Tungsten terminal acetylenes

The mer-(CO)3(dppe)W(C=CHPh), 3, prepared as described below, contains a vinylidene ligand, a ligand that occupies a central role in the chemistry of monohapto carbon ligands in organometallic chemistry. Chemical transformations relate the vinylidene ligand to acetylides, -vinyls, acyls, and carbynes. Low oxidation state monohapto vinylidenes of tungsten have recently been implicated as catalysts in the polymerization of terminal acetylenes. ... 

When alkynes are treated with catalytic amounts of a carbene complex, polymerization instead of metathesis can occur (Figure 3.44) [565,595,597,752-754]. The use of carbene complexes to catalyze alkyne polymerization enables much better control of the reaction than with heterogeneous or multi-component catalysts. Pure acetylene oligomers (n = 3-9) with terminal fcrf-butyl groups have been prepared with the aid of a tungsten carbene complex [755]. 

The tungsten carbene complex [(CO)5W=CHAr] (Ar = Ph, p-tol) reacts with 2-butyne to give stilbenes and [(CO)5W(MeC=CMe)]. Terminal alkynes, such as Bu C=CH, are however polymerized. Vinylidene complexes are proposed as intermediates since the acetylene-vinylidene rearrangement has ample precedence in stoichiometric reactions (Scheme 26). 

The polymerization kinetics of terminal alkynes have been determined. The reaction is initiated by tungsten carbene complexes (10) the chelating olefin is displaced by acetylene as the first step in the reaction, followed by formation of... 

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