Phosphorus Analogues of [Ni(bpy) 2 ]: Synthesis and Application in Carbon-Halogen Bond Activation.

The neutral, homoleptic pyridylphosphininenickel(0) complex [Ni(2-Py-4,6-Ph ₂ -PC ₅ H ₂ ) ₂ ] ( 1 ) has been obtained by reaction of the formal Ni(0) source [(IPr)Ni(H ₂ C═CHSiMe ₃ ) 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 ]BF ₄ , [ 1 (THF)]PF ₆ , and [ 1 ₂ ](BAr ^F ₄ ) ₂ . The structures of these salts reveal an interesting dependence on the nature of the anion. While [ 1 ]BF ₄ and [ 1 (THF)]PF ₆ show trigonal-bipyramidal coordination of Ni in the solid state, [ 1 ₂ ](BAr ^F ₄ ) ₂ exists as a dinuclear Ni(I) complex and possesses a bridging phosphinine moiety in a rare μ ₂ 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 λ ⁵ 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.