In this work we address the problem of isotacticity in a realistic heterogeneous Ziegler-Natta system by means of ab initio molecular dynamics. We focus on a previously identified 5-fold catalytic center, and we inspect its ability to select the appropriate olefin enantioface in the chain growth process. We study the first steps in the propene polymerization process and determine the energetics of the initial complexation phase for the different stereochemical orientations of the incoming propene. Then we analyze the subsequent insertions, which represent the crucial issue for the formation of a stereospecific polymer chain, and we find that the 5-fold catalytic center possesses a high degree of stereoselectivity. We examine the role of the agostic interaction, which can switch from alpha to beta and allow, even in the presence of a substrate, processes that can lead to chain termination.