Synthesis of methylidene complexes that contain a 2,6-Dimesitylphenylimido ligand and ethenolysis of 2,3-dicarbomethoxynorbornadiene

摘要

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*)(CH_2)(Me_2Pyr)(OR) (R = t-Bu, OCMe(CF_3)2, SiPh3, or 2,6-Me_2C_6H_3). Polymerization of 2,3-dicarbomethoxynorbornadiene (DCMNBD) with M? - -CHCMe_2Ph (M = Mo or W) initiators is slow as a consequence of a slow propagation step. However, W(NAr*)(CH_2)(Me_2Pyr)(OR) (R = SiPh_3 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.