Details

Autor(en) / Beteiligte

• Wan, Xiang
• Li, Man
• Liao, Rong‐Zhen

Titel

Ligand‐assisted Hydride Transfer: A Pivotal Step for CO2 Hydroboration Catalyzed by a Mononuclear Mn(I) PNP Complex

Ist Teil von

• Chemistry, an Asian journal, 2021-09, Vol.16 (17), p.2529-2537

Ort / Verlag

Weinheim: Wiley Subscription Services, Inc

Erscheinungsjahr

2021

Quelle

Wiley Online Library

Beschreibungen/Notizen

• A mononuclear Mn(I) pincer complex [Mn(Ph2PCH2SiMe2)2NH(CO)2Br] was disclosed to catalyze the pinacolborane (HBpin)‐based CO2 hydroboration reaction. Density functional calculations were conducted to reveal the reaction mechanism. The calculations showed that the reaction mechanism could be divided into four stages: (1) the addition of HBpin to the unsaturated catalyst C1; (2) the reduction of CO2 to HCOOBpin; (3) the reduction of HCOOBpin to HCHO; (4) the reduction of HCHO to CH3OBpin. The activation of HBpin is the ligand‐assisted addition of HBpin to the unsaturated Mn(I)‐N complex C1 generated by the elimination of HBr from the Mn(I) pincer catalyst. The sequential substrate reductions share a common mechanism, and every hydroboration commences with the nucleophilic attack of the Mn(I)‐H to the electron‐deficient carbon centers. The hydride transfer from Mn(I) to HCOOBpin was found to be the rate‐limiting step for the whole catalytic reaction, with a total barrier of 27.0 kcal/mol, which fits well with the experimental observations at 90 °C. The reactivity trend of CO2, HCOOBpin, HCHO, and CH3OBpin was analyzed through both thermodynamic and kinetic analysis, in the following order, namely HCHO>CO2>HCOOBpin≫CH3OBpin. Importantly, the very high barrier for the reduction of CH3OBpin to form CH4 reconciles with the fact that methane was not observed in this catalytic reaction. DFT calculations have been used to investigate the mechanism of the Mn(I)‐catalyzed CO2 hydroboration. A catalytic cycle consisting of four reaction stages was proposed based on our calculations. The reactivity trend of substrates for each reduction reaction was analyzed through both thermodynamic and kinetic analysis. The results presented in the current work will benefit the future rational design of related CO2 hydroboration reactions.