Bidentate [C,N] Schiff base ligand palladacycles: Synthesis, X-ray diffractometric analysis and survey of their catalytic activity

Abstract

Palladacycles have been synthesized from Pd(OAc)2 and Schiff base ligands via C-H activation, to render dinuclear acetate-bridged compounds. The latter are starting materials for the sequence of reactions leading to the ensuing complexes. Treatment of the µ-acetate dinuclear complexes with aqueous sodium chloride in a typical metathesis reaction, gave the corresponding µ-chloride dinuclear complexes. Reaction of the latter with triphenylphosphine or with bis(diphenylphosphino)methane (dppm) in a 1:2 ratio, and ammonium hexafluorophosphate, gave the single nuclear complexes in a bridge-splitting reaction. The compounds were characterized by microanalysis (CHN), IR and 1 H and 31 P{ 1 H} NMR spectroscopy. The crystal structures of two of them were determined by single-crystal X-ray diffraction. Additionally, the performance of the synthetized palladacycles as catalysts has been evaluated in the Suzuki-Miyaura cross-coupling reaction: they are suitable for the cross coupling of a rather large number of substrates in high yields under mild conditions.