A bi-nuclear Cu(II)-complex for selective epoxidation of alkenes: Crystal structure, thermal, photoluminescence and cyclic voltammetry

Abstract

Herein, we report the molecular and supramolecular structure, photoluminescence, redox behavior and product selective catalytic activity of [Cu2(oxalate)(1,10-phen)2Cl2] (where 1,10-phen = 1,10-phenanthroline) synthesized by using hydrophilic oxalate as bridging ligand and the hydrophobic 1,10-phen as the blocker ligand. Structural analysis reveals that this binuclear Cu(II)-complex crystallizes in achiral monoclinic P21/n space group and it has a 3D supramolecular structure. Each Cu-center displays five coordinated distorted square pyramidal geometry. Two such Cu centers are connected by oxalato-bridge to form the bi-nuclear-metal core and two 1,10-phen molecules block the outer periphery of the core and restrains further polymerization. These binuclear metallic units are connected by supramolecular hydrogen bonding and π⋯π interactions to form a 3D supramolecular architecture. The complex is stable up to 230 °C. A reversible redox couple centered at (E1/2) ∼ −27 mV with ΔEp ∼ 206 mV corresponding to the CuII/I couple was detected in the cyclic voltammogram of the complex in acetonitrile. The complex shows emission maxima at 451 and 480 nm upon excitation at 340 nm due to π-π* transition in the aromatic π-rings of 1,10-phenanthroline. Density functional analysis has been performed to explore the molecular structure and character of the orbitals within the complex. Due to the presence of five coordinated Cu-centers, the lewis acidic catalytic activity of the complex has been studied. It exhibits selective oxidation behavior for alkenes in presence of several oxidants. It shows 100% selectivity with 70% conversion for the oxidation of cis-cyclooctene to corresponding epoxide at 50 °C in presence of H2O2 as oxidant in acetonitrile.