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11Фталоцианины Phthalocyanines
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DOI: 10.6060/mhc2012.120360s
First Water-Soluble ^-Nitrido Dimer of Iron Phthalocyanine
Pavel A. Stuzhin,a@ Svetlana S. Ivanova,a Ilya Dereven'kov,a Sergey V. Makarov,a Radu Silaghi-Dumitrescu,b and Heiner Homborgc
aDepartment of Organic Chemistry, Ivanovo State University of Chemical Technology, RF-153000 Ivanovo, Russia b"Babes-Bolyai" University, RO-400028 Cluj-Napoca, Romania
cInstitute of Inorganic and General Chemistry, Christian-Albrechts-Universitat, D-24098 Kiel, Germany. @Corresponding author E-mail: stuzhin@isuct.ru
The first water soluble j-nitridodimer ofFe-phthalocyanine j-N(FeTSPc)2 has been prepared by two alternative routes: (i) by thermolysis of bis-azidocomplex of iron(III) tetrasulfophthalocyanine [(N3)2FeTSPc]- in acetic acid, and (ii) by sulfontion of j-nitridodiiron bisphthalocyanine ¡i-N(FePc)2 with chlorosulfonic acid.
Keywords: Tetrasulfophthalocyanine, iron complex, j-nitrido dimer.
The j-nitrido dimer of Fe-phthalocyanine j-N(FePc)2 was first reported and actively studied in the middle of the 1980s.[1,2] Recently it was established that its tert-butyl substituted derivative j-N(FePcfBu4)2 catalyses the oxidation of methane by H2O2 under very mild conditions (25-60oC),[3] and then a high catalytic activity was also demonstrated in the oxidation of other organic substrates.[4] It has been shown in theoretical work[5] that the ability of the j-nitrido moiety to serve as a remarkable charge reservoir and to stabilise the lower spin-states can enhance the catalytic activity of ji-nitrido dimers of Fe-porphyrazines in comparison with the corresponding j -oxo species. The water-soluble FeIII-tetrasulfophthalocyanine in its j -oxo form, j -O(FeTSPc)2, catalyses various redox-reactions in aqueous medium.[6] Among j -nitrido dimers so far only j -N(FePctBu4)2 and other species well-soluble in organic solvents due to presence
of alkyl residues were studied, including alkoxy[7] and alkylsulfonyl[8] substituted derivatives. We report here the synthesis of the first water-soluble derivative - the j-nitrido dimer of Fe-tetrasulfophthalocyanine, j-N(FeTSPc)2, which was prepared by two alternative routes (Scheme 1).
In the first approach Fe-tetrasulfophthalocyanine, which was prepared by cyclotetramerization of 4-sulfophthalic acid,[9] was used as a starting material. In neutral or basic water solutions this species exists as |-oxodimer |-O(FeTSPc)2,[6] but its dissolution in acetic acid leads to the monomeric acetate complex (AcO)FeTSPc. This is evidenced by the UV-vis spectrum in acetic acid, in which along the 0-band at 652 nm the lower intensity charge-transfer band is seen at 840 nm (Figure 1, spectrum 2). Such spectrum is characteristic for five-coordinated FeIn complexes of porphyrazines[10] and phthalocyanine[11] containing FeIn in the intermediate spin
HO,S
HO.S
.SO,H
-sew
'SO,H
u-O(FeTSPc),
u-N(FeTSPc),
u-N(FePc),
ArOH
HO,S
-SO,H
-SO-.H
(AcO)FeTSPc
N3
r(N,),FeTSPcr
Scheme 1. Synthetic routes to p,-nitridodimer of Fe-tetrasulfophthalocyanine, p,-N(FeTSPc)2. Макрогетероцикмм /Macroheterocycles 2012 5(2) 175-177 © ISUCT Publishing
^-Nitrido Dimer of Iron Tetrasulfophthalocyanine
state S=3/2. Thus for [(Cl)FePc] the Q-band at 655 nm (n-n* transition) is accompanied by a charge transfer band (n-dn) at 832 nm.[11] Addition of azide (NaN3 or HN3) leads to formation of a six-coordinated bisazido complex [(N3)2FeTSPc]- which can be followed by disappearance of the absorption bands of the pentacoordinated acetate complex at 652 and 840 nm and the appearance of a new very intense band at 673 nm (Figure 1, spectrum 3). Six-coordinated pseudohalide complexes of FeIII-phthalocyanine [(X)2FePc]- exhibit similar spectral features with the Q-band at 670-690 nm. Refluxing of the solution of the bisazido complex [(N3)2FeTSPc]- leads to its thermolysis with formation of the |-nitrido dimer, |-N(FeTSPc)2 (Figure 1, spectrum 4), similarly as in the case
of bisazido complexes of unsubstituted FeIII-phthalocyanine.
[2]
X, nm
Figure 1. UV-Vis spectra of |-oxo dimer |-O(FeTSPc)2 in water (1), acetate complex (AcO)FeTSPc formed in acetic acid (2); its conversion to bis azido complex [(N3)2FeTSPc]- (3)after addition of NaN and to |-nitrido dimer |-N(FeTSPc)2 (4) upon heating.
The second approach is based on our finding that the | -nitrido dimer of Fe-phthalocyanine | -N(FePc)2, prepared as described elsewhere,[1a2] unlike the |-oxo-dimer |-O(FePc)2, is very stable even in very strongly acidic media and can be chlorosulfonated with hot HSO3Cl (4 h at 150oC). After overnight staying of the reaction mixture the chlorosulfonic derivative | -N(FePc(SO2Cl)4)2 was isolated by pouring on ice and then hydrolysed with water at 80oC to give | -N(FeTSPc)2. Treatment of the sulfochloride |-N(FePc(SO2Cl)4)2 with dibutylamine gives the sulfamide derivative |-N(FePc(SO2NBu2)4)2. Elemental analysis and ESI mass-spectroscopy show the presence of four sulfonyl groups per Fe-phthalocyanine unit.
The UV-Vis spectrum of the obtained |-nitrido dimer |-N(FeTSPc)2 in acetic acid contains a broadened Q-band with a maximum at 640 nm and a shoulder at 680 nm (Figure 1, spectrum 4). The spectrum in water is shown in Figure 2 (left panel). Such spectral pattern is typical for single-atom ^-bridged dimeric Fe-phthalocyanines with exciton coupling between two adjacent n-chromophores. In comparison
with the |-oxodimer |-O(FeTSPc)2 the Q-band and the Soret bands in the UV-vis spectrum of |-N(FeTSPc)2 are bathochromically shifted (632 ^ 640 and 326 ^ 336 nm, respectively, Figure 2, left panel). Interestingly, the maximum of the Q-band in |-N(FeTSPc)2 has a similar position to that observed in dichlorometane solutions of alkylsulfonyl substituted derivatives |-N(FePc(SO2Alk)4)2 (Alk = tert-butyl, hexyl, XQ ~ 638 nm) and dibutylsulfonylamide |-N(FePc(SO2NBu2)4)2 (XQ = 634 nm). The difference in the electron-withdrawing properties of various sulfonyl groups is relatively small and the peripheral substituents in the phthalocyanine macrocycle have only weak influence on the spectral properties, which are more sensitive to the coordination mode and electronic structure of the metal center. The close position of the Q-band for the obtained sulfonated ^-nitrido dimer of Fe-phtalocyanine (~635-640 nm) with the non-oxidised ^-nitrido dimers bearing other sulfonyl substituents is indicative of their similar electronic structure.
The ^-nitrido dimers of Fe-phthalocyanine can contain two equivalent iron atoms either in the oxidation state +3.5 (FeIII'/-N-FeIII'/) or +4 (FeIV=N+=FeIV).[12] In the case of the unsubstituted derivative ^-N(FePc)2 the oxidation to cationic species [^-N(FePc)2]+ containing two FeIV occurs already at E'2=0.00 V and requires very mild oxidation agents such as ferrocenium cation, tetracyanoquinodimethane[1] or even iodine, while stronger oxidants, e.g. bromine, nitric acid or trifluoroacetic acid in air, lead to further oxidation involving macrocycle[2] yielding red-brown coloured complexes of FeIV with phthalocyanine cation-radical - [^-N((X)FePc+)2]+(X) (X = Br, CF3COO-, NO3-). Upon oxidation of the ^-bridge from (FenI/-N~FeIn/) to (FeIV=N+=FeIV) the Q-band maximum is shifted bathochromically by 10-20 nm,[1b8] while further oxidation of the macrocycle leads to red-brown species[2] due to appearance of absorption in the 500-550 nm region characteristic for cation-radicals.
We have studied the action of oxidants on the spectral properties of the obtained ^-nitridodimer of Fe-tetrasulfophthalocyanine. In the presence of hydroperoxide (H2O2 in basic medium) no changes were observed in its UV-vis spectrum in aqueous solution. Addition of bromine to its solution in acetic acid leads only to some broadening of the Q-band, while the position of its maximum remains changed. The Q-band at ~635-640 nm in ^-N(FeTSPc)2 can be associated with the presence of the (FeIn/-N-FeIII/2) bridge, since in the cationic oxidised species, containing (FeIV=N+=FeIV), it should be observed at longer wavelength (650-665 nm). Thus, for the oxidised alkylsulfonyl derivatives [^-N(FePc(SO2Alk)4)2]+ the Q-band is shifted from 638 to 647-657 nm,[8] and the addition of Br2 to solution of sulfamide derivative ^-N(FePc(SO2NBu2)4)2 in CH2Cl2 shifts the Q-band from 634 to 664 nm and broadens it. The electron-withdrawing sulfonyl groups presumably stabilise the phthalocyanine macrocycle to oxidation by bromine.
The ESR spectrum of ^-N(FeTSPc)2 aqueous solution (Figure 2, right panel) confirms the presence of the (FeIn/—N^ FenI/) bridge. It contains the characteristic triplet at g±=2.13, which is typical for ^-nitrido dimers of Fe-porphyrins[12] and Fe-porphyrazines[13] and originates from the hyperfine interaction of the unpaired electron with 14N nucleus on the ^-nitrido-bridge (AN±=2.60 mT). The complicated ESR pattern in the g~1.9-2.9
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Макрогетероциmbl /Macroheterocycles 2012 5(2) 175-177
P. A. Stuzhin et al.
2700
2900 3100 3300 3500
B, Gauss
Figure 2. UV-Vis (left) and ESR (right) spectra of |-oxo (1) and |-nitrido (2) dimers of Fe-tetrasulfophthalocyanine in water.
region might be connected with the additional interaction with the nitrogen atoms of the phthalocyanine macrocycle and coordination of oxygen as was observed for ц-nitrido dimer of Fe-porphyrazine.[13] The ESR spectrum exhibits also minor signals of the monomelic impurities, containing Fe111 in the spin states S = 1/2 and 3/2 (g3 at 2.3 and g± ~ 4.3, respectively), which can not be seen in UV-Vis spectrum
The value of the magnetic moment of ^-N(FeTSPc)2 in water solution ^eff = 2.14цв at 298 K (Evans method) also corresponds to the value expected for a system with one unpaired electron and is consistent with the data reported for the dimeric ц-nitrido Fe-complexes of other tetrapyrrolic macrocycles - ^-N(FePc)2 (^eff=2.13^B),[1] Fe-octaphenyl-porphyrazine (2.24цв)[13] and Fe-tetraphenylporphine ^eff=2.04^).[14]
In the NMR spectrum, the aromatic protons of the benzene rings are observed as overlapping multiplets in the region typical for diamagnetic phthalocyanines (7.6-8.7 ppm), implying negligible delocalization of the unpaired electron from the dz2 orbital onto the phthalocyanine macrocycle.[15]
In conclusion, we have prepared the ц-nitrido dimer of Fe-tetrasulfophthalocyanine, ^-N(FeTSPc)2 - the first water-soluble ц-nitrido dimer, and provide evidence that it contains an (Fein/—N—Feni/) bridging moiety. Further studies of this complex, including its redox properties and catalytic activity in aqueous solution, are in progress.
Acknowledgements. This work was supported by the Russian Foundation of Basic Research (grant Nr 12-03-00563).
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Received 08.03.2012 Accepted 19.05.2012
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