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Article Cite This: Inorg. Chem. 2017, 56, 14351-14356

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Convenient Synthesis of [closo-B10H9‑1-I]2− and [closo-B10H8‑1,10‑I2]2− Anions Edyta Rzeszotarska,† Irina Novozhilova,‡ and Piotr Kaszyński*,†,‡,§ †

Centre of Molecular and Macromolecular Studies, Polish Academy of Sciences, Sienkiewicza 112, 90363 Łódź, Poland Organic Materials Research Group, Department of Chemistry, Middle Tennessee State University, Murfreesboro, Tennessee 37132, United States § Faculty of Chemistry, University of Łódź, Tamka 12, 91403 Łódź, Poland Downloaded via UNIV OF CALIFORNIA SANTA BARBARA on June 28, 2018 at 22:03:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.

‡

S Supporting Information *

ABSTRACT: Two iodo derivatives, [closo-B10H9-1-I]2− (1) and [closo-B10H8-1,10I2]2− (2), were obtained from the parent [closo-B10H10]2− anion in a two-step process and about 60% and 80% overall yields, respectively. Molecular and crystal structures of 2[Pr4N] were established with XRD methods: I422; a = b = 10.1531(1) Å, c = 18.0149(2) Å; α = β = γ = 90°; Z = 2. Synthetic applications of 1[Bu4N] were demonstrated in a Pd(0)-catalyzed cross-coupling reaction with 4-MeOC6H4MgBr.

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INTRODUCTION One of the most effective ways to form a B−C bond in closoboranes involves a Pd-catalyzed cross-coupling reaction1 between an appropriate iodo-closo-borate and an organometallic reagent. This method has extensively been used for substitution of 12-vertex carboranes,2 derivatives of carbaborate anions, [closo-1-CB11H12]− (A, Figure 1)3−13 and [closo-1-CB9H10]−

typically controlled by stoichiometry and conditions of the reaction judiciously used considering their reactivity toward iodination, which increases in the order [closo-C2B10H12] < [closo-1-CB11H12]− < [closo-1-CB9H10]− < [closo-B12H12]2−. Related to the reactivity and symmetry of these clusters are the issues of regioselectivity and regiochemistry of substitution for mono- and polyiodo derivatives. Also, the isolation of pure isomers is increasingly more difficult with increasing electric charge of the cluster. In the series A−D (Figure 1), dianion [closo-B10H10]2− (D)26 is the most reactive toward electrophiles.27 In contrast to anions A−C, iodination of the [closo-B10H10]2− (D) dianion is very fast and kinetically indistinguishable for the introduction of the first three substituents.27,28 This inability to control the degree of cage iodination combined with the stereochemistry of the anion leads to complex mixtures of products, which can be separated by tedious electrophoresis29 or ion exchange chromatography,30 and some, such as [closo-B10H9-1-I]2− (1) and [closo-B10H8-1,10-I2]2− (2), have been characterized by NMR,30 IR,30 and XRD31,32 methods. Detailed analysis demonstrated that the apical isomer [closo-B10H9-1-I]2− (1) is the minor product (30%) between the two possible monoiodo isomers,30 when reaction was run at ambient temperature, and the equatorial isomer [closo-B10H9-2-I]2− is the sole product when iodination was conducted at −75 °C in EtOH.33

Figure 1. Structures of the selected closo-borate clusters: [closo-1CB11H12]− (A), [closo-1-CB9H10]− (B), [closo-B12H12]2− (C), and [closo-B10H10]2− (D).

(B),14−17 and dodecaborate anion [closo-B12H12]2− (C)18−20 with alkyl,8,9,12,15−17,19,20 aryl,3,5,13,14,18,19 and alkynyl4,5,7,10,11,20 groups. In contrast, there are no reports of similar coupling reactions for the [closo-B10H10]2− anion (D), the most synthetically available closo-borane,21 mainly due to the cumbersome access to its iodo derivatives. Ready availability of such iodo derivatives of D would certainly contribute to the development of structural and materials chemistry of [closoB10H10]2− anion, considering significant electronic interactions between apical π-substituents and 10-vertex closo-boranes.22−25 Iodo-closo-boranes are conveniently available for carboranes, [closo-C2B10H12], [closo-1-CB11H12]− and [closo-1-CB9H10]−2 and [closo-B12H12]2− dianions, by direct iodination of the clusters with a variety of reagents, such as I2, ICl, and NIS. The number of iodine atoms substituted on the closo-boranes is © 2017 American Chemical Society

The preparation of isomerically pure [closo-B10H9-1-I]2− (1) anion was demonstrated over four decades ago by taking advantage of high selectivity of electrophilic substitution with Received: September 29, 2017 Published: October 31, 2017 14351

DOI: 10.1021/acs.inorgchem.7b02477 Inorg. Chem. 2017, 56, 14351−14356

Article

Inorganic Chemistry

onstrated that [closo-B10H9-1-IPh]−[Et4N]+ (3[Et4N])36 is essentially insoluble in THF and therefore unreactive toward n-BuLi. Therefore, 3[Bu4N] salt was prepared in good yields by a modified literature procedure.36 The selectivity for monophenyliodination of [closo-B10H10]2− (D) with PhI(OAc)2 was accomplished by controlling the solubility of the desired product 3[Q] with the concentration of AcOH. Consequently, 30% aqueous AcOH was used for the preparation of 3[Bu4N] (Scheme 2).

phenyliodonium reagents,34 followed by cleavage of the resulting iodonium zwitterion [closo-B10H9-1-IPh]− (3, Figure 2).35 This method has never been reproduced in the literature

Figure 2. Reported preparation of 1.34,35

presumably due to inappropriate reaction conditions to prepare 3,36 and cumbersome on large-scale photolysis or electrolysis of 3 required to obtain 1.35 Recently, we have made significant advances in functionalization of closo-borates and optimized the preparation of 3.36 We have also demonstrated that the 12-iodonium zwitterion of [closo-1-CB11H12]− (A) undergoes a clean cleavage in the presence of RMgBr as an electron donor to yield the corresponding iodo derivative [closo-1-CB11H11-12-I]−.12,36 These two processes are now applied to obtain isomerically pure iodo derivatives 1 and 2. Here, we demonstrate a simple, convenient, and high yield access to isomerically pure mono- and diiodo derivatives [closoB10H9-1-I]2− (1) and [closo-B10H8-1,10-I2]2− (2). We provide XRD analysis of 2 and demonstrate a Pd-catalyzed arylation reaction of 1.

Scheme 2. Synthesis of [closo-B10H9-1-I]2− 2[R4N]+ (1[R4N])a

a Reagents and conditions: (i) PhI(OAc)2, [R4N]+X−, AcOH/H2O; (ii) n-BuLi, THF, −10 °C; (iii) [R4N]+X−.

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A subsequent reaction of 3[Bu4N] with n-BuLi in THF, followed by treatment of the reaction products with [Bu4N]+Br−, gave the desired monoiodo derivative 1[Bu4N] in 90% yield (Scheme 2). The presented synthesis of [closo-B10H9-1-I]2− (1) from 3 using n-BuLi constitutes a significant improvement of the reported preparation of the anion in either photochemical or electrochemical process.35 All three processes presumably involve a SET step and the formation of the 9-I-2 intermediate (9 electron iodine with two substituents; 3-(9-I-2), Scheme 3),

RESULTS AND DISCUSSION Synthesis. The preparative work began with the synthesis of the [closo-B10H8-1,10-I2]2− anion (2) from the bis-iodonium zwitterion [closo-B10H8-1,10-(IPh)2] (4, Scheme 1).36 Initial Scheme 1. Synthesis of [closo-B10H8-1,10-I2]2− 2[R4N]+ (2[R4N])a

Scheme 3. Proposed Mechanism for the Formation of 1 Reagents and conditions: (i) n-BuLi, THF, −10 °C, 1 h; (ii) [R4N]+X−. a

experiments with a Grignard reagent, used for a successful generation of [closo-1-CB11H11-12-I]− from [closo-1-CB11H1112-IPh],36 demonstrated full conversion of the bis-zwitterion 4, but the separation of the diiodide 2 was complicated by the formation of insoluble magnesium salts. Extraction of the acidic form of 2 from aqueous solutions to Et2O gave low yields of the desired product ultimately isolated as the 2[Et4N] salt. To simplify isolation of the anion, attention was turned to RLi reagents. Indeed, 4 in THF solutions reacted instantaneously upon dropwise addition of excess n-BuLi. After quenching of the reaction mixture with water and removing THF, the resulting clear aqueous solution of the lithium salts was treated with [Pr4N]+Cl− and the product was isolated as 2[Pr4N] in high yields. Similarly, 2[Bu4N] salt was obtained when [Bu4N]+Br− was used to precipitate the anion. 11B NMR analysis of the crude reaction mixture demonstrated a clean conversion of zwitterion 4 to dianion 2 with about 2 equiv of nBuLi per iodonium group. Synthesis of the monoiodo anion [closo-B10H9-1-I]2− (1) was less straightforward since it involved a salt of monoiodonium zwitterion [closo-B10H9-1-IPh]− (3). Initial experiments dem-

which falls apart, giving anion 1 and the phenyl radical. The latter is stabilized through subsequent reactions with the solvent or radical recombination. Analysis of the hexane wash of the aqueous solution of 2[Li] in the workup procedure by 1H NMR and MS methods revealed that biphenyl is the dominant component (>90%). The facile availability of iodio derivatives 1 and 2 opens up access to new derivatives of the [closo-B10H10]2− anion (D) through Pd(0)-catalyzed cross-coupling reactions. An example of such a process is an efficient arylation of 1[Bu4N] with 4MeOC6H4MgBr in the presence 1 mol % PEPPSI-IPr as a catalyst shown in Scheme 4. The resulting derivative 5 was isolated as the cesium salt, 5[Cs], in 75% yield. Other catalysts were completely ineffective. Thus, employing PPh3/PdCl2, previously used18 for the preparation of [closo-B12H11-1-Ph]−, 14352

DOI: 10.1021/acs.inorgchem.7b02477 Inorg. Chem. 2017, 56, 14351−14356

Article

Inorganic Chemistry Scheme 4. Synthesis of [closo-B10H9-1-Ar]2− 5a

of a tetrahedral nitrogen atom substituted with four propyl groups, each in an ideal all-trans conformation. The intracage dimensions of the [closo-B10H8-1,10-I2]2− anion, such as B−B bond distances and angles, are typical for the {closo-B10} derivatives26 (Table 1). Detailed analysis of data in Table 1 shows that the cage dimensions change upon substitution with the electronwithdrawing iodine atom (σp = 0.18 for I).38 Thus, the distance between the apical and equatorial boron atoms is diminishing and, in the monoiodo derivative 1, a larger effect is observed at the substituted apex. Consequently, the height of the square pyramids, B(1)···B(2-5), decreases form 1.100 Å in D to 1.059 Å in 2, which results in the overall contraction of the cage as measured by the B(1)···B(10) separation (3.717 Å in D to 3.628 Å in 2). Similar substituent effects on the cluster dimensions have been observed before, including derivatives of anions A39 and D.25 The B(1)−I bond distance is also sensitive to the substitution at the opposite apex: it is reduced from 2.208(6) Å in the monoiodo derivative 1 to 2.180(5) Å in the diiodo derivative 2 in response to the diminished electron density at the apical boron atom. Even further reduction of the B−I distance is observed upon replacement of the B(10)−H group in 1 with an electropositive C−Ph group in [closo-1-CB9H8-1Ph-10-I]− (dB−I = 2.163(6) Å, ΔdB−I = 0.046 Å).40 A similar substituent effect on the B−I distance is observed in the 12vertex series: the stronger electron-withdrawing substituent, the shorter the bond. For instance, in [closo-B12H11-1-I]2−, the B−I distance is dB−I = 2.226(3) Å (the longest in the series),41 while, in the carbaborate analogues, [closo-1-CB11H10-1-NH2-12-I]− and [closo-1-CB11H10-1-Quin-12-I], the B−I distances are significantly shorted (dB−I = 2.190(10) Å7 and 2.196(7) Å,42 respectively). In comparison with two other closo-borate dianions, the B−I distance in 1 is an intermediate between that in [closo-B12H11-1-I]2− (dB−I = 2.226(3) Å)41 and in [closoB6H6-1-I]− (dB−I = 2.174(3) Å).43)

a Reagents and conditions: (i) 4-MeOC6H4MgBr, PEPPSI-IPr, THF, reflux, 2 h.

PChx3/PdCl2, effective for B-alkylation of iodo derivatives of anions A and B,6,15−17 and (biphenyl-2-yl)PChx2/PdCl2 resulted in slow degradation of the starting 1, and formation of a complex mixture of starting 1 with several unidentified products not containing the desired 5, after 24 h. Molecular and Crystal Structures. Colorless crystals of 2[Pr4N] (tetragonal space group I422) were grown from MeOH/MeCN solutions at ambient conditions, and its solidstate structure was determined by X-ray diffraction analysis. Crystallographic data collection information is listed in the Supporting Information, while selected bond lengths and angles are collected in Table 1, and the molecular structure for 2[Pr4N] is shown in Figure 3. Table 1. Selected Interatomic Distances and Angles for Anion D[Q],a 1[Q],b and 2[Pr4N]c D[Q]a B(1)−I B(1)−B(2) avg B(1)···B(2-5)e B(2)−B(3) avg B(2)−B(6) avg B(6)−B(7) avg B(6)−B(10) avg B(10)···B(6-9)e B(1)···B(10) B−B(1)−I avg B−B(10)−X avg

1.702(3) 1.100 1.835(9) 1.813(6) 1.836(2) 1.700(3) 1.100 3.717 130.3(12)f

1[Q]b

2[Pr4N]

2.209(6) 1.678(11) 1.066 1.833(8) 1.806(9) 1.828(7) 1.692(4) 1.091 3.667 129.4(11) 130(6)f

2.180(5) 1.686(4)d 1.059 1.857(4)d 1.815(4) 1.857(4)d 1.686(4)d 1.059 3.628 128.9(2)d 128.9(2)d,g

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CONCLUSIONS We have developed a facile access to two isomerically pure iodo derivatives of the [closo-B10H10]2− anion, [closo-B10H9-1-I]2− (1) and [closo-B10H8-1,10-I2]2− (2), and demonstrated the utility of one of them in a Pd-catalyzed C−B cross-coupling reaction with an arylmagnesium reagent. The two iodo derivatives 1 and 2 are obtained from the corresponding phenyliodonium zwitterions, 3 and 4, respectively, in a reaction with n-BuLi in THF. While the selection of the counterion in the preparation of the diodide 2 is accomplished after the anion generation, the counterion for 1 is best selected at the stage of generation of the iodonium 3. The iodo derivatives 1 and 2 are considered as key intermediates for new ionic materials that are being pursued in our laboratory.

a

Q = 2,2′-bipyridinium, ref 37. bQ = methylenedipyridinium, ref 31. Except for unique in each molecule distances B−I, B−X and the cage size B(1)···B(10), all parameters are average values and the esd refers to the distribution of individual values. dUnique value; esd for the measurement. eThe height of the square pyramid. fX = H. gX = I. c

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Figure 3. Thermal ellipsoid representation of 2[Pr4N] showing [closoB10H8-1,10-I2] with one [Pr4N]+ cation (left), and the crystal packing viewed down the c axis with the cations removed for clarity (right). For selected geometrical parameters, see Table 1. The corresponding ellipsoids are at 50% probability.

EXPERIMENTAL SECTION

General. Reactions were carried out under Ar, and subsequent manipulations were conducted in air. NMR spectra were obtained at 500 MHz (1H), 125 MHz (13C), and 160 MHz (11B) in CD3CN and CDCl3. Chemical shifts were referenced to the solvent (1H and 13C: 1.94 and 118.26 ppm for CD3CN and 7.26 and 77.16 ppm for CDCl3),44 sodium 3-(trimethylsilyl)-1-propanesulfonate (D2O; 1H, δ = 0.0 ppm), or to an external sample of BF3·Et2O in CD3CN and CDCl3 (11B, δ = 0.0 ppm). The 11B NMR chemical shift of B(OH)3 in D2O was set at 19.5 ppm. The [closo-B10H10]2− 2[Et3NH]+ was obtained using a literature procedure:45 11B NMR (160 MHz, CD3CN) δ −27.8 (d, J = 130 Hz, 8B), 0.2 (d, J = 146 Hz, 2B).

The unit cell of 2[Pr4N] (a = 10.15310(10) Å, b = 10.15310(10) Å, c = 18.0149(2) Å) contains two molecules of [closo-B10H8-1,10-I2]2− and four cations [Pr4N]+. One molecule of [closo-B10H8-1,10-I2]2− and one cation [Pr4N]+ in their mutual orientations are shown in Figure 3. The cation consists 14353

DOI: 10.1021/acs.inorgchem.7b02477 Inorg. Chem. 2017, 56, 14351−14356

Article

Inorganic Chemistry Preparation of [closo-B10H9-1-I]2− 2[Bu4N]+ (1[Bu4N]). To a solution of monoiodonium derivative 3[Bu4N] (1.00 g, 1.77 mmol) in dry THF (18 mL), 2.5 M n-BuLi in hexanes (3.5 mL, 8.8 mmol) was added dropwise over the period of 5−10 min at −10 °C under argon. The reaction mixture was stirred at −5 °C for 1 h, and a small sample was analyzed by 11B NMR (more n-BuLi can be added if necessary to complete the reaction). Water (10 mL) was added, THF was removed under reduced pressure, and the clear solution was extracted with hexane (×3). The aqueous layer was treated with a concentrated solution of [Bu4N]+Br− (1.13 g, 3.5 mmol), and the resulting solid was collected by filtration, washed with hexane, and dried. The resulting crude product was recrystallized (MeOH/H2O) to give 1.16 g (90% yield) of salt 1[Bu4N] as colorless needles: mp 215−220 °C; 1H NMR (500 MHz, CD3CN) δ −0.1 to 0.9 (br m, 8H), 0.97 (t, J = 7.4 Hz, 24H), 1.36 (sext, J = 7.3 Hz, 16H), 1.56−1.64 (m, 16H), 3.07−3.13 (m, 16H), 3.62 (br q, J = 143 Hz, 1H); 11B NMR (160 MHz, CD3CN) δ −28.4 (d, J = 130 Hz, 4B), −24.8 (d, J = 131, 4B), −8.6 (s, 1B), 0.4 (d, J = 146 Hz, 1B) [lit.30 11B NMR (CD3CN) δ −28.8 (d, J = 127 Hz, 4B), −25.2 (d, J = 132, 4B), −8.9 (s, 1B), 0.0 (d, J = 168 Hz, 1B)]. Anal. Calcd for C32H81B10IN2: C, 52.72; H, 11.20; N, 3.84. Found: C, 52.56; H, 11.18; N, 3.75. Preparation of [closo-B10H8-1,10-I2]2− 2[R4N]+ (2[R4N]). General Procedure. To a suspension of [closo-B10H8-1,10-(IPh)2] (4, 2.10 g, 4.00 mmol)36 in dry THF (30 mL), 2.1 M n-BuLi in hexanes (9.0 mL, 18.9 mmol) was added dropwise at −10 °C under argon over 45 min period. The reaction mixture was stirred at −5 °C for 1 h, and a small sample was analyzed by 11B NMR (more n-BuLi can be added if necessary to complete the reaction). Water (10 mL) was added, and THF was removed from the resulting clear solution under reduced pressure. The solution was diluted with water to 20 mL and extracted with hexanes (×3). The aqueous layer was treated with a concentrated solution of tetraalkylammonium salt ([Bu4N]Cl or [Pr4N]Cl, 10 mmol; if necessary, the volume could be reduced to 20 mL by evaporation), placed in a refrigerator (−4 °C), and after 1 h, the resulting off-white precipitation was filtered, washed with hexane, and dried. The hexane wash was concentrated and the residue analyzed, revealing biphenyl as the main component (>90%): 1H NMR (500 MHz, CDCl3) δ 7.38 (t, J = 7.4 Hz, 1H), 7.48 (t, J = 7.5 Hz, 2H), 7.63 (t, J = 7.8 Hz, 2H); EI-MS, m/z 154 (M, 100). [closo-B10H8-1,10-I2]2− 2[Pr4N]+ (2[Pr4N]). Recrystallized from EtOH/MeCN or MeOH/MeCN (colorless crystals), 90−95% yield: mp > 250 °C; 1H NMR (500 MHz, CD3CN) δ 0.0−1.1 (br m, 8H), 0.99 (t, J = 7.2 Hz, 24H), 1.70 (sext, J = 7.6 Hz, 16H), 3.04−3.09 (m, 16H); 11B NMR (160 MHz, CD3CN) δ −24.5 (d, J = 132 Hz, 8B), −5.5 (s, 2B). Anal. Calcd for C24H64B10I2N2: C, 38.81; H, 8.69; N, 3.77. Found: C, 38.96; H, 8.79; N, 3.86. [closo-B10H8-1,10-I2]2− 2[Bu4N]+ (2[Bu4N]). Recrystallized from MeOH/CH2Cl2 (needles), 78−80% yield: mp 120−123 °C; 1H NMR (500 MHz, CD3CN) δ 0.0−1.1 (br m, 8H), 0.98 (t, J = 7.3 Hz, 24H), 1.35 (sext, J = 7.4 Hz, 16H), 1.57−1.64 (m, 16H), 3.05−3.09 (m, 16H); 11B NMR (160 MHz, CD3CN) δ −24.5 (d, J = 132 Hz, 8B), −5.6 (s, 2B) [lit.30 11B NMR (CD3CN) δ −24.8 (d, J = 133 Hz, 8B), −5.9 (s, 2B)]. Anal. Calcd for C32H80B10I2N2: C, 44.96; H, 9.43; N, 3.28. Found: C, 45.02; H, 9.61; N, 3.37. Preparation of [closo-B10H9-1-IPh]− [Bu4N]+ (3[Bu4N]). A solution of [closo-B10H10]2− 2[Et3NH]+ (0.968 g, 3.00 mmol) and NaOH (255 mg, 6.375 mmol) in water (8 mL) was concentrated to remove Et3N, and 30% aqueous AcOH (35 mL) was added, followed by solid [Bu4N]+[HSO4]− (2.04 g, 6.00 mmol; [Bu4N]+Cl− could also be used, but not the bromide). The resulting solution was cooled to 0 °C (ice-salt bath), and solid PhI(OAc)2 (0.966 g, 3.00 mmol) was added at once. The reaction was stirred for 1 h at 0 °C, water (20 mL) was added, and the solid was filtered. The resulting off-white solid was washed with H2O, and dried in vacuo. The crude material was dissolved in CH2Cl2 and evaporated with about 2 g of SiO2, and the powdery patty was deposited on the top of a short SiO2 plug. Washing the plug with CH2Cl2 removed bis-iodonium zwitterion 4, while the desired product was eluted with a CH2Cl2/MeCN (15:1) or with a CH2Cl2/AcOEt (10:1) mixture. The resulting crude oily product was

covered with diethyl ether to effect crystallization, giving 1.00−1.10 g (60−65% yield) of 3[Bu4N] as a yellowish solid: mp 97−102 °C; 1H NMR (500 MHz, CD3CN) δ −0.2−0.8 (br m, 8H), 0.97 (t, J = 7.3 Hz, 12H), 1.35 (sext, J = 7.4 Hz, 8H), 1.56−1.63 (m, 8H), 3.06−3.09 (m, 8H), 4.09 (br q, J = 148 Hz, 1H), 7.42 (t, J = 7.9 Hz, 2H), 7.59 (tt, J1 = 7.5 Hz, J2 = 1.0 Hz, 1H), 8.13 (dd, J1 = 8.3 Hz, J2 = 1.0 Hz, 2H); 11 B NMR (160 MHz, CD3CN) δ −27.6 (d, J = 131 Hz, 4B), −23.9 (d, J = 135, 4B), −2.1 (s, 1B), 8.9 (d, J = 154 Hz, 1B). Anal. Calcd for C22H50B10IN: C, 46.88; H, 8.94; N, 2.48. Found: C, 46.68; H, 8.79; N, 2.51. Preparation of [closo-B10H9-1-(C6H4OMe-4)]2− 2[Cs]+ (5[Cs]). To a solution of 3[Bu4N] (200 mg, 0.25 mmol) in dry THF (1 mL) was added 0.5 M 4-methoxyphenylmagnesium bromide (1.75 mL, 0.87 mmol) and PEPPSI-IPr catalyst (2 mg, 1 mol %). The mixture was refluxed for 2 h, water was added, and THF was removed under reduced pressure. The mixture was extracted with CH2Cl2 (×3). The combined extracts were dried (Na2SO4), and the solvent was evaporated. The oily residue was washed with hexane and Et2O, dissolved in small amounts of MeOH, and passed through an ionexchange column (Dowex 50WX4) using a MeOH/H2O mixture (1:1) until neutral pH of the eluate. The resulting solution was treated with excess CsOH·H2O (50 mg, 0.3 mmol), concentrated to about 1 mL volume, and cooled. The precipitate was collected by filtration, washed with acetone, and dried. The crude off-white product was recrystallized (MeCN), giving 105 mg (75% yield) of 5[Cs] as a white microcrystalline solid: mp > 250 °C; 1H NMR (500 MHz, D2O) δ −0.2 to 0.8 (br m, 8H), 3.09 (br q, J = 150 Hz, 1H), 3.75 (s, 3H), 6.69 (d, J = 8.6 Hz, 2H), 7.89 (d, J = 8.2 Hz, 2H); 13C NMR (125 MHz, D2O) δ 55.2, 113.4, 135.9, 156.9; 11B NMR (160 MHz, D2O) δ −29.6 (d, J = 124 Hz, 4B), −28.1 (d, J = 123, 4B), −4.4 (d, J = 140 Hz, 1B), 12.4 (s, 1B). Anal. Calcd for C7H16B10Cs2O: C, 17.15; H, 3.29. Found: C, 17.21; H, 3.65. Single Crystal X-ray Crystallography. A colorless bipyramidshaped crystal was mounted on a CryoLoop (Hampton Research) with a dab of vacuum grease. Intensity data were collected at 100 K on a dual source Rigaku SuperNova diffractometer with a Dectris Pilatus3 R 200 K-A detector (Cu Kα radiation, λ = 1.54184 Å), equipped with an Oxford Cryosystems Ltd. nitrogen flow apparatus (Cryostream 800 Series). Data collection and data reduction were carried out with CrysAlisPro (version 1.171.38.46, Rigaku Oxford Diffraction, 2015). Empirical absorption correction using spherical harmonics, as implemented in SCALE3 ABSPACK, was applied. The structure was solved by direct methods and refined by least-squares against |F|2 using programs SHELXT46 and SHELXL,46 respectively, as implemented in the SHELX-2017 suite of programs (http://shelx.uni-ac.gwdg.de/ SHELX/). Non-hydrogen atoms were refined anisotropically. Hydrogen atoms were refined in geometrically idealized positions using a riding model. The structure was refined as a two-component inversion twin using TWIN/BASF commands in SHELXL. The Flack absolute structure parameter x47,48 refined to 0.190(14). The absolute structure parameter49 y was then calculated separately using the OLEX2 program,50 to give the value of 0.192(4), indicating that the absolute structure has been assigned correctly. The final refinement converged with R1 = 0.0138 (I > 2σ(I)), ωR2 = 0.0365 (all data). Maximum and minimum peaks of residual density were 0.23 and −0.31 e Å−3, respectively. The structure was prepared using OLEX2,50 PLATON,51 and WinGX programs.52

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b02477. Table of crystallographic data for 2[Pr4N] (PDF) Accession Codes

CCDC 1574613 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing data_ 14354

DOI: 10.1021/acs.inorgchem.7b02477 Inorg. Chem. 2017, 56, 14351−14356

Article

Inorganic Chemistry

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Piotr Kaszyński: 0000-0002-2325-8560 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the NCN (OPUS 2016/17/B/ ST5/02801), FNP (TEAM-3), FNP (TEAM/2016-3/24), and the NSF (XRD facility, CHE-1626549) grants.

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b02477 Inorg. Chem. 2017, 56, 14351−14356