S. Fukuzumi et al., SELECTIVE ONE-ELECTRON AND 2-ELECTRON REDUCTION OF C-60 WITH NADH ANDNAD DIMER ANALOGS VIA PHOTOINDUCED ELECTRON-TRANSFER, Journal of the American Chemical Society, 120(32), 1998, pp. 8060-8068
The selective one-electron reduction of C-60 to C-60(.-) is attained t
hrough photoinduced electron transfer from an NADH analogue, 1-benzyl-
1,4-dihydronicotinamide (BNAH), and the dimer analogue [(BNA)(2)] to t
he triplet excited stare of C-60 The limiting quantum yield for format
ion of C-60(.-) in the case of (BNA)(2) exceeds unity; Phi(infinity) =
1.3. Ln this case, the initial electron transfer from (BNA)(2) to the
triplet excited state (C-3(60)) is followed by fast C-C bond cleavag
e in the resulting (BNA)(2)(.+) to give BNA(.) and BNA(+) and the seco
nd electron transfer from BNA(.) to C-60 yields BNA(+) and C-60(.-) wh
en (BNA)(2) acts as a two-electron donor to produce 2 equiv of C-60(.-
) When BNAH is replaced by 4-tert-butylated BNAH (t-BuBNAH), the photo
chemical reaction with C-60 yields not C-60(.-) but instead the tert-b
utylated anion (t-BuC60-) selectively. In this case, the initial elect
ron transfer from t-BuBNAH to C-3(60) is also followed by fast C-C bo
nd cleavage in t-BuBNAH(.+) to give t-Bu-., which is coupled with C-60
(.-) produced in the electron transfer to yield t-BuC60-. The selectiv
e two-electron reduction of C-60 to 1,2-dihydro[60]fullerene (1,2-C60H
2) is also attained with the use of another NADH analogue 10-methyl-9,
10-dihydroacridine (AcrH(2)), under visible light irradiation in deaer
ated benzonitrile solution containing trifluoroacetic acid. The studie
s on the quantum yields, the kinetic deuterium isotope effects, and th
e quenching of the triplet-triplet absorption of C-60 by AcrH(2) have
revealed that the photochemical reduction proceeds via photoinduced el
ectron transfer from 10-methyl-9,10-dihydroacridine to the triplet exc
ited state of C-60, which is followed by proton transfer from AcrH(2)(
.+) to C-60(.-) and a second electron transfer from the deprotonated a
cridinyl radical (AcrH(.)) to C60H. in the presence of trifluoroacetic
acid to yield the final products 10-methylacridinium ion (AcrH(+)) an
d 1,2-C60H2. The transient spectra of the radical ion pair formed in t
he photoinduced electron transfer have been detected successfully in l
aser flash photolysis of each NADH analogue-C-60 system. The mechanist
ic difference between the selective one- and two-electron reductions o
f C-60 is discussed On the basis of the difference in the redox and ac
id-base propel-ties of NADH and the dimer analogues.