Metal-ligand cooperation as key in formation of dearomatized Ni^(II)-H pincer complexes and in their reactivity towards CO and CO₂

The unique synthesis and reactivity of [(RPNP*)NiH] complexes, based on metal-ligand cooperation (MLC), is presented (RPNP* = deprotonated PNP ligand, R = iPr, tBu). Unexpectedly, the dearomatized complexes were obtained by reduction of the dicationic complexes [(RPNP)Ni(MeCN)])(BF4)2 with sodium amalgam, or by reaction of the free ligand with Ni(0)(COD)2. The iPr complex reacts with CO via MLC, to give a rare case of a distorted octahedral PNP-based pincer complex, the Ni(0) complex [(iPrPNP)Ni(CO)]. The dearomatized complexes also react with CO2 via MLC to form a rare example of 1-binding of CO2 to nickel, [(RPNP)Ni-1-CO2]. The iPr analog of this complex is capable of CO2 cleavage process involving C-O and C-P cleavage and C-C bond formation leading to the Ni-CO complex and to the new complex [(PiPr2NC2O2)Ni(P(O)iPr2)].