Study on the effect of auxiliary ligands in CoIII-NHC Complexes towards alkylation of amines using alcohols

Abstract

Here, we have presented a systematic study on the cobalt-mediated alkylation of amines using aromatic primary alcohols with sterically demanding substrates. In this context, we have employed two newly synthesized cobalt-NHC complexes Co1 and Co2, and pyridine appended (Co3-Co6) complexes to evaluate their catalytic efficiency. Among them, the pyridine-based benzimidazolin-2-ylidene Co-NHC complexes Co4 and Co6 showed high efficiency. However, the complex Co4, featuring a Cp*, exhibited lesser reactivity with sterically demanding ortho-substituted anilines, whereas complex Co6, with an acetylacetonate (acac) ligand, outperformed the rest. This outcome aligns with the steric mapping results of the employed catalysts. Furthermore, complex Co6 proved to be effective for the cyclization of 2-nitroaniline via coupling with various substituted benzyl alcohols.