Synthesis of Alkyne Metathesis Catalysts from Tris(dimethylamido)tungsten Precursors
Daniel Melcher, Òscar Àrias, Matthias Freytag, Peter G. Jones, Matthias Tamm
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 Me 2 (CF 3 )COH, Me(CF 3 ) 2 COH, and (CF 3 ) 3 COH, and also with silanols ( t BuO) 3 SiOH, and Ph 3 SiOH, all of which resulted in complexes of the type [PhC≡W(NHMe 2 )(NMe 2 )(OR) 2 ]. Full displacement of the amido ligands was also achieved in [PhC≡W(NHMe 2 ){OC(CF 3 ) 2 Me}{OSi(O‐ t Bu) 3 } 2 ] and [PhC≡W(NHMe 2 )(OSiPh 3 ) 3 ]. In addition, reaction of the three fluorinated alcohols with hexakis(dimethylamido)ditungsten yielded isomeric mixtures of bimetallic complexes [W 2 (NMe 2 ) 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 [W 2 (OR) 2 (NMe 2 ) 4 ] complexes require longer initiation times depending on the degree of fluorination of the tert ‐butoxide ligand.