Synthesis and Structure of [Li2C(PPh2 NSiMe3)(PPh2 S)]: A Geminal

Organometallics 2009, 28, 4617–4620 DOI: 10.1021/om900364j

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Synthesis and Structure of [Li2C(PPh2dNSiMe3)(PPh2dS)]: A Geminal Dianionic Ligand Jun-Hui Chen, Jiayi Guo, Yongxin Li, and Cheuk-Wai So* Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 637371 Singapore Received May 7, 2009 Summary: The (iminophosphoranyl)(thiophosphoranyl)methane [CH2(PPh2dNSiMe3)(PPh2dS)] (2) was obtained by the reaction of the phosphine-phosphinimine [Ph2PCH2(PPh2dNSiMe3)] (1) with sulfur in toluene. Treatment of 2 with BunLi in THF at -90 °C afforded the lithium (iminophosphoranyl)(thiophosphoranyl)methanide [Li{CH(PPh2dS)(PPh2dNSiMe3)}] (3). The geminal dianion derivative [Li2{C(PPh2dS)(PPh2d NSiMe3)}] (4) was synthesized by double deprotonation of 2 with a stoichiometric amount of ButLi in Et2O at -90 °C. The structures of compounds 2-4 have been determined by X-ray crystallography.

The chemistry of bis-phosphorus-stabilized methanide and geminal dianionic complexes has attracted much attention in the past few decades.1 In 1999, Cavell and co-workers2a and Ong and Stephan2b reported the synthesis and structure of the dilithium bis(iminophosphoranyl)methanediide complexes [Li2C(PPh2dNSiMe3)2]. The coordination chemistry of [C(PPh2dNSiMe3)2]2- was investigated exten*To whom correspondence should be addressed. E-mail: CWSo@ ntu.edu.sg. (1) Selected articles for bis-phosphorus-stabilized methanide complexes: (a) Karsch, H. H.; Schmidbaur, H. Z. Naturforsch., B: Anorg. Chem., Org. Chem. 1977, 32B, 762. (b) Karsch, H. H. Z. Naturforsch., B: Anorg. Chem., Org. Chem. 1979, 34B, 1171. (c) Karsch, H. H.; Appelt, A.; M€ uller, G. Organometallics 1986, 5, 1664. (d) Karsch, H. H.; Keller, U.; Gamper, S.; M€ uller, G. Angew. Chem., Int. Ed. Engl. 1990, 29, 295. (e) Karsch, H. H.; Ferazin, G.; Steigelmann, O.; Kooijman, H.; Hiller, W. Angew. Chem., Int. Ed. Engl. 1993, 32, 1739. (f) Karsch, H. H. Angew. Chem., Int. Ed. Engl. 1982, 21, 921. (g) Kamalesh Babu, R. P.; Kasani, A.; McDonald, R.; Cavell, R. G. Inorg. Chem. 2000, 39, 4981. (h) Kamalesh Babu, R. P.; Kasani, A.; McDonald, R.; Cavell, R. G. Organometallics 2001, 20, 1451. (i) Wei, P.; Stephan, D. W. Organometallics 2003, 22, 601. (j) Wei, P.; Stephan, D. W. Organometallics 2002, 21, 1308. (k) Hill, M. S.; Hitchcock, P. B. Dalton Trans. 2002, 4694. (l) Ahmed, S. A.; Hill, M. S.; Hitchcock, P. B. Organometallics 2006, 25, 394. (m) Al-Benna, S.; Sarsfield, M. J.; ThorntonPett, M.; Ormsby, D. L.; Maddox, P. J.; Bres, P.; Bochmann, M. Dalton Trans. 2000, 4247. (n) Rast€atter, M.; Zulys, A.; Roesky, P. W. Chem. Commun. 2006, 874. (o) Wiecko, M.; Roesky, P. W. Organometallics 2009, 28, 1266. (p) Berry, D. E.; Browning, J.; Dixon, K. R.; Hilts, R. W.; Pidcock, A. Inorg. Chem. 1992, 31, 1479. (q) Browning, J.; Bushnell, G. W.; Dixon, K. R.; Hilts, R. W. J. Organomet. Chem. 1992, 434, 241. (r) Suranna, G. P.; Mastrorilli, P.; Nobile, C. F.; Keim, W. Inorg. Chim. Acta 2000, 305, 151. (s) Blug, M.; Heuclin, H.; Cantat, T.; Le Goff, X.-F.; Mezailles, N.; Le Floch, P. Organometallics 2009, 28, 1969. Selected reviews for bis-phosphorus-stabilized geminal dianions: (t) Cantat, T.; Mezailles, N.; Auffrant, A.; Le Floch, P. Dalton Trans. 2008, 1957. (u) Jones, N. D.; Cavell, R. G. J. Organomet. Chem. 2005, 690, 5485. (2) (a) Kasani, A.; Kamalesh Babu, R. P.; McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed. 1999, 38, 1483. (b) Ong, C. M.; Stephan, D. W. J. Am. Chem. Soc. 1999, 121, 2939. (3) (a) Leung, W.-P.; Wang, Z.-X.; Li, H.-W.; Mak, T. C. W. Angew. Chem., Int. Ed. 2001, 40, 2501. (b) Hull, K. L.; Noll, B. C.; Henderson, K. W. Organometallics 2006, 25, 4072. (c) Orzechowski, L.; Jansen, G.; Harder, S. J. Am. Chem. Soc. 2006, 128, 14676. (d) Orzechowski, L.; Harder, S. Organometallics 2007, 26, 5501. (e) Kasani, A.; McDonald, R.; Ferguson, M.; Cavell, R. G. Organometallics 1999, 18, 4241. r 2009 American Chemical Society

sively. Main-group,3 transition-metal4 and lanthanide-metal5 bis(iminophosphoranyl)methanediide complexes were obtained by the salt elimination of [Li2C(PPh2dNSiMe3)2] with metal halide or by the double deprotonation of [CH2(PPh2d NSiMe3)2] with metal alkyl or amide. For example, the hafnium methanediide complex [(PPh2dNSiMe3)2CdHfCl2] was synthesized by treatment of [HfCl2{N(SiMe3)2}2] with [CH2(PPh2dNSiMe3)2].6 Dilithium bis(thiophosphoranyl)methanediide, [Li2C(PPh2dS)2], has also been synthesized, and it can serve as a synthon for the preparation of the palladium carbene complex [(Ph3P)PddC(PPh2dS)2] by reaction with PdCl2(PPh3).7 Recently, Le Floch and co-workers reported the syntheses of phosphine-iminophosphorane ligands containing at least two donor sites of different hardness.8 The fact that an iminophosphorane is isoelectronic with a thiophosphorane prompted our interest in the synthesis of a geminal dianion containing a hard nitrogen and soft sulfur coordination. In this paper, the syntheses of the lithium (iminophosphoranyl)(thiophosphoranyl)methanide [Li{CH(PPh2dNSiMe3)(PPh2dS)}] (3) and the dilithium derivative [Li2{C(PPh2d NSiMe3)(PPh2dS)}] (4) are reported.

Results and Discussion The reaction of the phosphine-phosphinimine [Ph2PCH2(PPh2dNSiMe3)] (1)9 with sulfur in toluene at 0 °C afforded the (iminophosphoranyl)(thiophosphoranyl)methane [CH2(PPh2dNSiMe3)(PPh2dS)] (2) (Scheme 1). It was anticipated that compound 2 could enhance the hemilabile character (4) (a) Kamalesh Babu, R. P.; McDonald, R.; Decker, S. A.; Klobukowski, M.; Cavell, R. G. Organometallics 1999, 18, 4226. (b) Kamalesh Babu, R. P.; McDonald, R.; Cavell, R. G. Organometallics 2000, 19, 3462. (c) Cavell, R. G.; Kamalesh Babu, R. P.; Kasani, A.; McDonald, R. J. Am. Chem. Soc. 1999, 121, 5805. (d) Kasani, A.; Kamalesh Babu, R. P.; McDonald, R.; Cavell, R. G. Angew. Chem., Int. Ed. 2001, 40, 4400. (e) Kasani, A.; McDonald, R.; Cavell, R. G. Chem. Commun. 1999, 1993. (f) Jones, N. D.; Lin, G.; Gossage, R. A.; McDonald, R.; Cavell, R. G. Organometallics 2003, 22, 2832. (5) Kasani, A.; Ferguson, M.; Cavell, R. G. J. Am. Chem. Soc. 2000, 122, 726. (6) Kamalesh Babu, R. P.; McDonald, R.; Cavell, R. G. Chem. Commun. 2000, 481. (7) Cantat, T.; Mezailles, N.; Ricard, L.; Jean, Y.; Le Floch, P. Angew. Chem., Int. Ed. 2004, 43, 6382. (8) (a) Boubekeur, L.; Ricard, L.; Mezailles, N.; Le Floch, P. Organmetallics 2005, 24, 1065. (b) Boubekeur, L.; Ulmer, S.; Ricard, L.; Mezailles, N.; Le Floch, P. Organometallics 2006, 25, 315. (c) Boubekeur, L.; Ricard, L.; Mezailles, N.; Demange, M.; Auffrant, A.; Le Floch, P. Organometallics 2006, 25, 3091. (d) Buchard, A.; Auffrant, A.; Klemps, C.; Vu-Do, L.; Boubekeur, L.; Le Goff, X. F.; Le Floch, P. Chem. Commun. 2007, 1502. (e) Buchard, A.; Komly, B.; Auffrant, A.; Le Goff, X. F.; Le Floch, P. Organometallics 2008, 27, 4380. (9) Gamer, M. T.; Roesky, P. W. Organometallics 2004, 23, 5540. Published on Web 07/10/2009

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Scheme 1. Synthesis of 2-4

Figure 1. Molecular structure of 2 with thermal ellipsoids at the 30% probability level.

compared with [CH2(PPh2dE)2] (E = NR, S; R = alkyl, aryl). [CH2(PPh2dE)2] (E = NR, S) were usually prepared by the reaction of (diphenylphosphino)methane with azide or sulfur in refluxing toluene.10 In contrast, reaction of 1 with sulfur in refluxing toluene gave a mixture of products that could not be identified. Similar (iminophosphoranyl)(thiophosphoranyl)methanes [CH2(PPh2dS)(PPh2dNR)] (R = 4-C6H4Me, 4-C6H4OMe, 2,4,6-C6H2Me3, 4-C6F4CHO, 4C6F4CN, 4-C5F4N, P(dO)(OPh)2, P(dS)(OEt)2, P(dS)(OPh)2) have been synthesized.11 Stalke and co-workers have also reported the synthesis of the hemilabile thiophosphoranyl ligand [(C5H4N-2)CH2PPh2(S)] by the reaction of [(C5H4N2)CH2PPh2] with sulfur.12 Compound 2 is a colorless crystalline solid, soluble in Et2O and toluene. It has been analyzed by NMR spectroscopy, X-ray crystallography, and elemental analysis. The 31P NMR spectrum of 2 shows two doublets at δ -5.23 and 36.7 ppm with 2JP-P0 = 17.3 Hz due to PPh2dNSiMe3 and PPh2dS, respectively. These are downfield shift compared with those of 1 (-26.7 (PPh2), -2.1 ppm (PPh2dNSiMe3)).9 The 31P NMR resonances of 2 are comparable to those of [CH2(PPh2dS){PPh2dN(4-C6H4OMe)}] (δ -4.8 (d), 36.2 ppm (d); 2JP-P0 =16 Hz).11a The 1H NMR spectrum of 2 shows one doublet of doublets for the methylene protons at δ 3.56 ppm (2JP-H =14.64, 12.36 Hz). The molecular structure of 2 is shown in Figure 1. Selected bond distances (A˚) and angles (deg) are given in Table 1. The P(1)-N(1) bond length (1.547(2) A˚) and P(2)-S(1) bond length (1.960(1) A˚) in 2 are comparable to those of [CH2(PPh2dS){PPh2dN(4-C6H4Me)}] (P-N = 1.556(4) A˚; P-S = 1.952(2) A˚).11a Treatment of 2 with BunLi in THF at -90 °C afforded the lithium (iminophosphoranyl)(thiophosphoranyl)methanide [Li{CH(PPh2dS)(PPh2dNSiMe3)}] (3), isolated as a colorless extremely air- and moisture-sensitive crystalline solid that was characterized by X-ray crystallography. The mole(10) (a) Appel, V. R.; Ruppert, I. Z. Anorg. Allg. Chem. 1974, 406, 131. (b) Grim, S. O.; Mitchell, J. D. Inorg. Chem. 1977, 16, 1762. (11) (a) Avis, M. W.; Goosen, M.; Elsevier, C. J.; Veldman, N.; Kooijman, H.; Spek, A. L. Inorg. Chim. Acta 1997, 264, 43. (b) Cadierno, V.; Díez, J.; García-Alvarez, J.; Gimeno, J. Organometallics 2008, 27, 1809. (12) Kling, C.; Ott, H.; Schwab, G.; Stalke, D. Organometallics 2008, 27, 5038.

cular structure of 3 is shown in Figure 2. Selected bond distances (A˚) and angles (deg) are given in Table 1. Compound 3 is a monomeric lithium complex that contains the six-membered metallacycle Li(1)-S(1)-P(1)-C(13)-P(2)N(1), formed by the ligand and the lithium atom. The Li(1) is also bound to the oxygen atoms of two THF molecules and displays tetrahedral geometry. The metallacycle adopts a twist-boat conformation in which S(1) and N(1) are displaced from the P(1)-C(13)-P(2)-Li(1) least-squares plane by 1.015 and 0.750 A˚, respectively. The C(13)-Li(1) distance (3.707 A˚) is significantly longer than that of [Li(THF){CH(PPh2dNSiMe3)2}] (2.560(8) A˚),13a showing that the negative charge is delocalized throughout the ligand. The C(13)-P bonds (1.708(4), 1.715(3) A˚) are significantly shorter than those in 2 (1.820(3), 1.831(3) A˚). On the other hand, the P-S (1.989(1) A˚) and P-N bonds (1.588(3) A˚) are slightly longer than those in 2. The Li(1)-N(1) bond (2.065(6) A˚) in 3 is shorter than the Li(1)-S(1) bond (2.484(6) A˚). Similar bis-phosphorus methanide complexes [Li{CH(PPh2dE)2}] (E = S, NSiMe3) have been synthesized and structurally characterized.13 The nature of the P-N bond in the methanide complex [Li{(C5H4N-2)CHPPh2(dNSiMe3)}] was recently studied by means of experimental charge density investigations.14 Compound 3 is soluble in hydrocarbon solvents and has been studied by NMR spectroscopy. The 31P NMR spectrum displays two doublets at δ 16.1 and 35.4 ppm (2JP-P0 = 21.7 Hz) due to PPh2dNSiMe3 and PPh2dS, respectively. The 13C NMR spectrum shows one doublet of doublets for the methanide carbon atom at δ 21.81 ppm (JP-C = 91.5, 126.4 Hz). In contrast, the 1H NMR spectrum shows a doublet for the methanide proton at δ 2.17 ppm (2JP-H = 3.68 Hz). The lack of coupling of the methanide proton to two nonequivalent phosphorus nuclei is unusual. The lithium salt of the geminal dianion [Li2{C(PPh2d S)(PPh2dNSiMe3)}] (4) was synthesized by double deprotonation of 2 with a stoichiometric amount of ButLi in Et2O at -90 °C. Other examples of the bis-phosphorus methanediide complexes [Li2{C(PPh2dE)2}] (E=S, NSiMe3) have been synthesized and structurally characterized.2,15 Compound 4 was isolated as a highly air- and moisture-sensitive colorless (13) (a) Gamer, M. T.; Roesky, P. W. Z. Anorg. Allg. Chem. 2001, 627, 877. (b) Browning, J.; Bushnell, G. W.; Dixon, K. R.; Pidcock, A. Inorg. Chem. 1983, 22, 2226. (14) Kocher, N.; Leusser, D.; Murso, A.; Stalke, D. Chem. Eur. J. 2004, 10, 3622. (15) Cantat, T.; Ricard, L.; Le Floch, P.; Mezailles, N. Organometallics 2006, 25, 4965.

Note


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Table 1. Selected Bond Distances (A˚) and Bond Angles (deg) for Compounds 2-4 Compound 2 C(13)-P(1) P(1)-N(1) N(1)-P(1)-C(13) C(13)-P(2)-S(1)

1.820(3) C(13)-P(2) 1.547(2) P(2)-S(1) 113.0(1) P(1)-C(13)-P(2) 111.1(9) P(1)-N(1)-Si(1) Compound 3

1.831(3) 1.960(1) 122.5(1) 138.5(2)

Li(1)-S(1) P(1)-S(1) C(13)-P(1) Li(1)-O(1) S(1)-Li(1)-N(1) N(1)-P(2)-C(13) C(13)-P(1)-S(1)

2.484(6) Li(1)-N(1) 1.989(1) P(2)-N(1) 1.708(4) C(13)-P(2) 1.972(12) Li(1)-O(2) 106.2(2) Li(1)-N(1)-P(2) 118.1(2) P(2)-C(13)-P(1) 116.0(1) P(1)-S(1)-Li(1) Compound 4

2.065(6) 1.588(3) 1.715(3) 1.964(7) 112.2(2) 122.7(2) 101.6(1)

Li(1)-C(13) Li(1)-N(2) Li(2)-S(1) Li(3)-C(13) Li(3)-N(1) Li(4)-N(1) C(13)-P(1) P(1)-S(1) C(41)-P(3) P(3)-S(2) C(13)-Li(1)-C(41) S(1)-Li(2)-S(2) N(1)-Li(3)-S(2) Li(1)-C(13)-Li(3) P(1)-C(13)-P(2) C(13)-P(2)-N(1) P(1)-S(1)-Li(2) P(2)-N(1)-Li(4) C(41)-P(3)-S(2) P(3)-S(2)-Li(2) P(4)-N(2)-Li(1)

2.213(10) 2.141(10) 2.498(9) 2.211(10) 2.179(9) 2.043(11) 1.677(5) 2.042(2) 1.680(5) 2.046(2) 103.4(4) 139.1(4) 153.8(4) 76.0(4) 131.7(3) 104.1(2) 89.3(3) 94.2(4) 108.6(2) 91.3(3) 88.4(3)

2.210(10) 2.445(9) 2.450(10) 2.206(10) 2.446(8) 2.011(11) 1.685(5) 1.617(4) 1.687(5) 1.611(4) 153.5(5) 103.6(4) 171.8(6) 76.2(4) 109.1(2) 76.5(2) 87.5(3) 130.6(3) 103.6(2) 76.1(2) 94.4(4)

Li(1)-C(41) Li(1)-S(1) Li(2)-S(2) Li(3)-C(41) Li(3)-S(2) Li(4)-N(2) C(13)-P(2) P(2)-N(1) C(41)-P(4) P(4)-N(2) N(2)-Li(1)-S(1) C(13)-Li(3)-C(41) N(1)-Li(4)-N(2) Li(1)-C(41)-Li(3) C(13)-P(1)-S(1) P(1)-S(1)-Li(1) P(2)-N(1)-Li(3) P(3)-C(41)-P(4) C(41)-P(4)-N(2) P(3)-S(2)-Li(3) P(4)-N(2)-Li(4)


crystalline solid which is soluble in hydrocarbon solvents. It has been characterized by NMR spectroscopy and X-ray crystallography. The 31P NMR signals of 4 (δ 11.8, 17.7 ppm, 2 JP-P0 =21.7, 26.0 Hz) show upfield shifts compared with those of 3. The 1H NMR spectrum of 4 displays resonances for the SiMe3 and phenyl protons. It is noteworthy that there is no 13C NMR signal for the carbenic carbon. Similarly, there is no 13C NMR signal for the carbenic carbon in [(PPh2dS)2CdPd(PPh3)].7


The molecular structure of 4 is shown in Figure 3. Selected bond distances (A˚) and angles (deg) are given in Table 1. Compound 4 crystallized as a dimer in which the lithium atoms Li(1) and Li(3) are bridged by the two carbon atoms C(13) and C(41) and coordinated with one nitrogen and one sulfur atom of each ligand. The other lithium atoms, Li(2) and Li(4), are bridged by two sulfur and two nitrogen atoms, respectively. The molecular structure of 4 is different from that of [Li2{C(PPh2dNSiMe3)2}], which has an octahedral Li4C2 cluster.2a On the other hand, it is similar to that of [Li2{C(PPh2dS)2}], except that Li(2) is coordinated with one THF solvent molecule and has a short Li(4) 3 3 3 C(41) distance (2.560 A˚).13 The ligand chains N-P-C-P-S are almost planar, and the ligand planes are orthogonal to each other (85.7°). The Li(1)-C(13) and Li(1)-C(41) bonds (2.213(10), 2.210(10) A˚) are similar to those of [Li2{C(PPh2dS)2}] (2.159(5), 2.196(5) A˚)15 but are significantly shorter than those of [Li2{C(PPh2dNSiMe3)2}] (2.441(7), 2.451(7) A˚).2b Since the Li(2) and Li(4) atoms are coordinated away from the C(13) and C(41) carbon atoms (Li(2)C(13) = 3.525 A˚, Li(2)-C(41) = 3.503 A˚; Li(4)-C(13) = 2.577 A˚, Li(4)-C(41) = 2.560 A˚), this allows stronger interaction between the C(13), C(41) and Li(1), Li(3) atoms. Similar to the case for [Li2{C(PPh2dE)2}] (E = S, NSiMe3),2,15 the structure of compound 4 also features short P-C(13) bonds (1.677(5), 1.685(5) A˚), a long P(1)-S(1) bond (2.042(2) A˚), and a long P(2)-N(1) bond (1.617(4) A˚). It is noteworthy that the average P-C bond lengths shorten from 1.826 A˚ in 2 and 1.712 A˚ in 3 to 1.681 A˚ in 4, while the P-N bond lengths increase from 1.547(2) A˚ in 2 and 1.588(3) A˚ in 3 to 1.611(4) A˚ in 4. In addition, the P-S bond lengths increase from 1.960(1) A˚ in 2 and 1.989(1) A˚ in 3 to 2.042(2) A˚ in 4. These are due to the negative hyperconjugation from carbon to phosphorus σ* orbitals in 3 and 4.

Experimental Section General Procedure. All manipulations were carried out under an inert atmosphere of dinitrogen gas by standard Schlenk techniques. Solvents were dried over and distilled over Na/K alloy prior to use. 1 was prepared as described in the literature.9 The 1H, 13C, and 31P NMR spectra were recorded on a JEOL

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Table 2. Crystallographic Data for Compounds 2-4 formula Mr color cryst syst space group a/A˚ b/A˚ c/A˚ R/deg β/deg γ/deg V/A˚3 Z dcalcd/g cm-3 μ/mm-1 F(000) cryst size/mm index range no. of rflns collected R1, wR2 (I > 2σ(I)) R1, wR2 (all data) goodness of fit., F2 no. of data/restraints/params largest diff peak, hole/e A˚-3

2

3

4

C31.5H35NP2SSi 549.70 colorless monoclinic C2/c 36.025(2) 15.835(6) 11.096(4) 90.00 106.50(4) 90.00 6069.1(4) 8 1.203 0.272 2328 0.34 0.30 0.20 -44 e h e 44 -19 e k e 19 -13 e l e 13 45 386 0.0467, 0.1218 0.0735, 0.1607 1.152 5996/200/368 0.531, -0.686

C36H46LiNO2P2SSi 653.77 colorless triclinic P1 10.234(4) 13.653(5) 13.805(5) 80.61(2) 73.13(2) 82.87(2) 1815.0(1) 2 1.196 0.241 696 0.54 0.52 0.50 -13 e h e 13 -18 e k e 18 -18 e l e 18 37 909 0.0646, 0.1713 0.1086, 0.2597 1.137 9595/39/492 0.648, -1.255

C63H73Li4N2OP4S2Si2 1146.17 colorless monoclinic C2/c 41.092(2) 12.539(5) 27.462(1) 90.00 114.82(3) 90.00 12 842.5(11) 8 1.186 0.260 4840 0.40 0.10 0.06 -48 e h e 49 -14 e k e 14 -32 e l e 32 43 672 0.0674, 0.1723 0.1522, 0.2477 1.000 11 367/474/ 811 1.190, -0.774

ECA 400 spectrometer. The NMR spectra were recorded in C6D6. The chemical shifts δ are relative to SiMe4 for 1H and 13C and 85% H3PO4 for 31P. Elemental analyses were performed by the Division of Chemistry and Biological Chemistry, Nanyang Technological University. Melting points were measured in sealed glass tubes and were not corrected. [H2C(PPh2dS)(PPh2dNSiMe3)] (2). A solution of sulfur (41 mg, 1.29 mmol) in toluene (5 mL) was added dropwise to a solution of 1 (0.61 g, 1.29 mmol) in toluene (1.5 mL) at 0 °C over a period of 2 h. The reaction mixture was stirred for 1 h at 0 °C. After concentration, 2 was obtained as colorless crystals. Yield: 0.52 g (80.1%). Mp: 62 °C. Anal. Found: C, 66.42; H, 6.17; N, 2.46. Calcd for C28H31NP2SSi: C, 66.78; H, 6.21; N, 2.78. 1H NMR (399.5 MHz): δ 0.23 (s, 9H, SiMe3), 3.56 (dd, 2H, 2 JP-H = 12.36, 14.64 Hz, PCH2P), 6.91-7.04 (m, 12H, Ph), 7.36-7.42 (m, 4H, Ph), 8.06-8.12 (m, 4H, Ph). 13C{1H} NMR (100.5 MHz): δ 4.51 (SiMe3), 39.86 (dd, JP-C = 45.1, 68.04 Hz, PCH2P), 131.08, 131.11, 131.39, 131.42, 131.70, 131.80, 132.88, 132.98, 134.01, 134.84, 135.68, 135.70, 136.66, 136.68 (Ph). 31 P{1H} NMR (161.7 MHz): δ -5.23 (d, PPh2dNSiMe3, 2 JP-P0 =17.3 Hz), 36.7 (d, PPh2dS, 2JP-P0 =17.3 Hz). ESI-MS: m/z: 504 [M þ Hþ]. [Li{CH(PPh2dS)(PPh2dNSiMe3)}] (3). n-Butyllithium (0.58 mL, 2 M in cyclohexane, 1.2 mmol) was added dropwise to 1 (0.5 g, 1.0 mmol) in THF (10 mL) at -90 °C. The resulting yellow solution was raised to ambient temperature and stirred for 17 h. Volatiles from the mixture were removed under reduced pressure, and the residue was extracted with THF/ hexane. After filtration and concentration of the filtrate, 3 was obtained as colorless crystals. Yield: 0.40 g (78%). Mp: 96 °C. Anal. Found: C, 65.91; H, 7.07; N, 1.96. Calcd for C28H30NLiP2SSi 3 2THF: C, 66.13; H, 7.10; N, 2.14. 1H NMR (399.5 MHz): δ 0.21 (s, 9H, SiMe3), 2.17 (d, 1H, 2JP-H =3.68 Hz, PCHP), 6.95-7.05 (m, 12H, Ph), 7.87-7.92 (m, 4H, Ph), 8.07-8.12 (m, 4H, Ph). 13C{1H} NMR (99.5 MHz): δ 4.47 (SiMe3), 21.81 (dd, JP-C = 91.5, 126.4 Hz, PCHP), 129.83, 129.85, 129.94, 129.97, 131.52, 131.64, 131.85, 131.96, 140.16, 140.21, 141.03, 141.08, 141.10, 141.16, 141.86, 141.91 (Ph). 31P{1H} NMR

(161.7 MHz): δ 16.1 (d, PPh2dNSiMe3, 2JP-P0 =21.7 Hz), 35.4 (d, PPh2dS, 2JP-P0 =21.7 Hz). [Li2{C(PPh2dS)(PPh2dNSiMe3)}] (4). tert-Butyllithium (1.17 mL, 1.7 M in pentane, 2.0 mmol) was added dropwise to 1 (0.5 g, 1.0 mmol) in diethyl ether (6.3 mL) at -90 °C. The resulting yellow solution was raised to ambient temperature and stirred for 1 h. Volatiles from the mixture were removed under reduced pressure, and the residue was extracted with THF/ hexane. After filtration and concentration of the filtrate, 4 was obtained as colorless crystals. Yield: 0.45 g (88%). Mp: 141 °C. Anal. Found: C, 64.97; H, 5.42; N, 2.45. Calcd for C56H58Li4N2P4S2Si2: C, 65.22; H, 5.67; N, 2.72. 1H NMR (395.9 MHz): δ 0.12 (s, 9H, SiMe3), 6.77-7.06 (m, 12H, Ph), 7.53-7.58 (m, 2H, Ph), 7.68-7.76 (m, 4H, Ph), 7.94-8.00 (m, 2H, Ph). 13C{1H} NMR (99.55 MHz): δ 4.66 (SiMe3), 128.92, 129.39, 129.51, 129.68, 129.77, 130.86, 130.97, 131.31, 131.41, 131.67, 131.78, 132.04, 132.15, 132.41, 132.58, 138.22, 140.98, 141.75, 141.80, 142.32, 142.51, 142.54, 143.07, 143.19 (Ph). 31P{1H} NMR (160.3 MHz): δ 11.8 (d, 2JP-P0 =21.7 Hz), 17.7 (d, 2JP-P0 =26.0 Hz). X-ray Data Collection and Structural Refinement. Intensity data for compounds 2-4 were collected using a Bruker APEX II diffractometer. The crystals of 2-4 were measured at 173(2) K. The structures were solved by direct phase determination (SHELXS-97) and refined for all data by full-matrix leastsquares methods on F2.16 All non-hydrogen atoms were subjected to anisotropic refinement and were generated geometrically and allowed to ride on their respective parent atoms. A summary of X-ray data is given in Table 2.

Acknowledgment. This work was supported by the Academic Research Fund Tier 1 (RG 47/08). Supporting Information Available: CIF files giving X-ray data for 2-4. This material is available free of charge via the Internet at http://pubs.acs.org. (16) Sheldrick, G. M. SHELXL-97; Universit€at G€ottingen, G€ottingen, Germany, 1997.

Synthesis and Structure of [Li2C(PPh2 NSiMe3)(PPh2 S)]: A Geminal

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