Noninnocent β-Diiminate Ligands: Redox Activity of a Bis(alkylimidazole)methane Ligand in Cobalt and Zinc Complexes

A new beta-diiminate ligand (the bis(1-methyl-4,5-diphenyl- 1H-imidazol-2-yl) methane anion, BMIMPh2-) is introduced, in which the ligand framework bears an extended imidazole-based pi-system in conjugation with a formal beta-diketiminates (NacNac) backbone. Bis-ligated transition metal complexes (Co, Zn) featuring this anionic ligand undergo a series of four consecutive single-electron oxidations that are all ligand-based. The singly and doubly oxidized complexes can be synthesized on a preparative scale and have been fully characterized by various spectroscopic techniques. This is in sharp contrast to the corresponding NacNac-based complexes in which only singly oxidized complexes were isolated and characterized. Single crystal X-ray structure determination revealed a correlation between the intra-ligand metrical parameters and the oxidation state of BMIMPh2-. These structural changes in the ligand framework make BMIMPh2- as a perceptible non-innocent ligand in contrast to NacNac type ligands.