Processes of making catalyst compositions are provided. In an exemplary embodiment, the processes include modifying an organoaluminum compound with a modifier that decreases the initial reducing strength of the organoaluminum compound, where the modifier can be an ether, an anhydride, an amine, an amide, a silicate, a silyl ether, a siloxane, an ester, a carbonate, a urea, a carbamate, a sulfoxide, a sulfone, a phosphoramide, or a combination thereof. The processes further include adding a transition metal complex to the mixture of the organoaluminum compound and the modifier; and obtaining a catalyst composition including the organoaluminum compound and the transition metal complex.