Conversion of Tungsten(IV) Oxo−Alkyne Complexes to Oxo−Vinylidene Complexes

A series of chiral tungsten(IV) oxo−alkyne complexes of the type Tp‘W(O)(I)(RC⋮CR‘) (R = R‘ = H ( 1 ); R = H, R‘ = Me ( 2 ); R = R‘ = Me ( 3 ); R = Me, R‘ = Ph ( 4 ); Tp‘ = hydridotris(3,5-dimethylpyrazolyl)borate) has been prepared. These complexes were synthesized by reaction of Tp‘W(O)(CO)(I) with Me 3 NO in the presence of an excess of alkyne. Phenylpropyne complex 4 was isolated as a 2:1 mixture of alkyne rotamers. For the propyne complex, a second route involving deprotonation of acetylene complex 1 followed by addition of MeI also produced complex 2 . The oxidation pathway to 2 with Me 3 NO resulted in a 1:1.5 ratio of alkyne rotamers, while the elaboration of 1 via deprotonation/methylation gave 2 in a 9:1 ratio of alkyne rotamers. Addition of n -BuLi to propyne complex 2 resulted in deprotonation of the terminal acetylene site, and electrophile addition then produced the vinylidene complexes Tp‘W( C CMe 2 )(O)(I) ( 5 ) and Tp‘W[ C C(Me)(H)](O)(I) ( 6 ) upon addition of MeI or HCl, respectively. X-ray structure determinations for alkyne complexes 2 and 4 and for vinylidene complex 5 are reported.