Synthesis, Characterization and Application of Some Transition Metal Complexes for Cross Coupling Reactions

Abstract

In recent years, transition metal based catalysts have gained large importance due to the inherent flexibility of the metals to be complex with different organic ligands. Schiff base which falls in the category of imines is a unique class of ligands with different donor atoms exhibiting fascinating coordination style to approach the numerous metals. Compounds with C-C bond have shown worldwide applications in various fields such as agrochemicals, pharmaceuticals, natural products, advanced materials and so on. The Suzuki-Miyaura reaction is one of the most frequently used reactions for the synthesis of biaryls using transition metal catalyst especially palladium. 3d-metal complexes act as an alternative to the high-cost palladium catalyst with comparable conversions. In this study, Schiff bases were synthesized using 4-aminoacetophenone, 2- amino-5-bromopyridine, 2-aminophenol, and 1,2-phenylenediamine with different substituted aldehydes (Salicylaldehyde, 2-hydroxy-3-methoxybenzaldehyde, 2- hydroxy-1-napthaldehyde). Complexes of 3d-transition metal (Mn, Fe, Co, Ni, Cu) were synthesized using Schiff base ligands. Also, we have described the synthesis of nano-iron (II) and nickel (II) complex of a Schiff base ligand, namely 1-((pyridin-2- ylimino)methyl)naphthalen-2-ol using sonochemical method. The immobilization of Schiff base copper complex onto graphene oxide was carried out to synthesize heterogeneous and eco-friendly catalysts. The synthesized complexes were analyzed using elemental analysis, FTIR, UV-Vis, NMR, Mass, TGA and magnetic susceptibility. The synthesized complexes were examined for their C-C coupling efficiency in Suzuki cross-coupling between phenylboronic acid and para substituted aryl halides. These complexes had a better advantage over phosphine complexes. The mild reaction condition, low cost of the reagent and non-toxic by-products of the reaction makes it versatile.