Complex formation of zinc-containing metalloporphyrins and nucleophilic substitution reactions involving pyridines

Article abstract of DOI:10.1007/s10593-012-1022-2

Linear correlations were found between the thermodynamic and kinetic parameters for the nucleophilic substitution and coordination of metalloporphyrins in various solvents with the participation of pyridines. Complex formation of zinc(II) tetraphenylporphyrin with n-donor ligands in chloroform at 25°C is proposed for use as a model system in the electronic spectroscopic investigation of the nucleophilicity and basicity of compounds capable of forming complexes of the n,? type.

Full text of DOI:10.1007/s10593-012-1022-2

Chemistry of Heterocyclic Compounds, Vol. 48, No. 3, June, 2012 (Russian Original Vol. 48, No. 3, March, 2012)
COMPLEX FORMATION OF ZINC-CONTAINING
METALLOPORPHYRINS AND NUCLEOPHILIC
SUBSTITUTION REACTIONS INVOLVING PYRIDINES
V. P. Andreev1*, P. S. Sobolev1, E. A. Larkina2, and E. P. Tkachevskaya2
Linear correlations were found between the thermodynamic and kinetic parameters for the nucleophilic
substitution and coordination of metalloporphyrins in various solvents with the participation of
pyridines. Complex formation of zinc(II) tetraphenylporphyrin with n-donor ligands in chloroform at
25°C is proposed for use as a model system in the electronic spectroscopic investigation of the
nucleophilicity and basicity of compounds capable of forming complexes of the n,ν type.
Keywords: donor-acceptor complexes, metalloporphyrins, pyridines, Hammett equation.
The present paper is a continuation of research of the quantitative relationships between the stability
constants of the complexes of zinc(II) tetraphenylporphin (Zn–TPP) and other metalloporphyrins (MP) with
various types of organic compounds, the rate constants for the nucleophilic substitution reactions, and the
physicochemical parameters characterizing these processes.
Earlier we showed [1-3] that the shifts (∆λ) of the absorption bands (λSoret 418.5 nm; λII 546.3 nm; λI 585
nm) of Zn–TPP complexes in chloroform during reaction with 3- and 4-substituted pyridines and also with the
N-oxides of pyridines, quinolines, and acridines correlate linearly with the logarithms of the stability constants
K of the complexes, the pKa values of the ligands (L) in water and other solvents, and the Hammett σ-constants
of substituents in the heterocycle. In addition, linear correlations are observed between the kinetic and
thermodynamic parameters of the Zn–TPP coordination process and certain nucleophilic substitution reactions
involving pyridines.
As model process [4] for investigation of the nucleophilicity of the reagents, we proposed to use their
complex formation with Zn–TPP in chloroform, and as a parameter of the nucleophilicity, which depends on the
basicity of the ligand, on the polarizability of the nucleophilic center and the molecule as a whole, and on the
electronic and spatial factors operating in the reagent, we proposed to use the stability constant K of the 1:1
Zn–TPP·L molecular complex and the ∆λ value. The aim of the present paper is to investigate the possibility of
using these data to predict the kinetic and thermodynamic parameters of coordination processes with other MPs.
_______
*To whom correspondence should be addressed, e-mail: andreev@psu.karelia.ru.
1Petrozavodsk State University, 33 Lenin Ave., Petrozavodsk 185910, Russia.
2M. V. Lomonosov Moscow Academy of Fine Chemical Technology, 86 Vernadskogo Ave., Moscow 119571,
Russia; e-mail: elenatkachevskaya@yandex.ru.
_________________________________________________________________________________________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 529-537, March, 2012. Original
article submitted March 21, 2011.
0009-3122/12/4803-0497©2012 Springer Science+Business Media, Inc.
497

We obtained experimental data for the coordination of the Zn–TPP complexes, zinc(II) protoporphyrin
dimethyl ester IX (Zn–PPDME IX), and zinc(II) chlorin e6 trimethyl ester (Zn–CTME e6).
H2C
H2C
Me
Me
Me
Me
N
N
N
N
N
N
N
N
N
N
N
N
CH2
Me
Zn
Zn
Zn
Me
Me
Me
Me
COOMe
COOMe
COOMe
Zn-PPDME IX
MeOOC
MeOOC
Zn-TPP
Zn-CTME e6
The stability constants K of the Zn–TPP molecular complexes with pyridine derivatives in chloroform
are concentration constants. Meanwhile, on account of the low concentration of the starting substances (2·10−5
for Zn–TPP and 10−4-10−3 M for the ligands) and also the absence of ionic forms in the solution it can be
assumed that the differences between the obtained values and the thermodynamic values are insignificant.
Good linear correlations are observed between log K, ∆λ, pKa, and the Hammett σ-constants (Table 1)
of studied MP, the stability constants of the complexes of pyridines with Zn–TPP being rather higher than for
those with Zn–PPDME IX. However, the electronic absorption spectra (EAS) of the complexes have individual
features. On the one hand, with decrease of the electron-donating properties of the substituents in the
heteroaromatic ring of the ligand the shifts of the maxima in the absorption bands for all three MPs (with the
exception of ∆λII for the Zn-CTME e6 complex with 4-dimethylaminopyridine) (Fig. 1) during coordination
with pyridines decrease in the following order: Zn–TPP > Zn–PPTME IX > Zn–CTME e6 (Table 1).
On the other hand, however, the ∆λ values vary in the order I > II > Soret for Zn–TPP, Soret > II > I for
Zn–PPDME, and e6 II > Soret > I for Zn–CTME, i.e., the sensitivity of ∆λ to the electronic effects of the
substituents in the ligand is an individual characteristic of the MP that depends not only on its nature but also on
the origin (type) of the absorption band.
Earlier, for the molecular complexes of heteroaromatic N-oxides of the n,ν type [3], we showed that the
maxima of the long-wave absorption bands in the electronic spectra undergo a larger bathochromic shift, the
longer the conjugation chain in the complex and the stronger the electron-donating properties of the substituent
in the molecule of the n-donor, and vice versa. This trend is confirmed by the increase of ∆λ for the complexes
of MP that we investigated from 4-cyano- to 4-dimethylaminopyridine and in the order Zn–TPP > Zn–PPDME
IX >Zn–CTME e6, since on account of their high polarizability the four phenyl rings in Zn–TPP must have
electron-donating properties during the formation of the MP–ligand complexes; conversely, during the
transition from Zn–PPDME IX to Zn–CTME e6 the accumulation of COOMe groups must lead to an increase
in their total electron-withdrawing effect. It is of importance that in the last case the second COOMe group is
only one methylene group away from the porphyrin ring (an increased -I effect), while the third is conjugated
with the ring and exhibits a negative mesomeric effect.
The increase of the nucleophilicity of the ligand due to the macrocyclic effect must lead to larger
projection of the zinc atom from the plane of the MP and to an increase of ∆λ. It is clear that the electron-
donating properties of the substituents in the porphyrin ring must favor this.
498

TABLE 1. The Stability Constants (K) of Molecular Complexes Zn–TPP
[2], Zn–PPDME IX, and Zn–CTME e6 with Pyridines in Chloroform at
25°C and the Shift of the Maxima (∆λ) of Absorption Bands I, II, and
Soret Bands in the Spectra of MP during Complex Formation
∆λ, nm
II
Substituent
in pyridine ligand
K, l/mol
I
Zn–TPP
20.4
Soret
4-Me2N
4-Me
H
22314 ± 878
6480 ± 240
3517 ± 150
803 ± 35
18.3
16.2
15.0
13.2
12.6
10.5
9.8
18.7
18.2
15.0
4-CN
7.7
Zn-PPDME IX
12.6
4-Me2N
4-Me
H
17150 ± 465
5095 ± 106
3330 ± 50
750 ± 25
14.0
12.0
11.7
10.0
16.3
14.2
13.7
10.8
10.9
10.5
8.9
4-CN
Zn-CTME e6
4.9
4-Me2N
4-Me
H
—
—
—
—
14.4
11.6
11.1
8.8
9.5
7.3
6.5
3.6
3.8
3.6
2.6
4-CN
_______
logKZn–TPP = 0.934 lgKZn– PPDME IX + 0.173, r = 0.999;
logKZn– PPDME IX = –0.927 σ + 3.496, r = 0.998;
logKZn– PPDME IX = 0.174 pKa + 2.594, r = 0.995;
ΔλI (Zn– PPDME IX) = 0.658 ΔλI (Zn–TPP) - 1.176, r = 0.975;
ΔλII (Zn– PPDME IX) = 0.757 ΔλII (Zn–TPP) - 0.064, r = 0.987;
ΔλSoret (Zn– PPDME IX) = 1.114 Δλ Soret (Zn–TPP) + 2.440, r = 0.992;
ΔλI (Zn– CTME e6) = 0.408 ΔλI (Zn–TPP) - 3.641, r = 0.973;
ΔλII (Zn–CTME e6) = 1.063 ΔλII (Zn–TPP) - 5.192, r = 0.990;
ΔλSoret (Zn–CTME e6)= 1.203 Soret (Zn–TPP) - 5.484, r = 0.998.
Fig. 1. The dependence of the shifts of the maxima of the absorption bands II (∆λII) of Zn–TPP [2]
(1 ∆λII = -3.64 σ + 15.30, r = 0.991), Zn–PPDME IX (2 ∆λII = -2.52 σ + 10.49, r = 0.999),
and Zn–CTME e6 (3 ∆λII = -3.81 σ + 11.11, r = 0.999) on the Hammett σ-constants upon
coordination of the MP with pyridines in CHCl3 at 25°C.
499

We compared the log K values that we obtained for the complex formation of Zn–TPP with pyridines in
chloroform with published data. It was found that they correlate linearly very well with log K determined by
spectrophotometry for the coordination of pyridines with Zn–TPP in methylene chloride and benzene, Cd–TPP
and Hg–TPP in chloroform and benzene (r = 0.994-0.999 [5], Fig. 2), and Zn–TPP and Zn(II)
octaethylporphyrin (Zn–OEP) in toluene (r = 0.985 and 0.974 respectively [6]).
Fig. 2. The dependence of log K (1) for Cd–TPP (log KCd–TPP, 0.1 M TBAP = 1.56 log KZn–TPP, 0.1M TBAP - 0.997,
r = 0.998) in CH2Cl2 [5] and (2) Zn–TPP (log KZn–TPP = 0.822 log KZn–TPP, 0.1M TBAP + 0.591, r = 0.996)
in CHCl3 (our data [2]) on log K for Zn–TPP (Х = 4-NMe2; 4-NH2; 4-Me; 3-Me; H; 4-CN; 3,5-Cl2;
3-CN; 3-Cl; 3-Br; 3-MeCO; 4-MeCO; 3,4-Me2; 0.1M solution of tetrabutyl perchlorate (TBAP) [5])
in CHCl3 for the coordination processes with pyridines.
It is necessary particularly to note that the 0.1 M additions of quaternary ammonium salts [5] to the
aprotic solvents required for sufficient electric conductivity in the solutions do not violate the linear correlations
described above and can make it possible to extend our proposed approach to electrochemical processes.
Thus, in the case of coordination-unsaturated Zn(II), Cd(II), and Hg(II) MPs it is possible on the basis
of our proposed scale of nucleophilicity in the presence of correlation equations to calculate the stability
constants of their complexes with n-donor ligands in various aprotic solvents. Unfortunately, we did not find
published data concerning the conformity of the ∆λ values to equations of the Hammett and Taft type for
various types of solvents and MPs. However, in our opinion, the linear correlations relating them to the log K,
pKa, σ-constants, and other physicochemical parameters dependent on the electron density at the nucleophilic
center must be fairly universal.
Table 2 gives examples of various nucleophilic substitution reactions [7-15] for which linear
correlations (r = 0.970-0.999) are fulfilled between log k (k is the reaction rate constant), on the one hand, and
log K and ∆λ (for complex formation between 3- and 4-substituted pyridines and Zn–TPP [2], Zn–PPDME IX,
and Zn–CTME e6), on the other.
500

TABLE 2. Nucleophilic Substitution Reactions with Pyridines for which
log k Correlates Linearly with log K and ∆λ for the Coordination of
Pyridines with Zn–, Cd–, and Hg–TPP, Zn–OEP [2, 5, 6], Zn–PPDME IX,
and Zn–CTME e6 in CHCl3, CH2Cl2, C6H6, and PhMe
Reaction
Conditions
Methanol,
YC6H4SO2Cl + XC5H4N → YC6H4SO2N+C5H4X + Cl–
Y= H, 4-Me, 4-MeO, 4-Cl, 4-NO2, 3-Cl, 3-NO2;
X = H, 4-Me, 3-Me, 3-CONH2, 4-CN
XC5H4N + CH3COOAc + H2O → AcOH + CH3COO– HN+C5H4X
35°С [7]
Aqueous solution,
X = H, 4-Me, 4-NMe2, 3-CONH2, 4-CN
25°С [8]
+
XC5H4N + RNHSO2OC6H4NO2 → RNHSO2 NC5H4X + –OC6H4NO2
CHCl3,
R = H, C6H5; X = H, 3-Me, 4-NMe2
XC5H4N + EtI → Et+NC5H4X I–
37°С [9]
Nitrobenzene,
X = H, 3-Me, 4-Me, 4-CN
60°С [10]
XC5H4N + RSO3F → RSO3+NC5H4X F–
Sulfolane,
XC5H4N + RI → R+NC5H4X I–
R = Me, Et; X = H, 3-Me, 4-Me, 4-CN
nitrobenzene,
2-nitropropane
25°С[11]
XC5H4N +C6H5SO2Cl + H2O → C6H5SO2OH + XC5H4N+Cl–
Aqueous solution,
X = H, 3-Me, 4-Me, 3-COOC2H5, 4-CN
XC5H4N +C6H5SO2Cl + H2O → C6H5SO2OH + XC5H4N+Cl–
15-35°С [12]
Acetonitrile,
X = H, 4-Me, 4-NMe2
(С6H5)2POCl + XC5H4N + H2O → (С6H5)2PO(OH) + XC5H4N+Cl–
25°С [13]
Acetonitrile,
X = H, 4-Me, 4-NMe2
25°С [14]
RO– + –PO3 NC5H4X → RPO42– + NC5H4X
Aqueous solution,
25°С [15]
X = H, 4-Me, 3-CONH2 (in the absence of and in the presence of Mg2+)
We note also that, as we have showen earlier [16], the shifts of the maxima (∆λ) in the absorption bands
of Zn–TPP in chloroform during reaction with anilines with substituents at positions 3 and 4 correlate linearly
with log K of the complexes, with the pKa values of the ligands in water, and with the σ-constants of the
substituents in the benzene ring. It was found that the rate constants of certain nucleophilic substitution
reactions (log k) with anilines in various solvents are also related by linear equations (r = 0.97-0.99) to the
stability constants of the complexes of anilines with Zn–TPP in chloroform at 25°C and also to the shifts of the
maxima in the absorption bands of the MP. Linear relationships between log K, log kcat, pKa, σ+, and ∆λ are also
observed for the rate constants (kcat) of the catalytic enzymatic oxidation of horseradish peroxidase [16].
Consequently, on the basis of the numerical values of K and ∆λ (according to the nucleo-
philicity/basicity scale that we introduced) for the coordination of Zn–TPP with various types of ligands
(coordination chemistry) it is possible to predict the rate both of nucleophilic substitution reactions (organic
chemistry) and of enzymatic reactions (biological chemistry) in various organic and aqueous solutions and vice
versa. This is based on the similarity of the structure and properties of the molecular complexes of Zn–TPP, of the
transition states (activated complexes) in SN reactions, and of the enzyme–substrate complexes when
ligands/nucleophiles/substrates of one type are used. We suppose that this approach can be extended also to
electrochemistry in so far as for anilines and phenols [16], for example, all the parameters mentioned above are
related linearly within the limits of compounds of one class to the half-wave potential (E1/2) for electrochemical
oxidation of the substrate and also to the ionization potentials of the highest occupied molecular orbital.
We have also determined the thermodynamic parameters for the coordination process of Zn–PPDME IX
with pyridines (Table 3).
According to the data in Table 3, in all cases ∆H0 has negative values and depends linearly on the basicity of
the ligands (∆H0Zn–PPDME IX = 2320 pKa - 29168, r = 0.999) and the Hammett σ-constants (∆H0Zn–PPDME IX = -12383
σ -17103, r = 0.999), their absolute values increasing with decrease of the pKa value of the ligand. This may
mean that the solvation–desolvation processes of the ligand play a very important role in the complex
501

formation of Zn–TPP and Zn–PPDME IX with pyridines in CHCl3, capable of forming both hydrogen bonds
and charge-transfer complexes [21]. In view of the fact that more basic ligands must be solvated by chloroform
more strongly their desolvation requires larger expenditure of energy.
In the transition from the most basic 4-dimethylaminopyridine to the least basic 4-cyanopyridine, the
∆S0 constants change their values from positive to negative and also depend linearly on the pKa values of the
ligands (∆S0Zn–PPDME IX = 11.24 pKa - 49.3, r = 0.998) and the Hammett σ-constants (∆S0Zn–PPDME IX = -60σ + 9.16,
r = 0.999) of the substituents in accordance with the expected order of variation of their solvation–desolvation
processes. However, the T∆S0 value changes somewhat faster in this series than the ∆H0 value, reducing the
possibility of complex formation with Zn–TPP and Zn–PPDME IX as the electron-withdrawing properties of
the substituents in the pyridine ring are increased.
Thus, despite the decrease of the negative value of the standard enthalpy for the complex formation of
Zn–TPP and Zn–PPDME IX with increase in the basicity of the ligands the thermodynamic stability of the
complexes (∆G0) increases due to increase in the entropy control of the coordination processes.
The enthalpy and entropy values for the formation of the Zn–TPP and Zn–PPDME IX complexes with
pyridines are fairly close, but in view of the very high correlation coefficients of the ∆H0 – ∆S0 relationship
(Zn–TPP, r = 0.9999, n = 6 [2]; Zn–PPDME IX, r = 0.9997) it is, in our opinion, possible to speak of a reliable
difference in the values of the isoequilibrium temperature (β 196 and 206 K respectively) for these two
processes.
Linear relationships are also observed between the activation parameters (∆H≠ and ∆S≠ [12]) for the
hydrolysis of benzenesulfonyl chloride, catalyzed by pyridines, on the one hand and ∆H0 and ∆S0 for the
coordination of Zn–TPP and Zn–PPDME IX with pyridines (they also correlate linearly with ∆H0 and ∆S0 [22]
for the dissociation of aqueous solutions of the cations of substituted pyridinium XC5H4N+) on the other. From
this, it can be concluded that simple correlation equations can be observed between the thermodynamic
parameters of the reactions SN and the complex formation processes of the MP.
Thus, in our opinion, the coordination of Zn–TPP in chloroform with ligands (ν-acceptors) like
nitrogen-containing heterocycles is a good model system for electron spectroscopic investigation of the
nucleophilicity and basicity (and possibly also oxidation-reduction characteristics) of compounds capable of
forming complexes of the n,ν type.
TABLE 3. The Thermodynamic Constants (∆H0, ∆S0) for the Complex
Formation of Zn–TPP and Zn–PPDME IX with Pyridines in CHCl3, the
Hammett σ-Constants of the Substituents, and the pKa Values of the Pyridines
in Water at 25°C
Substituent
in ligand
XC5H4N
Zn–TPP *
Zn–PPDME IX
рKа (Н2О) σ [19]
-ΔH0, kJ/mol ΔS0, J/(mol·K) -ΔH0, kJ/mol ΔS0, J/(mol·K)
4-Me2N
4-Me
H
9.71 [17]
5.98 [17]
5.29 [18]
-0.84
-0.17 14.36 ± 0.59
17.29 ± 0.17
8.65 ± 0.11
53.8 ± 0.4
6.92 ± 0.18
57.80 ± 2.6
21.50 ± 1.0
10.55 ± 0.7
-30.30 ± 1.8
25.0 ± 1.6 14.73 ± 0.26
8.9 ± 0.6 16.93 ± 0.16
-27.0 ± 1.6 25.10 ± 0.58
0
4-CN
1.86 [10] 0.628 [20] 24.50 ± 0.56
_______
*∆H0Zn–PPDME IX = 1.13 ∆H0Zn–TPP + 2.45, r = 0.988;
∆S0Zn–PPDME IX = 1.07 ∆S0Zn–TPP - 1.60, r = 0.988;
∆H0Zn–PPDME IX = 206 ∆S0Zn–PPDME IX - 19000, r = 0.9997.
The thermodynamic data for 4-Me2NPy, Py, and 4-CNPy were taken from our
work [2].
502

EXPERIMENTAL
The electronic spectra were recorded on an SF 2000-02 instrument. The stability constants of Zn–TPP
with pyridines in chloroform were determined as described in [1]. The thermodynamic constants of the complex
formation process were calculated graphically by means of the equation (Uhlig's first approximation [23]):
lnKT = -ΔH0298 / RT + ΔS0298 / R,
on the assumption that the ∆H and ∆S values remain constant in the investigated narrow temperature range
(273-313 K). The pyridine and its derivatives were purified as described in [10], and their physical constants
agreed with published data. The Zn–TPPs were obtained as described in [3]. The dimethyl ester of
protoporphyrin IX (PPDME IX) was synthesized from protohemin IX, which was subjected to simultaneous
removal of the iron and esterification by the action of iron(II) sulfate in MeOH with the passage of gaseous HCl
according to the method in [24].
Pheophorbide a Methyl Ester. The dried biomass of microalga Spirulina platensis (200.0 g) was
suspended in acetone and subjected to strong cooling in liquid nitrogen. The mixture was heated to room
temperature and extracted three times (in argon without access to light for 2 h) each time with the addition of a
fresh portion of acetone to the filtered biomass. The acetone extracts were combined and concentrated, and
water was added at the ratio of 100 ml of water to 500 ml of the extract. After 12 h, the precipitate, containing
chlorophyll a, was filtered off and dissolved in petroleum ether. The solution was passed through a layer of
Kieselgel 60 silica gel (0.063-0.100 μm) and evaporated to dryness. The obtained chlorophyll a was submitted
to transesterification in MeOH in the presence of 7.5% H2SO4 with simultaneous removal of the magnesium
ions. After the reaction, the solution was neutralized, extracted with CHCl3, and purified by column
chromatography on Kieselgel 60 silica gel with CHCl3 as eluent. After recrystallization from a mixture of
CHCl3 and petroleum ether, 331.3 mg of pheophorbide a methyl ester were obtained.
The data from the electronic and 1H NMR spectra agree with published data [25].
Chlorin e6 trimethyl ester (CTME e6) was obtained by the method described in [26] from
pheophorbide a methyl ester.
The zinc complexes of porphyrins were obtained by adding a saturated solution of zinc acetate in
MeOH to a solution of the starting metal-free porphyrin in CHCl3. After stirring for 30 min without access to
light, the formation of a metal complex was observed in the electronic spectrum of the mixture. The reaction
mixture was then washed with water, dried over Na2SO4, and filtered through a layer of silica gel. The solvent
was evaporated under vacuum, and the residue was reprecipitated from CHCl3 with petroleum ether.
Electronic spectra of Zn–CTME e6 (chloroform, λmax, nm): 412.8, 510.2, 640.2; Zn–PPDME IX
(chloroform, λmax, nm): 410.2, 538.8, 577.6.
REFERENCES
1.
2.
V. P. Andreev, Ya. P. Nizhnik, D. G. Bezruchko, and A. K. Morozov, Zh. Obshch. Khim., 75, 1379
(2005).
V. P. Andreev, V. V. Vapirov, Ya. P. Nizhnik, S. G. Tunina, and P. S. Sobolev, Zh. Org. Khim., 46,
1556 (2010).
3.
4.
5.
6.
7.
V. P. Andreev, Diss. Doct. Chem. Sci. [in Russian], Petrozavodsk (2007).
V. P. Andreev, Ya. P. Nizhnik, and N. Sh. Lebedeva, Zh. Org. Khim., 44, 1201 (2008).
К. М. Kadish and L. R. Shiue, Inorg. Chem., 21, 3623 (1982).
G. Szintay and A. Horvath, Inorg. Chim. Acta, 310, 175 (2000).
S. W. Hong, H. J. Koh, and I. Lee, J. Phys. Org. Chem., 12, 425 (1999).
503

8.
9.
С. Castro and E. A. Castro, J. Org. Chem., 46, 2939 (1981).
W. J. Spillane, G. Hogan, P. McGrath, J. King, and С. Brack, J. Chem. Soc., Perkin Trans. 2, 2099
(1996).
10.
11.
12.
13.
A. Fischer, W. J. Galloway, and J. Vaughan, J. Chem. Soc., 3591 (1964).
E. M. Arnett and R. Reich, J. Am. Chem. Soc., 102, 5892 (1980).
O. Rogne, J. Chem. Soc. B, 727 (1970).
V. A. Savelova, A. F. Popov, T. N. Solomoichenko, Yu. S. Sadovskii, Zh. P. Piskunova, and
O. V. Lobanova, Zh. Org. Khim., 36, 1502 (2000).
14.
V. A. Savelova, T. N. Solomoichenko, T. V. Ved', Yu. S. Sadovskii, and Yu. S. Simanenko, Zh. Org.
Khim., 29, 666 (1993).
15.
16.
D. Herschlag and W. P. Jenks, J. Am. Chem. Soc., 112, 1951 (1990).
V. P. Andreev, P. S. Sobolev, D. O. Zaitsev, N. A. Galibina, N. S. Zykina, L. Yu. Plyasunova, and
M. I. Romanova, Uch. Zap. PetrGU, Ser. Estestv. i Tekhn. Nauki, No. 6 (119), 7 (2011).
K. M. Kadish, L. R. Shiue, R. K. Rhodes, and L. A. Bottomley, Inorg. Chem., 20, 1274 (1981).
R. G. Garvey, J. H. Nelson, and R. O. Ragsdale, Coord. Chem. Rev., 3, 375 (1968).
H. Becker, Introduction to Electronic Theory of Organic Reactions [Russian translation], Mir, Moscow
1977.
17.
18.
19.
20.
21.
R. W. Hoffmann, Mechanisms of Organic Reactions [Russian translation], Khimiya, Moscow (1979).
L. J. Andrews and R. M. Keefer, Molecular Complexes in Organic Chemistry, Holden-Day, San
Francisco (1964).
22.
23.
I. R. Bellobono and M. A. Monetti, J. Chem. Soc., Perkin Trans. 2, 790 (1973).
B. P. Nikol'skii (editor), Physical Chemistry. Theoretical and Practical Handbook. Textbook for
Universities [in Russian], Khimiya, Leningrad (1987).
24.
J. E. Falk, Porphyrins and Metaloporphyrins, Vol. 2, Elsevier, Amsterdam-London-New York (1964),
p. 266.
25.
26.
A. S. Brandis, A. N. Kozyrev, and A. F. Mironov, Tetrahedron, 48, 6485 (1992).
S. Lötjönen and P. H. Hynninen, Synthesis, 541 (1980).
504