Dep. de Química, Facultad de Ciencias, Módulo 13, and Institute of Advanced Chemical Sciences (IadChem), Universidad Autónoma de Madrid, Campus de Excelencia UAM-CSIC, Cantoblanco, E-28049 Madrid, Spain.
Phys Chem Chem Phys. 2018 Jul 25;20(29):19552-19559. doi: 10.1039/c8cp03217c.
Carbon disulfide (CS2) and carbonyl sulfide (OCS) are indirect greenhouse gases that can be effectively trapped by classical, abnormal and remote nitrogen heterocyclic carbenes (NHCs), according to high level ab initio calculations. The process is described through a reaction profile involving two minima, a non-covalent complex and a covalently bound product, connected by a single transition state. Both CS2 and OCS react towards NHCs in a similar way, forming a new C-C bond and leading to very stable products with feasible barriers in many cases, although they vary significantly depending on the NHC structure. The barriers are larger than those reported for CO2, oscillating from barrierless processes up to a maximum of 57.9 kJ mol-1, whereas the products are more stabilized than those incorporating CO2. The lowest barriers for the CS2 + NHC reactions correspond to the largest C-C distances in the products, unlike the CO2 case. Remarkably, the most favored reactions, which are those involving a remote NHC, do not exhibit the highest interaction energies at the TS, but low distortion energy values of the OCS/CS2 moieties. The decomposition of the interaction energy allowed to confirmed that in fact the remote carbene is the less favored one in terms of the electrostatic and exchange terms. Substitution in CO2 of O by a more polarizable atom such as S have a great influence on the balance between the steric plus orbital interaction and the kinetic energy terms, thus making the products between NHCs and OCS/CS2 more stable. Both OCS and CS2 become better charge acceptors than CO2 on going from the starting complexes to the products.
根据高精度从头算，二硫化碳 (CS2) 和羰基硫 (OCS) 是间接温室气体，可被经典、异常和远程氮杂环卡宾 (NHC) 有效地捕获。该过程通过涉及两个最小值、非共价络合物和共价键合产物的反应轮廓来描述，由单个过渡态连接。CS2 和 OCS 以相似的方式与 NHC 反应，形成新的 C-C 键，并在许多情况下导致非常稳定的产物，尽管它们的势垒因 NHC 结构而异而有很大差异。这些势垒大于 CO2 的报道值，从无势垒过程到最大值 57.9 kJ mol-1 不等，而产物比包含 CO2 的产物更稳定。CS2 + NHC 反应的最低势垒对应于产物中最大的 C-C 距离，与 CO2 情况不同。值得注意的是，最有利的反应是涉及远程 NHC 的反应，它们在 TS 处的最高相互作用能，但 OCS/CS2 部分的扭曲能值较低。分解相互作用能允许确认，实际上远程卡宾在静电和交换项方面是最不受欢迎的。在 CO2 中用更具极化性的原子（如 S）取代 O，会极大地影响空间位阻加轨道相互作用和动能项之间的平衡，从而使 NHC 与 OCS/CS2 之间的产物更稳定。从起始络合物到产物，OCS 和 CS2 都比 CO2 更能成为更好的电子受体。
