Lutidine-Derived Ru-CNC Hydrogenation Pincer Catalysts with Versatile Coordination Properties

Lutidine-derived
bis-N-heterocyclic carbene (NHC) ruthenium CNC–pincer
complexes (Ru-CNC’s) were prepared. Depending on the synthetic
procedure, normal (1, 2) or mixed normal/abnormal
NHC-complexes (3) are formed. In the presence of phosphazene
base, Ru-CNC complexes activate nitriles to give ketimino compounds 4–6. Nitrile adduct 4 shows
reactivity toward strong bases to yield dearomatized complex 7, which heterolytically activates H2 to form the
bis-hydrido complex 8. Finally, these Ru-CNC’s
are active in catalytic hydrogenation of CO2 to formate
salts, and unlike the phosphine-containing Ru-PNP counterpart, they
also catalyze the selective hydrogenation of esters to alcohols.