Light Metal Pyrazolates Grafted onto Periodic Mesoporous Silica for Carbon Dioxide Capture and Transformation

High Resolution Image Download MS PowerPoint Slide Recent advances have shown that light metal pyrazolate complexes not only achieve high CO 2 uptake but are also able to convert epoxides and CO 2 to cyclic carbonates catalytically. Surface organometallic chemistry (SOMC) combines reactive metal complexes with the durability and robustness of a support material to form environmentally even more benign materials for CO 2 capture and conversion. In this study, light metal pyrazolates with a variety of oxidation states and ionic radii were grafted onto mesoporous silica SBA-15 500 affording the hybrid materials [Mg(pz t Bu2 ) 2 ] 2 @SBA-15 500, Al(pz t Bu2 ) 3 @SBA-15 500, Ti +IV (pz Me2 ) 4 @SBA-15 500, and Ti +III (pz t Bu2 ) 3 @SBA-15 500 . The hybrid materials were characterized via N 2 physisorption, elemental analysis, ICP/OES, DRIFTS, and solid-state NMR spectroscopy, suggesting successful grafting with monometallic surface species and revealing a CO 2 uptake of up to 11 wt%. In addition, Ti +IV (pz Me2 )[OSi(O t Bu) 3 ] 3 was synthesized as a model complex for surface species likely present for Ti +IV (pz Me2 ) 4 @SBA-15 500 . Complex Ti +IV (pz Me2 )[OSi(O t Bu) 3 ] 3 is also able to insert CO 2 under the formation of the carbamate complex Ti +IV (CO 2 ·pz Me2 )[OSi(O t Bu) 3 ] 3, emulating material CO 2 @Ti +IV (pz Me2 ) 4 @SBA-15 500 . All hybrid materials under study are active catalysts in the cycloaddition of epoxides with CO 2 to form cyclic carbonates. The magnesium hybrid material [Mg(pz t Bu2 ) 2 ] 2 @SBA-15 500 exceeds its homogeneous congener, featuring high conversion even for bulkier epoxides along with a desirable reusability.