Electrochemical benzylation of [60] fullerene fused lactones: unexpected formation of ring opening adducts and their photovoltaic properties

Introduction fullerene derivatives have attracted considerable attention in the past few years due to their potential applications in biology, materials and nano science There are many reports on the synthesis of functionalized fullerenes with new structures Among these methods, electrosynthesis is considered as a novel and effective strategy for the preparation of various fullerene derivatives due to its mild reaction conditions, good regioselectivity and relatively high yield In recent years, the electrochemical functionalization of fullerene fused heterocyclic compounds has attracted a lot of attention, because the electrochemical reduction makes the carbon heteroatom bond of the heterocyclic part on the framework of fullerene break and rearrange, which provides a new mode for the addition of fullerene derivatives The results show that different tetraaddition fullerene derivatives, such as 1,2,3,4-adduct and 1,2,3,16-adduct, can be formed by the reaction of fused fullerene heterocyclic anion with benzyl bromide (phch2br) Recently, Professor Wang Guanwu's research group of China University of science and technology reported the benzylation of δ - and γ - lactones fused by double anion [60] fullerenes Unexpectedly, three types of ring opening benzylation adducts were obtained and their photovoltaic properties were studied This achievement was published in org Lett (org Lett 2019, 21, 7346-7350) Figure 1 Electrochemical benzylation of [60] fullerene fused heterocycles previously reported and [60] fullerene fused lactones now reported by Professor Wang Guanwu (source: org Lett) Wang Guanwu studied in the Department of chemistry of Lanzhou University from September 1983 to June 1993, and obtained bachelor's degree, master's degree and doctor's degree respectively From July 1993 to April 2000, he successively engaged in postdoctoral research at Fudan University, Kyoto University, Kentucky University, University of Chicago and Yale University In May 2000, he was introduced to the Department of chemistry, University of science and technology of China through the "hundred talents plan" of Chinese Academy of Sciences in 1999, and won the National Science Fund for Distinguished Young Scholars in 2001 Currently, he is deputy editor in chief of mini reviews in Organic Chemistry (2017 to date), editorial board member of Organic Chemistry (2007 to date), current organic chemistry (2014 to date), Journal of Chemistry (2015 to date), and current organic chemistry (2016 to date) In 2004, he was selected as one of the first batch of national candidates for the "one million talents project in the new century" of seven ministries and commissions; in 2005, he was awarded the "seventh Anhui Youth Science and Technology Award" by the Organization Department of Anhui provincial Party committee, the Department of personnel of Anhui Province, and the Anhui Science and Technology Association; in 2005, he was granted the special allowance of the State Council; in 2007, he was awarded the "Wuxi apptec Life Chemistry Research Award"; in 2012, he was awarded the Asian award Core Program Lectureship Award; in 2017, he was interviewed by the chemical promotion center of the Ministry of science and technology of Taiwan (Visiting Lectureship) In recent years, research achievements in fullerene chemistry and green chemistry, such as fullerene mechanochemistry, fullerene free radical chemistry, fullerene electrochemistry, solvent-free organic synthesis, C-H bond activation, have been made in nature, chem SOC Rev., J am Chem SOC., angel Chem., int ed., chem SCI., ACS catalyst., org Lett., chem Commun., chem EUR J More than 220 papers were published in famous journals Research results of the project portfolio: electrochemical benzylation of [60] fullerene condensed lactone: unexpected formation of ring opening adduct and its photovoltaic performance Professor Wang Guanwu of University of science and technology of China has made a series of research results in the field of [60] fullerene electrochemistry in recent years In 2014, the research group took [60] fullerene indoline as the substrate, and obtained 1,2,3,16-addition mode fullerene tetraaddition derivatives (angelw Chem Int ed 2014, 53, 3006-3010) with high efficiency and selectivity through electrochemical synthesis Recently, they reported the reverse Baeyer Villiger reaction (chem SCI 2019, 10, 3012-3017) for the efficient electrochemical reduction of [60] fullerene fused lactones to [60] fullerene fused cyclones On the basis of these works, the author has studied the benzylation of δ - and γ - lactones fused by [60] fullerenes Unexpectedly, three types of ring opening benzylation adducts have been obtained and their photovoltaic properties have been studied Fig 2 Benzylation of δ - and γ - lactones fused by double anion [60] fullerenes and their photovoltaic properties (source: org Lett.) the author first studied [60] fullerene fused lactone 1, and electrolyzed 1 at − 1.34 V at a constant potential to obtain a unique open-loop structure 12 − At 25 ℃, 1 2 − was benzylated After 12 hours of reaction, 44% ring opening product 2 and 40% ring opening product 3 were obtained by accident The ratio of 2 and 3 is 1.1:1, which indicates that both the electronic effect and the spatial effect will affect the formation of the product In addition, 12 − and phch2br react for 3 h at 0 ℃, and then they are protonated with TFA to obtain ring opening product 4 with 58% yield The product 4 was obtained and the existence of intermediate a was proved Fig 3.12-benzylation (source: org Lett.) then, the author further studied with [60] fullerene fused lactone 5 Three similar ring opening products were also obtained Figure 4.52-benzylation (source: org Lett.) in order to better understand the regioselectivity of the reaction, the authors calculated the natural bond orbital charge distribution of intermediate a Among the non functionalized C60 carbon atoms, C2 (− 0.091) and C4 (− 0.090) are the two carbon atoms with the most negative charges, and they are more reactive with electrophilic reagents The reaction site is controlled by the charge density of carbon atom and the steric hindrance in the process of product formation Therefore, the regioselectivity of the product depends on the size of the attacking group and the stability of the product When intermediate a reacts with second molecule benzyl bromide, the most likely products are 2 and / or 3 In addition, the energy of product 2 is only 1.8 kcal mol − 1 higher than that of product 3, which is consistent with the regioselectivity of 1,2-adduct 2 and 1,4-adduct 3 Fig 5 Theoretical calculation (source: org Lett.) later, the author proposed the mechanism of the reaction: [60] fullerene condensed lactone 1 / 5 receives two electrons and is electrochemically reduced to form an open-loop double negative ion I with carbon oxygen bond breaking One negative charge of I is distributed on the C60 cage and the other is distributed on the oxygen atom of carboxylic acid radical Then, the first benzyl group is added to the oxygen atom of the carboxylate to obtain the monoanion II After that, the SN2 reaction between the monoanion II and the second molecule benzyl bromide resulted in the formation of 1,2-adduct 2 / 6 and 1,4-adduct 3 / 7, or the protonation of 1,2-hydrogenated fullerene 4 / 8 by TFA Figure 6 Possible reaction mechanism (source: org Lett.) finally, the author studied the application of three types of ring opening benzylation adducts in perovskite solar cells It was found that the PCE of the cell increased from 11.29% (no ETM device) to 12.02%, 12.57% and 15.25%, respectively, when the products 2, 3 and 4 were used as electronic transfer materials (ETMs) Especially as ETM device, the PCE (15.25%) of product 4 is slightly higher than that of PCBM (15.20%) Fig 7 (a) cell structure; (b) J-V curve (source: org Lett.) Professor Wang Guanwu's research group reported the benzylation of δ - and γ - lactones fused by double anion [60] fullerenes, and unexpectedly obtained three kinds of ring opening adducts, and proposed a reaction mechanism that may form ring opening adducts In addition, the representative fullerenes have been used as electron transport materials in perovskite solar cells, and show the potential to replace the commonly used electron transport material PCBM This article was recently published in org Lett (org Lett 2019, 21, 7346-7350) Niu Chuang, a doctoral student of University of science and technology of China, is the first author of this paper, and the corresponding authors are Professor Wang Guanwu and Professor Yang Shangfeng (thesis authors: Chuang Niu, Bairu Li, Zheng Chun Yin, Shangfeng Yang and Guan Wu Wang) The experimental part of the research work was completed by Niu Chuang, a doctoral student, and Yin Zhengchun, a master student The theoretical calculation part was completed by Niu Chuang, a doctoral student, and the battery part was completed by Li Bairu, a doctoral student of Professor Yang Shangfeng's research group Nowadays, people and scientific research have been paid more and more attention in the economic life China has ushered in the "node of science and technology explosion" Behind the progress of science and technology is the work of countless scientists In the field of chemistry, in the context of the pursuit of innovation driven, international cooperation has been strengthened, the influence of Returned Scholars in the field of R & D has become increasingly prominent, and many excellent research groups have emerged in China For this reason, CBG information adopts the 1 + X reporting mechanism CBG information website, chembeangoapp, chembeango official micro blog, CBG information wechat subscription number and other platforms jointly launch the column of "people and scientific research", approach the representative research groups in China, pay attention to their research, listen to their stories, record their demeanor, and explore their scientific research spirit.