Polykis(pyrazol-1-yl)benzenes: preparation, structure, and complexation with copper and palladium

A series of polykis(pyrazol-1-yl)benzenes, potential chelating ligands for transition metals, have been prepared by nucleophilic substitution of fluorine in 1,2-difluoro-, 1,2,3,4-tetrafluoro-, 1,2,4,5-tetrafluoro-, and hexafluorobenzenes. The observed substitution pattern indicated formation of early TS, making activation by fluorines ortho- to the site of nucleophilic attack dominant. Complexation of the synthesized ligands with copper(II) and palladium(II) was analyzed by ESI mass spectrometry. X-ray structures were determined for palladium(II) complex with 1,2-bis(pyrazol-1-yl)benzene and copper(II) complex with 1,4-difluoro-2,3-bis(pyrazol-1-yl)benzene, revealing an unusual seven-membered chelate cycle formation.