Architecting Silver-Organic Frameworks Based on Tetraimidazole-Functionalized Spirofluorene for the Cyclization of...

Exploiting efficient heterogeneous catalysts for the catalytic transformation of CO₂ to high-value oxazolidinones is significant, but it also remains a challenge to implement under mild conditions. In this work, two silver metal-organic frameworks (MOFs), namely TISF-Ag-1 and TISF-Ag-2, based on tetraimidazole-functionalized spirofluorene, i.e., 2,2',7,7'-tetra(1H-imidazol-1-yl)-9,9'-spirobi[fluorene] (TISF), have been prepared with different structures by anion regulation. Structural analysis indicates that TISF-Ag-1 exhibits a 4-connected, 2-fold interpenetrated 2D topology {4¹²·6³}, while TISF-Ag-2 shows a 7-connected 2D new topology {3⁹·4¹⁰·5²}. Additionally, TISF-Ag-1 can catalyze the cyclization of propargylic amines with CO₂ under solvent-free and ambient conditions (1 atm, 25 °C) with almost excellent yields, showing good reusability and good substrate adaptability. Comparatively, TISF-Ag-2 exhibits inferior activity, mainly due to counterion effects and a different network structure, highlighting the regulation of structure and catalytic activity by counterions. Significantly, TISF-Ag-1 has been applied for a gram-scale experiment with 68% yield. Investigations suggest that propargylamine is activated by the catalyst and DBU together, promoting the progress of the reaction. This work is highly anticipated to inspire the further rational design and preparation of MOFs for efficient CO₂ utilization under mild conditions.