TY - JOUR
T1 - Single- and two-state reactivity in the gas-phase C-H bond activation of norbornane by 'bare' FeO+
AU - Harris, Nathan
AU - Shaik, Sason
AU - Schroder, Detlef
AU - Schwarz, H. Helmut
PY - 1999
Y1 - 1999
N2 - The potential-energy surface for C-H bond activation of norbornane by 'bare' FeO+ is examined at the B3LYP/6-31G** level of theory. The free reactants combine to form norbornane/FeO+ ion-dipole clusters in which the FeO+ unit can bind at either the exo or endo face of norbornane. The transition structures for insertion of FeO+ into the exo and endo C-H bonds are located at least 9 kcal · mol-1 below the entrance channel, thus accounting for the observed unit efficiency of the C-H bond activation reported in previous gas-phase ion-cyclotron resonance experiments (Helv. Chim. Acta 1995, 78, 1013). Interesting features of the reaction profiles are crossovers of the high-spin sextet (S = 5/2) and low-spin quartet (S = 3/2) states en route to the transition structures (TS); this type of behavior has been termed two-state reactivity (Helv. Chim. Acta 1995, 78, 1393). The branchings between the endo and exo pathways are simulated by Rice- Ramsperger-Kassel-Marcus (RRKM) theory with the calculated harmonic frequencies. Additionally, hydrogen/deuterium kinetic isotope effects are computed using RRKM theory and compared with the experimental data. The simulated KIEs differ for high-spin and low-spin TSs, suggesting that isotope effects can be used as sensitive probes for diagnosing spin-crossover mechanisms.
AB - The potential-energy surface for C-H bond activation of norbornane by 'bare' FeO+ is examined at the B3LYP/6-31G** level of theory. The free reactants combine to form norbornane/FeO+ ion-dipole clusters in which the FeO+ unit can bind at either the exo or endo face of norbornane. The transition structures for insertion of FeO+ into the exo and endo C-H bonds are located at least 9 kcal · mol-1 below the entrance channel, thus accounting for the observed unit efficiency of the C-H bond activation reported in previous gas-phase ion-cyclotron resonance experiments (Helv. Chim. Acta 1995, 78, 1013). Interesting features of the reaction profiles are crossovers of the high-spin sextet (S = 5/2) and low-spin quartet (S = 3/2) states en route to the transition structures (TS); this type of behavior has been termed two-state reactivity (Helv. Chim. Acta 1995, 78, 1393). The branchings between the endo and exo pathways are simulated by Rice- Ramsperger-Kassel-Marcus (RRKM) theory with the calculated harmonic frequencies. Additionally, hydrogen/deuterium kinetic isotope effects are computed using RRKM theory and compared with the experimental data. The simulated KIEs differ for high-spin and low-spin TSs, suggesting that isotope effects can be used as sensitive probes for diagnosing spin-crossover mechanisms.
UR - http://www.scopus.com/inward/record.url?scp=0032862092&partnerID=8YFLogxK
U2 - 10.1002/(SICI)1522-2675(19991006)82:10<1784::AID-HLCA1784>3.0.CO;2-M
DO - 10.1002/(SICI)1522-2675(19991006)82:10<1784::AID-HLCA1784>3.0.CO;2-M
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AN - SCOPUS:0032862092
SN - 0018-019X
VL - 82
SP - 1784
EP - 1797
JO - Helvetica Chimica Acta
JF - Helvetica Chimica Acta
IS - 10
ER -