Synthesis of meso-Tetraaryl Triphyrins(2.1.1) - ACS Publications

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Synthesis of Meso-Tetraaryl Triphyrins(2.1.1) Kamakshya Nath Panda, Kishor Gulab Thorat, and Mangalampalli Ravikanth J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b02242 • Publication Date (Web): 18 Sep 2018 Downloaded from http://pubs.acs.org on September 19, 2018

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The Journal of Organic Chemistry

Synthesis of Meso-Tetraaryl Triphyrins(2.1.1) Kamakshya Nath Panda, Kishor G. Thorat and Mangalampalli Ravikanth* Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai - 400076, India [email protected] RECEIVED DATE

Abstract: A simple, straightforward [2+1] condensation of 5,6-diaryldipyrroethene dicarbinols with pyrrole under mild acid catalyzed conditions resulted in the formation of highly desirable aromatic β-free meso- tetraaryl [14]triphyrins(2.1.1) in 15-18% yields. The triphyrins(2.1.1) are very novel monoanionic tridentate ligands that form metal complexes readily as demonstrated here by preparing Re(I) complexes. Contracted porphyrinoids such as subporphyrins(1.1.1) and triphyrins(2.1.1) have earned remarkable attention in recent years because of their interesting spectral, electrochemical and coordination properties and also due to their potential applications in various technological fields as functional materials.1 Subporphyrins are 14π three pyrrole rings linked via three methine bridges.1–3 Subporphyrins, in general can be synthesized as only boron(III) complexes such as I (chart 1).3–5 Osuka et al. have made noteworthy contribution to the field of subporphyrin chemistry.3,5,6 The literature on subporphyrins revealed that the attempts to remove B(III) ion from subporphyrins to get free base subporphyrins led to the decomposition5 which limits the chemistry of subporphyrins(1.1.1). On the other hand, [14]triphyrin(2.1.1) is the next higher homologue of subporphyrin containing three pyrrole rings connected via four methine bridges.7 The triphyrins(2.1.1) can be obtained as free bases7 and can be used as ligands for coordination chemistry.[8–13] A literature survey revealed that the first triphyrin(2.1.1) reported was BCOD (bicyclo[2.2.2]octadine)-fused triphyrin(2.1.1) II (Chart 1) which was obtained serendipitously during the synthesis of BCOD -fused porphyrin.13 Yamada et al.14 reported a synthesis of series mesoarylated BCOD-fused triphyrins(2.1.1) by condensing BCODfused pyrrole with various aryl aldehydes under Lindsey’s conditions. Yamada et al.15 also synthesized β-substituted mesoarylated triphyrins(2.1.1) by condensing 3,4-diethylpyrrole and aryl aldehyde using high equivalents of BF3.OEt2. Recently, Srinivasan et al.16 synthesized β-free mesotetraaryl-substituted [14]triphyrin(2.1.1) III (Chart 1) by condensing 5,6-diphenyldipyrroethane and pentafluorobenzaldehyde using trifluoroacetic acid (TFA) as catalyst and DDQ as an oxidant in 5% yield. Srinivasan’s approach is serendipitous and limited for the synthesis of only one meso-tetraaryl triphyrin(2.1.1) and it is not a generalized method to prepare different meso-arylated [14]triphyrins(2.1.1) in decent yields.

Chart 1. Structures of the different reported triphyrins.

Chart 2. Structures of the synthesized triphyrins (1-4), and 1Re(I) and 2-Re(I)

Thus, it is highly desirable to develop a straightforward synthetic protocol to synthesize different meso-arylated [14]triphyrins(2.1.1) since such contracted macrocycles are excellent tridentate aromatic ligands, to develop rich coordination chemistry. Herein, we report straightforward, facile [2+1] synthetic protocol to prepare meso-arylated [14]triphyrins(2.1.1) 1-4 (Chart 2) using readily available precursors. To the best of our knowlegde, this is the first such generalized synthetic approach to prepare a range of meso-arylated [14]triphyrins(2.1.1). We also demonstrated that the [14]triphyrins(2.1.1) 1-4 are unique ligands to form metal complexes by syntheizing Re(I) complexes of [14]triphyrins(2.1.1) (Chart 2) under standard metalation conditions. The generalized [2+1] synthetic route for mesotetraarylated triphyrin(2.1.1) 1-4 is presented in Scheme 1. The

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required 5,6-diaryldipyrroethene (5a-c) were prepared over sequence of two steps by following our recently reported method.17 In the first step, the appropriate 5,6diaryldipyrroethene was treated with freshly prepared EtMgBr followed by appropriate acyl chloride in THF for 30 min. After standard work-up and column chromatographic purification afforded the acylated dipyrroethene (6a-d) in 67-78% yields. In the next step, the acylated dipyrroethenes (6a-d) were in situ reduced with NaBH4 in THF/CH3OH. Without isolating the corresponding dipyrroethene-dicarbinol (7a-d) was condensed with pyrrole (1 eq.) in the presence of 0.1 equivalent of trifluoroacetic acid in CH2Cl2 for 30 min under inert atmosphere followed by oxidation with DDQ in open air for additional 30 min. TLC analysis showed one major orange fluorescent spot corresponding to the desired meso-arylated triphyrins(2..1.1) 1-4. The crude compounds were subjected to basic alumina column chromatography and the desired meso-tetraarylated triphyrins 1-4 were obtained in 15-18% yields. The triphyrins(2.1.1) 1-4 were characterized by HR-MS and 1D/2D NMR spectroscopy. The respective molecular ion peak in HR-MS confirmed the identities of triphyrins(2.1.1) 1-4. The representative 1H NMR, spectrum of triphyrin(2.1.1) 1 is presented in Figure 1a. All protons of triphyrins(2.1.1) 1 were identified based on their position, integration, coupling constants and cross peak correlations observed in COSY and NOESY spectra as shown in Figure S1. In compound 1, the six protons of two meso-tolyl –CH3 groups appeared as singlet at 2.40 ppm showed NOE correlation with a doublet at 7.08 ppm which we identified as type e protons of meso-tolyl group. The doublet at 7.32 ppm was identified as type d protons of meso-tolyl group based on its cross-peak correlation with type e protons at 7.08 ppm. The type d protons resonance at 7.32 ppm showed NOE correlation with a doublet at 7.55 ppm which in turn showed cross-peak correlation with a doublet at 8.21 ppm. Thus, the resonances at 7.55 ppm and 8.21 ppm were due to type c and type

b protons of pyrrole rings (II and III), respectively. The mesophenyl rings showed three sets of resonances at 8.15 ppm (type f), 7.75 ppm (type g) and 7.69 ppm (type h) which were identified based on their correlations in NOESY and COSY spectra. The singlet observed at 7.64 ppm was identified as type a protons of pyrrole ring (ring I) based on its NOE correlation with type f protons. The inner NH proton was observed as broad resonance at 9.74 ppm. Although triphyrins(2.1.1) are 14π aromatic macrocycles, the unusual downfield shift of the inner NH proton was due to the presence of the strong intramolecular hydrogenbonding interaction with the imine nitrogen atom of the neighbouring pyrrole ring. The other meso-aryl triphyrins 2, 3 and 4 also showed similar NMR features. Thus, 1D and 2D NMR spectroscopy was used to deduce the molecular structures of meso-aryl triphyrins(2.1.1) 1-4 (Supporting Information). One of the meso-aryl triphyrins(2.1.1), the triphyrin 2 was further characterized by X-ray crystal structure analysis (Figure 1c). The crystal structure of 2 revealed that the triphyrin 2 contains three pyrrole units connected by four methine bridges. Out of the three pyrrole units, one is amino and other two are imino in nature. The amine pyrrole is attached to the meso-carbon of ethene bridge possesses strong hydrogen bonding interactions with imine pyrrole which is attached to the other end of ethene bridge leading to the planar arrangement of the triphyrin core.11 Thus, the triphyrin 2 shows almost planar arrangement except the other imine pyrrole which is slightly tilted (16.6 °) from mean plane defined by four meso carbons (C5, C10, C15 and C16). The phenyl substituents present on meso-carbons C15 and C16 possesses out of plane arrangement with plane of triphyrin making dihedral angle of ~77 ° each. Whereas, the phenyl substituents present on meso carbons C5 and C6 were found to make dihedral angles of 46.7° and 36.9° respectively, with plane of triphyrin 2.

Scheme 1. Synthesis of the [14]triphyrins 1-4 and Re(I) metal complexes 1- Re(I) and 2-Re(I).


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(a)

(c) (a)

(d) (b)

-CH3 a b

d

g

f

h

e

c

NH

(b)

f

g bh

-CH3

a d

c e

Figure 1. Partial 1H NMR spectra of compounds 1 (a) and 1-Re(I) (b) recorded in CDCl3, and single-crystal X-ray structure of compounds 2 (c) and 1-Re(I) (d); Top view (top) and side view (bottom), respectively (hydrogen atoms attached to the carbon atoms were omitted for clarity). To test the coordination behavior of meso-tetraaryl triphyrins(2.1.1), we treated the triphyrins 1 and 2 with Re(CO)5Cl in toluene at reflux for 6 h. The progress of the reaction was monitored by TLC analysis and absorption spectroscopy. We noted a clear color change from red to indigo as the Re(I) insertion progresses and absorption spectroscopy supported the formation of Re(I) complex. The crude compounds were subjected to neutral alumina column chromatography and afforded Re(CO)3 complexes of triphyrin(2.1.1), 1-Re(I) and 2Re(I) in 47-52% yields (Scheme 1). The molecular ion peak in HR-MS confirmed the identities of the complexes 1-Re(I) and 2Re(I). The Re(I) complexes 1-Re(I) and 2-Re(I) were characterized by 1D & 2D NMR spectroscopy and 1H NMR spectrum of 1-Re(I) is shown in Figure 1(b). The absence of inner NH resonance in 1H NMR and the presence of three strong resonances at 196.6, 163.3 and 158.7 ppm correponding to CO groups in 13C NMR (Figure S16) supports the formation of 1Re(I). Furthermore, most of the β-pyrrole and meso-aryl protons experienced an upfield shift in 1-Re(I) compared to free base triphyrin 1. For example, the type b pyrrole proton which appeared as doublet at 8.21 ppm in triphyrin 1 experienced upfield shift in 1-Re(I) and appeared at 7.68 ppm. The meso-aryl protons appeared slightly broader in 1-Re(I) which is in agreement with other Re(I) complexes of porphyrinoids reported in the literature.13 The Re(I) complex of triphyrin 1 was further characterized by X-ray crystallography (Figure 1(d)). The crystal structure of the 1-Re(I) revealed that the Re(I) ion was sitting above the plane (1.461 Å) of the macrocycle due to the small cavity size of the triphyrin. The Re(I) ion in 1-Re(I) was coordinated in octahedral fashion with three pyrrole nitrogens and the remaining three positions were occupied by three CO moieties, leading to the formation of bowl shaped structure of the triphyrin. The meso-aryl rings are inclined to different extents with respect to the plane of the triphyrin defined by four meso carbons (C5, C10, C15, and C16). The substituents present at

meso carbons C15 and C16 (70.4 and 84.6 °) were more deviated from the plane compared to the

-8.6 -7.6 -6.6 -5.6 -4.6 -3.6 -2.6

Figure 2. (a) Comparision of absorption spectra of triphyrin 1 (1 X 10-4 M) (blue solid line) and 1-Re(I) (1 x 10-4 M) (red solid line) and fluorescence spectrum of 1 (blue dashed line; λexc= 390 nm) in toluene at room temperature; b) Comparison of cyclic voltammograms of the compounds 1 and 1-Re(I) recorded in dry dichloromethane using TBAP (0.1 M) as supporting electrolyte with scan rate of 50 mVs-1 at 25 °C.

Energy (eV)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


EH-1 EH-1 EH EH EL EL EL+1

EL+1

LUMO

LUMO ΔE= 2.67 eV

ΔE= 1.94 eV

HOMO

1-Re(I)

HOMO

1

Figure 3. Energy level diagram for the compounds 1 and 1-Re(I) calculated by DFT.


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meso substituents present at C5 and C10 (47.9 and 53.6 °). The absorption spectrum of 1 (Figure 2a) indicates that the triphyrin(2.1.1) showed one strong Soret band at 390 nm and three Q-bands in the region of 450-600 nm. The absorption bands of meso-tetraaryl triphyrins(2.1.1) were appeared at lower wavelengths compared to meso-tetraaryl porphyrins due to their reduced π-conjugation. The triphyrins(2.1.1) 1-4 were weakly fluorescent with an emission band at ~560 nm. The 1-Re(I) showed similar absorption features like free base [14]triphyrin(2.1.1) with an intense Soret band which experienced slight blue-shift compared to free base triphyrin(2.1.1) 1 (Figure 2a). The triphyrins 1-4 and their Re(I) complexes 1-Re(I) and 2Re(I) showed two reversible reductions (Figure 2b) and one irreversible oxidation (Figure S41 and S42). The reduction potentials of Re(I) complexes were shifted towards less negative compared to their corresponding free base triphyrins indicating that Re(I) complexes were relatively electron deficient than respective free base triphyrins. The DFT (B3LYP/6-31g (d,p) for C, H, N, O atoms and B3LYP/LANL2DZ for Re) method suggested very similar structures for the triphyrins 1 and 1-Re(I) as those obtained by Xray crystallography (Figure S43) for 2 and 1-Re(I). The analysis of FMOs of 1 and 1-Re(I) revealed the destabilization of FMOs of the 1-Re(I) (Figure 3). The extent of destabilization of LUMO is more compared to the HOMO of 1-Re(I) leading to the increase in the band gap (ΔE) supporting the blue shifts in the absorption bands of the 1-Re(I) compared to 1. The more intense band in the region of 310-400 nm with relatively weak low energy bands in the region of 450-650 nm in 1-Re(I) can be assigned to metal to ligand charge transfer (MLCT) bands on the basis of TD-DFT calculations (Figures 3 and S44). In summary, we developed a simple, straightforward [2+1] condensation method for the synthesis of β-free mesotetraaryl triphyrins(2.1.1). This method is suitable and versatile to synthesize any desired meso-tetraaryl triphyrins(2.1.1) in decent yields. The triphyrins(2.1.1) are novel monoanionic tridentate contracted macrocycles which readily form metal complexes. Currently, we are synthesizing the meso-tetraaryl functionalized [14]triphyrins(2.1.1) to use them as synthons to prepare multicomponent systems.

electrodes. The high resolution mass spectra were recorded with a Q-TOF micro mass spectrometer. Single-crystal X-ray structure analyses were carried out on a Rigaku Saturn724 diffractometer conjugated with a low-temperature attachment. Data were collected at 100 K by means of graphite-monochromated Mo-Kα radiation (λα= 0.71073 Å) by ω-scan method. The data were reduced by using CrystalClear-SM Ex-pert 2.1 b24 software. The structures were solved by direct methods and refined by leastsquares against F2 employing the software packages SHELXL-97,18 SIR-92,19 and WINGX.20 All non-hydrogen atoms were refined anisotropically. CCDC No. 1855296, 1855624 and 1855623 for compounds 6b (E isomer), 2, and 1Re(I), respectively contains the supplementary crystallographic data of these compounds. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif Computational Details.

EXPERIMENTAL SECTION

Full geometry optimization of triphyrin(2.1.1) 1 and its Re(I) metal complex 1-Re(I) was carried out by using Gaussian 09 quantum chemical software.21 For compound 1, Density Functional Theory (DFT)22 method- B3LYP/6-31G(d, p)23 was used for all atoms, whereas for compound 1-Re(I), hybrid functional B3LYP coupled with LANL2DZ24 basis set for Re metal and 6-31G(d, p) for all other atoms were used for optimization in S0 state. The frequency calculations were done on S0 optimized geometries to substantiate genuine global minimum energy structures and found that the sum of imaginary frequencies zero for 1 and 1-Re(I). The optimized geometries were used to gain frontier molecular orbitals (FMOs) and were also subjected to singlet point TD-DFT calculations first 50 S0→Sn transitions to understand absorption properties of the triphyrin(2.1.1) 1 and its metal complex 1-Re(I).25–33 The integral equation formalism polarizable continuum model (PCM) within the self-consistent reaction field (SCRF) theory was used in the TD-DFT calculations to describe the solvation of the 1 and 1-Re(I) in toluene.34,35

Materials and Methods.

Syntheses.

The chemicals such as NaBH4 and DDQ were used as obtained from Aldrich. All other chemicals used for the synthesis were reagent grade unless otherwise specified. The 1 H NMR spectra were recorded in deuterated chloroform on 500 and 400 MHz Bruker instruments. The frequencies for 13C nucleus are 100.06 and 125.77 MHz for 400 MHz and 500 MHz instruments, respectively. Tetramethylsilane was used as an internal standard for 1H and 13C NMR. Absorption and fluorescence spectra recorded using a Perkin-Elmer Lambda35 and PC1 photon counting spectrofluorometer manufactured by ISS, USA instruments, respectively. Cyclic Voltammetry (CV) studies performed on the BAS electrochemical system using the three electrode configuration consisting of a glassy carbon (working electrode), platinum wire (auxiliary electrode) and saturated calomel (reference electrode)

General procedure for synthesis of triphyrins(2.1.1) 1-4. To the solution of appropriate diacylated dipyrroethene (0.18 mmol) in 10 mL THF:MeOH (9:1 v/v), NaBH4 (3.66 mmol) was added under N2 atmosphere. The reaction was stirred at room temperature for 15-20 min under N2 atmosphere. After completion of the reaction, as indicated by TLC analysis, the reaction was quenched with saturated aqueous solution of NH4Cl (50 mL) and extracted with diethyl ether (2 X 50 mL). The combined organic layers were dried over anhydrous sodium sulphate and the solvent was removed on rotary evaporator under high vacuo to afford dicarbinols (7a-7d) as yellow sticky solids. The appropriate crude dicarbinol without further purification was treated with 1 equivalent of pyrrole (0.18 mmol) in the presence of catalytic amount of TFA (0.1 eq. 0.018 mmol) in 100 mL CH2Cl2 under N2 atmosphere for


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30 min. DDQ (0.457 mmol) was added to the reaction mixture and stirring was continued for additional 30 min in open air. TLC analysis showed formation of one major orange fluorescent spot along with 2-3 more polar minor spots. The reaction mixture was subjected to basic alumina column chromatography using pet-ether:CH2Cl2 (85:15) and afforded the corresponding triphyrin(2.1.1) 1-4 as red crystalline solids in 15-18% yields.

as black crystalline solid. Similar procedure was adopted for synthesis of the compound 2-Re(I). Compound 1-Re(I). Yield: 47% (7 mg); mp: >300 C; 1H NMR (500 MHz, CDCl3) δ = 7.84 (d, J=1.6 Hz, 2H), 7.83 (d, J=2.1 Hz, 2H), 7.67 (d, J=4.7 Hz, 2H), 7.66 – 7.61 (m, 6H), 7.46 (s, 2H), 7.43 (d, J=7.8 Hz, 4H), 7.23 (d, J=4.7 Hz, 2H), 7.10 (d, J=7.7 Hz, 4H), 2.38 (s, 6H). 13C{1H}NMR (101 MHz, CDCl3) δ = 196.7, 163.6, 154.2, 141.0, 138.6, 137.5, 136.4, 133.0, 132.4, 128.6, 127.8, 127.4, 127.0, 124.8, 77.3, 77.0, 76.7, 21.3. HRMS (ESI) calcd. for C45H31N3O3Re: 848.1918 , found 848.1920 [M+H]+

Compound 1. Yield: 16% (17 mg); mp: 150-152 C; 1H NMR (400 MHz, CDCl3) δ = 9.74 (s, 1H), 8.21 (d, J=4.5 Hz, 2H), 8.15 (d, J=7.1 Hz, 4H), 7.76 (t, J=7.3 Hz, 4H), 7.70 (d, J=7.2 Hz, 2H), 7.64 (s, 2H), 7.55 (d, J=4.5 Hz, 2H), 7.32 (d, J=7.8 Hz, 4H), 7.08 (d, J=7.8 Hz, 4H), 2.41 (s, 6H). 13C{1H}NMR (126 MHz, CDCl3) δ = 153.7, 140.2, 136.0, 135.9, 134.6, 132.40, 130.3, 128.7, 128.2, 128.0, 127.0, 126.2, 125.4, 77.3, 77.0, 76.8, 21.3. HRMS (ESI) calcd. for C42H32N3: 578.2590, found 578.2591 [M+H]+

Compound 2-Re(I). Yield: 52% (8.5 mg); mp: >300 C; 1H NMR (500 MHz, CDCl3) δ = 7.85 (d, J=5.6 Hz, 4H), 7.72 (d, J=4.7 Hz, 2H), 7.64-7.66 (m, 6H), 7.56 (s, 4H), 7.48 (s, 2H), 7.27-7.29 (m, 8H); 13C{1H}NMR (126 MHz, CDCl3) δ = 194.7, 162.9, 158.9, 154.5, 141.5, 141.4, 138.5, 136.9, 133.1, 128.9, 128.2, 127.9, 127.0, 126.7, 125.2, 77.3, 77.0, 76.8; HRMS (ESI) calcd. for C43H27N3O3Re: 820.1595 , found 820.1607 [M+H]+.

Compound 2.Yield: 18% (19 mg); mp: 146-148 C .1H NMR (500 MHz, CDCl3) δ = 8.25 (d, J=4.5 Hz, 1H), 8.17 (d, J=7.2 Hz, 2H), 7.77 (t, J=7.4 Hz, 4H), 7.71 (t, J=7.3 Hz, 4H), 7.66 (s, 2H), 7.57 (d, J=4.4 Hz, 2H), 7.48 – 7.44 (m, 4H), 7.31 – 7.27 (m, 6H). 13C{1H}NMR (126 MHz, CDCl3) δ = 153.6, 145.0, 143.3, 138.3, 136.3, 135.1, 132.8, 130.7, 130.3, 129.0, 128.6, 126.7, 126.6, 77.5, 77.2, 77.0. HRMS (ESI) calcd. for C40H28N3: 550.2272, found 550.2278 [M+H] +.

General procedure for the preparation of compounds 6a6d. Freshly prepared ethyl magnesium bromide in THF (20 mL, 10.64 mmol, 0.53 M), was added dropwise to the solution of desired 5, 6-diaryl dipyrroethene (E and Z mixture) (1.77 mmol) in toluene (20 mL) under nitrogen. The resulting solution was stirred for 15-20 min at room temperature and then the corresponding acyl chloride (4.3 mmol) was added to this at 0 °C. The resulting mixture was stirred for 20-30 min at room temperature. The reaction mixture was quenched with ice cold solution of NH4Cl (100 mL) and extracted with ethyl acetate (3 X 50 mL). The combined organic layers were dried over anhydrous Na2SO4. The yellowish brown semisolid obtained after removal of solvent under vacuo was subjected to silica gel (60-120) column chromatography using pet ether/ethyl acetate (80:20) and afforded the compounds 6a-d as E and Z mixtures in 67-78% yields.

Compound 3. Yield: 15% (15.50 mg) mp: 148-150 C; 1H NMR (500 MHz, CDCl3) δ = 9.74 (s, 1H), 8.22 (d, J=4.5 Hz, 2H), 8.15 (d, J=7.5 Hz, 2H), 7.75 (t, J=7.4 Hz, 2H), 7.69 (t, J=7.3 Hz, 4H), 7.64 (s, 2H), 7.57 (d, J=4.5 Hz, 2H), 7.39-7.35 (m, 2H), 7.34 (d, J = 8.5 Hz, 2H), 6.83 (d, J=8.4 Hz, 2H), 6.10 – 4.89 (m, 4H), 3.87 (s, 6H); 13C{1H}NMR (126 MHz, CDCl3) δ = 153.7, 140.2, 136.0, 135.8, 134.6, 132.4, 130.3, 128.7, 128.2, 128.0, 127.0, 126.2, 125.4, 77.3, 77.0, 76.75, 35.0; HRMS (ESI) calcd. for C42H32N3O2: 610.2484, found 610.2489 [M+H]+ Compound 4. Yield: 18% (19 mg); mp: 154-156 C; 1H NMR (500 MHz, CDCl3) δ = 9.91 (s, 1H), 8.20 (d, J=4.5 Hz, 2H), 8.05 (d, J=8.0 Hz, 4H), 7.61 (s, 2H), 7.56 (d, J=7.8 Hz, 4H), 7.51 (d, J=4.5 Hz, 2H), 7.43 (dd, J=6.5 Hz, 2.9, 4H), 7.27 – 7.24 (m, 6H), 2.61 (s, 6H). 13C{1H}NMR (126 MHz, CDCl3) δ = 153.1, 144.6, 143.1, 140.8, 136.1, 135.5, 135.3, 133.7, 132.6, 130.3, 129.7, 129.2, 126.4, 126.4, 77.3, 77.0, 76.8, 21.4. HRMS (ESI) calcd. for C42H32N3: 578.2591, found 578.2591 [M+H]+

Compound 6a : Yield: (E/Z) 77% (1.25 g) mp: 101 °C; 1H NMR (400 MHz, CDCl3) δ = 9.18 (s, 2H), 8.51 (s, 1H), 8.06 (d, J=7.1 Hz, 1H), 7.94 – 7.83 (m, 4H), 7.79 – 7.69 (m, 2H), 7.59 – 7.30 (m, 15H), 6.99 (s, 9H), 6.80 (dd, J=4.0 Hz, 2.5 Hz, 2H), 6.58 (dd, J=4.1 Hz, 2.4 Hz, 1H), 6.08 (dd, J=4.0 Hz, 2.7 Hz, 2H), 5.52 (dd, J=4.0 Hz, 2.8 Hz, 1H), 2.49 (s, 1H), 2.29 (s, 6H). 13C{1H}NMR (126 MHz, CDCl3) δ = 184.4, 140.0, 139.0, 137.8, 137.4, 132.3, 132.1, 132.0, 131.3, 131.0, 130.7, 130.3, 130.0, 129.1, 129.0, 128.9, 128.5, 127.6, 120.2, 114.4, 77.5, 77.2, 77.0, 32.1, 29.9, 21.5, 14.3. HRMS (ESI) calcd. for C38H30KN2O2: 585.1956, found 585.1939 [M+K] +

Synthesis of 1-Re(I) and 2-Re(II). To the solution of 1 (10 mg, 0.018 mmol) in dry toluene, Re(CO)5Cl (65.8 mg, 0.182 mmol) was added and the resulting solution was heated at reflux for 6 h under inert atmosphere. After completion of reaction, as judged by TLC and UV-Vis absorption spectroscopy, the solvent was removed under high vacuo. The crude black residue was subjected to neutral alumina column chromatography using pet-ether/CH2Cl2, (95:5) and afforded Re(I) complex 1-Re(I)

Compound 6b: Yield: (E/Z) 72% (1.20 g) mp: 100-102 °C; 1 H NMR (500 MHz, CDCl3) δ = 9.15 (s, 2H), 8.42 (s, 1H), 7.91 – 7.83 (m, 4H), 7.53 (dd, J=6.0 Hz, 1.6 Hz, 4H), 7.46 (t, J=7.7 Hz, 6H), 7.19 – 7.15 (m, 6H), 7.12 – 7.09 (m, 4H), 6.82 (dd, J=4.0 Hz, 2.5 Hz, 2H), 6.11 (dd, J=3.9 Hz, 2.7, 2H). 13 C{1H}NMR (101 MHz, CDCl3) δ = 184.4, 142.0, 140.3,


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139.5, 139.3, 133.9, 133.8, 132.0, 131.4, 130.4, 129.1, 128.7, 128.5, 128.4, 128.0, 124.0, 120.1, 117.9, 114.6, 77.6, 77.2, 77.0. HRMS (ESI) calcd. for C36H27N2O2: 519.2091, found 519.2067 [M+H] +.

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(E isomer): mp: 102-104 C: H NMR (500 MHz, CDCl3) δ = 8.41 (s, 2H), 7.75 (d, J=7.4 Hz, 4H), 7.60 – 7.57 (m, 6H), 7.49 (dt, J=6.8 Hz, 5.3 Hz, 6H), 7.41 (t, J=7.6 Hz, 4H), 6.58 (dd, J=4.0 Hz, 2.4 Hz, 2H), 5.56 – 5.50 (dd, J=3.9 Hz, 2.4 Hz, 2H). 13 C{1H}NMR (101 MHz, CDCl3) δ = 184.0, 139.6, 138.9, 138.8, 138.3, 137.5, 132.0, 131.4, 131.4, 130.6, 130.2, 130.1, 129.6, 129.4, 129.1, 129.0, 128.5, 128.5, 128.4, 126.8, 119.1, 118.7, 115.8, 77.6, 77.2, 76.9. HRMS (ESI) calcd. for C36H26N2O2Na 541.1887, found 541.1896 [M+Na] +. o

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Compound 6c: Yield: (E/Z) 67% (1.05 g); mp: 102-104 °C; 1 H NMR (400 MHz, CDCl3) δ = 9.15 (s, 2H), 8.59 (s, 1H), 7.89 – 7.83 (m, 4H), 7.80 – 7.73 (m, 4H), 7.56 – 7.50 (m, 6H), 7.43 (dt, J=15.2 Hz, 7.5 Hz, 12H), 7.33 (q, J=3.1 Hz, 6H), 7.04 (dd, J=8.7 Hz, 3.4, 8H), 6.80 (dd, J=3.9 Hz, 2.5 Hz, 2H), 6.71 (d, J=8.8 Hz, 6H), 6.60 (dd, J=4.1 Hz, 2.5 Hz, 2H), 6.08 (dd, J=3.9 Hz, 2.7 Hz, 2H), 5.56 (dd, J=4.0 Hz, 2.8 Hz, 2H), 3.91 (s, 5H), 3.78 (s, 6H). 13C{1H}NMR (101 MHz, CDCl3) δ = 184.3, 183.9, 140.0, 138.5, 138.2, 132.7, 132.0, 131.9, 131.7, 131.1, 131.0, 129.1, 129.0, 128.5, 128.4, 123.7, 120.2, 119.8, 119.5, 115.7, 115.3, 114.4, 113.9, 77.6, 77.2, 76.9, 55.6, 55.4. HRMS (ESI) calcd. for C38H31N2O4: 579.2274, found 579.2278 [M+H] +.

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Compound 6d.Yield: (E/Z) 78% (1.20 g) mp: 101 °C; 1H NMR (500 MHz, CDCl3) δ = 9.19 (s, 2H), 8.42 (s, 1H), 7.79 (d, J=8.0, 4H), 7.67 (d, J=8.0, 2H), 7.61 – 7.56 (m, 1H), 7.48 (d, J=2.8, 1H), 7.30 – 7.24 (m, 2H), 7.16 (d, J = 5.2, 2H), 7.13 – 7.08 (m, 5H), 6.83 – 6.79 (m, 2H), 6.14 – 6.09 (m, 2H), 2.42 (s, 6H); 13C{1H}NMR (126 MHz, CDCl3) δ = 184.2, 142.7, 140.3, 139.1, 135.7, 132.5, 131.4, 130.2, 129.3, 129.2, 129.1, 128.3, 127.94, 119.7, 114.4, 77.5, 77.2, 77.0, 21.8; HRMS (ESI) calcd. for C38H30N2O2K : 585.1956, found 585.1939 [M+K] +.

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(11) SUPPORTING INFORMATION The Supporting Information is available free of charge on the ACS Publications website at DOI: 1H and 13C NMR spectra, 2D NMR spectra, HRMS spectra, Cyclic voltamograms, Computational details, and X-ray Crystallography data.

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ACKNOWLEDGEMENTS

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M.R. thanks the Science and Engineering Research Board, Government of India (EMR/2015/002196), for funding the project, K.N.P. thanks the UGC for the Junior Research Fellowship, and K.G.T. is thankful to IIT Bombay for a Postdoctoral Fellowship.

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Synthesis of meso-Tetraaryl Triphyrins(2.1.1) - ACS Publications

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