr., 1956, 9, 956. 20 K. Aurivillius and L. Folkmarson, Acta Chem. Scand., 1968, 22, 2529. 21 K. Brodersen, G. Göbel and G. Liehr, Z. Anorg. Allg. Chem., 1989, 575, 145. 22 B. Hämmerle, E. P. Müller, D. L. Wilkinson, G. Müller and P. Peringer, J. Chem. Soc., Chem. Commun., 1989, 1527. 23 P. A. W. Dean and D. G. Ibbott, Inorg. Nucl. Chem. Lett., 1975, 11, 119. 24 P. A. W. Dean and D. G. Ibbott, Can. J. Chem., 1976, 54, 177. 25 D. V. Toronto, A. L. Balch and D. S. Tinti, Inorg. Chem., 1994, 33, 2507. 26 S. S. M. Ling, N. Hadj-Bagheri, L. Manojlovic�-Muir, K. W. Muir and R. J. Puddephatt, Inorg. Chem., 1987, 26, 231; R. J. Puddephatt, L. Manojlovic�-Muir and K. W. Muir, Polyhedron, 1990, 9, 2967. 27 G. Ferguson, M. C. Jennings, H. A. Mirza and R. J. Puddephatt, Organometallics, 1990, 9, 1576. 28 A. Knoepfler-Mühlecker and P. Peringer, unpublished work. 29 G. Ferguson, B. R. Lloyd and R. J. Puddephatt, Organometallics, 1986, 5, 344. 30 P. S. Pregosin and R. W. Kunz, 31P and 13C NMR of Transition Metal Phosphine Complexes, eds. P. Diehl, E. Fluck and R. Kosfeld, Springer, Berlin, 1979. 31 D. A. Morgenstern, C. C. Bonham, A. P. Rothwell, K. V. Wood and C. P. Kubiak, Polyhedron, 1995, 14, 1129. 32 P. Peringer, J. Inorg. Nucl. Chem., 1980, 42, 1501. 33 G. M. Sheldrick, SHELXS 86, program for crystal structure solutions, University of Göttingen, 1986. 34 G. M. Sheldrick, SHELXL 93, program for refinement of crystal structures, University of Göttingen, 1993. Received 21st January 1997; Paper 7/00

ISSN:1477-9226    

DOI:10.1039/a700483d

出版商:RSC    

年代:1997

数据来源: RSC

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DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1611–1616 1611 Synthesis, co-ordination chemistry and crystallographic studies of some bis(aminophosphines) Tuan Q. Ly, Alexandra M. Z. Slawin and J. Derek Woollins *,† Department of Chemistry, Loughborough University, Loughborough LE11 3TU, UK 1,2-Bis(diphenylphosphinoamino)benzene 1 and 3,4-bis(diphenylphosphinoamino)toluene 2 have been prepared; 1 is oxidised by sulfur or selenium to C6H4(NHPPh2S)2-1,2 3 and C6H4(NHPPh2Se)2-1,2 4 and by sulfur and selenium to C6H4(NHPPh2S)(NHPPh2Se)-1,2 5. The napthalene compounds C10H6(NHPPh2S)2-1,8 6, C10H6(NHPPh2Se)2-1,8 7, C10H6(NHPPh2S)(NHPPh2Se)-1,8 8 and the ethane compound C2H4(NHPPh2S)2-1,2 9 have also been prepared.The co-ordination of 2 to Mo0, PdII, PtII and AuI, i.e. in cis-[Mo(CO)4L], cis-[MCl2L] (M = Pd or Pt) and [(AuCl)2L] [L = MeC6H3(NHPPh2)2-3,4] is also described. The crystals structures of representative examples have been determined. 1,2-Bis[(diphenylphosphino)methyl]benzene has been known for some time 1 and shown readily to form complexes containing seven-membered chelate rings.2,3 The related system 1,4- bis(diphenylphosphino)butane also complexes with a wide range of transition metals.4 There is substantial interest in the catalytic potential of chelating diphosphine–palladium/ platinum(II) complexes as they are known to be responsible for many types of selective chemical reactions.5,6 Molybdenum– bis(diphosphine) compounds 7,8 also have catalytic potential.9 Interestingly, there have been relatively few reports on noncarbon spacers between the carbon backbone and the adjacent phosphines.Similarly whilst the chemistry of acetylacetones is extensive, work on the non-carbon relatives R2P(E)NH(E)PR2 has been on a more modest scale until recently.10,11 Here, we report on the synthesis and complexation properties of some bidentate phosphines where amino groups are incorporated as spacers between the phosphorus atoms and the aromatic backbone.Examples of their co-ordination chemistry with molybdenum, palladium, platinum and gold are described. Experimental General Diethyl ether, light petroleum (b.p. 60–80 8C) and tetrahydrofuran were purified by reflux over sodium and distillation under nitrogen. Dichloromethane was heated to reflux over powdered calcium hydride and distilled under nitrogen. Chemicals from Aldrich and Lancaster were 3,4-diaminotoluene, 1,2- diaminobenzene, 1,8-diaminonaphthalene, triethylamine and chlorodiphenylphosphine which were purified by sublimation or distillation before use; 4-(dimethylamino)pyridine was used as received.The compounds [Mo(CO)4(pip)2] (pip = piperidine),12 [MCl2(cod)] (M = Pd or Pt, cod = cycloocta- 1,5-diene) 13 and [AuCl(tht)] (tht = tetrahydrothiophene) 14 were prepared using literature procedures. Infrared spectra were recorded from KBr discs on a Perkin- Elmer system 2000 spectrometer, 31P NMR spectra on a JEOL FX90Q operating at 36.21 MHz, 1H, 13C and 31P NMR spectra on Bruker instruments operating at 250, 62.9 and 101.3 MHz respectively, and fast atom bombardment (FAB) mass spectra by the Swansea mass spectrometer service.Preparations C6H4(NHPPh2)2-1,2 1. To 1,2-diaminobenzene (2.58 g, 23.9 mmol) in tetrahydrofuran (50 cm3) was added triethylamine (6.4 † E-Mail: j.d.woollins@lboro.ac.uk cm3, 47.8 mmol) and 4-(dimethylamino)pyridine (100 mg, 0.8 mmol).A tetrahydrofuran (50 cm3) solution of chlorodiphenylphosphine (8.6 cm3, 47.8 mmol) was added dropwise (white precipitate of NEt3HCl formed immediately). Stirring was continued for 3 h. The solution was filtered through a sintered Schlenk tube and the residue washed with tetrahydrofuran (2 × 30 cm3). The filtrate was evaporated to dryness and then the light brown oil was washed with diethyl ether (3 × 50 cm3) to give a light brown powder in a crude yield of 5.09 g (45%), m.p. 82–85 8C. NMR (CDCl3): 1H, d 7.37 (m, aromatic), 6.85 (m, aromatic) and 4.35 (2 H, d, NH); 13C, d 131.2, 130.9, 129, 128.5, 128.4, 121.9, 119.8 and 119.5; 31P, d 32.5. IR (KBr disc, cm21): 3328w, 3066vw, 3044w, 3001vw, 1648vw, 1593s, 1578m, 1492s, 1455m, 1433s, 1357w, 1338vw, 1291m, 1265w, 1245m, 1182w, 1154w, 1091s, 1068m, 1037m, 1025m, 998m, 939m, 904vs, 868m, 847m, 752vs, 738vs, 696vs, 619w, 572w, 515vs, 470vs, 438s, 422m, 361m, 348m and 302s. FAB mass spectrum: m/z 477, [M 1 H]1 (Found: C, 74.9; H, 5.6; N, 4.3.C30H26N2P2 requires C, 75.6; H, 5.5; N, 5.9%). MeC6H3(NHPPh2)2-3,4 2. To a tetrahydrofuran (50 cm3) solution of 3,4-diaminotoluene (3.8 g, 31.1 mmol) was added triethylamine (9 cm3, 64.6 mmol) and 4-(dimethylamino)- pyridine (200 mg, 1.6 mmol). A solution of chlorodiphenylphosphine (11 cm3, 60.3 mmol) in tetrahydrofuran (100 cm3) was added dropwise. Stirring was continued for 2 h. The solution was filtered through a sintered Schlenk tube and the residue washed with tetrahydrofuran (2 × 40 cm3).The filtrate was evaporated to dryness in vacuo. The product was washed with ether (2 × 50 cm3) and then dried in vacuo to give a yield of 14.1 g (93%), m.p. 71–73 8C. NMR (CDCl3): 31P, d 33.3 and 30.4; 1H, d 7.21 (m, aromatic), 6.90 (m, aromatic), 6.84 (d, aromatic), 6.50 (d, aromatic), 4.38 (d, J = 8 Hz, NH), 3.89 (1 H, d, NH) and 2.12 (3 H, s, CH3); 13C, d 128 (m, aromatic) and 19.8 (1 C, d, CH3). IR (KBr disc, cm21): 3329vw, 3320vw, 3067vw, 2954vw, 1656vw, 1647vw, 1608m, 1571w, 1504vs, 1479s, 1433vs, 1365m, 1325w, 1297s, 1262m, 1174m, 1114m, 1093s, 1069w, 1026w, 999w, 960m, 887s, 849m, 819m, 749s, 738vs, 696vs and 508s (Found: C, 73.9; H, 5.6; N, 5.5.C31H28N2P2 requires C, 75.9; H, 5.7; N, 5.7%). C6H4(NHPPh2S)2-1,2 3. Compound 1 (3.38 g, 7.1 mmol) was dissolved in tetrahydrofuran (50 cm3) and sublimed sulfur (462 mg, 14.4 mmol) was added. The yellow sulfur powder gradually disappeared and the flask felt warm as all the sulfur dissolved.The solvent was removed from the reaction mixture in vacuo and the white material washed with carbon disulfide (2 × 301612 J. Chem. Soc., Dalton Trans., 1997, Pages 1611–1616 cm3) and diethyl ether (2 × 30 cm3), yield 3.03 g (79%), m.p. 164–167 8C. 31P NMR (CDCl3): d 56.7. IR (KBr disc, cm21): 3312w, 3054w, 1640m, 1600m, 1561w, 1499s, 1436vs, 1382m, 1295ms, 1258w, 1206vw, 1104vs, 1049w, 1027vw, 998vw, 943w, 930vs, 896w, 806w, 750vs, 714vs, 692vs, 661w, 639vs, 631s, 614m, 565w, 509s, 496s, 451w, 439w and 407w.FAB mass spectrum: m/z 563, [M 1 Na]1; 541, [M 1 H]1; 540, M1; 324, [M 1 H 2 Ph2PS]1 and 291, [M 1 H 2 Ph2PS2]1 (Found: C, 65.3; H, 4.5; N, 5.2. C30H26N2P2S2 requires C, 66.6; H, 4.9; N, 5.2%). C6H4(NHPPh2Se)2-1,2 4. Compound 1 (4.52 g, 9.5 mmol) in toluene (150 cm3) and selenium (1.5 g, 19 mmol) were stirred for 1 h. A white precipitate formed within 10 min of addition of grey selenium. Tetrahydrofuran (100 cm3) was added to dissolve the product and the solution was then passed through Celite.The solvent was removed (Rotavap.) to yield 5.14 g (85%), m.p. 112–115 8C. 31P NMR (CDCl3): d 53.9 [1J(PSe) 764 Hz]. IR (KBr disc, cm21): 3308w, 3052vw, 1600w, 1561w, 1498s, 1478m, 1435vs, 1381m, 1311w, 1293m, 1255m, 1184w, 1100vs, 1049w, 1026vw, 998vw, 944w, 923s, 891w, 853vw, 805w, 750vs, 714s, 690vs, 618vw, 606vw, 559s, 545s, 522s, 508s, 489s and 387w. FAB mass spectrum: m/z 637, [M 1 H]1 and 636, M1 (Found: C, 56.2; H, 3.9; N, 4.4.C30H26N2P2Se2 requires C, 56.6; H, 4.1; N, 4.4%). C6H4(NHPPh2S)(NHPPh2Se)-1,2 5. The intermediate was prepared in the same way as compound 1, from 1,2- Diaminobenzene (1.36 g, 12.6 mmol), triethylamine (3.6 cm3, 26 mmol), 4-(dimethylamino)pyridine (55 mg, 0.4 mmol) and chlorodiphenylphosphine (4.5 cm3, 25.1 mmol). Sulfur (403 mg, 12.6 mmol) was added and stirred for 1 h followed by grey selenium (993 mg, 12.6 mmol) and allowed to react overnight.The solution was passed through Celite, then the solvent was removed in vacuo and the product washed with ether (2 × 40 cm3) to give a yield of 6.98 g (94%), m.p. 210–212 8C. 31P NMR (CDCl3): d 56.8 [5J(PP) 13] and 53.4 [5J(PP) 13, 1J(PSe) 764 Hz]. IR (KBr disc, cm21): 3310w, 3055vw, 1647w, 1596m, 1561w, 1499vs, 1479m, 1458w, 1436vs, 1382s, 1294vs, 1256m, 1184s, 1158m, 1101vs, 1070w, 1049w, 1026w, 998w, 943m, 929vs, 894m, 854vw, 809m, 790m, 750vs, 714vs, 691vs, 638s, 614m, 607m, 556s, 524s, 507s, 494s, 439w and 401w.FAB mass spectrum: m/z 611, [M 1 Na]1; 589, [M 1 H]1 and 588, M1 (Found: C, 61.0; H, 4.2; N, 4.7. C30H26N2P2SSe requires C, 61.2; H, 4.5; N, 4.8%). C10H6(NHPPh2S)2-1,8 6. This compound was prepared in the same way as for 3. 1,8-Diaminonaphthalene (1 g, 6.5 mmol), triethylamine (1.9 cm3, 14.3 mmol), 4-(dimethylamino)pyridine (80 mg, 0.6 mmol), chlorodiphenylphosphine (2.3 cm3, 12.8 mmol), and sulfur (500 mg, 16 mmol) were used to give a yield of 2.37 g (62%), m.p. 238–241 8C. 31P NMR (CDCl3): d 57.9. IR (KBr disc, cm21): 3147w, 3055vw, 1639vw, 1600w, 1577m, 1561vw, 1510vw, 1437vs, 1396s, 1310m, 1267vs, 1177vw, 1161vw, 1108vs, 1107vs, 1069vw, 1035vs, 998w, 922w, 893s, 836s, 766vs, 745vs, 730vs, 718vs, 690vs, 648s, 629vs, 613vs, 565s, 520vs, 502vs, 485s, 436m, 420s and 390s. FAB mass spectrum: m/z 591, [M 1 H]1 (Found: C, 68.5; H, 4.5; N, 4.6. C34H28N2P2S2 requires C, 69.1; H, 4.8; N, 4.7%).C10H6(NHPPh2Se)2-1,8 7. This compound was prepared in the same way as for 4. 1,8-Diaminonaphthalene (1.2 g, 7.6 mmol), triethylamine (2.2 cm3, 15.8 mmol), 4- (dimethylamino)pyridine (50 mg, 0.4 mmol), chlorodiphenylphosphine (2.6 cm3, 14.5 mmol), and grey selenium (1.2 g, 15 mmol) were used to obtain a yield of 1.2 g (22%), m.p. 260– 264 8C. 31P NMR (CDCl3): d 53.3 [1J(PSe) 792 Hz]. IR (KBr disc, cm21): 3127vw, 3049vw, 1598vw, 1575vw, 1475vw, 1436s, 1390s, 1309w, 1265s, 1097s, 1069w, 1034s, 1027m, 998w, 978vw, 921w, 892m, 867vw, 835m, 763vs, 742vs, 725vs, 712m, 689vs, 640w, 619w, 569s, 551vs, 515s, 497m, 481m, 460m and 382m.FAB mass spectrum: m/z 687, [M 1 H]1 and 686, M1 (Found: C, 58.8; H, 3.4; N, 4.1. C34H28N2P2Se2 requires C, 59.5; H, 4.1; N, 4.1%). C10H6(NHPPh2S)(NHPPh2Se)-1,8 8. This compound was prepared in the same way as for 5 where 1,8-diaminonaphthalene (755 mg, 4.8 mmol), triethylamine (1.4 cm3, 10 mmol), 4-(dimethylamino)pyridine (30 mg, 0.2 mmol), chlorodiphenylphosphine (1.6 cm3, 9.3 mmol), sulfur (125 mg, 3.9 mmol) and grey selenium (308 mg, 3.9 mol) were used to give a yield of 1.4 g (45%), m.p. 250–252 8C. 31P NMR (CDCl3): d 56.1 [5J(PP) 22] and 53.0 [5J(PP) 22, 1J(P]] Se) 792 Hz]. IR (KBr disc, cm21): 3143vw, 3054vw, 1642vw, 1613w, 1599w, 1576m, 1478w, 1436s, 1393s, 1309m, 1266s, 1162w, 1123vw, 1097s, 1070w, 1034s, 998m, 979vw, 921m, 892s, 835s, 764vs, 744vs, 728vs, 713vs, 690vs, 645m, 630s, 612s, 555s, 538s, 517s, 501s, 482m, 470m and 388s.FAB mass spectrum: m/z 639, [M 1 H]1 (Found: C, 63.9; H, 3.8; N, 4.0. C34H28N2P2SSe requires C, 63.9; H, 4.4; N, 4.4%). C2H4(NHPPh2S)2-1,2 9. This was prepared in the same way as for compound 3. 1,2-Diaminoethane (0.9 cm3, 13.5 mmol), triethylamine (4.2 cm3, 30.1 mmol), 4-(dimethylamino)pyridine (100 mg, 0.8 mmol), chlorodiphenylphosphine (5 cm3, 27.8 mmol) and sulfur (0.9 g, 28.1 mmol) were used to give a yield of 4.5 g (65%), m.p. 118–121 8C. 31P NMR (CDCl3): d 60.4. IR (KBr disc, cm21): 3368m, 3266w (br), 3052w, 2977w, 2937w, 2879w, 2739w, 2677w, 2603m, 2495m, 1476s, 1437vs, 1398s, 1384m, 1309w, 1201m, 1173m, 1105vs, 1083vs, 1037s, 997m, 863m, 853m, 807w, 754s, 742s, 716vs, 698vs, 692vs, 633s, 627s, 613s, 531s, 497s, 462w, 404w, 247m and 240w. FAB mass spectrum: m/z: 515, [M 1 Na]1; and 493, [M 1 H]1 (Found: C, 62.6; H, 4.9; N, 5.6. C26H26N2P2S2 requires C, 63.4; H, 5.3; N, 5.7%). cis-[Mo(CO)4{MeC6H3(PNHPPh2)2-3,4}].To a partially dissolved solution of [Mo(CO)4(pip)2] (99 mg, 262 mmol) in dichloromethane (15 cm3) was added 3,4-bis(diphenylphosphinoamino) toluene 2 (147 mg, 300 mmol). The cloudiness in the solution disappeared after 5 min of stirring. Stirring was continued for 2 h and then the solvent was removed in vacuo. The light yellow product was washed with light petroleum (2 × 20 cm3) and dried in vacuo to give a yield of 180 mg (98%), m.p. 208– 211 8C. 31P NMR (CDCl3): d 84.9 and 84.6 [2J(PP) 35 Hz].IR (KBr disc, cm21): 3333vw, 3054vw, 2924vw, 2853vw, 2026vs, 1947vs, 1911vs (br), 1608vw, 1585vw, 1509m, 1479m, 1433s, 1365w, 1295m, 1260w, 1217vw, 1181vw, 1159vw, 1125w, 1090s, 1071vw, 1027vw, 999vw, 963vw, 907m, 858vw, 815vw, 742s, 697vs, 647vw and 607s. FAB mass spectrum: m/z 700, M1 (Found: C, 59.6; H, 3.6; N, 4.0. C35H28MoN2O4P2 requires C, 60.0; H, 4.0; N, 4.0%). cis-[PdCl2{MeC6H3(PPh2)2-3,4}]. To solution of [PdCl2(cod)] (33 mg, 88 mmol) in dichloromethane (5 cm3) was added 3,4- bis(diphenylphosphinoamino)toluene 2 (44 mg, 90 mmol).The solvent was removed and the product washed with light petroleum (2 × 10 cm3) to give a crude yield of 56 mg (94%), decomp. 200–202 8C. 31P NMR (CDCl3): d 62.4 and 60.1 [2J(PP) 31 Hz]. IR (KBr disc, cm21): 3169w, 3052w, 2920vw, 2854vw, 1595vw, 1512m, 1481m, 1459w, 1435vs, 1389w, 1312m, 1262vw, 1222vw, 1183vw, 1160vw, 1128vw, 1101vs, 1027w, 998w, 817w, 744s, 711m, 691vs, 510vs, 469m and 295m.FAB mass spectrum: 691, [M 1 Na]1; 668, M1; 633, [M 2 Cl]1; 596, [M 2 2Cl]1 (Found: C, 55.1; H, 3.6; N, 4.0. C31H28Cl2N2P2Pd requires C, 55.8; H, 4.2; N, 4.2%). cis-[PtCl2{MeC6H3(NHPPh2)2-3,4}]. This was prepared in the same way as the palladium complex using [PtCl2(cod)] (100 mg, 267 mmol) and 3,4-bis(diphenylphosphinoamino)toluene 2 (133 mg, 271 mmol) to give a yield of 202 mg (100%), m.p.J. Chem. Soc., Dalton Trans., 1997, Pages 1611–1616 1613 Table 1 Selected IR and NMR spectroscopic data for compounds 1–9 Compound 31P NMR (d, J/H2) n(NH) n(PN) n(P]] E) 1 C6H4(NHPPh2)2 2 MeC6H3(NHPPh2)2 3 C6H4(NHPPh2S)2 4 C6H4(NHPPh2Se)2 5 C6H4(NHPPh2S)(NHPPh2Se) 6 C10H6(NHPPh2S)2 7 C10H6(NHPPh2Se)2 8 C10H6(NHPPh2S)(NHPPh2Se) 9 C2H4(NHPPh2S)2 32.5 33.3, 30.4 [2J(PP) 0] 56.7 53.9 [1J(PSe) 764] 56.8 [5J(PP) 13], 53.4 [5J(PP) 13, 1J(PSe) 764] 57.9 53.3 [1J(PSe) 792] 56.1 [5J(PP) 22], 53.0 [5J(PP) 22, 1J(PSe) 792] 60.4 3328m 3329w, 3320w 3312w 3308w 3310w 3147w 3127vw 3143vw 3368m 904vs, 738vs 887s, 738vs 930vs, 714vs 923vs, 714m 929vs, 714vs 893s, 730vs 892m, 725vs 892s, 728vs 1083vs, 716vs 639s 551m, 522m 638s, 556m, 524m 629vs 551s 645m, 555s 633s, 627s, 613s 279–280 8C. 31P NMR (CDCl3): d 39.0 and [2J(PP) 13, 1J(PPt) 3943 Hz] and 36.3 [2J(PP) 13, 1J(PPt) 3887 Hz]. IR (KBr disc, cm21): 3448w, 3211w, 3051vw, 2921vw, 2860vw, 1512w, 1481vw, 1459w, 1436vs, 1377vw, 1314w, 1129vw, 1101s, 1022vw, 998vw, 972vw, 891w, 815vw, 747m, 691vs, 583vw, 547w, 532m, 512vs, 486w, 469w, 444w, 317w, 305w, 283w, 253m and 246vs.FAB mass spectrum: m/z 779, [M 1 Na]1; 756, M1; 721, [M 2 Cl]1; and 684/685, [M 2 2Cl]1 [Found: C, 47.9; H, 3.6; N, 3.5. (C31H28Cl2N2P2Pt)2?CH2Cl2 requires C, 47.4; H, 3.7; N, 3.5%]. [(AuCl)2{MeC6H3(NHPPh2)2-3,4}]. This was prepared in the same way as the palladium complex using [AuCl(tht)] (60 mg, 187 mmol) and 3,4-bis(diphenylphosphinoamino)toluene 2 (47 mg, 96 mmol) to give a crude yield of 66 mg (72%), m.p. 146– 149 8C. NMR (CDCl3): 31P, d 60.9 and 59.6; 1H, d 7.21 (m, aromatic), 6.60 (m, aromatic), 6.50 (d, aromatic), 6.44 (d, aromatic), 5.45 (1 H, br s, NH), 5.33 (1 H, br s, NH) and 1.90 (3 H, s, CH3). IR (KBr disc, cm21): 3357vw, 2950vw, 2863vw, 1509s, 1436s, 1376w, 1294w, 1261vw, 1211vw, 1160vw, 1105s, 1027vw, 998vw, 969vw, 917vw, 886vw, 808w, 746m, 691vs, 531m, 498m, 419vw, 398w, 375vw, 352m, 334m, 326m, 303vs, 290s, 279vs, 254m, 247m and 227w. FAB mass spectrum: m/z 977, [M 1 Na]1; and 919, [M 2 Cl]1 (Found: C, 38.5; H, 3.2; N, 2.6.C31H28Au2Cl2N2P2 requires C, 39.0; H, 2.9; N, 2.9%). Crystallography Details of the data collections and refinements are summarised in Table 1. Data were collected at room temperature using Cu- Ka (l = 1.541 78 Å) and w scans with a Rigaku AFC7S diffractometer. Intensities were corrected for Lorentz-polarisation and for absorption (DIFABS15 or y-scans). The structures were solved by the heavy-atom method or by direct methods.For compound 4 only extremely small crystals were available, which led to a low number of observed reflections; only the P, Se and N atoms were refined anisotropically. In the other cases all of the non-hydrogen atoms were refined anisotropically. In 6 and 7 the absolute chirality was tested using the Flack parameter which refined to 0.02(1) and 0.08(1) respectively. In cis- [Mo(CO)4{MeC6H3(NHPPh2)2-3,4}] the methyl substituent on the aryl backbone was disordered over two sites with refined occupancies of 70 and 30%.In cis-[PtCl2{MeC6H3(NHPPh2)2- 3,4}] the dichloromethane solvate was present as two 50% occupancy molecules. The positions of the hydrogen atoms were idealised. Refinements were by full-matrix least squares based on F using TEXSAN.16 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 186/431. Results and Discussion The most efficient route for preparing Ph2PNHPPh2 with an amino spacer between the two phosphines is by treating PPh2Cl with NH(SiMe3)2.17 Surprisingly, little advantage has been taken of the ease of P]N bond-forming reactions in the synthesis of new phosphines, in part perhaps because of assumptions about the lability of the P]N bond. We have used this route to synthesize a range of diphosphine systems with amino spacers to aromatic backbones.Deprotonating the amines attached to the appropriate aromatic backbones, i.e. 3,4-diaminotoluene, 1,2-diaminobenzene, 1,8-diaminonaphthalene or 1,2-diaminoethane with triethylamine in the presence of a catalytic amount of 4-(dimethylamino)pyridine [equation (1), R = aryl] works effectively and we obtained the new PPh2Cl 1 R(NH2)2 2NEt3 R(NHPPh2)2 1 2NEt3HCl (1) phosphines in good yield. 1,2-Bis(diphenylphosphinoamino)- benzene 1 and 3,4-bis(diphenylphosphinoamino)toluene 2 are air stable indefinitely. Compounds 1 and 2 gave satisfactory microanalyses; 1 displayed a singlet in the 31P-{1H} NMR spectrum (d 32.5) and the expected 1H NMR spectrum (NH as a doublet at d 4.35), 2 displayed two peaks in the 31P-{1H} NMR spectrum (d 33.3 and 30.4) and a similar 1H NMR spectrum (NH as two doublets at d 4.38 and 3.89). The NMR shifts of 1 and 2 may be compared with those of 1,2-(Ph2PCH2)2C6H4 [31P-{1H}, d 213.5; 1H for CH2 at d 3.31]; the amino groups in 1 and 2 contribute to a significant difference in d values between the carbon- and nitrogen-based systems. It is noteworthy that the dP values in are similar to that of Ph2PNHPPh2 (d 33) suggesting that the neighbouring atom dominates the shift.Assignment of their IR spectra is difficult, but we can identify n(NH) at 3328 and 3329 cm21 and n(PN) at 904 and 887 cm21 for 1 and 2 respectively.The positive-ion FAB mass spectra gave the expected parent ions with appropriate isotopes distributions. The compound R2PNHPR2 may be oxidised by elemental sulfur or selenium in toluene at reflux to form Ph2P(S)NH- (S)PPh2 17 or Ph2P(Se)NH(Se)PPh2.18 As expected the new diphosphines described here were readily oxidised by sulfur or selenium at room temperature in tetrahydrofuran or toluene [equation (2)]. We tested this reaction using simple phenyl com- R(NHPPh2)2 1 E thf or ether R[NHP(E)Ph2]2 E = ��4 S8 or 2Se (2) pounds as well as naphthyl and ethyl backbones. The NMR and selected IR data for the new compounds are given in Table 1. The 31P-{1H} NMR spectra of 3, 6 and 9 displayed the expected singlets (d 56.7, 57.9 and 60.4 respectively) and are shifted around 30 ppm downfield on going from PIII to PV.The 1H NMR spectra contain the NH resonance (as a doublet at d 5.80, 6.76 and 3.28). Compounds 4 and 7 showed singlets with selenium satellites in the 31P-{1H} NMR spectrum [d 53.9, 1J(PSe) 764 and 53.3, 1J(PSe) 792 Hz].The n(PN) and n(PE) vibrations are assigned in Table 1. The mixed sulfur–selenium compound 5 has also been prepared by treating 1 with 1 mol of sulfur for 1 h followed by 11614 J. Chem. Soc., Dalton Trans., 1997, Pages 1611–1616 mole of selenium in tetrahydrofuran [equation (3)]. Compound C6H4(NHPPh2)2 1 ��8 S8 1 Se thf or ether C6H4[NHP(S)Ph2][NHP(Se)Ph2] (3) 5 showed two doublets with selenium satellites in the 31P-{1H} NMR spectrum {d (31P) 56.79 [5J(PP) 13] and 53.39 [1J(PSe) 764 Hz]}.Compounds 3–8 can easily be recrystallised from dichloromethane–diethyl ether; 9 was recrystallised from methanol or dichloromethane-diethyl ether. All the oxidised compounds in Table 1 are colourless. The crystal structures of compounds 4 and 6–9 confirmed the proposed formulations; comparative selected bond lengths Fig. 1 Crystal structure of compound 4 Fig. 2 Crystal structure of compound 6; 7 and 8 are isomorphous Fig. 3 Crystal structure of compound 9 are given in Table 3. In 4 the amino nitrogen atoms are approximately coplanar with the aryl backbone with one phosphorus also lying in this plane and the other phosphorus atom above the aryl backbone plane (Fig. 1). However, in 6–8 (which are isomorphous) a rather more symmetric arrangement is adopted (Fig. 2) with the phosphorus atoms being on opposite sides of the naphthalene plane.The pyramidalisation at nitrogen leads to these structures being chiral. This is most obvious in the case of 7, where the (R,R) conformation is clearly identi- fied. However in 6 although the pyramidalisation is clear at N(1) (R form) it is less pronounced at N(8). In 9 the crystal structure reveals (Fig. 3) two independent half molecules both of which are located on crystallographic centres of symmetry. There is a weak intermolecular hydrogen bond between the two independent molecules [H(ln*) ? ? ? S(2) 2.48, N(1*) ? ? ? S(2) 3.50 Å, N(1*)]H(ln*) ? ? ? S(2) 1448]. 3,4-Bis(diphenylphosphinoamino)toluene reacted immediately with [Mo(CO)4(pip)2] to displace the piperidines and form Fig. 4 Crystal structure of cis-[Mo(CO)4{MeC6H3(NHPPh2)2-3,4}]. Only the 70% occupancy substituent methyl group is shown Fig. 5 Crystal structure of cis-[PdCl2{MeC6H3(NHPPh2)2-3,4}]J. Chem. Soc., Dalton Trans., 1997, Pages 1611–1616 1615 Table 2 Details of the crystal data and refinements Compound 4 6 7 8 a 9 cis-[Mo(CO)4- {MeC6H3- (NHPPh2)2}] cis-[PdCl2- {MeC6H3- (NHPPh2}2] Empirical formula M Colour, habit Crystal size/mm Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 m(Cu-Ka)/mm21 F(000) Independent reflections Observed reflections Data: parameter ratio Minimum, maximum transmission P in weighting scheme Final R, R9 Largest D/s Largest difference peak, hole/e Å23 C30H26N2P2Se2 634.42 Clear, plate 0.15 × 0.15 × 0.10 Monoclinic C2/c (no. 15) 23.236(11) 9.061(14) 26.275(9) 96.44(4) 5497 8 1.53 4.63 2544 3061 1245 b 7.7 0.71, 1.0 0.004 0.095, 0.055 0.05 0.72, 20.77 C34H28N2P2S2 590.68 Clear, prism 0.15 × 0.23 × 0.32 Monoclinic P21 (no. 4) 9.809(4) 15.942(6) 10.381(4) 116.19(3) 1456 2 1.35 2.89 616 2263 1827 c 5.1 0.25, 1.0 0.003 0.060, 0.044 0.06 0.39, 20.35 C34H28N2P2Se2 684.48 Clear, plate 0.20 × 0.10 × 0.25 Monoclinic P21 (no. 4) 9.832(4) 16.030(3) 10.454(4) 116.47(3) 1475 2 1.54 4.46 688 2285 2197 c 6.1 0.87, 1.0 0.007 0.024, 0.026 0.01 0.20, 20.18 C34H28N2P2Se Clear, cube 0.24 × 0.26 × 0.26 Monoclinic P21 (no. 4) 9.828(5) 15.987(4) 10.417(5) 116.35(3) 1467 2 C26H26N2P2S2 492.57 Clear, block 0.20 × 0.20 × 0.26 Triclinic P1� (no. 2) 12.345(3) 12.698(2) 9.316(3) 105.05(2) 107.92(2) 103.44(2) 1262 2 1.30 3.22 516 3032 2519 c 8.7 0.63, 1.0 0.003 0.073, 0.066 0.02 0.39, 20.47 C35H28MoN2O4P2 698.5 Clear, needle 0.25 × 0.03 × 0.03 Triclinic P1� (no. 2) 10.718(2) 15.066(2) 10.214(1) 99.21(1) 93.27(1) 85.43(1) 1621 2 1.43 4.57 712 4812 2680 d 6.58 0.88, 1.0 0.007 0.042, 0.040 0.04 0.49, 20.29 C32H30Cl4N2P2Pd 752.8 Clear, block 0.10 × 0.10 × 0.20 Monoclinic P21/n (no. 14) 17.385(5) 8.760(3) 25.289(2) 109.68(1) 3626 4 1.38 7.85 1520 5809 3666 b 9.21 0.48, 1.0 0.003 0.082, 0.065 0.57 0.84, 21.39 a The sulfur and selenium atoms were disordered, although a full data set was obtained no refinement resulting in meaningful bond lengths and angles was possible.b I >1.5s(I ). c I >3.0s(I ). d I >2.0s(I ). a seven-membered-ring metal complex with molybdenum as shown in eqIts crystal structure reveals (Fig. 4) a [Mo(CO)4(pip)2] 1 MeC6H3(Ph2PNH)2-3,4 [Mo(CO)4{MeC6H3(NHPPh2)2-3,4}] (4) distorted octahedron with the carbonyl groups pushed away slightly by the phenyl groups of the phosphorus atoms. The seven-membered ring has some modest distortions from symmetric (Table 4) but (excluding the ME substituent) the molecule possesses approximate non-crystallographic C2 symmetry about an axis passing through the Mo atom and the middle of the C(1)]C(2) bond.Table 3 Comparative selected bond lengths (Å) and angles (8) for compounds 4, 6, 7 and 9. For 4, 6 and 7 the different P]E/P]N, etc. values are for the related bonds within the same molecule, whilst for 9 there are two independent half molecules with the one unique parameter reported for each independent molecule 4 6 7 9 * P]E P]N C]N N]P]E C]N]P E? ? ?E conformation 2.081(6) 2.107(5) 1.700(13) 1.638(13) 1.400(20) 1.413(19) 115.8(5) 114.3(5) 127.3(12) 124.5(12) anti 1.951(4) 1.957(4) 1.659(7) 1.655(7) 1.469(10) 1.464(1) 117.6(5) 114.2(3) 121.0(6) 121.6(6) anti 2.112(2) 2.111(8) 1.646(4) 1.676(4) 1.449(6) 1.439(6) 114.2(1) 116.8(2) 122.8(3) 120.8(3) anti 1.936(3) 1.943(2) 1.649(5) 1.654(5) 1.479(8) 1.523(8) 119.1(2) 118.3(2) 121.2(5) 123.5(4) anti * The second value of (e.g.P]E) comes from the second independent molecule throughout.Compound 2 reacts with [MCl2(cod)] to form the expected seven-membered chelate complex [equation (5), M = Pd or Pt]. [MCl2(cod)] 1 MeC6H3(Ph2PNH)2-3,4 [PdCl2{MeC6H3(NHPPh2)2-3,4}] (5) The palladium complex displayed an AX system in the 31P-{1H} NMR spectrum {d 62.4 and 60.1 [2J(PP) 31 Hz]} with the two phosphorus atoms coupling through the metal centre. Similarly the platinum complex displays an AX spectrum with platinum satellites in the 31P-{1H} NMR spectrum {d 39.0 [2J(PP) 13, 1J(PPt) 3943] and 36.3 [2J(PP) 13, 1J(PPt) 3887 Hz]}.The difference in the two inequivalent phosphorus peaks (Dd = 2.91 ppm) for the free phosphine is reduced (Dd = 0.27 ppm] for the metal complex. The crystal structure of the palladium complex reveals (Fig. 5) the seven-membered ring to have a similar geometry to that Table 4 Comparative selected bond lengths (Å) and angles (8) for the molybdenum and palladium complexes; L = MeC6H3(NHPPh2)2-3,4 cis-[Mo(CO)4L] cis-[PdCl2L] M]P(1) M]P(2) P(1)]N(1) P(2)]N(2) N(1)]C(1) N(2)]C(2) C(1)]C(2) P(1)]M]P(2) M]P(1)]N(1) M]P(2)]N(2) P(1)]N(1)]C(1) P(2)]N(2)]C(2) N(1)]C(1)]C(2) N(2)]C(2)]C(1) 2.516(2) 2.471(2) 1.688(6) 1.717(6) 1.415(9) 1.456(9) 1.382(10) 84.6(1) 115.6(2) 113.9(2) 128.4(5) 114.7(5) 124.5(7) 120.5(6) 2.234(2) 2.245(2) 1.700(7) 1.681(8) 1.462(11) 1.407(10) 1.386(11) 91.31(8) 114.0(2) 117.6(3) 113.2(5) 128.9(6) 118.7(8) 126.0(9)1616 J.Chem. Soc., Dalton Trans., 1997, Pages 1611–1616 in [Mo(CO)4{MeC6H3(NHPPh2)2-3,4}] with the aryl nitrogen atoms coplanar with respect to the backbone and with this backbone tilted with respect to the metal co-ordination plane; the bond lengths and angles follow similar trends in these two complexes. Gold phosphines have been intensively investigated as new antitumour drugs. More promising indications of anticancer activity were shown by a series of digold phosphine complexes e.g.[(AuCl)2(dppe)] (dppe = Ph2PCH2CH2PPh2).19 The reaction of [AuCl(tht)] with 3,4-bis(diphenylphosphinoamino)toluene led to [(AuCl)2{MeC6H3(NHPPh2)2-3,4}] in good yield as a light brown powder.The complex displays two resonances in its 31P-{1H} NMR spectrum (d 60.9 and 59.6) and the 1H NMR spectrum showed NH as two broad singlets at d 5.45 and 5.33. Assignment of the IR spectrum is difficult, but we can identify n(NH) at 3357 cm21 and n(PN) at 886 cm21 respectively. The positive-ion FAB mass spectrum gave the expected parent ion with appropriate isotope distribution and fragmentations. Acknowledgements We are grateful to Exxon Chemicals for support.References 1 A. M. Aguiar and M. G. R. Nair, J. Org. Chem., 1968, 33, 579. 2 M. Camalli, F. Caruso, S. Chaloupka, E. M. Leber, H. Rimml and L. M. Venanzi, Helv. Chim. Acta, 1990, 73, 2263. 3 M. Camalli, F. Caruso, H. Rimml and L. M. Venanzi, Inorg. Chem., 1995, 34, 673. 4 S. S. Sandhu, S. S. Sandhu and M. P. Gupta, Z. Anorg. Allg. Chem., 1970, 377, 348. 5 A. Zanardo, R. A. Michelin, F. Pinna and G. Strukul, Inorg. Chem., 1989, 28, 1648. 6 S. Gamguly and D. M. Roundhill, Organometallics, 1993, 12, 4825. 7 B. Chaudret, B. Delavaux and R. Poilblanc, Coord. Chem. Rev., 1988, 86, 191. 8 L. Haiduc, C. Silvetru, H. W. Roesky, H. G. Schmidt and M. Noltemeyer, Polyhedron, 1993, 12, 69. 9 J. S. Casas, A. Castineiras, I. Haiduc, A. Sanchez, J. Sordo and E. M. Vazquez-Lopez, Polyhedron, 1994, 13, 2873. 10 A. Laguna, M. Laguna, A. Rojo and M. Nieves Fraile, J. Organomet. Chem., 1986, 315, 269. 11 D. L. Hughes, N. J. Lazarowych, M. J. Maguire, R. H. Morris and R. L. Richards, J. Chem. Soc., Dalton Trans., 1995, 5. 12 J. D. Woollins (Editor), Inorganic Experiments, VCH, Weinheim, 1994. 13 D. Drew and J. R. Doyle, Inorg. Synth., 1991, 28, 346. 14 R. Uson, A. Laguna and M. Laguna, Inorg. Synth., 1989, 26, 85. 15 N. Walker and D. Stuart, DIFABS, Acta Crystallogr., Sect. A, 1968, 24, 351. 16 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corporation, Houston, TX, 1985 and 1992. 17 F. T. Wang, J. Najdzionek, K. L. Leneker, H. Wasserman and D. M. Braitsch, Synth. React. Inorg. Metal-Org. Chem., 1978, 8, 119. 18 P. Bhattacharyya, A. M. Z. Slawin, D. J. Williams and J. D. Woollins, J. Chem. Soc., Dalton Trans., 1995, 2489. 19 O. M. Ni Dhubhgaill and P. J. Sadler, in Metal Complexes in Cancer Therapy, ed. B. K. Keppler, VCH, Weinheim, 1993, p. 221. Received 2nd December 1996; Paper 6/08141J

ISSN:1477-9226    

DOI:10.1039/a608141j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 1617 Studies of octameric vinylsilasesquioxane by carbon-13 and silicon-29 cross polarization magic angle spinning and inversion recovery cross polarization nuclear magnetic resonance spectroscopy Christian Bonhomme,*,a Paul Tolédano,a Jocelyne Maquet,a Jacques Livage a and Laure Bonhomme-Coury†,b a Laboratoire Chimie de la Matière Condensée, Université Paris 6, 4 Place Jussieu, 75252 Paris Cedex 05, France b Laboratoire Céramiques et Matériaux Minéraux, Ecole Supérieure de Physique et Chimie Industrielles de la Ville de Paris, 10 rue Vauquelin, 75231 Paris Cedex 05, France The acidic hydrolysis of triethoxyvinylsilane Si(C2H3)(OEt)3 led to octavinyloctasilasesquioxane (C2H3SiO1.5)8 1 and to a transparent derived gel 2.Compound 1 was obtained as single crystals, suitable for X-ray analysis: trigonal, space group R3� , Z = 3, a = 13.533(2), c = 14.222(2) Å, g = 1208. Disorder of the methylene groups was observed.Compound 1 was carefully studied by IR spectroscopy and 29Si/13C cross polarization magic angle spinning (CP MAS) NMR spectroscopy. The CP dynamics of the various 13C sites were analysed by inversion recovery cross polarization (IRCP). Very different behaviours were observed for CH and CH2 signals and could be attributed to anisotropic reorientations of the vinyl groups. The IRCP sequence enabled a complete editing of the spectra and definite assignments of the observed lines.Owing to its highly resolved spectra and small intrinsic linewidths, it appears that compound 1 could act as a secondary reference for the set-up of the Hartmann–Hahn condition in 29Si CP NMR spectroscopy as well as a test for the set-up of the magic angle. All these results were applied to the study of the amorphous gel 2. Dipolar coupling constants were also strongly affected by local motions. During the last few years, spherosiloxanes, including octameric silasesquioxanes (RSiO1.5)8, have been extensively studied.Several review articles have been published.1–4 Special attention was paid to syntheses of new silasesquioxane structures 5,6 including heterometallic silasesquioxanes.2,7,8 This class of compounds has been used as models in different fields such as silicate/ zeolite chemistry, catalytic and analytical chemistry, etc. Therefore, silasesquioxanes have been studied by different spectroscopic techniques, i.e. X-ray diffraction,9–16 neutron diffraction, 17 vibrational spectroscopies 14,18 including normal coordinate analysis, liquid-state (1H, 29Si, 13C and 17O) NMR,6,19,20 etc. A few crystalline silasesquioxanes were studied by 29Si and 13C solid-state NMR spectroscopy, including the ‘Q8M8’ derivative (Me3SiOSiO1.5)8, which is now widely used for the set-up of 29Si cross polarization magic angle spinning (CP MAS) NMR.21,22 Moreover, interest in the use of these compounds as precursors for ceramics and macromolecular materials, by bridging organofunctional silasesquioxanes, has grown significantly very recently.4,23–25 Vinyl derivatives and heterofunctional compounds have been widely investigated by Martynova and co-workers 26,27 including X-ray diffraction studies.10 In this paper we present a complete study of the ‘cubane shaped’ octavinyloctasilasesquioxane (C2H3SiO1.5)8 1 by X-ray diffraction, infrared and 29Si/31C solidstate CP MAS NMR spectroscopy; 29Si CP MAS NMR spectroscopy was used to extract isotropic chemical shifts as well as chemical shift anisotropies (CSAs).Few CSA values related to small organosilicon molecules are available in the literature. Such CSAs may give information on the electronic environment around 29Si nuclei, local structure and molecular motion if present. The CP MAS NMR technique was not only used for enhancing the nuclear spin magnetization,28 but was also successfully used to edit the spectra, i.e.to assign without ambiguity the observed 13C resonances. The inversion recovery † E-Mail: laure.bonhomme@espci.fr cross polarization (IRCP) sequence can be compared to the well known editing sequences in liquid-state NMR, e.g. distortionless enhancements by polarization transfer (DEPT) and insensitive nuclei enhanced by polarization transfer (INEPT).29 Such editing techniques could act as invaluable tools of investigation for bridged-silasesquioxane amorphous materials. Indeed, the determination of the proton multiplicities of 13C sites is crucial for the complete characterization of these compounds.Moreover, the study of the CP dynamics allowed us to investigate local motion of the vinyl groups and to propose simple geometrical explanations for the astonishing CP behaviour of adjacent CH and CH2 groups. The results were applied to the study of an amorphous gel (compound 2) containing mostly vinyl T3 units(*), i.e. fully condensed C2H3Si*(OSi]] ] )3 entities.Results and Discussion Syntheses Synthesis of (C2H3SiO1.5)8 1 and the derived gel 2 are described in the Experimental section. Hydrolysis under acidic conditions and subsequent condensation of an organically modified silicon alkoxide, triethoxyvinylsilane Si(C2H3)(OEt)3 led to: (i) crystals (compound 1) with only fully condensed T3 units and (ii) gels (compound 2) containing a priori T0–3 units(*), C2H3Si*X32x- (OSi]] ] )x (X = OH or OEt, x = 0–3). Hydrolytic polycondensation of organotrichloro- (or methoxy-) silanes seems to be the main route of synthesis: Martynova and Chupakhina27 obtained octaorganooctasilasesquioxanes containing both methyl and vinyl groups by hydrolysis of SiMeCl3 and Si(C2H3)Cl3; Hendan and Marsmann19 presented the synthesis of mixed ethyl and vinyl derivatives starting from SiEtCl3 and Si(C2H3)Cl3.The use of modified silicon alkoxides SiR(OR9)3 (R = H or organic group, R9 = organic group) may open new synthetic routes to hydrido- and/or organo-silasesquioxanes.In particular,1618 J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 the choice of the experimental parameters (pH, temperature, solvent, concentration, nature of R9) allows a partial control of the hydrolysis–condensation process.30 Hydrolysis of such alkoxides leads to polymeric gels, which can act as ceramic precursors. 4 In this context, the formation of crystalline phases (such as compound 1) from media which usually lead to amorphous gels is a very interesting starting point for spectroscopic studies of such gels.This could be especially valuable for NMR studies of amorphous or poorly crystallized materials, which are extensively investigated by 13C/29Si/1H solid-state NMR techniques.31,32 In the case of compound 1 one unique crystalline phase is obtained, in contrast with the synthesis proposed by Baidina et al.10 [i.e. direct hydrolysis of Si(C2H3)Cl3] leading to octa- and deca-silasesquioxanes (C2H3SiO1.5)n with n = 8 or 10. However, in our case, the reaction yield for compound 1 remains poor.Crystal structure of compound 1 The molecular structure of compound 1, C16H24Si8O12, is shown in Fig. 1. Only the second vinyl carbons C(11) and C(21) are represented as the structure is disordered (see below). Selected bond lengths and angles are presented in Table 1. The main feature of the octameric cluster is the presence of a C3 axis containing atoms C(1) and Si(1).Disorder at the CH2 sites is present. Atom C(11) is bonded to C(1) (located on the C3 axis). Four positions for carbon atoms bonded to C(2) were found, corresponding to C(21)– C(24). Fractional occupancies of C(11) and C(21)–C(24) were refined for the structure solution. The occupancy of C(11) was found to be ��� . Such a characteristic has been previously clearly evidenced by Larsson,9 in the case of isomorphous homologues belonging to the hexagonal system and showing space group R3� [e.g.(RSiO1.5)8, R = Me, Et, Prn and Pri]. This has been also observed by Baidina et al.10 in the case of the octavinyl derivative (trigonal, space group R3�, a = 13.584, c = 14.364 Å, final R = 0.11). However, several differences between the molecular structure of the octavinyl derivative described in rempound 1 have to be noted. First, the Si]C bond lengths are shorter in our work than in ref. 10 to a rather important extent: Si(1)]C(1) and Si(2)]C(2) 2.03 Å in ref. 10, whereas we found 1.81(2) and 1.82(1) Å, respectively. Secondly, two distinct positions (with site occupancy ª ��� ) seem to be sufficient to describe the methylene carbon atom in the general position in ref. 10, whereas, in the case of compound 1 four disordered methylene positions C(21)–C(24) were found with site occupancies varying from 0.15 to 0.39 as estimations. The Si]O and Si]C bond lengths as well as O]Si]O, Si]O]Si and O]Si]C angles are in accord with values observed for well characterized octameric silasesquioxanes.11,12,14 The Si(2)] Table 1 Selected bond lengths (Å) and angles (8) with estimated standard deviations in parentheses for C16H24Si8O12 1.Symmetry codes as in Fig. 1 Si(1)]O(1) Si(2)]O(1) Si(2)]O(2) Si(2)]O(2V) Si(1)]C(1) Si(2)]C(2) 1.606(6) 1.596(6) 1.596(6) 1.616(6) 1.81(2) 1.82(1) C(1)]C(11) C(2)]C(21) C(2)]C(22) C(2)]C(23) C(2)]C(24) 1.25(3) 1.22(3) 1.26(3) 1.23(4) 1.27(4) O(1)]Si(1)]O(1II) O(1)]Si(2)]O(2) O(1)]Si(2)]O(2V) O(2)]Si(2)]O(2V) O(1)]Si(1)]C(1) O(1)]Si(2)]C(2) O(2)]Si(2)]C(2) O(2V)]Si(2)]C(2) 108.5(3) 108.5(3) 108.7(4) 108.6(3) 110.5(3) 110.0(5) 111.4(5) 109.7(5) Si(1)]O(1)]Si(2) Si(2)]O(2)]Si(2IV) Si(1)]C(1)]C(11) Si(2)]C(2)]C(21) Si(2)]C(2)]C(22) Si(2)]C(2)]C(23) Si(2)]C(2)]C(24) 150.5(4) 150.0(4) 127(2) 128(2) 121(2) 132(3) 125(3) C(2)]C angles have a mean value of 127(3)8, in agreement with the Si(1)]C(1)]C(11) angle [127(2)8]. All C]] C bond lengths are close to 1.25 Å (significantly shorter than usual, i.e. 1.33 Å). These observations justify the fact that positions C(21)–C(24) correspond to methylene sites but they are surely estimations. One unique C(21) position (occupancy = 1) cannot be defined. There are two non-equivalent distances between centrosymmetrically related silicon atoms within the molecule. Opposite Si atoms in general positions are 5.371(5) Å apart and those on the C3 axis are 5.360(1) Å apart. Such a slightly distorted cubane structure is accompanied by the absence of Si]O intermolecular contacts less than 3.7 Å and a low crystal density (Dc = 1.398 g cm23).An increase in the number of short intermolecular Si]O contacts led to more important distortions of the cubane cores as well as to an increase in crystal density.14 Larsson 9 showed also that the crystal density decreased from 1.51 g cm23 for (MeSiO1.5)8 to 1.09 g cm23 in (PrnSiO1.5)8. The main characteristic of compound 1 is the nonequivalence of the vinyl groups.The C(11) positions are related by C3 symmetry, whereas C(21)–C(24) are non-symmetryrelated. As X-ray diffraction is unable to distinguish between static and dynamic disorder the vinyl groups are either disordered or in motion. Vibrational spectroscopy Compounds 1 and 2 were analysed by infrared spectroscopy. Assignments of the main bands are given in Table 2, based on data from the literature.14,31,34 The IR spectrum of neat Si(C2H3)(OEt)3 was also used as a reference.The IR spectrum of compound 1 is characterized by a very strong band centred at 1113 cm21, assigned to nasym(Si]O]Si). This band is broad, compared to the other vibrations (Dw2� 1 ª 100 cm21). It is interesting that the other bands assigned to specific vibrations of the cubic siloxane cage (n < 780 cm21) are also rather broad, when compared to bands involving only the organic part of the molecule. This may reflect the small distortions of the cubane cage, lowering the symmetry of the entity from Oh.The band centred at 780 cm21 has a shoulder (756 cm21) which could indicate the presence of two Si]C bonding types, as already seen by X-ray analysis. Fig. 1 An ORTEP33 view of the structure of C16H24Si8O12 1, showing the atom labelling scheme. Of the second vinyl carbons only C(11) and C(21) are represented as well as their bonded hydrogens (calculated positions). The CH2 positions are disordered (see text). Symmetry codes: I x� , y� , z�; II y� , x 2 y, z; III y 2 x, x� , z; IV y, y 2 x, z�; V x 2 y, x, z�J.Chem. Soc., Dalton Trans., 1997, Pages 1617.1626 1619 The IR spectrum of the xerogel 2 is very similar to that for 1. All the bands (n < 2000 cm21) already assigned to vinyl vibrations for 1 are observed as five sharp signals centred at 1603, 1409, 1278, 1005 and 963 cm21. However, bands involving Si]O and Si]C vibrations are broadened, leading to a less resolved spectrum at low frequency.Such a broadening can be safely related to more disordered and/or distorted environments around Si atoms (compound 2 is amorphous to X-rays). Vibrations related to vinyl groups are much less sensitive to this disorder. Although not quantitative, this spectrum suggests that the xerogel contains very few residual ethoxy groups: no clear vibration is observed in the range 1350.1500 cm21 (relative to aliphatic CH2 and CH3 deformations). This gel is highly con- Fig. 2 The 29Si CP MAS NMR spectra of compound 1: (a) ¡®high¡� rotation speed, nrot (rotation speed) = 4000 Hz, X (29Si) (Larmor frequency) = 59.62 MHz, f (diameter of rotor) = 4 mm, Ns (number of scans) = 8, tCP (contact time) = 10 ms, r.d.(recycle delay) = 15 s, l.b. (line broadening) = 0 Hz; (b) ¡®intermediate¡� rotation speed, nrot = 500 Hz, X (29Si) = 79.50 MHz, f = 7 mm, Ns = 200, tCP = 10 ms, r.d. = 15 s, l.b. = 3 Hz, isotropic resonances labelled by arrows [(d) simulation of sideband patterns]; (c) static experiment, nrot = 0 Hz, X (29Si) = 59.62 MHz, f = 7 mm, Ns = 400, tCP = 10 ms, r.d.= 15 s, l.b. = 20 Hz [(e) simulations of Si(1) and Si(2) powder patterns convoluted by a gaussian broadening] Table 2 Selected infrared absorptions (cm21) of C16H24Si8O12 1 and the gel 2 1 2 Assignment* 3067w 3026w 1604m 1409m 1277m 1152 (sh) 1113vs (br) 1005m 970m 780m 756 (sh) 585s 465w 3063w 3024w 1603m 1409m 1278m 1129vs (br) 1043s (br) 1005m 963m 762m (br) 587m (br) 546m ¢� ¢© ¢­ 428m (br) nasym(CH2) n(CH) n(C]] C) d(CH2) in plane d(CH) in plane nasym(Si]O]Si) d(CH) out of plane d(CH2) out of plane n(Si]C) d(O]Si]O) 1d(Si]C]] C) nsym(Si]O]Si) * According to refs. 14, 31 and 34. w = Weak, m = medium, s = strong, br = broad, sh = shoulder, v = very, sym = symmetric, asym = asymmetric. densed (i.e. it contains mainly T3 units) as has been shown by solid-state 13C NMR spectroscopy (see below). Solid-state NMR spectroscopy Compound 1. Standard 29Si and 13C CP MAS experiments.Spectra of compound 1 obtained by 29Si and 13C CP MAS experiments (at various rotation speeds) are presented in Figs. 2 and 3, respectively. All NMR data, including isotropic chemical shift (29Si and 13C), shielding tensor principal components, linewidths, relative intensities and assignments are presented in Table 3. Few data concerning solid-state 29Si NMR results for silasesquioxanes are available. Most of the 29Si chemical shift data were obtained in solution including sophisticated two-dimensional experiments [i.e.incredible natural abundance double quantum transfer experiment (INADEQUATE)19] and leading to correlations between chemical shifts and geometrical parameters.6 Hoebbel and co-workers 22,35,36 studied several octa- and decasilasesquioxanes by means of solid-state techniques but published only isotropic chemical shift values. The determination of the principal components of the tensor s (chemical shift tensor) was mainly devoted to the structure elucidation of silicate minerals.37 To our knowledge, few papers dealing with shielding tensors of molecular organosilicon compounds have been published so far.Harris et al.38 presented 29Si NMR studies of various polysilanes, exhibiting different silicon environments. Compound 1 is characterized by two isotropic 29Si peaks [Fig. 2(a) and Table 3] characteristic of T3 units. The intensities of the lines are in the ratio 3 : 1 in good agreement with the presence of three equivalent Si(2) atoms to one Si(1) located on the C3 axis.This allows definite assignments for both resonances. It should be noted that a small shin the C3 axis was also observed in the case of the octamethyl cubane derivative (MeSiO1.5)8: 22 dSi(1) 266.5 and dSi(2) 265.9. These line intensities were obtained for a contact time of 10 ms, corresponding to an optimized value. An important experimental detail can be added: the Hartmann.Hahn condition was set up using compound 1, maximizing the intensities of both lines. In addition, another test for the Hartmann.Hahn set-up was the resolution of both lines (with small intrinsic linewidths, �£8.10 Hz), which was maximal at exact Hartmann.Hahn condition. In other words, compound 1 can be safely used as a standard for the set-up of CP experiments, a well resolved free induction decay (FID) being observed after eight scans (recycle delay = 15 s).At intermediate MAS rate (nrot = 1000 Hz, not shown here) two sets of spinning sidebands (with low intensities) were observed. Definitions of the shielding anisotropy (Ds) and asymmetry (h) are given in Table 3. The anisotropy was estimated to be 135 ppm for both Fig. 3 The 13C CP MAS NMR spectrum of compound 1 (a), with simulations of CH (b) and CH2 (c) patterns. Isotropic resonances are labelled by arrows: nrot = 1200 Hz, X (13C) = 75.46 MHz, f = 7 mm, Ns = 104, tCP = 5 ms, r.d.= 15 s, l.b. = 3 Hz. * Satellites corresponding to 1J(13C]29Si)1620 J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 Table 3 Silicon-29 and 13C CP NMR data for compounds 1 and 2 and cadmium acetylacetonate including isotropic shielding (siso), shielding-tensor components (sii), shielding anisotropy (Ds), asymmetry (h), linewidth, relative intensities and assignments a Compound siso s33 s22 s11 Ds dA h Linewidth/Hz Relative intensity (%) Assignment 1 (29Si) (13C) 2 (13C) [Cd(acac)2] (13C) 180.4 179.9 2138.0 2138.5 2128.8 2135 2129 2102.1 2100.6 1103.1 1102.7 2216.6 2214.6 2186.2 2205 2184 2196.4 2194.8 168.9 171.8 2110.4 2119.4 2116.0 2118 2124 255.1 253.5 168.9 165.1 292.0 281.9 284.5 283 280 255.1 253.5 134.2 134.2 2114.4 2114.0 285.9 2105 283 2141.3 2141.3 122.8 122.8 274.3 275.9 257.3 270 255 294.2 294.4 0.00 0.30 0.20 0.50 0.55 0.5 0.8 0.00 0.00 8 10 18 18 15 280 225 31 34 25 75 13 32 55 ª50 ª50 50 50 Si(1) Si(2) C(11) C(21) b C(1)/C(2) CH2 CH CH CH a s = 2d (in ppm); siso = ��� (s11 1 s22 1 s33); |s33 2 siso| > |s11 2 siso| > |s22 2 siso|; the errors in sii values are typically ±2 ppm; Ds = s33 2 ��� (s11 1 s22) = ��� dA; dA = s33 2 siso; h = (s22 2 s11)/dA; typical error in h is ±0.1.b Corresponding to the average value of s[C(21)]–s[C(24)]. 29Si sites. In order to get an accurate determination of (Ds, h) for each 29Si site, an experiment at much lower MAS rate (nrot = 500 Hz) and at higher field [X(29Si) = 79.5 MHz] was used [Fig. 2(b)]. Assuming that the shielding is the only magnetic influence on the intensities of the spinning sidebands, both patterns were analysed by a standard graphical procedure 39,40 [Fig. 2(d)]. Sets of (Ds, h) values were (134.2 ppm, ª0) for Si(1) and (134.2 ppm, ª0.2) for Si(2) leading to axial or nearly axial shielding tensors. However, the exact determination of h for axial or nearly axial symmetry using graphical methods is very difficult, whereas the shielding anisotropy is reasonably well defined.41 Therefore, the static powder spectrum [Fig. 2(c)] was simulated with a unique set of parameters (h1, h2) and fixed anisotropy (Ds = 134.2 ppm) [Fig. 2(e)]. The best simulation was obtained with h1 = 0.0 for Si(1) and h2 = 0.3 for Si(2). The static pattern could not be described by two tensors having the same h parameter. The shielding tensor relative to Si(2) is nonaxial whereas the Si(1) tensor can be considered as axial.However, the deviation from axiality for Si(2) remains rather low. The value of the anisotropy is in accord with values obtained for various organosilicon derivatives.38 The 13C NMR spectrum of compound 1 is characterized by three isotropic resonances centred at d 138.0, 138.5 and 128.8 [Fig. 3(a)]. The group of lines at d 138.0/138.5 and the line at d 128.8 are roughly in the ratio 1 : 1. The lines at d 138.0 and 138.5 are roughly in the ratio 1 : 3. This intensity analysis was done for a contact time tCP = 5 ms, corresponding to an optimized value.Indeed, all magnetizations reached their maximum for tCP > 5 ms as shown by a variable-contact-time experiment [T1r- (1H) ª 200 ms, i.e. T1r(1H) @ TC and TD, see below]. Both groups of lines are distinguished not only by isotropic chemical shifts but also by shielding anisotropies [Fig. 3(b), 3(c) and Table 3]. These observations indicate that each group of resonances may be assigned to CH or CH2 sites (direct definite assignment is not straightforward at this stage).The sideband pattern corresponding to d 128.8 [Fig. 3(b)] consists of narrow lines of equal width: this ascertains the set-up of the magic angle. It has been shown that off-axis sample spinning in the slow-spinning regime led to distorted sideband patterns and could result in misinterpretations of the spectra 42 (especially in the case of high 13C shielding anisotropies). Therefore, the resonances closely centred at d 138.0 and 138.5 do correspond to isotropic peaks and are not artifacts.In this sense compound 1 could be used as a secondary reference for precise magic angle set-up (at least on the 13C chemical shift scale). Shielding anisotropies (Ds) for C(1)/C(2), C(11) and C(21) (see Table 3) are small when compared to common values observed for rigid entities R1R2C]] CR3R4.43,44 This may suggest motional averaging at the vinyl sites leading to a drastic reduction in CSA values for every 13C site.45 This point will be carefully analysed by using the IRCP technique.Such a NMR sequence will allow also definite assignments for the observed lines. Investigation by IRCP techniques. A few sequences based on CP NMR allow one to edit 13C resonance lines in connection with the number of directly bonded protons. The most commonly used sequence is referred to in the literature as NQS (nonquaternary suppression). First introduced by Alla and Lippmaa46 and developed by Opella and Frey,47 it allows one to distinguish between rigid protonated groups (such as CH and CH2) and weakly coupled sites (such as carbonyl or quaternary C) by dipolar dephasing.Methyl has an intermediate behaviour due to fast reorientation, leading to a substantial reduction in the dipolar coupling strength. However, this sequence fails to distingish between ‘rigid’ CH and CH2 groups.48 Indeed, CH and CH2 have similar dipolar dephasing constants; moreover, these constants can largely be modulated by molecular motion.A second approach to spectral editing is related to solid-state J spectroscopy combined with multipulse on the 1H channel.49 However, so far, this has been applied mainly to species with high intrinsic mobilities and very rarely to rigid solid compounds. More recently, sequences based on polarization/ inversion of polarization have been widely developed in the framework of spectral editing.48,50 The IRCP sequence used in this work is presented in Fig. 4. It is derived from a standard CP sequence: after a contact time tCP (long enough to polarize all 13C nuclei), a 1808 phase shift is operated on the 13C channel. Owing to spin–temperature inversion, the obtained carbon-13 magnetization will invert during the inversion time ti. Then, the remaining 13C signal is acquired, including high-power decoupling. This experiment is also called CPPI (cross polarization with polarization inversion).48 It has been demonstrated that cross-polarization dynamics and polarization inversion dynamics are identical.51 In the case of strongly coupled sites (such as CH and CH2), analytical expres- Fig. 4 An IRCP sequence based on a standard 13C CP MAS experiment: 48 tCP = contact time (fixed) and ti = inversion time (variable)J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 1621 sions of the magnetizations during the inversion process have been derived for powdered samples at moderate MAS (!10 kHz), neglecting relaxation,48 equation (1) where M0 represents M(1 exp S2 ti TD D1 2n n 1 1 exp S2 3 2 ti TD D exp S2 ti 2 TC 2D2 1G (1) the maximal magnetization reached after tCP and n corresponds to the number of directly bonded protons in the CHn group.The inversion of polarization is characterized by two time constants which are related to different types of magnetization transfer: TC accounts for the coherent transfer of magnetization, involving the 13C nucleus and the directly bonded protons; it can be considered as an inverse measure of the strength of the heteronuclear dipolar coupling for CHn groups.It can be estimated for rigid CHn groups. Rapid molecular motion will lead to a reduction in dipolar coupling and will be related therefore to an increase in TC. Parameter TD is related to spin-diffusion processes, which involve all the remaining protons. Equation (1) is a generalization of that first derived by Müller et al.,52 accounting for magnetization oscillations in CP transfer for ferrocene single crystals.Generally, TC ! TD and the polarization inversion can be described by two regimes: the first (first tens of microseconds for ti) is dominated by a rapid decay of M(13CHn), characterized by TC. Then, a much slower regime of inversion follows (TD). As the dynamics of the two regimes are very different, a sharp turning point is observed. It corresponds to the end of the fast regime of inversion.Then, the magnetization reaches (1 2 n)(1 1 n)21M0 [equation (1)]. The CH and CH2 groups can be distinguished by the value of their turning point: 0 and 2��� M0, respectively. In this sense spectral editing is achieved. Moreover, it has been demonstrated that the criterion of the turning point is much less sensitive to molecular motions than are methods which rely only on the relative strengths of dipolar couplings (NQS sequence). In the case of weakly coupled sites (such as C]] O, quaternary C or rapidly rotating Me), the inversion of polarization is well described by an exponential process and one unique time constant, equation (2), again neglecting relaxation; TCH is the M(13C) = M0 F2 expS2 ti TCH D2 1G (2) standard cross-polarization constant.Equation (2) corresponds to the standard thermodynamic approach of cross-polarization dynamics.28 The IRCP sequence (13C) has been applied to the study of compound 1 and to gel 2. Our goal was to propose definite assignments for the 13C lines and possibly to obtain information about molecular motions.Spectra obtained for compound 1 (rotation speed = 4 kHz) with different increments of ti are presented in Fig. 5. At this rotation speed only two sets of spinning sidebands (with low intensities) are observed. The inversion of the normalized magnetization intensities is presented in Fig. 6. The total magnetization of the group of resonances centred at d 138.0 and 138.5 was considered.The IRCP sequence was also applied to a sample of cadmium acetylacetonate [Cd- (MeCOCHCOMe)2], i.e. [Cd(acac)2] (see Experimental section). In this compound the acetylacetonate ligands are stabilized in the enol form showing CH spin pairs with sp2 carbon atoms. This metalloorganic compound can act as a reference for ‘rigid’ Csp2H groups. Actually, two CH resonances are observed due to acetylacetonate moieties consistent with crystallographic data.53 Shift parameters are presented in Table 3.It is clearly seen that both inversions for ·dÒ ª 138 and d 128.8 present two regimes: a rapid one during the first 100 ms and a much slower one for higher values of ti. However, the turning points between the two regimes are obviously different. For d 128.8 it corresponds roughly to 0; for ·dÒ ª 138 it corresponds roughly to 2��� . Inversion curves were fitted using equation (1). Best fits were obtained with n = 1 (d 128.8) and 2 (·dÒ ª 138).Fits obtained with equation (2) involving a unique time constant were very poor. The extracted values of TC and TD are presented in Table 4. It is then possible to confirm assignments on the basis of the inversion curves. The resonance centred at d 128.8 is assigned to CH groups (n = 1); both resonances at d 138.0 and 138.5 are assigned to CH2 groups (n = 2). As indicated above, it is also obvious that TD @ TC. We should mention at this stage that the resonance at d 128.8 and its spinning sidebands are flanked by Fig. 5 The 13C IRCP MAS NMR spectra of compound 1 (tCP = 5 ms); ti = 0 ms corresponds to a standard CP MAS experiment (nrot = 4000 Hz, Ns = 48, l.b. = 10) Fig. 6 Evolution of the magnetizations (compound 1) versus inversion time ti. Fits are related to equation (1) (with n = 1 for CH and n = 2 for CH2). d, d 128.8; j, ·dÒ ª 1381622 J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 two satellites [see the insert in Fig. 3(a)]. The satellites are assigned to 13C nuclei coupled to 29Si [natural abundance 4.7% and |1J(13C]29Si)| = 136 ± 5 Hz]. The 13C INEPT study (see Experimental section) of the molecular precursor Si(C2H3)- (OEt)3 confirmed these results: (i) the CH2 signal was less shielded than the CH signal, (ii) |1J(13C]29Si)| = 119 Hz, in agreement with the value observed in the solid state. The signal centred at d 128.8 corresponds obviously to C(1) and C(2) resonances (see crystallographic section above).These resonances are not resolved as the isotropic chemical shifts must be very similar. The extracted value of TC for CH2 (Table 4) is clearly higher than those observed for ‘rigid’ aliphatic CH2 groups.48,54 Moreover, the magnetization related to CH2 in compound 1 is still positive for ti = 25 ms (Fig. 5), whereas the magnetization of CH2 in glycine (NH2CH2CO2H) is slightly negative for the same inversion time (see Experimental section). Owing to slightly shorter C]H bond lengths, a ‘rigid’ Csp2H2 group should invert more rapidly than a ‘rigid’ aliphatic Csp3H2 group.For compound 1 such experimental observations suggest motional reduction of the dipolar coupling between 13C and the directly bonded protons. As the dipolar constant TC is signifi- cantly affected, the frequency of the motion can be estimated to be n > 105 Hz.55 At this stage we can conclude that the apparent disorder observed for C(11) and C(21) by X-ray diffraction cannot be related to a static one.Indeed, in this case the behaviour of the rigid CH2 groups should be characterized by TC(CH2) < TC(CH) for [Cd(acac)2], which is obviously not the case (Table 4). Fast anisotropic motion of the vinyl groups (considered as rigid entities) around the Si(1)]C(1) and Si(2)]C(2) bonds may then be considered. The crystallographic refinements show that the local motion of the vinyl groups may consist of rapid jumps between discrete positions: three symmetry-related positions for C(11) and (at least) four for C(21).It is known that a continuous rotation of vinyl groups is not necessary to obtain averaging of dipolar coupling under reorientation. Rapid jumps between p positions (p > 3) located on a regular polygon lead exactly to the same averaging. By symmetry, the three C(11) positions (with equal occupancy) describe an equilateral triangle. The four C(21) positions describe a distorted square but refinement in this case is much less safe.If the approach of rapid motion of the vinyl groups is correct two points remain open: (i) TC for CH is much higher than TC observed for CH2 in compound 1 (see Table 4), which indicates a much stronger reduction of the dipolar coupling in the case of the CH spin pair; (ii) the fits of the IRCP curves (Fig. 6) obtained with equation (1) are less reliable for higher values of ti. Let us answer these two questions, considering reorientation of the vinyl groups around the Si]C bonds.(i) The approximate geometry of one vinyl group is represented in Fig. 7. Angles bi (i = 1–3) are those related to the atoms Si(1), C(1), C(11), H(1), H(2) and H(3) (see Fig. 1). Let us first consider the strong dipolar coupling between the CH spin pair. In a static configuration the dipolar tensor corresponding to CH is axially symmetric with the C]H bond direction as a unique axis.der rapid anisotropic reorientation around the Si]C direction (rapid jumps) the dipolar tensor remains axially symmetric but with the Si]C bond as a new Table 4 Extracted TC and TD values from 13C IRCP MAS NMR experiments according to equation (1) Compound 13C site TC/ms TD/ms 1 2 [Cd(acac)2] CH[C(1)/C(2)] CH2[C(11)/C(21)] CH CH2 CH 75 ± 4 30 ± 2 80* 30 ± 2 25 ± 0.6 3 ± 0.7 1.3 ± 0.2 3.5* 2.2 ± 0.3 0.43 ± 0.02 * Estimation, see text. unique axis.Then, the dipolar coupling ‘strength’ is modulated by the factor R = (3 cos2 b 2 1)/2, where b corresponds to the angle between the C]H bond and the axis of rotation.This result is general 45 and can be transposed for any second-rank tensor such as CSA and J coupling (when considering firstorder effects on the lineshapes). When the tensor is not axially symmetric the reduction factor for the interaction is a more complex function of the principal values of the tensor and the Euler angles between the principal axes and the reorientation direction.In the case of CH, b1 ª 638 so that |R| ª 0.2. In other words, this particular geometry of the CH pair leads to a very strong reduction in dipolar coupling under rapid reorientation. This can explain the high value of TC observed for the CH group in the IRCP experiment. The IRCP curves of [Cd(acac)2] (containing ‘rigid’ CH groups), compound 1 and ferrocene [Fe(h-C5H5)2] (adapted from ref. 56 and neglecting rotational echoes, see below) are presented in Fig. 8. We assume for this comparison that the C]H bond lengths are nearly equal for the three compounds.The rigid CH in [Cd(acac)2] experiences strong dipolar coupling leading to a low value of TC and rapid inversion during the first tens of ms. Ferrocene is characterized by rapid rotation around the internal axis with b = 908 (|R| = 0.5); 56 its evolution is intermediate between the rigid case of [Cd(acac)2] and the behaviour of the vinyl groups in compound 1 as expected from inspection of the R values.In the case of methylene groups (CH2), b2 ª 6 and b3 ª 548. This means that the C]H(2) bond is nearly collinear with the rotation axis whereas the C]H(3) bond is nearly at the magic angle. The C]H(2) dipolar coupling ‘strength’ is therefore almost unaffected by the motion (R ª 1). The removal of dipolar coupling from H(3) is almost complete. Therefore, the inversion of the CH2 magnetization is rapid during the first tens of microseconds (TC = 30 ms) but less than for a ‘rigid’ CH2 group. This TC value is comparable to values observed for rigid CH groups.We have shown that simple geometrical arguments may explain the different evolutions of CH and CH2 magnetizations. These results are at best qualitative since bi angles are estimated through the calculated positions of the H atoms. Conversely, theoretical analysis of the IRCP curves may lead to the determination of particular angles and bond lengths in the molecule. (ii) In the case of ferrocene the second stage of polarization inversion was modulated by strong rotational echoes.56 Indeed, the interactions between CH pairs are periodically refocused by MAS at times tn = (n2p/wrot) = (n/nrot) with n = 1, 2 etc., nrot being the spinning frequency.In our experiments, nrot = 4000 Hz and t1 = 250 ms, t2 = 500 ms, etc. Such echoes could explain the fact that the calculated curves in Fig. 6 are less reliable in the second stage of polarization inversion. Nevertheless, the order of magnitude for extracted TD values is correct.Fig. 7 Approximate geometry of the vinyl group corresponding to atoms Si(1), C(1) and C(11) and to related H atoms (calculated positions): b1 ª 63, b2 ª 6 and b3 ª 548J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 1623 The 13C CSA should also be modulated by vinyl reorientations. As stated above, CSA values for all carbon-13 sites are unusually small. However, the interpretation for the reduction of Ds is difficult.The CSA can be represented by a secondrank tensor, characterized by three initial principal values. Upon rapid reorientation, the reduction in CSA can be represented by a new tensor which is axially symmetric. The new principal values are functions of the initial values and Euler angles between the reorientation axis and the initial principal axes.45 In the case of compound 1 the orientations of the different CSA principal axes systems in the ‘static’ configuration of the cubane are not known.In other words, the Euler angles which orientate the initial tensor from the Si]C bond are not known. The IRCP results, concerning the reduction of dipolar tensors, are easier to analyse than the Ds reduction, as the CH direction corresponds to a principal direction of the initial dipolar tensor. Therefore, the IRCP results and Ds reduction cannot be directly related. As a conclusion the IRCP dynamics study allows a deep insight into the dipolar local fields.The 13C spectra can be edited completely (CH and CH2 distinction) though strong reduction of the dipolar coupling was present. Turning points in the IRCP curves are safe criteria for spectral editing. Reorientation of the vinyl groups could explain the different magnetization behaviours during the IRCP sequence. Moreover, the reorientation of the vinyl groups could be considered independently from the cubane core of the molecule as will be seen below.Finally, one should note that such different CP dynamics for closely spaced CH and CH2 may have a considerable influence on quantification by 13C CP MAS NMR spectroscopy and may lead to misinterpretations in spectral editing. One must be aware of specific molecular motions leading to strongly reduced dipolar coupling. Compound 2 (xerogel). Standard 29Si and 13C CP MAS experiments. The 29Si CP MAS spectrum (not shown) of compound 2 is characterized by a major peak centred at d 278 (linewidth ª 350 Hz), which corresponds to fully condensed T3 units C2H3Si*(OSi]] ] )3.A minor peak centred at d 272 is also observed and corresponds to T2 units C2H3Si*X(OSi]] ] )2 with X = OH or OEt. This demonstrates that the network of silicon entities is highly condensed. Spectra of compound 2 obtained by 13C CP MAS are presented in Fig. 9 (ti = 0 ms) and NMR data corresponding to the 13C vinyl resonances are presented in Table 3. The CP spectrum has two peaks located at d 135 and 129 and two minor resonances assigned to residual ethoxy groups (d 58 Fig. 8 Evolution of Csp2H magnetization versus inversion time ti (IRCP sequence) for: m, cadmium acetyloacetonate (‘rigid’ CH); ——, ferrocene, adapted from ref. 56 with TC = 50 ms and TD = 1.7 ms, |R| = 0.5; d, compound 1 (expansion of Fig. 6), |R| ª 0.2 and 17: CH2 and CH3, respectively). Low-speed sideband patterns related to vinylic 13C can be well simulated by two sets of average (Ds, h) CSA values (see Table 3 and Fig. 10). The Ds values are in agreement with those observed for compound 1, suggesting again rapid reorientation of vinyl groups around Si]C bonds. Investigation by 13C IRCP MAS NMR. The IRCP spectra obtained for ti = 30 and 50 ms are presented in Fig. 9. Evolution of both magnetizations (vinylic CH and CH2) is presented in Fig. 11. Simulations were obtained using two peaks with fixed isotropic chemical shift and linewidth. Only amplitudes were allowed to vary.The inversion of magnetization shows clearly two regimes for both resonances and equation (1) was used to extract TC and TD values. Once again, spectral editing is easy and the less shielded peak (d 135) can be safely assigned to CH2 [n = 2 in equation (1)]. The fit obtained for d 129 (using n = 1) is less safe because the turning point between the two regimes of inversion is higher than 0; TC and TD values are given as estimations. However, the CH IRCP behaviours for compounds 1 and 2 are identical during the first tens of ms.The TC values are in very close agreement with those extracted for CH and CH2 in compound 1. This indicates that the motion of the vinyl groups localized around Si]C bonds is independent of the rest of the structure (i.e. the cubane cage in the case of compound 1). The TD values are of the same order of magnitude but show some variations between compounds 1 and 2. This is not surprising as TD is strongly influenced by the 1H]1H interactions, which may vary considerably from one compound to another.Conclusion Octameric vinylsilasesquioxane 1 has been studied by X-ray diffraction and 29Si/13C CP MAS NMR spectroscopy. The X-ray data showed an uncertainty about the vinyl CH2 positions Fig. 9 The 13C CP and IRCP MAS NMR spectra of compound 2: nrot = 4000 Hz, X (13C) = 75.46 MHz, f = 4 mm, Ns = 600, tCP = 5 ms, r.d. = 6 s, l.b. = 30 Hz1624 J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 owing to static disorder or rapid reorientation by jumping.The latter is in accord with a careful analysis of CP dynamics, which revealed the rapid anisotropic reorientation of the vinyl groups around the Si]C bonds. The frequency of the motion was certainly higher than 105 Hz, leading to a strong reduction in dipolar coupling. Adjacent CH and CH2 groups showed very different residual dipolar coupling, as shown by IRCP. These observations were explained by the simple geometrical characteristics of the vinyl groups: the angle between the C]H and the Si]C bond axis was nearly the magic angle, leading to a very strong reduction in the dipolar coupling.Nevertheless, the CH polarization inversion showed two regimes as expected, allowing a complete spectral editing and definite assignments. The IRCP sequence can be safely used in solid-state NMR spectroscopy for the determination of proton multiplicities and can be compared to the liquid-state NMR sequences DEPT and Fig. 10 Low-rotation-speed 13C CP MAS spectrum (lower) of compound 2. Only the vinyl CH and CH2 patterns are simulated (upper): nrot = 1000 Hz, X (13C) = 75.46 MHz, f = 7 mm, Ns = 1688, tCP = 5 ms, r.d. = 6 s, l.b. = 10 Hz. Isotropic resonances are labelled by arrows Fig. 11 Evolution of the magnetizations (compound 2) versus inversion time ti for vinylic CH and CH2 signals: d, d 129; j, d 135 INEPT. The high resolution of the spectra of 1 allows one to use this compound as a safe secondary reference for the set-up of 29Si and 13C CP NMR experiments.The amorphous gel 2 was also studied by 29Si/13C CP NMR spectroscopy. It is a good example for applying NMR analysis techniques, which were carefully set with well defined compounds (such as crystals) to amorphous derived materials. The IRCP experiment also showed a strong reduction in dipolar coupling through motional averaging. Therefore, extreme caution should be taken when considering quantitative CP experiments.This could be especially important in the study of amorphous materials (bridged organofunctional silasesquioxanes, for instance), for which 13C CP NMR spectroscopy is used in the quantification of bridging reactions between the different cubane cores. Experimental Syntheses Compound 1 and derived gel 2. Triethoxyvinylsilane (Fluka) was used as received. The purity of this monomeric compound was checked by standard 13C and 29Si liquid-state NMR spectroscopy and INEPT29 [relative to SiMe4: dSi 258.7; dC(]] CH) 130.5; dC(]] CH2) 135.8; dC(CH2) 58.3; dC(CH3) 18.3; |1J(13C]29Si)| = 119 Hz as shown by 13C INEPT].Acidic water (HCl, 0.1 mol l21) (0.35 g, 19.7 mmol) was added to Si(C2- H3)(OEt)3 (2.50 g, 13.1 mmol) with vigorous stirring, without any solvent (H2O: Si = 1.5 : 1). After 2–3 min the mixture became homogeneous. At room temperature and after several days, single crystals of compound 1 were obtained as transparent parallelepipeds. These were extracted and washed with dried ethanol.They were insensitive to air moisture and found suitable for structure determination. Upon ageing the remaining liquid mixture led to a transparent gel which could be heated at 80 8C, leading to a dry amorphous powder called xerogel (compound 2). Such powders were studied without further treatment. The yield of the crystallized phase was estimated to be a few %. Several single crystals were analysed by X-ray diffraction, leading to one unique crystallographic structure, corresponding to compound 1.The IR spectrum was recorded and acted as ‘fingerprint’ of 1. Many experiments were repeated to obtain crystals, the molecular structure of which was systematically checked by IR spectroscopy. Cadmium acetylacetonate. Acetylacetone (pentane-2,4-dione, Fluka) (1 cm3, 9.68 mmol) was slowly added at room temperature and with stirring to an alkaline aqueous solution of cadmium chloride (6 cm3 of KOH solution at pH 14 1 20 cm3 of CdCl2 solution, [Cd21] = 0.25 mol l21).The white precipitate immediately obtained was filtered off and washed with iced water. Crystalline cadmium acetylacetonate was identified by X-ray diffraction: according to the crystallographic data given in ref. 53, a powder diffractogram was simulated using FULLPROF program.57 The experimental diffractogram and the simulation were strictly identical. Solid-state 13C CP MAS NMR (contact time = 2 ms, recycle delay = 6 s, number of scans = 856): dC(C]] O) 199.2, 193.8, 189.8 and 187.1; dC(]] CH) 102.1 and 100.6; dC(CH3) 30.2, 29.7 and 29.3.These isotropic chemical shifts are in very good agreement with those observed by Takegoshi et al.58 Spectroscopy Infrared spectra were recorded at room temperature as pressed KBr pellets with a Nicolet Fourier-transform spectrometer (range 400–4000 cm21); liquid 13C and 29Si NMR spectra at room temperature on Bruker AC-300 (13C, 75.46 MHz) and MSL-400 (29Si, 79.50 MHz) spectrometers, respectively, using a Bruker VSP probe.Chemical shifts are referenced to SiMe4. The 13C INEPT sequence 29 (including decoupling from 1H and refocusing) was also used to ascertain assignments (see ResultsJ. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 1625 and Discussion). Solid-state 13C and 29Si CP MAS experiments were carried out using Bruker MSL-300 and MSL 400 spectrometers (13C, 75.46; 29Si, 59.62 and 79.50 MHz) equipped with Bruker probes including external lock (4 and 7 mm probes).Zirconia rotors were used. Solid samples were spun at 0.5–4 kHz. Fluctuations in MAS speed were smaller than ±2 Hz over several hours. The magic angle was carefully set using the 79Br resonance of KBr. The matching condition for the Hartmann– Hahn cross-polarization (1H 908 pulse length: 5 ms for the 4 mm probe and 6.5 ms for the 7 mm probe) was set on adamantane (13C) and compound 1 (29Si). It should be noted that both radiofrequency channel levels have to be very carefully set.Indeed, it has been demonstrated that under mismatched conditions the results of IRCP sequences may be false.48 In order to check the matching of the Hartmann–Hahn condition, the IRCP seqence was tested on a glycine sample which acts as a typical ‘rigid’ methylene CH2 group (see Results and Discussion). The test was done periodically during all 13C IRCP MAS experiments. Contact times (tCP) were optimized by standard variablecontact- time experiments.Relaxation delays were 6–15 s. The 13C and 29Si shielding-tensor analyses,39 as well as deconvolution of lines, were obtained by using the WINFIT program developed by Massiot et al.40 Crystallography Crystals of compound 1 were prepared as described above, sealed in Lindemann capillaries and studied at 293 K. Crystal data. C16H24O12Si8, M = 633.04, trigonal, space group R3� (no. 148), a = 13.533(2), c = 14.222(2) Å, g = 1208, U = 1012(5) Å3 (by least-squares refinement for 25 reflections in the range 13.9 < q < 14.58, l = 0.710 69 Å), Z = 3, Dc = 1.398 g cm23, F(000) = 984.Colourless parallelepipeds. Crystal dimensions 0.4 × 0.3 × 0.3 mm, m(Mo-Ka) = 0.4 mm21. Data collection. Enraf-Nonius CAD-4 diffractometer, w–2q mode with w scan width = 0.80 1 0.34 tan q, w-scan speed 2– 20.1 min21, graphite-monochromated Mo-Ka radiation, 999 reflections measured (1 < q < 258; h 0–13, k 0–13; l216 to 16), 882 independent, giving 332 with I > 3s(I) (merging R = 0.0166).Two standard reflections were used (interva: 100 reflections and 60 min). Variation of standards: 1%. Structure solution and refinement. Direct methods (Si, O, C), full-matrix least-square refinements with anisotropic thermal parameters in the last cycles for all non-H atoms and hydrogens in calculated positions (assuming sp2 C atoms). Occupancies of C(11), C(21)–C(24) positions were also refined. As m(Mo-Ka) was rather low, no absorption correction was applied.Sixtyeight refined parameters. Extinction correction method:59 secondary extinction 36(9). The weighting scheme was w = 1. Final R and R9 values were 0.0503 and 0.0480; (D/s)max = 0.15. A final Fourier-difference calculation showed residual electron density in the range 20.2 to 10.15 e Å23. The SHELXS 86 60 system of computer programs was used for the direct methods. Refinement was performed with the CRYSTALS program.61 Atomic scattering factors, corrected for anomalous dispersion, were obtained from ref. 62.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 186/438. Acknowledgements We thank Professor P. Boch for his support and Professor R.M. Laine for providing different octameric silasesquioxanes. S. Mace is also gratefully acknowledged for experimental help. References 1 M. G. Voronkov and V. I. Lavrent9yev, Top. Curr. Chem., 1982, 102, 199. 2 F. J. Feher and T. A. Budzichowski, Polyhedron, 1995, 22, 3239. 3 R. H. Baney, M. Itoh, A. Sakakibara and T. Suzuki, Chem. Rev., 1995, 95, 1409. 4 D. A. Loy and K. J. Shea, Chem. Rev., 1995, 95, 1431. 5 C. L. Frye and W. T. Collins, J. Am.Chem. Soc., 1970, 92, 5586. 6 P. A. Agaskar and W. G. Klemperer, Inorg. Chim. Acta, 1995, 229, 355 and refs. therein. 7 F. J. Feher, T. A. Budzichowski and K. J. Weller, J. Am. Chem. Soc., 1989, 111, 7288. 8 F. J. Feher and K. J. Weller, Organometallics, 1990, 9, 2638. 9 K. Larsson, Ark. Kemi, 1960, 16, 203, 209, 215. 10 I. A. Baidina, N. V. Podberezskaya, V. I. Alekseev, T. N. Martynova, S. V. Borisov and A. N. Kanev, Zh. Strukt. Khim., 1979, 20, 648; N. V. Podberezskaya, S.A. Magarill, I. A. Baidina, S. V. Borisov, L. E. Gorsh, A. N. Kanev and T. N. Martynova, J. Struct. Chem. (Engl. Transl.), 1982, 23, 422. 11 G. Koellner and U. Müller, Acta Crystallogr., Sect. C, 1989, 45, 1106. 12 F. J. Feher and T. A. Budzichowski, J. Organomet. Chem., 1989, 373, 153. 13 H. B. Bürgi, K. W. Törnroos, G. Calzaferri and H. Bürgy, Inorg. Chem., 1993, 32, 4914. 14 G. Calzaferri, R. Imhof and K. W. Törnroos, J. Chem. Soc., Dalton Trans., 1994, 3123. 15 K. W. Törnroos, H.B. Bürgi, G. Calzaferri and H. Bürgy, Acta Crystallogr., Sect. B, 1995, 51, 155. 16 K. W. Törnroos, G. Calzaferri and R. Imhof, Acta Crystallogr., Sect. C, 1995, 51, 1732. 17 K. W. Törnroos, Acta Crystallogr., Sect. C, 1994, 50, 1646. 18 M. Bärtsch, P. Bornhauser, G. Calzaferri and R. Imhof, J. Phys. Chem., 1994, 98, 2817. 19 B. J. Hendan and H. C. Marsmann, J. Organomet. Chem., 1994, 483, 33. 20 J. Kowalewski, T. Nilsson and K. W. Törnroos, J. Chem. Soc., Dalton Trans., 1996, 1597. 21 E. 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Niu, Macromolecules, 1995, 28, 3894. 33 C. K. Johnson, ORTEP, Report ORNL-3794, Oak Ridge National Laboratory, Oak Ridge, TN, 1965. 34 G. Socrates, Infrared Characteristic Group Frequencies, Wiley, Chichester, 1994, p. 42. 35 D. Hoebbel, I. Pitsch, D. Heidemann, H. Jancke and W. Hiller, Z. Anorg. Allg. Chem., 1990, 583, 133. 36 I. Pitsch, D. Hoebbel, H. Jancke and W. Hiller, Z. Anorg. Allg. Chem., 1991, 596, 63. 37 A. R. Grimmer, R. Peter, E. Fechner and G. Molgedey, Chem. Phys. Lett., 1981, 77, 331. 38 R. K. Harris, T. N. Pritchard and E. G. Smith, J. Chem. Soc., Faraday Trans. 1, 1989, 85, 1853. 39 J. Herzfeld and A. E. Berger, J. Chem. Phys., 1980, 73, 6021. 40 D. Massiot, H. Thiele and A. Germanus, Bruker Rep., 1994, 140, 43. 41 N. J. Clayden, C. M. Dobson, L. Y. Lian and D. J. Smith, J. Magn. Reson., 1986, 69, 476. 42 E. M. Menger, D. P. Raleigh and R. G. Griffin, J. Magn. Reson., 1985, 63, 579. 43 T. M. Duncan, A Compilation of Chemical Shift Anisotropies, The Farragut Press, Chicago, 1990, p. C-13.1626 J. Chem. Soc., Dalton Trans., 1997, Pages 1617–1626 44 A. M. Orendt, J. C. Facelli, A. J. Beeler, K. Reuter, W. J. Horton, P. W. Cutts, D. M. Grant and J. Michl, J. Am. Chem. Soc., 1988, 110, 3386. 45 M. Mehring, Principles of High Resolution NMR in Solids, Springer, Berlin, 1983, p. 50. 46 M. Alla and E. Lippmaa, Chem. Phys. Lett., 1976, 37, 260. 47 S. J. Opella and M. H. Frey, J. Am. Chem. Soc., 1979, 101, 5854. 48 X. Wu and K. W. Zilm, J. Magn. Reson., 1993, A102, 205. 49 T. Terao, H. Miura and A. Saika, J. Am. Chem. Soc., 1982, 104, 5228. 50 X. Wu, S. T. Burns and K. W. Zilm, J. Magn. Reson., 1994, A111, 29. 51 X. Wu, S. Zhang and X. Wu, Phys. Rev. B, 1988, 37, 9827. 52 L. Müller, A. Kumar, T. Baumann and R. R. Ernst, Phys. Rev. Lett., 1974, 32, 1402. 53 E. N. Maslen, T. M. Greaney, C. L. Raston and A. H. White, J. Chem. Soc., Dalton Trans., 1975, 400. 54 C. Bonhomme, J. Maquet, J. Livage and G. Mariotto, Inorg. Chim. Acta, 1995, 230, 85. 55 F. Lauprêtre, L. Monnerie and J. Virlet, Macromolecules, 1984, 17, 1397. 56 J. Hirschinger and M. Hervé, Solid State NMR, 1994, 3, 121. 57 J. Rodrigues-Carvajal, FULLPROF 93, An Advanced Rietveld Code, Institut Laue-Langevin, Grenoble, 1993. 58 K. Takegoshi, K. J. Schenk and C. A. McDowell, Inorg. Chem., 1987, 26, 2552. 59 A. C. Larson, Crystallographic Computing, eds. F. R. Ahmed, J. R. Hall and C. P. Huber, Munksgaard, Copenhagen, 1970, p. 291. 60 G. M. Sheldrick, SHELXS 86, Program for the Solution of Crystal Structures, University of Göttingen, 1986. 61 D. J. Watkin, J. R. Carruthers and P. W. Betteridge, CRYSTALS, An Advanced Crystallographic Program System, Chemical Crystallography Laboratory, University of Oxford, 1988. 62 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4. Received 29th January 1997; Paper 7/00700K

ISSN:1477-9226    

DOI:10.1039/a700700k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1627–1632 1627 Electronic properties of hydroquinone-containing ruthenium complexes in diVerent oxidation states † Tia E. Keyes,a Pradeep M. Jayaweera,b John J. McGarvey b and Johannes G. Vos *,a a School of Chemical Sciences, Dublin City University, Glasnevin, Dublin 9, Ireland b Department of Chemistry, Queens University of Belfast, Belfast, UK Some novel bis(2,29-bipyridyl)ruthenium(II) complexes based on the ligands 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)- benzene (H2Lp) and 1,4-dihydroxy-2,3-bis(pyrazol-1-yl)benzene (H2Lo) have been prepared and characterized.The spectroscopic properties of the analogous H2Lp complex containing deuteriated 2,29-bipyridyl were also studied. The compounds have been oxidized and the electronic properties associated with both oxidation states examined in detail using resonance-Raman and UV/VIS/NIR spectroscopy. In the parent compounds the first redox process is hydroquinone based and the lowest-energy absorption is assigned to a hydroquinone to 2,29-bipyridyl interligand transition.The products obtained upon oxidation are best described as ruthenium(II)–quinone complexes and their lowest-energy transition is assigned to a RuII to quinone charge transfer. Recently, much attention has been paid to ruthenium– polypyridyl complexes1 bound to hydroquinone/quinone moieties. Most compounds reported are based upon 1,2- dihydroxy-type ligands where the hydroquinone moiety acts as a 1,2 chelate through two metal–oxygen bonds.In addition, some reports 2,3 deal with mixed nitrogen–oxygen donors where in the former the co-ordination of RuII to quinonoid rings via hydroxyl and amino moieties is examined and in the latter O,N co-ordination via a pyridyl nitrogen and a phenolic OH is observed. 1,4-Dihydroxyquinone complexes have been investigated to a considerably lesser extent.4 We have recently embarked on a systematic study of complexes where hydroquinone units in combination with other coordinating groups are bound to metal centres in a bidentate asymmetric mode.The aim of these studies is to investigate the electronic interaction between the hydroquinone and ruthenium–polypyridyl units. In previously reported cathecholate and hydroquinone complexes, electronic coupling between the ligands and the metal centre is expected to be strong and considerable orbital mixing complicates a detailed description of the properties of the compounds.2 Detailed investigation on both mono- and di-nuclear complexes 5 is needed to better understand the properties of dihydroxy-type ligands and their interactions with metal centres.Such investigations are not only of interest from the purely inorganic point of view, but are also expected to yield information on the behaviour of hydroquinone- type compounds in biological processes. Indeed recently we reported on the electrochemically induced intramolecular proton transfer in a ruthenium(II)–hydroquinone complex.6 In addition, the ruthenium(II)–polypyridyl complexes involving O,N bonds are expected to absorb well into the visible region and have therefore potential as dyes in sensitized solar cells.7 In this contribution we report on the synthesis and characterization of novel bis(bipyridyl)ruthenium complexes of the type [Ru(bipy)2L]1 where bipy is 2,29-bipyridyl and L is 1,4-dihydroxy-2,5-bis(pyrazol-1-yl)benzene (H2Lp) or 1,4- dihydroxy-2,3-bis(pyrazol-1-yl)benzene (H2Lo). Employing electrochemistry, spectroelectrochemistry and resonance- Raman spectroscopy, we have carried out a detailed study of the electrochemical and excited-state properties of these complexes in different oxidation states.† Supplementary data available (No. SUP 57224, 3 pp.): resonance- Raman spectra. See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. The synthesis and properties of the hydroquinones as polymer photostabilizers have been investigated by Catalan et al.8 This group also reported on the synthesis of rhodium and iridium carbonyl complexes of H2Lp.Experimental Techniques Metal complexes were purified on a semipreparative HPLC system using an Applied Chromatography Service (ACS) pump (model RR066) and model 353/UV/VIS detector together with a Magnum-9m Partisil cation-exchange column (10 mm × 25 cm). The mobile phase was acetonitrile–water (7 : 3, v/v) containing 0.15 mol dm23 KNO3.Absorption spectra were measured using a Shimadzu 3100 UV/VIS/NIR spectrophotometer interfaced with an Elonex PC-433. Electrochemistry was performed in HPLC-grade acetonitrile [dried over activated molecular sieve (type 3A)] using 0.1 mol dm23 tetraethylammonium perchlorate. The working electrode was a 3 mm Teflon-shrouded, glassy carbon electrode, the reference a saturated calomel electrode and the auxiliary electrode a platinum gauze.The cell employed was a three-electrode compartmentalized cell separated by glass frits. Solutions were degassed under argon for 20 min prior to experimentation. An EG&G PAR model 362 scanning potentiostat was employed for cyclic voltammetry (CV) and a model 264A polarographic analyser for differential pulse polarography (DPP). Data were recorded on a Linseis model 17100 x-y recorder at a scan rate of 100 mV s21 for CV and 10 mV s21 for DPP. Resonance-Raman experiments were recorded using an argon-ion laser as the excitation source in the region 355–528 nm, and a titanium–sapphire laser pumped by an argon-ion source for experiments carried out at wavelengths beyond 700 nm.Backscattering geometry was employed for the spectral1628 J. Chem. Soc., Dalton Trans., 1997, Pages 1627–1632 Table 1 The 400 MHz 1H NMR data (d) for the complexes in CD3CN Hydroquinone Pyrazole (pyridine) Complex [Ru(bipy)2(HLp)]1 Dd* [Ru(bipy)2(HLo)]1 Dd H3 7.00 20.27 — H5 — 6.39 20.37 H6 6.37 20.90 6.08 20.88 OH4 10.38 20.59 7.01 21.22 H39 6.44 21.34 6.39 21.27 H49 6.37 20.20 5.98 20.59 H59 8.24 0.00 6.89 20.13 H30 7.71 20.07 7.68 20.02 H40 6.46 20.11 6.45 20.12 H50 7.91 20.33 7.56 0.54 * Difference between resonances for complexes and free H2L.accumulations using a liquid-nitrogen cooled Charged-Coupled Devices multichannel array as the detector.9 Spectra of electrochemically generated species were recorded using a cell fitted with an optically transparent platinum-gauze electrode (62% transmittance) as working electrode.A silver wire was employed as a pseudo-reference electrode and a platinum wire as auxiliary. Tetrabutylammonium perchlorate (0.1 mol dm23 in dry acetonitrile) was used as supporting electrolyte. Materials p-Benzoquinone was recrystallized from water and dried prior to use. 1,4-Dioxane was dried by distillation over LiAlH4 and stored over activated molecular sieves prior to use. All other reagents (Aldrich) were used as received.The compounds H2Lo and H2Lp were synthesized and purified as described by Catalan et al.,8 [Ru(bipy)2Cl2]?2H2O and [Ru([2H8]bipy)2Cl2]?2H2O as described by Meyer and co-workers 10 and [2H8]2,29-bipyridyl as reported previously.11 [Ru(bipy)2(HLp)]PF6?2H2O. The compound H2Lp (0.15 g, 0.6 mmol) was dissolved in ethanol–water (1 : 1 v/v, 40 cm3) containing diethylamine (2%, v/v). This solution was deoxygenated with argon, heated and [Ru(bipy)2Cl2]?2H2O (0.275 g, 0.53 mmol) dissolved in ethanol–water (1 : 1 v/v, 40 cm3) was added slowly over 20 min.The mixture was heated under reflux in an argon atmosphere for 4 h after which time the dark purple solution was reduced in volume to approximately 10 cm3 and neutralized with sulfuric acid. It was allowed to stand for several hours and then filtered to remove any salt formed. A few drops of concentrated aqueous NH4PF6 were added and the resulting purple precipitate was filtered off.Two products were identified Fig. 1 The 400 MHz 1H NMR COSY-45 spectrum of [Ru(bipy)2- (HLp)]1 in CD3CN by HPLC. The first a mononuclear complex and the second dinuclear.5 The mononuclear product was obtained in a pure form after separation by semipreparative HPLC. It was recrystallized from acetone–water (1 : 1 v/v). Yield 60% (Found: C, 46.05; H, 3.35; N, 13.1. C32H29F6N8O4PRu requires C, 46.0; H, 3.5; N, 13.4%). The deuteriated analogue, [Ru([2H8]- bipy)2(Lp)]PF6 was prepared by the same method.[Ru(bipy)2(HLo)]NO3?2H2O. This complex was prepared as above except that no addition of NH4PF6 was required. On reduction of the solution volume after semipreparative HPLC the product precipitated spontaneously, and was collected as the nitrate salt. Yield 59% (Found: C, 51.05; H, 3.6; N, 16.35. Calc. for C32H29N9O7Ru: C, 51.05; H, 3.9; N, 16.75%). Results and Discussion General The complexes can be prepared and purified using standard synthetic techniques.Trace amounts of dinuclear complex formed during reaction can be removed by semipreparative HPLC. The properties of these dinuclear compounds will be dealt with in a separate publication.5 It is important to note that the complexes are unstable in acidic solution at pH < 4. Such decomposition has been reported elsewhere for phenolatebound complexes.12 Proton NMR spectroscopy (see below) and elemental analysis indicate that in the complex the free OH group is protonated and that as expected the co-ordinated hydroxyl group is deprotonated. 1H NMR spectroscopy Sharp, well defined resonances were observed for the complexes, confirming the presence of RuII and the absence of semiquinone radicals. Fig. 1 shows the 1H NMR correlation (COSY) spectra for [Ru(bipy)2(HLp)]1. A complete assignment of resonances was achieved by COSY 45 techniques, and comparison with the deuteriated analogue. However, although all bipyridyl resonances were identified, individual ring assignments were not made.The shifts pertaining to the hydroquinone ligands are shown in Table 1. The interpretation of the spectra for the complexes is straightforward and described for [Ru(bipy)2(HLp)]1; similar arguments may be applied to the other complex. Two singlets are observed for the hydroquinone moiety; COSY experiments show that they are in fact weakly coupled to one another. Both singlets exhibit an upfield shift with respect to free H2Lp.The first, H3, a moderate 20.27 ppm while the second, H6, exhibits a significant shift of 20.9 ppm. This large shift can be explained by a diamagnetic anisotropic interaction with a bipyridyl ring and indicates that the ruthenium centre is bound adjacent to this proton. Both H49 and in particular H39 of the co-ordinated pyrazole experience upfield shifts with respect to free H2Lp; again this shift may be attributed to diamagnetic anisotropic interaction of the pyrazole protons with the ring current of an adjacent bipyridyl ring.The protons of the remaining uncoordinated pyrazole H30, H40 and H50 show only weak upfield shifts, remaining essentially unchanged from those of free H2LpJ. Chem. Soc., Dalton Trans., 1997, Pages 1627–1632 1629 Table 2 Electrochemical and spectral data E/V vs. SCE Compounda [Ru(bipy)3]21 [Ru(bipy)2(HLp)]1 [Ru(bipy)2(HLo)]1 OH oxidation (V) — 0.42 0.44 Bipyridyl reduction 21.35 21.52, 21.80 21.60, 21.89 Metal oxidation 1.26 1.29 b 1.30 b Absorbance lmax/nm (log e) — 485 (3.76) 490 (3.63) a For H2Lp, E = 0.3 (pH 10) and 0.9 V (7) for OH oxidation; for H2Lo, 0.25 and 0.98 V respectively.b Irreversible. (see Table 1). The presence of an intramolecular hydrogen bond between the unco-ordinated OH and the pyrazole is maintained in [Ru(bipy)2(HLp)]1, confirmed by the downfield shift of the OH proton at d 10.38.8 The intramolecularity of this bridge was confirmed by the fact that the resonance is not affected by dilution.No such bridging is present for [Ru(bipy)2(HLo)]1, the OH resonance of which is observed at d 7.01; this is also observed for free H2Lo, where as a result of steric crowding the pyrazoles are turned out of the plane of the hydroquinone moiety. Electrochemical properties Table 2 displays the electrochemical properties of the complexes and the free hydroquinones. Fig. 2 shows the cyclic voltammogram for [Ru(bipy)2(HLp)]1. For the free H2L in neutral solution the first oxidation potential is around 0.9 V. In basic solution as a result of deprotonation of the hydroxyls this potential is dramatically cathodically shifted to around 0.3 V as a result of the large increase in electron density on the negatively charge oxygen groups.The quasi-reversible two-electron oxidation at 0.42 V for [Ru(bipy)2(HLp)]1 and at 0.44 V for [Ru(bipy)2- (HLo)]1 has been assigned to the hydroquinone–quinone oxidation. The two-electron nature of this wave was confirmed by bulk electrolysis/coulometry. It is interesting that despite the Fig. 2 Cyclic voltammogram of [Ru(bipy)2(HLp)]1 in acetonitrile, electrolyte NEt4ClO4, scan rate 100 mV s21 Fig. 3 The UV/VIS absorbance spectra of (a) [Ru(bipy)2(HLp)]1 and (b) [Ru(bipy)2(HLp)]1 (1 × 1024 mol dm3) in acetonitrile asymmetry of the ligand after co-ordination the oxidation occurs in a single two-electron step. The anodic shift of this potential with respect to the free H2L is expected as a result of co-ordination and is consistent with the behaviour observed for free H2L in basic solution.The O,N complexes bound to phenolic moieties reported by Ward and co-workers 3 show behaviour that is remarkably similar to that described here with an irreversible oxidation occurring at strongly anodic potential, 1.3 V in each case. For the present compounds the irreversibility of this oxidation is dependent on the potential scan rate, with the redox process becoming more reversible at faster scan rates.We associate the process with the metal-based RuII–RuIII oxidation. It is proposed that its irreversibility is related to decomposition of the ruthenium(III)–quinone complex. Electronic properties The absorption spectra are shown in Fig. 3 and the data in the visible part of the spectrum are listed in Table 2. The complexes exhibit intense absorbances at wavelengths <300 nm. On the basis of their intensities and by comparison with other ruthenium(II)–polypyridyl complexes 1 these are assigned as p–p* ligand-based transitions.The features around 330–350 nm for each complex are associated with p–p* transitions in hydroquinone moieties; similar absorbances are observed for H2L which show absorption maxima between 315 and 360 nm and for other complexes containing hydroquinone moieties.6 In line with other ruthenium(II)–polypyridyl complexes, the visible absorption at 480 nm is assigned as a metal to ligand charge transfer (m.l.c.t.) Ru(t2g) to bipy (p*) transition. This assignment is supported by the resonance-Raman and electrochemical data (see below).Table 2 shows that the position of the lowest-energy absorption maxima is red-shifted with respect to [Ru(bipy)3]21 and other complexes containing strong sdonor ligands.1 The values do not fully represent the true extent of the visible absorbance range of these compounds, since it is very broad and tails to approximately 700 nm (see Fig. 3). An intense shoulder tailing to the red from approximately 580 nm is observed. In agreement with Lever and co-workers 2 who reported similar transitions for their Ru(bipy)2–catecholate complexes, we attribute this transition to a p(L)–p*(bipy) transition. For Lever’s O,O9- and O,N-co-ordinated catecholate complexes a long-wavelength shoulder is observed at 667 nm.2 The absorbances associated with p(L)–p*(bipy) transitions for these complexes are at substantially longer wavelengths than observed for the present compounds.The reason for this is unclear, but the values obtained may indicate a higher energy for the hydroquinone ground state in our complexes. Spectroelectrochemistry Ultraviolet–visible spectroelectrochemistry was employed to obtain further information concerning the electrochemical and spectroscopic assignments. Oxidation of the solutions was carried out both by electrochemical methods and chemically by the addition of controlled amounts of Ce41. A typical example for the H2Lo complex is shown in Fig. 4. For the H2Lp complex similar features are observed. The spectral changes associated1630 J. Chem. Soc., Dalton Trans., 1997, Pages 1627–1632 with the first two-electron oxidation step are reversible, and unstable long-lived intermediates are not present as indicated by the clear isosbestic points at 327, 398, 446 and 614 nm. The figure shows that after the first two-electron oxidation the m.l.c.t. band at 490 nm blue shifts to approximately 416 nm, and a new feature appears at 700 nm for [Ru(bipy)2(Lo)]21.For [Ru(bipy)2(Lp)]21 a similar band is observed at 756 nm. The presence of significant absorption features between 400 and 500 nm in the spectrum of the oxidized compound suggests that in the complex the metal centre is still in the ruthenium(II) state, consistent with the interpretation of the electrochemical data. The oxidized complex is therefore most likely the analogous ruthenium(II)–quinone species.After oxidation of the hydroquinone to quinone the RuIIÆbipy(p2*) m.l.c.t. shifts to the blue as a result of the stabilization of the t2g level when the sdonating ability of the ligand is decreased. For both the H2Lo and H2Lp complexes the spectral changes associated with the oxidation at 1.3 V are irreversible, loss of the intense feature at between 700 and 800 nm and of the band at 416 nm is evident and a yellow complex is obtained.Preliminary characterization of this product suggests it to be a complex in which the pyrazole is bound to the Ru in a monodentate fashion. Resonance Raman Resonance-Raman spectroscopy has been used extensively to investigate the nature of the absorption and emission processes in ruthenium–polypyridyl complexes.13 In this study we have applied the technique to better understand the absorption features of the compounds and of their oxidized analogues. Fig. 5 shows the resonance-Raman spectra of (a) [Ru(bipy)2- (HLo)]1, (b) [Ru(bipy)2(HLp)]1 and (c) [Ru([2H8]bipy)2(HLp)]1 excited at 457.9 nm.Both the H2Lp and H2Lo complexes exhibit very similar features upon 457.9 nm excitation, suggesting that the ligand L is not involved in this transition. The enhanced features in spectra (a)–(c) at 1606, 1558, 1488, 1268, 1173 and 1023 cm21 are all characteristic of bipy, and this is confirmed by the spectral shifts induced in these bands on deuteriation of bipy.The shift on deuteriation is in the region of 30 cm21, with the exception of the band at 1486 cm21 which has an unusually Fig. 4 Spectroelectrochemistry of [Ru(bipy)2(HLo)]1 oxidized by addition of cerium(IV) sulfate. Spectra were recorded as a function of time between 0 and 20 min large isotopic effect of over 60 cm21. One feature, however, shows no isotopic effect, i.e. the low-intensity band at 1342 cm21. Interestingly the resonance-Raman spectrum of free H2L (SUP 57224), excited at 363.8 nm (i.e.in resonance with the hydroquinone p–p* transition), has as its most intense feature a band at 1342 cm21. We therefore conclude that excitation at 457.9 nm causes some pre-resonance enhancement of the ligand-based absorbance on the hydroquinone. In the lowfrequency end of the spectrum there are bands at 667 (isotope sensitive) and 374 cm21; the former has been tentatively associated with a ligand-deformation mode of bipy and the latter with a Ru]N stretching mode.14 The band at 374 cm21 shows only very weak resonance enhancement as the m.l.c.t.transition exerts little influence on the Ru]N bond. On the basis of these results we conclude that the broad absorption with a maximum near 480 nm is assigned as a RuIIÆbipy(p*) m.l.c.t. transition. This was anticipated, as the hydroquinone ligands possess no empty low-lying energy levels. Fig. 3 shows that, apart from the usual 400–500 nm band, the compounds exhibit a strong shoulder in their absorption spectrum at about 578 nm.To investigate the nature of that transition resonance-Raman spectra were recorded at 632.8 nm. This wavelength was chosen to avoid absorption into the lowenergy tail of the m.l.c.t. transition at 480 nm. Fig. 5(d ) shows the spectrum obtained for [Ru(bipy)2(HLp)]1 excited at 632.8 nm. What is immediately apparent is that this spectrum contains bipy-based features at 1606, 1557 and 1486 cm21 while in addition a number of new features are apparent in the lowfrequency region at 551, 486 and 433 cm21; the latter show no isotopic shifts on bipyridyl deuteriation. Also the band at 374 cm21 has disappeared.This latter feature has always been associated with m.l.c.t. transitions 15 in these compounds and its absence suggests that there is no contribution from such a pro- Fig. 5 Resonance-Raman spectra of (a) [Ru(bipy)2(HLp)]1, (b) [Ru- (bipy)2(HLo)]1, (c) [Ru([2H8]bipy)2(HLp)]1 excited at 457.4 nm and (d ) [Ru(bipy)2(HLp)]1 excited at 632.8 nm in acetonitrileJ.Chem. Soc., Dalton Trans., 1997, Pages 1627–1632 1631 cess. Based on a comparison with other oxygen-bound complexes 13,15 the band at 551 cm21 is assigned to Ru–O stretching vibrations and the last two to coupled Ru]O and ligand modes. These features are distinctly enhanced, suggesting the Ru–O bond is significantly influenced by the transition at 578 nm. These observations in conjunction with the simultaneous presence of bipy-centred modes, suggest that the absorption process we are probing in this experiment, namely the transition centred at 578 nm, is best described as a L(p) æÆ bipy(p*) interligand transition.Loss of electron density on the oxygen as the electron is transferred from the oxygen lone pair to bipy p* should have a significant effect on the Ru–O bond, resulting in enhancement of modes of this bond in line with what is observed. It is interesting that in the 632.8 nm spectra the intensities of the bipy vibrations around 1500 cm21 have changed with respect to those of the complex excited at 457.4 nm.A very similar effect was reported previously by Lever and co-workers 2 for O,O9-co-ordinated catechol complexes of RuII. For the latter compounds near-equal intensities of the bands at 1604 and 1557 cm21 were observed upon excitation at 457.9 nm, compared to a 1 : 3 intensity ratio upon excitation at 540 nm, attributed to the 457.4 nm line being pre-resonant with the RuIIÆbipy(p2*) transition near 480 nm.The change in intensity on excitation at wavelengths of >540 nm was ascribed to preresonance with the lower-energy RuIIÆbipy(p1*) transition. Our results suggest that the intraligand transition centred at 530 nm involves the bipy-based p1* orbital rather than the higherenergy p2* level. Furthermore the absence of the weak feature at 1342 cm21 seen upon 457.4 nm excitation is notable, and would appear to confirm the fact that this feature is associated with pre-resonance of internal high-energy hydroquinone transitions.Resonance-Raman studies were also carried out on the oxidized species. Spectra were recorded of solutions electrochemically oxidized by holding the potential at 0.6 V for 20 min or by the addition of Ce41. The spectra obtained for the Lp compound (a) and for its deuteriated analogue (b) upon excitation at 780 nm are given in Fig. 6. The spectroscopic features are clearly not associated with bipy, because of the absence of any isotopic effect on the frequency of the bands.The band at 1488 cm21 assigned to bipy in the spectrum in Fig. 5 remains enhanced for the oxidized complex, which might suggest that the spectrum of the latter still derives some intensity from resonance with the m.l.c.t. transition. However, comparison with the spectrum obtained for the deuteriated complex demonstrates that this mode exhibits no isotope effect. It is therefore unlikely that this band is bipy based. Another striking feature is the strong enhancement observed for the vibrational mode at 443 cm21.For the corresponding Lo complex a similar feature was observed at 445 cm21. It is likely that this is a Ru– O15 mode coupled to a Lp (or Lo) deformation. Some further, strongly enhanced features appear in Fig. 6(a) at 1647, 879 and 706 cm21. These bands are not observed in the spectra of the parent compounds and can therefore not be explained as hydroquinone vibrations. By comparison with other similar compounds13 we propose that these are associated with quinone stretching and deformation modes.This is a direct indication that the first redox process is hydroquinone based and that the product obtained in this oxidation is a ruthenium(II)– quinone complex. It is noteworthy that the resonance-Raman spectra of the oxidized complexes containing Lo and Lp are readily distinguishable. These observations again suggest that the ligand L is strongly involved in the spectroscopic process observed at about 750 nm for the oxidized species.Furthermore, resonance-Raman spectra of the oxidized complexes upon 457.9 nm excitation reveal that the Ru]N and bipy modes are still present. In addition the weak mode at 1342 cm21 present for the parent compound has disappeared (SUP 57224). Consistent with the electrochemical data, this suggests the presence of a ruthenium(II) moiety after oxidation and indicates the band at 700 nm is best described as a Ru(dp)Æ quinone(p*) m.l.c.t. transition.This interpretation is in agreement with observations for similar complexes 2,13 for which the primary electrochemistry occurs at the hydroquinone ligand. Conclusion The compounds reported in this work show some well defined spectroscopic and electrochemical properties. Electrochemical and spectroelectrochemical experiments show that the first redox process in these compounds is hydroquinone based.Resonance-Raman spectra provide direct evidence for a lowenergy hydroquinone to bipy charge-transfer transition. The absorption features of the compounds, far into the visible, make them in principle of interest for application as dyes in solar cells. However, for these particular compounds problems are expected to arise because of the presence of hydroquinonebased redox processes at low potentials. These features make these compounds interesting building blocks for supramolecular structures.We are at present engaged in the study of the dinuclear analogues. Acknowledgements The authors thank Forbairt and the EC-Joule programme for financial assistance. References 1 A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser and A. von Zelewsky, Coord. Chem. Rev., 1988, 84, 85; V. Balzani, A. Juris, M. Venturi, S. Campagna and S. Serroni, Chem. Rev., 1996, 96, 759. 2 M. Haga, E. S. Dodsworth and A. B. P. Lever, Inorg. Chem., 1986, 25, 447; H.Masui, A. B. P. Lever and P. R. Auburn, Inorg. Chem., 1991, 30, 2402. 3 J. C. Jeffery and M. D. Ward, J. Chem. Soc., Dalton Trans., 1992, 2119; J. C. Jeffery, E. Schatz and M. D. Ward, J. Chem. Soc., Dalton Trans., 1992, 1921; B. M. Holligan, J. C. Jeffery, M. K. Norgett, E. Schatz and M. D. Ward, J. Chem. Soc., Dalton Trans., 1992, 3345; Fig. 6 Resonance-Raman spectra of (a) [Ru(bipy)2(Lp)]21 and (b) [Ru([2H8]bipy)2(Lp)]21 at 0.6 V (after the first two-electron oxidation) excited at 780 nm in acetonitrile1632 J.Chem. Soc., Dalton Trans., 1997, Pages 1627–1632 D. A. Bardwell, D. Black, J. C. Jeffery, E. Schatz and M. D. Ward, J. Chem. Soc., Dalton Trans., 1993, 2321. 4 S. Ernst, P. Hanel, J. Jordanov, W. Kaim, V. Kasack and E. Roth, J. Am. Chem. Soc., 1989, 111, 1733; M. Haga, Inorg. Chim. Acta, 1983, 75, 29; A. M. El Handawy, Polyhedron, 1991, 10, 21 337; G. Juriga, M. Sattgast and M. E. McGuire, Inorg. Chim. Acta, 1991, 183, 39; M. J. Ridd, D. J. Gakowski, G. E. Sneddon and F. R. Keen, J. Chem. Soc., Dalton Trans., 1992, 1949. 5 T. E. Keyes and J. G. Vos, unpublished work. 6 R. Wang, T. E. Keyes, R. Hage, R. H. Schmehl and J. G. Vos, J. Chem. Soc., Chem. Commun., 1993, 1652. 7 B. O’Regan and M. Grätzel, Nature (London), 1991, 353, 737. 8 J. Catalan, F. Fabero, M. S. Guijarro, R. M. Claramount, M. D. Santa Maria, M. de la Concepcion Foces-Foces, F. H. Cano, J. Elguero and R. Sastre, J. Am. Chem. Soc., 1990, 112, 747; P. Cornago, C. Escolastico, M. D. Santa Maria, R. M. Claramount, D. Carmona, M. Esteban, L. A. Oro, C. Foces-Foces, A. L. Llamas- Siaz and J. Elguero, J. Organomet. Chem., 1994, 467, 293. 9 R. A. McNicholl, J. J. McGarvey, A. H. R. Al-Obaidi, S. E. J. Bell, P. M. Jayaweera and C. G. Coates, J. Phys. Chem., 1995, 99, 12 268. 10 B. P. Sullivan, D. J. Salmon and T. J. Meyer, Inorg. Chem., 1978, 17, 3334. 11 T. E. Keyes, F. Weldon, E. Muller, P. Pechy, M. Grätzel and J. G. Vos, J. Chem. Soc., Dalton Trans., 1995, 2705. 12 M. J. Clarke and M. G. Dowling, Inorg. Chem., 1991, 20, 3506. 13 A. B. P. Lever, H. Masui, R. A. Metcalf, D. J. Stufkens, E. S. Dodsworth and P. R. Auburn, Coord. Chem. Rev., 1993, 125, 317. 14 D. P. Strommen, P. K. Mallick, G. D. Danzer, R. S. Lumpkin and H. J. R. Kincaid, J. Phys. Chem., 1990, 94, 1357. 15 K. Burger, Coordination Chemistry: Experimental Methods, Butterworths, London, 1973; K. Nakamoto, IR and Raman Spectra of Inorganic and Coordination Compounds, Wiley-Interscience, New York, 4th edn., 1986. Received 22nd November 1996; Paper 6/07941E

ISSN:1477-9226    

DOI:10.1039/a607941e

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1633–1637 1633 Intermediates and products of the reaction of MoCl5 with ethanol: crystal structures of [MoOCl3(EtOH)] and H[MoOCl4]?2EtOH Christian Limberg,*,a Roland Boese b and Berthold Schiemenz a a Universität Heidelberg, Anorganisch-Chemisches Institut, Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany b Universität-GH Essen, Institut für Anorganische Chemie, Universitätsstrasse 3-5, D-45117 Essen, Germany An intermediate in the ethanolysis reactions of MoCl5, [MoOCl3(EtOH)] 2, has been isolated after the reaction of MoCl5 with 2 equivalents of EtOH and its crystal structure was determined.Treatment of MoCl5 with 2.5 equivalents of EtOH and subsequent cooling as well as the reaction of [Cl2OMo(m-OEt)2(m-HOEt)MoOCl2] 1 with HCl(g) yield a product which has been identified as H[MoOCl4]?2EtOH 3 by X-ray crystallography. The mechanisms leading to 1–3 are discussed. The reactions of 2 with donors have been investigated and [Cl2OMo- (m-OPr)2(m-HOPr)MoOCl2] 4 was obtained as a first derivative of 1 after the reaction of MoCl5 with PrOH.The reaction of MoCl5 with EtOH inspite of being seemingly trivial still causes confusion. In 1930 Wardlaw and Webb1 reported that at room temperature it results in the formation of a green oil containing MoOCl3 in one form or another as suggested by its reaction with [C5H5NH]Cl to yield [C5H5NH]- [MoOCl4]. On the other hand Butcher and Chatt 2 obtained a brown oil, the colour of which was rationalised later by Gibson and co-workers 3 as due to the presence of traces of moisture.However, on treatment with phosphines these two different oils yielded two different distortional isomers of [MoOCl2(PR3)3] with differing spectroscopic properties.3 In 1958 Bradley et al.4 described the synthesis of [{Mo(OEt)2Cl3}2] from the reaction of MoCl5 with an excess of EtOH at 278 8C, and recently after treatment of MoCl5 with 2.5 equivalents of EtOH in CHCl3 at room temperature we isolated the dimeric complex [Cl2OMo- (m-OEt)2(m-HOEt)MoOCl2] 1 in almost quantitative yield.5 The stoichiometry of the reaction has been verified by isolating the products EtCl and HCl, when the reaction was performed in a sealed vessel.These were the only products to be isolated having an appreciable volatility at 178 K. The failure to detect any diethyl ether enabled us to propose a reaction sequence (1) and MoCl5 1 2 EtOH 22HCl [Mo(OEt)2Cl3] 2EtCl [MoO(OEt)Cl2] [MoO(OEt)Cl2]EtOH 1 (1) to rule out a different possible mechanism for the decomposition of the postulated intermediate [Mo(OEt)2Cl3] therein via the pathway (2), which had been suggested previously to be [Mo(OR)2Cl3] [MoOCl3] 1 R2O (2) the essential reaction step in the methanolysis (R = Me) of MoCl5.6 Moreover the reaction generating complex 1 shows some peculiarities: after the addition of stoichiometric amounts of EtOH to MoCl5 a green solution is obtained turning brown while the volatiles are removed and finally yielding the orange complex 1.This redissolves giving an orange colour in CH2Cl2, switching to green again on treatment with gaseous, anhydrous HCl. This colour change can only be explained by the presence of highly reactive monomeric species stabilised by HCl (the variation between green and orange-brown is reminiscent of the different observations made by Wardlaw and Chatt already mentioned).In this contribution the isolation and crystal structures of two such reactive intermediates are described. Results and Discussion The reaction of MoCl5 with just 2 rather than 2.5 equivalents of EtOH should prevent the quantitative generation of complex 1 since not enough EtOH is available for the formation of the EtOH bridge present in it. In this case the stabilisation of a dimer once formed is impossible so that there should be a chance to isolate one or more of the monomeric intermediates.When a concentrated solution of MoCl5 in CH2Cl2 is treated with 2 equivalents of EtOH an unstable green solution is obtained, from which a greyish solid is precipitating continuously. Cooling of a freshly filtered solution to 278 8C results in the separation of considerable amounts of green crystals, which proved to be highly reactive, immediately liquidising in contact with traces of water (for instance at glass walls) to a brown oil. Crystals suitable for a structure analysis could be obtained by recrystallisation and in agreement with spectroscopic and other data these were found to consist of [MoOCl3(EtOH)] 2, the structure of which is shown in Fig. 1. Bond lengths and angles are presented in Table 1. Compound 2 exists as a discrete molecule showing a tetragonal-pyramidal geometry with the Mo placed 0.429 Å above the plane defined by Cl(1)–Cl(3) and O(1). At 1.641(2) Å the Mo]] O bond is remarkably short as compared to those of Table 1 Bond distances (Å) and angles (8) in complex 2 Mo]O(2) 1.641(2) Mo]H(10) 2.46(4) Mo]O(1) 2.102(2) Cl(1) ? ? ? H(10) 2.70(4) Mo]Cl(2) 2.3116(8) O(1)]C(1) 1.472(3) Mo]Cl(3) 2.3213(7) C(1)]C(2) 1.500(4) Mo]Cl(1) 2.3997(8) O(2)]Mo]O(1) 99.35(9) Cl(3)]Mo]Cl(1) 88.63(3) O(2)]Mo]Cl(2) 102.29(7) O(2)]Mo]H(10) 103.9(9) O(1)]Mo]Cl(2) 88.90(5) O(1)]Mo]H(10) 15.1(9) O(2)]Mo]Cl(3) 101.65(7) Cl(2)]Mo]H(10) 101.8(9) O(1)]Mo]Cl(3) 158.28(6) Cl(3)]Mo]H(10) 147.5(9) Cl(2)]Mo]Cl(3) 91.98(3) Cl(1)]Mo]H(10) 67.5(9) O(2)]Mo]Cl(1) 99.84(7) Mo]Cl(1)]H(10) 57.3(8) O(1)]Mo]Cl(1) 82.38(5) C(1)]O(1)]Mo 130.0(2) Cl(2)]Mo]Cl(1) 157.25(2) O(1)]C(1)]C(2) 110.0(2)1634 J.Chem. Soc., Dalton Trans., 1997, Pages 1633–1637 other molybdenum(V) compounds7 bearing ligands in trans position to the Mo]] O bond. Structural studies on a number of six-co-ordinate oxomolybdenum(V) complexes have shown that there is a significant lengthening of the molybdenum–ligand distance trans to the oxo-group (see ref. 1 in ref. 8). This lengthening is due to the trans influence of the oxo-group, which also facilitates the formation of five-co-ordinate species, especially in solutions of poorly co-ordinating solvents.8 Kinetic studies of substitution reactions of complexes such as [MoOCl3X2]n2 in dichloromethane9 suggest such five-co-ordinate species as intermediates and one such example is compound 2, although it is not formed in a substitution reaction. The absence of a ligand in trans position to the oxygen produces a definite electron deficiency at the Mo in 2 and enables participation of the lone pairs at the O atom in the bonding to Mo, formally producing a Mo]] ] O triple bond.This goes together with an increased bond order and force constant which is reflected by a comparatively high frequency for the n(Mo]] O) vibration being masked by the band for n(C]O) at 1013 cm21. Since normally EtOH ligands do not show a considerable trans influence it is not surprising that the Mo]Cl bonds are all of comparable length.The Mo]O(1) distance of 2.102(2) Å lies within the region characteristic for such bonds.10 The co-ordination number of five stresses the intermediate character of compound 2. Molybdenum complexes normally exhibit a marked tendency to obey the 18-electron rule and, moreover, the size of the Mo atom is such that six-fold coordination is commonly adopted.11 Lower co-ordination numbers are most likely to arise as a response either to the requirements of the 18-electron rule or to the presence of bulky ligands. 11 Neither of these factors seems to apply to 2 so that its five-co-ordination should mainly be a result of the strong trans influence of the oxo-group and the absence of ligands with relatively strong s-donor properties. Therefore its observed reactivity especially with regard to atmospheric water is only too understandable. Some five-co-ordinate complexes of the OMoCl3 fragment are known.8 A five-fold co-ordination of Mo in the solid state was demonstrated for the first time in 1975 for the complex [MoOCl3(S]] PPh3)] 12 in which the S]] PPh3 shows a marked trans influence unlike the EtOH ligand in 2.In contrast to 2 which forms an almost ideal square pyramid, [MoOCl3- (S]] PPh3)] is strongly distorted in favour of a trigonal bipyramid. This compound is inert towards a twenty-fold excess of S]] PPh3 and from extended investigations concerning formation of and equilibria between five- and six-co-ordinate chlorooxomolybdenum(V) complexes in CH2Cl2 it was concluded that the presence of a sulfur donor may assist formation of a five-co-ordinate complex in solution.8 The isolation of complex 2 in addition to the results obtained previously 5 unequivocally shows that the first steps in the mechanism of the reaction of MoCl5 with EtOH at room temperature should be as in equation (3).An intermediate [Mo- Fig. 1 Molecular structure of compound 2 MoCl5 1 EtOH 2HCl [Mo(OEt)Cl4] 2EtCl MoOCl3 1EtOH [MoOCl3(EtOH)] (3) 2 (OEt)2Cl3] is, at least at room temperature, not passed through.At low temperatures, however, the Mo]] O bond formation via elimination of EtCl might be suppressed enabling the formation of [Mo(OEt)2Cl3]. This compound is highly electron deficient (11 valence electrons for Mo) and needs stabilisation by an additional ligand extending its co-ordination number to six. This requirement can be met by dimerisation yielding the stable compound [{Mo(OEt)2Cl3}2] which has been isolated.4 A second possibility to trap [Mo(OEt)2Cl3] proved to be the addition of an ammonium chloride to the solution after annealing to 0 8C producing the isolable anion [Mo(OEt)2Cl4]2. Above 0 8C, however, complete decomposition occurs.13 The reaction of 2 with 0.5 equivalent of EtOH yields, after removing of all volatiles, 1 in quantitative yield providing additional support for the intermediate character of 2 during the synthesis of 1.This result encouraged attempts to isolate 2 directly from the green reaction mixture obtained after the addition of 2.5 equivalents of EtOH to a solution of MoCl5. If such a solution is cooled to 278 8C during 2 d grass-green crystals precipitate which, however, do not correspond to 2. After filtration at 278 8C they melt on annealing to temperatures above 210 8C forming an unstable green oil which upon evacuation of its crystallisation vessel slowly decomposes with evolution of HCl and EtOH (as detected by gas-phase IR spectroscopy) to yield the orange solid 1.Since this green solid is not formed upon addition of only 2 equivalents of EtOH to MoCl5 it should be richer in EtOH as compared to 2. However, because of its high sensitivity with respect to air, low melting point, paramagnetism and decomposition in vacuo this compound is very difficult to analyse. Fortunately its crystals grown at 240 8C and picked at 278 8C were suitable for X-ray diffraction analysis establishing the composition H[MoOCl4]?2EtOH 3 for the molecules in the crystal (see Fig. 2, Table 2), which is also in complete agreement with the analytical data obtained. All atoms apart from the proton representing the cation for the corresponding tetrachlorooxomolybdate anion were found.The presence of this proton is nevertheless unambiguous because of two reasons. First, if there was no cation present the Fig. 2 Molecular structure of complex 3; the proton representing the cation has been omittedJ. Chem. Soc., Dalton Trans., 1997, Pages 1633–1637 1635 Mo would be in the oxidation state 1VI which would be surprising considering the conditions of formation and decomposition. Secondly its UV/VIS spectrum compares well with those of other M1[MoOCl4]2 compounds.14,15 Since all other H atoms could be located the reasons why the additional acidic proton could not be detected are unclear.Significant electron density could be found neither in the surroundings at the EtOH molecules nor at the oxide ligand [at 1.668(4) Å the Mo]O(1) bond represents a very strong Mo]] O double bond]. Since the proton is not expected to be localised in complete isolation within the unit cell, the most likely explanation for its elusiveness would be its proximity to the Cl ligands resulting in a smeared electron density. The structure of the [MoOCl4]2 anion in 3 is similar to those determined previously.16 The strong Mo]] O bond exerts a powerful trans influence and the [MoOCl4]2 anion universally adopts a square-pyramidal geometry.Repulsion between the closely bound O atom and the chloride ligands increases the O]Mo]Cl angles [102.2(2), 101.7(2), 99.1(3), 103.1(3)8] which lie within the range defined as typical for oxo and nitrido complexes of the type [MXCl4]2 (X = N or O; M = Mo, Re, Ru or Os).17 The [MoOCl4]2 anion in 3 shows a slight distortion from C4v symmetry. A more pronounced distortion of this type had been observed in the compounds [N(PPh3)2]1[MoOCl4]2 16 and [N(PPh3)2]1[TcOCl4]2 18 and has been ascribed to the bulk of the N(PPh3)2 1 cations.In the unit cell of 3 besides the anions only H1 and EtOH are present which makes it understandable that the distortion is only weak in 3. Nevertheless the undistorted (though noncrystallographic) point symmetry of the anion in [AsPh4]- [MoOCl4] 19 appears to be unusual.Complex 3 represents another example of a five-co-ordinate molybdenum centre (see discussion above). It should be noted, though, that consistent with what has been said above, tetrachlorooxomolybdate anions tend to extend their co-ordination number to six,8 for instance by water, and are therefore unstable in the presence of moisture if they are not protected by bulky cations.16 One additional argument for the location of the proton missing from the crystal structure of complex 3 near the Cl ligands is the experimental finding that pumping on crystals of 3 yields HCl and EtOH so that 1 is formed after dimerisation of the resulting fragments.As mentioned earlier, an orange solution of 1 changes to bright green after treatment with gaseous HCl, which means that its Mo]Mo bond is cleaved producing the monomers H[MoOCl4] again. Quite a number of salts with the tetrachlorooxomolybdate anion are known to date,16 some of which have been mentioned in the above discussion.The parent acid of this series of salts in the free state has been mentioned only once before in the literature and was reported to be obtainable from the reaction of MoO3 with HCl–HI–water.15 Its characterisation was restricted to elemental analysis, magnetic susceptibility measurements, IR, electronic and X-ray powder spectra. From these data it was concluded that the solid-state structure of H[MoOCl4] should consist of a chloride-bridged dimer which is in clear contrast to the findings Table 2 Bond distances (Å) and angles (8) in complex 3 Mo]O(1) 1.668(4) C(1)]C(2) 1.46(2) Mo]Cl(4) 2.343(2) C(2)]O(2) 1.483(10) Mo]Cl(2) 2.338(2) C(3)]C(4) 1.543(13) Mo]Cl(1) 2.355(2) C(4)]O(3) 1.465(9) Mo]Cl(3) 2.376(2) O(1)]Mo]Cl(4) 102.2(2) O(1)]Mo]Cl(3) 103.1(3) O(1)]Mo]Cl(2) 101.7(2) Cl(4)]Mo]Cl(3) 87.43(8) Cl(4)]Mo]Cl(2) 156.12(6) Cl(2)]Mo]Cl(3) 87.82(6) O(1)]Mo]Cl(1) 99.1(3) Cl(1)]Mo]Cl(3) 157.82(6) Cl(4)]Mo]Cl(1) 87.71(6) C(1)]C(2)]O(2) 111.5(7) Cl(2)]Mo]Cl(1) 87.92(8) of this work.However, the UV/VIS spectrum compares well with that of 3, while the IR spectra are not comparable since that of 3 is dominated by the bands corresponding to the EtOH molecules. Taking into account all the results described above Scheme 1 can be deduced. As can be shown by NMR measurements on a CD2Cl2 solution of compound 2 in a flame-sealed NMR tube, quantitative decomposition occurs at room temperature with precipitation of oxomolybdenum chlorides within 3 d.The organic products remaining in solution thereafter could not be identified. As a solid 2 decomposes more slowly but should nevertheless be stored at 240 8C. By isolation of compounds 2 and 3 most of the characteristics of the reaction of MoCl5 with EtOH could be unravelled so that just by varying the reaction conditions appropriately one of four possible products can be obtained in good to quantitative yields. The five-fold co-ordination at the electrondeficient Mo in 2 invited investigations concerning reactions with p- and s-donors.Starting from comparable compounds such reactions lead to the corresponding six-co-ordinate addition products.8 On treatment of solutions of 2 in CH2Cl2 with gaseous CO, propylene or ethylene in each case the originally green solutions turned orange within 15 min and after removing the volatiles 1 could be isolated. This result can only be understood if it is assumed that these molecules initially coordinate at the free co-ordination site in 2 providing electron density to the Mo.This initiates elimination of HCl producing a 13-electron complex [MoO(OEt)Cl2L], which dimerises with elimination of L and co-ordination of an EtOH molecule from another molecule of 2. Scheme 2 shows this possible reaction pathway explaining the experimental results. Unfortunately there is uncertainty concerning the fate of the MoOCl3 which is expected to form simultaneously according to Scheme 2.However, employing the strong s donor OPPh3 as L which is capable of stabilising such fragments gave strong evidence for the formation of this side product, since a different reaction behaviour is observed in this case: the solution retains its green colour and after removing the volatiles a green oil is obtained. From the latter 1 can be extracted by diethyl ether in exactly the yield Scheme 1 (i) 278 8C, excess of EtOH; (ii) 4 EtOH, room temperature (r.t.) to 278 8C; (iii) 5 EtOH, r.t.to 278 8C; (iv) EtOH; (v) r.t., 5 EtOH; (vi) r.t., in vacuo; (vii) HCl (g)1636 J. Chem. Soc., Dalton Trans., 1997, Pages 1633–1637 expected from Scheme 2, leaving behind a green solid which proved to consist of [MoOCl3(OPPh3)2].20 These reactions demonstrate that it is not possible to attach a ligand at the free co-ordination site of compound 2 since as soon as the molybdenum centre receives additional electron density decomposition reactions occur.Accordingly 2 can only exist in its free state which yet again underlines its intermediate character. There are, however, many syntheses in the literature starting from uncharacterised MoCl5–EtOH mixtures 21 which must have contained, as the present work suggests, 1, 2 and/or 3 which are all interconvertible. Therefore 2 can serve as a soluble, weighable equivalent of the otherwise polymeric O]] MoCl3 in reactions with this fragment. These findings after studying the system MoCl5–EtOH of course suggested investigations concerning reactions with different alcohols. Surprisingly, a derivative of complex 1 could only be obtained in one case: treating MoCl5 with propanol produced [Cl2OMo(m-OPr)2(m-HOPr)MoOCl2] 4 (Scheme 3), while all other alcohols used, like methanol, allyl alcohol, Scheme 2 Scheme 3 phenol, pentafluorophenol and ButOH, produced inhomogeneous brown oils or simply MoOCl3 which precipitated.Experimental All manipulations were carried out with a vacuum line (at a background pressure <1024 mbar) or in a glove-box, or by means of Schlenk-type techniques involving the use of a dry argon atmosphere.Solvents were dried according to standard procedures; microanalyses were performed by the Analytische Laboratorien des Organisch-Chemischen Institutes der Universität Heidelberg. Infrared spectra were recorded with a Bruker IFS 66 FTIR spectrometer, 1H NMR spectra of solutions using a Bruker AC 200 instrument operating at 200 MHz.The deuteriated solvents had been condensed into the NMR tubes previously before the tubes were flame-sealed. The UV/VIS spectra were measured on a Perkin-Elmer Lambda 19 UV/VIS/ NIR spectrophotometer. The X-ray diffraction measurements were made on single crystals on a Siemens P4 (Nicolet Syntex) R3m/V four-circle diffractometer with graphite-monochromated Mo-Ka radiation (l 0.710 73 Å). Fast atom bombardment mass spectra were recorded with a Finnigan MAT 8230 instrument.Synthesis of [MoOCl3(EtOH)] 2 Molybdenum pentachloride (11.3 g, 0.041 mol) was placed in a Schlenk tube and suspended in CH2Cl2 (30 cm3). Ethanol (3.8 g, 0.082 mol) was added carefully within 1 h by means of a syringe, causing a considerable evolution of gas so that a second needle was needed as exhaust in the septum sealing the Schlenk tube. Shortly before the addition was complete a greyish solid formed which was filtered off after the last drop of EtOH had entered the tube.The filtrate was cooled to 278 8C causing 6.2 g (0.023 mol, 56%) of compound 2 to precipitate in the form of dark green crystals, which were freed from the solution via a cannula at 278 8C. They are extremely sensitive to air and show a good solubility in CH2Cl2, while they are only moderately soluble in CHCl3. They decompose on heating to 49 8C. By concentrating the filtrate and further cooling the yield could be improved, although the second fraction was not as pure as the first. When 2 was redissolved in CH2Cl2 and treated with 0.5 equivalent of EtOH after 5 min of stirring and removal of the volatiles, 1 was isolated in quantitative yield.Complex 2 (Found: C, 9.15; H, 2.35; Cl, 39.75. C2H6Cl3- MoO2 requires C, 9.1; H, 2.3; Cl, 40.25%); n& /cm21(KBr) 3413m (br), 2976w, 2933w, 1459w, 1381w, 1258w, 1082m, 1013s, 896m, 805m and 728m; 1H NMR (200 MHz, CD2Cl2, 20 8C, SiMe4): dH 3.7 (s, br) and 6.9 (s, br); electron-impact mass spectrum: m/z 200 (100, M1 2 EtCl), 165 (50, M1 2 EtCl 2 Cl), 149 (20, M1 2 OEt 2 2Cl), 130 (15, MoO2 1) and 114 (12%, MoO1); ESR (CH2Cl2) g = 1.956.Crystal structure of [MoOCl3(EtOH)] 2 Crystals of compound 2 were suspended in an oil in the glovebox, quickly selected under the microscope and frozen to 200 K. Crystal data. C2H6Cl3MoO2, M = 264.36, monoclinic, space group P21/n, a = 5.702(1), b = 8.237(1), c = 16.831(4) Å, b = 99.18(2)8, U = 780.40 Å3, 2.45 < q < 27.998, Z = 4, green plates, crystal size 0.50 × 0.40 × 0.20 mm, T = 200 K, m = 2.57 mm21, Dc = 2.250 g cm23, F(000) = 508.Data collection and processing. 2063 Reflections measured (qmax = 27.998), 1884 unique (Rint= 0.0180), 1709 with I > 2s(I), which were used in all calculations. Structure analysis and refinement. The structure was solved by direct methods and refined by full-matrix least-squares pro-J. Chem. Soc., Dalton Trans., 1997, Pages 1633–1637 1637 cedures based on F2, SHELXL 93,22 with anisotropic thermal parameters for all non-hydrogen atoms.An experimental absorption correction using y scans, Dy = 108, was applied. Atom H(10) was located from the Fourier-difference map and refined isotropically. All other hydrogen atoms were calculated by the use of a riding model. Final R1 = 0.0227 (based on F), and wR2 = 0.0536 (based on F2) for 78 parameters [w21 = s2(F) 1 0.003Fo 2]. The final difference-synthesis maximum and minimum were 0.489 and 20.444 e Å23, respectively.Synthesis of H[MoOCl4]?2EtOH 3 After the addition of 2.5 equivalents of EtOH to MoCl5 as described elsewhere 5 the reaction mixture was cooled to 278 8C, causing complex 3 to precipitate in the form of grassgreen crystals in 10% yield. These were freed from the solution via cannula at 278 8C. A better synthesis for 3 is the reaction of 1 with HCl. The compound 1?0.225CH2Cl2 (1.3 g, 2.51 mmol) was dissolved in CH2Cl2 (30 cm3) in a Schlenk tube and the solution frozen to 77 K. The reaction vessel was evacuated and an excess of HCl gas (7.5 mmol) cocondensed. The Schlenk tube was closed and the frozen reaction mixture warmed slowly to room temperature, turning green in the process.When annealing was complete the tube was cooled to 240 8C causing crystals of 3 (0.4 g, 1.15 mmol, 46%) to precipitate. They melt at approximately 210 8C and are very sensitive to air. n& /cm21(film) 3437vs (br), 2984s, 1597s, 1446m, 1392s, 1265s, 1081s, 1001vs, 868s and 805s.lmax(CH2Cl2) 710, 440 and 300 nm. 1H NMR (CD2Cl2): dH 2.36 (br, CH3) and 4.60 (br, CH2). Crystal structure of H[MoOCl4]?2EtOH 3 Crystals of complex 3 were transferred while cooling in a stream of argon from a Schlenk tube in which they had been generated to a glass apparatus allowing cooling and selection of a suitable crystal at the same time. The crystal chosen was surrounded with an inert oil and frozen on the diffractometer to 123 K.Crystal data. C4H13Cl4MoO3, M = 346.88, orthorhombic, space group Pna21, a = 8.447(2), b = 10.831(3), c = 13.359(2) Å, U = 1222.2(4) Å3, 2.42 < q < 32.328, Z = 4, green blocks, crystal size 0.37 × 0.32 × 0.24 mm, T = 123(2) K, m = 2.57 mm21, Dc = 1.885 g cm23, F(000) = 684. Data collection and processing. 2830 Reflections measured (qmax = 32.328), 2048 unique (Rint = 0.0608), 1944 with I > 2s(I), which were used in all calculations. Structure analysis and refinement. The structure was solved and refined and an absorption correction applied as for compound 2.All H atoms at the EtOH molecules could be located from the Fourier-difference map and were refined isotropically. Subsequently, the methyl and methylene hydrogens were treated as rigid groups and refined isotropically with 1.2 Ueq and 1.5 Ueq of the corresponding C atoms. Final R1 = 0.0430 (based on F), and wR2 = 0.1200 (based on F2) for 113 parameters [w21 = s2(F) 1 0.003Fo 2].The final difference-synthesis maximum and minimum were 0.4043 and 20.2187 e Å23, respectively. Atomic coordinates, thermal parameters, and bond lengths and angles for both structures 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 186/432. Synthesis of [Cl2OMo(Ï-OPr)2(Ï-HOPr)MoOCl2] 4 The synthesis was closely analogous to that one described for complex 14 using PrOH instead of EtOH (Found: C, 19.9; H, 4.1; Cl, 26.1.C9H22Cl4Mo2O5 requires C, 19.9; H, 4.05; Cl, 25.8%. n& /cm21(KBr) 3248m, 2968m, 2973w, 1461m, 1454m, 1395m, 1381m, 1266w, 1226w, 1100w, 1040m, 1010vs, 980vs, 942vs, 886s, 858m and 752m. 1H NMR (200 MHz, CD2Cl2, 20 8C, SiMe4): dH 0.96 [3 H, br, HO(CH2)2CH3], 1.08 [6 H, t, J(HH) 7.0 Hz, O(CH2)2CH3], 1.80 (2 H, br, HOCH2CH2CH3), 2.10 (4 H, m, OCH2CH2CH3), 3.60 (2 H, br, HOCH2CH2CH3) and 5.98 (4 H, br, OCH2CH2CH3).Acknowledgements We would like to thank the Fonds der Chemischen Industrie for providing a Liebig-Stipendium (to C. L.) and Professor Dr. G. Huttner for his constant, generous support. References 1 W. Wardlaw and H. W. Webb, J. Chem. Soc., 1930, 2100. 2 A. V. Butcher and J. Chatt, J. Chem. Soc. A, 1970, 2652. 3 A. P. Bashall, S. W. Bligh, A. J. Edwards, V. C. Gibson, M. McPartlin and O. B. Robinson, Angew. Chem., 1992, 104, 1664; Angew. Chem., Int. Ed. Engl., 1992, 31, 1607. 4 D. C. Bradley, R. K. Multani and W. Wardlaw, J. Chem. Soc., 1958, 4647. 5 C. Limberg, S. Parsons, A. J. Downs and D. J. Watkin, J. Chem. Soc., Dalton Trans., 1994, 1169. 6 N. T. Denisov, N. I. Shuvalova and V. F. Shuvalov, Russ. J. Phys. Chem. (Engl. Transl.), 1971, 45, 1585. 7 F. A. Schröder, Acta Crystallogr., Sect. B, 1975, 31, 2294. 8 P. M. Boorman, C. D. Garner and F. E. Mabbs, J. Chem. Soc., Dalton Trans., 1975, 1299. 9 C. D. Garner, M. R. Hyde, F. E. Mabbs and V. I. Routledge, J. Chem. Soc., Dalton Trans., 1975, 1175. 10 A. J. Blake, A. J. Downs, C. Limberg and S. Parsons, J. Chem. Soc., Dalton Trans., 1995, 3263. 11 M. L. H. Green, J. Organomet. Chem., 1995, 500, 127. 12 P. M. Boorman, C. D. Garner, F. E. Mabbs and T. J. King, J. Chem. Soc., Chem. Commun., 1974, 663. 13 D. P. Rillema and C. H. Brubaker, Inorg. Chem., 1969, 8, 1645. 14 C. D. Garner, I. H. Hillier, J. Kendrick and F. E. Mabbs, Nature (London), 1975, 258, 139. 15 H. K. Saha and M. C. Halder, J. Inorg. Nucl. Chem., 1971, 33, 705. 16 A. J. Blake, S. Parsons, A. J. Downs and C. Limberg, Acta Crystallogr., Sect. C, 1995, 51, 571. 17 K. Dehnicke and J. Strähle, Angew. Chem., Int. Ed. Engl., 1981, 20, 413. 18 F. A. Cotton, A. Davidson, V. W. Day, L. D. Gage and H. S. Trop, Inorg. Chem., 1979, 18, 3024. 19 F. Weller, U. Müller, U. Weiher and K. Dehnicke, Z. Anorg. Allg. Chem., 1980, 460, 191. 20 S. M Horner and S. Y. Tyree, Inorg. Chem., 1962, 1, 122. 21 Gmelin Handbook of Inorganic Chemistry, Syst. No. 53, Springer, Berlin, 8th edn., 1990, suppl. vol. B5, p. 377 ff.; suppl. vol. B6, p. 34 ff. 22 G. M. Sheldrick, SHELXL 93, A Program for Crystal Structure Refinement, University of Göttingen, 1993. Received 3rd January 1997; Paper 7/00083I

ISSN:1477-9226    

DOI:10.1039/a700083i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 1645 Complexes of silver(I), thallium(I), lead(II) and barium(II) with bis[3- (2-pyridyl)pyrazol-1-yl]phosphinate: one-dimensional helical chains and discrete mononuclear complexes Elefteria Psillakis, John C. JeVery, Jon A. McCleverty * and Michael D. Ward * School of Chemistry, University of Bristol, Cantock’s Close, Bristol BS8 1TS, UK Reaction of 3-(2-pyridyl)pyrazole with POBr3 in toluene–NEt3 afforded not the expected tris(pyrazolyl)phosphine oxide but the partially hydrolysed compound bis[3-(2-pyridyl)pyrazol-1-yl]phosphinate (as its triethylammonium salt).This compound has two potentially chelating N,N9-bidentate arms linked by an apical PO2 2 group. Reaction with AgNO3, Tl(O2CMe), Pb(NO3)2 or Ba(NO3)2 in dry MeCN followed by recrystallisation afforded crystals of the complexes [AgL]?2H2O, [TlL]?MeOH, [PbL2]?H2O and [(BaL2)3]?6MeCN?2H2O respectively, all of which have been crystallographically characterised.The compound [AgL]?2H2O contains infinite helical chains (AgL)• in which each ligand donates one N,N9-bidentate arm to each of two metals and each metal ion is four-co-ordinated by two arms from different ligands. The strands are held together in the crystal by a complex network of hydrogen bonds involving lattice water molecules and also by aromatic p-stacking interactions. The compound [TlL]?MeOH is likewise a one-dimensional helical polymer of TlL units, with each ligand bridging two metals and each Tl ion in a ‘2 1 3’ co-ordination geometry with two short bonds to ligands (<2.71 Å) and three longer, weak bonds (>2.87 Å): there is an obvious gap in the co-ordination sphere due to a stereochemically active lone pair.A combination of interstrand aromatic p-stacking interactions and hydrogen-bonding interactions involving the lattice MeOH molecule is present. The compound [PbL2]?H2O is in contrast a discrete mononuclear complex, four-co-ordinated just by one bidentate arm from each of the two ligands with the other bidentate arms pendant: again there is a stereochemically active lone pair.The metal geometry is approximately trigonal bipyramidal with the lone pair in an equatorial position. The lattice water molecule is hydrogen bonded to three different complex units. The compound [(BaL2)3]?6MeCN?2H2O contains mononuclear BaL2 and dinuclear Ba2L4 units: the former is ten-coordinate, with each ligand acting as an N4O donor and a phosphinate oxygen atom participating in co-ordination, whereas in the latter each BaII is nine-co-ordinated and two of the ligands are bridging, donating their four N atoms to one metal ion and a phosphinate oxygen atom to the other.The relationship between the steric and electronic preferences of the metal ions and the co-ordinating properties of the ligand, and how these interact to control self-assembly processes and determine the structures of complexes, is of fundamental interest in supramolecular and co-ordination chemistry.1 In this context many ligands which contain two bidentate compartments linked by a flexible bridge are known and their inherent flexibility means that they can adapt to the specific preferences of different metal ions in different ways.2–6 Often they form dinuclear helical complexes,2 but can co-ordinate in other ways if the stereoelectronic preferences of different metal ions demands it.3 A good example of this flexible co-ordination behaviour is provided by 2,29:69,20:60,2--quaterpyridine and its derivatives, which can form dinuclear double helicates with CuI and AgI4 but also co-ordinate in a planar tetradentate manner to metals which prefer square-planar or octahedral geometry.5 Other tetradentate ligands show similar behaviour.6 Use of metal ions which have no stereoelectronic geometric preferences arising from partially filled d shells allows examination of the possible co-ordination modes of a ligand in the absence of metal-directed requirements.We describe here the preparation of a simple bridging anion [L]2 containing two bidentate binding sites linked by a phosphinate bridge, which forms infinite one-dimensional single-stranded helical structures with AgI and TlI but discrete mononuclear complexes with PbII and BaII. The anion and all of the complexes have been crystallographically characterised. Experimental Syntheses (a) Trimethylammonium bis[3-(2-pyridyl)pyrazol-1-yl]phosphinate [NEt3H][L].To a solution of 3-(2-pyridyl)pyrazole 7 (5.45 g, 37.6 mmol) and dry triethylamine (5.0 g, 50 mmol) in dry toluene (40 cm3) maintained between 0 and 5 8C was added dropwise a solution of POBr3 (3.6 g, 12.5 mmol) in dry toluene (10 cm3) with constant stirring. The mixture was stirred at room temperature for 1 h and then heated to reflux for 10 h. After cooling, the mixture was filtered to remove NEt3HBr and the filtrate concentrated in vacuo, upon which a precipitate appeared.This was filtered off and dried; cooling of the remaining mother-liquor overnight afforded an additional crop of the product, which was finally recrystallised from MeCN– diethyl ether. Yield: 70% (Found: C, 57.2; H, 6.2; N, 21.2. Calc. for C22H28N7O2P?0.5Et2O: C, 57.3; H, 6.1; N, 21.2%). 1H NMR [(CD3)2CO, 300 MHz]: d 8.55 (2 H, ddd, J = 4.5, 1.6, 1.0, pyridyl H6), 8.16 (2 H, dd, J = 2.3, 0.5, pyrazolyl H5), 7.95 (2 H, d, J = 7.2, pyridyl H3), 7.76 (2 H, td, J = 6.9, 1.6, pyridyl H4), 7.25 (2 H, ddd, J = 6.8, 4.4, 1.1, pyridyl H5) and 6.89 (2 H, t, J = 2.2 Hz, pyrazolyl H4).n(P]] O) (KBr disc) 1167 cm21. (b) AgL. A mixture of [NEt3H][L] (0.45 g, 1.0 mmol) and AgNO3 (0.17 g, 1.0 mmol) in dry MeCN (8 cm3) was agitated in an ultrasound bath for 20 min. A white precipitate appeared which was filtered off, washed several times with MeCN and dried to give the product in 70% yield.X-Ray-quality crystals were grown by slow evaporation of a CHCl3 solution of the material (Found: C, 40.3; H, 2.6; N, 17.0. Calc. for C16H12- AgN6O2P?0.2CHCl3: C, 40.3; H, 2.5; N, 17.4%). n(P]] O) (KBr disc) 1168 cm21. (c) TlL. This was prepared and isolated in the same way as the silver complex above, from [NEt3H][L] (0.21 g, 0.47 mmol) and thallium(I) acetate (0.12 g, 0.47 mmol) in dry MeCN (101646 J. Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 cm3).The yield of the resulting white precipitate of TlL was 82%. X-Ray-quality crystals were grown by slow evaporation of a methanol or dichloromethane solution of the material (Found: C, 32.7; H, 2.1; N, 14.1. Calc. for C16H12N6O2PTl? 0.5CH2Cl2: C, 33.1; H, 2.1; N, 14.1%). FAB mass spectrum: m/z = 557 (40, TlL), 761 (100, Tl2L) and 1316 (10%, Tl2L3). n(P]] O) (KBr disc) 1168 cm21. (d ) PbL2. This was prepared and isolated in the same way as the silver complex above, from [NEt3H][L] (0.23 g, 0.50 mmol) and Pb(NO3)2 (0.17 g, 0.50 mmol) in dry MeCN (10 cm3).The yield of the resulting white precipitate of PbL2 was 98%. X-Ray-quality crystals were grown by slow evaporation of a concentrated CH2Cl2 solution of the material (Found: C, 41.3; H, 2.9; N, 18.3. Calc. for C32H24N12O4P2Pb?H2O: C, 41.3; H, 2.8; N, 18.1%). FAB mass spectrum: m/z = 559 (100, PbL), 910 (15, PbL2) and 933 (8%, PbL2 1 Na). n(P]] O) (KBr disc) 1168 and 1184 cm21. (e) BaL2. This was prepared and isolated in the same way as the silver complex above, from [NEt3H][L] (0.11 g, 0.25 mmol) and Ba(NO3)2 (0.065 g, 0.25 mmol) in dry MeCN (10 cm3).The yield of the resulting white precipitate of BaL2 was 73%. X-Ray-quality crystals were grown by slow evaporation of a concentrated MeCN solution of the material (Found: C, 43.7; H, 2.7; N, 19.4. Calc. for C32H24BaN12O4P2?H2O: C, 44.8; H, 3.0; N, 19.6%). FAB mass spectrum m/z = 489 (100, BaL) and 841 (20%, BaL2). n(P]] O) (KBr disc) 1171 cm21.Crystallography Suitable crystals were quickly transferred from the motherliquor to a stream of cold N2 at 2100 8C on a Siemens SMART diffractometer fitted with a CCD-type area detector. A detailed experimental description of the methods used for data collection and integration using the SMART system has been published. 8 Table 1 contains a summary of the crystal parmeters, data collection and refinement. In all cases the structures were solved by conventional heavy-atom or direct methods and refined by the full-matrix least-squares method on all F2 data using the SHELXTL 5.03 package 9 on Silicon Graphics Indigo-R4000 or Indy computers.In all cases, non-hydrogen atoms were refined with anisotropic thermal parameters; hydrogen atoms were included in calculated positions and refined with isotropic thermal parameters. The compound AgL crystallises with two molecules of water per complex formula unit. Each asymmetric unit contains 1.5 formula units, i.e.[AgL]1.5?3H2O. There is one complete Ag atom per asymmetric unit, with a second located on a C2 axis. One of the pyridyl rings [atoms N(61), C(62)–C(66)], although co-ordinated, is disordered over two slightly different orientations. Atom C(62), which is the position of attachment of the pyrazolyl ring, is common to both components of the disorder but the other five atoms were successfully separated into two components (which were restrained to be similar) in the ratio 53 : 47.Only the major component is shown in the Figures. The structural determination of [TlL]?MeOH was well behaved and presented no problems. In [PbL2]?H2O, three of the ligand carbon atoms [C(43), C(44) and C(64)] had unusually high thermal parameters (Ueq > 0.1 Å2). However attempts to split these atoms into disordered components (as in [AgL]?2H2O, above) were unsuccessful. Crystals of [(BaL2)3]?6MeCN?2H2O diffracted weakly so data were collected to 2q = 46.58, rather than 558 which was the limit for the others; however the structure solution and refinement presented no particular problems.The structure is actually [(BaL2)(Ba2L4)]?6MeCN?2H2O, containing a mononuclear BaL2 fragment and a dinuclear Ba2L4 fragment, both of which lie astride inversion centres. 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 186/442. Results and Discussion Ligand synthesis and crystal structure Reaction of 3,5-dimethylpyrazole (Hdmpz) with POBr3 has been previously reported to yield the tris(pyrazol-1-yl)- phosphine oxide (dmpz)3P]] O, which acts as a facial tridentate ligand similar in its co-ordination behaviour to a tris(pyrazolyl) borate.10 It was found to be prone to partial hydrolysis to give the bis(pyrazol-1-yl)phosphinate [(dmpz)2PO2]2 which could co-ordinate as an N,N,O-donor terdentate ligand.10,11 We performed the reaction of 3-(2-pyridyl)pyrazole (HR) with POBr3 and NEt3 to try and prepare the hexadentate podand R3P]] O in which three bidentate pyridylpyrazolyl arms are linked at the apical P]] O group, in a comparable manner to the hexadentate podand [R3BH]2 which we have studied extensively recently.8,12 Instead partial hydrolysis occurred during the synthesis or work-up to give the bis(pyrazol-1-yl)phosphinate [NEt3H][R2PO2] (the anion of which is hereafter referred to as L2; Scheme 1).The P]] O stretching band in the IR spectrum of the product was at a rather low frequency for a phosphine oxide and the elemental analysis indicated formation of [NEt3H]- [R2PO2] rather than R3P]] O. This happened despite the use of ‘dry’ reagents, probably during the work-up and recrystallisation when the reaction mixture was handled in air.In subsequent syntheses no special precautions were taken to exclude moisture during work-up and purification, so that [NEt3H]- [R2PO2] could be prepared deliberately. The formulation of the material was confirmed by X-ray analysis (Fig. 1, Table 2). Each bidentate arm has a transoid conformation, with the pyridyl ring being twisted by 88 with respect to the plane of the adjacent pyrazolyl ring in each case. The two molecules in the unit cell are associated by a weak C]H? ? ? N hydrogen-bonding interaction across the inversion centre, with the C? ? ? N separation being 3.42 Å.There is a much stronger N]H? ? ? O hydrogen-bonding interaction between the [NEt3H]1 cation and one of the phosphinate oxygen atoms, with the N? ? ? O separation being 2.70 Å. The geometry about each phosphorus atom is rather distorted from tetra- Scheme 1 (i) POBr3, toluene, NEt3, reflux; (ii ) moistureJ.Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 1647 Table 1 Summary of crystal parameters, data collection and refinement for the five new compounds [NEt3H][L] [AgL]1.5?3H2O [TlL]?MeOH [PbL2]?H2O [BaL2]?[Ba2L4]?6MeCN?2H2O Formula C22H28N7O2P C24H24Ag1.5N9O6P1.5 C17H16N6O3PTl C32H26N12O5P2Pb C108H94Ba3N42O14P6 M 453.48 742.78 587.70 927.78 2802.09 System, space group Triclinic, P1� Monoclinic, C2/c Triclinic, P1� Triclinic, P1� Triclinic, P1� a/Å 8.9275(14) 13.930(3) 8.3653(12) 7.8328(12) 10.663(3) b/Å 10.997(3) 24.258(4) 8.598(2) 11.263(2) 14.729(4) c/Å 13.916(3) 17.670(2) 13.869(2) 20.800(6) 20.674(9) a/8 94.751(11) — 99.540(9) 83.17(2) 100.27(2) b/8 105.663(13) 97.670(8) 100.627(9) 81.50(3) 101.54(4) g/8 112.23(2) — 96.684(14) 70.398(11) 107.18(3) U/Å3 1191.2(4) 5917(2) 955.7(3) 1704.9(6) 2940(2) Z 2 8 2 2 1 Dc/g cm23 1.264 1.668 2.042 1.807 1.583 m/mm21 0.148 1.138 8.566 5.103 1.156 F(000) 480 2976 560 908 1406 Crystal size/mm 0.70 × 0.10 × 0.05 0.30 × 0.25 × 0.20 0.60 × 0.25 × 0.15 0.25 × 0.10 × 0.05 0.25 × 0.15 × 0.05 2q Range for data collection/8 3–55 3–55 3–55 4–55 3–46.5 Reflections collected (total, independent, Rint) 7570, 5196, 0.025 18 751, 6735, 0.041 6110, 4193, 0.030 11 096, 7578, 0.043 10 518, 7890, 0.067 Data, restraints, parameters 5194, 0, 296 6735, 209, 444 4193, 0, 255 7575, 0, 477 7881, 0, 779 Final R1, wR2 a,b 0.043, 0.110 0.041, 0.095 0.021, 0.055 0.051, 0.105 0.062, 0.111 Weighting factors (a, b) b 0.0311, 0.84 0.0428, 0.83 0.0318, 1.41 0, 14.65 0.0166, 0 Largest peak, hole/e Å23 10.241, 20.364 10.897, 21.230 10.718, 21.046 10.855, 21.383 10.641, 20.704 a Structure was refined on Fo 2 using all data; the value of R1 is given for comparison with older refinements based on Fo with a typical threshold of F > 4s(F). b wR2 = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� where w21 = [s2(Fo 2) 1 (aP)2 1 bP] and P = [max(Fo 2, 0) 1 2Fc 2]/3.hedral, with the O]P]O angle being 1258 and the other angles being correspondingly slightly compressed.Otherwise the structure has no unusual features. One-dimensional helical polymers with AgI and TlI Reaction of [NEt3H][L] with AgNO3 in dry MeCN afforded a white precipitate the elemental analyses of which were consistent with a 1 : 1 metal : ligand stoichiometry (and retention of some of the solvent of crystallisation). Ligands with two or more bidentate N-donor compartments commonly assemble around CuI or AgI to give oligonuclear double helicates in which the metal ions are in a pseudo-tetrahedral geometry,1,2,13 Fig. 1 Crystal structure of the anion in [NEt3H][L], showing the weak hydrogen bonding leading to association of two anions across an inversion centre Table 2 Selected bond lengths (Å) and angles (8) for the anion of [NEt3H][L] P(1)]O(2) P(1)]O(1) P(1)]N(11) P(1)]N(31) 1.4647(13) 1.4795(13) 1.724(2) 1.727(2) N(11)]C(15) N(11)]N(12) N(12)]C(13) C(21)]N(22) N(22)]C(23) 1.361(2) 1.367(2) 1.330(2) 1.334(2) 1.341(2) O(2)]P(1)]O(1) O(2)]P(1)]N(11) O(1)]P(1)]N(11) 125.13(8) 110.07(7) 104.39(7) O(2)]P(1)]N(31) O(1)]P(1)]N(31) N(11)]P(1)]N(31) 106.06(8) 107.40(7) 101.35(7) and we consequently thought that a simple double helix Ag2L2 would be the most likely structure for this complex.The crystal structure of [AgL]?2H2O (Fig. 2, Table 3) shows that the complex is indeed helical, but is also an infinite onedimensional polymer. Each Ag1 ion is as expected in a fourco- ordinate environment, arising from two bidentate N,Nchelating arms from two separate ligands, with the Ag]N distances lying in the range 2.211–2.520 Å [apart from Ag(2)]N(61B) in the minor disordered component which is 2.63 Å].Each ligand therefore bridges two wever instead of formation of a discrete 2 : 2 helical complex which would require the two ligands to be ‘in register’ with each other, each ligand is ‘slipped’ with respect to the adjacent ligands to give an infinite chain. The asymmetric unit contains one unique silver atom [Ag(1)] and another half atom on a C2 axis [Ag(2)].The sequence of silver atoms along the chain is therefore . . . 1]2]1]1]2]1 . . . with the structure repeating after every three silver atoms; there are C2 axes through Ag(2) and midway between the two equivalent adjacent Ag(1) atoms. The Ag(1) ? ? ? Ag(19) and Ag(1) ? ? ? Ag(2) distances are 6.857 and 5.450 Å respectively. There are interligand aromatic stacking interactions (3.2–3.6 Å) both within each helical strand and between strands. This is a common feature of helical complexes 1 but one which is not essential for helicate formation:14 the matching of metal-ion co-ordination geometry and ligand donor properties is probably more important.A consequence of the ligand arrangement is that all of the anionic phosphinate groups lie in a line along one face of the strand, such that each infinite helical strand has polar and non- Fig. 2 Crystal structure of the one-dimensional helical chain of [AgL]?2H2O1648 J. Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 polar faces. This results in two types of interstrand association in the crystal, which can be called ‘face-to-face’ and ‘back-toback’, illustrated in Figs. 3 and 4. The two polar faces of adjacent strands are associated via a complicated network of hydrogen bonding involving the phosphinate oxygen atoms and water molecules (Fig. 3).Some of the water hydrogen atoms were disordered so this depiction of the hydrogen-bonding network is necessarily somewhat arbitrary, but it illustrates clearly the interstrand cross-linking assisted by the water molecules. In the ‘back-to-back’ association (Fig. 4) the non-polar faces of two adjacent strands are together, resulting in an interleaved ‘herring-bone’ type of pattern in which T-stacking edge-to-face interactions between the strands are apparent. The structure is therefore stabilised by both inter- and intra-strand p-stacking interactions as well as the interstrand hydrogen bonding. Interestingly the complex was recrystallised from CHCl3, although the solvent was not predried and the solution was left to stand in air: the presence of trace quantities of moisture is obviously of fundamental importance for the formation of these crystals.Reaction of [NEt3H][L] with thallium(I) acetate in dry MeCN leads to a white precipitate the elemental analytical and mass spectroscopic data of which again indicated a 1 : 1 formulation, i.e.TlL. The crystal structure of [TlL]?MeOH is shown in Fig. 5. Again the complex is an infinite one-dimensional chain, simi- Fig. 3 Association of chains in [AgL]?2H2O via a hydrogen-bonding network involving the phosphinate groups and lattice water molecules Table 3 Selected bond lengths (Å) and angles (8) for [AgL]?2H2O Ag(1)]N(31) Ag(1)]N(11) 2.211(3) 2.252(3) Ag(1)]N(21) Ag(1)]N(41) 2.406(3) 2.515(3) Ag(2)]N(61A)a Ag(2)]N(61A9) Ag(2)]N(61B) 2.238(13) b 2.238(13) b 2.631(12)c Ag(2)]N(61B9) Ag(2)]N(52) Ag(2)]N(529) 2.631(12)c 2.288(3) 2.288(3) N(31)]Ag(1)]N(11) N(31)]Ag(1)]N(21) N(11)]Ag(1)]N(21) 156.18(10) 131.63(10) 71.67(10) N(31)]Ag(1)]N(41) N(11)]Ag(1)]N(41) N(21)]Ag(1)]N(41) 70.21(10) 114.08(10) 102.15(10) N(61A9)]Ag(2)]N(61A) N(61A9)]Ag(2)]N(52) N(61A)]Ag(2)]N(52) N(61A9)]Ag(2)]N(529) N(61A)]Ag(2)]N(529) N(52)]Ag(2)]N(529) 83.0(10)b 130.9(4)b 75.8(4)b 75.8(4)b 130.9(4)b 148.35(14) N(52)]Ag(2)]N(61B9) N(529)]Ag(2)]N(61B9) N(52)]Ag(2)]N(61B) N(529)]Ag(2)]N(61B) N(61B9)]Ag(2)]N(61B) 135.3(3)c 66.4(3)c 66.4(3)c 135.3(3)c 110.5(5)c a For the atoms co-ordinated to Ag(2) the prime denotes a symmetryrelated atom; thus N(61A) and N(61A9) are related by a C2 operation. The suffixes A and B denote the two different disordered components of the pyridyl ring N(61), C(62)–C(66) which was disordered over two orientations.b Major component of disorder (57%).c Minor component of disorder (43%). lar to that of AgL. The co-ordination geometry is difficult to describe, as there is a wide spread of bond lengths from the TlI to various donor atoms, covering the range 2.68–3.08 Å (Table 4). In thallium(I) complexes with tris(pyrazolyl)borate ligands the metal ion is in a three-co-ordinate pyramidal geometry with Tl]N distances of 2.5–2.7 Å and there is a stereochemically active lone pair occupying the ‘vacant’ site of the tetrahedral co-ordination sphere.15–17 If other potential donor atoms are also present 15,16 these tend to interact more weakly, with Tl]L separations of above 3 Å.The primary co-ordination geometry is therefore trigonal pyramidal, with additional long-range interactions when required. In TlL there is no such clear demarcation between ‘strong’ and ‘weak’ co-ordinate bonds. In Fig. 5 the two shortest Tl]N interactions to N(41) and N(12) (2.68 and 2.71 Å respectively) are indicated by solid lines, as these correspond to the distances of ‘strong’ bonds observed in other complexes.15–17 The three longer interactions [to N(21), N(32) and O(1); 2.872, 2.956 and 3.087 Å respectively] are indicated as dashed lines; the gap in the co-ordination sphere, occupied by the stereochemically active lone pair, is clear.Fig. 6 shows the crystal packing of the helical chains. It is clear that both face-to-face (separation ca. 3.7 Å) and edge-toface stacking interactions between aromatic rings occur.There is also weak hydrogen bonding between the phosphinate oxygen atoms of one chain [O(1)] and the C]H hydrogen atoms H(35) of another chain and H(44) of a third chain, with O? ? ? H distances of 2.45 and 2.37 Å respectively. In addition there are methanol solvent molecules in the lattice (one per Tl atom) which are involved in three hydrogen-bonding interactions as both donor and acceptor (Fig. 7), thereby acting as a bridge between two chains in the same way as the water molecules in the structure of the silver(I) complex described earlier.The methanol OH interacts with the phosphinate oxygen atom O(2) of one chain (non-bonded O? ? ? O separation 2.71 Å) and the methanol oxygen atom simultaneously acts as a hydrogenbond acceptor from two CH hydrogen atoms of a different chain [C(23) and C(25); non-bonded O? ? ? C separations 3.42 and 3.36 Å respectively]. This structure is therefore similar to that of [AgL]?2H2O in that one-dimensional helical chains are formed which are stabilised in the crystal by both inter- and Fig. 4 Interaction between the two hydrophobic faces of the helical chains in [AgL]?2H2O Fig. 5 Crystal structure of the one-dimensional helical chain of [TlL]?MeOH. The metal ions are all crystallographically equivalentJ. Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 1649 intra-strand p stacking and by inter- and intra-strand hydrogen bonding via solvent molecules.Helicates have become widespread in co-ordination chemistry in the last decade as interest has grown in self-assembly methods to prepare large, high-nuclearity structures with sophisticated molecular architectures that are unattainable by more conventional synthetic methods.1,2 The majority of such complexes are discrete double or triple helicates containing a small number of metal centres, usually two or three. Considerably rarer are infinite one-dimensional helical structures,18 which arise (as here) when the bridging ligands are ‘slipped’ relative to one another and which are of particular interest not just for the self-assembly processes which produce them, but also because of their striking anisotropy which may find applications in the areas of one-dimensional conductors (‘molecular wires’) or new magnetic materials. Discrete mononuclear complex units may also give rise to one-dimensional helical chains, not through bridging ligands, but through association in such a way that the component parts are twisted slightly with respect to one another in the same sense along the ‘axis of assembly’, such that helicity arises.19 These types of co-ordination polymer may be contrasted with the polymeric structures that arise from dinucleating bridging ligands with a ‘back-to-back’ arrangement of binding sites.20 Discrete mononuclear complexes with PbII and BaII The reaction of [NEt3H][L] with Pb(NO3)2 afforded in nearquantitative yield a material with elemental analysis and FAB mass spectrum indicating the formulation PbL2.Two views of the crystal structure of [PbL2]?H2O are in Figs. 8 and 9 and Fig. 6 Crystal packing of the helical chains in [TlL]?MeOH Table 4 Selected bond lengths (Å) and angles (8) for [TlL]?MeOH Tl(1)]N(41A) Tl(1)]N(12) 2.682(3) 2.709(3) Tl(1)]N(21) Tl(1)]N(32A) Tl(1)]O(1) 2.872 2.956 3.087 N(41A)]Tl(1)]N(12) N(41A)]Tl(1)]N(21) N(41A)]Tl(1)]N(32A) N(41A)]Tl(1)]O(1) N(12)]Tl(1)]N(21) 82.06(8) 77.7 59.8 83.9 58.7 N(12)]Tl(1)]N(32A) N(12)]Tl(1)]O(1) N(21)]Tl(1)]N(32A) N(21)]Tl(1)]O(1) N(32A)]Tl(1)]O(1) 139.1 59.2 96.3 116.9 124.4 Parameters which have no calculated estimated standard deviations involve atoms that were considered by the software to be beyond normal bonding distance; they were calculated from the final atomic coordinates after refinement.show that, in contrast to the complexes of AgI and TlI, PbL2 is a simple mononuclear complex albeit one with some unusual features.As with the thallium(I) complex, the description of the co-ordination geometry is not straightforward because of the presence of a wide range of metal–donor atom separations (2.54–3.11 Å). However these are fairly clearly split into two sets of four, with one set of four short bonds (2.54–2.69 Å), (Table 5) and four long bonds (2.85–3.11 Å). Comparison with the crystal structures of other lead(II) complexes shows that this is common behaviour,16,21 and that the lead(II) ion is best considered here as basically four-co-ordinate with four additional long, weak interactions. Each ligand has one bidentate arm coordinated to the metal centre with one arm ‘pendant’ but still weakly interacting with the metal.In Figs. 8 and 9 therefore only the four shorter interactions are shown as bonds and it is clear from Fig. 9 in particular that the lone pair of the PbII is stereochemically active. The four co-ordinated N atoms occupy very approximately the two axial sites and two of the three equatorial sites of a trigonal bipyramid.This geometric description is limited by the nonideal bite angles of the bidentate arms and the other steric constraints inherent in the structure [for example, the ‘axial’ pair of Fig. 7 Hydrogen-bonding interactions involving the solvent MeOH and adjacent stacked chains in [TlL]?MeOH Fig. 8 Crystal structure of [PbL2]?H2O Table 5 Selected bond lengths (Å) and angles (8) for [PbL2]?H2O Pb]N(81) Pb]N(41) 2.539(6) 2.613(6) Pb]N(32) Pb]N(72) 2.638(6) 2.692(6) N(81)]Pb]N(41) N(81)]Pb]N(32) N(41)]Pb]N(32) 77.9(2) 83.0(2) 63.8(2) N(81)]Pb]N(72) N(41)]Pb]N(72) N(32)]Pb]N(72) 64.3(2) 80.1(2) 135.8(2)1650 J.Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 atoms N(32) and N(72) subtend an angle of 135.88 at the Pb] but seems to be preferable to the alternative extreme of squarepyramidal geometry. The geometry about the PbII is similar to that observed in [Pb(HBR3)(NO3)] [HR = 3-(2-pyridyl)pyrazole]. 16 The disposition of the two pendant arms is interesting. They are approximately planar, with the lone pairs of the potentially co-ordinating nitrogen atoms cisoid and facing inwards towards the metal, rather than transoid as would be expected for electronic reasons if the pendant arm were not interacting with the metal.22 However these lone pairs are not pointed directly towards the metal ion, but point to the space ‘above’ it (Fig. 9) which is occupied by the metal lone pair. The interaction of the pendant groups with the metal is therefore strong enough to ensure that these donor atoms point approximately inwards but not strong enough to make them point exactly at the metal centre and this vindicates the decision to treat these four interactions as of secondary importance. The lattice water molecule is involved in both donor and acceptor hydrogen-bonding interactions involving different complex units.It acts as a hydrogen-bond donor (Ow]H? ? ?Op, where w denotes water and p phosphinate) to two phosphinate oxygen atoms of different complex units [O(11) from one unit and O(12) from the second], with O? ? ? O separations of 2.79 and 2.80 Å respectively. The water oxygen atom also acts as a hydrogen-bond acceptor, forming a weak C]H? ? ? O interaction (C ? ? ? O 3.14 Å) with H(86) with a third complex unit. The lattice water molecule therefore plays an important role in determining the crystal packing.The reaction of [NEt3H][L] with Ba(NO3)2 afforded in good yield a material with elemental analysis and FAB mass spectrum indicating the formulation BaL2. Crystallisation from MeCN afforded crystals of [(BaL2)3]?6MeCN?2H2O the structure of which (Figs. 10 and 11) is surprisingly complicated. The unit cell contains independent mononuclear (BaL2, Fig. 10) and Fig. 9 Alternative view of the crystal structure of [PbL2]?H2O, emphasising the presence of pendant ligand arms and the stereochemically active lone pair Fig. 10 Crystal structure of the BaL2 fragment of [(BaL2)3]? 6MeCN?2H2O dinuclear (Ba2L4, Fig. 11) units, both of which lie astride inversion centres; i.e. the asymmetric unit contains half of the monomer and half of the dimer, giving the overall formulation [(BaL2)(Ba2L4)]?6MeCN?2H2O for the crystalline material. We see here that the phosphinate oxygen atoms can co-ordinate under the appropriate conditions.10,11 Thus, the monomer [BaL2] is ten-co-ordinate with an N8O2 donor set and each ligand pentadentate.In the dimer [Ba2L4] each BaII is nineco- ordinate with an N8O donor set from one tetradentate (N4) ligand and one pentadentate (N4O) ligand the four N atoms of which are co-ordinated to one metal ion whilst the O is coordinated to the second one. The two pentadentate ligands are therefore bridging, allowing formation of the [Ba2L4] dimer. The bond distances (Table 6) are in the normal range for barium complexes.23 Interestingly, the lengths of the Ba]O bonds in the mononuclear complex unit BaL2 (both 3.14 Å) are significantly longer than that in the dinuclear complex unit Ba2L4 (2.73 Å).This is a reflection of the electroneutrality principle: in the BaL2 unit there are two long Ba]anionic O interactions, compared to one short interaction and one non-co-ordinated phosphinate group [Ba(1) ? ? ? O(4) 3.39 Å] for each metal centre of Ba2L4. Also noteworthy is the presence of aromatic pstacking interactions between different ligands in the dinuclear fragment.The water molecule in each asymmetric unit forms an O]H? ? ? O hydrogen bond to the phosphinate oxygen atom O(5) of the mononuclear BaL2 unit, with a separation between the two oxygen atoms of 2.71 Å. Barium(II) commonly forms nine- or ten-co-ordinate complexes with multidentate nitrogen- or oxygen-donor ligands, especially if they carry a negative charge.23 The comparison between the barium(II) and lead(II) structures is interesting, as the charges are the same and the ionic radii (1.35 and 1.20 Å respectively) are comparable: the lower co-ordination numbers and softer donor sets commonly seen for PbII presumably reflect the presence of a lone pair of valence electrons in the coordination sphere.The co-ordination geometry about Ba(2), in the mononuclear unit BaL2, may be approximately described as a bicapped square prism, with the oxygen atoms as the caps and the square planes N(112), N(92), N(12B), N(10A) and N(11C), N(92A), N(121), N(101).The irregular nine-co-ordination in the Ba2L2 unit does not obviously correspond to any of the simple limiting cases of nine-co-ordinate geometries. Conclusion The anion [L]2 affords a surprising diversity of structures, exhibiting a variety of different co-ordination modes, in its complexes with non-transition-metal ions: N2, N4 and N4O modes have all arisen. We have seen how [L]2 can give both onedimensional helicates when acting as a bridge between two metal ions and discrete mononuclear complexes when all donor atoms bind to the same metal ion.In this respect it is similar to Fig. 11 Crystal structure of the Ba2L4 fragment of [(BaL2)3]? 6MeCN?2H2OJ. Chem. Soc., Dalton Trans., 1997, Pages 1645–1651 1651 other versatile ligands such as 2,29 : 69,20 : 60,2--quaterpyridine. In three of the four structures complex hydrogen-bonding networks involving solvent molecules help to stabilise the crystal lattice.Depending on the electronic demands of the metal centre, the anionic phosphinate oxygen atom may be pendant or may co-ordinate, giving [L]2 the option of behaving as a solely N-donor or mixed N,O-donor ligand. We are currently attempting to extend its co-ordination chemistry to transition metals and lanthanides. Acknowledgements We thank the EPSRC for a grant to purchase the diffractometer. References 1 E. C.Constable, Prog. Inorg. Chem., 1994, 42, 67; D. Philp and J. F. Stoddart, Angew. Chem., Int. Ed. Engl., 1996, 35, 1155; D. S. Lawrence, T. Jiang and M. Levett, Chem. Rev., 1995, 95, 2229; D. B. Amabilino and J. F. Stoddart, Chem. Rev., 1995, 95, 2725; J.-M. Lehn, Supramolecular Chemistry, VCH, Weinheim, 1995. 2 R. W. Saalfrank, R. Harbig, J. Nachtrab, W. Bauer, K.-P. Zeller, D. Stalke and M. Teichert, Chem. Eur. J., 1996, 2, 1363; L. J. Charbonniere, G. Bernardinelli, C. Piguet, A.M. Sargeson and A. F. Williams, J. Chem. Soc., Chem. Commun., 1994, 1419; C. Piguet, G. Bernardinelli, B. Bocquet, O. Schaad and A. F. Williams, Inorg. Chem., 1994, 33, 4112; A. Bilyk, M. M. Harding, P. Turner and P. W. Hambley, J. Chem. Soc., Dalton Trans., 1994, 2783; A. Juris and R. Ziessel, Inorg. Chim. Acta, 1994, 225, 251; C. O. Dietrich-Buchecker, J.-P. Sauvage, A. De Cian and J. Fischer, Table 6 Selected bond lengths (Å) and angles (8) for [(BaL2)3]? 6MeCN?2H2O Ba(1)]O(2A) Ba(1)]N(72) Ba(1)]N(12) Ba(1)]N(52) Ba(1)]N(32) 2.730(6) 2.869(8) 2.871(9) 2.872(9) 2.914(8) Ba(1)]N(21) Ba(1)]N(61) Ba(1)]N(41) Ba(1)]N(81) 2.946(9) 3.043(8) 3.055(9) 3.088(8) Ba(2)]N(112) Ba(2)]O(6) Ba(2)]N(92) 2.852(8) 3.140(7) 2.870(8) Ba(2)]N(121) Ba(2)]N(101) 3.062(8) 3.055(9) O(2A)]Ba(1)]N(72) O(2A)]Ba(1)]N(12) N(72)]Ba(1)]N(12) O(2A)]Ba(1)]N(52) N(72)]Ba(1)]N(52) N(12)]Ba(1)]N(52) O(2A)]Ba(1)]N(32) N(72)]Ba(1)]N(32) N(12)]Ba(1)]N(32) N(52)]Ba(1)]N(32) O(2A)]Ba(1)]N(21) N(72)]Ba(1)]N(21) N(12)]Ba(1)]N(21) N(52)]Ba(1)]N(21) N(32)]Ba(1)]N(21) O(2A)]Ba(1)]N(61) N(72)]Ba(1)]N(61) N(12)]Ba(1)]N(61) 128.8(2) 80.8(2) 115.3(3) 92.7(2) 70.9(2) 173.0(2) 119.3(2) 111.8(2) 69.6(2) 111.9(2) 79.6(2) 73.2(2) 55.9(3) 125.8(3) 118.5(3) 85.3(2) 116.7(2) 122.5(3) N(52)]Ba(1)]N(61) N(32)]Ba(1)]N(61) N(21)]Ba(1)]N(61) O(2A)]Ba(1)]N(41) N(72)]Ba(1)]N(41) N(12)]Ba(1)]N(41) N(52)]Ba(1)]N(41) N(32)]Ba(1)]N(41) N(21)]Ba(1)]N(41) N(61)]Ba(1)]N(41) O(2A)]Ba(1)]N(81) N(72)]Ba(1)]N(81) N(12)]Ba(1)]N(81) N(52)]Ba(1)]N(81) N(32)]Ba(1)]N(81) N(21)]Ba(1)]N(81) N(61)]Ba(1)]N(81) N(41)]Ba(1)]N(81) 53.7(3) 69.9(2) 164.9(2) 151.8(2) 66.7(2) 116.1(2) 68.9(2) 54.9(2) 128.4(2) 66.7(2) 144.8(2) 54.7(2) 70.0(2) 117.1(2) 68.5(2) 68.0(2) 126.8(2) 62.7(2) N(112)]Ba(2)]N(92) N(112A)]Ba(2)]N(92) N(112)]Ba(2)]N(101A) N(112A)]Ba(2)]N(101A) N(92)]Ba(2)]N(101A) N(92A)]Ba(2)]N(101A) N(112)]Ba(2)]N(121A) N(92)]Ba(2)]N(121A) N(112)]Ba(2)]N(121) N(92)]Ba(2)]N(121) N(101A)]Ba(2)]N(121) 66.7(2) 113.3(2) 73.9(2) 106.1(2) 126.4(2) 53.6(2) 125.5(2) 71.4(2) 54.5(2) 108.6(2) 72.6(2) N(101)]Ba(2)]N(121) N(112)]Ba(2)]O(6A) N(92)]Ba(2)]O(6A) N(101)]Ba(2)]O(6A) N(121)]Ba(2)]O(6A) N(112)]Ba(2)]O(6) N(92)]Ba(2)]O(6) N(92A)]Ba(2)]O(6) N(101)]Ba(2)]O(6) N(121)]Ba(2)]O(6) 107.4(2) 123.7(2) 122.5(2) 70.9(2) 72.4(2) 56.3(2) 57.5(2) 122.5(2) 109.1(2) 107.6(2) J.Chem. 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ISSN:1477-9226    

DOI:10.1039/a700475c

出版商:RSC    

年代:1997

数据来源: RSC