Ruthenium N-heterocyclic carbene complexes: Versatile catalysts precursors for olefin metathesis, olefin cyclopropanation, and radical reactions

N-heterocyclic carbenes are divalent carbon species, which are commonly used as neutral, two-electron ligands with a negligible p-back-bonding tendency. They behave as phosphine mimics, yet they are better s-donors and they form stronger bonds to metal centres than most phosphines. Their electronic and steric properties are liable to ample modification simply by varying the substituents on the nitrogen atoms. Therefore, N-heterocyclic carbenes constitute a promising new class of ligands available for catalyst engineering and fine tuning, and a great deal of attention has been paid to them recently.
We found that the 18-electron complex RuCl2(p-cymene)(PCy3) was a versatile and efficient promoter for the ring-opening metathesis polymerisation of both strained and low-strain cyclic olefins when activated by a suitable carbene precursor such as trimethylsilyl-diazomethane. RuCl2(p-cymene)(PCy3) was also an excellent catalyst for ATRP (Atom Transfer Radical Polymerisation) of methyl methacrylate and styrene. Here, we present preliminary results obtained in olefin metathesis, olefin cyclopropanation, and radical reactions (ATRP and
Kharasch addition) when tricyclohexylphosphine was substituted by an N-heterocyclic ligand.