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Dibenzidecaphyrins (1.0.0.1.1.1.0.0.1.1) and Their Bis-BF2 Complexes Sunit Kumar, Kishor Gulab Thorat, and Mangalampalli Ravikanth J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.8b01812 • Publication Date (Web): 02 Nov 2018 Downloaded from http://pubs.acs.org on November 2, 2018

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The Journal of Organic Chemistry

Dibenzidecaphyrins Complexes

(1.0.0.1.1.1.0.0.1.1)

and

Their

Bis-BF2

Sunit Kumar,a Kishor G Thorata and Mangalampalli Ravikantha* a

Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India, E-mail: [email protected]

Abstract: The

largest

dibenziporphyrinoids

discovered

till

date,

dibenzidecaphyrins

(1.0.0.1.1.1.0.0.1.1), were synthesized in 8-10% yields by condensing m-phenylene based pentapyrrane with pentafluorobenzaldehyde under mild reaction conditions. The crystal structure obtained for one of the decaphyrin macrocycle revealed that the macrocycle adopts figure-of-eight conformation and showed nonaromatic features. The decaphyrin macrocycles were further characterized by various spectral, electrochemical techniques and computational studies.

The

dibenzidecaphyrin macrocycle showed half the number of proton NMR resonances, indicating the high symmetry of the macrocycle. The decaphyrins showed a broad absorption in 600-900 nm region along with a well-defined band at 448 nm and the macrocycles were stable under redox conditions. The decaphyrins were treated with BF3.OEt2/triethylamine in CH2Cl2 at reflux temperature, followed by column chromatography, to afford bis-BF2 complexes of decaphyrin in 34-40% yields. The spectral and DFT studies supported a figure-of-eight conformation for the bis-BF2 complexes and electrochemical studies indicated that the bis-BF2 complexes were electron deficient compared to the free base decaphyrin macrocycles.

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INTRODUCTION Expanded porphyrins are defined as macrocycles that contain pyrrole, furan, thiophene or other five or six membered heterocyclic or carbocyclic subunits interconnected either directly or through one or more meso carbons maintaining minimum 17 atoms in the ring pathways.1,2 Over the years, several research groups explored the chemistry of expanded porphyrins in terms of their different synthetic strategies structure-property relationships and applications in various technological fields3 Due to availability of more number of coordinating atoms and bigger cavity size, the core modified expanded porphyrins gained tremendous attention in metal coordination, anion binding, sensing and anion transport chemistry.1-3 The attention on expanded porphyrins has been continuously growing because of their ability to act as sensitizers for photodynamic therapy (PDT),4 as contrast agents in magnetic resonance imaging (MRI),5 as radiation therapy enhancer,6 and also as nonlinear optical (NLO) material and for investigation of issues related to aromaticity.7 The expanded porphyrins are conformationally flexible and prefer to exist in different conformations depending upon their ring size.8 In general, the expanded porphyrins which are larger than heptaphyrins becomes more flexible and try to attend different conformations/shapes leading to more complexity in their stuctures.2a The control over conformation of expanded porphyrins is important since the structural arrangement define the electronic, optical and coordination properties of expanded porphyrins.. A perusal of literature reveals that, there are only few examples of large expanded porphyrins which have been structurally characterized. These includes Sessler’s turcasarin,9 Setsune’s helical [64]hexadecaphyrin,10 Chandrashekar’s aromatic core-modified [34]octaphyrin,11 Vogel’s figure eight [32]octaphyrin12 and Osuka’s the crescent shaped [44]decaphyrin as well as the intramolecular helical [56]dodecaphyrin13 to name just a few


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of the important expanded macrocycles. Furthermore, expanded carbaporphyrinoids containing one or more internal carbon donor atoms along with other heteroatom donors such as nitrogen, oxygen, sulphur, selenium, tellurium etc. in the coordination core are very rare and little is known about their electronic, structural and coordination properties.14 Recently, we reported the synthesis of [28] m-benzihexaphyrins15 1a-d by (3+3) condensation of readily available precursors such as 1,3-dithienylbenzene diol with different 16-hetero tripyrranes under simple acid catalyzed macrocycle forming conditions (Figure 1). The [28] m-benzihexaphyrins are highly stable nonaromatic macrocycles and absorbs in the region of 500-950 nm but have a weak tendency to form coordination complexes (1a-d). We also prepared stable doubly N-fused nonaromatic expanded dibenziporphyrins (2a-d) by (5+3) condensation of 1,3-bis(2-thienyl)benzene diol with m-phenylene based pentapyrrane under mild acid catalyzed conditions.16 These doubly fused expanded dibenziporphyrins (2a-d) did not have appropriate coordination environment to form complexes. In continuation of our work on expanded benziporphyrinoids, in this paper, we report the

synthesis

of

stable

first

example

of

largest

non-aromatic

dibenzidecaphyrins

(1.0.0.1.1.1.0.0.1.1) (3a-c) by condensing the readily available m-phenylene based pentapyrrane with pentafluorobenzaldehyde under mild acid catalyzed conditions. The macrocycles (3a-c) readily forms bis-BF2 complexes (4a-c) upon treatment with BF3.OEt2 in the presence of triethylamine in CHCl3 under reflux conditions. The spectral and electrochemical studies indicate that both dibenzidecaphyrins (3a-c) and their bis-BF2 complexes (4a-c) retain figure-of-eight conformations in solution as well.



Figure

1:

Structures

of

expanded

benziporphyrins,

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N-fused

dibenziporphyrinoids,

dibenzidecaphyrins and bis-BF2 dibenzidecaphyrins. RESULTS AND DISCUSSION The target dibenzidecaphyrins (3a-c) and their bis BF2 complexes (4a-c) were prepared by using reported procedure17 as shown in the Schemes 1 and 2, respectively. The desired m-phenylene based pentapyrranes (5a-c) were prepared from corresponding 1,3-dithienylbenzene diols (6a-c) by following our earlier reported procedure.16 The reaction was carried out by condensing one equivalent of appropriate pentapyrrane 5a with one equivalent of various aldehydes such as p-tolualdehyde, p-nitrobenzaldehyde, anisaldehyde, p-bromobenzaldehyde, pentafluorobenzaldehyde in CH2Cl2 in the presence of catalytic amount of TFA for 1 h under inert


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atmosphere followed by oxidation with DDQ in open air. The progress of the reaction was followed by TLC analysis and absorption spectroscopy. Interestingly, we did not notice the formation of the desired decaphyrin macrocycle in condensation of pentapyrranes with different aldehydes except pentafluorobenzaldehyde which showed a very clear green colored major spot on TLC and two well defined absorption bands in the region of 300-900 nm. The crude compound was subjected to basic alumina column chromatography and a dark green compound was collected. The HR-MS analysis showed a peak at 1678.5054 corresponding to [M+H] + molecular ion peak of the desired dibenzidecaphyrin macrocycle 3a. The formation of compound 3a was further confirmed by X-ray crystallography (vide infra). The reaction was repeated several times by varying different acids and their concentration. The best yield of 10% for macrocycle 3a was obtained when we used 0.5 equivalent of TFA for condensation and 2 equivalents of DDQ for the oxidation. It is worth mentioning that we did not notice formation of any macrocycle when the condensation

of

pentapyrranes

was

carried

out

with

aldehydes

other

than

pentafluorobenzaldehyde. The decaphyrin macrocycles 3b and 3c were prepared similarly by condensing appropriate pentapyrrane (5b-c) with pentafluorobenzaldehyde under similar reaction conditions. The bis BF2 complexes of decaphyrins 4a-c were prepared by treating appropriate decaphyrin macrocycle 3a-c with 60 equiv. of BF3.OEt2 in CHCl3 in the presence of triethylamine base at reflux for 6 h. As the reaction progressed, the color of the reaction mixture was turned to more dark green and absorption spectroscopy showed different features from free base macrocycle indicating the formation of the desired bis BF2 complexes 4a-c (Scheme 2).

Column

chromatography of the crude reaction mixture afforded the desired BF2 complexes in 34-40% yields which was later identified as the bis BF2 complexes of dibenzidecaphyrin 4a-c by HR-MS and detailed 1D and 2D NMR spectroscopy.



Scheme 1: Synthesis of dibenzidecaphyrin 3 (a-c).

Scheme 2: Synthesis of bis BF2 complex of dibenzidecaphyrin 4 (a-c).


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X-ray crystallography of dibenzidecaphyrin 3a: The identity of the dibenzidecaphyrin 3a was unambiguously confirmed by single crystal X-ray diffraction analysis. The diffraction quality single crystals of 3a were grown by slow evaporation of n-hexane into chloroform solution of 3a at room temperature over a period of 7 days and the crystal structure obtained for 3a is presented in Figure 2. The important crystallographic data are enlisted in Tables S1 and S2. The decaphyrin macrocycle 3a crystallizes in C2/c space group of monoclinic system, containing six independent molecules in a unit cell. It is evident from the Xray structure (Figure 2) that the macrocycle 3a was highly ruffled and attains a figure-of-eight structure which was observed in other reported expanded porphyrins.17 The asymmetric unit of the molecule indicates the presence of overall half symmetry due to a two-fold rotational axis. The Xray structure reveals that the four thiophene rings in the molecule were connected to two phenylene rings at 1, 3-positions and the sulphur atoms of thiophene rings were pointing outwards and inwards alternately with respect to the macrocycle core. The C-C bond lengths within the mphenylene rings exhibit the characteristic benzene like features with C-C bond length varying from 1.360(8) to 1.395(8) Å. However, the C-C bonds between m-phenylene rings and thiophene rings have single bond character implying the lack of π-delocalization in the macrocycle leading to a non-aromatic system. The rest of the molecule displays typical conjugated bond features within the macrocycle as confirmed from the C-C, C-N and C-S bond lengths. Furthermore, intramolecular hydrogen bonding interactions N2-H2..N1 (H2..N1 2.22 Å) and N2-H2..S2 (H2..S2 2.34 Å) were observed. The torsional angles between meso- tert-butylbenzene rings adjacent to the porphyrinato thiophene group are (C4C5C6C15) 130° and (C42C31C32C33) 138° respectively, which are much higher than those of the pentafluorophenyl rings present on the dipyrromethene unit (C19C20C21C26 = 108°). Thus, the crystal structure reveals that the



dibenzidecaphyrin was distorted and adopts a figure-of-eight conformation similar to other reported expanded porphyrinoids.18 (a)

(b)

Figure 2: Stick representation of the single-crystal X-ray structure of dibenzidecaphyrin 3a (a) Perspective view; (b) Side view. All of the hydrogen atoms and meso aryls have been omitted for clarity. NMR Studies: The dibenzidecaphyrins 3(a-c) and their bis BF2 complexes 4(a-c) were characterized in detail by using 1D and 2D NMR spectroscopy (see Supporting Information). The partial 1H NMR spectrum of 3a is presented in Figure 3. It is clear from the Figure 3 that compound 3a shows fewer proton NMR resonances than one would expect for such a large macrocycle indicating that the macrocycle is a highly symmetric molecule. Thus, in the 1H NMR spectrum of macrocycle 3a, the eight protons of four pyrrole rings appeared as two sets of resonances at 6.91 (type h) and 7.86 (type i) ppm; the eight protons of four thiophene rings appeared as two sets of resonances at 6.01 (type d) and 6.44 (type e) ppm and the six protons of two benzene rings appeared as two sets


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of resonances at 6.93-6.97 (type a and c) and 7.14 (type b) ppm. The two pyrrole inner -NH protons appeared in the downfield region at 14.07 ppm.

Figure 3: Partial 1H NMR spectrum of macrocycle 3a recorded in CDCl3 at room temperature.

Figure 4: 1H-1H COSY NMR spectrum of compounds 4a recorded in CDCl3 at room temperature.



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All these resonances were identified and assigned based on position, integration, coupling constant and proton to proton cross correlations in 1H-1H COSY and NOESY spectra (Supporting information). The appearance of macrocyclic ring protons such as pyrrole, thiophene and benzene protons in 6-8 ppm region and the pyrrole inner NH protons at ~14 ppm supports the non-aromatic nature of the macrocycle and these features are in agreement with other reported nonaromatic/anti-aromatic macrocycles in the literature.19 The other two decaphyrin macrocycles 3b and 3c were also characterized and identified all resonances by 1D and 2D NMR spectra. The NMR spectrum of the BF2 complex 4a was much more resolved as evident in 1H-1H COSY spectrum shown in Figure 4. In macrocycle 3a, the type a and c protons of the benzene ring appeared as a multiplet in the region of 6.93-6.97 (type a and c) ppm, but these were well separated in the BF2 complex 4a and the protons appeared as two sets of peaks at 6.91 (type a) and 7.32 (type c) ppm. In the BF2 complex 4a, the inner -NH protons which appeared at 14.07 ppm in free base macrocycle 3a were completely absent due to complexation with BF2 units. The pyrrole, thiophene and benzene protons in BF2 complex 4a experienced slight upfield or downfield shifts compared to the corresponding protons in free base macrocycle 3a indicating the alteration of the electronic properties of the decaphyrin macrocycle due to complexation with the BF2 units (Figure S33). The BF2 complex 4a was further characterized by

11

B and

19

F NMR. In

11

B NMR, the

macrocycle 4a showed a typical triplet due to coupling with two fluorides at 1.82 ppm whereas in 19

F NMR, the macrocycle showed a broad resonance at -130.49 ppm (See supporting information).

The significant downfield shifts of 11B and

19

F NMR resonances in macrocycle 4a compared to

standard BF2 complex of meso-phenyl dipyrrin (BODIPY) was attributed to a macrocyclic ring current effect.20 The bis BF2 complexes 4b and 4c also showed similar NMR features. Thus, the


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NMR spectral features were in agreement with the molecular structures of macrocycles 3 (a-c) and 4 (a-c).

Absorption and electrochemical studies: The absorption and electrochemical properties of macrocycles 3a-c and their bis-BF2 complexes 4a-c were investigated and data are presented in Table S3. The comparison of absorption spectra and the cyclic voltamograms of 3a and 4a are presented in Figure 5a and Figure 5b respectively. Both macrocycles showed typical nonaromatic absorption features in 300-900 nm region. The macrocycle 3a showed a broad band in region of 600-900 nm and a relatively well-defined sharp band at 490 nm, whereas macrocycle 4a exhibited a slightly hypsochromically shifted broad band at 700 nm and ill-defined broad band in the region of 300-500 nm. Furthermore, BF2 complexation slightly altered absorption features of the decaphyrin macrocycle indicating that macrocycle 4a also adopts a figure-of-eight conformation like its free base decaphyrin precursor 3a. The compounds 3b/3c and 4b/4c also showed similar absorption features with slight shifts in their peak maxima (Table S3). We explored the sensing ability of macrocycle 3a towards different anions and cations. Our preliminary studies indicated that the free base decaphyrin 3a did not show any sensing ability for anions but showed specific sensing for Hg2+ ion over various other metal ions (Figure S38). Thus, we noticed significant changes in the absorption spectrum of macrocycle 3a only upon addition of Hg2+ ion and no major changes were observed with other metal ions such as K+, Na+, Li+, Ca2+, Mn2+, Cd2+, Zn2+, Co2+, Ni2+, Cu2+, Fe2+, Fe3+, Cr3+. The color of solution was also changed from light green to dark green upon addition of Hg2+ ion to macrocycle 3a. We carried out systematic absorption spectral titration of macrocycle 3a upon increasing addition of Hg2+ ion as shown in Figure 5b. The sequential addition of Hg2+ ion to chloroform solution of macrocycle



3a resulted in the decrease of absorption band at 448 nm and appearance of new band at 479 nm and significant increase of broad absorption band at 731 nm along with a clear isosbestic point at 464 nm suggesting the presence of two species which we attributed to the free base macrocycle 3a and its Hg2+ complex 3a+Hg2+. Furthermore, the binding constant of 7.35 x 103 M-1 was evaluated for macrocycle 3a and Hg2+ ion interaction using Benesi-Hilderbrand equation. Job’s plot analysis supported 1:2 stoichiometry between macrocycle 3a and Hg2+ ion (Figure 5c). However, we could not establish 1:2 stoichiometry by HR-MS analysis due to our instrument limitations. The redox properties of 3a and 4a were investigated in dichloromethane by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Macrocycle 3a showed one quasireversible reduction at -0.90 V; one irreversible reduction at -1.38 V and three quasi-reversible oxidations at 0.66 V, 0.72 V and 1.04 V. Thus, the macrocycle 3a show relatively easier oxidations and harder reductions indicating that it is an electron rich macrocycle. The bis-BF2 complex 4a also exhibited similar redox features. Complex 4a showed one reversible reduction at -0.69 V; one irreversible reduction at -1.28 V and three quasi-reversible oxidations at 0.77 V, 0.86 V and 1.02 V as shown in Figure 5d. Furthermore, a comparison of the redox potential for 3a and 4a indicates that the reductions were observed at less negative potential whereas oxidations were noted at more positive potential in complex 4a compared free base decaphyrin macrocycle 3a. This indicates that the bis-BF2 complex 4a is easier to reduce but more difficult to oxidize compared to free base decaphyrin macrocycle 3a. The decaphyrin macrocycles 3b/3c and their BF2 complexes 4b/4c also exhibited similar redox features like 3a/4a (Table S3).


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Figure 5: (a) Overlaid absorption spectra of compound 3a (black line) and compound 4a (red line) recorded in a chloroform (5×10-6 M) solution. (b) Absorption spectral change of macrocycle 3a (5 x 10-6 M) upon addition of increasing equivalent of Hg2+ ions (0-5 equiv.) in CHCl3 solution at room temperature. (c) Job’s plot for the evaluation of binding stoichiometry between macrocycle 3a and Hg2+ in CH3Cl solution at 448 nm (The total [compound 3a] + [Hg2+] = 5×10-6 M.) Where nHg2+ is mole fraction of the Hg2+ ion added and A is Absorbance of compound 3a in the presence of Hg2+and A0 is absorbance of compound 3a in the absence of Hg2+ which forms 1:2 complexes and (d) comparison of cyclic voltamograms (black line) and differential pulse voltamograms (red line) of compounds 3a and 4a recorded in CH2Cl2 at a scan rate of 50 mVs-1 using saturated calomel electrode as reference electrode and 0.1 M TBAP as the supporting electrolyte.



DFT studies. DFT calculations were performed to further investigate the structural, spectral and electrochemical properties of the compounds 3a-c and 4a-c. The comparison of the DFT (B3LYP/6-31g (d,p)) optimized structures of the compound 3a and its bis-BF2 complex 4a is presented in Figure 6 and for compounds 3b-c and their bis-BF2 complexes 4b-c were included in supporting information (Figures S41-S42). DFT studies indicated a very similar structure for compound 3a as that obtained from single X-ray crystal. Furthermore, the optimized geometries of the compounds 3b and 3c shows similar structural features of macrocyclic core as that of compound 3a suggesting no influence of change in meso substituents on structural properties of dibenzidecaphyrin core. Upon bis-BF2 complexation of 3a, we noted that the two dipyrrin moieties of dibenzidecaphyrin macrocycle became more planar but rest of the dibenzidecaphyrin macrocycle that includes four thiophene and two p-phenylene rings was deviated from the plane of the BF2 dipyrrin moieties resulted in more distorted geometry of compound 4a compared to compound 3a. Similar observations were noted for other bis BF2 complexes of dibenzidecaphyrins 4b and 4c with respect to their corresponding free base dibenzidecaphyrins 3b and 3c, respectively. The observed illdefined blue shifted absorption bands of bis-BF2 complexes 4a-c compared to their free bases 3ac can be attributed to the structural deformation in 4a-c (Figures 5, S35 and S36).


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a)

b)

N1’ N2’

N1

S2’

N1’ B1’

S2

N1

S1

F1

B1

F2

N2

N1’ S2’ N2’

N1

B1 N2

S1’

S1

S2

S2

N2’

N2 S1’

S2’

F2’

B1’

F1’

S1 S1’

Figure 6. Comparison of DFT optimized geometries of compound 3a (a) and its bis-BF2 complex 4a (b); Top-perspective views and Bottom- side views (Note: Hydrogen atoms and meso substituents in side views were removed for clarity). Analysis of the frontier molecular orbitals of the compound 3a suggested that HOMO (Highest Occupied Molecular Orbitals) is mainly localized on four thiophene rings, two dipyrrin units and little density on pentafluorobenzene rings present at the meso positions but no orbital density on two p-phenylene units of macrocycle. Also, LUMO (Lowest Unoccupied Molecular Orbitals) in 3a localized mainly on dipyrrin units and thiophene rings away from the p-phenylene units which supports poor π-orbital overlap in dibenzidecaphyrin 3a. However, HOMO of the compound 4a is localized on one of the dipyrrin units and thiophene rings leaving no orbital density on rest of the macrocycle. In LUMO of the 4a, the transfer of most of the charge density to other



Page 16 of 27

part of the macrocycle was observed. The HOMO and LUMO of the compound 4a were found to be stabilized compared to the HOMO and LUMO of 3a suggesting 4a is difficult to oxidize but easier to reduce compared to 3a. The redox properties were also in agreement with these observations. The increase in band gap in 4a supports the blue shifted absorption bands of 4a compared to 3a. Similar observations were noted for the compounds 3b-c and 4b-c (Figures S43S44 ).

a)

b)

LUMO E=-6.3794 eV

LUMO E=-6.4080 eV

ΔE= 0.895 eV

HOMO E=-7.2741 eV

ΔE= 0.944 eV

HOMO E=-7.3517 eV

Figure 7. Selected frontier molecular orbitals (isovalue = 0.02) with orbital energies and band gap of the compounds 3a (a) and 4a (b) calculated using B3LYP/6-31g (d,p) level of theory.


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CONCLUSIONS: In conclusion, we successfully prepared the first examples of dibenzidecaphyrins (1.0.0.1.1.1.0.0.1.1) from a readily available m-phenylene based pentapyrranes as the key precursors under mild reaction conditions. The dibenzidecaphyrin macrocycles were not formed when we used any other substituted aldehydes other than pentafluorobenzaldehyde. These macrocycles are the largest expanded benziporphyrinoids known in the literature so far. The crystal structure obtained for one of the decaphyrin macrocycles revealed that the macrocycle adopts a figure-of-eight conformation. The decaphyrin macrocycles show few resonances in the proton and 13

C NMR spectra due to the presence of high symmetry. The free base decaphyrin macrocycles

exhibits typical non-aromatic absorption features and are stable under electrochemical redox conditions. The decaphyrin macrocycles readily forms bis-BF2 complexes upon treatment with BF3.OEt2 at reflux conditions. The NMR, absorption, electrochemical and DFT studies support the retention of fight-of-eight conformation for bis-BF2 complexes of the dibenzidecaphyrin macrocycle.

MATERIALS AND METHODS General Experimental: The chemicals such as pentafluorobenzaldehyde, and 2,3-dichloro-5,6dicyano-1,4-benzoquinone (DDQ) were procured from Sigma-Aldrich and used as obtained. All other chemicals used for the synthesis/studies were obtained from local suppliers and were reagent/spectroscopic grade unless otherwise specified. Column chromatography purifications were done using basic alumina (Al2O3). The characterization of the compounds using various spectral techniques such as NMR, absorption, cyclic voltammetry were performed as described previously.16



X-ray crystal structure analysis: The X-ray crystal analysis and crystal refinements were performed as described previously.16 The CCDC No. 1824344 contains the supplementary crystallographic data for this paper. 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: The density functional theory (DFT) calculations for the compounds 3ac and 4a-c were carried out as described previously.21 The stability of the optimized geometries of the all compounds 3a-c and 4a-c was established with vibrational analyses, and found that the sum of imaginary frequencies were zero for all the molecules.

Compound 3a: Samples of pentapyrrane16 5a (200 mg, 0.30 mmol) and pentafluorobenzaldehyde (235 mg, 1.20 mmol) were dissolved in dichloromethane (100 mL) and nitrogen was bubbled through the solution for 15 min. TFA (17 mg, 0.15 mmol) was added and the solution was stirred, protected from light for 1h under inert atmosphere. The reaction was then oxidized with DDQ (137 mg, 0.60 mmol) for 2 h in open air. The crude compound was purified by basic alumina column chromatography using petroleum ether/ dichloromethane (80:20) to afford 3 as dark green solid (50 mg, 10 % yield). mp: > 300 °C. 1H NMR (400 MHz, CDCl3, δ in ppm): 1.37 (s, 36H, CH3), 6.01 (d, J = 5.0 Hz, 4H, thienyl d), 6.44 (d, J = 5.0 Hz, 4H, thienyl e), 6.91 (d, J = 4.0 Hz, 4H, pyrrolyl h), 6.93-6.97 (m, 4H, aryl a and c), 7.14 (dd, J = 8.0 Hz, 4H, aryl b), 7.32 (d, J = 8.0 Hz, 8H, tert-butylbenzene f), 7.38 (d, J = 8.0 Hz, 8H, tert-butylbenzene g), 7.86 (bs, 4H, pyrrolyl i), 14.07 (bs, 2H, inner -NH); 19F NMR (376.4 MHz, CDCl3, δ in ppm): -137.84 (q, 1J (F-F) = 26.3 Hz, 4F), -155.21 (q, 1J (F-F) = 22.5 Hz, 2F), -161.90 (td, 1J (F-F) = 15.0 Hz, 4F); 13C NMR (125 MHz, CDCl3, δ in ppm): 29.8, 31.5, 34.9, 70.7, 30.4, 113.4, 121.1, 123.5, 123.9, 124.3, 124.7, 124.9, 125.6, 126.3, 128.3, 129.1, 129.2, 130.7, 131.3, 131.6, 133.4, 134.2, 136.8, 137.1, 138.8,


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142.7, 144.8, 146.9, 148.3, 148.7, 152.0, 160.0; UV-vis (in CHCl3, λmax/nm, log ε) = 355 (4.7), 448 (5.1) and 735 (4.4); HRMS (ESI-TOF) m/z: [M+H]+ calcd. for C102H79F10N4S4 1677.5022, found 1678.5054. Compound 3b: The compound 3b was prepared by following the same procedure as given for compound 3a by using pentapyrrane16 5b (200 mg, 0.31 mmol), pentafluorobenzaldehyde (243 mg, 1.24 mmol) and DDQ (141 mg, 0.62 mmol). The crude compound was purified by basic alumina column chromatography and obtained the desired macrocycle 3b using petroleum ether/ dichloromethane (75:25) as a dark green color solid (40 mg, 8% yield). mp: > 300 °C. 1H NMR (500 MHz, CDCl3, δ in ppm): 1.30 (d, J = 7.0 Hz, 24H, -CH3), 2.97 (sep, J = 7.0 Hz, 4H, -CH), 6.01 (d, J = 5.0 Hz, 4H, thienyl d), 6.43 (d, J = 5.0 Hz, 4H, thienyl e), 6.91 (d, J = 4.0 Hz, 4H, pyrrolyl h), 6.93-6.96 (m, 4H, aryl a and c), 7.13 (d, J = 8.0 Hz, 4H, aryl b), 7.25 (d, J = 8.0 Hz, 8H, iso-propylbenzene f), 7.32 (d, J = 8.0 Hz, 8H, iso-propylbenzene g), 7.86 (bs, 4H, pyrrolyl i), 14.07 (bs, 2H, inner -NH); 19F NMR (376.4 MHz, CDCl3, δ in ppm): -137.84 (q, 1J (F-F) = 26.3 Hz, 4F), -155.23 (q, 1J (F-F) = 22.5 Hz, 2F), -161.90 (td, 1J (F-F) = 15.0 Hz, 4F); 13C NMR (100 MHz, CDCl3, δ in ppm): 24.1, 29.8, 34.1, 90.4, 114.2, 121.2, 123.6, 124.2, 126.1, 126.3, 128.4, 129.1, 131.6, 133.4, 134.2, 137.5, 139.4, 142.7, 148.3, 148.7, 149.7, 160.0; UV-vis (in CHCl3, λmax/nm, log ε) = 356 (4.6), 448 (5.1) and 739 (4.3); HRMS (ESI-TOF) m/z: [M+H]+ calcd. for C98H70F10N4S4 1620.4318, found 1621.4345. Compound 3c: The compound 3c was prepared by following the same procedure as given for compound 3a by using pentapyrrane16 5c (200 mg, 0.34 mmol), pentafluorobenzaldehyde (266 mg, 1.36 mmol) and DDQ (155 mg, 0.68 mmol). The crude compound was purified by basic alumina column chromatography and obtained the desired macrocycle 3c using petroleum ether/ dichloromethane (75:25) as a dark green color solid (40 mg, 8% yield). mp: > 300 °C. 1H NMR



(500 MHz, CDCl3, δ in ppm): 2.42 (s, 12H, -CH3), 6.02 (d, J = 5.0 Hz, 4H, thienyl d), 6.43 (d, J = 5.0 Hz, 4H, thienyl e), 6.91-6.96 (m, 8H, pyrrolyl h, aryl a and c), 7.11-7.14 (m, 4H, aryl b), 7.20 (d, J = 7.8 Hz, 8H, tolyl g), 7.31 (d, J = 7.8 Hz, 8H, tolyl f), 7.85 (bs, 4H, pyrrolyl i), 14.06 (bs, 2H, inner -NH); 13C NMR (125 MHz, CDCl3, δ in ppm): 29.8, 123.7, 128.8, 129.5, 131.5, 134.1; 19

F NMR (376.4 MHz, CDCl3, δ in ppm): -137.84 (q, J (F-F) = 26.3 Hz, 4F), -155.23 (q, J (F-F)

= 22.5 Hz, 2F), -161.90 (td, J (F-F) = 15.0 Hz, 4F); UV-vis (in CHCl3, λmax/nm, log ε) = 356 (4.7), 448 (5.2) and 740 (4.5); HRMS (ESI-TOF) m/z: [M+H]+ calcd. for C90H55F10N4S4 1509.3144, found 1510.3177. Compound 4a: Compound 3a (50 mg, 0.03 mmol) was dissolved in chloroform (20 mL) and TEA (150 mg, 1.48 mmol) was added to the solution. BF3.OEt2 (255 mg, 1.80 mmol) was then added to the reaction mixture and the resulted reaction mixture was refluxed at 80 °C for 6 h. The solvent was removed in a rotary evaporator, and the crude compound was purified by basic alumina column chromatography using petroleum ether/dichloromethane (70:30) to afford pure compound 4a as dark green solid (21 mg, 40% yield); mp: > 300 °C. 1H NMR (500 MHz, CDCl3, δ in ppm): 1.30 (s, 36H, -CH3), 6.27 (d, J = 5.2 Hz, 4H, thienyl d), 6.44 (d, J = 5.2 Hz, 4H, thienyl e), 6.91 (t, J = 8.0 Hz, 2H, aryl a), 7.06 (d, 4H, J = 4.0 Hz, pyrrolyl h), 7.16-7.17 (m, 12H, aryl b, tertbutylbenzene f), 7.27 (d, J = 8.0 Hz, 8H, tert-butylbenzene g), 7.32 (bs, 2H, aryl c), 7.36 (bs, 4H, pyrrolyl i); 11B NMR (160.4 MHz, CDCl3, δ in ppm): 1.82 (t, 1J (B-F) = 30.8 Hz, 2B); 19F NMR (470.5 MHz, CDCl3, δ in ppm): -130.49 (bs, 4F), -137.04 (q, 1J (F-F) = 24.1 Hz, 4F), -153.91 (q, 1

J (F-F) = 21.1 Hz, 2F), -161.38 (td, 1J (F-F) = 21.5 Hz, 4F); 13C NMR (125 MHz, CDCl3, δ in

ppm): 29.8, 31.4, 34.9, 121.9, 122.3, 123.2, 124.7, 124.8, 129.4, 123.9, 134.2, 135.0, 135.5, 138.4, 140.6, 142.5, 144.8, 148.4, 153.2, 157.3; UV-vis (in CHCl3, λmax/nm, log ε) = 463 (4.8) and 696 (4.6); HRMS (ESI-TOF) m/z: [M+H]+ calcd. for C102H77B2F14N4S4 1773.5016, found 1773.5029.


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Compound 4b: The compound 4b was prepared by following the same procedure as given for compound 4a by using compound 3b (50 mg, 0.03 mmol), TEA (155 mg, 1.54 mmol) and BF3.OEt2 (262 mg, 1.85 mmol). The crude compound was purified by basic alumina column chromatography and obtained the desired macrocycle 4b using petroleum ether/ dichloromethane (60:40) as a dark green color solid (18 mg, 34% yield); mp: > 300 °C. 1H NMR (400 MHz, CDCl3, δ in ppm): 1.24 (d, J = 7.0 Hz, 24H, -CH3), 2.90 (sep, J = 7.0 Hz, 4H, -CH), 6.27 (d, J = 5.2 Hz, 4H, thienyl d), 6.74 (d, J = 5.2 Hz, 4H, thienyl e), 6.91 (t, J = 8.0 Hz, 2H, aryl a), 7.06 (d, 4H, J = 4.0 Hz, pyrrolyl h), 7.11-7.18 (m, 20H, aryl b, iso-propylbenzene f, g), 7.31 (bs, 2H, aryl c), 7.367.37 (m, 4H, pyrrolyl i); 11B NMR (160.4 MHz, CDCl3, δ in ppm): 1.83 (t, 1J (B-F) = 30.4 Hz, 2B); 19F NMR (470.5 MHz, CDCl3, δ in ppm): -129.76 (bs, 4F), -137.08 (q, 1J (F-F) = 24.1 Hz, 4F), -153.98 (q, 1J (F-F) = 21.1 Hz, 2F), -161.39 (td, 1J (F-F) = 21.5 Hz, 4F); 13C NMR (125 MHz, CDCl3, δ in ppm): 23.9, 29.8, 34.1, 53.5, 122.0, 122.3, 123.2, 124.7, 125.9, 129.5, 133.2, 134.2, 135.0, 135.1, 135.6, 138.4, 141.0, 142.5, 144.8, 148.4, 150.9, 157.3; UV-vis (in CHCl3, λmax/nm, log ε) = 462 (4.9) and 701 (4.7); HRMS (ESI-TOF) m/z: [M]+ calcd. for C98H68B2F14N4S4 1716.4311, found 1716.4317. Compound 4c: The compound 4c was prepared by following the same procedure as given for compound 4a by using compound 3c (50 mg, 0.03 mmol), TEA (155 mg, 1.54 mmol) and BF3.OEt2 (262 mg, 1.85 mmol). The crude compound was purified by basic alumina column chromatography and obtained the desired macrocycle 4c using petroleum ether/ dichloromethane (60:40) as a dark green color solid (19 mg, 35% yield); mp: > 300 °C. 1H NMR (500 MHz, CDCl3, δ in ppm): 2.45 (s, 12H, -CH3), 6.28 (d, J = 5.2 Hz, 4H, thienyl d), 6.73 (d, J = 5.2 Hz, 4H, thienyl e), 6.91 (t, J = 8.0 Hz, 2H, aryl a), 7.06-7.18 (m, 24H, pyrrolyl h aryl b, iso-propylbenzene f, g), 7.27 (bs, 2H, aryl c), 7.37-7.38 (m, 4H, pyrrolyl i); 11B NMR (160.4 MHz, CDCl3, δ in ppm): 1.80



Page 22 of 27

(t, 1J (B-F) = 30.8 Hz, 2B); 19F NMR (470.5 MHz, CDCl3, δ in ppm): -130.76 (bs, 4F), -137.08 (q, 1

J (F-F) = 24.1 Hz, 4F), -153.89 (q, 1J (F-F) = 21.1 Hz, 2F), -161.32 (td, 1J (F-F) = 21.5 Hz, 4F); C NMR (100 MHz, CDCl3, δ in ppm): 21.5, 29.8, 122.0, 123.2, 124.5, 128.6, 133.1, 134.0, 135.4,

13

140.2, 140.7, 142.4, 148.4, 157.5; UV-vis (in CHCl3, λmax/nm, log ε) = 462 (4.8) and 703 (4.6); HRMS (ESI-TOF) m/z: [M+H]+ calcd. for C90H53B2F14N4S4 1605.3135, found 1605.3137.

ASSOCIATED CONTENT Supporting Information: It contains characterization data (HRMS, 1H,

13

C,

19

F,

11

B, 2D

NMR and DFT studies) data for all the reported compounds and crystallographic data for compound 3a.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Fax: 91-22-5723480. Tel: 91-22-5767176. ORCID Mangalampalli Ravikanth: 0000-0003-0193-6081 Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS M.R. thanks Science & Engineering Research Board, Government of India (EMR/2015/002196), S.K. thanks the UGC for fellowship and K.G.T. thanks to the IIT Bombay India for an institute post-doctoral fellowship.


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and Their Bis-BF2 Complexes - ACS Publications - American

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