The First Structurally Characterized Homofullerene (Fulleroid)

Kiely, Andrew F.; Haddon, Robert C.; Meier, Mark S.; Selegue, John P.; Brock, Carolyn Pratt; Patrick, Brian O.; Wang, Guan‐Wu; Chen, Yongsheng

doi:10.1021/ja991692y

Cited by 63 publications

(133 citation statements)

References 17 publications

(26 reference statements)

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“…Furthermore, from the point of view of aromaticity, the curved buckybowls are very attractive systems since they exhibit a compromise between strain and conjugation. The C 60 NH system [45,46] represents a possible case of homoaromaticity [47] in fullerenes, while C 60 F 18 [48±50] is a flattened fullerene possessing a benzenelike six-membered ring whose aromaticity is worth analysis. First, we analyze the changes in local aromaticities on going from planar PAHs such as benzene, naphthalene, and pyracyclene to curved PAHs such as C 20 H 10 , C 26 H 12 , and C 30 H 12 , and on to C 60 .…”

Section: Introductionmentioning

confidence: 99%

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

Poater

Fradera

Duran

et al. 2003

Chemistry A European J

153

144

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In this work we quantify the local aromaticity of six-membered rings in a series of planar and bowl-shaped polycyclic aromatic hydrocarbons (PAHs) and fullerenes. The evaluation of local aromaticity has been carried out through the use of structurally (HOMA) and magnetically (NICS) based measures, as well as by the use of a new electronically based indicator of aromaticity, the para delocalization index (PDI), which is defined as the average of all the Bader delocalization indices between para-related carbon atoms in six-membered rings. The series of PAHs selected includes C(10)H(8), C(12)H(8), C(14)H(8), C(20)H(10), C(26)H(12), and C(30)H(12), with benzene and C(60) taken as references. The change in the local aromaticity of the six-membered rings on going from benzene to C(60) is analyzed. Finally, we also compare the aromaticity of C(60) with that of C(70), open [5,6]- and closed [6,6]-C(60)NH systems, and C(60)F(18).

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Section: Introductionmentioning

confidence: 99%

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

Poater

Fradera

Duran

et al. 2003

Chemistry A European J

153

144

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“…Hence, the addition chemistry of C 70 involves both chemo-and regioselectivity. [5][6][7][8] However, the addition of carbene to the equatorial bond of C 70 (to form C 2v -C 71 H 2 ) has not been detected.We were prompted to synthesize this elusive C 2v C 71 H 2 isomer for several reasons: 1) The hydrogen-atom chemical shifts of the carbene adducts are useful for probing the local ring currents of C 70 and its hexaanion. [3,4] This relatively high bond strain in turn makes the polar regions the most reactive sites of the molecule.…”

mentioning

confidence: 99%

Addition of Carbene to the Equator of C₇₀ To Produce the Most Stable C₇₁H₂ Isomer: 2 aH‐2(12)a‐Homo(C₇₀‐D_5h(6))[5,6]fullerene

Shu

Lü

et al. 2010

Angew Chem Int Ed

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Unlike C 60 , in which all carbon-atom environments are identical, C 70 has five distinct carbon-atom environments, which give rise to eight distinct CÀC bond types. Hence, the addition chemistry of C 70 involves both chemo-and regioselectivity. The synthetic chemistry of C 70 is centered on the areas near the poles, [1, 2] as these areas have the highest curvature and hence high bond strain. [3,4] This relatively high bond strain in turn makes the polar regions the most reactive sites of the molecule. The equatorial region of C 70 , on the other hand, has little curvature and hence lower bond strain. Thus, the carbon atoms at the equator are much less reactive, as there is a much higher activation barrier to be overcome before reactions can occur. For example, carbene (CH 2 ) has been added to the polar region of C 70 , and several isomers of C 71 H 2 have been synthesized and fully characterized. [5][6][7][8] However, the addition of carbene to the equatorial bond of C 70 (to form C 2v -C 71 H 2 ) has not been detected.We were prompted to synthesize this elusive C 2v C 71 H 2 isomer for several reasons: 1) The hydrogen-atom chemical shifts of the carbene adducts are useful for probing the local ring currents of C 70 and its hexaanion. [7,[9][10][11] Computations show that the equatorial six-membered ring of C 70 has the largest diamagnetic ring current, [11,12] but no solid experimental evidence exists. 2) Theoretical studies have indicated that the sidewall of nanotubes can be opened by chemical modifications of divalent groups, such as carbene, [13] as was also confirmed indirectly by Umeyama et al.[14] C 70 can be considered as the shortest (5,5) nanotube; fully characterized C 2v C 71 H 2 would provide us with direct hard evidence of the structure of nanotube carbene adducts.3) The density functional computations in this study show that the C 2v structure has the lowest energy of all possible isomers of C 71 H 2 and is an open [6,6] homofullerene. Addition at the [6,6] junction of fullerenes mostly results in [6,6] closed adducts;[15] [6,6] open homofullerenes are stable only in special cases. [16,17] Herein we report the synthesis, characterization, and theoretical studies of the missing C 71 H 2 isomer-a homofullerene with a CH 2 group attached to the C 70 equator. Access to this elusive C 2v C 71 H 2 isomer not only enabled satisfactory clarification of the local electron delocalization of the C 70 equatorial rings and provided unambiguous support for nanotube-sidewall opening, but also provided a new member of the homofullerene family. Moreover, the pyrogenic synthesis proved to be a highly efficient approach to overcome the high activation barriers to the formation of the thermodynamically most stable isomers, as also demonstrated, for example, by the synthesis of C 60 Cl 8 and C 60 Cl 12 , in which the C 60 cage violates the isolated pentagon rule (IPR), [18] and by the synthesis of the stable unconventional fulleride C 64 H 4 . [19] The structures of all chemically possible C 70 -fullerenebased isom...

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“…Fulleroids were alternatively generated via [4+4] intramolecular cycloaddition reactions followed by a retro [2+2+2] ring-opening of the fullerene framework. [10] The addition of carbenes to metallofullerenes [1b, 11] and C 70 [12] also resulted in the formation of fulleroids. Furthermore, the manganese(III) acetate-mediated radical reaction of I h -Sc 3 N@C 80…”

Section: Angewandte Chemiementioning

confidence: 99%

The Cycloaddition Reaction of I_h‐Sc₃N@C₈₀ with 2‐Amino‐4,5‐diisopropoxybenzoic Acid and Isoamyl Nitrite to Produce an Open‐Cage Metallofullerene

et al. 2011

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The unique structural and electronic properties of endohedral metallofullerenes (EMFs) make them candidates for applications in nanoscience and biomedicine, and the functionalization of EMFs has attracted increasing attention. [1] Various types of transformations, such as Diels-Alder reactions, 1,3dipolar cycloadditions, photochemical silylation, alkylation and carbene additions, Bingel reactions, and free-radical reactions have been reported to take place on the outer surface of EMFs. [1] Icosahedral (I h ) Sc 3 N@C 80 , the most abundant EMF, can undergo most, but not all, of the abovementioned reactions. [2] For example, the Bingel reaction of I h -Y 3 N@C 80 [3a,c] and I h -Gd 3 N@C 80 [3b] has been reported to yield methanofullerene derivatives, but the same attempted cyclopropanation reaction with I h -Sc 3 N@C 80 was not successful. [3a] The [2+2] cycloaddition of benzyne, which is known to occur with C 60[4a] and C 70 , [4b] has only recently been reported to occur with EMFs. [5] Herein, we report that the [2+2] cycloaddition of I h -Sc 3 N@C 80 with 4,5-diisopropoxybenzyne generated in situ from 2-amino-4,5-diisopropoxybenzoic acid and isoamyl nitrite in 1,2-dichlorobenzene (ODCB) in the presence of air produces an unprecedented open-cage metallofullerene.The reaction of I h -Sc 3 N@C 80 with 2-amino-4,5-diisopropoxybenzoic acid and isoamyl nitrite in a molar ratio of 1:5:6 in ODCB at 60 8C for 12 h under argon atmosphere afforded an isomeric mixture of [2+2] cycloadducts 1 and 2 in 29 % combined yield along with 48 % of recovered I h -Sc 3 N@C 80 (Scheme 1). The ratio of cycloadducts 1 and 2 was 29:71 (8 %:21 %) based on the 1 H NMR spectrum of the mixture.Scheme 1. Reaction of I h -Sc 3 N@C 80 with 2-amino-4,5-diisopropoxybenzoic acid and isoamyl nitrite under argon or air. Scandium atoms: *; nitrogen atoms: *.

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The First Structurally Characterized Homofullerene (Fulleroid)

Cited by 63 publications

References 17 publications

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

Addition of Carbene to the Equator of C₇₀ To Produce the Most Stable C₇₁H₂ Isomer: 2 aH‐2(12)a‐Homo(C₇₀‐D_5h(6))[5,6]fullerene

The Cycloaddition Reaction of I_h‐Sc₃N@C₈₀ with 2‐Amino‐4,5‐diisopropoxybenzoic Acid and Isoamyl Nitrite to Produce an Open‐Cage Metallofullerene

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The First Structurally Characterized Homofullerene (Fulleroid)

Cited by 63 publications

References 17 publications

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

An Insight into the Local Aromaticities of Polycyclic Aromatic Hydrocarbons and Fullerenes

Addition of Carbene to the Equator of C70 To Produce the Most Stable C71H2 Isomer: 2 aH‐2(12)a‐Homo(C70‐D5h(6))[5,6]fullerene

The Cycloaddition Reaction of Ih‐Sc3N@C80 with 2‐Amino‐4,5‐diisopropoxybenzoic Acid and Isoamyl Nitrite to Produce an Open‐Cage Metallofullerene

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Addition of Carbene to the Equator of C₇₀ To Produce the Most Stable C₇₁H₂ Isomer: 2 aH‐2(12)a‐Homo(C₇₀‐D_5h(6))[5,6]fullerene

The Cycloaddition Reaction of I_h‐Sc₃N@C₈₀ with 2‐Amino‐4,5‐diisopropoxybenzoic Acid and Isoamyl Nitrite to Produce an Open‐Cage Metallofullerene