Ansa-zirconocene diamide complex rac-Me2Si(CMB)(2)Zr(NMe2)(2) (rac-1, CMB = 1-C5H2-2-Me-4-Bu-t) reacts with AlR3 (R = Me, Et, i-Bu) and then with [CPh3](+) [B(C6F5)(4)](-) (2) in toluene in order to in situ generate cationic alkylzirconium species. In the sequential NNR-scale reactions of rac-1 with various amount of AlMe3 and 2, rac-1 transforms first to rac-Me2Si(CMB)(2)Zr(Me)(NMe2) (rac-3) and [rac-Me2Si(CMB)(2)ZrMe](+) (rac-4) by the reaction with AlMe3, and then to [rac-Me2Si(CMB)(2)ZrMe](+) (5(+)) cation by the reaction of the resulting mixtures with 2. The activities of propylene polymerizations by rac-1/Al(i-Bu)(3)/2 system are dependent on the type and concentration of AlR3, resulting in the order of activity: rac-1/Al(i-Bu)(3)/2 > rac-1/AlEt3/2 > rac-1/lMAO much greater than rac-1/AlMe3/2 system. The bulkier isobutyl substituents make inactive catalytic species sterically unfavorable and give rise to more separated ion pairs so that the monomers can easily access to the active sites. The dependence of the maximum rate (R-p,R-max) on polymerization temperature (T-p) obtained by rac-1/Al(i-Bu)(3)/2 system follows Arrhenius relation, and the overall activation energy corresponds to 0.34 kcal/mol. The molecular weight (MW) of the resulting isotactic polypropylene (iPP) is not sensitive to Al(i-Bu), concentration The analysis of regiochemical errors of iPP shows that the chain transfer to Al(i-Bu), is a minor chain termination. The 1,3-addition of propylene monomer is the main source of regiochemical sequence and the [mr] sequence is negligible, as a result the meso pentad ([mmmm]) values of iPPs are very high ([mmmm] > 94%). These results can explain the fact that rac-1/Al(i-Bu)(3)/2 system keeps high activity over a wide range of [Al(iBu)(3)]/[Zr] ratio between 32 and 3,260.