A silica supported catalyst system can be prepared that includes the product of admixing a magnesium alkoxide with a group 4, 5, or 6 transition metal complex to form a magnesium transition metal alkoxide adduct having the general formula: MgM(OR)2(OR1)pClq wherein M is a group 4, 5, or 6 transition metal; R is an alkyl or aryl moiety; R1 is a alkyl or aryl moiety having from 1 to 10 carbons, and p and q are 0 or an integer such that p+q equals the highest formal oxidation state of M; contacting the magnesium transition metal alkoxide adduct with a silica template to form a silica supported catalyst precursor; contacting the silica supported catalyst precursor chlorinating agent to form a chlorinated catalyst precursor; and contacting the chlorinated catalyst precursor with an aluminum alkyl to form a silica supported catalyst.