Group 14 Substituted Carbyne Complexes—An Almost Complete Set

Organometallics 2011, 30, 139–144 DOI: 10.1021/om100896r

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Group 14 Substituted Carbyne Complexes;An Almost Complete Set: [Mo(tCAPh3)(CO)2(Tp*)] (Tp* = Hydrotris(dimethylpyrazolyl) borate; A = Si, Ge, Sn, Pb but A 6¼ C) Richard L. Cordiner, Anthony F. Hill,* Rong Shang and Anthony C. Willis Research School of Chemistry, Institute of Advanced Studies, Australian National University, Canberra, Australian Capital Territory, Australia Received September 16, 2010

The successive reactions of [Mo(tCBr)(CO)2(Tp*)] (Tp* = hydrotris(3,5-dimethylpyrazol-1yl)borate) with nBuLi and ClAPh3 (A = Ge, Sn, Pb) afford the carbyne complexes [Mo(tCAPh3)(CO)2(Tp*)] but fail in the case of ClCPh3 and ClSiPh3. The silicon analogue [Mo(tCSiPh3)(CO)2(Tp*)] may, however, be obtained via a multistep Fischer-Mayr synthesis. [Mo(tCPbPh3)(CO)2(Tp*)] is the first example of a plumbyl alkylidyne complex. Introduction Carbyne complexes LnMtCR have been obtained with a wide range or organic substituents “R”, including alkyl, aryl, alkenyl, acyl, and alkynyl groups.1 For alkylidyne complexes bearing hydrocarbon substituents the three most commonly employed synthetic routes are (i) Fischer’s archetypal alkoxide abstraction from an alkoxycarbene complex,2 (ii) Schrock’s R-hydrogen abstraction/elimination routes,3 and (iii) Schrock’s alkyne cleavage reactions with [W2(OtBu)6].4 Carbyne complexes bearing heteroatom substituents are somewhat less widely represented, in part because routes ii and iii are seldom appropriate while Fischer’s protocol requires in the first instance that the carbyne substituent be introduced via nucleophilic attack at a carbonyl ligand, thereby placing some limitations on the range of potential heteroatom nucleophiles. This approach has been widely employed in the case of aminomethylidynes5 but for few other heteroatom groups. Heterocarbonyl ligands (CS, CSe, CTe, CNR) bound to especially π-basic metal centers (typically octahedral d6)

may undergo attack at the heteroatom β to the metal, an approach that has afforded access to amino6 and chalcogenolato carbynes.7 The discovery of halocarbyne complexes by Lalor8 significantly increased the range of potential carbyne substituents that could be introduced via nucleophilic halide substitution,1a a process that may in some cases be catalytically mediated by palladium phosphine complexes.9 However, recently we reported that halocarbyne complexes could in effect undergo “umpolung” via lithium/halogen exchange with nBuLi to generate lithium carbido complexes in which the carbido carbon displayed nucleophilic character10 toward a wide range of electrophiles (Scheme 1). This builds upon the

(1) For reviews on alkylidyne complexes see: (a) Caldwell, L. M. Adv. Organomet. Chem. 2008, 57, 1. (b) Kim, H.-S.; Angelici, R. J. Adv. Organomet. Chem. 1987, 27, 51. (c) Mayr, A.; Hoffmeister, H. Adv. Organomet. Chem. 1991, 32, 227. (d) Mayr, A.; Ahn, S. Adv. Transition Met. Coord. Chem. 1996, 1, 1. (e) Transition Metal Carbyne Complexes; Kreissl, F. R., Ed.; Kluwer: Dordrecht, The Netherlands, 1992; NATO ASI Series C392. (f) Gallop, M. A.; Roper, W. R. Adv. Organomet. Chem. 1986, 25, 121. (g) Jia, G. Coord. Chem. Rev. 2007, 251, 2167. (h) Da Re, R. E.; Hopkins, M. D. Coord. Chem. Rev. 2005, 249, 1396. (i) Fischer, H.; Hofmann, P.; Kreissl, F. R.; Schrock, R. R.; Schubert, U.; Weiss, K. Carbyne Complexes; VCH: Weinheim, Germany, 1988. (2) Fischer, E. O.; Kreis, G.; Kreiter, C. G.; M€ uller, J.; Huttner, G.; Lorenz, H. Angew. Chem., Int. Ed. Engl. 1973, 12, 564. (3) (a) Schrock, R. R. Chem. Commun. 2005, 2773. (b) Schrock, R. R. Chem. Rev. 2002, 102, 145. (c) Schrock, R. R. Dalton Trans. 2001, 2541. (4) Listemann, M. L.; Schrock, R. R. Organometallics 1985, 4, 74. (5) (a) Fischer, E. O.; Huttner, G.; Kleine, W.; Frank, A. Angew. Chem. 1975, 87, 781. (b) Schubert, U.; Neugebauer, D.; Hofmann, P.; Schilling, B. E. R.; Fischer, H.; Motsch, A. Chem. Ber. 1981, 114, 3349. (c) Filippou, A. C.; Portius, P.; Jankowski, C. J. Organomet. Chem. 2001, 617, 656. (d) Lungwitz, B.; Filippou, A. C. J. Organomet. Chem. 1995, 498, 91. (e) Anderson, S.; Hill, A. F.; Ng, Y. T. Organometallics 2000, 19, 15. (f) Cook, D. J.; Hill, A. F. Organometallics 1997, 16, 5616. (g) Anderson, S.; Hill, A. F. J. Organomet. Chem. 1990, 394, C24.

(6) (a) Pombeiro, A. J. L.; Guedes da Silva, M. F. C.; Michelin, R. A. Coord. Chem. Rev. 2001, 218, 43. (b) Gamble, A. S.; White, P. S.; Templeton, J. L. Organometallics 1991, 10, 693. (c) Filippou, A. C.; Gruenleitner, W.; Herdtweck, E. J. Organomet. Chem. 1989, 373, 325. (d) Filippou, A. C.; Fischer, E. O.; Gruenleitner, W. J. Organomet. Chem. 1990, 386, 333. (e) Filippou, A. C.; Gruenleitner, W.; Kiprof, P. J. Organomet. Chem. 1991, 410, 175. (f) Filippou, A. C.; Wagner, C.; Fischer, E. O.; Voelkl, C. J. Organomet. Chem. 1992, 438, C15. (7) (a) Dombek, B. D.; Angelici, R. J. Inorg. Chem. 1976, 15, 2397. (b) Greaves, W. W.; Angelici, R. J. Inorg. Chem. 1981, 20, 2983. (c) Greaves, W. W.; Angelici, R. J.; Helland, B. J.; Klima, R.; Jacobson, R. A. J. Am. Chem. Soc. 1979, 101, 7618. (d) Kim, H. P.; Kim, S.; Jacobson, R. A.; Angelici, R. J. Organometallics 1986, 5, 2481. (e) Cade, I. A.; Hill, A. F.; McQueen, C. M. A. Organometallics 2009, 28, 6639. (f) Fortune, J.; Manning, A. R. Organometallics 1983, 2, 1719. (8) Lalor, F. J.; Desmond, T. J.; Cotter, G. M.; Shanahan, C. A.; Ferguson, G.; Parvez, M.; Ruhl, B. J. Chem. Soc., Dalton Trans. 1995, 1709. (a) Lalor, F. J.; O'Neill, S. A. J. Organomet. Chem. 2003, 684, 249. (b) Chaona, S.; Lalor, F. J.; Ferguson, G.; Hunt, M. M. J. Chem. Soc., Chem. Commun. 1988, 1606. (c) Desmond, T.; Lalor, F. J.; Ferguson, G.; Parvez, M. J. Chem. Soc., Chem. Commun. 1984, 75. (d) Weber, L.; Dembeck, G.; Boese, R.; Blaeser, D. Organometallics 1999, 18, 4603. (e) Weber, L.; Dembeck, G.; Boese, R.; Blaser, D. Chem. Ber. 1997, 130, 1305. (f) Woodworth, B. E.; Templeton, J. L. J. Am. Chem. Soc. 1996, 118, 7418. (g) Jamison, G. M.; White, P. S.; Templeton, J. L. Organometallics 1991, 10, 1954. (h) Etienne, M.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 2324. (i) Cordiner, R. L.; Hill, A. F.; Wagler, J. Organometallics 2008, 27, 4532. (9) (a) Armitt, D. J.; Bruce, M. I.; Gaudio, M.; Zaitseva, N. N.; Skelton, B. W.; White, A. H.; Le Guennic, B.; Halet, J.-F.; Fox, M. A.; Roberts, R. L.; Hartl, F.; Low, P. J. Dalton Trans. 2008, 6763. (b) Bruce, M. I.; Cole, M. L.; Gaudio, M.; Skelton, B. W.; White, A. H. J. Organomet. Chem. 2006, 691, 4601. (c) Cordiner, R. L.; Gugger, P. A.; Hill, A. F.; Willis, A. C. Organometallics 2009, 28, 6632. (10) Cordiner, R. L.; Hill, A. F.; Wagler, J. Organometallics 2008, 27, 5177.

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Scheme 1. Umpolung of Halocarbyne Reactivity (M = Mo, W; X = Cl, Br; Nu-; Eþ = Generalized Nucleophiles and Electrophiles)10

work of Templeton11 and Cummins,12 who had previously demonstrated the synthetic utility of group 6 anionic carbido complexes. With this alternative mode of reactivity now easily available, we have addressed the question of carbyne complexes in which the carbyne substituent is a heavier element of group 14. A small number of silyl carbynes have been reported,13 while (11) (a) Enriquez, A. J.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 2001, 123, 4992. (b) Jamison, G. M.; Bruce, A. E.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 5057. (12) (a) Peters, J. C.; Odom, A. L.; Cummins, C. C. Chem. Commun. 1997, 1995. (b) Greco, J. C.; Peters, J. C.; Baker, T. A.; Davis, W. M.; Cummins, C. C.; Wu, G. J. Am. Chem. Soc. 2001, 123, 5003. (c) Agapie, T.; Diaconescu, P. L.; Cummins, C. J. Am. Chem. Soc. 2002, 124, 2412. (13) (a) Fischer, E. O.; Hollfelder, H.; Kreissl, F. R. Chem. Ber. 1979, 112, 2177. (b) Fischer, E. O.; Hollfelder, H.; Friedrich, P.; Kreissl, F. R.; Huttner, G. Angew. Chem., Int. Ed. 1977, 16, 401. (c) Uedelhoven, W.; Eberl, K.; Kreissl, F. R. Chem. Ber. 1979, 112, 3376–89. (d) Andersen, R. A.; Chisholm, M. H.; Gibson, J. F.; Reichert, W. W.; Rothwell, I. P.; Wilkinson, G. Inorg. Chem. 1981, 20, 3934. (e) Ahmed, K. J.; Chisholm, M. H.; Huffman, J. C. Organometallics 1985, 4, 1168. (f) Savage, P. D.; Wilkinson, G.; Motevalli, M.; Hursthouse, M. B. Polyhedron 1987, 6, 1599. (g) Jeffery, J. C.; Ruiz, M. A.; Stone, F. G. A. J. Organomet. Chem. 1988, 355, 231. (h) Caulton, K. G.; Chisholm, M. H.; Streib, W. E.; Xue, Z. J. Am. Chem. Soc. 1991, 113, 6082. (i) Seidel, S. W.; Schrock, R. R.; Davis, W. M. Organometallics 1998, 17, 1058. (j) Giannini, L.; Solari, E.; Dovesi, S.; Floriani, C.; Re, N.; Chiesi-Villa, A.; Rizzoli, C. J. Am. Chem. Soc. 1999, 121, 2784. (k) Wadepohl, H.; Arnold, U.; Pritzkow, H.; Calhorda, M. J.; Veiros, L. F. J. Organomet. Chem. 1999, 587, 233. (l) Safronova, A. V.; Bochkarev, L. N.; Stolyarova, N. E.; Grigor'eva, I. K.; Malysheva, I. P.; Basova, G. V.; Fukin, G. K.; Kursky, Y. A.; Khorshev, S. Y.; Abakumov, G. A. Russ. Chem. Bull. 2003, 52, 2140. (m) Balazs, G.; Sierka, M.; Scheer, M. Angew. Chem., Int. Ed. 2005, 44, 4920. (n) Hock, A. S.; Schrock, R. R. Chem. Asian J. 2007, 2, 867. (o) Jamison, G. M.; White, P. S.; Harris, D. L.; Templeton, J. L. In Transition Metal Carbyne Complexes; Kreissl, F. R., Ed.; Kluwer Academic: Dordrecht, The Netherlands, 1992; Proceedings of the NATO Advanced Research Workshop on Transition Metal Carbyne Complexes, Wildbad Kreuth, Germany, p 201. (p) Hill, A. F. In Transition Metal Carbyne Complexes; Kreissl, F. R., Ed.; Kluwer Academic: Dordrecht, The Netherlands, 1992, Proceedings of the NATO Advanced Research Workshop on Transition Metal Carbyne Complexes, Wildbad Kreuth, Germany, p 239. (14) Safronova, A. V.; Bochkarev, L. N.; Stolyarova, N. E.; Grigor’eva, I. K.; Malysheva, I. P.; Basova, G. V.; Fukin, G. K.; Baranov, E. V.; Kurskii, Y. A.; Abakumov, G. A. Russ. Chem. Bull. 2006, 55, 218. (15) The implausible complex (TPP)Sn{CtRe(CO)3}2 has been claimed but is almost certainly (TPP)Sn{OReO3}2: Noda, I.; Kato, S.; Mizuta, M.; Yasuoka, N.; Kasai, N. Angew. Chem., Int. Ed. Engl. 1979, 18, 83. (16) Selected leading references: (a) Van Beelen, D. C.; Wolters, J.; De Vos, D. Main Group Met. Chem. 1998, 21, 55. (b) Wrackmeyer, B.; Kehr, G.; Wettinger, D.; Milius, W. Main Group Met. Chem. 1993, 16, 445. (c) Dallaire, C.; Brook, M. A.; Bain, A. D.; Frampton, C. S.; Britten, J. F. Can. J. Chem. 1993, 71, 1676. (d) Wrackmeyer, B.; Horchler von Locquenghien, K. Main Group Met. Chem. 1990, 13, 387. (e) Moloney, M. G.; Pinhey, J. T.; Roche, E. G. Tetrahedron Lett. 1986, 27, 5025. (f) Nast, R.; Grouhi, H. J. Organomet. Chem. 1980, 186, 207. (f) Nast, R.; Grouhi, H. J. Organomet. Chem. 1979, 182, 197. (g) Puddephatt, R. J.; Thistlethwaite, G. H. J. Organomet. Chem. 1972, 40, 143. (h) Siebert, W.; Davidsohn, W. E.; Henry, M. C. J. Organomet. Chem. 196917, 65. (i) Davies, A. G.; Puddephatt, R. J. J. Chem. Soc. C 1968, 317. (j) Beermann, C.; Hartmann, H. Z. Anorg. Allg. Chem. 1954, 276, 20.

Cordiner et al.

very rare examples of germyl-14 and stannyl-substituted14a,15 carbynes have been obtained recently via extension of Schrock’s alkyne cleavage approach.3,4 Carbyne complexes bearing lead, the most metallic of nonmetals, as a substituent are unknown. Indeed, alkynyl plumbanes have received comparatively little attention16 and structural data are limited to the diyne Ph3PbCtCCtCPbPh317 and the very recent report of the plumbous derivative [PbII(CtCPh){(NRCMe)2CH}] (R = C6H3iPr2-2,6).18 The lack of interest in alkynyl plumbanes as synthetic reagents presumably reflects their increased toxicity (cf. widely employed alkynyl stannanes) and the potentially explosive nature of heavy-metal acetylides.19 We have therefore investigated the possibility that carbynes of the heavier group 14 elements might be accessible via the umpolung approach and have attempted to prepare, for the first time, the complete analogous series [Mo(tCAPh3)(CO)2(Tp*)] (A = C (1), Si (2), Ge (3), Sn (4), Pb (5); Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate) that includes each and every group 14 element. This goal has not been completely realized. The more exotic germanium, tin, and lead derivatives were readily obtained, while the silicon example 2, though accessed, required an alternative synthetic route and the more mundane carbon congenor 1 remains elusive.

Results and Discussion The successive treatment of [Mo(tCBr)(CO)2(Tp*)] (6) with nBuLi (to afford [Mo(tCLi)(CO)2(Tp*)] (7)) and Me3SiCl affords the silyl carbyne complex [Mo(tCSiMe3)(CO)2(Tp*)] (8) in high yield.10 This complex is an analogue of the complexes [M(tCSiMe2Ph)(CO)2(Tp*)] (M = Mo, W) reported previously by Templeton and obtained via a FischerMayr approach.13o We now find that a similar strategy employing ClAPh3 (A = Ge, Sn, Pb) affords the new carbyne complexes [Mo(tCAPh3)(CO)2(Tp*)] (A = Ge (3), Sn (4), Pb (5); Scheme 2), including the first example of a leadsubstituted carbyne complex and very rare examples of germanium and tin carbynes. Somewhat surprisingly, the same reaction employing ClSiPh3 failed, with the only isolated organometallic species being the previously reported bimetallic complexes [Mo2(μ-C2)(CO)4(Tp*)2] (9)20 and [Mo2(μ-CCH2)(CO)4(Tp*)2] (10).13o,21 The complex 9 typically arises from outer-sphere single electron oxidation of [Mo(tCLi)(CO)2(Tp*)], while 10 arises from proton abstraction via the intermediacy of the parent methylidyne complex [Mo(tCH)(CO)2(Tp*)] (11), which dimerizes under ambient conditions.13o,21 Given that no problems accompany the synthesis of [Mo(tCSiMe3)(CO)2(Tp*)] (8), it would seem that electron transfer begins to compete effectively with diamagnetic (electrophile/nucleophile) pathways when steric factors become intrusive. This would also account for the failure to isolate the trityl derivative [Mo(tCCPh3)(CO)2(Tp*)] (1), given that Gomberg’s Ph3C• radical (and its dimer) has extensive (17) Brouty, C.; Spinat, P.; Whuler, A. Acta Crystallogr., Sect. B: Struct. Crystallogr. Cryst. Chem. 1980, 36, 2624. (18) Jana, A.; Sarish, S. P.; Roesky, H. W.; Schulzke, C.; Doring, A.; John, M. Organometallics 2009, 28, 2563. (19) Dewhurst, R. D.; Hill, A. F.; Smith, M. K. Organometallics 2006, 25, 2388. (20) Colebatch, A. L.; Cordiner, R. L.; Hill, A. F.; Nguyen, K. T. H. D.; Shang, R.; Willis, A. C. Organometallics 2009, 28, 4394. (21) Colebatch, A. L.; Hill, A. F.; Shang, R.; Willis, A. C. Organometallics 2010, 29, 6482. (22) Gomberg, M. J. Am. Chem. Soc. 1901, 23, 496.

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Scheme 2. Synthesis of Tetrel-Substituted Carbynes

Figure 1. Molecular structure of [Mo(tCSnPh3)(CO)2(Tp*)] (4) in the crystal form (60% displacement ellipsoids, hydrogen atoms omitted for clarity). Selected bond lengths (A˚) and angles (deg): N11-Mo1 = 2.334(2), N21-Mo1 = 2.223(2), N31-Mo1 = 2.226(2), C1-Mo1 = 1.795(3), C1-Sn1 = 2.136(3), C2-Mo1 = 1.997(3), C3-Mo1 = 2.006(3); Mo1-C1-Sn1 = 172.80(15), N11-Mo1-N31 = 81.58(8), N11-Mo1-N21 = 79.33(8), N31Mo1-N21 = 84.49(8), C3-Mo1-C2 = 86.07(12), C3Mo1-C1 = 84.73(12), C2-Mo1-C1 = 83.26(11). Scheme 3. Synthesis of [Mo(tCSiPh3)(CO)2(Tp*)] (2) via Acylate Oxide Abstraction

chemistry.22 This is in contrast to the reaction of [Mo(tCLi)(CO)2(Tp*)] with iodomethane, which cleanly affords [Mo(tCMe)(CO)2(Tp*)] (12).10 Previously, Templeton13o,23 and we13p have reported that the Mayr modification24 of Fischer’s acylate oxide abstraction protocol25,5b could be extended to silyl carbynes. Acccordingly, the required complex [Mo(tCSiPh3)(CO)2(Tp*)] (2) was prepared via the multistep sequence outlined in Scheme 3. Although the overall yield was rather poor (9.4%) and was not optimized, it served to provide the missing benchmark compound 2. Complexes 2-5 were each crystallographically characterized. Although the crystals selected for diffractometry were not crystallographically isomorphous, to the naked eye the derived ORTEP representations are essentially indistinguishable. Accordingly, only a single displacement ellipsoid view of 4 (Figure 1) and displacement ellipsoid and space-filling representations of 5 (Figure 2) are presented. All four molecular structures have similar features with regard to the “Tp*Mo(CO)2” unit, which is unremarkable other than to note the usual trans influence of the carbyne ligand upon the trans pyrazolyl donors, the Mo-N bond lengths of which are in each case elongated relative to the remaining two N-Mo bond lengths. (23) Jamison, G. M.; Bruce, A. E.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 5057. (24) Mayr, A.; McDermott, G. A. Organometallics 1985, 4, 608. (25) (a) Fischer, H.; Fischer, E. O. J. Organomet. Chem. 1974, 69, C1. (b) Himmelreich, D.; Fischer, E. O. Z. Naturforsch. 1982, 37B, 1218.

Figure 2. (a) Molecular structure of [Mo(tCPbPh3)(CO)2(Tp*)] (5) in the crystal form (60% displacement ellipsoids, hydrogen atoms omitted for clarity). The molecule straddles a crystallographic mirror plane that bisects the intercarbonyl angle (asterisks indicate symmetry-derived positions). (b) Space-filling representation of 5 (Tp* light gray, PbPh3 dark gray, tC black). Selected bond lengths (A˚) and angles (deg): Pb1-C1 = 2.217(6), Pb1-C21 = 2.210(4), Pb1-C31 = 2.213(7), Mo1N11 = 2.217(3) Mo1-C11 = 1.999(5), Mo1-N21 = 2.349(5), Mo1-C1 = 1.798(6); C21-Pb1-C1 = 111.66(14), C21-Pb1C21* = 112.8(2), C21-Pb1-C31 = 103.46(14), C1-Pb1-C31 = 113.3(2), N11-Mo1-N11* = 80.49(19), N11-Mo1-N21 = 82.39(12), C11-Mo1-C1 = 84.78(19), C11-Mo1-C11* = 86.8(3), Pb1-C1-Mo1 = 169.7(3).

This may be quantified by “TR”, the ratio of the Mo-N bond trans to the carbyne vs the average value for the cis pyrazolyl groups, and while it is significant for each complex, the effect is comparable in magnitude for each (1.05-1.06).

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Table 1. Selected Structural and Spectroscopic Data param -1 a

νCO (cm )

kCO (N m-1)b δC(MoC)c r(MotC) (A˚) — MoCA (deg) r(C-A) (A˚) TRd c

2 (Si)

3 (Ge)

4 (Sn)

5 (Pb)

2000 1893 15.92 351.8 1.809 174.6 1.864 1.05

1999 1914 15.44 344.1 1.786 176.0 1.952 1.06

1997 1913 15.42 349.9 1.795 172.8 2.136 1.05

1996 1911 15.39 345.5 1.798 169.7 2.217 1.06

a Measured in THF. b Cotton-Kraihanzel forcePconstant (mdyn/A˚);18 Measured in CDCl3 (ppm). d TR = 2r(MoNtrans)/ r(MoNcis).

Structural data for poly(pyrazolyl)borate-ligated carbyne complexes have been reviewed recently,1a and Table 1 collates structural and spectroscopic data of interest, from which it can be seen that the typically short MotC alkylidyne bond length is essentially invariant down the group, within the limits of precision (6 esd, ca. 0.02 A˚). There is, however, a marginal trend in the deformation of the MotC-A angle on descending the group, though such deformations for carbyne complexes are typically attributed to crystal-packing effects rather than electronic origins1a and angles as small as 163
have been observed in related systems.26 As noted above, structural data for alkynyl plumbanes are limited to Ph3PbCtCCtCPbPh3 (Pb-C = 2.203 A˚)17 and [PbII(CtCPh){(NRCMe)2CH}] (Pb-C = 2.275 A˚).18 The remaining examples of compounds with two-coordinate carbon bound to lead for which structural data are available are the five-coordinate anionic cyanide complex [Pb(CN)(2,6-bis(1-(salicyloylhydrazono)ethyl)pyridine]- (Pb-C = 2.358 A˚)27 and the isonitrile adduct [Pb{Si(SiMe3)3}2(CNtBu)] (Pb-C = 2.496 A˚).28 Thus, the Pb-C bond length of 2.217(6) A˚ observed in 5 is most similar to those for the alkynyl plumbanes, though the steric congestion associated with accommodating the bulky “CMo(CO)2(Tp*)” group no doubt moderates this. Bonding within the MotC-Pb linkage would therefore appear to be in all respects entirely conventional and there is no need to invoke any mesomeric contribution to the bonding. Furthermore, the geometry adopted by 5 is not dissimilar to those observed for 2-4, other than minor differences in the phenyl substituent conformations. Thus, although 5 is novel, there would not appear to be anything untoward as a result of including this 6p element as a carbyne substituent. Carbyne complexes bearing 6p main-group elements as substituents are unknown, and 5p examples are limited to the methyltellurolatocarbynes [Mo(tCTeMe)(CO)2(Tp*)]10 and [Os(tCTeMe)(CO)2(PPh3)2]SbF6,29 stannylcarbynes 4, and [PhnSn{CtW(OtBu)3}4-n] (n=2, 3)13a and the unstable iodocarbynes [M(tCI)(CO)2(Tp*)] (M=Mo,8 W11). The isolation of 5, which is thermally stable though mildly light sensitive, suggests that further chemistry may follow for these heavier main-group elements. In conclusion, the halocarbyne umpolung strategy has allowed the synthesis and comparative characterization of the first almost complete set of group 14 substituted carbyne (26) (a) Caldwell, L. M.; Hill, A. F.; Wagler, J.; Willis, A. C. Dalton Trans. 2008, 3538. (b) Caldwell, L. M.; Hill, A. F.; Rae, A. D.; Willis, A. C. Organometallics 2008, 27, 341. (27) Pedrido, M.; Romero, M. J.; Bermejo, M. R.; Gonzalez-Noya, A. M.; Maneiro, M.; Rodriguez, M. J.; Zaragoza, G. Dalton Trans. 2006, 5304. (28) Klinkhammer, K. Polyhedron 2002, 21, 587. (29) Roper, W. R. J. Organomet. Chem. 1986, 300, 167.

complexes, including the first to bear a 6p element. The few reactivity studies on silylcarbynes have on occasion revealed interesting divergences with hydrocarbyl carbynes,13 while the reactivity of germyl, stannyl, and plumbyl carbynes is yet to be explored, a matter we are now attending to.

Experimental Section General Considerations. All manipulations were carried out under a dry and oxygen-free nitrogen atmosphere using standard Schlenk, vacuum-line, and inert-atmosphere drybox (argon) techniques, with dried and degassed solvents which were distilled from either calcium hydride (CH2 Cl 2) or sodiumpotassium alloy and benzophenone (ethers and paraffins). NMR spectra were obtained at 25
C on a Varian Gemini 300BB spectrometer (1H at 299.95 MHz and 13C at 75.428 MHz, referenced to external SiMe4; 119Sn at 111.85 Hz, referenced to external SnMe4). Elemental microanalysis was performed by the microanalytical service of the Australian National University. Electrospray (ESI) mass spectrometry was performed by the Research School of Chemistry mass spectrometry service. Typically a sample was dissolved in dichloronmethane and then diluted with methanol or acetonitrile. Data for X-ray crystallography were collected with a Nonius Kappa CCD diffractometer. The complex [Mo(tCBr)(CO)2(Tp*)] (1)10 was prepared according to the indicated published procedure. All other reagents were used as received from commercial sources. Synthesis of [Mo(tCSiPh3)(CO)2(Tp*)] (2) (Not Optimized). A solution of LiSiPh3 in THF was prepared as follows: under an atmosphere of dry argon, a lithium dispersion (2.00 g, 30% in parrafin oil) was placed in a Schlenk tube and washed with hexane by decantation (4  30 mL). To the residue was added chlorotriphenylsilane (5.00 g, 16.9 mmol) and five small roughened glass beads and a magnetic stirbar. Tetrahydrofuran (50 mL) was added and the mixture stirred vigorously for 2 h. In a separate round-bottom flask equipped with a pressure-equalized dropping funnel was placed [Mo(CO)6] (3.75 g, 14.2 mmol) and THF (100 mL). The solution of LiSiPh3 obtained above was transferred to the dropping funnel via cannula filtration and then added dropwise to the stirred suspension of [Mo(CO)6] over a period of 15 min (monitored by IR spectroscopy). The mixture was then cooled (dry ice/propanone), and to this was added trifluoroacetic anhydride (2.00 mL, d = 1.511 g/mL, 14.4 mmol) over a period of 15 min. The mixture was maintained at this temperature for 25 min and then warmed slowly to room temperature over 1 h. The mixture was recooled to -78
C, and then solid K[Tp*] (5.00 g, 14.9 mmol) was added in one portion. The mixture was stirred at this temperature for 12 h and then warmed to room temperature and freed of volatiles under reduced pressure. The orange residue was chromatographed (silica gel), first with hexane as eluent to give re-formed [Mo(CO)6]. Subsequent elution with a mixture of dichloromethane and hexane (1:2) afforded an orange-yellow band, which was collected and freed of volatiles. The residue was then recrystallized from dichloromethane and hexane (-18
C) to provide light orangeyellow crystals. Yield 0.96 g (1.33 mmol, 9.4%). Anal. Found: C, 60.05; H, 5.18; N, 11.39. Calcd for C36H37BMoN6O2Si: C, 60.01; H, 5.18; N, 11.66. IR (cm-1): Nujol, 1991, 1906 νCO, 1540 νCN; hexane, 2005, 1923 νCO, 1540 νCN; THF, 2000, 1917 νCO, 1540 νCN. NMR (CD2Cl2, 25
C): 1H, δH 2.29, 2.30 (s  2, 3 H  2, pzCH3), 2.21, 2.38 (s  2,6 H  2, pzCH3), 5.73 (s, 1 H, pzH), 5.84 (s, 2 H, pzH), 7.35-7.66 (m, 15 H, C6H5); 13C{1H}, δC 351.8 (MotC), 288.8 (CO), 151.8, 151.5, 145.9, 145.6 (C3,5(pz)), 136.4, 134.1. 130.0, 128.2 (C6H5), 106.6, 106.4 (C4(pz)), 14.38, 12.65 (1 C  2, pzCH3), 16.25, 12.99 (2 C  2, pzCH3). ESI-MS: m/z 692.5 [M - CO]þ, 664.5 [M - 2CO]þ. Crystal data for 2: C36H37BMoN6O2Si, Mr = 720.57, T = 200(2) K, triclinic, space group P1 (No. 2), a = 10.3477(2) A˚, b = 12.1245(3) A˚, c = 14.3177(3) A˚, R = 101.4756(11)
, β = 91.0133(14)
, γ = 95.6878(13)
, V = 1750.44(7) A˚3, Z = 2, Fcalcd = 1.367 Mg m-3,

Article μ(Mo KR) = 0.450 mm-1, pale yellow plate, 0.04  0.12  0.38 mm, 31 719 measured reflections with 2θmax = 52.7
, 7135 independent reflections, 7115 absorption-corrected data used in F2 refinement, 424 parameters, R1 = 0.0313, wR2 = 0.0845 for 5504 reflections with I > 2σ(I) (CCDC 793429). Synthesis of [Mo(tCGePh3)(CO)2(Tp*)] (3). An oven-baked Schlenk tube was allowed to cool under an atmosphere of dry nitrogen and then charged with [Mo(tCBr)(CO)2(Tp*)] (0.400 g, 0.74 mmol) and tetrahydrofuran (20 mL). The stirred solution was cooled to -78
C and then treated with a solution of nBuLi in hexane (0.30 mL, 2.5 M, 0.75 mmol) and stirred for 15 min. Solid chlorotriphenylgermane (0.251 g, 0.74 mmol) was added in a single portion, and the mixture was warmed slowly to 0
C to afford an orange solution which was stirred at this temperature for 30 min. The solvent was then removed under reduced pressure, the residue was extracted with dichloromethane, and the combined extracts were filtered through diatomaceous earth, diluted with petroleum spirit (40-60
C bp), and slowly concentrated to afford a yellow solid that was then recrystallized from a mixture of dichloromethane and hexane (-18
C). Yield: 0.34 g (0.44 mmol, 59%). Anal. Found: C, 56.80; H, 4.66; N, 10.90. Calcd for C36H37BGeMoN6O2: C, 56.52; H, 4.87; N, 10.98. IR (cm-1): Nujol, 2549 w νBH, 1990 s, 1903 vs νCO, 1541 νCN; THF, 1999 s, 1914 vs νCO, 1543 νCN. NMR (C6H6, 25
C): 1H, δH 2.04, 2.32 (s  2, 3 H  2, pzCH3), 2.05, 2.48 (s  2, 6 H  2, pzCH3), 5.36 (s, 1 H, pzH), 5.57 (s, 2 H, pzH), 7.15 (m, 9 H, H3-5(C6H5)), 7.84 (m, 6 H, H2,6(C6H5)); 13C{1H}, δC 344.1 (MotC), 229.2 (CO), 151.4, 151.2,144.7, 144.6 (C3,5(pz)), 137.0 (C1(C6H5)), 135.6 (C2,6(C6H5)), 129.5 (C4(C6H5)), 128.7 (C3,5(C6H5)), 106.7, 106.5 (C4(pz)), 14.40, 12.41 (1 C  2, pzCH3), 16.49,12.65 (2 C  2, pzCH3). ESI-MS (positive ion, MeCN): m/z 805 [M þ MeCN]þ, 738 [M - CO]þ, 709 (Base) [M - 2CO]þ. Crystal data for 3 3 C6H6: C36H37BGeMoN6O2 3 C6H6, Mr = 843.18, T = 200(2) K, triclinic, space group P1 (No. 2), a = 8.2963(2) A˚, b = 10.2762(2) A˚, c = 23.7893(4) A˚, R = 82.7608(11)
, β = 88.3253(9)
, γ = 80.2278(9)
, V = 1982.72(7) A˚3, Z = 2, Fcalcd = 1.412 Mg m-3, μ(Mo KR) = 1.118 mm-1, yellow block, 0.13  0.14  0.15 mm, 88 354 measured reflections with 2θmax = 55
, 9104 independent reflections, 9104 absorption-corrected data used in F2 refinement, 478 parameters, R1 = 0.0342, wR2 = 0.0823 for 7088 reflections with I > 2σ(I) (CCDC 793430). Synthesis of [Mo(tCSnPh3)(CO)2(Tp*)] (4). An oven-baked Schlenk tube was cooled under an atmosphere of dry nitrogen and then charged with [Mo(tCBr)(CO)2(Tp*)] (0.400 g, 0.74 mmol) and tetrahydrofuran (50 mL). The stirred solution was cooled to -78
C and then treated with a solution of nBuLi in hexane (0.30 mL, 2.5 M, 0.75 mmol) and stirred for 15 min. Solid chlorotriphenylstannane (0.285 g, 0.74 mmol) was then added in a single portion, and the mixture was warmed slowly to room temperature to provide a dark red-brown solution (νCO 1998, 1914 cm-1 with minor unidentified peaks at 1920 sh and 1854 cm-1). The solvent was removed under reduced pressure, the residue was extracted with dichloromethane, and the combined extracts were filtered through diatomaceous earth. The solvent was removed in vacuo and the residue extracted with petroleum spirit (40-60
C bp). Slow concentration of the combined, filtered extracts afforded a yellow-orange powder that was dried in vacuo. Yield: 0.46 g (0.57 mmol, 77%). Anal. Found: C, 53.07; H, 4.88; N, 10.52. Calcd for C36H37BMoN6O2Sn: C, 53.30; H, 4.60; N, 10.36. IR (cm-1): Nujol, 1993 s, 1902 vs νCO, 154 3νCN; CH2Cl2, 1999 s, 1914 vs νCO; THF, 1998, 1914 νCO. NMR (C6H6, 25
C): 1H, δH 2.04, 2.34 (s  2, 3 H  2, pzCH3), 2.05, 2.57 (s  2,6 H  2, pzCH3), 5.36 (s, 1 H, pzH), 5.54 (s, 2 H, pzH), 7.18 (m, 9 H, H3-5(C6H5)), 7.79 (m, 6 H, H2,6(C6H5), 3JSnH = 51 Hz); 13C{1H}, δC 349.9 (MotC), 229.4 (CO), 152.9, 152.5, 151.4, 150.9 (C3,5(pz)), 144.7 (C1(C6H5)), 137.5 (C2,6(C6H5)), 129.5 (C4(C6H5)), 129.1 (C3,5(C6H5)), 107.4, 106.5 (C4(pz)), 14.40,12.41 (1 C  2, pzCH3), 16.63, 12.60 (2 C  2, pzCH3). 119Sn{1H} NMR (CDCl3): δSn -228.4 (1JSnC = 540 (tC), 40 (CO), 53 Hz (C1Ph)). ESI-MS (positive ion, MeCN):

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m/z 812 [HM]þ, 786 [HM - CO]þ, 756 [M - 2CO]þ, 351 (base) [SnPh3]þ. Crystal data for 4: C36H37BMoN6O2Sn, Mr = 811.17, T = 200(2) K, triclinic, space group P1 (No. 2), a = 10.4624(1) A˚, b = 12.2445(2) A˚, c = 14.5125(2) A˚, R = 102.9271(8)
, β = 92.8843(10)
, γ = 94.5805(10)
, V = 1801.79(4) A˚3, Z = 2, Fcalcd = 1.495 Mg m-3, μ(Mo KR) = 1.081 mm-1, yellow block, 0.10  0.14  0.18 mm, 50 451 measured reflections with 2θmax = 60
, 10 546 independent reflections, 10 545 absorption-corrected data used in F2 refinement, 536 parameters, 180 restraints, R1 = 0.0265, wR2 = 0.0707 for 8021 reflections with I > 2σ(I) (CCDC 793431). Synthesis of [Mo(tCPbPh3)(CO)2(Tp*)] (5). An oven-baked Schlenk tube was cooled under an atmosphere of dry nitrogen and then charged with [Mo(tCBr)(CO)2(Tp*)] (0.400 g, 0.74 mmol) and tetrahydrofuran (50 mL). The stirred solution was cooled to -78
C and then treated with a solution of nBuLi in hexane (0.30 mL, 2.5 M, 0.75 mmol) and stirred for 15 min. Solid chlorotriphenylplumbane (0.350 g, 0.74 mmol) was then added in a single portion, and the mixture was warmed to 0
C and stirred for 15 min to provide a dark red-brown solution. The solvent was removed under reduced pressure and the residue extracted with dichloromethane. The combined extracts were filtered through diatomaceous earth, diluted with petroleum spirit (40-60
C bp), and slowly concentrated to afford a crude gray-brown solid which was recrystallized twice from a mixture of dichloromethane and hexane (-18
C) to afford orange crystals that were dried in vacuo. Yield: 0.204 g (0.23 mmol, 31%). Anal. Found: C, 47.82; H, 4.39; N, 9.01. Calcd for C36H37BMoN6O2Pb: C, 48.06; H, 4.15; N, 9.34. IR (cm-1): Nujol, 2545 νBH, 1983 s, 1897 vs νCO, 1541 νCN; CH2Cl2, 1996 s, 1911 vs νCO, 1542 νCN; THF, 2003, 1920 νCO. NMR (C6H6, 25
C): 1H, δH 2.05, 2.35 (s  2, 3 H  2, pzCH3), 2.07, 2.59 (s  2, 6 H  2, pzCH3), 5.37 (s, 1 H, pzH), 5.54 (s, 2 H, pzH), 7.18 (m, 9 H, H3-5(C6H5)), 7.82 (m, 6 H, H2,6(C6H5), 3JPbH = 87 Hz); 13C{1H}, δC 345.5 (MotC), 229.2 (CO), 154.1, 151.5, 150.9, 150.3 (C3,5(pz)), 144.6 (C1(C6H5)), 137.7 (C2,6(C6H5)), 130.7 (C4(C6H5)), 129.8 (C3,5(C6H5)), 106.7, 106.5 (C4(pz)), 14.45,12.41 (1 C  2, pzCH3), 16.59, 12.60 (2 C  2, pzCH3). ESI-MS (positive ion, MeCN): m/z 922 [NaM]þ, 908 [NaM þ MeCN - 2CO]þ, [HM]þ, [HM - CO]þ, 867 [NaM 2CO]þ, 844 [M - 2CO]þ, 439 (base) [PbPh3]þ. Crystal data for 5: C36H37BMoN6O2Pb, Mr = 899.68, T = 200(2) K, orthorhombic, space group Pnma, a = 15.4068(2) A˚, b = 15.9388(3) A˚, c = 14.5102(3) A˚, V = 3563.21(11) A˚3, Z = 4, Fcalcd = 1.677 Mg m-3, μ(Mo KR) = 5.111 mm-1, pale orange plate, 0.02  0.09  0.32 mm, 43 568 measured reflections with 2θmax = 55
, 4217 independent reflections, 4216 absorption-corrected data used in F2 refinement, 237 parameters, 10 restraints, R1 = 0.0332, wR2 = 0.0880 for 3164 reflections with I > 2σ(I) (CCDC 793432). Crystal Data for 13 3 0.5C6H6. From one of many protracted attempts to obtain crystals of 4 suitable for crystallography, a rogue crystal was selected that was not representative of the bulk sample but was modeled to be a benzene hemisolvate of the stannyloxy complex [Mo(OSnPh3)(dO)2(Tp*)] (13): C36H40BMoN6O3Sn, Mr = 830.19, T = 200(2) K, triclinic, space group P1 (No. 2), a = 8.0951(3) A˚, b = 9.9690(5) A˚, c = 23.1787(11) A˚, R = 82.3925(18)
, β = 88.749(2)
, γ = 77.050(2)
, V = 1806.84(14) A˚3, Z = 2, Fcalcd = 1.526 Mg m-3, μ(Mo KR) = 1.082 mm-1, yellow plate, 0.02  0.11  0.37 mm, 47 328 measured reflections with 2θmax = 50
, 6424 independent reflections, 6423 absorption-corrected data used in F2 refinement, 433 parameters, R1 = 0.0792, wR2 = 0.0688 for 4271 reflections with I > 2σ(I) (CCDC 793433). Since there are only two previous reports of structurally characterized mononuclear stannyloxy complexes,30 a brief discussion of the structural features is

(30) (a) Kondracka, M.; Herntrich, T.; Merzweiler, K. Z. Anorg. Allg. Chem. 2004, 630, 1798. (b) Grutzmacher, H.; Pritzkow, H. Chem. Ber. 1993, 126, 2409.

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provided as Supporting Information, as it falls outside the scope of the present discussion.

Acknowledgment. We gratefully acknowledge the financial assistance of the Australian Research Council (Nos. DP0557815 and DP0881692).

Cordiner et al. Supporting Information Available: CIF files giving crystallographic data for 2 (CCDC 793429), 3 3 C6H6 (CCDC 793430), 4 (CCDC 793431), 5 (CCDC 793432), and 13 3 0.5C6H6 (CCDC 793433) and text and figures giving a brief discussion of the structural features of 13 3 0.5C6H6. This material is available free of charge via the Internet at http://pubs.acs.org.