REACTIONS OF ALKYNES AND CARBENE EQUIVALENTS WITH OXO(SALEN)CHROMIUM(V) COMPLEXES

Alkynes are oxidized by oxo(salen)chromium(V) triflate and related com plexes 2 to form 1,2-diones. The oxidation of diphenylacetylene procee ds by formation of an intermediate which reacts more rapidly with a se cond equivalent of oxometal complex to form benzil. The intermediate i s most likely a metallaoxetene or a related species, such as a metallo carbene. Reactions of phosphorus or nitrile ylides with 2 proceed to f orm carbonyl compounds (and phosphine oxide or nitrile) in a manner co nsistent with participation of similar intermediates. The reactions ap pear to be related mechanistically to alkene epoxidation by the same o xometal complexes.