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

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) A and Ni–C distances of 1.884(5) and 1.875(5) A. 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 Bronsted acids and the Lewis acid BF3.