A study of the mechanism of iron carbonyl-catalyzed isomerization of 1- pentene in the gas phase using time-resolved infrared spectroscopy

Gregory T. Long, Eric Weitz*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

After generation of Fe(CO)3 by 308-nm gas-phase photolysis of Fe(CO)5, 1-pentene adds to Fe(CO)3 to form Fe(CO)32-1-pentene) with a bimolecular rate constant of k(a) = (4 ± 1) x 10-10 cm3 molecule-1 s- 1. Rapid β-hydrogen transfer, by way of intramolecular C-H bond insertion to form HFe(CO)33-C5H9), follows rate-limiting addition of 1-pentene to Fe(CO)3 and proceeds with a lower bound of k1 ≥ 109 s-1. Under experimental conditions, HFe(CO)33-C5H9) decays on a millisecond time scale with concurrent formation of Fe(CO)32-pentene)2 by addition of 1- pentene to an Fe(CO)32-pentene) intermediate. It is Fe(CO)32- pentene) that is in equilibrium with HFe(CO)33-C5H9) that adds 1- pentene to form Fe(CO)32-pentene)2, which may contain an isomerized olefin. CO may add to Fe(CO)32-pentene) that is in equilibrium with HFe(CO)33-C5H9) to form Fe(CO)42-pentene). Fe(CO)42-pentene) remains stable on the time scale of catalytic turnover and its formation serves as a termination pathway for thermal catalysis. This system is compared to the analogous propene system (Long, G. T.; Wang, W.; Weitz, E. J. Am. Chem. Soc. 1995, 117, 12810). The major difference in behavior between these systems is attributed to an ~3 orders of magnitude shift in the equilibrium constant toward HFe(CO)3(π-allyl) relative to Fe(CO)3(olefin) when the starting olefin is 1-pentene instead of propene. The magnitude of the equilibrium constants indicates that there is an ~4 kcal mol-1 greater enthalpy difference between HFe(CO)33-C5H9) and Fe(CO)32-pentene) than for the corresponding species in the propene system.

Original languageEnglish (US)
Pages (from-to)1431-1442
Number of pages12
JournalJournal of the American Chemical Society
Volume122
Issue number7
DOIs
StatePublished - Feb 23 2000

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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