Kinetic Isotope Effects upon the Hydrolysis of Pyridine Arylboranes

Davis, Robert Earl; Kenson, Robert E.

doi:10.1021/ja00982a019

Cited by 5 publications

(2 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The most obvious feature is that they are all inverse. This feature is not surprising since hydrolysis of sodium borohydride (27), hydrolysis of pyridine alkylboranes (28), and the methanolysis of lithium borohydride (29) all have inverse isotope effects. In the reduction of ketones by borohydride, it has been shown (30,46) that the rate determining step is transfer of the first hydrogen (Fig.…”

Section: The Terms Steric Approach Control Andmentioning

confidence: 97%

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Wigfield¹,

Phelps²

1972

Can. J. Chem.

View full text Add to dashboard Cite

Definitions for the terms steric approach control and product deuelopment control in relation to the degree of bonding in the transition state are put forward. Kinetic deuterium isotope effects in the reduction of a graded series of ketones by NaBH, and NaBD, have been measured. These effects are inverse, and show no systematic dependence on the degree of steric hindrance of the ketone. This evidence appears to invalidate the steric approach control-product development control explanation of the axial to equatorial product ratios (1). The primary isotope effect is very small, which is consistent with an early transition state in these reductions, as demanded by other explanations of product ratios, but since several other factors causing small isotope effects may be applicable, the evidence does not constitute proof of an early transition state.The main conclusions of this work have already been published in preliminary form (2).Les notions de "steric approach control" et 'kroduct deuelopment control" en relation avec le degri. de liaison dans I'ttat de transition, sont precisees. Les effets isotopiques du deuterium sur la cinbtique de reduction d'une serie de cetones par NaBH, et NaBD,, ont Ct C mesurts. Ces effets sont inverses et ne montrent aucune dependance systematique avec le degrt d'empschement sttrique de la cCtone. Cette mise en evidence montre que I'explication des rapports du produit axial et equatorial par le "steric approach control" et "product development control", n'est pas valable (1). L'effet isotopique primaire, trts faible, est compatible avec un debut d'6tat de transition dans ces rbductions. Ce rbsultat, deji mentionnt dans d'autres etudes, ne constitue pas une preuve puisque de nombreux autres facteurs peuvent Etre la cause de ces faibles effets isotopiques. Les conclusions principales de ce travail ont deja Ct C publikes dans une note preliminaire (2).

show abstract

Section: The Terms Steric Approach Control Andmentioning

confidence: 97%

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Wigfield¹,

Phelps²

1972

Can. J. Chem.

View full text Add to dashboard Cite

show abstract

“…Previous studies have revealed a high sensitivity of the kinetic stability of amine−boranes to changes in structure. Indeed, substitution in the coordination spheres of nitrogen and/or boron in compounds of the type R n NH 3 - n ·BH y X 3 - y , where R may be an alkyl, aryl, or heterocyclic group, n and y have possible values of 0, 1, 2, and 3, and X represents a hydride, halide, cyanide, or azide ligand, has been shown to have profound effects on both the rate and mechanism of hydride oxidation. − In addition, recent studies have shown differences in the stoichiometry of reaction of BH 3 adducts of secondary and tertiary amines with hypochlorous acid wherein secondary amine−boranes are found to undergo hydride oxidation and tertiary amine−boranes to be subject to B-chlorination. − …”

Section: Introductionmentioning

confidence: 99%

Acid-Catalyzed Amine−Borane Reduction of Nitrite

Bell

Kelly

1996

Inorg. Chem.

View full text Add to dashboard Cite

The rate of reduction of nitrite by trimethylamine-borane was followed by observing the decrease in nitrite absorbance under pseudo-first-order conditions. The reaction is acid-catalyzed and exhibits a first-order dependence on both amine-borane and total nitrite concentration. The molar equivalence of NaNO(2) to (CH(3))(3)NBH(3) = 2:1. Equimolar amounts of hydrogen and nitrous oxide are formed, and the molar ratio of nitrite reacted to N(2)O produced is 2:1. In concentrated HCl or H(2)SO(4), a correlation of rate with the Hammett acidity function, h(o), is observed. The reaction is subject to a pronounced inversesolvent isotope effect (k(D)()2(O)/k(H)()2(O) approximately 2.7) and a modest normal substrate effect (k((CH)()3())()3(N.BH)()3/k((CH)()3())()3(N.BD)()3 approximately 1.4). The reaction is first-order in H(3)O(+) in the region pH 0.7-2.7, but a second-order dependence is observed above pH 4 with the transition occurring at pH approximately pK(a) for HNO(2). Results are consistent with a mechanistic model involving preequilibration protonation of molecular nitrous acid followed by rate-limiting hydride attack on H(2)ONO(+) or free NO(+) to produce nitrosyl hydride as a reactive intermediate.

show abstract

Inkrementenmethode zur Vorausberechnung der ¹H‐chemischen Verschiebungen von Bicyclo[2,2,1]hepten‐Derivaten

Doerffel

Kasper²,

Zimmermann³

1974

J. Prakt. Chem.

View full text Add to dashboard Cite

show abstract

Kinetic Isotope Effects upon the Hydrolysis of Pyridine Arylboranes

Cited by 5 publications

References 5 publications

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Acid-Catalyzed Amine−Borane Reduction of Nitrite

Inkrementenmethode zur Vorausberechnung der ¹H‐chemischen Verschiebungen von Bicyclo[2,2,1]hepten‐Derivaten

Contact Info

Product

Resources

About

Kinetic Isotope Effects upon the Hydrolysis of Pyridine Arylboranes

Cited by 5 publications

References 5 publications

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Deuterium Isotope Effects in the Reduction of Cyclohexanones. The Concepts of Steric Approach Control and Product Development Control

Acid-Catalyzed Amine−Borane Reduction of Nitrite

Inkrementenmethode zur Vorausberechnung der 1H‐chemischen Verschiebungen von Bicyclo[2,2,1]hepten‐Derivaten

Contact Info

Product

Resources

About

Inkrementenmethode zur Vorausberechnung der ¹H‐chemischen Verschiebungen von Bicyclo[2,2,1]hepten‐Derivaten