Synthesis and Reactions of Platinum(III) Complexes with Protoporphine Ligands in Mixtures of Acetic and Sulfuric Acids

Article abstract of DOI:10.1023/A:1024756424980

Unusual stable platinum complexes (Cl)Pt^IIIPwere obtained by the reaction of K₂[PtCl₆] with porphyrin H₂P (full methyl ethers of proto-, meso-, deutero-, and hematoporphyrin) in a 1:2 molar ratio in boiling pyridine. The forms of existence, kinetics and mechanism of dissociation of metal porphyrins in AcOH-(0.3-2.1) M H₂SO ₄ mixtures were studied at 300-330 K. The reaction has first-order with respect to metal porphyrin, low E values (21-48 kJ/mol), and negative ΔS^≠ values (-145- to -224 J mol^-1 K ^-1). The dependence of the formal first-order rate constants on H₂SO₄ concentration is linear at low values of this latter (up to 1.5 M). The mechanism of the electron density redistribution produced by functional substitution in β positions of the macroring was studied to establish that the character of the dependence of the dissociation rate on the macroring nature is determined by restricted π-electron density transfer from the metal atom to a coordinated N atom.

Full text of DOI:10.1023/A:1024756424980

Russian Journal of General Chemistry, Vol. 73, No. 2, 2003, pp. 283 287. Translated from Zhurnal Obshchei Khimii, Vol. 73, No. 2, 2003,
pp. 304 309.
Original Russian Text Copyright
2003 by Lomova, Andrianova.
Synthesis and Reactions of Platinum(III) Complexes
with Protoporphine Ligands in Mixtures
of Acetic and Sulfuric Acids
S. T. Lomova and L. G. Andrianova
Institute of Solution Chemistry, Russian Academy of Sciences, Ivanovo, Russia
Received March 6, 2001
III
Abstract Unusual stable platinum complexes (Cl)Pt P were obtained by the reaction of K [PtCl ] with
2
6
porphyrin H P (full methyl ethers of proto-, meso-, deutero-, and hematoporphyrin) in a 1: 2 molar ratio in
2
boiling pyridine. The forms of existence, kinetics and mechanism of dissociation of metal porphyrins in
AcOH (0.3 2.1) M H SO mixtures were studied at 300 330 K. The reaction has first-order with respect to
2
4
S
values ( 145 to 224 J mol 1 K ). The
1
metal porphyrin, low E values (21 48 kJ/mol), and negative
dependence of the formal first-order rate constants on H SO concentration is linear at low values of this
2
4
latter (up to 1.5 M). The mechanism of the electron density redistribution produced by functional substitution
in positions of the macroring was studied to establish that the character of the dependence of the dissocia-
tion rate on the macroring nature is determined by restricted -electron density transfer from the metal atom
to a coordinated N atom.
According to published data [1, 2], functional
substitution in a porphyrin ligand incorporated in a
metal porphyrin significantly affects the electronic
structure and geometry of the coordination center,
which shows up in changed forms of existence of the
complexes in solutions and quantitative characteristics
of their reactivity, in particular, dissociation under the
action of acids. However, the magnitudes and direc-
tions of these changes strongly depend on the nature
of the central metal atom. Therefore, studies on the
properties of functional derivatives of porphine com-
plexes with unexplored metals are topical. Of parti-
cular interest are transition metals that form either
donor or dative bonds with ligands in addition to
viously, the stabilization of Pt(III) in protoporphyrin
complexes results from intramolecular transfer of elec-
tron density onto the complex-forming atom from the
macroring, the electron density in which is increased
owing to the presence of eight alkyl and pseudoalkyl
III
groups. Evidence for the composition of the (Cl)Pt P
complexes comes from the electronic absorption
spectra of porphyrin complexes of platinum in dif-
ferent oxidation states. The spectra of the complexes
II
III
IV
Pt TPP [3], (Cl)Pt P, and (Cl) Pt TPP contain two
2
visible absorption bands with
35 nm [4, 5].
max
These bands undergo equidistant shifts to the long-
wave region along this series. Moreover, the follow-
III
ing text shows that nonplanar (Cl)Pt P complexes
usual
donor acceptor bonds.
with a five-coordinate platinum cation significantly
II
IV
differ in stability from Pt and Pt complexes with a
In this work we used the example of platinum
III
planar PtN coordination entity.
4
complexes with protoporphyrin ligands [(Cl)Pt P] to
study the effect of the nature of functional groups in
Platinum(III) complexes with protoporphine li-
gands have similar absorption spectra in organic sol-
vents, their mixtures with AcOH, and 100 % AcOH
(Fig. 1), which implies that the acidity of AcOH is
insufficient for protonation of donor N atoms and for
dissociation of the complexes. In these media, the
complexes form molecular solutions and do not form
the
positions of two pyrrole moieties on the re-
activity of the complexes toward proton in H SO4
2
AcOH mixed proton-donor solvents.
A special feature of the synthesis of (Cl)PtIIIP
complexes is the use of a Pt(IV) compound as a com-
plex-forming agent, which is reduced to Pt(III) during
the synthesis. A similar complex-formation reaction of
K PtCl with tetraphenylporphine (H TPP) yields a
H-associated species known for (Cl) PtTPP and other
2
metal porphyrins in aqueous H SO [5, 6]. The elec-
2
4
2
6
2
III
IV
tronic absorption spectra of Pt complexes with pro-
toporphyrin ligands in concentrated H SO (Figs. 1
platinum(IV) complex (Cl) Pt TPP, whereas, the re-
2
action of K PtCl with H TPP in boiling PhCN for
2
4
2
4
2
II
2+
3
0 h, a platinum(II) porphyrin Pt TPP [3, 4]. Ob-
and 2) are actually the spectra of the H4P cations
1
070-3632/03/7302-0283$25.00 2002 MAIK Nauka/Interperiodica

284
LOMOVA, ANDRIANOVA
5
49.5
559.1
5
59.3
5
28.5
A
5
25.5
A
1
3
5
38.4
2
1
8
9
4
2
7
,
nm
,
nm
Fig. 2. Electronic absorption spectra of (Cl)PtDP in (1)
(8) AcOH 1.5 M H SO mixture and (9) 17.5 M H SO
4
Fig. 1. Electronic absorption spectra of (Cl)PtMP in
2
4
2
(
(
1) methanol, (2) AcOH, (3) 17.5 M H SO , and (4) of
Cl)PtGP in the EtOH 10% AcOH mixture.
at 298 K. Time, s: (1) 0, (8) 40, (2) (7) intermediate
time moments.
2
4
formed by dissociation of platinum(III) porphyrins.
In nonaqueous acetic acid with small H SO mono-
Ka
+
CH COOH + H SO
CH COOH2 + HSO4, (5)
3
2
4
3
+ 2
0
2
4
Ka = [CH COOH ] /C .
H SO
2 4
(6)
3
2
hydrate additives at temperatures higher than 298 K,
III
(
[
Cl)Pt P complexes dissociate by Pt N bonds
Taking into account Eqs. (4) and (6), we can draw
kinetic equation (7) for dissociation of the complexes
in sulfuric acid with a concentration lower than 1.5 M.
Eqs. (1) and (2); Fig. 2] at a measurable rate (see
table). The constancy of the formal first-order rate
constants confirms the form of kinetic equation (3)
for limiting stage (1). Reaction (2) is very fast. There-
fore, the unprotonated porphyrin is not accumulated in
the reaction mixture, and its electronic spectrum is not
observed (Fig. 2).
V = (1/K )kC(Cl)PtPC
+ 2
.
[C H OH ]
2 5 2
(7)
a
Equation (7) allows estimation of the true (Cl)PtIIIP
dissociation rate constants, and, from their tempera-
ture dependence, true activation parameters. With the
pK and acidity functions of the AcOH H SO mixed
(
Cl)PtP + 2H+
H P + 2H+
H P + (Cl)Pt
2+
,
(1)
(2)
(3)
2
a
2
4
solvent at 298 K (see [2] and references therein), by
the Hammett equation we estimated the true (Cl)PtMP
and (Cl)PtDP dissociation rate constants at (5.6 1.6)
2+
H P ,
4
2
V = kappC(Cl)PtP
.
7
and (2.8 0.8) 108 s mol l , respectively.
1
2 2
10
The kapp f(C0
Temperature dependences of pK and H are absent
a 0
) dependence is linear at low
H SO
2
4
from the literature. The dissociation of platinum(III)
porphyrins in the mixed solvents under study is cha-
racterized by moderate values of E and by negative
H SO concentrations at all the temperatures under
2
4
study, implying that the reaction is first-order with
respect to C0
.
H SO
2
4
values of
S
(see table).
0
At H SO concentrations higher than 1.5 M, the
V = kC(Cl)PtP
C
.
4
(4)
2
4
H SO
2
0
kapp f(C
) dependence is no longer linear (Fig. 3),
H SO
2
4
However, in the AcOH medium sulfuric acid acts
as a weak electrolyte [Eqs. (5) and (6)].
which results from the fact that Eq. (6) is not valid at
increased concentrations of sulfuric acid. The activa-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 2 2003

SYNTHESIS AND REACTIONS OF PLATINUM(III) COMPLEXES
285
Kinetic parameters of dissociation of platinum(III) protoporphyrin complexes in the AcOH H SO mixed solvent
2
4
kapp 10 , s 1
3
Concentration
of N SO ,
E,
kJ/mol
S ,
2
4
J mol 1 K 1
M
298.2 K
308.2 K
318.2 K
328.2 K
(Cl)PtMP
0
0
0
.31
.50
.74
1.58 0.04
1.9 0.1
2.6 0.1
2.46 0.08
3.4 0.16
4.3 0.16
3.81 0.09
6.3 0.57
6.86 0.3
34.6 1
48 3
37.85 0.5
190 3
145 10
175 2
(Cl)PtPP
1
1
2
.63
.91
.10
5.0 0.1
6.15 0.16
10.2 0.8
7.3 0.1
8.0 0.1
13.45 1.0
10.6 0.8
10.5 1.0
18 1
30 1
21 1
23 1.6
197 3
224 4
215 5
(Cl)PtDP
0
0
1
1
.42
.81
.22
.63
5.7 0.2
6.3 0.2
7.27 0.4
7.3 0.2
8.6 0.3
10.06 0.7
10.2 0.7
11.4 0.6
12.9 0.7
16.1 0.9
14.4 0.7
17.8 0.4
32 1
37 1
27 1
35 1.4
189 3
170 4
203 4
176 5
(Cl)PtGP
1
2
2
2
3
.49
.00
.55
.73
.67
0.87 0.00
1.00 0.04
1.055 0.01
2.89
1.40 0.04
1.41 0.02
1.51 0.04
2.22 0.03
1.90 0.02
2.12 0.05
21 2
3.386 0.01
2.68 0.01
2.97 0.04
51 4
37 0
27 3
28.3 1
78.6
187 1
220 10
215 1
37.7
3.07
23 2
59 2
80.1
32.2
tion characteristics of the metal porphyrin acid system
see table), the first-order dissociation kinetic equa-
tion (3), and the dependence of rate constant on
metal cations [7], chromium(III) [8], manganese(III)
[9], and for manganese(III) protoporphyrin complexes
[10].
(
0
C
are similar to those for earlier studied reac-
H SO
2
4
tions of H TPP complexes with double-charged 3d-
According to data in the table and in [4, 5], the
2
2
98
k
103,
4
app
s 1
10
3
5
6
2
2
6
1
1
2
3
0
c
, M
4
H SO
2
Fig. 3. Dependence of the dissociation rate constants k
of (1) (3) (Cl)PtMP, (4) (Cl)PtPP, (5) (Cl)PtDP, and (6) (Cl)PtGP
app
on the initial concentration of H SO in AcOH. T, K: (1), (4 6) 298.2, (2) 308.2, and (3) 318.2.
2
4
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 2 2003

286
LOMOVA, ANDRIANOVA
platinum(III) complexes under study are much less
stable with respect to solvated protons as compared
phyrin complex can be explained in the same way, if
the vinyl and methylated hyroxyalkyl groups are
considered as pseudoalkyl substituents. However, in
fact, an unexpected sharp increase in stability is
observed [order (8)]. This probably points to electron-
acceptor properties of the substituents CH(OCH )CH
II
IV
to Pt TPP and (Cl) Pt TPP which are stable in cold
2
concentrated H SO . This is obviously explained by
2
4
III
the fact that the central Pt atom in (Cl)Pt P com-
plexes is displaced toward the Cl acido ligand, thus
preventing formation of Pt N dative back bonds
characteristic of bi- and tetravalent platinum com-
plexes.
3
3
and CH=CH with respect to nitrogen n-electron pairs,
2
as the involvement of these substituents into inter-
action with the macroring not compensated for by
strengthened dative
stability of the metal porphine. The electron-acceptor
properties of the CH(OCH )CH groups can also be
enhanced by their specific solvation (hydrogen bonds)
in a mixture of AcOH and H SO .
bonds significantly increases
As seen from the table, the kinetic stability of the
complexes, measured by kapp(298 K), decreases along
3
3
series (8) for all compositions of the AcOH H SO4
2
mixed solvent.
2
4
(Cl)PtGP > PtTPP >> (Cl)PtMP > (Cl)PtDP. (8)
The appearance of Pt N dative back bonds in
the PtTPP and (Cl) PtTPP complexes with a planar
2
The kinetic stability of platinum(III) H PP and
2
coordination entity PtN results in a sharp positive
4
H MP complexes varies in the same order as that
2
2
+
2+
2+
jump of the kinetic stability of these complexes in
solutions [4, 5].
described in [11 16] for similar Mg , Cd , Zn ,
and Fe3+ complexes. The stability order of manga-
nese(III) protoporphyrin complexes [10] is similar to
order (8) in that meso- and deuteroporphyrin com-
plexes are much more labile than hemato- and proto-
porphyrins. However, (Cl)MnPP is more stable than
Thus, our study of the reactivity of platinum por-
phyrins toward proton provides, on the one hand,
indirect quantitative evidence for the unusual trivalent
state of platinum in monomeric complexes, and, on
the other, adds to our view of the electronic effects of
substituents in aromatic macrorings. It must be em-
phasized that the complicated electronic and geo-
metric structure of the reaction center in platinum(III)
porphyrins determines the specificity of the electronic
effect of substituents as compared to that in classical
substitution reactions of functional derivatives of
benzene: The first-type substituents CH(OCH )CH
2
+
(
Cl)MnGP. In contrast to Pt and Mn complexes, Cu
2
+
and Ni mesoporphyrin complexes dissociate slower
than protoporphyrin ones [14, 15, 17].
Thus, the above stability order is observed only for
complexes in which M N dative back bonding is
2
+
2+
2+
either impossible (Mg , Cd , and Zn complexes)
3
+
3+
3+
or hindered (complexes of Fe , Mn , and Pt with
a nonplanar coordination center). It should be noted
that the activation of a metal porphyrin acid reacting
system involves cleavage of M N donor acceptor
bonds and protonation of two coordinated N atoms
3
3
and CH=CH become electron-acceptors.
2
EXPERIMENTAL
[
Eq. (1)]. We can assume that the increased kinetic
The electronic absorption spectra were recorded on
SF-26, Specord M-40, and Specord M-400 instru-
ments. The IR spectra were taken on a Specord M-80
spectrophotometer and analyzed by a comparison with
the spectra of porphyrins, their complexes, and Pt
complexes with acyclic ligands [18 21].
stability of (Cl)PtMP compared to (Cl)PtDP results
from the +I effect of -CH CH substituents and
2
3
strengthening of Pt N donor acceptor interaction.
Such interaction would prevent conjugation of nitro-
gen n-electron pairs with the macroring and thus
facilitate considerably solvoprotolytic dissociation of
the complexes. However, this is not the fact. This
result implies prevalence of the +I effect of substi-
tuents on the electron pairs of Pt N bonds. In the
case of manganese(III) complexes, introduction of two
ethyl radicals in the deuteroporphyrin macroring has
almost no effect on the kinetic stability of the com-
plex, i.e. the contributions into the stability of the
complex of the effect of two CH CH substituents
Sulfuric acid monohydrate was prepared from
H SO (chemically pure grade) and oleum (chemically
2
4
pure grade), following water content by potentiometry
[22]. Acetic acid (100%) was prepared from glacial
AcOH by fractional unfreezing. The water contents of
individual solvents were no higher than 0.02 0.03%.
The mixed solvents AcOH H SO were prepared by
2
4
the gravimetric method. The accuracy of temperature
measurements in the kinetic experiments was 0.1 K.
2
3
on the state of nitrogen n-electron pairs and Pt N
bonds mutually compensate each other.
The chlorine contents were determined by burning
the samples in oxygen, and the Pt contents, by atomic
adsorption spectroscopy on an AASIN spectrometer
The increased stability of the (Cl)PtGP and
(
Cl)PtPP complexes compared to the deuteropor-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 2 2003

SYNTHESIS AND REACTIONS OF PLATINUM(III) COMPLEXES
287
and by thermal analysis on a 1000D derivatograph.
Chloro)platinum(III)porphyrins (full methyl
ethers) were obtained by complex formation between
3. Andrianova, L.G. and Lomova, T.N., Abstracts of
Papers, I Int. Conf. on Biocoordination Chemistry,
Ivanovo, 1994, p. 116.
(
4
. Tyulyaeva, E.Yu. and Lomova, T.N., Abstracts of
Papers, XIX Vserossiskoe Chugaevskoe soveshchsnie
po khimii kompleksnykh soedinenii (XIX Russian
Tchugaev Conf. on Chemistry of Coordination
Compounds), Ivanovo, 1999, p. 157.
H P and K PtCl at a 1:2 molar ratio in boiling
2
2
6
pyridine within 30 min. To a cooled reaction mixture,
CHCl and water were added until the chloroform
3
layer separated. This layer was washed with water
many times to remove excess salt and pyridine and
5
6
. Tyulyaeva, E.Yu., Cand. Sci. (Chem.) Dissertation,
Ivanovo, 1999.
. Lomova, T.N., Mozhzhyhina, E.G., Shormanova, L.P.,
and Berezin, B.D., Zh. Obshch. Khim., 1989, vol. 59,
no. 10, p. 2317.
then subjected to chromatography on an Al O3
2
column (Brockmann activity grade II), eluent CHCl3
EtOH (2%).
Full methyl ethers of porphyrins were obtained and
purified by the standard procedure [23].
7
. Berezin, B.D., Drobysheva, A.N., and Venedik-
tov, E.A., Koord. Khim., 1976, vol. 2, no. 3, p. 346.
(
Chloro)mesoporphyrinplatinum(III) (Cl)PtMP.
1
IR
18 [ (Pt Cl)]; 720 (bending vibrations of pyrrole
rings); 838 [ (Cmeso H)]; 964, 986, 1100, 1455
skeleton vibrations of pyrrole rings); 1122 [ (C O)];
spectrum,
cm :
456
[ (Pt N)];
8. Lomova, T.N., Berezin, B.D., Oparin, L.V., and
Zvezdina, V.V., Zh. Neorg. Khim., 1982, vol. 27,
no. 3, p. 683.
9. Lomova, T.N. and Berezin, B.D., Zh. Neorg. Khim.,
1979, vol. 24, no. 6, p. 1574.
10. Klyueva, M.E., Lomova, T.N., and Berezin, B.D., Zh.
Obshch. Khim., 1991, vol. 61, no. 5, p. 1244.
11. Drobysheva, A.N. and Berezin, B.D., Zh. Neorg. Khim.,
6
(
1
[
2
171 [(CH ) COO]; 1362, 1387 [ (CH )]; 1476
2 2 3
(CH )]; 1735 [ (C=O)]; 2870, 2880 [ (CH )]; 2935,
2
3
970 [ (Cmeso H)]. Electronic absorption spectrum,
max, nm: in MeOH 420.0, 529.7, 561.8; in AcOH
60, 528, 415. Found, %: Cl 4.84; Pt 23.6 0.1.
5
1
974, vol. 19, no. 3, p. 837.
2. Berezin, B.D. and Drobysheva, A.N., Zh. Fiz. Khim.,
974, vol. 48, no. 11, p. 2742.
C H ClN O Pt. Calculated, %: Cl 4.2; Pt 23.7.
3
6
40
4
4
1
1
1
(
Chloro)protoporphyrinplatinum(III) (Cl)PtPP.
1
3. Karmanova, L.P., Drobysheva, A.N., and Bere-
IR spectrum, cm : 461 [ (Pt N)]; 630 [ (Pt Cl)];
zin, B.D., Zh. Fiz. Khim., 1977, vol. 51, no. 3, p. 629.
7
[
26 (bending vibrations of pyrrole rings); 838
(Cmeso H)]; 971, 992, 1100, 1460 (skeleton vibra-
14. Berezin, B.D., Drobysheva, A.N., and Venedik-
tov, E.A., Koord. Khim., 1976, vol. 2, no. 4, p. 491.
15. Drobysheva, A.N. and Berezin, B.D., Zh. Fiz. Khim.,
1977, vol. 51, no. 1, p. 21.
16. Drobysheva, A.N., Karmanova, L.P., and Bere-
zin, B.D., Zh. Fiz. Khim., 1977, vol. 51, no. 6, p. 1344.
tions of pyrrole rings); 1124 [ (C O)]; 1655 [vinyl
C=C)]; 1370, 1388 [ (CH )]; 1475 [ (CH )]; 1718
(
3
2
[
[
(C=O)]; 2870, 2880 [ (CH )]; 2935, 2975
(Cmeso H)]; 3080 [vinyl
3
(C H)]. Electronic
absorption spectrum, max, nm: in EtOH: 420, 530,
62; in AcOH: 418, 530, 560.
5
1
1
1
7. Drobysheva, A.N. and Berezin, B.D., Zh. Fiz. Khim.,
978, vol. 52, no. 7, p. 1755.
8. Kincaid, J. and Nakamoto, K., J. Inorg. Nucl. Chem.,
975, vol. 37, no. 1, p. 85.
1
(
Chloro)deuteroporphyrinplatinum(III)
Cl)PtDP. Electronic absorption spectrum, max, nm:
in CHCl : 558.9, 527.1, 417.1; in AcOH: 415.1,
(
1
3
9. Cheremisina, I.M., Zh. Strukt. Khim., 1978, vol. 19,
5
26, 556.4.
no. 2, p. 336.
(
Chloro)hematoporphyrinplatinum(III)
20. Lavallee, D.K., Inorg. Chem., 1978, vol. 17, no. 2,
p. 232.
(
Cl)PtGP. Electronic absorption spectrum (EtOH +
1
0% AcOH), max, nm: 564.3, 531.3, 416.7.
21. Kitagawa, T. and Ozaki, Yu., in Structure and
Bonding 64, Berlin: Springer, 1987, p. 71.
REFERENCES
2
2. Gillespie, R.J. and Robinson, E.A., Nonaqueous Sol-
vents, New York: Wiley, 1968. Translated under the
title Nevodnye rastvoriteli, Moscow: Khimiya, 1971,
p. 109.
1
2
. Berezin, B.D., Shormanova, L.P., and Tzvetkov, T.A.,
Zh. Fiz. Khim., 1979, vol. 59, no. 11, p. 2716.
. Lomova, T.N., Shormanova, L.P., and Klyueva, M.E.,
Uspehi khimii porfirinov (Progress in Porphyrin
Chemistry), St. Petersburg: Nauchno-Issled. Inst.
Khimii S.-Peterb. Gos. Univ., 1997.
23. Koifman, O.I., Askarov, K.A., Berezin, B.D., and
Enikolopyan, N.S., Porfiriny: struktura, svoistva,
sintez (Poprphyrins: Structure, Properties, Synthesis),
Moscow: Nauka, 1985, p. 175.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 73 No. 2 2003