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Single‐ and Two‐State Reactivity in the Gas‐Phase C−H Bond Activation of Norbornane by `Bare' FeO +
Author(s) -
Harris Nathan,
Shaik Sason,
Schröder Detlef,
Schwarz Helmut
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19991006)82:10<1784::aid-hlca1784>3.0.co;2-m
Subject(s) - norbornane , chemistry , kinetic isotope effect , deuterium , reactivity (psychology) , computational chemistry , stereochemistry , atomic physics , medicine , physics , alternative medicine , pathology
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.