Chelated bis(NHC) complexes of saturated (imidazolin-2-ylidene) NHC ligands: structural authentication and facile ligand fragmentation

The CH₂-linked bis(NHC) complexes [{(^SMesIm)₂CH₂}PdBr₂] and [{(^SMesIm)₂CH₂}Pd(NCMe)₂][PF₆]₂ are reported. These represent the first structurally characterized chelated, saturated bis(NHC) complexes. The complexes are subject to facile ligand fragmentation during their synthesis. Longer (CH₂)_n-linkers in the imidazolin-2-ylidene-based series of ligands afforded the pendant imidazolinium mono(NHC) complexes [{(^SMesImH)(^SMesIm)(CH₂)_n}PdBr₃] by reaction of the diimidazolinium salts (n = 2, 3) with palladium acetate. These did not react to give the bis(NHC) complexes, as was the case for [{(^SMesImH)(^SMesIm)CH₂}PdX₃] (X = Br, I). Disilver(I) complexes [{(^SMesIm)₂(CH₂)_n}₂Ag₂][PF₆]₂n = 1 and 3, were also prepared.