C−H Bond Activation of Arenes by - American Chemical Society

Jul 14, 2010 - Vladimir I. Bregadze, Irina D. Kosenko, Irina A. Lobanova, Zoya A. Starikova, ... Compounds, Russian Academy of Sciences, Vavilov Stree...
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5366

Organometallics 2010, 29, 5366–5372 DOI: 10.1021/om100385m

C-H Bond Activation of Arenes by [8,80 -μ-I-3,30 -Co(1,2-C2B9H10)2] in the Presence of Sterically Hindered Lewis Bases† Vladimir I. Bregadze, Irina D. Kosenko, Irina A. Lobanova, Zoya A. Starikova, Ivan A. Godovikov, and Igor B. Sivaev* A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Street 28, 119991, Moscow, Russian Federation Received April 30, 2010

Reactions of the iodonium derivative of cobalt bis(dicarbollide) anion [μ-8,80 -I-3,30 -Co(1,2C2B9H10)2] with Lewis bases in aromatic solvents were studied. The reactions proceed through the iodonium bridge opening, and the structure of the reaction products depends strongly on the nature of the Lewis base and solvent used. The reactions with conventional Lewis bases (L) give the corresponding products of Lewis base addition, [8-L-80 -I-3,30 -Co(1,2-C2B9H10)2], whereas the reactions with sterically hindered Lewis bases (L*) result in activation of the C-H bond of the aromatic solvent with formation of the corresponding aryl derivatives [8-Ar-80 -I-3,30 -Co(1,2-C2B9H10)2]-. Activated arenes, such as toluene, could react with [μ-8,80 -I-3,30 -Co(1,2-C2B9H10)2] without Lewis bases, whereas strongly deactivated arenes do not give C-H activation products even in the presence of sterically hindered Lewis bases.

Introduction The boron-based Lewis acids BX3 (X= F, Cl, Br) and B(C6F5)3 are popular tools in modern organic synthesis.1 The electrophilicity of the classical boron Lewis reagents is rather strong but limited. This is exemplified by the lack of reaction with arenes by an electrophilic aromatic substitution mechanism. Increasing the cationic character by removing the halide or its replacement by a stabilizing R3N group enhances the electrophilic reactivity at boron.2 Boron cations can be classified into three structural classes based on the coordination number at boron. Borinium cations R2Bþ are two-coordinate and typically are ligated by bulky, strongly π-donating substituents that effectively shield the boron cation from the solvent and anion. Borenium cations LR2Bþ are three-coordinate species that comprise two σbound substituents (R) and one dative interaction with a ligand (L) that serves to occupy a third coordination site as well as to reduce some of the electron deficiency at boron. The third, and the most common, class of boron cations is that of the tetrahedral, four-coordinate boronium cations L2R2Bþ, with two coordination sites occupied by σ-bound substituents and the other two populated by neutral donor ligands. Borenium cations with weakly stabilizing substituents can be classified as superelectrophiles, combining a

monocationic charge with an unoccupied p orbital.3 The unfilled p orbitals of the boron atom in borinium cations can become partially occupied as a result of π-donation from covalently bound substituents, analogous to the isoelectronic allenes. Bidentate ligation of boron generates a “chelate-restrained” borinium cation in which electrophilicity is enhanced by the nonlinear geometry at boron, resulting in an empty boron p orbital that cannot be stabilized by ligand π-donation.4 In the chemistry of polyhedral boron hydrides, boroncentered cations were postulated to be key intermediates of an electrophile-induced nucleophilic substitution mechanism that is responsible for formation of a variety of boron-substituted derivatives. 5 Boron-centered cations can be easily generated by abstraction of a hydride by treatment with Lewis or Br€ onsted acids. Similar to the chelaterestrained borinium cations, these species have an unstabilized p orbital and are strong electrophiles. It was shown recently that chelate-restrained borinium cations are able to activate C-H bonds of arenes with formation of arylboron derivatives.4 In this contribution we describe reactions of arenes with a quasi-borinium cation generated from the iodonium derivative of cobalt bis(dicarbollide), [μ-8,80 -I-3,30 -Co(1,2-C2B9H10)2], by the treatment with sterically hindered Lewis bases.

Results and Discussion †

Part of the Dietmar Seyferth Festschrift. *To whom correspondence should be addressed. E-mail: sivaev@ ineos.ac.ru. (1) (a) Ishihara, K. In Lewis Acids in Organic Synthesis; Yamamoto, H., Ed.; Wiley-VCH: Weinheim, Germany, 2000; pp 89-133. (b) Erker, G. Dalton Trans. 2005, 1883. (2) (a) K€ olle, P.; N€ oth, H. Chem. Rev. 1985, 85, 399. (b) Piers, W.; Bourke, S. C.; Conroy, K. D. Angew. Chem., Int. Ed. 2005, 44, 5016. (3) Olah, G. A.; Klump, D. A. Superelectrophiles and Their Chemistry; Wiley: New York, 2008. pubs.acs.org/Organometallics

Published on Web 07/14/2010

Conditions and selectivity of formation of quasi-borinium cations through abstraction of hydride strongly depend on (4) Del Grosso, A.; Pritchard, R. G.; Muryn, C. A.; Ingleson, M. J. Organometallics 2010, 29, 241. (5) (a) Bregadze, V. I.; Timofeev, S. V.; Sivaev, I. B.; Lobanova, I. A. Russ. Chem. Rev. 2004, 73, 433. (b) Semioshkin, A. A.; Sivaev, I. B.; Bregadze, V. I. Dalton Trans. 2008, 977. r 2010 American Chemical Society

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Scheme 1

the hydride character of hydrogen atoms in specific polyhedral boron hydrides. The cobalt bis(dicarbollide) anion [3,30 Co(1,2-C2B9H11)2]- (1) and its derivatives are characterized by remarkable thermal and chemical stability, highly delocalized negative charge, low nucleophilicity and strong acidity of their conjugated acids, and easy modification through substitution of hydrogen atoms.6 The strong hydride character of hydrogen atoms located at positions 8 and 80 of the metallacarborane cage and their participation in electrophileinduced nucleophilic substitution reactions are well established. It is also noteworthy that AlCl3 enables C-H activation of benzene with 1 to give the ortho-phenylene-bridged derivative [μ-8,8-(1,2-C6H4)-3,30 -Co(1,2-C2B9H10)2]-, presumably involving B(8)- and B(80 )-centered cationic centers generated by abstraction of hydride with AlCl3.7 Another example is the reaction of 1 with benzene in the presence of dimethyl sulfate and sulfuric acid, giving the phenyl derivative [8-Ph-3,30 -Co(1,2-C2B9H10)(1,2-C2B9H11)]-.8 In search of milder reaction conditions we concentrated our attention on the reactions of the iodonium bridge opening in [μ-8,80 -I-3,30 -Co(1,2-C2B9H10)2] (2). The iodonium derivative is easily accessible by reaction of the monoiodo derivative [8-I-3,30 -Co(1,2-C2B9H10)(1,2-C2B9H11)]- with AlCl3 in benzene.9 Reactions of 2 with Lewis bases presumably proceed through the iodonium bridge opening with generation of a quasi-borinium cation at position 8 of the metallacarborane cage followed by attack with a Lewis base, resulting in bifunctional derivatives [8-L-80 -I-3,30 -Co(1,2-C2B9H10)2] (6) (a) Hawthorne, M. F.; Young, D. C.; Wegner, P. A. J. Am. Chem. Soc. 1965, 87, 1818. (b) Hawthorne, M. F.; Young, D. C.; Andrews, T. D.; Hove, D. V.; Pilling, R. L.; Pitts, A. D.; Reinjes, M.; Warren, L. F.; Wegner, P. A. J. Am. Chem. Soc. 1968, 90, 879. (c) Sivaev, I. B.; Bregadze, V. I. Collect. Czech. Chem. Commun. 1999, 64, 783, and references therein. (7) Plesek, J.; Hermanek, S. Collect. Czech. Chem. Commun. 1978, 43, 1325. (8) Plesek, J.; Hermanek, S.; Franken, A.; Cisarova, I.; Nachtigal, C. Collect. Czech. Chem. Commun. 1997, 62, 47.  (9) Plesek, J.; Stibr, B.; Hermanek, S. Collect. Czech. Chem. Commun. 1984, 49, 1492.

(L = NH3 , NEt3 , Py, NtCR (R = Me, Ph, CHdCH 2), SMe2, O(CH2CH2)2O).9-11 On the other hand, combinations of sterically hindered Lewis acids and Lewis bases, termed frustrated Lewis pairs, do not form classical Lewis acid-Lewis base adducts, but are able to activate various small molecules (H2, CO2, carbonyl compounds, alkenes, dienes, alkynes).12 In the present work we studied reactions of 2 with Lewis bases in aromatic solvents. Reactions of 2 with unhindered Lewis bases such as pyridine and morpholine result smoothly in the corresponding charge-compensated ammonium derivatives [8-C5H5N80 -I-3,30 -Co(1,2-C2B9H10)2] (3a)13 and [8-O(CH2CH2)2NH80 -I-3,30 -Co(1,2-C2B9H10)2] (3b) (Scheme 1). The solid-state structure of morpholinium derivative 3b 3 CH2Cl2 was determined by single-crystal X-ray diffraction (Figure 1). The dicarbollide ligands in 3b are mutually rotated by 47.7°, producing a cisoid-conformation of the anion. The B-I (2.218(6) A˚) and B-N (1.590(6) A˚) distances fall within the range of the corresponding distances for known derivatives of cobalt bis(dicarbollide) anion (Cs[8,80 -I23,30 -Co(1,2-C2B9H10)2] (2.205 A˚),14 (BEDT-TTF)2[8-I-3, 3 0 -Co(1,2-C 2 B 9 H 10 )(1 0 ,2 0 -C 2 B 9 H 11 )] (2.240 A˚ ), 15 (TTF)[8,80 -I2-3,30 -Co(1,2-C2B9H10)2] (2.216 A˚),16 (BMDT-TTF)4[8,8 0 -I 2 -3,3 0 -Co(1,2-C 2 B 9 H 10 )2 ] (2.175 and 2.206 A˚ ), 16 (10) Knyazev, S. P.; Kirin, V. N.; Chernyshev, E. A. Dokl. Chem. 1996, 350, 252. (11) Selucky, P.; Plesek, J.; Rais, J.; Kyrs, M.; Kadlekova, L. J. Radioanal. Nucl. Chem. 1991, 149, 131. (12) (a) Stephan, D. W. Dalton Trans. 2009, 3129. (b) Stephan, D. W.; Erker, G. Angew. Chem., Int. Ed. 2010, 49, 46. (13) See Supporting Information. (14) Sivy, P.; Preisinger, A.; Baumgartner, O.; Valach, F.; Koren, B.; Matel, L. Acta Crystallogr. 1986, 42C, 28. (15) Kazheva, O. N.; Alexandrov, G. G.; Kravchenko, A. V.; Starodub, V. A.; Sivaev, I. B.; Lobanova, I. A.; Bregadze, V. I.; Buravov, L. I.; Dyachenko, O. A. J. Organomet. Chem. 2007, 692, 5033. (16) Kazheva, O. N.; Alexandrov, G. G.; Kravchenko, A. V.; Starodub, V. A.; Lobanova, I. A.; Sivaev, I. B.; Bregadze, V. I.; Titov, L. V.; Buravov, L. I.; Dyachenko, O. A. J. Organomet. Chem. 2009, 694, 2336.

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Figure 1. Molecular structure of 3b. Selected bond lengths [A˚]: Co(1)-C(1) 2.042(4), Co(1)-C(2) 2.039(4), Co(1)-C(1 0 ) 2.050(4), Co(1)-C(20 ) 2.061(4), Co(1)-B(4) 2.095(5), Co(1)B(7) 2.129(5), Co(1)-B(8) 2.132(5), Co(1)-B(40 ) 2.070(5), Co(1)-B(70 ) 2.119(5), Co(1)-B(80 ) 2.141(5), C(1)-C(2) 1.619(6), C(10 )-C(20 ) 1.618(6), B(8)-I(1) 2.218(6), B(80 )-N(1) 1.590(6), N(1)-C(3) 1.498(5), N(1)-C(6) 1.501(5).

Bregadze et al.

Figure 2. Molecular structure of anion 4. Selected bond lengths [A˚]: Co(1)-C(1) 2.019(3), Co(1)-C(2) 2.022(3), Co(1)-C(10 ) 2.015(3), Co(1)-C(20 ) 2.021(3), Co(1)-B(4) 2.114(3), Co(1)B(7) 2.118(3), Co(1)-B(8) 2.148(3), Co(1)-B(40 ) 2.097(3), Co(1)-B(70 ) 2.115(3), Co(1)-B(80 ) 2.175(3), C(1)-C(2) 1.628(4), C(10 )-C(20 ) 1.629(4), B(8)-I(1) 2.210(3), B(80 )-C(3) 1.570(4).

(BEDT-TTF)2[8,80 -I2-3,30 -Co(1,2-C2B9H10)2] (2.220 A˚),16 and [8-(PhCH2)2NH-3,30 -Co(1,2-C2B9H10)(10 ,20 -C2B9H11)] (1.599 A˚)17). In the case of sterically hindered Lewis bases, such as 2,2,6,6-tetramethylpiperidine, 2,6-di-tert-butyl-4-methylpyridine, or triphenylphosphine, no reaction was found at room temperature; however a short heating time results in C-H activation of benzene with formation of the corresponding phenyl derivative [8-Ph-80 -I-3,30 -Co(1,2-C2B9H10)2]- (4) (Scheme 1). The 11B NMR spectrum of 4 contains a characteristic singlet at 12 ppm corresponding to the arylated boron atom at position 8 of the metallacarborane cage.18,19 The solid-state molecular structure of 4 was deduced from X-ray crystallographic studies of its trimethylammonium salt (Me3NH)[4] (Figure 2). The dicarbollide ligands in 4 are mutually rotated by 178.7°, producing a transoid-conformation of the anion. The B-I (2.210(3) A˚) and B-C (1.570(4) A˚) distances fall within the range of the corresponding distances for known derivatives of cobalt bis(dicarbollide) anion (2.205-2.240 A˚14-16 and 1.577 A˚,8 respectively). The C-H activation of more active aromatics, such as toluene, does not require the presence of a Lewis base and proceeds simply on heating a solution of 2 in toluene at 70 °C to give a mixture of all possible isomers in the ratio 2.5:1.8:1.0 (estimated by integration of methyl group signals in the 1H NMR spectrum). This reaction allows one to suggest an equilibrium between the bridged iodonium derivative 2 and the open iodo-quasi-borinium form 20 (Scheme 2). Unfortunately our attempts to detect 20 by 1H and 11B VT NMR spectroscopy of 2 in benzene-d6 were unsuccessful,

which could be explained by high reactivity of this particle and shift of the equilibrium to more stable 2. Reaction of 2 with anisole gave a mixture of O- and C-substituted products; the p-methoxy derivative [8-(4-MeOC6H4)80 -I-3,30 -Co(1,2-C2B9H10)2]- (5) was isolated by repeated column chromatography on silica. Reactions of 2 with deactivated aromatics, such as acetophenone and nitrobenzene, gave O-substituted products (based on the characteristic signal of O-substituted boron in the 11B NMR spectra) rather than products of arene C-H activation. Purification and characterization of these products is in progress. Using sterically hindered mesitylene as the solvent, no reaction was observed in the absence of Lewis acid. In the presence of 2,2,6,6-tetramethylpiperidine the product of the arene C-H activation, [8-(2,4,6-Me3C6H2)-80 -I-3,30 -Co(1,2C2B9H10)2]- (6), was isolated in a low yield as the 2,2,6,6tetramethylpiperidinium salt (Scheme 1). It was reported earlier that no C-H activation was found from the treatment of 1 with AlCl3 in mesitylene.20 In the presence of triphenylphosphine as Lewis base, the reaction of 2 in mesitylene results in the triphenylphosphonium derivative [8-Ph3P-80 -I3,30 -Co(1,2-C2B9H10)2] (7) (Scheme 1). The solid-state structure of 7 was determined by single-crystal X-ray diffraction (Figure 3). The dicarbollide ligands in 7 are mutually rotated by 172.0°, adopting a transoid-conformation. The B-P distance (1.987(5) A˚) in 7 is somewhat longer than the corresponding distances in known triphenylphosphonium derivatives of polyhedral boron hydrides ((Bu4N)[B12H11PPh3] (1.928 A˚),21 [nido-9-Ph3P-7,8C2B9H11] (1.912 A˚),22 [3-H-3,3,8-(PPh3)3-closo-3,1,2-RuC2B9H10] (1.942 A˚),23 [3-(μ-CO)-8-PPh3-closo-3,1,2-NiC2B9H10]2 (1.938 A˚),24 [2-(Me2CO)-2,11-(Ph3P)2-closo-2,1-PdTeB10H9]

 (17) Sicha, V.; Plesek, J.; Kvicalova, M.; Cisarova, I.; Gr€ uner, B. Dalton Trans. 2009, 851. (18) Rojo, I.; Teixidor, F.; Vi~ nas, C.; Kivek€as, R.; Sillanp€a€a, R. Chem.;Eur. J. 2003, 9, 4311. (19) 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.

(20) Korshak, V. V.; Katz, G. A.; Petrovskii, P. V.; Komarova, L. G.; Bekasova, N. I. Organomet. Chem. USSR 1989, 2, 518. (21) Bernard, R.; Cornu, D.; Luneau, D.; Naoufal, D.; Scharff, J.-P.; Miele, P. J. Organomet. Chem. 2005, 690, 2745. (22) Kim, K. M.; Do, Y.; Knobler, C. B.; Hawthorne, M. F. Bull. Korean Chem. Soc. 1989, 10, 321. (23) Tutusaus, O.; Nu~ nez, R.; Vi~ nas, C.; Teixidor, F.; Mata, I.; Molins, E. Inorg. Chem. 2004, 43, 6067.

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Scheme 2

Figure 3. Molecular structure of 7. Selected bond lengths [A˚]: Co(3)-C(1) 2.032(4), Co(3)-C(2) 2.019(4), Co(3)-C(1 0 ) 2.017(4), Co(3)-C(20 ) 2.031(4), Co(3)-B(4) 2.120(4), Co(3)B(7) 2.107(5), Co(3)-B(8) 2.167(5), Co(3)-B(40 ) 2.126(4), Co(3)-B(70 ) 2.108(4), Co(3)-B(80 ) 2.194(4), C(1)-C(2) 1.620(5), C(10 )-C(20 ) 1.606(5), B(8)-I(1) 2.202(5), B(80 )-P(1) 1.987(5).

(1.942 A˚),25 [2-(H2O)-2,7-(Ph3P)2-closo-2,1-PdTeB10H9][BF4] (1.950 A˚),26 [2-(CO)-2,11-(Ph3P)2-closo-2,1-PdTeB10H9][BF4] (1.941 A˚),26 [2-I-2,7-(Ph3P)2-closo-2,1-PdTeB10H9] (1.961 A˚)27), but significantly shorter than in classical Lewis acid-Lewis base adduct Ph3P-B(C6F5)3 (2.180 A˚).28 The reaction of 2 with triphenylphosphine oxide in mesitylene results in the corresponding phosphonium derivative [8-Ph3PO-80 -I-3,30 -Co(1,2-C2B9H10)2] (8) (Scheme 1). Singlecrystal X-ray crystallographic studies of 8 revealed a gaucheconformation of the dicarbollide ligands with a rotation angle of 114.5° (Figure 4). The B-O (1.462(3) A˚) and O-P (1.5492(19) A˚) distances in 8 were found to be longer and shorter, respectively, than the corresponding distances in [Et3POBO2C6H4][CB11H6Br6] (1.380 and 1.595 A˚),4 but much shorter and longer, respectively, than the corresponding distances in Lewis (24) King, R. E., III; Miller, S. B.; Knobler, C. B.; Hawthorne, M. F. Inorg. Chem. 1983, 22, 3548. (25) Ferguson, G.; Gallagher, J. F.; McGrath, M.; Sheehan, J. P.; Spalding, T. R.; Kennedy, J. D. J. Chem. Soc., Dalton Trans. 1993, 27. (26) Sheehan, J. P.; Spalding, T. R.; Ferguson, G.; Gallagher, J. F.; Kaitner, B.; Kennedy, J. D. J. Chem. Soc., Dalton Trans. 1993, 35. (27) Ferguson, G.; Gallagher, J. F.; Sheehan, J. P.; Spalding, T. R.; Kennedy, J. D.; Macias, R. J. Chem. Soc., Dalton Trans. 1993, 3147. (28) Jacobsen, H.; Berke, H.; D€ oring, S.; Kehr, G.; Erker, G.; Fr€ ohlich, R.; Meyer, O. Organometallics 1999, 18, 1724. (29) Burford, N.; Spence, R. E. v. H.; Linden, A.; Cameron, T. S. Acta Crystallogr. 1990, C46, 92.

Figure 4. Molecular structure of 8. Selected bond lengths [A˚]: Co(1)-C(1) 2.015(3), Co(1)-C(2) 2.042(3), Co(1)-C(1 0 ) 2.023(3), Co(1)-C(20 ) 2.037(3), Co(1)-B(4) 2.082(3), Co(1)B(7) 2.107(3), Co(1)-B(8) 2.140(3), Co(1)-B(40 ) 2.082(3), Co(1)-B(70 ) 2.105(3), Co(1)-B(80 ) 2.142(3), C(1)-C(2) 1.609(4), C(10 )-C(20 ) 1.603(4), B(8)-I(1) 2.211(3), B(80 )-O(1) 1.462(3) A˚, O(1)-P(1) 1.5492(19).

acid-Lewis base adducts F3B-OPPh3 (1.516 and 1.522 A˚)29 and (C6F5)3B-OPEt3 (1.533 and 1.4973 A˚).30 The short B-O and long O-P distances are well consistent with the structure of phosphonium rather than the quasi-borenium cation. It should be noted that all reactions are very sensitive to traces of moisture, and use of non-anhydrous solvents results in formation of the hydroxy derivative [8-HO-80 -I-3,30 Co(1,2-C2B9H10)2]- as the side product. This derivative was earlier prepared by iodination of [8-HO-3,30 -Co(1,2C2B9H10)(10 ,20 -C2B9H11)]- as well as by reaction of [8-I-3,30 Co(1,2-C2B9H10)(10 ,20 -C2B9H11)]- with sulfuric acid.31

Summary Reactions of the iodonium derivative of cobalt bis(dicarbollide) anion [μ-8,80 -I-3,30 -Co(1,2-C2B9H10)2] with Lewis bases results in the opening of the iodonium bridge with generation of a quasi-borinium cation. The character of (30) Beckett, M. A.; Brassington, D. S.; Coles, S. J.; Hursthouse, M. B. Inorg. Chem. Commun. 2000, 3, 530. (31) (a) Kosenko, I. D.; Lobanova, I. A.; Sivaev, I. B.; Bregadze, V. I. Reported at 2nd Ukr. Student Conf. “Karazinski Khimichni Chitannya2010”, Kharkiv, April 19-22, 2010; p 33 (http://www-chemistry.univer. kharkov.ua/files/Abstracts_2010.pdf). (b) Kosenko, I. D.; Lobanova, I. A.; Sivaev, I. B.; Bregadze, V. I. Unpublished results.

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Table 1. Crystal Data and Structure Refinement for [8-O(CH2CH2)2NH-80 -I-3,30 -Co(1,2-C2B9H10)2] 3 CH2Cl2 (3b), (Me3NH)[8-Ph-80 -I3,30 -Co(1,2-C2B9H10)2] (4), [8-Ph3P-80 -I-3,30 -Co(1,2-C2B9H10)2] (7), and [8-Ph3PO-80 -I-3,30 -Co(1,2-C2B9H10)2] (8)

empirical formula fw color and habit temp (K) cryst syst space group a [A˚] b [A˚] c [A˚] R [deg] β [deg] γ [deg] V [A˚3] Z λ (A˚) Dx (g/cm3) μ (mm-1) no. of reflns collected no. of indep rflns no. of rflns with I > 2σ(I) no. of params goodness of fit on F 2 R1 (I > 2σ(I)), wR2

(3b)

(7)

(8)

(4)

C9H31B18Cl2CoINO 620.66 red plate 120(2) monoclinic P21/c (No. 14) 10.727(3) 13.456(4) 17.082(5) 90.00 90.152(7) 90.00 2465.6(13) 4 0.71073 1.672 2.672 22 647 5319 3087 298 0.992 0.0403, 0.0588

C22H35B18CoIP 710.88 red plate 120(2) monoclinic P21/c (No. 14) 17.814(3) 10.1078(17) 18.926(3) 90.00 112.264(3) 90.00 3153.7(9) 4 0.71073 1.497 1.591 30 722 7611 4169 388 1.001 0.0397, 0.0677

C22H35B18CoIOP 726.88 orange needle 100(2) triclinic P212121 (No. 19) 8.8339(3) 16.6204(5) 22.3821(7) 90.00 90.00 90.00 3286.21(18) 4 0.71073 1.469 1.531 39 546 8704 7662 478 1.016 0.0312, 0.0601

C13H35B18CoIN 585.83 orange plate 100(2) monoclinic P21/n (No. 14) 12.370(2) 10.7016(17) 20.203(3) 90.00 102.012(3) 90.00 2615.9(7) 4 0.71073 1.488 1.843 23 633 5067 5067 318 0.999 0.0258, 0.0471

reaction products depends strongly on the nature of the Lewis base and solvent used. The reactions with simple Lewis bases (L) give the corresponding products of Lewis base addition, [8-L-80 -I-3,30 -Co(1,2-C2B9H10)2], whereas the reactions with sterically hindered Lewis bases (L*) result in activation of the C-H bond of the arene solvent with formation of the corresponding aryl derivatives [8-Ar-80 -I-3,30 Co(1,2-C2B9H10)2]-. Activated arenes, such as toluene, could react with [μ-8,80 -I-3,30 -Co(1,2-C2B9H10)2] without Lewis bases, whereas deactivated arenes do not give C-H activation products even in the presence of sterically hindered Lewis bases. In general, reactivity of the quasi-borinium cation formed resembles that of “chelate-restrained” borinium cations.

Experimental Section The 1H, 11B, 11B{1H}, and 13C NMR spectra were collected using Bruker AM300, Bruker Avance-400, and Bruker Avance600 spectrometers. The residual signal of the NMR solvent relative to tetramethylsilane was taken as the internal reference for 1H NMR and 13C NMR spectra. 11B NMR spectra were referenced using BF3 3 Et2O as external standard. The electron ionization mass spectra were obtained with a Kratos MS890 instrument operating in a mass range of m/z 50-800. The negative ion electrospray ionization mass spectra were obtained with a microOTOF II instrument (Bruker Daltonics) operating in a mass range of m/z 50-3000. [μ-8,80 -I-3,30 -Co(1,2-C2B9H10)2] (2) was prepared according to the literature procedure.9 The reaction progress was monitored by thin-layer chromatography (Merck F254 silica gel on aluminum plates). Acros Organics silica gel (0.060-0.200 mm) was used for column chromatography. All solvents were carefully dried and purified by standard techniques.32 Elemental analyses were performed at the Laboratory of Microanalysis of the Institute of Organoelement Compounds. X-ray Single-Crystal Diffraction. Single-crystal X-ray diffraction experiments were carried out with a Bruker SMART 1000 CCD area detector for 3 at 120 K and a Bruker APEX II CCD area detector for 4 and 8 at 100 K and for 7 at 100 K, respectively. The low temperature of the crystals was maintained (32) Armarego, W. L. F.; Chai, C. L. L. Purification of Laboratory Chemicals; Butterworth-Heinemann, 2003.

with a Cryostream (Oxford Cryosystems) open-flow N2 gas cryostat. In all the experiments graphite-monochromated Mo KR radiation (λ = 0.71073 A˚) was used. Reflection intensities were integrated using SAINTPlus software33 for 3 and Bruker SAINT software34 for 4, 7, and 8, respectively. Absorption corrections for all structures were applied semiempirically using the SADABS program.35 The structures were solved by direct methods and refined by the full-matrix least-squares method against F2 in anisotropic approximation for non-hydrogen atoms. All carborane hydrogen atoms were located from the difference Fourier syntheses, whereas the H(C) atoms were placed in geometrically calculated positions. All hydrogen atom positions in structures 3, 4, and 7 were refined in isotropic approximation in a riding model. In structure 8 the carborane hydrogen atoms were refined in isotropic approximation. All calculations were performed using the SHELXTL software.36 Details concerning the crystal data collection and refinement parameters are summarized in Table 1. Crystallographic data for the structures 3, 4, 7, and 8 have been deposited with the Cambridge Crystallographic Data Centre (CCDC 774445, 775445, 774443, and 774444, respectively). 8-(N-Morpholine)-80 -iodo-1,10 ,2,20 -tetracarba-3-commo-cobalta-closo-tricosaborane(20) 3 CH2Cl2 (3b). Morpholine (0.24 mL, 2.77 mmol) was added to a solution of [8,8 0 -μ-I-3,3 0 -Co(1,2-C2B9H10)2] (0.20 g, 0.44 mmol) in 25 mL of anhydrous benzene. The reaction mixture was stirred at room temperature for 24 h. The solvent was removed under vacuum, and the residue was purified by column chromatography on silica with CH2Cl2 as eluent. The major fraction was collected, dried under vacuum, and recrystallized from a mixture of CH2Cl2 and n-hexane to give a red product (0.13 g, 54.5%). Anal. Calcd for C9H31B18Cl2CoINO: B, 31.35; C, 17.42; H, 5.03; N, 2.26. Found: B, 31.43; C, 17.09; H, 4.96; N, 2.23. 1H NMR (33) SAINTPlus, Data Reduction and Correction Program, v.6.01; Bruker Analytical X-ray Systems Inc.: Madison, WI, 1998. (34) APEX II, V.2.0-1, SAINT, v.7.23A; Bruker Analytical X-ray Systems Inc.: Madison, WI, 2005. (35) Sheldrick, G. M. SADABS, v.2.01, Bruker/Siemens Area Detector Absorption Correction Program; Bruker Analytical X-ray Systems Inc.: Madison, WI, 1998. (36) (a) Sheldrick, G. M. Programs SHELXS97 (crystal structure solution) and SHELXL97 (crystal structure refinement); University of Gottingen: Germany, 1997. (b) Sheldrick, G. M. SHELXTL, v.5.10, Structure Determination Software Suite; Bruker Analytical X-ray Systems Inc.: Madison, WI, 1998.

Article (acetone-d6, 400 MHz): 6.61 (s, 1 H, NH), 4.68 (s, 2 H, CHcarb), 4.49 (s, 2 H, CHcarb), 4.13 (m, 2 H, B-NHþ(CH2CH2)2O, J = 13.1 Hz, J = 2.6 Hz), 3.99 (m, 2 H, B-NHþ(CH2CH2)2O, J = 12.6 Hz, J = 1.5 Hz), 3.66 (m, 2 H, B-NHþ(CH2CH2)2O, J = 13.1 Hz), 3.25 (m, 2 H, B-NHþ(CH2CH2)2O, J = 12.6 Hz, J = 3.3 Hz). 13C NMR (acetone-d6, 150 MHz): 65.1 (O(CH2CH2)2NH), 55.4 (B-NHþ(CH2CH2)2O), 53.2 (Ccarb), 51.7 (Ccarb). 11B NMR (acetone-d6, 128 MHz): 14.1 (s, 1 B, B(8)-N), 3.5 (d, 1 B, J = 145 Hz), 0.2 (d, 1 B, J = 143 Hz), -0.9 (d, 2 B, J = 147 Hz), -2.9 (s, 1 B, B(80 )-I), -4.6 (d, 4 B, J = 151 Hz), -7.4 (d, 2 B, J = 144 Hz), -15.5 (d, 2 B, J = 137 Hz), -16.4 (d, 2 B, J = 140 Hz), -22.4 (d, 2 B, J = 157 Hz). EI-MS: 535.3 [M]þ, 409.5 [M - I]. Trimethylammonium 8-Phenyl-80 -iodoicosahydro-1,10 ,2,20 -tetracarba-3-commo-cobalta-closo-tricosaborate ((Me 3 NH)[4]). Triphenylphosphine (0.175 g, 0.67 mmol) was added to a solution of [8,80 -μ-I-3,30 -Co(1,2-C2B9H10)2] (0.30 g, 0.66 mmol) in 20 mL of anhydrous benzene. The reaction mixture was heated under reflux for 20 min. The solvent was evaporated. The residue was dissolved in 5 mL of acetone, treated with an excess of aqueous solution of [Me3NH]Cl, and put into a refrigerator for a few hours. The precipitate formed was filtered off and purified by column chromatography on silica with a solvent mixture of CH2Cl2 and MeCN (10:1) as eluent. The major fraction was collected and dried under vacuum to give an orange product (0.29 g, 74.4%). Anal. Calcd for C13H35B18CoIN: B, 33.21; C, 26.65; H, 6.02; N, 2.39. Found: B, 33.25; C, 26.12; H, 5.97; N, 2.28. 1H NMR (acetone-d6, 400 MHz): 7.31 (d, 2 H, o-Ph), 7.18 (t, 2 H, m-Ph), 7.11 (m, 1 H, p-Ph), 4.51 (s, 2 H, CHcarb), 3.81 (s, 2 H, CHcarb), 3.21 (s, 9H, Me3NHþ). 11B NMR (acetone-d6, 128.3 MHz): 12.3 (s, 1 B, B(8)-C), 3.8 (d, 1 B, J = 137 Hz), 0.9 (d, 1 B, J = 138 Hz), -3.9 (d, 6 B, J = 136 Hz), -4.8 (d, 2 B, J = 135 Hz), -6.1 (s, 1 B, B(80 )-I), -18.1 (d, 4 B, J = 153 Hz), -22.2 (d, 1 B, J = 140 Hz), -22.9 (d, 1 B, J = 137 Hz). Cesium 8-Phenyl-80 -iodoicosahydro-1,10 ,2,20 -tetracarba-3commo-cobalta-closo-tricosaborate (Cs[4]). 2,2,6,6-Tetramethylpiperidine (0.18 mL, 1.11 mmol) was added to a solution of [8,80 -μ-I-3,30 -Co(1,2-C2B9H10)2] (0.10 g, 0.22 mmol) in 20 mL of anhydrous benzene. The reaction mixture was heated under reflux for 20 min. The solvent was evaporated. The residue was dissolved in 5 mL of acetone, treated with an excess of an aqueous solution of CsCl, and put into a refrigerator for a few hours. The precipitate formed was filtered off and purified by column chromatography on silica with a solvent mixture of CH2Cl2 and MeCN (10:1) as eluent. The major fraction was collected and dried under vacuum to give the orange product (0.08 g, 54.8%). 1H NMR (acetone-d6, 400 MHz): 7.33 (d, 2 H, o-Ph), 7.21 (t, 2 H, m-Ph), 7.14 (m, 1 H, p-Ph), 4.54 (s, 2 H, CHcarb), 3.84 (s, 2 H, CHcarb). 13C NMR (acetone-d6, 75 MHz): 149.4 (B-CPh), 131.9 (o-Ph), 127.3 (m-Ph), 125.8 (p-Ph), 60.2 (Ccarb), 53.4 (Ccarb). 11B NMR (acetone-d6, 128 MHz): 12.7 (s, 1 B, B(8)-C), 4.2 (d, 1 B, J=143 Hz), 1.3 (d, 1 B, J=141 Hz), -3.5 (d, 6 B, J = 136 Hz), -4.4 (d, 2 B, J = 135 Hz), -5.7 (s, 1 B, B(80 )-I), -17.7 (d, 4 B, J = 150 Hz), -21.8 (d, 1 B, J = 143 Hz), -22.6 (d, 1 B, J = 139 Hz). ESI-MS, negative: 526.2 [M]. Cesium 8-Tolyl-80 -iodoicosahydro-1,10 ,2,20 -tetracarba-3-commo-cobalta-closo-tricosaborate. (a) A solution of [8,80 -μ-I-3,30 Co(1,2-C2B9H10)2] (0.30 g, 0.66 mmol) in 15 mL of anhydrous toluene was heated at 70 °C for 20 min. The residue was dissolved in 5 mL of acetone, treated with an excess of an aqueous solution of CsCl, and put into a refrigerator for a few hours. The precipitate formed was filtered off and purified by column chromatography on silica with a solvent mixture of CH2Cl2 and MeCN (8:1) as eluent. The major fraction was collected and dried under vacuum to give an orange product (0.20 g, 44.5%). (b) Triphenylphosphine (0.13 g, 0.50 mmol) was added to a solution of [8,80 -μ-I-3,30 -Co(1,2-C2B9H10)2] (0.30 g, 0.66 mmol) in 15 mL of anhydrous toluene. The reaction mixture was heated at 70 °C for 30 min. The solvent was evaporated. The residue was dissolved in 5 mL of acetone, treated with an excess of an aqueous solution of CsCl, and put

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into a refrigerator for a few hours. The precipitate formed was filtered off and purified by column chromatography on silica. The elution with CH2Cl2 gave compound 7 in 12.5% yield (0.14 g). The subsequent elution with a mixture of CH2Cl2 and MeCN (12:1) gave the tolyl derivative as a mixture of isomers in 58.3% yield (0.03 g). 1 H NMR (acetone-d 6 , 400 MHz): 7.37-6.93 (m, 4 H, C6H4Me), 4.51 (s, 2 H, CHcarb), 3.83 (s, 2 H, CHcarb), 2.27 (s, C6H4Me), 2.22 (s, C6H4Me), 2.16 (s, C6H4Me). 11B NMR (acetone-d6, 128 MHz): 12.4 (s, 1 B, B(8)C), 3.87 (d, 1 B, J = 147 Hz), 0.6 (d, 1 B, J = 141 Hz), -4.0 (d, 8 B, J = 135 Hz), -6.2 (s, 1 B, B(80 )-I), -18.2 (d, 4B, J = 153 Hz), -22.8 (m, 2 B). ESI-MS, negative: 540.9 [M], 525.8 [M - CH3], 448.6 [M - C6H4CH3]. 2,2,6,6-Tetramethylpiperidinium 8-(2,4,6-Trimethylphenyl)80 -iodoicosahydro-1,10 ,2,20 -tetracarba-3-commo-cobalta-closotricosaborate ((TMP)[6]). 2,2,6,6-Tetramethylpiperidine (0.19 mL, 1.10 mmol) was added to a solution of [8,80 -μ-I-3,30 -Co(1,2C2B9H10)2] (0.30 g, 0.66 mmol) in 30 mL of anhydrous mesitylene. The reaction mixture was heated at 80 °C for 1 h, allowed to cool to room temperature, and treated with 200 mL of n-hexane. The oil formed was separated, dissolved in 5 mL of acetone, treated with 50 mL of water, and put into a refrigerator for a few hours. The precipitate formed was filtered off and subjected to repeated column chromatography on silica (CH2Cl2-MeCN, 10:1) to give an orange product (0.09 g, 19.3%). Anal. Calcd for C22H51B18CoIN: B, 27.40; C, 37.21; H, 7.24; N, 1.97. Found: B, 37.15; C, 36.82; H, 7.27; N, 1.88. 1H NMR (acetone-d6, 400 MHz): 6.74 (s, 2 H, C6H2Me3), 4.36 (s, 2 H, CHcarb), 3.78 (s, 2 H, CHcarb), 2.57 (s, 6 H, C6H2Me3), 2.12 (s, 3 H, C6H2Me3), 1.92-1.83 (m, 6 H, CH2(CH2CMe2)2NþH2), 1.57 (s, 12 H, CH2(CH2CMe2)2NþH2). 13 C NMR (acetone-d6, 75 MHz): 141.3 (o-C(C6H2Me3)), 134.8 (pC(C6H2Me3)), 130.6 (m-C(C6H2Me3)), 58.5 (Ccarb), 58.1 (CH2(CH2CMe2)2NþH2), 51.4 (Ccarb), 38.0 (CH2(CH2CMe2)2NþH2), 26.8 (CH2(CH2CMe2)2NþH2), 26.1 (C6H2Me3), 19.8 (C6H2Me3), 15.9 (CH2(CH2CMe2)2NþH2). 11B NMR (acetone-d6, 128 MHz): 11.3 (s, 1 B, B(B)-C), 2.1 (d, 1 B, J = 159 Hz), 0.7 (d, 1 B, J = 168 Hz), -4.2 (m, 9 B), -17.1 (d, 2 B, J = 162 Hz), -18.4 (d, 2 B, J = 158 Hz), -20.7 (d, 1 B), -22.7 (d, 1 B, J = 146 Hz). ESI-MS, negative: 568.2 [M]; positive: 142.2 [M]. Cesium 8-(4-Methoxyphenyl)-80 -iodoicosahydro-1,10 ,2,20 -tetracarba-3-commo-cobalta-closo-tricosaborate (Cs[5]). Triphenylphosphine (0.115 g, 0.44 mmol) was added to a solution of [8,80 -μ-I-3,30 -Co(1,2-C2B9H10)2] (0.20 g, 0.44 mmol) in 20 mL of anhydrous anisole. The reaction mixture was heated at 80 °C for 20 min, allowed to cool to room temperature, treated with 200 mL of n-hexane, and put into a refrigerator for 10 h. The oil formed was separated, dissolved in 5 mL of acetone, and treated with an excess of an aqueous solution of CsCl. The precipitate was filtered off and subjected to repeated column chromatography on silica (CHCl3-MeCN, 6:1) followed by repeated crystallization from a mixture of Et2O and n-hexane to give the pure orange product (0.04 g, 13.1%). Anal. Calcd for C11H27B18CoCsIO: B, 28.25; C, 19.19; H, 3.95. Found: B, 28.12; C, 27.95; H, 3.88. 1H NMR (acetone-d6, 400 MHz): 7.21 (d, 2 H, C6H4OMe, J = 7.9 Hz), 6.77 (d, 2 H, C6H4OMe, J = 7.9 Hz), 4.51 (s, 2 H, CHcarb), 3.81 (s, 2 H, CHcarb), 3.73 (s, 3 H, OMe). 13 C NMR (acetone-d6, 75 MHz): 158.4 (C-OMe) 133.0 (B-(C(CHCH)2C)OMe), 113.0 (B-(C(CHCH)2C)OMe), 60.2 (Ccarb), 54.3 (O-Me), 53.6 (Ccarb). 11B NMR (acetone-d6, 128 MHz): 12.6 (s, 1 B, B(8)-C), 3.9 (d, 1 B, J = 141 Hz), 0.6 (d, 1 B, J = 142 Hz), -3.9 (d, 6 B, J = 145 Hz), -4.9 (m, 3 B), -18.3 (d, 4 B, J = 153 Hz), -22.9 (m, 2B). ESI-MS, negative: 556.2 [M]. 8-Triphenylphosphine-80 -iodo-1,10 ,2,20 -tetracarba-3-commocobalta-closo-tricosaborane(20) (7). (a) Triphenylphosphine (0.57 g, 2.21 mmol) was added to a solution of [8,80 -μ-I-3,30 Co(1,2-C2B9H10)2] (0.20 g, 0.44 mmol) in 20 mL of anhydrous mesitylene. The reaction mixture was heated at 80 °C for 2 h, allowed to cool to room temperature, and treated with 200 mL of n-hexane. The oil formed was separated and purified by column chromatography on silica with benzene as eluent.

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The major fraction was collected, dried under vacuum, and recrystallized from a mixture of benzene and n-hexane to give an orange product (0.18 g, 57.1%). Anal. Calcd for C22H35B18CoIP: B, 27.37; C, 37.17; H, 4.96; P, 4.34. Found: B, 27.43; C, 36.92; H, 4.92; P, 4.28. 1H NMR (acetone-d6, 400 MHz): 7.77 (m, 15 H, B-Ph3), 4.80 (s, 2 H, CHcarb), 3.94 (s, 2 H, CHcarb). 13 C NMR (acetone-d6, 75 MHz): 134.8 (d, JC-P = 9 Hz, p-C(Ph)), 133.0 (d, o-C(Ph), JC-P = 3 Hz), 129.4 (d, m-C(Ph), JC-P = 3 Hz), 124.4 (d, Cipso(Ph), JC-P = 70 Hz), 57.7 (Ccarb), 50.5 (Ccarb). 11B NMR (acetone-d6, 128 MHz): 4.2 (m, 2 B), -1.2 (d, 1 B, B(8)-P), -2.0 (m, 5 B), -4.5 (d, 2 B, J = 145 Hz), -7.0 (d, 2 B, J = 148 Hz), -14.5 (d, 2 B, J = 160 Hz), -15.6 (d, 2 B, J = 155 Hz), -18.0 (d, 1 B), -22.9 (d, 1 B). 31P NMR (acetone-d6, 162 MHz): 9.1-6.5 (m, P-B). EI-MS: 710.6 [M], 581.6 [M - I], 449.3 [M - PPh3], 321.1 [M - I - PPh3]. 8-Triphenylphosphine Oxide-80 -iodo-1,10 ,2,20 -tetracarba-3commo-cobalta-closo-tricosaborane(20) (8). Triphenylphosphine oxide (0.30 g, 1.08 mmol) was added to a solution of [8,80 -μ-I3,30 -Co(1,2-C2B9H10)2] (0.10 g, 0.22 mmol) in 20 mL of anhydrous mesitylene. The reaction mixture was heated under reflux for 10 min, allowed to cool to room temperature, and treated with 200 mL of n-hexane. The oil formed was separated and purified by column chromatography on silica (CH2Cl2-benzene, 1:1) and recrystallized from a mixture of CH2Cl2 and n-hexane to give an orange product (0.03 g, 18.6%). Anal. Calcd for C22H35B18CoIOP: B, 26.77; C, 36.35; H, 4.85; P, 4.26. Found: B, 26.84; C, 36.18; H, 4.78; P, 4.22. 1H NMR (acetone-d6, 400 MHz): 7.89-7.73 (m, 15 H, B-Oþ-P(C6H5)3), 4.52 (s, 2 H, CHcarb), 4.32 (s, 2 H, CHcarb). 11B NMR (acetone-d6, 128 MHz): 19.9

Bregadze et al. (s, 1 B, B(8)-OPPh3), 2.3 (d, 1 B, J = 146 Hz), -0.6 (d, 1 B, J = 152 Hz), -3.8 (m, 7 B), -7.4 (d, 2 B, J = 147 Hz), -16.2 (d, 2 B, J = 120 Hz), -18.2 (d, 2 B, J = 130 Hz), -23.0 (d, 1 B), -26.4 (d, 1 B). 31P NMR (acetone-d6, 162 MHz): 53.2 (s). EI-MS: 726.0 [M], 600.5 [M - I], 466.4 [M - PPh3]. Cesium 8-Hydroxy-80 -iodoicosahydro-1,10 ,2,20 -tetracarba-3commo-cobalta-closo-tricosaborate. A solution of [8,80 -μ-I-3,30 Co(1,2-C2B9H10)2] (0.10 g, 0.22 mmol) in 15 mL of wet acetone was stirred at room temperature for 2 h. The reaction mixture was treated with an excess of an aqueous solution of CsCl. The formed precipitate was filtered off and dried in vacuo to give the orange product (0.05 g, 40%). Anal. Calcd for C4H21B18CoIO: B, 32.51; C, 8.03; H, 3.54. Found: B, 32.57; C, 7.62; H, 3.48. 1H NMR (acetone-d6, 400 MHz): 4.42 (s, 2 H, CHcarb), 4,25 (s, 2 H, CHcarb). 11B NMR (acetone-d6, 128 MHz): 22.2 (s, 1 B, B(8)OH), -0.8 (d, 1 B), -5.6 (m, 9 B), -7.7 (s, 1 B, B(80 )-I), -18.2 (d, 2 B), -20.4 (d, 2 B), -23.4 (d, 1 B), -27.6(d, 1 B). ESI-MS, negative: 466.2 [M], 339.1 [M - I].

Acknowledgment. Financial support from the Russian Foundation for Basic Research (10-03-00698 and 10-0391331) is highly acknowledged. Supporting Information Available: Crystallographic data as CIF files, synthesis and spectral data of [8-C5H5N-80 -I-3,30 Co(1,2-C2B9H10)2], and crystal packing of [8-O(CH2CH2)2NH-80 -I-3,30 -Co(1,2-C2B9H10)2] (3). This material is available free of charge via the Internet at http://pubs.acs.org.