Pore-engineering of single-site Ti(IV) embedded Zr-MOFs for enhanced catalytic hydroboration of large size carbonyl substrates

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 di-carboxylate ligands chelated single-site Ti(IV) within co-ordination-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.