Regioselectivity in Diels–Alder Cycloadditions of ^#6094C₆₈ Fullerene with a Triplet Ground State

Abstract

To achieve a full control on the regioselectivity of chemical additions to fullerenes is a major goal in the field of the reactivity of carbon nanostructures. In this work, we computationally analyze the regioselectivity of the Diels-Alder (DA) reaction of cyclopentadiene to the hollow non-isolated pentagon rule (IPR) #6094 C68 fullerene, which possesses a triplet ground state. Our aim is to check whether the typically favored [6,6]-addition in fullerenes can be shifted to [5,6] bonds in #6094 C68 due to the change in their ground states.Our results show that the [5,5] adduct is the thermodynamic reaction product whereas the kinetic product is the [5,6] bond of type F, adjacent to a pentalene unit. As compared to the singlet state, in the triplet state, the Gibbs barrier for the attack to the [5,6] bond of #6094 C68 is reduced by about 5 kcal•mol -1 , the DA cycloaddition becoming more regioselective. Our energy decomposition analysis shows that the change of regioselectivity in the DA reaction of hollow fullerenes from the usual [6,6] bond to the [5,6] bond in #6094 C68 is driven by higher stabilizing orbital interactions in the latter bond favored by the spin density accumulation around the two pentalene units of the cage. The findings of this investigation complement those of earlier studies on the regioselectivity of IPR fullerenes and endohedral metallofullerenes.

Diels–Alder Cycloaddition on Nonisolated-Pentagon-Rule C2v(19 138)–C76 and YNC@C2v(19 138)–C76: The Difference in Regioselectivity Caused by the Inner Metallic Cluster

“…The mentioned functionals have been widely utilized for the reaction energy and energy barrier calculations in Diels−Alder reactions of fullerenes. 15,18,19,29,30 The Gaussian 09 program was employed throughout this work. 31 Figure 1.…”

“…In the case of Diels–Alder reactions of D 3 h –C 68 and Sc 3 N@ D 3 h –C 68 with three pairs of fused pentagons, it is found that the [5,5]-bond and the [5,6]-bond of type-F in the free C 68 fullerene are thermodynamically and kinetically favored, respectively, while the [5,5]-bond is the most thermodynamically and kinetically reactive site upon encapsulation of the metallic cluster . Very recently, a computational analysis on the Diels–Alder reaction of cyclopentadiene (Cp) to the hollow non-IPR #6094 C 68 with a triplet ground state revealed that the [5,5]-adduct is the thermodynamic reaction product, whereas the kinetic product originates from the [5,6]-bond of type-F, which is similar to that on D 3 h –C 68 . It seems that the C–C bonds in the adjacent pentagon pair exhibit high chemical reactivity in both free and endohedral fullerenes, and the exohedral addition on the highly strained region stabilizes the whole molecular system …”

A Palladium Complex as an Asymmetric π-Lewis Base Catalyst for Activating 1,3-Dienes

“…It has been well explored that transition metals can serve as π-Lewis acids by accepting π-electrons of unsaturated systems to umpolung their reactivity toward diverse nucleophiles (Scheme a). − In addition, the empty antibonding molecular orbitals of double bonds (π*) are able to accept electrons from the d-orbitals of transition metals via back-bonding (Scheme b); − however, the synthetic potential via such a π-Lewis base activation mode has been significantly underdeveloped. Several metals (including W, Re, Os, and Mo) can coordinate in a η 2 fashion to arenes or even 1,3-dienes stoichiometrically and donate their electrons to render a subsequent attack on suitable electrophiles (Scheme c). − In addition, a few types of metals with low valence also have been demonstrated to catalyze the coupling reactions of 1,3-dienes − or even alkenes , with electrophilic carbonyls and imines, where an oxidative cyclization pathway was generally involved (Scheme d). Despite these advances, establishing a general activation mode and broadening the application of transition metals as exact π-Lewis base catalysts, which can directly enhance the nucleophilicity of alkenes or even umpolung the reactivity of electron-deficient alkenes beyond organic σ-type Lewis bases, still remain to be disclosed in the chemistry field.…”

Revealing the Origin of Π‐facial and Regioselectivity in the Diels‐Alder Reaction of Unsymmetrical, Cage‐annulated 1,3‐Cyclohexadiene with Ethyl Propiolate Dienophile: a DFT Study

“…Further, the potential energy surface (PES) for the DA reactions of EP with HPDD and HHDD has been studied to evaluate the formation of kinetic products of these reactions. [26][27][28][29][30] Non-Covalent Interactions analysis [31] (NCI) has been utilized to explain the stereo-and regioselectivity for such DA reactions.…”

“…The molecular electrostatic potential (MESP) analysis is an important tool to examine the preferential approach of a dienophile to the dissymmetric π‐faces of dienes. Further, the potential energy surface (PES) for the DA reactions of EP with HPDD and HHDD has been studied to evaluate the formation of kinetic products of these reactions [26–30] . Non‐Covalent Interactions analysis [31] (NCI) has been utilized to explain the stereo‐ and regioselectivity for such DA reactions.…”