Homoleptic Organoderivatives of High-Valent Nickel(III)

Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu4](2)[Ni-II(C6X5)(4)] [X=F (1), Cl (2)] have been prepared by low-temperature treatment of the halo-complex precursor [NBu4](2)[NiBr4] with the corresponding organolithium reagent LiC6X5. Compounds 1 and 2 are electrochemically related by reversible one-electron exchange processes with the corresponding organometallate(III) compounds [NBu4][Ni-III(C6X5)(4)] [X = F (3), Cl (4)]. The potentials of the [Ni-III(C6X5)(4)](-)/[Ni-II(C6X5)(4)](2-) couples are +0.07 and -0.11 V for X=F or Cl, respectively. Compounds 3 and 4 have also been prepared and isolated in good yield by chemical oxidation of 1 or 2 with bromine or the amminium salt [N(C6H4Br-4)(3)][SbCl6]. The [Ni-III(C6X5)(4)](-) species have SP-4 structures in the salts 3 and 4, as established by single-crystal X-ray diffraction methods. The [Ni-II(C6F5)(4)](2-) ion in the parent compound 1 has also been found to exhibit a rather similar SP-4 structure. According to their SP-4 geometry, the Ni-III compounds (d(7)) behave as S = 1/2, systems both at microscopic (EPR) and macroscopic levels (ac and dc magnetization measurements). The spin Hamiltonian parameters obtained from the analysis of the magnetic behavior of 3 and 4 within the framework of ligand field theory show that the unpaired electron is centered mainly on the metal atom, with > 97% estimated d(z2) contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C6X5-C6X5 coupling compounds.