Cubane: Difference between revisions

{{Short description|Organic compound (C8H8) with a cube carbon structure}}

| Watchedfields = changed

| verifiedrevid = 443545029

| Name = Cubane

| ImageFileL1 = Cuban.svg

| ImageNameL1 = Structural formula of cubane

| ImageFileR1 = Cubane molecule ball.png

| ImageNameR1 = Ball-and-stick model of cubane

| PIN = Cubane<ref name=iupac2013>{{cite book | title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = [[Royal Society of Chemistry|The Royal Society of Chemistry]] | date = 2014 | location = Cambridge | page = 169 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4 | quote = The retained names adamantane and cubane are used in general nomenclature and as preferred IUPAC names.}}</ref>

| SystematicName = Pentacyclo[4.2.0.0^2,5.0^3,8.0^4,7]octane

| OtherNames =

|Section1={{Chembox Identifiers

| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}

| CASNo_Ref = {{cascite|correct|??}}

| UNII_Ref = {{fdacite|correct|FDA}}

| UNII = Z5HM0Q7DK1

| ChEBI_Ref = {{ebicite|correct|EBI}}

| InChI = 1/C8H8/c1-2-5-3(1)7-4(1)6(2)8(5)7/h1-8H

|Section2={{Chembox Properties

| Formula = {{chem2|C8H8}}

| MolarMass = 104.15 g/mol

| Density = 1.29 g/cm³

| Appearance = Transparent<ref name=ch>{{cite web | url=https://www.ch.ic.ac.uk/local/projects/b_muir/Cubane/Cubanepro/Start.html | title=Start }}</ref> crystalline solid

| MeltingPtC = 133.5

| MeltingPt_ref = <ref name = Biegasiewicz />

| BoilingPtC = 161.6

| BoilingPt_ref = <ref name= Biegasiewicz />

|Section8={{Chembox Related

| OtherFunction = [[Cuneane]]<br />[[Dodecahedrane]]<br />[[Tetrahedrane]]<br />[[Prismane]]<br />[[Prismane C8]]

| OtherFunction_label = [[hydrocarbon]]s

| OtherCompounds = [[Octafluorocubane]]<br />[[Octanitrocubane]]<br />[[Octaazacubane]]

'''Cubane''' is a synthetic [[hydrocarbon]] compound with the [[Chemical formula|formula]] {{chem2|C8H8}}. It consists of eight [[carbon]] atoms arranged at the corners of a [[Cube (geometry)|cube]], with one [[hydrogen]] atom attached to each carbon atom. A solid [[crystal]]line substance, cubane is one of the [[Platonic hydrocarbon]]s and a member of the [[prismanes]]. It was first synthesized in 1964 by [[Philip Eaton]] and Thomas Cole.<ref name="eaton-1964" /> Before this work, Eaton believed that cubane would be impossible to synthesize due to the "required 90 degree [[molecular geometry|bond angles]]".<ref>{{cite book |last1=Teachers |first1=University of New South Wales Summer School for Chemistry |title=Approach to Chemistry: Lectures and Workshop Reports of the ... Summer School for Chemistry Teachers |date=1963 |publisher=The University |page=98 |url=https://books.google.com/books?id=cFA0AQAAIAAJ |language=en}} "This compound was described only a few months ago and, curiously enough, it is quite easy to make, although only a year ago I would have predicted that it would be difficult, or even impossible, to synthesize."</ref><ref>{{cite book |last1=Moore |first1=John W. |last2=Stanitski |first2=Conrad L. |last3=Jurs |first3=Peter C. |title=Chemistry: The Molecular Science |date=2002 |publisher=Harcourt College Publishers |isbn=978-0-03-032011-8 |page=372 |url=https://books.google.com/books?id=XjcvAQAAIAAJ |language=en}} "This sharp bond angle creates severe bond strain in cubane, a compound thought previously impossible to synthesize because of the required 90° bond angles."</ref> The cubic shape requires the carbon atoms to adopt an unusually sharp 90° bonding angle, which would be highly [[strain (chemistry)|strained]] as compared to the [[tetrahedral molecular geometry#Tetrahedral bond angle|109.45° angle]] of a [[tetrahedral geometry|tetrahedral]] carbon. Once formed, cubane is quite [[kinetic stability|kinetically stable]], due to a lack of readily available decomposition paths. It is the simplest hydrocarbon with [[octahedral symmetry]].

Having high potential energy and kinetic stability makes cubane and its derivative compounds useful for controlled energy storage. For example, [[octanitrocubane]] and [[heptanitrocubane]] have been studied as high-performance explosives. These compounds also typically have a very high [[density]] for hydrocarbon molecules. The resulting high [[energy density]] means a large amount of energy can be stored in a comparably smaller amount of space, an important consideration for applications in fuel storage and energy transport. Furthermore, their geometry and stability make them suitable [[isostere]]s for benzene rings.<ref>{{Cite journal |last=Wiesenfeldt |first=Mario P. |last2=Rossi-Ashton |first2=James A. |last3=Perry |first3=Ian B. |last4=Diesel |first4=Johannes |last5=Garry |first5=Olivia L. |last6=Bartels |first6=Florian |last7=Coote |first7=Susannah C. |last8=Ma |first8=Xiaoshen |last9=Yeung |first9=Charles S. |last10=Bennett |first10=David J. |last11=MacMillan |first11=David W. C. |date=June 2023 |title=General access to cubanes as benzene bioisosteres |url=https://www.nature.com/articles/s41586-023-06021-8 |journal=Nature |language=en |volume=618 |issue=7965 |pages=513–518 |doi=10.1038/s41586-023-06021-8 |issn=1476-4687|pmc=10680098 }}</ref>

The classic 1964 synthesis starts with the conversion of [[2-cyclopentenone]] to 2-bromo[[cyclopentadienone]]:<ref name="eaton-1964"/><ref name=eaton1964 />

[[File:Cyclopentenone to 2-bromocyclopentadienone.png|500px|class=skin-invert]]

[[Allylic]] [[bromination]] with [[N-Bromosuccinimide|''N''-bromosuccinimide]] in [[carbon tetrachloride]] followed by addition of molecular bromine to the [[alkene]] gives a 2,3,4-tribromocyclopentanone. Treating this compound with [[diethylamine]] in [[diethyl ether]] causes [[elimination reaction|elimination]] of two equivalents of [[hydrogen bromide]] to give the diene product.

[[File:CubaneSynthesis.png|thumb|left|500px|Eaton's 1964 synthesis of cubane]]{{clear left}}

The construction of the eight-carbon cubane framework begins when 2-bromocyclopentadienone undergoes a spontaneous [[Diels-Alder reaction|Diels-Alder dimerization]]. One ketal of the [[Endo-exo isomerism|''endo'' isomer]] is subsequently selectively deprotected with aqueous [[hydrochloric acid]] to '''3'''.

In the next step, the ''endo'' isomer '''3''' (with both [[alkene]] groups in close proximity) forms the cage-like isomer '''4''' in a [[photochemical]] [2+2] [[cycloaddition]]. The [[haloketone|bromoketone]] group is converted to ring-contracted [[carboxylic acid]] '''5''' in a [[Favorskii rearrangement]] with [[potassium hydroxide]]. Next, the thermal [[decarboxylation]] takes place through the [[acid chloride]] (with [[thionyl chloride]]) and the [[tert-butyl|''tert''-butyl]] [[perester]] '''6''' (with [[Tert-Butyl hydroperoxide|''tert''-butyl hydroperoxide]] and [[pyridine]]) to '''7'''; afterward, the acetal is once more removed in '''8'''. A second Favorskii rearrangement gives '''9''', and finally another decarboxylation gives, via '''10''', cubane ('''11''').

A more approachable laboratory synthesis of disubstituted cubane involves bromination of the ethylene ketal of [[cyclopentanone]] to give a tribromocyclopentanone derivative. Subsequent steps involve dehydrobromination, Diels-Alder dimerization, etc.<ref>{{Cite journal|doi=10.1071/C97021|title=Dimethyl Cubane-1,4-dicarboxylate: A Practical Laboratory Scale Synthesis|year=1997|last1=Bliese|first1=Marianne|last2=Tsanaktsidis|first2=John|journal=Australian Journal of Chemistry|volume=50|issue=3|page=189}}</ref><ref>{{Cite web|last=Fluorochem|first=Inc|date=July 1989|title=Cubane Derivatives for Propellant Applications|url=https://apps.dtic.mil/sti/pdfs/ADA210368.pdf|url-status=live|archive-url=https://web.archive.org/web/20210709185435/https://apps.dtic.mil/sti/pdfs/ADA210368.pdf |archive-date=2021-07-09 }}</ref>

[[File:Cuban4.svg|Alternative synthesis of a disubstituted cubane|555x555px|class=skin-invert|center]]

The resulting cubane-1,4-dicarboxylic acid is used to synthesize other substituted cubanes. Cubane itself can be obtained nearly quantitatively by photochemical decarboxylation of the thiohydroxamate ester (the [[Barton decarboxylation]]).<ref>{{Cite journal |last=Eaton |first=Philip E. |date=1992 |title=Cubane: Ausgangsverbindungen für die Chemie der neunziger Jahre und des nächsten Jahrhunderts |url=https://onlinelibrary.wiley.com/doi/10.1002/ange.19921041105 |journal=Angewandte Chemie |language=de |volume=104 |issue=11 |pages=1447–1462 |doi=10.1002/ange.19921041105|bibcode=1992AngCh.104.1447E }}</ref>

==Derivatives==

{{see also|Cubane-type cluster}}

The synthesis of the octaphenyl [[derivative (chemistry)|derivative]] from tetraphenylcyclobutadiene nickel bromide by Freedman in 1962 pre-dates that of the parent compound. It is a sparingly soluble colourless compound that melts at 425–427&nbsp;°C.<ref name= Biegasiewicz /><ref name=freedman1961 /><ref name=freedman1962 /><ref name=freedman1965 /> A [[hypercubane]], with a [[hypercube]]-like structure, was predicted to exist in a 2014 publication.<ref>{{cite journal|last=Pichierri|first=F.|journal=Chem. Phys. Lett.|date=2014|volume=612|pages=198–202|doi=10.1016/j.cplett.2014.08.032|title= Hypercubane: DFT-based prediction of an ''O_h''-symmetric double-shell hydrocarbon|bibcode=2014CPL...612..198P}}</ref><ref>{{Cite web | url=http://www.compchemhighlights.org/2014/12/hypercubane-dft-based-prediction-of-oh.html |title = Hypercubane: DFT-based prediction of an Oh-symmetric double-shell hydrocarbon}}</ref> Two isomers of [[cubene]] have been synthesized, and a third analyzed [[computational chemistry|computationally]]. The alkene in ''ortho''-cubene is exceptionally reactive due to its [[pyramidalization|pyramidalized geometry]]. At the time of its synthesis, this was the most pyramidalized alkene to have been made.<ref>{{cite journal |title= Cubene (1,2-dehydrocubane) |first1= Philip E. |last1= Eaton |first2= Michele |last2= Maggini |journal= J. Am. Chem. Soc. |year= 1988 |volume= 110 |issue= 21 |pages= 7230–7232 |doi= 10.1021/ja00229a057 }}</ref> The ''meta''-cubene isomer is even less stable, and the ''para''-cubene isomer probably only exists as a [[diradical]] rather than an actual diagonal bond.<ref>{{cite book |title= Strained Hydrocarbons |url= https://archive.org/details/strainedhydrocar00hypo_746 |url-access= limited |editor-first= Helena |editor-last= Dodziuk |chapter= 2.3 A Theoretical Approach to the Study and Design of Prismane Systems |first1= Ruslan M. |last1= Minyaev |first2= Vladimir I. |last2= Minkin |first3= Tatyana N. |last3= Gribanova |publisher= Wiley |year= 2009 |isbn= 9783527627141 |page= [https://archive.org/details/strainedhydrocar00hypo_746/page/n76 55] }}</ref><!-- not sure how to format this; want to reference the section/page of relevance, but it's in a collected work that already consumes the book's overall ed/title and chapter's author/title -->

In 2022, both [[heptafluorocubane]] and [[octafluorocubane]] were synthesized.<ref>{{cite journal |vauthors=Sugiyama M, Akiyama M, Yonezawa Y, Komaguchi K, Higashi M, Nozaki K, Okazoe T |date=August 2022 |title=Electron in a cube: Synthesis and characterization of perfluorocubane as an electron acceptor |journal=Science |volume=377 |issue=6607 |pages=756–759 |doi=10.1126/science.abq0516 |pmid=35951682 |bibcode=2022Sci...377..756S |s2cid=251515925}}</ref> Octafluorocubane is of theoretical interest because of its unusual [[electronic structure]],<ref>Pichierri, F. Substituent effects in cubane and hypercubane: a DFT and QTAIM study. ''Theor Chem Acc'' 2017; 136: 114. {{doi|10.1007/s00214-017-2144-5}}</ref> which is indicated by its susceptibility to undergo reduction to a detectable [[anion]] {{chem|C|8|F|8|-}}, with a free electron trapped inside the cube, in effect making it the world's smallest box.<ref>{{cite journal |vauthors=Krafft MP, Riess JG |date=August 2022 |title=Perfluorocubane-a tiny electron guzzler |journal=Science |volume=377 |issue=6607 |pages=709 |doi=10.1126/science.adc9195 |pmid=35951708 |bibcode=2022Sci...377..709K |s2cid=251517529|url=https://hal.science/hal-03873082 }}</ref>

==Cubylcubanes and oligocubanes==

Cubene (1,2-dehydrocubane) and 1,4-cubanediyl(1,4-dehydrocubane) are enormously strained compounds which both undergo [[nucleophilic addition]] very rapidly, and this has enabled chemists to synthesize cubylcubane. X-ray diffraction structure solution has shown that the central cubylcubane bond is exceedingly short (1.458 Å), much shorter than the typical C-C single bond (1.578 Å). This is attributed to the fact that the exocyclic orbitals of cubane are s-rich and close to the nucleus.<ref>{{cite journal |last1=Gilardi |first1=Richard. |last2=Maggini |first2=Michele. |last3=Eaton |first3=Philip E. |title=X-ray structures of cubylcubane and 2-tert-butylcubylcubane: short cage-cage bonds |journal=Journal of the American Chemical Society |date=1 October 1988 |volume=110 |issue=21 |pages=7232–7234 |doi=10.1021/ja00229a058 |issn=0002-7863}}</ref> Chemists at the [[University of Chicago]] extended and modified the sequence in a way that permits the preparation of a host of [n]cubylcubane oligomers.<ref>{{cite journal |last1=Eaton |first1=Philip E. |title=Cubanes: Starting Materials for the Chemistry of the 1990s and the New Century |journal=Angewandte Chemie International Edition in English |date=1992 |volume=31 |issue=11 |pages=1421–1436 |doi=10.1002/anie.199214211 |language=en |issn=1521-3773}}</ref> The [n]cubylcubanes are rigid molecular rods with the particular promise at the time of making [[liquid crystals]] with exceptional UV transparency. As the number of linked cubane units increases, the solubility of [n]cubylcubane plunges; as a result, only limited chain length (up to 40 units) have been synthesized in solutions. The skeleton of [n]cubylcubanes is still composed of enormously strained carbon cubes, which therefore limit its stability. In contrast, researchers at [[Penn State University]] showed that poly-cubane synthesized by solid-state reaction is 100% sp³ carbon bonded with a tetrahedral angle (109.5°) and exhibits exceptional optical properties (high [[refractive index]]).<ref>{{cite journal |last1=Huang |first1=Haw-Tyng |last2=Zhu |first2=Li |last3=Ward |first3=Matthew D. |last4=Wang |first4=Tao |last5=Chen |first5=Bo |last6=Chaloux |first6=Brian L. |last7=Wang |first7=Qianqian |last8=Biswas |first8=Arani |last9=Gray |first9=Jennifer L. |last10=Kuei |first10=Brooke |last11=Cody |first11=George D. |last12=Epshteyn |first12=Albert |last13=Crespi |first13=Vincent H. |last14=Badding |first14=John V. |last15=Strobel |first15=Timothy A. |title=Nanoarchitecture through Strained Molecules: Cubane-Derived Scaffolds and the Smallest Carbon Nanothreads |journal=Journal of the American Chemical Society |date=21 January 2020 |volume=142 |issue=42 |pages=17944–17955 |doi=10.1021/jacs.9b12352 |pmid=31961671 |s2cid=210870993 |issn=0002-7863}}</ref>

[[Cuneane]] may be produced from cubane by a [[metal-ion-catalyzed σ-bond rearrangement]].<ref name=March /><ref name=kindler />

[[File:Cuban_zu_Cunean.svg|176x176px|class=skin-invert]]

With a rhodium catalyst, it first forms ''syn''-tricyclooctadiene, which can thermally decompose to cyclooctatetraene at 50–60&nbsp;°C.<ref>{{Cite journal |last1=Cassar |first1=Luigi |last2=Eaton |first2=Philip E. |last3=Halpern |first3=Jack |date=1970 |title=Catalysis of symmetry-restricted reactions by transition metal compounds. Valence isomerization of cubane |url=https://pubs.acs.org/doi/abs/10.1021/ja00714a075 |journal=Journal of the American Chemical Society |language=en |volume=92 |issue=11 |pages=3515–3518 |doi=10.1021/ja00714a075 |issn=0002-7863}}</ref>

[[File:Cubane_to_cyclooctatetraene.svg|400x400px|class=skin-invert]]

*[[Tetrahedrane]]

==References==

{{reflist|colwidth=30em

|refs=

<ref name= Biegasiewicz >{{cite journal| last1 = Biegasiewicz | first1 = Kyle | last2 = Griffiths | first2 = Justin | last3 = Savage | first3 = G. Paul | last4 = Tsanakstidis | first4 = John | last5 = Priefer | first5 = Ronny | year = 2015 | title = Cubane: 50 years later | journal = Chemical Reviews| volume = 115 | issue = 14 | pages = 6719–6745 | doi=10.1021/cr500523x | pmid=26102302}}</ref>

<ref name="eaton-1964">{{cite journal|title=Cubane|first1=Philip E.|last1=Eaton|first2=Thomas W.|last2=Cole|journal=[[J. Am. Chem. Soc.]]|date=1964|volume=86|issue=15|pages=3157–3158|doi=10.1021/ja01069a041}}</ref>

<ref name=eaton1964 >{{cite journal|title=The Cubane System|first1=Philip E.|last1=Eaton|first2=Thomas W.|last2=Cole|journal=[[J. Am. Chem. Soc.]]|date=1964|volume=86|issue=5|pages=962–964|doi=10.1021/ja01059a072}}</ref>

<ref name=March>{{cite book|first1=Michael B.|last1=Smith|first2=Jerry|last2=March|title=March's Advanced Organic Chemistry|url=https://archive.org/details/organicchemistry00mich_115|url-access=limited|edition=5th|publisher=John Wiley & Sons|date=2001|page=[https://archive.org/details/organicchemistry00mich_115/page/n1477 1459]|isbn=0-471-58589-0}}</ref>

<ref name=kindler>{{cite journal|title=Studien über den Mechanismus chemischer Reaktionen, XXIII. Hydrierungen von Nitrilen unter Verwendung von Terpenen als Wasserstoffdonatoren|first1=K.|last1=Kindler|first2=K.|last2=Lührs|journal=[[Chem. Ber.]]|volume=99|date=1966|pages=227–232|doi=10.1002/cber.19660990135}}</ref>

<ref name=freedman1961>{{cite journal|title=Tetraphenylcyclobutadiene Derivatives. II.1 Chemical Evidence for the Triplet State|first=H. H.|last=Freedman|journal=[[J. Am. Chem. Soc.]]|date=1961|volume=83|issue=9|pages=2195–2196|doi=10.1021/ja01470a037}}</ref>

<ref name=freedman1962>{{cite journal|title=Tetraphenylcyclobutadiene Derivatives. IV.1 "Octaphenylcubane"; A Dimer of Tetraphenylcyclobutadiene|first1=H. H.|last1=Freedman|first2=D. R.|last2=Petersen|journal=[[J. Am. Chem. Soc.]]|date=1962|volume=84|issue=14|pages=2837–2838|doi=10.1021/ja00873a046}}</ref>

<ref name=freedman1965>{{cite journal|title=Structure of the Dimer of tetraphenylcyclobutadiene|first1=G. S.|last1=Pawley|first2=W. N.|last2=Lipscomb|first3=H. H.|last3=Freedman|journal=[[J. Am. Chem. Soc.]]|date=1964|volume=86|issue=21|pages=4725–4726|doi=10.1021/ja01075a042}}</ref>

}}

==External links==

* [http://www.synarchive.com/syn/14 Eaton's cubane synthesis at SynArchive.com]

* [http://www.synarchive.com/syn/189 Tsanaktsidis's cubane synthesis at SynArchive.com]

* [http://www.ch.ic.ac.uk/local/projects/b_muir/Cubane/Cubanepro/Start.html Cubane chemistry at Imperial College London]

[[Category:Polycyclic nonaromatic hydrocarbons]]

[[Category:Molecular geometry]]

[[Category:Theoretical chemistry]]

[[Category:Cyclobutanes]]

[[Category:Substances discovered in the 1960s]]

[[Category:Pentacyclic compounds]]

[[Category:Cubes]]