Tetra- and penta-coordinated aluminum complexes with bis-amidine ligands and their reactivity for efficient CO2 transformation to cyclic carbonates

Abstract

The development of efficient catalysts for CO₂ transformation into value-added products is crucial for sustainable chemistry. In this work, we report the synthesis and characterization of a new series of tetra- and penta-coordinated aluminum complexes supported by bis-amidine ligands featuring a rigid naphthalene bridge and their application as catalysts in the reaction of carbon dioxide with epoxides to form cyclic carbonates. Interestingly, while tetra- and penta-coordinated aluminum complexes bearing methyl groups are efficient when used with TBAI as a co-catalyst, their iodo analogs proved to be inefficient in mono-component catalysis, requiring the use of additional TBAI. Computational results of the proposed systems reveal the necessity of achieving a delicate balance between the nucleophilic properties of iodide atoms and the steric configuration of the complexes. Experimental and computational studies offer valuable insights into the role of ligand structure in aluminum-based catalysts, highlighting the potential of main-group metals in CO₂ fixation.