We present an overview of the phosphonothioate hydrolytic chemistry
promoted by molybdenum organometallics as well as new results on solvent
effects. The metallocene bis(η
$ ^{5}$
-cyclopentadienyl)
molybdenum(IV) dichloride (Cp
$_{2}$
MoCl
$_{2}$
C=η
$^{5}$
-C
$_{5}$
H
$_{5}$
) and the
methylated analog, (CH
$_{3}$
Cp)
$_{2}$
MoCl
$_{2}$
hydrolyzes the compound O,S-diethyl phenylphosphonothioate
(DEPP) whose core functional group mimics the neurotoxin VX. This is one of the
few examples of phosphonothioate degradation yielding exclusively the desired
P-S bond scission under mild aqueous conditions (pH 7,
25°C). The solvent composition affects the
monomer-dimer equilibrium of aquated molybdocenes which in turn dictates the
rate of DEPP hydrolysis. Kinetic and equilibrium results are presented to show
that the monomer is the active species. Moreover, photoelectron spectroscopy
data indicate that while the methylated
(CH
$_{3}$
Cp)
$_{2}$
MoCl
$_{2}$
has a higher monomer concentration compared to
Cp
$_{2}$
MoCl
$_{2}$
, the former has a
diminished electrophilic molybdenum center that is key in phosphonothioate
hydrolysis.
