Base-Catalyzed Insertion of Dioxygen into Rhodium−Hydrogen Bonds: Kinetics and Mechanism

The reaction between molecular oxygen and rhodium hydrides L(OH)RhH+ (L = (NH3)4, trans-L1, and cis-L1, where L1 = cyclam) in basic aqueous solutions rapidly produces the corresponding hydroperoxo complexes. Over the pH range 8 < pH < 12, the kinetics exhibit a first order dependence on [OH−]....

Full description

Saved in:
Bibliographic Details
Published in:Inorganic chemistry 2010-02, Vol.49 (3), p.781-785
Main Authors: Szajna-Fuller, Ewa, Bakac, Andreja
Format: Article
Language:English
Subjects:
Ammonia - chemistry
Catalysis
Hydrogen - chemistry
Hydrogen Bonding
Hydrogen-Ion Concentration
Kinetics
Organometallic Compounds - chemistry
Oxidation-Reduction
Oxygen - chemistry
Rhodium - chemistry
Thermodynamics
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:The reaction between molecular oxygen and rhodium hydrides L(OH)RhH+ (L = (NH3)4, trans-L1, and cis-L1, where L1 = cyclam) in basic aqueous solutions rapidly produces the corresponding hydroperoxo complexes. Over the pH range 8 < pH < 12, the kinetics exhibit a first order dependence on [OH−]. The dependence on [O2] is less than first order and approaches saturation at the highest concentrations used. These data suggest an attack by OH− at the hydride with k = (1.45 ± 0.25) × 103 M−1 s−1 for trans-L1(OH)RhH+ at 25 °C, resulting in heterolytic cleavage of the Rh−H bond and formation of a reactive Rh(I) intermediate. A competition between O2 and H2O for Rh(I) is the source of the observed dependence on O2. In support of this mechanism, there is a significant kinetic isotope effect for the initial step, L1(OH(D))RhH(D)+ + OH(D)− ⇄ k − 1 k 1 L1(OH(D))RhI + H(D)2O, k 1H/k 1D = 1.7, and k −1H/k −1D = 3.0. The activation parameters for k 1 for trans-L1(OH)RhH+ are ΔH ‡ = 64.6 ± 1.3 kJ mol−1 and ΔS ‡ = 40 ±4 J mol−1 K−1.
ISSN:0020-1669
1520-510X
DOI:10.1021/ic901808t