Trinuclear Zn(II) and Cu(II) Homo and Heterotrimetallic Complexes Involvingd-Glucopyranosyl and Biscarboxylate Bridging Ligands. A Substrate Binding Model of Xylose Isomerases

Abstract

Reactions of MCl(2).nH(2)O with N,N'-bis(D-glucopyranosyl)-1,4,7-triazacyclononane ((D-Glc)(2)-tacn), which was formed from D-glucose and 1,4,7-triazacyclononane (tacn) in situ, afforded a series of mononuclear divalent metal complexes with two beta-D-glucopyranosyl moieties, [M((D-Glc)(2)-tacn)Cl]Cl (M = Zn (11), Cu (12), Ni (13), Co (14)). Complexes 11-14 were characterized by analytical and spectroscopic measurements and X-ray crystallography and were found to have a distorted octahedral M(II) center ligated by the pentacoordinate N-glycoside ligand, (beta-D-glucopyranosyl)(2)-tacn, and a chloride anion. Each D-glucose moiety is tethered to the metal center through the beta-N-glycosidic bond with tacn and additionally coordinated via the C-2 hydroxyl group, resulting in a lambda-gauche five-membered chelate ring. When L-rhamnose (6-deoxy-L-mannose) was used instead of D-glucose, the nickel(II) complex with two beta-L-rhamnopyranosyl moieties, [Ni((D-Man)(2)-tacn)(MeOH)]Cl(2) (15), was obtained and characterized by an X-ray analysis. Reactions of 11 (M = Zn) with [Zn(XDK)(H(2)O)] (21) or [Cu(XDK)(py)(2)] (22) (H(2)XDK = m-xylylenediamine bis(Kemp's triacid imide)) yielded homo and heterotrimetallic complexes formulated as [Zn(2)M'((D-Glc)(2)-tacn)(2)(XDK)]Cl(2) (M' = Zn (31), Cu (32)). The similar reactions of 12 (M = Cu) with complex 21 or 22 afforded [Cu(2)M'((D-Glc)(2)-tacn)(2)(XDK)]Cl(2) (M' = Cu (33), Zn (34)). An X-ray crystallographic study revealed that complexes 31 and 34 have either Zn(II)(3) or Cu(II)Zn(II)Cu(II) trimetallic centers bridged by two carboxylate groups of XDK and two D-glucopyranosyl residues. The M...M' separations are 3.418(3)-3.462(3) A (31) and 3.414(1)-3.460(1) A (34), and the M...M'...M angles are 155.18(8) degrees (31) and 161.56(6) degrees (34). The terminal metal ions are octahedrally coordinated by the (D-Glc)(2)-tacn ligand through three nitrogen atoms of tacn, two oxygen atoms of the C-2 hydroxyl groups of the carbohydrates, and a carboxylate oxygen atom of XDK ligand. The central metal ions sit in a distorted octahedral environment ligated by four oxygen atoms of the carbohydrate residues in the (D-Glc)(2)-tacn ligands and two carboxylate oxygen atoms of XDK. The deprotonated beta-D-glucopyranosyl unit at the C-2 hydroxyl group bridges the terminal and central ions with the C-2 mu-alkoxo group, with the C-1 N-glycosidic amino and the C-3 hydroxyl groups coordinating to each metal center. Complexes 31-34 are the first examples of metal complexes in which D-glucose units act as bridging ligands. These structures could be very useful substrate binding models of xylose or glucose isomerases, which promote D-glucose D-fructose isomerization by using divalent dimetallic centers bridged by a glutamate residue.

Hydrogen Bonds as Structural Directive towards Unusual Polynuclear Complexes: Synthesis, Structure, and Magnetic Properties of Copper(II) and Nickel(II) Complexes with a 2‐Aminoglucose Ligand

“…The vicinal functional groups feature several donor atoms capable of forming stable complexes with transition metals [7] and offer several possibilities to introduce additional donor groups into the sugar backbone. Well-known modification strategies are N-glycosylation of polyamines [8,9] and nucleophilic substitution of bromoethyl-O-glycosides. [10] TEMPO oxidation of the secondary hydroxyl group at C6 results in the formation of uronic acids.…”

“…[17][18][19][20] In particular, their copper(II) compounds show a considerable tendency to self-aggregate affording oxoidobridged oligonuclear complexes with unexpected magnetic properties induced by hydrogen bonding between the constituting glucose ligands. [17] The formation of oxygen bridged polynuclear compounds is a general feature for transitionmetal complexes with carbohydrate derivatives as ligands, [21,8] which is usually prevented by the presence of appropriate coligands to coordinatively saturate the metal ion. Nevertheless very little is known about relevant carbohydrate-based polynuclear complexes.…”

catena-Poly[[aquazinc(II)]-μ-N,N′-bis(2-cyano-3-ethoxy-3-oxoprop-1-enyl)benzene-1,2-diaminido]

“…These findings are in agreement with its embedding in the centre of a distorted octahedron. With respect to the flexibility of Zn(ii) in the formation of different complex geometries the complex fits within Fuchs et al (2014), Barnard et al (2009), Ryu et al (2003, or Tanase et al (2001), even if for the latter case larger structural deviations are observed due to larger structural differences in the ligand constitution.…”

“…The structures of Zn II complexes with ligands stabilizing comparable complex geometries can be found in Barnard et al (2009), Ryu et al (2003) or Tanase et al (2001). In Tanase et al (2001), the ligands show comparable N,N,O,O-coordination with respect to a different ligand backbone whereas in Ryu et al (2003) and Barnard et al (2009), the ligands with N,N,N,N-coordination are diaminobenzene derivatives.…”

“…In Tanase et al (2001), the ligands show comparable N,N,O,O-coordination with respect to a different ligand backbone whereas in Ryu et al (2003) and Barnard et al (2009), the ligands with N,N,N,N-coordination are diaminobenzene derivatives. In Fuchs et al (2014), a mononuclear Zn complex is presented with the same ligand but a dmso molecule in the coordination sphere of the metal stabilizing a different complex geometry.…”