Iron Complex Cleaves C–H and O–H Bonds

A novel diiron(IV) complex exceeds the bond-breaking capabilities of its predecessors by being able to cleave strong C–H and O–H bonds, reports a research team led by Lawrence Que Jr. of the University of Minnesota, Twin Cities, and Eckard Münck of Carnegie Mellon University (Nat. Chem., DOI: 10.1038/nchem.162). The chemists note that the complex is the first iron complex that can activate the O–H bonds of aliphatic alcohols. They obtained the complex, which has a bridging oxo group between the iron atoms, by electrochemically oxidizing a diiron(III) precursor. The diiron(IV) complex cleaves C–H bonds with bond energies as high as 100 kcal/mol. For example, under anaerobic conditions the complex oxidizes cyclohexane to cyclohexene and 1,3-cyclohexadiene. The lack of a hydroxylated product is probably due to the bridging oxo group, the researchers suggest, because forming an alcohol would require breaking both Fe–O bonds. As for cleaving O–H bonds, oxidation of tert-butyl alcohol to form acetone indicates that the diiron complex targets the hydroxyl group instead of one of the weaker C–H bonds.