One-Pot Syntheses of Irida-Polycyclic Aromatic Hydrocarbons† Cite This: Chem

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One-Pot Syntheses of Irida-Polycyclic Aromatic Hydrocarbons† Cite This: Chem Chemical Science View Article Online EDGE ARTICLE View Journal | View Issue One-pot syntheses of irida-polycyclic aromatic hydrocarbons† Cite this: Chem. Sci.,2019,10, 10894 a a a b a All publication charges for this article Yu Xuan Hu,‡ Jing Zhang,‡ Xiaoyan Wang, Zhengyu Lu, Fangfang Zhang, have been paid for by the Royal Society Xiaofei Yang,a Zhihua Ma,a Jun Yin, *a Haiping Xia b and Sheng Hua Liu *a of Chemistry Metalla-analogues of polycyclic aromatic hydrocarbons (PAHs) have captivated chemists with their fascinating structures and unique electronic properties. To date, metallabenzene, metallanaphthalene and metallaanthracene have been reported. Metalla-analogues with more complicated fused rings have rarely been reported. Herein, we have successfully synthesized a series of new iridafluoranthenes and fused-ring iridafluoranthenes ranging from pentacyclic to heptacyclic metallaaromatic hydrocarbons in Received 6th August 2019 high yields under mild reaction conditions for the first time. Their photophysical and redox properties Accepted 12th October 2019 were also explored using UV-vis spectroscopy and electrochemistry combined with TD-DFT DOI: 10.1039/c9sc03914g calculations. The present work may offer an important guideline for the design and construction of new rsc.li/chemical-science polycyclic metallaaromatic hydrocarbons and metalla-nanographenes. Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Introduction carbeneiridium compound by using an intramolecular C–H activation reaction.6b In 2018, they further developed irida- Polycyclic aromatic hydrocarbons (PAHs), as important compo- phenanthrene, iridanaphthalene and iridaanthracene from nents in the eld of organic chemistry, have attracted a signi- their corresponding methoxy(alkenyl)carbeneiridium inter- * cant amount of attention due to their wide range of applications mediates via reactions of [IrCp Cl(NCMe) (PMe3)]PF6 with 8 in organic light-emitting diodes,1 eld-effect transistors2 and diarylpropargyl alcohols. In the present work, we have organic photovoltaic cells.3 Since the rst metallabenzene proposed a one-pot synthetic route to obtain a series of pure This article is licensed under a (Scheme 1) was reported by Roper et al. in 1982,4 scientists have iridauoranthenes in high yields (70–87%) by using * devoted enormous efforts to developing transition metal-con- IrCp Cl2(PMe3) and 9-ethynyl-9- uorenol derivatives as taining metalla-aromatics.5 However, only very limited systems, reagents (Scheme 2), all of which were successfully embedded 6 7 Open Access Article. Published on 14 October 2019. Downloaded 9/26/2021 1:58:11 AM. including metallanaphthalene, metallaanthracene, metal- laphenanthrenes,8 metallabenzynes,9 metallanaphthalynes,10 metallaanthracynes, metallaphenanthrynes11 and metal- lapentalenes,12 have been reported over the past few decades. Moreover, metalla-analogues of PAHs containing multiple fused rings have rarely been reported until now. Among these devel- oped systems, only a handful of examples involve irida-PAHs. In 2017, Wright et al. successfully synthesized the rst iri- daanthracene complex.7 In another recent breakthrough, Bolano˜ et al. reported a novel iridanaphthalene compound in a high yield of 74% from its corresponding methoxy(alkenyl) aKey Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal University, Wuhan 430079, P. R. China. E-mail: [email protected]; [email protected] bDepartment of Chemistry, Shenzhen Grubbs Institute, Southern University of Science and Technology, Shenzhen 518055, P. R. China † Electronic supplementary information (ESI) available: Crystallographic details and NMR and HRMS data. CCDC 1940387, 1940396, 1940398, 1940533, 1940389, 1940391, 1940392, 1940394, 1940397 and 1940400. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c9sc03914g ‡ These authors contributed equally to this work. Scheme 1 Organic PAHs and metalla-analogues. 10894 | Chem. Sci.,2019,10,10894–10899 This journal is © The Royal Society of Chemistry 2019 View Article Online Edge Article Chemical Science occurred, which is followed by further coordination of alkynol compound L1 to form an allenylidene intermediate (A). Subsequently, nucleophilic attack by the oxygen atom of methanol on the Ca of the allenylidene followed by proton transfer at Cb gives the (methoxyalkenylcarbene)iridium intermediate 1a. Intramolecular C–Hactivationthenoccurred aer treatment with AgPF6 to remove another chloride and to generate the ultimate product complex 1.Fortunately,we successfully isolated the intermediate 1a and obtained its single crystal (Fig. S2†) to further verify the reaction mecha- nism we proposed above. In addition, it is well documented in theliteraturethatcarbenecomplexeslike1a could easily be formed from a reaction between allenylidene intermediates and alkynol pro-ligands.15 Additionally, the structure of the uorenyl ligand of 1a was symmetric, so pure products could be obtained in the subsequent ring-closing reaction due to the equivalent C–Hactivationsites(Ha and Hb in Scheme S3†)in 1a. Interestingly, when asymmetric compounds (L7–L9)reac- * 7– ted with Cp IrCl2(PMe3), the corresponding pure complexes 9 were obtained in high yields above 90%. In addition, we also – Scheme 2 Synthesis of target complexes 1 9. successfully isolated carbene intermediates 7a and 8a and obtained their structures by single crystal X-ray crystallog- † 7–9 Creative Commons Attribution-NonCommercial 3.0 Unported Licence. raphy (Fig. S3 ). The complexes were obtained by CH into a fused ve-membered ring to achieve higher conjuga- metalation of the benzene ring that is directly fused to the ve- tion. In the solid state all the new compounds are stable in air membered ring and remote from the fused ring “f”. Metalation and can be stored in contact with the atmosphere for half of this benzene ring results in the formation of a six- a year without any signs of decomposition. To the best of our membered metallacyclic ring. Presumably this is favoured over knowledge, the present work is the rst case involving CH metalation of the fused benzene ring “f” because metal- synthesis of metallauoranthenes to date. Specically, ation of this ring would give a seven-membered metallacycle, compounds L5–L9 were used to produce complexes 5–9 with the formation of which is expected to be less favourable. Aer the most abundant fused rings and high conjugation, which treating 8a with AgPF6, ring-closed product 8 was successfully This article is licensed under a did not involve any isomerization and thus maintained high produced in a high yield of 93%. yield and high purity. In addition, diverse polycyclic metal- The structures of complexes 1–9 were veried by using laarenes, including four tetracyclic complexes (1–4)andpen- nuclear magnetic resonance (NMR) spectroscopy and high- tacyclic (7), hexacyclic (5, 6 and 8) and heptacyclic (9) resolution mass spectrometry (HRMS). Typically, for complex 1, Open Access Article. Published on 14 October 2019. Downloaded 9/26/2021 1:58:11 AM. complexes, have been presented in this work. Although there the proton signals corresponding to the pentam- are several reports on nitrogen- or oxygen-containing poly- ethylcyclopentadienyl group can be observed at d ¼ 1.84 ppm 13 13 cyclic metallaaromatics, this series of new structures that and the C(CH3) signals are located at d ¼ 100.0 and 9.7 ppm, containmorethanfourfusedringsinthepolycyclicskeletons respectively. The characteristic signals of group P(CH3)3 are consisting of a metal atom and carbon atoms only, is located at d ¼ 1.21 ppm in the 1H NMR spectrum and at d ¼ 13.8 1 13 unprecedented. ppm (d, JC–P ¼ 41.6 Hz) in the C NMR spectrum, respectively. The 31P NMR spectrum also shows two signals at À35.3 ppm (s, À 1 ¼ Results and discussion P(CH3)3) and 144.3 ppm (hept, JP–F 712.3 Hz, PF6), respectively. Additionally, the downeld signal observed at d ¼ As depicted in Scheme 2, the target complexes (1–9)were 250.5 ppm in the 13C NMR spectrum corresponds to C1, which synthesized by a one-pot method in high yield (70–87%) under is a typical metal-bonded carbon atom. Similar spectra were mild reaction conditions. Specically, as shown in Scheme obtained for complexes 2–9 and their NMR data were consistent 6b,c,8 S1,† asolutionofCp*IrCl2(PMe3), NaPF6 and a pro-ligand (L1– with those reported in the literature. L9, respectively) in methanol was stirred at room temperature We successfully obtained single crystals of 1–3, 5, 6, 8 and 9 overnight, and then methanol was removed under vacuum and to further conrm their structures. As shown in Fig. 1a and b, the residue was dissolved in dichloromethane. Subsequently, the tetracyclic skeleton of complex 1 exhibited good planarity. AgPF6 was added and the mixture was further stirred for 5 The sum of the angles in the iridium-containing six-membered minutes to obtain the corresponding target complex (1–9). ring was 720.0, which is consistent with the ideal value of Furthermore, we propose a possible reaction mechanism a planar six-membered ring. The bond lengths of Ir1–C1 and according to the previous report of Bolano˜ et al.14 by taking Ir1–C5 were 1.984 and 2.056 A,˚ respectively, while the corre- complex 1 as an example. As shown in Scheme S3,† initially, sponding bond lengths in complexes 2, 3, 5, 6, 8 and 9 were ˚ ˚ de-coordination of one chloride from Cp*IrCl2(PMe3) 1.954–1.992 A and 2.034–2.071 A, respectively. These bond This journal is © The Royal Society of Chemistry 2019 Chem. Sci.,2019,10,10894–10899 | 10895 View Article Online Chemical Science Edge Article C3–C4–C5. The iridium-containing polycyclic skeletons observed in the crystal structures of 3, 6 and 8 also show excellent planarity (Fig. 1d, g and h), while the polycyclic frameworks of 5 and 9 exhibit some distortion (Fig. 1e, f, i and j), which is presumably caused by the intramolecular repulsion between the hydrogen atoms connected with C12 and C20 in 5 and C14 and C27 in 9.
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