Convenient Route to Monocarba-closo-dodecaborate Anions

Jun 2, 2016 - Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, ...
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Convenient Route to Monocarba-closo-dodecaborate Anions Naoki Tanaka, Yoshiaki Shoji,* and Takanori Fukushima Laboratory for Chemistry and Life Science, Institute of Innovative Research, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan S Supporting Information *

A B S T R A C T : M o n o c a r b a - c l o s o - d o d e c a b o r a t e a n io n [HCB11H11]− (1) and its derivatives are superb anionic species with remarkably high chemical stability and low nucleophilicity. Here we report a convenient two-step synthesis of 1, starting from nido-decaborane(14) (2) through the formation of arachno[CB9H14]− (3). In this protocol, the use of Me3NH+ as a countercation of 1 and 3 enables facile cation exchange, thus greatly enhancing access to the carbaborate anions. We also demonstrate an efficient perchlorination reaction of 1 into [HCB11Cl11]− (4). The detailed synthetic protocols as well as the full analytical data presented herein should provide a general and reliable recipe for the synthesis of these anionic species.

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INTRODUCTION

RESULTS AND DISCUSSION Scheme 1 outlines the new route to monocarba-closododecaborate anion 1 and its perchlorinated derivative 4. We set a Me3NH+ salt of [HCB11H11]− (Me3NH+·1) as a target compound (Scheme 1) because tertiary ammonium ions can be easily removed by neutralization. The choice of Me3NH+ was key in this synthetic protocol. As the first step, the precursor Me3NH+·3 was prepared from nido-decaborane(14) 2 using the Brellochs reaction with slight modification.22 The ESI-TOF MS spectrum (negative mode) of the resulting Me3NH+·3 showed clear ion peaks of [CB9H14]− (calcd for CB9H14− [M]− m/z = 123.20; found 123.20) (Figure S1, SI). The 1H NMR spectrum (400 MHz) of Me3NH+·3 at 25 °C in acetone-d6 showed a singlet signal at 3.21 ppm, due to the methyl groups of Me3NH+, and multiple BH signals appeared from 3.00 to −1.50 ppm (Figure S2, SI). The 11B NMR spectrum (128 MHz) of Me3NH+·3 at 25 °C in acetone-d6 showed five doublet signals at −1.6, −10.6 to −13.2, −29.0, and −39.9 ppm along with one triplet signal at −23.0 ppm (Figure S3, SI), indicating the formation of a Cs-symmetric arachno-[CB9H14]− skeleton.23,24 In 13C NMR spectroscopy (100 MHz), a signal due to the bridgehead carbon of [CB9H14]− appeared in the upfield region (−4.9 ppm) (Figure S4, SI). Finally, the molecular structure of Me3NH+·3 was unambiguously determined based on an X-ray analysis of a single crystal obtained by the slow diffusion of hexane vapor into an AcOEt solution of Me3NH+·3 (Figure 1). The arachno-[CB9H14]− framework is virtually identical to those reported previously.23,24 In the crystal, Me3NH+·3 formed a contact ion pair, where two short N−B contacts were observed for N1−B9 [3.227(2) Å] and N1−B6 [3.397(2) Å] (Figure 1). These interatomic distances are significantly shorter than the sum of the van der Waals radii (3.47 Å).25 Me3NH+·3

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Icosahedral monocarba-closo-dodecaborate anion [HCB11H11] (1) and its derivatives, which exhibit remarkably high chemical stability as well as low nucleophilicity,1−4 have many applications, including the creation of highly reactive cationic species,2,4−9 molecular super Brønsted acids,10−12 electrolyte materials,13−15 and even pharmaceutical agents.16,17 To date, several synthetic routes to closo-carbaborate anions have been developed.3,4,18−21 In 1967, Knoth and co-workers reported a five-step synthesis of 1 starting from nido-decaborane(14) (2),18,19 although it requires harsh reaction conditions and hazardous reagents such as sodium cyanide and sodium metal. More recently, Kennedy and co-workers showed that the reaction of arachno-[CB9H14]− (3) with BH3·SMe2 affords 1, where two BH groups are inserted into 3 to form the vertices of 1.21 This synthetic protocol has been the most convenient route to construct the closo-carbaborate skeleton. However, there is still room for improvement because this protocol uses lipophilic Et4N+ as a countercation of 1 and 3, which is unfavorable for further ion exchange with other cations, in particular, hydrophilic cations. In fact, we previously faced this problem during our research on the development of low-valent boron cations with closo-carbaborate-based anions.8 In the present work, we newly established a convenient route to the synthesis of 1 (Scheme 1), which may overcome the above problems. We also show that 1 is successfully converted into an undecachloro closo-carbaborate anion ([HCB11Cl11]−, 4), which has an exceptionally weakly coordinating nature, thereby enabling the synthesis of extremely reactive cationic species.8−10 The new synthetic protocols for 1 and 4 reported here are straightforward and thus greatly enhance the availability of these particular anionic species. © XXXX American Chemical Society

Received: April 17, 2016

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DOI: 10.1021/acs.organomet.6b00309 Organometallics XXXX, XXX, XXX−XXX

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Scheme 1. Synthesis of the Salts of arachno-[CB9H14]− (3), closo-[HCB11H11]− (1), and closo-[HCB11Cl11]− (4) from nidoB10H14 (2)

together with signals due to [HCB11H11]− (CH: 2.23 ppm and BH: 2.15−1.05 ppm) (Figure S6, SI). The 11B NMR spectrum of Me3NH+·1, involving three doublet signals at −7.32, −13.8, and −16.9 ppm (Figure S7, SI), agrees with its icosahedral closo-carbaborate skeleton. Neutralization of Me3NH+·1, accompanied by the formation of volatile trimethylamine, facilitated the exchange of the countercation of 1 (Scheme 1b). For example, Na+·1 was obtained when Me3NH+·1 was treated with sodium hydride in refluxing THF under argon for 24 h, although the isolation of this salt was not successful because of its highly hygroscopic nature. However, the addition of cesium chloride to the reaction mixture, followed by recrystallization from water, enabled the isolation of Cs+·1 as colorless crystals (80% yield). Importantly, the synthesis of Cs+·1 could be achieved more efficiently from Me3NH+·3 when Me3NH+·1 was subjected to neutralization and cation exchange sequentially without the isolation of Me3NH+·1 by recrystallization (Scheme 1b). As a consequence, the isolated yield of Cs+·1 (81%) from Me3NH+· 3 can be greatly improved. As a related work, Lavallo, Guo, and co-workers recently reported that the reduction of Me3NH+·1 with Mg metal in DME yields solvated crystals of Mg2+·12.26 Halogenated derivatives of 1 are an important class of weakly coordinating anions. In particular, perchlorinated [HCB11Cl11]− (4) has high chemical stability as well as low nucleophilicity, which enables the isolation of extremely reactive cationic species such as molecular super Brønsted acid2−12 and twocoordinate cationic boron species.8 Here, we also investigated the perchlorination reaction of 1 into 4 (Scheme 1b). While this reaction has been reported to proceed in refluxing SO2Cl2 (boiling point = 69 °C) for 1 day,27 in our case it required an even higher temperature and a longer reaction time to complete the reaction. Thus, a SO2Cl2 solution of Cs+·1 was heated at 115 °C under argon in a pressure-tight vessel (Figure S19) for 1 week. At this stage, the MALDI-TOF MS spectrum (negative mode) of the reaction mixture still showed ion peaks of partially chlorinated derivatives [HCB11ClxH11−x]− (x = 8, 9, and 10) together with those of 4 (Figure S17, SI). When the reaction was continued for an additional 1 week under the same conditions, only the ion peaks of 4 were observed in MALDITOF MS spectrometry of the reaction mixture. When the resultant mixture was recrystallized from water, Cs+·4 was

Figure 1. Molecular structure of Me3NH+·3 with atomic displacement parameters set at 50% probability. Color code: boron = pink, carbon = gray, nitrogen = blue, and hydrogen = white. Selected bond lengths (Å): C1−B1 = 1.726(3), C1−B2 = 1.668(3), C1−B3 = 1.734(3), B1− B2 = 1.779(3), B1−B4 = 1.782(3), B1−B6 = 1.863(3), B2−B3 = 1.776(3), B2−B4 = 1.747(3), B2−B5 = 1.748(3), B3−B5 = 1.783(3), B3−B8 = 1.856(3), B4−B5 = 1.811(3), B4−B6 = 1.781(3), B5−B7 = 1.783(2), B5−B8 = 1.776(3), B6−B7 = 1.746(3), B6−B9 = 1.897(3), B7−B8 = 1.738(3), B7−B9 = 1.735(3), B8−B9 = 1.895(3), N1−B6 = 3.397(2), N1−B9 = 3.227(2).

undergoes slow decomposition under air and moisture within a few months, and therefore this compound should be stored in an argon or nitrogen atmosphere. Me3NH+·3 was converted into Me3NH+·1 with the use of BH3·SMe2 (Scheme 1a). For example, treatment of Me3NH+·3 with an excess amount of BH3·SMe2 in refluxing 1,2-C2H4Cl2 under argon, followed by successive treatment with NaH in THF at 60 °C under argon and Me3NH+Cl− in water at 0 °C, afforded Me3NH+·1 as a white powder (74% yield). The ESITOF MS spectrum (negative mode) of Me3NH+·1 displayed ion peaks of [CB11H12]− (calcd for CB11H12− [M]− m/z = 143.20; found 143.20) (Figure S5, SI). The 1H NMR spectrum (400 MHz) of Me3NH+·1 in acetone-d6 at 25 °C showed one singlet signal of the methyl groups of Me3NH+ at 3.22 ppm, B

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washed with hot water and dried under reduced pressure [the 11B NMR spectrum of the residue showed that the crude product contained a boron-containing byproduct together with 1 (Figure S18, SI)]. Under argon, the residue was added to a THF suspension (3.0 mL) of NaH (226 mg, 9.43 mmol), and the resulting mixture was stirred for 24 h under reflux. After the mixture was allowed to cool to 0 °C, water (3.0 mL) was slowly added dropwise. After THF was removed by partial evaporation of the mixture under reduced pressure, the resulting white precipitates were removed by filtration. Then, Me3NH+Cl− (541 mg, 5.66 mmol) was added to this filtrate at 0 °C. The resulting white precipitate was collected by filtration, washed with water, and dried under reduced pressure, to give Me3NH+·1 (567 mg, 2.79 mmol) in 74% yield: dp > 450 °C. FT-IR (KBr): ν (cm−1) 3185, 3038, 2746, 2536, 1469, 1415, 1386, 1090, 1064, 1022, 975, 886, 749, 718. 1H NMR (400 MHz, acetone-d6): δ (ppm) 3.22 (s, 9H), 2.23 (s, 1H), 2.15−1.00 (m). 11B NMR (128 MHz, acetone-d6): δ (ppm) −7.32 (d, 1B, JBH = 139 Hz), −13.8(d, 5B, JBH = 133 Hz), −16.9 (d, 5B, JBH = 151 Hz). 13C NMR (100 MHz, acetone-d6): δ (ppm) 51.7, 46.4. ESI-TOF MS: calcd for CB11H12 [M]− m/z = 143.20; found 143.20. The ESI-TOF MS, 1H, 11B, and 13C NMR spectra of Me3NH+· 1 are shown in Figures S5, S6, S7, and S8, respectively. Cation Exchange of Me3NH+·1 into Cs+·1. Under argon, NaH (18 mg, 7.38 × 10−1 mmol) was added to a THF solution (2.0 mL) of Me3NH+·1 (100 mg, 4.92 × 10−1 mmol), and the mixture was stirred for 24 h under reflux. After the reaction mixture was allowed to cool to 0 °C, water (2.0 mL) was slowly added dropwise. The resulting solution was partially evaporated under reduced pressure to remove volatile materials, and then CsCl (124 mg, 7.38 × 10−1 mmol) was added. When the resulting solution was allowed to stand at 5 °C, colorless crystals formed, which were collected by filtration, washed with water (1.0 mL), and dried under reduced pressure, to give Cs+·1 (109 mg, 3.95 × 10−1 mmol) in 80% yield: dp > 450 °C. FT-IR (KBr): ν (cm−1) 3060, 2547, 1455, 1145, 1092, 1065, 1029, 861, 717. 1H NMR (400 MHz, acetone-d6): δ (ppm) 2.23 (s, 1H). 11B NMR (128 MHz, acetone-d6): δ (ppm) −7.23 (d, 1B, JBH = 138 Hz), −13.7 (d, 5B, JBH = 136 Hz), −16.8(d, 5B, JBH = 150 Hz). 13C NMR (100 MHz, acetone-d6): δ (ppm) 50.7. ESI-TOF MS: calcd for CB11H12 [M]− m/ z = 143.20; found 143.20. Anal. Calcd for CH12B11Cs: C, 4.35; H, 4.38. Found: C, 4.33; H, 4.43. The ESI-TOF MS, 1H, 11B, and 13C NMR spectra of Cs+·1 are shown in Figures S9, S10, S11, and S12, respectively. Synthesis of Cs+·1 from Me3NH+·3 without the Isolation of Me3NH+·1. Under argon, BH3·SMe2 (29.2 mL, 495 mmol) was added to a dry 1,2-C2H4Cl2 solution (58 mL) of Me3NH+·3 (3.89 g, 21.2 mmol), and the mixture was stirred for 4 days under reflux. After the reaction mixture was allowed to cool to 25 °C, it was evaporated to dryness under reduced pressure. The residue was washed with hot water and dried under reduced pressure. Under argon, the residue was added to a THF suspension (50 mL) of NaH (1.25 g, 52.1 mmol), and the resulting mixture was stirred for 24 h under reflux. After the reaction mixture was allowed to cool to 0 °C, water (50 mL) was slowly added dropwise. After THF was removed by partial evaporation of the mixture under reduced pressure, the resulting white precipitates were removed by filtration. CsCl (4.36 g, 25.9 mmol) was then added to this filtrate. When the resulting solution was allowed to stand at 5 °C, colorless crystals formed, which were collected by filtration, washed with water (5.0 mL), and dried under reduced pressure, to give Cs+·1 (4.69 g, 17.0 mmol) in 81% yield. Synthesis of Cs+·4. In a pressure-tight vessel (Figure S19), a SO2Cl2 solution (30 mL) of Cs+·1 (1.63 g, 5.91 mmol) was stirred under argon at 115 °C for 2 weeks. After the resulting solution was allowed to cool to 25 °C, it was evaporated to dryness under reduced pressure. The residue was recrystallized from water to give Cs+·4 as colorless crystals (3.02 g, 4.61 mmol) in 78% yield: dp > 450 °C. FTIR (KBr): ν (cm−1) 3024, 2993, 1611, 1339, 1254, 1123, 1040, 1016, 958, 901, 736, 717, 671. 1H NMR (400 MHz, acetone-d6): δ (ppm) 4.33 (s, 1H). 11B NMR (128 MHz, acetone-d6): δ (ppm) −2.97 (s, 1B), −10.4 (s, 5B), −13.5 (s, 5B). 13C NMR (100 MHz, acetone-d6): δ (ppm) 46.7. ESI-TOF MS (negative mode): calcd for CHB11Cl11 [M]− m/z = 521.77; found 521.77. Anal. Calcd for CHB11Cl11Cs: C,

isolated as colorless crystals in high yield (78%). Thus, the present perchlorination conditions, while they require a long reaction time, lead to the efficient formation of Cs+·4.

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CONCLUSION In conclusion, we have demonstrated convenient synthetic protocols for the salts of [HCB11H11]− (1) and [HCB11Cl11]− (4), where a Me3NH+ salt of arachno-[CB9H14]− (3) plays a crucial role as a synthetic intermediate. The detailed procedures and full analytical data presented here should provide a general and reliable recipe for the synthesis of carbaborate anions, thus significantly enhancing the availability of these superb anionic species, even for nonspecialists.

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EXPERIMENTAL SECTION

Materials. Unless otherwise noted, all commercial reagents were used as received. nido-B10H14 (2) was purchased from Wako Pure Chemical Industries, Ltd. Caution: Compound 2 is toxic, and thus all the manipulations using 2 must be performed in a f ume hood. 1,2-C2H4Cl2 was dried over CaH2 and freshly distilled prior to use. Methods. Decomposition points (dp) were recorded on a Yanaco MP-500D melting-point apparatus. Infrared spectra were recorded at 25 °C on a JASCO model FT/IR-660Plus Fourier transform infrared spectrometer. NMR spectroscopy measurements were carried out on a Bruker model AVANCE-400 spectrometer (400.0 MHz for 1H, 128.3 MHz for 11B, 100.6 MHz for 13C, and 376.4 MHz for 19F), where chemical shifts (δ) were determined with respect to residual solvent for 1H (residual nondeuterated acetone: 1H(δ) = 2.05 ppm), external BF3OEt2 in acetone-d6 for 11B (11B(δ) = 0.0 ppm), and residual solvent for 13C (acetone-d6: 13C(δ) = 29.84, 206.26 ppm). The absolute values of the coupling constants are given in hertz (Hz), regardless of their signs. Multiplicities are abbreviated as singlet (s), doublet (d), triplet (t), quartet (q), multiplet (m), and broad (br). Mass spectrometry measurements were carried out on a Bruker micrOTOF II mass spectrometer equipped with an electrospray ionization (ESI) probe or on a Shimadzu AXIMA-CFR Plus with a MALDI-TOF mass spectrometer. Synthesis of Me3NH+·3. Compound 2 (2.00 g, 16.4 mmol) was added to an aqueous solution (50 mL) of KOH (3.37 g, 60.1 mmol) at 0 °C. To this mixture was slowly added HCHO (37% solution in water, stabilized with 10% MeOH, 21.0 mL) using a syringe pump over a period of 6 h at 0 °C, and the resulting mixture was stirred for 24 h at 25 °C. After MeOH was partially removed by evaporating the solution under reduced pressure, an aqueous solution (20 mL) of KCl (20.0 g) was added. The resulting aqueous solution was extracted with Et2O (5 times). Then, water (100 mL) was added to the combined Et2O extract. After Et2O was removed by partial evaporation of the mixture under reduced pressure, Me3NH+Cl− (3.32 g, 34.7 mmol) was added. The resulting white precipitate was collected by filtration, washed with water, and dried under reduced pressure, to give Me3NH+·3 as a white powder (1.64 g, 8.94 mmol) in 54% yield: dp 184 °C. FT-IR (KBr): ν (cm−1) 3073, 3035, 3024, 2969, 2946, 2797, 2749, 2548, 2519, 2499, 2423, 2348, 1960, 1469, 1414, 1385, 1193, 1059, 1013, 981, 932, 850, 815, 795, 760, 721, 695, 675, 643, 617. 1H NMR (400 MHz, acetone-d6): δ (ppm) 3.21 (s, 9H), −1.32 to 3.00 (m), −2.00 (s, 1H), −3.95 (m, 1H). 11B NMR (128 MHz, acetoned6): δ (ppm) −1.63 (d, 1B, JBH = 132 Hz), −10.6 (d, 1B, JBH = 150 Hz), −13.2(d, 2B, JBH = 143 Hz), −23.0 (t, 1B, JBH = 113 Hz), −29.0 (d, 2B, JBH = 137 Hz), −39.9(d, 2B, JBH = 141 Hz). 13C NMR (100 MHz, acetone-d6): δ (ppm) 45.4, −4.89. ESI-TOF MS (negative mode): calcd for CB9H14 [M]− m/z = 123.20; found 123.20. The ESITOF MS, 1H, 11B, and 13C NMR spectra of Me3NH+·3 are shown in Figures S1, S2, S3, and S4, respectively. Synthesis of Me3NH+·1. Under argon, BH3·SMe2 (5.35 mL, 90.6 mmol) was added to a dry 1,2-C2H4Cl2 solution (12 mL) of Me3NH+· 3 (700 mg, 3.77 mmol), and the mixture was stirred for 4 days under reflux. After the reaction mixture was allowed to cool to 25 °C, it was evaporated to dryness under reduced pressure. The residue was C

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(6) Reed, C. A.; Kim, K.-C.; Bolskar, R. D.; Mueller, L. J. Science 2000, 289, 101−104. (7) Kato, T.; Stoyanov, E.; Geier, J.; Grützmacher, H.; Reed, C. A. J. Am. Chem. Soc. 2004, 126, 12451−12457. (8) (a) Shoji, Y.; Tanaka, N.; Mikami, K.; Uchiyama, M.; Fukushima, T. Nat. Chem. 2014, 6, 498−503. (b) Shoji, Y.; Tanaka, N.; Hashizume, D.; Fukushima, T. Chem. Commun. 2015, 51, 13342− 13345. (c) Alain, A. E.; Shoji, Y.; Fukushima, T.; Bryce, D. L. Inorg. Chem. 2015, 54, 11889−11896. (9) (a) Gunbas, G.; Hafezi, N.; Sheppard, W. L.; Olmstead, M. M.; Stoyanova, I. V.; Tham, F. S.; Meyer, M. P.; Mascal, M. Nat. Chem. 2012, 4, 1018−1023. (b) Stoyanov, E. S.; Gunbas, G.; Hafezi, N.; Mascal, M.; Stoyanova, I. V.; Tham, F. S.; Reed, C. A. J. Am. Chem. Soc. 2012, 134, 707−714. (10) Reed, C. A. Chem. Commun. 2005, 1669−1677. (11) (a) Juhasz, M.; Hoffmann, S.; Stoyanov, E.; Kim, K.-C.; Reed, C. A. Angew. Chem., Int. Ed. 2004, 43, 5352−5355. (b) Stoyanov, E. S.; Hoffmann, S. P.; Juhasz, M.; Reed, C. A. J. Am. Chem. Soc. 2006, 128, 3160−3161. (12) Nava, M.; Stoyanova, I. V.; Cummings, S.; Stoyanov, E. S.; Reed, C. A. Angew. Chem., Int. Ed. 2013, 52, 1−5. (13) Pospíšil, L.; King, B. T.; Michl, J. Electrochim. Acta 1998, 44, 103−108. (14) Carter, T. J.; Mohtadi, R.; Arthur, T. S.; Mizuno, F.; Zhang, R.; Sirai, S.; Kampf, J. W. Angew. Chem., Int. Ed. 2014, 53, 3173−3177. (15) Nafady, A. J. Electroanal. Chem. 2015, 755, 1−6. (16) Hawthorne, M. F. Angew. Chem., Int. Ed. Engl. 1993, 32, 950− 984. (17) Wilbur, D. S.; Hamlin, D. K.; Srivastava, R. R.; Chyan, M.-K. Nucl. Med. Biol. 2004, 31, 523−530. (18) (a) Knoth, W. H. J. Am. Chem. Soc. 1967, 89, 1274−1275. (b) Knoth, W. H. Inorg. Chem. 1971, 10, 598−605. (19) Plešek, J.; Jelínek, T.; Drdáková, E.; Heřmánek, S.; Štíbr, B. Collect. Czech. Chem. Commun. 1984, 49, 1559−1562. (20) Batsanov, A. S.; Fox, M. A.; Goeta, A. E.; Howard, J. A. K.; Hughes, A. K.; Malget, J. M. J. Chem. Soc., Dalton Trans. 2002, 2624− 2631. (21) Franken, A.; Bullen, N. J.; Jelínek, T.; Thornton-Pett, M.; Teat, S. J.; Clegg, W.; Kennedy, J. D.; Hardie, M. J. New J. Chem. 2004, 28, 1499−1505. (22) Brellochs, B. In Davidson, M. G.; Hughes, A. K.; Marder, T. B.; Wade, K., Eds. Contemporary Boron Chemistry; Royal Society of Chemistry: Cambridge, England, 2000; pp 212−214. (23) Štibr, B.; Jelínek, T.; Plešek, J.; Heŕmánek, S. J. Chem. Soc., Chem. Commun. 1987, 0, 963−964. (24) Brellochs, B.; Baćkovský, J.; Štíbr, B.; Jelínek, T.; Holub, J.; Bakardjiev, M.; Hnyk, D.; Hofmann, M.; Císarová, I.; Wrackmeyer, B. Eur. J. Inorg. Chem. 2004, 3605−3611. (25) Mantina, M.; Chamberlin, A. C.; Valero, R.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem. A 2009, 113, 5806−5812. (26) McArthur, S. G.; Geng, L.; Guo, J.; Lavallo, V. Inorg. Chem. Front. 2015, 2, 1101−1104. (27) Gu, W.; McCulloch, B. J.; Reibenspies, J. H.; Ozerov, O. V. Chem. Commun. 2010, 46, 2820−2822. (28) APEX 2, version 2011.11-3; Bruker AXS Inc.: Madison, WI, USA, 2011. (29) SAINT, version V7.60A; Bruker AXS Inc.: Madison, WI, USA, 2009. (30) REQAB; Molecular Structure Corporation: The Woodlands, TX, USA, 2008. (31) Altomare, A. M.; Burla, C.; Camalli, M.; Cascarano, G. L.; Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl. Crystallogr. 1999, 32, 115−119. (32) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64, 112−122.

1.83; H, 0.15; Cl, 59.55. Found: C, 1.96; H, 0.16; Cl, 59.11. The ESITOF MS, 1H, 11B, and 13C NMR spectra of Cs+·4 are shown in Figures S13, S14, S15, and S16, respectively. To confirm the reproducibility of this perchlorination reaction, we independently synthesized Cs+·4 by a procedure similar to that described above using different amounts of Cs+·1: for example, starting from 1.20 (4.35 mmol) and 0.50 g (1.81 mmol) of Cs+·1, Cs+·4 was obtained in 72% and 68% yields, respectively. Single-Crystal X-ray Diffraction Analysis. Single crystals of Me3NH+·3 were obtained from AcOEt/hexane as colorless block crystals. A single crystal of Me3NH+·3 was coated with immersion oil (type B: code 1248, Cargille Laboratories, Inc.) and then mounted on a micromount. The diffraction data of this crystal were collected at 90 K under a stream of cold nitrogen gas on a Bruker model APEX2 platform-CCD X-ray diffractometer system28 using graphite-monochromated Mo radiation (λ = 0.710 73 Å). The intensity data were collected by an ω-scan method with 0.5° oscillation for each frame. The Bragg spots were integrated using the ApexII program package,29 and the empirical absorption correction (multiscan) was applied using the REQAB program.30 The structure was solved by direct methods (SIR97)31 and refined by full-matrix least-squares (SHELXL−97).32 The anisotropic temperature factors were applied to all non-hydrogen atoms. All the hydrogen atoms, except for those of the methyl groups of Me3NH+, were assigned by a Fourier map and isotropically refined. Crystal data for C4H24B9N (Me3NH+·3): colorless block, 0.22 × 0.18 × 0.11 mm3, monoclinic, P21, a = 6.4166(5), b = 10.3935(8), c = 9.5956(7) Å, β = 100.278(1)°, V = 629.67(8) Å3, Z = 2, ρcalcd = 0.968 g cm−3, T = 90 K, 2θmax = 58.4°, Mo Kα radiation, λ = 0.710 73 Å, μ = 0.044 mm−1, 4578 reflections measured, 2208 unique reflections, 190 parameters, R1 = 0.0301 (I > 2σ(I)), wR2 = 0.0857 (all data), CCDC 1457854.

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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.organomet.6b00309. Experimental and analytical data (PDF) Crystallographic data for Me3NH+·3 (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (Y. Shoji). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas “π-Figuration” (26102008) and KAKENHI (26708004) from The Ministry of Education, Culture, Sports, Science, and Technology, Japan. N.T. is grateful for a JSPS Young Scientist Fellowship (15J11698). The authors thank the Material Analysis Suzukake-dai Center, Technical Department, Tokyo Institute of Technology, for the support of NMR and MALDI-TOF MS measurements.

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REFERENCES

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DOI: 10.1021/acs.organomet.6b00309 Organometallics XXXX, XXX, XXX−XXX