Facile Conversion of Ni(II) Cyclopropylchlorins into Novel β

Dec 19, 2016 - A series of β-substituted Ni(II) cyclopropylchlorins was converted into the corresponding Ni(II) and free base porphyrins using TFA an...
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Facile Conversion of Ni(II) Cyclopropylchlorins into Novel β‑Substituted Porphyrins through Acid-Catalyzed Ring-Opening Reaction Nitika Grover,† Nivedita Chaudhri,† and Muniappan Sankar* Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India S Supporting Information *

ABSTRACT: The conversion of cyclopropylchlorins into porphyrins represents a key step in the synthetic manipulation of macrocycles with tunable physical and chemical properties. Herein, we report a facile method for the synthesis of novel β-substituted porphyrins from cyclopropylchlorins. A series of Ni(II) cyclopropylchlorins was converted into the corresponding Ni(II) and free base porphyrins using TFA and H2SO4 under mild reaction conditions in good yields (75−86%). The new chlorins and porphyrins were characterized by various spectroscopic techniques and the single-crystal X-ray diffraction method. The reaction proceeds very fast (80% yield. In efforts to extend the versatility of synthetic route, chlorins, viz. NiTPPBr2C(COOEt)2 and NiTPPBr2C(CN)(COOEt), were synthesized and further treated with TFA under similar conditions as described above. An attempt to convert these free base chlorins into respective free base porphyrins failed due to protonation of the inner core nitrogens of chlorins. Thus, the free base porphyrins (1−7) were synthesized by addition of conc. H2SO4 to corresponding Ni(II) chlorins where ring opening followed by demetalation took place. The conversion of chlorins into porphyrins occurs within 5 min after adding TFA or H2SO4 with instant color change from green to red. The desired porphyrins were obtained in good yields (82−85%). Thus, the above procedure can be used for a variety of chlorin derivatives without loss of efficiency. To extend this work, we examined the reactivity of NiOPP(NO2) with the above-mentioned active methylene compounds which results in the synthesis of a new class of hexasubstituted cyclopropylchlorins (Scheme 2). These chlorins were further treated with TFA to get the corresponding β-pentasubstituted porphyrins (5a−7a). The proposed ring-opening process is shown in Scheme 3. Being inspired by the examples of bromo-substituted tetraphenylchlorins (Scheme 1), we engaged in the synthesis of bromosubstituted octaphenylchlorins from NiOPP(NO2)Br2. It was not successful because the reactant was completely insoluble in DMSO. As an alternative route, we attempted the bromination of NiOP−chlorin in order to obtain the desired product. Interestingly, we obtained the corresponding porphyrin (NiOPPBr 2 CH(COOEt) 2 (6a)) instead of chlorin (NiOPPBr2C(COOEt)2) due to in situ formation of HBr which catalyzes the ring-opening reaction with a yield of >80% (Scheme 2). However, the dibromination of NiOPPC(CN)(COOEt) resulted in a mixture of inseparable products. These reactions are an example of Michael addition followed by a simple oxidation. There are many oxidizing agents employed in organic chemistry,15 whereas only a few examples have been successfully used for oxidation of chlorins into porphyrins.16 Notably, we obtained porphyrins from chlorins without use of any oxidizing agent. Thus, the proposed mechanism (Scheme 3) describes a new type of reaction as well as opens a new route to prepare β-substituted porphyrins which previously were difficult to access by standard synthetic methods. Crystal Structure Discussion. The unambiguous identification of porphyrins, viz. NiTPPBr2CH(COOEt)2 (2a) and H2TPPBr2CH(COOEt)2 (2), were performed by single-crystal X-ray diffraction studies. The single crystals were obtained by slow diffusion of hexane into the corresponding porphyrins in CHCl 3 . Figure 1 clearly shows the product to be dibromodiethylmalonate-substituted meso-tetraphenylporphyrins. The two COOEt groups are oriented trans to each other and antipodal to the β-dibromo functionality. The crystallographic data of both above-mentioned porphyrins are listed in Table S1 in the Supporting Information (SI). The top and side

Figure 1. ORTEP diagrams (top and side views) of (a) NiTPPBr2CH(COOEt)2 (2a) and (b) H2TPPBr2CH(COOEt)2 (2).

ORTEP views of MTPPBr2CH(COOEt)2 (M = Ni(II) and 2H) are shown in Figure 1. However, the conformation is clearly nonplanar with significant up and down out of plane displacement of all four meso positions, i.e., both porphyrins exhibited a ruffled conformation of the porphyrin core. The selected average bond lengths and bond angles of MTPPBr2CH(COOEt)2 (M = Ni(II) and 2H) are listed in Table S2 in the SI. Interestingly, NiTPPBr2CH(COOEt)2 (2a) has shown a ruffled conformation with a higher magnitude of the displacement of the β-pyrrole carbons (ΔCβ = ± 0.7 Å) as compared to H2TPPBr2CH(COOEt)2 (2), which has a ruffled conformation with a ΔCβ value of ±0.576 Å (Figure 1 and Table S2 in SI). DFT Calculations. DFT calculations at the B3LYP/6-31G level using Gaussian09 were performed on a model of synthesized porphyrins to evaluate the extent of delocalization of the frontier molecular orbitals (FMOs).17 The frontier molecular orbitals of compound H2TPPCH(COOEt)2 (1) are shown in Figure 2. DFT calculations indicate that both the HOMO and the LUMO have a significant contribution of the macrocyclic core for β-substituted electron-deficient porphyrins.21 The optimized geometries and frontier molecular orbital diagrams of other systems are shown in Figures S1−S4 in the SI. The electronic effects of the β-substituents and the influence

Figure 2. Frontier molecular orbitals of H2TPPCH(COOEt)2 (1) using DFT calculations at the B3LYP/6-31G level. D

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 1. UV−Vis and Fluorescence Spectral Data in CH2Cl2 at 298 Ka λabs

a

porphyrin

B band

H2TPPCH(COOEt)2 (1) H2TPPBr2CH(COOEt)2 (2) H2TPPCH(CN)(COOEt) (3) H2TPPBr2CH(CN)(COOEt) (4) H2OPPCH(COOEt)2 (5) H2OPPBr2CH(COOEt)2 (6) H2OPPCH(CN)(COOEt) (7)

418(5.48) 424(5.61) 418(5.49) 427(5.22) 441(5.36) 460(5.27) 442(5.40)

Q band(s) 515(4.09), 521(4.38), 517(4.14), 528(4.06), 537(4.14), 560(3.95), 538(4.11),

550(3.59), 597(3.75), 552(3.66), 596(3.77), 584(3.88), 614(3.99), 589(3.95),

592(3.47), 648(3.25) 657(3.79) 595(3.57), 649(3.50) 648(3.61) 612(sh), 687(3.51) 712(3.83) 683(3.58)

λem

ϕf

656, 720 666, 719(sh) 660, 722 655, 724 711 760(w) 709

0.090 0.004 0.082 0.0003 0.009 0.0009 0.014

The values in parentheses refer to log ε, w = weak, sh = shoulder.

Figure 3. (a) Comparative UV−vis absorption spectra of NiTPPC(COOEt)2 and NiTPPCH(COOEt)2 (1a); Q band intensity is enhanced for clarity. (b) Comparative UV−vis spectra of diethylmalonate appended free base porphyrins (1 and 2, 5 and 6) in CH2Cl2 at 298 K.

All newly synthesized mixed substituted free base porphyrins (1−7) and their Zn(II) complexes (1b−7b) were characterized by fluorescence spectroscopy to elucidate the role of βsubstitution and the effect of nonplanarity. The emission spectra of these porphyrins were recorded in CH2Cl2 at 298 K. The emission spectral data of free base porphyrins (1−7) are given in Table 1, whereas for Zn(II) complexes (1b−7b) they are presented in Table S3 in the SI. Notably, a highly redshifted emission band with feeble fluorescence intensity was observed for bromo-substituted porphyrins in comparison to H2TPP. H2TPPBr2CH(COOEt)2 (2) exhibited a 10 nm red shift as compared to H2TPPCH(COOEt)2 (1), whereas H2OPPBr2CH(COOEt)2 (6) is much more red shifted (49 nm) relative to H2OPPCH(COOEt)2 (5). The same trend in fluorescence intensity and spectral shift was observed for Zn(II) complexes (1b−7b). The increased red shift in the fluorescence spectra and decreased quantum yield of bromo-substituted porphyrins were due to enhanced nonplanarity as evidenced by X-ray crystallographic studies and the heavy atom effect of Br groups.20a Quantum yields (ϕ) were calculated by using the equation

of nonplanarity of the macrocyclic core (as evidenced from DFT calculations and single-crystal X-ray structures) on the pophyrin π-system are further examined by various spectroscopic techniques and cyclic voltammetric studies. Electronic Spectral Studies. The optical absorption spectra of porphyrins, chlorins, and their metal complexes have been recorded in CH2Cl2 at 298 K, which show their characteristic features. Table 1 lists the electronic spectral data of free base porphyrins in CH2Cl2 at 298 K. The chlorin derivatives displayed a strong absorption band in the longwavelength region (Qy band) which readily disappeared after the addition of TFA or H2SO4 which clearly indicates the conversion of chlorin into porphrin as shown in Figure 3a. The optical absorption spectra of porphyrin and their metal complexes are influenced by the presence of a β-substituent and core metal ions.18 All free base porphyrins exhibited one B band and three or four Q bands. H2TPPBr2CH(COOEt)2 (2) displayed a 6 nm red shift in the Soret band and 9 nm in the Qx(0,0) band relative to H2TPPCH(COOEt)2 (1), whereas H2TPPBr2CH(CN)(COOEt) (4) exhibited a 9 nm red shift in the B band as compared to H2TPPCH(CN)(COOEt) (3) due to inductive and/or resonating effect of electron-withdrawing substituents such as cyano and bromo groups.19 A similar trend was observed in the case of octaphenylporphyrin (OPP) derivatives. Notably, H2OPPBr2CH(COOEt)2 (6) exhibited a 19 nm red shift in the Soret band as well as 25 nm in the Q band as compared to H2OPPCH(COOEt)2 (5), as shown in Figure 3b. This is possibly due to electron-donating β-phenyl substituents (+I effect) which can destabilize the HOMO as well as the nonplanarity of the porphyrin core.20 Figure S5 in the SI shows the comparative UV−vis spectra of H2TPPCH(CN)(COOEt) (3), H2TPPBr2CH(CN)(COOEt) (4), and H2OPPCH(CN)(COOEt) (7) in CH2Cl2 at 298 K. A similar trend was observed for Ni(II) and Zn(II) metal complexes as shown in Table S3 and Figures S6 and S7 in the SI.

ϕsample = (ϕref × A sample × εref )/(A ref × εsample)

and follows the order H2TPPCH(COOEt)2 (1) > H2TPPCH(CN)(COOEt) (3) > H2OPPCH(CN)(COOEt) (7) > H2OPPCH(COOEt)2 (5) > H2TPPBr2CH(COOEt)2 (2) > H2OPPBr2CH(COOEt)2 (6) > H2TPPBr2CH(CN)(COOEt) (4). The lower quantum yields can be attributed to rapid ISC, which is a characteristic feature of ruffled porphyrins.19 NMR Studies. All porphyrins and chlorins exhibited characteristic chemical shifts arising from β-pyrrole protons, β-substituent protons, meso-phenyl, and imine protons for free base porphyrins. Figures S8−S28 in the SI show the 1H NMR E

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Figure 4. 1H NMR spectra of (a) NiOPPC(COOEt)2 and (b) NiOPPCH(COOEt)2 (5a) showing proton signal shift during the conversion of chlorin into porphyrin.

spectra of all newly synthesized porphyrinoids. The ethyl groups of malonate in chlorins exhibited two separate signals due to torsional and intrinsic angle strain in the cyclopropyl ring (Figure 4). Both −CH2 showed two separate quartets, and likewise both −CH3 groups showed two separate triplets, whereas as the angle strain is relieved after addition of TFA and H2SO4 then only either one multiplet or one quartet appeared for two −CH2 groups and one triplet appeared for two −CH3 groups as shown in Figure 4. The β-pyrrole resonances of these synthesized free base TPPs are 0.11−0.22 ppm upfield shifted as compared to H2TPP(NO2). Similarly, bromo-substituted TPPs (2 and 4) are also 0.11−0.18 ppm upfield shifted than that of H2TPP(NO2)Br2. The β-pyrrole resonances of H2OPPCH(COOEt)2 (5) and H2OPPCH(CN)(COOEt) (7) are marginally upfield shifted (Δδ = 0.1−0.12 ppm) as compared to H2TPP(NO2). Figure 5 shows the 1H NMR spectra of the imino proton region of free base-synthesized porphyrins in CDCl3 at 298 K. The core imino protons resonate at higher region as compared to their nitro-substituted porphyrins. Nonplanarity of the octaphenyl macrocycle causes the broad feature of the imino protons to resonate at a downfield region relative to planar tetraphenylporphyrins. The reason for the largest downfield shift of −NH of H2OPPBr2CH(COOEt)2) (6) is due to the enhanced nonplanarity induced by bulky β-substituents. The 13C NMR spectra of free base porphyrins were recorded in CDCl3 at 298 K. Figures S29−S47 in the SI represent 13C NMR spectra of all newly synthesized porphyrins. However, we were unable to record 13C NMR spectra of ZnOPPBr2(COOEt)2 due to very poor solubility in deuterated solvents (CDCl3 and DMSO-d6). The number and position of carbon signals in the spectra are in accordance with proposed structures of target porphyrins. The 13C NMR signal for

Figure 5. Representative 1H NMR spectra of imino proton region of synthesized free base porphyrins (1−7).

carbonyl carbon appeared in the range of 160−170 ppm, whereas for the porphyrin macrocycle signals appeared in the range of 110−150 ppm for all synthesized porphyrins. The three signals were assigned to CH(COOEt)2 and CH(CN)(COOEt) groups in the range of 60−10 ppm. The MALDITOF mass spectra of all derivatives have been recorded using 2(4′-hydroxybenzeneazo)benzoic acid (HABA) as matrix. The positive ion mode mass spectra of synthesized porphyrins are shown in Figures S48−S67 in the Supporting Information, and F

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

CN, COOEt) have shown marginal anodic shift, whereas reduction potentials shifted more anodically (ΔEred = 210 mV) as compared to unbrominated porphyrins due to the nonplanar conformation of the porphyrin core as well as the nonplanarity of the porphyrin core. Octaphenylporphyrin derivatives have shown lower oxidation potentials as compared to the corresponding meso-tetraphenylporphyrins. The first oxidation potential of free base octaphenylporphyrins is 200−310 mV cathodically shifted as compared to the respective mesotetraphenylporphyrins possibly due to destabilization of HOMOs in the case of octaphenylporphyrins (Figures 8 and S70 in the SI). Interestingly, these β-substituted porphyrins have shown the following trend in the first oxidation potentials: MOPPBr2CH(COOEt) 2 < MOPPCH(CN)(COOEt) < MOPPCH(COOEt) 2 < MTPPCH(COOEt) 2 < MTPPCH(CN)(COOEt) < MTPPBr2CH(COOEt)2 < MTPPBr2CH(CN)(COOEt). This trend can be explained on the basis of the nonplanarity and electron-withdrawing/donating effect of β-substituents. In general, OPP derivatives have shown lower oxidation potentials as compared to TPPs due to the positive I effect of Ph groups and nonplanar conformation of the macrocyclic core. Among CH(COOEt)2 and CH(CN)(COOEt), the latter has shown a higher electron-withdrawing ability due to the strong electronwithdrawing nature of the CN group as compared to that of COOEt.

the molecular ion peaks are in accordance with the proposed structures. The bromo-substituted porphyrins show the isotopic pattern as shown in the inset of Figures S49, S53, S56, S58, S60, S63, and S66 in the SI which are matching with the simulated ones. Electrochemical Studies. The electrochemical redox properties of all synthesized chlorins and porphyrins were investigated in CH2Cl2 containing 0.1 M TBAPF6 as supporting electrolyte at 298 K. The comparative cyclic voltammograms of NiOPPC(COOEt)2 (chlorin) and the corresponding porphyrin (NiOPPCH(COOEt)2 (5a)) are shown in Figure 6. The halfwave potentials for each redox process are summarized in Table 2.

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CONCLUSIONS In summary, we present a novel, straightforward approach to obtain β-functionalized OPP and TPP derivatives in good yields (75−86%) under mild reaction conditions with atom economy. Seven different series of β-substituted porphyrins and their metal (Ni(II) and Zn(II)) complexes have been synthesized and characterized by various spectroscopic techniques. The crystal structures of MTPPBr2CH(COOEt)2 (M = Ni(II) and 2H) revealed the ruffled conformation of the porphyrin core. These mixed tri/penta-β-substituted porphyrins exhibited a considerable red shift in their B and Q bands as compared to MTPPs. The downfield shift of the imino proton resonances (Δδ = 0.12−1.45 ppm) reflects the conformational change from quasi-planar to nonplanar in these porphyrins as well as the electronic effects of substituents. The broader range of the first ring redox potentials (from 0.77 to 1.21 V for oxidation and from −0.94 to −1.40 V for reduction) shows the redox tunability achieved by means of mixed tri- and penta-βsubstitution on the TPP skeleton. Notably, OPP derivatives have lower oxidation potentials as compared to TPP derivatives with a dramatic reduction in the HOMO−LUMO gap. Overall, these porphyrinoids exhibited red-shifted electronic spectral features with varying degrees nonplanar conformation and tunable redox properties as well as porphyrin core basicity. Our approach provides easy access to a number of βsubstituted porphyrins which are difficult to prepare by conventional synthetic approaches. Utilization of these porphyrins in nonlinear optics (NLO), dye-sensitized solar cells (DSSC), and catalytic applications is in progress.

Figure 6. Comparative cyclic voltammograms of Ni(II) complexes of chlorin and the corresponding porphyrin in CH2Cl2 containing 0.1 M TBAPF6 at 298 K.

In general, Ni(II) complexes of chlorins have lower oxidation potentials as compared to that of corresponding porphyrins due to the nonplanar conformation of the chlorin core, whereas there is no significant difference in the first ring reduction potentials (Figure 6). Thus, the potential separation in E1/2 values between the first oxidation and the reduction (HOMO− LUMO gap) is higher for porphyrins with respect to their corresponding chlorins. The first oxidation potentials of Ni(II) porphyrins are 150−240 mV anodically shifted as compared to Ni(II) chlorins. The redox potentials of the porphyrin π-system are affected by the electronic nature of the β-substituent, the nature of the core metal ion, and the conformation of the macrocyclic ring.21 The influence of different electron-withdrawing and -donating substituents for diethylmalonate-appended Ni(II) porphyrins is shown in Figure 7. Figure S69 in the SI shows the comparative cyclic voltammograms of diethylmalonate-appended free base and Zn(II) porphyrins. The effect of ethylcyanoacetate on the ring potentials is shown in Figure S70 in the SI. The first ring oxidation potential of synthesized porphyrin shows the following trend according to the difference in electronegativity, i.e., Zn(II) < H2(Free base) < Ni(II). Notably, the first reduction potentials are more anodically shifted as compared to the first oxidation potentials. The first ring oxidation potentials of H2TPPBr2CH(COOEt)(R) (R = CN, COOEt) are 60−70 mV anodically shifted due to the nonplanarity of the porphyrin core, while reduction potentials are 150−210 mV anodically shifted as compared to the corresponding unbrominated porphyrins, viz. H2TPPCH(COOEt)(R) (R = CN, COOEt), due to electron-withdrawing bromo groups. Notably, the first ring oxidation potentials of H2OPPBr2CH(COOEt)(R) (R =

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EXPERIMENTAL SECTION

Chemicals. Pyrrole and ethylcyanoacetate were purchased from Alfa Aesar, U.K., and used as received. Diethylmalonate was purchased from SD Fine Chemicals Ltd., India. Benzaldehyde, N-bromosuccinimde (NBS), Zn(OAc)2·2H2O, K2CO3, TBAPF6, CaH2, P2O5, and

G

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry Table 2. Electrochemical Redox Dataa of Porphyrinoids in CH2Cl2 at 298 K oxidation (V)

a

reduction (V)

porphyrin

I

II

ΔE1/2

I

H2TPPCH(COOEt)2 (1) H2TPPBr2CH(COOEt)2 (2) H2TPPCH(CN)(COOEt) (3) H2TPPBr2CH(CN)(COOEt) (4) H2OPPCH(COOEt)2 (5) H2OPPBr2CH(COOEt)2 (6) H2OPPCH(CN)(COOEt) (7) NiTPPC(COOEt)2 NiTPPCH(COOEt)2 (1a) NiTPPBr2C(COOEt)2 NiTPPBr2CH(COOEt)2 (2a) NiTPPC(CN)(COOEt) NiTPPCH(CN)(COOEt) (3a) NiTPPBr2C(CN)(COOEt) NiTPPBr2CH(CN)(COOEt) (4a) NiOPPC(COOEt)2 NiOPPCH(COOEt)2 (5a) NiOPPBr2CH(COOEt)2 (6a) NiOPPC(CN)(COOEt) NiOPPCH(CN)(COOEt) (7a) ZnTPPCH(COOEt)2 (1b) ZnTPPBr2CH(COOEt)2 (2b) ZnTPPCH(CN)(COOEt) (3b) ZnTPPBr2CH(CN)(COOEt) (4b) ZnOPPCH(COOEt)2 (5b) ZnOPPBr2CH(COOEt)2 (6b) ZnOPPCH(CN)(COOEt) (7b)

1.02 1.08 1.06 1.13 0.83d 0.82 0.90b 0.85 1.03 0.94 1.18 0.96 1.10 1.06 1.21d 0.79 0.94 0.98 0.97 0.98 0.86 0.90 0.89 0.94 0.73 0.73 0.77

1.25 1.22 1.27 1.24

2.21 2.06 2.20 2.12 2.06 1.84 1.98 2.14 2.30 2.17 2.32 2.12 2.32 2.00 2.21 2.26 2.19 2.09 2.13 2.19

−1.19 −0.98 −1.14 −0.99 −1.23d −1.02b,d −1.08 −1.29 −1.27 −1.23b −1.14 −1.16b −1.22 −0.94 −1.10 −1.27 −1.25 −1.11 −1.16 −1.21

2.30 2.20 2.13 2.04 1.97 2.05

−1.40b −1.31b −1.19b −1.31 −1.24b −1.28

1.21b 1.19 1.32 1.21 1.30 1.26b 1.32 1.23 1.16 1.21 1.21 1.20 1.22 1.14 1.18 1.18 1.15 0.87 0.90 0.90

II

III

−1.15 −1.36 −1.23

−1.36

−1.34

−1.38 −1.40 −1.50 −1.51 −1.27 −1.31 −1.53 −1.63

−1.60b

−1.60b −1.49b −1.42 −1.52 −1.51b −1.49

Versus Ag/AgCl reference electrode. bIrreversible peaks. cData obtained from DPV. dRepresents two electron process, ΔE1/2 = Ioxidation − Ireduction.

Figure 8. HOMO−LUMO variation of synthesized free base porphyrins. used as received. NBS was recrystallized from hot water and dried for 8 h at 70 °C under vacuum. TBAPF6 was recrystallized twice from hot ethanol and dried under vacuum for 2 days at 25 °C. All solvents employed in this work (like hexane, ethanol, CHCl3, etc.) were distilled and dried prior to use. Precoated thin-layered silica gel chromatographic plates were purchased from E. Merck and used as received. H2TPP, H2TPP(NO2), H2TPP(NO2)Br2, H2TPPBr 4, H2OPP, and their metal complexes were synthesized according to the literature methods.14,21 Instruments and Methods. Optical absorption spectra were recorded on an Agilent Cary 100 spectrophotometer using a pair of quartz cells of 3.5 mL volume and 10 mm path length. Fluorescence spectra were recorded on Hitachi F-4600 spectrofluorometer using a quartz cell of 10 mm path length. NMR spectra were recorded on JEOL ECX 400 MHz and Bruker AVENCE 500 MHz spectrometers in CDCl3 at 298 K. MALDI-TOF-MS spectra were measured using a Bruker UltrafleXtreme-TN MALDI-TOF/TOF spectrometer using 2(4′-hydroxybenzeneazo)benzoic acid (HABA) as a matrix in positive ion mode. X-ray-quality single crystals of NiTPPBr2CH(COOEt)2

Figure 7. Comparative cyclic voltammograms of Ni(II) complexes of diethylmalonate-appended porphyrins in CH2Cl2 using TBAPF6 as supporting electrolyte at 298 K. liq. Br2 were purchased from HiMedia, India. Ni(OAc)2·4H2O, Pd(PPh3)4, and phenylboronic acid were purchased from SigmaAldrich, India, and used as received. Silica gel (100−200 mesh), DMSO, and THF were purchased from Thomas Baker, India, and H

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

(m, 2H, −OCH2), 1.23−1.19 (m, 3H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 165.074, 143.058, 142.820, 142.276, 140.217, 139.521, 135.068, 133.571, 132.856, 132.360, 128.928, 127.994, 127.717, 126.897, 119.165, 117.305, 116.276, 62.787, 29.616, 13.865. MALDI-TOF-MS (m/z): found 782.089 [M + H]+, calcd 782.206. Anal. Calcd for C49H33N5O2Ni: C, 75.21; H, 4.25; N, 8.95. Found: C, 75.39; H, 5.31; N, 8.90. 2-(Ethyl-1′-cyano-2′-propanoate)-12,13-dibromo-5,10,15,20tetraphenylporphyrinatonickel(II) (NiTPPBr2CH(CN)(COOEt)) (4a). Yield: 82% (41 mg, 0.044 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 424(5.20), 540(4.00), 576(3.68). 1H NMR (400 MHz, CDCl3) δ: 8.86(s, 1H, β-H), 8.70(d, 3JH,H = 8 Hz, 1H, β-H), 8.60(d, 3JH,H = 4 Hz, 1H, β-H), 8.57−8.53 (dd, 3JH,H = 8 Hz, 4 Hz, 2H, β-H), 8.02−7.93(m, 4H, meso-o-Ph), 7.81−7.74(m, 4H, meso-o-Ph), 7.69−7.60 (m, 12H, meso-m,p-Ph), 4.74 (s, 1H, −CH), 4.18−4.03(m, 2H, −OCH2), 1.19(t, 3JH,H = 8 Hz, 3H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 165.978, 144.069, 143.983, 143.859, 143.173, 140.522, 139.425, 139.293, 138.701, 138.148, 136.403, 136.260, 135.402, 134.229, 133.895, 133.505, 133.218, 133.133, 133.009, 132.818, 129.300, 128.480, 128.337, 127.641, 127.383, 124.876, 120.175, 118.459, 118.230, 118.039, 116.289, 63.359, 38.025, 30.064. MALDI-TOF-MS (m/z): found 938.378 [M + H]+, calcd 938.027. Anal. Calcd for C49H31N5O2Br2Ni: C, 62.59; H, 3.32; N, 7.45. Found: C, 62.68; H, 3.40; N, 7.44. General Procedure for the Conversion of Ni(II) Cyclopropyltetraphenylchlorins into Corresponding Free Base Tetraphenylporphyrins. A 100 mg (0.121 mmol) amount of 5,10,15,20-tetraphenyl-[2:3]-[bis(ethoxycarbonyl)-methano]porphyrinatonickel(II) was dissolved in a minimum amount of CHCl3. To this, 1.5 mL of conc. H2SO4 was added dropwise and stirred for 5 min at 0 °C. Then 50 mL of water was added slowly to the reaction mixture with constant stirring. The organic layer was washed with water (2 × 100 mL), 10% aqueous ammonia solution (25 mL), and finally distilled water (100 mL) in order to remove excess ammonia. The organic layer was passed over anhydrous sodium sulfate and purified on a silica gel column using CHCl3 as eluent. The desired product (1) was collected as the first fraction, and the yields were found to be ∼80% for all cases. 2-(1′,3′-Diethyl-2′-propanedioate)-5,10,15,20-tetraphenylporphyrin (H2TPPCH(COOEt)2) (1). Yield: 82% (77 mg, 0.099 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 418(5.48), 515(4.09), 550(3.59), 592(3.47), 648(3.25). 1H NMR (400 MHz, CDCl3) δ: 8.89 (s, 1H, β-H), 8.84−8.80 (m, 4H, β-H), 8.76 (d, 3JH,H = 4 Hz, 1H, β-H), 8.61(d, 3JH,H = 4 Hz, 1H, β-H), 8.22− 8.19 (m, 6H, meso-o-Ph), 8.11 (d, 3Jo‑H,m‑H = 8 Hz, 2H, meso-o-Ph), 7.77−7.72 (m, 12H, meso-m,p-Ph), 4.96 (s, 1H, −CH), 4.20−4.13 (m, 4H, −OCH2), 1.18 (t, 3JH,H = 8 Hz, 6H, −CH3), −2.73 (s, 2H, −NH). 13 C NMR (100 MHz, CDCl3) δ: 168.697, 142.419, 141.914, 141.571, 134.754, 134.687, 134.611, 133.714, 128.566, 127.812, 127.288, 126.849, 126.735, 126.649, 120.433, 120.356, 120.290, 119.298, 61.280, 52.928, 13.874. MALDI-TOF-MS (m/z): found 773.123 [M + H]+, calcd 773.312. Anal. Calcd for C51H40N4O4: C, 79.25; H, 5.22; N, 7.25. Found: C, 79.46; H, 5.10; N, 7.16. 2-(1′,3′-Diethyl-2′-propanedioate)-12,13-dibromo-5,10,15,20tetraphenylporphyrin (H2TPPBr2CH(COOEt)2) (2). Yield: 81% (77 mg, 0.082 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 424(5.61), 521(4.38), 597(3.75), 657(3.79). 1H NMR (400 MHz, CDCl3) δ: 8.86−8.55 (m, 5H, β-H), 8.22−8.07 (m, 8H, meso-oPh), 7.83−7.71 (m, 12H, meso-m,p-Ph), 4.80 (s, 1H, −CH), 4.19−4.09 (m, 4H, −OCH2), 1.17 (t, 3JH,H = 8 Hz, 3H, −CH3), −2.83 (t (br), 2H, −NH). 13C NMR (100 MHz, CDCl3) δ: 168.668, 141.924, 141.628, 141.409, 141.056, 140.798, 137.395, 135.335, 135.278, 135.202, 134.830, 134.058, 129.462, 128.794, 128.499, 128.346, 128.251, 128.091, 127.641, 127.450, 127.374, 126.935, 126.877, 120.881, 120.290, 119.851, 119.632, 61.642, 29.797, 14.036. MALDI-TOF-MS (m/z): found 930.351 [M + 2H]+, calcd 930.112. Anal. Calcd for C51H38N4O4Br2: C, 65.82; H, 4.12; N, 6.02. Found: C, 65.72; H, 3.96; N, 6.18. 2-(Ethyl-1′-cyano-2′-propanoate)-5,10,15,20-tetraphenylporphyrin (H2TPPCH(CN)(COOEt) (3). Yield: 81% (83 mg, 0.1 mmol).

(2a) and H2TPPBr2CH(COOEt)2 (2) were obtained by vapor diffusion of hexane into the CHCl3 solution of compounds. CCDC Nos. for NiTPPCH(COOEt)2Br2 and H2TPPCH(COOEt)2Br2 are 1443237 and 1443238, respectively. Single-crystal XRD data was collected on a Bruker Apex-II CCD diffractometer. Ethyl groups of COOEt were disordered. The ground state geometry optimization in gas phase was carried out by DFT calculations using the B3LYP functional with the 6-31G basis set. Electrochemical measurements were carried out using CH instruments (CHI 620E). A three-electrode assembly was used consisting of a platinum working electrode, Ag/ AgCl as a reference electrode, and a Pt wire as a counter electrode. The porphyrin concentration was maintained at ∼1 mM during electrochemical measurements. The whole experiment was performed under inert atmosphere. All tetraphenylchlorins were synthesized according to the literature methods, and the spectral data are matching with the reported literature.3 General Procedure for the Conversion of Ni(II) Cyclopropyltetraphenylchlorins into Corresponding Ni(II) Tetraphenylporphyrins. A 50 mg (0.06 mmol) amount of 5,10,15,20tetraphenyl-[2:3]-[bis(ethoxycarbonyl)methano]porphyrinatonickel(II) was dissolved in a minimum amount of CHCl3. To this solution, a few drops of TFA were added slowly, and the reaction mixture was stirred at 0 °C for 5 min. The reaction mixture was allowed to warm to room temperature, and water was added to the reaction mixture. The organic layer was washed with (1:1) water−ammonia mixture and finally with distilled water (100 mL) in order to remove excess ammonia. The organic layer was dried over sodium sulfate, and the solvent was removed under reduced pressure. The crude solid was purified using column chromatography using CHCl3 to afford the title compound as a bright purple solid. The similar procedure was employed for the preparation of NiTPPCH(CN)(COOEt) (3a), NiTPPBr2CH(COOEt)2 (2a), and NiTPPBr2CH(CN)(COOEt) (4a), and the yields are found to be ∼85% in all cases. 2-(1′,3′-Diethyl-2′-propanedioate)-5,10,15,20tetraphenylporphyrinatonickel(II) (NiTPPCH(COOEt)2) (1a). Yield: 86% (43 mg, 0.052 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 417(5.29), 524(3.64). 1H NMR (400 MHz, CDCl3) δ: 8.82(s, 1H, β-H), 8.72−8.64(m, 6H, β-H), 8.01− 7.97(m, 6H, meso-o-Ph), 7.88(d, 3Jo‑H,m‑H = 8 Hz, 2H, meso-o-Ph), 7.71−7.61(m, 12H, meso-m,p-Ph), 4.88(s, 1H, −CH), 4.18−4.10(m, 4H, −OCH2), 1.20(t, 3JH,H = 4 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 168.544, 143.497, 142.839, 140.636, 140.036, 138.853, 136.355, 133.762, 132.923, 132.418, 127.860, 127.469, 127.011, 126.592, 119.184, 118.898, 117.715, 61.461, 29.797, 14.046. MALDI-TOF-MS (m/z): found 828.859 [M]+, calcd 828.225. Anal. Calcd for C51H38N4O4Ni: C, 73.84; H, 4.62; N, 6.75. Found: C, 73.74; H, 5.85; N, 6.55. 2-(1′,3′-Diethyl-2′-propanedioate)-12,13-diromo-5,10,15,20tetraphenylporphyrinatonickel(II) (NiTPPBr2CH(COOEt)2) (2a). Yield: 85% (43 mg, 0.043 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 423(5.27), 540(4.12), 577(sh). 1H NMR (400 MHz, CDCl3) δ: 8.79−8.50 (m, 5H, β-H), 7.93 (d, 3Jo‑H,m‑H = 8 Hz, 3H, meso-o-Ph), 7.82 (t, 3Jo‑H,m‑H = 8 Hz, 5H, meso-o-Ph), 7.67− 7.61 (m, 12H, meso-m,p-Ph), 4.77 (s, 1H, −CH), 4.16−4.08 (m, 4H, −OCH2), 1.16 (t, 3JH,H = 8 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 168.191, 143.611, 139.845, 139.502, 139.273, 137.004, 135.669, 133.991, 133.838, 138.180, 132.961, 132.704, 128.728, 128.365, 128.146, 127.698, 127.231, 119.632, 61.766, 52.947, 29.921. MALDI-TOF-MS (m/z): found 985.303 [M + H]+, calcd 985.053; found 1008.413 [M + H + Na]+, calcd 1008.043. Anal. Calcd for C51H36N4O4Br2Ni: C, 62.04; H, 3.68; N, 5.67. Found: C, 65.16; H, 3.40; N, 5.44. 2-(Ethyl-1′-cyano-2′-propanoate)-5,10,15,20tetraphenylporphyrinatonickel(II) (NiTPPCH(CN)(COOEt)) (3a). Yield: 83% (42 mg, 0.053 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 417(5.27), 532(4.09). 1H NMR (400 MHz, CDCl3) δ: 8.92 (s, 1H, β-H), 8.72−8.62 (m, 6H, β- H), 7.97− 7.95 (m, 7H, meso-o-Ph), 7.82 (d, 3Jo‑H,m‑H = 8 Hz, 1H, meso-oPh),7.83−7.60 (m, 12H, meso-m,p-Ph), 4.80 (s, 1H, −CH), 4.21−4.05 I

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

7.86−7.72(m, 12H, meso-m,p-Ph), 4.92(s, 1H, −CH), 4.22−4.15(m, 2H, −OCH2), 0.88(t, 3JH,H = 5 Hz, 3H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 150.800, 147.311, 142.724, 134.515, 132.742, 130.244, 128.918, 127.889, 126.544, 124.275, 124.094, 121.650, 116.867, 63.263, 38.559, 32.190. MALDI-TOF-MS (m/z): found 788.177 [M + H]+ calcd 788.199. Anal. Calcd for C49H33N5O2Zn: C, 74.57; H, 4.21; N, 8.87. Found: C, 74.66; H, 4.32; N, 8.91. 2-(Ethyl-1′-cyano-2′-propanoate)-12,13-dibromo-5,10,15,20tetraphenylporphyrinatozinc(II) (ZnTPPBr2CH(CN)(COOEt)) (4b). Yield: 74% (20 mg, 0.021 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 425(5.58), 553(4.25), 593(sh). 1H NMR (500 MHz, CDCl3) δ: 9.08(s, 1H, β-H), 8.85−8.82(q, 3JH,H = 5 Hz, 2H, β-H), 8.77(d, 3JH,H = 4 Hz, 1H, β-H), 8.65(d, 3JH,H = 4 Hz, 1H, β-H), 8.17−7.99(m, 8H, meso-o-Ph), 7.87−7.67(m, 12H, meso-m,p-Ph), 4.86(s, 1H, −CH), 4.22−4.13(m, 2H, −OCH2), 1.22(t, 3JH,H = 5 Hz, 3H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 167.686, 153.985, 150.953, 148.455, 141.618, 140.646, 139.302, 134.725, 133.962, 132.360, 128.613, 128.060, 126.935, 124.466, 122.578, 115.141, 113.987, 63.549, 47.360, 32.324. MALDI-TOF-MS (m/z): found 944.96 [M + H]+, calcd 944.02. Anal. Calcd for C49H31N5O2Br2Zn: C, 62.15; H, 3.30; N, 7.40. Found: C, 62.40; H, 3.54; N, 7.48. Synthesis of [2:3]-[Bis(ethoxycarbonyl)methano]5,7,8,10,15,17,18,20-octaphenylchlorinatonickel(II) [NiOPPC(COOEt)2]. K2CO3 (270 mg, 1.96 mmol) and diethylmalonate (598 μL, 3.92 mmol) were taken in 4.5 mL of DMSO and stirred for 1.5 h under inert atmosphere at reflux. To this solution, 200 mg (0.196 mmol) of NiOPP(NO2) was added, and stirring was continued for an additional 2 h at 80 °C. The reaction mixture was cooled to RT and diluted with CH2Cl2. The organic layer was washed with saturated brine solution and passed over sodium sulfate. The crude solid was purified on a silica column using CHCl3 to afford the title compound as a bright purple solid. Yield: 47% (104 mg, 0.092 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 431(5.16), 524(3.78), 582(sh), 631(4.46). 1H NMR (400 MHz, CDCl3) δ: 7.78 (s, 2H, β-H), 7.33 (d, 3Jo‑H,m‑H = 8 Hz, 6H, meso-o-Ph), 7.13−6.99(m, 14H, meso-o and m,p-Ph), 6.84−6.74 (m, 20H, β-Ph), 4.23(s, 2H, βH), 4.10−4.04(q, 3JH,H = 4 Hz, 8 Hz, 2H, −OCH2), 3.09−3.04(q, 3JH,H = 4 Hz, 8 Hz, 2H, −OCH2), 1.10(t, 3JH,H = 8 Hz, 3H, −CH3), 0.32(t, 3 JH,H = 8 Hz, 3H, −CH3). MALDI-TOF-MS (m/z): found 1132.36 [M]+, calcd 1132.35. Anal. Calcd for C75H54N4O4Ni: C, 79.44; H, 4.80; N, 4.94. Found: C, 79.41; H, 4.90; N, 5.03. Synthesis of [2:3]-[(Cyano)(ethoxycarbonyl)methano]5,7,8,10,15,17,18,20-octaphenyl-chlorinatonickel(II) (NiOPPC(CN)(COOEt)). K2CO3 (203 mg, 1.47 mmol) and ethylcyanoacetate (188 μL, 1.76 mmol) were taken in THF under inert atmosphere and refluxed for 2 h. The solution was cooled to RT, and then 150 mg (0.147 mmol) of NiOPP(NO2) was added, and stirring was continued overnight at 50 °C. The reaction mixture was diluted with CH2Cl2, and the organic layer was washed with saturated brine solution and passed over sodium sulfate. The solvent was evaporated to dryness, and the crude chlorin was purified using column chromatography using CHCl3 to afford the title compound as a bright purple solid. Yield: 44% (70 mg, 0.064 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 430(5.08), 524(3.73), 629(4.36). 1H NMR (400 MHz, CDCl3) δ: 7.81(s, 1H, β-H), 7.38(d, 3Jo‑H,m‑H = 8 Hz, 4H, meso-o-Ph), 7.19−6.98(m, 16H, meso-o and m,p-Ph), 6.83−6.60 (m, 20H, β-Ph), 4.34(s, 2H, β-H), 4.23−4.18(q, 3JH,H = 8 Hz, 8 Hz, 2H, −OCH2), 0.88(t, 3JH,H = 4 Hz, 3H, −CH3). MALDI-TOF-MS (m/z): found 1085.33 [M]+, calcd 1085.32. Anal. Calcd for C73H49N5O2Ni: C, 80.67; H, 4.54; N, 6.44. Found: C, 80.80; H, 3.50; N, 6.43. General Procedure for the Conversion of Ni(II) Cyclopropyloctaphenylchlorins into Corresponding Ni(II) Octaphenylporphyrins. A 60 mg (0.053 mmol) amount of NiOPPC(COOEt)2 was dissolved in a minimum amount of CHCl3. To this solution, a few drops of TFA were added slowly at 0 °C, and the reaction mixture was stirred for 5 min. The reaction mixture was allowed to warm to room temperature, and water was added to the reaction mixture. The organic layer was washed with (1:1) water− ammonia mixture and finally with distilled water (100 mL). Organic

Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 418(5.49), 517(4.14), 552(3.66), 595(3.57), 649(3.50). 1H NMR (400 MHz, CDCl3) δ: 8.99 (s, 1H, β-H), 8.87 (s, 2H, β-H), 8.83−8.78 (m, 3H, β-H), 8.79(d, 3JH,H = 8 Hz, 1H, β-H), 8.22−8.17 (m, 8H, meso-o-Ph), 7.79−7.75 (m, 12H, meso-m,p-Ph), 4.85 (s, 1H, −CH), 4.21−4.10 (m, 2H, −OCH2), 1.18 (t, 3JH,H = 8 Hz, 3H, −CH3), −2.74 (s, 2H, −NH). 13C NMR (100 MHz, CDCl3) δ: 165.484, 141.943, 141.723, 140.970, 134.649, 133.943, 133.752, 129.166, 128.184, 128.041, 127.946, 127.250, 126.926, 120.919, 120.642, 119.145, 116.666, 63.177, 38.054, 13.493. MALDI-TOF-MS (m/z): found 725.186 [M]+, calcd 725.279. Anal. Calcd for C49H35N5O2: C, 81.08; H, 4.86; N, 9.65. Found: C, 81.25; H, 4.72; N, 9.43. 2-(Ethyl-1′-cyano-2′-propanoate)-12,13-dibromo-5,10,15,20-tetraphenylporphyrin (H2TPPBr2CH(CN)(COOEt)) (4). Yield: 77% (73 mg, 0.082 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 427(5.22), 528(4.06), 596(3.77), 648(3.61). 1H NMR (400 MHz, CDCl3) δ: 8.69−8.67(dd, 3JH,H = 4 Hz, 4 Hz, 2H, βH), 8.42−8.41(dd, 3JH,H = 4 Hz, 4 Hz, 2H, β-H), 8.09−7.96(m, 9H, βH and meso-o-Ph), 7.78−7.68(m, 12H, meso-m,p-Ph), 4.88(s, 1H, −CH), 4.40−4.35(q, 3JH,H = 4 Hz, 8 Hz, 2H, −OCH2), 1.37 (t, 3JH,H = 8 Hz, 3H, −CH3), 2.07(s, 2H, −NH). 13C NMR (100 MHz, CDCl3) δ: 167.133, 156.054, 146.309, 141.390, 137.471, 134.363, 130.377, 128.594, 124.618, 114.372, 64.360, 48.866, 23.161. MALDI-TOF-MS (m/z): found 884.296 [M]+, calcd 884.635. Anal. Calcd for C49H33N5O2Br2: C, 66.60; H, 3.76; N, 7.93. Found: C, 66.56; H, 3.65; N, 7.72. General Procedure for the Synthesis of Zn(II) Complexes from Free Base Porphyrins. A 25 mg amount of free base tetraphenylporphyrins was dissolved in 15 mL of CHCl3. To this, 10 equiv of Zn(OAc)2·2H2O in 2 mL of MeOH solution was added, and the resulting mixture was refluxed for 30 min. The organic layer was washed with water to remove excess metal salt. The crude porphyrins were purified by column chromatography. The yields were found to be 70−75%. The melting point for all Zn(II) was >300 °C. 2-(1′,3′-Diethyl-2′-propanedioate)-5,10,15,20tetraphenylporphyrinatozinc(II) (ZnTPPCH(COOEt)2) (1b). Yield: 75% (20 mg, 0.024 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 419(5.61), 549(4.23), 586(sh). 1H NMR (500 MHz, CDCl3) δ: 9.01(s, 1H, β-H), 8.94−8.91(m, 4H, β-H), 8.86(d, 3JH,H = 5 Hz, 1H, βH), 8.68(d, 3JH,H = 5 Hz, 1H, β-H), 8.22−8.19(m, 6H, meso-o-Ph), 8.11(d, 3Jo‑H,m‑H = 5 Hz, meso-o-Ph), 7.80−7.69(m, 12H, meso-m,p-Ph), 5.02(s, 1H, −CH), 4.23−4.15(m, 4H, −OCH2), 1.22(t, 3JH,H = 5 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 169.126, 150.505, 150.314, 147.921, 146.329, 142.810, 135.898, 135.154, 134.525, 133.466, 132.446, 132.275, 131.636, 128.365, 127.630, 127.126, 126.640, 121.548, 121.243, 120.347, 61.709, 53.385, 29.816. MALDI-TOF-MS (m/z): found 835.175 [M + H]+, calcd 835.266. Anal. Calcd for C51H38N4O4Zn: C, 73.25; H, 4.58; N, 6.70. Found: C, 73.38; H, 4.71; N, 6.62. 2-(1′,3′-Diethyl-2′-propanedioate)-12,13-dibromo-5,10,15,20tetraphenylporphyrinatozinc(II) (ZnTPPBr2CH(COOEt)2) (2b). Yield: 73% (19 mg, 0.020 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 424(5.48), 553(4.11), 590(sh). 1H NMR (500 MHz, CDCl3) δ: 8.96(s, 1H, β-H), 8.85(s, 2H, β-H), 8.78(d, 3JH,H = 5 Hz, 2H, β-H), 8.63(d, 3JH,H = 5 Hz, 2H, β-H), 8.19(d, 3Jo‑H,m‑H = 5 Hz, meso-o-Ph), 8.10−8.06(m, 6H, meso-o-Ph), 7.76−7.71(m, 12H, meso-m,p-Ph), 4.97(s, 1H, −CH), 4.23−4.17(m, 4H, −OCH2), 1.24(t, 3JH,H = 5 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 169.030, 151.668, 151.315, 150.915, 148.579, 142.477, 142.314, 142.038, 135.316, 134.715, 134.515, 134.191, 133.457, 132.132, 128.461, 128.051, 127.727, 127.193, 126.897, 126.669, 125.248, 62.033, 32.047, 22.808. MALDI-TOF-MS (m/z): found 991.317 [M + H]+ calcd 991.047. Anal. Calcd for C51H36N4O4Br2Zn: C, 61.62; H, 3.65; N, 5.64. Found: C, 61.60; H, 3.72; N, 5.62. 2-(Ethyl-1′-cyano-2′-propanoate)-5,10,15,20tetraphenylporphyrinatozinc(II) (ZnTPPCH(CN)(COOEt)) (3b). Yield: 71% (19 mg, 0.024 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 420(5.54), 550(4.16), 589(sh). 1H NMR (500 MHz, CDCl3) δ: 9.16(s, 1H, β-H), 8.94−8.92(m, 4H, β-H), 8.89(d, 3JH,H = 5 Hz, 1H, βH), 8.73(d, 3JH,H = 5 Hz, 1H, β-H), 8.21−8.15(m, 8H, meso-o-Ph), J

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

meso-o-Ph), 7.35−7.19(m, 12H, meso-m,p-Ph), 6.92−6.81(m, 20H, βPh), 4.11(s, 1H, −CH), 3.95−3.85(m, 2H, −OCH2), 1.00(t, 3JH,H = 5 Hz, 3H, −CH3), −1.77(s, 2H, -NH). 13C NMR (100 MHz, CDCl3) δ: 165.226, 143.783, 143.621, 140.827, 140.398, 138.606, 136.355, 135.984, 135.707, 135.230, 132.227, 131.331, 127.317, 127.008, 126.592, 126.239, 125.686, 125.362, 122.225, 120.919, 119.632, 116.647, 62.767, 37.482, 14.046. MALDI-TOF-MS (m/z): found 1030.803 [M + H]+, calcd 1030.412. Anal. Calcd for C73H51N5O2: C, 85.11; H, 4.99; N, 6.80. Found: C, 85.41; H, 4.70; N, 6.73. Synthesis of 2-(1′,3′-Diethyl-2′-propanedioate)-12,13-dibromo5,7,8,10,15,17,18,20-octaphenylporphyrinatonickel(II) (NiOPPBr2CH(COOEt)2). A 90 mg (0.087 mmol) amount of NiOPPC(COOEt)2 was dissolved in CHCl3. To this, 5 equiv of liquid Br2 was added dropwise over a period of 10 min and continued to stir for 10 min at room temperature. At the end, the excess of bromine was quenched by washing with 10% aqueous solution of Na2S2O5. The organic layer was washed with water and passed over sodium sulfate. The solvent was removed using a rotary evaporator, and the crude porphyrin was purified by silica gel column chromatography using CHCl3 as eluent. The yield was found to be 80% (89 mg, 0.069 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 453(5.09), 582(4.05), 624(3.9). 1H NMR (400 MHz, CDCl3) δ: 8.16(s, β-H), 7.57(d, 3Jo‑H,m‑H = 4 Hz, 2H, meso-o-Ph), 7.50(t, 3JH,H = 4 Hz, 6H, meso-o-Ph), 7.21−7.06(m, 12H, meso-m,p-Ph), 6.84−6.67(m, 20H, β -Ph), 4.10(s, 1H, −CH), 4.00−3.90(m, 4H, −OCH2), 1.04(t, 3 JH,H = 8 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 168.191, 148.769, 147.949, 147.501, 146.376, 144.956, 143.659, 143.182, 143.020, 142.810, 139.740, 139.387, 138.663, 138.281, 137.242, 136.975, 136.413, 136.107, 135.488, 134.935, 134.481, 131.588, 131.321, 127.974, 127.193, 126.859, 126.716, 126.659, 126.601, 126.468, 125.896, 125.600, 125.534, 120.471, 61.518, 52.127, 31.732. MALDI-TOF-MS (m/z): found 1314.730 [M + Na]+, calcd 1314.737. Anal. Calcd for C75H52N4O4Br2Ni: C, 69.74; H, 4.06; N, 4.34. Found: C, 69.89; H, 4.22; N, 4.40. Synthesis of 2-(1′,3′-Diethyl-2′-propanedioate)-12,13-dibromo5,7,8,10,15,17,18,20-octaphenylporphyrin (H2OPPBr2CH(COOEt)2) (6). H2OPPBr2CH(COOEt)2 (6) was prepared by simple sulfuric acid demetalation of 60 mg (0.046 mmol) of NiOPPBr2CH(COOEt)2 (6a) by using a conventional procedure. The yield of the product was found to be 76% (44 mg 0.035 mmol). Melting point > 300 °C. UV− vis (CH2Cl2): λmax(nm) (log ε) 460(5.27), 560(3.95), 614(3.99), 712(3.83). 1H NMR (400 MHz, CDCl3) δ: 8.00−7.96(m, 4H, meso-oPh), 7.86(s, 1H, β -H), 7.80−7.75(m, 4H, meso-o-Ph), 7.29−7.21(m, 12H, meso-m,p-Ph), 6.92−6.77(m, 20H, β -Ph), 4.07(s, 1H, −CH), 3.97−3.88(m, 4H, −OCH2), 1.02(t, 3JH,H = 8 Hz 6H, −CH3), −1.58(s, 2H, −NH). 13C NMR (100 MHz, CDCl3) δ: 168.277, 142.782, 140.188, 138.625, 138.348, 137.967, 137.280, 137.213, 135.507, 135.411, 132.055, 131.998, 131.798, 127.164, 127.097, 126.659, 126.563, 126.497, 126.249, 125.896, 61.089, 52.327, 13.893. MALDI-TOF-MS (m/z): found 1235.888 [M + H]+, calcd 1235.064. Anal. Calcd for C75H54N4O4Br2: C, 72.94; H, 4.41; N, 4.54. Found: C, 72.70; H, 4.48; N, 4.66. General Procedure for the Synthesis of Zn(II) Complexes from Free Base Porphyrins. A 25 mg (0.022 mmol) amount of Zn(II) complexes of octaphenylporphyrins was prepared using conventional methods as described for tetraphenylporphyrins, and the yields were found to be 75−80%. Melting points for all derivatives were >300 °C. 2-(1′,3′-Diethyl-2′-propanedioate)-5,7,8,10,15,17,18,20octaphenylporphyrinatozinc(II) (ZnOPPCH(COOEt)2) (5b). Yield: 76% (20 mg, 0.018 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 435(5.41), 564(4.21). 1H NMR (500 MHz, CDCl3) δ: 8.50(s, 1H, βH), 8.42(t, 3JH,H = 5 Hz, 2H, β -H), 7.81−7.72(m, 8H, meso-o-Ph), 7.24−7.11(m, 12H, meso-m,p-Ph), 6.95−6.93(m, 4H, β-Ph), 6.87− 6.77(m, 16H, β-Ph), 4.27(s, 1H, −CH), 4.03−3.96(m, 4H, −OCH2), 1.06(t, 3JH,H = 5 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 169.069, 151.677, 148.684, 147.053, 146.739, 146.584, 141.704, 141.618, 141.542, 140.045, 138.482, 137.948, 137.747, 135.545, 135.411, 135.307, 135.164, 135.068, 134.954, 132.189, 132.074, 131.656, 131.378, 127.021, 126.897, 126.478, 126.373, 125.810,

layer was dried over sodium sulfate, and the solvent was removed for dryness. The crude product was purified by column chromatography using CHCl3. The similar procedure was employed for NiOPPCH(CN)(COOEt) (7a), and the yield was found to be ∼80% in both cases. 2-(1′,3′-Diethyl-2′-propanedioate)-5,7,8,10,15,17,18,20octaphenylporphyrinatonickel(II) NiOPPCH(COOEt)2 (5a). Yield: 82% (49 mg, 0.043 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 434(5.07), 552(3.98), 591(3.66). 1H NMR (400 MHz, CDCl3) δ: 8.30(s, 1H, β-H), 8.20(d, 3JH,H = 4 Hz, 1H, β-H), 8.11(d, 3JH,H = 4 Hz, 1H, β-H), 7.50(d, 3Jo‑H,m‑H = 8 Hz, 2H, meso-o-Ph), 7.45−7.38(m, 6H, meso-o-Ph), 7.19−6.97(m, 14H, mesom,p-Ph), 6.90−6.65(m, 20H, β-Ph), 4.17(s, 1H, −CH), 4.05−3.94(m, 4H, −OCH2), 1.08(t, 3JH,H = 8 Hz, 6H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 168.487, 148.389, 147.740, 146.977, 146.920, 144.460, 143.964, 141.695, 140.360, 139.416, 139.082, 137.385, 136.374, 133.962, 133.752, 131.626, 127.050, 126.706, 126.144, 126.077, 125.553, 119.384, 119.050, 118.812, 61.452, 52.670, 29.816. MALDI-TOF-MS (m/z): found 1132.070 [M]+, calcd 1132.350. Anal. Calcd for C75H54N4O4Ni: C, 79.44; H, 4.80; N, 4.94. Found: C, 79.39; H, 4.67; N, 4.82. 2-(Ethyl-1′-cyano-2′-propanoate)-5,7,8,10,15,17,18,20octaphenylporphyrinatonickel(II) (NiOPPCH(CN)(COOEt)) (7a). Yield: 80% (40 mg, 0.037 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 435(5.23), 553(4.15), 590(sh). 1H NMR (400 MHz, CDCl3) δ: 8.40(s, 1H, β-H), 8.21(d, 3JH,H = 4 Hz, 1H, βH), 8.12(d, 3JH,H = 4 Hz, 1H, β-H), 7.52−743(m, 2H, meso-o-Ph), 7.41−7.38(m, 6H, meso-o-Ph), 7.21−7.15(m, 4H, meso-m,p-Ph), 7.08− 7.02 (m, 8H, meso-m, p-Ph), 6.81−6.64(m, 20H, β-Ph), 5.30(s, 1H, −CH), 4.04 (s, 2H, −OCH2), 1.11(t, 3JH,H = 4 Hz, 3H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 165.245, 148.569, 147.396, 147.168, 144.393, 141.027, 139.797, 139.054, 137.109, 136.784, 134.000, 133.609, 133.466, 132.685, 131.540, 131.369, 126.773, 126.201, 125.705, 119.594, 116.533, 62.853, 37.825, 31.961. MALDI-TOF-MS (m/z): found 1086.619 [M + H]+, calcd 1085.331. Anal. Calcd for C73H49N5O2Ni: C, 80.67; H, 4.54; N, 6.44. Found: C, 80.65; H, 4.58; N, 6.51. General Procedure for the Conversion of Ni(II) Cyclopropyloctaphenylchlorins into Corresponding Free Base Octaphenylporphyrins. A 50 mg (0.044 mmol) amount of NiOPPC(COOEt)2 was dissolved in a minimum amount of CHCl3. To this, a few drops of conc. H2SO4 was added and stirred for 5 min at 0 °C. Then distilled water was added slowly to the reaction mixture. The organic layer was washed with water (2 × 50 mL), then with 10% aqueous ammonia solution (25 mL), and finally with distilled water (100 mL). The organic layer was dried using anhydrous sodium sulfate, and the crude product was purified on a silica gel column using CHCl3 as eluent. The desired porphyrin was collected as a single fraction. The similar procedure was employed for H2OPPCH(CN)(COOEt) (7), and the yield was found to be ∼75% for both cases. 2-(1′,3′-Diethyl-2′-propanedioate)-5,7,8,10,15,17,18,20-octaphenylporphyrin (H2OPPCH(COOEt)2) (5). Yield: 75% (35 mg, 0.0325 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 441(5.36), 537(4.14), 584(3.88), 612(sh), 687(3.51). 1H NMR (400 MHz, CDCl3) δ: 8.29(s, 2H, β-H), 8.23(s, 1H, β-H), 7.92−7.78(m, 8H, meso-o-Ph), 7.31−7.16(m, 12H, meso-m,p-Ph), 6.93−6.75(m, 20H, β-Ph), 4.23(s, 1H, −CH), 3.99−3.88(m, 4H, −OCH2), 1.01(t, 3JH,H = 8 Hz, 6H, −CH3), −1.80(bs, 2H, −NH). 13C NMR (100 MHz, CDCl3) δ: 168.468, 141.065, 140.722, 140.598, 138.949, 136.107, 135.650, 135.354, 135.297, 131.702, 131.626, 131.521, 131.369, 127.193, 127.050, 126.563, 126.497, 126.458, 126.277, 126.220, 126.134, 125.591, 125.553, 125.505, 125.305, 121.777, 120.528, 120.080, 61.652, 52.289, 14.065. MALDI-TOF-MS (m/z): found 1077.816 [M + H]+, calcd 1077.437. Anal. Calcd for C75H56N4O4: C, 83.62; H, 5.24; N, 5.20. Found: C, 83.43; H, 5.09; N, 5.06. 2-(Ethyl-1′-cyano-2′-propanoate)-5,7,8,10,15,17,18,20-octaphenylporphyrin (H2OPPCH(CN)(COOEt)) (7). Yield: 76% (36 mg, 0.035 mmol). Melting point > 300 °C. UV−vis (CH2Cl2): λmax(nm) (log ε) 442(5.40), 538(4.11), 589(3.95), 683(3.58). 1H NMR (500 MHz, CDCl3) δ: 8.29(s, 1H, β-H), 8.23(s, 2H, β-H), 7.93−7.75(m, 8H, K

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry 125.209, 124.866, 61.423, 32.028, 22.999. MALDI-TOF-MS (m/z): found 1139.668 [M + H]+, calcd 1139.351. Anal. Calcd for C75H54N4O4Zn: C, 78.97; H, 4.77; N, 4.91. Found: C, 78.75; H, 4.84; N, 4.93. 2-(Ethyl-1′-cyano-2′-propanoate)-5,7,8,10,15,17,18,20octaphenylporphyrinatozinc(II) (ZnOPPCH(CN)(COOEt)) (7b). Yield: 81% (21 mg, 0.020 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 435(5.39), 564(4.19). 1H NMR (500 MHz, CDCl3) δ: 8.64(s, 1H, βH), 8.45(s, 2H, β-H), 7.85−7.72(m, 8H, meso-o-Ph), 7.25−7.10(m, 12H, meso-m,p-Ph), 6.97−6.66(m, 20H, β-Ph), 4.09(s, 1H, −CH), 4.03−3.96(m, 2H, −OCH2), 1.06(t, 3JH,H = 7 Hz, 3H, −CH3). 13C NMR (100 MHz, CDCl3) δ: 165.684, 152.097, 147.854, 147.511, 147.206, 146.901, 146.527, 145.127, 141.456, 141.132, 139.740, 138.205, 137.919, 137.805, 137.557, 135.392, 135.697, 132.580, 131.636, 131.407, 128.451, 127.74, 127.269, 127.050, 126.554, 126.258, 126.087, 125.867, 125.505, 125.343, 122.664, 122.034, 62.758, 31.952, 22.798. MALDI-TOF-MS (m/z): found 1092.668 [M + H]+, calcd 1092.325. Anal. Calcd for C73H49N5O2Zn: C, 80.18; H, 4.52; N, 6.40. Found: C, 80.17; H, 4.58; N, 6.33. 2-(1′,3′-Diethyl-2′-propanedioate)-12,13-dibromo5,7,8,10,15,17,18,20-octaphenylporphyrinatozinc(II) (ZnOPPBr2CH(COOEt)2) (6b). Yield: 79% (21 mg, 0.016 mmol). UV−vis (CH2Cl2): λmax(nm) (log ε) 456(5.13), 584(3.92), 632(sh). 1H NMR (500 MHz, CDCl3) δ: 8.28(s, 1H, β-H), 7.87−7.82(m, 4H, meso-o-Ph), 7.74− 7.69(m, 4H, meso-o-Ph), 7.21−7.14(m, 12H, meso-m,p-Ph), 6.84− 6.72(m, 20H, β-Ph), 4.24(s, 1H, −CH), 3.99−3.96(m, 4H, −OCH2), 1.06(t, 3JH,H = 6.5 Hz, 6H, −CH3). MALDI-TOF-MS (m/z): found 1295.192 [M + H] + , calcd 1295.172. Anal. Calcd for C75H52N4O4Br2Zn: C, 69.38; H, 4.04; N, 4.31. Found: C, 69.58; H, 4.15; N, 4.44.

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N.C. thank the Ministry of Human Resource development (MHRD) and Council of Scientific and Industrial Research (CSIR), India, respectively, for senior research fellowship.

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(1) (a) Karpuschkin, T.; Kappes, M. M.; Hampe, O. Binding of O2 and CO to Metal Porphyrin Anions in the Gas Phase. Angew. Chem., Int. Ed. 2013, 52, 10374−10377. (b) Clave, G.; Chatelain, G.; Filoramo, A.; Gasparutto, D.; Saint-Pierre, C.; Le Cam, E.; Pietrement, O.; Guerineau, V.; Campidelli, S. Synthesis of a Multibranched Porphyrin−Oligonucleotide Scaffold for the Construction of DNAbased Nano-architectures. Org. Biomol. Chem. 2014, 12, 2778−2783. (c) Luo, J.; Chen, L.-F.; Hu, P.; Chen, Z.-N. Tetranuclear Gadolinium(III) Porphyrin Complex as a Theranostic Agent for Multimodal Imaging and Photodynamic Therapy. Inorg. Chem. 2014, 53, 4184−4191. (d) Zardi, P.; Caselli, A.; Macchi, P.; Ferretti, F.; Gallo, E. Synthesis of Biologically Relevant Compounds by Ruthenium Porphyrin Catalyzed Amination of Benzylic C−H Bonds. Organometallics 2014, 33, 2210−2218. (e) Beletskaya, I.; Tyurin, V. S.; Tsivadze, A. Y.; Guilard, R.; Stern, C. Supramolecular Chemistry of Metalloporphyrins. Chem. Rev. 2009, 109, 1659−1713. (f) Tanaka, T.; Osuka, A. Conjugated Porphyrin Arrays: Synthesis, Properties and Applications for Functional Materials. Chem. Soc. Rev. 2015, 44, 943− 969. (g) Suslick, K. S.; Rakow, N. A.; Kosal, M. E.; Chou, J. H. The Materials Chemistry of Porphyrins and Metalloporphyrins. J. Porphyrins Phthalocyanines 2000, 4, 407−413. (h) Wang, C.; Dai, Y.; Feng, G.; He, R.; Yang, W.; Li, D.; Zhou, X.; Zhu, L.; Tan, L. J. Addition of Porphyrins to Cigarette Filters To Reduce the Levels of Benzo[a]pyrene (B[a]P) and Tobacco-Specific N-Nitrosamines (TSNAs) in Mainstream Cigarette Smoke. J. Agric. Food Chem. 2011, 59, 7172−7177. (i) Wang, X.-D.; Wolfbeis, O. S. Optical Methods for Sensing and Imaging Oxygen: Materials, Spectroscopies and Applications. Chem. Soc. Rev. 2014, 43, 3666−3761. (j) Harada, R.; Matsuda, Y.; Okawa, H.; Kojima, T. A Porphyrin Nanotube: SizeSelective Inclusion of Tetranuclear Molybdenum−Oxo Clusters. Angew. Chem., Int. Ed. 2004, 43, 1825−1828. (k) Kojima, T.; Harada, R.; Nakanishi, T.; Kaneko, K.; Fukuzumi, S. Porphyrin Nanotubes Based on Self-Assembly of Mo(V)-Dodecaphenylporphyrin Complexes and Inclusion of Mo-Oxo Clusters: Synthesis and Characterization by X-ray Crystallography and Transmission Electron Microscopy. Chem. Mater. 2007, 19, 51−58. (2) (a) Hombrecher, H. K.; Gherdan, V. M.; Ohm, S.; Cavaleiro, J. A. S.; Neves, M. G. P. M. S.; Condesso, M. F. Synthesis and Electrochemical Investigation of β-alkyloxy Substituted Meso-tetraphenylporphyrins. Tetrahedron 1993, 49, 8569−8578. (b) Giuntini, F.; Faustino, M. A. F.; Neves, M. G. P. M. S.; Tome, A. C.; Silva, A. M. S.; Cavaleiro, J. A. S. Synthesis and Reactivity of 2-(porphyrin-2-yl)-1,3dicarbonyl Compounds. Tetrahedron 2005, 61, 10454−10461. (c) Serra, V. I. V.; Pires, S. M. G.; Alonso, C. M. A.; Neves, M. G. P. M. S.; Tome, A. C.; Cavaleiro, J. A. S. Meso-tetraarylporphyrins Bearing Nitro or Amine Groups: Synthetic Strategies and Reactivity Profile. Top. Heterocycl. Chem. 2013, 33, 35−78. (d) Jaquinod, L.; Gros, C.; Olmstead, M. M.; Antolovich, M.; Smith, K. M. First Syntheses of Fused Pyrroloporphyrins. Chem. Commun. 1996, 1475− 1476. (e) Gros, C. P.; Jaquinod, L.; Khoury, R. G.; Olmstead, M. M.; Smith, K. M. Approaches to β-fused Porphyrinoporphyrins: Pyrroloand Dipyrromethaneporphyrins. J. Porphyrins Phthalocyanines 1997, 1, 201−212. (3) (a) Shea, K. M.; Jaquinod, L.; Khoury, R. G.; Smith, K. M. Dodecasubstituted metallochlorins (metallodihydroporphyrins). Chem. Commun. 1998, 759−760. (b) Jaquinod, L.; Gros, C.; Khoury, R. G.; Smith, K. M. A Convenient Synthesis of Functionalized Tetraphenylchlorins. Chem. Commun. 1996, 2581−2582. (c) Shea, K. M.; Jaquinod, L.; Smith, K. M. Dihydroporphyrin Synthesis: New Methodology. J. Org. Chem. 1998, 63, 7013−7021. (d) Taniguchi, M.; Kim, M. N.; Ra, D.; Lindsey, J. S. Synthesis of β-Linked Diporphyrins and Their Homo- and Hetero-Bimetallic Complexes. J. Org. Chem. 2005, 70, 275−285.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02333. UV−vis absorption, emission, and 1H NMR spectra of all synthesized compounds, 13C NMR spectra and MALDITOF mass spectra for all compounds, CV figures, electronic and electrochemical data tables, optimized geometries and FMOs diagrams (PDF)

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REFERENCES

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Phone:+91-1332-284753. Fax: +91-1332-273560. ORCID

Muniappan Sankar: 0000-0001-6667-3759 Author Contributions †

N.G. and N.C.: These authors contributed equally to this work. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We sincerely thank the reviewers for the valuable comments and suggestions to improve our manuscript quality. We are grateful to Prof. Raymond Butcher, Inorganic and Structural Chemistry, Howard University, Washington, D.C., USA, for structural refinements. We thank Ms. Kumari Anshul for her kind help during the synthesis. We are grateful for the financial support provided by Council of Scientific and Industrial Research (01(2694)/12/EMR-II), the Science and Engineering Research Board (SB/FT/CS-015/2012), and the Board of Research in Nuclear Science (2012/37C/61/BRNS). N.G. and L

DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.6b02333 Inorg. Chem. XXXX, XXX, XXX−XXX