Tuning the size of supramolecular M4L4 tetrahedra by ligand connectivity

Article abstract of DOI:10.1039/c2dt30888f

Triangular triscatechol ligands are prepared in facile reaction sequences. The catechol units are either bound to the triangular backbone through their 3- or 4-position. With titanium(iv) ions, the ligands form metallosupramolecular M₄L₄

Full text of DOI:10.1039/c2dt30888f

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PAPER
Tuning the size of supramolecular M4L4 tetrahedra by ligand connectivity†
Markus Albrecht,*a Yuli Shang,a Kensuke Hasui,a,b Verena Gossen,a Gerhard Raabe,a Kazukuni Taharab
and Yoshito Tobeb
Received 24th April 2012, Accepted 1st June 2012
DOI: 10.1039/c2dt30888f
Triangular triscatechol ligands are prepared in facile reaction sequences. The catechol units are either
bound to the triangular backbone through their 3- or 4-position. With titanium(IV) ions, the ligands form
metallosupramolecular M4L4 tetrahedra which are characterized by ESI MS and proton NMR. Quantum-
chemical calculations reveal that connectivity at the catechol in the 3-position results in highly condensed
structures while attachment in the 4-position affords container molecules providing huge internal cavities.
Introduction
Recently, nanospheres, nanocontainers or nanovessels became
attractive targets for preparative chemists. Due to their internal
cavity they are able to bind guests and subsequently they might
act as mediators for reactions or unusual species can be stabi-
lized in their interior. In order to make container molecules,
“covalent” or “non-covalent” strategies can be envisaged.1
Fig. 1 Schematic presentation of the self-assembly of an M4L4 tetra-
hedron from four triangular ligands and four metal ions.
In the field of non-covalent formation of spherical hollow
molecules, metal-coordination based self-assembly proved to be
efficient.2 Work by Fujita3 or Raymond4 shows not only the
aesthetics of this chemistry but also its potential for e.g. supra-
molecular catalysis.
3- to 4-position results in a dramatic structural change of the
metal complexes leading to much bigger metallosupramolecular
aggregates with much bigger cavities.
Over the years, we investigated the formation of supramole-
cular self-assembled structures like helicates or metallosupra-
molecular M4L4 tetrahedra (Fig. 1).5 To obtain the latter,
triangular ligands with three catechol units which span the faces
of the polyhedron were prepared. Metal coordination at the
corners results in the formation of the metallocontainers.6
As one possible site for coordination, catechols were fre-
quently used. However, usually the catechol is connected to the
ligand framework through the 3-position of its aromatic ring
(Type I, Fig. 2). Representative examples are ligands A7 and B8
which early on were used for the self-assembly of triple stranded
helicates or C9 and D10 which lead to M4L6 or M4L4 tetrahedra,
respectively. A rare example for substitution in the 4-position
(type II) is ligand E,11 which forms heteronuclear hierarchically
assembled helicate-type structures.
Results and discussion
The ligands L1-H6–L3-H6 consist of central triangular rigid and
planar platforms which bear three catechol ligands through
methylene connections. The synthetic approaches are straight
forward starting from brominated triangular starting materials as
outlined in Scheme 1.
Ligands L1-H6 and L2-H6 are obtained from tris(4-bromo-
phenyl) amine 1. The bromide is exchanged by lithium and the
intermediately formed organometallic reagent is either quenched
with 2,3-dimethoxybenzaldehyde 2a or 3,4-dimethoxybenzalde-
hyde 2b resulting in the formation of the tris alcohols 3a (47%)
or 3b (45%) as mixtures of stereoisomers. Reaction with acetic
anhydride leads to the acetates 4a or 4b in quantitative yield.
The acetate groups are removed by hydrogenation using palla-
dium on charcoal as catalyst resulting in 5a (93%) or 5b (90%).
Finally, the catechol ligand units are liberated by cleavage of the
methyl ethers with BBr3. Ligands L1-H6 and L2-H6 are obtained
in 98% or 80% yield, respectively.
Herein, three novel triangular triscatechol ligands (Fig. 3) with
connection through the 3-(L1) as well as the 4-position (L2, L3)
are presented. Simple shifting of the attaching units from the
aInstitut für Organische Chemie, Landoltweg 1, 52074, Aachen,
Germany. E-mail: markus.albrecht@oc.rwth-aachen.de
bDivision of Frontier Materials Science, Graduate School of
Engineering Science, Osaka University, Toyonaka, Osaka 560-8531,
Japan
L3-H6 is synthesized in a Friedel–Crafts reaction of 1,3,5-tris-
(bromomethyl)benzene 6 with veratrole 7 in the presence of zinc
chloride. Derivative 8 is obtained in a 37% yield. In the final
step, methyl ethers are cleaved to afford ligand L3-H6 in a 90%
†Electronic supplementary information (ESI) available. See DOI:
10.1039/c2dt30888f
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Fig. 3 Triangular ligands for the formation of M4L4 tetrahedra with
connection of the catechol through the 3-(L1) and 4-position (L2, L3).
for the complex. Most characteristic is the signal of the methy-
lene unit, which appears as singlet (δ = 3.84) for L1-H6. Upon
metal coordination the two protons of CH2 become diastereo-
topic and are observed as doublets at δ = 4.04 and 3.03 ppm
(J = 12.7 Hz). The spectra of the complex do not change signifi-
cantly depending on the counter cations. The compounds are
stable in D2O and Na8[(L1)4Ti4] was measured at variable temp-
erature. Up to 353 K the spectrum did not show significant
changes. This reveals a high thermodynamic stability of the
complex and also a high configurational stability. No coalesc-
ence of the diastereotopic methylene protons could be observed.
In case of the complex K8[(L2)4Ti4] the situation proved to be
more complicated. The complex was prepared by the standard
method in methanol and an orange red solution was formed.
Upon removal of the solvent under vacuum a red solid was iso-
lated, which could not be dissolved again. This probably indi-
cates collapsing of the container upon evacuation leading to an
insoluble coordination polymer. An alternative explanation
might be that the once precipitated tetrahedron possesses only a
low solubility. Therefore, K8[(L2)4Ti4] was prepared in situ in
methanol-d4 and a proton NMR spectrum was recorded. Fig. 5
compares the 1H NMR spectra of the ligand L2-H6 and of
K8[(L2)4Ti4]. Again, the expected splitting is observed for the
phenyl spacers and the catechol units. The signals shift signifi-
cantly upon complex formation. Most characteristic is the beha-
viour of the signal of the methylene groups which shows one
singlet at δ = 3.64 for the ligand. In the complex K8[(L2)4Ti4],
diastereotopic behaviour is observed and two doublets are found
at δ = 3.56 and 3.43 (J = 13.4 Hz).
Fig. 2 Different connection modes – Type I or II – for catechol units
and examples A–D for Type I and E for Type II ligands.
yield. All prepared ligands are characterized by standard analyti-
cal techniques.
Complexes are obtained by the reaction of four equivalents of
ligand, titanoyl bisacetylacetonate and an alkali metal carbonate.
Usually formation of M4L4 coordination compounds proceeds
close to quantitative and the supramolecular aggregates are iso-
lated in high yield (Scheme 2). As counter cations only alkaline
metals were introduced in this study .
With ligand L1-H6 three alkaline metal salts (Li, Na, K) were
prepared and were characterized by 1H NMR spectroscopy,
ESI MS, and elemental analysis. ESI MS shows peaks corres-
ponding to the salts of the M4L1 tetrahedron. Varying amounts
4
of counterions (which might be exchanged by protons) and of
1
solvent molecules are observed. The H NMR spectra of L1-H6
(a) and of the complexes M8[(L1)4Ti4] (M: Li (b), Na (c), K (d))
in methanol-d4 are shown in Fig. 4.
In the spectrum of the ligand the two doublets of the triaryl
amine are observed at δ = 7.04 and 6.84 (J = 8.2 Hz).
Upon coordination those signals are shifted to δ = 7.51 and 6.76
(M = Li). The resonances of the catechol unit are found at
δ = 6.65–6.48 (m) for the ligand and at δ = 6.42, 6.32 and 6.19
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Fig. 4 Proton NMR spectra of L1-H6 (a) and M8[(L1)4Ti4] (M: Li (b),
Na (c), K (d)) in methanol-d4.
Fig. 5 Proton NMR spectra of K8[(L2)4Ti4] (a) and L2-H6 (b) in
methanol-d4.
Scheme 1 Preparation of the ligands L1-H6–L3-H6.
Scheme 2 Preparation of tetrahedral tetranuclear titanium(IV) com-
plexes from ligands L1-H6–L3-H6.
Negative ESI MS of K8[(L2)4Ti4] recorded in methanol-d4/D2O
shows characteristic peaks for the complex (e.g. m/z = 673.18
{K2D2[(L2)4Ti4]}4−) as well as aggregates incorporating solvent
molecules (e.g. m/z = 693.82 {K2D2[(L2)4Ti4](D2O)4}4− or
1443.27 {K6[(L2)4Ti4](D2O)2}2−).
Fig. 6 Comparison of the structures of the octaanions [(L1)4Ti4]8− and
[(L2)4Ti4]8− obtained at the HF level of theory employing the SDD/
MDF10 basis set and ECPs for Ti and TZVP for all other elements.
As no crystals of a quality sufficient for X-ray structure
determination could be obtained, computational methods were
used to analyze the structures. The calculations were performed
on the Hartree–Fock level of theory employing the TZVP basis
set in combination with SDD/MDF10 for the titanium(IV) ions.12
The computationally obtained structures of the two octaanions
[(L1)4Ti4]8− and [(L2)4Ti4]8− are shown in Fig. 6. The catechol
ligands connected at the 3-position ([(L1)4Ti4]8−) lead to an
average Ti–Ti distance of 15.629 Å. Due to the twist at the
complex units, the ligands are bent inwards in this case. The
connection at the 4-position ([(L2)4Ti4]8−) results in both a
slightly larger Ti–Ti distance and a larger, expanded cavity.
[(L1)4Ti4]8− possesses a highly condensed structure resulting in
a very compact stable arrangement. The large cavity of
[(L2)4Ti4]8− is caused by the position of the catechol connection
forcing the triangular spacer away from the center of the con-
tainer molecule. To estimate the volume of the tetrahedron, the
center of the container was determined. Then the distance to the
nearest atom was taken as a radius. The volume of the resulting
sphere was estimated and gives an impression of the cavity size.
The smaller tetrahedron has a volume of 449 Å3 and the bigger
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dissolved in methanol, DMSO or water. Fig. 7 shows a represen-
tative part of the ESI MS spectrum depicting triple anionic peaks
with varying amounts of sodium cations and protons.
The 1H NMR spectra of the free ligand L3-H6 and of
Na8[(L3)4Ti4] in methanol-d4 are shown for comparison in
Fig. 8. Again the aromatic protons reveal characteristic shifting
upon coordination of the ligand. The diastereotopic behaviour of
the methylene unit (occurring as a singlet at δ = 3.68) is found
in the coordination compound Na8[(L3)4Ti4] in form of two
doublets at δ = 3.55 and 3.52 (J = 15.1 Hz).
Conclusions
In here we presented three new triangular ligands which are able
to form metallosupramolecular M4L4 tetrahedra. Three catechol
units are connected through their 3- or 4-position to methylene
groups attached to a central triaryl amine or 1,3,5-benzene
moiety. Connection in the 3-position results in highly condensed
tetrahedra, while shifting of the connecting unit to the 4-position
results in a dramatic expansion of the container. Thus, a simple
structural modification allows a change of the overall structure of
the supramolecular aggregate. The described complexes as well
as related derivatives will be used for the investigation of their
application in host guest chemistry.
Fig. 7 Part of the negative ESI MS of Na8[(L3)4Ti4] showing complex
peaks with the charge 3−.
Experimental section
NMR spectra were recorded on a Varian Mercury 300 or Inova
400 spectrometer. FT-IR spectra were recorded on a Perkin-
Elmer PE 1760 FT spectrometer. Mass spectra were taken on a
Varian MAT212 and Finnigen SSQ 7000 mass spectrometer.
Elemental analyses were obtained with an Elementar Vario EL
analyser. The calculations have been performed with the
program package Gaussian‘09 on the HF level of theory in com-
bination with SDD/MDF10 for Ti(IV) and TZVP for all other
atoms.1
Synthesis of 3a. A 15% solution of tBuLi in hexane (25 mL,
18 mL) was added to a mixture of 2.89 g (6 mmol) tris(4-bromo-
phenyl)amine 1 in 50 mL dry ether at −78 °C under nitrogen.
The immediately formed suspension was stirred for 3 h at
−78 °C and then a solution of 5.98 g (36 mmol) 2,3-dimethoxy-
benzaldehyde 2a in 15 mL of ether was added. The reaction
mixture was stirred and overnight warmed up to room tempera-
ture. 3 M HCl (5 mL) was added and the precipitate was filtered
and washed with ethanol and ether. After column chromato-
graphy (silica, CH2Cl2–EtOAc 5 : 1) 3a was obtained as a white
solid. Yield: 2.08 g (2.80 mmol, 47%). Melting point: 177 °C.
1H NMR (400 MHz, CDCl3): δ = 7.18 (m, 6H), 7.04 (m, 3H),
6.97–6.92 (m, 9H), 6.85 (m, 3H), 5.94 (d, J = 5.3 Hz, 3H),
3.83 (s, 9H), 3.61 (s, 9H), 2.92 (d, J = 5.3 Hz, 3H) ppm.
13C NMR (400 MHz, CDCl3): δ = 152.5 (C), 146.6 (C),
146.2 (C), 138.2 (C), 137.6 (C), 127.3 (CH), 124.0 (CH),
123.7 (CH), 119.5 (CH), 111.8 (CH), 72.1 (CH), 60.5 (CH3),
55.8 (CH3) ppm. IR (KBr): ν = 3291, 2935, 2832, 1600, 1503,
1476, 1429, 1312, 1265, 1219, 1079, 1006, 910, 837, 807, 778,
755, 700 cm−1. MS (EI, 70 eV): m/z = 743.5 [M]+.
C45H45NO9·1/2H2O: C 71.79, H 6.16, N 1.86; found C 71.3,7 H
6.15, N 1.79.
Fig. 8 Proton NMR spectra of Na8[(L3)4Ti4] (a) and L3-H6 in metha-
nol-d4.
one a volume of 1304 Å3. Upon removal of structurally stabili-
zing solvent molecules within the big container the cavity col-
lapses leading to a coordination polymer.
The models also show that the supramolecular containers
possess big openings which should allow a fast exchange of
solvent molecules or other guest species.
Our search for a stable extended tetrahedron with connectivity
in the 4-position led us to the ligand L3-H6. This ligand is some-
what smaller than L2-H6. Preparation of the Na8[(L3)4Ti4]
complex resulted in a red solid which after isolation could be
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Synthesis of 3b. 482 mg (1 mmol) of 1 was dissolved in
15 mL ether and 4.1 mL of a 15% tBuLi solution in hexane at
−78 °C was added. The mixture was stirred for 3 h before an
ether solution of 3,4-dimethoxybenzaldehyde 2b (997 mg,
6 mmol) was added. The reaction mixture was warmed up and
stirred overnight at room temperature. After addition of 10 mL of
3 M HCl, the phases were separated. The organic phase was
washed with brine, dried over Na2SO4 and taken to dryness. The
remaining product was purified by column chromatography
(silica gel, pentane–ethyl acetate 1 : 1). Yield: 338 mg (45%).
1H NMR (300 MHz, CDCl3): δ = 7.25 (m, 6H), 7.05 (m, 6H),
6.98–6.82 (m, 9H), 5.74 (m, 3H), 3.87 (s, 12H), 2.17 (m, 3H)
ppm. 13C NMR (300 MHz, CDCl3): δ = 149.0 (C), 148.4 (C),
146.5 (C), 138.1 (C), 136.5 (C), 127.4 (CH), 123.8 (CH),
118.8 (CH), 110.9 (CH), 109.7 (CH), 75.7 (CH), 55.9 (CH3)
ppm. IR (KBr): ν = 3333, 2922, 2107, 1599, 1501, 1439, 1321,
(t, J = 7.9 Hz, 3H), 6.83 (d, J = 8.4 Hz, 6H), 6.71 (dd, J = 7.9,
1.5 Hz, 3H), 6.67 (dd, J = 7.9, 1.5 Hz, 3H), 3.82 (s, 6H),
3.78 (s, 9H), 3.64 (s, 9H) ppm. 13C NMR (300 MHz, CDCl3,):
δ = 152.8 (C), 147.1 (C), 145.9 (C), 135.3 (C), 135.1 (C),
129.5 (CH), 123.8 (CH), 123.8 (CH), 122.5 (CH), 110.5 (CH),
60.4 (CH3), 55.7 (CH3), 35.2 (CH2) ppm. IR (KBr): ν = 2999,
2927, 2832, 1601, 1583, 1502, 1475, 1311, 1270, 1218, 1154,
1107, 1069, 1002, 937, 838, 799, 774, 746, 689 cm−1. MS (EI,
70 eV): m/z = 695.7 [M]+. C45H45NO6: C 77.67, H 6.52,
N 2.01; found C 77.25, H 6.53, N 1.97.
5b: Yield: 72 mg (90%). 1H NMR (400 MHz, CDCl3):
δ = 6.95 (d, J = 8.6 Hz, 6H), 6.88 (d, J = 8.6 Hz, 6H), 6.74
(m, 3H), 6.68–6.64 (m, 6H), 3.77–3.70 (m, 24H) ppm.
IR (KBr): ν = 2998, 2925, 2851, 1594, 1504, 1458, 1414, 1325,
1258, 1234, 1137, 1025, 944, 912, 860, 795, 744, 673 cm−1
.
MS (ESI+): m/z = 696.3 [M + H]+. HRMS calculated for
1264, 1183, 1107, 1015, 959, 872, 808, 754, 716 cm−1
.
C45H46O6N: 696.3319; found: 696.3317.
MS (ESI+): m/z = 726.2 [M − OH]+. C39H33NO6·4/3H2O:
Synthesis of L1-H6. At 0 °C 0.2 mL BBr3 was added to a
solution of 5a (43 mg, 0.07 mmol) in 5 mL of dichloromethane.
The mixture was warmed up and stirred overnight at room
temperature. 2 mL of methanol was added. The mixture was
taken to dryness and the residue was dissolved in ethyl acetate
(20 mL). After washing with aqueous HCl (pH = 4), drying
(Na2SO4) and evaporation of the solvent, L1-H6 was obtained as
gray solid. Yield: 37 mg (98%). Melting point: 96–97 °C.
1H NMR (300 MHz, CD3OD): δ = 7.04 (d, J = 8.2 Hz, 6H),
6.84 (d, J = 8.2 Hz, 6H), 6.65–6.48 (m, 9H), 3.84 (s, 6H) ppm.
13C NMR (300 MHz, CD3OD): δ = 145.9 (C), 144.7 (C),
142.9 (C), 135.4 (C), 129.1 (CH), 128.2 (C), 123.4 (CH),
121.0 (CH), 118.9 (CH), 112.7 (CH), 34.5 (CH2) ppm. IR
(KBr): ν = 3474, 1599, 1499, 1357, 1322, 1274, 1168, 1106,
1067, 975, 831, 807, 769, 737, 696 cm−1. MS (ESI+): m/z =
612.4 [M + H]+. C39H33NO6·3H2O: C 70.36, H 5.90, N 2.20;
found C 70.45, H 5.30, N 1.94.
C 70.39, H 6.26, N 1.82; found C 70.35, H 5.97, N 1.64.
Synthesis of 4a. A solution of 3a (160 mg, 0.22 mmol) in
5 mL acetic anhydride was heated to reflux for 5 h. After cooling
to room temperature the solvent was removed in vacuum and the
residue was dissolved in dichloromethane. The organic phase
was washed with a saturated solution of sodium bicarbonate and
dried over sodium sulfate. The solvent was evaporated and 4a
was obtained as a white solid. Yield: 187 mg (quant.). Melting
point: 82–85 °C. 1H NMR (400 MHz, CDCl3): δ = 7.10 (d,
J = 8.6 Hz, 6H), 7.05 (s, 3H), 6.98 (t, J = 8.0 Hz, 3H), 6.92 (dd,
J = 8.0, 1.7 Hz, 3H), 6.85 (d, J = 8.6 Hz, 6H), 6.78 (m, 3H),
3.77 (s, 9H), 3.69 (s, 9H), 2.05 (s, 9H) ppm. 13C NMR
(400 MHz, CDCl3): δ = 169.8 (C), 152.6 (C), 146.8 (C),
146.0 (C), 134.4 (C), 134.3 (C), 128.1 (CH), 124.0 (CH),
123.8 (CH), 118.5 (CH), 111.8 (CH), 71.7 (CH), 60.4 (CH3),
55.8 (CH3), 21.5 (CH3) ppm. IR (KBr): ν = 2963, 2938, 2834,
1738, 1602, 1587, 1505, 1478, 1430, 1369, 1315, 1268, 1224,
1176, 1073, 1008, 805, 783, 749 cm−1. MS (EI, 70 eV): m/z =
869.5 [M]+. C51H51NO12·1/2H2O: C 69.69, H 5.96, N 1.59;
found C 69.38, H 5.90, N 1.58.
Synthesis of L2-H6. 50 mg (0.08 mmol) of 5b was dissolved
in 10 mL of dichloromethane and 0.2 mL of BBr3 was added at
0 °C. The mixture was stirred at room temperature overnight.
The reaction was quenched by addition of methanol. After
evaporating the solvent in vacuum the residue was dissolved in
20 mL of ethyl acetate, washed with water and dried over
sodium sulfate. Finally the ethyl acetate was removed in vacuum
to obtain L2-H6 as a brown solid. Yield: 35 mg (80%). 1H NMR
(400 MHz, CD3OD): δ = 6.93 (m, 6H), 6.80 (m, 6H), 6.74
(m, 3H), 6.58 (d, J = 8.0 Hz, 3H), 6.43 (dd, J = 8.0, 2.0 Hz,
3H), 3.64 (s, 6H) ppm. 13C NMR (400 MHz, CD3OD):
δ = 145.9 (C), 144.7 (C), 143.0 (C), 136.1 (C), 133.1 (C),
129.1 (CH), 123.5 (CH), 119.7 (CH), 115.6 (CH), 114.8 (CH),
40.1 (CH2) ppm. IR (KBr): ν = 3333, 2922, 2853, 2107, 1599,
1501, 1439, 1321, 1264, 1183, 1107, 1062, 1015, 959, 872, 808,
754, 716, 676 cm−1. MS (ESI−): m/z = 610.2 [M − H]−. HRMS
calculated for C39H32O6N: 610.2224; found 610.2235.
Synthesis of 4b. 200 mg of 3b (0.27 mmol) was heated in
3 mL of acetic anhydride to reflux for 5 h. After evaporation of
the solvent the residue was dissolved in 10 mL dichloromethane,
washed with a saturated solution of sodium bicarbonate and
dried over sodium sulfate. The dichloromethane was removed in
vacuum and the product was used for the next reaction without
1
further purification. Yield: quant. H NMR (400 MHz, CDCl3):
δ = 7.17 (pseud. d, J = 8.7 Hz, 6H), 7.00 (pseud. d, J = 8.7 Hz,
6H), 6.92–6.80 (m, 9H), 6.78 (s, 3H), 3.87 (s, 9H), 3.86 (s, 9H),
2.15 (s, 9H) ppm.
Synthesis of 5a and 5b. 100 mg (0.11 mmol) of trisacetate 4a
or 4b, 10 mg of Pd/C and 4 mL of triethylamine were stirred in
25 mL of EtOH–EtOAc (4 : 1) under a hydrogen atmosphere
(45 bar) for 24 h. After filtration the solvent was removed and
the residue was dissolved in dichloromethane. Washing with
saturated aqueous NaHCO3, drying (Na2SO4) and evaporation of
solvent yields the products as white solids.
Synthesis of 8. A Schlenk flask was charged with 1,3,5-tris-
(bromomethyl)benzene (1.80 g, 5 mmol) and 5 mL veratrole.
The solution was degassed at room temperature, heated to
105 °C and nitrogen was bubbled through for 5 min. Under a
nitrogen atmosphere, 150 mg anhydrous ZnCl2 was added. The
mixture was stirred at 150 °C for 2 h under N2. The mixture was
5a: Yield: 74 mg (93%). Melting point: 110–111 °C. 1H NMR
(300 MHz, CDCl3): δ = 6.96 (d, J = 8.4 Hz, 6H), 6.90
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evaporated close to dryness under vacuum. 100 mL dichloro-
methane was added and the solution was washed three times
with a saturated solution of sodium bicarbonate. The organic
layer was isolated, dried over sodium sulfate and evaporated to
obtain a brown crude product. Silica column chromatography,
eluting with CH2Cl2–EtOAc (20 : 1) yielded the product as
white solid. Yield: 986 mg (1.9 mmol, 37%). 1H NMR
(400 MHz, CDCl3): δ = 6.87 (s, 3H), 6.78 (m, 3H), 6.70–6.64
(m, 6H), 3.85 (m, 15H), 3.78 (s, 9H) ppm. 13C NMR (400 MHz,
CDCl3): δ = 148.8 (C), 147.3 (C), 141.6 (C), 133.7 (C),
127.1 (CH), 120.8 (CH), 112.2 (CH), 111.1 (CH), 55.9 (CH3),
55.7 (CH3), 41.4 (CH2) ppm. IR (KBr): ν = 2935, 2834,
1593, 1510, 1450, 1341, 1259, 1233, 1137, 1025, 943, 852, 806,
740, 660 cm−1. MS (EI, 70 eV): m/z = 528.4 [M]+. MS (ESI−)
m/z = 527.0 [M − H]−. HRMS calculated for C33H36O6Na:
551.2404; found: 551.2418.
916, 844, 810, 777, 742, 714 cm−1. MS (ESI−): m/z = 654.14
{H4[(L1)4Ti4]}4−, 665.13 {Na2H2[(L1)4Ti4]}4, 676.12 {Na4-
[(L1)4Ti4]}4, 694.10 {H4[(L1)4Ti4](MeOH)5}4−, 705.09 {Na2H2-
[(L1)4Ti4](MeOH)5}4−
,
716.08 {Na4[(L1)4Ti4](MeOH)5}4−
,
733.05 {H4[(L1)4Ti4](MeOH)10}4−, 744.04 {Na2H2[(L1)4Ti4]-
(MeOH)10}4−, 755.03 {Na4[(L1)4Ti4](MeOH)10}4−. C156H108
-
N4Na8O24Ti4·20H2O: C 59.33, H 4.72, N 1.77; found C 59.25,
H 4.79, N 1.71.
K8[(L1)4Ti4]. Yield: quant. 1H NMR (300 MHz, CD3OD):
δ = 7.42 (m, 24H), 6.67 (m, 24H), 6.34 (d, J = 7.2 Hz, 12H),
6.25 (t, J = 7.2 Hz, 12H), 6.10 (d, J = 7.2 Hz, 12H), 3.95 (d,
J = 12.3 Hz, 12H), 2.95 (d, J = 12.3 Hz, 12H) ppm. IR (KBr):
ν = 3585, 1702, 1600, 1503, 1478, 1449, 1355, 1281, 1116,
1054, 836, 745, 714 cm−1. MS (ESI−): m/z = 654.14 {H4[(L1)4-
Ti4]}4−, 673.12 {K2H2[(L1)4Ti4]}4−, 692.10 {K4[(L1)4Ti4]}4−
,
713.07 {K2H2[(L1)4Ti4](MeOH)5}4−
,
732.05 {K4[(L1)4Ti4]-
Synthesis of L3-H6. At 0 °C 0.4 mL BBr3 was added to a
solution of 8 (283 mg, 0.53 mmol) in 20 mL dichloromethane.
The mixture was stirred overnight at room temperature and 5 mL
of methanol was added. The solvent was evaporated and the
residue then was dissolved in 20 mL ethyl acetate and washed
with water. The organic phase was dried over sodium sulfate and
the solvent removed in vacuum. Yield: 214 mg (0.48 mmol,
, , 771.01
(MeOH)5}4− 752.02 {K2H2[(L1)4Ti4](MeOH)10}4−
{K4[(L1)4Ti4](MeOH)10}4−. C156H108N4K8O24Ti4·20H2O·MeOH:
C 56.81, H 4.62, N 1.69; found C 57.03, H 4.69, N 1.51.
K8[(L2)4Ti4] (prepared in situ in methanol-d4). 1H NMR
(300 MHz, CD3OD): δ = 6.97 (m, 24H), 6.74 (m, 24H),
6.35 (m, 12H), 6.14–6.12 (m, 24H), 3.56 (d, J = 13.4 Hz, 12H),
3.43 (d, J = 13.4 Hz, 12H) ppm. MS (ESI−): m/z =
1
90%). H NMR (300 MHz, CD3OD): δ = 6.78 (s, 3H), 6.65 (m,
664.4 {D4[(L2)4Ti4](CD3OD)}4−, 673.18 {K2D2[(L2)4Ti4]}4−
,
3H), 6.55 (s, 3H), 6.46 (m, 3H), 3.68 (s, 6H) ppm. 13C NMR
(300 MHz, CD3OD): δ = 144.6 (C), 142.9 (C), 141.8 (C),
133.2 (C), 126.6 (CH), 119.9 (CH), 115.7 (CH), 114.9 (CH),
40.7 (CH2) ppm. IR (KBr): ν = 3359, 2915, 1720, 1600, 1515,
1439, 1352, 1275, 1186, 1105, 958, 861, 811, 786, 748, 704,
660 cm−1. MS (ESI−): m/z = 443.20 [M − H]−. C27H24O6·H2O:
C 70.12, H 5.67; found C 70.26, H 5.88.
693.82 {K2D2[(L2)4Ti4](D2O)4}4−, 701.82 {K2D2[(L2)4Ti4](D2O)2-
(CD3OD)2}4−, 713.00 {K3D[(L2)4Ti4](D2O)6}4−, 723.09 {K3D-
[(L2)4Ti4](D2O)8}4−
,
732.55{K4[(L2)4Ti4](D2O)8}4−
,
742.73
{K4[(L2)4Ti4](D2O)10}4−, 752.00 {K3D[(L2)4Ti4](D2O)12(CD3-
OD)}4−, 1362.09 {D6[(L2)4Ti4](D2O)5}2−, 1443.27 {K6[(L2)4Ti4]-
(D2O)2}2−, 1464.73 {K5D[(L2)4Ti4](D2O)6}2−, 1485.18 {K4D2-
[(L2)4Ti4](D2O)8(CD3OD)}2−, 1525.18 {K4D2[(L2)4Ti4](D2O)12-
(CD3OD)}2−
.
General procedure for the preparation of titanium(IV) complexes
Na8[(L3)4Ti4]. Yield: quant. 1H NMR (600 MHz, CD3OD):
δ = 6.56 (s, 12H), 6.42 (dd, J = 7.7 Hz, 1.5Hz, 12H), 6.29 (d,
J = 7.7 Hz, 12H), 6.04 (d, J = 1.5 Hz, 12H), 3.55 (d, J = 15.1 Hz,
12H), 3.52 (d, J = 15.1 Hz, 12H) ppm. IR (KBr): ν = 1597,
1483, 1423, 1340, 1254, 1215, 1116, 1023, 958, 866, 817, 758,
710 cm−1. MS (ESI−): m/z = 650.10 {H5[(L3)4Ti4]}3−, 657.43
{NaH4[(L3)4Ti4]}3−, 664.42 {Na2H3[(L3)4Ti4]}3−, 672.08 {Na3H2-
[(L3)4Ti4]}3−, 679.41 {Na4H[(L3)4Ti4]}3−, 690.10 {Na3H2[(L3)4Ti4]-
1 eq. ligand, 1 eq. TiO(acac)2 and 1 eq. M2CO3 (M = Na, K, Li)
were dissolved in methanol and stirred overnight. After evapo-
ration of the solvent a red solid was obtained.
Li8[(L1)4Ti4]. Yield: quant. 1H NMR (300 MHz, CD3OD):
δ = 7.51 (m, 24H), 6.76 (m, 24H), 6.42 (m, 12H), 6.32 (m,
12H), 6.19 (m, 12H), 4.04 (d, J = 12.7 Hz, 12H), 3.03 (d,
J = 12.7 Hz, 12H) ppm. IR (KBr): ν = 3585, 1602, 1503, 1448,
(H2O)3}3−
,
695.44 {Na2KH2[(L3)4Ti4](H2O)3}3−
,
697.43
1321, 1255, 1106, 1059, 1011, 918, 845, 777, 741, 714 cm−1
.
{Na4H[(L3)4Ti4](H2O)3}3−, 702.76 {Na3KH[(L3)4Ti4](H2O)3}3−
,
MS (ESI−): m/z = 654.14 {H4[(L1)4Ti4]}4−, 657.15 {Li2H2-
[(L1)4Ti4]}4−, 660.15 {Li4[(L1)4Ti4]}4−, 694.10 {H4[(L1)4Ti4]-
704.76 {Na5[(L3)4Ti4](H2O)3}3−
,
710.09 {Na4K[(L3)4Ti4]-
(H2O)3}3−. C108H72Na8O24Ti4·20H2O: C 52.11, H 4.53; found
C 52.50, H 4.96.
(MeOH)5}4−
, , 700.10
697.10 {Li2H2[(L1)4Ti4](MeOH)5}4−
{Li4[(L1)4Ti4](MeOH)5}4−, 733.06 {H4[(L1)4Ti4](MeOH)10}4−
,
736.06 {Li2H2[(L1)4Ti4](MeOH)10}4−, 739.06 {Li4[(L1)4Ti4]-
(MeOH)10}4−. C156H108N4Li8O24Ti4·23H2O·MeOH: C 60.52,
H 5.11, N 1.80; found C 60.25, H 4.81, N 1.63.
Acknowledgements
This work was supported by the DFG (international research
training school SELECA) and the JSPS.
Na8[(L1)4Ti4]. Yield: quant. 1H NMR (300 MHz, CD3OD):
δ = 7.42 (m, 24H), 6.67 (m, 24H), 6.31 (m, 12H), 6.22 (t, J =
7.6 Hz, 12H), 6.19 (d, J = 7.6 Hz, 12H), 3.94 (d, J = 12.4 Hz,
1
12H), 2.93 (d, J = 12.4 Hz, 12H) ppm. H NMR (300 MHz,
Notes and references
D2O): δ = 7.41 (m, 24H), 6.62 (m, 24H), 6.56 (m, 12H), 6.45
(t, J = 7.6 Hz, 12H), 6.18 (d, J = 7.6 Hz, 12H), 3.79 (d, J =
12.5 Hz, 12H), 3.15 (d, J = 12.5 Hz, 12H) ppm. IR (KBr): ν =
3590, 3396, 1602, 1503, 1447, 1322, 1254, 1106, 1058, 1011,
1 (a) D. J. Cram and J. M. Cram, Container Molecules and their Guests,
RSC, Cambridge, 1994; (b) Special issue on nanocontainers: M. Albrecht
and F. E. Hahn, Chemistry of Nanocontainers, Top. Curr. Chem. Vol.,
2012, 319.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 9316–9322 | 9321

View Article Online
2 (a) B. H. North, Y.-R. Zheng, K.-W. Chi and P. J. Stang, Acc. Chem.
Res., 2009, 42, 1554; (b) S. Leininger, B. Olenyuk and P. J. Stang, Chem.
Rev., 2000, 100, 853–907.
3 (a) M. Fujita, Chem. Soc. Rev., 1998, 27, 417; (b) M. Yoshizawa,
J. K. Klosterman and M. Fujita, Angew. Chem., 2009, 121, 3470.
4 Recent examples: (a) M. D. Pluth, R. G. Bergman and K. N. Raymond,
J. Am. Chem. Soc., 2008, 130, 6362; (b) C. J. Brown, R. G. Bergman and
K. N. Raymond, J. Am. Chem. Soc., 2009, 131, 17530;
(c) J. S. Mugridge, R. G. Bergman and K. N. Raymond, J. Am. Chem.
Soc., 2010, 132, 1182.
7 E. J. Enemark and T. D. P. Stack, Angew. Chem., Int. Ed. Engl., 1995, 34,
996–998.
8 M. Albrecht and S. Kotila, Angew. Chem., Int. Ed. Engl., 1996, 35,
1208–1210.
9 M. Ziegler, J. L. Brumaghim and K. N. Raymond, Angew. Chem., Int.
Ed., 2000, 39, 4119–4121.
10 M. Albrecht, I. Janser and R. Fröhlich, Chem. Commun., 2005, 157.
11 (a) X. Sun, W. J. Darren, D. Caulder, R. E. Powers, K. N. Raymond and
E. H. Wong, Angew. Chem., Int. Ed., 1999, 38, 1303–1306; (b) X. Sun,
D. W. Johnson, D. Caulder, K. N. Raymond and E. H. Wong, J. Am.
Chem. Soc., 2001, 123, 2752–2763; (c) X. Sun, D. W. Johnson,
K. N. Raymond and E. H. Wong, Inorg. Chem., 2001, 40, 4504–4506.
See also (d) S. Hiraoka, Y. Sakata and M. Shionoya, J. Am. Chem. Soc.,
2008, 130, 10058–10059.
12 M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria, M. A. Robb,
J. R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G. A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H. P. Hratchian, A. F. Izmaylov,
J. Bloino, G. Zheng, J. L. Sonnenberg, M. Hada, M. Ehara, K. Toyota,
R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, T. Vreven, J. A. Montgomery, Jr., J. E. Peralta, F. Ogliaro,
M. Bearpark, J. J. Heyd, E. Brothers, K. N. Kudin, V. N. Staroverov,
R. Kobayashi, J. Normand, K. Raghavachari, A. Rendell, J. C. Burant,
S. S. Iyengar, J. Tomasi, M. Cossi, N. Rega, J. M. Millam, M. Klene,
J. E. Knox, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli,
J. W. Ochterski, M. J. Martin, K. Morokuma, V. G. Zakrzewski,
G. A. Voth, P. Salvador, J. J. Dannenberg, S. Dapprich, A. D. Daniels,
Ö. Farkas, J. B. Foresman, J. V. Ortiz, J. Cioslowski and D. J. Fox,
GAUSSIAN 09 (Revision A.1), Gaussian, Inc., Wallingford CT, 2009.
5 (a) M. Albrecht, I. Janser and R. Fröhlich, Chem. Commun., 2005, 157;
(b) M. Albrecht and R. Fröhlich, Bull. Chem. Soc. Jpn., 2007, 80,
797–808.
6 (a) M. Albrecht, Angew. Chem., Int. Ed., 1999, 38, 3463–3465;
(b) A. J. Amoroso, J. C. Jefferey, P. L. Jones, J. A. McCleverty,
P. Thornton and M. D. Ward, Angew. Chem., Int. Ed. Engl., 1995, 34,
1443; (c) R. L. Paul, A. J. Amoroso, P. L. Jones, S. M. Couchman,
Z. R. Reeves, L. H. Rees, J. C. Jefferey, J. A. McCleverty and
M. D. Ward, J. Chem. Soc., Dalton Trans., 1999, 1563; (d) C. Brückner,
R. E. Powers and K. N. Raymond, Angew. Chem., Int. Ed., 1998, 37,
1837; (e) D. Caulder, C. Brückner, R. E. Powers, S. König, T. N. Parac,
J. A. Leary and K. N. Raymond, J. Am. Chem. Soc., 2001, 123, 8923;
(f) R. W. Saalfrank, H. Glaser, B. Demleitner, F. Hampel,
M. M. Chowdhry, V. Schünemann, A. X. Trautwein, G. B. M. Vaughan,
R. Yeh, A. V. Davis and K. N. Raymond, Chem.–Eur. J., 2001, 8, 493;
(g) For a study on different cavity sizes of molecular tetrahedrons see:
R. A. Bilbeisi, J. K. Clegg, N. Elgrishi, X. de Hatten, M. Devillard,
B. Breiner, P. Mal and J. R. Nitschke, J. Am. Chem. Soc., 2012, 134,
5110–5119.
9322 | Dalton Trans., 2012, 41, 9316–9322
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