Jose Sancho

Acetylene metathesis by tungsten(VI) alkylidyne complexes

Abstract W(CCMe3)(OCMe3)3 reacts with acetylenes at a rate which is first order in tungsten and first order in acetylene. The rate increases by approximately an order of magnitude upon replacing a phenyl substituent in the acetylene with an alkyl substituent. The metathesis of PhCCEt is slower than either the metathesis of PhCCTol or PrCCEt because the intermediate benzylidyne complex reacts with PhCCEt in largely a degenerate fashion. W(CCMe3)(OCMe3)3 will metathesize PrCCEt in the presence of acetonitrile, ethyl acetate, phenol, and triethylamine, and so far has been used successfully to metathesize EtCCCH2NMe2 and to cross-metathesize Me3SiOCH2CCCH2OSiMe3 with 3-hexyne. W(CCMe3)-(NPr12)3 is as effective a catalyst as W(CCMe3)(OCMe3)3.