A New Totally Flat N(sp2)C(sp2)N(sp2) Pincer Palladacycle: Synthesis and Photoluminescent Properties

Abstract
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 Li2PdCl4 in methanol at room temperature affords the pincer palladacycle (C5H4N-2-CC(Cl)-8-C9H6κNCN)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 π-stacking between alternate pyridine−quinoline moieties (3.448 Å). The pairs are also connected by π-stacking with an interpair distance of 3.452 Å 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.

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