This invention relates to the field of olefin polymerization catalyst compositions, and methods for the polymerization and copolymerization of olefins, including polymerization methods using a catalyst composition. One aspect of this invention is the formation and use of a catalyst composition comprising a stannoxy-substituted half-sandwich metallocene and an activator for olefin polymerization processes. For example, this invention encompasses the preparation of (⁵-C₅H₅)Ti(OSnPh₃)Cl₂, its contact with an activator, for example, zinc-impregnated chlorided alumina, to form a catalyst composition, and the use of this catalyst composition for polymerizing olefins or acetylenes.