A new totally flat N(sp(2))C(sp(2))N(sp(2)) pincer palladacycle: synthesis and photoluminescent properties

The Sonogashira coupling of 2-bromopyridine with 8-quinolinyl-acetylene affords 2-pyridinyl-8-quinolinyl-acetylene (1) in high yields. The chloropalladation of 1 with Li(2)PdCl(4) in methanol at room temperature affords the pincer palladacycle (C(5)H(4)N-2-C=C(Cl)-8-C(9)H(6)kappaN,kappaC,kappaN)PdCl (2) in 63% yield. The X-ray molecular structure of (2) shows that it is totally flat and that it is associated in pairs though pi-stacking between alternate pyridine-quinoline moieties (3.448 A). The pairs are also connected by pi-stacking with an interpair distance of 3.452 A between quinoline-quinoline moieties. A very low fluorescence emission was also revealed by the pincer palladacycle 2 in both solution and the solid state, which has been ascribed to an excimeric emission due to the particular structure (rigid and totally flat) of 2 in the solid state.