Modulating Hetero-Multimetallic Atoms in Covalent Organic Frameworks for Efficient Oxidization of Olefin Compounds
In the field of synthetic chemistry, modulating the quantity and location of different metal centers to achieve synergistic, tandem, or cooperative effects has always been a technical challenge. Hetero-multinuclear catalysts have garnered significant attention due to their advantages such as high selectivity, cascading production, and specific chemical transformations. However, their high structural complexity makes the synthesis process extremely difficult. Covalent Organic Frameworks (COFs), as materials with periodic molecular ordering and open architectures, show great potential in the preparation of heterometallic catalysts. However, the random distribution of functional units in traditional COFs makes it difficult to achieve modular and interrelated arrangements of metal ions, thereby limiting their catalytic performance.
To address this issue, a research team from Northeast Normal University in China proposed a molecular coordination imprint strategy. By modulating the quantity and location of individual metal centers in COFs, they successfully achieved efficient catalysis through multi-metallic assemblies. This study not only provides new insights into the synthesis of heterometallic catalysts but also offers an efficient catalyst for the sustainable oxidation of olefin compounds.
Source of the Paper
The paper was co-authored by Qinghao Meng, Panzhe Qiao, Dan Deng, and others, with the research team primarily affiliated with the Faculty of Chemistry at Northeast Normal University and the Shanghai Synchrotron Radiation Facility. The paper was published on March 13, 2025, in the journal Chem, titled “Modulating Hetero-Multimetallic Atoms in Covalent Organic Frameworks for Efficient Oxidization of Olefin Compounds.”
Research Process
1. Proposal and Implementation of the Molecular Coordination Imprint Strategy
The research team first proposed a molecular coordination imprint strategy, using Cu²⁺ ions as templates to modulate the coordination environment of metal centers in COFs. The specific steps are as follows: - Step 1: Cu²⁺ ions were coordinated with phenol units (C–O), Schiff base imine units (C=N), and pyridine or pyrimidine units in COFs to form tri-coordination (2N, 1O) and di-coordination (1N, 1O) sites. - Step 2: Template Cu²⁺ ions were removed using an ethylene diamine tetraacetic acid disodium salt (EDTA-2Na) solution, releasing the coordination sites. - Step 3: Other metal ions (such as Pd²⁺, Fe³⁺, Zn²⁺, etc.) were introduced into the COFs to form multi-metallic assemblies.
2. Synthesis and Characterization of Multi-Metallic COFs
The research team used 2,5-diaminopyrimidine (mi) and 2,5-diaminopyridine (di) as linkers, bonding with triformylphloroglucinol (TP) through amine linkages to synthesize two-dimensional COFs with a high density of nitrogen atoms as coordination sites for metal ions. By modulating the molar ratio of mi to di, they successfully prepared COF samples with different metal ratios. Techniques such as powder X-ray diffraction (PXRD), nitrogen adsorption-desorption isotherms, and scanning transmission electron microscopy (STEM) were used to characterize the crystallinity, porosity, and metal distribution of the COFs in detail.
3. Catalytic Performance Testing
The research team used Cu²⁺/Pd²⁺-doped COFs as the research object to test their catalytic performance in olefin oxidation reactions. The specific experimental conditions were: 1 mmol of styrene substrate and 0.64 mol% catalyst were incubated in 4 mL of a DMF/water mixture (volume ratio of 7:1) at 25°C and 1 bar O₂ atmosphere for 8 hours. The conversion rate and product selectivity were evaluated using nuclear magnetic resonance (NMR) and chromatography analysis.
Main Results
Successful Implementation of the Molecular Coordination Imprint Strategy: Through the Cu²⁺ ion template strategy, the research team successfully modulated the coordination environment of metal centers in COFs, forming tri-coordination and di-coordination sites, thereby achieving efficient catalysis through multi-metallic assemblies.
High Catalytic Performance of Multi-Metallic COFs: Cu²⁺/Pd²⁺-doped COFs exhibited excellent catalytic activity in olefin oxidation reactions, with a conversion rate of up to 94% and a turnover frequency (TOF) of 1,184.9 h⁻¹, significantly outperforming existing commercial catalysts (PdCl₂/CuCl₂).
Stability and Reusability of the Catalyst: After 10 cycles of use, the catalyst’s activity remained above 90%, demonstrating its good stability and reusability.
Conclusion and Significance
This study successfully modulated the coordination environment of multi-metallic centers in COFs through a molecular coordination imprint strategy, achieving efficient and sustainable olefin oxidation reactions. This achievement not only provides new insights into the synthesis of heterometallic catalysts but also offers efficient catalysts for industrial production and environmental protection. Additionally, the study highlights the great potential of COFs in the field of catalysis, laying the foundation for the future development of more high-performance catalysts.
Research Highlights
Innovative Molecular Coordination Imprint Strategy: By introducing Cu²⁺ ions as templates, the research team successfully modulated the coordination environment of metal centers in COFs, achieving efficient catalysis through multi-metallic assemblies.
High Catalytic Performance: Cu²⁺/Pd²⁺-doped COFs exhibited excellent catalytic activity in olefin oxidation reactions, with conversion rates and TOF significantly surpassing those of existing catalysts.
Good Stability and Reusability: After multiple cycles of use, the catalyst’s activity remained at a high level, indicating its promising industrial application prospects.
Other Valuable Information
The research team also revealed the electron transfer process of Cu²⁺ and Pd²⁺ ions in the catalytic reaction through density functional theory (DFT) calculations, further validating the catalytic mechanism. Furthermore, the study demonstrates the broad application prospects of COFs in the field of catalysis, providing important references for the future development of more high-performance catalysts.
This research not only holds significant scientific value but also provides efficient catalysts for industrial production and environmental protection, showcasing the great potential of COFs in the field of catalysis.