Sulfur-bridged phenol dimer 32 is converted into P–S–P ligand 5, mono- and dinuclear palladium complexes of which are selectively synthesized and characterized by X-ray crystallography.
Thiacalix [4]arenes bearing two amino groups instead of two hydroxy groups of p-tert-butylthiacalix[4]arene(2) at the distal 1,3-(5b) and proximal 1,2-positions (5c) are regioselectively synthesized via the nucleophilic aromatic substitution (S N Ar) reaction of lithium benzylamide with tetra-O-methylsulfinylcalix[4]arenes 4(rctt) and 4(rcct), respectively. The S N Ar reaction selectively proceeds at the benzene rings between two neighboring sulfinyl groups of a trans conformation. This is rationalized by the cooperative coordination of a methoxy group with a neighboring sulfinyl oxygen atom toward the metal ion to form a six-membered chelate, through which the amide ion attacks the aromatic nucleus. The N,O-hybrid thiacalixarenes 5b and 5c adopt cone conformations in their acetonitrile inclusion crystals. The distances between adjacent N and/or O atoms of their narrow-rim substituents indicate that the four substituents form a circular hydrogen-bond network but it is weaker than that of original thiacalixarene 2. Compound 5c also adopts a cone conformation in the guest-free crystal. This, combined with the fact that tetraaminated p-tertbutylthiacalix[4]arene 5a adopts a 1,3-alternate conformation in its guest-free crystal, indicates that the intramolecular O/N hydrogen bonds, not to mention the O/O hydrogen bond, in compound 5c play a crucial role in maintaining a cone conformation in the crystal.
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