Effect of the chemical modification of the tetrapyrrole macrocycle on the reactivity of porphyrins in complexation with Pt4+ and Pd 2+ cations

Article abstract of DOI:10.1134/S0036023607020180

The reactions of 5,10,15,20-tetraphenylporpine, 5,10,15-triphenyl-20-(4- hexadecanoxyphenyl)porphine, 5,10,15,20-tetra-(4-butoxyphenyl)porphine, and 2,3,7,8,12,13,17,18-ocaethylporphine with H₂PtCl₆ in boiling phenol and with PdCl₂ in boiling dimethylformamide are studied by spectrophotometry. Due to a strong electronic effect of the substituents, the reactivity of the tetrapyrrole macrocycle during porphyrinate formation changes by more than two orders of magnitude. Platinum(II) 5,10,15-triphenyl-20-(4-hexadecanoxyphenyl)porphinate and palladium(II) 5,10,15,20-tetra-(4-butoxyphenyl)porphinate have been synthesized and identified for the first time. Nauka/Interperiodica 2007.

Full text of DOI:10.1134/S0036023607020180

ISSN 0036-0236, Russian Journal of Inorganic Chemistry, 2007, Vol. 52, No. 2, pp. 250–253. © Pleiades Publishing, Inc., 2007.
Original Russian Text © N.V. Chizhova, N.Zh. Mamardashvili, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 2, pp. 292–295.
PHYSICAL METHODS OF INVESTIGATION
Effect of the Chemical Modification of the Tetrapyrrole
Macrocycle on the Reactivity of Porphyrins in Complexation
with Pt4+ and Pd2+ Cations
N. V. Chizhova and N. Zh. Mamardashvili
Institute of Solution Chemistry, Russian Academy of Sciences, ul. Akademicheskaya 1, Ivanovo, 153045 Russia
Received April 18, 2006
Abstract—The reactions of 5,10,15,20-tetraphenylporpine, 5,10,15-triphenyl-20-(4-hexadecanoxyphe-
nyl)porphine, 5,10,15,20-tetra-(4-butoxyphenyl)porphine, and 2,3,7,8,12,13,17,18-octaethylporphine with
H2PtCl6 in boiling phenol and with PdCl2 in boiling dimethylformamide are studied by spectrophotometry. Due
to a strong electronic effect of the substituents, the reactivity of the tetrapyrrole macrocycle during porphyrinate
formation changes by more than two orders of magnitude. Platinum(II) 5,10,15-triphenyl-20-(4-hexadecanox-
yphenyl)porphinate and palladium(II) 5,10,15,20-tetra-(4-butoxyphenyl)porphinate have been synthesized and
identified for the first time.
DOI: 10.1134/S0036023607020180
Porphyrins and related tetrapyrrole macrocycles are the reactions of I and II with K2PtCl2 in boiling ben-
known to manifest their photochromic and catalytic
properties being complexed with metals. Complexes of
porphyrins with platinum and palladium, which are
widely used in various areas of science and technology
for the creation of controlled functional materials [1, 2],
are of special interest.
zene. Buchler and colleagues [4] wrote that the yields
of platinum(II) and palladium(II) tetraphenylporphyri-
nates can be increased to 80% by carrying out the reac-
tion in boiling benzonitrile and using PtCl2 and PdCl2 as
reactants. Platinum(II) and palladium(II) 5,10,15,20-
tetra(benzo-15-crown-5)porphyrinates were synthe-
sized in 84 and 87% yields, respectively, under similar
conditions. It should be mentioned that Rothemund and
Menotti [6] found that the reaction of PdCl2 with II in
boiling dimethylformamide resulted in a partial hydro-
genation of the tetrapyrrole macrocycle and yielded the
Several methods for the synthesis of platinum(II)
and palladium(II) porphyrinates with 5,10,15,20-tet-
raphenylporphine (I) and 2,3,7,8,12,13,17,18-octaeth-
ylporphine (II) are described in works [3–5].According
to [3], platinum(II) 5,10,15,20-tetraphenylporpyrinate
(III) and platinum(II) 2,3,7,8,12,13,17,18-octaeth-
ylporphyrinate (IV) were synthesized in ~20% yield by corresponding dihydroporphyrin as an admixture.
R1
M
å = ç2, R = R2 = C6H5 (I);
1
å = Pt2+, R1 = R2 = C6H5 (III);
å = H2, R1 = C6H4-4-OC16H33, R2 = C6H5 (V);
å = H2, R1 = R2 = C6H4-4-OC4H9 (VI);
å = Pt2+, R1 = C6H4-4-OC16H33, R2 = C6H5 (VII);
å = Pt2+, R1 = R2 = C6H4-4-OC4H9 (VIII);
å = Pd2+, R1 = C6H4-4-OC16H33, R2 = C6H5 (IX);
å = Pd2+, R1 = R2 = C6H4-4-OC4H9 (X);
å = Pd2+, R1 = R2 = C6H5 (XI);
N
N
N
N
N
N
M
R2
N
R2
N
å = Zn2+, R1 = R2 = C6H5 (XIII).
M = H2 (II),
R2
å = Pt2+ (IV),
å = Pd2+ (XII).
For the purpose of creating porphyrin-containing for the synthesis of platinum(II) and palladium(II) ms-
photochromic systems able to respond to external and β-substituted porphyrinates and studied the effect
action, in the present work we developed new methods of chemical modification of the tetrapyrrole macrocy-
250

EFFECT OF THE CHEMICAL MODIFICATION OF THE TETRAPYRROLE MACROCYCLE
251
Electronic absorption spectra of the Pt2+ and Pd2+ porphyri-
nates in chloroform
cle on the reactivity of I, II, 5,10,15-triphenyl-20-(4-
hexadecanoxyphenyl)porphine (V), and 5,10,15,20-
tetra-(4-butoxyphenyl)porphine (VI) in complexing
H2PtCl6 in boiling phenol and PdCl2 in boiling dimeth-
ylformamide. Platinum(II) 5,10,15-triphenyl-20-(4-
hexadecanoxyphenylporphyrinate (VII), platinum(II)
5,10,15,20-tetra-(4-butoxyphenyl)porphyrinate (VIII),
palladium(II) 5,10,15-triphenyl-20-(4-hexadecanox-
yphenyl)porphyrinate (IX), and palladium(II)
Band I
Band II
Soret band λ,
Ìnm ( logε )
Compound
λ, nm ( logε ) λ, nm ( logε )
III
540 (4.10)
541 (3.92)
536 (4.53)
539 (4.18)
540 sh
510 (4.40)
511 (4.11)
502 (4.12)
510 (4.41)
512 (4.58)
523 (4.54)
526 (4.58)
523 (4.53)
512 (4.32)
558 (4.36)
402 (5.48)
402 (4.84)
381 (5.31)
402 (5.46)
407 (5.56)
417 (5.61)
421 (5.67)
417 (5.63)
400 (5.24)
420 (5.19)
III*
IV
5,10,15,20-tetra-(4-butoxyphenyl)porphyrinate
have been synthesized for the first time.
(X)
VII
VIII
IX
EXPERIMENTAL
531 sh
Porphyrin ligands V and VI were synthesized
according a known procedure [7]. The complex forma-
tion of the metal cation with the porphyrin ligand was
monitored by spectrophotometry and thin-layer chro-
matography (TLC). The spectrophotometric procedure
was as follows: aliquot volumes were taken from the
reaction mixture at certain time intervals and dissolved
in a certain amount of dimethylformamide, and the
solution was placed in a cell. Electronic absorption
spectra were recorded on a Specord M40 spectropho-
X
535 sh
XI
531 sh
XII
XIII*
545 (4.76)
597 (4.99)
* The data are borrowed from [9, 7], respectively.
For PtC36N4H44 anal. calcd. (%): C, 59.37; N, 7.67;
tometer at 298 K. Electron-impact mass spectra were H, 6.07.
measured on an MX-1310 mass spectrometer at an ion-
izing electron energy of 70 eV and an ionization cham-
ber temperature of 150–200°C. Thin-layer chromatog-
raphy was carried out on Silufol plates (G/UV254) using
hexane–chloroform (1 : 2) as the eluent. IR spectra
were recorded on a Specord M80 spectrometer as KBr
pellets. The solvents were purified according to [8].
Synthesis of platinum(II) 5,10,15,20-tetraphe-
nylporphyrinate (III). A mixture of porphyrin I (0.05 g,
0.0813 mmol), H2PtCl6 × 6H2O (0.244 mmol), and phe-
nol (6 g) was refluxed for 2 h; the melt was cooled, dis-
solved in dimethylformamide (20 ml), and poured into
water. A precipitate that formed was filtered off,
washed with water, and dried. The residue was chro-
matographed on silica gel 40/100 (Cçël3 : C6H12 (1 : 2)
as eluent). The yield was 0.05 g (0.0619 mmol, 76%).
Rf = 0.76.
Found (%): C, 59.40; N, 7.70; H, 6.10 .
Mass spectrum (m/z): 727.6 (Irel = 82%) [M+].
IR (cm–1): 3049 w, 2958 s, 2926 m, 2868 w, 1735 s,
1564 w, 1455 m, 1391 w, 1266 m, 1238 m, 1156 s, 1058 w,
993 w, 875 m, 835 m, 734 m, 467 w, 442 w.
Platinum(II) 5,10,15-triphenyl-20-(4-hexadecan-
oxyphenyl)porphyrinate (VII). Porphyrin V (0.05 g)
and H2PtCl6 · 6H2O (0.091 g) were taken in a molar ratio
of 1 : 3. The reaction time was 4 h. The yield was 0.05 g
(0.0477 mmol, 80%), Rf = 0.71.
For PtC60N4H59O anal. calcd. (%): C, 68.80; N,
5.35; H, 5.69.
Found (%): C, 68.77; N, 5.32; H, 5.66.
Mass spectrum (m/z): 1046.3 (Irel = 92%) [M+].
IR (cm–1): 3055 w, 3022 w, 2923 s, 2852 m, 1727 w,
1656 w, 1598 m, 1455 m, 1359 (m), 1317 m, 1287 m,
1184 m, 1078 m, 1019 s, 797 m, 754 w, 714 m, 701 m,
1667 w, 430 w.
For C44N4H28 anal. calcd. (%): C, 65.41; N, 6.94; H,
3.50.
Found (%): C, 65.38; N, 6.92; H, 3.47.
Mass spectrum (m/z): 807.2 (Irel = 76%) [M+].
IR (cm–1): 3060 w, 3028 w, 2824 m, 2852 w, 1809 w,
1733 w, 1633 m, 1591 m, 1441 m, 1360 m, 1317 m,
1176 w, 1077 m, 1019 s, 796 m, 754 m, 713 m, 668 m,
434 w.
Porphyrinates IV, VII, and VIII were synthesized
similarly.
Platinum(II) 2,3,7,8,12,13,17,18-octaethylporphy-
rinate (IV). Porphyrin II (0.05 g) and H2PtCl6 · 6H2O
(0.145 g) were taken in a molar ratio of 1 : 3. The reaction
time was 9 h. The yield was 0.05 g (0.0687 mmol, 76%),
Rf = 0.69.
Platinum(II)
5,10,15,20-tetra(4-butoxyphe-
nyl)porphyrinate (VIII). Porphyrin VI (0.05 g) and
H2PtCl6 (0.086 g) in the molar ratio of 1 : 3. Reaction
time: 12 h.Yield: 0.05 g (0.0456 mmol, 78%). Rf = 0.70.
For PtC N H O anal. calcd. (%): C, 65.73; N,
60
4 60 4
5.08; H, 5.53.
Found (%): C, 65.70; N, 5.11; H, 5.50.
Mass spectrum (m/z): 1095.1 (Irel = 79%) [M+].
IR spectrum (cm–1): 2957 m, 2929 m, 2870 w, 1607 s,
1507 s, 1464 m, 1358 m, 1285 m, 1244 s, 1174 s, 1107 w,
1076 w, 1021 m, 1009 m, 967 w, 820 m, 798 m, 714 w,
647 w, 560 w, 437 w.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 52 No. 2 2007

252
CHIZHOVA, MAMARDASHVILI
Mass spectrum (m/z): 636.1 (Irel = 69%) [M+].
Palladium(II) 5,10,15-triphenyl-20-(4-hexade-
canoxyphenyl)porphyrinate (IX). A mixture of porphy-
rin V (0.1 g) and PdCl2 (0.21 g) in a molar ratio of 1 : 10
was dissolved in dimethylformamide (60 ml) and
refluxed for 5 min. The mixture was cooled, a precipi-
tate was filtered off, and the filtrate was poured into
water. The precipitate was filtered off, washed with
water, and chromatographed on silica gel 40/100
(CHCl3 : C6H12(1 : 2) as eluent). The yield was 0.09 g
(0.0938 mmol, 80%), Rf = 0.74.
IR (cm–1): 3049 w, 2958 s, 2926 m, 2867 w, 1738 w,
1671 w, 1553 w, 1452 m, 1388 w, 1310 w, 1263 m,
1233 s, 1154 s, 1142 m, 1107 w, 1057 m, 989 m, 937 w,
832 m, 753 m, 732 m, 715 m, 608 w, 457 w.
RESULTS AND DISCUSSION
The reduction of Pt4+ to Pt2+ occurs during the reac-
tions of H2PtCl6 with compounds I, II, V, and VI. We
found that in the reaction of compound I with H2PtCl6
in boiling phenol, porphyrinate III is formed ~15 times
more rapidly than in the with K2PtCl4 in boiling ben-
zonitrile [9]. It is worth mentioning that the reactivity of
the tetrapyrrole macrocycle toward Pt4+ decreases sub-
stantially (maximally sixfold) under the inductive
effect of electron-releasing substituents arranged in the
both ms- (I, V, VI) and β- (II) positions of the molecule.
According to the mechanism of porphyrin coordination
by metal cations in nonaqueous media [10], metal por-
phyrins are formed due to the bimolecular collision of
the porphyrin ligand and solvated salt. The rate of the
complexation process depends on two factors, namely,
(1) the strength of the N–H bonds of the reaction center
of the porphyrin and (2) coordination interaction
between the metal cation and nitrogen atoms of the por-
phyrin. The effect of these factors depends on the spe-
cifics of the process. The decrease in the complexation
rate observed on going from I to II, V, and VI indicates
that the strength of the N–H bonds of the porphyrin
ligand makes the key contribution to the energy of the
transition state. Electron-releasing substituents
increase the density of the N–H bonds, thus decreasing
the reactivity of the tetrapyrrole macrocycle to Pt4+.
This is confirmed by the consecutive increase in the
time of formation of porphyrinates III, VII, and VIII
with an increase in the number of the alkyloxy groups
(n) in the phenyl fragments (n = 0 (III), 1 (VII), 4
(VIII)).
The fact that the formation rate of palladium(II) por-
phyrinates IX, X, and XI in the reactions of the corre-
sponding ligands with PdCl2 in dimethylformamide
changes in the opposite direction indicates that the
coordination interaction of the metal cation with the
nitrogen atom of the porphyrin makes the key contribu-
tion to the energy of the transition state of the complex
formation process. The electron-releasing substituents
increase the electron density on the tertiary nitrogen
atoms of the macrocycle, thus enhancing the coordina-
tion interaction of the cation of the solvate complex
with the porphyrin in the transition state. The latter is
accompanied by an increase in the reaction rate (maxi-
mally by ~120 times).
For PdC60N4H59O anal. calcd. (%): C, 75.17; N, 5.85;
H, 6.22.
Found (%): C, 75.15; N, 5.82; H, 6.19.
Mass spectrum (m/z): 954.4 (Irel = 97%) [M+].
IR (cm–1): 3049 w, 3022 w, 2922 s, 2851 m, 1803 w,
1598 m, 1568 m, 1441 m, 1353 m, 1312 m, 1287 m,
1194 m, 1076 m, 1014 s, 797 m, 753 m, 713 m, 701 m,
667 w, 461 w.
Palladium(II)
5,10,15,20-tetra-(4-butoxyphe-
nyl)porphyrinate (X), palladium(II) 5,10,15,20-tet-
raphenylporphyrinate
(XI),
and palladium(II)
2,3,7,8,12,13,17,18-octaethylporphyrinate (XII) were
synthesized in a similar manner.
Palladium(II)
5,10,15,20-tetra-(4-butoxyphe-
nyl)porphyrinate (X). Porphyrin VI (0.1 g) and PdCl2
(0.2 g) in a molar ratio of 1 : 10. Reaction time: 1 min.
Yield: 0.08 g (0.0794 mmol, 76%). Rf = 0.73.
For PdC N H O anal. calcd. (%): C, 71.51; N,
60
4 60 4
5.56; H, 6.01.
Found (%): C, 71.49; N, 5.52; H, 5.98.
Mass spectrum (m/z): 1007.3 (Irel = 83%) [M+].
IR (cm–1): 3039 w, 2956 m, 2926 m, 2870 w, 1607 s,
1505 s, 1465 m, 1353 m, 1285 m, 1243 s, 1174 s, 1107 w,
1074 w, 1009 m, 798 w, 714 w, 643 w, 543 w, 452 w.
Palladium(II) 5,10,15,20-tetraphenylporphyri-
nate (XI). Porphyrin I (0.1 g) and PdCl2 (0.29 g) in a
molar ratio of 1 : 10. Reaction time: 2 h. Yield: 0.08 g
(0.111 mmol, 73%). Rf = 0.78.
For PdC44N4H28 anal. calcd. (%): C, 73.48; N, 7.79;
H, 3.93.
Found (%): C, 73.46; N, 7.77; H, 3.90.
Mass spectrum (m/z): 718.1 (Irel = 87%) [M+].
IR (cm–1): 3053 w, 3016 w, 2923 m, 2852 w, 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.
Palladium(II) 2,3,7,8,12,13,17,18-octaethylpor-
phyrinate (XII). Porphyrin II (0.1 g) and PdCl2 (0.33 g)
in a molar ratio of 1 : 10. Reaction time: 2 min. Yield:
0.09 g (0.141 mmol, 75%). Rf = 0.73.
The synthesis of palladium(II) octaethylporphyri-
nate (XII) needs special attention. The reaction of octa-
ethylporphine II with PdCl2 in boiling dimethylforma-
mide yields porphyrinate XII in 75% yield. No forma-
For PdC36N4H44 anal. calcd. (%): C, 67.63; N, 8.74;
H, 6.95.
Found (%): C, 67.61; N, 8.77; H, 6.92.
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EFFECT OF THE CHEMICAL MODIFICATION OF THE TETRAPYRROLE MACROCYCLE
253
tion of side dihydroporphyrins was observed under
these conditions, unlike in [6].
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spectra and elemental analysis match completely to the
structures of the synthesized compounds. The hypsoch-
romic shift of the absorption bands in the electronic
absorption spectra of the platinum(II) and palladium(II)
porphyrinates (III, IV, VII–XII) relative to the metal
porphyrins containing the metal ion with a closed elec-
tronic shell (for instance, zinc(II)) is caused by the
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ACKNOWLEDGMENTS
8. Organikum (VEB Deutscher Verlag der Wissenschaften,
1976; Mir, Moscow, 1979).
This work was supported by the Russian Foundation
for Basic Research (project no. 05-03-32055) and the
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