For all these reasons, we decided to model a hypothetical system in which the irreversible activation steps occurred at similar rates (Table , entries 1, 3 and 5; Table , entries 5-6), while the Me3Al dissociation steps involving 3c and 3b were identical but more favorable than for 3e such that no one product dominated ( Note that the specific features shown in Figure concur with experimental data on both propene polymerization (bell-shaped polymerization rate data at constant [Zr]) 2f and catalyst activation (i.e. saturation) behavior in the case of the SBI complex. In this hypothetical case the amount of active catalyst 2e never exceeds 3 mol% of total Zr under all conditions. This is in good but fortuitous agreement with estimates of active site concentration (ca. 8 mol%) estimated from kinetics of propene polymerization involving SBIZrMe2 and MAO (2400:1). 2a-b