Evaluation of ruthenium‐based catalytic systems for the controlled atom transfer radical polymerisation of vinyl monomers

Only [RuCl2(p-cymene)(PR3)] complexes where the phosphine ligand, PR3, is both strongly basic and bulky proved to be effective catalysts for the controlled atom transfer radical polymerisation (ATRP) of methyl methacrylate and styrene. The best phosphine ligands were typically P(i-Pr)3, P(cyclohexyl)2Ph, P(cyclohexyl)3, and P(cyclopentyl)3. Less basic and/or bulky phosphines led to ineffective systems for ATRP. Tricyclohexylarsine gave rise to a highly efficient catalyst system. However, related complexes in which the phosphine ligand was replaced by tricyclohexylstibine, nitrogen (piperidine and 4-cyanopyridine) and carbon ligands (alkyl isocyanides) proved to be inefficient. The observation of a direct relationship between the p-cymene lability (measured by TGA) and catalyst activity suggests that p-cymene release is a prerequisite for the polymerisation process.