Bis(N‐heterocyclic carbene) Dipalladium Complexes: Synthesis, Solid‐State Conformational Studies and Solution Behaviour

Abstract

AbstractNew palladium(II) bis(N‐heterocyclic carbene) (NHC) complexes have been prepared via metallomacrocyclic AgI ligand transfer agents. Reaction of 1,4‐bis(3‐isopropylimidazolium)xylene (1a) hexafluorophosphate with Ag2O gives a AgI macrocyclic NHC complex in which two silver ions are sandwiched between two dipodal ligands (2a). The NHC moieties adopt a cisoid conformation relative to one another. Upon transfer to palladium to give [{PdCl2(MeCN)}2(bis‐NHC)] (3a) the NHC ligands in the complexes adopt a mixture of cisoid and transoid conformers in the solid state, which have been characterized by X‐ray crystallography. In CD3CN solution the cisoid and transoid conformers interconvert and exhibit resonances for a single averaged form.DFT calculations indicate an interconversion barrier of 56 kJ mol–1. In CDCl3 solution two different isomers are observed which have been assigned to isomers of a chloride‐bridged dimer (4a) following dissociation of the acetonitrile ligands. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)