Quantifying the barrier for the movement of cyclobis(paraquat- p -phenylene) over the dication of monopyrrolotetrathiafulvalene
Quantifying the barrier for the movement of cyclobis(paraquat- p -phenylene) over the dication of monopyrrolotetrathiafulvalene
复制标题
量化环双（百草枯-对亚苯基）相对于单吡咯四硫富瓦烯的二价移动的障碍
DOI：
10.1039/d1ob02263f
复制
发表时间：
2022
影响因子：
3.2
通讯作者：
Jeppesen, Jan O.
中科院分区：
文献类型：
--
作者：
Kristensen, Rikke;Neumann, Mathias S.;Andersen, Sissel S.;Stein, Paul C.;Flood, Amar H.;Jeppesen, Jan O.
合成了一种用于测量双分子氧化（0 ~+2）产生的静电势垒高度的双[2]准轮烷1 <$CBPQT·4PF 6和双[2]轮烷2·4PF 6。这两个系统都有四吡咯四硫富瓦烯（MPTTF）和氧亚苯基（OP）作为环双（百草枯-对亚苯基）（CBPQT 4+）的站点。它们在一端有一个大的终止子，而24+中的第二个终止子由硫代乙基（SEt）和硫代二甘醇（TDEG）取代基组成，而在1 μ CBPQT 4+中，SEt基团已被体积较小的硫代甲基（SMe）取代。当比较两个系统的物理性质时，MPTTF单元上的取代基的这种看似很小的差异导致了深刻的变化，从而允许首次测量[2]伪轮烷中CBPQT 4+环在MPTTF 2+单元上的去滑移。利用循环伏安法和核磁共振氢谱研究了1 <$CBPQT·MPTTF 4+和2·MPTTF 4+的转换机理，发现MPTTF单元氧化后，CBPQT 4+首先移动到OP位，分别生成1 <$CBPQT·OP 6+和2·OP 6 +.研究了1 <$CBPQT·MPTTF 4+和1 <$CBPQT·OP 6+中发生的络合/解络合过程的动力学，从而确定了当CBPQT 4+移动穿过中性MPTTF单元（17.0 kcal mol−1）或二氧化MPTTF 2+单元（24.0 kcal mol−1）时过渡态的自由能。这些结果表明，MPTTF单元氧化成MPTTF 2+使CBPQT 4+环必须克服的能垒增加了7.0 kcal mol−1，以使解络合发生。
A bistable [2]pseudorotaxane 1⊂CBPQT·4PF6 and a bistable [2]rotaxane 2·4PF6 have been synthesised to measure the height of an electrostatic barrier produced by double molecular oxidation (0 to +2). Both systems have monopyrrolotetrathiafulvalene (MPTTF) and oxyphenylene (OP) as stations for cyclobis(paraquat-p-phenylene) (CBPQT4+). They have a large stopper at one end while the second stopper in 24+ is composed of a thioethyl (SEt) group and a thiodiethyleneglycol (TDEG) substituent, whereas in 1⊂CBPQT4+, the SEt group has been replaced with a less bulky thiomethyl (SMe) group. This seemingly small difference in the substituents on the MPTTF unit leads to profound changes when comparing the physical properties of the two systems allowing for the first measurement of the deslipping of the CBPQT4+ ring over an MPTTF2+ unit in the [2]pseudorotaxane. Cyclic voltammetry and 1H NMR spectroscopy were used to investigate the switching mechanism for 1⊂CBPQT·MPTTF4+ and 2·MPTTF4+, and it was found that CBPQT4+ moves first to the OP station producing 1⊂CBPQT·OP6+ and 2·OP6+, respectively, upon oxidation of the MPTTF unit. The kinetics of the complexation/decomplexation process occurring in 1⊂CBPQT·MPTTF4+ and in 1⊂CBPQT·OP6+ were studied, allowing the free energy of the transition state when CBPQT4+ moves across a neutral MPTTF unit (17.0 kcal mol−1) or a di-oxidised MPTTF2+ unit (24.0 kcal mol−1) to be determined. These results demonstrate that oxidation of the MPTTF unit to MPTTF2+ increases the energy barrier that the CBPQT4+ ring must overcome for decomplexation to occur by 7.0 kcal mol−1.