Reactions of microcrystalline fullerene C₆₀ with amino and aza macrocyclic ligands under solvent-free conditions

ABSTRACT

We evaluated the reactivity under solvent-free conditions of 2-aminomethyl-15-crown-5 (AM15C5), 2-aminomethyl-18-crown-6 (AM18C6), 1,4,8,12-tetraazacyclopentadecane (TACPD) and rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (tet b) with microcrystalline fullerene C₆₀. The reactions of nucleophilic addition were carried out at temperatures of about 160°C for 5 h in the case of crown ethers and TACPD, and at 180–190°C for 24 h in the case of tet b. Characterization of the products obtained was performed by using Fourier-transform infrared (FTIR) and Raman spectroscopy, laser desorption/ionization time-of-flight (LDI-TOF) mass spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). To provide an additional insight into the reactivity of macrocyclic compounds with C₆₀ molecules, we employed theoretical calculations in the frame of density functional theory (DFT). According to the results of SEM imaging, macrocyclic reagents are generally unable to deeply penetrate into the bulk of fullerene microcrystals (with a possible exception of TACPD). According to TGA measurements, the reaction efficiency is very low for tet b, whereas the average content of organic fraction in C₆₀-AM15C5 and C₆₀-AM18C6 reaches about 29%, and in C₆₀-TACPD, almost 40%. According to LDI-TOF mass spectral analysis, the products of TACPD, tet b and AM15C5 reactions with fullerene have oligomeric or polymeric structure. By using DFT theoretical calculations, the latter observation was explained by enhanced reactivity of secondary amino groups toward nucleophilic addition onto fullerene cage.

KEYWORDS:

• fullerene C₆₀
• Crystalline powder
• Amino-substituted crown ethers
• Tetraazamacrocyclic ligands
• Solvent-free reactions

Acknowledgements

Financial support from the National Autonomous University of Mexico (grant DGAPA-IN200516) and from the National Council of Science and Technology of Mexico (CONACYT, grant 250655) is greatly appreciated. The authors thank Dr. Edgar Alvarez-Zauco (Facultad de Ciencias, UNAM) for the opportunity to use TGA equipment, as well as Dr. Roberto Sato and M.Sc. Guadalupe Bañuelos-Muñeton (Laboratorio Universitario de Caracterización Espectroscópica, LUCE_CCADET_UNAM) for measuring Raman spectra. D. E. T.-A. is indebted to CONACYT and the Masters Degree Program in Chemical Sciences of UNAM for a M. Sc. scholarship.

Declarations of interest

None

Additional information

Funding

Consejo Nacional de Ciencia y Tecnología 250655, Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México IN200516