Ni(ii) complexes of the phosphine-oxime Ph2PC6H4-2-CHNOH

Abstract

We report the solution and structural chemistry of nickel(II) complexes of the phosphine-oxime Ph₂PC₆H₄-2-CHNOH (PCHNOH). PCHNOH invariably binds in a bidentate manner as illustrated by cis-Ni(PCHNOH)₂Cl₂ and cis-[Ni(PCHNOH)₂]²⁺ (as its BF₄⁻ salt). Treatment of PCHNOH with Ni(OAc)₂(H₂O)₄ gave charge-neutral trans-[Ni(PCHNO)₂]⁰. Treatment of trans-[Ni(PCHNO)₂]⁰ with BF₃ gave [Ni(PCHNO)₂BF₂]BF₄. The cation features a planar NiP₂N₂ center wherein the pair of oximate groups are linked by the difluoroboryl center. The 1 : 1 complexes of the oxime and the oximate are illustrated by [Ni(PCHNOH)Cl₂]₂ and [Ni(C₆F₅)(PCHNO)]₂, which feature five- and four-coordinate Ni(II) centers, respectively. All complexes in this series hydrolyze to give the trinickel oxo-phosphine-oximate complex [Ni₃(PCHNO)₃O]⁺. One feature of the PCHNOH ligand is its wide bite angle combined with its protic OH center. These aspects are manifested in the structures of Ni(PCHNOH)₂Cl₂ and [Ni(PCHNOH)Cl₂]₂, which show intramolecular hydrogen bonding to terminal chloride ligands.