TY - JOUR
T1 - Structural and Kinetic Studies of Intermediates of a Biomimetic Diiron Proton-Reduction Catalyst
AU - Wang, Shihuai
AU - Aster, Alexander
AU - Mirmohades, Mohammad
AU - Lomoth, Reiner
AU - Hammarström, Leif
N1 - Funding Information:
We thank Sascha Ott and Sonja Pullen (Uppsala University) for contributing to the synthesis of the diiron biomimetic catalyst and for discussions. This work was supported by the Swedish Research Council (grant 2016-04271) and the Olle Engkvist Byggmä Foundation (grant 2016/3). S.W. gratefully acknowledges a grant from the Chinese Scholarship Council.
PY - 2018/1/16
Y1 - 2018/1/16
N2 - One-electron reduction and subsequent protonation of a biomimetic proton-reduction catalyst [FeFe(μ-pdt)(CO)6] (pdt = propanedithiolate), 1, were investigated by UV-vis and IR spectroscopy on a nano- to microsecond time scale. The study aimed to provide further insight into the proton-reduction cycle of this [FeFe]-hydrogenase model complex, which with its prototypical alkyldithiolate-bridged diiron core is widely employed as a molecular, precious metal-free catalyst for sustainable H2 generation. The one-electron-reduced catalyst was obtained transiently by electron transfer from photogenerated [Ru(dmb)3]+ in the absence of proton sources or in the presence of acids (dichloro- or trichloroacetic acid or tosylic acid). The reduced catalyst and its protonation product were observed in real time by UV-vis and IR spectroscopy, leading to their structural characterization and providing kinetic data on the electron and proton transfer reactions. 1 features an intact (μ2,κ2-pdt)(μ-H)Fe2 core in the reduced, 1-, and reduced-protonated states, 1H, in contrast to the Fe-S bond cleavage upon the reduction of [FeFe(bdt)(CO)6], 2, with a benzenedithiolate bridge. The driving-force dependence of the rate constants for the protonation of 1- (kpt = 7.0 × 105, 1.3 × 107, and 7.0 × 107 M-1 s-1 for the three acids used in this study) suggests a reorganization energy >1 eV and indicates that hydride complex 1H is formed by direct protonation of the Fe-Fe bond. The protonation of 1- is sufficiently fast even with the weaker acids, which excludes a rate-limiting role in light-driven H2 formation under typical conditions.
AB - One-electron reduction and subsequent protonation of a biomimetic proton-reduction catalyst [FeFe(μ-pdt)(CO)6] (pdt = propanedithiolate), 1, were investigated by UV-vis and IR spectroscopy on a nano- to microsecond time scale. The study aimed to provide further insight into the proton-reduction cycle of this [FeFe]-hydrogenase model complex, which with its prototypical alkyldithiolate-bridged diiron core is widely employed as a molecular, precious metal-free catalyst for sustainable H2 generation. The one-electron-reduced catalyst was obtained transiently by electron transfer from photogenerated [Ru(dmb)3]+ in the absence of proton sources or in the presence of acids (dichloro- or trichloroacetic acid or tosylic acid). The reduced catalyst and its protonation product were observed in real time by UV-vis and IR spectroscopy, leading to their structural characterization and providing kinetic data on the electron and proton transfer reactions. 1 features an intact (μ2,κ2-pdt)(μ-H)Fe2 core in the reduced, 1-, and reduced-protonated states, 1H, in contrast to the Fe-S bond cleavage upon the reduction of [FeFe(bdt)(CO)6], 2, with a benzenedithiolate bridge. The driving-force dependence of the rate constants for the protonation of 1- (kpt = 7.0 × 105, 1.3 × 107, and 7.0 × 107 M-1 s-1 for the three acids used in this study) suggests a reorganization energy >1 eV and indicates that hydride complex 1H is formed by direct protonation of the Fe-Fe bond. The protonation of 1- is sufficiently fast even with the weaker acids, which excludes a rate-limiting role in light-driven H2 formation under typical conditions.
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U2 - 10.1021/acs.inorgchem.7b02687
DO - 10.1021/acs.inorgchem.7b02687
M3 - Article
C2 - 29297686
AN - SCOPUS:85041807639
VL - 57
SP - 768
EP - 776
JO - Inorganic Chemistry
JF - Inorganic Chemistry
SN - 0020-1669
IS - 2
ER -