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Bridge-splitting Kinetics, Equilibria and Structures of trans-bis-cyclooctene Complexes of Platinum(II)

Otto, Stefanus; Roodt, Andreas and Elding, Lars Ivar LU (2003) In Dalton Transactions p.2519-2525
Abstract
Cyclooctene (C8H14, cot) complexes of platinum(II) have been synthesised and characterised by means of multinuclear NMR, UV-Vis spectroscopy and X-ray crystallography. The bridge-splitting equilibrium constants of the dinuclear, chloride-bridged trans-[PtCl2(cot)]2, 1, in dichloromethane solvent at 298 K with MeOH, MeCN and cot, yielding trans-[PtCl2(cot)(MeOH)], 2, trans-[PtCl2(cot)(MeCN)], 3, and trans-[PtCl2(cot)2], 4, were determined by UV-Vis measurements as K12= 0.0169 ± 0.0015, K13= 9.7 ± 0.9 and K14= 2.05 ± 0.06 mol–1 dm3, respectively. Substitution of one cyclooctene from 4 by MeOH gives K42= 0.110 ± 0.009 and by MeCN K43= 2.25 ± 0.03. The bis-cyclooctene complexes 1 and 4 react quantitatively with chloride to give [PtCl3(cot)]–,... (More)
Cyclooctene (C8H14, cot) complexes of platinum(II) have been synthesised and characterised by means of multinuclear NMR, UV-Vis spectroscopy and X-ray crystallography. The bridge-splitting equilibrium constants of the dinuclear, chloride-bridged trans-[PtCl2(cot)]2, 1, in dichloromethane solvent at 298 K with MeOH, MeCN and cot, yielding trans-[PtCl2(cot)(MeOH)], 2, trans-[PtCl2(cot)(MeCN)], 3, and trans-[PtCl2(cot)2], 4, were determined by UV-Vis measurements as K12= 0.0169 ± 0.0015, K13= 9.7 ± 0.9 and K14= 2.05 ± 0.06 mol–1 dm3, respectively. Substitution of one cyclooctene from 4 by MeOH gives K42= 0.110 ± 0.009 and by MeCN K43= 2.25 ± 0.03. The bis-cyclooctene complexes 1 and 4 react quantitatively with chloride to give [PtCl3(cot)]–, 5. The kinetics for bridge-splitting of 1 with MeOH, MeCN and cot was studied by conventional and cryo-stopped-flow spectroscopy. Second-order rate constants at 298 K are 0.128 ± 0.003, 4.93 ± 0.02 and 0.0637 ± 0.0009 mol–1 dm3 s–1, respectively. The corresponding activation parameters are H= 43.7 ± 1.8, 42.0 ± 0.8 and 39.6 ± 0.9 kJ mol–1 and S=–115 ± 6, –91 ± 3 and –135 ± 3 J K–1 mol–1, indicating associative activation with a relatively large -TS contribution to G. Crystal and molecular structures of 1, 4, and the tetraphenylphosphonium salt of 5 have been determined, indicating a moderate ground-state trans influence of cyclooctene. The molecular structure of 4 with two CC double bonds coordinated trans to each other and perpendicular to the platinum coordination plane, features a significant Pt–C bond lengthening compared to cyclooctene complexes with chloride or nitrogen trans to cyclooctene, leading to high reactivity and thermodynamic instability. Equilibrium data confirm that the thermodynamic stability of a cyclooctene coordinated trans to another cyclooctene is much lower than trans to a ligand with less -back-bonding capacity. (Less)
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Contribution to journal
publication status
published
subject
keywords
Kinetics, Bridge splitting, Bis cyclooctene complexes, Plarinum
in
Dalton Transactions
issue
12
pages
2519 - 2525
publisher
Royal Society of Chemistry
external identifiers
  • wos:000183430100023
  • scopus:9644291944
ISSN
1477-9234
DOI
language
English
LU publication?
yes
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cf1b6edb-0bf2-4fde-89e3-4880d738d3dd (old id 128375)
date added to LUP
2007-07-09 14:07:26
date last changed
2018-05-29 10:18:08
@article{cf1b6edb-0bf2-4fde-89e3-4880d738d3dd,
  abstract     = {Cyclooctene (C8H14, cot) complexes of platinum(II) have been synthesised and characterised by means of multinuclear NMR, UV-Vis spectroscopy and X-ray crystallography. The bridge-splitting equilibrium constants of the dinuclear, chloride-bridged trans-[PtCl2(cot)]2, 1, in dichloromethane solvent at 298 K with MeOH, MeCN and cot, yielding trans-[PtCl2(cot)(MeOH)], 2, trans-[PtCl2(cot)(MeCN)], 3, and trans-[PtCl2(cot)2], 4, were determined by UV-Vis measurements as K12= 0.0169 ± 0.0015, K13= 9.7 ± 0.9 and K14= 2.05 ± 0.06 mol–1 dm3, respectively. Substitution of one cyclooctene from 4 by MeOH gives K42= 0.110 ± 0.009 and by MeCN K43= 2.25 ± 0.03. The bis-cyclooctene complexes 1 and 4 react quantitatively with chloride to give [PtCl3(cot)]–, 5. The kinetics for bridge-splitting of 1 with MeOH, MeCN and cot was studied by conventional and cryo-stopped-flow spectroscopy. Second-order rate constants at 298 K are 0.128 ± 0.003, 4.93 ± 0.02 and 0.0637 ± 0.0009 mol–1 dm3 s–1, respectively. The corresponding activation parameters are H= 43.7 ± 1.8, 42.0 ± 0.8 and 39.6 ± 0.9 kJ mol–1 and S=–115 ± 6, –91 ± 3 and –135 ± 3 J K–1 mol–1, indicating associative activation with a relatively large -TS contribution to G. Crystal and molecular structures of 1, 4, and the tetraphenylphosphonium salt of 5 have been determined, indicating a moderate ground-state trans influence of cyclooctene. The molecular structure of 4 with two CC double bonds coordinated trans to each other and perpendicular to the platinum coordination plane, features a significant Pt–C bond lengthening compared to cyclooctene complexes with chloride or nitrogen trans to cyclooctene, leading to high reactivity and thermodynamic instability. Equilibrium data confirm that the thermodynamic stability of a cyclooctene coordinated trans to another cyclooctene is much lower than trans to a ligand with less -back-bonding capacity.},
  author       = {Otto, Stefanus and Roodt, Andreas and Elding, Lars Ivar},
  issn         = {1477-9234},
  keyword      = {Kinetics, Bridge splitting,Bis cyclooctene complexes, Plarinum},
  language     = {eng},
  number       = {12},
  pages        = {2519--2525},
  publisher    = {Royal Society of Chemistry},
  series       = {Dalton Transactions},
  title        = {Bridge-splitting Kinetics, Equilibria and Structures of trans-bis-cyclooctene Complexes of Platinum(II)},
  url          = {http://dx.doi.org/},
  year         = {2003},
}