Homoleptic Organoderivatives of High‐Valent Nickel(III)

Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu 4 ] 2 [Ni II (C 6 X 5 ) 4 ] [X=F ( 1 ), Cl ( 2 )] have been prepared by low‐temperature treatment of the halo‐complex precursor [NBu 4 ] 2 [NiBr 4 ] with the corresponding organolithium reagent LiC 6 X 5 . Compounds 1 and 2 are electrochemically related by reversible one‐electron exchange processes with the corresponding organometallate(III) compounds [NBu 4 ][Ni III (C 6 X 5 ) 4 ] [X=F ( 3 ), Cl ( 4 )]. The potentials of the [Ni III (C 6 X 5 ) 4 ] − /[Ni II (C 6 X 5 ) 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(C 6 H 4 Br‐4) 3 ][SbCl 6 ]. The [Ni III (C 6 X 5 ) 4 ] − species have SP ‐4 structures in the salts 3 and 4 , as established by single‐crystal X‐ray diffraction methods. The [Ni II (C 6 F 5 ) 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   z   2contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C 6 X 5 C 6 X 5 coupling compounds.