Efficient Catalytic Reduction of 4-Nitrophenol Using Copper(II) Complexes with N,O-Chelating Schiff Base Ligands.

Hassan Wafi Garba,Nor Azam Endot,Muhammad Sabiu Abdullahi,Mohamad Shazwan Shah Jamil

doi:10.3390/molecules26195876

Abstract

The reduction of 4-nitrophenol to 4-aminophenol by sodium borohydride was used as a model to test the catalytic activity of copper(II) complexes containing N,O-chelating Schiff base ligands. In this study, a series of copper(II) complexes containing respective Schiff base ligands, N′-salicylidene-2-aminophenol (1), N′-salicylidene-2-aminothiazole (2), and N,N′-bis(salicylidene)-o-phenylenediamine (3), were synthesized and characterized by elemental analysis, Fourier transform infrared (FT-IR), UV-Visible (UV-Vis) and electron paramagnetic resonance (EPR) spectroscopies. The results from the 4-nitrophenol reduction showed that 3 has the highest catalytic activities with 97.5% conversion, followed by 2 and 1 with 95.2% and 90.8% conversions, respectively. The optimization of the catalyst amount revealed that 1.0 mol% of the catalyst was the most optimized amount with the highest conversion compared to the other doses, 0.5 mol% and 1.5 mol%. Recyclability and reproducibility tests confirmed that all three complexes were active, efficient, and possess excellent reproducibility with consistent catalytic performances and could be used again without a major decrease in the catalytic activity.

Highlights

Schiff bases are versatile ligands and have been employed extensively as chelating agents in coordination chemistry, as they readily form stable complexes with most of the transition metals
The results indicate that all complexes show highly reproducible data with consistent catalytic activity
The synthesized products were characterized by melting point, UV-Vis, Fourier transform infrared (FT-IR), and electron paramagnetic resonance (EPR) spectroscopies

Summary

Introduction

Schiff bases are versatile ligands and have been employed extensively as chelating agents in coordination chemistry, as they readily form stable complexes with most of the transition metals. Previous studies have reported the use of Schiff bases and their corresponding metal complexes in numerous applications, such as catalytic [1,2,3] luminescence [4,5], and antimicrobial [6,7,8] activities. Owing to their structural diversity and simple preparation methods, various Schiff base ligands have been synthesized and studied, with the aim to expand their potential in a variety of applications. Metal acetate is regarded as the most convenient starting material for complexation with Schiff bases because it is soluble in alcohols and is a salt of a weak acid [10]

Objectives

Methods

Results

Conclusion