Bulletin of the Korean Chemical Society

Korean Chemical Society (대한화학회)
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Kinetics and Stereochemistry of CO Substitution Reactions of Half-Open Chromocene Carbonyls(Ⅰ): Reactions of Cp($C_{5}H_{7}$)CrCO and Phosphines

  • Chung, Jong-Jae (Department of Chemistry, College of Natural Sciences, Kyungpook National University) ;
  • Roh, Byung-Gill (Department of Chemistry, College of Natural Sciences, Kyungpook National University) ;
  • Park, Yu-Chul (Department of Chemistry, College of Natural Sciences, Kyungpook National University)
  • Published : 1993.04.20
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Abstract

The CO substitution reactions in the complex, $Cp(S-C_5H_7)CrCO$ with $PR_3(PR_3=PMePh_2,\;P(OCH_3)_3,\;PMe_2Ph)$ were investigated spectrophotometrically at various temperatures. From the reaction rates, it was suggested that the CO substitution reaction takes place by first-order (dissociative) pathway. Activation parameters in decaline are ${\Delta}H^{\neq}\;=\;24.58\;kcal\;{\cdot}\;mol^{-1},\;{\Delta}S^{\neq}\;=\;3.05 cal\;{\cdot}\;mol^{-1}{\cdot}K^{-1}$. Unusually low value of ${\Delta}S^{\neq}$ suggests an ${\eta}^5-S\;{\to}\;{\eta}^5-U$ conversion of the pentadienyl ligand. This was confirmed by the extended-Huckel molecular orbital (EHMO) calculations, which revealed that the total energy Of $Cp(S-C_5H_7)CrCO$ is about 6.84 kcal/mol more stable than that of $Cp(U-C_5H_7)CrCO$ and the energy of $[Cp(U-C_5H_7)CrCO^{\neq}$ transition state is about 4.25 kcal/mol lower than that of $[Cp(S-C_5H_7)Cr]^{\neq}$ transition state.

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References

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