Infrared spectra of the CH3-CrF, CH2=WHF, and CH=WH2F molecules:: Reversible photochemical interconversion by α-hydrogen transfer

Group 6 methylmetal fluoride, methylidene, and methylidyne complexes (CH3-MF, CH2 = MHF, and CH equivalent to MH2F) are formed by reaction of the laser-ablated metal atoms and methyl fluoride during condensation in excess argon and have been identified by matrix infrared spectroscopy. The CH3-CrF molecule is much more stable and is the only product found for Cr, and all three comparable energy products are observed for Mo, but only the more stable CH2=WHF and CH-WHY forms are trapped for W. The last molecules are photoreversible, owing to a-hydrogen transfer between carbon and metal atoms. The methylidene complexes are formed on ultraviolet irradiation (240-380 nm) at the expense of the methylidyne complexes, and the process is reversed on visible irradiation (lambda > 420 nm). Calculations show that one a-H is distorted toward the metal atom, which provides evidence of strong agostic interaction in the methylidene ground state molecules.