Optically Active Polyoxotungstates Bearing Chiral Organophosphonate Substituents

Abstract

Divacant Keggin-type polyoxotungstates [γ-XW10O36]8– with X = Si or Ge, were functionalized with chiral phosphoryl groups. The hybrid compounds [(R*PO)2(γ-XW10O36)]4– with R = N-protected aminoalkyl groups or O-protected amino acid derivatives, were isolated. The solution characterization of the products was performed by different techniques: 183W, 31P, 13C, and 1H NMR spectroscopy, electrospray ionization mass spectrometry, UV/Vis spectroscopy, and circular dichroism (CD). The experimental data confirm the covalent grafting of the organic moieties onto the polyanionic surface. A chirality transfer, from the pendant organic arm to the inorganic framework is apparent from CD studies. Multiple Cotton effects were observed in the region of charge-transfer transitions pertaining to W–O bonds. Furthermore, the 183W NMR spectra are consistent with the expected C2 symmetry, resulting from introduction of two organic stereocenters. The title complexes were used in the presence of hydrogen peroxide to perform the oxidation of methyl p-tolyl sulfide. Implications for the design of enantioselective catalysts based on these derivatives are discussed

Synthesis and structural characterization of BINOL-modified chiral polyoxometalates

“…16,17 The 29 Si NMR spectrum of R-I in acetonitrile-d 3 showed a single signal at −84.22 ppm (Fig. 11f-h To the best of our knowledge, I was the first example of structurally characterized chiral ligandmodified monomeric Keggin-type POM.…”

Optically Active Tripodal Dendritic Polyoxometalates: Synthesis, Characterization and Their Use in Asymmetric Sulfide Oxidation with Hydrogen Peroxide

“…These compounds oxidized methyl p-tolyl sulfide to the corresponding chiral sulfoxide with up to 75 % conversion and a maximum of 8 % ee. [16] In addition, our preliminary results showed that the dendritic POM compound was more selective (14 vs. 4 % ee) than the non-dendritic counterpart. Bonchio and co-workers also observed the dependence of the enantioselectivity of the reaction on the nature of the ligand.…”

Synthesis and biological activity of an Anderson polyoxometalate bis‐functionalized with a Bombesin‐analog peptide

“…Among the available targeting biomolecules, such as monoclonal antibodies, aptamers, and receptor‐specific substrates, peptides are flexible molecules which can display high affinity toward a receptor and impart a high cell penetrating capability, with low immunogenicity . Peptides are suitable pendants for POMs and can be covalently grafted via amide bonds . On the other hand, as observed for the targeted proteins mentioned above, they can also establish multiple weak interactions with the POM surface, being these usually more efficient upon increasing of size and charge density of the polyanion, or when using transition metal‐substituted POMs with free coordination positions on the metal ions …”