An ortho-palladated dimethylbenzylamine complex as a highly efficient turnover catalyst for the decomposition of P=S insecticides. Mechanistic studies of the methanolysis of some P=S-containing phosphorothioate triesters

Article abstract of DOI:10.1039/b508917d

An ortho-palladated complex Pd(dmba)(py)(OTf) (9), or Pd(N,N- dimethylbenzylamine)(pyridine)-(trifluoromethanesulfonate), was synthesized and its solution properties in methanol studied as a function of _s ^spH. In neutral solution the triflate dissociates from the complex to give a dominant form Pd(dmba)(py)(HOCH₃), and in acid the pyridine dissociates to give Pyr-H⁺ and Pd(dmba)(HOCH₃)(HOCH ₃). Under basic conditions, Pd(dmba)(py)(HOCH₃) ionizes to give Pd(dmba)(py)(^-OCH₃) from which the pyridine can dissociate to yield a mixture of a bis-methoxy-bridged dimer (Pd(dmba)( ^-OCH₃))₂ (15-dimer), and its monomer Pd(dmba)(HOCH₃)-(^-OCH₃). Kinetic studies under buffered conditions reveal that 9 is an effective catalyst for the methanolysis of fenitrothion and other P=S pesticides. The active form of the catalyst is a basic one having one associated methoxide generated with an apparent _s^spK_a of 10.8. Analysis of the change in the UV/vis spectrum as a function of _s^spH generates a spectrophotometric _s^sK_a of 10.8 ±0.1. This catalytic system is shown to promote the methanolysis of fenitrothion (3), diazinon (4), quinalphos (5), coumaphos (10) and dichlofenthion (11) at 0.05 mol dm^-3 triethyl amine buffer, _s^spH 10.8, 25°C, under turnover conditions where the [phosphorothioate]/[9] ratio is 48.6, 13.4, 13.4, 18.6, and 48.6 respectively. In all cases, the products were derived from displacement of the leaving group by methoxide, the second-order turnover rate constants being 36.9, 0.45, 0.12, > 146.7 and 44.3 dm ³ mol^-1 s^-1 respectively. An associative mechanism for the catalyzed methanolysis of the P=S pesticides is proposed where a transiently coordinated S=P substrate is intramolecularly attacked by the Pd^II-coordinated methoxide. The Royal Society of Chemistry 2005.

Full text of DOI:10.1039/b508917d

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A R T I C L E
An ortho-palladated dimethylbenzylamine complex as a highly
=
efficient turnover catalyst for the decomposition of P S insecticides.
=
Mechanistic studies of the methanolysis of some P S-containing
phosphorothioate triesters†
Zhong-Lin Lu, Alexei A. Neverov and R. Stan Brown*
Department of Chemistry, Queen’s University, Kingston, Ontario, Canada K7L 3N6.
E-mail: rsbrown@chem.queensu.ca; Fax: 613-533-6669; Tel: 613-533-2400
Received 23rd June 2005, Accepted 25th July 2005
First published as an Advance Article on the web 15th August 2005
An ortho-palladated complex Pd(dmba)(py)(OTf) (9), or Pd(N,N-dimethylbenzylamine)(pyridine)-
(trifluoromethanesulfonate), was synthesized and its solution properties in methanol studied as a function of sspH.
In neutral solution the triflate dissociates from the complex to give a dominant form Pd(dmba)(py)(HOCH3), and in
acid the pyridine dissociates to give Pyr–H+ and Pd(dmba)(HOCH3)(HOCH3). Under basic conditions,
Pd(dmba)(py)(HOCH3) ionizes to give Pd(dmba)(py)(−OCH3) from which the pyridine can dissociate to yield a
mixture of a bis-methoxy-bridged dimer (Pd(dmba)(−OCH3))2 (15-dimer), and its monomer Pd(dmba)(HOCH3)-
(−OCH3). Kinetic studies under buffered conditions reveal that 9 is an effective catalyst for the methanolysis of
=
fenitrothion and other P S pesticides. The active form of the catalyst is a basic one having one associated methoxide
generated with an apparent sspKa of 10.8. Analysis of the change in the UV/vis spectrum as a function of sspH
generates a spectrophotometric sspKa of 10.8 0.1. This catalytic system is shown to promote the methanolysis of
fenitrothion (3), diazinon (◦4), quinalphos (5), coumaphos (10) and dichlofenthion (11) at 0.05 mol dm−3 triethyl
amine buffer, sspH 10.8, 25 C, under turnover conditions where the [phosphorothioate]/[9] ratio is 48.6, 13.4, 13.4,
18.6, and 48.6 respectively. In all cases, the products were derived from displacement of the leaving group by
methoxide, the second-order turnover rate constants being 36.9, 0.45, 0.12, >146.7 and 44.3 dm3 mol−1 s−1
=
respectively. An associative mechanism for the catalyzed methanolysis of the P S pesticides is proposed where a
II
=
transiently coordinated S P substrate is intramolecularly attacked by the Pd -coordinated methoxide.
As part of an ongoing program to provide effective methods
Introduction
for the destruction of OP-based pesticides and chemical war-
In a recent series of papers Kazankov, Ryabov and co-workers1
fare agents,2 we previously investigated La3+(−OCH3)-catalyzed
reported studies of metallacycles such as 1 (M = Pt, Pd; X = Cl;
methanolysis of phosphate triesters such as paraoxon (6) and
Z = pyridine, DMSO) and 2 (M = Pt, Pd; X = Cl; Z = pyridine),
and reported that the latter oximes are remarkably good catalysts
for the hydrolysis of sulfur-containing organophosphate (OP)
triesters of which the pesticides fenitrothion (3), diazinon (4)
and quinalphos (5) are but three examples.
its phosphorothioate analogue (7)2a–c as well as the propensity
of some aza complexes of Zn2+(−OCH3) and Cu2+(−OCH3) to
catalyze the methanolysis of 6 and 3.2d La3+, being a ‘hard’
metal ion in the Pearson ‘hard/soft’ sense,3 cannot promote the
=
methanolysis of the P S pesticides, but the somewhat ‘softer’
Zn2+ ion can, although not nearly as well as Cu2+.
Indeed, as little as 1 mM of the Cu2+(−OCH3) complex of 1,5,9-
triazacyclododecane (8, M = Cu), catalyzes4 the methanolysis
of 3 at near neutral sspH (8.75)5,6 with a t1/2 of ca. 57 s accounting
for an 8.4 × 108-fold acceleration relative to the background
reaction.
In an effort to ascertain whether the non-oxime metallacycles
(1) described by Ryabov, Kazankov and co-workers1 can pro-
† Electronic supplementary information (ESI) available: X-ray crystallo-
graphic analysis reports for Pd(dmba)(py)(Cl) and Pd(dmba)(py)(OTf).
See http://dx.doi.org/10.1039/b508917d
=
mote the methanolysis of P S pesticides as efficiently as does the
Cu2+(−OCH3) complex 8, we prepared the benzyldimethylamine
T h i s j o u r n a l i s
T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 5
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7
3 3 7 9
©

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pyridine trifluoromethanesulfonate palladacycle complex 9
(Pd(dmba)(py)(OTf)), and studied its catalysis of the methanol-
recrystallized from a mixture of hexanes and dichloromethane
to afford 120.0 mg of crystals, yield 92.3%.
IR (KBr, cm−1): 2916 (m), 1603 (s), 1448 (vs), 1306 (vs), 1261
(vs), 1158 (vs), 1029 (vs), 1017 (vs), 843 (m), 740 (m), 630 (m),
514 (m). Mp: 199 ◦C. 1H-NMR (ppm, 400 MHz, d4-methanol):
d 8.94 (d, J = 8.0 Hz, 2H), 8.15 (t, J = 8.0 Hz, 1H), 7.69 (m,
2H), 7.02 (m, 2H), 6.73 (t, J = 8.0 Hz, 1H), 5.92 (d, J = 8.0 Hz,
1H), 4.08 (s, 2H), 2.83 (s, 6H). 19F-NMR (ppm, 376.47 MHz,
d4-methanol): d 80.57. MS (FAB): m/z 319.09 (M − OTf). Anal.
calc. for C15H15N2F3O3PdS: C 38.60, H 3.24, N 6.00%. Found:
C 38.14, H 3.57, N 5.96%.
=
ysis of fenitrothion and the related P S pesticides 4, 5, 10
(coumaphos) and 11 (dichlofenthion). The following represents
our findings in this project.
(c) X-Ray crystal structure determination
Crystals of 9 and its chloride precursor suitable for diffraction
measurements were prepared by recrystallization from a mixture
of n-hexane and dichloromethane. A single crystal of each was
mounted on a glass fiber with grease and cooled to −93 ◦C in a
stream of nitrogen gas controlled with a Cryostream Controller
700. Data collection was performed on a Bruker SMART CCD
1000 X-ray diffractometer with graphite-monochromated Mo
˚
Ka radiation (k = 0.71073 A), operating at 50 kV and 30 mA
Experimental
over 2h ranges of ca. 4.60–56.62◦. No significant decay was
observed during the data collection.
(a) Materials and methods
Data were processed using the Bruker AXS Crystal Structure
Analysis Package, Version 5.10.10 Neutral atom scattering
factors were taken from Cromer and Waber.11a The raw intensity
data were integrated using the program SAINT-Plus, which
corrects for Lp and decay. Absorption corrections were applied
using the program SADABS.11b
Given in Table 1 are the structural data for the data collection
and refinement for 9 and its precursor chloride complex
Pd(dmba)(py)(Cl), which was obtained by the same procedure.
In Table 2 are presented selected bond lengths, bond angles and
torsional angles for the two complexes. An ORTEP diagram of
9 at the 50% probability level is given in Fig. 1. Full structural
details for each complex are given as ESI.†
Methanol (99.8% anhydrous), sodium methoxide (0.5 mol dm−3
solution in methanol) and silver triflate (AgOTf) and paraoxon
6 were purchased from Aldrich and used without fur-
ther purification. HClO4 (70% aqueous solution) was pur-
chased from BDH. Fenitrothion (3, O,O-dimethyl O-(3-
methyl-4-nitrophenyl) phosphorothioate), diazinon (4, O,O-
diethyl O-(2-isopropyl-4-methyl-6-pyrimidinyl) phosphoroth-
ioate) and quinalphos (5, O,O-diethyl O-(2-quinoxalyl) phos-
phorothioate) were gifts from Professor Erwin Buncel and
Professor Gary van Loon of this department. Phosphoroth-
ioate 7 was synthesized by a slight modification of the re-
ported procedure7 from 4-nitrophenylthiol. Coumaphos (10, O-
(3-chloro-4-methyl-2-oxo-2H-chromen-7-yl) O,O-diethyl phos-
phorothioate) and dichlofenthion (11, O,O-diethyl O-(2,4-
dichlorophenyl) phosphorothioate) were purchased from Chem
Service Inc.
CCDC reference numbers (CCDC 278462 and 278463). See
http://dx.doi.org/10.1039/b508917d for crystallographic data
in CIF or other electronic format.
Caution: all of the phosphorus substrates described herein are
acetylcholinesterase inhibitors: compounds 3, 4, 5, 10, and 11
have oral LD50 values of 250, 66, 62, 16, and 270 mg kg−1 in rats8
respectively.
1H NMR and 31P NMR spectra were determined at 400 MHz
and 161.97 MHz using a Bruker Avance-400 NMR spectrome-
ter. 1H NMR spectra were referenced to the CD2H peak of d4-
methanol appearing at d 3.31. 31P NMR spectra were referenced
to an external standard of 70% phosphoric acid in water, and
up-field chemical shifts are negative. Elemental analyses were
performed by Canadian Microanalytical Service Ltd., Delta,
British Columbia, Canada. Mass spectra were determined
using a VG Quattro mass spectrophotometer equipped with an
electrospray source. IR spectra were obtained on thin films or
NaBr pellets and melting points were measured on a Fisher-
Johns melting point apparatus.
Fig. 1 ORTEP presentation of the molecular structure of 9. Displace-
ment ellipsoids for non-H atoms are shown at the 50% probability level
and H atoms are represented by circles of arbitrary size.
(b) Preparation of Pd(dmba)(py)(OTf) complex (9)
Complex 9 was prepared from the monomeric complex
Pd(dmba)(py)(Cl) (dmba = N,N-dimethylbenzylamine), itself
being prepared according to the literature procedure9 and puri-
fied through recrystallization from a hexanes–CH2Cl2 mixture.
To a solution of 98.6 mg of the Pd(dmba)(py)(Cl) complex
(0.278 mmol) in dichloromethane (20 ml) was added solid
AgOTf (89.2 mg, 0.347 mmol). The mixture was stirred at room
temperature for 3 h and then filtered through Celite. The Celite
was washed with another 10 ml of dichloromethane and the
combined organic layers stripped of solvent by rotary evapora-
tion under reduced pressure. The pale white solid residue was
(d) Kinetic and titrimetric methods
The CH3OH2+ concentration was determined using a Radiome-
ter Vit 90 Autotitrator equipped with a Radiometer GK2322
combination (glass/calomel) electrode calibrated with Fisher
Certified Standard aqueous buffers (pH = 4.00 and 10.00)
s
as described in our recent papers.2,4,12,13 Values of pH were
s
calculated by subtracting a correction constant of −2.24 from
the experimental meter reading as reported by Bosch et al.6
3 3 8 0
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7

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Table 1 Experimental data for the X-ray diffraction study on complex 9 and its chloride precursor Pd(dmba)(py)(Cl)
Parameter
Pd(dmba)(py)(OTf) (9)
Pd(dmba)(py)(Cl)
Formula
C15H17F3N2O3PdS
468.77
180(2)
C14H17ClN2Pd
355.15
180(2)
Formula weight
T/K
˚
k/A
0.71073
0.71073
Space group
P21/c
Pbca
Crystal system
Monoclinic
9.1402(17)
12.351(2)
5.852(3)
Orthorhombic
9.5463(18)
16.258(4)
18.117(4)
90
˚
a/A
˚
b/A
˚
c/A
a/◦
b/◦
c /◦
90
97.942(3)
90
1772.3(6)
4
1.757
90
90
3
˚
V/A
2811.7(11)
8
1.678
Z
q/g cm−3
l/mm−1
1.211
1.493
F(000)
936
1424
Crystal size/mm
h range/◦
Index ranges
0.5 × 0.06 × 0.06
2.10–28.31
−10 ꢀ h ꢀ 12
−16 ꢀ k ꢀ 16
−20 ꢀ l ꢀ 20
11 759
0.5 × 0.2 × 0.1
2.25–28.28
−12 ꢀ h ꢀ 12
−19 ꢀ k ꢀ 21
−23 ꢀ l ꢀ 24
18 463
Reflections collected
Independent reflections
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2r(I)]
4005 (Rint = 0.0290)
4005/0/294
1.041
3377 (Rint = 0.0478)
3377/0/231
0.928
R1 = 0.0300, wR2 = 0.0601
R1 = 0.0329, wR2 = 0.0595
−3
˚
Largest diff. peak and hole/e A
0.685 and −0.645
0.984 and −0.630
◦
◦
˚
Table 2 Selected bond lengths (A), bond angles ( ) and torsion angles ( ) for Pd(dmba)(py)(OTf) (9) and Pd(dmba)(py)(Cl)
Parameter
Pd(dmba)(py)(OTf)
Pd(dmba)(py)(Cl)
Pd(1)–C(6)
Pd(1)–N(2)
Pd(1)–N(1)
Pd(1)–O(1) or Pd(1)–Cl(1)
1.958(3)
2.035(2)
2.075(2)
2.212(2)
1.987(3)
2.043(2)
2.082(2)
2.4312(9)
C(6)–Pd(1)–N(2)
C(6)–Pd(1)–N(1)
N(2)–Pd(1)–N(1)
C(6)–Pd(1)–O(1) or C(6)–Pd(1)–Cl(1)
N(2)–Pd(1)–O(1) or N(2)–Pd(1)–Cl(1)
N(1)–Pd(1)–O(1) or N(1)–Pd(1)–Cl(1)
C(6)–Pd(1)–N(2)–C(10)
N(1)–Pd(1)–N(2)–C(10)
Cl(1)–Pd(1)–N(2)–C(14) or O(1)–Pd(1)–N(2)–C(14)
Pd(1)–O(1)–S(1)–C(15)
92.50(10)
82.78(10)
175.20(9)
175.89(9)
89.22(8)
95.55(9)
70.0(2)
60.2(2
67.9(2)
122.4(2)
94.20(12)
81.95(12)
176.05(10)
175.51(9)
89.51(7)
94.30(7)
−55.4(3)
−68.5(3)
−51.0(2)
s
s
(i) Spectrophotometric titration. A stock solution was pre-
pared by dissolving 4.0 mg of 9 in 1.71 ml of anhydrous methanol
and a 0.025 ml aliquot of this was diluted to 2.5 ml through the
addition of a 1.0 mmol dm−3 LiClO4 in methanol solution such
that the final [9] = 5 × 10−5 mol dm−3. The sspH of the resulting
solution was adjusted by addition of aliquots of (0.125–1.25) ×
10−3 mol dm−3 solutions of NaOMe, the sspH measured and the
UV/visible spectra recorded from 220–450 nm.
duplicate solutions were prepared, one for pH measurements,
and the second portion being used for kinetics. In all cases, sspH
values measured before and after reaction were consistent to
within 0.1 units.
The pseudo-first-order rate constants (kobs) were evaluated by
fitting the absorbance vs. time traces to a standard exponential
model. The stock solution of the palladium complex (9) was
prepared in pure methanol at 1 × 10−3 mol dm−3. In order to
determine the kinetic order in [9], a series of kinetic runs was
s
s
undertaken at pH 11.54 (2,2,6,6-tetramethylpiperidine buffer)
(ii) Kinetics. The kinetics of methanolysis of 3 promoted
by [9] were monitored as a function of sspH by observing
the rate of appearance of 3-methyl-4-nitrophenol at 318 nm
or of 3-methyl-4-nitrophenolate at 404 nm using an OLIS-
modified Cary 17 UV/visible spectrophotometer. All reactions
using 2 × 10−5 mol dm−3 fenitrothion in the presence of varying
[complex] from (0.4 to 4) × 10−5 mol dm−3. The pseudo-first-
obs
max
order rate constants (k ) given in Table 3 were obtained by
extrapolating to a [buffer] = 0.0 mol dm−3 and when plotted
against [9] gave a straight line, the gradient of which was
taken as the second-order catalytic rate constant (ko2bs). The
sspH dependence of the catalytic rate constant was determined
were followed to at least three half-times at 25
0.1 ◦C
under buffered conditions. Buffers were prepared from N-
methylmorpholine (sspKa = 8.23), trimethylamine (sspKa = 9.60),
triethylamine (sspKa = 10.78), and 2,2,6,6-tetramethylpiperidine
(sspKa = 11.86). The total [buffer] varied between (1 and 3) ×
10−3 mol dm−3 and the buffers were partially neutralized with
70% HClO4. To avoid any chloride ion contamination from
the glass electrode that might affect the metal ion reactions,
obs
max
by obtaining the k pseudo-first-order rate constants for the
methanolysis of 2 × 10−5 mol dm−3 fenitrothion between sspH 8.2
and 12.2 in the presence of a single concentration of 9 (2.0 ×
10−5 mol dm−3). The k2obs second-order rate constants given in
obs
max
Table 4 and plotted in Fig. 2 were obtained as k /[9].
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7
3 3 8 1

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Table 3 Concentration dependence for the pseudo-first-order rate
constant of the methanolysis of 3 promoted by 9 and corrected
The kinetics of methanolysis of substrates 6 and 7 were
s
also studied at pH 10.80. The concentration of 9 for these
s
for buffer effects at [3] = 2.0 × 10−5 mol dm−3
,
sspH 11.54, 2,2,6,6-
determinations was set at (0.2 to 1) × 10−3 mol dm−3, substrate
6 was set at 2 × 10−5 mol dm−3 and substrate 7 at 4.03 ×
10−5 mol dm−3, respectively.
tetramethylpiperidine buffer, 25 ◦C
obs
max
[9]/mol dm−3 (× 105)
k
/s−1 a,b
(iii) NMR turnover experiments. Catalytic turnover of the
methanolysis of an excess of substrates 3, 4, 5, 10, and 11 relative
4.0
3.0
2.0
1.6
1.2
0.8
0.4
(1.23 0.01) × 10−1
(1.04 0.05) × 10−1
(6.80 0.08) × 10−2
(5.56 0.07) × 10−2
(4.93 0.07) × 10−2
(2.77 0.07) × 10−2
(8.73 0.66) × 10−3
1
s
to [9] was investigated using H and 31P NMR at pH 10.80
under buffered conditions. A typical experiment iss described
for diazinon. To 0.35 ml of triethylamine buffer (0.1 mol dm−3,
sspH 10.80) and 0.27 ml of d4-methanol (added as an NMR
lock signal) was added 0.070 ml of a stock solution of 4.0 ×
10−2 mol dm−3 diazinon (4) in methanol. To the resulting mixture
was added 0.020 ml of a 1.05 × 10−2 mol dm−3 stock solution of
9. At this point, the concentration of 4 was 3.9 × 10−3 mol dm−3
and that of 9 was 2.9 × 10−4 mol dm−3 ([4]/[9] = 13.4). The
kinetics were followed by determining the rate of loss of the
a Rate constants determined at three different [buffer] from (1–3) ×
10−3 mol dm−3, and extrapolated to zero [buffer]. b Errors are calculated
from the standard deviation of the mean.
Table 4 Observed maximal pseudo-first-order rate constants (kobs ) for
the methanolysis of 3 cat◦alyzed by 9 at [3] = 2.0 × 10−5 mol dm−3m,ax[9] =
2.0 × 10−5 mol dm−3, 25 C as a function of sspHa
1
diazinon H NMR signal at 6.82 ppm and the rate of increase
of the product 2-isopropyl-6-methylpyrimidin-4-olate signal at
6.10 ppm, the general time course for these being shown in Fig. 4.
Independent fitting of the two sets of intensity vs. time data to
a standard exponential model gave the pseudo-first-order rate
constant presented in Table 5. The completion of the reaction
was also confirmed by 31P NMR since the signal for diazinon 4
at d 60.8 ppm14 was completely replaced by that of the product
obs
max
sspH (amine buffer)
k
/s−1 b
8.22 (N-methylmorpholine)
8.54 (N-methylmorpholine)
9.05 (trimethylamine)
9.54 (trimethylamine)
10.23 (trimethylamine)
10.49 (triethylamine)
10.87 (triethylamine)
11.29 (triethylamine)
11.49 (2,2,6,6-tetrapiperidine)
11.91 (2,2,6,6-tetrapiperidine)
12.23 (2,2,6,6-tetrapiperidine)
(1.86 0.15) × 10−4
(4.48 0.23) × 10−4
(9.80 0.20) × 10−4
(3.21 0.15) × 10−3
(1.65 0.04) × 10−2
(2.09 0.05) × 10−2
(3.76 0.09) × 10−2
(6.86 0.07) × 10−2
(6.82 0.10) × 10−2
(7.99 0.32) × 10−2
(8.17 0.55) × 10−2
O,O-diethyl O-methyl phosphorothioate at d 69.70 ppm (lit.15
d
69.85).
obs
a Observed second-order rate constants (ko2bs) are computed as k /2 ×
max
10−5 mol dm−3 and are plotted in Fig. 3 against sspH. b Errors are
calculated from the standard deviation of the mean of duplicate runs.
Fig. 4 Turnover experiment for the methanolysis of diazinon 4
(3.9 × 10−3 mol dm−3) in the presence of 9 (2.9 × 10−4 mol dm−3),
CH3OH–CD3OD (3 : 2), 0.05 M TEA buffer (sspH = 10.80) monitored
by 1H NMR. Open circles (᭺) = disappearance of d 6.83 ppm signal of
4; filled circles (᭹) = appearance of d 6.10 ppm signal attributable to
2-isopropyl-6-methylpyrimidin-4-olate product.
NMR turnover experiments for the rate of methanolysis of 3
(stock solution 7.3 × 10−2 mol dm−3), 5 (stock solution 4.0 ×
10−2 mol dm−3), 10 (stock solution 2.8 × 10−2 mol dm−3), and
11 (stock solution 7.3 × 10−2 mol dm−3) promoted by 9 were
conducted in the same way as with 4 by injecting 70 ll of the
various stock solutions into buffered d4-methanol along with
10 ll (for 3, 10 and 11) or 20 ll (for 5) of the stock solution of 9.
The 1H and 31P NMR data for the substrates and corresponding
products are listed in Table 6, while the kinetic constants and
turnover numbers are listed in Table 5.
Fig. 2◦ Plot of kmax vs. [9] for the methanolysis of 3 (2.0 × 10−5 mol dm−3
)
at 25 C, buffer 2,2,6,6-tetrapiperidine (1–3) × 10−3 mol dm−3, extrap-
olated to zero [buffer], sspH 11.54. Maximal second-order rate constant
(km2 ax) for catalyzed reaction from the gradient of the plot is (3.30 0.11)
× 103 dm3 mol−1 s−1
.
Results
(a) Kinetics of methanolysis of 3
(i) Preliminary experiments. In preliminary experiments to
determine the propensity of 9 to catalyze the methanolysis of
fenitrothion 3, we attempted to use phenol buffers such as
pentafluorophenol (sspKa = 9.24),2 2,3,5-trichlorophenol (sspKa =
10.64)2b and 2,5-dichlorophenol (sspKa = 11.06),2b but each of
these exhibits strong inhibition of the catalysis presumably
through binding to the metal complex. Amine buffers such as N-
methylmorpholine, trimethylamine, triethylamine and 2,2,6,6-
tetramethylpiperidine (sspKa values given in the Experimental
Fig. 3 Plot of log ko2bs vs. sspH for the methanolysis of 3 at [3] = 2.0 ×
10−5 mol dm−3, catalyzed by 9 ([9] = 2.0 × 10−5 mol dm−3) at 25 ◦C. The
line through the data computed from the fit to eqn. (2), gives a km2 ax of
4.13 × 103 dm3 mol−1s−1, and a kinetic sspKa of 10.87.
3 3 8 2
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7

View Article Online
Table 5 1H NMR turnover conditional rate constants for the methanolysis of different phosphorothioate esters catalyzed by 9 at 0.05 mol dm−3
TEA, pH 10.8, 25 ◦
C
Phosphorothioate esters/mol dm−3
TON
k
obs/s−1
ko2bs/dm3 mol−1 s−1
3
7.3 × 10−3
3.9 × 10−3
3.9 × 10−3
2.8 × 10−3
7.3 × 10−3
48.6
13.4
13.4
18.6
48.6
(5.35 0.6) × 10−3
(1.30 0.1) × 10−4
(3.53 0.3) × 10−5
>2.2 × 10−2
36.9a
0.45b
4
5
10
11
0.12b
>146.7a
44.3a
(6.65 0.3) × 10−3
a [9] = 1.5 × 10−4 mol dm−3
.
b [9] = 2.9 × 10−4 mol dm−3
.
Table 6 NMR spectral data of the turnover experiment for the methanolysis of different phosphorothioate esters catalyzed by 9 at 0.05 M TEA,
CH3OH–CD3OD (3 : 2), pH 10.80, 25 ◦
C
1H NMR (aromatic protons), d/ppm
31P NMR, d/ppm
Substrate
Substrate
Product
Substrate
Product
3
8.04 (1H), 7.21 (2H)
6.82 (1H)
8.69 (1H), 8.12 (1H), 7.98 (1H), 7.85 (2H)
7.85 (1H), 7.26 (2H)
7.54 (1H), 7.35 (2H)
7.98 (1H), 6.58 (2H)
6.10 (1H)
8.20 (1H), 7.84 (1H), 7.59 (1H), 7.37 (2H)
7.58 (1H), 6.79 (1H), 6.63 (1H)
7.27 (1H), 7.07 (1H), 6.84 (1H)
66.18
60.76
61.57
62.73
63.29
73.29a
69.70b
69.70b
69.67b
69.60b
4
5
10
11
a Authentic product O,O,O-trimethyl phosphorothioate reported15 31P NMR d 73.40 ppm. b Authentic product O,O-diethyl O-methyl phosphoroth-
ioate reported15 31P NMR d 69.85 ppm.
section) were found to inhibit the catalysis far less, but to
obtain the accurate kobs constants at [buffer] = 0 mol dm−3,
the kinetics were always measured at 1, 2 and 3 mmol dm−3
buffer concentrations and the buffer-independent catalytic rate
The appearance of the plot suggests a catalytic process where
a basic form of the catalyst is active as in eqn. (1), from which
can be derived the kinetic expression given in eqn. (2). NLLSQ
fitting of the data gives a km2 ax of 4.13 × 103 dm3 mol−1 s−1 and a
kinetic sspKa of 10.8 0.1, the best fit line through the data also
being shown in Fig. 3.
obs
constant (k ) was determined either from linear extrapolations
max
(at lower pH) or curve fittings (at higher pH) of the plots of kobs
vs. [buffer] to zero buffer.
Methanol stock solutions of 9 in the absence of buffer are
stable for at least 10 d. The stability of 9 was also checked
(1)
s
at pH 10.54 and the same activity was demonstrated over
s
at least 500 min, which is a time period sufficient for any of
ko2bs = km2 ax (10−pKa /(10−pH + 10−pKa ))
(2)
s
the kinetic experiments described here. Above pH 11.00, the
s
The catalysis of the methanolysis of 3 by palladacycle 9 is such
that one can calculate that a 1 mmol dm−3 solution of 9, at sspH
values of 9.05 and 12.3, gives t1/2 values for methanolysis of 3 of
13.0 s and 166 ms respectively.
complex exhibits some ageing process which diminished its
activity, but we did not investigate this process in any detail
other than to determine the kinetics under conditions where
the ageing was minimal. The catalyzed reaction is also inhibited
by the presence of Cl−. We started the catalytic study with the
chloride complex Pd(dmba)(py)(Cl), but it immediately became
clear that at higher concentrations of catalyst there was an
inhibitory effect suggestive of dissociated Cl− attaching itself
(b) Spectrophotometric titration of 9
s
As a function of increasing pH, the UV spectrum of 9 in
methanol has an absorbance sincrease at 252 nm, a decrease
at 231 nm and an isosbestic point at 238 nm. The change in
absorbance at 231 nm of a 5 × 10−5 mol dm−3 solution of 9 in
II
to the Pd preventing access of the methoxide or substrate, both
of which are required for the catalysis. Further experiments (not
shown) using 1 × 10−5 mol dm−3 of fenitrothion in the presence
of 2 × 10−4 mol dm−3 Pd(dmba)(py)(OTf) and 1 × 10−4 mol dm−3
NaOCH3 (sspH 11.50) with varying [n-Bu4Cl] showed asymptotic
reduction in the kobs vs. [Cl−] plots suggestive of a one site
inhibition with Kinhibition = (1.1 0.1) × 10 −3 mol dm−3. Owing to
the inhibitory effect of Cl−, all of the following catalytic studies
used Pd(dmba)(py)(OTf) (9).
methanol as a function of sspH was fit to eqn. (3) to generate a
s
s
spectrophotometric pKa of 10.8
0.1, an Abs0 of 0.649 and
a DAbs of −0.056. The dashed line through the data given in
Fig. 5 is constructed on the basis of this fit.
Abs = Abs0 + DAbs(10−pKa /(10−pH + 10−pKa ))
(3)
(c) NMR turnover experiments for the methanolysis of 3, 4, 5,
12 and 13 promoted by 9
(ii) Dependence of the kinetic values for the methanolysis
s
of 3 on [9] and pH. The concentration dependence for the
s
methanolysis of 3 was initially measured at sspH 11.54 (2,2,6,6-
NMR experiments were performed in a 2 : 3 CD3OD–CH3OH
solution containing triethylamine buffer (0.05 mol dm−3) at
sspH 10.80, with [9] = (1.5–2.9) × 10−4 mol dm−3 and the
concentrations of substrates 3, 4, 5, 10, and 11 being (2.8–7.3) ×
10−3 mol dm−3, affording [phosphorothioate]/[catalyst] ratios
of 48.6, 13.4, 13.4, 18.6, and 48.6 respectively (see Table 5).
For the slower substrates, the higher concentration of catalyst
was used. The rates of the reactions were monitored by 1H
NMR by observing the changes in the peak intensities of the
appropriate aromatic protons. The completions of the reactions
were also verified by 31P NMR which showed that each of the
obs
max
tetramethylpiperidine buffer) with the k values being given
in Table 3 and plotted in Fig. 2. The plot is linear, indicative
of the kinetically active monomeric form of 9. The second rate
constant (ko2bs) is evaluated as the gradient of the linear plot,
(3.30 0.11) × 103 dm3 mol−1 s−1.
obs
max
The pseudo-first-order rate constants (k ) for the methanol-
ysis of 3 promoted by a 2.0 × 10−5 mol dm−3 solution of 9 at 11
different sspH values between sspH 8.22 and 12.23 are presented in
Table 4. The corresponding second-order rate constants, ko2bs, are
obs
obtained as k /(2 × 10−5 mol dm−3) and are plotted in Fig. 3.
max
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7
3 3 8 3

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was said to be the catalytically active form in promoting the
hydrolysis of p-nitrophenyl acetate16 for which the catalytic
rate constants plateaued above the pKa of 4.18. On the other
hand, in a later study of the hydrolysis of N-t-BOC–methionine
p-nitrophenyl ester promoted by 12, it was reported1b that
there was a pronounced [−OH] dependent increase in the kcat
values above pH 7.5. Since the proposed mechanism proceeded
via the S-coordinated palladacycle 13, it was suggested that
either the pKa of the Pd(OH2) was shifted markedly upward
when coordinated to S, or that the reaction involved attack of
external HO−.
Fig. 5 Plot of the absorbance of 9 at 231 nm ([9] = 5.0 × 10−5 mol dm−3
,
1 mmol dm−3 LiClO4 in methanol solution, T = 25 ◦C) as a function of
sspH showing a spectrophotometric sspKa of 10.8 0.1. Dashed line from
fit of the data to eqn. (3).
starting phosphorothioate materials had been replaced by a
single methoxylated product.
Listed in Table 6 are the 1H NMR starting material and
product signals used to determine the kinetics of decomposition
of the various substrates under turnover conditions. In all cases,
the intensity vs. time data adhered to good first-order behaviour
for at least three half-times, and standard fitting of the data to an
exponential model yielded the pseudo-first-order rate constants
given in Table 5 along with the turnover numbers.
The behaviour of
9
and its chloride precursor
Pd(dmba)(py)(Cl) in methanol solution has both similarities to
and differences from the situation in water.1b,9,16 We assume that
the triflate of 9 is completely dissociated in methanol, to give
the methanol analogue 12–HOCH3. Furthermore, we assume
that the Cl of Pd(dmba)(py)(Cl) is somewhat less dissociated in
methanol to form 12–HOCH3 due to the fact there is a common
ion rate suppression of the latter’s catalysis of the methanolysis
of fenitrothion. However, we have been unable to detect an
=
(d) Kinetics of methanolysis of P O substrates paraoxon (6)
and O,O-diethyl S-p-nitrophenyl phosphorothioate 7
=
The methanolyses of these P O substrates promoted by 9
were very slow, compared with the above P S counterparts.
ionization event attributable to a low sspKa for the conversion of
=
II
II
s
s
Pd –HOCH3 to Pd –−OCH3. For example, the measured pH
The absorbance vs. time trace for the reaction of paraoxon at
sspH = 10.80, with [9] = 2.0 × 10−3 mol dm−3 and [6] = 4.02 ×
10−5 mol dm−3, showed no change after 33 h. Assuming that
less than 5% of the reaction would have been observable, we
set an upper limit for the kobs of 5.3 × 10−6 s−1. Methanolysis
of the S-p-nitrophenyl phosphorothioate derivative 7 (2.0 ×
10−5 mol dm−3) at sspH = 10.80 promoted by 2.0 × 10−4 mol dm−3
9 gave an easily monitored reaction, the kobs being 3.83 × 10−5 s−1.
Relative to the background methoxide reaction at sspH = 10.80,2b
the acceleration is an unimpressive 236-fold.
values of solutions comprising (0.5 to 5) × 10−4 mol dm−3
9
in methanol are all above neutrality (8.38), being 9.83–10.55
indicating that there is no ionization of PdII –HOCH3 having a
s
s
low pKa. Additionally, the potentiometric titration profile for
a solution of 5.0 × 10−4 mol dm−3 9 in methanol, containing a
s
sufficient amount of added HClO4 that the starting pH was
3, shows no detectable ionizable protons (outside thosse for the
strong acid region) having a sspKa value of between 3 and 10.
Some indication of the solution behaviour of 9/12 as a
s
s
1
function of pH is obtained from H NMR studies of a 6.2 ×
10−3 mol dm−3 solution of 9 in d4-methanol under three sets
of conditions: (a) immediately after formulation; (b) after the
addition of 1 equiv. of neat HClO4; and, (c) after the addition
of NaOCH3 to the solution from (a). In Scheme 1 are shown
the various species supported by the solution NMR spectra
under the above conditions. We have used the characteristic
peaks of the pyridine resonances and those of the benzylic
CH2 group since they are visibly sensitive to changes in the
Discussion
(a) Structure of 9 and its chloride precursor Pd(dmba)(py)(Cl)
The solid state structure of 9 is shown in Fig. 1 with selected
structural details, bond lengths and angles being given in Tables 1
and 2 along with those for the chloride precursor whose structure
is not shown here but is given in the ESI.† Both structures
are very similar to those reported for the analogous Pd(py)Cl
oximes9 in terms of the overall square planar geometry and
1
coordination environment. The H NMR spectrum of the first
solution gives evidence of a single observable material that we
assign as palladacycle 12–HOCH3. As is the reported case in
water,1,9 under acidic conditions some pyridine dissociates from
II
the bond lengths and angles about the Pd . The triflate in 9 is
singly-coordinated to the Pd trans to the aryl–Pd with the C(6)–
Pd(1)–O(1) angle being 175.89(9)◦. The torsional angle between
the pyridine plane and the palladium C1 plane is 24.6◦. The
trifluoromethyl group is tilted toward the pyridine ring with a
torsion angle C(15)–S(1)–O(1)–Pd(1) of −122.36(17)◦.
1
the complex (ca. 55% observed by H NMR), leaving two Pd-
containing species in solution as well as some visible precipitate.
The species in solution are 12–HOCH3 (ca. 45%, calculated
from integration of phenyl and pyridine protons) along with
32% of the palladacycle 14 without an associated pyridine [1H
NMR (d, ppm): ca. 7.00, 4H; 3.98, 2H; 2.80 6H]. The latter
has a limited solubility in methanol at these concentrations
producing some precipitate, but when the isolated precipitate
is redissolved in fresh d4-methanol, the product proved to be the
same palladacycle without pyridine (14).
(b) Solution behaviour of 9 as a function of sspH
The aqueous solution behaviour of Pd(dmba)(py)(Cl) is re-
ported to involve complete replacement of the Cl with H2O,
the latter reported to have a pKa of 4.18 in water9,16 to
yield the hydroxo-coordinated compound, Pd(dmba)(py)(−OH)
(12). At pH values lower than 3, and greater than 10, the
pyridine dissociates from the palladium, presumably due to its
protonation at low pH, and through replacement by HO− at
high pH. In the intermediate pH range, Pd(dmba)(py)(−OH)
A second solution containing 7.2 × 103 mol dm−3 of 9
was treated with 0.5 equiv. and then a second 0.5 equiv.
of NaOMe. After the first addition of base, the 1H NMR
spectrum gave evidence of the presence of 12–HOCH3 (signals
3 3 8 4
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7

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Scheme 1
slightly broadened) along with some dissociated pyridine, with (d) Turnover experiments
considerably broadened resonances, and an equivalent amount
of palladacycle having a benzylic resonance at ca. 3.86 ppm, and
having two distinct N–CH3 resonances at 2.73 and 2.78 ppm.
Further addition of base intensified the signals of free pyridine
and the latter palladacycle which is probably a composite of at
least two forms: 15–(HOCH3)(−OCH3), which itself is in equi-
librium with a 15-dimer, as in Scheme 1. The 12–−OCH3 form
must be in rapid equilibrium with 12–HOCH3, but dissociation
of pyridine from the former to give 15–(HOCH3)(−OCH3) must
be rather slow on the NMR timescale. Since the palladacycle
benzylic CH2 resonances and two N–CH3 resonances are fairly
sharp, the dominant equilibrium structure probably comprises
the 15-dimer in syn and anti forms. It is of note that the dimer
of the chloride complex (Pd(dmba)Cl)2, when dissolved in d4-
methanol containing an excess of NaOCH3, produces a 1H
NMR spectrum which is virtually identical to the spectrum of
what we propose as the 15-dimer including the two different
intensity N–CH3 resonances, thus supporting the syn and anti
dimers as being the source of the latter resonances.
=
The methanolysis of five P S pesticides (fenitrothion (3), di-
azinon (4), quinalphos (5), coumaphos (10) and dichlofenthion
(11)), catalyzed by 9 under turnover conditions was investigated
by 1H and 31P NMR under buffered conditions (0.05 M
triethylamine, sspH 10.80, ambient temperature) in d4-methanol.
The particular sspH value and buffer conditions were chosen to
s
match the kinetic and spectroscopic pKa values of 10.8, but
s
the conditional rate constants determined from solutions under
buffered NMR conditions that are reported in Table 5 are lower
than we previously obtained under spectroscopic conditions
extrapolated to zero [buffer]. By way of comparison, the ko2bs for
the catalyzed methanolysis of 3 under spectroscopic conditions
at sspH 10.8 is ca. 1880 dm3 mol−1 s−1, while that obtained from
the NMR experiment is some 50-fold lower at 36.9 dm3 mol−1 s−1.
The drop in reactivity is due to the large concentration of
inhibitory buffer in the NMR experiment, which is required to
control the sspH, as well as the larger concentrations of substrate
and catalyst which can alter the solution properties. Neverthe-
less, these are still very effective catalytic systems for the decom-
position of these classes of pesticides, capable of forming non-
toxic, methoxylated products under turnover conditions with
good first-order kinetics and without any product inhibition.
All of the above indicates that there is no observable dis-
sociation of a proton from the metal-coordinated methanol at
low sspH. In fact, the spectrophotometric titration of a solution
comprising 5 × 10−5 mol dm−3 of 9 in methanol between sspH 10
s
s
and 13 indicates a spectrophotometric pKa of 10.85, a value
(e) Conclusions and postulated reaction mechanism
consistent with the kinetic sspKa discussed below.
Given in Scheme 2 is a predicted mechanism for the reaction
which is consistent with all the available data. The available
information suggests that palladacycle 9, when introduced into
methanol solution predominantly exists as a mono-methanol
complex (Pd(dmba)(py)(HOCH3), 12–HOCH3 in Schemes 1
and 2). The catalytically active form is a basic one (12–−OCH3
and/or 15) generated by the ionization of a Pd-bound methanol
having an sspKa of 10.8. The mechanism in Scheme 2 is proposed
(c) Kinetics of catalyzed methanolysis of 3 promoted by 9
The kobs vs. concentration plot for the methanolysis of 3 catalyzed
s
s
by varying [9] at pH 11.4 is linear and the gradient is defined
as ko2bs. The second-order catalytic rate constants at other pH
s
s
values listed in Table 4 were computed from the kobs values
obtained at a single concentration of catalyst, and extrapolated
obs
max
obs
max
II
II
to zero buffer concentration to give k , with k /(catalyst) =
to be an associative one (typical for Pt and Pd complexes where
ko2bs. The log of the ko2bs values, when plotted against pH as
in Fig. 3, and fit to the expression in eqn. (2) gives a skinetic
sspKa of 10.87 and a maximal second-order rate constant of
4.13 × 103 dm3 mol−1 s−1. This value can be compared with
the second-order rate constant for the same process catalyzed
by 8:Cu2+(−OCH3) of 12.2 dm3 mol−1 s−1.4 While 9 is apparently
more active than 8:Cu2+(−OCH3) by about 300-fold, the latter,
steric factors are not large)17 involving pre-equilibrium binding
s
=
of the P S to form a transient five-coordinate complex (16) that
undergoes intramolecular attack of the coordinated methoxide
on P. Whether the reaction involves a stepwise mechanism,
through a five-coordinate phosphorane intermediate or via
concerted displacement of the leaving group, cannot be ascer-
tained on the basis of the available evidence, although we note
that the La3+- and Zn2+-catalyzed methanolysis of phosphate
and phosphorothioate triesters was recently shown2b to involve
concerted displacement of aryloxy leaving groups. Turnover of
s
s
owing to its lower pKa, is about equally as effective at that
sspH. For example, solutions of 1 mmol dm−3 in each catalyst,
8:Cu2+ or 9, when compared at the same pH value of 8.75
s
s
=
catalyze the methanolysis of 3 with t1/2 values of 57 and 19 s,
corresponding to an acceleration over the background reaction
of 8.4 × 108-fold and 4.9 × 109-fold respectively.
the catalyst requires displacement of the P S product from 17,
again probably through an associative process with solvent,
II
followed by deprotonation of the Pd -coordinated methanol.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7
3 3 8 5

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Scheme 2
The palladacycle system studied here has some interesting
(c) G. M. Kazankov, V. S. Sergeeva, E. N. Efremenko, L. Alexandrova,
S. D. Varfolomeev and A. D. Ryabov, Angew. Chem., Int. Ed., 2000,
39, 3117; (d) G. M. Kazankov, V. S. Sergeeva, A. A. Borisenko, A. I.
Zatsman and A. D. Ryabov, Russ. Chem. Bull. Int. Ed., 2001, 50,
1844.
2 (a) J. S. Tsang, A. A. Neverov and R. S. Brown, J. Am. Chem. Soc,
2003, 125, 7602; (b) T. Liu, A. A. Neverov, J. S. W. Tsang and R. S.
Brown, Org. Biomol. Chem., 2005, 3, 1525; (c) J. S. W. Tsang, A. A.
Neverov and R. S. Brown, Org. Biomol. Chem., 2004, 2, 3457; (d) W.
Desloges, A. A Neverov and R. S. Brown, Inorg Chem., 2004, 43,
6752.
3 M. B. Smith and J. March, Advanced Organic Chemistry, Wiley
Interscience, New York, 2001, 5th edn., pp. 338–342 and refs. cited
therein.
4 A. A. Neverov and R. S. Brown, Org. Biomol. Chem., 2004, 2,
2245.
5 For the designation of pH in non-aqueous solvents we use the forms
described by Bosch and co-workers6 based on the recommendations
of the IUPAC, in Compendium of Analytical Nomenclature: Definitive
Rules 1997, Blackwell, Oxford, UK, 1998, 3rd edn. If one calibrates
the measuring electrode with aqueous buffers and then measures
the pH of an aqueous buffer solution, the term wwpH is used; if the
electrode is calibrated in water and the ‘pH’ of the neat buffered
methanol solution then measured, the term swpH is used; and if the
electrode is calibrated in the same solvent and the ‘pH’ reading is
made, then the term sspH is used.
6 E. Bosch, F. Rived, M. Roses and J. Sales, J. Chem. Soc., Perkin
Trans. 2, 1999, 1953; F. Rived, M. Rose´s and E. Bosch, Anal. Chim.
Acta, 1998, 374, 309; E. Bosch, P. Bou, H. Allemann and M. Rose´s,
Anal. Chem., 1996, 68, 3651; I. Canals, J. A. Portal, E. Bosch and M.
Rose´s, Anal. Chem., 2000, 72, 1802.
properties that might make it a method of choice for the
II
=
decomposition of P S pesticides on larger scale. Since Pd is
considered ‘soft’ in the Pearson ‘hard/soft’ sense,3 the system is
=
selective for P S-containing organophosphates as is evidenced
=
by the fact that it is ineffective for a typical P O substrate,
paraoxon. It does show some reactivity toward O,O-diethyl S-p-
nitrophenyl phosphorothioate (k2 = 0.38 dm mol−1 s−1), but this
is less than exhibited by our previously reported2b La3+ dimer
or Zn2+:[1,5,9-triazacyclododecane] catalysts, for which the rate
constants are 12.4 and 0.84 dm mol−1 s−1 respectively. Since
the reaction medium is methanol the hydrophobic organophos-
II
phates and these Pd catalysts are far more soluble than they
are in aqueous solution. Finally, because the reaction is actually
a transesterification reaction and not a hydrolysis reaction, the
final triester product is neutral and is thus substantially non-
II
inhibitory. While it is true that the Pd system here is more
expensive on a per mole basis than the previous La3+ catalysts
or the triazacyclodecane Zn2+(−OCH3) or Cu2+(−OCH3) systems
reported earlier,2,4 the covalent attachment of the metal to the
aryl group and the fact that the catalytic cycle does not involve
II
a Pd to Pd0 redox change suggest that it should be possible
to create polymer-bound or solid-supported18 versions of the
catalytic system that can be recovered for re-use. All of the above
suggest that further investigation of this class of catalysts should
=
generate practical methods for the destruction of P S pesticides.
7 S.-B. Hong and F. M. Raushel, Biochemistry, 1996, 35, 10 904.
8 The Merck Index, Merck & Co. Inc., Rahway, NJ, USA, 1989;
Pesticide and Metabolite Standard Catalogue, Chem Services Inc.,
West Chester, Pennsylvania, 2001–2004.
9 A. Ryabov, V. A. Polyakov and A. K. Yatsimirsky, J. Chem. Soc.,
Perkin Trans. 2, 1983, 1503.
10 Bruker AXS Crystal Structure Analysis Package, Version 5.10
(SMART NT (Version 5.053), SAINT-Plus (Version 6.01),
SHELXTL (Version 5.1)), Bruker AXS Inc., Madison, WI, USA,
1999.
11 (a) D. T. Cromer and J. T. Waber, International Tables for X-Ray
Crystallography, Kynoch Press, Birmingham, UK, 1974, vol. 4,
Table 2.2 A; (b) G. M. Sheldrick, SADABS, Program for area detector
adsorption correction, Institute for Inorganic Chemistry, University
of Go¨ttingen, Germany, 1996.
Acknowledgements
The authors gratefully acknowledge the financial assistance
of the Natural Sciences and Engineering Research Council of
Canada, Queen’s University and the United States Department
of the Army, Army Research Office, Grant No. W911NF-04-1-
0057 and the Defense Threat Reduction Agency, Joint Science
and Technology Office (06012384BP).19 In addition, we are
grateful to Dr Riu-Yao Wang of the Queen’s Chemistry X-Ray
Structure Determination Laboratory for structure determina-
tions of Pd(dmba)(py)(Cl) and Pd(dmba)(py)(OTf).
References and notes
1 (a) A. D. Ryabov, G. M. Kazankov, S. A. Kurzeev, P. V. Samuleev and
V. A. Polyakov, Inorg. Chim. Acta, 1998, 280, 57; (b) S. A. Kurzeev,
G. M. Kazankov and A. D. Ryabov, Inorg. Chim. Acta, 2000, 305, 1;
12 A. A. Neverov, G. Gibson and R. S. Brown, Inorg. Chem., 2003, 42,
228.
13 G. Gibson, A. A. Neverov and R. S. Brown, Can. J. Chem., 2003, 81,
495.
3 3 8 6
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7

View Article Online
14 R. D. Mortimer and B. A. Dawson, J. Agric. Food Chem., 1991, 39,
911.
18 D. E. Bergbreiter, Chem. Rev., 2002, 102, 3345; D. E. Bergbreiter,
P. L. Osburn, A. Wilson and E. M. Sink, J. Am. Chem. Soc.,
2000, 122, 9058; H. P. Dijkstra, M. Q. Slagt, A. McDonald, C. A.
Kruithof, R. Kreiter, A. M. Mills, M. Lutz, A. L. Speck, W. Klopper,
G. P. M. Van Klink and G. Van Koten, J. Catal., 2005, 229,
322.
15 S. Ryu, J. A. Jackson and C. M. Thompson, J. Org. Chem., 1991, 56,
4999.
16 A. K. Yatsimirsky, G. M. Kazankov and A. D. Ryabov, J. Chem.
Soc., Perkin Trans. 2., 1992, 1295.
17 M. Schmu¨lling, A. D. Ryabov and R. van Eldik, J. Chem. Soc., Dalton
Trans., 1994, 1257; H. Holmann, B. Hellquist and R. van Eldik, Inorg
Chim. Acta, 1991, 18, 25.
19 The content of the information does not necessarily reflect the
position or the policy of the federal government, and no official
endorsement should be inferred.
O r g . B i o m o l . C h e m . , 2 0 0 5 , 3 , 3 3 7 9 – 3 3 8 7
3 3 8 7