An Amine-Assisted Ionic Monohydride Mechanism Enables Selective Alkyne <i>cis</i>-Semihydrogenation with Ethanol: From Elementary Steps to Catalysis
作者:Zhidao Huang、Yulei Wang、Xuebing Leng、Zheng Huang
DOI:10.1021/jacs.1c01472
日期:2021.3.31
protonolysis of the Ir–C(vinyl) bond. Instead, mechanistic data are consistent with an anion-involved alcoholysis pathway involving ionization of (NCP)IrCl(vinyl) via EtOH-for-Cl substitution and reversible protonation of Cl– ion with an Ir(III)-bound EtOH, followed by β-H elimination of the ethoxy ligand and C(vinyl)–H reductive elimination. The use of an amine is key to the monohydride mechanism by promoting
Z-烯烃在炔烃半加氢反应中的选择性合成取决于催化剂对起始原料和产物的反应性差异。在这里,我们报告了通过配位诱导的离子一氢化物机制用乙醇对炔烃进行Z选择性半氢化。EtOH 配位驱动的 Cl –在钳形 Ir(III) 氢氯化物络合物 (NCP)IrHCl ( 1 ) 中解离形成阳离子一氢化物,[(NCP)IrH(EtOH)] + Cl –,它选择性地与炔烃反应相应的Z-烯烃,从而克服竞争性热力学主导烯烃Z - E异构化和过度还原。然而,建立催化循环的挑战在于醇解步骤;炔烃插入产物 (NCP)IrCl(乙烯基) 与 EtOH 的反应确实发生,但非常缓慢。令人惊讶的是,醇解不是通过 Ir-C(乙烯基)键的直接质子分解进行的。相反,机理数据与涉及阴离子的醇解途径一致,包括 (NCP)IrCl(vinyl) 通过 EtOH-for-Cl 取代电离和 Cl -离子与 Ir(III) 结合的 EtOH 的可逆质子化,然后是