(Pyrazolylborato)zinc−Aldehyde Complexes

Walz, Rainer; Ruf, Michael; Vahrenkamp, Heinrich

doi:10.1002/1099-0682(20011)2001:1<139::aid-ejic139>3.0.co;2-6

Cited by 15 publications

(10 citation statements)

References 31 publications

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“…Neither the aldehyde ν(CO) band (1713 → 1715 cm -1 ) nor the aldehyde CH 1 H NMR resonanance (10.08 → 10.10 ppm) show significant changes upon coordination, however, leading to the conclusion that the aldehyde function is not coordinated to zinc. In case of 9 both the aldeyhde ν(CO) band (1671 → 1659 cm -1 ) and the aldehydic proton resonance (9.99 → 10.20 ppm) are shifted by the expected amounts in comparison to those of free formylphenolate . Thus both the phenolate and the aldehyde function of salicylic aldehyde seem to be coordinated, in analogy to the situation in the complex Tp Cum,Me Zn(OC 6 H 4 CHO) .…”

Section: Resultsmentioning

confidence: 83%

“…In case of 9 both the aldeyhde ν(CO) band (1671 → 1659 cm -1 ) and the aldehydic proton resonance (9.99 → 10.20 ppm) are shifted by the expected amounts in comparison to those of free formylphenolate . Thus both the phenolate and the aldehyde function of salicylic aldehyde seem to be coordinated, in analogy to the situation in the complex Tp Cum,Me Zn(OC 6 H 4 CHO) . The resulting structural assignments are given in Figure .…”

Section: Resultsmentioning

confidence: 88%

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Sulfur-Rich Zinc Chemistry: New Tris(thioimidazolyl)hydroborate Ligands and Their Zinc Complex Chemistry Related to the Structure and Function of Alcohol Dehydrogenase

2001

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The 1-substituted tris(2-thioimidazolyl)hydroborate ligands Tt(R) were prepared as the potassium salts from KBH(4) and the corresponding 1-R-2-thioimidazole for R = t-Bu and C(6)H(4)-p-CH(CH(3))(2) (Cum). Their reactions with zinc salts yielded the tetrahedral complexes Tt(R)Zn-X with X = F, Cl, ONO(2) and (Tt(t)()(-)(Bu))(2)Zn. With zinc perchlorate the labile perchlorate complexes Tt(R)Zn-OClO(3) were obtained. They served as starting materials for the incorporation of substrates which are relevant for the chemistry of horse liver alcohol dehydrogenase: Ethanol led to [Tt(t)()(-Bu)Zn.EtOH] ClO(4).EtOH, p-nitrophenol (NitOH) yielded Tt(Cum)Zn-ONit. Pyridine-2-carbaldehyde and salicylic aldehyde were incorporated as N(pyridine) and O(phenolate) coligands with possible additional O(aldehyde) coordination. Substituted pyridyl methanols (R-PyCH(2)OH) yielded the trinuclear complexes [(Tt(t)()(-Bu))(2)Zn(3)(R-PyCH(2)O)(2)] (ClO(4))(2) with bridging Tt and pyridylmethoxide ligands. Preliminary experiments on the functional modeling of alcohol dehydrogenase have shown that TtZn complexes promote both the dehydrogenation of 2-propanol and the hydrogenation of pentafluorobenzaldehyde.

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Section: Resultsmentioning

confidence: 83%

Section: Resultsmentioning

confidence: 88%

Sulfur-Rich Zinc Chemistry: New Tris(thioimidazolyl)hydroborate Ligands and Their Zinc Complex Chemistry Related to the Structure and Function of Alcohol Dehydrogenase

2001

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“…In addition to the hydrolytic cleavages with Tp*Zn−OH we had also found its nucleophilic addition to electron-poor aldehydes with formation of α-hydroxyalkoxide complexes …”

Section: Resultsmentioning

confidence: 96%

Pyrazolylborate−Zinc−Hydrosulfide Complexes and Their Reactions

Rombach

Vahrenkamp

2001

Inorg. Chem.

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Four new hydrosulfide complexes Tp*Zn-SH of substituted pyrazolylborate ligands (Tp*) were prepared by reactions of Tp*Zn-OH with H(2)S, and three of them were structurally characterized. Unlike the Tp*Zn-OH complexes they do not react with esters, phosphates, or CO(2), e.g. for thiolytic cleavage reactions. They also cannot be deprotonated, as various bases induce precipitation of ZnS and release of anionic Tp*. Acidic organic X-OH compounds (carboxylic acids, trinitrophenol, hexafluoroacetylacetone) replace the SH groups with formation of Tp*Zn-OX. Thiols undergo an entropy-driven SH substitution to yield the Tp*Zn-SR complexes. Like the Tp*Zn-SR complexes the Tp*Zn-SH complexes are quite reactive toward alkylation with methyl iodide, yielding Tp*Zn-I and CH(3)SH. The kinetic investigation of the methylation of Tp(Ph,Me)Zn-SH has shown it to be a clean second-order reaction, thereby indicating that the SH group is alkylated in the zinc-bound state.

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“…We had observed before , that the enzyme−substrate interactions of these enzymes can be modeled by zinc complexes in which the aldehydic and alcoholic functions are attached to zinc in a chelating fashion. As the second donor of the chelating alcohol or aldehyde ligands we had used pyridine nitrogen 52 or phenolate oxygen, and even in the pocket within encapsulating pyrazolylborate ligands could the increase of the coordination number of zinc be realized. With this in mind, complexes L ·Zn−OC 6 H 4 - o -CHO ( 13 ) and L ·Zn−O−C 6 H 4 - o -CH 2 OH ( 14 ) were synthesized from 1 and the potassium salts of o -formylphenol and o -(hydroxymethyl)phenol.…”

Section: Resultsmentioning

confidence: 99%

“…Their formyl and hydroxymethyl groups represent the oxidized and reduced forms of the substrates (aldehyde/alcohol) which are interconverted by the zinc-containing alcoholdehydrogenase enzymes. We had observed before 52,53 that the enzyme-substrate interactions of these enzymes can be modeled by zinc complexes in which the aldehydic and alcoholic functions are attached to zinc in a chelating fashion. As the second donor of the chelating alcohol or aldehyde ligands we had used pyridine nitrogen 52 or phenolate oxygen, 53 The relevant spectroscopic data for 13 and 14 [ν(COaldehyde) and δ(CHO) as well as δ(CH 2 OH)] do not differ significantly from those of the free substrates and hence speak against a zinc coordination by the CHO or CH 2 OH groups.…”

Section: Resultsmentioning

confidence: 99%

A Sterically Hindered N,N,O Tripod Ligand and Its Zinc Complex Chemistry

Trösch

Vahrenkamp

2001

Inorg. Chem.

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The new ligand bis(2-picolyl)(2-hydroxy-3,5-di-tert-butylbenzyl)amine (HL) was prepared from bis(2-picolyl)amine and 2,4-di-tert-butyl-6-(chloromethyl)phenol. It acts as a tetradentate N,N,O tripod ligand ensuring 5-fold coordination in all its zinc complexes L.Zn-X. The central complex of the series was [L.Zn(OH(2))]ClO(4) (1) obtained from zinc perchlorate. Together with the more labile complex L.Zn-C(2)H(5) (2), obtained from diethyl zinc, it was used as a starting material for ligand substitutions. In the presence of bases, 1 was converted to L.Zn-OH (3), [L.Zn(py)]ClO(4) (4), and [(L.Zn)(3)(mu(3)-CO(3))]ClO(4) (5). Metathetical reactions produced the neutral complexes L.Zn-X with X = Br (6), OAc (7), OC(6)H(5) (8), SC(6)H(5) (9), OP(O)(OPh)(2) (10), p-nitrophenolate (11), 1-methyluracilate (12), o-formylphenolate (13), and o-hydroxymethylphenolate (14). Structure determinations of 1, 5, 7, 10, 11, 13, and 14 confirmed the strictly monodentate attachment of all units X in L.Zn-X. The hydrolytic cleavage of tris(p-nitrophenyl) phosphate by 1 was investigated preparatively and kinetically. L.Zn-OH was found to be the hydrolytically active nucleophile. The second-order rate constant for the cleavage reaction was found to be slightly lower than the values for related systems, reflecting the steric hindrance in the tert-butyl-substituted ligand L.

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(Pyrazolylborato)zinc−Aldehyde Complexes

Cited by 15 publications

References 31 publications

Sulfur-Rich Zinc Chemistry: New Tris(thioimidazolyl)hydroborate Ligands and Their Zinc Complex Chemistry Related to the Structure and Function of Alcohol Dehydrogenase

Sulfur-Rich Zinc Chemistry: New Tris(thioimidazolyl)hydroborate Ligands and Their Zinc Complex Chemistry Related to the Structure and Function of Alcohol Dehydrogenase

Pyrazolylborate−Zinc−Hydrosulfide Complexes and Their Reactions

A Sterically Hindered N,N,O Tripod Ligand and Its Zinc Complex Chemistry

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