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Mechanosynthesis of Pd(II) photosensitizers under solvent-free conditions in a ball mill

Cyclopalladated complexes and their derivatives have been successfully used in many areas of materials science and biological chemistry [1, 2]. Although these compounds' reactivity and optical properties depend primarily on the cyclopalladated substrate, such features can also be tuned by an appropriate choice of ancillary ligands [3]. Their preparation and modification are usually carried out in solution, but the number of reports on the solid-state synthesis of these organometallic complexes is steadily increasing. To improve the optical properties of dipalladated azobenzenes, [{; ; (DMF)PdCl}; ; 2(-AZB-2H)], their derivatives were prepared with 4- styrylpyridine and 1, 10-phenanthroline by the solvent-free ball-milling method. Reactions with 4-styrylpyridine gave planar complexes, while substitution of DMF ligands in dipalladated azobenzenes by 1, 10-phenanthroline led to the breaking of one PdN bond, allowing the rotation of a phenyl ring and the positioning of both Pd atoms on the same side of the azobenzene ligand. Two Pd atoms in phenanthroline products are linked by the azobenzene ligand and additionally by the Cl-bridge. Ball milling has been shown to be a clean and highly efficient method for the solid-state synthesis of derivatives of dipalladated azobenzenes, although the formation of phenanthroline derivatives requires very complex intramolecular transformations. References [1] J. Dupont, C.S. Consorti, J. Spencer, The Potential of Palladacycles: More than Just Precatalysts. Chem. Rev. 105 (2005) 2527–2572. [2] Palladacycles: Synthesis, Characterization and Applications. (Eds. Dupont, J. ; Pfeffer, M.), Wiley-VCH, Weinheim, 2008. [3] M. Ghedini, I. Aiello, A. Crispini, A. Golemme, M. La Deda, D. Pucci, Coord. Chem. Rev. 290 (2006) 1373– 1390.

mechanochemistry ; solid-state ; cyclopalladates

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