Organometallic Supramolecular Chemistry with Monosaccharides: Triethylammoniumμ-Chloro-bis{chloro(η5-cyclopentadienyl)(methyl 4,6-O-benzylidene-β-D-glucopyranosidato-1κO2,1:2κO3)zirconate}

Abstract

The reaction of [CpZrCl 3 (thf) 2 ] with methyl 4,6-Obenzylidene-b-d-glucopyranoside (bMeBGH 2 , 1) in the presence of Et 3 N results in the formation of the zirconate complex [Et 3 NH][(CpZrCl) 2(2). X-ray structure analyses were performed from the ligand precursor b-MeBGH 2 1 as well as from 2. Compound 1 crystallizes in the monoclinic chiral space group P2 1 . The molecules show a flat arrangement including the benzylidene protecting group, and are packed in columns. The columns are held together in pairs by the formation of hydrogen bonds between the hydroxy functions in positions 2 and 3. Compound 2 crystallizes in the orthorhombic space group P2 1 2 1 2 1 . The b-MeBG ligands are chelating the Zr atoms through the oxygen atoms in positions 2 and 3 of the glucopyranosidato ligand revealing a 1-zircona-2,5-dioxolane moiety each; the oxygen atom in position 3 is linked to both of the Zr atoms. Additionally one chloro ligand is bridging the two Zr centers. Two terminally bound chloro ligands stick out from the two Zr atoms into a chiral U-shaped cavity constructed by the two b-MeBG ligands. The cavity incorporates the tertiary ammonium cation [Et 3 NH] , which is bound to one of the terminal chloro ligands through a hydrogen bond. The inclusion of the [Et 3 NH] cation in the U-shaped cavity, even in solution, is demonstrated by NMR spectroscopic data.

Monosaccharide Ligands in Organotitanium and Organozirconium Chemistry

“…The reaction of CpZrCl 3 with the modified methyl glucopyranoside also reveals a dinuclear metal complex, m-chloro-bis{chloro(h 5 -cyclopentadienyl)(methyl-4,6-Obenzylidene-b-D-glucopyranosidato-1kO 2 ,1:2kO 3 -zirconate} (7 À ), composed of two bridging sugar ligands and two chlorido (cyclopentadienyl)metal units [6] (Scheme 9.6 and Figure 9.5).…”

“…The uncoordinated glucopyranoside b-MeBnGluH 2 has a dihedral angle O2-C2-C3-O3 of 64.2 [6]. Compound 1 has dihedral angles of 66.97 and 68.81 .…”

“…This value is considerably smaller than that measured for the dihedral angle in b-MeBnGluH 2 . In addition a reduction of the dihedral angle O2-C2-C3-O3 of the free ligand upon coordination has been shown for the glucopyranosidato ligand in the zirconate complex [6]. A coordination of one titanium atom to one chelating allopyranosidato ligand was therefore plausible, but, as the results indicate, such as structure was not obtained (Figure 9.2).…”

“…In this host-guest arrangement the triethylammonium cation is fixed inside the cavity through a hydrogen bond to one of the terminal chlorido ligands in the cavity. It has been found in 1 H NMR experiments that the encapsulated triethylammonium cation is rapidly exchanged with external [Et 3 NH] þ [6]. Recent results demonstrate that external amines also undergo a rapid exchange with the amine of the hosted ammonium cation.…”

A Novel Field of Research: Bioorganometallic Chemistry, Origins, and Founding Principles

“…Among the first transition metal complexes (excluding Hg compounds) with metal-carbon σ-bonds to carbohydrates were cobalt carbonyl and Cp(OC) 2 Fe complexes [231][232][233][234]. These systems were also studied as intermediates in oxo reactions of unsaturated sugars [235][236][237]. Subsequently, metal carbene complexes of carbohydrates were synthesized [238][239][240][241][242].…”