New type of photoluminescent iridium complex: Novel synthetic route for cationic trans-bis(2-phenylpyridinato)iridium(III) complex

Article abstract of DOI:10.1002/ejic.200600888

A new type of iridium(III) complex [trans-Ir(ppy)₂(PPh ₃)₂]⁺ (1) has been prepared by a novel synthetic method and its structural and photoluminescent characteristics have been compared with those of the cis analogue, [cis-Ir(ppy)₂(PPh ₃)-(P(OPh)₃)]⁺ (2) which has also been newly prepared in this study. Wiley-VCH Verlag GmbH & Co. KGaA, 2006.

Full text of DOI:10.1002/ejic.200600888

SHORT COMMUNICATION
DOI: 10.1002/ejic.200600888
New Type of Photoluminescent Iridium Complex: Novel Synthetic Route for
Cationic trans-Bis(2-phenylpyridinato)iridium(III) Complex
Chong Shik Chin,*[a] Min-Sik Eum,[a] Song yi Kim,[a] Choongil Kim,[a] and
Sung Kwon Kang[b]
Keywords: Isomerization / Iridium / Photoluminescence / Synthetic methods / Bis(ppy) complex
A new type of iridium(III) complex [trans-Ir(ppy)2(PPh3)2]+ (1)
has been prepared by a novel synthetic method and its struc-
tural and photoluminescent characteristics have been com-
pared with those of the cis analogue, [cis-Ir(ppy)2(PPh3)-
(P(OPh)3)]+ (2) which has also been newly prepared in this
study.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
Introduction
Studies on iridium(III) complexes of 2-phenylpyridinato
(ppy) and related ligands have been extensively carried out
as their characteristic luminescent properties seem to be uti-
lizable in the display industry.[1] There are three different
types of compounds reported thus far: tris-ppy complexes,
fac- and mer-Ir(ppy)3;[1c,2] bis-ppy complexes, cis-
Ir(ppy)2(L)(LЈ);[3] and mono-ppy complexes, trans,cis-
Ir(ppy)(PR3)2(L)(LЈ) [trans-(PR3)2, cis-(L)(LЈ)].[1a] Emission
characteristics such as λmax, ΦPL, and τ are somewhat suc-
cessfully controlled by modifying the ppy ligand and by in-
troducing diverse ancillary ligands (L and LЈ).[1–4]
Results and Discussion
Synthesis
There has been no report of trans-Ir(ppy)2(L)(LЈ) con-
taining two ppy ligands trans to each other probably be-
Complex 1, [trans-Ir(ppy)2(PPh3)2]+(OTf), is synthesized
cause of the lack of the established synthetic procedures, in high yield following the procedure depicted in Equation
although these trans bis-ppy complexes are expected to (1) where the ppy ligands are added to the metal one by
show emission properties that are comparable with those of one. Complex 3 was chosen as the starting material because
cis-Ir(ppy)2(L)(LЈ); the properties may also be tunable by of its unique reactivity that results from the four equatorial
modifying the ppy ligand and by varying ancillary ligands. ligands (H)2(MeCN)2. These equatorial ligands can be
The trans-M(ppy)2 moiety is only observed in four-coordi- readily replaced by two anionic hydrocarbyls and two other
[5,6]
nate Pt(ppy)2
and Pd(ppy)2,[6] which also emit strongly neutral ligands.[7] The mono-ppy complex [Ir(ppy)-
in the visible region.
(H)(NCMe)(PPh3)2]+ (4) has to be isolated in good purity
for the next step (4Ǟ5) to obtain 1 in high purity and yield.
An analogous mono-ppy complex [Ir(ppy)(H)(OC-
Me2)(PPh3)2]+ was previously prepared.[8] The two ligands
(H)(MeCN) of 3 are readily replaced with one ppy ligand
to give complex 4 by facile dissociation of the MeCN ligand
along with H2 evolution. Complex 4, however, does not re-
act further with ppyH in refluxing toluene. The reaction
mixture of 4 and ppyH in C3H7OC2H4OH (b.p. 150 °C)
heated at reflux affords 1 with unknown materials, whereas
the reaction in refluxing C2H5OC2H4OH (b.p. 133 °C) gives
We now report the synthesis of new complexes [trans-
Ir(ppy)2(PPh3)2]+ (1) with the two nitrogen atoms cis to
each other and [cis-Ir(ppy)2(PPh3){P(OPh)3}]+ (2) and their
emission characteristics.
[a] Chemistry Department, Sogang University,
Seoul 121-742, Korea
Fax: +82-2-701-0967
E-mail: cschin@sogang.ac.kr
a
stable complex [trans-Ir(ppy)(ppyH)(H)(PPh3)2]+ (6)
[b] Chemistry Department, Choong-Nam University,
Daegeon 305-764, Korea
[Equation (2)] which does not undergo further reaction. Re-
placement of the labile MeCN ligand by ppyH was also
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2006, 4979–4982
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4979

C. S. Chin, M.-S. Eum, S. y. Kim, C. Kim, S. K. Kang
SHORT COMMUNICATION
observed in the reaction of [IrI(NCMe)(CO)(PPh3)2]+ at
25 °C to give [IrI(CO)(ppyH)(PPh3)2]+ which undergoes
oxidative addition of ppyH to produce [Ir(ppy)(H)-
(CO)(PPh3)2]+ at the elevated temperature.[9] Insertion of a
bulky alkyne into the Ir–H bond of 4 makes abstraction of
the bulky alkenyl ligand, –CH=CH–p-C6H4CH3, of 5 facile
to give 1. Alkyne insertion into the Ir–H bond of 6 has
not been observed yet. Formation of stable hydrocarbon
CH2=CH–p-C6H4CH3 may facilitate the production of 1
from 5. Attempts to replace one PPh3 of 1 with P(OPh)3 to
prepare [trans-Ir(ppy)2(PPh3){P(OPh)3}]+ have been unsuc-
cessful thus far.
Newly prepared complexes 1, 1F2, 1F2Me, 2, 2F2,
2F2Me, 4, 5, and 6 have been unambiguously characterized
by detailed spectral (1H-, 13C-, 31P NMR, IR, TOF mass)
and elemental analysis data and also crystal X-ray diffrac-
tion data analysis for 1 and 2. Assignment of the spectral
signals is mostly straightforward (see Supporting Infor-
mation for spectra and detailed assignments).
Crystal Structures
Complex 2, [cis-Ir(ppy)2(PPh3){P(OPh)3}]+(OTf), has
been synthesized [Equation (3)] in order to compare its
Figures 1 and 2 show the two nitrogen atoms that are cis
properties with those of 1. Attempts to prepare [cis- to each other in trans-isomer 1 but trans to each other in
Ir(ppy)2(PPh3)2]+ have been unsuccessful, probably because cis-isomer 2. Figure 2 shows the two ppy groups being
PPh3 is too large for the cis-Ir(ppy)2 moiety to have two pushed away from the two phosphorus ligands, which re-
PPh3 in the cis position[10] (see below for the crystal struc- sults in a notable difference between the two Ir–N distances
ture of 2). Although monophosphorus ligand complexes (2.089 and 2.042 Å) and the N–Ir–N bond angle (164°),
such as cis-Ir(ppy)2(PR3)(X) (X = Cl, CN; R = Ph, nBu, which is far smaller than 180°. It seems less likely for cis-
OPh)[3c] have been previously prepared, no report of a bis- bis(ppy) complex 2 to maintain two bulky PPh3 groups in
(phosphorus base ligand) complex such as [cis-Ir(ppy)2- the cis position without severe steric hindrance. Density
(PR3){P(OPh)3}]+ (2) has been made.
function theory calculations suggest that the HOMO of
[12]
Complexes 1F2, 1F2Me, 2F2, and 2F2Me have also been Ir(ppy)3,[1c,11] Ir(ppy)2L2,[1f,11] and Pt(ppy)L2 involve dπ-
prepared by the same procedures shown in Equations (1) orbitals of the metal and whose energy level is closely re-
and (3) to investigate the effects that modification of the lated to the bond lengths between the metal and the ligands.
ppy ligand would have on the emission characteristics of Both Ir–N and Ir–C distances for 1 are very close to those
complexes 1 and 2.
of fac-Ir(ppy)3 and fac-Ir(tpy)3 (see Table 1) where all N
4980
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4979–4982

Photoluminescent [trans-Ir(ppy)2(PPh3)2]+ Complex
SHORT COMMUNICATION
atoms are trans to the C atoms. The Ir–N distances are cis-Ir(tpy)2(P–P) (Table 1). The Ir–P [phosphite, P(OPh)3]
longer in trans complex 1 than those in cis complexes 2 and distances are shorter than those in Ir–P [phosphane, PPh3,
(PPh2CH2)2BPh2] (see Table 1).
Emission Spectral Data
Both trans- and cis- complexes (1 and 2, respectively) dis-
play relatively strong emission in the green–blue color re-
gion (see λmax in Table 2). trans-Bis(PPh3) complex 1 shows
the λmax emission at a somewhat longer wavelength than
that of cis-(PPh3)[P(OPh)3] complex 2. This small difference
in λmax may be due to the P(OPh)3 in 2 since cis-Ir(ppy)2-
X(PPh3) complexes show their emission at longer wave-
lengths than do cis-Ir(ppy)2X[P(OPh)3] complexes.[3c]
Table 2. Photoluminescence spectroscopic data in degassed MeCN
at 25 °C for [trans-Ir(ppy)2(PPh3)2]+ (1), [trans-Ir(F2ppy)2-
(PPh3)2]+ (1F2), [trans-Ir(F2Meppy)2(PPh3)2]+ (1F2Me), [cis-Ir-
(ppy)2(PPh3){P(OPh)3}]+ (2), [cis-Ir(F2ppy)2(PPh3)2]+ (2F2) and
[cis-Ir(F2Meppy)2 (PPh3)2]+ (2F2Me). [Ir] = 1·10–5 .
Complex
λmax [nm]
ΦPL
τ [µs]
Figure 1. ORTEP drawing of [trans-Ir(ppy)2(PPh3)2]+ (1) with ther-
mal ellipsoids drawn at the 50% probability level. Selected bond
lengths [Å]: Ir1–C42 = 2.050(5); Ir1–C30 = 2.052(5); Ir1–N31 =
2.160(4); Ir1–N19 = 2.168(4); Ir1–P2 = 2.3802(12); Ir1–P1 =
2.3891(12). Selected bond angles [°]: C30–Ir–N31 = 178.99(16);
C42–Ir–N19 = 178.81(17); P1–Ir–P2 = 179.19(4).
1
470, 497
452, 479
450, 475
458, 488
444, 473
442, 470
0.24
0.36
0.37
0.18
0.91
0.72
4.4
4.8
3.5
0.31
2.8
2.9
1F2
1F2Me
2
2F2
2F2Me
It is well-established that λmax emission bands for cis-
Ir(ppy)2(L)(LЈ) are shifted to shorter wavelengths when the
ppy ligand is F-substituted on the phenyl ring and Me-sub-
stituted on the pyridyl ring.[1c,g,3b,4] It is noticed that the
blueshifts, which result from the exchange of a ppy ligand
to either a F2ppy or F2Meppy ligand, are greater for the
trans complexes (1, 1F2, 1F2Me) than they are for the cis
complexes (2, 2F2, 2F2Me) (see Table 2). It is also noticed
that quantum yields are significantly larger for F2ppy (1F2)
and F2Meppy (1F2Me) complexes than for ppy (1) com-
plexes. A striking increase in ΦPL is observed when the ppy
ligand of 2 is replaced with either a F2ppy or F2Meppy
ligand (Table 2).
In conclusion, a new type of iridium(III) complex [trans-
Ir(ppy)2(PPh3)2]+ (1) has been prepared by a novel synthetic
method and its structural and photoluminescent character-
istics have been compared with those of the cis analogue,
[cis-Ir(ppy)2(PPh3){P(OPh)3}]+ (2), which has also been
newly prepared in this study. No significant differences have
been found for their photoluminescent properties because
of the geometric differences between trans-1 and cis-2. Sky
Figure 2. ORTEP drawing of [cis-Ir(ppy)2(PPh3){P(OPh)3}]+ (2)
with thermal ellipsoids drawn at the 50% probability level. Selected
bond lengths [Å]: Ir–N1 = 2.089(11); Ir–N13 = 2.042(11); Ir–C12
= 2.072(13); Ir–C24 = 2.071(12); Ir–P25 = 2.307(3); Ir–P47 =
2.433(3). Selected bond angle [°]: N1–Ir–N13 = 164.3(4); C12–Ir–
P25 = 169.3(4); C24–Ir–P47 = 177.0(4).
Table 1. Structural and Photoemission data for [trans-Ir(ppy)2(PPh3)2]+ (1), [cis-Ir(ppy)2(PPh3){P(OPh)3}]+ (2) and related complexes.
Complex
Ir–C [Å]
Ir–N [Å]
Ir–P [Å]
λmax [nm]
[trans-(ppy)2Ir(PPh3)2]+ (1)
2.050, 2.052
2,160, 2.168
2.089, 2.042
2.167
2.380, 2.389
2.307, 2.433
470, 497
458, 488
545
510
512
[cis-(ppy)2Ir(PPh3){P(OPh)3}]+ (2) 2.072, 2.071
[1d]
fac-Ir(ppy)3
2.035
2.024
[a],[1c]
fac-Ir(tpy)3
mer-Ir(tpy)3
2.132
2.076, 2.086, 2.020[c]
2.047, 2.057
2.151,[d] 2.044, 2.065
2.082, 2.083
[a],[1c]
cis-(tpy)2Ir(P–P)[a,b],[1f]
2.420, 2.431
468
[a] tpy = 2-(p-tolyl)pyridinato. [b] P–P = (PPh2CH2)2BPh2. [c] trans to N. [d] trans to C.
Eur. J. Inorg. Chem. 2006, 4979–4982
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
4981

C. S. Chin, M.-S. Eum, S. y. Kim, C. Kim, S. K. Kang
SHORT COMMUNICATION
W. J. Finkenzeller, H. Yersin, Chem. Mater. 2005, 17, 1745–
1752; e) M. K. Nazeeruddin, R. Humphrey-Baker, D. Berner,
S. Rivier, L. Zuppiroli, M. Graetzel, J. Am. Chem. Soc. 2003,
125, 8790–8797; f) J. Li, P. I. Djurovich, B. D. Alleyne, M. You-
sufuddin, N. N. Ho, J. C. Thomas, J. C. Peters, R. Bau, M. E.
Thompson, Inorg. Chem. 2005, 44, 1713–1727.
blue color emission can be obtained by replacing the ppy
ligands of 1 or 2, which produce greenish–blue light, with
either F2ppy or F2Meppy ligands. New synthetic methods
are currently under investigation to replace the PPh3 axial
ligand of 1 with a variety of ligands to prepare [trans-
Ir(ppy)2(L)(LЈ)]+,0 (L, LЈ = neutral or anionic C, N, P, O-
base) which would show diverse luminescent characteristics.
Finally, we wish this study to open a new research field that
deals with light emitting iridium complexes containing two
ppy ligands and related cyclometalated ligands trans to each
other.
[2] K. A. King, P. J. Spellane, R. J. Watts, J. Am. Chem. Soc. 1985,
107, 1431–1432.
[3] a) W. J. Finkenzeller, P. Stößel, H. Yersin, Chem. Phys. Lett.
2004, 397, 289–295; b) C. Adachi, R. C. Kwong, P. I. Djurov-
ich, V. Adamovich, M. A. Baldo, M. E. Thompson, S. R. For-
rest, Appl. Phys. Lett. 2001, 79, 2082–2084; c) C.-L. Lee, R. R.
Das, J.-J. Kim, Curr. Appl. Phys. 2005, 5, 309–313; d) Q. Zhao,
S. Liu, M. Shi, C. Wang, M. Yu, L. Li, F. Li, T. Yi, C. Haung,
Inorg. Chem. 2006, 45, 6152–6160.
[4] a) C.-H. Yang, K.-H. Fang, C.-H. Chen, I.-W. Sun, Chem.
Commun. 2004, 2232–2233; b) R. Ragni, E. A. Plummer, K.
Brunner, J. W. Hofstraat, F. Babudri, G. M. Farinola, F. Naso,
L. De Cola, J. Mater. Chem. 2006, 16, 1161–1170; c) T. Tsu-
zuki, N. Shirasawa, T. Suzuki, S. Tokito, Adv. Mater. 2003, 15,
1455–1458.
Supporting Information (see footnote on the first page of this arti-
cle): 1H-, 13C-, 31P NMR spectra for 1–6. Experimental details with
1H-, 13C-, 31P NMR, FTIR, TOF-Mass spectral and EA data. PL
decay diagrams. CCDC-617305 (1) and -617304 (2) contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[5] a) L. Chassot, E. Müller, A. von Zelewsky, Inorg. Chem. 1984,
23, 4249–4253; b) M. Maestri, D. Sandrini, V. Balzani, L.
Chassot, P. Jolliet, A. von Zelewsky, Chem. Phys. Lett. 1985,
122, 375–379; c) L. Chassot, A. von Zelewsky, Inorg. Chem.
1987, 26, 2814–2818.
Acknowledgments
[6] P. Jolliet, M. Gianini, A. von Zelewsky, G. Bernadinelli, H.
Stoeckli-Evans, Inorg. Chem. 1996, 35, 4883–4888.
[7] a) C. S. Chin, H. Lee, S. Noh, H. Park, M. Kim, Organometal-
lics 2003, 22, 2119–2123; b) C. S. Chin, M. Kim, H. Lee, S.
Noh, K. M. Ok, Organometallics 2002, 21, 4785–4793.
[8] X. Li, T. Vogel, C. D. Incarvito, R. H. Crabtree, Organometal-
lics 2005, 24, 62–76.
The authors wish to thank the Korea Research Foundationfor their
financial support of this study through the Basic Science Research
Institute program grant No. 2005–015-C00222and Prof. B. Lee,
Physics Dept., Sogang Univ. for the loan of the apparatus for mea-
surements of PL lifetime.
[9] F. Neve, M. Ghedini, G. De Munno, A. Crispini, Organometal-
lics 1991, 10, 1143–1148.
[1] a) N. Herron, N. S. Radu, E. M. Smith, Y. Wang, US Patent
2005/0048312 A1; b) S. Lamansky, M. E. Thompson, V. Ad-
amovich, P. I. Djurovich, C. Adachi, M. A. Baldo, S. R. For-
[10] [cis-Ir(ppy)2(PPh2Me)2]+ will be reported elsewhere.
[11] P. J. Hay, J. Phys. Chem. A 2002, 106, 1634–1641.
rest, R. Kwong, US Patent 2002/0182441 A1; c) A. B. Tamayo, [12] J. Brooks, Y. Babayan, S. Lamansky, P. I. Djurovivh, I. Tsyba,
B. D. Alleyne, P. I. Djurovich, S. Lamansky, I. Tsyba, N. N.
Ho, R. Bau, M. E. Thompson, J. Am. Chem. Soc. 2003, 125,
7377–7387; d) J. Breu, P. Stössel, S. Schrader, A. Starukhin,
R. Bau, M. E. Thompson, Inorg. Chem. 2002, 41, 3055–3066.
Received: September 4, 2006
Published Online: November 6, 2006
4982
www.eurjic.org
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2006, 4979–4982