Construction of preorganized polytopic ligands via palladium-promoted cross-coupling reactions

Rigid preorganized multitopic ligands have been designed and synthesized. The Pd(O)-catalyzed cross-coupling reactions between ethynylated derivatives of bipyridine or terpyridine and the corresponding bipyridine or terpyridine halides or triflates provide access to various homo-ditopic, hetero-ditopic, homo-tritopic, and hetero-tritopic ligands bearing acetylene or diphenylacetylene central units in fair to excellent yields. Optimal conditions mere found with [Pd(PPh(3))(2)Cl-2], CuI in THF and diisopropylamine at rt, or with [Pd(PPh(3))(4)] in benzene and diisopropylamine at 80 degrees C. When a phenylethynyl group is present in the molecule, the relevant conditions involve [Pd(PPh(3))(4)] in n-propylamine at 60 degrees C. Oxidative dimerization of the ethynylated derivatives in the presence of cupric salts and oxygen gives the corresponding homo-ditopic ligands bearing diacetylene or diphenyldiacetylene as a spacer in good yields. These methods provide a practical approach to the rational design of multichelating ligands for coordination of redox and photoactive transition metals.