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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 N2 sorption analysis, X-ray photoelectron spectroscopy (XPS), thermal gravimetric analysis (TGA), high-resolution 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.
Ganji et al. (Wed,) studied this question.