Reactions of Tungsten
Acetylide–Silylene Complexes
with Pyridines: Direct Observation of Silylene/Silyl Migration in
Tungsten Acetylide and Carbyne/Vinylidene Frameworks
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Abstract
Reaction of acetylide–silylene complex Cp*(CO)<sub>2</sub>W(SiPh<sub>2</sub>)(CC<sup><i>t</i></sup>Bu) (<b>1a</b>) with 4-(dimethylamino)pyridine (DMAP) gave an equilibrium
mixture
of DMAP-stabilized silylene acetylide complexes <i>trans-</i> and <i>cis</i>-Cp*(CO)<sub>2</sub>W(SiPh<sub>2</sub>·DMAP)(CC<sup><i>t</i></sup>Bu) (<i><b>trans</b></i><b>-4</b> and <i><b>cis</b></i><b>-4</b>).
The corresponding reaction using Cp*(CO)<sub>2</sub>W(SiPh<sub>2</sub>)(CCSiMe<sub>3</sub>) (<b>2</b>) produced the novel DMAP-coordinated
silenylcarbyne/silylvinylidene complex Cp*(CO)<sub>2</sub>W[CC(SiPh<sub>2</sub>·DMAP)(SiMe<sub>3</sub>)] (<b>6a</b>) as a major
product, which was equilibrated with <i>trans-</i> and <i>cis</i>-Cp*(CO)<sub>2</sub>W(SiPh<sub>2</sub>·DMAP)(CCSiMe<sub>3</sub>) (<i><b>trans</b></i><b>-5a</b> and <i><b>cis</b></i><b>-5a</b>) via silylene/silyl migration.
The novel structures of <i><b>cis</b></i><b>-4</b> and <b>6a</b> were revealed by X-ray crystallography. A mixture
of <b>2</b> and pyridine exhibited interesting temperature-dependent
NMR spectral changes, indicating the formation of <i>trans-</i> and <i>cis</i>-Cp*(CO)<sub>2</sub>W(SiPh<sub>2</sub>·py)(CCSiMe<sub>3</sub>) (<i><b>trans</b></i><b>-5b</b> and <i><b>cis</b></i><b>-5b</b>) and Cp*(CO)<sub>2</sub>W[CC(SiPh<sub>2</sub>·py)(SiMe<sub>3</sub>)] (<b>6b</b>) at low temperature, while a mixture of <b>1a</b> and pyridine
showed no such spectral changes
