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Synthesis and spectroscopic characterization of super-stable rhenium(V)porphyrins
Accepted Manuscript Synthesis and spectroscopic characterization of super-stable rhenium(V)porphyrins N.G. Bichan, E.Yu. Tyulyaeva, I.A. Khodov, T.N. Lomova PII: DOI: Reference:
S0022-2860(14)00004-0 http://dx.doi.org/10.1016/j.molstruc.2013.12.074 MOLSTR 20263
To appear in:
Journal of Molecular Structure
Received Date: Revised Date: Accepted Date:
25 October 2013 25 December 2013 28 December 2013
Please cite this article as: N.G. Bichan, E.Yu. Tyulyaeva, I.A. Khodov, T.N. Lomova, Synthesis and spectroscopic characterization of super-stable rhenium(V)porphyrins, Journal of Molecular Structure (2014), doi: http:// dx.doi.org/10.1016/j.molstruc.2013.12.074
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Synthesis and spectroscopic characterization of super-stable rhenium(V)porphyrins Bichan N. G., Tyulyaeva E. Yu.*, Khodov I. A., Lomova T. N. Federal Government Institution of Sciences G.A. Krestov Institute of Solution Chemistry of Russian academy of Science, Akademicheskaya St., 1 Ivanovo 153045 Russian Federation *Corresponding author: [email protected] Akademicheskaya St., 1 Ivanovo 153045 Russian Federation
Abstract. The preparation of rhenium(V) porphyrin complexes {µ-oxobis[(oxo)(5,10,15,20-tetraphenyl-21H,23H-porphinato)rhenium(V)] [O=ReTPP]2O (1), (oxo)(phenoxo)(2,3,7,8,12,13,17,18-octaethyl-5-monophenyl-21H,23Hporphinato)rhenium(V) O=Re(PhO)MPOEP (2), (cloro)(oxo)(2,3,7,8,12,13,17,18octaethyl-5,15-diphenyl-21H,23H-porphinato)rhenium(V) O=Re(Cl)5,15DPOEP (4), and (oxo)(phenoxo)(2,3,7,8,12,13,17,18-octaethyl-21H,23Hporphinato)rhenium(V) O=Re(PhO)OEP (5)} by the interaction of H2ReCl6 with corresponding porphyrin in boiling phenol is described. (Cloro)(oxo)(2,3,7,8,12,13,17,18-octaethyl-5-monophenyl-21H,23Hporphinato)rhenium(V) O=Re(Cl)MPOEP (3) and (oxo)(chloro)(2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphinato)rhenium(V) O=Re(Cl)OEP (6) have been prepared by the reaction of axial-ligand substitution from (2) and (5), respectively. Compounds (24) were newly synthesized. Characterization of the compounds (1–6) reported herein was made mainly by UV–Visible, IR, 1Н NMR, 1H–1H 2D COSY, 1H–1H 2D DOSY, 1H–1H 2D ROESY, 1H–1H 2D TOCSY spectroscopic techniques and elemental analysis. The stability of the complexes in solutions when exposed to strong acids at the presence of atmospheric oxygen has been estimated. Compounds (24) and (6) show them super-stable since they do not undergo dissociation along M−N bonds in concentrated H2SO4 under heating up to 363 K. Compounds (3) and (4) undergo one-electron oxidation to form stable -cation radicals O=Re(HSO4)P+ under these conditions. The products of the reaction between all studied porphyrins and concentrated H2SO4 were isolated in CHCl3 by reprecipitation onto ice and proved to be rhenium(V) complexes O=Re(HSO4)P.
1. Introduction Rhenium and its compounds are of great interest as a model of radioactive technetium used in photodynamic therapy [1, 2]. Rhenium coordination compounds have practical application because of their high catalytic and biological activity in various processes [35]. A large number of studies are devoted to porphyrinoids and phthalocyanines of rhenium in various oxidation states [6]. Along with other similar compounds with metal cations of high oxidation states, rheniumporphyrins exhibit a variety of coordination properties and structures together with high stability so they are promising in the development of technical catalyst systems similar to rhodium- and iridiumporphyrin systems reported earlier [7]. To date the systematic studies of porphyrin complexes of rhenium in the 5+ oxidation state reported in [8, 9] are the most important. The spectral characteristics of rhenium(V) complexes with octaethylporphyrin and a variety of tetraarylporphyrins ReO(P)X (X = anion) prepared by the reaction of ReCl5 with porphyrin (H2P) in refluxing trichlorobenzene have been reported by Buchler et al. [8b]. Homborg et al. [9c] represents crystal structure of hexa-coordinated ReV phthalocyaninates
(P
is
phthalocyanine
dianion
Pc)
and
ReV
tetraphenylporphyrinates (P is 5,10,15,20-tetraphenyl-21H,23H-porphyrin dianion TPP) ReO(P)X synthesized in diglyme using Re2O7. In the papers mentioned above the µ-oxo-dimer species [ReO(P)]2O are the result of either alcoholysis of ReO(P)X and ReCl3(P) or dissolving of mononuclear species in pyridine. Earlier we have reported [10] an efficient method for the direct obtaining of [ReO(TPP)]2O which is a convenient starting material for a variety of mononuclear species. We have also shown [11] that the stability of the coordination center of the ReO(TPP)X sharply depends on the nature of a second acido ligand X. In this connection our study is focused on the synthesis and identification of some porphyrin derivatives of rhenium(V) including new ones, which do not undergo MN bond dissociation in concentrated sulfuric acid under heating up to
363 K, in order to obtain super-stable porphyrin compounds with high opportunity of practical applications. Since oxidation states of rhenium cations in metalloporphyrins obtained during a one-pot synthesis can be varied, the separation and identification of complexes with different structures are often hampered. Because of the nature of metalloporphyrins the proton resonances are gathered in the aromatic region of 59 ppm, that is why and 2-D NMR spectroscopy along with other spectroscopic methods is used conveniently in order to detect the impurities and confirm individual compounds. The replacement of axial ligands and substituents at various positions of the macrocycle as well as dimerization result in clearly assignable cross-peaks in the 2-D NMR spectra. Therefore, this method can be used as a starting point for further research of the structure of new compounds.
2. Experimental (1) [O=ReTPP]2O (2) O=Re(PhO)MPOEP: R1 = phenyl, R2 = H, X = OPh (3) O=Re(Cl)MPOEP: R1 = phenyl, R2 = H, X = Cl (4) O=Re(Cl)5,15DPOEP: R1 = R2 = phenyl, X = Cl (26)
(5) O=Re(PhO)OEP: R1 = R2 = H, X = OPh (6) O=Re(Cl)OEP: R1 = R2 = H, X = Cl
2.1. Preparation of (1) [10] Yield: 75 %. UV-Visible (CHCl3), λmax, nm (log ε): 620 (sh), 582 (4.51), 461 (5.34), 333 (4.88). IR (solid random layer, ν, cm–1): phenyl groups, 702, 754 (γ C– H); 1072, 1179 (δ C–H); 1485, 1575, 1597 (ν C=C); 3022, 3056 (ν C–H); pyrrole groups, 801 (γ C–H); 1018 (C3–C4, ν C–N, δ C–H); 1341 (ν C–N); 1440 (ν C=N); coordination centre, 463 (Re–N); 723, 854 (Re–O–Re); 961 (Re=O).
1
H NMR (CDCl3, δ, ppm, J, Hz): 9.07 (d, 8Hо, J = 7.6), 8.79 (s, 16Hβ), 8.01
(t, 8Hm, J = 7.6), 7.6 (t, 8Hp, J = 7.6), 7.47 (d, 8Hо’, J = 7.6), 7.04, 6.87 (t, t, 8Hm’, J = 7.6, J = 7.6). 1
H NMR (C6D6, , ppm, J, Hz): 9.18 (s, 16Hβ), 8.1 (d, 8Hо, J = 7.1), 8.0 (t,
8Hо’, J = 7.1), 7.47 (m, 16Hm,p, J = 7.6), 6.85 (t, 2Hm’, J = 7.3), 6.67 (t, 2Hm’, J = 7.3), 6.42 (d, 2Hp’, J = 8.3), 6.32 (d, 2Hp’, J = 8.6). 1
H NMR (CD3COOD, , ppm, J, Hz), monomer species O=Re(OAc)TPP:
9.51 (s, 8Hβ), 8.51 (d, 4Ho, J = 7.3), 8.37 (d, 4Ho, J = 7.3), 7.9 (m, 8Hm, 4Hp). 1
H NMR (D2SO4, δ, ppm): 9.13 (m, 8Hβ), 8.52, 8.23 (t, t, 8Hо), 8.06 (t, 8Hm,
1
H–1H 2D COSY (C6D6, , ppm, J, Hz): 8.1 (d, 8Hо, J = 7.1) − 7.47 (m,
4 Hp). 16Hm,p), 8.0 (t, 8Hm, J = 7.1) − 7.47 (m, 16Hm,p), 6.85 (m, 2Hm’, J = 7.3) − 6.42 (d 2Hp, J = 8.3), 6.67 (t, 2H m’, J = 7.3) − 6.32 (d 2Hp,, J = 8.6). 1
H–1H 2D COSY (CD3COOD, , ppm, J, Hz): O=Re(OAc)TPP: 8.51 (d,
4Ho, J = 7.32) 7.93 (m, 12Hm,p), 8.37 (d, 4Ho, J = 7.3) 7.93 (m, 12Hm,p). For C88H56N8O3Re2 anal. calcd. (%): C, 64.22; H, 3.41; N, 6.81. Found (%): C, 63.14; H, 3.52; N, 5.59.
2.2. Preparation of (2) 2,3,7,8,12,13,17,18-octaethyl-5-monophenyl-21H,23H-porphyrin (H2MPOEP) and H2ReCl6 in 1 : 5 molar ratio were refluxed in phenol at 454 K for 5 h. After reaction completion detected by a disappearance of H2MPOEP band and by termination of changes in the UV-Visible spectrum of the reaction mixture in chloroform, the contents of the reaction vessel was cooled and, after dilution with water, the products were extracted into chloroform. The solution was repeatedly washed with warm water to remove phenol, concentrated by partly evaporation of the solvent, and chromatographed on a column with Al2O3 (Brockman activity II) using CH2Cl2. This gave two zones namely a pink zone and a diffuse green-brown zone. The substances isolated from the second zones were chromatographed once
again on a silica gel (40/100 Chemapol) column, elution being performed first with benzene
and
then
with
CHCl3
C2H5OH
mixture (1
:
1).
Complex
O=Re(PhO)MPOEP was in the green zone. Yield: 75 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 595 (3.64), 477 (4.02), 348 (4.38). IR (KBr, ν, cm–1): phenyl groups, 707, 741 (γ C–H); 1074, 1101 (δ C–H); 1546, 1600, 1631 (ν C=C); 3024, 3059 ( C–H); pyrrole groups, 799 (γ C–H); 1058 (C3–C4, ν C–N, δ C–H); 1378 (ν C–N); 1464 (ν C=N); alkyl groups: 1340, 1401 (δ C–H); methine groups: 1253, 1269 (δ C–H), 842, 853 ( C–H); coordination centre, 464 (Re–N); 946 (Re=O); 668 (Re–O); 1486 (OPh). 1
H NMR (CDCl3, δ, ppm, J, Hz): 10.70 (m, 3H, meso); 8.45 (d, 1Hо, J =
6.7), 8,35 (d, 1Hо, J = 7.3), 7.79 (m, 2Hm), 7.95 (d, 1Hp, J = 7.3), 4.28, 3.84, 3.74, 3.67, 3.58 (m, s, s, s, s, 16 Н, CH2), 1.57, 1.28, 0.90 (s, s, m 24 Н, CH3). 1
H NMR (CD3COOD, δ, ppm, J, Hz): 11.06 (m, 3H, meso); 8.50 (t, 1Hо ,J =
6.7), 8.31 (t, 1Hо, J = 7.3), 7.88 (m, 2Hm), 7.62 (t, 1Hp); 4.41, 4.26, 3.95, 3.87, 3.71, 3.51 (m, m, s, s, s, s 16 Н, CH2), 1.32, 0.92 (m, m 24 Н, CH3); 7.07 (s, 2Ho (OPh)), 6.93 (s, 2Hm (OPh)), 6.83 (s, 1Hp (OPh)). For С48H53N4O2Re anal. calcd. (%): C, 63.79; H, 5.87; N, 6.20. Found (%): C, 64.57; H, 6.14; N, 5.84.
2.3. Preparation of (3) Gaseous HCl was passed through the solution of 2 in dichloromethane within 10 min. Solution color was changed from yellow-green to deep wine-red. Yield: 100 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 620 (3.67), 520 (4.13), 351 (4.73). IR (KBr, ν, cm–1): phenyl groups, 705, 740 (γ C–H); 1059, 1097 (δ C–H`); 1547, 1599, 1630 (ν C=C); 3024, 3060 (ν C–H); pyrrole groups, 801 (γ C–H); 1059 (C3–C4, ν C–N, δ C–H); 1383 (ν C–N); 1464 (ν C=N); alkyl groups: 1340, 1401 (δ C–H); methine groups: 1261 (δ C–H), 865, 908 ( C–H); coordination centre: 464 (Re–N); 946 (Re=O).
1
H NMR (CDCl3, δ, ppm, J, Hz): 10.88 (m, 3H, meso); 8.36 (t, 1Hо, J = 7.0),
7.92 (t, 1Hо, J = 7.6), 7.76 (m, 2Hm), 7.55 (q, 1Hp, J = 7.3), 4.27, 3.87, 3.79, 2.94 (m, m, m, m 16 Н, CH2), 2.08, 1.34, (t, m 24Н, CH3). 1
H–1H 2D COSY (CDCl3, , ppm, J, Hz): 8.36 (t, 1Hо, J = 7.0) − 7.76 (m,
2Hm), 7.92 (t, 1Hо, J = 7.6) − 7.76 (m, 2Hm), 7.76 (m, 2Hm) − 7.55 (q, 1Hp, J = 7.3); 4.27 (m, 6H, СH2) − 2.08 (t, 8H, CН3), 3.87 (m, 6H, СH2) − 1.34 (m, 16H, CН3), 3.79 (m, 4H, СH2) − 1.34 (m, 16H, CН3), 2.94 (m, 2H, СH2) − 1.34 (m, 16H, CН3). 2.4. Preparation of (4) Compound (4) was prepared and purified by the same procedure described above for (2), but H2MPOEP was replaced by 2,3,7,8,12,13,17,18-octaethyl-5,15diphenyl-21H,23H-porphyrin (H2DPOEP). CHCl3 was used in place of CH2Cl2 in chromatography. Time of the reaction was 6 h. Yield: 75 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 625 (3.70), 525 (4.15), 354 (4.75). IR (KBr, ν, cm–1): phenyl groups, 702, 742 (γ C–H); 1073, 1125 (δ C–H); 1491, 1532, 1600 (ν C=C); 3022, 3059 (ν C–H); pyrrole groups, 800 (γ C–H); 1062 (C3–C4, ν C–N, δ C–H); 1384 (ν C–N); 1465 (ν C=N); alkyl groups: 1341, 1400 (δ C–H); methine groups: 1274 (δ C–H), 838, 861 ( C–H); coordination centre: 467 (Re–N); 962 (Re=O). 1
H NMR (CDCl3, δ, ppm, J, Hz): 10.82 (m, 2H, meso); 8.29 (d, 2Hо, J =
8.1), 8.20 (d, 2Hо, J = 8.1), 7.91 (m, 2Hм), 7.85 (m, 2Hм), 7.73 (q, 1Hp, J = 7.3), 7.55 (q, 1Hp, J = 7.3), 4.20, 2.70 (m, br. s 16 Н, CH2), 1.95, 1.56 (t, br. s, 24Н, CH3). 1
H–1H 2D COSY, (CDCl3, , ppm, J, Hz): 8.29 (d, 2 Hо, J = 8.1) − 7.91 (m,
2Hm), 8.20 (d, 2Hо, J = 8.0) − 7.85 (m, 2Hm), 7.91 (m, 2Hм) − 7.73 (q, 1Hp, J = 7.3), 7.85 (m, 2Hm) − 7.55 (q, 1Hp, J = 7.3), 4.20 (m, 10H, СH2) − 1.95 (t, 10 H, CН3), 4.20 (m, 10H, СH2) − 1.56 (br. s, 14H, CН3), 2.70 (br. s, 6H, СH2) − 1.95 (t, 10H, CН3). For С36H44N4OClRe anal. calcd. (%): C, 62.51; H, 5.64; N, 5.41. Found (%): C, 6.08; H, 5.45; N, 61.05.
2.5. Preparation of (5) Compound (5) was prepared and purified by the same procedure described above for (2), but H2MPOEP was replaced by 2,3,7,8,12,13,17,18-octaethyl21H,23H-porphyrin (H2OEP). Time of the reaction was 9 h. Yield: 70 %. UV-Visible (CH2Cl2), λmax, nm: 613, 580, 469, 343. IR (KBr, ν, cm–1): pyrrole groups, 747 (γ C–H); 1057 (C3–C4, ν C–N, δ C– H); 1376 (ν C–N); 1468 (ν C=N); alkyl groups: 1317 (δ C–H); methine groups: 1223, 1273 (δ C–H), 844, 873 ( C–H); coordination centre, 454, 466 (Re–N); 959 (Re=O); 670 (Re–O); 1451, 1589 (OPh). 1
H NMR (C6D6, δ, ppm): 10.77 (m, 4H, meso), 9.51 (m, 8H, meso); 4.43 (m,
32Н, CH2), 4.03 (m, 16Н, CH2), 1.83 (m, Н, CH3); 7.04 (s, 2Ho (OPh)), 6.95 (s, 2Hm (OPh)), 6.85 (s, 1Hp (OPh)). 1
H–1H 2D COSY (C6D6, , ppm): 4.43 (m, 32Н, СH2) − 1.83 (m, 16Н, CН3),
4.03 (m, СH2) − 1.83 (m, CН3). For С42H49N4O2Re anal. calcd. (%): C, 60.94; H, 5.93; N, 6.77. Found (%): C, 62.17; H, 6.31; N, 7.15. 2.6. Preparation of (6) Gaseous HCl was passed through the solution of (5) in dichloromethane within 10 min. Solution color was changed from yellow-green to pink. Yield: 100 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 620 (3.90), 518 (4.30), 347 (4.92). IR (KBr, ν, cm–1): pyrrole groups, 747 (γ C–H); 1057 (C3–C4, ν C–N, δ C– H); 1376 (ν C–N); 1468 (ν C=N); alkyl groups: 1316 (δ C–H); methine groups: 1223, 1271 (δ C–H); 846, 854, 871 ( C–H); coordination centre: 467 (Re–N); 965 (Re=O). 1
H NMR (CDCl3, δ, ppm): 10.94 (m, 4H, meso); 4.36 (m, 16 Н, CH2), 2.13
(m, 24 Н, CH3).
1
H–1H 2D COSY (CDCl3, , ppm): 4.36 (m, 16 Н, СH2) − 2.13 (m, 24 Н,
СH3). Solid amorphous samples of (1−6) were isolated from solutions by solvent evaporation at room temperature. 2.7. Spectroscopy The UV-Visible spectra were measured on Agilent 8453 UV-Visible spectrophotometers; IR spectra were recorded on a VERTEX 80v spectrometer; elemental analysis was performed on a CHNSO Analyzer Flash EA 1112 Series. The solid layers of complexes for IR spectroscopy were formed by evaporation of the CHCl3 solvent from a solution of the complex on a silicon plate. All NMR experiments were performed on a Bruker Avance III-500 NMR spectrometer equipped with a 5 mm probe using standard Bruker TOPSPIN Software. Temperature control was performed using a Bruker variable temperature unit (BVT-2000) in combination with a Bruker cooling unit (BCU-05) to provide chilled air. Experiments were performed at 298 K without sample spinning. 1
H NMR (500 MHz) spectra were recorded using 90° pulses and relaxation
delay of 1 s; spectral width was 19.13 ppm; 128 scans were acquired. Proton NMR is relative to deuterium solvent peaks. The two-dimensional Double Quantum Filtered Correlation Spectroscopy (2D DQF-COSY) [12] spectra was acquired with a 19.13 ppm spectral window in the direct dimension F1 with 2048 complex data points and a 19.13 ppm spectral window in the indirect dimension F2 with 256 complex points. The spectra were acquired with 16 scans and relaxation delay of 2 s. Two-dimensional Total Correlation Spectroscopy (2D ge-TOCSY) [13] and Rotating frame nuclear Overhauser effect Spectroscopy (2D ge-ROESY) [14] experiments were performed with pulsed filtered gradient techniques. The spectra were recorded in a phasesensitive mode using Echo/Antiecho-TPPI gradient selection with 2048 points in the F2 direction and 512 points in the F1 direction. Spin-lock delay values for 2D
ge-ROESY and 2D ge-TOCSY were 200 msec. The spectra were acquired with 6472 scans and relaxation delay of 2 s. The two-dimension Diffusion Order Spectroscopy (2D DOSY) spectra were recorded with PGSTE pulse sequence using a bipolar gradient pulses and the insertion of a supplementary delay (LED) [15]. The PGSTE sequence was used with a diffusion delay of 0.1 s, a total diffusion-encoding pulse width of 5 ms. For each of 32 gradient amplitudes, 64 transients of 16384 complex data points were acquired. 3. Results and discussion Rhenium(V) complexes with H2OEP and its meso-phenyl substituted porphyrins were prepared according to Scheme 1.
Scheme 1. Synthesis of rhenium(V) octaethylporphyrin complexes: R = C2H5; *-in an amount of impurity
3.1 UV–Visible absorption spectra There is a weak absorption at ~350 nm in the UV–Visible spectrum of the μoxo dimer complex (1) [10]. The view of UV–Visible spectra of (24) and (6) (Fig. 1) characterize these compounds as the monomeric species. Unlike the absorption spectra of μ-oxo dimer the UV–Visible spectra of monomeric species demonstrate the intense B(0,0) band at 350 nm. UV–Visible absorption
spectroscopic changes during the reversible transfer of the monomer and μ-oxodimer forms were used for a quantitative study of the reaction of compound (1) with AcOH in benzene [16]. Similarly, the electronic absorption spectra of individual complexes (26) are differed in the presence of the additional bands in the range of 300800 nm in particular charge transfer bands at max=440480 nm [17]. In the UV–Visible spectra of (5) in C6H6 and CH2Cl2 (Fig. 1 curves 1, 2) the Soret band is more intense compared with the charge-transfer band. This fact also suggests the predominance of the monomeric species. However, the intensity difference of these bands is decreased in passing from CH2Cl2 (Fig. 1, curves 2) to benzene (Fig. 1, curves 1). Since benzene promotes to the μ-oxo-dimer formation [18], on the basis of 2D NMR study we can certainly say that complex (5) exists as an equilibrium mixture of monomeric and μ-oxo-dimer forms in benzene. The position of the bands in the UV–Visible spectra of the resulting compounds depends on the nature of the macrocyclic and axial ligands. Thus, the peaks maxima in the spectrum of compound (2) are red-shifted by 58 nm respectively from the spectrum of compound (5). The band hypsochromic shift of the complexes with MO bond is associated with its higher covalence compared with the MCl bond. In the case of Cl-containing compounds (3), (4) and (6) the introduction of the phenyl substituents in the meso-positions of the macrocycle results in the red shift of the most of the bands in the spectra of the compounds. These spectra exhibit Soret band respectively at 351, 354 and 347 nm, and the charge transfer band – at 520, 525 and 518 nm respectively. The similar dependence of UV–Visible spectra on the number of meso-phenyl substituents in the macrocycle is typical for octaethyl-substituted porphyrins of manganese(III) [19]. The Soret band repositioning after replacing the axial ligand OPh with Cl is ~5 nm, while the charge transfer band in this case is red-shifted more significantly - about 45–50 nm. The same tendency is observed in the case of oxo-complexes of molybdenum(V) with H2TPP while going from O=Mo(OH)TPP to O=Mo(Cl)TPP [20].
3.2 Confirmation of structure by IR and NMR studies Regardless of the nature of the singly-charged axial ligand the main intense bands corresponding to the stretching vibrations of macrocyclic ligands bonds are found in the IR spectra of resulting octaethyl-porphyrin complexes (Experimental). Additionally, the spectra contain the bands proving the coordination nature of these compounds. Thus, bands with frequencies 464, 470, 467, 466 and 467 cm–1 can be attributed to the vibrations of the Re–N bonds in (2), (3), (4), (5) and (6), respectively. The maxima positions are practically independent on the nature of the singly-charged axial ligand as well as on the number of phenyl substituents in the porphyrin ligand. This indicates the same coordination type and electronic state of the coordination centre of investigated rhenium(V) complexes. An additional band at 454 сm–1 and a weak signal at 619 сm–1 are observed in the range of stretching vibrations of Re–N bonds in the IR spectrum of (5). These bands are analogous to the signals in the IR spectrum of compound (1) but absent in the IR spectrum of (6). A strong absorption at 650550 cm1 has been shown to attribute to the vibrations of MoOMo bonds in [O=MoTPP]2O [18]. This means that at the atmosphere conditions compound (5) in KBr contains the impurity of μ-oxo dimer species at very small equilibrium concentration according to the low intensity of signal in the IR spectrum. 1
Н NMR spectrum of compound (5) in C6D6 (Fig. 2) exhibits two signals of
meso-protons at 10.77 and 9.51 ppm. The absence of correlation between these signals in the 1H–1H 2D COSY (Fig. 3) and 1H–1H 2D ROESY spectra in C6D6 indicates that they belong to different compounds. Furthermore, these data are supported by a 1H–1H 2D DOSY spectrum of the compound (5), where the separation according to the diffusion coefficients also demonstrated the presence of two compounds in solution was found. According to [20] and signal assignment in 1H NMR of compound (1) (Experimental) the signals of meso-protons at 10.77 ppm can be assigned to the monomeric species of the
complex (5), whereas up-shifted signal to its μ-oxo-dimer [O=ReOEP]2O, which is present in small amount and is in equilibrium with (5). It should be noted that 1H–1H 2D DOSY spectrum of compound 6 obtained by passing of gaseous HCl through the solution of (5) in dichloromethane (Fig. 4), is the spectrum of the individual monomeric species without μ-oxo-dimer impurity. The individuality of compounds (24) and (6) reported herein and the absence of dimer species of these compounds in solutions were confirmed by spectroscopic techniques: 1Н ЯМР, 1H–1H 2D DOSY, 1H–1H 2D COSY, 1H–1H 2D ROESY spectroscopic studies (Experimental). There are cross-peaks corresponding only to the interaction of −СН2− and −СН3 protons in the 1H–1H 2D COSY of 6 in CDCl3. In the 1H–1H 2D COSY spectra of (3) and (4) the correlations between Hо, Hm and Hp in meso-phenyl substituents of macrocycle appear. Additional signals, which can be attributed to the protons of the axial ligands are not detected. In 1Н NMR (Fig. 2a), 1H–1H 2D COSY (Fig. 3) and 1H–1H 2D ROESY spectra (Fig. 5) the presence of −OPh in compounds (2) and (5) is supported by the availability of proton signals with the chemical shifts closed to those of the o-, mand p-protons in the phenol molecule [21]. The intense bands corresponding to the stretching vibrations of bonds in phenoxy-ligand (1451, 1589 and 1486 cm–1) and Re–O bond (670 and 668 сm–1) in the IR spectra of compound (2) and (5) (Fig. 6а) also demonstrate the presence of axial-bounding −OPh in the first coordination sphere of the complexes. At the same time, the bands mentioned above do not appear in the IR spectra of compounds (3), (4) and (6) (Fig. 6b). Axial-bounding oxo-ligand in the first coordination sphere can be fixed by a signal of Re=O vibrations at 950 cm–1 in the IR spectra of all studied compounds (Experimental). 3.3 Stability in solutions
In order to estimate the stability in solutions, the synthesized complexes were exposed to strong acids, atmospheric oxygen and high temperatures. Rhenium(V)porphyrins exhibit high stability for long time without changing in organic solvents. Compounds (24) and (6) are stable along M−N bonds in 18.5M H2SO4 under heating up to 363 K. The compounds were reprecipitated onto ice from sulfuric acid solutions after heating under mentioned temperature within 6 h and they UV-Visible spectra in CH2Cl2 (Table 1) did not exhibit the bands of noncoordinated H2TPP or its protonated species H4TPP2+. These spectra are similar to spectra of the investigated compounds in CH2Cl2, but the charge transfer band is shifted to 498 nm. The analogy of the compound spectra in CH2Cl2 both when dissolved and after reprecipitation from sulfuric acid indicates the same coordination type of the compounds. According to experimental data (section 2) the position of the charge transfer band in the O=Re(X)P spectra depends on the nature of axial ligand X. The spectrum of compound (3) in CH2Cl2 exhibits this band at 520 nm, while the transition to the compound (2) with −OPh as axial ligand results in this band at 477 nm. Absorption maximum in the spectra of O=Mo(Cl)TPP, O=Mo(OPh)TPP and O=Mo(OH)TPP are respectively at 500, 475 and 450 nm, according to [18, 22]. When compounds
(24) and (6) are exposed to hot sulfuric acid, HSO4 ions, which are in large excess in solution, substitute the axially coordinated monodentate ligands with formation of O=Re(HSO4)P, as well as in the case of the compound (1) [11]. That’s why all the reprecipitated complexes have the charge transfer band at 498 nm in their spectra. The appearance of a new stretching vibration band of metaloxygen bond at 670 cm1 in the IR spectrum (demonstrated at Fig. 7 using the compound (3) as an
example) is also evidence of the HSO4 presence in the coordination sphere of the compounds resulted in the reaction with H2SO4. Besides mentioned maintaining of the type spectra of the complexes after their extraction from sulfuric acid in the unchanged state, spectra of compounds (3)
and (4) in sulfuric acid sharply vary within the time (Table 1). It is typical for solutions of the complexes in 16.8–18.2M H2SO4 at 318 ÷ 348 K. A new UV– Visible spectrum of the resulting compound is identified as the spectrum of metalloporphyrin, which is one-electron oxidized along the porphyrin -ring system (Scheme 2) according to [23–25].
Scheme 2. Oxidation of compound 3 (R1 = phenyl, R2 = H) and compound 4 (R1 = R2 = phenyl) in aerated H2SO4. R = C2H5 The chemical generation of the one-electron oxidized species of metalloporphyrins under the expose of oxygen dissolved in H2SO4 (solubility of O2 in 17.5M H2SO4 is 27.5 lm3 [26]) according to equation analogous to Scheme 2, has been studied earlier for complexes of H2TPP with Ru(IV) [24] and Pd(II) [25]. UV-Visible spectra have been found to be the best feature of the radical species of metalloporphyrins [23] therefore identification of -cation radicals was carried out using the method of electron absorption spectroscopy. The addition of the second phenyl substituent at meso-position of the macrocycle going from (3) to (4) is followed by the saddle strain of macrocycle [27, 28], but does not result in significant difference in the properties of these compounds (Table 1). The oxidation ability of complexes in this case is provided by the presence of eight electron-donor -alkyl groups in -ring systems of both compounds. The UV–Visible spectra of compounds (2) and (6) in concentrated H2SO4 do not exhibit the bands of -cation radical. The stability to oxidation along macrocycle in the case of the compound (2) is conditioned by stronger covalent binding ReO compared with ReCl (in compound (3)) preventing the
displacement of OPh and its substitution on the HSO4 (see eq. 1). The latter
becomes possible, as well as in the case of the unsubstituted at the meso-positions compound (6), only under the heating in an acidic medium with pouring onto ice
when the instant formation of the complexes with axial ligand HSO4 takes place (Table 1). 4. Conclusions Thus, we have described the preparation of rhenium(V) porphyrin complexes by the reaction of H2ReCl6 with - 5,10,15,20-tetraphenyl-21H,23Hporphyne H2TPP, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyne H2OEP and its 5-phenyl and 5,15-diphenyl-meso-derivatives, H2MPOEP and H25,15DPOEP. The compounds were characterized by a variety of spectroscopic techniques. The monomer porphyrin complexes of rhenium(V) are super-stable along M−N bonds in proton-donating solutions (AcOH, AcOHH2SO4, H2SO4–H2O). In acid media, they exist as the initial species or undergo the reactions of substitution of the corresponding acid anion for the anion axial ligand. Together with the macrocycle variation such transformation of the coordination sphere results in significant changes in physical and chemical properties of rhenium(V)porphyrins. Under the convenient electron-excessing state of the macrocycle, the complexes with hydrosulfate ion undergo one-electron oxidation, which occur in aerated sulfuric acid forming a stable -cation radicals. The stability of the compounds, the high activity of the axial positions in the ligand substitution reactions and the possibility of oxidation along the macrocycle, which have been confirmed in this report, promise great prospects for practical use of the complexes in the catalysis of the redox processes as well as in the formation of self-assembled donor-accepter complexes for biomedicine and optoelectronics.
Acknowledgements. Financial support was from grants of the President of the Russian Federation for support of scientific schools NSh-3993.2012.3 and the Russian Foundation for Basic Research, Projects No. 12-03-00775 and 12-03-00967.
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Copper(II)
Figure captions
Fig. 1. UV–Visible spectra of 5 in C6H6 (1) and CH2Cl2 (2); 6 in CH2Cl2 (3) Fig. 2. 1Н NMR spectra of compound 5 in C6D6 (a); compound 6 in CDCl3 (b) (*Hmeso signal for μ-oxo dimer species of 5) Fig. 3. 1H–1H 2D COSY of compound 5 in C6D6 Fig. 4. 1H–1H 2D DOSY of compound 6 in C6D6 Fig. 5. 1H–1H 2D ROESY of compound 5 in C6D6 Fig. 6. IR spectra of compounds 5 (a) and 4 (b) in KBr Fig. 7. IR spectra of compound 3 in KBr before (a) and after (b) the reaction with 18.2M H2SO4
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Table 1. Absorption bands (max, nm) in UV-Visible spectra of compounds 24 and 6 CH2Cl2 H2SO4 CH2Cl2, dissolution after 6 h after under 338 K reprecipitation 498, 350 498, 350a 480, 368b 625, 525, 354 860, 465, 333 515, 319 500, 350a 4 467, 368b 620, 518, 347 800, 453, 325 453, 325c 498, 350 6 (a) - after 1 h; (b)- -cation radical in C2H5OH; (c) - in 1 min after dissolution 2 3
595, 477, 348 620, 520, 351
875, 460, 327 875, 450, 327
875, 460, 327 515, 319
Highlights
1. Rhenium(V) porphyrins were synthesized. 1
2. UV–Visible, IR, Н, 2D NMR spectra for title compounds were studied. 3. The compounds do not undergo MN bonds dissociation in strong acids. 4. The compounds form the stable -cation radicals O=Re(HSO4)P . +
S0022-2860(14)00004-0 http://dx.doi.org/10.1016/j.molstruc.2013.12.074 MOLSTR 20263
To appear in:
Journal of Molecular Structure
Received Date: Revised Date: Accepted Date:
25 October 2013 25 December 2013 28 December 2013
Please cite this article as: N.G. Bichan, E.Yu. Tyulyaeva, I.A. Khodov, T.N. Lomova, Synthesis and spectroscopic characterization of super-stable rhenium(V)porphyrins, Journal of Molecular Structure (2014), doi: http:// dx.doi.org/10.1016/j.molstruc.2013.12.074
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Synthesis and spectroscopic characterization of super-stable rhenium(V)porphyrins Bichan N. G., Tyulyaeva E. Yu.*, Khodov I. A., Lomova T. N. Federal Government Institution of Sciences G.A. Krestov Institute of Solution Chemistry of Russian academy of Science, Akademicheskaya St., 1 Ivanovo 153045 Russian Federation *Corresponding author: [email protected] Akademicheskaya St., 1 Ivanovo 153045 Russian Federation
Abstract. The preparation of rhenium(V) porphyrin complexes {µ-oxobis[(oxo)(5,10,15,20-tetraphenyl-21H,23H-porphinato)rhenium(V)] [O=ReTPP]2O (1), (oxo)(phenoxo)(2,3,7,8,12,13,17,18-octaethyl-5-monophenyl-21H,23Hporphinato)rhenium(V) O=Re(PhO)MPOEP (2), (cloro)(oxo)(2,3,7,8,12,13,17,18octaethyl-5,15-diphenyl-21H,23H-porphinato)rhenium(V) O=Re(Cl)5,15DPOEP (4), and (oxo)(phenoxo)(2,3,7,8,12,13,17,18-octaethyl-21H,23Hporphinato)rhenium(V) O=Re(PhO)OEP (5)} by the interaction of H2ReCl6 with corresponding porphyrin in boiling phenol is described. (Cloro)(oxo)(2,3,7,8,12,13,17,18-octaethyl-5-monophenyl-21H,23Hporphinato)rhenium(V) O=Re(Cl)MPOEP (3) and (oxo)(chloro)(2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphinato)rhenium(V) O=Re(Cl)OEP (6) have been prepared by the reaction of axial-ligand substitution from (2) and (5), respectively. Compounds (24) were newly synthesized. Characterization of the compounds (1–6) reported herein was made mainly by UV–Visible, IR, 1Н NMR, 1H–1H 2D COSY, 1H–1H 2D DOSY, 1H–1H 2D ROESY, 1H–1H 2D TOCSY spectroscopic techniques and elemental analysis. The stability of the complexes in solutions when exposed to strong acids at the presence of atmospheric oxygen has been estimated. Compounds (24) and (6) show them super-stable since they do not undergo dissociation along M−N bonds in concentrated H2SO4 under heating up to 363 K. Compounds (3) and (4) undergo one-electron oxidation to form stable -cation radicals O=Re(HSO4)P+ under these conditions. The products of the reaction between all studied porphyrins and concentrated H2SO4 were isolated in CHCl3 by reprecipitation onto ice and proved to be rhenium(V) complexes O=Re(HSO4)P.
1. Introduction Rhenium and its compounds are of great interest as a model of radioactive technetium used in photodynamic therapy [1, 2]. Rhenium coordination compounds have practical application because of their high catalytic and biological activity in various processes [35]. A large number of studies are devoted to porphyrinoids and phthalocyanines of rhenium in various oxidation states [6]. Along with other similar compounds with metal cations of high oxidation states, rheniumporphyrins exhibit a variety of coordination properties and structures together with high stability so they are promising in the development of technical catalyst systems similar to rhodium- and iridiumporphyrin systems reported earlier [7]. To date the systematic studies of porphyrin complexes of rhenium in the 5+ oxidation state reported in [8, 9] are the most important. The spectral characteristics of rhenium(V) complexes with octaethylporphyrin and a variety of tetraarylporphyrins ReO(P)X (X = anion) prepared by the reaction of ReCl5 with porphyrin (H2P) in refluxing trichlorobenzene have been reported by Buchler et al. [8b]. Homborg et al. [9c] represents crystal structure of hexa-coordinated ReV phthalocyaninates
(P
is
phthalocyanine
dianion
Pc)
and
ReV
tetraphenylporphyrinates (P is 5,10,15,20-tetraphenyl-21H,23H-porphyrin dianion TPP) ReO(P)X synthesized in diglyme using Re2O7. In the papers mentioned above the µ-oxo-dimer species [ReO(P)]2O are the result of either alcoholysis of ReO(P)X and ReCl3(P) or dissolving of mononuclear species in pyridine. Earlier we have reported [10] an efficient method for the direct obtaining of [ReO(TPP)]2O which is a convenient starting material for a variety of mononuclear species. We have also shown [11] that the stability of the coordination center of the ReO(TPP)X sharply depends on the nature of a second acido ligand X. In this connection our study is focused on the synthesis and identification of some porphyrin derivatives of rhenium(V) including new ones, which do not undergo MN bond dissociation in concentrated sulfuric acid under heating up to
363 K, in order to obtain super-stable porphyrin compounds with high opportunity of practical applications. Since oxidation states of rhenium cations in metalloporphyrins obtained during a one-pot synthesis can be varied, the separation and identification of complexes with different structures are often hampered. Because of the nature of metalloporphyrins the proton resonances are gathered in the aromatic region of 59 ppm, that is why and 2-D NMR spectroscopy along with other spectroscopic methods is used conveniently in order to detect the impurities and confirm individual compounds. The replacement of axial ligands and substituents at various positions of the macrocycle as well as dimerization result in clearly assignable cross-peaks in the 2-D NMR spectra. Therefore, this method can be used as a starting point for further research of the structure of new compounds.
2. Experimental (1) [O=ReTPP]2O (2) O=Re(PhO)MPOEP: R1 = phenyl, R2 = H, X = OPh (3) O=Re(Cl)MPOEP: R1 = phenyl, R2 = H, X = Cl (4) O=Re(Cl)5,15DPOEP: R1 = R2 = phenyl, X = Cl (26)
(5) O=Re(PhO)OEP: R1 = R2 = H, X = OPh (6) O=Re(Cl)OEP: R1 = R2 = H, X = Cl
2.1. Preparation of (1) [10] Yield: 75 %. UV-Visible (CHCl3), λmax, nm (log ε): 620 (sh), 582 (4.51), 461 (5.34), 333 (4.88). IR (solid random layer, ν, cm–1): phenyl groups, 702, 754 (γ C– H); 1072, 1179 (δ C–H); 1485, 1575, 1597 (ν C=C); 3022, 3056 (ν C–H); pyrrole groups, 801 (γ C–H); 1018 (C3–C4, ν C–N, δ C–H); 1341 (ν C–N); 1440 (ν C=N); coordination centre, 463 (Re–N); 723, 854 (Re–O–Re); 961 (Re=O).
1
H NMR (CDCl3, δ, ppm, J, Hz): 9.07 (d, 8Hо, J = 7.6), 8.79 (s, 16Hβ), 8.01
(t, 8Hm, J = 7.6), 7.6 (t, 8Hp, J = 7.6), 7.47 (d, 8Hо’, J = 7.6), 7.04, 6.87 (t, t, 8Hm’, J = 7.6, J = 7.6). 1
H NMR (C6D6, , ppm, J, Hz): 9.18 (s, 16Hβ), 8.1 (d, 8Hо, J = 7.1), 8.0 (t,
8Hо’, J = 7.1), 7.47 (m, 16Hm,p, J = 7.6), 6.85 (t, 2Hm’, J = 7.3), 6.67 (t, 2Hm’, J = 7.3), 6.42 (d, 2Hp’, J = 8.3), 6.32 (d, 2Hp’, J = 8.6). 1
H NMR (CD3COOD, , ppm, J, Hz), monomer species O=Re(OAc)TPP:
9.51 (s, 8Hβ), 8.51 (d, 4Ho, J = 7.3), 8.37 (d, 4Ho, J = 7.3), 7.9 (m, 8Hm, 4Hp). 1
H NMR (D2SO4, δ, ppm): 9.13 (m, 8Hβ), 8.52, 8.23 (t, t, 8Hо), 8.06 (t, 8Hm,
1
H–1H 2D COSY (C6D6, , ppm, J, Hz): 8.1 (d, 8Hо, J = 7.1) − 7.47 (m,
4 Hp). 16Hm,p), 8.0 (t, 8Hm, J = 7.1) − 7.47 (m, 16Hm,p), 6.85 (m, 2Hm’, J = 7.3) − 6.42 (d 2Hp, J = 8.3), 6.67 (t, 2H m’, J = 7.3) − 6.32 (d 2Hp,, J = 8.6). 1
H–1H 2D COSY (CD3COOD, , ppm, J, Hz): O=Re(OAc)TPP: 8.51 (d,
4Ho, J = 7.32) 7.93 (m, 12Hm,p), 8.37 (d, 4Ho, J = 7.3) 7.93 (m, 12Hm,p). For C88H56N8O3Re2 anal. calcd. (%): C, 64.22; H, 3.41; N, 6.81. Found (%): C, 63.14; H, 3.52; N, 5.59.
2.2. Preparation of (2) 2,3,7,8,12,13,17,18-octaethyl-5-monophenyl-21H,23H-porphyrin (H2MPOEP) and H2ReCl6 in 1 : 5 molar ratio were refluxed in phenol at 454 K for 5 h. After reaction completion detected by a disappearance of H2MPOEP band and by termination of changes in the UV-Visible spectrum of the reaction mixture in chloroform, the contents of the reaction vessel was cooled and, after dilution with water, the products were extracted into chloroform. The solution was repeatedly washed with warm water to remove phenol, concentrated by partly evaporation of the solvent, and chromatographed on a column with Al2O3 (Brockman activity II) using CH2Cl2. This gave two zones namely a pink zone and a diffuse green-brown zone. The substances isolated from the second zones were chromatographed once
again on a silica gel (40/100 Chemapol) column, elution being performed first with benzene
and
then
with
CHCl3
C2H5OH
mixture (1
:
1).
Complex
O=Re(PhO)MPOEP was in the green zone. Yield: 75 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 595 (3.64), 477 (4.02), 348 (4.38). IR (KBr, ν, cm–1): phenyl groups, 707, 741 (γ C–H); 1074, 1101 (δ C–H); 1546, 1600, 1631 (ν C=C); 3024, 3059 ( C–H); pyrrole groups, 799 (γ C–H); 1058 (C3–C4, ν C–N, δ C–H); 1378 (ν C–N); 1464 (ν C=N); alkyl groups: 1340, 1401 (δ C–H); methine groups: 1253, 1269 (δ C–H), 842, 853 ( C–H); coordination centre, 464 (Re–N); 946 (Re=O); 668 (Re–O); 1486 (OPh). 1
H NMR (CDCl3, δ, ppm, J, Hz): 10.70 (m, 3H, meso); 8.45 (d, 1Hо, J =
6.7), 8,35 (d, 1Hо, J = 7.3), 7.79 (m, 2Hm), 7.95 (d, 1Hp, J = 7.3), 4.28, 3.84, 3.74, 3.67, 3.58 (m, s, s, s, s, 16 Н, CH2), 1.57, 1.28, 0.90 (s, s, m 24 Н, CH3). 1
H NMR (CD3COOD, δ, ppm, J, Hz): 11.06 (m, 3H, meso); 8.50 (t, 1Hо ,J =
6.7), 8.31 (t, 1Hо, J = 7.3), 7.88 (m, 2Hm), 7.62 (t, 1Hp); 4.41, 4.26, 3.95, 3.87, 3.71, 3.51 (m, m, s, s, s, s 16 Н, CH2), 1.32, 0.92 (m, m 24 Н, CH3); 7.07 (s, 2Ho (OPh)), 6.93 (s, 2Hm (OPh)), 6.83 (s, 1Hp (OPh)). For С48H53N4O2Re anal. calcd. (%): C, 63.79; H, 5.87; N, 6.20. Found (%): C, 64.57; H, 6.14; N, 5.84.
2.3. Preparation of (3) Gaseous HCl was passed through the solution of 2 in dichloromethane within 10 min. Solution color was changed from yellow-green to deep wine-red. Yield: 100 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 620 (3.67), 520 (4.13), 351 (4.73). IR (KBr, ν, cm–1): phenyl groups, 705, 740 (γ C–H); 1059, 1097 (δ C–H`); 1547, 1599, 1630 (ν C=C); 3024, 3060 (ν C–H); pyrrole groups, 801 (γ C–H); 1059 (C3–C4, ν C–N, δ C–H); 1383 (ν C–N); 1464 (ν C=N); alkyl groups: 1340, 1401 (δ C–H); methine groups: 1261 (δ C–H), 865, 908 ( C–H); coordination centre: 464 (Re–N); 946 (Re=O).
1
H NMR (CDCl3, δ, ppm, J, Hz): 10.88 (m, 3H, meso); 8.36 (t, 1Hо, J = 7.0),
7.92 (t, 1Hо, J = 7.6), 7.76 (m, 2Hm), 7.55 (q, 1Hp, J = 7.3), 4.27, 3.87, 3.79, 2.94 (m, m, m, m 16 Н, CH2), 2.08, 1.34, (t, m 24Н, CH3). 1
H–1H 2D COSY (CDCl3, , ppm, J, Hz): 8.36 (t, 1Hо, J = 7.0) − 7.76 (m,
2Hm), 7.92 (t, 1Hо, J = 7.6) − 7.76 (m, 2Hm), 7.76 (m, 2Hm) − 7.55 (q, 1Hp, J = 7.3); 4.27 (m, 6H, СH2) − 2.08 (t, 8H, CН3), 3.87 (m, 6H, СH2) − 1.34 (m, 16H, CН3), 3.79 (m, 4H, СH2) − 1.34 (m, 16H, CН3), 2.94 (m, 2H, СH2) − 1.34 (m, 16H, CН3). 2.4. Preparation of (4) Compound (4) was prepared and purified by the same procedure described above for (2), but H2MPOEP was replaced by 2,3,7,8,12,13,17,18-octaethyl-5,15diphenyl-21H,23H-porphyrin (H2DPOEP). CHCl3 was used in place of CH2Cl2 in chromatography. Time of the reaction was 6 h. Yield: 75 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 625 (3.70), 525 (4.15), 354 (4.75). IR (KBr, ν, cm–1): phenyl groups, 702, 742 (γ C–H); 1073, 1125 (δ C–H); 1491, 1532, 1600 (ν C=C); 3022, 3059 (ν C–H); pyrrole groups, 800 (γ C–H); 1062 (C3–C4, ν C–N, δ C–H); 1384 (ν C–N); 1465 (ν C=N); alkyl groups: 1341, 1400 (δ C–H); methine groups: 1274 (δ C–H), 838, 861 ( C–H); coordination centre: 467 (Re–N); 962 (Re=O). 1
H NMR (CDCl3, δ, ppm, J, Hz): 10.82 (m, 2H, meso); 8.29 (d, 2Hо, J =
8.1), 8.20 (d, 2Hо, J = 8.1), 7.91 (m, 2Hм), 7.85 (m, 2Hм), 7.73 (q, 1Hp, J = 7.3), 7.55 (q, 1Hp, J = 7.3), 4.20, 2.70 (m, br. s 16 Н, CH2), 1.95, 1.56 (t, br. s, 24Н, CH3). 1
H–1H 2D COSY, (CDCl3, , ppm, J, Hz): 8.29 (d, 2 Hо, J = 8.1) − 7.91 (m,
2Hm), 8.20 (d, 2Hо, J = 8.0) − 7.85 (m, 2Hm), 7.91 (m, 2Hм) − 7.73 (q, 1Hp, J = 7.3), 7.85 (m, 2Hm) − 7.55 (q, 1Hp, J = 7.3), 4.20 (m, 10H, СH2) − 1.95 (t, 10 H, CН3), 4.20 (m, 10H, СH2) − 1.56 (br. s, 14H, CН3), 2.70 (br. s, 6H, СH2) − 1.95 (t, 10H, CН3). For С36H44N4OClRe anal. calcd. (%): C, 62.51; H, 5.64; N, 5.41. Found (%): C, 6.08; H, 5.45; N, 61.05.
2.5. Preparation of (5) Compound (5) was prepared and purified by the same procedure described above for (2), but H2MPOEP was replaced by 2,3,7,8,12,13,17,18-octaethyl21H,23H-porphyrin (H2OEP). Time of the reaction was 9 h. Yield: 70 %. UV-Visible (CH2Cl2), λmax, nm: 613, 580, 469, 343. IR (KBr, ν, cm–1): pyrrole groups, 747 (γ C–H); 1057 (C3–C4, ν C–N, δ C– H); 1376 (ν C–N); 1468 (ν C=N); alkyl groups: 1317 (δ C–H); methine groups: 1223, 1273 (δ C–H), 844, 873 ( C–H); coordination centre, 454, 466 (Re–N); 959 (Re=O); 670 (Re–O); 1451, 1589 (OPh). 1
H NMR (C6D6, δ, ppm): 10.77 (m, 4H, meso), 9.51 (m, 8H, meso); 4.43 (m,
32Н, CH2), 4.03 (m, 16Н, CH2), 1.83 (m, Н, CH3); 7.04 (s, 2Ho (OPh)), 6.95 (s, 2Hm (OPh)), 6.85 (s, 1Hp (OPh)). 1
H–1H 2D COSY (C6D6, , ppm): 4.43 (m, 32Н, СH2) − 1.83 (m, 16Н, CН3),
4.03 (m, СH2) − 1.83 (m, CН3). For С42H49N4O2Re anal. calcd. (%): C, 60.94; H, 5.93; N, 6.77. Found (%): C, 62.17; H, 6.31; N, 7.15. 2.6. Preparation of (6) Gaseous HCl was passed through the solution of (5) in dichloromethane within 10 min. Solution color was changed from yellow-green to pink. Yield: 100 %. UV-Visible (CH2Cl2), λmax, nm (log ε): 620 (3.90), 518 (4.30), 347 (4.92). IR (KBr, ν, cm–1): pyrrole groups, 747 (γ C–H); 1057 (C3–C4, ν C–N, δ C– H); 1376 (ν C–N); 1468 (ν C=N); alkyl groups: 1316 (δ C–H); methine groups: 1223, 1271 (δ C–H); 846, 854, 871 ( C–H); coordination centre: 467 (Re–N); 965 (Re=O). 1
H NMR (CDCl3, δ, ppm): 10.94 (m, 4H, meso); 4.36 (m, 16 Н, CH2), 2.13
(m, 24 Н, CH3).
1
H–1H 2D COSY (CDCl3, , ppm): 4.36 (m, 16 Н, СH2) − 2.13 (m, 24 Н,
СH3). Solid amorphous samples of (1−6) were isolated from solutions by solvent evaporation at room temperature. 2.7. Spectroscopy The UV-Visible spectra were measured on Agilent 8453 UV-Visible spectrophotometers; IR spectra were recorded on a VERTEX 80v spectrometer; elemental analysis was performed on a CHNSO Analyzer Flash EA 1112 Series. The solid layers of complexes for IR spectroscopy were formed by evaporation of the CHCl3 solvent from a solution of the complex on a silicon plate. All NMR experiments were performed on a Bruker Avance III-500 NMR spectrometer equipped with a 5 mm probe using standard Bruker TOPSPIN Software. Temperature control was performed using a Bruker variable temperature unit (BVT-2000) in combination with a Bruker cooling unit (BCU-05) to provide chilled air. Experiments were performed at 298 K without sample spinning. 1
H NMR (500 MHz) spectra were recorded using 90° pulses and relaxation
delay of 1 s; spectral width was 19.13 ppm; 128 scans were acquired. Proton NMR is relative to deuterium solvent peaks. The two-dimensional Double Quantum Filtered Correlation Spectroscopy (2D DQF-COSY) [12] spectra was acquired with a 19.13 ppm spectral window in the direct dimension F1 with 2048 complex data points and a 19.13 ppm spectral window in the indirect dimension F2 with 256 complex points. The spectra were acquired with 16 scans and relaxation delay of 2 s. Two-dimensional Total Correlation Spectroscopy (2D ge-TOCSY) [13] and Rotating frame nuclear Overhauser effect Spectroscopy (2D ge-ROESY) [14] experiments were performed with pulsed filtered gradient techniques. The spectra were recorded in a phasesensitive mode using Echo/Antiecho-TPPI gradient selection with 2048 points in the F2 direction and 512 points in the F1 direction. Spin-lock delay values for 2D
ge-ROESY and 2D ge-TOCSY were 200 msec. The spectra were acquired with 6472 scans and relaxation delay of 2 s. The two-dimension Diffusion Order Spectroscopy (2D DOSY) spectra were recorded with PGSTE pulse sequence using a bipolar gradient pulses and the insertion of a supplementary delay (LED) [15]. The PGSTE sequence was used with a diffusion delay of 0.1 s, a total diffusion-encoding pulse width of 5 ms. For each of 32 gradient amplitudes, 64 transients of 16384 complex data points were acquired. 3. Results and discussion Rhenium(V) complexes with H2OEP and its meso-phenyl substituted porphyrins were prepared according to Scheme 1.
Scheme 1. Synthesis of rhenium(V) octaethylporphyrin complexes: R = C2H5; *-in an amount of impurity
3.1 UV–Visible absorption spectra There is a weak absorption at ~350 nm in the UV–Visible spectrum of the μoxo dimer complex (1) [10]. The view of UV–Visible spectra of (24) and (6) (Fig. 1) characterize these compounds as the monomeric species. Unlike the absorption spectra of μ-oxo dimer the UV–Visible spectra of monomeric species demonstrate the intense B(0,0) band at 350 nm. UV–Visible absorption
spectroscopic changes during the reversible transfer of the monomer and μ-oxodimer forms were used for a quantitative study of the reaction of compound (1) with AcOH in benzene [16]. Similarly, the electronic absorption spectra of individual complexes (26) are differed in the presence of the additional bands in the range of 300800 nm in particular charge transfer bands at max=440480 nm [17]. In the UV–Visible spectra of (5) in C6H6 and CH2Cl2 (Fig. 1 curves 1, 2) the Soret band is more intense compared with the charge-transfer band. This fact also suggests the predominance of the monomeric species. However, the intensity difference of these bands is decreased in passing from CH2Cl2 (Fig. 1, curves 2) to benzene (Fig. 1, curves 1). Since benzene promotes to the μ-oxo-dimer formation [18], on the basis of 2D NMR study we can certainly say that complex (5) exists as an equilibrium mixture of monomeric and μ-oxo-dimer forms in benzene. The position of the bands in the UV–Visible spectra of the resulting compounds depends on the nature of the macrocyclic and axial ligands. Thus, the peaks maxima in the spectrum of compound (2) are red-shifted by 58 nm respectively from the spectrum of compound (5). The band hypsochromic shift of the complexes with MO bond is associated with its higher covalence compared with the MCl bond. In the case of Cl-containing compounds (3), (4) and (6) the introduction of the phenyl substituents in the meso-positions of the macrocycle results in the red shift of the most of the bands in the spectra of the compounds. These spectra exhibit Soret band respectively at 351, 354 and 347 nm, and the charge transfer band – at 520, 525 and 518 nm respectively. The similar dependence of UV–Visible spectra on the number of meso-phenyl substituents in the macrocycle is typical for octaethyl-substituted porphyrins of manganese(III) [19]. The Soret band repositioning after replacing the axial ligand OPh with Cl is ~5 nm, while the charge transfer band in this case is red-shifted more significantly - about 45–50 nm. The same tendency is observed in the case of oxo-complexes of molybdenum(V) with H2TPP while going from O=Mo(OH)TPP to O=Mo(Cl)TPP [20].
3.2 Confirmation of structure by IR and NMR studies Regardless of the nature of the singly-charged axial ligand the main intense bands corresponding to the stretching vibrations of macrocyclic ligands bonds are found in the IR spectra of resulting octaethyl-porphyrin complexes (Experimental). Additionally, the spectra contain the bands proving the coordination nature of these compounds. Thus, bands with frequencies 464, 470, 467, 466 and 467 cm–1 can be attributed to the vibrations of the Re–N bonds in (2), (3), (4), (5) and (6), respectively. The maxima positions are practically independent on the nature of the singly-charged axial ligand as well as on the number of phenyl substituents in the porphyrin ligand. This indicates the same coordination type and electronic state of the coordination centre of investigated rhenium(V) complexes. An additional band at 454 сm–1 and a weak signal at 619 сm–1 are observed in the range of stretching vibrations of Re–N bonds in the IR spectrum of (5). These bands are analogous to the signals in the IR spectrum of compound (1) but absent in the IR spectrum of (6). A strong absorption at 650550 cm1 has been shown to attribute to the vibrations of MoOMo bonds in [O=MoTPP]2O [18]. This means that at the atmosphere conditions compound (5) in KBr contains the impurity of μ-oxo dimer species at very small equilibrium concentration according to the low intensity of signal in the IR spectrum. 1
Н NMR spectrum of compound (5) in C6D6 (Fig. 2) exhibits two signals of
meso-protons at 10.77 and 9.51 ppm. The absence of correlation between these signals in the 1H–1H 2D COSY (Fig. 3) and 1H–1H 2D ROESY spectra in C6D6 indicates that they belong to different compounds. Furthermore, these data are supported by a 1H–1H 2D DOSY spectrum of the compound (5), where the separation according to the diffusion coefficients also demonstrated the presence of two compounds in solution was found. According to [20] and signal assignment in 1H NMR of compound (1) (Experimental) the signals of meso-protons at 10.77 ppm can be assigned to the monomeric species of the
complex (5), whereas up-shifted signal to its μ-oxo-dimer [O=ReOEP]2O, which is present in small amount and is in equilibrium with (5). It should be noted that 1H–1H 2D DOSY spectrum of compound 6 obtained by passing of gaseous HCl through the solution of (5) in dichloromethane (Fig. 4), is the spectrum of the individual monomeric species without μ-oxo-dimer impurity. The individuality of compounds (24) and (6) reported herein and the absence of dimer species of these compounds in solutions were confirmed by spectroscopic techniques: 1Н ЯМР, 1H–1H 2D DOSY, 1H–1H 2D COSY, 1H–1H 2D ROESY spectroscopic studies (Experimental). There are cross-peaks corresponding only to the interaction of −СН2− and −СН3 protons in the 1H–1H 2D COSY of 6 in CDCl3. In the 1H–1H 2D COSY spectra of (3) and (4) the correlations between Hо, Hm and Hp in meso-phenyl substituents of macrocycle appear. Additional signals, which can be attributed to the protons of the axial ligands are not detected. In 1Н NMR (Fig. 2a), 1H–1H 2D COSY (Fig. 3) and 1H–1H 2D ROESY spectra (Fig. 5) the presence of −OPh in compounds (2) and (5) is supported by the availability of proton signals with the chemical shifts closed to those of the o-, mand p-protons in the phenol molecule [21]. The intense bands corresponding to the stretching vibrations of bonds in phenoxy-ligand (1451, 1589 and 1486 cm–1) and Re–O bond (670 and 668 сm–1) in the IR spectra of compound (2) and (5) (Fig. 6а) also demonstrate the presence of axial-bounding −OPh in the first coordination sphere of the complexes. At the same time, the bands mentioned above do not appear in the IR spectra of compounds (3), (4) and (6) (Fig. 6b). Axial-bounding oxo-ligand in the first coordination sphere can be fixed by a signal of Re=O vibrations at 950 cm–1 in the IR spectra of all studied compounds (Experimental). 3.3 Stability in solutions
In order to estimate the stability in solutions, the synthesized complexes were exposed to strong acids, atmospheric oxygen and high temperatures. Rhenium(V)porphyrins exhibit high stability for long time without changing in organic solvents. Compounds (24) and (6) are stable along M−N bonds in 18.5M H2SO4 under heating up to 363 K. The compounds were reprecipitated onto ice from sulfuric acid solutions after heating under mentioned temperature within 6 h and they UV-Visible spectra in CH2Cl2 (Table 1) did not exhibit the bands of noncoordinated H2TPP or its protonated species H4TPP2+. These spectra are similar to spectra of the investigated compounds in CH2Cl2, but the charge transfer band is shifted to 498 nm. The analogy of the compound spectra in CH2Cl2 both when dissolved and after reprecipitation from sulfuric acid indicates the same coordination type of the compounds. According to experimental data (section 2) the position of the charge transfer band in the O=Re(X)P spectra depends on the nature of axial ligand X. The spectrum of compound (3) in CH2Cl2 exhibits this band at 520 nm, while the transition to the compound (2) with −OPh as axial ligand results in this band at 477 nm. Absorption maximum in the spectra of O=Mo(Cl)TPP, O=Mo(OPh)TPP and O=Mo(OH)TPP are respectively at 500, 475 and 450 nm, according to [18, 22]. When compounds
(24) and (6) are exposed to hot sulfuric acid, HSO4 ions, which are in large excess in solution, substitute the axially coordinated monodentate ligands with formation of O=Re(HSO4)P, as well as in the case of the compound (1) [11]. That’s why all the reprecipitated complexes have the charge transfer band at 498 nm in their spectra. The appearance of a new stretching vibration band of metaloxygen bond at 670 cm1 in the IR spectrum (demonstrated at Fig. 7 using the compound (3) as an
example) is also evidence of the HSO4 presence in the coordination sphere of the compounds resulted in the reaction with H2SO4. Besides mentioned maintaining of the type spectra of the complexes after their extraction from sulfuric acid in the unchanged state, spectra of compounds (3)
and (4) in sulfuric acid sharply vary within the time (Table 1). It is typical for solutions of the complexes in 16.8–18.2M H2SO4 at 318 ÷ 348 K. A new UV– Visible spectrum of the resulting compound is identified as the spectrum of metalloporphyrin, which is one-electron oxidized along the porphyrin -ring system (Scheme 2) according to [23–25].
Scheme 2. Oxidation of compound 3 (R1 = phenyl, R2 = H) and compound 4 (R1 = R2 = phenyl) in aerated H2SO4. R = C2H5 The chemical generation of the one-electron oxidized species of metalloporphyrins under the expose of oxygen dissolved in H2SO4 (solubility of O2 in 17.5M H2SO4 is 27.5 lm3 [26]) according to equation analogous to Scheme 2, has been studied earlier for complexes of H2TPP with Ru(IV) [24] and Pd(II) [25]. UV-Visible spectra have been found to be the best feature of the radical species of metalloporphyrins [23] therefore identification of -cation radicals was carried out using the method of electron absorption spectroscopy. The addition of the second phenyl substituent at meso-position of the macrocycle going from (3) to (4) is followed by the saddle strain of macrocycle [27, 28], but does not result in significant difference in the properties of these compounds (Table 1). The oxidation ability of complexes in this case is provided by the presence of eight electron-donor -alkyl groups in -ring systems of both compounds. The UV–Visible spectra of compounds (2) and (6) in concentrated H2SO4 do not exhibit the bands of -cation radical. The stability to oxidation along macrocycle in the case of the compound (2) is conditioned by stronger covalent binding ReO compared with ReCl (in compound (3)) preventing the
displacement of OPh and its substitution on the HSO4 (see eq. 1). The latter
becomes possible, as well as in the case of the unsubstituted at the meso-positions compound (6), only under the heating in an acidic medium with pouring onto ice
when the instant formation of the complexes with axial ligand HSO4 takes place (Table 1). 4. Conclusions Thus, we have described the preparation of rhenium(V) porphyrin complexes by the reaction of H2ReCl6 with - 5,10,15,20-tetraphenyl-21H,23Hporphyne H2TPP, 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyne H2OEP and its 5-phenyl and 5,15-diphenyl-meso-derivatives, H2MPOEP and H25,15DPOEP. The compounds were characterized by a variety of spectroscopic techniques. The monomer porphyrin complexes of rhenium(V) are super-stable along M−N bonds in proton-donating solutions (AcOH, AcOHH2SO4, H2SO4–H2O). In acid media, they exist as the initial species or undergo the reactions of substitution of the corresponding acid anion for the anion axial ligand. Together with the macrocycle variation such transformation of the coordination sphere results in significant changes in physical and chemical properties of rhenium(V)porphyrins. Under the convenient electron-excessing state of the macrocycle, the complexes with hydrosulfate ion undergo one-electron oxidation, which occur in aerated sulfuric acid forming a stable -cation radicals. The stability of the compounds, the high activity of the axial positions in the ligand substitution reactions and the possibility of oxidation along the macrocycle, which have been confirmed in this report, promise great prospects for practical use of the complexes in the catalysis of the redox processes as well as in the formation of self-assembled donor-accepter complexes for biomedicine and optoelectronics.
Acknowledgements. Financial support was from grants of the President of the Russian Federation for support of scientific schools NSh-3993.2012.3 and the Russian Foundation for Basic Research, Projects No. 12-03-00775 and 12-03-00967.
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Copper(II)
Figure captions
Fig. 1. UV–Visible spectra of 5 in C6H6 (1) and CH2Cl2 (2); 6 in CH2Cl2 (3) Fig. 2. 1Н NMR spectra of compound 5 in C6D6 (a); compound 6 in CDCl3 (b) (*Hmeso signal for μ-oxo dimer species of 5) Fig. 3. 1H–1H 2D COSY of compound 5 in C6D6 Fig. 4. 1H–1H 2D DOSY of compound 6 in C6D6 Fig. 5. 1H–1H 2D ROESY of compound 5 in C6D6 Fig. 6. IR spectra of compounds 5 (a) and 4 (b) in KBr Fig. 7. IR spectra of compound 3 in KBr before (a) and after (b) the reaction with 18.2M H2SO4
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Table 1. Absorption bands (max, nm) in UV-Visible spectra of compounds 24 and 6 CH2Cl2 H2SO4 CH2Cl2, dissolution after 6 h after under 338 K reprecipitation 498, 350 498, 350a 480, 368b 625, 525, 354 860, 465, 333 515, 319 500, 350a 4 467, 368b 620, 518, 347 800, 453, 325 453, 325c 498, 350 6 (a) - after 1 h; (b)- -cation radical in C2H5OH; (c) - in 1 min after dissolution 2 3
595, 477, 348 620, 520, 351
875, 460, 327 875, 450, 327
875, 460, 327 515, 319
Highlights
1. Rhenium(V) porphyrins were synthesized. 1
2. UV–Visible, IR, Н, 2D NMR spectra for title compounds were studied. 3. The compounds do not undergo MN bonds dissociation in strong acids. 4. The compounds form the stable -cation radicals O=Re(HSO4)P . +