New phenanthroline iron complexes: Synthesis and catalytic activity in alkane oxidation with hydrogen peroxide

New binuclear iron complexes with labile coordination sites, [Fe2OL4(H2O)(2)](ClO4)(4) where L stands for hydrophobic phenanthroline (phen) bearing electronegative and lipophilic substituents (Cl, Br, C2H5, C6H5, C6H13), are synthesized. The stereospecificity, alcohol/ketone ratio, regioselectivity, and substituent effect in the hydroxylation of alkanes (cyclohexane, adamantane, cis-1,2-dimethylcyclohexane) with hydrogen peroxide catalyzed by these complexes are studied. The said parameters, as well as a decrease in the alkane oxidation regioselectivity with increasing hydrogen peroxide concentration, are similar to the respective parameters for mononuclear iron complexes of tetradentate ligands. The results confirm that regardless of the nature of chelating ligands, the same mechanism operates in both cases, namely, the transfer of an oxygen atom with the participation of ferryl intermediates.