Infrared spectra and density functional calculations of the M←NCCCH3, η2–M(NC)–CH3, CH3–MNC, CH2[dbnd]M(H)NC, and CH[tbnd]M(H)2NC complexes produced by reactions of Group 6 metal atoms with acetonitrile

Abstract

The M←NCCH3, η2–M(NC)–CH3, CH3–MNC, CH2M(H)NC, and HCM(H)2NC complexes are produced by reactions of laser-ablated Group 6 metal atoms with acetonitrile and identified from the matrix IR spectra through isotopic substitution and comparison to frequencies calculated by density functional theory in the harmonic approximation (B3LYP/6-311++(3df,3pd) and BPW91/6-311++G(3df,3pd), this all-electron set for Cr, and SDD for Mo and W). Good general agreement is shown in tables for all observed frequencies and these calculations. The products follow the reaction path proposed earlier for Group 4 and 5 metal reactions, which are supported by density functional energy calculations. The M←NCCH3 complex strengthens the assumption that the lone electron pair on the N-end first attracts the metal atom. The π-complexes show that the back-donation of the Group 6 metal is weaker than those of Zr and Group 5 metals. The observed products clearly show the increasing preference for the higher oxidation-state complex with increasing atomic number of the Group 6 metal, and subsequent photolysis increases the yields for the higher oxidation-state complexes. The methylidyne isocyanide HCW(H)2NC has a Cs structure similar to the HCW(H)2X complexes prepared earlier.