A Sterically Demanding Iminopyridine Ligand Affords Redox-Active Complexes of Aluminum(III) and Gallium(III)

The combination of an electrophilic metal center with a redox active ligand set has the potential to provide reactivity unique from transition metal redox chemistry. In this report, substituted iminopyridine complexes containing monoanionic and dianionic MeIPMes ligands have been characterized structurally and electronically. Green (MeIPMes –)­AlCl2 (1), (MeIPMes –)­AlMe2 (2), and (MeIPMes –)­GaCl2 (5) have a doublet spin state which results from the anion radical form of MeIPMes. Purple (MeIPMes 2–)­AlCl­(OEt2) (3), (MeIPMes 2–)­AlMe­(OEt2) (4), and (MeIPMes 2–)­GaCl­(OEt2) (6) are each diamagnetic. We have also investigated the solvent dependence of the decomposition of the MeIPMes anion radical. Complexes 1 and 2 can be obtained from benzene and hexanes whereas the use of ether solvents results in the formation of undesirable (CH2IPMes –)­AlCl2 (1a) and (CH2IPMes –)­AlCl2 (2a) formed by loss of a hydrogen atom from the MeIPMes – ligand. Electrochemical measurements indicate that 1, 2, and 5 are redox active.