The 1,3-dipolar cycloaddition of an azomethine ylide (Prato reaction) with M(3)N@I(h)-C(80) (denoted as M(3)N@C(80); M = Sc, Lu, Y, Gd) was carried out to obtain fulleropyrrolidinebis(carboxylic acid) derivatives as scaffolds for the preparation of various functionalized M(3)N@C(80) 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(3)N@C(80), the initial addition gave a [6,6]-adduct of the I(h)-C(80) 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(80), and interestingly, in the reactions of Y(3)N@C(80) and Gd(3)N@C(80), 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(3)N@C(80), Y(3)N@C(80), and Gd(3)N@C(80). The utility of the obtained Prato adducts was confirmed by preparation of a highly water-soluble Gd(3)N@C(80) derivative.

Terpyridine ligands are widely used in chemistry and material sciences owing to their ability to form stable molecular complexes with a large variety of metal ions. In that context, variations of the substituents on the terpyridine ligand allow modulation of the material properties. Applying the Stille cross-coupling reaction, we prepared with good yields a new series of terpyridine ligands possessing quinoline-type moieties in ortho, meta, and para positions and dimethylamino substituents at central or distal positions. The corresponding cobalt(II) complexes were synthesized and fully characterized by elemental analysis, single-crystal X-ray crystallography, mass spectrometry, and UV-vis, H NMR, and Fourier transform infrared (FT-IR) spectroscopy as well as by cyclic voltammetry (CV). Density functional theory (DFT) calculations were performed to investigate the electronic structure of all the Co(II) bis-terpyridyl molecular complexes. In this work, we show that terpyridine ligand functionalization allows tuning the redox potentials of the Co(III)/Co(II), Co(II)/Co(I), and Co(I)/Co(I) (tpy) couples over a 1 V range.