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Iridium Complexes Containing Bis(imidazoline thione) and Bis(imidazoline selone) Ligands for Visible-Light-Induced Oxidative Coupling of Benzylamines to † ‡ † † ‡ ‡ Jaewon Jin, Hee-Won Shin, Joon Hyun Park, Ji Hoon Park, Eunchul Kim, Tae Kyu Ahn,*, † † ‡ Do Hyun Ryu,*, and Seung Uk Son*, , † ‡ Department of Chemistry and Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea

*S Supporting Information

ABSTRACT: Novel iridium(III) complexes containing bis- (N-heterocyclic ), bis(imidazoline thione) L2, and bis(imidazoline selone) L3 were prepared. The iridium complexes bearing L2 and L3 showed the significant absorption of visible light with maximum intensity at ∼460 nm. Bis(2-(2′-benzothienyl)pyridinato)iridium(III) complexes (Ir-6) with L3 showed excellent ability as a photosensitizer of visible light. Under blue LED irradiation with maximum emission at 460 nm, 0.25 mol % Ir-6 showed 94% conversion of benzylamine for 5 h at room temperature. Through mechanistic studies, it was suggested that the photoinduced oxidative coupling of benzylamine by Ir-6 follows a singlet pathway. The excellent performance of Ir-6 originated from the efficient visible light absorption at 460 nm and the enhanced triplet state due to the heavy-atom effect of L3. This work shows that bis(imidazoline thione) and bis(imidazoline selone) can be efficient ligands for tuning the optical properties of iridium(III) complexes.

■ INTRODUCTION in photoinduced oxidative coupling of benzylamines to imines Recently, chemical reactions triggered by sustainable energy in the presence of oxygen. sources such as solar energy and the relevant photoactive systems have attracted the attention of scientists.1 Over the past ■ RESULTS AND DISCUSSION decade, iridium(III) complexes bearing the 2-phenylpyridinato Scheme 1 shows the synthetic methods for new iridium 2 (ppy) ligand have shown interesting optical properties. complexes. First, the bis(ppy)iridium chloride dimer (ppy = 2- Numerous iridium(III) complexes with various geometric and phenylpyridinato) was prepared using the method described in electronic ligands have been prepared.3 In addition, two or the literature.10 Bis(N-heterocyclic carbene)-2AgBr (L1- more kinds of ligands have been introduced to iridium 2AgBr) was prepared by the reaction of the corresponding 4 − 11 complexes. The enhanced spin orbit coupling due to the imidazolium salt with silver oxide (Ag2O). The reaction of ff heavy-atom e ect of iridium has been shown to result in the [(ppy)2IrCl]2 with L1-2AgBr in 2-ethoxyethanol resulted in the ffi + 11,12 e cient mixing of singlet and triplet states and to promote formation of the complex [(ppy)2L1Ir] (Ir-1). Bis- intersystem crossing.2,3,5 The major studies of these iridium (imidazoline thione) L2 and bis(imidazoline selone) L3 were complexes have focused on the phosphorescent properties for prepared by the reaction of the corresponding imidazolium salt organic light emitting diode (OLED) devices.6 with elementary sulfur and .13a Imidazoline thiones Due to their unique optical properties, iridium complexes and selones have been used as versatile ligands toward various 12 have recently been applied as photocatalysts and photo- transition metals. The reaction of [(ppy)2IrCl]2 with L2 and 1,7 + + initiators. For example, iridium complexes were applied as a L3 resulted in the formation of [(ppy)2L2Ir] or [(ppy)2L3Ir] 1 8 1 photosensitizer to generate a singlet oxygen ( O2), which can complexes (Ir-2, Ir-3). As observed in the literature, H NMR be used for various purposes, including photodynamic cancer peaks from protons in benzyl carbon and imidazoline rings of therapy (PDT).9 However, one of the drawbacks of iridium L2 and L3 shifted (0.3−0.5 ppm) downfield through 13 complexes is their low absorption of visible light. The shift of coordination. Moreover, X-ray photoelectron spectroscopy absorption bands to a visible light range can be induced (XPS) revealed that the S 2p and Se 3d orbital peaks of L2 and − through the screening of ligands. L3, respectively, shifted to higher energies by 1.6 2.0 eV in In this work, we report the preparation of iridium complexes containing bis(N-heterocyclic carbene), bis(imidazoline thi- Received: May 18, 2013 one), and bis(imidazoline selone) ligands and their properties Published: June 28, 2013

© 2013 American Chemical Society 3954 dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959 Organometallics Article

Scheme 1. Synthesis of Iridium(III) Complexes Containing Bis(N-heterocyclic carbene), Bis(imidazoline thione), and Bis(imidazoline selone) Ligands

Figure 1. UV/vis absorption (solid line) and normalized emission × −5 − (dotted line) spectra of 1 10 M Ir-1 Ir-6 in CH2Cl2. iridium complexes. (Figure S1, Supporting Information) Three − Table 1. Optical and Electrochemical Properties of further iridium complexes (Ir-4 Ir-6) were prepared using the Iridium(III) Complexes Ir-1−Ir-6 in CH Cl 2-(2′-benzothienyl)pyridinato ligand (btpy)14 instead of ppy. 2 2 Chart 1 summarizes the iridium complexes prepared in this oxidn λ ε λ Δ ° a b c d abs, (nm, em G es potential HOMO Ees work. compd M−1cm−1) (nm) (eV) (V) (eV) (eV) a Ir-1 380, 5900 473 2.68 1.16 −5.60 −2.92 Chart 1. Iridium(III) Complexes Used in This Study Ir-2 431, 4600 486 2.60 1.05 −5.49 −2.89 Ir-3 428, 2600 499 2.54 1.01 −5.45 −2.91 Ir-4 419, 9000 577 2.17 1.02 −5.46 −3.29 Ir-5 464, 9900 604 2.09 0.96 −5.40 −3.31 Ir-6 461, 11000 603 2.09 0.91 −5.35 −3.26 aΔ ° G es (the free energy of excited states above the ground states) values were calculated by the method in ref 19. bPotential (vs Ag/Ag+) of the first oxidative wave. cHOMO energy calculated by the potential of the oxidative wave.19 dExcited state energy calculated by HOMO + Δ ° G es.

a − The counteranion, PF6 , is omitted.

The analogue of Ir-1 having fluorine groups in the ppy ligand has been reported to show poor absorption in a range of visible light.11 Similarly, Ir-1 has shown very poor absorption of visible light (Figure 1 and Table 1) The introduction of L2 and L3, instead of L1 resulted in a significant red shift of the absorption − Figure 2. Cyclic voltammograms of Ir-1 Ir-6 in CH2Cl2. band to ∼430 nm. However, the absorption intensity and shift degree of Ir-2 and Ir-3 were not sufficient for the efficient absorption of visible light. In comparison to Ir-1, Ir-4 showed a 1), while those of Ir-2 and Ir-3 shifted to lower values: +1.05 red-shifted absorption at 419 nm. Moreover, Ir-5 and Ir-6 and +1.01 V, respectively. A similar trend was observed in the showed significant absorption (ε = 9900−11000 M−1 cm−1)at series Ir-4−Ir-6. These observations imply that L3 and L2 ∼460 nm and the a emission at ∼600 nm with a 140 nm Stokes provided a more electron rich effect, in comparison with L1. shift (Figure 1 and Table 1). Considering the significant absorption of visible light by Ir- Figure 2 shows the electrochemical properties of Ir-1−Ir-6 in 1−Ir-6, we investigated the photosensitizing performance of methylene chloride. The reduction peaks were overlapped with iridium complexes under visible light irradiation. It has been the reduction range of CH2Cl2, implying that the iridium reported that the photoinduced oxidative coupling of benzyl- complexes are relatively electron rich systems. The oxidation results in the formation of imines.15 Although a visible- potential of Ir-1 was observed at +1.16 V (vs Ag/Ag+) (Table light-induced system has been reported, the reaction temper-

3955 dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959 Organometallics Article ature was relatively high, at ∼80 °C.16 The system working at room temperature was relatively less explored.17 Table 2 summarizes the performance of Ir-1−Ir-6 in the visible-light- induced oxidative coupling of benzylamine to .

Table 2. Visible-Light-Induced Oxidative Coupling of a Amines in the Presence of Iridium Complexes Ir1−Ir-6

Figure 3. Two main mechanisms for the photoinduced oxidative coupling of benzylamine to imine.

b c singlet oxygen, which induces the oxidative coupling of entry cat./amt (mol %) yield (%) benzylamine to imine. Both mechanisms work depending on 1 Ir-1/0.1 benzylamine 20 the optical and electrochemical properties of the photo- 2 Ir-2/0.1 benzylamine 24 sensitizers. 3 Ir-3/0.1 benzylamine 36 In the photoredox pathway, the energy levels of the reactants 4 Ir-4/0.1 benzylamine 36 and photosensitizer should match well. In this work, the excited 5 Ir-5/0.1 benzylamine 45 state energy level of the photosensitizer should be located at an 6 Ir-6/0.1 benzylamine 70 energy level higher than the LUMO of oxygen. The HOMO 7 Ir-6/0.25 benzylamine 94 (90) energy level of benzylamine should be located at an energy level d 8 no cat. benzylamine NR higher than that of the photosensitizer or the oxidized e 9 Ir-6/0.25 benzylamine NR photosensitizer. On the basis of the oxidation potentials and 10 Ir-6/0.25 4-methoxybenzylamine 99 (92) emission spectra of iridium complexes, their excited state 11 Ir-6/0.25 4-methylbenzylamine 95 (92) energy levels were calculated in the range of −2.9 to −3.3 12 Ir-6/0.25 4-chlorobenzylamine 89 (83) eV,19,20 which matches well with the LUMO level (∼−3.6 eV) 13 Ir-6/0.25 4-fluorobenzylamine 76 (71) of oxygen.17,21 In comparison, the HOMO energy values of 14 Ir-6/0.25 1-phenylethylamine 61 (58) iridium complexes are higher than that (∼−6.5 eV) of 15 Ir-6/0.25 (2-thienyl)methylamine 60 (56) benzylamine.17,21 Thus, it can be reasoned that the reduction a Reaction conditions: 1 mmol of amine, 1 atm of O2, blue LED of oxidized iridium complexes by benzylamine is not favorable. b irradiation, 3 mL of CH2Cl2, 5 h, room temperature. In mol % with It is reported that the enhanced triplet states facilitate energy respect to amine. cConversion yield based on 1H NMR spectroscopy 8 d e transfer to triplet oxygen species, generating a singlet oxygen. (isolated yield in parentheses). NR = no reaction. The glassware was Considering the phosporescent emission properties of Ir-5 and completely covered with Al foil. Ir-6, we conducted photophysical studies for the direct detection of possible singlet oxygen under the laser irradiation We used a conventional blue LED (0.9 mW/cm2) with a of 460 nm wavelength. As expected, typical emissions at 1270 maximum emission at 460 nm as a light source. As shown in nm from singlet oxygen generated by Ir-5 and Ir-6 were entries 1−6 in Table 2, 0.1 mol % of Ir-1−Ir-6 showed observed in methylene chloride. Figure 4 shows the emission relatively different activities as photosensitizers in the oxidative decay curves of singlet oxygen generated by Ir-5 and Ir-6 with × −5 coupling of benzylamine. First, Ir4−Ir-6 showed better the same concentration (1 10 M). The calculated lifetime − of singlet oxygen by Ir-5 and Ir-6 was 91 μs, which exactly performances, in comparison with Ir1 Ir-3. Second, the 22 iridium complexes with L2 and L3 (Ir-2, Ir-3, Ir-5, Ir-6) matches the value reported in methylene chloride. Interest- showed better activities, in comparison with Ir-1 and Ir-4. ingly, the intensity of the generated singlet oxygen by Ir-6 was These observations can be rationalized by the absorption 2.4 times higher than that by Ir-5. We believe that the superior efficiencies of iridium complexes for visible light. Interestingly, although Ir-5 and Ir-6 have similar optical and electrochemical properties, they showed quite different performances as photosensitizers in the oxidative coupling of benzylamine in the presence of oxygen. (entries 5 and 6 in Table 2). To understand this observation, we conducted mechanistic studies on the photochemical process. Two main mechanisms, (1) a photoredox pathway1b,15a,16 and (2) a singlet oxygen pathway,18 have been reported for the photo- oxidation of amine to imine in the presence of oxygen. As shown in Figure 3, in the photoredox pathway (oxidative quenching cycle), the excited iridium complex transfers an •− electron to oxygen to form the reduced O2 . The oxidized iridium complex obtains an electron via the oxidation of amine •+ to form a radical cation, RNH2 . Finally, the reaction of the •− •+ reduced O2 and the oxidized RNH2 species results in the 16 formation of imine. In comparison, in the singlet oxygen Figure 4. Emission (1270 nm) decay curves of the singlet oxygen pathway, the excited iridium complex in the triplet state can generated by Ir-5 and Ir-6 in CH2Cl2 under laser irradiation (460 nm transfer energy to the triplet oxygen molecule to form active wavelength).

3956 dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959 Organometallics Article performance of Ir-6 over Ir-5 resulted from the additional electrode. The counter electrode was a platinum wire. Ag/AgNO3 + heavy-atom effect of selenium in L3, in comparison with sulfur (Ag/Ag ) was used as the reference electrode. 0.1 M Bu4NPF6 in 23 ff methylene chloride was used as the electrolyte. in L2. The dramatic heavy-atom e ects of selenium have been 1 reported in the optical properties of phosphorescent dyes, in In order to obtain the decay curve of singlet oxygen ( O2) comparison with the case for sulfur.23 This observation matches phosphorescence, an optical parametric oscillator (OPO) laser (Spectra-Physics, basiScan) pumped by Nd:YAG (Spectra-Physics, well with the results in the photoinduced chemical conversions λ − INDI-40-10) was utilized as an excitation source ( ex 450 560 nm). by Ir-5 and Ir-6 (entries 5 and 6 in Table 2). The direct The time duration (fwhm) of the excitation pulse was 7 ns, and the observation of singlet oxygen species and the intensity trend pulse energy was controlled by a neutral density filter set from 1.0 to 1 strongly support the assumption that the photoinduced 0.1 mJ/pulse. The phosphorescence of O2 was investigated by the oxidative coupling of benzylamine in this work was conducted characteristic peak at 1270 (1268) nm using a monochromator through a singlet oxygen pathway. Moreover, the gradual (Princeton Instruments, SP2300) equipped with an NIR-PMT addition of benzylamine to the generated singlet oxygen species (Hamamatsu, H10330-75). The output signal from an NIR-PMT showed a decrease of life times with a 2.6 × 108 M−1 s−1 was recorded with a 500 MHz digital oscilloscope (Agilent, DSO-X quenching rate at 298 K (Figure S2 in the Supporting 3054A). A cutofffilter was used to remove scattered excitation light. Synthetic Procedure for Ir-1 and Ir-4. [(ppy)2IrCl]2 and Information). 10,14 ′ A 0.25 mol % amount of Ir-6 showed 94% conversion of [(btpy)2IrCl]2 were prepared using the literature method. 1,1 - Dimethyl-3,3′-methylenediimidazolium dibromide was prepared using benzylamine to the corresponding imine in 5 h at room the literature method.11 1,1′-Dimethyl-3,3′-methyleneimidazolium temperature under blue LED irradiation. It is noteworthy that dibromide (32 mg, 0.094 mmol) and Ag O (65 mg, 0.28 mmol) the 0.25 mol % phenothiazine-based organic dyes that have 2 were added to 2-ethoxyethanol (5 mL). [(ppy)2IrCl]2 (50 mg, 0.047 been recently developed showed 83% conversion of benzyl- mmol) was added. The reaction mixture was refluxed for 12 h in the 17 amine in 12 h under the same conditions. In control dark. After it was cooled to room temperature, the solution was filtered fi experiments, benzylamine showed no reaction in the absence of through a glass lter. An excess of NH4PF6 (0.10 g, 0.61 mmol in 20 Ir-6 under blue LED irradiation (entry 8 in Table 2). mL of water) was added to form yellow precipitates, which were Moreover, when the glassware was covered with aluminum retrieved by filtration, washed with excess water, and then dried under foil in the presence of Ir-6 under blue LED irradiation, no vacuum. The product (Ir-1)waspurified by flash column chromatography using a 9/1 mixture of CH2Cl2 and CH3CN as an conversion was observed (entry 9 in Table 2). These 1 δ observations demonstrate that the chemical conversion of eluent. Isolated yield: 64%. H NMR (300 MHz, acetone-d6): 8.49 (d, J = 7.2 Hz, 2H), 8.20 (d, J = 7.8 Hz, 2H), 7.98 (t, J = 7.2 Hz, 2H), benzylamine in this work was triggered through the photo- 7.79 (d, J = 7.8 Hz, 2H), 7.52 (s, 2H), 7.21 (t, J = 7.5 Hz, 2H), 7.16 (s, sensitizing of Ir-6. A 0.25 mol % amount of Ir-6 showed good 2H), 6.87 (t, J = 7.2 Hz, 2H), 6.75 (t, J = 7.5 Hz, 2H), 6.42 (d, J = 7.5 activity for various benzylamine derivatives and, interestingly, Hz, 2H), 6.36 (s, 2H), 2.93 (s, 6H) ppm. 13C NMR (75 MHz, δ showed higher conversion yields for more electron rich acetone-d6): 169.7, 164.0, 162.7, 153.3, 144.7, 137.4, 131.7, 128.6, benzylamines (entries 7 and 10−13 in Table 2). 1-Phenyl- 124.4, 123.8, 123.0, 121.4, 121.3, 120.0, 62.6, 36.8 ppm. HRMS for + + ethylamine with steric hindrance at the benzyl carbon site and M ,[C31H28N6Ir] : calcd 677.2005, obsd 677.2007. Anal. Calcd for (1-thienyl)methylamine with a heteroatom showed 61% and C31H28N6IrPF6: C, 45.31; H, 3.43; N, 10.23. Found: C, 45.40; H, 3.70; 60% conversions, respectively. N, 10.14. Mp: 328 °C dec. For the synthesis of Ir-4, [(btpy)2IrCl]2 was used instead of 1 δ ■ CONCLUSION [(ppy)2IrCl]2. Isolated yield: 58%. H NMR (300 MHz, acetone-d6): 8.53 (d, J = 7.5 Hz, 2H), 8.05 (t, J = 7.5 Hz, 2H), 7.80 (d, J = 7.5 Hz, This work shows that bis(imidazoline thione) and bis- 2H), 7.73 (d, J = 7.2 Hz, 2H), 7.60 (s, 2H), 7.24 (s, 2H), 7.13 (t, J = (imidazoline selone) can be used as ligands to tune the optical 7.5 Hz, 2H), 7.11 (t, J = 7.2 Hz, 2H), 6.85 (t, J = 7.2 Hz, 2H), 6.57 (s, properties of iridium(III) complexes. The introduction of 2H), 6.21 (d, J = 7.2 Hz, 2H), 2.99 (s, 6H) ppm. 13C NMR (75 MHz, δ bis(imidazoline thione) and bis(imidazoline selone) to iridium acetone-d6): 166.5, 160.9, 158.0, 154.2, 147.7, 142.6, 138.8, 136.9, complexes resulted in significant absorption in the visible light 125.6, 125.1, 124.3, 123.7, 122.9, 121.8, 121.0, 119.6, 62.6, 37.0 ppm. + + + range. Especially, the complex [(btpy)2L3Ir] (Ir-6) showed HRMS for M ,[C35H28N6S2Ir] : calcd 789.1446, obsd 789.1444. Anal. the highest performance as a photosensitizer in the visible-light- Calcd for C35H28N6S2IrPF6: C, 45.01; H, 3.02; N, 9.00. Found: C, ° induced oxidative coupling of benzylamine to imine. It was 44.86; H, 3.27; N, 8.73. Mp: 290 C dec. speculated that the superior performance of Ir-6 resulted from Synthetic Procedure for Ir-2, Ir-3, Ir-5, and Ir-6. L2 and L3 were prepared using the literature method.13 For the synthesis of Ir-2, the additional heavy-atom effect of the L3 ligand. We believe [(ppy)2IrCl]2 (50 mg, 0.047 mmol) and L2 (25 mg, 0.10 mmol) were that further various iridium(III) complexes can be prepared by added to methylene chloride. The reaction mixture was refluxed for 12 designing new imidazoline thione and imidazoline selone h in the dark. The solvent was then removed by rotary evaporation. ligands. The resultant solid was dissolved in methanol. An excess of NH4PF6 (0.10 g, 0.61 mmol in 20 mL of water) was added to form yellow ■ EXPERIMENTAL SECTION precipitates which were retrieved by filteration, washed with excess fi General Considerations. 1H and 13C NMR spectra for new water, and dried under vacuum. The product, Ir-2, was puri ed by compounds were obtained using a Varian 300 MHz spectrometer. recrystallization in a mixture of methylene chloride and diethyl . 1 δ Mass spectral data were obtained from the Korea Basic Science Isolated yield: 51%. H NMR (300 MHz, acetone-d6): 8.78 (d, J = Institute (Daegu) on a JEOL JMS 700 high-resolution mass 7.2 Hz, 2H), 8.17 (d, J = 8.4 Hz, 2H), 7.98 (t, J = 7.5 Hz, 2H), 7.73 (d, spectrometer. Elemental analysis was performed on a CE EA1110 J = 7.5 Hz, 2H), 7.70 (s, 2H), 7.33 (s, 2H), 7.28 (t, J = 7.2 Hz, 2H), instrument. The UV/vis absorption spectra were recorded using a 6.83 (t, J = 7.8 Hz, 2H), 6.73 (s, 2H), 6.71 (t, J = 7.2 Hz, 2H), 6.17 (d, 13 δ JASCO V-630 spectrophotometer. Emission spectra were recorded J = 7.8 Hz, 2H), 3.24 (s, 6H) ppm. C NMR (75 MHz, acetone-d6): using a JASCO FP-6200 spectrofluorometer. 168.9, 157.6, 150.9, 144.0, 138.4, 131.0, 130.1, 124.8, 123.4, 122.3, + + Cyclic voltammetry measurements were carried out using a CH 122.0, 120.0, 119.8, 59.7, 35.6 ppm. HRMS for M ,[C31H28N6S2Ir] : − instruments Model CHI600 potentiostat and 5 mM Ir1 Ir6 in calcd 741.1446, obsd 741.1448. Anal. Calcd for C31H28N6S2IrPF6:C, CH2Cl2. A conventional three-electrode assembly was used to record 42.03; H, 3.19; N, 9.49. Found: C, 42.23; H, 3.49; N, 9.34. Mp: 204 cyclic voltammograms under argon. Carbon was used as the working °C dec.

3957 dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959 Organometallics Article For the synthesis of Ir-3, L3 was used instead of L2. Isolated yield: ■ REFERENCES 1 δ 71%. H NMR (300 MHz, acetone-d6): 9.24 (d, J = 7.2 Hz, 2H), 8.19 (d, J = 7.8 Hz, 2H), 7.99 (t, J = 7.5 Hz, 2H), 7.78 (s, 2H), 7.74 (d, (1) Recent reviews: (a) Piers, W. E. Organometallics 2011, 30, 13. J = 7.5 Hz, 2H), 7.52 (s, 2H), 7.29 (t, J = 7.2 Hz, 2H), 6.84 (t, J = 7.2 (b) Narayanam, J. M. R.; Stephenson, C. R. J. Chem. Soc. Rev. 2011, Hz, 2H), 6.84 (s, 2H), 6.72 (t, J = 7.8 Hz, 2H), 6.13 (d, J = 7.5 Hz, 40, 1259. (c) Kudo, A.; Miseki, Y. Chem. Soc. Rev. 2009, 38, 253. 13 δ (d) Eisenberg, R. Science 2009, 324, 44. Selected examples: 2H), 3.41 (s, 6H) ppm. C NMR (75 MHz, acetone-d6): 174.3, 151.9, 143.6, 137.6, 130.3, 129.6, 126.6, 124.3, 123.4, 123.0, 121.6, (e) Miyake, Y.; Nakajima, K.; Sasaki, K.; Saito, R.; Nakanishi, H.; 120.9, 119.4, 68.9, 36.8 ppm. HRMS for M+,[C H N Se Ir]+: calcd: Nishibayashi, Y. Organometallics 2009, 28, 5240. (f) Du, P.; Knowles, 31 28 6 2 K.; Eisenberg, R. J. Am. Chem. Soc. 2008, 130, 12576. 837.0335, obsd 837.0335. Anal. Calcd for C31H28N6Se2IrPF6: C, 38.01; H, 2.88; N, 8.58. Found: C, 38.24; H, 3.20; N, 8.84. Mp: 217 °C dec. (2) (a) Baldo, M. A.; Thompson, M. E.; Forrest, S. R. Nature 2000, 403, 750. (b) Adachi, C.; Baldo, M. A.; Thomson, M. E.; Forrest, S. R. For the synthesis of Ir-5, [(btpy)2IrCl]2 was used instead of 1 δ J. Appl. Phys. 2001, 90, 5048. Recent review: (c) Chi, Y.; Chou, P.-T. [(ppy)2IrCl]2. Isolated yield: 41%. H NMR (300 MHz, acetone-d6): 9.05 (d, J = 7.5 Hz, 2H), 8.04 (t, J = 7.8 Hz, 2H), 7.82 (d, J = 7.5 Hz, Chem. Soc. Rev. 2010, 39, 638. 2H), 7.75 (d, J = 7.8 Hz, 2H), 7.74 (s, 2H), 7.38 (s, 2H), 7.22 (t, J = (3) Recent review: Ulbricht, C.; Beyer, B.; Friebe, C.; Winter, A.; 7.5 Hz, 2H), 7.14 (t, J = 7.2 Hz, 2H), 6.83 (t, J = 7.2 Hz, 2H), 6.74 (s, Schubert, U. S. Adv. Mater. 2009, 21, 4418. 2H), 6.09 (d, J = 7.5 Hz, 2H), 3.22 (s, 6H) ppm. 13C NMR (75 MHz, (4) Selected examples: (a) Yang, C.-H.; Mauro, M.; Polo, F.; δ Watanabe, S.; Muenster, I.; Fröhlich, R.; De Cola, L. Chem. Mater. acetone-d6): 165.6, 161.6, 155.8, 151.3, 145.4, 142.4, 139.1, 135.0, 125.3, 124.9, 123.8, 123.0, 122.2, 120.5, 120.1, 119.0, 64.1, 35.1 ppm. 2012, 24, 3684. (b) Baranoff, E.; Curchod, B. F. E.; Frey, J.; Scopelliti, + + R.;Kessler,F.;Tavernelli,I.;Rothlisberger,U.;Gratzel,̈ M.; HRMS for M ,[C35H28N6S4Ir] : calcd 853.0888, obsd 853.0889. Anal. Nazeeruddin, M. K. Inorg. Chem. 2012, 51, 215. (c) Brulatti, P.; Calcd for C35H31N6S4IrPF6: C, 42.12; H, 2.83; N, 8.42. Found: C, 42.47; H, 2.95; N, 8.20. Mp: 205 °C dec. Gildea, R. J.; Howard, J. A. K.; Fattori, V.; Cocchi, M.; Williams, J. A. For the synthesis of Ir-6, [(btpy)2IrCl]2 and L3 were used instead G. Inorg. Chem. 2012, 51, 3813. 1 − of [(ppy)2IrCl]2 and L2. Isolated yield: 68%. H NMR (300 MHz, (5) Recent paper on spin orbit coupling analysis of Ir(III) δ acetone-d6): 9.38 (d, J = 7.5 Hz, 2H), 8.04 (t, J = 7.5 Hz, 2H), 7.85 complexes: Koseki, S.; Kamata, N.; Asada, T.; Yagi, S.; Nakazumi, (s, 2H), 7.83 (d, J = 8.4 Hz, 2H), 7.75 (d, J = 8.1 Hz, 2H), 7.56 (s, H.; Matsushita, T. J. Phys. Chem. C 2013, 117, 5314. 2H), 7.21 (t, J = 7.2 Hz, 2H), 7.14 (t, J = 7.2 Hz, 2H), 6.89 (s, 2H), (6) Reviews: (a) Costa, R. D.; Orti, E.; Bolink, H. J.; Monti, F.; 6.83 (t, J = 7.5 Hz, 2H), 6.09 (d, J = 8.1 Hz, 2H), 3.40 (s, 6H) ppm. Accorsi, G.; Armaroli, N. Angew. Chem., Int. Ed. 2012, 51, 8178. 13 δ C NMR (75 MHz, acetone-d6): 165.5, 160.9, 159.3, 153.1, 147.7, (b) Holder, E.; Langeveld, B. M. W.; Schubert, U. S. Adv. Mater. 2005, 145.4, 142.4, 138.9, 135.5, 125.4, 124.9, 123.9, 123.0, 121.7, 120.9, 17, 1109. + + (7) Selected examples: (a) Sato, S.; Morikawa, T.; Kajino, T.; Ishitani, 119.2, 62.1, 37.0 ppm. HRMS for M ,[C35H28N6S2Se2Ir] : calcd O. Angew. Chem., Int. Ed. 2013, 52, 988. (b) Soman, S.; Bindra, G. S.; 948.9777, obsd 948.9780. Anal. Calcd for C35H31N6S4IrPF6: C, 38.50; H, 2.58; N, 7.70. Found: C, 38.85; H, 2.91; N, 8.03. Mp: 232 °C dec. Paul, A.; Groarke, R.; Manton, J. C.; Connaughton, F. M.; Schulz, M.; Experimental Procedure for Photochemical Reactions. In a Dini, D.; Long, C.; Pryce, M. T.; Vos, J. G. Dalton Trans. 2012, 41, 10 mL vial, amine (1.0 mmol) and iridium complex were dissolved in 12678. (c) Lu, Z.; Yoon, T. Angew. Chem., Int. Ed. 2012, 51, 10329. ́ CH2Cl2 (3 mL). After a magnetic spin bar was added, the vial was (d) Lalevee, J.; Blanchard, N.; Tehfe, M.-A.; Peter, M.; Morlet-Savary, sealed using a rubber septum. The reaction mixture was stirred under F.; Fouassier, J. P. Macromol. Rapid Commun. 2011, 32,917. an O2 atmosphere (using an O2 balloon) with irradiation of a blue (e) Larraufie, M.-H.; Pellet, R.; Fensterbank, L.; Goddard, J.-P.; λ 2 ̂ LED ( max 460 nm, 0.9 mW/cm ) strip at room temperature. The Lacote, E.; Malacria, M.; Ollivier, C. Angew. Chem., Int. Ed. 2011, 50, reaction temperature was carefully maintained using a water bath. After 4463. (f) BiSalle, B. F.; Bernhard, S. J. Am. Chem. Soc. 2011, 133, 5 h, the reaction mixture was directly analyzed by 1HNMR 11819. (g) Jasimuddin, S.; Yamada, T.; Fukuju, K.; Otsuki, J.; Sakai, K. spectroscopy. The products were isolated by flash column Chem. Commun. 2010, 46, 8466. (h) Nagib, D. A.; Scott, M. E.; chromatography using neutral alumina. The NMR spectra of the MacMillan, D. W. C. J. Am. Chem. Soc. 2009, 131, 10875. imine products in Table 2 exactly matched with those in our recent (8) (a) Sun, J.; Zhao, J.; Guo, H.; Wu, W. Chem. Commun. 2012, 48, paper.17 4169. (b) Takizawa, S.; Aboshi, R.; Murata, S. Photochem. Photobiol. Sci. 2011, 10, 895. (c) Djurovich, P. I.; Murphy, D.; Thompson, M. E.; ■ ASSOCIATED CONTENT Hernandez, B.; Gao, R.; Hunt, P. L.; Selke, M. Dalton Trans. 2007, 3763. *S Supporting Information (9) DeRosa, M. C.; Crutchley, R. J. Coord. Chem. Rev. 2002, 233, 351. (10) (a) Nonoyama, M. Bull. Chem. Soc. Jpn. 1974, 47, 767. Figures giving the XPS spectra of L2, L3, Ir-2, Ir-3, Ir-5, and Ir- ’ 6 and the quenching curves of singlet oxygen species with (b) Mauro, M.; Paoli, G. D.; Otter, M.; Donghi, D.; D Alfonso, G.; De Cola, L. Dalton Trans. 2011, 40, 12106. benzylamine. This material is available free of charge via the (11) Yang, C.-H.; Beltran, J.; Lemaur, V.; Cornil, J.; Hartmann, D.; Internet at http://pubs.acs.org. Sarfert, W.; Fröhlich, R.; Bizzarri, C.; De Cola, L. Inorg. Chem. 2010, 49, 9891. ■ AUTHOR INFORMATION (12) Although the structural data were not converged due to the disorder in the side ring of the benzothiophene moiety, the Corresponding Author connectivity of the bis(NHC) ligand to Ir in Ir-4 was clearly confirmed *E-mail: [email protected] (S.U.S.); [email protected] (T.K.A.); by single-crystal X-ray analysis. [email protected] (D.H.R.). (13) (a) Jia, W.-G.; Huang, Y.-B.; Lin, Y.-J.; Wang, G.-L.; Jin, G.-X. Notes Eur. J. Inorg. Chem. 2008, 4063. (b) Jia, W.-G.; Huang, Y.-B.; Lin, Y.-J.; fi Jin, G.-X. Dalton Trans. 2008, 5612. (c) Crossley, I. R.; Hill, A. F.; The authors declare no competing nancial interest. Humphrey, E. R.; Smith, M. K. Organometallics 2006, 25, 2242. (d) Kim, H. R.; Jung, I. G.; Yoo, K.; Jang, K.; Lee, E. S.; Yun, J.; Son, S. ■ ACKNOWLEDGMENTS U. Chem. Commun. 2010, 46, 758. (e) Choi, J.; Park, S. Y.; Yang, H. Y.; Kim, H. J.; Ihm, K.; Nam, J. H.; Ahn, J. R.; Son, S. U. Polym. Chem. This work was supported by grants NRF-2011-0029186 2011, 2, 2512. (f) Choi, J.; Ko, J. H.; Jung, I. G.; Yang, H. Y.; Ko, K. (Midcareer Researcher Program) and NRF-2012-1040282 C.; Lee, J. Y.; Lee, S. M.; Kim, H. J.; Nam, J. H.; Ahn, J. R.; Son, S. U. (Priority Research Centers Program). S.U.S. thanks the WCU Chem. Mater. 2009, 21, 2571. (g) Choi, J.; Kang, N.; Yang, H. Y.; Kim, program for the grant R31-2008-10029. H. J.; Son, S. U. Chem. Mater. 2010, 22, 3586.

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(14) Lalevee,́ J.; Dumur, F.; Mayer, C. R.; Gigmes, D.; Nasr, G.; Tehfe, M.-A.; Telitel, S.; Morlet-Savary, F.; Graff, B.; Fouassier, J. P.. Macromolecules 2012, 45, 4134. (15) (a) Lang, X.; Ji, H.; Chen, C.; Ma, W.; Zhao, J. Angew. Chem., Int. Ed. 2011, 50, 3934. (b) Mitsumoto, Y.; Nitta, M. J. Org. Chem. 2004, 69, 1256. (16) Su, F.; Mathew, S. C.; Möhlmann, L.; Antonietti, M.; Wang, X.; Blechert, S. Angew. Chem., Int. Ed. 2011, 50, 657. (17) Park, J. H.; Ko, K. C.; Kim, E.; Park, N.; Ko, J. H.; Ryu, D. H.; Ahn, T. K.; Lee, J. Y.; Son, S. U. Org. Lett. 2012, 14, 5502. (18) Jiang, G.; Chen, J.; Huang, J.-S.; Che, C.-M. Org. Lett. 2009, 11, 4568. Δ ° (19) The free energy values of excited states ( G es) above the ground states of complexes were calculated using the following Δ ° χ′ χ′ Δν 2 −1 equations; G es = E0 + and =( 1/2) (16kBT ln 2) . For definitions of terms, see more details in: (a) Opperman, K. A.; Mecklenburg, S. L.; Meyer, T. J. Inorg. Chem. 1994, 33, 5295. (b) Kober, E. M.; Caspar, J. V.; Lumpkin, R. S.; Meyer, T. J. J. Phys. Chem. 1985, 90, 3722. (20) HOMO energy values were calculated by the following − − − equation: HOMO (eV) = 4.8 [Eox E1/2(ferrocene)]. E1/2(Fc/ Fc+) was observed at +0.36 V. Kim, J. H.; Park, J. H.; Lee, H. Chem. Mater. 2003, 15, 3414. (21) The LUMO energy level of oxygen and HOMO energy level of benzylamine were calculated by density functional theory (DFT) calculations. Refer to the Supporting Information in ref 17. (22) Byteva, I. M. Zh. Prikl. Spektrosk. 1979, 31, 333. (23) Recent examples: (a) McCormick, T. M.; Calitree, B. D.; Orchard, A.; Kraut, N. D.; Bright, F. V.; Detty, M. R.; Eisenberg, R. J. Am. Chem. Soc. 2010, 132, 15480. (b) Ohulchanskyy, T. Y.; Donnelly, D. J.; Detty, M. R.; Prasad, P. N. J. Phys. Chem. B 2004, 108, 8668.

3959 dx.doi.org/10.1021/om4004412 | Organometallics 2013, 32, 3954−3959