Coordination properties of (chloro)aluminum-5,15-diphenyloctaalkylporphyrin in the reactions with small organic molecules

Article abstract of DOI:10.1134/S1070328410050015

The reactions of aluminum porphyrinate ((Cl)AIP) with organic molecules L (imidazole, pyridine, pyrimidine, and pyrazine) in benzene were studied using spectral and quantum-chemical methods. The structures and stabilities of the molecular complexes (Cl)Al(L)_nP in solutions were determined. The influence of the nature of the macrocyclic ligand and organic base on the coordination properties of aluminum porphyrinate was observed. The degree of deformation of the metalloporphyrin and its molecular complexes was estimated. A good correlation between the experimental and calculated characteristics Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S1070328410050015

ISSN 1070ꢀ3284, Russian Journal of Coordination Chemistry, 2010, Vol. 36, No. 5, pp. 323–329. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © S.V. Zaitseva, S.A. Zdanovich, O.I. Koifman, 2010, published in Koordinatsionnaya Khimiya, 2010, Vol. 36, No. 5, pp. 323–329.
Coordination Properties of (Chloro)aluminumꢀ5,15ꢀ
Diphenyloctaalkylporphyrin in the Reactions
with Small Organic Molecules
S. V. Zaitsevaa, *, S. A. Zdanovicha, and O. I. Koifmana, b
a Institute of Solution Chemistry, Russian Academy of Sciences, Akademicheskaya 1, Ivanovo, 153045 Russia
b Ivanovo State University of Chemical Technology, Ivanovo, Russia
*Eꢀmail: svz@iscꢀras.ru
Received September 9, 2009
Abstract—The reactions of aluminum porphyrinate ((Cl)AIP) with organic molecules L (imidazole, pyriꢀ
dine, pyrimidine, and pyrazine) in benzene were studied using spectral and quantumꢀchemical methods. The
structures and stabilities of the molecular complexes (Cl)Al(L)nP in solutions were determined. The influꢀ
ence of the nature of the macrocyclic ligand and organic base on the coordination properties of aluminum
porphyrinate was observed. The degree of deformation of the metalloporphyrin and its molecular complexes
was estimated. A good correlation between the experimental and calculated characteristics
DOI: 10.1134/S1070328410050015
One of the main factors defining the catalytic activꢀ the molecular complexes were described in detail
ity of metal porphyrinates is the presence of an addiꢀ [6
tional axial ligand in the complex along with the macꢀ
rocyclic ligand nature. The study of the influence of
the nature of small organic molecules on the coordiꢀ
nation properties of highꢀcharge metal porphyrinates
evoke increased interest.
⎯8].
Electronic absorption (UV) spectra were recorded
on a Caryꢀ50 spectrophotometer in the range from 380
to 700 nm as plots and tables for the subsequent mathꢀ
ematical processing. Changes in the absorbance for a
series of solutions at a constant concentration of aluꢀ
minum porphyrinate and various base concentrations
were detected at the working wavelengths 407–411
The purpose of the present work is to study the
intermolecular interactions of aluminum porphyriꢀ
nate ((Cl)AIP) with monoꢀ and diatomic bases (L),
namely, imidazole (Im), pyridine (Py), pyrimidine
(Prm), and pyrazine (Prz), in benzene at 298 K using
spectrophotometric titration [1] and computer simuꢀ
lation [2–5].
and 421–422 nm in cells with l= 1 cm. The inaccuracy
of temperature maintenance did not exceed 1 K.
The dependences presented below were processed
using the leastꢀsquares method. The relative error in
Кst determination did not exceed 8–10%.
Quantumꢀchemical calculations were performed
by the PM3 method [2–4] using the PC version [9] of
the Gamess program package [10]. The condition for
the end of calculations was a specified gradient of
0.0004 kJ mol–1 l–1. The initial data were prepared and
the calculation results were processed using the
ChemCraft program, version 1.3, developed by
G.A. Zhurko [11]. The angles and bonds of the averꢀ
aged structure of the planar metalloporphyrins [12]
were used in the initial approximation for the porphyꢀ
rin macrocycle, and the bond lengths and angles of the
phenyl and alkyl substituents of the porphyrin and of
the organic bases from [13] were used. The butyl subꢀ
stituents in the initial approximation were specified as
transꢀisomers in the retarded conformation. The mean
plane of the phenyl fragments is oriented at the right
angle to the mean plane of the macrocycle. When
modeling the molecular complex, the orientation of
the organic bases was performed in such a way that the
Bu
Cl
Bu
N22
Al
N23
N21
N24
Bu
(Cl)AlP
EXPERIMENTAL
The formation of the mixedꢀligand complex
(Cl)Al(L)nP was carried out in benꢀ
zene at 298 K. The experimental procedure and calcuꢀ
(Cl)AIP + Ln
lation of the stability (equilibrium) constants (Кst) of
323

324
ZAITSEVA et al.
А
424 nm
411 nm
A
1.0
0.8
0.6
0.4
(b)
0
1.0
cIm
2.0
10–4, mol/l
3.0
×
(a)
350
375
400
425
450
λ
, nm
–6
–3
Fig. 1. (a) Change in the UV spectra of (Cl)AlP in the reaction with imidazole (
c
from 5.2
×
10 to 6.22 × 10 mol/l) and (b) the
corresponding titration curve at Δλ = 424 nm.
mean plane of the axial ligand would be perpendicular
to the mean plane of the porphyrin macrocycle and
the nitrogen atom with a lone electron pair would be
directed toward the aluminum atom.
1H NMR (CDCl3),
, ppm: 10.07 s (2H, mesoꢀH),
7.83 m, 9.15 m, 10.60 m (10H, Ph–H), 3.12 m (36H,
C4H9), 2.45 s (12H, CH3); hexamethyldisilane was
used as the internal standard.
δ
Synthesis of the chloride complex of aluminum with
5,15ꢀdiphenylꢀ3,7,13,17ꢀtetramethylꢀ2,8,12,18ꢀtetꢀ
rabutylporphyrin ((Cl)AIP). A weighed sample of 5,15ꢀ
diphenylꢀ2,8,12,18ꢀtetrabutylꢀ3,7,13,17ꢀtetramethꢀ
ylporphyrin (10 mg) was dissolved in anhydrous pyriꢀ
dine (30 ml), a 50ꢀfold excess of AlCl3 was added, and
the reaction mixture was refluxed for 6 h. After coolꢀ
ing, water (100 ml) and acetic acid (30 ml) were added.
The precipitate that formed was filtered off, washed
with warm water, and dissolved in a minimum volume
of CHCl3. The solution was loaded in a column with
Al2O3 (Brockmann activity II) for chromatography.
The eluent was CHCl3. The dry complex was isolated
after polar chromatography using the vacuum distillaꢀ
tion off of CHCl3. The yield was 61%.
RESULTS AND DISCUSSION
The introduction of a base into a solution of alumiꢀ
num porphyrinate (c(Cl)AIP from 4.85
×
10–6 to 6.62
×
10–6 mol/l) results in the formation of the aluminum
porphyrinate complex with the axial ligand
(Cl)Al(L)nP. This process is accompanied by a change
in the intensity and shift of the main absorption bands
(В, Q1, and Q2) in the UV spectrum of the (Cl)AlP
complex (Fig. 1), which makes it possible to deterꢀ
mine the equilibrium constant and composition of the
complex. The amount of the axial ligand (
mixedꢀligand complex was determined from the slope
ratio of the linear plot of log[(Aeq o)/(A∞ eq)] vs.
logcL [1], where A0 eq, and ∞ are the absorbances of
n) in the
–
A
– A
UV (benzene), λmax, nm (log ε): 581.0 (4.55), 543.0
(4.61), 411.0 (5.50).
,
A
A
solutions at the working wavelength for the metalꢀ
loporphyrin, equilibrium mixture, and molecular
complex, respectively (Fig. 2). For all bases chosen,
For C52H60AlClN4
n
was established to be 0.82–1.02, that is, . Thus, the
composition of the complex corresponds to
(Cl)Al(L)nP.
≈
1
anal. calcd. (%): C, 77.73;
Found (%): C, 77.65;
H, 7.53;
H, 7.58;
N, 6.97.
N, 7.01.
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COORDINATION PROPERTIES
325
Aeq
log
∝
–
–
A0
Aeq
A
Prz
1.0
Prm
Py
Im
0.5
0
1.5
2.0
2.5
3.0
3.5
4.0
logcL
–0.5
–1.0
Fig. 2. Plot of log[(
A – A )/(A – A )] vs. logc for the intermolecular reactions of (Cl)AlP with the organic bases.
eq 0 ∝ eq L
The stability constants of the molecular complexes (regression equation logKst = 0.263Δλ – 0.021;
r =
formed (Table 1) increase in the series (Cl)Al(Prz)P < 0.99) between the stability of the molecular complex
and the shift of the band (Δλmax) in its UV spectrum
(Fig. 4).
(Cl)Al(Prm)P < (Cl)Al(Py)P < (Cl)Al(Im)P, which
can be due to the influence of the base nature. The
higher the basicity of the axial ligand, the more stable
An analysis of the data in Table 1 and earlier pubꢀ
lished results [16] shows that the presence of
the OC4H9 groups in the phenyl fragments and
more substantial steric strains of the macrocycle of
(Cl)Alꢀ5,15ꢀ(paraꢀbutyloxyphenyl)ꢀ2,8,12,18ꢀtetraꢀ
the complex (Table 1). The
рКа value [14] and the proꢀ
ton affinity ( prot) of isolated base molecules calcuꢀ
E
lated by the AM1 quantumꢀchemical method [5] were
accepted as the basicity parameters (Table 1). It is necꢀ
essary to use calculated values, because, on the one
hand, the basicity of small molecules can change on
going from the aqueous phase to the organic medium.
On the other hand, the regularities of рКа changing in
inert organic solvents are retained in the gaseous phase
[15].
butylꢀ3,7,13,17ꢀtetramethylporphyrin
((Cl)Al(pꢀ
BuOPh)P) increase the basicity of the porphyrin
ligand and, as consequence, decrease the coordination
ability of the compound in the reaction with organic
bases. The stability of the molecular complexes
(Cl)Al(
pꢀBuOPh)P is two times lower than that of
(Cl)Al(L)P.
The analogous dependences of logKst on
st on prot were obtained on the basis of the calcuꢀ
lated and experimental characteristics and are
described by the equations logKst = 0.076pKa2
0.331pKa + 2.179 (correlation coefficient = 0.94)
and logKst = 0.005Ep2rot + 1.373Eprot + 105.73 (
рКа and of
logK
E
The degree of deformation of the aluminum porꢀ
phyrinate macrocycle and its changes during the interꢀ
molecular interaction with bases were determined by
the PM3 quantumꢀchemical method. The optimized
(Cl)AlP molecule is sterically strained and has the
–
r
r
=
0.99), respectively (Fig. 3). A linear correlation mixed type of deformation: “cupola” and “saddle”
Table 1. Stability constants and some energy characteristics of the (Cl)Al(L)P molecular complexes
298 K
st
–3
–1
Complex
pK
–Eprot.base, kcal/mol
–E
,
kcal/mol
Δλ
, nm
K
×
10 , mol
l
a
Al–L
max (B)
(Cl)Al(Im)P
(Cl)Al(Py)P
(Cl)Al(Prm)P
(Cl)Al(Prz)P
2.65 0.19
0.278 0.022
0.121 0.011
0.071 0.012
6.65
5.29
1.30
0.60
169.36
162.79
155.54
151.77
9.83
6.59
5.00
4.21
13
9
8
7
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326
ZAITSEVA et al.
log Kst
log Kst
3.5
(b)
(а)
3.5
3.0
2.5
Im
Im
3.0
2.5
Py
Py
Prz
Prz
Prm
2.0
1.5
2.0
Prm
1.5
0
2
4
6
8
Ka
–170 –165 –160 –155 –150
E
p
b, kcal/mol
Fig. 3. Dependences of the stability of the (Cl)Al(L)P complexes on pKa (a) and the calculated energy of protonation of the
organic bases (b).
(Figs. 5, 6). The coordination center represents a tetꢀ lengths in the methylene bridges, and the slope angles
ragonal pyramid with a rhombus in the base (N4) and of the pyrrole fragments to the XY plane are different
is characterized by the symmetry C4 . The perimeter of ([16], Fig. 5, Table 2).The difference in the degrees of
ν
N4 (PN4) is 11.665 Å. The aluminum atom is shifted to
deformation of the (Cl)AlP macrocycle and (Cl)Al(pꢀ
one of the mesoꢀcarbon atoms and shifts from the N4
plane toward the acido ligand by 0.506 Å. A considerꢀ
able deviation of the skeletal atoms of the macrocycle
BuOPh)P, along with the electronic effect of the subꢀ
stituents, reflects the stability of their molecular comꢀ
plexes.
from its mean plane (XY) along the
Z axis is observed
The energetically favorable structure of compound
(Cl)Al(L)P calculated by computer simulation is well
consistent with the experimental data. A molecule of
the base (L) is oriented in the transꢀposition toward
the acido ligand (Fig. 5). The formation of (Cl)Al(L)P
is accompanied by a change in steric strains of the
macrocycle (Table 2). The predominant type of deforꢀ
mation of the molecule is “saddle,” whereas the
cupola component is negligible (Figs. 5, 6). The sizes
(Fig. 5).
It was found on the basis of the calculated data that
steric strains of an isolated (Cl)AlP molecule were less
(Fig. 5, Table 2) than those in (Cl)Al(
The average value of deviations of the skeletal atoms of
the macrocycle from XY along the axis ( av) in the
latter is by 0.038 Å greater than that in (Cl)AlP. The
type of deformation for the both complexes is nearly
the same. However, the PN and Zav values, the shift
nꢀBuOPh)P [16].
Z
Δ
Z
of coordination plane N4 increase (Table 2). The
values for (Cl)Al(L)P decrease by 0.020–0.026 Å. The
formation of the ꢀAl–L bond is accompanied by the
Δ
Zav
Δ
4
of the Al atom from the N4 (Al–Ct) plane, the plane
angles of the tetrapyrrole macrocycle, the bond
σ
shortening of the Al–N bond and Al–Ct distance and
the elongation of the Al–Cl bond in the coordination
center of the macrocycle. The stronger is the Al–L
bond, the weaker is Al–Cl (Table 2). A correlation
between the Al–L bond length (dAl–L) and the stability
of the (Cl)Al(L)P complex is observed. The depenꢀ
dence is linear and described by the regression equaꢀ
logKst
3.5
Im
3.0
2.5
tion: logKst = –23.39dAl–L + 59.47 (r = 0.98) (Fig. 7a).
An analysis of the calculated energies of the Al–L
Py
bond ( b) (Table 2) made it possible to obtain the Еb
E
–
values for the molecular complexes increasing in the
series (Cl)Al(Prz)P < (Cl)Al(Prm)P < (Cl)Al(Py)P <
(Cl)Al(Im)P. We have found that the more negative is
Prz
Prm
2.0
1.5
the bond energy, the higher is the
This dependence is described by the regression equaꢀ
tion: log st = –0.278 b + 0.671 ( = 0.99) (Fig. 7b).
Kst value (Table 1).
5
10
15
Δλ, nm
K
E
r
Thus, the regularities obtained suggest that the
determining factors of the coordination properties of
aluminum porphyrinate are the nature of the base and
Fig. 4. Dependence of log
K of the (Cl)Al(L)P complexes
st
on the shift of the absorption band in the UV spectra.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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COORDINATION PROPERTIES
327
(Cl)AlP
(Cl)AlP(Im)
(Cl)AlP(Prz)
Fig. 5. Structures of (Cl)AlP and its molecular complexes with imidazole and pyrazine calculated by the PM3 quantumꢀchemical
method.
Δ
Z
,
Å
Δ
Z
,
Å
Å
Δ
Z, Å
(Сl)AlP
(Сl)Al(Py)P
(Сl)Al(Im)P
0.25
0.15
0.05
0.25
0.15
0.05
0.25
0.15
0.05
–0.05
–0.15
–0.05
–0.15
0
10
20 –0.05
–0.15
0
10
20
0
10
20
Atom no.
Atom no.
Atom no.
Δ
Z
,
Å
Δ
Z, Å
Δ
Z,
(Сl)Al(
nꢀBuOPh)P
(Сl)Al(Prm)P
(Сl)Al(Prz)P
0.25
0.15
0.05
0.25
0.15
0.05
0.35
0.25
0.15
0.05
–0.05
–0.15
–0.05
–0.15
–0.05
–0.15
0
10
20
0
10
20
0
10
20
Atom no.
Atom no.
Atom no.
Fig. 6. Deviations of the skeletal atoms of the porphyrin macrocycle along the
Z
axis (
Δ
Z) from its mean plane for the (Cl)Al(pꢀ
BuOPh), (Cl)AlP, and (Cl)Al(L)P complexes according to the PM3 quantumꢀchemical calculation: designate the nitrogen
ؠ
atoms, and
•
are the carbon atoms.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 36
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328
ZAITSEVA et al.
macrocyclic ligand and the degree of deformation of
the latter.
logKst
3.5
Im
(a)
3.0
2.5
2.0
1.5
ACKNOWLEDGMENTS
The authors are grateful to Prof. A.S. Semeikin
(Ivanovo State University of Chemical Technology,
Ivanovo, Russia) for kindly presented 5,15ꢀdiphenylꢀ
3,7,13,17ꢀtetramethylꢀ2,8,12,18ꢀtetrabutylporphyrin.
This work was supported by the program for fundaꢀ
mental research of the Russian Federation “Theoretiꢀ
cal and Experimental Investigation of the Chemical
Bond Nature and Mechanisms of the Most Important
Chemical Reactions and Processes” and the Russian
Foundation for Basic Research (project no. 09ꢀ03ꢀ
00736ꢀa).
Py
(a)
Prz
Prm
2.38
2.41
2.44
d(Al–L),
2.47
Å
logKst
3.5 Im
3.0
(b)
Py
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2.5
Prm
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***
Complex
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Δ
Z , Å
av
21
23
22
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21
23
24
Al–N
Al–N
Al–N
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N –N
Al–Cl
2.306
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4.197
2.421
1.832
1.818
2.413
4.167
4.196
2.420
1.833
1.818
2.414
4.166
4.195
Notes: * The atoms in the macrocycle are enumerated according to the IUPAC nomenclature.
** Ct is the center of the N coordination plane.
4
*** Perimeter of the N coordination plane.
4
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COORDINATION PROPERTIES
329
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2010