Chemical structure and reactions of axially coordinated iridium(III) porphyrins

Article abstract of DOI:10.1134/S0036023615020199

Effect of modification of the axial (fifth and sixth) coordination sites on the physicochemical properties and reactivity of iridium(III) complexes with 5,10,15,20-tetraphenyl-21H,23H-porphine was studied. Oxidation reactions of (Cl)(H₂O)IrTPP

Full text of DOI:10.1134/S0036023615020199

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2015, Vol. 60, No. 2, pp. 157–165. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © E.Yu. Tyulyaeva, E.G. Mozhzhukhina, N.G. Bichan, T.N. Lomova, 2015, published in Zhurnal Neorganicheskoi Khimii, 2015, Vol. 60, No. 2, pp. 194–202.
COORDINATION
COMPOUNDS
Chemical Structure and Reactions
of Axially Coordinated Iridium(III) Porphyrins
E. Yu. Tyulyaeva, E. G. Mozhzhukhina, N. G. Bichan, and T. N. Lomova
Krestov Institute of Solution Chemistry, Russian Academy of Sciences,
Akademicheskaya ul. 1, Ivanovo, 153045 Russia
eꢀmail: tnl@iscꢀras.ru
Received July 17, 2014
Abstract—Effect of modification of the axial (fifth and sixth) coordination sites on the physicochemical
properties and reactivity of iridium(III) complexes with 5,10,15,20ꢀtetraphenylꢀ21H,23Hꢀporphine was
studied. Oxidation reactions of (Cl)(H2O)IrTPP in protic solvents by atmospheric oxygen (on assistance of
protons at high concentration) preceded by ligand substitution at the axial position were studied. It was found
that (Cl)(H2O)IrTPP in 100% AcOH undergoes slow oneꢀelectron oxidation at the aromatic ligand to form
π
cation radical (CH3COO)(CH3COOH)IrTPP•+. The reaction was studied in 100% AcOH (H2O content
0.078%) at 288–308 K, its kinetic parameters were obtained. The (Cl)(H2O)IrTPP reaction product in
CF3COOH was identified as complex (CF3COO)2IrIVTPP oxidized at the central metal cation. It was experꢀ
imentally confirmed that the reaction in 99% CF3COOH at 298 K proceeds in two stages: the substitution of
axial Cl– and H2O by excess CF3COO– (
eff = (8.0 0.5)
10–5
for comparison.
k
eff = (1.8 0.1)
×
10–3 s–1) and the oxidation of iridium to Ir(IV)
(k
×
s
–1). Data on similar Re(III) complexes (PhO)ReTPP and (Cl)ReTPP are presented
DOI: 10.1134/S0036023615020199
Variable valence in chemical compounds is one of mula) in protolytic solvents AcOH and CF3COOH
the reasons of structure variety of iridium coordination and to reveal the effect of modification at the fifth and
compounds, in particular, complexes with tetrapyrrole sixth axial coordination sites in molecule on the physꢀ
ligands. Few Ir(I) porphyrin complexes are presented icochemical properties and reactivity of the comꢀ
in the literature by several works. Among described plexes. We also obtained data for similar Re3+ complexes
compounds are intermediate [IrI(CO)3]2OEP in the
presented for comparison. Only few works in the literaꢀ
ture were dedicated to the physical chemistry of Re3+
complexes with tetrapyrrole ligands: for derivatives of
course of (Cl)(CO)IrIIIOEP synthesis from
[Ir(cod)Cl]2 (cod is cyclooctadiene) and H2OEP [1],
tetracoordinated bis[iridium(I)] complex with Nꢀ
transꢀdifluorophthalocyanine transꢀ
[Re(F)2pc2–]– and
Nꢀconfused porphyrin ReIII(NFP)OL (P = TPP2–
)
confused porphyrin (NCTPP) I (CO)4 (NCTPP is
Ir2
[14, 15].
the dianion of Nꢀconfused 5,10,15,20ꢀtetraphenylꢀ
21H,23Hꢀporphine) [2], and donorꢀacceptor SAT
EXPERIMENTAL
(sitting a top) complex ꢀ(5,10,15,20ꢀtetraphenylporꢀ
μ
phine)ꢀbisꢀchloroiridium(I) [3]. Oxidation state 3+
and CN = 6 are more typical for iridium [4]. Strucꢀ
tures with central Ir(III) atom were studied for comꢀ
pounds of classes hexaphyrins [5], corroles [6, 7], porꢀ
phyrins [8–11], and Nꢀconfused porphyrins [2].
(5,10,15,20ꢀtetraphenylporphinato)chloroaquairiꢀ
dium(III) (Cl)(H2O)IrIIITPP [16]. A mixture of
H2TPP (0.00360 g), (Н3O)2IrCl6 (0.01115 g) (molar
ratio 1 : 5), and phenol (2.0 g) was heated under reflux
for 3 h. Reaction completion was detected by the disꢀ
appearance of Н2ТРР in the reaction mixture using
thinꢀlayer chromatography (TLC) (Silufol, chloroꢀ
form). The reaction mixture was cooled, dissolved in
chloroform, and washed many times with warm disꢀ
tilled water in a separating funnel to remove phenol.
The chloroform solution was concentrated and chroꢀ
matographed on Brockmann activity grade II alumina
using chloroform as an eluent. There were three zones.
The substances of the first and the third zones were
According to [5–11], Ir(III) porphyrinoids display
catalytic and redox activity, which depends on the
state of axial coordination sites on the metal atom.
Porphyrin complexes show distinct photoluminescent
properties [12, 13]. There is a rapidly growing interest
in the chemistry of aromatic macroheterocyclic iridꢀ
ium compounds in recent years due to the noted feaꢀ
tures.
The aim of this work is to study the state and reacꢀ purified repeatedly. Trace amounts of compound of
tions of 5,10,15,20ꢀtetraphenylꢀ21H,23Hꢀporphine unknown composition from the second zone were disꢀ
(
H2TPP) complexes with trivalent iridium cation (forꢀ carded.
157

158
TYULYAEVA et al.
Table 1. 1H NMR spectra of (L)(X)IrTPP in CDCl3 depending on solvent used for chromatography
δ
, ppm,
J, Hz
Solvents
Product ratio
H
Ho, Hm, Hp
axial ligands
β
Benzene–CHCl3
9.06
8.17 (d, 8Ho,
J
= 7),
H2O 2.18 (s, 2H)
(Cl)(H2O)IrTPP
(s, 8H ) 7.75 (m, 12Hm,p
)
β
(Cl)(H2O)IrTPP : (OH)(H2O)IrTPP = 10 : 1
EtOH–CH3COOH
8.9
(s, 8H )
β
8.58 (d, 8Ho,
J
= 7),
H2O 0.35 (s, 2H)
OH –1.41 (s, 1H)
(OH)(H2O)IrTPP
7.52 (t, 8Hp),
7.36 (t, 4Hm)
9.06
8.17
CH3COOH 1.78
(d, 3H, CH3, J = 7.3)
(s, 8H ) (d, 8Ho,
J
= 7.3),
β
7.75 (m, 12Hm,p
)
(Cl)(CH3COOH)IrTPP
(Cl)(CH3COOH)IrTPP : (Cl)(EtOH)IrTPP :
(OH)(EtOH)IrTPP = 3 : 1 : 1
9.02 8.1 (d, 8Ho, = 7.3),
J
EtOH 3.53
(m, 2H, CH2)
(s, 8H ) 7.75 (m, 12Hm,p
)
β
(Cl)(EtOH)IrTPP
9.09
8.22
EtOH 3.63 (m, 2H, CH2)
(s, 8H ) (d, 8Ho, J = 7.3),
OH –1.2 (s, 1H)
(OH)(EtOH)IrTPP
β
7.75 (m, 12Hm,p
)
X
X = Cl, L = H2O, (Cl)(H2O)IrTPP
X = OH, L = H2O, (OH)(H2O)IrTPP
X = Cl, L = CH3COOH, (Cl)(CH3COOH)IrTPP
X = Cl, L = C2H5OH, (Cl)(EtOH)IrTPP
X = OH, L = C2H5OH, (OH)(EtOH)IrTPP
N
N
Ir
N
N
L
The substance from the first zone was purified by
chromatography on silica gel L 100/250 using chloroꢀ
form and next ethanol–chloroform (1 : 1, v/v). A
crimson zone containing iridium(I) complex with
molecular porphyrin ligand (SAT complex)
[IrCl(H2О)2]2Н2ТРР [16] was isolated. The individuꢀ
ality of the purified compound was confirmed by TLC
on Silufol plates with the use of chloroform Rf = 0.94.
The IR spectrum of the compound of the main
zone eluted from chromatographic column with
C2H5OH–1% CH3COOH (a solid chaotic layer,
cm–1): phenyl substituents, 702 m, 754 s
(C–H));
1045, 1072 m, 1207 s (C–H)); 1488, 1597 m, 1622
(C=C)); 3026, 3054 ( (C–H)); pyrrole fragments,
802 s (C–H)); 1277 ( (C–N)); 1320 ( (C=N));
2853 m, 2924 s (C–H)); 1441 m skeletal vibrations
of pyrrole rings; coordination center, 465 (νs(Ir–N))
and 526 (νas(Ir–N)); 573 and 662 (νas(Ir–O) and
ν
,
(γ
(
δ
(ν
ν
(γ
ν
ν
(ν
UVꢀvis (benzene, λmax, nm, (log )): 420 (5.11), 482
ε
(3.27), 518 (3.73), 544 (3.73), 594 (3.25), 652 (3.1).
νs(Ir–O)); 1351 ( (O–H)).
δ
1H NMR spectra depending on the nature of L and
The compound from the third zone was repeatedly
chromatographed on alumina using chloroform. The
main zone was adsorbed in the upper part of the colꢀ
umn. The substance from this zone was eluted with
benzene–CHCl3. The obtained compound was idenꢀ
tified by UVꢀvis spectrum as the complex of composiꢀ
tion (Cl)(H2O)IrIIITPP. Yield 7%. UVꢀvis (CHCl3,
X– are presented in Table 1.
(5,10,15,20ꢀTetraphenylꢀ21H,23Hꢀporphinato)(phenꢀ
oxo)rhenium(III) (PhO)ReTPP and (5,10,15,20ꢀtetꢀ
raphenylꢀ21H,23Hꢀporphinato)chlororhenium(III)
(Cl)ReTPP were prepared similarly to [17]. H2TPP and
H2ReCl6 in molar ratio 1 : 2 were heated under reflux in
phenol at 454 K. The reaction completion was
detected after 2 h by the termination of alterations in
the UVꢀvis spectrum of reaction mixture sampled in
λmax, nm, (log )): 395 (shoulder 3.91), 418 (5.78), 476
ε
(shoulder 3.60), 508 (shoulder 3.73), 549 (4.42), 588
(3.81), 640 (3.63).
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 2 2015

CHEMICAL STRUCTURE AND REACTIONS
159
chloroform. The reaction mixture was cooled and disꢀ
The reaction rates of complexes in AcOH and
solved in chloroform. The solution in CHCl3 was CF3COOH were determined from the drop of comꢀ
washed many times with warm distilled water in a sepꢀ pound concentrations monitored by spectrophotomeꢀ
arating funnel to remove phenol, concentrated by parꢀ try. The measurements were performed in 1ꢀcm path
tial removal of the solvent, and chromatographed on length cells placed into a special thermostated chamꢀ
an Al2O3 column (Brockmann activity grade II) using ber of the spectrophotometer. Accuracy of solution
chloroform. Two zones were obtained: green and temperature determination was 0.1 K. Solutions of
green–brown. The substances isolated from the first complexes in sulfuric acid were prepared immediately
and the second zones were subjected to repeated chroꢀ prior to thermostating. The kinetics of complexes oxiꢀ
matography.
dation reactions was studied by the isolation method.
Rate constants and activation energies (keff Eeff
were determined using dependences log[(A0 )/(
)] vs , lnkeff vs. 1/ , respectively, standard deviaꢀ
tions were found by least squares using Microsoft
Excel software. Here A0 , and are the optical
densities of solutions at working wavelength at time (
equal to 0, current , and the time of reaction compleꢀ
tion; is temperature. Activation entropy
reaction was determined by the Eyring equation in appliꢀ
cation to liquid systems for the second standard state.
100% Acetic acid was prepared by fractional
defrost of glacial AcOH (water content of 0.078% was
determined by the Karl Fischer titration).
,
)
The chromatography of the substance from the
–
A
A –
green zone on a column with silica gel (40/100 Cheꢀ
mapol) using benzene as an eluent afforded an indiꢀ
vidual orange zone containing (Cl)ReTPP. The zone
∞
τ
A
.
T
T
∞
containing
μ
ꢀoxoꢀdimeric form of Re5+ compound
,
A
A
∞
τ
[O=ReTPP]2O and concentrated at the top of the colꢀ
umn was eluted with a CHCl3–C2H5OH (1 : 1).
τ)
τ
≠
The chromatography of substance from the green–
brown zone on a silica gel column using benzene as an
eluent gave a pink zone of (PhO)ReTPP. Next,
[O=ReTPP]2O was eluted with a CHCl3–C2H5OH
(1 : 1).
T
) of
(ΔSeff
Solid amorphous samples of the complexes were
isolated from solutions by solvent evaporation at ambiꢀ
ent temperature. The individuality and chromatoꢀ
graphic purity of the products were confirmed by TLC
on silica gel Silufol plates using benzene. For
(Cl)ReTPP Rf = 0.80, for (PhO)ReTPP Rf = 0.83.
RESULTS AND DISCUSSION
The prepared compounds were identified as pentaꢀ
coordinated rhenium(III) complexes (X)ReTPP and
hexacoordinated iridium(III) complexes (L)(X)IrTPP
from the hypsoꢀtype UVꢀVis spectra typical of porꢀ
phyrin complexes of triply charged metal cations [18]
and from the data of IR and 1H NMR spectroscopy that
agree well with those reported in [16, 17]. The results of
identification of axial ligands X and L are given below.
(Cl)ReTPP. Yield 0.5%. UVꢀvis (CHCl3, λmax
nm): 555 (shoulder), 525, 495 (shoulder), 416. UVꢀvis
,
(AcOH, λmax, nm): 540 (shoulder), 520, 480, 437
ν
(shoulder), 417. IR (300–2000 cm–1, as KBr pellet,
,
cm–1): phenyl substituents, 705, 759 (
1172 ( (C–H)); 1466, 1595, 1614 ( (C=C)); pyrrole
fragments, 799 ( (C–H)); 1029 (C3–C4 ( (C–N),
(C–H)); 1350 ( (C–N)); 1377 ( (C=N)); coordinaꢀ
γ(C–H)); 1075,
δ
ν
The high reactivity of iridium(III) complexes at the
axial directions was shown in the literature by the
examples of Ir(CO)(Cl)OEP reactions with pyridine,
γ
ν
δ
ν
ν
tion center, 408 (Re–N); 374, 392 (Re–Cl).
Nꢀ(nꢀbutyl)imidazole, and (carboxy)imidazole [12]
(PhO)ReTPP. Yield 7%. UVꢀvis (CHCl3, λmax
,
and transformation of waterꢀsoluble aqua and hydroxy
derivatives of Ir(III) tetra(sulfophenyl)porphyrins in
aqueous and methanolic solutions [10, 19]. The analꢀ
ysis of relative signal intensities in the 1H NMR spectra
of iridium complexes (Table 1) indicates the obvious
dependence of axial ionic and molecular ligands in the
compounds on solvents used at the complex purificaꢀ
tion stage. The solvent also affects the number of comꢀ
pounds present in solution. Thus, the purification of
iridium complex with a benzene–CHCl3 mixture (on
repeated chromatography) leads to emergence of sigꢀ
nals in 1H NMR spectrum in CDCl3 at 2.18, 0.35 ppm
nm, (log
425 (4.3). IR (solid chaotic layer,
substituents, 702, 758 ( (C–H)); 1068, 1178 (
H)); 1487, 1578, 1600 ( (C=C)); 2956, 3060 (
H)); pyrrole fragments, 806 ( (C–H)) 997 (C3–C4,
(C–N), (C–H)); 1340 ( (C–N)); 1377 ( (C=N))
ε)): 660 (shoulder), 551 (2.3), 436 (shoulder),
ν
, cm–1): phenyl
(C–
(C–
γ
δ
ν
ν
γ
;
ν
δ
ν
ν
;
coordination center, 418 (Re–N); 663 (Re–O); axial
ligand, 1265, 1462, 1542 (–OPh). 1Н NMR (CDCl3,
δ, ppm: 8.95 (d, 8H ), 8.25, 8.15 (d, m, 8Hо); 7.80 (m,
β
8Hm), 7.55 (m, 4Hp), 3.63 (s, 2Ho (OPh)), 4,71 (s, 2Hm
(OPh)), 5,37 (s, 1Hp (OPh)).
UVꢀvis, IR, and NMR spectra were recorded on an and –1.41 ppm related by us to the proton signals of
Agilent 8453 UVꢀVis and a Specord Mꢀ400 spectrophoꢀ coordinated H2O and hydroxide ion OH–, respectively
tometers, a VERTEX 80v spectrometer, and a Bruker [20, 21]. At the same time, the presence of two distinct
AVANCEꢀ500 radiospectrometer (using TMS as an singlets of pyrrole H protons at = 9.06 and 8.9 ppm
δ
internal reference), respectively. Solid layers of comꢀ and two sets of resonβances for the Ho, Hm, and Hp proꢀ
plexes for IR spectral study were prepared by evaporaꢀ tons of meso phenyl substituents indicates the presence
tion of CHCl3 solvent from a solution of complex on a of (H2O)(Cl)IrTPP and (H2O)(OH)IrTPP at equilibꢀ
silicon plate.
rium in the solution in a 10 : 1 ratio.
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160
TYULYAEVA et al.
A
1
0
400
500
600
700
800
λ
, nm
Fig. 1. UVꢀvis spectrum of (Cl)(H O)IrTPP in 100% AcOH at 298 K and τ (s) varied from 0 to 3600.
2
When C2H5OH–1% CH3COOH was used for the
The IR spectrum of (PhO)ReTPP shows absorpꢀ
chromatography of iridium(III) complex with tion with maximum at 418 cm–1 corresponding to
1
H2TPP, its H NMR spectrum (in CDCl3) displays vibrations of Re–N bonds and the maximum for
(Cl)ReTPP is shifted to 408 cm–1. The latter feature
probably results from the decrease in the Re–N bond
force constant because of the participation of electron
new peaks of resonances of C2H5OH (3.53 and 3.63
ppm), CH3COOH (1.78 ppm), and hydroxide ion OH–
(–1.2 ppm). The IR spectrum of the compound eluted
from chromatographic column with C2H5OH–1%
CH3COOH shows absorption with maxima at 573 and
662 cm–1 and a distinct peak at 1351 cm–1 (O–H
bending vibrations), which indicate the presence of
coordinated ethanol molecules in the structure of the
complex.
pairs of Cl in conjugation with Re
d orbitals. Ligand
π
–OPh was detected by the presence of signals of
o
ꢀ, mꢀ
,
1
and
pꢀprotons in the H NMR spectrum of complex
(PhO)ReTPP, which are shifted upfield as compared
with the proton signals of free phenol like in the case
of iridium complexes [22]. The presence of phenoxy
ligand in (PhO)ReTPP is confirmed by a new intense
absorption in the IR spectrum of the compound
(medium intensity bands within all spectrum) at 1285
1
The H NMR spectrum of compound isolated by
chromatography with C2H5OHꢀ1% CH3COOH
exhibits three singlets (9.02, 9.06, and 9.09 ppm)
cm–1 in maximum that corresponds to
(C–O) vibraꢀ
ν
related to
H and three doublets of phenyl ortho proꢀ
tons (8.1, 8.β17, and 8.22 ppm). These signals correꢀ
spond to three different iridium(III) compounds. The
signals of the most distant from the porphyrin macroꢀ
cycle para and meta protons of the phenyl substituents
display the least shift and appear as one large multiplet
tions. Furthermore, the spectrum of (PhO)ReTPP in the
region of C=C bond vibrations of aromatic benzene
ring (1487, 1578, and 1600 cm–1) exhibits supplemenꢀ
tary absorption bands of the same nature related to
phenyl incorporated into coordinated phenoxy ligand.
These are the absorption bands with frequencies 1462
and 1542 cm–1. Axial ligand vibrations in (Cl)ReTPP
are probably related to absorption bands at 374, 392
cm–1 (342 cm–1 in the spectrum of [ReCl6]2– [23]).
at = 7.75 ppm. The computation of relative integrated
δ
intensities for the signals of protons of the same kind
and the number of protons of axial ligands allows us to
suppose the presence in solution of a mixture of porꢀ
phyrin
complexes
(Cl)(CH3COOH)IrTPP,
The composition of (L)(X)IrTPP at the axial posiꢀ
tion varies when the compounds are placed into soluꢀ
tion. In glacial acetic acid, Ir(III) complexes form
molecular solutions without proton transfer [24]. The
spectrum of (Cl)(H2O)IrTPP is similar to the UVꢀvis
(Cl)(EtOH)IrTPP, and (OH)(EtOH)IrTPP in 3 : 1 : 1
ratio (Table 1).
It should be noted that an upfield shift of proton
signals of axial ligands in 1H NMR spectrum (as comꢀ
pared with the signals of free molecules) under the spectrum in chloroform but contains bathochromiꢀ
action of porphyrin ligand ring current is observed for cally shifted by ~10 nm
bands (Fig. 1, = 0). At
Q
τ
T
≥
all considered iridium compounds.
288 K, the spectrum transforms in time with retention of
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 2 2015

CHEMICAL STRUCTURE AND REACTIONS
161
A0 – A
∞
logꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
A – A
τ
∞
3
1.2
0.8
0.4
5
2
4
1
0
300
900
τ, s
Fig. 2. Dependence log[(
A
–
A
)/(
A
–
A
)] vs
. for reaction of (Cl)(H O)IrTPP in 100% AcOH at Т, K: 288 (1), 293 (2), 298 (3),
τ
0
∞
τ
∞
2
303 (
4), 308 (
5
). = 0.992–0.997.
ρ
distinct isosbestic points (Fig. 1): the intensity of the tution of axial ligands. Indeed, CF3COO– has lower
Soret band (418 nm) and longꢀwavelength bands with affinity to metal porphyrin as compared with
maxima at 557 and 595 nm decreases, new bands at 438 CH3COO– because of strong electronꢀwithdrawing
and 770–850 nm appear and grow. The presence of effect of three fluorine atoms. Therefore, the reaction
isosbestic points at 392, 428, 492, and 688 nm (Fig. 1) of complete substitution of initial axial ligands instantly
indicates the single initial form of the complex, proceeds in AcOH but carries on in time in the case of
(CH3COO)(CH3COOH)IrTPP, which undergoes trifluoroacetic acid, which is demonstrated by the presꢀ
transformation into the second colored compound in ence of the complicated Soret band in UVꢀvis spectrum
the absence of other colored forms (with allowance in the initial period (Fig. 3a), which becomes symmetꢀ
made for the constant total concentration of interconꢀ rical band with maximum at 402 nm in the course of
verting compounds). Such changes in UVꢀvis specꢀ transformation. Rate constant
trum are typical for the reactions of oneꢀelectron oxiꢀ CF3COOH at 298 K is (1.8 0.1)
k
eff of this process in 99%
×
10–3 s–1
.
dation of metal porphyrins with atmospheric oxygen
in the presence of acids [21, 25–28] to form their catꢀ
ion radicals (equation (1)). The final spectrum of reacꢀ
tion product coincides with the spectrum of an oxiꢀ
dized form of iridium(III) complex with 5,10,15ꢀtrisꢀ
pentafluorophenylcorrole, (PPh3)IrTPFC+, prepared
by electrochemical oxidation of (PPh3)IrTPFC with
The second series of spectral curves (Fig. 3b)
exhibits decrease in the intensity of band at 402 nm
and growth of absorption at λmax = 355 and 685 nm in
the region of 450–500 nm. Similar hypsochromic shift
of the Soret band by more than 30 nm and emergence
of band at 685 nm is observed upon electrochemical
π
tꢀ4BPA tris(4ꢀbromophenylammonium) hexachloroꢀ
antimonate and identified by ESR [29].
Table 2. Kinetic parameters for (Cl)(H2O)IrTPP oxidation
in acetic acid (CH O = 0.078%)
(CH3COO)(CH3COOH)IrTPP + О2 + Н+
2
(1)
→
(CH3COO)(CH3COOH)IrTPP•+ + HO•2.
T, K
keff
×
103, s–1
The reaction (1), which formally has first order
toward metal porphyrin concentration (Fig. 2), was
studied in AcOH (H2O content 0.078%) within temꢀ
perature range 288–308 K, kinetic parameters of the
oxidation reaction are represented in Table 2.
288
293
298
303
308
1.8 0.1
2.5 0.1
3.5 0.1
4.8 0.2
6.6 0.2
On dissolution of (Cl)(H2O)IrTPP in CF3COOH
the Soret band is broadened and exhibits two maxima
at λmax = 405 and 410 nm (Fig. 3, = 0). At 298 K,
,
τ
gradually changed in time spectra produce sequenꢀ
tially two series of curves with isosbestic points (Fig. 3).
One can suppose that the complication of spectral patꢀ
tern of complex transformation in CF3COOH is assoꢀ
ciated with the presence of slow initial stage of substiꢀ
#
E
eff = 48 2 kJ/mol,
= –299 5 J/(mol K)
ΔSeff
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 2 2015

162
TYULYAEVA et al.
(а)
A
1.2
0.6
1.0
0
400
λ
420
, nm
0.5
0
A
300
400
500
600
(b)
700
800
λ, nm
1.0
0.5
0
300
400
500
600
700
800
λ
, nm
Fig. 3. UVꢀvis spectrum of (Cl)(H O)IrTPP in 99% CF COOH at 298 K and τ (s) varied from 0 to 340 (a), from 341 to 7000 (b).
2
3
The last spectrum was recorded after 24 h.
oxidation of (Py)2IrTPFC and (TMA)2IrTPFC (Py is initial (Cl)(H2O)IrTPP with CF3COOH (Fig. 3b,
pyridine, TMA is trimethylamine) [29] and chroꢀ equation (2)) is a oneꢀelectron oxidation of
mium(III) porphyrinoids [30, 31] and indicates oneꢀ (CF3COO)(CF3COOH)IrIIITPP
into
keff is equal
electron oxidation of the complex at the central metal (CF3COO)2IrIVTPP, oxidation rate constant
×
atom. Thus, the second sequential stage of reaction of to (8.0 0.5)
10–5 s–1 for 99% CF3COOH at 298 K.
–
+
L + X + H
(Cl)(H2O)IrTPP
(CF3COO)(CF3COOH)IrTPP
CF COOH
3
(2)
O
2
(CF3COO)2IrIVTPP
HO•2
It is seen from the noted above that the macrocycle state could not be employed to study kinetics of the
always remains within complex as distinct from the total reaction of Ir(III) complexes in trifluoroacetic
initial axial ligands. To confirm this statement, the acid. Therefore, one may consider the acquisition of
compounds after completion of reaction in AcOH and two separated in time series of spectral curves in experꢀ
CF3COOH were isolated into chloroform, washed out iment as a success, which allowed us to obtain kinetic
from the acids, and tested spectrophotometrically: the constant for each of two consecutive stages of the comꢀ
bands of initial Ir(III) compounds in molecular form plex reaction.
(420 and 555 nm) were detected.
(Cl)ReTPP is stable in glacial AcOH, its electronic
The comparison of rates of the two consecutive absorption spectrum in this medium is similar to that
reactions shows that the principle of quasiꢀstationary in chloroform (Experimental) and does not change on
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 2 2015

CHEMICAL STRUCTURE AND REACTIONS
163
of the band of initial (Cl)ReTPP and its
cal, which is stable even in organic solvent.
π
cation radiꢀ
A
(PhO)ReTPP, in contrast to (Cl)ReTPP, dissociꢀ
ates at the Re–N bonds to give dication Н4ТРР2+
(equation (3), Fig. 5): slowly in 100% AcOH at 298 K
and quickly, upon dissolution, in media containing
sulfuric acid (AcOH–H2SO4, H2SO4–H2O).
(PhO)ReTPP + 4HX
(3)
→
H4TPP2+ + [ReOPh]2+ + 4X–.
Different stability of two axial complexes of rheꢀ
nium porphyrin indicates the strong binding of Cl–
and –OPh in the complexes in acidic solvents, which
differs rhenium from iridium in the corresponding
compounds.
2
1
3
400
500
600
700
λ
, nm
Variation of the central atom in the isostructural
metal porphyrins is one of the factors that change
reactivity upon oxidation in aerated acids. (Cl)RhTPP
Fig. 4. UVꢀvis spectrum of (Cl)ReTPP in AcOH–3 M
H SO immediately after dissolution ( ) and after keeping for
), in CHCl after reprecipitation on ice ( ).
1
2
4
in mixed solvent AcOH–3–5 M H2SO4 produces H+
ꢀ
3 h at 298 K (
2
3
3
associated form (O2)RhTPP⋅⋅⋅H
+⋅⋅⋅R containing coorꢀ
dinated O2 ligand and undergoes oxidation to give
π
cation radical (HSO4)RhTPP+• only in media with
high proton concentration, concentrated H2SO4 [26].
heating to 328 K. The Soret and
shifted hypsochromically by 5 nm relative to the specꢀ
Q (0,0) bands are
trum in chloroform. In AcOH–3 M H2SO4 at 308 K, At the same time, (Cl)(H2O)IrTPP slowly produces
an oxidized at the macrocycle form even in 100%
AcOH without preliminary formation of H+ꢀassociꢀ
ated form. (Cl)MnTPP is the least stable compound at
the M–N bond as compared with its structural analogs
and dissociates at the macrocycle without formation of
stable radical forms in AcOH–3–5 M H2SO4 [32, 33].
The lability of manganese complex with macrocyclic
its spectrum displays bathochromic shift of
680 nm and that of band to the region from 418 to
440 nm, as well as increase in the total background of
absorption in the visible region (Fig. 4, lines and ).
These changes indicate unambiguously the formation
of
cation radical (Cl)ReTPP•+
Q band to
B
1
2
π
.
The electronic absorption spectrum of the final
compound transferred into chloroform and purified
from protic solvents (Fig. 4, line
ligand is explained by lower contribution of N
reverse dative bond into complex stability in comꢀ
3) shows the presence parison with other noted complexes [34, 35].
←
M
π
A
1
0
450
550
650
λ
, nm
Fig. 5. UVꢀvis spectrum of (PhO)ReTPP in 100% AcOH at 298 K and
τ
(s) varied from 0 to 2280.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 60 No. 2 2015

164
TYULYAEVA et al.
In the context of medium acidity necessary for oxiꢀ conducted using the instruments of the Upper Volga
dation reaction, the stable in protic solvents at the M–N Regional Center for Physicochemical Research.
bond (Cl)MTPP complexes with the same polyhedron
(with no regard for weakly bonded molecular ligands
like H2O) can be arranged in the series (4) in agreeꢀ
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