Metal–Ligand Cooperation as Key in Formationof Dearomatized NiII–H Pincer Complexes and in TheirReactivity toward CO and CO2

摘要

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.