3 research outputs found
Analysis of Hydrogen Atom Abstraction from Ethylbenzene by an Fe<sup>V</sup>O(TAML) Complex
It was shown previously
(<i>Chem. Eur. J</i>. <b>2015</b>, 21, 1803) that
the rate of hydrogen atom abstraction, <i>k</i>, from ethylbenzene
(EB) by TAML complex [Fe<sup>V</sup>(O)ÂB*]<sup>−</sup> (<b>1</b>) in acetonitrile exhibits a large kinetic isotope effect
(KIE ∼ 26) in the experimental range 233–243 K. The
extrapolated tangents of lnÂ(<i>k</i>/<i>T</i>)
vs <i>T</i><sup>–1</sup> plots for EB-<i>d</i><sub>10</sub> and EB gave a large, negative intercept difference,
IntÂ(EB) – IntÂ(EB-<i>d</i><sub>10</sub>) = −34.5
J mol<sup>–1</sup> K<sup>–1</sup> for <i>T</i><sup>–1</sup> → 0, which is shown to be exclusively
due to an isotopic mass effect on tunneling. A decomposition of the
apparent activation barrier in terms of electronic, ZPE, thermal enthalpic,
tunneling, and entropic contributions is presented. Tunneling corrections
to Δ<i>H</i><sup>⧧</sup> and Δ<i>S</i><sup>⧧</sup> are estimated to be large. The DFT
prediction, using functional B3LYP and basis set 6-311G, for the electronic
contribution is significantly smaller than suggested by experiment.
However, the agreement improves after correction for the basis set
superposition error in the interaction between EB and <b>1</b>. The kinetic model employed has been used to predict rate constants
outside the experimental temperature range, which enabled us to compare
the reactivity of <b>1</b> with those of other hydrogen abstracting
complexes
Revised Mechanism for a Ruthenium-Catalyzed Coupling of Aldehyde and Terminal Alkyne
Ruthenium
catalysts have been found to be of great use for many
kinds of reactions. Understanding the details of the catalytic cycle
allows to not only rationalize experimental results but also to improve
upon reactions. Herein, we present a detailed computational study
of a ruthenium-catalyzed coupling between a terminal alkyne and an
aldehyde. The reaction under examination facilitates novel access
to olefins with the concurrent loss of a single carbon as carbon monoxide.
The reaction was first developed in 2009, but the tentative mechanism
initially proposed was proven to be contradictory to some experimental
data obtained since then. Using a combination of computational investigations
and isotope-labeling experiments, several potential mechanisms have
been studied. In contrast to the [2+2] cycloaddition mechanism suggested
for similar catalysts, we propose a new consensus pathway that proceeds
through the formation of a ruthenium–vinylidene complex that
undergoes an aldol-type reaction with the aldehyde to yield the product
olefins. Computational insights into the influence of different reagents
used to optimize reaction conditions and the intricacies of decarbonylation
of a Ru–CO complex affecting catalyst turnover are highlighted
TAML Activator/Peroxide-Catalyzed Facile Oxidative Degradation of the Persistent Explosives Trinitrotoluene and Trinitrobenzene in Micellar Solutions
TAML activators are well-known for
their ability to activate hydrogen
peroxide to oxidize persistent pollutants in water. The trinitroaromatic
explosives, 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitrobenzene
(TNB), are often encountered together as persistent, toxic pollutants.
Here we show that an aggressive TAML activator with peroxides boosts
the effectiveness of the known surfactant/base promoted breakdown
of TNT and transforms the surfactant induced nondestructive binding
of base to TNB into an extensive multistep degradation process. Treatment
of basic cationic surfactant solutions of either TNT or TNB with TAML/peroxide
(hydrogen peroxide and <i>tert</i>-butylhydroperoxide, TBHP)
gave complete pollutant removal for both in <1 h with >75% of
the
nitrogen and ≥20% of the carbon converted to nitrite/nitrate
and formate, respectively. For TNT, the TAML advantage is to advance
the process toward mineralization. Basic surfactant solutions of TNB
gave the colored solutions typical of known Meisenheimer complexes
which did not progress to degradation products over many hours. However
with added TAML activator, the color was bleached quickly and the
TNB starting compound was degraded extensively toward minerals within
an hour. A slower surfactant-free TAML activator/peroxide process
also degrades TNT/TNB effectively. Thus, TAML/peroxide amplification
effectively advances TNT and TNB water treatment giving reason to
explore the environmental applicability of the approach