Cyclopalladated Complexes of Perylene Imine: Formation of Acetato-Bridged Dinuclear Complexes with 6,6-and 5,6-Membered Metallacycles

Perylene-3-carbaldehyde (1) was condensed with 4-ethylaniline to give 3-perilenylmetilen-4'-ethylaniline (2). The metalation reaction of 2 with palladium acetate, in toluene at 60 degrees C, produced a mixture of palladium complexes where the two major components, 3 and 4, have been characterized as acetate-bridged dimers. Complex 3 is made of two identical six-membered endo cyclometalated Pd(C boolean AND N) moieties, in which the palladium is bound to the peri site with anti arrangement. Compound 4 is the first example combining six- and five-membered metallacycles in a dinuclear compound and adopts an unusual syn arrangement of metal ligands. The X-ray structures of 3 and 4 show pi-pi stacking of perylenyl rings, intermolecular for 3 and intramolecular for 4. The intramolecular pi-pi stacking in 4 has a detrimental effect on luminescence. The imine 2 and all the palladium complexes exhibit fluorescence associated with the perylene fragment, with emission quantum yields, in solution at room temperature, in the range 0.04-0.13 (and emission lifetimes similar to 5 ns). The similarity of the luminescence spectral pattern of the imine and their metalated complexes to that of perylene, although red-shifted, strongly suggests a perylene-dominated intraligand pi-pi* emissive state, metal-perturbed by interaction of the palladium fragment.