“Carborane”的意思、由来-开放百科全书

Carboranes are electron-delocalized (non-classically bonded) clusters composed of boron, carbon and hydrogen atoms that may also contain other metallic and nonmetallic elements in the cluster framework.^[1] Like many of the related boron hydrides, these clusters are polyhedra or fragments of 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-), three (hypho-), or more vertices. Carboranes are a notable example of heteroboranes.

Carboranes having as few as 5 and as many as 14 atoms in the cage framework (15 if metal atoms are included) are known, but the majority have two cage carbon atoms; of these, the best-known series is that of the closo-C₂B_nH_n+2 systems where n = 3 to 12. However, carboranes having 1 to 6 cage carbon atoms have been prepared, as have a number of carborane mono- and dianions. The icosahedral CB₁₁H₁₂^- anion is a strong acid, and its polychlorinated derivative H(CHB₁₁Cl₁₁) is a superacid.

The icosahedral charge-neutral closo-carboranes, 1,2-, 1,7-, and 1,12-C₂B₁₀H₁₂ (respectively ortho-, meta-, and para-carborane in the informal nomenclature) are particularly stable and are commercially available.^[2] These boron-rich clusters exhibit unique organomimetic properties with chemical reactivity matching classical organic molecules, yet are structurally similar to metal-based inorganic and organometallic species^[3]

The C₂B₁₀H₁₂ isomers, together with other carborane clusters and metallacarboranes (see below) are utilized in a wide range of applications including heat-resistant polymers, recovery of radioactive metals from nuclear waste, catalysis, novel electroactive materials, and medical applications. Like other electron-delocalized polyhedral clusters, the electronic structure of these cluster compounds can be described by the Wade-Mingos rules.

As noted above, carboranes are closely related to boron hydrides (boranes), and thus are structurally very different from hydrocarbons, owing to the fact that carbon atoms have one more valence electron than do boron atoms (a notable feature of carboranes is that the cage carbon atoms often are directly bound to as many as 6, or even more, neighboring atoms, quite unlike the hydrocarbons).

Carboranes and boranes adopt 3-dimensional cage (cluster) geometries in order to facilitate their electron-delocalized nonclassical bonding, whereas hydrocarbons are typically chains or rings; for example, B₄H₁₀ has an arachno cage geometry while the butane isomers n- and iso-C₄H₁₀, with 4 more electrons than B₄H₁₀, adopt linear or branched chain structures. Examples of nido and arachno- carboranes include 2,3-C₂B₄H₈ and 1,3-C₂B₇H₁₃, respectively. Geometrical isomers of carboranes can exist, necessitating the use of the numerical prefixes in a compound's name; this is illustrated by the 1,2-, 1,7-, and 1,2-C₂B₁₀H₁₂ icosahedral clusters referred to earlier. For general overviews of carborane chemistry see "Chemistry of the Elements", pp. 181–189^[4] and "Advanced Inorganic Chemistry, Sixth Edition, pp. 131-174"^[5]. A recent comprehensive treatment of this area, with references updated annually, can be found in reference [1]. Electron-delocalized bonding in boranes and carboranes is discussed extensively in ^[6]

Preparation

Carboranes have been prepared by many different routes, the most common being addition of alkynyl reagents to boron hydride clusters to form dicarbon carboranes. For example, the high-temperature reaction of pentaborane(9) with acetylene affords several closo-carboranes as well as other products:

When the reaction is conducted at lower temperatures, an open-cage carborane is obtained:

Other procedures generate carboranes containing three or four cage carbon atoms (refs. [1],[4],[5])

Monocarba derivatives

Monocarboranes are clusters with B_nC cages. The 12-vertex derivative is best studied, but several are known.

Typically they are prepared by the addition of one-carbon reagents to boron hydride clusters. One-carbon reagents include cyanide, isocyanides, and formaldehyde. For example, monocarbadodecaborate ([CB₁₁H₁₂]^-) is produced from decaborane and formaldehyde, followed by addition of borane dimethylsulfide.^[7]^[8]

Dicarba clusters

Dicarbaboranes can be prepared from boron hydrides using alkynes as the source of the two carbon centers. In addition to the closo-C₂B_nH_n+2 series mentioned above, several open-cage dicarbon species are known including nido-C₂B₃H₇ (isostructural and isoelectronic with B₅H₉) and arachno-C₂B₇H₁₃.

Syntheses of icosahedral closo-dicarbadodecaborane derivatives (R₂C₂B₁₀H₁₀) employ alkynes as the R₂C₂ source and decaborane (B₁₀H₁₄) to supply the B₁₀ unit.

Tricarba, tetracarba, pentacarba, and hexacarba clusters

Carboranes having more than two carbon atoms in the skeletal framework, obtained in a variety of ways, include derivatives of nido-C₃B₃H₇, nido-C₃B₈H₁₁, nido-C₄B₂H₆, nido-C₄B₄H₈, nido-C₅BH₆⁺, and arachno-H₆C₆B₆Et₆ (reference [1]).

Isomerism

Many dicarbaboranes exist as isomers that differ in the relative location of the carbon centers. In addition to the three previously mentioned icosahedral C₂B₁₀H₁₂ compounds, isomerism is also found in some smaller closo-carborane systems, e.g., 1,2- and 1,6-C₂B₄H₆, 2,3- and 2,4-C₂B₅H₇, 1,2- and 1,6-C₂B₆H₈, and 2,3- and 2,4-C₂B₅H₇, as well as in open-cage carboranes such as 2,3- and 2,4-C₂B₄H₈ and 1,2 and 1,3-C₂B₉H₁₃.

In general, isomers having non-adjacent cage carbon atoms are more thermally stable than those with adjacent carbons, so that heating tends to induce mutual separation of the carbon atoms in the framework. This is illustrated by the thermal isomerization of 1,2- to 1,6-C₂B₄H₆ and of 1,2- to 1,7-C₂B₁₀H₁₂. Formation of the 1,12-C₂B₁₀H₁₂ (para-carborane) isomer requires much higher temperatures (ca. 600C), accompanied by some decomposition (refs. [1], [4], and [5]).

Reactions

Carboranes undergo a wide variety of reactions. Deprotonation of closo-dicarbadodecaboranes using organolithium reagents gives the dilithio derivatives.^[10]

These dilithiated compounds react with a variety of electrophiles, e.g. chlorophosphines, chlorosilanes, and sulfur.^[11]

Base-induced degradation of carboranes give anionic nido derivatives, which can be employed as ligands for transition metals, generating metallacarboranes, which are carboranes containing one or more transition metal or main group metal atoms in the cage framework, discovered in 1965 ^[12]. The bulk of the work on metallacarboranes has centered on 12-vertex MC₂B₉ and M₂C₂B₈ clusters and 7-vertex MC₂B₄ and M₂C₂B₃ (triple-decker^[13] and multidecker sandwich^[14]) clusters, but metallacarboranes of 6 to 15 vertices have also been prepared^[15], as have clusters with varying numbers of carbon, boron, and metal atoms (see refs. [1], [4[, and [5]). Diborolyl-metal complexes featuring MC₃B₂ and M₂C₃B₂ cages, representing another type of metallacarborane, have also been extensively studied ^[16]

Research

Dicarbollide complexes have been evaluated for many applications for many years, but commercial applications are rare. The bis(dicarbollide) [Co(C₂B₉H₁₁)₂]^- has been used as a precipitant for removal of ¹³⁷Cs⁺ from radiowastes.^[17]

The medical applications of carboranes have been explored.^[18] C-functionalized carboranes represent a source of boron for boron neutron capture therapy.^[19]

The compound H(CHB₁₁Cl₁₁) is a superacid, forming a isolable salt with protonated benzene, C₆H{{su|b=7|p=+}}.^[21] It protonates fullerene, C₆₀.^[22]

See also

References

1. ^Grimes, R. N., Carboranes 3rd Ed., Elsevier, Amsterdam and New York (2016) {{ISBN|9780128018941}}
2. ^{{cite journal | author = Jemmis, E. D. | authorlink = Eluvathingal Devassy Jemmis | title = Overlap control and stability of polyhedral molecules. Closo-Carboranes | journal = Journal of the American Chemical Society | year = 1982 | volume = 104 | issue = 25 | pages = 7017–7020 | doi = 10.1021/ja00389a021 }}
3. ^{{cite journal | author = Spokoyny, A. M. | title = New ligand platforms featuring boron-rich clusters as organomimetic substituents | journal =Pure and Applied Chemistry | year = 2013 | volume = 85 | issue = 5 |pages = 903–919 | doi = 10.1351/PAC-CON-13-01-13 | pmc = 3845684 }}
4. ^{{Greenwood&Earnshaw2nd}}
5. ^Advanced Inorganic Chemistry, Sixth Edition, F. A. Cotton, G. Wilkinson, C. A. Murillo, and M. Bochmann, Wiley Interscience, 1999, Chapter 5 (R. N. Grimes).
6. ^Lipscomb W.N. Boron Hydrides. Benjamin, New York (1963)|
7. ^{{cite journal|title=1-B₉H₉CH^- and B₁₁H₁₁CH^-|author=W. H. Knoth|journal=J. Am. Chem. Soc.|year=1967|volume=89|pages=1274–1275|doi=10.1021/ja00981a048}}
8. ^{{cite journal|authors=Tanaka, N.; Shoji, Y.; Fukushima, T.|title=Convenient Route to Monocarba-closo-dodecaborate Anions. |journal=Organometallics|year=2016|volume=35|pages=2022–2025|doi=10.1021/acs.organomet.6b00309}}
9. ^{{cite journal|journal=Acta Crystallogr.|year=1966|volume=20|pages=631–638|doi=10.1107/S0365110X66001531|title=Further Refinements of Some Rigid Boron Compounds|author=G. S. Pawley}}
10. ^{{cite journal|authors=Popescu, A.-R.; Musteti, A. D.; Ferrer-Ugalde, A.; Viñas, C.; Núñez, R.; Teixidor, F.|title=Influential Role of Ethereal Solvent on Organolithium Compounds: The Case of Carboranyllithium|journal=Chemistry – A European Journal|year=2012|volume=18|pages=3174–3184|doi=10.1002/chem.201102626}}
11. ^{{cite journal|author=Jin, G.-X.|title=Advances in the Chemistry of Organometallic Complexes with 1,2-Dichalcogenolato-o-Carborane Ligands|journal=Coord. Chem. Rev.|year=2004|volume=248|pages=587–602|doi=10.1016/j.ccr.2004.01.002}}
12. ^Hawthorne, M. F.; Young, D. C.; Wegner, P. A. J. Am. Chem. Soc. 1965, 87, 1818
13. ^Beer, D. C.; Miller, V. R.; Sneddon, L. G.; Grimes, R. N.; Mathew, M.; Palenik, G. J. J. Am. Chem. Soc. 1973, 95, 3046
14. ^Wang, X.; Sabat, M.; Grimes, R. N. J. Am. Chem. Soc. 1995, 117, 12227
15. ^{{cite journal|authors=Deng, L.; Xie, Z.|title=Advances in the Chemistry of carboranes and metalBach, B.; Nie, Y.; Pritzkow, H.; Siebert, W. J. Organomet. Chem. 2004, 689, 429lacarboranes with more than 12 vertices|journal=Coord. Chem. Rev.|year=2007|volume=251|pages=2452–2476|doi=10.1016/j.ccr.2007.02.009}}
16. ^Bach, B.; Nie, Y.; Pritzkow, H.; Siebert, W. J. Organomet. Chem. 2004, 689, 429
17. ^{{cite journal|authors=Dash, B. P.; Satapathy, R.; Swain, B. R.; Mahanta, C. S.; Jena, B. B.; Hosmane, N. S.|title=Cobalt bis(dicarbollide) anion and its derivatives|journal=J. Organomet. Chem.|year=2017|volume=849-850|pages=170–194|doi=10.1016/j.jorganchem.2017.04.006}}
18. ^{{cite journal|authors=Issa, F.; Kassiou, M.; Rendina, L. M.|title= Boron in drug discovery: carboranes as unique pharmacophores in biologically active compounds|journal=Chem. Rev. |year=2011|volume=111|pages=5701–5722|doi=10.1021/cr2000866}}
19. ^{{cite journal | author = Soloway, A. H. |author2=Tjarks, W. |author3=Barnum, B. A. |author4=Rong, F.-G. |author5=Barth, R. F. |author6=Codogni, I. M. |author7=Wilson, J. G. | year = 1998 | title = The Chemistry of Neutron Capture Therapy | journal = Chemical Reviews | volume = 98 | issue = 4 | pages = 1515–1562 | doi = 10.1021/cr941195u| pmid = 11848941}}
20. ^{{cite journal |author1=Crowther, D. J. |author2=Baenziger, N. C. |author3=Jordan, R. F. | title = Group 4 metal dicarbollide chemistry. Synthesis, structures and reactivity of electrophilic alkyl complexes (Cp*)(C₂B₉H₁₁)M(R), M = Hf, Zr | journal = Journal of the American Chemical Society | year = 1991 | volume = 113 | issue = 4 | pages = 1455–1457 | doi = 10.1021/ja00004a080 }}
21. ^{{cite book |author1=Olah, G. A. |author2=Prakash, G. K. S. |author3=Sommer, J. |author4=Molnar, A. | title = Superacid Chemistry | edition = 2nd | year = 2009 | publisher = Wiley | page = 41 | isbn = 978-0-471-59668-4 }}
22. ^{{cite journal | author = Reed Christopher A | year = 2013 | title = Myths about the Proton. The Nature of H⁺ in Condensed Media | journal = Acc. Chem. Res. | volume = 46 | issue = 11| pages = 2567–2575 | doi = 10.1021/ar400064q | pmid=23875729 | pmc=3833890}}