XII Iberian Meeting of Electrochemistry XVI Meeting of the ...

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XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PE 07 Electrochemical behaviour of novel scorpionate and pyrazole dioxovanadium complexes Telma F.S. Silva, 1 Konstantin V. Luzyanin, 1 Luísa M.D.R.S. Martins, 1,2 Armando J.L. Pombeiro 1 1 Centro de Química Estrutural, Complexo I, Instituto Superior Técnico, Av. Rovisco Pais, 1049- 001 Lisboa, Portugal. 2 Área Departamental de Engenharia Química, ISEL, R. Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal. tsilva@dem.isel.ipl.pt The coordination chemistry of vanadium, in particular with multidentate ligands, is receiving much attention namely on account of its involvement in various biological and catalytic processes, and the search for novel V complexes with pharmacological and catalytic significance is a matter of a high current interest. 1 In view of the significance of V-chemistry with poly(pyrazolyl)borate ligands towards mimicking biocatalytic behaviours and also in pursuit of our interest on transition metal complexes bearing scorpionate ligands, we have embarked upon the syntheses of oxovanadium complexes with such ligands and with those of the related tris(pyrazolyl)methane family, 2 namely the dioxovanadium(V) complexes [VO 2 (3,5- Me 2 Hpz) 3 ][BF 4 ] 1 (pz = pyrazolyl), [VO 2 {SO 3 C(pz) 3 ] 2, [VO 2 {HB(3,5-Me 2 pz) 3 }] 3 or [VO 2 {HC(pz) 3 }][BF 4 ] 4, and the oxovanadium(IV) complex [VO{HB(pz) 3 }{H 2 B(pz) 2 }] 5. We are now reporting the results of our study of the redox behaviour, by cyclic voltammetry and controlled potential electrolysis (at a platinum electrode, 25 ºC, in a 0.2 M [ n Bu 4 N][BF 4 ]/CH 2 Cl 2 or DMSO solution), of the obtained vanadium complexes, which allowed us to get an insight into the net electron-donor ability of such ligands and in the redox V(V)/V(IV) or V(IV)/V(III) interplay, essential for the vanadium versatility as a catalyst. Acknowledgments: This work has been partially supported by the Fundação para a Ciência e a Tecnologia (F CT), Portugal, and its PPCDT (F EDER funded) programme. TFSS is grateful to F CT for a PhD grant (no. SFRH/BD/48087/2008). References [1] A.S. Tracey, G.R. Willsky, E.S. Takeuchi, Vanadium Chemistry, Biochemistry, Pharmacology and Practical Applications, CRC Press, 2007. [2] Silva, T.F.S.; Luzyanin, K.V.; Kirillova, M.V.; Guedes da Silva, M.F.; Martins, L.M.D.R.S.; Pombeiro, A.J.L., Adv. Synth. Catal., 2010, 352, 171. September, 811, 2010. ISEL - Lisbon 98
XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society PE 08 Electrochemical behaviour of para-substituted 3-(phenylhydrazo)pentane-2,4-diones Maximilian N. Kopylovich, a K amran T. Mahmudov, a M. Fátima C.Guedes da Silva, a,b Luísa M. D. R. S. Martins, a,c Maxim L. Kuznetsov, a Telma F. S. Silva, a João J. R. Fraústo da Silva, a Armando J. L. Pombeiro a a Centro de Química Estrutural, Complexo I, IST, TU Lisbon, Av. Rovisco Pais, 1049001 Lisboa, Portugal. b Universidade Lusófona de Humanidades e Tecnologias, ULHT Lisbon, Campo Grande 376, 1749-024 Lisboa, Portugal. c Área Departamental de Engenharia Química, ISEL, R. Conselheiro Emídio Navarro, 1959-007 Lisboa, Portugal kamran_chem@mail.ru The electrochemical behaviour of unsubstituted 3-(phenylhydrazo)pentane-2,4-dione (H L 1 ) and its para-substituted chloro (H L 2 ), carboxy (H L 3 ), fluoro (H L 4 ) and nitro species (H L 5 ) were studied using cyclic voltammetry and the results were interpreted by theoretical calculations at the DFT/HF hybrid level. The substituent at the aromatic ring has a stronger influence on the oxidation potential (E p/2 ox ) than on the reduction one (E p/2 Red ), in accord with the HOMO and LUMO compositions, the former with an important contribution of the aromatic component and the latter being essentially localized at the other part of the molecule. Theoretical studies can account for the irreversibility of the redox processes and allow to propose conceivable mechanisms involving single-electron anodically induced dimerization and two-electron cathodically induc Trends between the Hammett's p , normal n p, inductive I , resonance R , negative p and positive p + polar conjugation and Taft's o p substituent constants and reduction and oxidation potentials were recognized. A good fit was found for p . p 2 E p/2 ox / V 1.4 1.0 0.6 0.2 p = 4.55E ox p/2 r 2 = 0.903, n = 5 1.05 1.10 1.15 1.20 1.25 1.30 Fig.1- Plot of the p substituent constant versus E p/2 ox for HL 1-5 . The obtained correlations or trends should be used to tune various properties of HL such as acidity, coordination ability, biological activity, etc., what can be of interest for both fundamental studies and practical applications. Acknowledgements: This work has been partially supported by the Foundation for Science and Technology (F CT September, 811, 2010. ISEL - Lisbon 99
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