In accordance with the present invention, there is provided a transition metal olefin polymerization catalyst component characterized by the formula: ##STR00001## where, M is a Group IV or a Group IV transition metal, B is a bridge group containing at least two carbon atoms, A' and A'' are organogroups, each containing a heteroatom selected from the group consisting of oxygen, sulfur, nitrogen and phosphorus, X is selected from the group consisting of chlorine, bromine, iodine, a C.sub.1-C.sub.20 alkyl group, a C.sub.6-C.sub.30 aromatic group and mixtures thereof, and n is 1, 2 or 3. The invention also encompasses a method for the polymerization of an ethylenically unsaturated monomer which comprises contacting a transition metal catalyst component as characterized by formula (1) above and an activating co-catalyst component in a polymerization reaction zone with an ethylenically unsaturated monomer under polymerization conditions to produce a polymer product.