Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2023 Feb 7;8(7):6391–6401. doi: 10.1021/acsomega.2c06638

Facile Synthesis of β-Tetracyano Vanadyl Porphyrin from Its Tetrabromo Analogue and Its Excellent Catalytic Activity for Bromination and Epoxidation Reactions

Mannar R Maurya 1,*, Ved Prakash 1, Tawseef Ahmad Dar 1, Muniappan Sankar 1,*
PMCID: PMC9948182  PMID: 36844578

Abstract

graphic file with name ao2c06638_0020.jpg

Complex 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[VIVOTPP(CN)4], 2} has been prepared by nucleophilic substitution of β-bromo groups of the corresponding 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[VIVOTPP(Br)4], 1} using CuCN in quinoline. Both complexes show biomimetic catalytic activity similar to enzyme haloperoxidases and efficiently brominate various phenol derivatives in the presence of KBr, H2O2, and HClO4 in the aqueous medium. Between these two complexes, 2 exhibits excellent catalytic activity with high turnover frequency (35.5–43.3 s–1) due to the strong electron-withdrawing nature of the cyano groups attached at β-positions and its moderate nonplanar structure as compared to 1 (TOF = 22.1–27.4 s–1). Notably, this is the highest turnover frequency value observed for any porphyrin system. The selective epoxidation of various terminal alkenes using complex 2 has also been carried out, and the results are good, specifying the importance of electron-withdrawing cyano groups. Catalysts 1 and 2 are recyclable, and the catalytic activity proceeds through the corresponding [VVO(OH)TPP(Br)4] and [VVO(OH)TPP(CN)4] intermediates, respectively.

Introduction

Vanadium-dependent haloperoxidase (V-HPO) enzymes are known to play a key role in the oxidation of X– (X– = halide ions) in the presence of hydrogen peroxide.1 During the oxidation of X–, also observed in the functional model as well as in kinetics studies, the in situ generated oxido(peroxido)vanadium(V) species allows nucleophilic attack of the halide ion, followed by the release of HOX/X2, which actually halogenate the substrates (Scheme 1).2−7

Scheme 1. Functional Model Considering the Oxidovanadium(IV) or Dioxidovanadium(V) Complex for the Generation of HOX and Subsequent Non-Catalytic Bromination.

Scheme 1

Open in a new tab

Since oxidative halogenation occurs in the acidic medium, homogeneous functional models generally decompose at lower pH. Even metal complexes of unsubstituted porphyrins generally tend to undergo degradation8 in oxidation- and oxidative bromination-type reactions, while complexes with β- and meso-functionalized porphyrins not only make them stable9 toward degradation but also tune them to attain good thermal and chemical stabilities.10,11 The high stability and recyclability of β- and meso-functionalized vanadyl porphyrins even at low pH (ca. 1.5)12 are therefore suitable for developing new haloperoxidase mimetic catalysts. Furthermore, a highly electron-deficient porphyrin coordinated to the vanadyl center shows an excellent catalytic reaction due to an increase in the Lewis acidic nature of the complex.12 Based on the biomimetic haloperoxidase reaction, recently, we developed a method for the self-catalyzed oxidative bromination of β-positions of the pyrrole ring of complex [VIVOTPP] in excellent yield under mild conditions without brominating the meso-phenyl rings.12 Furthermore, the brominated [VIVOTPP(Br)8] and [VIVOTPP] are highly active recyclable catalysts for the oxidative bromination of phenol derivatives.

Despite tremendous progress in synthetic organic chemistry over the past many years, bromination of phenol derivatives remains an area of focus owing to the use of its products in further reactions in industries as intermediates for fine chemicals and pharmaceuticals.13,14 Porphyrins act as multifaceted ligands coordinating with various metals to form metalloporphyrins with many catalytic applications.15−17 In living systems, porphyrins and their analogues perform many vital functions like oxygen transport and storage, photosynthesis, and electron transfer and as cofactors to many enzymes.18−20 Porphyrins have also been found to possess remarkable applications in the fields of solar energy,21 medicine,22 sensing,23 catalysis,24 and nonlinear optics.25

Furthermore, we observed that all bromo groups of the vanadium(IV) complex of tetrabrominated β-positions of the pyrrole, i.e., 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[VIVOTPP(Br)4], 1}, can easily be cyanated to obtain 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrinatooxidovanadium(IV) {[VIVOTPP(CN)4], 2} in a single step under suitable reaction conditions. Therefore, we present herein two alternate methods for the synthesis of [VIVOTPP(CN)4], 2: (i) a single-step direct cyanation of [VIVOTPP(Br)4], 1, using CuCN in quinoline, and (ii) reaction of VOSO4 with free-base H2TPP(CN)4; the isolation of the free base is a multi-step process (Scheme 2).26 The catalytic potential of both complexes (1 and 2) has been explored for the oxidative bromination of phenol derivatives. Complex 2 has also been utilized as a catalyst for selective epoxidation of olefins.

Scheme 2. Synthetic Route to Prepare Free-Base H2TPP(CN)4.

Scheme 2

Open in a new tab

Results and Discussion

Synthesis and Characterization of Complexes

Complex [VIVOTPP(Br)4] (1) can easily be prepared by reacting H2TPPBr4 with VOSO4·xH2O in refluxing DMF under an argon atmosphere.27−29 Synthesis of [VIVOTPP(CN)4] (2) has been achieved by the direct cyanation of [VIVOTPP(Br)4] (1) via nucleophilic substitution with CuCN in quinolone under an argon atmosphere (Scheme 3) in a single step. This method has earlier been applied by some of us for the synthesis of [CuIITPP(CN)4].30 Alternatively, the reaction of free-base H2TPP(CN)4 with VOSO4·xH2O in DMF under reflux conditions for 30 h also gives 2. However, isolation of free-base H2TPP(CN)4 itself is a tedious three-step process, as shown in Scheme 2. Moreover, the overall yield of 2 is about 23% compared to 29% from the first method. Therefore, the first method is much better and time saving.

Scheme 3. Synthetic Routes for 2 and Molecular Structure of Synthesized Oxidovanadium(IV) Complexes 1 and 2.

Scheme 3

Open in a new tab

UV–vis and IR Spectral Studies

The UV–vis spectrum of 1 in CH2Cl2 exhibits a single Soret band at 435 nm, which is almost similar to that of H2TPPBr4 (436 nm), and two Q bands (560 and 604 nm) compared to three in the case of H2TPPBr4 (533, 612, and 685 nm). Thus, the first Q band is 27 nm red-shifted while the second Q band is 8 nm blue-shifted relative to H2TPPBr4 upon metalation with the vanadium ion. Replacement of bromo groups at β-positions of the porphyrin ring by the cyano group of 1 caused the shifting of the Soret band to 442 nm in 2 (Figure 1), which is expected due to the more electron-withdrawing nature of the −CN group as compared to −Br. Similarly, the two Q bands also shifted to higher wavelengths by 17 and 21 nm, respectively, and appeared at 577 and 625 nm. Furthermore, the peak at 625 nm is relatively more intense in the case of 2 compared to the corresponding Q band of 1. Two weak shoulder peaks arose at ca. 425 and 530 nm in 2, which is possibly due to the charge transfer from the porphyrin ring to the −CN group (highly electron-withdrawing group). In the IR spectrum, characteristic peaks due to the ν(V=O) and ν(C–Br) stretches were located at 1010 and 619 cm–1 (Figure S1), respectively. The cyano groups present on the β-positions of the porphyrin ring caused the appearance of ν(V=O) at 1015 cm–1 in 2, which is 5 cm–1 higher than that found in 1. The absence of ν(C–Br) and the presence of the ν(C≡N) stretch at 2230 cm–1 (Figure S2) again validated the replacement of all bromo groups by CN.

Figure 1.

Figure 1

Open in a new tab

UV–vis spectra of [VIVOTPP(Br)4] (1) and [VIVOTPP(CN)4] (2) in CH2Cl2 at 298 K.

Mass Spectrometry and Thermogravimetric Study

The found and calculated MALDI-TOF mass values for both complexes [1, m/z: found 995.99 [M]+ (calcd. 995.24) and 2, m/z: found 779.53 [M]+ (calcd. 779.15)] (Figures S3 and S4) are in good agreement and support the formation of expected complexes. As thermal stability has been considered one of the important parameters in terms of the catalytic suitability of complexes, the thermogravimetric profiles of these complexes were obtained. Both complexes are thermally stable (decomposition temperature: 230 °C for 1 and 275 °C for 2), and within these two, 2 is more stable than 1 (Figures S5 and S6), which may be attributed to the higher strength of C–C bonds (346 kJ/mol) and C≡N bonds (887 kJ/mol) relative to C–Br bonds (285 kJ/mol). Increasing the temperature further, both complexes decomposed exothermically in two overlapping steps. Complex 1 finally stabilized at 530 °C with a residue of 9.1%, while 2 stabilized at 430 °C with a residue of 10.5%. These values are close to the theoretical values of 9.04 and 11.68%, respectively, for V2O5.

Electrochemical Study

The electrochemical study of [VIVOTPP] has been well explored in non-aqueous medium.31 To understand the electrochemistry of synthesized complexes, we recorded a cyclic voltammogram of these compounds in distilled CH2Cl2 at 298 K using Ag/AgCl as the reference electrode and TBAPF6 as the supporting electrolyte. The cyclic voltammogram of 1 exhibited two oxidation peaks at 1.27 and 1.45 V, while 2 displayed the corresponding oxidation peaks at 1.46 and 1.84 V, respectively. Similarly, two reduction peaks were obtained at −0.84 and −1.07 V in 1 and at −0.22 and −0.64 V in 2 (Figure 2). Table 1 provides all parameters. The first and second oxidation potentials in the case of 2 are 0.19 and 0.39 V, anodically shifted compared to 1, whereas the first and second reduction potentials of 2 are 0.62 and 0.43 V, anodically shifted compared to 1. Therefore, cyclic voltammetry supports the more electron-deficient nature of 2 compare to 1.31,32

Figure 2.

Figure 2

Open in a new tab

Above: cyclic voltammograms of 1 and 2 in triple-distilled CH2Cl2 at 298 K using Ag/AgCl as the reference electrode and 0.1 M TBAPF6 as the supporting electrolyte. Below: redox reactions of complexes 1 and 2.

Table 1. Electrochemical Redox Dataa of 1 and 2 in CH2Cl2.

  oxidation(V)
 reduction(V)
  
porphyrina II I I II ΔE (V)b
[VIVOTPP(Br)4], 1 1.45 1.27 –0.84 –1.07 2.11
[VIVOTPP(CN)4], 2 1.84 1.46 –0.22 –0.64 1.68
Open in a new tab
a

vs. the Ag/AgCl reference electrode and the Pt working and Pt wire auxiliary electrodes. 0.1 M TBAPF6 as the supporting electrolyte at 298 K.

b

ΔE = Ioxidation – Ireduction.

DFT Optimization Study

A DFT optimization study using the B3LYP functional and the LANL2DZ basis set was carried out for 1 and 2 in the gas phase. The optimized geometries of 1 and 2 are compared in Figure 3. Both 1 and 2 exhibited nonplanar, saddle shape conformation, with 1 being relatively more distorted due to bulkier bromine atoms. In the case of 1, Δ24 was found to be ±0.3829 Å while a similar value in the case of 2 was found to be ±0.2302 Å only. ΔCβ (carbon atoms having −Br or −CN substituents were taken as β) values were calculated to be ±0.8545 Å and ±0.538 Å for 1 and 2, respectively. Similarly, ΔCβ′ (carbon atoms attached to −H atoms were taken as β′) values for 1 and 2 were calculated to be ±0.725 and ±0.418 Å, respectively. Likewise, the ΔM (M = metal) values in 1 and 2 were calculated to be 0.538 and 0.529 Å, respectively. Various bond distance values in 1 were calculated to be 1.593 Å (V=O), 1.379 Å (Cβ–Cβ), and 1.372 Å (Cβ′–Cβ′). The corresponding bond distances in 2 were found to be 1.591, 1.396, and 1.370 Å.

Figure 3.

Figure 3

Open in a new tab

B3LYP/LANL2DZ set-optimized geometries of 1 and 2 in the gaseous phase showing top and side views (where β-hydrogens and meso-phenyl substituents have been removed for clarity).

EPR Study

The X-band EPR spectra of [VIVOTPP(Br)4] (1) and [VIVOTPP(CN)4] (2) were recorded in toluene at 100 K (Figure 4). The spectra of both complexes exhibit similar eight lines, indicating the presence of vanadium metal (I = 7/2) at the porphyrin center in +4 oxidation state with one unpaired electron. The spin Hamiltonian parameters were obtained from the simulated EPR spectra of complexes 1 and 2, which are in close agreement with the corresponding experimentally observed spectrum. For complex 1, g∥ and g⊥ were found to be 1.9603 and 1.9825, respectively. The corresponding calculated values were 1.9603 and 1.9841, respectively. The A∥ and A⊥ values were found to be 159.6 × 10–4 and 56.0× 10–4 cm–1, respectively, while the calculated values were 159.2 × 10–4 and 56.6 × 10–4 cm–1, respectively. Similarly, for 2, g∥ and g⊥ were found to be 1.9605 and 1.983 (calc.: 1.9605 and 1.9879), respectively, while A∥ and A⊥ values were found to be 160.2 × 10–4 and 57.2 × 10–4 cm–1 (calc.: 160.6 × 10–4, 57.3 × 10–4 cm–1), respectively. The g|| < g⊥ and A|| ≫ A⊥ relationships are normal for the axially compressed d1xy configuration;33,34 thus, complexes 1 and 2 are both axially compressed. Furthermore, we cannot observe any super hyperfine splitting from pyrrolic-N since the unpaired electron resides on a σ-non-bonding orbital pointing away from these N atoms, which are present in the equatorial (xy) plane.34

Figure 4.

Figure 4

Open in a new tab

X-band EPR spectra of [VIVOTPP(Br)4] (1) and [VIVOTPP(CN)4] (2) in toluene at 100 K (blue) and their corresponding simulated spectra (red). EPR parameter: microwave frequency, 9.388 GHz; incident microwave power, 0.717 mW.

Catalytic Activity—Oxidative Bromination of Phenol Derivatives

Oxidative bromination of various phenol derivatives was carried out considering complex 2 as a representative. Since the hydroxyl group at the phenyl ring is o- and p-directing, the bromination occurs on one or both of these positions depending on the situation. Considering 4-methylphenol as a representative, the following parameters were varied to optimize the reaction conditions for 10 mmol (1.08 g) of 4-methylphenol: (i) three different amounts of catalyst 2 (0.00020, 0.00040, and 0.00060 g), (ii) three different amounts of KBr (10, 20, and 30 mmol), (iii) three different amounts of oxidant 30% aqueous H2O2 (10, 20, and 30 mmol), and (iv) three different amounts of 70% aqueous HClO4 (10, 20, and 30 mmol). Furthermore, reaction was carried out in water (20 mL) at room temperature. Table 2 presents the details of conversion under each specified condition. Mainly one product, i.e., 2-bromo-4-methylphenol, was formed at the optimized reaction conditions. However, the 100% conversion led to the formation of additional derivative di-bromo-4-methylphenol along with the initial product when the reaction time was extended. These products were confirmed by GC–MS (Figures S7 and S8).

Table 2. Oxidative Bromination of 4-Methylphenol (1.08 g, 10 mmol) Using [VIVOTPP(CN)4] (2) as the Catalyst under Different Reaction Conditions.

              % selectivity
entry catalyst (mg, μmol) KBr (g, mmol) H2O2 (g, mmol) HClO4 (g, mmol) time (min) % conversion mono-bromo di-bromo
1 0.20, 0.256 1.19, 10 1.13, 10 1.43, 10 120 70 100  
2 0.40, 0.513 1.19, 10 1.13, 10 1.43, 10 120 68 100  
3 0.60, 0.769 1.19, 10 1.13, 10 1.43, 10 120 62 100  
4 0.20, 0.256 1.19, 10 1.70, 15 1.43, 10 120 92 100  
5 0.20, 0.256 1.19, 10 2.27, 20 1.43, 10 120 95 100  
6 0.20, 0.256 1.78, 15 2.27, 20 1.43, 10 60 90 100  
7 0.20, 0.256 2.38, 20 2.27, 20 1.43, 10 60 99 100  
9 0.20, 0.256 1.78, 15 1.70, 15 1.43, 10 60 93 100  
10 0.20, 0.256 2.38, 20 1.70, 15 1.43, 10 60 87 100  
11 0.20, 0.256 1.78, 15 1.70, 15 2.13, 15 60 93 100  
12 0.20, 0.256 1.78, 15 2.27, 20 2.13, 15 60 99 100  
13 0.20, 0.256 2.38, 20 2.27, 20 2.13, 15 30 97 100  
14 0.20, 0.256 1.78, 15 2.27, 20 2.86, 20 30 99 100  
15 0.20, 0.256 2.38, 20 2.27, 20 2.86, 20 15 98 100  
16 0.20, 0.256 2.38, 20 2.27, 20 2.86, 20 20 100 98 2
17 0.20, 0.256 2.38, 20 2.27, 20 2.86, 20 30 100 85 15
Open in a new tab

The best-suited conditions for the maximum conversion of 10 mmol of 4-methylphenol (1.08 g) were found to be as follows: catalyst 2 (0.00020 g, 0.256 μmol), KBr (2.38 g, 20 mmol), 30% aqueous H2O2 (2.267 g, 20 mmol), 70% aqueous HClO4 (2.87 g, 20 mmol, added in two equal portions of 1.43 g, each at interval of 5 min), and water (20 mL) (entry 15, Table 2). Notably, conversion reached 98% under these reaction conditions within 15 min with a TOF value of 42.5 s–1, which is found to be very high as compared to any known vanadyl complex till date (Table S1).16,27 There is no indication of the self bromination of 2 within this short period. This was further confirmed by the UV–visible spectrum (Figure 1) and MALDI-TOF mass spectrum (discussed in later sections) of the recovered complex after the catalytic reaction.

Oxidative bromination of other phenol derivatives (phenol, 4-tert-butylphenol, 2,4-dimethyl-phenol, 2,6-dimethylphenol, 2,4-di-tert-butylphenol, 2-tert-butyl-4-methyl-phenol, 4-bromophenol, 2,4-dichlorophenol, 4-methoxyphenol) (Table 3) was also carried out under similar reaction conditions as optimized for 4-methylphenol. Percentage conversion in most cases reaches above 95% except for 2,6-dimethylphenol (82%) and 2,4-dichlorophenol (85%). Generally, the monobromo product is obtained selectively, except in phenol and 4-methoxyphenol where the selectivities of the monobromo product are 55 and 76%, respectively. It was found that electron-donating groups enhance the reactivity of phenol, thereby resulting in relatively higher yields and high turnover frequency (TOF) for electron-rich phenols.

Table 3. Oxidative Bromination of Different Phenol Derivatives Using [VIVOTPP(CN)4] (2) as the Catalyst.

graphic file with name ao2c06638_0016.jpg

entry substrate time (min) conv. (%) TOF (s–1) products selectivity (%)
1. phenol 15 97 42.0 4-bromophenol 55
          2-bromophenol 45
2. 4-methylphenol 15 98 42.5 2-bromo-4-methylphenol 100
3. 2-iso-propyl-5-methylphenol 15 95 41.2 2-bromo-3-methyl-6-iso-propylphenol 11
  4-bromo-3-methyl-6-iso-propylphenol 43
  2,4-dibromo-3-methyl-6-iso-propylphenol 46
4. 4-tert-butylphenol 15 99 42.9 2-bromo-4-tert-butylphenol 100
5. 2,4-dimethylphenol 15 100 43.3 2-bromo-4,6-di-methylphenol 100
6. 2,6-dimethylphenol 15 82 35.5 2,6-di-methyl-4-bromophenol 100
7. 2,4-di-tert-butylphenol 15 96 41.6 2,4-di-tert-butyl-6-bromophenol 100
8. 2-tert-butyl-4-methylphenol 15 95 41.2 2-bromo-4-methyl-6-tert-butylphenol 100
9. 4-bromophenol 15 96 41.6 2,4,-di-bromophenol 100
10. 2,4-dichlorophenol 15 85 36.8 2-bromo-4,6-di-chlorophenol 100
11. 4-methoxyphenol 15 100 43.3 2-bromo-4-methoxyphenol 76
          2,6-dibromo-4-methoxyphenol 24
Open in a new tab

Compared to 2, complex 1 shows a bit lower conversion, but the selectivity trend of monobromo derivatives is the same (Table 4) as observed for 2. The better performance of complex 2 compared to 1 is possibly due to better electron-withdrawing cyano groups and moderate nonplanarity.35−39 Compared to the previously reported non-substituted vanadyl porphyrin [VIVOTPP] (TOF = 10.6–15.1 s–1),12 the catalytic activity of 1 (TOF = 22.1–27.4 s–1) is found to be much better while that of 2 (TOF = 35.5–43.3 s–1) is excellent.

Table 4. Oxidative Bromination of Different Phenol Derivatives Using [VOTPP(Br)4] (1) as the Catalyst.

graphic file with name ao2c06638_0017.jpg

entry substrate time (min) conversion (%) TOF (s–1) products selectivity (%)
1. phenol 15 94 26.0 4-bromophenol 58
          2-bromophenol 42
2. 4-methylphenol 15 95 26.3 2-bromo-4-methylphenol 100
3. 2-iso-propyl-5-methylphenol 15 93 25.7 2-bromo-3-methyl-6-iso-propylphenol 8
  4-bromo-3-methyl-6-iso-propylphenol 48
  2,4-dibromo-3-methyl-6-iso-propylphenol 44
4. 4-tert-butylphenol 15 97 26.8 2-bromo-4-tert-butylphenol 100
5. 2,4-dimethylphenol 15 99 27.4 2-bromo-4,6-di-methylphenol 100
6. 2,6-dimethylphenol 15 80 22.1 2,6-di-methyl-4-bromophenol 100
7. 2,4-di-tert-butylphenol 15 95 26.3 2,4-di-tert-butyl-6-bromophenol 100
8. 2-tert-butyl-4-methylphenol 15 94 26.0 2-bromo-4-methyl-6-tert-butylphenol 100
9. 4-bromophenol 15 93 25.7 2,4,-di-bromophenol 100
10. 2,4-dichlorophenol 15 82 22.7 2-bromo-4,6-di-chlorophenol 100
11. 4-methoxyphenol 15 99 27.4 2-bromo-4-methoxyphenol 80
          2,6-dibromo-4-methoxyphenol 20
Open in a new tab

To understand the conversion of a monobromo product to a dibromo analogue by extending time, we analyzed the product selectivity with an extended time period in the case of 4-methylphenol for both catalysts. It was observed that the % selectivity of 2,6-dibromo-4-methylphenol increases with the elapse of time and, after ca. 28 h, only 2,6-dibromo-4-methylphenol was observed in the reaction mixture (Figure 5). This is due to further bromination of the mono brominated product. This observation invigorated us to extend this study to another mono-substituted phenol (i.e., 4-methoxyphenol) where the possibility of further electrophilic (Br+) substitution exists and the same trend is found (Figure S9). In the case of phenol, the initially formed 2-bromophenol as well as 4-bromophenol both converted to 2,4-dibromophenol (Figure S10).

Figure 5.

Figure 5

Open in a new tab

Time courses of the product selectivity change of the brominated product of 4-methylphenol using (a) catalyst 1 and (b) catalyst 2.

Reactivity of Complexes 1 and 2 with Brominating Reagents in the Absence of a Brominating Substrate

As observed earlier during the oxidative bromination, complex [VIVOTTP] used as the catalyst underwent self-bromination in the absence of a substrate and gave β-octabrominated complex [VIVOTTP(Br)8].12 Under similar optimized reaction conditions, i.e., when a mixture of 2.5 mmol of KBr, 2.5 mmol of H2O2, and 1.0 mmol of HClO4 in 3 mL of water was used and a solution of 0.05 mmol of complex 1 in 2 mL of dichloromethane was added, the stirring of reaction for 36 h at room temperature also gave complex [VIVOTTP(Br)8] (Scheme 4), which was confirmed by UV–vis spectroscopy [UV–vis (CHCl3) λmax (nm): 362, 464, 590, 628] (Figure 6) as well as MALDI-TOF mass spectrometry [m/z: found 1310.04 [M]+ (calcd. 1310.44) (Figure S11). Interestingly, complex 2 showed no observable change in the UV–vis spectrum under similar reaction conditions, indicating no bromination at the unsubstituted β-position. This is possibly due to the strong electron-withdrawing nature of tetracyano substituents that oppose the electrophilic (Br+) substitution at the β-position.

Scheme 4. Self-Catalytic Oxidative Bromination Behavior of Complex 1 to Give Octabromo Derivative [VIVOTTP(Br)8].

Scheme 4

Open in a new tab

Figure 6.

Figure 6

Open in a new tab

UV–vis spectral change during the self-catalytic reaction of catalyst 1.

Catalytic Activity—Epoxidation of Olefins

As epoxidation of olefins was already reported for catalyst 1,29 the catalytic potential of 2 was also established here for the epoxidation of various olefins. We have chosen styrene as a representative alkene, and the following parameters were varied to optimize the reaction conditions: for 5 mmol (0.52 g) of styrene: (i) three different amounts of the catalyst (0.0005, 0.001, and 0.0015 g), (ii) three different amounts of the oxidant 30% aqueous H2O2 (10, 15, and 20 mmol), (iii) three different amounts of NaHCO3 (promoter) (1.5, 2.0, and 2.5 mmol) at various compositions of solvents (MeCN/H2O) (5:0, 3:1, 2:1, 3:2, and 4:3). Furthermore, the reaction was carried out at two temperatures (i.e., 50 and 60 °C). Table 5 presents the details of conversion under each specified condition (optimization parameters). The best-suited reaction conditions were concluded to be as follows (entry 8, Table 5): styrene 0.52 g, 5 mmol; catalyst 2 0.0005 g, 0.641 μmol; oxidant H2O2 2.26 g, 20 mmol; promotor NaHCO3 0.168 g, 2.0 mmol, in a 3:2 MeCN:H2O mixture (v/v) at 60 °C. Under these conditions, a maximum of 92% conversion of styrene to styrene epoxide selectively was achieved within 1 h of reaction time.

Table 5. Oxidation of Styrene (0.52 g, 5 mmol) Using [VIVOTPP(CN)4] (2) as the Catalyst in 1 h Reaction Time under Different Reaction Conditions.

entry catalyst (mg, μmol) H2O2 (g, mmol) NaHCO3 (g, mmol) MeCN/H2O temp. (°C) % conversion selectivity
1. 0.5, 0.641 1.13, 10 0.168, 2 3:2 60 80 100
2. 1.0, 1.28 1.13, 10 0.168, 2 3:2 60 83 100
3. 1.5, 1.92 1.13, 10 0.168, 2 3:2 60 69 100
4. 0.5, 0.641 1.70, 15 0.168, 2 3:2 60 88 100
5. 0.5, 0.641 2.26, 15 0.126, 1.5 3:2 60 67 100
6. 0.5, 0.641 2.26, 20 0.126, 1.5 3:2 60 78 100
7. 0.5, 0.641 2.26, 20 0.210, 2.5 3:2 60 61 100
8. 0.5, 0.641 2.26, 20 0.168, 2 3:2 60 92 100
9. 0.5, 0.641 2.26, 20 0.168, 2 2:1 60 76 100
10. 0.5, 0.641 2.26, 20 0.168, 2 4:3 60 53 100
11. 0.5, 0.641 2.26, 20 0.168, 2 3:1 60 65 100
12. 0.5, 0.641 2.26, 20 0.168, 2 5:0 60 49 100
13. 0.5, 0.641 2.26, 20 0.168, 2 3:2 50 75 100
14.   2.26, 20 0.168, 2 3:2 60 40 100
15.   2.26, 20   3:2 60 15 100
16. 0.5, 0.641 2.26, 20   3:2 60 39 100
Open in a new tab

Under the above optimized reaction conditions, epoxidation of other alkenes was also tested (Table 6) and corresponding epoxides were obtained selectively with good conversion. Controlled experiments (i.e., in the absence of catalyst and/or promoter NaHCO3) were also performed, and the results demonstrate that the oxidant is essential to achieving good catalytic conversion while the promoter is essential to achieving selectivity toward the formation of epoxide. It is observed that, in the absence of catalyst 2, conversion is only 40% under the optimized reaction conditions, while in the absence of NaHCO3 (promoter), conversion was found to be 39% under the same conditions. In the absence of both catalyst 2 and NaHCO3 (promoter), the conversion was limited only to 15%.

Table 6. Oxidation of Various Olefins Using Catalysts 2 under Optimized Reaction Conditions with 100% Selectivity for the Epoxide Formation.

graphic file with name ao2c06638_0018.jpg

graphic file with name ao2c06638_0019.jpg

Open in a new tab

Recyclability of Catalysts during Oxidative Bromination and Epoxidation

Catalysts 1 and 2 were recovered after the first cycle of bromination reaction using column chromatography, as detailed in the Experimental Section. The efficiency of both recovered catalysts was examined again for the oxidative bromination of 4-methylphenol under conditions similar to those used for the first cycle. Recycled 1 exhibited 94% conversion of 4-methylphenol with a TOF of 26.0 s–1, while recycled 2 exhibited a conversion of 96% and a TOF of 41.6 s–1. The minor loss in catalytic efficiency can be explained by the fact that the recovery process of a very small amount of catalyst, especially in homogeneous catalysis, is not 100% efficient and inevitably leads to a small loss of the catalyst. Catalyst recyclability was repeated four times, and only a small decrease in conversion was noticed. Even in the fourth cycle, catalysts 1 and 2 showed 85 and 86% conversion, respectively (Figure 7).

Figure 7.

Figure 7

Open in a new tab

Bar diagram showing catalytic recyclability along with % conversion at every cycle of catalytic reaction (bromination of 4-methylphenol) using 1 (green) and 2 (gray).

The recyclability of catalysts 2 was also tested four times for the epoxidation of styrene under similar optimized reaction conditions as fixed for epoxidation, and again, only a minor decrease in efficiency (Figure 8) was noted.

Figure 8.

Figure 8

Open in a new tab

Bar diagram showing catalytic recyclability along with % conversion at every cycle of catalytic reaction (epoxidation of styrene) using 2.

Recovery of Catalysts after Catalytic Reaction and Their Characterization

The UV–vis spectra of the recovered catalysts slightly differ (Figure 9) from the respective fresh catalyst. The MALDI-TOF mass spectra of these recovered catalysts show the formation of a stable intermediate [VVO(OH)TPP(Br)4] (1a) [(m/z) found: 1011.247, [M]− calc: 1011.81)] and [VVO(OH)TPP(CN)4] (2a) [(m/z): 795.167, [M–H]− calc: 795.15], i.e., oxido-hydroxidovanadium(V) analogues of complexes 1 and 2 (Figures S12 and S13). This observation further suggests that catalysts change their structures after catalytic oxidative bromination reaction.

Figure 9.

Figure 9

Open in a new tab

(a) UV–vis spectra of 1 before (blue) and after (red) catalytic reaction and (b) UV–vis spectra of 2 before (blue) and after (red) catalytic reaction.

Catalyst 2 after epoxidation of styrene was also recovered and purified through column chromatography, and its UV–vis spectrum and MALDI-TOF mass spectrum were recorded. While the mass spectrum matches well with the sample recovered after bromination reaction, the UV–vis spectrum showed one extra band at ca. 270 nm (Figure S14), which is possibly the presence of a trace amount of styrene epoxide as styrene epoxide exhibits a UV band at ca. 260 nm (Figure S15).

Reactivity of [VIVOTPP(CN)4] (2) in DMSO-d6—A 51V NMR Study and Possible Catalytic Mechanism

In order to understand the mechanistic pathway for the epoxidation of organic substrates, we performed a 51V NMR study of complex 2 under different conditions. The 51V NMR spectra of 2 were recorded as (i) fresh sample dissolved in DMSO-d6 (Figure 10a), (ii) after adding H2O2 and NaHCO3 to (a) (Figure 10b), (iii) sample (b) after heating for 1 h at 60 °C (Figure 10c), and (iv) after adding excess styrene to (c) (Figure 10d). Thus, as expected pure paramagnetic complex 2 dissolved in DMSO-d6 gave no peak in 51V NMR. However, upon addition of 0.44 mmol of 30% aqueous H2O2 and 0.37 mmol of NaHCO3, two NMR signals were observed at −621.4 and −636.4 ppm with an intensity ratio of 9.5:0.5. Based on the UV–vis and MALDI-TOF spectral studies of the recovered catalyst (see previous section), the former signal may be assigned due to the generation of [VVO(OH)TPP(CN)4] while the weak signal at −636.4 ppm might be due to oxidoperoxidovanadium(V) species.40,41 Heating the reaction mixture for 1 h at 60 °C, the minor signal at −636.4 ppm disappeared, possibly due to breaking of the peroxide species to a relatively better stable intermediate [VVO(OH)TPP(CN)4]. The signal at −621.4 ppm completely disappeared upon addition of excess of styrene to the above solution. The styrene containing the above solution was also subjected to MALDI-TOF mass spectrometry, and the resulting spectrum (Figure S16) shows the appearance of a new but weak signal due to original complex 2 along with the signal due to [VVO(OH)TPP(CN)4]. These two observations hint toward the further reaction of [VVO(OH)TPP(CN)4] with styrene and converting it back to the original complex to some extent. Thus, it is reasonable to propose that during styrene epoxidation, catalyst 2 passes through highly unstable intermediate oxidoperoxidovanadium(V) to a relatively better stable oxidohydroxidovanadium(V) intermediate. The oxidohydroxidovanadium(V) complex upon further reaction with H2O2 in the presence of NaHCO3 again forms the highly unstable oxidoperoxidovanadium(V) species,42 and the reaction continues.

Figure 10.

Figure 10

Open in a new tab

51V NMR spectra of [VIVOTPP(CN)4] (2) (6.4 μmol) in DMSO-d6 (a) in the presence of a fresh sample, (b) after adding 0.44 mmol of 30% aq. H2O2 and 0.37 mmol of NaHCO3 to (a), (c) after heating the solution in (b) for 1 h at 60 °C, and (d) after adding excess of styrene to (c) and heating at 60 °C for 10 min.

The oxidative bromination only partly follows the reaction mechanism generally followed by vanadium complexes (Scheme 1). Complex 2 reacts with H2O2 to give the corresponding oxidoperoxidovanadium(V) intermediate, which in the presence of H3O+ (i.e., aqueous HClO4) possibly changes to oxidohydroperoxidovanadium(V) porphyrin. Both species are possibly highly unstable, the latter of which catalyzes the oxidation of Br– to HOBr; a brominating reagent and a catalyst are converted to a better stable [VVO(OH)TPP(CN)4]. Like epoxidation, the reaction continues in the presence of H2O2 and HClO4.

Conclusions

A simplified method was developed to synthesize a highly electron-deficient β-tetracyano-meso-tetraphenylporphyrin vanadyl complex, [VIVOTPP(CN)4] (2) from β-tetrabromo-substituted vanadyl porphyrin [VIVOTPP(Br)4] (1) by nucleophilic substitution reaction. The catalytic potential of complexes 1 and 2 was tested for the oxidative bromination of phenol and its derivatives. Catalyst 2, being more electron deficient, was found as the best catalyst for the oxidative bromination reaction having a TOF value of 43.3 s–1, the highest TOF found for any catalyst till date. Although catalysts 1 and 2 are homogeneous catalysts, they are recyclable and their recyclability was checked up to four cycles. Catalyst 2 was also utilized for the selective epoxidation of olefins, and conversions were good to excellent. As evidenced by UV–vis, MALDI-TOF mass, and 51V NMR studies, both catalysts are recyclable and both catalytic reactions pass through the corresponding [VVO(OH)TPP(Br)4] or [VVO(OH)TPP(CN)4] intermediate.

Experimental Section

Materials

VOSO4, N-bromosuccinimide (HiMedia, India), CuCN (SD Fine Chemicals, India), various alkenes (Alfa Aesar, India), 30% aqueous H2O2, silica gel (100–200 mesh) (Rankem, India), and HPLC-grade DMF (SRL) were used as received. Tetrabutylammonium hexafluorophosphate (TBAPF6) (Merck) was recrystallized two times from hot ethanol before use. H2TPPBr4 was prepared from H2TPP using recrystallized N-bromosuccinimide.9 Dry CH2Cl2 used in cyclic voltammetry analysis was distilled twice after drying over phosphorus pentoxide (P2O5) and from calcium hydride (CaH2) for the third time.

Instrumentation

Elemental analysis was carried out using an Elementar vario EL II instrument. Mid-IR range IR spectra were recorded using a Perkin-Elmer spectrometer as KBr pellet. UV–vis spectra were recorded using an Agilent Cary 100 spectrophotometer. Cyclic voltammetric measurements were performed on a CHI 620E instrument, using a three-electrode assembly that consisted of Ag/AgCl as the reference electrode, Pt disk as the working electrode, and Pt wire as the counter electrode. All electrochemical measurements were carried out in triple-distilled CH2Cl2 using TBAF6 as the supporting electrolyte, Pt as the working electrode, Ag/AgCl as the reference electrode, and Pt wire as the counter electrode at 298 K. Using HABA as a matrix, MALDI-TOF spectra were recorded on a Bruker UltrafleXtreme-TN MALDI-TOF mass spectrometer. SII EXSTAR 6300 was used to obtain thermogravimetric analysis with a heating rate of 10 °C/min under a normal aerial atmosphere using aluminum powder as reference. EPR spectra were recorded in EMXmicro A200-9.5/12/S/W, BRUKER BIOSPIN, and simulated by WINEPR SimFonia. Reaction products obtained from the catalytic reaction were identified using a Shimadzu 2010 Plus gas chromatograph endowed with an Rtx-1 capillary column (30 m × 0.25 mm × 0.25 μm) and an FID detector. The product identities were confirmed using a Perkin-Elmer GC–MS (Clarus 500). The percent (%) conversion of the substrate and the selectivity of the products were calculated from the GC data using the formulae

graphic file with name ao2c06638_m001.jpg

Synthesis of [VIVOTPP(Br)4], 1

Complex 1 was synthesized by the method reported by us previously.29 Yield 85% (271 mg, 0.272 mmol). UV–vis (CH2Cl2): λmax (nm) (log ε): 335 (3.98), 435 (5.28), 560 (4.00), 604 (3.80). MALDI-TOF-MS (m/z): found 995.99 [M]+, calcd. 995.24. Anal. calcd. for C44H24Br4N4OV: C, 53.10; H, 2.43; N, 5.63. Found C, 52.99; H, 2.46; N, 5.22.

Synthesis of [VIVOTPP(CN)4], 2

Method A

Complex 1 (100 mg, 0.1005 mmol) was dissolved in 15 mL of quinoline, and CuCN (900 mg, 10.05 mmol, ca. 100 equiv.) was added. The reaction mixture was stirred for 10 min and then heated with stirring at 190 °C for 3 h under an argon atmosphere. The reaction mixture was cooled to ambient temperature and filtered using a G-4 crucible. The filtrate was diluted with chloroform (30 mL) and washed with 10 M HCl solution (3 × 25 mL) followed by water (3 × 25 mL). After drying the chloroform layer with sodium sulfate, the solvent was removed by a rotary evaporator. The crude product was dissolved in chloroform and purified over silica (100–200 mesh) using chloroform as the eluent. The last and major band of three fractions was collected and identified as 2. Complex 2 was obtained in pure form by rotatory evaporation of the solvent. Yield 32% (25 mg, 0.0321 mmol). UV–vis (CH2Cl2): λmax (nm) (log ε): 443 (5.31), 578 (3.81), 625 (4.67). MALDI-TOF-MS (m/z): found 779.53 [M]+, calcd. 779.15. Anal. calcd. for C48H24N8OV: C, 73.94; H, 3.10; N, 14.37. Found: C, 73.75; H, 3.01; N, 14.22.

Method B

Alternatively, 2 was also prepared as follows: ligand 2,3,12,13-tetracyano-5,10,15,20-tetraphenylporphyrin (300 mg, 0.420 mmol) was dissolved in DMF (75 mL). A large excess of VOSO4 hydrate (1027.5 mg, 6.3 mmol) was added to it, and the mixture was stirred for 10 min and then refluxed for 30 h under an argon atmosphere. The reaction mixture was cooled to room temperature and distilled water (150 mL) was added, and the product mixture was allowed to settle as precipitate. It was then filtered using the G-4 crucible and dried under vacuum for 8 h. The crude product was re-dissolved in CHCl3 and purified over silica (100–200) mesh using chloroform as the eluent. Compound 2 was obtained in pure form by rota-evaporating the eluent in 55% yield (212 mg, 0.273 mmol). UV–vis (CH2Cl2): λmax (nm) (log ε): 437 (5.31), 635 (4.67). MALDI-TOF-MS (m/z): found 779.53 [M]+, calcd 779.15. Anal. calcd. for C48H24N8OV: C, 73.94; H, 3.10; N, 14.37. Found: C, 73.79; H, 2.96; N, 14.20.

Catalytic Activity—Oxidative Bromination of Phenol Derivatives

In a typical reaction, 4-methylphenol, a representative (1.08 g, 10 mmol), KBr (2.38 g, 20 mmol), 30% aqueous H2O2 (2.26 g, 20 mmol), and water (20 mL) were taken in a 50 mL reaction flask. Complex 2 (0.00020 g, 0.262 μmol) and HClO4 (1.43 g, 10 mmol) were added, and the mixture was stirred at room temperature. An additional 10 mmol of HClO4 was added after 5 min. After 15 min, the reaction mixture was extracted with hexane and the hexane layer was injected (ca. 0.25 μL) into the gas chromatograph. The products were finally analyzed by GC–MS and identified by the electronic library available. Similar reactions were performed using 0.402 μmol of catalyst 1.

Recovery and Reuse of Catalysts

After completing the first cycle of the catalytic reaction as mentioned above in five different batches for both substrates (i.e., styrene and phenol), CHCl3 was added to each reaction mixture and washed with distilled water (3 × 10 mL) and organic layer separated. Both catalysts were recovered by silica column chromatography using CHCl3:hexane (3:7, v/v) for 1 and CHCl3 for 2 as eluent. Their identities were confirmed by UV–vis and MALDI-TOF mass spectrometry (Figures S12 and S13). The recovered catalysts were used for the next cycle of catalytic reaction.

Acknowledgments

M.R.M. and M.S. thank the Science and Engineering Research Board (SERB), New Delhi, India, for the financial support (Grant No. CRG/2018/000182 to M.R.M. and SERB/CRG/2020/005958 to M.S.). M.S. thanks the Council of Scientific and Industrial Research, New Delhi, for the financial support (CSIR/01(3058)/21/EMR-II). V.P. thanks University Grants Commission (UGC), New Delhi, India, for the fellowship.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.2c06638.

  • Characterization data, NMR spectra, MALDI-TOF mass spectra, TGA, catalytic information, TOF (h–1) values for oxidative bromination of thymol/terpenes with different catalysts known in the literature (PDF)

The authors declare no competing financial interest.

Supplementary Material

ao2c06638_si_001.pdf (828.6KB, pdf)

References

  1. Leblanc C.; Vilter H.; Fournier J. B.; Delage L.; Potin P.; Rebuffet E.; Michel G.; Solari P. L.; Feiters M. C.; Czjzek M. Vanadium haloperoxidases: From the discovery 30 years ago to X-ray crystallographic and V K-edge absorption spectroscopic studies. Coord. Chem. Rev. 2015, 301-302, 134–146. 10.1016/j.ccr.2015.02.013. [DOI] [Google Scholar]
  2. a) Butler A.; Baldwin A. H. Vanadium bromoperoxidase and functional mimics. Struct. Bonding 1997, 89, 109–132. 10.1007/3-540-62874-6_10. [DOI] [Google Scholar]; b) Plass W.; Bangesh M.; Nica S.; Buchholz A. Model Studies of Vanadium-Dependent Haloperoxidation: Structural and Functional Lessons, Synthetic and Computational Models of Supramolecular Interactions and the Formation of Peroxo Species. ACS Symp. Ser. 2007, 974, 163–177. 10.1021/bk-2007-0974.ch013. [DOI] [Google Scholar]
  3. a) Clague M. J.; Keder N. L.; Butler A. Biomimics of vanadium bromoperoxidase: Vanadium(V)-Schiff base catalyzed oxidation of bromide by hydrogen peroxide. Inorg. Chem. 1993, 32, 4754. 10.1021/ic00074a017. [DOI] [Google Scholar]; b) Butler A. Mechanistic considerations of the vanadium haloperoxidases. Coord. Chem. Rev. 1999, 187, 17–35. 10.1016/S0010-8545(99)00033-8. [DOI] [Google Scholar]
  4. Nica S.; Pohlmann A.; Plass W. Vanadium(V) Oxoperoxo Complexes with Side Chain Substituted N-Salicylidenehydrazides: Modeling Supramolecular Interactions inVanadium Haloperoxidases. Eur. J. Inorg. Chem. 2005, 2032–2036. 10.1002/ejic.200401060. [DOI] [Google Scholar]
  5. Wischang D.; Hartung J.; Hahn T.; Ulber R.; Stumpf T.; Fecher-Trost C. Vanadate(v)-dependent bromoperoxidase immobilized on magnetic beads as reusable catalyst for oxidative bromination. Green Chem. 2011, 13, 102–108. 10.1039/C0GC00499E. [DOI] [Google Scholar]
  6. Maurya M. R. Probing the synthetic protocols and coordination chemistry of oxido-, dioxido-, oxidoperoxido-vanadium and related complexes of higher nuclearity. Coord. Chem. Rev. 2019, 383, 43–81. 10.1016/j.ccr.2018.12.010. [DOI] [Google Scholar]
  7. Tótaro R. M.; Williams P. A. M.; Apella M. C.; Blesa M. A.; Baran E. J. Bromination of phenol red mediated by vanadium (V) peroxo complexes at pH 6.5. J. Chem. Soc. Dalton Trans. 2000, 4403–4406. 10.1039/b005733i. [DOI] [Google Scholar]
  8. Chang C. K.; Kuo M. S. Reaction of Iron(III) Porphyrins and Iodosoxylene; The Active Oxene Complex of Cytochrome P-450. J. Am. Chem. Soc. 1979, 101, 3413–3415. 10.1021/ja00506a063. [DOI] [Google Scholar]
  9. Vicente M.; Smith K. Syntheses and Functionalizations of Porphyrin Macrocycles. Curr. Org. Synth. 2014, 11, 3–28. 10.2174/15701794113106660083. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Suslick K. S.; Bhyrappa P.; Chou J. H.; Kosal M. E.; Nakagaki S.; Smithenry D. W.; Wilson S. R. Microporous Porphyrin Solids. Acc. Chem. Res. 2005, 38, 283–291. 10.1021/ar040173j. [DOI] [PubMed] [Google Scholar]
  11. Suslick K. S.; Rakow N. A.; Kosal M. E.; Chou J. H. The materials chemistry of porphyrins and metalloporphyrins. J. Porphyrins Phthalocyanines 2000, 04, 407–413. . [DOI] [Google Scholar]
  12. Maurya M. R.; Prakash V.; Avecilla F.; Sankar M. Selective Bromination of β-Positions of Porphyrin by Self-Catalytic Behaviour of VOTPP: Facile Synthesis, Electrochemical Redox Properties and Catalytic Application. Eur. J. Inorg. Chem. 2021, 1685–1694. 10.1002/ejic.202100116. [DOI] [Google Scholar]
  13. Weissermel K.; Arpe H. J.; Industrial Organic Chemistry, VCH, 1997, 10.1002/9783527616688. [DOI] [Google Scholar]
  14. Rao A. S.; Paknikar S. K.; Kirtane J. G. Recent advances in the preparation and synthetic applications of oxiranes. Tetrahedron 1983, 39, 2323–2367. 10.1016/S0040-4020(01)91961-1. [DOI] [Google Scholar]
  15. Yamazaki S. Metalloporphyrins and related metallomacrocycles as electrocatalysts for use in polymer electrolyte fuel cells and water electrolyzers. Coord. Chem. Rev. 2018, 373, 148–166. 10.1016/j.ccr.2017.09.016. [DOI] [Google Scholar]
  16. Dar T. A.; Uprety B.; Sankar M.; Maurya M. R. Robust and electron deficient oxidovanadium(IV) porphyrin catalysts for selective epoxidation and oxidative bromination reactions in aqueous media. Green Chem. 2019, 21, 1757–1768. 10.1039/C8GC03909G. [DOI] [Google Scholar]
  17. Han Y.; Fang H.; Jing H.; Sun H.; Lei H.; Lai W.; Cao R. Singly versus Doubly Reduced Nickel Porphyrins for Proton Reduction: Experimental and Theoretical Evidence for a Homolytic Hydrogen-Evolution Reaction. Angew. Chem., Int. Ed. 2016, 55, 5457–5462. 10.1002/anie.201510001. [DOI] [PMC free article] [PubMed] [Google Scholar]
  18. Hardison R. C. A brief history of hemoglobins: Plant, animal, protist, and bacteria. Proc. Natl. Acad. Sci. U. S. A. 1996, 93, 5675–5679. 10.1073/pnas.93.12.5675. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Mauzerall D.Porphyrins, Chlorophyll, and Photosynthesis. In Photosynthesis I; Springer Berlin Heidelberg: Berlin, Heidelberg, 1977, 117–124. [Google Scholar]
  20. Feierabend J.; Dehne S. Fate of the porphyrin cofactors during the light-dependent turnover of catalase and of the photosystem II reaction-center protein D1 in mature rye leaves. Planta 1996, 198, 413–422. 10.1007/BF00620058. [DOI] [Google Scholar]
  21. Birel Ö.; Nadeem S.; Duman H. Porphyrin-Based Dye-Sensitized Solar Cells (DSSCs): a Review. J. Fluoresc. 2017, 27, 1075–1085. 10.1007/s10895-017-2041-2. [DOI] [PubMed] [Google Scholar]
  22. Ethirajan M.; Chen Y.; Joshi P.; Pandey R. K. The role of porphyrin chemistry in tumor imaging and photodynamic therapy. Chem. Soc. Rev. 2011, 40, 340–362. 10.1039/B915149B. [DOI] [PubMed] [Google Scholar]
  23. Ding Y.; Zhu W.-H.; Xie Y. Development of Ion Chemosensors Based on Porphyrin Analogues. Chem. Rev. 2017, 117, 2203–2256. 10.1021/acs.chemrev.6b00021. [DOI] [PubMed] [Google Scholar]
  24. Barona-Castaño J.; Carmona-Vargas C.; Brocksom T.; de Oliveira K. Porphyrins as Catalysts in Scalable Organic Reactions. Molecules 2016, 21, 310–336. 10.3390/molecules21030310. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Senge M. O.; Fazekas M.; Notaras E. G. A.; Blau W. J.; Zawadzka M.; Locos O. B.; Ni Mhuircheartaigh E. M. Nonlinear optical properties of porphyrins. Adv. Mater. 2007, 19, 2737–2774. 10.1002/adma.200601850. [DOI] [Google Scholar]
  26. Bhyrappa P.; Sankar M.; Varghese B. Mixed Substituted Porphyrins: Structural and Electrochemical Redox Properties. Inorg. Chem. 2006, 45, 4136–4149. 10.1021/ic052035b. [DOI] [PubMed] [Google Scholar]
  27. Kumar R.; Chaudhary N.; Sankar M.; Maurya M. R. Electron deficient nonplanar β-octachlorovanadylporphyrin as a highly efficient and selective epoxidation catalyst for olefins. Dalton Trans. 2015, 44, 17720–17729. 10.1039/C5DT02349A. [DOI] [PubMed] [Google Scholar]
  28. Kumar P. K.; Bhyrappa P.; Varghese B. An improved protocol for the synthesis of antipodal β-tetrabromo-tetraphenylporphyrin and the crystal structure of its Zn(II) complex. Tetrahedron Lett. 2003, 44, 4849–4851. 10.1016/S0040-4039(03)01143-2. [DOI] [Google Scholar]
  29. Dar T. A.; Tomar R.; Mian R. M.; Sankar M.; Maurya M. R. Vanadyl β-tetrabromoporphyrin: synthesis, crystal structure and its use as an efficient and selective catalyst for olefin epoxidation in aqueous medium. RSC Adv. 2019, 9, 10405–10413. 10.1039/C8RA09825E. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Kumar R.; Saxena A.; Sankar M. Mixed β-bromo/cyano tetrasubstituted-meso-tetraphenylporphyrin Cu(II) complexes: Synthesis and electrochemical studies. J. Porphyrins Phthalocyanines 2016, 20, 1420–1425. 10.1142/S1088424616501169. [DOI] [Google Scholar]
  31. Kadish K. M.; Morrison M. M. Substituent effects on the redox reactions of tetraphenylporphyrins. Bioinorg. Chem. 1977, 7, 107–115. 10.1016/S0006-3061(00)80061-7. [DOI] [PubMed] [Google Scholar]
  32. Kadish K. M. The Electrochemistry of Metalloporphyrins in Nonaqueous Media. Prog. Inorg. Chem. 2007, 34, 435–605. 10.1002/9780470166352.ch5. [DOI] [Google Scholar]
  33. Ghosh S. K.; Patra R.; Rath S. P. Axial Ligand Coordination in Sterically Strained Vanadyl Porphyrins: Synthesis, Structure, and Properties. Inorg. Chem. 2008, 47, 9848–9856. 10.1021/ic800714w. [DOI] [PubMed] [Google Scholar]
  34. Smith T. S. II; LoBrutto R.; Pecoraro V. L. Paramagnetic spectroscopy of vanadyl complexes and its applications to biological systems. Coord. Chem. Rev. 2002, 228, 1–18. 10.1016/S0010-8545(01)00437-4. [DOI] [Google Scholar]
  35. Langeslay R. R.; Kaphan D. M.; Marshall C. L.; Stair P. C.; Sattelberger A. P.; Delferro M. Catalytic Applications of Vanadium: A Mechanistic Perspective. Chem. Rev. 2019, 119, 2128–2191. 10.1021/acs.chemrev.8b00245. [DOI] [PubMed] [Google Scholar]
  36. Sabuzi F.; Pomarico G.; Floris B.; Valentini F.; Galloni P.; Conte V. Sustainable bromination of organic compounds: A critical review. Coord. Chem. Rev. 2019, 385, 100–136. 10.1016/j.ccr.2019.01.013. [DOI] [Google Scholar]
  37. Pessoa J. C.; Correia I. Salan vs. salen metal complexes in catalysis and medicinal applications: Virtues and pitfalls. Coord. Chem. Rev. 2019, 388, 227–247. 10.1016/j.ccr.2019.02.035. [DOI] [Google Scholar]
  38. Galloni P.; Mancini M.; Floris B.; Conte V. A sustainable two-phase procedure for V-catalyzed toluene oxidative bromination with H2O2-KBr. Dalton Trans. 2013, 42, 11963–11970. 10.1039/c3dt50907a. [DOI] [PubMed] [Google Scholar]
  39. McLauchlan C. C.; Murakami H. A.; Wallace C. A.; Crans D. C. Coordination environment changes of the vanadium in vanadium-dependent haloperoxidase enzymes. J. Inorg. Biochem. 2018, 186, 267–279. 10.1016/j.jinorgbio.2018.06.011. [DOI] [PubMed] [Google Scholar]
  40. a Balcells D.; Maseras F.; Ujaque G. Computational Rationalization of the Dependence of the Enantioselectivity on the Nature of the Catalyst in the Vanadium-Catalyzed Oxidation of Sulfides by Hydrogen Peroxide. J. Am. Chem. Soc. 2005, 127, 3624–3634. 10.1021/ja0435384. [DOI] [PubMed] [Google Scholar]; b Kravitz J. Y.; Pecoraro V. L.; Carlson H. A. Quantum Mechanics/Molecular Mechanics Calculations of the Vanadium Dependent Chloroperoxidase. J. Chem. Theory Comput. 2005, 1, 1265–1274. 10.1021/ct050132o. [DOI] [PubMed] [Google Scholar]; c Schneider C. J.; Penner-Hanh J. E.; Pecoraro V. L. Elucidating the Protonation Site of Vanadium Peroxide Complexes and the Implications for Biomimetic Catalysis. J. Am. Chem. Soc. 2008, 130, 2712–2713. 10.1021/ja077404c. [DOI] [PubMed] [Google Scholar]
  41. Maurya M. R.; Haldar C.; Kumar A.; Kuznetsov M.; Avecilla F.; Costa Pessoa J. Vanadium complexes having [VO]2+, [VO]3+ and [VO2]+ cores with hydrazones of 2,6-diformyl-4-methylphenol: synthesis, characterization, reactivity, and catalytic potential. Dalton Trans. 2013, 42, 11941–11962. 10.1039/c3dt50469g. [DOI] [PubMed] [Google Scholar]
  42. a) Maiti S. K.; Dinda S.; Banerjee S.; Mukherjee A. K.; Bharracharyya R. Oxidoperoxidotungsten(VI) Complexes with Secondary Hydroxamic Acids: Synthesis, Structure and Catalytic Uses in Highly Efficient, Selective and Ecologically Benign Oxidation of Olefins, Alcohols, Sulfides and Amines with H2O2 as a Terminal Oxidant. Eur. J. Inorg. Chem. 2008, 2008, 2038. 10.1002/ejic.200701043. [DOI] [Google Scholar]; b) Bagherzadeh M.; Aminia M.; Parastar H.; Jalali-Heravi M.; Ellern A.; Woo L. K. Inorg. Chem. Commun. 2012, 20, 86–89. 10.1016/j.inoche.2012.02.023. [DOI] [Google Scholar]; c) Lane B. S.; Vogt M.; DeRose V. J.; Burgess K. Manganese-Catalyzed Epoxidations of Alkenes in Bicarbonate Solutions. J. Am. Chem. Soc. 2002, 124, 11946–11954. 10.1021/ja025956j. [DOI] [PubMed] [Google Scholar]; d) Richardson D. E.; Yao H.; Frank K. M.; Bennett D. A. Equilibria, Kinetics, and Mechanism in the Bicarbonate Activation of Hydrogen Peroxide: Oxidation of Sulfides by Peroxymonocarbonate. J. Am. Chem. Soc. 2000, 122, 1729–1739. 10.1021/ja9927467. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao2c06638_si_001.pdf (828.6KB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES