Reversible anion-templated self-assembly of [2+2] and [3+3] metallomacrocycles containing a new dicopper(i) motif

Article abstract of DOI:10.1039/c1cc11206f

A new dicopper(i) complex is reported that can be incorporated into extended architectures through multitopic carboxylate linkers; reversible carboxylate templation under pH control led to the formation of [2+2] and [3+3] metallomacrocycles.

Full text of DOI:10.1039/c1cc11206f

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COMMUNICATION
Reversible anion-templated self-assembly of [2+2] and [3+3]
metallomacrocycles containing a new dicopper(I) motifwz
Emily F. V. Dry, Jack K. Clegg, Boris Breiner, Daniel E. Whitaker, Roman Stefaky and
Jonathan R. Nitschke*
Received 28th February 2011, Accepted 23rd March 2011
DOI: 10.1039/c1cc11206f
A new dicopper(I) complex is reported that can be incorporated
into extended architectures through multitopic carboxylate
linkers; reversible carboxylate templation under pH control led
to the formation of [2+2] and [3+3] metallomacrocycles.
Recent years have seen major advances in the creation of
complex self-assembled architectures from simple building
blocks.1 Subtle alterations in components’ geometries2 or the
identities of metal ions3 can result in major changes in a
product’s structure. The use of multiple ‘chemically orthogonal’
linkages has been exploited to generate structures in which
1 1 and its schematic
Synthesis of [Cu2L12MeCN2]
each different kind of linkage contributes to the overall
structure.4 We have recently shown how subcomponent
self-assembly,5 the simultaneous formation of both dynamic
covalent (CQN) and dative (ligand-M) bonds under
thermodynamic control, can yield complex and functional
dynamic systems.6 Here we describe a new self-assembled
dicopper(I) complex for use as a building block in the formation
of extended multinuclear architectures including the anion
templated assembly7 of both a 52-membered [2+2] and a
78-membered [3+3] metallomacrocycle.
Scheme
representation (right).
The reaction of 6-(diphenylphosphino)picolinaldehydez
with aniline and copper(I) yielded a dicopper(I) complex of
the form [Cu2L1 MeCN2]ꢀ2BF4, 1 (Scheme 1).z
2
The pyridyl imine ligands L1 each have three donor atoms,
shared between the two copper centres, with the pyridyl and
imine donors chelating the first CuI, while the diphenylpho-
sphine moiety bridges to the second metal ion. Both copper(I)
centres thus adopt a pseudotetrahedral coordination geometry
with an N3P coordination sphere,8 in which the third nitrogen
donor is provided by an acetonitrile molecule. The metal
centres are separated by 3.1698(14) A, a distance greater than
Fig. 1 Schematic representation of the X-ray crystal structure of
1ꢀ2HSO4ꢀ2MeCN, R = H. Counterions and solvent omitted for clarity.
twice copper(I)’s van der Waals radius (2.80 A).9 The ligands
are oriented in a head-to-tail arrangement, rendering this
complex C2-symmetric, as reflected both in the solution
NMR spectra and the solid-state X-ray structure (Fig. 1).
Complex 1 has two modes of linkage for the formation of
more complex structures. Firstly, the coordinated acetonitrile
molecules can be replaced by multi-functional ligands capable
of linking dimetallic units together.10 Secondly, the dynamic-
covalent imine bonds11,12 can be exploited by substitution for
a multi-functional amine.5 These two types of modification
can be carried out independently, increasing the diversity of
structures available using this motif.
University of Cambridge, Department of Chemistry, Lensfield Road,
Cambridge, UK CB2 1EW. E-mail: jrn34@cam.ac.uk
w This article is part of a ChemComm ‘Supramolecular Chemistry’
web-based themed issue marking the International Year of Chemistry
2011.
z Electronic supplementary information (ESI) available: Synthesis and
characterisation data, specific details of X-ray studies. CCDC
815065–815067. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c1cc11206f
The reaction of 1 with disodium terephthalate (Na2L2)
yielded the terephthalate-linked tetranuclear species
[(Cu2L1)2L2], 2 (Fig. 2). Its X-ray structure (Fig. 2) revealed
y Present address: CEMES-CNRS, 29, rue Jeanne Marvig, BP 94347,
31055 Toulouse Cedex 4, France.
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6021–6023 6021

formation of a 26 membered [1+1] metallomacrocycle 3,
whose ligand L3 is the Schiff-base condensation product of
two phosphino-aldehyde residues with the dianiline
(Scheme 2).
The flexible polyethylene glycol chain enables the ligand to
encircle the dicopper motif of 1, giving complex 3 (Scheme 2).
The 1H NMR of 3 indicated that it exists as the majority
product (85%) in a dynamic combinatorial library (DCL)12
also containing higher oligomeric species. This library
persisted even after repeated recrystallisations.
Employing both dianiline and terephthalate together
resulted in the exclusive formation of the [2+2] metallomacro-
cyclic product [Cu4L3 L2]ꢀ2BF4, 4 (Scheme 3). Both the
2
terephthalate (L2) and the dianiline (L3) link the two dicopper(I)
domains forming a 52-membered metallomacrocyclic ring.
Once again the Cuꢀ ꢀ ꢀCu distances are reduced relative to those
found in 1 with a separation of 2.9083(14) A observed in the
X-ray structure (Fig. 3).
Fig. 2 Schematic representation of the X-ray crystal structure of
2ꢀ2BF4ꢀ1.5H2Oꢀ2C4H10OꢀMeCN formed by the reaction of 1 with
disodium terephthalate. Counter-ions and solvent omitted for clarity.
Scheme 2 In the absence of templation, the reaction of aldehyde,
diamine and Cu(I) gave 85% [1+1] metallomacrocycle [Cu2L3]ꢀ2BF4, 3.
dicarboxylate bridges between dicopper units.z The bridging
mode also effected a shortening of the Cuꢀ ꢀ ꢀCu distance by
0.31 A to 2.8580(6) A.
The ability to link more than one dicopper(I) domain
together using diamines was investigated by the use of the
dianiline triethyleneglycol bis(p-aminophenyl)ether in place of
aniline in the synthesis of 1. This reaction resulted in the
Fig. 3 Schematic representation of the X-ray structure of 4ꢀ2BF4ꢀ
4MeCN. Counterions, solvent and disorder removed for clarity.
Scheme 3 The addition of terephthalate to a solution of 3 yields [2+2] metallomacrocycle 4; addition of 1,3,5-tris(4-carboxyphenyl)benzene
yielded [3+3] metallomacrocycle 5. Both 4 and 5 could be reversibly interconverted to 3 through acid/base cycling.
c
6022 Chem. Commun., 2011, 47, 6021–6023
This journal is The Royal Society of Chemistry 2011

exploiting the dual functionality of this system are being
investigated.
We thank the Marie Curie IIF scheme of the 7th EU
Framework Program (J.K.C.), the Walters-Kundert Charitable
Trust (J.R.N.) and the EPSRC for funding and S.P. Black for
helpful suggestions.
Notes and references
z 1ꢀ2HSO4ꢀ2MeCN: formula C56H52Cu2N8O8P2S2,
M
1218.20,
triclinic, P1, a 12.360(3), b 14.495(3), c 16.258(3) A, a 95.16(3)1,
b 91.69(3)1, g 105.61(3)1, V 2789.5(10) A3,
2, T 180(2) K,
N 60 657, Nind 12 532 (Rmerge 0.1261), R1(F) 0.0829, wR2(F2) 0.2499.
formula C114H106B2Cu4F8-
ꢀ
Z
2ꢀ2BF4ꢀ1.5H2Oꢀ2C4H10OꢀMeCN:
N9O7.50P4, M 2273.74, orthorhombic, pbam, a 12.147(2), b 18.712(4),
c 23.253(5) A, V 5285.3(18) A3, Z 2, T 180(2) K, N 51 480, Nind
6686(Rmerge 0.0377), R1(F) 0.0372, wR2(F2) 0.0967. 4ꢀ2BF4ꢀ4MeCN:
ꢀ
2513.92, triclinic, P1,
formula C124H112B2Cu4F8N12O12P4,
M
a 11.583(2), b 16.843(3), c 19.661(4) A, a 66.03(3)1, b 78.91(3)1,
g 88.69(3)1, V 3433.1(14) A3, Z 1, T 180(2) K, Nind 12 082(Rmerge
0.0748), R1(F) 0.0812, wR2(F2) 0.2437. SQUEEZE applied.
Fig. 4 CAChe MM213 model of [3+3] metallomacrocycle 5.
While in the solid state 4 crystallised in an achiral meso
form, with the two coordinating domains of each L3 arranged
on the same (cis) side of the molecule, in solution two species
are observed in a ratio of 66 : 34. The second species occurs
when the two binding domains are arranged mutually trans
across the plane of the molecule forming a helix with two
different enantiomers (P vs. M) present in a racemic (rac)
mixture.
The meso and rac species exhibit different 1H NMR spectra
(see Fig. S3–S5 in the ESIz). Two-dimensional NMR
experiments confirmed that both species were [2+2] metallo-
macrocycles, which interconvert slowly on the NMR
timescale.
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1
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In conclusion, a new dicopper(I) complex has been synthe-
sised, whose symmetrical structure incorporates dynamic
covalent imine bonds and coordinatively unsaturated metal
centres. Weakly coordinated solvent molecules can be displaced
with anionic ligands to form extended structures, while the
dynamic nature of the imine bonds can be exploited to form
metallomacrocylic species incorporating dianiline groups.
Employing both of these features has allowed for the anion
templated synthesis of [2+2] and [3+3] metallomacrocycles.
These metallomacrocycles can be readily and reversibly
broken down and reformed by subsequent addition of an acid
and a base. Other complex assemblies that are accessible by
c
This journal is The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 6021–6023 6023