Aqueous Phase Organometallic Catalysis Using (MeCp)2Mo(OH) (H2O+. Intramolecular Attack of Hydroxide on Organic Substrates

Article abstract of DOI:10.1021/om0342558

The hydrolysis of esters and difunctional ethers catalyzed by Cp′₂Mo(OH)(H₂O)⁺ (1) (Cp′ = η⁵-C₅H₄CH₃) and the stoichiometric oxidation of CO to CO₂ in the presence of 1 are described. These reactions, combined with the previously reported nitrile hydrations and phosphate esters hydrolyses catalyzed by 1, demonstrate that 1 is an effective homogeneous catalyst for hydration, hydrolysis, and oxidation reactions in aqueous solution under mild conditions (pH ～7, ～80°C). Each reaction is proposed to proceed by intramolecular attack of the hydroxide ligand on a bound substrate. The intramolecular nature of the reaction is supported by the ester hydrolysis activation parameters (ΔH? = 5.9 ± 0.7 kcal/mol and ΔS? = -48 ± 9 eu), the lack of H/D exchange, and the significant increase (10⁶-10⁸) in the rate of hydrolysis over uncatalyzed hydrolysis.

Full text of DOI:10.1021/om0342558

1738
Organometallics 2004, 23, 1738-1746
Aqu eou s P h a se Or ga n om eta llic Ca ta lysis Usin g
(MeCp )2Mo(OH)(H2O)+. In tr a m olecu la r Atta ck of
Hyd r oxid e on Or ga n ic Su bstr a tes
Kerry L. Breno, Michael D. Pluth, Christopher W. Landorf, and David R. Tyler*
Department of Chemistry, University of Oregon, Eugene, Oregon 97403
Received October 22, 2003
The hydrolysis of esters and difunctional ethers catalyzed by Cp′2Mo(OH)(H2O)+ (1) (Cp′
) η5-C5H4CH3) and the stoichiometric oxidation of CO to CO2 in the presence of 1 are
described. These reactions, combined with the previously reported nitrile hydrations and
phosphate esters hydrolyses catalyzed by 1, demonstrate that 1 is an effective homogeneous
catalyst for hydration, hydrolysis, and oxidation reactions in aqueous solution under mild
conditions (pH ∼7, ∼80 °C). Each reaction is proposed to proceed by intramolecular attack
of the hydroxide ligand on a bound substrate. The intramolecular nature of the reaction is
supported by the ester hydrolysis activation parameters (∆Hq ) 5.9 ( 0.7 kcal/mol and ∆Sq
) -48 ( 9 eu), the lack of H/D exchange, and the significant increase (106-108) in the rate
of hydrolysis over uncatalyzed hydrolysis.
Sch em e 1. In tr a m olecu la r Atta ck of a Hyd r oxy
Liga n d on a Bou n d Nitr ile to F or m a n Am id a te
In ter m ed ia te Lea d in g to Hyd r a tion of th e Nitr ile
In tr od u ction
Aqueous phase homogeneous catalysis is a burgeoning
field, and the investigation of new, water-soluble cata-
lysts is an active area of research.1 As part of our
development of new, water-soluble catalysts, we are
exploring the aqueous chemistry of the Cp′2Mo(OH)-
(H2O)+ (1) (Cp′ ) η5-C5H4CH3) complex.2-6 In a recent
paper, we reported that this complex was a catalyst for
nitrile hydration reactions in aqueous solution (eq 1).3
tramolecular attack of hydroxide on a bound ester ligand
is a key step in the cis-Cu(H2O)2L2+-catalyzed hydrolysis
of carboxylic esters and phosphate diesters.10-13 Like-
wise, intramolecular hydroxide attack is a proposed step
in the hydrolysis of phosphate diesters with the Ni-
(tren)(OH)(OH2)+ catalyst.12-14 These reports prompted
our investigation into whether intramolecular attack of
the hydroxide ligand in the Cp′2Mo(OH)(H2O)+ complex
on a bound substrate was a general reaction and, if so,
if it could be exploited in other catalytic cycles. In this
paper we report the results of our investigation.
A key step in the proposed mechanism was the in-
tramolecular attack of a coordinated hydroxy ligand on
a bound nitrile substrate (Scheme 1). This step has a
precedent in the hydration of acetonitrile to acetamide
catalyzed by [Co(cyclen)(OH2)2]3+, which was shown to
proceed by a route involving intramolecular hydroxide
attack on a coordinated nitrile.7 The intramolecular
attack of hydroxide on bound substrates in Co(III) aquo/
hydroxy complexes is not limited to the hydration of
nitriles but extends to the hydrolysis of phosphate
esters, amides, and amino acid esters, as well.8-10
Similar intramolecular reactions with various sub-
strates occur in other systems. For example, the in-
Exp er im en ta l Section
Gen er a l P r oced u r es. All experiments were performed
under a nitrogen atmosphere using standard glovebox tech-
niques or a Schlenk line. All liquid substrates were degassed
using three freeze-pump-thaw cycles, except for H2O and
D2O, which were purged with nitrogen for at least 30 min prior
to use. All NMR samples were prepared in an inert atmos-
phere and were sealed with septum caps or J -Young screw-
caps. Reactions were brought to the required temperature
* Corresponding author. E-mail: dtyler@uoregon.edu.
(1) Cornils, B.; Hermann, W. A. Aqueous-Phase Organometallic
Catalysis: Concepts and Applications; Wiley-VCH: Weinheim, 1998.
(2) Balzarek, C.; Weakley, T. J . R.; Kuo, L. Y.; Tyler, D. R.
Organometallics 2000, 19, 2927-2931.
(3) Breno, K. L.; Pluth, M. D.; Tyler, D. R. Organometallics 2003,
22, 1203-1211.
(4) Breno, K. L.; Tyler, D. R. Organometallics 2001, 20, 3864-3868.
(5) Balzarek, C.; Tyler, D. R. Angew. Chem., Int. Ed. 1999, 38, 2406-
2408.
(8) Kim, J . H.; Chin, J . J . Am. Chem. Soc. 1992, 114, 9792-9795.
(9) Sutton, P. A.; Buckingham, D. A. Acc. Chem. Res. 1987, 20, 357-
364.
(10) Chin, J . Acc. Chem. Res. 1991, 24, 145-152.
(11) Chin, J .; J ubian, V. Chem. Commun. 1989, 839-841.
(12) Morrow, J . R.; Trogler, W. C. Inorg. Chem. 1988, 27, 3387-
3394.
(6) Balzarek, C.; Weakley, T. J . R.; Tyler, D. R. J . Am. Chem. Soc.
2000, 122, 9427-9434.
(7) Kim, J . H.; Britten, J .; Chin, J . J . Am. Chem. Soc. 1993, 115,
3618-3622.
(13) Morrow, J . R.; Trogler, W. C. Inorg. Chem. 1989, 28, 2330-
2333.
(14) De Rosch, M. A.; Trogler, W. C. Inorg. Chem. 1990, 29, 2409-
2416.
10.1021/om0342558 CCC: $27.50 © 2004 American Chemical Society
Publication on Web 03/19/2004

Catalysis Using (MeCp)2Mo(OH)(H2O)+
Organometallics, Vol. 23, No. 8, 2004 1739
using an oil bath. 1H, 2H, and 13C NMR spectra were measured
A catalyst stock solution was prepared by adding [Cp′2Mo-
(µ-OH)2MoCp′2][OTs-]2 (0.1128 g, 127 µmol) to 25 mL of D2O.
2-Methoxyacetonitrile (100 µL,1.34 mmol) was then added to
500 µL (2.55 µmol) of the stock solution and sealed in a screw-
cap NMR tube. The resulting solution turned a light pink color.
The sample was heated at 85 °C for 7 days in an oil bath. The
1H NMR resonances (D2O) before heating were at δ 4.41 (s,
2H, CH3OCH2CN) and 3.50 (s, 3H, CH3OCH2CN). During
heating, the following 1H NMR resonances (D2O) for 2-meth-
oxyacetamide appeared: δ 4.22 (s, 2H, CH3OCH2CONH2) and
3.43 (s, 3H, CH3OCH2CONH2). In addition, methanol (δ 3.35,
s, 3H), glycolic acid (δ 3.99, s, 2H), and an unidentified peak
at δ 3.86 (s) were detected. After heating, only a slight pink
coloration remained in the sample. The kinetics of the reaction
were modeled by GIT.15 A minimum of three reproducible trials
were collected for rate data.
1
2
on a Varian Inova 300 (299.95 MHz for H, 46.04 MHz for H,
and 75.42 MHz for 13C). IR spectra were measured on a Nicolet
Magna IR 530 spectrometer. An Orion model 230 pH meter
with a Corning NMR Micro Combo pH electrode was used to
take pH readings, and all pD values reported herein are
uncorrected. Mass spectra were recorded from an Agilent 1100
series LC/MS with an electrospray head. Gas chromatography
data were recorded using a 100 µL sample loop (Alltech) on a
model 1022 Perkin-Elmer autosystem gas chromotograph with
a 6 ft Alltech Carbosphere 80/100 1/8 in. stainless steel column
using helium as the carrier gas.
Ma ter ia ls. All substrates were used without purification
except for acetone (Aldrich 99.5+%), which was dried and
distilled with type 4A molecular sieves (Fischer), and aceto-
nitrile (Fischer Scientific 99.9%), which was dried and distilled
over CaH2. H2O and D2O were degassed with scrubbed
nitrogen for at least 30 min. D2O (99.9% D) and CD3C(O)CD3
(99.9% D) were obtained from Cambridge Isotope Laboratory.
Carbon monoxide (chemically pure) was obtained from Air
Liquid. All remaining materials were obtained from Aldrich.
The dimer [Cp′2Mo(µ-OH)2MoCp′2][OTs]2 was prepared as
described previously.5
Ethyl ether (100 µL, 963 µmol) was added to 1 mL (5.10
µmol of [Cp′2Mo(µ-OH)2MoCp′2][OTs-]2) of the stock solution
described above in an NMR tube. The sample was heated to
75 °C and monitored by NMR spectroscopy for a week. There
were no detectable changes in the sample.
Oxid a tion of Ca r bon Mon oxid e. Distilled water (or alter-
natively D2O) was added to 0.0450 g of [Cp′2Mo(µ-OH)2MoCp′2]-
[OTs-]2 (50.0 µmol) in a 5 mL volumetric flask in the glovebox.
This solution was transferred to a Fisher-Porter bottle and
subsequently removed from the inert atmosphere. The bottle
was charged with 41 psi CO and heated in an oil bath at 81-
85 °C for 21 h. During heating, the solution changed from a
dark brown-green to a bright yellow. An aliquot of the solution
was evaporated to yield a yellow-orange solid. IR (KBr): 3087,
2006, 1631, 1486, 1456, 1382, 1184, 1039, 1012, 814, 691, and
570 cm-1. MS (m/z+, relative intensity): 285.0 (100%) and
738.0 (8%), corresponding to Cp′2Mo(CO)H+ (2) and the cluster
2[Cp′2Mo(CO)H]+[OTs]-. The isotope patterns of the two ions
seen in mass spectroscopy are consistent with the structures
proposed above. 1H NMR(300 MHz, d6-acetone): δ 7.68 (d, 2H,
J ) 4.05 Hz, o-Ar S3OC6H4CH3), 7.36 (d, 2H, J ) 3.90 Hz, m-Ar
S3OC6H4CH3), 5.54 (m, 4H, J ) 5.6 Hz, Cp′), 5.44 (m, 4H, J )
5.6 Hz, Cp′), 2.39 (s, 3H, -CH3, S3OC6H4CH3), -8.09 (s, 1H,
Mo-H, Cp′2Mo(CO)H). Two hours after the completion of
heating, the pH of the solution was 3.90; after 125 h, the pH
of the solution had risen to 5.56.
Ca r boxylic Ester Hyd r olysis. The hydrolysis of ethyl
acetate is used as a representative procedure for the hydrolysis
of carboxylic esters. Experimental details for the hydrolysis
of other carboxylic esters can be found in the Supporting
Information. A minimum of three reproducible trials were
collected for rate data. [Cp′2Mo(µ-OH)2MoCp′2][OTs-]2 (0.0125
g, 14.1 µmol) and ethyl acetate (30 µL, 308 µmol) were added
to 1.10 mL of D2O. The resulting solution was bright green in
color and was heated at 80 °C for 17 h. In the first NMR
spectrum, taken before heating, traces of ethanol were detected
in the sample and these resonances increased in intensity
1
throughout the heating. H NMR (300 MHz, D2O, pD ) 3.7):
δ 4.13 (q, 2H, J ) 7.2 Hz CH3CH2(O)COCH3), 2.08 (s, 3H, CH3-
CH2(O)COCH3), 1.23 (t, 3H, J ) 7.2 Hz CH3CH2(O)COCH3),
3.65 (q, 2H, J ) 5.7 Hz CH3CH2OH), and 1.18 (t, 3H, J ) 6.3
Hz CH3CH2OH). For the kinetic studies, the above procedure
was repeated with and without buffer and monitored for over
800 h. For the buffered sample, [Cp′2Mo(µ-OH)2MoCp′2][OTs-]2
(0.00217 g, 2.45 µmol), ethyl acetate (5 µL, 46.9 µmol), and
hemi-sodium morpholinosulfonic acid (NaMOPS; 0.0217 g, 49.3
µmol) were added to 1.10 mL of D2O.
In a separate reaction, the headspace gas was analyzed to
determine the gaseous products of the reaction of 1 with CO.
[Cp′2Mo(µ-OH)2MoCp′2][OTs-]2 (0.1003 g, 113 µmol) was added
to 5.0 mL of H2O (0.28 mol) in the glovebox. This solution was
transferred to a Fisher-Porter bottle and then removed from
the glovebox. The bottle was charged with 40 psi CO and
heated in an oil bath at 82 °C for 20 h. The reaction was
allowed to equilibrate to room temperature for 30 min (while
being stirred vigorously) before GC analysis of the gas in the
headspace of the reaction vessel. The gases in the headspace
were sampled six times at different pressures by GC and
compared to the calibration curve determined for CO2. The
total amount of CO2 calculated to be in the gas phase of the
reaction was 198 ( 8 µmol or 87 ( 4% of the total CO2
predicted by the proposed equation (eq 7, Results).
Nitr ile Hyd r a tion . The hydration of acetonitrile is pre-
sented here as a representative procedure for the hydration
of nitriles. (See ref 3 for more complete experimental notes on
nitrile hydration.) [Cp′2Mo(µ-OH)2MoCp′2][OTs-]2 (0.0407 g,
45.9 µmol) was added to 5 mL of D2O, and then a 750 µL
aliquot of this solution (containing 12.78 µmol of total mono-
meric molybdenum complex) was added to 100 µL of acetoni-
trile (1.91 mmol). The resulting solution, which immediately
turned pink, was flame sealed while frozen in liquid nitrogen.
The sample was heated at 75 °C for 9 days in an oil bath.
1
Before heating, the H NMR (D2O) resonance of the substrate
was at δ 2.08 (s, 3H, CH3CN); after heating for 9 days, a new
resonance appeared at 1.98 (s, 3H, CH3CONH2). After heating
for 9 days, the 13C NMR (D2O) showed four resonances at δ
177.3 (s, CH3CONH2), 119.2 (s, CH3CN), 21.4 (s, CH3CONH2),
and 1.0 (CH3CN). After 30 days of heating, only the 13C
resonances at δ 177.3 and 21.4 remained.
In h ibition a n d Com p etitive Rea ction s. A study of
reaction rates as a function of metal complex concentration
was not possible with the above reactions due to the presence
of interfering inhibition or competition reactions. The hydra-
tion of nitriles is inhibited by the amide hydration product.3
In addition, the ester (or ether) hydrolysis reaction is competi-
tive with H/D exchange of the alcohol product and inhibited
by acid coordination to the catalyst.5 Thus, changing the
Eth er Hyd r olysis. Ethyl vinyl ether (1.5 mL, 16 mmol) was
reacted with 103 mg (116 µmol) of 1 in 10 mL of H2O in a
Schlenk flask. The flask was heated to 80 °C for 8 h. The
resulting solution was then washed with CDCl3 and extracted.
The extract was examined by NMR. The products of the
1
reaction extracted were ethanol and acetaldehyde. H NMR-
(300 MHz, CDCl3): δ 3.65 (q, 2H, J ) 5.7 Hz CH3CH2OH),
1.18 (t, 3H, J ) 6.3 Hz CH3CH2OH), and 2.20 (t, 3H, CH3C-
(O)H). A minimum of three reproducible trials were collected
for rate data.
(15) (a) Stabler R. N.; Chesick, J . Int. J . Kinet. 1978, 10, 461. (b)
McKinney, R. J .; Weigert F. J . Quantum Chemistry Program Ex-
change, Program # QCMPO22. (c) Weigert, F. J . Comput. Chem. 1987,
11, 273.

1740 Organometallics, Vol. 23, No. 8, 2004
Breno et al.
F igu r e 1. 1H NMR spectra of ethyl acetate hydrolysis. The initial spectrum is shown at the bottom with increasing time
shown vertically. Resonances of ethyl acetate are marked “a”, ethanol “b”, and acetic acid “c.” The * resonances are attributed
to the catalyst.
amount of catalyst in solution changed the rate of the inhibit-
ing/competing reactions and complicated the catalyst depen-
dence.
Resu lts
Ca r boxylic Ester Hyd r olysis. Simple unactivated
carboxylic esters were hydrolyzed to their respective
alcohols and carboxylic acids using catalyst 1 in aqueous
solution (eq 2). As an example of this reactivity, the
hydrolysis of ethyl acetate to ethyl alcohol and acetic
acid was monitored by NMR spectroscopy, and the
results are shown in Figure 1. The figure shows the
disappearance of the ethyl acetate resonances at 4.13,
2.08, and 1.23 ppm and the commensurate increase in
the ethyl alcohol (3.65 and 1.18 ppm) and acetic acid
(2.05 ppm) resonances. The product assignments were
confirmed by comparison to NMR samples of authentic
compounds in D2O.
F igu r e 2. Disappearance of ethyl acetate and appearance
of ethanol in the hydrolysis of ethyl acetate with catalyst
1 at 65 °C. The hydrolysis reaction (buffered to pH 7.1) is
shown with triangles. The unbuffered hydrolysis reaction
is shown with circles. The curves are exponential fits of
the concentration vs time data.
Ta ble 1. Ra tes of Eth yl Aceta te Hyd r olysis a t
Va r iou s Tem p er a tu r es, p H 7.1
During the course of the reaction, the color of the
solution changed from green-brown to bright green. In
addition, the pD over the first 24 h of the reaction
decreased to pD 3.7, consistent with the color change
in the catalyst solution. (Solutions of the catalyst are
brown at neutral pH but green when acidic.) The
pseudo-first-order rate constant for hydrolysis was (4.3
( 0.2) × 10-6 s-1 at 65 °C. However, the reaction was
inhibited by the drop in pH as the acetic acid formed.
With the addition of the noncoordinating buffer Na-
MOPS, the pH of the reaction mixture remained 7.1 over
the course of the reaction. Under these conditions, the
reaction was not inhibited, and the carboxylic ester
hydrolysis pseudo-first-order rate constant was (7.6 (
0.9) × 10-6 s-1 (65 °C, pH 7.1), as obtained from an
exponential decay fit of the data shown in Figure 2. This
rate constant indicates a substantial increase (∼106) in
the rate of hydrolysis compared to that for ethyl acetate
in the absence of catalyst at neutral pH.16
initial rate
temp (°C)
kobs (10-5 s-1
)
k (10-3 M-1 s-1
)
(10-3 M/h)
94
74
70
66
23
2.2 ( 0.2
1.0 ( 0.1
0.79 ( 0.09
0.76 ( 0.10
0.20 ( 0.07
4.8 ( 0.5
2.1 ( 0.2
1.7 ( 0.2
1.6 ( 0.2
0.43 ( 0.15
3.6 ( 0.4
1.6 ( 0.2
1.3 ( 0.1
1.2 ( 0.2
0.34 ( 0.1
The rates of ethyl acetate hydrolysis with catalyst 1
at neutral pD were evaluated at various temperatures
between 23 and 95 °C. The results are shown in Table
1. In this table, kobs is the pseudo-first-order rate
constant for hydrolysis. The second-order rate constant
is given by k.
The Eyring plot for these data is shown in Figure 3,
from which ∆Hq ) 5.9 ( 0.7 kcal/mol and ∆Sq ) -48 (
9 eu were determined. (The large negative activation
entropy is indicative of a constrained transition state
and will be discussed in terms of the proposed mecha-
nism of the reaction.) As mentioned, ethyl acetate is not
the only carboxylic ester to be hydrolyzed with catalyst
1. The hydrolyses of other esters such as butyl butyrate,
(16) Schmeer, G.; Sturm, P. Phys. Chem. 1999, 1, 1025-1030.

Catalysis Using (MeCp)2Mo(OH)(H2O)+
Organometallics, Vol. 23, No. 8, 2004 1741
hydrolyzed at 75 °C using 1 as a catalyst according to
the reactions shown in Scheme 2.3 Methanol and glycolic
acid were detected as products by NMR, as authenti-
cated by additions of pure compound to the reaction
mixture. Because glycolic acid and methanol are prod-
ucts of ether hydrolysis and nitrile hydration, it is
evident that both reactions proceed with catalyst 1. The
kinetics of the reaction were modeled by GIT4 using eqs
3-6. The rate constant of ether hydrolysis, kapp, was
determined from the modeling to be 3.75 × 10-3 M-1
s-1
.
kapp
catalyst + 2-methoxyacetonitrile
8
catalyst + methanol + 2-hydroxyacetonitrile (3)
k4
98
F igu r e 3. Eyring plot for the hydrolysis of ethyl acetate
catalyzed by Cp′2MoOH(OH2)+. Error bars represent one
sigma.
catalyst + 2-hydroxyacetonitrile
catalyst + 2-hydroxyacetamide (4)
k5
Sch em e 2. Hyd r olysis of 2-Meth oxya ceton itr ile
P r om oted by Ca ta lyst 1
2-hydroxyacetamide
98 glycolic acid + NH3 (5)
k2
catalyst + 2-hydroxyacetamide
98
inhibition product (6)
Unactivated ethers did not reveal any reactivity detect-
able by NMR at 75 °C over the course of 7 days, and it
is concluded that unactivated ethers such as diethyl
ether do not hydrolyze under the mild conditions
presented here. This observation is consistent with the
fact that catalyst 1 and THF can be mixed in a solution
without hydrolysis of the solvent or a change in the
catalyst.
Nitr ile Hyd r a tion . Our previous work3 showed that
1 is a catalyst for the hydration of nitriles to their
corresponding amides without subsequent hydrolysis to
the carboxylic acids. For example, acetonitrile was
hydrated to acetamide, but no acetic acid was detected.3
To probe the generality of this result, a variety of
monofunctional and bifunctional nitriles were hydrated
with catalyst 1. For convenience in discussing these
results in the context of a generalized mechanism,
selected results are presented again in Table 2.
norbornenyl acetate, vinyl acetate, and methyl cyanoace-
tate were followed by 1H and/or 13C NMR spectroscopy.
In each case, the products of hydrolysis, the respective
acids and alcohols, were observed and confirmed by the
addition of authentic samples (see Supporting Informa-
tion). The bidentate coordination of acetate to the Cp′2-
Mo2+ unit was observed by ES-MS in the hydrolysis of
norbornenyl acetate. The parent peak at 321 m/z is
attributed to species 3. This finding has mechanistic
significance because the metal-coordinated acetate prod-
uct is observed in both cobalt- and copper-catalyzed
hydrolysis reactions.11
Oxid a tion of Ca r bon Mon oxid e. Catalyst 1 under-
goes a stoichiometric reaction with CO in aqueous
solution to form CO2, as detected and quantified by gas
chromatography. The experimental CO2 yield was cal-
culated to be 87 ( 4% based on the stoichiometry in eq
7. (The remaining CO2 is likely dissolved in solution and
accounts for the increase in the pH over time after the
solution is vented in a glovebox (see Experimental
Section).) Initially, the solution of 1 was brownish-green,
but during the reaction the solution became bright
Eth er Hyd r olysis. The initial investigation of ethers
began with unsaturated ethers. It was observed that,
in aqueous solutions of 1, vinyl ethyl ether hydrolyzed
to form ethanol and acetaldehyde. The products were
identified by extraction with CDCl3 and subsequent
comparison of their 1H NMR spectra with authentic
samples. The substituted ether 2-methoxyacetonitrile

1742 Organometallics, Vol. 23, No. 8, 2004
Ta ble 2. Hyd r a tion of Nitr iles w ith th e [Cp ′2Mo(OH)(OH2)]+ Ca ta lyst
Breno et al.
substrate
(M)
[1]
(M)
k2 (10-6
temp
(°C)
initial rate
substrate
acetonitrile
acrylonitrile
benzonitrile
3-bromopropionitrile
4-cyanopyridine
3-hydroxypropionitrile
isobutyronitrile
M-1 s-1
)
(10-3 mol product/L‚h)
0.91
0.72
0.89
1.09
0.33
2.43
1.87
2.23
0.010
0.010
0.009
0.009
0.009
0.009
0.009
0.009
3.05
2.32
0.20
1.42
7.44
14.2
2.38
3.67
82
75
85
90
90
90
85
85
8.75
13.1
33.6
15.2
6.29
329
22.8
256
2-methoxyacetonitrile
yellow. The yellow solid was isolated, and spectroscopic
analysis showed it to be [Cp′2Mo(CO)H][OTs] (2). The
nonmethylated [Cp2Mo(CO)H]+ complex is well known,
and the spectroscopic data are essentially identical.17-20
The NMR showed that the molybdocene unit is intact
with resonances at 5.54 and 5.44 for the bound cyclo-
strated the stability and utility of water-soluble molyb-
docene hydroxides in the catalytic hydration reactions
of nitriles.3 The results reported here extend these
earlier studies to include the hydration, hydrolysis, and
oxidation reactions of other substrates in aqueous
solution. One of the most interesting features in these
reactions is the role of the hydroxide ligand, which is
shown below to be involved in intramolecular reactions
with the bound substrates.
Th e Ca ta lyst. Prior work demonstrated that, in
aqueous solution, complex 4 is in equilibrium with
catalyst 1 (eq 8; Keq ) 7.9 × 10-2 M at 23 °C, pD 7.8).2,30
A prior study also determined that species 1 was the
1
pentadienyl ligands. In addition the H NMR showed a
resonance at -8.09 ppm, consistent with the hydride
resonance of [Cp2Mo(CO)H]+, -8.3 ppm.19 The infrared
spectrum showed a peak at 2006 cm-1 that is charac-
teristic of a CO stretch in a molybdenum hydride/
carbonyl.18-20 Mass spectroscopy of the yellow solution
showed m/z peaks at 285.0 (100%) with an isotope
pattern consistent with a single Mo atom, as well as a
second peak at 738.0 (8%) with an isotope pattern
consistent with two Mo atoms (see Supporting Informa-
tion). It is suggested that these peaks are due to the
Cp′2Mo(CO)H+ species (predicted parent peak ) 285)
and the electrospray-induced cluster [Cp′2Mo(CO)H+]2-
[OTs]- (predicted parent peak ) 738). In summary, the
spectroscopic evidence indicates that the yellow solid is
[Cp′2Mo(CO)H][OTs] (2) and the reaction is as written
in eq 7.
active catalyst by studying the reaction rates as a
function of metal complex concentration.5 Unfortu-
nately, a similar direct method could not be used to
determine the catalyst for the reactions in this study
due to the presence of interfering inhibition or competi-
tion reactions (see Experimental Section). There is
indirect evidence, however, that 1 is indeed the catalyti-
cally active species. Thus, in the case of nitrile hydra-
tion, when the amount of 1 in solution is decreased by
the addition of [N(n-Bu)4+][BF4-] to the solution (and
the amount of 4 accordingly increased; eq 8), the rate
of nitrile hydration is decreased, as monitored by NMR.3
Ca r boxylic Ester Hyd r olysis. In the absence of
catalysts, carboxylic esters do not readily hydrolyze at
neutral pH. For example, in the absence of a catalyst,
the rate constant for ethyl acetate hydrolysis in water
Discu ssion
To carry out homogeneous aqueous catalysis, water-
solublizing groups such as sulfonated phosphines are
often incorporated into the catalyst to impart water
solubility. Although far less extensively studied, orga-
nometallic complexes with aquo or hydroxy ligands
provide alternative means for water-solubilizing cata-
lysts.8,21-28 Among such complexes, the presence of early
transition metals is rare.2,27 The oxophilic nature of the
earlier transition metals is thought to lead to limited
water stability, reduced selectivity, and low reactivity
in catalysis.29 However, recent studies on 1 demon-
is only 2.47 × 10-10 s-1 16
. One of the catalysts previously
used to hydrolyze carboxylic esters is a tetra-amino-
(17) Igarashi, T.; Ito, T. Chem. Lett. 1985, 1699-1702.
(18) Adams, M. A.; Folting, K.; Huffman, J . C.; Caulton, K. G. Inorg.
Chem. 1979, 18, 3020-3023.
coordinated zinc complex, ZOH.28 This catalyst is only
(19) Nakamura, T.; Minato, M.; Ito, T.; Tanaka, M.; Osakada, K.
Bull. Chem. Soc. J pn. 1997, 70, 169-174.
(20) Ito, T.; Haji, K.; Suzuki, F.; Igarashi, T. Organometallics 1993,
12, 2325-2331.
(21) Abura, T.; Ogo, S.; Watanabe, Y.; Fukuzumi, S. J . Am. Chem.
Soc. 2003, 125, 4149-4154.
(22) Ogo, S.; Abura, T.; Watanabe, Y. Organometallics 2002, 21,
2964-2969.
(23) Ogo, S.; Makihara, N.; Kaneko, Y.; Watanabe, Y. Organome-
tallics 2001, 20, 4903-4910.
(24) Makihara, N.; Ogo, S.; Watanabe, Y. Organometallics 2001, 20,
497-500.
efficient at catalyzing the hydrolysis of activated esters
(25) Ogo, S.; Makihara, N.; Watanabe, Y. Organometallics 1999, 18,
5470-5474.
(29) Morales, D.; Elena Navarro Clemente, M.; Perez, J .; Riera, L.;
Riera, V.; Miguel, D. Organometallics 2002, 21, 4934-4938.
(30) Compared to the η5-C5H5 analogue, the methyl groups on the
cyclopentadienyl ligands sterically hinder formation of the dimer and
promote hydrolysis to the monomeric species (Keq ) 3.5 × 10-2 M at
23 °C, pD 3.5 for the η5-C5H5-containing molecule).
(26) Bernhard, P.; Helm, L.; Ludi, A.; Merbach, A. E. J . Am. Chem.
Soc. 1985, 107, 312-317.
(27) Crane, T. W.; White, P. S.; Templeton, J . L. Inorg. Chem. 2000,
39, 1081-1091.
(28) Chin, J .; Zou, X. J . Am. Chem. Soc. 1984, 106, 3687-3688.

Catalysis Using (MeCp)2Mo(OH)(H2O)+
Organometallics, Vol. 23, No. 8, 2004 1743
such as methyl triflate; it does not hydrolyze methyl
acetate, for example.31 However, both activated and
unactivated esters undergo hydrolysis with catalysts
containing cis-diaquo ligands. For example, with Cu-
(II) catalysts, particularly 5, methyl acetate and p-
nitrophenyl acetate are readily hydrolyzed. Interest-
ingly, the hydrolysis of the unactivated methyl acetate
is at least 2 orders of magnitude faster than the
hydrolysis of p-nitrophenyl acetate, indicating that the
leaving group departure is not rate-determining.11 Co-
(III) cis-diaqua complexes are similarily effective cata-
lysts. Both cis-[Co(trpn)(OH2)2]3+ and [Co(trien)(OH2)-
(OH)]2+ are hydrolysis catalysts for carboxylic esters and
amino acid esters. The hydrolysis is promoted by direct
coordination of the carbonyl group; without this coor-
dination, little rate acceleration occurs. It is not surpris-
ing therefore that, because they bind carbonyl groups
effectively, cis-diaquo Mo(IV) complexes are effective
carboxylic ester hydrolysis catalysts. The ability of the
cis-diaquo Mo(IV) unit to bond to carbonyl groups is
demonstrated by the observation of 3 in the ES-MS
spectrum of an aqueous mixture containing norbornenyl
acetate and catalyst 1. In summary of this section, the
similarity between all of the effective hydrolysis cata-
lysts is the presence of cis-diaquo ligands. This struc-
tural feature is important for two reasons. First, it
provides a labile ligand that can be easily replaced by
a carbonyl group of an entering ester. Second, with
many catalysts, including catalyst 1, the second “aquo
ligand” is a hydroxy ligand at neutral pH. This hydroxy
ligand can facilitate hydrolysis by acting as a general
base or acting as an internal nucleophile (see the
mechanism section below). Note that decreasing the pH
of the solution will lead to the protonation of the hydroxy
ligand, making a less effective base or nucleophile. The
lower concentration of effective catalyst at acidic pH
leads to a decrease in the rate of hydrolysis, as evident
with the unbuffered (acidic) ester hydrolysis reactions
(kobs ) (7.6 ( 1.0) × 10-6 at pH 7.1 and (4.3 ( 0.2) ×
10-6 unbuffered).
Eth er Hyd r olysis. Activated, difunctional ethers
hydrolyze in aqueous solution with catalyst 1, but under
similar conditions, monofunctional ethers do not hydro-
lyze. The likely reason is that the ether functionality is
a weak ligand and is sterically hindered, which prevents
coordination of the ether. Because only difunctional
ethers hydrolyze, it is suggested that precoordination
of the second functional group to the catalyst is required.
For example, methoxyacetonitrile likely coordinates to
the catalyst via the nitrogen of the nitrile functional
group. It is suggested that hydrolysis of the ether
functional group occurs after this coordination. It is
noted that the ether hydrolysis reactivity parallels the
coordination ability of the second functional group. For
example, the hydrolysis of methoxyacetonitrile is faster
than vinyl ethyl ether because the nitrile is a better
ligand. Interestingly, a similar mechanism is employed
to describe the hydrolysis of amino acid esters with Co-
(III) catalysts.32 In this case, the other functional group
(i.e., the amide group) binds to the catalyst and the
amide or amino acid ester is then hydrolyzed.32
P h osp h a te Ester Hyd r olysis. Catalysts for the
aqueous phase hydrolysis of phosphate esters are used
for endonuclease mimics, and they are used to decom-
mission pesticides and chemical warfare agents.14,33,34
Hydrolysis of phosphate esters is extremely slow due
to the stability of the phosphate ester over that of
carboxylic ester, ether, or amide linkages. The base-
catalyzed hydrolysis of NaOP(O)(OCH3)2 is only 6.8 ×
10-12 M-1 s-1 at 25 °C, and the water hydrolysis of
dimethyl phosphate has been calculated to be a nearly
stagnant 5.8 × 10-16 s-1 at pH 7, 70 °C. It has been
reported that the cis-diaquo complexes of Co(III) are
effective catalysts for the hydrolysis of dimethyl phos-
phate at 60 °C and pD 6.3 (6.2 × 10-7 M-1 s-1, [Co-
(cyclen)(OH2)2]3+). Note that two aquo ligands are
required for efficient catalysis, as [Co(tetren)(OH2)]3+
does not catalyze the hydrolysis of phosphate esters.8
Interestingly, the hydrolysis of bis(p-nitrophenyl)phos-
phate (BNPP) with Cu(i-Pr3[9]aneN3)2+ at pH 7.2
proceeds with a similar rate constant (8.56 × 10-7 M-1
s-1). Under similar conditions, Kuo et al. investigated
the hydrolysis of phosphate diesters and triesters using
Cp2MoCl2 as a precatalyst that forms Cp2MoOH(OH2)+
at neutral pH. They reported a rate constant for
hydrolysis of dimethyl phosphate of approximately 1.0
× 10-7 M-1 s-1 at pD 3-7. It is interesting to note that
for each of these effective catalysts the rate enhance-
ment is significant, a 108 enhancement over the hydro-
lytic process at neutral pH. As discussed in the mecha-
nistic section below, the rate enhancement and coordi-
nated hydrolysis products indicate that phosphate hy-
drolysis utilizes the cis-aquo ligand functionality to
coordinate the phosphate and the second aquo (or
hydroxy) ligand site to perform an intramolecular
nucleophilic attack on the bound substrate.
Nitr ile Hyd r a tion . The hydration of nitriles is an
industrially important reaction, particularly in the
context of acrylonitrile, where side products of olefin
hydration often produce substantial impurities. While
many catalysts have been used to hydrate nitriles35-42
(also see Table 1 in ref 3), catalyst 1 is highly chemose-
lective for the nitrile hydration over olefin hydration.
The hydration reaction is straightforward, and no
subsequent hydrolysis of the amide occurs (except in the
special case of 2-methoxyacetonitrile3). It is interesting
to note that the most effective hydration catalysts have
an open coordination site and an internal hydroxide that
can participate in the hydrolysis.
Oxid a tion of Ca r bon Mon oxid e. As part of another
investigation into using 1 as a catalyst for Reppe
(33) Kuo, L. Y. Abstr. Pap.-Am. Chem. Soc. 2000, 220th, INOR-
489.
(34) Kuo, L. Y.; Perera, N. M. Inorg. Chem. 2000, 39, 2103-2106.
(35) Ghaffar, T.; Parkins, A. W. J . Mol. Catal. A: Chem. 2000, 160,
249-261.
(36) J ensen, C. M.; Trogler, W. C. J . Am. Chem. Soc. 1986, 108, 723-
729.
(37) Villain, G.; Constant, G.; Gaset, A.; Kalck, P. J . Mol. Catal.
1980, 7, 355-364.
(38) Villain, G.; Gaset, A.; Kalck, P. J . Mol. Catal. 1981, 12, 103-
111.
(39) Yoshida, T.; Matsuda, T.; Okano, T.; Kitani, T.; Otsuka, S. J .
Am. Chem. Soc. 1979, 101, 2027-2038.
(40) Djoman, M. C. K. B.; Ajjou, A. N. Tetrahedron Lett. 2000, 41,
4845-4849.
(41) Bennett, M. A.; Yoshida, T. J . Am. Chem. Soc. 1973, 95, 3030-
3031.
(31) Menger, F. M.; Ladika, M. J . Am. Chem. Soc. 1987, 109, 3145-
3146.
(32) Angelici, R. J .; Hopgood, D. J . Am. Chem. Soc. 1968, 90, 2514-
2517.
(42) Murahashi, S.; Sasao, S.; Saito, E.; Naota, T. J . Org. Chem.
1992, 57, 2521-2523.

1744 Organometallics, Vol. 23, No. 8, 2004
Breno et al.
Sch em e 3. Rea ction of Ca ta lyst 1 a n d Ca r bon Mon oxid e w ith P r op osed Ca r boxylic Acid In ter m ed ia te
Sch em e 4. Ca ta lytic Hyd r a tion P a th w a ys
carbonylation, it was observed that 1 reacted with CO
to form an inactive species. Analysis showed that the
products were CO2 and Cp′2MoH(CO)+ (2). This reaction
is interesting because the catalyst mimics catalysts for
the water-gas shift reaction (WGSR) (eq 9).43
P r op osed Mech a n ism . The major theme thoughout
the reactions reported herein is that complexes with cis-
diaquo ligands are often effective hydration catalysts.
It is evident that the lability of the first aquo ligand
and the hydrolysis assistance imparted by the second
ligand increase the catalytic activity of such complexes.
The intimate mechanism of the reactions can be ex-
plored by careful examination of each reaction. Catalyst
1 could catalyze the hydration/hydrolysis reactions in
at least four different ways. First, catalyst 1 could
simply act as a Lewis acid promoter for hydrolysis by
coordinating the substrate (Scheme 4a). This is reason-
able because, after ligand coordination, the electrophilic
center on the ligand would be primed for attack by
external water. Indeed, this has been shown to be an
accurate description of the mechanism of rate enhance-
ment of ester hydrolysis using monoaquo catalysts such
as [Co(tetren)(OH2)]3+.8 When Lewis acid activation is
the mechanism of acceleration, the rate of hydrolysis is
typically enhanced by 2-3 orders of magnitude.46 Note,
however, that [Co(tetren)(OH2)]3+ is an ineffective cata-
lyst for the hydration of phosphate diesters, a reaction
observed to be accelerated by catalyst 1. Furthermore,
Kuo et al. have observed that the rate of organophos-
phate ester hydrolysis catalyzed by [Cp2Mo(OH)(H2O)]+
is 108 times greater than the hydrolysis in water alone.34
Clearly, to account for the improved rate of hydrolysis,
the metal must play a more active role than simple
substrate coordination and activation.
CO + H2O f CO2 + H2
(9)
The typical WGSR catalytic cycle is comprised of four
steps (illustrated in Scheme 3 for the case of 1): (a) CO
is coordinated to the metal center, (b) nucleophilic attack
of hydroxide (or water) occurs on the coordinated CO,
(c) decarboxylation of the newly formed carboxylic acid
group yields a metal hydride, and (d) the metal hydride
reductively eliminates H2.44 The reaction of CO with 1
is apparently similar, but the fourth step, elimination
of H2, does not occur. With complex 1, the monohydride,
Cp′2MoH+, does not react with the acidic solution to
form H2. Rather, a second carbon monoxide molecule
binds irreversibly to the open coordination site, trapping
the intermediate and forming an unreactive species, 2.
An incomplete cycle is not unprecedented, as [Ru(dppe)-
+
(CO)(H2O)3]2 reacts with CO to form the cationic
hydride [Ru(dppe)(CO)3H]+ and CO2.45
The reaction of 1 with CO is relatively facile, with
30% conversion to 2 in 1 h at 80 °C under 1 atm of CO.
Note that species 2 has been fully characterized by
NMR, MS, and IR spectroscopy (see Experimental
Section). In addition, 2 was independently synthesized
by reacting Cp′2MoH(OTf) with CO (eq 10). Interest-
ingly, 2 is completely unreactive under all anaerobic
reaction conditions investigated. (Thus, it is stable in
acidic and in basic solution below pH 9; it does not react
with olefins, nitriles, alcohols, or esters at 80 °C.)
A second possible mechanism involves the metal-
bound hydroxide as a nucleophile in an intermolecular
attack on an unactivated (noncoordinated) substrate
(Scheme 4b). However, this possibility seems remote,
as metal-bound hydroxides are not known as good
nucleophiles. Sutton and Buckingham report that metal
(43) Ford, P. C. Acc. Chem. Res. 1981, 14, 31-37.
(44) Hutchings, G. J .; Gottschalk, F.; Hunter, R.; Orchard, S. W. J .
Chem. Soc., Faraday Trans. 1 1989, 85, 363-371.
(45) Hargreaves, M. D.; Mahon, M. F.; Whittlesey, M. K. Inorg.
Chem. 2002, 41, 3137-3145.
(46) Hendry, P.; Sargeson, A. M. Aust. J . Chem. 1986, 39, 1177-
1186.

Catalysis Using (MeCp)2Mo(OH)(H2O)+
Organometallics, Vol. 23, No. 8, 2004 1745
Sch em e 5. P r op osed Gen er a l Mech a n ism of
In tr a m olecu la r Hyd r oxid e Atta ck w ith Ca ta lyst 1
It is proposed that formation of the cyclic intermediate
is the slow step in the catalytic pathway.48 The activa-
tion parameters, ∆Hq ) 5.9 ( 0.7 kcal/mol and ∆Sq )
-48 ( 9 eu, measured for the hydrolysis of ethyl acetate
with catalyst 1 are consistent with a geometrically
constrained transition state. With Cu(i-Pr[9]aneN3)2+
,
the hydrolysis of phosphodiesters was reported to
proceed via an intramolecular nucleophilic attack with
activation parameters ∆Hq ) 10.59 kcal/mol and ∆Sq )
-26.2 eu.49 (In this case, the bite angle of the tris(amino)
ligand in the copper catalyst constrains the bound
phosphate ester and hydroxide, in essence preorganizing
the ligands and thereby making the activation entropy
less negative.) Interestingly, Kuo measured the activa-
tion parameters for phosophate ester hydrolysis with
Cp2MoCl2 and found ∆Hq ) 9.8 kcal/mol and ∆Sq ) -49
eu. He ascribed the catalytic activity to an intermolecu-
lar attack (4a) but could not rule out an intramolecular
pathway with a constrained transition state.
The acceleration of hydrolysis by a factor of 108 as
reported by Kuo for phosphate diesters using 1 and
acceleration of carboxylic ester hydrolysis by a factor of
106 using 1 are both consistent with the dual activation
mechanism in Scheme 5.50 In systems that likely
undergo the same intramolecular nucleophillic attack
using other catalysts (such as [Co(cyclen)(OH2)2]3+), the
rate of dimethyl phosphate hydrolysis is on the order
of 1010 times greater than that of water hydrolysis.8 In
summary, the high rate of acceleration shown by these
catalyst systems is best explained by the dual activation
pathway in Scheme 4d and Scheme 5.
hydroxides are only good (bimolecular) nucleophiles
when the substrate is very electrophilic, as in the case
of SO2 or CO2, or when the leaving group is particularly
strong such as in activated esters, acid chlorides, or
anhydrides.9 Clearly, in the hydrolysis of ethyl acetate
(as in nearly all of the reactions reported herein) there
is neither a good leaving group nor a highly electrophilic
substrate, and thus this mechanism cannot account for
the catalytic activity.
A third mechanism can be postulated, based on the
activity of the bound hydroxide ligand. If the substrate
is coordinated to the metal center, the bound hydroxide
ligand could act as a general base catalyst (Scheme 4c).
If such were the case, an increased rate of hydrolysis
via Lewis acid activation as well as general base
catalysis would be expected. If general base catalysis
were an important factor, the addition of buffer should
increase the reaction rate due to the increased likelihood
of general base catalysis by the buffer itself.28 However,
this was not observed experimentally. In fact, the
addition of a noncoordinating buffer such as NaMOPS
resulted in no net change in the reaction rate.47 In
addition, if this mechanism were operative, H/D ex-
change should occur at the R-position to the electrophilic
atom due to formation of an enolate type species.
However, no exchange was observed in the hydration
of nitriles. (Unfortunately, the H/D exchange in the
products (post-hydrolysis) of ester hydrolysis precludes
using this analysis with the other substrates.)
The final and most likely mechanism of hydrolysis
involves both Lewis acid activation of the substrate and
intramolecular nucleophillic attack by the bound hy-
droxy ligand (Scheme 4d). The coordination of the
substrate in place of a labile aquo ligand is the first step
in the hydration (Scheme 5). The intramolecular attack
of the hydroxide is facilitated by the juxtaposition of the
ligands and the consequent high probability of orbital
overlap.9 Intramolecular hydroxide attack leads to the
formation of a constrained cyclic intermediate. The
molybdocene intermediate has not been isolated due to
its reactivity, but it was observed in mass spectrometry
analysis of the products of norborenyl acetate hydrolysis
(see species 3). It is noteworthy that the ability to
stabilize the cyclic intermediate accounts for the in-
creased reactivity of [Co(trpn)(OH2)2]3+ over [Co(tren)-
(OH2)2]3+ in phosphate ester hydrolysis.10
Finally, it is noted that other researchers have used
substitutionally inert complexes to confirm intramo-
lecular hydroxide attack via isotope studies.9,12 How-
ever, the lability of the aquo and hydroxy ligands in
catalyst 1 prevented isotopic analysis because the
coordinated ligands exchanged with the solvent on a
shorter time scale than hydrolysis.
Con clu sion
Complex 1 is a catalyst for the hydrolysis of carboxylic
esters, ethers, and phosphate esters, the hydration of
nitriles, and a stoichiometric reagent for the oxidation
of carbon monoxide. In evaluating the structure/activity
relationship of 1 and other hydration catalysts, it is
apparent that cis-aquo/hydroxy ligands are ideally
suited for catalyzing the hydrolysis/hydration/oxidation
of organic substrates because the labile aquo ligand can
be easily displaced to coordinate various functional
groups and the second ligand (often a hydroxide) can
promote hydration by way of an intramolecular attack
(48) In fact, the formation of the cyclic intermediate with amide
substrates seems to be preventing amide hydrolysis. Interestingly,
although catalyst 1 hydrolyzes difficult substrates such as phosphate
esters and hydrates nitriles, the hydrolysis of amides was not observed
under any reaction conditions used in this study. It does not seem
plausible that hindrance of amide coordination to the catalyst is the
problem because amide coordination is a noted inhibitor of nitrile
hydrolysis (see ref 3). Therefore, the intramolecular hydroxide attack
(to form the four-membered cyclic species) would seem to be problem-
atic. The absence of amide hydrolysis by 1 counters the common belief
that the hydrolysis behavior of carboxylic esters (particularly activated
esters) can be used as models for amide hydrolysis by peptidases (see
ref 10).
(47) At high concentrations of NaMOPS, it is possible that the
concentration of monomeric catalyst 1 would decrease due to an
equilibrium shift due to salt effects. However, this was not observed
with the concentrations of buffer used in this experiment.
(49) Deck, K. M.; Tseng, T. A.; Burstyn, J . N. Inorg. Chem. 2002,
41, 669-677.
(50) Kuo, L. Y.; Barnes, L. A. Inorg. Chem. 1999, 38, 814-817.

1746 Organometallics, Vol. 23, No. 8, 2004
Breno et al.
on a bound substrate. Even early transition metals,
typically dismissed as too oxophilic, can be used to form
cis-diaqua type complexes, which are active catalysts.
From the enhanced reactivity, activation parameters,
and lack of H/D exchange, it is likely that the hydration,
hydrolysis, and oxidation reactions proceed via an
intramolecular hydroxide attack. The observations pre-
sented here promote the increased understanding of
aqueous organometallic mechanisms and could be useful
for the development of artificial hydrolytic enzymes and
efficient catalysts for the destruction of chemical weap-
ons.
Ack n ow led gm en t is made to the NSF for the sup-
port of this research and to Professor Louis Kuo for
helpful discussions. K.L.B. acknowledges a DOE GAANN
fellowship for partial support.
Su p p or tin g In for m a tion Ava ila ble: Experimental de-
tails on the hydrolysis of other carboxylic esters and the mass
spectrum of the products from the reaction of 1 with CO are
available free of charge via the Internet at http://pubs.acs.org.
OM0342558