Ruthenium Metathesis Catalysts with Saturated Unsymmetrical N-Heterocyclic Carbene Ligands

The facile synthesis of two new unsymmetrical N-heterocyclic carbene (NHC) ligands from commercially available monosubstituted diamines is presented. The resultant unsymmetrical NHC ligands have been complexed to ruthenium to give novel olefin metathesis initiators. Of particular interest, the new complexes (7a and 8a) gave significantly different E:Z ratios in cross-metathesis reactions and gave an improved selectivity in diastereoselective ring-closing metathesis, in comparison to the corresponding Grubbs 2 (2) and Hoveyda−Grubbs (3) complexes.