Reaction of [70]Fullerene with Tetraethyl Methylenediphosphonate or Diethyl (Cyanomethyl)phosphonate Revisited

Abstract

The reaction of C70 with CH2(PO3Et2)2 or CH2(PO3Et2)CN in the presence of NaH has been reinvestigated. The reaction of C70 with the former phosphonate affords five products. Products 1–3 have molecular structures C70>CH(PO3Et2), whereas products 4 and 5 have molecular structures C70>C(PO3Et2)2. In contrast, only one product 6, with a molecular structure C70>C(PO3Et2)CN, could be isolated from the reaction of C70 with CH2(PO3Et2)CN and NaH. Ultrasonication was used to shorten the reaction times and increase the product yields. No product resulting from addition to the C7–C21 bond of C70 was observed in either cycloaddition reaction. Accordingly, the previously reported major products 3 and 6, which were assigned as the C7–C21 isomers, should be reassigned as the C1–C2 isomers. This correction is very important for understanding the reactivity of C70. Our reassignments are further supported by theoretical calculations. The newly isolated minor products 1, 2, and 4 were identified as the C5–C6 isomers. The present work proves that the reactivity order of the bonds in C70 for these two reactions is C1–C2 > C5–C6. These results resolve the confusion caused by previous incorrect product assignments.

Reductive Activation of C70 Equatorial Carbons and Structurally Characterized C70 δ-Adduct with Closed [5,6]-Ring Fusion

“…It is noteworthy that the d -bound o -BrCH 2 C 6 H 4 CH 2 C 70 – could in principle result in both δ- and γ-isomers. However, calculations at the B3LYP/6-31G level predicted energy levels of 0.0, 2.9, 9.0, and 19.5 kcal/mol for the α-, β-, δ-, and γ-isomers, respectively, implying that the γ-isomer is unlikely to be stable, rationalizing the unavailability of this isomer, which is consistent with previous work …”

“…The chemistry of fullerenes is governed by the release of the strain energy caused by the deviation from the planarity of sp 2 -hybridized carbon atoms. , The principle is well observed for the reactions of C 70 , where the more strained carbons in the polar region (types a – c in Figure ) are more reactive with preferential formation of derivatives at the most and second most curved bonds (α- and β-bonds, Figure ) for ortho-addition reactions. − In contrast, the less strained carbon atoms in the flat equatorial region of C 70 are inert with very limited reports so far on the addition at the δ-bond. ,, Notably, the δ-adduct is the fifth most stable isomer predicted theoretically using C 70 H 2 as a model, next only to the α- and β-adducts and two para isomers with additions at d , d -carbons across the equator and a , c -carbons, which have all been obtained in significant amounts, − ,,, suggesting that the unavailability of the δ-isomer is likely due to the kinetic rather than thermodynamic factor.…”

Regioselective Oxazolination of C702– and Formation of cis-1 C70 Adduct with Respect to the Apical Pentagon

“…The formation of a C1–C2 C 70 adduct is further supported by the UV–vis spectroscopic measurement (Figure S5, Supporting Information), which has been shown to be sensitive to the addition pattern rather than the types of addends. ,− The UV–vis spectrum of the compound shows the typical absorptions for C1–C2 adducts, with absorption bands at 343, 400, 465, 538, and 660 nm.…”