A banana-shaped dinuclear complex with a tris(benzene-o-dithiolato) ligand

Article abstract of DOI:10.1039/b926939h

Reaction of the C₃-symmetric triazine bridged tris(benzene-o-dithiol) ligand H₆-1 with Ti⁴⁺ leads to the unexpected formation of the dinuclear complex (Me₃PhN) ₄[Ti₂(1)₂] while other C₃-symmetric ligands are reported to form either mono- or tetranuclear complexes.

Full text of DOI:10.1039/b926939h

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A banana-shaped dinuclear complex with a tris(benzene-o-dithiolato)
ligandw
Florian Hupka and F. Ekkehardt Hahn*
Received 22nd December 2009, Accepted 9th April 2010
First published as an Advance Article on the web 23rd April 2010
DOI: 10.1039/b926939h
Reaction of the C3-symmetric triazine bridged tris(benzene-
o-dithiol) ligand H6-1 with Ti4+ leads to the unexpected forma-
tion of the dinuclear complex (Me3PhN)4[Ti2(1)2] while other
C3-symmetric ligands are reported to form either mono- or
tetranuclear complexes.
Supramolecular self-assembly facilitates the creation of large
and complex structures from relatively simple precursors.1,2
Based on reversible weak interactions, such as hydrogen
bonding or metal–ligand interactions, an array of self-assembled
structures have been synthesized and this type of coordination
chemistry has been reviewed.3–9 Some of these structures
possess an internal cavity, whose interior provides a specific
chemical environment, distinctly different from the exterior
surrounding.10–13 The development of new container mole-
cules which can be used as reaction chambers or for trapping
of short living reaction intermediates currently constitutes an
Scheme 1 Synthesis of the dinuclear complex (Me3PhN)4[Ti2(1)2].
important synthetic target.
Raymond et al.14 and Albrecht et al.15 have synthesized
C3-symmetric tricatechol ligands, suitable for the formation of
tetranuclear clusters of type [M4L4]mꢀ. However, if the back-
bone in such ligands is flexible enough, the entropically
favored mononuclear complexes of type [ML]nꢀ are formed.16
Recently, we have described the formation of a tetranuclear
cluster derived from a C3-symmetric tris(bdt)6ꢀ ligand (bdt =
benzene-o-dithiolato dianion)17 while a similar ligand with a
more flexible backbone leads to the formation of the mono-
nuclear complex.18 The tetranuclear cluster has been shown to
serve as a container molecule capable to encapsulate small
cationic guest molecules. Here we describe a C3-symmetric
tris(benzene-o-dithiol) ligand (H6-1) which is surprisingly
Fig.
1
High-resolution
electrospray
mass
spectrum
of
capable of forming a dinuclear complex when reacted with
Ti(OPr)4 and Me3PhNCl.
Hx(Me3PhN)y[Ti2(1)2], for peak assignment see text.
spectrometry data confirm the [Ti2(1)2]4ꢀ stoichiometry. Fig. 1
shows the ESI mass spectrum with major peaks at m/z = 473.0
Ligand H6-1 has been prepared according to previously
published procedures.19,20 Two equivalents of H6-1 react with
two equivalents of Ti(OPr)4z in the presence of Na2CO3 in
methanoly resulting in the formation of a deep red solution
(lmax = 540 nm), typical for the [Ti(bdt)3]2ꢀ chromophore.21
Addition of Me3PhNCl to the methanol solution yields a deep
red precipitate which was identified as the dinuclear com-
plex [Ti2(1)2]4ꢀ (Scheme 1). The high-resolution ESI(ꢀ) MS
[Ti2(1)2]4ꢀ, 631.0 {H[Ti2(1)2]}3ꢀ, 676.0 {(Me3PhN)[Ti2(1)2]}3ꢀ
and 1082.1 {(Me3PhN)2[Ti2(1)2]}2ꢀ
,
.
Single crystals of (Me3PhN)4[Ti2(1)2]ꢁ2DMSOꢁ6DMF suitable
for an X-ray diffraction analysis were obtained by slow
diffusion of diethyl ether into a solution of (Me3PhN)4[Ti2(1)2]
in MeOH/DMF/DMSO (10 : 1 : 1, v : v : v).z Fig. 2 shows
the molecular structure of the trianion [Me3PhNCTi2(1)2]3ꢀ
,
with one Me3PhN+ cation encapsulated within the interior of
Institut fur Anorganische und Analytische Chemie,
¨
the cavity.
Universitat Munster, Corrensstraße 30, D-48149 Munster,
¨
¨
¨
To the best of our knowledge, complex [Ti2(1)2]4ꢀ con-
stitutes the first example of two C3-symmetric ligands forming a
dinuclear complex, with two ligand arms of each ligand coordi-
nating to one metal center and the remaining one coordinating to
the second metal center (and vice versa).
Germany. E-mail: fehahn@uni-muenster.de; Fax: +49-251-8333108;
Tel: +49-251-8333111
w Electronic supplementary information (ESI) available: Details of the
crystal structure determination. CCDC 759471. For ESI and crystallo-
graphic data in CIF or other electronic format see DOI: 10.1039/
b926939h
ꢂc
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Fig. 4 1H NMR spectra (400 MHz, 25 1C, d, ppm) of Me3PhNCl
(top), ligand H6-1 (middle) and complex (Me3PhN)4[Ti2(1)2] (bottom)
in DMF-d7 (* = DMF, & = H2O).
Fig. 2 Molecular structure of the complex anion [Me3PhNCTi2(1)2]3ꢀ
(left ORTEP drawing with 50% probability ellipsoids; right space filling
model), hydrogen atoms, solvent molecules and cations (except for the
encapsulated Me3PhN+) have been omitted for clarity. Selected bond
lengths [A] and angles [1]: range Ti1–S 2.391(2)–2.446(2), Ti1A–S
2.381(2)–2.449(2), Ti1ꢁ ꢁ ꢁTi2 18.956(2); bite angle SꢀTi1ꢀS
81.00(6)–83.02(6), SꢀTi1AꢀS 80.62(6)–82.92(6).
outside maintaining no remarkable interactions with the
complex anion.
Encapsulation and release from the cavity in solution is too
fast to be detected by NMR spectroscopy. Even at low
temperatures neither a broadening of the proton resonances
nor a chemical shift to higher field was observed for the
Me3PhN+ cation as would be expected for the encapsulated
ion (Fig. 4).
Complex (Me3PhN)4[Ti2(1)2]ꢁ2DMSOꢁ6DMF crystallizes
ꢀ
in the centrosymmetric space group P1. Each titanium atom
The small numbers of resonances in the 1H NMR spectrum
of (Me3PhN)4[Ti2(1)2] (Fig. 4, bottom) indicate the presence of
only one highly symmetric species in solution. The spectrum
reveals the characteristic set of signals for the proton resonances
of the benzene-o-dithiolato donor unit reflecting the AMX
spin system at d = 7.11 (dd), 6.46 (dd) and 6.22 (t) ppm.
The resonance for the amide protons is detected as a singlet at
d = 14.27 ppm and is shifted to low field compared to the
value recorded for the free ligand (Dd = 3.27 ppm). This
observation indicates, in contrast to the findings in the solid
state, the formation of intramolecular N–Hꢁ ꢁ ꢁS hydrogen
bonds in solution.
is coordinated by six sulfur atoms in a strongly distorted
octahedral fashion with a calculated twist angle of f = 36.11
(Ti1) and f = 36.81 (Ti2). Both titanium atoms exhibit the
same absolute configuration, namely D in the depicted com-
plex anion. Each {TiS6} moiety in complex anion [Ti2(1)2]4ꢀ
shows two long (Nꢁ ꢁ ꢁS separations in the range of 3.5 A) and
one short Nꢁ ꢁ ꢁS separation (B2.9 A) indicative for the
formation of just one N–Hꢁ ꢁ ꢁS hydrogen bond per {TiS6} unit.
The side view of the crystal structure (Fig. 3, left) shows an
uncommon banana like shape where both ligands point in the
same direction. Remarkable is the very long Ti–Ti distance of
about 19 A which is about twice as large as seen for other
dinuclear helical complexes.19d–g
In conclusion, we have described the use of a novel tris-
(benzene-o-dithiol) ligand to form a self-assembled M2L2
complex, the first dinuclear complex based on a C3-symmetric
ligand showing a banana-shape geometry. This homochiral
complex possesses an internal cavity which can encapsulate
one Me3PhN+ cation which was detected in the solid state but
not in solution. Further studies concerning the possibility to
encapsulate other small molecules are underway.
Since the separation of the triazine moieties measures about
9 A, the two ligands span a large groove and the complex
anion can serve as a molecular host. The molecular structure
determination shows one Me3PhN+ cation located inside this
cavity (Fig. 3, right), while the other three cations remain
This work was supported by the Fonds der Chemischen
Industrie and the NRW International Graduate School of
Chemistry. We thank Dr A. Hepp for measuring the NMR
spectra and Dr H. Luftmann for measuring the mass spectra.
Notes and references
z Commercially available Ti(OPr)4 (Aldrich) was used without further
purification. 2,3-Di(isopropylmercapto)benzoic acid chloride19 and
2,4,6-tris(p-aminoanilino)-1,3,5-triazine20 were prepared as described
previously.
y Preparation of 2,4,6-tris{p-[2,3-di(isopropylmercapto)benzamido-
anilino]}-1,3,5-triazine: freshly prepared 2,3-di(isopropylmercapto)-
benzoic acid chloride (1.0 g, 3.47 mmol) was dissolved in THF
(20 mL) and this solution was added to a solution of 2,4,6-tris-
(p-aminoanilino)-1,3,5-triazine (462 mg, 1.16 mmol) and Et3N (1.20 mL,
8.70 mmol) in THF (40 mL). The reaction mixture was stirred for 12 h
Fig. 3 Plot of the [Ti2(1)2]4ꢀ anion in a side view showing its banana-
shape and plot of the [Me3PhNCTi2(1)2]3ꢀ anion viewed down the
Ti–Ti axis (right).
ꢂc
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at ambient temperature. Subsequently, insoluble material was removed
by filtration and the solvent was removed from the filtrate under
vacuum. The solid residue was purified by column chromatography
(silica gel, CH2Cl2/ethyl acetate 1 : 1, v : v). Yield: 1.18 g (1.02 mmol,
88%); 1H NMR (400.1 MHz, CDCl3, ppm): d = 7.55 (m, 12H,
phenylene-H), 7.42 (m, 3H, bdt-H), 7.30 (m, 6H, bdt-H), 3.43
(m, 6H, CH(CH3)2), 2.92 (s, br, 3H, N–H), 1.34 (d, 3J = 6.6 Hz,
18H, CH(CH3)2), 1.16 (d, 3J = 6.6 Hz, 18H, CH(CH3)2). 13C NMR
(100.6 MHz, CDCl3, ppm): d = 170.8 (C(O)NH), 168.1 (triazene-C),
149.6, 146.8, 139.0, 137.5, 133.0, 132.9, 132.0, 129.2, 125.6, 124.5
(phenylene- and bdt-C), 44.7 (SCH), 40.0 (SCH), 26.9 (CH(CH3)2),
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26.5 (CH(CH3)2). MS (MALDI, positive ions): m/z = 1156 [M + H]+
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,
.
Preparation of ligand H6-1: dry, freshly distilled THF (60 mL) was
added to a mixture of 2,4,6-tris{p-[2,3-di(isopropylmercapto)benzamido-
anilino]}-1,3,5-triazine (1.18 g, 1.02 mmol), sodium (352 mg, 15.3 mmol)
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under vacuum. Yield: 755 mg (0.84 mmol, 82%); 1H NMR (400.1 MHz,
DMF-d7, ppm): d = 11.0 (s, br, 3H, N-H), 10.55 (s, 3H, N-H), 7.88
(s, br, 12H, phenylene-H), 7.67 (dd, 3J = 7.7, 4J = 1.0, 3H, bdt-H),
7.49 (dd, 3J = 7.7, 4J = 1.0, 3H, bdt-H), 7.17 (t, 3J = 7.7, 3H, bdt-H),
5.61 (s, br, 6H, S-H). 13C NMR (100.6 MHz, DMF-d7, ppm): d =
168.0 (C(O)NH), 137.4 (triazine-C), 135.0, 134.9, 132.1, 130.9, 128.4,
126.7, 126.3, 126.0, 125.4, 121.1 (phenylene- and bdt-C). MS
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Preparation of (Me3PhN)4[Ti2(1)2]: a sample of Ti(OPr)4 (15.7 mg,
0.055 mmol) was added to a solution of H6-1 (50 mg, 0.055 mmol) and
Na2CO3 (11.7 mg, 0.110 mmol) in degassed methanol (20 mL). The
solution was stirred under argon at ambient temperature for 12 h and
filtered. Addition of Me3PhNCl (18.9 mg, 0.11 mmol) to the filtrate
yielded a dark red precipitate, which was isolated by filtration, washed
with methanol (2 ꢃ 10 mL) and dried under vacuum. Yield: 57 mg
(0.03 mmol, 55%); 1H NMR (400 MHz, DMF-d7, ppm): d = 14.27
(s, 6H, (C(O)NH)), 7.78 (d, 3J = 8.0 Hz, 8H, Me3NPh-H), 7.71
(d, 3J = 8.6 Hz, 12H, phenylene-H), 7.55 (d, 3J = 8.6 Hz, 12H,
phenylene-H), 7.52 (t, 3J = 8.0 Hz, 8H, Me3NPh-H), 7.41 (m, 4H,
Me3NPh-H), 7.11 (dd, 3J = 7.7 Hz, 4J = 1.2 Hz, 6H, bdt-H), 6.42
(dd, 3J = 7.7 Hz, 4J = 1.2 Hz, 6H, bdt-H), 6.18 (t, 3J = 7.7 Hz, 6H,
bdt-H), 3.56 (s, 36H, PhNMe-H); 13C NMR (400 MHz, DMF-d7, ppm):
d = 167.7 (C(O)NH), 163.5 (triazine-C), 160.1, 157.5 (C–S), 147.5
(Me3NPh-C), 135.9, 134.9 (phenylene-C), 130.7, 130.6, 120.3
(Me3NPh-C), 119.6, 119.5 (phenylene-C), 114.7, 114.1, 113.4, 112.6
(bdt-C), 57.1 (PhNMe3-C); MS (ESI, negative ions) m/z: 473.0
[Ti2(1)2]4ꢀ, 631.0 {H[Ti2(1)2]}3ꢀ, 676.0 {(Me3PhN)[Ti2(1)2]}3ꢀ, 1082.1
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-
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a = 84.555(4)1, b = 78.851(4)1, g = 87.166(4)1, V = 7788.8(8) A3,
ꢀ
space group P1, Z = 2, 45 721 measured intensities, 26 396 unique
intensities (Rint = 0.0687), all reflections used in refinement against
|F2|, R = 0.0900, wR = 0.2586 (for all data).
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ꢂc
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3746 | Chem. Commun., 2010, 46, 3744–3746