Stereochemistry of nickel(II) complexes with N-glycosylamine ligands from 1,3-diaminopropane and aldopentoses. Correlation between configurational structures and circular dichroism spectra

摘要

Reactions of [Ni(tn)(3)]X-2 . 2H(2)O (tn = 1,3-diaminopropane, X = Cl or Br) with aldopentoses afforded a series of mononuclear nickel(II) complexes with N-glycosylamine ligands, [Ni(aldose-tn)(2)]X-2 [aldose-tn = 1-(N-aldosyl)-amino-3-aminopropane, aldose = D-xylose (D-Xyl) 1, D-lyxose (D-Lyx) 2, D-ribose (D-Rib) 3, or D-arabinose (D-Ara) 4], which were characterized by elemental analysis, electronic absorption and circular dichroism (CD) spectroscopy, and X-ray crystallography. Compound 4b, [Ni(D-Ara-tn)(2)]Br-2 . 2H(2)O, was shown by an X-ray analysis to have a C-2 symmetrical mononuclear nickel(II) structure ligated by two tridentate N-glycosylamine ligands, 1-amino-3-(N-D-arabinosyl)propane. The two N-glycosylamines are co-ordinated to the metal through the primary amino and N-glycosidic secondary amino groups and the C-2 hydroxy group of the sugar moiety in a meridional mode, resulting in a Lambda-C-2-helical configuration around the metal centre. The sugar rings adopt an unusual alpha-C-1(4) chair conformation and the sugar-chelate ring conformation is delta. The co-ordination behavior of D-ribose was confirmed by an X-ray analysis of an analogous compound, [Ni(D-Rib-men)(3)]Br-2 . 2CH(3)OH 5 [D-Rib-men = 1-methylamino-2-(N-D-ribosyl)aminoethane], derived from the reaction of [Ni(men)(3)]Br-2 with D-ribose [men : 1-amino-2-(N-methylamino)ethane]. The D-ribose moiety forms an alpha-N-glycosidic bond with the primary amino group of men, and adopts an alpha-C-4(1) chair form, the sugar-chelate ring conformation being delta. The CD spectra of 1-4 were measured in the region 9000-50 000 cm(-1) and clearly indicated the structural features of the complexes; the Cotton effects at around 10 000 cm(-1) (the first absorption band of the d-d transitions) reflected the conformation of the sugar chelate or the absolute configuration of the N-glycosidic nitrogen atom, and those at around 40 000-46 000 cm(-1) (charge-transfer bands) demonstrated the C-2 chiral configuration around the metal centre. These assignments were also confirmed by the CD spectra of known compounds. [References: 47]