Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Palladium-Catalyzed Selective Mono-/Tetraacetoxylation of o‑Carboranes with Acetic Acid via Cross Dehydrogenative Coupling of Cage B−H/O−H Bonds Tao-Tao Xu, Ke Cao,* Ji Wu, Cai-Yan Zhang, and Junxiao Yang State Key Laboratory Cultivation Base for Nonmetal Composite and Functional Materials & School of Materials Science and Engineering, Southwest University of Science and Technology, 59 Qinglong Road, Mianyang, 0086-621010 Sichuan, People’s Republic of China S Supporting Information *
ABSTRACT: A selective mono-/tetraacetoxylation of o-carboranes with acetic acid via cross dehydrogenative coupling of cage B−H/O−H bonds has been developed, and a series of mono- and tetraacetoxylated o-carboranes have been synthesized with moderate to good yields as well as good selectivity. Mechanistic studies indicate that the acetoxyl originates from acetic acid directly, and a nucleophilic addition of PdIV-oxo species and dehydration process is proposed.
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INTRODUCTION Carboranes are a class of boron hydride clusters with threedimensional aromaticity relative to benzene, which have proved to be important building blocks in pharmaceuticals,1 functional materials,2 and supramolecular chemistry3 as well as coordination chemistry.4 To further broaden the application of carboranes, establishing a compound library of carboranes with diverse functional groups is an important project, which would offer a toolbox to explore their latent properties and applications. Therefore, developing methodologies for selective boron functionalization is eagerly desired. For o-carborane, the 10 B−H bonds are not fully equal and have slight differences in reactivity, which makes selective boron functionalization more difficult and complicated.5 Hence, developing an efficient synthetic method, especially via direct B−H activation, for selective boron functionalization of o-carboranes has been a burgeoning subject and has attracted much interest from chemists in recent years.5b,6 To address the selective direct B−H functionalization of ocarborane, Xie and co-workers have realized selective B(4,5) functionalization by utilizing a carboxylic acid as a traceless directing group.7 Recently, with aldehyde as a transient directing group, selective arylation on B(4,5) was also achieved by the Yan group.8 On the other hand, on the basis of the inherent electrophilic characteristics and the slight difference in electrophilic reactivity of H−B(8,10) and H−B(9,12) bonds, we have achieved selective monofunctionalization on B(8) and B(9) via electrophilic B−H activation. 9 These results demonstrated that a transition-metal-catalyzed B−H activation © XXXX American Chemical Society
strategy is an efficient protocol for selective boron functionalization of carboranes.10 However, an electrophilic synthon is needed in most of these transformations. Transition-metal-catalyzed cross dehydrogenation coupling reactions have been powerful tools in the construction of carbon−carbon and carbon−heteroatom bonds with high efficiency in synthetic organic chemistry.11 As the coupling partner does not require prefunctionalization, this direct chemical transformation of C−H bonds renders more succinct and atom-economical synthetic routes in comparison with traditional synthetic protocols. With this concept in mind, we decided to explore the direct selective functionalization of B−H bonds of o-carborane via cross dehydrogenative coupling. Recently, we have reported a silver tuned selective mono-/ tetraacetoxylation of o-carboranes with iodobenzene diacetate (PIDA) as the acetoxyl source via palladium-catalyzed electrophilic B−H activation.9c In order to further enhance the atom economy of this transformation, we anticipated accomplishing such an acetoxylation via a cross dehydrogenative coupling process with acetic acid under oxidative conditions (Scheme 1).12 Herein, we are pleased to present our work.
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RESULTS AND DISCUSSION To begin our research, 1,2-Me2-o-carborane (1a) was selected to screen the conditions, and the results are summarized in Table 1. Considering that AgOAc could be as a Lewis acid to Received: January 10, 2018
A
DOI: 10.1021/acs.inorgchem.8b00038 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry Scheme 1. Strategies for Selective Acetoxylation of o-Carboranes
tune the monoacetoxylation in our previous work,9c we therefore anticipated utilizing the dual role of AgOAc, including Lewis acidity and oxidability, to examine the conditions. To our delight, the selective monoacetoxylation on B(8) and B(9) could be obtained with 42% yield along with 50% conversion of 1a in acetic acid at 40 °C after 48 h (entry 1). The yield was slightly reduced when Cu(OAc)2 was used instead (entry 2). Both the yield and conversion ratio were enhanced distinctly when AgOAc and Cu(OAc)2 were loaded (entry 3). However, the yield was not further improved after many efforts. A control experiment demonstrated that Pd(OAc)2 and an oxidant are essential for this transformation (entries 4 and 5). Thereafter, iodosobenzene (PhIO) was introduced to this reaction, and the conversion ratio of 1a was increased to 85%, although the expected product was only afforded with 45% yield (entry 6). When the reaction was carried out in dichloromethane along with 2 equiv of Cu(OAc)2, the target product was obtained in 69% yield with a 75% conversion ratio of 1a (entry 8). With the optimized conditions in hand, the scope of ocarboranes was then examined, and the results are shown in Table 2. We can see that o-carboranes with alkyl, benzyl, and aryl groups substituted on Ccage were all compatible with this transformation and gave the corresponding products with moderate to good yields. Additionally, electron-donating groups were more favorable than electron-withdrawing groups for this selective monoacetoxylation (2e−h). Subsequently, selective monoacyloxylation with carboxylic acids was then explored. However, when the reaction was carried out with benzoic acid in 1,2-dichloroethane, the benzoylation proceeded very sluggishly and gave the expected product in only 8% yield. After many efforts, the benzoylation
Table 1. Palladium-Catalyzed Monoacetoxylation of 1,2Me2-o-carboranea
entry
catalyst
1
Pd(OAc)2
2
Pd(OAc)2
3
Pd(OAc)2
4 5 6 7
Pd(OAc)2 Pd(OAc)2 Pd(OAc)2
8
Pd(OAc)2
oxidant 2 equiv AgOAc 2 equiv Cu(OAc)2 2 equiv AgOAc 2 equiv Cu(OAc)2 2 equiv AgOAc 2 equiv PhIO 2 equiv AgOAc 1.5 equiv PhIO 2 equiv Cu(OAc)2 1.5 equiv PhIO
solvent
yield (%) (conversion ratio (%))b
AcOH
42 (50)
AcOH
36 (45)
AcOH
60 (62)
AcOH
trace
AcOH AcOH DCM/ AcOHc
trace 45 (85) 59 (68)
DCM/ AcOHc
69 (75)
a
Unless noted otherwise, reactions were carried out using 0.25 mmol of 1a, 10 mol % of Pd(OAc)2, and 1 mL of AcOH at 40 °C for 48 h under an argon atmosphere. bIsolated yields calculated on the basis of consumed 1a, and the conversion ratios of 1a are given in parentheses. c 0.5 mL of AcOH in 1 mL of dichloromethane (DCM).
Table 2. Palladium-Catalyzed Monoacetoxylation of o-Carboranesa,b
a All reactions were carried out on a 0.25 mmol scale in 1.5 mL of DCM/AcOH (v/v 2/1) at 40 °C for 48 h under an argon atmosphere. bIsolated yields were calculated on the basis of the consumed 1a; the conversion ratio of 1a and the ratio of B(8) and B(9) isomers are given in parentheses.
B
DOI: 10.1021/acs.inorgchem.8b00038 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry could be enhanced to 34% yield with 2 equiv of AgNO3 in toluene at 80 °C for 24 h. Other carboxylic acids such as 4chlorobenzoic acid and cyclohexanecarboxylic acid also displayed poor reactivity, and the corresponding products were obtained in lower yield (Scheme 2).
conducted with 4.4 equiv of PhIO in acetic acid, the expected 3a was formed with 25% yield (entry 1). The yield was slightly improved when 0.2 equiv of Pd(OAc)2 was loaded (entry 2). Other oxidants such as t-BuOOH and K2S2O8 displayed lower efficiency (entries 3 and 4). Fortunately, when the reaction was carried out in acetic anhydride, 3a was afforded in 52% yield after 96 h (entry 5). Furthermore, the tetraacetoxylation was complete within 24 h when the reaction was conducted at 80 °C with 5 equiv of PhIO and gave the desired product in 55% yield (entries 6 and 7). With the optimized conditions in hand, the generality of this selective tetraacetoxylation was then explored. As we can see from Table 4, for Ccage-dialkyl-substituted o-carboranes, the tetraacetoxylation proceeded smoothly, and the expected products were formed in moderate yields (3a−c). When a phenyl was decorated on Ccage, the o-carboranes were also compatible with this transformation and gave the corresponding products in moderate to good yields (3d−f). However, when 1,2-Ph2-o-carborane was used, the tetraacetoxylation product was only formed in 44% yield (3g). Comparing with our previous work,9c we can see that this transformation was performed with slightly lower efficiency. The main reason is due to the formed triacetoxylation product, which hardly transforms further to the tetraacetoxylated product. Meanwhile, this result also demonstrated that the direct boron acetoxylation via cross dehydrogenative coupling process is more challenging without an electrophilic partner. Interestingly, benzyl-substituted o-carboranes were well compatible with this acetoxylation, and the desired products were obtained in good yields (3h−j). However, when the benzyl was substituted with a methoxy group, the excessive acetoxylation product was obtained and only gave 3k in 55% yield. In contrast, the benzyl with an electron-withdrawing group displayed relatively lower reactivity (3l). To understand the mechanism and exclude the possibility of in situ formed PIDA via dehydration of PhIO with acetic acid,13 the reaction of PhIO with acetic acid was conducted at 80 °C for 2 h, and then the 1H NMR was recorded in acetic acid-D4.
Scheme 2. Selective Monoacyloxylation of 1,2-Me2-ocarborane
On the basis of the selective monoacetoxylation of ocarboranes via cross dehydrogenative coupling, selective tetraacetoxylation on B(8,9,10,12) was then examined, and the results are summarized in Table 3. When the reaction was Table 3. Palladium-Catalyzed Tetraacetoxylation of 1,2-Me2o-carboranea
entry 1 2 3 4 5 6 7
Pd(OAc)2 0.1 0.2 0.2 0.2 0.2 0.2 0.2
equiv equiv equiv equiv equiv equiv equiv
oxidant 4.4 4.4 4.4 2.0 4.4 4.4 5.0
equiv equiv equiv equiv equiv equiv equiv
PhIO PhIO t-BuOOH K2S2O8 PhIO PhIO PhIO
solvent
yield (%)b
AcOH AcOH AcOH AcOH AcOH/Ac2Oc AcOH/Ac2Oc AcOH/Ac2Oc
25 30 10 trace 52d 49e 55e
a
Unless noted otherwise, reactions were carried out on a 0.25 mmol scale in 2 mL of solvent at 60 °C for 24 h under an argon atmosphere. b Isolated yields. cv/v 1/1. dReaction for 96 h. eReaction at 80 °C.
Table 4. Palladium-Catalyzed Tetraacetoxylation of o-Carboranesa,b
a All reactions were carried out on a 0.25 mmol scale in 2 mL of AcOH/Ac2O (v/v 1/1) at 80 °C for 24−48 h under an argon atmosphere. bIsolated yields.
C
DOI: 10.1021/acs.inorgchem.8b00038 Inorg. Chem. XXXX, XXX, XXX−XXX
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Inorganic Chemistry
anhydride,16,9c which would be the primary transition state due to the reduced electrophilic reactivity of other B−H bonds induced by the electron-withdrawing effect of acetoxyl.
By comparison with the 1H NMR of PhIO and PIDA (Scheme 3), we can see that the PhIO was untouched in acetic acid and there was no PIDA formed. This result demonstrates that the acetoxyl originates from acetic acid directly.
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CONCLUSIONS In conclusion, a selective mono-/tetraacetoxylation of ocarboranes via cross dehydrogenative coupling of B−H and O−H bonds was developed, and a series of mono-/ tetraacetoxylated o-carboranes anchored with diverse groups have been synthesized in moderate to good yields. The formation of PdIV-oxo species and a nucleophilic addition/ dehydration process was proposed for this acetoxylation. Meanwhile, the selective monoacetoxylation might be ascribed to the coordination effect of copper with the B−H bond, and a cyclopalladation process might be the key route to facilitate the tetraacetoxylation. This work has disclosed a direct and atomeconomical strategy for the construction of B−O bonds via cross dehydrogenative coupling of B−H/O−H bonds, which has important value in the design of reactions for the construction of carbon−boron and boron−heteroatom bonds of carboranes by a cross dehydrogenative coupling process.
1
Scheme 3. Comparison of H NMR Spectra of PIDA, PhIO, and a Mixture of PhIO and AcOH Reacted at 80 °C for 2 h
Subsequently, two control experiments with AcOH and AcOD were performed under the standard conditions, and a primary KIE of 1.06 was observed (Scheme 4). This result indicates that the cleavage of the O−H bond is not involved in the rate-determining step and a cooperative process might also take place.
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EXPERIMENTAL SECTION
General Information. All reactions under standard conditions were monitored by thin-layer chromatography (TLC) on gel F254 plates. Silica gel (200−300 mesh) was used for column chromatography, and the distillation range of petroleum ether was 60−90 °C. 1H NMR, 13C{1H} and 11B{1H} NMR spectra were recorded on Bruker 600 MHz instruments. All 1H NMR and 13C{1H} NMR spectral data are reported in ppm relative to tetramethylsilane (TMS) as internal standard, and 11B{1H} NMR spectral data are referenced to external BF3·Et2O. HRMS data were measured by ESI techniques. General Procedure for Selective Monoacetoxylation of oCarboranes. In a 10 mL dried flask were sequentially placed ocarborane (0.25 mmol), AcOH (0.5 mL), CH2Cl2 (1 mL), Pd(OAc)2 (5.6 mg, 0.025 mmol), Cu(OAc)2 (0.5 mmol, 91 mg), and PhIO (82.5 mg, 0.375 mmol) under an argon atmosphere. After the reaction mixture was stirred at 40 °C for 48 h, it was cooled to room temperature and extracted with ethyl acetate (60 mL). The organic phase was washed with water (3 × 10 mL), NaHCO3(aq) (3 × 10 mL), and brine (3 × 10 mL) in sequence and then dried over anhydrous Na2SO4. After evaporation of the solvent, both isomers were separated by column chromatography on 200−300 mesh silica gel with petroleum ether/EtOAc 20/1. General Procedure for Selective Tetraacetoxylation of oCarboranes. In a 10 mL dried flask were sequentially placed ocarborane (0.25 mmol), AcOH (1 mL), Ac2O (1 mL), Pd(OAc)2 (11.2 mg, 0.05 mmol), and PhIO (275 mg, 1.25 mmol) under an argon atmosphere. After the reaction mixture was stirred at 80 °C for 24−48 h until palladium black was formed, it was cooled to room temperature and extracted with ethyl acetate (60 mL). The organic phase was washed with water (3 × 10 mL), NaHCO3(aq) (3 × 10 mL), and brine (3 × 10 mL) in sequence and then dried over anhydrous Na2SO4. After evaporation of the solvent, the residue was purified by column chromatography on 200−300 mesh silica gel with CH2Cl2/EtOAc 20/1 to 10/1 as eluent. 1,2-Dimethyl-9-acetoxyl-o-carborane (2a-B9). 2a-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.06 (s, 3H), 2.04 (s, 3H), 2.01 (s, 3H); 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 68.9, 61.9, 23.7, 22.6, 21.2. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 9.5 (1B, BOAc), −5.8 (1B), −10.3 (4B), −10.9 (2B), −11.8 (2B). HRMS: calculated for C6B10H19O2 (M + H)+ 231.23827; found 231.23854. 1,2-Dimethyl-8-acetoxyl-o-carborane (2a-B8). 2a-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.07 (s, 3H), 2.04 (6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.5, 68.5, 22.9, 22.5. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.7 (1B, BOAc),
Scheme 4. Kinetic Isotopic Effect
On the basis of the experimental results, a plausible mechanism is proposed in Scheme 5 (with B(9)−H as an Scheme 5. Plausible Mechanism for Acetoxylation
example). Due to the more electrophilic reactivity of H− B(8,9,10,12) bonds, the electrophilic palladation of a B−H bond of H−B(8,9,10,12) takes place first to give I, and then the PdIV-oxo species II would form by oxidation with PhIO,14 followed by nucleophilic addition of PdIV-oxo with the O atom of acetic acid and a dehydration process to form the PdIV intermediate III; subsequently reductive elimination gives product 2 and releases Pd(OAc)2 to the next catalytic cycle. We consider that the coordinate complex IV might be formed and suppress the secondary electrophilic palladation to hinder multiacetoxylation, as discussed in our previous work.15 On the other hand, the acetoxyl might act as a directing group to give the palladacyclic intermediate V in the presence of acetic D
DOI: 10.1021/acs.inorgchem.8b00038 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry −5.6 (2B), −9.2 (1B), −10.4 (2B), −11.8 (2B), −13.3 (1B), −14.3 (1B). HRMS: calculated for C6B10H19O2 (M + H)+ 231.23827; found 231.23826. μ-1,2-Tetramethylene-9-acetoxyl-o-carborane (2b-B9). 2b-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.49−2.44 (m, 4H), 2.01 (s, 3H), 1.60−1.58 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 68.6, 61.6, 32.9, 30.9, 22.6, 19.9, 19.3. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 8.8 (1B, BOAc), −6.3 (1B), −9.9 (2B), −10.5 (2B), −11.9 (2B), −13.7 (2B). HRMS: calculated for C8B10H21O2 (M + H)+ 257.25392; found 257.25396. μ-1,2-Tetramethylene-8-acetoxyl-o-carborane (2b-B8). 2b-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.45−2.43 (m, 4H), 2.08 (s, 3H), 1.60−1.56 (m, 4H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.5, 68.2, 32.5, 22.6, 19.6. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 5.8 (1B, BOAc), −6.2 (2B), −10.6 (2B), −12.0 (4B), −17.7 (1B). HRMS: calculated for C8B10H21O2 (M + H)+ 257.25392; found 257.25386. μ-1,2-Dibenzyl-9-acetoxyl-o-carborane (2c-B9). 2c-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.25−7.23 (m, 2H), 7.08−7.07 (m, 2H), 3.77 (s, 2H), 3.72 (s, 2H), 2.04 (s, 3H). 13 C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 129.2, 128.8, 128.7, 127.7, 127.6, 67.3, 60.3, 37.8, 35.7, 22.6. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 9.3 (1B, BOAc), −5.7 (2B), −10.3 (4B), −11.9 (2B), −12.6 (1B). HRMS: calculated for C12B10H21O2 (M + H)+ 305.25392; found 305.25391. μ-1,2-Dibenzyl-8-acetoxyl-o-carborane (2c-B8). 2c-B8 was isolated as a white solid.1H NMR (600 MHz, CDCl3, ppm): δ 7.24−7.22 (m, 2H), 7.06−7.05 (m, 2H), 3.72 (s, 2H), 3.71 (s, 2H), 2.07 (s, 3H). 13 C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.5, 128.8, 128.7, 127.6, 66.4, 37.3, 22.5. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 5.3 (1B, BOAc), −5.7 (2B), −10.6 (2B), −11.9 (2B), −12.7 (2B), −16.9 (1B). HRMS: calculated for C12B10H21O2 (M + H)+ 305.25392; found 305.25403. 1,2-Diphenyl-9-acetoxyl-o-carborane (2d-B9). 2d-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.45−7.43 (m, 2H),7.41−7.40 (m, 2H), 7.25−7.21 (m, 2H), 7.15−7.12 (m, 4H), 2.06 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.0, 130.9, 130.5, 130.3, 130.2, 129.1, 128.3, 128.2, 80.9, 73.7, 22.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 11.8 (1B, BOAc), −3.3 (2B), −9.9 (2B), −11.0 (3B), −13.4 (2B). HRMS: calculated for C16B10H23O2 (M + H)+ 355.26957; found 355.26974. 1,2-Diphenyl-8-acetoxyl-o-carborane (2d-B8). 2d-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.47−7.45 (m, 4H), 7.23−7.21 (m, 2H), 7.15−7.12 (m, 4H), 2.16 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.6, 130.9, 130.3, 130.1, 128.3, 80.3, 22.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.9 (1B, BOAc), −2.9 (2B), −9.9 (2B), −11.2 (2B), −12.3 (1B), −13.5 (1B), −17.3 (1B). HRMS: calculated for C16B10H23O2 (M + H)+ 355.26957; found 355.26956. 1,2-Bis(4-chlorophenyl)-9-acetoxyl-o-carborane (2e-B9). 2e-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.38−7.37 (m, 2H), 7.35−7.33 (m, 2H), 7.16−7.15 (m, 4H), 2.05 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.0, 137.1, 132.2, 131.8, 128.8, 128.7, 127.6, 79.9, 72.8, 22.6. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 12.0 (1B, BOAc), −3.1 (2B), −9.9 (2B), −10.8 (3B), −13.6 (2B). HRMS: calculated for C16B10H21Cl2O2 (M + H)+ 423.19163; found 423.19155. 1,2-Bis(4-chlorophenyl)-8-acetoxyl-o-carborane (2e-B8). 2e-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.40−7.38 (m, 4H), 7.16−7.14 (m, 4H), 2.15 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.6, 137.1, 132.1, 128.8, 128.5, 79.3, 22.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.7 (1B, BOAc), −3.1 (2B), −10.3 (2B), −11.6 (2B), −12.8 (1B), −13.7 (1B), −17.8 (1B). HRMS: calculated for C16B10H21Cl2O2 (M + H)+ 423.19163; found 423.19186. 1,2-Bis(4-methoxylphenyl)-9-acetoxyl-o-carborane (2f-B9). 2f-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.37−7.35 (d, J = 12 Hz, 2H), 7.33−7.31 (d, J = 12 Hz, 2H), 6.65− 6.63 (m, 4H), 3.72 (s, 6H), 2.05 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 160.9, 160.8, 132.5, 132.1, 122.8, 121.4, 113.6,
113.5, 81.8, 74.4, 55.3, 22.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 11.6 (1B, BOAc), −3.7 (2B), −9.9 (2B), −11.4 (3B), −13.4 (2B). HRMS: calculated for C18B10H27O4 (M + H)+ 415.29070; found 415.29066. 1,2-Bis(4-methoxylphenyl)-8-acetoxyl-o-carborane (2f-B8). 2f-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.38−7.37 (d, J = 6 Hz, 4H), 6.64−6.63 (d, J = 6 Hz, 4H), 3.72 (s, 6H), 2.15 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.7, 160.9, 132.4, 132.1, 122.6, 113.5, 81.2, 55.3, 22.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.6 (1B, BOAc), −3.4 (2B), −10.1 (1B), −11.5 (2B), −13.9 (3B), −17.6 (1B). HRMS: calculated for C18B10H27O4 (M + H)+ 415.29070; found 415.29071. 1,2-Bis(4-methylbenzyl)-9-acetoxyl-o-carborane (2g-B9). 2g-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.17−7.16 (m, 4H), 7.11−7.09 (m, 4H), 3.61 (s, 2H), 3.58 (s, 2H), 2.36 (s, 6H), 1.94 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 169.9, 138.0, 137.9, 132.3, 131.7, 130.2, 130.1, 129.4, 129.3,75.3, 68.4, 41.2, 39.0, 22.6, 21.1. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 9.7 (1B, BOAc), −5.5 (2B), −11.1 (2B), −11.9 (2B), −13.4 (2B), −17.0 (1B). HRMS: calculated for C20B10H31O2 (M + H)+ 413.32491; found 413.32495. 1,2-Bis(4-methylbenzyl)-8-acetoxyl-o-carborane (2g-B8). 2g-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.17−7.16 (m, 4H), 7.11−7.10 (m, 4H), 3.60 (s, 4H), 2.36 (s, 6H), 2.02 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.4, 137.9, 131.7, 130.3, 129.3, 74.5, 40.6, 22.7, 21.2. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.8 (1B, BOAc), −5.2 (2B), −11.9 (3B), −13.4 (3B), −15.9 (1B). HRMS: calculated for C20B10H31O2 (M + H)+ 413.32491; found 413.32550. 1,2-Bis(4-bromobenzyl)-9-acetoxyl-o-carborane (2h-B9). 2h-B9 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.51−7.49 (m, 2H), 7.36 (brs, 2H), 7.27−7.26(m, 1H), 7.25−7.24 (m, 1H), 7.18−7.16 (m, 2H), 3.60 (s, 2H), 3.57 (s, 2H), 1.96 (s, 3H). 13 C{1H} NMR (150 MHz, CDCl3, ppm): δ 169.9, 137.0, 136.4, 133.2, 131.6, 131.5, 130.3, 130.2, 129.0, 128.9, 122.7, 122.6, 74.2, 67.4, 41.1, 38.9, 22.6, 21.2. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 9.9 (1B, BOAc), −5.2 (2B), −10.8 (2B), −11.9 (3B), −13.5 (2B). HRMS: calculated for C18B10H24Br2O2Na (M + Na)+ 563.09658; found 563.09711. 1,2-Bis(4-bromobenzyl)-8-acetoxyl-o-carborane (2h-B8). 2h-B8 was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.51−7.49 (m, 2H), 7.37 (brs, 2H), 7.28−7.25(m, 2H), 7.18−7.17 (m, 2H), 3.58 (s, 4H), 2.04 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.4, 136.4, 133.3, 131.5, 130.3, 129.1, 122.7, 73.5, 40.4, 22.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.9 (1B, BOAc), −4.8 (2B), −10.9 (1B), −12.0 (1B), −13.3 (3B), −16.1 (2B). HRMS: calculated for C18B10H24Br2O2Na (M + Na)+ 563.09658; found 563.09692. 1,2-Dimethyl-8/9-benzoyl-o-carborane (2i). 2i was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 8.07−8.05 (m, 2H), 8.03−8.00 (m, 2H), 7.56−7.51 (m, 2H), 7.49−7.38(m, 4H), 2.09 (s, 2H), 2.08 (s, 8H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 165.9, 165.4, 132.8, 132.6, 131.5, 131.2, 130.2, 130.1, 128.2, 128.1, 68.6, 63.9, 61.9, 23.7, 23.0, 21.2. HRMS: calculated for C11H21B10O2 (M + H)+ 295.24666; found 295.24738. 1,2-Dimethyl-8/9-(4-chlorobenzoyl)-o-carborane (2j). 2j was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 8.00−7.98 (m, 2H), 7.95−7.93 (m, 1H), 7.41−7.38 (m, 2H), 7.38− 7.35(m, 1H), 2.09−2.07 (brs, 10H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 164.9, 164.6, 139.2, 138.9, 131.5, 131.4, 129.9, 129.7, 128.6, 128.5, 69.2, 68.7, 62.1, 23.7, 23.0, 21.2. HRMS: calculated for C11H20B10O2Cl (M + H)+ 329.20769; found 329.20752. 1,2-Dimethyl-8/9-cyclohexanecarboxyl-o-carborane (2k). 2k was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.32− 2.25 (m, 1H), 2.23−2.19 (m, 1H), 2.06 (s, 2H), 2.03 (s, 7H), 1.93− 1.84 (m, 4H), 1.75−1.68 (m, 4H), 1.62−1.59 (m, 3H), 1.43−1.32 (m, 3H), 1.30−1.20 (m, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 175.6, 175.2, 68.9, 68.4, 61.5, 43.9, 28.9, 28.8, 25.8, 25.4, 23.7, 22.9, 21.4. HRMS: calculated for C11H27B10O2 (M + H)+ 301.29361; found 301.29425. E
DOI: 10.1021/acs.inorgchem.8b00038 Inorg. Chem. XXXX, XXX, XXX−XXX
Article
Inorganic Chemistry 1,2-Dimethyl-8,9,10,12-tetraacetoxyl-o-carborane (3a). 3a was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.11 (s, 6H), 2.09(s, 6H), 2.08 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.6, 50.1, 22.3, 21.7. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 3.2 (2B, BOAc), −2.2 (2B, BOAc), −16.5 (4B), −19.2 (2B). HRMS: calculated for C12B10H24O8Na (M + Na)+ 427.2368; found 427.2361. μ-1,2-Trimethylene-8,9,10,12-tetraacetoxyl-o-carborane (3b). 3b was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.60−2.56 (m, 4H), 2.55−2.54 (m, 2H), 2.09 (s, 12H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.6, 61.7, 33.5, 32.9, 22.4, 22.3. 11 1 B{ H} NMR (192 MHz, CDCl3, ppm): δ 2.3 (2B, BOAc), −0.4 (2B, BOAc), −18.5 (4B), −19.9 (2B). HRMS: calculated for C13B10H24O8Na (M + Na)+ 439.2365; found 439.2360. μ-1,2-Tetramethylene-8,9,10,12-tetraacetoxyl-o-carborane (3c). 3c was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 2.50 (brs, 4H), 2.08 (s, 12H), 1.61 (brs, 4H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.6, 49.5, 31.2, 22.3, 19.3. 11 1 B{ H} NMR (192 MHz, CDCl3, ppm): δ 2.7 (2B, BOAc), −1.3 (2B, BOAc), −16.7 (4B), −22.6 (2B). HRMS: calculated for C14B10H26O8Na (M + Na)+ 453.2521; found 453.2517. 1-Methyl-2-phenyl-8,9,10,12-tetraacetoxyl-o-carborane (3d). 3d was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.73−7.72 (d, J = 6 Hz, 2H), 7.48−7.45 (dd, J = 6 Hz, 1H), 7.40−7.38 (dd, J = 6 Hz, 2H), 2.12 (brs, 9H), 2.09 (s, 3H), 1.75 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.2, 169.6, 169.5, 132.0, 131.0, 129.0, 128.6, 59.3, 53.6, 22.4, 21.4. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.5 (1B, BOAc), 3.9 (1B, BOAc), −1.8 (2B, BOAc), −16.3 (4B), −20.9 (2B). HRMS: calculated for C17B10H26O8Na (M + Na)+ 489.2505; found 489.2523. 1-Phenyl-2-benzyl-8,9,10,12-tetraacetoxyl-o-carborane (3e). 3e was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.80−7.79 (d, J = 6 Hz, 2H), 7.54−7.51 (dd, J = 6 Hz, 1H), 7.47−7.44 (dd, J = 6 Hz, 2H), 7.25−7.21 (m, 3H), 6.84−6.83 (m, 2H), 3.11 (s, 2H), 2.09 (s, 6H), 2.07 (s, 3H), 2.06 (s, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.4, 169.4, 134.6, 132.4, 131.3, 129.9, 129.2, 128.5, 128.1, 60.7, 58.3, 39.1, 22.4, 22.3. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.2 (1B, BOAc), 3.9 (1B, BOAc), −1.9 (2B, BOAc), −17.5 (4B), −22.4 (2B). HRMS: calculated for C23B10H30O8Na (M + Na)+ 565.2844; found 565.2830. 1-n-Butyl-2-phenyl-8,9,10,12-tetraacetoxyl-o-carborane (3f). 3f was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.71−7.69 (d, J = 12 Hz, 2H), 7.48−7.44 (dd, J = 12 Hz, 1H), 7.40− 7.36 (dd, J = 12 Hz, 2H), 2.12 (s, 6H), 2.11 (s, 3H), 2.09 (s, 3H), 1.81−1.77 (m, 2H), 1.41−1.37 (m, 2H), 1.09−1.05 (m, 2H), 0.73− 0.70 (t, J = 6 Hz, 3H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.2, 169.6, 169.5, 132.1, 131.0, 129.0, 128.5, 60.7, 58.6, 32.9, 31.8, 22.4, 22.0, 13.4. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 4.2 (2B, BOAc), −1.8 (2B, BOAc), −16.9 (4B), −21.3 (2B). HRMS: calculated for C20B10H32O8Na (M + Na)+ 531.2994; found 531.2986. 1,2-Diphenyl-8,9,10,12-tetraacetoxyl-o-carborane (3g). 3g was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.51− 7.49 (m, 4H), 7.23−7.22 (m, 2H), 7.14−7.12 (m, 4H), 2.16 (s, 6H), 2.12 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.2, 169.5, 131.5, 130.6, 128.4, 128.3, 61.9, 22.5, 22.4. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 5.3 (2B, BOAc), −1.9 (2B, BOAc), −15.9 (4B), −21.9 (2B). HRMS: calculated for C22B10H28O8Na (M + Na)+ 551.2672; found 551.2680. 1,2-Dibenzyl-8,9,10,12-tetraacetoxyl-o-carborane (3h). 3h was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.36− 7.34 (m, 6H), 7.24−7.22 (m, 4H), 3.69 (s, 4H), 2.02 (s, 6H), 2.00 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.3, 134.3, 130.2, 128.9, 128.4, 60.2, 55.9, 39.4, 22.3, 22.2. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 3.7 (2B, BOAc), −1.8 (2B, BOAc), −17.7 (4B), −20.6 (2B). HRMS: calculated for C24B10H32O8Na (M + Na)+ 579.2977; found 579.2986. 1,2-Bis(4-methylbenzyl)-8,9,10,12-tetraacetoxyl-o-carborane (3i). 3i was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.16−7.15 (m, 4H), 7.12−7.10 (m, 4H), 3.64 (s, 4H), 2.34 (s, 6H), 2.02 (s, 6H),2.00 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ
170.0, 169.3, 138.2, 131.4, 130.1, 129.5, 56.1, 39.1, 22.3, 22.2, 21.1. 11 1 B{ H} NMR (192 MHz, CDCl3, ppm): δ 3.3 (2B, BOAc), −2.1 (2B, BOAc), −18.1 (4B), −21.1 (2B). HRMS: calculated for C26B10H37O8 (M + H)+ 587.34135; found 587.34137. 1,2-Bis(2-methylbenzyl)-8,9,10,12-tetraacetoxyl-o-carborane (3j). 3j was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.25−7.23 (m, 2H), 7.22−7.18 (m, 6H), 3.74 (s, 4H), 2.45 (s, 6H), 2.03 (s, 6H)1.98 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.1, 137.3, 132.8, 131.8, 131.1,128.6, 126.1, 55.4, 36.4, 22.3, 22.2, 20.2. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 3.3 (2B, BOAc), −2.4 (2B, BOAc), −18.4 (6B). HRMS: calculated for C26B10H37O8 (M + H)+ 587.34135; found 587.34113. 1,2-Bis(4-methoxylbenzyl)-8,9,10,12-tetraacetoxyl-o-carborane (3k). 3k was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.15 (brs, 2H), 7.13 (brs, 2H), 6.87 (brs, 2H), 6.86 (brs, 2H), 3.80 (s, 6H), 3.62 (s, 4H), 2.04 (s, 6H), 2.01 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.3, 159.5, 131.3, 126.5,114.2, 60.4, 56.2,55.2, 38.7, 22.4, 22.3. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 3.3 (2B, BOAc), −2.2 (2B, BOAc), −18.0 (4B), −20.9 (2B). HRMS: calculated for C26B10H37O10 (M + H)+ 619.33118; found 619.33099. 1,2-Bis(4-bromobenzyl)-8,9,10,12-tetraacetoxyl-o-carborane (3l). 3l was isolated as a white solid. 1H NMR (600 MHz, CDCl3, ppm): δ 7.50−7.49 (d, J = 6 Hz, 4H), 7.11−7.10 (d, J = 6 Hz, 4H), 3.62 (s, 4H), 2.03 (s, 6H), 2.01 (s, 6H). 13C{1H} NMR (150 MHz, CDCl3, ppm): δ 170.1, 169.3, 133.1, 132.2, 131.8, 122.9,60.4, 55.1,38.8, 22.3, 22.2. 11B{1H} NMR (192 MHz, CDCl3, ppm): δ 3.5 (2B, BOAc), −2.1 (2B, BOAc), −18.0 (4B), −20.9 (2B). HRMS: calculated for C26B10H31O8Br2 (M + H)+ 739.13107; found 739.13110.
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ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.8b00038. 1 H, 13C, and 11B NMR spectra (PDF)
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AUTHOR INFORMATION
Corresponding Author
*E-mail for K.C.:
[email protected]. ORCID
Ke Cao: 0000-0003-0348-2386 Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work is supported by the NSFC (No. 21602182), Sichuan Provincial Science and Technology Department (No. 2016TD0014), Sichuan Provincial Education Department (No.16ZB0133), and Longshan academic talent research supporting program of SWUST (17LZX324). KeeCloud Biotech is acknowledged for HRMS analysis.
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REFERENCES
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