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)(2)W(SiPh2)((CCBu)-Bu-t) (1a) with 4-(dimethylamino)-pyridine (DMAP) gave an equilibrium mixture of DMAP-stabilized silylene acetylide complexes trans- and cis-Cp*-(CO)(2)W(SiPh2 center dot DMAP)((CCBu)-Bu-t) (trans-4 and cis-4). The corresponding reaction using Cp*(CO)(2)W(SiPh2)(CCSiMe3) (2) produced the novel DMAP-coordinated silenylcarbyne/silylvinylidene complex Cp*(CO)(2)W[CC(SiPh2 center dot DMAP)(SiMe3)] (6a) as a major product, which was equilibrated with trans- and cis-Cp*(CO)(2)W(SiPh2 center dot 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)(2)W(SiPh2 center dot py)(CCSiMe3) (trans-5b and cis-5b) and Cp*(CO)(2)W[CC(SiPh2 center dot py)(SiMe3)] (6b) at low temperature, while a mixture of la and pyridine showed no such spectral changes.