Liu Xiaoqing, Wang Xiaojing, Li Yao, Yu Tianhao, Zhao Weizhen, Liu Lei
School of Environment and Safety Engineering, North University of China, Taiyuan, 030051, P. R. China.
Phys Chem Chem Phys. 2021 Jun 2;23(22):12541-12548. doi: 10.1039/d1cp00479d. Epub 2021 May 17.
Sterically hindered frustrated Lewis pairs (FLPs) have the ability to activate hydrogen molecules, and their reactivity is strongly determined by the geometric parameters of the Lewis acids and bases. A recent experimental study showed that ionic liquids (ILs) could largely improve the effective configuration of FLPs. However, the detailed mechanistic profile is still unclear. Herein, we performed molecular dynamics (MD) simulations to reveal the effects of ILs on the structures of FLPs, in particular, the association of Lewis acids and bases. For this purpose, mixed systems were adopted consisting of the ILs [Cmim][NTf] (n = 6, 10, 14), [Cmim][PF] and [Cmim][CTf] and the typical FLP (tBu)P/B(CF) for MD simulations. Radial distribution functions (RDFs) results show that toluene competes with (tBu)P to interact with B(CF), resulting in a relatively low effective (tBu)P/B(CF) complex, while [Cmim][NTf] shows less competition with (tBu)P, which increases the amount of effective FLPs. Spatial distribution functions (SDFs) results show that toluene forms a continuum solvation-shell, which hinders the interactions between (tBu)P and B(CF), while [Cmim][NTf] leaves relatively large empty spaces, which are accessible for (tBu)P or B(CF) molecules, resulting in higher probabilities of effective FLP structures. Lastly, we find that the longer alkyl chain length of [Cmim] cations, the higher the amount of effective (tBu)P/B(CF) pairs, and the anion [CTf] shows negative effects, for which even less effective (tBu)P/B(CF) pairs have been found compared to those of toluene.
空间位阻受阻路易斯对（FLPs）具有活化氢分子的能力，其反应活性很大程度上由路易斯酸和碱的几何参数决定。最近的一项实验研究表明，离子液体（ILs）可以极大地改善FLPs的有效构型。然而，详细的机理仍然不清楚。在此，我们进行了分子动力学（MD）模拟，以揭示离子液体对FLPs结构的影响，特别是路易斯酸和碱的缔合。为此，采用了由离子液体[Cmim][NTf]（n = 6、10、14）、[Cmim][PF]和[Cmim][CTf]以及典型的FLP（tBu）P/B（CF）组成的混合体系进行MD模拟。径向分布函数（RDFs）结果表明，甲苯与（tBu）P竞争与B（CF）相互作用，导致有效（tBu）P/B（CF）络合物相对较少，而[Cmim][NTf]与（tBu）P的竞争较少，这增加了有效FLPs的数量。空间分布函数（SDFs）结果表明，甲苯形成连续的溶剂化壳，阻碍了（tBu）P与B（CF）之间的相互作用，而[Cmim][NTf]留下相对较大的空隙，（tBu）P或B（CF）分子可以进入，从而导致有效FLP结构的概率更高。最后，我们发现[Cmim]阳离子的烷基链长度越长，有效（tBu）P/B（CF）对的数量越高，而阴离子[CTf]显示出负面影响，与甲苯相比，发现的有效（tBu）P/B（CF）对更少。
