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Reaction Mechanism for Olefin Exchange at Chloro Ethene Complexes of Platinum(II)

Plutino, Maria R. ; Otto, Stefanus ; Roodt, Andreas and Elding, Lars Ivar LU (1999) In Inorganic Chemistry 38(6). p.1233-1238
Abstract
Synopsis  In methanol solutions of Zeise's salt, the parent complex [PtCl3(C2H4)]- as well as its solvolysis product, trans-[PtCl2(C2H4)(MeOH)], exchange rapidly with free ethene. The olefin exchange process, which is largely entropy controlled, involves the substitution labile site trans to the coordinated ethene.    Abstract   Complex equilibria in methanol/chloroform/dichloromethane solutions containing Zeise's anion, [PtCl3(C2H4)]- (1), the solvento species, trans-[PtCl2(C2H4)(MeOH)] (2), and the dinuclear complex, trans-[PtCl2(C2H4)]2 (3), have been studied by UV−vis, 1H, and 195Pt NMR spectroscopy, giving average values of KCl = (1.6 ± 0.2)103 M-1 and KS =... (More)
Synopsis  In methanol solutions of Zeise's salt, the parent complex [PtCl3(C2H4)]- as well as its solvolysis product, trans-[PtCl2(C2H4)(MeOH)], exchange rapidly with free ethene. The olefin exchange process, which is largely entropy controlled, involves the substitution labile site trans to the coordinated ethene.    Abstract   Complex equilibria in methanol/chloroform/dichloromethane solutions containing Zeise's anion, [PtCl3(C2H4)]- (1), the solvento species, trans-[PtCl2(C2H4)(MeOH)] (2), and the dinuclear complex, trans-[PtCl2(C2H4)]2 (3), have been studied by UV−vis, 1H, and 195Pt NMR spectroscopy, giving average values of KCl = (1.6 ± 0.2)103 M-1 and KS = (0.16 ± 0.02) M-1 for the equilibrium constants between 2 and 1 and 3 and 2, respectively. The bridged complex 3 is completely split into monomeric solvento complexes 2 in methanol and in chloroform or dichloromethane solutions with [MeOH] > 0.5 M. Ethene exchange at the mononuclear complexes 1 and 2 was studied by 1H NMR line-broadening experiments in methanol-d4. Observed overall exchange rate constants decrease with an increase in free chloride concentration due to the displacement of the rapid equilibrium between 1 and 2 toward the more slowly exchanging parent chloro complex 1. Ethene exchange rate constants at 298 K for complexes 1 and 2 are kex1 = (2.1 ± 0.1)103 M-1 s-1and kex2 = (5.0 ± 0.2)105 M-1 s-1, respectively, with corresponding activation parameters ΔH1⧧ = 19.1 ± 0.3 kJ mol-1, ΔS1⧧ = −117 ± 1 J K-1 mol-1, ΔH2⧧ = 10.2 ± 0.4 kJ mol-1, and ΔS2⧧ = −102 ± 2 J K-1 mol-1. The activation process is largely entropy controlled; the enthalpy contributions only amounting to ≈30% of the free energy of activation. Ethene exchange takes place via associative attack by the entering olefin at the labile site trans to the coordinated ethene, which is either occupied by a chloride or a methanol molecule in the ground state. The intimate mechanism might involve a two-step process via trans-[PtCl2(C2H4)2] in steady state or a concerted process via a pentacoordinated transition state with two ethene molecules bound to the platinum(II) (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Olefin exchange, Zeise's anion, Platinum(II) olefin complexes, Reaction mechanism, Fast kinetics, Activation parameters
in
Inorganic Chemistry
volume
38
issue
6
pages
6 pages
publisher
The American Chemical Society
external identifiers
  • scopus:0000978933
ISSN
1520-510X
DOI
10.1021/ic981020t
language
English
LU publication?
yes
id
4b9aa62d-d166-4618-bd4c-4ed822330e62
date added to LUP
2016-12-17 19:04:21
date last changed
2017-03-20 20:07:08
@article{4b9aa62d-d166-4618-bd4c-4ed822330e62,
  abstract     = {Synopsis  In methanol solutions of Zeise's salt, the parent complex [PtCl3(C2H4)]- as well as its solvolysis product, <i style="font-family: Helvetica, Arial, sans-serif; font-size: 13px;">trans</i>-[PtCl2(C2H4)(MeOH)], exchange rapidly with free ethene. The olefin exchange process, which is largely entropy controlled, involves the substitution labile site trans to the coordinated ethene.    Abstract   Complex equilibria in methanol/chloroform/dichloromethane solutions containing Zeise's anion, [PtCl3(C2H4)]- (1), the solvento species, trans-[PtCl2(C2H4)(MeOH)] (2), and the dinuclear complex, trans-[PtCl2(C2H4)]2 (3), have been studied by UV−vis, 1H, and 195Pt NMR spectroscopy, giving average values of KCl = (1.6 ± 0.2)103 M-1 and KS = (0.16 ± 0.02) M-1 for the equilibrium constants between 2 and 1 and 3 and 2, respectively. The bridged complex 3 is completely split into monomeric solvento complexes 2 in methanol and in chloroform or dichloromethane solutions with [MeOH] &gt; 0.5 M. Ethene exchange at the mononuclear complexes 1 and 2 was studied by 1H NMR line-broadening experiments in methanol-d4. Observed overall exchange rate constants decrease with an increase in free chloride concentration due to the displacement of the rapid equilibrium between 1 and 2 toward the more slowly exchanging parent chloro complex 1. Ethene exchange rate constants at 298 K for complexes 1 and 2 are kex1 = (2.1 ± 0.1)103 M-1 s-1and kex2 = (5.0 ± 0.2)105 M-1 s-1, respectively, with corresponding activation parameters ΔH1⧧ = 19.1 ± 0.3 kJ mol-1, ΔS1⧧ = −117 ± 1 J K-1 mol-1, ΔH2⧧ = 10.2 ± 0.4 kJ mol-1, and ΔS2⧧ = −102 ± 2 J K-1 mol-1. The activation process is largely entropy controlled; the enthalpy contributions only amounting to ≈30% of the free energy of activation. Ethene exchange takes place via associative attack by the entering olefin at the labile site trans to the coordinated ethene, which is either occupied by a chloride or a methanol molecule in the ground state. The intimate mechanism might involve a two-step process via trans-[PtCl2(C2H4)2] in steady state or a concerted process via a pentacoordinated transition state with two ethene molecules bound to the platinum(II)},
  author       = {Plutino, Maria R.  and Otto, Stefanus  and Roodt, Andreas and Elding, Lars Ivar},
  issn         = {1520-510X},
  keyword      = {Olefin exchange,Zeise's anion,Platinum(II) olefin complexes,Reaction mechanism,Fast kinetics,Activation parameters},
  language     = {eng},
  month        = {03},
  number       = {6},
  pages        = {1233--1238},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {Reaction Mechanism for Olefin Exchange at Chloro Ethene Complexes of Platinum(II)},
  url          = {http://dx.doi.org/10.1021/ic981020t},
  volume       = {38},
  year         = {1999},
}