Effect of the nature of the tetrapyrrole macrocycle on the transmetallation of Zn2+ and Cd2+ porphyrins with PdCl2 in dimethylformamide

Article abstract of DOI:10.1134/S0036023611030089

Transmetallation of zinc (Zn²⁺) and cadmium (Cd²⁺) complexes of 5,10,15,20-tetraphenylporphin, 5,10,15,20-tetra(4-chlorophenyl) porphyrin, 5,10,15,20-tetra(4-methoxyphenyl)porphyrin, tetrabenzoporphyrin, and octaphenyltetraazaporphyrin with PdCl₂ in DMF was studied by spectrophotometry. The influence of the nature of the tetrapyrrole macrocycle on the reactivity of Zn²⁺ porphyrins toward palladium chloride in boiling DMF was established. Palladium(II) complexes of 5,10,15,20- tetraphenylporphyrin, 5,10,15,20- tetra(4-chlorophenyl)porphyrin, 5,10,15,20-tetra(4-methoxyphenylporphyrin), and tetrabenzoporphyrin were prepared and identified. Pleiades Publishing, Ltd., 2011.

Full text of DOI:10.1134/S0036023611030089

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2011, Vol. 56, No. 3, pp. 484–488. © Pleiades Publishing, Ltd., 2011.
Original Russian Text © N.V. Chizhova, N.Zh. Mamardashvili, 2011, published in Zhurnal Neorganicheskoi Khimii, 2011, Vol. 56, No. 3, pp. 523–527.
PHYSICAL CHEMISTRY
OF SOLUTIONS
Effect of the Nature of the Tetrapyrrole Macrocycle
on the Transmetallation of Zn2+ and Cd2+ Porphyrins
with PdCl2 in Dimethylformamide
N. V. Chizhova and N. Zh. Mamardashvili
Institute of Solution Chemistry, Russian Academy of Sciences, Akademicheskaya ul. 1, Ivanovo, 153045 Russia
Received September 22, 2009
Abstract—Transmetallation of zinc (Zn2+) and cadmium (Cd2+) complexes of 5,10,15,20ꢀtetraphenylporꢀ
phin, 5,10,15,20ꢀtetra(4ꢀchlorophenyl)porphyrin, 5,10,15,20ꢀtetra(4ꢀmethoxyphenyl)porphyrin, tetrabenꢀ
zoporphyrin, and octaphenyltetraazaporphyrin with PdCl2 in DMF was studied by spectrophotometry. The
influence of the nature of the tetrapyrrole macrocycle on the reactivity of Zn2+ porphyrins toward palladium
chloride in boiling DMF was established. Palladium(II) complexes of 5,10,15,20ꢀtetraphenylporphyrin,
5,10,15,20ꢀ tetra(4ꢀchlorophenyl)porphyrin, 5,10,15,20ꢀtetra(4ꢀmethoxyphenylporphyrin), and tetrabenꢀ
zoporphyrin were prepared and identified.
DOI: 10.1134/S0036023611030089
Porphyrins and related tetrapyrrole macrocycles boiling benzonitrile was reported [3, 4]. Complexes
I
and Pd2+ tetrabenzoporphyrin (PdТBP) (II) were preꢀ
pared by a similar procedure in dimethylformamide
(DMF) [5, 6].
are known to exhibit photochromic and catalytic
properties when exist as metal complexes. Of particuꢀ
lar interest are porphyrin complexes with palladium,
which are widely used in various fields of science and
technology for the development of new functional
materials [1,2].
Analysis of published data and our results shows
that transmetallation of labile complexes is a promisꢀ
ing way for the preparation of palladium complexes
with tetrapyrrole macrocycles. In particular, we synꢀ
thesized PdTBP and Pd2+ octaphenyltetraazaporꢀ
phyrin (PdOPhTAP) (III) from Cd and Mg porphyꢀ
rins [7, 8].
A method for the synthesis of palladium (Pd2+) comꢀ
plexes of 5,10,15,20ꢀtetraphenylporphin (PdТPhP) (I)
and 5,10,15,20ꢀtetra(benzoꢀ15ꢀcrownꢀ5)porphyrin
by the reaction of the porphyrin ligand with PdCl2 in
In order to develop efficient methods for the synꢀ
thesis of Pd2+ porphyrins, in this work, we studied the
reactions of 5,10,15,20ꢀtetraphenylporphyrin comꢀ
A
1
plexes of Zn2+ (ZnТPhP) (VI and Сd2+ (CdТPhP)
)
3
1.0
0.8
0.6
0.4
0.2
(VII),
5,10,15,20ꢀtetra(4ꢀchlorophenyl)porphyrin
complexes of Zn2+ (ZnT(4ꢀClPh)P) (VIII
)
and Cd2+
2
(CdT(4ꢀClPh)P) (IX), and 5,10,15,20ꢀtetra(4ꢀmethoꢀ
2
xyphenyl)porphyrin complexes of Zn2+ (ZnT(4ꢀ
1
OCH3Ph)P) (X) )
and Cd2+ (CdT(4ꢀOCH3Ph)P) (XI
with palladium chloride in DMF. The effect of benzo
and aza substitution on the reactivity of Zn2+ tetrabenꢀ
zoporphyrin (ZnTBP) (XII), Cd2+ tetrabenzoporphyꢀ
rin (CdTBP) (XIII), and Zn2+ octaphenyltetraazaporꢀ
3
phyrin (ZnOPhTAP) (XIV) with PdCl2 in DMF was
studied.
0
500
550
600
650
, nm
λ
Owing to the considerable difference between
the UV–Vis spectra of the starting compounds and
the resulting Pd2+ porphyrins (figure, Table 1), it
was possible to study transmetallation by spectroꢀ
photometry.
UV–Vis spectra in DMF: (
1) ZnTPhP, (2) CdTPhP, and
(3) PdTPhP.
484

EFFECT OF THE NATURE OF THE TETRAPYRROLE MACROCYCLE
485
plates. The solvents were purified by published proceꢀ
dures [14].
R
Synthesis of Pd2+ 5,10,15,20ꢀtetraphenylporphyrin
(I). (a) A mixture of complex VI (0.05 g) and PdCl2
(0.13 g) in the molar ratio 1 : 10 was dissolved in DMF
(20 mL), and the mixture was refluxed for 4 min,
cooled, and poured in water. The precipitate was filꢀ
tered off, washed with water, dried, and chromatoꢀ
graphed on alumina with chloroform elution. Yield
0.043 g (0.0598 mmol), 81%. Rf = 0.78 (elution with
hexane–chloroform (1 : 2)).
N
N
N
N
N
N
R
M
R
R
M
N
N
М = Pd2+, R = C6H5 (
М = Zn2+, R = C6H5 (VI),
М = Cd2+, R = С6Н5 (VII)
I
),
M = Pd2+
M = Zn2+
M = Cd2+
(II),
(XII),
(XIII),
1H NMR (
, ppm, CDCl3): 8.84 (s, 8 H, pyrrole
δ
,
ring), 8.20 (d, 8H, ortho), 7.81 (t, 8H, meta), 7.76 (t,
4H, para).
M = Pd2+, R = C6H4ꢀ4ꢀCl (IV),
M = Zn2+, R = C6H4ꢀ4Cl (VIII),
M = Cd2+, R = C6H4ꢀ4Cl (IX),
The 1H NMR spectrum of the starting ZnTPhP (
,
δ
ppm, CDCl3): 8.97 (s, 8H), 8.25 (d, 8H), 7.81 (t, 8H),
7.77 (t, 4 H).
М = Pd2+, R = C6H4ꢀ4ꢀOCH3 (
M = Zn2+, R = C6H4ꢀ4ꢀOCH3 (
M = Cd2+, R = C6H4ꢀ4ꢀOCH3 (XI),
V
),
(b) Complex VII (0.05 g) and PdCl2 (0.037 g) (1 :
3 mol/mol) were refluxed in DMF (20 mL) for 2 min.
Yield 0.04 g (0.0556 mmol), 81%. Rf = 0.78.
X
),
For PdC44N4H28 anal. calcd. (%): C, 73.48; N,
7.79; H, 3.93.
R
R
N
M
N
R
Found (%): C, 73.46; N, 7.77, H, 3.90.
R
N
N
N
MS:
IR (
m
ν
/
z
= 718.1 (
I
rel = 87%) [M+].
N
N
, cm–1): 3053 (w), 3016 (w), 2923 (m), 2852 (w),
N
R
R
1803 (w), 1598 (m), 1538 (w), 1490 (w), 1441 (m),
1353 (m), 1311 (w), 1209 (w), 1177 (w), 1075 (m),
1015 (s), 836 (w), 796 (m), 752 (m), 701 (m), 667 (w),
528 (w), 466 (w).
R
R
M = Pd2+, R = C6H5 (III),
M = Zn2+, R = C6H5 (XIV).
Pd2+ tetrabenzoporphyrin (II) was synthesized by a
modification of a reported procedure [7]. A mixture of
complex XIII (0.05 g) and PdCl2 (0.14 g) (molar ratio
1 : 10) in DMF (80 mL) was refluxed for 10 min and
cooled, the precipitate was filtered off, and the filtrate
was poured in water. The precipitate was filtered off,
washed with water and ethanol, and chromatographed
on alumina (elution with pyridine–diethyl ether (1 : 4)).
The yield of complex II was 0.037 g (0.06 mmol), 75%.
Rf = 0.62 (elution with diethyl ether).
EXPERIMENTAL
The Zn2+ and Cd2+ porphyrins (VI
–
XI) were synꢀ
thesized from appropriate porphyrin ligands [9, 10] by
the Adler method [11]. The Zn2+ and Cd2+ porphyrins
(
XII–XIV) were prepared by the Linstead method [12,
13]. The transmetallation reactions of Zn2+ and Cd2+
porphyrins with PdCl2 in DMF were monitored by
spectrophotometry and TLC. The spectrophotometric
procedure was as follows: samples of equal volume
were taken from the reaction mixture at specified
intervals and dissolved in specified amounts of DMF,
and the solutions were placed in the spectrophotometꢀ
ric cell. The UV–Vis spectra were recorded on a Caryꢀ
100 spectrophotometer at 298 K. Electron impact
mass spectra were run on an MXꢀ1310 massꢀspectroꢀ
metric setup at an ionizing energy of 70 eV and ionizaꢀ
For PdC36H20N4 anal. calcd. (%): C, 70.31; N,
9.11; H, 3.28.
Found (%): C, 70.25; N, 9.07; H, 3.24.
1Н NMR (
9.93 (s, 8H), 8.32 (s, 8H).
IR (
, cm–1): 2922, 2847 (νС–Н, –С6Н4), 1727, 1606,
δ, ppm, [D6] DMSO): 11.30 (s, 4H),
ν
1568 (νC=C, –C6H4), 1460 (νC=N), 1430, 1372,
1323 (νC–N), 1257, 1122 (δC–H, –C6H4), 1066, 1011
(
⎯
γC–C
С6Н4), 454 (νPd–N
Synthesis of Pd2+ 5,10,15,20ꢀtetra(4ꢀchloropheꢀ
, δC–H), 831 (γC–H, pyrrole ring), 755, 706 (γС–Н,
).
tion chamber temperature of 150–200 С. Elemental
analysis was performed on a Flash EA 1112 analyzer.
The H NMR spectra were recorded on a Bruker AV
IIIꢀ500 instrument, IR spectra were measured on an
Avatar 360ꢀFTꢀIRꢀESP instrument for KBr pellets.
°
1
nyl)porphyrin (IV). (a) Complex VIII (0.05 g), PdCl2
(0.11 g) (1 : 10 mol/mol) in DMF (10 mL) was
refluxed for 5 min. Yield 0.041 g (0.0478 mmol), 78%.
Rf = 0.89.
TLC analysis was performed on Silufol (G/UV254
)
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 56 No. 3 2011

486
CHIZHOVA, MAMARDASHVILI
Table 1. UV–Vis spectra of Pd2+, Zn2+, and Cd2+ porphyrins
Band I
Band II
Soret band
Compound
Solvent
CHCl3
λ
, nm (logε)
PdTPhP
PdTPhP
ZnTPhP
CdTPhP*
555 sh
554 sh
598 (4.29)
614 [0.218]
555 sh
523 (4.43)
522 (4.41)
558 (4.62)
415 (5.47)
415 (5.44)
423 (5.70)
431 [2.72]
416 (5.43)
415 (5.40)
421 [2.84]
434 [2.68]
419 (5.43)
419 (5.40)
422 [2.79]
431 [2.91]
408 (5.18)
425 (5.48)
433 (5.53)
350 (4.26)
375 (5.05)
DMF
DMF
DMF
CHCl3
DMF
DMF
DMF
CHCl3
DMF
DMF
DMF
DMF
DMF
DMF
CHCl3
CHCl3
572 [0.253]
524 (4.42)
523 (4.40)
559 [0.41]
573 [0.22]
525 (4.44)
525 (4.39)
561 [0.31]
576 [0.32]
556 (3.80)
577 (4.20)
585 (4.23)
560 (3.83)
580 (4.36)
PdT(4ꢀClPh)P
PdT(4ꢀClPh)P
ZnT(4ꢀClPh)P*
CdT(4ꢀClPh)P*
PdT(4ꢀOCH3Ph)P
PdT(4ꢀOCH3Ph)P
ZnT(4ꢀOCH3Ph)P*
CdT(4ꢀOCH3Ph)P*
PdTBP
554 sh
598 [0.23]
615 [0.14]
558 (3.64)
560 (3.63)
603 [0.25]
622 [0.38]
606 (4.97)
624 (5.05)
629 (5.02)
616 (4.28)
637 (5.11)
ZnTBP
CdTBP
PdOPhTAP[8]
ZnOPhTAP
* Relative intensities are presented.
(b) Complex IX (0.05 g) and PdCl2 (0.03 g) (1 :
3 mol/mol) were refluxed in DMF (10 mL) for 2 min.
Yield 0.04 g, 81%. Rf = 0.89.
(c) Tetra(4ꢀchlorophenyl)porphyrin (0.05 g) and
PdCl2 (0.035 g) (1 : 3 mol/mol) were refluxed in DMF
(20 mL) for 1 min. Yield 0.043 g (0.050 mmol), 76%.
Rf = 0.89.
Found (%): C, 68.84; N, 6.63; H, 4.27.
1Н NMR (
, ppm, CDCl3): 8.86 (s, 8H), 8.10 (d,
8H), 7.30 (d, 8H), 4.11 (s, 12H).
IR (
, cm–1): 2927 (m), 2830 (w), 2029 (w), 1607
(s), 1506 (s), 1462 (m), 1353 (s), 1289 (m). 1249 (s),
1175 (s), 1111 (w), 1016 (s), 799 (s), 714 (m), 608 (m),
500 (w).
δ
ν
For PdC44N4H24Cl4 anal. calcd. (%): Cl, 16.56; Pd,
12.41.
RESULTS AND DISCUSSION
Found (%): Cl, 16.61; Pd, 12.39.
Transmetallation of Zn2+ tetraphenylporphyrin
1Н NMR (
δ
, ppm, CDCl3): 8.83 (s, 8H), 8.11 (d,
8H), 7.77 (d, 8H).
IR (
, cm–1): 2923 (m), 2846 (w), 1906 (w), 1739
with Сu2+ in boiling pyridine and Cd2+ and Hg2+ tetꢀ
raphenylporphyrins with Zn2+ in pyridine at 25
C was
°
ν
described in detail [15]. It was show that the exchange
(w), 1637 (w), 1541 (w), 1487 (s), 1449 (w), 1352 (m),
1256 (w), 1092 (s), 1013 (s), 885 (w), 806 (s), 716 (m),
506 (m).
with Hg2+ tetraphenylporphyrin is 17 times faster than
with Cd2+
.
The studies carried out upon sampling showed that
the reaction of Zn porphyrin (VI) with PdCl2 taken in
1 : 3 molar ratio in boiling DMF gives Pd porphyrin (I)
Synthesis of Pd2+ 5,10,15,20ꢀtetra(4ꢀmethoxypheꢀ
nyl)porphyrin (V). (a) Complex
X (0.05 g) and PdCl2
(0.11 g) (1 : 10 mol/mol) were refluxed in DMF
(15 mL) for 5 min. Yield 0.04 g (0.048 mmol), 77%.
Rf = 0.81.
(b) Complex XI (0.05 g) and PdCl2 (0.031 g) (1 :
3 mol/mol) were refluxed in DMF (15 mL) for 2 min.
Yield 0.039 g (0.046 mmol), 79%. Rf = 0.81.
(c) Tetra(4ꢀmethoxyphenyl)porphyrin (0.05 g) and
PdCl2 (0.036 g) (molar ratio 1 : 3) were refluxed in
DMF (30 mL) for 20 s. Yield 0.041 g (0.049 mmol),
72%, Rf = 0.81.
within 15 min. The UV–Vis spectrum of the sample
taken from the reaction mixture after 15 min and dissolved
in DMF exhibits bands with λI = 554, λII = 522 nm, while
the bands for starting VI with maxima at 598 and
558 nm (figure) have disappeared. The hypsochromic
shift of the Soret band in the UV–Vis spectrum of I with
respect to Zn porphyrin in DMF was 8 nm (Table 1).
When the reaction time increased to 20 min, the UV–
Vis spectral pattern of complex
I did not change.
Under similar conditions, the degree of conversion of
chloro and methoxy derivatives of Zn2+ porphyrins to
the corresponding Pd porphyrins was ~25–30%. The
For PdC48N4H36O4 anal. calcd. (%): C, 68.70; N,
6.68; H, 4.32.
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EFFECT OF THE NATURE OF THE TETRAPYRROLE MACROCYCLE
487
Table 2. Effect of the nature of the tetrapyrrole macrocycle on
the transmetallation of Zn2+ and Cd2+ porphyrins by PdCl2 in
boiling DMF
UV–Vis spectra of samples in DMF exhibit, apart
from the bands with maxima at 555, 524 and 558,
525 nm for the reaction products, also the bands for
the starting Zn chloro and methoxy porphyrins at
λmax = 598, 559 and 603, 561 nm. As the reaction time
was increased to 1 h, the product yield increased but
still no complete transformation of the starting metal
porphyrins to the final products took place. The
observed decrease in the reactivity of Zn tetrapheꢀ
nylporphyrin upon the substitution is probably due to
Starting
compound
Reactant
molar ratio
Reaction time
15 min
ZnTPhP
1 : 3
CdTPhP
1 : 3
1 : 3
2 min
ZnT(4ꢀClPh)P
15 min–degree
of conversion ~ 25%
enhancement of the N
the case of VIII, +J effect in
increased to a 10ꢀfold excess, the deactivating effect of
M
σ
ꢀbond (+C effect in
CdT(4ꢀClPh)P
1 : 3
2 min
X). As the salt amount is
ZnT(4ꢀOCH3Ph)P 1 : 3
15 min–degree
of conversion ~30%
substituents is levelled up and Pd porphyrins (
I, IV,
CdT(4ꢀOCH3Ph)P 1 : 3
2 min
4 min
5 min
5 min
and ) are formed in boiling DMF after 4–5 min.
V
ZnTPhP
1 : 10
1 : 10
An opposite situation is observed for complexation
of the tetraphenylporphin ligand and its derivative
with PdCl2 in DMF [5]. According to published data
[16], electronꢀdonating substituents, which increasing
the electron density on the tertiary nitrogen atoms of
the macrocycle, enhance the coordination interaction
of the solvato complex cation with porphyrin in the
transition state, and the reaction rate thus increases.
Our studies demonstrated that the introduction of
chlorine atoms (+C effect) and electronꢀdonating
methoxy groups (+J effect) in the paraꢀposition of the
tetraphenylporphin benzene rings increases the rate of
complexation with PdCl2 in DMF by ~2 orders of magꢀ
nitude as compared with the starting porphyrin [5].
ZnT(4ꢀClPh)P
ZnT(4ꢀOCH3Ph)P 1 : 10
ZnTBP
1 : 10
1 h–degree
of conversion ~25%
CdTBP
1 : 10
10 min
ZnOPhTAP
MgOPhTAP*
1 : 20
1 : 20
2 h–no reaction
1 h
* Data from [8].
The data from elemental analysis, UV–Vis, IR,
and NMR spectroscopy fully correspond to the strucꢀ
tures of the synthesized compounds. The hypsochroꢀ
mic shift of the UV–Vis bands of Pd2+ porphyrins (
I–
It is known [17] that benzo and aza substitution staꢀ
bilize Zn porphyrins. This was also supported by our
studies. The degree of conversion of Zn tetrabenꢀ
zoporphyrin (XII) to Pd(II) porphyrin at 1 : 10 molar
ratio of the reactants in boiling DMF at the reaction
time of 1 h is only ~25%. Zinc octaphenylporphyrin
V
) with respect to the starting Zn2+ and Cd2+ porphyꢀ
rins (VI XIV) can be attributed to strong ꢀdative
interaction between the metal ion and the porphyrin
–
π
macrocycle of the
d –eg(π*) type (Table 1). In the
π
1H NMR spectrum of Pd tetraphenylporphyrin, the
signals of the pyrrole rings and orthoꢀprotons are
shifted upfield by 0.13 and 0.05 ppm relative to the
spectrum of the starting Zn porphyrin.
(
XIV) does not form the corresponding palladium porꢀ
phyrin(III) even on longꢀterm refluxing (2 h) with a
20ꢀfold excess of PdCl2
.
The obtained results indicate that in the case of tetꢀ
rapyrrole macrocycles that are usually prepared by
template cyclotetramerization as metal porphyrin
complexes, the palladium complexes are conveniently
synthesized via transmetallation of their labile comꢀ
plexes (Table 2). In the case of tetrapyrrole macrocyꢀ
cles that are readily formed as free ligands, it is more
expedient to use the complexation of the porphyrin
ligand with the metal cation classical for porphyrins.
On going from the covalently bonded Zn porphyꢀ
rins to less stable ionic Cd porphyrins [17], the rate of
metal exchange with Pd increases. Irrespective of the
chemical modification of the macrocycle, the rates of
formation of Pd2+ porphyrins (
I
,
IV
DMF almost coincide. The transmetallation of Cd
porphyrins (VII IX XI) by PdCl2 in DMF at lower
, V) in boiling
,
,
temperature has not been studied. Palladium tetrabenꢀ
zoporphyrin is formed in boiling DMF ~5 times more
slowly than complex I at 1 : 10 molar ratio of the reacꢀ
tants. Cd2+ octaphenyltetraazaporphyrin is not formed
by the Linstead method [13]. Cd2+ octaphenyltetꢀ
raazaporphyrin formed from the corresponding ligand
and cadmium acetate in DMF is unstable in the solid
state. During the isolation, the complex is converted to
the octaphenyltetraazaporphyrin ligand. Therefore, it
is expedient to obtain Pd2+ octaphenyltetraazaporphyꢀ
rin from Mg octaphenyltetraazaporphyrin [8].
ACKNOWLEDGMENTS
This work was supported by the Russian Foundation
for Basic Research (project no. 08ꢀ03ꢀ90000 Bel._a).
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