Esteban Urriolabeitia

4-arylidene-5(4H)-oxazolones, -imidazolones and -thiazolones have been regioselectively palladated at the ortho position of the 4-arylidene ring through C-H bond activation promoted by Pd(OAc)2. The reaction is general for the three substrates and tolerates electron-withdrawing and -releasing substituents at different positions of the 4-arylidene moiety (ortho-, meta-, para). Oxazolones and imidazolones structurally analogous to the well-known chromophore of the Kaede protein have also been studied. The interaction of the light with these orthopalladated complexes will be presented here.
Two main types of behaviors have been found, depending of the ancillary ligands accompanying the oxazolones or imidazolones around the Pd(II) center.

On the one hand, mononuclear derivatives with labile ligands such as acetonitrile, or with chelating ligands such as acetylacetonate, are fluorescent when irradiated with visible light. The fluorescence of these complexes is compared with that of the free ligands, and the influence of the Pd(II), the nature of the heterocycle, the substituents in the orthopalladated heterocyclic ligand, and the auxiliary ligands in the fluorescence is discussed. On the other hand, orthopalladated dinuclear clam-shell derivatives with carboxylate bridges react with visible light affording cyclobutanes through [2+2]-photocycloaddition of the C=C bonds of the arylidene unit. This Pd-templated photocylcloaddition allows fully stereoselective access to new derivatives of diaminotruxillic acids, not achievable by conventional photochemical procedures. The scope of the photocycloaddition and the release of the organic ligand through different methods will also be presented.

Carlos Cativiela, Esteban P. Urriolabeitia (ISQCH, CSIC-University of Zaragoza, Spain)
Alexandra Pop, Cristian Silvestru (Babes-Bolyai University, FCIC, Cluj-Napoca, Romania)