Single Electron Transfer-Promoted Photochemical Reactions of Secondary N-Trimethylsilylmethyl-N-benzylamines Leading to Aminomethylation of Fullerene C-60

초록

Photoreactions between C-60 and secondary N-trimethylsilylmethyl-N-benzylamines were explored to evaluate the feasibility of a new method for secondary amino-methylation of electron acceptors. The results show that photoreactions of C-60 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 a-trimethylsilyl group. The aminomethyl radicals formed in this manner then couple with C-60 or C-60(center dot-) 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 alpha-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 a-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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