A Binuclear Cerium-Based Metal–Organic Framework as an Artificial Monooxygenase for the Saturated Hydrocarbon Aerobic Oxidation with High Efficiency and High Selectivity

Abstract

Artificial enzymatic systems have emerged in the field of biomimetic catalysis by constructing specific catalytic centers of enzymes. Inspired by the high activity of natural monooxygenase for the oxidation transformation, several binuclear Cu/Fe-based metal−organic frameworks (MOFs) have been frequently used as oxidation catalysts, yet rarely reports of MOFs with other metals nodes have been reported to date. In this work, by the ingenious decoration of binuclear Ce−O−Ce moieties and anthraquinone groups with good oxygen activation ability in one framework, an MOF-supported artificial binuclear cerium monooxygenase was obtained for the highly selective oxidation of inert C(sp 3 )−H bonds. The single-crystal structural study reveals that the molecule-level modularity with a binuclear Ce−O−Ce moiety design in the MOF creates a confined microenvironment to offer the ordered distribution of highly dense substrate-accessible active sites throughout the architecture. After photoexcitation, the Ce−O−Ce moieties trigger a ligand-to-metal charge-transfer (LMCT) event to form an oxygen bridge radical, which abstracts a hydrogen atom from the C(sp 3 )−H bond to generate a carbon-centered radical through a typical hydrogen atom transfer (HAT) process. These carbon-centered radicals rapidly combine the reactive oxygen species (ROS) produced by the anthraquinone groups via an energy transfer (EnT) process to generate the alkyl peroxy radical intermediates, which are easily trapped by another unsaturated coordinated cerium ions to further facilitate their hydrolysis for the selective formation of carbonyl products. This anthraquinone-functionalized metal−organic framework containing binuclear cerium catalytic centers resembling the active sites of natural monooxygenase exhibits the unique catalytic selectivity (>97%) and high activity, which represent the first example of the MOF constructed from metals different from that of natural monooxygenase for applying to the oxidation of alkanes, expanding the selection range of metal centers in the artificial monooxygenase. Taking advantage of the heterogeneity of the MOF, the Ce−MOF was recycled five times without a decrease in its selectivity and activity and possessed broader applicability for the substrate with inert C−H bonds, providing a blueprint for designing new artificial monooxygenase for the inert alkane oxidation.

Enzyme-Inspired Coordination Polymers for Selective Oxidization of C(sp3)–H Bonds via Multiphoton Excitation

“…As the sum of the van der Waals radii between two Cu(I) atoms is about 2.80 Å, 36,37 the Cu•••Cu separation in the Cu-Cl-bpyc polymer demonstrated the cuprophillic interactions, similar to that in natural monooxygenases. 38,39 While several mono- oxygenases mimicking well-defined catalytic active sites have been designed, 40,41 Cu-Cl-bpyc represents the first example of coordination polymers that duplicated the active sites of Cu 2 (μ 2 -S) 2 monooxygenases, highlighting the similarity to natural enzymes and the high density of the activity sites. 42 The one-dimensional chains are aligned parallel via π-stacking interactions to form three-dimensional (3D) networks (Figures S1−S3) and characterized by scanning electron microscopy (SEM), where Cu-X-bpyc (X = Cl, Br, I) exhibits a similar lamellar structure (Figures S10−S12).…”

The Emergence of the Ubiquity of Cerium in Heterogeneous Oxidation Catalysis Science and Technology

“…The growth in the development and application of cerium-containing materials since about 1980 has truly been remarkable. Cerium has been applied to many of the major fields of fundamental and applied catalysis and continues to be exploited for its redox and defect structural properties in many emerging technology applications as well, including CO 2 conversion [169], advanced fuel cell technologies [170], biomimetic catalysis [171], and the manufacture of sustainable aviation fuels [172,173]. The application of cerium oxide to catalysis, which started as a redox promoter and then as an "inert" support for metal catalysts, has grown into a dynamic field of rational catalyst design based on the increased understanding of cerium's unique redox properties, structural versatility, and agency as a catalyst constituent.…”

A 2D Dy-based metal–organic framework derived from benzothiadiazole: structure and photocatalytic properties

“…31,32 These sites can be coordinated by solvent molecules and are expected to contribute to photocatalytic activity as Lewis acid sites in organic photocatalysis. 33–35…”

“…Therefore, we judge that MOL 1 is a potential photocatalyst that can be applied to photocatalytic organic reactions. 34,35…”

“…3b), it has been found that it can produce the O 2 ˙ − radical under light irradiation to participate in the subsequent reaction. 35,38 As a commonly used MOF structure, MIL-100 is usually modified and applied to photocatalysis, often producing superoxide radicals. Compared with its oxidation ability, it cannot effectively promote the reaction in this paper.…”