Synthesis and ESR study of Co and Ni hydrazides and hydroxamates containing 2,6-di-tert-butylphenol moiety in the ligands

Abstract

A series of Co and Ni hydrazides and hydroxamates containing the 2,6-di-tert-butylphenol moiety as a potential free radical precursor in the ligand environment of the complexes were synthesized. ESR spectroscopy was used to study the dependence of the stability of metal complexes incorporating a paramagnetic center in the ligand on the type of the coordination environment of the metal and the nature of the ligand. The complexes, in which a saturated aliphatic bridging group separates the 2,6-di-tert-butylphenol moiety and the coordination environment of the metal, can undergo oxidation to produce stable paramagnetic species with an unpaired electron in the ligand environment. The interaction of the free radical center in the ligand with the coordination environment of the metal is practically absent (excepting the weak spin-spin interaction). Metal complexes incorporating a hydrazine moiety conjugated with the 2,6-di-tert-butylphenol substituent do not produce detectable stable paramagnetic forms with a free radical in the ligand.