Effect of structural change in viologen acceptors on the rate of single electron transfer from tributylphosphine.
The "flexible" 3 and "rigid" cyclic viologens 4, diquarternary salts of 2,2'-bipyridine and 1,10-phenanthroline, respectively, were treated with tributylphosphine (1) in acetonitrile containing a large amount of methanol under an argon atmosphere. A single electron transfer (SET) easily occurred from the latter to the former, the SET to 4 being 10(5)-10(6) times faster than the SET to 3. The reorganization energy lambda for the latter SET is thought to be larger than that for the former SET, because 3 undergoes a structural change upon the one-electron reduction to its radical cation, whereas the one-electron reduction of 4 takes place without a structural change. Taking into account the difference in lambda, and also taking into account the bond formation energy brought about by the follow-up reaction of the phosphine radical cation 1*(+) with methanol, the observed kinetics were well interpreted in terms of the Marcus theory.
Yasui
Shinro
S
Tezukayama University, Gakuen-Minami, Nara, Japan. yasui@tezukayama-u.ac.jp
Itoh
Kenji
K
Ohno
Atsuyoshi
A
Tokitoh
Norihiro
N