Editing Buckminsterfullerene (section)

==Chemical reactions and properties==
{{chem|C|60}} undergoes six reversible, one-electron reductions, ultimately generating {{chem|C|60|6-}}. Its [[oxidation]] is irreversible. The first reduction occurs at ≈−1.0&nbsp;[[Volt|V]] ([[Ferrocene|Fc]]/{{chem|Fc|+}}), showing that C<sub>60</sub> is a reluctant electron acceptor.  {{chem|C|60}} tends to avoid having double bonds in the pentagonal rings, which makes electron [[delocalization]] poor, and results in {{chem|C|60}} not being "[[superaromatic]]". C<sub>60</sub> behaves like an electron deficient [[alkene]]. For example, it reacts with some nucleophiles.<ref name="buckminsterfullerene3"/><ref name=Reed/>

=== Hydrogenation ===
C<sub>60</sub> exhibits a small degree of aromatic character, but it still reflects localized double and single C–C bond characters. Therefore, C<sub>60</sub> can undergo addition with hydrogen to give polyhydrofullerenes. C<sub>60</sub> also undergoes [[Birch reduction]]. For example, C<sub>60</sub> reacts with lithium in liquid ammonia, followed by ''tert''-butanol to give a mixture of polyhydrofullerenes such as C<sub>60</sub>H<sub>18</sub>, C<sub>60</sub>H<sub>32</sub>, C<sub>60</sub>H<sub>36</sub>, with C<sub>60</sub>H<sub>32</sub> being the dominating product. This mixture of polyhydrofullerenes can be re-oxidized by [[2,3-Dichloro-5,6-dicyano-1,4-benzoquinone|2,3-dichloro-5,6-dicyano-1,4-benzoquinone]] to give C<sub>60</sub> again.

A selective hydrogenation method exists. Reaction of C<sub>60</sub> with 9,9′,10,10′-dihydroanthracene under the same conditions, depending on the time of reaction, gives C<sub>60</sub>H<sub>32</sub> and C<sub>60</sub>H<sub>18</sub> respectively and selectively.<ref name="InorgChem">{{cite book| title = Inorganic Chemistry| edition = 3rd| chapter = Chapter 14: The group 14 elements| author1 = Catherine E. Housecroft| author2 = Alan G. Sharpe| publisher = Pearson| year = 2008| isbn = 978-0-13-175553-6}}</ref>

===Halogenation===
Addition of [[fluorine]], [[chlorine]], and [[bromine]] occurs for C<sub>60</sub>. Fluorine atoms are small enough for a 1,2-addition, while Cl<sub>2</sub> and Br<sub>2</sub> add to remote C atoms due to [[steric factor]]s. For example, in C<sub>60</sub>Br<sub>8</sub> and C<sub>60</sub>Br<sub>24</sub>, the Br atoms are in 1,3- or 1,4-positions with respect to each other. Under various conditions a vast number of halogenated derivatives of C<sub>60</sub> can be produced, some with an extraordinary selectivity on one or two isomers over the other possible ones. Addition of fluorine and chlorine usually results in a flattening of the C<sub>60</sub> framework into a drum-shaped molecule.<ref name="InorgChem" />

===Addition of oxygen atoms===
Solutions of C<sub>60</sub> can be oxygenated to the [[epoxide]] C<sub>60</sub>O. Ozonation of C<sub>60</sub> in 1,2-xylene at 257K gives an intermediate ozonide C<sub>60</sub>O<sub>3</sub>, which can be decomposed into 2 forms of C<sub>60</sub>O. Decomposition of C<sub>60</sub>O<sub>3</sub> at 296&nbsp;K gives the epoxide, but photolysis gives a product in which the O atom bridges a 5,6-edge.<ref name="InorgChem" />

[[File:Addition of O atom into C60 Scheme.png|none|300px]]

===Cycloadditions===
The [[Diels–Alder reaction]] is commonly employed to functionalize C<sub>60</sub>. Reaction of C<sub>60</sub> with appropriate substituted diene gives the corresponding adduct.

The Diels–Alder reaction between C<sub>60</sub> and 3,6-diaryl-1,2,4,5-tetrazines affords C<sub>62</sub>. The C<sub>62</sub> has the structure in which a four-membered ring is surrounded by four six-membered rings.

[[File:3D structure of C62 derivative from C60 update.jpg|thumb|A C<sub>62</sub> derivative [C<sub>62</sub>(C<sub>6</sub>H<sub>4</sub>-4-Me)<sub>2</sub>] synthesized from C<sub>60</sub> and 3,6-bis(4-methylphenyl)-3,6-dihydro-1,2,4,5-tetrazine]]

The C<sub>60</sub> molecules can also be coupled through a [2+2] [[cycloaddition]], giving the dumbbell-shaped compound C<sub>120</sub>. The coupling is achieved by high-speed vibrating milling of C<sub>60</sub> with a catalytic amount of [[potassium cyanide|KCN]]. The reaction is reversible as C<sub>120</sub> dissociates back to two C<sub>60</sub> molecules when heated at {{convert|450|K}}. Under high pressure and temperature, repeated [2+2] cycloaddition between C<sub>60</sub> results in polymerized fullerene chains and networks. These polymers remain stable at ambient pressure and temperature once formed, and have remarkably interesting electronic and magnetic properties, such as being [[ferromagnetism|ferromagnetic]] above room temperature.<ref name="InorgChem" />

===Free radical reactions===
Reactions of C<sub>60</sub> with [[free radicals]] readily occur. When C<sub>60</sub> is mixed with a disulfide RSSR, the radical C<sub>60</sub>SR• forms spontaneously upon irradiation of the mixture.

Stability of the radical species C<sub>60</sub>Y<sup>•</sup> depends largely on [[steric factor]]s of Y. When ''tert''-butyl halide is photolyzed and allowed to react with C<sub>60</sub>, a reversible inter-cage C–C bond is formed:<ref name="InorgChem" />

[[File:Free radical reaction of fullerene with tert-butyl radical.png|none|600px]]

===Cyclopropanation (Bingel reaction)===
Cyclopropanation (the [[Bingel reaction]]) is another common method for functionalizing C<sub>60</sub>. Cyclopropanation of C<sub>60</sub> mostly occurs at the junction of 2 hexagons due to steric factors.

The first cyclopropanation was carried out by treating the β-bromomalonate with C<sub>60</sub> in the presence of a base. Cyclopropanation also occur readily with [[diazomethane]]s. For example, diphenyldiazomethane reacts readily with C<sub>60</sub> to give the compound C<sub>61</sub>Ph<sub>2</sub>.<ref name="InorgChem" /> [[Phenyl-C61-butyric acid methyl ester|Phenyl-C<sub>61</sub>-butyric acid methyl ester]] derivative prepared through cyclopropanation has been studied for use in [[organic solar cells]].

===Redox reactions===
====C<sub>60</sub> anions====
{{See also|Fullerides}}
The [[LUMO]] in C<sub>60</sub> is triply degenerate, with the [[HOMO]]–[[LUMO]] separation relatively small. This small gap suggests that reduction of C<sub>60</sub> should occur at mild potentials leading to fulleride anions, [C<sub>60</sub>]<sup>''n''−</sup> (''n''&nbsp;=&nbsp;1–6). The midpoint potentials of 1-electron reduction of buckminsterfullerene and its anions is given in the table below:

{| class="wikitable"
! colspan=2|Reduction potential of C<sub>60</sub> at 213&nbsp;K
|-
! Half-reaction !! ''E''° (V)
|-
| C<sub>60</sub> + e<sup>−</sup> ⇌ {{chem|C|60|-}} || −0.169
|-
| {{chem|C|60|-}} + e<sup>−</sup> ⇌ {{chem|C|60|2-}} || −0.599
|-
| {{chem|C|60|2-}} + e<sup>−</sup> ⇌ {{chem|C|60|3-}} || −1.129
|-
| {{chem|C|60|3-}} + e<sup>−</sup> ⇌ {{chem|C|60|4-}} || −1.579
|-
| {{chem|C|60|4-}} + e<sup>−</sup> ⇌ {{chem|C|60|5-}} || −2.069
|-
| {{chem|C|60|5-}} + e<sup>−</sup> ⇌ {{chem|C|60|6-}} || −2.479
|}

C<sub>60</sub> forms a variety of [[charge-transfer complexes]], for example with [[tetrakis(dimethylamino)ethylene]]:
:C<sub>60</sub> + C<sub>2</sub>(NMe<sub>2</sub>)<sub>4</sub> → [C<sub>2</sub>(NMe<sub>2</sub>)<sub>4</sub>]<sup>+</sup>[C<sub>60</sub>]<sup>−</sup>
This salt exhibits [[ferromagnetism]] at 16&nbsp;K.

====C<sub>60</sub> cations====
C<sub>60</sub> oxidizes with difficulty. Three reversible oxidation processes have been observed by using [[cyclic voltammetry]] with ultra-dry [[methylene chloride]] and a supporting electrolyte with extremely high oxidation resistance and low nucleophilicity, such as [<sup>n</sup>Bu<sub>4</sub>N] [AsF<sub>6</sub>].<ref name=Reed>{{cite journal |doi=10.1021/cr980017o|title=Discrete Fulleride Anions and Fullerenium Cations|year=2000|last1=Reed|first1=Christopher A.|last2=Bolskar|first2=Robert D.|journal=Chemical Reviews|volume=100|issue=3|pages=1075–1120|pmid=11749258 |s2cid=40552372 |url=https://escholarship.org/uc/item/60b5m71z}}</ref>

{| class="wikitable"
! colspan=2|Reduction potentials of C<sub>60</sub> oxidation at low temperatures
|-
! Half-reaction !! ''E''° (V)
|-
| C<sub>60</sub> ⇌ {{chem|C|60|+}} || +1.27
|-
| {{chem|C|60|+}} ⇌ {{chem|C|60|2+}} || +1.71
|-
| {{chem|C|60|2+}} ⇌ {{chem|C|60|3+}} || +2.14
|}

===Metal complexes===
{{main|Fullerene ligand}}
C<sub>60</sub> forms complexes akin to the more common alkenes. Complexes have been reported [[molybdenum]], [[tungsten]], [[platinum]], [[palladium]], [[iridium]], and [[titanium]].  The pentacarbonyl species are produced by [[photochemical reaction]]s.

: M(CO)<sub>6</sub> + C<sub>60</sub> → M(''η''<sup>2</sup>-C<sub>60</sub>)(CO)<sub>5</sub> + CO (M = Mo, W)

In the case of platinum complex, the labile ethylene ligand is the leaving group in a thermal reaction:
: Pt(''η''<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>)(PPh<sub>3</sub>)<sub>2</sub> + C<sub>60</sub> → Pt(''η''<sup>2</sup>-C<sub>60</sub>)(PPh<sub>3</sub>)<sub>2</sub> + C<sub>2</sub>H<sub>4</sub>

[[Titanocene]] complexes have also been reported:
: (''η''<sup>5</sup>-[[Cyclopentadienyl|Cp]])<sub>2</sub>Ti(''η''<sup>2</sup>-(CH<sub>3</sub>)<sub>3</sub>SiC≡CSi(CH<sub>3</sub>)<sub>3</sub>) + C<sub>60</sub> → (''η''<sup>5</sup>-Cp)<sub>2</sub>Ti(''η''<sup>2</sup>-C<sub>60</sub>) + (CH<sub>3</sub>)<sub>3</sub>SiC≡CSi(CH<sub>3</sub>)<sub>3</sub>

Coordinatively unsaturated precursors, such as [[Vaska's complex]], for [[adduct]]s with C<sub>60</sub>:

: ''trans''-Ir(CO)Cl(PPh<sub>3</sub>)<sub>2</sub> + C<sub>60</sub> → Ir(CO)Cl(''η''<sup>2</sup>-C<sub>60</sub>)(PPh<sub>3</sub>)<sub>2</sub>

One such iridium complex, [Ir(''η''<sup>2</sup>-C<sub>60</sub>)(CO)Cl(Ph<sub>2</sub>CH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>OCH<sub>2</sub>Ph)<sub>2</sub>] has been prepared where the metal center projects two electron-rich 'arms' that embrace the C<sub>60</sub> guest.<ref name="SupraChem">{{cite book| title = Supramolecular Chemistry| edition = 2nd|author1=Jonathan W. Steed |author2=Jerry L. Atwood |name-list-style=amp | publisher = Wiley| year = 2009| isbn = 978-0-470-51233-3}}</ref>

===Endohedral fullerenes===
{{main|Endohedral fullerene|Endohedral hydrogen fullerene}}

Metal atoms or certain small molecules such as H<sub>2</sub> and noble gas can be encapsulated inside the C<sub>60</sub> cage. These endohedral fullerenes are usually synthesized by doping in the metal atoms in an arc reactor or by laser evaporation. These methods gives low yields of endohedral fullerenes, and a better method involves the opening of the cage, packing in the atoms or molecules, and closing the opening using certain [[organic reactions]]. This method, however, is still immature and only a few species have been synthesized this way.<ref>{{cite journal | last1 = Rodríguez-Fortea | first1 = Antonio | last2 = Balch | first2 = Alan L. | last3 = Poblet | first3 = Josep M. | year = 2011 | title = Endohedral metallofullerenes: a unique host–guest association | journal = Chem. Soc. Rev. | volume = 40 | issue = 7| pages = 3551–3563 | doi = 10.1039/C0CS00225A | pmid = 21505658}}</ref>

Endohedral fullerenes show distinct and intriguing chemical properties that can be completely different from the encapsulated atom or molecule, as well as the fullerene itself. The encapsulated atoms have been shown to perform circular motions inside the C<sub>60</sub> cage, and their motion has been followed using [[NMR spectroscopy]].<ref name="SupraChem" />