A new type of chiral porphyrin: Organopalladium porphyrins with chiral chelating diphosphine ligands

Peripherally palladated Ni(II) porphyrins have been prepared using enantiopure chiral chelating diphosphines as supporting ligands on the attached Pd(II) fragment. Both enantiomers of the following complexes have been obtained in good yields, using oxidative addition of the bromoporphyrin starting material 5-bromo-10,20-diphenylporphyrinatonickel(II) (NiDPPBr (1)) to the [Pd0L] complex generated in situ from Pd2dba3 and the chiral ligand L: [PdBr(NiDPP)(CHIRAPHOS)] (2a,b) [CHIRAPHOS = 2,3-bis(diphenylphosphino)butane], [PdBr(NiDPP)(Tol-BINAP)] (3a,b) [Tol-BINAP) = 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl] and [PdBr(NiDPP)(diphos)] [diphos = 1,2-bis(methylphenylphosphino)benzene] (4a,b). The induced asymmetry in the porphyrin was readily detected by 1H NMR and CD spectroscopy. The porphyrin chiroptical properties are strongly dependent upon the structure of the chiral ligand, such that a monosignate CD signal, and symmetric and asymmetric exciton couplets were observed for 4a, 2b, and 3a,b, respectively.

Graphical abstractPeripherally palladated Ni(II) porphyrins with chiral ligands, [PdBr(NiDPP)(CHIRAPHOS)], [CHIRAPHOS = 2,3-bis(diphenylphosphino)butane], [PdBr(NiDPP)(Tol-BINAP)] [Tol-BINAP) = 2,2′-bis(di-p-tolylphosphino)-1,1′-binaphthyl] and [PdBr(NiDPP)(diphos)] [diphos = 1,2-bis(methylphenylphosphino)benzene] have been prepared. The induced asymmetry in the porphyrin was readily detected by 1H NMR and CD spectroscopy. The three types of chiral ligand influence the CD spectral profiles in individual ways.Figure optionsDownload full-size imageDownload as PowerPoint slide