Advanced

Trans effect and trans influence of triphenyl stibine and -phosphine in platinum(II) complexes. A comparative mechanistic and structural study

Wendt, Ola LU and Elding, Lars Ivar LU (1997) In Journal of the Chemical Society. Dalton Transactions 1997(24). p.4725-4731
Abstract (Swedish)
The kinetics and mechanism of the reactions between trans-[PtI3(PPh3)]– and trans-[PtI3(SbPh3)]– with pyridine, 2- and 4-methylpyridine in acetonitrile solvent have been studied by stopped-flow spectrophotometry. The crystal and molecular structures of the tetrabutylammonium salts of the two anions have been determined. Substitution of iodide trans to stibine is reversible and takes place via parallel direct and solvolytic pathways; substitution in the phosphine complex occurs with negligible back reaction. The kinetic data indicate that triphenyl-stibine and -phosphine should be placed in a series of decreasing trans effect, C2H4 > SbPh3 > CO > P(OMe)3 > PPh3 > AsEt3, i.e. SbPh3 has a much larger trans effect than that of... (More)
The kinetics and mechanism of the reactions between trans-[PtI3(PPh3)]– and trans-[PtI3(SbPh3)]– with pyridine, 2- and 4-methylpyridine in acetonitrile solvent have been studied by stopped-flow spectrophotometry. The crystal and molecular structures of the tetrabutylammonium salts of the two anions have been determined. Substitution of iodide trans to stibine is reversible and takes place via parallel direct and solvolytic pathways; substitution in the phosphine complex occurs with negligible back reaction. The kinetic data indicate that triphenyl-stibine and -phosphine should be placed in a series of decreasing trans effect, C2H4 > SbPh3 > CO > P(OMe)3 > PPh3 > AsEt3, i.e. SbPh3 has a much larger trans effect than that of PPh3; stibine complexes in the present study react ca. 16 times faster than their phosphine analogues. The activation parameters are typical of associatively activated processes, and in the case of the stibine complex they indicate that very little bond breaking has occurred in the transition state. In the ground states there is a clear-cut difference in the Pt–I distances trans to the pnictogen, 2.637(2) Å in the stibine complex and 2.662(3) Å in the phosphine complex, indicating that SbPh3 has a smaller ground-state trans influence and hence is a weaker σ donor than PPh3. Since the kinetic trans effect is a combination of ground-state labilisation and transition-state stabilisation, it is concluded that the large trans effect of stibine is due to a better π acceptance. Based on a comparison of Sb–C distances and C–Sb–C angles in free and co-ordinated stibine, this is proposed to be due to a higher d character of the π* orbitals on stibine as compared to phosphine, leading to a better overlap between antimony π* and platinum 5d π orbitals. (Less)
Abstract
The kinetics and mechanism of the reactions between trans-[PtI3(PPh3)]– and trans-[PtI3(SbPh3)]– with pyridine, 2- and 4-methylpyridine in acetonitrile solvent have been studied by stopped-flow spectrophotometry. The crystal and molecular structures of the tetrabutylammonium salts of the two anions have been determined. Substitution of iodide trans to stibine is reversible and takes place via parallel direct and solvolytic pathways; substitution in the phosphine complex occurs with negligible back reaction. The kinetic data indicate that triphenyl-stibine and -phosphine should be placed in a series of decreasing trans effect, C2H4 > SbPh3 > CO > P(OMe)3 > PPh3 > AsEt3, i.e. SbPh3 has a much larger trans effect than that of... (More)
The kinetics and mechanism of the reactions between trans-[PtI3(PPh3)]– and trans-[PtI3(SbPh3)]– with pyridine, 2- and 4-methylpyridine in acetonitrile solvent have been studied by stopped-flow spectrophotometry. The crystal and molecular structures of the tetrabutylammonium salts of the two anions have been determined. Substitution of iodide trans to stibine is reversible and takes place via parallel direct and solvolytic pathways; substitution in the phosphine complex occurs with negligible back reaction. The kinetic data indicate that triphenyl-stibine and -phosphine should be placed in a series of decreasing trans effect, C2H4 > SbPh3 > CO > P(OMe)3 > PPh3 > AsEt3, i.e. SbPh3 has a much larger trans effect than that of PPh3; stibine complexes in the present study react ca. 16 times faster than their phosphine analogues. The activation parameters are typical of associatively activated processes, and in the case of the stibine complex they indicate that very little bond breaking has occurred in the transition state. In the ground states there is a clear-cut difference in the Pt–I distances trans to the pnictogen, 2.637(2) Å in the stibine complex and 2.662(3) Å in the phosphine complex, indicating that SbPh3 has a smaller ground-state trans influence and hence is a weaker σ donor than PPh3. Since the kinetic trans effect is a combination of ground-state labilisation and transition-state stabilisation, it is concluded that the large trans effect of stibine is due to a better π acceptance. Based on a comparison of Sb–C distances and C–Sb–C angles in free and co-ordinated stibine, this is proposed to be due to a higher d character of the π* orbitals on stibine as compared to phosphine, leading to a better overlap between antimony π* and platinum 5d π orbitals. (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), Triprhenyl stibine, Triphenyl phosphine, Trans effect series, Trans influence, Stopped-flow kinetics, Reaction mechanism, Tetrabutyl ammonium salt, Crystal structure
in
Journal of the Chemical Society. Dalton Transactions
volume
1997
issue
24
pages
7 pages
publisher
Royal Society of Chemistry
external identifiers
  • scopus:33748837232
ISSN
1472-7773
DOI
10.1039/A706617A
language
English
LU publication?
yes
id
05a8ee14-4ef0-4f91-9a46-a213fc5dfe69
date added to LUP
2016-12-31 22:44:01
date last changed
2017-03-28 12:01:50
@article{05a8ee14-4ef0-4f91-9a46-a213fc5dfe69,
  abstract     = {The kinetics and mechanism of the reactions between trans-[PtI3(PPh3)]– and trans-[PtI3(SbPh3)]– with pyridine, 2- and 4-methylpyridine in acetonitrile solvent have been studied by stopped-flow spectrophotometry. The crystal and molecular structures of the tetrabutylammonium salts of the two anions have been determined. Substitution of iodide trans to stibine is reversible and takes place via parallel direct and solvolytic pathways; substitution in the phosphine complex occurs with negligible back reaction. The kinetic data indicate that triphenyl-stibine and -phosphine should be placed in a series of decreasing trans effect, C2H4 > SbPh3 > CO > P(OMe)3 > PPh3 > AsEt3, i.e. SbPh3 has a much larger trans effect than that of PPh3; stibine complexes in the present study react ca. 16 times faster than their phosphine analogues. The activation parameters are typical of associatively activated processes, and in the case of the stibine complex they indicate that very little bond breaking has occurred in the transition state. In the ground states there is a clear-cut difference in the Pt–I distances trans to the pnictogen, 2.637(2) Å in the stibine complex and 2.662(3) Å in the phosphine complex, indicating that SbPh3 has a smaller ground-state trans influence and hence is a weaker σ donor than PPh3. Since the kinetic trans effect is a combination of ground-state labilisation and transition-state stabilisation, it is concluded that the large trans effect of stibine is due to a better π acceptance. Based on a comparison of Sb–C distances and C–Sb–C angles in free and co-ordinated stibine, this is proposed to be due to a higher d character of the π* orbitals on stibine as compared to phosphine, leading to a better overlap between antimony π* and platinum 5d π orbitals.},
  author       = {Wendt, Ola and Elding, Lars Ivar},
  issn         = {1472-7773},
  keyword      = {Platinum(II),Triprhenyl stibine,Triphenyl phosphine,Trans effect series,Trans influence,Stopped-flow kinetics,Reaction mechanism,Tetrabutyl ammonium salt,Crystal structure},
  language     = {eng},
  month        = {12},
  number       = {24},
  pages        = {4725--4731},
  publisher    = {Royal Society of Chemistry},
  series       = {Journal of the Chemical Society. Dalton Transactions},
  title        = {Trans effect and trans influence of triphenyl stibine and -phosphine in platinum(II) complexes. A comparative mechanistic and structural study},
  url          = {http://dx.doi.org/10.1039/A706617A},
  volume       = {1997},
  year         = {1997},
}