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

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 α-H transfer on an excited potential energy surface. The higher valence of group 6 metals sustains a second α-H transfer to form the CH⋮MH 2 X (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⋮MH 2 X - 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.