The selective one-electron reduction of C60 to C60 •- is attained through photoinduced electron transfer from an NADH analogue, 1-benzyl-1,4-dihydronicotinamide (BNAH), and the dimer analogue [(BNA)2] to the triplet excited state of C60. The limiting quantum yield for formation of C60 •- in the case of (BNA)2 exceeds unity; Φ∞ = 1.3. In this case, the initial electron transfer from (BNA)2 to the triplet excited state (3C60*) is followed by fast C−C bond cleavage in the resulting (BNA)2 •+ to give BNA• and BNA+ and the second electron transfer from BNA• to C60 yields BNA+ and C60 •-, when (BNA)2 acts as a two-electron donor to produce 2 equiv of C60 •-. When BNAH is replaced by 4-tert-butylated BNAH (t-BuBNAH), the photochemical reaction with C60 yields not C60 •- but instead the tert-butylated anion (t-BuC60 -) selectively. In this case, the initial electron transfer from t-BuBNAH to 3C60* is also followed by fast C−C bond cleavage in t-BuBNAH•+ to give t-Bu•, which is coupled with C60 •- produced in the electron transfer to yield t-BuC60 -. The selective two-electron reduction of C60 to 1,2-dihydro[60]fullerene (1,2-C60H2) is also attained with the use of another NADH analogue, 10-methyl-9,10-dihydroacridine (AcrH2), under visible light irradiation in deaerated benzonitrile solution containing trifluoroacetic acid. The studies on the quantum yields, the kinetic deuterium isotope effects, and the quenching of the triplet−triplet absorption of C60 by AcrH2 have revealed that the photochemical reduction proceeds via photoinduced electron transfer from 10-methyl-9,10-dihydroacridine to the triplet excited state of C60, which is followed by proton transfer from AcrH2 •+ to C60 •- and a second electron transfer from the deprotonated acridinyl radical (AcrH•) to C60H• in the presence of trifluoroacetic acid to yield the final products 10-methylacridinium ion (AcrH+) and 1,2-C60H2. The transient spectra of the radical ion pair formed in the photoinduced electron transfer have been detected successfully in laser flash photolysis of each NADH analogue−C60 system. The mechanistic difference between the selective one- and two-electron reductions of C60 is discussed on the basis of the difference in the redox and acid−base properties of NADH and the dimer analogues.

The formation of organofullerenes of the type R2C60 and R(R‘)C60 from C60 2- and alkyl halides (RX or R‘X) in benzonitrile was mechanistically investigated for 15 different alkyl halides which vary in electrophilicity and electron acceptor ability. The first step in the reaction leads to RC60 - via an electron-transfer mechanism, followed by formation of R2C60 or R(R‘)C60 via an SN2 mechanism. Evidence of the mechanism comes from comparison of rate constants for the stepwise addition of two R groups to C60 2- with rate constants for the genuine electron transfer and SN2 reactions. The formation of t-BuC60 - and PhCH2C60 - after the first R group addition was confirmed by electrospray ionization mass spectroscopy. The t-BuC60 - derivative will not react further with excess t-BuI, but this is not the case for the less sterically hindered PhCH2Br, which adds to t-BuC60 - in benzonitrile to give t-Bu(PhCH2)C60. A protonation of t-BuC60 - with trifluoroacetic acid can also occur to give 1,4-t-Bu(H)C60, which rearranges rapidly to yield 1,2-t-Bu(H)C60. Rate constants for the second alkylation of t-BuC60 - with a variety of different alkyl halides are compared with values of genuine SN2 reactions and indicate that the second step in the fullerene alkylation reaction proceeds via an SN2 mechanism. The rate constants of electron transfer from C60 2- to RX span a range of 105, but are insensitive to the steric effect of the alkyl group, i.e., they depend only on the electron-acceptor ability of RX. In contrast, the SN2 rate constants of t-BuC60 - with RX are highly susceptible to the steric effect of the alkyl group and no reaction at all takes place between t-BuC60 - and t-BuI. Thus, the first addition of one sterically hindered alkyl group to C60 2- occurs via electron transfer and cannot be followed by further addition of a second sterically hindered group (via an SN2 reaction). This is not the case for less sterically hindered alkyl groups such as benzyl bromide which can add via an SN2 reaction to yield C60 adducts with two different alkyl groups.