CALIXARENE METALLORECEPTORS - SYNTHESIS AND MOLECULAR RECOGNITION PROPERTIES OF UPPER-RIM FUNCTIONALIZED CALIX[4]ARENES CONTAINING AN ORGANOPALLADIUM BINDING-SITE

The compound -chloroacetamido)-25,26,27,28-tetrapropoxycalix[4] arene, 4, was prepared in the cane conformation by the published method. Com pound 4 was reacted with alpha,alpha'-m-xylenedithiol and sodium ethox ide under high-dilution conditions in ethanol solution. The resulting macrobicyclic calix[4]arene. HL1, 5, contains a symmetrically disposed macrocyclic loop across the upper rim of the calix[4]arene. Palladati on of 5 yielded [Pd(L-1)(CH3CN)][BF4], 6. Similarly )acetamido]-25,26, 27,28-tetrapropoxycalix[4]arene, 8, was used to prepare HL2, 9. Compou nd 9 is similar to 5 but contains an aromatic spacer group separating the xylyl fragment from the calixarene unit. Palladation of 9 yielded [Pd(L-2)(CH3CN)][BF4(]), 11. All new compounds and complexes were char acterized in solution by H-1 NMR spectroscopy, and the molecular struc ture of 5 was verified by a single-crystal X-ray diffraction study. Co mpound 5 crystallized in the space group P2(1)/c with a = 23.5095(1) A ngstrom, b = 9.9090(1) Angstrom, c = 23.3586(1) Angstrom, beta = 91.53 (1)degrees, V = 5439.59(8) Angstrom(3), and Z = 4. The structure was r efined to R(F) = 10.13% and R-w(F-2) = 21.91% for 5799 reflections wit h F-0(2) > 2 sigma(F-0(2)). Compounds 6 and 1 are calix[4]arene-based metalloreceptors containing an organopalladium binding site and a hydr ophobic cavity provided by the calix[4]arene. Binding of a substrate t hrough sigma-binding to the palladium center and interaction within th e hydrophobic site were demonstrated in solution by H-1 NMR spectrosco py. These multiple receptor-substrate interactions are used by 11 for the molecular recognition of 4-phenylpyridine in the presence of 2-phe nylpyridine or 3-phenylpyridine.