(IP)2Ga(III) complexes facilitate net two-electron redox transformations (IP = α-iminopyridine)

Area of Science:

• Organometallic Chemistry
• Coordination Chemistry
• Redox Chemistry

Background:

• Previous studies on aluminum complexes with iminopyridine ligands showed varied one- and two-electron redox behavior, including accessible mixed-valent states.
• Understanding the redox properties of related gallium complexes is crucial for comparative inorganic chemistry and materials science.

Purpose of the Study:

• To investigate the redox behavior of gallium complexes with iminopyridine ligands.
• To compare the thermodynamic accessibility of different oxidation states between gallium and aluminum analogs.
• To elucidate the structural and electronic factors governing the redox chemistry of these metal complexes.

Main Methods:

• Reactions of M(+)[(IP(2-))(2)Ga](-) (where IP = iminopyridine, M = cation) with oxidants like pyridine N-oxide, ferrocenium, and TEMPO.
• Synthesis of gallium complexes via reaction of reduced iminopyridine with GaCl(3).
• Cyclic voltammetry measurements to assess the thermodynamic stability of mixed-valent states.

Main Results:

• Gallium complexes exclusively undergo two-electron redox reactions, yielding products like (IP(-))(2)Ga(OH), [(IP(-))(2)Ga](+), and (IP(-))(2)Ga(TEMPO).
• Only the (IP(-))(2)GaX and [(IP(2-))(2)Ga](-) oxidation states were found to be thermodynamically accessible for gallium.
• Cyclic voltammetry revealed that the mixed-valent state [(IP(2-))(IP(-))Ga](+) is not significantly stabilized against disproportionation, unlike potential aluminum analogs.

Conclusions:

• The redox chemistry of gallium iminopyridine complexes is characterized by a strong preference for two-electron processes, limiting accessible oxidation states.
• Structural differences, specifically a larger dihedral angle between ligand planes in gallium complexes, likely reduce electronic coupling, impacting mixed-valent state stability.
• The observed differences in redox behavior between gallium and aluminum highlight the influence of metal identity and ligand geometry on electronic structure and reactivity.