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(SiPh ₂)(CC^tBu) (1a) with 4-(dimethylamino)pyridine (DMAP) gave an equilibrium mixture of DMAP-stabilized silylene acetylide complexes trans- and cis-Cp*(CO)₂W(SiPh₂·DMAP)(CC ^tBu) (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)(CCSiMe ₃) (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(SiPh ₂·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.