Electrophilic Halogenation of closo-1, 2-C2B8H10

Article pubs.acs.org/IC

Electrophilic Halogenation of closo-1,2‑C2B8H10

Mario Bakardjiev,† Aleš Růzǐ čka,‡ Zdeňka Růzǐ čková,‡ Josef Holub,† Oleg L. Tok,† and Bohumil Štíbr*,† Institute of Inorganic Chemistry, Academy of Sciences of the Czech Republic, 250 68 Ř ež, Czech Republic Department of General and Inorganic Chemistry, Faculty of Chemical Technology, University of Pardubice, Studentská 573, 532 10 Pardubice, Czech Republic

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ABSTRACT: Initial studies on electrophilic halogenation of the dicarbaborane closo-1,2-C2B8H10 (1) have been carried out to reveal that the substitution takes place at B7 and B10 vertexes, which are the most removed from the CH positions. The course of the halogenation is strongly dependent on the nature of the halogenation agent and reaction conditions. Individual reactions led to the isolation of the monosubstituted compounds 1,2-C2B8H9-10-X (2) (where X = F, I) and 1,2-C2B8H9-7-X (3) (where X = Cl, I). Disubstituted carboranes 1,2C2B8H8-7,10-X2 (4) (where X = Cl, Br, I) were obtained under more forcing conditions. Individual halo derivatives were characterized by mass spectrometry and high-field NMR (11B, 1H,13C) spectroscopy combined with two-dimensional [11B−11B]COSY, 1H{11B(selective)}, and [11B−1H]-correlation NMR techniques. All of the derivatives bearing a halogen substituent in the B10 position exhibit a remarkable antipodal 13C and 1H NMR shielding at the CH1 vertex, increasing in the order H < I < Br < Cl < F. The structures of 1,2-C2B8H8-7,10-X2 derivatives (where X = Cl, I, 4b,d) were established by X-ray diffraction analyses.

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INTRODUCTION Halogenation reactions in the 10-vertex dicarbaborane series have so far been very scarce except for 1,6-C2B8H10, which produced solely 8-X derivatives (where X = Cl, Br, I) on electrophilic halogenation1 taking place at the negative Bpositions which are not adjacent to the cluster carbon atoms. The remaining C2B8H10 dicarbaboranes (1,2- and 1,10-isomers) have not yet been examined from the viewpoint of electrophilic B substitution, although a series of 1,10-C2B8H9-2-X derivatives (for X = Cl, Br, I) has been obtained on thermal rearrangement of the 1,6-C2B8H9-8-X compounds.1 In the much more explored o-carborane (1,2-C2B10H12) series, electrophilic substitution takes place in a similar manner. The electron-delocalized character of the o-carborane cage renders it, much like aromatic hydrocarbons, susceptible to attack by halogen electrophiles, and this and other properties have led to the development of useful routes to B-halogenated species.2 The typical channel of these reactions under milder reaction conditions is the formation of mono- and disubstituted species with halogen functions at the 9- and 9,12-positions antipodal to the C1,2 vertexes. Thus, reactions of Cl2 and Br2 with o-carborane, typically in the presence of AlCl3, afford 1,2C2B10H11-9-X and 1,2-C2B10H10-9,12-X2 derivatives. It should be noted that iodination proceeds much more slowly and requires elevated temperatures. However, a direct, straightforward approach that offers significant synthetic advantages utilizes the reaction of elemental I2 with 1,2-RC2B10H11 derivatives (R = H, Me, Ph) at 270 °C in sealed tubes without solvent. Under these conditions, even the corresponding 1RC2B10H7-8,9,10,12-I4 derivatives are obtained in high yield together with minor amounts of tri- and diiodo species.3,4 With halomethanes, the same substitution sequence is observed as with elemental halogens; for example, a quite convenient © XXXX American Chemical Society

method is refluxing o-carborane in CCl4 or over AlCl3 to give the 9,12-Cl2 derivative in high yield. In short, halogenation leads to substitution at negative B sites most removed from the positively charged carbon vertexes.2 In this work we are going to present initial studies on the halogenation of 1,2-C2B8H10 (1), which is a smaller analogue of o-carborane, never explored as a substrate for halogenation reactions. Full use of the recently published convenient synthesis of this basic carborane5 will be made together with discussion on some interesting NMR and structural aspects of this new chemistry.

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RESULTS AND DISCUSSION Syntheses. Halogenation reactions of the parent carborane 1 examined in this work are outlined in Scheme 1. Attempts at monosubstitution have led to the formation of either C2B8H810-X (2) (where X = F, I, path A) or 1,2-C2B8H8-7-X (3) (where X = Cl, I, path B) compounds. Thus, interaction between 1 and SbF5 in refluxing hexane, a modification of the fluorination procedure applied to o-carborane,6 afforded C2B8H8-10-F (2a) as the sole product. A long-term (72 h), room-temperature, AlCl3-catalyzed chlorination with CCl4 led to the isolation of a single product, which was identified by NMR as the monosubstituted 1,2-C2B8H8-7-Cl (3b) (path B). On the other hand, room-temperature bromination of 1 with elemental Br2/AlCl3 in CS2 did not lead to specific formation of the monosubstituted product but only to dibromination. An inseparable 3:1 mixture of monoiodinated derivatives 1,2C2B8H8-10-I (2d) and 1,2-C2B8H9-7-I (3d) has been obtained from direct AlCl3-promoted iodination of 1 by elemental iodine Received: March 14, 2017

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DOI: 10.1021/acs.inorgchem.7b00627 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Scheme 1. Mono- and Dihalogenation Reactions of closo-1,2C2B8H10 (1)

Figure 2. ORTEP view at the 50% probability level of closo-1,2C2B8H8-7,10-I2 (4d). Selected bond lengths (Å); and angles (deg): C1−C2 1.531(4), C1−B3 1.606(4), C1−B4 1.605(4), C2−B3 1.785(4), B3−B4 1.858(4), C2−B6 1.719(3), B3−B6 1.825(4), B4− B7 1.816(4), B6−B10 1.693(3), B7−I1 2.167(2), B10−I2 2.136(2); C2−C1−B3 69.33(17), C2−C1−B4 105.66(18), B3−C1−B4 70.69(17), B3−C1−B5 110.41(19), B4−B3−B6 102.09(17), B6− B3−B7 61.36(14), B6−B9−B8 90.43(15), B6−B9−B10 57.14(13), B6−B10−B9 65.88(15), B6−B10−B8 101.12(17).

in refluxing benzene (paths A + B). It is not recommended to separate the 2d + 3d mixture by LC chromatography, because of apparent activation of B positions in the cage of 1 to hydrolysis and B degradation on the silica gel support. Nevertheless, the NMR data for individual compounds 2d or 3d could be reliably estimated from the spectrum of the corresponding mixture. Disubstituted derivatives 1,2-C2B8H8-7,10-X2 (for X = Cl, Br, 4b,c) (yields 87 and 78%, path C of Scheme 1) were isolated by similar halogenation procedures at reflux temperatures or via heating in a Pyrex tube at 80 °C. The diiodo derivative 1,2C2B8H8-7,10-I2 (4d) was formed in 90% yield as a single product on treatment of 1 with ICl in refluxing CH2Cl2 in the presence of a catalytic amount of AlCl3. Structural Studies. The structures of the dihalo derivatives 4b,d were established unambiguously by X-ray diffraction analyses, as shown in Figures 1 and 2. Along with the recently

published5 structure for 1-Ph-closo-1,2-C2B8H9, these are two more crystallographic studies reported for the closo-1,2dicarbaborane series. As previously confirmed also in the electron diffraction study on 1,7 the carborane cage in 4b,d approximates the expected bicapped Archimedean antiprismatic geometry with two adjacent carbon vertexes in the apical and equatorial sites. In effect, the carbon atoms are compressed toward the center of the cluster relative to the positions they would have in a regular bicapped square antiprism. The two Cl and I substituents are situated in cage positions B7 and B10, as anticipated from NMR measurements. The C1−C2 distance approaches that found for the 1-Ph-1,2-derivative,5 and the C2−C1−B3 angle at 69.33(17)° is larger than those found for structurally established derivatives of 1,2-C2B10H12 with pentacoordinate carbon apexes.2 NMR Spectroscopy. The structures of all the halo derivatives of 1 isolated in this work are in agreement with the results of multinuclear 11B, 1H, and 13C NMR measurements. [11B−11B]-COSY,8 [11B−1H]-correlation, and 1H{11B(selective)}9 NMR experiments led in most cases to complete 1 H assignments for individual cage BH vertexes. Surveys of the 11 B NMR spectra for the 10-X and 7-X halogenated compounds of structures 2−4 are given in Figures 3 and 4. It is clearly seen that the spectra of the Cs-symmetry 10-X derivatives 2 display a set of 1:2:(2 + 2) doublets together with one low-field B10 singlet, while all other compounds bearing the 7-X functionality (asymmetrical structures 3 and 4) exhibit eight different resonances, of which one or two are singlets, as expected. The 1H and 13C NMR spectra (see Figures 5 and 6) exhibit two distinct CH1 and CH2 singlet resonances, of which namely the 13C signal associated with C1 shows a broad variation (range of Δδ(13C1) = −1.9 to −13.8 ppm) due to the strong antipodal (A)10 shielding by the 10-X substituent, as shown in Figure 5. There is a downward trend for an increase in the remote-controlled 13C A shielding by X in the series I < Br < Cl < F, which is consistent with the increasing ability of the X substituent to donate nonbonding electrons to C1 in the cage of 1. It should also be noted that the contribution of the γ effect of either 7-X or 10-X substituents to the 13C shift at both C vertexes is smaller.

Figure 1. ORTEP view at the 30% probability level of closo-1,2C2B8H8-7,10-Cl2 (4b). Selected bond lengths (Å) and angles (deg): C1−C2 1.504(18), C1−B3 1.61(2), C1−B4 1.59(2), C2−B3 1.775(18), B3−B4 1.87(3), C2−B6 1.700(16), B3−B6 1.84(2), B4− B7 1.84(2), B6−B10 1.667(14), B7−Cl1 1.802(11), B10−Cl2 1.783(10); C2−C1−B3 69.3(10), C2−C1−B4 106.0(10), B3−C1− B4 71.6(10), B3−C1−B5 112.7(10), B4−B3−B6 99.8(9), B6−B3−B7 60.1(7), B6−B9−B8 90.3(7), B6−B9−B10 56.6(6), B6−B10−B9 65.7(7), B6−B10−B8 102.7(8). B

DOI: 10.1021/acs.inorgchem.7b00627 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 5. Graphical intercomparison of the 13C NMR chemical shifts and (Δδ) for compounds of structures 2−4 in cluster positions CH1 and CH2 (for numbering see Scheme 1). The figure demonstrates trends for a strong antipodal 13C shielding at the CH1 site due to the presence of 10-X substituents.

Figure 3. Graphical intercomparison of the 11B NMR chemical shifts (given as δ(11B) (Δδ))/1JBH in Hz)/δ(1H)cageBH) and relative intensities for monosubstituted compounds of structures 2 and 3 in individual cluster positions (for numbering see Scheme 1). Singlets of the substituted vertexes are shown in red; other signals (in black) are doublets. Assignments were made by [11B−11B]-COSY, 1H{11B(selective)}, and [11B−1H]-correlation measurements.

Figure 6. Graphical intercomparison of the 1H NMR chemical shifts and relative intensities for compounds of structures 2−4 in individual cluster positions CH1 and CH2 (for numbering see Scheme 1). The figure demonstrates similar trends for antipodal 1H shielding at the H1 site due to the presence of 10-X substituents.

Figure 4. Graphical intercomparison of the 11B NMR chemical shifts (given as δ(11B) (Δδ))/1JBH in Hz)/δ(1H)cageBH) and relative intensities for disubstituted compounds of structure 4 in individual cluster positions (for numbering see Scheme 1). Singlets of the substituted vertexes are shown in red; other signals (in black) are doublets. Assignments were made by [11B−11B]-COSY, 1H{11B(selective)}, and [11B−1H]-correlation measurements.

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CONCLUSIONS Even closo-1,2-C2B8H10 (1), a smaller analogue of the popular o-carborane, undergoes electrophilic halogenation at boron vertexes most remote from both carbon vertexes with a maximum number of two substituents under the relatively mild conditions employed. However, in comparison to the isoelectronic [1-CB9H10]− 11,12 and 1-SB9H913 compounds, carborane 1 seems to be less reactive, most likely due to the presence of two positively charged carbon vertexes.2 The B7 and B10 positions, being most removed from the carbon vertexes, are preferred for electrophilic attack, perhaps unlike the aforementioned monoheteroborane compounds, in which the lower-belt B6 position is typically activated in the first step of a similar substitution. The positioning of at least one halogen substituent on the B10 atom in the isolated halo derivatives of 1 has created a good setting for demonstrating the remote-

As shown in Figure 6, there is a similar trend for increasing A shielding by X in the series H < I < Br < Cl in the 1H NMR spectra as well. The effect is not as pronounced as that in the corresponding 13C spectra, as it is transmitted through one more bond (C−H). Nevertheless, this observation is consistent with the increasing ability of the 10-X substituent to donate nonbonding electrons to CH1 in the cage of 1 as well. Here again, the contribution of the 7-X substitution in compounds 3b,d to the γ-shielding in CH1 and CH2 vertexes is less marked; the combined contribution of the γ effect of both X substituents in the disubstituted compounds 4 to the 1H shift at the CH vertexes is also smaller, as expected. C

DOI: 10.1021/acs.inorgchem.7b00627 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry controlled 13C antipodal (A) NMR shift for a series of halogens residing on the B vertex opposite to the carbon apex. Due to the remarkable sensitivity of the 13C nucleus to electronic changes, this A effect was found to be considerably strong, confirming the electron donation ability of individual halogens into the cluster, decreasing in the series F > Cl > Br > I, as expected. Moreover, it is evident that compounds isolated in this study can be employed as starting materials marked with a halogen label for various substitution reactions, for example alkylation and metal incorporation, which may perhaps help refresh interest in this scarcely investigated area of 10-vertex boron cluster chemistry.

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EXPERIMENTAL SECTION

Materials and Methods. All reactions were carried out under an argon atmosphere. Dichloromethane and hexane were dried over CaH2 and freshly distilled before use. Other conventional chemicals were of reagent or analytical grade and were used as purchased. Mass spectra were recorded in the M+ mode. NMR spectroscopy was performed at 400 and 600 MMz (for 1H), inclusive of standard [11B−11B]-COSY8 (all theoretical cross peaks were observed) and 1 H{11B(selective)}9 NMR experiments, leading to complete assignments of all resonances to individual cage BH units. Chemical shifts are given in ppm to high frequency (low field) of Ξ = 32.083971 MHz (nominally F3B·OEt2 in CDCl3) for 11B (quoted ±0.5 ppm), Ξ = 25.144 MHz for 13C (quoted ±0.5 ppm), and Ξ = 100 MHz for 1H (quoted ±0.05 ppm), Ξ is defined as in ref 14, and the solvent resonances were used as internal secondary standards. The starting carborane 1 has been prepared according to the recently reported method.5 closo-1,2-C2B8H9-10-F (2a). To a mixture of 435 mg (2 mmol) of SbF5 and hexane (5 mL) was added 121 mg (1 mmol) of carborane 1 in small portions with stirring and cooling to 0 °C. When the addition of the reagent was complete, the reaction mixture was heated at reflux for 4 h. The mixture was then treated with water (10 mL) with shaking. The organic layer was then dried over CaCl2, evaporated, and subjected to LC chromatograhy on a silica gel support using 10% CH2Cl2 in hexane as the mobile phase (observed partial decomposition during the elution). The fraction of Rf ≈ 0.25 identified by NMR as 2a was evaporated and vacuum-sublimed to give 23 mg (16%) of the product. For NMR data, see Figures 3, 5, and 6. For 2a: EIMS m/z (max) calcd 139, found 139. Anal. Calcd for FC2B8H9 (mol wt 138.57): C, 17.33; H, 8.62. Found: C, 17.01; H, 8.50. closo-1,2-C2B8H9-7-Cl (3b). A solution of carborane 1 (150 mg, 1.24 mmol) in CCl4 (10 mL) was treated with anhydrous AlCl3 (∼10 mg), and the mixture was stirred for 120 h at room temperature. After this time, monitoring by 11B NMR indicated the formation of 3b as a sole product. The CCl4 was evaporated, and the residual solids were extracted with hexane. The extract was evaporated to dryness and subjected to vacuum sublimation at ∼100 °C (bath) to isolate 175 mg (91%) of 3b. For NMR data, see Figures 3, 5, and 6. For 3b: EIMS m/ z (max) calcd 155, found 155. Anal. Calcd for ClC2B8H9 (mol wt 155.03): C, 15.49; H, 5.85. Found: C, 15.27; H, 5.71. closo-1,2-C2B8H8-7,10-Cl2 (4b). A solution of carborane 1 (121 mg, 1.0 mmol) in CCl4 (10 mL) was treated with anhydrous AlCl3 (∼10 mg), and the mixture was heated at 85 °C in a Pyrex tube equipped with a Teflon stopper for 72 h. The CCl4 was then evaporated, and the residual solids were extracted with hexane. The extract was evaporated to dryness and subjected to vacuum sublimation at ∼110 °C (bath) to isolate 165 mg (87%) of 4b as a white, crystalline compound. For NMR data, see Figures 4−7. For 4b: EIMS m/z (max) calcd 189, found 189. Anal. Calcd for Cl2C2B8H8 (mol wt 189.48): C, 12.68; H, 4.26. Found: C, 12.10; H, 4.20. closo-1,2-C2B8H8-7,10-Br2 (4c). A solution of carborane 1 (121 mg, 1.0 mmol) in CS2 (10 mL) was treated with anhydrous AlCl3 (∼10 mg), and a solution of Br2 (384 mg, 2.4 mmol) in CS2 (15 mL) was added. After it was stirred for 1 h at ambient temperature the mixture was heated at 85 °C in a Pyrex tube equipped with a Teflon

Figure 7. Examples of authentic NMR spectra of closo-1,2-C2B8H87,10-Cl2 (4b): (a) 400 MHz 1H NMR spectrum; (b) 150.91 MHz 13C NMR spectrum; (c) 128.3 MHz 11B NMR spectrum; (d) 128.3 MHz 11 1 B{ H} NMR spectrum. stopper for 24 h. The volatiles were then evaporated, and the residual solids were extracted with hexane. The extract was evaporated to dryness and subjected to vacuum sublimation at ∼110 °C (bath) to isolate 217 mg (78%) of 4b as a white, crystalline compound. For NMR data, see Figures 4−6. For 4b: EIMS m/z (max) calcd 279, found 279. Anal. Calcd for Br2C2B8H8 (mol wt 278.38): C, 8.63; H, 2.90. Found: C, 8.54; H, 2.81. closo-1,2-C2B8H9-10-I (2d) and closo-1,2-C2B8H9-7-I (3d). A solution of carborane 1 (121 mg, 1.0 mmol) in benzene (10 mL) was treated with anhydrous AlCl3 (∼10 mg) and elemental I2 (280 mg, 1.1 mmol) and heated at reflux for 72 h. After the mixture was cooled to room temperature, a saturated aqueous solution of sodium thiosulfate (10 mL) was added to remove residual halogen and aluminum trichloride. The aqueous layer was separated and washed with diethyl ether (3 × 5 mL), the washings being added to the organic layer. The combined organics were dried over anhydrous magnesium sulfate. Removal of solvent in vacuo afforded a mixture of 2d and 3d (200 mg, total yield 81%). For NMR data, see Figure 4. For 2d + 3d: EIMS m/z (max) calcd 247, found 247. Anal. Calcd for IC2B8H9 (mol wt 246.48): C, 9.75; H, 3.68. Found: C, 9.69; H, 3.49. closo-1,2-C2B8H8-7,10-I2 (4d). To ca. 10 mL of dichloromethane were added 1 (133 mg, 1.1 mmol), iodine monochloride (360 mg. 2.2 mmol), and aluminum trichloride (30 mg, 0.22 mmol). The reaction mixture was refluxed for 24 h with stirring. The mixture was then worked up as in the preceding experiment to afford 356 mg (87%) of 4d, which was recrystallized from boiling hexane. For NMR data, see Figure 5. For 4d: EIMS m/z (max) calcd 373, found 372. Anal. Calcd for I2C2B8H8 (mol wt 372.38): C, 6.45; H, 2.17. Found: C, 6.41; H, 2.09. X-ray Crystallography. The X-ray data for the dichloro derivative 4b (off-color crystals by slow evaporation of a hexane solution) were obtained at 150 K using an Oxford Cryostream low-temperature device and a Nonius KappaCCD diffractometer with Mo Kα radiation (λ = 0.71073 Å), a graphite monochromator, and the ϕ and χ scan mode. Data reductions were performed with DENZO-SMN.15 The absorption was corrected by integration methods.16 Structures were solved by direct methods (Sir92)17 and refined by full-matrix least squares based on F2 (SHELXL97).18 Full sets of diffraction data for diiodo derivative 4d (off-color crystals by slow evaporation of a hexane solution) were collected at 150(2) K with a Bruker D8-Venture diffractometer equipped with Cu radiation (Cu Kα; λ = 1.54178 Å) or Mo radiation (Mo Kα; λ = 0.71073 Å) microfocus X-ray (IμS) sources, a Photon CMOS detector, and Oxford Cryosystem cooling device for data collection. The frames were integrated with the Bruker SAINT software package using a narrow-frame algorithm. Data were corrected for absorption effects using the multiscan method D

DOI: 10.1021/acs.inorgchem.7b00627 Inorg. Chem. XXXX, XXX, XXX−XXX

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(6) Lebedev, V. N.; Balagurova, E. V.; Polyakov, A. V.; Yanovski, A. I.; Struchkov, Yu.; Zakharkin, L. I. Selective Fluorination of o- and mcarboranes. Synthesis of 9-Monofluoro-, 9,12-Difluoro-1,8,9,12-Trifluoro-, and 8,9,10,12-Tetrafluoro-o-carboranes and 9-Monofluoro-, and 9,10-Difluoro-m-carboranes. Molecular Struc-ture of 8,9,10,12Tetrafluoro-o-carborane. J. Organomet. Chem. 1990, 385, 307−318. (7) Hnyk, D.; Rankin, D. W. H.; Robertson, H. E.; Hofmann, M.; Schleyer, P.v.R. Molecular Structure of 1,2-Dicarba-closo-decaborane(10) as Studied by the Concerted Use of Electron Diffraction and Ab Initio Calculations. Inorg. Chem. 1994, 33, 4781−4786. (8) Venable, T. L.; Hutton, W. C.; Grimes, R. N. Two-Dimensional Boron-11-Boron-11 Nuclear Magnetic Resonance Spectroscopy as a Probe of Polyhedral Structure: Application to Boron Hydrides, Carboranes, Metallaboranes, and Metallacarboranes. J. Am. Chem. Soc. 1984, 106, 29−37. (9) Fontaine, X. L. R.; Kennedy, J. D. Identification of the endo,exo Isomer of 6,9-(PMe2Ph)2-arachno-B10H12 by Nuclear Magnetic Resonance Spectroscopy. J. Chem. Soc., Dalton Trans. 1987, 1573− 1575. (10) Heřmánek, S. Boron-11 NMR Spectra of Boranes, Main-Group Heteroboranes, and Substituted Derivatives. Factors Influencing Chemical Shifts of Skeletal Atoms. Chem. Rev. 1992, 92, 325−362 and references therein.. (11) Ivanov, S. V.; Rockwell, J. J.; Miller, S. M.; Anderson, O. P.; Solntsev, K. A.; Strauss, S. H. Reactions of CB9H10− with Electrophiles, Including the Regioselective Mono- and Dihalogenation of the Lower Belt. Inorg. Chem. 1996, 35, 7882−7891. (12) Ivanov, S. V.; Lupinetti, A. J.; Solntsev, K. A.; Strauss, S. H. Fluorination of Deltahedral closo-Borane and Carborane Anions with N-fluoro Reagents. J. Fluorine Chem. 1998, 89, 65−72. (13) Smith, W. L.; Meneghelli, B. J.; Thompson, D. A.; Klymko, P.; McClure, N.; Bower, M.; Rudolph, R. W. Directive Effects in The Electrophilic Substitution of Deltahedral Boranes and Heteroboranes. Deuteration and Halogenation of 1-Thiadecaborane(9) and Thiadodecaborane(11). Inorg. Chem. 1977, 16, 3008−3012. (14) Mc Farlane, W. A 13C and 31P Magnetic Double Resonance Study of Organo-Phosphorus Compounds. Proc. R. Soc. London Ser. A 1968, 306, 175−199. (15) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data Collected in Oscillation Mode. Methods Enzymol. 1997, 276, 307−326. (16) Coppens, P. In Crystallographic Computing; Ahmed, F. R., Hall, S. R., Huber, C. P., Eds.; Munksgaard: Copenhagen, 1970; pp 255− 270. (17) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A. Completion and Refinement of Crystal Structures with SIR92. J. Appl. Crystallogr. 1993, 26, 343−350. (18) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. Adv. 2015, 71, 3−8.

(SADABS). Obtained data were treated with XT-version 2014/5 and SHELXL-2014/7 software implemented in the APEX3 v2016.5-0 (Bruker AXS) system.18 Hydrogen atoms were mostly localized on a difference Fourier map; however, to ensure uniformity of treatment of the crystal, all hydrogens were recalculated into idealized positions (riding model) and assigned temperature factors Uiso (H) = 1.2Ueq(pivot atom) or 1.5Ueq(methyl). H atoms in carborane cages were placed with C−H and B−H distances of 1.1 Å. Crystallographic data for 4b: C2H8B8Cl2, Mr = 189.46, orthorhombic, P212121, a = 6.7760(2) Å, b = 11.2621(5) Å, c = 12.2790(5) Å, β = 90°, Z = 4, V = 937.04(6) Å3, Dc = 1.343 g cm−3, μ = 0.613 mm−1, Tmin/Tmax = 0.876/ 0.911; −8 ≤ h ≤ 7, −14 ≤ k ≤ 14, −15 ≤ l ≤ 14; 7492 reflections measured (θmax = 27.5°), 2112 independent (Rint = 0.0411), 1715 with I > 2σ(I), 109 parameters, S = 1.058, R1(obsd data) = 0.1071, wR2(all data) = 0.2690; max, min residual electron density 1.561, −0.515 e Å−3. Crystallographic data for 4d: C2H8B8I2, Mr = 372.36, monoclinic, P21/c, a = 6.730(2) Å, b = 12.763(3) Å, c = 12.528(3) Å, β = 94.78(3)°, Z = 4, V = 1072.4(5) Å3, Dc = 2.306 g cm−3, μ = 5.797 mm−1, Tmin/Tmax = 0.5263/0.7460; −9 ≤ h ≤ 9, −17 ≤ k ≤ 17, −15 ≤ l ≤ 17; 29099 reflections measured (θmax = 30.06°), 3113 independent (Rint = 0.0308), 2838 with I > 2σ(I), 109 parameters, S = 1.147, R1(obsd data) = 0.0234, wR2(all data) = 0.0536; max, min residual electron density 0.556, −1.441 e Å−3. Crystallographic data for structural analyses have been deposited with the Cambridge Crystallographic Data Centre, CCDC deposition no. 1511525 for 4b and 1536096 for 4d.

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ASSOCIATED CONTENT

Accession Codes

CCDC 1511525 and 1536096 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, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for B.S.: [email protected]. ORCID

Bohumil Štíbr: 0000-0003-4010-4106 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was supported by the Grant Agency of the Czech Republic (project no. 16-01618S).

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REFERENCES

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DOI: 10.1021/acs.inorgchem.7b00627 Inorg. Chem. XXXX, XXX, XXX−XXX