Jump to main content
Jump to site search

Issue 12, 2003
Previous Article Next Article

Bridge-splitting kinetics, equilibria and structures of trans-biscyclooctene complexes of platinum(II)

Author affiliations

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 ΔH = 43.7 ± 1.8, 42.0 ± 0.8 and 39.6 ± 0.9 kJ mol−1 and ΔS = −115 ± 6, −91 ± 3 and −135 ± 3 J K−1 mol−1, indicating associative activation with a relatively large -TΔS contribution to ΔG. 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 C[double bond, length as m-dash]C 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 π-back-bonding capacity.

Graphical abstract: Bridge-splitting kinetics, equilibria and structures of trans-biscyclooctene complexes of platinum(ii)

Back to tab navigation

Supplementary files

Publication details

The article was received on 04 Mar 2003, accepted on 17 Apr 2003 and first published on 13 May 2003


Article type: Paper
DOI: 10.1039/B302482M
Citation: Dalton Trans., 2003, 2519-2525
  •   Request permissions

    Bridge-splitting kinetics, equilibria and structures of trans-biscyclooctene complexes of platinum(II)

    S. Otto, A. Roodt and L. I. Elding, Dalton Trans., 2003, 2519
    DOI: 10.1039/B302482M

Search articles by author

Spotlight

Advertisements