Phosphorus Analogues of [Ni(bpy)₂]: Synthesis and Application in CarbontextendashHalogen Bond Activation

The neutral, homoleptic pyridylphosphininenickel(0) complex [Ni(₂-Py-4,6-Ph₂-PC₅H₂)₂] (1) has been obtained by reaction of the formal Ni(0) source [(IPr)Ni(H₂C═CHSiMe₃)₂] with 2 equiv of 2-(2′-pyridyl)-4,6-diphenylphosphinine (L). Compound 1 can be oxidized both electrochemically and through the use of ferrocenium salts, to afford the corresponding Ni(I) complexes [1]BF₄, [1(THF)]PF₆, and [1₂](BAr^F₄)₂. The structures of these salts reveal an interesting dependence on the nature of the anion. While [1]BF₄ and [1(THF)]PF₆ show trigonal-bipyramidal coordination of Ni in the solid state, [1₂](BAr^F₄)₂ exists as a dinuclear Ni(I) complex and possesses a bridging phosphinine moiety in a rare μ₂ mode. Reactions of 1 with halobenzenes highlight the noninnocent behavior of the aromatic phosphinine ligand, leading to the formation of oxidized Ni complexes but not to classical oxidative addition products. The reaction of 1 with bromobenzene affords the λ⁵ phosphinine 2 and the bipyramidal Ni(I) complex [1]Br, whereas a more unconventional oxidation product 3 is formed from the reaction of 1 and iodobenzene.