Cyclometallated PTII complexes of 2-(2-thienyl)-4-(cycloalkylimino)-substituted quinazolines

Article abstract of DOI:10.1016/j.mencom.2016.03.015

The title complexes were prepared based on 2-(thiophen-2-yl)-4-(morpholin-4-yl)- and 2-(thiophen-2-yl)-4-(piperidin-1-yl)-substituted quinazolines and found to exhibit luminescent properties.

Full text of DOI:10.1016/j.mencom.2016.03.015

Mendeleev
Communications
Mendeleev Commun., 2016, 26, 129–130
ii
Cyclometallated Pt complexes of 2-(2-thienyl)-
4-(cycloalkylimino)-substituted quinazolines
a,b
a
a,b
Emiliya V. Nosova,* Tatyana N. Moshkina, Dmitry S. Kopchuk,
b
a,b
a,b
Galina N. Lipunova, Pavel A. Slepukhin and Valery N. Charushin
a
b
Department of Organic and Biomolecular Chemistry, Ural Federal University, 620002 Ekaterinburg,
Russian Federation
I. Ya. Postovsky Institute of Organic Synthesis, Ural Branch of the Russian Academy of Sciences,
6
20990 Ekaterinburg, Russian Federation. Fax: +7 343 374 1189; e-mail: emily74@rambler.ru
DOI: 10.1016/j.mencom.2016.03.015
X
N
The title complexes were prepared based on 2-(thiophen-
O
N
N
2
1
-yl)-4-(morpholin-4-yl)- and 2-(thiophen-2-yl)-4-(piperidin-
-yl)-substituted quinazolines and found to exhibit lumine-
NH
S
S
N
O
Pt
scent properties.
Me
O
X = O, CH2
Me
Nitrogen-containing six-membered heteroaromatic compounds,
pyridines, quinolines, quinazolines and their aza and benzo
analogues, are of interest as ligands to obtain organometallic
complexes, photo- and electroluminescent compounds and various
organic materials. Indeed, many p-deficient aza-aromatic systems
basedonazinesandbenzazines, includingpyridines, pyrimidines,
quinolines and quinoxalines, have already been used as key
components for the formation of electron transport layers in
electroluminescent materials.1
amination;10 however, an electron-donating thienyl substituent
at the 2-position of quinazoline deactivates the bicyclic system,
thus making it reluctant toward direct amination. Quinazolines
2a and 2b were synthesized by the conversion of 2-(thiophen-
2-yl)quinazolin-4-one 1 into a 4-chloro derivative followed by
substitution of the chlorine atom under the action of cyclo-
alkylimines (Scheme 1).
Ligands 2a and 2b were cyclometallated on reflux in acetic
acid containing potassium tetrachloroplatinate according to a
11
Cyclometallated platinum(ii) complexes of aza-aromatic com-
pounds have gained attention due to their high stability and
typical procedure, resulting in the formation of dimeric complexes
2
intense emission. Platinum(ii) complexes with pyridine deriva-
X
tives have been intensively studied since these organometallic
materials demonstrate high quantum yields and large Stokes
shifts. It is known that, in these complexes, a ligand not only
provides strong binding with a metal, but it is also supposed to
O
N
N
NH
i, ii
N
3
S
S
be a sensitizer, facilitating energy transfer to the metal center.
N
In particular, 2-(2-thienyl)pyridines (thpy) undergo cyclometal-
ii
1
2a X = O
b X = CH2
lation, and the thpy complexes of Pt proved to exhibit enhanced
2
4
lifetimes. Aryl substituents were incorporated at the 5-position
5
X
N
of the pyridine ring in order to expand the aromatic system,
and the same effect can be achieved by benzene ring annelation.
Note that the Pt complexes of benzazines provide a good basis to
develop electronic devices, which are capable of working in both
iii, iv, v
N
6
visible and near-IR spectral regions. The data on cyclometallated
S
platinum complexes based on ligands from the benzazine family
N
7
are scarcely available, while the cyclometallated platinum(ii)
complexes of quinazolines have never been reported.
O
Pt
Me
O
4
-Morpholino- and 4-piperidino-2-(thiophen-2-yl)-substi-
tuted quinazolines 2a and 2b, respectively, have not so far
been described, whereas a 6-methoxy analogue of 2a has been
mentioned. 2-(Thiophen-2-yl)-4-piperazinoquinazoline, which
Me
8
3a X = O
b X = CH2
3
is a close analogue of 2a and 2b, has been obtained previously
through nucleophilic substitution of the chlorine atom at the
Scheme 1 Reagents and conditions: i, POCl , reflux, 2 h, then NaHCO ,
3
3
4
-position of 2,4-dichloroquinazoline followed by a cross-coupling
H O; ii, morpholine or piperidine, MeCN, reflux, 10 h; iii, K PtCl , AcOH,
2
2
4
9
reaction with 2-thienylboronic acid. It has also been shown that
-morpholinoquinazoline can be obtained by oxidative alkyl-
reflux, 10 h; iv, DMSO, reflux, 5 min; v, sodium acetylacetonate, acetone,
reflux, 16 h.
4
©
2016 Mendeleev Communications. Published by ELSEVIER B.V.
–
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on behalf of the N. D. Zelinsky Institute of Organic Chemistry of the
Russian Academy of Sciences.

Mendeleev Commun., 2016, 26, 129–130
PtL(m-Cl)] . The latter were treated with DMSO to afford the Table 1 Spectroscopic data of ligands 2 and complexes 3 in acetonitrile.
2
[
intermediate monomeric complexes PtL(DMSO)Cl, which were
converted directly (without purification) into complexes 3a and
Compound
labs/nm
lem/nma
Stokes shift/nm
3
b on treatment with an excess of sodium acetylacetonate in
2a
2b
3a
3b
295, 335
502
508
584
579
167
173
204
202
acetone (Scheme 1).
296, 335
1
The structures of 2a,b and 3a,b were studied by H NMR
spectroscopy and mass spectrometry. The formation of com-
plexes 3a,b resulted in the disappearance of a one-proton signal
of the thiophene ring and caused downfield shifts for the H(8)
resonance signal of the quinazoline system. Moreover, the
characteristic resonances of the acetylacetonate CH proton at
314, 355, 380
314, 354, 377
a
Excitation at 335 nm for 2a,b and at 380 nm for 3a,b.
5
.57–5.58 ppm and the signals of two methyl groups were
1
Pt(1)
observed in the H NMR spectra. Molecular ion peaks in the
mass spectra of complexes 3a,b were recorded. An excellent
correlation between experimental and calculated picks in the
mass spectra of 3a,b has been found (see Figures S6 and S8,
Online Supplementary Materials).
3
.573 Å
Pt(1)
†
According to the XRD data, compound 3a is crystallized in the
centrosymmetric space group. The Pt ion has a typical distorted
squared coordination. Bond lengths in the Pt chelate indicate at a
strong conjugation in the 1,3-dicarbonyl system. As a result of
the CH···O contact between C(9) an O(1) atoms (Figure 1), the
benzene ring of the quinazoline system is turned toward the
Pt(1)O(1)O(2)N(1)C(12) plane at an angle of 21°. In crystals, two
molecules proved to form dimers on the twofold axes with the
interatomic distance Pt···Pt [1–x, y, 0.5–z] of 3.57 Å (Figure 2),
which suggests the presence of Pt–Pt interaction in the crystal state.
Figure 2 Dimer 3a formation in a crystal.
In conclusion, the cyclometallated platinum(ii) complexes
[Pt(L)(acac)] with quinazolines have been prepared, and the
spectroscopic data of quinazoline ligands 2 and their Pt com-
plexes 3 have been compared. Further studies for the synthesis of
new luminescent materials based on ligands 2 are in progress.
ii
Pt complexes 3 exhibit the long-wave shift of emission
This work was supported by the Russian Foundation for
Basic Research (grant no. 14-03-00340), the Ural Branch of
the Russian Academy of Sciences (project no. 15-21-3-7) and
the Council of the President of the Russian Federation (grant
no. NSh-3656.2014.3).
maximum compared to the starting ligands 2 (Table 1). Upon
photoexcitation at the lowest energy band, the complexes and
ligands were found to exhibit low-intensity luminescence with a
large Stokes shift. The maxima in photoluminescence spectra of
the complexes are red-shifted with respect to those observed for
the ligand precursors.
Online Supplementary Materials
Supplementary data associated with this article can be found
in the online version at doi:10.1016/j.mencom.2016.03.015.
C(8)
C(22)
C(7)
C(23)
C(9)
C(6)
O(1)
Pt(1)
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2
–3
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CCDC 1439844 contains the supplementary crystallographic data for
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Received: 7th September 2015; Com. 15/4725
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