The effect of π-bonding ligands on the metal ion-catalysed decarboxylation of acetonedicarboxylic acid

Hay, Robert W.; Leong, K. N.

doi:10.1039/c19670000800

Cited by 2 publications

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“…There are examples in the literature of other organic reactions that are catalyzed by Lewis acids in water. As early as 1951 it was shown that simple transition metal ions catalyze the decarboxylation of dimethyloxaloacetic acid . There are also many studies on the metal-ion catalyzed hydrolysis of esters, amides, and phosphates…”

Section: Introductionmentioning

confidence: 99%

Lewis Acid Catalysis of a Diels−Alder Reaction in Water

1996

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Here we report the first detailed study of a Diels-Alder (DA) reaction that is catalyzed by Lewis acids in water. The effect of Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ ions as Lewis acid catalysts on the rate and endo-exo selectivity of the DA reaction between the bidentate dienophiles 3-phenyl-1-(2-pyridyl)-2-propen-1-ones (1a-e) and cyclopentadiene (2) in water has been studied. Relative to the uncatalyzed reaction in acetonitrile, catalysis by 0.010 M Cu(NO 3) 2 in water accelerates the reaction by a factor of 79 300. The kinetics of the catalyzed reaction were analyzed in terms of equilibrium constants for complexation of the Lewis acid with 1a-e and rate constants for the reaction of the resulting complexes with 2. The rate enhancement imposed upon the uncatalyzed DA reaction of substrates 1 with 2 by water is much more pronounced than that for the catalyzed reaction. The increase of the endo-exo selectivity induced by water in the uncatalyzed process is completely absent for the Lewis acid catalyzed reaction. The modest solvent and substituent effects observed for the catalyzed reaction indicate that the change in charge separation during the activation process is not larger than the corresponding change for the uncatalyzed reaction.

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Section: Introductionmentioning

confidence: 99%

Lewis Acid Catalysis of a Diels−Alder Reaction in Water

1996

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“…That the formation of special ternary complexes enhances the rate of the metal ion-catalyzed decarboxylation of oxaloacetate or dimethyloxaloacetate is well known. Effective ligands are 2,2'bipyridyl [37], 1,lO-phenanthroline [38,39], and pyridine [40] ; they all contain n-systems. Of interest in this connection is also that the hydrolysis of diisopropyl fluorophosphate is catalyzed by several Cu2+ complexes, among which the Cu2+-bipyridyl I : 1 complex is especially effective.…”

Section: Discussionmentioning

confidence: 99%

“…Effective ligands are 2,2'-bipyridyl [37], 1,lO-phenanthroline [38,39], and pyridine [40] ; they all contain n-systems. Of interest in this connection is also that the hydrolysis of diisopropyl fluorophosphate is catalyzed by several Cu2+ complexes, among which the Cu2+-bipyridyl I : 1 complex is especially effective.…”

Section: Discussionmentioning

confidence: 99%

Ternary Complexes in Solution

Huber

Griesser

Prijs

et al. 1969

European Journal of Biochemistry

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The stability constants of the ternary Cuz+ complexes, ethylenediamine-Cu2+-pyrocatechol and histamine-Cua+-pyrocatechol dianion, were determined. Both complexes are more stable than one would expect on pure statistical reasons. The imidazole-containing ternary Cuz+ complex is, however, especially stable. For the equilibrium, Cu(histamine), + Cu(pyrocatechol), ~2[(histamine)Cu(pyrocatechol)], the constant is log X = 4.86 (I = 0.1; T = 25"), while the statistical value is 0.6. These results were compared with those taken (or calculated) from the literature; it is concluded that the n-system of the ligands is important for such a great increase in stability. Furthermore, the Cuz+-histamine I : 1 complex selectively binds to 0-ligands rather than to N-ligands. Thus, the first coordinated ligand has an influence on the kind of the second to be coordinated, i. e. the Cua+-histamine 1 : 1 complex shows discriminating qualities. The significance of these results is discussed with regard to Cu-proteins, since it is suggested for several enzymes that the imidazole group of histidine is involved with the binding of metal ions.I n general, ternary complexes, i.e. mixed ligand metal ion complexes, can be considered as models [2] for enzyme-metal ion-substrate complexes [3,4]. Furthermore, such ternary complexes probably occur in biological fluids that contain several ligands as well as different metal ions. Investigations of the stability of ternary complexes may, therefore, help toward understanding the driving forces which lead to the formation of such complexes in biological systems. The importance of mixed complexes in nature is evident, since a great deal of biochemical reactions occur in such complexes, i.e. within the coordination sphere of metal ions [3,4].I n addition, the investigation of ternary Cu2+ complexes, containing an imidazole group as binding site, is of special interest, since it is suggested for several proteins which interact with Cua+ and for natural Cu-proteins that the imidazole group of histidine binds to copper. Thus, the Cuz+ complexes of several histidine-containing peptides

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The effect of π-bonding ligands on the metal ion-catalysed decarboxylation of acetonedicarboxylic acid

Cited by 2 publications

References 0 publications

Lewis Acid Catalysis of a Diels−Alder Reaction in Water

Lewis Acid Catalysis of a Diels−Alder Reaction in Water

Ternary Complexes in Solution

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