Hybrid Organic–Inorganic Rotaxanes, Including a Hetero-Hybrid [3]Rotaxane Featuring Two Distinct Heterometallic Rings and a Molecular Shuttle

Article abstract of DOI:10.1002/anie.201805439

[2] and [3] hybrid rotaxanes are reported based on {Ti₇M} rings (M is a trivalent metal such as Fe^III or Ga^III). NMR studies show that [2]rotaxanes can act as molecular shuttles, while EPR studies of [3]rotaxanes show weak interactions between the paramagnetic components of the supramolecular assemblies.

Full text of DOI:10.1002/anie.201805439

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Accepted Article
Title: Hybrid organic-inorganic rotaxanes, including a hetero-hybrid
[3]rotaxane featuring two distinct heterometallic rings and a
molecular shuttle
Authors: Richard Winpenny, Grigore Timco, Antonio Fernandez,
Andreas Kostopoulos, Jodie Charlton, Selena Lockyer,
Thomas Hailes, Ralph Adams, Eric McInnes, Floriana Tuna,
Inigo Vitorica-Yrzebal, and George Whitehead
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To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201805439
Angew. Chem. 10.1002/ange.201805439
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http://dx.doi.org/10.1002/ange.201805439

Angewandte Chemie International Edition
10.1002/anie.201805439
COMMUNICATION
Hybrid organic-inorganic rotaxanes, including a hetero-hybrid
[
3]rotaxane featuring two distinct heterometallic rings and a
molecular shuttle
Grigore A. Timco,* Antonio Fernandez, Andreas K. Kostopoulos, Jodie F. Charlton, Selena Lockyer,
Thomas R. Hailes, Ralph Adams, Eric J. L. McInnes, Floriana Tuna, Inigo J. Vitorica-Yrzebal, George
F. S. Whitehead and Richard E. P. Winpenny*
III
II
III
Abstract: [2] and [3] hybrid rotaxanes are reported based on {Ti
7
M}
Mn to Mn . The structure of the {Ti M } ring is an octagon of
7
III
III
rings (where M = a trivalent metal such as Fe or Ga }. NMR studies
show that [2]rotaxanes can act as molecular shuttles, while EPR
studies of [3]rotaxanes show weak interactions between the
paramagnetic components of the supramolecular assemblies.
metal sites with each edge bridged by an oxide and two
pivalates, and is unchanged from the simple ring formed using
+
[9]
n-Pr
2 2
NH as the template. Here two rings are present, linked
by the ten-carbon chain of the organic thread.
Hybrid organic-inorganic rotaxanes consist of an organic
template about which a cyclic coordination compound or metal
[
1,2]
[3]
ring can be grown. They differ from metallocrowns and other
[
4]
metal rings in that the design of the organic template, or thread,
is such that bulky groups or stoppers are included to prevent the
thread leaving the ring. This allows inclusion of coordinating
groups at the end of the threads, building complex structures
[
5]
including [4], [5] and [7]-rotaxanes. It is also possible to add
II
[6]
additional paramagnetic centres such as Cu ions or organic
[
7]
radicals. While there are several mechanically interlocked
[8]
molecules featuring metal ions, they remain unusual. Here we
III
[9]
report a new family of hybrid rotaxanes, based on {Ti
7
M } rings.
Figure 1. Representation of the structure 2 in the crystal. [A] is represented as a
spacefilling model with the remainder ball and stick. T-Butyl moieties omitted
for clarity. Ti = grey, Ga = light grey, O = red, N = blue, C = dark grey, H = white
The long term aim here is to create complex diamagnetic hosts
into which we can dope supramolecular assemblies containing
multiple paramagnetic centres, allowing implementation of
We wished to examine if hybrid molecular shuttles could be
[
10,11]
universal gates for quantum information processing.
[
1]
prepared by this route. Therefore, we used dibenzyl-1,8-
diamine [(PhCH NH (CH in the reaction used to give 2.
The simplest possible route to a [3]rotaxane is to use a di-amine
where there is a long chain between the amine centres and large
groups at each the end to act as stoppers. Therefore, we
2
2
)
2
2
)
8
C
The aliphatic chain is too short to allow a [3]rotaxane to form, so
t
the [2]rotaxane, {[
C][Ti
7
GaO
8
(O
2
C Bu)16]}
5
forms (Figure 2). As
III
III
dissolved an oxo-centered triangle of a trivalent metal (Fe , Ga ,
5
contains two ammonium “stations” we can then study the
III
III
Cr or Mn ) in pivalic acid in the presence of dibenzyldecane-
motion use 2-dimensional exchange spectroscopy (EXSY)
1
,10-diamine [(PhCH
2
NH
2
)
2
(CH
2
)
10
A]
and trimethylacetic
[16]
7
experiments to study the motion of the {Ti Ga} ring along the
i
anhydride; [Ti(OPr)
4
] is then added. All manipulations were
organic thread and find that it exchanges between the two
carried out under nitrogen with rigorous exclusion of water. The
2 2 4
ammonium stations. EXSY measurements at 310 K in C D Cl
t
t
oxo-centered triangles were: Fe
3
O(O
2
C Bu)
6
(H
2
O)
3
](O
2
C Bu).
-1
gave a rate of exchange of 0.15 s for shuttling corresponding to
t
[12]
t
t
[9]
BuCO
2
H;
O(O
O(O
result
MO (O
[Ga
(HO
3
O(O
2
C Bu)
7
(CH
3
CN)]
0.5
BuCO
2
H;
‡
-1
a free energy of activation ΔG of 19.4 kcal mol . This is
t
t
[13]
[
[
Cr
3
2
C Bu)
7
2
C Bu)
2
]
generated
in
situ;
7
comparable with the motion of {Cr Co} rings along an organic
[
14]
Mn
3
2
CMe)
7
(HO
2
CMe)]
the
n
.
[1]
thread. (Figure S1).
The
is
formation
of
III
a
[3]rotaxane,
While this chemistry is beautifully simple, as a route to
supramolecular assemblies it is limited by the availability and
solubility of organic threads containing multiple amine groups.
An alternative route is via synthesis of rotaxanes and pseudo-
t
III
III
III
{
(
[
A][(Ti
7
8
2
C Bu)16)]
2
} (M = Fe
1
, Ga
2
, Cr
3
or Mn
4
)
t
Figure 1). The synthesis of
4
used [TiO(O
2
C Bu)
2
]
8
as the
[
15]
i
starting material as the reaction involving [Ti(OPr)
4
] reduced
[
5]
rotaxanes that contain coordinating groups. Therefore we
prepared a [2]rotaxane containing PyCH
2
NH
2
CH
2
2
CH Ph B as
t
III
III
[
a]
Dr. Grigore A, Timco, Dr. Antonio Fernandez, Andreas Kostopoulos,
the thread giving {[
Figure 3a). As
B
][(Ti
7
MO
8
(O
2
C Bu)16)]} (M = Fe
6
, Ga
can be
] gives the
(Figure
7)
Selena Lockyer, Thomas P. Hailes, Dr Ralph Adams, Prof Eric. J. L.
McInnes, Dr Robin G. Pritchard, Dr Christopher A. Muryn, Dr Inigo J.
Vitorica-Yrzebal, Dr. George F. S. Whitehead, Prof. Richard E. P.
Winpenny
(
B
is terminated by a pyridine group, 6
t
used as a ligand and reaction of
6
with [Cu
2
(O
2
C Bu)
4
t
III
t
assembly, [Cu
2
(O
2
C Bu)
4
]{[
B][Ti
7
Fe O
8
(O
2
C Bu)16]}
2
8
The School of Chemistry, The University of Manchester
Oxford Road, Manchester, M13 9PL, United Kingdom
Email: richard.winpenny@manchester.ac.uk,
3
b), which is a [3]rotaxane. The {Cu
2
} “lantern” structure is
similar to those found as bridges in other supramolecular
[
17]
assemblies.
Supporting information for this article is given via a link at the end of
the document.
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Angewandte Chemie International Edition
10.1002/anie.201805439
COMMUNICATION
The [2]rotaxane
6
can also be used as a ligand for monometallic
copper(II)
Cu(hfac)
complexes
such
as
Cu(hfac)
2
giving
III
t
[
2
]{[
B
][Ti
7
Fe O
8
(O
2
C Bu)16
]
9
(Hhfac 1,1,1,6,6,6-
=
hexafluoroacetylacetonate) (Figure 3c). To interpret the EPR
spectra of we also synthesised the isostructural compound
Cu(hfac) ]{[
Cu(hfac)
8
III
t
[
2
7 8 2
B][Ti Ga O (O C Bu)16] 10 via reaction of 7 with
2
.
The ability to grow isostructural but different heterometallic rings
around similar threads has also allowed us to make a hetero-
heterometallic-hybrid [3]rotaxane. Using
A
as the thread we can
Ni} ring around one ammonium
group (see SI for experimental details), and then grow a {Ti Fe}
ring around the second ammonium giving:
][Cr C Bu)16][Ti C Bu)16]} 11 which has the
same structure as compounds 1 – 4 (Figure 1). Synthesis of
3]rotaxanes with different rings as components is unusual, and
[
4]
first grow the very stable {Cr
7
7
t
t
{
[
A
7
NiF
8
(O
2
7 8 2
FeO (O
Figure 2. Representation of the structure of 4 in the crystal. [C] is represented as
a spacefilling model with the remainder ball and stick. T-Butyl moieties omitted
for clarity. Ti = grey, Ga = light grey, O = red, N = blue, C = dark grey, H = white
[
the ability to grow a supramolecule with two heterometallic
components is unique. Evidence for the hetero-heterometallic
rings is provided by full elemental analysis, EPR spectroscopy
(
see below) and the reaction chemistry to give 11
.
EPR spectroscopy on the paramagnetic rotaxanes
definitively shows incorporation of the paramagnetic ions (Figure
III
S2); the exception is
4
as Mn is EPR silent at the frequencies
we have used. Spectra of the [2]rotaxane
6 are those of an
III
isolated high spin Fe ion (S = 5/2) with axial (|D|) and rhombic
-
1
(
E) zero-field splitting parameters of 0.17 and 0.045 cm ,
respectively. There are some minor spectral changes in the
3]rotaxane that can be modelled as small changes in E.
Similarly, spectra of
[
1
3
can be modelled as a single S = 3/2 (D =
-
1
III
-
0.53, E = 0.03 cm ) due to Cr . The larger |D
M
| and smaller
M}, and also the
magnitudes of D and E, are typical for monometallic {MO
rhombicity (E/D) for M = Fe cf. Cr in {Ti
7
6
}
[
18,19]
complexes, e.g. [M(diketonates)
3
].
7
The DCr value in {Ti Cr} is
[
20]
ca. significantly larger than that in the parent {Cr
7
M} family: this
carboxylate
must be
a
function of the {Cr(O
)
4
(O)
2
}
vs.
carboxylate
{
Cr(O
)
4
(F) } crystal fields. The implication is that oxide is
2
acting as a better π-donor, resulting in a weaker crystal field and
hence larger ZFS via mixing with excited states, and that this is
more important than the greater charge.
There is no direct evidence of any interaction between the {Ti
components in spectra of the homo-[3]rotaxanes and (Figure
S2), with only slight broadenings or minor changes in ZFS
7
M}
1
3
[
5]
compared to isolated {Ti
7
M}, nor in that of the hetero-
[
3]rotaxane 11 (Figure S3) which comprises a superposition of
features for {Ti
7
Fe} (S = 5/2) and {Cr
7
Ni} (S = ½ ground state with
Ni} ring appear
7
Ni} rings. Test calculations
[
16]
g = 1.8) . The exchange interactions in the {Cr
7
[
4]
to be unchanged from isolated {Cr
-
1
show that interactions of > 0.01 cm would introduce observable
changes, hence giving a gross upper limit to any interaction
(Figure S3). This is unsurprising: the nearest ring…ring
distances are ca. 14 Å which would correspond to dipolar
-
3
-1
interactions of ca. 20 MHz (of the order 10 cm ) and there is no
obvious through-bond exchange pathway. Previous pulsed EPR
studies on [3]rotaxanes of {Cr
7
Ni} rings with tri-aryl threads
Figure 3. Representation of the structures of a. 6, b. 8 and c. 9 in the crystal. [B]
(ring…ring ca. 1.6 nm) gave interactions of the order of 10
is represented as a space filling model with the remainder ball and stick. T-Butyl
moieties omitted for clarity. Ti = grey, Fe = maroon, Cu = light blue, Ga = light
grey, O = red, N = blue, C = dark grey, F, green, H = white
[
21]
MHz.
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Angewandte Chemie International Edition
10.1002/anie.201805439
COMMUNICATION
However, spectra of
9
, which has {Ti
7
Fe} bound to Cu(II) via the
[4]
5]
E. J. L. McInnes, G. A. Timco, G. F. S. Whitehead, R. E. P. Winpenny,
Angew. Chem. Int. Ed., 2015, 54, 14244-14269.
pyridyl head-group on the thread
B, do show evidence of
[
A. Fernandez, J. Ferrando-Soria, E. M. Pineda, F. Tuna, I. J. Vitorica-
Yrezabal, C. Knappke, J. Ujma, C. A. Muryn, G. A. Timco, P. E. Barran,
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2015, 54, 10858-10861.
exchange coupling, with a clear additional splitting compared to
a simple superposition spectrum (Figure 4). Simulation gives an
-
1
exchange interaction of J = -0.03 cm (-2JŝFe.ŝCu exchange
[6]
-
1
Hamiltonian). This is similar to the J = -0.016 cm found by EPR
II
t
[6]
2 7 8 2
for the [Cu(hfac) ]{[B][Cr Ni O (O C Bu)16] analogue and, as
[
7]
M. –E. Boulon, A. Fernandez Mato, E. M. Pineda, N. F. Chilton, G. Timco,
A. J. Fielding, R. E. P. Winpenny, Angew. Chem. Int. Ed. 2017, 56, 3876-
with that system, the mechanism is unclear given the lack of
covalent interaction between the components (the leading
3
879.
J. E. M. Lewis, P. D. Beer, S. J. Loeb, S. M. Goldup, Chem. Soc. Rev.
018, 46, 2577-2591.
-
1
component of the dipolar interactions is of ca. -0.003 cm ).
[8]
9]
2
These results show we can prepare diamagnetic [3]rotaxanes
into which we will, in the future, dope paramagnetic [3]rotaxanes,
seeking to perform two-qubit gates in orientated single crystals.
The preparation of compound 11, where we have included two
distinct heterometallic rings without exchange of metals between
the two rings suggests this approach is promising.
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Figure 4. Q-band (34.0463 GHz) EPR spectrum of a powder sample of
9 (top;
black) measured at 5 K. Calculated spectra (red) with: SFe = 5/2, gFe = 2.00, DFe
=
-
1
-
=
0.19, |EFe| = 0.04 cm (E/D = 0.21), SCu = 1/2, gCu(x,y,z) = 2.05,2.05,2.30, and JFeCu
-0.03 cm-1 (middle) and nil (bottom). Calculated spectra with allowed (black)
and forbidden (red) transitions used a 150 G intrinsic linewidth and strain in the
-1
zero-field splitting matrix and J of 0.01 cm .
.
Acknowledgements
This work was supported by the University of Manchester, the
EPSRC(UK, EP/L018470/1) and the EPSRC National EPR
Facility. We also thank EPSRC (UK) for funding an X-ray
diffractometer (grant number EP/K039547/1).
Keywords: rotaxanes, heterospin, qubits, quantum gate,
quantum computing, quantum information processing
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Angewandte Chemie International Edition
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COMMUNICATION
Table of Contents
COMMUNICATION
Grigore A. Timco,* Antonio Fernandez, Andreas
Kostopoulos, Jodie F. Charlton, Selena Lockyer,
Thomas R. Hailes, Ralph Adams, Eric J. L. McInnes,
Floriana Tuna, Inigo J. Vitorica-Yrzebal, George F. S.
Whitehead and Richard E. P. Winpenny*
Page No. – Page No.
Hybrid organic-inorganic rotaxanes, including a
hetero-hybrid [3]rotaxane featuring two distinct
heterometallic rings and a molecular shuttle
7
New [2] and [3]rotaxanes are reported based on {Ti M} rings.
This article is protected by copyright. All rights reserved.