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    Home > One pot synthesis of iridium heteropolycyclic aromatic hydrocarbons

    One pot synthesis of iridium heteropolycyclic aromatic hydrocarbons

    • Last Update: 2019-11-13
    • Source: Internet
    • Author: User
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    The metal heteroanalogues of PAHs are unique in the field of organometallic chemistry due to their unique structures and electronic properties So far, the structures of metal benzene, metal naphthalene and metal anthracene have been reported, but there are few reports of metal heteroanalogues with larger dense rings Recently, Liu Shenghua group of central China Normal University has successfully synthesized a series of iridium heterofluoranthene and polyphenyl fused iridium heterofluoranthene derivatives in high yield under mild reaction conditions for the first time, with the number of fused rings ranging from four to seven (DOI: 10.1039 / c9sc03914g) Prof Liu Shenghua, research group brief introduction: since the establishment of the research group, the research group has been engaged in the synthesis, reactivity and Performance Research of organometallic compounds for a long time, including the research on the synthesis and properties of Organometallic Molecular Wires and molecular switches, AIE and intelligent response luminescent materials, and heteropolycyclic aromatic hydrocarbons At present, the research group has published more than 150 papers in domestic and foreign academic journals, including JACS, chem SCI., chem Commun., org Lett And other internationally renowned academic journals At present, the research group has 2 professors, 5 doctors and 15 masters Prof Liu Shenghua, professor and doctoral supervisor of central China Normal University He obtained bachelor's degree in organic chemistry from Jiangxi University (now Nanchang University) in 1984, master's degree in organic chemistry from Wuhan University in 1994, doctor's degree in organic chemistry from Wuhan University in 1999 and postdoctoral research from Hong Kong University of science and technology in 1999-2002 In 2004, it was selected into the New Century Excellent Talents plan of the Ministry of education, and in 2012, it was selected into the discipline leader plan of Wuhan city Up to now, he has presided over more than 10 national and provincial research projects, including 6 national natural science funds, 1 major scientific and technological innovation project of colleges and universities, and 1 New Century Excellent Talents plan of the Ministry of education In 2010, he won the second prize of natural science of Hubei Province (the first adult) Leading scientific research achievements: as an important part of organic compounds, iridium heteropolycyclic aromatic hydrocarbons (iridium heteropolycyclic aromatic hydrocarbons) synthesized by one pot method have attracted more and more attention due to its wide application prospects in organic light-emitting diodes, field-effect transistors, organic solar cells and other fields On the other hand, since Roper et al reported the first case of metal benzene in 1982, metal heteroaromatics have gradually attracted the attention and research of scientists In recent years, metal naphthalene (alkyne), metal anthracene (alkyne), metal phenanthrene (alkyne) and the metal carbaryl compounds proposed by Xia Haiping's research group have been successively synthesized and reported (Figure 1) However, up to now, there are few reports of heteropahs with larger condensed ring structure, especially iridium heteropahs Fig 1 In 2017, Wright et al Successfully synthesized the first iridium heterofluoranthene compound In 2018, Bola ñ o et al Obtained a group of iridium carbenes through the reaction of [ircp * Cl (NCME) (PME 3)] pf 6 with diarylpyrynyl alcohol, and further activated the ring by hydrocarbon to obtain iridium heteronaphthalene, iridium heteroanthracene and iridium heterophenanthrene, and first reported the structure of iridium heteronaphthalene The reaction conditions of this synthesis method are mild, but there are isomers in the products, which are difficult to separate In this work, Liu Shenghua's group synthesized and separated the first iridium heterofluoranthene compound and its polyphenyl fused derivatives in high yield (70% - 87%) from ircp * Cl 2 PME 3 and 9-ethynyl-9-fluorenol derivatives from the perspective of one pot synthesis The highest number of fused rings is seven, which is the largest one in the reported heteropolyaromatic system Fig 2 synthesis of target complex 1-9 (source: Chemical Science) as shown in Fig 2, ircp * Cl 2 PME 3, sodium hexafluorophosphate and 9-ethynyl-9-fluorenol derivatives (l1-l9) were stirred overnight in methanol at room temperature, and then the methanol was vacuumed dry, silver hexafluorophosphate and a proper amount of dichloromethane were added and stirred at room temperature 5 Minutes, the target product (1 - 9) can be obtained Referring to the previous work of Bola ñ o et al, the author proposed the possible reaction mechanism of iridium heterofluoranthene As shown in Figure 3, under the action of sodium hexafluorophosphate, the metal raw material ircp * Cl 2 PME 3 first removes a chlorine atom; then alkynol compound L1 is coordinated with it to obtain diene intermediate, which then reacts with a molecular methanol to obtain carbene compound 1A; finally 1A Under the action of silver hexafluorophosphate, another chlorine atom is removed, and then the intramolecular hydrocarbon is activated to close the ring to obtain the target product 1 Fig 3 the possible synthesis mechanism of iridium heterofluoranthene (source: Chemical Science) in the synthesis of compounds 1-6, because the ligand l1-l6 used has symmetry, the generation of isomers has been successfully avoided When asymmetric ligand l7-l9 is used, the target product 7-9 can still be obtained in high yield Intermediate compounds 7a and 8A (Fig 4) have been successfully cultured It is found that iridium atom can form six membered ring by metal cyclization with benzene ring adjacent to five membered ring in fluorene group, and seven membered ring by metal cyclization with benzene ring "F" (Fig 2), and This reaction is more likely to form iridium hetero six membered ring Fig 4 crystal structure of intermediate 7a (left) and 8A (right) (source: Chemical Science) the structure of compounds 1-9 was determined by NMR and HRMS, and most of them were further confirmed by X-ray single crystal diffraction (Fig 5) The single crystal structure diagram shows that the four ring framework of compound 1 has very good planarity, and the sum of the internal angles of the iridium hetero six ring is 720.0 °, which is in good agreement with the ideal value of the sum of the internal angles of the plane six ring The bond length of ir1-c1 bond and ir1-c5 bond in the single crystals of these compounds are 1.954-1.992 Å and 2.034-2.071 Å, respectively, which is equivalent to the bond length of previously reported iridium heteroaromatic compounds The fused ring skeletons of single crystals 2, 3, 6 and 8 also have good planarity In contrast, the condensed ring skeleton of 5 and 9 crystals is distorted to a certain extent, which may be caused by the larger intramolecular hydrogen repulsion Fig 5 single crystal structure of compounds 1-3, 5, 6, 8 and 9 (source: Chemical Science) Next, the author tested the UV-Vis absorption spectrum of compounds 1-9 (Fig 6) When the substituents are changed, compound 1 - 4 has a similar absorption wavelength When the conjugated structure is extended, the maximum absorption wavelength of compound 5 - 9 has a significant red shift compared with compound 1 The author further calculated the time-dependent density functional theory (TD-DFT) of compounds 1-9, and the simulated absorption data (Table 1) is highly consistent with the experimental data The results show that the maximum absorption of these compounds is due to the synergistic effect of the internal electronic transition of the ligand and the metal to ligand electronic transition, which also shows that iridium plays an important role in the electronic transition process of the compounds Fig 6 UV visible absorption spectrum (source: Chemical Science) table 1 UV visible absorption data and TD-DFT results (source: Chemical Science) In order to further understand the electronic properties of these compounds, the authors used platinum disk electrode as working electrode, platinum wire as counter electrode and silver wire as reference electrode to test the cyclic voltammograms of these compounds in dichloromethane Compounds 1 - 9 have multiple electron redox processes, and the first electron reduction processes of all compounds show good reversibility In contrast compound 1, when the fused ring skeleton is connected with the electron donor, the oxidation potential and reduction potential move to the cathode; when the fused ring skeleton is connected with the electron acceptor, the oxidation potential and reduction potential move to the anode However, when the conjugated framework is expanded, the oxidation potential moves to the cathode and the reduction potential moves to the anode The calculated energy levels of Homo and LUMO (Table 2) are in good agreement with the change trend of the first oxidation potential and the first reduction potential of these compounds, that is to say, the introduction of electron donor will increase the HOMO and LUMO energy levels, while the introduction of electron acceptor is just the opposite; the expansion of conjugated system can reduce the LUMO energy level and increase the HOMO energy level In summary, Liu Shenghua group synthesized a series of novel iridium heterofluoranthene derivatives in high yield under mild conditions by one pot synthesis method This work not only enriches the metal heteropahs system, but also is expected to open a new way for the design and synthesis of larger metal heteropahs and even metal heteronano graphene This achievement was recently published on Chemical Science (DOI: 10.1039 / c9sc03914g) Dr Hu Yuxuan and Dr Zhang Jing, Ph.D students, are the co first authors, and Prof Liu Shenghua and Prof Yin Jun, Ph.D students, are the corresponding authors The above research work is strongly supported by Xia Haiping, Professor of South University of science and technology, and supported by the general program of NSFC 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.
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