Syntheses, Structures, and Reactivity of Low Spin Iron(III) Complexes Containing a Single Carboxamido Nitrogen in a [FeN₅L] Chromophore

Abstract

A new pentacoordinate ligand based on TPA (tris-(2-pyridylmethyl)amine), namely, N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide (PaPy(3)H), has been synthesized. The iron(III) complexes of this ligand, namely, [Fe(PaPy(3))(CH(3)CN)](ClO(4))(2) (1), [Fe(PaPy(3))(Cl)]ClO(4) (2), [Fe(PaPy(3))(CN)]ClO(4) (3), and [Fe(PaPy(3))(N(3))]ClO(4) (4), have been isolated and complexes 1-3 have been structurally characterized. These complexes are the first examples of monomeric iron(III) complexes with one carboxamido nitrogen in the first coordination sphere. All four complexes are low spin and exhibit rhombic EPR signals around g = 2. The solvent bound species [Fe(PaPy(3))(CH(3)CN)](ClO(4))(2) reacts with H(2)O(2) in acetonitrile at low temperature to afford [Fe(PaPy(3))(OOH)](+) (g = 2.24, 2.14, 1.96). When cyclohexene is allowed to react with 1/H(2)O(2) at room temperature, a significant amount of cyclohexene oxide is produced along with the allylic oxidation products. Analysis of the oxidation products indicates that the allylic oxidation products arise from a radical-driven autoxidation process while the epoxidation is carried out by a distinctly different oxidant. No epoxidation of cyclohexene is observed with 1/TBHP.