Encapsulating Electron-Rich Pd NPs with Lewis Acidic MOF: Reconciling the Electron-Preference Conflict of the Catalyst for Cascade Condensation via Nitro Reduction

Abstract

Cascade reactions take advantage of step-saving and facile operation for obtaining chemicals. Herein, catalytic hydrogenation of nitroarene coupled condensation with β-diketone to afford β-ketoenamines is achieved by an integrated nanocatalyst, Pd-e@UiO-66. The catalyst has the structure of an acid-rich metal–organic framework (MOF), UiO-66-encapsulated electron-rich Pd nanoparticles, and it reconciles the electron-effect contradiction of cascade catalytic reactions: catalytic hydrogenation requires an electron-rich catalyst, while condensation requires electron-deficient Lewis acid sites. The catalyst showed good activity, high chemoselectivity, and universal applicability for the synthesis of β-ketoenamines using nitroarenes. More than 30 β-ketoenamines have been successfully prepared with up to 99% yield via the methodology of relay catalysis. The catalyst exhibited excellent stability to maintain its catalytic performance for more than five cycles. Furthermore, we conducted an in-depth exploration of the reaction mechanism with theoretical calculations.

Locking Effect in Metal@MOF with Superior Stability for Highly Chemoselective Catalysis

“…The results of XPS and X-ray absorption structure (XAS) fully demonstrate the regulation of electron-rich states of Au species arising from the locking effect. Considering the electron status of MNP catalysts related to hydrogenation of the nitro group − and combining the catalytic activity by the locking effect presented above, we speculate that the binding energy of Au 4f is related to the catalytic performance, and the negative Au NPs may contribute to higher selective activity.…”

A semi-encapsulated PdRh alloy heterojunction for the selective catalytic hydrogenation of nitrophenylacetylene to nitrostyrene

“…The peaks of Pd 3d can be deconvoluted from the strong peak of Zr 3p, and they are ascribed to the doublets of Pd (II) and Pd (0). 23 Likewise, the four peaks of Rh emerge for Rh 3d3/2 and Rh 3d5/2, and are divided into two sets of doublets of Rh (0) species and Rh (III) species (Fig. 3a and b).…”

Opportunities and Challenges of Metal–Organic Framework Micro/Nano Reactors for Cascade Reactions

“…Simply mixing the two catalysts will result in a less selectivity reaction. Sun et al demonstrated that Pd-e@UiO-66 can be applied to the catalytic hydrogenation of nitroarene coupled condensation with β-diketone to afford β-ketoenamines . The Pd NPs act as an electron-rich catalyst, while unsaturated Zr 4+ sites serve as electron-deficient sites within this MOF-MNRs nanoreactor, which exhibits excellent selectivity and activity.…”