Mechanism of stereospecific polymerization of α-olefins by late-transition metal and octahedral group 4 metal catalysts

In the last few years remarkable advances have been made in the field of non-cyclopentadienyl complexes as homogeneous olefin polymerization catalysts. In this paper we summarize some recent literature data concerning the stereochemical mechanism of α-olefin polymerization promoted by late transition metal systems and bi- and tetra-dentate imine phenolate group 4 metal complexes. NMR analysis of the fine structure of suitably labelled polymers, obtained by using isotopically enriched catalysts or monomers, provided valuable information on the regiochemistry and stereochemistry of the polymerization. In particular, 13C was introduced in different points of the polymer chain as a sort of magnifying lens to observe fine aspects of the microstructure, and to establish a chronology in the sequence of the monomer insertions.