Carboranes reactions

B-signals , Computational studies ofnttfo-[C4B7Hn] carboranes and nido-8-vertex boranes and carboranes , Applications of IGLO/GIAO NMR computations of carborane systems products of trimethylamine/c/o o-carborane reactions carborane C chemical shifts and Extension of the borane-carbocation continuum to cage systems . ... 

Nonicosahedral carboranes can be prepared from the icosahedral species by similar degradation procedures or by reactions between boranes such as B H q and B H with acetylenes. The degradative reactions for intermediate C2B H 2 species (n = 6-9) have been described in detail (119). The small closo-Qr Yi 2 species (n = 3-5 are obtained by the direct thermal reaction (500—600°C) of B H using acetylene in a continuous-flow system. The combined yields approach 70% and the product distribution is around 5 5 1 of 2,4-C2B3H2 [20693-69-0] to l,6-C2B Hg [20693-67-8] to 1,5-C2B3H3 [20693-66-7] (120). A similar reaction (eq. 60) employing base catalysts, such as 2 6-dimethylpyridine at ambient temperature gives nido-2 >-(Z, ... 

The silacarborane analogue of C,C-dimethyl-o / o-carborane, closo-l]l-((C i]) -l]lSi[ fri [128270 8 ] h.3.s been reported (179). This o-sdacarborane, which has an icosahedral framework much like o-carborane and is reported to be stable to air and moisture, was obtained in low yield from the reaction of decaborane and bis (dimethyl amino)metbyl silane in refluxing benzene. 

Main Group Element Carborane Derivatives. Main group element carborane derivatives have been reviewed (231). Only a few alkaline-earth element metaHacarborane derivatives have been characterized. The icosahedral beryUacarborane, /(9j (9-3-[(CH3)3N]-3,l,2-BeC2B H, shown in Figure 24a, has been prepared via the reaction of nido-1 and Be(CH3)2 [0(C2H3)2]2 followed by reaction of the diethyletherate product and... 

Treatment of a carborane derivative of thiirane with A-bromosuccinimide gives a j3-bromodisulfide (79MI50601). Chlorination of CM-2,3-di-f-butylthiirane by f-butyl hypochlorite proceeded differently to the reaction with chlorine itself (Scheme 41) (74JA3146). 

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). 

C/o50-carboranes are the most numerous and the most stable of the carboranes. They are colourless volatile liquids or solids (depending on mol wt.) and can be prepared from an alkyne and a borane by pyrolysis, or by reaction in a silent electric discharge. This route, which generally gives mixtures, is particularly useful for small c/o50-carboranes (n = 5-7) and for some intermediate c/ow-carboranes (n = 8-11), e.g. 

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 ... 

Cluster expansion reactions with diborane provide an alternative route to intermediate closo-carboranes, e.g. ... 

A convenient route to three-carbon carboranes is the hydroboration of an alkyne with a preformed dicarbaborane. For example, reaction of ethyne (or propyne) with arachno-4,5-C2B7Hi3 (70) in hexane at 120°C gives a mixture of tri- and tetra-carbaboranes, e.g. (71), (72), (73), (74) in modest yield. Access to other... 

The three isomeric icosahedral carboranes (76-78) are unique both in their ease of preparation and their great stability in air, and consequently their chemistry has been the most fully studied. The 1,2-isomer in particular is available on the multikilogram scale. It is best prepared in bulk by the direct reaction of ethyne with decaborane in the presence of a Lewis base, preferably Et2S ... 

The reaction, which is quite general for closo-carboranes, involves the reductive opening of an n-vertex c/o50-cluster followed by metal... 

The structure of the bimetallic 10-vertex cluster was shown by X-ray diffraction to be (84). When the icosahedral carborane l,2-C2BioHi2 was used, the reaction led to the first supraicosahedral metallocarboranes with 13- and 14-vertex polyhedral structures (85)-(89). Facile isomerism of the 13-vertex monometallodicarbaboranes was observed as indicated in the scheme above (in which = CH and O = BH). 

A particularly elegant route to metallacarbor-anes is the direct oxidative insertion of a metal centre into a c/oso-carborane cluster the reaction uses zero-valent derivatives of Ni, Pd and Pt in a concerted process which involves a nett transfer of electrons from the nucleophilic metal centre to the cage ... 

Many novel cluster compounds have now been prepared in this way, including mixed metal clusters. Further routes involve the oxidative fusion of dicarbon metallacarborane anions to give dimetal tetracarbon clusters such as (103) and (104) O (jjg insertion of isonitriles into inetallaborane clusters to give monocarbon meiallacarboranes such as (105) and the reaction of small ii/t/o-carboranes with alane adducts such as Et3NAlH3 to give the commo species (106) ... 

The reactions of the Group VIII di- and triborolyl or carboranes sandwiches are directed basically to their extension to multidecker derivatives. 

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