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

The CH2-linked bis(NHC) complexes [{((S)MesIm)(2)CH2}PdBr2] and [{((S)MesIm)(2)CH2} 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 [{((S)MesImH)((S)MesIm)(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 [{((S)MesImH)((S)MesIm)CH2} PdX3] (X = Br, I). Disilver(I) complexes [{((S)MesIm)2(CH2)n} 2Ag(2)][PF6](2) n = 1 and 3, were also prepared.