An activated solid catalyst component is disclosed formed from a magnesium compound, a titanium compound, an organosilicon compound, a supportive electron donor, and at least one internal electron donor. The solid catalyst component is activated to include titanium and carbon bonds by reaction with an activation agent, such as an aluminum compound. In one embodiment, small amounts of polymer are polymerized with the catalyst component during activation. The activated catalyst component is stable and, when formed, can later be used to produce various polyolefin polymers. The activated catalyst component has controlled reaction kinetics so that the catalyst does not overheat and degrade during initial polymerization.