Tuning of ruthenium N-heterocyclic carbene catalysts for ATRP

Depending on the substituents, R1 and R2, ruthenium(II)–p-cymene complexes bearing N-heterocyclic carbene ligands are either efficient catalysts for the well-controlled atom transfer radical polymerisation of methyl methacrylate and styrene, or promote a redox-initiated free-radical process.