Strong Oxophilicity of Zr Species in Zr⁴⁺-Exchanged Montmorillonite Boosted Meerwein–Ponndorf–Verley Reduction of Renewable Carbonyl Compounds

Abstract

Meerwein−Ponndorf−Verley (MPV) reduction of biomass-derived carbonyl compounds is a greatly promising route for biomass valorization. Robust, facile-prepared, and cost-effective inorganic Zr-based catalysts for this transformation remain highly desirable. Herein, Zr-containing montmorillonite (denoted as Zr-MMT) was constructed by the ion exchange of Zr 4+ with the interlayer cations of montmorillonite (MMT). Very interestingly, as an inorganic catalyst, the prepared Zr-MMT showed high catalytic activity for MPV reduction of various biomass-derived carbonyl compounds. Systematic investigations revealed that the excellent performance of Zr-MMT predominantly originated from more positively charged Zr species ([Zr x (OH) y (H 2 O) n ] (4x−y)+ ), which could boost the activation of the carbonyl group and simultaneously promote the hydrogen transfer process assisted by suitable basic sites on MMT. Notably, the preparation of Zr-MMT avoided the utilization of surfactants or expensive organic ligands, and the prepared Zr-MMT showed better or comparable catalytic performance than most reported Zr-containing catalysts, significantly enabling it to be more practical.

“Domino” synthesis of bio-derived anethole over facile-prepared hafnium phosphonate frameworks with efficient bifunctional acid sites

“…Importantly, strong hydrophobicity was very conducive to the reaction process and would prevent water formation during the reaction, which might poison the active acid sites of the catalyst. 48…”

“…Importantly, strong hydrophobicity was very conducive to the reaction process and would prevent water formation during the reaction, which might poison the active acid sites of the catalyst. 48 The microscopic morphology of PA-Hf-SO 3 H (1.5 : 1) was investigated by electron microscopy of different types. SEM images (Fig.…”

A functionalized Hf(iv)–organic framework introducing an efficient, recyclable, and size-selective heterogeneous catalyst for MPV reduction

“…This conclusion was similar with previous reports. 4,8,9,24,26 Therefore, the advanced catalytic performance of CSMCRI-KNC 0 over HfCl 4 , linker, and pristine Hf-UiO-66 MOF was due to the survival of dual active sites, like the LA metal center and hydrogen-bond-donating (HBD) sites of the linker. 46 The LA originated from the metal centers Hf 4+ , while the HBD sites arose because of the availability of -OH, and -NH groups in the linker.…”

“…[5][6][7] The MPV reaction involves the formation of a six-membered ring transition state in which both the reducing alcohol and the carbonyl compound are coordinated to the metal center (Lewis acidic site). 8,9 The assistance of basic sites has also been proposed for the formation of the sixmembered ring. 9 The MPV reduction is one of the traditional technologies for redox reactions, and can realize the selective hydrogenation of carbonyl groups through hydrogen transfer between ketones (aldehydes) and alcohols.…”

“…8,9 The assistance of basic sites has also been proposed for the formation of the sixmembered ring. 9 The MPV reduction is one of the traditional technologies for redox reactions, and can realize the selective hydrogenation of carbonyl groups through hydrogen transfer between ketones (aldehydes) and alcohols. 10 The MPV reduction has been extensively applied in various significant organic syntheses to produce structurally important organic molecules, 11 especially in the fields of asymmetric synthesis and biomass conversion.…”