Phosphorus-Containing Hybrid Calixphyrins: Promising Mixed-Donor Ligands for Visible and Efficient Palladium Catalysts
摘要:
Phosphorus-sulfur-containing hybrid calixphyrins were prepared by the BF3-promoted dehydrative condensation between sigma4-2,5-bis[(pyrrol-2-yl)methyl]phosphole and 2,5-bis[hydroxy(phenyl)methyl]thiophene. X-ray crystallographic analysis of the Pd-P,N2,S-hybrid calixphyrin complex revealed that the Pd center was coordinated by the four heteroatoms to adopt a distorted square planar geometry. The Pd complex, displaying a characteristic reddish purple color in solution, catalyzed the Heck reaction of bromoarenes with n-butyl acrylate with high efficiency at elevated temperatures.
The 5,10-porphodimethene-type P,S,N-2-hybrid calixphyrins bearing p-methoxyphenyl or p-(trifluoromethyl)phenyl groups at the sp(2)-hybridized meso carbons and their palladium(II) and rhodium(l) complexes were prepared and characterized. The electronic effects of the meso-aryl substituents on the redox properties of the pi-conjugated Subunits were evaluated for both the free bases and the palladium complexes, and the hemilabile nature of the P,S,N-2-Calixphyrin platforms in the rhodium complexes was revealed.