Complexation of the Triply-Bonded Dirhenium(II) Complex Re 2 Cl 4 (μ-dppm) 2 (dppm ) Ph 2 PCH 2 PPh 2 ) by Up to Three Acetylene Molecules Mani Ganesan, Keng-Yu Shih, † Phillip E. Fanwick, and Richard A. Walton* Department of Chemistry, Purdue UniVersity, 1393 Brown Building, West Lafayette, Indiana 47907-1393 Received September 3, 2002 The triply bonded dirhenium(II) synthons Re 2 X 4 (µ-dppm) 2 (X ) Cl, Br; dppm ) Ph 2 PCH 2 PPh 2 ) react with acetylene at room temperature in CH 2 Cl 2 and acetone to afford the bis(acetylene) complexes Re 2 X 4 (µ-dppm) 2 (µ:η 2 ,η 2 -HCCH)- (η 2 -HCCH) (X ) Cl (3), Br(4)). Compound 3 has been derivatized by reaction with RNC ligands in the presence of TlPF 6 to give unsymmetrical complexes of the type [Re 2 Cl 3 (µ-dppm) 2 (µ:η 2 ,η 2 -HCCH)(η 2 -HCCH)(CNR)]PF 6 (R ) Xyl (5), Mes (6), t-Bu (7)), in which the RCN ligand has displaced the chloride ligand cis to the η 2 -HCCH ligand. The reaction of 3 with an additional 1 equiv of acetylene in the presence of TlPF 6 gives the symmetrical all-cis isomer of [Re 2 Cl 3 (µ-dppm) 2 (µ:η 2 ,η 2 -HCCH)(η 2 -HCCH) 2 ]PF 6 (8). The two terminal η 2 -HCCH ligands in 8 are very labile and can be displaced by CO and XylNC to give the complexes [Re 2 Cl 3 (µ-dppm) 2 (µ:η 2 ,η 2 -HCCH)(L) 2 ]Y (L ) CO when Y ) PF 6 (9); L ) CO when Y ) (PF 6 ) 0.5 /(H 2 PO 4 ) 0.5 (10); L ) XylNC when Y ) PF 6 (11)). These substitution reactions proceed with retention of the all-cis stereochemistry. Single-crystal X-ray structure determinations have been carried out on complexes 3, 5, 8, 10, and 11. In no instance have we found that the acetylene ligands undergo reductive coupling reactions. Introduction Several examples of the binding of alkynes to compounds that contain Mo-Mo and W-W quadruple bonds (σ 2 π 4 δ 2 configuration) and electron-poor triple bonds (σ 2 π 4 config- uration) have been reported in which the alkynes assume η 2 - and µ:η 2 ,η 2 -coordination modes. 1-7 In addition, in some circumstances the triply bonded dimetal complexes have been found to participate in important C-C bond coupling and metathesis reactions. 1-3,6-10 In contrast to this fairly extensive body of data, reactions of alkynes with the synthons that contain the electron-rich triple bond (σ 2 π 4 δ 2 δ* 2 configura- tion) have not previously reported although we have de- scribed the reactions of acetylene and other alkynes with carbonyl, isocyanide, and mixed carbonyl-isocyanide com- plexes derived from the triply bonded synthons Re 2 X 4 (µ- dppm) 2 (X ) Cl, Br; dppm ) Ph 2 PCH 2 PPh 2 ). 11-15 To * To whom correspondence should be addressed. E-mail: rawalton@ purdue.edu. † Present address: W. R. Grace Co., 7500 Grace Drive, Columbia, MD 21044. (1) Cotton, F. A.; Walton, R. A. Multiple Bonds Between Metal Atoms, 2nd ed.; Oxford University Press: Oxford, U.K., 1993; and references therein. (2) (a) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Rothwell, I. P. J. Am. Chem. Soc. 1982, 104, 4389. (b) Chisholm, M. H.; Folting, K.; Hoffman, D. M.; Huffman, J. C. J. Am. Chem. Soc. 1984, 106, 6794. (3) Cotton, F. A.; Schwotzer, W.; Shamshoum, E. S. Organometallics 1983, 2, 1167. (4) Kerby, M. C.; Eichhorn, B. W.; Dovikew, L.; Vollhardt, K. P. C. Inorg. Chem. 1991, 30, 156. (5) Byrnes, M. J.; Chisholm, M. H.; Galluci, J.; Wilson, P. J. Organo- metallics 2002, 21, 2240. This recent report cites the pertinent literature in the field. (6) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. J. Am. Chem. Soc. 1984, 106, 6806. (7) Chisholm, M. H.; Conroy, B. K.; Huffman, J. C. Organometallics 1986, 5, 2384. (8) (a) Chisholm, M. H.; Eichhorn, B. W.; Folting, K.; Huffman, J. C. Organometallics 1989, 8, 49. (b) Chisholm, M. H.; Eichhorn, B. W.; Huffman, J. C. Organometallics 1989, 8, 67. (9) (a) Schrock, R. R.; Listemann, M. L.; Sturgeoff, L. G. J. Am. Chem. Soc. 1982, 104, 4291. (b) Listemann, M. L.; Schrock, R. R. Organometallics 1985, 4, 74. (10) Chamberlin, R. L. M.; Rosenfeld, D. C.; Wolczanski, P. T.; Lobkovsky, E. B. Organometallics 2002, 21, 2724. (11) (a) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. J. Am. Chem. Soc. 1993, 115, 9319. (b) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. Organometallics 1994, 13, 1235. (12) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. Organometallics 1993, 12, 347. (13) (a) Shih, K.-Y.; Fanwick, P. E.; Walton, R. A. J. Chem. Soc., Chem. Commun. 1994, 861. (b) Kort, D. A.; Shih, K.-Y.; Wu, W.; Fanwick, P. E.; Walton, R. A. Organometallics 1995, 14, 448. Inorg. Chem. 2003, 42, 1241-1247 10.1021/ic020532b CCC: $25.00 © 2003 American Chemical Society Inorganic Chemistry, Vol. 42, No. 4, 2003 1241 Published on Web 01/24/2003