Research Projects within the Ott group
The Ott group is currently working on the following projects:
Molecular and supramolecular systems in the context of Artificial Phostosynthesis
- Functional Models of the [FeFe]-Hydrogenase active site
- Phostosensitizer for Artificial Photosynthesis
- Catalytic Water Oxidation (in collaboration with Anders Thapper)
Low valent Phosphorous Compounds
Functional Models of the [FeFe]-Hydrogenase active site
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Molecular hydrogen may well become the energy carrier of the future and the reversible inter-conversion of protons to molecular hydrogen is thus a key process for future energy schemes. We have taken inspiration from Nature who catalyzes this transformation by a class of enzymes termed hydrogenases (H2ases), in particular the [FeFe] H2ases.
We prepare bioinorganic model complexes of the [FeFe] H2ase's active site that contribute in the quest to understand the catalytic mechanism of the enzyme. At the same time, we utilize this knowledge to design and synthesize new catalysts that are structurally based on the [FeFe] H2ase motif. The catalytic performance of our complexes is tested by a variety of spectroscopic and electrochemical techniques.
We are also interested to utilize our catalysts in conjunction with suitable photosensitizers to drive the reduction of protons by light. Such light-driven hydrogen production schemes are vital for the sustainable production of hydrogen as a carbon-free solar fuel.
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- M Beyler; S Ezzaher; M Karnahl; M-P Santoni; R Lomoth; S Ott, Pentacoordinate iron complexes as functional models of the distal iron in [FeFe] hydrogenases. Chem. Commun. 2011, 47 (42), 11662. link
- D Streich; Y Astuti; M Orlandi; L Schwartz; R Lomoth; L Hammarström; S Ott, High-Turnover Photochemical Hydrogen Production Catalyzed by a Model Complex of the [FeFe]-Hydrogenase Active Site. Chem. Eur. J. 2010, 16 (1), 60. link
- S Ott; M Kritikos; B Åkermark; L Sun; R Lomoth, A Biomimetic Pathway for Hydrogen Evolution from a Model of the Iron Hydrogenase Active Site. Angew. Chem., Int. Ed. 2004, 43 (8), 1006. link
- S Kaur-Ghumaan; L Schwartz; R Lomoth; M Stein; S Ott, Catalytic Hydrogen Evolution from Mononuclear Iron(II) Carbonyl Complexes as Minimal Functional Models of the [FeFe] Hydrogenase Active Site. Angew. Chem., Int. Ed. 2010, 49 (43), 8033. link
We use Metal-organic frameworks (MOFs) for immobilization of molecular catalysts relevant for energy conversion processes. MOFs are considered to be “inert” with exceptionally high thermal and chemical stability, and can provide a robust platform for the incorporation of potentially labile molecular catalysts. In the context of light-to-fuel conversion schemes, protection of catalytically active species by a MOF matrix can enhance their performance.
In our recent work, we have incorporated a molecular proton reduction catalyst with structural similarities to the [FeFe]-hydrogenase active sites into a highly robust Zr(IV)-based metal-organic framework (MOF). In conjunction with a photosensitizer and a sacrificial electron donor, the new MOF-cat catalyzes photochemical hydrogen evolution in water at pH 5 with substantially improved initial rates and overall hydrogen producti
on when compared to a reference system of the same molecular catalyst in solution.
Building on these initial results we are currently extending the project towards integration of other molecular catalysts and photosensitizers into MOFs. We further interface MOF-catalysts with electrodes and semiconductor materials. Mechanistic aspects as well as improved performance of the catalyst systems will be investigated (photo-) electrochemically, leading to a deep understanding of this new heterogeneous catalyst platform.
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- Pullen, S.; Fei, H.; Orthaber, A.; Cohen, S. M.; Ott, S. Journal of the American Chemical Society 2013, 135, 16997.
- Fei, H.; Pullen, S.; Wagner, A.; Ott, S.; Cohen, S. M. Chemical Communications 2015, 51, 66.
Photosensitizers for Artificial Photosynthesis
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Photosensitizers based on bis(tridentate) ruthenium(II) complexes provide a suitable scaffold for the construction of supramolecular rod-like molecular arrays (dyads and triads) for vectorial electron transfer. In addition to this geometrical requirement, sufficiently long excited state lifetimes and appropriate redox potentials of the ground and excited state are required for efficient electron transfer.
We have designed polypyridyl tridentate ligands with 6-membered chelate rings (dqp-analogs) that exhibit coordination bite angles close 180°. As a result, [Ru(dqp)2]2+ shows a remarkably long lifetime of the 3MLCT state (3.0 μs), four orders of magnitude longer than [Ru(tpy)2]2+.
Studies of the excited state dynamics together with quantum chemical calculations of [Ru(dqp)2]2+ suggest that extension of the lifetime results from a less accessible 3MLCT-3MC crossing point in the excited state energy surface.
Using homoleptic and heteroleptic [Ru(dqp)2]2+- analogs featuring the ligands dqxp, Ninp and dqp, we demonstrated that the redox properties of the ground and excited state of this family of complexes can be tuned by varying the electronics of the lateral subunits of the ligand (Inorg. Chem. 2013, 52, 5128-5137). Such novel ligands are readily accessible by different carbon-carbon and carbon-heteroatom couplings.
[Ru(dqxp)2]2+ represents a more potent oxidant in its excited state than [Ru(dqp)2]2+ by 500 mV, with a lifetime of 255 ns. This complex discloses suitable photophysical and redox properties of the excited state, especially for light induced vectorial charge transfer schemes that require high oxidative power.
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- GA Parada; LA Fredin; M-P Santoni; M Jäger; R Lomoth; L Hammarström; O Johansson; P Persson; S Ott, Tuning the Electronics of Bis(tridentate)ruthenium(II) Complexes with Long-Lived Excited States: Modifications to the Ligand Skeleton beyond Classical Electron Donor or Electron Withdrawing Group Decorations. Inorg. Chem. 2013, 52 (9), 5128. link
This project is in collaboration with Anders Thapper
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We have developed an oxygen evolving water oxidation catalyst that can be driven by visible light in aqueous solutions at pH 7. The catalyst is based on amorphous cobalt oxide nanoparticles and uses methylenediphosphonate (M2P) as an additional ligand. The ruthenium complex Ru(bpy)32+ is used as the photosensitizer and peroxosulfate (S2O82-) as the sacrificial electron acceptor (Scheme below). The presence of a ligand allows for an anchoring point where photosensitizer and catalyst can be linked together.
We are currently working on linking the photosensitizer to the cobalt catalyst by using a modified photosensitizer containing M2P groups. We are also in parallel modifying the photosensitizer to be able to be attached to the semiconductor surface in aqueous media.
- Shevchenko, D.; Anderlund, M. F.; Thapper, A.; Styring, S. Energy Envir. Sci. 2011, 4, 1284-1287. link
- Risch, M.; Shevchenko, D.; Anderlund, M. F.; Styring, S.; Heidkamp, J.; Lange, K. M.; Thapper, A.; Zaharieva, I. Int. J. Hydrogen Energy 2012, 37, 8878-8888.
- H-Y Wang; J Liu; J Zhu; S Styring; S Ott; A Thapper, A Ru-Co hybrid material based on a molecular photosensitizer and a heterogeneous catalyst for light-driven water oxidation. Phys. Chem. Chem. Phys. 2014, 16 (8), 3661. link
- H-Y Wang; E Mijangos; S Ott; A Thapper, Water Oxidation Catalyzed by a Dinuclear Cobalt–Polypyridine Complex. Angew. Chem., Int. Ed. 2014, 53 (52), 14499. link
Phospholes are the phosphorus analogues of pyrroles, i.e. five-membered ring system that contain one phosphorus heteroatom. Although known for 60 years by the pioneering work of Wittig and Geissler, the chemistry of phospholes has experience a remarkable renaissance over the last ten years due to their applicability in organic electronics applications, in particular, in organic light-emitting diodes (OLEDs). Building on our expertise in acetylenic phosphaalkenes (introduce link here), we established a convenient access to P=C substituted phospholes (see scheme). The presence of two differently hybridized P-centers gives rise to a rich chemistry, and the possibility to tune the compounds’ electronic properties over a large range.
In addition, we have recently established a new synthetic sequence to phospholes from diacetylenic ketones and so-called phospha Wittig Horner reagents. Using this route, alkene-bridged bis-phospholes that are not available by any other route can selectively be prepared.
With our unique approaches to phospholes and oxa-phospholes we explore these compounds potential in the field of organic electronics.
Selected References: Go to Top
- Arkhypchuk, A. I.; Orthaber, A.; Mihali, V. A.; Ehlers, A. W.; Lammertsma, K.; Ott, S., Oxaphospholes and Bis-Phospholes from Phosphinophosphonates and α,β-Unsaturated Ketones. Chem. Eur. J. 2013, 19 (41), 13692–13704. link
- Arkhypchuk, A. I.; Santoni, M.-P.; Ott, S., Cascade Reactions Forming Highly Substituted, Conjugated Phospholes and 1,2-Oxaphospholes. Angew. Chem., Int. Ed. Engl. 2012, 51 (31), 7776-7780. link
- Arkhypchuk, A. I.; Mijangos, E.; Lomoth, R.; Ott, S., Redox Switching in Ethenyl-Bridged Bisphospholes. Chem. Eur. J. 2014, 20 (49), 16083-16087. link
- Öberg, E.; Orthaber, A.; Lescop, C.; Réau, R.; Hissler, M.; Ott, S., Phosphorus Centers of Different Hybridization in Phosphaalkene-Substituted Phospholes. Chem. Eur. J. 2014, 20 (27), 8421–8432. link
- A Kreienbrink; MB Sarosi; R Kuhnert; P Wonneberger; AI Arkhypchuk; P Lonnecke; S Ott; E Hey-Hawkins, Carbaborane-based alkynylphosphanes and phospholes. Chem. Commun. 2015, 51 (5), 836. link
Acetylenic PhosphaAlkenes (APAs)
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The fusion of molecular acetylene (C≡C) chemistry with low-valent phosphorus chemistry, in particular phosphaalkenes (P=C), brings about an unprecedented class of compounds. Acetylenic PhosphaAlkenes (APAs) are the first examples of molecular structures where heavier main group elements are incorporated into oligoacetylenes.
We currently develop the synthesis of APAs I-IV, study their properties by spectroscopic, crystallographic, electrochemical and theoretical methods and explore their suitability for the construction of larger assemblies based on the APA motif.
APAs offer a variety of properties that are not attainable with classical all-carbon based designs. Amongst those are their rich coordination chemistry, and the fact that APAs usually feature HOMO-LUMO gaps that are considerably smaller than those of their all-carbon congeners.
At present, the APA-project can be classified as basic research. On the other hand, applications within single-molecule electronics or as molecular materials for organic electronics and photonics devices are certainly feasible and will be explored in the future.
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- B Schäfer; E Öberg; M Kritikos; S Ott, Incorporating Phosphaalkenes into Oligoacetylenes. Angew. Chem., Int. Ed. Engl. 2008, 47 (43), 8228. link
- X-L Geng; S Ott, Exploitation of an unprecedented silica-promoted acetylene-allene rearrangement for the preparation of C,C-diacetylenic phosphaalkenes. Chem. Commun. 2009, (46), 7206. link
- X-L Geng; S Ott, Acetylene-Expanded Dendralene Segments with Exotopic Phosphaalkene Units. Chem. Eur. J. 2011, 12153. link