Dual role of para-phenyl substituents in aromatic imine ligand complexes of cobalt and iron

The voltammetric bahavior of bis complexes of CO(II) and Fe(II) with the ligand 2,6-bis-(4-phenyl-2-pyridyl)-4-phenyl-pyridine (terosite) has been studied in acetonitrile using D. C. and A. C. polarography and cyclic voltammetry. The cobalt(II) complex undergoes three one-electron reductions to the +1, 0 and −1 formal oxidation states, respectively, and one-electron oxidation to Co(site)3+2. The bis(terosite)iron(II) complex is reduced in two steps to the +1 and zero formal oxidation states and also exhibits a one-electron oxidation to Fe(site)3+2. Comparison of half-wave potentials with the corresponding complexes of cobalt and iron with the ligands 2,6-bis(2-pyridyl)pyridine (terpyridine) and 2,6-bis(2-pyridyl)4-phenylpyridine (terosine) shows that the ligand para phenyl groups can function as both weak electron donors and acceptors. Spectroscopic and magnetic data is also given.