Metal–Ligand Cooperation as Key in Formation of Dearomatized Ni(II)–H Pincer Complexes and in Their Reactivity toward CO and CO(2)

[Image: see text] The unique synthesis and reactivity of [((R)PNP*)NiH] complexes (1a,b), based on metal–ligand cooperation (MLC), are presented ((R)PNP* = deprotonated PNP ligand, R = (i)Pr, (t)Bu). Unexpectedly, the dearomatized complexes 1a,b were obtained by reduction of the dicationic complexes [((R)PNP)Ni(MeCN)](BF(4))(2) with sodium amalgam or by reaction of the free ligand with Ni(0)(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 CO(2) via MLC to form a rare example of η(1) binding of CO(2) to nickel, complexes 4a,b. An unusual CO(2) 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 [(P(i)Pr(2)NC(2)O(2))Ni(P(O)(i)Pr(2))] (5b). All complexes have been fully characterized by NMR and X-ray crystallography.