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Kinetics and Mechanism for Chloride Anation of Some Platinum(IV) Aqua Complexes in the Presence of Platinum(II))

Elding, Lars Ivar LU and Gustafson, Lena (1976) In Inorganica Chimica Acta 19(1). p.31-38
Abstract (Swedish)
Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law:

rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x... (More)
Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law:

rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x [PtCl42−][PtCl5H2O−]

The usual interpretation of k‴ as the stability constant for a five-coordinate complex PtCl53− is ruled out by other experiments, which indicate a much smaller stability constant than that obtained from the kinetics. This is also supported by a stopped-flow study at 25°C in 0.5 M perchloric acid medium of the substitution of bromide by chloride in trans-Pt(NH3)4Br2 for large concentrations of entering ligand and in the presence of Pt(NH3)42+. A modified reaction mechanism is suggested which can describe all experimental results. The primary step is the formation of a dimer complex from the platinum(IV) substrate complex and the simple platinum(II) complex, hydrated in the axial positions. This dimer might decompose directly to a platinum(II) complex and a platinum(IV) aqua complex. Alternatively, it might react with the incoming ligand to form a new dinuclear complex, which decomposes to the platinum(II) complex and the substituted platinum(IV) complex. (Less)
Abstract
Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law:

rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x... (More)
Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law:

rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x [PtCl42−][PtCl5H2O−]

The usual interpretation of k‴ as the stability constant for a five-coordinate complex PtCl53− is ruled out by other experiments, which indicate a much smaller stability constant than that obtained from the kinetics. This is also supported by a stopped-flow study at 25°C in 0.5 M perchloric acid medium of the substitution of bromide by chloride in trans-Pt(NH3)4Br2 for large concentrations of entering ligand and in the presence of Pt(NH3)42+. A modified reaction mechanism is suggested which can describe all experimental results. The primary step is the formation of a dimer complex from the platinum(IV) substrate complex and the simple platinum(II) complex, hydrated in the axial positions. This dimer might decompose directly to a platinum(II) complex and a platinum(IV) aqua complex. Alternatively, it might react with the incoming ligand to form a new dinuclear complex, which decomposes to the platinum(II) complex and the substituted platinum(IV) complex. (Less)
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Contribution to journal
publication status
published
subject
keywords
Chloride anation , Platinum(IV) aqua complex, Reaction mechanism
in
Inorganica Chimica Acta
volume
19
issue
1
pages
8 pages
publisher
Elsevier
external identifiers
  • scopus:0008697161
ISSN
0020-1693
DOI
10.1016/S0020-1693(00)91070-3
language
English
LU publication?
yes
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f319bf99-44a2-4828-bf86-699ab0bce726
date added to LUP
2017-02-19 17:45:52
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2017-11-14 09:50:19
@article{f319bf99-44a2-4828-bf86-699ab0bce726,
  abstract     = {Chloride anations of PtCl5H2O−, trans-PtCl4(H2O)2 and trans-Pt(CN)4ClH2O− in the presence of PtCl42− have been studied at 50°C in 1.00M perchloric acid medium. It is shown that PtCl5H2O− is formed as the primary reaction product in the two last-mentioned anations. This is not compatible with the generally used mechanism for platinum(II)-catalyzed platinum (IV) substitutions, which gives PtCl62− as the direct reaction product for these two reactions. Other examples of formation of aqua complex intermediates in previously studied platinum(II)-catalyzed platinum (IV) substitutions can be found by examination of data from the literature. The chloride anation of PtCl5H2O− follows the rate law:<br/><br/> rate = (k′ + k″ [Cl−]) / (1 + k‴[Cl−]) x [PtCl42−][PtCl5H2O−]<br/><br/>The usual interpretation of k‴ as the stability constant for a five-coordinate complex PtCl53− is ruled out by other experiments, which indicate a much smaller stability constant than that obtained from the kinetics. This is also supported by a stopped-flow study at 25°C in 0.5 M perchloric acid medium of the substitution of bromide by chloride in trans-Pt(NH3)4Br2 for large concentrations of entering ligand and in the presence of Pt(NH3)42+. A modified reaction mechanism is suggested which can describe all experimental results. The primary step is the formation of a dimer complex from the platinum(IV) substrate complex and the simple platinum(II) complex, hydrated in the axial positions. This dimer might decompose directly to a platinum(II) complex and a platinum(IV) aqua complex. Alternatively, it might react with the incoming ligand to form a new dinuclear complex, which decomposes to the platinum(II) complex and the substituted platinum(IV) complex.},
  author       = {Elding, Lars Ivar and Gustafson, Lena},
  issn         = {0020-1693},
  keyword      = {Chloride anation ,Platinum(IV) aqua complex,Reaction mechanism},
  language     = {eng},
  number       = {1},
  pages        = {31--38},
  publisher    = {Elsevier},
  series       = {Inorganica Chimica Acta},
  title        = {Kinetics and Mechanism for Chloride Anation of Some Platinum(IV) Aqua Complexes in the Presence of Platinum(II))},
  url          = {http://dx.doi.org/10.1016/S0020-1693(00)91070-3},
  volume       = {19},
  year         = {1976},
}