Promotion of phosphoester hydrolysis by MoO2Cl2L (L = bipyridine derivatives, H2O, no ligand), MoO2(CH 3)2L (L = bipyridine derivatives) and related inorganic-organic hybrids in aqueous media Dedicated to Professor Maria José Calhorda on the occasion of her 65th birthday.

Article abstract of DOI:10.1016/j.jorganchem.2013.12.029

The compounds MoO₂Cl₂L (L = 2,2′-bipyridine (bipy) (1); 4,4′-di-tert-butyl-2,2′-bipyridine (di- ^tBu-bipy) (2)), [MoO₂Cl₂(H₂O) ₂]·(diglyme)₂ (3), MoO₂Cl₂ (4), MoO₂(CH₃)₂L (L = bipy (5); di- ^tBu-bipy (6)), [MoO₃(bipy)]_n (7), {[MoO ₃(bipy)][MoO₃(H₂O)]}_n (8), [Mo ₈O₂₂(OH)₄(di-^tBu-bipy)₄] (9) and MoO₃ (10) were tested as phosphoester bond hydrolysis promoters in aqueous media. Sodium para-nitrophenylphosphate (pNPP) was used as a model substrate for the phosphoester bond hydrolysis reaction, which was performed at 55 °C, using D₂O as solvent and 100 or 10 mol% of the chosen promoter. The progression of all the reactions was monitored by ¹H NMR spectroscopy. All studied systems promote phosphoester bond hydrolysis. The best performance was obtained with MoO₂Cl ₂L compounds (1-4) and with the inorganic-organic hybrid {[MoO ₃(bipy)][MoO₃(H₂O)]}_n (8). The studied compounds originate either homogeneous or solid/liquid biphasic systems. For the biphasic systems (1, 2, 5-9), the solid phase was recovered at the end of the reaction and characterized by FT-IR spectroscopy.

Full text of DOI:10.1016/j.jorganchem.2013.12.029

Journal of Organometallic Chemistry 760 (2014) 42e47
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Promotion of phosphoester hydrolysis by MoO2Cl2L (L ¼ bipyridine
derivatives, H2O, no ligand), MoO2(CH3)2L (L ¼ bipyridine derivatives)
and related inorganiceorganic hybrids in aqueous media
Ana C. Gomes a, Martyn Pillinger a, Patrique Nunes b, Isabel S. Gonçalves a,
,
Marta Abrantes b
*
a Department of Chemistry, CICECO, University of Aveiro, Campus Universitário de Santiago, 3810-193 Aveiro, Portugal
b Centro de Química Estrutural, Complexo Interdisciplinar, Instituto Superior Técnico, Universidade de Lisboa, 1049-001 Lisbon, Portugal
a r t i c l e i n f o
a b s t r a c t
The compounds MoO2Cl2L (L ¼ 2,20-bipyridine (bipy) (1); 4,40-di-tert-butyl-2,20-bipyridine (di-tBu-bipy)
Article history:
(2)), [MoO2Cl2(H2O)2]$(diglyme)2 (3), MoO2Cl2 (4), MoO2(CH3)2L (L
¼
bipy (5); di-tBu-bipy (6)),
Received 30 September 2013
Received in revised form
12 December 2013
[MoO3(bipy)]n (7), {[MoO3(bipy)][MoO3(H2O)]}n (8), [Mo8O22(OH)4(di-tBu-bipy)4] (9) and MoO3 (10)
were tested as phosphoester bond hydrolysis promoters in aqueous media. Sodium para-nitro-
phenylphosphate (pNPP) was used as a model substrate for the phosphoester bond hydrolysis reaction,
which was performed at 55 ꢀC, using D2O as solvent and 100 or 10 mol% of the chosen promoter. The
progression of all the reactions was monitored by 1H NMR spectroscopy. All studied systems promote
phosphoester bond hydrolysis. The best performance was obtained with MoO2Cl2L compounds (1e4)
and with the inorganiceorganic hybrid {[MoO3(bipy)][MoO3(H2O)]}n (8). The studied compounds orig-
inate either homogeneous or solid/liquid biphasic systems. For the biphasic systems (1, 2, 5e9), the solid
phase was recovered at the end of the reaction and characterized by FT-IR spectroscopy.
Ó 2014 Elsevier B.V. All rights reserved.
Accepted 14 December 2013
Dedicated to Professor Maria José Calhorda
on the occasion of her 65th birthday.
Keywords:
Molybdenum
Oxides
Bipyridine ligands
Phosphoester hydrolysis
1. Introduction
Chemically, organophosphate pesticides are esters of phos-
phoric acid (phosphoesters). The chemistry of pesticides is
Organophosphorus pesticides are the most widely used type of
pesticide in the world. They constitute a vast category of chemicals
specifically designed for the control of pests, weeds or plant dis-
eases. Their application is still the most effective and accepted
means for the protection of plants from pests, and has contributed
significantly to enhanced agricultural productivity and crop yields
[1a]. Unfortunately, organophosphate pesticides are also the most
important cause of severe toxicity and death from acute poisoning
worldwide, with more than 200,000 deaths each year in devel-
oping countries [1a,b]. Moreover, their accumulation in the envi-
ronment is a recognized ecological threat with harmful effects on
human beings or other mammalian species due to possible long-
term exposure to sublethal doses. The toxic effect of organophos-
phorus pesticides has a cumulative nature and entails various
degenerative disorders of the nervous system. Additionally,
organophosphorus pesticides are strong mutagens, causing multi-
ple chromosomal aberrations and carcinogenesis [1c].
entwined with that of nerve agents (chemical weapons, such as
sarin) since they possess similar structural features and formulas.
Whereas pesticides are less immediately toxic when compared
with nerve agents, their heavier use and looser monitoring is
perhaps cause for greater concern [1a].
Hydrolysis products of organophosphate pesticides are either
non-toxic, or have a substantially lower toxicity than the original
substrates [1c]. Thus, hydrolysis is considered to be an interesting
strategy to eliminate organophosphate pesticides. In the absence of
a catalyst or enzyme, phosphoester hydrolysis may be extremely
slow under normal conditions. For this reason, over time, a growing
interest in the metal promoted hydrolysis of phosphoesters has
arisen. In recent years, a range of metal complexes containing Cu2þ
,
Ln3þ, Co3þ, Zn2þ, Mn2þ, Fe3þ and Zr4þ has proven to exhibit high
activity toward phosphoester cleavage [2].
Molybdenum is an essential trace element for plant growth and is
commonly used in the form of oxides as fertilizer to avoid molyb-
denum deficiencies in soils worldwide [3], making molybdenum an
attractive candidate for metal promoted hydrolysis of phosphoesters.
To the best of our knowledge, the use of molybdenum-containing
* Corresponding author. Fax: þ351 21 846 4455.
E-mail address: marta.abrantes@ist.utl.pt (M. Abrantes).
0022-328X/$ e see front matter Ó 2014 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.12.029

A.C. Gomes et al. / Journal of Organometallic Chemistry 760 (2014) 42e47
43
compounds as promoters of phosphoester hydrolysis had until
recently been limited to molybdocene derivatives (Cp02MoCl2) [4],
molybdates ðMoO42ꢁÞ [5aec] and polyoxometalates [5deh], even
though molybdenum is known to be a crucial component of both
natural and synthetic catalysts [3,5h,6]. For molybdocene deþrivatives
the reactive agents were proposed to be [Cp02Mo(OH)(H2O)] , which
are formed by rapid hydrolysis of the MoeCl bonds in Cp02MoCl2.
Phosphoester hydrolysis was not catalytic, possibly due to the high
stability of Cp02Mo-phosphate products [4a,c].
The effect of molybdates on phosphoester hydrolysis was orig-
inally studied in the context of organic phosphate estimation by
colorimetry [5aec]. Recently, a growing interest in the phos-
phoesterase activity of molybdates has arisen, due in part to the
promising potential of polyoxomolybdates as therapeutic agents
[5deh,7]. For molybdates, reactive species responsible for phos-
The promoters MoO2Cl2(bipy) (1) [10a], MoO2Cl2(di-tBu-bipy) (2)
[10b], [MoO2Cl2(H2O)2]$(diglyme)2 (3) [10c], MoO2Cl2 (Sigmae
Aldrich) (4), MoO2(CH3)2(bipy) (5) [10d,e], MoO2(CH3)2(di-tBu-bipy)
(6) [10f], [MoO3(bipy)]n (7) [10g], {[MoO3(bipy)][MoO3(H2O)]}n (8)
[10h], [Mo8O22(OH)4(di-tBu-bipy)4] (9) [10i] and MoO3 (Sigmae
Aldrich, >99.5%) (10) were synthesized according to the published
procedures or obtained from commercial sources and used as
received.
FT-IR spectra were recorded as KBr pellets using a Unicam-
Mattson 7000 spectrophotometer equipped with a DTGS CsI de-
tector. Solution NMR spectra were recorded on a Bruker Avance IIþ
300 MHz (UltraShieldTM Magnet) spectrometer at ambient tem-
perature. Chemical shifts are given in ppm relative to TMS (1H).
2.2. Molybdenum-promoted hydrolysis assays
phoester hydrolysis were proposed to be polyoxomolybdates such
6ꢁ
Sodium para-nitrophenylphosphate (3.0 mg, 8 ꢂ 10ꢁ3 mmol)
and dioxane (internal standard, 0.8 mg, 9 ꢂ 10ꢁ3 mmol) were
dissolved in deuterated water in a 5 mm NMR tube bearing a
magnetic stirring bar, and heated at 55 ꢀC. The molybdenum
compound (10 or 100 mol% relative to pNPP) was added, and the
progression of the reaction monitored over time by 1H NMR.
Attention: The magnetic stirring bar was removed immediately
before the NMR measurement, and then reintroduced immediately
after the measurement. The relative amounts of pNPP and para-
nitrophenol (pNPh) in the reaction medium were followed by
quantification of the respective areas in comparison to the area of
the internal standard. The pH of the solution was measured at the
described times and reaction temperature. The pD value of the
solution was obtained by adding 0.4 to the pH reading. Before
addition of the catalyst the reaction medium had a pD of 7.4.
Addition of the metal complexes studied causes significant differ-
ences in the pD of the reaction medium. Reactions were not buff-
ered to understand the real impact of each compound per se in the
hydrolysis reaction.
as the heptamolybdate anion [Mo7O24
]
that form upon mild
acidification of molybdate solutions. These results showed that
negatively charged and saturated complexes could efficiently hy-
drolyze phosphoester bonds [5f]. Previously, the metal complexes
that were found to be active as catalysts for the hydrolysis of
phosphoester bonds were generally coordinatively unsaturated
and/or positively charged [2a,8], which were assumed to be
essential properties for Lewis acid activation via coordination of
phosphoryl oxygen(s) to the metal ion.
Very recently, we showed that phosphoester bond hydrolysis of
para-nitrophenylphosphate (pNPP), a commonly used model sub-
strate, could be accelerated by using the complex MoO2Cl2(DMF)2
(DMF ¼ dimethylformamide) in water under mild conditions, even
when catalytic amounts of complex are used [9]. In that work we
found that, at high concentrations of MoO2Cl2(DMF)2, hydrolysis of
the MoeCl bonds in the molecular precursor led to the precipita-
tion of a molybdenum oxide structure formulated as Mo2O6(DMF).
The latter compound dissolved as the reaction progressed, leading
to the formation of hydrolytically active isopolyoxomolybdate and
phosphomolybdate species. Encouraged by these results, we
decided to explore the phosphoester hydrolysis promoting poten-
tial of other complexes of the type MoO2X2Ln, in the hope of finding
more active systems and/or gaining a better understanding of the
chemistry of the complexes in aqueous solution and the influence
of the ligands X and L. We herein report the performance of the
complexes MoO2Cl2L (L ¼ 2,20-bipyridine (bipy), 4,40-di-tert-butyl-
2,20-bipyridine (di-tBu-bipy), H2O, no ligand) and MoO2(CH3)2L
(L ¼ bipy, di-tBu-bipy) in the hydrolysis of pNPP. The hybrid mo-
lybdenum oxide materials [MoO3(bipy)]n, {[MoO3(bipy)][MoO3(-
H2O)]}n and [Mo8O22(OH)4(di-tBu-bipy)4] have also been studied
since these have been shown in previous work to be products of the
hydrolysis of the complexes MoO2Cl2L. The family of compounds to
be screened was completed by inclusion of the purely inorganic
compounds MoO3 and MoO2Cl2.
2.3. Promoter recovery
At the end of the reaction monitoring, biphasic solideliquid
systems were centrifuged (Table 1). The obtained solid was washed
with water, methanol and diethyl ether and air-dried. Identification
of the solids was performed by FT-IR spectroscopy. Recovered solids
were numbered with an asterisk. For example, the solid recovered
from a reaction with 1 was identified as 1*. Additional scaled-up
(5ꢂ) reactions were performed with 1 and 5, which allowed
enough solid to be recovered for use in a second run.
3. Results and discussion
Compounds 1e10 were synthesized according to literature
procedures (1e3 and 5e9) or obtained commercially (4 and 10) as
described in the Experimental section [10]. Their structures are
illustrated in Chart 1. Reaction of MoO2Cl2 with THF afforded
MoO2Cl2(THF)2, and further addition of one equivalent of bidentate
nitrogen donor ligand L (L ¼ bipy or di-tBu-bipy) resulted in the
formation of the complex MoO2Cl2L (1 and 2) [10a,b]. Treatment of
the latter compounds with Grignard reagent at low temperature
gave the dimethyl derivatives MoO2(CH3)2L (5 and 6) (L ¼ bipy or
di-tBu-bipy) [10def]. [MoO2Cl2(H2O)2]$(diglyme)2 (3) was pre-
pared by reflux of an aqueous solution of HCl with MoO3 and
addition of diglyme [10c]. The one dimensional organiceinorganic
hybrid material [MoO3(bipy)]n (7) was prepared by oxidative
decarbonylation of Mo(CO)4(bipy) [10g]. The molybdenum oxide/
bipyridine hybrid material {[MoO3(bipy)][MoO3(H2O)]}n (8) [10h]
2. Experimental
2.1. Materials and methods
Na2MoO4$2H2O (Fluka, >99%), MoO2Cl2 (SigmaeAldrich), bipy,
di-tBu-bipy (98%, SigmaeAldrich), diethylene glycol dimethylether
(diglyme, 99%, Fluka), hexane (99%, SigmaeAldrich), acetone (99.5%,
Fluka), diethyl ether (99.8%, SigmaeAldrich), dichloromethane
(99.9%, SigmaeAldrich), acetonitrile (99.5%, SigmaeAldrich),
pentane (99%, SigmaeAldrich), methylmagnesium chloride solution
(CH3MgCl, 3 M in THF, Fluka), para-nitrophenylphosphate disodium
salt hexahydrate (pNPP, 99%, Alfa Aesar), D2O (Euroiso-top, 99.96%),
and 1,4-dioxane (Fischer Chemical, 99.99%) were obtained from
commercial sources and used as received.

44
A.C. Gomes et al. / Journal of Organometallic Chemistry 760 (2014) 42e47
Table 1
Characterization of the hydrolysis reaction system regarding phases and possible
identification of the solid phase at the end of the reaction.a
IDb
Promoter
System type
Solid identificationd
1
2
3
MoO2Cl2(bipy)
Biphasic (S/L)c
Biphasic (S/L)c
Monophasic
[MoO3(bipy)]n (1*)
MoO2Cl2(di-tBu-bipy)
[MoO2Cl2(H2O)2]$
(diglyme)2
MoO2Cl2(di-tBu-bipy) (2*)
e
4
5
6
MoO2Cl2
Monophasic
e
MoO2(CH3)2(bipy)
Biphasic (S/L)c
Biphasic (S/L)c
MoO2(CH3)2(bipy) (5*)
MoO2(CH3)2
MoO2(CH3)2(di-tBu-bipy)
(di-tBu-bipy) (6*)
[MoO3(bipy)]n (7*)
[MoO3(bipy)]n (8*)
7
8
[MoO3(bipy)]n
{[MoO3(bipy)]
[MoO3(H2O)]}n
[Mo8O22(OH)4
(di-tBu-bipy)4]
MoO3$H2O
Biphasic (S/L)c
Biphasic (S/L)c
9
Biphasic (S/L)c
[Mo8O22(OH)4
(di-tBu-bipy)4] (9*)
e
Scheme 1. Mo-promoted hydrolysis reaction studied in this work.
10
Monophasic
a
Reaction conditions: 100 mol% of promoter relative to pNPP, 55 ꢀC, D2O, dioxane
reaction performed in the absence of promoter (blank) and previ-
ously reported datafor MoO2Cl2(DMF)2 (DMF¼ dimethylformamide)
and Na2MoO4 [9]. The dichloro complexes 1e4 and MoO2Cl2(DMF)2
present similar hydrolysis promotion profiles, indicating that the
neutral ligands L (bipy, di-tBu-bipy, H2O, no ligand, DMF) in the
compounds MoO2Cl2L have no significant impact on the promoter
capacity of the systems. However, after the half reaction time all the
systems perform significantly better thanNa2MoO4. Interestingly, the
dimethyl derivatives 5 and 6 are also hydrolysis promoters, although
they perform significantly slower than their dichloro counterparts.
Thus, although the presence of Cl ligands, which could be prone to
hydrolysis and substitution by oxygen ligands, is not mandatory for
the activity of monomeric systems, it seems to be important for the
system performance. Furthermore, for the MoO2(CH3)2L compounds
studied, the use of the ligand di-tBu-bipy has a clear positive effect
when compared with the use of the ligand bipy.
as internal standard.
b
Promoter identification number.
Solid/liquid biphasic system.
By FT-IR spectroscopy. Please see the Experimental section for a description of
c
d
the recovery procedure.
and the octanuclear complex [Mo8O22(OH)4(di-tBu-bipy)4] (9) [10i]
were obtained by reaction of 1 and 2 with H2O, respectively.
Compounds 1e10 were tested as phosphoester bond hydrolysis
promoters. Sodium para-nitrophenylphosphate (pNPP) was used as
a model substrate for the phosphoester bond hydrolysis reaction,
which was performed at 55 ꢀC, using D2O as solvent and 100 mol%
of the chosen promoter (Scheme 1). The progression of all the re-
actions was monitored by 1H NMR spectroscopy (see Experimental
section for details and Fig. 1). Over time, the 1H NMR spectra of the
reaction solutions show that the amount of pNPP (doublets at
and 7.31) decreases with the concomitant increase of the hydrolysis
product para-nitrophenol (pNPh) (doublets at 8.15 and 6.89).
The results regarding MoO2X2L compounds 1e6 are depicted in
Fig. 2. For comparison purposes this figure also includes results of the
d 8.21
Performing the reaction with catalytic amounts of 1 and 2
(10 mol% of complex relative to pNPP; homogeneous reaction
conditions, i.e., one monophasic liquid phase) also enables an
accelerated pNPP hydrolysis, but at a slower rate (Fig. 2). A similar
behavior was reported for the complex MoO2Cl2(DMF)2 [9].
d
Chart 1. Molybdenum-containing compounds used in this work.

A.C. Gomes et al. / Journal of Organometallic Chemistry 760 (2014) 42e47
45
bipy)}2] [10h,12], and the octanuclear compound 9 [10h]. However,
the changes noted in the spectrum of 2* are not consistent with any
of these structures. For the remaining biphasic systems, the FT-IR
spectra of the recovered solids (5*, 6* and 9*) were identical to
those exhibited by the promoters initially used (Fig. S2). The
dichloro compounds 1, 3, 4 and MoO2Cl2(DMF)2 all resulted in
acidic pD values of 1.4, which indicates that hydrolysis of the MoeCl
bonds had occurred to give HCl and an acidic solution. By contrast, a
pD value of 6.4 was obtained after addition of MoO2Cl2(di-tBu-bipy)
(2). This is consistent with the FT-IR result and indicates that the
presence of the di-tBu-bipy ligands renders the complex less sol-
uble and/or more stable towards hydrolysis of the MoeCl bonds.
Despite this contrasting behavior of
2 (vs. 1, 3, 4 and
MoO2Cl2(DMF)2), it presents a similar hydrolysis promotion profile
to the other four dichloro compounds, as noted above (Fig. 2).
Additional scaled-up (5ꢂ) reactions were performed with 1 and
5, which allowed enough solid to be recovered for use in a second
run. As noted above, 1* was identified as 7, while 5* was identified
as 5. The isolated yields (in mol%, calculated assuming that 1* ¼ 7
and 5* ¼ 5) after the scaled-up runs were 51% for 1* and 58% for 5*.
The hydrolytic performances of the two recovered solids (100 mol%
relative to pNPP) were similar to their “fresh” counterparts (i.e., 7
and 5, respectively) (Fig. 4).
The stability of MoO2(CH3)2(di-tBu-bipy) (6), [MoO3(bipy)]n (7)
and [Mo8O22(OH)4(di-tBu-bipy)4] (9) has been described in previ-
ous work in which the compounds were used as catalysts for the
liquid-phase epoxidation of olefins at 55 ꢀC with tert-butylhy-
droperoxide as oxidant under non-aqueous conditions [10f,g,i].
Specifically, MoeCH3 and MoeN bonds in the soluble homoge-
neous catalyst 6 were found to be chemically stable under the re-
actions conditions used, even in the present of peroxides and
alcohols [10f]. In the present study we have found that this stability
seems to extend to aqueous media. In parallel with the present
work, the catalytic olefin epoxidation systems with 7 and 9 were
always biphasic and the IR spectra of the recovered solids were
identical to those of the as-synthesized compounds [10g,i].
Fig. 1. Representative 1H NMR spectra (300 MHz, detail 6.5e9.0 ppm and 3.5e
6.0 ppm) of the pNPP hydrolysis reaction. Reaction conditions: 100 mol% of 8 relative
to pNPP, 55 ꢀC, D2O, 1,4-dioxane as internal standard.
Among the studied polynuclear systems (7e9), the best system
is the hybrid {[MoO3(bipy)][MoO3(H2O)]}n (8), which equals the
performance of the mononuclear systems bearing chloro ligands (1
and 2) and surpasses the commercial molybdenum oxide 10
(Fig. 3).
When the amount of promoter used is 100 mol% relative to
pNPP, compounds 1e10 originate either homogeneous (3, 4 and 10)
or solid/liquid biphasic (1, 2, 5e9) systems (Table 1). For the
biphasic systems, the solid phase (denoted N*) was recovered at the
end of the reaction (please see the Experimental section for details)
and characterized by FT-IR spectroscopy. Our previous studies on
the reaction of the complexes MoO2Cl2L (L ¼ bipy, di-tBu-bipy) with
water (which resulted in the isolation of the hybrid materials 8 and
9) [10h,i], together with the synthesis and characterization of
[MoO3(bipy)]n (7) by oxidative decarbonylation of Mo(CO)4(bipy)
[10g], helped in the identification of the recovered solids. The FT-IR
spectra of 1*, 7* and 8* were all identical to that for the as-prepared
material 7 (Fig. S1 in the Supplementary data). For the dichloro
complex 2, the spectrum of the recovered solid 2* showed some
differences from that for 2 (Fig. S2), although there was still a good
match between the two spectra concerning the characteristic Moe
O vibrations between 850 and 950 cmꢁ1 and the organic ligand
modes between 1000 and 1700 cmꢁ1. Three possible products of
the reaction of 2 with water are the oxo-bridged dinuclear species
[{MoO2Cl(di-tBu-bipy)}2(m2-O)] [11] and [{MoO2(m2-O)(di-tBu-
Fig. 2. Hydrolysis profile of pNPP either in the absence of promoter (B), or with
MoO2X2(bipy) (X ¼ Cl (1, (100 mol%) or (10 mol%)), CH3 (5, )), MoO2X2(di-tBu-bipy)
(X ¼ Cl (2,
(100 mol%) or (10 mol%)), CH3 (6, )), [MoO2Cl2(H2O)2]$(diglyme)2
(3, ꢂ), MoO2Cl2 (4, -), MoO2Cl2(DMF)2
( ) or Na2MoO4 ( ). Reaction conditions:
100 mol% promoter relative to pNPP (unless otherwise indicated), 55 ꢀC, D2O, dioxane
as internal standard. Reaction pD after promoter addition in parenthesis: 1 (1.4), 2
(6.4), 3 (1.4), 4 (1.4), 5 (7.4), 6 (7.4), MoO2Cl2(DMF)2 (1.4), Na2MoO4 (7.4).

46
A.C. Gomes et al. / Journal of Organometallic Chemistry 760 (2014) 42e47
polynuclear compound studied, {[MoO3(bipy)][MoO3(H2O)]}n (8),
performs much better than molybdic acid (MoO3$H2O) and as good
as the mononuclear dichloro derivatives. While MoO2Cl2 and
MoO3$H2O both give rise to monophasic (homogeneous) systems,
the complexes MoO2X2L (1,2,5,6; X ¼ Cl, CH3) and compound 8 give
rise to biphasic systems (when 100 mol% of promoter is used
relative to pNPP), and it was possible to recover and identify the
solid phases. Whereas both MoO2Cl2(bipy) (1) and 8 are trans-
formed into the one-dimensional organiceinorganic hybrid mate-
rial [MoO3(bipy)]n, which in a separate experiment only performed
moderately as a promoter of pNPP hydrolysis, complexes 5, 6 and,
to a lesser extent, 2 were recovered unchanged. Future work may
focus on complex 2, investigating the possibility of promoter
recycling and reuse.
Acknowledgments
We are grateful to the Fundação para a Ciência e a Tecnologia
(FCT, Portugal), the Programa Operacional Ciência e Inovação (POCI)
2010, Orçamento do Estado (OE), European Union, Fundo Europeu
de Desenvolvimento Regional (FEDER), QREN, COMPETE, the
Associate Laboratory CICECO (PEst-C/CTM/LA0011/2013), and CQE
(PEst-OE/QUI/UI0100/2013) for continued support and funding,
including the R&D Project PTDC/QEQ-SUP/1906/2012 and the
research grant BPD/UI89/4864/2013 provided within this project.
The authors also thank the Portuguese NMR Network (IST-UTL
Center) (RECI/QEQ-QIN/0189/2012) for providing access to the
NMR facilities.
Fig. 3. Hydrolysis profile of pNPP either in the absence of promoter (B), or with
[MoO3(bipy)]n (7, ), {[MoO3(bipy)][MoO3(H2O)]}n (8, ), [Mo8O22(OH)4(di-tBu-bipy)4]
(9, ), or MoO3 (10, ). Reaction conditions: 100 mol% promoter relative to pNPP, 55 ꢀC,
D2O, dioxane as internal standard. The reaction pD after promoter addition was 7.4 in
all cases.
4. Conclusions
Insecticidal organophosphates and related nerve agents can be
detoxified by hydrolysis of their phosphoester bonds. In the present
work we have shown that various types of oxomolybdenum com-
pounds, ranging from simple mononuclear complexes of the type
MoO2X2L to polynuclear compounds, can promote the hydrolysis of
the benchmark substrate sodium para-nitrophenylphosphate
(pNPP). The performance of the dichloro derivatives MoO2Cl2L (1,2;
L ¼ bipyridine ligand) matches that of MoO2Cl2, and is superior to
that of Na2MoO4. A disadvantage of MoO2Cl2 vs. the bipyridine
adducts is that it is less stable and more difficult to handle. The best
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.jorganchem.2013.12.029.
References
[1] (a) S.V. Kumar, Md. Fareedullah, Y. Sudhakar, B. Venkateswarlu, E. Ashok
Kumar, Arch. Appl. Sci. Res. 2 (2010) 199e215;
(b) M. Eddleston, N.A. Buckley, P. Eyer, A.H. Dawson, Lancet 371 (2008) 597e
607;
(c) M. Sirotkina, I. Lyagin, E. Efremenko, Int. Biodeterior. Biodegrad. 68 (2012)
18e23.
[2] (a) K. Kim, O.G. Tsay, D.A. Atwood, D.G. Churchill, Chem. Rev. 111 (2011)
5345e5403;
(b) F. Aguilar-Pérez, P. Gómez-Tagle, E. Collado-Fregoso, A.K. Yatsimirsky,
Inorg. Chem. 45 (2006) 9502e9517.
[3] U.C. Gupta, Molybdenum in Agriculture, Cambridge University Press, Cam-
bridge, 1997.
[4] (a) L.Y. Kuo, S. Kuhn, D. Ly, Inorg. Chem. 34 (1995) 5341e5345;
(b) L.Y. Kuo, L.A. Barnes, Inorg. Chem. 38 (1999) 814e817;
(c) T.J. Ahmed, L.N. Zakharov, D.R. Tyler, Organometallics 26 (2007) 5179e
5187.
[5] (a) H. Weil-Malherbe, R.H. Green, Biochem. J. 49 (1951) 286e292;
(b) L. Lutwak, J. Sacks, J. Biol. Chem. 200 (1953) 565e569;
(c) H. Weil-Malherbe, Biochem. J. 55 (1953) 741e745;
(d) E. Ishikawa, T. Yamase, J. Inorg. Biochem. 100 (2006) 344e350;
(e) E. Cartuyvels, K.V. Hecke, L.V. Meervelt, C. Görller-Walrand, T.N. Parac-
Vogt, J. Inorg. Biochem. 102 (2008) 1589e1598;
(f) G. Absillis, R.V. Deun, T.N. Parac-Vogt, Inorg. Chem. 50 (2011) 11552e
11560;
(g) G. Absillis, E. Cartuyvels, R.V. Deun, T.N. Parac-Vogt, J. Am. Chem. Soc. 130
(2008) 17400e17408;
(h) E. Ishikawa, T. Yamase, Eur. J. Inorg. Chem. (2013) 1917e1925.
[6] G.P. Chisole, P.M. Maitlis, Metal-catalysis in Industrial Organic Processes, Royal
Society of Chemistry Publishing, Cambridge, 2008.
[7] U. Kortz, M. Pope, Inorg. Chem. 34 (1995) 2160e2163.
[8] (a) G. Feng, D. Natale, R. Prabaharan, J.C. Mareque-Rivas, N.H. Williams,
Angew. Chem. Int. Ed. 45 (2006) 7056e7059;
(b) H.-J. Schneider, J. Rammo, R. Hettich, Angew. Chem. Int. Ed. Engl. 32 (1993)
1716e1719;
(c) A. O’Donoghue, S.Y. Pyun, M.-Y. Yang, J.R. Morrow, J.P. Richard, J. Am.
Chem. Soc. 128 (2006) 1615e1621;
(d) M. Komiyama, S. Kina, K. Matsumura, J. Sumaoka, S. Tobey, V.M. Lynch,
E. Anslyn, J. Am. Chem. Soc. 124 (2002) 13731e13736;
Fig. 4. Hydrolysis profile of pNPP with 1*
( ), [MoO3(bipy)]n (7, ), 5* ( ) and
MoO2(CH3)2(bipy) (5, ). Reaction conditions: 100 mol% promoter relative to pNPP,
55 ꢀC, D2O, dioxane as internal standard. The reaction pD after promoter addition was
7.4 in all cases.

A.C. Gomes et al. / Journal of Organometallic Chemistry 760 (2014) 42e47
47
ꢀ
(e) N. Mitic, S.J. Smith, A. Neves, L.W. Guddat, L.R. Gahan, G. Schenk, Chem.
M.J. Calhorda, C.C. Romão, I.S. Gonçalves, A.D. Lopes, M. Pillinger, Chem. Eur. J.
8 (2002) 2370e2383;
Rev. 106 (2006) 3338e3363;
(f) A. Neves, M. Lanznaster, A.J. Bortoluzzi, R.A. Peralta, A. Casellato,
E.E. Castellano, P. Herrald, M.J. Riley, G. Schenk, J. Am. Chem. Soc. 129 (2007)
7486e7487.
(f) F.E. Kühn, A.M. Santos, A.D. Lopes, I.S. Gonçalves, E. Herdtweck, C.C. Romão,
J. Mol. Catal. A Chem. 164 (2000) 25e38;
(g) T.R. Amarante, P. Neves, A.C. Coelho, S. Gago, A.A. Valente, F.A.A. Paz,
M. Pillinger, I.S. Gonçalves, Organometallics 29 (2010) 883e892;
(h) M. Abrantes, T.R. Amarante, M.M. Antunes, S. Gago, F.A.A. Paz,
I. Margiolaki, A.E. Rodrigues, M. Pillinger, A.A. Valente, I.S. Gonçalves, Inorg.
Chem. 49 (2010) 6865e6873;
[9] C. Tomé, M.C. Oliveira, M. Pillinger, I.S. Gonçalves, M. Abrantes, Dalton Trans.
42 (2013) 3901e3907.
[10] (a) W.M. Carmichael, D.A. Edwards, G.W.A. Fowles, P.R. Marshall, Inorg. Chim.
Acta 1 (1967) 93e96;
(b) F.E. Kühn, A.D. Lopes, A.M. Santos, E. Herdtweck, J.J. Haider, C.C. Romão,
A.G. Santos, J. Mol. Catal. A Chem. 151 (2000) 147e160;
(c) F.J. Arnaiz, R. Aguado, J. Sanzaparicio, M. Martinezripoll, Polyhedron 13
(1994) 2745e2749;
(d) G.N. Schrauzer, L.A. Hughes, N. Strampach, P.R. Robinson, E.O. Schlemper,
Organometallics 1 (1982) 44e47;
(i) T.R. Amarante, P. Neves, C. Tomé, M. Abrantes, A.A. Valente, F.A.A. Paz,
M. Pillinger, I.S. Gonçalves, Inorg. Chem. 51 (2012) 3666e3676.
[11] C.A. Gamelas, A.C. Gomes, S.M. Bruno, F.A.A. Paz, A.A. Valente, M. Pillinger,
C.C. Romão, I.S. Gonçalves, Dalton Trans. 41 (2012) 3474e3484.
[12] T.R. Amarante, P. Neves, F.A.A. Paz, M. Pillinger, A.A. Valente, I.S. Gonçalves,
Inorg. Chem. Commun. 20 (2012) 147e152.
(e) F.E. Kühn, M. Groarke, E. Bencze, E. Herdtweck, A. Prazeres, A.M. Santos,