Ruthenium(IV) and Osmium(II) Tetraphenylporphine Complexes: Synthesis and Oxidation Reactions

Article abstract of DOI:10.1023/A:1025162321560

The Ru(IV) and Os(II) complexes (PhO)₂RuTPP and OsTPP were synthesized from tetraphenylporphine (H₂TPP) and K ₂RuO₄ or K₂OsO₄ (taken in the molar ratio of 1:30) in boiling phenol. The kinet

Full text of DOI:10.1023/A:1025162321560

Russian Journal of Coordination Chemistry, Vol. 29, No. 8, 2003, pp. 564–568. Translated from Koordinatsionnaya Khimiya, Vol. 29, No. 8, 2003, pp. 605–610.
Original Russian Text Copyright © 2003 by Tyulyaeva, Lomova, Mozhzhukhina.
Ruthenium(IV) and Osmium(II) Tetraphenylporphine
Complexes: Synthesis and Oxidation Reactions
E. Yu. Tyulyaeva, T. N. Lomova, and E. G. Mozhzhukhina
Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
Received July 10, 2002
Abstract—The Ru(IV) and Os(II) complexes (PhO)2RuTPP and OsTPP were synthesized from tetraphe-
nylporphine (H2TPP) and K2RuO4 or K2OsO4 (taken in the molar ratio of 1 : 30) in boiling phenol. The kinetics
of oxidation reactions of these complexes in solutions of HOAc (acetic), H2SO4, and HOAc–H2SO4 acids was
studied. It was found that in the aerated HOAc–H2SO4 mixture heated above 340 K, these complexes are oxi-
dized with participation of different reaction sites: the Ru(IV) complex is oxidized at macrocycle to give the π-
.
radical-cation (PhO)2RuíPP + , while in the Os(II) complex, the metal atom is oxidized to form the Os(III)
complex. In the first case, the reaction follows the activation mechanism, whereas in the second case, the acti-
vation energy of the reaction is zero.
The platinum metals are known to exhibit high com- vent as eluent. The individual nature and chromato-
plexing properties and form kinetically inert complexes graphic purity were confirmed by the thin-layer chro-
[1]. Since ruthenium and osmium occur in different
oxidation states, they can produce various complexes
with different ligands, in particular, with porphyrins.
The following complexes were synthesized and their
structures and physicochemical properties were
matography on Silufol silica gel using chloroform as a
solvent.
(Diphenoxo)tetraphenylporphinatoruthenium(IV)
(PhO)2RuTPP was synthesized in 56% yield. The
electronic absorption spectrum (CHCl3), λmax, nm
(logε): 625–650 (b), 560 (3.43), 531.6 (3.64), 410
(4.58). IR (KBr), ν, cm–1: 401 (Ru–O), 444 (Ru–N),
benzene ring vibrations 701, 752, γ(CH); 1070, 1176
δ(CH); 1487, 1597 ν(C=C); 3020, 3053 ν(CH); pyrrole
ring vibrations 794 γ(CH); 1009 (C(3)–C(4), ν(C–N),
δ(CH)); 1350 ν(C–N); 1441 ν(C=N); 1527 (skeletal
vibrations of pyrrole ring), 2853, 2923 ν(CH). 1H NMR
(CDCl3), δ, ppm: 2.17 d (4H, Ó-OC6H5), 2.26 m (6H,
m-, p-OC6H5), 7.73 t (12H, m-, p-C6H5), 8.19 m (8H,
o-C6H5), 8.69 t (8H, C4H2N).
reported:
(CO)(L)MIIP
[2,
3],
(Cl)MIIITPP,
[(X)MIVTPP]2O [4–7], [(O)2åVIP] [8] (M is Os, Ru; P
are dianions of octaphenylporphine (OEP), tetraphe-
nylporphine (TPP); L is Py, Me, etc; X is Br, Cl, CF3,
COO, HSO4). At the same time, such characteristics as
the thermodynamic stability and kinetical inertness
were not studied.
The reactions of formation of porphyrin complexes
of the platinum metals and their dissociation under the
action of acids are irreversible [2–9], and that is why the
thermodynamic stability constants of these complexes
cannot be experimentally determined. In this work, the
Ru(IV) and Os(II) complexes with tetraphenylporphine
(H2TPP) of the composition (PhO)2RuTPP and OsTPP
were synthesized and the kinetics of their reactions
with the HOAc, H2SO4, and HOAc–H2SO4 acids is
studied.
Tetraphenylporphinatoosmium(II) OsTPP was
synthesized with the yield of 50%. The electronic
absorption spectrum (CHCl3), λmax, nm: 635.7 594.8,
551.5, 525 (sh), 500.4, 406.3, with alternating intensi-
ties of the bands numbered starting from the long-wave
band: VI > III > II > IV > V > I (Fig. 1). IR spectrum
(KBr) ν, cm–1: 463 ν(Os–N), benzene ring vibrations
702, 752 γ(CH); 1071, 1177 δ(CH); 1488, 1597
ν(C=C); 3025, 3054 ν(CH); pyrrole ring vibrations 799
γ(CH); 1009 (C(3)–C(4), ν(C–N), δ(CH)); 1351 ν(C–
N); 1441 ν(C=N); 1540 (skeletal vibrations of pyrrole
EXPERIMENTAL
The ruthenium(IV) and osmium(II) complexes with
the 1 : 1 composition of porphyrin and the metal cation
were synthesized by reacting H2Têê (0.01 mg) with
K2RuO4 or K2OsO4 (taken in the molar ratio of 1 : 30)
in boiling phenol. The starting metal salts were pre-
pared by fusing metallic Ru (0.07 mg) or Os (0.08 mg)
together with KNO3 (0.05 mg) in the presence of KOH.
1
ring), 2852, 2923 ν(C–H), H NMR (CDCl3), δ, ppm:
7.68 m (4H, p-C6H5), 7.77 m (8H, m-C6H5), 8.16 m
(8H, o-C6H5), 9.05 t (8H, C4H2N).
The electronic absorption spectra were recorded
The complexes were purified by column chromatogra- on SF-26 and Specord M-400 spectophotometers, IR
phy on Al2O3 (II Brockmann activity) using CHCl3 sol- and 1H NMR spectra were measured on Specord M80
1070-3284/03/2908-0564$25.00 © 2003 åÄIä “Nauka /Interperiodica”

RUTHENIUM(IV) AND OSMIUM(II) TETRAPHENYLPORPHINE COMPLEXES
565
and Bruker spectrometers (200 MHz, hexamethyldisil-
oxane), respectively.
A
Interaction of the complexes with sulfuric acid was
kinetically studied by spectrophotometric methods.
The solutions were thermostatted in a standard U4
water thermostat, the accuracy of the temperature mea-
surements being ±0.1 K.
A highly concentrated sulfuric acid was prepared
from a reagent grade H2SO4 and a monohydrate by a
gravimetric technique, the monohydrate was prepared
from a reagent grade oleum and H2SO4 with potentio-
metric monitoring of concentration [10]. The concen-
tration of aqueous sulfuric acid was determined by the
acid–base titration with the maximum accuracy of
0.15%. Solutions of metalloporphyrins in the çéÄÒ–
H2SO4 of different compositions were obtained by mix-
ing metalloporphyrin solutions of the known concen-
trations in glacial HOAc, 10 M H2SO4 solution in gla-
cial HOAc, and glacial HOAc. The content of water in
individual H2SO4 and HOAc was determined potentio-
metrically [10] and by the Fisher titration method,
respectively, and did not exceed 0.02–0.03%. The same
content of water was produced by the fractional freez-
ing-out technique.
5
4
3
2
1
500
600
700 λ, nm
Fig. 1. Electronic absorption spectra of OsTPP in (1) chlo-
roform, (2) HOAc, (3) 97.5% H SO , and (4, 5) in the
HOAc–9 M H SO mixture, after termination of the reac-
2
4
2
4
tion with an acid at (5) 350 K.
at 521 and 592 nm are contained in the visible region.
The spectra of the obtained Ru(IV) and Os(II) com-
plexes also differ in the oxidation states of the central
metal atom.
RESULTS AND DISCUSSION
The known Ru and Os porphyrin complexes were
synthesized from the metal carbonyls of a mixed com-
position. In this work, we followed the original proce-
dure and used the refined metal powders, which were
oxidized to the respective anionic oxo complexes
[MO4]2– and then used in the reaction with tetraphe-
nylporphine. This reaction occurs in several stages of
the ligand substitution in the first coordination sphere
of the initial complex and is accompanied by the redox
reaction involving the phenol solvent. The overall pro-
cess can be written as follows:
The covalently bonded OPh acido ligands in the
1
Ru(IV) complex are identified by the IR and H NMR
spectra. The additional absorption maximum at 401 cm–1
corresponds to the vibration of the Ru–O bond [11, 13].
The spectra of free ç2íêê and OsTPP do not show this
1
band. In the H NMR spectra of the Ru complex, the
chemical shifts (δ) 2.17 and 2.26 ppm are due to pro-
tons of the coordinated phenoxo ligands. The same con-
clusion was made when examining the 1H NMR spectra
of the (C6H5)FeTpTP complex (TpTP is the tetra(p-
tolyl)porphine dianion) with phenyl at the fifth coordi-
nation site [14] and the (Py)2RuOEP complex with the
coordinated pyridine (δ = 2.04 ppm) [11]. The chemical
shifts from (Ph and Py) protons and the (PhO)2RuTPP
macrocycle (7.73 and 8.19 ppm) considerably differ.
The authors of [15] believe that a significant distance
between the protons with δ ≈ 2 ppm and the macrocycle
plane protons suggests that these protons belong to the
axial ligand. Thus, ruthenium porphyrin is a haxacoor-
dinated complex.
2K2RuO4 + H2TPP + 3C6H5OH
(C6H5O)2RuTPP + C6H4O2
+ 4KOH + RuO2 + H2O,
(1)
K2OsO4 + H2TPP + C6H5OH
(2)
OsTPP + C6H4O2 + 2KOH + H2O.
In this case, the complexation reactions (Eqs. (1)
and (2)) result in the 1 : 1 Ru(IV) and Os(II) complexes
with tetraphenylporphine. The metal complexes in the
indicated oxidation states are easily identified by the
As follows from the spectral data, OsTPP does not
electronic absorption spectra (Fig. 1, 1), which agrees contain the coordinated acido ligands. However, taking
with the data on the known Ru and Os complexes (in account of the coordinating properties of Os(II) [1] and
different oxidation states) with the other porphyrins a comparatively long wave of the maximum of the
[11, 12]. For instance, the (Py)2RuIIOEP and (CH3)RuI- Q(0,0) band (551.5 nm), one can assume that in solu-
IIOEP complexes in benzene exhibit the B(0,0) and tions of OsTPP, the OsII atom has coordination number
Q(0,0) bands (the Soret band and more intense low- 6 due to coordination of the donor molecules of a sol-
energy band) at 395, 521 and 394, 503 nm, respectively. vent. It is most likely that the coordinated molecules are
In the (OCH3)2RuTPP, the Soret band is bathochromi- the H2O molecules contained in the solvents. At the
1
cally shifted (410 nm), and two bands with the maxima same time, the OsTPP H NMR spectrum does not
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

566
TYULYAEVA et al.
In a mixture of solvents çéÄÒ–H2SO4, the com-
A
plexes under study each occur as two different forms
obtained when the composition of the mixture is
changed. With small amounts of H2SO4, the initial
molecular form of the complexes prevails (Fig. 2, 1–3)
and this form remains unchanged after its isolation
from the acidic solution. With an increase in the H2SO4
concentration to 3 and 9 mol/l, a new form of the Ru
and Os complexes appear in the solution, respectively.
The electronic absorption spectrum becomes more
resolved in the near-IR region, while the intense band at
551.5 and 531.6 nm (in CHCl3) is smoothed out. The
final transformation into the product, whose spectrum
contains the absorption bands with maxima in the range
of 630–660 nm (Fig. 1, 5 and Fig. 2, 5), occurs in the
course of thermostatting the solutions at 345–360 K.
The products of the Ru(IV) and Os(II) complex trans-
formation are identified by comparing their electronic
absorption spectra with those of different oxidized
forms of metalloporphyrins reported in [16, 18]. In the
number and position of the bands, the spectrum of the
product of the (PhO)2RuTêê transformation concides
4
2
5
1
3
500
600
700 λ, nm
Fig. 2. Electronic absorption spectra of (Phé) Ruíêê in
2
the HOAc–H SO mixture with c
(mol/l): (1) 0, (2)
2
4
H2SO4
–3
10 , (3) 0.1, (4, 5) 3.0, after termination of the reaction
with an acid at (5) 355 K.
exhibit a weak absorption with the chemical shift 2.15
ppm due to protons of H2O contained in a solvent as
was observed in the spectra of the coordinatively satu-
rated metalloporphyrins we studied, namely, AgTPP,
(Cl)AlTPP, (Cl)2PtTPP, and some others. Moreover,
according to the data of [11, 16], the coordination of the
Ru(II) and Os(II) complexes with the molecular ligands
capable of forming the dative π-bonds with the metal
atom results in a considerable bathochromic shift of the
Q(0,0) band. Thus, the bands Q(0,0) and Q(0,1) (the
vibration satellite of the Q(0,0) band) for the
(Py)2OsOEP and (Py)(CO)OsOEP complexes lie at
510, 482, and 550, 525 nm, respectively.
.
+
with that of the π-radical-cation RuíêP obtained by
the chemical oxidation of RuTPP. The higher degree of
.
+
the Ru oxidation in (PhO)2RuTêP appears as diffu-
sion of the absorption bands in its spectrum as com-
pared to the spectrum of the reduced (regarding a
.
+
metal) analog of RuíêP .
The electronic absorption spectrum of the product of
OsTPP transformation (Fig. 3) fully coincides with that
of the cationic osmium complex [(CO)(Py)OsIIIOEP]+.
The latter complex is synthesized by electrochemical
oxidation of the (CO)(Py)OsIIOEP complex [16].
Taking into account the oxidizing properties of the
aerated sulfuric acid [19, 20], one can represent the
overall equations of the reactions occurring in solutions
of (PhO)2Ruíêê and OsTPP solutions in acetic acid
The electronic absorption spectra of the Ru(IV) and
Os(II) complexes are of “hypso-hyper” type (hypso-
chromic shift of the Q(0,0) band and additional bands
in the near-IR region, Fig. 1, 1–4), which suggests the
dπ
eg(π*) interaction and the intramolecular trans-
fer of the electron density from the a1u and a2u orbitals with the added H2SO4 as
of porphyrin to the eg(dπ) orbital of a metal on absorp-
tion of light quanta [17]. The mixed σπ type of coordi-
.
.
(PhO) RuTP + + HO2,(3)
P
2
(PhO)2RuTPP + é2 + H+
nation bonds provides grounds to consider these com-
plexes as very stable compounds.
.
OsIIíPP + é2 + ç+
OsIIIíPP+ + çO2 .
(4)
In glacial acetic acid, the (PhO)2RuTêê and OsTPP
complexes form molecular solutions (Fig. 1, 2 and
Fig. 2, 1). Both complexes dissolve in aqueous H2SO4
with c > 17 mol/l. The Ru complex is stable in this
medium for a long time and when heated to 400 K.
However, the electronic absorption spectrum shows
considerable changes in the region of the Soret band: its
intensity decreases, while the intensity of the absorp-
tion at 438 nm increases, which indicates a steady equi-
librium of two colored forms. The bands in the visible
region remain. The OsTPP complex undergoes trans-
formation accompanied by the spectral changes: the
intense band in the visible region (Fig. 1, 1, 2) exhibits
Reactions (3) and (4) were kinetically studied, and
their rates can be expressed by a full kinetic equation
–dccomplex/dτ = kccomplexcn cHm+ ,
(5)
O2
where n and m are the orders in the O2 and H2SO4 con-
centrations and by a formal first-order kinetic equation
obtained by the excess concentration method
–dccomplex/dτ = keffccomplex
.
(6)
The effective rate constants of reactions (3) and (4)
calculated by optimization of a linear dependence in
coordinates log((A0 – A∞)/(Aτ – A∞)) vs. τ by the least-
hypsochromic shift and a new absorption is observed at squares method with Microsoft Excel program and the
715–720 nm in the near-IR region (Fig. 1, 3). effective activation parameters are listed in Tables 1 and 2.
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

RUTHENIUM(IV) AND OSMIUM(II) TETRAPHENYLPORPHINE COMPLEXES
567
In this case, A0, Aτ, and A∞ are the optical densities of
A
solutions of the Ru and Os complexes at the operating
wave lengths of 556 and 436 nm, respectively, at time
0, τ and after the reaction termination. One can see
from Table 1 that the effective activation parameters of
reaction (3) vary greatly with the changing H2SO4 con-
centration, which underlies the difference between the
oxidation reactions of the complexes and reactions of
their dissociation under the action of acids [19].
As was experimentally found, the reaction rate does
not depend on the O2 concentration, i.e., in reaction (5),
n = 0. As for the other oxidation reactions with the aer-
ated H2SO4, keff in reaction (3) increases with the
increasing initial concentration of H2SO4 (Table 1). A
linear correlation was found between the logarithms of
keff and cH0 SO (correlation parameters are given in
2
4
Table 3). It thus follows that the reaction order in the
H2SO4 concentration is almost unity (m = 1 in Eq. (5)).
The numerical values of the rate constants k were found
λ, nm
III
+
Fig. 3. Electronic absorption spectrum of Os TPP (prod-
II
uct of the Os TPP oxidation) in chloroform.
by optimizing equation logkeff = logcH0 SO + logk
2
4
obtained from Eqs. (5) and (6) with account of the deter-
mined orders in the components and are listed in the
same table.
sented in Table 2. One can see that this reaction has zero
order in the concentration of protons, i.e., the full
kinetic equation is identical to Eq. (6) and keff = k. In the
investigated narrow temperature interval, which makes
it possible to reliably determine the rate constants by
The OsTPP oxidation reaction (4) occurs in acetic
acid with small amounts of H2SO4 (7–9 mol/l) at 346–
352 K. The kinetic parameters of reaction (4) are pre- the method used, the reaction rate does not depend on
Table 1. Effective rate constants, activation energies and entropies of the (PhO)2RuTPP oxidation to the π-radical-cation in
the HOAc–H2SO4 mixture
keff × 105, s–1 (pkeff)
c0H SO , mol/l
E, kJ/mol
∆S≠, J/(mol K)
2
4
351 K
354 K
356 K
1.0
3.0
4.0
3.2 ± 0.4 (4.5)
10.3 ± 3.0 (4.0)
15.2 ± 5.0 (3.8)
6.4 ± 0.8 (4.2)
15.7 ± 1.4 (3.8)
17.1 ± 2.5 (3.7)
143.6
87.4
24.4
69.5
–85.1
13.6 ± 3.7 (3.9)
16.7 ± 2.6 (3.8)
–260.5
Table 2. Effective parameters of the OsIITPP oxidation to OsIIITPP+ in the HOAc–H2SO4 mixture
keff × 104, s–1
c0H SO in HOAc, mol/l
2
4
343 K
346 K
349 K
352 K
343–352 K**
7.0
7.2
3.29 ± 0.09
2.59 ± 0.06
3.95 ± 0.09
1.0 ± 0.1
3.2 ± 0.16
3.5 ± 0.2
3.24 ± 0.04
3.0 ± 0.3
3.0 ± 0.1
2.6 ± 0.1
7.5
3.0 ± 0.7
7.7
2.9 ± 0.16
2.18 ± 0.07
2.13 ± 0.05
2.0 ± 0.7
8.0
2.2 ± 0.2
2.16 ± 0.03
8.5
1.7 ± 0.2
1.89 ± 0.06
1.8 ± 0.1
9.0
7.0–9.0*
2.6 ± 1
3.2 ± 0.2
2.5 ± 0.3
* The average k values in the whole range of the H SO concentrations under study.
eff
2
4
** The average k values in the whole temperature interval under study.
eff
RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 29 No. 8 2003

568
TYULYAEVA et al.
Table 3. Parameters of the linear correlation (logkeff = const1logc0
+ const2), rate constants (k), energies (E) and entro-
H2SO4
pies (∆S≠) of the formation of the (PhO)2RuTPP•+ π-radical-cation
Approximation
T, K
const1
const2
k, s–1 mol–1
l
E, kJ/mol
110 ± 24
∆S≠, J/(mol K)
–28 ± 68
reliability, R2
351
354
356
1.11
0.71
0.74
–4.50
–4.21
–4.19
0.998
1
0.986
2.6 ± 1.6
3.3 ± 1.9
4.4 ± 2.9
temperature, which suggests a zero activation energy
and the capability of a system not to overcome the
energy barrier in the pathway to the products of a sim-
ple limiting stage. Therefore, one can conclude that in
the latter stage, the transfer of the electron or proton
having wave functions occurs.
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and Berezin, B.D., Zh. Obshch. Khim., 1989, vol. 59,
no. 10, p. 2317.
In conclusion, one should note that reaction (4) can
be used in practice for the synthesis of the osmium(III)
porphyrin complexes.
22. Lomova, T.N., Klyueva, M.E., and Berezin, B.D., Izv.
Vyssh. Uchebn. Zaved., Khim. Khim. Tekhnol., 1988,
vol. 31, no. 12, p. 75.
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