Transmethylation of a four-coordinate nickel(i) monocarbonyl species with methyl iodide

Abstract

Three distinct oxidation states of a nickel carbonyl species, formally Ni(II), +1 and 0, (compounds 1, 2 and 3 respectively) have been realized using a (PNP)Ni scaffold (PNP⁻ = N[2-PⁱPr₂-4-Me-C₆H₃]₂⁻). X-ray diffraction (XRD) studies of these carbonyl complexes show a geometrical change about the nickel center from square planar (1) to pyramidal (2) and pseudotetrahedral (3). Interestingly, the Ni–C bond distance of 2 is longer than that of 1 and 3 due to the electron population of the antibonding d_x²−y² orbital. A difference in the reactivity of these nickel carbonyl species was clearly observed. Reaction of the monovalent nickel carbonyl species (2) with CH₃I revealed the formation of (PNP)NiCOCH₃ (4) via C–C bond coupling while the zerovalent congener (3) underwent an oxidative ligand substitution reaction.