Reversible carbon monoxide binding at copper(I) P-S-X (X = N, O) coordination polymers

Article abstract of DOI:10.1016/j.jorganchem.2012.05.032

Reaction of Ph₂PCH₂CH₂S(2-C ₆H₄NH₂) (1) or Ph₂PCH ₂CH₂S(2-C₆H₄OMe) (2) with CuCl and AgSbF₆ in the presence of THF affords

Full text of DOI:10.1016/j.jorganchem.2012.05.032

Journal of Organometallic Chemistry 715 (2012) 39e42
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Reversible carbon monoxide binding at copper(I) PeSeX (X ¼ N, O) coordination
polymers
,
,
*
Christopher W. Tate a, Antony D. Gee a b, Ramon Vilar a, Andrew J.P. White a, Nicholas J. Long a
a Department of Chemistry, Imperial College, London SW7 2AZ, UK
b Department of Chemistry, Kings College, Strand, London WC2R 2LS, UK
a r t i c l e i n f o
a b s t r a c t
Article history:
Reaction of Ph2PCH2CH2S(2-C6H4NH2) (1) or Ph2PCH2CH2S(2-C6H4OMe) (2) with CuCl and AgSbF6 in the
presence of THF affords {[Cu(1)THF](SbF6)}n (3) and {[Cu(2)THF](SbF6)}n (4). In the solid state, THF-
inclusive 3 exists as a one dimensional zigzag coordination polymer in which each PeSeN ligand is
connected to two copper(I)-centres. Both 3 and 4 are able to bind CO reversibly in solution or can be
desolvated at 110 ꢀC in vacuo to give {[Cu(1)](SbF6)}n (7) and {[Cu(2)](SbF6)}n (8). These solvent-free
compounds have been found to bind carbon monoxide reversibly over multiple cycles in solution and
in the solid state, under mild conditions.
Received 7 March 2012
Received in revised form
15 May 2012
Accepted 20 May 2012
Keywords:
Carbon monoxide
Coordination polymer
Copper
Ó 2012 Elsevier B.V. All rights reserved.
1. Introduction
tripodal bis(imidazole)thioethers [14]. In general, when ligands
inclusive of thioether substituents are coordinated to CuI, the
Although metal compounds that can reversibly bind carbon
monoxide have long been known, several new and interesting
examples have been published in recent years [1e5]. The ongoing
interest in CO-coordinating agents is driven not only by the ubiq-
uity of CO as a ligand in organometallic chemistry but also by the
possibility of their varied and wide-ranging application as CO
sources/sensors, molecular switches and in biologically related
systems for example. Copper(I) species in particular have a rich
history in the reversible binding of CO and are used in this context
in the industrially important COSORB process [6e10].
More recently, our group has reported the use of a Tp*Cu
complex (Tp* ¼ tris(3,5-dimethylpyrazolyl)borate) in the pre-
concentration of 11CO for subsequent release to palladium cata-
lysed coupling reactions and use in the area of positron emission
tomography [11]. We have also described reversible CO binding at
several first-row transition metal complexes of a new PeSeN
ligand [12]. In extension of this work, we have chosen to look at
copper(I) complexes of potentially tridentate ligands containing
hard and soft donor functionalities.
resulting complexes often adopt multimeric structures, may
contain unsaturated or weakly coordinated metal centres and
frequently exhibit reactivity toward small molecules [15e19]. The
formation of unsaturated, yet structurally stable, CuI species can
allow for reversible CO binding in the solid state and there are
examples of solid supported copper complexes for which this is
true, however, unsupported metal complexes that bind CO in
solution often do not bind CO as crystalline solids due to lattice
constraints [20,21]. We report here a rare example of a copper(I)
coordination polymer containing a PeSeN ligand together with
a PeSeO ligand analogue and describe their behaviour toward CO
in solution and in the solid state.
2. Results and discussion
Ph2PCH2CH2S(2-C6H4NH2) (1) and Ph2PCH2CH2S(2-C6H4OMe)
(2) (Fig. 1) were synthesised by deprotontion of the relevant C2-
substituted arylthiol precursors followed by reaction with (2-
chloroethyl)diphenyl-phosphine [12,22,23].
A mixture of one
Previously reported examples of copper(I) CO binding
complexes have been based on a variety of ligand types including
those containing mixed donor ligands such as Schiff bases [13] or
equivalent of 1 or 2 and CuCl was reacted with AgSbF6 in the
presence of THF to give species of the formulation {[Cu(1)
THF](SbF6)}n (3) and {[Cu(2)THF](SbF6)}n (4), respectively (Fig. 2).
The 31P NMR spectra of these complexes revealed broad singlets
at chemical shifts located downfield with respect to the free ligands
(3: ꢁ6.7 ppm, 4: ꢁ4.1 ppm) and the presence of a single molecule of
THF per Cu(ligand) unit was confirmed by analysis of the relevant
* Corresponding author. Tel.: þ44 (0)207 5945781; fax: þ44 (0)207 5945804.
E-mail address: n.long@imperial.ac.uk (N.J. Long).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2012.05.032

40
C.W. Tate et al. / Journal of Organometallic Chemistry 715 (2012) 39e42
In a separate experiment, it was possible to directly desolvate 3
or 4 by heating solid samples at 110 ꢀC in vacuo. Complete removal
of THF to give 7 and 8, respectively, was achieved in 2 h under these
conditions. Other than the absence of THF, the 1H NMR spectra
showed little change in the chemical shifts and patterns of diag-
nostic resonances compared with data recorded for 3 and 4 and
matched those obtained in the solution studies reported above,
indicating that this process occurs without any significant decom-
position. The singlet peaks found in the 31P NMR spectra
(7: ꢁ5.3 ppm, 8: ꢁ3.4 ppm) were also subtly shifted from chemical
shift values obtained for the THF-inclusive complexes and this
possibly suggests that no major structural rearrangements take
place upon desolvation. Elemental analysis conducted on 7 and 8
confirm their THF-free assignment.
To assess the ability of these compounds to bind CO in the solid
state, a stream of CO (1 atm) was passed over finely powdered
samples for 10 min. This resulted in the complete conversion of 7
and 8 to the carbonyl species 5 and 6, respectively, which were
identified by elemental analysis of the solids and NMR and IR
spectroscopy in CD2Cl2. Solid samples of 5 and 6 were stable in
a stream of N2 (1 atm), however, CO could be fully removed under
vacuum conditions (1 ꢂ 10ꢁ3 mbar) at room temperature. Revers-
ible binding of carbon monoxide was recorded for both compounds
in the solid state over at least 5 cycles. Bubbling N2 through THF
solutions of 5 and 6 obtained via this route furnished the parent
complexes 3 and 4. A summary of the relationship between
compounds 3e8 is shown in Scheme 1.
Fig. 1. The PeSeN and PeSeO ligands 1 and 2.
1H NMR spectra. Solid samples of 3 and 4 could be dried in vacuo at
room temperature and stored under N2 for weeks without loss of
THF. The molecular structure of 3 is shown in Fig. 3 and was
determined by single crystal X-ray diffraction of crystals grown
from 1:1 THF/hexane at room temperature.
In contrast to the facial coordination modes seen in the recently
reported iron, cobalt and nickel complexes of 1 [12], here in the
copper species the tridentate PeSeN ligand acts in a bridging
manner, the nitrogen and phosphorus donor atoms coordinating to
one copper centre whilst the sulphur donor coordinates to an
adjacent copper atom, forming a cationic chain polymer that
extends along the crystallographic c axis direction (Fig. 3). The
orientation of the ligands along the chain puts the N(1) hydrogen
atoms all on one “side” of the chain (the back as viewed in Fig. 3),
and the SbF6 anions serve to bridge adjacent, glide-related, N(1)
centres via NeH/F hydrogen bonds. Unfortunately, the anions
were found to be disordered (see supporting information) and so
the geometries (which have been calculated using the major
occupancy orientation) have to be considered as indicative only;
the [N/F], [H/F] distances (Å) and the [NeH/F] angle (ꢀ) are
3.011(6), 2.13, 165 and 3.120(8), 2.41, 136. There are no NeH/F
links between chains. The geometry at the copper centre is
severely distorted tetrahedral with angles in the range 96.31(9) to
122.35(3)ꢀ, and the eight-membered chelate ring has a twist-boat-
chair conformation [24].
3. Conclusion
Several copper(I) species containing PeSeX (X ¼ N, O) hetero-
donor ligands 1 and 2 have been synthesised and characterised.
Interestingly, the molecular structure of THF-inclusive 3 has
revealed it to be a one dimensional zigzag coordination polymer in
the solid state. In solution, compounds 3 and 4 can be converted, in
a facile and reversible manner, to the carbonyl species 5 and 6
which can in turn undergo decarbonylation to give 7 and 8. Alter-
natively, the latter solvent-free compounds are obtained by des-
olvation of 3 or 4 using a combination of heat and vacuum
conditions. Notably, compounds 7 and 8 were found to bind CO gas
reversibly under mild conditions in solution and in the solid state
over multiple cycles.
The versatile carbon monoxide trap and release properties of
these compounds may be useful in a variety of applications
although initially we intend to assess their suitability for use as
11CO-trapping agents in systems developed for the radiolabelling of
drug molecules [11,25,26].
Although crystallographic evidence was not obtained for 4, it is
likely that this compound has a solid-state structure analogous to 3.
This is inferred by the strong similarities observed in their NMR
spectra and the closely matching CO binding properties of both
compounds, although no further supporting evidence was
obtained.
By bubbling CO through DCM solutions of 3 or 4 the new cop-
per(I) carbonyl species {[Cu(1)CO](SbF6)}n (5) and {[Cu(2)
CO](SbF6)}n (6) were formed. The generation of compounds con-
taining terminal CueCO bonds was confirmed by infrared spec-
troscopy (5: 2091 cmꢁ1, 6: 2114 cmꢁ1) and 1H NMR spectroscopy in
CD2Cl2 revealed the presence of free THF indicating that it is
replaced in its metal binding sites by CO. Release of CO was ach-
ieved by bubbling N2 through DCM solutions of the respective
carbonyl complexes to give {[Cu(1)](SbF6)}n (7) and {[Cu(2)](SbF6)}n
(8). Subsequent reaction with CO resulted in complete reconversion
to 5 and 6 and the reversible gas binding process between these
species was found to be reproducible over at least 5 cycles. Alter-
natively, addition of an equal volume of THF to DCM solutions of 5
or 6 followed by application of an N2 stream led to the reformation
of the parent complexes 3 and 4 (Scheme 1).
4. Experimental
4.1. General
All air and moisture-sensitive compounds were manipulated
under an inert atmosphere of nitrogen using conventional Schlenk
or glove-box techniques. General solvents were passed through
drying columns and freeze-thaw degassed before use. Deuterated
solvents were purchased from the Cambridge Isotope Laboratories.
All other chemicals were purchased from commercial sources and
used as received. Compound 1 was synthesised according to
a literature procedure [12]. NMR spectra were recorded on a Bruker
Av-400 or DRX-400 MHz NMR spectrometer. 1H and 13C spectra
were referenced to residual proton resonances in the deuterated
solvent, while 31P{1H} spectra were referenced to an external H3PO4
standard. NMR spectroscopic resonances are reported in ppm at
298 K unless otherwise stated. Infrared absorption spectra were
Fig. 2. Preparation of 3 and 4.

C.W. Tate et al. / Journal of Organometallic Chemistry 715 (2012) 39e42
41
Fig. 3. Part of one of the extended cationic chains present in the crystals of 3. Selected bond lengths (Å) and angles (ꢀ); CueN(1) 2.152(3), CueP(10) 2.2180(9), CueO(30) 2.145(3),
CueS(7A) 2.4172(9), N(1)eCueP(10) 119.14(8), N(1)eCueO(30) 98.73(11), N(1)eCueS(7A) 99.18(8), P(10)eCueO(30) 116.31(8), P(10)eCueS(7A) 122.35(3), O(30)eCueS(7A)
96.31(9).
collected with
a
Perkin Elmer RX FT-IR spectrometer using
was added in one portion and the resulting suspension was stirred
for 30 min. Filtration and subsequent removal of the solvent in
vacuo gave a green solid. Hexane (1 ml) was added followed by THF
(5 ml) and the resulting solution was heated briefly to reflux and
then allowed to cool to room temperature. A green solution was
filtered from the precipitated white product which was washed
with Et2O (2 ꢂ 5 ml) and dried in vacuo. Yield ¼ 0.28 g, 68%. 31P{1H}
NMR (CD2Cl2): ꢁ6.7 (s). 1H NMR (CD2Cl2): 7.93e9.93 (m, 14H), 5.08
(s, 2H), 3.84 (s, 4H), 3.26 (s, 2H), 2.37 (s, 2H), 1.98 (4H). 13C{1H} NMR
(CD2Cl2): 133.67 (s),133.11 (d,15 Hz),132.13 (s),131.48 (s),130.21 (d,
10 Hz), 129.57 (s), 128.39 (s), 126.17 (s). Anal. Calcd. for
C24H28CuF6NOPSSb: C, 40.65; H, 3.98; N, 1.98. Found: C, 40.55; H,
3.81; N, 1.87. Crystal data for 3: M ¼ 708.79, monoclinic, P21/c (no.
14), a ¼ 10.36016(6), b ¼ 23.69555(15), c ¼ 11.23626(7) Å,
a nitrogen purged cell containing KBr discs. Elemental analyses
were performed by Stephen Boyer, Science Centre, London Metro-
politan University, London.
4.2. Procedures
4.2.1. Preparation of Ph2PCH2CH2S(2-C6H4OMe) (2)
KPPh2 (20.3 ml, 10 mmol) was added dropwise to a solution of
1,2-dichloroethane (4.8 ml, 61 mmol) in THF (80 ml) at ꢁ78 ꢀC. The
resulting yellow solution was allowed to reach room temperature
and was then stirred for 12 h. Removal of the solvent in vacuo led to
the isolation of an off-white glassy solid. Addition of Cs2CO3 (3.3 g,
10 mmol), MeCN (80 ml) and 2-methoxybenzenethiol (1.43 g,
10 mmol) was followed by heating of the mixture to reflux for 2
days. The resulting suspension was filtered through celite and the
solvent was removed in vacuo to give 2 as a white solid.
Yield ¼ 2.95 g, 83%. 31P{1H} NMR (CD2Cl2): ꢁ17.1 (s). 1H NMR
(CD2Cl2): 7.36 (m, 10H), 7.18 (m, 1H), 7.11 (m, 1H), 6.86 (m, 2H), 3.80
(s, 3H), 2.92 (m, 2H), 2.33 (m, 2H). Anal. Calcd. for C21H21OPS: C,
71.57; H, 6.01. Found: C, 71.41; H, 5.79.
b
¼ 99.8468(6)ꢀ, V ¼ 2717.75(3) Å3, Z ¼ 4, Dc ¼ 1.732 g cmꢁ3
, m(Cu-
K
a
) ¼ 10.665 mmꢁ1, T ¼ 173 K, colourless needles, Oxford Diffrac-
tion Xcalibur PX Ultra diffractometer; 5306 independent measured
reflections (Rint ¼ 0.0265), F2 refinement, R1(obs) ¼ 0.0326,
wR2(all)
¼
0.0840, 4860 independent observed absorption-
corrected reflections [jFoj > 4
s
(jFoj), 2qmax ¼ 145ꢀ], 390 parame-
ters. CCDC 885922.
4.2.3. Preparation of {[Cu(2)THF](SbF6)}n (4)
4.2.2. Preparation of {[Cu(1)THF](SbF6)}n (3)
2 (0.2 g, 0.57 mmol) and CuCl (0.056 g, 0.57 mmol) were
combined and dissolved in DCM (20 ml). AgSbF6 (0.2 g, 0.58 mmol)
1 (0.2 g, 0.59 mmol) and CuCl (0.058 g, 0.59 mmol) were
combined and dissolved in DCM (20 ml). AgSbF6 (0.2 g, 0.58 mmol)
Vac., 110 o
- THF
C
1
3
1
7
{[Cu( )THF](SbF6)}n ( )
{[Cu( )](SbF6)}n ( )
2
4
2
8
{[Cu( )THF](SbF6)}n ( )
{[Cu( )](SbF6)}n ( )
+ CO, DCM
- THF
+ CO
- CO
= Reversible CO binding
in DCM and solid state
+ THF, N2
- CO
{[Cu(1)CO](SbF6)}n (5)
{[Cu(2)CO](SbF6)}n (6)
Scheme 1. Reversible binding of carbon monoxide in solution and in the solid state.

42
C.W. Tate et al. / Journal of Organometallic Chemistry 715 (2012) 39e42
was added in one portion and the resulting suspension was stirred
for 30 min. Filtration and subsequent removal of the solvent in
vacuo gave a green solid. THF (5 ml) was added and the resulting
solution was heated briefly to reflux. Removal of the solvent gave 4
as a white solid which was washed with Et2O (2 ꢂ 5 ml) and dried
in vacuo. Yield ¼ 0.25 g, 61%. 31P{1H} NMR (CD2Cl2): ꢁ4.1 (s, broad).
1H NMR (CD2Cl2): 7.75e7.24 (m, 12H), 7.09 (d, JHeH ¼ 8 Hz, 1H), 6.97
(d, JHeH ¼ 8 Hz, 1H), 4.08 (s, 4H), 3.67 (s, 3H), 3.19 (s, 2H), 2.50 (s,
2H), 2.09 (s, 4H). Anal. Calcd. for C25H29CuF6O2PSSb: C, 41.47; H,
4.04. Found: C, 41.49; H, 3.96.
Acknowledgements
We thank the EPSRC and GSK for funding this research.
Appendix A. Supporting material
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2012.05.032.
References
4.2.4. Preparation of {[Cu(1)CO](SbF6)}n (5)
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CD2Cl2) solution of 3 or passed over finely powdered samples of 7
for 10 min to give 5. 31P{1H} NMR (CD2Cl2): ꢁ2.1 (s). 1H NMR
(CD2Cl2): 7.70 (d, JHeH ¼ 7 Hz, 1H), 7.61e7.13 (m, 13H), 4.92 (s, 2H),
3.17 (s, 2H), 2.71e1.90 (m, 2H), 3.72 (s, 4H), 1.88 (s, 4H).
IR ¼ 2091 cmꢁ1 (CO). Anal. Calcd. for C21H20CuF6NOPSSb: C, 37.93;
H, 3.03; N, 2.11. Found: C, 37.89; H, 2.91; N, 1.87.
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4.2.5. Preparation of {[Cu(2)CO](SbF6)}n (6)
A stream of CO (1 atm) was either bubbled through a DCM (or
CD2Cl2) solution of 4 or passed over finely powdered samples of 8
for 10 min to give 6. 31P{1H} NMR (CD2Cl2): ꢁ1.1 (s, broad). 1H NMR
(CD2Cl2): 8.00e6.80 (m, 14H), 3.81 (s, 3H), 3.73 (s, 4H), 3.15 (s, 2H),
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4.2.6. Preparation of {[Cu(1)](SbF6)}n (7)
Solid 3 was finely powdered and then heated for 2 h at 110 ꢀC in
vacuo to give 7. Alternatively, 7 was obtained by bubbling a stream
of N2 through a DCM (or CD2Cl2) solution of 5 for 10 min. 31P{1H}
NMR (CD2Cl2): ꢁ5.3 (s). 1H NMR (CD2Cl2): 7.95e6.84 (m, 14H), 5.03
(s, 2H), 3.24 (s, 2H), 2.46 (s, 2H). Anal. Calcd. For C20H20CuF6NPSSb:
C, 37.71; H, 3.17; N, 2.20. Found: C, 37.82; H, 3.25; N, 2.29.
4.2.7. Preparation of {[Cu(2)](SbF6)}n (8)
Solid 4 was finely powdered and then heated for 2 h at 110 ꢀC in
vacuo to give 8. Alternatively, 8 was obtained by bubbling a stream
of N2 through a DCM (or CD2Cl2) solution of 6 for 10 min. 31P{1H}
NMR (CD2Cl2): ꢁ3.4 (s, broad). 1H NMR (CD2Cl2): 7.70e7.23 (m,
12H), 7.08 (t, JHeH ¼ 8 Hz,1H), 6.96 (d, JHeH ¼ 8 Hz,1H), 3.61 (s), 3.28
(s), 2.65 (s). Anal. Calcd. for C21H21CuF6OPSSb: C, 38.69; H, 3.25.
Found: C, 38.69; H, 3.34.
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