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Equilibria, Kinetics and Mechanism for Rapid Substitution Reactions trans to Triphenyl Silyl in Platinum(II) Complexes

Wendt, Ola LU and Elding, Lars Ivar LU (1997) In Inorganic Chemistry 36(26). p.6028-6032
Abstract (Swedish)
Fast substitution of chloride for bromide and iodide trans to triphenylsilyl in trans-PtCl(SiPh3)(PMe2Ph)2 has been studied by stopped-flow spectrophotometry in acetonitrile solution. Substitution is reversible with an observable solvent path via the solvento complex trans-[Pt(SiPh3)(MeCN)(PMe2Ph)2]+, which has also been synthesized and characterized in solution. Rate constants for the forward and reverse direct substitution pathways are 2900 ± 100 and 7500 ± 300 for bromide and 14300 ± 1100 and 81000 ± 11000 M-1 s-1 for iodide as nucleophile. The solvento complex reacts ca. 103 times faster with iodide than the parent chloride complex, and its reactivity is some 2 orders of magnitude higher than the most reactive solvento species of... (More)
Fast substitution of chloride for bromide and iodide trans to triphenylsilyl in trans-PtCl(SiPh3)(PMe2Ph)2 has been studied by stopped-flow spectrophotometry in acetonitrile solution. Substitution is reversible with an observable solvent path via the solvento complex trans-[Pt(SiPh3)(MeCN)(PMe2Ph)2]+, which has also been synthesized and characterized in solution. Rate constants for the forward and reverse direct substitution pathways are 2900 ± 100 and 7500 ± 300 for bromide and 14300 ± 1100 and 81000 ± 11000 M-1 s-1 for iodide as nucleophile. The solvento complex reacts ca. 103 times faster with iodide than the parent chloride complex, and its reactivity is some 2 orders of magnitude higher than the most reactive solvento species of platinum(II) studied so far. Halide substitution occurs with negative volumes and entropies of activation, but the nucleophilic discrimination is low, and the leaving ligand plays the most important role in the activation process, indicating an Id mechanism. Triphenylsilyl has a very high trans effect, comparable to that of ethene and methylisocyanide, due to extensive bond-weakening in the ground state, probably enforced by π-acception in the transition state. Due to electronic and solvational effects the platinum(II) silyl moiety acts as a hard or borderline metal center in acetonitrile, the thermodynamic stability sequence of its halide complexes being Cl > Br > I, i.e. the reverse of what is usually observed for platinum(II) complexes (Less)
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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Platinum(II), Triphenyl Silyl, Fast kinetics, trans effect, Stopped flow, Kinetics and mechanism, Id Mechanism, Reverse stability sequence, Activation parameters
in
Inorganic Chemistry
volume
36
issue
26
pages
5 pages
publisher
The American Chemical Society
ISSN
1520-510X
DOI
10.1021/ic971008l
language
Swedish
LU publication?
yes
id
e1d231d0-f701-4e90-b698-5c80cdce6c61
date added to LUP
2016-12-31 20:11:00
date last changed
2017-03-28 12:07:02
@article{e1d231d0-f701-4e90-b698-5c80cdce6c61,
  abstract     = {Fast substitution of chloride for bromide and iodide trans to triphenylsilyl in trans-PtCl(SiPh3)(PMe2Ph)2 has been studied by stopped-flow spectrophotometry in acetonitrile solution. Substitution is reversible with an observable solvent path via the solvento complex trans-[Pt(SiPh3)(MeCN)(PMe2Ph)2]+, which has also been synthesized and characterized in solution. Rate constants for the forward and reverse direct substitution pathways are 2900 ± 100 and 7500 ± 300 for bromide and 14300 ± 1100 and 81000 ± 11000 M-1 s-1 for iodide as nucleophile. The solvento complex reacts ca. 103 times faster with iodide than the parent chloride complex, and its reactivity is some 2 orders of magnitude higher than the most reactive solvento species of platinum(II) studied so far. Halide substitution occurs with negative volumes and entropies of activation, but the nucleophilic discrimination is low, and the leaving ligand plays the most important role in the activation process, indicating an Id mechanism. Triphenylsilyl has a very high trans effect, comparable to that of ethene and methylisocyanide, due to extensive bond-weakening in the ground state, probably enforced by π-acception in the transition state. Due to electronic and solvational effects the platinum(II) silyl moiety acts as a hard or borderline metal center in acetonitrile, the thermodynamic stability sequence of its halide complexes being Cl > Br > I, i.e. the reverse of what is usually observed for platinum(II) complexes},
  author       = {Wendt, Ola and Elding, Lars Ivar},
  issn         = {1520-510X},
  keyword      = {Platinum(II),Triphenyl Silyl,Fast kinetics,trans effect,Stopped flow,Kinetics and mechanism,Id Mechanism,Reverse stability sequence,Activation parameters},
  language     = {swe},
  month        = {12},
  number       = {26},
  pages        = {6028--6032},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {Equilibria, Kinetics and Mechanism for Rapid Substitution Reactions trans to  Triphenyl Silyl in Platinum(II) Complexes},
  url          = {http://dx.doi.org/10.1021/ic971008l},
  volume       = {36},
  year         = {1997},
}