Mechanism of Titanocene Metallacyclobutane Cleavage and the Nature of the Reactive Intermediate

Article abstract of DOI:10.1021/ja00250a021

The mechanism of titanocene metallacyclobutane cleavage to give a titanocene methylidene is examined in detail.The reaction of titanocene metallacyclobutanes with acetylenes or olefins displays either first- or second-order kinetics depending upon the metallacycle, its reaction temperature, and the trapping reagent.The rate-determining step for cleavage is the formation of an olefin-titanocene methylidene complex.Evidence for this complex is presented by competition experiments and kinetic studies of titanocene methylidene phosphine adducts.Deuterium isotope effect studies on an α-d₂ metallacycle reveal a preference for cleavage toward placing deuterium in the liberated olefin.The studies presented allow for the rational control of the catalytic activity of titanocene metallacyclobutanes.