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 }2 Ag2 ][PF6 ]2 n = 1 and 3, were also prepared.