The Electrochemical Behavior of the Low-valent Transititon-metal Complexes. I. Nickel-2,2′-Dipyridyl Complexes.

Abstract
The electrochemical behavior of zero-valent nickel-2,2′-dipyridyl complexes (Ni(dipy)2, Ni(CH2CHCN)2-(dipy), and Ni(NCCHCHCN)2(dipy)) was examined in a hexamethylphosphoric triamide solution by polarographic and ESR measurements. In the polarography, these complexes were first reduced at a very anodic potential (E1⁄2: about −0.6–−0.8 V vs. Ag wire). At this reduction step, the anion radical of the complex was observed for all the complexes by means of ESR analysis. The spectra of the anion radicals and their g-values suggested the localization of an unpaired electron on the ligand side. The addition of 2,2′-dipyridyl to the solution increased the height of the second wave, the half-wave potential of which was also more anodic than that of free 2,2′-dipyridyl, and the anion radical of 2,2′-dipyridyl was observed at this reduction step. It was concluded that the dianion species formed at the second reduction step dissociated to give the 2,2′-dipyridyl anion radical, and that the anion radical of the complex was reproduced in the presence of excess 2,2′-dipyridyl.