New bis(N,N-trimethylsilylarylamidinate) zirconium dichloride complexes with various carbon substituents were prepared, and their solid as well as solution state structures were studied. In the polymerization of propylene, after activation by MAO, these catalysts provided two fractions. Ether soluble polymers were obtained at a low activity as sticky polymers with lower molecular weights, except with the o-OMe substituted complex. The solid fractions were composed of a highly isotactic polymer and a moderately syndiotactic polymer. An interesting linear correlation was found between the rates of the 2,1 and 3,1 insertions for the ether soluble fractions.