Chemistry of nickel tetrafluoropyridyl derivatives: their versatile behaviour with Brønsted acids and the Lewis acid BF3

Abstract

Treatment of trans-[NiF(2-C₅NF₄)(PEt₃)₂] (C₅NF₄ = tetrafluoropyridyl) (1) with HCl effects the formation of the air stable chloride complex trans-[NiCl(2-C₅NF₄)(PEt₃)₂] (2). The reaction of 2 with excess HCl slowly yields 2,3,4,5-tetrafluoropyridine (4). On reaction of 4 with [Ni(COD)(PEt₃)₂], the C–F activation product trans-[NiF(2-C₅NF₃H)(PEt₃)₂] (5) is formed instantly. The bifluoride compound trans-[Ni(FHF)(2-C₅NF₄)(PEt₃)₂] (6) is obtained on treatment of 1 with Et₃N·3HF. Reaction of 2 with HBF₄ yields the binuclear complex [NiCl{μ-κ²(C,N)-(2-C₅NF₄)}(PEt₃)]₂ (7). The X-ray crystal structure of 7 reveals a “butterfly”-shaped dimeric complex with square-planar coordination at both nickel atoms, with Ni–N distances of 1.965(4) and 1.955(4) Å and Ni–C distances of 1.884(5) and 1.875(5) Å. Treatment of 1 with BF₃·OEt₂ in the presence of acetonitrile yields the cationic compound trans-[Ni(2-C₅NF₄)(NCMe)(PEt₃)₂]BF₄ (8), while reaction of trans-[Ni(OTf)(2-C₅NF₄)(PEt₃)₂] (3) with NaBAr′₄ and acetonitrile gives trans-[Ni(2-C₅NF₄)(NCMe)(PEt₃)₂]BAr′₄ (9) [Ar′ = 3,5-C₆H₃(CF₃)₂]. The studies reported in this paper provide methods for the synthesis of tetrafluoropyridines substituted in the 2-position and demonstrate the behaviour of nickel derivatives with Brønsted acids and the Lewis acid BF₃.