Reactive intermediates formed during olefin polymerization by methylalumoxane-activated ansa-zirconocene catalysts: identification of a chain-carrying intermediate by NMR methods.

Addition of 1-hexene to methylalumoxane-activated catalyst systems based on rac-Me(2)Si(ind)(2)ZrMe(2) causes, concurrent with polyhexene formation and diminution of the otherwise prevalent cation [rac-Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMe(2)](+), formation of a hitherto unobserved species [rac-Me(2)Si(ind)(2)Zr(mu-R)(mu-Me)AlMe(2)](+), where R is a Zr-bound polyhexyl chain. As hexene is increasingly consumed, this cation decays, mainly back to [rac-Me(2)Si(ind)(2)Zr(mu-Me)(2)AlMe(2)](+) and, in part, to some species containing a Zr-bound allylic chain end.