Department of Chemistry, Stanford University, Stanford, CA, USA.
Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, WA, USA.
Nat Chem. 2019 Oct;11(10):940-947. doi: 10.1038/s41557-019-0313-y. Epub 2019 Aug 26.
The ability to functionalize hydrocarbons with CO could create opportunities for high-volume CO utilization. However, current methods to form carbon-carbon bonds between hydrocarbons and CO require stoichiometric consumption of very resource-intensive reagents to overcome the low reactivity of these substrates. Here, we report a simple semi-continuous cycle that converts aromatic hydrocarbons, CO and alcohol into aromatic esters without consumption of stoichiometric reagents. Our strategy centres on the use of solid bases composed of an alkali carbonate (MCO, where M = K or Cs) dispersed over a mesoporous support. Nanoscale confinement disrupts the crystallinity of MCO and engenders strong base reactivity at intermediate temperatures. The overall cycle involves two distinct steps: (1) CO-promoted C-H carboxylation, in which the hydrocarbon substrate is deprotonated by the supported MCO and reacts with CO to form a supported carboxylate (RCOM); and (2) methylation, in which RCOM reacts with methanol and CO to form an isolable methyl ester with concomitant regeneration of MCO.
用 CO 功能化烃类化合物可以为大量利用 CO 创造机会。然而，目前在烃类化合物和 CO 之间形成碳-碳键的方法需要使用化学计量的、资源密集型试剂来克服这些底物的低反应性。在这里，我们报告了一种简单的半连续循环，可在不消耗化学计量试剂的情况下将芳烃、CO 和醇转化为芳基酯。我们的策略集中在使用由碱碳酸盐（MCO，其中 M = K 或 Cs）分散在介孔载体上组成的固体碱。纳米尺度的限制破坏了 MCO 的结晶度，并在中等温度下产生了强碱性反应性。整个循环涉及两个不同的步骤：（1）CO 促进的 C-H 羧化，其中烃底物被负载的 MCO 脱质子，并与 CO 反应形成负载的羧酸盐（RCOM）；（2）甲基化，其中 RCOM 与甲醇和 CO 反应，形成可分离的甲酯，同时再生 MCO。
