The Origins of the Differences between Alkyne Hydroalkoxylations Catalyzed by 8-Quinolinolato- and Dipyrrinato-Ligated RhI Complexes: A DFT Mechanistic Study

作者：Liu, Zheyuan; Guo, Jiandong; Song, Chunyu; Hu, Wenping; Dang, Yanfeng^*; Wang, Zhi-Xiang^*

来源：European Journal of Inorganic Chemistry, 2017, 2017(20): 2713-2722.

DOI：10.1002/ejic.201700181

• Hydroalkoxylation of alkyne
• Density functional calculations
• Rhodium
• 8-Quinolinolato ligands
• Dipyrrinato ligands
• Enols

Hydroalkoxylations of terminal alkynes with methanol, catalyzed by 8-quinolinolato-and dipyrrinato-ligated RhI complexes, afford anti-Markovnikov (Z)- and (E)-enol ethers, respectively. Herein we performed a DFT study to gain insight into the mechanisms of the two reactions, aiming at understanding why and how the two ligands differ. Of the two possible mechanisms, namely, C-beta-HT and Rh-HT, characterized by a Rh-I Fisher carbene and vinyl Rh-III-H hydride complex, respectively, the hydroalkoxylation with 8-quinolinolato prefers the C-beta-HT mechanism, while that with dipyrrinato favors the Rh-HT mechanism. The root cause for the mechanistic difference is that the O atom in 8-quinolinolato, due to its large electronegativity and exposure, is more favorable than the N atom in dipyrrinato in stabilizing the protic hydrogen as methanol undergoes a 1,3-addition, thus the addition in the former is much easier than that in the latter. Consequently, the addition in the hydroalkoxylation with dipyrrinato controls the reaction selectivity, giving the (E)-enol ether. In contrast, the selectivity of the hydroalkoxylation with 8-quinolinolato is determined by the RhI Fisher carbene to undergo a 1,2-hydrogen transfer, leading to the (Z)-enol ether. Furthermore, a DMA solvent molecule substantially facilitates the methanol addition in the reaction with dipyrrinato but not in the reaction with 8-quinolinolato.

• 出版日期2017-5-26
• 单位中国科学院大学; 天津大学