Activation of η 5 -Cyclopentadienyl Ligands toward Nucleophilic Attack through η 5 f η 3 Ring Slippage. Kinetics, Thermodynamics, and NMR Spectroscopy Walter Simanko, Valentin N. Sapunov, Roland Schmid, and Karl Kirchner* Institute of Inorganic Chemistry, Technical University of Vienna, Getreidemarkt 9, A-1060 Vienna, Austria Scot Wherland* Department of Chemistry, Washington State University, Pullman, Washington 99164-4630 Received February 19, 1998 Summary: The kinetics of the reactions of the complexes [Ru(η 5 -C 5 H 5 )(η 4 -C 5 H 4 O)(L)]CF 3 SO 3 (L ) CH 3 CN, pyri- dine, thiourea) with PMe 3 have been studied in acetone. The novel reaction products [Ru(η 3 -C 5 H 5 )(η 4 -C 5 H 4 O)- (PMe 3 )(L)]CF 3 SO 3 formed are fluxional in solution due to an intramolecular enantiomeric equilibrium likely proceeding through a five-coordinate η 1 -C 5 H 5 inter- mediate. Of the various bonding modes the cyclopentadienyl ligand can adopt in organotransition metal complexes, the η 5 , η 3 , and η 1 fashions are of particular interest, in view of their ability to interconvert through ring slip- page. 1 A decrease in hapticity implies a decrease in the number of electrons donated to the metal and creates vacant sites for further reactions to utilize. This feature is arguably the key property for understanding the catalytic efficiency of cyclopentadienyl complexes. For a number of years the η 3 -C 5 H 5 ligand itself proved to be a controversial species, until it was detected in the X-ray structure of W(η 5 -C 5 H 5 )(η 3 -C 5 H 5 )(CO) 2 . 2 In contrast to available reports on η 5 to η 1 slippage, 1,3 direct observation of an η 5 to η 3 interconversion is still outstanding. Nevertheless, the possibility of the occur- rence of η 3 intermediates has been postulated frequently as a mechanistic rationale for a number of organome- tallic rearrangement reactions, 4 simply to adhere to the 18e rule. Among such reactions are R- and -hydrogen abstractions, 5,6 photochemically induced C-H, Si-H, and C-C bond cleavages, 7 cyclopentadienyl ligand transfers, 8 and ligand substitution. 3d,9 Surprisingly, for inter- or intramolecular nucleophilic attack at C 5 H 5 ligands, 10 transient η 3 or η 1 coordination has hitherto not been considered, despite the fact that η 5 -C 5 H 5 is known to be rather inert toward nucleophilic attack. 11 However, the η 3 or η 1 modes should appreciably enhance the reactivity of the C 5 H 5 ligand. Unfortunately, the few reports dealing with additions, substitutions, and migrations of nucleophiles onto the C 5 H 5 ligand do not allow any definite conclusions to be drawn as to the involvement of ring slippages. 10 Here we report the synthesis and characterization of the novel η 3 -C 5 H 5 complexes [Ru(η 3 -C 5 H 5 )(η 4 -C 5 H 4 O)(PMe 3 )(L)]CF 3 SO 3 (L ) CH 3 CN, pyridine, thiourea), which are precursors of the 1,1′-disubstituted ruthenocene [Ru(η 5 -C 5 H 4 PMe 3 )(η 5 - C 5 H 4 OH)]CF 3 SO 3 (10), formed by endo migration of PMe 3 (Scheme 1). 12 Thus, kinetic and thermodynamic (1) O’Connor, J. M.; Casey, C. P. Chem. Rev. 1987, 87, 307. (2) Huttner, G.; Brintzinger, H. H.; Bell, L. G.; Friedrich, P.; Bejenke, V.; Neugebauer, D. J. Organomet. Chem. 1978, 145, 329. (3) (a) Anderson, G. K.; Cross, R. J.; Fallis, S.; Rocamora, M. Organometallics 1987, 6, 1440. (b) Green, M. L. H.; Michaelidou, D. M.; Moutford, P.; Suarez, A. G.; Wong, L.-L. J. Chem. Soc., Dalton Trans. 1993, 1593. (c) Antonelli, D. M.; Gomes, P. T.; Green, M. L. H.; Martins, A. M.; Mountford, P. J. Chem. Soc., Dalton Trans. 1997, 2435. (d) Casey, C. P.; O’Connor, J. M.; Haller, K. J. J. Am. Chem. Soc. 1985, 107, 1251. (e) Werner, H.; Ku ¨ hn, A. Angew. Chem. 1979, 91, 447. (f) Goel, A. B.; Goel, S.; VanDer Veer, D.; Clark, H. C. Inorg. Chim. Acta 1981, 53, L117. (4) (a) Yan, X.; Cherenga, A. N.; Metzler, N.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 1997, 2091. (b) Green, J. C.; Parkin, R. P. G.; Yan, X.; Haaland, A.; Scherer, W.; Tafipolsky, M. A. J. Chem. Soc., Dalton Trans. 1997, 3219. (c) Butts, M. D.; Bergman, R. G. Organo- metallics 1994, 13, 1899. (5) (a) Marks, T. J.; Kolb, J. R. J. Am. Chem. Soc. 1975, 97, 3397. (b) Brintzinger, H. H.; Bercaw, J. E. J. Am. Chem. Soc. 1970, 92, 3397. (c) Slocum, D. W.; Beach, D. L.; Ernst, C. R.; Fellows, R.; Moronski, M.; Conway, B.; Bencini, J.; Siegel, A. J. Chem. Soc., Chem. Commun. 1980, 1043. (d) Roman, E.; Astruc, D.; Des Abbayes, H. J. Organomet. Chem. 1981, 219, 211. (e) Slocum, D. W.; Engelmann, T. R.; Fellows, R. L.; Moronski, M.; Duraj, S. J. Organomet. Chem. 1984, 260, C21. (f) Slocum, D. W.; Moronski, M.; Gooding, R.; Duraj, S. J. Organomet. Chem. 1984, 260, C26. (6) Yang, G. K.; Bergman, R. G. Organometallics 1985, 4, 129. (7) (a) Green, M. L. H.; Berry, M.; Couldwell, C.; Prout, K. Nouv. J. Chim. 1977, 1950. (b) Berry, M.; Elmitt, K.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 1979, 1950. (c) Ephritikhine, M.; Green, M. L. H. J. Chem. Soc., Chem. Commun. 1976, 926. (d) Rest, A. J.; Whitwell, I.; Graham, W. A. G.; Hoyano, J. K.; McMaster, A. D. J. Chem. Soc., Chem. Commun. 1984, 624. (e) Yang, H.; Kotz, K. T.; Asplund, M. C.; Harris, C. B. J. Am. Chem. Soc. 1997, 119, 9564. (8) (a) Peng, M. H.; Brubaker, C. H., Jr. J. Organomet. Chem. 1977, 135, 333. (b) Lee, J. G.-S.; Brubaker, C. H., Jr. Inorg. Chim. Acta 1977, 25, 181. (9) (a) Vest, P.; Anhaus, J.; Bajaj, H. C.; van Eldik, R. Organome- tallics 1991, 10, 818. (b) Rerek, M. E.; Basolo, F. J. Am. Chem. Soc. 1984, 106, 5908. (c) Cramer, R.; Seiwell, L. P. J. Organomet. Chem. 1975, 92, 245. (10) (a) Arif, A. M.; Cowley, A. H.; Nunn, C. M.; Pakulski, M. J. Chem. Soc., Chem. Commun. 1987, 994. (b) Benfield, F. W. S.; Green, M. L. H. J. Chem. Soc., Dalton Trans. 1974, 1324. (c) Forschner, T. C.; Cooper, N. J. J. Am. Chem. Soc. 1989, 111, 7420. (d) McNally, J. M.; Cooper, N. J. J. Am. Chem. Soc. 1989, 111, 4500. (e) Hughes, R. P.; Maddock, S. M.; Rheingold, A. L.; Liable-Sands, L. M. J. Am. Chem. Soc. 1997, 119, 5988. (f) Herber, U.; Bleuel, E.; Gevert, O.; Laubender, M.; Werner, H. Organometallics 1998, 17, 10. (11) Davies, S. G.; Green, M. L. H.; Mingos, D. M. P. Tetrahedron 1978, 34, 3047. (12) (a) Kirchner, K.; Taube, H. J. Am. Chem. Soc. 1991, 113, 7039. (b) Kirchner, K.; Mereiter, K.; Schmid, R.; Taube, H. Inorg. Chem. 1993, 32, 5553. (c) Simanko, W.; Vallant, T.; Mereiter, K.; Schmid, R.; Kirchner, K.; Coddington, J.; Wherland, S. Inorg. Chem. 1996, 35, 5923. 2391 Organometallics 1998, 17, 2391-2393 S0276-7333(98)00119-8 CCC: $15.00 © 1998 American Chemical Society Publication on Web 05/21/1998