Willans, Charlotte E., Anderson, Kirsty M., Paterson, Martin J., Junk, Peter C., Barbour, Leonard J., and Steed, Jonathan W. (2009) Bis(N-heterocyclic carbene) dipalladium complexes: synthesis, solid-state conformational studies and solution behaviour. European Journal of Inorganic Chemistry, 2009 (19). pp. 2835-2843.

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Abstract

New 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.

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