Acta Chim. Sinica ›› 2018, Vol. 76 ›› Issue (2): 113-120.DOI: 10.6023/A17070328 Previous Articles     Next Articles

Article

Ir(III)螯合物催化醚的硅氢化反应中负氢来源的机理研究

张琪a,b, 刘奥c, 于海珠c, 傅尧a   

  1. a 中国科学技术大学化学系 合肥 230026;
    b 合肥工业大学工业与装备技术研究院 合肥 230009;
    c 安徽大学化学化工学院 合肥 230601
  • 收稿日期:2017-09-03 出版日期:2018-02-15 发布日期:2018-01-09
  • 通讯作者: 于海珠, 傅尧 E-mail:yuhaizhu@ahu.edu.cn;fuyao@ustc.edu.cn
  • 基金资助:

    项目受国家自然科学基金(Nos.21572212,21672001,21702041),国家自然科学基金委员会与中国工程物理研究院联合基金(No.U1530262)和深圳超级计算中心和中国科学技术大学计算中心给予计算资源资助.

Hydride Source in Ethers Hydrosilylation Reaction Catalyzed by Brookhart's Ir(Ⅲ) Pincer Complex

Zhang Qia,b, Liu Aoc, Yu Haizhuc, Fu Yaoa   

  1. a Department of Chemistry, University of Science and Technology of China, Hefei 230026;
    b Institute of Industry & Equipment Technology, Hefei University of Technology, Hefei 230009;
    c School of Chemistry & Chemical Engineering, Anhui University, Hefei 230601
  • Received:2017-09-03 Online:2018-02-15 Published:2018-01-09
  • Contact: 10.6023/A17070328 E-mail:yuhaizhu@ahu.edu.cn;fuyao@ustc.edu.cn
  • Supported by:

    Project supported by the National Natural Science Foundation of China (Nos. 21572212, 21672001, 21702041), Joint Foundation of National Natural Science Foundation of China and Academy of Engineering Physics (No. U1530262), and the supercomputing system of National Supercomputing Center in Shenzhen and USTC.

The hydrosilylative reduction with silane is a popular defunctionalization strategy to convert biomass into chemicals and energies because of the mild reaction conditions. Among these, the reduction of C-O bond is particularly important because of its application in sugar biomass reduction. The (C6F5)3 B/silane catalytic system has been frequently used in the reduction of C-O bonds in the past years. However, Brookhart et al. reported alkyl ethers reduction by using Ir(Ⅲ) pincer catalyst and reductant HSiEt3. This work provides a novel hydrosilylation catalyst for C-O reduction and an effective method for sugar biomass deoxygenation. According to the previous mechanistic proposals on similar Ir catalysed hydrosilylation reactions, the iridium dihydride complex, iridium silyl hydride complex, silane adduct iridium complex and iridium silyl trihydride complex might possibly act as the hydride source. We carried out the theoretical study on Brookhart's Ir(Ⅲ) Pincer Complex/HSiEt3 catalyzed hydrosilylation reaction of EtOEt yielding ethane and EtOSiEt3. The density functional theory (DFT) calculations in our study indicate that the iridium dihydride complex is the best hydride source. Our calculation result is consistent well with experimental observations in Brookhart's experiment. For example, the phenomenon that adding iridium dihydride complex into the reaction system increases the reaction rate is understandable because the complex is involved in the rate-determining step. From the Distortion/Interaction analysis, we found that hydride transfer steps on the other three possible hydride sources are disfavoured by the HSiEt3/-SiEt3 group (derived from HSiEt3) bonded with Ir center. The iridium silyl hydride complex is unfavourable because the Ir-H bond is strengthened and the pincer ligand is distorted. For the silane adduct iridium complex, the coordination of HSiEt3 destabilizes iridium complex intermediate for entropy increases and trans effect, and destabilizes the related transition state by damaging its pincer ligand. Further, the corresponding hydride transfer transition state from iridium silyl trihydride is highly unstable and Si-H bond always reform automatically. What's more important, the moderate bond dissociation energy of Ir-hydride, small steric hindrance and the promotion effect of SiEt3 group coordination with ether all facilitate the hydride transfer on the iridium dihydride complex.

Key words: hydrosilylation, iridium, hydride, pincer, DFT