Synthesis of lutetium(iii)-porphyrin complexes: old problems and new excellent conditions found

Article abstract of DOI:10.1039/c6nj02424f

A convenient method for the preparation of very attractive and almost unknown lutetium(iii)-porphyrins was developed. Systematic investigations involving a broad spectrum of solvents (DMF, TCB, imidazole, sulfolane, and a CHCl₃/MeOH mixture), as well as studies concerning the influence of temperature and the reaction time on the yield, were performed. Under the optimized experimental conditions found within the study for [5,10,15,20-tetraphenylporphyrinato]lutetium(iii) chloride (sulfolane, reflux, 0.5 h; 88% yield), the synthesis of some other more complex derivatives was demonstrated.

Full text of DOI:10.1039/c6nj02424f

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Synthesis of lutetium(III)–porphyrin complexes: old problems
and new excellent conditions found
Bartosz Kalota,a Agnieszka Mikusb and Stanisław Ostrowski*,b
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
www.rsc.org/
A convenient method for preparation of very attractive and somewhat troublesome. Except one case,12d these yields (for
almost unknown lutetium(III)–porphyrins was developed. Syste- the reactions carried out in imidazole) have not been
matic investigations involving a broad spectrum of solvents (DMF, determined (or not determined correctly12a) and the products
TCB, imidazole, sulfolane, and CHCl3/MeOH mixture), as well as have never been fully character-ized.
studies concerning the influence of temperature and the reaction
time on the yield were performed. Under optimized experimental
conditions found within the study for [5,10,15,20-
tetraphenylporphyrinato]lutetium(III) chloride (sulfolane, reflux,
0.5 h; 88% yield), the synthesis of some other more complex
derivatives was demonstrated.
In the last decades the interest of using lanthanide(III)–porphy-
rins has significantly increased.1 They are applied in
noninvasive blood glucose monitoring,2 as labels for
Scheme 1. Synthesis of chloro-lutetium(III)-5,10,15,20-
tetraphen-ylporphyrin ([Lu-TPP]Cl).
immunoassays,3 fluorescence probes of biomolecules,4 near-
Hence, we have undertaken systematic investigations to
infrared polymer electroluminescent devices,5 or imaging
develop a convenient method for preparation of this type of
probes,6 NMR shift reagents,7 and contrast agents8 of in vivo
complexes. We used a broader spectrum of solvents. The
magnetic resonance. These complexes exhibit large Stokes’
influence of the temperature and the reaction time were also
shift, thus their luminescence is strongly NIR-shifted (the shift
studied. Well-known meso-tetraphenylporphyrin (m-TPP,
1)
is ca 50 nm for fluorescence and ca 200 nm for phosphore-
scence).9 Additionally, small structure modification of the
porphyrin ligand allows for flexible adjustment of
photophysical and photochemical properties of the complex. It
was also found that luminescence of certain lanthanide(III)–
porphyrins is oxygen sensitive, giving an excellent possibility
for designing of attractive oxygen and pressure sensitive
luminophores that are desired in various applications.10
was chosen as a model compound for this optimization. The
product obtained therefrom, chloro-lutetium(III)-5,10,15,20-
tetraphenylporphyrin ([Lu-TPP]Cl,
very desired materials for various utilizations.13,14 It is worth
mentioning that although this simple complex has been
2), and its derivatives, are
2
reported in the recent literature,13 neither the yield nor the
physico-chemical and spectroscopic data for it were provided.
To obtain high yield of m-TPP–lutetium(III) complex, we
have carried out a series of experiments using solvents such as
DMF, TCB, imidazole, sulfolane, and CHCl3/MeOH mixture. At
the beginning, the reagents were always preheated in these
solvents to reflux temperature (see Table 1 and experimental
details). In the first reaction, m-TPP and LuCl3×6H2O were
refluxed in a mixture of CHCl3 and MeOH. This mixture was
often used for preparation of porphyrin complexes,15 among
others, in our laboratory.16 Many desired products were
obtained by this way with good yield. Contrary, in our case
none of the product was being observed and most of the m-
TPP was recovered. Prolonging the reaction time gave the
Syntheses of lanthanide(III)–porphyrins, by replacement of
two central hydrogen atoms in the macrocycle ligand with lan-
thanide ion (Scheme 1), were often carried out in 1,2,4-
trichlorobenzene (TCB)7,11 or imidazole.12,13 However,
utilization of these solvents has certain limitations: synthesis in
TCB is time-consuming (yields ca 30-60%); while in the case of
imidazole, product isolation from the post-reaction mixture is
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same effect and only progressive degradation of the substrate
occurred slowly (Table 1).
In the next set of experiments carried out in DMF we were
changing the reaction time between 2 h and 20 h, and we
were able to improve the yield from 5% to 16% only, despite
that after 10 h most of m-TPP was consumed. We found that
the isolation of the product from this solvent was rather
problematic because it underwent continuous degradation
during the purification process. This could be influenced by
ligand exchange in the lutetium(III)–complex as DMF may act
as an efficient ligand herein (P-Lu(III)–Cl → P-Lu(III)–DMF).
Earlier, this type of reactions in DMF were described in the
literature and the Authors declared unlikely good yields (38%;
for Lu(III)-TBP).10b It is somewhat surprising.
Table 1. Optimization of the synthesis of [Lu-TPP]Cl.
Solvent,
Temperature
Reaction
timea
Recovery
of m-TPP
Yield
CHCl3/MeOH, 10:1
CHCl3/MeOH, 10:1
DMF
2 h
–
ca 83%
ca 75%
90%
4 h
–
2 h
< 5%
6%
DMF
4 h
ca 85%
b
DMF
6 h
7.5%
11%
b
b
DMF
9 h
Only a slightly better results were obtained during the opti-
mization process in TCB. After 20 h of heating under reflux, we
achieved the best yield, 23%. Contrary to the investigations in
DMF, the product isolation was very easy in this case, and
prac-tically all the not converted substrate could be recovered.
When we added after 20 h new portion of LuCl3×6H2O, the
yield raised to 32%, and 64% of m-TPP was recovered, thus
giving good balance of the reaction (see last entry in this
series, Table 1).
DMF
16 h
20 h
2 h
10%
DMF
16%
8%c
b
TCB
3.5%
5.5%
8.5%
13%
b
TCB
4 h
b
TCB
6 h
b,c
b,c
b,c
TCB
8 h
TCB
16 h
20 h
25 hd
2 h
22%
TCB
23%
A very promising yields were observed when imidazole was
used as a solvent (b.p. 256 °C). The conversion was rather fast,
TCB
32%
64%
b
ca 20%e
ca 29%e
ca 36%e
ca 49%e
ca 54%e
ca 65%e
63%
however, after 15–20
h we noticed the progressive
imidazole
imidazole
imidazole
imidazole
imidazole
imidazole
sulfolane, 180°C
sulfolane, 180°C
sulfolane, 215°C
sulfolane, 215°C
sulfolane, 215°C
sulfolane, 250°C
sulfolane, 250°C
sulfolane, 250°C
sulfolane, reflux
sulfolane, reflux
sulfolane, reflux
sulfolane, reflux
degradation of the product (TLC monitoring). In the best case,
we were able to figure out the yield on the basis of TLC as
approximately over 70%, but this yield dropped during the
work-up and isolation on column chromatography. Probably
we have here the same inconveniences observed earlier for
DMF (degradation by ligand exchange) because imidazole can
also be ligated effectively by the Lu(III) system.17 Thus, again
the isolation was problematic herein.
b
b
b
6 h
7 h
12 h
15 h
20 h
1 h
17%
tracesc
27%
2 h
74%
8%
We found that the solvent (probably its polarity) and tem-
perature have a large effect on the yield of [Lu-TPP]Cl. Hence,
we have decided to carry out the final set of experiments in
sulfolane, which is polar enough and it allows for optimization
in a broad range of temperature, up to 285 °C. Interestingly, in
the first reaction performed at 250 °C (2 h) we observed fast
conversion of m-TPP into desired product, and only very small
amount of substrate was detected (Table 1). Thus, sulfolane
was relevant for this conversion. Further studies by changing
the temperature in the range of 180–285 °C and the reaction
time (20 min to 2 h) allowed us to find the best conditions
(reflux, 0.5 h; 88% yield), however in all reactions the yields
were very good. At high temperature, prolonging the reaction
time after complete conversion of the substrate, led to a slow
decomposition of the product (e.g., at 250 °C: 1 h – 85%, 2 h –
77%; see Table 1).
1 h
81%
9%
1.5 h
2 h
80%
7%
82%
–
0.5 h
1 h
86%
6.5%
traces
traces
31%
tracesc
tracesc
tracesc
85%
2 h
77%
20 min
30 min
40 min
1 h
62%
88%
88%
86%
a
Usually, the reactions were carried out up to 20 h (for CHCl3/MeOH –
up to 4 h, for sulfolane – up to 2 h) or to complete conversion of the
substrate; if not other mentioned – in reflux (temperature of solvents:
CHCl3/ /MeOH (10:1) – ca 62 °C, DMF – 153 °C, TCB – 214 °C, imidazole
The above results show that temperature is also important
parameter herein. On the other hand, the synthesis in TCB,
which is very convenient as far as isolation of product is con-
cerned, was limited by the lower boiling point of this solvent.
We came back to these studies and decided to carry out an
addi-tional experiment in TCB in a tube sealed with a Rotaflo
stop-cock, which allows to reach the temperature of 285 °C
under higher pressure. It was ’half-successful’ experiment
because the yield was improved up to 29% only. However, it is
– 256 °C, sulfolane – 285 °C); reaction scale – ca 6.0 mg TPP (ca 1.0×
10-
2
mmol) in 1 mL of solvent (for imidazole – 1.0 g); before work-up of
the reaction mixtures containing DMF, imidazole, or sulfolane
chloroform was added and the solvent was washed out with water,
b
see ref. [18]. The recovery of substrate was not determined. c These
selected reactions were performed in preparative scale (up to 0.1
mmol), see ref. [18]. After 20 h the next portion of LuCl3×6H2O was
d
e
added. The yield was not determined exactly because the product
was contaminated partially due to its spontaneous decomposition.
2 | J. Name., 2012, 00, 1-3
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worth men-tioning that most of the remaining porphyrin was Figure 2. Typical UV-Vis spectrum of the formation of metallo-
recovered. porphyrin: (a) free base porphyrin, (b) product
Thus, with this new efficient method in hands (elaborated
4.
The course of the reactions may be followed by examining
for sulfolane; typical procedure is given for
2
),18 we prepared the UV-Vis absorption spectra of the reaction mixture.
some other more complex porphyrin derivatives which we Completion of the reaction is indicated by the disappearance
need for our further luminescence investigations being in of the four visible absorption bands of the free base porphyrin
progress in our laboratories: [5,10,15,20-tetrakis(3- at 517, 553, 591, 648 nm and the appearance of bands
fluorophenyl)porphyrinato]lutetium(III) chloride (
nitrophenyl)-10,15,20-triphenylporphyrinato]lutetium(III)
chloride 46%), {5-[4-nitro-3-(toluene-4-
sulphonylmethyl)phenyl]-10,15,20-triphenyl-
porphyrinato}lutetium(III) chloride (
3
, 77%), [5-(4- characteristic for the metalloporphyrin: 516, 553 (intensive),
592 nm (see example for nitro-derivative 4; Figure 2).
(
4,
Synthetic approach to lutetium(III)–porphyrins from meso-
tetraphenylporphyrin (and its derivatives) was investigated: in
5
, 46%) (see Fig. 1). The various solvents, in a broad range of temperature and the re-
yields were not so high as compared to compound
one can say these complexes are easily accessible.
2
, however, action time. Detailed studies allow us to optimize the reaction
conditions for this process, thus a new, fast, and high-yielded
method was developed (sulfolane, reflux, 0.5 h; 88% yield for
m-TPP).18 The polarity of the solvent, temperature, and the
short reaction time (30–40 min) have a large effect on the
yield and should be mentioned herein. This method is general,
tolerating the variation of the substitution pattern in the meso-
phenyl rings (see more complex derivatives prepared with this
protocol).
An alternative convenient preparative procedure (for the
reaction carried out in TCB in a sealed tube under higher
pressure) was also elaborated. In this case, the conversion rate
was lower, however, the isolation of product was very easy
and almost all of the remaining porphyrin was recovered, thus
giving good balance of the reaction.
The interest of using lanthanide(III)–porphyrins has signifi-
cantly increased in many areas of chemistry, thus the ability to
access these types of porphyrin complexes is of great import-
ance. They are being sought for current investigations. Taking
into account high yield and preparative simplicity of the
Figure 1. Structures of other chloro-lutetium(III) porphyrin com- presented method, it may well receive future attention.
plexes obtained in sulfolane.
Acknowledgements
This work was supported by Grant No 168/S/00, UP-H in
Siedlce.
Notes and references
1
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6
7
S. Haye and P. Hambright, J. Chem. Soc., Chem. Commun.,
1988, 666.
CHCl3 and finally CHCl3/MeOH, 20:1) to give product
– 25.4 mg (88%).
Products 3-5 were prepared by the same procedure. In some
reactions presented in Table 1 even CHCl3/MeOH (10:1) mix-
ture was used as eluent at the end of chromatography sepa-
2; yield
(a) Ch.-P. Wong, R. F. Venteicher and W. D. Horrocks Jr., J. Am.
Chem. Soc., 1974, 96, 7149; (b) W. D. Horrocks Jr. and Ch.-P.
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1984, 168, 70.
8
9
ration. For preparation of
– see ESI.
Data for products. 2: This compound was described in the li-
2 in TCB at 285°C (under pressure)
L. A. Martarano, Ch.-P. Wong, W. D. Horrocks Jr. and A. M.
Ponte Goncalves, J. Phys. Chem., 1976, 80, 2389.
terature three years ago,13 however it was not characterized.
10 (a) J. M. Vanderkooi, G. Maniara, T. J. Green and D. F. Wilson,
J. Biol. Chem., 1987, 262, 5476; (b) S. A. Vinogradov and D. F.
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Inorg. Chem. Commun., 2008, 11, 1051; (b) Ch.-P. Wong and
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Res. Chinese U., 2004, 20, 807; (b) M. Gouterman, C. D. Schu-
maker, T. S. Srivastava and T. Yonetani, Chem. Phys. Lett.,
mp > 300°C.
–7.80 (m, 8H, H-Ph), 7.79–7.57 (m, 12H, H-Ph).
δ
H (CDCl3) ca 8.70 (broad s, 8H, Hβ-pyrrole), 8.16
λ
max (CHCl3) /
nm 588, 551, 509, 420 (Soret band). MS (APPI–photospray(+),
AcOEt/CHCl3), m/z (% rel. int.) 878 (3), 877 (14), 876 (44), 875
(78) [isotope (M–Cl+AcOEt)+]; 850 (4), 849 (15), 848 (55), 847
(100) [isotope (M–Cl+OAc)H+]. MS (APPI–photospray(–),
AcOEt/CHCl3), m/z (% rel. int.) 908 (5), 907 (12), 906 (36), 905
(56) [isotope (M–Cl+2×OAc)–]; 885 (9), 884 (21), 883 (44),
882 (54), 881 (100) [isotope (M+OAc)–]; 848 (3), 847 (9), 846
(18) [isotope (M–Cl+OAc)–]. The molecular formula was
confirmed by comparing the theoretical and experimental
isotope patterns for the (M+OAc)– ion (C46H31N4ClO2Lu); it
was found to be identical within the experimental error
limits. 3: semicrystalline. δH (CDCl3) 8.61 (s, 8H, Hβ-pyrrole),
1976, 40, 456; (c) T. S. Srivastava, Bioinorg. Chem., 1978, 8,
61; (d) I. K. Shushkevich, S. S. Dvornikov, T. F. Kachura and K.
N. Solov'ev, J. Appl. Spectrosc., 1981, 35, 1109.
13 E. G. Ermolina, R. T. Kuznetsova, T. A. Solodova, E. N. Tel'mi-
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sakova and Y. V. Korovin, Dyes Pigments, 2013, 97, 209.
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2007, 251, 2386; (b) N. Andre´, T. B. Jensen, R. Scopelliti, D.
Imbert, M. Elhabiri, G. Hopfgartner, C. Piguet and J.-C. G.
Bünzli, Inorg. Chem., 2004, 43, 515; (c) M. M. Ayhan, A. Singh,
C. Hirel, A. G. Gürek, V. Ahsen, E. Jeanneau, I. Ledoux-Rak, J.
Zyss, Ch. Andraud and Y. Bretonnière, J. Am. Chem. Soc., 2012,
134, 3655.
15 (a) J.-H Fuhrhop and K. M. Smith, in Porphyrins and Metallo-
porphyrins, ed. K. M. Smith, Elsevier, Amsterdam, 1975, Cha-
pter H, pp. 757-861. (b) K. M. Kadish, K. M. Smith and R. Gui-
lard (eds.), Handbook of Porphyrin Science, World Scientific
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16 (a) S. Ostrowski and Y. K. Shim, Bull. Korean Chem. Soc., 2001,
22, 9; (b) S. Ostrowski, A. Mikus, Y. K. Shim, J.-Ch. Lee, E.-Y.
Seo, K.-I. Lee and M. Olejnik, Heterocycles, 2002, 57, 1615;
8.40–8.29, 8.25–8.04, and 7.79–7.57 (3×m, 16H, H-Ar). λmax
(CHCl3) / nm 586, 550, 513, 417 (Soret band). MS (APPI–
photospray(+), AcOEt), m/z (% rel. int.) 1037 (2), 1036 (8),
1035 (11) [isotope (M–Cl+ 2×AcOEt)+]; 1009 (5), 1008 (18),
1007 (31) [isotope (M–Cl+OAc +AcOEt)H+]; 950 (2), 949 (14),
948 (46), 947 (68) [isotope (M–Cl+AcOEt)+]; 922 (5), 921 (20),
920 (61), 919 (97) [isotope (M– Cl+OAc)H+]; 785 (9), 784 (13),
783 (40), 782 (67), 781 (68), 780 (100) [isotope (M–C6H4F–
F)+]. MS (APPI–photospray(–), AcOEt), m/z (% rel. int.) 1037
(3), 1036 (9), 1035 (19) [isotope (M–Cl+2×AcOEt)–]; 1010 (2),
1009 (8), 1008 (12) [isotope (M–Cl+AcOH+AcOEt)H–]; 979 (5),
978 (17), 977 (26) [isotope (M–Cl+2×OAc)–]); 860 (6), 859
(15), 858 (24) [isotope (M–HCl)–]; 783 (11), 782 (37), 781
(71), 780 (65), 779 (100) [isotope (M–C6H4F–HF)–]. The
molecular formula was confirmed by comparing the
theoretical and experimental isotope patterns for the (M–
HCl)– ion (C44H23N4F4Lu); it was found to be identical within
the experimental error limits. 4: mp > 300°C.
(part of AB, J 5.5 Hz, 2
Hβ-pyrrole), 8.92–8.83 (m, Hβ-
pyrrole), 8.65–8.57, 8.08–7.92, and 7.80–7.65 (3 m, H-Ar).
max (CHCl3) / nm 592, 553, 516, 422 (Soret band). MS (APPI–
δH (CDCl3) 9.11
(c) S. Ostrowski, D. Szerszeń and M. Ryszczuk, Synthesis, 2005
819; (d) S. Ostrowski and A. M. Raczko, Helv. Chim. Acta,
2005, 88, 974; (e) P. Wyrębek and S. Ostrowski, J. Porphyrins
Phthalocyanines, 2007, 11, 822; (f) S. Ostrowski and S. Grzyb,
Tetrahedron Lett., 2012, 53, 6355.
,
̴
×
×
λ
photospray(+), AcOEt/MeOH), m/z (% rel. int.) 923 (6), 922
(21), 921 (65), 920 (100) [isotope (M–Cl+AcOEt)+]; 877 (3),
876 (7), 875 (8), 874 (15) [isotope (M–Cl–NO2+AcOEt)+]; 871
(3), 870 (5), 869 (5), 868 (8) [isotope MH+]. The molecular for-
mula was confirmed by comparing the theoretical and experi-
mental isotope patterns for the (M–Cl+AcOEt)+ ion
(C48H35N5O4Lu); it was found to be identical within the experi-
mental error limits. 5: mp > 300°C. δH (CDCl3) 9.00–8.33 (m,
Hβ-pyrrole and H-Ar), 8.12–7.89 (m, H-Ar), 7.78–7.10 (m, H-
17 W. D. Horrocks Jr. and E. G. Hove, J. Am. Chem. Soc., 1978,
100, 4386.
18 Experimental details. For General – see ESI. Some more com-
plex porphyrin ligands were obtained according to known
procedures described in the previous literature: 5,10,15,20-
tetrakis(3-fluorophenyl)porphyrin,19 5-(4-nitrophenyl)-10,15,
20-triphenylporphyrin,20 5-[4-nitro-3-(toluene-4-sulphonyl-
methyl)phenyl]-10,15,20-triphenylporphyrin.21
Ar), ca 4.80 (broad s, CH2), ca 2.40 (broad s, CH3).
/
λmax (CHCl3)
nm 593, 552, 516, 424 (Soret band). MS (ESI(+),
Synthesis of [Lu-TPP]Cl in sulfolane in reflux. Typical proce-
dure. – meso-TPP (21.6 mg, 0.0351 mmol) and LuCl3
×
6H2O
AcOEt/MeOH), m/z (% rel. int.) 1179 (3), 1178 (4), 1177 (7),
1176 (12) [isotope (M–Cl+ 2×AcOEt)+]; 1091 (4), 1090 (18),
1089 (57), 1088 (100) [isotope (M–Cl+AcOEt)+]; 1002.7 (0.8),
1002.2 (1.3), 1001.7 (2.4), 1001.2 (5), 1000.7 (7), 1000.2 (6)
[isotope (M–Cl)22+]. HR-MS (ESI): calcd for C56H43N5O6SLu
(43.2 mg, 0.1109 mmol) in 4 mL of sulfolane were heated (un-
der argon) in reflux (285°C) in round-bottomed light-shielded
flask (10 mL), equipped with a reflux condenser, over a period
of 30–40 min (TLC monitoring; in turn: n-hexane, CHCl3, and
CHCl3/MeOH, 20:1). Then, the reaction mixture was cooled
to room temperature, 10 mL of CHCl3 was added, and it was
washed with water (20 mL) in a separatory funnel. The water
[(M–Cl+AcOEt)+]
– 1088.2342, found – 1088.2322. MS
(ESI(+), AcOCH(CH3)2/CH2Cl2), m/z (% rel. int.) 1207 (5), 1206
(11), 1205(20), 1204 (30) [isotope (M–Cl+2×AcOCH(CH3)2)+];
1106 (6), 1105 (10), 1104 (22), 1103 (65), 1102 (100) [isotope
(M–Cl+AcOCH(CH3)2)+]. HR-MS (ESI): calcd for C57H45N5O6SLu
[(M–Cl+AcOCH(CH3)2)+] – 1102.2498, found – 1102.2479.
phase was extracted with CHCl3 (3
× 2 mL) and the combined
organic layers were dried with anhydrous MgSO4. After eva-
porating the solvent, the column chromatography was per-
formed using gradient mixture as eluent (from n-hexane to 19 B. Łopuszyńska, K. Piechocka, A. Mikus, S. Ostrysz and S.
Ostrowski, Macroheterocycles, 2013, , 245.
6
4 | J. Name., 2012, 00, 1-3
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DOI: 10.1039/C6NJ02424F
Journal Name
COMMUNICATION
20 W. J. Kruper Jr., T. A. Chamberlin and M. Kochanny, J. Org.
Chem., 1989, 54, 2753.
21 S. Ostrowski, N. Urbańska and A. Mikus, Tetrahedron Lett.,
2003, 44, 4373.
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A convenient high-yielded method for preparation of
very attractive lutetium(III)–porphyrins was developed
(in sulfolane at reflux temperature, 0.5 h, up to 88%).