Towards a phosphorescent cyclometalated iridium complex containing a modified polymerizable acetylacetonato ligand

Article abstract of DOI:10.1016/j.inoche.2007.10.029

A convenient synthesis of the complex [Ir(ppy)₂(phC6-acac)] (1, ppy = 2-phenylpyridyl, phC6-acac = 11-(2,5-dibromo-4-hexyloxy-phenoxy)-undecane-2,4-dione) from [{Ir(μ-Cl)(ppy)₂}₂], phC6-acacH and silver trifluoroacetate as the halide abstractor in refluxing acetone is described. The crystal and molecular structure of 1 was determined by X-ray crystallography.

Full text of DOI:10.1016/j.inoche.2007.10.029

Available online at www.sciencedirect.com
Inorganic Chemistry Communications 11 (2008) 231–234
www.elsevier.com/locate/inoche
Towards a phosphorescent cyclometalated iridium complex containing
a modified polymerizable acetylacetonato ligand
Marion Graf a, Valeria Gancheva b,c, Manuel Thesen b, Hartmut Kruger b, Peter Mayer a,
¨
Karlheinz Sunkel a,*
¨
a Department Chemie der Ludwig-Maximilians-Universita¨t Mu¨nchen, Butenandtstraße 5–13, D-81377 Mu¨nchen, Germany
b Fraunhofer Institut fu¨r Angewandte Polymerforschung, Geiselbergstraße 69, D-14476 Potsdam-Golm, Germany
c Bulgarian Academy of Sciences, Institute of Polymers, Acad. G. Bontchev Str. 103A, BG-1113 Sofia, Bulgaria
Received 29 June 2007; accepted 18 October 2007
Available online 15 December 2007
Abstract
A convenient synthesis of the complex [Ir(ppy)2(phC6-acac)] (1, ppy = 2-phenylpyridyl, phC6-acac = 11-(2,5-dibromo-4-hexyloxy-
phenoxy)-undecane-2,4-dione) from [{Ir(l-Cl)(ppy)2}2], phC6-acacH and silver trifluoroacetate as the halide abstractor in refluxing ace-
tone is described. The crystal and molecular structure of 1 was determined by X-ray crystallography.
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Iridium; Cyclometalated complex; Photoluminescence; Crystal structure
In the last years the photophysical and photochemical
properties of cyclometalated iridium(III) complexes have
been extensively investigated. Because of their high lumines-
cence quantum yields and short phosphorescence lifetimes
these compounds are suitable for various applications in
photochemistry and in organic light-emitting devices
(OLEDs) and exhibit still the efficient phosphorescent dyes
in this field up to now, e.g. [1–16]. In this light, one of the
best green-light-emitting complexes is the compound
fac-[Ir(ppy)3)] yielding a high quantum efficiency [17].
Moreover the more efficient green-light-emitting complex
[Ir(ppy)2(acac)] as the phosphorescent dopant was reported
[18]. Therefore, complexes of the formula [Ir(ppy)2(acac)]
(acac = modified acetylacetonates) should obviously
provide better luminescent properties. Many efforts were
undertaken to chemically modify this type of complex to
reach proper luminescence properties, e.g. [10] and to incor-
porate chemical functionalities which are useful to link
these complexes covalently to phosphorescent polymer
OLED materials. In this paper we report the preparation
and structural characterization of a new compound in this
area, [Ir(ppy)2(phC6-acac)] (1, ppy = 2-phenylpyridyl,
phC6-acac = 11-(2,5-dibromo-4-hexyloxy-phenoxy)-unde-
cane-2,4-dione). Thus compound 1 was prepared from
[{Ir(l-Cl)(ppy)2}2], phC6-acacH, triethylamine as the base
and silver trifluoroacetate as the halide abstractor in reflux-
ing acetone. All manipulations were performed under a dry
argon atmosphere using conventional Schlenk techniques.
Solvents and reagents were used as received, [{Ir(l-
Cl)(ppy)2}2] was prepared according to the literature pro-
cedure [19]. The precursor of the ligand, phC6-acacH =
11-(2,5-dibromo-4-hexyloxy-phenoxy)-undecane-2,4-dione
was obtained by a specially developed preparation [20]. 1H
NMR spectra were recorded on a Jeol EX 400 (1H:
400 MHz) or a Jeol Eclipse 400 NMR spectrometer (1H:
400 MHz). The spectra were referenced to external SiMe4
(1H). IR spectra were recorded as KBr pellets on a Mattson
Perkin Elmer 983 G spectrometer. Mass spectra were
obtained on a JMS-700 spectrometer from Jeol. Microanal-
yses (C, H, N) were performed by the University of Munich
microanalytical laboratory.
*
Corresponding author. Tel.: +49 89 2180 77773.
E-mail address: karlheinz.suenkel@cup.uni-muenchen.de (K. Sunkel).
¨
1387-7003/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2007.10.029

232
M. Graf et al. / Inorganic Chemistry Communications 11 (2008) 231–234
˚
A mixture of [{Ir(l-Cl)(ppy)2}2] (0.500 g, 0.47 mmol),
0.71073 A). The structure was solved by direct methods
(SIR 97) [21] and refined by full-matrix least-squares
calculations on F2 (SHELXL-97) [22]. Anisotropic dis-
placement parameters were refined for all non-hydrogen
atoms. Crystal data: C45H49Br2IrN2O4 FW = 1033.91, tri-
(ppy = 2-phenylpyridine), phc6-acaH = 11-(2,5-dibromo-4-
hexyloxy-phenoxy)-undecane-2,4-dione (0.498 g, 0.93 mmol),
and AgO2CCF3 (0.206 g, 0.933 mmol) were dissolved in
30 mL of acetone and refluxed under nitrogen for 3 h.
The mixture was cooled to room temperature and the pre-
cipitated AgCl was separated by filtration. Then the solvent
was removed in vacuo to dryness. The remaining residue
was dissolved in 10 mL of dichloromethane and chromato-
graphed over an alumina column (25 Â 2 cm) with dichlo-
romethane as the eluent. The first yellow band was
collected and evaporated to dryness, dissolved in 5 mL of
CH2Cl2 and precipitated with hexane. Crystals suitable
for X-ray diffraction studies were obtained by slow diffu-
sion of ethanol into a concentrated solution of the com-
pound in dichloromethane. (Yield: 210 mg, 48%). Anal.
Calc. for C45H49Br2IrN2O4 (MW 1033.91) C, 52.28; H,
ꢀ
clinic, space group P1, a = 7.5953(2), b = 13.8109(3), c =
˚
19.9793(5) A, a = 84.3394(12), b = 79.3392(14), g =
3
˚
89.2467(13)°, V = 2049.54(9) A , Z = 2, Dcalc = 1.675 g
cmÀ3, T = 200(2) K, 37,708 reflections were collected, of
which 7721 (Rint = 0.045 [I > 2r(I)] were unique.
The molecular structure of 1 is illustrated in Fig. 1
including important bond lengths and angles in the cap-
tion. The iridium complex exhibits two cyclometalated
phenylpyridine ligands and the diketonate ligand in a
pseudooctahedral coordination sphere at the metal center.
The Ir–C bond lengths, ranging from 1.983(6) to
˚
1.987(6) A, are within the range reported for other mono-
1
4.78; N, 2.71%. Found: C, 51.98; H, 5.00; N, 2.67%. H
nuclear complexes containing the Ir(ppy)2 moiety [10].
The Ir–N bond lengths are in the range of 2.033(6)–
NMR (270 MHz, CDCl3): d8.49 (dd, J = 1.4 Hz, J =
1.0 Hz, 2H), 8.47 (dd, J = 1.41 Hz, J = 1.05 Hz, 2H), 7.82
(t, J = 8.72 Hz, 2H), 7.70 (m, 2H), 7.52 (m, 2H), 7.02 (d,
J = 3.03 Hz, 2H), 6.79 (m, 2H), 6.66 (m, 2H), 6.31 (m,
1H), 6.24 (m, 1H), 5.18 (s, 1H, OC–CH–CO), 3.92 (m,
6H), 1.97 (t, J = 7.43 Hz, 2H), 1.79 (s, 3H, CH3–CO),
1.72 (m, 2H), 1.30 (m, 10H), 1.11 (m, 2H), 0.98 (m, 2H),
0.90 (t, J = 6.98 Hz, 3H,–CH2–CH3). IR (KBr): 629w,
669w, 729s, 752s, 793w, 1030s, 1062s, 1156w, 1210s,
1264s, 1302w, 1358s, 1422s, sh, 1456s, 1478s, 1492s,
1514s, 1580vs, 1605s, 2855s, 2925s, br, cmÀ1. MS (70 eV):
1033 (M+, 193Ir).
˚
2.036(6) A. Furthermore, the C–C and C–N bond lengths
and angles are within normal ranges and in accordance
with corresponding parameters described for other simi-
larly constituted complexes [14]. The Ir–O bond lengths
˚
are 2.151(4) and 2.164(5) A, respectively. Furthermore,
the C–O bond lengths are in agreement with the literature
reports, e.g. [12].
The absorption and room-temperature emission spec-
trum of 1 recorded in dichloromethane is shown in
Fig. 2. In the absorption spectrum the intense bands
1
around 300 nm can be assigned to spin-allowed (p–p*)
Complex 1 was prepared from the reaction of [{Ir(l-
Cl)(ppy)2}2] with 2 equiv. of silver trifluoroacetate, 1 equiv.
of the diketone, and triethylamine as the base in refluxing
acetone (Scheme 1). The new compound was separated
by column chromatography and purified by crystallization
from ethanol/dichloromethane. Elemental analysis, mass
transitions, and bands at 339, 365, and 406 nm correspond
to spin-allowed MLCT bands. The two bands at 457 and
1
485 nm can be assigned to the formally spin-forbidden
3MLCT transition as reported for [Ir(ppy)2(acac)] [15].
The peak wavelength of phosphorescent emission of com-
pound 1 was observed at 520 nm and is comparable to sim-
ilar constituted cyclometalated iridium complexes
containing the acetylacetonate ligand, e.g. [4,15]. The new
green-emitting complex [Ir(ppy)2(phC6-acac)] (1) will be
used now in applications for phosphorescent polymer
OLED systems. By the hexyloxy-spacer the phosphores-
1
spectrum, and the H NMR spectroscopic data confirmed
the constitution of compound 1. Crystals for the X-ray
diffraction study were selected by means of a polariza-
tion microscope, mounted on the tip of a glass fiber,
and investigated on a Nonius KappaCCD diffractometer
using graphite-monochromated MoKa radiation (k =
O
C6H13
Br
Br
Br
O
O
C7H14
C6H13
Cl
Cl
N
O
C7H14
O
Ir
Ir
2
2 AgO2CCF3
2
Ir
2 AgCl
2 CF3CO2H
N
N
O
O
O
Br
2
2
2
(1)
Scheme 1.

M. Graf et al. / Inorganic Chemistry Communications 11 (2008) 231–234
233
˚
Fig. 1. ORTEP view of 1 with thermal ellipsoids are drawn at 50% probability level. Selected bond lengths (A) and angles (°): Ir(1)–N(1) 2.033(6), Ir(1)–
˚
N(2) 2.036(6), Ir(1)–C(7) 1.987(6), Ir(1)–C(18) 1.983(6), Ir(1)–O(1) 2.164(5), Ir(1)–O(2) 2.151(4) A; O(1)–Ir–O(2) 88.21(18), O(1)–Ir–N(1) 94.5(2), O(1)–Ir–
N(2) 89.2(2), O(1)–Ir–C(7) 175.0(2), O(1)–Ir–C(18) 90.6(2), O(2)–Ir–N(1) 88.70(19), O(2)–Ir–N(2) 95.97(19), O(2)–Ir–C(7) 89.5(2), O(2)–Ir–C(18) 176.4(2),
N(1)–Ir–N(2) 174.1(2), N(1)–Ir–C(7) 81.0(2), N(1)–Ir–C(18) 94.8.(2), N(2)–Ir–C(7) 95.5(2), N(2)–Ir–C(18) 80.6(2), C(7)–Ir–C(18) 91.9(3)°.
References
4
3
2
1
0
UVvis
PL
excitation 365 nm
[1] X. Li, Z. Chen, Q. Zhao, L. Shen, F. Li, T. Yi, Y. Cao, C. Huang,
Inorg. Chem. 46 (2007) 5518.
[2] C.-H. Yang, K.-H. Fang, W.-L. Su, S.-P. Wang, S.-K. Su, I.-W. Sun,
J. Organomet. Chem. 691 (2006) 2767.
[3] I.R. Laskar, S.-F. Hsu, T.-M. Chen, Polyhedron 24 (2005) 189.
[4] M.-L. Xu, W.-L. Li, Z.-W. An, Q. Zhou, G.-Y. Wang, Appl.
Organometal. Chem. 19 (2005) 1225.
[5] K.K.-W. Lo, J.S.-W. Chan, C.-K. Chung, V.W.-H. Tsang, N. Zhu,
Inorg. Chim. Acta 357 (2004) 3109.
[6] P. Coppo, E.A. Plummer, L. De Cola, J. Chem. Soc., Chem.
Commun. (2004) 1774.
[7] A. Tsuboyama, T. Takiguchi, S. Okada, M. Osawa, M. Hoshino, K.
Ueno, J. Chem. Soc., Dalton Trans. (2004) 1115.
520
[8] J.D. Slinker, A.A. Gorodetsky, M.S. Lowry, J. Wang, S. Parker, R.
Rohl, S. Bernhard, G.G. Malliaras, J. Am. Chem. Soc. 126 (2004)
2763.
300
400
500
600
wavelength / [nm]
[9] M.-K. Lau, K.-M. Cheung, Q.-F. Zhang, Y. Song, W.-T. Wong, I.D.
Williams, W.-H. Leung, J. Organomet. Chem. 689 (2004) 2401.
[10] S. Jung, Y. Kang, H.-S. Kim, Y.-H. Kim, C.-L. Lee, J.-J. Kim, S.-K.
Lee, S.-K. Kwon, Eur. J. Inorg. Chem. (2004) 3415.
[11] A.J. Sandee, C.K. Williams, N.R. Evans, J.E. Davies, C.E. Boothby,
A. Ko¨hler, R.H. Friend, A.B. Holmes, J. Am. Chem. Soc. 126 (2004)
7041.
Fig. 2. Absorption spectrum and photoluminescence for [Ir(ppy)2(phC6-
acac)] (1) in dichloromethane at room temperature.
cent complex will be covalently, but non-conjugatedly
linked to the polymer backbone.
[12] M.C. DeRosa, D.J. Hodgson, G.D. Enright, B. Dawson, C.E.B.
Evans, R.J. Crutchley, J. Am. Chem. Soc. 126 (2004) 7619.
[13] A. Beeby, S. Bettington, I.D.W. Samuel, Z. Wang, J. Mater. Chem.
13 (2003) 80.
[14] A.B. Tamayo, B.D. Alleyne, P.I. Djurovich, S. Lamansky, I. Tsyba,
N.N. Ho, R. Bau, M.E. Thompson, J. Am. Chem. Soc. 125 (2003) 7377.
[15] S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, R.
Kwong, I. Tsyba, M. Brotz, B. Mui, R. Bau, M.E. Thompson, Inorg.
Chem. 40 (2001) 1704.
Supplementary material
CCDC 650267 contains the supplementary crystallo-
graphic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Cen-
tre via www.ccdc.cam.ac.uk/data_request/cif.
[16] V.V. Grushin, N. Herron, D.D. LeCloux, W.J. Marshall, V.A.
Petrov, Y. Wang, J. Chem. Soc., Chem. Commun. (2001) 1494.
[17] M.A. Baldo, S. Lamansky, P.E. Burrows, M.E. Thompson, Appl.
Phys. Lett. 75 (1999) 4.
[18] C. Adachi, M.A. Baldo, M.E. Thompson, S. Forrest, J. Appl. Phys.
90 (2001) 5048.
[19] S. Sprouse, K.A. King, P.J. Spellane, R.J. Watts, J. Am. Chem. Soc.
106 (1984) 6647.
[20] Synthesis of PhC6-acacH: (a) 2,5-Dibromo-4-hexyloxy-phenol: In a
100-mL-3-necked round bottom flask were placed 1.00 g (3.73 mmol)
2,5-dibromohydrochinone and 20 mL of ethanol. Then 0.84 g of
KOH pellets (14.9 mmol) and hexylbromide (1.86 mmole) were
Acknowledgements
The authors are grateful to the BMBF for funding with-
in the CARO-Project (01 BD 0685) and to the Department
of Chemistry and Biochemistry of the Ludwig Maximilians
University Munich for supporting these investigations.
V.G. and H.K. thank the NATO for funding a part of
the work at Fraunhofer IAP within the CLG-Project
(CBP.EAP.CLG 981997).

234
M. Graf et al. / Inorganic Chemistry Communications 11 (2008) 231–234
added. The reaction mixture was refluxed for 24 h, filtered hot, and
hexamethylphosphamide were added by syringe. The reaction mixture
was cooled to 0 °C and 0.13 g (1.30 mmol) of acetylacetone were
injected. After 20 min 0.91 mL (1.46 mmol) 1.6 M butyllithium-
solution in hexane were added slowly and the mixture stirred for
another 20 min at 0 °C. Then 0.7 g (1.37 mmol) of 1,4-dibromo-2-(6-
bromo-hexyloxy)-5-hexyloxy-benzene solved in 2 mL of dry THF
were injected. The reaction mixture was stirred for 20 h at room
temperature and after acidification it was solved in ethyl acetate. The
organic layer was washed with sodium bicarbonate solution and
water and finally dried over Na2SO4. After removal of the solvent, the
pure product was obtained by column chromatography using petrol
ether/ethyl acetate (10:1) as the eluent. The product was obtained as a
white powder. (Yield 56%) Anal. Calc. for C23H34Br2O4(MW 543.33):
C, 51.70; H, 6.41; Br, 29.91% Found: C, 53.29; H, 6.46%. 1H NMR
(500 MHz, CDCl3) (a) keto-form (12%) d 7.08 (ss, 2H); 3.94 (tt, 4H);
3.57 (s, 2H); 2.51 (t, 2H); 2.24 (s, 3H); 1.80 (m, 4H); 1.62 (m, 2H); 1.48
(m, 4H); 1.35 (m, 8H); 0.91 (t, 3H). (b) enol-form (88%) d 7.08 (ss,
2H); 5.49 (s, 1H); 3.94 (tt, 4H); 2.27 (t, 2H); 2.05 (s, 3H); 1.80 (m, 4H);
1.62 (m, 2H); 1.48 (m, 4H); 1.35 (m, 8H); 0.91 (t, 3H).
cooled to room temperature. Subsequently it was diluted with
dichloromethane and washed several times with water. The organic
layer was dried over Na2SO4. After removing the solvent, the
compound was purified by column chromatography on SiO2 using
hexane/ethyl acetate (4:1) as the eluant. The procedure yields the pure
product as a white powder. (Yield 62%) Anal. Calc. for C12H16Br2O2
(MW 352.07): C, 40.94; H, 4.58; Br, 45.39%. Found: C, 41.06; H,
1
4.65%. H NMR (500 MHz, CDCl3) d7.24 (s, 1H); 6.98 (s, 1H); 5.20
(s, 1H); 3.93 (t, 2H); 1.80 (m, 2H); 1.48 (m, 2H); 1.34 (m, 4H); 0.91 (t,
3H). (b) 1,4-Dibromo-2-(6-bromo-hexyloxy)-5-hexyloxy-benzene: In a
100-mL-3-necked-round bottom flask with nitrogen inlet 1.10 g
(3.13 mmol) 2,5-dibromo-4-hexyloxy-phenol and 30 mL of cyclohexa-
none were placed. Subsequently 1.30 g (9.40 mmol) of potassium
carbonate, a catalytic amount of potassium iodide, and 31.3 mmol of
1,6-dibromohexane were added. The reaction mixture was refluxed
for 3 h. Then the mixture was filtered hot. After distillation of spare
1,6-dibromohexane crystallisation (at least twice) from hexane gave
the pure product as slight yellow powder. (Yield 61%) Anal. Calc. for
C
19H28Br3O2 (MW 528.14): C, 41.97; H, 5.28; Br, 46.53% Found: C,
[21] A. Altomare, M.C. Burla, M. Camalli, G.L. Cascarano, C. Giaco-
vazzo, A. Guagliardi, A.G.G. Moliterni, G. Polidore, R. Spagna,
SIR97: a new tool for crystal structure determination and refinement,
J. Appl. Crystallogr. 32 (1999) 115.
[22] G.M. Sheldrick, SHELXL-97, Program for Crystal Structure Refine-
ment, University of Go¨ttingen, Go¨ttingen, Germany, 1997.
42.23; H, 5.42%. 1H NMR (500 MHz, CDCl3) d 7.08 (s, 2H); 3.95 (tt,
4H); 3.43 (t, 2H); 1.80 (m, 8H); 1.53 (m, 2H); 1.48 (m, 2H); 1.35 (m,
4H); 0.91 (t, 3H). (c) 11-(2,5-Dibromo-4-hexyloxy-phenoxy)-unde-
cane-2,4-dione: In a 25-mL-3-necked-round bottom flask with septum
64 mg (2.67 mmol) of sodium hydride were placed. The equipment
was evacuated and flushed with argon. 5 mL of dry THF and 50 lL of