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6.55 Å. N5C-Ru. Y43W. 4.46 Å. W7. 3.77 Å. Y8W. 8.35 Å. F40W. 6.27 Å. Y55W. 6.98 Å. W57. 10.42 Å. R60C-Re. Thermodynamic Considerations. Bimetallic pathway strongly favored under most conditions Strong acid and/or less positive E°  (Co 3+/2+ ) favor monometallic route

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Catalysts for solar fuels

6.55 Å

N5C-Ru

Y43W

4.46 Å

W7

3.77 Å

Y8W

8.35 Å

F40W

6.27 Å

Y55W

6.98 Å

W57

10.42 Å

R60C-Re

Thermodynamic Considerations

Bimetallic pathway strongly favored under most conditions

Strong acid and/or less positive E° (Co3+/2+) favor monometallic route

Both can be competitive under intermediate conditions

Ni(cyclam) TON

Fujita, E.; Creutz, C.; Sutin, N. Brunschwig, B. S. Inorg. Chem.1993, 32, 2657-2662.

Hu, X.; Brunschwig, B. S.; Peters, J. C. J. Am. Chem. Soc.2007, 129, 8988-8998.

Kellett, R. M.; Spiro, T. G. Inorg. Chem.1985, 24, 2373-2377.

Chao, T.-H.; Espenson, J. H. J. Am. Chem. Soc.1978, 100, 129-133.

Aqueous Co(P) Electrocatalysts

NSF Center for Chemical Innovation: CCI Solar

Interdisciplinary collaboration focused on building and understanding a self-contained water splitting system powered by the sun as a

source of clean, sustainable energy

Selected Nonaqueous H2 Evolution Studies

Aqueous electrocatalysis (>90% Faradaic H2 yield) at moderate overpotentials (<0.6 V)

Catalysis likely occurs at CoII/I interface (limited mechanistic details reported)

Several electronic absorptions in UV-visible region: oxidation state sensitive photoprobes

Distance (C60 and C5) = 38.4 Å

Catalysts for Solar Fuels

Covalently tethered or adsorbed electrocatalyst on a light-absorbing nanostructured cathode stable to (moderately) reducing conditions

Electrocatalytic H2 evolution occurs near Co2+/1+ couple

Simulations and thermodynamics favor bimetallic pathway

Ongoing Flash-Quench Spectroscopic Studies

Kellet, R.; Spiro, T. G. Inorg. Chem. 1985, 24, 2373-2377.

Reductive Quenching: [Ru(bpy)3]1+ from MeODMA

J. L. Dempsey, J. R. Winkler, H. B. Gray manuscript in preparation.

Hu, X.; Brunschwig, B. S.; Peters, J. C. J. Am. Chem. Soc.2007, 129, 8988-8998.

Connolly, P.; Espenson, J. H. Inorg. Chem.1986, 25, 2684-2688.

Spectroelectrochemistry: CoI(TMPyP)┐3+ in CH3CN

Nanostructured anode or adsorbed thin film electrocatalyst stable to strongly oxidizing conditions

Currently investigating timescale to confirm reduction at CoII site in [Co(TMPyP)]4+

Reductive quenching of [RuII(bpy)3]2+ promising for CoI(P) generation in situ

Efforts to expand range of conditions to pH 5-8 continue

Bulk photolysis experiments ongoing to confirm H2 evolution via homogeneous catalyst

SEC-derived difference spectrum (blue; Pt mesh, 0.1 M TBAH in MeCN)

UV-vis absorption spectrum of [CoII(TM4PyP)]4+ in MeCN (orange)

K. E. Plass, M. A. Filler, J. M. Spurgeon, B. M. Kayes, S. Maldonado,

B. S. Brunschwig, H. A. Atwater, N. S. Lewis Adv. Mater 2009, 21, 325-328

Juris; Balzani; Barigeletti; Campagna; Belser; von ZelewskyCoord. Chem. Rev.1988, 84, 85-277.

Hoffman, M. Z.; Bolletta, F.; Moggi, L.; Hug, G. L. J. Phys. Chem. Ref. Data1989, 18, 219-543.

Bryan D. Stubbert, Bert T. Lai, and Harry B. Gray

Division of Chemistry and Chemical Engineering, California Institute of Technology

Very Long Range Membrance Electron Transfer

CO2 Reduction Catalysts: Very High h

Roles of Ligand-N H–Bonding

Non-rigidity and Preferred Conformations

Two main isomerization routes: inversion at Ni–N<

N–H deprotonation to Ni–N< (Ni2+ and Ni3+)

Ni–N(R)< cleavage to Ni–N< (3° NL< and Ni1+)

Goal: understand tryptophan electron transfer through OmpA as model membrane protein for PSII

OmpA

Photosystem II

Pautsch, A.; Schulz, G. E. Nat. Struct. Biol.1998, 5, 1013-1017.

Maimon, E.; Zilbermann, I.; Cohen, H.; Kost, D.; van Eldik, R.; Meyerstein, D. Eur. J. Inorg. Chem.2005, 4997.

Soibinet, M.; Dechamps-Olivier, I.; Guillon, E.; Barbier, J.-P.; Aplincourt, M.; Chuburu, F.; Le Baccon, M.; Handel, H. Polyhedron2005, 24, 143-150.

Ikeda, R.; Soneta, Y.; Miyamura, K. Inorg. Chem. Comm.2007, 10, 590-592.

Currently moving towards heterobimetallic ligands to facilitate oxygen atom or hydroxyl group transfer in a two electron process

Nelson, et al.Nat. Rev. Mol. Cell Bio. 2005, 6, 818.

Babini, et al.J. Am. Chem. Soc.2000, 122, 4532.

Winkler, et al.Pure Appl. Chem.1999, 71, 1753.

Gray, et al.Annu. Rev. Biochem.1996, 65, 537.

Single pendant arm donors afford similar results: diminished reactivity and minor decrease in overpotential

Catalytic CO2 Reduction: [NiL4]2+

Fisher, B.; Eisenberg, R. J. Am. Chem. Soc.1980, 102, 7361.

Bhugun, I.; Lexa, D.; Saveant, J.-M. J. Am. Chem. Soc.1996, 118, 1769.

Grodkowski, J.; Neta, P.; Fujita, E.; Mahammed, A.; Simkhovich, L.; Gross, Z.

J. Phys. Chem. A2002, 106, 4772.

Benson, E. E.; Kubiak, C. P.; Sathrum, A. J.; Smieja, J. M. et al. Chem. Soc. Rev.2009, in press.

Targeting Cooperative C–O Cleavage

Acknowledgements

Team GCEP: Kyle M. Lancaster, Keiko Yokoyama, A. KatrineMuseth, Rose Bustos

Bruce Brunschwig & Jay Winkler

Jillian Dempsey & Lionel Cheruzel

Gray and Lewis research groups

Additional funding:

OmpA ET Pathway: Follow the Hopping Hole

CO Dehydrogenase

Ni(h1-CO2) interaction

H-bond stabilization

Fe for “O” transfer

Jeoung & DobbekScience2007, 318, 1461

>106 × CO2:H2O selectivity!!

Ethylene-bridged bis(cyclam)Ni24+ lowers overpotential

Modest gain possibly at the expense of selectivity

Exogenous Lewis bases (e.g., pyridine) lower overpotential

Reduced pyridinium catalysis not observed

N-substitution induces conformational change: counterintuitive decrease in overpotential, but diminished reactivity

Shih, C.; et al. (2008) Science320, 1760-1762.

Electron transfer rates: hopping mechanism >> tunneling mechanism

Tryptophan residues provide launch pads and landing sites

OmpA has several well-positioned residues for long range ET

ET dynamics investigated with time resolved laser flash photolysis

Beley, M.; Cellis, J.-P.; Ruppert, R.; Sauvage, J.-P. J. Am. Chem. Soc.1986, 108, 7641

Flash-quench laser photolysis studies (pH 5)

Data consistent with CoIP generation [Ru(bpy)3]2+ bleach convolutes data (480 nm)

Plausible CO2 Reduction Mechanism at Ni


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