Solid-state synthesis, spectroscopic and electrochemical properties of symmetric a 3 type corroles with meso-3-Chloro-4-fluorophenyl groups and its Co III, Mn III and Cu III complexes Текст научной статьи по специальности «Химические науки»

Corroies

Корролы

Макрогэтэроцмклы

Статья

Paper

http://macroheterocycles.isuct.ru

DOI: 10.6060/mhc150250z

Solid-State Synthesis, Spectroscopic and Electrochemical Properties of Symmetric A3 Type Corroles with meso-3-Chloro-4-fluorophenyl Groups and Its Co111, Mn111 and Cu111 Complexes

Peng Zhang, Minzhi Li, Yu Jiang, Li Xu, Xu Liang,@1 and Weihua Zhu@2

School of Chemistry and Chemical Engineering, Jiangsu University, ZhenJiang 212013, China @1Corresponding author E-mail: [email protected] @2Corresponding author E-mail: [email protected]

Solid-state synthesis of A3 type 5,10,15-(3-chloro-4-fluorophenyl)corrole, and its Co111, Mn111 and Cu111 complexes having asymmetric meso-substituents were successfully synthesized and separated. Structural characterization by MS and 1H NMR and the spectroscopic properties by UV-vis, magnetic circular dichorism (MCD) spectra were investigated in this study. Electrochemical properties were also studied to in-depth understand the electronic structures of these corrole or metallo-corrole complexes.

Keywords: Corrole, solid-state synthesis, spectroscopy, electrochemistry.

Твердофазный синтез, спектральные и электрохимические свойства симметричного коррола А3 типа с мезо—3—хлор— 4—фторфенильными группами и его Co111, Mn111 и Cu111 комплексов

Пенг Жанг, Минжи Ли, Ю Джианг, Ли Ксу, Ксу Лианг,@1 Вейхуа Жу@2

Школа химии и химической инженерии, Университет Цзянсу, 212013 Чжэньцзян, Китай @1E-mail: [email protected] @2E-mail: [email protected]

Проведен твердофазный синтез 5,10,15-(3-хлоро-4-фторфенил)коррола А3 типа и его комплексов с Co111, Mn111 и Cu111 с асимметричными заместителями в мезо-положениях. Структура полученных соединений была подтверждена с помощью масс-спектрометрии и спектральных методов (ЭСП, спектроскопии Н ЯМР и магнитного кругового дихроизма). Для более глубокого понимания электронной структуры полученного коррола и его металлокомплексов были изучены их электрохимические свойства.

Ключевые слова: Коррол, твердофазный синтез, спектроскопия, электрохимия.

Introduction

The porphyrinoid complexes have received the considerable amount of attention in recent years, since their optical and biological properties could lead to applications as functional dyes in a number of different high-technology fields, such as organic solar cells, photodynamic therapy, heat absorbers, and organic catalysis.[1] Corroles, the porphyrin analogues with a direct pyrrole-pyrrole bond and an extra N-H proton on the inner ligand perimeter, are best known for forming the basic structure of vitamin B12.[2] In recent decades, there has been a strong research focus on the use of corroles as functional ligands, largely due to their ability to stabilize higher oxidation states of the coordinated metals, which can be applied as potential catalysts such as: Cr(V), Fe(IV), Co(IV), and even Mn(V) or Co(V).[3] On the other hand, high-valence metallo-corrole complexes applied for combined photodynamic therapy (PDT) and bioimaging applications in living cells has recently been explored.[4] Recently, the synthesis of corrole is mainly focused on the acid-catalyzed reaction by Gryko,[5a-5d] or solid-state Al2O3 supported reaction was also succeeded by Collman.[5e] However, in spite of research interests of corroles, the number of either spectroscopic or electrochemical investigations on the electronic structure of free base corroles and their metallo-complexes have been limited. Especially, the corrole analogues having asymmetric meso-substituents were less studied and reported previously. All these advantages promoted us to synthesize new corrole analogues containing asymmetric meso-substituents. In this paper, asymmetric 3-chloro-4-fluorobenzaldehyde was selected as the key starting materials to synthesis free base corrole via solid-state synthetic procedure. Spectroscopic properties studied by UV-vis absorptions, magnetic circular dichroism (MCD) spectrums and the electronic structures of these corrole analogues were also in-depth studied by cyclic voltammetry measurements.

Experimental

Chemicals

Analytical pure iV,jV-dimethylmethanamide (DMF) for electrochemical measurements was purchased from the Aladdin Reagent Company of Shanghai, and freshly distilled before use. All other chemicals and solvents were analytical pure grade and were purchased from the Shanghai Guoyao Company. All solvents were dried and distilled prior to use.

Materials and Instruments

Cyclic voltammetry was performed in a three-electrode cell using a Chi-730C electrochemistry station. A glassy carbon disk electrode was utilized as the working electrode while a platinum wire and a saturated calomel electrode (SCE) were employed as the counter and reference electrodes, respectively. The working and counter electrodes were made from platinum mesh and the reference electrode was an SCE. The working and reference electrodes were placed in one compartment while the counter electrode was placed in the other. UV-visible absorption spectra were recorded with a HP 8453A diode array spectrophotometer.

All of the electrochemical measurements were carried out under a nitrogen atmosphere. Magnetic circular dichroism (MCD) spectra were measured with a JASCO J-820 equipped with a 1.6 T (tesla) permanent magnet by using both the parallel and anti-parallel fields. The conventions of Piepho and Schatz are used to describe MCD intensity and the Faraday terms.[7] MALDI-TOF mass spectra (MS) were collected using Bruker Daltonics autoflex II MALDI-TOF MS spectrometer. 1H NMR spectra were recorded on a Bruker AVANCE 400 spectrometer (operating at 400.13 MHz) using the residual solvent as an internal reference for 1H (5 = 7.26 ppm for CDCl3 and 5.32 ppm for CD2Cl2).

Synthesis of 5,10,15-(3-chloro-4-fluorophenyl)corrole (1). Neutrilized Al2O3 (3 g) was added to a mixture of 10 mL CH2Cl2 solution of 3-chloro-4-fluorobenzaldehyde (1.59 g, 10 mmol). Freshly distilled pyrrole (0.90 mL, 13 mmol) was slowly added and heated again at 60 °C for 4h under N2 after fully removed of CH2Cl2. After cooled to the room temperature, 25 mL CH2Cl2 was added to the same mixture and the Al2O3 was removed by filtration. Then, chronail (1.00 g, 40 mmol) was added to solution and stirred at 50 °C for 1h. Purification perfomed on the silica gel column chromatography (CH2Cl2:hexane = 1:1) and finally recrystallized from CH2Cl2 and hexane to give 5,10,15-(3-chloro-4-fluorophenyl) corrole 1 (330 mg, 14.5 %). m/z (MALDI-TOF-mass) 685.63 (Calcd. [M+H]+ = 684.94). UV-vis (CH2Cl2) Xmax nm: 414 (136000), 571 (10700), 613 (7800), 644 (7800). 2H NMR (CDCl3, 298 K) 8H ppm: 9.03 (2H, br s), 8.88 (2H, br s), 8.59 (4H, br s), 8.42 (2H, br s), 8.22 (2H, br s), 8.04 (1H, br s), 7.64 (4H, br s), -2.79 (3H, br s).

Synthesis of Co(III)PPh3-5,10,15-(3-chloro-4-fluorophenyl) corrole (2a). H3-5,10,15-(3-chloro-4-fluorophenyl)corrole 1 (68 mg, 0.1 mmol) was dissolved in a 40 mL of methanol/CH2Cl2 (1:1) mixture containing triphenylphosphine (131 mg, 0.5 mmol, 5.0 eq) and Co(CH3COO)2-4H2O (190 mg, 0.75 mmol). The mixture was slowly increased to 60 °C and kept for 1.5h. After removal of the solvent, purification by silica gel column chromatography (CH2Cl2:hexane = 1:1), and recrystallization (CH2Cl2/hexane) to give the pure Co(III)-5,10,15-(3-chloro-4-fluorophenyl)corrole 2a (92 mg, 92.0%). m/z (MALDI-TOF-mass) 740.14 (Calcd. [M]+ = 739.85). UV-vis (CH2Cl2) Xmax nm: 385 (43500), 410 (34800), 556 (9500), 582 (6700). 1H NmR^CD^, 298 K) 8H ppm: 8.82 (2H, d, J= 3.6 Hz), 8.45 (2H, d, J=4.8 Hz), 8.20 (2H, d, J = 4.4 Hz), 8.09 (2H, d, J = 4.4 Hz), 7.52~7.47 (m, PPh3), 7.17 (4H, br s), 6.76 (5H, br s).

Synthesis of Mn(III)-5,10,15-(3-chloro-4-fluorophenyl)cor-role (2b). H3-5,10,15-(3-chloro-4-fluorophenyl)corrole 1 (68 mg, 0.1 mmol) was dissolved in 20 mL of distilled DMF mixture containing Mn(CH3COO)2-4H2O (183 mg, 0.75 mmol), and the mixture was heated at 110 °C for 30 mins. After removal of DMF under low pressure, the purification was carried by silica gel column chromatography (CH2Cl2), alumina gel chromatography (CH2Cl2:ethylacetate = 4:1) and the target compound was obtained after recrystallization by CH2Cl2 and hexane to give the pure Mn(III)-5,10,15-(3-chloro-4-flu oro phenyl)corrole 2b (76 mg, 69.0%). m/z (MALDI-TOF-mass) 735.20 (Calcd. [M]+ = 735.85). UV-vis (CH2Cl2) Xmax nm: 404 (37500), 428 (35600), 495(11100),

570(7500), 62442(88m0a0x).

Synthesis ofCu(III)-5,10,15-(3-chloro-4-fluorophenyl)corrole (2c). H3-5,10,15-(3-chloro-4-fluorophenyl)corrole 1 (136 mg, 0.2 mmol) was dissolved in a 40 mL methanol/CH2Cl2 (1:1) mixture containing Cu(CH3COO)2-H2O (200 mg, 1 mmol), and the mixture was refluxed at 60 °C for 2h. After removal of the solvent, the purification was carried by silica gel column chromatography (CH2Cl2), alumina gel chromatography (CH2Cl2:ethylacetate = 4:1) and recrystallization (CH2Cl2 and hexane to give the pure Cu(III)-5,10,15-(3-chloro-4-fluorophenyl)corrole 2c (112 mg, 75.0%). m/z (MALDI-TOF-mass) 744.60 (Calcd. [M]+ = 744.50). UV-vis (CH2Cl2) Xmax nm: 410 (60100), 540 (4200), 620 (2700). 1H NMR (CD2Cl 298! K) 8„ ppm: 7.90 (2H, d, J = 4.0 Hz), 7.78 (2H, d,

J= 4.4 Hz), 7.64~7.61 (5H, m), 7.53~7.49 (1H, m), 7.37~7.29 (5H, m), 7.26 (2H, d, J = 4.8 Hz).

Results and Discussion

Synthesis and Characterization

The synthetic procedure is shown in Scheme 1. The solid-state synthetic procedure using Al2O3 supported materials promoted that the less of acid media produced a simple purification system. The MALDI-TOF-mass spectra of 1 reveals a strong parent peak at m/z=685.63 (Calcd [M+H]+=684.94), providing direct evidence that the target H3-5,10,15-(3-chloro-4-fluorophenyl)corrole 1 was successfully obtained. Similar MALDI-TOF-mass peaks were also observed in the case of metallo-corroles 2a, 2b and 2c. The proton signals which appeared in the 1H NMR spectra of 1 was similar with that of regular triarylcorrole from litera-tures.[5] The uncertain proton integration value of PPh3 of 2a is probably due to the partial removal of the axial ligands during the purification or measurement. 1H NMR spectra of 1, 2a and 2c are shown in Figure 1.

Spectroscopic Properties

The optical spectroscopy of corroles can be described in terms of perturbations to an ML=0, ±1, ±2, ±3, ±4, ±5, ±6, ±7 sequence of MOs associated with the parent C15H153- perimeter for the 15-atom 18-n-electron system of the inner ligand perimeter. Moffitt[6] and Michl[7] demonstrated that when the symmetry of aromatic and heteroaromatic n-systems are lowered by perturbations to the structure, the alignments of the nodal patterns of the MOs of the parent perimeter are retained. This can be used to predict the effect of structural perturbations on the relative energies of the frontier n-MOs. The HOMO and LUMO of the parent C15H153- perimeter for corroles have ML=±4 and ±5 properties, respectively. By analogy with Gouterman's four-orbital model it can be demonstrated that this leads to allowed B and forbidden Q bands based on allowed AML=±1 and forbidden AML=±9 transitions.

UV-visible absorption spectroscopy is one of the most useful methods for characterizing porphyrins and their analogues. The UV-vis absorption spectra of H3-5,10,15-(3-chloro-4-fluorophenyl)corrole 1 (Figure 2, bottom) reveal an intense Soret band absorptions at 414 nm, and three

CHO

Solvent free N' Catalyst free CI H

F

2a M = Co(lll)PPh3 2b M = Mn(lll) 2c M = Cu(lll)

Scheme 1. Synthesis of H3-5,10,15-(3-chloro-4-fluorophenyl)corrole 1, and its metal complexes 2.

Figure 1. 1H NMR spectra of 1 (up) in CDCl3, 2a (middle) and 2c (bottom) in CD2Cl2.

Figure 2. UV-vis absorption (bottom) and MCD spectra (top)

of H3-Corrole 1 in CH2Cl2.

weak Q band absorptions at 571, 613 and 644 nm. The additional information provided by the MCD technique181 is derived from three highly characteristic spectral features, the Faraday A1, B0, and C0 terms.[9] The oppositely signed coupled pair of Faraday B0 terms observed at 410 (negative) and 435 nm (positive) at the Soret band region, 544 (negative), 578 (negative), 612 (positive), 644 nm (positive) at the Q band region. Based on the intensity and the sign of the MCD signals of 1, Qx(0-0), Qx(0-1), Qy(0-0), Qy(0-1) bands were assigned to the B0-terms observed at 644, 612, 578, 544 nm in non-polar solvent CH2Cl2, respectively. The observed positive sign of the low energy Qx band and negative sign for higher energy Qy band in the positivepositive-negative-negative manners are uncharacteristic of porphyrinoids and indicative of the larger energy difference between the LUMO and LUMO+1 orbitals (n* orbitals) the HOMO and HOMO-1 n MOs (n orbitals). In the spectra of lowsymmetry porphyrinoids, pairs of coupled oppositely signed Faraday B0 terms replace the derivative-shaped Aj-terms that are observed in the spectra of radially symmetric metal porphyrinoid complexes.181

The metal coordinated corrole analogues generally exhibit different shape of the absorptions of the UV-vis spectra compared with free-base corroles, due to the metal-ligand or the ligand-metal transition interaction was occured in these coordinated corrole complexes. Co(III)PPh3 corrole 2a (Figure 3, bottom) exhibits intense Soret band absorptions at 386 nm with an extra shoulder band at around 410 nm, and two Q bands appeared at 556 and 582 nm, respectively. The decreased number of the Q bands of 2a can be assigned as the change of the molecular symmetry via metal-coordination. The MCD spectra of compound 2a (Figure 3, up) in CH2Cl2 are revealed by the Faraday B0-terms in the corresponding MCD spectra centered at 385 (negative) and 410 nm (positive) at the Soret band region, 556 (negative), 582 nm (positive) at the Q band region. The MCD spectra of 2a reveal intense signals in the Q band region and weak signals in the Soret band region, that is different from the regular free-base corrole and its analogues, probably due to the intramolecular metal-ligand transitions. The Mn(III)-coordinated corrole 2b (Figure 4, bottom) reveals broader

region of absorptions in the UV-vis spectrum. Two Soret band absorptions appeared at 408, 428 nm, and two Q band absorptions appeared at 570, 640 nm, respectively. The MCD spectra of compound 2b (Figure 4, up) in CH2Cl2 are revealed by the Faraday B0-terms in the corresponding MCD spectra centered at 400 (negative) and 432 nm (positive) at the Soret band region, 572 (negative), 644 nm (positive) at the Q band region. The Cu(III)-coordinated corrole 2c (Figure 5, bottom) reveals intense Soret band at 410 nm, where a shoulder band appeared at around 430 nm. Two weak Q band absorptions were appeared at 540, and 620 nm. The MCD spectra of compound 2c (Figure 5, up) in CH2Cl2 are revealed by the Faraday B0-terms in the corresponding MCD spectra centered at 410 (positive) and 433 nm (negtive) at the Soret band region, 540 (negative), 575 nm (positive), 620 nm (positive) at the Q band region.

Electrochemical Properties

In order to in-depth understand the electronic structure of H3-corrole 1 (Figure 6) and its metallo-coordinated

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Figure 5. UV-vis absorption (bottom) and MCD spectra (top) of Cu(III)-Corrole 2c in CH2Cl2.

Figure 6. Cyclic voltammetry measurement of H3-corrole 1 in DMF containing 0.1 M TBAP, scan rate: 0.1 V/s.

Figure 8. Cyclic voltammetry measurement of Mn(III)-corrole 2b in DMF containing 0.1 M TBAP, scan rate: 0.1 V/s.

Figure 7. Cyclic voltammetry measurement of Co(III)PPh3-corrole 2a in DMF containing 0.1 M TBAP, scan rate: 0.1 V/s.

Figure 9. Cyclic voltammetry measurement of Cu(III)-corrole 2c in DMF containing 0.1 M TBAP, scan rate: 0.1 V/s.

complexes 2a (Figure 7), 2b (Figure 8) and 2c (Figure 9), respectively. Cyclic voltammetry measurements were carried out in DMF containing 0.1 M TBAP. H3-corrole 1 reveals a clear reversible redox at E1/2=-1.70 V which can be assigned as [H3-Corrole]/[H3-Corrole]- from the reduction of the corrole ring, and the oxidation part of 1 turned to be irreversible due to the decomposition of H3-corrole 1 during the oxidation processes of CV measurements. In the case of Co(III)PPh3-corrole 2a, two reversible reduction processes were observed at E1/2 = -0.40 and -1.48 V, respectively. These two processes of 2a can be assigned as [Co(III)-Corrole]+/[Co(II)-Corrole] and [Co(II)-Corrole]/ Co(II)-Corrole]-, respectively. The oxidation processes of 2a are also irreversible. The Mn(III)-corrole 2b also reveal two reversible reduction processes at E1/2=-1.14 V for [Mn(II)-Corrole]-/[Mn(I)-Corrole]2- and E1/2=-1.84 V for ring reduction [Mn(I)-Corrole]2-/[Mn(I)-Corrole]3-, respectively. The oxidation processes of 2b reveal only one reversible curve

at E1/2=0.34 V assigned as [Mn(m)-Corrole]/[Mn(II)-Corrole]". Finally, the Cu(III)-corrole 2c only reveals two reversible reduction E1/2=0.08 and -1.75 V, that can be assigned as [Cu(III)-Corrole]/[Cu(II)-Corrole]- and ring reduction [Cu(II)-Corrole]-/[Cu(II)-Corrole]2-. All electrochemistry results are simlar with other A3 type H3-meso-p-fluorophenylcorrole or H3-meso-m-chlorophenylcorrole and their metallo-complexes,[10] that indicate mirror effect of the unsymmetric introduction of fluoro- or chloro-substituents at meso-phenyl positions.

Conclusions

In this

paper, A3 type 5,10,15-(3-chloro-4-fluorophenyl)corrole having asymmetric meso-3-chloro-4-fluorophenyl-substituents was successfully obtained via a solid-state synthetic procedure. The Co(III)PPh3,

Mn(III) and Cu(III) coordinated corrole complexes were also successfully synthesized and isolated for the first time. Spectroscopic properties were studied by UV-vis absorption and magnetic circular dichroism spectroscopy, as well as cyclic voltammetry measurements were carried out. Considering that development of new synthetic pathways and investigations on the electronic structures of corroles are very useful design and analysis of chromophores, our results in this research will offer useful information for the future corrole chemistry.

Acknowledgements. Financial support was provided by the National Scientific Foundation of China (No. 21171076).

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Received 28.02.2015 Accepted 01.04.2015