Lutidine-derived Ru-CNC hydrogenation pincer catalysts with versatile coordination properties

Abstract

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.