Silver and Palladium Complexes Containing Ditopic N‑Heterocyclic Carbene–Thione Ligands

• Published in: Organometallics 2012-09, Vol.31 (18), p.6595-6607
• Main Authors: Slivarichova, Miriam, Reading, Eamonn, Haddow, Mairi F, Othman, Hafiizah, Owen, Gareth R
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om300615e

The mixed donor N-heterocyclic carbene (NHC)/thione ligand precursors [1-(3-R-2H-imidazol-1-yl-2-thione)methyl-3-R-2H-imidazol-2-ium]X, [HCS R ]X (R = methyl, benzyl; X = Br, I), have been utilized to prepare a range of silver and palladium complexes. The coordination of CS R to silver(I) salts has been explored, providing dimeric complexes of the type [AgX(CS R )]2 (where R = methyl, benzyl; X = Br, I). Structural characterization of [AgX(CS Bn )]2 revealed a bidentate coordination mode for the mixed donor ligand and dinuclear structures where the silver centers are bridged by two bromido centers. Palladium complexes bearing one or two CS R ligands have additionally been prepared either directly, utilizing [Pd(OAc)2] as precursor, or via transmetalation strategies. The dicationic complexes [Pd(CS R )2][X]2 and neutral complexes [PdX2(CS R )] (where R = methyl, benzyl; X = Br, I, PF6) have been synthesized and fully characterized. The CS R ligand in the aforementioned complexes does not undergo transformation of the NHC unit to a urea function, which had been found to occur in the previously reported copper complexes. Palladium complexes containing both NHC/thione and bis-phosphine ligands were also prepared. Complexes of the type [Pd(CS Me )(L2)][X]2 and [PdX(CS Me )(L2)][X] (where L2 = dppe, dppp; X = Br, OAc, I, PF6) were obtained. The presence of the bis-phosphine appears to destabilize the coordination of the NHC/thione ligand and as a consequence leads to its elimination from the complex.