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.