Peroxo-Bridged Dinuclear Cobalt(III) Complexes Containing N-Glycoside Ligands from Tris(2-aminoethyl)amine and d-Glucose or Maltose

Abstract

Peroxo-bridged dinuclear cobalt(III) complexes, [{Co((d-Glc)2-tren)}2(μ-O2)]X3·5H2O (X = Cl (2·5H2O), Br (3·5H2O)) and [{Co((Mal)2-tren)}2(μ-O2)]Cl3·6H2O (4·6H2O), were prepared from CoX2·6H2O, tris(2-aminoethyl)amine, and d-glucose (d-Glc) or maltose (α-d-glucopyranosyl-(1→4)-d-glucose; Mal), and were characterized by elemental analysis, UV−vis absorption, circular dichroism, 1H and 13C NMR spectroscopic techniques, and X-ray absorption and crystallographic analyses, where (aldose)2-tren is bis(N-aldosyl-2-aminoethyl)(2-aminoethyl)amine (aldose = d-Glc, Mal). The structure of 2 and 4 were determined by X-ray crystallography to consist of two Co(III) ions bridged by a peroxo unit: 2·4H2O·CH3OH, orthorhombic, P212121 (No. 19), a = 19.384(8) Å, b = 23.468(5) Å, c = 13.195(5) Å, V = 6002(2) Å3, Z = 4, Dcalcd = 1.440 g cm-3, T = −99 °C, R = 0.078, Rw = 0.085 for 4961 reflections with I > 3σ(I); 4·2.25H2O·3.75CH3OH, monoclinic, P21 (No. 4), a = 12.819(7) Å, b = 49.168(18) Å, c = 14.973(6) Å, β = 104.59(4)°, V = 9130(7) Å3, Z = 4, Dcalcd = 1.459 gcm-3, T = −136 °C, R = 0.101 for 6837 reflections with I > 2σ(I). The hydrogen bondings between the sugar moieties deviates the Co−O−O−Co torsional angle from planarity to 100.4(6)° (2) and av 102(1)° (4). The electronic structures of the twisted Co2(μ-O)2 core were discussed on the basis of extended Hückel MO calculations. The present discrete complexes have a tetravalent sugar domain around the dinuclear center and clearly demonstrated distinct sugar−sugar interactions which could be a minimal model for so-called sugar clusters of glycoproteins on cell surfaces.