Supramolecular metallacycles with a 'pseudo double-paracyclophane' structure based on flexible π-conjugated linkers

Article abstract of DOI:10.1039/c5cc03778f

The straightforward synthesis of new supramolecular metallacycles having a 'pseudo double-paracyclophane' structure is presented. They are obtained from the reaction of a pre-assembled Cu(i) bimetallic precursor bearing short intermetallic distances with

Full text of DOI:10.1039/c5cc03778f

View Article Online
View Journal
ChemComm
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: C. Lescop, W.
Shen, M. El Sayed Moussa and Y. Yao, Chem. Commun., 2015, DOI: 10.1039/C5CC03778F.
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the Ethical guidelines still
apply. In no event shall the Royal Society of Chemistry be held
responsible for any errors or omissions in this Accepted Manuscript
or any consequences arising from the use of any information it
contains.
www.rsc.org/chemcomm

Please do not adjust margins
Page 1 of 4
ChemComm
View Article Online
DOI: 10.1039/C5CC03778F
Chemical Communications
COMMUNICATION
Supramolecular metallacycles with ‘pseudo double-
paracyclophane’ structure based on flexible π-conjugated linkers.
Received 00th January 20xx,
Accepted 00th January 20xx
W. Shen, M. El Sayed Moussa, Y. Yao, C. Lescop*
DOI: 10.1039/x0xx00000x
Dedicated to the Pr. Dr. Manfred
Scheer for his 60th birthday
www.rsc.org/
The straightforward synthesis of new supramolecular
metallacycles having ‘pseudo double-paracyclophane’ structure is
presented. They are obtained from the reaction of a pre-
assembled Cu(I) bimetallic precursor bearing short intermetallic
distances with cyano-capped homoditopic π-conjugated linkers
having flexible central cores.
Coordination driven supramolecular synthetic chemistry is
a
powerful approach for the construction of discrete and stable
complex molecular architectures such as macrocycles or cages, a
topic which is currently of considerable interest.1,2 Typically, the
design of such coordination-based systems relies on reaction of
multitopic metal centers and rigid organic linkers whose symmetry
and connectivity are selected considering the overall shape of the
target assembly (defining the “Directional-Bonding Approach”2g).
The associations between these sub-units are directed by non-
covalent
interactions
(metal-ligand
bonds,
metal-metal
interaction…) that have to be strongly directional and kinetically Scheme 1. a) Molecular structure of the pre-assembled molecular clip A,
Synthesis of the supramolecular assemblies C-E; b) Synthesis of the
labile to allow reasonably predictable, reproducible and selective
syntheses. In so doing the topology of the ensuing products can be
supramolecular metallacycles 5-8 and structure of the linkers 1-4.
reasonably controlled and directed. In this field, we have previously
described the general coordination-driven supramolecular synthesis
of a series of stacked supramolecular assemblies C,3 D4 and E5
(Scheme 1a). They were obtained from the reaction of the pre-
assembled bimetallic Cu(I) U-shape molecular clip A6 (Scheme 1a)
bearing hemilabile bridging phosphane coordination mode for the
2,5-bis(2-pyridyl)phosphole ligand B6 and short intermetallic
distances (2.551(1) Å, revealing cuprophillic interactions) with,
respectively, a large variety of homoditopic rigid organic π-
conjugated linkers, with the metal-based linear linker [Au(CN)2]- and
with a series of cyano-capped monotopic π-conjugated ligands.
These results suggested that the stabilizing non-covalent interlinker
lateral interactions (π-π interaction, aurophilic interaction)
generated within these self-assembled structures could play a key
role in the selective coordination driven synthetic processes
conducted on pre-assembled polymetallic molecular clip A bearing
short intermetallic distances, possibly complementing the
“Directional-Bonding Approach” syntheses rules. This hypothesis
has triggered us to explore whether such specificity of the
molecular clip A could be exploited allowing a general access to
original discrete supramolecular architectures. In this work, we
have focused our attention on the reaction of ditopic linkers
bearing central flexible fragments and terminal cyano capped π-
conjugated moieties with the molecular clip A (Scheme 1b). Indeed,
employing such flexible donor linkers challenges the coordination
driven supramolecular chemistry principles as
noticeable amount of the pre-programmed assembling information
that serves as basis of product predictivity is generally
a loose of a
a
anticipated.7 This induces a lower selectivity in self-assembly
supramolecular processes resulting in a mixture of unpredictable
products whose yields and relative ratio may mostly depend upon
minor experimental variations. This assumption a priori weakens
the interest of polytopic flexible donor linkers in coordination
Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Université de Rennes
1, Campus de Beaulieu, 35042 Rennes Cedex (France). E-mail: christophe.lescop
@univ-rennes1.fr Fax: (+33) 2-23-23-69-39; Tel: (+33) 2-23-23-50-02
† Footnotes relating to the title and/or authors should appear here.
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 1
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 2 of 4
View Article Online
DOI: 10.1039/C5CC03778F
Chemical Communications
COMMUNICATION
Fig. 1. a) General and b) lateral views of the X-ray crystal structures of the tetracationic supramolecular metallacycles 5-8 ; c) view of the stacking patterns of 5-8
observed in single crystals. (counteranions and solvent molecules have been omitted for clarity).
driven supramolecular syntheses and still a limited number of NMR spectrum of the crude reactions, as well as those recorded for
examples exits that employ such linkers to generate discrete the crystalline samples dissolved in CD2Cl2, show singlets at ca. + 8
structures.7
ppm that are similar to the signals registered for the precursor A as
In a first step, we have focused our attention on the reaction of the well as those recorded for the supramolecular assemblies C-E
1
molecular clip A with the cyano-capped homoditopic linkers 1-4 (Scheme 1a). Moreover H NMR spectra presented a simple single
set of signals, revealing highly symmetrical assemblies 5-8 in which
the acetonitrile ligands carried by the molecular clip A have been
(Scheme 1b) carrying both ‘rigid’ π-conjugated systems and
‘flexible’ linear -(CH2)n- aliphatic moieties of various lengths (shorter
(1,3) or longer terminal π-systems (2,4); shorter, n=4 (1,2) or longer,
n=6 (3,4) central aliphatic fragments). The new homoditopic linkers
1-4 were synthesized in medium to good yields according to a
sequence of Sonogashira coupling and Wadsworth-Emmons
reactions.8 Their room temperature 1:1 reaction in CH2Cl2 with the
molecular clip A afforded after purification the supramolecular
assemblies 5-8 (Scheme 1b), respectively, as orange polycrystalline
air stable powders in medium to good yields.8 The derivatives 5-8
are readily soluble in chlorinated solvents (CHCl3, CH2Cl2). Their
multinuclear NMR characterizations8 indicate that the CuI2(B)2
moiety is maintained along these reactions. Indeed, the 31P{1H}
substituted affording molecular species bearing
a
1/1
(CuI2(B)2/linker ratio. The molecular structures of the assemblies 5-8
were established due to X-ray diffraction studies8 performed on
single crystals9 obtained at room temperature from pentane
diffusion into CH2Cl2 solutions. These four derivatives crystallize in
the P-1 space group of the triclinic system (Table S1) with an
inversion centre located in the centre of the tetracationic
derivatives 5-8. Unexpectedly, in spite of the various lengths of the
linkers 1-4 and their flexible aliphatic central cores, assemblies 5-8
are metallocyclophanes formed from the coordination of two
flexible linkers on two CuI2(B)2 moieties (Fig. 1). In these solid state
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 2
Please do not adjust margins

Page 3 of 4
ChemComm
Please do not adjust margins
Journal Name
COMMUNICATION
-
structures, the four BF4 counterions and the co-crystallization
CH2Cl2 solvent molecules are located outside the self-assembled
molecules. In each metallocyclophane, the four Cu(I) atoms lie in
the same plane and the metric parameters of the dicationic CuI2(B)2
cores are very similar to those of the corresponding free molecular
clip A and related tetracationic π-stacked rectangles C (Table S2)3
suggesting a strain-free coordination of the linkers 1-4 on the
[Cu2(B)2]2+ units. In these assemblies, the -(CH2)n- central aliphatic
strings have different configurations, reflecting their relative
flexibility (Fig. 1) : in the case of the derivative 5, a gauche
configuration is observed for each aliphatic chain of the two linkers
1 while in the metallacycles 6-8 the two aliphatic fragments are
mostly parallel with an 'eclipsed' configuration. No short contacts
are observed between the central aliphatic strings. Probably as a
result of a steric congestion of the imbricated -(CH2)n- fragments
located in the central part of the metallocyclophanes, the lateral
offset of the neighbouring π-systems are larger within derivatives 5-
8 than in the supramolecular rectangles C, but it does not forbid
intramolecular π-π interaction to occur. The π-π interaction is weak
in the case of assembly 5 (quite large inter π-planes distances, ca.
3.7 Å, and limited area of π-surface involved are observed; see Fig.
S7) but it is more significant for derivative 7 based on the same
short π- systems but having a longer and 'eclipsed' aliphatic central
fragments. Assemblies 6,8 based on linkers having longer π-systems
present very similar features: the π-conjugated fragments are
almost planar (maximum deviation to the mean plane: 6, 0.252 Å; 8,
0.209 Å), parallel (angle between the mean plane of two interacting
π-moiety: 6, 5.22°; 8, 1.71°) and participate in similar π-π
interactions (inter π-planes distances : ca. 3.4 - 3.5 Å) with large
area of their surface involved (see Fig. S7). Therefore in these
assemblies, despite the different configurations presented by the
aliphatic moieties of the linkers, the π-fragments of the
homoditopic linkers participate to intramolecular π-π interaction,
similarly to what is observed in the metallocyclophanes C3 (Scheme
1a). As a result, solid state arrangements of the aliphatic and
aromatic fragments of the ligands 2-4 in self-assembled derivatives
6-8 induces the formation of unprecedented ‘pseudo double-
paracyclophane’ structure (see Fig. 1b) having large lengths (6, 52.4
Å; 8, 52.3 Å). In addition, a remarkable feature observed in the solid
state structure of most of the π-stacked supramolecular assemblies
of type C and E (Scheme 1a) is their self-organization within infinite
π-stacked columns due to intermolecular π-π interactions,3
affording a very general approach to arrange symmetrical linear π-
conjugated organic systems in infinite molecular networks in which
all the π-systems overlap. Interestingly, intermolecular π-π
interactions (inter π-planes distances: ca. 3.3 - 3.5 Å) are also
observed in the solid state structure of the derivatives 5, 6 and 8
leading to the supramolecular organization of these self-assembled
View Article Online
DOI: 10.1039/C5CC03778F
Fig. 2 a) Synthesis of the derivatives 11 and 12, b) X-ray crystal structures of b)
the cationic coordination polymer 11 and c) the tetracationic derivative 12 (H
atoms, counteranions and solvent molecules have been omitted for clarity).
suberonitrile (n=6) 10 led in good yields after treatment clear
orange powders to the derivative 12. Conversely to 11, the
compound 12 is readily soluble in chlorinated solvents and NMR
spectroscopies8 suggest that during this reaction occurred only a
partial substitution of the acetonitrile ligands carried by the CuI2(B)2
fragment in A. This is confirmed by the crystal structure of 12,
determined from single crystals grown with pentane vapour
diffusion in CH2Cl2 solutions of 12.8 In contrast to the polymeric
assembly 11, the derivative 12 is a molecular species in which two
CuI2(B)2 fragments are connected due to the coordination of one
equivalent of the linker 10 on one metal center of each CuI2(2)2
fragment while the second CuI metal center is still coordinated to
an acetonitrile ligand (Fig. 2c). Note that up to 10 equivalents of 10
were reacted with the molecular clip B but the derivative 12 was
the only species that was obtained in the solid state. Finally,
derivatives 11 and 12 are isolated in the solid state as no specific
intermolecular contacts between isolated molecular entities are
observed. Although the (CuI)2 nodes retain a U-shape topology in
the assemblies 11 and 12 no metallacycle is formed showing that
the geometry of the bimetallic molecular clip A is not directing
exclusively the formation of metallacycle structures. These solid
state structures confirm that the molecular clip A does not present
any specific proneness to afford systematically supramolecular
metallacycles due to its reaction on homoditopic linkers and
highlight the key role played by the intramolecular π-π interactions
between the π-walls of the linkers to allow the selective formation
of supramolecular metallacycles based on the flexible linkers 1-4.
These results demonstrate that according to a rational design of the
individual molecular building blocks, the syntheses rules requested
to apply a coordination-driven supramolecular synthesis can be
metallacycles in infinite columns bearing discrete stacks of four supplemented by the intentional occurrence of non-covalent lateral
aromatic moieties separated by imbricated -(CH2)n- fragments (Fig.
1c).10
π-π interactions between the assembled subunits to give a general
access to original supramolecular assemblies. This is allowed due to
the use of pre-assembled polymetallic molecular clip bearing
specific molecular organization such as those encountered in the U-
shape molecular clip A (short intermetallic distances, structural
rigidity and hemilability of the N,P,N ligand B).3 In the near future,
the versatility of this approach will be studied, extending the scope
of the polytopic linkers used with the variation of the ''ratio''
rigid/flexible fragment, of the nature of the flexible moiety and of
the connectivity of the linkers. The characterisation of large series
of new discrete supramolecular assemblies bearing original
structural features and functionnalities is expected.
In order to confirm the critical importance of the π-conjugated
fragments in the core of the linkers 1-4 to drive the formation of
supramolecular metallacycles 5-8, we have reacted the molecular
clip A with the cyano-capped homoditopic linkers 9, 10 bearing only
-(CH2)n- cores. Reacting adiponitrile (n=4) 9 (Fig. 2a) with the
molecular clip A in CH2Cl2 in a 1:1 ratio afforded derivative 11 (71%
yield),8 which was characterized by an X-ray diffraction study.9 This
compound is a one dimensional coordination polymer (Fig 2b) in
which two consecutive CuI2(B)2 fragments are connected by one
linker 9. The 1:1 reaction of the precursor A with the longer linker
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
ChemComm
Page 4 of 4
COMMUNICATION
Journal Name
2012, 14, 3367; c) L. Carlucci, G. Ciani, P. Macchi, D. M.
Proserpio, S. Rizzato, Chem. Eur. J.,DO1I9: 9109.,1039/C5CC03778F
V,iew2A3r7tic;le dO)nlinLe.
Carlucci, G. Ciani, D. M. Proserpio, S. Rizzato, Chem. Eur. J.,
2002, , 1519; e) L-P. Xue, X-H. Chang, L-F. Ma, L-Y. Wang,
RSC Adv., 2014, , 60883; f) A. Granzhan, C. Schouwey, T.
This work was supported by the Ministère de la Recherche et de
l’Enseignement Supérieur, the CNRS and the ANR (ANR-12-IS07-
0002 P-OPTOELECTR-MOLMAT). C.L. thanks the Alexander von
Humboldt Foundation for a fellowship for experienced researcher.
5
8
4
Riis-Johannessen, R. Scopelliti, K. Severin, J. Am. Chem. Soc.,
2011, 133, 7106.
For experimental details, spectroscopic and X-Ray diffraction
data, see SI.
Careful examination of the several crystallization batches
and unit cell determination of single crystals randomly
selected did not evidence the formation of other
polymorphs.
Notes and references
8
9
1
a) M. Liu, W. Liao, C. Hu, S. Du, H. Zhang, Angew. Chem. Int.
Ed., 2012, 51, 1585; b) Q. F. Sun, S. Sato, M.Fujita, Nat.
Chem,. 2012,
Chen, M. Wu, K. Su, M. Hong, Chem. Sci., 2012,
A. Bilbeisi, J. K. Clegg, N. Elgrishi, X. d. Hatten, M. Devillard, B.
Breiner, P. Mal, J. R. Nitschke, J. Am. Chem. Soc. 2012, 134
4
, 330; c) K. Xiong, F. Jiang, Y. Gai, D. Yuan, L.
3
, 2321; d) R.
10 Concerning the assembly
distances between the -moieties of the linkers
are too large for intermolecular interactions.
7
,
solid state intermolecular
,
π
3
(ca. 4.8 Å)
5110; f) M. Otte, P. F. Kuijpers, O. Troeppner, I. Ivanovic´-
Burmazovic´, J. N. H. Reek, B. d. Bruin, Chem. Eur. J., 2013,
19, 10170; g) S. Pasquale, S. Sattin, E. C. Escudero-Adan, M.
π-π
Martinez-Belmonte, J. d. Mendoza, Nat. Commun., 2012,
785; h) Q. F. Sun, J. Iwasa, D. Ogawa, Y. Ishido, S. Sato, T.
Ozeki, Y. Sei, K. Yamaguchi, M. Fujita, Science, 2010, 328
3,
,
1144; i) D. Fujita, K. Suzuki, S. Sato, M. Yagi- Utsumi, Y.
Yamaguchi, N. Mizuno, T. Kumasaka, M. Takata, M. Noda, S.
Uchiyama, K. Kato, M. Fujita, Nat. Commun., 2012, 3, 1093; j)
D. Fujita, H. Yokoyama, Y. Ueda, S. Sato, M. Fujita, Angew.
Chem. Int. Ed., 2015, 54, 155; k) S. Löffler, J. Lübben, L.
Krause, D. Stalke, B. Dittrich, G.H. Clever, J. Am. Chem. Soc.,
2015, 137, 1060; l) F. Dielsmann, C. Hiendl, F. Hastreiter, E.V.
Peresypkina, A. Virovets, R.M. Gschwind, M. Scheer, Angew.
Chem. Int. Ed., 2014, 49, 13605; m) R. Zhu, J. Lübben, B.
Dittrich, G.H. Clever, Angew. Chem. Int. Ed., 2015, 54, 2796;
n) C. Gütz, R. Hovorka, C. Klein, Q-Q. Jiang, C. Bannwarth, M.
Engeser, C. Schmuck, W. Assenmacher, W. Mader, F. Topic,
K. Rissanen, S. Grimme, A. Lützen, Angew. Chem. Int. Ed.,
2014, 53, 1693; o) J.B. Pollock, T.R. Cook, G.L. Schneider, P.J.
Stang, Chem. Asian J., 2013, 8, 2423; p) X. Yan, T. R. Cook , J.
B. Pollock , P. Wei, Y. Zhang, Y. Yu, F. Huang, P. J. Stang, J.
Am. Chem. Soc., 2014, 136, 4460; q) Yan , J.-F. Xu, T. R. Cook,
F. Huang , Q-Z. Yang , C-H. Tung, P. J. Stang, Nature Chem.,
2014, 24, 8717; r) Z-. Li, Y. Zhang, C-W. Zhang, L-J. Chen, C.
Wang, H. Tan, Y. Yu, X. Li, H.-B. Yang, J. Am. Chem. Soc.,
2014, 136, 8577; s) J. Taesch, F. Topic, K. Rissanen, V. Heitz,
Chem. Commun., 2012, 48, 5118; t) S. Y-L. Leung, A. Y-Y.
Tang, C-H. Tao, H-S. Chow, V. W-W. Yam, J. Am. Chem. Soc.
2012, 134, 1047.
2
a) M. Han, D. M. Engelhard, G. H. Clever, Chem. Soc. Rev.,
2014, 43, 1848; b) M. Yoshizawa, J. Klosterman, J., Chem.
Soc. Rev., 2014, 43, 1885; c) M. M. J. Smulders, I. A. Riddell,
C. Browne, J. R. Nitschke, Chem. Soc. Rev,. 2013, 42, 1728; d)
K. Harris, D. Fujita, M, Fujita, Chem. Commun,. 2013, 49
,
6703; e) T. R. Cook, Y. R. Zheng, P. J. Stang, Chem. Rev. 2013,
113, 734; f) H. Amouri, C. Desmarets, J. Moussa, Chem.Rev.
2012, 112, 2015; g) S. Leininger, B. Olenyuk, P. J. Stang,
Chem. Rev. 2000, 100, 853; h) L. Xu, Y.-X. Wang, L-J. Chen, H.-
B. Yang, Chem. Soc. Rev., 2015, 44, 2148; i) L. Xu, L.-J. Chen,
H.-B. Yang, Chem. Commun., 2014, 50, 5156.
3
a) B. Nohra, S. Graule, C. Lescop, R. Réau, J. Am. Chem. Soc.,
2006, 128, 3520; b) Y. Yao, W. Shen, B. Nohra, C. Lescop, R.
Réau, Chem. Eur. J., 2010, 16, 7143.
4
5
6
V. Vreshch, W. Shen, B. Nohra, S-K Yip, V.W-W. Yam, C.
Lescop, R. Réau, Chem. Eur. J., 2012, 2, 466.
M. El Sayed Moussa, K. Guillois, W. Shen, R. Réau, J.
Crassous, C. Lescop, Chem. Eur. J., 2014, 20, 14853.
a) F. Leca, C. Lescop, E. Rodriguez-Sanz, K. Costuas, J-F. Halet,
R. Réau, Angew. Chem. Int. Ed., 2005, 44, 4362; b) B. Nohra,
E. Rodriguez-Sanz, C. Lescop, R. Réau, Chem. Eur. J., 2008,
14, 3391.
7
a) S. M. J. Wang, L. Zhao, T. C. W. Mak, Dalton Trans., 2010,
39, 2108; b) L. Cunha-Silva, M. J. Hardie, Cryst. Eng. Comm.,
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins