Cage Shrinkage of Fullerene via a C₂ Loss: from IPR C₉₀(28)Cl₂₄ to Nonclassical, Heptagon-Containing C₈₈Cl_22/24

Abstract

A new case of chlorination-promoted fullerene cage shrinkage is reported. Chlorination of C90 (isolated pentagon rule isomer no. 28) with VCl4 afforded C88Cl22 with a nonclassic carbon cage (NCC) containing 1 heptagon and 13 pentagons including 2 fused pairs flanking the heptagon. The pathway of C2 abstraction from the C90 cage is suggested on the basis of density functional theory calculations.

C100 is Converted into C94Cl22 by Three Chlorination‐Promoted C2 Losses under Formation and Elimination of Cage Heptagons

“…Later, chlorination‐promoted C 2 loss reactions (C2Ls) below 400 °C were reported for several higher fullerenes 7. A single C 2 loss in the course of chlorination of C 86 (16) and C 90 (28) (isomer numbering in parentheses is according to the spiral algorithm1) yielded NC fullerene chlorides C 84 ( NC 1)Cl 32 7a and C 88 ( NC 1)Cl 22 ,7b respectively (the numeral after NC indicates the number of heptagons in the carbon cage). In C 96 , both single and double C 2 losses have been reported that gave, respectively, C 94 ( NC 1)Cl 28 and C 92 ( NC 2)Cl 32 7c.…”

“…In ref. 7b, certain mechanistic considerations have been presented regarding C 2 elimination in the chlorinated form. Without chlorination, pyrolytic degradation of higher fullerenes such as C 76 , C 78 , and C 84 into C 60 and C 70 is known to proceed only above 1000 °C8 and no clear mechanism has been suggested so far.…”

“…The C2L2 case, which yields a heptagon with three adjacent pentagons including one fused pair thereof, is implicated in a two‐step transformation from C 96 (80) to C 92 ( NC 2)Cl 32 7c. C2L3 leads to a heptagon flanked by two pairs of fused pentagons and has been observed in C 86 (16), C 90 (28), and C 96 (114), having produced C 84 ( NC 1)Cl 30 ,7d C 88 ( NC 1)Cl 22 ,7b and C 94 ( NC 1)Cl 28 ,7c respectively.…”

General rules for predicting the local aromaticity of carbon polyhedra

“…The commonly accepted explanation for the existence of non-classical fullerenes involves a combination of the following: (a) those fullerenes with a lower number of pentagon-pentagon bonds are usually more stable than those with a higher number of pentagon-pentagon bonds -this is known as the pentagon adjacent penalty rule (PAPR) [3][4][5]; (b) in fullerenes composed of squares and hexagons, it is energetically favorable when all squares are surrounded by hexagons -this is known as the isolated-square rule (ISR) [6,7]; (c) those isomers with a lower number of square-square bonds have an energetic advantage over those with a higher number of square-square bonds -this is known as the square adjacency penalty rule (SAPR) [8]. Recently, both from the experimental and the theoretical sides, the study of non-classical fullerenes has been attracting increasing interest [9][10][11][12][13][14][15][16][17].…”

Capturing C90 Isomers as CF3 Derivatives: C90(30)(CF3)14, C90(35)(CF3)16/18, and C90(45)(CF3)16/18

“…[9] Several theoretical calculations have been performed to establisht he relative stability of C 90 isomers and estimate their relative populations in the experimental mixtures.…”