Scheme 3 Activation Mechanism This is because the dissociation of Me3Al from the primary kinetic product [SBIZrMe2AlMe2] [7,4] (3b) is the least unfavorable of the dissociation equilibria (Table , entries 6-8) so that the overall rate and extent of formation of 2b with kobs = (k1K1/k1+k-1)[Zr] (with k1 ~ k-1) is much greater than any other competing sequence of steps.