Iodo carboranes

The only compounds of this type are some phenyliodonium salts with a carbo-ranyl group, obtained from 9-o-, 9-m- and 2-p-iodocarboranes which were converted into (dichloroiodo) and then into [bis(trifluoroacetoxy)iodo]carboranes these were coupled with benzene in presence of acid [84]. 

Halogen-substituted mercuracarborands can be prepared from their halogenated substituted carborands <2001AGE2124>. f/oro-9,12-l2-l,2-C2B8Hio 22 can be deprotonated and treated with mercuric iodide to give the bis-iodo-tetramer 23 in 78% yield (Equation 3). The starting bis-iodo-carborane 22 is prepared by electrophilic iodinaton of the 9,12-vertices of 1,2-carborane. 

Organozinc Compounds in the Cross-coupling Reaction with Iodo-carboranes... 

SCHEME 6.8 lodination of /)-carborane (3). 2-Iodo-/)-carborane (47), diiodo-/)-carborane (48a-e), and decaiodo-/)-carborane (49). 

Cross-coupling of 9-iodo-o-carborane and 9-iodo-m-carborane with RZnX proceeds in diethyl ether or THF in high yields following the Scheme 10. Organozinc compounds containing methoxycarbonyL, keto, and nitrile groups were synthesized from the... 

We have shown for the first time 12 that not only c/oso-carboranes, but also iodo-nido-7,8-dicarbaundecaborates containing an iodine atom in the polyhedral skeleton or in the pentagonal plane of the polyhedron enter into cross-coupling reactions with organomagnesium and organozinc compounds catalyzed by palladium complexes. It is known that ifo-7,8-dicarbaundecaborates are strong BH-acids (pKa = 21.1), due to the presence of the axial hydrogen atom. 

Similar to fluorination, iodination of o-carborane (1) has been carried out primarily through electrophilic iodination or by nucleophilic deboronation followed by reconstruction of the carbo-rane cage with BI3 (Scheme 6.2) (Yamazaki et al., 2005). Depending on the stoichiometric quantity of molecular iodine (Ij), the electron-rich borons 9 and 12 of 1 can be iodinated easily in the presence of AICI3 to give 9-iodo-o-carborane (17) and/or 9,12-diiodo-o-carborane (18) (Li et al., 1991 Yamazaki et al., 2005), whereas the reaction of compound 14 with boron triiodide (BI3) afforded 3-iodo-o-carborane (19, 74% yield) (Yamazaki et al., 2005). 

SCHEME 6.2 Iodination of o-carborane (1). Dianion (14), 9-iodo-o-carborane (17), 9,12-diiodo-o-carborane (18), 3 -iodo-o-carborane (19), and octaiodo-o-carborane (20). 

SCHEME 6.3 lodination of 3-iodo-o-carborane (19) and 3,6-diiodo-o-carborane (22). 3,9,12-Triiodo-o-carborane (21), 3,6,9-triiodo-o-carborane (23), 3,6,9,12-tetraiodo-o-carborane (24), and decaiodo-o-carborane (25). 

Depending on the temperature and the reaction time, the solvent-free iodination of 1 with I2 in a sealed tube allowed the regioselective synthesis of 9-iodo-o-carborane (17, 97% yield), 9,12-diiodo-o-carborane (18, 62% yield), and 8,9,10,12-tetraiodo-o-carborane (26, 93% yield. Scheme 6.4) (Barbera et al., 2008 Vaca et al., 2006). Shorter reaction times were reqnired when mono/di-C-alkyl- and mono/di-C-aryl-substituted o-carboranes were iodinated nsing the same method (Barbera et al., 2008). Tetraiodination of 1,2-diphenyl-o-carborane (27) and 1,2-dimethyl-o-carborane (28) required only 3.5 h and 2.5 h, respectively, to give 29 and 30. These results were in agreement with previous studies showing that the presence of methyl substituents at the carbon atoms increased the electron density at the boron atoms of 1 (Boer et al., 1966 Pbtenza and Lipscomb, 1966). 

SCHEME 6.7 lodination and bromination of m-carborane (2). 9-Iodo-m-carborane (42), 9,10-diiodo-m-carborane (43), octaiodo-m-carborane (44), 9-bromo-m-carborane (45), and 9,10-dibromo-m-carborane (46). 

SCHEME 6.10 Bromination of 9-iodo-m-carborane (42). 9-Bromo-m-carborane (45). 

Reaction of 9-iodo-o-carborane (17) with TBAF yielded 5-iodo- (55, 94% yield), and 6-iodo-nido-o-carborane (56) (Scheme 6.13) (Fox and Wade, 1999). On the other hand, reaction of the trimethylammonium salt of 4 (57) with 1 equivalent of I2 resulted in 9-iodo- 7(( -o-carborane (58, 88% yield), whereas reaction with 2.5 equivalents of I2 afforded 9,ll-diiodo- 7(( -o-carborane (59,... 

SCHEME 6.13 Synthesis of halogenated wirfo-o-carborane derivatives (56-60). 9-Iodo-o-carborane (17), 5-iodo- i(fo-o-carborane derivative (55), 6-iodo-n/trimethylammonium salt of nido-o-carborane (57), 9-iodo-n/[Pg.119]

Stanko and Iroshnikova reported the first radiolabeling of iodo-o-c/oYO-carborane (Scheme 6.2) via isotopic exchange reaction nsing Na I and iron (II) sulfate as a catalyst (Stanko and Iroshnikova, 1970). Adapting a method by Marshall et al. for Pd-catalyzed cold halogen exchange, as described... 

CTAs that are carborane cluster radioiodinated may be attractive candidates for radiotherapeutic and diagnostic applications. Such molecules may be less susceptible to dehalogenation, and thns, snperior to conventional carbon radioiodinated nucleosides, such as the various radioactive variants of 5-iodo-2 -deoxyuridine (see Section 6.1 for discussion). 

Eriksson, L., Tohnachev, V. and Sjdberg, S. 2003. Eeasibility of palladium-catalyzed isotopic exchange between sodium [ I]I and 2-iodo-para-carborane. J. Labelled Gontp. Radiophamt., 46, 623-31. 

Li, J., Logan, C. F., and Jones, M., Jr. 1991. Simple syntheses and alkylation reactions of 3-iodo-o-carborane and 9,12-diiodo-o-carhorane. Inorg. Chem., 30,4866-8. 

The coupling of a phosphorus atom to a boron atom can be done by synthesis of the iodo-substi-tuted carborane and subsequent palladium-catalyzed cross-coupling reaction (Figure 22.4) [24]. Unfortunately, this reaction only works with the meta- and para-carborane and not with the ortho isomer, because of cleavage of 9-iodo-ortAo-carborane with triethylamine in toluene at SS-W C. Attachment of an iodine atom to the B9 atom is done via electrophilic iodation. The mechanism is similar to the Friedel-Crafts reaction using AICI3 as the Lewis acid. 

Several other substrates were tested using l,2-bis(diphenylphosphino)-ortfto-carborane(12) as ligand. Yields between 65% and full conversion were obtained (Table 22.31). It is remarkable that with bromoiodo-substituted compounds the reaction takes place only at the iodo-substituted position. The use of (C6F5)2PCH2CH2P(QF5)2 gave lower yields in some reactions, but may be suitable for other reactions. 

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