A new family of pyrazolyl-based anionic bidentate ligands and crystal structure of bis(N-phenyl-2-pyrazolyl-1-carboximidothioato)copper(II)

Article abstract of DOI:10.1016/j.jorganchem.2005.01.019

Three new N,S-donor bidentate pyrazolyl-based ligands abbreviated as [PhNCSPz]^-, 1, [PhNCSPz^Me2]^-, 2, and [PhNCSPz^Ph2]^-, 3, have been synthesized in THF by direct mixing of phenylisothiocyanide with suspension of appropriate sodium-pyrazolate salts and characterized by the common spectroscopic and analytical methods. The Cu(II) complexes of these anionic chelate ligands have been characterized and the crystal structure of Cu(PhNCSPz)₂, 4, has been determined. The space group of complex is P2₁c, with a = 5.9313(3), b = 21.206(1) ?, c = 8.0667(4) ?, β = 103.822(1)°.

Full text of DOI:10.1016/j.jorganchem.2005.01.019

Journal of Organometallic Chemistry 690 (2005) 2128–2132
www.elsevier.com/locate/jorganchem
A new family of pyrazolyl-based anionic bidentate ligands and
crystal structure of bis(N-phenyl-2-pyrazolyl-1-
carboximidothioato)copper(II)
a,
a
a
b
Moayad Hossaini Sadr *, Ali Reza Jalili , Habib Razmi , Seik Weng Ng
a
Department of Chemistry, Azarbaijan University of Tarbiat Moallem, Tabriz, Iran
Department of Chemistry, University of Malaya, 50603 Kuala Lumpur, Malaysia
b
Received 10 January 2005; accepted 12 January 2005
Available online 22 February 2005
Abstract
Three new N,S-donor bidentate pyrazolyl-based ligands abbreviated as [PhNCSPz]ꢀ, 1, [PhNCSPzMe2]ꢀ, 2, and [PhNCSPzPh2]ꢀ,
3, have been synthesized in THF by direct mixing of phenylisothiocyanide with suspension of appropriate sodium-pyrazolate salts
and characterized by the common spectroscopic and analytical methods. The Cu(II) complexes of these anionic chelate ligands have
been characterized and the crystal structure of Cu(PhNCSPz)2, 4, has been determined. The space group of complex is P21c, with
˚
˚
a = 5.9313(3), b = 21.206(1) A, c = 8.0667(4) A, b = 103.822(1)ꢀ.
ꢁ 2005 Elsevier B.V. All rights reserved.
Keywords: Pyrazolyl-based ligands; Polypyrazolylborate; Copper complexes; Model compounds
1. Introduction
the form of pyrazolato anion [2–7]. The realm of pyraz-
olyl-based ligands, similar to those of the well known
classical polypyrazolylborate congeners, is completely
fertile and wide and their complexes may exhibit inter-
esting roles such as catalysts, models, pharmaceuticals,
etc. [8–15].
There are a lot of publications on coordination chem-
istry of pyrazole-based chelating ligands which present
versatile coordination geometry and nuclearity [1]. The
suitable structure and high stability of pyrazoles, in
addition to the ability of their deprotonated form to
act as powerful nucleophiles in substitution reactions,
have made them as good candidates for incorporation
in the design of new ligands. The easy control of the
electronic and steric properties of the pyrazolyl-derived
ligands by introducing different substituents in the pyr-
azolyl rings is another advantage and expands the do-
main of pyrazole-type ligands. Pyrazoles also can
behave as endo- or exo-bidentate bridging ligands in
Recently we have reported some copper(I) complexes
containing tetrathiometallate and polypyrazolylborate
ligands, providing N2S2 coordination environment
around copper atoms. In sight of structural and spectro-
scopic similarities between our complexes and active
sites of copper proteins, we introduced them as model
compounds [16–18]. As a result of high tendency of an-
ionic S-donor ligands, specially tetrathiomolybdate or
tetrathiotangustate, to reduce Cu(II) to Cu(I) [19], our
try to synthesis Cu(II) complexes containing tetrathio-
metallate and polypyrazolylborate ligands was led to
failure. In fact, complexes containing Cu(II)–S bonds
show a tendency to undergo redox reactions which nor-
mally converts Cu(II) to Cu(I) [20]. Particularly, Cu(II)–
*
Corresponding author. Tel.: +98 412 4524993/5424991; fax: +98
412 452 4991/4525193.
E-mail addresses: sadr@azaruniv.edu, hosainis@yahoo.com (M.H.
Sadr).
0022-328X/$ - see front matter ꢁ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.01.019

M.H. Sadr et al. / Journal of Organometallic Chemistry 690 (2005) 2128–2132
2129
thiolate complexes containing N-donors from pyrazolyl-
derived ligands are rare and according to our knowl-
edge, the compound [Cu(HB(3,5-iPr2Pz)3)(SCPh3)] is
the only structurally characterized example [21]. Contin-
uing our interest to copper complexes containing N2S2
chromophors, herein we report the novel N,S-donor
bidentate ligands 1–3 (Fig. 1) and their Cu(II) com-
plexes, 4–6. The compound 4 is monomeric and the
co-ordination environment around copper(II) atom is
trans-N2S2 forming a perfect square planar geometry
(Fig. 2).
FT BRUKER or SHIMADZU IR-470 infrared spectro-
photometers using pressed KBr disks with polystyrene
as reference. UV–Vis spectra were obtained on a JASCO
model 7850 spectrophotometer.
2.2. Synthesis of Na[PhNCSPz] (1)
A solution of pyrazole (0.68 g, 10 mmol) in 25 ml dry
THF was treated with solid NaH (55%, 0.44 g, 10 mmol)
under Ar atmosphere. After stirring for 3 h, PhNCS
(1.2 ml (d = 1.13 g/ml), 10 mmol) was added into the
resulting suspension of NaPz and the reaction was con-
tinued overnight at r.t. The suspension was filtered using
a fritted funnel and the collected white solid (PhNCSPz)
washed with cold THF (2 · 10 ml) and n-hexane
(2 · 25 ml) and dried in vacuo (2.13 g, 95%);
m.p. = 250 ꢀC (commence of melting along with color
change and decomposition). IR (KBr, cmꢀ1): 3127w
broad, m(C–H), 1595s, 1557vs, 1509s, 1446w, 1388s,
1315m, 1241vs, 1187s, 1170w, 1089s, 1043s, 986s, 931s,
2. Experimental
2.1. General considerations
All operations were carried out under a pure dinitro-
gen or argon atmosphere using Schlenk techniques. All
reagents and solvents were purchased from commercial
sources and the solvents were dried by standard proce-
dure [22] and were degassed by three freeze-pump-thaw
cycles. 1H and 13C NMR spectra were recorded on
BRUKER DRX500 AVANCE spectrometer. Peaks
were assigned on the basis of chemical shift, integration,
and coupling patterns. IR spectra were recorded on a
1
915w, 904w, 767s, 704s, 632m. H NMR (DMSO-d6, d
ppm, J Hz): 6.26 (dd, JH–H = 3 and 5, 1H, 4-H in Pz),
3
6.88 (tt, JH–H = 3 and 19, 1H, 4-H in Ph), 7.01 (d,
3
3JH–H = 3, 1H, 3-H or 5-H in Pz), 7.04 (d, JH–H = 5,
1H, 3-H or 5-H in Pz), 7.21 (t, JH–H = 19.0, 3H, in
Ph), 7.43 (t, JH–H = 3, 1H, in Ph); 13C NMR (DMSO-
d6, d): 104.66, 120.64, 121.66, 122.95, 127.39, 127.57,
130.41, 139.39, 153.10, 167.71. Anal. Calc. for
C10H8N3NaS: C, 53.33; H, 3.56; N, 18.67; S, 14.22.
Found: C, 52.83; H, 3.40; N, 19.17; S, 14.10%.
Ph
Me
Me
N
Ph
N
N
N
N
N
N
2.3. Synthesis of Na[PhNCSPzMe2] (2)
N
S
N
S
S
PhNCS (1.2 ml, 10 mmol) was added to a stirred sus-
pension of Na(3,5-Me2Pz) (1.18 g, 10 mmol) in THF
(40 ml). After being refluxed for 6 h, the suspension was
cooled to r.t. and filtered using a fritted funnel and the col-
lected white solid Na[PhNCSPzMe2] was washed with cold
THF (2 · ml) and n-hexane (2 · 25 ml) and dried in vacuo
(2.22 g, 88%); m.p. = 300 ꢀC (commence of melting along
with color change and decomposition). IR (KBr, cmꢀ1):
1634m, 1606m, 1498s, 1476m, 1447m, 1384s, 1322m,
1135m (b), 999vs, 829w, 689s, 656m, 546m (b), 473m.
1H NMR (DMSO-d6, d ppm, J Hz): 2.11 (b, 3H, CH3 in
3,5-(CH3)2Pz). 2.39 (b, 3H, CH3 in 3,5-(CH3)2Pz), 6.25
(1)
(2)
(3)
Fig. 1. Pyrazolyl-based ligands PzRSꢀ, 1, PzMe2RSꢀ, 2, and PzPh2RSꢀ,
3, (R = PhNC).
3
(t, JN–H = 4, 1H, 4-H in 3,5-(CH3)2Pz), 6.85 (t,
3JH–H = 19, 1H, 4-H in Ph), 7.00 (d, JH–H = 18.0, 2H, 2-
H and 6-H in Ph), 7.19 (t, 2 H, 3-H and 5-H in Ph). Anal.
Calc. for C12H12N3NaS: C, 56.92; H, 4.74; N, 16.6; S,
12.65. Found: C, 57.41; H, 4.69; N, 16.2; S, 12.51%.
2.4. Synthesis of Na[PhNCSPzPh2] (3)
PhNCS (1.2 ml, 10 mmol) was added to a stirred sus-
pension of Na(3,5-Ph2Pz) (2.42 g, 10 mmol) in THF
(60 ml). After being refluxed for 8 h, the suspension was
Fig. 2. Structure of the [Cu(PhNCSPz)2], 4, showing the numbering
scheme.

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M.H. Sadr et al. / Journal of Organometallic Chemistry 690 (2005) 2128–2132
cooled to r.t. and filtered using a fritted funnel and the col-
lected white solid Na[PhNCSPzPh2] was washed with cold
THF (2 · 1 ml) and n-hexane (2 · 25 ml) and dried in va-
cuo (2.94 g, 78%); m.p. = 350 ꢀC (commence of melting
along with color change and decomposition). IR (KBr,
cmꢀ1): 2800–3400s (broad multipet), m(C–H), 15991w,
1541m, 1496s, 1461s, 1384s, 1344w, 1316w, 1295w,
1272w, 1075m, 1057w, 976s, 916w, 754vs, 698s, 688s. 1H
NMR (DMSO-d6, d): 7.02 (t, J = 20, 1H, 4-H in PhNCS),
7.19 (s, 1H, 4-H in Pz), 7.25 (t, J = 20, 2H, 3-H and 5-H in
PhNCS), 7.34 (t, J = 19, 2H, 4-H in PhPz), 7.45 (t, J = 19,
4H, 3-H and 5-H in PhPz), 7.57 (d, J = 20, 2H, 2-H and 6-
H in PhNCS), 7.84 (d, J = 19, 4H, 2H, 2-H and 6-H in
PhPz). 13C NMR (DMSO-d6, d): 99.617, 123.14, 123.91,
125.10, 127.79, 127.97, 127.82, 131.47, 138.42, 149.88,
168.21. Anal. Calc. for C22H16N3NaS: C, 70.03; H, 4.24;
N, 11.14; S, 8.49. Found: C, 70.45; H, 4.32; N, 11.03; S,
8.61%.
m(C–H), 1659w, 1635w, 1601w, 1568w, 1494m, 1462s,
1447m, 1272w, 916m, 753vs, 688vs. Electronic spectrum
(DMF, k nm, absorbance): 281 (2). Anal. Calc. for
C44H32CuN6S2: C, 68.44; H, 4.15; N, 10.89; S, 8.04.
Found: C, 68.66; H, 4.07; N, 11.01; S, 7.95%.
2.8. X-ray crystallography
Diffraction studies of the complex 4 were performed
on a Bruker 2001 SMART CCD diffractometer. Mo
˚
Ka radiation (k = 0.71073 A) was employed for data
collection at 113 K. Crystal data, structure solution
and refinement for 4 are summarized in Table 1.
3. Result and discussion
3.1. Ligand synthesis
2.5. Synthesis of CuL2, L = [PhNCSPz]ꢀ (4)
The ligands 1–3 were readily prepared in THF from
the reactions of equimolar amounts of phenylisothiocy-
anide and the corresponding sodium pyrazolates
Na(3,5-R2Pz), as illustrated in the following equation:
Solid Na[PhNCSPz] (0.45 g, 2.0 mmol) and CuBr2
(0.22 g, 1 mmol) were added into acetone (30 ml) and
stirred for 4 h. The resulting deep violet solution was fil-
tered and the solvent removed in vacuo (yield 0.42 g,
90%): IR (KBr, cmꢀ1): 3132w and 3120w, m(C–H),
1593vs, 1500w, 1460w, 1431s, 1391m, 1339m, 1278m,
1216m, 1201m, 1102m, 1073s, 942vs, 910m, 780s,
763m, 693s, 609m. Electronic spectrum (DMF, nm,
absorbance): 320 (1.52), 290 (sh), 266 (1.83), 256
(1.34). Anal. Calc. for C20H16CuN6S2: C, 51.34; H,
3.42; N, 17.97; S, 13.69. Found: C, 51.01; H, 3.52; N,
18.10; S, 13.44%.
NaPzR2 þPhNCS ! Naþ½PhNCSPzR2ꢁꢀ ðR ¼ H;Me;PhÞ
ð1Þ
Deprotonation of pyrazoles to form the NaPzR2, can
be facilitated by application of an alkali or a base (typi-
cally, triethylamine) or by means of interaction of pyraz-
ole with n-butyllithium, pyrazole with an alkali metal in
THF, or pyrazole with an alkali metal hydride [2]. The
salts 1–3 were isolated in high yield (78–95%) as white
powders after separating by filtration and subsequent
washing with cold THF and n-hexane. They are stable
in dry air for months and show sufficient solubility in
ꢀ
] (5)
2.6. Synthesis of CuL2, L = [PhNCSPzMe2
A mixture of Na[PhNCSPzMe2] (0.51 g, 2.0 mmol)
and CuBr2 (0.22 g, 1 mmol) was stirred in acetone
(40 ml) for 6 h. The precipitated NaBr was separated
by filtration and the filtrate was dried in vacuo (yield
0.45 g, 87%): IR (KBr, cmꢀ1): 2900–3100w (multipletes),
m(C–H), 1607vs, 1590vs, 1486w, 1467w, 1415m, s,
1380w, 1347s, 1336s, 1269w, 1206s, 1054m, 991w,
940s, 811m, 794w, 769m, 756m, 698s. Electronic spec-
trum (DMF, k nm, absorbance): 426 (0.25), 312 (1.40),
267 (2.0), 258 (1.35). Anal. Calc. for C24H24CuN6S2:
C, 55.01; H, 4.58; N, 16.05; S, 12.22. Found: C, 54.91;
H, 4.63; N, 16.25; S, 12.00%.
Table 1
Crystallographic data for compound 1
Chemical formula
Formula weight
C20H16CuN6S2
467.5
P21/c
Crystal system, space group
Unit cell dimensions
˚
a (A)
5.9313(3)
21.206(1)
8.0667(4)
103.822(1)
985.22(8)
2
˚
b (A)
˚
c (A)
b (ꢀ)
3
˚
V (A )
Z
Dcalc (g cmꢀ3
)
1.578
1.340
l (mmꢀ1
Crystal size (mm)
)
0.59 · 0.22 · 0.18
26.4
8176
ꢀ
2.7. Synthesis of CuL2, L = [PhNCSPzPh2
]
(6)
hmax (ꢀ)
Reflections collected
Independent reflections
Parameters
1999
133
A mixture of Na[PhNCSPzMe2] (0.38 g, 1.0 mmol)
and CuBr2 (0.11 g, 0.5 mmol) was refluxed in acetone
(40 ml) for 8 h. The precipitated NaBr was separated
by filtration and the filtrate was dried in vacuo (yield
0.31 g, 80%): IR (KBr, cmꢀ1): 2863–3136b (multipletes),
R [I > 2r]
Rw (all data)
Goodness-of-fit on F2
Electron density extremes (e A
0.026
0.031
1.05
ꢀ0.38 to 0.19
ꢀ3
˚
)

M.H. Sadr et al. / Journal of Organometallic Chemistry 690 (2005) 2128–2132
2131
Table 2
common solvents such as dichloromethane, acetone or
˚
Selected bond lengths (A) and angles (ꢀ) for (1)
tetrahydrofuran. The formation of the ligands from reac-
tants can be easily controlled by solid state IR spectros-
copy: the absence of –SCN pick at the region 2000–
2100 cmꢀ1 along with the appearance of some new bands
other than those of corresponding pyrazolates, clearly
verifies the production of the ligands. It is also important
to note that we have successfully used a similar method
to prepare other new bidentate ligands such as
Na+[PhNCSBtz]ꢀ (Btz = benzotriazole) or Na+[PhNC-
SImz]ꢀ (Imz = imidazole) from the reactions of PhNCS
and NaBtz or NaImz, respectively, an observation that
illustrates the general applicability of our methodology.
The contribution of PhNCS in preparation of new N,S-
donor ligands has also been reported by Shen and Yao
[23] and they have been considered the activation of
PhNCS by organolanthanoid complexes as driving force
of reaction.
Cu1–S1
S1–Cu–S1i
S1–Cu–N1
2.281(1)
180
85.8(1)
Cu1–N1
N1–Cu–N1i
S1–Cu–N1i
1.954(2)
180
94.2(1)
Symmetry code (i): 1 ꢀ x, 1 ꢀ y, 1 ꢀ z.
four-coordinate perfect square planar with bond angles
of 85.8ꢀ, 94.2ꢀ and 180ꢀ for S1–Cu–N1, S1–Cu–N1i,
and S1–Cu–S1i (or N1–Cu–N1i), respectively. The
molecular geometry, bond angles and Cu–N dis-
tances(1.954 A) in 4 are comparable to those of
[Cu(H2B(3,5-Me2Pz)2)2] [17] or [Cu(H2B(3,5-(CF3)2-
˚
˚
Pz) ) ] [24]. Both of the Cu–S (2.281 A) distances in 4
2 2
are equal and are similar to those found for (NEt4)2[Bp-
CuMoS4Cu2(l-Bp0)2Cu2MoS4CuBp0] [17] or (NEt4)2-
[MS4(CuBp0)2] (M = Mo, W; Bp0 = H2B(3,5-Me2Pz)2)
[18]. The structure of 4 is also very similar to that of the
anionic cis-CuN2S2 complex, [Cu(SCH2CH(CO2Me)
NHCH2)2]ꢀ, which has been introduced as a synthetic
model for the copper proteins such as poplar plastocya-
nin [25]. Even if, the bonding parameters about Cu atom
in 4 are somewhat different from those of the mentioned
metalloproteins, they match better than the previously
reported complexes [25–28].
The structure of the complex 5 has also been deter-
mined, and the copper atom has a distorted tetrahedral
geometry with bond angles varying from 86.93ꢀ to
151.59ꢀ and average Cu–N and Cu–S distances of
1.976 and 2.237 A, respectively; The complete data for
this structure will be published elsewhere as necessitated
by our joint collaborators.
3.2. Preparation of copper complexes
The complexes 4–6 were prepared in acetone or tetra-
hydrofuran through one-pot reaction by mixing of the
corresponding ligands with CuBr2 in 2:1 molar ratio,
in nearly quantitative yield (Eq. (2)), even though, syn-
thesis of the complexes by the self assembly method
via direct mixing of reactants was also successful (Eq.
(3))
2Na½PhNCSPzR2ꢁ þ CuBr2 ! CuL2 þ 2NaBr
˚
ðL ¼ ½PhNCSPzR2ꢁÞ
ð2Þ
ð3Þ
2PzR2 þ 2PhNCS þ CuCl ! CuL2 þ 2HCl
ðL ¼ ½PhNCSPzR2ꢁÞ
3.4. Conclusion
All compounds 4–6 are completely air stable and 4 and
5 is highly but 6 slightly soluble in most of laboratory sol-
vents such as acetone, tetrahydrofuran, dichlorometh-
ane, acetonitrile. . . The complexes were characterized
by a combination of analytical and spectroscopic tech-
niques, including IR, UV–Vis, CHN elemental analysis.
IR spectra of the complexes are also useful, as explained
The compounds 1–3 are new anionic bidentate li-
gands which can be easily prepared and stored for
months in dry air without any significant decomposi-
tion, according to their physical properties and IR spec-
troscopy. So, there is a vast possibility to do more
research on these ligands by synthesizing new similar li-
gands via displacing the pyrazolyl moiety of the ligands
with different similar pyrazole-type nucleophiles. Hence,
coordination chemistry of the ligands will be structurally
as well as functionally fruitful and interesting.
1
for the ligands. H and 13C NMR spectra of the com-
plexes were not very informative as a result of the pres-
ence of paramagnetic Cu(II) atom (d9).
As a result of structural similarity, the complexes 4–6,
can be considered as structural models for type I mono-
nuclear Cu-proteins such as poplar plastocyanin,
cuperedoxin, cytochrome c oxides, etc. [20,26,29,30].
In addition to comparability of pyrazole (as N-donor
in 4–6) and imidazole of amino acids of living systems,
the bonding parameters and co-ordination environment
of Cu atom in 4 are similar to those reported for copper
proteins. It is also fascinating that, according to our
knowledge, the compounds 4–6 are among the rare com-
plexes which contain stable Cu(II)–S (from thiolates)
3.3. Structure of [Cu(PhNCSPz)2], 4
Single crystals suitable for an X-ray diffraction study
of [Cu(PhNCSPz)2] were obtained by slow evaporation
of a concentrated THF (or acetone) solution of the title
compound at room temperature. An ORTEP diagram
of 4 is presented in Fig. 2 and a selection of bond lengths
and angles is given in Table 2. In the solid state, the struc-
ture of the title compound consists of monomeric trans-
CuN2S2 units and the geometry around Cu atom is a

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M.H. Sadr et al. / Journal of Organometallic Chemistry 690 (2005) 2128–2132
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geometry, high ligand field stabilization energy, and
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(b) R. Uson, L.A. Oro, M.T. Pinillos, M. Royo, E. Pastor,
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Acknowledgements
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We thank the Research Office of Azarbaijan Univer-
sity of Tarbiat Moallem and the University of Malaya
for supporting this study. We thank Mr. H. R. Bijhan-
zade of Tarbiat Modares University for the NMR spec-
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Appendix A. Supplementary data
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Crystallographic data, excluding structure factors,
have been deposited at Cambridge Crystallographic
Data Center, CCDC No. 250916. Copies of this infor-
mation may be obtained free of charge from the Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK
(fax: +44-1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk). Supplementary
data associated with this article can be found, in the on-
line version at doi:10.1016/j.jorganchem.2005.01.019.
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