School of Science and Technology, University of New England, Armidale, NSW 2351, Australia.
School of Rural Medicine, University of New England, Armidale, NSW 2351, Australia.
J Phys Chem A. 2023 Jul 13;127(27):5713-5722. doi: 10.1021/acs.jpca.3c03166. Epub 2023 Jun 27.
We report that bifunctional molecules containing hydroxyl and carbonyl functional groups can undergo an effective transfer hydrogenation via an intramolecular proton-coupled hydride transfer (PCHT) mechanism. In this reaction mechanism, a hydride transfer between two carbon atoms is coupled with a proton transfer between two oxygen atoms via a cyclic bond rearrangement transition structure. The coupled transfer of the two hydrogens as H and H is supported by atomic polar tensor charges. The activation energy for the PCHT reaction is strongly dependent on the length of the alkyl chain between the hydroxyl and carbonyl functional groups but relatively weakly dependent on the functional groups attached to the hydroxyl and carbonyl carbons. We investigate the PCHT reaction mechanism using the Gaussian-4 thermochemical protocol and obtain high activation energy barriers (Δ) of 210.5-228.3 kJ mol for chain lengths of one carbon atom and 160.2-163.9 kJ mol for chain lengths of two carbon atoms. However, for longer chain lengths containing 3-4 carbon atoms, we obtain Δ values as low as 101.9 kJ mol. Importantly, the hydride transfer between two carbon atoms proceeds without the need for a catalyst or hydride transfer activating agent. These results indicate that the intramolecular PCHT reaction provides an effective avenue for uncatalyzed, metal-free hydride transfers at ambient temperatures.
我们报告称，含有羟基和羰基官能团的双功能分子可以通过分子内质子耦合氢转移（PCHT）机制进行有效的转移加氢。在这种反应机制中，两个碳原子之间的氢转移与两个氧原子之间的质子转移通过环状键重排过渡态结构耦合。两个氢原子 H 和 H 的耦合转移由原子极性张量电荷支持。PCHT 反应的活化能强烈依赖于羟基和羰基官能团之间的烷基链长度，但相对较弱地依赖于连接到羟基和羰基碳原子上的官能团。我们使用 Gaussian-4 热化学方案研究了 PCHT 反应机制，并获得了高的活化能垒（Δ），对于一个碳原子的链长为 210.5-228.3 kJ mol，对于两个碳原子的链长为 160.2-163.9 kJ mol。然而，对于含有 3-4 个碳原子的更长链长，我们得到的 Δ 值低至 101.9 kJ mol。重要的是，两个碳原子之间的氢转移不需要催化剂或氢转移活化剂。这些结果表明，分子内 PCHT 反应为在环境温度下进行无催化剂、无金属的氢转移提供了一种有效的途径。
