Stable and metastable self-assembled rings based on trans-chelated Pd II

Article abstract of DOI:10.1002/zaac.201300168

In contrast to the large number of self-assembled ring and cage structures based on cis-chelated square-planar metal complexes as connecting nodes, the use of trans-chelated square-planar building blocks is vastly underrepresented in supramolecular coordination chemistry. We here report of a strategy for the formation of self-assembled ring structures based on the trans-chelating ligand 1, 2-bis(2-pyridylethinyl)-benzene coordinated to Pd^II in a 1:1 fashion and bis-monodentate pyridyl bridging ligands. Depending on the angle between the two N-donor functionalities of the bridging ligands, three- or two-membered rings are quantitatively formed in solution. Whereas the former species show a high thermodynamic stability, the latter rings are of only kinetic stability if the bridging ligand is also able to form a coordination cage as an alternative product. The assembly and transformation of the supramolecular structures was characterized by ¹H NMR spectroscopy and high-resolution FTICR-ESI mass spectrometry, augmented by semiempiric PM6 geometry optimizations. Copyright

Full text of DOI:10.1002/zaac.201300168

ARTICLE
DOI: 10.1002/zaac.201300168
Stable and Metastable Self-Assembled Rings based on trans-chelated PdII
Fernanda A. Pereira,[a] Thomas Fallows,[a] Marina Frank,[a] Anqi Chen,[a] and
Guido H. Clever*[a]
Keywords: Supramolecular chemistry; Self-assembly; Chelates; Coordination cages; Palladium
Abstract. In contrast to the large number of self-assembled ring and tween the two N-donor functionalities of the bridging ligands, three-
cage structures based on cis-chelated square-planar metal complexes or two-membered rings are quantitatively formed in solution. Whereas
as connecting nodes, the use of trans-chelated square-planar building the former species show a high thermodynamic stability, the latter rings
blocks is vastly underrepresented in supramolecular coordination
chemistry. We here report of a strategy for the formation of self-as-
sembled ring structures based on the trans-chelating ligand 1,2-bis(2-
are of only kinetic stability if the bridging ligand is also able to form
a coordination cage as an alternative product. The assembly and trans-
formation of the supramolecular structures was characterized by 1H
pyridylethinyl)-benzene coordinated to PdII in a 1:1 fashion and bis- NMR spectroscopy and high-resolution FTICR-ESI mass spectrome-
monodentate pyridyl bridging ligands. Depending on the angle be-
try, augmented by semiempiric PM6 geometry optimizations.
Introduction
Self-assembled rings composed of metal cations and organic
linkers represent a class of discrete coordination compounds
that mainly contributed to the success story of supramolecular
host-guest systems in recent years.[1] The archetypes of these
2-dimensional rings, and the 3-dimensional cages derived
thereof, consist of square-planar coordinated d8-metal cations
(PdII or PtII) carrying one cis-chelating diamine ligand
(Fujita[2]) or two cis-coordinating phosphine ligands (Stang[3]
)
which leave the two remaining coordination sites in a cis-rela-
tionship. In combination with linear bis-monodentate bridging
ligands, the 90° angle offered by these metal nodes thus leads
to the construction of supramolecular squares or rectangles
(Figure 1a).[4,5] In the prototypical example, the reaction of
[Pd(cis-ethylenediamine)(solvent)2]2+ with 4,4’-bipyridine
thus yields a tetranuclear square-shaped ring.[2] Numerous de-
signs of supramolecular rings and cages following this simple
principle have been presented by Fujita, Stang, Lippert,[6,7]
Hahn,[8] Hupp,[9] Long[10] and many other groups since
then.[11] Notably, almost all structures containing square-
planar coordinated metal nodes that carry one such ligand with
the role of blocking two of the four coordination sites have
the latter one occupying cis-positions. Although few examples
containing trans-coordinated palladium or platinum have been
reported,[12,13] most of these examples contain non-chelating
spectator ligands such as halides or bulky phosphines.
Figure 1. Schematic comparison of the self-assembly of a) cis-chelated
square-planar coordinated metal cations with linear linkers to give
squares and b) trans-chelated square-planar coordinated metal cations
with bent linkers to give rings of different sizes and thermodynamic
stabilities.
* Jun.-Prof. Dr. G. H. Clever
Fax: +49-551-3933373
E-Mail: gclever@gwdg.de
[a] Institute for Inorganic Chemistry
Georg-August University Göttingen
Tammannstr. 4
Examples of supramolecular structures containing trans-co-
ordinating chelate ligands wrapped around a square-planar co-
ordinated metal ion are quite rare. Recently, we became inter-
37077 Göttingen, Germany
Homepage: www.clever-lab.de
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Stable and Metastable Self-Assembled Rings based on trans-chelated PdII
ested in the rigid, trans-chelating ligand 1,2-bis(2-pyridyl- in 2001[14] but so far only rarely used in coordination chemis-
ethinyl)-benzene 2 which has been described by Bosch et al. try.[15–22] Furthermore, no reports are covering the use of this
system in supramolecular chemistry so far.[23]
Results and Discussion
Based on the trans-chelating abilities of ligand 2 and two
different bridging ligands, we designed two circular supra-
molecular assemblies using molecular modeling techniques
(Figure 1b).
The synthesis of the literature known ligand 2a[14] as well
as an electron-rich derivative 2b and an electron-deficient de-
rivative 2c were carried out according to standard procedures
(Scheme 1a).
Subsequently, the ligands were converted into the 1 : 1 com-
plexes [Pd(2a-c)(CD3CN)2](BF4)2 which serve as the building
blocks for the subsequent assembly of the ring structures. Elec-
tron-deficient ligand 2c was found to smoothly react to the
needed precursor [Pd(2c)(CD3CN)2](BF4)2 when mixed with
the metal source [Pd(CD3CN)4](BF4)2 in
a 1 : 1 ratio
(Scheme 1b). For the electron-rich ligands 2a and 2b, however,
this method proved to be unsuitable since the reaction was
shown to yield the 1 : 2 complex [Pd(2a,b)2](BF4)2 which is
not able to convert to the desired ring compounds upon ad-
dition of the bridging ligands, presumably due to kinetic
reasons (Scheme 1c).
Therefore, a two-step strategy was employed to prepare the
needed precursors [Pd(2a,b)(CD3CN)2](BF4)2 starting with the
previously described clean conversion of the ligands into the
chloride-containing palladium complexes [Pd(2a,b)(Cl)2][15]
by reaction of 2a,b with one equivalent of [Pd(CH3CN)2(Cl)2]
(Scheme 1d). Subsequently, the chlorido ligands were removed
from the metal center and substituted by acetonitrile ligands
by the addition of two equivalents of AgBF4. This step had to
be carried out with care (reaction at room temperature in
CD3CN, no evaporation of the solvent) directly followed by
Scheme 1. Synthesis of a) the trans-chelating ligands described
in this study and b) the mononuclear precursor complex
[Pd(2c)(CD3CN)2](BF4)2 from the electron-deficient ligand 2c. c)
Since the electron-rich ligands 2a and 2b give the dead-end complexes
[Pd(2a,b)2](BF4)2 with [Pd(CD3CN)4](BF4)2 as a metal source, a two-
step procedure d) was followed for obtaining the desired mononuclear
precursor complexes [Pd(2a,b)(CD3CN)2](BF4)2.
1
Figure 2. Comparison of H NMR spectra of ligands 2c, 2a and their PdII complexes [Pd(2c)(CD3CN)2](BF4)2, [Pd(2a)(CD3CN)2](BF4)2 and
[Pd(2a)2](BF4)2 (300 MHz, 298 K, CD3CN, * = CHCl3).
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addition of the bridging ligands, since attempts to isolate [Pd(2a)(CD3CN)2](BF4)2, which proved helpful in the synthe-
the species [Pd(2a,b)(CD3CN)2](BF4)2 again were leading sis of the self-assembled rings because it allowed a batchwise
to the formation of the unwanted dead-end product judgment about the quality of the unstable intermediate
[Pd(2a,b)2](BF4)2.
[Pd(2a)(CD3CN)2](BF4)2 by NMR spectroscopy.
The transformation of ligands 2c and 2a into the
The preparation of the precursors [Pd(2a–c)(CD3CN)2](BF4)2
precursor
complexes
[Pd(2c)(CD3CN)2](BF4)2
and in CD3CN was followed by the addition of one equivalent of
[Pd(2a)(CD3CN)2](BF4)2 as well as the non-reactive com- the bridging ligand. According to Figure 1b and Scheme 2, the
1
pound [Pd(2a)2](BF4)2 could be clearly followed by H NMR addition of bis-monodentate ligand 3 which is able to offer
monitoring (Figure 2).[24] In particular, it can be seen that all two pyridine donor sites in a 120° angle was leading to the
ligand proton signals undergo downfield shifts upon metal quantitative formation of the three-membered rings 4a-c.
complexation. Furthermore, the spectrum of [Pd(2a)2](BF4)2
The clean formation of these rings was clearly indicated by
1
can be clearly distinguished from the 1:1 complex the changes observed in the H NMR spectra upon reaction
(Figure 3). In particular, the signal of proton H6 of trans-che-
lating ligand 2a was found to undergo a tremendous downfield
shift upon ring formation. In contrast to the formation of
[Pd(2a)2](BF4)2 from [Pd(2a)(CD3CN)2](BF4)2, proton H5 was
also receiving a downfield shift upon formation of 4a, thereby
showing, that no [Pd(2a)2](BF4)2 is formed as a side product.
This is even true after keeping compound 4a for a long time
in solution at room temperature.
1
Furthermore, all H NMR signals of the bridging ligand 3
were found to undergo a downfield shift upon formation of
rings 4a–c. Again, this indicates the coordination of the bridg-
ing ligand to the metal atoms of the {Pd(2a–c)} fragments.
In addition, the high-resolution FTICR-ESI mass spectrum
of the 1:1 reaction mixture of [Pd(2a)(CD3CN)2](BF4)2 and 3
in CD3CN unambiguously supports the formation of the three-
membered ring 4a by showing intense peaks for the cationic
species [4a+2BF]4+, [4a+3BF]3+ and [4a+4BF]2+ (Figure 4).
The measured isotope pattern is in perfect agreement with a
simulation for the trinuclear compound 4a.
Following the same protocol, we synthesized the
two-membered
ring
6a
starting
from
precursor
[Pd(2a)(CD3CN)2](BF4)2 and bridging ligand 5 (Scheme 3).[25]
Again, the 1H NMR spectrum indicated the formation of one
major product bearing the signals from the 2a and 5 subunits
Scheme 2. Quantitative self-assembly of molecular 3-rings 4a–c
from 1:1 mixture of mononuclear precursor complexes
a
[Pd(2a–c)(CD3CN)2](BF4)2 and bridging ligand 3.
1
Figure 3. Comparison of H NMR spectra of [Pd(2a,c)(CD3CN)2](BF4)2 and their respective three-membered rings (4a,c) with the spectrum of
3 (300 MHz, 298 K, CD3CN).
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Stable and Metastable Self-Assembled Rings based on trans-chelated PdII
Figure 4. FTICR-ESI mass spectrum of 4a.
ligand 5, were almost unaffected by the ring formation which
can be satisfyingly explained by their remote position with re-
spect to the coordination sites in ring 6a.
By leaving the solution of 6a in CD3CN standing at room
temperature for an extended period (several days) and subse-
quent re-examination by NMR spectroscopy and ESI-mass
spectrometry, we made an intriguing observation: After this
time period, compound 6a had quantitatively converted into a
1:4 mixture of the previously described interpenetrated double
[25–27]
cage structure [2Cl+BF4@Pd458](BF4)5
and compound
1
[Pd(2a)2](BF4)2 (Figure 6). According to the H NMR results
Scheme 3. Quantitative self-assembly of a molecular 2-ring 6a
from 1:1 mixture of mononuclear precursor complex
a
[Pd(2a)(CD3CN)2](BF4)2 and bridging ligand 5.
in the expected 1:1 integral ratio (Figure 5). In well accordance
with the observations made for the formation of 4a, the signal
of proton H6 of ligand 2a was found to undergo a strong down-
field shift upon ring formation. In addition, all the pyridine
proton signals of bridging ligand 5 were found to undergo a
significant downfield shift upon complexation to the PdII cat-
Figure 6. The comparison of the thermal stabilities of the self-assembled
rings reveals that a) the three-membered ring 4a–c is stable upon heating
and/or prolonged standing in solution at room temperature whereas the
two-membered ring 6a was observed to quantitatively transform
into
a
previously described interpenetrated double cage
[2Cl+BF4@Pd458](BF4)5 and [Pd(2a)2](BF4)2 in the presence of chlor-
ions. In contrast, protons Ha–Hc, assigned to the backbone of ide (latter stemming from remaining AgCl in the reaction mixture).[25,26]
1
Figure 5. Comparison of H NMR spectra of 5, [Pd(2a)(CD3CN)2]2+ and the two-membered ring 6a (300 MHz, 298 K, CD3CN).
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F. A. Pereira, T. Fallows, M. Frank, A. Chen, G. H. Clever
ARTICLE
(Figure 7) and mass spectrometric data (Figure 8), the double of the trans-coordinating ligand 2a-c by the formation of
cage unambiguously contains two chloride anions bound in the [Pd(2a-c)2](BF4)2. Whereas ligand 5 has a clear tendency to
outer two of its three pockets. This chloride must stem from self-assemble to a highly-symmetric cage structure, the 120°
AgCl remaining in the reaction mixture after the preparation donor-site angle offered by ligand 3 in the drawn cisoid confor-
of the precursor [Pd(2a)(CD3CN)2](BF4)2 according to mation (and even less so the 180° angle of its transoid confor-
Scheme 1d. Furthermore, the dissolution of solid AgCl by the mation) are rather unsuitable for the formation of a spherical
double cage structure in acetonitrile is in full accordance with cage structure based on the square-planar coordination of PdII
our previous findings which have shown, that the double cage under compliance with the principle of maximum site occu-
[3BF4@Pd458](BF4)5 binds chloride with an extraordinary pancy.[28]
high affinity by an allosteric binding mechanism.[26] We thus
Since all attempts to obtain single crystals of the rings 4a–
assume that the formation of the thermodynamically very c and 6a suitable for X-ray crystallographic structure determi-
stable chloride-containing double cage structure as well as the nation remained unsuccessful, we applied molecular modelling
formation of the stable compound [Pd(2a)2](BF4)2 are the for obtaining plausible structures of the rings 4a (with the me-
thermodynamic driving forces for the quantitative conversion thoxyethoxy groups of ligand 3 truncated) and 6a (Fig-
of the ring 6a, latter being a kinetic product.
ure 9).[29] The obtained models show, that a nearly perfect
Following this argument, it is quite interesting to ask why square-planar coordination environment around the metal
the three-membered rings 4a–c are so stable. A plausible ex- atoms as well as unstrained local structures of the bridging
planation is based on the fate of the 2:1 mixture of ligand 3 ligands can be well accommodated together within the antici-
and PdII cations that would be released upon full consumption pated structure of the rings. The three-membered ring 4a is
Figure 7. Comparison of the 1H NMR spectra of double cage [2Cl+BF4@Pd458](BF4)5, compound [Pd(2a)2](BF4)2 and the result of the thermal
conversion of the metastable compound 6a upon prolonged standing at room temperature (300 MHz, 298 K, CD3CN).
Figure 8. FTICR-ESI mass spectrum of a) two-membered ring 6a and b) the same solution after long-time standing at room temperature showing
signals of double cage [2Cl+BF4@Pd458](BF4)5 and [Pd(2a)2](BF4)2.
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Stable and Metastable Self-Assembled Rings based on trans-chelated PdII
roughly of C3-symmetry (subject to the relative tilt direction
Experimental Section
of the central 1,4-phenylene rings of the bridging ligands). The
side-view shows, that the ring is perfectly flat with respect to
the pyridine rings of the bridging ligands. The trans-chelating
ligands are oriented perpendicular to this plane. The distance
between the palladium atoms is 12.3 Å, the Pd–Pd–Pd angle
is 60.0°.
Synthesis of 1,4-bis(5-(2-methoxyethoxy)-pyridine-3-yl)benzene
(3): 3-bromo-5-(2-methoxyethoxy)pyridine (100 mg, 431 μmol,
2 equiv.), 1,4-benzenediboronic acid dipinacol ester (71 mg, 215 μmol,
1 equiv.), potassium carbonate (297 mg, 2.15 mmol, 10 equiv.) and
Pd(dppf)Cl2 (9.6 mg, 11.7 μmol, 0.05 equiv.) were added to a Schlenk
tube under N2. Toluene (2 mL) and water (1 mL) were added and the
mixture was degassed and afterwards stirred at 85 °C for 96 h. The
mixture was poured in water and washed with ethyl ether (4 ϫ 25 mL).
The organic layer was filtered through celite and the solvents were
removed in vacuo to yield a brown solid (75.0 mg, 197 μmol). Yield:
1
91%. H NMR (300 MHz, CD3CN): δ = 3.38 (s, 6 H, Hg), 3.81–3.67
(m, 4 H, Hf), 4.26 (m, 1.7 Hz, 4 H, He), 7.58 (dd, 2.7, 2.0 Hz, 2 H,
Hb), 7.82 (s, 4 H, Ha), 8.29 (d, 2.8 Hz, 2 H, Hc), 8.51 (s, 2 H, Hd).
ESI HRMS: m/z ([C22H25N2O4]+) found: 381.1808 calcd.: 381.1809.
Synthesis of 1,2-bis(tert-butyldimethylsilyloxy)-4,5-bis(pyridine-2-
ylethinyl)benzene (2b): The reaction was carried out under N2. To
4,5-bis(tert-butyldimethylsilyloxy)-1,2-diiodobenzene (246 mg, 423
μmol, 1 equiv.), Pd(PPh3)2Cl2 (31.7 mg, 45 μmol) and CuI (5.4 mg, 28
μmol) was added dry Et3N (8 mL). The mixture was degassed and
2-ethinyl-pyridine (108.9 mg, 1.06 mmol, 2.5 equiv.) was added and
afterwards stirred at 60 °C for 2 h. The solvent was evaporated in
vacuo to give a dark brown oil which was redissolved in dichlorometh-
ane and purified by flash chromatography on silica gel (hexane/ethyl
acetate, 1:1) to give a brown oil (71.5 mg, 132 μmol). Yield: 32%. 1H
NMR (CD3CN): δ = 0.30 (s, 12 H, Si-CH3), 1.02 (s, 18 H, tBu), 7.15
(s, 2 H, H2), 7.34 (ddd, 7.3, 4.9, 1.6 Hz, 2 H, H5), 7.81–7.70 (m, 4
H, H3, H4), 8.64 (ddd, 4.9, 1.8, 1.0 Hz, 2 H, H6). ESI HRMS: m/z
([C32H41N2O2Si2]+) found: 541.2698 calcd. 541.2701.
Figure 9. Results of the geometry optimization of the self-assembled
rings a) 4a and b) 6a viewed from two different perspectives (semiem-
piric PM6 level of theory, Gaussian’09, in the structure of 6a, the C2
geometry of the dibenzosuberone ligand was preserved according to
its X-ray structure[25] by fixing the dihedral angles of the ethylene
bridge with the annelated benzene rings because PM6 was found to
show shortcomings in correctly describing the conformation of the
seven-membered ring).[29]
Synthesis of N-(4-bromophenyl)-4,5-diiodophthalimide: Two equiv-
alents of 4-bromo-aniline were combined with 1 equiv. of the precursor
4,5-diiodophthalic anhydride at 180 °C for 5 min giving a brown syrup
as raw material which was purified by flash chromatography on silica
gel (DCM/Hexane 10:1) to give a white solid (316 mg, 570 μmol).
In the two-membered ring 6a, the mean plane through the
bridging ligands is likewise perpendicular to the trans-chelat-
ing ligands’ ring planes, although the bridging ligands are
slightly twisted showing a local C2-symmetry. The global sym-
metry of the ring 6a is D2. The distance between the palladium Yield: 23%. 1H NMR (CDCl3): δ = 7.32 (d, 8.7 Hz, 2 H, H7), 7.63
(d, 8.7 Hz,
2 H, H8), 8.43 (s, 2 H, H2). ESI HRMS: m/z
atoms is 16.6 Å in this case the transannular distance between
the carbonyl oxygen atoms is 9.6 Å.
([C14H6BrI2NO2Na]+) found: 575.7556 calcd. 575.7563.
Synthesis of N-(4-bromophenyl)-4,5-bis(pyridine-2-ylethinyl)-
phthalimide (2c): In a Schlenk finger under N2 was added N-(4-bro-
mophenyl)-4,5-diiodophthalimide (228 mg, 412 μmol, 1 equiv.),
PdCl2(PPh3)2 (17 mg, 24.1 μmol, 0.05 equiv.) and CuI (4.6 mg, 24.1
μmol, 0.05 equiv.). Anhydrous THF (12 mL) was added and the sys-
tem degassed before addition of 2-ethinyl-pyridine (104 mg, 101 μmol,
2.1 equiv.) and 5 equiv. of Et3N. The reaction was left running over-
night at room temperature. After evaporation of the solvents the raw
material was purified by flash chromatography on silica gel (CHCl3/
MeOH 70:1) to give a yellow solid (257 mg, 509 μmol). Yield: 62%.
1H NMR (CD3CN): δ = 7.46–7.39 (m, 4 H, H5, H7), 7.74–7.70 (m, 2
H, H8), 7.88–7.85 (m, 4 H, H3, H4), 8.21 (s, 2 H, H2), 8.69 (dt, 4.9,
1.4 Hz, 2 H, H6). ESI HRMS: m/z ([C28H15BrN3O2]+) found:
Conclusions
Herein, we showed that trans-chelated square-planar PdII
building blocks are suited for the quantitative formation of
novel two- and three-membered ring compounds by a self-as-
sembly process in solution using two different bis-mono-
dentate bridging ligands. Depending on the nature of the latter
ligands, the rings are thermodynamically stable or only kinetic
products, that further transform into tetranuclear double cage
structures and mononuclear complexes. Our approach for ring
formation is in contrast to the vast number of reported self-
assembled rings and cages based on cis-chelated PdII or PtII 504.0328 calcd. 504.0342.
cations. We thus believe that the underrepresented class of
Synthesis of [Pd(2a,b)(CD3CN)2](BF4)2: PdCl2(CH3CN)2 (62.3
trans-chelated building blocks in self-assembled structures
might contribute to the structural and functional diversity of
supramolecular assemblies. In particular, we are interested in
expanding the rich possibilities of functionalizing and derivat-
izing the trans-chelating ligand and the introduction of stereo-
isomerism and chirality by the desymmetrization of its two
arms.
μmol, 1.4 equiv.) in CH2Cl2 (5 mL) was added to 2a-b (45 μmol,
1 equiv.) in CH2Cl2 (5 mL). The mixture was stirred at room tempera-
ture for 30 min and the solvent was evaporated in vacuo. The raw
products were redissolved in dichloromethane and purified by flash
chromatography on silica gel (dichloromethane/methanol, 20:1) to give
[PdCl2(2a,b)] as a solid (23 μmol, 50–52%). The exchange of chlor-
ides for acetonitrile ligands was made with a AgBF4 solution. A
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ARTICLE
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2.8 mM solution of [PdCl2(2a,b)] in CD3CN (6.3 μmol in 2.25 mL)
was prepared and added to a 11.24 mM solution of AgBF4 in CD3CN
(23.6 μmol in 2.10 mL) in 1:2 equivalence. The mixture was shaken
well and kept in a dark place for 1 h at room temperature. AgCl pre-
cipitatet as a grey solid. 1H NMR [Pd(2a)(CD3CN)2](BF4)2 (CD3CN):
δ = 7.64 (ddd, 7.5, 5.8 1.6 Hz, 2 H, H5), 7.71 (dd, 5.8, 3.3 Hz, 2 H,
H2), 7.96–7.88 (m, 4 H, H3, H1), 8.09 (td, 7.8, 1.5 Hz, 2 H, H4), 8.90
(ddd, 5.8, 1.5, 0.7 Hz, 2 H, H6). 1H NMR [Pd(2b)(CD3CN)2](BF4)2
(CD3CN): δ = 0.35 (s, 12 H, Si-CH3), 1.06 (s, 18 H, tBu), 7.45 (s, 2
H, H2), 7.62 (ddd, 2 H, 5 H), 7.89 (d, 2 H, H3), 8.07 (td, 2 H, H4),
8.89 (m, 2 H, H6).
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Synthesis of [Pd(2c)(CD3CN)2](BF4)2: [Pd(CH3CN)4](BF4)2 (12
μmol, 1.2 equiv.) and 2c (10 μmol, 1 equiv.) were combined in 1 mL
of CD3CN to form a 1 mM solution of [Pd(2c)(CD3CN)2](BF4)2 1H
NMR (CD3CN): δ = 7.44–7.39 (m, 2 H, H7), 7.76–7.70 (m, 2 H, H8),
7.82 (ddd, 7.6 5.9, 1.6 Hz, 2 H, H5), 8.07 (ddd, 7.9, 1.6, 0.7 Hz, 2 H,
H3), 8.24 (ts, 7.8, 1.5 Hz, 2 H, H4), 8.46 (s, 2 H, H2), 9.04 (ddd, 5.9,
1.5, 0.7 Hz, 2 H, H6).
[11] F. Würthner, C.-C. You, C. R. Saha-Möller, Chem. Soc. Rev. 2004,
Synthesis of three-membered Ring (4a): A solution of 3 (50 μL, 7 m)
in CD3CN and a solution of [Pd(2a)(CD3CN)2]2+ (500 μL, 0.7 m) in
CD3CN were combined in a 1:1 ratio. The mixture was shaken well
and left at room temperature for 10 min. to form 4a. 1H NMR
(CD3CN): δ = 3.22 (s, 18 H, Hg), 3.48–3.54 (m, 12 H, Hf), 4.09–4.15
(m, 12 H, He), 7.83–7.77 (m, 12 H, H5, Hb), 7.91–7.96 (m, 6 H, H2),
7.96–7.91 (m, 6 H, H2), 8.02–7.98 (m, 18 H, H3, Ha), 8.07 (td, 7.8,
1.5 Hz, 6 H, H4), 8.22–8.17 (m, 6 H, H1), 8.93 (d, 4.2 Hz, 6 H, Hc),
9.29 (d, 3 Hz, 6 H, Hd), 9.57 (d, 6.3 Hz, 6 H, H6). ESI HRMS: m/z
([C126H108N12O12Pd3B2F8]4+) found: 618.6391 calcd.: 618.6356.
33, 133–146.
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org. Chem. 2002, 41, 2296–2300.
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2003, 3, 263–266.
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363, 3987–3992.
Synthesis of three-membered Ring (4c): A solution of 3 (1.03 mL,
3 mM) in CD3CN and a solution of [Pd(2c)(CD3CN)2]2+ (300 μL,
10.3 mM) were combined in CD3CN. The mixture was shaken well
and left at room temperature for 10 min. to form 4c. 1H NMR
(CD3CN): δ = 3.21 (s, 18 H, Hg), 3.54–3.51 (m, 12 H, Hf), 4.13–4.10
(m, 12 H, He), 7.44 (d, 8.7 Hz, 6 H, H7), 7.61 (d, 8.4 Hz, 6 H, H8),
7.78–7.73 (m, 12 H, H5, Hb), 7.88 (s, 12 H, Ha), 8.11–7.99 (m, 12 H,
H4, H3), 8.68 (s, 6 H, H2), 8.81 (d, 2.5 Hz, 6 H, Hc), 9.24–9.21 (m, 6
H, Hd), 9, 49 (d, 5.9 Hz, 6 H, H6).
[22] M. Jung, Y. Suzaki, T. Saito, K. Shimada, K. Osakada, Polyhe-
dron 2012, 40, 168–174.
Synthesis of two-membered Ring (6a): A solution of 5[25] (250 μL,
2.8 m) in CD3CN and a solution of [Pd(2a)(CD3CN)2]2+ were com-
bined in CD3CN (1 mL, 0.7 m). The mixture was shaken well and left
for 5 min at room temperature to form 6a. 1H NMR (CD3CN): δ =
3.28 (s, 4 H, Hh), 7.41 (d, 4 H, Hb), 7.53 (ddd, 8.1, 5.8, 0.7 Hz, 4 H,
H5), 7.76–7.67 (m, 8 H, Hd, Hc), 7.95–7.86 (m, 8 H, H3, H2), 8.08–
7.99 (m, 8 H, H4, He), 8.18–8.10 (m, 4 H, H1, Ha), 9.16–9.12 (m, 4
H, Hf), 9.26 (dd, 1.6, 0.9 Hz, 4 H, Hg), 9.42 (m, 4 H, H6). ESI MS:
m/z ([C98H60N8O2Pd2BF4)]3+) found: 560.4133 calcd.: 560.4324.
[23] A similar ligand was used to form self-assembled dinuclear rec-
tangular boxes, however, showing a different, non-chelating bind-
ing mode: T. Kawano, J. Kuwana, C.-X. Du, I. Ueda, Inorg.
Chem. 2002, 41, 4078–4080.
[24] Batch by batch, the 1H NMR spectrum of the in situ prepared
[Pd(2a)(CD3CN)2](BF4)2 may contain a second set of signals of
varying intensity which might be assigned to chloride containing
species being in equilibrium with the target compound. Neverthe-
less, these solutions could also be used for the subsequent ring
formation.
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John, G. H. Clever, Angew. Chem. Int. Ed. 2012, 51, 2191–2194.
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2013, 19, 2114–2121.
[27] J. M. Dieterich, G. H. Clever, R. A. Mata, Phys. Chem. Chem.
Phys. 2012, 14, 12746–12749.
Acknowledgments
This work was supported by the Deutsche Forschungsgemeinschaft
(DFG) IRTG 1422 (Metal Sites in Biomolecules). FAP thanks the DFG
and MF the Evonik Foundation for PhD fellowships. TF thanks the
Erasmus Program for financial support.
[28] S. De, K. Mahata, M. Schmittel, Chem. Soc. Rev. 2010, 39, 1555–
1575.
[29] 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. Mont-
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Received: March 22, 2013
Published Online: May 24, 2013
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