SYNTHESIS, STRUCTURE AND REACTIVITY OF COBALT(III) COMPLEXES WITH TRIDENTATE IMINO-OXIME AND AMINO-OXIME LIGANDS

The tridentate iminooximes HL(2) and HL(1) have been prepared by conde nsation of biacetyl monoxime with 2-(2-aminoethyl)pyridine and 2-(amin omethyl)pyridine, respectively. They reacted with cobalt(II) ion in th e presence of oxygen to give the complexes [Co(III)L(2)]ClO4 (L = L(1) or L(2)). The iminooxime may be hydrogenated in the presence of NaBH4 to yield the corresponding aminooximes HL(3) and HL(4), which, on rea ction with Co-II, formed the complexes [Co(III)L(HL)][ClO4](2) (L = L( 3) or L(4)). All these complexes have been structurally characterized by single-crystal X-ray diffraction. The cobalt has an octahedral envi ronment with the iminooxime ligands in mer configuration and the amino oxime, ones in fac configuration. The reduction of [Co(III)L(2)(2)]ClO 4 with NaBH4 produces a nucleophilic cobalt(I)species which, on reacti on with MeI, gives a. stable organocobalt dinuclear complex, previousl y reported. On the contrary, the reduction of [Co(III)L(2)(1)]ClO4 inv olves. hydrogenation of the ligand from imino- to amino oxime, with th e formation of a stable cobalt(II) species. Under these conditions, no reduction to Co-I was observed. The different reactivity is attribute d to the more strained co-ordination in [Co(III)L(2)(1)]ClO4 with resp ect to that in [Co(III)L(2)(2)]ClO4.