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

Abstract

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: *.

Effective derivatization and extraction of insoluble missing lanthanum metallofullerenes La@C2n (n = 36–38) with iodobenzene

“…It has been widely accepted that the absorption spectra of fullerene adducts reflect sensitively the cage structure and the addition position rather than the nature of the addends [6,[9][10][11][12][13][14]. In fact, the respective three regioisomers of La@C 72 (C 6 H 3 Cl 2 )-I, La@C 74 (C 6 H 3 Cl 2 )-I, and La@C 74 (C 6 H 3 Cl 2 )-II show similar features in their absorption spectra, respectively.…”

Lewis Acid–Base Adducts of Sc2C2@C3v(8)-C82/N-Heterocyclic Carbene: Toward Isomerically Pure Metallofullerene Derivatives

“…2b is likely a kinetically favorable labile product that cannot be isolated from the solution. The crystallographic results of 2a unambiguously demonstrate that one polarized C−C single bond is formed between the normal carbene site C2N of the NHC and a specific [5,6,6]-carbon atom out of 17 types of nonequivalent cage carbon atoms of Sc 2 C 2 @ C 3v (8)-C 82 . Theoretical calculations demonstrate that the high regioselectivity, the unexpected addition pattern, and the quantitative formation of monoadducts are synergistic results from the cage geometry and electron distribution on the cage.…”

“…In summary, the reaction between Sc 2 C 2 @C 3v (8)-C 82 and 1 proceeds in a highly regioselective manner, which affords only two adducts (2a and 2b) quantitatively. The NHC moiety links to a specific [5,6,6]-carbon atom of Sc 2 C 2 @C 3v (8)-C 82 using its normal carbene site (C2N) in the final product 2a, which is rationalized theoretically as a consequence of the synergistic effect of electron distribution and cage geometry. In addition, 2b is also theoretically predicted to be a normal carbene monoadduct, with the addition site locating at one of the type 2 cage carbon atoms of Sc 2 C 2 @C 3v (8)-C 82 .…”

“…Even for the highly symmetric Sc 3 N@I h -C 80 , which has only two types of nonequivalent carbon atoms on the cage, its chemical reactions with different reagents normally generate two monoadduct isomers, together with numerous di-and multiadducts. For instance, the benzyne addition of Sc 3 N@C 80 afforded at least two monoadducts together with several multiadducts 4,5 and, even worse, its trifluoromethylation produced a mixture of di-and multiadducts with the number of addends ranging from 2 to 18. 6−9 Analogously, trifluoromethylation of the low-symmetric Y@C 82 affords at least two monoadducts and three multiadducts.…”

“…The N-heterocyclic carbene (NHC) moiety links to the fullerene cage via a C−C single bond of 1.520 Å, verifying the formation of a Lewis acid−base adduct. It is surprising to see that the normal carbene site C2N of the NHC links to a specific [5,6,6]-carbon atom (type 1 in Figure 1) out of the 17 kinds of nonequivalent cage carbon atoms of Sc 2 C 2 @C 3v (8)-C 82 .…”