Carborane 1206475 220993039 2008-06-22T15:40:15Z DOI bot 6652755 Citation maintenance. You can [[WP:DOI|use this bot]] yourself! Please [[User:DOI_bot/bugs|report any bugs]]. [[Image:O-carborane-3D-balls.png|thumb|right|[[Ball-and-stick model]] of ''o''-carborane]] [[Image:Carborane-acid-3D-balls.png|thumb|right|Ball-and-stick model of the carborane acid anion. (acidic proton not displayed)<br><br>Colour scheme:<br>[[hydrogen]] − white,<br>[[chlorine]] − green,<br>[[boron]] − pink,<br>[[carbon]] − black.]] A '''carborane''' is a cluster composed of [[boron]] and [[carbon]] atoms. Like many of the related [[boranes]], these clusters are [[polyhedra]] and are similarly classified as ''closo-, nido-, arachno-, hypho-,'' etc. based on whether they represent a complete (''closo-'') polyhedron, or a polyhedron that is missing one (''nido-''), two (''arachno-''), or more vertices. Interesting examples of '''carboranes''' are the extremely stable [[icosahedral]] [[closo cluster|closo]]-carboranes.<ref>{{cite journal | title = Overlap control and stability of polyhedral molecules. Closo-Carboranes | author = Eluvathingal D. Jemmis | journal = [[J. Am. Chem. Soc.]] | year = 1982 | volume = 104 | pages = 7017–7020 | doi =10.1021/ja00389a021}}</ref> A prominent example is the charge-neutral C<sub>2</sub>B<sub>10</sub>H<sub>12</sub> or '''''o''-carborane''' with the prefix ''o'' derived from [[ortho]], which has been explored for use in a wide range of applications from heat-resistant polymers to medical applications. This compound is called super [[aromatic]] because it obeys [[Huckel's rule]] and exhibits high thermal stability. At 420 °C ''o''-carborane converts to the meta isomer. In comparison, [[benzene]] requires a >1000 °C to induce skeletal rearrangement. Like arenes, carboranes also undergo [[electrophilic aromatic substitution]]. :[[Image:O-carborane.png|150px|o-carborane, hydrogen atoms connected to boron omitted for clarity]] Another important carborane is the negatively charged CHB<sub>11</sub>H<sub>12</sub><sup>—</sup>, which has been used to make solid [[superacid]]s. The carborane superacid H(CHB<sub>11</sub>Cl<sub>11</sub>) <ref>Note that the image the acidic proton is not the one bonded to the carborane but that it is the counterion not displayed</ref> is one million times stronger than sulfuric acid. The reason for this high acidity is that the acid anion CHB<sub>11</sub>Cl<sub>11</sub><sup>-</sup> is very stable and substituted with electronegative substituents. H(CHB<sub>11</sub>Cl<sub>11</sub>) is the only acid known to [[protonation|protonate]] C<sub>60</sub> [[fullerene]] without decomposing it. <ref>{{cite journal | title = The Strongest Isolable Acid | author = Mark Juhasz, Stephan Hoffmann, Evgenii Stoyanov, Kee-Chan Kim, Christopher A. Reed | journal = [[Angewandte Chemie International Edition]] | volume = 43 | pages = 5352–5355 | year = 2004 | format = | doi = 10.1002/anie.200460005}}</ref> <ref>{{cite journal | title = Carborane acids. New "strong yet gentle" acids for organic and inorganic chemistry | author = Christopher A. Reed | journal = [[Chem. Commun.]] | volume = 2005 | pages = 1669–1677 | doi = 10.1039/b415425h | url = http://www.reedgrouplab.ucr.edu/publications/Chem%20Comm%202005%201669.pdf | format = Full article (reprint) | year = 2005}}</ref>. ==Dicarbadodecaborane== The most heavily studied carborane is C<sub>2</sub>B<sub>10</sub>H<sub>12</sub>, m. p. 320 C. It is often prepared from the reaction of [[acetylene]] with [[decaborane]]. A variation on this method entails the use of [[dimethyl acetylenedicarboxylate]] to give C<sub>2</sub>B<sub>10</sub>H<sub>10</sub>(CO<sub>2</sub>C H<sub>3</sub>)<sub>2</sub>, which can be degraded to the C<sub>2</sub>B<sub>10</sub>H<sub>12</sub>.<ref>{{cite journal | author = Kutal, C. R.; Owen, D. A.; Todd, L. J. | title = Closo-1,2-dicarbadodecaborane(12) | journal = [[Inorganic Syntheses]] | year = 1968 | volume = 11 | pages = 19–23 | doi = 10.1002/9780470132425.ch5}}</ref> === History === The 1,2-closo-dicarbadodecaboranes (usually simply called carboranes), were reported simultaneously by groups at Olin Corporation and the Reaction Motors Division of Thiokol Chemical Corporation working under the U.S. Air Force <!--contracts AF 33(600-32702, June 11,1956-May 10,1958, and AF 33(616),5639-March 1,1958-October 12,1960)--> and published in 1963.<ref>{{cite journal | author = T. L. Heying, J. W. Ager, S. L. Clark, D. J. Mangold, H. L. Goldstein, M. Hillman, R. J. Polak, and J. W. Szymanski | title = A New Series of Organoboranes. I. Carboranes from the Reaction of Decaborane with Acetylenic Compounds | journal = [[Inorganic Chemistry (journal)|Inorganic Chemistry]] | year = 1963 | volume = 2 | pages = 1089–1092 | doi = 10.1021/ic50010a002}}</ref> <ref>{{cite journal | author = H. Schroeder, T. L. Heying, J. R. Reiner | title = A New Series of Organoboranes. II. The Chlorination of 1,2-Dicarbaclosododecaborane(12)" [[Inorganic Chemistry (journal)|Inorganic Chemistry]] | year = 1963 | volume = 2 | pages = 1092–1096 | doi = 10.1021/ic50010a003 | journal = Inorganic Chemistry}}</ref><ref>{{cite journal | author = T. L. Heying, J. W. Ager, S. L. Clark, R. P. Alexander, S. Papetti, J. A. Reid, S. I. Trotz | title = A New Series of Organoboranes. III. Some Reactions of 1,2-Dicarbaclosododecaborane(12) and its Derivatives | [[Inorganic Chemistry (journal)|Inorganic Chemistry]] | year = 1963 | volume = 2 | pages = 1097–1105 | doi = 10.1021/ic50010a004 | journal = Inorganic Chemistry}}</ref> <ref>{{cite journal | author = S. Papetti, T. L. Heying | title = A New Series of Organoboranes. IV. The Participation of the 1,2-Dicarbaclosododecaborane(12) Nucleus in Some Novel Heteratomic Ring Systems | journal = [[Inorg. Chem.]] | year = 1963 | volume = 2 | pages = 1105–1107 | doi = 10.1021/ic50010a005}}</ref> <ref>{{cite journal | author = M. M. Fein, J. Bobinski, N. Mayes, N. Schwartz, M. S. Cohen | title = Carboranes. I. The Preparation and Chemistry of 1-Isopropenylcarborane and its Derivatives (a New Family of Stable Closoboranes) | journal = Inorg. Chem.]] | year = 1963 | volume = 2 | pages = 1111–1115 | doi =10.1021/ic50010a007}}</ref><ref>{{cite journal | author = M. M. Fein, D. Grafstein, J. E. Paustian, J. Bobinski, B. M. Lichstein, N. Mayes, N. N. Schwartz, M. S. Cohen | title = Carboranes. II. The Preparation of 1- and 1,2-Substituted Carboranes | journal = [[Inorg. Chem.]] | year = 1963 | volume = 2 | pages = 1115–1119 | doi = 10.1021/ic50010a008}}</ref> <ref>{{cite journal | author = D. Grafstein, J. Bobinski, J. Dvorak, H. Smith, N. Schwartz, M. S. Cohen, M. M. Fein | title = Carboranes. III. Reactions of the Carboranes | journal = [[Inorg. Chem.]] | year = 1963 | volume = 2 | pages = 1120–1125 | doi = 10.1021/ic50010a009}}</ref><ref>{{cite journal | author = D. Grafstein, J. Bobinski, J. Dvorak, J. E. Paustian, H. F. Smith, S. Karlan, C. Vogel, M. M. Fein | title = Carboranes. IV. Chemistry of Bis-(1-carboranylalkyl) Ethers | journal = [[Inorg. Chem.]]| year = 1963 | volume = 2 | pages = 1125–1128 | doi = 10.1021/ic50010a010}}.</ref><ref>{{cite journal | author = D. Grafstein, J. Dvorak | title = Neocarboranes, a New Family of Stable Organoboranes Isomeric with the Carboranes | journal = [[Inorg. Chem.]] | year = 1963 | volume = 2 | pages = 1128–1133 | doi = 10.1021/ic50010a011}}</ref> Simultaneously a group from the USSR published similar work. Heretofore, decaborane derivatives were thought to be thermally unstable and reactive with air and water. These groups demonstrated the unprecedented stability of the 1,2-closo-dodecaborane group, presented a general synthesis, and described the transformation of substituents without destroying the carborane cluster. and demonstrated the ortho to meta isomerization. ===Dicarbollide=== Numerous studies have been made on derivatives of the so-called dicarbollide anion, [B<sub>9</sub>C<sub>2</sub>H<sub>11</sub>]<sup>2-</sup>. This anion forms [[sandwich compound]]s with many metal ions and some exist in otherwise unusual oxidation states. The dianion is a nido cluster prepared by degradation of the parent dicarborane:<ref>Plešek, J.; Heřmánek, S.; Štíbr, B. Inorganic Syntheses, 1983, volume 22, pages 231-124.</ref> :B<sub>10</sub>C<sub>2</sub>H<sub>12</sub> + 3 CH<sub>3</sub>OH + KOH → KB<sub>9</sub>C<sub>2</sub>H<sub>12</sub> + B(OCH<sub>3</sub>)<sub>3</sub> + H<sub>2</sub>O + H<sub>2</sub> ===Carborynes=== '''Carboryne''', or 1,2-dehydro-o-carborane, is an unstable derivative of ortho-carborane with the formula B<sub>10</sub>C<sub>2</sub>H<sub>10</sub>. The hydrogen atoms on the C2 unit in the parent ''o''-carborane are missing. The compound resembles and is [[Isolobal principle|isolobal]] with [[benzyne]] <ref>{{cite journal | title = 1,2-Dehydro-o-carborane | author = Henry L. Gingrich, Tirthankar Ghosh, Qiurong Huang, and [[Maitland Jones]] | journal = [[J. Am. Chem. Soc.]] | year = 1990 | volume = 112 | issue = 10 | pages = 4082–4083 | doi = 10.1021/ja00166a080}}</ref><ref>{{cite journal | title = Structure and Bonding in B10X2H10 (X = C and Si). The Kinky Surface of 1,2-Dehydro-o-Disilaborane | author = E. D. Jemmis and B. Kiran | journal = [[J. Am. Chem. Soc.]] | year = 1997 | issue = 19 | pages = 4076–4077 | doi = 10.1021/ja964385q | volume = 119}}</ref><ref>{{cite journal | title = Control of Stability through Overlap Matching: closo-Carboranes and closo-Silaboranes | author = B. Kiran, A. Anoop, E. D. Jemmis | journal = [[J. Am. Chem. Soc.]] | year = 2002 | volume = 124 | pages = 4402–4407 | doi = 10.1021/ja016843n}}</ref>. A carboryne compound was first generated in 1990 starting from o-carborane. The hydrogen atoms connected to carbon are removed by [[n-butyllithium]] in [[tetrahydrofuran]] and the resulting lithium [[dianion]] is reacted with [[bromine]] at 0[[°C]] to form the bromo monoanion. :[[Image:Carboryne synthesis.png|600px|Carboryne synthesis, main chemical bonds involving carbon in red]] Heating the reaction mixture to 35 °C releases carboryne, which can subsequently be trapped with suitable [[dienes]]: :[[Image:Carboryne reactions.png|600px|carboryne reactions]] such as [[anthracene]] (to afford a [[trypticene]]-like molecule) and [[furan]] in 10 to 25% [[chemical yield]]. Carborynes react with [[alkyne]]s to '''benzocarboranes''' <ref>{{cite journal | title =Nickel-Mediated Regioselective [2 + 2 + 2] Cycloaddition of Carboryne with Alkynes | author =Liang Deng, Hoi-Shan Chan, and Zuowei Xie | journal = [[J. Am. Chem. Soc.]] | year = 2006 | volume = 128 | issue = 24 | pages = 7728–7729 | doi = 10.1021/ja061605j}}</ref><ref>{{cite journal | title = Theoretical Study of the Insertion Reactions of Benzyne- and Carboryne- Ni Complexes | author = Eluvathingal D Jemmis and Anakuthil Anoop | url = http://www.mhpcc.hpc.mil/research/appbriefs/2004/2004MHPCCAppBriefs.pdf | journal = MHPCC Application Briefs | year = 2004 | pages = 51}}</ref> in an adaptation of the above described procedure. O-carborane is deprotonated with [[n-butyllithium]] as before and then reacted with dichloro-di(triphenylphosphino) nickel to a nickel coordinated carboryne. This compound reacts with 3-hexyne in an [[alkyne trimerization]] to the benzocarborane. :[[Image:BenzocarboraneSynthesis.png|600px|benzocarborane synthesis]] Single crystal [[X-ray diffraction]] analysis of this compound shows considerable [[bond length]] alternation in the benzene ring (164.8 [[picometre|pm]] (!) to 133.8 pm) ruling out [[aromaticity]]. == References == {{reflist|2}} == External links == * [http://www.reedgrouplab.ucr.edu/projects/strong_gentle.html The Reed Group] [[Category:boron compounds]] [[Category:Cluster chemistry]] [[Category:Superacids]] [[de:Carborane]] [[es:Carborano]] [[fr:Carborane]] [[ko:카보레인]] [[it:Carborani]] [[ja:カルボラン酸]] [[pl:Kwas karboranowy]] [[pt:Carborano]] [[sv:Carboransyra]] [[zh:碳硼烷]]