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Article

Synthesis of B-Substituted Anthracenyl and Pyrenyl Derivatives of ortho-Carborane

by
Akim V. Shmal’ko
,
Sergey A. Anufriev
*,
Kyrill Yu. Suponitsky
,
Evgeniia P. Antoshkina
,
Igor B. Sivaev
* and
Vladimir I. Bregadze
A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, 28 Vavilov Str., 119991 Moscow, Russia
*
Authors to whom correspondence should be addressed.
Inorganics 2025, 13(5), 138; https://doi.org/10.3390/inorganics13050138
Submission received: 31 March 2025 / Revised: 23 April 2025 / Accepted: 25 April 2025 / Published: 27 April 2025
(This article belongs to the Special Issue Boron-Based Low-Dimensional Nanoclusters and Nanomaterials)
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Abstract

:
Isomeric B-substituted anthracenyl and pyrenyl derivatives of ortho-carborane containing polycyclic aromatic substituents both in the position of the carborane cage most distant from the carbon atoms (position 9) and in the neighboring position (position 3) were synthesized by Pd-catalyzed cross-coupling of the corresponding iodo derivatives of ortho-carborane with polycyclic aryl zinc bromides. The derivative containing two pyrenyl substituents at the positions most distant from the carbon atoms of the ortho-carborane cage, 9,12-di(pyren-1′-yl)-ortho-carborane, was obtained in a similar way starting from 9,12-diiodo-ortho-carborane. The solid-state structures of the pyrene-containing derivatives 3-pyren-1′-yl-ortho-carborane, 9-pyren-1′-yl-ortho-carborane, and 9,12-di(pyren-1′-yl)-ortho-carborane were determined by single-crystal X-ray diffraction.

Graphical Abstract

1. Introduction

Aryl derivatives of ortho-carborane 1,2-C2B10H12 are of great interest for various applications, from the design of new drugs [1,2,3,4] to the development of new materials [5,6,7,8,9,10,11]. This gives rise to a demand for the development of convenient methods for the synthesis of various aryl derivatives of ortho-carborane. There is a great difference between derivatives containing aryl substituents at the carbon and boron vertices of the carborane cage, both in methods of their synthesis and in the cage effect on the properties of the aryl substituent. Methods for the synthesis of C-aryl carboranes are well developed and can be divided into two groups. The first involves the reaction of decaborane derivatives 6,9-arachno-B10H12L2 (L = SR2, NR3, MeCN) with various arylacetylenes to form the corresponding C-aryl-ortho-carboranes [12]. However, this approach gives low yields when using some sterically hindered alkynes, especially those containing two aromatic groups [13,14,15,16,17,18,19,20]. The second group includes cross-coupling reactions of C-organometallic derivatives of ortho-carborane with aryl halides. In particular, C-aryl derivatives of ortho-carborane can be prepared by the Ullmann-type copper-coupling reactions [14,21,22,23]. A variation in this method involves light-promoted Cu-catalyzed C-arylation of ortho-carborane [24]. A more efficient alternative method is based on Ni-catalyzed cross-coupling reactions of aryl iodides with carboranyl Grignard reagents [25,26,27,28].
The synthesis of B-aryl derivatives of ortho-carborane is a somewhat more complex task. They were first obtained in minor yields by the reaction of the reduced form of ortho-carborane with aryl Grignard reagents 15 years later than the C-aryl derivatives [29]. Later, a more convenient synthetic method was proposed based on Pd-catalyzed cross-coupling reactions of iodo derivatives of ortho-carborane with aryl Grignard reagents (Kumada cross-coupling). In this way, both 9-aryl and 9,12-diaryl derivatives of ortho-carborane can be obtained, containing substituents in the positions of the carborane cage most distant from the carbon atoms [30,31,32,33,34,35,36,37,38,39]. For the synthesis of the B-aryl derivatives with functional groups sensitive to organomagnesium reagents, a simple and efficient method for one-pot Pd-catalyzed cross-coupling of 9-iodo-ortho-carborane with in situ generated organozinc compounds was proposed [40].
Similarly, 3-aryl derivatives of ortho-carborane containing a substituent at a position adjacent to both carbon atoms of the carborane cage can also be prepared by Pd-catalyzed cross-coupling of 3-iodo-ortho-carborane with aryl Grignard reagents [41,42]. At the same time, it was found that reactions of 3-iodo-ortho-carborane with organometallic reagents, which are “hard” nucleophiles, in the presence of a catalytic amount of [Pd(PPh3)4] can lead to the loss of halogen with the formation of 1,3-dehydro-ortho-carborine [43]. This can be avoided by using in situ generated organozinc derivatives [44]. The use of 3-iodo-ortho-carborane in Suzuki cross-coupling reactions gives good results only in the case of arylboronic acids containing electron-donating substituents [45]. 3-Aryl derivatives of ortho-carborane can also be prepared by Pd-catalyzed cross-coupling of 3-pinacolboron derivative of ortho-carborane [46] with aryl bromides [47] or photocatalytic arylation of 3-diazonium-ortho-carborane tetrafluoroborate [48]. At the same time, despite the rather large variety of methods for obtaining B-aryl derivatives of ortho-carborane, phenyl derivatives predominate among the synthesized compounds, while polycyclic aromatic derivatives are represented mainly by naphthyl derivatives, and there are only a few examples of B-substituted ortho-carborane derivatives with both tricyclic (anthracene [41,47,48]) and tetracyclic (pyrene [49]) aromatic substituents.
In this contribution we describe the synthesis of a series of new B-substituted polycyclic aromatic derivatives of ortho-carborane with anthracen-2-yl- and pyren-1-yl substituents, as well as the solid-state structures of the synthesized pyrenyl derivatives.

2. Results and Discussion

2.1. Synthesis and Characterization

For the synthesis of B-substituted polycyclic aryl derivatives of ortho-carborane, the Pd-catalyzed cross-coupling reaction of the corresponding carboranyl iodides with aryl zinc reagents obtained in situ by the Co-catalyzed reaction of aryl bromides with zinc dust [50] was applied. Previously, we used this approach to prepare 3- and 9-aryl derivatives of ortho-carborane with various substituents on the phenyl ring [40,44].
In this study, anthracen-2-yl and pyren-1-yl zinc bromides were prepared by the reaction of the corresponding polycyclic aromatic bromides with allyl zinc chloride/bromide that was generated from zinc dust and allyl chloride in the presence of 25 mol.% of CoBr2 and a catalytic amount of trifluoroacetic acid in acetonitrile (Scheme 1).
The reaction of the prepared anthracen-2-yl zinc bromide with 9-iodo-ortho-carborane (1) in acetonitrile in the presence of 2 mol.% of [(Ph3P)2PdCl2] and catalytic amounts of trifluoroacetic acid results in 9-(anthracen-2′-yl)-ortho-carborane (2), which was isolated in 72% yield after gradient column chromatography on silica (Scheme 2).
The 11B NMR spectrum of 9-(anthracen-2′-yl)-ortho-carborane in acetone-d6 contains a singlet of the C-substituted boron atom at 7.2 ppm and five doublets with a total integral ratio of 1:1:2:2:2:2, which is in good agreement with the symmetry of the C-substituted ortho-carborane. The 1H NMR spectrum contains broadened singlets of two nonequivalent carborane CH groups at 4.59 and 4.68 ppm as well as a characteristic set of signals of the asymmetrically substituted anthracenyl group at 7.4–8.5 ppm. The 13C NMR spectrum contains signals of the carborane cage at 51.5 and 55.9 ppm and signals of the anthracene substituent in the area of 120–140 ppm.
In a similar way, the reaction of pyren-1-yl zinc bromide with 9-iodo-ortho-carborane (1) in acetonitrile gives 9-(pyren-1′-yl)-ortho-carborane (3), which was isolated in 78% yield (which is significantly higher than that recently reported in the Grignard reagent synthesis (28%) [49]) (Scheme 2). The 11B NMR spectrum of 3 is almost identical to that of the anthracene derivative 2 and shows a singlet of the C-substituted boron atom at 7.2 ppm and five doublets with a total integral ratio of 1:1:2:2:2:2. The 1H NMR spectrum contains broadened singlets of the carborane CH groups at 4.73 and 4.78 ppm as well as a set of signals of the pyrenyl group in the region of 8.0–9.0 ppm. The 13C NMR spectrum contains signals of the carborane cage at 53.3 and 55.8 ppm and signals of the pyrene substituent in the field of 125–135 ppm.
The same approach can be used for the synthesis of the 9,12-disubstituted pyrene derivative of ortho-carborane: the reaction of pyren-1-yl zinc bromide with 9,12-diiodo-ortho-carborane (4) in the presence of 4 mol.% of [(Ph3P)2PdCl2] in acetonitrile produces 9,12-di(pyren-1′-yl)-ortho-carborane (5), isolated in 68% yield after repeated column chromatography on silica (Scheme 3). It is worth noting the very poor solubility of compound 5 and the very poor visualization of its spots on TLC plates using PdCl2 solution, which is usually used for the detection of carboranes [40,44,51,52,53,54], which makes it difficult to both monitor the progress of the reaction and purify the goal product in the presence of a large number of fluorescent pyrene-based organic by-products.
The 11B NMR spectrum of 9,12-di(pyren-1′-yl)-ortho-carborane in CD2Cl2 contains a singlet of the C-substituted boron atoms at 8.7 ppm and three doublets with a total integral ratio of 2:2:4:2. The 1H NMR spectrum contains a broadened singlet of the carborane CH groups at 4.06 ppm as well as the signals of the pyrene substituents in the region of 7.5–9.3 ppm. It is worth noting the strong downfield shift of the signal of two BH hydrogens to 3.74 ppm (Figure S16). This may indicate the preservation in solution of the intramolecular CH⋯HB interactions between the pyrene substituents and the carborane cage found in the crystal structure of 5 (See below). In the 13C NMR spectrum, the carborane cage signal appears at 59.8 ppm, whereas signals of the pyrene substituents are located in the field of 120–135 ppm.
It should be noted that, unlike 1,2-di(pyrenyl)benzene, which was obtained as a mixture of syn- and anti-isomers [55], in this case a single isomer is formed, which was identified as the syn-isomer by single crystal X-ray diffraction (See below). The reason for this is not entirely clear, but it is worth noting the significantly greater length of the B-B bond in carborane (1.827(6) Å) compared to the C-C bond in the benzene derivative (1.396(3) Å), as well as the somewhat larger angle between the Bcarb-Cpyr and Cbenz-Cpyr bonds in these derivatives (64.8° vs. 59.8°), which should facilitate the possibility of mutual rotation of the pyrene substituents. The formation of only one isomer was also reported in the case of 1,2-bis(pyren-1′-yl)-ortho-carborane, but the mutual orientation of the substituents was not determined [56].
The reaction of anthracen-2-yl zinc bromide with 3-iodo-ortho-carborane (6) in acetonitrile in the presence of 2 mol.% of [(Ph3P)2PdCl2] and catalytic amounts of trifluoroacetic acid leads to 3-(anthracen-2′-yl)-ortho-carborane (7), which was isolated in 83% yield after column chromatography on silica (Scheme 4).
The 11B NMR spectrum of 3-(anthracen-2′-yl)-ortho-carborane in acetone-d6 contains a singlet of the C-substituted boron atom at −4.5 ppm and four doublets with a total integral ratio of 2:1:1:3:3. The 1H NMR spectrum contains a broadened singlet of the carborane CH groups at 4.87 ppm as well as a set of signals of the anthracenyl group at 7.4–8.6 ppm. It should be noted that the spectral pattern of the anthracenyl substituent changes compared to compound 2, which consists, in particular, in the low-field shift of the C(1)’H hydrogen singlet from 8.0 ppm to ~8.5 ppm, indicating a decrease in the electron-donating effect of the substituent [57]. This is in good agreement with the electronic effects of ortho-carboranyl groups substituted at different positions of the cage [58]. The 13C NMR spectrum contains a signal of the carborane cage at 58.9 ppm and signals of the anthracene substituent in the area of 125–145 ppm.
In a similar way, the reaction of pyren-1-yl zinc bromide with 3-iodo-ortho-carborane (6) in acetonitrile gives 3-(pyren-1′-yl)-ortho-carborane (8), which was isolated in 86% yield after column chromatography on silica. The 11B NMR spectrum of 3 is almost identical to that of the anthracene derivative 2 and shows a singlet of the C-substituted boron atom at −4.3 ppm and four doublets with a total integral ratio of 2:1:1:3:3. The 1H NMR spectrum contains a broadened signal of the carborane CH groups at 5.13 ppm and a set of signals of the pyrenyl group in the region of 8.1–9.3 ppm. The pronounced downfield shift of the CH-carborane group signal compared to the 9-substituted derivative 3 is similar to that observed in the corresponding phenyl derivatives of ortho-carborane [59,60]. The 13C NMR spectrum contains a signal of the carborane cage at 59.8 ppm and signals of the pyrene substituent in the range of 125–136 ppm.

2.2. Solid-State Structure and Crystal Packing

The solid-state structures of compounds 3, 5, and 8 were determined by single-crystal X-ray diffraction. In all cases, an asymmetric unit cell contains one molecule of compound. The pyrene substituents in all molecules adopt nearly planar geometry. For monosubstituted ortho-carboranes 3 and 8 (Figure 1), the orientation of the pyrene substituent relative to the carborane cage is similar. In 3-(pyren-1′-yl)-ortho-carborane 8, the projection of the pyrene substituent onto the C(1)-C(2)-B(4)-B(8)-B(7) pentagon of the carborane cage nearly coincides with the B(8)-X (X is the center of the C(1)-C(2) bond) line. The deviation angle (φ) is equal to 10.2(3)° (Figure 1). In 9-(pyren-1′-yl)-ortho-carborane 3, the angle of the corresponding projection onto the B(8)-B(4)-B(5)-B(10)-B(12) pentagon with the B(4)-X (X is the center of the B(10)-B(12) bond) line is equal to 11.0(2)°. It leads to an appearance of the close intramolecular non-bonded H⋯H contacts (Table 1, Figure 1). Using the PBE0/def2tzvp level of approximation, geometry optimization of molecules 3 and 8 was carried out, followed by the topological analysis of the calculated electron density by means of R. Bader’s topological theory “Atoms in Molecules” [61]. This way of theoretical analysis of molecular structure and energetic characteristics was utilized in our previous studies on substituted carboranes and metallacarboranes [62,63,64].
The orientation of the pyrene substituent in the calculated molecules differs somewhat from that in the experimental structures (Table 1). This can be explained by the influence of the crystal packing effect. However, the same H⋯H contacts (with slightly different distances) are observed in the calculated molecular geometries. Their energies, estimated using the Espinosa-Leconte correlation [65,66], make an additional contribution to the stabilization of the molecular geometry.
Similarity of the solid-state structures of 3- and 9-(pyren-1′-yl)-ortho-carboranes is also observed in their crystal structures. In both cases, crystal packing is formed by columns in which molecules are connected by weak stacking interaction between perene fragments. Connection between columns is provided by H⋯H and H⋯π interactions between the carborane and pyrene fragments and H⋯π interactions between the pyrene fragments, as well as ordinary van-der-Waals interactions. From Figure 2 and Figure 3, it is seen that the structures of columns and relative orientation of columns connected by the H⋯π interactions between pyrenes (green ovals in Figure 2 and Figure 3) are very similar. Moreover, exactly the same atoms are involved in stacking interactions inside the columns and interactions between two closest columns (detailed information is provided in the Supplementary Materials), while other intercolumnar interactions are somewhat different.
Compound 5, 9,12-di(pyren-1-yl)-ortho-carborane, contains two pyrene substituents in vicinal positions (Figure 4). In accord with the above description of monosubstituted carboranes, the orientation of the pyrene substituents in 5 was described using φ1 and φ2 angles. The pyrene fragment at the B9 atom is located above the B(8)-B(4)-B(5)-B(10)-B(12) pentagon, and its projection nearly coincides with the B(10)-X1 line (X1 is the center of the B(8)-B(4) bond). The second pyrene fragment at the B(12) atom is above the B(7)-B(8)-B(9)-B(10)-B(11) pentagon, and its projection also nearly coincides with the B(10)-X2 line (X2 is the center of the B(7)-B(8) bond), as shown at the bottom of Figure 4 and given in Table 2. It should be noted that the B(9)-B(12) bond in compound 5 (1.827(6) Å) is somewhat longer than in most known 9,12-diaryl derivatives of ortho-carborane (1.798–1.814 Å) [31,33,38,40], 9,12-di(p-hydroxyphenyl)-ortho-carborane (1.824(6) Å) [33], and 8,9,10,12-tetraphenyl-ortho-carborane (1.822(4) Å) [38].
In contrast to monosubstituted carboranes 3 and 8, in disubstituted carborane 5, substituents are oriented more symmetrically (φ angles are close to zero), and, as presented in Table 2, calculated geometry is nearly identical to the experimental one. This can be attributed to the vicinal location of the substituents. Bulky pyrene fragments restrict their ability to rotate around the B-C bond and are less sensitive to the crystal packing forces. Crystal packing diagram of compound 5 and all close and shortened intermolecular contacts are presented in the Supplementary Materials (Figure S54, Table S1).

3. Materials and Methods

3.1. General Methods

9-Iodo-ortho-carborane (1) [67], 9,12-diiodo-ortho-carborane (4) [68], 3-iodo-ortho-carborane (6) [69], and bis(triphenylphosphine)palladium dichloride [(Ph3P)2PdCl2] [70] were prepared according to the literature procedures. Anhydrous cobalt dibromide was prepared from cobalt bromide hexahydrate by heating at 160 °C under vacuum for 3 h and stored under an argon atmosphere. Acetonitrile was dried using standard procedure [71]. All other chemical reagents were purchased from Sigma Aldrich, Acros Organics, and BLDPharm and used without purification. All reactions were carried out in an argon atmosphere. The reaction progress was monitored by thin-layer chromatography (Merck F254 silica gel on aluminum plates) and visualized using 0.5% PdCl2 in 1% HCl in aq. MeOH (1:10). Acros Organics silica gel (0.060–0.200 mm) was used for column chromatography. The NMR spectra at 400.1 MHz (1H), 128.3 MHz (11B), and 100.0 MHz (13C) were recorded with a Varian Inova-400 spectrometer. The signals in the 1H and 13C NMR spectra were referenced to Me4Si, whereas the signals in the 11B NMR spectra were referenced to BF3·Et2O. The signal assignment in 11B{1H} NMR spectra was performed using 11B{1H}-11B{1H} DQCOSY experiments. All spectra were processed in MestRenova version 12.0.0-20080. High-resolution mass spectra were recorded on an LCMS-9030 device (Shimadzu, Japan) using electrospray ionization mass spectrometry (ESI-MS). Measurements were carried out in positive (capillary voltage 3.5 kV) and negative (−3.0 kV) ion mode; samples were dissolved in acetonitrile and injected into the mass spectrometer chamber from an HPLC system LC-40 Nexera (Shimadzu, Japan). The following parameters were used: Mass scanning range: m/z 50–1500; external calibration with solution NaI in MeOH/H2O; drying and heating gases (nitrogen) (each 10 dm3/min); nebulizing gas (nitrogen) (3 dm3/min); interface temperature: 300 °C; flow rate: 0.4 cm3/min. Molecular ions in the spectra were analyzed and matched with the appropriately calculated m/z and isotopic profiles in the LabSolutions v.5.114 program.

3.2. General Procedure for Synthesis of 9-Polycyclicaryl-ortho-Carboranes

A slightly modified procedure previously used for the synthesis of 9-aryl derivatives of ortho-carborane [40] was applied. Allyl chloride (82 μL, 77 mg, 1.00 mmol) and trifluoroacetic acid (25 μL) were added to a blue mixture of zinc powder (490 mg, 7.50 mmol) and anhydrous CoBr2 (55 mg, 0.25 mmol) in 5 mL of freshly distilled acetonitrile. The resulting dark orange mixture was stirred at room temperature for 15 min. Then the corresponding polycyclic aryl bromide (2.50 mmol) was added, and the slurry was stirred at room temperature for another 45 min. Then 9-iodo-ortho-carborane (270 mg, 1.00 mmol) and [(Ph3P)2PdCl2] (14 mg, 0.02 mmol) were added, and the reaction mixture was stirred at room temperature overnight. Then the mixture was filtered, and the residue was washed with hot acetone (until traces of carborane-containing products disappeared on TLC). The organic phases were combined, concentrated under reduced pressure with the addition of silica, and subjected to column chromatography on silica to give the corresponding 9-polyaryl derivatives of ortho-carborane.

3.2.1. 9-(Anthracen-2′-yl)-ortho-carborane (2)

2-Anthracenyl bromide (643 mg, 2.50 mmol) and 9-iodo-ortho-carborane (1) (270 mg, 1.00 mmol) were used as starting materials; a mixture of n-hexane: ethyl acetate (from 9:1 to 9:2, v/v) was used as eluent for gradient column chromatography; a pale-yellow crystalline solid was obtained (230 mg, yield 72%). 1H{11B} NMR (400 MHz, acetone-d6): δ 8.46 (1H, s, CHAr), 8.43 (1H, s, CHAr), 8.03 (3H, m, CHAr), 7.92 (1H, d, J = 8.6 Hz, CHAr), 7.51 (1H, d, J = 8.3 Hz, CHAr), 7.46 (1H, d, J = 6.4 Hz, CHAr), 7.45 (1H, d, J = 6.7 Hz, CHAr), 4.68 (1H, br s, CHCarb), 4.59 (1H, br s, CHCarb), 2.61 (1H, br s, BHCarb), 2.45 (6H, br s, BHCarb), 2.20 (2H, br s, BHCarb) ppm. 13C{1H} NMR (100 MHz, acetone-d6): δ 137.4 (CAr-B), 132.8 (CAr), 132.63 (CHAr), 132.59 (CAr), 132.5 (CAr), 132.2 (CAr), 130.8 (CHAr), 129.0 (CHAr), 128.9 (CHAr), 127.4 (CHAr), 126.9 (CHAr), 126.4 (CHAr), 126.0 (2xCHAr), 55.9 (CHCarb), 51.5 (CHCarb) ppm; 11B NMR (128 MHz, acetone-d6): δ 7.2 (1B, s, B(9)-C), −2.8 (1B, d, J = 147 Hz, B(12)), −8.9 (2B, d, J = 149 Hz, B(8,10)), −13.5 (2B, d, J = 155 Hz, B(4,5)), −14.2 (2B, d, J = 145 Hz, B(7,11)), −14.8 (2B, d, J = 176 Hz, B(3,6)) ppm. 1H NMR (400 MHz, CDCl3): δ 8.38 (1H, s, CHAr), 8.34 (1H, s, CHAr), 8.00 (1H, s, CHAr), 7.97 (2H, m, CHAr), 7.87 (1H, d, J = 7.2 Hz, CHAr), 7.50 (1H, d, J = 8.7 Hz, CHAr), 7.41 (2H, m, CHAr), 3.69 (1H, br s, CHCarb), 4.58 (1H, br s, CHCarb) ppm; 11B NMR (128 MHz, CDCl3): δ 7.8 (1B, s, B(9)-C), −2.0 (1B, d, J = 152 Hz, B(12)), −8.6 (2B, d, J = 152 Hz, B(8,10)), −13.7 (2B, d, J = 180 Hz, B(4,5)), −14.1 (2B, d, J = 147 Hz, B(7,11)), −15.2 (2B, d, J = 166 Hz, B(3,6)) ppm. HRMS-ESI (m/z): obsd. 320.2567 [M]+, calcd. for C16H20B10: 320.2571 [M]+.

3.2.2. 9-(Pyren-1′-yl)-ortho-carborane (3)

1-Pyrenyl bromide (703 mg, 2.50 mmol) and 9-iodo-ortho-carborane (1) (270 mg, 1.00 mmol) were used; as starting materials a mixture of n-hexane: ethyl acetate (9:1.5, v/v) was used as eluent for column chromatography; a white crystalline solid was obtained (268 mg, yield 78%). 1H{11B} NMR (400 MHz, acetone-d6): δ 9.03 (1H, d, J = 9.4 Hz, CHAr), 8.34 (1H, d, J = 7.8 Hz, CHAr), 8.21 (2H, d, J = 7.7 Hz, CHAr), 8.14 (1H, d, J = 8.0 Hz, CHAr), 8.13 (1H, d, J = 9.6 Hz, CHAr), 8.09 (2H, d, J = 5.3 Hz, CHAr), 8.02 (1H, t, J = 7.7 Hz, CHAr), 4.78 (1H, br s, CHCarb), 4.73 (1H, br s, CHCarb), 2.85 (1H, br s, BHCarb), 2.71 (2H, br s, BHCarb), 2.66 (2H, br s, BHCarb), 2.54 (2H, br s, BHCarb), 2.29 (2H, br s, BHCarb) ppm. 13C{1H} NMR (100 MHz, acetone-d6): δ CAr-B not observed, 134.4 (CHAr), 134.3 (CAr), 132.4 (CAr), 131.8 (CAr), 131.6 (CAr), 128.4 (CHAr), 128.3 (CHAr), 128.2 (CHAr), 127.2 (CHAr), 126.6 (CHAr), 125.8 (CAr), 125.6 (CHAr), 125.5 (CAr), 125.4 (CHAr), 125.0 (CHAr), 55.8 (CHCarb), 53.3 (CHCarb) ppm; 11B NMR (128 MHz, acetone-d6): δ 7.2 (1B, s, B(9)-C), −2.2 (1B, d, J = 147 Hz, B(12)), −8.5 (2B, d, J = 149 Hz, B(8,10)), −13.1 (2B, d, J = 160 Hz, B(4,5)), −14.1 (2B, d, J = 142 Hz, B(7,11)), −14.9 (2B, d, J = 166 Hz, B(3,6)) ppm. 1H{11B} NMR (400 MHz, CDCl3): δ 8.96 (1H, d, J = 9.4 Hz, CHAr), 8.31 (1H, d, J = 7.9 Hz, CHAr), 8.13 (2H, t, J = 6.8 Hz, CHAr), 8.07 (1H, d, J = 5.8 Hz, CHAr), 8.05 (1H, d, J = 7.9 Hz, CHAr), 8.03 (1H, d, J = 9.6 Hz, CHAr), 8.00 (1H, d, J = 8.8 Hz, CHAr), 7.96 (1H, t, J = 7.7 Hz, CHAr), 3.74 (1H, br s, CHCarb), 3.68 (1H, br s, CHCarb), 2.94 (1H, br s, BHCarb), 2.80 (2H, br s, BHCarb), 2.69 (2H, br s, BHCarb), 2.51 (2H, br s, BHCarb), 2.33 (2H, br s, BHCarb) ppm; 11B NMR (128 MHz, CDCl3): δ 7.8 (1B, s, B(9)-C), −1.4 (1B, d, J = 152 Hz, B(12)), −8.1 (2B, d, J = 152 Hz, B(8,10)), −13.2 (2B, d, J = 162 Hz, B(4,5)), −14.1 (2B, d, J = 148 Hz, B(7,11)), −15.3 (2B, d, J = 157 Hz, B(3,6)) ppm. HRMS-ESI (m/z): obsd. 344.2572 [M]+, calcd. for C18H20B10: 344.2571 [M]+.

3.3. Synthesis of 9,12-Bis(pyren-1′-yl)-ortho-Carborane (5)

Allyl chloride (82 µL, 77 mg, 1.00 mmol) and trifluoroacetic acid (25 μL, catalytic amount) were added to a blue mixture of zinc dust (490 mg, 7.50 mmol) and anhydrous CoBr2 (55 mg, 0.25 mmol) in 5 mL of freshly distilled acetonitrile. The resulting dark orange mixture was stirred at room temperature for 15 min, after which 1-pyrenyl bromide (703 mg, 2.50 mmol) was added, and the slurry was stirred at room temperature for another 45 min. Then 9,12-diiodo-ortho-carborane (4) (198 mg, 0.50 mmol) and [(Ph3P)2PdCl2] (14 mg, 0.02 mmol, catalytic amount) were added. Then the mixture was filtered, and the residue was washed with hot acetone (until traces of carborane-containing products disappeared on TLC). The organic phases were combined, concentrated under reduced pressure with the addition of silica, and subjected to column chromatography on silica using a mixture of n-hexane: ethyl acetate (from 9:1.5 to 100% ethyl acetate, v/v) as eluent. The carborane-containing fraction was collected and subjected to column chromatography using a mixture of n-hexane: dichloromethane mixture (1:1, v/v) as eluent to give a white crystalline solid (186 mg, yield 68%). 1H{11B} NMR (400 MHz, CD2Cl2): δ 9.03 (2H, d, J = 9.3 Hz, CHAr), 8.08 (6H, m, CHAr), 7.92 (6H, m, CHAr), 7.78 (2H, d, J = 8.9 Hz, CHAr), 7.71 (2H, d, J = 8.0 Hz, CHAr), 4.06 (2H, br s, CHCarb), 3.74 (2H, br s, BHCarb), 2.78 (6H, br s, BHCarb) ppm; 13C{1H} NMR (100 MHz, CD2Cl2): δ CAr-B not observed, 134.4 (CHAr), 134.1 (CAr), 131.9 (CAr), 131.2 (CAr), 131.1 (CAr), 128.2 (CHAr), 127.9 (CHAr), 127.7 (CHAr), 126.8 (CHAr), 126.0 (CHAr), 125.3 (CAr), 125.1 (CHAr), 124.9 (CHAr), 124.5 (CAr), 124.3 (CHAr), 59.8 (CHCarb) ppm; 11B NMR (128 MHz, CD2Cl2): δ 8.7 (2B, s, B(9,12)-C), −8.4 (2B, d, J = 153 Hz, B(8,10)), −13.4 (4B, d, J = 135 Hz, B(4,5,7,11)), −15.7 (2B, m, B(3,6)) ppm. HRMS-ESI (m/z): obsd. 567.3109 [M+Na]+, calcd. for C34H28B10Na: 567.3102 [M+Na]+.

3.4. General Procedure for Synthesis of 3-Polycyclicaryl-ortho-Carboranes

A slightly modified procedure previously used for the synthesis of 3-aryl derivatives of ortho-carborane [44] was applied. Allyl chloride (82 μL, 77 mg, 1.00 mmol) and trifluoroacetic acid (25 μL) were added to a blue mixture of zinc powder (490 mg, 7.50 mmol) and anhydrous CoBr2 (55 mg, 0.25 mmol) in 5 mL of freshly distilled acetonitrile. The resulting dark orange mixture was stirred at room temperature for 15 min. Then the corresponding polycyclic aryl bromide (2.50 mmol) was added, and the slurry was stirred at room temperature for another 45 min. Then 9-iodo-ortho-carborane (6) (270 mg, 1.00 mmol) and [(Ph3P)2PdCl2] (14 mg, 0.02 mmol) were added, and the reaction mixture was stirred at room temperature overnight. Then the mixture was filtered, and the residue was washed with hot acetone (until traces of carborane-containing products disappeared on TLC). The organic phases were combined, concentrated under reduced pressure with the addition of silica, and subjected to column chromatography on silica to give the corresponding 3-polyaryl derivatives of ortho-carborane.

3.4.1. 3-(Anthracen-2′-yl)-ortho-carborane (7)

2-Anthracenyl bromide (643 mg, 2.50 mmol) and 3-iodo-ortho-carborane (6) (270 mg, 1.00 mmol) were used as starting materials; a mixture of n-hexane: ethyl acetate (9:1.5, v/v) was used as eluent for column chromatography; a pale-green crystalline solid was obtained (265 mg, yield 83%).
1H{11B} NMR (400 MHz, acetone-d6): δ 8.55 (1H, s, CHAr), 8.50 (2H, s, CHAr), 8.07 (3H, m, CHAr), 7.77 (1H, d, J = 8.6 Hz, CHAr), 7.51 (2H, m, CHAr), 4.87 (2H, br s, CHCarb), 2.58 (2H, br s, BHCarb), 2.51 (2H, br s, BHCarb), 2.44 (2H, br s, BHCarb), 2.29 (2H, br s, BHCarb), 2.20 (1H, br s, BHCarb) ppm. 13C{1H} NMR (100 MHz, acetone-d6): δ CAr-B not observed, 135.5 (CHAr), 133.2 (CAr), 132.9 (CAr), 132.5 (CAr), 132.0 (CAr), 129.7 (CHAr), 129.1 (CHAr), 129.0 (CHAr), 128.4 (CHAr), 127.5 (CHAr), 126.8 (CHAr), 126.7 (CHAr), 126.5 (CHAr), 58.9 (CHCarb) ppm; 11B NMR (128 MHz, acetone-d6): δ −3.0 (2B, d, J = 148 Hz, B(9,12)), −4.5 (1B, s, B(3)-C), −8.8 (1B, d, J = 149 Hz, B(8)), −12.5 (3B, d, J = 154 Hz, B(4,7,6/10)), −13.3 (3B, d, J = 164 Hz, B(5,6/10,11)) ppm. 1H{11B} NMR (400 MHz, CDCl3): δ 8.44 (1H, s, CHAr), 8.43 (1H, s, CHAr), 8.28 (1H, s, CHAr), 8.02 (3H, m, CHAr), 7.61 (1H, d, J = 8.6 Hz, CHAr), 7.51 (2H, m, CHAr), 3.85 (2H, br s, CHCarb), 2.54 (4H, br s, BHCarb), 2.46 (2H, br s, BHCarb), 2.27 (2H, br s, BHCarb), 2.22 (1H, br s, BHCarb) ppm. 11B NMR (128 MHz, CDCl3): δ −2.3 (2B, d, J = 149 Hz, B(9,12)), −4.9 (1B, s, B(3)-C), −8.4 (1B, d, J = 152 Hz, B(8)), −12.8 (3B, d, J = 156 Hz, B(4,7,6/10)), −13.5 (3B, d, J = 161 Hz, B(5,6/10,11)) ppm. HRMS-ESI (m/z): obsd. 320.2569 [M]+, calcd. for C16H20B10: 320.2571 [M]+.

3.4.2. 3-(Pyren-1′-yl)-ortho-carborane (8)

1-Pyrenyl bromide (703 mg, 2.50 mmol) and 3-iodo-ortho-carborane (6) (270 mg, 1.00 mmol) were used as starting materials; a mixture n-hexane: ethyl acetate (9:1.5, v/v) was used as eluent for column chromatography; a white crystalline solid was obtained (296 mg, yield 86%).
1H{11B} NMR (400 MHz, acetone-d6): δ 9.27 (1H, d, J = 9.4 Hz, CHAr), 8.40 (1H, d, J = 7.8 Hz, CHAr), 8.33 (3H, m, CHAr), 8.23 (2H, m, CHAr), 8.16 (1H, m, CHAr), 8.10 (1H, m, CHAr), 5.13 (2H, br s, CHCarb), 2.94 (1H, br s, BHCarb), 2.62 (2H, br s, BHCarb), 2.58 (1H, br s, BHCarb), 2.49 (2H, br s, BHCarb), 2.31 (2H, br s, BHCarb), 2.23 (1H, br s, BHCarb) ppm; 13C{1H} NMR (100 MHz, acetone-d6): δ CAr-B not observed, 136.5 (CAr), 133.3 (CAr), 132.9 (CHAr), 132.3 (CAr), 131.5 (CAr), 129.5 (CHAr), 128.8 (CHAr), 128.1 (CHAr), 127.4 (CHAr), 127.2 (CHAr), 126.5 (CHAr), 126.3 (CHAr), 125.33 (CAr), 125.27 (CHAr), 59.8 (CHCarb). 11B NMR (128 MHz, acetone-d6): δ −2.9 (2B, d, J = 150 Hz, B(9,12)), −4.3 (1B, s, B(3)-C), −8.4 (1B, d, J = 150 Hz, B(8)), −11.9 (3B, d, J = 159 Hz, B(4,7,6/10)), −13.1 (3B, d, J = 158 Hz, B(5,6/10,11)) ppm. 1H{11B} NMR (400 MHz, CDCl3): δ 9.15 (1H, d, J = 8.9 Hz, CHAr), 8.24 (3H, m, CHAr), 8.13 (2H, m, CHAr), 8.07 (3H, m, CHAr), 4.10 (2H, br s, CHCarb), 2.98 (1H, br s, BHCarb), 2.69 (2H, br s, BHCarb), 2.56 (3H, br s, BHCarb), 2.33 (3H, br s, BHCarb) ppm; 11B NMR (128 MHz, CDCl3): δ −2.1 (2B, d, J = 146 Hz, B(9,12)), −4.5 (1B, s, B(3)-C), −8.0 (1B, d, J = 146 Hz, B(8)), −12.1 (3B, d, J = 154 Hz, B(4,7,6/10)), −13.2 (3B, d, J = 145 Hz, B(5,6/10,11)) ppm. HRMS-ESI (m/z): obsd. 344.2565 [M]+, calcd. for C18H20B10: 344.2571 [M]+.

3.5. Single Crystal X-Ray Diffraction Study

Crystals of 3 and 8 were obtained by slow crystallization from acetone, whereas crystals of 5 were grown from dichloromethane. The single-crystal X-ray diffraction experiments were carried out using a SMART APEX2 CCD diffractometer (λ(Mo-Kα) = 0.71073 Å, graphite monochromator, ω-scans) at 100 K. Collected data were processed by the SAINT and SADABS programs incorporated into the APEX2 program package [72]. The structures were solved by the direct methods and refined by the full-matrix least-squares procedure against F2 in anisotropic approximation. The refinement was carried out with the SHELXTL program [73]. The details of data collection and crystal structure refinement are summarized in Table 3 along with CCDC numbers, which contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif.

4. Conclusions

Isomeric B-substituted anthracenyl and pyrenyl derivatives of ortho-carborane containing polycyclic aromatic substituents both in the position of the carborane cage most distant from the carbon atoms (position 9) and in the neighboring position (position 3) were synthesized by Pd-catalyzed cross-coupling of the corresponding iodo derivatives of ortho-carborane with polycyclic aryl zinc bromides. The derivative containing two pyrenyl substituents at the positions most distant from the carbon atoms of the ortho-carborane cage, 9,12-di(pyren-1′-yl)-ortho-carborane, was obtained in a similar way starting from 9,12-diiodo-ortho-carborane. The solid-state structures of the pyrene-containing derivatives 3-pyren-1′-yl-ortho-carborane, 9-pyren-1′-yl-ortho-carborane, and 9,12-di(pyren-1′-yl)-ortho-carborane were determined by single-crystal X-ray diffraction. Luminescence properties of the synthesized derivatives are under investigation and will be published elsewhere.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/inorganics13050138/s1, Figures S1–S53: NMR spectra of compounds 2, 3, 5, 7, and 8; Figures S54–S63: HRMS spectra of compounds 2, 3, 5, 7, and 8; Figure S64: Crystal packing of 9,12-bis(pyren-1′-yl)-ortho-carborane (5); Table S1. Close and shortened contacts (Å) of central molecule of compound 5 with its closest environment in the crystal and types of intermolecular interactions; Table S2: Close and shortened contacts (Å) of central molecule of compound 8 with its closest environment in the crystal and types of intermolecular interactions; Table S3: Close and shortened contacts (Å) of central molecule of compound 3 with its closest environment in the crystal and types of intermolecular interactions. References [74,75] are cited in the supplementary materials.

Author Contributions

Synthesis and purification, A.V.S.; synthesis, NMR studies, and manuscript preparation, S.A.A.; HRMS studies and manuscript preparation, E.P.A.; single crystal X-ray diffraction, quantum chemical calculations, and manuscript preparation, K.Y.S.; supervision, manuscript concept and preparation, I.B.S.; project administration, V.I.B. All authors have read and agreed to the published version of the manuscript.

Funding

This research was supported by Russian Science Foundation (25-43-00072).

Institutional Review Board Statement

Not applicable.

Informed Consent Statement

Not applicable.

Data Availability Statement

Crystallographic data for the structures of 3-pyren-1′-yl-ortho-carborane (8), 9-pyren-1′-yl-ortho-carborane (3), and 9,12-di(pyren-1′-yl)-ortho-carborane (5) were deposited in the Cambridge Crystallographic Data Centre as supplementary publications CCDC 2435229 (for 8), 2435230 (for 3), and 2435231 (for 5). The Supplementary Materials contain NMR and mass spectra for compounds 2, 3, 5, 6, and 7.

Acknowledgments

The NMR and mass spectra of all synthesized compounds were obtained using equipment from the Center for Molecular Structure Studies at A.N. Nesmeyanov Institute of Organoelement Compounds, operating with financial support from the Ministry of Science and Higher Education of the Russian Federation.

Conflicts of Interest

The authors declare no conflicts of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results.

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Inorganics 13 00138 sch001
Scheme 1. Preparation of anthracen-2′-yl and 9-pyren-1′-yl zinc bromides.
Scheme 1. Preparation of anthracen-2′-yl and 9-pyren-1′-yl zinc bromides.
Inorganics 13 00138 sch001
Inorganics 13 00138 sch002
Scheme 2. Synthesis of 9-anthracen-2′-yl- and 9-pyren-1′-yl-ortho-carboranes.
Scheme 2. Synthesis of 9-anthracen-2′-yl- and 9-pyren-1′-yl-ortho-carboranes.
Inorganics 13 00138 sch002
Inorganics 13 00138 sch003
Scheme 3. Synthesis of 9,12-di(pyren-1′-yl)-ortho-carborane.
Scheme 3. Synthesis of 9,12-di(pyren-1′-yl)-ortho-carborane.
Inorganics 13 00138 sch003
Inorganics 13 00138 sch004
Scheme 4. Synthesis of 3-anthracen-2′-yl- and 3-pyren-1′-yl-ortho-carboranes.
Scheme 4. Synthesis of 3-anthracen-2′-yl- and 3-pyren-1′-yl-ortho-carboranes.
Inorganics 13 00138 sch004
Inorganics 13 00138 g001
Figure 1. Top. General view of the pyren-1-yl derivatives of ortho-carborane 8 (left) and 3 (right) showing atomic numbering. Thermal ellipsoids are drawn at a 50% probability level. Close intramolecular non-bonded H⋯H contacts are shown by dashed lines. Bottom. Projection of the pyrene substituent (shown by the dashed green line) onto the corresponding pentagon of the carborane cage. Angle between the line connecting the boron atom with the center of the opposite bond (X) and the dashed green line is designated as φ.
Figure 1. Top. General view of the pyren-1-yl derivatives of ortho-carborane 8 (left) and 3 (right) showing atomic numbering. Thermal ellipsoids are drawn at a 50% probability level. Close intramolecular non-bonded H⋯H contacts are shown by dashed lines. Bottom. Projection of the pyrene substituent (shown by the dashed green line) onto the corresponding pentagon of the carborane cage. Angle between the line connecting the boron atom with the center of the opposite bond (X) and the dashed green line is designated as φ.
Inorganics 13 00138 g001
Inorganics 13 00138 g002
Figure 2. Crystal packing fragment of compound 3. Top: view in the ab crystallographic plane. Bottom-left: intercolumnar H⋯π interaction; bottom-right view of the column along axis c. Close intermolecular non-bonded contacts are shown by dashed lines.
Figure 2. Crystal packing fragment of compound 3. Top: view in the ab crystallographic plane. Bottom-left: intercolumnar H⋯π interaction; bottom-right view of the column along axis c. Close intermolecular non-bonded contacts are shown by dashed lines.
Inorganics 13 00138 g002
Inorganics 13 00138 g003
Figure 3. Crystal packing fragment of compound 8. Top: view in the bc crystallographic plane. Bottom-left: intercolumnar H⋯π interaction; bottom-right view of the column along axis a. Close intermolecular non-bonded contacts are shown by dashed lines.
Figure 3. Crystal packing fragment of compound 8. Top: view in the bc crystallographic plane. Bottom-left: intercolumnar H⋯π interaction; bottom-right view of the column along axis a. Close intermolecular non-bonded contacts are shown by dashed lines.
Inorganics 13 00138 g003
Inorganics 13 00138 g004
Figure 4. Top. General view of carborane 5 showing atomic numbering. Thermal ellipsoids are drawn at a 50% probability level. Close intramolecular non-bonded H⋯H contacts are shown by dashed lines. Bottom. Projection of the pyrene substituents (shown by dashed green lines) onto corresponding pentagons of the carborane cage. Angles between the lines connecting the boron atom with the center of opposite bonds (X1,2) and dashed green lines are designated as φ1,2.
Figure 4. Top. General view of carborane 5 showing atomic numbering. Thermal ellipsoids are drawn at a 50% probability level. Close intramolecular non-bonded H⋯H contacts are shown by dashed lines. Bottom. Projection of the pyrene substituents (shown by dashed green lines) onto corresponding pentagons of the carborane cage. Angles between the lines connecting the boron atom with the center of opposite bonds (X1,2) and dashed green lines are designated as φ1,2.
Inorganics 13 00138 g004
Table 1. Selected geometrical characteristics (angles in deg., distances in Å) of molecules 8 and 3 defining relative orientation of the pyrene and ortho-carborane fragments. Experiment vs. theory *.
Table 1. Selected geometrical characteristics (angles in deg., distances in Å) of molecules 8 and 3 defining relative orientation of the pyrene and ortho-carborane fragments. Experiment vs. theory *.
Compound 8Compound 3
X-Ray Calcd.X-RayCalcd.
Angle φ **10.2(4)34.311.0(2)36.3
C(4)-H(4A)⋯H(1)-C(1)2.051.93 [−2.6]--
C(15)-H(15A)⋯H(8)-B(8)1.942.18 [−1.9]--
C(4)-H(4A)⋯H(12)-B(12)--2.252.06 [−2.2]
C(15)-H(15A)⋯H(4)-B(4)--1.892.23 [−1.4]
* Energies of H⋯H contacts (in kcal/mol) are obtained by Espinosa-Lecomte correlation and are given in brackets; for experimental structures, C-H and B-H bond lengths are normalized at 1.08 and 1.18 Å, respectively, which correspond to neutron diffraction data and nearly coincide with calculated distances. ** Definition of angle φ is shown at the bottom of Figure 1.
Table 2. Selected geometrical characteristics (angles in deg., distances in Å) of molecule 5 defining relative orientation of the pyrene and ortho-carborane fragments. Experiment vs. theory *.
Table 2. Selected geometrical characteristics (angles in deg., distances in Å) of molecule 5 defining relative orientation of the pyrene and ortho-carborane fragments. Experiment vs. theory *.
X-RayCalcd.
Angle φ1 **4.6(4)1.6
Angle φ2 **0.5(4)1.5
C(4)-H(4A)⋯H(10)-B(10)2.022.08 [−2.2]
C(15)-H(15A)⋯H(8)-B(8)2.182.14 [−2.0]
C(4′)-H(4′A)⋯H(10)-B(10)2.092.08 [2.2]
C(15′)-H(15B)⋯H(8)-B(8)2.112.14 [−2.0]
* Energies of H⋯H contacts (in kcal/mol) are obtained by Espinosa-Lecomte correlation and are given in brackets; for experimental structures, C-H and B-H bond lengths are normalized at 1.08 and 1.18 Å, respectively, which correspond to neutron diffraction data and nearly coincide with calculated distances. ** Definition of angles φ1 and φ2 is shown at the bottom of Figure 4.
Table 3. Crystallographic data for compounds 3, 5, and 8.
Table 3. Crystallographic data for compounds 3, 5, and 8.
358
Formula C18H20B10C34H28B10C18H20B10
FW344.44544.66344.44
Crystal systemOrthorhombicMonoclinicOrthorhombic
Space groupP212121P21/nFdd2
a, Å7.2182(2)8.6601(8)21.9384(16)
b, Å14.4891(5)35.244(3)47.186(4)
c, Å17.2004(6)9.7598(9)6.9542(5)
α, deg.909090
β, deg.90109.323(4)90
γ, deg.909090
V, Å31798.91(10)2811.1(4)7198.9(9)
Z4416
ρcryst, g·cm−31.2721.2871.271
F(000)71211282848
μ, mm−10.0640.0680.063
θ range, deg.1.84–27.032.29–26.082.05–27.35
Rflns. collected23,98429,49318,983
Indep. rflns./Rint3937/0.05225557/0.11213927/0.0660
Completeness to theta θ, %10099.899.6
Ref. parameters297437297
GOF (F2)1.0431.0301.031
Rflns. with I > 2σ(I)337431243488
R1(F) (I > 2σ(I)) a0.03970.07600.0438
wR2(F2) (all data) b0.09120.18970.1028
Largest diff. peak/hole, e·Å−30.164/−0.2370.390/−0.2870.197/−0.203
CCDC Number2,435,2302,435,2312,435,229
a R1 = Σ|Fo − |Fc||/Σ(Fo); b wR2 = (Σ[w(Fo2 − Fc2)2]/Σ[w(Fo2)2]½.
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Shmal’ko, A.V.; Anufriev, S.A.; Suponitsky, K.Y.; Antoshkina, E.P.; Sivaev, I.B.; Bregadze, V.I. Synthesis of B-Substituted Anthracenyl and Pyrenyl Derivatives of ortho-Carborane. Inorganics 2025, 13, 138. https://doi.org/10.3390/inorganics13050138

AMA Style

Shmal’ko AV, Anufriev SA, Suponitsky KY, Antoshkina EP, Sivaev IB, Bregadze VI. Synthesis of B-Substituted Anthracenyl and Pyrenyl Derivatives of ortho-Carborane. Inorganics. 2025; 13(5):138. https://doi.org/10.3390/inorganics13050138

Chicago/Turabian Style

Shmal’ko, Akim V., Sergey A. Anufriev, Kyrill Yu. Suponitsky, Evgeniia P. Antoshkina, Igor B. Sivaev, and Vladimir I. Bregadze. 2025. "Synthesis of B-Substituted Anthracenyl and Pyrenyl Derivatives of ortho-Carborane" Inorganics 13, no. 5: 138. https://doi.org/10.3390/inorganics13050138

APA Style

Shmal’ko, A. V., Anufriev, S. A., Suponitsky, K. Y., Antoshkina, E. P., Sivaev, I. B., & Bregadze, V. I. (2025). Synthesis of B-Substituted Anthracenyl and Pyrenyl Derivatives of ortho-Carborane. Inorganics, 13(5), 138. https://doi.org/10.3390/inorganics13050138

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