Advanced

Protonolysis of Dialkyl and Alkylaryl Platinum(II) Complexes and Geometrical Isomerization of the Derived Monoorgano-Solvento Complexes: Clear-Cut Examples of Associative and Dissociative Pathways in Platinum Chemistry

Romeo, Rafaello; Plutino, Maria Rosaria and Elding, Lars Ivar LU (1997) In Inorganic Chemistry 36(25). p.5909-5916
Abstract (Swedish)
Synopsis
Protonolysis of the title compounds involves rate-determining proton transfer to the substrate. Subsequent isomerization is dissociative. Activation volumes for the two processes have opposite signs. A new kinetic β-hydrogen accelerating effect for isomerization favoring the fluxionality of a T-shaped 14-electron intermediate is reported.

Abstract
Abstract Image
Protonolysis of the complexes cis-[PtR2(PEt3)2] (R = Me, Et, Prn, Bun, CH2C(Me)3, CH2Si(Me)3) and cis-[Pt(R)(R‘)(PEt3)2] (R = Ph, 2-MeC6H4, 2,4,6-Me3C6H2; R‘ = Me) in methanol selectively cleaves one alkyl group, yielding cis-[Pt(R)(PEt3)2(MeOH)]+ and alkanes. The reactions occur as single-stage conversions from the substrate to the product. There is... (More)
Synopsis
Protonolysis of the title compounds involves rate-determining proton transfer to the substrate. Subsequent isomerization is dissociative. Activation volumes for the two processes have opposite signs. A new kinetic β-hydrogen accelerating effect for isomerization favoring the fluxionality of a T-shaped 14-electron intermediate is reported.

Abstract
Abstract Image
Protonolysis of the complexes cis-[PtR2(PEt3)2] (R = Me, Et, Prn, Bun, CH2C(Me)3, CH2Si(Me)3) and cis-[Pt(R)(R‘)(PEt3)2] (R = Ph, 2-MeC6H4, 2,4,6-Me3C6H2; R‘ = Me) in methanol selectively cleaves one alkyl group, yielding cis-[Pt(R)(PEt3)2(MeOH)]+ and alkanes. The reactions occur as single-stage conversions from the substrate to the product. There is no evidence by UV and by low-temperature 1H and 31P NMR spectroscopy for the presence of significant amounts of Pt(II) or Pt(IV) intermediate species. Reactions are first order with respect to complex and proton concentrations and are strongly retarded by steric congestion at the Pt−C bond, varying from k2 = (2.65 ± 0.08) × 105 M-1 s-1 for R = R‘ = Et to k2 = 9.80 ± 0.44 M-1s-1 for R = R‘= CH2Si(Me)3. Low enthalpies of activation and largely negative volumes of activation are associated with the process. The mechanism involves a rate-determining proton transfer either to the metal−carbon σ bond (SE2 mechanism) or to the metal center (SE(oxidative) mechanism), followed by fast extrusion of the alkane and simultaneous blocking of the vacant coordination site by the solvent to generate cis-[Pt(R)(PEt3)2(MeOH)]+ species. The subsequent slower process, cis to trans isomerization of cis-[Pt(R)(PEt3)2(MeOH)]+, is characterized by high values of enthalpies of activation, positive entropies of activation, and largely positive volumes of activation. The reaction is shown to proceed through the dissociative loss of the weakly bonded molecule of solvent and the interconversion of two geometrically distinct T-shaped 14-electron 3-coordinate intermediates. The presence of β-hydrogens on the residual alkyl chain produces a great acceleration of the rate (R = Me, ki = 0.0026 s-1; R = Et, ki = 44.9 s-1) as a consequence of the stabilization of the 3-coordinate [Pt(R)(PEt3)2]+ transition state through an incipient agostic interaction. The results of this work, together with those of a previous paper, give a rationale of the “elusive” nature of these compounds. The following factors concur:  (i) electron release by the phosphine ligands, (ii) steric repulsion and distortion of the square-planar configuration, and (iii) interaction of the metal with β-hydrogens. (Less)
Abstract
Synopsis
Protonolysis of the title compounds involves rate-determining proton transfer to the substrate. Subsequent isomerization is dissociative. Activation volumes for the two processes have opposite signs. A new kinetic β-hydrogen accelerating effect for isomerization favoring the fluxionality of a T-shaped 14-electron intermediate is reported.

Abstract
Protonolysis of the complexes cis-[PtR2(PEt3)2] (R = Me, Et, Prn, Bun, CH2C(Me)3, CH2Si(Me)3) and cis-[Pt(R)(R‘)(PEt3)2] (R = Ph, 2-MeC6H4, 2,4,6-Me3C6H2; R‘ = Me) in methanol selectively cleaves one alkyl group, yielding cis-[Pt(R)(PEt3)2(MeOH)]+ and alkanes. The reactions occur as single-stage conversions from the substrate to the product. There is no evidence by UV... (More)
Synopsis
Protonolysis of the title compounds involves rate-determining proton transfer to the substrate. Subsequent isomerization is dissociative. Activation volumes for the two processes have opposite signs. A new kinetic β-hydrogen accelerating effect for isomerization favoring the fluxionality of a T-shaped 14-electron intermediate is reported.

Abstract
Protonolysis of the complexes cis-[PtR2(PEt3)2] (R = Me, Et, Prn, Bun, CH2C(Me)3, CH2Si(Me)3) and cis-[Pt(R)(R‘)(PEt3)2] (R = Ph, 2-MeC6H4, 2,4,6-Me3C6H2; R‘ = Me) in methanol selectively cleaves one alkyl group, yielding cis-[Pt(R)(PEt3)2(MeOH)]+ and alkanes. The reactions occur as single-stage conversions from the substrate to the product. There is no evidence by UV and by low-temperature 1H and 31P NMR spectroscopy for the presence of significant amounts of Pt(II) or Pt(IV) intermediate species. Reactions are first order with respect to complex and proton concentrations and are strongly retarded by steric congestion at the Pt−C bond, varying from k2 = (2.65 ± 0.08) × 105 M-1 s-1 for R = R‘ = Et to k2 = 9.80 ± 0.44 M-1s-1 for R = R‘= CH2Si(Me)3. Low enthalpies of activation and largely negative volumes of activation are associated with the process. The mechanism involves a rate-determining proton transfer either to the metal−carbon σ bond (SE2 mechanism) or to the metal center (SE(oxidative) mechanism), followed by fast extrusion of the alkane and simultaneous blocking of the vacant coordination site by the solvent to generate cis-[Pt(R)(PEt3)2(MeOH)]+ species. The subsequent slower process, cis to trans isomerization of cis-[Pt(R)(PEt3)2(MeOH)]+, is characterized by high values of enthalpies of activation, positive entropies of activation, and largely positive volumes of activation. The reaction is shown to proceed through the dissociative loss of the weakly bonded molecule of solvent and the interconversion of two geometrically distinct T-shaped 14-electron 3-coordinate intermediates. The presence of β-hydrogens on the residual alkyl chain produces a great acceleration of the rate (R = Me, ki = 0.0026 s-1; R = Et, ki = 44.9 s-1) as a consequence of the stabilization of the 3-coordinate [Pt(R)(PEt3)2]+ transition state through an incipient agostic interaction. The results of this work, together with those of a previous paper, give a rationale of the “elusive” nature of these compounds. The following factors concur:  (i) electron release by the phosphine ligands, (ii) steric repulsion and distortion of the square-planar configuration, and (iii) interaction of the metal with β-hydrogens. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Platinum(II), Reaction Mechanism, Associative reaction, Dissocative reaction, High-pressure stopped flow, Fast reactions, Activation parameters, cis-trans isomerization, Protonolysis, Platinum(II), Associative processes, Dissociative processes, High-pressure stopped-flow, Activation volumes
in
Inorganic Chemistry
volume
36
issue
25
pages
8 pages
publisher
The American Chemical Society
ISSN
1520-510X
DOI
10.1021/ic9704905
language
English
LU publication?
yes
id
6e2dba7f-585d-4b34-b9f9-39c24b998a29
date added to LUP
2016-12-31 23:05:39
date last changed
2017-04-25 22:25:58
@article{6e2dba7f-585d-4b34-b9f9-39c24b998a29,
  abstract     = {Synopsis<br/>Protonolysis of the title compounds involves rate-determining proton transfer to the substrate. Subsequent isomerization is dissociative. Activation volumes for the two processes have opposite signs. A new kinetic β-hydrogen accelerating effect for isomerization favoring the fluxionality of a T-shaped 14-electron intermediate is reported.<br/><br/>Abstract<br/>Protonolysis of the complexes cis-[PtR2(PEt3)2] (R = Me, Et, Prn, Bun, CH2C(Me)3, CH2Si(Me)3) and cis-[Pt(R)(R‘)(PEt3)2] (R = Ph, 2-MeC6H4, 2,4,6-Me3C6H2; R‘ = Me) in methanol selectively cleaves one alkyl group, yielding cis-[Pt(R)(PEt3)2(MeOH)]+ and alkanes. The reactions occur as single-stage conversions from the substrate to the product. There is no evidence by UV and by low-temperature 1H and 31P NMR spectroscopy for the presence of significant amounts of Pt(II) or Pt(IV) intermediate species. Reactions are first order with respect to complex and proton concentrations and are strongly retarded by steric congestion at the Pt−C bond, varying from k2 = (2.65 ± 0.08) × 105 M-1 s-1 for R = R‘ = Et to k2 = 9.80 ± 0.44 M-1s-1 for R = R‘= CH2Si(Me)3. Low enthalpies of activation and largely negative volumes of activation are associated with the process. The mechanism involves a rate-determining proton transfer either to the metal−carbon σ bond (SE2 mechanism) or to the metal center (SE(oxidative) mechanism), followed by fast extrusion of the alkane and simultaneous blocking of the vacant coordination site by the solvent to generate cis-[Pt(R)(PEt3)2(MeOH)]+ species. The subsequent slower process, cis to trans isomerization of cis-[Pt(R)(PEt3)2(MeOH)]+, is characterized by high values of enthalpies of activation, positive entropies of activation, and largely positive volumes of activation. The reaction is shown to proceed through the dissociative loss of the weakly bonded molecule of solvent and the interconversion of two geometrically distinct T-shaped 14-electron 3-coordinate intermediates. The presence of β-hydrogens on the residual alkyl chain produces a great acceleration of the rate (R = Me, ki = 0.0026 s-1; R = Et, ki = 44.9 s-1) as a consequence of the stabilization of the 3-coordinate [Pt(R)(PEt3)2]+ transition state through an incipient agostic interaction. The results of this work, together with those of a previous paper, give a rationale of the “elusive” nature of these compounds. The following factors concur:  (i) electron release by the phosphine ligands, (ii) steric repulsion and distortion of the square-planar configuration, and (iii) interaction of the metal with β-hydrogens.},
  author       = {Romeo, Rafaello and Plutino, Maria Rosaria and Elding, Lars Ivar},
  issn         = {1520-510X},
  keyword      = {Platinum(II),Reaction Mechanism,Associative reaction,Dissocative reaction,High-pressure stopped flow,Fast reactions,Activation parameters,cis-trans isomerization,Protonolysis,Platinum(II),Associative processes,Dissociative processes,High-pressure stopped-flow,Activation volumes},
  language     = {eng},
  month        = {12},
  number       = {25},
  pages        = {5909--5916},
  publisher    = {The American Chemical Society},
  series       = {Inorganic Chemistry},
  title        = {Protonolysis of Dialkyl and Alkylaryl Platinum(II) Complexes and Geometrical Isomerization of the Derived Monoorgano-Solvento Complexes: Clear-Cut Examples of Associative and Dissociative Pathways in Platinum Chemistry},
  url          = {http://dx.doi.org/10.1021/ic9704905},
  volume       = {36},
  year         = {1997},
}