Synthesis and metal complexes of thiourea ligands containing carbohydrate-derived substituents

Article abstract of DOI:10.1002/hlca.201200386

Two glucose-derived thiourea derivatives, 2a and 2b, were prepared by addition of the corresponding amino sugars to a solution of 4-nitrobenzoyl isothiocyanate (Scheme 1). The thioureas were isolated as colorless solids in good yields and were fully characterized by NMR spectroscopy, optical rotation, elemental analysis, and also by single-crystal X-ray diffraction. Attempts to obtain Cu^II and Ni^II bis(chelate) complexes with these thioureas failed. However, the C(1)-protected thiourea derivative 2a reacted with orthopalladated acetato-bridged dimers to afford the corresponding monomeric Pd^II complexes 3 and 4 (Scheme 2). In these compounds, the thiourea coordinates to the metal as monoanionic O,S chelate ligand, which was confirmed by X-ray crystallography. Copyright

Full text of DOI:10.1002/hlca.201200386

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Synthesis and Metal Complexes of Thiourea Ligands Containing
Carbohydrate-Derived Substituents
by Michelle Sternberga), Jçrg Rustb), Christian W. Lehmannb), and Fabian Mohr*a)
a) Fachbereich C – Anorganische Chemie, Bergische Universitꢀt Wuppertal, Gaußstr. 20, D-42119
Wuppertal (phone: þ 49-202-4393641; fax: þ 49-202-4393052; e-mail: fmohr@uni-wuppertal.de)
b) Max-Planck-Institut fꢁr Kohlenforschung, Kaiser-Wilhelm-Platz 1, D-45470 Mꢁlheim an der Ruhr
Two glucose-derived thiourea derivatives, 2a and 2b, were prepared by addition of the corresponding
amino sugars to a solution of 4-nitrobenzoyl isothiocyanate (Scheme 1). The thioureas were isolated as
colorless solids in good yields and were fully characterized by NMR spectroscopy, optical rotation,
elemental analysis, and also by single-crystal X-ray diffraction. Attempts to obtain CuII and NiII
bis(chelate) complexes with these thioureas failed. However, the C(1)-protected thiourea derivative
2a reacted with orthopalladated acetato-bridged dimers to afford the corresponding monomeric PdII
complexes 3 and 4 (Scheme 2). In these compounds, the thiourea coordinates to the metal as
monoanionic O,S chelate ligand, which was confirmed by X-ray crystallography.
Introduction. – Acylthioureas of the type RC(¼O)NHC(¼S)NR2R3 are readily
deprotonated at the N-atom and may subsequently react with many metal compounds
giving metallacyclic compounds in which the thioureas act as monoanionic, O,S
chelating ligands or, in the case of gold(I), as monoanionic Sꢀ ligands (Fig. 1).
Fig. 1. General structures of metal complexes containing thioureato ligands
Examples of these types of compounds containing CuII, NiII, PdII, PtII, ZnII, CoIII,
HgII and RhIII have been reported by various groups over the past years [1 – 15]. In most
cases, R1 corresponds to an aryl group and R2 and R3 are alkyl chains or part of a
ꢂcycloalkeneꢃ such as morpholine or pyrrolidine. Recent work from our group has
shown that these ligands may also act as monoanionic ligands coordinating only
through the S-atom to a gold(I) center [16]. The coordination chemistry of thioureas
derived from primary amines (i.e., R2 ¼ H) is significantly less developed; only two
papers containing structural data for some PdII and PtII complexes are available
[17][18]. Interest in this class of compounds has arisen from their potential application
ꢄ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

Helvetica Chimica Acta – Vol. 96 (2013)
281
as selective extraction agents for metal separation and chromatography [4][10][19][20]
and also for their antimicrobial [2][3][21], antimalarial [16][22], and antitumor
activity [16][23].
Derivatives of sugars are ꢂbiocompatibleꢃ ligands which are of interest in metal
complexes for medical applications [24] and also for asymmetric catalysis [25]. The
sugar moiety may impart H2O solubility to the metal complex and/or can be recognized
by biological sugar receptors. Examples for sugar functionalized ligands include Schiff
bases derived from the condensation of amino sugars with pyridine-2-carboxaldehyde
or 2-hydroxynaphthalene-1-carboxaldehyde [26][27]. Other groups have studied Mo
and Mn complexes containing sugar-substituted pyridine-2-methanols [28] or salen-
type ligands (salen ¼ bis(salicyclidene)ethylenediamine) [29] in asymmetric syntheses.
A detailed study of the antitumor activity of some PtII complexes containing glucose
derivatives in the backbone has also been reported [30]. Given our interest in the
coordination chemistry of thioureas and related sulfur species [1][16][31 – 36], we
wished to prepare some sugar-substituted thioureas and study their reactions with
metal compounds. The results of these studies are reported herein.
Results and Discussion. – The glucose-based substituted thiourea derivatives 2a and
2b were prepared by addition of the amino sugars 1a [37] and 1b [38] to a solution of 4-
nitrobenzoyl isothiocyanate generated in situ from the corresponding acyl chloride and
KSCN in acetone (Scheme 1). The thioureas 2a and 2b were isolated as colorless solids
in good yields and were fully characterized by NMR spectroscopy, optical rotation,
elemental analysis, and also by single-crystal X-ray diffraction. The spectroscopic data
was fully consistent with the proposed structures. Two distinct signals for the two NH
1
groups were observed in the H-NMR spectra of both compounds at d(H) ca. 9 ppm
(C(¼O)NHC(¼S)] and 11 (C(¼S)NHCH). The signal of the latter was a d due to
coupling with the HꢀC(2) of the carbohydrate ring. The H-atom resonances of the
carbohydrate ring in both compounds could be unambiguously assigned by using 2D-
NMR spectra. Particularly diagnostic was the magnitude of the coupling constant of the
signal of HꢀC(2), since this indicated the configuration of the carbohydrate ring at this
position.
Scheme 1

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Helvetica Chimica Acta – Vol. 96 (2013)
The molecular structures of both compounds 2a and 2b were confirmed by X-ray
diffraction (Fig. 2,a and 2,b; Table). In both cases, the thiourea unit is attached to the
pyranose ring in the equatorial position at C(2) under retention of the glucose
configuration. The carbohydrate ring is rotated by ca. 908 relative to the thiourea unit,
whilst the aromatic ring lies almost in the plane of the thiourea moiety. Both structures
are very similar in terms of bond lengths and angles as well as in the orientation of the
C¼O and C¼S units with respect to each other. In both compounds, the
HNC(¼S)NHC(¼O) unit lies in one plane and is rotated such that the chalcogen
atoms lie on opposite sides (Fig. 3). This conformation is (in both molecules) held in
place by an intramolecular H-bond between N(1) and O(1) with H ··· O distances of
ca. 1.97 and 1.82 ꢅ, respectively. A similar structural arrangement including such
an intramolecular H-bond has also been found in the cyclohexyl (Cy) derivative
4-O2NC6H4C(¼O)NHC(¼S)NHCy [39]. In addition to this intramolecular H-bond, a
further intermolecular H-bond between N(2)ꢀH and the pyranose ring O-atom in 2a
(H ··· O 2.48 ꢅ) or the solvated-ethanol O-atom in 2b (H ··· O 2.43 ꢅ) is observed. The
OH group of the ethanol solvent molecule is involved in a further OꢀH ··· O H-bond to
the carbonyl O-atom of the C(6) O-acetyl protecting group.
Fig. 2. Molecular structure of a) 2a and b) 2b. Arbitrary atom numbering; 50% probability ellipsoids; the
EtOH of solvation for 2b is omitted for clarity.

Helvetica Chimica Acta – Vol. 96 (2013)
283
Fig. 3. Superposition of the molecular structures of 2a and 2b. The r.m.s. of the fitted pyranose ring atoms
is 0.067 ꢅ.
Table. Crystal Data and Structure Refinement for Compounds 2a, 2b, and 4
2a
2b
4
Empirical formula
Mr
C21H25N3O11S
527.50
C24H31N3O13S
601.58
C38H36N4O13PdS
895.17
Crystal system
Space group
tetragonal
P43212
monoclinic
P21
monoclinic
P21
a [ꢅ]
b [ꢅ]
c [ꢅ]
b [8]
V [ꢅ3]
Z
11.3362(3)
11.3362(3)
37.866(3)
11.003(4)
10.502(4)
12.739(5)
103.97(3)
1428.5(9)
2
1.399
0.183
632.0
5.3581(11)
28.747(6)
12.166(3)
93.311(3)
1870.8(7)
2
1.589
0.626
916.0
4866.1(4)
8
1.440
0.198
2208.0
Density (calc.) [Mg/m3]
Absorption coefficient [mmꢀ1
F(000)
]
Crystal size [mm]
2V range [8]
Reflections collected
Independent reflections
R(int)
0.21 ꢁ 0.18 ꢁ 0.04 0.06 ꢁ 0.05 ꢁ 0.01 0.036 ꢁ 0.028 ꢁ 0.001
6.48 – 58.82
11365
5.86 – 58.82
6456
1.82 – 31.17
50201
5611
4916
11998
0.0412
0.0718
0.0707
Data, restraints, parameters
Goodness-of-fit on F2
Final R indices (I > 2s(I))
5611, 0, 329
1.076
R1 ¼ 0.0568,
wR2 ¼ 0.1078
R1 ¼ 0.0760,
wR2 ¼ 0.1128
4916, 1, 380
0.720
11998, 1, 519
1.160
R1 ¼ 0.0590,
wR2 ¼ 0.1081
R1 ¼ 0.1768,
wR2 ¼ 0.1300
0.01(18)
R1 ¼ 0.0520,
wR2 ¼ 0.1352
R1 ¼ 0.0725,
wR2 ¼ 0.1662
0.03(3)
R indices (all data)
Absolute structure parameter (Flack) [40] 0.05(12)
Largest diff. peak and hole [e ꢅꢀ3
]
0.23 and ꢀ 0.30 0.37 and ꢀ 0.32 2.18 and ꢀ 2.53
We initially attempted the reaction of 2a and 2b with [Cu(OAc)2] in the hope to
obtain homoleptic bis(chelate) complexes containing the deprotonated thioureas.
However, in both cases examination of the reaction mixture by electrospray mass

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spectrometry showed a multitude of signals, the majority of which could not be
assigned. We were able to identify signals corresponding to CuII adducts of the
thioureas accompanied by loss of one or more acetate groups or loss of the entire
carbohydrate unit. Similar results were also obtained with [Ni(OAc)2]. It seemed,
therefore, that under these conditions, the ligands undergo fragmentation and also lose
the acetate groups. From these preliminary experiments, it also became clear that the
tetraacetate derivative 2b had a much greater tendency to undergo fragmentation than
2a, we therefore focused our attention on the reactivity of 2a with acetato-bridged
cyclopalladated compounds. Similar reactions of thiourea derivatives with cyclo-
palladated acetato-bridged dimers have been previously reported by us [32]. Thus, the
reaction of 2a with 1/2 equiv. of the cyclopalladated dimers gave the yellow PdII
complexes 3 and 4 in good yields (Scheme 2). The compounds were characterized by
1H-NMR spectroscopy, elemental analysis and, in the case of 4 by X-ray crystallog-
1
raphy. The H-NMR spectra of 3 and 4 revealed that the signal of the NH H-atom
between the CO and CS groups had disappeared, consistent with deprotonation of the
thiourea unit. The second NH signal was still visible as a d due to coupling with the
carbohydrate ring HꢀC(2). The coupling constant for this NH H-atom (ca. 9.3 Hz) was
equal in both the Pd-complexes as well as in the unchelated thioureas, indicating that
the configuration at C(2) of the sugar moiety died not change during the reaction. This
was further confirmed by an X-ray diffraction study of 4 (Table). The molecule
crystallizes in space group P21 and consists of a Pd-atom coordinated to the ortho-C-
atom of the phenyl substituent at the quinoline derivative, the N-atom of the quinoline
unit, as well as the S- and O-atoms of the deprotonated thiourea ligand (Fig. 4).
Overall, the coordination geometry about the Pd center is, as expected, square planar.
The thiourea ligand is deprotonated at N(1) and forms a planar O,S-chelate ring, typical
for this type of ligand. The bond lengths and angles about the Pd-atom in 4 are similar
to those observed previously in other cyclopalladated thioureato complexes [32].
Scheme 2

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285
Fig. 4. Molecular structure of 4. Arbitrary atom numbering; 50% probability ellipsoids; H-atoms are
omitted for clarity.
Conclusions. – We prepared and fully characterized two carbohydrate-substituted
thioureas and examined their reactivity with metal species. Reactions with metal
acetates led to fragmentation of the ligands and not to the expected bis(chelate) metal
complexes. However, the reaction with cyclometallated palladium(II) complexes
cleanly afforded monomeric palladium(II) compounds containing the sugar-substitut-
ed thiourea as a monoanionic, O,S-chelate ligand, which was confirmed by an X-ray
crystallographic study. Further studies of this class of complexes are continuing in our
laboratories and will be reported in due time.
Experimental Part
General. All experiments were carried out under ambient conditions with no exclusion of air and
moisture. The amino sugars 1a and 1b as well as the cyclopalladated nitrosamine [Pd(O2CMe){4-
MeꢀC6H3ꢀN(Me)NO}]2 were prepared as described in [32][37][38]. [Pd(O2CMe){2-C6H4ꢀC8H5Nꢀ4-
COOMe}]2 was prepared by treating palladium(II) acetate with commercial methyl 2-phenylquinoline-4-
carboxylate in AcOH as described for the hexadecyl analogue [41]. All other chemicals and solvents
were from commercial sources (Acros Organics, Alfa Aesar, or SigmaꢀAldrich) and were used as
received. Optical rotations: PerkinꢀElmer-241 polarimeter (10 cm, 1 ml cell); [a]2D5 determined at 589 nm
(Na-d line). NMR Spectra: Bruker-Avance-400 at 400 spectrometer; (1H) and 101 MHz (13C); d in ppm
rel. to Me4Si as internal standard, J in Hz. Elemental analyses were performed by the staff of the
microanalytical facility at the University of Wuppertal.
Single-Crystal X-Ray diffraction. Crystal diffraction data for 2a and 2b were collected at 150 K with
an Oxford-Diffraction-Gemini-E-Ultra diffractometer, equipped with an EOS-CCD area detector and a
four-circle kappa goniometer. For the data collection, the Mo-source emitting graphite-monochromated
MoKa radiation (l 0.71073 ꢅ) was used. Data integration, scaling, and empirical absorption corrections
were carried out with the CrysAlis Pro program package [42]. Diffraction data for 4 were collected at
100 K with a Bruker-APEX-II diffractometer positioned in front of a FR591 rotating Mo-anode equipped
with focussing multilayer optics. The structures were solved with direct methods and refined by full-
matrix-least-squares against F2. The non-H-atoms were refined anisotropically, and H-atoms were placed
at idealized positions and refined with the riding model. All calculations were carried out with the
program Olex2 [43]. Important crystallographic data and refinement details are summarized in the
Table1).
1
)
CCDC-915384 (2a), -915384 (2b), and -915383 (4) contain the supplementary crystallographic data
for this paper. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/
data_request/cif.

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Methyl 2-Deoxy-2-{{[(4-nitrobenzoyl)amino]thioxomethyl}amino}-b-d-glucopyranoside 3,4,6-Tria-
cetate (2a). To a soln. of KSCN (0.31 g, 3.13 mmol) in acetone (40 ml) was added 4-nitrobenzoyl chloride
(0.58 g, 3.13 mmol), and the resulting mixture was heated to reflux for 1 h. Then the yellow suspension
was cooled to r.t., a soln. of protected amino sugar 1a (1.00 g, 3.13 mmol) in acetone (40 ml) was added,
and the mixture was stirred for an additional 3 h at r.t. The almost colorless suspension was poured into
0.1m HCl (200 ml), and the resulting precipitate was isolated by filtration, washed with H2O (200 ml),
and dried in air: 2a (1.22 g, 74%). Colorless solid. X-Ray-quality crystals were obtained by recrystallizing
a sample from EtOH. [a]2D5 ¼ þ2.9 (c ¼ 1, CH2Cl2). 1H-NMR (400 Hz, CDCl3): 2.06, 2.07, 2.13 (s,
3 AcO); 3.55 (s, MeO); 3.79 (m, HꢀC(5)); 4.22 (dd, J ¼ 12.2, 2.8, 1 HꢀC(6)); 4.33 (dd, J ¼ 12.2, 4.7,
1 HꢀC(6)); 4.68 (d, H, J ¼ 7.9, HꢀC(1)); 4.87 (q, J ¼ 8.8, HꢀC(2)); 5.21 (t, J ¼ 9.2, HꢀC(4)); 5.36 (t, J ¼
9.4, HꢀC(3)); 8.06 (d, H, J ¼ 8.8, 2 arom. H); 8.38 (d, J ¼ 8.8, 2 arom. H); 9.22 (s, C(O)NH); 10.74 (d, J ¼
9.4 Hz, C(S)NH). 13C-NMR (101 MHz, CDCl3): 20.61, 20.74 (Me); 57.02 (MeO); 58.86 (C(2)); 62.00
(C(6)); 68.09 (C(4)); 72.00 (C(5)); 72.54 (C(3)); 101.50 (C(1)); 124.18, 128.93 (arom. C); 136.90
(CC(O)); 150.68 (CNO2); 164.71 (CO); 169.33, 170.54, 170.69 (MeCO); 180.91 (CS). Anal. calc. for
C21H25N3O11S (527.12): C 47.81, H 4.78, N 7.97, S 6.08; found: C 47.91, H 4.92, N 7.94, S 5.82.
2-Deoxy-2-{{[(4-nitrobenzoyl)amino]thioxomethyl}amino}-b-d-glucopyranose 1,3,4,6-Tetraacetate
(2b). As described for 2a, with KSCN (0.43 g, 4.40 mmol), 4-nitrobenzoyl chloride (0.82 g, 4.40 mmol),
and amino sugar 1b (1.53 g, 4.40 mmol): 2b (1.81g, 74%). Colorless solid. [a]2D5 ¼ þ21.01 (c ¼ 1, CH2Cl2).
1H-NMR (400 Hz, CDCl3): 2.07, 2.09, 2.13, 2.15 (s, 4 AcO); 3.94 (m, HꢀC(5)); 4.19 (dd, J ¼ 12.3, 2.6,
1 HꢀC(6)); 5.35 (dd, J ¼ 12.5, 4.7, 1 HꢀC(6)); 5.08 (q, J ¼ 8.7, HꢀC(2)); 5.24 (t, J ¼ 9.1, HꢀC(4)); 5.39 (t,
J ¼ 9.2, HꢀC(3)); 5.96 (d, J ¼ 8.2, HꢀC(1)); 8.07 (d, J ¼ 8.8, 2 arom. H); 8.37 (d, J ¼ 8.8, 2 arom. H); 9.24
(s, C(O)NH); 10.77 (d, J ¼ 9.3, C(S)NH). 13C-NMR (101 MHz, CDCl3): 20.58; 20.67; 20.71; 21.00 (Me);
57.82 (C(2)); 61.64 (C(6)); 67.38 (C(4)); 72.11 (C(3)); 72.90 (C(5)); 92.12 (C(1)); 124.17, 128.99 (arom.
C); 136.65 (CC(O)); 150.72 (CNO2); 164.47 (CO); 169.14, 169.31, 170.35, 170.64 (MeCO); 181.24 (CS).
Anal. calc. for C22H25N3O12S · EtOH (587.14): C 47.02, H 4.97, N 7.15, S 5.46; found: C 47.64, H 5.03, N 7.39,
S 5.26.
{Methyl 2-Deoxy-2-{{[(4-nitrobenzoyl-kO)amino](thioxo-kS)methyl}amino}-b-d-glucopyranosidato
1,3,4,6-tetraacetate}{2-[4-(methoxycarbonyl)quinolin-2-yl-kN]phenyl-kC]palladium (4). A mixture of 2
(0.07 g, 0.134 mmol) and the palladacycle [Pd(O2CMe){2-C6H4ꢀC8H5Nꢀ4-COO2Me}]2 (0.05 g,
0.061 mmol) in MeCN (20 ml) was heated to reflux for 30 min. The resulting yellow soln. was
concentrated, and the residue was washed with H2O and Et2O and subsequently dried in air: 4 (0.48 g,
1
88%). Yellow solid. [a]2D5 ¼ ꢀ105.6 (c ¼ 1, CH2Cl2). H-NMR (400 Hz, CDCl3)2): 2.10 (br. s, 9 H, Me);
3.56 (s, MeOꢀC(1)); 3.80 (m, HꢀC(5)); 4.11 (s, COOMe); 4.18 (dd, J ¼ 12.2, 1.8, 1 HꢀC(6)); 4.36 (dd, J ¼
12.5, 4.8, 1 HꢀC(6)); 4.62 (d, J ¼ 7.8, HꢀC(2)); 4.90 (m, HꢀC(1)); 5.33 (m, HꢀC(3), HꢀC(4)); 6.91 (d,
J ¼ 9.3, NH); 7.01 (m, Hc, Hb); 7.35 (d, J ¼ 7.6, Hd); 7.54 (d, J ¼ 7.6, Ha); 7.61 (m, Hf, Hg); 8.25 (m, 4 arom.
H, C6H4NO2); 8.65 (d, J ¼ 7.3, Hh); 8.94 (d, J ¼ 7.1, Hi); 9.07 (d, J ¼ 8.1, He). Anal. calc. for
C38H38N4O13PdS (896,12): C 50.87, H 4.27, N 6.24, S 3.57; found: C 50.58, H 4.56, N 6.30, S 3.53.
{Methyl 2-Deoxy-2-{{[(4-nitrobenzoyl-kO)amino](thioxo-kS)methyl}amino}-b-d-glucopyranosidea-
to 1,3,4,6-tetraacetate}{5-methyl-2-[methyl(nitroso-kN)amino]phenyl-kC]palladium (3): As described for
4, with 2a (0.09 g, 0.174 mmol) and palladacycle [Pd(O2CMe){4-MeꢀC6H3ꢀN(Me)NO}]2 (0.05 g,
0.079 mmol): 3 (0.41 g, 66%). Yellow solid. [a]2D5 ¼ ꢀ67.6 (c ¼ 1, CH2Cl2). H-NMR (400 Hz, CDCl3)2):
1
2.04, 2.07, 2.13 (s, 3 Me); 2.22 (s, Me); 3.50 (s, MeOꢀC(1)); 3.60 (s, MeN); 3.79 (m, HꢀC(5)); 4.19 (dd,
J ¼ 12.2, 2.5, 1 HꢀC(6)); 4.36 (dd, J ¼ 12.5, 5.0, 1 HꢀC(6)); 4.49 (d, J ¼ 7.9, HꢀC(1)); 4.91 (m, HꢀC(2));
2
)
Atom numbering:

Helvetica Chimica Acta – Vol. 96 (2013)
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5.22 (q, J ¼ 9.7, HꢀC(4)); 5.31 (m, HꢀC(3)); 6.72 (d, J ¼ 9.3, NH); 6.84 (d, J ¼ 8.0, Hd); 6.93 (dd, J ¼ 8.0,
2.3, Hc); 7.05 (d, J ¼ 2.3, Ha); 8.28 (d, J ¼ 8.8, 2 arom. H of C6H4NO2), 8.41 (d, J ¼ 8.8 Hz, 2 arom. H of
C6H4NO2). Anal. calc. for C29H36N5O12PdS (784.11): C 44.36, H 4.62, N 8.92, S 4.08; found: C 44.24, H
4.89, N 8.78, S 3.96.
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Received July 23, 2012