Divergent Carbonylation Reactivity Preferences of Nickel Complexes Containing Amido Pincer Ligands: Migratory Insertion versus Reductive Elimination

Abstract

The reactivity of a series of nickel(II) hydride, alkyl, and anilide complexes supported by amido diphosphine ligands, including symmetrical [N(o-C6H4PR2)2]− (R = Ph (1a), iPr (1c), Cy (1d)) and unsymmetrical [N(o-C6H4PPh2)(o-C6H4PiPr2)]− (1b), with carbon monoxide is described. Exposure of a benzene solution of [1a–d]NiH to carbon monoxide under ambient conditions leads to reductive elimination of diarylamine to give quantitatively zerovalent nickel dicarbonyl complexes [H·1a–d]Ni(CO)2 (2). Migratory insertion of CO into the Ni-R bonds of [1]NiR in benzene solutions affords Ni(II)-acyl derivatives [1]NiC(O)R (R = Me (3), Et (4), n-hexyl (5), 2-norbornyl (6)). Interestingly, further carbonylation of acyl 3a and 4a generates [RC(O)N(o-C6H4PPh2)2]Ni(CO)2 (R = Me (7a), Et (8a)) as a result of C–N bond-forming reductive elimination whereas no reaction occurs for 3b–c or 4b–c under similar conditions. Carbonylation of the anilide complexes [1]NiNHPh produces carbamoyl [1]Ni[C(O)NHPh] (9) as the final product irrespective of the identity of the phosphorus substituents. The decisive factors on the generation of these divergent carbonylation products are discussed.