Time-Resolved Vibrational Spectroscopy of [FeFe]-Hydrogenase Model Compounds

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• 作者：Jamie L. Bingaman ; Casey L. Kohnhorst ; Glenn A. Van Meter ; Brent A. McElroy ; Elizabeth A. Rakowski ; Benjamin W. Caplins ; Tiffany A. Gutowski ; Christopher J. Stromberg ; Charles Edwin Webster ; Edwin J. Heilweil
• 刊名：The Journal of Physical Chemistry A
• 出版年：2012
• 出版时间：July 12, 2012
• 年：2012
• 卷：116
• 期：27
• 页码：7261-7271
• 全文大小：554K
• 年卷期：v.116,no.27(July 12, 2012)
• ISSN：1520-5215

文摘

Model compounds have been found to structurally mimic the catalytic hydrogen-producing active site of Fe鈥揊e hydrogenases and are being explored as functional models. The time-dependent behavior of Fe₂(渭-S₂C₃H₆)(CO)₆ and Fe₂(渭-S₂C₂H₄)(CO)₆ is reviewed and new ultrafast UV- and visible-excitation/IR-probe measurements of the carbonyl stretching region are presented. Ground-state and excited-state electronic and vibrational properties of Fe₂(渭-S₂C₃H₆)(CO)₆ were studied with density functional theory (DFT) calculations. For Fe₂(渭-S₂C₃H₆)(CO)₆ excited with 266 nm, long-lived signals (蟿 = 3.7 卤 0.26 渭s) are assigned to loss of a CO ligand. For 355 and 532 nm excitation, short-lived (蟿 = 150 卤 17 ps) bands are observed in addition to CO-loss product. Short-lived transient absorption intensities are smaller for 355 nm and much larger for 532 nm excitation and are assigned to a short-lived photoproduct resulting from excited electronic state structural reorganization of the Fe鈥揊e bond. Because these molecules are tethered by bridging disulfur ligands, this extended di-iron bond relaxes during the excited state decay. Interestingly, and perhaps fortuitously, the time-dependent DFT-optimized exited-state geometry of Fe₂(渭-S₂C₃H₆)(CO)₆ with a semibridging CO is reminiscent of the geometry of the Fe₂S₂ subcluster of the active site observed in Fe鈥揊e hydrogenase X-ray crystal structures. We suggest these wavelength-dependent excitation dynamics could significantly alter potential mechanisms for light-driven catalysis.