Recent Developments in the Syntheses of Aluminum Complexes Based on Redox-Active Ligands

• Importance of redox-active ligands. • Application of redox-active ligands in aluminum chemistry. • Recent development in the synthesis of aluminum complexes supported by imino-pyridine ligands. • Recent development in the synthesis of aluminum complexes supported by BIAN ligands. • Recent development in the synthesis of aluminum complexes supported by formazanate ligands. Applications of aluminum as a catalyst for organic/inorganic transformation reactions are ideal because of its easy availability, inexpensiveness, and non-toxicity. However, successful implementation of Al(III) complexes as catalysts require an easy reduction-oxidation cycle between Al(III) and Al(I). Nevertheless, molecular complexes of Al(I) are not common, often require special efforts for their synthesis and isolation. Additionally, the Al(I)→Al(III) oxidation reaction is facile whereas the corresponding Al(III)→Al(I) reduction occurs only under highly reducing conditions. This creates a problem in developing Al(I)/Al(III) couple catalytic cycle for practical application. But, for aluminum complexes to be applicable in redox transformations, complexes must readily undergo reversible oxidation and reduction processes. One can envision applying a redox-active ligand where instead of aluminum the ligand would be reversibly oxidized and reduced to perform a certain electron transfer process. So, the development of a large pool of aluminum complexes supported by redox-active ligands is very important. In this review article, we have summarized recent developments on the syntheses of aluminum complexes with some redox-active ligands. This may help in designing new catalysts for future applications.