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 CH2=MHX (X = F, Cl, Br, I) and CH2=MH2 methylidene complexes exhibit agostic bonding effects of CH2 and MH2 distortion. The reactions proceed through the CH3-MX insertion product followed by alpha-H transfer on an excited potential energy surface. The higher valence of group 6 metals sustains a second alpha-H transfer to form the CH MH2X (M = Mo, W, X = H, F, Cl, Br) methylidyne complexes, and electron capture by group 5 CH2=MHX (M = Nb, Ta, X = H, F, Cl, Br) methylidene complexes gives rise to the analogous CH MH2X- 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.