Using visible light to initiate one-pot synergy / cascade reactions is an environmentally friendly and energy saving strategy. In this manuscript we reported that MIL-101 (Fe) can act as a multifunctional catalyst to realize the oxidative condensation between o-phenylenediamines and alcohols for the synthesis of benzimidazoles under visible light. The deposition of plasmonic Au nanoparticles (Au NPs) on MIL-101 (Fe) led to a significantly improved activity. Both controlled experiments and results of electron spin resonance (ESR) showed that the production of benzimidazoles from o-phenylenediamines and alcohols involves three successive steps, namely the oxidative dehydrogenation of alcohols to produce aldehydes, the condensation between o-phenylenediamines and those to be produced Aldehydes the Schiff bases and their oxidation with the formation of benzimidazoles via a superoxide radical (O2 • -) mediated path. The promoting effect of plasmonic Au NPs for this reaction can be attributed to an effective transfer of the hot electrons excited by surface plasmon resonance (SPR) to the lowest unoccupied molecular orbital (LUMO) of MIL-101 (Fe), which leads to the generation of more active O2 • – radicals. This study not only offers an environmentally friendly and sustainable route for the synthesis of benzimidazoles, but also shows the great potential of using rationally designed plasmonic metal NPs / MOFs nanocomposites as multifunctional catalysts for light-initiated one-pot tandem / cascade reactions.

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