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 (d⁷) 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 contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C₆X₅? C₆X₅ coupling compounds.