TY - JOUR
T1 - A study of the mechanism of iron carbonyl-catalyzed isomerization of 1- pentene in the gas phase using time-resolved infrared spectroscopy
AU - Long, Gregory T.
AU - Weitz, Eric
PY - 2000/2/23
Y1 - 2000/2/23
N2 - 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)3(η2-1-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)3(η3-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)3(η3-C5H9) decays on a millisecond time scale with concurrent formation of Fe(CO)3(η2-pentene)2 by addition of 1- pentene to an Fe(CO)3(η2-pentene) intermediate. It is Fe(CO)3(η2- pentene) that is in equilibrium with HFe(CO)3(η3-C5H9) that adds 1- pentene to form Fe(CO)3(η2-pentene)2, which may contain an isomerized olefin. CO may add to Fe(CO)3(η2-pentene) that is in equilibrium with HFe(CO)3(η3-C5H9) to form Fe(CO)4(η2-pentene). Fe(CO)4(η2-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)3(η3-C5H9) and Fe(CO)3(η2-pentene) than for the corresponding species in the propene system.
AB - 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)3(η2-1-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)3(η3-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)3(η3-C5H9) decays on a millisecond time scale with concurrent formation of Fe(CO)3(η2-pentene)2 by addition of 1- pentene to an Fe(CO)3(η2-pentene) intermediate. It is Fe(CO)3(η2- pentene) that is in equilibrium with HFe(CO)3(η3-C5H9) that adds 1- pentene to form Fe(CO)3(η2-pentene)2, which may contain an isomerized olefin. CO may add to Fe(CO)3(η2-pentene) that is in equilibrium with HFe(CO)3(η3-C5H9) to form Fe(CO)4(η2-pentene). Fe(CO)4(η2-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)3(η3-C5H9) and Fe(CO)3(η2-pentene) than for the corresponding species in the propene system.
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U2 - 10.1021/ja9914341
DO - 10.1021/ja9914341
M3 - Article
AN - SCOPUS:0033996734
VL - 122
SP - 1431
EP - 1442
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
SN - 0002-7863
IS - 7
ER -