Evaluation of [12C/11C]carbon monoxide binding to copper(I) tris(pyrazolyl)borate complexes

Article abstract of DOI:10.1002/ejic.201301475

The copper(I) coordination chemistry of tris(3-R-5-R′-pyrazolyl) borate ligands (Tp^R,R′) bearing substituent groups attached to the pyrazole rings has been investigated under nitrogen and carbon monoxide atmospheres [1 (Tp^Ph,SMe) R =

Full text of DOI:10.1002/ejic.201301475

FULL PAPER
DOI:10.1002/ejic.201301475
Evaluation of [12C/11C]Carbon Monoxide Binding to
Copper(I) Tris(pyrazolyl)borate Complexes
Steven Kealey,*[a] Andrew J. P. White,[b] Antony D. Gee,[c] and
Nicholas J. Long*[b]
Keywords: Copper / Carbonyl ligands / Tridentate ligands / Isotopic labelling
The copper(I) coordination chemistry of tris(3-R-5-RЈ-pyr-
azolyl)borate ligands (TpR,RЈ) bearing substituent groups at-
tached to the pyrazole rings has been investigated under ni-
trogen and carbon monoxide atmospheres [1 (TpPh,SMe) R =
Ph, RЈ = SCH3; 2 (TpPy) R = 2-pyridyl, RЈ = H; 3 (TpPhos,Me) R
= 2-(diphenylphosphinyl)phenyl, RЈ = CH3]. The reactivity is
strongly dependent on the coordinating potential of the sub-
stituent groups; in the absence of CO, 1 formed an insoluble
complex [Cu(TpPh,SMe)]n (1b), 2 formed a multinuclear spe-
cies [Cu(TpPy)]n (2a; tetrameric in solution, dimeric in the so-
lid state) and 3 formed a discrete complex [Cu(TpPhos,Me)]
(3a). Under a CO atmosphere, 1 displayed irreversible CO
binding to form the complex [Cu(TpPh,SMe)CO] (1c),
2
showed reversible CO binding between 2a and the mononu-
clear species [Cu(TpPy)CO] (2b), and 3 did not bind to CO,
but instead formed 3a. The reactivity of the copper com-
plexes of 1 and 2 with [11C]carbon monoxide has been exam-
ined in the radiochemistry laboratory to investigate the re-
versibility of 11CO binding. The solid-state structures of
[Tl(TpPh,SMe)] (1a), 1c and 2a were elucidated by X-ray crys-
tallography.
ity and the sub-micromolar quantities of 11CO being pro-
duced. Over recent years, a number of elegant techniques
have been developed to improve 11CO reactivity, most no-
tably the use of high-pressure microautoclave reactors,[5]
highly active carbonylation catalysts,[6] 11CO-trapping mo-
lecules[7] and soluble delivery gases.[8] Our group has been
interested in the use of transition-metal-containing com-
plexes that can selectively bind to CO in solution for appli-
cation in 11C-radiolabelling experiments. We found that a
copper(I) complex supported by the tripodal “scorpionate”
ligand tris(3,5-dimethylpyrazolyl)borate (Tp*) was able to
trap 11CO efficiently through the formation of the copper(I)
carbonyl species [Cu(Tp*)11CO] (Scheme 1).
Introduction
Positron emission tomography (PET) is a molecular im-
aging technique that uses radiolabelled compounds as mo-
lecular probes to observe biological processes in vivo. Al-
though PET is most frequently used in disease diagnos-
tics,[1] especially oncology, it is increasingly being used in
the early phases of the drug development process as it can
provide useful information on the distribution and tissue
concentration of candidate molecules.[2] Tracer synthesis re-
mains one of the biggest challenges in the field owing to
the short half-lives of the common positron-emitting radio-
nuclides (18F: 109 min, 11C: 20 min, 15N: 10 min, 15O:
2 min) and the limited array of radiolabelling reagents that
are available.[3] [11C]Carbon monoxide (11CO) is a useful
11C-labelling reagent, which may be incorporated into a
wide range of biologically-active molecules through metal-
catalysed carbonylation reactions;[4] however, the wide-
spread use of this gas had been hindered by its poor solubil-
[a] Institute of Psychiatry, King’s College London,
Denmark Hill, London, SE5 8AF, UK
E-mail: steven.kealey@kcl.ac.uk
Scheme 1. Copper(I)–scorpionate complex used for 11CO trapping.
http://www.kcl.ac.uk/iop/index.aspx
[b] Department of Chemistry, Imperial College London,
London, SW7 2AZ, UK
11CO release could subsequently be triggered by the ad-
dition of a competing ligand, which allowed palladium-me-
diated [11C]carbonylation reactions to be performed in si-
tu.[7a,9] Here, we report our study into the use of second-
generation tris(pyrazolyl)borate ligands bearing 3,5-pyraz-
olyl substituents and their reactivity towards CuI and
12/11CO (Figure 1).
E-mail: n.long@imperial.ac.uk
http://www.ch.ic.ac.uk/long/
[c] Division of Imaging Sciences and Biomedical Engineering,
King’s College London, The Rayne Institute, St Thomas’s
Hospital,
London, SE1 7EH, UK
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201301475.
Eur. J. Inorg. Chem. 2014, 1896–1905
1896
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
coordination, Tp ligands impart electron density on the CuI
ion, which is then available for Cu(d)–CO(π*) back-bond-
ing; the extent of the back-bonding can be quantified by
measurement of the CO stretch (νCO) by IR spectroscopy.
A number of second-generation Tpx ligands that contain
substituent groups attached to the pyrazole rings have been
synthesised. Of the known [Cu(Tpx)CO] complexes
(Table 1), the pyrazole ring substituents can be split into
three categories: electron releasing (alkyl), electron neutral
(aryl) and electron-withdrawing (halogenated alkyl) on the
basis of νCO. It is noteworthy that, with the exception of
the halogenated species, no Tp complexes that contain het-
eroatom substituents directly bound to the pyrazole rings
have been reported. Such species may possess new elec-
tronic and coordinating properties arising from the hetero-
atom lone electron pairs and may be desirable for radio-
chemistry applications by facilitating rapid 11CO capture.
I. New Tp Ligand Synthesis
Substituted Tpx ligands are synthesised by condensation
reactions of the substituted pyrazole with a metal borohyd-
ride. We reasoned that the previously reported methylthio-
substituted pyrazole 3(5)-phenyl-5(3)-methylthiopyrazole
(iii)[24] could be converted to a new, potentially electron-
releasing Tp species by this pathway. Accordingly, com-
pound iii was formed in two steps by reaction of aceto-
phenone (i) with carbon disulfide and methyl iodide[25] to
give the α-ketoketene-S,S-diacetal (ii), followed by reaction
with hydrazine hydrate. The pyrazole was then converted
into the corresponding Tp ligand [K(TpPh,SMe)] (1) by reac-
tion with KBH4 (Scheme 2). Given the unknown reactivity
of the pyrazole with the borohydride anion and the high
reaction temperatures (Ͼ200 °C) required for Tp synthesis,
this reaction was performed under a nitrogen atmosphere
to avoid oxidation and decomposition of the product. The
3,5-disubstitution pattern of iii meant that over-reaction to
form the tetrakis(pyrazolyl)borate could not occur owing to
steric limitations. During heating of the reaction mixture, a
white precipitate formed, which, after cooling, was isolated
and recrystallised from tetrahydrofuran/hexane (THF/hex-
ane). The formation of 1 was confirmed by mass spectrome-
Figure 1. Second-generation Tpx ligands under investigation.
Results and Discussion
Tris(pyrazolyl)borate (Tp) ligands are adept at stabilising
copper(I) carbonyl complexes through both steric and elec-
tronic effects. From a steric perspective, the three N donor
atoms of the Tp ligand can enforce a tridentate geometry
around the CuI ion and leave a vacant site for a carbonyl
ligand to bind and achieve the preferred four-coordinate
pseudotetrahedral environment around the CuI centre. On
Table 1. Carbonyl stretching frequencies of known [Cu(Tpx)CO]
complexes.
1
try (TpPh,SMe at m/z = 579) and H NMR spectroscopy, in
[a] Tetrakis(pyrazolyl)borate ligand.
Scheme 2. Synthetic pathway to [K(TpPh,SMe)] (1).
Eur. J. Inorg. Chem. 2014, 1896–1905
1897
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
which the signal of the BH proton was evident as a broad gated for their potential to stabilise the copper centre by
multiplet centred at δ = 5.43 ppm.
chelation upon loss of the carbonyl ligand (Scheme 3).
During poly(pyrazolyl)borate synthesis, steric factors are
known to determine the regiochemistry of the resultant li-
gand (a notable exception is the TpBr,Ph,Br ligand, for which
electronic factors override).[26] Steric control is a conse-
quence of the relative energies of the five-centre cyclic tran-
sition state that is thought to occur during N–B bond for-
mation.[27] Accordingly, 3,5-disubstituted pyrazoles give rise
to ligands in which the boron atom is bound to the least
sterically hindered nitrogen atom of the pyrazolyl ring; this
results in Tp ligands in which the bulkiest substituents oc-
cupy the 3-position, furthest from the boron atom. In the
case of 1, the phenyl group was expected to occupy the 3-
position. To confirm this regiochemistry, structural charac-
terisation by X-ray crystallography was performed on the
corresponding thallium complex [Tl(TpPh,SMe)] (1a), which
was formed by the 1:1 reaction of 1 with thallium nitrate.
Single crystals were obtained by slow diffusion of pentane
vapour into a chloroform solution of 1a. The solid-state
structure (Figure 2) confirms the 3-phenyl-5-methylthio dis-
tribution for all three pyrazole rings. This is in agreement
with the predictions made upon steric grounds and may be
further enforced by electronic effects in which the electron-
releasing methylthio group is able to increase the nucleophi-
licity of its vicinal nitrogen atom, thus making it more reac-
tive toward the borohydride anion.
Scheme 3. Potential stabilisation of copper(I) by a hemilabile Tpx
ligand.
The choice of appended donor group and the length and
flexibility of the linker unit are likely to be important fac-
tors in the effectiveness of such a system. If the competing
donor group binds too favourably to the copper atom, then
it would be impossible to displace it with CO. On the other
hand, if the donor group has little affinity towards the cop-
per centre, decarbonylation may not be facilitated under
mild conditions. The relative strength of ligand binding to
CuI ions is in the following order: R–CϵNϽCOϽPR3. In
the absence of any nitrile-appended Tp ligands in the litera-
ture, the TpPy ligand reported by Ward et al.[28] that bears
2-pyridyl donor groups was chosen as an analogous N-do-
nor species (Figure 1, centre). This species is a potentially
tris-chelating hexadentate ligand that consists of three bi-
dentate N,NЈ donor arms. For comparison, the reactivity of
a tris(pyrazolyl)borate ligand bearing PPh3 donor groups
tethered to the 3-pyrazolyl position (TpPhos,Me; Figure 1,
right), which was previously synthesised in our group,[29]
was also investigated. The reactivity all three [K(Tpx)] li-
gands (Figure 1) towards CuCl was studied under N2 and
CO atmospheres.
III. CuI Reactivity of Tpx Ligands
(i) TpPh,SMe
The addition of acetonitrile to CuCl and 1 under an at-
mosphere of nitrogen immediately produced a white pre-
cipitate (1b), which is insoluble in water and all common
organic solvents. Mass spectrometry of 1b showed frag-
ments with the expected m/z ratios and isotope patterns for
[(TpPh,SMe) + 2H]+, [Cu(TpPh,SMe) + H]+, [Cu2(TpPh,SMe
)
2
+ H]+ and [Cu3(TpPh,SMe)2]+, and elemental analysis gave a
good match for a 1:1 Cu/TpPh,SMe complex. This suggests
that a [Cu(TpPh,SMe)]n coordination polymer forms to
satisfy the tetracoordinate requirements of the CuI ion. This
may be achieved by bridging of the N donors between adja-
Figure 2. Crystal structure of [Tl(TpPh,SMe)] (1a).
II. Donor-Appended Tp Ligands
The [Cu(Tp*)] trapping system described previously[7a] cent metal sites and/or coordination of the sulfur lone elec-
uses ligand addition to displace 11CO from the CuI–11CO tron pairs.
complex. It was proposed that the incorporation of compet-
The reaction of 1 with CuCl under an atmosphere of CO
ing donor groups into the Tp ligand framework may allow did not lead to the formation of 1b; instead, the copper(I)
reversible carbonylation/decarbonylation to be achieved carbonyl complex [Cu(TpPh,SMe)CO] (1c) formed [Equation
and could form part of a reusable 11CO trapping system. To (1)], as indicated by a sharp νCO absorption at ν =
˜
this end, hemilabile scorpionate ligands containing donor 2081 cm–1 in the solution IR spectrum. Filtration and con-
groups tethered to the 3-pyrazolyl position were investi- centration of the solution to dryness yielded the intact carb-
Eur. J. Inorg. Chem. 2014, 1896–1905
1898
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
onyl complex 1c as a white solid as evidenced by solid-state
In the solid-state structures of both the thallium (1a) and
1
IR spectroscopy (νCO at ν = 2087 cm–1), H and 11B NMR copper carbon monoxide (1c) complexes of TpPh,SMe (Fig-
˜
spectroscopy and elemental analysis. ESI mass spectrome- ures 2 and 3, respectively), the tridentate boron ligand
try showed the expected isotope pattern for [M – CO]+ at adopts
a near C3-symmetric arrangement about the
m/z =581; carbonyl dissociation is thought to occur in the boron···metal axis. The differences between the ligand con-
spectrometer. When compared with other [Cu- formations unsurprisingly stem from the coordination of
(Tpx)CO] complexes in Table 1, the CO stretching fre- the metal atoms. Whereas the B···Tl separation in 1a is
quency of 1c is found to be the highest of all of the aryl- 3.612(2) Å [the thallium atom is ca. 1.83 Å out of the N(1)–
appended Tp ligands and is only slightly lower than that of N(3)–N(5) plane], the copper centre in 1c is ca. 0.6 Å closer
the electron-poor fluorinated species, which suggests that to the boron atom of the ligand with a B···Cu separation
the ligand is a relatively weak electron donor. This may be of 3.014(3) Å [the metal atom is ca. 1.15 Å out of the N(1)–
caused by poor orbital overlap between the lone pair of the N(3)–N(5) plane]. In the close literature analogues
third row sulfur atoms and the conjugated π system of the [Tl(TpPh)][31] and [Cu(Tp2Ph)CO],[10b] the B···Tl and B···Cu
pyrazole rings. As such, the inductive electron-withdrawing separations of ca. 3.61 and 3.08 Å, respectively, are very
effect of the electronegative sulfur atoms may outweigh the similar to those observed here. This difference in the B···M
electron-releasing resonance effect. The 13C{1H} NMR separation is also reflected in the M–N bond lengths, which
spectrum of 1c was recorded using a sample prepared from are ca. 0.5 Å longer in the thallium complex than in the
13C-enriched CO, which allowed the normally weak carb- copper species (Table 2). Associated with this difference in
onyl peak to be observed. The Cu–13CO resonance appears the metal position is a pseudo “grabbing” distortion of the
as a broad singlet at δ = 174.8 ppm, which is comparable tridentate boron ligand (see Supporting Information).
to that reported for [Cu(Tp2Ph)CO].[30] Notably, the related
Table 2. Comparative selected bond lengths [Å] and angles [°] for
3,5-dialkyl-substituted Tpx complexes [Cu(Tp2iPr)CO],
1a [M = Tl] and 1c [M = Cu].
[Cu(TptBu,iPr)CO][30] and [Cu(Tp*)CO] (see Supporting In-
formation) show multiplets owing to the coupling of the
1a [M = Tl]
1c [M = Cu]
13C nuclei to 63Cu (I = 3/2, abundance = 69%, γ = 7.11) M–N(1)
2.6100(19)
2.5594(16)
2.5910(16)
–
2.074(2)
2.072(2)
2.051(2)
1.794(3)
3.014(3)
and 65Cu (I = 3/2, abundance = 31%, γ = 7.60) nuclei.
M–N(3)
M–N(5)
M–C(40)
M···B
3.612(2)
N(1)–M–N(3)
74.78(5)
76.01(5)
–
75.66(5)
–
–
91.39(8)
93.24(8)
122.41(10)
91.64(8)
121.58(10)
127.15(10)
N(1)–M–N(5)
N(1)–M–C(40)
N(3)–M–N(5)
N(3)–M–C(40)
N(5)–M–C(40)
(1)
Solid-State Structures of 1a and 1c
In 1c, each of the three arms of the ligand are tilted
towards the copper centre compared with those of the thal-
lium centre in 1a; as a result, the pendant phenyl rings are
pulled “inwards” and the S-methyl units are pushed “out-
wards”. The average separation between the phenyl ring
centroids is ca. 8.02 Å in 1a and 7.58 Å in 1c, and the
average separation between the sulfur atoms is ca. 4.28 Å
in 1a and 4.51 Å in 1c.
The solid-state structure of 1c (Figure 3) was elucidated
by X-ray crystallography of crystals grown by slow evapora-
tion of dichloromethane.
(ii) TpPy
The reaction of the pyridyl-donor-appended ligand
[K(TpPy)] (2) with CuCl under a nitrogen atmosphere
yielded an orange solution, which was filtered and concen-
trated to dryness [Equation (2)]. Elemental analysis of the
resultant orange powder (2a) provided an excellent match
for a compound of the formula [Cu(TpPy)]n. ESI mass spec-
trometry showed a peak at m/z = 1016, which corresponds
to a dinuclear species [Cu2(TpPy)2 + H]+, and the highest
cluster at m/z = 1079 corresponds to the trinuclear species
[Cu3(TpPy)2]+. The 1H NMR spectrum of 2a showed signifi-
cant broadening at room temperature, which prompted us
to perform a variable-temperature study (Figure 4) by cool-
ing the CD2Cl2 solution.
Figure 3. Crystal structure of [Cu(TpPh,SMe)CO] (1c).
Eur. J. Inorg. Chem. 2014, 1896–1905
1899
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
1
Figure 4. Variable-temperature H NMR spectrum of [Cu(TpPy)]n (2a).
coordination at each copper centre is postulated to occur
through the coordination of the N,NЈ arms of each TpPy
ligand to multiple CuI centres. Therefore, the broadening of
1
the signals of the room-temperature H NMR spectrum of
2a arises from the fluxional behaviour of the bidentate li-
gand arms. Ward et al. have previously reported on the size
mismatch between the TpPy ligand and copper(I) ion.[32]
Interestingly, they found that the analogous reaction of
[K(TpPy)] with [Cu(MeCN)4][PF6] under a nitrogen atmo-
sphere yielded not 2a but a brown complex of the formula
[Cu3(TpPy)2][PF6]. This difference in the reactivity of TpPy
between CuI sources suggests that the counteranion plays
an important role in the reactivity; the formation of the
neutral complex [Cu(TpPy)]4 (2a) may result from the
favourable thermodynamic driving force of KCl precipi-
tation.
(2)
As the temperature was lowered, the broad aromatic
peaks at δ = 5.5–8.5 ppm de-coalesced. At 243 K (–30 °C),
a complex spectrum was obtained in which the aromatic
protons produced a total relative integral of 24. The pres-
ence of a mononuclear species in solution could effectively
be ruled out as a single TpPy ligand contains only 18 aro-
matic protons. The observed spectrum can be explained by
considering there to be four nonequivalent TpPy molecules
in solution [Cu4(TpPyA)(TpPyB)(TpPyC)(TpPyD)], in which
the three donor arms of each Tp ligand are chemically
equivalent; this produces six chemical environments per li-
Solid-State Structure of 2a
The recrystallisation of 2a from THF provided single
gand and, hence, a total of 24 separate resonances. These crystals suitable for analysis by X-ray diffraction. In con-
chemical environments have been assigned for the 1H NMR trast to the structure from the solution-state NMR analysis,
1
spectrum recorded at 243 K with the aid of the H COSY the solid-state structure of 2a (Figure 5) reveals a dimeric
spectrum (see Supporting Information).
complex of the formula [Cu(TpPy)]2. Here, each CuI ion is
The predisposition of 2a to form
a
tetranuclear coordinated to a bidentate N,NЈ donor arm from each Tp
[Cu(TpPy)]4 species in solution most likely arises from a size ligand. Unlike in [Cu3(TpPy)2][PF6],[32] in which every bi-
mismatch between the large TpPy ligand cavity and the dentate arm is coordinated, each Tp ligand in 2a has two
small CuI ion. As such, the coordination of one of the pyr- coordinated arms (one at each CuI ion) and one uncoordi-
idyl donor arms to achieve a pseudotetrahedral array nated arm that points away from the metal centre. The re-
around the metal ion would place considerable strain on sultant structure is a C2-symmetric dimer with a central 12-
the ligand. Similarly, the chelation of two N,NЈ donor arms membered ring. This ring has a boatlike conformation with
cannot provide a stable tetrahedral arrangement around the the base formed by Cu(1), N(4A), N(3A), Cu(1A), N(4)
central metal atom as there is insufficient flexibility to allow and N(3), such that the B···B separation is 5.103(8) Å. The
the two arms to be mutually perpendicular. Instead, tetra- geometry at the copper centre is severely distorted tetrahe-
Eur. J. Inorg. Chem. 2014, 1896–1905
1900
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
dral (Table 3), and the restricted bite angles of the chelating our to return, and the νCO band weakened considerably,
ligands [N(2)–Cu(1)–N(11) 80.49(13)°, N(4A)–Cu(1)– which suggests that decarbonylation to 2a occurred. Fur-
N(21A) 79.79(13)°] result in an enlarged angle between the ther studies on the carbonylation/decarbonylation of 2b
coordinated pyrazolyl nitrogen atoms [N(2)–Cu(1)–N(4A) showed that this process was reversible (Figure 6). Bubbling
135.87(13)°]. The Cu–N bond lengths clearly show the dif- CO through a solution of 2a for 5 min caused a sharp νCO
ference between the pyrazolyl and pyridyl nitrogen atoms; band to appear at ν = 2081 cm–1 (Figure 6, a). Three vac-
˜
the Cu–N(pz) bonds are ca. 0.1 Å shorter than their Cu– uum/nitrogen cycles caused this band to considerably
N(py) counterparts.
weaken (Figure 6, b), and another three vacuum/nitrogen
cycles made it weaker still (Figure 6, c). Bubbling CO
through the solution again for five minutes caused νCO to
reappear as a strong band (Figure 6, d).
Figure 6. Solution IR spectra of [Cu(TpPy)]n (2a)/[Cu(TpPy)CO]
(2b) in DCM.
Figure 5. Crystal structure of [Cu(TpPy)]2 (2a).
The 1H NMR spectrum of the carbonyl adduct 2b in
CD2Cl2 was recorded. This spectrum is remarkably dif-
ferent to the complex spectrum observed for the carbonyl-
free species 2a and is comparable to that observed for the
mononuclear species [Cu(TpPh,SMe)CO] (1c). With the aid
Table 3. Selected bond lengths [Å] and angles [°] for [Cu(TpPy)]2
(2a).
Cu(1)–N(2)
Cu(1)–N(4A)
2.023(3)
1.982(3)
Cu(1)–N(11)
Cu(1)–N(21A)
2.109(4)
2.127(3)
1
of the H COSY spectrum, the spectrum was assigned as
N(2)–Cu(1)–N(11)
N(2)–Cu(1)–N(21A) 125.66(12) N(11)–Cu(1)–N(4A)
80.49(13) N(2)–Cu(1)–N(4A)
135.87(13)
128.30(12)
shown in Figure 7. In 2b, the three ligand arms are equiva-
lent, and the six different aromatic protons occupy distinct
chemical environments. The 3-pyridyl proton is furthest
downfield at δ = 8.70 ppm, whereas the 4-pyrazolyl proton
is characteristically upfield of all of the other aromatic reso-
N(11)–Cu(1)–N(21A) 110.04(14) N(4A)–Cu(1)–N(21A) 79.79(13)
N(1)–B(1)–N(3)
N(3)–B(1)–N(5)
110.1(3)
111.4(3)
N(1)–B(1)–N(5)
106.1(3)
The reactivity of 2a towards CO was investigated. The nances at δ = 6.71 ppm. The equivalence of the three ligand
bubbling of CO through a dichloromethane (DCM) solu- arms supports the hypothesis based on the IR data that a
tion of 2a for five minutes caused the orange solution to C3-symmetric species forms in which the three pyrazolyl N
become more yellow. This colour change was accompanied donor atoms bind to the copper centre and a terminal carb-
by the appearance of a sharp νCO absorption band at ν = onyl ligand occupies the fourth coordination site. However,
˜
2081 cm–1. This value falls within the range typically seen attempts to obtain single crystals under a CO atmosphere
for aryl-appended [Cu(Tpx)CO] species (Table 1) and indi- for X-ray analysis were unsuccessful.
cates that the monomeric carbonyl species [Cu(TpPy)CO]
The reversible carbonylation of 2b can be contrasted with
(2b) formed. In an attempt to isolate 2b, the solution was the behaviour of [Cu(TpPh,SMe)CO] (1c), which was found
concentrated in vacuo; however, this caused the orange col- to be stable to decarbonylation under vacuum. This differ-
1
Figure 7. H NMR spectrum of [Cu(TpPy)CO] (2b) at 300 K.
Eur. J. Inorg. Chem. 2014, 1896–1905
1901
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
ence in reactivity cannot be attributed to an unusually weak gand Tp* (4), reported previously for 11CO trapping, was
CuI–CO bond, as solution IR spectroscopy of 2b shows νCO investigated for comparison. Experiments were performed
to be in the normal range for stable [Cu(Tpx)CO] com- in acetonitrile and toluene solutions with [Cu(Tpx)] com-
plexes; therefore, the difference likely results from stabilisa- plexes formed in situ through the reaction of [K(Tpx)] with
tion of the decarbonylated species by multicentre coordina- CuCl under an atmosphere of nitrogen. 11CO was delivered
tion of the bidentate N,NЈ-donor arms. A similar trend in through the solution, and the vial was sealed and heated
CO reactivity has been observed previously for the N,N,N for 5 min to promote 11CO release. By measuring the radio-
macrocycle
1,4-diisopropyl-1,4,7-triazacyclononane activity of the vial and untrapped gases before and after
(TACN),[33] for which irreversible carbonylation of the [Cu- heating, the extent of 11CO trapping and release could be
(TACN)]+ complex could be rendered reversible by the ad- calculated (Table 4).
dition of a –CH2Py N-donor arm to the ligand back-
Table 4. 11CO trapping and release of [Cu(Tpx)] complexes.
bone.[34] In this case, the pyridyl donor group was able to
stabilise the CO-free species by chelation at the CuI centre.
It is also noteworthy that reversible carbonylation has been
observed to occur in the CuI complex formed from the cor-
Solvent
11CO trap [%][a]
11CO release [%][b]
1b
1b
acetonitrile
toluene
acetonitrile
toluene
acetonitrile
toluene
2Ϯ0
77Ϯ2
6Ϯ1
14Ϯ4
84Ϯ2
100Ϯ0
not measured
6Ϯ1
99Ϯ1
100Ϯ0
43Ϯ6
51Ϯ5
responding pyrazole precursor to 2, 3-(2-pyridyl)-5-methyl- 2a
pyrazole.[35]
2a
4a
(iii) TpPhos,Me
4a
[a] Average of two runs. 11CO trapping was performed at 20 °C. [b]
The reactivity of the phosphine-appended scorpionate li-
gand [K(TpPhos,Me)] (3) with copper under a nitrogen atmo-
sphere has previously been reported [Equation (3)].[29] This
11CO release was performed at 70 (acetonitrile) or 90 °C (toluene).
As expected, the 11CO trapping of 1b in acetonitrile was
very poor owing to the insolubility of this complex. In tolu-
ene solution, however, the formation of 1b was hindered by
the poor solubility of the [K(TpPh,SMe)] starting material.
11CO trapping of the resultant suspension proceeded with
high11COincorporation,whichsuggeststhat[Cu(TpPh,SMe)11-
CO] formed in solution, as seen previously with 12CO.
However, this complex was resistant to 11CO release upon
heating. In both acetonitrile and toluene solutions, 2a
showed poor 11CO trapping, most likely because of stabili-
sation of the CO-free complex by competitive binding of
the pyridyl groups. As a consequence, 11CO release was fa-
cilitated and proceeded quantitatively in both solvents. Pre-
vious studies on 4a have shown that it exists as a [Cu-
(Tp*)]2 dimer in the solid state, whereas it is extensively
dissociated in solution.[36] As such, CO is able to approach
the copper(I) ion to form the mononuclear [Cu(Tp*)CO]
species.[12] This is reflected by the excellent 11CO trapping
efficiency of 4a in acetonitrile and quantitative 11CO trap-
ping in toluene. Despite the high affinity of this complex
for 11CO at room temperature, approximately half of the
11CO was displaced upon subsequent heating. This demon-
strates the utility of this complex for 11CO sequestration
prior to metal-catalysed [11C]carbonylation reactions.
yielded
a
mononuclear complex of the formula
[Cu(TpPhos,Me)] (3a) in which the ligand coordinates to the
CuI centre in a κ4-N3,P fashion through the coordination
of three pyrazolyl donors and one phosphino group with
the two remaining phosphine groups uncoordinated (Fig-
ure 8). On the basis of the known coordinating behaviour
of copper(I) (PR3 Ͼ CO), it was predicted that under an
atmosphere of CO, the carbonyl species 3b would not form.
Indeed, prolonged CO bubbling did not result in any ob-
servable νCO band in the solution IR spectrum, and analysis
of the recovered solid showed that the CO-free complex 3a
had formed. As such, this compound was not selected for
investigation in the radiochemistry laboratory with 11CO.
(3)
Conclusions
Tris(pyrazolyl)borate ligands containing donor groups
tethered to the 3- or 5-pyrazolyl positions have been found
to display varied coordinating behaviour with CuI and CO,
depending on the coordinating properties of the substituent
Figure 8. [Cu(TpPhos,Me)] (3a).
(iv) Radiochemistry
The 11CO trapping/release efficiencies of the copper(I) groups. A new tris(pyrazolyl)borate ligand that contains
complexes of TpPh,SMe and TpPy were investigated in the methylthio and phenyl donor groups tethered to the 5- and
radiochemistry laboratory. The 3,5-dimethyl-appended li- 3-pyrazolyl positions, respectively, has been formed. The
Eur. J. Inorg. Chem. 2014, 1896–1905
1902
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
corresponding CuI–carbonyl complex was stable to decarb-
onylation under vacuum, but despite the presence of poten-
tially electron-releasing substituents, this species did not
display increased Cu–CO back-bonding as evidenced by the
relatively high νCO frequency. A tris(pyrazolyl)borate com-
plex containing 2-pyridyl groups tethered to the 3-pyrazolyl
position reacted with CuCl to form multinuclear species in
solution and the solid state, as evidenced by 1H NMR spec-
troscopy and X-ray crystallography. This species could re-
melt to form. The temperature was gradually increased to 220 °C,
and stirring of the mixture at this temperature for 2 h caused a
white solid to precipitate. After cooling, ethanol (20 mL) was
added, and the solid was broken up with a spatula and sonicated
to produce a white powder, which was collected by filtration, puri-
fied by precipitation from THF/hexane and dried in vacuo (1.305 g,
1
2.1 mmol, 66%). IR (KBr disc): ν
= 2448 (BH) cm–1. H NMR
˜
max
3
(400 MHz, [D6]acetone, 25 °C): δ = 7.75 (d, JH,H = 7.1 Hz, 6 H,
3
3
o-Ph), 7.22 (dd, JH,H = 7.2 Hz, JH,H = 7.2 Hz, 6 H, m-Ph), 7.16
(m, 3 H, p-Ph), 6.55 (s, 3 H, 4-pz), 5.43 (br m, 1 H, BH), 2.34 (s,
versibly bind to CO to form a mononuclear [Cu(TpPy)CO] 9 H, CH3) ppm. 13C{1H} NMR (126 MHz, [D6]acetone, 25 °C): δ
= 151.8 (s, 3-pz), 144.3 (s, 5-pz), 136.1 (s, i-Ph), 129.1 (s, m-Ph),
127.2 (s, p-Ph), 126.0 (s, o-Ph), 103.4 (s, 4-pz), 17.5 (s, CH3) ppm.
11B NMR (128 MHz, [D6]acetone, 25 °C): δ = –5.6 (br s, BH) ppm.
MS (ESI–): m/z = 579 [TpPh,SMe]–.
compound in which the pyridyl groups are non-coordinat-
ing. tris(pyrazolyl)borate complex containing tri-
phenylphosphine groups bound to the 3-pyrazolyl position
did not display any CO binding; the CuI ion instead pre-
ferred to chelate to one of the donor phosphine groups to
A
[Tl(TpPh,SMe)] (1a): A solution of TlNO3 (0.103 g, 0.39 mmol) in
form a stable mononuclear complex. In the radiochemistry water (15 mL) was added to a stirred solution of 1 (200 mg,
laboratory, 11CO binding studies showed good 11CO uptake
0.32 mmol) in THF (10 mL), which caused the immediate precipi-
for [Cu(TpPh,SMe)]n in toluene; however, this species was
tation of a white solid. The solid was collected by filtration, washed
with methanol (10 mL) and dried in vacuo to give a white powder
stable to decarbonylation upon heating. The reversibility of
(0.213 g, 0.27 mmol, 84%). C30H28BN6S3Tl (783.98): calcd. C 46.0,
11CO binding to [Cu(TpPy)]n was demonstrated; however,
H 3.60, N 10.7; found C 46.0, H 3.50, N 10.7. IR (nujol): ν
=
˜
max
the initial uptake was low, and it is thus unsuitable for 11CO
trapping applications. The established ligand Tp* was
found to offer excellent 11CO uptake in toluene, and good
11CO release could be achieved at 90 °C. As such, of the
complexes under investigation, the [Cu(Tp*)] system offers
2498 (BH) cm–1. H NMR (400 MHz, CDCl3, 25 °C): δ = 7.61 (d
1
3
3
3JH,H = 7.0 Hz, 6 H, o-Ph), 7.41 (dd, JH,H = 7.3 Hz, JHH
=
3
7.3 Hz, 6 H, m-Ph), 7.35 (t, JH,H = 7.3 Hz, 3 H, p-Ph), 6.37 (s, 3
H, 4-pz), 5.41 (br m, 1 H, BH), 2.56 (s, 9 H, CH3) ppm.
1H{11B}(400 MHz, CDCl3, 57 °C): As above except the broad BH
the best all-round performance for application in [11C]carb- multiplet becomes a sharper singlet at δ = 5.41 ppm. 13C{1H}
NMR (101 MHz, CDCl3, 25 °C): δ = 153.1 (s, 3-pz), 145.7 (s, 5-
pz), 133.5 (s, i-Ph), 128.8 (s, m-Ph), 127.9 (s, p-Ph), 126.9 (d, JC,Tl
onylation radiolabelling experiments.
4
= 108.2 Hz, o-Ph), 103.1 (s, 4-pz), 17.2 (s, CH3) ppm. 11B NMR
(400 MHz, CDCl3, 25 °C): δ = –6.9 (br s) ppm. MS (ESI–): m/z =
579 [TpPh,SMe]–. Single crystals suitable for X-ray analysis were
grown by vapour diffusion of pentane into a chloroform solution
of this complex. Crystal data for 1a: C30H28BN6S3Tl, M = 783.94,
monoclinic, P21/c (no. 14), a = 12.8755(2), b = 14.4834(2), c =
Experimental Section
General: Manipulations of air- and moisture-sensitive compounds
were performed with a conventional vacuum/nitrogen/carbon mon-
oxide Schlenk line. Solvents were distilled from standard drying
agents under an atmosphere of nitrogen directly prior to use, with
the exception of anhydrous acetonitrile and toluene for radiochem-
istry experiments, which were purchased from Romil and used as
received. NMR spectra were collected by using Bruker DRX-400
or AV-500 spectrometers at the Department of Chemistry, Imperial
College, London. Chemical shifts are reported in parts per million
and were referenced to the residual proton signals in the solvents.
[D2]Dichloromethane, [D]chloroform and [D6]acetone were dried
with 4 Å molecular sieves and stored under nitrogen. Mass spectra
were recorded with a Micromass Autospec Q spectrometer by Mr.
J. Barton and Mr. G. Tucker of the Department of Chemistry, Im-
perial College. Infrared absorption spectra were collected with sam-
ples either as KBr discs or in solution by using a Perkin–Elmer RX
FTIR spectrometer. Elemental analyses were performed by Stephen
Boyer at the London Metropolitan University. Reagents were pur-
chased from the Aldrich Chemical Company with the exception of
[K(Tp*)] (Strem Chemicals Inc.) and used without further purifica-
tion. Compound ii was synthesised according to literature pro-
cedures.[25] 3(5)-Phenyl-5(3)-methylthiopyrazole (iii) was synthe-
sised by the reaction of ii with hydrazine hydrate according to the
literature procedure.[24,25] Potassium hydrotris[3-(2Ј-pyridyl)pyrazo-
lyl]borate [K(TpPy)] (2)[28] and potassium hydrotris{3-[2-(diphenyl-
phosphanyl)phenyl]-5-methylpyrazolyl}borate [K(TpPhos,Me)] (3)[29]
were synthesised according to literature procedures.
17.3040(3) Å, β = 109.588(2)°, V = 3040.12(9) Å3, Z = 4, Dc
=
1.713 gcm–3, μ(Mo-Kα) = 5.550 mm–1, T = 173 K, colourless plate-
like needles, Oxford Diffraction Xcalibur 3 diffractometer; 10124
independent measured reflections (Rint = 0.0463), F2 refinement,[37]
R1(obs) = 0.0226, wR2(all) = 0.0557, 7500 independent observed
absorption-corrected reflections [|Fo|Ͼ 4σ(|Fo|), 2θmax = 65°], 374
parameters.
[Cu(TpPh,SMe)]n (1b): MeCN (20 mL) was added to CuCl (0.016 g,
0.16 mmol) and 1 (0.100 g, 0.16 mmol) to form a white suspension,
which was stirred overnight. The solution was allowed to settle and
filtered. The remaining white solid was washed with degassed water
(10 mL) then THF (2ϫ 10 mL) and dried in vacuo to give 1b as a
white powder (0.053 g, 0.08 mmol, 51%). C30H28BCuN6S3
(643.44): calcd. C 56.0, H 4.39, N 13.1; found C 56.2, H 4.24, N
13.2. MS (TOF ES+): m/z (%) = 581 (100) [TpPh,SMe + 2H]+, 684
(50) [Cu(TpPh,SMe) + H]+, 1287 (40) [Cu2(TpPh,SMe
)
+ H]+, 1349
2
(40) [Cu3(TpPh,SMe)2]+ (all fragments display the expected isotope
patterns).
[Cu(TpPh,SMe)CO] (1c): CO was bubbled through a suspension of
1 (0.100 g, 0.16 mmol) and CuCl (0.016 g, 0.16 mmol) in THF for
30 min. IR spectroscopy of the THF solution indicated the forma-
tion of the carbonyl adduct (νCO at ν = 2081 cm–1). The suspension
˜
was allowed to settle and filtered to give a clear, colourless filtrate,
which was concentrated to dryness to produce a white powder
(0.064 g, 0.10 mmol, 60%). C31H28BCuN6OS3 (670.09): calcd. C
55.5, H 4.21, N 12.5; found C 55.4, H 4.30, N 12.4. IR (KBr disc):
Potassium
Hydrotris[3-phenyl,5-methylthio(pyrazolyl)]borate
[K(TpPh,SMe)] (1): A finely ground mixture of iii (3.00 g, 15.8 mmol)
and KBH4 (0.17 g, 3.2 mmol) was heated to 90 °C, which caused a
Eur. J. Inorg. Chem. 2014, 1896–1905
1903
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
1
3
4
ν
= 2500 (BH), 2087 (CO) cm–1. H NMR (400 MHz, CD2Cl2,
3JH,H = 7.3 Hz, JH,H = 4.9 Hz, JHH = 0.8 Hz, 3 H, 4-Py), 6.71
˜
max
3
3
25 °C): δ = 7.69 (d, JH,H = 6.8 Hz, 6 H, o-Ph), 7.43 (m, 9 H, m,p-
Ph), 6.32 (s, 3 H, 4-pz), 5.19 (br m, 1 H, BH), 2.59 (s, 9 H, CH3)
ppm. 11B NMR (400 MHz, CD2Cl2, 25 °C): δ = –9.1 (br s, BH)
ppm. MS (ESI+): m/z = 581 [TpPh,SMe + 2H]+, 684 [Cu(TpPh,SMe)-
CO + 14]+.
(d, JH,H = 2.3 Hz, 3 H, 4-pz), 4.64 (br m, 1 H, BH) ppm.
[Cu(TpPhos,Me)] (3a): Under an atmosphere of CO, THF (10 mL)
was added to a mixture of [K(TpPhos,Me)] (3) (0.100 g, 0.09 mmol)
and CuCl (0.009 g, 0.09 mmol), and a yellow solution immediately
formed. Solution IR spectroscopy did not show any signs of a carb-
onyl absorption in the 2000–2100 cm–1 region. 31P{1H} NMR spec-
troscopy of the reaction solution indicated the formation of 3a.
The solution was filtered and concentrated to dryness in vacuo to
give a pale yellow solid. C66H55BCuN6P3 (1098.31): C 72.1, H 5.04,
[Cu(TpPh,SMe)13CO] (1c): CD2Cl2 and CH2Cl2 were added to an
NMR tube containing 1 (0.037 g, 0.06 mmol) and CuCl (0.006 g,
0.06 mmol). [13C]CO was bubbled through the suspension for
1 min. 13C{1H} NMR (400 MHz, CD2Cl2, 25 °C): δ = 174.8 (br s,
CO), 153.0 (s, 3-pz), 144.8 (s, 5-pz), 133.4 (s, i-Ph), 128.3 (s, m,p-
Ph), 127.6 (s, o-Ph), 103.4 (s, 4-pz), 17.0 (s, CH3) ppm. Single crys-
tals suitable for X-ray analysis were grown by slow evaporation of
this solution. Crystal data for 1c: C31H28BCuN6OS3, M = 671.12,
monoclinic, P21/c (no. 14), a = 12.8579(3), b = 14.7465(3), c =
17.5158(4) Å, β = 111.388(3)°, V = 3092.43(13) Å3, Z = 4, Dc =
1.441 gcm–3, μ(Mo-Kα) = 0.945 mm–1, T = 173 K, colourless plates,
Oxford Diffraction Xcalibur 3 diffractometer; 10320 independent
measured reflections (Rint = 0.0786), F2 refinement,[37] R1(obs) =
0.0606, wR2(all) = 0.1138, 5760 independent observed absorption-
corrected reflections [|Fo|Ͼ 4σ(|Fo|), 2θmax = 65°], 392 parameters.
N 7.64; found C 72.0, H 5.10, N 7.58. IR (KBr disc): ν
= 2509
˜
max
(BH) cm–1. 1H NMR (400 MHz, CDCl3, 25 °C): δ = 7.94 (d, JH,H
3
= 7.6 Hz, 3 H, 6-Ph), 7.18 (m, 9 H, 5-Ph + p-Ph), 7.11 (ddd, 3JH,H
3
4
= 7.5 Hz, JH,H = 7.5 Hz, JH,H = 1.0 Hz, 3 H, 4-Ph), 7.06 (dd,
3
3JH,H = 7.5 Hz, JHH = 7.5 Hz, 12 H, m-Ph), 6.95 (m, 15 H, 3-Ph
+ o-Ph), 5.98 (s, 3 H, 4-pz), 4.79 (br m, 1 H, BH), 2.31 (s, 9 H,
CH3) ppm. 31P{1H} NMR (162 MHz, CD2Cl2, 25 °C): δ = –7.4 (s)
ppm. 31P{1H} NMR (162 MHz, CD2Cl2, –90 °C): δ = –14.64 (br
s, 2 P, PPh2), 0.0 (s, 1 P, PPh2–Cu) ppm. 11B NMR (128 MHz,
CD2Cl2, 25 °C): δ = –5.4 (br s) ppm. MS (ESI+): m/z = 1099
[Cu(TpPhos,Me)]+.
[Cu(TpPy)]n (2a): CH2Cl2 (15 mL) was added to a mixture of 2
(0.121 g, 0.25 mmol) and CuCl (0.025 g, 0.25 mmol) to form an
orange solution. After stirring for 30 min, the mixture was allowed
to settle, filtered, and concentrated in vacuo to give an orange pow-
der (0.208 g, 0.20 mmol, 81%). C24H19BCuN9 (507.83): C 56.8, H
Radiochemistry: Experiments were performed at the Imanova Cen-
tre for Imaging Sciences, Hammersmith Hospital, London. Manip-
ulations were performed in a lead-shielded hot cell to minimise
exposure to radiation. [11C]Carbon dioxide (11CO2) was produced
with a Siemens Eclipse HP cyclotron by 11 MeV proton bombard-
ment (5 μA beam current for 2 min) of a target containing nitrogen
and 1% oxygen to yield Ͻ1 GBq of 11CO2. The 11CO2 was con-
verted to 11CO by using a commercially-available Eckert and
Ziegler modular lab apparatus according to the following pro-
cedure: 11CO2 was delivered from the cyclotron in a stream of he-
lium gas and trapped in a stainless steel loop containing molecular
sieves at room temperature. 11CO2 was released by heating the loop
to 400 °C as helium was passed through at a rate of 20 mL/min.
The resultant 11CO2/helium gas stream was passed through a
quartz tube containing molybdenum powder at 850 °C to convert
11CO2 to 11CO (conversion ca. 60–70%). Unreacted 11CO2 was re-
moved by passing the gas stream through a column containing
Ascarite®.
3.77, N 24.8; found C 56.7, H 3.73, N 24.9. IR (KBr disc): ν
=
˜
max
2430 (BH) cm–1. 1H NMR (400 MHz, CD2Cl2, 25 °C): δ = 8.23 (br
s, 3 H, 3-Py), 7.68 (br m, 6 H, 5-Py + 6-Py), 7.12 (br s, 6 H, 4-Py
+ 5-pz), 6.48 (br s, 3 H, 4-pz), 4.63 (br m, 1 H, BH) ppm. MS
(ESI+): m/z = 1016 [Cu2(TpPy)2]+, 1079 [Cu3(TpPy)2]+. 1H NMR
3
(400 MHz, CD2Cl2, –30 °C): δ = 8.52 [d, JH,H = 4.4 Hz, 3 H, (3-
3
Py)A], 8.31 [br s, 3 H, (3-Py)B], 8.22 [d, JH,H = 4.6 Hz, 3 H,
3
3
(3-Py)C], 8.08 [d, JH,H = 4.0 Hz, 3 H, (3-Py)D], 8.01 [d, JH,H
=
8.1 Hz, 3 H, (6-Py)A], 7.84 [m, 3 H, (5-Py)C], 7.67 [m, 15 H,
(5-Py)A,B,D + (6-Py)B,C], 7.31 [d, 3JH,H = 1.7 Hz, 3 H, (5-pz)B], 7.27
3
[d, JH,H = 8.0 Hz, 3 H, (6-Py)D], 7.23 [m, 3 H, (4-Py)C], 7.12 [m,
3
9 H, (4-Py)A,B,D], 6.92 [d, JH,H = 1.9 Hz, 3 H, (5-pz)C], 6.84 [s, 3
3
H, (5-pz)D], 6.75 [br s, 3 H, (5-pz)A], 6.72 [d, JH,H = 1.7 Hz, 3 H,
3
(4-pz)B], 6.58 [d, JH,H = 1.9 Hz, 3 H, (4-pz)C], 6.29 [s, 3 H,
CuCl (11 μmol) and [K(Tpx)] (11 μmol) were weighed into a 3 mL
V-bottomed glass vial, which was fitted with a rubber septum cap
then flushed with nitrogen for 10 min through the inlet and vent
needles. Anhydrous solvent (1.0 mL) was added, and the vial was
shaken for 30 s. The 11CO/helium gas stream was delivered to the
trapping solution at 20 mL/min, and the waste gases were collected
in a gas bag situated in a dose calibrator (Capintec Inc) to provide
real-time radioactivity measurement of the untrapped gases. Fol-
lowing 11CO delivery, the vial was sealed and heated for five min-
utes at 70 (for acetonitrile) or 90 °C (for toluene), after which the
heating was stopped, and a helium gas stream was bubbled through
the vial to displace any released 11CO into the waste gas bag. The
sample vial was removed from the hot cell, and its radioactivity
was measured in a dose calibrator (Isomed 2000). From these mea-
surements, the extent of 11CO trapping and 11CO release was calcu-
lated.
3
(4-pz)A], 5.64 [d, JH,H = 1.9 Hz, 3 H, (4-pz)D], 4.40 [br s, 4 H,
(BH)A,B,C,D] ppm. Single crystals suitable for X-ray analysis were
grown by recrystallisation from THF. Crystal data for 2a:
C48H38B2Cu2N18·3(C4H8O), M = 1231.98, monoclinic, C2/c (no.
15), a = 28.4631(15), b = 14.6250(4), c = 14.1652(5) Å, β =
94.329(4)°, V = 5879.8(4) Å3, Z = 4, Dc = 1.392 gcm–3, μ(Cu-Kα)
= 1.393 mm–1, T = 173 K, yellow platelike needles, Oxford Diffrac-
tion Xcalibur PX Ultra diffractometer; 5639 independent measured
reflections (Rint = 0.0404), F2 refinement,[37] R1(obs) = 0.0585,
wR2(all) = 0.2142, 3991 independent observed absorption-corrected
reflections [|Fo|Ͼ 4σ(|Fo|), 2θmax = 150°], 431 parameters.
[Cu(TpPy)CO] (2b): A solution of 2a in CH2Cl2 (15 mL) was pre-
pared in situ from CuCl (0.025 g, 0.25 mmol) and 2 (0.121 g,
0.25 mmol) under an atmosphere of nitrogen. The orange solution
was filtered, and CO gas was bubbled through the filtrate for 5 min.
This caused the solution to become yellow-orange. IR (CH2Cl2):
CCDC-966952 (for 1a), -966953 (for 1c) and -966954 (for 2a) con-
tain the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
ν
= 2081 (s, CO) cm–1. Successive vacuum/nitrogen cycles
˜
max
caused the νCO band to become progressively weaker. Bubbling of
CO through this solution caused the νCO band to reappear as a
1
strong absorption. H NMR (400 MHz, CD2Cl2, 25 °C): δ = 8.70
3
3
(d, JH,H = 4.3 Hz, 3 H, 3-Py), 7.87 (d, JH,H = 7.9 Hz, 3 H, 6-Py),
Supporting Information (see footnote on the first page of this arti-
7.80 (d, 3JH,H = 2.1 Hz, 3 H, 5-pz), 7.77 (m, 3 H, 5-Py), 7.29 (ddd, cle): Additional crystallographic and NMR spectroscopic data.
Eur. J. Inorg. Chem. 2014, 1896–1905
1904
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.eurjic.org
FULL PAPER
[13] C. E. Ruggiero, C. J. Carrano, W. E. Antholine, J. W. Whittaker,
C. J. Cramer, W. B. Tolman, J. Am. Chem. Soc. 1993, 115,
11285–11298.
Acknowledgments
A. D. G. acknowledges financial support from (i) the Department
of Health via the National Institute for Health Research (NIHR),
Comprehensive Biomedical Research Centre award to Guy’s & St
Thomas’ NHS Foundation Trust in partnership with King’s Col-
lege London and King’s College Hospital NHS Foundation Trust
and (ii) The Centre of Excellence in Medical Engineering funded
by the Wellcome Trust and the Engineering and Physical Sciences
Research Council (EPSRC) under grant number WT 088641/Z/09/
Z.
[14] R. R. Conry, G. Ji, A. A. Tipton, Inorg. Chem. 1999, 38, 906–
913.
[15] J. L. Schneider, S. M. Carrier, C. E. Ruggiero, V. G. Young,
W. B. Tolman, J. Am. Chem. Soc. 1998, 120, 11408–11418.
[16] M. I. Bruce, A. P. P. Ostazewski, J. Chem. Soc., Chem. Com-
mun. 1972, 1124–1125.
[17] O. M. Abu Salah, M. I. Bruce, J. Organomet. Chem. 1975, 87,
C15–C18.
[18] H. V. R. Dias, H. J. Kim, H. L. Lu, K. Rajeshwar, N. R. deTac-
coni, A. Derecskei-Kovacs, D. S. Marynick, Organometallics
1996, 15, 2994–3003.
[19] H. V. R. Dias, H. J. Kim, Organometallics 1996, 15, 5374–5379.
[20] H. V. R. Dias, T. K. H. H. Goh, Polyhedron 2004, 23, 273–282.
[21] A. Caballero, M. M. Diaz-Requejo, T. R. Belderrain, M. C.
Nicasio, S. Trofimenko, P. J. Perez, J. Am. Chem. Soc. 2003,
125, 1446–1447.
[22] H. Brunner, U. P. Singh, T. Boeck, S. Altmann, T. Scheck, B.
Wrackmeyer, J. Organomet. Chem. 1993, 443, C16–C18.
[23] H. V. R. Dias, H. L. Lu, Inorg. Chem. 1995, 34, 5380–5382.
[24] S. M. S. Chauhan, H. Junjappa, Synthesis 1975, 798–801.
[25] a) K. T. Potts, M. J. Cipullo, P. Ralli, G. Theodoridis, J. Org.
Chem. 1982, 47, 3027–3038; b) K. T. Potts, P. Ralli, G. Theodo-
ridis, P. Winslow, Org. Synth. 1986, 64, 189.
[26] G. P. A. Yap, F. Jove, J. Urbano, E. Alvarez, S. Trofimenko,
M. M. Diaz-Requejo, P. J. Perez, Inorg. Chem. 2007, 46, 780–
787.
[27] S. Trofimenko, Scorpionates: Polypyrazolylborate Ligands and
Their Coordination Chemistry, Imperial College Press, 1999.
[28] A. J. Amoroso, A. M. Cargill Thompson, J. C. Jeffery, P. L.
Jones, J. A. McCleverty, M. D. Ward, J. Chem. Soc., Chem.
Commun. 1994, 2751–2752.
[1] M. E. Phelps, Proc. Natl. Acad. Sci. USA 2000, 97, 9226–9233.
[2] P. M. Matthews, E. A. Rabiner, J. Passchier, R. N. Gunn, Br. J.
Clin. Pharmacol. 2012, 73, 175–186.
[3] P. W. Miller, N. J. Long, R. Vilar, A. D. Gee, Angew. Chem. Int.
Ed. 2008, 47, 8998–9033; Angew. Chem. 2008, 120, 9136.
[4] a) B. Langstrom, O. Itsenko, O. Rahman, J. Labelled Compd.
Radiopharm. 2007, 50, 794–810; b) S. Kealey, A. Gee, P. W.
Miller, J. Labelled Compd. Radiopharm., DOI: 10.1002/
jlcr.3150.
[5] a) T. Kihlberg, B. Langstrom, F. T. J. Eriksson, Method and
Apparatus for Production and Use of [11C]Carbon Monoxide
in Labelling Synthesis Patent Application PCT/SE02/01222; b)
E. D. Hostetler, H. D. Burns, Nucl. Med. Biol. 2002, 29, 845–
848.
[6] K. Dahl, M. Schou, N. Amini, C. Halldin, Eur. J. Org. Chem.
2013, 1228–1231.
[7] a) S. Kealey, P. W. Miller, N. J. Long, C. Plisson, L. Martarello,
A. D. Gee, Chem. Commun. 2009, 3696–3698; b) H. Audrain,
L. Martarello, A. Gee, D. Bender, Chem. Commun. 2004, 558–
559.
[8] J. Eriksson, J. van den Hoek, A. D. Windhorst, J. Labelled
Compd. Radiopharm. 2012, 55, 223–228.
[9] a) S. Kealey, C. Plisson, T. L. Collier, N. J. Long, S. M. Hus-
bands, L. Martarello, A. D. Gee, Org. Biomol. Chem. 2011, 9,
[29] S. Kealey, N. J. Long, P. W. Miller, A. J. P. White, A. D. Gee,
Dalton Trans. 2008, 2677–2679.
[30] K. Fujisawa, T. Ono, Y. Ishikawa, N. Amir, Y. Miyashita, K.
Okamoto, N. Lehnert, Inorg. Chem. 2006, 45, 1698–1713.
3313–3319; b) L. E. Jennings, S. Kealey, P. W. Miller, A. D. [31] Z. Ciunik, T. Ruman, M. Lukasiewicz, S. Wolowiec, J. Mol.
Gee, N. J. Long, J. Labelled Compd. Radiopharm. 2011, 54, Struct. 2004, 690, 175–180.
135–139; c) G. Buscemi, P. W. Miller, S. Kealey, A. D. Gee, N. J. [32] P. L. Jones, J. C. Jeffery, J. P. Maher, J. A. McCleverty, P. H.
Long, J. Passchier, R. Vilar, Org. Biomol. Chem. 2011, 9, 3499–
Rieger, M. D. Ward, Inorg. Chem. 1997, 36, 3088–3095.
[33] P. Chaudhuri, K. Oder, J. Organomet. Chem. 1989, 367, 249–
258.
3503.
[10] a) S. Kiani, J. R. Long, P. Stavropoulos, Inorg. Chim. Acta
1997, 263, 357–366; b) S. Imai, K. Fujisawa, T. Kobayashi, N. [34] L. M. Berreau, J. A. Halfen, V. G. Young, W. B. Tolman, Inorg.
Shirasawa, H. Fujii, T. Yoshimura, N. Kitajima, Y. Moro-oka,
Inorg. Chem. 1998, 37, 3066–3070.
[11] a) N. Kitajima, K. Fujisawa, C. Fujimoto, Y. Moro-oka, Chem.
Lett. 1989, 18, 421–424; b) N. Kitajima, K. Fujisawa, C. Fujim-
oto, Y. Moro-oka, S. Hashimoto, T. Kitagawa, K. Toriumi, K.
Tatsumi, A. Nakamura, J. Am. Chem. Soc. 1992, 114, 1277–
1291.
Chim. Acta 2000, 297, 115–128.
[35] K. Singh, J. R. Long, P. Stavropoulos, Inorg. Chem. 1998, 37,
1073–1079.
[36] C. Mealli, C. S. Arcus, J. L. Wilkinson, T. J. Marks, J. A. Ibers,
J. Am. Chem. Soc. 1976, 98, 711–718.
[37] a) SHELXTL, Bruker AXS, Madison, WI; b) SHELX-97:
G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
Received: November 21, 2013
[12] M. I. Bruce, A. P. P. Ostazewski, J. Chem. Soc., Dalton Trans.
1973, 2433–2436.
Published Online: February 27, 2014
Eur. J. Inorg. Chem. 2014, 1896–1905
1905
© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim