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Ruperto Carola‐Symposium 2008

Small Molecule Activation and

Bioenergy Conversion

October 23‐24, 2008

Internationales Wissenschaftsforum Heidelberg (IWH) Ruprecht‐Karls‐Universität Heidelberg

Organized by: Doris Kunz and Katja Heinze

Funded by: Klaus‐Georg und Sigrid Hengstberger Prize 2007

Small Molecule Activation and Bioenergy Conversion Ruperto Carola-Symposium 2008 Table of Contents

Table of Contents Lectures L1 Hydrocarbon activation at platinum: From molecular complexes to metal-organic

frameworks ..................................................................................................................... 1

L2 Non-Heteroatom C1 Organolanthanide Chemistry......................................................... 2

L3 Subvalent Fe-complexes – a new venue for nucleophilic metal catalysis...................... 3

L4 Carbon Dioxide Coordination, Activation, and Functionalization at Reactive Uranium Complexes....................................................................................................... 4

L5 Rare earth metal catalyzed CO2/epoxide copolymerization........................................... 5

L6 Biomimetic CH Activation and Water Oxidation .......................................................... 6

L7 The Electrochemistry of Enzymes that Catalyze Oxidation and Production of H2........ 7

L8 Molecular devices for photocatalytic hydrogen production........................................... 8

L9 Multiresponsive, Photo- and Electrochemically Active Assemblies Based on Ferrocenyl-functionalised Terpyridine Ligands ............................................................. 9

L10 Molybdenum Dinitrogen Complexes with Multidentate Phosphine Ligands: Application in Synthetic Nitrogen Fixation ................................................................. 10

L11 Biomimetic Approaches to Artificial Photosynthesis: Controlling Coupled Electron Transfers ....................................................................................................................... 11

Posters P1 Quinones by Cu-catalysed Oxidation of Isochromanes with Molecular Oxygen ........ 15

P2 Towards the activation of H2O2: Synthesis of new pyridine based complexes of Platinum and Gold........................................................................................................ 16

P3 Oxidative Transformation of Aromatics Aided by Gold Complexes........................... 17

P4 High-Throughput Reaction Monitoring of Enantioselective Hydrogenations with On-Column Reaction Chromatography........................................................................ 18

P5 Oxidative Addition Reactions of Alkyl Halides to a Highly Nucleophilic Rhodium Complex ....................................................................................................................... 19

P6 Chromium-based Molecular Catalysts for the Production of Polyethylenes with Medium and Ultra-High Molecular Weight ................................................................. 20

P7 Nitrate reductase active site models investigated by DFT ........................................... 21

P8 Synthesis and Characterisation of Highly Fluorescent Bisdipyrido Imidazolium Salts .............................................................................................................................. 22

P9 Bis(terpyridine)-Ruthenium-Complexes as Building Blocks for Peptides: Electron- and Energy Transfer ..................................................................................................... 23

P10 Photo-induced electron transfer – a tool in single-molecule fluorescence spectroscopy ................................................................................................................. 24

P11 Small molecule activation with metal and metal oxide clusters: matrix isolation and quantum chemical calculations .................................................................................... 25

Small Molecule Activation and Bioenergy Conversion Ruperto Carola-Symposium 2008

Programme

Small Molecule Activation and Bioenergy Conversion Ruperto Carola-Symposium 2008 Programme

Programme

Wednesday, 22. October 2008 Arrival

* * *

Thursday, 23. October 2008

„Coordination Chemistry and Small Molecule Activation”

Chairperson: Doris Kunz

9:00 Welcome

9:15 Mats Tilset, University of Oslo „Hydrocarbon activation at platinum: From molecular complexes to metal-

organic frameworks”

10:15 Coffee break

10:30 Reiner Anwander, Eberhard-Karls Universität Tübingen „Non-Heteroatom C1 Organolanthanide Chemistry”

11:30 Bernd Plietker, Universität Stuttgart, „Subvalent Fe-complexes – a new venue for nucleophilic metal catalysis”

12:30 Lunch break

14:00 Karsten Meyer, Friedrich-Alexander Universität Erlangen-Nürnberg „Carbon Dioxide Coordination, Activation, and Functionalization at Reactive

Uranium Complexes”

15:00 Kai C. Hultzsch, Rutgers, The State University of New Jersey „Rare earth metal catalyzed CO2/epoxide copolymerization”

16:00 Coffee break

16:30 Robert H. Crabtree, Yale University „Biomimetic CH Activation and Water Oxidation”

17:30 Poster session

18:30 Dinner buffet (bis ca. 19 Uhr)

19:30 A chemical guided tour through Heidelberg with refreshment at local brewery

* * *

Small Molecule Activation and Bioenergy Conversion Programme Ruperto Carola-Symposium 2008

Friday, 24. October 2008

„Coordination Chemistry and Bioenergy Conversion” Chairperson: Katja Heinze

9:00 Fraser A. Armstrong, University of Oxford „The Electrochemistry of Enzymes that Catalyze Oxidation and Production of H2”

10:00 Sven Rau, Friedrich-Alexander Universität Erlangen-Nürnberg „Molecular devices for photocatalytic hydrogen production“

11:00 Coffee break

11:30 Ulrich Siemeling, Universität Kassel „Multiresponsive, Photo- and Electrochemically Active Assemblies Based on

Ferrocenyl-functionalised Terpyridine Ligands”

12:30 Lunch break

14:00 Felix Tuczek, Christian Albrechts Universität Kiel „Molybdenum Dinitrogen Complexes with Multidentate Phosphine Ligands:

Application in Synthetic Nitrogen Fixation”

15:00 Poster session, coffee and cake served

16:30 Leif Hammarström, Uppsala University „Biomimetic Approaches to Artificial Photosynthesis: Controlling Coupled

Electron Transfers”

17:30 Final discussion

18:30 Departure

* * *

Samstag, 25. October 2008

about 10:00 Guided tour to the Heidelberg Castle and/or Carl Bosch Museum


Lecture Abstracts


1

L1

Hydrocarbon activation at platinum: From molecular complexes to metal-

organic frameworks

Mats Tilset

Department of Chemistry, University of Oslo P.O.Box 1033 Blindern, N-0315 Oslo, Norway e-mail: [email protected]

The so-called Shilov system, based on Pt(II) salts in acidic aqueous media, was shown to activate and functionalize unreactive C-H bonds as early as in the 1970’s.1 These findings inspired vigorous activities aimed at reacting hydrocarbon C-H bonds with well-defined molecular transition-metal species in solution. Today, Pt may still be one of the metals that shows the greatest promise, although practical applications remain a still unrealized goal. In this contribution, results from research activities in Pt-mediated C-H activation2 in our group will be highlighted with the original Shilov system as a back-drop, with examples from recent3 and ongoing mechanistic work. It will also be demonstrated that the structural motif of the Pt complexes that can react with C-H bonds can be incorporated into 3-dimensional network structures in so-called MOF (metal-organic framework) materials.4

Pt complex

Pt-L1

Pt-L-1

Pt-L0

Pt-N

Pt-MOF with related structural motif

References

(1) Shilov, A. E.; Shul'pin, G. B. Activation and catalytic reactions of saturated hydro-

carbons in the presence of metal complexes; Kluwer Academic: Dordrecht, 2000.

(2) Lersch, M.; Tilset, M. Chem. Rev. 2005, 105, 2471-2526.

(3) Wik, B. J.; Ivanovic-Burmazovic, I.; Tilset, M.; van Eldik, R. Inorg. Chem. 2006, 45, 3613-3621.

(4) Szeto, K. C.; Kongshaug, K. O.; Jakobsen, S.; Tilset, M.; Lillerud, K. P. Dalton Trans., 2008, 2054-60.


2

L2

Non-Heteroatom C1 Organolanthanide Chemistry

L. C. H. Gerber, M. Zimmermann, R. Litlabø, H. M. Dietrich, K. W. Törnroos, R. Anwander

Department of Chemistry, University of Bergen, Allégaten 41, N-5007 Bergen, Norway

e-mail: [email protected]

Multiple hydrogen abstraction from metal-bonded alkyl ligands has been discussed as a

delicate case of C–H bond activation in group 4–Al organometallics and has been associated

with deactivation pathways of Ziegler-Natta-type polymerization catalysts.1-3 We found that

mixtures containing both highly reactive [Ln–CH3] moieties and [Ln–(CH3)x–Al]

heterobimetallic linkages undergo similar C–H bond activation.4-7 Accordingly, hydrogen

abstraction led to the first structurally authenticated [Ln–CH2] and [Ln–CH] moieties.4-6 In

the absence of sterically demanding ligands, the high charge densities of the hard carbon

functionalities CH22– and CH3– imply cluster formation (Figure 1).7

La

HCCH

HC

La

La

La

CHLa

CH

HC

LaLa

La

CH

CH

CH

LaCH

0 3–

Figure 1. Core structures of rare-earth metal methine clusters

Literature:

[1] P. R. Sharp, S. J. Homes, R. Schrock, M. R. Churchill, H. J. Wasserman, J. Am. Chem. Soc. 1981, 103, 965–966.

[2] A. Herzog, H. W. Roesky, Z. Zak, M. Noltemeyer, Angew. Chem. Int. Ed. Engl. 1994, 33, 967–968.

[3] D. W. Stephan, Organometallics 2005, 24, 2548–2560. [4] H. M. Dietrich, H. Grove, K. W. Törnroos, R. Anwander, J. Am. Chem. Soc. 2006, 128,

1458–1459. [5] H. M. Dietrich, K. W. Törnroos, R. Anwander, J. Am. Chem. Soc. 2006, 128, 9298–

9299. [6] M. Zimmermann, J. Takats, G. Kiel, K. W. Törnroos, R. Anwander, Chem. Commun.

2008, 612–614. [7] L. C. H. Gerber, E. Le Roux, K. W. Törnroos, R. Anwander, Chem. Eur. J., in press.


3

L3

Subvalent Fe-complexes – a new venue for nucleophilic metal catalysis

Bernd Plietker

Institut für Organische Chemie, Universität Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart


Catalysis by means of readily abundant and inexpensive iron complexes has faced an

increasing interest in chemical research.[1] Amongst the complexes used low or subvalent

ferrates represent an interesting class of potential catalysts.[2] The high electron density that is

accumulated on the metal center allows their use as nucleophiles in various chemical

transformations. However, althought stoichiometric applications of e.g. subvalent iron-

complexes like Na2[Fe(CO)4] are known in organic synthesis for more than 30 years[3]

catalytic applications are almost unknown. In the present talk some of our recent results in the

use of the related subvalent iron-complex [Bu4N][Fe(CO)3(NO)] will be presented. This

nucleophilic metal species allows for allylic substitutions following either a σ-[4] or a π-allyl[5]

mechanism as well as for an efficient transesterification[6] under neutral conditions. First

mechanistic investigations as well as applications will be presented.

R2 R1

[Fe]

Nu

R2 R1 O R1

Nu

[Fe(CO)3(NO)]O R1

[Fe]

EWG

R2 R1 O R1

Actδ+δ+

δ- δ+δ-

ActEWG

Nu Nu

Allylic Subst itut ion T ransesteri f ication

Literature:

[1] Iron-catalysis in organic synthesis (Ed.: B. Plietker), Wiley-VCH, Weinheim-New York, 2008. [2] A. Dieskau, B. Plietker, manuscript submitted for publication. [3] J. P. Collman, Acc. Chem. Res. 1975, 8, 342. [4] (a) B. Plietker, Angew Chem. 2006, 118, 1497; Angew. Chem. Int. Ed. 2006, 45, 1469; (b) B. Plietker, Angew. Chem. 2006, 118, 6200; Angew. Chem. Int. Ed. 2006, 45, 6053. [5] B. Plietker, A. Dieskau, K. Möws, A. Jatsch, Angew. Chem. 2008, 120, 204; Angew. Chem. Int. Ed. 2008, 47, 198. [6] S. Magens, M. Ertelt, A. Jatsch, B. Plietker, Org. Lett. 2008, 10, 53.


4

L4

Carbon Dioxide Coordination, Activation, and Functionalization at

Reactive Uranium Complexes

Suzanne C. Bart and Karsten Meyer

Department of Chemistry & Pharmacy, Friedrich-Alexander University Erlangen-Nürnberg

Inorganic Chemistry, Egerlandstr. 1, D- 91058 Erlangen


The hexadentate tris-aryloxide triazacyclononane ligand, (t-BuArO)3tacn3–, and its sterically more demanding and protective adamantyl and diamantane derivatives have provided access to reactive coordination compounds of uranium, [((RArO)3tacn)U] (R = t-Bu, Ad, Di), in oxidation states III, IV, V, and VI and custom-tailored ligand environments. These complexes display a pronounced reactivity towards small molecules of biological and industrial relevance. In this seminar, reactions are presented that result in carbon dioxide coordination, activation, splitting, and functionalization. It is shown that charge-separated complexes of uranium are particularly reactive species that often lead to unprecedented chemistry.

Literature:

[1] S.C. Bart, C. Anthon, F.W. Heinemann, E. Bill, N.M. Edelstein, and K. Meyer, J. Am. Chem. Soc. 2008, 130, ASAP article. DOI: 10.1021/ja804263w

[2] O.P. Lam, C. Anthon, F.W. Heinemann, J.M. O'Connor, and K. Meyer, J. Am. Chem. Soc. 2008, 130, 6567 – 6776.

[3] I. Castro-Rodriguez and K. Meyer, J. Am. Chem. Soc. 2005, 127, 11242 – 11243. [4] I. Castro-Rodriguez, H. Nakai, L. Zakharov, A.L. Rheingold and K. Meyer,

Science 2004, 305, 1757 – 1759.


5

L5

Rare earth metal catalyzed CO2/epoxide copolymerization

Kai C. Hultzsch

Department of Chemistry & Chemical Biology, Rutgers, The State University of New Jersey,

610 Taylor Road, Piscataway, NJ 08854-8087, USA


The utilization of CO2 as a C1 feedstock is an appealing goal in contemporary catalysis

research, because CO2 is naturally abundant, inexpensive, nontoxic and nonflammable. In

particular, the metal-catalyzed copolymerization of CO2 and epoxides has been studied

extensively, because the resulting polycarbonates are biodegradable polymers with attractive

material properties,[1] potentially as a substitute for petrochemical based polymers, e.g.

polyethylene or polypropylene.

The organometallic chemistry of the rare earth elements has attracted significant attention in

particular due to their high catalytic activity for a wide range of organic transformations[2] and

polymerizations.[3] Although rare metal complexes are well known to activate epoxides and

CO2, CO2/epoxide copolymerization catalysts have been reported only recently.[4,5]

In this talk we will discuss the chemistry associated with these catalysts and applications in

other organic transformations.

Literature:

[1] G. W. Coates, D. R. Moore, Angew. Chem. Int. Ed. 2004, 43, 6618-6639.

[2] G. A. Molander, J. A. C. Romero, Chem. Rev. 2002, 102, 2161-2185.

[3] H. Yasuda, Top. Organomet. Chem. 1999, 2, 255-283.

[4] a) D. Cui, M. Nishiura, Z. Hou, Macromolecules 2005, 38, 4089-4095. b) D. Cui, M.

Nishiura, O. Tardif, Z. Hou, Organometallics 2008, 27, 2428-2435.

[5] a) D. V. Vitanova, F. Hampel, K. C. Hultzsch, J. Organomet. Chem. 2005, 690, 5182-

5197. b) B. B. Lazarov, F. Hampel, K. C. Hultzsch, Z. Anorg. Allg. Chem. 2007, 633,

2367-2373.


6

L6

Biomimetic CH Activation and Water Oxidation

R. H. Crabtree

Yale Chemistry Department


A manganese terpyridine catalyst equipped with a molecular recognition function hydroxy-

lates alkyl CH bonds with almost complete regio and diastereoselectivity. The same catalyst

also oxidizes water.

N

N

N

Mn O

O Mn

NO

O

O

OO•

HO

OHMe

IV

IV COOH COOH

HOH

N

N

N

Mn O

O Mn

O•IV

IV

:OH2


7

L7

The Electrochemistry of Enzymes that Catalyze

Oxidation and Production of H2

Fraser A. Armstrong

Department of Chemistry, Inorganic Chemistry Laboratory, South Parks Road, Oxford OX1 3QR, England


Hydrogenases are microbial enzymes which catalyse the oxidation and production of dihydrogen, H2. The minimal active site comprises an Fe atom coordinated by thiolate and the simple diatomic species CO and CN. In almost all cases the complete active site contains a second Fe (in the so-called [FeFe]- hydrogenases) or a Ni ([NiFe] hydrogenases). Most hydrogenases also contain a sequence of Fe-S clusters to mediate long-range electron transfer to and from the buried active site. Hydrogenases are highly electroactive when adsorbed on certain materials- giving a reversible hydrogen electrode devoid of Pt. Not only does this activity enable their complex properties to be unravelled by precise electrochemical techniques, but it provides leads for new technologies such as fuel cells, H2 production, non-Pt electrocatalysts, photo-H2 particles and novel redox catalysts for organic transformations. Unlike Pt, hydrogenases receive CO as a reversible inhibitor, and this gives the enzymes an advantage. However, for the enzymes, O2 is usually a potent inactivator: O2 sensitivity is generally acknowledged to be the major issue confronting technological exploitation of these enzymes, and it is one of many issues limiting development of small molecule catalysts. Electrochemical experiments are providing new information on the mechanism of reaction with O2 during catalysis of H2-cycling and suggesting how inhibition may be overcome. The data may guide the genetic engineering of microorganisms that are able to produce H2 in the presence of O2.

Literature:

[1] K. A. Vincent, A. Parkin, F. A. Armstrong, Chem. Rev. 2007, 107, 4366-4413. [2] K. A. Vincent, X. Li, C. F. Blanford, N. A. Belsey, J. H. Weiner, F. A. Armstrong,

Nature Chem. Biol. 2007, 3, 761-762. [3] J. A. Cracknell, K. A. Vincent, M. Ludwig, O. Lenz, B. Friedrich, F. A. Armstrong, J.

Amer. Chem. Soc. 2008, 130, 424-425. [4] J. A. Cracknell, K. A. Vincent, F. A. Armstrong, Chem. Rev. 2008, 108, 2439-2461. [5] G. Goldet, A.Wait, J. A. Cracknell, B. Friedrich, M. Ludwig, O. Lenz, F. A. Armstrong,

J. Amer. Chem. Soc. 2008, 130, 11106-11113. [6] A. Parkin, G. Goldet, C. Cavazza, J. C. Fontecilla-Camps, F. A. Armstrong, J. Amer.

Chem. Soc.2008, 130, advance article on web 10-09-08.


8

L8

Molecular devices for photocatalytic hydrogen production

Johannes G. Vos, Sven Rau

Institute for Inorganic Chemistry, FAU Erlangen, Egerlandstr. 1


Photocatalytic splitting of water is an elegant way to capture the energy of sun light and

transfer it directly into hydrogen which is a storable resource. The use of molecular catalysts

allows a design of its components which will lead to an optimised catalytic system. Currently

several molecular devices are known which contain a light absorbing ruthenium polypyridyl

centre, a redoxactive bridging ligand and catalytically active metal centre.1,2 The focus of this

presentation will be on the interaction between these essential components in a

heterodinuclear Ruthenium-Palladium complex containing tetrapyridophenazines as bridging

ligands.3 This interplay has been characterised by NMR, X-ray, UV-vis, emission, spectro-

electrochemistry and resonance Raman spectroscopy and DFT calculations. Based on these

complementary techniques a mechanism for the photoinduced hydrogen formation will be

discussed.

NN

Ru

NN N

N2+

N

N N

NMLn

photoredoxcentre- light absorption- charge transfer- oxidation of donor

bridging ligand- coordination of

both metal centres- electron storage

catalytic metalsite- recocnition of substrate- coordination of substrate- suseptible to reduction by

reduced bridging ligand Literature:

[1] A. J. Esswein, D. G. Nocera, Chem. Rev. 2007, 107, 4022-4047

[2] S. Rau, D. Walther, J. G. Vos, Dalton Trans., 2007, 915-919

[3] S. Rau, B. Schäfer, D. Gleich, E. Anders, M. Rudolph, M. Friedrich, H. Görls, W.

Henry, J. G. Vos, Angew. Chem., Int. Ed. 2006, 45, 6215-6218


9

L9

Multiresponsive, Photo- and Electrochemically Active Assemblies Based on

Ferrocenyl-functionalised Terpyridine Ligands

Ulrich Siemeling

Institute of Chemistry, University of Kassel, Heinrich-Plett-Str. 40, 34132 Kassel, Germany


Terpyridine ligands of the type Fc’-X-tpy’ (Fc’ = ferrocenyl or octamethylferrocenyl, X =

rigid spacer, tpy’ = 4’-substituted 2,2’:6’,2’’-terpyridine; Figure 1) were prepared,

crystallographically characterised and used for the synthesis of di- and trinuclear

bis(terpyridine) RuII complexes. These multiresponsive donor−sensitiser assemblies were

investigated by (spectro-)electrochemistry, UV/Vis, transient absorption and luminescence

spectroscopy, and an energy level scheme was derived on the basis of the data collected.[1]

Intramolecular quenching of the photoexcited RuII complexes by the redox-active Fc’ groups

can occur reductively and by energy transfer. Both the redox potential of the donor and the

nature of the spacer X have a decisive influence on the excited state lifetimes and emission

properties of the complexes. Some of the complexes show room temperature luminescence,

which is very unusual for this type of compounds.

N

N

N

Fe

ferrocenyl group(variable redox potential)

rigid π-spacer(variable length)

= H or Me

Figure 1. Schematic representation of the ligands used in this study.

Literatur:

[1] U. Siemeling, J. Vor der Brüggen, U. Vorfeld, B. Neumann, A. Stammler, H.-G.

Stammler, A. Brockhinke, R. Plessow, P. Zanello, F. Laschi, F. Fabrizi de Biani, M.

Fontani, S. Steenken, M. Stapper, G. Gurzadyan, Chem. Eur. J. 2003, 9, 2819.


10

L10

Molybdenum Dinitrogen Complexes with Multidentate Phosphine Ligands:

Application in Synthetic Nitrogen Fixation

Felix Tuczek

Institut für Anorganische Chemie, Christian Albrechts Universität Kiel, Otto Hahn Platz 6/7

D-24098 Kiel


The realization of a truly catalytic process of ammonia synthesis on the basis of the Chatt

cycle represents a significant goal. Recently we have performed a complete quantum-

chemical investigation of this cycle and found a close mechanistic relationship to the Schrock

cycle which has been theoretically treated before.[1,2] As evident from this investigation as

well as experimental studies,[3] a basic problem of the classic Chatt-type Mo/W bis-

(dinitrogen) complexes with diphosphine coligands is the presence of two coordination sites

for external substrates which in the course of the reactive cycle leads to the bonding of Lewis

bases deriving from the added acid or the solvent. It is therefore desirable to employ a

polydentate ligand which, in addition to a stable equatorial phosphine ligation, also occupies

the trans-position of the dinitrogen ligand by a neutral donor atom (P or N).[4,5] The talk

summarizes our attempts to prepare such ligands and corresponding molybdenum complexes

and describes their geometric, electronic-structural and spectroscopic properties. The

reactivities of these systems are discussed from the perspective of synthetic nitrogen fixation.

Literature:

[1] Stephan, G.; Sivasankar, Ch.; Tuczek, F. Chem. Eur. J. 2008, 14, 644.

[2] Studt, F.; Tuczek, F. Angew. Chem. Int. Ed. 2005, 44, 5639.

[3] Mersmann, K.; Hauser, A.; Tuczek, F. Inorg. Chem. 2006, 45, 5044, and ref.s cited

therein

[4] Stephan, G.; Näther, C.; Sivasankar, Ch.; Tuczek, F. Inorg. Chim. Acta 2008, 361, 1008.

[5] Dreher, A.; Stephan, G.; Tuczek, F., in Metal Ion Controlled Reactivity; Vol. 61 of Adv.

Inorg. Chem.(2008); C. Hubbard and R. v. Eldik; Eds; in press.


11

L11

Biomimetic Approaches to Artificial Photosynthesis:

Controlling Coupled Electron Transfers

Stenbjörn Styring and Leif Hammarström

Department of Photochemistry and Molecular Science


Light-induced charge separation in molecular assemblies has been widely investigated in the

context of artificial photosynthesis. Important progress has been made in the fundamental

understanding of electron and energy transfer, and in stabilizing charge separation by multi-

step electron transfer.

In the Swedish Consortium for Artificial Photosynthesis, we build on principles from

the natural enzymes Photosystem II and Fe-hydrogenases. An important theme in this

biomimetic effort is that of coupled electron transfer reactions, which have so far received

only little attention: (1) each absorbed photon leads to charge separation on a single-electron

level only, while catalytic water splitting and hydrogen production are multi-electron

processes. There is thus the need for controlling accumulative electron transfer on molecular

components; (2) water splitting and proton reduction at the potential catalysts necessarily

requires the management of proton release and/or uptake. Far from being just a stoichiometric

requirement this controls the electron transfer processes by proton-coupled electron transfer

(PCET); (3) redox-active links between the photosensitizers and the catalysts are required to

rectify the accumulative electron transfer reactions, and will often be the starting points of

PCET.

Our recent results along these lines will be presented.

Literature:

[1] L. Hammarström and S. Styring. Phil. Trans. B, 2008, 363, 1283-1291.

[2] L. Hammarström, Current Opinion in Chemical Biology 2003, 7, 666-673.


Poster Abstracts


15

P1 Quinones by Cu-catalysed Oxidation of Isochromanes with Molecular

Oxygen

Hashmi, A. S. K., Heidelberg, Ackermann, M., Heidelberg

Prof. Dr. A. Stephen K. Hashmi, Organisch-Chemisches Institut Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany

[email protected], http://www.hashmi.de

The syntheses of quinones and hydroquinones from phenolprecursers is a well-known and

established method in organic chemistry. Since most of the old-fashioned oxidizing agents

such as PbO, HgO or Br2 suffer from toxicity and pollution, new oxidizing methods with

“green” chemicals have been developed during the past years. One very attractive oxidizing

agent for phenols is molecular oxygen which is able to transform simple phenols to the

corresponding quinones by a copper-catalyst.[1] Whereas this reaction was not very successful

with lots of more complicated phenols in general, we found out, that isochromane derivatives

react easily in the described manner.

Several alkyl and aryl substituents have been tested in this reaction with success. Functional

groups which might suffer from unselective oxidation by treatment with other oxidizing

agents were tolerated under these conditions without further oxidation.

Moreover, a subsequent reduction of the quinones lead to the hydroquinone

derivatives. This transformation proceeds under very mild conditions and in good yields. In

summary it is a further application for isochromanes which can be synthesized easily by

goldcatalysed phenol synthesis according to Hashmi et al.[2]

[1] K. Takehira, M. Shimizu, Y. Watanabe, H. Orita, T. Hayakawa, Tetrahedron Lett. 1989, 30, 6691.

[2] A. S. K. Hashmi, T. M. Frost, J. W. Bats, J. Am. Chem. Soc. 2000, 122, 11553.


16

P2

Towards the activation of H2O2: Synthesis of new pyridine based complexes

of Platinum and Gold Christian Lothschütz, A. Stephen K. Hashmi

Ruprecht-Karls Universität Heidelberg, Organisch-Chemisches Institut

Im Neuenheimer Feld 274, 69120 Heidelberg


Oxidations are important reactions both for synthetic chemists and for industrial processes.

Nevertheless there are only a few reactions known dealing with late transition metals.

Especially the use of hydrogenperoxid or more complex organic peroxides e.g. tert-butyl

hydroperoxide is rarely discussed. On the basis of the work of Strukul et al. we here report the

synthesis of novel ligands and complexes, modified by pentfluorophenyl or bromo-

tetrafluorophenyl groups.1 These compounds have been prepared in a few steps from readily

available starting materials in good yields. (Figure 1)

Figure 1: Crystal structure of a modified Pt(II) complex

The activation of the oxidant might occur via hydrogen bonds, enabling the oxygen transfer to

coordinated substrates.

Literature:

[1] E. Pizzo, P. Sgarbossa, A. Scarso, R. A. Michelin and G. Strukul, Organometallics 2006, 25, 3056. M. Colladon, A. Scarso, P. Sgarbossa, R. A. Michelin and G. Strukul, J. Am. Chem. Soc. 2007, 129, 7680.

N N N F

F

F

F

Br

PtCl Cl


17

P3

Oxidative Transformation of Aromatics Aided by Gold Complexes

Daniel Serra a, Nikolai Vinokurov,a Christoph Jäkela,b

aCatalysis Research Laboratory, Im Neuenheimer Feld 584, 69120 Heidelberg, Germany

BASF SE, GCB/C - M313, 67056 Ludwigshafen, Germany

Methods for the efficient iodination of aromatic systems are of general interest in Organic

Chemistry, due to the use of iodine-substituted aromatic compounds for the formation of

carbon-carbon and carbon-heteroatom bonds.[1,2] However, direct iodination of arenes requires

oxidation of less electrophilic iodine to more reactive species, like I+ or the use of

stoichiometric amounts of Lewis acids, which complicates the work-up and can result in a

decreased selectivity of the process.

Herein, we describe a method for the direct iodination of aromatic compounds without an

additional oxidant. The mild reaction conditions might allow access to a number of important

intermediates for the synthesis of various pharmaceutical and bioactive compounds.[3] In

addition, we found that arylgold (III) complexes react with aromatic amines leading to C-N

bond formation.

1 J. K. Stille, Angew. Chem. Int. Ed. Engl. 1986, 25, 508. 2 J. P. Wolfe, S. L. Buchwald, Org. Synth. 2004, 10, 423.; P. J. Patt, J. F. Hartwig J. Am.

Chem. Soc.; 1994, 116, 5969. 3 K. C. Nicolaou, P. G. Bulger, D. Sarlah, Angew. Chem. Int. Ed. 2005, 44, 4442.


18

P4

High-Throughput Reaction Monitoring of Enantioselective Hydrogenations

with On-Column Reaction Chromatography

Sven K. Weber, Sabrina Bremer, Oliver Trapp

Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg Im Neuenheimer Feld 270, 69120 Heidelberg

e-mail: [email protected] Searching for highly-efficient and effective chiral catalysts is of great economic and ecologic impact. As the mechanism of catalytic reactions is mainly controlled by structural parameters[1] the prerequisite for a directed design of catalysts is the understanding of the reaction kinetics and activation parameters. Therefore comprehensive experimental kinetic data of a broad variety of substrates are necessary to identify rate-controlling elementary steps and to develop mechanistic models. Microfluidic devices integrating chemical synthesis and analysis on the same chip represent a promising approach for parallelized high-throughput (ht) kinetic measurements of catalysts with minute material consumption, yet they are mostly slow, expensive and limited to study single reactions, because competing reactions lead to indefinable reaction kinetics. Recently we showed[2, 3] for hydrogenations over highly active Pd nanoparticles that the synchronous combination of catalysis and separation makes it possible to efficiently perform ht reaction rate measurements (147 reactions/hour) of substrate libraries.

EnantioselectiveOn-column

Synthesis & Separation

stationary phase

mobile phase

dissolved state

catalysis

Ki, chem°

Ki, phys°

Ki, chem°

Ki, phys°

k-1cat

catk1

PimobEi

mob

Eidiss

Pidiss

Eicat

Picat

fused-silica capillarylength 50 cm, ID 250 µm

coating 250 nm

The Reactor

chiral stationary phase& catalytic activity

EnantioselectiveOn-column

Synthesis & Separation

stationary phase

mobile phase

dissolved state

catalysis

Ki, chem°

Ki, phys°

Ki, chem°

Ki, phys°

k-1cat

catk1

PimobEi

mob

Eidiss

Pidiss

Eicat

Picat

fused-silica capillarylength 50 cm, ID 250 µm

coating 250 nm

The Reactor

chiral stationary phase& catalytic activity

Scheme 1 - Enantioselective On-Column Synthesis and Separation

Here we demonstrate the extension of these techniques to enantioselective synthesis and in particular the screening of enantioselective catalysts by combining separation selectivity and catalytic activity in a single chromatographic column (on-column reaction chromatography, Scheme 1). Literature: [1] C. T. Campbell, Nature 2002, 432, 282. [2] O. Trapp, S. K. Weber, S. Bauch, W. Hofstadt, Angew. Chem., Int. Ed. 2007, 46, 7307. [3] O. Trapp, S. K. Weber, S. Bauch, T. Baecker, W. Hofstadt, B. Spliethoff, Chem. Eur. J.

2008, DOI: 10.1002/chem.200701780.


19

P5

Oxidative Addition Reactions of Alkyl Halides to a Highly Nucleophilic

Rhodium Complex

Barbara Wucher, Michael Moser, Doris Kunz* and Frank Rominger

Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg,

Im Neuenheimer Feld 270, D-69120 Heidelberg, Germany


The highly nucleophilic [Rh(bimca)(CO)] complex and its reactivity towards oxidative

addition of alkyl halides will be presented. The CNC pincer type ligand 3,6-di-tert-butyl-1,8-

bis(3-methylimidazolin-2-yliden-1-yl)carbazolide (bimca) was generated in situ by

deprotonation of the imidazolium salt (bimca)•2HBF4. Conversion of the meridionally

coordinated ligand with [Rh(µ-Cl)(CO)2]2 yielded the [Rh(bimca)(CO)] complex 1.[1] Strong

σ-donor and weak π-acceptor properties caused by the ligand give the rhodium center a highly

nucleophilic character which makes the complex very attractive for oxidative addition

reactions of alkyl halides. As shown previously, oxidative addition of methyl iodide occurs

much faster compared to similar rhodium complexes.[2] In our current interest is the oxidative

addition of higher alkyl halides which normally takes place only under harsh reaction

conditions and concurrent CO-insertion.

NN N

NNRhCO

NN N

NNRhCO

I

xs. RI

toluene

1 2

R

For example the addition of ethyl iodide to [Rh(bimca)(CO)] in toluene already occurs at rt

yielding [Rh(bimca)I(CO)(R)] 2 (R = Et). It is remarkable that neither CO-insertion nor β-H-

elimination is observed. This and other reactions with higher alkyl halides will be presented.

Literature:

[1] M. Moser, B. Wucher, D. Kunz, F. Rominger, Organometallics 2007, 26, 1024-1030.

[2] J. A. Gaunt, V. C. Gibson, A. Haynes, S. K. Spitzmesser, A. J. P. White, D. J. Williams, Organometallics 2004, 23, 1015-1023.


20

P6

Chromium-based Molecular Catalysts for the Production of Polyethylenes

with Medium and Ultra-High Molecular Weight

Stefan Marka, Alexander Kurekb, Rolf Mülhauptb, Markus Endersa*

aAnorganisch-Chemisches Institut der Universität Heidelberg, Im Neuenheimer Feld 270, D-

69120 Heidelberg, bFreiburger Materialforschungszentrum, Universität Freiburg


Polyethylenes with a wide range of mechanical properties are produced commercially with

Phillips-, Ziegler- or Metallocene catalysts. For the further improvement of PE-materials it is

necessary to develop highly active catalytic systems which allow for the variation of several

molecular properties like molecular weight distribution or co-monomer incorporation.

Ultra-high molecular weight polyethylene (UHMWPE) is a unique polymer with outstanding

physical and mechanical properties that make this material attractive for engineering and

special applications. However conventional processing methods such as injection or blow

molding cannot be used for this material because of its high melt viscosity. Therefore polymer

blends which combine the low melt viscosity of HDPE with the mechanical advantages of

UHMW-PE are desirable.

[N]

R

Cr CH3

C2 spacer

N-donor

substituents for stericand electronic control

vacant coordination site

+ cationic complex


21

P7

Nitrate reductase active site models investigated by DFT

Matthias Hofmann

Anorganisch-Chemisches Institut, Im Neuenheimer Feld 270, D-69120 Heidelberg


Nitrate reductases (NRs) have a key role within the biological nitrogen cycle by catalyzing the

reduction of nitrate to nitrite. Dissimilatory nitrate reduction is a bacterial mode of energy

generation under anoxic conditions. Molybdenum dependent NR may be members of the

sulfite oxidase (eukariotic NR) or DMSO reductase families (prokaryotic NR). The active

sites of structurally characterized enzymes show a remarkable diversity. The first examples

suggest an oxygen atom transfer mechanism between Mo and substrate. Model coplexes have

already been investigated computationally [1]. The recent report of a sulfur atom in the sixth

position in close distance to the cystein sulfur atom [2] led to various mechanistic

speculations for which model computations will be presented.

HN

N NH

HN

O

SS

O P

O

H2NO

OOR

S

MoS S

S

Sprotein

OH

S

MoS S

S

O

protein

OC

S

MoS S

S

O

protein

O

O

S

MoS S

OH/OH2

O Cys

protein

NR

sulfite oxidase family dmso reductase family

metallo-pterin

D. desulfuricans NapR. spaeroides NapAB

E. coli NarGHI E. coli NarGH

S

MoS S

S

Sprotein

S

D. desulfuricans NapA

MoSS S

SO

SCys

S

MoSS S

S

SSCys O

MoSS S

S

SSCys

O

???+ NO3 - NO2

Literature:

[1] M. Hofmann, J. Biol. Inorg. Chem. 2007, 12, 989-1001.

[2] S. Najmudin, P. Gonzáles, J. Trinão, C. Coelho, A. Mukhopadhyay, N. M. F. S. A.

Cerqueira, C. C. Romão, I. Moura, J. J. G. Moura, C. D. Brondino, M. J. Romão, J. Biol.

Inorg. Chem. 2008, 13, 737-753.


22

P8

Synthesis and Characterisation of Highly Fluorescent

Bisdipyrido Imidazolium Salts

Christine Deißler, Verena Gierz, Frank Rominger, Doris Kunz*

Organisch-Chemisches Institut, Ruprecht-Karls-Universität Heidelberg,

Im Neuenheimer Feld 270, 69120 Heidelberg, Germany


2,2´-Bisformamidinium salts A can be considered as the formal oxidation products of tetra-

aminoethylenes B. Along with an increasing stabilisation of the formamidinium ions, e.g. by

an aromatic character, the corresponding tetraaminoethylenes B become strong oxidants.[1],[2]

N R

N R

R

R

RN

RN

R NR N

R

R

R

R

++ 2dimerizationN R

N R

R

R

NR

NR

R

RX -2

- 2 e−,

+ 2 e−,

X-+ 2

X -- 2

A B C Compounds B can be prepared by dimerisation of carbenes C. Oxidation of B leads to the

formamidinium salts A. This approach is not suitable for the synthesis of arylated

bisimidazolium salts. Recently, an interesting but highly substrate specific FeCl3 catalysed

reaction towards ethylene bridged monopyrido bisimidazolium salts was published.[3]

By developing a more general route we were able to synthesise and structurally characterise

the highly stable bisdipyrido imidazolium salts 1 (R = H) and 2 (R = tBu) which show a

strong green-yellow fluorescence in the daylight.[4]

2 BF4-N

N

N

N+ +

R

R

R

R

1 (R = H)2 (R = tBu)

Literature:

[1] N. Wiberg, Angew. Chem. Int. Ed. Engl. 1968, 10, 766-779.

[2] G. P. McGlacken, T. A. Khan, Angew. Chem. Int. Ed. 2008, 47, 1819-1823.

[3] M. Ostermeier, C. Limberg, B. Ziemer, V. Karunakaran, Angew. Chem. Int. Ed. 2007,

46, 5329-5331.

[4] C. Deißler, F. Rominger, D. Kunz, unpublished results.


23

P9

Bis(terpyridine)-Ruthenium-Complexes as Building Blocks for Peptides:

Electron- and Energy Transfer

Katja Heinze, Klaus Hempel

Department of Inorganic Chemistry, University of Heidelberg Im Neuenheimer Feld 270, 69120 Heidelberg, Germany


The heteroleptic complex [(HOOC–tpy)Ru(tpy–NH2)](PF6)2 (tpy = 2,2’;6’,2’’-terpyridine)

has been incorporated into multicomponent systems and the electron and energy transfer

characteristics of the systems were studied.

(PF6)2

HO

Ru N N

N

NN

NNO H

H

(PF6)2

Ru N N

N

NN

NNO H

HNHFe

Ferrocene moieties were attached on the N-terminal end, the C-terminal end or on both ends

of the ruthenium complex via amide bonds using solution phase peptide synthesis.

Ru N N

N

NN

NNO

HNH

O

(PF6)2

O

HO

NH

O

R

0,1

The next two series of multicomponent systems are peptidic chains composed of

bis(terpyridine)ruthenium(II) acceptor units and organic chromophores as donor moieties (R =

coumarin, naphthaline, anthracene, fluorine units) linked directly by amide bonds or with a

glycine spacer inserted in between the donor and acceptor. These dyads were prepared by

Solid-Phase Peptide Synthesis (SPPS) techniques.

All multicomponent systems were studied by UV/Vis and NMR spectroscopy, steady-state

luminescence, luminescence decay and electrochemistry, as well as by DFT calculations.

[1] K. Heinze, K. Hempel, M. Beckmann, Eur. J. Inorg. Chem. 2006, 2040-2050.

[2] K. Heinze, K. Hempel, submitted.


24

P10

Photo-induced electron transfer – a tool in single-molecule fluorescence

spectroscopy

Alexander Kiel1, Manoj Kumbhakar2, Haridas Pal2, Andrij Mokhir3, Roland Krämer3, Dirk-

Peter Herten1

1Single-molecule spectroscopy, BIOQUANT / CellNetworks, Univ. Heidelberg, Im

Neuenheimer Feld 267 / BQ007, D-69120 Heidelberg 2RPC Division, Bhaba Atomic Research Centre, Mumbai, 400 085 India

3Inorganic Chemistry, Univ. Heidelberg, Im Neuenheimer Feld 271, 69120 Heidelberg


In the past two decades, the use of photo-physical processes to

design novel fluorescent sensors and probes has become

increasingly important with the advent of single-molecule

fluorescence spectroscopy (SMFS). The photo-physical toolbox

now allows studying complex interaction between different

molecules on the nanometer scale and below. Here, we present

different DNA-based probes to study photo-induced electron

transfer (PET) in transition metal complexes as well as through

π-stacked DNA double strands. In both cases, SMFS was used to

measure the kinetics of the different underlying processes. One

probe was designed to observe complexation of individual Cu2+-

ions and to measure the kinetics of Cu(II)-complex formation in thermodynamic equilibrium.

The other was used to study a combination of fluorescence resonance energy transfer (FRET)

and PET revealing electron transfer dynamics through the π-stack of double stranded DNA.

Our experiments demonstrate that photo-physical processes, like electron or energy transfer,

are key in probe design to investigate complex molecular processes on single-molecule level.

Literature:

[1] A. Kiel, J. Kovacs, A. Mokhir, R. Krämer, D.P. Herten. Angew. Chem. Intl. Ed 2007,

46, 3363-3366.

[2] M. Kumbakhar, A. Kiel, H. Pal, D.P. Herten. submitted 2008.


25

P11 Small molecule activation with metal and metal oxide clusters: matrix

isolation and quantum chemical calculations H.-J. Himmel, O. Hübner

Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120

Heidelberg e-mail: [email protected]

The matrix isolation technique is now well established as a valuable method for the isolation and characterization of reactive intermediates.[1] A combination of experimental (spectroscopic) results and quantum chemical calculations is used to shed light on some key steps of model catalytic reactions. The Heidelberg matrix isolation equipment is unique in allowing absorption measurements in the range 5 – 25000 cm−1 as well as scattering measurements (Raman and fluorescence) on the same matrix sample. We are using the matrix isolation technique to study the activation and fixation of small molecules (e.g. H2, N2, CO, CH4 and C2H6) by small metal and metal oxide clusters. The analysis of the electronic excitation spectra of these species is important since the facile access to low-lying electronically excited states is generally responsible for the high reactivity of metal atom dimers and clusters.[2] In the last years we studied in detail the Ti2 molecule and its reactivity towards N2. While no reaction occurs between Ti atoms in their electronic ground state and N2, the relatively weakly bound Ti2 molecule (with a dissociation energy of ca. 115 kJ mol−1)[3] cleaves the strong N2-triple bond in one step without a significant activation barrier to give the rhomboedric Ti2(µ-N)2 nitride.[4,5] This nitride is amenable to further N2 activation with formation of a [{(N2)4Ti}2(µ-N)2(µ-η2:η2-N2)] complex in pure N2 matrices featuring a strongly activated N2 unit (N2

2−).[6] Transition metal oxides are important components of many catalysts. In first studies we compared the electronic ground state and excited states of the rhomboedric oxides Ni2O2 and [Ni2O2]+.[7] [Ni2O2]+ was shown to react in the gas-phase with ethane and higher alkenes with formation of [Ni2O2H2]+ and (presumably) the corresponding alkenes.[8] By contrast, [Ni2O2]+ does not react with H2 and CH4. In future matrix isolation experiments the reactions of neutral Ni2O2 with H2, CH4 and C2H6 will be explored. Literature: [1] See, for example: a) H.-J. Himmel, A. J. Downs, T.M. Greene, Chem. Rev. 2002, 102, 4191-4241. b) H.-J. Himmel, On the Track of Reaction Mechanisms: Characterization and Reactivity of Metal Atom Dimers in Inorganic Chemistry in Focus II, Eds. G. Meyer, D. Naumann, L. Wesemann, Wiley-VCH 2005. c) H.-J. Himmel, M. Reiher, Angew. Chem. 2006, 118, 6412 – 6437; Angew. Chem. Int. Ed. 2006, 45, 6264 – 6288. [2] a) H.-J. Himmel, L. Manceron, A. J. Downs, Angew. Chem. 2002, 114, 829 – 832; Angew. Chem. Int. Ed. 2002, 41, 796 - 799. b) A. Köhn, H.-J. Himmel, B. Gaertner, Chem. Eur. J. 2003, 9, 3909 – 3919. [3] a) H.-J. Himmel, A. Bihlmeier, Chem. Eur. J. 2004, 10, 627 – 633. b) O. Hübner, H.-J. Himmel, L. Manceron, W. Klopper, J. Chem. Phys. 2004, 121, 7195 – 7206. [4] a) H.-J. Himmel, O. Hübner, W. Klopper, L. Manceron, Angew. Chem. 2006, 118, 2865 – 2868; Angew. Chem. Int. Ed. 2006, 45, 2799 – 2802. b) H.-J. Himmel, O. Hübner, L. Manceron, Phys. Chem. Chem. Phys. 2006, 8, 2000 – 2011. [5] J. C. Green, H.-J. Himmel, New J. Chem. 2006, 30, 1253 – 1262. [6] O. Hübner, L. Manceron, H.-J. Himmel, publication in preparation. [7] O. Hübner, H.-J. Himmel, submitted for publication. [8] K. Koszinowski, M. Schlangen, D. Schröder, H. Schwarz, Eur. J. Inorg. Chem. 2005, 2464 – 2469.

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