A strong-field pentadentate ligand in iron-based alkane oxidation catalysis and implications for iron(iv) oxo intermediates

Abstract

The pentadentate ligand bis(pyridylmethyl)(bipyridylmethyl)amine BPAbipy 1 and the iron(II) complex [Fe(1)(CH3CN)](ClO4)2 have been prepared. The strong field ligand 1 stabilises the low spin iron(II) complex, resulting in a high redox potential of 1.01 V for the Fe(II)/Fe(III) redox couple (vs. SCE). High valent iron complexes are destabilised by strong field ligands and the reaction of [Fe(1)(CH3CN)](ClO4)2 with PhIO is believed to result in a short-lived iron(IV) oxo complex, which is rapidly reduced to the oxo-bridged dinuclear iron(III) complex [(Fe(1))2(μ-O)](ClO4)4. The catalytic properties of the iron(II) complex [Fe(1)(CH3CN)](ClO4)2 for the oxidation of cyclohexane with various amounts of H2O2 has been evaluated. Moderate catalytic activities, comparable to other iron(II) complexes featuring pentadentate ligands but significantly lower than the tetradentate BPMEN ligand, have been observed.