Metal-Ligand Multiple Bonds in High-Spin Complexes

The chemistry of late first row transition metals supported by dipyrromethane and dipyrromethene ligands bearing sterically bulky substituents was explored. Transition metal complexes (Mn, Fe, Co, Ni, Zn) of the dipyrromethane ligand 1,9-dimesityl-5,5-dimethyldipyrromethane (dpma) were prepared. Structural and magnetic characterization (SQUID, EPR) of the bis-pyridine adducts (dpma)Mn(py)2, (dpma)Fe(py)2, and (dpma)Co(py)2 showed each tetrahedral divalent ion to be high-spin, while square planar (dpma)NiII(py)2 and tetrahedral (dpma)Zn(py)2 were shown to be diamagnetic. Electrochemical experiments revealed oxidative events at common potentials independent of metal identity or spin state, consistent with ligand-based oxidation.