Regioselective aromatic substitution reactions of cyclometalated Ir(III) complexes: Synthesis and photochemical properties of substituted Ir(III) complexes that exhibit blue, green, and red color luminescence emission

Article abstract of DOI:10.1021/ic101164g

In this manuscript, the regioselective halogenation, nitration, formylation, and acylation of Ir(tpy)₃ and Ir(ppy)₃ (tpy = 2-(4/-tolyl)pyridine and ppy = 2-phenylpyridine) and the subsequent conversions are described. During attempte

Full text of DOI:10.1021/ic101164g

806 Inorg. Chem. 2011, 50, 806–818
DOI: 10.1021/ic101164g
Regioselective Aromatic Substitution Reactions of Cyclometalated Ir(III)
Complexes: Synthesis and Photochemical Properties of Substituted Ir(III)
Complexes That Exhibit Blue, Green, and Red Color Luminescence Emission
Shin Aoki,*,†,‡ Yasuki Matsuo,† Shiori Ogura,† Hiroki Ohwada,† Yosuke Hisamatsu,† Shinsuke Moromizato,†
Motoo Shiro,§ and Masanori Kitamura†,‡
‡
†Faculty of Pharmaceutical Sciences, and Center for Technologies against Cancer (CTC), Tokyo University of
§
Science, 2641 Yamazaki, Noda, Chiba, 278-8510 Japan, and Rigaku Corporation, X-ray Research Laboratory,
3-9-12 Matsubaracho, Akishima, Tokyo, 196-8666 Japan
Received June 9, 2010
In this manuscript, the regioselective halogenation, nitration, formylation, and acylation of Ir(tpy)3 and Ir(ppy)3 (tpy =
2-(40-tolyl)pyridine and ppy = 2-phenylpyridine) and the subsequent conversions are described. During attempted
bromination of the three methyl groups in fac-Ir(tpy)3 using N-bromosuccinimide (NBS) and benzoyl peroxide (BPO),
three protons at the 50-position (p-position with respect to the C-Ir bond) of phenyl rings in tpy units were substituted by Br,
as confirmed by 1H NMR spectra, mass spectra, and X-ray crystal structure analysis. It is suggested that such substitution
reactions of Ir complexes proceed via an ionic mechanism rather than a radical mechanism. UV-vis and luminescence
spectra of the substituted Ir(III) complexes are reported. The introduction of electron-withdrawing groups such as CN and
CHO groups at the 50-position of tpy induces a blue shift of luminescence emission to about 480 nm, and the introduction of
electron-donating groups such as an amino group results in a red shift to about 600 nm. A reversible change of emission for
the 50-amino derivative of Ir(tpy)3, Ir(atpy)3, between red and green occurs upon protonation and deprotonation.
Introduction
Synthesis of various cyclometalated Ir complexes is typi-
cally conducted by heating Ir(III) salts such as IrCl3 with the
corresponding ligands that had been prepared in advance.
Alternative synthetic methods would be the direct and
regioselective modification of the metalated ligands after
the Ir complexes are prepared, which would afford novel
Cyclometalated complexes play central roles as triplet emit-
ters in the production of organic light-emitting diodes (OLEDs)
because of their excellent luminescence properties.1,2 Iridium-
(III) complexes such as fac-Ir(tpy)3 1 and fac-Ir(ppy)3
2
(tpy=2-(40-tolyl)pyridine and ppy=2-phenylpyridine) shown
in Chart 1 have long-lived excited states and high luminescence
quantum yields (Φ) of 0.1-0.9,1,2 mainly because of low-lying
metal to ligand charge transfer (MLCT) (e.g., Φ for 2 has been
reported to be 0.4).2f,h,k They are in widespread use in emission
materials3 and also as components of photoreductants,4
photosensitizers,5 oxygen sensors,6 and photoredox catalysts.7
In addition, several Ir complexes that emit blue-8 and red-
color9 luminescence have been developed by choosing cyclo-
metalating ligands. To our knowledge, however, examples of
luminescent iridium complexes that reversibly respond to the
surrounding environment (e.g., pH and metal cations) are
rare.1e,10,11
(2) (a) Sprouse, S.; King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem.
Soc. 1984, 106, 6647–6653. (b) Ohsawa, Y.; Sprouse, S.; King, K. A.; DeArmond,
M. K.; Watts, R. J. J. Phys. Chem. 1987, 91, 1047–1054. (c) Dedeian, K.; Djurovich,
P. I.; Garces, F. O.; Carlson, G.; Watts, R. J. Inorg. Chem. 1991, 30, 1685–1687.
€
(d) Colombo, M. G.; Brunold, T. C.; G€udel, H. U.; Forstch, M.; B€urg, H.-B. Inorg.
Chem. 1994, 33, 545–550. (e) Baldo, M. A.; Lamansky, S.; Burrows, P. E.;
Thompson, M. E.; Forrest, S. R. Appl. Phys. Lett. 1999, 75, 4–6. (f) Lamansky,
S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Kwong, R.; Tsyba, I.; Bortz, M.;
Mui, B.; Thompson, M. E. Inorg. Chem. 2001, 40, 1704–1711. (g) Lamansky, S.;
Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H.-E.; Adachi, C.; Burrows, P. E.;
Forrest, S. R.; Thompson, M. E. J. Am. Chem. Soc. 2001, 123, 4304–4312.
(h) Grushin, V. V.; Herron, N.; LeCloux, D. D.; Marshall, W. J.; Petrov, V. A.; Wang,
Y. Chem. Commun. 2001, 1494–1495. (i) Markham, J. P. J.; Lo, S.-C.; Magennis,
S. W.; Burn, P. L.; Samuel, I. D. W. Appl. Phys. Lett. 2002, 80, 2645–2647. (j) Lo,
S.-C.; Male, N. A. H.; Markham, J. P. J.; Magennis, S. N.; Barn, P. L.; Salata, O. T.;
Samuel, J. D. W. Adv. Mater. 2002, 14, 975–979. (k) Tamayo, A. B.; Alleyne, B. D.;
Djurovich, P. I.;Lamansky, S.; Tsyba, I.; Ho, N. N.; Bau, R.; Thompson, M. E. J. Am.
Chem. Soc. 2003, 125, 7377–7387. (l) Tsuboyama, A.; Iwawaki, H.; Furugori, M.;
Mukaide, T.; Kamatani, J.; Igawa, S.; Moriyama, T.; Miura, S.; Takiguchi, T.; Okada,
S.; Hoshino, M.; Ueno, K. J.Am.Chem. Soc. 2003, 125, 12971–12979. (m) Jung, S.;
Kang, Y.; Kim, H.-S.;Kim, Y.-H.; Lee, C.-L.; Kim, J.-J.;Lee, S.-K.;Kwon,S.-K.Eur.
J. Inorg. Chem. 2004, 3415–3423. (n) Kapturkiewicz, A.; Angulo, G. Dalton Trans.
2003, 3907–3913. (o) Kapturkiewicz, A.; Chen, T.-M.; Laskar, I. R.; Nowacki, J.
Electrochem. Commun. 2004, 6, 827–831. (p) Lowry, M. S.; Hudson, W. R.; Pascal,
R. A., Jr.; Bernhard, S. J. Am. Chem. Soc. 2004, 126, 14129–14135.
*To whom correspondence should be addressed. E-mail: shinaoki@
rs.noda.tus.ac.jp.
(1) (a) Baldo, M. A.; O’Brien, D. F.; You, Y.; Shoustikov, A.; Thompson,
M. E.; Forrest, S. R. Nature 1998, 395, 151–154. (b) Chou, P.-T.; Chi, Y. Eur.
J. Inorg. Chem. 2006, 3319–3332. (c) Evans, R. C.; Douglas, P.; Winscom, C. J.
Coord. Chem. Rev. 2006, 250, 2093–2126. (d) Flamigni, L.; Barbieri, A.; Sabatini,
C.; Ventura, B.; Barigelletti, F. Top. Curr. Chem. 2007, 281, 143–203. (e) Lo, K. K.-W.;
Louie, M.-W.; Zhang, K. Y. Coord. Chem. Rev. 2010, 254, 2603–2622. (f) Zhao, Q.;
Li, F.; Huang, C. Chem. Soc. Rev. 2010, 39, 3007–3030.
r
pubs.acs.org/IC
Published on Web 01/07/2011
2011 American Chemical Society

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 807
derivatives that otherwise would not be possible to obtain.
For example, Stossel et al. reported in a patent12 on the
regioselective halogenation and nitration of cyclometalated
Ir(III) complexes, although details of the reaction mecha-
nisms involved in the substitutions were not reported, nor
Chart 1
(3) (a) Maestri, M.; Sandrini, D.; Balzani, V.; Chassot, L.; Jolliet, P.; von
€
Zelewsky, A. Chem. Phys. Lett. 1985, 122, 375–379. (b) Bar, L.; Gliemann, G.;
Chassot, L.; von Zelewsky, A. Chem. Phys. Lett. 1986, 123, 264–267.
(c) Sandrini, D.; Maestri, M.; Balzani, V.; Chassot, L.; von Zelewsky, A.
J. Am. Chem. Soc. 1987, 109, 7720–7724. (d) Chassot, L.; von Zelewsky, A.
Inorg. Chem. 1987, 26, 2814–2818. (e) Brooks, J.; Babayan, Y.; Lamansky, S.;
Djurovich, P. I.; Tsyba, I.; Bau, R.; Thompson, M. E. Inorg. Chem. 2002, 41,
3055–3066.
(4) King, K. A.; Spellane, P. J.; Watts, R. J. J. Am. Chem. Soc. 1985, 107,
1431–1432.
Chart 2
(5) (a) Abdel-Shafi, A.; Bourdelande, J. L.; Ali, S. S. Dalton Trans. 2007,
2510–2516. (b) Djurovich, P. I.; Murphy, D.; Thompson, M. E.; Hernandez, B.;
Gao, R.; Hunt, P. L.; Selke, M. Dalton Trans. 2007, 3763–3770. (c) Hsieh, J.-M.;
Ho, M.-L.; Wu, P.-T.; Tsai, T.-T.; Chi, Y. Chem. Commun. 2006, 615–617.
(6) (a) Di Marco, G.; Lanza, M.; Mamo, A.; Stefio, I.; DiPietro, C.;
Romeo, G.; Campagna, S. Anal. Chem. 1998, 70, 5019–5023. (b) DeRosa,
M. C.; Mosher, P. J.; Yap, G. P. A.; Focsaneanu, K.-S.; Crutchley, R. J.; Evanc,
C. E. B. Inorg. Chem. 2003, 42, 4864–4872. (c) Zhang, S.; Hosaka, M.;
Yoshihara, T.; Negish, K.; Iida, Y.; Tobita, S.; Takeuchi, T. Cancer Res. 2010,
70, 4490–4498.
(7) Nagiv, D. A.; Scott, M. E.; MacMillan, D. W. C. J. Am. Chem. Soc.
2009, 131, 10875–10877.
(8) (a) Collin, J.-P.; Dixon, I. M.; Sauvage, J.-P.; Williams, J. A. G.;
Barigelletti, F.; Flamigni, L. J. Am. Chem. Soc. 1999, 121, 5009–5016.
(b) Nazeeruddin, M. K.; Humphry,-Baker, R.; Berner, D.; Rivier, S.; Zuppiroli,
L.; Graetzel, M. J. Am. Chem. Soc. 2003, 125, 8790–8797. (c) Coppo, P.;
Plummer, E. A.; DeCola, L. Chem. Commun. 2004, 1774–1775. (d) Laskar, I. R.;
Hsu, S.-F.; Chen, T.-M. Polyhedron 2005, 24, 189–200. (e) You, Y.; Park, S. Y. J.
Am. Chem. Soc. 2005, 127, 12438–12439. (f) Dedeian, K.; Shi, J.; Forsyth, E.;
Morton, D. C.; Zavalij, P. Y. Inorg. Chem. 2007, 46, 1603–1611. (g) Song, Y.-H.;
Chiu, Y.-C.; Chi, Y.; Cheng, Y.-M.; Lai, C.-H.; Chou, P.-T.; Wong, K.-T.; Tsai,
M.-H.; Wu, C.-C. Chem.;Eur. J. 2008, 14, 5423–5434. (h) Yang, L.; Okuda, F.;
Kobayashi, K.; Nozaki, K.; Tanabe, Y.; Ishii, Y.; Haga, M. Inorg. Chem. 2008, 47,
7154–7165.
(9) (a) Ostrowski, J. C.; Robinson, M. R.; Heeger, A. J.; Bazan, G. C.
Chem. Commun. 2002, 784–785. (b) Okada, S.; Okinaka, K.; Iwawaki, H.;
Furugori, M.; Hashimoto, M.; Mukaide, T.; Kamatani, J.; Igawa, S.; Tsuboyama,
A.; Takiguchi, T.; Ueno, K. Dalton Trans. 2005, 1583–1590. (c) Hwang, F.-M.;
Chen, H.-Y.; Chen, P.-S.; Liu, C.-S.; Chi, Y.; Shu, C.-F.; Wu, F.-I.; Chou, P.-T.;
Peng, S.-M.; Lee, G.-H. Inorg. Chem. 2005, 44, 1344–1353. (d) Obara, S.;
Itabashi, M.; Okuda, F.; Tamaki, S.; Tanabe, Y.; Ishii, Y.; Nozaki, K.; Haga, M.
Inorg. Chem. 2006, 45, 8907–8921. (e) Fang, C.-H.; Chen, Y.-L.; Yang, C. H.;
Chi, Y.; Yeh, Y.-S.; Li, E. Y.; Cheng, Y.-M.; Hsu, C.-J.; Chou, P.-T.; Chen, C.-T.
Chem.;Eur. J. 2007, 13, 2686–2694. (f) Tian, N.; Thiessen, A.; Schiewek, R.;
Schmitz, O. J.; Hertel, D.; Meerholz, K.; Holder, E. J. Org. Chem. 2009, 74,
2718–2725.
(10) (a) Licini, M.; Gareth Williams, J. A. Chem. Commun. 1999, 1943–
1944. (b) Arm, K. J.; Leslie, W.; Gareth Willaims, J. A. Inorg. Chim. Acta 2006,
359, 1222–1232. (c) Zhao, Q.; Liu, S.; Shi, M.; Li, F.; Jing, H.; Yi, T.; Huang, C.
Organometallics 2007, 26, 5952–5930. (d) Chen, H.; Zhao, Q.; Wu, Y.; Li, F.;
Yang, H.; Yi, T.; Huang, C. Inorg. Chem. 2007, 462, 11075–11081. (e) Brandel,
J.; Sairenji, M.; Ichikawa, K.; Nabeshima, T. Chem. Commun. 2010, 46, 3958–
3960.
were the structures of the functionalized Ir complexes, and
their photochemical properties.13
Recently, we have attempted to brominate the three methyl
groups of 1 using N-bromosuccinimide (NBS) (3.3 equiv) and
benzoyl peroxide (BPO) (0.6 equiv) in CCl4 to obtain the Ir
complex having three 2-(40-bromomethylphenyl)pyridine
units as an important intermediate for the synthesis of a
new luminescent sensor for inositol 1,4,5-trisphosphate (Ins-
(1,4,5)P3).14,15 Very interestingly, we found that the three
methyl groups of fac-Ir(tpy)3 were not brominated under
these conditions and that the product was 3a, in which three
protons at the 50-position (p-position with respect to the C-Ir
bond) of phenyl rings in tpy units were substituted by Br
(Chart 2), as described below.
(11) For ruthenium(II) complexes, whose emission spectra change ac-
cording to pH, see: (a) Grigg, R.; Amilaprasadh Norbert, W. D. J. J. Chem.
Soc., Chem. Commun. 1992, 1300–1302. (b) Cargill Thompson, A. M. W.;
Smailes, M. C. C.; Jeffrey, J. C.; Ward, M. D. J. Chem. Soc., Dalton Trans. 1997,
737–743. (c) Higgins, B.; DeGraff, B. A.; Demas, J. N. Inorg. Chem. 2005, 44,
6662–6669.
(12) (a) Stossel, P.; Spreitzer, H.; Bach, I. U.S. Patent. US 2005/0253135
A1. (b) Stossel, P.; Spreitzer, H.; Becker, H. U.S. Patent. US 2006/7125998
B2.
(13) For halogenation and nitration of ruthenium, osmium, and cobalt
complexes such as [Ru(bpy)2(ppy)]þ (bpy = 2,20-bipyridine), see: (a) Collman,
J. P. Angew. Chem. Int. Ed. 1965, 4, 132–138. (b) Gillard, R. D.; Hill, R. E. E.;
Maskill, R. J. Chem. Soc. A. 1970, 1447–1451. (c) Clark, G. R.; Headford, C. E. L.;
Roper, W. R.; Wright, L. L.; Yap, V. P. D. Inorg. Chim. Acta 1994, 220, 261–272. (d)
Chodorowski-Kimmes, S.;Beley, M.;Collins, J.-P.;Sauvage, J.-P. Tetrahedron Lett.
1996, 37, 2963–2966. (e) Coudret, C.; Fraysse, S.; Launay, J.-P. Chem. Commun.
1998, 663–664. (f) Clark, A. M.; Rickard, C. E. F.; Roper, W. R.; Wright, L. J. J.
Organomet. Chem. 2000, 598, 262–275.
(14) For our previous luminescent sensor for Ins(1,4,5)P3, see: Aoki, S.;
Zulkefeli, M.; Shiro, M.; Kohsako, M.; Takeda, K.; Kimura, E. J. Am.
Chem. Soc. 2005, 127, 9129–9139.
(15) For reviews about receptors and sensors of phosphates and other
anions, see: (a) Kimura, E.; Koike, T.; Shionoya, M. In Structure and
Bonding: Metal Site in Proteins and Models; Sadler, J. P., Ed.; Springer: Berlin,
1997; Vol. 89, pp 1-28. (b) Kimura, E.; Kikuta, E. J. Biol. Inorg. Chem. 2000, 5,
139–155. (c) Aoki, S.; Kimura, E. Rev. Mol. Biotech. 2002, 90, 129–155.
(d) Aoki, S.; Kimura, E. In Comprehensive Coordination Chemistry II; Que, L.
Jr., Tolman, W. B., Eds.; Elsevier Ltd: New York, 2004; Vol. 8, pp 601-640.
(e) Aoki, S.; Kimura, E. Chem. Rev. 2004, 104, 769–787. (f) Kitamura, M.;
Nishimoto, H.; Aoki, K.; Tsukamoto, M.; Aoki, S. Inorg. Chem. 2010, 49, 5316–
5327. (g) Krivickas, S. J.; Tamanini, E.; Todd, M. H.; Watkinson, M. J. Org. Chem.
2007, 172, 8280–8289. (h) Archibald, S. J. Annu. Rep. Prog. Chem., Sect. A 2008,
104, 272–296. (i) Zeng, Z.; Torriero, A. A. J.; Belousoff, M. J.; Bond, A. M.; Spiccia,
L. Chem.;Eur. J. 2009, 15, 10988–10996. (j) Belousoff, M. J.; Gasser, G.;
Graham, B.; Tor, Y.; Spiccia, L. J. Biol. Inorg. Chem. 2009, 14, 287–300.

808 Inorganic Chemistry, Vol. 50, No. 3, 2011
Aoki et al.
Table 1. Results for the Halogenation of 1 and 2
entry
Ir complex
reagent (eq.)
solvent
conditions
product
yielda (%)
1
2
3
4
5
6
7
8
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
NBS (3.3), BPO (0.6)
NBS (3.3)
NBS (3.3)
NBS (3.3)
NBS (3.3)
(nBu)4NBr3 (4.0)
NIS (4.0)
NIS (3.3)
CCl4
CCl4
reflux, 1 day
reflux, 12 h
r.t., 10 min
r.t., 10 min
r.t., 10 min
r.t., 1 h
3a
3a
3a
3a
3a
3a
3b
3b
3b
5
4a
4a
4a
4b
4b
6
64
61
96
82
80
71
89
60
70
52
55
76
62
55
32
61
MeCN
CH2Cl2
Acetone
MeCN
MeCN
CCl4
MeCN
MeCN
CCl4
r.t.,1 day
reflux, 2 h
r.. 16 hr
r.t., 1 day
reflux, 1 day
reflux, 12 h
reflux, 1 h
reflux, 1 day
reflux, 1 day
reflux, 1 day
9
(BnMe3)N ICl2 (4.0)
3
10
11
12
13
14
15
16
NCS (6.9)
NBS (3.3), BPO (0.6)
NBS (3.3)
NBS (3.3)
CCl4
MeCN
MeCN
MeCN
MeCN
NIS (3.3)
(BnMe3)N ICl2 (6.6)
NCS (6.4)
3
a Isolated yield.
In this manuscript, the results of the regioselective halogena-
tion (giving 3-6), formylation (giving 7 and 8), acetylation
(giving 9 from 2), and nitration (giving 10 and 11) of 1 and 2
and their subsequent conversions are reported (Chart 2).
Among the various derivatives prepared in this work, car-
boxy and amino derivatives represent potentially useful
intermediates for introduction of various functionalities onto
Ir complexes. Thus, it was expected that the well-defined C3-
symmetric structure of a cyclometalated Ir(III) complex
could be a potential platform for design and synthesis of
useful luminescent and photochemical tools in photochem-
istry, biological chemistry, analytical chemistry, medicinal
chemistry, material science, and related area. In addition, the
tris(50-amino) derivative of Ir(tpy)3, Ir(atpy)3 12 (atpy=2-(50-
amino-40-tolyl)pyridine), was prepared from 10. The findings
indicate that 12 emits a red luminescence at about 600 nm,
and its emission is blue-shifted to about 500 nm upon the
addition of a sufficiently strong acid to protonate the amino
groups of 12. The pH-dependent and reversible change in the
emission of 12 is also reported.
(silica gel) TLC plate and Fuji Silysia Chemical FL-100D, respec-
tively. Density Functional Theory (DFT) calculations were per-
formed using Gaussian 03 at the B3LPY/LanL2DZ basis level.
Synthesis. Improved Method for the Synthesis of fac-
Tris[2-(40-tolyl)pyridine]iridium(III) (1)2c,d,f-h,k,l,3,16 (Chart 1). A
mixture of 2-(40-tolyl)pyridine (7.6 g, 45.0 mmol), Na2SO4
(5 g, 35.2 mmol), and IrCl3 3H2O (529 mg, 1.50 mmol) in
3
dioxane/H2O (1/1, 120 mL) was stirred at the reflux temperature
for 1 day. After cooling to room temperature, the mixture was
concentrated under reduced pressure. After adding 30 mL of water,
the solution was extracted with CHCl3 three times. The combined
organic layer was concentrated under reduced pressure, to which
Na2SO4 (5 g, 35.2 mmol) and dioxane/H2O (1/1, 120 mL) were
added, and the resulting mixture was stirred at the reflux tempera-
ture for 1 day. After repeating this treatment once more, the
mixture was concentrated under reduced pressure. After adding
30 mL of water, the solution was extracted three times with CHCl3.
The combined organic layer was dried over Na2SO4, filtered, and
concentrated under reduced pressure, and the resulting residue was
purified by silica gel column chromatography (CHCl3/hexane, 3:2)
to afford 1 as a yellow powder (972 mg, 93% yield).
fac-Tris[2-(50-bromo-40-tolyl)pyridine]iridium(III) (3a) (Entry 1
in Table 1). N-Bromosuccinimide (35 mg, 196 μmol) and benzoyl
peroxide (10 mg, 41 μmol) were added to a solution of 1 (41 mg,
59 μmol) in CCl4 (2.5 mL), and the whole was stirred at the reflux
temperature for 1 day. After cooling to room temperature, the
insoluble materials were removed by filtration. The filtrate was
concentrated under reduced pressure, and the resulting residue
was purified by silica gel column chromatography (hexane/
AcOEt, 1:3) to afford 3a as a yellow powder (35 mg, 64% yield).
Mp >300 °C. IR (KBr): ν = 3026, 2917, 1601, 1560, 1468, 1421,
1354, 1256, 1157, 1065, 1034, 879, 780, 748, 605 cm-1. 1H NMR
(300 MHz, CDCl3/TMS): δ = 7.80 (d, J = 7.7 Hz, 3H), 7.75 (s,
3H), 7.61 (t, J = 7.1 Hz, 3H), 7.41 (d, J = 4.4 Hz, 3H), 6.87 (t,
J = 6.1 Hz, 3H), 6.65 (s, 3H), 2.18 (s, 9H). MS (m/z). Calcd for
C36H27Br3IrN3 (Mþ): 932.9364 Found: 932.9351. Anal. Calcd
for C36H27Br3IrN3: C, 46.32; H, 2.91; N, 4.50%. Found: C,
46.45; H, 2.73; N, 4.41%.
Experimental Section
General Information. IrCl3 3H2O and Cu(NO3)2 3H2O were
3
3
purchased from KANTO CHEMICAL Co., Inc. Anhydrous
acetonitrile (MeCN) and dimethylformamide (DMF) were ob-
tained by distillation from CaH2. All aqueous solutions were
prepared using deionized water. Melting points were measured
€
on a Buchi 510 Melting Point Apparatus and a YANACO
MP-33 Micro Melting Point Apparatus and listed without
corrections. For measurement of UV-vis and luminescence
spectra in aqueous solution at given pHs, buffer solutions
(CAPS, pH 10.0; CHES, pH 9.0; EPPS, pH 8.0; HEPES, pH
7.0; MES, pH 6.0; acetic acid/sodium acetate, pH 5.0, 4.0, and
3.0) were used, and the ionic strengths were appropriately
adjusted with NaNO3. The Good’s buffer reagents (Dojindo)
were obtained from commercial sources: MES (2-morpholino-
ethanesulfonic acid, pKa = 4.8), HEPES (2-[4-(2-hydroxyethyl)-
1-piperazinyl]ethanesulfonic acid, pKa = 7.5), EPPS (3-[4-(2-
hydroxyethyl)-1-piperazinyl]propanesulfonic acid, pKa = 8.0),
CHES (2-(cyclohexylamino)ethanesulfonic acid, pKa = 9.5),
CAPS (3-(cyclohexylamino)propanesulfonic acid, pKa = 10.4).
IR spectra were recorded on a JASCO FTIR410 and a Perkin-
Elmer FTIR-Spectrum 100 (ATR) at room temperature. 1H
NMR (300 MHz) were recorded on a JEOL Always 300 spectro-
meter. Elemental analyses were performed on a Perkin-Elmer
CHN 2400 analyzer. Thin-layer chromatography (TLC) and silica
gel column chromatographies were performed using a Merck 5554
fac-Tris[2-(50-bromo-40-tolyl)pyridine]iridium(III) (3a) (Entry 3
in Table 1). N-Bromosuccinimide (17 mg, 93 μmol) was added to
a solution of 1 (20 mg, 28 μmol) in MeCN (5 mL) in the dark.
After stirring at room temperature for 10 min, the reaction mix-
ture was concentrated under reduced pressure, and the resulting
(16) (a) McDonald, A. R.; Lutz, M.; von Chrzanowski, L. S.; van Klink,
G. P. M.; Spek, A. L.; van Koten, G. Inorg. Chem. 2008, 47, 6681–6691.
(b) Stossel, P.; Fortte, R.; Parham, A.; Breuning, E.; Heil, H.; Vestweber, H. U.S.
Patent US 2008/0312396 A1. An improved method for the synthesis of 1 by us is
described in the Experimental Section.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 809
residue was purified by silica gel column chromatography
(CHCl3) to afford 3a as a yellow powder (25 mg, 96% yield).
fac-Tris[2-(50-iodo-40-tolyl)pyridine]iridium(III) (3b) (Entry 7
in Table 1). N-Iodosuccinimide (39 mg, 172 μmol) was added to
a solution of 1 (30 mg, 43 μmol) in MeCN (7.5 mL) in the dark.
After stirring at the reflux temperature for 1 day, the reaction
mixture was concentrated under reduced pressure, and the
resulting residue was purified by silica gel column chromato-
graphy (hexane/CHCl3, 2:1) to afford 3b as a yellow powder
(41 mg, 89% yield). Mp > 300 °C. IR (KBr): ν = 3220, 2853,
1594, 1472, 1421, 1295, 1264, 1194, 1155, 1136, 1006, 874, 828,
under reduced pressure, and the resulting residue was purified
by silica gel column chromatography (hexane/CHCl3, 1:2) to
afford 6 as a yellow powder (19 mg, 61% yield). Mp > 300 °C.
IR (KBr): ν = 3632, 3077, 2923, 2852, 1720, 1600, 1563, 1477
cm-1. 1H NMR (300 MHz, CDCl3/TMS): δ = 7.88 (d, J = 8.2
Hz, 3H), 7.71 (td, J = 8.2, 1.6 Hz, 3H), 7.55 (d, J = 2.2 Hz, 3H),
7.07 (dd, J = 4.4 Hz, 3H), 6.82-6.92 (m, 6H). MS (m/z). Calcd
for C33H18Cl6IrN3 (Mþ): 856.9222, Found: 856.9232. Anal.
Calcd for C33H18Cl6IrN3 2.5CHCl3: C, 43.39; H, 2.10; N,
3
4.28%. Found: C, 43.06; H, 1.92; N, 4.64%.
fac-Tris[2-(50-formyl-40-tolyl)pyridine]iridium(III) (7) (Chart 4).
Phosphorus oxychloride (0.3 mL) was added dropwise to DMF
(3 mL), and the resulting mixture was stirred at room tempera-
ture for 1 h, after which 1 (100 mg, 145 μmol) was added to
obtain a yellow solution. After stirring at 80 °C for 16 h, the
deep-red colored reaction mixture was allowed to cool at 0 °C,
and 1 M NaOH (9 mL) was then added. After stirring at room
temperature for 12 h, the yellow solid was isolated by filtration
and washed with 10 mL of water to afford 7 as a yellow powder
(109 mg, 98% yield). Mp > 300 °C. IR (KBr): ν = 3444, 2921,
2846, 2723, 1673, 1601, 1577, 1473, 1207, 1066, 929, 782, 750
783, 751, 739, 641, 583 cm-1 1H NMR (300 MHz, CDCl3/
.
TMS): δ = 7.99 (s, 3H), 7.79 (d, J = 8.2 Hz, 3H), 7.60 (t, J = 8.2
Hz, 3H), 7.40 (d, J = 5.5 Hz, 3H), 6.86 (t, J = 5.9 Hz, 3H), 6.68
(s, 3H), 2.21 (s, 9H). MS (m/z). Calcd for C36H27I3IrN3 (Mþ):
1074.8945, Found: 1074.8938. Anal. Calcd for C36H27I3IrN3: C,
40.24; H, 2.53; N, 3.91%. Found: C, 40.61; H, 2.22; N, 4.04%.
fac-Tris[2-(50-bromophenyl)pyridine]iridium(III) (4a) (Entry 12
in Table 1). N-Bromosuccinimide (18 mg, 100 μmol) was added to
a solution of 2 (20 mg, 31 μmol) in CCl4 (10 mL) in the dark. The
reaction mixture was stirred at the reflux temperature for 12 h and
concentrated under reduced pressure. The resulting residue was
purified by silica gel column chromatography (hexane/CHCl3, 1:2)
to afford 4a as a yellow powder (21 mg, 76% yield). Mp > 300 °C.
IR (KBr): ν = 3033, 3012, 2987, 2948, 2854, 2339, 1733, 1716,
1
cm-1. H NMR (300 MHz, CDCl3/TMS): δ = 10.19 (s, 3H),
8.09 (s, 3H), 8.03 (d, J = 8.4 Hz, 3H), 7.71 (t, J = 8.3 Hz, 3H),
7.45 (d, J = 5.3 Hz, 3H), 6.97 (t, J = 5.4 Hz, 3H), 6.70 (s, 3H),
2.44 (s, 9H). MS (m/z) Calcd for C39H30IrN3O3 (Mþ): 779.1894,
Found: 779.1891. Anal. Calcd for C39H30IrN3O3: C, 59.98; H,
3.87; N, 5.38%, Found: C, 59.94; H, 3.44; N, 5.48%.
1
1698, 1683, 1652, 1558, 1540, 1471, 1417 cm-1. H NMR (300
MHz, CDCl3/TMS): δ= 7.84(d, J = 7.9 Hz, 3H), 7.73 (d, J = 1.8
Hz, 3H), 7.64 (t, J = 8.3 Hz, 3H), 7.48 (d, J = 5.5 Hz, 3H), 6.92
(t, J = 7.5 Hz, 3H), 6.91 (dd, J = 8.2, 1.8 Hz, 3H), 6.66 (dd, J =
8.1, 1.5 Hz, 3H). MS (m/z). Calcd for C33H21Br3IrN3 (Mþ):
886.8870, Found: 886.8860. Anal. Calcd for C33H21Br3IrN3: C,
44.15; H, 2.39; N, 4.74%. Found: C, 44.23; H, 2.36; N, 4.68%.
fac-Tris[2-(50-iodophenyl)pyridine]iridium(III) (4b) (Entry 14
in Table 1). N-Iodosuccinimide (39 mg, 173 μmol) was added to
a solution of 2 (34 mg, 53 μmol) in CH2Cl2 (13 mL) in the dark,
and the reaction mixture was stirred at the reflux temperature
for 1 day. The reaction mixture was concentrated under reduced
pressure, and the resulting residue was purified by silica gel
column chromatography (hexane/CHCl3, 1:2) to afford 4b as a
yellow powder (30 mg, 55% yield). Mp >300 °C. IR (KBr): ν =
3038, 2244, 1600, 1557, 1467, 1414, 1306, 1251, 1133, 1059, 1024,
872, 823, 780, 750, 737, 685, 637, 568 cm-1. 1H NMR (300 MHz,
CDCl3/TMS): δ = 7.90 (d, J = 1.8 Hz, 3H), 7.84 (d, J = 7.9 Hz,
3H), 7.65 (td, J = 7.1, 1.6 Hz, 3H), 7.46 (d, J = 4.4 Hz, 3H), 7.07
(dd, J = 8.1, 1.8 Hz, 3H), 6.93 (t, J = 6.1 Hz, 3H), 6.55 (d,
J = 7.9 Hz, 3H). MS (m/z). Calcd for C33H21I3IrN3 (Mþ):
1030.8476, Found: 1030.8469. Anal. Calcd for C33H21I3IrN3: C,
38.39; H, 2.05; N, 4.07%. Found: C, 38.54; H, 1.85; N, 4.01%.
fac-Tris[2-(30,50-dichloro-40-tolyl)pyridine]iridium(III) (5)
(Entry 10 in Table 1). N-Chlorosuccinimide (30 mg, 224 μmol)
was added to a solution of 1 (24 mg, 33 μmol) in MeCN (8 mL) in
the dark, and the whole reaction mixture was stirred at room
temperature for 1 day. The reaction mixture was concentrated
under reduced pressure, and the resulting residue was purified
by silica gel column chromatography (hexane/CHCl3, 1:2) to
afford 5 as a yellow powder (16 mg, 52% yield). Mp. > 300 °C.
IR (KBr): ν = 3648, 2946, 2921, 2852, 2337, 1733, 1716, 1698,
1683, 1652, 1558, 1540, 1506, 1455 cm-1. 1H NMR (300 MHz,
CDCl3/TMS): δ = 7.84 (d, J = 8.4 Hz, 3H), 7.67 (td, J = 8.0,
1.6 Hz, 3H), 7.60 (s, 3H), 7.02 (d, J = 4.6 Hz, 3H), 6.82 (td,
J = 6.6, 1.1 Hz, 3H), 2.33 (s, 9H). MS (m/z). Calcd for
C36H24Cl6IrN3 (Mþ): 898.9722, Found: 898.9702. Anal. Calcd
for C36H24Cl6IrN3: C, 47.86; H, 2.68; N, 4.65%. Found: C,
47.66; H, 2.39; N, 4.52%.
fac-Tris{2-[(50-hydroxymethyl)-40-tolyl]pyridine}iridium(III)
3
2.5H2O (15) (Chart 4). NaBH4 (51 mg, 1.4 mmol) was added to
a solution of 7 (53 mg, 68 μmol) in EtOH (7 mL). The reaction
mixture was stirred at room temperature for 12 h. The insolu-
ble compounds were isolated by filtration and washed with
water to afford 15 as a yellow powder (53 mg, 94% yield).
Mp > 300 °C. IR (KBr): ν = 3421, 1596, 1472, 1426, 1261, 1160,
1
1068, 993, 923, 877, 785, 750, 633 cm-1. H NMR (300 MHz,
DMSO-d6/TMS): δ = 8.01 (d, J = 8.4 Hz, 3H), 7.74 (t, J = 9.0
Hz, 3H), 7.64 (s, 3H), 7.33 (d, J = 4.8 Hz, 3H), 7.02 (t, J = 7.0
Hz, 3H), 6.50 (s, 3H), 4.36 (s, 6H), 1.97 (s, 9H). MS (m/z). Calcd
for C39H36IrN3O3 (Mþ): 785.2362, Found: 785.2366. Anal.
Calcd for C39H36IrN3O3 2.5H2O: C, 56.30; H, 4.97; N,
3
5.05%, Found: C, 56.13; H, 4.46; N, 4.98%.
fac-Tris{2-[(50-hydroxymethyl)phenyl]pyridine}iridium(III)
3
0.5H2O (16) (Chart 4). Phosphorus oxychloride (0.3 mL) was
added to DMF (1.5 mL), and the resulting mixture was stirred at
room temperature for 1 h, to which 2 (50 mg, 76 μmol) was
added. After stirring at 80 °C for 16 h, the deep-red colored
reaction mixture was allowed to cool at 0 °C, and 1 M NaOH
(4.5 mL) was then added. After stirring at room temperature for
12 h, the yellow solid was isolated by filtration and washed with
10 mL of water to afford 8 as a yellow powder (50 mg, 88%
yield). Mp > 300 °C. IR (KBr): ν = 2954, 2921, 2850, 1720,
1666, 1579, 1475, 1411, 1355, 1245, 1027, 784, 752, 485, 410
cm-1. 1H NMR (300 MHz, CDCl3/TMS): δ = 9.88 (s, 3H), 8.19
(d, J = 1.5 Hz, 3H), 8.10 (d, J = 8.4 Hz, 3H), 7.76 (td, J = 7.3,
1.5 Hz, 3H), 7.52 (d, J = 4.8 Hz, 3H), 7.26 (dd, J = 7.7, 1.6 Hz,
3H), 7.04 (t, J = 6.1 Hz, 3H), 6.98 (d, J = 7.7 Hz, 3H). MS (m/z).
Calcd for C36H24IrN3O6 (Mþ): 739.1447, Found: 739.1459.
NaBH4 (16 mg, 423 μmol) was added to a solution of 8
(15 mg, 20 μmol) in EtOH (1.5 mL). The reaction mixture was
stirred at room temperature for 7 h. The insoluble compounds were
filtered off and washed with water to afford 16 as a yellow powder
(13 mg, 86% yield from 8). Mp > 300 °C. IR (KBr): ν = 3221,
2854, 1595, 1541, 1473, 1454, 1422, 1296, 1265, 1195, 1007, 829, 740,
642 cm-1. 1H NMR (300 MHz, DMSO-d6/TMS): δ = 8.08 (d, J =
8.1 Hz, 3H), 7.76 (t, J = 6.9 Hz, 3H), 7.67 (s, 3H), 7.44 (d, J = 5.1
Hz, 3H), 7.09 (t, J = 6.6 Hz, 3H), 6.60-6.67 (m, 6H), 4.33 (s, 6H).
MS (m/z). Calcd for C36H30IrN3O3 (Mþ): 743.1893, Found:
fac-Tris[2-(30,50-dichlorophenyl)pyridine]iridium(III) 2.5CHCl3
3
(6) (Entry 16 in Table 1). N-Chlorosuccinimide (23 mg, 174 μmol)
was added to a solution of 2 (18 mg, 27 μmol) in MeCN (5 mL) in
the dark and the whole reaction mixture was stirred at the reflux
temperature for 1 day. The reaction mixture was concentrated
743.1902. Anal. Calcd for C36H30IrN3O3 0.5H2O: C, 57.36; H,
3
4.14; N, 5.57%, Found: C, 57.09; H, 4.27; N, 5.78%.

810 Inorganic Chemistry, Vol. 50, No. 3, 2011
Aoki et al.
fac-Tris[2-(50-carboxyl-40-tolyl)pyridine]iridium(III) 3H2O (17)
(Chart 4). A mixture of NaClO2 (320 mg, 3.6 mmol) and
NaH2PO4 2H2O (1.11 g, 7.1 mmol) in water (4 mL) was added
(s, 9H). MS (m/z). Calcd for C39H33IrN6O3 (Mþ): 823.2141,
Found: 823.2150. Anal. Calcd for C39H33IrN6O3 2.5H2O: C,
3
3
53.78; H, 4.40; N, 9.65%, Found: C, 54.11; H, 4.39; N, 9.38%.
fac-Tris[2-(50-cyano-40-tolyl)pyridine]iridium(III) H2O (22)
3
dropwise to a solution of 7 (309 mg, 0.40 mmol) and 2-methyl-
2-butene (830 mg, 12 mmol) in DMSO (16 mL) at room tempera-
ture. After stirring at room temperature for 12 h, the mixture
was concentrated under reduced pressure, to which 1 M aq. HCl
was added. The resulting solid was filtered off and washed with
water and MeOH to afford 17 as a yellow powder (260 mg, 74%
yield). Mp > 300 °C. IR (KBr): ν = 3415, 2965, 1683, 1583,
1473, 1238, 1054, 1031, 781 cm-1. 1H NMR (300 MHz, CDCl3/
TMS): δ = 8.23 (s, 3H), 8.16 (d, J = 8.2 Hz, 3H), 7.84 (t, J = 7.9
Hz, 3H), 7.42 (d, J = 5.9 Hz, 3H), 7.17 (t, J = 7.1 Hz, 3H), 6.57
(s, 3H), 2.24 (s, 9H). MS (m/z). Calcd for C39H30IrN3O6 (Mþ):
3
(Chart 5). Ac2O (2 mL) was added to 21 (22 mg, 25 μmol),
and the reaction mixture was stirred at 140 °C for 2 h. The
reaction mixture was concentrated under reduced pressure, and
the resulting residue was washed with water to afford 22 as a
yellow powder (20 mg, quant.). Mp > 300 °C. IR (KBr): ν =
2921, 2212, 1759, 1585, 1473, 1424, 1382, 1315, 1270, 1240, 1215,
1158, 1065, 1021, 914, 888, 783, 666, 640 cm-1. 1H NMR (300
MHz, CDCl3/TMS): δ = 7.88 (d, J = 8.4 Hz, 3H), 7.82 (s, 3H),
7.72 (t, J = 7.2 Hz, 3H), 7.42 (d, J = 4.8 Hz, 3H), 7.00 (t, J = 6.0
Hz, 3H), 6.66 (s, 3H), 2.31 (s, 9H). MS (m/z). Calcd for
C39H27IrN6 (Mþ): 770.1903, Found: 770.1904. Anal. Calcd
827.1742, Found: 827.1735. Anal. Calcd for C39H30IrN3O6
3H2O: C, 53.05; H, 4.11; N, 4.76%, Found: C, 52.75; H, 3.78; N,
4.51%.
3
for C39H27IrN6 H2O: C, 59.37; H, 3.70; N, 10.65%, Found:
C, 59.04; H, 3.96; N, 10.61%.
3
fac-Tris[2-(50-carboxylphenyl)pyridine]iridium(III) 3H2O (18)
(Chart 4). A mixture of NaClO2 (220 mg, 2.3 mmol) and
NaH2PO4 2H2O (0.76 g, 4.9 mmol) in water (3 mL) was added
fac-Tris[2-(50-aminomethyl-40-tolyl)pyridine]iridium(III) 3H2O
(20) (Chart 5). BH3 THF (2 mL, 1.08 M) was added to a
3
3
3
solution of 22 (48 mg, 62 μmol) in THF (1 mL). After stirring
at room temperature for 1 day, 1 M aq. HCl (1 mL) was added
to the reaction mixture, followed by addition of 1 M aq. NaOH
(3 mL). The solution was extracted with CHCl3, and the
combined organic layer was dried over Na2SO4, filtered, and
concentrated under reduced pressure to afford 20 as a yellow
powder (22 mg, 42% yield). Mp > 300 °C. IR (KBr): ν = 3365,
2925, 1662, 1585, 1561, 1472, 1425, 1385, 1263, 1242, 1208, 1158,
3
dropwise to a solution of 8 (15 mg, 20 μmol) and 2-methyl-2-
butene (570 mg, 8.2 mmol) in MeCN (1 mL) at 70 °C. After
stirring for 12 h, the mixture was cooled to room temperature
and concentrated under reduced pressure. The resulting solid
was washed with water and MeOH to afford 18 as a yellow
powder (10 mg, 59% yield). Mp > 300 °C. IR (KBr): ν = 3064,
3046, 1716, 1698, 1683, 1671, 1652, 1635, 1587 cm-1. 1H NMR
(300 MHz, CDCl3/TMS): δ = 8.35 (s, 3H), 8.16 (d, J = 8.2 Hz,
3H), 7.83 (t, J = 7.0 Hz, 3H), 7.66 (d, J = 5.3 Hz, 3H), 7.30 (d,
J = 7.9 Hz, 3H), 7.07 (t, J = 6.4 Hz, 3H), 6.85 (d, J = 7.9 Hz,
3H). MS (m/z). Calcd for C36H24IrN3O6 (Mþ): 785.1272,
1068, 1021, 931, 885, 750, 701 cm-1 1H NMR (300 MHz,
.
CDCl3/TMS): δ = 7.70 (d, J = 7.7 Hz, 3H), 7.48 (t, J = 7.5
Hz, 3H), 7.43 (d, J = 4.0 Hz, 3H), 7.06 (s, 3H), 6.74 (t, J = 6.0
Hz, 3H), 6.55 (s, 3H), 3.65 (s, 6H), 2.00 (s, 9H). MS (m/z). Calcd
for C39H39IrN6 (Mþ): 782.2842, Found: 782.2842. Anal. Calcd
Found: 785.1268. Anal. Calcd for C36H24IrN3O6 3H2O: C,
3
51.42; H, 3.84; N, 5.00%, Found: C, 51.20; H, 3.43; N, 4.95%.
Compound 19 MeOH (Chart 4). N,N-Diisopropylethyl-
for C39H39IrN6 3H2O: C, 55.90; H, 5.41; N, 10.03%, Found: C,
55.54; H, 4.97; N, 9.66%.
3
3
fac-Tris[2-(50-acetylphenyl)pyridine]iridium(III) 4H2O (9)
amine, (iPr)2NEt, (56 mg, 433 μmol) and PyBOP (226 mg, 434
μmol) were added to a solution of 17 (90 mg, 107 μmol) and
N-tert-butyloxycarbonyl-1,2-ethylenediamine17 (69 mg, 431 μmol)
in DMF (15 mL). The reaction mixture was stirred at room
temperature for 10 h. The reaction mixture was concentrated
under reduced pressure, and the resulting residue was extracted
three times with CHCl3. The combined organic layer was dried
over Na2SO4, filtered, and concentrated under reduced pres-
sure, and the resulting residue was purified by silica gel column
chromatography (CHCl3/MeOH, 10:1) to afford 19 (87 mg,
64% yield) as a yellow powder. Mp > 300 °C. IR (KBr): ν =
2934, 1631, 1586, 1530, 1474, 1424, 1366, 1248, 1164, 1072, 998,
912, 778, 752, 672 cm-1. 1H NMR (300 MHz, CDCl3/TMS): δ
= 7.87 (d, J = 8.2 Hz, 3H), 7.76 (s, 3H), 7.55 (t, J = 7.5 Hz, 3H),
7.36 (d, J = 5.0 Hz, 3H), 6.83 (t, J = 6.2 Hz, 3H), 6.69 (s, 3H),
6.43 (brs, 3H), 5.11 (brs, 3H), 3.47-3.54 (m, 6H), 3.30-3.40 (m,
6H), 2.24 (s, 9H), 1.39 (s, 27H). MS (m/z). Calcd for C60H72Ir-
N9O9 (Mþ): 1256.5177 Found: 1256.5155. Anal. Calcd for
3
(Chart 6). Acetyl chloride (5 μL, 70 μmol) and AlCl3 (10 mg,
74 μmol) were added to a solution of 2 (9 mg, 14 μmol) in
1,2-dichloroethane (4 mL). The reaction mixture was stirred at
0 °C for 10 min. The insoluble compounds were collected by
filtration and washed with water to afford 9 as a yellow powder
(8 mg, 67%). Mp > 300 °C. IR (KBr): ν = 3461, 3044, 1664,
1578, 1528, 1476, 1411, 1354, 1300, 1245, 1159, 1061, 1027, 962,
827, 784, 751, 714, 670 cm-1 1H NMR (300 MHz, CDCl3/
.
TMS): δ = 8.32 (d, J = 1.8 Hz, 3H), 8.09 (d, J = 8.2 Hz, 3H), 7.72
(td, J= 7.5, 1.5 Hz, 3H), 7.51 (d, J= 4.8 Hz, 3H), 7.37 (dd, J=8.1,
1.8 Hz, 3H), 7.00 (t, J = 6.6 Hz, 3H), 6.84 (d, J = 7.9 Hz, 3H), 2.51
(s, 9H). MS (m/z). Calcd for C39H30IrN3O3 (Mþ): 781.1911,
Found: 781.1901. Anal. Calcd for C39H30IrN3O3 4H2O: C, 54.92;
H, 4.49; N, 4.92%, Found: C, 54.47; H, 4.03; N, 4.90%.
3
fac-Tris[2-(50-nitro-40-tolyl)pyridine]iridium(III) CH2Cl2 (10)12
3
(Chart 7). Cu(NO3)2 3H2O (25 mg, 103 μmol) was added to a
3
solution of 1 (48 mg, 69 μmol) in Ac2O (2 mL) at 0 °C, and the
reaction mixture was stirred at room temperature for 1 day.
After 5 mL of water was added, the solution was extracted three
times with CHCl3. The combined organic layer was dried over
Na2SO4, filtered, and concentrated under reduced pressure, and
the resulting residue was purified by silica gel column chroma-
tography (CH2Cl2) to afford 10 as an orange powder (56 mg,
89% yield). Mp > 300 °C. IR (KBr): ν = 2803, 1591, 1563,
1547, 1489, 1422, 1364, 1283, 1199, 1161, 1069, 1023, 918, 822,
C60H72IrN9O9 MeOH: C, 56.90; H, 5.95; N, 9.79%. Found:
3
C, 56.53; H, 5.82; N, 9.42%.
fac-Tris[2-(50-hydroxyimino-40-tolyl)pyridine]iridium(III) 2.5H2O
3
(21) (Chart 5). Hydroxylamine monohydride (31 mg, 445 μmol)
was added to a solution of 7 (39 mg, 49 μmol) in MeOH (8 mL).
The reaction mixture was stirred at room temperature for 2 h.
The reaction mixture was concentrated under reduced pressure,
and the resulting residue was washed with water to afford 21 as a
yellow powder (41 mg, 96% yield). Mp > 300 °C. IR (KBr): ν =
2982, 2214, 1662, 1583, 1521, 1473, 1424, 1383, 1263, 1242, 1221,
786, 759, 719, 699, 637 cm-1 1H NMR (300 MHz, CDCl3/
.
TMS): δ = 8.44 (s, 3H), 8.04 (d, J = 8.2 Hz, 3H), 7.79 (t, J = 7.7
Hz, 3H), 7.45 (d, J = 5.0 Hz, 3H), 7.05 (t, J = 6.8 Hz, 3H), 6.71
(s, 3H), 2.44 (s, 9H). MS (m/z). Calcd for C36H27IrN6O6 (Mþ):
1
1158, 1068, 936, 889, 827, 782, 749, 673 cm-1. H NMR (300
MHz, Acetone-d6/TMS): δ = 9.88 (s, 3H), 8.25 (s, 3H), 8.07 (d,
J = 8.2 Hz, 3H), 8.00 (s, 3H), 7.78 (t, J = 7.5 Hz, 3H), 7.60 (d,
J = 5.1 Hz, 3H), 7.06 (t, J = 5.9 Hz, 3H), 6.75 (s, 3H), 2.15
832.1629. Found: 832.1616. Anal. Calcd for C36H27IrN6O6
CH2Cl2: C, 48.47; H, 3.19; N, 9.17%. Found: C, 48.38; H, 2.89;
N, 8.96%.
3
fac-Tris[2-(50-nitrophenyl)pyridine]iridium(III) (11)12 (Chart 7).
(17) Demonchauxi, P.; Ganellinl, C. R.; Dunn, P. M.; Haylett, D. G.;
Jenkinson, D. H. Eur. J. Med. Chem. 1991, 26, 915–920.
Cu(NO3)2 3H2O (22 mg, 92 μmol) was added to a solution of 2
3

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 811
˚
(40 mg, 61 μmol) in Ac2O (2 mL) at 0 °C. The reaction mixture
was stirred at room temperature for 1 day. After adding water
(5 mL), the solution was extracted three times with CHCl3. The
combined organic layer was dried over Na2SO4, filtered, and
concentrated under reduced pressure, and the resulting residue
was purified by silica gel column chromatography (CH2Cl2)
to afford 11 as an orange powder (50 mg, quant.). Mp > 300 °C.
IR (KBr): ν = 2923, 2854, 1563, 1492, 1322, 1106, 1047, 1027,
Cubic, space group P213 (#198), a = 22.5283(4) A, V =
11433.7(4) A , Z = 12, Dcalc = 1.872 g/cm3, 7069 measured
3
˚
reflections, 6945 reflections with I > 2σ(I), 2θmax = 50.96°, R1
(wR2) = 0.035 (0.0949), GOF = 1.054, Flack parameter =
0.03(1). CCDC 770685 contains the supplementary crystallo-
graphic 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.
1
881, 786, 754 cm-1. H NMR (300 MHz, CDCl3/TMS): δ =
Crystal Data for 3b. C36H27I3IrN3 1.67(CHCl3), Mr =
1273.57, a yellow crystal, crystal size 0.12 ꢀ 0.10 ꢀ 0.08 mm,
3
8.54 (d, J = 2.4 Hz, 3H), 8.12 (d, J = 7.9 Hz, 3H), 7.84 (t, J =
7.7 Hz, 3H), 7.67 (dd, J = 8.4, 2.0 Hz, 3H), 7.51 (d, J = 5.5 Hz,
3H), 7.12 (t, J = 5.7 Hz, 3H), 6.90 (d, J = 8.2 Hz, 3H). MS (m/z).
Calcd for C33H21IrN6O6 (Mþ): 790.1177, Found: 790.1146.
Anal. Calcd for C33H21IrN6O6: C, 50.19; H, 2.68; N, 10.64%,
Found: C, 49.84; H, 2.61; N, 10.37%.
˚
Cubic, space group P213 (#198), a = 22.9303(4) A, V =
12056.6(4) A , Z = 12, Dcalc = 2.105 g/cm3, 7347 measured
3
˚
reflections, 7133 reflections with I > 2σ(I), 2θmax = 50.6°, R1
(wR2) = 0.040 (0.1085), GOF = 1.051, Flack parameter =
0.016(8). CCDC 770686 contains the supplementary crystal-
lographic 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.
fac-Tris[2-(50-amino-40-tolyl)pyridine]iridium(III) 2H2O (12)
3
(Chart 7). A mixture of 10 (60 mg, 72 μmol) and SnCl2 2H2O
3
(244 mg, 1.1 mmol) in EtOH (10 mL) was stirred at 50 °C. After
5 min, NaBH4 (82 mg, 2.16 mmol) was added. After stirring the
solution was stirred at reflux temperature for 30 min and at
room temperature for 30 min, a solution of (Boc)2O (157 mg,
720 μmol) was added, and the whole mixture was stirred at
reflux temperature for 3 h. After cooling to room temperature,
the insoluble materials were filtered off. After 5 mL of water
was added to the filtrate, the solution was three times extracted
with CHCl3. The combined organic layer was dried over
Na2SO4, filtered, and concentrated under reduced pressure,
and the resulting residue was purified by silica gel column
chromatography (CHCl3) to afford 24 (67 mg, 89% yield from
Measurements of UV-vis Absorption and Luminescence Spectra.
Steady-state UV/vis absorption were recorded on a JASCO
V-550 and V-630BIO UV-vis spectrophotometer and lumines-
cence excitation and emission spectra were recorded on a
JASCO FP-6500 and FP-6200 spectrofluorometer, respectively,
at 25.0 ( 0.1 °C. Solution samples were degassed for 10 min
before UV-vis and luminescence measurements. The quantum
yields of luminescence (Φ) were determined by comparison with
the integrated corrected emission spectrum of a quinine sulfate
standard, whose emission quantum yield in 0.1 M H2SO4 was
assumed to be 0.55 (excitation at 366 nm). For the calculation of
emission quantum yields, the following equation was used, in
which Φs and Φr depict the quantum yields of the sample and
reference compound, ηs and ηr are the refractive indexes of the
solvents used for the measurements of the sample and reference,
As and Ar are the absorbance of the sample and the reference,
and Is and Ir stand for the integrated areas under the emission
spectra of the sample and reference, respectively (all Ir com-
pounds for luminescence measurements were excited at 366 nm
in this manuscript). For the determination of Φs in mixed
solvent systems, the η values of main solvents were used for
calculation.
1
10) as a yellow powder. Mp > 300 °C. H NMR (300 MHz,
CDCl3/TMS): δ = 8.08 (s, 3H), 7.84 (d, J = 7.8 Hz, 3H), 7.48
(t, J = 7.2 Hz, 3H), 7.40 (d, J = 5.1 Hz, 3H), 6.75 (t, J =
6.3 Hz, 3H), 6.61 (s, 3H), 6.11 (s, 3H), 2.02 (s, 9H), 1.51 (s, 27H).
MS (m/z). Calcd for C51H57IrN6O6(Mþ): 1040.3938 Found:
1040.3940.
A mixture of TMSCl (31 mg, 285 μmol) and NaI (43 mg,
285 μmol) in MeCN (5 mL) was stirred at room temperature for
15 min, to which 24 (50 mg, 48 μmol) was added. After the whole
was stirred at room temperature for 10 min, the insoluble
compounds were filtered off and washed with CHCl3 and
hexane to afford green compounds, which were purified by
ionic exchange column chromatography (IRA-400 (OH- form))
to give 12 as a red powder (34 mg, 81% from 24). Mp > 300 °C.
IR (KBr): ν = 3319, 1596, 1542, 1468, 1427, 1393, 1294, 1264,
2
2
Φs ¼ Φrðηs ArIsÞ=ðηr AsIrÞ
Cyclic Voltammetry (CV). Cyclic voltammetry measurements
were performed with a BAS model 660A electrochemical analy-
zer at room temperature in DMF containing 0.1 M nBu4N(PF6)
as the supporting electrolyte in a standard one-component cell
under an argon atmosphere equipped with 3-mm outer diameter
glassy carbon working electrode, and a platinum wire counter
electrode, and the Ag/AgCl referenced electrode (Ag/AgCl in
MeCN containing 0.01 M AgNO3 and 0.1 M nBu4N(ClO4)).
All solutions were deoxygenated by argon bubbling for at least
10 min, immediately before measurements.
1
1181, 1061, 781, 747 cm-1. H NMR (300 MHz, DMSO- d6/
TMS): δ = 7.76 (d, J = 7.8 Hz, 3H), 7.67 (t, J = 7.2 Hz, 3H),
7.31 (d, J = 4.8 Hz, 3H), 7.03 (s, 3H), 6.95 (t, J = 6.0 Hz, 3H),
6.33 (s, 3H), 4.09 (br, 6H), 1.81 (s, 9H). MS (m/z). Calcd for
C36H33IrN6 (Mþ): 740.2365, Found: 740.2367. Anal. Calcd for
C36H33IrN6 2H2O: C, 55.58; H, 4.79; N, 10.80%, Found: C,
55.61; H, 4.86; N, 11.11%.
3
Crystallographic Study of 3a and 3b. Fine crystals were ob-
tained from slow evaporation of 3a (C36H27Br3IrN3 CHCl3)
3
and 3b (C33H21Br3IrN3) in CHCl3. All measurements were made
on a Rigaku RAXIS-RAPID imaging plate area detector with
graphite monochromated Mo-KR radiation at 120.1 K for 3a
and 100.1 K for 3b. The structures were solved by direct
methods18 and refined by full-matrix least-squares techniques.
All calculations were performed using the CrystalStructure
(Version 3.8, Rigaku & RAC (2007)) except for refinements,
which were performed with SHELXL-97.19
Results and Discussion
Halogenation of 1 (Ir(tpy)3) and 2 (Ir(ppy)3). After
refluxing a mixture of 1 with NBS and BPO in CCl4 for
1 day, a single product was obtained. Its 1H NMR
(CDCl3/TMS, 300 MHz) spectra (Figure S1 in the Sup-
porting Information) indicated that the methyl groups
of 1 were not brominated (Chart 2) because three methyl
groups were still detected and a singlet signal, corre-
sponding to the 50-proton (H(50)) on the phenyl ring of
the tpy unit, had disappeared, in comparison with data
for the starting material 1 (for the assignment, see Chart 2).
The mass spectrum of the product gave a fragment at
m/z = 933, which corresponds to the tribrominated deriv-
ative of 1 (Figure S1c in the Supporting Information),
Crystal Data for 3a. C36H27Br3IrN3 1.18(CHCl3), Mr =
3
1074.43, a yellow crystal, crystal size 0.17 ꢀ 0.12 ꢀ 0.07 mm,
(18) Burla, M. C.; Caliandro, R.; Camalli, M.; Carrozzini, B.; Cascarano,
G. L.; De Caro, L.; Giacovazzo, C.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 2005, 38, 381–388.
(19) Sheldrick, G. M. SHELX-97, Program for the Refinement of Crystal
€
€
Structures; University of Gottingen: Gottingen, Germany, 1997.

812 Inorganic Chemistry, Vol. 50, No. 3, 2011
Aoki et al.
suggesting that the product is 3a, in which the protons at
the 50-positions of the phenyl rings in the three tpy units
had been substituted with Br.
The halogenation of 1 (Ir(tpy)3) and 2 (Ir(ppy)3) was
examined under several different reaction conditions, and
the results are summarized in Table 1. As stated above,
the bromination of 1 and 2 with NBS in the presence of a
catalytic amount of BPO in CCl4 (under reflux tempera-
ture for 1 day) gave the corresponding tribrominated
compounds, 3a and 4a, respectively, in moderate chemi-
cal yields (entries 1 and 11 in Table 1).
When the bromination was conducted with only NBS
(3.3 equiv) in CCl4, 3a and 4a were produced in moderate
yields (entries 2 and 12). Interestingly, when 1 and 2 were
brominated with NBS in more polar solvents such as
MeCN, CH2Cl2, or acetone (entries 3-5 and 13), the
reaction was much faster than those in CCl4. In addition,
the treatment of 1 with tetrabutylammonium tribromide
((nBu)4NBr3) in MeCN also gave 3a (entry 6). These
results suggest that this bromination likely proceeds via
an ionic mechanism rather than a radical mechanism, as
described below.
Figure 1. Top view(a) and sideview(b) ofstick drawings of 3a(Ir(50-Br-
tpy)3). The three tpy units are shown in light blue, green-yellow, and light
green, Ir in red, and Br in orange.
In the case of the iodination of 1 and 2 (to give 3b and
4b), similar results were obtained, as shown in Table 1
(entries 7-9 and 14-15). Treatment of 1 and 2 with NCS
(3.3 equiv) in MeCN gave the several products. To
investigate this aspect in detail, we treated 1 and 2 with
6 equiv of NCS and obtained 30,50-hexachloro complexes
5 and 6 in moderate yields, as shown in Table 1 (entries 10
and 16). We assume that, because Cl atoms have smaller
diameters than Br or I, this allowed the second aromatic
substitution at the 30-position. On the other hand, the
fluorination of 1 and 2 with 1-fluoro-2,6-dichloropyridi-
nium tetrafluoroborate or N-fluoro-N0- (chloromethyl)-
triethylenediamine bis(tetrafluoroborate) afforded a
complex mixture of products.
Table 2. Representative Parameters for the Crystal Structure Analysis of 3a
and 3b
3a
3b
C (20)-Ir
N (1)-Ir
2.02 2.01
2.13 2.14
˚
bond lengths (A) (averaged values)
C (50)-Br(or I) 1.91 2.11
dihedral angles (deg) (averaged values) C-Ir-C
85.9 85.4
95.8 94.3
95.4 94.9
C-Ir-N
N-Ir-N
Crystal Structures of Tribrominated and Triiodinated
Ir(tpy)3, 3a and 3b. The structure of 3a was confirmed by
an X-ray crystal structure analysis, as shown in Figure 1,
which shows that the 50-position of the three phenyl
groups are all substituted with Br. The averaged N-
Chart 3
˚
(tpy)-Ir and C(tpy)-Ir bond distances are 2.13 A and
2.02 A, which are almost identical to the reported values
˚
for 1, 2, and related Ir complexes.2d,g,h,k,l,9b The averaged
˚
C-Br bond distance was 1.91 A.
The crystal structure of 3b is displayed in Figure S2
in the Supporting Information, which shows that the 50-
positions of the three phenyl groups were all substituted
mechanism. Moreover, treatment of 13 with NBS alone
resulted in a negligible reaction, providing support for
the conclusion that the major mechanism involved in the
50-halogenation of Ir complexes (e,g., 1 f 3a in Chart 2) is
somewhat different from that of the radical-mediated
halogenation of 13 (f14) in Chart 3.
Aromatic substitution reactions of activated benzenes
were previously reported by Carreno and Ruano et al.20
For example, the reaction of electron-rich benzene deriv-
atives such as 3-isopropyl-1,2,4-trimethoxybenzene and
1,2,4-trimethoxybenzene with NBS or NIS in CCl4 or
MeCN gives the corresponding halogenated products as
major products, respectively. It is very likely that the
˚
with I. The averaged N(tpy)-Ir (2.14 A) and C(tpy)-Ir
(2.01 A) bond distances are almost identical to those of
˚
the aforementioned 3a (Figure 1), and the averaged I-C
bond length was 2.11 A, which is slightly longer than that
˚
of the Br-C bond in 3a. Representative parameters for
the crystal structure analysis of 3a and 3b are listed in
Table 2.
Proposed Mechanism for the Selective Substitution Re-
actions of 1 and 2. As listed in Table 1, halogenation at the
50-position of tpy and ppy ligands in 1 and 2 proceeds in
the absence of radical initiators such as BPO, suggesting
an ionic mechanism rather than a radical mechanism.
Indeed, the reaction of 2-(40-tolyl)pyridine (tpy) 13 with
NBS and BPO in CCl4 resulted in the bromination of the
methyl group to afford 14 (Chart 3) possibly via a radical
(20) (a) Carreno, M. C.; Ruano, J. L. G.; Sanz, G.; Toledo, M. A.;
Urbano, A. J. Org. Chem. 1995, 60, 5328–5331. (b) Carreno, M. C.; Ruano,
J. L. G.; Sanz, G.; Toledo, M. A.; Urbano, A. Tetrahedron Lett. 1996, 37, 4081–
4084.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 813
Chart 4
Chart 5
methoxy groups of these substrates serve as electron-
donating groups to activate the benzene rings of these
substrates. Considering the above facts, we assume that
C-Ir bonds in 1 (Ir(ppy)3) and 2 (Ir(tpy)3) exhibit electron-
donating effect and activate the phenyl rings of the
metalated ligands to facilitate electrophilic substitution
reactions at the p-position (50-position) with respect to the
C-Ir bonds.21-23
Formylation and Acetylation of Ir Complexes. Formyla-
tions of 1 and 2 were carried out with DMF and POCl3
(Vilsmeier reaction) to yield tris(formyl) derivatives 7 and
8 in good yields (Chart 4). The reduction of 7 and 8 with
NaBH4 gave the corresponding alcohols 15 and 16. A
Pinnick oxidation (NaClO4, 2-methyl-2-butene, in MeCN/
0.1 M aq. NaH2PO4) of 7 and 8 afforded the correspond-
ing carboxylic acids 17 and 18, respectively. The con-
densation of 17 with (mono-Boc)ethylenediamine17 in the
(21) The HOMO energy level and electron orbital density of 2 were
calculated by using density functional theory (DFT) calculation (B3LYP/
LanL2DZ) (ref 22). Supporting Information, Figure S3 displays that the
phenyl group of the ppy unit has larger HOMO orbitals than those of the
pyridine ring and that the 30- and 50-position of the ppy units have large
HOMO orbitals, which may allow substitution reactions at those positions.
(22) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, Jr., J. A.; Vreven, T.; Kudin, K. N.;
Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci,
B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada,
M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian,
H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.;
Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski,
J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg,
J. J.;Zakrzewski, V. G.;Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.;
Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.;
Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill,
P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, Revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
presence of Et3N and PyBOP (benzotriazol-1-yloxytri-
pyrrolidinophosphonium hexafluorophosphate) in DMF
yielded 19, which could be an important intermediate to
synthesize C3-symmetric bioactive molecules.
These successful conversions of 7 and 8 prompted us
to attempt to introduce various other functionalities onto
the Ir complexes. Although we attempted the reductive
amination of 7 with NH4Cl and NaBH3CN to obtain
the tris(aminomethyl) compound 20 (Chart 5), this reac-
tion failed to proceed. Alternatively, 7 was converted to
the tris(hydroxyimino) derivative 21 by treatment with
NH2OH HCl, followed by the reaction with Ac2O to
afford the tris(cyano) derivative 22. Reduction of the CN
3
groups of 22 with BH3 THF gave 20 in moderate yield
(reduction of 22 to 20 with NaBH4 þ TiCl4 or LiAlH4 was
3
not successful).
We also carried out the acetylation of 1 and 2 with AcCl
and AlCl3 in CH2Cl2 (Chart 6). The triacetylated com-
pound 9 was obtained from 2, while the product from
1 was tetrakis[2-(40-tolylpyridine)(μ-dichloro)]diiridium
(23) In our preliminary experiments, it was suggested that halogenations
(e.g.; NBS, MeCN at 70 °C) of Ir(tpy)2(bpy) (bpy = 2,20-bipyridyl) also
proceed as 1 and 2 do. Details will be reported elsewhere.

814 Inorganic Chemistry, Vol. 50, No. 3, 2011
Aoki et al.
Chart 6
Figure 3. (a) UV-vis spectra of 1 (plain curve), 7 (bold curve), 10 (thin
curve), 19 (bold dashed curve), and 22 (dashed curve) in degassed CH2Cl2
at 25 °C. (b) Emission spectra of 1 (plain curve), 7 (bold curve), 10 (thin
curve), 19 (bold dashed curve), and 22 (dashed curve) in degassed CH2Cl2
at 25 °C (excitation at 366 nm). [Ir complex] = 10 μM. A.u. is arbitrary
units and emission intensity was normalized with the absorbance of each
compound at 366 nm, which was used for excitation of all Ir complexes.
460 nm can be assigned to metal-to-ligand charge transfer
(MLCT). Excitation spectra of these four Ir complexes
are shown in Figure S4a in the Supporting Information.
As shown in Figure 2b and Table 3, the luminescence
quantum yields (φ) of 3b and 5 were lower than that of 1.24
Figure 3 shows UV-vis spectra and emission spectra
for 1, 7, 10, 19, and 22 (excitation spectra are shown in
Figure S4b in the Supporting Information). We conclude
that the introduction of electron-withdrawing moieties
such as formyl and cyano groups at 50-position of Ir(tpy)3
(e.g., 7 and 22), is responsible for the blue shift in the
emission wavelength.
The UV-vis spectra of 7 and 22 exhibited a larger
absorption at wavelength >350 nm than those of 1 and
10, as shown in Figure 3a. For comparison, we collected
UV-vis spectra of benzaldehyde, anisole, and anisalde-
hyde. As shown in Figure S5 in the Supporting Information,
Figure 2. (a) UV-vis spectra of 1 (plain curve), 3a (bold curve), 3b
(dashed curve), and 5 (bold dashed curve) in degassed CH2Cl2 at 25 °C. [Ir
complex] = 10 μM. (b) Emission spectra of 1 (plain curve), 3a (bold
curve), 3b (dashed curve), and 5 (bold dashed curve) in degassed CH2Cl2
at 25 °C (excitation at 366 nm). [Ir complex] = 10 μM. A.u. is arbitrary
units and emission intensity was normalized with the absorbance of each
compound at 366 nm, which was used for excitation of all Ir complexes.
1
complex 23,2a,k,p,9f as confirmed by H NMR spectra,
although the mechanism for this reaction is not clear at
present.
UV-vis and Luminescence Spectra of Substituted Ir
Complexes. UV-vis and luminescence spectra of substi-
tuted Ir complexes, 1, 3a, 3b, 5, 7, 10, 19, and 22, were
obtained, and the results are shown in Figures 2 and 3.
The UV-vis spectra of 3a, 3b, and 5 were nearly identical
to a spectrum of 1 (Figure 2a). Small shoulders at around
(24) It is known that the nitro group works as a strong quencher of
luminescent dye (see: Munkholm, C.; Parkinson, D.-R.; Walt, D. R. J. Am.
Chem. Soc. 1990, 112, 2608–2612. Ueno, T.; Urano, Y.; Kojima, H.; Nagano, T.
J. Am. Chem. Soc. 2006, 128, 10640–10641, and references cited therein).
Concerning emission spectra of hexachlorinated and triiodinated Ir complexes 3b
and 5, such halogen substituents may facilitate thermal deactivation via non-
radiative pathway, as suggested by the reviewer.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 815
a
Table 3. Photochemical Properties of the Substituted Ir(tpy)3 in CH2Cl2
complex
λmax (absorption)
λ
max (emission)
φ
1
287, 373 nm
286, 376 nm
252, 377 nm
226, 366 nm
289, 347 nm
281, 375 nm
286, 365 nm
281, 366 nm
512 nm
506 nm
505 nm
500 nm
477 nm
0.50
0.49
0.04
0.13
0.58
≈ 0
3a
3b
5
7
10
19
22
499 nm
478 nm
0.40
0.46
a [Ir complex] = 10 μM.
Chart 7
Figure 5. Photograph showing solutions of 22 (30 μM), 1 (30 μM),
H3 12 (100 μM), and acid-free 12 (100 μM) in degassed DMSO/CH2Cl2
3
(1/5) at 25 °C (excitation at 365 nm).
Introduction of Amino Groups on Ir(tpy)3 and Lumines-
cence Properties Altered by the Protonation/Deprotona-
tion of Its Amino Groups. It has been reported that the
luminescence properties of Ir complexes can be altered by
certain ligands and their substituent groups.1,2,8,9 In the
past decade, considerable efforts have been made to
develop efficient luminescent Ir complexes that are able
to emit all of the primary colors: red, green, and blue. It
has been reported that the incorporation of electron-
withdrawing substituents such as F and CN results in
an increase in the energy gap between the highest occu-
pied molecular orbital (HOMO) and the lowest unoccu-
pied molecular orbital (LUMO), resulting in a blue-shift
in the emission wavelength when compared to the parent
complexes.6,25 In contrast, several examples of red-color
luminescent Ir complexes have also been reported.9 It
should be noted that only few examples of luminescent
iridium complexes that reversibly respond to the sur-
rounding environment have been reported.1e,f,10
On the basis of the aforementioned results, we assumed
that electron-donating units such as an amino group may
induce red-shift in the emission of Ir complexes. There-
fore, we carried out the nitration (HNO3 or Cu(NO3)2
3
3H2O and Ac2O) of 1 and 2 to obtain 10 and 11 according
to a previously reported procedure12 and successive re-
duction of the nitro groups (Chart 7). Hydrogenation of
10 with H2 and Pd/C gave partially reduced compounds,
mono- and bis(amino) complexes. The nitro groups of 10
were then reduced with SnCl2 2H2O and NaBH4 to give
Figure 4. Change in emission spectra of 12 (10 μM) in degassed DMSO
at 25 °C (excitation at 366 nm) upon the repeated addition of acid (1 M
HCl in 1,4-dioxane) and base (1 M DBU in 1,4-dioxane). (a) 12 before the
addition of Hþ, (b) (a) þ HCl, (c) (b) þ DBU, (d) (c) þ HCl, (e) (d) þ
DBU, and (f) (e) þ HCl (excitation at 366 nm). A.u. is in arbitrary units.
(Inset) Change in luminescence intensity at 508 nm of 12 caused by the
repeated addition of HCl and DBU.
3
12, which is abbreviated as Ir(atpy)3 in this manuscript.
Since the purification of 12 after reduction was difficult,
the three amino groups of 12 were protected with Boc in
situ, and 12 was isolated as 3-Boc protected derivative 24,
which was easily purified by silicagel colum chromato-
graphy. The three Boc groups of 24 were removed by
treatment with TMSCl and NaI to afford the HI salt of
12, which was purified by ionic exchange column chro-
matography (IRA-400, HO- form) to give acid-free 12.
anisaldehyde exhibits a strong absorption at >250 nm,
possibly because of conjugation between the electron-
withdrawing formyl group and the electron-donating
methoxy group. A comparison of Supporting Informa-
tion, Figure S5 and Figure 3a are consistent with the
electron-donating characteristics of C-Ir bonds.
(25) For example, Lasker et al. introduced methoxy and fluoro groups on
Ir(ppy)3 complex, but these complexes emit blue-color luminescence (ref 8d).

816 Inorganic Chemistry, Vol. 50, No. 3, 2011
Aoki et al.
Chart 8
Interestingly, the luminescence of a solution of 12 in
DMSO was found to be red, with an emission maximum
at around 600 nm, as displayed in Figure 4 (bold curve a)
and Figure 5 (right) ([12]=100 μM, excitation at 366 or
365 nm).26 Figure 5 shows blue colored luminescence
from 22 (left), a yellow-green emission from 1 (second
left), and a red emission from 12 (right). Moreover, the
addition of Hþ to 12 induced a significant blue-shift
(about 100 nm) in its luminescence emission, as the result
of the protonation of the three amino groups (Chart 8),
resulting in green emission at 508 nm, as shown in Figure 4
(plain curve b) and Figure 5 (the second from the right).27
When a base, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU),
was added, the red colored emission was recovered. As
depicted in Figure 4 and the inset, these processes were
reversible with negligible decrease in emission intensity at
each step. The luminescent quantum yields (φ) of 12 and
H3 12 in DMSO were determined to be 9.4 ꢀ 10-3 and
3
0.23, respectively. The lower φ value of acid-free 12 can be
attributed to the energy gap law because of the increase in
the wavelength of the emission peak.28,29
We carried out cyclic voltammetry (CV) measurements
of 22, 1, and 12,30 from which potential gaps between the
first oxidation and reduction of these Ir complexes were
estimated to be 3.1 V (for 22), 2.9 V (for 1), and 2.6 V
(for 12), suggesting the relationship of these values with the
order of their emission wavelength. CV curves of 12 and
Figure 6. Change in the emission spectra of 12 (100 μM) in degassed
DMSO/100 mM buffer (from pH 3 to 9) (1/6) at 25 °C. (Inset) pH-
Dependent plot of emission intensity of 12 (100 μM) at 531 nm (closed
circle) in degassed DMSO/100 mM buffer (1/6). Excitation at 366 nm. A.
u. is in arbitrary unit.
because protonation/deprotonation processes of amino
groups are much faster than redox reactions on the electrode
in given measurement conditions.
triprotonated H3 12 (prepared from 12 þ 3 equiv, HClO4)
3
were undertaken to compare HOMO and LUMO levels
of these two species. However, it was found that these two
CV curves are almost identical (data not shown), possibly
Next, luminescence spectra of 12 in aqueous solutions
at pH 3-9 were measured ([12] = 100 μM, exitation at
366 nm). Asshown inFigure 6, a stronggreen emissionwas
observed at acidic pH (531 nm at pH 3-4 and 517 nm at
pH 5). In contrast, the emission shifted to about 600 nm at
pH 5-6 with significant decrease in green emission at
about 530 nm.31,32 These results indicate that protonated
amino groups function as electron-withdrawing groups to
cause blue shift of the emission to about 500 nm. Figure 7
clearly displays that 12 responds to the pH of the aqueous
solutions, changing from a yellow-green emission at an
acidic pH to a red emission at neutral and basic pH.
(26) Luminescence emission spectra of 12 in organic solvents such as
DMSO (and DMSO/H2O), DMF, CH2Cl2, 1,4-dioxane, and THF are
shown in Figure S6 in the Supporting Information. Although we could
not observe apparent relationships between λmax and quantum yields of its
emission and the chemical properties of these solvents such as dielectric
constants (εr) and normalized empirical parameters of solvent polarity (ENT ),
it seems that less polar solvents afford larger emission intensity.
(27) UV-vis spectral change of 12 by protonation and deprotonation are
shown in Figure S7 in the Supporting Information which shows a blue shift
(ca. 40 nm) of absorption upon addition of excess amount of HCl.
(28) (a) Cummings, S. D.; Eisenberg., R. J. Am. Chem. Soc. 1996, 118,
1949–1960. (b) Meyer, T. J. Pure Appl. Chem. 1986, 58, 1193–1206.
(29) Preliminary results of DFT calculation of 12 and H3 12 suggest that
(31) The pH-dependent change in UV/vis spectra of 12 (10 μM) in
DMSO/100 mM buffer (pH 3-10) is shown in Figure S10 in the Supporting
Information.
3
the difference of the energy gaps between HOMO and LUMO between these
species are very small. A detailed calculation is now underway.
(30) Typical CV curves of 1, 22, and 12 in DMF containing 0.1 M
nBu4N(PF6) at 25 °C are shown in Figure S8 in the Supporting Information.
A summary of potential gaps of the first oxidation and reduction of 1, 22, and
12 in comparison with those of benzonitrile and aniline are displayed in
Figure S9 in the Supporitng Information.
(32) Note that emission intensity of H3 12 and acid-free 12 in solvent
3
systems containing water (such as DMSO/H2O) are lower than those in other
organic solvent systems (see Figure S6 in the Supporting Information),
possibly because of the greater polarity of water than those of other organic
solvents.

Article
Inorganic Chemistry, Vol. 50, No. 3, 2011 817
Figure 7. Photograph showingsolutions of 100 μM 12 in degassedDMSO/100 mMbuffer (frompH4 to 10) (1/6) (fromleft toright) excited byUV light at
365 nm at 25 °C.
of three amino groups of 12 induces large blue-shift of its
emission.
The results of emission titrations of 12 (100 μM) with
0.1 M aq. HCl and organic Bronsted acids such as tri-
fluoroacetic acid (CF3CO2H, TFA), and methanesulfo-
nic acid (CH3SO3H) in DMSO at 25 °C are shown in
Figure S11 in the Supporting Information, which indicate
that the first protonation at one of three amino groups of
12 induces a blue-shift of its emission from about 590 nm
to about 520 nm and that the second and third protona-
tions promote emission enhancement at about 510-520
nm. It was also found that CH3SO3H (pKa = -0.6 in H2O
and pKa = 1.6 in DMSO),33 CF3CO2H (pKa = 0.5 in
H2O33 and pKa = 3.45 in DMSO),34 and HCl (pKa = -8
in H2O and pKa = 1.8 in DMSO)34 cause considerable
emission enhancement of 14.35 On the other hand, negli-
gible change was observed upon addition of chloroacetic
acid (ClCH2CO2H, pKa = 2.87 in H2O at 25 °C)33 and
citric acid (pKa = 3.13, 4,76, and 6.40 in H2O)33 under the
same conditions and addition of BF3 Et2O in CH2Cl2,
3
Figure 8. Emission spectra of 12 (100 μM) in degassed DMSO/H2O
which is a Lewis acid (Figure S11 in the Supporting
Information), possibly because of weaker acidities than
(1/6) in the presence of (a) 300 μM HCl (pH ∼3.9), (b) 200 μM HCl (pH
∼4.6), (c) 100 μM HCl (pH ∼5.3), and (d) 0 μM HCl (pH 7.3) at 25 °C.
Excitationat366nm. A.u. is in arbitraryunit. (Inset) Photograph showing
solutions of Figures 8a, 8b, 8c, and 8d (from left to right) excited by UV
light at 365 nm.
those of aforementioned acids. These functions may be
applicable for use in photochemical, analytica, and bio-
logical devices.
Unfortunately, we could not determine the accurate
pKa values of H3 12 because of its low solubility in water
Conclusion
3
containing DMSO or MeCN at 25 °C. By potentimetric
pH titration14,15 of a suspension of 12 in DMSO/water
(5/95) with I = 0.1 (NaNO3) at 25 °C (data not shown),
In this manuscript, we report on regioselective electrophilic
aromatic substitution reactions at the 50-positions (p-position
with respect to C-Ir bond) of phenyl rings in Ir(tpy)3 and
Ir(ppy)3, including halogenation, formylation, acetylation,
and nitration. Further chemical conversions were also carried
out to afford triamine derivatives (12, 19, 20), tricarboxylic
acids (17, 18), and triols (15, 16).
In addition, UV-vis and luminescence spectra (exitation
and emission) of 1 (Ir(tpy)3) and its derivatives synthesized in
this work are reported. By introducing electron-withdrawing
groups at the 50-position of Ir(tpy)3, the emission wavelength
underwent a blue shift (7 and 22, see Figure 3b). On the other
hand, the introduction of amino groups (electron-donating
groups) at the 50-position of Ir(tpy)3 (12) resulted in a
three pKa values of H3 12 were roughly estimated to be in
3
the range of 4 to 5.5 (Chart 8), which are almost identical
to the pKa values of 4-5 estimated by pH-dependent
luminescence spectral change shown in Figure 6 and its
inset (the pKa value of anilinium cation in water is
reported to be 4.60).33
Emission spectra of 12 (100 μM) in the absence and the
presence (1 to 3 equiv.) of HCl were undertaken in DMSO
and water (1/6). As shown in Figure 8, emission of mono-
(H 12), di- (H2 12), and triprotonated (H3 12) species
3
3
3
of 12 exhibit emission maxima at about 510-520 nm
(green to green-yellow emissions), and only acid-free 12
exhibits an emission maximum at about 590 nm (red
emission). These results strongly suggest that protonation
(34) Bordwell, F. G. Acc. Chem. Res. 1988, 21, 456–463.
(35) As shown in Supporting Information, Figure S11, emission enhance-
ment of 12 upon addition of aq. HCl is smaller than that upon addition of
MeSO3H regardless of the stronger acidity of HCl than that of MeSO3H,
possibly because of the existence of water in the solvent system (see Figure S6
in the Supporting Information and ref 32 in this manuscript).
(33) Speight, J. G. Lange’s Handbook of Chemistry, 16th ed.; McGraw-Hill:
New York, 2005.

818 Inorganic Chemistry, Vol. 50, No. 3, 2011
Aoki et al.
significant red shift in the luminescence emission (at ca.
590-600 nm) compared to its parent complex 1. Moreover,
it was found that the emission of 12 can be converted to a
green color upon protonation of its amino groups in a
reversible manner (Figure 4-8).
This information will be useful for the future design and
synthesis of novel luminescence metal complexes and their
applications in inorganic chemistry, material sciences, photo-
chemistry, biological chemistry, analytical chemistry, medic-
inal chemistry, and related fields.
Acknowledgment. This study was supported by grants-
in-aid from the Ministry of Education, Culture, Sports,
Science and Technology (MEXT) of Japan (Nos. 18390009,
19659026, and 20750081) and “Academic Frontier” proj-
ect for private universities: matching fund subsidy from
MEXT, 2009-2013. M.K. is also thankful for a Sasakawa
Scientific Research Grant from the Japan Science Society.
Supporting Information Available: Figures S1-S11, and
Tables and CIF files (Tables S1∼S8) for 3a and 3b. This material
is available free of charge via the Internet at http://pubs.acs.org.