A novel coordination mode of κ1-N-Br-pyridylbenz-(imida, oxa or othia)-zole to Pt(ii): Synthesis, characterization, electrochemical and structural analysis

Article abstract of DOI:10.1039/c9ra01856e

Herein, three novel Pt(ii) complexes with formula [trans-Pt(Br-PyBenz-X)(Cl)₂(DMSO)] (1-3) having Br-pyridylbenz-(imida, oxa or othia)-zole (L_1-3) derivatives as potential bidentate ligands, under an unusual κ¹-N-coordinat

Full text of DOI:10.1039/c9ra01856e

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A novel coordination mode of k1-N-Br-
pyridylbenz-(imida, oxa or othia)-zole to Pt(II):
synthesis, characterization, electrochemical and
structural analysis†
Cite this: RSC Adv., 2019, 9, 14033
ab
*
Juan Nicasio-Collazo,
Gonzalo Ramırez-Garcıa,a Marcos Flores-A´lamo,c
´ ´
Silvia Gutierrez-Granados,a Juan M. Peralta-Hernandez,a Jose Luis Maldonado,b
J. Oscar C. Jimenez-Halla
´
´
´
a
a
*
and Oracio Serrano
Herein, three novel Pt(II) complexes with formula [trans-Pt(Br-PyBenz-X)(Cl)2(DMSO)] (1–3) having Br-
pyridylbenz-(imida, oxa or othia)-zole (L1–3) derivatives as potential bidentate ligands, under an unusual
k1-N-coordination mode are reported. All compounds were obtained straightforwardly via reaction of
corresponding LPB1–3 and [Pt(Cl)2(DMSO)2] (DMSO ¼ dimethyl sulfoxide), at 100 ꢀC in acetonitrile,
respectively. 1–3 complexes were characterized by analytical and spectroscopic data: melting point, FT-
IR, Raman, UV/Vis and NMR experiments. Cyclic voltammetry studies show an irreversible two-electron
process at ꢁ0.50 and ꢁ0.51 V, which was ascribed to the Pt(II)/Pt(IV) couple, for complexes 2 and 3. The
crystal structure of complex 2 was elucidated by single-crystal X-ray diffraction, where the platinum
atom exhibits a square plane geometry, where LPB2 adopts an unusual mono-coordinated mode via an
N-k1-benzoxazole ring. According to DFT calculations the first N-coordination exchanging one DMSO
molecule is favourable, while the second N-coordination is highly impeded.
Received 11th March 2019
Accepted 22nd April 2019
DOI: 10.1039/c9ra01856e
rsc.li/rsc-advances
complexes with pyridyl-imidazole ligands, which were used as
electroluminescent materials in light-emitting electrochemical
cells devices. Later, Wang et al.14 reported an elegant work on
Introduction
Benzimidazole and its derivatives are important heterocyclic
compounds. These ligands have been found to exhibit biolog-
ical activities and clinical applications.1 In the last decades,
transition metal complexes with benzimidazole derivatives have
shown attractive chemical properties2,3 and numerous applica-
tions in catalysis,4–6 biological activity,7 organic light-emitting
diodes8,9 and photovoltaics.10 Furthermore, N,N0-donor
chelating ligand pyridyl-benzimidazole has been used as
a bipyridine analogue in a wide variety of complexes with
different metal ions such as Ir(III),11,12 Ru(II),13 Pt(II),14 respec-
tively. Barnham and Ruiz et al.11 reported that a series of Ir(III),
Ru(II) and Pt(II) inhibited in vitro aggregation of the peptide
fragment amyloid Ab1–42, representing a potential use as
therapeutic agents for Alzheimer's disease. Recently, Espino,
Bolink and Orti et al.12 reported the synthesis of iridacycle
the synthesis of pyridyl-benzimidazole ligands, which display
uorescent emission in the purple/blue region at room
temperature and phosphorescent emission in the blue/green
region at 77 K. Fan et al.15 showed that W(0) species exhibit
enhanced phosphorescence, at room temperature, from MLCT
excited stated with quantum yields on the order of 10ꢁ3. Addi-
tionally, Housecro and Bolink et al.16 reported an elegant
synthesis of cyclometalated Ir(III) compounds having pyridyl-
benzoxa and thiazole derivatives (LBP), giving an efficient and
stable red-emission, with active layers lifetimes greater than
1000 h. Furthermore, Ward et al.13 described a series of Re-
carbonyl, Pt-acetylide and Ru-bipyridine complexes with LBP
ligands. Particularly, Pt species showed luminescence in the
range 553–605 nm arising from the 3MLCT state, with emissive
lifetime up to 500 ns and quantum yields up to 6% in CH2Cl2 at
room temperature. Studies reported by DeStefano et al.17,18 on
Pt- and Zn-LBP complexes showed that they exhibit a color blue
luminescence in the solid state and in solution.
a
´
Departamento de Quımica, Universidad de Guanajuato, Cerro de La Venada S/N, CP
36040, Guanajuato, Gto, Mexico. E-mail: oraciosinh@ugto.mx
bResearch Group of Optical Properties of Materials (GPOM), Centro de Investigaciones
In early reports, Westcott et al.7 showed that the reaction of
[Pt(Cl2)(COE)]2 (COE ¼ cis-cyclooctene) or K2PtCl4 with LPB
ligands gives the expected [cis-Pt(Cl)2(LPB)] complexes (Chart
1a). Later, when benzimidazole fragment is in position three
with respect to pyridine, the reaction lead to the monodentate
´
´
en Optica, AP 37000, Leon, Guanajuato, Mexico. E-mail: nicasio.collazo@cio.mx
c
´
´
´
Facultad de Quımica, Universidad Nacional Autonoma de Mexico (UNAM), Circuito
´
´
Exterior S/N, Coyoacan, Cd. Universitaria, CP 04510, Ciudad de Mexico, Mexico
† Electronic supplementary information (ESI) available. CCDC 1849220. For ESI
and crystallographic data in CIF or other electronic format see DOI:
10.1039/c9ra01856e
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[cis-Pt(Cl)2(LPB)2], where coordination to the metal occurs via desired compound, instead, the starting materials are recov-
the pyridine ring (Chart 1e). Part of our research has been ered. The replaced of dimethyl for an chloride–platinum
focused on understanding the reactivity of 2-(6-bromopyridyl-2- complexes with general formula [PtCl2(COE)2] or [PtCl2(COD)]
yl)-1-phenylbenzimidazole, LPB1, ligand towards dialkyl–palla- does not show a positive effect on the reactivity towards LPB1–3
,
dium complexes. A few years ago, we reported the synthesis of according to the NMR analysis of the proton and platinum
seven-membered palladacycles through selective C–Br bond spectra. This suggest, that bromine atom into the LPB1–3 ligands
activation of
a Br-pyridine-benzimidazole derivative and plays an interesting role on the complex formation according to
concomitant C–C coupling bond, where no-innocent cyclo- Westcott report's (Charts 1a and e). Later, when PPh3 was added
octadiene ligand (COD) plays an essential role (Chart 1b).19 Also, to the reaction mixture, an spontaneous formation of complex
a ve-membered palladacycles synthesis can be achieved when [PtCl2(PPh3)2] takes place in quantitative yield, according to the
the COD is displaced by a phosphine ligand (Chart 1c). In 2018, 31P and 195Pt NMR experiments.21 Given the low reactivity of
we reported a direct synthesis on rollover palladacycles was organoplatinum species, we carried out the reaction with Pt
achieved via C–H bond activation reaction in remote position coordination species like [PtCl2(DMSO)2] or [PtCl2(THT)2]
on Br-pyridyl-benzothiazole (LPB2) by PdCl2, where the dime- (DMSO ¼ dimethyl sulfoxide; THT ¼ tetrahydro-thiophene)
thylformamide plays an important role on the reaction with LPB1–3, retrieving the starting materials even under
pathway.20 However, to the best of our knowledge, well- drastic reaction conditions (150 C). Similar results have been
ꢀ
characterized transition metal complexes containing LPB described by Zucca et al.22
ligands showing a N-k1-coordinated mode still relatively scarce
On the other hand, the use of K2PtCl4 with one equivalent of
in the literature.7 Here in, we report our DFT calculations and LPB2 in DMSO, did not show any reactivity under temperatures
ꢀ
ꢀ
experimental results on the reactivity of Br-Pyridylbenz-(imida, below 100 C. When the temperature was increased to 150 C,
oxa or othia)-zole ligands toward platinum complexes.
the 1H NMR spectrum showed only signals assigned to the free
ligand. Nevertheless, the 195Pt NMR spectrum showed a new
signal at ꢁ3526 ppm, differing from K[PtCl3(DMSO)] or
[PtCl2(DMSO)2] signals which appeared at ꢁ2959 and
ꢁ3450 ppm, respectively.23
Results and discussion
Our rst attempts were addressed to obtain a dialkyl–platinum
complexes, through a stochiometric reaction of [Pt(COD)(Me)2]
with LPB1–3, using CH2Cl2 as solvent at room temperature.
However, under these conditions the reaction do not give the
Later, a stochiometric reaction of [PtCl2(COD)] with LPB2, in
THT solution at 150 ꢀC during a week, gave a yellow solid in
a yellow solution. 195Pt NMR spectrum showed a signal at
ꢁ3360 ppm, suggesting the formation of an analogous specie.
Similar results were obtained when [PtCl2(COD)] complex was
used as platinum source in solution of THT at 150 ꢀC of
temperature. Given the mentioned scarce reactivity, we decided
to study the solvent effect of CH2Cl2, CHCl3, isopropyl alcohol or
2-ethoxyethanol at temperatures below to 100 ꢀC, using
[PtCl2(DMSO)2] as platinum source and one equivalent of LPB2
;
however, under these conditions the starting materials were
recovered in quantitative amounts.
To our delight, when the reaction was carried out, in aceto-
nitrile at 100 ꢀC, it leads to a pale yellow solid (Scheme 1).
Temperature plays an important role, since a complex was not
produced when the mixture was at temperatures below to 60 ꢀC.
Also, the solvent effect is not trivial since formation of metallic
platinum was observed when isopropyl alcohol or 2-ethox-
yethanol were used instead of acetonitrile.
Scheme
1
Synthetic route of [trans-PtCl2(DMSO)(LPB1–3)], 1–3,
Chart 1
species.
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Unfortunately, all compounds show very low solubility in
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common organic solvents, the NMR experiments were carried out
in DMSO-d6. All experimental measurements were recorded
immediately, aer DMSO-d6 addition, in order to avoid ligand
exchange between Pt(II) complexes and DMSO-d6.24,25 Thus, under
1
our conditions, only complexes 2–3 were soluble enough. The H
NMR spectrum of 2 revealed a signal at 2.54 ppm with integrates to
6 protons, the signal was assigned to methyl protons, giving
a singlet corresponding to DMSO fragment. In the region of 7.47 to
8.36 ppm seven signals appeared, assigned to aromatic protons
corresponding to the LPB2 free fragment. 13C{1H} NMR spectrum
showed a characteristic signal for the methyl group in 40.4 ppm
assigned to the coordinate DMSO. In the aromatic region, four
signals appeared in 120.5, 122.9, 130.6 and 140.9 ppm assigned to
the carbons of phenyl fragment, and three signals in 111.5, 125.3
and 126.6 ppm assigned to the pyridyl fragment, according to 2D
NMR experiments. Finally, the 195Pt NMR gave an intense signal at
ꢁ3455 ppm, without any other signicative signals, assuming the
formation of only one platinum complex. The 1H NMR spectrum of
complex 3 shows a singlet at 2.54 ppm, which is assigned to the
methyl groups in the DMSO fragment. In the aromatic region
between 7.53 to 8.35 ppm, seven well dened signals are observed
and allocated into two sets: (i) three signals corresponding to the
Fig. 1 The molecular structure of complex 2 (the thermal ellipsoids
are drawn at 60% probability). Selected bond lengths [A˚] and angles (ꢀ);
Cl(1)–Pt(1) 2.2990(12); Cl(2)–Pt(1) 2.3022(12); N(1)–Pt(1) 2.051(3);
Pt(1)–S(1) 2.2108(11); N(1)–Pt(1)–S(1) 179.52(10); N(1)–Pt(1)–Cl(1)
87.00(10); S(1)–Pt(1)–Cl(1) 93.47(4); N(1)–Pt(1)–Cl(2) 89.68(10); S(1)–
Pt(1)–Cl(2) 89.84(4); Cl(1)–Pt(1)–Cl(2) 174.85(5).
pyridine fragment (7.85, 7.99 and 8.35 ppm) and four signals for derivatives were the coordination to metal center occurs via
benzothiazole fragment (7.53, 7.59, 8.12 and 8.19 ppm). 13C{1H} pyridine ring. To the best of our knowledge, our results
NMR spectrum shows a signal at d 40.4 ppm for methyl group of demonstrated the inuence of Br atom avoiding pyridin's
DMSO. Additionally, the signals at 119.8, 130.3 and 141.1 ppm are nitrogen coordination to Pt metal center.
assigned to C–H for pyridine fragment and the signals at 122.7,
The redox properties of all compounds were studied by cyclic
123.5, 126.3 and 126.9 are assigned to C–H in benzothiazole frag- voltammetry with a golden electrode in anhydrous DMF solution
ment, according to the 2D NMR H–13C. In good agreement with of 0.1 mol Lꢁ1 NBu4BF4 as the supporting electrolyte (Fig. 2).
1
the latter, the 195Pt NMR spectrum shows one signal at ꢁ3455 ppm.
Two reduction steps occur in all the analyzed free ligands
UV-Vis spectra of the LPB1–3 ligands showed a maximum and for complexes 2 and 3 (Fig. 2, peaks i and ii). First, the wave
absorption peak between 313–321 nm (Fig. S1†), which could be (i) is assigned to the irreversible reductive cleavage of the C–Br
1
assigned to p / p* absorption (spin allowed S0 / IL transi- bond in the halopyridine moiety (see Table S2† for potential
tion).26 A hypochromic effect was observed in all UV-Vis spectra values).30 The wave (ii) is associated to wave (iii), and this couple
of 1–3, attributed to the Pt coordination towards the LPB1–3 is assigned to one-electron reversible redox transition response.
ligands, respectively. Additional experimental evidence onto Pt- This reduction/oxidation process is attributed to the N]C bond
complexes synthesis was conrmed via melting point (decom- of the benz(imida, oxa or othia)zole rings, giving rise to stable
position to black solid), IR and Raman spectroscopies. Thus, radical anions in which nitrogen has the negative charge and
the ligand bands of the complexes are slightly shied with the resulting carbon radical is stabilized by the adjacent
respect to free ligands. The main IR and Raman bands of heteroatom and the pyridine ring.31
complexes 1–3 are listed in ESI (see Table S1†). Identication of
An additional cathodic peak was observed at ꢁ2.4 V only
the n(Pt–N), n(Pt–Cl) and n(Pt–S) at ca. 319, 330 and 283 cmꢁ1 when the free LPB3 ligand was analyzed (Fig. 2d). This irrevers-
bands were compared among them and in relation to the ible reduction is expected to occur on the pyridine ring.32
[PtCl2(DMSO)2] complex.27–29
However, we were unable to observe this wave for other ligands
Additionally, suitable crystals of complex 2 were grown from at the encompassed potentials in the electroactive window. It
slow evaporation of acetonitrile solution. Fig. 1 shows the could be attributed to the strongest donating character of the
molecular structure of compound 2. The Pt(II) ion in [trans- benzothiazole, favoring the pyridine reduction with respect to
PtCl2(L2)(DMSO)] exhibited distorted square plane geometry the analogous benzoxazole or benzimidazole compounds,
around Pt center where the ligand LPB2 was coordinated to the which include most electronegative heteroatoms. This shi
metal through a N atom in benzoxazole unit and the N atom of towards more negative potentials was also observed by Kap-
Br-pyridine remained free. The chlorine atoms adopted trans turkiewicz et al.26 for unsubstituted 2-(2-pyridyl)benzazole
conguration, and the remaining position was occupied by the ligands. In the case of complex 3, the mentioned peak at ꢁ2.4 V
sulfur atom of the DMSO molecule coordinated to the metal disappears due to the coordination of the N at the pyridine with
center. Westcott et al.7 have reported the synthesis and char- the metal center of Pt(II) (Fig. 2d). The peak (v), present in the
acterization of cis-dichloroplatinum complexes containing cyclic voltammograms of all the free ligands at potentials
mono coordinated piridynbenzimidazole, oxazole and thiazole between 887 and 916 mV is attributed to the irreversible
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Fig. 2 Cyclic voltammograms of (a) PtCl2(DMSO)2; (b) LPB1 free ligand and complex 1; (c) LPB2 free ligand and complex 2; (d) LPB3 free ligand and
complex 3. Scan rate 300 mV sꢁ1 cathodic direction.
oxidation of the nitrogen atom at the azole ring, which also coordinate moieties were reduced to well-known tetracoordi-
coordinates with the platinum center, and in consequence it nate complexes (Fig. 3a and b), we obtained that those of mode
was not noticed when the complexes were analyzed. Further- A were more stable than those of mode B for about 4 to
more, the wave (vi), observed when LPB2 and LPB3 ligands were 9 kcal molꢁ1 (see ESI†).
analyzed, can be attributed to the irreversible oxidation of O and
We conducted NBO calculations at the same level of theory,
S, respectively (Fig. 2c and d). Such wave was not detected for for complexes containing LPB2 ligand, aiming to understand
LPB1 due to the presence of the phenyl substituents attached to this preference for coordination. We found that the N / Pt
the N. It should be noted that 1 shows very limited solubility in donation and back-donation are stronger for mode A stabilizing
DMF. The absence of any peaks in voltammogram for complex 1 by 9.63 and 6.21 kcal molꢁ1, respectively, than for mode B
(Fig. 2b) is due to the immediate settling to the bottom of the according to our analysis (See ESI†). Although there is an
cell when dispersed in solvent. Peak (vii) is only detected in the increase in the Br / Pt donation in mode B stabilizing by
cyclic voltammograms of [PtCl2(DMSO)2], due an irreversible 10.54 kcal molꢁ1 than for mode A, there is an increasing steric
Pt(II)/Pt(IV) oxidation. These experiments show that the coordi- hindrance between Br and Cl vicinal atoms which deforms the
nation between the 2 or 3 and the platinum center does not have square planar geometry of the metal centre. Furthermore, we
any effects on the oxidation state of the metal, remaining as calculated the reaction energies for the exchange of the N,N-
Pt(II). Finally, the peak (viii) is also observed only when the donor ligand and solvent molecules in [PtCl2(DMSO)2] as shown
[PtCl2(DMSO)2] and its complexes where analyzed and it is
assigned to the irreversible two-electron oxidation of the chlo-
ride anions.
Finally, we have performed theoretical calculations using the
M06-L density-functional in combination with triple-z quality
basis sets for carrying out geometry optimizations (see ESI† for
further details). We have expressed energy values at the
(SMD:DMSO)M06-L/def2-tzvpp level for discussing our results
herein. Initially, we investigated the coordination mode for
complexes [trans-PtCl2(DMSO)(LBP1–3)] (1–3). Since penta-
Fig. 3 Platinum complexes having ligand LBP1–3 in a mono-coordi-
nation mode k1-N.
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Table 1 Calculated reaction energies (kcal molꢁ1) of the following
molecule is favorable, under our experimental conditions, and
the second N-coordination releasing the second DMSO is highly
impeded. Finally, we demonstrated that effect of solvent,
temperature, the bromine atom at the auxiliary ligands and
platinum complexes source kind, plays an important role in the
formation on this unusual mononuclear species.
reaction channels at the M06-L/mix-basis levela
Experimental
General considerations
Manipulations of air and moisture compounds were performed
under nitrogen atmosphere using standard Schlenk techniques.
˚
Acetonitrile was dried over 3 A molecular sieves before use.
K2PtCl4 was purchased from Pressure Chemical Co (USA). All
materials were used as received from commercial suppliers
19
26
33–35
without further purication. Compounds LPB1
,
L
PB2
, LPB3,
and [Pt(Cl)2(DMSO)2]36 were prepared according to the literature.
NMR spectra were recorded on a Bruker Ultra Shield 500 and
Bruker AV-400 MHz spectrometer at room temperature. H and
X¼
NC6H5
O
S
NH
1
DHR1
DGR1
DHR2
DGR2
ꢁ6.2
ꢁ4.0
17.6
5.6
ꢁ2.0
ꢁ0.4
18.4
6.7
ꢁ1.9
0.4
16.6
4.9
ꢁ5.7
ꢁ3.5
16.1
4.2
13C{1H} chemical shi (d) are given in part per million (ppm)
relative to tetramethylsilane (TMS) and the solvent resonance
were used as internal standards and 195Pt relative to K2PtCl4
(Solution in D2O). Elemental analysis experiments were carried
out on 2400 CHNS/O Series II System PerkinElmer. IR spectra
were recorded on a PerkinElmer Spectrum 100 FT-IR infrared
spectrometer using KBr pellets. Raman spectra were recorded on
a Renishaw InVia microscope Raman spectrometer. Raman
measurements were acquired with an excitation line provided by
a diode laser at 457 nm, by means of a 20ꢂ microscope's objec-
tive with a 0.4 numerical aperture; 2 s of integration time, and 20
accumulations were selected. UV-Vis absorption spectrum was
collected using a spectrophotometer Perking Elmer, lambda 900,
Waltham, MA, USA. Cyclic voltammetry studies were conducted
a
DH and DG are in kcal molꢁ1
.
in Table 1. The rst N-coordination exchanging one DMSO
molecule is favourable because of the negative values indicating
exothermicity (and exergonicity) where the second N-
coordination releasing the second DMSO is highly impeded.
This is in line with our experimental evidence. The effect of
substituents X ¼ NPh, O or S; is also signicant: heteroatoms
with a more activating effect on the benz(imida, oxa or othia)
zole ring make more available the lone-pair of the nitrogen that
donates to the platinum.
at room temperature in
a BASi Epsilon-EC potentiostat/
galvanostat with included soware system. A gold working elec-
trode (2 mm), a platinum wire auxiliary electrode, and Ag/AgCl
reference electrode were used in a standard three-electrode
conguration. The measurements were carried out in 5 mL of
DMF solutions of the compound (3.0 ꢂ 10ꢁ3 mol Lꢁ1) containing
0.05 mol Lꢁ1 tetrabuthylammonium tetrauoroborate (NBu4BF4)
as the supporting electrolyte. X-ray crystallographic studies were
collected at Oxford Diffraction Gemini “A” diffractometer.
Moreover, according to our calculations, the use of a more
labile ligand like cyclooctene in order to promote its exchange
with the second N-coordination (see eqn (S1)†) will not favour
the reaction (DHR ¼ 18.0 kcal molꢁ1; DGR ¼ 6.0 kcal molꢁ1). We
also corroborate that reported reactions using [PtCl4]2ꢁ for
obtaining the desired bidentate complexes (see eqn (S2)†)
avoiding DMSO as solvent give exothermic (exergonic) reactions
(DHR ¼ ꢁ14.8 kcal molꢁ1; DGR ¼ ꢁ17.4 kcal molꢁ1).
Synthesis of ligands
Conclusions
2-(6-Bromopyridin-2-yl)-1-phenyl-1H-benzimidazole (LPB1).
In summary, we have demonstrated that reactivity of potential N-Phenyl-o-phenylenediamine (533 mg, 3 mmol) and 6-bromo-
bidentate 2-(6-Br-2-pyridyl)-benz-(imida, oxa or othia)-zole pyridincarboxaldehyde (558 mg, 3 mmol) were dissolved in
ligands (LPB1–3) with an equivalent of [PtCl2(DMSO)2] complex, 20 mL of ethanol. Then, the reaction mixture was stirred at
in acetonitrile at 100 ꢀC, yields the complexes with general room temperature in an open ask and monitored by TLC. On
formula [trans-PtCl2(LPB1–3)(DMSO)], 1–3, respectively. LPB1–3 the completion of the reaction, solvent was removed, and the
fragment ligands are bonded to the platinum center under an crude product reaction was dissolved in DMF (10 mL) and NaCN
unusual N-k1-coordination mode. Furthermore, cyclic voltam- (147 mg, 3 mmol) was added. Then, the reaction was stirred at
metry studies show an irreversible two-electron process at ꢁ0.50 room temperature in an open ask and monitored by TLC. On
and ꢁ0.51 V, which was ascribed to the Pt(II)/Pt(IV) couple, for the completion on the reaction, the mixture was quenched with
complexes 2 and 3. According to performance theoretical water and extracted with diethyl ether. The organic phase was
calculation the rst N-coordination exchanging one DMSO collected, dried over MgSO4, and concentrated. The product was
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puried by ash column chromatography on silica gel with 1582, 1557, 1500, 1456, 1445, 1407, 1389, 1333 (C–N), 1265,
hexanes/ethyl acetate as (6 : 1) eluent, yielding a brown powder 1208, 1167, 1152, 1122 (S]O) cmꢁ1
.
1
(753 mg, 2.15 mmol). Yield 80%. Mp ¼ 112–114 ꢀC. H NMR
[trans-Pt(Cl)2(L2)(DMSO)] (2). The synthesis was following
(CDCl3, 500 MHz): d ¼ 8.16 (d, 1H, J ¼ 7.7 Hz), 7.90 (d, 1H, J ¼ the general procedure, ligand LPB2 (500 mg, 1.8 mmol) was
8.0 Hz), 7.58 (t, 1H, J ¼ 7.8 Hz), 7.55–7.46 (m, 4H), 7.41–7.26 (m, reacted with [Pt(Cl)2(DMSO)2] (767 mg, 1.8 mmol), to afford
7H), 7.21 (d, 1H, J ¼ 8.0 Hz) ppm. 13C{1H} NMR (CDCl3, 126 a brown solid (1070 mg, 1.7 mmol). Yield 95%. C14H13BrCl2-
MHz): d ¼ 149.96, 148.77, 142.69, 140.76, 138.76, 138.06, 137.58, N2O2PtS (619.22 molꢁ1): calcd. C 27.16; H 2.12; N 4.52; found C
1
129.31, 128.50, 128.18, 127.71, 124.42, 123.45, 123.02, 120.38, 27.45; H 1.98, N 4.49. Mp ¼ 196–198 ꢀC. H NMR (500 MHz,
111.21 ppm. IR (KBr) ~n ¼ 3042, 1595, 1577, 1557, 1501, 1435, DMSO-d6) d ¼ 8.36 (dd, J ¼ 7.6, 0.8, 1H), 8.02 (t, J ¼ 7.8, 1H),
1389, 1328, 1267, 1200, 1151, 1117, 1072, 988, 846, 797, 760, 7.93–7.86 (m, 3H), 7.52 (td, J ¼ 7.6, 1.2, 1H), 7.47 (td, J ¼ 7.6, 1.2,
738, 699, 656, 624, 573 cmꢁ1
.
1H), 2.54 (s, 6H) ppm. 13C{1H} NMR (126 MHz, DMSO-d6) d ¼
2-(6-Bromopyridin-2-yl)benzoxazole (LPB2). The synthesis 159.81, 150.49, 145.93, 141.65, 141.07, 140.95, 130.62, 126.68,
was similar to that described for L1, and the starting materials 125.36, 122.96, 120.52, 111.52, 40.43 ppm. 195Pt NMR (107 MHz,
were 2-aminophenol (327 mg,
3
mmol) and 6-bromo-2- DMSO-d6) d ¼ ꢁ3455 ppm. IR (~n) ¼ (3037, 3009, C–H) 2991,
pyridinecarboxaldehyde (558 mg, 3 mmol), and NaCl (147 mg, 2926, 2917, 1534, 1401, 1354, 1305 (S–C), 1299 (C–N), 1156,
3 mmol), to afford a white solid (310 mg, 1.1 mmol). Yield 43%. 1133, 1020 (S]O) cmꢁ1
.
1H NMR (CDCl3, 500 MHz): d ¼ 8.26 (dd, 1H, J ¼ 7.6, 1.0 Hz),
[trans-Pt(Cl)2(L3)(DMSO)] (3). The synthesis was following
7.83–7.77 (m, 1H), 7.70 (t, 1H, J ¼ 7.8 Hz), 7.63 (dd, 1H, J ¼ 7.2, the general procedure, ligand LPB2 (500 mg, 1.7 mmol) was
1.9 Hz), 7.60 (dd, 1H, J ¼ 7.9, 0.9 Hz), 7.37 (pd, 2H, J ¼ 7.4, 1.5 reacted with [Pt(Cl)2(DMSO)2] (725 mg, 1.7 mmol), to afford
Hz) ppm. 13C{1H} NMR (CDCl3, 126 MHz): d ¼ 160.05, 151.14, a brown solid (1050 mg, 1.6 mmol). Yield 96%. Mp ¼ 204–
146.82, 142.63, 141.69, 139.27, 130.24, 126.46, 125.16, 122.31, 206 C. C14H13BrCl2N2OPtS2 (635.28 molꢁ1): calcd. C 26.47; H
ꢀ
120.85, 111.48 ppm. IR (KBr) ~n ¼ 3049, 1576, 1549, 1509, 1421, 2.06; N 4.41; found C 26.71; H 1.91, N 4.39.1H NMR (500 MHz,
1315, 1249, 1154, 1120, 996, 988, 864, 794, 757, 643, 531 cmꢁ1
.
DMSO-d6) d ¼ 8.35 (dd, J ¼ 7.6, 0.8, 1H), 8.19 (dd, J ¼ 7.9, 1.5,
1H), 8.12 (d, J ¼ 7.7, 1H), 7.99 (t, J ¼ 7.8, 1H), 7.85 (dd, J ¼ 7.9,
Mp ¼ 182–184 ꢀC.
2-(6-Bromopyridin-2-yl)benzothiazole
(LPB3).
and
2-Amino- 0.8, 1H), 7.59 (ddd, J ¼ 8.3, 7.2, 1.3, 1H), 7.53 (ddd, J ¼ 8.3, 7.1,
thiophenol
(321
mg,
3
mmol)
6-bromo-2- 1.2, 1H), 2.54 (s, 6H) ppm. 13C{1H} NMR (126 MHz, DMSO-d6)
pyridinecarboxaldehyde (558 mg, 3 mmol) were dissolved in d ¼ 166.82, 153.61, 151.47, 141.10, 135.46, 130.34, 126.91,
20 mL of ethanol, the reaction mixture was stirred over night at 126.37, 123.52, 122.74, 119.82, 40.43 ppm. 195Pt NMR (107 MHz,
room temperature, the product precipitates from ethanol DMSO-d6) d ¼ ꢁ3455 ppm. IR (~n) ¼ (3037, 3009, C–H), 2992,
without any further purication, to afford a pale yellow solid 2926, 2917, 1401, 1384, 1305 (S–C), 1299 (C–N), 1156, 1133, 1020
(856 mg, 295 mmol). Yield 98%. Mp ¼ 192–194 ꢀC. 1H NMR (S]O) cmꢁ1
(CDCl3, 500 MHz): d ¼ 8.32 (dd, 1H, J ¼ 7.8, 0.9 Hz), 8.09 (d, 1H,
J ¼ 8.1 Hz), 7.99–7.91 (m, 1H), 7.70 (t, 1H, J ¼ 7.7 Hz), 7.56 (d,
1H, J ¼ 7.9 Hz), 7.56–7.48 (m, 1H), 7.44 (t, 1H, J ¼ 7.6 Hz) ppm.
.
13C{1H} NMR (CDCl3, 126 MHz): d ¼ 167.59, 154.29, 152.54,
X-ray crystallography
141.86, 139.33, 136.48, 129.75, 126.60, 126.10, 123.88, 122.22, X-ray powder diffraction experiments were acquired in Diffrac-
119.59 ppm. IR (KBr) ~n ¼ 3092, 3062, 3045, 1578, 1541, 1475, tometer Model D2 PHASER-Bruker. Single crystal of complex
1452, 1427, 1408, 1349, 1281, 1247, 1238, 1159, 1131, 1111, was mounted on a glass ber and analyzed with an Oxford
1085, 1075, 1005, 983, 929, 891, 818, 759, 738, 649, 623 cmꢁ1
.
Diffraction Gemini “A” diffractometer with a CCD area detector,
˚
a sealed tube X-ray source (lMoKa ¼ 0.71073 A), and a graphite
monochromator. The double pass method of scanning was
used to exclude any noise. The collected frames were integrated
with the CrysAlis Pro and CryAlis RED soware package (Agilent
General procedure for the synthesis of [trans-Pt(Cl)2(Ln)(DMSO)]
In a sealed tube was charged with LPBn (0.120 mmol), [Pt(Cl)2(- Technologies); analysis of the integrated data did not reveal any
DMSO)2] (0.120 mmol) and acetonitrile (15 mL). The reaction decay. Final cell parameters were determined by a global
mixture was heated at 100 ꢀC for 24 h and cooled down slowly to renement of reections; data were corrected for absorbance by
room temperature. Thus, a solid precipitate was observed. The analytical numeric absorption correction,37 employing a multi-
solid was ltered and washed with Et2O giving the platinum faceted crystal model based on expression upon the Laue
complexes in good yield. All complexes were obtained in gram symmetry using equivalent reection. Structure solution and
scale with good yields (up to 70%) and were characterized by renement were carried out with SHELXS-2014 and SHELXL-
FTIR, Raman, NMR, UV-Vis spectroscopies and melting point.
2014;38,39 Mercury CSD 39 and the WinGX suite were used for
[trans-Pt(Cl)2(L1)(DMSO)] (1). The synthesis was following molecular graphics and presentation of single-crystal diffrac-
the general procedure, ligand LPB1 (500 mg, 1.4 mmol) was tion data.40,41 Full-matrix least-squares renement was carried
2
2 2
reacted with [PtCl2(DMSO)2] (603 mg, 1.4 mmol) giving a pale- out by minimizing (Fo ¼ Fc ) . All non-hydrogen atoms were
yellow solid (649 mg, 1 mmol). Yield 70%. C20H18BrCl2N3OPtS rened anisotropically. Crystallographic data have been
(694.33 molꢁ1): calcd. C 34.60; H 2.61; N 6.05; found C 34.66; H deposited at the Cambridge Crystallographic Data Center as
2.57, N 5.93. Mp ¼ 206–208 ꢀC. IR (~n) ¼ (3091, 3064, C–H) 1595, ESI† number CCDC 1849220.
14038 | RSC Adv., 2019, 9, 14033–14039
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Paper
RSC Advances
C. E. Housecro, E. C. Constable and H. J. Bolink, J. Am.
Chem. Soc., 2017, 139, 3237–3248.
Conflicts of interest
17 M. R. DeStefano and D. K. Geiger, Acta Crystallogr., Sect. C:
Struct. Chem., 2016, 72, 491–497.
There are no conicts to declare.
18 M. R. DeStefano and D. K. Geiger, Acta Crystallogr., Sect. C:
Struct. Chem., 2017, 73, 697–702.
Acknowledgements
19 J. Nicasio-Collazo, E. Alvarez, J. C. Alvarado-Monzon,
G. Andreu-de-Riquer, J. O. Jimenez-Halla, L. M. De Leon-
Rodriguez, G. Merino, U. Morales, O. Serrano and
J. A. Lopez, Dalton Trans., 2011, 40, 12450–12453.
Authors thank to the Laboratorio Nacional UG-CONACYT,
´
Martın Olmos and Christian Albor for their technical assis-
tance. J. N.-C. thanks the Postdoctoral fellowship from Uni-
´
versidad de Guanajuato (UG-DAIP-Excelencia Academica 2015).
´
´
´
´
20 M. E. Tovar-Ramırez, R. Ramırez-Zuniga, J. Nicasio-Collazo,
O. S. is gratefully to UG for nancial support this research
´
K. Wrobel, J. G. Alvarado-Rodrıguez, K. Wrobel and
´
(DAIP-Excelencia Academica 2015, grant 002/2015, and DAIP-
O. Serrano, ChemistrySelect, 2018, 3, 4133–4139.
21 L. Rigamonti, C. Manassero, M. Rusconi, M. Manassero and
A. Pasini, Dalton Trans., 2009, 0, 1206–1213.
22 L. Maidich, G. Dettori, S. Stoccoro, M. A. Cinellu, J. P. Rourke
and A. Zucca, Organometallics, 2015, 34, 817–828.
23 L. G. Marzilli, Y. Hayden and M. D. Reily, Inorg. Chem., 1986,
25, 974–978.
´
2018). J. L. M. thanks Ce-MIE-Sol 207450/27 (Mexico) and
CONACyT-SENER B-S-69369 (Bilateral grant Mexico-England),
´
Fondo Sectorial CONACYT-SENER-Sustentabilidad energetica.
Notes and references
1 W. Akhtar, M. F. Khan, G. Verma, M. Shaquiquzzaman,
M. A. Rizvi, S. H. Mehdi, M. Akhter and M. M. Alam, Eur. J.
Med. Chem., 2017, 126, 705–753.
2 B. Pashaei, H. Shahroosvand, M. Graetzel and
M. K. Nazeeruddin, Chem. Rev., 2016, 116, 9485–9564.
3 J. S. Pap, A. Draksharapu, M. Giorgi, W. R. Browne, J. Kaizer
and G. Speier, Chem. Commun., 2014, 50, 1326–1329.
4 A. O. Ogweno, S. O. Ojwach and M. P. Akerman, Appl. Catal.,
A, 2014, 486, 250–258.
5 M. Zhang, R. Gao, X. Hao and W.-H. Sun, J. Organomet.
Chem., 2008, 693, 3867–3877.
6 S. O. Ojwach, A. O. Ogweno and M. P. Akerman, Catal. Sci.
Technol., 2016, 6, 5069–5078.
24 D. S. Martin, Inorg. Chim. Acta, Rev., 1967, 1, 87–97.
25 R. J. Mureinik, Coord. Chem. Rev., 1978, 25, 1–30.
26 R. Czerwieniec, A. Kapturkiewicz, J. Lipkowski and
J. Nowacki, Inorg. Chim. Acta, 2005, 358, 2701–2710.
27 E. D. Risberg, J. Mink, A. Abbasi, M. Y. Skripkin, L. Hajba,
´
¨
P. Lindqvist-Reis, E. Bencze and M. Sandstrom, Dalton
Trans., 2009, 0, 1328–1338.
28 I. A. Emenko, A. P. Kurbakova, Z. D. Matovic and
G. Ponticelli, Transition Met. Chem., 1994, 19, 640–642.
29 B. Morzyk-Ociepa, K. Szmigiel, I. Turowska-Tyrk, M. Malik-
Gajewska, J. Banach and J. Wietrzyk, Polyhedron, 2018, 153,
88–98.
30 M. S. Mubarak and D. G. Peters, J. Electroanal. Chem., 1997,
425, 13–17.
31 E. K. Beloglazkina, I. V. Yudin, A. G. Majouga, A. A. Moiseeva,
A. I. Tursina and N. V. Zyk, Russ. Chem. Bull., 2006, 55, 1803–
1809.
7 X.-F. He, C. M. Vogels, A. Decken and S. A. Westcott,
Polyhedron, 2004, 23, 155–160.
¨
8 J.-H. Zhao, Y.-X. Hu, H.-Y. Lu, Y.-L. Lu and X. Li, Org.
Electron., 2017, 41, 56–72.
9 J. Hu, C. Zhao, T. Zhang, X. Zhang, X. Cao, Q. Wu, Y. Chen,
D. Zhang, Y. Tao and W. Huang, Adv. Opt. Mater., 2017, 5,
1700036.
10 W.-K. Huang, C.-M. Lan, Y.-S. Liu, P.-H. Lee, S.-M. Chang and
E. W.-G. Diau, J. Chin. Chem. Soc., 2010, 57, 1151–1156.
11 G. S. Yellol, J. G. Yellol, V. B. Kenche, X. M. Liu,
K. J. Barnham, A. Donaire, C. Janiak and J. Ruiz, Inorg.
Chem., 2015, 54, 470–475.
32 A. A. Isse, G. Berzi, L. Falciola, M. Rossi, P. R. Mussini and
A. Gennaro, J. Appl. Electrochem., 2009, 39, 2217–2225.
33 Y.-W. Wu, J.-T. Wang, C. Jiang, W.-X. Chai and L. Song, Asian
J. Chem., 2015, 27, 1529–1531.
34 H.-S. Jung and S.-H. Kim, Bull. Korean Chem. Soc., 2014, 35,
280–282.
35 S. Kottukulam Subran, S. Banerjee, A. Mondal and P. Paira,
New J. Chem., 2016, 40, 10333–10343.
12 M. Martinez-Alonso, J. Cerda, C. Momblona, A. Pertegas,
J. M. Junquera-Hernandez, A. Heras, A. M. Rodriguez,
G. Espino, H. Bolink and E. Orti, Inorg. Chem., 2017, 56,
10298–10310.
36 R. Romeo, L. M. Scolaro, V. Catalano and S. Achar, Inorg.
Synth., 2007, 32, 153–158.
37 R. C. Clark and J. S. Reid, Acta Crystallogr., Sect. A: Found.
Crystallogr., 1995, 51, 887–897.
13 N. M. Shavaleev, Z. R. Bell, T. L. Easun, R. Rutkaite,
L. Swanson and M. D. Ward, Dalton Trans., 2004, 0, 3678–
3688.
14 Q. D. Liu, W. L. Jia and S. Wang, Inorg. Chem., 2005, 44,
1332–1343.
38 G. M. Sheldrick, Acta Crystallogr., Sect. A: Found. Adv., 2015,
71, 3–8.
39 G. M. Sheldrick, Acta Crystallogr., Sect. C: Struct. Chem., 2015,
71, 3–8.
40 C. F. Macrae, P. R. Edgington, P. McCabe, E. Pidcock,
G. P. Shields, R. Taylor, M. Towler and J. van de Streek, J.
Appl. Crystallogr., 2006, 39, 453–457.
15 J. J. Lee, C. P. Yap, T. S. Chwee and W. Y. Fan, Dalton Trans.,
2017, 46, 11008–11012.
16 C. D. Ertl, C. Momblona, A. Pertegas, J. M. Junquera-
Hernandez, M. G. La-Placa, A. Prescimone, E. Orti,
41 L. J. Farrugia, J. Appl. Crystallogr., 1999, 32, 837–838.
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