JACS: "molecular machine" refers to "Lewis acid"

1、 Background: on October 5, 2016, the Royal Swedish Academy of Sciences announced that Jean Pierre Sauvage, sir J Fraser Stoddart and Bernard L Feringa shared the 2016 Nobel Prize for chemistry, in recognition of the three "inventing a molecular machine with controllable action and capable of performing tasks after energy is given" Molecular switch is an important part of molecular machine, and diarylethene structure as an important molecular switch model is favored by chemists The study of chemical catalysis and polymerization by using the on-off process of diarylethene structure has attracted much attention Photo acid generator (PAG) is a kind of compound which can produce new acid structure under light condition It is widely used in polymerization initiation stage Compared with chemical feeding process, PAG has the advantages of controllable space, convenient and fast However, the current research on PAG is mainly focused on the design and synthesis of the photoinduced process of visible light radiation At the same time, most of the reported photoacid structures are confined to br ø nsted Acid rather than Lewis acid Typical Lewis catalysts, such as aluminum trichloride, titanium tetrachloride, stannic chloride and boron trifluoride, can realize processes such as Diels alder reaction, Friedel Crafts reaction and Mukaiyama aldol reaction, but br ø nsted Acid is difficult to realize the catalytic process of the above reactions Therefore, the design of Lewis acid generator with photoinduced change is more valuable in theory and application 2 Research content recently, Professor Tsuyoshi Kawai of the University of advanced science and technology of Nara, Japan, designed and synthesized a photoinduced Lewis acid generator based on the structure of diarylethene The relevant research results were published on J am Chem SOC (DOI: 10.1021 / JACS 9b11821) (photo source: J am Chem SOC.) 3 Research methods in the previous reports, the design mechanism of photoinduced br ø nsted Acid generator is shown in the figure below Under the ultraviolet radiation, the electronic transition of diarylethenylethylene in open state (o) occurs, and then it is converted to closed state (c), and then C occurs elimination reaction to realize br ø nsted Synthesis of acid (photo source: J am Chem SOC.) based on the analysis of the above structure, the author designed and synthesized the following diarylethene structure 1o Under the irradiation of UV light, 1c structure was obtained by o-ring-closing Since 1C could not achieve the elimination reaction, and the trifluoromethylsulfonate (cf3so3 -) was a group with strong leaving ability, 1c realized charge separation and obtained the Lewis acid-base pair form of 1C + / cf3so3 + Due to the change of structure, this process can only realize the transition from open to closed, but not from closed to open For this reason, the author has also carried out a comparative experiment, when the trifluoromethylsulfonic acid group is changed into the methoxy group without leaving ability, the typical reversible change of molecular switch can be realized For this reason, the author used 1H NMR and 13C NMR to study the change of 1C + hydrogen spectrum and the change process of carbon chemical shift in detail, and further confirmed the rationality of 1C + structure (photo source: J am Chem SOC.) at the same time, the author also carried out a catalytic experiment with 1o They found that 1o could realize the homopolymerization of epoxicosahexane When acetonitrile was used as solvent, polyether chain with terminal group 1C could be prepared, which fully confirmed that this process was a cationic polymerization process induced by 1C + The Mukaiyama aldol reaction was also carried out to prepare products with medium yield 4 The author realized the design and synthesis process of the photoinduced Lewis acid generator based on diarylethene by using the ingenious change of functional groups, and proved the rationality of its existence by means of NMR, and made a simple prospect of its induced catalytic process.