A method of forming a polyolefin catalyst component which includes chlorinating magnesium ethoxide, and then treating the solid first with an electron donor, particularly diethyl phthalate or di-isobutyl phthalate, at a relatively low donor level, and then second with a titanating agent, such as titanium tetrachloride, to produce a catalyst component. The catalyst component is activated with an aluminum alkyl cocatalyst. An organosilane compound can be added as a stereoselectivity control agent. The activated catalyst is used in the polymerization of olefins, particularly propylene, to obtain a polymer product with a broad molecular weight distribution.