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Low temperature kinetic study of very fast substitution reactions at platinum(II) trans to olefins

Otto, S and Elding, Lars Ivar LU (2002) In Journal of the Chemical Society. Dalton Transactions p.2354-2360
Abstract
Ultra-fast substitution of chloride for bromide, iodide, azide and thiocyanate trans to ethene in Zeise's anion, [PtCl3(C2H4)](-), 1, has been investigated in methanol solvent by use of cryo temperature diode array stopped-flow spectrophotometry. Reactions follow the usual two-term rate law for square-planar substitutions, k(obs)=k(1)+k(2)[Y] (where k(1)=k(MeOH) [MeOH]), with k(1)=118+/-10 s(-1) and k(2)=(5.1+/-0.2) x 10(2), (3.51+/-0.07) x 10(3), (11.8+/-0.2) x 10(3), and (56+/-4) x 10(3) mol(-1) dm(3) s(-1) for Y=Br-, I-, N-3(-) and SCN-, respectively, at 223 K. Activation parameters for MeOH, Br-, I- and N-3(-) are DeltaH(not equal)=23+/-2, 21+/-2, 17+/-1.0 and 11.9+/-1.5 kJ mol(-1) and DeltaS(not equal)=-124+/-10, -96+/-9, -98+/-4 and... (More)
Ultra-fast substitution of chloride for bromide, iodide, azide and thiocyanate trans to ethene in Zeise's anion, [PtCl3(C2H4)](-), 1, has been investigated in methanol solvent by use of cryo temperature diode array stopped-flow spectrophotometry. Reactions follow the usual two-term rate law for square-planar substitutions, k(obs)=k(1)+k(2)[Y] (where k(1)=k(MeOH) [MeOH]), with k(1)=118+/-10 s(-1) and k(2)=(5.1+/-0.2) x 10(2), (3.51+/-0.07) x 10(3), (11.8+/-0.2) x 10(3), and (56+/-4) x 10(3) mol(-1) dm(3) s(-1) for Y=Br-, I-, N-3(-) and SCN-, respectively, at 223 K. Activation parameters for MeOH, Br-, I- and N-3(-) are DeltaH(not equal)=23+/-2, 21+/-2, 17+/-1.0 and 11.9+/-1.5 kJ mol(-1) and DeltaS(not equal)=-124+/-10, -96+/-9, -98+/-4 and -111+/-6 J K-1 mol(-1), respectively. Recalculation of k(1) to second-order units gives the sequence of nucleophilicity MeOH<Br-<I-<N-3(-)<SCN-(1:100:700:2500:12000) at 223 K. This nucleophilic discrimination decreases with increasing temperature. Chloride for iodide substitution trans to allyl alcohol, vinyltrimethylsilane and cyclooctene at [PtCl3(L)](-), (L=CH2CHCH2OH, 2; CH2CHSiMe3, 3; C8H14,4) follow the same rate law with k(1)=116&PLUSMN;5, 31.0&PLUSMN;0.3 and 23.6&PLUSMN;0.1 s(-1) and k(2)= (2.65&PLUSMN;0.06) x 10(3), (0.273&PLUSMN;0.005) x 10(3) and (0.119&PLUSMN;0.002) x 10(3) mol(-1) dm(3) s(-1) at 223 K. Activation parameters are &UDelta;H-&NOTEQUAL;(k(MeOH))=24.4&PLUSMN;1.3, 28.4&PLUSMN;0.6 and 29.9&PLUSMN;0.8 kJ mol(-1), &UDelta;S-&NOTEQUAL;(k(MeOH)) =-120&PLUSMN;5, -114&PLUSMN;2 and, -108&PLUSMN;3 J K-1 mol(-1), &UDelta;H-&NOTEQUAL;(k(2))=19.9&PLUSMN;1.2, 24.6&PLUSMN;1.7 and 24&PLUSMN;3 kJ mol(-1) and &UDelta;S-&NOTEQUAL;(k(2))=-8&PLUSMN;5, -84&PLUSMN;7 and -93&PLUSMN;10 J K-1 mol(-1), for 2, 3 and 4 respectively. The free energies of activation are dominated by the -T&UDelta;S&NOTEQUAL; terms. The crystal and molecular structures of Bu4N[PtCl3(CH2CHSiMe3)] and Bu4N[PtCl3(C8H14)] show slight Pt-Cl bond lengthening to 2.314(2) &ANGS; and 2.3238(16) &ANGS; trans to the olefins, similar to that found trans to ethene in Zeise's anion. All experiments support a model for the very fast substitution reactions trans to the olefins in which ground state labilisation is much less significant than transition state stabilisation. Extrapolation to ambient temperature together with literature data for related reactions in methanol solvent gives a quantitative measure of the trans effect of ethene as: SR2<Me2SO<AsEt3<PR3<P(OR)(3)<C2H4(1:5:400:3500:7000:3 x 10(6)). The relative trans effect of the olefins studied is C2H4&SIM;CH2CHCH2OH>CH(2)CHSiMe(3)similar toC(8)H(14), spanning a factor of between 5 and 30 depending on the nucleophile, a (Less)
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Contribution to journal
publication status
published
subject
keywords
Fast kinetics , Olefin complex, Structure, Platinum(II), Substitution reaction
in
Journal of the Chemical Society. Dalton Transactions
issue
11
pages
2354 - 2360
publisher
Royal Society of Chemistry
external identifiers
  • wos:000175858100019
  • scopus:0036015079
ISSN
1472-7773
DOI
10.1039/b200197g
language
English
LU publication?
yes
id
f1cbbced-ae71-4dd1-aaef-eb5b3e245c2a (old id 337134)
date added to LUP
2007-11-08 08:56:35
date last changed
2017-09-03 04:29:16
@article{f1cbbced-ae71-4dd1-aaef-eb5b3e245c2a,
  abstract     = {Ultra-fast substitution of chloride for bromide, iodide, azide and thiocyanate trans to ethene in Zeise's anion, [PtCl3(C2H4)](-), 1, has been investigated in methanol solvent by use of cryo temperature diode array stopped-flow spectrophotometry. Reactions follow the usual two-term rate law for square-planar substitutions, k(obs)=k(1)+k(2)[Y] (where k(1)=k(MeOH) [MeOH]), with k(1)=118+/-10 s(-1) and k(2)=(5.1+/-0.2) x 10(2), (3.51+/-0.07) x 10(3), (11.8+/-0.2) x 10(3), and (56+/-4) x 10(3) mol(-1) dm(3) s(-1) for Y=Br-, I-, N-3(-) and SCN-, respectively, at 223 K. Activation parameters for MeOH, Br-, I- and N-3(-) are DeltaH(not equal)=23+/-2, 21+/-2, 17+/-1.0 and 11.9+/-1.5 kJ mol(-1) and DeltaS(not equal)=-124+/-10, -96+/-9, -98+/-4 and -111+/-6 J K-1 mol(-1), respectively. Recalculation of k(1) to second-order units gives the sequence of nucleophilicity MeOH&lt;Br-&lt;I-&lt;N-3(-)&lt;SCN-(1:100:700:2500:12000) at 223 K. This nucleophilic discrimination decreases with increasing temperature. Chloride for iodide substitution trans to allyl alcohol, vinyltrimethylsilane and cyclooctene at [PtCl3(L)](-), (L=CH2CHCH2OH, 2; CH2CHSiMe3, 3; C8H14,4) follow the same rate law with k(1)=116&amp;PLUSMN;5, 31.0&amp;PLUSMN;0.3 and 23.6&amp;PLUSMN;0.1 s(-1) and k(2)= (2.65&amp;PLUSMN;0.06) x 10(3), (0.273&amp;PLUSMN;0.005) x 10(3) and (0.119&amp;PLUSMN;0.002) x 10(3) mol(-1) dm(3) s(-1) at 223 K. Activation parameters are &amp;UDelta;H-&amp;NOTEQUAL;(k(MeOH))=24.4&amp;PLUSMN;1.3, 28.4&amp;PLUSMN;0.6 and 29.9&amp;PLUSMN;0.8 kJ mol(-1), &amp;UDelta;S-&amp;NOTEQUAL;(k(MeOH)) =-120&amp;PLUSMN;5, -114&amp;PLUSMN;2 and, -108&amp;PLUSMN;3 J K-1 mol(-1), &amp;UDelta;H-&amp;NOTEQUAL;(k(2))=19.9&amp;PLUSMN;1.2, 24.6&amp;PLUSMN;1.7 and 24&amp;PLUSMN;3 kJ mol(-1) and &amp;UDelta;S-&amp;NOTEQUAL;(k(2))=-8&amp;PLUSMN;5, -84&amp;PLUSMN;7 and -93&amp;PLUSMN;10 J K-1 mol(-1), for 2, 3 and 4 respectively. The free energies of activation are dominated by the -T&amp;UDelta;S&amp;NOTEQUAL; terms. The crystal and molecular structures of Bu4N[PtCl3(CH2CHSiMe3)] and Bu4N[PtCl3(C8H14)] show slight Pt-Cl bond lengthening to 2.314(2) &amp;ANGS; and 2.3238(16) &amp;ANGS; trans to the olefins, similar to that found trans to ethene in Zeise's anion. All experiments support a model for the very fast substitution reactions trans to the olefins in which ground state labilisation is much less significant than transition state stabilisation. Extrapolation to ambient temperature together with literature data for related reactions in methanol solvent gives a quantitative measure of the trans effect of ethene as: SR2&lt;Me2SO&lt;AsEt3&lt;PR3&lt;P(OR)(3)&lt;C2H4(1:5:400:3500:7000:3 x 10(6)). The relative trans effect of the olefins studied is C2H4&amp;SIM;CH2CHCH2OH&gt;CH(2)CHSiMe(3)similar toC(8)H(14), spanning a factor of between 5 and 30 depending on the nucleophile, a},
  author       = {Otto, S and Elding, Lars Ivar},
  issn         = {1472-7773},
  keyword      = {Fast  kinetics ,Olefin complex,Structure,Platinum(II),Substitution reaction},
  language     = {eng},
  number       = {11},
  pages        = {2354--2360},
  publisher    = {Royal Society of Chemistry},
  series       = {Journal of the Chemical Society. Dalton Transactions},
  title        = {Low temperature kinetic study of very fast substitution reactions at platinum(II) trans to olefins},
  url          = {http://dx.doi.org/10.1039/b200197g},
  year         = {2002},
}