Regioselective Synthesis and Characterization of Tris- and Tetra-Prato Adducts of M₃N@C₈₀ (M = Y, Gd)

Abstract

The tris- and tetra-adducts of M3N@I h -C80 metallofullerenes were synthesized and characterized for the first time. The 1,3-dipolar cycloaddition (Prato reaction) of Y3N@I h-C80 and Gd3N@I h-C80 with an excess of N-ethylglycine and formaldehyde provided tris- and tetra-fulleropyrrolidine adducts in a regioselective manner. Purification by HPLC and analyses of the isolated peaks by NMR, MS, and vis-NIR spectra revealed that the major products were four tris- and one tetra-isomers for both Y3N@I h-C80 and Gd3N@I h-C80. Considering the large number of possible isomers (e.g., at least 1140 isomers for the tris-adduct), the limited number of isomers obtained indicated that the reactions proceeded with high regioselectivity. NMR analyses of the Y3N@I h-C80 adducts found that the tris-adducts were all-[6,6]- or [6,6]­[6,6]­[5,6]-isomers and that some showed mutual isomerization or remained intact at room temperature. The tetra-adduct obtained as a major product was all-[6,6] and stable. For the structural elucidation of Gd3N@I h-C80 tris- and tetra-adducts, density functional theory (DFT) calculations were performed to estimate the relative stabilities of tris- and tetra-adducts formed upon Prato functionalization of the most pyramidalized regions of the fullerene structure. The most stable structures corresponded to additions on the most pyramidalized (i.e., strained) bonds. Taking together the experimental vis-NIR spectra, NMR assignments, and the computed relative DFT stabilities of the potential tris- and tetra-adducts, the structures of the isolated adducts were elucidated. Electron resonance (ESR) measurements measurements of pristine, bis-, and tris-adducts of Gd3N@C80 suggested that the rotation of the endohedral metal cluster slowed upon increase of the addition numbers to C80 cage, which is favored for accommodating the Gd atoms of the relatively large Gd3N cluster inner space at the sp3 addition sites. This is presumably related to the high regioselectivity in the Prato addition reaction driven by the strain release of the Gd3N@C80 fullerene structure.

Unexpected formation of 1,2- and 1,4-bismethoxyl Sc3N@Ih-C80 derivatives via regioselective anion addition: an unambiguous structural identification and mechanism study

“…[1][2][3][4] Exohedral functionalization of EMFs has shown its effectiveness to broaden their applications by generation a variety of useful derivatives. During the last decades, many synthetic methods have been applied to modify EMFs, among which cycloadditions, such as the BingelHirsch reaction, 5,6 [2+2] benzyne addition, 7, 8 1,3dipolar reaction, [9][10][11][12] DielsAlder reaction, 13 carbene addition 14 and so on, 5,15,16 have been widely utilized. Results show that the chemical properties of EMFs are much different from those of empty fullerenes, resulting in a fact that some chemical reactions which are effective to C 60 do not work on EMFs.…”

Multicomponent Reactions Among Alkyl Isocyanides, sp Reactants, and sp2 Carbon Cages

“…33 In functionalized NCFs, fully ordered clusters were mostly achieved via direct and strong interactions between the functional group and the cage (e.g., multiadditions or formal charge on the ligand and cage, etc.). 16b 21c 24 34 Our work demonstrated that weak intermolecular interactions between the organic ligands and the NCF cage can also restrict the cluster motion in the solid state of synthetically straightforward monoadducts, which provides a new direction of materials design for magnetic and quantum applications.…”

Regulating the electronic and spin structure of endohedral metallofullerenes: a case investigation of Sc3N@C80 and Sc3C2@C80

“…In particular, in 2020, Semivrazhskaya et al synthesized regioselective tris-and tetra-Prato adducts of M 3 N@C 80 (M = Y, Gd) to design new nitride EMF-based materials. 35 Coincidentally, the group of Aroua systematically investigated the Prato reaction of M 3 N@I h -C 80 (M = Sc, Lu, Y, Gd) with reversible isomerization. 36 At present, paramagnetic endohedral EMFs with unpaired electrons have drawn more attention owing to their extraordinary configurations and unique spin properties, making them promising candidates for quantum information processing, molecular machines, [37][38][39][40] etc.…”