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An iron-iron hydrogenase mimic with appended electron reservoir for efficient proton reduction in aqueous media

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Science Advances  22 Jan 2016:
Vol. 2, no. 1, e1501014
DOI: 10.1126/sciadv.1501014
  • Fig. 1 Molecular structures of 1Ph and 1.

    (A) Crystal structure of 1Ph with displacement ellipsoids at 50% probability. (B) DFT-calculated (BP86, def2-TZVP) structure of 1.

  • Fig. 2 Redox behavior of 1 in the absence of acid.

    (A) Cyclic voltammogram (0.1 V s−1) of 1.0 mM 1 in CH2Cl2 containing 0.1 M nBu4NPF6 on a mercury working electrode. (Inset) Epc variation with scan rate. (B) Room temperature EPR spectrum of 13− in toluene. The singlet at 3299 G is of unknown origin. (C) IR spectral evolution during the reduction of 1 mM 1 in CH2Cl2 containing 0.1 M nBu4NPF6.

  • Fig. 3 Fluorescence quenching and TR-IR of 1(ZnTPP)2.

    (A) Fluorescence quenching titration of a constant concentration of 80 μM ZnTPP with increasing equivalents 1 in CH2Cl2. Fluorescence intensity (λem = 645 nm) versus equivalents 1 and (inset) versus the ratio of free ZnTPP showing full static quenching. (B) Spectral evolution during TR-IR of 1(ZnTPP)2. (C) Rise and decay profiles plus global biexponential fitting from TR-IR at four wavelength maxima (only two are shown for clarity). mOD, milli optical density.

  • Fig. 4 DFT-calculated properties of 1 and 12−.

    Illustration of the DFT-calculated (BP86, def2-TZVP) frontier orbitals (top) and spin density distributions (bottom) of 1 and 12 (triplet). Selected bond lengths (middle) of 1, 1, and 12 illustrate both Fe–S bond elongation followed by rupture, and aromatization of the phosphole backbone upon monoreduction and direduction. SOMO, singly occupied molecular orbital; LUMO, lowest unoccupied molecular orbital.

  • Fig. 5 Catalysis in dichloromethane.

    Cyclic voltammetry (0.1 V s−1) of 1.0 mM 1 in CH2Cl2 containing 0.1 M nBu4NPF6 and 4.0 mM Et3NHBF4 on a mercury working electrode. (Inset) A catalytic wave that increases in amplitude with increasing acid concentration.

  • Fig. 6 Redox behavior of 1 in the presence of acid.

    (A) Cyclic voltammogram (0.1 V s−1) of 1.0 mM 1 in CH2Cl2 containing 0.1 M nBu4NPF6 and 4.0 mM Et3NHBF4 on a mercury working electrode. (B) Peak potential analysis depicting the pure kinetic (KP) zone. (C) IR spectral evolution (first redox wave) during the reduction of 1 mM 1 in CH2Cl2 containing 0.1 M nBu4NPF6 and 4.0 mM Et3NHBF4 on a AuHg working electrode.

  • Fig. 7 Catalytic mechanism in dichloromethane.

    (A) IR spectral evolution (second redox wave and catalytic wave combined) during the reduction of 1 mM 1 in CH2Cl2 containing 0.1 M nBu4NPF6 and 4.0 mM Et3NHBF4 on a AuHg working electrode. (B) Proposed mechanism of proton reduction by (activated) 1 in dichloromethane. SEC, spectroelectrochemistry; RDS, rate-determining step.

  • Fig. 8 Catalysis in 1 M H2SO4.

    Cyclic voltammograms of 2.0 μM 1 in 1 M H2SO4 on a AuHg working electrode at different scan rates. (A) Under a nitrogen atmosphere. (B) Under air.

  • Fig. 9 Catalysis in acidified 1 M Na2SO4.

    (A) Cyclic voltammograms of 2.0 μM 1 in 1 M Na2SO4 (pH adjusted with concentrated H2SO4) on a AuHg working electrode at 0.1 V s−1 at different pH values. (B) Half-wave potential versus pH. (C) Plateau current density versus proton concentration.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/2/1/e1501014/DC1

    Materials and Methods

    Fig. S1. Solution IR spectra of 1, 1Ph, and Et21·(BF4)2 in dichloromethane.

    Fig. S2. 1H NMR (400 MHz) of 1 in CD2Cl2.

    Fig. S3. 31P NMR (162 MHz) of 1 in CD2Cl2.

    Fig. S4. 1H1H correlation spectroscopy (COSY; 300 MHz) of 1 in CD2Cl2.

    Fig. S5. Nuclear Overhauser effect spectroscopy (NOESY; 300 MHz) of 1 in CD2Cl2.

    Fig. S6. 1H NMR (400 MHz) of 1Ph in CD2Cl2.

    Fig. S7. 31P NMR (162 MHz) of 1Ph in CD2Cl2.

    Fig. S8. FD mass analysis of 1.

    Fig. S9. FD mass analysis of 1Ph.

    Fig. S10. X-ray diffraction structure of 1Ph with displacement ellipsoids at 50% probability.

    Fig. S11. Bulk electrolysis of 10 μmol 1 on a carbon sponge electrode.

    Fig. S12. Integrated data from fig. S11.

    Fig. S13. Cyclic voltammograms of 0.5 mM 1.

    Fig. S14. Cyclic voltammograms of 0.5 mM 1, starting from −1.6 V to the cathodic peak, then cycling over the reoxidation wave.

    Fig. S15. Simulation of cyclic voltammograms (DigiElch) from fig. S13 (scan rate, 0.1 V s−1).

    Fig. S16. Simulation of cyclic voltammograms (DigiElch) from fig. S13 (scan rate, 1.0 V s−1).

    Fig. S17. UV-vis spectra of 1 and ZnTPP at a path length of 10 mm.

    Fig. S18. UV-vis titration of a constant concentration of 80 μM ZnTPP with increasing equivalents 1.

    Fig. S19. Output of the fitting procedure.

    Fig. S20. Fluorescence quenching titration of a constant concentration of ZnTPP with 1.

    Fig. S21. UV-vis spectrum of the sample used in the TR-IR experiment (path length, 500 μm).

    Fig. S22. Rise and decay profiles plus global biexponential fitting from TR-IR at four wavelength maxima.

    Fig. S23. Cyclic voltammograms of 0.5 mM 1 and 4.0 mM Et3NHBF4.

    Fig. S24. Cyclic voltammograms of 0.5 mM 1 and 8.0 mM Et3NHBF4.

    Fig. S25. Cyclic voltammograms of 0.5 mM 1 and 16 mM Et3NHBF4.

    Fig. S26. Cyclic voltammograms of 0.5 mM 1 and 32 mM Et3NHBF4.

    Fig. S27. 1H NMR (400 MHz) of 1 in CD2Cl2 in the absence and presence of 4 eq of Et3NHBF4.

    Fig. S28. Cathodic peak potential versus ln(scan rate).

    Fig. S29. Cathodic peak potential versus ln([acid]2).

    Fig. S30. Simulation of cyclic voltammograms from fig. S23.

    Fig. S31. Differential spectral evolution (pyridine region shown) going from 1 to 2.

    Fig. S32. Differential spectral evolution (pyridine region shown) going from 2 to 3 and then to 13.

    Fig. S33. Cyclic voltammogram of 1 mM 1 and 4.0 mM Et3NHBF4 and fits for the simulated model.

    Fig. S34. Cyclic voltammograms of 1.0 mM 1Ph.

    Fig. S35. Cyclic voltammograms of 1.0 mM 1Ph in the presence of 8.0 mM Et3NHBF4.

    Fig. S36. Cathodic peak potential versus ln(scan rate) and ln([acid]).

    Fig. S37. Foot-of-the-wave analysis of the voltammograms in Fig. 8A.

    Fig. S38. Synthesis and structure of Et21·(BF4)2.

    Fig. S39. 1H NMR (400 MHz) of Et21·(BF4)2 in CD2Cl2.

    Fig. S40. 31P NMR (162 MHz) of Et21·(BF4)2 in CD2Cl2.

    Fig. S41. Cyclic voltammograms of 2 μM Et21·(BF4)2 in 0.1 M Na2SO4.

    Fig. S42. Peak current versus scan rate for the adsorption waves in fig. S41.

    Fig. S43. Cyclic voltammogram of 1 M H2SO4 (background currents).

    Fig. S44. Cyclic voltammogram of 2 μM phosphole ligand in 1 M H2SO4.

    Table S1. Comparison of the IR and NMR data of 1, 1Ph, and reference compounds.

    Table S2. Fitted parameters (DigiElch) for the redox processes of 1 in the absence of acid.

    Table S3. Calculated molar extinction coefficients and R2 value of the fit.

    Table S4. Titration setup (with equivalents 1 with respect to ZnTPP) measured and corrected intensity at 645 nm and free ZnTPP concentration.

    Table S5. Fitted parameters for cyclic voltammogram as shown in figs. S23 to S26.

    Table S6. Comparison of reduced and protonated 4,4′-bipyridine species with species formed during spectroelectrochemical reduction in the presence of acid.

    Table S7. Model parameters for cyclic voltammogram as shown in fig. S33.

    Table S8. TON during one cyclic voltammogram scan at various scan rates.

    References (4648)

  • Supplementary Materials

    This PDF file includes:

    • Materials and Methods
    • Fig. S1. Solution IR spectra of 1, 1ph, and Et21·(BF4)2 in dichloromethane.
    • Fig. S2. 1H NMR (400 MHz) of 1 in CD2Cl2.
    • Fig. S3. 31P NMR (162 MHz) of 1 in CD2Cl2.
    • Fig. S4. 1H1H correlation spectroscopy (COSY; 300 MHz) of 1 in CD2Cl2.
    • Fig. S5. Nuclear Overhauser effect spectroscopy (NOESY; 300 MHz) of 1 in CD2Cl2.
    • Fig. S6. 1H NMR (400 MHz) of 1ph in CD2Cl2.
    • Fig. S7. 31P NMR (162 MHz) of 1ph in CD2Cl2.
    • Fig. S8. FD mass analysis of 1.
    • Fig. S9. FD mass analysis of 1ph.
    • Fig. S10. X-ray diffraction structure of 1ph with displacement ellipsoids at 50% probability.
    • Fig. S11. Bulk electrolysis of 10 μmol 1 on a carbon sponge electrode.
    • Fig. S12. Integrated data from fig. S11.
    • Fig. S13. Cyclic voltammograms of 0.5 mM 1.
    • Fig. S14. Cyclic voltammograms of 0.5 mM 1, starting from −1.6 V to the cathodic peak, then cycling over the reoxidation wave.
    • Fig. S15. Simulation of cyclic voltammograms (DigiElch) from fig. S13 (scan rate, 0.1 V s−1).
    • Fig. S16. Simulation of cyclic voltammograms (DigiElch) from fig. S13 (scan rate, 1.0 V s−1).
    • Fig. S17. UV-vis spectra of 1 and ZnTPP at a path length of 10 mm.
    • Fig. S18. UV-vis titration of a constant concentration of 80 μM ZnTPP with increasing equivalents 1.
    • Fig. S19. Output of the fitting procedure.
    • Fig. S20. Fluorescence quenching titration of a constant concentration of ZnTPP with 1.
    • Fig. S21. UV-vis spectrum of the sample used in the TR-IR experiment (path length, 500 μm).
    • Fig. S22. Rise and decay profiles plus global biexponential fitting from TR-IR at four wavelength maxima.
    • Fig. S23. Cyclic voltammograms of 0.5 mM 1 and 4.0 mM Et3NHBF4.
    • Fig. S24. Cyclic voltammograms of 0.5 mM 1 and 8.0 mM Et3NHBF4.
    • Fig. S25. Cyclic voltammograms of 0.5 mM 1 and 16 mM Et3NHBF4.
    • Fig. S26. Cyclic voltammograms of 0.5 mM 1 and 32 mM Et3NHBF4.
    • Fig. S27. 1H NMR (400 MHz) of 1 in CD2Cl2 in the absence and presence of 4 eq of Et3NHBF4.
    • Fig. S28. Cathodic peak potential versus ln(scan rate).
    • Fig. S29. Cathodic peak potential versus ln(acid2).
    • Fig. S30. Simulation of cyclic voltammograms from fig. S23.
    • Fig. S31. Differential spectral evolution (pyridine region shown) going from 1 to 2.
    • Fig. S32. Differential spectral evolution (pyridine region shown) going from 2 to 3 and then to 13−.
    • Fig. S33. Cyclic voltammogram of 1 mM 1 and 4.0 mM Et3NHBF4 and fits for the simulated model.
    • Fig. S34. Cyclic voltammograms of 1.0 mM 1ph.
    • Fig. S35. Cyclic voltammograms of 1.0 mM 1ph in the presence of 8.0 mM Et3NHBF4.
    • Fig. S36. Cathodic peak potential versus ln(scan rate) and ln(acid).
    • Fig. S37. Foot-of-the-wave analysis of the voltammograms in Fig. 8A.
    • Fig. S38. Synthesis and structure of Et21·(BF4)2.
    • Fig. S39. 1H NMR (400 MHz) of Et21·(BF4)2 in CD2Cl2.
    • Fig. S40. 31P NMR (162 MHz) of Et21·(BF4)2 in CD2Cl2.
    • Fig. S41. Cyclic voltammograms of 2 μM Et21·(BF4)2 in 0.1 M Na2SO4.
    • Fig. S42. Peak current versus scan rate for the adsorption waves in fig. S41.
    • Fig. S43. Cyclic voltammogram of 1 M H2SO4 (background currents).
    • Fig. S44. Cyclic voltammogram of 2 μM phosphole ligand in 1 M H2SO4.
    • Table S1. Comparison of the IR and NMR data of 1, 1ph, and reference compounds.
    • Table S2. Fitted parameters (DigiElch) for the redox processes of 1 in the absence of acid.
    • Table S3. Calculated molar extinction coefficients and R2 value of the fit.
    • Table S4. Titration setup (with equivalents 1 with respect to ZnTPP) measured and corrected intensity at 645 nm and free ZnTPP concentration.
    • Table S5. Fitted parameters for cyclic voltammogram as shown in figs. S23 to S26.
    • Table S6. Comparison of reduced and protonated 4,4′-bipyridine species with species formed during spectroelectrochemical reduction in the presence of acid.
    • Table S7. Model parameters for cyclic voltammogram as shown in fig. S33.
    • Table S8. TON during one cyclic voltammogram scan at various scan rates.
    • References (46–48)

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