Schrock molybdenum catalyst, alkyne metathesis

In the early 1980s, Schrock prepared a series of tungsten- and molybdenum-based carbyne complexes, and demonstrated that they are viable catalysts for performing stoichiometric and catalytic alkyne metathesis [7]. With the defined carbyne complexes, he laid the foundation for the mechanistic understanding of alkyne metathesis, and was the first to demonstrate that vinyl-substituted carbyne complexes are stable [8] and that alkyne metathesis could be performed in the presence of C=C double bonds. 

Alkynes can also undergo metathesis. The preferred catalysts for alkyne metathesis are Schrock catalysts—catalysts that contain molybdenum or tungsten as the transition metal. 

Schrock RR, Czekelius C. Recent advances in the syntheses 136. and applications of molybdenum and tungsten alkylidene and alkylidyne catalysts for the metathesis of alkenes and alkynes. 

Schrock, R.R. and Czekelius, C. (2007) Recent advances in the syntheses and applications of molybdenum and tungsten alkylidene and alkylidyne catalysts for the metathesis of alkenes and alkynes. Adv. Synth. Catal, 349, 55-77. Zhang, W. and Moore, J.S. (2007)... 

In 1976 Fischer had tested the ROMP reactions of cycloalkanes with carbyne tungsten(O) complexes as catalysts (6). With addition of Lewis acids as cocatalysts the Fischer type carbyne complexes were active in cycloalkane metathesis polymerisation. Fischer type carbyne complexes are also active catalysts for alkyne polymerisations, as found by Katz in 1984 (7). The catalytic reactions of Schrock type carbyne tungsten(VI) or molybdenum(VI) complexes were focussed on alkyne metatheses reactions (8). 

Schrock and Fischer type carbyne tungsten or molybdenum complexes are very interesting catalysts for alkene metathesis or alkyne polymerisation reactions. Within the first reaction steps they form carbene complexes and on these carbene complexes further metathesis or polymerisation occur. 

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