Effect of Lewis Acids on the Catalyst Activity for Alkene Metathesis, Z-/E- Selectivity and Stability of Tungsten Oxo Alkylidenes

Abstract Lewis acids increase the catalytic activity of classical heterogeneous catalysts and molecular d 0 tungsten oxo alkylidenes in a variety olefin metathesis processes. The formation labile adducts between metal complex acid has been observed experimentally suggested to be involved catalyst increase. In this contribution, DFT (M06) calculations have performed determine role on activity, Z-/E- selectivity stability by comparing three W(E)(CHR)(2,5-dimethylpyrrolide)(O-2,6-dimesithylphenoxide) (E = oxo, imido or oxo-Lewis adduct) alkylidenes. Results show that alkylidene—Lewis influences reactivity due both steric electronic effects. addition E group increases its bulkiness decreases Z -selectivity. Moreover, interaction ligand donating ability former toward metal. This is important when either trans same plane competing for orbitals. Therefore, weakening facilitates cycloaddition cycloreversion steps it stabilizes productive trigonal bipyramid metallacyclobutane isomer. two factors complex. electron tuneability coordination also applies deactivation particularly key ?-hydride elimination step. process, transition states pseudo oxo. presence Gibbs energy barrier significantly. Overall, optimization each step reaction makes more reactive deactivation.