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 ^MeIP_Mes ligands have been characterized structurally and electronically. Green (^MeIP_Mes^–)­AlCl₂ (<b>1</b>), (^MeIP_Mes^–)­AlMe₂ (<b>2</b>), and (^MeIP_Mes^–)­GaCl₂ (<b>5</b>) have a doublet spin state which results from the anion radical form of ^MeIP_Mes. Purple (^MeIP_Mes^2–)­AlCl­(OEt₂) (<b>3</b>), (^MeIP_Mes^2–)­AlMe­(OEt₂) (<b>4</b>), and (^MeIP_Mes^2–)­GaCl­(OEt₂) (<b>6</b>) are each diamagnetic. We have also investigated the solvent dependence of the decomposition of the ^MeIP_Mes anion radical. Complexes <b>1</b> and <b>2</b> can be obtained from benzene and hexanes whereas the use of ether solvents results in the formation of undesirable (^CH2IP_Mes^–)­AlCl₂ (<b>1a</b>) and (^CH2IP_Mes^–)­AlCl₂ (<b>2a</b>) formed by loss of a hydrogen atom from the ^MeIP_Mes^– ligand. Electrochemical measurements indicate that <b>1</b>, <b>2</b>, and <b>5</b> are redox active