DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 831–834 831 Reaction of tris[(diphenylphosphino)dimethylsilyl]methane with molybdenum hexacarbonyl and deprotonation to give a salt with a planar carbanion. Crystal structures of (Ph2PMe2Si)3CH and [Li(tmen)2][C(SiMe2PPh2)3], tmen 5 N,N,N9,N9-tetramethylethane- 1,2-diamine Anthony G. Avent, Dominique Bonafoux, Colin Eaborn,* Sushil K. Gupta, Peter B. Hitchcock and J. David Smith * School of Chemistry, Physics and Environmental Science, University of Sussex, Brighton, UK BN1 9QJ.E-mail: C.Eaborn@sussex.ac.uk; J.D.Smith@sussex.ac.uk Received 17th November 1998, Accepted 21st January 1999 The compound (Ph2PMe2Si)3CH I reacted (i) with [Mo(CO)6] to give cis-[Mo(CO)4{(Ph2PMe2Si)3CH}] 1 in which two phosphine groups are co-ordinated to molybdenum and one is free, and (ii) with LiBu in the presence of N,N,N9,N9-tetramethylethane-1,2-diamine (tmen) to give [Li(tmen)2][C(SiMe2PPh2)3] 2, which contains discrete planar carbanions and no Li–P co-ordination. The crystal structures of compounds I and 2 have been determined and 1 has been characterised spectroscopically.We have been able to isolate a wide range of novel types of organometallic compounds by attaching the bulky ligands C(SiMe3)3 or C(SiMe2Ph)3 to metal centres.1 Recently the emphasis in our research has moved towards use of ligands of the type C(SiMe3)2(SiMe2X) and C(SiMe2X)3 that have similar bulk around the metal centre to which they are attached but also contain groups X bearing lone pairs capable of coordinating intra- or inter-molecularly to the metal.Those used previously include C(SiMe3)2(SiMe2X) with X = OMe2 or SMe 3 and C(SiMe2X)3 with X = OMe4 or NMe2.5,6 In particular, the lithium derivative LiC(SiMe2NMe2)3, made by metallation of the ligand precursor (Me2NMe2Si)3CH, adopts a linear polymeric structure in which the planar lithium ion, co-ordinated by three NMe2 groups, is well separated from the planar carbanionic centre.Moreover, the highly unusual Grignard reagent (Me2NMe2Si)3CMgI has a planar carbanionic centre without specific interaction with the magnesium atom. We now describe the synthesis of the analogous phosphorus-containing ligand precursor I, the molybdenum complex 1, and the lithium derivative 2 obtained from the reaction between I and LiBu/tmen (tmen = N,N,N9,N9-tetramethylethane-1,2-diamine). Results and discussion The precursor I was obtained in good yield from the reaction between (BrMe2Si)3CH7 and KPPh2 in tetrahydrofuran (thf) and characterised by multinuclear NMR spectroscopy.The 1H NMR spectrum showed the expected signals assigned to SiMe2, CH and Ph protons. The 13C and 29Si spectra showed complex multiplets which were simulated by the PANIC program. The signal from the ipso-carbon of the phenyl group was analysed as the A part of an AXY2 system, with the 12C/13C isotope shift at phosphorus |dX 2 dY| = 0.028.The signal from the ortho carbon was also analysed as the A part of an AXY2 spin system but with |dX 2 dY| = 0.009; that from the meta-carbon was analysed as the A part of an AXX92 spin system, as the isotope shift is attenuated over three bonds. The presence of a 13C nucleus in a methyl site makes the two remote 31P nuclei magnetically inequivalent so that the CH3 signal appears as the A part of an AXYY9 system with |dX 2 dY| = 0.006. The 29Si signal was analysed as the A part of an AXY2 system with |dX 2 dY| (arising from the 29Si/28Si isotope shift at P) = 0.011.The 29Si satellites from the quartet assigned to the tertiary carbon showed that the coupling constant 1JSiC is 33.2 Hz [cf. 38.7 Hz for (Me3Si)3CH8 and 42 Hz for (Me2NSiMe2)3CH5]. The phosphorus chemical shift, d 251, is close to that, d 256.8, for diphenyl(trimethylsilyl)phosphine.9 Crystals of compound I suitable for an X-ray study were obtained from heptane–thf. The reaction between compound I and molybdenum hexacarbonyl gave a white solid which was judged to be the complex cis-[Mo(CO)4{(Ph2PMe2Si)3CH}] 1 from (i) the mass spectrum, which showed the successive loss of four carbonyl groups from the molecular ion, (ii) the presence of four bands in the carbonyl stretching region of the infrared spectrum as required for C2v symmetry, and (iii) the presence in the 29Si and 31P NMR spectra of two signals with intensities in the ratio 2 : 1.These are attributed respectively to complexed SiA,BMe2PPh2 fragments (with dP 221, about 30 ppm to higher frequency than the signal for I), and uncomplexed SiCMe2PPh2 fragments (with dP close to that for I).The bidentate co-ordination of the ligand in 1 gives a six-membered MoPSiCSiP metallacycle and leaves one free SiMe2PPh2 fragment. The presence of three signals in each region of the 1H and 13C spectra, corresponding to the methyl and phenyl substituents in uncomplexed SiCMe2PPh2 groups and SiA,BMe2PPh2 groups on either side of the ring, shows that the chelate structure is preserved in solution and is not fluxional on the NMR timescale.In several other complexes MoL(CO)4 the ligand L containing three phosphorus centres, e.g. (Ph2P)3CH10 or (Ph2PCH2)3CCH3,11,12 is bidentate. Compound I was readily metallated by LiBu in the presence of tmen. The product 2 was obtained as pale yellow832 J. Chem. Soc., Dalton Trans., 1999, 831–834 Table 1 Bond lengths (Å) and angles (8) in (Ph2PSiMe2)3CH I and [(Ph2PSiMe2)3C]2 Si–C Si–Me P–Si P–Ph (Ph2PSiMe2)3CH I 1.898(5) a 1.871(6) a 2.275(2) a 1.837(5) a [(Ph2PSiMe2)3C]2 1.809(7) a 1.879(8) a 2.323(3) a 1.837(8) a Si–C–Si Ph–P–Ph Si–P–Ph Me–Si–Me C–Si–Me C–Si–P Me–Si–P Si1 114.7(3) 101.9(2) 101.1(2) 106.5(3) 107.1(3) 116.1(2) 111.5(3) 107.9(2) 103.4(2) 110.1(2) Si2 112.1(3) 101.9(2) 107.9(2) 98.7(2) 106.3(3) 116.1(2) 110.8(3) 108.0(2) 111.5(2) 103.4(2) Si3 114.5(3) 103.0(2) 97.7(2) 106.8(2) 104.6(3) 118.1(2) 110.6(3) 107.3(2) 109.4(2) 106.3(2) Si1 120.7(4) 102.4(3) 106.0(3) 101.4(3) 104.0(4) 114.9(4) 116.6(3) 112.7(2) 105.3(3) 101.8(3) Si2 120.2(4) 105.2(4) 106.3(3) 102.2(3) 105.9(4) 114.6(3) 117.2(3) 114.1(3) 103.3(2) 99.8(3) Si3 118.6(4) 102.2(4) 104.2(3) 106.8(3) 103.4(4) 116.6(3) 114.7(3) 110.8(3) 102.3(3) 107.8(3) a Mean value.Numbers in parentheses indicate the precision of individual measurements, none of which diVered significantly from the mean.crystals from warm toluene and shown by an X-ray study to be ionic, with a lattice consisting of discrete [Li(tmen)2]1 cations and [C(SiMe2PPh2)3]2 anions. The CSi3 core of the carbanion is planar, like those in [Li(thf)4][C(SiMe2- C6H4Me-o)3] 13 and [Li(12-crown-4)2][C(SiMe3)(SiMeBut 2)- (SiMe2F)].14 The ionic structure of 2 contrasts with the polymeric structure of the amino derivative LiC(SiMe2NMe2)3,5 and the molecular structure of the recently described compound [LiP{C(SiMe3)2}(C6H4CH2NMe2)2] 3,15 which has a planar carbanionic centre and lithium co-ordinated both by the lone pair on phosphorus and by those on the two nitrogen atoms.The 31P NMR spectrum of a thf solution of compound 2 consisted of a singlet at d 239.4. The absence of Li–P coupling and the small diVerence between the chemical shifts of 2 and of the precursor I indicate that in solution, as in the solid, the phosphorus atoms in 2 are not co-ordinated to lithium. The structures of the anion of compound 2 and the corresponding protonated species I are shown in Figs. 1 and 2. (The cation in 2 is similar to that described in several other compounds and is not discussed further here.) Bond lengths and angles are given in Table 1. For each species the individual Si–C, Si–Me, P–Si and P–C bond lengths diVer insignificantly from the corresponding mean values, but there is considerably more variation in the bond angles, which means that neither the Fig. 1 Molecular structure of (Ph2PMe2Si)3CH I.anion in 2 nor the corresponding protonated species I has any crystallographic symmetry. The anion has one SiMe2PPh2 group on one side of the CSi3 plane and two on the other. {There is a similar configuration of SiMe2C6H4Me-o groups in the anion [C(SiMe2C6H4Me-o)3]2.13} In contrast, the molecule I is propeller-shaped, with approximate C3 symmetry and all the SiMe2PPh2 groups lying on the side opposite the C–H bond. The Si–C1 distances are much shorter in the anion (mean 1.809 Å) than in the protonated species I (mean 1.898 Å) showing that the anionic charge is delocalised into C1–Si bonds, probably by negative hyperconjugation.16 Data for a number of related species are given in Table 2.The Si–C1 distances in the silyl-stabilised carbanions are all short compared with those in the corresponding silyl-substituted methanes. The bond lengths show little systematic variation with the nature of the substituent X.The Si–P bonds are longer in the anion than in I, and in other organosilylphosphines or organosilylphosphine complexes. 20 The P–C bond lengths are in the normal range, 2.20– 2.29 Å, and all the Si–Me bond lengths are, within experimental error, the same as those in SiMe4 [1.875(2) Å].21 The Si–C–Si angles are larger in the anion than in the protonated species, as expected if the ionic charge is delocalised over the CSi3 system [cf. C(SiMe3)3 17 and C(SiMe2Ph)3 1b derivatives].The other mean bond angles in I are similar (within 48) to those in the anion of 2 but there is more scatter in the protonated than Fig. 2 Structure of the anion of [Li(tmen)2][C(SiMe2PPh2)3] 2.J. Chem. Soc., Dalton Trans., 1999, 831–834 833 in the unprotonated species. The geometry at phosphorus is pyramidal with C–P–C and C–P–Si angles less than the tetrahedral value, as found in other silylphosphine complexes.20 The chemistry of the compounds described here shows several novel features.(a) Although the organolithium compound 2 reacted in the normal way with a stoichiometric amount of MeOH-d4 to give the expected (Ph2PMe2Si)3CD in high yield, reactions with other electrophiles e.g. MeI or I2 resulted in cleavage of Si–P bonds. Similar cleavages have been observed for Ph2PSiMe3 20 but it is remarkable that attack at the Si–P bond in 2 appears to occur more readily rather than that at the carbanionic centre. (b) There is a considerable diVerence in reactivity between Si–N or Si–S bonds on the one hand and Si–P bonds on the other.Whereas the compounds LiC(SiMe2NMe2)3 4,5 and LiC- (SiMe3)2(SiMe2SMe)3 could each be used as a reagent for the transfer of the C-centred ligands to other metals, reactions of compound 2 with HgBr2 and PtCl2 did not proceed cleanly. Tetraphenyldiphosphine P2Ph2 was always obtained as the principal product but the additional presence of PPh2H in some cases may indicate that PPh2Li and PPh2Br are intermediates in the ligand degradation.It has not been possible to isolate the silicon-containing products in a pure state. (c) The isolation of complex 1 suggests that in the absence of electrophiles the compound I has some potential as a mono-, di- or tri-dentate ligand towards transition metals. This area of chemistry is however likely to be restricted by ligand degradation and by slow attack of I on the thf commonly used as a solvent. (d) The stability of compound I in the absence of electrophiles is also shown by the fact that it reacts in the normal way with metal methyl derivatives, e.g.with LiBu to give the compound 2. Experimental Air and moisture were excluded as far as possible from all reactions by the use of standard Schlenk techniques and Ar as blanket gas. Solvents were dried by normal procedures and distilled immediately before use. The NMR spectra were recorded at 300.13 (1H), 125.8 (13C), 99.4 (29Si), 121.4 (31P) and 32.53 MHz (95Mo) and chemical shifts are relative to SiMe4 for H, C and Si, H3PO4 for P, and X 6.515 for Mo.The 29Si spectra were obtained by inverse gated decoupling and signals from ternary carbon were detected by the DEPT procedure. Coupling constants derived from PANIC simulation are accurate to ±0.2 Hz. The EI mass spectra were recorded at 70 eV: m/z values are given for 1H, 12C, 28Si and 98Mo. Syntheses (Ph2PMe2Si)3CH I. A solution of KPPh2 (130 cm3, 0.5 M in thf) was added dropwise to (BrMe2Si)3CH (9.08 g, 21.3 mmol) in thf (100 cm3) at room temperature and the mixture stirred for 4 h.The solvent was removed under vacuum, the residue extracted with benzene (3 × 20 cm3), the extract filtered, the solvent removed, and the residue recrystallised from thf– heptane (10 : 1) to give colourless needles of compound I (14.2 Table 2 Si–C1 Distances (Å) in compounds HC(SiMe2X)3 and anions [C(SiMeX)3]2 X Me Ph PPh2 NMe2 OMe Br HC(SiMe2X)3 1.887(6) 1.895(1) 1.898(5) 1.884(5) Ref. 17 19(a) This work 19(b) [C(SiMeX)3]2 1.818(10)–1.822(10) 1.800(3)–1.812(3) 1.809(7) 1.793(6) 1.805(4) Ref. 17 13 a This work 54 a For C(SiMe2C6H4Me-o)3. g, 89%), mp 192 8C (Found: C, 68.1; H, 6.4; P, 13.8. C43H49P3Si3 requires C, 69.5; H, 6.4; P, 12.5%). No carbon- or phosphoruscontaining impurity was detected by NMR spectroscopy. dH (C6D6) 0.51 (18 H, s, SiMe2), 1.20 (1 H, q, 3JPH 3.5 Hz, CH), 6.98 (18 H, m, m- and p-H) and 7.52 (12 H, m, o-H). dC 1.9 (DEPT q, 1JSiC 33.2, 2JCP 11.1, CH), 2.0 (m, 2JCP 8.1, 4JCP 9.4, 0.4, 4JPP 9.4, SiMe2), 127.7 (p-C), 128.8 (m, 3JCP 6.5, 4JPP 9.4, m-C), 134.6 (m, 2JCP 18.4, 4JPP 9.4, o-C) and 136.5 (m, ipso-C, 1JCP 18.6, 5JCP 20.5, 4JPP 9.4 Hz).dSi 2.8 (1JSiP 27.2, 3JSiP 23.9 Hz). dP 250.6. m/z 557 (5, M 2 PPh2), 370 (75, P2Ph4), 185 (80, PPh2) and 183 (100%, PPh2 2 H2). Compound I reacted slowly (during 1 week) with thf at room temperature with formation of some P2Ph4, the presence of which was deduced from the 31P NMR spectrum.cis-[Mo(CO)4{(Ph2PMe2Si)3CH}] 1. A suspension of [Mo- (CO)6] (0.712 g, 2.69 mmol) and I (2.00 g, 2.69 mmol) in toluene (150 cm3) was slowly heated to reflux, then maintained at reflux for 3 h to give a red solution. The solution was allowed to cool to room temperature and the solvent removed to leave a yellow solid which was judged to be complex 1 (2.34 g, 90%), mp 101 8C (Found: C, 52.9; H, 5.4; Mo, 9.9; P, 9.4. C47H49- MoO4P3Si3 requires C, 59.3; H, 5.2; Mo, 10.1; P, 9.7%).The low value for the carbon analysis is puzzling since the NMR data were fully consistent with the proposed structure. n& max/cm21 2018s, 1950 (sh), 1925s and 1880s. dH (C6D6) 0.15 (6 H, d, 3JPH 3.5, SiMe), 0.31 (6 H, d, 3JPH 6.6, SiMe), 0.36 (6 H, d, 3JPH 2.3, SiMe), 0.93 (1 H, d, 3JPH 5.3 Hz, CH), 6.8–7.2 (18 H, m, m- and p-H), 7.26 (4 H, m, o-H), 7.50 (4 H, m, o-H) and 7.76 (4 H, m, o-H). dC 0.64 (d, 2JCP 14.4, SiMe2), 2.16 (dd, 2JCP 9.6, 4JCP 1.2, SiMe2), 3.25 (d, 2JCP 9.3, SiMe2), 3.45 (q, 2JCP 7.2, CH), 128.06 (A of AXX9, 3JCP 9.6, 2JPP ca. 2, m-CA,B), 128.42 (s, p-C), 128.46 (A of AXX9, 3JCP 9.4, 2JPP ca. 2, m-CA,B), 128.57 (s, p-C), 129.05 (s, p-C), 129.14 (d, 3JCP 7.0, m-CC), 133.61 (A of AXX9, 2JCP 10.3, 2JPP ca. 2, o-CA,B), 134.69 (d, 2JCP 18.5, o-CC), 134.84 (d, 1JCP 17.5, ipso-C), 135.24 (d, 1JCP 24.0, ipso-C), 135.36 (A of AXX9, 2JCP 12.3, 2JPP ca. 2, o-CA,B), 137.56 (d, 1JCP 25.6, ipso- C), 206.4 (t, 2JCP 7.6, cis-CO), 215.9 (dd, 2JCP-trans 22.2, 2JCP-cis 9.4, trans-CO) and 216.3 (t, 2JCP 7.6 Hz, cis-CO).dSi 22.2 (2 Si, d, 1JSiP 18.7, SiA,B) and 0.1 (1 Si, dt, 1JSiP 30.9, 3JSiP 7.2 Hz, SiC). dP 248.7 (1 P, t, 4JPP 2.0, PC) and 217.7 (2 P, d, 4JPP 2.0 Hz, PC). dMo 21290 (Dn2� 1 500 Hz). m/z 924 (8, M 2 CO), 896 (30 M 2 2CO), 868 (100, M 2 3CO), 840 (55, M 2 4CO) and 682 (50, M 2 3CO 2 PHPh2) and 654 (80%, M 2 4CO 2 PHPh2). [Li(tmen)2][C(SiMe2PPh2)3] 2. A solution of LiBu (3.23 mmol) in hexane (1.3 cm3) was added to a mixture of I (2.0 g, 2.7 mmol) and tmen (4.5 cm3, 30 mmol) in toluene (30 cm3) at room temperature.After about 30 min an orange solid separated. This was filtered oV, washed first with light petroleum (bp 40–60 8C, 2 × 10 cm3) then with benzene (3 × 10 cm3), and recrystallised from warm toluene to give pale yellow air- and moisture-sensitive plates of compound 2 (1.73 g, 65%), mp 187 8C (decomp.) (Found: C, 66.1; H, 8.2; N, 5.7.C55H80- LiN4P3Si3 requires C, 67.3; H, 8.2; N, 5.7%). dH (thf-d8) 0.16 (18 H, s, SiMe2), 25 (24 H, s, NMe2), 2.31 (8 H, s, CH2), 6.91–7.37 (20 H, m, Ph) and 7.66–7.73 (10 H, m, Ph). dC 4.75 (m, SiMe2), 4.8 (DEPT, q, 1JSiC 59.7, 2JCP 20.3 Hz, CSi3), 46.1 and 58.8 (free tmen, displaced by solvent), 125.3 (s), 127.8 (m) and 134.8 (m). dSi 20.9. dP 239.4. Reactions of complex 2 With CD3OD. The compound CD3OD (0.4 cm3) in benzene (5 cm3) was added to a suspension of 2 (0.94 g, 0.95 mmol) in benzene (10 cm3) to give a clear solution immediately.The solvent was removed to leave the deuteriated species (Ph2PMe2- Si)3CD as a white solid (0.54 g, 76%). m/z 558.188 (M 2 PPh2); C31H38DP2Si3 requires m/z 558.190. The 13C and 31P NMR spectra were identical with those for I; the proportion of I834 J. Chem. Soc., Dalton Trans., 1999, 831.834 estimated from the signal at d 1.2 in the 1H NMR spectrum was less than 10%. With MeI. A solution of MeI (0.36 mmol) in thf (0.72 cm3) was added to compound 2 (0.32 mmol) in thf (10 cm3) at 270 8C.The mixture was allowed to warm to room temperature and stirred for 2 h. After removal of the solvent the residue was extracted with light petroleum to give, according to the 31P NMR spectrum and integration of the 1H spectrum, a mixture of PPh2Me (51%), and PPh2H/P2Ph4 (49%), identified by comparison of the 31P chemical shifts with those of commercially available samples and with values in the literature.23 With an eight-fold excess of MeI, 2 gave a white solid which was shown by its 1H, 13C and 31P NMR spectra18 to be [PMe2Ph2]I, isolated in 87% yield.Positive FAB MS: m/z 557 (2, [PPh2Me2]2I) and 215 (90, PPh2Me2). With I2. A solution of I2 (0.7 mmol) in thf (0.8 cm3) was added to compound 2 (0.7 mmol) in thf (10 cm3) at 278 8C, and the mixture allowed to warm to room temperature. A white solid was filtered oV and the 31P NMR spectrum of the filtrate showed the presence of P2Ph4 as the only detectable phosphorus-containing thf-soluble product.The solid was not investigated further. With metal halides. The reaction of compound 2 with PtCl2 gave P2Ph4 and that with HgBr2 gave Hg, P2Ph4 (75% of thfsoluble products) and PPh2H (25%). Unidentified white solids were obtained in both reactions and their NMR spectra showed that they contained neither phosphorus nor aromatic protons. Crystallography Details are given in Table 3. All non-hydrogen atoms were refined anisotropically. The H atoms were included in riding mode with Uiso(H) = 1.2Ueq(C) except for Me groups which were fixed at idealised geometry but with the torsion angles defining the H atom position refined and Uiso(H) = 1.5Ueq(C).The high value of R for complex 2 is a consequence of the weak diVraction from a thin plate. Table 3 Crystallographic data and details of structure refinement for compounds I and 2 Empirical formula Formula weight T/K l/A Crystal system Space group a/A b/A c/A b/8 U/A3 Z m/mm21 q Range/8 Reflections collected Unique reflections Reflections with I > 2s(I) R1, wR2 [I > 2s(I)] (all data) Data/restraints/parameters I C43H49P3Si3 743.0 173(2) 0.71073 Monoclinic P21/n (no. 14) 18.314(4) 10.398(3) 21.859(7) 100.61(2) 4091(2) 4 0.26 2.22 5170 4993 (Rint = 0.0357) 3229 0.053, 0.107 0.105, 0.136 4992/0/446 2 C55H80LiN4P3Si3 981.4 173(2) 0.71073 Monoclinic P21/n (no. 14) 15.023(4) 16.592(4) 23.174(11) 90.78(3) 5776(3) 4 0.20 2.23 8371 8027 (Rint = 0.0698) 4106 0.090, 0.145 0.189, 0.179 8026/0/595 CCDC reference number 186/1330.See http://www.rsc.org/suppdata/dt/1999/831/ for crystallographic files in .cif format. Acknowledgements The authors thank the EPSRC for financial support, the EU for the award of a Marie-Curie Fellowship to D. 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