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Pseudo-rotation mechanism for fast olefin exchange and substitution processes at orthometalated C,N-complexes of platinum(II)

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Author

Summary, in English

Bridge splitting in chloroform of the orthometalated chloro-bridged complex [Pt(mu-Cl)(2-Me2NCH2C6H4)](2) (1), with ethene, cyclooctene, allyl alcohol and phosphine according to 1 + 2L --> 2 [PtCl(2-Me2NCH2C6H4)(L)], where L = C2H4 (3a), C8H14, (3b), CH2CHCH2OH (3c), and PPh3 (4a and 4b) gives monomeric species with L coordinated trans or cis to aryl. With olefins the thermodynamically stable isomer with L coordinated cis to aryl is formed directly without an observable intermediate. With phosphine and pyridine, the kinetically controlled trans-product isomerizes slowly to the more stable cis-isomer. Bridge splitting by olefins is slow and first-order in 1 and L, with largely negative DeltaS(double dagger). Substitution of ethene cis to aryl by cyclooctene and allyl alcohol to form 3b and 3c, and substitution of cot from 3b by allyl alcohol to form 3c are first order in olefin and complex, ca. six orders of magnitude faster than bridge cleavage due to a large decrease in DeltaH(double dagger), and with largely negative DeltaS(double dagger). Cyclooctene exchange at 3b is first-order with respect to free cyclooctene and platinum complex. All experimental data for olefin substitution and exchange are compatible with a concerted substitution/isomerization process via a turnstile twist pseudo-rotation in a short-lived labile five-coordinated intermediate, involving initial attack on the labile coordination position trans to the sigma-bonded aryl. Bridge-cleavage reactions of the analogous bridged complexes occur similarly, but are much slower because of their ground-state stabilization and steric hindrance.

Publishing year

2004

Language

English

Pages

3662-3668

Publication/Series

Dalton Transactions

Issue

21

Document type

Journal article

Publisher

Royal Society of Chemistry

Topic

  • Inorganic Chemistry

Keywords

  • Olefin exchange
  • Fast reactions
  • Pseudo-rotation mechanism

Status

Published

ISBN/ISSN/Other

  • ISSN: 1477-9234