This journal is c The Royal Society of Chemistry 2013 Chem. Commun., 2013, 49, 8955--8957 8955 Cite this: Chem. Commun., 2013, 49, 8955 Synthesis and properties of boron complexes of [14]triphyrins(2.1.1)† Daiki Kuzuhara,* a ZhaoLi Xue, a Shigeki Mori, b Tetsuo Okujima, c Hidemitsu Uno, c Naoki Aratani a and Hiroko Yamada* ad Boron complexes of [14]triphyrins(2.1.1) were prepared from free- base [14]triphyrins(2.1.1) with phenylboron dichloride. The absorption spectrum of the meso-free b-alkyl–triphyrin boron complex in CH 2 Cl 2 showed a broad weak band at around 640 nm assigned to transition from B-phenyl to the triphyrin, while that of the meso-aryl benzo- triphyrin boron complex showed only Soret and Q bands. Triphyrin, a ring-contracted porphyrin lacking one of the pyrrole moieties from the parent porphyrin framework, is a new family of porphyrinoids. The first triphyrin compounds were reported in 1972 as subphthalocyanines prepared from phthalonitrile in the presence of BCl 3 . 1 Subsequently, subporphyrazine, replacing the isoindole moieties of subphthalocyanine by pyrrole rings, was reported in 1995. 2 In 2006, Osuka et al. reported the tribenzosubporphyrin replacing all nitrogen atoms at the meso-positions of subphthalo- cyanines by methine carbon atoms. 3 Then, Kobayashi and Osuka independently developed the synthetic protocols for meso-aryl substituted subporphyrins. 4,5 These subphthalocyanines and sub- porphyrins have been obtained only as boron complexes with a dome-shaped conformation. 6 In addition, subporphyrins have shown tuneable optical properties by meso-substitutions and bright fluorescence. 7 Recently, planar divalence borenium subporphyrin derivatives were reported as carborane anion salts. 8 However, the boron atoms of all subphthalocyanine and subporphyrin complexes have never been removed from the core cavities to afford the free- base subphthalocyanines and subporphyrins to date (Fig. 1). In 2008, we have succeeded in the preparation of [14]triphyrins- (2.1.1) by an acid-catalyzed condensation under modified Lindsey’s conditions. 9 Subsequently, we and another group have reported meso- 10 and pyrrolic b-position-free 11 triphyrins. These [14]triphyrins- (2.1.1) have nearly planar structures with a 14p-electron aromatic system and include no metals on the inside of the macrocycles, and they work as monoanionic–tridentate ligands. The manganese( I), 10 rhenium( I), 9b,10 iron(II), 12 iron( III), 12 ruthenium( II), 9b platinum( II) 13 and platinum( IV) 13 complexes have been already reported; thus the [14]triphyrin(2.1.1) frameworks are flexible and adjustable to various metal ions. 14 On the other hand, subpyriporphyrins and N-fused porphyrins have as coordination systems the monoanionic– tridentate ligand structures, similar to the [14]triphyrins(2.1.1). These porphyrinoid ligands could react with phenyl boron dichloride to give the corresponding boron complexes. 15,16 In particular, the boron-insertion into subpyriporphyrins was accompanied by the change of the aromaticity from the non-aromatic structure at free- base to the aromatic structure at the boron complex. In this regard, the introduction of boron atoms into [14]triphyrins(2.1.1) is impor- tant for the triphyrin and tridentate porphyrinoid chemistry. Herein, we report the synthesis, optical and electrochemical properties and crystal structures of boron( III) complexes of [14]triphyrins(2.1.1). The synthetic scheme of boron complexes (2ÁBF 4 and 4ÁBF 4 ) is shown in Scheme 1.‡ Free-base triphyrins 1 and 3 were reacted with phenylboron dichloride to give 2ÁCl and 4ÁCl , respectively. Anion exchange, then, was performed by treatment with AgBF 4 to give 2ÁBF 4 and 4ÁBF 4 in 91% and 85% yields, respectively. Compounds 2ÁBF 4 and 4ÁBF 4 showed no reversibility of removal of the boron atom and they were stable under strong acidic conditions such as conc. Fig. 1 Structures of boron complexes of triphyrin analogs. a Graduate School of Materials Science, Nara Institute of Science and Technology, 8916-5, Ikoma, Nara 630-0192, Japan. E-mail: [email protected], [email protected]; Fax: +81-743-72-6042; Tel: +81-743-72-6041 b Department of Molecular Science, Integrated Center for Sciences, Ehime University, Matsuyama 790-8577, Japan c Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577, Japan d CREST, JST, Chiyoda-Ku, Tokyo 102-0075, Japan † Electronic supplementary information (ESI) available. CCDC 942292 and 942293. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3cc44788j Received 26th June 2013, Accepted 4th August 2013 DOI: 10.1039/c3cc44788j www.rsc.org/chemcomm ChemComm COMMUNICATION Published on 21 August 2013. Downloaded by University of California - Santa Barbara on 10/09/2013 11:04:42. View Article Online View Journal | View Issue
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This journal is c The Royal Society of Chemistry 2013 Chem. Commun., 2013, 49, 8955--8957 8955
Cite this: Chem. Commun.,2013,49, 8955
Synthesis and properties of boron complexes of[14]triphyrins(2.1.1)†
Boron complexes of [14]triphyrins(2.1.1) were prepared from free-
base [14]triphyrins(2.1.1) with phenylboron dichloride. The absorption
spectrum of the meso-free b-alkyl–triphyrin boron complex in CH2Cl2showed a broad weak band at around 640 nm assigned to transition
from B-phenyl to the triphyrin, while that of the meso-aryl benzo-
triphyrin boron complex showed only Soret and Q bands.
Triphyrin, a ring-contracted porphyrin lacking one of the pyrrolemoieties from the parent porphyrin framework, is a new family ofporphyrinoids. The first triphyrin compounds were reported in 1972as subphthalocyanines prepared from phthalonitrile in the presenceof BCl3.1 Subsequently, subporphyrazine, replacing the isoindolemoieties of subphthalocyanine by pyrrole rings, was reported in1995.2 In 2006, Osuka et al. reported the tribenzosubporphyrinreplacing all nitrogen atoms at the meso-positions of subphthalo-cyanines by methine carbon atoms.3 Then, Kobayashi and Osukaindependently developed the synthetic protocols for meso-arylsubstituted subporphyrins.4,5 These subphthalocyanines and sub-porphyrins have been obtained only as boron complexes with adome-shaped conformation.6 In addition, subporphyrins haveshown tuneable optical properties by meso-substitutions and brightfluorescence.7 Recently, planar divalence borenium subporphyrinderivatives were reported as carborane anion salts.8 However, theboron atoms of all subphthalocyanine and subporphyrin complexeshave never been removed from the core cavities to afford the free-base subphthalocyanines and subporphyrins to date (Fig. 1).
In 2008, we have succeeded in the preparation of [14]triphyrins-(2.1.1) by an acid-catalyzed condensation under modified Lindsey’sconditions.9 Subsequently, we and another group have reported
meso-10 and pyrrolic b-position-free11 triphyrins. These [14]triphyrins-(2.1.1) have nearly planar structures with a 14p-electron aromaticsystem and include no metals on the inside of the macrocycles, andthey work as monoanionic–tridentate ligands. The manganese(I),10
and platinum(IV)13 complexes have been already reported; thus the[14]triphyrin(2.1.1) frameworks are flexible and adjustable to variousmetal ions.14 On the other hand, subpyriporphyrins and N-fusedporphyrins have as coordination systems the monoanionic–tridentate ligand structures, similar to the [14]triphyrins(2.1.1). Theseporphyrinoid ligands could react with phenyl boron dichloride togive the corresponding boron complexes.15,16 In particular, theboron-insertion into subpyriporphyrins was accompanied by thechange of the aromaticity from the non-aromatic structure at free-base to the aromatic structure at the boron complex. In this regard,the introduction of boron atoms into [14]triphyrins(2.1.1) is impor-tant for the triphyrin and tridentate porphyrinoid chemistry. Herein,we report the synthesis, optical and electrochemical properties andcrystal structures of boron(III) complexes of [14]triphyrins(2.1.1).
The synthetic scheme of boron complexes (2�BF4 and 4�BF4) isshown in Scheme 1.‡ Free-base triphyrins 1 and 3 were reacted withphenylboron dichloride to give 2�Cl and 4�Cl, respectively. Anionexchange, then, was performed by treatment with AgBF4 to give2�BF4 and 4�BF4 in 91% and 85% yields, respectively. Compounds2�BF4 and 4�BF4 showed no reversibility of removal of the boron atomand they were stable under strong acidic conditions such as conc.
Fig. 1 Structures of boron complexes of triphyrin analogs.
a Graduate School of Materials Science, Nara Institute of Science and Technology,
[email protected]; Fax: +81-743-72-6042; Tel: +81-743-72-6041b Department of Molecular Science, Integrated Center for Sciences, Ehime University,
Matsuyama 790-8577, Japanc Graduate School of Science and Engineering, Ehime University, Matsuyama 790-8577,
Japand CREST, JST, Chiyoda-Ku, Tokyo 102-0075, Japan
† Electronic supplementary information (ESI) available. CCDC 942292 and942293. For ESI and crystallographic data in CIF or other electronic format seeDOI: 10.1039/c3cc44788j
8956 Chem. Commun., 2013, 49, 8955--8957 This journal is c The Royal Society of Chemistry 2013
HCl, HPF6 and HBF4. These compounds were soluble in halogenatedand polar solvents such as chloroform, acetonitrile and methanol.These boron complexes were characterized using NMR spectra,high-resolution TOF-mass spectra and X-ray single crystal diffrac-tion analysis.
1H NMR spectra of 2�BF4 and 4�BF4 in CDCl3 are shown in Fig. 2.B-phenyl protons of 2�BF4 were observed at 3.24 (ortho), 5.99 (meta)and 6.27 (para) ppm, which show the characteristic of high-field shiftsdue to a diatropic ring current of the triphyrin macrocycle. The signalsof the axial phenyl ring of 4�BF4 were observed at 4.00 (ortho), 6.28(meta) and 6.52 (para) ppm. The chemical shift of the ortho protonsof 2�BF4 shows the highest field-shift in the boron porphyrinoidanalogues, to the best of our knowledge, where the correspondingprotons are observed at 4.57 ppm for subporphyrin,8 5.66 ppmfor subphthalocyanines,17 4.87 ppm for subpyriporphyrin15 and3.50 ppm for N-fused porphyrins.16 11B NMR spectra of 2�BF4 and4�BF4 showed peaks at�14.2 and�11.2 ppm, respectively, affectedby the diatropic macrocyclic ring current.
The crystal structures of 2�BF4 and 4�BF4 are shown in Fig. 3 andbond distances are summarized in Table 1. There are two crystal-lographically independent molecules of 2�BF4 in a unit cell. Theboron atom has the tetrahedral structure and coordinates with thethree nitrogen atoms and one phenyl carbon atom. Compounds2�BF4 and 4�BF4 show the bowl-shaped structure similar to
subporphyrins8 compared to the nearly planar structure of free-basetriphyrins 1 and 3. The average B–N distances are 1.527 (1.530) Å for2�BF4 and 1.541 Å for 4�BF4, and B–C bond lengths are 1.617(3)(1.616(3)) Å for 2�BF4 and 1.621(4) Å for 4�BF4. These bond lengthsare similar to the subporphyrin.8 Bowl depths, determined by thedistance between boron atoms and the mean plane made by allpyrrolic b-carbons, are 0.93 (0.96) Å for 2�BF4 and 1.03 Å for 4�BF4.The distances between boron atoms and the mean planes of threenitrogen atoms were 0.58 (0.53) Å for 2�BF4 and 0.57 Å for 4�BF4. Itshould be noted that 2�BF4 indicated the smallest bowl depth in thereported tridentate boron triphyrins, due to the larger cavity ofthe triphyrin macrocycle. This related to the larger downfield-shiftof the o-phenyl protons due to the stronger influence of themacrocyclic ring current.
Absorption and emission spectra of these boron triphyrins 2�BF4
and 4�BF4 in CH2Cl2 are shown in Fig. 4. The absorption spectra of4�BF4 showed a typical shape of porphyrinoid with the Soret band at434 (e = 1.1 � 105 M�1 cm�1) and Q-band at 505 (0.70 � 104), 539(1.3 � 104) and 570 (3.0 � 104) nm. The fluorescence peak of 4�BF4
was observed at 668 nm with a fluorescence quantum efficiency of5.5%. In contrast, the absorption of 2�BF4 exhibited three bandsconsisting of Soret-like, Q-like and additional forbidden bands.Soret-like and Q-like bands were observed at 340 nm (e = 1.3 �105 M�1 cm�1), 480 (0.79 � 104) and 512 (1.0 � 104). Furthermorethe additional broad weak band was observed around 615 nm andabsorption coefficient was 160 M�1 cm�1. Such kind of weak bandwas not observed for 4�BF4 even at the high concentration solutionand also for the previously reported boron-included porphyrinoids.No emission of 2�BF4 was observed.
To understand the optical properties, DFT calculations wereperformed at the B3LYP/6-31G** level using Gaussian 09 program(Fig. S1, ESI†).18 Geometry optimization calculations were carriedout using the structure of 2a+ with six methyl groups at pyrroleb-positions for simplicity. The highest occupied molecular orbital(HOMO) and the lowest unoccupied molecular orbital (LUMO) of 4+
Scheme 1 Synthesis of boron complexes of triphyrins 2�BF4 and 4�BF4.
Fig. 2 1H NMR spectra of (a) 2�BF4 and (b) 4�BF4 in CDCl3.
Fig. 3 X-ray crystal structures of (a) 2�BF4 and (b) 4�BF4. Solvents and hydrogenatoms are omitted for clarity. Thermal ellipsoids represent a 50% probability.For 2�BF4, two crystallographically independent molecules exist in the unit cell.One of the molecules is shown here.
Table 1 Specific bond lengths, distances, and chemical shift of 2�BF4 and 4�BF4
a The average bond distances between the boron and nitrogen atoms. b Thebond distances between the mean plane of three nitrogen atoms and theboron atom. c The 1H NMR signals of the ortho-position hydrogen.
This journal is c The Royal Society of Chemistry 2013 Chem. Commun., 2013, 49, 8955--8957 8957
were distributed in the benzotriphyrin macrocycle similar to thoseof 3 (Fig. S2, ESI†). Therefore, it gave the common absorptionspectra with Soret and Q-bands. By contrast, we found that HOMOand HOMO � 1 orbitals of 2a+ were located at the B-phenyl moietyand HOMO � 2, HOMO � 3, LUMO and LUMO + 1 orbitals weredistributed in a triphyrin macrocycle. This is probably because theHOMO and HOMO � 1 energy levels of 1a were lowered by theremoval of benzene moieties from tribenzotriphyrin 3. TD-DFTcalculations were also performed at B3LYP/6-31G(d,p)//B3LYP/6-31G(d,p). Compound 2a+ consists of the transitions from HOMOto LUMO and HOMO � 1 to LUMO with weak oscillator strengthsof 0.0054 at 584 nm and 0.0013 at 560 nm, respectively (Fig. S2,ESI†). According to these calculation results, the weak band of 2+
was assignable to the transition from the B-phenyl to the triphyrinmoiety. Oscillator strengths at longest wavelength regions of 4+
are assignable to the Q-bands containing of HOMO to LUMO( f = 0.140, 540 nm) and HOMO to LUMO + 1 ( f = 0.052, 531 nm)(Fig. S3, ESI†).
To investigate the electrochemical properties, we have measuredthe cyclic voltammetry in acetonitrile containing (nBu)4NPF6 as theelectrolyte at room temperature (Fig. S4, ESI†). Two reversiblereduction potentials were observed at �0.83 and �1.38 V (vs.Fc/Fc+) for 2�BF4 and �0.78 and �1.16 V for 4�BF4, respectively.One reversible oxidation peak of 4�BF4 was observed at 1.27 V, whileno oxidation peak of 2�BF4 was observed in the measurementregion. All oxidation and reduction signals showed anode-shiftscompared to the parent free-base triphyrins.
We have succeeded in the preparation of [14]triphyrins(2.1.1)boron complexes 2�BF4 and 4�BF4 from free-base triphyrins. These
boron triphyrins have 14p-electron aromatic characteristics andrepresent the dome-shaped structures. The optical properties of2�BF4 and 4�BF4 gave different results based on the attachedsubstituents on triphyrins; 4�BF4 showed only Soret- and Q-bands,while 2�BF4 showed other forbidden bands by transitions fromHOMO (B-phenyl moiety) to LUMO (triphyrin moiety) andHOMO � 1 (B-phenyl moiety) to LUMO (triphyrin moiety).Further derivatization of the substituents on triphyrin coresand axial substituents on the boron atom is under investigationfor the development of boron containing triphyrin chemistry.
This work was supported by the JSPS Postdoctoral Fellowshipfor Foreign Researchers (to Z.-L.X.) and partly supported byGrants-in-Aid (No. 24655034 to H.Y. and D.K.) and the GreenPhotonics Project in NAIST sponsored by the MEXT (Japan).
Notes and references‡ Crystallographic data for 2�BF4: C36H43BN3�BF4, M = 615.37, mono-clinic, space group P21 (#4), a = 9.3059(2), b = 24.7965(5), c = 14.9207(3) Å,b = 109.9720(10)1, V = 3235.94(12) Å3, T = 103 K, Z = 4, R1 = 0.0489,wR2 = 0.1123, GOF = 1.043. Crystallographic data for 4�BF4: C58H37BN3�BF4�3(CHCl3), M = 1231.70, orthorhombic, space group Pnma (#62), a =18.9212(3), b = 21.2650(3), c = 13.7069(2) Å, V = 5515.11(14) Å3, T = 103 K,Z = 4, R1 = 0.0561, wR2 = 0.1422, GOF = 1.060. CCDC 942292 for 2�BF4 and942293 for 4�BF4.
1 A. Meller and A. Ossko, Monatsh. Chem., 1972, 103, 150.2 M. S. Rodrıguez-Morgade, S. Esperanza, T. Torres and J. Barbera,
Chem.–Eur. J., 2005, 11, 354.3 Y. Inokuma, J. H. Kwon, T. K. Ahn, M.-C. Yoo, D. Kim and A. Osuka,
Angew. Chem., Int. Ed., 2006, 45, 961.4 (a) Y. Inokuma, Z. S. Yoon, D. Kim and A. Osuka, J. Am. Chem. Soc.,
2007, 129, 4747; (b) Y. Inokuma and A. Osuka, Dalton Trans.,2008, 2517; (c) A. Osuka, E. Tsurumaki and T. Tanaka, Bull. Chem.Soc. Jpn., 2011, 84, 679.
5 N. Kobayashi, Y. Takeuchi and A. Matsuda, Angew. Chem., Int. Ed.,2007, 46, 758.
6 P. J. Brothers, Chem. Commun., 2008, 2090.7 (a) Y. Inokuma, S. Easwaramoorthi, S. Y. Jang, K. S. Kim, D. Kim and
A. Osuka, Angew. Chem., Int. Ed., 2008, 47, 4840; (b) S. Easwaramoorthi,J.-Y. Shin, S. Cho, P. Kim, Y. Inokuma, E. Tsurumaki, A. Osuka andD. Kim, Chem.–Eur. J., 2009, 15, 12005; (c) M. Kitano, S. Hayashi,T. Tanaka, H. Yorimitsu, N. Aratani and A. Osuka, Angew. Chem.,Int. Ed., 2012, 51, 5593; (d) T. Tanaka, M. Kitano, S. Hayashi, N. Arataniand A. Osuka, Org. Lett., 2012, 14, 2694; (e) M. Kitano, S. Hayashi,T. Tanaka, N. Aratani and A. Osuka, Chem.–Eur. J., 2012, 18, 8929.
8 E. Tsurumaki, S. Hayashi, F. S. Tham, C. A. Reed and A. Osuka,J. Am. Chem. Soc., 2011, 133, 11956.
9 (a) Z.-L. Xue, Z. Shen, J. Mack, D. Kuzuhara, H. Yamada, T. Okujima,N. Ono, X.-Z. You and N. Kobayashi, J. Am. Chem. Soc., 2008,130, 16478; (b) Z.-L. Xue, J. Mack, H. Lu, L. Zhang, X.-Z. You,D. Kuzuhara, M. Stillman, H. Yamada, S. Yamauchi, N. Kobayashiand Z. Shen, Chem.–Eur. J., 2011, 17, 4396.
10 D. Kuzuhara, H. Yamada, Z. Xue, T. Okujima, S. Mori, Z. Shen andH. Uno, Chem. Commun., 2010, 47, 722.
11 K. S. Anju, S. Ramakrishnan and A. Srinivasan, Org. Lett., 2011, 13, 2498.12 Z. Xue, D. Kuzuhara, S. Ikeda, Y. Sakakibara, K. Ohkubo, N. Aratani,
T. Okujima, H. Uno, S. Fukuzumi and H. Yamada, Angew. Chem.,Int. Ed., 2013, 52, 7306.
13 Z. Xue, D. Kuzuhara, S. Ikeda, T. Okujima, S. Mori, H. Uno andH. Yamada, Inorg. Chem., 2013, 52, 1688.
14 D. Kuzuhara and H. Yamada, Heterocycles, 2013, 87, 1209.15 (a) R. Mysliborski, L. Latos-Grazynski, L. Szterenberg and T. Lis,
Angew. Chem., Int. Ed., 2006, 45, 3670; (b) K. S. Kim, J. M. Lim,R. Mysliborski, M. Pawlicki, L. Latos-Grazynski and D. Kim, J. Phys.Chem. Lett., 2011, 2, 477.
16 A. Młodzianowska, L. Latos-Grazynski, L. Szterenberg andM. Stepien, Inorg. Chem., 2007, 46, 6950.
17 J. Rauschnabel and M. Hanack, Tetrahedron Lett., 1995, 36, 1629.18 M. Frisch, et al., Gaussian 09, Gaussian, Inc., Wallingford, CT, 2009.
Fig. 4 (a) Absorption spectra of 1 (blue) and 2�BF4 (red) in CH2Cl2; (b) absorption(solid line) and fluorescence (dotted line) spectra of 3 (blue) and 4�BF4 (red) inCH2Cl2. The obtained fluorescence was excited at the Soret band.
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