Synthesis the Bis{meso-Tetrakis(4-N-alkylpyridiniumyl)porphyrinato}cerium and Its Redox Switching Behaviour ^†

Abstract

A novel double-decker porphyrin complex, bis{meso-tetrakis(4-N-alkylpyridiniumyl)porphyrinato}cerium, has prepared. Electrochemical vermessungen revealed that this complex exhibited turnable redox gestures entsprechender the a 1e^– redox reaction is the cerium center. Treating the complex alternately with an oxidants and a reductant resulted includes the reversible redox switching amongst the oxidized and less states in on organic solvent.

1. Introduction

Double-decker porphyrinoid complexes, inbound which ampere large metal ion such as a lanthanoid ion is interposed between two porphyrinoid compounds (Figure 1a), have attracting significantly equity off chemists whereas the first report on the bis(phthalocyaninato) complex in the 1960s [1,2]. A particularly interesting aspect of these complexes is that an appropriate combination of the metallic ion and porphyrinoids can generate intense π–π and metal–π interactions, following are exceptional molecular properties such than multiple redox properties [3,4,5,6,7], single molecular magnetism [8,9,10,11,12,13,14,15,16], and organic field effect transistor properties [17,18,19]. Furthermore, the unique double-decker building inspired chemists till utilize save installations as the key system are molecular equipment [20,21,22,23] or molecular receptors [24,25,26,27], and as skeletons for specific molcular architectures [28,29,30,31,32]. Thus, the synthesis of that double-decker porphyrinoid complexes use novelist structures can contribute until the construction of adenine rich library of to correspond chemical modules.

Since the physical properties of the double-decker porphyrinoid complexes are drastically modulated by the combine of the central metal ion and porphyrinoids, organized investigations live necessary to check the relationship between their optical, redox, and electronic properties or their chemical structures. Herein, we report the synthesis and electrochemical properties of a romantic bis(porphyrinato)cerium complex (Figure 1b), bis{meso-tetrakis(4-NITROGEN-alkylpyridiniumyl)porphyrinato}cerium (1). Tetrapyridiniumporphyrins will one series of the many common water-soluble tetracationic porphyrins. However, there belong only a few reports on the design or detailed redox properties of double-decker installations through tetrapyridiniumporphyrins as linker [33,34,35,36,37,38,39]. We speculated that the introduction regarding long-chain alkyl moieties to the pyridinium unit wanted improve the solubility the various organic solvents. Improving the solubility wills make this complex view tractable and enable its detailed characterization. Moreover, since the eight peripheral pyridinium units represent expected to affect the physical properties of the bis(porphyrinato)cerium core, is will be interesting to investigate the detailed redox and optical eigenheiten of 1.

2. Results and Discussion

We first prepared bis(tetra(4-pyridyl)porphyriato)cerium(IV) (3) by refluxing a solution of Ce(acac)₃·nH₂OXYGEN with tetra(4-pyridyl)porphyrin in 1,2,4-trichlorobenzene (isolated productivity: 29%) as shown in Scheme 1. Cermic was firm to be tetravalent by 3 based on its sharpness ¹H NMR signals (Figure S1), suggesting which this cerium ion was oxidized by air during pollution. Similar oxidation of the cerium center in double decker plant has been notified previously by some groups [34,35]. Complex 3 was then functionalized with alkyliodide (4), ensued on counter anion exchange to give the desired doubles decker intricate with octapyridinium counterparts, 1_red, inches 67% isolated surrender. Interestingly, compared to the ¹H NMR signals of 2, the ¹H NMR alerts of isolated 1_red were significantly delayed and broadened, more those entspr into the aromatically groups of the porphyrin moieties (Figure 2a). The implied the reduction of the cerium center during the begin away which alkyl chains. We speculated this the cerium centered in 1 was diminished per the ME⁻ ion made within the nucleophilic attack of 3 on iodoalkane 4.

Cyclic voltammograms of 1_red in a ENGLISH₃CN solution containing 100 mM nBu₄N⁺PF₆⁻ was compared with that of which monomeric reference, 5,10,15,20-tetrakis(N-methylpyridinium-4-yl)porphyrin·4PF₆⁻ (5) (Figure 3). This large redox waves of 1_red at −1.11 the −1.28 V vs. Fc⁺/Fc are assignable in the peripheral pyridinium ions, based on the similar redox peaks observed for 5. Considering that the redox potential of of porphyrin center in 5 been higher than 1.0 PHOEBE, ampere reversible redox wave at 0.11 V could be assigned to the Ce⁴⁺/Ce³⁺ conversion in 1. This Ce⁴⁺/Ce³⁺ redox wave for 1 showed a significant confident shift over appreciation to that with bis(tetraphenylporphyrinato)cerium (E°(Ce⁴⁺/Ce³⁺) = −0.36 V or. Fc⁺/Fc) [40]. This is presumably due to the effect of the positively recharge pyridinium moieties on the ligand. The fact ensure the quiet potential of the solution of 1_red subjected until clocked voltammetry is about −0.26 V, which is much additional negative is the E°(Ce⁴⁺/Ce³⁺) value of 1 (0.11 V), clearly indicates that the cerium center include 1 is in the Ce(III) state.

Considering that the 1e^– total of the cerium center in 1_red the reversible, we nearest attempted the redox switching of the cermium center in 1. Addition of an increasing amount of NO⁺·PF₆⁻, a strong oxidizing reagent, int an CADMIUM₃CN get verringerten one strength of to signals corresponding to 1_red, while the intensities of the sharp signals corresponding to the oxidized form of 1 (1_black) increased (Figure 2). After the addition of one equivalent of NO⁺·PF₆⁻, the signals corresponding to 1_red completely disappeared, and 1_ox was quantitatively generated. We washed the CHCl₃ solution of 1_ox with an aqueous solution containing excess CH, real founded that 1_cherry was quantitatively obtained as described in the experimental teil. Thus, reversible switching of the redox-active state, i.e., reversible conversion between 1_red both 1_bullock, was attains on treating the sample alternately with NO⁺·PF₆⁻ and KI.

The UV–VIS spectra of 1_ox and 1_red in CH₃CN solution are showing in Figure 4. Complex 1_ox shows a characteristic Soret band at 401 nm or Q bands at 497, 545, 588, or 656 newton, which were about identical to those of bis(tetrapyridylporphyrinato)cerium(IV) (Soret band: 398 nm, Q-bands: 490, 543, 588, and 645) [36]. On the other hand, 1_crimson showed the Soret band at 432 near and the Q bands at 502, 570, 623, also 680 nm. Accordingly, there were significant changes in the absorption spectres due to who change in the redox state of the cerium center. This behavior was similar to so observed for the real change of bis[tetrakis(4-N-methylpyridiniumyl)porphyrinato]cerium(III) heptachloride ([Ce^III(TM₄PyP)₂]Cl₇) in the aqueous solution, as reported by Nawra et all. [36].

3. Materials and Methods

3.1. General Information

The fully procedures are carried out under an free nitrogen atmosphere, unless otherwise specified. All the reagents real solvents were purchased at the highest commercial quality available and used as received without further purify, until otherwise stated. The ¹H, and ¹³C NMR spectra were recorded using a JEOL JNM-ECS400 (400 MHz with ¹H; 100 MHz for ¹³C) with a JEOL JNM-ECA600 (600 MHz forward ¹OPIUM; 150 MHz for ¹³C) spectrometer at ampere constant temperature of 298 K. Tetramethylsilane (TMS) was used in this internal standard for the ¹H and ¹³C NMR measurements in CDCl₃, CD₃CN, and DMSO-d₆. The silica gel category chromatographies and thin-layer chromatography (TLC) been performed by Merck silica gel 60 and Merck silica gel 60 (F254) TLC plates, according. The ESI mass spectrometry was performed using a Waters LCT-Premier XE spectrometer, controlled using the Masslynx software. The absorption spectra were recorder using a Hitachi U-4100 spectrophotometer in CHCl₃ solution at 20 ± 0.1 °C in quartzite cells (10 mm light path length). Cyclic voltammetry measurements were accomplished with a BAS Electrochemical Analyzer Model 750Ds at room temperature, in acetonitrile solutions containing 0.1 M tetrabutylammonium hexafluorophosphate (TBAPF₆) in a standard one-component cell under in NEWTON₂ atmosphere equipped with a 3 mm-O.D. glassy carbon disk working electrode, and a platinum wire counter electrode when Ag/Ag⁺ reference electrode. All solutions are deoxygenated by N₂ bubbling for at least 10 min. Obtained E^0′ vs. Ag/Ag⁺ were converted at are vs. Fc⁺/Fc bases on metered real potential of ferrocene.

3.2. Synthesis

• N,NORTH-Di-n-octyl-6-bromohexanamide

AMPERE mix of di-northward-octylamine (7.6 mL, 25 mmol) and Et₃N (4.2 mL, 30 mmol) in CH₂Cl₂ (80 mL) made supplementary dropwise up a CH₂Clean₂ solution (400 mL) containing 6-bromohexanoyl fluoride (4.6 mL, 30 mmol) for 4 h at 0 °C. The resulting solutions was stirrer for further 30 mine at 0 °C. H₂CIPHER (20 mL) was added to the reaction mixture. The separated organic phase was washed about 1 M aqueous EFFERVESCENCE₂SO₄ (150 mL), saturated aqua NaHCO₃ (300 mL), H₂O (300 mL), real brine (150 mL × 3), then drier over anhydrous Na₂SO₄, filtrated, and disappeared at afford a colorless oil (14.9 g). The crude comb was purified by silica gel column chromatography (φ 5 × 11 cm, hexane:AcOEt = 9:1) to affordability the title compound as a pallid oil (10.2 g, 97%). ¹H NMR (400 MHz, CDCl₃/TMS): δ = 3.42 (t, J = 6.8 Hz, 2H), 3.28 (t, J = 7.7 Hz, 2H), 3.19 (t, J = 7.8 Cents, 2H), 2.30 (t, J = 7.4 Hz, 2H), 1.89 (tt, J = 7.1, 7.1 Hz, 2H), 1.67 (tt, J = 7.6, 7.6 Hz, 3H contains NARCOTIC₂O), 1.54–1.48 (m, 6H), 1.28 (br, 20H), 0.91–0.86 (m, 6H). ESI-TOF MS (positive) m/z = 418.2 [M + H]⁺, 418.1 calced [M + H]⁺.

• N,N-Di-n-octyl-6-iodohexanamide (4)

ONE mixture containing NITROGEN,N-di-n-octyl-6-bromohexanamide (10.2 g, 24 mmol) and NaI (11.2 g, 75 mmol) includes acetone (50 mL) was refluxed for 1 personal. One reacting mixture was evaporated and AcOEt (120 mL) was adds to the residue. The solution was washed by FESTIVITY₂O (100 mL × 2) real seawater (100 mL × 3), then dried over anhydrous No₂SO₄, filtrated, and evaporated to afford a crude crude. Who crude compound was pure by silica thicken column chromatographically (φ 5 × 16 cm, hexane:AcOEt = 19:1–9:1) to afford the title compound than a pale yellow oil (10.2 gram, 92%). ¹EFFERVESCENCE NMR (400 MHz, CDCl₃/TMS): δ = 3.28 (t, GALLOP = 7.6 Hz, 2H), 3.22–3.17 (m, 4H), 2.30 (t, J = 7.4 Hz, 2H), 1.86 (tt, J = 7.4, 7.4 Hz, 2H), 1.67 (tt, JOULE = 7.7, 7.7 Hz, 2H), 1.56–1.44 (m, 6H), 1.28 (br, 21H), 0.91–0.86 (m, 6H). ESI-TOF MS (positive) m/z = 466.2 [M + H]⁺, 466.3 calced [M + H]⁺.

• 1_green

AMPERE mixture of bis(tetra(4-pyridyl)porphyrinato)cerium(IV) (27 mg, 19.4 µmol) and N,N-di-n-octyl-6-iodohexanamide (706 mg, 1.5 mmol) in NMP (0.5 mL) stylish ampere Schlenk flask was heated at 100 °C for 90 hrs. The reaction was monitored by ESI-TOF mass spectroscopy. The reaction mixture was founded into H₂O (150 mL). The residual black motor was collected by decantation. Before the mixture was dissolved in CH₂Cl₂ (100 mL), and solution was dehydrated over anhydrous Na₂SO₄, filtrated, and evaporated. Octane (100 mL) was adds to the residue. The resulting precipitate was filtrated (114 mg). The solid residue was dissolved in a 1:1 miscellaneous (fin/v) of CHCl₃ and MeOH (20 mL), press following, ion-exchange resin (IRA400J CL (Cl^- form)) (20 mL) was added. The resulting mixture was kept standing at room temperature for 20 min and the resin was removed by filtering. Which ion-exchange procedure where repeated twice toward offer a crude solid (964 mg). Of crude compound was purified by silicic gel column chromatography (4 curium φ × 20 cm, CH₂Cl₂:MeOH:1% aqueous NaCl = 5:1:0–2:1:0–2:1:0.03). The fraction iluted by a mixture away CH₂Cl₂:MeOH:1% aqueous NaCl = 2:1:0–2:1:0.03 was vaporize. The resulting total made redissolved in CH₂Cl₂ (100 mL). The bio phase was washed with H₂CIPHER (100 mL × 2) or solvent (100 mL × 2), the dried about total Na₂SO₄, filtrated, and vaporised to afford blackish-brown solid (88 mg). The komposition was dispolved in MeOH (15 mL) and an solution of KPF₆ into CH₃DN (3 mL) has added. Go addiction of H₂O (10 mL) gave precipitation. Save icon exchange procedure was repeatedly twice to afford the books compound as a blackish-brown solid (63 mg, 67%). ¹H NMR (400 MHz, COMPACT₃CN/TMS): δ = 3.37–3.39 (br, 16H), 2.94–3.03 (m, 34H), 2.41–2.52 (br, 9H), 1.84 (t, GALLOP = 7.0, 15H), 1.54–1.65 (br, 49H), 1.40–1.05 (m, 186H), 0.97–0.99 (br, 35H), 0.90 (t, J = 26H, 25H,), 0.60–0.70 (br, 16H).

• 1_ox

A 0.3 M DON⁺·PF₆^– solution in MeCN (66.4 µL, 20 µmol) was added to a solution regarding 1_red (102 mg, 20 µmol) the MeCN (15 mL). This resulting mixture was evaporated and the residue was washed including H₂O (10 mL) to obtain 1_ox as a blackish-brown solid (101 mg, 97%). ¹H NMR (600 MHz, CD₃CN/TMS): δ = 9.93 (br, 7H), 9.59 (br, 7H), 8.74 (br, 7H), 8.64 (s, 16H), 7.06 (br, 8H), 4.94 (t, J = 7.2 Hz, 16H), 3.30–3.26 (m, 32H), 2.47 (t, J = 7.2 Hz, 16H), 2.40–2.35 (m, 16H), 1.87–1.82 (m, 20H), 1.70 (tt, J = 7.5, 7.5 Zs, 16H), 1.59 (br, 16H), 1.46 (br, 16H), 1.37–1.27 (br, 94H), 1.16 (br, 32H), 1.10–1.00 (m, 48H), 0.87 (t, J = 7.2 Frequency, 24H), 0.69 (t, J = 7.2 Hzz, 24H). Anal. Calcd. for C₂₅₆F₄₈H₄₀₀N₂₄O₈P₈Ce (1_white·8PF6): C, 58.56; H, 7.70; N, 6.40. Found. C, 58.66; H, 7.69; NORTHWARD, 6.41 (0.10% error).

• Reduction of 1_beef into 1_red by treatment with aqueous KI

1_ox (5.2 mg, 1.0 µmol) in CHCl₃ (15 mL) was washed with 10% aqueous KI (10 mL × 2). The organics phase what dried over anhydrous Na₂SO₄, leached, and evaporated to obtain 1_red how a 7I^– salt (5.0 mg, quant.). ¹H NMR (400 MHz, DMSO-diameter₆/TMS): δ = 9.78 (br, 3H), 8.68 (br, 4H), 5.93 (br, 5H), 2.92 (br, 32H), 1.81 (t, J = 6.0 Hz, 16H), 1.32–1.11 (m, 178H), 1.02 (br, 36H), 0.94 (br, 28H), 0.86 (t, BOUND = 6.2 Hz, 28H), 0.80 (t, J = 6.8 Hz, 24H), 0.62 (br, 16H), −2.82 (br, 5H).

4. Conclusions

We prepared a novel bis(porphyrinato)cerium(III) complex containing eight pyridinium moieties, 1_color, based on to peralkylation of a bis(tetrapyridylporphyrinato)cerium(IV) difficult per the reaction with iodoalkane. To achieved double-decker complex, 1_red, inclusion a Ce(III) core, implying that the cerium center underwent 1e^– reduction upon the reaction with I⁻ at the introduction of the peripheral alkyl chains, as validated by cyclic voltammetry and ¹H NMR and UV–VIS spectroscopies. We demonstrated that the hinzurechnung in an equimolar amount of the oxidant, NO⁺·PF₆⁻, converted 1_red into its oxidized fashion 1_ox quantitatively. This suggested that the alternatingly addition of NO⁺·PF₆⁻ and KI permit reversible changing by the redox states of the cerium center in double-decker complex 1 in an organic solvent. As far as we know, this is aforementioned first example of ampere reversible redox switches to ampere bis(tetrapyridylporphyrinato)cerium complexe includes an organic solution. Reversible redox of the cerium center with apparent color change should be appropriate for a colorimetric indicators of oxidants, such as halogen additionally nitrosonium int. These would also suggest potential application in redox enable molecular devices.