Chelation versus Binucleation: Metal Complex Formation with the Hexadentate all‐cis‐N¹,N²‐Bis(2,4,6‐trihydroxy‐3,5‐diaminocyclohexyl)ethane‐1,2‐diamine

Abstract

The hexadentate ligand all-cis-N(1),N(2)-bis(2,4,6-trihydroxy-3,5-diaminocyclohexyl)ethane-1,2-diamine (L(e)) was synthesized in five steps with an overall yield of 39% by using [Ni(taci)(2)]SO(4).4H(2)O as starting material (taci=1,3,5-triamino-1,3,5-trideoxy-cis-inositol). Crystal structures of [Na(0.5)(H(6)L(e))](BiCl(6))(2)Cl(0.5).4H(2)O (1), [Ni(L(e))]Cl(2).5H(2)O (2), [Cu(L(e))](ClO(4))(2).H(2)O (3), [Zn(L(e))]CO(3).7H(2)O (4), [Co(L(e))](ClO(4))(3) (5c), and [Ga(H(-2)L(e))]NO(3).2H(2)O (6) are reported. The Na complex 1 exhibited a chain structure with the Na(+) cations bonded to three hydroxy groups of one taci subunit of the fully protonated H(6)(L(e))(6+) ligand. In 2, 3, 4, and 5c, a mononuclear hexaamine coordination was found. In the Ga complex 6, a mononuclear hexadentate coordination was also observed, but the metal binding occurred through four amino groups and two alkoxo groups of the doubly deprotonated H(-2)(L(e))(2-). The steric strain within the molecular framework of various M(L(e)) isomers was analyzed by means of molecular mechanics calculations. The formation of complexes of L(e) with Mn(II), Cu(II), Zn(II), and Cd(II) was investigated in aqueous solution by using potentiometric and spectrophotometric titration experiments. Extended equilibrium systems comprising a large number of species were observed, such as [M(L(e))](2+), protonated complexes [MH(z)(L(e))](2+z) and oligonuclear aggregates. The pK(a) values of H(6)(L(e))(6+) (25 degrees C, mu=0.10 M) were found to be 2.99, 5.63, 6.72, 7.38, 8.37, and 9.07, and the determined formation constants (log beta) of [M(L(e))](2+) were 6.13(3) (Mn(II)), 20.11(2) (Cu(II)), 13.60(2) (Zn(II)), and 10.43(2) (Cd(II)). The redox potentials (vs. NHE) of the [M(L(e))](3+/2+) couples were elucidated for Co (-0.38 V) and Ni (+0.90 V) by cyclic voltammetry.

Formation of lithium, sodium and potassium complexes with 1,3,5-triamino-1,3,5-trideoxy-cis-inositol (taci)

“…Coordination of an alkali metal cation to a protonated taci frame has been observed previously by Bartholomä et al (2010). Coordination of an alkali metal cation to a protonated taci frame has been observed previously by Bartholomä et al (2010).…”

Hafnium-Based Contrast Agents for X-ray Computed Tomography

“…Two clear trends were identified: progression toward lanthanides with higher atomic number and the introduction of shorter carboxylate substituents, e.g., acetate instead of propionate, led to the highly stable complex Na 3 [Lu 3 (H −3 taci-ta) 2 ] (5) containing lutetium and the taci-ta ligand (Table 1). A synthetic sequence based on all-cis-2,4,6tris(benzyloxy)-1,3,5-cyclohexanetriamine (9) 18 as the key intermediate derived from the nickel complex 8 19 delivered 5 after acetate introduction via tert-butyl bromoacetate, deprotection, and complex formation with the respective lanthanide chloride in the presence of sodium hydroxide in methanol (Scheme 1).…”

Poly[[(μ4-1,3,5-triamino-1,3,5-trideoxy-cis-inositol)sodium] bromide]

“…However, binding of divalent transition metal cations such as Cu 2+ usually occurs via three axial amino groups (Reiss et al, 1998). The binding of Na + to a protonated bis-taci unit (where two tacimoieties are connected via a O-CH 2 -CH 2 -O bridge) occurred via the axial hydroxy groups (Bartholomä et al, 2010).…”