Synthesis and Characterization of an Iridium Triphyrin Complex

Sep 23, 2016 - Daiki Kuzuhara , Shinsuke Kawatsu , Wataru Furukawa , Hironobu Hayashi , Naoki Aratani , Hiroko Yamada. European Journal of Organic ...
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Synthesis and Characterization of an Iridium Triphyrin Complex Songlin Xue,† Daiki Kuzuhara,*,‡ Naoki Aratani,† and Hiroko Yamada*,† †

Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan ‡ Department of Physical Science and Materials Engineering, Iwate University, 4-3-5 Ueda, Morioka 020-8551, Japan S Supporting Information *

ligand. We revealed that the valence of iridium is changed from IrI to IrIII with transformation of the COD ligand. In addition, the optical and electrochemical properties of the iridium complex will be discussed. The synthetic scheme of TriP-IrIII (2) is shown in Scheme 1. Compound 1 was reacted with [IrCl(cod)]2 in degassed N,N-

ABSTRACT: A sandwich complex of iridium(III) benzotriphyrin (2) has been synthesized from free-base benzotriphyrin (1) and [IrCl(cod)]2 (COD = 1,5cyclooctadiene). The COD ring was transformed from 1,5-COD to an η1,η3-C8H12 unit as a π-allyl ligand associated with the valence change of iridium from IrI to IrIII, as revealed by X-ray diffraction analysis. The Soret-like band of 2 was blue-shifted and broadened compared with that of 1, indicating strong electronic interactions between triphyrin and the iridium ion. Compound 2 also showed very broad absorption in the range of 500−800 nm, which can be assigned to a mixture of Q and metal-to-ligand charge-transfer bands.

Scheme 1. Synthesis of 2

I

n the past decade, contracted porphyrinoids, relatively new members of the porphyrin family, have attracted the attention of researchers for their potential applications in a variety of fields because of their coordination abilities and catalysis activities.1 Triphyrins consist of three pyrrole or related compounds and show unique optical and electronic properties compared with the parent porphyrin.2,3 Among the reported triphyrins, we and others have developed the synthesis and metalation of [14]triphyrins(2.1.1) and related compounds. 2 [14]Triphyrins(2.1.1) generally have a 14π-electron system and have one-valence tridentate coordination structures. Thus, the [14]triphyrins(2.1.1) make it possible to prepare the various metal complexes with BIII, MnI, ReI, RuII, FeII, PdII, PtII, and PtIV ions, to date.2b,3 We have chosen an iridium complex of triphyrin (TriP-IrIII) as the next target because iridium complexes have received much attention for their applications for example as catalysts for organic synthesis4 and organic light-emitting diodes.5,6 Iridium complexes coordinated by porphyrin,7 corrole,8a,b benzonorrole,8c and N-confused porphyrin9 have been reported to date. 1,5-Cyclooctadiene (COD) has been known as an important and fundamental ligand for diverse metal complexes.10 In particular, the COD ligand enables us to make stable metal complexes.11 In porphyin families, iridium porphyrin complexes with the COD ligand have barely been reported. Shinokubo and co-workers reported iridium complexes of dipyridylporphyrin with [IrCl(cod)]2.12 However, the unexpected η1,η3-C8H10Ocoordinated iridium complex was isolated. Also, the iridium center was oxidized from IrI to IrIII during the reaction. Herein, we report the metalation of benzotriphyrin 1 with [IrCl(cod)]2. This is the first example of an iridium complex of [14]triphyrins(2.1.1) containing an η1,η3-C8H12 ring as a π-allyl © 2016 American Chemical Society

dimethylformamide (DMF) at 130 °C under a nitrogen atmosphere. The crude material was purified by silica gel column chromatography with chloroform as an eluent to give the iridium complex 2 in 46% yield as a major product. The structure of 2 was characterized by high-resolution matrix-assisted laser desorption/ionization time-of-flight (HR-MALDI-TOF) mass spectroscopy, X-ray diffraction analysis, 1H and 13C NMR spectroscopy, and 1H−1H COSY NMR spectroscopy. The HR-MALDITOF mass spectrum of 2 showed the parent ion peaks at m/z 999.3159 [calcd for C60H45IrN3: m/z 999.3164 ([M]+); Figure S1]. We also detected a minor product of m/z 1015.3108 by HRMALDI-TOF mass spectroscopy in trace (Figure S2). This might have one oxygen atom in complex 2 (2-O). We examined the formation of 2-O from 2 under a couple of reaction conditions: (a) refluxed in DMF under an ambient atmosphere for 12 h; (b) stirred in CH2Cl2 in the presence of 30% H2O2 for 24 h; (c) stirred in CH2Cl2/meta-chloroperbenzoic acid (mCPBA) for 12 h; (d) stirred in CH2Cl2 under light and ambient atmosphere for 24 h. However, we were not successful in isolating 2-O. The structure of complex 2 was confirmed by X-ray crystallography (Figure 1). It is clearly shown that the IrIII ion is in a fac-coordination fashion and is sandwiched between one COD ring and one triphyrin macrocycle in the same manner as TriP-Fe-Cp complexes.3c The iridium center is coordinated to three nitrogen atoms on the triphyrin macrocycle and to one Received: August 3, 2016 Published: September 23, 2016 10106

DOI: 10.1021/acs.inorgchem.6b01841 Inorg. Chem. 2016, 55, 10106−10109

Communication

Inorganic Chemistry

ppm (Figure 2a). Isoindole and phenyl ring protons of 2 were observed in the range of 6.5−8.5 ppm as scattered signals because of low molecular symmetry (Figure 2a). We also measured 1H NMR spectra in C2D2Cl4 at 50, 75, and 100 °C for investigation of the molecular dynamics of complex 2 (Figure S9). The COD ring maintained the shape and position of the signals even at 100 °C, indicating that the rotations of triphyrin and COD are suppressed around the metal ion. These results corresponded with the results of X-ray diffraction analysis. The UV−vis absorption spectra of 1 and 2 in CH2Cl2 are shown in Figure 3. We reported that 1 showed typical porphyrin-

Figure 1. Crystal structure of 2: (a) top view; (b) side view with selected label atoms. Hydrogen atoms are omitted for clarity. The thermal ellipsoids represent 50% probability.

carbon sp3 (C57) and three π-allylic carbon (C60, C53, and C54) atoms on the C8H12 ring. The bond lengths are 1.418 Å (C53− C60), 1.452 Å (C53−C54), 1.523 Å (C54−C55), 1.494 Å (C55−C56), 1.523 Å (C56−C57), 1.504 Å (C57−C58), 1.511 Å (C58−C59), and 1.493 Å (C59−C60). These bond lengths imply that part of C53−C54 and C53−C60 form a π-allyl structure and other carbon atoms form C−C single bonds, indicating transformation of the COD ring from 1,5-COD to an η1,η3-C8H12 ring. In addition, the valence of the iridium center is changed from IrI to IrIII. A similar phenomenon has been reported by the porphyrinate ligands.12 The bond lengths between the iridium center and each carbon atom of the π-allyl ligand are 2.186 Å (C60−Ir), 2.090 Å (C53−Ir), and 2.193 Å (C54−Ir) and the bond length between iridium and C57 is 2.116 Å (Figure 1b), which are similar to those of known π-allyl COD ring iridium complexes.12,13 The 1H NMR spectra of 1 and 2 are shown in Figures 2 and S4. Initially, we tried to characterize the 1H NMR signals at room

Figure 3. UV−vis absorption spectra of 1 (red line) and 2 (blue line) in CH2Cl2.

like absorption.2a,b,3a,15 The magnetic circular dichroism and time-dependent denstiy functional theory (TD-DFT) calculations of the free base 1 suggested that Soret- and Q-like bands of 1 are composed of four frontier orbitals (HOMO, HOMO−1, LUMO, and LUMO+1) like typical porphyrinoid systems by the theory of Gouterman’s four-orbital model.15 In contrast, Soretlike bands of 2 were observed at 346 and 390 nm, which exhibited a blue shift and broadened compared with those of 1. A similar phenomenon was reported on TriP-Fe-Cp because of strong electronic interactions between the triphyrin ligand and metal ions.3c At the Q-band region, 2 showed very broad absorption at 526 and 658 nm and the absorption edge reached around 800 nm. In order to investigate the absorption properties of 2, TDDFT calculation was performed. The results of TD-DFT calculation showed that broadened peaks of 2 between 450 and 800 nm can be assigned to a mixture of metal-to-ligand charge-transfer (MLCT) and Q bands (Figures S10 and S11 and Table S1). Unfortunately, we could not observe phosphorescence from compound 2 under an argon atmosphere at room temperature. The electrochemical properties of 1 and 2 were examined by cyclic voltammetry (CV) and differential-pulse voltammetry in CH2Cl2 at room temperature, containing 0.1 M nBu4NPF6 as an electrolyte (Figure S12). Complex 2 showed two reversible reduction waves with potentials at −1.36 and −1.71 V (vs Fc/ Fc+), respectively. The first reversible oxidation wave was observed at 0.42 V, and the second quasi-reversible oxidation wave was observed at 1.10 V. The absolute potential differences between the first oxidation and first reduction (HOMO− LUMO) gaps of 1 and 2 by CV experiments are 2.40 and 1.78 eV, respectively. In summary, we have successfully synthesized and characterized a novel triphyrin iridium sandwich complex with an η1,η3COD ring ligand. The absorption spectrum of 2 showed blueshifted and broad absorption in the Soret-band region and broad absorption in the Q-band region. TD-DFT calculations

Figure 2. 1H NMR spectra of (a) 2 in CD2Cl2 at 193 K and (b) 1 in CDCl3 at 293 K. The asterisks indicate residual solvent peaks.

temperature. However, we could not get assignable signals because of the broadened spectrum, especially for peaks belonging to the phenyl group protons; even free rotation of the phenyl groups should be inhibited by isoindoles.14 Those signals were finally assigned by NOESY at room temperature and 1 H−1H COSY at 193 K (Figures S7 and S8). The protons of the COD ring of 2 were observed in the range of 0.0−4.0 ppm, reflecting the diamagnetic ring current effect of triphyrin. For the 1 H−1H COSY NMR spectrum, the protons of the π-allyl part of the COD ring are observed at 3.84 (f), 2.89 (d), and 2.41 (e) 10107

DOI: 10.1021/acs.inorgchem.6b01841 Inorg. Chem. 2016, 55, 10106−10109

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Inorganic Chemistry

Chem., Int. Ed. 2013, 52, 3360−3363. (e) Pawlicki, M.; Hurej, K.; Szterenberg, L.; Latos-Grazyński, L. Synthesis and Switching the Aromatic Character of Oxatriphyrins(2.1.1). Angew. Chem., Int. Ed. 2014, 53, 2992−2996. (f) Pawlicki, M.; Garbicz, M.; Szterenberg, L.; Latos-Grażyński, L. Oxatriphyrins(2.1.1) Incorporating an orthoPhenylene Motif. Angew. Chem., Int. Ed. 2015, 54, 1906−1909. (3) (a) Xue, Z. L.; Mack, J.; Lu, H.; Zhang, L.; You, X. Z.; Kuzuhara, D.; Stillman, M.; Yamada, H.; Yamauchi, S.; Kobayashi, N.; Shen, Z. The Synthesis and Properties of Free-Base [14]Triphyrin(2.1.1) Compounds and the Formation of Subporphyrinoid Metal Complexes. Chem. - Eur. J. 2011, 17, 4396−4407. (b) Xue, Z. L.; Kuzuhara, D.; Ikeda, S.; Okujima, T.; Mori, S.; Uno, H.; Yamada, H. Synthesis and Characterization of New Platinum(II) and Platinum(IV) Triphyrin Complexes. Inorg. Chem. 2013, 52, 1688−1690. (c) Xue, Z. L.; Kuzuhara, D.; Ikeda, S.; Sakakibara, Y.; Ohkubo, K.; Aratani, N.; Okujima, T.; Uno, H.; Fukuzumi, S.; Yamada, H. η 5 Cyclopentadienyliron(II)−[14]Triphyrin(2.1.1) Sandwich Compounds: Synthesis, Characterization, and Stable Redox Interconversion. Angew. Chem., Int. Ed. 2013, 52, 7306−7309. (d) Xue, Z. L.; Wang, Y. M.; Mack, J.; Zhu, W. H.; Ou, Z. P. Synthesis, Characterization, and Electrochemistry of the Manganese(I) Complexes of meso-Substituted [14]Tribenzotriphyrins(2.1.1). Chem. - Eur. J. 2015, 21, 2045−2051. (e) Xue, Z. L.; Wang, Y. M.; Mack, J.; Fang, Y. Y.; Ou, Z. P.; Zhu, W. H.; Kadish, K. M. Synthesis and Characterization of Palladium(II) Complexes of meso-Substituted [14]Tribenzotriphyrin(2.1.1). Inorg. Chem. 2015, 54, 11852−11858. (4) (a) Kawabata, S.; Tokura, H.; Chiyojima, H.; Okamoto, M.; Sakaguchi, S. Asymmetric Hydrosilane Reduction of Ketones Catalyzed by an Iridium Complex Bearing a Hydroxyamide-Functionalized NHC Ligand. Adv. Synth. Catal. 2012, 354, 807−812. (b) Modugno, G.; Monney, A.; Bonchio, M.; Albrecht, M.; Carraro, M. Transfer Hydrogenation Catalysis by a N-Heterocyclic Carbene Iridium Complex on a Polyoxometalate Platform. Eur. J. Inorg. Chem. 2014, 2014, 2356−2360. (c) Brown, J. A.; Cochrane, A. R.; Irvine, S.; Kerr, W. J.; Mondal, B.; Parkinson, J. A.; Paterson, L. C.; Reid, M.; Tuttle, T.; Andersson, S.; Nilsson, G. N. The Synthesis of Highly Active Iridium(I) Complexes and their Application in Catalytic Hydrogen Isotope Exchange. Adv. Synth. Catal. 2014, 356, 3551−3562. (d) Ebe, Y.; Nishimura, T. Iridium-Catalyzed Branch-Selective Hydroarylation of Vinyl Ethers via C−H Bond Activation. J. Am. Chem. Soc. 2015, 137, 5899−5902. (5) Lamansky, S.; Djurovich, P.; Murphy, D.; Abdel-Razzaq, F.; Lee, H. E.; Adachi, C.; Burrows, P. E.; Forrest, S. R.; Thompson, M. E. Highly Phosphorescent Bis-Cyclometalated Iridium Complexes: Synthesis, Photophysical Characterization, and Use in Organic Light Emitting Diodes. J. Am. Chem. Soc. 2001, 123, 4304−4312. (6) Tsuboyama, A.; Iwawaki, H.; Furugori, M.; Mukaide, T.; Kamatani, J.; Igawa, S.; Moriyama, T.; Miura, S.; Takiguchi, T.; Okada, S.; Hoshino, M.; Ueno, K. Homoleptic Cyclometalated Iridium Complexes with Highly Efficient Red Phosphorescence and Application to Organic Light-Emitting Diode. J. Am. Chem. Soc. 2003, 125, 12971−12979. (7) Kanemitsu, H.; Harada, R.; Ogo, S. A water-soluble iridium(III) porphyrin. Chem. Commun. 2010, 46, 3083−3085. (8) (a) Palmer, J. H.; Day, M. W.; Wilson, A. D.; Henling, L. M.; Gross, Z.; Gray, H. B. Iridium corroles. J. Am. Chem. Soc. 2008, 130, 7786− 7787. (b) Palmer, J. H.; Durrell, A. C.; Gross, Z.; Winkler, J. R.; Gray, H. B. Near-IR Phosphorescence of Iridium(III) Corroles at Ambient Temperature. J. Am. Chem. Soc. 2010, 132, 9230−9231. (c) Maurya, Y. K.; Ishikawa, T.; Kawabe, Y.; Ishida, M.; Toganoh, M.; Mori, S.; Yasutake, Y.; Fukatsu, S.; Furuta, H. Near-Infrared Phosphorescent Iridium(III) Benzonorrole Complexes Possessing Pyridine-based Axial Ligands. Inorg. Chem. 2016, 55, 6223−6230. (9) Toganoh, M.; Konagawa, J.; Furuta, H. Bis[iridium(I)] Complex of Inverted N-Confused Porphyrin. Inorg. Chem. 2006, 45, 3852−3854. (10) (a) Mena, I.; Jaseer, E. A.; Casado, M. A.; Garcı ́a-Orduña, P.; Lahoz, F. J.; Oro, L. A. Terminal and Bridging Parent Amido 1,5Cyclooctadiene Complexes of Rhodium and Iridium. Chem. - Eur. J. 2013, 19, 5665−5675. (b) Vrieze, K.; Volger, H. C.; Praat, A. P. Nuclear magnetic resonance studies in coordination chemistry V. Kinetic studies

predicted the presence of several MLCT bands between 450 and 800 nm. In electrochemical studies, complex 2 showed two oxidation and two reduction waves. Further studies about the electrochemical mechanism during synthesis of the iridium complex and the catalytic activity of 2 are currently underway.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01841. X-ray crystallographic data in CIF format (CIF) Synthetic details, HR-MALDI-TOF mass, NMR, and UV−vis absorption spectra, DFT calculation report, and cyclic and differential-pulse voltammograms (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was partly supported by CREST JST, Grants-in-Aid for Scientific Research (Grants 26105004, 16H02286, and 16K17950), the Green Photonics Project in NAIST, the NAIST Presidential Special Fund, and the program for promoting the enhancement of research universities in NAIST supported by MEXT. The authors thank to Y. Nishikawa in NAIST for HR-MALDI mass spectrometry measurement. The authors also thank F. Asanoma in NAIST for the NMR measurements.

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REFERENCES

(1) (a) de la Torre, G.; Vázquez, P.; Agulló-López, F.; Torres, T. Role of Structural Factors in the Nonlinear Optical Properties of Phthalocyanines and Related Compounds. Chem. Rev. 2004, 104, 3723−3750. (b) Torres, T. From Subphthalocyanines to Subporphyrins. Angew. Chem., Int. Ed. 2006, 45, 2834−2837. (c) Inokuma, Y.; Osuka, A. Subporphyrins: emerging contracted porphyrins with aromatic 14π-electronic systems and bowl-shaped structures: rational and unexpected synthetic routes. Dalton Trans. 2008, 19, 2517−2526. (d) Osuka, A.; Tsurumaki, E.; Tanaka, T. Subporphyrins: A Legitimate Ring-Contracted Porphyrin with Versatile Electronic and Optical Properties. Bull. Chem. Soc. Jpn. 2011, 84, 679−697. (e) Yamada, H.; Kuzuhara, D. Synthesis and Characterization of Triphyrins: A New Family of Porphyrinoids. Heterocycles 2013, 87, 1209−1240. (f) Xue, Z. L.; Qian, Y. Y.; Chan, K. S. Triphyrin catalyzed direct C−H arylation of benzene with aryl halides. Tetrahedron Lett. 2014, 55, 6180−6183. (g) Mase, K.; Ohkubo, K.; Xue, Z.; Yamada, H.; Fukuzumi, S. Catalytic two-electron reduction of dioxygen catalysed by metal-free [14]triphyrin(2.1.1). Chem. Sci. 2015, 6, 6496−6504. (2) (a) Xue, Z. L.; Shen, Z.; Mack, J.; Kuzuhara, D.; Yamada, H.; Okujima, T.; Ono, N.; You, X. Z.; Kobayashi, N. A Facile One-Pot Synthesis of meso-Aryl-Substituted [14]Triphyrin(2.1.1). J. Am. Chem. Soc. 2008, 130, 16478−16479. (b) Kuzuhara, D.; Yamada, H.; Xue, Z. L.; Okujima, T.; Mori, S.; Shen, Z.; Uno, H. New synthesis of meso-free[14]triphyrin(2.1.1) by McMurry coupling and its derivatization to Mn(I) and Re(I) complexes. Chem. Commun. 2011, 47, 722−724. (c) Anju, K. S.; Ramakrishnan, S.; Srinivasan, A. meso-Aryl Triphyrin(2.1.1). Org. Lett. 2011, 13, 2498−2501. (d) Kuzuhara, D.; Sakakibara, Y.; Mori, S.; Okujima, T.; Uno, H.; Yamada, H. Thiatriphyrin (2.1.1): A Core-Modified Contracted Porphyrin. Angew. 10108

DOI: 10.1021/acs.inorgchem.6b01841 Inorg. Chem. 2016, 55, 10106−10109

Communication

Inorganic Chemistry of exchange reactions involving 1,5-cyclooctadiene complexes of rhodium(I). J. Organomet. Chem. 1968, 14, 185−200. (c) Rinehart, R. E.; Lasky, J. S. The Isomerization of 1,3-Cyclooctadiene to 1,5Cyclooctadiene via the Rhodium(I) π-Complex. J. Am. Chem. Soc. 1964, 86, 2516−2518. (11) (a) Gassner, F.; Dinjus, E.; Görls, H.; Leitner, W. CO2 Activation. 7. Formation of the Catalytically Active Intermediate in the Hydrogenation of Carbon Dioxide to Formic Acid Using the [{(COD)Rh(μH)}4]/Ph2P(CH2)4PPh2 Catalyst: First Direct Observation of Hydride Migration from Rhodium to Coordinated 1,5-Cyclooctadiene. Organometallics 1996, 15, 2078−2082. (b) Sun, Y. M.; Yan, X. M.; Mettlach, N.; Endle, J. P.; Kirsch, P. D.; Ekerdt, J. G.; Madhukar, S.; Hance, R. L.; White, J. M. Precursor chemistry and film growth with (methylcyclopentadienyl) (1,5-cyclooctadiene)iridium. J. Vac. Sci. Technol., A 2000, 18, 10−16. (c) Jain, A.; Chi, K. M.; Hampden-Smith, M. J.; Kodas, T. T.; Farr, J. D.; Paffett, M. F. Chemical vapor deposition of copper via disproportionation of hexafluoroacetylacetonato (1,5-cyclooctadiene) copper (I), (hfac)Cu(1, 5-COD). J. Mater. Res. 1992, 7, 261−264. (12) Yoshida, K.; Nakashima, T.; Yamaguchi, S.; Osuka, A.; Shinokubo, H. Peripherally cyclometalated iridium complexes of dipyridylporphyrin. Daltan. Trans. 2011, 40, 8773−8775. (13) Madrahimov, S. T.; Markovic, D.; Hartwig, J. F. The Allyl Intermediate in Regioselective and Enantioselective Iridium-Catalyzed Asymmetric Allylic Substitution Reactions. J. Am. Chem. Soc. 2009, 131, 7228−7229. (14) Makarova, E. A.; Shimizu, S.; Matsuda, A.; Luk’yanets, E. A.; Kobayashi, N. meso-Aryl tribenzosubporphyrina totally substituted subporphyrin species. Chem. Commun. 2008, 18, 2109−2111. (15) Sung, Y. M.; Lim, J. M.; Xue, Z. L.; Shen, Z.; Kim, D. Comparative photophysical properties between bicyclo[2.2.2]octadiene (BCOD)and benzo-fused free-base triphyrins (2.1.1). Chem. Commun. 2011, 47, 12616−12618.

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DOI: 10.1021/acs.inorgchem.6b01841 Inorg. Chem. 2016, 55, 10106−10109