Induction of Olefin Metathesis by Acetylenes.

Acetylenes induce phenylmethoxycarbene pentacarbonyltungsten to initiate metatheses of cis-2-pentene, cyclooctene, cycloheptene, and cyclopentene, but too much quenches the reactions. The first three of these transformations are remarkably stereoselective, yielding olefins that are 94 to 97 cis. These observations accord with the hypothesis that Scheme 1 is the mechanism of acetylene polymerization. They also provide a functional equivalent an acetylene of the organometallic cocatalysts like ethylaluminum dichloride, unique in operating in the absence of strong Lewis acid metal-halides. Author