Reactions of Tungsten Acetylide–Silylene Complexes with Pyridines: Direct Observation of Silylene/Silyl Migration in Tungsten Acetylide and Carbyne/Vinylidene Frameworks

Reaction of acetylide–silylene complex Cp*(CO)2W(SiPh2)(CCtBu) (1a) with 4-(dimethylamino)pyridine (DMAP) gave an equilibrium mixture of DMAP-stabilized silylene acetylide complexes trans- and cis-Cp*(CO)2W(SiPh2·DMAP)(CCtBu) (trans-4 and cis-4). The corresponding reaction using Cp*(CO)2W(SiPh2)(CCSiMe3) (2) produced the novel DMAP-coordinated silenylcarbyne/silylvinylidene complex Cp*(CO)2W[CC(SiPh2·DMAP)(SiMe3)] (6a) as a major product, which was equilibrated with trans- and cis-Cp*(CO)2W(SiPh2·DMAP)(CCSiMe3) (trans-5a and cis-5a) via silylene/silyl migration. The novel structures of cis-4 and 6a were revealed by X-ray crystallography. A mixture of 2 and pyridine exhibited interesting temperature-dependent NMR spectral changes, indicating the formation of trans- and cis-Cp*(CO)2W(SiPh2·py)(CCSiMe3) (trans-5b and cis-5b) and Cp*(CO)2W[CC(SiPh2·py)(SiMe3)] (6b) at low temperature, while a mixture of 1a and pyridine showed no such spectral changes.