title: Dicyclopalladated complexes of asymmetrically substituted azobenzenes: synthesis, kinetics and mechanisms.
abstract: Two series of new dicyclopalladated complexes {(DMF)PdCl(μ-R(1)C6H3N═NC6H3R(2))PdCl(DMF)} of 4,4'-functionalized azobenzenes with substituents of varying electron-donating or electron-withdrawing strength (R(1) = H, NMe2; R(2) = H, Cl, Br, I, OMe, PhNH, CO2H, SO3Na, or NO2) have been synthesized and fully characterized. (1)H 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 (1)H 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 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 steps. The rate-determining step in both palladations is the breaking of the ortho C-H bond, which has been confirmed as an electrophilic substitution process by Hammett correlations and DFT calculations.
authors.affiliation: Division of Physical Chemistry, Ruđer Bošković Institute , Bijenička 54, HR-10000 Zagreb, Croatia.
authors.forename: Marina
authors.initials: M
authors.lastname: Juribašić
authors.forename: Ana
authors.initials: A
authors.lastname: Budimir
authors.forename: Snježana
authors.initials: S
authors.lastname: Kazazić
authors.forename: Manda
authors.initials: M
authors.lastname: Curić
mesh_terms: D001391:Azo Compounds / Q000737:chemistry*; D060326:Chemistry Techniques, Synthetic; D018360:Crystallography, X-Ray; D004583:Electrons; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D011789:Quantum Theory; D013050:Spectrometry, Fluorescence
chemical_list: D001391:Azo Compounds; D009942:Organometallic Compounds; D010165:Palladium; C009850:azobenzene