期刊
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
卷 133, 期 6, 页码 1859-1869出版社
AMER CHEMICAL SOC
DOI: 10.1021/ja108395g
关键词
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资金
- NSF [CHE0909587]
- NIH [GM62309]
- Ministry of Education, Culture, Sports, Science, and Technology, Japan [20108010]
- KOSEF/MEST [R31-2008-000-10010-0]
- Harry and Cleio Greer Fellowship
- Grants-in-Aid for Scientific Research [20108001, 20108010] Funding Source: KAKEN
- Division Of Chemistry
- Direct For Mathematical & Physical Scien [0909587] Funding Source: National Science Foundation
The electron-transfer and hydride-transfer properties of an isolated manganese(V)-oxo complex, (TBP(8)Cz)Mn-V(O) (1) (TBP(8)Cz=octa-tert-butylphenyl-corrolazinato) were determined by spectroscopic and kinetic methods. The manganese(V)-oxo complex 1 reacts rapidly with a series of ferrocene derivatives ([Fe(C5H4Me)(2)], [Fe(C5HMe4)(2)], and ([Fe(C5Me5)(2)] = Fc*) to give the direct formation of [(TBP(8)Cz)Mn-III(OH)](-) ([2-OH])(-), a two-electron-reduced product. The stoichiometry of these electron-transfer reactions was found to be (Fc derivative)/1 = 2:1 by spectral titration. The rate constants of electron transfer from ferrocene derivatives to 1 at room temperature in benzonitrile were obtained, and the successful application of Marcus theory allowed for the determination of the reorganization energies (lambda) of electron transfer. The lambda values of electron transfer from the ferrocene derivatives to 1 are lower than those reported for a manganese(IV)-oxo porphyrin. The presumed one-electron-reduced intermediate, a Mn-IV complex, was not observed during the reduction of 1. However, a Mn-IV complex was successfully generated via one-electron oxidation of the Mn-III precursor complex 2 to give [(TBP(8)Cz)Mn-IV](+) (3). Complex 3 exhibits a characteristic absorption band at lambda(max) = 722 nm and an EPR spectrum at 15 K with g'(max) = 4.68, g'(mid) = 3.28, and g'(min) = 1.94, with well-resolved Mn-55 hyperfine coupling, indicative of a d(3) Mn-IV S=3/2 ground state. Although electron transfer from [Fe(C5H4Me)(2)] to 1 is endergonic (uphill), two-electron reduction of 1 is made possible in the presence of proton donors (e.g., CH3CO2H, CF3CH2OH, and CH3OH). In the case of CH3CO2H, saturation behavior for the rate constants of electron transfer (k(et)) versus acid concentration was observed, providing insight into the critical involvement of H+ in the mechanism of electron transfer. Complex 1 was also shown to be competent to oxidize a series of dihydronicotinamide adenine dinucleotide (NADH) analogues via formal hydride transfer to produce the corresponding NAD(+) analogues and [2-OH](-). The logarithms of the observed second-order rate constants of hydride transfer (k(H)) from NADH analogues to 1 are linearly correlated with those of hydride transfer from the same series of NADH analogues to p-chloranil.
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