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

Treatment of trans-[NiF(2-C5NF4)(PEt3)(2)] (C5NF4=tetrafluoropyridyl) (1) w ith HCl effects the formation of the air stable chloride complex trans-[NiC l(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)], t he C-F activation product trans-[NiF(2-C5NF3H)(PEt3)(2)] (5) is formed inst antly. The bifluoride compound trans-[Ni(FHF)(2-C5NF4)(PEt3)(2)] (6) is obt ained on treatment of 1 with Et3N . 3HF. Reaction of 2 with HBF4 yields the binuclear complex [NiCl{mu-kappa(2)(C,N)-(2-C5NF4)}(PEt3)](2) (7). The X-r ay 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) Angstrom and Ni-C distances of 1.884(5) and 1.875(5) An gstrom. Treatment of 1 with BF3. OEt2 in the presence of acetonitrile yield s the cationic compound trans-[Ni(2-C5NF4)(NCMe)(PEt3)(2)]BF4 (8), while re action of trans-[Ni(OTf)(2-C5NF4)(PEt3)(2)] (3) with NaBAr'(4) and acetonit rile 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 b ehaviour of nickel derivatives with Bronsted acids and the Lewis acid BF3.