Temperature and Solvent Effects on H2 Splitting and Hydricity: Ramifications on CO2 Hydrogenation by a Rhenium Pincer Catalyst

• DOI: 10.1021/jacs.0c11110
• Publication Date: 2021-01-01T07:29:31Z
• Authors: Jenny Hu; Quinton J. Bruch; Alexander J. M. M...
• Keywords: formic acid; carbon dioxide; rhenium; 01 natural sciences; 7. Clean energy; Catalysis; 0104 chemical sciences; hydricity; outer sphere; Homogeneous Catalysis; thermodynamic; H2 splitting; formate; 13. Climate action; pincer; Organometallic Compounds; Kinetics and Mechanism - Organometallic Reactions; hydrogenation

The catalytic hydrogenation of carbon dioxide holds immense promise for applications in sustainable fuel synthesis and hydrogen storage. Mechanistic studies that connect thermodynamic parameters with the kinetics catalysis can provide new understanding guide predictive design improved catalysts. Reported here are thermochemical kinetic analyses a pincer-ligated rhenium complex (tBuPOCOP)Re(CO)2 (tBuPOCOP = 2,6-bis(di-tert-butylphosphinito)phenyl) catalyzes CO2 to formate faster rates at lower temperatures. Because catalyst follows prototypical "outer sphere" mechanism, comprehensive temperature solvent effects on H2 splitting hydride transfer steps expected be relevant many other Strikingly large entropy associated cleavage results strong dependence concentration [(tBuPOCOP)Re(CO)2H]− present during catalysis, which is further impacted by changing from toluene tetrahydrofuran acetonitrile. New methods determining hydricity metal hydrides temperatures than 298 K developed, providing insight into how influence favorability catalysis. These insights guided selection conditions high activity (up 364 h–1 1 atm or 3330 20 1:1 H2:CO2). In cases where highest individual barrier, entropic contributions outer sphere lead unique dependence: increases as decreases (200-fold increase upon cooling 50 0 °C) (4-fold 100 °C). Ramifications structure–function relationships discussed, including comparisons between mechanisms "metal–ligand cooperation" mechanisms.