ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Quantum-chemical calculations employing a density-functional theory/Hartree-Fock hybrid method (B3LYP) have been used to explore the mechanistic details of the C—C and C—H bond-activation processes in propane mediated by a bare Fe+ ion. While the theoretically predicted results are in complete accord with all available experimental data, they give rise to a different mechanistic picture than envisaged previously. In contrast to earlier speculation, the activation barriers for the initial insertion steps of Fe+ into a C—H or C—C bond are found to be significantly below the Fe+ + C3H8 channel. The rate-determining steps for both, the C—C and the C—H bond activation branches of the [FeC3H8]+ potential-energy surface rather occur late on the respective reaction coordinates and are connected with saddle points of concerted rearrangement processes. The C—C bond activation, which leads to the exothermic reductive elimination of methane, occurs via the C—C inserted species and not as a side channel originating from a C—H inserted ion, as assumed hitherto. For the C—H bond-activation processes, which finally results in the exothermic expulsion of molecular hydrogen, two energetically similar reaction channels for an [1,2]-elimination exist. The results clearly show, that an [1,3]-H2-elimination mechanism cannot compete with the [1,2]-elimination paths, in line with the experimental findings. Overall, a lower energy demand for the reductive elimination of methane compared to the loss of H2 is obtained, straightforwardly explaining the preference of the former process observed experimentally.
Additional Material:
2 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19960790717
