NICKEL-COMPLEXES CONTAINING CATECHOLATE, BENZOQUINONE AND SEMIQUINONERADICAL LIGANDS

Quinone complexes of nickel have been prepared by treating Ni(CO)(4) w ith 3,6-di-tert-butyl-1,2-benzoquinone (3,6-DBBQ). Reactions carried o ut with stoichiometric quantities of 3,6-DBBQ lead to the formation of monomeric, square planar Ni(3,6-DBSQ)(2). Spins of the radical semiqu inone ligands are coupled antiferromagnetically to result in near diam agnetism. Electrochemical characterization has shown that the complex undergoes reduction in two one-electron steps. Chemical reduction with CoCp2 results in the formation of (CoCp2)[Ni(3,6-DBCat)(2)]. EPR spec tra recorded on this product show anisotropy that is consistent with t he Ni(III) formulation. Reactions carried out with Ni(CO)(4) and an ex cess of 3,6-DBBQ lead to the formation of Ni(3,6-DBBQ)(3,6-DBSQ)(2). C rystallographic characterization (Ni(3,6-DBBQ)(3,6-DBSQ)(2); orthorhom bic, Ccca, a = 20.092(6), b = 24.335(8), c = 18.340(4) Angstrom, V = 8 967(4) Angstrom(3), Z = 4) has shown that the metal is octahedral and that the benzoquinone and semiquinone ligands are differentiable by ch aracteristic C-O, C-C and Ni-O bond lengths. Magnetic properties are s lightly temperature dependent due to either weak antiferromagnetic Ni- SQ exchange or offsetting Ni-SQ (ferromagnetic) and SQ-SQ (antiferroma gnetic) exchange interactions. (C) 1997 Elsevier Science S.A.