Spectroscopic and electron-transfer reactivity studies of bulky bis(N-cycloalkyl-3,5-tBu2-salicylaldiminato)copper(II) complexes: Generation of uncoordinated and coordinated phenoxyl radicals

This work summarizes the results of our studies on the spectral, magnetic, electrochemical and chemical redox properties of N-cycloalkyl-3,5-tBu2-salicylaldimine ligands [cycloalkyl = cyclo-C5H9(HL1), cyclo-C6H11 (HL2), cyclo-C7H13 (HL3), cyclo-C8H15 (HL4), 1-adamantyl (HL5), 2-adamantyl (HL6)] and their copper(II) complexes (1–6). The compounds have been characterized by IR, 1H NMR, UV–vis, EPR spectroscopy, electrochemical and magnetic susceptibility measurements. The geometry of 1–6, according to their EPR (gII and gII/AII) and visible spectral data, exhibit a significant amount distortion from slightly distorted square-planar to pseudo-tetrahedral. The cyclic voltammetric studies of 1–6 reveal that as the extent of the tetrahedral distortion of CuII center increases on going from 1 to 5, the values of CuII/CuI potentials became more negative. The compounds have been oxidized electrochemically and chemically and the generated relatively stable uncoordinated phenoxyl [HLx]+ and coordinated Cu(II)-phenoxyl radical [1–6]+ species have been characterized by UV/vis and EPR spectroscopy.