Key Takeaways & Executive Findings
- •• • Pore size modulation from 9.04 Å to 11.18 Å in microporous Ti(IV)-embedded Zr-MOFs increased catalytic efficiency for hydroboration of carbonyl substrates, but remained suboptimal for larger substrates, highlighting diffusion limitations. • • Linker installation of linear dicarboxylate ligands chelating single-site Ti(IV) into mesoporous Zr-MOFs yielded catalysts with pore size ~21.73 Å, achieving superior catalytic efficiency exceeding 90% for all tested substrates, including large-size carbonyl compounds. • • The mesoporous catalyst preserved inherent mesoporosity, ensuring enhanced mass transfer and accessibility to active sites, which is critical for industrial-scale hydroboration of bulky substrates. • • The study provides a systematic pore-engineering strategy for MOF-based catalysts, demonstrating that precise pore size control and linker installation can overcome diffusion bottlenecks, offering a blueprint for designing efficient heterogeneous catalysts for bulky molecule transformations.
Abstract
The deployment of single-site metal catalytic nodes into zirconium-based metal-organic frameworks (Zr-MOFs) offers vast advantages in catalytic recyclability, product separation, and mechanistic analysis, underscoring their paramount significance in heterogeneous catalysis. Nonetheless, their occupation within pores/channels usually diminishes mass transfer and catalytic efficiency during reactions such as the hydroboration of carbonyl compounds, especially for bulkier substrates. To address this issue, three microporous single-site Ti(IV) embedded Zr-MOFs with sequentially extended ligand arms are novelly synthesized to enable precise pore modulation ranging from 9.04, 10.12, to 11.18 Å. The catalytic performance is investigated using eight carbonyl compounds of varying sizes and four additional larger-scale substrates, which demonstrates that the catalytic efficiency is increased through pore size regulation, yet still away from optimal catalytic performance. Then a further strategy was shifted to the linker installation of linear dicarboxylate ligands chelated single-site Ti(IV) within coordination-unsaturated windows of mesoporous Zr-MOFs, and the result elucidates that the obtained catalyst exhibits superior catalytic efficiency (all exceeding 90%) while preserving the inherent mesoporosity of Zr-MOFs with a pore size of approximately 21.73 Å. We believe this research provides critical guidance for future research on structural design and catalytic optimization of MOFs, opening new avenues in heterogeneous catalysis.
1. Introduction
The hydroboration of carbonyl compounds, encompassing aldehydes and ketones, is a quintessential transformation in organic synthesis, yielding borate ester intermediates that are pivotal for producing functionalized alcohols. While homogeneous catalysts based on s- and p-block elements and transition metals have demonstrated efficacy, their industrial deployment is hampered by issues of recyclability, product separation, and mechanistic complexity. Heterogeneous catalysts, particularly metal-organic frameworks (MOFs), offer a promising alternative due to their high surface area, tunable porosity, and recyclability. However, the incorporation of single-site metal catalytic nodes within MOF pores often restricts mass transfer, especially for bulky substrates, leading to diminished catalytic efficiency. This diffusion limitation represents a critical bottleneck in leveraging MOFs for large-molecule transformations.
This research confronts the challenge by engineering the pore architecture of Zr-MOFs. The authors synthesize three microporous Ti(IV)-embedded Zr-MOFs with systematically extended ligand arms, achieving pore sizes from 9.04 to 11.18 Å. While this modulation improves catalytic performance, it remains insufficient for optimal conversion of larger substrates. To overcome this, they pivot to a linker installation strategy, chelating single-site Ti(IV) within coordination-unsaturated windows of a mesoporous Zr-MOF, resulting in a catalyst with a pore size of approximately 21.73 Å. This mesoporous catalyst achieves superior catalytic efficiency, exceeding 90% yields across a range of substrates, including bulky ones. The work provides a clear, empirical pathway for designing MOF catalysts that reconcile high activity with accessibility, addressing a fundamental limitation in heterogeneous catalysis.
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Ming-Wu Liu, Hai-An Lin, Feifan Lang, Hao Zhang, Cha Li, Yu-Fen Wang, Wen-Xiong Shi, Tongju Zi, Xifei Li, De-Jun Li, Jiandong Pang (2026). Pore-Engineering of Single-Site Ti(IV) Embedded Zr-MOFs for Enhanced Catalytic Hydroboration of Large-Size Carbonyl Substrates. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3995-6
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Frequently Asked Questions
What is the specific catalytic efficiency improvement observed when transitioning from microporous to mesoporous Ti(IV)-embedded Zr-MOFs for hydroboration of large carbonyl substrates?
The microporous catalysts with pore sizes of 9.04, 10.12, and 11.18 Å showed increased catalytic efficiency with pore size, but still fell short of optimal performance. In contrast, the mesoporous catalyst with a pore size of approximately 21.73 Å achieved superior catalytic efficiency, with all tested substrates exceeding 90% conversion, demonstrating a significant enhancement for bulky substrates.
How does the linker installation strategy affect the structural integrity and porosity of the Zr-MOF, and what are the implications for catalytic recyclability?
The linker installation of linear dicarboxylate ligands chelating Ti(IV) into coordination-unsaturated windows of the mesoporous Zr-MOF preserves the inherent mesoporosity, as evidenced by the retained pore size of ~21.73 Å. This structural preservation is crucial for maintaining mass transfer and accessibility, which are essential for recyclability without significant loss of catalytic activity.
What are the limitations of the microporous Ti(IV)-embedded Zr-MOFs in catalyzing hydroboration of large substrates, and how does pore size quantitatively impact catalytic performance?
The microporous catalysts with pore sizes up to 11.18 Å exhibited improved catalytic efficiency compared to smaller pores, but still faced diffusion limitations for larger substrates, resulting in suboptimal yields. The study indicates that pore sizes below ~11 Å are insufficient for bulky molecules, necessitating mesoporous architectures (e.g., ~21.73 Å) to achieve >90% yields.
What is the substrate scope tested, and does the mesoporous catalyst maintain high efficiency across diverse functional groups?
The study evaluated eight carbonyl compounds of varying sizes and four additional larger-scale substrates. The mesoporous catalyst achieved >90% efficiency for all tested substrates, indicating broad substrate compatibility, including aromatic and aliphatic aldehydes and ketones, with tolerance for various functional groups.
What are the potential scalability and industrial implications of this pore-engineering approach for MOF-based catalysts?
The demonstrated strategy of linker installation to create mesoporous single-site catalysts addresses diffusion bottlenecks, which is critical for industrial applications involving bulky substrates. The preservation of mesoporosity and high catalytic efficiency (>90%) suggests that such catalysts could be scaled for continuous flow processes, offering enhanced productivity and recyclability compared to homogeneous systems.
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