PdII Complexes of Tridentate PCP N‐Heterocyclic Carbene Ligands: Structural Aspects and Application in Asymmetric Hydroamination of Cyano Olefins

Abstract

AbstractThe synthesis of the ligand precursor 1,3‐bis{(R)‐1‐[(S)‐2‐(diphenylphosphanyl)ferrocenyl]ethyl}imidazolium iodide ([PCPH]I, 1) was extended to the electronically and sterically modified ligand precursors 1,3‐bis{(R)‐1‐[(S)‐2‐{[3,5‐bis(trifluoromethyl)phenyl]phosphanyl}ferrocenyl]ethyl}imidazolium iodide ([3,5‐CF3‐PCPH]I, 6), and 1,3‐bis[(R)‐1‐{(S)‐2‐[bis(3,5‐dimethylphenyl)phosphanyl]ferrocenyl}ethyl]imidazolium iodide ([3,5‐Me‐PCPH]I, 7). Palladium complexes were prepared starting from [Pd(OAc)2]3 in THF to afford [PdI(PCP)]OAc (8), [Pd(OAc)(3,5‐CF3‐PCP)]I (9), and [PdI(3,5‐Me‐PCP)]OAc (10), in excellent yields. The crystal structures of the ligand precursor [3,5‐CF3‐PCPH]I (6), the complex [PdI(3,5‐CF3‐PCP)]PF6 (14), as well as the dicationic complex [Pd(NCCH3)(PCP)](PF6)2 (11), were determined by X‐ray diffraction. Complex 11 and its derivative [Pd(NCCH3)(3,5‐Me‐PCP)](PF6)2 (13) have been tested as catalysts in the asymmetric addition of, for example, thiomorpholine tomethacrylonitrile giving selectivities up to 63 and 75 % ee, respectively, at –80 °C. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)