Near-Infrared Phosphorescent Iridium(III) Benzonorrole Complexes

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Near-Infrared Phosphorescent Iridium(III) Benzonorrole Complexes Possessing Pyridine-based Axial Ligands Yogesh Kumar Maurya,‡ Takahiro Ishikawa,‡ Yasunori Kawabe,‡ Masatoshi Ishida,‡ Motoki Toganoh,‡ Shigeki Mori,§ Yuhsuke Yasutake,† Susumu Fukatsu,† and Hiroyuki Furuta*,‡ ‡

Department of Chemistry and Biochemistry, Graduate School of Engineering and Center for Molecular Systems, Kyushu University, Fukuoka 819-0395, Japan † Graduate School of Arts and Sciences, The University of Tokyo, Tokyo 153-8902, Japan § Integrated Center for Sciences, Ehime University, Matsuyama 790-8577, Japan S Supporting Information *

ABSTRACT: Novel near-infrared phosphorescent iridium(III) complexes based on benzo-annulated N-linked corrole analogue (termed as benzonorrole) were synthesized. The structures of the complexes revealed octahedral coordination geometries involving an organometallic iridium− carbon bond with two external axial ligands. Interestingly, the iridium(III) complex exhibits near-infrared phosphorescence at room temperature at wavelengths beyond 900 nm. The significant redshift of the emission, as compared to the corrole congener, is originated from the ligand-centered triplet character. The fine-tuning of the photophysical properties of the complexes was achieved by introducing electron-donating and electron-withdrawing substituents on the axial pyridine ligands.

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INTRODUCTION Phosphorescent transition metal complexes exhibiting nearinfrared (NIR) light at room temperature are one of the major focuses of research and development recently in terms of the various applications such as organic light-emitting diodes,1 photocatalysts,2 oxygen sensors,3 biological imaging,4 and so forth. To date, various types of NIR phosphorescent materials based on the d6, d8, and d10 transition metal complexes have been reported by taking advantage of strong spin−orbit coupling that allows efficient population of the triplet manifold.5 As representative examples, platinum(II) complexes with the porphyrin-related macrocycles (e.g., porphyrin (1), phthalocyanine, chlorin, calixphyrin, etc., in Chart 1) demonstrated inherent high stability and strong phosphorescent emission in the NIR region with long emission lifetime up to the microsecond time scale.6 Utilizing the large πconjugated porphyrin-based macrocycles as metal coordination ligands could be one promising approach, since the NIR phosphorescence is frequently originated from the intraligand charge transfer (3ILCT) in the complexes. The emission energy is highly dependent on the ligand orbitals (e.g., highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)) and can be thus controlled by utilizing an appropriate macrocycle. In this regard, cyclometalated d6 octahedral iridium(III) complexes can also be considered as the most efficient and versatile class of phosphorescent materials (e.g., [Ir(ppy)3]3+).7 Neutral iridium(III) complexes supported by rigid and planar π-conjugated macrocycles reveal high chemical stability and provide the ability to tune the emission wavelength. In fact, © XXXX American Chemical Society

corrole (2) serves as a trianionic tetradentate NNNN ligand providing a smaller metal coordination site than porphyrin.8 It has been reported that a halogenated freebase corrole emits phosphorescence at low temperature (77 K) based on the heavier atom effect.9 This heavy atom substitution approach on the corrole frameworks indeed works in the various metallocorroles such as aluminum(III), gold(III), rhodium(III), gallium(III), and tin(IV) as NIR phosphorescence emittors.10 Among them, the nonsubstituted iridium(III) corrole complex (Ir-2a) reported by Gross and Gray et al.11a−c emits remarkably red-shifted phosphorescence at λem ≈ 792 nm under ambient condition relative to that of octaethylporphyrin Ir(III) complex (Ir-1) (λem = 655 nm).12 Kar et al. have recently reported the iridium(III) corrole complexes emitting phosphorescence around 880 nm in the tetrahydrofuran (THF) solution.11d When the Ir(III) corrole complex was functionalized with a BODIPY unit, the phosphorescence enhancement occurs via efficient through-bond energy transfer.11e In view of the fascinating structural effects on the photophysical properties in the Ir(III) corrole complexes, neutral organometallic iridium(III) carbacorrole with a CNNN core (such as 3 and 4)13 should be an interesting hybrid target to investigate the effect of the iridium−carbon bond on the triplet excited state in pursuit of the deep NIR phosphorescence. In this study, we synthesized novel iridium(III) N-linked corrole complexes (Ir-6a−e, Scheme 1) possessing various substituted pyridines as axial ligands. The benzo-annulated NReceived: April 6, 2016

A

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Chart 1

Lash et al., synthesis of organoiridium(III) carbaporphyrins is scarcely achieved due to the high reactivity of organoiridium species.15 For the key process of inner CH activation of 5, a low-valent iridium(I) cyclooctadiene dimer reagent was used to facilitate the oxidative addition.16 It is noted that the reaction medium (i.e., toluene) is also crucial for the preparation of complexes Ir-6; the reaction in THF solution used in the literature yielded a complicated mixture.11b,c Finally, refluxing the toluene solution of 5 with 1.25 equiv of iridium(I) metal salt in the presence of base as well as the corresponding axial pyridine derivatives afforded the desired products in 59−90% yields. Meanwhile, by using the same protocol, the iridium(III) corrole congeners (Ir-2a-e) were also prepared (see the details in Supporting Information). The resulting iridium(III) complexes were fully characterized by using various spectroscopies (e.g., 1H, 13C, and 19F NMR, UV/vis, high-resolution mass) and X-ray crystallographic analysis. The molecular structure of Ir-6a has been confirmed by Xray crystallographic analysis (Figure 1a and Figure S10, Tables 1 and 2).17 The benzonorrole core of the complex is almost planar (mean deviation of 0.039 Å, where the plane is defined by 23 atoms), and the two pyridine molecules occupy the apical positions at the iridium atomic center. The Ir−C bond (1.928 Å) is shorter than the Ir−Npyrrole one (2.007, 1.990, and 1.963 Å) due to the strong σ-donor nature of the inner carbon atom. Two axial pyridines are found to be faced in parallel to the bay area of the benzonorrole with the Ir−Npyridine bond distances of 2.073 and 2.077 Å. Compared to Ir-2a,11c the average Ir− Npyridine bond distance of Ir-6a is slightly longer by 0.016 Å. This implies that the Lewis acidity of the iridium center of Ir-6a can be altered by the lateral coordination environment of the benzonorrole. As a matter of fact, almost similar structural features were observed in the complex Ir-6c possessing N,N′dimethylaminopyridines (Figure 1b and Figure S10).17 The above structural features of Ir-6a and Ir-6c were wellreproduced in the theoretical models obtained by the density functional theory (DFT: B3LYP/6-31G*-LanL2DZ) calculations (Table S1). The bonding interaction between the iridium

Scheme 1. Synthesis of Iridium(III) Benzonorrole Complexes, Ir-6a-e with Various 4-Substituteda Pyridines As Axial Ligands

a

Ar = pentafluorophenyl group.

linked carbacorrole analogue (5) used as the ligand platform has some advantages including the scalable synthetic route and the unique optical properties.14 In addition, this skeletal modified corrole analogue can provide a CNNN-type organometallic coordination environment inside the macrocycle. Thus, the resulting organoiridium complexes Ir-6a−e should be of importance to gain insight into the structure for designing NIR phosphorescent carbaporphyrinoids with a metal−carbon bond. To fine-tune the excited state to achieve the emission in the deep NIR region, the concepts of electropositivity/negativity motifs in the complexes through axial pyridine ligands were introduced. For comparative purposes, the structure and the photophysical properties of regular iridium(III) corrole complexes (Ir-2a−e) were also investigated.

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RESULTS AND DISCUSSION The synthetic route for the complexes Ir-6a-e is shown in Scheme 1. According to the one and only report on the preparation of iridium(III) azuliporphyrin complex (Ir-7) by B

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

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Figure 1. X-ray single crystal structures of complexes (a) Ir-6a and (b) Ir-6c with the 50% thermal ellipsoid probabilities. Co-crystallized solvent molecules and meso-aryl rings were omitted for clarity.

Table 1. Crystallographic Details of Ir-6a and Ir-6c formula cryst syst space group R wR2 (all data) GOF a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) volume, Å3 Z T (K) Dcalc(g/cm3) F000 2θmax no. of reflections measd (unique) no. variables CCDC no.

Ir-6a

Ir-6c

C58H36F15IrN6 tetragonal I41/a 0.0740 0.1540 1.219 36.913(10) 36.913(10) 15.452(4) 90 90 90 21 055(13) 16 100 1.633 10 208 56 12 683 772 1465093

C61H44F15IrN8 triclinic P1̅ 0.0467 0.1096 1.066 11.0104(17) 15.3207(16) 19.061(3) 66.406(6) 89.660(8) 70.254(6) 2742(7) 2 100 1.655 1356 56 13 230 861 1465092

Table 2. Selected Bond Lengths around Iridium Metal Center of Ir-6a, Ir-6c, and Ir-2a

bond distance (Å)

Ir-6a

Ir-6c

Ir-2a11c

Ir1−N1 Ir1−N2 Ir1−N3 Ir1−C17/N4 Ir1−N5 Ir1−N6

1.963(5) 2.007(6) 1.990(6) 1.928(6) 2.073(5) 2.077(5)

1.961(4) 2.014(3) 1.978(5) 1.917(3) 2.078(4) 2.084(4)

1.947(2) 1.979(2) 1.976(2) 1.953(2) 2.052(2) 2.066(2)

Ho: ortho), 5.68 (Py-Hm: meta), and 6.54 ppm (Py-Hp: para) can also be explained by the aromatic ring current effect. The shifts varied depending on substituents on the pyridine rings (cf. Supporting Information). The high-resolution electrospray ionization (HR-ESI) mass spectroscopy of the complexes indicated the presence of two axial pyridine ligands on the iridium center. For instance, the complex Ir-6a exhibited an ion peak at m/z = 1194.1102 [M]+, which is consistent with the theoretical value (calcd. for C51H20F15IrN6; 1194.1139). Likewise, the other series of complexes, Ir-6b-e, were also characterized by mass spectroscopy. The UV−vis absorption spectra for Ir-6a−e in toluene revealed a split Soret-like band and well-structured Q-like bands, which represent the distinct aromatic character of the complexes (Figure 3). In particular, the vibronic 0−0 lowest energy band of Ir-6a located at λmax = 664 nm is higher in

center and pyridinic nitrogen atoms was dependent upon the electron donor ability of the pyridine ligands, which may induce the alteration of the photophysical properties (vide infra). The 1H NMR spectrum of Ir-6a supports the proposed structure revealed in the solid state (Figure 2a). Although the degree of aromaticity is slightly weaker than that of Ir-2a, the distinct diatropicity of Ir-6a is retained as evident from the characteristic resonance shifts of β-pyrrolic protons (β-H) that appear in the lower-field region (δ = 7.4−8.2 ppm). The 1 H−1H COSY spectrum of Ir-6a supports the assignment of aromatic protons of a phenylene ring and β-pyrrole moieties (Figure 2b). On the one hand, the cross couplings for the doublet/triplet resonance peaks at 8.24, 7.15, 7.38, and 7.27 ppm are attributed to the phenylene protons. On the other hand, the upfield shifts of the axial pyridine C−Hs at 3.56 (PyC

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

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transitions with small oscillator strengths (Figure S21 and Table S2). For the cases of Ir-6a−c, the HOMO−LUMO transitions are predominantly governed by the typical ππ* transitions (Figure S19). The theoretical HOMO−LUMO energy gaps of Ir-6a−e are considerably narrower than those of Ir-2a−e, which results in the redshifts of the emission maxima (Figures S21 and S22). The smaller HOMO−LUMO gaps are originated from the destabilization of the HOMO energy. The lifted degeneracy of the HOMO pair gives rise to an allowed S0−S1 transition with moderate oscillator strength ( f ≈ 0.14; Table S2). Similar electronic effects of the substituents of pyridine were seen in the corrole complexes (Figure S22 and Table S3). As with the corrole complex Ir-2a, the complexes Ir-6a−e exhibited distinct phosphorescent emission at room temperature (Figures 4 and S12). Notably, the emission wavelength is

Figure 2. (a) Partial 1H NMR spectrum of Ir-6a in CD2Cl2 at 298 K, (b) 1H−1H COSY spectrum in the peripheral CHs region of Ir-6a in CD2Cl2 at 298 K.

Figure 4. Normalized phosphorescence spectra of Ir-6a−e at room temperature in toluene solution; λex = 670 nm.

longer than 900 nm, which is remarkably red-shifted compared to that of the corrole congener Ir-2a (λmax = 792 nm in toluene).11b This shift could be originated from the substantial 3 LC character of the benzonorrole ligand 5 containing a structurally perturbed N-linked indole unit.18 Similarly to the absorption spectra, the emission wavelengths varied depending on the electron-donating ability of the substituents on the pyridine moieties. Also note that the corresponding Stokes shifts are significantly larger than those of a series of corroles Ir2a−e (Tables 3 and 4). The phosphorescence of Ir-6a−e was significantly enhanced at low temperature without spectral change (e.g., the peak height of λem of Ir-6a was intensified 2 times at 190 K), which suggests the dominance of the triplet excited-state due to the strong spin−orbit coupling (Figure S13). The polarized organometallic bond and the perturbed πconjugated pathway via N-linkage present in Ir-6a−e may play roles in the shift of the energies of the lowest triplet states. The phosphorescence quantum yields ΦPL of Ir-6a−e in toluene solution at 298 K were determined to be 0.35−0.62%, which are rather small as compared to that of Ir-2a (ΦPL = 1.2%; Tables 3 and 4). The emissive lifetimes were estimated to be in the range of 0.15−0.50 μs by the time-correlated single photon counting (TCSPC). These are shorter than those of Ir2a−e (Figures S14 and S15).20 In an effort to understand the relaxation process, the overall radiative and nonradiative rate constants kr and knr were calculated for Ir-6a−e. It was found that the relative quantum yields of Ir-6a−e are likely to be governed by the nonradiative deactivation processes (knr). In

Figure 3. UV−vis absorption spectra of Ir-6a−e in toluene.

intensity than that of the 1−0 band. Such a trend in the transition nature is opposite to that of the corrole complex Ir2a (Figure S11).11b As expected, replacement of the substituents on the axial pyridine ligand caused the shifts of transition energies; for the electron-rich derivatives (i.e., Ir-6b and Ir-6c), the peak of the lowest transition is red-shifted slightly, whereas the electron-deficient derivatives (i.e., Ir-6d and Ir-6e) show blue shifts of the corresponding bands. In the low-energy region of the spectra from Ir-6d and Ir-6e, a very broad shoulder band is seen. This suggests the intramolecular charge transfer (CT) of the forbidden transition nature arising from the strong electron-withdrawing ability of 4cyano- and 4-carbethoxy-substituted pyridine derivatives upon photoexcitation. The molecular energy diagrams of the complexes Ir-6d and Ir-6e support the presence of the CT D

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 3. Photophysical Dataa of Ir-6a−e complex Ir-6a Ir-6b Ir-6c Ir-6d Ir-6e

λabs (nm) (ε/1 × 104 M−1 cm−1)b λem (nm) 664 669 677 660 662

(1.72) (1.70) (1.71) (1.66) (1.69)

931 933 944 920 925

ΦPLc (1 × 10−2) 0.43 0.51 0.35 0.61 0.62

τPL (μs)d kr (1 × 104 s−1) 0.147 0.152 0.165 0.497 0.256

2.93 3.36 2.12 1.23 2.42

knr (1 × 106 s−1)

Stokes shift (cm−1)

ΔES‑T (eV)e

6.79 6.56 6.04 2.00 3.88

4319.1 4229.6 4177.8 4282.0 4294.9

0.85 0.85 0.84 0.07 0.26

Measured in toluene. bWavelength of the lowest Q-bands. cQuantum yield was calculated by using IR-1040 (Φ = 0.012 in CH2Cl2, λex = 570 nm) as reference.19 dDetermined by TCSPC method with excitation at 530 nm. eObtained by the TD-DFT calculations (B3LYP/6-31G**/LANL2DZ).

a

Table 4. Photophysical Dataa of Ir-2a−e complex Ir-2a Ir-2b Ir-2c Ir-2d Ir-2e

λabs (nm) (ε /1 × 104 M−1 cm−1)b λem (nm) 620 628 641 612 616

(1.07) (0.95) (0.84) (1.47) (1.32)

792 797 807 788 793

ΦPLc (1 × 10−2)

τPL (μs)d

kr (1 × 104 s−1)

knr (1 × 105 s−1)

Stokes shift (cm−1)

ΔES‑T (eV)e

1.20 2.63 1.27 3.09 2.68

2.59 1.94 1.52 4.25 6.45

0.46 1.36 0.84 0.73 0.42

3.8 5.0 6.5 2.3 1.5

3502.8 3376.5 3209.1 3649.5 3623.4

0.78 0.76 0.75 0.05 0.35

Measured in toluene. bWavelength of the lowest Q-bands. cQuantum yield was calculated by using Ir-2a (Φ = 0.012 in toluene, λex = 496.5 nm) as reference.2 dDetermined by TCSPC method with excitation at 530 nm. eObtained by the TD-DFT calculations (B3LYP/6-31G**/LANL2DZ).

a

Dry toluene and THF (stabilizer free) was purchased from KANTO and used as received. Thin-layer chromatography (TLC) was performed on aluminum sheet coated with silica gel 60 F254 (Merck). Preparative separation was performed by silica gel flash column chromatography (KANTO Silica Gel 60N, spherical, neutral, 40−50 μm) or silica gel gravity column chromatography (KANTO Silica Gel 60N, spherical, neutral, 63-210 μm). The benzonorrole ligand 514 and iridium corrole complex Ir-2a11b,c were prepared according to the reported protocol. 1H, 13C, and 19F NMR spectra were recorded in CDCl3 and CD2Cl2 solutions on a JEOL ECX500 NMR spectrometer (500 MHz for 1H) and a Bruker Advance III HD600SB spectrometer (600 MHz for 1H; 564 MHz for 19F, and 150 MHz for 13C). Chemical shifts were reported relative to CDCl3 (δ = 7.26 ppm) and CD2Cl2 (δ = 5.32 ppm) for 1H in parts per million and CDCl3 (δ = 77.16 ppm) and CD2Cl2 (δ = 53.8 ppm) for 13C in parts per million. Trifluoroacetic acid (0.02% in CDCl3) was used as an external reference for 19F (δ = −76.5 ppm). UV−vis−NIR spectra were measured on a Shimadzu UV-3150PC spectrometer. Fluorescence spectra were recorded on an SPEX Fluorolog-3-NIR spectrometer (HORIBA) with NIR-PMT R5509 photomultiplier tube (Hamamatsu) in a 10 mm quartz fluorescence cuvette. Highresolution mass (HRMS) spectra were measured with a JEOL JMST100CS (ESI mode).

contrast to the limited variations of kr, the value of knr significantly varied, probably due to the inherent structural effect of the axial pyridine moieties. In fact, a similar trend of the decay rates was seen in the corrole derivatives (Table 4). According to the energy-gap law, knr = α exp(−βΔE); the constant knr increases with a decrease in the energy gap (ΔE) between the emissive excited state and the ground state (α and β are constants).21 The rate constants knr values of Ir-6a−e are significantly larger than those of Ir-2a−e. These lower quantum yields, and shorter emission lifetimes for Ir-6a−e could be owing to the electronic perturbations of the π-conjugated ligand via N-linkage fashion, which consequently reduces the energy gap of S0−S1 transition. Lowering the inherent energies of emission could thus facilitate the rapid excited-state depopulation via nonradiative processes. Observation of the larger Stokes shift vales for Ir-6a−e is also consistent with the above analysis.

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CONCLUSION

In summary, we have prepared a series of iridium(III) benzonorrole complexes Ir-6a−e, possessing various substituted pyridine axial ligands, as novel NIR-emitting materials. Compared with the iridium(III) corrole congeners, Ir-6a−e exhibit phosphorescence in the deep NIR beyond 900 nm under ambient conditions. Moreover, axial pyridine ligands on the complexes can control the inherent stability and solubility in organic solvents. The substitution of the axial pyridine in the complexes enables to fine-tune their photophysical properties as well. Importantly, the N-linked mutation of the corrole framework can cause a drastic change in the photophysical properties, for example, lower energy emission. It is however still necessary to improve the overall quantum yield of emission. The study would contribute to design new organoiridium(III) complexes based on the porphyrinoids for promising applications including efficient NIR-emitting devices.

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THEORETICAL CALCULATIONS DFT calculations were performed with the Gaussian09 program package without symmetry treatment.22 Initial structures were based on the X-ray crystal structure of the related compounds. The geometries were fully optimized using Becke’s three-parameter hybrid functional combined with the Lee−Yang−Parr correlation functional, denoted as the B3LYP level of DFT, with the 6-31G(d, p) and LANL2DZ (for Ir) basis set for all calculations.23 Experimental absorption spectra were analyzed by the time-dependent DFT (TD-DFT) calculations with the same level. Ground-state geometries were verified by the frequency calculations, where no imaginary frequency was found. X-ray Crystallography. Single-crystal X-ray structural analyses for Ir-6a and Ir-6c were performed on a Saturn equipped with a CCD detector (Rigaku) using Mo Kα (graphite, monochromated, λ = 0.710 69 Å) radiation. The data were corrected for Lorentz, polarization, and absorption effects. The structure was solved by the direct method of

EXPERIMENTAL SECTION

Materials and Instruments. All reactions were performed in dried vessels under Ar or N2. Commercially available solvents and reagent were used without further purification unless otherwise mentioned. CH2Cl2 was dried by passing through a pad of alumina. E

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

J = 7.6 Hz, 1H), 7.14 (t, J = 7.5 Hz, 1H), 5.19 (d, J = 7.7 Hz, 4H), 3.40 (d, J = 7.6, 1.4 Hz, 4H), 3.13 (s, 6H); 13C NMR (151 MHz, CD2Cl2, ppm): δ 173.72, 164.88, 149.62, 147.79, 147.09 (d, JCF = 242 Hz), 146.25 (d, JCF = 244 Hz), 144.72, 144.08, 143.75, 141.79 (d, JCF = 253 Hz), 141.22 (d, JCF = 257 Hz), 138.33 (d, J = 251 Hz), 138.06 (d, JCF = 251 Hz), 134.92, 134.80, 134.22, 131.44, 130.94, 124.82, 123.67, 123.45, 123.09, 121.40, 120.37, 119.56, 117.35 (t, J = 19 Hz), 116.82 (t, J = 19 Hz), 115.47 (t, J = 18 Hz), 112.80, 111.58, 110.99, 109.68, 108.75, 101.74, 90.43, 55.57; 19F NMR (565 MHz, CD2Cl2, ppm): δ −139.90 (dd, J = 25.4, 7.9 Hz, 2F), −140.20 to ca. −140.38 (m, 4F), −155.91 to ca. −156.04 (m, 1F), −156.47 (t, J = 20.7 Hz, 1F), −157.43 to ca. −157.55 (m, 1F), −163.64 to ca. −163.81 (m, 2F), −164.06 to ca. −164.24 (m, 2F), −164.80 to ca. −165.01 (m, 2F); UV/vis/NIR (toluene): λmax/nm (ε × 10−3 [M−1 cm−1]) = 394 (31.3), 411 (32.1), 431 (35.6), 578 (6.94), 620 (11.0), 669 (17.0); HRMS (ESI+): Found: m/z 1254.136 98. Calcd for C 53H 24 F 15 IrN 6 O 2 ([M]+ ): m/z 1254.13505, with error: +1.94 ppm. Synthesis of Ir-6c. Benzonorrole (15 mg, 0.0177 mmol), [Ir(cod) (OMe)]2 (14.7 mg, 0.0221 mmol), K2CO3 (50 mg, 0.362 mmol), and 4-(dimethylamino)pyridine (43.3 mg, 0.354 mmol) was dissolved in toluene (3 mL) under Ar at room temperature. After it was stirred for 10 min, the reaction mixture was heated to 100 °C and was stirred further for 40 min. The resulting solution was allowed to cool to room temperature and passed through the alumina pad in CH2Cl2, and the solvents were evaporated in vacuo. Further, the desired product was purified by passing through a silica gel column with CH2Cl2/hexane (v/v = 20/80) as eluent. The product was recrystallized from CH2Cl2/hexane to give green colored compound in 88.5% yield (20 mg). 1 H NMR (600 MHz, CD2Cl2, ppm): δ 8.19 (d, J = 7.6 Hz, 1H), 8.02 (d, J = 3.8 Hz, 1H), 7.97 (d, J = 4.7 Hz, 1H), 7.86 (d, J = 4.7 Hz, 1H), 7.80 (d, J = 4.6 Hz, 1H), 7.77 (d, J = 4.6 Hz, 1H), 7.35 (d, J = 7.5 Hz, 1H), 7.33 (d, J = 3.5 Hz, 1H), 7.21 (d, J = 7.6 Hz, 1H), 7.11 (t, J = 7.5 Hz, 1H), 4.80 (d, J = 7.1 Hz, 4H), 3.18 (d, J = 7.2 Hz, 4H), 2.28 (s, 12H); 13C NMR (151 MHz, CD2Cl2, ppm): δ 176.28, 152.36, 148.08, 146.99, 144.77, 144.17, 143.76, 135.05, 134.68, 134.28, 131.28, 130.69, 129.34, 128.58, 124.60, 123.36, 122.96, 122.82, 121.36, 119.80, 119.29, 112.61, 111.53, 111.16, 109.08, 105.55, 101.04, 89.93, 38.63 (The resonances for meso-aryl carbons were not clearly shown due to the 13C−F coupling with adjacent fluorine atoms); 19F NMR (565 MHz, CD2Cl2, ppm): δ −139.08 (dd, J = 25.5, 7.9 Hz, 2F), −139.52 (td, J = 24.2, 7.9 Hz, 4F), −155.71 (t, J = 20.7 Hz, 1F), −156.23 (t, J = 20.7 Hz, 1F), −157.21 (t, J = 20.7 Hz, 1F), −163.25 to ca. −163.38 (m, 2F), −163.65 to ca. −163.79 (m, 2F), −164.37 to ca. −164.51 (m, 2F); UV/vis/ NIR (toluene): λmax/nm (ε × 10−3 [M−1 cm−1]) = 394 (30.2), 435 (37.2), 583 (6.64), 628 (11.59), 677 (17.1); HRMS (ESI+): Found: m/z 1280.19458. Calcd for C55H30F15IrN8 ([M]+): m/z 1280.19832, with error: −3.73 ppm. Synthesis of Ir-6d. Benzonorrole (15 mg, 0.0177 mmol), [Ir(cod) (OMe)]2 (14.7 mg, 0.0221 mmol), K2CO3 (50 mg, 0.362 mmol), and 4-cyanopyridine (36.9 mg, 0.354 mmol) were dissolved in toluene (3 mL) under Ar at room temperature. After it was stirred for 10 min, the reaction mixture was heated to 100 °C and was stirred further for 40 min. The resulting solution was allowed to cool to room temperature and passed through the alumina pad in CH2Cl2, and the solvents were evaporated in vacuo. Further, the desired product was purified by passing through a silica gel column

SHELXS-97 and refined using the SHELXL-97 program. All the positional parameters and thermal parameters of nonhydrogen atoms were refined anisotropically on F2 by the fullmatrix least-squares method. Hydrogen atoms were placed at the calculated positions and refined riding on their corresponding carbon atoms. Synthesis of Iridium(III) Complexes. All the iridium(III) benzonorrole and corrole complexes (Ir-6a−e and Ir-2a−e) were prepared by following a similar protocol. The synthetic procedures and the detailed characterized data of Ir-2a−e are given in the Supporting Information. Synthesis of Ir-6a. Benzonorrole (15 mg, 0.0177 mmol), [Ir(cod) (OMe)]2 (14.7 mg, 0.0221 mmol), K2CO3 (50 mg, 0.362 mmol), and pyridine (28.6 μL, 0.354 mmol) were dissolved in toluene (3 mL) under Ar at room temperature. After it was stirred for 10 min, the reaction mixture was heated to 100 °C and was stirred further for 45 min. After it cooled to room temperature, the reaction mixture was passed through the alumina pad in CH2Cl2, and the solvents were evaporated in vacuo. Further, the desired product was purified by passing through a silica gel column with CH2Cl2/hexane (v/v = 15/85) as eluent. The product was recrystallized from CH2Cl2/hexane to give green colored compound in 89.8% yield (19 mg). 1 H NMR (500 MHz, CD2Cl2, ppm): δ 8.24 (d, J = 7.7 Hz, 1H), 8.09 (d, J = 3.9 Hz, 1H), 8.07 (d, J = 4.8 Hz, 1H), 7.95 (d, J = 4.7 Hz, 1H), 7.83 (d, J = 4.7 Hz, 1H), 7.79 (d, J = 4.7 Hz, 1H), 7.46 (d, J = 3.9 Hz, 1H), 7.38 (t, J = 7.5 Hz, 1H), 7.26 (d, J = 7.7 Hz, 1H), 7.15 (t, J = 7.6 Hz, 1H), 6.54 (t, J = 7.5 Hz, 2H), 5.68 (t, J = 7.2 Hz, 4H), 3.56 (d, J = 5.5 Hz, 4H); 13C NMR (151 MHz, CD2Cl2): δ 172.40, 149.15, 147.85, 146.92 (d, JCF = 240 Hz), 146.23 (d, JCF = 244 Hz), 144.69, 144.00, 143.70, 141.30 (d, JCF = 256 Hz), 141.25 (d, JCF = 240 Hz), 138.11 (d, J = 255 Hz), 135.91, 134.92, 134.87, 134.23, 131.51, 131.05, 124.91, 123.80, 123.69, 123.53, 123.20, 121.51, 120.58, 119.70, 117.17 (t, JCF = 19 Hz), 116.75 (t, JCF = 20 Hz), 115.41 (t, JCF = 20 Hz), 112.90, 111.79, 110.75, 108.59, 102.12, 90.63; 19 F NMR (565 MHz, CD2Cl2, ppm): δ −139.33 (dd, J = 25.0, 7.8 Hz, 2F), −139.49 to ca. −139.66 (m, 4F), −155.14 (t, J = 20.6 Hz, 1F), −155.62 (t, J = 20.6 Hz, 1F), −156.64 (t, J = 20.6 Hz, 1F), −162.84 to ca. −163.00 (m, 2F), −163.25 to ca. −163.43 (m, 2F), −164.04 to ca. −164.23 (m, 2F); UV/vis/ NIR (toluene): λmax/nm (ε × 103 [M−1 cm−1]) = 405 (31.6), 429 (33.4), 448 (33.3), 570 (5.54), 618 (9.67), 664 (17.2); HRMS (ESI + ): Found: m/z 1194.11026. Calcd for C51H20F15IrN6([M]+): m/z 1194.11392, with error: −3.65 ppm. Synthesis of Ir-6b. Benzonorrole (15 mg, 0.0177 mmol), [Ir(cod) (OMe)]2 (14.7 mg, 0.0221 mmol), K2CO3 (50 mg, 0.362 mmol), and 4-methoxypyridine (35.9 μL, 0.354 mmol) were dissolved in toluene (3 mL) under Ar at room temperature. After it was stirred for 10 min, the reaction mixture was heated to 100 °C and was stirred further for 40 min. The resulting solution was allowed to cool to room temperature and passed through the alumina pad in CH2Cl2, and the solvents were evaporated in vacuo. Further, the desired product was purified by passing through a silica gel column with CH2Cl2/hexane (v/v = 20/80) as eluent. The product was recrystallized from CH2Cl2/hexane to give green colored compound in 81% yield (18 mg). 1 H NMR (600 MHz, CD2Cl2, ppm): δ 8.22 (d, J = 7.7 Hz, 1H), 8.07 (d, J = 3.9 Hz, 1H), 8.05 (d, J = 4.7 Hz, 1H), 7.93 (d, J = 4.7 Hz, 1H), 7.83 (d, J = 4.7 Hz, 1H), 7.80 (d, J = 4.7 Hz, 1H), 7.42 (d, J = 3.8 Hz, 1H), 7.37 (t, J = 7.5 Hz, 1H), 7.25 (d, F

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry with CH2Cl2/hexane (v/v = 40/60) as eluent. The product was recrystallized from CH2Cl2/hexane to give green colored compound in 59.1% yield (13 mg). 1 H NMR (500 MHz, CD2Cl2, ppm): δ 8.27 (d, J = 7.8 Hz, 1H), 8.14 (t, J = 4.2 Hz, 2H), 8.01 (d, J = 4.7 Hz, 1H), 7.87 (d, J = 4.8 Hz, 1H), 7.82 (d, J = 4.8 Hz, 1H), 7.57 (d, J = 3.9 Hz, 1H), 7.43 (t, J = 7.6 Hz, 1H), 7.30 (d, J = 7.7 Hz, 1H), 7.21 (d, J = 7.5 Hz, 1H), 5.89 (d, J = 7.0 Hz, 4H), 3.60 (d, J = 7.0 Hz, 4H); The nature of the labile axial pyridine ligands in solution hampered to obtain clear 13C NMR spectrum; 19F NMR (466 MHz, CD2Cl2, ppm): δ −139.53, −139.91 (d, J = 21.5 Hz), −140.03 to ca. −140.35 (m), −154.58, −155.06, −156.06, −156.13, −162.58 (d, J = 26.8 Hz), −163.08 (d, J = 23.4 Hz), −163.12 to ca. −163.30 (m), −163.88 (d, J = 27.5 Hz), −163.93 to ca. −164.06 (m); UV/vis/NIR (toluene): λmax/nm (ε × 10−3 [M−1 cm−1]) = 398 (31.6), 423 (30.5), 443 (33.9), 568 (6.27), 612 (9.15), 660 (16.6); HRMS (ESI+): Found: m/z 1036.03025. Calcd for C41H10F15IrN4 ([M−2 pyridines]+): m/z 1036.02952, with error: +0.3 ppm. Synthesis of Ir-6e. Benzonorrole (15 mg, 0.0177 mmol), [Ir(cod)(OMe)]2 (14.7 mg, 0.0221 mmol), K2CO3 (50 mg, 0.362 mmol), and 4-carbethoxypyridine (53 μL, 0.354 mmol) were dissolved in toluene (3 mL) under Ar at room temperature. After it was stirred for 10 min, the reaction mixture was heated to 100 °C and was stirred further for 40 min. The resulting solution was allowed to cool to room temperature and passed through the alumina pad in CH2Cl2, and the solvents were evaporated in vacuo. Further, the desired product was purified by passing through a silica gel column with CH2Cl2/hexane (v/v = 20/80) as eluent. The product was recrystallized from CH2Cl2/hexane to give green colored compound in 84.4% yield (20 mg). 1 H NMR (600 MHz, CD2Cl2, ppm): δ 8.26 (d, J = 7.7 Hz, 1H), 8.13 (d, J = 4.8 Hz, 1H), 8.12 (d, J = 3.9 Hz, 1H), 8.01 (d, J = 4.7 Hz, 1H), 7.86 (d, J = 4.8 Hz, 1H), 7.82 (d, J = 4.7 Hz, 1H), 7.54 (d, J = 3.9 Hz, 1H), 7.40 (t, J = 7.9 Hz, 1H), 7.30 (d, J = 7.7 Hz, 1H), 7.18 (t, J = 7.5 Hz, 1H), 6.21 (d, J = 7.1 Hz, 4H), 3.93 (q, J = 7.1 Hz, 4H), 3.68 (d, J = 7.2 Hz, 4H), 1.00 (t, J = 7.1 Hz, 6H); 13C NMR (151 MHz, CD2Cl2, ppm): δ 170.53, 163.00, 150.16, 147.28, 147.07 (d, JCF = 240 Hz), 146.30 (d, JCF = 247 Hz), 144.61, 143.94, 143.70, 141.93 (d, JCF = 261 Hz), 141.35 (d, JCF = 253 Hz), 138.48 (d, JCF = 252 Hz), 137.14, 134.99, 134.71, 134.17, 131.60, 131.17, 125.15, 124.09, 124.04, 123.40, 122.84, 121.49, 120.95, 119.90, 116.96 (t, JCF = 19 Hz), 116.63 (t, JCF = 19 Hz), 115.27 (t, JCF = 19 Hz), 113.04, 112.01, 110.37, 108.38, 102.62, 91.01, 62.34, 13.91 (d, J = 16.8 Hz); 19F NMR (565 MHz, CD2Cl2, ppm): δ −139.22 (dd, J = 25.3, 7.8 Hz, 2F), −139.56 (dd, J = 24.4, 7.9 Hz, 4F), −154.88 (t, J = 20.7 Hz, 1F), −155.30 to ca. −155.43 (m, 1F), −156.37 to ca. −156.50 (m, 1F), −162.71 to ca. −162.86 (m, 2F), −163.14 to ca. −163.29 (m, 2F), −163.98 to ca. −164.12 (m, 2F); UV/vis/NIR (toluene): λmax/nm (ε × 10−3 [M−1 cm−1]) = 400 (31.5), 425 (32.4), 444 (33.8), 570 (6.02), 614 (9.29), 662 (16.9); HRMS (ESI+): Found: m/z 1338.160 84. Calcd for C57H28F15IrN6O4 ([M]+): m/z 1338.156 18, with error: +4.67 ppm.

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The detailed synthetic procedures, NMR, mass spectroscopic data, absorption/emission spectra, and DFTcalculations (PDF) Crystallographic data for Ir-6a (CIF) Crystallographic data for Ir-6c (CIF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The work was supported by Grant-in-Aids (15K13646 to H.F., 16K05700 to M.I. 25246021 to S.F.) from Japan Society for the Promotion of Science (JSPS). The authors thank to Dr. M. Watanabe for the help of NMR measurements.

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REFERENCES

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S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b00853. G

DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.6b00853 Inorg. Chem. XXXX, XXX, XXX−XXX