Design and Exploration of Catalytic Activity of Two-DimensionalSurface-Engineered Graphene Oxide Nanosheets in the Transannulationof N-Heterocyclic Aldehydes or Ketones with Alkylamines

摘要

In this work, pharmaceutically and biologically important compounds containing imidazo[1,5-a]pyridine nuclei have been synthesized via transannulation of N-heteroaryl aldehydes or ketones with alkylamines using a graphene oxide-supported copper catalyst. The nanocatalyst was fabricated by the covalent immobilization of 4-aminoantipyrine onto an amine-functionalized graphene oxide nanosupport followed by its metallation with copper acetate. Structural analysis by transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and X-ray diffraction demonstrates that the two-dimensional sheet-like structure of graphene oxide is maintained even after the chemical modifications, whereas XPS revealed crucial information related to elemental composition and surface electronic states of the metal present in the catalyst. Apart from this, Fourier transform infrared spectroscopy helped in identifying the degree of oxidation and the presence of oxygenated groups in graphene oxide nanocomposites. As a heterogeneous catalyst, this graphene oxide-supportedcopper complex showed moderate to good catalytic activity in the C(sp³)–H bond activation/amination of a variety of substrates.This superior catalytic performance originated from the unique 2-dimensionalstructure of graphene oxide-based material which provided space betweengraphitic overlayers due to appropriate positioning of metal on theirbasal planes, decreasing the diffusion resistances of reactant surfaces,thus making it function as a nanoreactor. More importantly, this nanomaterialcould be recovered easily and reused repeatedly by simple washingwithout chemical treatment with no appreciable loss in its catalyticactivity, showing good potential for increasing the overall turnovernumber of this synthetically useful catalyst.