Dicyclopalladated Complexes of Asymmetrically Substituted Azobenzenes: Synthesis, Kinetics and Mechanisms (CROSBI ID 195827)
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Juribašić, Marina ; Budimir, Ana ; Kazazić, Snježana ; Ćurić, Manda
engleski
Dicyclopalladated Complexes of Asymmetrically Substituted Azobenzenes: Synthesis, Kinetics and Mechanisms
Two series of new dicyclopalladated complexes {; ; ; (DMF)PdCl(mu-R1C6H3N=NC6H3R2)PdCl(DMF)}; ; ; of 4, 4’-functionalized azobenzenes with substituents of varying electron-donating or electron-withdrawing strength (R1=H, NMe2 ; R2=H, Cl, Br, I, OMe, PhNH, CO2H, SO3Na, NO2) have been synthesized and fully characterized. 1H NMR spectroscopy along with the ESI mass spectrometry unambiguously identified the new complexes in the solution and their solid-state structures were determined by X-ray crystallography. The presence of easily exchangeable solvent ligands was confirmed by 1H NMR spectroscopy, X-ray experiments and ESI mass spectrometry. The complexes were additionally characterized by UV-vis and fluorescence spectroscopies. The effect of different 4, 4’-substituents on the formation rate of mono- and dicyclopalladated azobenzenes was studied by the UV-vis spectroscopy. The experimental results are complemented by the quantum-chemical (DFT) calculations in order to rationalize the kinetic results as well as substituent effects on the reaction rates. It was found that the mono- and dicyclopalladation reactions of azobenzenes proceed in two consecutive processes, adduct formation and palladation step. The rate-determining step in both palladations is the breaking of the ortho C–H bond that has been confirmed as an electrophilic substitution process by Hammett correlations and DFT calculations.
azobenzenes; dicyclopalladation; kinetics; mechanism; DFT
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