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 b oth strongly basic and bulky proved to be effective catalysts for the contr olled atom transfer radical polymerisation (ATRP) of methyl methacrylate an d styrene. The best phosphine ligands were typically P(i-Pr)(3), P(cyclohex yl)(2)Ph, P(cyclohexyl)(3), and P(cyclopentyl)(3). Less basic and/or bulky phosphines led to ineffective systems for ATRP. Tricyclohexylarsine gave ri se to a highly efficient catalyst system. However, related complexes in whi ch the phosphine ligand was replaced by tricyclohexylstibine, nitrogen (pip eridine and 4-cyanopyridine) and carbon ligands (alkyl isocyanides) proved to be inefficient. The observation of a direct relationship between the p-c ymene lability (measured by TGA) and catalyst activity suggests that p-cyme ne release is a prerequisite for the polymerisation process.