Application of Microwave Irradiation in Carbon Nanostructures

Abstract

Fullerenes Under Microwave Irradiation IntroductionSince Krätschmer and co-workers discovered a procedure for the preparation of bulk quantities of C 60 [1] in the early 1990s, the physical properties of fullerenes have been intensively investigated. However, members of this new family of compounds are insoluble or sparingly soluble in most solvents [2] and, consequently, C 60 is difficult to handle. Chemical functionalization allows the preparation of soluble C 60 derivatives that maintain the electronic properties of fullerenes. For this reason, the chemistry and derivatization of fullerenes has continued to attract attention aimed at preparing derivatives with interesting physical properties and biological activities [3]. New materials based on C 60 derivatives have shown promise in the fields of material science [4], solar energy conversion [5], nonlinear optical behavior [6], superconductivity [7], ferromagnetism [8], medicinal chemistry [9], and HIV-1 protease inhibition [10].Among the suitable procedures for the functionalization of fullerenes (Scheme 23.1) [11], cycloadditions provide a powerful tool as C 60 behaves as an electron-deficient olefin with a relatively low-lying LUMO (−3.14 eV) [12,13].As a consequence, a large variety of cycloaddition reactions have been carried out [12, 14] in which C 60 (1) is the reactive 2π component. In this context, [1 + 2]-, [2 + 2]-, [3 + 2]-, and [4 + 2]-cycloadditions have all been performed (Scheme 23.2) and the conditions for cycloadduct formation depend strongly on the gap between the controlling orbitals. For this reason, it is frequently necessary to use harsh conditions involving several hours (or days) under reflux in high-boiling solvents. As microwave irradiation has been successfully used in cycloaddition reactions solving problems concerning reversibility and decomposition of reagents and/or products, it was evident to use this methodology in fullerene chemistry as most fullerene derivatives are prepared by Diels-Alder [15] or 1,3-dipolar cycloaddition reactions [16].Microwaves in Organic Synthesis, Third Edition.

Modulation of the exfoliated graphene work function through cycloaddition of nitrile imines

“…It should be noted that with less reactive dipoles, the use of microwave irradiation (MWI) has proven to be very useful in cycloaddition reactions 19,20 as well as in fullerene and carbon nanotube chemistry. 21 The application of MWI allows the formation of cycloadducts in a few minutes. Significantly, in contrast to other fullerene derivatives, the resulting 2-pyrazolinefullerenes show better, or at least equivalent, electron affinity when compared to the parent C 60 and they also exhibit remarkable thermal stability.…”