Quantitative relations holding in coordination of (tetraphenylporphyrinato) zinc(II) and nucleophilic substitution with anilines

Article abstract of DOI:10.1134/S1070428012060048

Thermodynamic parameters (ΔG°, ΔS°) of quasi-isoenthalpic coordination of (tetraphenylporphyrinato) zinc(II) with anilines (except for 4-halo derivatives) in chloroform at 273-313 K in the absence of steric factors are linearly related to shifts of their

Full text of DOI:10.1134/S1070428012060048

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2012, Vol. 48, No. 6, pp. 772–779. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © V.P. Andreev, P.S. Sobolev, D.O. Zaitsev, 2012, published in Zhurnal Organicheskoi Khimii, 2012, Vol. 48, No. 6, pp. 776–783.
Quantitative Relations Holding in Coordination
of (Tetraphenylporphyrinato)zinc(II) and Nucleophilic
Substitution with Anilines
V. P. Andreeva, P. S. Soboleva, and D. O. Zaitsevb
a Petrozavodsk State University, pr. Lenina 33, Petrozavodsk, 185910 Russia
e-mail: andreev@psu.karelia.ru
b Karelian State Pedagogical Academy, Petrozavodsk, Russia
Received October 5, 2010
Abstract—Thermodynamic parameters (ΔG°, ΔS°) of quasi-isoenthalpic coordination of (tetraphenylpor-
phyrinato)zinc(II) with anilines (except for 4-halo derivatives) in chloroform at 273–313 K in the absence of
steric factors are linearly related to shifts of their absorption bands in the electronic spectra in reactions with
anilines, as well as with logarithms of the stability constants of the complexes, pKa values of the ligands in
water, and Hammett substituent constants σ+. Linear relations were also found between thermodynamic and
kinetic parameters of some nucleophilic substitution reactions and complex formation of (tetraphenylpor-
phyrinato)zinc(II) with anilines.
DOI: 10.1134/S1070428012060048
log(K/k) = 2.77 + 2.73 Σσ* – 0.94 EN; r = 0.983. (2)
The present article continues our studies on quanti-
tative relations between the stability constants of com-
plexes formed by (tetraphenylporphyrinato)zinc(II)
(Zn-TPP) with various organic compounds, rate con-
stant of nucleophilic substitution, and physicochemical
parameters characterizing these processes. We previ-
ously showed [1–3] that shifts of absorption maxima
(Δλ) in the electronic spectra of Zn-TPP in chloroform
upon reaction with 3- and 4-substituted pyridines, as
well as with pyridine, quinoline, and acridine N-ox-
ides, are linearly related to logarithms of the stability
constants (K) of the complexes, pKa of ligands (L) in
water and other solvents, and Hammett constants σ of
substituent in the heteroring.
The goal of the present work was to analyze kinetic
and thermodynamic parameters of coordination of
Zn-TPP with substituted anilines Ia–Iv in chloroform.
NR1R2
X
Ia–Iv
R1 = R2 = H, X = H (a), 3-Me (b), 4-Me (c), 4-Et (d),
3-MeO (e), 4-MeO (f), 4-H2N (g), 3-O2N (h), 4-F (i),
4-Cl (j), 4-Br (k), 4-I (l), 3-Cl (m), 2-Cl (n), 4-O2N (o); R2 =
X = H, R1 = Me (p), Et (q); Ph (r); R1 = R2 = Et, X = H (s);
R1 = R2 = Me, X = H (t), 4-CHO (u), 4-EtOC(O) (v).
Using the extended Taft equation (1), modified by
Litvinenko et al. [4] for amines, we succeeded [5] in
obtaining correlation (2) between logK in benzene
(determined by calorimetry), Σσ*, EN, and logk for the
reaction of phenacyl bromide with amines in benzene
at 25°C.
We found that shifts of the absorption maxima (Δλ)
in the electronic spectra observed in reactions of
Zn-TPP with anilines in chloroform are linearly related
(r = 0.95–0.98) to logarithms of the stability con-
stants of the complexes (ΔλII = 3.26logK + 6.85), pKa
values of the ligands in water (ΔλII = 1.11pKa + 9.15),
and Hammett constants σ of substituents in the ben-
zene ring of anilines (ΔλII = 2.92σ + 14.12) provided
that steric factors are lacking (see table).
logk = logk0 + ρ* Σσ* + δ EN,
(1)
Here, k is the rate constant, the term ρ* Σσ*
describes the inductive effect of all substituents on the
nitrogen atom, and δEN characterizes steric factor (δEs
in the Taft equation).
The experimental stability constants (K) of the
Zn-TPP complexes with aniline derivatives in chloro-
772

QUANTITATIVE RELATIONS HOLDING IN COORDINATION
773
Stability constants (K) and thermodynamic parameters (∆G°, ∆H°, ∆S°) for the formation of molecular complexes of Zn-TPP
with anilines in chloroform at 25°C, shifts of the absorption maxima of the I, II, and Soret bands (Δλ) in the spectra of
Zn-TPP upon complex formation, substituent constants σ+, and pKa of anilines in water at 25°C
∆λ, nm
pKa, 25°C
[8, 9]
–∆H°,
kJ/mol
∆S°,
– ∆G°,d
kJ/mol
Ligand
K
σ+ [6, 7]
J mol–1 K–1
I
II
Soret
Ia
Ib
Ic
Id
Ie
If
141±2
174±3
199±2
161±8
112±3
343±3
0776±11
049±1
164±3
138±3
109±3
124±4
072±2
036±1
103±2
189±4
020.4±0.8
0.000
–0.066a (–0.069)
–0.311–
–0.295–
0.047a (0.115)
–0.778–
–1.3–00
0.674a (0.710)
–0.073–
0.114
4.60
4.72
5.07
–
16.0
17.0
16.8
16.5
15.2
17.3
13.9
14.5
14.8
13.8
13.7
15.4
15.8
12.0
14.4
13.7
13.5
13.0
13.1
12.8
13.3
14.7
12.2
07.9
11.7
09.6
10.0
10.2
–
14.80±0.78
14.82±0.10
15.06±0.50
–
–8.27±2.35–
–6.78±0.32–
–6.55±1.30–
–
12.26
12.80
13.10
–
4.23
5.34
09.7
10.4
11.2
–
14.81±0.15 –10.63±0.660– 11.64
14.44±0.25
14.75±0.15
14.87±0.19
13.47±0.05
13.66±0.60
0.46±1.06
5.86±0.27
14.46
16.51
09.64
12.70
12.20
Ig
Ih
Ii
6.16b, 6.08c 18.6
2.46
4.65
14.9
17.2
16.2
16.0
14.8
15.4
15.5
15.7
17.0
15.0
11.3
14.8
–17.3±0.62–
–2.57±0.27–
–4.68±2.00–
09.4
09.4
08.9
08.8
09.0
09.1
–
Ij
3.98
Ik
Il
0.150
3.88
15.62±0.15 –13.23±0.3–00 11.62
14.24±0.60 –7.72±2–.00 11.94
0.135
3.79
Im
In
Ip
Iq
It
0.399
3.52
14.59±0.10 –13.35±0.26–0 10.59
14.60±0.17 –19.51±0.5–00 08.87
14.81±0.27 –11.51±0.6–00 11.38
–
2.64
–
4.85
–
5.11
–
14.76±0.06
–5.69±0.04–
12.98
–
5.06
b1.61b
10.2
07.9
09.3
14.78±0.48 –24.52±1.3–00 07.47
Iu
Iv
003.66±0.06 (0.22) CHO [8]
44.6±7. (0.45) COOEt
12.30±1.23
10.90±10.0
–30.5±5–.00
–5.0±2–.0
03.21
9.4
2.61 [10]
a
b
c
d
Substituent constant σ+meta; Hammett constants σ are given in parentheses.
Ionic strength 0.10 (Ig) [11], 0.14 (Iu) [12].
At 20°C [13].
∆G° = ∆H° – T∆S°.
form are concentration-dependent. On the other hand,
taking into account low concentration of the initial
compounds (2×10–5 M for Zn-TPP and 10–4 to 10–3 M
for ligands, except for In, It, and Iu) and the absence
of ionic species in solution, we presume that the
experimental values insignificantly differ from the
thermodynamic constants. We believe that the obtained
stability constants of the Zn-TPP complexes with
anilines (except for Iu and Iv) characterize 1 : 1
molecular n,v-complexes with a dative N–Zn bond. In
particular, linear correlation between pKa of the ligands
in water and logK in chloroform (see table), as well as
the X-ray diffraction data [14] (CSD refcodes
HAMLAI and JIVNIL), confirmed that protonation
and coordination of ligands Ia–It with Zn-TPP involve
the same center, i.e., nitrogen atom in the amino group.
with isoquinoline N-oxide [3], the angle between the
porphyrin macroring plane and aromatic ring in the
ligand in the above complexes of both types is about
30°. However, in our case the formation of such ad-
ducts is hardly probable because of low concentration
and weak nucleophilicity of anilines (even 1:1 com-
plexes are very unstable). Furthermore, interaction of
Zn-TPP with the second ligand molecule should return
the zinc atom to the macroring cavity, so that the
position and intensity of absorption bands in the elec-
tronic spectra of more symmetric 1 :2 complexes
should differ only slightly from the spectrum of
Zn-TPP itself, and the stability constants of 1:1 com-
plexes determined by electronic spectroscopy should
not be affected. In fact, an isosbestic point was ob-
served in the spectra upon gradual addition of a ligand
to a solution of Zn-TPP (c = 2×10–5 M) until complete
complexation, and the intensity of absorption bands
belonging to the components occurring in equilibrium
In addition, crystalline 1 : 2 n,v-complexes of
Zn-TPP with aniline and 2-methylaniline were report-
ed [14] (HAMCIH, HAMMEN). As in the 1:1 adduct
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

ANDREEV et al.
774
conformed to the Bouguer–Lambert–Beer law. The
formation of crystalline 1:2 complexes is likely to be
determined by the conditions of their isolation (slow
evaporation in air of a solution containing metal
porphyrin and aniline at a given ratio); in some cases,
stable crystalline clathrates and solvates can be ob-
tained in such a way.
The coordination process involving 2- or N-substi-
tuted anilines In, Ip, Iq, Is, and It, in which the
substituent exerts steric shielding of the coordination
center, cannot be described properly by the Hammett
equation. In this case, steric constants should be used,
e.g., as in modified Taft equation (1). The complexes
formed by the above ligands with Zn-TPP (except for
the most basic ligand Iq) are characterized by con-
siderably lower stability constants as compared to
aniline, whereas N,N-diethylaniline failed to bind all
Zn-TPP molecules even at a ligand-to-Zn-TPP ratio of
150000:1; therefore, we were unable to determine the
molar absorption coefficient ε and hence the K value
for the complex.
We failed to determine K and Δλ values for the
complex with 4-nitroaniline (Io) due to its poor solu-
bility in chloroform (calculation of the molar absorp-
tion coefficient of the complex required a higher con-
centration of Io to convert all metal porphyrin mole-
cules in solution into molecular complex). Diphenyl-
amine (Ir) (pKa 0.78 [15]), like 2,6-dimethyl-4-nitro-
pyridine N-oxide (pKa –0.86 [5]) and 2,6-dichloro-
pyridine (pKa –2.57 [16]), even in a saturated solution
did not produce appreciable variations in the electronic
absorption spectra of Zn-TPP, in contrast to such even
weaker bases as 4-nitro- (pKa –1.7), 3-methyl-4-nitro-
(pKa –0.97), and 2-methyl-4-nitropyridine N-oxides
(pKa –0.967) [5]. This may be due to joint effect of
electronic and especially steric factors which sharply
reduce nucleophilicity of the nitrogen atom and
hamper bond formation with the metal ion. Probably,
weakly basic and weakly nucleophilic anilines like
diphenylamine react with Zn-TPP in solution to give
only n,π- and π,π-complexes whose electronic absorp-
tion spectra differ insignificantly from the spectra of
the metal porphyrin; therefore, such complexes could
not be detected by electronic spectroscopy.
Taking into account similarity in the structures of
Zn-TPP complexes with anilines and transition states
in nucleophilic substitution reactions [5] with the latter
as nucleophiles, we made an attempt to reveal quanti-
tative relations between the parameters characterizing
these processes. It was found that the rate constants k
for nucleophilic substitution by anilines in methanol–
acetonitrile mixtures (50–100%) at 35°C [17] [Eq. (3)],
rate constants k2, kXY, and kXZ for the aminolysis of
benzoic anhydrides in methanol at 25–45°C [18]
[Eq. (4)], and rate constants for the reaction of trans-β-
chlorovinyl 3-nitrophenyl ketone with anilines (X =
4-H2N, 4-MeO, 4-Me, 4-Br, 3-Cl, 3-O2N) in isopropyl
alcohol at 25°C [19] are linearly related to the complex
formation constants of anilines with Zn-TPP in chloro-
form at 25°C (logk = 2.69logK – 6.29; r = 0.99) and
shifts of the absorption maxima (Δλ) of the metal
porphyrin (Fig. 1).
Unlike pyridines and heteroaromatic N-oxides
[1–3], the behavior of anilines upon complexation with
Zn-TPP is described much better with the use of sub-
stituent constants σ+ (logK = –0.57σ+ + 2.13; r = 0.99,
n = 11) rather than Hammett constants σ (r = 0.91). It
was specially noted [6] that the necessity of using
constants σ+ is determined by the presence of just
vacant orbital rather than positive charge on the reac-
tion center. We must emphasize that the residual
positive charge on the zinc atom in Zn-TPP is too
small to polarize aniline molecules to an appreciable
extent via Coulomb forces.
XC6H4NH2
+
YC6H4CH2OSO2C6H4Z
ZC6H4SO3
(3)
XC6H4NH2CH2C6H4Y
+
X = H, Me, 4-MeO, 4-Cl, 3-O2N; Y = H, 4-Cl;
Z = H, 4-Me, 4-Cl, 3-O2N.
2XC6H4NH2
+
Y(Z)C6H4COOBz
kXY
XC6H4NHCOC6H4Y XC6H4NH3
+
+
BzO–
k2
(4)
kXZ
XC6H4NHBz
+ XC6H4NH3 +
ZC6H4COO–
Exclusion of compounds In, Ip, Iq, It (steric
factors), and Il (iodine atom very strongly differs from
other substituents in polarizability) gives a good linear
correlation between logK and Δλ (logK = 0.307ΔλI –
2.88; n = 13, r = 0.97; logK = 0.27ΔλII – 1.59, n = 13,
r = 0.97). Likewise, the complex formation is well
described by the equation logK = 0.31pKa + 0.82 (n =
12, r = 0.97) provided that N-substituted anilines In,
Ip, Iq, and It–Iv are not taken into account.
X = H, 4-MeO, 4-Me, 4-Br, 3-Cl; Y (Z) = H, 4-MeO,
4-Me, 3-Cl, 4-O2N.
The experimental stability constants of the Zn-TPP
complexes with anilines, determined at different tem-
peratures (273–313 K), were used to calculate thermo-
dynamic parameters of the complex formation process
(see table). It should be noted that the ΔH° values for
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

QUANTITATIVE RELATIONS HOLDING IN COORDINATION
775
logk
anilines Ia–Ih, Im, In, Ip, Iq, and It are fairly similar
(–14.5 to –15 kJ/mol; ΔH° –14.76±0.14 kJ/mol; n =
2
av
2
12), i.e., the complexation of anilines with Zn-TPP is
a quasi-isoenthalpic process (in the complexation with
pyridines, ΔH° ranges from –8 to –25 kJ/mol and is
linearly related to the ligand basicity [2]). Presumably,
the reason is much weaker nucleophilicity (basicity) of
anilines compared to pyridines.
1
1
0
–1
–2
–3
In going from most basic p-phenylenediamine (Ig)
to least basic 3-nitroaniline (Ih), the parameter ΔS°
changes from positive (for anilines Ia–Ih and Im with
primary amino group) to negative and shows a linear
correlation with the substituent constants σ+ (ΔS° =
–11.46σ+ – 8.84; r = 0.995, n = 8). For the anilines
constituting a quasi-isoenthalpic series, including
2-chloroaniline, ΔS° is linearly related to logK (ΔS° =
19.35logK – 49.9; r = 0.999, n = 12). Thus, even
though the possibility for coordination is enthalpy-
controlled (major contribution to ΔG°), the selectivity
of complex formation (i.e., the relation between K and
aniline structure) is determined by variation of the
entropy. In the coordination with pyridines, ΔS° is
linearly related to the ligand basicity [2], but it varies
over a broader range, from –27 to 54 J mol–1 K–1.
10
12
14
16
18 Δλ, nm
Fig. 1. Plots of logk for the reaction of trans-β-chlorovinyl
3-nitrophenyl ketone (3-O2NC6H4COCH=CHCl) with
anilines Ic, If–Ih, Ik, and Im in isopropyl alcohol at 25°C
[19] versus shifts of the absorption maxima of the (1) first
(ΔλI, logk = 0.82ΔλI – 11.83; r = 0.99) and (2) second bands
(ΔλII, logk = 0.89ΔλII – 14.94; r = 0.99) in the electronic
spectrum of Zn-TPP upon complex formation with anilines
in chloroform.
the benzene ring of 4-methylaniline (EDACUI,
ISAYAC01) or of an acetyl group into 4-bromoaniline
(PBRANL01, ICAMUU, ICANAB) [14] shortens the
C–N bond and reduces the angle θ (α approaches
120°), indicating sp3→sp2 rehybridization of the nitro-
gen atom.
In molecules of anilines having alkyl groups or
+M-substituents, the angle θ between the benzene ring
plane and the amino group ranges from 22 to 49°, and
it increases as the size of the neighboring substituents
increases, reaching 89.74° in hexakis(dimethylamino)-
benzene (GENFAG) [14]. By contrast, accumulation of
–M-substituents in the benzene ring [NO2, COOH,
C≡CH, C≡N, CHO, C(O)R] reduces the angle θ to
0–10°, the molecule becomes more planar, and the
nitrogen atom approaches sp2 hybridization.
Thus, according to the X-ray diffraction data, hy-
bridization of the amino nitrogen atom in anilines (sp2
or sp3) in crystal is determined by electronic properties
of substituents in the benzene ring. Subsequently, we
would like to demonstrate by complex formation of
Zn-TPP with various ligands that the parameters opera-
tive in X-ray analysis are applicable to characterization
of chemical and biochemical processes occurring in
solution with participation of low-molecular com-
pounds. For instance, X-ray diffraction data obtained
for crystalline samples are widely used in the deter-
mination of native structures of high-molecular sub-
stances such as proteins [22].
The fact that ΔS° for coordination with primary
anilines Ia–Ih and Im changes in parallel with elec-
tron-donor power of substituents in the benzene ring
may be attributed to some extent (unlike pyridines) to
gradual increase in the p-character of the lone electron
pair on the nitrogen atom due to electron density
transfer to the benzene ring (sp3→sp2 rehybridization).
This should change steric environment of the reaction
center (ligand molecule becomes more planar), while
N→Zn dative bonding should require stronger struc-
tural rearrangement to ensure the reverse rehybridiza-
tion (sp2→sp3). Analogous pattern was observed by us
previously for the oxygen atom in heteroaromatic
N-oxides upon formation of n,v-complexes with BF3,
CuCl2, ZnCl2, and Zn-TPP [3, 20, 21].
Analysis of the X-ray diffraction data [14] for
anilines, their salts, and molecular complexes showed
that the formation of a new bond involving LEP on the
amino nitrogen atom is accompanied by extension of
the C–N bond from 1.340–1.406 to 1.433–1.485 Å and
that the bond angles α at the nitrogen atom correspond
to sp3 hybridization (~109°). The distances rC–N and
angles α and θ in free aniline ligands can be used to
estimate the degree of sp3 (α ≈ 109°, θ = 20–50°) and
sp2 hybridization (α = 120°, θ = 0°) of the nitrogen
atom. For example, introduction of a nitro group into
Obviously, coordination of metal porphyrins with
anilines having sp2-nitrogen atom (sp2→sp3 rehybrid-
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

ANDREEV et al.
776
ization during complex formation) should be accom-
panied by electron density transfer from the benzene
ring with charge localization on the nitrogen atom. As
the degree of conjugation between the amino group
and π-system of the aromatic ring decreases (electron-
donor power of substituents increases), the entropy
ΔS° for the complexation with Zn-TPP gradually be-
comes less and less negative, approaches zero for com-
pound If (X = 4-OMe), and becomes positive for
ligand Ig (X = 4-H2N). In the latter case, the degree of
electron density localization on the nitrogen atom is
sufficient (for some reason) to make the initial state of
the system more ordered than the final state. This may
be due to solvation of the reactants.
p-dimethylaminobenzaldehyde hydrobromide
(MABZAL10) is protonated at the amino group,
whereas the reaction of Iu with a softer and bulkier
Lewis acid, dichloro(diphenyl)tin (BUHKEU) [14]
gives rise to n,v-dative bond with participation of the
carbonyl oxygen atom.
Coordination through the carbonyl oxygen atom is
indirectly supported by the facts that the stability con-
stant of the complex with ethyl p-dimethylaminoben-
zoate (Iv) is twice as high as that found for N,N-di-
methylaniline, though ethoxycarbonyl group is elec-
tron-withdrawing, and that the ΔH° value (–10.9 kJ×
mol–1) is even higher than ΔH° for p-dimethylamino-
benzaldehyde (it differs from the average ΔH° values
for other anilines coordinated to Zn-TPP at the amino
nitrogen atom). The ΔS° value for ester Iv (–5.0 J ×
mol–1 K–1) considerably differs from the corresponding
value for p-dimethylaminobenzaldehyde, which may
be due to replacement of the aldehyde hydrogen atom
by +M ethoxy group. Dative bonds between the zinc
atom in Zn-TPP and benzoic acid esters in crystal
(SEMRAD, SEMREH, SEMRIL) [14] are formed
through the carbonyl oxygen atom in the ligand.
Decrease of ΔS° in the series aniline > N-methyl-
aniline > N,N-dimethylaniline from –8.27 to –24.52 J×
mol–1 K–1 (sp3-hybridization) is likely to result prima-
rily from steric interactions, for the number of degrees
of freedom of atoms adjacent to the amino group in the
complex should decrease as the size of substituents on
the nitrogen atom increases.
The alkyl groups in N,N-diethylaniline (Is, pKa 6.56
[13]) are so bulky that the stability constant of its com-
plex with Zn-TPP (we failed to determine its value) is
much lower than for p-dimethylaminobenzaldehyde
(K = 3.66) having an electron-withdrawing CH=O
group (σ– = +1.13, σp = +0.44 [6, 23]). Unfortunately,
compound It is liquid under normal conditions, but the
X-ray diffraction data showed that N,N-diethyl-3,4-
dinitroaniline molecules in crystal exist as two con-
formers with cis and trans arrangement of methyl
groups in the ethyl fragments relative to the aromatic
ring plane, which hampers coordination of nitrogen to
the zinc atom.
As might be expected, the stability constants of the
Zn-TPP complexes with anilines in chloroform in-
crease as the temperature decreases. On the other hand,
the data in Fig. 2 suggest that ΔG and the stability
constants at 0 K should not depend on the ligand
structure. The plots of ΔG versus substituent constants
σ+ at different temperatures (Fig. 3) cross each other at
σ+ ≈ –0.8 (ΔH ≈ –14.5 KJ/mol), i.e., for the corre-
sponding ligand ΔGT = ΔG° = ΔH° (ΔS° = 0), and
variation of the Gibbs energy for the coordination
process should not depend on the temperature. In fact,
the ΔG value for 4-methoxyaniline (σ+OMe = –0.778)
changes very weakly with temperature.
Unlike other anilines, the complexation with p-di-
methylaminobenzaldehyde (Iu) is characterized by
considerably lower ΔH° value (–12.3 KJ/mol) and
very low value of ΔS° (–30.5 J mol–1 K–1; see table).
We believe that ligand Iu is coordinated with participa-
tion of a different donor center, carbonyl oxygen atom.
Specific attention should be given to 4-haloanilines
Ii–Il, for which ΔH° ranges from –13.47 to –15.62 kJ×
mol–1. Figure 4 shows that anilines Ii–Il do not fit
ΔS°—σ+ and ΔG°—σ+ correlations found for other
4- and 3-substituted anilines with primary amino
group. The temperature dependence of ΔG indicates
that ΔG values and the stability constants become
independent of the nature of 4-haloaniline at about
180 K rather than at 0 K.
It is known that the LEP on the nitrogen atom
directly linked to a strong –M-substituent is displaced
toward the electronegative atom so considerably that
dative bonds with Lewis acids involve just that atom
[6]. We showed that 4-(4-dimethylaminostyryl)pyri-
dine N-oxide reacts with HCl, BF3, CuCl2, ZnCl2, and
Zn-TPP in various organic solvents at the N-oxide
oxygen atom rather than at the nitrogen atom in the
dimethylamino group [3]. Nevertheless, first protona-
tion of this compound occurs at the dimethylamino
group [24, 25]. According to the X-ray diffraction data,
At first glance, extrapolation of thermodynamic
data obtained for a narrow temperature range for com-
plexation in solution to a temperature beyond phase
transition of the solvent may seem improper. However,
we only emphasize very high accuracy of crossing of
the straight lines at a single point (Fig. 2) near 0 K for
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

QUANTITATIVE RELATIONS HOLDING IN COORDINATION
777
most 3- and 4-substituted anilines and quite different
temperature dependence of ΔG for 4-haloanilines.
of activation ΔH≠ (21–63 kJ/mol) and high negative
entropies of activation ΔS≠ (–105 to –196 J mol–1 K–1),
which is consistent with published data for SN2 reac-
tions [6, 7, 27]. The parameters ΔH≠ and ΔS≠ give rise
to isokinetic relationship. Unlike the parameters char-
acterizing coordination of anilines to Zn-TPP, the ΔH°
value for the aminolysis is constant (–14.8 kJ/mol) and
ΔS° is small in absolute value (6 to –17 J mol–1 K–1);
the reason is that SN2 reactions involve more essential
reorganization of electron shells of atoms in the
substrate and nucleophile upon formation of transition
state as compared to complex formation with Zn-TPP.
High negative ΔS≠ values are intrinsic to reactions in
which the transition state is much more ordered and
compact than the initial system. Therefore, a linear
correlation exists between ΔG≠ for the aminolysis of
benzoic anhydrides in methanol and ΔG° for the com-
Furthermore, the basicity of 4-haloanilines in water
at 25°C decreases in the series F > Cl > Br > I (see
table), while the stability constants of their complexes
with Zn-TPP in chloroform at the same temperature
show a somewhat different order, F > Cl > I > Br (in
keeping with the substituent constants σ+). Unlike C,
N, and O atoms belonging to the second row of the
Periodic Table, halogen atoms differ considerably in
the size of their orbitals; therefore, specificities of
static (electronic effects) and dynamic (e.g., solvation
by aprotic solvents) polarization of molecules contain-
ing different halogen substituents cannot be interpreted
in a simple fashion.
Unusual basicity series of 4-haloanilines in water
(F > Cl > Br > I; i.e., fluorine atom appears to be the
strongest electron donor) is explained by the fact that
the +M-effect of halogen atoms (which is maximal for
fluorine) is stronger than the –I-effect which changes
in the opposite direction [26]. However, such inter-
pretation cannot rationalize the observed variations of
the stability constants and thermodynamic parameters.
Presumably, the reason should be sought among spec-
ificities of dynamic polarization of the reactants [pro-
tonation of anilines in water (pKa) and coordination of
anilines to Zn-TPP in chloroform (logK)]. In terms of
the Pearson hard and soft acids and bases principle,
bromine atom is likely to be solvated best with chloro-
form (better than other halogens and amino group),
which leads to additional displacement of electron
density from the nitrogen atom to bromine and hence
reduces nucleophilicity of the amino group as com-
pared to 4-iodoaniline. An indirect support is that
4-bromoaniline molecule in crystal is characterized by
the smallest angle between the benzene ring and amino
group planes (CLANIC05, EJAYET, IDAHUR,
PBRANL01) [14], i.e., it is the most planar. Therefore,
4-bromoaniline (minimal K value in the series of
4-haloanilines) requires the highest energy for com-
plexation with Zn-TPP (sp2 →sp3 rehybridization).
Solvation of amino group in water is much stronger
than solvation of halogen atom, and the basicity series
in water differs from the series of the stability con-
stants in chloroform. This problem will be the subject
of our further studies.
ΔG, kJ/mol
–7
It
–9
Ih
Im
Ip
–11
–13
–15
–17
–19
Ie
Ia
Ib
Iq, Ic
If
Ig
–50
50
150
250
T, °C
Fig. 2. Temperature dependences of ΔG for complex forma-
tion of Zn-TPP with anilines in chloroform.
ΔG, kJ/mol
–9
3
4
2
1
–11
–13
–15
–17
We also compared thermodynamic parameters for
the aminolysis of benzoic anhydrides in methanol and
complexation of anilines with Zn-TPP in chloroform.
The nucleophilic substitution process [k2, kXY, kXZ;
Eq. (4)] [18] is characterized by fairly low enthalpies
–1.5
–1.0
–0.5
0
0.5
σ
Fig. 3. Plots of ΔG for complex formation of Zn-TPP with
anilines Ia–Ic, Ie–Ih, and Im versus substituent constants σ+
at (1) 283, (2) 288, (3) 298, and (4) 313 K.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

ANDREEV et al.
778
ΔS°, J mol–1 K–1
(a)
ΔG°, kJ/mol
(b)
10
–8
–10
–12
–14
–16
5
Il
Ik
0
Ii
Ij
Ij
Ii
–5
Ik
–10
Il
–18
–20
–15
–20
–1.5
–1.0
–0.5
0.0
0.5
σ+
–1.5
–1.0
–0.5
0.0
0.5
σ+
Fig. 4. Plots of (a) ΔS° (ΔS° = –11.46σ+ – 8.84; r = 0.995, n = 8) and (b) ΔG° (ΔG° = 3.36σ+ – 12.11; r = 0.997, n = 8) for complex
formation of Zn-TPP with anilines Ia–Ic, Ie–Ih, and Im and 4-haloanilines Ii–Il in chloroform versus substituent constants σ+.
plexation of anilines with Zn-TPP in chloroform,
whereas ΔH≠ (ΔS≠) shows no correlation with ΔH°
(ΔS°). Nevertheless, the data on complex formation of
anilines with Zn-TPP may be used to predict relative
rate constants k and Gibbs energies of activation ΔG≠
for nucleophilic substitution with participation of
anilines.
This study was performed under financial support
by the Presidium of the Russian Academy of Sciences
(program no. 18) and by the Russian Foundation
for Basic Research (project no. 12-03-97 013-
r_povolzh’e_a).
REFERENCES
We previously presumed [3] that the X-ray diffrac-
tion data for 1:1 complexes, namely the distances from
the centroid of the Zn-TPP macroring to the zinc atom
and from the latter to the ligand nitrogen atom, may be
used as parameters characterizing nucleophilicity of
the ligand. In fact, 3-nitroaniline forms a stronger com-
plex with Zn-TPP than 2-chloroaniline (see table) and
is characterized by longer distance r1 and shorter
distance r2 [14]. We plan to examine the structure of
Zn-TPP complexes with various ligands by X-ray
diffraction with a view to check the above hypothesis
for generality.
1. Andreev, V.P., Nizhnik, Ya.P., Bezruchko, D.G., and Mo-
rozov, A.K., Russ. J. Gen. Chem., 2005, vol. 75,
p. 1309.
2. Andreev, V.P., Vapirov, V.V., Nizhnik, Ya.P., Tuni-
na, S.G., and Sobolev, P.S., Russ. J. Org. Chem., 2010,
vol. 46, p. 1563.
3. Andreev, V.P., Doctoral (Chem.) Dissertation, Petro-
zavodsk, 2007.
4. Litvinenko, L.M., Popov, A.F., and Gel’bina, Zh.P.,
Dokl. Akad. Nauk SSSR, 1972, vol. 203, p. 343.
5. Andreev, V.P., Nizhnik, Ya P., and Lebedeva, N.Sh.,
Russ. J. Org. Chem., 2008, vol. 44, p. 906.
6. Dneprovskii, A.S. and Temnikova, T.I., Teoreticheskie
osnovy organicheskoi khimii (Theoretical Foundations
of Organic Chemistry), Leningrad: Khimiya, 1991,
pp. 86, 90, 115.
7. Becker, H., Einführung in die Elektronentheorie
organisch–chemischer Reaktionen, Berlin: Wissen-
schaften, 1974, 3rd ed. Translated under the title Vvede-
nie v elektronnuyu teoriyu organicheskikh reaktsii,
Moscow: Mir, 1977, p. 87.
EXPERIMENTAL
Aniline and its derivatives were purified as de-
scribed in [28]; their physical constants coincided with
published data. The electronic absorption spectra were
measured on an SF 2000-02 spectrophotometer. The
stability constants of the complexes of Zn-TPP with
anilines in chloroform were determined as reported in
[1]. The thermodynamic parameters for the complex
formation process were determined graphically with
account taken of the first Ulich approximation [29]:
8. Wepster, B.M., Rec. Trav. Chim. Pays–Bas, 1952,
vol. 71, p. 1171.
9. Biggs, A.I., J. Chem. Soc., 1961, p. 2572.
10. Van de Graaf, B., Hoefnagel, A.J., and Wepster, B.M.,
J. Org. Chem., 1981, vol. 46, p. 653.
lnKT = –ΔH° /RT + ΔS° /R,
298
298
assuming that ΔH and ΔS remain constant in the
11. Willi, A.V., Z. Phys. Chem. (BRD), 1961, vol. 27,
examined temperature range (273–313 K).
p. 233.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012

QUANTITATIVE RELATIONS HOLDING IN COORDINATION
779
12. Robaszewska, W. and Gabowski, Z.R., Roszn. Chem.,
22. Popov, E.M., Problema belka (Protein Problem),
Sorokina, T.I., Ed., Moscow: Nauka, 1997, vol. 3, p. 74;
Popov, E.M., Usp. Khim., 1995, vol. 64, p. 1995;
Sluchanko, N.N. and Gusev, N.B., Usp. Biol. Khim.,
2010, vol. 50, p. 74.
1959, vol. 33, p. 781.
13. Svoistva organicheskikh soedinenii. Spravochnik
(Properties of Organic Compounds. Reference Book),
Potekhin, A.A., Ed., Leningrad: Khimiya, 1984, p. 517.
23. Gordon, A.J. and Ford, R.A., The Chemist’s Com-
panion, New York: Wiley, 1972. Translated under the
title Sputnik khimika, Moscow: Mir, 1976, p. 172.
14. Cambridge
www.ccdc.cam.ac.uk
15. Dolman, D. and Stewart, R., Can. J. Chem., 1967,
Structural
Database;
http://
24. Korzhenevskaya, N.G. and Rybachenko, V.I., Russ. J.
Gen. Chem., 1999, vol. 69, p. 421.
vol. 45, p. 903.
16. Cook, M.J., Dassanyake, N.L., Johnson, C.D., Kat-
ritzky, A.R., and Toone, T.W., J. Chem. Soc., Perkin
Trans. 2, 1974, p. 1069.
17. Lee, I., Sohn, S.C., Kang, C.H., and Oh, Y.J., J. Chem.
Soc., Perkin. Trans. 2, 1986, p. 1631.
25. Schroeder, G., Rybachenko, V.I., Chotii, K.Yu.,
Kovalenko, V.V., Grebenyuk, L.V., Lenska, B., and
Eitner, K., Russ. J. Gen. Chem., 2003, vol. 73, p. 455.
26. Reutov, O.A., Kurts, A.L., and Butin, K.P., Organi-
cheskaya khimiya (Organic Chemistry), Moscow:
Binom, 2005, vol. 1, p. 310.
18. Lee, B.C., Yoon, J.H., Lee, C.G., and Lee, I., J. Phys.
Org. Chem., 1994, vol. 7, p. 273.
27. Johnson, S.L., Adv. Org. Chem., 1960, vol. 60, p. 237.
19. Litvinenko, L.M., Popov, A.F., Kostenko, L.I., and
Nosovskaya, T.D., Zh. Org. Khim., 1973, vol. 9, p. 552.
28. Boulton, P.D. and Hall, F.M., J. Chem. Soc. B, 1969,
p. 259.
20. Andreev, V.P. and Nizhnik, Ya.P., Koord. Khim., 2007,
vol. 33, p. 703.
29. Fizicheskaya khimiya. Teoreticheskoe i prakticheskoe
rukovodstvo (Physical Chemistry. Theoretical and
Practical Guide), Nikol’skii, B.P., Leningrad: Khimiya,
1987, p. 374.
21. Andreev, V.P., Vapirov, V.V., Nizhnik, Ya.P., Aleshi-
na, L.A., and Semenova, T.A., Russ. J. Gen. Chem.,
2008, vol. 78, p. 973.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 48 No. 6 2012