Abstract
The structure and reactivity of intermediates in the photocatalytic cycle of a proton reduction catalyst, [Fe2(bdt)(CO)6] (bdt = benzenedithiolate), were investigated by time-resolved spectroscopy. The singly reduced catalyst [Fe2(bdt)(CO)6]-, a key intermediate in photocatalytic H2 formation, was generated by reaction with one-electron reductants in laser flash-quench experiments and could be observed spectroscopically on the nanoseconds to microseconds time scale. From UV/vis and IR spectroscopy, [Fe2(bdt)(CO)6]- is readily distinguished from the two-electron reduced catalyst [Fe2(bdt)(CO)6]2- that is obtained inevitably in the electrochemical reduction of [Fe2(bdt)(CO)6]. For the disproportionation rate constant of [Fe2(bdt)(CO)6]-, an upper limit on the order of 107 M-1 s-1 was estimated, which precludes a major role of [Fe2(bdt)(CO)6]2- in photoinduced proton reduction cycles. Structurally [Fe2(bdt)(CO)6]- is characterized by a rather asymmetrically distorted geometry with one broken Fe-S bond and six terminal CO ligands. Acids with pKa ≥ 12.7 protonate [Fe2(bdt)(CO)6]- with bimolecular rate constants of 4 × 106, 7 × 106, and 2 × 108 M-1 s-1 (trichloroacetic, trifluoroacetic, and toluenesulfonic acids, respectively). The resulting hydride complex [Fe2(bdt)(CO)6H] is therefore likely to be an intermediate in photocatalytic cycles. This intermediate resembles structurally and electronically the parent complex [Fe2(bdt)(CO)6], with very similar carbonyl stretching frequencies.
| Original language | English |
|---|---|
| Pages (from-to) | 17366-17369 |
| Number of pages | 4 |
| Journal | Journal of the American Chemical Society |
| Volume | 136 |
| Issue number | 50 |
| DOIs | |
| Publication status | Published - Dec 17 2014 |
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ASJC Scopus subject areas
- Chemistry(all)
- Catalysis
- Biochemistry
- Colloid and Surface Chemistry
Cite this
Direct observation of key catalytic intermediates in a photoinduced proton reduction cycle with a diiron carbonyl complex. / Mirmohades, Mohammad; Pullen, Sonja; Stein, Matthias; Maji, Somnath; Ott, Sascha; Hammarström, Leif; Lomoth, Reiner.
In: Journal of the American Chemical Society, Vol. 136, No. 50, 17.12.2014, p. 17366-17369.Research output: Contribution to journal › Article
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TY - JOUR
T1 - Direct observation of key catalytic intermediates in a photoinduced proton reduction cycle with a diiron carbonyl complex
AU - Mirmohades, Mohammad
AU - Pullen, Sonja
AU - Stein, Matthias
AU - Maji, Somnath
AU - Ott, Sascha
AU - Hammarström, Leif
AU - Lomoth, Reiner
PY - 2014/12/17
Y1 - 2014/12/17
N2 - The structure and reactivity of intermediates in the photocatalytic cycle of a proton reduction catalyst, [Fe2(bdt)(CO)6] (bdt = benzenedithiolate), were investigated by time-resolved spectroscopy. The singly reduced catalyst [Fe2(bdt)(CO)6]-, a key intermediate in photocatalytic H2 formation, was generated by reaction with one-electron reductants in laser flash-quench experiments and could be observed spectroscopically on the nanoseconds to microseconds time scale. From UV/vis and IR spectroscopy, [Fe2(bdt)(CO)6]- is readily distinguished from the two-electron reduced catalyst [Fe2(bdt)(CO)6]2- that is obtained inevitably in the electrochemical reduction of [Fe2(bdt)(CO)6]. For the disproportionation rate constant of [Fe2(bdt)(CO)6]-, an upper limit on the order of 107 M-1 s-1 was estimated, which precludes a major role of [Fe2(bdt)(CO)6]2- in photoinduced proton reduction cycles. Structurally [Fe2(bdt)(CO)6]- is characterized by a rather asymmetrically distorted geometry with one broken Fe-S bond and six terminal CO ligands. Acids with pKa ≥ 12.7 protonate [Fe2(bdt)(CO)6]- with bimolecular rate constants of 4 × 106, 7 × 106, and 2 × 108 M-1 s-1 (trichloroacetic, trifluoroacetic, and toluenesulfonic acids, respectively). The resulting hydride complex [Fe2(bdt)(CO)6H] is therefore likely to be an intermediate in photocatalytic cycles. This intermediate resembles structurally and electronically the parent complex [Fe2(bdt)(CO)6], with very similar carbonyl stretching frequencies.
AB - The structure and reactivity of intermediates in the photocatalytic cycle of a proton reduction catalyst, [Fe2(bdt)(CO)6] (bdt = benzenedithiolate), were investigated by time-resolved spectroscopy. The singly reduced catalyst [Fe2(bdt)(CO)6]-, a key intermediate in photocatalytic H2 formation, was generated by reaction with one-electron reductants in laser flash-quench experiments and could be observed spectroscopically on the nanoseconds to microseconds time scale. From UV/vis and IR spectroscopy, [Fe2(bdt)(CO)6]- is readily distinguished from the two-electron reduced catalyst [Fe2(bdt)(CO)6]2- that is obtained inevitably in the electrochemical reduction of [Fe2(bdt)(CO)6]. For the disproportionation rate constant of [Fe2(bdt)(CO)6]-, an upper limit on the order of 107 M-1 s-1 was estimated, which precludes a major role of [Fe2(bdt)(CO)6]2- in photoinduced proton reduction cycles. Structurally [Fe2(bdt)(CO)6]- is characterized by a rather asymmetrically distorted geometry with one broken Fe-S bond and six terminal CO ligands. Acids with pKa ≥ 12.7 protonate [Fe2(bdt)(CO)6]- with bimolecular rate constants of 4 × 106, 7 × 106, and 2 × 108 M-1 s-1 (trichloroacetic, trifluoroacetic, and toluenesulfonic acids, respectively). The resulting hydride complex [Fe2(bdt)(CO)6H] is therefore likely to be an intermediate in photocatalytic cycles. This intermediate resembles structurally and electronically the parent complex [Fe2(bdt)(CO)6], with very similar carbonyl stretching frequencies.
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U2 - 10.1021/ja5085817
DO - 10.1021/ja5085817
M3 - Article
AN - SCOPUS:84919361193
VL - 136
SP - 17366
EP - 17369
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 50
ER -