CONSTRUCTION OF PREORGANIZED POLYTOPIC LIGANDS VIA PALLADIUM-PROMOTEDCROSS-COUPLING REACTIONS

Rigid preorganized multitopic ligands have been designed and synthesiz ed. The Pd(O)-catalyzed cross-coupling reactions between ethynylated d erivatives of bipyridine or terpyridine and the corresponding bipyridi ne or terpyridine halides or triflates provide access to various homo- ditopic, hetero-ditopic, homo-tritopic, and hetero-tritopic ligands be aring acetylene or diphenylacetylene central units in fair to excellen t 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 pr esent in the molecule, the relevant conditions involve [Pd(PPh(3))(4)] in n-propylamine at 60 degrees C. Oxidative dimerization of the ethyn ylated derivatives in the presence of cupric salts and oxygen gives th e corresponding homo-ditopic ligands bearing diacetylene or diphenyldi acetylene as a spacer in good yields. These methods provide a practica l approach to the rational design of multichelating ligands for coordi nation of redox and photoactive transition metals.