Prato Reaction of M<sub>3</sub>N@<i>I</i><sub><i>h</i></sub>‑C<sub>80</sub> (M = Sc, Lu,
Y, Gd) with Reversible Isomerization
- Publication date
- Publisher
Abstract
The 1,3-dipolar cycloaddition of an azomethine ylide
(Prato reaction)
with M<sub>3</sub>N@<i>I</i><sub><i>h</i></sub>-C<sub>80</sub> (denoted as M<sub>3</sub>N@C<sub>80</sub>; M = Sc,
Lu, Y, Gd) was carried out to obtain fulleropyrrolidinebis(carboxylic
acid) derivatives as scaffolds for the preparation of various functionalized
M<sub>3</sub>N@C<sub>80</sub> materials. The formation of two monoadduct
isomers (the [6,6]- and [5,6]-adducts) were detected by HPLC and identified
by NMR and vis/NIR spectroscopies. In each Prato reaction with M<sub>3</sub>N@C<sub>80</sub>, the initial addition gave a [6,6]-adduct
of the <i>I</i><sub><i>h</i></sub>-C<sub>80</sub> cage, and subsequently, a [5,6]-adduct was obtained by complete
or partial thermal isomerization via a rearrangement reaction. The
reaction rate of the latter thermal conversion of the adducts was
dependent on the size of the metal cluster inside C<sub>80</sub>,
and interestingly, in the reactions of Y<sub>3</sub>N@C<sub>80</sub> and Gd<sub>3</sub>N@C<sub>80</sub>, this conversion was found to
be reversible for the first time. Detailed kinetic studies provided
the enthalpy and entropy barriers for the reactions of the adducts
of Lu<sub>3</sub>N@C<sub>80</sub>, Y<sub>3</sub>N@C<sub>80</sub>,
and Gd<sub>3</sub>N@C<sub>80</sub>. The utility of the obtained Prato
adducts was confirmed by preparation of a highly water-soluble Gd<sub>3</sub>N@C<sub>80</sub> derivative