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

The reactivity of a series of nickel­(II) hydride, alkyl, and anilide complexes supported by amido diphosphine ligands, including symmetrical [N­(<i>o</i>-C₆H₄PR₂)₂]⁻ (R = Ph (<b>1a</b>), ^<i>i</i>Pr (<b>1c</b>), Cy (<b>1d</b>)) and unsymmetrical [N­(<i>o</i>-C₆H₄PPh₂)­(<i>o</i>-C₆H₄P^<i>i</i>Pr₂)]⁻ (<b>1b</b>), with carbon monoxide is described. Exposure of a benzene solution of [<b>1a</b>–<b>d</b>]­NiH to carbon monoxide under ambient conditions leads to reductive elimination of diarylamine to give quantitatively zerovalent nickel dicarbonyl complexes [H·<b>1a</b>–<b>d</b>]­Ni­(CO)₂ (<b>2</b>). Migratory insertion of CO into the Ni-R bonds of [<b>1</b>]­NiR in benzene solutions affords Ni­(II)-acyl derivatives [<b>1</b>]­NiC­(O)­R (R = Me (<b>3</b>), Et (<b>4</b>), <i>n</i>-hexyl (<b>5</b>), 2-norbornyl (<b>6</b>)). Interestingly, further carbonylation of acyl <b>3a</b> and <b>4a</b> generates [RC­(O)­N­(<i>o</i>-C₆H₄PPh₂)₂]­Ni­(CO)₂ (R = Me (<b>7a</b>), Et (<b>8a</b>)) as a result of C–N bond-forming reductive elimination whereas no reaction occurs for <b>3b</b>–<b>c</b> or <b>4b</b>–<b>c</b> under similar conditions. Carbonylation of the anilide complexes [<b>1</b>]­NiNHPh produces carbamoyl [<b>1</b>]­Ni­[C­(O)­NHPh] (<b>9</b>) 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