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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 14, Number 5
BKCSDE 14(5)
May 20, 1993 

Kinetics and Stereochemistry of CO Substitution Reactions of Half-Open Chromocene Carbonyls(Ⅲ) : Reactions of Cp*(η5-C5H7)CrCO and Phosphines
Jong-Jae Chung*, Byung-Gill Roh, Yu-Chul Park
The CO substitution reactions in the complex, Cp*(C5H7)CrCO with PR3(PR3=PMePh2, P(OCH3)3, PMe2Ph) were investigated spectrophotometrically at various temperatures. For the reaction rates, it was suggested that the CO substitution reaction took place by first-order (dissociative) pathway. Activation parameters in decaline are △H≠= 21.99±2.4 kcal/mol, △S≠= 8.9±7.1 cal/mol·k. Unusually low value of △S≠, suggested an η5-S→ η5-U conversion of the pentadienyl ligand. At various temperature, the rates of reaction for the Cp(pdl)CrCO complexes increase in the order Cp*(C5H7)-CrCO < Cp(C5H7)CrCO < Cp(2,4-C7H11)CrCO, which can be attributed to the usual steric acceration or electronic influence for the ligand substitution of metal complexes. This suggestion was confirmed by the extended-Huckel molecular orbital (EHMO) calculations, which revealed that the energy of [Cp*(U-C5H7)Cr]≠ transition state is about 4.93 kcal/mol lower than that of [Cp(S-C5H7)Cr]≠ transition state, and the arrangement of the overlap populations between Cr and the carbon of CO is Cp*(C5H7)CrCO > Cp(C5H7)CrCO > Cp(2,4-C7H11)CrCO.
549 - 554
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