Iron-ligand coordination in tandem radical cyclizations: Synthesis of benzo[b]thiophenes by a one-pot reaction of iron 1,3-diketone complexes with 2-thiosalicylic acids

Article abstract of DOI:10.1002/chem.201100377

Iron-the mediator: 1,3-Diketone ligands coordinated to iron undergo unprecedented tandem reactions with 2-thiosalicylic acids to give 2-substituted 3-hydroxylbenzo[b]thiophenes in up to 98 % yield. A similar reaction with 2-mercaptonicotinic acid gave a thieno[2,3-b]pyridine derivative in 72 % yield (see scheme). A mechanism involving redox transformation and tandem radical cyclization of the coordinated ligands is proposed. Copyright

Full text of DOI:10.1002/chem.201100377

COMMUNICATION
DOI: 10.1002/chem.201100377
Iron–Ligand Coordination in Tandem Radical Cyclizations: Synthesis of
Benzo[b]thiophenes by a One-pot Reaction of Iron 1,3-Diketone Complexes
with 2-Thiosalicylic Acids
Sharon Lai-Fung Chan, Kam-Hung Low,* Chen Yang, Samantha Hui-Fung Cheung, and
Chi-Ming Che*[a]
Metal–ligand coordination endows the coordinated li-
gands with intriguing reactivities toward nucleophilic or
electrophilic attacks and/or redox transformations;[1] this
relies on the Lewis acidity and/or redox properties of metal
ions and can be harnessed for the synthesis of complex or-
ganic compounds.[1b] Of particular importance is the iron–
ligand coordination with applications in organic synthesis, in
view of the recent surge of interest in iron-catalyzed/mediat-
ed organic reactions.[2] Reasons for this are the natural
abundance and biocompatibility of iron, both of which are
essential to the development of sustainable chemical cataly-
sis.
dents in the chemistry of metal complexes of 1,3-diketones,
a family of coordination compounds that have received nu-
merous attention.[1,6]
Our initial finding presented herein came from a hydro-
thermal reaction of FeACHTNUGTRNEUNG(acac)3 (1A; acac=acetylacetonate)
with 2-thiosalicylic acid (2a, 2 equiv) in ethylene glycol
(EG) at 1208C for 12 h; this unexpectedly afforded FeII
complex 3, which contains coordinated benzo[b]thiophene
derivatives (Scheme 1). A reaction of 1B with 2a led to the
We report an unexpected tandem reaction of iron-bound
1,3-diketone ligands with 2-thiosalicylic acids to selectively
afford 2,3-disubstituted benzo[b]thiophenes. This reaction is
likely to proceed by an iron-mediated tandem radical cycli-
zation pathway. Benzo[b]thiophene derivatives have applica-
tions in material science and the pharmaceutical industry,
with the 2,3-disubstituted benzo[b]thiophene core as a key
structural unit in pharmaceutical drugs, such as Raloxifene.[3]
Whereas various methods for the synthesis of benzo[b]thio-
phenes, including metal-catalyzed cyclization, are known,[3a]
only a few use 1,3-diketones as precursors. A recently re-
ported synthesis of benzo[b]thiophenes from 1,3-diketones
through tandem reactions requires dithiodibenzoyl chlori-
de[4a] or 2-(chlorosulfanyl)benzoyl chloride.[4b] Application of
iron-mediated/catalyzed cyclization in benzo[b]thiophene
synthesis constitutes a challenge. To the best of our knowl-
edge, iron-mediated tandem radical cyclizations are sparse[5]
and the formation of benzo[b]thiophenes through a tandem
reaction of coordinated 1,3-diketone ligands has no prece-
Scheme 1. The unexpected syntheses of FeII- and FeIII-complexes 3 and 4
from hydrothermal reactions.
isolation of FeIII complex 4 (Scheme 1). Complex 3 has been
structurally characterized by X-ray diffraction analysis[7]
À
À
(Figure 1) and the Fe O2 and Fe O1 distances were deter-
mined to be 2.039(4) and 2.074(4) ꢀ, respectively, compara-
[a] Dr. S. L.-F. Chan, Dr. K.-H. Low, C. Yang, S. H.-F. Cheung,
Prof. C.-M. Che
State Key Laboratory on Synthetic Chemistry
Department of Chemistry
and Open Laboratory of Chemical Biology
of the Institute of Molecular Technology
for Drug Discovery and Synthesis
The University of Hong Kong, Pokfulam Road (Hong Kong)
Fax : (+852)2857-1586
E-mail: cmche@hku.hk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100377.
Figure 1. ORTEP drawing for 3 with omission of hydrogen atoms (ther-
mal ellipsoid probability level: 30%).
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II
À
Table 1. The one-pot reaction of iron 1,3-diketone complexes 1B–1J with
2a to afford 2-substituted 3-hydroxybenzo[b]thiophenes 5.
ble to the corresponding Fe O distances (2.046–2.057 ꢀ) in
[Fe(CF3COCHCOCF3)2A
CTHUNGTRENNUNG
was also determined, but the data were not of a sufficiently
high quality (see Figure S1 in the Supporting Information).
The magnetic susceptibility of 3 (5.67 mB) reveals a high-spin
FeII electronic configuration. Complexes 3 and 4 constitute a
rare type of metal complexes of 1,3-diketones integrated
into the benzo[b]thiophene core. We could find no other ex-
amples of structurally characterized metal complexes of this
type in the literature.[6]
We conceived that the reaction of 1A or 1B with 2a to
give 3 or 4, involving an iron-mediated cyclization to gener-
ate the benzo[b]thiophene core, could be developed into a
synthetically useful one-pot reaction upon treatment of the
in situ formed 3 or 4 with aqueous HCl to release the coor-
dinated benzo[b]thiophene ligands. Remarkably, such a one-
pot reaction starting from treatment of 1A with 2a (1 equiv)
in EG at 1208C for 4 h led to the isolation of 2-acetyl-3-hy-
droxybenzo[b]thiophene (5Aa) in 97% yield based on 2a
(Scheme 2). When the solvent was changed from EG to a
Entry
Complex 1
R1
Product
Yield [%]
72
R2
1
2
3
4
5
6
1B
1B’
1C
1D
1E
1F
CF3
5Ba
5Ba
5Aa
23
<5
Me
CF3
CF3
CF3
CF3
5Ca
5Da
5Ea
5Fa
77
64
39
31
7
8
1G
1H
CF3
CF3
5Ga
5Ha
81
76
9
1I
CF3
CF3
5Ia
47
98
10
1J
Me
5Aa
47% yield, entry 9, Table 1). The one-pot reaction of 1J
with 2a afforded 5Aa in 98% isolated yield (entry 10,
Table 1).
The substituted 2-thiosalicylic acids 2b–2e reacted with
complex 1A to give the multisubstituted benzo[b]thiophenes
5Ab–5Ae (Scheme 3). These products were isolated in
62–65% yields for 2b and 2c with electron-donating OMe or
Me groups and in 90–93% yields for 2c and 2e with elec-
tron-withdrawing Cl or F groups.
3-Mercaptonaphthalene-2-carboxylic acid (7) underwent
similar reactions with complexes 1B, 1C, 1E, and 1I, afford-
ing the corresponding disubstituted naphthoACHTNUTRGNE[NUG 2,3-b]thio-
Scheme 2. Synthesis of 2,3-disubstituted benzo[b]thiophene 5Aa and tri-
ketone 6 from 1A and 2a.
mixture of EG/water (1:1), the yield of 5Aa was not signifi-
cantly reduced, indicating the compatibility of the reaction
with moisture. When the reaction was performed at 788C
with EtOH as solvent, the related triketone product 6 was
isolated in 53% yield. Neither 5Aa nor 6 was detected from
phenes (8) in up to 95% yield (Table 2). We also examined
reactions of H
ditions.
ACHTUNGTRENNUNG(acac) or NaCAHTUNGTERN(NUGN acac) with 2a under similar con-
We then extended the one-pot reaction of 1A and 2a to
iron 1,3-diketone complexes 1B–1J and obtained a series of
2-substituted
3-hydroxybenzo[b]thiophenes
5Aa–5Ia
(Table 1). Complex 1B with phenyl and CF3 groups gave
5Ba in 72% yield (entry 1, Table 1). A Me instead of the
CF3 substituent in 1B led to the formation of a mixture of
5Ba and 5Aa (entry 2, Table 1). For complexes 1C–1H with
aryl (naphthyl or substituted phenyl) and CF3 groups, 5
were isolated in 64–81% yields (entries 3, 4, 7, 8, Table 1),
except when the aryl group contained an electron-withdraw-
ing pCl or pCF3 substituent (entries 5, 6, Table 1). Thienyl
groups in complex 1I could be tolerated in the reaction, af-
fording 5Ia that contains two thiophene rings (isolated in
Scheme 3. Cyclization reactions with substituted 2-thiosalicylic acids.
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Iron-Mediated Benzothiophene Formation
COMMUNICATION
Table 2. One-pot reactions of iron 1,3-diketone complexes 1B, 1C, 1E, 1I
with 7 to afford disubstituted naphthoACTHNUTRGNEUNG[2,3-b]thiophenes 8.
Entry
Complex 1
Product
Yield [%]
R1
R2
1
2
3
4
1B
1C
1E
1I
CF3
8B
8C
8E
8I
90
80
74
95
CF3
CF3
CF3
a similar one-pot reaction of complex 1A with 2-mercaptoni-
cotinic acid (9). From this reaction, the product 10A with a
pharmaceutically attractive thieno
isolated in 72% yield (Scheme 4).
[2,3-b]pyridine core[9] was
ACHTUNGTRENNUNG
Scheme 5. Proposed mechanism for the benzo[b]thiophene ring forma-
tion.
mation of a mixture of 5Ba and 5Aa for 1B’ (Table 1) can
be explained by a competitive 1,3-acyl shift of acetyl and
benzoyl groups. 5) Fe(CF3COCHCOtBu)3 and 2a in the one-
pot reaction did not afford the corresponding product 5, as
the bulky tBu group would disfavor the nucleophilic attack
to form II. 6) Complexes 1E and 1F, which have electron-
withdrawing pCl or pCF3 groups and are less prone to un-
dergo nucleophilic attack to form II, gave products 5 in rela-
tively low yields (Table 1). 7) Replacement of the SH group
in 2a with OH or NH2 groups did not result in similar
tandem reactions.
Scheme 4. Synthesis of 2,3-disubstituted thienoACTHUNRTGNEUNG[2,3-b]pyridine.
A proposed mechanism for the formation of 5 from 1 and
2 via intermediates I–V is depicted in Scheme 5 with 1A and
2a as examples. This tandem reaction could initially gener-
ate I upon coordination of 2a through the thiolate group,
followed by condensation of the 1,3-diketone with benzoic
acid to generate II and its enol form, III. Oxidation of III,
by FeIII and trace amount of peroxide in the solvent (EG) is
likely to generate the radical intermediate IV, which could
undergo cyclization to give V with ligand 6, and FeIII is re-
duced to FeII. After detachment, compound 6 would under-
go 1,3-acyl shift and hydrolysis to give 5Aa, as reported in
the literature.[4] This proposed mechanism is supported by
the following evidence: 1) Compound 5Aa was not obtained
from the reaction of 2a with the substitutionally inert Ru-
To study the effect of peroxide on the cyclization reaction,
we examined the reaction of 2a with PhC(O)OOC(O)Ph
(1 equiv) in the presence of 1A (1 equiv), which gave 5Aa in
81% yield (Scheme 6). When 1A was replaced by NaACHTUNGTRENNUNG(acac)
(3 equiv), 5Aa was formed as a minor product in only 23%
yield, and the major product was a disulfide derived from 2a
(35%). Interestingly, a reaction with 0.5 equivalents of 1A
A
E
(acac)2, Zn
E
(acac)2,
in the presence of Na
80% yield (Scheme 6).
ACHTUNGTRNE(NUNG acac) (1.5 equiv) afforded 5Aa in
U
ACHTUNGTRENNUNG
A
We have applied the iron-mediated tandem reaction to
the synthesis of tetra- and pentacyclic compounds. A one-
pot reaction of complex 1G with 2a, involving in situ genera-
tion, also reacted with 2a to give 5Aa, albeit in 16–26%
yields. 3) 5Aa was not detected when the reaction was con-
ducted in air, thus disfavoring oxidation of III to IV by O2.
4) Products 5 obtained for 1B–1J (Table 1) result from the
1,3-acyl shift of the CF3CO group instead of the R1CO
(R1 =aryl) group, consistent with the higher electrophilicity
expected for the carbonyl C atom in CF3CO; also, the for-
1
tion of 5Ga (as revealed by H NMR measurements) and
subsequent treatment with tBuOK, resulted in the isolation
of the tetracyclic product 11 (compounds with such a tetra-
cyclic core have been studied as estrogen receptor b (ERb)
selective ligands)[10] in 56% yield (Scheme 7). A similar re-
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K.-H. Low, C.-M. Che et al.
Scheme 6. Formation of 5Aa in the presence of peroxide.
Scheme 8. Cyclization reactions with FeCl3 as starting material.
these neutral, air-stable, and highly phosphorescent Pt com-
plexes have a potential application as the emissive dopant in
organic light-emitting diodes. In literature, examples on cy-
clometalated Pt complexes with O O ligands, other than
acac or substituted acac systems, are sparse.[11] The 2-acyl-3-
hydroxylbenzo[b]thiophenes can serve as bidentate ligand
systems analogue to acac.[12] Complexes 13 and 14 with the
deprotonated phenylpyridine (ppy) ligand and deprotonated
5Aa (for 13) and 5Ha (for 14) as the O O ligand were pre-
pared in 64% and 50% yields, respectively, by adapting lit-
erature procedures.[11a] These two complexes have been
characterized by spectroscopic methods.[13] Crystals of 13
were obtained by diffusion of diethyl ether into a dichloro-
methane solution and characterized by X-ray crystallogra-
phy (Figure 2).[7] The complex has a square planar geometry
and the pyridine ring is trans to the O2 on the benzo[b]thio-
II
II
II
À
À
À
phene with Pt N, Pt O1, and Pt O2 distances of
1.992(4), 2.098(2), and 2.002(3) ꢀ, respectively, comparable
to the corresponding Pt N (1.983(5)–2.006(6) ꢀ), Pt O1
(2.064(4)–2.083(4) ꢀ), and Pt O2 (1.990(4)–1.998(4) ꢀ)
II
II
À
À
II
À
Scheme 7. One-pot formation of tetracyclic 11 and pentacyclic 12.
distances in [Pt
G
(dpm)] (thpy=2-(2’thienyl)pyridine,
Hdpm=dipivaloylmethane).[11a]
action with 7 gave the new pentacyclic compound 12, which
was isolated in 32% yield (Scheme 7).
Note that the one-pot reaction can be performed directly
with FeCl3, 1,3-diketone, and NaOAc without the need to
prepare the pure FeIII complexes 1 from these reagents; this
could be particularly beneficial when the 1,3-diketone com-
plexes are difficult to be isolated. Treatment of a 1:3:3:1
mixture of 2a/HACHTUNGTRENNUNG(acac)/NaOAc/FeCl3 in EG at 1208C for 4 h
gave 5Aa in 95% isolated yield (Scheme 8), similar to the
result obtained for the reaction with 1A. This FeCl3/1,3-di-
ketone/NaOAc method has been extended to prepare 5Ba,
10A, and 11 in 69, 71, and 35% yields, respectively
(Scheme 8).
The electrochemistry and photophysics of cyclometalated
platinum complexes with 2-phenylpyridyl (C N) and 1,3-di-
ketone (O O) ligands have been reported, revealing that
Figure 2. ORTEP drawing for 13 with omission of hydrogen atoms (ther-
mal ellipsoid probability level: 30%).
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Iron-Mediated Benzothiophene Formation
COMMUNICATION
The room-temperature (298 K) absorption and emission
spectra of dichloromethane solutions of 13 and 14 are
shown in Figure 3. The emission spectra were recorded upon
ligand. The tunability of the emission wavelength of these
(C N)PtACHTNUTRGNE(UNG O O) complexes by using the benzo[b]thiophene
ligand system is attractive in the context of developing new
phosphorescent PtII dopant materials. Further investigation
on the use of the benzo[b]thiophene ligand system for the
design and synthesis of other types of functional transition-
metal complexes is in progress.
We have demonstrated an interesting type of tandem radi-
cal cyclization reaction, which involves an iron-mediated
redox transformation and occurs at the coordinated ligands
with product yields of up to 98%. Tandem radical cycliza-
tions are an important class of reactions of great utility in
organic synthesis[5] and the use of redox-active FeIII reagents
is promising in this endeavor. PtII complexes with ppy and
deprotonated 5Aa or 5Ha ligands have been prepared to
reveal the potential use of the benzo[b]thiophene ligand
system in the design of new Pt-based phosphorescent mate-
rials.
Acknowledgements
This work was supported by The University of Hong Kong, the Universi-
ty Grants Council of HKSAR (the Area of Excellence Scheme: AoE 10/
01P), and the Hong Kong Research Grants Council (HKU 1/CRF/08;
HKU 700809; HKU 700810). We thank Lap Szeto for assistance in X-ray
crystal-structure determination.
Keywords: coordination complexes · cyclization · iron ·
platinum · radical reactions
[1] a) E. C. Constable, Metals and Ligand Reactivity, Wiley-VCH, Wein-
heim, 1996; b) L. S. Hegedus, Transition Metals in the Synthesis of
Complex Organic Molecules, 2nd ed., University Science Books,
Sausalito, 1999.
Figure 3. Absorption (solid line) and emission (dashed line) spectra for
13 (top) and 14 (bottom) in dichloromethane (6.0ꢂ10À5 M) at 298 K.
[2] a) C. Bolm, J. Legros, J. Le Paih, L. Zani, Chem. Rev. 2004, 104,
6217–6254; b) A. Correa, O. Garcꢃa MancheÇo, C. Bolm, Chem.
Soc. Rev. 2008, 37, 1108–1117; c) S. Enthaler, K. Junge, M. Beller,
Angew. Chem. 2008, 120, 3363–3367; Angew. Chem. Int. Ed. 2008,
47, 3317–3321; d) B. Plietker, Iron Catalysis in Organic Chemistry,
Wiley-VCH, Weinheim, 2008; e) R. H. Morris, Chem. Soc. Rev.
2009, 38, 2282–2291.
[3] a) A. R. Katritzky, C. A. Ramsden, E. F. V. Scriven, R. J. K. Taylor,
G. Jones, Comprehensive Heterocyclic Chemistry-III, Vol. 3, Elsevier,
Oxford, 2008; b) I. F. Perepichka, D. F. Perepichka, Handbook of
Thiophene-Based Materials, Wiley, New York, 2009.
[4] a) P. Gopinath, S. Nilaya, T. R. Debi, V. Ramkumar, K. M. Mura-
leedharan, Chem. Commun. 2009, 7131–7133; b) J. Młochowski, P.
Potaczek, Phosphorus Sulfur Silicon Relat. Elem. 2009, 184, 1115–
1123.
[5] a) I. Ryu, N. Sonoda, D. P. Curran, Chem. Rev. 1996, 96, 177–194;
b) B. B. Snider, Chem. Rev. 1996, 96, 339–363; c) A. Gansꢄuer, T.
Lauterbach, S. Narayan, Angew. Chem. 2003, 115, 5714–5731;
Angew. Chem. Int. Ed. 2003, 42, 5556–5573; d) K. C. Nicolaou, D. J.
Edmonds, P. G. Bulger, Angew. Chem. 2006, 118, 7292–7344;
Angew. Chem. Int. Ed. 2006, 45, 7134–7186; e) G. J. Rowlands, Tet-
rahedron 2010, 66, 1593–1636.
excitation at the lowest absorption band (lexc =430 nm).
Molar extinction coefficients of low-energy transitions (350–
430 nm) for 13 and 14 are in the range of 5000 to
13000 LmolÀ1 cmÀ1, similar to those of other (C N)Pt com-
plexes reported in the literature;[14] these transitions are at-
tributed to mixed metal-to-ligand (C N) charge transfer
(MLCT) and ligand centered charge-transfer transitions.
The profiles of the absorption spectra of the complexes
[Pt
ACHTUNGTRENNUNG(ppy)ACHTUNGTRENNUNG
results of DFT calculations on [Pt
N
ACHTUNGTRENNUNG
that the LUMO is predominantly C N in character. Com-
plex 13 shows an emission maximum at 564 nm with a quan-
tum yield of 0.28 (at 1.0ꢂ10À5 m) at 298 K; this is tentatively
3
assigned to be originated from a mixed LC–MLCT excited
state. Complex 14 shows an emission maximum at 615 nm
with a quantum yield of 0.016 (at 1.0ꢂ10À5 m) at 298 K. A
red-shifted lmax of the Pt complexes is observed by changing
the O O ligand from acac (lmax =486 nm) to deprotonated
5Aa (lmax =564 nm) and to 5Ha (lmax =615 nm); this can be
reasoned as the lowering of energy of the excited state due
to the extended conjugation in the benzo[b]thiophene
[6] a) M. Moreno-MaÇas, J. Marquet, A. Vallribera, Tetrahedron 1996,
52, 3377–3401; b) C. Pettinari, F. Marchetti, A. Drozdov in Compre-
hensive Coordination Chemistry-II, Vol. 1 (Eds.: J. A. McCleverty,
T. J. Meyer, A. B. P. Lever), Elsevier, Amsterdam, 2004, p. 97;
Chem. Eur. J. 2011, 17, 4709 – 4714
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4713

K.-H. Low, C.-M. Che et al.
c) P. A. Vigato, V. Peruzzo, S. Tamburini, Coord. Chem. Rev. 2009,
253, 1099–1201, and references therein.
D. Roberto, R. Ugo, F. De Angelis, S. Fantacci, Chem. Commun.
2010, 46, 2414–2416.
[7] CCDC-803511 (3) and 808327 (13) contain the supplementary crys-
tallographic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[12] E. N. Shepelenko, L. S. Minkina, S. G. Kochin, A. V. Khokhlov,
V. A. Bren, A. D. Garnovskii, Zh. Obshch. Khim. 1987, 57, 2342–
2346.
1
[13] 13: H NMR (400 MHz, CD2Cl2, 258C, TMS): d=9.07 (d, J=5.6 Hz,
[8] K. E. Preuss, J. Wu, M. Jennings, Acta. Crystallogr. Sect. E 2005, 61,
m430–m432.
[9] J. K. Shirey, Z. Xiang, D. Orton, A. E. Brady, K. A. Johnson, R. Wil-
liams, J. E. Ayala, A. L. Rodriguez, J. Wess, D. Weaver, C. M. Nis-
wender, P. J. Conn, Nat. Chem. Biol. 2008, 4, 42–50.
1H), 8.20 (d, J=7.9 Hz, 1H), 7.85–7.81 (m, 1H), 7.76–7.74 (m 1H),
7.68–7.60 (m, 3H), 7.50 (dd, J=7.7, 1.0 Hz, 1H), 7.42–7.40 (m, 1H),
7.27–7.26 (m, 1H), 7.17–7.14 (m, 2H), 2.41 ppm (s, 3H); 14:
1H NMR (400 MHz, CD2Cl2, 258C, TMS): d=9.23 (d, J=5.4 Hz,
1H), 8.54 (s, 1H), 8.26 (d, J=8.0 Hz, 1H), 8.04–7.88 (m, 5H), 7.72–
7.63 (m, 6H), 7.52–7.50 (m, 1H), 7.42–7.41 (m, 1H), 7.29–7.28 (m,
1H), 7.18–7.09 ppm (m, 2H).
[10] C. P. Miller, M. D. Collini, H. A. Harris, Bioorg. Med. Chem. Lett.
2003, 13, 2399–2403.
[11] a) J. Brooks, Y. Babayan, S. Lamansky, P. I. Djurovich, I. Tsyba, R.
Bau, M. E. Thompson, Inorg. Chem. 2002, 41, 3055–3066; b) M.
Ghedini, T. Pugliese, M. La Deda, N. Godbert, I. Aiello, M. Amati,
S. Belviso, F. Lelj, G. Accorsi, F. Barigelletti, Dalton Trans. 2008,
4303–4318; c) A. Valore, A. Colombo, C. Dragonetti, S. Righetto,
[14] K. P. Balashev, M. V. Puzyk, V. S. Kotlyar, M. V. Kulikova, Coord.
Chem. Rev. 1997, 159, 109–120.
Received: February 2, 2011
Published online: March 23, 2011
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Chem. Eur. J. 2011, 17, 4709 – 4714