Boron−Oxygen Bond Formation by Palladium-Catalyzed Etheration of

Jul 24, 2009 - ... M. V. Lomonosov Moscow State University, Leninskye Gory, 119992 ...... (f) Sasaki , T.; Guerrero , J. M.; Tour , J. M. Tetrahedron ...
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Organometallics 2009, 28, 4758–4763 DOI: 10.1021/om9001044

Boron-Oxygen Bond Formation by Palladium-Catalyzed Etheration of 2-Iodo-para-carborane Kuanysh Z. Kabytaev,†,§ Sergey N. Mukhin,†,§ Ivan V. Glukhov,‡ Zoya A. Starikova,‡ Vladimir I. Bregadze,*,‡ and Irina P. Beletskaya*,† †

Chemistry Department, M. V. Lomonosov Moscow State University, Leninskye Gory, 119992 Moscow, Russian Federation, and ‡A. N. Nesmeyanov Institute of Organoelement Compounds, 28 Vavilov Street, 119991 Moscow, Russian Federation. §These authors contributed equally to this work. Received February 11, 2009

For the first time, the palladium-catalyzed etheration of 2-iodo-p-carborane with phenolates and alkoxides has been demonstrated. The reactions of 2-iodo-1,12-dicarba-closo-dodecaborane (2-iodop-carborane) with sodium salts of phenol, p-cresol, R- and β-naphthol, 3-methyl-4-chlorophenol, and 3,4-dimethylphenol using the Pd(dba)2/BINAP (dba = dibenzylideneacetone; BINAP = rac-2,20 -bis(diphenylphosphino)-1,10 -binaphthyl) system in dioxane at 90 °C afforded the corresponding 2p-carboranyl aryl ethers in good to high yields. 2-Methoxy-p-carborane and 2-ethoxy-p-carborane have also been obtained in good yield. The structures of 2-(4-methylphenoxy)-p-carborane and 2-methoxyp-carborane have been established by X-ray diffraction studies. Introduction Polyhedral boron compounds and particularly icosahedral carboranes, being known for 45 years, still attract the attention of chemists working in different fields including medicine1 and materials science2 and also in the construction of molecular devices.3 One of the most important features of carboranes is their ability to undergo an electrophilic substitution, which allows considering them as nonplanar aromatic compounds. However, the mechanism of such reactions should be different from that for their arene counterparts. One of the most important reactions of this kind is electrophilic iodination *To whom correspondence should be addressed. E-mail: beletska@ elorg.chem.msu.ru (I.P.B.); [email protected] (V.I.B.). (1) (a) Soloway, A. H.; Tjarks, W.; Barnum, B. A.; Rong, F.-G.; Barth, R. F.; Codogni, I. M.; Wilson, J. G. Chem. Rev. 1998, 98, 1515. (b) Hawthorne, M. F.; Maderna, A. Chem. Rev. 1999, 99, 3421. (c) Valliant, J. F.; Guenther, K. J.; King, A. S.; Morel, P.; Schaffer, P.; Sogbein, O. O.; Stephenson, K. A. Coord. Chem. Rev. 2002, 232, 173. (d) Endo, Y.; Iijima, T.; Yamakoshi, Y.; Fukasawa, H.; Miyaura, C.; Inada, M.; Kubo, A.; Itai, A. Chem. Biol. 2001, 8, 341. (e) Bregadze, V. I.; Sivaev, I. B.; Glazun, S. A. Anti-Cancer Agents Med. Chem. 2006, 6, 75. (f) Yinghuai, Z.; Peng, A. T.; Carpenter, K.; Maguire, J. A.; Hosmane, N. S.; Takagaki, M. J. Am. Chem. Soc. 2005, 127, 9875. (2) (a) Yang, X.; Jiang, W.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc. 1992, 114, 9719. (b) Mueller, J.; Base, K.; Magnera, T. F.; Michl, J. J. Am. Chem. Soc. 1992, 114, 9721. (c) Schoberl, U.; Magnera, T. E.; Harrison, R. M.; Fleischer, F.; Pflug, J. L.; Schwab, P. F. H.; Meng, X.; Lipiak, D.; Noll, B. C.; Allured, V. S.; Rudalevige, T.; Lee, S.; Michl, J. J. Am. Chem. Soc. 1997, 119, 3907. (d) Schwab, P.; Levin, M. D.; Michl, J. Chem. Rev. 1999, 99, 1863. (e) Farha, O. K.; Spokoyny, A. M.; Mulfort, K. L.; Hawthorne, M. F.; Mirkin, C. A.; Hupp, J. T. J. Am. Chem. Soc. 2007, 129, 12680. (f ) Simon, Y. C.; Ohm, C.; Zimny, M. J.; Coughlin, E. B. Macromolecules 2007, 40, 5628. (3) (a) Tour, J. M. J. Org. Chem. 2007, 72, 7477. (b) Morin, J.-F.; Sasaki, T.; Shirai, Y.; Guerrero, J. M.; Tour, J. M. J. Org. Chem. 2007, 72, 9481. (c) Morin, J.-F.; Shirai, Y.; Tour, J. M. Org. Lett. 2006, 8, 1713. (d) Sasaki, T.; Tour, J. M. Tetrahedron Lett. 2007, 48, 5821. (e) Sasaki, T.; Tour, J. M. Org. Lett. 2008, 10, 897. (f) Sasaki, T.; Guerrero, J. M.; Tour, J. M. Tetrahedron 2008, 64, 8522. (g) Sasaki, T.; Morin, J.-F.; Lu, M.; Tour, J. M. Tetrahedron Lett. 2007, 48, 5817. pubs.acs.org/Organometallics

Published on Web 07/24/2009

leading to monosubstituted o-, m-, and p-carboranes.4,5 The forming B-I bond proved to be closer to aromatic Csp2-I (or to Csp2-Cl) than to the B-I bond in alkyl or aryl boron halides.6 However, this bond is significantly less reactive than the Csp2-I bond or even less reactive than Csp2-Cl, and its reactivity decreases in the series 2-iodo-p-carborane > 9-iodo-m-carborane > 9-iodo-o-carborane.6 A certain analogy between the B-I bond and sp2 C-Hal bonds promoted the development of Pd-catalyzed boroncarbon bond-forming reactions similarly to Kumada,4 Suzuki,7 Negishi,8 Sonogashira,5,8 and Heck9 reactions. Recently, we have successfully accomplished amination10 and amidation11 B-N bond-forming reactions of p- and m-iodo-carboranes with different amines (aliphatic, aromatic, and NH-heterocycles) and amides (aliphatic, lactams, (4) (a) Zakharkin, L. I.; Kalinin, V. N. Izv. Akad. Nauk SSSR, Ser. Khim. 1966, 575. (b) Seickhaus, J. F.; Semenuk, N. S.; Knowles, T. A.; Schroeder, H. Inorg. Chem. 1969, 8, 2452. (c) Zakharkin, L. I.; Kovredov, A. I.; Ol'shevskaya, V. A.; Shaugumbekova, Zh. S. J. Organomet. Chem. 1982, 226, 217. (5) Jiang, W.; Knobler, C. B.; Curtis, C. E.; Mortimer, M. D.; Hawthorne, M. F. Inorg. Chem. 1995, 36, 3491. (6) (a) Marshall, W. J.; Young, R. J., Jr.; Grushin, V. V. Organometallics 2001, 20, 523. (b) Vi~nas, C.; Barbera, G.; Oliva, J. M.; Teixidor, F.; Welch, A. J.; Rosair, G. M. Inorg. Chem., 2001, 40, 6555. (7) Eriksson, L.; Beletskaya, I. P.; Bregadze, V. I.; Sivaev, I. B.; Sjoberg, S. J. Organomet. Chem. 2002, 657, 267. (8) (a) Yang, X.; Jiang, W.; Knobler, C. B.; Mortimer, M. D.; Hawthorne, M. F. Inorg. Chim. Acta 1995, 240, 371. (b) Beletskaya, I. P.; Bregadze, V. I.; Ivushkin, V. A.; Petrovskii, P. V.; Sivaev, I. B.; Sj€oberg, S.; Zhigareva, G. G. J. Organomet. Chem. 2004, 689, 2920. (c) Beletskaya, I. P.; Bregadze, V. I.; Ivushkin, V. A.; Zhigareva, G. G.; Petrovskii, P. V.; Sivaev, I. B. Russ. J. Org. Chem. 2005, 41, 1359. (9) Eriksson, L.; Winberg, K.-J.; Claro, R. T.; Sjoberg, S. J. Org. Chem. 2003, 68, 3569. (10) Beletskaya, I. P.; Bregadze, V. I.; Kabytaev, K. Z.; Zhigareva, G. G.; Petrovskii, P. V.; Glukhov, I. V.; Starikova, Z. A. Organometallics 2007, 26, 2340. (11) Mukhin, S. N.; Kabytaev, K. Z.; Zhigareva, G. G.; Glukhov, I. V.; Starikova, Z. A.; Bregadze, V. I.; Beletskaya, I. P. Organometallics 2008, 27, 5937. r 2009 American Chemical Society

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Figure 1. General view of molecules of 4 (a) and 1 (b) in the crystal. Thermal ellipsoids are shown for p = 50%.

and aromatic) analogously to Buchwald-Hartwig amination12 and amidation13 of aryl iodides. During the course of our amination studies employing t-BuONa as a base, we have observed the formation of unusual 2-hydroxy-para-carborane along with the expected amination product.10 This compound was isolated and characterized by X-ray crystallography. We have shown that tert-butoxide was the source of a hydroxy group; however no formation of 2-hydroxy-p-carborane was observed in the presence of NaOH or KOH in aqueous or organic solvents.10 This result is somewhat contradictory to that obtained in aromatic substitution in the presence of a similar Pd catalyst,14 where only aryl-tert-butyl ether was obtained. It should be mentioned that the formation of phenols is a much more difficult task, which requires employment of sophisticated monodentate ligands.15 The direct Pd-catalyzed hydroxylation and etheration of iodo-carborane still needs to be explored due to the poor selectivity and low yields of the oxidation method (the only exception is exhaustive oxidative hydroxylation16). We suppose that formation of a hydroxy derivative employing t-BuONa as a hydroxy group source is the best available procedure thus far. On the basis of these observations, it was reasonable to propose the palladium-catalyzed etheration of iodo-carboranes with alkoxides and phenolates. Indeed, we have shown that 2-iodo-p-carborane can successfully be etherated by phenolates and alkoxides in the presence of the Pd(dba)2/ BINAP system.

Results and Discussion Using a similar catalytic system (Pd(dba)2/BINAP in dioxane at 90 °C) to that applied for amination and hydroxylation of 2-iodo-p-carborane,10 we examined the reaction (12) (a) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046. (b) Wolfe, J. P.; Wagaw, S.; Marcous, J.-F.; Buchwald, S. L. Acc. Chem. Res. 1998, 31, 805. (13) (a) Fujita, K.; Yamashita, M.; Puschmann, F.; Alvarez-Falcon, M. M.; Incarvito, C. D.; Hartwig, J. F. J. Am. Chem. Soc. 2006, 128, 9044. (b) Ikawa, T.; Barder, T. E.; Biscoe, M. R.; Buchwald, S. L. J. Am. Chem. Soc. 2007, 129, 13001. (14) Palucki, M.; Wolfe, J. P.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119, 3395. (15) Anderson, K. W.; Ikawa, T.; Tundel, R. E.; Buchwald, S. L. J. Am. Chem. Soc. 2006, 128, 10694. (16) Herzog, A.; Knobler, C. B.; Hawthorne, M. F. J. Am. Chem. Soc. 2001, 123, 12791.

Scheme 1. Etheration of 2-Iodo-p-carborane

in the presence of two alkoxides: MeONa and EtONa. In both reactions, only the product of alkoxylation was formed without any traces of hydroxylation product, as proved by 11B NMR studies. The structure of 2-MeO-p-carborane is shown in Figure 1. The reaction of 2-I-p-C2B10H11 with various phenols and naphthols except for β-naphthol under the same conditions proceeded very smoothly to give the products in good to high isolated yields. In the case of β-naphthol, the reaction was not completed within 3 days, but no byproduct was detected. The structure of 2-(4-methylphenoxy)-p-carborane is given in Figure 1. To validate our protocol, we have performed the test reaction in the absence of catalyst. No reaction occurred after 48 h of stirring, as confirmed by 11B NMR spectroscopy. It is known that palladium-catalyzed etheration of aryl halides by alcohols or phenols requires the application of electron-rich and bulky monodentate ligands,17 while in the case of 2-iodo-p-carborane, this process proceeds well with the same catalyst as that used in amination reaction. The amination of aryl halides in the presence of MeONa, i-PrONa, or t-BuONa employing the Pd/BINAP catalyst system gives the amination product only.18 Thus, apparently, there are some differences between palladium-catalyzed coupling reactions of 2-iodo-p-carborane and aryl halides. Unfortunately, the main obstacle for gaining insights into the catalytic cycle of cross-coupling processes with iodo-carborane is an impossibility to detect or isolate the intermediate oxidative addition step,6 which is well characterized for aryl halides. (17) (a) Parrish, C. A.; Buchwald, S. L. J. Org. Chem. 2001, 66, 2498. (b) Vorogushin, A. V.; Huang, X.; Buchwald, S. L. J. Am. Chem. Soc. 2005, 127, 8146. (c) Burgos, C. H.; Barder, T. E.; Huang, X.; Buchwald, S. L. Angew. Chem., Int. Ed. 2006, 45, 4321. (d) Schwarz, N.; Pews-Davtyan, A.; Alex, K.; Tillack, A.; Beller, M. Synthesis 2007, 23, 3722. (e) Mann, G.; Shelby, Q.; Roy, A. H.; Hartwig, J. F. Organometallics 2003, 22, 2775. (18) Prashad, M.; Hu, B.; Lu, Y.; Draper, R.; Har, D.; Repic, O.; Blacklock, T. J. J. Org. Chem. 2000, 65, 2612–2614.

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Scheme 2. Reaction of 2-Iodo-p-carborane with Phenols

Kabytaev et al. Table 2. Selected Bond Lengths (A˚) and Angles (deg) for Crystal Structures of 1 and 4

B(2)-C(1) B(2)-B(3) B(2)-B(6) B(2)-B(7) B(2)-B(11) B(2)-O(13) O(13)-C(14) B(2)-O(13)-C(14)

1

4

1.744(2) 1.804(2) 1.802(2) 1.780(2) 1.781(2) 1.3884(16) 1.4324(14) 119.76(10)

1.721(2) 1.798(2) 1.799(2) 1.784(2) 1.777(2) 1.4016(19) 1.3789(17) 127.42(11)

Table 1. Reaction of 2-Iodo-p-carborane with Phenolsa

Figure 2. Formation of puckered layers in 4 through C-H 3 3 3 π interactions.

a Reaction conditions: 0.37 mmol of 2-iodo-para-carborane and catalyst were added to 1.48 mmol of the corresponding phenol pretreated with 1.11 mmol of NaH in 3 mL of dioxane, 90 °C. b Yield determined by 11B NMR is 98%.

Of all dicarba-closo-dodecaborane isomers (p-, m-, and o-carboranes), only the 2-iodo derivative of p-carborane gives the coupling products with alcohols and phenols under the mentioned conditions. 9-Iodo-m-carborane is not reactive enough, though it can participate in amination19 and amidation11 reactions. It was found that 9-iodo-o-carborane quantitatively decomposes under basic conditions, forming nido-undecaborate.20 (19) Kabytaev, K. Z.; Bregadze, V. I.; Beletskaya, I. P. Unpublished results  br, B. J.; Waksman, L.; Sneddon, L. (20) Plesek, J.; Hermanek, S.; Stı´ G. Inorg. Synth. 1983, 22, 231.

It is known that reaction of aryl halides with alcohols or phenols can be effectively catalyzed by copper complexes and nanoparticles.21 However, all our attempts to perform the reaction of 2-iodo-p-carborane with t-BuONa in the presence of copper complexes were unsuccessful. It deserves mentioning that p-carborane derivatives substituted by one alkoxy or aryloxy group at the boron atom have not been known until now. Thus, only closo-2,3,4,5,6,7,8,9,10,11-decahydroxy-1,12-bis(sulfonic acid)-1,12-dicarbadodecaborane(12) was prepared by Hawthorne.16 Exhaustive methylation of this compound by methyl triflate furnished closo-B-decamethoxy-1,12-bis(methylsulfonate)p-carborane. Description of Structures. The structures of studied compounds, 2-methoxy-p-carborane (1) and 2-(4-methylphenoxy)-p-carborane (4), are shown in Figure 1. The selected bond lengths and angles are given in Table 2. From Table 2, it is apparent that, in general, the geometrical parameters of the studied molecules are quite similar. The main difference is the B(2)-C(1) bond length, which in 4 is 0.023 A˚ shorter than that in 1. As it is known from the literature for the carborane derivatives, containing atoms with electron lone pairs (LP) (oxygen, nitrogen, sulfur, etc.) bonded to carboranes, the electron back-donation of LP to the antibonding orbital of the bond of the icosahedron can occur.22 On the basis of the literature analysis of the studied (21) (a) Beletskaya, I. P.; Cheprakov, A. V. Coord. Chem. Rev. 2004, 248, 2337. (b) Hosseinzadeh, R.; Tajbakhsh, M.; Mohadjerani, M.; Alikarami, M. Synlett 2005, 7, 1101. (c) Kidwai, M.; Mishra, N. K.; Bansal, V.; Kumar, A.; Mozumdar, S. Tetrahedron Lett. 2007, 48, 8883. (22) Teixidor, F.; Flores, M. A.; Vi~ nas, C.; Sillanp€a€a, R.; Kivek€as, R. J. Am. Chem. Soc. 2000, 122, 1963.

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Figure 3. Formation of infinite chains in the crystal of 1. Table 3. Crystal Data and Structure Refinement for 1 and 4 1 formula mol wt cryst color, habit cryst size, mm cryst syst space group

4

C3H14B10O 174.24 Colorless, plate 0.13  0.11  0.08 monoclinic C 2/c

C9H18B10O 250.33 Colorless, block 0.17  0.13  0.11 monoclinic P 2(1)/n

a, A˚ b, A˚ c, A˚ R, deg β, deg γ, deg V, A˚3 Z Dcalcd, g cm-3 2θmax, deg abs coeff., μ(Mo KR), mm-1 no. reflns collected completeness no. indep reflns no. obsd reflns (I > 2σ(I)) no. of params R1 (on F for obsd reflns) wR2 (on F2 for all reflns)

26.432(5) 6.5980(17) 12.095(2) 90.00 108.445(7) 90.00 2001.0(7) 8 1.157 56 0.057 8250 0.998 2406 (Rint = 0.0322) 1561 172 0.0412 0.1127

7.0460(8) 10.8128(12) 18.763(2) 90.00 94.115(2) 90.00 1425.8(3) 4 1.166 58 0.060 15 385 0.999 3799 (Rint = 0.0453) 2679 226 0.0524 0.1159

Weighting Scheme

w-1=σ2(Fo2) + (aP)2 + bP, P = 1/3(Fo2 + 2Fc2)

a b F(000) GOOF largest diff peak and hole, e A˚-3

0.06 0 720 1.014 0.244 and -0.196

Cell Constants

compounds it is reasonable to propose that the antibonding orbital of the B(2)-C(1) bond should be involved in such interaction, for which the highest difference in bond length is observed.23 Thus, it is possible to suggest that the bond length variation is caused by the difference in the extent of the LP-carborane charge transfer. Analysis of the bond lengths also shows that variation of the bond lengths in the Bcarb-O-C fragment takes place, which can indicate that (23) Glukhov, I. V.; Lyssenko, K. A.; Korlyukov, A. A.; Antipin, M. Yu. Faraday Discuss. 2007, 135, 203.

0.02 1.0 520 0.998 0.349 and -0.225

the LP of oxygen atoms are involved in conjugation with the aromatic ring. It is clear from the values of the O(13)C(14) bond lengths that for 1 it is 0.053 A˚ longer than that in 4, while the B(2)-O(13) bond, in contrast, is shorter by 0.014 A˚. Thus, it is possible to conclude that the conjugation of oxygen LP with the aromatic ring leads to the decrease in the extent of the charge transfer to the antibonding orbital of the B(2)-C(1) bond. The crystal packings of two studied p-carboranes derivatives are different. Thus, in the crystal of 4 molecules form weak intermolecular C-H 3 3 3 π interactions by both C-H

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hydrogen atoms of the carborane moiety, which are more acidic than the B-H ones. This type of interaction for carboranes plays an important role in the formation of crystal structures, as described in a number of papers dedicated to the cocrystals of carboranes.24 Distances between the hydrogen atoms and centroids of the aromatic rings are equal to 2.489 and 2.514 A˚ for interactions formed by H(1) and H(12) atoms, respectively. The mentioned interactions lead to the formation of a sandwich-like structure (see Figure 2), in which a given carborane icosahedron is surrounded by two aromatic rings in a metallocene fashion. This results in the formation of puckered layers, which are interlinked by weak van der Waals interactions only. In the crystal of 1 molecules are held together by CH 3 3 3 O interactions of two types (see Figure 3): C(12)H(12) 3 3 3 O(13C) (H(12) and C(14)-H(14A) 3 3 3 O(13A). Geometrical parameters of the hydrogen bonds: C(12)H(12), H(12) 3 3 3 O(13C), and C(12) 3 3 3 O(13C) bond lengths are equal to 0.968, 2.551, and 3.276(2) A˚, respectively. The C(12)-H(12)-O(13C) angle is 132°. C(14)-H(14A), H(14A) 3 3 3 O(13A), and C(14) 3 3 3 O(13A) bond lengths are equal to 0.980, 2.659, and 3.475(2) A˚. The C(14)-H(14A)-O(13A) angle is 141°. These interactions are rather weak, but they lead to the formation of infinite chains parallel to b axis. These chains are interlinked by van der Waals interactions only.

Conclusion We have described an efficient method for introduction of an alkoxy or aryloxy group at a boron atom of p-carborane. Using the Pd(dba)2/BINAP system in dioxane at 90 °C, the etheration of 2-iodo-p-carborane at the boron atom with various O-nucleophiles (sodium salts of phenols, MeONa, and EtONa) was accomplished for the first time. Importantly, p-carboranes substituted by one alkoxy or aryloxy group at the boron atom have not been known until now.

Experimental Section General Comments. All reactions were performed under argon in oven-dried glassware. Flash chromatography was carried out on Merck silica gel 60 (4360 mesh), and Merck silica 60 F254 was used for thin-layer chromatography (TLC). Carborane spots were visualized on TLC by dipping in a 0.5% w/v PdCl2 in 10% concentrated HCl/MeOH solution followed by heating, which gave black spots on a yellow background. All starting phenols were recrystallized before use. Dioxane was dried over sodium benzophenone ketyl and distilled under argon prior to use. The 1H, 13C, and 11B NMR spectra were recorded on a Bruker AMX-400 spectrometer at 400, 100.61, and 128.3 MHz, respectively, from solutions in CDCl3; all shifts are given in units of ppm. The mass spectra were obtained on a Finnigan SSQ-7000 instrument. Elemental analyses were performed in the Microanalytical Laboratory of INEOS RAS, Moscow, Russia. General Experimental Procedures. A phenol was added (1.48 mmol) to a suspension of NaH (60% dispersion in mineral oil; 44.4 mg, 1.11 mmol) in dioxane (3 mL). The mixture was stirred at 90 °C for 30 min, and then 2-iodo-p-carborane (100 mg, 0.37 mmol), Pd(dba)2 (10.6 mg, 5.0%), and BINAP (11.6 mg, 5.0%) were added to the mixture. The stirring was continued at 90 °C for 24-72 h, depending on the phenol substrate. The reaction was monitored by TLC using petroleum ether as (24) Blanch, R. J.; Williams, M.; Fallon, G. D.; Gardiner, M. G.; Kaddour, R.; Raston, C. L. Angew. Chem., Int. Ed. Engl. 1997, 36, 504.

Kabytaev et al. eluent. The reaction was stopped after all 2-iodo-p-carborane was consumed. The resulting mixture was diluted with dichloromethane and filtered through a paper filter, and the solvent was carefully removed under vacuum. The crude product was purified by flash chromatography on silica gel using petroleum ether or chloroform as eluent (h=10 cm, i=2 cm). 2-Methoxy-1,12-dicarba-closo-dodecaborane (1). The mixture of MeONa (60 mg, 1.11 mmol), 2-iodo-p-carborane (100 mg, 0.37 mmol), Pd(dba)2 (10.6 mg, 5.0%), and BINAP (11.6 mg, 5.0%) was stirred for 72 h at 90 °C in dioxane and then worked up as stated in General Procedures. Yield: 63%; colorless oil crystallizes upon cooling. 11B NMR: -24.5 (d, 1B, J=169 Hz), -18.3 (d, 2B, J = 171 Hz), -17.4 (d, 2B, J = 128 Hz), -16.9 (d, 2B, J=172 Hz), -15.4 (d, 2B, J=155 Hz), 3.3 (s, 1B). 1H NMR: 0.9-3.1 (m, 9H, B-H), 2.64 (s, 1H, cage C-H), 3.04 (s, 1H, cage C-H), 3.58 (s, 3H, Me). Anal. Calcd for C3H14B10O: C, 20.68; H, 8.10. Found: C 20.59; H 8.21. 2-Ethoxy-1,12-dicarba-closo-dodecaborane (2). Ethanol was added by micropipet (35.5 μL, 28 mg, 0.6 mmol) to a suspension of NaH (60% dispersion in mineral oil; 24 mg, 0.6 mmol) in dioxane (1 mL). The mixture was stirred at 90 °C for 30 min, and then 2-iodo-p-carborane (54 mg, 0.2 mmol), Pd(dba)2 (6 mg, 5.0%), and BINAP (6 mg, 5.0%) were added to the mixture. The stirring was continued for 22 h at 90 °C in dioxane and then worked up as stated in General Procedures. Yield: 61%, colorless oil. 11B NMR: -24.3 (d, 1B, J = 167 Hz), -18.4 (d, 2B, J = 122 Hz), -16.9 (d, 2B, J = 140 Hz), -15.3 (d, 2B, J = 64 Hz), -14.7 (d, 2B, J = 184 Hz), 3.1 (s, 1B). 1H NMR: 1.0-3.0 (m, 9H, B-H), 1.29 (t, 3H, CH3, J=7.0 Hz), 2.67 (s,1H, cage C-H), 3.06 (s, 1H, cage C-H), 3.84 (q, 2H, CH2, J=7.0 Hz). 13C NMR: 17.1, 59.4, 64.9, 66.4. Anal. Calcd for C4H16B10O: C, 25.52; H, 8.57. Found: C, 25.69; H, 8.33. 2-(Phenoxy)-1,12-dicarba-closo-dodecaborane (3). Yield: 66%, colorless oil. 11B NMR: -23.7 (d, 1B, J=169 Hz), -18.0 (d, 2B, J = 170 Hz), -16.7 (d, 4B, J = 172 Hz), -14.8 (d, 2B, J = 175 Hz), 1.9 (s, 1B). 1H NMR: 1.4-3.3 (m, 9H, B-H), 2.73 (s, 1H, carborane cage C-H), 3.22 (s, 1H, carborane cage C-H), 7.097.11 (m, 3H, benzene ring), 7.34 (t, 2H, benzene ring, J = 7.9 Hz). 13 C NMR: 59.9, 64.8, 120.2, 123.0, 129.6, 157.4. Anal. Calcd for C8H16B10O: C, 40.66; H, 6.82; B, 45.75. Found: C, 41.03; H, 6.73; B, 45.73. MS: m/z 236 [M]þ. 2-(4-Methylphenoxy)-1,12-dicarba-closo-dodecaborane (4). Yield: 68%, colorless crystalline solid, mp 43-44 °C. 11B NMR: -23.8 (d, 1B, J=158 Hz), -18.0 (d, 2B, J=168 Hz), -16.7 (d, 4B, J= 171 Hz), -14.9 (d, 2B, J = 171 Hz), 2.0 (s, 1B). 1H NMR: 1.4-3.1 (m, 9H, B-H), 2.35 (s, 3H, Me group), 2.72 (s, 1H, carborane cage C-H), 3.21 (s, 1H, carborane cage C-H), 6.98 (d, 2H, benzene ring, J = 8.5 Hz), 7.13 (d, 2H, benzene ring, J = 8.5 Hz). 13C NMR: 20.7, 59.9, 64.7, 119.9, 130.0, 132.3, 155.3. Anal. Calcd for C9H18B10O: C, 43.18; H, 7.25; B, 43.18. Found: C, 42.99; H, 7.09; B, 43.28. 2-(3,4-Dimethylphenoxy)-1,12-dicarba-closo-dodecaborane (5). Yield 92%, white crystalline solid, mp 54 °C. 11B NMR: -23.9 (d, 1B, J = 171 Hz), -18.1 (d, 2B, J = 174 Hz), -16.8 (d, 4B, J = 171 Hz), -14.9 (d, 2B, J = 175 Hz), 2.0 (s, 1B). 1H NMR: 1.43.3 (m, 9H, B-H), 2.24 (s, 3H, Me), 2.26 (s, 3H, Me) 2.72 (s,1H, cage C-H), 3.20 (s, 1H, cage C-H), 6.81-6.85 (m, 2H, benzene ring), 7.07 (d, 1H, benzene ring, J = 8.0 Hz). 13C NMR: 19.0, 20.0, 59.8, 64.7, 117.2, 121.4, 130.4, 131.0, 137.9, 155.4. Anal. Calcd for C10H20B10O: C, 45.43; H, 7.63. Found: C, 45.59; H, 7.76. 2-(r-Naphthoxy)-1,12-dicarba-closo-dodecaborane (6). Yield: 85%, yellowish crystalline solid, mp 72-73 °C. 11B NMR: -23.7 (d, 1B, J = 166 Hz), -18.0 (d, 2B, J = 144 Hz), -16.7 (d, 4B, J=171 Hz), -14.8 (d, 2B, J=170 Hz), 2.2 (s, 1B). 1H NMR: 1.4-3.3 (m, 9H, B-H), 2.75 (s, 1H, cage C-H), 3.32 (s,1H, cage C-H), 7.28 (t, 1H, naphthoxy, J=3.5 Hz), 7.44 (t, 1H, naphthoxy, J=7.9 Hz), 7.50-7.54 (m, 2H, naphthoxy), 7.60 (d, 1H, naphthoxy, J = 8.2 Hz), 7.83-7.87 (m, 1H, naphthoxy), 8.10-8.16 (m, 1H, naphthoxy). 13C NMR: 60.0, 65.0, 114.3,

Article 122.2, 122.8, 125.6, 125.7, 125.8, 126.3, 127.6, 127.8, 134.9. Anal. Calcd for C12H18B10O: C, 50.33; H, 6.34; B, 37.75. Found: C, 50.54; H, 6.36; B, 37.40. 2-(β-Naphthoxy)-1,12-dicarba-closo-dodecaborane (7). Yield: 36%, colorless crystalline solid, mp 67-68 °C. 11B NMR: -23.6 (d, 1B, J = 161 Hz), -17.9 (d, 2B, J = 176 Hz), -16.7 (d, 4B, J=172 Hz), -14.8 (d, 2B, J = 165 Hz), 2.0 (s, 1B). 1H NMR: 1.4-3.3 (m, 9H, B-H), 2.75 (s, 1H, cage C-H), 3.27 (s, 1H, cage C-H), 7.26-7.29 (m, 1H, naphthoxy), 7.42 (t, 1H, naphthoxy, J=7.5 Hz), 7.46-7.50 (m, 2H, naphthoxy), 7.78-7.84 (m, 3H, naphthoxy). 13C NMR: 60.0, 64.8, 115.7, 121.4, 124.5, 126.3, 127.1, 127.7, 129.6, 130.1, 134.4, 155.2. Anal. Calcd for C12H18B10O: C, 50.33; H, 6.34; B, 37.75. Found: C, 50.29; H, 6.36; B, 37.60. 2-(3-Methyl-4-chlorophenoxy)-1,12-dicarba-closo-dodecaborane (8). Yield: 95%, colorless oil. 11B NMR: -23.7 (d, 1B, J= 160 Hz), -18.0 (d, 2B, J=145 Hz), -16.7 (d, 4B, J=151 Hz), -14.9 (d, 2B, J = 164 Hz), 1.8 (s, 1B). 1H NMR: 1.4-3.3 (m, 9H, B-H), 2.37 (s, 3H, Me), 2.74 (s, 1H, cage C-H), 3.20 (s, 1H, cage C-H), 6.86 (dd, 1H, benzene ring, J = 2.8 Hz and J = 8.8 Hz), 6.94 (d, 1H, benzene ring, J = 2.7 Hz), 7.27 (s, 1H, benzene ring). 13C NMR: 20.3, 60.0, 64.7, 118.8, 122.6, 128.2, 129.8, 137.3, 155.9. Anal. Calcd for C9H17B10OCl: C, 37.96; H, 6.02. Found: C, 37.80; H, 5.86. Control Experiment: Reaction of 2-Iodo-p-carborane with Sodium tert-Butoxide with No Catalyst. The mixture of t-BuONa (29 mg, 0.3 mmol) and 2-iodo-p-carborane (27 mg, 0.1 mmol) was stirred for 48 h at 100 °C in dioxane. The resulting mixture was diluted with diethyl ether and filtered through a paper filter, and then solvent was carefully removed under vacuum. The residue was dissolved in CDCl3 and analyzed by 11 B NMR spectroscopy. Only starting material was found. Attempt to Perform Copper-Catalyzed Reaction of 2-Iodo-pcarborane with tert-Butoxide. The mixture of t-BuONa (29 mg, 0.3 mmol), 2-iodo-p-carborane (27 mg, 0.1 mmol), CuI (2 mg, 10% mol), and phenanthroline (2 mg, 10% mol) or trans-1,2diaminocyclohexane (1.2 mg, 10% mol) was stirred for 24 h at 100 °C in dioxane. The resulting mixture was diluted with diethyl ether and filtered through a paper filter, and then solvent was carefully removed under vacuum. The residue was dissolved in CDCl3 and analyzed by 11B NMR spectroscopy. No new product was formed. Attempt to Perform Reaction of 9-Iodo-m-carborane with Phenol. Phenol was added (28 mg, 0.3 mmol) to a suspension of NaH (60% dispersion in mineral oil; 8 mg, 0.2 mmol) in dioxane (1 mL). The mixture was stirred at 90 °C for 20 min, and then 9-iodo-m-carborane (27 mg, 0.1 mmol), Pd(dba)2 (3 mg, 5.0%), and BINAP (3 mg, 5.0%) were added to the mixture. The stirring was continued at 90 °C for 48 h. The

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resulting mixture was diluted with chloroform and filtered through a paper filter, and then solvent was carefully removed under vacuum. The residue was dissolved in CDCl3 and analyzed by 11B NMR spectroscopy. No reaction product was observed. X-ray Crystal Structure Determination of Compounds 1 and 4. Crystals of 1 were obtained by cooling of 1 in liquid state (oil) to 4 °C. The crystals of 4 suitable for X-ray study were grown by diffusion of warm hexane into a hot chloroform solution. Single-crystal X-ray diffraction experiments for 1 and 4 were carried out with a Bruker SMART 1000 CCD area detector diffractometer, using graphite-monochromated Mo KR radiation (λ = 0.71073 A˚, ω-scans) at 120 K. The low temperature of the crystals was maintained with a Cryostream (Oxford Cryosystems) open-flow N2 gas cryostat. Reflection intensities were integrated using SAINT software25 and absorption correction was applied semi-empirically using SADABS program.26 The structures were solved by the direct method and refined by full-matrix least-squares against F2 in anisotropic (for nonhydrogen atoms) approximation. All carborane hydrogen atoms were located from difference Fourier syntheses; the H(C) atoms were placed in geometrically calculated positions. All calculations were performed on an IBM PC/AT using SHELXTL software.27 Crystallographic data and refinement parameters for compounds are presented in Table 3.

Acknowledgment. Financial support by the Russian Foundation for Basic Research and support of the President of the Russian Federation for leading schools (project NSh-3019.2008.3) are acknowledged. We thank Dr. Alexei D. Averin for acquiring NMR spectra. Supporting Information Available: Crystallographic data for structures 1 and 4 (atomic coordinates, bond lengths, bond angles, and thermal parameters). This material is available free of charge via the Internet at http://pubs.acs.org. These data have also been deposited at the Cambridge Crystallographic Data Centre (CCDC). Deposition numbers for the structures 1 and 4 are 712095 and 712094. These data can be obtained free of charge on application to the CCDC (e-mail deposit@ccdc. cam.ac.uk). (25) (a) SAINTPlus, Data Reduction and Correction Program, v. 6.01; Bruker AXS: Madison, WI, 1998. (b) SMART, Bruker Molecular Analysis Research Tool, v. 5.059; Bruker AXS: Madison, WI, 1998. (26) Sheldrick, G. M. SADABS, Bruker/Siemens Area Detector Absorption Correction Program, v.2.01; Bruker AXS: Madison, WI, 1998. (27) Sheldrick, G. M., SHELXTL-97, Version 5.10; Bruker AXS Inc.: Madison, WI, 1997.