Infrared Spectra of the CH3−CrF, CH2WHF, and CH⋮WH2F Molecules: Reversible Photochemical Interconversion by α-Hydrogen Transfer

Abstract

Group 6 methylmetal fluoride, methylidene, and methylidyne complexes (CH3−MF, CH2MHF, and CH⋮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 CH2WHF and CH⋮WH2F forms are trapped for W. The last molecules are photoreversible, owing to α-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 (λ > 420 nm). Calculations show that one α-H is distorted toward the metal atom, which provides evidence of strong agostic interaction in the methylidene ground state molecules.