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 (MeIPMes2–)­AlCl­(OEt2) (3), (MeIPMes2–)­AlMe­(OEt2) (4), and
(MeIPMes2–)­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.