Plane sites prochiral

It is interesting to note that the interaction of a prochiral reactant with a chiral step-kink site and with an adsorbed chiral modifier each fiilfills the three-point contact model required for chiral recognition [102-104]. At a step-kink site, the reactant adsorbed in the pro-(l ) geometry contacts the surface plane, the step, and the kink in a way that is not equivalent to the pro-(S) adsorbate. Similarly, in the modifier-reactant interaction between methyiacetoacetate and pyroglutamate, it is proposed that the reactant has three key points of contact comprising the metal-molecule interaction and two intermolecular H-bonds with the modifier [101]. 

Complexes with C -symmetry (e.g., 2, Figure 9.6) have an internal vertical mirror plane bisecting the ligand from back to front. The two coordination sites formed after activation are mirror images, and therefore show opposite selectivity for the coordination and insertion of the prochiral monomer. This means that the preferred propylene face for coordination changes after every insertion step, which affords a syndiotactic polypropylene microstructure. 

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