Acceleration Effect of Bases on Mn Pincer Complex-Catalyzed CO₂ Hydroboration

Abstract

Herein, we report a comprehensive study of CO 2 hydroboration catalyzed by Mn pincer complexes. The traditional metal−ligand cooperation (MLC) mechanism based on the H− Mn−N−Bpin pincer complex is not viable due to the competing abstraction of the Bpin group from the H−Mn−N−Bpin complex by NaO t Bu. Instead, we propose an ionic mechanism based on the H−Mn−N−Na species with a low energy span (22.5 kcal/mol) and unveil the acceleration effect of bases. The X groups in the H− Mn−N−X catalyst models are further modulated, and the steric hindrance and H→B donor−acceptor interactions of the X group increase the energy barrier of the hydride transfer. The hydrogen bond and electrostatic interactions of the X group can accelerate the hydride transfer to HCOOBpin and HCHO molecules except for the nonpolar CO 2 molecule. Based on these discoveries, we designed a pyridine-based Mn pincer catalyst system, which could achieve CO 2 hydroboration in low-temperature and base-free conditions through a metal−ligand cooperation mechanism.

Hydroboration of CO2 to Methyl Boronate Catalyzed by a Manganese Pincer Complex: Insights into the Reaction Mechanism and Ligand Effect

“…Additionally, Findlater and Gade explored the hydroboration reaction of ketones catalyzed by cheap metal complexes and proved that it mainly proceeds through the inner-sphere reaction mode, , which may also be applicable to the Leitner’s catalytic system. Recently, Liao and Li et al presented some meaningful insights into Leitner’s catalytic system in their works. , The outer-sphere reaction mechanism of CO 2 hydroboration was explored by Liao, and the reduction reactivities of CO 2 , HCOOBpin, HCHO, and CH 3 OBpin were compared. Li et al proposed an ionic mechanism based on the H–Mn–N–Na species with a low energetic span (22.5 kcal/mol) and unveiled the acceleration effect of bases.…”

“…Recently, Liao and Li et al presented some meaningful insights into Leitner's catalytic system in their works. 70,71 The outersphere reaction mechanism of CO 2 hydroboration was explored by Liao, and the reduction reactivities of CO 2 , HCOOBpin, HCHO, and CH 3 OBpin were compared. Li et al proposed an ionic mechanism based on the H−Mn−N−Na species with a low energetic span (22.5 kcal/mol) and unveiled the acceleration effect of bases.…”

Theoretical Study on the Hydrogenolysis of Polyurethanes to Improve the Catalytic Activities

“…In accordance with our previous theoretical studies, − this research was carried out with the DFT ωB97X-D method using the Gaussian 09 program . Geometries were optimized in the THF solvent using the def2-SVP basis sets. , The single-point energy refinements were further performed with the def2-TZVPP basis sets. , Thermal corrections and entropy contributions to the Gibbs free energies were obtained with the ωB97X-D/def2-SVP method.…”

Challenges and Prospects in the Catalytic Conversion of Carbon Dioxide to Formaldehyde

“…The carbonyl dissociation mechanism mainly includes Regarding the same Mn pincer complex, Li, Schaefer, and co-workers reported a novel ionic mechanism for CO 2 hydroboration in the presence of sodium tert-butoxide (NaO t Bu). [62] The ionic mechanism also contains three tandem stages. Differently, the HÀ MnÀ NÀ Bpin pincer species generated by the reaction of the Mn pincer complex and HBpin in the traditional mechanism is not viable under basic conditions due to abstraction of the Bpin group by NaO t Bu, while the generated HÀ MnÀ NÀ Na pincer species leads to a more favorable ionic mechanism.…”

“…The carbonyl dissociation mechanism mainly includes three catalytic cycles: hydroboration of CO 2 to yield the intermediate product HCOOBpin, hydroboration of HCOOBpin to yield HCHO and O(Bpin) 2 , and hydroboration of HCHO to yield methyl boronate (CH 3 OBpin). Regarding the same Mn pincer complex, Li, Schaefer, and co‐workers reported a novel ionic mechanism for CO 2 hydroboration in the presence of sodium tert ‐butoxide (NaO t Bu) [62] . The ionic mechanism also contains three tandem stages.…”