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)­(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)­(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.