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Mechanistic Information from Pressure Acceleration of Hydride Formation via Proton Binding to a Cobalt(I) Macrocycle

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Etsuko Fujita,*^† James F. Wishart,^† and Rudi van Eldik*^‡

Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, and Institute for Inorganic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058 Erlangen, Germany

Inorg. Chem., 2002, 41 (6), pp 1579–1583

DOI: 10.1021/ic011109q

Publication Date (Web): February 22, 2002

Section:

Catalysis, Reaction Kinetics, and Inorganic Reaction Mechanisms

Abstract

The effect of pressure on proton binding to the racemic isomer of the cobalt(I) macrocycle, CoL⁺ (L = 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene), has been studied for a series of proton donors using pulse radiolysis techniques. The second-order rate constants for the reaction of CoL⁺ with proton donors decrease with increasing pK_a of the donor acid, consistent with a reaction occurring via proton transfer. Whereas the corresponding volumes of activation (ΔV) are rather small and negative for all acids (proton donors) with pK_a values below 8.5, significantly larger negative activation volumes are found for weaker acids (pK_a > 9.5) containing OH groups as proton donors. In the latter case, the observed ΔV for these protonation reactions show a correlation with the reaction volumes (ΔV°_ion) for the ionization of the weak acids with a slope of 0.44, indicating that bond dissociation of the weak acid molecule bound to the metal center proceeds approximately halfway at the transition state along the reaction coordinate in terms of volume changes.

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This article has been cited by 1 ACS Journal articles (1 most recent appear below).

Transition State Characterization for the Reversible Binding of Dihydrogen to Bis(2,2'-bipyridine)rhodium(I) from Temperature- and Pressure-Dependent Experimental and Theoretical Studies
Etsuko Fujita, Bruce S. Brunschwig, Carol Creutz, James T. Muckerman, Norman Sutin, David Szalda, and Rudi van Eldik
Inorganic Chemistry2006 45 (4), 1595-1603
- Transition State Characterization for the Reversible Binding of Dihydrogen to Bis(2,2'-bipyridine)rhodium(I) from Temperature- and Pressure-Dependent Experimental and Theoretical Studies
  Etsuko Fujita, Bruce S. Brunschwig, Carol Creutz, James T. Muckerman, Norman Sutin, David Szalda, and Rudi van Eldik
  Inorganic Chemistry2006 45 (4), 1595-1603
  Thermodynamic and kinetic parameters for the oxidative addition of H2 to [RhI(bpy)2]+ (bpy = 2,2‘-bipyridine) to form [RhIII(H)2(bpy)2]+ were determined from either the UV−vis spectrum of equilibrium mixtures of [RhI(bpy)2]+ and [RhIII(H)2(bpy)2]+ or from ...
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