A3type phthalocyanine-based homoleptic lanthanide(III) double-decker π-radical complexes bearing functional hydroxy groups: Synthetic approach, spectral properties and electrochemical study

Article abstract of DOI:10.1002/ejic.201000511

The sandwich lanthanide(III) complexes ^BnO,BuPc₂Ln (^BnO,BuPc = 2-benzyloxy-9,10,16,17,23,24-hexa-n- butylphthalocyaninate; Ln = Eu, Lu) (1a, 1b) were obtained from [Ln(acac) ₃]·nH₂O and ^BnO,Bu

Full text of DOI:10.1002/ejic.201000511

FULL PAPER
DOI: 10.1002/ejic.201000511
A3B-Type Phthalocyanine-Based Homoleptic Lanthanide(III) Double-Decker
π-Radical Complexes Bearing Functional Hydroxy Groups:
Synthetic Approach, Spectral Properties and Electrochemical Study
Victor E. Pushkarev,*[a,b] Alexander Yu. Tolbin,[a] Nataliya E. Borisova,[b]
Stanislav A. Trashin,[a] and Larisa G. Tomilova*[a,b]
Keywords: Phthalocyanines / Lanthanides / Sandwich complexes / Double-decker complexes / Pi radicals
The sandwich lanthanide(III) complexes BnO,BuPc2Ln (BnO,BuPc ising structural building blocks and stable phenolic hydroxy
= 2-benzyloxy-9,10,16,17,23,24-hexa-n-butylphthalocyanin-
ate; Ln = Eu, Lu) (1a, 1b) were obtained from [Ln(acac)3]·
nH2O and BnO,BuPcH2 by heating these compounds in n-
hexadecanol, and then treating the reaction solution with
H2SO4 to yield the corresponding neutral double-decker
complexes HO,BuPc2Ln (HO,BuPc = 9,10,16,17,23,24-hexa-n-
butyl-2-hydroxyphthalocyaninate) (2a, 2b), which are prom-
group containing π-radical species. A combination of UV/
Vis/NIR, NMR spectroscopy, MALDI-TOF mass spectro-
metry, cyclic voltammetry and spectroelectrochemistry pro-
vided unambiguous characterization of the newly prepared
bis(phthalocyanines), and also allowed their stability and be-
havior in solution to be investigated.
thetic procedures available for such compounds are based
on the template complexation either of two different
phthalonitriles with a lanthanide salt[8a] or of phthaloni-
triles with the corresponding monophthalocyanines.[8b–8d]
Alternatively, the procedures involve direct interaction of a
half-sandwich REE compound, formed in situ, with lithium
phthalocyaninate,[8e] which usually give mixtures of prod-
ucts in comparatively low yields that are hard to separate.
In our recent work[9] we have reported the development
of effective synthetic pathways to A3B phthalocyanines and
their selective transformation to covalently bridged clam-
shell-type complexes. The accessibility of these clamshell-
type compounds allowed us to demonstrate the possibility
of obtaining novel sandwich-type structures through com-
plexation with Lu salt.[10]
In this paper we describe the development of an optimal
synthetic route to bis(phthalocyanines) bearing functional
OH groups, which can then be used as structural building
blocks. Moreover, the physicochemical and redox properties
of these compounds are of great interest since these mole-
cules represent stable π-radical species that contain phenolic
OH groups as peripheral substituents.
Introduction
Since their synthesis for the first time more than 40 years
ago[1] sandwich-type phthalocyanines of rare-earth elements
(REE) have become an important class of tetrapyrrolic co-
ordinating compounds, include several different types of
structures,[2] and have a wide range of applications.[3] Intro-
duction of functional groups on the periphery of these mo-
lecules allows them to be coupled with different surfaces
including carbon nanotubes[4] and also makes them promis-
ing building blocks for the creation of nanoscale structures
that are useful in multibit information storage,[5] gas sens-
ing,[6] nonlinear optics[7] and other advanced areas.
Controlling the number and location of functional
groups on the phthalocyanine–REE complexes requires the
synthesis of asymmetrically substituted derivatives, in par-
ticular, complexes with A3B-type ligands. To the best of our
knowledge, there have been no well-characterized homolep-
tic REE–phthalocyanine sandwich complexes containing
functionalized A3B ligands reported to date, although a few
examples of heteroleptic complexes are known.[8] The syn-
[a] Institute of Physiologically Active Compounds, Russian
Academy of Sciences,
142432 Chernogolovka, Moscow Region, Russian Federation
Fax: +7-496-524-9508
Results and Discussion
E-mail: pushkarev@org.chem.msu.ru
[b] Department of Chemistry, M. V. Lomonosov Moscow State
University,
Synthesis of Homoleptic Double-Decker Complexes 1 and 2
Treatment of the metal-free phthalocyanine HO,BuPcH2
with benzyl chloride in dimethylformamide in the presence
of sodium hydride at room temperature gave the protected
ligand BnO,BuPcH2 (Scheme 1) within 30 min.
119991 Moscow, Russian Federation
Fax: +7-495-939-0290
E-mail: tom@org.chem.msu.ru
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201000511.
View this journal online at
wileyonlinelibrary.com
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A3B-Type Phthalocyanine-Based Homoleptic Lanthanide(III) Complexes
Scheme 1. Synthesis of double-decker complexes.
The reaction of BnO,BuPcH2 with Ln(acac)3·nH2O (Ln = of BnO,BuPcH2 with a lutetium salt at 210 °C (Scheme 1,
Eu, Lu) in n-hexadecanol, a method that is similar to a pathway B) selectively yielded the double-decker complex
procedure developed earlier in our group[11] for the synthe- 1b. An increase in the reaction temperature favors the for-
sis of lanthanide(III) complexes based on symmetrical mation of triple-decker complexes, as observed in the case
2,3,9,10,16,17,23,24-octabutylphthalocyanine (BuPcH2), led of compound 1a. Treatment of complexes 1a and 1b with
to the selective formation of double-decker complexes 1a concentrated sulfuric acid followed by pouring into ice and
and 1b. An important feature of the synthesis technique re- precipitation gave the target bis(phthalocyanine) complexes
ported herein concerns the synthesis of europium complex 2a and 2b. Complex 2b was produced in a quantitative
1a, which was prepared by heating the starting reagents at yield, whereas in the case of 2a HO,BuPcH2 was also ob-
180 °C in the presence of lithium methoxide (Scheme 1, served in the product mixture, reflecting the lower stability
pathway A) instead of DBU that was required for the syn- of 2a with respect to 2b. Thus, this synthetic scheme af-
thetic procedure reported in ref.[11] This allowed the reac- forded compounds 2a and 2b in good overall yields
tion time to be decreased from 2–3 h to 20 min, while also (Table 1). It is worth mentioning that all attempts to obtain
generating a higher yield of the target compound. These 2 directly from HO,BuPcH2 were not successful, and led to
advantages that result from the use of lithium methoxide in the gradual thermal decomposition of the initial free-base
the synthetic procedure instead of DBU may derive from phthalocyanine even under an inert gas, which is also con-
the noncoordinating nature of the lithium methoxide: the sistent with the low thermal stability of 2; the control ex-
tendency of DBU to form coordinating bonds with the lan- periments confirmed this hypothesis (Footnote S1 in the
thanide ion of the intermediate half-sandwich mono- Supporting Information).
(phthalocyanine) compound[12] should create steric hin-
Table 1. Yields and high-resolution MALDI-TOF mass spectrome-
try data for complexes 1 and 2.
drance at the metal centre that prevents further complex-
ation. In addition, reduction of the reaction time appears
to be an essential factor that influences the product yield
because of the thermal lability of the benzyloxy substituents
in compounds 1. It is noteworthy that when the reaction
was carried out without basic additives the process selecti-
vity substantially decreases due to the formation of the cor-
Formula
Yield [%]
m/z [M]+[a]
1a
1b
2a
2b
C126H140N16O2Eu
C126H140N16O2Lu
C112H128N16O2Eu
C112H128N16O2Lu
81
78
71
98
2061.7041 (2062.0557)
2084.7595 (2085.0786)
1881.5466 (1881.9618)
1904.5760 (1904.9847)
responding triple-decker mixture. In contrast, complexation [a] Calculated values given in parentheses.
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V. E. Pushkarev, L. G. Tomilova et al.
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Newly prepared homoleptic double-decker complexes 1 Electronic Absorption Spectra
and 2 have been characterized by MALDI-TOF mass spec-
trometry, electronic absorption and 1H NMR spectroscopic
The UV/Vis spectroscopic study of bis(phthalocyanine)
techniques. The MALDI-TOF mass spectra of these com- complexes 1 and 2 confirms that they are neutral π-radical-
pounds (Table 1, Figures 1 and S1–S3 in the Supporting In- containing species. The spectra were recorded on C6H6
formation), with DCTB {2-[(2E)-3-(4-tert-butylphenyl)-2- solutions of the complexes, and the data are summarized in
methylprop-2-enylidene]malonitrile} as the matrix, revealed Table 2. Figure 2 displays the UV/Vis spectra of the hydroxy
intense molecular ion [M]+ peaks with characteristic iso- derivatives 2 that are characterized by split Soret bands in
topic patterns that are in good accordance with the simu- the 327–356 nm region, weaker π-radical bands at 471–
lated spectra. It is also noteworthy that no additional frag- 485 nm, and a strong single Q-band at 673–684 nm that has
mentation of the [M]+ ion was observed under laser ioniza- nicely resolved vibrational satellites. Furthermore, an ex-
tion with DCTB for compounds 1 that bear chemically la- pected hypsochromic shift of the absorption bands in the
bile benzyloxy groups (Figure 1), although spectra recorded spectrum for the Eu complex with respect to the bands in
with DHB (2,5-dihydroxybenzoic acid) as the matrix dis- the spectrum for the Lu complex is clearly observed,
played secondary ion peaks.
whereas the deprotection of the peripheral OH groups has
Figure 1. MALDI-TOF mass spectra of compounds 1a (a) and 2a (b) and isotopic patterns for the corresponding molecular ions (insets).
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A3B-Type Phthalocyanine-Based Homoleptic Lanthanide(III) Complexes
Figure 2. Electronic absorption spectra of compounds 2a and 2b in C6H6.
virtually no effect on the band positions, which reflects the ures 3, 4, S6–S13 and Table S2 in the Supporting Infor-
similar electron-donating properties of benzyloxy and hy- mation) were recorded at room temperature with the com-
droxy substituents (Table 2). Investigation of the transmit- plexes dissolved in a CDCl3/[D6]DMSO (1:1, v/v) mixture
tance spectra in the NIR region also revealed no difference in the presence of 1–2 vol.-% hydrazine hydrate, which re-
between the hydroxy and benzyloxy complexes, showing the duces the π-radical species to the corresponding dianions.
same positions for the red valence (RV) and intervalence
(IV) bands (Figures S4, S5 and Table S1 in the Supporting
Information). Note that certain spectral changes in the NIR
regions in the spectra of the Eu and Lu complexes are ob-
served, namely, a bathochromic shift of the RV band,
whereas the IV band shifts hypsochromically. Such changes
are in good accordance with previously published data in
the literature for HOMO–LUMO molecular orbital sub-
structure of bis(phtahlocyanine) sandwich complexes.[13]
The full assignment of NMR signals was made on a basis
of published data[11] for the symmetrically substituted com-
1
plexes BuPc2Ln (Ln = Eu, Lu) and H–1H COSY experi-
ments. Thus, in the spectrum of compound 1a (Figure 3)
the aromatic protons of the phthalocyanine rings HAr are
revealed as a sum of singlets at δ = 11 ppm. The peaks
associated with the α-HAr protons overlap with the HAr sig-
nal and have intercorrelated signals with the β-HAr protons
(Figure 4) that enabled their assignment, while the signal at
δ = 10.75 ppm is assigned to the αЈ-HAr protons. The sig-
nals in the δ = 7.5–8.5 ppm region are clearly due to the
aromatic protons of the benzyloxy substituent (HPh), and
their assignment was also provided by the 2D NMR spec-
trum (Figure 4). The CH2 protons of the benzyloxy groups
are revealed as signals at δ = 6.45 and 6.8 ppm and have
cross-peaks in the COSY spectrum; these peaks are as-
signed to the exo- and endo-protons, respectively, as the
exo-protons are subjected to a greater degree of deshielding
than the endo-protons, because they are closer to the para-
magnetic EuIII ion. The signals in the aliphatic region be-
longing to the butyl chain protons can be assigned clearly
from the COSY spectrum (Figure S6) and show a good cor-
Table 2. Electronic absorption data for double-decker complexes 1
and 2 in C6H6.
λmax [nm] (I/Imax
)
B (Soret)
π-Radical
Qvib
Q
1a 331 (0.980) 356 (0.852) 485 (0.251) 615 (0.344) 684 (1.000)
1b 327 (0.749) 351 (0.753) 471 (0.213) 606 (0.228) 673 (1.000)
2a 329 (0.917) 355 (0.776) 483 (0.257) 614 (0.330) 684 (1.000)
2b 327 (0.766) 351 (0.709) 471 (0.211) 607 (0.227) 673 (1.000)
NMR Spectra
relation with data obtained for the BuPc2Eu complex.[11]
A
During the last decades NMR spectroscopy has become
an important tool in the structural determination of sand-
wich-type bis(phthalocyanine) complexes as the difficulties
associated with radical extinction and insufficient solubility
to enable spectrum acquisition have been overcome. For the
freshly prepared double-decker compounds 1 and 2 that
were prepared as inseparable mixture of structural isomers,
similar approach was applied to fully assign the peaks in the
NMR spectrum of the lutetium complex 1b (Figures S7–
S9 in the Supporting Information); however, no additional
deshielding of the protons was observed, in contrast to 1a,
due to the diamagnetic nature of the LuIII ion.
The 1H NMR spectra of the double-decker complexes 2a
and for which it is impossible to form single crystals suit- and 2b are characterized by the disappearance of benzyloxy
able for X-ray analysis, the role of NMR spectroscopy is group signals (Figures S10–S13 and Table S2 in the Sup-
1
crucial. The H NMR spectra of complexes 1 and 2 (Fig- porting Information) that are present in the spectra for 1a
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V. E. Pushkarev, L. G. Tomilova et al.
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Figure 3. 1H NMR spectrum of compound 1a (aromatic region) in CDCl3/[D6]DMSO (1:1, v/v) with the addition of 1–2 vol.-%
N2H4·H2O; “ϫ” indicates signals from residual CHCl3.
Figure 4. 1H–1H COSY NMR spectrum of compound 1a (aromatic region) in CDCl3/[D6]DMSO (1:1, v/v) with the addition of 1–2 vol.-
% N2H4·H2O; “ϫ” indicates signals from residual CHCl3.
and 1b. The protons of the phthalocyanine core are slightly β-HAr proton signal demonstrated unexpected significant
shielded by 0.1–0.2 ppm indicating the similar electron-do- deshielding compared to the corresponding peak in the
nating properties of the benzyloxy and hydroxy substitu- spectrum of the benzyloxy-protected compound 1a, and
ents. However, in the case of the europium complex 2a the also revealed the dependence of the chemical shift and peak
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A3B-Type Phthalocyanine-Based Homoleptic Lanthanide(III) Complexes
resolution on the solvent system used for data collections
(Figures S10, S10a, S10b and Table S3 in the Supporting
Information).
The NMR data can be rationalized by taking into ac-
count two processes competing in solution, namely, the
dissociation of the hydroxy groups in 2a and 2b and the
reduction of the complexes to negatively charged diamag-
netic species. The first process seems to dominate for 2a
resulting in the delocalization of negative charge over the
bis(phthalocyanine) moiety, while the remaining radical
moves to the oxygen atom and, consequently, may influence
the nearby protons. Furthermore, the signal of the β-pro-
tons should reveal a greater downfield shift than that of the
α-protons, since they are strongly influenced by the core
macrocyclic π-conjugated system. In turn, due to the
smaller Lu ionic radius compared to the Eu ion, 2b is char-
acterized by a closer ligand arrangement then 2a. This en-
hances the π–π interactions facilitating radical delocaliza-
tion and, consequently, results in the lower acidity of the
hydroxy groups that assists the reduction process men-
tioned above. Thus, direct radical extinction takes place for
2b, which causes no significant changes in chemical shifts
of the signals of the remaining protons compared with cor-
responding peaks in the spectrum of benzyloxy-protected
1b. Nevertheless, these statements require more detailed
physicochemical studies, which lie beyond the scope of the
current investigation.
Electrochemistry
The redox properties of bis(phthalocyanine) complexes 1
and 2 were studied in o-dichlorobenzene (DCB) by cyclic
voltammetry (CV) with a platinum disk electrode in the po-
tential range from –2.4 to 1.1 V (vs. Fc/Fc+). The com-
pounds underwent up to three quasi-reversible (ip ≈ v1/2
,
∆Ep ≈ 0.1 V) reduction processes, labeled R1, R2, and R3,
as well as one reversible and one irreversible, i.e. no back
peak was observed, oxidation processes labeled Ox1 and
Ox2, respectively. Table 3 lists the half-wave potentials
(E1/2), and Figure 5 shows the CV curves for the reversible
couples.
Table 3. Half-wave potentials for 1 and 2 in DCB.
E1/2 [V] (vs. Fc/Fc+)
[a]
Figure 5. Cyclic voltammograms for reversible couples in DCB
R3
R2
R1
Ox1
Ox2
containing 0.2  [BuN4][BF4], with scan rate = 0.20 Vs–1: (A) 1a
(
(
BnO,BuPc2Eu); (B) 2a (HO,BuPc2Eu); (C) 1b (BnO,BuPc2Lu); (D) 2b
1a
1b
2a
2b
–1.76
–1.74
–2.10
–2.12
–0.57
–0.66
–0.57
–0.67
–0.15
–0.23
–0.20
–0.29
1.02
1.05
0.76
0.86
HO,BuPc2Lu).
–2.16
of 1, and especially the gaps between the first two oxidation
[a] Approximate values.
and reduction peaks lie close to the literature values[14,15]
The negative shift of the redox potentials for the Eu (a) for similar phthalocyanine complexes.
with respect to the Lu (b) complexes is in good agreement
Debenzylation of complexes 1 to generate the corre-
with previous reports,[14,15] and can be explained by the in- sponding complexes 2 results in a cathodic shift of the Ox1,
creased interaction between the phthalocyanine rings due Ox2 and R1, R2 peaks by 50–60 mV, 200–250 mV and 5–
to the distance between the macrocycles shortening along 15 mV, 340–380 mV, respectively. This shift indicates a no-
with a decreasing REE ionic radius. The redox potentials ticeable destabilization of complexes 2 compared to com-
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V. E. Pushkarev, L. G. Tomilova et al.
FULL PAPER
plexes 1, since less energy is required for the oxidation and could remain undetectable due to the poor electrochemical
more for the reduction processes. A similar effect has been reversibility of R2 due to the presence of the hydroxy
noted previously[14] for phthalocyanines with electron-do- groups.
nating peripheral groups, and an opposite effect has been
mentioned[16] in the case of acceptor substituents. The shift
Spectroelectrochemistry
of the R2 peak by ca. 350 mV in the voltammograms of
complexes 2 compared to the corresponding peak in the
voltammograms of 1 is stronger than expected from the de-
benzylation. The electron-donating effect of the hydroxy
groups can be enhanced by the solvent and electrolyte that
can induce polarization along the H–O bond, apparently
leading to the formation of ionic pairs, thus increasing the
negative charge on the oxygen atoms. However, taking into
account the completely identical UV/Vis/NIR spectra of the
initial neutral forms of 1 and 2, and also the very similar
UV/Vis spectra of both the one-electron-reduced and -oxid-
ized forms, as described in the next section, the redox cou-
ple labeled as R2 for 2 could be considered as an analogue
of the R3 reduction observed for 1, whereas the real R2
It is well known that phthalocyanines reveal strong
changes in their electronic absorption spectra while under-
going oxidation and reduction, providing opportunities for
different applications. UV/Vis spectral changes for complex
2a (HO,BuPc2Eu) during controlled potential electrolysis at
+0.15 and –0.85 V (Figure 6) reflect the transformation of
the neutral double-decker phthalocyanine to the one-elec-
tron-oxidized and -reduced forms,[15,17] respectively. The
data for 1a (BnO,BuPc2Eu) obtained under the same condi-
tions gave identical band positions for all redox states
(Table 4).
Table 4. Electronic absorption data for the neutral, oxidized, and
reduced forms of 1a and 2a.
State
λmax [nm]
B (Soret) π-Radical Qvib
Q
1a
2a
[
BnO,BuPc2Eu]0 331, 357
492
510
618
649
687
732
[
[
BnO,BuPc2Eu]+ 328, 372
BnO,BuPc2Eu]–
347
598[a] 645, 693sh
[
[
[
HO,BuPc2Eu]0 332, 357
HO,BuPc2Eu]+ 331, 371
491
508
618
649
687
734
HO,BuPc2Eu]–
346
595[a] 645, 691sh
[a] Approximate position.
Thus, the removal of the benzyloxy protecting group in
1 that leads to the hydroxy-substituted complexes 2 does
not noticeably change the distances between the energy
levels, at least for those that give rise to bands found in the
UV/Vis spectra, but the energy of the whole system is prob-
ably increased since considerable cathodic shifts of the re-
dox potentials were observed. After complete electrolysis,
the initial neutral forms of the phthalocyanines were fully
recovered by back oxidation/reduction. This demonstrates
the good stability of the oxidized and reduced forms in
solution, also implying that the double-decker complexes
obtained are promising electrochromic materials.
Conclusions
Starting from 2-benzyloxy-9,10,16,17,23,24-hexa-n-but-
ylphthalocyanine we have prepared a series of A3B-type
ligand based homoleptic REE–bis(phthalocyanine) com-
plexes, including hydroxy-substituted derivatives, which
are inaccessible directly from the corresponding
9,10,16,17,23,24-hexa-n-butyl-2-hydroxyphthalocyanine li-
gand. The phenolic hydroxy group containing complexes
were found to be stable π-radicals as well as conventional
bis(phthalocyanines), which is unambiguously supported by
spectral as well as electrochemical data. An investigation of
the application of these complexes as synthetic building
blocks is currently underway and will be discussed else-
where.
Figure 6. UV/Vis spectral changes for 2a (HO,BuPc2Eu) in DCB con-
taining 0.4  [BuN4][BF4] during (A) controlled potential oxidation
(+0.15 V) and (B) reduction (–0.85 V).
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A3B-Type Phthalocyanine-Based Homoleptic Lanthanide(III) Complexes
wall of the cell to avoid it interfering with the light beam. A Luggin
Experimental Section
capillary and a capillary for argon purging were placed close to the
working electrode. A reference Ag|AgCl electrode was connected
to the cell through a salt bridge. A Pt-counter electrode with a
surface area larger than the area of the working electrode was
placed in a separate compartment and connected to the working
space through a glass tube fitted with a frit. Sample solutions con-
tained 0.4 moldm–3 of [Bu4N][BF4] and 0.01 mmoldm–3 of sample.
Pure argon was passed through the sample solution to remove oxy-
gen and to stir the solution gently during the electrolysis process.
General: Column chromatography was carried out on silica gel col-
umns (Merck, Silicagel 60, 0.040–0.063 mm) with the eluents indi-
cated. Preparative TLC was performed with flexible plates: Merck
Silica Gel 60, Merck Silica Gel 60 F254, and Merck Aluminium
Oxide F254 neutral. Gel permeation chromatography was ac-
complished on polymeric support Bio-Beads S-X1 (BIORAD) with
C6H6 as the eluent. The electrolyte for voltammetric and spectro-
electrochemical studies, [Bu4N][BF4] (Sigma–Aldrich), was recrys-
tallized twice from ethyl acetate/hexane (9:1, v/v) and dried under
vacuum at 70 °C, the o-dichlorobenzene (DCB, 99%, Sigma–Ald-
rich, HPLC-grade) for these studies was used as received. All other
reagents and solvents were obtained or distilled according to stan-
dard procedures. The compounds [M(acac)3]·nH2O,[18] 4,5-dibu-
tylphthalonitrile[19] and 4-benzyloxyphthalonitrile[9a] were prepared
according to literature procedures. The salts [M(acac)3]·nH2O and
Mg(OAc)2·4H2O were dried immediately before use in vacuo, in a
desiccator, at 50 °C for 5 h and at 110 °C for 10 h, respectively. The
BuPcH2 ligand as well as the corresponding magnesium complex
BuPcMg were obtained as by-products during the synthesis of
HO,BuPcH2, and had spectral characteristics that are identical to
published data.[11,20] All the reactions were monitored by TLC and
UV/Vis and were continued until complete disappearance of start-
ing reagents was observed, unless otherwise specified.
Preparation of [HO,BuPcMg]: A mixture of 4,5-dibutylphthalonitrile
(547.2 mg, 2.28 mmol), 4-benzyloxyphthalonitrile (88.9 mg,
0.38 mmol) and lithium methoxide (187.7 mg, 4.94 mmol) in
isoamyl alcohol (15 mL) was heated under reflux for about 3 h.
The solution was cooled to room temperature and concentrated
under reduced pressure. The residue was washed with MeOH (3ϫ
50 mL), dried at 50 °C for 1 h, then dissolved in concentrated
H2SO4 and poured onto ice. The resulting precipitate was filtered
off, washed with water to obtain a neutral pH, and dried at 80 °C
for 2 h. The obtained solid powder (254 mg, and according to
MALDI-TOF spectrometry a mixture of HO,BuPcH2 and BuPcH2,
which was poorly soluble and hard to separate) was suspended in
DCB (10 mL), then DBU (0.329 mL, 1.33 mmol) and Mg(OAc)2·
4H2O (244 mg, 1.14 mmol) were added, and the mixture was then
kept under reflux for 2 h. The resulting solution was concentrated
under reduced pressure, and 50 mL of MeOH was subsequently
added. The precipitate formed after 2 h was filtered off. The mother
liquor was treated with acetic acid to obtain a neutral pH, and
another fine precipitate formed that according to MALDI-TOF
was pure HO,BuPcMg. Both precipitates were washed with boiling
80% aqueous MeOH (3ϫ 50 mL), filtered, and dried in vacuo. The
first precipitate (which according to MALDI-TOF spectrometry
was a mixture of HO,BuPcMg and BuPcMg) was dissolved in CHCl3
and subjected to chromatography on silica gel. The by-product
BuPcMg was separated from the mixture with CHCl3/pyridine
(100:1) as the eluent, and then the column was eluted with CHCl3/
Py (20:1) to isolate the HO,BuPcMg complex, the solvent evapo-
rated, and the residue dried in vacuo. The total reaction yield for
Electronic absorption (UV/Vis) spectra were recorded with a Ther-
moSpectronic Helios-α spectrophotometer with 0.5 cm quartz cells
with the samples dissolved in C6H6, CHCl3, CCl4 or DCB. UV/
Vis/NIR measurements were made with a Hitachi-230 instrument
with 0.5 cm quartz cells with the samples dissolved in CCl4.
MALDI-TOF mass spectra were taken with a VISION-2000 mass
spectrometer with 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-
enylidene]malonitrile (DCTB) or 2,5-dihydroxybenzoic acid (DHB)
as the matrix. High-resolution MALDI mass spectra were recorded
with a Bruker ULTRAFLEX II TOF/TOF instrument with DCTB
1
1
as the matrix. H NMR and H–1H COSY spectra were recorded
with a Bruker AVANCE 400 spectrometer (400.13 MHz) with the
initial ligand samples dissolved in [D8]THF. The complex samples
were dissolved in a CDCl3/[D6]DMSO (1:1, v/v) mixture to which
N2H4·H2O (1–2 vol.-%) was added at 20 °C, unless otherwise speci-
fied. Chemical shifts are given in ppm relative to SiMe4. Coupling
constants J are given in Hz. FT-IR spectra were recorded on KBr-
matrix pellets with a Nicolet NEXUS IR-FURJE spectrometer
with a resolution of 2 cm–1.
1
HO,BuPcMg was 158.8 mg (47%). H NMR ([D8]THF): δ = 8.64–
9.33 (m, 9 H, Pc-H), 3.95 (br. t, J = 7.3 Hz, 12 H, α-CH2), 1.95–
2.12 (m, 12 H, β-CH2), 1.52–1.64 (m, 12 H, γ-CH2), 1.13 (br. t, J
= 7.3 Hz, 18 H, CH ) ppm. FT-IR (KBr): ν = 3220–3450 (OH)
˜
3
cm–1. UV/Vis (C6H6): λmax (I/Imax) = 355 (0.868), 627 (0.332), 688
(1.000) nm. MS (MALDI-TOF, DHB): calcd. for C56H65N8OMg
[M + H]+ 889.5; found 889.1.
Electrochemical measurements were carried out with an IPC-Pro
potentiostat (Econix, Russia). Cyclic voltammetry (CV) was per-
formed in a conventional three-electrode cell with a Pt-disk
(2.0 mm in diameter) working and Pt-foil counter electrodes. The
Ag|AgCl reference electrode was connected to the solution through
a salt bridge and a Luggin capillary, the tip of which was placed
close to the working electrode. The junction potentials were cor-
rected for by a ferrocenium+/ferrocene (Fc+/Fc) couple. The sample
(0.1–0.5 mmoldm–3) was dissolved in a 0.2 moldm–3 solution of
[Bu4N][BF4] in DCB, the solution was purged with argon for
20 min before measurements were taken. The open circuit potential
of the working electrode when immersed in the phthalocyanine
solutions was approximately –0.3 V. The scan rate was varied from
0.05 to 1.00 Vs–1. All measurements were performed at ambient
temperature (22Ϯ1 °C).
Preparation of [HO,BuPcH2]: The magnesium complex HO,BuPcMg
(25 mg, 0.028 mmol) was dissolved in concentrated H2SO4 and kept
for 5 min, then poured onto ice. The precipitate was filtered,
washed consecutively with H2O, to obtain a neutral pH, and 80%
aqueous MeOH (3ϫ 20 mL), and dried in vacuo. Yield 22 mg
(98%). 1H NMR ([D8]THF): δ = 8.73–9.24 (m, 9 H, Pc-H), 3.86
(br. t, J = 7.3 Hz, 12 H, α-CH2), 2.05–2.19 (m, 12 H, β-CH2), 1.54–
1.66 (m, 12 H, γ-CH2), 1.19 (br. t, J = 7.3 Hz, 18 H, CH3) ppm.
FT-IR (KBr): ν = 3210–3400 (OH) cm–1. UV/Vis (C H ): λ
˜
6
6
max
(I/Imax) = 347 (0.757), 614 sh (0.348), 649 (0.523), 669 (0.934), 705
(1.000) nm. MS (MALDI-TOF, DHB): calcd. for C56H66N8O
[M]+ 866.5; found 866.2.
Preparation of [BnO,BuPcH2]: NaH (10 mg, 0.417 mmol) was added
to a solution of HO,BuPcH2 (72 mg, 0.083 mmol) in DMF (3 mL),
and the mixture was stirred under sonication at ambient tempera-
ture for 30 min. After that, benzyl chloride (0.04 mL, 0.348 mmol)
was added, and stirring was continued for another 1 h. The solu-
Spectroelectrochemical experiments were performed with a quartz
electrochemical cell composed of three separated compartments.
The rectangular compartment with a path length of 9.3 mm con-
tained a Pt-net working electrode, which was placed near the side-
Eur. J. Inorg. Chem. 2010, 5254–5262
© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
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V. E. Pushkarev, L. G. Tomilova et al.
FULL PAPER
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tion was treated with H2O (10 mL), a precipitate formed, which
was filtered and washed consecutively with H2O (3ϫ 30 mL) and
MeOH (2ϫ 30 mL). Yield 65 mg (82%). UV/Vis (C6H6): λmax
(I/Imax) = 348 (0.690), 614sh (0.283), 650 (0.455), 670 (0.889), 706
(1.000) nm. MS (MALDI-TOF, DHB): calcd. for C63H72N8O
[M]+ 956.6, [M – Bn]+ 865.5; found 956.5, 865.5.
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ligand BnO,BuPcH2 (25 mg, 0.026 mmol), MeOLi (3 mg,
0.078 mmol), [Eu(acac)3]·3H2O (6.5 mg, 0.013 mmol) and 100 mg
of n-hexadecanol (cetyl alcohol) was heated under argon to 180 °C
for 20 min (Scheme 1, pathway A). In the same fashion, a mixture
of BnO,BuPcH2 (25 mg, 0.026 mmol), [Lu(acac)3]·3H2O (6.8 mg,
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insoluble components were filtered off, and the solvents evapo-
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(4ϫ 30 mL) and dried in vacuo. The greenish solids that were ob-
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chromatography from which the green bands containing the target
double-decker complexes were collected.
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concentrated H2SO4 (2 mL) and immediately poured onto ice. The
precipitates were filtered, washed consecutively with H2O to obtain
a neutral pH and 80% aqueous MeOH (3ϫ 30 mL), and then dried
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The reaction yields for compounds 1 and 2 are given in Table 1.
Supporting Information (see footnote on the first page of this arti-
cle): MALDI-TOF and HR mass spectra, UV/Vis/NIR spectra and
data, 1H and 1H–1H COSY NMR spectra and data for the double-
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We thank Dr. Natalia V. Pashkova and Dr. Ivan A. Belogorokhov
for recording the NIR spectra of complexes 1 and 2. Financial
support from the Russian Foundation for Basic Research (Grant
No. 08-03-00753) and the Program for Fundamental Research of
the Presidium of the Russian Academy of Sciences (“Development
of Synthetic Methods for Chemical Compounds and Creation of
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Received: May 8, 2010
Published Online: October 4, 2010
5262
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Eur. J. Inorg. Chem. 2010, 5254–5262