Synthesis, structure, and reactivity of [C5Me5CoLL '] complexes with L = pyridine and L ' = olefin or L-L ' = bipyridine

The bis(olefin) complex [C5Me5Co(C2H3SiMe3)(2)] (6) reacts with pyridine at 22 degrees C to give the pyridine olefin complex [C5Me5Co(C2H3SiMe3)(C5H5N )] (7) The addition of excess pyridine does not result in the formation of a bis(pyridine) adduct. Thermolysis of solutions of 7 in benzene-d(6) resul ts in catalytic H/D exchange which incorporates deuterium from the solvent into coordinated olefin. Pyridine dissociation generates a 16-electron inte rmediate which is formulated as the reactive species. At long times deutera tion of the coordinated pyridine is also observed via shuttling of deuteriu m from the solvent to the olefin ligand and then to the pyridine. The react ion of 6 with pyridine-d(5) results in the analogue 7-d(5). Thermolysis of 7-d(5) shows preference for H/D exchange at the ortho positions of coordina ted pyridine, which has been explained by the formation of eta(2)-coordinat ed intermediates. Reaction of 4-phenylpyridine with 6 yields the analogous pyridine adduct [C5Me5Co(C2H3SiMe3)(4-C6H5-C5H4N)] (12), which was characte rized by X-ray structural analysis. H/D exchange catalysis is also observed using this pyridine derivative. In a reaction of bipyridine with 6 clean o lefin substitution is observed at 22 degrees C to generate violet, highly a ir sensitive [C5Me5Co(bipy)] (13). Complex 13 has been characterized by X-r ay structural analysis.