Reductive Benzylation of C₆₀ Imidazoline with a Bulky Addend

Abstract

Reductive benzylation of C60 imidazoline with a bulky addend affords two 1,2,3,16-adducts (2 and 4) and one 1,2,3,4-adduct (3). Experimental and computational results indicate that the sterically favored 2 is more stable than the electronically favored 3. However, an opposite stability order is shown for the dianions of 2 and 3.

Electronic vs Steric Effects on the Stability of Anionic Species: A Case Study on the Ortho and Para Regioisomers of Organofullerenes

“…The distinct [5,6]-double bond nature in 2 •− is blurred in BnC 60 − after removing the methoxy group, as the bond length is predicted to be elongated from 1.394 to 1.417 Å (Gaussian 09 at HF/6-31G level). Meanwhile, the single [6,6]-bond in 2 •− would possess a significant double bond nature in BnC 60 − , as the bond length is predicted to be shortened from 1.511 to 1.395 Å by calculations at the same level.…”

“…The extra stability for 4 •− is likely related to the unique bond delocalization in the equatorial region of C 70 cage, 20 which may construct a cyclopentadiene structure with the [5,6]-double bond in the polar region to delocalize the acquired charge. 21 Figure 8 shows the partial structures with bond labeling for 2 •− and 4 •− calculated at the HF/6-31G level.…”

“…[5,6]-double bond in the singly and doubly reduced species of 5, and the charge-induced cleavage of the methoxy group would be therefore unlikely. It indicates that the 1,2,4,15-configuration for C 60 adducts is an electronically preferential one, where the para addition manner in the derivatives should be due to the electronic factor, rather than the steric factor.…”

“…4 Second, the fullerene derivatives are typically of electrochemical activity, rendering them suitable for the study of anionic species. 5 Although the steric factor plays an important role in formation of neutral fullerene para adducts, the preliminary result on sterically favored C 60 imidazoline derivatives indicates that such a factor has little effect in stabilizing the anionic species compared with the electronic factor, 6 suggesting an important difference between the steric and electronic factors. Herein, we report the stability examination of the anionic species of organofullerenes 1−5 (Scheme 1), which shows a distinct difference between the ortho and para adducts and may help to obtain a better understanding on the electronic vs steric effects toward the stabilization of anionic species.…”

“…For fullerene derivatives, 1,2 the electronically favored products are the ortho adducts, as all the double bonds are positioned between the two hexagons, retaining the electronic structure of pristine fullerenes. While the sterically favored ones are the para adducts, in which an electronically unfavored [5,6]double bond is introduced, 3 but this increased energy can be compensated for by a decrease in steric hindrance when bulky addends are involved. The effects of the electronic and steric factors on the stabilization of neutral organic molecules have been well studied.…”