2 research outputs found
Theoretical Investigation of the Gas-Phase Reaction of CrO<sup>+</sup> with Propane
Transition
metal oxide cations (e.g., MO<sup>+</sup>) have been
shown to oxidize small alkanes in the gas phase. The chromium oxide
cation is of particular interest because it is more reactive than
oxides of earlier transition metals but is more selective than oxides
of later transition metals. The reaction of CrO<sup>+</sup> with propane
has been shown to produce a number of products: propanol, propene,
ethene, and hydrogen. Few theoretical studies exist for reactions
of simple transition metal oxide cations with larger alkanes. We have
analyzed the potential energy surfaces associated with the reaction
of CrO<sup>+</sup> with propane using two DFT methods, B3LYP and M06-L.
Energetically viable reaction paths leading to each experimentally
observed product have been characterized. Each reaction path begins
with formation of a reactive intermediate in which either an α-
or β-hydrogen from propane is extracted by the oxygen atom of
CrO<sup>+</sup>. While pathways leading to formation of hydrogen and
ethene were found to occur on a single spin surface, energetically
viable pathways to forming propanol and propene require a transition
from the quartet spin surface to the sextet surface. The minimum-energy
crossing points between the quartet and sextet surfaces were found
to be well below the energy level of the reactants and structurally
resemble the initial reactive intermediates
Simple Mechanism for the Dimerization of Ethylene by Gas-Phase CrOH<sup>+</sup>
Dimerization of ethylene by gas-phase chromium hydroxide
(CrOH<sup>+</sup>) has been experimentally observed. Recent theoretical
work suggests the most likely mechanism associated with this process
involves formation of a metallacycle intermediate and involves two
spin-inversion processes. We propose a different mechanism that involves
the formation of a chromium-aqua complex. While the energetics of
this new mechanism are similar to previously proposed mechanisms,
all intermediates and transition states remain on the same spin surface
as both the reactants and products