Homogeneous Catalytic Oxidation of Unactivated Primary and Secondary Alcohols Employing a Versatile “Helmet” Phthalocyaninato Iron Complex Catalyst Without Added Organic Solvent

Abstract

We have examined catalytic oxidations of non-benzylic alcohols under solvent-free conditions with the goal of discovering greener alternatives to current synthetic protocols for these transformations. An iron(III) complex bearing a bicyclic pentadentate 14,28-[1,3-diiminoisoindolinato]phthalocyaninato (diiPc) ligand and an axial water ligand has been shown to function as a very effective catalyst in oxidation reactions of three secondary aliphatic alcohols (2-pentanol, 2,4-dimethyl-3-pentanol and cyclohexanol), one primary aliphatic alcohol (1-pentanol), and one bifunctional allyl alcohol (5-hydroxymethylfurfural) with tert-butylhydroperoxide (TBHP) in the absence of added organic solvent. All reactions proceed with high turnover numbers and turnover frequency relative to related systems. Selectivity for the desired aldehyde and ketone products is excellent. The presence of only water as the monodentate axial ligand in the catalyst provides solubility in non-aromatic substrates, in contrast to diiPc complexes of FeIII where the axial monodentate ligand is a mixture of methanol and water strongly favoring methanol.