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

• Published in: Inorganica Chimica Acta 2012-07, Vol.390, p.129-134
• Main Authors: Khattar, Raghvi, Hundal, M.S., Mathur, Pavan
• Format: Article
• Language: English
• Subjects: Alkynes; bisbenzimidazole; Catalyst; Crystal structure; Fe (III) complex
• ISSN: 0020-1693; 1873-3255
• DOI: 10.1016/j.ica.2012.04.015

A new Oxo-diferric complex has been synthesized using N-picolyl bis-benzimidazolyl ligand. Structural work reveals that the two Iron atoms occupy a six coordination, four coordination sites. Complex has been utilized for the oxidation of aromatic alkynes in the presence of tert-butyl hydroperoxide. The major products formed are the dicarbonyl derivative and acetylenic ketone. [Display omitted] ► New N-picolylated bis benzimidazole ligand is synthesized. ► A dimeric oxo bridged iron complex is synthesized and characterized structurally. ► Iron (III) dimeric complex is used for the oxidation of aromatic alkynes. ► Dicarbonyl and α,β-acetylenic ketone are the major products of oxidation. ► Oxidation reaction follows radical mechanism. 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 (H2O2) 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.