Effects of base on both an electron-transfer reaction from an NADH model compound, 1-benzyl-1,4dihydronicotinamide (BNAH) to [Fe(NN)3] 3+ (N-N = 2,2′-bipyridine and 1,10-phenanthroline) and a hydride transfer from BNAH to tetracyanoethylene (TCNE) in acetonitrile have been examined. The stoicheiometry of the electron transfer from BNAH to [Fe(N-N)3]3- in the absence of a base indicates that BNAH is a one-electron donor. In the presence of a base, however, BNAH acts as an apparent twoelectron donor, when the two-electron transfer proceeds via a multistep process; a fast one-electron transfer from BNAH to [Fe(NN) 3]3+ occurred, followed by the rate-determining deprotonation of BNAH + by base and the subsequent fast electron transfer from BNA to [Fe(N-N)3]3+. The rate constants for the proton transfer from BNAH+- to a series of pyridine derivatives have been determined. In the reduction of TCNE by BNAH, BNAH appears to be a two-electron donor in both the absence and presence of a base. Rates of the reduction of TCNE by BNAH increased with increasing base concentration, suggesting the involvement of BNAH+ as an intermediate in the hydride transfer from BNAH to TCNE. The kinetic analyses have led to the evaluation of the proton transfer rate constants for the deprotonation of BNAH+ with various bases, which accord with those obtained from the electron-transfer reactions of BNAH with [Fe(NN)3]3+ in the presence of bases. Based on the Brönsted plot of the proton transfer rate constants as well as the variation of the primary kinetic isotope effects k H/kD with the pKa, of the base, the pK a value for BNAH+ has been evaluated as 3.6 ±0.4.
|Number of pages||7|
|Journal||Journal of the Chemical Society. Perkin Transactions 2|
|State||Published - 1984|