Syntheses, structures and electrochemistry of manganese(III) complexes derived from N, N′- o-phenylenebis(3-ethoxysalicylaldimine): Efficient catalyst for styrene epoxidation

Abstract

Syntheses, characterizations, electrochemistry and catalytic properties for styrene epoxidation of three manganese(III) compounds [Mn IIIL 1(H 2O)(MeOH)](ClO 4) ( 1) [Mn IIIL 1(N 3)(H 2O)]·dmf ( 2) [Mn IIIL 1(Cl)(H 2O)] ( 3) derived from the Schiff base compartmental ligand N, N′- o-phenylenebis(3-ethoxysalicylaldimine) (H 2L 1) are reported. The three compounds are characterized by elemental analyses, IR, mass and UV–Vis spectra and conductance values. Single crystal X-ray structures of 1 and 2 have been determined. The structures of 1 and 2 show that these are mononuclear compounds having a salen type structure. In both structures, a dinuclear species is formed by bifurcated hydrogen bonding involving coordinated water molecule. The coordination of chloride in 3 is shown by conductance measurements. The compounds have also been characterized by UV–Vis and mass spectroscopic studies. Cyclic voltammetric and square wave voltammetric studies of the three compounds reveal that these undergo Mn(III)/Mn(II) reduction reversibly with the order of the ease of reduction as 3 > 2 > 1. This order has been explained proposing the composition of active species in solution. Catalytic properties for epoxidation of styrene by all the three complexes using PhIO and NaOCl as oxidant have been studied. The order of both the styrene conversion and styrene epoxidation using the three title compounds is 3 > 1 > 2. Again, it has been observed that more efficient conversion and epoxidation take place when PhIO is used as oxidant.