Computational Studies of 1,3-Dipolar [3 + 2]-Cycloaddition Reactions of Fullerene-C60 with Nitrones

Richard Tia Jacob Amevor

doi:10.4172/jtco.1000117

Abstract

Solubility of fullerene-C60 improves with functionalization. 1,3-dipolar [3+2]-cycloaddition reactions of fullerene-C60 with substituted nitrones, a versatile method for fullerene functionalization, were investigated at the MO6/6-31G*//PM3 level of theory to elucidate the effect of electron-releasing (-CH3, -CH2CH3, -CH2CH2CH3, C6H5CH2) substituents and electronwithdrawing substituents (-F, -Cl, -Br, -NC, and -NO2) on the energetics of the reaction; the regio- and stereo-selectivity of the mono- and bis-addition of nitrones; and global reactivity descriptors of the molecular systems to rationalize and predict their chemical reactivity and site selectivity. The results show that electron-withdrawing groups on the nitrones increase the activation barrier of the reaction whereas electron-donating groups decrease the activation barriers. However, electron-withdrawing groups on the nitrones result in more stable products compared to the electron-donating groups. It was found that the reactions with electron-donating substituents on the nitrone are normal electron demand reactions, with C60 as the dipolarophile and the substituted nitrones as the dipoles while the reactions with electron-withdrawing substituents on the nitrones are inverse electron demand reactions. The chemical hardness values show greater positive values for adducts with electron-withdrawing substituents on the nitrone and smaller negative values for adducts with electron-donating substituents on the nitrone, confirming the trend that larger activation barriers accompany reactions with electron-withdrawing substituents on the nitrone while electron-donating substituents lower activation barriers. The activation barriers of the second nitrone addition (bisadduct formation) were found to be lower than the barriers for the first nitrone addition (monoadduct formation). Stereo-chemically, syn-bisaddition was found to be thermodynamically and kinetically stable favoured over anti-bisaddition. Electron donating and electron-withdrawing substituents have a marked effect on the energetics of the reaction.

Highlights

Over the past decades, the field of fullerene chemistry has developed remarkably, driven by the structural novelty and the intriguing properties of fullerenes that offer a wide variety of new possibilities in a diverse range of applications
Fullerene-C60 has many potential applications such as in synthetic chemistry, artificial photosynthesis, non-linear optics, surface coatings, superconductivity devices, and cosmetics to slow down the aging of the human skin
The high capability of C60 to act as an electron acceptor or even as electron accumulator has led to the synthesis of a large number of compounds in which the fullerene is covalently linked to photoactive groups serving as potential electron donors [6]

Summary

Introduction

The field of fullerene chemistry has developed remarkably, driven by the structural novelty and the intriguing properties of fullerenes that offer a wide variety of new possibilities in a diverse range of applications. Even though fullerenes have been among the most studied molecules in science over the last two decades since its preparation in multigram amounts, many important reactions in the arsenal of organic chemistry have not been extensively applied to fullerenes synthetically, despite the unprecedented chemical structures that could be formed. In view of the above, this work aims at exploring (1) mono- and bis-1,3-dipolar cycloaddition of nitrone and its substituted derivatives to fullerene C60 (Scheme 2); (2) the effect of electron-releasing (CH3, CH2CH3, CH2CH2CH3, C6H5CH2) substituents and electron-withdrawing substituents (F, Cl, Br, NC, and NO2-) on the energetics of the reaction; (3) the regio- and stereo-selectivity of the mono- and bis-addition and (4) global reactivity descriptors of the molecular systems to rationalize and predict their chemical reactivity and site selectivity.

Results and Discussion

20 Naphthyl Naphthyl Naphthyl

Conclusions