Solvent Dependence of the Monomer–Dimer Equilibrium of Ketone-Substituted Triscatecholate Titanium(IV) Complexes

Article abstract of DOI:10.1002/chem.202001053

Hierarchical helicates based on ketone-substituted titanium(IV)triscatecholates show different monomer-dimer behavior depending on different solvents. The dimerization constants of a whole series of differently alkyl-substituted complexes is analyzed to show that the solvent has a very strong influence on the dimerization. Hereby, effects like solvophobicity/philicity, sterics, electronics of the substituents and weak side-chain—side-chain interactions seem to act in concert.

Full text of DOI:10.1002/chem.202001053

A Journal of
Accepted Article
Title: Solvent dependence of the monomer-dimer equilibrium of ketone-
substituted triscatecholate titanium(IV) complexes.
Authors: A. Carel N. Kwamen, Judith Jenniches, Iris M. Oppel, and
Markus Albrecht
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.202001053
Link to VoR: http://dx.doi.org/10.1002/chem.202001053
Supported by

10.1002/chem.202001053
Chemistry - A European Journal
FULL PAPER
Solvent dependence of the monomer-dimer equilibrium of ketone-
substituted triscatecholate titanium(IV) complexes.
A. Carel N. Kwamen,[a] Judith Jenniches,[b] Iris M. Oppel,[b] and Markus Albrecht*[a]
[a]
A. C. N. Kwamen, Prof. Dr. M. Albrecht
Institut für Organische Chemie
RWTH Aachen University
Landoltweg 1, Aachen 52074, Germany
E-mail: markus.albrecht@oc.rwth-aachen.de
J. Jenniches, Prof. Dr. I. M. Oppel
Institut für Anorganische Chemie
RWTH Aachen University
[b]
Landoltweg 1, Aachen 52074, Germany
Supporting information for this article is given via a link at the end of the document.
Abstract: Hierarchical helicates based on ketone-substituted
titanium(IV)triscatecholates show different monomer-dimer behavior
depending on different solvents. The dimerization constants of a
whole series of differently alkyl-substituted complexes is analyzed to
show that the solvent has a very strong influence on the dimerization.
Hereby, effects like solvophobicity/philicity, sterics, electronics of the
substituents and weak side chain-side chain interactions seem to act
in concert.
Scheme 1. Hierarchical formation of helicate type complexes by incorporation
of a metal ion into the spacer of the helicating ligand.
Introduction
Over the last 50 years Supramolecular Chemistry evolved to an
important independent branch of chemistry combining principles
of the traditional disciplines (inorganic, organic, physical
chemistry) and connecting those to biochemistry, material
science or nanotechnology.1
More than 30 years ago Lehn introduced the helicates as
coordination compounds in which two or more linear ligand
strands wrap around two or more metal ions.2 If the helicating
ligands are not covalently linked but contain a non-covalent
connecting point (e. g. a metal ion or a hydrogen bond), helicate
type coordination compounds may be formed in a hierarchical
process (Scheme 1).3 Several “hierarchical” helicates as well as
closely related cluster helicates have been described in the
literature.4
In 2005 we described a hierarchical helicate based on 3-carbonyl-
substituted catecholate ligands forming initially a mononuclear
triscatecholate titanium(IV) complex which in the presence of
lithium counter cations dimerizes to a triple-lithium bridged
coordination compound. The carbonyl may be an aldehyde,
ketone, thioester or ester.5 For several reasons no dimer
formation has been observed for amide derivatives yet: with
secondary amides an NH…Ocatecholate hydrogen bond is blocking
the lithium binding site, while tertiary amides are sterically too
demanding for dimer formation (Scheme 2).
Scheme 2. The lithium dependent monomer-dimer equilibrium based on
carbonyl-substituted titanium(IV) triscatecholates.
The hierarchically formed triscatecholate titanium(IV) helicates
are exceptional in comparison to other hierarchical helicates. In
the solid, the dimeric helicates are present while in solution the
lithium bridged systems slowly reach the thermodynamic
equilibrium between monomer and dimer.6
The equilibrium ratio between monomer and dimer depends on
the strength of lithium binding in the dimer or the ease of lithium
removal, respectively. Thus, the kinds of carbonyl donors as well
as of the solvents are highly influential on the equilibrium state. In
addition, weak side-chain interactions significantly can contribute
to dimer stabilization or destabilization.6
To illustrate the solvent dependence: the complexes of 2,3-
dihydroxybenzaldehyde as ligand at room temperature show
dimerization constants of Kdim = 10 (methanol-d4), 950 (THF-d8)
or 1330 (acetone-d6). In DMSO-d6 or D2O only monomer and in
acetonitrile-d3 only dimer is observed.5 Thus depending on the
1
This article is protected by copyright. All rights reserved.

10.1002/chem.202001053
Chemistry - A European Journal
FULL PAPER
solvent, the whole spectrum from monomer to dimer can be
detected by NMR spectroscopy at ambient conditions (Figure 1).
Intense recent studies were focusing on the ester or thioester
derivatives in DMSO-d6 or methanol-d4 solution, respectively.
Those solvents provide dimer stability windows which make a
comparative investigation within the oxo-6 or thioester5 series
depending on different side-chains possible. However, it would be
of major interest to perform related studies which simultaneously
allow the evaluation of the influence of the side chain as well as
of different solvents.
lithium carbonate to obtain the hierarchical helicates Li[Li3(1)6Ti2]
which in solution are in equilibrium with the monomeric species
Li2[(1)3Ti] (Scheme 3).5
Scheme 3. Preparation of the ligands discussed in this study.
The catechol ligands bear ketone substituents of the n-alkane
series from methyl to dodecyl (1a-l-H2), -branched substituents
(1m-o-H2), secondary substituents (1p-s-H2), and substituents
with phenyl groups (1t,u-H2).7
Figure 1. Stability domains in which the lithium dependent monomer dimer
equilibrium of carbonyl substituted triscatecholate titanium(IV) complexes can
be observed depending on the carbonyl moiety as well as on the solvent. The
results of the present study on ketone derivatives are highlighted in the box.
Therefore, our focus now was shifted back to the ketone based
catecholate ligands 1-H2 and found out that they are ideal
candidates for the systematic investigation of the dimer stability
with variation of the substituents as well as of the solvents. Some
of the ketone derivatives were already studied in methanol-d4.5a
Some new complexes are added in here and significantly different
dimerization behavior is observed depending on the solvents
DMSO-d6, methanol-d4, acetonitrile-d3, THF-d8 and acetone-d6.
Figure 2. Structure of the anion [Li3(1o)6Ti2]- as observed in the crystal of
K[Li3(1o)6Ti2] (side (a) and top view (b)) and of [Li3(1s)6Ti2]- (side (c) and top
view (d)). Grey: C, white: H, red: O, blue: Li, yellow: Ti, the cyclohexylmethyl
substituents are shown in black.
Results and Discussion
The crystal structure of the ethyl ketone Li[Li3(1b)6Ti2] has been
described earlier.5a In addition, the structure of the more sterically
demanding cyclohexyl methyl K[Li3(1o)6Ti2] and cyclhexyl
substituted complex Li[Li3(1s)6Ti2] have been obtained now.
Figure 2a shows the side view of the anion [Li3(1o)6Ti2]- revealing
the connecting bis-titanium tris-lithium centre while the top view
(Figure 2b) shows the relative orientation of the cyclohexylmethyl
The required ligands 1-H2 were prepared by Grignard addition of
alkyl Grignard reagents to dimethoxybenzaldehyde 2 followed by
Jones oxidation of the alcohols 3 and final ether cleavage of the
protecting groups at 4. The obtained ligands 1-H2 (3 eq) were
coordinated to titanoylbis(acetylacetonate) in the presence of
2
This article is protected by copyright. All rights reserved.

10.1002/chem.202001053
Chemistry - A European Journal
FULL PAPER
substituents. Hereby the cyclohexyl rings adopt roughly an
alternating position with the “plane” of the six membered ring
orientated parallel or orthogonal to the Ti-Ti axis. This allows a
close packing with H…H distances of 2.29-2.98 Å between
neighboring T-shaped cyclohexyl rings. All cyclohexyl moieties
adopt the chair conformation with an equatorial position of the
methylene unit.8
Li[Li3(1s)6Ti2] is the sterically most crowded hierarchically formed
dimer of this kind which has been structurally characterized so far.
Due to the limited space around the central core the cyclohexyl
planes have to orientate parallel to the Ti…Ti axis. In addition, the
dimer has to “stretch” resulting in a somewhat longer Ti…Ti
distance of 5.562(1) Å in [Li3(1s)6Ti2]- compared to 5.444(1) Å in
[Li3(1o)6Ti2]-.
Dimerization constants of the complexes Li[Li3(1a-u)6Ti2] were
determined by proton NMR at 295 K in DMSO-d6, methanol-d4,
acetonitrile-d3, THF-d8 and acetone-d6 (Table 1).
Figure 3. Dimerization constants Kdim (at 295 K) of the complexes Li[Li3(1a-
u)6Ti2 in DMSO-d6, methanol-d4, acetonitrile-d3, THF-d8 and acetone-d6.
Table 1. Solvent dependent dimerization constants Kdim for the equilibrium
between two monomers Li2[(1)3Ti] and one dimer Li[Li3(1)6Ti2] as obtained at
295 K by proton NMR integration at a concentration of 2•10-3 mol L-1.
Ligand (R)
1a (Me)
DMSO-d6
monomer
CD3OD
3890
± 505
785[a]
CD3CN
715
± 84
THF-d8
1430
± 177
1960
± 247
3170
± 408
4000
± 521
6215
± 822
6075
± 802
3260
± 420
4960
± 651
2570
± 328
5480
± 721
2780
± 356
5270
± 692
7570
± 1007
3150
± 406
2180
± 276
9720
± 1301
6390
± 845
7970
± 1061
6390
± 845
950
(D3C)2C=O
1240
± 152
1b (Et)
monomer
35 ± 3
3260
± 420
7460
± 990
5400
± 710
5520
± 727
3120
± 402
3640
± 472
3890
± 505
5515
± 677
5250
± 70
5825
± 83
5155
± 677
600
± 70
700
± 83
540
28590
± 3913
54150
± 7979
30780
± 4219
36980
± 5082
16560
± 2245
18030
± 2448
12320
± 1659
19250
± 2618
15900
± 2884
12350
± 1665
8560
1c (Pr)
1110[a]
1500[a]
1015[a]
965[a]
1d (Bu)
55 ± 5
1e (Pent)
1f (Hex)
1g (Hept)
1h (Oct)
1i (Non)
1j (Dec)
1k (Undec)
1l (Dodec)
1m (iBu)
25 ± 2
180 ± 19
90 ± 9
725[a]
115 ± 12
110 ± 11
90 ± 9
1425[a]
1125 ±
137
665[a]
85 ± 8
740
± 88
1200[a]
80 ± 8
± 1142
1090
± 132
2950
± 378
175 ± 18
135 ± 14
95 ± 9
175 ±
18
100
± 10
55 ± 5
1n
(CH2cyBu)
1o
(CH2cyHex)
1p (iPr)
6690
± 887
± 63
25 ± 2
7 ± 1
4 ± 1
1730
± 216
505
± 58
375
± 42
965
± 116
130
± 13
1040
± 126
2000
± 252
4700
± 615
2560
± 326
1q (3-Pent)
1r (cyPent)
1s (cyHex)
1t (Ph)
monomer
160 ± 17
monomer
160 ± 17
50 ± 5
Figure 4. Kdim (at 295 K) of the complexes Li[Li3(1a-u)6Ti2 as observed in
different solvents.
40 ± 4
30 ± 3
70 ± 7
Table 1 and Figure 3,4 summarize the obtained dimer stabilities.
It is obvious that the dimerization constants rise in the order
DMSO-d6 < methanol-d4 < acetonitrile-d3 ≤ THF-d8 < acetone-d6
as it is roughly summarized in the highlighted box in Figure 1. The
observed trend in dimerization constants can neither be
correlated with the polarity of the solvent (Reichardt polarity
parameters: ET = 45.1 (DMSO), 55.4 (MeOH), 45.6 (MeCN), 37.4
(THF) and 42.2 (Aceton))9 nor with the ability to dissolve lithium
455 ± 52
± 114
675
± 79
1u (Bz)
146 ±
15
290
± 32
985 ± 119
[a] From reference 5a.
3
This article is protected by copyright. All rights reserved.

10.1002/chem.202001053
Chemistry - A European Journal
FULL PAPER
cations.10 However, the dimerization tendency roughly follows the
lipophobicity/philicity of the respective solvent. Alkanes are not
soluble in DMSO, they show low solubility in methanol and
acetonitrile and they are more or less miscible with THF and
acetone. Thus, more hydrophilic solvents stabilize the highly
charged monomer with two “free” lithium counter cations in which
oxygen atoms are exposed to the surface of the complex while
lipophilic solvents prefer the less charged dimer with the oxygen
atoms buried within the complex.
This results in low dimerization constants of the complexes with
branched side chains.
THF-d8: Starting with the methyl ketone the dimerization constant
gradually increases until it reaches the pentyl derivative. The
hexyl and higher n-alkyl substituted complexes show a strong
even/odd behavior with the even alkyl groups resulting in higher
and the odd in lower dimerization constants. This even-odd
behavior is an indication for a direct interaction between the alkyl
chains.12 The Kdim’s of the -branched derivatives are related to
the dimerization constants of the n-alkyls while the bulky
secondary ketones result in unusually high ones (even higher
than the n-alkyls).
Acetone-d6: The dimerization behavior of the n-alkanes in
acetone-d6 indicates a strong influence of the electron donating
alkyl groups from methyl to ethyl to n-propyl leading to increasing
Kdim’s. With longer alkyl chains the dimerization constants
gradually decrease showing some even/odd alternating behavior.
Due to higher steric demands the -branched systems possess
somewhat lower and the -branched very low dimerization
constants.
Different trends can be observed for the dimerization constants
based on the different solvents (Figure 4):
DMSO-d6: The Kdim’s in DMSO-d6 follow trends as observed
earlier for the corresponding esters.6 For the methyl- as well as
ethylketones only monomers are observed while with gradually
increasing numbers of carbon atoms of the n-alkyl substituent Kdim
increases reaching a maximum for the hexyl compound. With
longer n-alkyls Kdim stepwise decreases again. Figure 5 shows a
comparison of the dimerization constants of the n-alkyl-
substituted ketone (blue) and ester derivatives (red) revealing
similar shapes of the trend lines (dotted lines).
Our investigations show that there is a strong solvent dependence
of the monomer dimer equilibrium of Li[Li3(1a-u)6Ti2] based on
different effects in different solvents resulting in very different
stability patterns of the set of compounds in the investigated
solvents.13 DMSO-d6, acetonitrile-d3 and acetone-d6 show more
or less easy to explain patterns of Kdim: initially Kdim increases with
growing chain length while it decreases with longer chains. This
may be due to an entropy effect as observed for the
corresponding n-alkyl esters.
The solvents methanol-d4 and THF-d8 behave in an unexpected
way: In case of methanol-d4 only steric effects seem to be
influential, leading to lower Kdim’s with bulkier side chains. In THF-
d8 higher dimer stability is observed with more bulky groups. This
observation may be due to a direct attractive interaction between
the side chains in this solvent. Bulkier groups are able to have
direct contact to each other while less bulky groups have to adopt
their conformation appropriately.14 This interpretation is supported
by the observation of an even odd behavior of the dimerization
constants in case of the long n-alkyl chains.
Figure 5. Kdim of the n-alkyl (blue) and n-alkoxy (red) substituted complexes
plotted against the chain length (number of C or C+O atoms) of the respective
side-chain. The dotted lines represent the respective trend lines.
The branched compounds show in most cases much lower
dimerization tendencies than the linear ones with the exception of
the isobutyl and cyclopentyl substituted complexes. The
complexes with aromatic side chains prefer the formation of the
monomer due to the high solvophilicity of aromatics in DMSO. The
exceptionally high Kdims of the isobutyl and cyclopentyl ketones
may be due to some interactions between the side chains in the
dimeric helicates (e.g. dispersion11) in addition to solvophobic
effects. The isobutyl complex hereby may be compared to the
corresponding isopropyl ester in which stabilizing dispersive
interactions have been verified.6
Conclusion
The monomer dimer equilibrium of ketocatechol based
hierarchical helicates Li2[(1)3Ti]/Li[Li3(1)6Ti2] is an ideal tool to
investigate weak interactions of different side chains in different
solvents. 15 Thus it represents an interesting alternative to Wilcox
molecular balance.16 Variation of the solvent leads to dramatically
different patterns of the stability constants revealing the influence
of effects like sterics, electronics and side chain-side chain
interactions. Often the concerted influence of all the effects is
obvious. However, in methanol-d4 only sterics seem to be
responsible for the dimer stability. Some observed dimerization
constants are exceptionally high (Li[Li3(1m,r)6Ti2] in DMSO-d6,
Li[Li3(1p)6Ti2] in acetonitrile-d3 and Li[Li3(1m, p-s)6Ti2] in THF-d8).
In those cases, some attractive side chain-side chain interactions
between the bulky groups seem to become important, which may
be based on London dispersion.17
Methanol-d4:5a In methanol-d4 there seems to be virtually no
difference in the electronic influence of different substituents. The
observed dimerization constants lead to the impression that here
only sterics are controlling the dimer stability. The methyl ketone
as the sterically least demanding group results in the highest Kdim
.
The longer n-alkyl derivatives show very similar dimer stabilities.
However, it is reduced in the complexes with sterically more
demanding - and even more with -branched side chains.
Acetonitrile-d3: In this solvent the dimerization constant
gradually increases from the methyl to the n-propyl ketone and
after this reaches a plateau starting with butyl. A drop in Kdim is
found for the hexyl to octyl substituted derivatives. The initial
increase of Kdim can be attributed to the increasing donor ability of
the substituents while later on mainly steric effects are important.
Keywords: self assembly • helicate • thermodynamics •
intermolecular interaction • solvent effect
4
This article is protected by copyright. All rights reserved.

10.1002/chem.202001053
Chemistry - A European Journal
FULL PAPER
[1] (a) J.-M. Lehn, Supramolecular Chemistry – Concepts
Puttreddy, J. S. Ward, K. Rissanen, R. Fröhlich, M. Albrecht,
and Perspective, VCH, Weinheim, 1994; (b) F. Biedermann, Chem. Eur. J. 2020, 26, 1396-1405.
H. J. Schneider, Chem. Rev. 2016, 116, 5216–5300. [7] For a recent example of catechol-based helicates see:
(a) J.-M. Lehn, A. Rigault, J. Siegel, J. Harrowfield,
[2]
Y. Yamasaki, H. Shio, T. Amimoto, R. Sekiya, T. Haino,
Chem. Eur. J. 2018, 24, 8558-8568.
[8] See for comparison the complexes with
cyclohexylesters: M. Schlottmann, D. Van Craen, J. Baums,
I. Funes Ardoiz, C. Wiederhold, I. M. Oppel, M. Albrecht,
Inorg. Chem. 2020, 59, 3, 1758-1762.
B. Chevrier D. Moras, Proc. Natl. Acad. Sci. USA, 1987, 84,
2565-2569; (b) C. Piguet, G. Bernardinelli, G. Hopfgartner,
Chem. Rev., 1997, 97, 2005-2062; (c) M. Albrecht, Chem.
Rev., 2001, 101, 3457-3497. For selected highlights in
helicate chemistry see: (d) M. J. Hannon, V. Moreno, M. J.
Prieto, E. Moldrheim, E. Sletten, I. Meistermann, C. J. Isaac, [9] C. Reichardt, Chem. Rev. 1994, 94, 2319-2358.
K. J. Sanders, A. Rodger, Angew. Chem. Int. Ed. 2001, 40,
880-884; (e) J. R. Nitschke, D. Schultz, G. Bernardinelli, D.
Gerard, J. Am. Chem. Soc. 2004, 126, 16538-16543; (f) S.
E. Howson, A. Bolhuis, V. Brabec, G. J. Clarkson, J.
Malina, A. Rodger, P. Scott, Nat. Chem. 2012, 4, 31–36; (g)
J.-F. Ayme, J. E. Beves, D. A. Leigh, R. T. McBurney, K.
Rissanen, D. Schultz, Nat. Chem. 2012, 4, 15-20; For
catechol-based helicates see: (h) E. J. Enemark, T. D. P.
Stack, Angew. Chem., Int. Ed. Engl. 1995, 34, 996-998; (e)
M. Albrecht, S. Kotila, Angew. Chem., Int. Ed. Engl. 1995,
34, 2134-2137; (i) B. Kersting, M. Meyer, R. E. Powers, K.
N. Raymond, J. Am. Chem. Soc. 1996, 118, 7221-7222; (j)
U. Kiehne, A. Lützen, Eur. J. Org. Chem. 2007, 5703-5711;
(k) Y. Yamasaki, H. Shio, T. Amimoto, R. Sekiya, T. Haino
Chem. Eur. J. 2018, 24, 8558 – 8568.
[10] M. M. Markowitz, W. N. Hawley, D. A. Boryta, R. F.
Harris, Journal of Chemical and Engeneering Data, 1961, 6,
325-327.
[11] For dispersion effects in supramolecular chemistry see:
(a) T. Liu, H.-J. Schneider, Angew. Chem. Int. Ed. 2002, 41,
1368-1370; (b) H.-J. Schneider, Acc. Chem. Res. 2015, 48,
1815-1822; (c) L. Yang, J. B. Brazier, T. A. Hubbard, D. M.
Rogers, S. L. Cockroft, Angew. Chem. Int Ed Engl. 2016,
55, 912-916; (d) see also: S. Rösel, C. Balestrieri, P. R.
Schreiner, Chem. Sci. 2017, 8, 405-410.
[12] (a) R. Boese, H.-C. Weiss, D. Bläser, Angew. Chem.
Int. Ed. 1999, 38, 988-992; (b) see also: A. Baeyer, Ber.
Dtsch. Chem. Ges. 1877, 10, 1286-1288.
[13] For solvent influence on alkyl-alkyl interactions see: L.
Yang, C. Adam, G. S. Nichol, S. L. Cockroft, Nature
Chemistry 2013, 5, 1006-1010.
[3] M. Albrecht, Hierarchically assembled titanium(IV)
helicates. in Synergy in Supramolecular Chemistry.
Nabeshima, T., CRC Press, Boca Raton, 2015, chapter 2,
19-32
[14] See for comparison: P. R. Schreiner, L. V. Chernish, P.
A. Gunchenko, E. Y. Tikhonchuk, H. Hausmann, M.
Serafin, S. Schlecht, J. E. P. Dahl, R. M. K. Carlson, A. A.
Fokin, Nature 2011, 477, 308−311.
[4]
(a) M. H. W. Lam, S. T. C. Cheung, K.-M. Fung, W.-
T. Wong, Inorg. Chem. 1997, 36, 4618-4619; (b) T. Konno,
K. Takuda, T. Suzuki, K.-I. Okamoto, Bull. Chem. Soc. Jap.
1998, 71, 1049-1054; (c) X. Sun, D. W. Johnson, D.
Caulder, R. E. Powers, K. N. Raymond, E. H. Wong,
Angew. Chem. Int. Ed., 1999, 38, 1303-1306; (d) Y. Sakata,
S. Hiraoka, M. Shionoya, Chem. Eur. J., 2010, 16, 3318-
3325; (e) S. Hiraoka, Y. Sakata, M. Shionoya, J. Am. Chem.
Soc., 2008, 130, 10058–10059; (f) K. Yoneda, K. Adachi,
K. Nishio, M. Yamasaki, A. Fuyuhiro, M. Katada, S.
Kaizaki, S. Kawata, Angew. Chem. Int. Ed. 2006, 45, 5459–
5461; (g) G. N. Newton, T. Onuki, T. Shiga, M. Noguchi, T.
Matsumoto, J. S. Mathieson, M. Nihei, M. Nakano, L.
Cronin, H. Oshio, Angew. Chem. Int. Ed. 2011, 50, 4844 –
4848; (h) M. Okamura, M. Kondo, R. Kuga, Y. Kurashige,
T. Yanai, S. Hayami, V. K. K. Praneeth, M. Yoshida, K.
Yoneda, S. Kawata, S. Masaoka, Nature 2016, 530, 465 –
468; (i) T. Nakagawa, H. Danjo, M. Kawahata, K.
[15] See for comparison: C. A. Hunter, Angew. Chem. Int.
Ed. 2004, 43, 5310–5324.
[16] a) S. Paliwal, S. Geib, C.S.Wilcox, J. Am. Chem. Soc.
1994, 116, 4497-4498; b) E. Kim, S. Paliwal, C. S. Wilcox,
J. Am. Chem. Soc. 1998, 120, 11192–11193.
[17] K. Mꢀller-Dethlefs, P. Hobza, Chem. Rev. 2000, 100,
143−167.
Yamaguchi, Tetrahedron 2019, 75, 315-323.
[5]
(a) M. Albrecht, S. Mirtschin, M. de Groot, I. Janser,
J. Runsink, G. Raabe, M. Kogej, C. A. Schalley, R.
Fröhlich, J. Am. Chem. Soc., 2005, 127, 10371-10387; (b)
A. C. N. Kwamen, G. S. de Macedo, C. Wiederhold, I. M.
Oppel, M. Albrecht, Chem. Eur. J. 2020, doi:
10.1002/chem.201905212.
[6]
(a) D. Van Craen, W. H. Rath, M. Huth, L. Kemp, C.
Räuber, J. Wollschläger, C. Schalley, A. Valkonen, K.
Rissanen, M. Albrecht, J. Am. Chem. Soc. 2017, 139,
16959–16966. (b) A. C. N. Kwamen, M. Schlottmann, D.
Van Craen, E. Isaak, J. Baums, L. Shen, A. Massomi, C.
Räuber, B. P. Joseph, G. Raabe, C. Göb, I. M. Oppel, R.
5
This article is protected by copyright. All rights reserved.

10.1002/chem.202001053
Chemistry - A European Journal
FULL PAPER
Entry for the Table of Contents
The behavior of the monomer dimer equilibrium of hierarchical helicates formed from keto-catechole ligands strongly depends on the
solvent which is used. Based on the respective solvents, different side chain-side chain interaction modes like sterics,
solvophobicity/philicity and probably even London dispersion become highly influential for the stabilization or destabilization of the
dimers.
6
This article is protected by copyright. All rights reserved.