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

Abstract

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-C₆H₄PⁱPr₂)]⁻ ([Ph-PNP-ⁱPr]⁻). Treatment of NiCl₂(DME) with H[Ph-PNP-ⁱPr] in THF at room temperature produced [Ph-PNP-ⁱPr]NiCl as green crystals in 82% yield. Salt metathesis of [Ph-PNP-ⁱPr]NiCl with LiNHPh(THF) in THF at −35 °C generated cleanly [Ph-PNP-ⁱPr]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, CCSiMe₃, CCPh, CH₂CN). In addition, [Ph-PNP-ⁱPr]NiNHPh also behaves as a nucleophile to react with acetyl chloride to yield [Ph-PNP-ⁱPr]NiCl and N-phenylacetamide quantitatively. Carbonylation of [Ph-PNP-ⁱPr]NiNHPh with carbon monoxide affords cleanly the carbamoyl derivative [Ph-PNP-ⁱPr]Ni[C(O)NHPh]. The relative bond strengths of Ni–E in [Ph-PNP-ⁱPr]NiEPh (E = NH, O, S, CC) are assessed and discussed.