PdII complexes of tridentate PCP N-heterocyclic carbene ligands: Structural aspects and application in asymmetric hydroamination of cyano olefins

Article abstract of DOI:10.1002/ejic.200500612

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-CF ₃-PCPH]I (6), the complex [PdI(3,5-CF₃-PCP)]PF₆ (14), as well as the dicationic complex [Pd(NCCH₃)(PCP)](PF ₆)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 to methacrylonitrile giving selectivities up to 63 and 75 % ee, respectively, at -80°C. Wiley-VCH Verlag GmbH & Co. KGaA, 2005.