Matrix Preparation and Spectroscopic and Theoretical Investigations of Simple Methylidene and Methylidyne Complexes of Group 4-6 Transition Metals

摘要

A new generation of simple methylidene complexes has been prepared by reactions of excited group 4-6 transition metal atoms with methyl halides and methane in solid argon. These CH_2=MHX (X = F, Cl, Br, I) and CH_2=MH_2 methylidene complexes exhibit agostic bonding effects of CH_2 and MH_2 distortion. The reactions proceed through the CH_3-MX insertion product followed by a-H transfer on an excited potential energy surface. The higher valence of group 6 metals sustains a second a-H transfer to form the CHident to MH_2X (M = Mo, W, X = H, F, Cl, Br) methylidyne complexes, and electron capture by group 5 CH_2 =MHX (M = Nb, Ta, X = H, F, Cl, Br) methylidene complexes gives rise to the analogous CH ident to MH_2X~- methylidyne anion complexes. These simple organometallic complexes are identified by matrix infrared spectra through isotopic substitution and by comparison with vibrational characteristics calculated by DFT. Periodic trends in agostic interactions are illustrated for different metals and halogen substituents. Complementary investigations for group 3 and for group 7-9 transition metals and for early lanthanide and actinide metals are also discussed and compared.