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

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-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)