Open Air Direct Oxidative Coupling of Alcohols and Amines to Imines Catalyzed by Ruthenium Nanoclusters Supported on a Mesoporous Carbon (CMK-8) in/on Water

Abstract

We present a green and efficient protocol for the synthesis of various imines including challenging α,β-unsaturated imines directly from alcohols and amines via a tandem oxidative cross-coupling strategy. The reaction is catalyzed by ruthenium nanoclusters supported on a cubic ordered mesoporous carbon (CMK-8) under ambient air pressure (622 Torr) and mild aqueous conditions without requiring a base or other additives. The catalyst shows excellent activity and selectivity for a broad range of alcohols and amines, giving the desired imines in excellent yield and high purity. The catalyst was characterized by various analytical techniques such as N 2 sorption analysis, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), highresolution transmission electron microscopy (TEM), high-angle annular dark-field scanning TEM, and the corresponding elemental mapping. The results revealed that the catalyst has a large surface area, uniform pore size distribution with ordered cubic arrangement, and active Ru species with very small sizes (mostly less than 1 nm), which most likely accounts for its exceptional catalytic performance. Hot filtration and recycling tests demonstrated that the catalyst operated heterogeneously and remained active for at least three cycles.