Synthesis, structure and oxidation of alkynes using a μ-oxo diiron complex with the ligand bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-yl methyl) ether

Article abstract of DOI:10.1016/j.ica.2012.04.015

New ligand bis (1-(pyridin-2-ylmethyl)-benzimidazol-2-ylmethyl ether and its μ-oxo diferric complex has been synthesized and characterized. The dimeric [LClFe-O-FeCl₃] has been characterized crystallographically, and shows that iron atoms occupy inequivalent coordination sites. One of the Fe (III) atom is coordinated by two benzimidazole nitrogens, one ether oxygen and bridging oxide oxygen, forming the equatorial plane while one Cl^- ion and the oxygen atom of a DMF molecule occupy the axial fifth and the sixth coordination positions. The second Fe (III) is tetrahedrally coordinated by three Cl^- ions and the bridging oxide oxygen O. The bridging oxide anion is unsymmerically coordinated to the two Iron (III) atoms. Oxidation of aromatic alkynes was investigated using this complex as catalyst with small amount of tert-butyl hydroperoxide (TBHP) and Hydrogen peroxide (H ₂O₂) as an alternate source of oxygen. Isolated products were characterized by GC-Mass. Solvent, temperature, Stoichiometry and oxidant variation are studied and reaction conditions have been optimized. Dicarbonyl and α,β-acetylenic ketone are the major product and depend on the nature of the alkyne employed.