Bioinspired Hydrogen Bond Motifs in Ligand Design:  The Role of Noncovalent Interactions in Metal Ion Mediated Activation of Dioxygen

Borovik, A. S.

doi:10.1021/ar030160q

Cited by 392 publications

(282 citation statements)

References 69 publications

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“…1 Direct reaction of (L) with [Cu(NCCH 3 ) 4 ]BF 4 in CH 2 Cl 2 gives [Cu(L)NCCH 3 ]BF 4 (1) (Fig. 1) in 46% yield as an intense yellow-coloured powder, and was characterised by 1 H-NMR, MS and elemental analysis.…”

Section: Resultsmentioning

confidence: 99%

Syntheses of copper(i)cis-1,3,5-tri-iminocyclohexane complexes

et al. 2006

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Copper(I) complexes of the ligand cis-1, 3,5-tris(cinnamylideneamino)cyclohexane (L) have been prepared from a versatile precursor complex, [Cu I (L)NCMe]BF 4 , which incorporates a labile acetonitrile ligand that can be exchanged to give a range of new Cu(L)X complexes (where X = Cl, Br, NO 2 , SPh). 1 H NMR spectra and X-ray structures of the Cl, Br and NO 2 complexes show L coordinated in a symmetric fashion about the copper centre. The complexes have been further characterised using UV/Visible spectroscopy and cyclic voltammetry. CuLCl shows an electrochemically reversible Cu I/II redox couple at 0.51 V (vs. Ag/AgCl) while the CuLNO 2 complex shows an analogous quasi-reversible wave at 0.41 V (vs. Ag/AgCl).

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Section: Resultsmentioning

confidence: 99%

Syntheses of copper(i)cis-1,3,5-tri-iminocyclohexane complexes

et al. 2006

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“…A recent proposal has suggested that in some cases H-bond(s) to the terminal oxo ligand could be used in stabilizing metal-oxo complexes. 18 The H-bonds would decrease the multiple bond character of the M-oxo unit, resulting in highspin complexes with longer M-O bondssproperties such as those found in [Fe III H 3 buea(O)] 2-. These predictions are consistent with the results presented here.…”

Section: Discussionmentioning

confidence: 99%

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H₃buea)Fe^III^-X]ⁿ^- (X = S^2-, O^2-, OH^-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes

et al. 2006

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Iron L-edge, iron K-edge, and sulfur K-edge X-ray absorption spectroscopy was performed on a series of compounds [Fe III H3buea(X)] n-(X ) S 2-, O 2-, OH -). The experimentally determined electronic structures were used to correlate to density functional theory calculations. Calculations supported by the data were then used to compare the metal-ligand bonding and to evaluate the effects of H-bonding in Fe III-O vs Fe III-S complexes. It was found that the Fe III-O bond, while less covalent, is stronger than the Fe III-S bond. This dominantly reflects the larger ionic contribution to the Fe III-O bond. The H-bonding energy (for three H-bonds) was estimated to be -25 kcal/mol for the oxo as compared to -12 kcal/mol for the sulfide ligand. This difference is attributed to the larger charge density on the oxo ligand resulting from the lower covalency of the Fe-O bond. These results were extended to consider an Fe IV-O complex with the same ligand environment. It was found that hydrogen bonding to Fe IV-O is less energetically favorable than that to Fe III-O, which reflects the highly covalent nature of the Fe IV-O bond.

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“…[9] We sought to utilize this self-organization by incorporating these tripodal scaffolds into a titanium-phosphonate material. The synthetic strategy is outlined in Scheme 1.…”

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A Tripodal Peptidic Titanium Phosphonate as a Homochiral Porous Solid Medium for the Heterogeneous Enantioselective Hydration of Epoxides

Milo

Neumann

2010

Adv Synth Catal

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A porous, homochiral titanium-phosphonate material based on a tripodal peptide scaffold was used as a heterogeneous reaction medium for the enantioselective hydration (> 99%) of styrene oxide. This titanium-phosphonate material, which was shown to contain confined chiral spaces, was prepared by polymerization of l-leucine onto a tris(2-aminoethyl)amine initiator, followed by capping with phosphonate groups and completed by non-aqueous condensation with titanium isopropoxide. Circular dichroism confirmed that the peptide tethers yielded a secondary structure. X-ray powder diffraction and transmission electron microscopy supported by a semi-empirical model showed the likely formation of a porous, lamellar material that was quantified by nitrogen adsorption.Keywords: catalyst design; enantioselectivity; hydrolysis; organic-inorganic composites; peptidesThe common strategy to carry out asymmetric catalysis for the preparation of enantiomerically enriched products, a cornerstone of modern synthetic chemistry, is to design homogeneous (soluble) metal-based and more recently also organic catalysts comprised of chiral ligands. The advantages of using insoluble catalyst systems, especially related to the practicality of recovering expensive catalysts, have also led to considerable efforts in the area of asymmetric heterogeneous catalysis. The typical approach utilized in this area is the covalent or non-covalent immobilization of known homogeneous catalysts onto supports.[1] More recently, we have also seen the incorporation of chiral ligands and chiral complexes into metal-organic framework materials, that is chiral MOFs, to yield what has been termed self-supported catalysts. Here, polytopic chiral ligands having both catalytically active and cross-linking sites are used for preparing homochiral materials that can be used in self-supported heterogeneous catalysis. [2] Another observation related to asymmetric catalysis is that, in principle, by carrying out reactions in chiral reaction media, enantiomerically enriched products can be attained. Historically, in homogeneous chiral media only low levels of enrichment have been observed, [3] although recently chiral ionic liquids were used as solvents for reactions that yielded high enantioselectivities, presumably due to their ionic nature.[4] Quite surprisingly there have been no reports on the use of porous, heterogeneous and homochiral media for asymmetric transformations. A quite singular example of asymmetric catalysis using insoluble peptidic, but non-porous media, is the epoxidation of a,b-unsaturated ketones on polypeptides (JuliaColonna reaction). [5] Based on the assumption that a more confined chiral environment may induce improved enantioselectivity, in this research we were interested in preparing porous, homochiral materials that can be used as heterogeneous media for enantioselective transformations. This would be the first step in the development of a general methodology for the preparation of chiral products from racemic or prochiral substrat...

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Bioinspired Hydrogen Bond Motifs in Ligand Design: The Role of Noncovalent Interactions in Metal Ion Mediated Activation of Dioxygen

Cited by 392 publications

References 69 publications

Syntheses of copper(i)cis-1,3,5-tri-iminocyclohexane complexes

Syntheses of copper(i)cis-1,3,5-tri-iminocyclohexane complexes

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H₃buea)Fe^III^-X]ⁿ^- (X = S^2-, O^2-, OH^-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes

A Tripodal Peptidic Titanium Phosphonate as a Homochiral Porous Solid Medium for the Heterogeneous Enantioselective Hydration of Epoxides

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Bioinspired Hydrogen Bond Motifs in Ligand Design: The Role of Noncovalent Interactions in Metal Ion Mediated Activation of Dioxygen

Cited by 392 publications

References 69 publications

Syntheses of copper(i)cis-1,3,5-tri-iminocyclohexane complexes

Syntheses of copper(i)cis-1,3,5-tri-iminocyclohexane complexes

X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H3buea)FeIII-X]n- (X = S2-, O2-, OH-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes

A Tripodal Peptidic Titanium Phosphonate as a Homochiral Porous Solid Medium for the Heterogeneous Enantioselective Hydration of Epoxides

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X-ray Absorption Spectroscopy and Density Functional Theory Studies of [(H₃buea)Fe^III^-X]ⁿ^- (X = S^2-, O^2-, OH^-): Comparison of Bonding and Hydrogen Bonding in Oxo and Sulfido Complexes