Synthesis of Methylidene Complexes that Contain a 2,6-Dimesitylphenylimido Ligand and Ethenolysis of 2,3-Dicarbomethoxynorbornadiene

Monoalkoxide pyrrolide (MAP) complexes that contain a 2,6-dimesitylphenylimido (NAr*) ligand react with ethylene to yield unsubstituted metallacyclobutanes that are in equilibrium with methylidene complexes, W­(NAr*)­(CH₂)­(Me₂Pyr)­(OR) (R = t-Bu, OCMe­(CF₃)₂, SiPh₃, or 2,6-Me₂C₆H₃). Polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) with MCHCMe₂Ph (M = Mo or W) initiators is slow as a consequence of a slow propagation step. However, W­(NAr*)­(CH₂)­(Me₂Pyr)­(OR) (R = SiPh₃ or 2,6-dimethylphenyl) complexes react readily with 1 equiv of DCMNBD to give a monoinsertion product. The facile reaction between the monoinsertion product and ethylene then allows these complexes to be catalyts for the ring-opening cross-metathesis (ethenolysis) of DCMNBD and DCMNBE (2,3-dicarbomethoxynorbornene) with minimal formation of polymer.