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Theoretical Studies on Water Splitting Using Transition Metal Complexes
KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , xii, 66 p.
Series
TRITA-BIO-Report, ISSN 1654-2312 ; 2014:6
National Category
Theoretical Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-145191ISBN: 978-91-7595-069-3 (print)OAI: oai:DiVA.org:kth-145191DiVA: diva2:717140
Public defence
2014-06-13, Albanova FB53, Roslagstullsbacken 21, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20140526

Available from: 2014-05-26 Created: 2014-05-14 Last updated: 2014-05-26Bibliographically approved
List of papers
1. Water Oxidation Catalysis: Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes
Open this publication in new window or tab >>Water Oxidation Catalysis: Influence of Anionic Ligands upon the Redox Properties and Catalytic Performance of Mononuclear Ruthenium Complexes
Show others...
2012 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 51, no 6, 3388-3398 p.Article in journal (Refereed) Published
Abstract [en]

Aiming at highly efficient molecular catalyts for water oxidation, a mononuclear ruthenium complex Ru-II(hqc)(pic)(3) (1; H(2)hqc = 8-hydroxyquinoline-2-carboxylic acid and plc = 4-picoline) containing negatively charged carboxylate and phenolate donor groups has been designed and synthesized. As a comparison, two reference complexes, Ru-II(pdc)(pic)(3) (2; H(2)pdc = 2,6-pyridine-dicarboxylic acid) and Ru-II(tpy)(pic)(3) (3; tpy = 2,2':6',2 ''-terpyridine), have also been prepared. All three complexes are fully characterized by NMR, mass spectrometry (MS), and X-ray crystallography. Complex 1 showed a high efficiency toward catalytic water oxidation either driven by chemical oxidant (Ce-IV in a pH 1 solution) with a initial turnover number of 0.32 s(-1), which is several orders of magnitude higher than that of related mononuclear ruthenium catalysts reported in the literature, or driven by visible light in a three-component system with [Ru(bpy)(3)](2+) types of photosensitizers. Electrospray ionization MS results revealed that at the Rum state complex 1 undergoes ligand exchange of 4-picoline with water, forming the authentic water oxidation catalyst in situ. Density functional theory (DFT) was ernployed to explain how anionic ligands (hqc and pdc) facilitate the 4-picoline dissociation compared with a neutral ligand (tpy). Electrochemical measurements show that complex 1 has a much lower E(Ru-III/Ru-II) than that of reference complex 2 because of the introduction of a phenolate ligand. DFT was further used to study the influence of anionic ligands upon the redox properties of mononuclear aquaruthenium species, which are postulated to be involved in the catalysis cycle of water oxidation.

Keyword
Molecular Catalysts, Excited-States, Density, Thermochemistry, Solvation, Dioxygen, Kinetics, Energy, Cells, Dimer
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-95121 (URN)10.1021/ic201348u (DOI)000301624500008 ()2-s2.0-84863338735 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation
Note
QC 20120515Available from: 2012-05-15 Created: 2012-05-14 Last updated: 2017-12-07Bibliographically approved
2. Where does the water go?: A computational study on the reactivity of a ruthenium(V) oxo complex (bpc)(bpy)RuVO
Open this publication in new window or tab >>Where does the water go?: A computational study on the reactivity of a ruthenium(V) oxo complex (bpc)(bpy)RuVO
2014 (English)In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 16, 11182-11185 p.Article in journal (Refereed) Published
Abstract [en]

Two possible reactive sites (the oxo site and the Ru site) for water on a high-valent ruthenium(V) oxo complex were examined. Our results suggest that the reaction on the ruthenium (via a seven coordinate intermediate) has both a lower barrier and a product with a lower free energy than the product of addition at the oxo.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-145656 (URN)10.1039/C4CP01183J (DOI)000336796800010 ()2-s2.0-84901281183 (Scopus ID)
Note

Q 20140527

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
3. A computational study of the mechanism for water oxidation by (bpc)(bpy)(RuOH2)-O-II
Open this publication in new window or tab >>A computational study of the mechanism for water oxidation by (bpc)(bpy)(RuOH2)-O-II
2014 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 43, no 36, 13776-13782 p.Article in journal (Refereed) Published
Abstract [en]

A mechanistic study on the catalytic cycle water oxidation with 1 [(bpc)(bpy)(RuOH2)-O-II](+) (Hbpc = 2,2'-bipyridine-6-carboxylic acid, bpy = 2,2'-bipyridine) is described in this paper. Stepwise oxidation via proton-coupled electron transfer gives 3 [(bpc)(bpy)Ru-IV=O](+). An active 4 [(bpc)(bpy)Ru-V=O](2+), which is involved in the OO bond formation is generated from further 1e(-) oxidation of 3. Another different possible reaction at 4 was investigated and new destructive paths involving overoxidation of the metal were identified. The most viable path for OO bond formation via a water nucleophilic attack at the oxo of 4 is found to be the rate-determining step in this water oxidation catalytic cycle, and the hydro-peroxo 6 [(bpc)(bpy)-(RuOOH)-O-III](+) is generated accompanied with a proton transfer. The super-oxo 7(side-on) [(bpc)(bpy)(RuOO)-O-IV](+) and 8(side-on) [(bpc)(bpy)(RuOO)-O-V](2+), both low spin species, are generated by further oxidations of 6. Through an intersystem crossing they can transform to their high spin states, 9(end-on) [(bpc)(bpy)(RuOO)-O-IV](+) and 12(end-on) [(bpc)(bpy)(RuOO)-O-V](2+), respectively. Following a dissociative pathway O-2 is readily generated from both 9(end-on) and 12(end-on).

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-145657 (URN)10.1039/c4dt02113d (DOI)000341282100035 ()2-s2.0-84906302977 (Scopus ID)
Note

Updated from manuscript to article in journal.

QC 20141009

Available from: 2014-05-26 Created: 2014-05-26 Last updated: 2017-12-05Bibliographically approved
4. Pendant amine bases speed up proton transfers to metals by splitting the barriers
Open this publication in new window or tab >>Pendant amine bases speed up proton transfers to metals by splitting the barriers
2012 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 48, no 37, 4450-4452 p.Article in journal (Refereed) Published
Abstract [en]

By using density functional theory on [FeFe]-hydrogenase mimics we deconvolute the function of pendant amine bases in proton transfer to and from the metal center. By dividing the high free energy barrier into one high enthalpy-low entropy barrier and one with a low enthalpy-high entropy, a lower free energy barrier is reached.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-95128 (URN)10.1039/c2cc00044j (DOI)000302559100017 ()2-s2.0-84859588310 (Scopus ID)
Note
QC 20120515Available from: 2012-05-15 Created: 2012-05-14 Last updated: 2017-12-07Bibliographically approved
5. Mechanistic studies on proton transfer in a [FeFe] hydrogenase mimic complex
Open this publication in new window or tab >>Mechanistic studies on proton transfer in a [FeFe] hydrogenase mimic complex
2013 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 21, 7816-7822 p.Article in journal (Refereed) Published
Abstract [en]

Four different pathways for deprotonation of [(mu-pdt){Fe(CO)(3)}{Fe(CO)(kappa(2)-Me2PCH2N(Me)CH2PMe2)}] (pdt = propane-1,3-dithiolate) [1H(mu)](1+) were examined, including (1) the "Direct" deprotonation; (2) the "Indirect" deprotonation via the pendant amine N; (3) the "Indirect" deprotonation via the distal metal Fe; and (4) the "Indirect" deprotonation via the dithiolate S. Only deprotonation of the "Indirect" pathway via the pendant amine N is feasible at room temperature. The most favorable migration destination for the bridging hydride in [1H(mu)](1+) is the pendant amine N (activation energy barrier 16.1 kcal mol(-1)). Migrations to the other two possible sites including the distal metal Fe (34.6 kcal mol(-1)) and the S in the dithiolate group (41.5 kcal mol(-1)) were hindered by high proton shuttling barriers. Once the migration barriers of those three "Indirect" pathways are overcome, the following deprotonations from all three positions including the distal atom Fe, the dithiolate S and the pendant amine N, are all feasible. The results also demonstrate a large difference for deprotonation of the hydride from the terminal and bridging sites. The low energy of the virtual orbital associated with the antibonding M-H interaction of [1H(Fe)](1+) implies the high activity for the interaction with aniline.

Keyword
[FeFe]hydrogenases, Bridging hydride, Bridging sites, Mechanistic studies, Migration barriers, Pendant amines, Room temperature, Virtual orbitals
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-123637 (URN)10.1039/c3dt33087g (DOI)000318792400038 ()2-s2.0-84877762775 (Scopus ID)
Funder
Swedish Research Council
Note

QC 20130618

Available from: 2013-06-18 Created: 2013-06-13 Last updated: 2017-12-06Bibliographically approved
6. Catalytic activation of H2 under mild conditions by an [FeFe]-hydrogenase model via an active μ-hydride species
Open this publication in new window or tab >>Catalytic activation of H2 under mild conditions by an [FeFe]-hydrogenase model via an active μ-hydride species
Show others...
2013 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 135, no 37, 13688-13691 p.Article in journal (Refereed) Published
Abstract [en]

A [FeFe]-hydrogenase model (1) containing a chelating diphosphine ligand with a pendant amine was readily oxidized by Fc+ (Fc = Cp 2Fe) to a FeIIFeI complex ([1]+), which was isolated at room temperature. The structure of [1]+ with a semibridging CO and a vacant apical site was determined by X-ray crystallography. Complex [1]+ catalytically activates H2 at 1 atm at 25 C in the presence of excess Fc+ and P(o-tol) 3. More interestingly, the catalytic activity of [1]+ for H2 oxidation remains unchanged in the presence of ca. 2% CO. A computational study of the reaction mechanism showed that the most favorable activation free energy involves a rotation of the bridging CO to an apical position followed by activation of H2 with the help of the internal amine to give a bridging hydride intermediate.

Keyword
Activation free energy, Apical positions, Bridging hydride, Catalytic activation, Computational studies, Diphosphine ligand, Reaction mechanism, Room temperature
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-133266 (URN)10.1021/ja408376t (DOI)000330163000020 ()2-s2.0-84884498203 (Scopus ID)
Funder
Knut and Alice Wallenberg Foundation
Note

QC 20140224

Available from: 2013-10-30 Created: 2013-10-29 Last updated: 2017-12-06Bibliographically approved

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