Deoxygenative hydrogenation of amides to amines homogeneously catalyzed by a complex of an Earth-abundant metal is presented. This manganese-catalyzed reaction features high efficiency and selectivity. A plausible reaction mechanism, involving metal–ligand cooperation of the manganese pincer complex, is proposed based on NMR studies and relevant stoichiometric reactions.

The unique synthesis and reactivity of [(RPNP*)NiH] complexes (1a,b), based on metal–ligand cooperation (MLC), are presented (RPNP* = deprotonated PNP ligand, R = iPr, tBu). Unexpectedly, the dearomatized complexes 1a,b were obtained by reduction of the dicationic complexes [(RPNP)Ni(MeCN)](BF4)2 with sodium amalgam or by reaction of the free ligand with Ni0(COD)2. Complex 1b reacts with CO via MLC, to give a rare case of a distorted-octahedral PNP-based pincer complex, the Ni(0) complex 3b. Complexes 1a,b also react with CO2 via MLC to form a rare example of η1 binding of CO2 to nickel, complexes 4a,b. An unusual CO2 cleavage process by complex 4b, involving C–O and C–P cleavage and C–C bond formation, led to the Ni–CO complex 3b and to the new complex [(PiPr2NC2O2)Ni(P(O)iPr2)] (5b). All complexes have been fully characterized by NMR and X-ray crystallography.

Acridine-based PNP pincer complexes have been previously utilized for several environmentally benign catalytic processes. In light of the recent growth in interest in base-metal catalysis, we report here the synthesis of acridine-PNP pincer complexes of Ni, Co, Fe, and Mn. We also report here the noninnocent redox nature of these complexes that results in the dimerization of pincer complexes by forming a C–C bond at the C9 position of the acridine ring.