Single Electron Transfer-Promoted Photochemical Reactions of Secondary N-Trimethylsilylmethyl-N-benzylamines Leading to Aminomethylation of Fullerene C₆₀

Abstract

Photoreactions between C60 and secondary N-trimethylsilylmethyl-N-benzylamines were explored to evaluate the feasibility of a new method for secondary aminomethylation of electron acceptors. The results show that photoreactions of C60 with these secondary amines in 10% EtOH-toluene occur to form aminomethyl-1,2-dihydrofullerenes predominantly through a pathway involving single electron transfer (SET)-promoted formation of secondary aminium radicals followed by preferential loss of the α-trimethylsilyl group. The aminomethyl radicals formed in this manner then couple with C60 or C60(•-) to form radical or anion precursors of the aminomethyl-1,2-dihydrofullerenes. In contrast to thermal and photochemical strategies developed previously, the new SET photochemical approach using α-trimethylsilyl-substituted secondary amines is both mild and efficient, and as a result, it should be useful in broadening the library of substituted fullerenes. Moreover, the results should have an impact on the design of SET-promoted C-C bond forming reactions. Specifically, introduction of an α-trimethylsilyl group leads to a change in the chemoselectivity of SET-promoted reactions of secondary amines with acceptors that typically favor aminium radical N-H deprotonation, leading to N-C bond formation. Finally, symmetric and unsymmetric fulleropyrrolidines are also generated in yields that are highly dependent on the electronic properties of arene ring substituents in amines, irradiation time, and solvent.

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“…40 For the mechanism of surface initiated polymerization, the exposed amine radicals serve as good electron donors, which are beneficial to the photochemical single electron transfer from amines to alkenes. 46 Upon the polymerization process, the presence of radicals could alter the chemoselectivity of electron donor amino groups with acceptors that typically favor amine radical N–H deprotonation, giving rise to the formation of N–C bonds. 40,46 Simultaneously, based on the radical chain propagation mechanism, free radicals migrate from the N centers to the C centers for subsequent polymerization.…”

“…46 Upon the polymerization process, the presence of radicals could alter the chemoselectivity of electron donor amino groups with acceptors that typically favor amine radical N–H deprotonation, giving rise to the formation of N–C bonds. 40,46 Simultaneously, based on the radical chain propagation mechanism, free radicals migrate from the N centers to the C centers for subsequent polymerization. 40 Coupling termination occurs when two free radicals are covalently bound due to their strong interaction.…”