A terminal nickel(II) anilide complex featuring an unsymmetrically substituted amido pincer ligand: synthesis and reactivity

This work describes preparation and reaction chemistry of a terminal nickel(II) anilide complex supported by an unsymmetrically substituted diarylamido diphosphine ligand, [N(o-C6H4PPh2)(o-(C6H4PPr2)-Pr-i)](-) ([Ph-PNP-Pr-i]-). Treatment of NiCl2(DME) with H[Ph-PNP-Pr-i] in THF at room temperature produced [Ph-PNP-Pr-i]NiCl as green crystals in 82% yield. Salt metathesis of [Ph-PNP-Pr-i] NiCl with LiNHPh(THF) in THF at -35 degrees C generated cleanly [Ph-PNP-Pr-i] NiNHPh as a greenish blue solid. The anilide complex deprotonates protic (e.g., PhOH and PhSH) and aprotic (e.g., trimethylsilylacetylene, phenylacetylene, and acetonitrile) acids in benzene at room temperature to give quantitatively [Ph-PNP-iPr]NiX (X = OPh, SPh, C equivalent to CSiMe3, C equivalent to CPh, CH2CN). In addition, [Ph-PNP-Pr-i]NiNHPh also behaves as a nucleophile to react with acetyl chloride to yield [Ph-PNP-Pr-i]NiCl and N-phenylacetamide quantitatively. Carbonylation of [Ph-PNP-Pr-i]NiNHPh with carbon monoxide affords cleanly the carbamoyl derivative [Ph-PNP-Pr-i]Ni[C(O) NHPh]. The relative bond strengths of Ni-E in [Ph-PNP-Pr-i]NiEPh (E equivalent to NH, O, S, C equivalent to C) are assessed and discussed.