Catalyst compositions useful for the polymerization of olefins are
disclosed. These compositions comprise a Group 8-10 metal complex
comprising a bidentate or variable denticity ligand comprising one or two
nitrogen donor atom or atoms independently substituted by an aromatic or
heteroaromatic ring(s), wherein the ortho positions of said ring(s) are
substituted by aryl or heteroaryl groups. Also disclosed are processes for
the polymerization of olefins using the catalyst compositions.