Cyclometalated platinum complexes: High-yield synthesis, characterization, and a crystal structure

Article abstract of DOI:10.1016/j.jorganchem.2005.05.042

The one-pot reaction of K₂PtCl₄ and various 2-arylpyridines, H?N, in a 3:1 (v/v) mixture of 2-ethoxyethanol and H₂O at 80 °C for 16 h affords cyclometalated platinum complexes, Pt(?N)(H?N)(Cl), in high yield. These have been fully characterized and, in one case, the X-ray structure has been determined.

Full text of DOI:10.1016/j.jorganchem.2005.05.042

Journal of Organometallic Chemistry 690 (2005) 4090–4093
www.elsevier.com/locate/jorganchem
Note
Cyclometalated platinum complexes: High-yield
synthesis, characterization, and a crystal structure
a
c
c
Jian-Yang Cho , Kyrill Yu. Suponitsky b,c, Jennifer Li , Tatiana V. Timofeeva ,
a
Stephen Barlow , Seth R. Marder
a,
*
a
Center for Organic Photonics and Electronics and School of Chemistry and Biochemistry, Georgia Institute of Technology,
Atlanta, GA 30332-0400, USA
b
Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, Russia
c
Department of Natural Sciences, New Mexico Highlands University, Las Vegas, NM 87701, USA
Received 20 April 2005; received in revised form 25 May 2005; accepted 26 May 2005
Available online 11 July 2005
Abstract
The one-pot reaction of K2PtCl4 and various 2-arylpyridines, HCꢀN, in a 3:1 (v/v) mixture of 2-ethoxyethanol and H2O at 80 ꢁC
for 16 h affords cyclometalated platinum complexes, Pt(CꢀN)(HCꢀN)(Cl), in high yield. These have been fully characterized and, in
one case, the X-ray structure has been determined.
ꢂ 2005 Elsevier B.V. All rights reserved.
Keywords: Cyclometalated metal complexes; Platinum; Phosphorescent; 2-Aryl-pyridine; Crystal structure
1. Introduction
[Pt(CꢀN)(l-Cl]2 dimers, which were themselves obtained
from the reaction of K2PtCl4 and HCꢀN [3,6]. Here we
show that the products of K2PtCl4 and HCꢀN
{CꢀN = ppy, 2-(2,4-difluorophenyl)pyridine (4,6-dfppy),
2-benzo[b]thiophen-2-yl-pyridine (btp), and 1-phenyl-
isoquinoline (piq)} under the conditions of Ref. [3]
are, in fact, mononuclear species of the type
Pt(CꢀN)(HCꢀN)(Cl).
Cyclometalated complexes are important in catalysis
[1] and polymerization processes; iridium [2] and plati-
num [3,4] examples have attracted attention as phos-
phors for organic light-emitting diodes (OLEDs), and
platinum species have potential medicinal applications
due to their cytotoxic [5] and luminescence properties.
The synthesis [3] and use in OLEDs [4] of phosphores-
cent complexes with general structure Pt(CꢀN)(OꢀO),
where CꢀN is
a
cyclometalated ligand such as
2. Experimental
0
2-phenylpyridinato-N; C2 (ppy) and OꢀO is a b-diketo-
nate, were recently reported. The Pt(CꢀN)(OꢀO) species
of Ref. [3] were obtained from intermediate Pt com-
plexes reported, without characterizing data, to be
2.1. General
K2PtCl4 (Strem) and Hppy and 2-ethoxyethanol (Al-
drich) were used without further purification. H-4,6-
dfppy, Hbtp, and Hpiq were prepared via the Suzuki
coupling reactions of commercial available boronic
acids with 2-bromopyridine or 1-chloroisoquinoline.
*
Corresponding author. Tel.: +21 404 385 6048; fax: +21 404 894
5909.
E-mail address: seth.marder@chemistry.gatech.edu (S.R. Marder).
0022-328X/$ - see front matter ꢂ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2005.05.042

J.-Y. Cho et al. / Journal of Organometallic Chemistry 690 (2005) 4090–4093
4091
2.2. Pt(ppy)(Hppy)(Cl) (1)
7.15–8.14 (m, 12H), 6.98 (br s, 1H), 6.88 (br s, 1H),
6.11 (d, J = 6.6 Hz, 1H). HRMS-ESI (m/z): [M ꢁ Cl]+
calcd for C26H17N2S2Pt, 616.04755; found, 616.0526.
Anal. Calc. for C26H17ClN2PtS2: C, 47.89; H, 2.63; N,
4.30. Found: C, 48.03; H, 2.55; N, 4.16%.
K2PtCl4 (3.0 g, 7.2 mmol) and 2-phenylpyridine
(2.80 g, 18.1 mmol) in a 3:1 (v/v) mixture of 2-ethoxy-
ethanol (75 mL) and H2O (25 mL) were heated at
80 ꢁC for 16 h under nitrogen atmosphere. The reaction
mixture was allowed to cool down to room tempera-
ture and concentrated under reduced pressure. Et2O
was added to the resulting residue and a yellow solid
was formed. The solid was collected by vacuum filtra-
tion. The solid was dissolved in CH2Cl2 and washed
with H2O. The organic solvent was removed under re-
duced pressure. The residue was re-dissolved in mini-
mal amount of CH2Cl2 and MeOH (ꢀ50 times in
volume) was added. The mixture was stirred at room
temperature overnight. A yellow solid was collected
by vacuum filtration and washed with MeOH. The
product was dried under vacuum to give a bright yel-
low solid (3.04 g, 77.3%), data for which were consis-
tent with the literature [7–9].
2.5. Pt(piq)(Hpiq)(Cl) (4)
K2PtCl4 (1.67 g, 4.0 mmol) and 1-phenyl-isoquinoline
(2.06 g, 10.0 mmol) in a 3:1 (v/v) mixture of 2-ethoxyeth-
anol (51 mL) and H2O (17 mL) were heated at 80 ꢁC for
16 h under N2 atmosphere. The reaction was allowed to
cool down to room temperature and concentrated under
reduced pressure. The resulting orange brown precipi-
tate was collected by vacuum filtration and washed with
H2O and hexanes to give an orange–brown solid (2.20 g,
85.6%). The analytically pure product was recrystallized
from CH2Cl2. 1H NMR (300 MHz, CDCl3,): 9.53
(d, J = 6.3 Hz, 1H), 9.03 (d, J = 6.3 Hz, 1H), 8.72 (d,
J = 8.5 Hz, 1H), 8.15–8.19 (m, 1H), 7.97 (d,
J = 8.2 Hz, 1H), 7.91–7.94 (m, 1H), 7.66–7.85 (m, 5H),
7.54–7.62 (m, 2H), 7.43–7.51 (m, 2H), 7.31–7.38 (m,
2H), 7.19–7.25 (m, 1H), 7.03–7.09 (m, 1H), 6.87 (td,
J = 7.7, 1.4 Hz, 1H), 6.37 (dd, J = 7.7, 1.1 Hz, 1H).
HRMS-ESI (m/z): [M ꢁ Cl]+ calcd for C30H21N2Pt,
604.13471; found, 604.1371. Anal. Calc. for
C30H21ClN2Pt: C, 56.30; H, 3.31; N, 4.38. Found: C,
56.27; H, 3.33; N, 4.34%.
2.3. Pt(4,6-dfppy)(H-40,60-dfppy)(Cl) (2)
K2PtCl4 (2.0 g, 4.8 mmol) and 2-(2,4-difluorophe-
nyl)pyridine (2.54 g, 12.0 mmol) in a 3:1 (v/v) mixture
of 2-ethoxyethanol (54 mL) and H2O (18 mL) were
heated at 80 ꢁC for 16 h under N2 atmosphere. The
reaction mixture was allowed to cool down to room
temperature and concentrated under reduced pressure.
H2O was added and the resulting yellow precipitate
was collected by vacuum filtration and washed with
H2O and hexanes to give a yellow solid (2.57 g,
87%). 1H NMR (300 MHz, CDCl3, d): 9.60 (d,
J = 5.8 Hz, 1H), 9.19 (d, J = 5.2 Hz, 1H), 8.41 (dd,
J = 14.8, 8.5 Hz, 1H), 7.96 (t, J = 7.7 Hz, 1H), 7.89
(d, J = 8.2 Hz, 1H), 7.77 (t, J = 7.7 Hz, 1H), 7.65 (d,
J = 8.0 Hz, 1H), 7.44 (t, J = 6.0 Hz, 1H), 7.09 (t,
J = 6.0 Hz, 1H), 6.87 (m, 1H), 6.73 (m, 1H), 6.47
(m, 1H), 5.62 (d, J = 8.8 Hz, 1H). HRMS-FAB (m/z):
[M]+, calc. for C22H13ClN2PtF4, 610.03302; found,
610.03414. Anal. Calc. for C22H13ClN2PtF4: C,
43.18; H, 2.14; N, 4.58. Found: C, 43.20; H, 2.20;
N, 4.51%.
2.6. Pt(piq)(acac)
A mixture of 4 (1.0 g, 1.6 mmol), 2,4-pentanedione
(0.34 g, 3.4 mmol), and Na2CO3 (1.65 g, 15.6 mmol) in
20 mL of 2-ethoxyethanol was heated at 100 ꢁC over-
night under N2 atmosphere. The reaction was allowed
to cool down to room temperature and H2O was added.
The mixture was extracted with CH2Cl2. The organic
layer was washed with H2O and dried over anhydrous
MgSO4. The organic solvent was removed under re-
duced pressure. The crude product was purified by col-
umn chromatography (silica gel, dichloromethane as
eluting solvent) to give an orange brown solid (0.50 g,
64.2%). 1H NMR (300 MHz, CDCl3, d): 8.93 (d,
J = 6.6 Hz, 1H), 8.85 (d, J = 8.5 Hz, 1H), 8.07 (dd,
J = 8.0, 1.4 Hz, 1H), 7.59–7.82 (m, 4H), 7.40 (d,
J = 6.3 Hz, 1H), 7.23 (td, J = 7.1, 1.4 Hz, 1H), 7.15
(td, J = 7.1, 1.4 Hz, 1H), 5.47 (s, 1H), 2.010 (s, 3H),
2.005 (s, 3H). 13C{1H} NMR (75 MHz, CDCl3, d):
185.76, 184.00, 168.44, 146.09, 141.43, 139.10, 137.25,
131.01, 130.45, 129.25, 128.41, 128.09, 127.36, 126.10,
125.80, 123.14, 119.44, 102.49, 28.43, 27.26. HRMS-EI
(m/z): [M]+ calcd for C20H17NO2Pt, 498.09071; found,
498.09022. Anal. Calc. for C20H17NO2Pt: C, 48.19; H,
3.44; N, 2.81. Found: C, 48.13; H, 3.36; N, 2.71%.
Pt(ppy)(acac) (0.35 g, 84.3%) was obtained from 1 under
analogous conditions.
2.4. Pt(btp)(Hbtp)(Cl) (3)
K2PtCl4 (2.0 g, 4.8 mmol) and 2-benzo[b]thiophen-2-
yl-pyridine (2.3 g, 12.0 mmol) in a 3:1 (v/v) mixture of 2-
ethoxyethanol (54 mL) and H2O (18 mL) were heated at
80 ꢁC for 16 h under N2 atmosphere. The reaction was
allowed to cool down to room temperature and concen-
trated under reduced pressure. H2O was added and the
resulting brown precipitate was collected by vacuum fil-
tration, and washed with H2O, methanol, and hexanes
to give a brown solid (3.0 g, 95.4%). 1H NMR
(300 MHz, CDCl3,d): 9.56 (br s, 1H), 9.36 (br s, 1H),

4092
J.-Y. Cho et al. / Journal of Organometallic Chemistry 690 (2005) 4090–4093
2.7. Crystallography
as
a
minor side-product in
a
synthesis of
[Bu4N]+[Pt(ppy)Cl2]ꢁ [9].
We studied a red prism (0.15 · 0.10 · 0.10 mm) of 4
(C30H21N2ClPt, fw = 640.03) which was obtained by
recrystallization from CH2Cl2/MeOH using a SMART
Complexes 1–4 can be used as starting materials for
Pt(CꢀN)(OꢀO) species (as can the species claimed as
[Pt(CꢀN)(l-Cl)]2 in reference 3). Pt(ppy)(acac) is ob-
tained in 84% yield from 1 using a modification of the
conditions reported in reference 3, and the new com-
pound Pt(piq)(acac) is obtained in 64% yield from 4.
An X-ray structure of 4 (Fig. 2) provides further sup-
port for its formulation as Pt(CꢀN)(HCꢀN)(Cl). The
bond lengths and angles around the platinum atom are
similar to those in the structure of 1 [5a,9]; the Pt–Cl
bonds are significantly elongated as a consequence of
the trans effect of the C(1) atom. The chelating piq li-
˚
1000 CCD diffractometer (k(Mo Ka) = 0.71073 A,
graphite monochromator, x-scans) at 120 K. The crystal
ꢀ
was found to belong to the triclinic space group P1, with
˚
˚
a = 10.1817(17) A, b = 10.2249(17) A, c = 12.054(2) A,
˚
a = 89.539(3)ꢁ, b = 71.474(3)ꢁ, c = 72.195(3)ꢁ, V =
3
1127.4(3) A , Z = 2, qcalc = 1.885 g cmꢁ3, F(000) = 620,
˚
and l = 6.365 mmꢁ1. Data (10,992 reflections, 5317 inde-
pendent reflections, Rint = 0.0286) were collected in the h
range 1.79–28.00ꢁ (ꢁ13 6 h 6 13,ꢁ13 6 k 6 13,ꢁ15 6
l 6 15). Refinement (307 parameters) converged to give
GOF(F2) = 0.995, R1(F) = 0.0310 (for 4560 data with
I > 2r(I)), and wR2(F2) = 0.0724 (all data), with residual
electron density maxima and minima of 1.519 and
˚
gand in 4 is less planar (mean deviation 0.189 A) than
the ppy ligand of 1, presumably due to steric repulsion
between the closest hydrogen atoms (attached to C(5)
and C(9)). The shortest intermolecular contacts are
ꢁ1.016 e Aꢁ3, respectively. SAINT Plus [10], SADABS
˚
[11], and SHELXTL-97 [12] software packages were used.
3. Results and discussion
The reaction of K2PtCl4 with Hppy, H-4,6-dfppy,
Hbtp, and Hpiq in 1:2.5 mole ratio in 3:1 (v/v) 2-ethoxy-
ethanol/H2O at 80 ꢁC for 16 h gives products 1–4,
respectively (Fig. 1) in high yield. NMR data, high-res-
olution mass spectrometry, elemental analysis, and the
crystal structure determination of 4 indicate that these
species have the general formula Pt(CꢀN)(HCꢀN)(Cl).
2–4 are new compounds (although the products of the
reaction of H-4,6-dfppy and Hbtp with K2PtCl4 under
conditions identical to ours have previously been re-
ported, without characterizing data, to be [Pt(CꢀN)(l-
Cl)]2 dimers [3], as has the product of Hppy and
K2PtCl4). 1 has previously been characterized as a sig-
nificant side-product of the reaction of 1:1 K2PtCl4
and Hppy (1:1 dioxane/water; 72 h at room temperature;
72 h at reflux) to give [Pt(ppy)(l-Cl)]2 [7]; it has also
been obtained in 59% yield from the reaction of
Pt(COD)Cl2 with excess Hppy in the presence of
NaOAc in 95% ethanol [8], in 40% yield from the reac-
tion of [Et4N]+[Pt(NH3)Cl3]ꢁ and Hppy in water [5], and
˚
Fig. 2. ORTEP view (50%) of 4. Selected parameters (A,ꢁ): Pt(1)–C(1)
2.001(4), Pt(1)–N(1) 2.025(4), Pt(1)–N(2) 2.026(4), Pt(1)–Cl(1)
2.4084(12), C(1)–Pt(1)–N(2) 95.94(15), N(1)–Pt(1)–N(2) 177.01(14),
C(1)–Pt(1)–Cl(1) 175.23(12), N(1)–Pt(1)–Cl(1) 96.91(11), N(2)–Pt(1)–
Cl(1) 86.00(10).
Fig. 1. Structures of complexes 1–4.

J.-Y. Cho et al. / Journal of Organometallic Chemistry 690 (2005) 4090–4093
4093
Fig. 3. Comparison of UV–vis. absorption and luminescence spectra for 1–4 in CH2Cl2.
˚
3.301(6) A (C(12)–C(15)) and 3.192(6) A (C(4)–C(15)).
There are also weak intermolecular C–H. . .p interac-
˚
tions (2.47 A between H(28a) and the centroid of the
C(1)–C(6) ring).
We have also recorded UV–vis. absorption and lumi-
nescence spectra for 1–4; these are compared in Fig. 3.
˚
(d) C. Shu, A. Leitner, J.F. Hartwig, Angew. Chem. Int., Ed.
Engl. 43 (2004) 4797.
[2] (a) S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq,
H.E. Lee, C. Adachi, P.E. Burrows, S.R. Forrest, M.E. Thomp-
son, J. Am. Chem. Soc. 123 (2001) 4304;
(b) A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide, J.
Kamatani, S. Igawa, T. Moriyama, S. Miura, T. Takiguchi, S.
Okada, M. Hoshino, K. Ueno, J. Am. Chem. Soc. 125 (2003)
12971.
[3] J. Brooks, Y. Babayan, S. Lamansky, P.I. Djurovich, I. Tsyba,
R. Bau, M.E. Thompson, Inorg. Chem. 41 (2002) 3055.
[4] (a) V. Adamovich, J. Brooks, A. Tamayo, A.M. Alexander, P.I.
Djurovich, B.W. DÕAndrade, C. Adachi, S.R. Forrest, M.E.
Thompson, New J. Chem. 26 (2002) 1171;
4. Supplementary information
Crystallographic data for 4 have been deposited with
the Cambridge Crystallographic Data Centre (CCDC
No. 269303 for complex 4). Copies of this information
may be obtained free of charge from The Director,
CCDC, 12 Union Road, Cambridge, CB21EZ, UK
(Fax: +44 1223 336-033; e-mail: deposit@ccdc.cam.
ac.uk or http://www.ccdc.cam.ac.uk).
(b) B.W. DÕAndrade, J. Brooks, V. Adamovich, M.E. Thompson,
S.R. Forrest, Adv. Mater. 14 (2002) 1032.
[5] (a) T. Okada, I.M. El-Mehasseb, M. Kodaka, T. Tomohiro, K.-
I. Okamoto, H. Okuno, J. Med. Chem. 44 (2001) 4661;
(b) I.M. El-Mehasseb, M. Kodaka, T. Okada, T. Tomohiro, K.
Okamoto, H. Okuno, J. Inorg. Biochem. 84 (2001) 157.
[6] A previous study B.N. Cockburn, D.V. Howe, T. Keating,
B.F.G. Johnson, J. Lewis, J. Chem. Soc., Dalton Trans. (1973)
404, showed that the product of K2PtCl4 and HCꢀN (under
different reaction conditions from those of reference 3) was
[Pt(CꢀN)(l-Cl)]2 for the case where HCꢀN = benzo[h]quinoline,
that analogous dimers could be obtained from the reaction of
Na2PdCl4 and a range of HCꢀN ligands (compositions proven by
elemental analysis), and that these dimers could be converted to
M(CꢀN)(OꢀO) complexes.
Acknowledgements
This material is based upon work supported in part
by the STC Program of the National Science Founda-
tion under Agreement Number DMR-0120967. We also
thank the NSF (award No. CHE-0211419) and the Na-
tional Institute of Health (RIMI program, award No.
1P20MD001104-01).
[7] D.S.C. Black, G.B. Deacon, G.L. Edwards, Aus. J. Chem. 47
(1994) 217.
[8] C.A. Craig, F.O. Garces, R.J. Watts, R. Palmans, A.J. Frank,
Coord. Chem. Soc. 97 (1990) 193.
[9] M.M. Mdleleni, J.S. Bridgewater, R.J. Watts, P.C. Ford, Inorg.
Chem. 34 (1995) 2334.
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