The carbon-carbon bond formation of C60 with Group 14 organometallic compounds is attained through photoinduced electron transfer from Group 14 organometallic compounds acting as electron donors to the triplet excited state of C60. The electron donors employed in this study are ketene silyl acetals and allylic stannanes. When an unsymmetric allylic stannane, e.g. prenyltributyltin (Me2C=CHCH2SnBu3) is employed, the allylic group is introduced selectively at the α-position to yield C60-1,2-CH2CH=CMe2 under irradiation of the visible light and no γ adduct has been formed. Such regioselectivity is characteristic of the reactions of prenyltributyltin via electron transfer, where the C-Cδ bond formation occurs after cleavage of the Sn-C bond. A comparison of the observed rate constants determined from the dependence of the quantum yields on the concentrations of electron donors, as well as the quenching of the triplet excited state of C60 by the electron donors with those predicted for the electron transfer processes, indicates that the photoreduction proceeds via photoinduced electron transfer from the electron donors to the triplet excited state of C60. The radical ion pair generated in the photoinduced electron transfer from ketene silyl acetal to the triplet excited state of C60 has been successfully detected as transient absorption spectra in the visible and near-IR region with use of the laser flash photolysis.
- Group 14 organometallic compounds
- Photoinduced electron transfer
- Radical ion pair intermediates