No abstract

A series of isomers of bis(N-methylpyrrolidine)-C(60) 2 (Prato bisadducts) was prepared by the 1,3-dipolar cycloaddition of N-methylazomethine ylide to C(60). Six isomers were separated and characterized by ESI-MS, UV/vis, and (1)H and (13)C NMR spectroscopy. The structures of these bisadducts were assigned based on (1) comparison of their molecular symmetries with their (1)H and (13)C NMR spectra, (2) comparison of their UV/vis spectra with those of corresponding Bingel-Hirsch bisadducts, and (3) the order of deshielding of the methylene and N-methyl (1)H NMR resonances. Prato bisaddition is less chemoselective than Bingel-Hirsch bisaddition to C(60).

Complex monolayer formation between three amphiphiles: cetyltrimethylammonium bromide (CTAB), octadecylamine (ODA), dioctadecyldimethylammonium bromide (DOAB), and tetrakis(4-sulfonatophenyl)porphine (TPPS) at the air/water interface were investigated. It was found that TPPS could form complex monolayers with the amphiphiles at the air/water interface through the electrostatic interaction at pH ) 3.1. The complex monolayer could be deposited onto solid substrates using a Langmuir-Schaefer (LS) transfer method to form well-defined LS films. Although TPPS existed as a monomer in aqueous solution at pH 3.1, it could form a J-aggregate in the complex monolayers with the amphiphiles. It is interesting to note that the LS films showed strong split Cotton effect in the circular dichroism (CD) spectra although TPPS and the amphiphiles are all achiral. It was found that only if the chirality of the LS film was related to the J-aggregate formation of TPPS in the LS film, i.e., only when the TPPS formed J-aggregate, can a CD signal be detected. Further investigation through AFM measurements revealed that the nanothread formed in the LS films was responsible for the chirality of the LS film.

3He NMR spectrometry has been used to examine bisaddition to C60 containing an encapsulated 3He atom (3He@C60) using three types of reactions:  (1) cyclopropanation with diethyl bromomalonate and base to give dicarbethoxymethanofullerenes (Bingel−Hirsch reaction), (b) addition of azomethine ylides to give N-methylfulleropyrrolidines (Prato−Wudl reaction), and (c) reduction to give C60H4. 3He NMR spectra of crude reaction mixtures in all three series showed well-separated resonances for each of the bisadducts, spread out over more than 2 ppm. The major isomeric bisadducts from the first two reactions were separated and characterized, and the 3He NMR spectra of the individual major bisadducts from 3He@C60 were obtained (five isomers from reaction 1, four isomers from reaction 2). Although the absolute chemical shifts in the two series of bisadducts differ, the relative chemical shifts are significantly but not perfectly correlated. Bisadducts with appended ligands on opposite hemispheres of C60 (7, 6, and 5) tend to have 3He NMR resonances downfield of the bisadducts with appended ligands on the same hemisphere (bisadducts 2 and 3). Unfortunately, the equatorial isomer 4, a major product from the Hirsch addition reaction, was not obtained in sufficient quantity for study from the Prato reaction. Well-separated resonances were also seen for the isomeric compounds of composition 3He@C60H4 from reaction of the fullerene with diimide, but the individual isomers were not separated. The very large differences in the 3He NMR chemical shifts of the isomeric bisadducts in all three reactions demonstrate that the magnetic field felt by the 3He atom due to the ring currents in the residual π-system is extremely sensitive to the pattern of ligation on the C60 surface. These results provide further support for the assertion that 3He NMR is a very sensitive probe of patterns of chemical addition to fullerenes, and suggest that this technique will prove to be generally useful in determining the ratio as well as the identity of isomeric fullerene bisadducts.