C-F Bond activation at Ni(0) and simple reactions of square planar Ni(II) fluoride complexes

The reaction of Ni(COD)(2)(COD = 1,5-cyclooctadiene) with triethylphosphine and pentafluoropyridine in hexane has been shown previously to yield trans-[NiF(2-C(5)NF(4))(PEt(3))(2)](1a) with a preference for reaction at the 2-position of the heteroaromatic. The corresponding reaction with 2,3,5,6-tetrafluoropyridine was shown to yield trans-[NiF(2-C(5)NF(3)H)(PEt(3))(2)](1b). In this paper, we show that reaction of Ni(COD)(2) with triethylphosphine and pentafluoropyridine in THF yields a mixture of 1a and 1b. Competition reactions of Ni(COD)(2) with triethylphosphine in the presence of mixtures of heteroaromatics in hexane reveal a kinetic preference of k(pentafluoropyridine):k(2,3,5,6-tetrafluoropyridine)= 5.4:1. Treatment of 1a and 1b with Me(3)SiN(3) affords trans-[Ni(N(3))(2-C(5)NF(4))(PEt(3))(2)](2a) and trans-[Ni(N(3))(2-C(5)NHF(3))(PEt(3))(2)](2b), respectively. The complex trans-[Ni(NCO)(2-C(5)NHF(3))(PEt(3))(2)](3b) is obtained on reaction of with Me(3)SiNCO and by photolysis of under CO, while trans-[Ni(eta(1)-C [triple bond CPh)(2-C(5)NF(4))(PEt(3))(2)](4a) is obtained by reaction of phenylacetylene with 1a. Addition of KCN, KI and NaOAc to complex 1a affords trans-[Ni(X)(2-C(5)NF(4))(PEt(3))(2)](5a X = CN, 6a X = I, 7a X = OAc), respectively. The PEt(3) groups of complex are readily replaced by addition of 1,2-bis(dicyclohexylphosphino)ethane (dcpe) to produce [NiF(2-C(5)F(4)N)(dcpe)](8a). Addition of dcpe to trans-[Ni(OTf)(2-C(5)F(4)N)(PEt(3))(2)](10a), however, yields the salt [Ni(2-C(5)F(4)N)(dcpe)(PEt(3))](OTf)(9a) by substitution of only one PEt(3) and displacement of the triflate ligand. The structures of 2b, 4a, 7a and 8a were determined by X-ray crystallography. The influence of different ancillary ligands on the bond lengths and angles of square-planar nickel structures with polyfluoropyridyl ligands is analysed.