Electrochemical investigation of intramolecular interactions in molecules with two (or more) redox centers

1. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 1 Electrochemical investigation of intramolecular interactions in molecules with two (or more) redox centers Motto: Electrochemical experimental data are very rich in information, the problem is with their decoding J. Heyrovský Institute of Physical Chemistry, Praha, Czech Republic Molecular electrochemistry departmentjiri.ludvik@jh-inst.cas.cz

2. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 2 more redox centers - molecular wires - "conductivity" of moleculesconnection X differences between surface (new phase) and solution (molecular) electrochemistry electric conductivity of a SAM or single molecule (STM) and intramolecular electronic interaction (mutual sensing, ΔE, Δ3D, ...) *Molecules with two (or more) redox centers:independent communicating strong interaction A  known B  known AB  ? BA  ??? unpredictable! *primary detection by experimental (electrochemical) approach (Hammett) *correlation with spectroscopies and with theoretical (quantum chemical) approach

3. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 3 Dicarbonyl Aromatic Compounds 1

4. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 4 Oximes all mono-oximes: 4 el (E1) 2 el (E2) Hayati Celik, Guler Ekmekci, Jiri Ludvík, Jiri Pícha and Petr Zuman: J.Phys.Chem.B 2006, 110 6785-6796. H. Celik, J. Ludvik and P. Zuman: Electrochimica Acta 51 (2006) 5845-5852.

5. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 5 Oximes of 1,2-diketones two isomers: 1-phenyl-1,2-propanedione- 1-oxime i pH 0 - 7 2 el 4 el E standard mechanism :

6. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 6 pH 5 - 7 i pH 0 - 4 1-phenyl-1,2-propanedione- 2-oxime 2 el 4 el E change of mechanism : Hayati Celik, Jiří Ludvík, Petr Zuman: Electrochemistry Communnication 8 (2006) 1749-1752. Hayati Celik, Jiri Ludvik and Petr Zuman: Electrochim. Acta 52 (2007) 1990-2000..

7. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 7 Observed difference between dcP or CV and CPE(Controlled-potential Electrolysis) i pH 0 - 4 4 el 2 el E time scale: voltammetric techniques - seconds preparative electrolysis - 103 seconds with higher pH k increases

8. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 8 Proposed mechanism for 2-oxime in acidic media: a) Electrooxidation of product Proofs – supports: Anodic CV peak: the enol form is oxidized to ketoimin b) Analogy Benzil:

9. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 9 Why such a difference between the two isomers? kinetic or thermodynamic problem? ? 1-oxime fast 2-oxime slow cooperation with theoretical chemists is necessary

10. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 10 molecular and electronic structure imine of 1-oxime imine of 2-oxime diprotonated benzil transoid transoid cisoid HOMO LUMO dihedral angle  isolated oxime nearly planarity  delocalized system

11. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 11 Conclusions No.1  Two mechanisms: 1-oxime Sequentially H e e H standard oxime mechanism low interaction 2-oxime Simultaneously 2H + 2e „benzil“ mechanism strong interaction  strong interaction between two redox centers – new quality - difficult to predict  AB ≠ BA  "symmetric" behavior of non-symmetric molecules - more general feature?

12. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 12 2 Ferrocene derivatives

13. Ph Ph P = O Fe e - COOH Ph Ph P Fe e - COOH J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 13 2.1 ferrocenes as ET "sensors" phosphino-ferrocene carboxylic acid Hybrid bridging ligand:soft (P) and hard (COOH) donor groups  strong coordination P  M  interaction COO – M depends on pH  solubility in water - Two redox centers: FeII / Fe III and PIII / PV - Oxidation of PIII to PV proceeds via the FeII / Fe III redox couple by anintramolecular ET A1(multielectron) A2(one-electron) PIII:strong interaction – full delocalization (non-bonding el. pair involved)

14. Ph Ph Ph Ph CO P P CO Cr Fe O CO Fe C e - CO C N N R R R carbene - chelate amide R Ph Ph CO P CO Cr Fe CO CO CO C O N R R phosphine complex J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 14 Aminocarbenes with a P-chelating phosphinoferrocenyl substituent combining different redox centers: ferrocene Cr-carbonyl complex carbene(reducible) Aminocarbene chelates: two successive 1el. oxidations of one delocalized systemcommunicating over carbene P-complexes: two independent 1el. waves, non communicating Amides: only ferrocene reversible redox system intramolecular ET E1=0.33; E2=0.88 V (Cr) E1= -0.13 E2=0.23 V E1=0.20; E2=0.35 V (P=O) Complexes with very low Eox  cooperative effect of N and P Meca, L., Dvořák, D., Ludvík, J., Císařová, I., Štěpnička, P., Organometallics. 2004,23, 2541-2551.

15. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 15 2.2 more redox centers Dinuclear ruthenium sawhorse-type complexes - promissing for liquid crystals ferrocenecarboxylates as bridging ligands bridging and terminal or terminal groups 3 (5) redox centers M.Auzias, G.Suess-Fink, P.Štěpnička, J.Ludvík: Inorg.Chim.Acta 2007,360, 2023.

16. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 16 Fc moiety as a terminal group: two overlapped 1-el, rev. oxidn. of two Fc (no communication) + one 1-el, irev. oxidn. of di-Ru core 2xFc

17. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 17 phosphine – strong el. donor: oxidn of RuRu-core prior to Fc-oxidn Fc moiety as a bridging ligand: two close separated 1-el, rev. oxidn. of two Fc  rather limited communication between Fc + irev. oxidn. of di-Ru core 2xFc 2xFc Generally: Fc first, RuRu-core second The first oxidation makes the following one(s) more difficult  discontinuity in changes of the redox potentials

18. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 18 Conclusions No.2 Ferrocene moiety: "entrance" to the molecule (intramolecular ET) part of a broader delocalized system "sensor" reflecting the electron properties of the rest of the molecule reflecting the extent of delocalization

19. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 general conclusions Molecules with more redox centers - understanding of possibilities of electronic "coupling" of more redox centers (new electronic properties, tuning of redox potentials, new design) - experimental estimation - measuring of electronic "conductivity" of spacers in the molecule, of electron delocalization, mutual interaction, extent of the push-pull effect, intramolecular electron transfer etc. Molecular electrochemistry - good experimental tool for learning more about fundamentals of redox chemistry electronic structure of molecules intramolecular interactions generation of radical intermediates and their characterization The data can reveal even very subtle effects and anomalities provoke questions suggest answers but an independent proof is necessary - suitable approach for co-operation

20. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 acknowledgements diketones: Petr Zuman, Clarkson University, USA Stanislav Záliš, J. Heyrovský Institute quantum-chemical calculations ferrocenes: Petr Štěpnička, Charles University Prague Financial support: Research center LC-510 and the project KONTAKT No. M 00209 (Ministry of Education, Youth and Sports of the Czech Republic)

21. J. Heyrovský Institute of Physical Chemistry – Prague Beograd 2010 p-nitrobenzoic acid in DMF - autoprotonation 1e 0.8e Thank you for your attention