Coordination Modes, Oxidation, and Protonation Levels of 2,6-Pyridinediimine and 2,2′:6′,2′-Terpyridine Ligands in New Complexes of Cobalt, Zirconium, and Ruthenium. An Experimental and Density Functional Theory Computational Study

The syntheses and molecular and electronic structures of the following complexes have been established by single crystal X-ray crystallography and UV-vis-NIR spectroscopy, and verified by density functional theory calculations (DFT B3LYP): [(eta(5)-Cp)(2)Zr-IV(tpy(2-))](0) (S = 0) 1, [(eta(5)-Cp)(2)Zr-IV-((OMe)pdi(2-))](0) (S = 0) 2, [Co-II((OMe)pdi(center dot))(eta(2)-BH4)](0) (S = 0) 4, [Ru-II((OMe)pdi-H)Cl(PPh3)(2)](0) (S = 0) 5, cis-[Ru-II((OMe)pdi(0))Cl-2(PPh3)](0) (S = 0) 6, and [Run(II)(eta(2)-(OMe)pdi(0))(eta(2)-(OMe)pdi-H)(2)](0) (S = 0) 7, with (tpy(0)) being neutral 2,2':6',2'-terpyridine, (tpy(center dot))(1-) its pi radical anion, (tpy(2-))(2-) its dianion; ((OMe)pdi(0)) neutral 2,6-bis(4-methoxyphenylmethylimine)pyridine, ((OMe)pdi(center dot))(1-) its radical anion and ((OMe)pdi(2-))(2-) its dianion; ((OMe)pdi-H)(1-) represents the deprotonated form of the ((OMe)pdi(0)) ligand where deprotonation takes place at the meta-position of the pyridine ring. Density functional theory calculations using the B3LYP functional were performed, establishing geometry optimized molecular and electronic structures. The structural parameter Delta = [(average distance C-py-C-imine) - (av. distance C-py - N-py + av. distance C-imine-N-imime)] is introduced for the characterization of the oxidation level of pdi (and analogously of tpy) ligands of M(pdi) (or M(tpy)) motifs for first row transition metals. The M(L-0) unit in second and third row low-valent transition metal ion complexes may exhibit significant pi-backdonation M -> L-0 structural effects.