Destruction of chemical warfare agent simulants by air and moisture stable metal NHC complexes

Article abstract of DOI:10.1039/c7dt04805j

The cooperative effect of both NHC and metal centre has been found to destroy chemical warfare agent (CWA) simulants. Choice of both the metal and NHC is key to these transformations as simple, monodentate N-heterocyclic carbenes in combination with silver or vanadium can promote stoichiometric destruction, whilst bidentate, aryloxide-tethered NHC complexes of silver and alkali metals promote breakdown under mild heating. Iron-NHC complexes generated in situ are competent catalysts for the destruction of each of the three targetted CWA simulants.

Full text of DOI:10.1039/c7dt04805j

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Destruction of chemical warfare agent simulants
by air and moisture stable metal NHC complexes†
Cite this: DOI: 10.1039/c7dt04805j
a
Catherine Weetman,a Stuart Notmanb and Polly L. Arnold
*
The cooperative effect of both NHC and metal centre has been found to destroy chemical warfare agent
(CWA) simulants. Choice of both the metal and NHC is key to these transformations as simple, monoden-
tate N-heterocyclic carbenes in combination with silver or vanadium can promote stoichiometric
destruction, whilst bidentate, aryloxide-tethered NHC complexes of silver and alkali metals promote
breakdown under mild heating. Iron–NHC complexes generated in situ are competent catalysts for the
destruction of each of the three targetted CWA simulants.
Received 20th December 2017,
Accepted 17th January 2018
DOI: 10.1039/c7dt04805j
rsc.li/dalton
Introduction
Since the first deployment of chemical warfare agents (CWAs)
during the First World War, research into efficient decontami-
nation routes has become necessary for immediate appli-
cations, and also for the destruction of CWA stockpiles as set
out in the 1992 Chemical Weapons Convention Treaty
(demiliterisation).1–5 Whilst a variety of fast and effective
decontamination routes have been identified, these generally
Scheme 1 Three pathways for sulfur-mustard destruction.
contain
a mixture of flammable solvents and corrosive
reagents and can be impractical for transportation or deconta-
mination of expensive equipment. For example, DS2 is a com-
bination of nucleophilic diethylenetriamine/ethylene glycol/
monomethyl ether/sodium hydroxide mixtures and whilst it is
a broadband decontaminant it is highly corrosive towards
many materials.6 Alternate decontamination solutions con-
taining basic hypochlorite (bleach)-based microemulsions are
very effective for sulfur mustard decontamination7,8 however
these are also deemed too corrosive and environmentally unac-
ceptable for widespread use.9 Therefore new reagents that have
a low environmental impact and can be used in different situ-
ations on different classes of warfare agents are desirable.10
Sulfur mustard (HD), bis-2-chloroethyl sulfide, is a potent
vesicant with a long environmental persistence that makes
decontamination challenging.6,11–13 Generally destruction of
HD can occur via three different pathways (Scheme 1).
Currently known dehydrohalogenation procedures can be pro-
blematic due to the reversible addition of HCl14,15 and con-
sidered too slow in comparison to the other decontamination
pathways16 whilst at ambient temperatures hydrolysis is
limited by the low aqueous solubility of HD.17 Oxidation is
currently one of the most effective pathways of deconta-
mination; however care must be taken to form the mono-
oxidation product, as the sulfone is a potent vesicant in its
own right.
The other major class, nerve agents, are organophospho-
nate compounds that were originally developed as pesticides
until their highly toxic nature was recognised. Nerve agents
can be divided into two main classes: non-persistent G- (e.g.
Sarin) and persistent V- (e.g. VX) series, where the persistence
relates to the relative ease of degradation or propensity to
remain in the environment.
Traditional routes for decontamination of VX have centred
arounds its susceptibility towards nucleophilic attack, but again
the control of product formation is imperative. In the simplest
case addition of H2O yields several products,18,19 but the for-
mation of EA-2192 is of concern as it is nearly as toxic as VX and
is less reactive towards further nucleophilic attack (Scheme 2).10
N-Heterocyclic carbenes (NHCs) have transformed modern
organometallic chemistry.20 The strongly Lewis basic σ-donor
ligands have been shown to bind to many metals leading to
aEaStCHEM School of Chemistry, The University of Edinburgh, King’s Buildings,
Edinburgh, EH9 3FJ, UK. E-mail: Polly.Arnold@ed.ac.uk
bDefence Science Technology Laboratory (DSTL), Porton Down, Salisbury,
SP4 0JQ Wilts, UK
†Electronic supplementary information (ESI) available: Synthetic details for the
compounds; kinetic data for the catalysis. Crystal structure data for the
vanadium–NHC decomposition product. CCDC 1580495. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/c7dt04805j
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vages, respectively. Whilst these simulants are less toxic than
the actual CWAs, they are still considered to be very toxic
(paraoxon-ethyl: LD50 in Rat = 0.716 mg kg−1) and must be
handled with great care. Reactions are carried out on a small
scale with no more than 5 µL of the chosen CWA simulant, to
manage the risks associated with these compounds.
Results and discussion
Candidate metal–NHC complexes
Scheme 2 Pathways for VX destruction by hydrolysis.
Copper and silver NHC complexes were initially targeted due
to their high water-stability and ability to undergo redox reac-
tions, thus providing a good baseline for how metal–NHC com-
plexes may react with CWA simulants. This focused on the use
of previously reported, commercially available unsaturated
NHCs (denoted IR, and derived from the imidazolium chloride
salts IPr·HCl, IMes·HCl and ICy·HCl) and saturated NHCs
(denoted SIR, and derived from the imidazolinium salts
SIPr·HCl, and SIMes·HCl) and a bidentate aryloxide-functiona-
lised imidazolium salt (HOArIPr·HCl), Fig. 2. The silver NHC
complexes AgCl(IR) (R = Dipp 1-Ag, Mes 2-Ag, Cy 3-Ag), AgCl
(SIR) (R = Dipp 4-Ag, Mes 5-Ag)38 and corresponding copper
NHC complexes CuCl(IR) (R = Dipp 1-Cu, Mes 2-Cu, Cy 3-Cu),
CuCl(SIR) (R = Dipp 4-Cu, Mes 5-Cu)39 are readily obtained
from reactions with the corresponding metal oxide. Due to the
potential for oxidation destruction pathways the use of the
highly oxidising but remarkably air-stable vanadyl NHC com-
plexes VOCl3(IR) (R = Dipp 1-V, Mes 2-V, Cy 3-V), Fig. 2, (1–3)-V
were isolated from the stoichiometric addition of VOCl3 to the
free carbene.33,40 It is of note that whilst the saturated ana-
logues of the vanadium NHC complexes were also isolated
they were found to be unstable towards moisture, and there-
fore were not used in this study (see ESI†).
In addition, metal complexes of the bidentate aryloxide
NHC were also made; 6-Ag was made from silver(I)oxide,41 and
the sodium (6-Na) and potassium (6-K) complexes were made
from the corresponding MOtBu (M = Na or K) salt in situ prior
to use.
Reactions of each compound shown in Fig. 2 with each of
the three CWA simulants were monitored by 1H NMR spec-
troscopy. Reactions used stoichiometric, excess, or catalytic
amounts of the complexes and were accelerated by either heat
or photolysis.
widespread applications, notably their use in homogeneous
catalysis with late transition metals for alkene metathesis and
C–C coupling reactions.21 In relation to decontamination and
demiliterisation of CW agents, the range of reactivity available
to NHCs and their highly tuneable nature makes them attrac-
tive candidates for these processes due to their ability to act as
strong nucleophiles in organocatalysis, as well as organic
bases.22 Oxidative CWA destruction pathways can also be con-
sidered in combination with right choice of metal centre.
Many coinage metal NHC complexes made for medicinal
applications display very high water stability,23 while homo-
geneous catalysts based on Pd and V show both a high stability
towards oxidation24–28 and great efficacy as oxidation
catalysts,29–31 in particular vanadium doped silica has been
previously shown to be effective for the oxidation of CEES. The
redox couple of VO2+/VO2+ (vanadyl) complexes is +1.00 V,32
and it has been demonstrated that the complex VOCl3(IMes) is
air-stable.33
We have been studying the cooperative reactivity of metal–
NHC complexes in which the metal–C bond is relatively labile,
and can give rise to reactions of both the metal and NHC. We
have previously shown a range of carbon–element bond for-
mation and cleavage reactions.34–36
Herein we report the effectiveness of a range of air and
moisture stable metal NHC complexes for the stoichiometric
and catalytic destruction of both H- (mustards) and V- (nerve)
type chemical warfare agent (CWA) simulants shown in Fig. 1.
The use of simulants is required due to strictly controlled pro-
duction, acquisition, retention or use of warfare agents under
Schedule 1 of the Chemical Weapons Convention (CWC).
Previous research has shown 2-chloroethyl ethyl sulphide
(CEES, referred to as half mustard) is an effective simulant for
HD,37 whilst paraoxon-ethyl and profenofos are used to simu-
late VX as these contain the desirable P–O and P–S bond clea-
Fig. 1 CWA simulants targeted for decontamination.
Fig. 2 M–NHC complexes used in this study.
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Fig. 3 Kinetic rate data for the decomposition of CEES by (1–5)-Ag
showing first order dependence on CEES and that 1-Ag is by far the
fastest reagent for its destruction.
Scheme 3 Reactions of (1–5)-Ag with CWA simulants showing the
major decontamination products.
It is proposed that the photolysis cleaves the silver–NHC
bond, thus releasing the silver ion, a potent oxidant for CEES,
and the free carbene which is active for the dehydrohalogena-
tion of CEES, giving two routes for the destruction of the CWA
simulant, Scheme 4a. Reactions of equimolar amounts of
Ag2O and AgCl and CEES were also carried out as control reac-
tions, however they were insoluble in the reaction medium
and no decomposition was observed at 80 °C or under photo-
lysis. It is suggested that the NHC plays an important role by
both helping solubilise the metal cation whilst also acting as a
reagent in its own right.
This hypothesis is backed up by the products formed from
the reaction of the free base NHC (Scheme 4b). The equimolar
reaction between IPr and CEES at room temperature shows
10% conversion to EVS, the dehydrohalogenation product,
within 5 minutes. However, storage for a further hour at room
temperature or at 80 °C for 24 h showed no further destruction
of CEES, presumably because the remaining NHC decomposed
during prolonged contact with air and moisture. A trial reac-
Destruction by group 11 metal–NHC complexes
Stoichiometric simulant degradation reactions were followed
in 0.5 mL of CDCl3. Reactions were monitored at intervals by a
combination of NMR spectroscopy (1H and 31P where relevant),
UV-Vis spectroscopy and GC mass spectrometry. As shown in
Scheme 3, complexes (1–5)-Ag showed no reactivity at room
temperature or after prolonged heating at 80 °C with any of
the simulants. However, upon exposure to low-intensity UV
light (254 nm, 6 W) the reactions with CEES showed the con-
version of CEES into new compounds after 1 h, according to
1H NMR spectroscopic analysis. No reaction of the V agent
simulants was observed even after prolonged exposure to
either 254 nm or 364 nm UV radiation.
Full destruction of CEES was observed after 5 h when using
an excess of 1-Ag (5 eq.). The 1H NMR spectra show several
new species in solution. Through a combination of HSQC,
HMBC, COSY and DOSY 2D NMR spectroscopy experiments
the major product was identified as the mono-oxidation
product, CEES-O (Scheme 3). The two other major products
are attributed to the dehydrohalogenation of CEES and
include ethyl(vinyl)sulfide (EVS) and 1,4-thioxane (1,4-TO)
which results from the dehydrohalogenation of partially hydro-
lysed CEES.10 An approximate product distribution was 80%
CEES-O: 8% EVS: 10% 1,4-TO, with several minor products
accounting for the remaining 2%.
The fate of complex 1-Ag was also determined by NMR spec-
troscopy and ICP-OES spectrometry as the imidazolium chloride
salt IPr·HCl, and a silver- and sulfur- containing material which
was observed to precipitate during the reaction. The scale of
these reactions (demanded for safety reasons) make unambigu-
ous analysis difficult, but it is most likely to be silver sulfate.
Kinetic analyses of the reactions of (1–5)-Ag with CEES were
carried out to examine the influence of the sterics and elec-
tronics of the NHC on the reaction. Reactions between (1–5)-Ag
and CEES in CDCl3 in a quartz tube were monitored by 1H
NMR spectroscopy with mesitylene as an internal standard.
NMR spectra were recorded for each sample after 30 minutes
periods of UV (254 nm) radiation. The data fitted to a first-
order dependence on CEES (Fig. 3), show that 1-Ag is the
fastest of all the silver NHC complexes (Fig. S6–10†).
Scheme 4 Destruction of CEES mediated by the silver cation (oxi-
dation, route a) or by the released NHC IPr (dehydrohalogenation,
route b).
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tion using artificial sunlight from a commercially available
SAD lamp provided ca. 40% decomposition of CEES within the
same 5 h time frame.
The analysis of observed rates gives a reactivity in decreas-
ing order for the NHC of IPr > ICy > IMes > SIPr > SIMes.
Saturated NHCs (SIR) are better σ-donors than the unsaturated
(IR) analogues.42 Thus although the free (SIR) carbene could
be considered more reactive for the dehydrohalogenation reac-
tion, the efficacy of complexes (1–5)-Ag appears to be domi-
nated by the reaction that cleaves the Ag–NHC bond.
To further confirm this cooperative effect reactions between
the metal and the NHC reactions were carried out using the
analogous copper NHC complexes. Following the same proto-
col for the silver complexes, the Cu(I) analogues (1–5)-Cu were
combined with 1 equivalent of CEES in the presence of UV
Scheme 5 Reactions of (1–3)-V with CWA simulants showing the major
decontamination products.
1
light (254 nm). After 1 h the H NMR spectra confirm that the
product diethyldisulfide (EESS) is formed (Scheme 5b). VOCl3
has been recently shown to effect the oxychlorination of cyclo-
hexane,44 but if anything, is only a minor contributor here (see
ESI† for proposed mechanism).
The complexes (1–3)-V also react with the two V-agent simu-
lants shown in Fig. 1. Scheme 5c shows the reaction of (1–3)-V
with both paraoxon-ethyl and profenofos yield substituted
phenol products arising from P–OAr bond cleavage and sub-
sequent hydrolysis through trace moisture in the reaction
mixture. These were identified by GC-MS trace after 3 h of
exposure to UV light (254 nm) (Scheme 5c), with complete
decomposition of both V agent simulants observed after 24 h.
Cu–NHC bonds have been broken, showing broad, paramagne-
tically-shifted resonances which are attributed to the for-
mation of Cu(II) ions arising from aerobic oxidation after
release into solution. GC-MS data indicate that no degradation
of CEES has occurred in any of the reactions studied.
Prolonged exposure of the reactions to UV light show only
background reactivity, ca. 10% decomposition of CEES. Since
the Cu+1/Cu0 redox couple is significantly less oxidising than
the Ag+1/Ag0 couple (+0.52 V vs. +0.80 V),32 these observations
suggest that both the oxidising metal and the basic NHC are
responsible for the CEES destruction. We note that the degra-
dation products arise from both oxidation and dehydrohalo-
genation, suggesting that the metal cation also plays a role in
facilitating dehydrohalogenation. Presumably coordination of
the sulfur to the silver cation renders the CEES active towards
attack by the liberated NHC.
Destruction by complexes of tethered-NHCs
To test the hypothesis that a combination of metal and NHC
afford enhanced dehydrohalogenation of the H-agent, three
different metal complexes of a hemilabile, bidentate aryloxy-
NHC, 6-Ag, 6-Na and 6-K shown in Fig. 2, were made and
tested (see ESI† for details).
No reaction between stoichiometric quantities of 6-Ag and
CEES was observed at room temperature by 1H NMR spec-
troscopy, but after 1 h at 80 °C, 25% conversion to the product
of dehydrohalogenation, EVS, was observed. This was charac-
terised by the characteristic alkene hydrogens of the product
(Scheme 6a). The complete conversion of CEES to EVS can be
achieved using a catalytic amount of 6-Ag if additional Ag2O is
added within 5 h, thus rendering the system catalytic in NHC.
Destruction by vanadium NHC complexes
Complexes (1–3)-V produce efficient stoichiometric destruction
of CEES in 5 hours under UV light (254 nm), Scheme 5a. The
reactions appear to involve reduction by the vanadium centre
1
as the H NMR spectra of the reaction mixtures show contact-
shifted resonances due to the paramagnetic vanadium centre,
and must be separated from vanadium-containing materials
for identification. Reactions monitored by GC-MS also show
the conversion of CEES to new products (Scheme 5a). The
major decomposition product is CEES-O (60%), with 2-chloro-
ethylethyldisulfide (CEESS) a minor product. Two features are
notable: there is no evidence of dehydrohalogenation, and hex-
achloroethane (PCA) is also formed during the reaction.
The observation of PCA production is notable since it is
usually observed to form in samples of CEES that have been
stored for long periods of time (tens of years to the best of our
knowledge),17 although there are only a few literature reports
of the chlorination of CEES. In these cases the di, tri, and tet-
rachlorinated sulfides are reported to form, along with hexa-
chloroethane which results from the reaction with excess
chlorine radicals.43 Here however, repetition of the reactions
between 2-V and CEES in C6D6 confirm the PCA derives from
Scheme 6 Reactions of 6-M with CWA simulants showing the major
solvent decomposition, as after 3 h, the new decomposition decontamination products.
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Table 1 Catalytic destruction of CWA simulants with in situ catalyst for-
mation from air stable components showing the major products from
each reaction
CWA simulant
Entry
IR·HCl
MXn
CEES
Paraoxon-ethyl
Profenofos
1
2
3
4
5
6
7
8
9
IPr·HCl
IPr·HCl
IPr·HCl
IMes·HCl
IMes·HCl
IMes·HCl
ICy·HCl
ICy·HCl
ICy·HCl
NiCl2
FeBr2
FeCl3
NiCl2
FeBr2
FeCl3
NiCl2
FeBr2
FeCl3
EESS
EESS
CEES-O
EESS
EESS
CEES-O
EESS
BES
CEES-O
Reaction conditions used 1 µmol of NHC·HCl and metal salt, with
4 µmol of KOtBu and 20 µmol of CWA simulant in 1 mL of MeCN at
80 °C.
Scheme 7 Proposed mechanism for the destruction of CEES catalysed
by 6-Ag.
The proposed mechanism for this reaction is outlined in
Scheme 7, showing how the combination of the silver centre
and the NHC can be effective for the destruction of CEES.
Furthermore, similar reactivity can be obtained with the
alkali metal NHC complexes 6-Na and 6-K, which give 30%
and 15% destruction of CEES in 1 h, respectively (at 80 °C).
Again, the selective formation of EVS was identified by 1H
NMR spectroscopy. The kinetic data (Fig. S27†) suggest a small
induction period (possibly due to complex formation) and first
order dependence on base. It is possible to double the rate of
reaction by doubling the amount of alkali metal base. Once
formed, these Group 1 salts show moderate moisture instabil-
ity; decomposition of 6-K occurs over one hour after exposure
to air so whilst cheaper, they are less desirable as decontami-
nation reagents than the silver complexes.
The reactivity of complexes 6-M towards both paraoxon-ethyl
and profenofos nerve simulants under analogous reaction con-
ditions also proved successful; cleavage of P–OAr bond was
identified by 31P NMR spectroscopy after 20 h at 80 °C
(Scheme 6b). A proposed mechanism is outlined in Scheme 8, in
which the nucleophilic carbene attacks the phosphorus centre,
leading to M–OAr bond formation then P–OAr bond cleavage.
Scheme 9 Catalytic breakdown of CEES using an in situ generated
NHC–Fe(II) catalyst.
which the active catalyst is generated in situ, from the use of
air stable components (NiCl2, FeBr2 and FeCl3) with imidazo-
lium salts (IPr·HCl, IMes·HCl and ICy·HCl) was carried out.
Use of equimolar amounts of MCln and IR·HCl with a fourfold
excess of KOtBu leads to the formation of NHC–MXn (where
X = Cl or OtBu) in situ, to which each of the chosen CWA simu-
lants were then added 20-fold excess (i.e. 5 mol% catalyst
loading w.r.t. simulant) and monitored over a period of 24 h at
80 °C using a combination of UV/vis, GC-MS and NMR
spectroscopy.
In all cases catalytic destruction of the chosen simulants
was observed after mild heating at 80 °C for 24 hours. In terms
of CEES destruction, use of the Fe(III) complex results in oxi-
dation to CEES-O as the major product (Table 1, entries 3, 6
and 9) whilst EESS and PCA were identified as the major pro-
ducts for Ni(II) and Fe(II) reactions (Table 1, entries 1, 2, 4, 5,
and 7), except for FeBr2 reactions in which oxybis(ethylsulfane)
(BES) was identified (Table 1, entry 8; Scheme 9). In the case of
the nerve simulants P–OAr cleavage was identified as the
major product through GC-MS analysis.
Catalytic CWA destruction
NHC complexes of earth-abundant iron and nickel have shown
widespread uses in homogeneous catalysis. Their combination
with the simple bases KOtBu was studied as a potential
destruction method. Thus, a series of catalytic reactions in
Attempts to render the (1–3)-V systems catalytic proved to
be unsuccessful, but the reactions underline the capability of
the oxidising metal in these CWA destructions.
Conclusions
Air- and moisture stable NHC complexes have been shown to
be effective for the destruction of CWA simulants. The coopera-
Scheme 8 Proposed mechanism for the destruction of nerve agents
with 6-M complexes.
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tive effect of both the NHC and metal centre is vital to the
success of these decontamination reactions. Comparison of
the simple commercially available imidazoline/imidazolinium
silver NHC complexes, (1–5)-Ag, these were found to provide
efficient destruction under UV conditions in 5 h, primarily to
the oxidation product, CEES-O, and also to the dehydrohalo-
genation product. The choice of metal centre is key for these
transformations as reactions with complexes (1–3)-V provide
complete destruction of CEES within 5 h and allowed for
destruction of nerve simulants through cleavage of P–OAr
bond to form substituted phenols. Preliminary studies using
artificial sunlight (from a commercially available SAD lamp)
also show reasonable levels of CEES decomposition within the
same 5 h timeframe, presumably a result which could be
improved with suitable ligand tuning.
4 J. Paxman and R. Harris, A Higher Form of Killing: The Secret
History of Chemical and Biological Warfare, Arrow, London,
2001.
5 J. L. McWilliams and R. J. Steel, Gas! The Battle for Ypres,
1915, Vanwell Publishing Limited, Canada, 1985.
6 Y. C. Yang, J. A. Baker and J. R. Ward, Chem. Rev., 1992, 92,
1729–1743.
7 F. M. Menger and A. R. Elrington, J. Am. Chem. Soc., 1991,
113, 9621–9624.
8 F. M. Menger and A. R. Elrington, J. Am. Chem. Soc., 1990,
112, 8201–8203.
9 I. A. Fallis, P. C. Griffiths, T. Cosgrove, C. A. Dreiss,
N. Govan, R. K. Heenan, I. Holden, R. L. Jenkins,
S. J. Mitchell, S. Notman, J. A. Platts, J. Riches and
T. Tatchell, J. Am. Chem. Soc., 2009, 131, 9746–9755.
Examination of the cooperative effect of metal centre and 10 B. M. Smith, Chem. Soc. Rev., 2008, 37, 470–478.
NHC through use of a hemi-labile bidentate aryloxide tethered 11 E. Marshall, Science, 1984, 224, 130–132.
NHC complex (6-M) shows clean destruction to EVS at 80 °C 12 J. P. Fitch, E. Raber and D. R. Imbro, Science, 2003, 302,
within a few hours. The rate of destruction is increased, and
the reaction rendered catalytic in NHC via addition of further 13 L. M. Eubanks, T. J. Dickerson and K. D. Janda, Chem. Soc.
equivalents of alkali metal base or silver(I) oxide. Catalytic Rev., 2007, 36, 458–470.
destruction of all three CWA simulants can also be achieved 14 G. W. Wagner, P. W. Bartram, O. Koper and K. J. Klabunde,
using in situ generated iron or nickel NHC complexes. This J. Phys. Chem. B, 1999, 103, 3225–3228.
new class of CWA simulant degradants show promise, and 15 G. W. Wagner, O. B. Koper, E. Lucas, S. Decker and
1350–1354.
further work is in progress to improve reactivity while retaining
the air-stability of the metal–NHC complexes.
K. J. Klabunde, J. Phys. Chem. B, 2000, 104, 5118–
5123.
16 Y. Y. Liu, C. T. Buru, A. J. Howarth, J. J. Mahle,
J. H. Buchanan, J. B. DeCoste, J. T. Hupp and O. K. Farha,
J. Mater. Chem. A, 2016, 4, 13809–13813.
17 N. B. Munro, S. S. Talmage, G. D. Griffin, L. C. Waters,
A. P. Watson, J. F. King and V. Hauschild, Environ. Health
Perspect., 1999, 107, 933–974.
Conflicts of interest
There are no conflicts to declare.
18 Y. J. Jang, K. Kim, O. G. Tsay, D. A. Atwood and
D. G. Churchill, Chem. Rev., 2015, 115, PR1–PR76.
19 K. Kim, O. G. Tsay, D. A. Atwood and D. G. Churchill,
Chem. Rev., 2011, 111, 5345–5403.
20 W. A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1290–
1309.
21 T. M. Trnka and R. H. Grubbs, Acc. Chem. Res., 2001, 34,
18–29.
22 C. M. Crudden and D. P. Allen, Coord. Chem. Rev., 2004,
248, 2247–2273.
23 D. Bourissou, O. Guerret, F. P. Gabbai and G. Bertrand,
Chem. Rev., 2000, 100, 39–91.
24 J. C. Y. Lin, R. T. W. Huang, C. S. Lee, A. Bhattacharyya,
W. S. Hwang and I. J. B. Lin, Chem. Rev., 2009, 109, 3561–
3598.
Acknowledgements
We thank DSTL for financial support, and the EPSRC for
funding through EP/J018139/1 and the UK Catalysis Hub EP/
K014714/1. This project has also received funding from the
European Research Council (ERC) under the European
Union’s Horizon 2020 research and innovation programme
(grant agreement No 740311). We thank Karlotta van Rees and
Peter Saghy for assistance with the synthesis of the silver and
copper complexes, Euan Doidge for ICP-OES analysis,
University of Edinburgh NMR spectroscopy and Mass spec-
trometry departments for support.
25 S. P. Nolan, Acc. Chem. Res., 2011, 44, 91–100.
26 S. Gaillard, C. S. J. Cazin and S. P. Nolan, Acc. Chem. Res.,
2012, 45, 778–787.
Notes and references
1 J. B. Tucker, War of Nerves: Chemical Warfare from World 27 I. J. B. Lin and C. S. Vasam, Coord. Chem. Rev., 2007, 251,
War I to Al-Qaeda, Pantheon Books, New York, 2006. 642–670.
2 K. Coleman, History of Chemical Warfare Pelgrave, 28 P. L. Arnold, M. S. Sanford and S. M. Pearson, J. Am. Chem.
Macmillan, Basingstoke, 2005. Soc., 2009, 131, 13912–13913.
3 E. Croddy, Chemical and Biological Warfare, Springer-Verlag, 29 D. A. Bulushev, L. Kiwi-Minsker, V. I. Zaikovskii and
New York, 2001. A. Renken, J. Catal., 2000, 193, 145–153.
A
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Dalton Transactions
Paper
30 Y. Maeda, N. Kakiuchi, S. Matsumura, T. Nishimura, 38 P. de Fremont, N. M. Scott, E. D. Stevens, T. Ramnial,
T. Kawamura and S. Uemura, J. Org. Chem., 2002, 67, 6718–
6724.
31 A. Lattanzi, A. Senatore, A. Massa and A. Scettri, J. Org.
Chem., 2003, 68, 3691–3694.
32 W. M. Haynes, CRC Handbook of Chemistry and Physics,
CRC Press, USA, 93rd edn, 2012.
33 C. D. Abernethy, G. M. Codd, M. D. Spicer and
M. K. Taylor, J. Am. Chem. Soc., 2003, 125, 1128–1129.
34 Z. R. Turner, R. Bellabarba, R. P. Tooze and P. L. Arnold,
J. Am. Chem. Soc., 2010, 132, 4050–4051.
O. C. Lightbody, C. L. B. Macdonald, J. A. C. Clyburne,
C. D. Abernethy and S. P. Nolan, Organometallics, 2005, 24,
6301–6309.
39 F. Lazreg, D. B. Cordes, A. M. Z. Slawin and C. S. J. Cazin,
Organometallics., 2015, 34, 419–425.
40 S. Zhang, W. C. Zhang, D. D. Shang, Z. Q. Zhang and
Y. X. Wu, Dalton Trans., 2015, 44, 15264–15270.
41 D. D. Yang, Y. G. Tang, H. B. Song and B. Q. Wang,
Organometallics, 2015, 34, 2012–2017.
42 V. H. L. Wong, A. J. P. White, T. S. A. Hor and K. K. Hii,
Chem. Commun., 2015, 51, 17752–17755.
43 F. G. Mann and W. J. Pope, J. Chem. Soc., 1922, 121, 594–
603.
35 P. L. Arnold, Z. R. Turner, R. Bellabarba and R. P. Tooze,
J. Am. Chem. Soc., 2011, 133, 11744–11756.
36 P. L. Arnold, T. Cadenbach, I. H. Marr, A. A. Fyfe, N. L. Bell,
R. Bellabarba, R. P. Tooze and J. B. Love, Dalton Trans., 44 W. F. Wu, Z. H. Fu, X. Wen, Y. J. Wang, S. Zou, Y. Meng,
2014, 43, 14346–14358.
37 V. Kumar and E. V. Anslyn, Chem. Sci., 2013, 4, 4292–4297.
Y. C. Liu, S. R. Kirk and D. L. Yin, Appl. Catal., A, 2014, 469,
483–489.
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