Bromo-substituted Mn(II) and Mn(III)-tetraarylporphyrins: synthesis and properties

Article abstract of DOI:10.1080/00958972.2018.1519186

Mono-, tetra-, and octa-bromo substituted Mn(II)- and Mn(III)-tetraarylporphyrins were synthesized by reactions of manganese(II) chloride with corresponding porphyrin ligands or their Cd(II)-complexes in DMF. With the use of the metal exchange reaction, the time of the Mn-porphyrins formation is significantly reduced with increase in yield of final products in comparison with the complexation reaction. Mn(III)-tetraarylporphyrins reduce to the Mn(II)-porphyrins in DMF in the presence of NaOH and in pure DMF. The obtained compounds were identified using UV–vis and ¹H NMR spectroscopy, mass-spectrometry, and elemental analysis.

Full text of DOI:10.1080/00958972.2018.1519186

Journal of Coordination Chemistry
ISSN: 0095-8972 (Print) 1029-0389 (Online) Journal homepage: http://www.tandfonline.com/loi/gcoo20
Bromo-substituted Mn(II) and Mn(III)-
tetraarylporphyrins: Synthesis and properties
Natalya Vasil’evna Chizhova, Olga Valentinivna Maltсeva, Svetlana
Veniaminovna Zvezdina, Nugzar Zhoraevich Mamardashvili & Oscar
Iosiphovich Koifman
To cite this article: Natalya Vasil’evna Chizhova, Olga Valentinivna Maltсeva, Svetlana
Veniaminovna Zvezdina, Nugzar Zhoraevich Mamardashvili & Oscar Iosiphovich Koifman (2018):
Bromo-substituted Mn(II) and Mn(III)-tetraarylporphyrins: Synthesis and properties, Journal of
Coordination Chemistry, DOI: 10.1080/00958972.2018.1519186
To link to this article: https://doi.org/10.1080/00958972.2018.1519186
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Bromo-substituted Mn(II) and Mn(III)-tetraarylporphyrins:
Synthesis and properties
NATALYA VASIL’EVNA CHIZHOVA†, OLGA VALENTINIVNA MALTСEVA†,
SVETLANA VENIAMINOVNA ZVEZDINA†, NUGZAR ZHORAEVICH MAMARDASHVILI*† and
OSCAR IOSIPHOVICH KOIFMAN‡
†Laboratory of Coordination Chemistry of Macrocyclic Compounds, G. A. Krestov Institute of Solution Chemistry
of the Russian Academy of Sciences, Russian Federation
‡Research Institute of Macroheterocycles, Ivanovo State University of Chemistry and Technology,
Russian Federation; Laboratory of New Materials on the Basis of Macrocyclic Compounds, G. A. Krestov Institute
of Solution Chemistry of the Russian Academy of Sciences, Russian Federation
Mono-, tetra- and octa-bromo substituted Mn(II)- and Mn(III)-tetraarylporphyrins were
synthesized by reactions of manganese(II) chloride with corresponding porphyrin ligands or their
Cd(II)-complexes in DMF. With the use of the metal exchange reaction, the time of the Mn-
porphyrins formation is significantly reduced with increase in yield of final products in
comparison with the complexation reaction. Mn(III)-tetraarylporphyrins reduce to the Mn(II)-
porphyrins in DMF in the presence of NaOH and in pure DMF. The obtained compounds were
identified using UV-Vis and 1H NMR spectroscopy, mass-spectrometry and elemental analysis.
Keywords: Bromo-substituted porphyrins; Complexation; Metal-exchange reaction; Mn(II)- and
Mn(III)-Tetraarylporphyrins; Spectroscopy
1. Introduction
Manganese is a biometal necessary for life of organisms [1]. A large number of works in this
field are conducted at the intersection of chemistry, biology and medicine. The variety of
manganese porphyrin especially electronic structure of molecules, their spectral, electrochemical
and complex formation properties make it important to study these compounds in terms of the
development of theoretical and applied aspects of coordination and bioorganic chemistry.
Manganese is essential to perform functions of reproductive, central nervous and endocrine
systems. Manganese porphyrins possess the ability to bind free radicals. Mn(III)-porphyrins are
usually the most important representative class of metalloporphyrins with catalytic activity in
epoxidation of alkenes [2]. The oxidation of sulfides by hydroperite in the presence of the
*Corresponding author. Email: ngm@isc-ras.ru

Mn(III)-tetra-(4-hydroxyphenyl)porphyrin was studied [3]. According to Miskelly and
coworkers [4] and DeFreitas-Silva and coworkers [5], the Mn(III)-5-(3-bromo-4-amino)phenyl-
10,15,20-tris-phenyl-2,3,7,8,12,13,17,18-octabromoporphyrin could be used as a biomimetic
catalyst of cyclohexane oxidation [5]. Catalytic activity and oxidative stability of a series of
pyridyl-substituted manganese porphyrins has been investigated [6].
Electrochemical and electrocatalytic properties of alkyl-substituted porphyrins and their
complexes with Mn(III) were investigated [7]. Recently, manganese porphyrins possessing
properties of molecular magnetism and capable of nanoporous structures have been prepared and
used for the design of new functional materials.
Manganese complexes with tetraphenylporphin were described [8, 9]. Complexes of the
Mn(III)
with
tetrabenzoporphyrin,
tetraphenyltetrabenzoporphyrin
and
octaphenyltetraazaporphyrin were described [10-12]. In present work, the coordination reactions
of the 5,10,15,20-tetraphenylporphyrin 1, 2-bromo-5,10,15,20-tetraphenylporphyrin 2, 2,3,12,13-
tetrabromo-5,10,15,20-tetraphenylporphyrin 3, 5,10,15,20-tetra-(4-bromophenyl)porphyrin 4 and
2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin 5 with manganese(II) chloride
(MnCl2) (eqns. 1 and 2) and the metal exchange reactions of cadmium porphyrin complexes
(6-10) (eqns. 3 and 4) with MnCl2 in DMF were investigated. The metal exchange reaction
significantly reduced the time and temperature of the Mn-porphyrins formation in comparison
with the complexation reaction. Obtained bromo-substituted Mn(II) and Mn(III)-
tetraarylporphyrins were identified using UV-Vis and 1H NMR spectroscopy, mass-spectrometry
and elemental analysis.
H 2P + M nC l2
M nP + 2H C l
(1)
O 2, C l-
(C l)M nP
M nP
(2)
(3)
(4)
M nP + C dC l2
C dP + M nC l2
O 2, C l-
(C l)M nP
M nP

2. Experimental
2.1. Materials and physical measurements
DMF, СНCl3, C6H14, Cd(OAc)2, KOAc, Al2O3 active basic (0.063-0.200 mm) were used without
purification; MnCl2 was annealed at 200 °С for 4 h. Tetraphenylporphyrin 1 and tetra-(4-
bromophenyl)porphyrin 4 (“Porphychem”) were used in the experiment. 2-Bromo-5,10,15,20-
tetraphenylporphyrin 2 was obtained by an optimized procedure [13]. 2,3,12,13-Tetrabromo-
5,10,15,20-tetraphenylporphyrin 3 was synthesized by an optimized procedure [14]. The
structure of tetrabromosubstituted porphyrin 3 was proved by X-ray diffraction analysis [14].
2,3,7,8,12,13,17,18-Octabromotetraphenylporphyrin
5
was synthesized from Cu(II)
tetraphenylporphyrin. Cd(II) tetraphenylporphyrins 6-10 were synthesized according to the
methods given [15]. Tables S1 and S2 show the characteristics of the UV-Vis spectra of 1-10.
The significant difference in UV-vis spectra of basis porphyrin, their Cd-complexes and formed
Mn-porphyrins made it possible to use spectrophotometric method for investigating
complexation and metal-exchange reactions.
UV-Vis spectra were recorded on a Cary 100 (Varian) spectrophotometer at room
1
temperature. H NMR spectra were recorded on a Bruker AV III-500 spectrometer (internal
standard was tetramethylsilane (TMS)). Mass spectra were obtained on a Maldi TOF Shimadzu
Biotech Axima Confidence mass spectrometer (matrix – dihydroxybenzoic acid). Elemental
analysis was performed on a Flash EA 1112 analyzer.
2.2. Synthesis of Cu(II) 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin
To 0.025 g (0.0296 mmol) of copper tetraphenylporphyrin in a mixture of 10 ml of CHCl3 and
1 ml of DMF was added 0.105 g (0.592 mmol) of NBS and stirred at room temperature for 10 h.
The reaction mixture was evaporated to a minimum 10 ml of DMF, H2O and NaClsolid was
added. Dark brown precipitate was filtered off, washed with water and dried, then
chromatographed on Al2O3 with CHCl3, and precipitated from C2Н5OH. Yield: 68% (0.026 g,
0.0199 mmol). Mass spectrum, m/z (Irel,%) 1306.6 (98) [M]+ was calculated for C44H20N4Br8Cu -
1307.5. UV-Vis spectrum in CHCl3, λ, nm (log ε): 626 sh., 581 (4.33), 467 (5.21), 447 sh.
2.3. Synthesis of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin 5 was
synthesized according to optimized synthesis procedure [16]. The dark green 5 is formed when

the copper complex in CHCl3 is treated with mixture of choric and sulfuric acids (4:3) for 2 h at
room temperature. Mass spectrum, m/z (Irel,%): 1245.4 (62) [M]+ was calculated for
1
C44H22N4Br8 - 1246.1. H NMR (CDCl3, δ, p.p.m.): 8.22 d. (8H, ortho-C6H5), 7.79 m. (12H,
meta-C6H5 and para-C6H5), -1.65 s. (2H, NH-protons).
2.4. Synthesis of 5,10,15,20-tetraphenylporphyrin chloride Mn(III) (11)
0.02 g (0.0276 mmol) of 6 was dissolved in 40 ml of DMF and 0.07 g (0.552 mmol) of MnCl2
was added. The reaction mixture was held at room temperature for 30 min, both distilled H2O
and NaClsolid were added to precipitate the product which was filtered off. Finally, dark green
precipitate was washed with water, dried and precipitated (powdery) from hexane. Yield: 95%
(0.0185 g, 0.0263 mmol). Found %: C 74.98; H 3.97; N 7.88; Cl 4.97. C44H28N4ClMn.
Calculated %: C 75.16; H 4.01; N 7.97; Cl 5.04. Mass spectrum, m/z (Irel,%): 667.37 (98)
1
[M-Cl]+ was calculated for C44H28N4Mn - 667.7. H NMR (CDCl3, δ, p.p.m.): 8.30 dr. s. (8H,
pyrrole ring), 8.09 br. s. (8H, ortho-C6H5), 7.75 br. s. (12H, meta-C6H5 and para-C6H5).
2.5. Synthesis of 2-bromo-5,10,15,20-tetraphenylporphyrin chloride Mn(III) (12)
0.02 g (0.0249 mmol) of 7, 0.06 g (0.498 mmol) of MnCl2 and 40 ml of DMF was stirred 70 min
at room temperature. The dark green precipitate was processed in a similar manner to 11. Yield:
92% (0.018 g, 0.0230 mmol). Found %: C 67.42; H 3.42; N 10.15. C44H27N4ClBrMn. Calculated
%: C 67.58; H 3.48; N 10.22. Mass spectrum, m/z (Irel,%): 745.22 (95) [M-Cl]+ was calculated
for C44H27N4BrMn - 746.6. 1H NMR (CDCl3, δ, p.p.m.): 8.20, br. s. (7H, pyrrole ring), 8.01 br. s.
(8H, ortho-C6H5), 7.55 br. s. (12H, meta-C6H5 and para-C6H5).
2.6. Synthesis of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin chloride Mn(III) (13)
(a) 0.02 g (0.0215 mmol) of 3, 0.054 g (0.430 mmol) of MnCl2 and 20 ml of DMF was refluxed
in a flask for 20 min. After processing, the reaction mixture was dissolved in chloroform,
evaporated and precipitated from hexane (dark green precipitate). Yield: 77% (0.017 g,
0.0166 mmol). (b) 0.02 g (0.0192 mmol) of 8, 0.048 g (0.384 mmol) of MnCl2 and 15 ml of
DMF were warmed to a boil and boiled for 25 s (dark green precipitate). Yield: 90% (0.018 g,
0.0173 mmol). They were processed similarly to (a). Found %: C 51.72; H 2.34; N 5.41.
C44H24N4ClBr4Mn. Calculated %: C 51.88; H 2.38; N 5.50. Mass spectrum, m/z (Irel,%):

983.01 (97) [M-Cl]+ was calculated for C44H24N4Br4Mn - 983.3. 1H NMR (DMSO d6, δ, p.p.m.):
8.80 br. s. (4H, pyrrole ring), 8.27 br. s. (8H, ortho-C6H5), 6.75 br. s. (12H, meta-C6H5 and para-
C6H5).
2.7. Synthesis of 5,10,15,20-tetra-(4-bromophenyl)porphyrin chloride Mn(III) (17)
(a) 0.02 g (0.0215 mmol) of 4 was dissolved in 10 ml of DMF, 0.054 g (0.430 mmol) of MnCl2
was added and the reaction mixture was refluxed with stirring for 15 min. Dark green precipitate
was obtained and processed in a similar manner to 11. Yield: 74% (0.016 g, 0.0157 mmol).
(b) 0.02 g (0.0192 mmol) of 9, 0.048 g (0.384 mmol) of MnCl2 and 10 ml of DMF were heated
to a boil and boiled for 20 s. Yield: 89% (0.0175 g, 0.0171 mmol). Found %: C 51.75; H 2.32;
N 5.43. C44H24N4ClBr4Mn. Calculated %: C 51.88; H 2.38; N 5.50. Mass spectrum m/z (Irel,%):
1
982.68 (75) [M-Cl]+ was calculated for C44H24N4Br4Mn - 983.3. H NMR (CDCl3, δ, p.p.m.):
8.60 br. s. (8H, pyrrole ring), 8.35 br. s. (16H, ortho-C6H5 and meta-C6H5).
2.8. Synthesis of 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetraphenylporphyrin chloride
Mn(III) (19)
(a) 0.02 g (0.0161 mmol) of 5, 0.0316 g (0.322 mmol) of potassium acetate, 0.04 g (0.32 mmol)
of MnCl2 and 20 ml of DMF was stirred for 2 min. A dark brown precipitate was obtained.
Yield: 75% (0.016 g, 0.0120 mmol). (b) 0.02 g (0.0148 mmol) of 10, 0.037 g (0.296 mmol) of
MnCl2 and 20 ml of DMF was stirred for 30 s. Yield: 81% (0.016 g, 0.0120 mmol). Found %:
C 39.49; H 1.45; N 4.12. C44H20N4ClBr8Mn. Calculated %: C 39.61; H 1.51; N 4.20. Mass
spectrum m/z (Irel,%): 1298.25 (98) [M-Cl]+ was calculated for C44H20N4Br8Mn - 1298.8.
1H NMR (CDCl3, δ, p.p.m.): 8.05 br. s. (8H, ortho-C6H5), 7.47 m. (12H, meta-C6H5 and para-
C6H5).
2.9. Synthesis of tetraphenylporphyrins Mn(II)
Mn(II)-tetraphenylporphyrin 14 is formed by shaking a DMF solution (4 ml) of 11 (0.002 g,
0.00284 mmol) with solid NaOH (0.3 g, 7.5 mmol) in a sealed cell for 1 h. Similar to 14 Mn(II)-
porphyrins 15 and 18 were obtained from 12 and 17 in DMF in the presence of NaOH within 10
and 5 min, respectively. Mn(II)-porphyrin 16 is formed by shaking a DMF solution (4 ml) of 13
(0.002 g, 0.00195 mmol) for 30 min. Similar to 16 Mn(II)-porphyrin 20 was obtained from 19

within 5 min. Mn(II) porphyrins, when separated from the reaction mixture, are partially or
completely oxidized to Mn(III) porphyrins. Table S3 shows the characteristics of the UV-Vis
spectra of the Mn(II)-porphyrins.
3. Results and discussion
The reaction of formation between porphyrin ligands (H2P) and Mn(II)X2 (X = Cl-, CH3COO-) in
organic solvents is accompanied by formation of Mn(III)-porphyrins [(X)Mn(III)P] [17]. As a
rule, the complex formation process cannot be stopped at the stage of the Mn(II)-porphyrin
formation. Exceptions are tetraphenylporphyrins with a large number of electron-withdrawing
chlorine atoms in the macrocycle [18]. Therefore, investigationn of the effect of bromine atoms
in the pyrrole and phenyl rings of tetraphenylporphyrins on the ability to form manganese
complexes in various degrees of oxidation is needed.
5,10,15,20-Tetraphenylporphyrin chloride Mn(III) 11 and 2-bromo-5,10,15,20-
tetraphenylporphyrin chloride Mn(III) 12 were synthesized earlier [19] by complexation of
corresponding porphyrin ligands with MnCl2 in boiling DMF within 80 and 65 minutes,
respectively. 2,3,12,13-Tetrabromo-5,10,15,20-tetraphenylporphyrin chloride Mn(III) 13 was
formed by interaction of porphyrin 3 with MnCl2 in DMF for 2.5 h.
Manganese(II)-tetraphenylporphyrins (scheme 1) were obtained by using the method
described in the works [20,21]. The alkaline dimethylformamide (a solid NaOH in DMF) was
taken as the reducing agent. The studies shown that the Mn(II)-tetraphenylporphyrin 14 is
formed by shaking of the DMF solution of the compound 11 (С ~ 10-4mol/L) with NaOH (CNaOH
~ 10-1 mol/L) in a sealed cell within ~ 1 hour. UV-Vis spectrum of the compound 14 in the
system DMF+NaOH has Q bands with λmax 617, 576, 533 and Soret band with λmax 442 nm (the
spectra of “normal type” [22]). These bands arise as a result of electrons transition from higher
occupied orbitals of symmetry a1u and a2u into the lower vacant orbitals eg*of the porphyrin [23].
The 2-Bromo-5,10,15,20-tetraphenylporphyrin Mn(II) 15 is formed in the corresponding DMF
solution of the Mn(III)-porphyrin in the presence of a solid NaOH within ~ 10 min. The
compounds 14-15 are oxidized into the Mn(III)-complexes when isolated from the reaction
mixture. Chromatography of Mn(III)-porphyrins 14-15 on basic aluminum oxide (eluent-
chloroform) results in the formation of a mixture of Mn(II) and Mn(III) complexes.

R
R
3
3
R
R
R1
R1
R3
R3
R 2
R 2
N
H
N
N
N
N
N
R
R
R
M
R
H
N
N
R2
R2
R 3
R 3
R 2
R 2
R 3
R 3
R
R
R=R1=R2=R3=H 1,
М=Cd(II), R=R1=R2=R3=H 6,
R1=Br, R=R2=R3=H 2,
R1=R2=Br, R=R3=H 3,
R=Br, R1=R2=R3=H 4,
R1=R2=R3=Br, R=H 5,
М=Cd(II), R1=Br, R=R2=R3=H 7,
М=Cd(II), R1=R2=Br, R=R3=H 8,
М=Cd(II), R=Br, R1=R2=R3=H 9,
М=Cd(II), R1=R2=R3=Br, R=H 10,
M=(Сl)Mn(III), R=R1=R2=R3=H 11,
M=(Сl)Mn(III), R1=Br, R=R2=R3=H 12,
M=(Сl)Mn(III), R1=R2=Br, R=R3=H 13,
M=Mn(II), R=R1=R2=R3=H 14,
M=Mn(II), R1=Br, R=R2=R3=H 15,
M=Mn(II), R1=R2=Br, R=R3=H 16,
M=(Сl)Mn(III), R=Br, R1=R2=R3=H 17,
M=Mn(II), R=Br, R1=R2=R3=H 18,
M=(Сl)Mn(III), R1=R2=R3=Br, R=H 19,
M=Mn(II), R1=R2=R3=Br, R=H 20.
Scheme 1. Porphyrins in this study.
We showed that a mixture of Mn(II)- and Mn(III)-porphyrins is formed upon interaction
of porphyrin 3 with MnCl2 within 20 min [19]. This can be explained by the combined effects of
the reaction medium and the electron-withdrawing effect of bromine. Due to residual water,

boiling DMF is hydrolyzed [24], which results in the formation of reducing agents such as
formate and hydroxide [20, 21, 25] (eqn. 5):
СН(O)N(CH3)2 + H2O → СН(O)O- → СО + ОН-
(5)
When a mixture of manganese tetrabromoporphyrins is dissolved in chloroform,
oxidation of Mn(II) to Mn(III) is observed within 10 min. 2,3,12,13-Tetrabromo-5,10,15,20-
tetraphenylporphyrin Mn(II) 16 is formed in the corresponding Mn(III)-porphyrin DMF solution
within 20-30 min (figure 1). Thus, Mn(III)-porphyrin is formed in the aprotic solvent (CHCl3),
and in a strongly coordinating solvent of the basic character (DMF), Mn(II)-porphyrin can be
obtained.
The studies show that complexation of para-bromosubstituted porphyrin 4 with MnCl2
(molar ratio of reagents of 1:20) in boiling DMF occurs within 15 min with the formation of
5,10,15,20-tetra-(4-bromophenyl)porphyrin chloride Mn(III) 17. The UV-Vis spectrum of the
formed compound in chloroform has bands with λmax at 617, 581 525 477, 416, 402 and 375 nm.
While the bands of 1 with λmax at 646, 590, 550, 515 and 418 nm disappear. The synthesized
compound 17 and Mn(III)-porphyrins 11-13 possess the hyper-type UV-Vis spectrum [22] with a
large number of well-defined bands (figure 2, table S3).
When 17 is dissolved in DMF, full reduction Mn(III) → Mn(II) is not observed. In the
UV-Vis spectrum of the DMF solution along with max 608, 570, 437 and 418 nm, corresponding
to the Mn(II)-porphyrin, weak bands characteristic of the Mn(III)-porphyrin are observed
(figure 3). Mn(II)-5,10,15,20-tetra-(4-bromophenyl)porphyrin 18 is formed by adding solid
alkali (NaOH) to the DMF solution.
When octabromosubstituted porphyrin 5 is refluxed with MnCl2 in DMF for 30 s, the
initial porphyrin is present along with the Mn(II)- and Mn(III)-porphyrins in the reaction
mixture. The increase of the reaction time to 5 min or more does not lead to complete conversion
of the starting porphyrin into the corresponding manganese complexes. A mixture of
octabromosubstituted Mn(II)- and Mn(III)-porphyrins was synthesized in the presence of
potassium acetate (molar ratio of H2P / KOAc = 1:20). When the mixture of Mn(II)- and
Mn(III)-porphyrins is dissolved in chloroform a complete oxidation of the Mn(II)-porphyrins
into the Mn(III)-porphyrins occurs with formation of Mn(III)-2,3,7,8,12,13,17,18-octabromo-
5,10,15,20-tetraphenylporphyrin 19 (figure 4). On the other hand, 2,3,7,8,12,13,17,18-

octabromo-5,10,15,20-tetraphenylporphyrin Mn(II) 20 was formed by dissolving the Mn(II)- and
Mn(III)-porphyrins mixture in DMF.
The permetallation method of labile complexes of porphyrins [26] is widely used for the
synthesis of various metalloporphyrins. In labile complexes of porphyrins and phthalocyanine,
i.e. for ionic complexes (Li2P, Na2P, Li2Pc), there is no hindrance for exchange reactions. These
reactions for lithium porphyrins (Li2P) and lithium phthalocyanines (Li2Pc) with p, d and f-metal
salts are used in the synthesis of the corresponding MPs and MPCs [27]. Na-
tetraphenylporphyrin (Na2TPP) also easily exchanges Na+ in solutions [28]. Further studies on
cation exchange were focused on porphyrin complexes with a significant degree of ionicity of
MN bonds. These include the Mg(II), Cd(II), Hg(II), Pb(II) and Zn(II) complexes [27, 29]. It was
also noted that metal exchange occurs if more stable complexes are formed during the reaction
[30]. Further investigations show the use of the metal exchange method for synthesis of various
metalloporphyrins leads to a significant decrease in reaction time and increase in the yield of
final products [10-12, 31, 32].
We investigated the metal exchange reaction of 6-10 Cd(II) complexes with MnCl2 in
DMF under conditions comparable to the reaction of the corresponding porphyrin ligands with
the metal cations. Mn(III)-porphyrin 11 is formed by interaction of the Cd(II)-
tetraphenylporphyrin solution in DMF with MnCl2 at room temperature for 30 min. There are
bands with max at 603, 568, 521, 466, 416, 399 and 378 nm in the UV-Vis spectrum of the
formed compound (figure 5). The metal exchange reaction of Cd(II)-porphyrin 7 with MnCl2 in
DMF results in formation of mono-bromosubstituted Mn(III)porphyrin 12 under comparable
conditions for 70 min.
Para- and β-tetrabromosubstituted manganese porphyrins were synthesized at room
temperature for 7-8 h. The reaction time is reduced to 20-25 s by refluxing 8 and 9 solutions with
MnCl2 in DMF.
The mixture of Mn(II) and Mn(III)-porphyrins was synthesized by reaction of 10 with
manganese chloride (molar ratio 1:20) in boiling DMF for 30 s. In a solution of CHCl3 the
oxidation of Mn(II) → Mn(III) was observed for several hours. When Mn(II) and Mn(III)-
porphyrins
are
dissolved
in
DMF,
2,3,7,8,12,13,17,18-octabromo-5,10,15,20-
tetraphenylporphyrin Mn(II) 20 is formed.

1
The synthesized compounds were identified by UV-Vis spectroscopy, H NMR
spectroscopy, mass-spectrometry and elemental analysis.
A characteristic feature of the (X)Mn(III) structure is the presence of a strong interaction
of manganese with the porphyrin due to the (NMn) p()-d()-interaction, which coincides in
direction with the -bond. The insertion of the acido-ligands into the internal coordination sphere
of Mn(III)-tetraphenylporphyrins changes significantly the geometry of the molecules, which
leads to appearance of an additional band (max ~ 478-505 nm) and increase in the number of
bands compared to Mn(II)-complexes (table S3). The Mn(III)-porphyrins are paramagnetic. This
1
leads to the fact that in the H NMR spectra of the Mn(III)-tetraphenylporphyrins, the signals of
the pyrrole and phenyl rings are considerably broadened compared to the diamagnetic nitride
complexes of the Mn(V)-porphyrins [33].
The signals with a value of m/z 667.3, 746.2, 982.9 982.7 and 1298.2, in the mass spectra
of Mn(III)-porphyrins 11-13, 17 and 18, correspond to the molecular ions obtained as a result of
the M-Cl bond dissociation in corresponding Mn-porphyrins (figures S1-S5, experimental).
4. Conclusion
The reactions of the β- and para-bromophenyl substituted porphyrins coordination with MnCl2
and the metal exchange reaction of their cadmium complexes with MnCl2 were investigated in
DMF. Use of the metal exchange reaction significantly reduced the time of manganese porphyrin
formation and increased yield of final products in comparison with the reaction of the
corresponding porphyrin ligand complexation with Mn(II)-cations.
The metal exchange method of labile Cd-porphyrins made it possible to obtain Mn(III)-
tetraphenylporphyrin and its monobromo-substituted manganese(III) complex at room
temperature. The Mn(III)-tetraphenylporphyrins reduce to Mn(II)-porphyrins in DMF in the
presence of NaOH and in pure DMF. With an increase in the number of electron-acceptor
bromines (-I eff) in the pyrrole rings of Mn(III)-porphyrins, the reduction of Mn(III) → Mn(II) is
enhanced. Bromine atoms in the phenyl rings of the macrocycle exert less influence on the
formation of Mn(II)-porphyrins.

Acknowledgements
This work was supported by the Russian Scientific Foundation (project number 14-23-00204-P)
and the RFBR (grant number №18-03-00048_a), and employed with the equipment of the
Shared Facilities Center “Upper Volga Regional Center of Physicochemical Studies”.
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Figure 1. UV-Vis spectra of -bromosubstituted manganese porphyrins: (a) compound 13 in
CHCl3, (b) compound 16 in DMF (Ccomplexes ~ 1.5×10-5 mol/L).
Figure 2. UV-Vis spectra in chloroform: (a) the porphyrin 4, (b) 17.

Figure 3. The changes of the UV-Vis spectra of the DMF solution of 17: (a) at dissolution,
(b) after 1.5 h.
Figure 4. The UV-Vis spectra in chloroform: (a) of the mixture of octabromo-substituted
manganese porphyrins at dissolution, (b) of the Mn(III) porphyrin 19.

Figure 5. The UV-Vis spectra in chloroform: (a) of the Cd(II)-tetraphenylporphyrin, (b) of the
Mn(III)-tetraphenylporphyrin.
Graphical abstract