Carbon–hydrogen bond activation in cyclopentadienyl dimethyl tungsten nitrosyl and carbonyl

Abstract

Mechanisms for generating tungsten carbene complexes from CpW(NO)(CH₃)₂, Cp*W(NO)(CH₃)₂ and [CpW(CO)(CH₃)₂]⁻ by methane elimination were studied by density functional (B3LYP) computations. Based on the calculations, a one-step (σ-bond metathesis like) mechanism is preferred in nitrosyl complexes, while a two-step (oxidative addition then reductive elimination) mechanism is preferred in the carbonyl complex. The one-step mechanism is strongly assisted by the metal as the transition state for this mechanism has a W–H distance that is only ≈0.1 Å longer than the W–H single bond in the oxidative addition intermediate. Stronger π backbonding of the NO ligand is responsible for the difference.