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Thermodynamics of complexes formation of dicyclopalladated 4‐dimethylaminoazobenzene with nitrogen ligands in solution

Palladacycles are a long-standing topic of research due to their wide application in organic transformations and catalysis, in materials science and, recently, in the design of photosensitizers and biomolecular labels. [1] In this context, we have focused our research on the organopalladium compounds with azobenzenes that exhibit strong light absorption and emission in the visible and near infrared regions, which qualifies them as good candidates for chromogenic and fluorogenic room-temperature (bio)sensors. [2] In addition, azobenzenes easily react with different PdII precursors yielding mono- or dicyclopalladated complexes, and their physical properties can be modulated by an appropriate selection of ancillary ligands or by varying the substituents on the azobenzene. [1, 3] In this work we have studied for the first time the complexes formation of dicyclopalladated 4- dimethylaminoazobenzene with different nitrogen ligands, 4-substituted pyridine derivatives (Figure 1). Thermodynamic properties of those processes were evaluated by means of UV-Vis and microcalorimetric titrations in DMF and DMSO at 25 °C and it was found that one or two nitrogen containing ligands can bound to dicyclopalladated azobenzene. Results will be discussed in terms of electron-donating and electron-withdrawing properties of substituents in the 4-position of pyridine derivatives as well as the solvent donor abilities.

thermodynamics ; dicyclopalladated azobenzene ; nitrogen ligands ; UV-Vis ; ITC

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