5 research outputs found
Stereochemical Inversion of Phosphonothioate Methanolysis by La(III) and Zn(II): Mechanistic Implications for the Degradation of Organophosphate Neurotoxins
The utility of phosphonothioate methanolysis to degrade
organophosphate neurotoxins has prompted the stereochemical investigation
of this useful transformation. The methanolysis of enantiomerically
pure <i>O</i>,<i>S</i>-diethyl phenylphosphonothioate
(<b>5</b>) was studied both in the presence and in the absence
of metal ions known to catalyze the phosphonothioate → phosphonate
transformation. This report outlines the syntheses of enantiomerically
pure <b>5</b> and its methanolysis product <i>O</i>-ethyl <i>O</i>-methyl phenylphosphonate (<b>7</b>). Compound <b>7</b> results from exclusive P–S scission
of <b>5</b>, which is the desired mode of phosphonothioate methanolysis
(<i>E</i><sub>a</sub> = 14.5 ± 0.5 kcal/mol). The stereochemical
analysis of the phosphonothioate methanolysis was done for the first
time with β-cyclodextrin, and it shows complete inversion on
the phosphorus center upon methoxide displacement of ethanethiolate.
The presence of LaÂ(III) or ZnÂ(II) complexes do not alter this S<sub>N</sub>2-like substitution which sheds new light on the mechanism
of methanolysis of phosphonothioates
Stereochemical Inversion of Phosphonothioate Methanolysis by La(III) and Zn(II): Mechanistic Implications for the Degradation of Organophosphate Neurotoxins
The utility of phosphonothioate methanolysis to degrade
organophosphate neurotoxins has prompted the stereochemical investigation
of this useful transformation. The methanolysis of enantiomerically
pure <i>O</i>,<i>S</i>-diethyl phenylphosphonothioate
(<b>5</b>) was studied both in the presence and in the absence
of metal ions known to catalyze the phosphonothioate → phosphonate
transformation. This report outlines the syntheses of enantiomerically
pure <b>5</b> and its methanolysis product <i>O</i>-ethyl <i>O</i>-methyl phenylphosphonate (<b>7</b>). Compound <b>7</b> results from exclusive P–S scission
of <b>5</b>, which is the desired mode of phosphonothioate methanolysis
(<i>E</i><sub>a</sub> = 14.5 ± 0.5 kcal/mol). The stereochemical
analysis of the phosphonothioate methanolysis was done for the first
time with β-cyclodextrin, and it shows complete inversion on
the phosphorus center upon methoxide displacement of ethanethiolate.
The presence of LaÂ(III) or ZnÂ(II) complexes do not alter this S<sub>N</sub>2-like substitution which sheds new light on the mechanism
of methanolysis of phosphonothioates
Aqueous Chemistry of the Metallocene [Cp<sub>2</sub>MoCl<sub>2</sub>]BF<sub>4</sub>: Evidence of Autocatalytic Molybdenum(V) Reduction in Water
The
aqueous chemistry of the air-stable MoÂ(V) metallocene [Cp<sub>2</sub>MoCl<sub>2</sub>]ÂBF<sub>4</sub> (<b>1</b>) yields an
unexpected autocatalytic reduction when water is added to an acetonitrile
solution of <b>1</b>. While <b>1</b> yields the expected
stable Cp–Mo ligation and rapid chloride hydrolysis in water,
a MoÂ(V) → MoÂ(IV) reduction to the metallocene Cp<sub>2</sub>MoCl<sub>2</sub> (<b>2</b>) was evident. Under acidic conditions
(pH ∼2) or trace amounts of water this reduction was slow enough
to be monitored spectroscopically, and it is shown to be autocatalytic
in aqueous <b>2</b>. No reaction occurs when <b>1</b> and <b>2</b> are in the dichloride form in acetonitrile (i.e., no water).
It is hypothesized that the added water serves two roles. First it
initially reduces a small population of <b>1</b> to <b>2</b>, and then as the aquated MoÂ(IV) metallocene, it catalyzes the reduction
of the remaining MoÂ(V) in water. This is the first aqueous investigation
of the MoÂ(V) metallocene, and it shows a novel and unprecedented autocatalytic
reduction that is mediated by water
Phosphonothioate Hydrolysis Turnover by Cp<sub>2</sub>MoCl<sub>2</sub> and Silver Nanoparticles
The metallocene bisÂ(cyclopentadienyl)ÂmolybdenumÂ(IV) dichloride
(Cp<sub>2</sub>MoCl<sub>2</sub>; Cp = η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) is the first organometallic compound to promote the
hydrolysis of phosphonothioates with selective P–S scission
in a stoichiometric fashion. This report shows that silver nanoparticles
capped with borohydride ions promote turnover in this hydrolytic process,
as indicated by <sup>31</sup>P NMR studies on the reaction of <i>O</i>,<i>S</i>-diethyl phenylphosphonothioate (DEPP)
with Cp<sub>2</sub>MoCl<sub>2</sub> (pH 7). This is the first example
of the joint use of nanoparticles and molybdenum metallocenes to promote
phosphonothioate hydrolysis. Initial results indicate the turnover
may be due to free Ag<sup>+</sup>(aq) ions present in the solution
that arise either from the slow dissolution of the nanoparticles or
from interactions with the Ag nanoparticle surface
Phosphonothioate Hydrolysis Turnover by Cp<sub>2</sub>MoCl<sub>2</sub> and Silver Nanoparticles
The metallocene bisÂ(cyclopentadienyl)ÂmolybdenumÂ(IV) dichloride
(Cp<sub>2</sub>MoCl<sub>2</sub>; Cp = η<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>) is the first organometallic compound to promote the
hydrolysis of phosphonothioates with selective P–S scission
in a stoichiometric fashion. This report shows that silver nanoparticles
capped with borohydride ions promote turnover in this hydrolytic process,
as indicated by <sup>31</sup>P NMR studies on the reaction of <i>O</i>,<i>S</i>-diethyl phenylphosphonothioate (DEPP)
with Cp<sub>2</sub>MoCl<sub>2</sub> (pH 7). This is the first example
of the joint use of nanoparticles and molybdenum metallocenes to promote
phosphonothioate hydrolysis. Initial results indicate the turnover
may be due to free Ag<sup>+</sup>(aq) ions present in the solution
that arise either from the slow dissolution of the nanoparticles or
from interactions with the Ag nanoparticle surface