Ruthenium N-Heterocyclic Carbene Complexes for the Catalysis of Nonmetathesis Organic Transformations

Ruthenium N-heterocyclic carbene (NHC) complexes have been at the forefront of the development of NHCs into the ubiquitous ligands now found in organometallic catalysis. This chapter reveals quite clearly not only a continued growth in interest in Ru-NHC catalysis, but more obviously, a very significant diversification of catalytic applications. The hydrogenation chemistry of half-sandwich Ru complexes containing primary amino functionalized NHC ligands has been developed principally by the Morris group. Some of the Ru-NHC catalysts active for transfer hydrogenation have also been used in the direct hydrogenation. There has been significant interest and significant developments in the use of Ru-NHC complexes for the so-called borrowing hydrogen reactions, which brings about temporary oxidation of alcohols to aldehydes and ketones, which are then utilized for the formation of new C-C and C-N bonds. Neutral half-sandwich complexes of the form [Cp*LRu(NHC)Cl] have been employed in the racemization of chiral alcohols.