Synthesis, structure and reactivity of palladium(II) complexes of chiral N-heterocyclic carbene-imine and -amine hybrid ligands.

The synthesis and structures of chiral N-heterocyclic carbene (NHC)-N-donor complexes of silver(I) and palladium(II) are reported. The X-ray structure of an NHC-imine silver(I) complex ((nPr)CN(CHPh))AgBr exhibits an Ag(2)Br(2) dimer motif where the imine group is not coordinated to the silver atom. Reaction between 2 and [PdCl(2)(MeCN)(2)] gives the palladium(II) complex (kappa(2)-(nPr)CN(CHPh))PdCl(2) that contains a chelating NHC-imine ligand as shown by single-crystal X-ray diffraction. Slow hydrolysis of related complexes (kappa(2)-(nPr)CN(CHPh))PdCl(2) and (kappa(2)-((Ph)(2)CH)CN(CHPh))PdCl(2) using triethylammonium chloride and water lead to the precipitation of single crystals of insoluble NHC-amino palladium(II) complexes (kappa(2)-(nPr)CN(H(2)))PdCl(2) and (kappa(2)-((Ph)(2)CH)CN(H(2)))PdCl(2), respectively. In the solid state, complexes 6 and 7 both exhibit intermolecular hydrogen bonding between chlorine and an amino-hydrogen atom resulting in an infinite chain structure. Substitution of an amino hydrogen for an ethyl group gives the soluble complex (kappa(2)-(iPr)CN((H)Et))PdCl(2). Reaction between two equivalents of 2 and [PdCl(2)(MeCN)(2)] gives the di-NHC complex (kappa(1)-(nPr)CN(CHPh))(2)PdCl(2) that does not contain a coordinated imine as shown by single crystal X-ray diffraction. Conproportionation between 5 and an equivalent of [PdCl(2)(MeCN)(2)] to does not occur at temperatures up to 100 degrees C in CD(3)CN.