Role(s) of TMA in polymerization

Quenched-flow data for propene polymerization with rac -Me 2 Si(2-Me-4-Ph-1-indenyl) 2 ZrCl 2 /MAO support a picture where removal of MAO qualitatively changes the kinetic profile from a mainly enthalpic to a mainly entropic barrier. DFT studies suggest that a not previously recognized singly-bridged end-on coordination mode of Me 6 Al 2 to catalytically active centers may be kinetically relevant as a resting state. In contrast, the more traditional doubly-bridged complex of Me 3 Al is proposed to be more relevant to chain transfer to cocatalyst. A new TMA-metallocene binding mode is presented and its role in entropy compensation in insertion chemistry discussed.