Carborane lead

As with the simple boranes, the closo carboranes are generally more thermally stable than the corresponding nido and arachno species. Thermal decomposition of nido and arachno carboranes often leads to one or more closo carborane. For example, pyrolysis of 2,3-C2B4Hg is another route to 2,3-C2B3H2 [30347-95-6], l,2-C2B4Hg [20693-68-9] and l,6-C2B4Hg [20693-67-8], and 1,5-C2B3H3 [20693-66-7] (123). 

The reaction of (fluoroalkenyl)carboranes with potassium permanganate in acetone leads to formation of a-diketones [119. These compounds react by photochemical reaction in which the radical formation at boron is followed by addition to the double bond [120] (equation 92). 

Pyrolysis of nido- or nrac/ino-carboranes or their reaction in a silent electric discharge also leads to c/o50-species either by loss of Ht or disproportionation ... 

The first examples of DNA metallointercalators containing a 1,2- or 1,7-carborane thiolato ligand have been reported.349 For example, treatment of [Pt(OTf)(terpy)]+ (terpy = 2,2 6, 2 -terpyr-idine) with l-HSCH2-l,2-C2B10Hii leads to the formation of [Pt(l-SCH2-l,2-C2BioHn)(terpy)]+ (143). The DNA-binding properties of several complexes have also been described. 

Dehydrobenzene or benzyne 158 can be trapped by all manner of species. 1,2-Dehydro-o-carborane 159 has been shown to undergo many of the same reactions as its two-dimensional relative, 1,2-dehydrobenzene. Although dehydroaromatic molecules can be formed in a variety of ways, synthetic pathways to 1,2-dehydro-o-carborane are quite limited. An effective procedure reported so far78 first forms the dianion by deprotonation of o-carborane with 2 equiv. of butyllithium. Precipitated dilithium carborane is then treated with 1 equiv. of bromine at 0°C to form the soluble bromo anion 160. Thermolysis of 160 with anthracene, furan, and thiophene as substrates leads to the adducts 161-164.79 80 1,2-Dehydro-o-carborane reacts with norbomadiene to give both homo 2+4 and 2+2 addition, leading to three products 165-167, in a 7 1 ratio79. An acyclic diene, 2,3-dimethyl-... 

ICOSAHEDRAL CARBORANES AND INTERMEDIATES LEADING TO THE PREPARATION OF CARBAMETALLIC BORON HYDRIDE DERIVATIVES... 

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. 

The reaction leading to 20 was used to prepare 25 (Scheme 3.2-13) [35], starting from diethyl(propyn-l-yl)borane which served as a versatile reagent for the synthesis of other carboranes (vide infra). l,l-Bis(diethyl-boryl)propene 23 can be detected and isolated, whereas it was not possible to identify l,l,l-tris(diethylboryl)propane 24 in the reaction mixture. 

The stability of the liquid carboranes depends on the substituents R at carbon and boron. The axial (endo) hydrogen atom is acidic and involved in 3c2e bonding to one of the basal boron atoms. In the 1H NMR it exhibits a high field shift near S = —1.4. Deprotonation of 55 with potassium or Bu Li leads to the anion (55-H)-, which is isolobal with C5H5. Reactions of 55 and (55-H) with appropriate metal complexes lead to metallacarboranes with sandwich structures [67, 69],... 

A one pot route to nido-1,6-diiodo-tctracarba-nuio-hcxaborane derivatives is depicted in Scheme 3.2-32. After iodoboration of the alkynes with BI3 the dehaloge-nation of the alkenyl derivatives presumably leads to dimerization and rearrangement to give structurally characterized 1,6-diiodo-nido-carboranes 56d [81]. 

Dehalogenation of unsaturated organohalogenoboranes also leads to nido-Ctfii and nido-C4B4 carboranes. The nido-C5B cluster s apex boron forms very strong bonds with Lewis acids BX3. 

The phenyl modified polymers show a significant decrease In weight loss compared to their all methyl analog (6). In a study of the thermal breakdown of phenyl substituted carborane-slloxane polymers, It has been reported that the presence of phenyl groups In carborane-siloxanes leads to cross-linking and less loss of weight ( ) ... 

Applied to icosahedral carboranes as the starting materials, it leads to metallocarborane based on 13- or 14-vertex polyhedra, e.g. (35, 70),... 

Refluxing Cjq with the metallacyclic carboranyliridium dihydride complex 13 in a toluene-acetonitrile mixture yields the complex 14, which contains two different polyhedral clusters as ligands (Scheme 7.7) [28]. The strong trans-influence of the o-bonded carborane ligand leads to a distortion of the iridacyclopropane moiety. The Ir-C bond trans to the carborane is significantly longer than the other Ir-C bond (2.229 vs. 2.162 A). This distortion can be utilized for the selective insertion... 

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