Carboranes preparation

Reactions of boron hydrides must be carried out with special care. If properly conducted, the reactions reported here proceed without difficulty, but fires which do occur as the result of equipment failures or similar incidents are usually vigorous. It is recommended that all carborane preparations be carried out in areas designated for the use of hazardous materials. 

Eleutherobin, via ring-closing diene metathesis, 11, 229 Eleven-membered rings with G-G bonds, 3, 706-707 via ring-closing diene metathesis, 11, 227 Eleven-vertex carboranes, preparation, 3, 63, 3, 97 Elimination reactions... 

G in the presence of a catalytic amount of a Lewis base such as dimethylether, (GH2)20. In addition to the gas-phase pyrolysis of diborane, can be prepared by a solution-phase process developed at Union Garbide Gorp. Decaborane is a key intermediate in the preparation of many carboranes and metaHa derivatives. As of this writing, this important compound is not manufactured on a large scale in the western world and is in short supply. Prices for decaborane in 1991 were up to 10,000/kg. 

Garboranes. The term carborane is widely used in American Hterature as a contraction of the lUPAC approved nomenclature carbaborane. The first carboranes, isomers of C2B2H, and were prepared in the mid-1950s at Olin Mathiesen. These carboranes were obtained as a mixture... 

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 related mono-A/-alkylated carboranes, 7-(NH2R)-7-CB2qH22, can be prepared by treatment of decaborane(14) with alkyl isocyanides (125). 

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... 

The carboranyl alcohol can also be prepared from the stannyl carborane and an aldehyde using Pd2(dba)3-CHCl3/dppe. The carborane is stable to Brpnsted and Lewis acids and to LiAlH.. 

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. 

Other convenient routes to carboranes, selected from the growing number of recently reported syntheses, are as follows. Monocarbon carboranes can be prepared in good yield by the transition-metal catalysed hydroboration of alkenes followed by thermal rearrangement of the intermediate product, c.gP" ... 

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 ... 

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) ... 

A final class of high burning rate proplnts combines the high density and high impulse difluoramino compds in their binders with the carborane derivatives. Jones (Ref 79) described the preparation of TVOPA (1,2,3-tris [1,2-bis-(difluoramino)ethoxy] propane, 1PCA (1-iso-propenyl-carboranyl-acetone) and NFPA (2,3-bis(difluoramino) propyl acrylate) and proplnts... 

Metallocarboranes and metalloboranes, discussed in 6.5.4, may be prepared from metal halides and carborane anions. Selected examples of complexes formed by thermal—or otherwise—induced polyhedral rearrangements of existing metallocarboranes are given in a few equations, and some other individual compounds are listed in tables. 

Neutral carboranes and boranes react with transition-metal complexes forming metallocarboranes or metalloboranes, respectively. However, most metallocarboranes and metalloboranes are prepared from transition-metal halides and anionic carborane and borane species ( 6.5.3.4) or by reacting metal atoms and neutral boranes and carboranes. These reactions are oxidative addition reactions ( 6.5.3.3). 

Metal-vapor synthesis also prepares metallaboranes and metallacarboranes with oxidation of the metal. Thermally generated Ni, Co and Fe atoms react with the nido-carborane 2,6-C2B7H, and either cyclopentadiene, toluene, mesitylene, or... 

The original synthesis of metallacarborancs is effected by deprotonation of nido-carborane anions in a manner like that employed to prepare ferrocene, e.g. ... 

Because the complexes listed in Tables 1-8 are all prepared with metal halides and carborane anions, only one example for each type of metallocarborane (number of B atoms) is given in the following representative equations for clarity, the skeletal framework in the equations have numbered positions and H atoms are omitted ... 

Macrocyclic thioethers which contain a carborane backbone have also been prepared and the silver(I) complexes obtained. The reaction of AgN03 with the sulfur-containing macrocyclic ligand... 

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