How Niobium and Tantalum Complexes of the Type M(CHCMe3)(PR3)2Cl3 Can Be Modified To Give Olefin Metathesis Catalysts

Abstract

Complexes of the type M(CHR)L2X3 ( M= Nb or Ta, R = CMe3 or Ph, L = a tertiary phosphine, X = Cl or Br) react with terminal olefins to give the organic products of β-hydride rearrangement of the four possible intermediate metallacyclobutane complexes. We see no metathesis products or cyclopropanes. When L = THF or py, the complex reacts with ethylene to give ~10% metathesis product, with 1-butene to give ~50% metathesis products, and with cis-2-pentene to give exclusively metathesis products. Ta(CHCMe3)(THF)2Cl3 is a short-lived metathesis catalyst for cis-2-pentene. Complexes of the type M(CHCMe3)(OCMe3)2Cl(PMe3) react with terminal and internal olefins to give only metathesis products and are longer lived (ca. 35 turnovers) metathesis catalysts for cis-2-pentene. The major chain termination steps in metathesis of a terminal olefin are decomposition (probably intermolecular) of intermediate methylene complexes and rearrangement of intermediate metallacyclobutane complexes. The major chain termination step in metathesis of cis-2-pentene is rearrangement of an alkylidene ligand in an intermediate alkylidene complex to an olefin. © 1981, American Chemical Society. All rights reserved.