Synthesis of Alkyne Metathesis Catalysts from Tris(dimethylamido)tungsten Precursors

Abstract

Benzylidyne tungsten systems bearing a combination of alkoxide and amide ligands were readily obtained by partial alcoholysis of amido‐supported tungsten complexes. Benzylidyne tris(dimethylamido)tungsten was treated with fluorinated alcohols Me2(CF3)COH, Me(CF3)2COH, and (CF3)3COH, and also with silanols (tBuO)3SiOH, and Ph3SiOH, all of which resulted in complexes of the type [PhC≡W(NHMe2)(NMe2)(OR)2]. Full displacement of the amido ligands was also achieved in [PhC≡W(NHMe2){OC(CF3)2Me}{OSi(O‐tBu)3}2] and [PhC≡W(NHMe2)(OSiPh3)3]. In addition, reaction of the three fluorinated alcohols with hexakis(dimethylamido)ditungsten yielded isomeric mixtures of bimetallic complexes [W2(NMe2)4(OR)2], which bear two electron‐donating ligands and one electron‐withdrawing ligand per tungsten atom. All amido‐substituted compounds are active in the self‐metathesis of 5‐benzyloxy‐2‐pentyne, although [W2(OR)2(NMe2)4] complexes require longer initiation times depending on the degree of fluorination of the tert‐butoxide ligand.