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.