Carbon–hydrogen bond activation in cyclopentadienyl dimethyl tungsten nitrosyl and carbonylBased on the presentation given at Dalton Discussion No. 4, 10–13th January 2002, Kloster Banz, Germany. Theoretical studies of inorganic and organometallic reaction mechanisms. Part 21.1

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 A longer than the W–H single bond in the oxidative addition intermediate. Stronger π backbonding of the NO ligand is responsible for the difference.