Chemical Reactions of Cationic Metallofullerenes: An Alternative Route for Exohedral Functionalization

Abstract

The chemistry of cationic forms of clusterfullerenes remainl ess explored than that of the corresponding neutralo ra nionic species. In the presentw ork, M 3 N@I h -C 80 (M = Sc or Lu) cationsw ere generated by both electrochemical and chemical oxidationm ethods. The as-obtained cations successfully underwentt he typical Bingel-Hirsch reactiont hat fails with neutral Sc 3 N@I h -C 80 .T wo isomeric Sc 3 N@I h -C 80 cation derivatives, [5,6]-open and [6,6]open adducts,w ere synthesized, and the former has never been prepared by meanso faB ingel-Hirsch reactionw ith neutralc lusterfullerenes.I nt he case of the Lu 3 N@I h -C 80 cation,h owever,o nly a[ 6,6]-open adduct was obtained. Densityf unctional theory (DFT) calculations indicated that the oxidized M 3 N@I h -C 80 was much more reactive than the neutralc ompound upon addition of the diethylb romomalonate anion.T he Bingel-Hirschr eaction of M 3 N@I h -C 80 cationso ccurredb ym eanso fa nu nusual outer-sphere single-electron transfer( SET) processf rom the diethyl bromomalonate anion to the stable intermediate [M 3 N@C 80 (C 2 H 5 COO) 2 CBr]C.R emarkably,t he diethyl bromomalonate anion was found to act as both an ucleophile and an electrond onor.

Bingel–Hirsch Addition of Diethyl Bromomalonate to Ion‐Encapsulated Fullerenes M@C60 (M=Ø, Li+, Na+, K+, Mg2+, Ca2+, and Cl−)

“…[18] The Gibbs energy reactionb arrier of 25.5 and1 6.4 kcal mol À1 for the BH cycloadditiont ot he [6,6] bond of C 60 and Li + @C 60 are not far from the barriers reported in previousc omputationals tudies of BH additions ( Figure 2). [13,19] To be consistent with results shown later on, we included the effect of the Na + counterionofthe diethylbromomalonate anion in the comparison of both attacks. From now on, we will focus our study on the [6,6] attack owing to the highere nergy barriero ft he [5,6] attack in both systems, plus the fact that, to the best of our knowledge,d irect [5,6] attacks have never been observed for BH additions to C 60 .…”

“…They were able to react Y 3 N@I h -C 80 and Er 3 N@I h -C 80 with diethylb romomalonate under mild conditions but failed to functionalize Sc 3 N@I h -C 80 and Lu 3 N@I h -C 80 .V eryr ecently,t he same group showedt hat the oxidized forms of these two EMFs successfully underwent the BH reaction generating [5,6] and [6,6] open adducts. [13] Scheme 1i llustrates the mechanism of the BH reactioni na model M@C 60 EMF,i nw hichw eh ave introduced the nomenclature used throughout the manuscript. Accordingly,f or each speciesw ith an endohedrali on M( M= Ø, Li + ,N a + ,K + ,M g 2 + , Ca 2 + ,a nd Cl À ,w here Ø@C 60 stands for C 60 without any endohedral metal), the reaction mechanism starts with the formation of the reactantc omplex (M-R)f rom reactants at infinite distance (M-Rinf).…”

“…Otherwise, if the nucleophilic attack is carried out by C 3 or C 4 ,t he [5,6] product is obtained.W es hall see in as ubsequent section of the manuscript that this is not going to occur in practiceowing to their higher associated Gibbs energy barriers. In fact, the [5,6] addition in BH reactions has been reported only for af ew EMFs, [13][14] although in some cases, the [6,6] adducts could be further convertedt o [ 5,6] products by heating. [15] The functionalized EMF product can be considered a closed-cage methanofullerene M-P or an open-cage fulleroid M-P' depending on the C 1 -C 2 distance.…”

“…They were able to react Y 3 N@ I h ‐C 80 and Er 3 N@ I h ‐C 80 with diethyl bromomalonate under mild conditions but failed to functionalize Sc 3 N@ I h ‐C 80 and Lu 3 N@ I h ‐C 80 . Very recently, the same group showed that the oxidized forms of these two EMFs successfully underwent the BH reaction generating [5,6] and [6,6] open adducts [13] …”

Tuning Photoinduced Electron Transfer in POM‐Bodipy Hybrids by Controlling the Environment: Experiment and Theory

“…To investigate how the kinetics of CS and CR depend on the medium containing the POM-hybrid system, we used ar ecently proposed strategy to determine the associated reorganization energies, l and free energy barriers, DG°. [21] According to Marcus theory,the rate constant for an electron transfer process of as upramolecular system in the nonadiabatic limit (i.e.w hen its different elements are poorly electronically coupled) can be expressed by Equations (1). [22,23] In the current case,c onsidering the electron decoupling between the organic and inorganic moieties, [12] it is likely that the electron transfer would occur through space.…”