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

Abstract

Abstract The 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‐CF 3 ‐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‐CF 3 ‐PCP)]I ( 9 ), and [PdI(3,5‐Me‐PCP)]OAc ( 10 ), in excellent yields. The crystal structures of the ligand precursor [3,5‐CF 3 ‐PCPH]I ( 6 ), the complex [PdI(3,5‐CF 3 ‐PCP)]PF 6 ( 14 ), as well as the dicationic complex [Pd(NCCH 3 )(PCP)](PF 6 ) 2 ( 11 ), were determined by X‐ray diffraction. Complex 11 and its derivative [Pd(NCCH 3 )(3,5‐Me‐PCP)](PF 6 ) 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)