Deconstructive Cycloaromatization Strategy towards N,O-Bidentate Ligands and Their Four-Coordinate Organoboron Complexes

doi:10.21203/rs.3.rs-1130793/v1

Download PDF

Article

Deconstructive Cycloaromatization Strategy towards N,O-Bidentate Ligands and Their Four-Coordinate Organoboron Complexes

https://doi.org/10.21203/rs.3.rs-1130793/v1

This work is licensed under a CC BY 4.0 License

Version 1

posted

You are reading this latest preprint version

The innovative construction of novel N,O-bidentate ligands and N,O π-conjugated four-coordinate organoboron complexes represent a long-standing challenge for chemists. Here, we report an unprecedented and straightforward approach for the construction of N,O-bidentate ligands and their organoboron complexes via the merge of ring deconstruction with cycloaromatization of indolizines and cyclopropenones. Without any catalysts, our method is able to deliver a series of polyaryl 2-(pyridin-2-yl)phenol ligands, N,O π-conjugated organoboron (BF₂ and BAr₂) complexes with good functional-group compatibility which are difficult or even impossible to synthesize with previous methods. Importantly, the formed N,O-bidentate ligands were easy to scale up and derive with valuable drugs and active molecules. In addition, the photoluminescence measurements and the HOMO/LUMO gap have been investigated, the results have revealed that N,O π-conjugated tetracoordinate boron complexes display bright fluorescence, large Stokes shifts, and good quantum yields (Φ_lum = 0.15–0.45). The method proposed by the paper will inspire the development of various N,O-bidentate metal and boron complexes, which is expected to move the area of catalysis chemistry and material science forward.

Bidentate ligands and their organoboron complexes represent one of the most important classes of organic compounds, which are extensively utilized in medicinal chemistry, homogeneous catalysis, materials chemistry, and so on.^[1–3] In particular, N,N-bidentate ligands and their organoboron (BF₂, BAr₂) complexes have been thoroughly developed for their readily available, good catalytic activity, and chemselectivity. ^[4–13] For example, N,N-bidentate organic BF₂ complexes boradipyrromethene (BODIPY) are considered as outstanding representatives. They have successfully provided significant contributions to the development of many applications such as fluorescent indicators, biological ଂuoroprobes, organic light-emitting devices (OLED), and photosensitizers, because of the particular properties related to high fluorescence intensity, quantum yields, and exceptional stability (Scheme 1a, left).^[14–19]

Scheme 1 | Access to N,O-bidentate ligands and their organic boron complexes.

N,O-bidentate organoboron (BF₂, BAr₂) complexes that are nonetheless reckoned to be underexplored should also have significant advances in optical material and labeling reagents (Scheme 1a, right).^[20–26] However, the synthesis of these fluorescent N,O-bidentate ligands and their organic boron (BF₂, BAr₂) complexes are extremely difficult owing to the lack of efficient methods, which makes their development far behind that of N,N-bidentate organic BF₂ complexes BODIPY. Thus, the development of convenient transformation to prepare those fluorescent compounds with functional diversity is still highly desirable. In this regard, 2-(pyridin-2-yl)phenol is a class of important N,O-bidentate ligand accompanied with tremendous development potential.^[27–37] Generally, the synthesis of such BF₂ complexes with 2-(pyridin-2-yl)phenol ligands require multi-step sequence transformation (Suzuki coupling, deprotection, and coordination) from the prefunctionalized procedures pyridinyl halides/surrogates and aryl organometallic reagents (Scheme 1b).^[38–40] Recently, Jiao successfully achieved PdCl₂ and N-hydroxyphthalimide cocatalyzed C_sp2-H hydroxylation of 2-phenylpyridine by dioxygen activation.^[41] Glory developed copper-catalyzed one-shot synthesis of N,O-bidentate organic BF₂ complexes from 2-phenylpyridine derivatives (Scheme 1b).^[42] But there are still some limitations needed to be addressed: 1) Multi-step synthesis is needed, and some precursors need complex pre-functionalization; 2) Metal catalysts are necessary, and metal- and oxidant-free systems have not been established; 3) Relatively narrow substrate scope. More challenging structures such as fluorescent polyaryl 2-(pyridin-2-yl)phenol ligands and their BF₂ and BAr₂ complexes cannot be synthesized. To meet these challenges, we proposed a deconstructive cycloaromatization strategy, which could quickly access polyaryl 2-(pyridin-2-yl)phenol ligands and their four-coordinate organoboron complexes.

Deconstructive functionalization has long been an integral part of organic synthesis, allowing rapid construction of scaffolds of complex molecular via ingenious cleavage and reorganization of chemical bond, which widely serves as a momentous synthetic strategy for multifarious fields.^[43–52] In particular, the ring deconstruction-rearomatization reaction is considered to be a challenging chemical transformation, also known as "scaffold hopping" (Scheme 1c).^[53–54] To date, the sequence deconstruction-cycloaromatization of indolizines has never been proposed,^[55–62] though several complexes and valuable molecules can be constructed through this strategy (Scheme 1c). Considering the great applicative prospects of N,O-bidentate ligands and their organic boron complexes, we disclose unprecedented metal-free deconstructive cycloaromatization between indolizines and cyclopropenones that can furnish a three-carbon unit as a key building block,^[63–68] providing practical polyaryl N,O-bidentate ligands and their organic BX₂ (X = F, Ar) complexes in one-pot. Of note, some representative four-coordinate organoboron complexes show interesting photophysical properties.

Condition optimization.

We have long been committed to developing new methods to construct nitrogen-containing heterocyclic derivatives.^[69–73] Thus, easily available 2-phenylindolizine and diphenylcyclopropenone were chose as the model substrates to conduct the reaction under 120 ^oC in DCM for 18 h (Table 1). Surprisingly, the sequence deconstructive recycloaromatization product was secured with a prominent yield (95%) without any catalysts and additives (Table 1, entry 1). Lowering the reaction temperature to 100 ^oC and 80 ^oC resulted in decreasing yields of polyaryl N,O-bidentate ligand (Table 1, entry 2). These results indicated that deconstructive aromatization was driven by heat. Then, a series of solvents, such as DCE, toluene, and DMSO were tested and they showed worse results than standard conditions (Table 1, entry 3). Performing the reaction at nitrogen atmosphere affected the reaction efficiency slightly and afforded the polyaryl 2-(pyridin-2-yl)phenol in 88% yield (Table 1, entry 4). Finally, the radical inhibitor TEMPO and BHT were added to the reaction, respectively, the hardly changed yields indicated that a free radical process was not involved in the transformation.

Synthesis of polyaryl N,O-bidentate ligands.

With the optimal conditions in hands, we began to evaluate the substrate adaptability of this deconstructive-cycloaromatization reaction, as summarized in Scheme 2. Firstly, various substituted indolizines were applied to get the target products under the optimized conditions. The 2-phenylindolizine with substituents at its pyridine ring, such as methyl, methoxy, ethyl, and ester, could give the desired N,O-bidentate ligands 3b-3e in 68%-93% yields. To our delight, products 3f and 3g were also obtained with high yields when alkyls replaced aryl group at C-2 position of indolizines. Both electron-donating and electron-withdrawing groups at para-position of benzene were well tolerated to deliver the corresponding N,O-bidentate ligands 3h-3r with moderate to high yields, in which product 3r was detected by single-crystal X-ray diffraction to figure out its concrete structure (CDCC 2101314). Similarly, when the meta- and ortho- positions of phenyl ring were equipped with various substituents, regardless of whether mono- or di-substituted, products 3s-3aa were all achieved in satisfactory yields (70%-91%). And the reaction was not severely affected by the service of 2-(4-fluorophenyl)-7-methylindolizine and 2-(4-chlorophenyl)-8-methylindolizine (3ab, 85%; 3ac, 86%). It was found that thienyl-, furyl-, and pyridyl-substituted indolizines was effectively leading to 70-81% yields of 3ad-3af. Then several cyclopropenones were entrusted with the mission to complete this deconstructive-cycloaromatization reaction. In comparison to the model substrate, cyclopropenones with methyl and methoxyl group on phenyl ring also offered the ideal products 3ag-3ai in nice yields. When it came to dithienylcyclopropenone, the reaction result made us amused with 82% yield of 3aj. It was worth mentioning that dithienylcyclopropenone and 2-(thiophen-2-yl)indolizine proved to be successful substrates for the procedure of deconstructive- cycloaromatization under metal- and oxidant-free conditions, affording N,O-bidentate ligand 3ak in 60% yield.

Scheme 2 | Access to polyaryl N,O-bidentate ligands via deconstructive aromatization. Reactions were performed in 0.3 mmol scale. 1 (0.30 mmol), 2 (0.33 mmol, 1.1 equiv), DCM (3.0 mL), 120 ^oC, 18 h.

Synthesis of organoboron (BF ₂ and BPh₂) complexes.

Organoboron compounds have important value and are widely used in numerous fields, including organic synthesis, catalysis, drug discovery, materials science, and so on. Among them, organic BF₂ and BAr₂ complexes have gathered much interests. Inspired by the above success on the construction of N,O- bidentate ligand via the merge of ring deconstruction with cycloaromatization of indolizines and cyclopropenones, we continued to expand this one-pot protocol to build valuable N,O-bidentate organic BF₂ and BAr₂ complexes (Scheme 3). For instance, 2-phenylindolizine and diphenylcyclopropenone could proceed smoothly in the presence of BF₃·OEt₂ and triethylamine, giving N,O-bidentate organic BF₂ complex 4a in 80% yield under metal-free conditions. Moreover, a few indolizine derivatives were subsequently examined for forming N,O-bidentate organic BF₂ complexes 4b-4f, and producing the BF₂ complexes in 60%-82% yields, in which the crystal structure of 4b were obtained (CDCC 2101316). Similarly, different cyclopropenones were proved to be reliable candidates, furnishing the BF₂ complexes 4g and 4h in moderate yields. To our delight, when BPh₃ participated in this reaction with model reactants, the targeted N,O-bidentate organic BPh₂ complexes 5a were achieved in nice yields without any other catalysts and additives. Also, the indolizines bearing various groups, such as different-substituted phenyl, furyl, and pyridyl, could also provide the corresponding BPh₂ complexes 5b-5f in good yields (65%-82%). More importantly, we found that a variety of boric acid can also directly participate in the reaction as a boron source, leading to four-coordinate organoboron complexes by one-pot method. The results proved that different substituted phenylboronic acids were tolerable in the presence of K₃PO₄ and the expected diarylboron complexes (5g-5m) were afforded in good yields (77%−90%). Besides phenyl, other arylboronic acids, such as thienyl, furyl, naphthyl, and carbazolyl boronic acid, could enable to forge target products 5n-5q in 77%-86% yields. The crystal structure of 5q was analyzed (CDCC 2121318). Next, we introduced triphenylamine groups to indolzine and used it to get the corresponding BPh₂-complexs 5r and 5s successfully with good yields. Finally, bisindolizine derivative prepared via Suzuki-coupling of iodoindolizine and 1,4-phenylenebisboronic acid finished the deconstructive-cycloaromatization and provided product 5t in 84% yield. Notably, compound 5t contains two four-coordinate organoboron centers.

Synthesis of polyaryl phenolic esters.

Then, we turned our attention to put acetic acid into the reaction edifice, the assumed polyaryl 2-(pyridin-2-yl)phenol derivatives were produced in one-pot (Scheme 4). For example, when acetic acid was used, essential 2-(pyridin-2-yl)phenol derivatives 6a-6d were got in 60%-75% yields with variant indolizines, and the crystal structure data of 6c has arrived in our hand (CDCC 2101315). This novel deconstructive aromatization strategy provides a convenient, direct and practical access to synthesize complex N,O-bidentate ligand and their derivatives in one-pot. metal- and oxidant-free conditions.

As we know, phenol derivatives are not only indispensable components of many drugs, but also good synthetic intermediates. Therefore, the polyaryl 2-(pyridin-2-yl)phenols synthesized by the present method were easily incorporated into several drug molecules and bioactive units via esterification process under mild conditions (Scheme 4). We firstly employed a simple pyrazolecarboxylic acid, which is an intermediate of YW2065 (anti-CRC molecule), and fortunately, the desired esterification product 6e was yielded in 82% yield. Then two approved drugs indometacin and febuxostat with complicated structure could combine with polyaryl 2-(pyridin-2-yl)phenol, generating the corresponding derivatives 6f and 6g in high yields, respectively. Herein, we developed a rapid method for the construction of complex framework polyaryl 2-(pyridin-2-yl)phenols and successfully applied it to the modification of several pharmaceuticals and biologically active molecules.

Scheme 4 | Synthesis of polyaryl phenolic esters derivatives and incorporation of N,O-bidentate ligand into drugs and active molecules. Conditions: [a] 1 (0.3 mmol, 1.0 equiv), 2a (0.33 mmol, 1.1 equiv), AcOH (0.36 mmol, 1.2 equiv), DCM (3.0 mL), 120 ^oC, 18 h. [b] 3 (0.2 mmol), RCOOH (0.3 mmol, 1.5 equiv), DCC (0.3 mmol, 1.5 equiv), DMAP (0.2 mmol, 1 equiv), DCM, r.t., 24 h.

Further transformations of products.

In order to further evaluate the practicability and expansibility of this deconstructive aromatization reaction, we expanded the scale of this metal and additive-free transformation to 8 mmol (Scheme 5). Surprisingly, we easily and efficiently acquired the final product 3a in 81% yield (2.6 g) by direct filter and wash with MeOH. The further transformations were studied. When halogenating agents, N-fluorobenzenesulfonimide (NFSI), 1,3-dichloro-5,5-dimethylhydantoin (DCDMH), and N-bromosuccinimide (NBS), were stirred with N,O-bidentate ligand at 80 ^oC respectively, the corresponding halogenated products 7a-7c were given with 78%-96% yields, which could be purified readily by recrystallization (hexane and DCM). The obtained halogenated N,O-bidentate ligands were easily ordinated with arylboronic acids to produce the corresponding four-coordinate organoboron complexes (8a-8c). Next, three different boric acids were coupled with brominated N,O-bidentate ligand, generating 9a-9c with good yields. Reaction could also occur between N,O-bidentate ligand and perfluorotriphenylborane to cater for product 10 in 90% yield.

Scheme 5 | Further transformation of N,O-bidentate ligands. Conditions: [a] 1a (10 mmol), 2a (11 mmol, 1.1 equiv), DCM (25 mL), 120 ^oC, 18 h.[b] 3a (0.3 mmol), NFSI (0.36 mmol, 1.2 equiv), DCM (3 mL), 80 ^oC, 12 h. [c] 3a (0.3 mmol), NBS or DCDMH (0.36 mmol, 1.2 equiv), DCM (3 mL), 80 ^oC, 12 h. [d] 7a, 7b, or 7c (0.3 mmol),Ph-B(OH)₂ (1.5 mmol, 5 equiv), K₃PO₄ (3 mmol, 10 equiv). [e] 8b (0.3 mmol), boric acid (0.45 mmol, 1.5 equiv), Pd(PPh₃)₄ (0.03 mmol, 0.1 equiv), K₂CO₃ (0.6 mmol, 2.0 equiv), THF:H₂O (10:1, 3 mL), 90 ^oC, 12 h. [f] 3a (0.3 mmol), perfluorotriphenylborane (0.36 mmol, 1.2 equiv), DCM (3 mL), 80 ^oC, 12 h.

Photophysical property investigations

To prove the promising applications as optical material of the four-coordinate organoboron complexes, we next investigated the photophysical properties of N,O-bidentate BPh₂ complexs prepared by this method (Scheme 6 and Table 2). Clearly, the selected four-coordinate organoboron complexes (5a, 5i, 5q, 5t, and 8a) display bright blue fluorescence in DCM, while compounds 9b and 5s display light green fluorescence and 5r displays intensive yellow fluorescence under UV light irradiation (365 nm) (Scheme 6a). The detailed spectra datas were shown in Scheme 6. Absorption spectra of 5a in different solvent shows that DCM is the best solvent for these N,O-bidentate BPh₂ complexes (Scheme 6b). The absorption maximum wavelengths of the selected comlexes range from 311 nm to 347 nm in DCM solution (Scheme 6c). In fluorescence emission spectra, their maximum photoluminescence wavelength are concentrated at 473 nm to 570 nm (Scheme 6d). Different substituent groups weakly affect on emission wavelength and fluorescence intensity, while compounds 9b, 5s, and 5r have remarkable red shifts. It is worthy to note that compound 5r displays the emission maxima at 570 nm (Scheme 6d). Interestingly, these organoboron complexs exhibits large Stokes shifts ranging from 139 nm to 223 nm, and such large Stokes shifts makes them appealing in valuable applications (Table 2). Finally, density functional theory (DFT) calculations were conducted at the B3LYP/6-31G(d) level using the Gaussian 03 package for further study the optoelectronic properties.^[74] The calculated HOMO and LUMO energy levels of selected compounds (5a, 5r, 5s, 5t, and 9b) were summarized at Scheme 6e and Table 2. The results disclosed that the HOMO−LUMO gaps of these four-coordinate organoboron complexes are in the range from 2.99 to 3.70 eV.

Proposed mechanism

Based on the results of our experiments and previous reports,^[75] a plausible mechanism is depicted in Scheme 7. First, a resonance is occurred between cyclopropenone 2a and its ionic form 2a', which reacts with 2-phenyl indolizine 1a in high temperature to give intermediate I. Then, charge transfer occurs on the nitrogen atom in indolizine to form ion intermediate II. Subsequently, the intermediate III was obtained via the cleavage of C-N bond. Intermediate III isomerized to more stable intermediates IV. Finally, the intramolecular positive and negative ions interact to produce intermediate V, which further undergoes aromatization to obtain the final product 3a. 3a could react with BF₃ and BPh₃ (or arylboronic acid) to give N,O-bidentate organic BF₂ and BAr₂ complexes 4a and 5a.

In conclusion, we have developed an efficient and unprecedented access to produce novel polyaryl N,O-bidentate ligands without any metals or other additives via deconstructive cycloaromatization reaction from indolizines and cyclopropenones. Furthermore, this strategy provides a convenient and one-pot synthesis of novel N,O-bidentate organic BF₂ and BPh₂ compounds, in which the optical properties and HOMO/LUMO gap of these tetracoordinate organoboron compounds are explored. Notably, these N,O π-conjugated boron complexes exhibit bright fluorescence, and large Stokes shifts, which could have appealing applications in bioassays and optoelectronic devices. We envision that this work will open new access to the construction of polyaryl N,O-bidentate ligands and inspire the discovery of various N,O-bidentate metal and boron complexes.

Supporting Information

Supporting Information is available. Experimental details, characterization data and NMR spectra of new compounds.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (22001045), the Science Foundation for Distinguished Young Scholars for GuangDong Province (2020B1515020026), the Innovation and Strong School Project of Guangdong Pharmaceutical University (2019KQNCX061, 2021ZDZX2028), Guangdong Cosmetics Engineering & Technology Research Center, GDPU-HKU Zhongshan Biomedical Innovation Platform, Special funds of key disciplines construction from Guangdong and Zhongshan cooperating.

Clevenger, A. L.; Stolley, R. M.; Aderibigbe, J.; Louie, J. Trends in the Usage of Bidentate Phosphines as Ligands in Nickel Catalysis. Chem. Rev. 2020, 120, 6124–6196.
Rej, S.; Ano, Y.; Chatani, N. Bidentate Directing Groups: An Efficient Tool in C–H Bond Functionalization Chemistry for the Expedient Construction of C–C Bonds. Chem. Rev. 2020, 120, 1788–1887.
Daugulis, O.; Roane, J.; Tran, L. D. Bidentate, Monoanionic Auxiliary-Directed Functionalization of Carbon–Hydrogen Bonds. Acc. Chem. Res. 2015, 48, 1053–1064.
Xiao, X.; Tian, W.; Imran, M.; Cao, H.; Zhao, J. Controlling the triplet states and their application in external stimuli-responsive triplet–triplet-annihilation photon upconversion: from the perspective of excited state photochemistry. Chem. Soc. Rev. 2021, 50, 9686–9714.
Yogo, T.; Urano, Y.; Ishitsuka, Y.; Maniwa, F.; Nagano, T. Highly Efficient and Photostable Photosensitizer Based on BODIPY Chromophore. J. Am. Chem. Soc. 2005, 127, 12162–12163.
Oleynik, P.; Ishihara, Y.; Cosa, G. Design and Synthesis of a BODIPY-α-Tocopherol Adduct for Use as an Off/On Fluorescent Antioxidant Indicator. J. Am. Chem. Soc. 2007, 129, 1842–1843.
Erten-Ela, S.; Yilmaz, M. D.; Icli, B.; Dede, Y.; Icli, S.; Akkaya, E. U. A Panchromatic Boradiazaindacene (BODIPY) Sensitizer for Dye-Sensitized Solar Cells. Org. Lett. 2008, 10, 3299–3302.
Ozlem, S.; Akkaya, E. U. Thinking Outside the Silicon Box: Molecular AND Logic As an Additional Layer of Selectivity in Singlet Oxygen Generation for Photodynamic Therapy. J. Am. Chem. Soc. 2009, 131, 48–49.
Domaille, D. W.; Zeng, L.; Chang, C. J. Visualizing Ascorbate-Triggered Release of Labile Copper within Living Cells using a Ratiometric Fluorescent Sensor. J. Am. Chem. Soc. 2010, 132, 1194–1195.
Li, D.; Zhang, H.; Wang, Y. Four-coordinate organoboron compounds for organic light-emitting diodes (OLEDs). Chem. Soc. Rev. 2013, 42, 8416–8433.
Lu, H.; Mack, J.; Yang, Y.; Shen, Z. Structural modification strategies for the rational design of red/NIR region BODIPYs. Chem. Soc. Rev., 2014, 43, 4778–4823.
Patra, A.; Patalag, L. J.; Jones, P. G.; Werz, D. B. Extended benzene-fused oligo-BODIPYs: in three steps to a series of large, arc-shaped, near-infrared dyes. Angew. Chem., Int. Ed. 2021, 60, 747–752.
Chen, P. Z.; Niu, L. Y.; Chen, Y. Z.; Yang, Q. Z. Difluoroboron β-diketonate dyes: Spectroscopic properties and applications. Coord. Chem. Rev. 2017, 350, 196–216.
Jin, J.; Xia, H.; Zhang, F.; Wang, Y. Lewis-Base Boryl Radicals Enabled Borylation, Radical Catalysis and Reduction Reactions. Chin. J. Org. Chem. 2020, 40, 2185–2194.
Tian, Y. M.; Guo, X. N.; Braunschweig, H.; Radius, U.; Marder, T. B. Photoinduced Borylation for the Synthesis of Organoboron Compounds. Chem. Rev. 2021, 121, 3561–3597.
Mellerup, S. K.; Wang, S. Boron-based stimuli responsive materials. Chem. Soc. Rev. 2019, 48, 3537–3549.
Ji, L.; Griesbeck, S.; Marder, T. B. Recent developments in and perspectives on three-coordinate boron materials: a bright future. Chem. Sci. 2017, 8, 846–863.
Lorbach, A.; Hubner, A.; Wagner, M. Aryl(hydro)boranes: versatile building blocks for boron-doped π-electron materials. Dalton Trans. 2012, 41, 6048–6063.
Wang, H.; Wang, H.; Wang, Z.; Tang, L.; Zeng, G.; Xu, P.; Chen, M.; Xiong, T.; Zhou, C.; Li, X. Covalent organic framework photocatalysts: structures and applications. Chem. Soc. Rev. 2020, 49, 4135–4165.
Frath, D.; Massue, J.; Ulrich, G.; Ziessel, R. Luminescent Materials: Locking π-Conjugated and Heterocyclic Ligands with Boron(III). Angew. Chem., Int. Ed. 2014, 53, 2290–2310.
Itoh, K.; Okazaki, K.; Fujimoto, M. The Structure of 1,3-Enaminoketonatoboron Difluorides in Solution and in the Solid State. Aust. J. Chem. 2003, 56, 1209–1214.
Zhou, Y.; Xiao, Y.; Chi, S.; Qian, X. Isomeric Boron–Fluorine Complexes with Donor–Acceptor Architecture: Strong Solid/Liquid Fluorescence and Large Stokes Shift. Org. Lett. 2008, 10, 633–636.
Feng, J.; Liang, B.; Wang, D.; Xue, L.; Li, X. Novel Fluorescent Dyes with Fused Perylene Tetracarboxlic Diimide and BODIPY Analogue Structures. Org. Lett. 2008, 10, 4437–4440.
Xia, M.; Wu, B.; Xiang, G. Synthesis, structure and spectral study of two types of novel fluorescent BF₂ complexes with heterocyclic 1,3-enaminoketone ligands. J. Fluorine Chem. 2008, 129, 402–408.
Ma, R. Z.; Yao, Q. C.; Yang, X.; Xia, M. Synthesis, characterization and photoluminescence properties of strong fluorescent BF2 complexes bearing (2-quinolin-2-yl)phenol ligands J. Fluorine Chem. 2012, 137, 93–98.
Balijapalli, U.; Manickam, S.; Thirumoorthy, K.; Sundaramurthy, K. N.; Sathiyanarayanan, K. I. (Tetrahydrodibenzo[a,i]phenanthridin-5-yl)phenol as a Fluorescent Probe for the Detection of Aniline. J. Org. Chem. 2019, 84, 11513–11523.
Jia, X.; Peng, P. N-(4-Thiazolylmethyl)Morpholine N-Oxide as N,O-Bidentate Ligand for Copper-Catalyzed Ullmann-Type N-Arylation of Azoles/Amines with Aryl Halides. Asian J. Org. Chem. 2019, 8, 1548–1554.
Shen, Y. C.; Li, Y. X.; Wen, X. J.; Feng, X. M. Application of N-Oxides in Asymmetric Catalytic Reactions. Chin. J. Org. Chem. 2005, 25, 272–281.
Speiser, F.; Braunstein, P.; Saussine, L. Dinuclear Nickel Complexes with Bidentate N,O Ligands: Synthesis, Structure, and Catalytic Oligomerization of Ethylene. Inorg. Chem. 2004, 43, 4234–4240.
Zuideveld, M. A.; Wehrmann, P.; Röhr, C.; Mecking, S. Remote Substituents Controlling Catalytic Polymerization by Very Active and Robust Neutral Nickel(II) Complexes. Angew. Chem., Int. Ed. 2004, 43, 869–873.
Connor, E. F.; Younkin, T. R.; Henderson, J. I.; Waltman, A. W.; Grubbs, R. H. Synthesis of neutral nickel catalysts for ethylene polymerization-the influence of ligand size on catalyst stability. Chem. Commun. 2003, 2272–2273.
Jenkins, J. C.; Brookhart, M. A Highly Active Anilinoperinaphthenone-Based Neutral Nickel(II) Catalyst for Ethylene Polymerization. Organometallics 2003, 22, 250–256.
Hicks, F. A.; Jenkins, J. C.; Brookhart, M. Synthesis and Ethylene Polymerization Activity of a Series of 2-Anilinotropone-Based Neutral Nickel(II) Catalysts. Organometallics 2003, 22, 3533–3545.
Ju, C.-W.; Li, B.; Li, L.; Yan, W.; Cui, C.; Ma, X.; Zhao, D. Modular Synthesis of Pentagonal and Hexagonal Ring-Fused NBN-Phenalenes Leading to an Excited-State Aromatization-Induced Structural Planarization Molecular Library. J. Am. Chem. Soc. 2021, 143, 5903–5916.
Ma, R.-Z.; Yao, Q.-C.; Yang, X.; Xia, M. Synthesis, characterization and photoluminescence properties of strong fluorescent BF2 complexes bearing (2-quinolin-2-yl)phenol ligands. J. Fluorine Chem. 2012, 137, 93–98.
Kim, N. G.; Shin, C. H.; Lee, M. H.; Do, Y. Four-coordinate boron compounds derived from 2-(2-pyridyl)phenol ligand as novel hole-blocking materials for phosphorescent OLEDs. J. Organomet. Chem. 2009, 694, 1922–1928.
Zhang, Z.; Zhang, Z.; Ye, K.; Zhang, J.; Zhang, H.; Wang, Y. Diboron complexes with bis-spiro structures as high-performance blue emitters for OLEDs. Dalton Trans. 2015, 44, 14436–14443.
Noda, H.; Bode, J. W. Synthesis of Chemically and Configurationally Stable Monofluoro Acylboronates: Effect of Ligand Structure on their Formation, Properties, and Reactivities. J. Am. Chem. Soc. 2015, 137, 3958–3966.
Zhao, D.; You, J.; Hu, C. Recent Progress in Coupling of Two Heteroarenes. Chem. Eur. J. 2011, 17, 5466–5492.
Yang, Y.; Lan, J.; You, J. Oxidative C–H/C–H Coupling Reactions between Two (Hetero)arenes. Chem. Rev. 2017, 117, 8787–8863.
Yan, Y.; Feng, P.; Zheng, Q.-Z.; Liang, Y.-F.; Lu, J.-F.; Cui, Y.; Jiao, N. PdCl₂ and N-Hydroxyphthalimide Co-catalyzed C_sp2-H Hydroxylation by Dioxygen Activation. Angew. Chem., Int. Ed. 2013, 52, 5827–5831.
Tan, G.; Schrader, M. L.; Daniliuc, C.; Strieth-Kalthoff, F.; Glorius, F. C–H Activation Based Copper-Catalyzed One-Shot Synthesis of N,O-Bidentate Organic Difluoroboron Complexes. Angew. Chem., Int. Ed. 2020, 59, 21541–21545.
Ma, X.-X.; Song, Q.-L. Recent progress on selective deconstructive modes of halodifluoromethyl and trifluoromethyl-containing reagents. Chem. Soc. Rev. 2020, 49, 9197–9219.
Roque, J. B.; Kuroda, Y.; Göttemann, L. T; Sarpong, R. Deconstructive diversification of cyclic amines. Nature 2018, 564, 244–248.
Morcillo, S. P. Radical-Promoted C–C Bond Cleavage: A Deconstructive Approach for Selective Functionalization. Angew. Chem., Int. Ed. 2019, 58, 14044–14054.
Wang, H.; Toh, R. W.; Shi, X.; Wang, T.; Cong, X.; Wu, J. Photo-mediated selective deconstructive geminal dihalogenation of trisubstituted alkenes. Nat. Commun. 2020, 11, 4462.
Zhang, L.; Cao, T.; Jiang, H.; Zhu, S. Deconstructive Reorganization: De Novo Synthesis of Hydroxylated Benzofuran. Angew. Chem., Int. Ed. 2020, 59, 4670–4677.
Hu, F.; Wang, L.; Xua, L.; Li, S.-S. Aromatization-driven deconstruction/refunctionalization of unstrained rings. Org. Chem. Front. 2020, 7, 1570–1575.
Wang, Y.; Zheng C.; You, S. L. Iridium-Catalyzed Asymmetric Allylic Dearomatization by a Desymmetrization Strategy. Angew. Chem., Int. Ed. 2017, 56, 15093–15097.
Murakami, M.; Ishida, N. Potential of Metal-Catalyzed C–C Single Bond Cleavage for Organic Synthesis. J. Am. Chem. Soc. 2016, 138, 13759–13769.
Zhao, K.; Yamashita, K.; Carpenter, J. E.; Sherwood, T. C.; Ewing, W. R.; Cheng, P. T. W.; Knowles, R. R. Catalytic Ring Expansions of Cyclic Alcohols Enabled by Proton-Coupled Electron Transfer. J. Am. Chem. Soc. 2019, 141, 8752–8757.
Chen, Y.; Du, J.; Zuo, Z. Selective C–C bond scission of ketones via visiblelight-mediated cerium catalysis. Chem. 2020, 6, 266–279.
Xu, Y.; Dong, G. Deconstructive Functionalization of Ketones via an LMCT-Promoted C–C Cleavage. Chem. 2020, 6, 10–11.
Chen, P. H.; Billett, B. A.; Tsukamoto, T.; Dong, G. “Cut and Sew” Transformations via Transition-Metal-Catalyzed Carbon–Carbon Bond Activation. ACS Catal. 2017, 7, 1340–1360.
Xu, C.; Yin, G.; Jia, F.-C.; Wu, Y.-D.; Wu, A.-X. Merging Annulation with Ring Deconstruction: Synthesis of (E)-3-(2-Acyl-1H-benzo[d]imidazol-4-yl)acrylaldehyde Derivatives via I2/FeCl3-Promoted Dual C(sp3)–H Amination/C–N Bond Cleavage. Org. Lett. 2021, 23, 2559–2564.
Tan, Z.; Ci, C.; Yang, J.; Wu, Y.; Cao, L.; Jiang, H.; Zhang, M. Catalytic Conversion of N-Heteroaromatics to Functionalized Arylamines by Merging Hydrogen Transfer and Selective Coupling. ACS Catal. 2020, 10, 5243–5249.
Chattopadhyay, B.; Gevorgyan, V. Transition-Metal-Catalyzed Denitrogenative Transannulation: Converting Triazoles into Other Heterocyclic Systems. Angew. Chem., Int. Ed. 2012, 51, 862–872.
Davies, H. M. L.; Alford, J. S. Reactions of metallocarbenes derived from N-sulfonyl-1,2,3-triazoles. Chem. Soc. Rev. 2014, 43, 5151–5162.
Teders, M.; Gómez-Suárez, A.; Pitzer, L.; Hopkinson, M. N.; Glorius, F. Diverse Visible-Light-Promoted Functionalizations of Benzotriazoles Inspired by Mechanism-Based Luminescence Screening. Angew. Chem., Int. Ed. 2017, 56, 902–906.
Tatarov, A.; Kurbatov, S.; Borodkin, G.; Goumont, R.; Terrier, F. S_EAr–S_NAr couplings of indolizines and related pyrrole derivatives with superelectrophilic nitrobenzoxadiazoles. Tetrahedron 2010, 66, 995–1006.
Wang, R.-N.; Wang, S.-W.; Li, D.-Y.; Ye, F.-Y.; Leng, Y.-T.; Wu, Y.-S.; Chang, J.-B.; Wu, Y.-J. Radical ring opening reaction of pyridine fused heterocycles with IBA-N3 catalyzed by tetra-n-butylammonium iodide. Tetrahedron 2019, 75, 2298–2305.
Watanabe, K.; Terao, N.; Kii, I.; Nakagawa, R.; Niwa, T.; Hosoya, T. Indolizines Enabling Rapid Uncaging of Alcohols and Carboxylic Acids by Red Light-Induced Photooxidation. Org. Lett. 2020, 22, 5434–5438.
Li, R.; Li, B.; Zhang, H.; Ju, C.-W.; Qin, Y.; Xue, X.-S.; Zhao, D. A ring expansion strategy towards diverse azaheterocycles. Nat. Chem. 2021, 13, 1006–1016.
Xie, F.; Yu, S.; Qi, Z.; Li, X. Nitrone Directing Groups in Rhodium(III)-Catalyzed C–H Activation of Arenes: 1,3-Dipoles versus Traceless Directing Groups. Angew. Chem., Int. Ed. 2016, 55, 15351–15355.
Wang, X.; Seidel, F. W.; Nozaki, K. Synthesis of Polyethylene with In-Chain α,β-Unsaturated Ketone and Isolated Ketone Units: Pd-Catalyzed Ring-Opening Copolymerization of Cyclopropenone with Ethylene. Angew. Chem., Int. Ed. 2019, 58, 12955–12959.
Zhao, W.-T.; Gao, F.; Zhao, D. Intermolecular σ-Bond Cross-Exchange Reaction between Cyclopropenones and (Benzo)silacyclobutanes: Straightforward Access towards Sila(benzo)cycloheptenones. Angew. Chem., Int. Ed. 2018, 57, 6329–6332.
Liu, Y.; Tian, Y.; Su, K.; Wang, P.; Guo, X.; Chen, B. Rhodium(iii)-catalyzed [3 + 3] annulation reactions of N-nitrosoanilines and cyclopropenones: an approach to functionalized 4-quinolones. Org. Chem. Front. 2019, 6, 3973–3977.
Shi, Y.; Xing, H.; Huang, T.; Liu, X.; Chen, J.; Guo, X.; Li, G.; Wu, Y. Divergent C–H activation synthesis of chalcones, quinolones and indoles. Chem. Commun. 2020, 56, 1585–1588.
Song, D.; Huang, C.; Liang, P.; Zhu, B.; Liu, X.; Cao, H. Lewis acid-catalyzed regioselective C–H carboxamidation of indolizines with dioxazolones via an acyl nitrene type rearrangement. Org. Chem. Front. 2021, 8, 2583–2588.
Wang, Y.; Zheng, H.; Xu, J.; Zhuang, C.; Liu, X.; Cao, H. Access to diverse primary, secondary, and tertiary amines via the merger of controllable cleavage of triazines and site-selective functionalization. Org. Chem. Front. 2021, 8, 4706–4714.
Zhou, J.; Li, W.; Zheng, H.; Pei, Y.; Liu, X.; Cao, H. Visible Light-Induced Cascade Cyclization of 3-Aminoindazoles, Ynals, and Chalcogens: Access to Chalcogen-Containing Pyrimido[1,2-b]-indazoles. Org. Lett. 2021, 23, 2754–2759.
Liu, X.; Song, D.; Zhang, Z.; Lin, J.; Zhuang, C.; Zhan, H.; Cao, H. Regioselective C–H dithiocarbamation of indolizines with tetraalkylthiuram disulfide under metal-free conditions. Org. Biomol. Chem. 2021, 19, 5284–5288.
Liu, X.; Li, W.; Liu, H.; Cao, H. Application on the Construction of Imidazo[1,2-a]pyridines C-3 Canbon-Hetero Bonds by Visible-Light Catalysis and Electrochemistry. Chin. J. Org. Chem. 2021, 41, 1759–1773.
Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, M.; Fukuda, R.; Hasegawa, J.; Ishida, J.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, O.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, Revision E.01; Gaussian, Inc.: Pittsburgh PA, 2004.
Nechaev, I. V.; Cherkaev, G. V. Radical and Ionic Reactions of Indolizin-1-ols: Synthesis of 3-Arylsulfanyl-, 3-(Tropon-2-yl)- and 3-(Tropolon-5-ylazo)-1-hydroxyindolizines from 3,3-Difluorocyclopropenes. J. Org. Chem. 2021, 86, 7687–7700.

Tables 1-2 are available in the Supplementary Files section.

There is NO Competing Interest.

Tables.docx
SINatureComm.pdf
Supporting information
Onlinefloatimage9.png
Table of Contents GraphicThe innovative construction of novel N,O-bidentate ligands and N,O π-conjugated four-coordinate organoboron complexes represent a long-standing challenge for chemists. Here, we report an unprecedented and straightforward approach for the construction of N,O-bidentate ligands and their organoboron complexes via the merge of ring deconstruction with cycloaromatization of indolizines and cyclopropenones. Without any catalysts, our method is able to deliver a series of polyaryl 2-(pyridin-2-yl)phenol ligands, N,O π-conjugated organoboron (BF₂ and BAr₂) complexes with good functional-group compatibility which are difficult or even impossible to synthesize with previous methods. Importantly, the formed N,O-bidentate ligands were easy to scale up and derive with valuable drugs and active molecules. In addition, the photoluminescence measurements and the HOMO/LUMO gap have been investigated, the results have revealed that N,O π-conjugated tetracoordinate boron complexes display bright fluorescence, large Stokes shifts, and good quantum yields (Φ_lum=0.15–0.45). The method proposed by the paper will inspire the development of various N,O-bidentate metal and boron complexes, which is expected to move the area of catalysis chemistry and material science forward.

Download PDF

Version 1

posted

You are reading this latest preprint version

Deconstructive Cycloaromatization Strategy towards N,O-Bidentate Ligands and Their Four-Coordinate Organoboron Complexes

Status:

Version 1

Abstract

Figures

Introduction

Results And Discussion

Photophysical property investigations

Proposed mechanism

Conclusion

Declarations

References

Tables

Additional Declarations

Supplementary Files

Status:

Version 1