Synthesis of unsymmetrical 5,6-POCOP′-type pincer complexes of nickel(ii): impact of nickelacycle size on structures and spectroscopic properties

Abstract

This report describes the synthesis and characterization of a family of unsymmetrical pincer complexes of nickel(II), featuring both 5- and 6-membered nickelacycles. The room temperature reaction of NiBr₂(NCCH₃)_x with bis(phosphinite) ligand, 1-(i-Pr₂PO),3-(i-Pr₂POCH₂)-C₆H₄ (POCHOP′), results in direct nickelation at the 2-position of the aromatic ring to give (5,6-POCOP′)NiBr (5,6-POCOP′ = κ^P,κ^C,κ^P′-2-(i-Pr₂PO),6-(i-Pr₂POCH₂)-C₆H₃). This complex undergoes salt metathesis reactions with M′X to give the corresponding charge neutral derivatives, (5,6-POCOP′)NiX (X = OSO₂CF₃, OSO₂(4-CH₃-C₆H₄), CH₃, and CCCH₃), whereas the abstraction of bromide by AgBPh₄ in acetonitrile gave the cationic derivative, [(5,6-POCOP′)Ni(NCCH₃)][BPh₄]. The new complexes have been characterized by multinuclear NMR spectroscopy and X-ray diffraction studies. The reactivities of the new complexes (5,6-POCOP′)NiX (X = Br, OSO₂CF₃) have been explored briefly to establish the nucleophilicity of the X ligand and the substitutional lability of the phosphinite moiety in the 6-membered cycle.