V. Grosshenny et al., CONSTRUCTION OF PREORGANIZED POLYTOPIC LIGANDS VIA PALLADIUM-PROMOTEDCROSS-COUPLING REACTIONS, Journal of organic chemistry, 62(5), 1997, pp. 1491-1500
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.