Kinetic control of the transmetalation of labile metalloporphyrins in individual and mixed solvents

Article abstract of DOI:10.1134/S003602361205004X

Transmetalation reactions of cadmium complexes of tetraphenylporphine (CdTPP, I) and tetra-benzoporphine (CdTBP, II) in individual and mixed solvents have been investigated. For individual solvents, provided that the reaction proceeds via the same mechani

Full text of DOI:10.1134/S003602361205004X

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 5, pp. 744–750. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © D.B. Berezin, O.V. Shukhto, N.V. Lazareva, 2012, published in Zhurnal Neorganicheskoi Khimii, 2012, Vol. 57, No. 5, pp. 812–819.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Kinetic Control of the Transmetalation of Labile Metalloporphyrins
in Individual and Mixed Solvents
D. B. Berezin, O. V. Shukhto, and N. V. Lazareva
Research Institute of Chemistry of Macroheterocycles, Ivanovo State University of Chemistry and Technology,
pr. Engel’sa 7, Ivanovo, 153000 Russia
Received October 14, 2010
Abstract—Transmetalation reactions of cadmium complexes of tetraphenylporphine (CdTPP, I) and tetraꢀ
benzoporphine (CdTBP, II) in individual and mixed solvents have been investigated. For individual solvents,
provided that the reaction proceeds via the same mechanism, its rate generally increases as the donor number
increases in the order DMSO < DMF < PrOHꢀ1 < MeCN (CdTPP–Zn(OAc) –Solv system). On passing to
2
the CdTPP–Cu(OAc) –Solv system, the reaction rate order changes to DMSO < PrOHꢀ1 < MeCN < DMF
2
because the transmetalation mechanism changes from mixed to associative, as follows from the reaction order
with respect to the salt being zero. The effect of the DMSO–DMF mixed solvent on the transmetalation reacꢀ
1
tion is limited to changing the reaction rate through alteration of the stability of the [CuX (Solv )
2
n
–
m
– 2
2
(
Solv ) ] solvated salts. The trans effect of the ligands in the solvated salts does not increase the transmetalaꢀ
m
tion rate.
DOI: 10.1134/S003602361205004X
Possessing a wide variety of unique properties, cesses involving the dissociation of the complex,
metal complexes of porphyrins (metalloporphyrins, including transmetalation [6].
MPs) are promising components for new materials
and devices in chemical technology, electronics, and
medicine [1, 2]. The transmetalation reaction (1) proꢀ
vides means to obtain MPs that are difficult to syntheꢀ
size directly via the complexation reaction (2), making
use of more readily available labile complexes (M(II) =
Cd, Hg, Pb).
Ph
N
N
N
N
Ph
Cd
Ph
МР + М'X (Solv)m –
n
→
n –
M'P + МX (Solv)m n, (1)
n
Ph
I
H P + MX (Solv)
2
2
n – 2
R
–2Solv
#
(2)
[
H P⋅⋅⋅MX (Solv)
n – 4
]
2
2
N
N
N
N
MP + 2HX + (n – 4)Solv.
R
Cd
R
Cadmium complexes of porphyrins, such as comꢀ
pounds and II, are among the most readily synthesizꢀ
I
able MPs and are convenient objects for investigating
the kinetics and mechanism of reaction (1). They are
less stable than most MPs and dissociate in acidoproꢀ
tolytic media (under the action of a molecular acid
HX) and solvoprotolytic media (under the action of
R
II
In order to optimize the conditions for the syntheꢀ
sis of the MP compꢀlexes via reaction (1) and gain a
deeper insight into the transmetalation mechanism, it
+
the solvated proton H(Solv)) [1, 3, 4]. The comparaꢀ
tively low stability of the cadmium porphyrins is due to is essential to study various factors in the transmetalaꢀ
the low degree of covalence of their Cd–N coordinaꢀ tion reaction. There have been reports on how transꢀ
tion
σ
bonds, whose ionicity is fairly high, and to the metalation depends on the porphyrin structure in the
large ionic radius of the metal (1.01 Å), which does not initial MP [6–9], on the nature of the metal ion being
match the size of the coordination cavity of the porꢀ replaced [10, 11], on the nature of the metal ion being
phyrin ligand (2.01 Å). It is owing to their low stability introduced [6, 12], and on the nature of the salt anion
that the cadmium porphyrins decompose to an Н2Р [9, 13]. Likely mechanisms have been suggested for
ligand and a metal ion and are very active in other proꢀ metal ion exchange in labile MPs [6, 9, 14]. At the
744

KINETIC CONTROL OF THE TRANSMETALATION
745
Table 1. Dependence of kinetic parameters of transmetalation in the CdTPP–M(OAc) system on the properties of the meꢀ
2
dium at 298 K (cM(OAc)2 = 2.76
10–4 mol/L)
×
Solvent
ꢀPrOH
Property
DMSO
DMF
n
MeCN
C H
6
6
*
*
*
*
*
*
DN
AN
ε
29.8
19.3
46.68
3.96
71.3
6.4
26.6
16.0
36.7
3.8
77.4
19.5
32.0
37.5
20.1
1.6
75.1
14.1
18.9
36.0
3.4
52.9
20.9
0.1
8.2
2.3
0
89.9
~0
μ
, D
VM
ER
5.7
Cu(OAc)2
2.76 ± 0.70
~1
3
–1
–1
kapp
nsalt
×
10 , s
0.48**
~0***
61 ± 14
59.66**
0
32 ± 2
3.12 ± 0.29
–
No reaction*****
Ea, kJ/mol
26 ± 3
77 ± 27
Zn(OAc)2
1.20 ± 0.03
1.4
3
kapp
nsalt
×
10 , s
0.16 ± 0.01****
0.74**
~1
7.60 ± 0.51
1.2
No reaction*****
–
–
Ea, kJ/mol
–
4.0 ± 0.5
52 ± 15
Notes:
*Data from [15, 19].
* Calculated using the Arrhenius equation or an experimental kapp
** The order of the reaction decreases with decreasing temperature.
*
*
= f(csalt) function.
–3
*
*** csalt = 2.7
×
10 mol/L;
***** Reaction with M(Acac)2.
same time, the solvent effect as a significant factor in vents, which was determined by the Fischer method,
the reaction rate and mechanism [15] has not been did not exceed the value specified in [18]. The salts
properly investigated at the quantitative level. There Cu(OAc) , Zn(OAc) , and Cu(NO3)2 were recrystalꢀ
2
2
have been only comparisons of the Cd/Co and Cd/Zn lized from the respective acids; Cu(Acас)2, from benꢀ
exchange rates in dimethyl sulfoxide (DMSO) and zene. The resulting crystals were vacuumꢀdried at
p
≈
acetonitrile (MeCN) for blood porphyrins [16].
133 Pa and
T
= 80 С. Benzene (С Н6, analytical
°
6
grade) was boiled with Р2О5 and distilled.
For this reason, we carried out a spectroscopic and
kinetic study of the Cd/Cu and Cd/Zn transmetalaꢀ
Reaction (1) was monitored spectrophotometriꢀ
tion reactions for the cadmium tetraphenylporphine cally on a Hitachi U3000 spectrophotometer. A salt
solution in the solvent to be examined, with a preset
solute concentration, was placed in a temperatureꢀ
controlled cell. After the preset temperature was estabꢀ
complex (CdTPP,
dimethylformamide (DMF), DMSO, and MeCN
Table 1) and the same study of the Cd/Cu transmetaꢀ
I) in nꢀpropanol (nꢀPrOH), N,Nꢀ
(
lation reaction for CdTPP and cadmium tetrabenꢀ lished, an equal volume of a thermostated solution of
a cadmium complex in the same solvent was added.
The time variation of the concentrations of the MP
and M'P complexes as a result of transmetalation was
monitored as the increase in absorbance for the longꢀ
wavelength absorption band of the resulting M'P.
zoporphine (CdTBP, II) in the DMF–DMSO mixed
solvent (Table 2) in wide temperature and concentraꢀ
tion ranges.
EXPERIMENTAL
Reaction (1) was conducted in the presence of a
1
0ꢀ to 100ꢀfold excess of a salt to ensure that it obeys
Compounds
I and II were synthesized, purified,
the pseudoꢀfirstꢀorder rate equation
and identified using standard procedures [17]. Solꢀ
vents were pretreated as recommended in [18]. DMSO
pure grade) was held over calcined BaO; DMF (anaꢀ
lytical grade), over calcined MgSO4. Both were then
vacuumꢀdistilled (bp 60 and 40 , respectively).
–
dcMP = k c ; kapp
app MP
/
d
τ
=
kvcsalt
.
(3)
(
Kinetic parameters were calculated using equaꢀ
tions of formal kinetics.
≈
≈
°С
Acetonitrile (reagent grade) was dried by boiling with
P2O5 and was distilled using a reflux condenser, and
RESULTS AND DISCUSSION
the fraction boiling above 80.5
°
С was collected.
n
ꢀPrOH was boiled with anhydrous K CO and was
The organic solvents DMSO, DMF,
n
ꢀPrOH, and
2
3
then distilled, and the fraction with bp 97 С was colꢀ MeCN are polar coordinating media and have a large
lected. The residual water content of the organic solꢀ dielectric constant of
°
ε
= 20–40, a high dipole
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 5 2012

746
BEREZIN et al.
Table 2. Kinetic parameters of the transmetalation reaction (1) of complexes
DMF–DMSO
I
and II with Cu(OAc) and Cu(NO ) in the
2 3 2
103,
s–1
k
×
10 ,
–3
Ea
kJ/mol
,
Δ
S#
,
Porphyrin
, mol/L)
Salt
, nm)
csalt
mol/L
,
Solvent,
DMSO/DMF, vol %
kapp
×
v
T, K
–1
–1
(
c
(
λ
s
L mol
J/(mol K)
CdTPP (
I
)
Cu(OAc)2 1.38
×
×
×
10–3
10–3
10–3
0/100
25/75
308
Very rapidly
–
–
–
5
(2.76
×
10 ) (541)
3.29 ± 0.15 7.74 ± 0.35
2.02 ± 0.18 28.14 ± 2.51
1.79 ± 0.11 15.73 ± 0.98
1.02 ± 0.18 14.21 ± 2.53
Very rapidly
3.41 ± 0.16 7.61 ± 0.36
2.38 ± 0.09 28.20 ± 1.07
1.99 ± 0.10 15.30 ± 0.77
1.19 ± 0.20 14.10 ± 2.37
53.10*
5
7
0/50
5/25
100/0
0/100
2
.07
.76
–
–
25/75
50/50
75/25
100/0
0/100
2
298
298
113 ± 19
–95**
25/75
50/50
75/25
2.60*
3
3
3
08 3.59 ± 0.29 7.72 ± 0.62
18 9.05 ± 0.09
28 52.84 ± 0.13
298
1.90*
69 ± 13
61 ± 4
–73**
3
3
3
08 2.62 ± 0.03 27.66 ± 0.32
18 4.76 ± 0.07
28 13.47 ± 0.80
298
1.60*
–102**
3
3
3
08 2.17 ± 0.03 15.17 ± 0.21
18 4.25 ± 0.06
28 9.25 ± 0.18
1
00/0
308 1.37 ± 0.02 14.47 ± 0.21 61 ± 14
–107**
–
3
3
18 3.79 ± 0.04
28 5.94 ± 0.16
3.45
×
10–3
0/100
308
Very rapidly
–
2
5
7
5/75
0/50
5/25
3.69 ± 0.09 38.96 ± 0.19
2.94 ± 0.11 31.04 ± 1.06
2.45 ± 0.08 25.87 ± 0.52
1.46 ± 0.21 15.42 ± 2.03
8.30*
1
00/0
0/100
CdTBP (II) Cu(OAc)2 1.43
×
10–3
298
45 ± 2
–158 ± 7
–
5
(1.43
×
10 ) (630)
328 2.86 ± 0.94
3
3
38 4.88 ± 1.64
48 7.55 ± 2.64
25/75
50/50
75/25
298
4.78*
50 ± 13 –147 ± 15
52 ± 11 –147 ± 12
328 1.62 ± 0.40
338 3.45 ± 0.78
348 4.73 ± 0.72
298
2.48*
328 1.04 ± 0.18
338 2.19 ± 0.38
348 3.15 ± 0.27
298
4.34*
39 ± 2
–184 ± 6
328 1.45 ± 0.24
338 2.15 ± 0.32
348 3.34 ± 0.44
1
00/0
0/100
25/75
Very slowly
CdTBP (II) Cu(NO ) 1.43
×
10–3
298 9.78 ± 0.70
2.06 ± 0.47
–
–
3
2
–5
(
1.43 10 ) (630)
×
5
7
0/50
5/25
1.09 ± 0.17
1.79 ± 0.31
100/0
2.28 ± 0.18
Notes: * Calculated using the Arrhenius equation or an experimental concentration dependence.
* Estimated data.
*
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 5 2012

KINETIC CONTROL OF THE TRANSMETALATION
747
moment of
μ
= 1.6–4.0 D, and a large donor number sociation mechanism (reaction (4)), as is indicated by
of DN = 14–30 (Table 1) [15]. However, these solvents the fact that the order of the reaction n with respect to
cannot be assigned to one class of media because they the salt is close to unity.
differ in their acid–base, donor–acceptor, and solvaꢀ
S
tion properties. DMSO, DMF, and MeCN are dipolar
CdP
+
Cu(OAc) (S)n
2
– 2
aprotic (DA) solvents [15], have a high polarity (
ε
>
S
35, μ ≥ 3.5 D) and a high solvating power toward catꢀ
≠
ions, and are practically indifferent toward anionic
species. Owing to their high solvating power, these
compounds have a large DN value and a small accepꢀ
tor number (AN) (Table 1) [15]. The alcohols, includꢀ
N
N
N
S
Cd
AcO
S
S
AcO
slowly
Cu
S
N
ing
n
ꢀPrOH, are weakly protonꢀdonating solvents.
Possessing moderate polarity characteristics (
ε μ
,
) and
rapidly
a high electronꢀdonating power (DN), they have a
large AN exceeding their DN [15].
CuP + Cd(OAc) (S) .
2
n
(4)
Because the solvents examined here belong to difꢀ
According to the current views of the transmetalaꢀ
ferent classes, we failed to establish a general relationꢀ tion mechanism [5, 6, 9, 12, 20], a decrease in the
ship between the transmetalation rate and the particuꢀ coordinating power of the solvent is favorable for the
lar properties of the medium. However, for the DA solꢀ associative pathway of the process because of the increase
vents examined, the rate of reaction (1) in the in the stability of the intermediate of reaction (1). Howꢀ
CdTPP–Zn(OAc) –Solv system typically increases ever,
n is close to unity not only for the strongly coorꢀ
2
with an increasing DN (Table 1): DMSO < DMF < dinating solvent DMF, but also for the CdTPP–
PrOHꢀ1 < MeCN. The corresponding apparent rate Zn(OAc) –Solv systems in which Solv is a weakly
2
–
4
constant (kapp) ratios for csalt = 2.76
Ӷ
×
10 mol/L are coordinating solvent: for
nꢀPrOH and MeCN, n is
0.02 : 0.1 : 0.15 : 1. The rate of the reaction in ~1.4 and ~1.2, respectively. Therefore, in all of the solꢀ
DMSO is the lowest, although the rate constant for vents, the reaction proceeds via the same mixed mechꢀ
this solvent was measured at a higher salt concentraꢀ anism. In all cases, the intermediate, whose formation
tion (Table 1). nꢀPropanol is very different from the would imply the associative pathway of reaction (1),
other media since it is a protogenic solvent [15].
did not show itself in the spectrum.
A coordinating solvent is involved in reaction (1) as
a component of the solvation complexes of the enterꢀ
The kinetic study of reaction (1) in the CdTPP–
Cu(OAc) –Solv system demonstrated that the
2
ing metal (M') and leaving metal (M), МХ (Solv)
m
n
–
m
increasing order of reaction rates, DMSO < PrOHꢀ1 <
MeCN < DMF, does not correlate with the physicoꢀ
chemical properties of the media (Table 1). While the
and М'Х (Solv)n m, thus determining the stability of
m
–
these complexes [19]. It is believed that the rate of
transmetalation in various solvents is determined by
the electronꢀdonating power of the medium and, to a
lesser extent, by its polarity [5]. For example, in the
fact that nꢀPrOH does not fit in with the above kinetic
order of media can be explained by this alcohol
belonging to protogenic rather than DA solvents [15],
DMF, in which the transmetalation reaction proceeds
at the highest rate, is a typical DA solvent. Considering
the high electronꢀdonating power of DMF, it was
expected that transmetalation in this solvent would be
much slower than in MeCN, which is the weakest
electron donor and has the smallest molar volume
VM = 52.9 versus 71.3, 75.1, and 77.4 for DMSO,
ꢀPrOH, and DMF, respectively), the latter factor
being favorable for the spatial accessibility of the reacꢀ
tion sites. The transmetalation rate in DMSO was
expected to be approximately the same as in DMF. In
fact, the transmetalation rates in these solvents, which
lowꢀpolarity solvent pyridine (Py:
ε
= 12.3
, = 2.37 D),
μ
which has a high coordinating power (DN = 33.1), the
Zn/Cu transmetalation reaction of ZnTPP proceeds
very slowly, needs an elevated temperature, and occurs
only via a dissociative mechanism [10]. In polar solꢀ
vents with a less pronounced electronꢀdonating funcꢀ
tion, the rate of reaction (1) is much higher. The
Cd/Zn and Cd/Co transmetalation reactions of blood
(
n
porphyrins in MeCN (
erably faster than the same reactions in DMSO (
6.7, DN = 29.8) [16]. This is explained by the lower
ε
= 36, DN = 14.1) are considꢀ
ε
=
4
capability of MeCN to form solvation complexes.
Pyridineꢀlike solvents, DMF, and DMSO indeed form
the most stable complexes, the nitrile solvates are the
least stable, and the alcohol complexes occupy an
intermediate position; that is, the stability constant Kst
decreases in the following order: Py (1700
DMF (190 40) < DMSO (37 ) < ꢀBuOH (18
MeCN (4) [19].
are very similar in polarity (
ε,
μ), donor–acceptor
properties (DN, AN), and other characteristics in the
CdTPP–Cu(OAc) –Solv system, differ most greatly
2
(by more than 2 orders of magnitude) in the solvent
series examined, as follows from the apparent rate
±
100) <
–1
±
±
9
n
±
1) <
constant data (kapp, s ) measured under comparable
conditions (Table 1). The apparent rate constant ratios
–4
We demonstrated in earlier works [9, 12] that most for reaction (1) at csalt = 2.76
×
10 mol/L in the solꢀ
of the transmetalation reactions of cadmium porphyꢀ vent series DMSO–PrOHꢀ1–MeCN–DMF is 0.008 :
rins in DMSO proceed via a mixed, association–disꢀ 0.046 : 0.05 : 1.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 5 2012

748
BEREZIN et al.
–logkapp
z
0
3
.5
1
OAc–
M2+
OAc–
y
L
L
LT
3
.0
.5
.0
.5
.0
.5
2
L
T
2
2
1
1
0
x
3
4
Fig. 2. Structure of the transꢀactive asymmetric salt solꢀ
vate.
failed. This is evidence that the polarity of the medium
is a significant factor in transmetalation.
However, the key reason why the transmetalation
rate order changes on passing from the CdTPP–
Cu(OAc) –Solv system to the CdTPP–Cu(Acac) –
2
2
Solv system is that the mechanism of reaction (1) in
DMF changes from mixed to associative, as is indiꢀ
cated by the reaction order with respect to the salt
becoming zero under these conditions (Fig. 1), as distinct
from what is observed for, e.g., propanol (Table 1). In all
0
2
.0
2.5
3.0
3.5 4.0
–logcM(ОAc)2
of the systems examined here, n is temperatureꢀindeꢀ
Fig. 1. Graphical determination of the order of the transꢀ
pendent; that is, the temperatureꢀinduced changes
exert no effect on the pathway of reaction (1), as disꢀ
tinct from what was observed earlier in DMSO [9].
metalation reaction in the CdTPP–CuОAc system:
2
(
1
) DMSO, tan
tan = 1.2; ( ) DMF, tan
MeCN refer to the CdTPP–ZnОAc2 system.
α
= 0; (
2
) PrOHꢀ1, tan
α
= 1; (
3
) MeCN,
α
4
α
= 0;
T
= 298 K. The data for
A specific feature of transmetalation in nꢀPrOH is
a very low activation energy both for the Cu(OAc)2
solution (16–29 kJ/mol) and for the Zn(OAc) soluꢀ
2
Although the organic solvents examined here, parꢀ tion (4–12 kJ/mol). This is likely due to the effective
ticularly DMF and DMSO, have similar individual solvation of the anionic species by this solvent. The Еа
in other solvents is
parameters characterizing their polarity, structuredꢀ value for the reaction of Cu(OАc)
2
markedly larger: 77 kJ/mol for MeCN and 61 kJ/mol
for DMSO (Table 1).
ness, and acid–base and donor acceptor properties,
they may differ in terms of complex multiparametric
characteristics [15]. One of these characteristics is soꢀ
Interest in mixed solvents is due to the discovery of
called reaction field energy ЕR [19], which depends on new properties of these media. In essence, any mixed
1
2
solvent (Solv ꢀSolv ) of particular composition is an
the dielectric constant, dipole moment, and molar
volume and takes into account the energy of molecular
interaction in the solvent, whose degree decreases with
increasing ER. According to reference data, ЕR
increases in the following order of solvents: toluene
individual liquid medium with a new set of properties
[
15]. In addition to changing the coordinating power
and polarity of the medium, which determine the
composition and stability of the solvation shell of the
metal and, accordingly, the reactivity of this shell in
reactions (1) and (2) and other coordination react
ions, the solvent effect can show itself in polarization
of the solvation shells of the reactants. An example of
this polarization is the trans effect of solvent ligands in
(
0.05) < nꢀPrOH (3.6) < Py (5.7) (DMSO (6.4) <
DMF (19.5) < MeCN (20.9). Clearly, DMF and
MeCN have the largest ER values, which are well above
the same values for DMSO, Py, and particularly toluꢀ
ene. On the whole, this increasing order of ER is in
agreement with the increasing order of reaction rates
mixed solvated salts of
which means that the
d
metals [5]. The trans effect,
π
ꢀligand LT polarizes the M–L
for CdTPP in the CdTPP–Cu(ОAc) –Solv system,
2
bond that is trans to this ligand [21], weakens this bond
many times, thus enhancing the reactivity of the solꢀ
except for nꢀPrOH, which is a proton donor medium.
The transmetalation reaction proceeds most rapidly in vate (Fig. 2).
DMF and MeCN and much less rapidly in DMSO
There have been kinetic studies of the complexꢀ
ation reaction (2) of tetraphenyltetrabenzoporphine
E
and Py, which are lowꢀ R
media, and it practically
does not take place in nonpolar aprotic solvents, such
as arenes. Attempts to carry out reaction (1) in the phine (H(NꢀMe)(
CdTPP–Cu(Acас) –Solv system in benzene (
tate in DMF–DMSO, DMF–Py, and DMSO–Py
= 333 K solvents, which are ꢀligands. It was demonstrated [5]
(
H TPTBP) [5, 22] and
N
ꢀmethylꢀ
β
ꢀoctaethylporꢀ
2
β
ꢀEt)8P) [23] with copper(II) aceꢀ
ε
=
2
2.28,
μ
= 0) at a 100ꢀfold excess of the salt and
T
π
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 5 2012

KINETIC CONTROL OF THE TRANSMETALATION
749
2
98, L mol–1 s–1
kapp, s–1
k
v
50
60
4
3
2
1
0
0
0
0
5
0
1
b
c
40
30
20
10
a
0
20
40
60
80
100
S2
S1
Solvent composition, vol %
Fig. 3. Rate constant kv of the complexation reaction
between H(NꢀMe)( ꢀEt)8P and Cu(OAc)2 as a function
of the solvent composition: ( ) DMF–Py, ( ) DMSO–Py,
and ( ) DMF–DMSO [23].
β
3
a
b
2
c
0
20
40
60
80 100
сDMSO, vol %
that, as a consequence of the trans effect in the solꢀ
vated salt, the rate of reaction (2) varies nonlinearly
with the solvent composition and the rate constant
versus composition curves for the mixed systems show
extremums (Fig. 3).
Fig. 4. Apparent rate constant of transmetalation (kapp) as
a function of the composition of the DMSO–DMF solꢀ
vent (csalt
/
cCdP = 100,
T
= 298 K): (
1
) CdTPP–Cu(OAc)2;
(
2
) CdTBP–Cu(NO ) ; and (
3) CdTBP–Cu(OAc)2.
3
2
On passing from individual
π
ꢀcoordinating solꢀ
vents to a mixed one, the largest trans effect–induced
increase in the rate of reaction (2) is observed in the
DMF–DMSO system, which can be as large as two
orders of magnitude [5]. It has been claimed in a numꢀ
ber of works [6, 11, 24] that the complexation and
transmetalation reactions of metalloporphyrins obey
the same rules. For example, for both reactions, the
true rate constant depends on the salt concentration
because of the changes in the structure and stability of
the solvated salt [5. 19].
–
decreasing coordinating power of the salt anion (AcO <
–
N
O ).
3
2
app
98
The character of the nonlinear dependence of
k
on the composition of the mixed solvent is mainly
determined by the gradual alteration the structure of
1
2
the solvated salt CuX (Solv )
(Solv ) caused by
2
n
–
m
– 2
m
the changing composition of the medium. For examꢀ
ple, the solvated salt can undergo the following changes:
Cu(OAc) (DMSO)4
→
Cu(OAc) (DMSO) (DMF)
→
2
2
3
We investigated the transmetalation reaction (1) in Cu(OAc) (DMSO) (DMF)2, and so on. The transmetꢀ
2
2
the CdTPP(I)–Cu(ОAc) , CdTBP(II)–Cu(ОAc)2
,
alation rate constants for the mixed solvents do not
and CdTBP(II)–Cu(NO3)2 system in the DMSO– exceed the rate constants for individual DMSO and
2
DMF (Fig. 4); that is, the trans effect in the solvated
salts does not shows itself in reaction (1), unlike the
trans effect in reaction (2). This is likely due to the fact
that the mechanism of transmetalation is more comꢀ
plicated than the mechanism of complexation involvꢀ
ing H2P [1, 5, 9, 14].
DMF solvent (Table 2). Figure 4 plots the apparent
2
98
rate constant of transmetalation (
k
) as a function of
app
the DMSO–DMF solvent composition. Clearly, the
rate of the reaction in pure DMF under conditions of
a threefold excess of the salt over the cadmium porꢀ
phyrin decreases in the following order (Table 2):
Figure 5 shows a typical logarithmic plot of the apparꢀ
ent rate constant of reaction (1) versus the salt concentraꢀ
2
app
98
CdTPP–Cu(OAc) (
2
k
= 53.10
= 9.78
×
10–3 s–1)
>
2
app
98
tion for the CdTPP–Cu(ОAc)2 system at
Т = 308 K and
CdTBP–Cu(NO3)2
(
k
×
10–3 s–1)
>
different compositions of the DMF–DMSO solvent.
1
2
98
–
3 –1
CdTBP–Cu(OAc) (
2
k
= 8.30
×
10 s ) . As was The order of the reaction with respect to the copꢀ
app
demonstrated in earlier works [9, 11, 13], the transꢀ per(II) salt is practically invariable (
n 0.4) in the solꢀ
≈
metalation rate increases with a decreasing rigidity of vent composition range from 25 to 100% DMSO, in
the macrocycle (CdTBP < CdTPP) and with a which the reaction rate changes insignificantly (Fig. 4),
and falls to 0.13 and below on passing to the 0–25%
1
Calculated by extrapolation.
DMSO range, in which the react ion rate increases by
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 57 No. 5 2012

750
BEREZIN et al.
4
. D. B. Berezin and O. V. Shukhto, Izv. Vyssh. Uchebn.
Zaved., Khim. Khim. Tekhnol. 46 (8), 34 (2003).
–
logkapp
3
3
2
2
2
2
2
.2
5
. D. B. Berezin, Macrocyclic Effect and the Structural
Chemistry of Porphyrins (URSS, Moscow, 2010) [in
Russian].
4
.0
.8
.6
.4
.2
.0
3
2
6
. P. Hambright, in The Porphyrin Handbook, Ed. by
K. M. Kadish, K. M. Smith, and R. Guilard (Acaꢀ
demic, New York, 2000), Vol. 3, p. 129.
1
7. D. K. Lavallee, B. A. Kopelove, and O. P. Anderson,
J. Am. Chem. Soc. 100 (10), 3025 (1978).
. S. Cromer, P. Hambright, J. Grodkowski, and P. Neta,
8
J. Porphyrins Phthalocyanines , 45 (1997).
1
2.4
2.5
2.6
2.7
2.8
2.9
9. D. B. Berezin, O. V. Shukhto, and M. S. Reshetyan,
–logcCu(OAc)2
Russ. J. Gen. Chem. 80 (3), 518 (2010).
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0. C. Grant and P. Hambright, J. Am. Chem. Soc. 91 (15),
195 (1969).
11. E. Haye and P. Hambright, Inorg. Chem. 23 (26), 4777
(1984).
4
Fig. 5. Graphical determination of the order of the transꢀ
metalation reaction in the CdTPP–Cu(OAc)2 system in
the DMSO–DMF solvent: DMSO : DMF (vol %) = (
1)
2
5 : 75, ( ) 50 : 50, ( ) 75 : 25, and ( ) 100 : 0; = 308 K.
2
3
4
T
12. D. B. Berezin, O. V. Shukhto, M. S. Nikol’skaya, and
B. D. Berezin, Russ. J. Coord. Chem. 31 (2), 95 (2005).
1
3. L. Orzel, M. Wolak, L. Fiedor, et al., in Abstr. Inorganic
Reaction Mechanism Meeting (IRMMꢀ35), Krakow,
Poland, 2005, p. 50.
a factor of 20. The decrease in the order of the reaction
with respect to the salt on passing from the strongly
coordinating solvent DMSO to the less strongly coorꢀ
dinating solvent DMF is due to the increase in the
contribution from the associative pathway of transꢀ
metalation to the mixed mechanism of reaction (1)
14. B. D. Berezin, O. V. Shukhto, and D. B. Berezin, Russ.
J. Inorg. Chem. 47, 1187 (2002).
1
5. Yu. Ya. Fialkov, Solvent as a Means of Controlling a
Chemical Process (Khimiya, Leningrad, 1990) [in Rusꢀ
sian].
[
9]. Elucidation of the structural aspects of this effect
would provide explanation for the fact that the rate of
the transmetalation reaction involving Cu(OAc)2 in
DMF is higher than the rate of the same reaction in
the other solvents.
16. S. V. Zvezdina, M. B. Berezin, and B. D. Berezin, Russ.
J. Inorg. Chem. 51, 112 (2006).
1
7. K. A. Askarov, B. D. Berezin, R. P. Evstigneeva, et al.,
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by N. S. Enikolopyan (Nauka, Moscow, 1985) [in Rusꢀ
sian].
Thus, the only effective solventꢀbased way of conꢀ
trolling the rate of reaction (1) is by selecting a polar
medium with a comparatively low coordinating power 18. A. Gordon and R. Ford, The Chemist’s Companion: A
for processes taking place via the mixed mechanism
5, 9], and a medium with a relatively large reaction
Handbook of Practical Data, Techniques, and References
(Wiley, New York, 1972; Mir, Moscow, 1976).
[
field energy (ЕR) for the associative mechanism of the 19. B. D. Berezin and O. A. Golubchikov, Coordination
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Metal Salts (Nauka, Moscow, 1992) [in Russian].
2
0. K. B. Yatsimirskii and Ya. D. Lampeka, Physical Chemꢀ
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