Mechanistic study of β-methyl and β-hydrogen elimination in the zirconocene compounds CP′2ZrR(μ-CH3)B(C6F5)3 (Cp′ = Cp, Cp*; R = CH2CMe3, CH2CHMe2)

A kinetics study of beta-methyl elimination reactions of the compounds Cp2ZrNp(mu-Me)B(C6F5)(3) (in various solvents) and Cp*2ZrNp(mu-Me)B(C6F5)(3) (in CD2Cl2) shows that the reactions are accelerated by polar solvents and by steric crowding in the Cp* system, results consistent with previous findings and conclusions that the methyl migrations are accompanied in a concerted process by borate anion departure from the inner coordination sphere of the metal ion. Surprisingly, however, the isobutyl compound CP*Zr-2(i-Bu)(mu-Me)B(C6F5)(3), which is expected to undergo beta-methyl elimination by analogy with an extensive literature on chain transfer processes during propylene polymerization, undergoes very rapid beta-hydrogen elimination only.