Luminescent Tetrahedral Molecular Cages Containing Ruthenium(II) Chromophores

Article abstract of DOI:10.1021/acs.inorgchem.8b01157

We have designed linear metalloligands which contain a central photoactive [Ru(N^∞N)₃]²⁺ unit bordered by peripheral metal binding sites. The combination of these metalloligands with Zn(II) and Fe(II) ions leads to heterometallic tetrahedral cages, which were studied by NMR spectroscopy, mass spectrometry, and photophysical methods. Like the parent metalloligands, the cages remain emissive in solution. This approach allows direct incorporation of the favorable properties of ruthenium(II) polypyridyl complexes into larger self-assembled structures.

Full text of DOI:10.1021/acs.inorgchem.8b01157

Article
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
pubs.acs.org/IC
Luminescent Tetrahedral Molecular Cages Containing Ruthenium(II)
Chromophores
Ena T. Luis, Hasti Iranmanesh, Kasun S. A. Arachchige, William A. Donald, Gina Quach,‡
†
†
†,§
†
‡
,†
Evan G. Moore, and Jonathon E. Beves*
†
School of Chemistry, UNSW Sydney, Sydney, 2052 Australia
‡
School of Chemistry and Molecular Biosciences, the University of Queensland, Brisbane, Queensland, 4072 Australia
*
S Supporting Information
∧
2+
ABSTRACT: We have designed linear metalloligands which contain a central photoactive [Ru(N N) ] unit bordered by
3
peripheral metal binding sites. The combination of these metalloligands with Zn(II) and Fe(II) ions leads to heterometallic
tetrahedral cages, which were studied by NMR spectroscopy, mass spectrometry, and photophysical methods. Like the parent
metalloligands, the cages remain emissive in solution. This approach allows direct incorporation of the favorable properties of
ruthenium(II) polypyridyl complexes into larger self-assembled structures.
60−63
and molecular cages,41,64−68 and photocatalysis
1
. INTRODUCTION
MOFs
has been recently reported within a molecular cage formed
with ruthenium(II) polypyridyl chromophores bridged by
Self-assembled discrete supramolecular structures have dem-
1
−4
onstrated valuable applications in sensing,
separations or
and for control-
Metallosupramo-
5
−7
8−10
69
2+
selective encapsulation,
drug delivery,
palladium(II) ions. We reported [Ru(tpy)
]
2
units (tpy =
1
1−17
ling substrate reactivity and catalysis.
2,2′:6′,2″-terpyridine) functionalized with pendant pyridyl
1
8−27
lecular cages
often assemble predictable three-dimen-
groups which could be assembled into discrete cages with
70
sional architectures programmed by the coordination prefer-
ences of metal ions and geometries of organic linker units.
Early examples of catalytic metallosupramolecular cages
exploited the size restriction of the cavities to facilitate the
palladium(II) ions, although these cages are not emissive at
room temperature, as expected for this class of bistridentate
71
complexes. Herein, we report three new metallosupramo-
28−30
lecular cages based on metalloligands bearing a photoactive
reaction occurring inside.
Recent focus has turned to
∧
2+
[
Ru(N N) ] motif where the useful photophysical properties
transition-metal-catalyzed reactions, with the active species
3
31−37
38,39
are maintained in the cage structures.
Complex [Ru(phen) (1)](PF
functionalized with additional binding sites for metal ions,
with the installation of 4-pyridyl groups allowing the assembly
encapsulated within,
or appended to,
the central
cavity. While co-encapsulation has proven to be an effective
approach for catalysis within cages, preorganizing the active
units into the components of the cage structure itself is
potentially a more robust method to ensure the catalyst cannot
dissociate from the cage structure. Examples of luminescent
2
) (Scheme 1) can be
6 2
72
72
of hetereodimetallic one-dimensional coordination polymers.
In this work, a bidentate chelating site was chosen to direct the
assembly of a discrete tetrahedral structure in conjunction with
4
0−48
cages
have been reported, and recent work has
demonstrated photoinduced energy transfer between cages
73−75
4
9−51
an octahedral metal ion, inspired by the work of Lindoy,
and bound guests.
The ruthenium(II) complex [Ru-
51,76−82
83−86
87−89
2
+
Nitschke,
Raymond,
and Lusby.
(
bpy)3] (bpy = 2,2′-bipyridine) is perhaps the best known
5
2
photosensitizer, and in recent years has continued to show its
53−59
versatility in catalyzing a variety of photoredox reactions.
These types of chromophores have been incorporated into
Received: April 27, 2018
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01157
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Scheme 1. Synthetic Route to Racemic Complexes [Ru(phen) (3)](PF ) and [Ru(phen) (4)](PF ) and the Numbering
2
6 2
2
6 2
Scheme Adopted
1
Figure 1. Partial H NMR spectra (500 MHz, CD CN) of (a) [Ru(phen) (4)](PF ) ; (b) [Ru(phen) (3)](PF ) ; (c) [Ru(phen) (6)](PF ) ; (d)
3
2
6
2
2
6
2
2
6 2
[
Ru(phen) (7)](PF ) .
2 6 2
2
. EXPERIMENTAL SECTION
synchrotron X-ray radiation (λ = 0.71073 Å) (MX1 Beamline at the
Australian Synchrotron). Single crystals of 2,2′:5′,3″:6″,2‴-quaterpyr-
2
.1. General. Synthetic schemes and detailed spectroscopic
idine {1.5(C H N )} were measured on a Bruker kappa-II CCD
1
20 15
4
assignments are given in the Supporting Information. H and
diffractometer using IμS Incoatec Microfocus Source with Mo Kα
radiation (λ = 0.710723 Å).
13
1
C{ H} NMR assignments were made using 2D-NMR methods
(
COSY, HSQC, HMBC) and are unambiguous unless stated
{
[Ru(phen) (3)](PF ) ·0.5MeCN}. C H F N10.5P2Ru, M =
2 6 2 55 37.5 12
90
otherwise. 5-Bromo-2,2′-bipyridine, 5,5′-dibromo-2,2′-bipyridine
1
=
236.46, red platelets, triclinic, space group P1
̅
, a = 12.290(3) Å, b
9
0
91
(
1), 5-bromo-2-(1,3-dioxolan-2-yl)pyridine, 2-(1,3-dioxolan-2-
14.930(3) Å, c = 15.050(3) Å, α = 109.38(3)°, β = 100.72(3)°, γ =
9
2
3
−3
yl)-5-pyridineboronic acid pinacol ester, and [Ru(phen) (1)]-
2
95.73(3)°, V = 2523.4(10) Å , Z = 2, ρ = 1.627 g cm , μ(Mo Kα)
calc
1
72
−
(
PF6)2 were prepared by reported procedures.
.2. Single Crystal X-ray Diffraction. A summary of crystallo-
= 0.471 mm , T = 100(2) K, 84 390 reflections collected.
Refinement of 726 parameters using 11 909 independent reflections
2
2
graphic data and refinement parameters is shown in Table S2. Data
were deposited with the Cambridge Structural Database (CCDC
against F converged at final R = 0.0776 (R all data = 0.0886), wR =
1
1
2
0.2198 (wR all data = 0.2367), GooF = 1.065.
2
entries: 1839130 and 1839131). Single crystals of {[Ru(phen) (3)]-
{1.5(2,2′:5′,3″:6″,2‴-Quaterpyridine)}. C H N , M = 310.35,
2
20 14
4
(
PF ) ·0.5(MeCN)} were measured by Si<111> monochromated
colorless plate, monoclinic, space group P2 /c, a = 26.627(4) Å, b =
6
2
1
B
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Inorganic Chemistry
Article
Figure 2. Left: an ORTEP representation of the complex cation in the single crystal X-ray structure of {[Ru(phen) (3)](PF ) ·0.5MeCN}, with
2
6 2
thermal ellipsoids shown at 30% probability. Ru: teal, C: gray, N: blue, H: white. Right: a CPK representation of the face-to-face and edge-to-face
π−π stacking interactions, with alternating complexes shown in red and blue. Anions and solvent molecules are omitted for clarity.
Scheme 2. Formation of Tetrahedral Cage [Fe-5]20+
a
a
Only three of the six ligands are shown for clarity.
7
.2406(10) Å, c = 11.7009(15) Å, α = 90°, β = 102.112(10)°, γ = 90°,
3
−3
V = 2205.7(5) Å , Z = 6, ρ = 1.402 g cm , μ(Mo Kα) = 0.086
mm , T = 150(2) K, 19 035 reflections collected. Refinement of 325
parameters using 4816 independent reflections against F converged
calc
−
1
2
at final R = 0.0524 (R all data = 0.0947), wR = 0.1494 (wR all data
1
1
2
2
=
0.1932), GooF = 1.029.
3
. RESULTS AND DISCUSSION
3.1. A Sexipyridine-Functionalized Metalloligand. We
aimed to selectively install a ruthenium complex into a specific
site of a linear ligand with three identical bidentate domains.
This required a synthetic strategy where the desired
ruthenium-containing chromophore is synthesized first,
followed by elaboration directly upon the complex to introduce
the additional binding sites. This approach is essential to
ensure the ruthenium center, which can be generally
considered to be substitution inert, is selectively placed in a
single binding site of the ligand, with the remaining bidentate
sites available for coordination with labile metal ions for self-
assembly. We have previously shown heteroleptic ruthenium-
Figure 3. Full HR-ESI mass spectrum of cage [Zn-5](PF6) in
20
MeCN. Inset: observed and theoretical isotope pattern for {[Zn-
5
+
5
](PF ) } .
6 15
(
II) polypyridyl complexes functionalized with bromo
substituents are suitable for palladium(0)-mediated cross-
7
2
coupling reactions, and here the complex [Ru(phen) (1)]-
bipyridine, Scheme 1) was used. The required coupling
2
(
PF ) (phen = 1,10-phenanthroline; 1 = 5,5′-dibromo-2,2′-
partner, 5-(2,2′-bipyridine)boronic acid pinacol ester (2) was
6
2
C
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Scheme 3. Synthesis of the Racemic Complex [Ru(phen) (7)](PF ) and the Numbering Scheme Adopted
2
6 2
Scheme 4. Synthesis of Cage [Zn-8]20+
a
a
Only three of the six ligands are shown for clarity.
synthesized from 5-bromo-2,2′-bipyridine. This borylation was
carried out by lithiation, quenching with tributylborate,
followed by the addition of pinacol. The boronic ester has
previously been synthesized using a Miyaura coupling
salt from an aqueous workup with KPF . Attempts to prepare
6
the free sexipyridine ligand (3) by reaction of 1 and 2 under
identical conditions, or in other solvent mixtures (e.g., DMSO,
dioxane/i-PrOH, DMF/DME/water), did not afford the
desired compound. Instead, the major species identified in
the reaction mixture were free 1 and 2,2′:5′,3″:6″,2‴-
quaterpyridine. The latter was isolated, and its single crystal
X-ray structure determined (see section S7.2). This finding
suggests that the bromo-functionalized ligand is relatively
activated toward cross-coupling, with respect to dehalogena-
tion, when coordinated to the ruthenium(II) center. The
simpler model compound [Ru(phen) (4)](PF ) (4 = 3,3′:
9
5
method; however, attempts to reproduce this reaction gave
the homocoupled 2,2′:5′,3″:6″,2‴-quaterpyridine product as
the major isolated species. See the Supporting Information for
9
3
details.
The metalloligand [Ru(phen) (3)](PF ) (3 = 2,2′:5′,3″:
2
6 2
6
″,2‴:5‴,3⁗:6⁗,2⁗′-sexipyridine) was synthesized by palla-
dium(0)-catalyzed Suzuki coupling reaction between [Ru-
phen) (1)](PF ) and boronic ester 2. The reaction was
(
2
6 2
2
6 2
carried out with Cs CO and Pd(PPh ) in DMF at 120 °C for
6′,2″:5″,3‴-quaterpyridine) was prepared in 61% yield using
an analogous procedure with 3-pyridineboronic acid neopentyl
glycol ester.
2
3
3 4
4
5 min in a microwave reactor. The metalloligand complex
−
[Ru(phen) (3)](PF ) was isolated in 84% yield as the PF
2 6 2 6
D
DOI: 10.1021/acs.inorgchem.8b01157
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the C37−C40 bond, and atom C53 is 170°). One of the
terminal bpy units is involved in weak face-to-face π−π
stacking with the central bpy unit of an adjacent complex
(
centroid-to-plane distance of 3.485 Å), whereas the other
terminal bpy unit is engaged in closer edge-to-face interactions
centroid of ring containing N10 to C3i = 3.33(1) Å,
(
centroid···H−C = 2.58 Å, i = 1 = x, y, z). The terminal bpy
ligand not involved in face-to-face stacking is the more planar,
with the two pyridyl rings almost perfectly coplanar (angle
between the least-squares planes of the two rings = 2.96°; the
angle between the least-squares planes of the two rings of the
other terminal bpy unit is 11.14°). Coplanarity is expected for
free 2,2′-bipyridine units due to favorable intramolecular N···
HC interactions. The complexes are assembled via weak
9
6−98
phenyl−phenyl embraces
between the equivalent phenan-
throline ligands of adjacent complexes (plane-to-plane
separation 3.464 Å).
The [Ru(phen) (3)](PF ) complex was self-assembled into
2
6 2
molecular cages by reaction with labile metal(II) ions. The self-
assembly was attempted with a variety of first row transition
metalsiron(II), cobalt(II), cobalt(III), nickel(II), and zinc-
Figure 4. A semi-empirical (PM3) model of cage [Zn-8]20+
Hydrogen atoms are omitted for clarity. Zn(II) (purple) and Ru(II)
.
(
II)to probe a number of possible structures from different
(
teal) are shown as balls; all bonds are shown as sticks. The Ru(II)
preferred coordination geometries. However, using iron(II)
and zinc(II) gave the most success in the self-assembly, while
the other metal ions produced species that were difficult to
identify or isolate.
ions are modeled as Δ isomers and the Zn(II) ions as Λ isomers. The
top zinc(II) ion is shown coordinated to three separate residues
colored red, green, and blue.
As an example, 3 equiv of [Ru(phen) (3)](PF ) and 2
2
6 2
Table 1. Summary of Calculated Diffusion Coefficients and
a
equiv of Fe(BF ) ·6H O were reacted in acetonitrile at 80 °C
4 2 2
Hydrodynamic Radii Measured by NMR in CD CN
3
for 24 h, followed by anion metathesis with aqueous KPF . The
6
diffusion coefficient/
hydrodynamic
radius/Å
resulting red solid was collected on Celite and washed with
water, then dissolved in acetonitrile. The self-assembled
structures are consistent with the [Fe L ](PF ) stoichiometry
expected for the tetrahedral cage [Fe-5](PF6)20 (Scheme 2).
High resolution electrospray ionization (ESI) mass spectrom-
etry revealed highly charged 4+, 5+, and 6+ species for
iron(II)-containing cages corresponding to the loss of
−
10
2
−1
compound
10 m s
[
[
[
[
[
Ru(phen) (3)](PF )
10.4 ± 0.5
11.7 ± 0.3
5.51 ± 0.05
5.60 ± 0.05
4.35 ± 0.08
6.2 ± 0.3
5.4 ± 0.2
11.6 ± 0.1
11.4 ± 0.1
14.7 ± 0.3
2
6
2
4
6
6 20
Ru(phen) (7)](PF )
2
6
2
Fe-5](PF6)20
Zn-5](PF6)20
Zn-8](PF6)
20
a
Hydrodynamic radii calculated using the Stokes−Einstein equation.
counterions, in each case matching calculated isotope patterns
1
(
see Figures S3 and S4). The H NMR spectrum of the
Complexes [Ru(phen) (3)](PF ) and [Ru(phen) (4)]-
reaction of [Ru(phen) (3)](PF ) with Fe(BF ) ·6H O
2 6 2 4 2 2
2
6
2
2
1
13
(
PF ) were characterized in detail by H and C NMR,
(Figure S17) shows a mixture of species in solution, so we
monitored the assembly process over time to investigate
whether this was due to prematurely terminating the reaction
before thermodynamic equilibrium had been reached.
6
2
electrospray ionization mass spectrometry (ESI-MS), absorp-
tion and emission properties, and for [Ru(phen) (3)](PF )
2
6 2
1
also by single crystal X-ray diffraction. The H NMR spectra
are shown in Figure 1, and all signals were assigned using the
The reaction of [Ru(phen) (3)](PF ) with Fe(BF ) ·6H O
2 6 2 4 2 2
94
1
methods previously described. Upon exchange of bromo
in CD CN was monitored by H NMR at 80 °C for several
3
1
groups for pyridyl functional groups, the H NMR signals of
days (Figure S19). Upon initial mixing of the reagents, a broad
1
the phenanthroline ligands are largely unaffected by the
changes in the bpy ligand. The signals corresponding to the
central bpy unit are in similar environments in [Ru(phen)2-
featureless H NMR spectrum is observed, consistent with a
kinetic mixture of different oligomeric products. After heating,
the spectrum becomes simpler with sharper signals suggesting
the presence of several similar products. After 24 h, no further
(
3)](PF6)2 and [Ru(phen) (4)](PF ) , with the protons
2 6 2
1
shifted further upfield in the model complex. Similarly,
comparison of the signals for the B rings (see Scheme 1 for
atom labeling) in the complexes shows that the protons are
shifted further downfield in [Ru(phen) (3)](PF ) , with the
changes in the H NMR spectrum were observed, and the
reaction appears to be complete and that the end product
mixture is a thermodynamic minimum. The reaction was
treated with aqueous KPF , and the resulting precipitate was
2
6 2
6
B3
most pronounced change shown for H upon substituting a
pyridyl ring in the 2-position, causing a shift of 1.05 ppm.
Single crystals of [Ru(phen) (3)](PF ) suitable for X-ray
collected on Celite, washed with water, and redissolved in
CD CN. It is clear one of the species present in the reaction is
3
removed (decomposed) by this procedure; for example, the
signal at 9.0 ppm disappears after workup. The number of
separate signals in the spectrum after workup indicated the
major product formed has low symmetry (i.e., not T
symmetry). The concentration dependence of the mixture
2
6 2
crystallography were grown by slow diffusion of diethyl ether
into an acetonitrile solution of the complex. The structure is
shown in Figure 2 and contains a single complex in the
asymmetric unit. The spy ligand (3) in the structure is slightly
bent due to coordination of the ruthenium(II) center to the
central bipyridyl unit (angle between atom C26, the center of
was also studied in CD CN (Figure S23), and although signals
3
became sharper at lower concentrations, no evidence for a
E
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II
Figure 5. All samples were measured in acetonitrile at 298 K with [Ru ] ≈ 0.06 mM. (a, b) Absorption spectra of the metalloligands and the
respective cages formed with Zn(II) and Fe(II) metal centers. Extinction coefficients are normalized to the concentration of ruthenium(II) centers
present for comparison. The Zn(II) cages display the same absorption profiles as the mononuclear complexes, showing that self-assembly with
Zn(II) has no effect on absorption energies. (c, d) Normalized emission (λex = 450 nm) of the metalloligands and their respective cages formed
with Zn(II) and Fe(II) metal centers. The cages retain the emissive properties of the ligands, with some quenching which is more prevalent in cage
[
Zn-8](PF ) .
6 20
change in the product distribution was observed over the
concentration range studied (∼0.2 to 1 mM). The related
reaction of [Ru(phen) (3)](PF ) and Zn(NTf ) in acetoni-
stereochemistry of the vertices simply due to the geometrical
arrangement of the groups.
To alleviate some of the complexity caused by this
2
6 2
2 2
trile gave a self-assembled product with highly charged HR-
ESI-MS signals corresponding to sequential loss of PF6 anions
isomerism, [Ru(phen) (3)](PF ) was prepared as the
2
6 2
−
enantiopure Λ isomer. This was achieved by resolving
2
+
99
72
from the tetrahedral cage [Zn-5](PF ) (Figure 3), and the
[Ru(phen) (py) ] (py = pyridine) into its enantiomers,
6
20
2 2
1
H NMR spectrum was also consistent with the product
followed by chelation of 1 to form Λ-[Ru(phen) (1)](PF ) .
2
6 2
distribution similar to that described with iron(II) (Figure
S17).
The Suzuki coupling with 2 was also carried out in the
microwave as for the racemic complex, giving Λ-[Ru(phen)
-
2
2
0+
It is known that related, but smaller, tetrahedral cages
formed with short, rigid ligands can exist as mixtures of
stereoisomers which differ only in the stereochemistry of the
(3)](PF
6
)
2
in 47% yield. The formation of cage [Fe-5] with
(3)](PF re-
the enantiopure metalloligand Λ-[Ru(phen)
)
6 2
2
1
sulted in some simplification of the H NMR spectrum
compared to that of the cage assembled with the racemate
(Figure S20). There was a significant increase in the
proportion of the product with the signal at 9.0 ppm, which
was removed during workup, as occurred for the racemic case.
The final isolated sample has a relatively simple spectrum and
suggests a single major tetrahedral cage species. Circular
dichroism spectra of Λ-[Ru(phen) (3)](PF ) and its self-
7
8,79
20+
vertices (Λ or Δ).
However, in the case of cage [M-5]
,
the ruthenium(II) center on the metalloligands can also be Λ
or Δ configuration. This combination will give rise to the
possibility of many diastereomers with a large number of
slightly different proton environments to result in the observed
complicated spectrum. Free rotation about the carbon−carbon
bonds between the bpy units of the metalloligand would allow
2
6 2
the [Ru(phen) (bpy)] units to rotate to avoid any unfavorable
assembled [Fe-5](PF ) cage are essentially identical (Figure
2
6 20
steric clashes between neighboring units. This may result in
ruthenium(II) centers on adjacent metalloligands being
sufficiently close to cause noticeable differences in their H
NMR environments, but not so restricted that the stereo-
chemistry of one center can dictate the stereochemistry of the
next. Similarly, the stereochemistry of the ruthenium(II)
centers can be expected to have little influence on the
S31), indicating that the only chirality in the cage arises from
the ruthenium(II) centers; i.e., the orientation of the metal
ions at the vertices is not influenced by the chirality of the
metalloligand.
3.2. A Cage with Capped Vertices. To use the assembled
cages for photoredox applications, two key requirements are
(i) the photophysical properties of the ruthenium(II)
1
F
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chromophores must be preserved in the assembled species and
125 °C (Figure S22). At higher temperatures, the aromatic
signals do significantly sharpen, yet are unable to reach a
completely symmetrical fast exchange regime. Significantly, on
cooling the sample back to room temperature, a spectrum
identical to that prior to heating was obtained, verifying the
observed changes are not due to irreversible decomposition of
the cage and suggesting a highly robust structure.
(
(
ii) the cages must not disassemble, even at very low
catalytic) concentrations. Transition metal centers such as
iron(II) can be highly effective for quenching ruthenium(II)
excited states by acting as effective electron acceptors/
1
00−102
10
donors.
A safer option is to opt for d metal ions as
the vertices of the cage, such as zinc(II), which are generally
resistant to redox processes. However, the d10 configuration
leads to two consequences: the Zn−N bonds are typically
labile, and there are no strong coordination geometry
preferences around the zinc(II) center. These issues create
20+
The self-assembly of cage [Zn-8] was also monitored in
CD CN with the reaction mixture maintained at 50 °C for 5
3
days (Figure S21). Immediately after mixing, the aldehyde is
consumed, as expected, and significant shifts in the signals of
the methylene linkers of the tren residue are observed. The
difficulties with using zinc(II) ions for self-assembly. We were
3
̈
rthner and co-workers, who prepared an
1
inspired by Wu
aromatic region of the H NMR spectrum did not display any
impressive tetrahedral cage with zinc(II) vertices and the
pyridylimine chemistry used extensively by
further changes after 5 h of heating. However, the aliphatic
region did continue to undergo significant changes. Initially, a
series of relatively sharp signals between 4.0 and 2.5 ppm are
observed, potentially due to partially condensed tren units
7
7,80,103−106
Nitschke.
In that example, a perylene bisimide
featuring 2-pyridylcarboxaldehyde substituents was condensed
with a tridentate capping unit, tren (tren = tris(2-aminoethyl)-
amine), and a source of zinc(II) ions to form tris-
(
that would still be expected to be reasonable ligands for
zinc(II)). Following extensive heating, the methylene groups
are able to adopt a wide range of relative conformations which
must be close in energy in part due to the flexible coordination
geometry of the zinc(II) center. After workup, all of the sharp
signals from the aliphatic region are removed, suggesting these
may be structures that feature free amine groups that might
result in higher solubility in water.
(
pyridylimine) binding units as the vertices of the cage. A
:0.9:0.7 ratio of diastereomeric cages was reported at 50 °C in
1
CD CN, consistent with the poor transfer of chiral information
3
3
between the vertices expected for long ligands. We would
expect a similar situation for our ruthenium(II)-containing
cages prepared using the same approach, although these cages
would be significantly smaller. Suzuki coupling of [Ru(phen)2-
3
.3. Molecular Modeling. In order to estimate the size of
(
1)](PF ) and a pyridyl unit with a protected aldehyde group
20+
6
2
the tetrahedral cage [Zn-8] , a simple PM3 model was
calculated and is shown in Figure 4. The estimated length of
one edge of the tetrahedron is approximately 26 Å, and the
and a boronic ester gave [Ru(phen) (6)](PF ) which was
2
6 2
deprotected to generate the desired dialdehyde complex
[
(
Ru(phen) (7)](PF ) in 85% yield over these two steps
2 6 2
3
central cavity has a volume of approximately 340 Å .
Scheme 3). The complexes were also fully characterized by
3.4. Diffusion NMR Studies. Diffusion NMR, often
1
13
H and C NMR, electrospray ionization mass spectrometry
presented as DOSY plots, is a powerful tool for differentiating
species on the basis of their rates of diffusion, and for
estimating their relative sizes. It has become a standard tool of
1
(
ESI-MS), and absorption and emission properties. The H
NMR spectra are shown in Figure 1, and display similar trends
as [Ru(phen) (3)](PF ) and [Ru(phen) (4)](PF ) upon
2
6 2
2
6 2
supramolecular chemists for characterizing molecular cages
substituting pyridyl groups for the bromo functionalities, with
107−110
B3
and capsules.
We measured the diffusion coefficients of
the signal of H being shifted downfield by 0.38 ppm on
the mononuclear [Ru(phen) (3)](PF ) and [Ru(phen) (7)]-
2
6 2
2
substitution.
To prepare the desired cage [Zn-8]20+, 3 equiv of
(PF ) complexes, in addition to the self-assembled cage
6 2
structures formed from these components; the data are shown
in Table 1. The measured diffusion coefficients of the
mononuclear complexes correspond to hydrodynamic radii of
[
Ru(phen) (7)](PF ) , 2 equiv of tren, and 2 equiv of
2 6 2
Zn(NTf ) were reacted in acetonitrile at 50 °C for 5 h,
2
2
followed by anion exchange with aqueous KPF as described
6
5
.4 and 6.2 Å. From the X-ray crystal structure of
previously (Scheme 4). High resolution ESI-MS (Figures S5
and S6) showed a series of highly charged (7+, 6+, 5+, 4+)
signals with isotope patterns matching the calculated patterns
[
Ru(phen) (3)](PF ) , the smallest box that encapsulates
2
6 2
the cation is approximately 25.6 × 9.6 × 10.7 Å which might
suggest a hydrodynamic radius ∼ 8 Å if this volume is
approximated as a sphere. The observed hydrodynamic radius
is a little shorter, perhaps not surprising given the complex is
far from being approximately a sphere.
for sequential loss of PF6− from [Zn-8](PF ) . Additional
6 20
higher mass signals of the same charge were observed for each
of these signals, possibly corresponding to the encapsulation of
1
neutral solvent molecules. The aromatic region of the H
As expected, the self-assembled structures have smaller
diffusion coefficients than the mononuclear metalloligands. For
NMR spectrum (Figure S18) is considerably simpler than
2
0+
those of the [M-5] cages, in part due to this cage having
fewer proton environments. The signals are broad and
consistent with a collection of equilibrated isomers. The
concentration dependence of the mixture was also studied in
2
0+
20+
cages [Fe-5]
and [Zn-5] , these correspond to hydro-
dynamic radii of 11.6 and 11.4 Å, respectively. For cage [Zn-
2
0+
8
]
, the expected length (from a PM3 model) for one edge of
the tetrahedron is approximately 26 Å. Such a tetrahedron
which would fit inside a sphere of radius 16 Å and, as this is a
more reasonable approximation for a sphere, we observe good
agreement with the calculated hydrodynamic radius (14.7 Å).
It must be emphasized that, in estimating sizes, no
consideration has been given to the volume of the many
anions present which must diffuse with the cationic cage, and it
is remarkable that there is any agreement at all with predicted
sizes. That said, there is no doubt the mononuclear complexes
CD CN (Figure S24), and although some hydrolysis was
3
observed at low (∼0.1 mM) concentrations, no significant
change in the product distribution was observed. This is also
consistent with the formation of discrete species of the same
size, as opposed to mixtures of oligomers which might be
expected to show more pronounced concentration depend-
ence.
Using variable temperature NMR in DMSO-d , we
6
1
monitored the H NMR spectrum over a range from 25 to
G
DOI: 10.1021/acs.inorgchem.8b01157
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
have been assembled into much larger structures, consistent
with the proposed tetrahedral cages.
ORCID
Jonathon E. Beves: 0000-0002-5997-6580
3
.5. Photophysical Properties. Finally, we turn our
attention to the photophysical properties of the cages. Figure
a shows the absorption spectra of [Ru(phen) (3)](PF ) ,
Present Address
§
School of Chemistry and Molecular Biosciences, The
University of Queensland, Brisbane, Queensland, 4072
Australia.
5
2
6 2
[
Fe-5](PF ) , and [Zn-5](PF ) , normalized for the
6 20 6 20
concentration of ruthenium(II) in all cases. The absorption
Author Contributions
spectra of [Ru(phen) (3)](PF ) and [Zn-5](PF6)20 are
2
6 2
essentially identical as the coordination of zinc(II) to the
terminal bpy groups will not generate a new chromophore. In
both compounds, the MLCT band has a maximum absorption
at 450 nm and the ligand-centered transitions appear at higher
energies, with the extended conjugation of ligand 3 resulting in
the absorbance band at 350 nm. In cage [Fe-5](PF ) ,
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Notes
The authors declare no competing financial interest.
6
20
coordination of the iron(II) ions shifts the energy of this
ligand-centered transition. Figure 5b makes the same
comparison between [Ru(phen) (7)](PF ) and [Zn-8]-
ACKNOWLEDGMENTS
■
This work was supported by the Australian Research Council
DP160100870] and UNSW Sydney. E.T.L. thanks the
Australian government for an Australian Postgraduate Award
scholarship. Access to the Australian Synchrotron was possible
by a Collaborative Access Program (MXCAP9824/10598).
2
6 2
[
(
PF ) . Here, some change in the absorption spectrum is
6 20
observed as an aldehyde group is being replaced with an imine,
which has some influence on the electronic properties of the
ruthenium(II) center. Panels (c) and (d) in Figure 5 compare
the emission data for the mononuclear complexes with the
cage structures, normalized for absorption at 450 nm. In cages
REFERENCES
■
[
Zn-5](PF6)
and [Fe-5](PF ) , minimal quenching is
20 6 20
(1) Turega, S.; Whitehead, M.; Hall, B. R.; Meijer, A. J.; Hunter, C.
A.; Ward, M. D. Shape-, size-, and functional group-selective binding
of small organic guests in a paramagnetic coordination cage. Inorg.
Chem. 2013, 52 (2), 1122−32.
́
2) Neelakandan, P. P.; Jimenez, A.; Nitschke, J. R. Fluorophore
incorporation allows nanomolar guest sensing and white-light
observed relative to the mononuclear parent complexes and
both cages remain strongly emissive in solution. The emission
energy of [Fe-5](PF ) is blue-shifted compared to both [Zn-
6
20
(
5
](PF6)20 and its parent complex. Cage [Zn-8](PF ) also
6 20
remains emissive in solution, although it experiences a
noticeably greater level of quenching compared to the [M-
emission in M L cage complexes. Chem. Sci. 2014, 5 (3), 908−915.
4
6
(
3) Frischmann, P. D.; Kunz, V.; Wurthner, F. Bright Fluorescence
̈
5](PF6)20 cages.
and Host-Guest Sensing with a Nanoscale M L Tetrahedron
4
6
Accessed by Self-Assembly of Zinc-Imine Chelate Vertices and
Perylene Bisimide Edges. Angew. Chem., Int. Ed. 2015, 54, 7285−
7289.
4
. CONCLUSIONS
Using a metalloligand approach, we have installed inert
luminescent [Ru(bpy) ]-like complexes on the linker units of
(4) Zhang, M.; Xu, H.; Wang, M.; Saha, M. L.; Zhou, Z.; Yan, X.;
Wang, H.; Li, X.; Huang, F.; She, N.; Stang, P. J. Platinum(II)-Based
Convex Trigonal-Prismatic Cages via Coordination-Driven Self-
Assembly and C60 Encapsulation. Inorg. Chem. 2017, 56 (20),
3
tetrahedral molecular cages. These cages retain the photo-
physical properties of the parent complexes and are not
susceptible to disassembly, even at low concentrations. The
formation of a complicated mixture of stereoisomers, even
where the stereochemistry of the ruthenium centers was
controlled, prevents a detailed analysis of their host−guest
chemistry, but we anticipate this approach will prove useful for
preparing functional molecular photoreactors.
1
(
2498−12504.
5) Xuan, W.; Zhang, M.; Liu, Y.; Chen, Z.; Cui, Y. A chiral
quadruple-stranded helicate cage for enantioselective recognition and
separation. J. Am. Chem. Soc. 2012, 134 (16), 6904−7.
(6) Zhang, W. Y.; Lin, Y. J.; Han, Y. F.; Jin, G. X. Facile Separation
of Regioisomeric Compounds by a Heteronuclear Organometallic
Capsule. J. Am. Chem. Soc. 2016, 138 (33), 10700−7.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01157.
(7) Taylor, C. G. P.; Piper, J. R.; Ward, M. D. Binding of chemical
warfare agent simulants as guests in a coordination cage:
contributions to binding and a fluorescence-based response. Chem.
Commun. 2016, 52 (37), 6225−6228.
■
*
S
(8) Lewis, J. E. M.; Gavey, E. L.; Cameron, S. A.; Crowley, J. D.
Stimuli-responsive Pd2L4 metallosupramolecular cages: towards
Synthetic procedures, NMR and ESI-MS data, and
additional experimental details are reported (PDF)
targeted cisplatin drug delivery. Chem. Sci. 2012, 3 (3), 778−784.
(
9) Cullen, W.; Turega, S.; Hunter, C. A.; Ward, M. D. pH-
dependent binding of guests in the cavity of a polyhedral coordination
cage: reversible uptake and release of drug molecules. Chem. Sci. 2015,
6 (1), 625−631.
Accession Codes
CCDC 1839130 and 1839131 contain the supplementary
crystallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(10) Xu, W.-Q.; Fan, Y.-Z.; Wang, H.-P.; Teng, J.; Li, Y.-H.; Chen,
C.-X.; Fenske, D.; Jiang, J.-J.; Su, C.-Y. Investigation of Binding
Behavior between Drug Molecule 5-Fluoracil and M L -Type
4
4
Tetrahedral Cages: Selectivity, Capture, and Release. Chem. - Eur. J.
017, 23 (15), 3542−3547.
11) Otte, M.; Kuijpers, P. F.; Troeppner, O.; Ivanovic-
2
(
Burmazovic,
́ ́
I.; Reek, J. N. H.; de Bruin, B. Encapsulation of Metalloporphyrins in
AUTHOR INFORMATION
Corresponding Author
E-mail: j.beves@unsw.edu.au.
■
*
a Self-Assembled Cubic M L Cage: A New Molecular Flask for
8
6
Cobalt−Porphyrin-Catalysed Radical-Type Reactions. Chem. - Eur. J.
2013, 19 (31), 10170−10178.
H
DOI: 10.1021/acs.inorgchem.8b01157
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
12) Brown, C. J.; Toste, F. D.; Bergman, R. G.; Raymond, K. N.
Supramolecular Catalysis in Metal-Ligand Cluster Hosts. Chem. Rev.
015, 115, 3012−3035.
13) Yang, L.; Jing, X.; He, C.; Chang, Z.; Duan, C. Redox-Active
(32) Brown, C. J.; Miller, G. M.; Johnson, M. W.; Bergman, R. G.;
Raymond, K. N. High-Turnover Supramolecular Catalysis by a
Protected Ruthenium(II) Complex in Aqueous Solution. J. Am. Chem.
Soc. 2011, 133 (31), 11964−11966.
2
(
M8L6 Cubic Hosts with Tetraphenylethylene Faces Encapsulate
Organic Dyes for Light-Driven H Production. Chem. - Eur. J. 2016,
(33) Otte, M.; Kuijpers, P. F.; Troeppner, O.; Ivanovic-Burmazovic,
́ ́
2
I.; Reek, J. N. H.; de Bruin, B. Encapsulated Cobalt−Porphyrin as a
Catalyst for Size-Selective Radical-type Cyclopropanation Reactions.
Chem.-Eur. J. 2014, 20 (17), 4880−4884.
2
(
2 (50), 18107−18114.
14) Cullen, W.; Misuraca, M. C.; Hunter, C. A.; Williams, N. H.;
Ward, M. D. Highly efficient catalysis of the Kemp elimination in the
cavity of a cubic coordination cage. Nat. Chem. 2016, 8 (3), 231−6.
(
(34) García-Simon, C.; Gramage-Doria, R.; Raoufmoghaddam, S.;
́
Parella, T.; Costas, M.; Ribas, X.; Reek, J. N. H. Enantioselective
Hydroformylation by a Rh-Catalyst Entrapped in a Supramolecular
Metallocage. J. Am. Chem. Soc. 2015, 137 (7), 2680−2687.
15) Martí-Centelles, V.; Lawrence, A. L.; Lusby, P. J. High Activity
and Efficient Turnover by a Simple, Self-Assembled “Artificial Diels−
Alderase”. J. Am. Chem. Soc. 2018, 140 (8), 2862−2868.
(35) Kaphan, D. M.; Levin, M. D.; Bergman, R. G.; Raymond, K. N.;
(
16) Zhang, D.; Jamieson, K.; Guy, L.; Gao, G.; Dutasta, J.-P.;
Toste, F. D. A supramolecular microenvironment strategy for
Martinez, A. Tailored oxido-vanadium(V) cage complexes for
selective sulfoxidation in confined spaces. Chem. Sci. 2017, 8 (1),
transition metal catalysis. Science 2015, 350 (6265), 1235−1238.
(36) Jing, X.; Yang, Y.; He, C.; Chang, Z.; Reek, J. N. H.; Duan, C.
7
(
89−794.
Control of Redox Events by Dye Encapsulation Applied to Light-
Driven Splitting of Hydrogen Sulfide. Angew. Chem., Int. Ed. 2017, 56
17) Cullen, W.; Metherell, A. J.; Wragg, A. B.; Taylor, C. G. P.;
Williams, N. H.; Ward, M. D. Catalysis in a Cationic Coordination
Cage Using a Cavity-Bound Guest and Surface-Bound Anions:
Inhibition, Activation, and Autocatalysis. J. Am. Chem. Soc. 2018, 140
(
39), 11759−11763.
(
37) Jing, X.; He, C.; Yang, Y.; Duan, C. A Metal−Organic
Tetrahedron as a Redox Vehicle to Encapsulate Organic Dyes for
(
8), 2821−2828.
18) Dalgarno, S. J.; Power, N. P.; Atwood, J. L. Metallo-
supramolecular capsules. Coord. Chem. Rev. 2008, 252 (8), 825−841.
19) Han, M.; Engelhard, D. M.; Clever, G. H. Self-assembled
coordination cages based on banana-shaped ligands. Chem. Soc. Rev.
014, 43 (6), 1848−60.
20) Cecot, G.; Marmier, M.; Geremia, S.; De Zorzi, R.;
Photocatalytic Proton Reduction. J. Am. Chem. Soc. 2015, 137 (11),
(
3
(
967−3974.
38) Wang, Q. Q.; Gonell, S.; Leenders, S. H.; Durr, M.; Ivanovic-
(
Burmazovic, I.; Reek, J. N. Self-assembled nanospheres with multiple
endohedral binding sites pre-organize catalysts and substrates for
highly efficient reactions. Nat. Chem. 2016, 8 (3), 225−30.
2
(
(
39) Leenders, S. H. A. M.; Durr, M.; Ivanovic-Burmazovic, I.; Reek,
̈
́ ́
Vologzhanina, A. V.; Pattison, P.; Solari, E.; Fadaei Tirani, F.;
Scopelliti, R.; Severin, K. The Intricate Structural Chemistry of
M
J. N. H. Gold Functionalized Platinum M L -Nanospheres and
1
2 24
Their Application in Cyclization Reactions. Adv. Synth. Catal. 2016,
58 (9), 1509−1518.
40) Chepelin, O.; Ujma, J.; Wu, X.; Slawin, A. M.; Pitak, M. B.;
II
2nLn-Type Assemblies. J. Am. Chem. Soc. 2017, 139 (24), 8371−
3
(
8
381.
(
21) Therrien, B.; Suss-Fink, G.; Govindaswamy, P.; Renfrew, A. K.;
Coles, S. J.; Michel, J.; Jones, A. C.; Barran, P. E.; Lusby, P. J.
Luminescent, enantiopure, phenylatopyridine iridium-based coordi-
nation capsules. J. Am. Chem. Soc. 2012, 134 (47), 19334−7.
Dyson, P. J. The “complex-in-a-complex” cations [(acac) M⊂Ru (p-
iPrC H Me) (tpt) (dhbq) ] : A trojan horse for cancer cells. Angew.
2
6
6
+
6
4
6
2
3
Chem., Int. Ed. 2008, 47 (20), 3773−6.
22) Mattsson, J.; Govindaswamy, P.; Furrer, J.; Sei, Y.; Yamaguchi,
K.; Suss-Fink, G.; Therrien, B. Encapsulation of Aromatic Molecules
(41) Schmidt, A.; Hollering, M.; Han, J.; Casini, A.; Kuhn, F. E. Self-
(
assembly of highly luminescent heteronuclear coordination cages.
̈
Dalton Trans. 2016, 45 (31), 12297−300.
in Hexanuclear Arene Ruthenium Cages: A Strategy to Build Up
Organometallic Carceplex Prisms with a Dangling Arm Standing Out.
Organometallics 2008, 27, 4346−4356.
(42) Li, X.-Z.; Zhou, L.-P.; Yan, L.-L.; Yuan, D.-Q.; Lin, C.-S.; Sun,
Q.-F. Evolution of Luminescent Supramolecular Lanthanide M L
2
n 3n
Complexes from Helicates and Tetrahedra to Cubes. J. Am. Chem. Soc.
017, 139 (24), 8237−8244.
43) Rota Martir, D.; Escudero, D.; Jacquemin, D.; Cordes, D. B.;
Slawin, A. M. Z.; Fruchtl, H. A.; Warriner, S. L.; Zysman-Colman, E.
(
23) Schmitt, F.; Freudenreich, J.; Barry, N. P.; Juillerat-Jeanneret,
2
(
L.; Suss-Fink, G.; Therrien, B. Organometallic cages as vehicles for
intracellular release of photosensitizers. J. Am. Chem. Soc. 2012, 134
(
2), 754−7.
24) Kilbas, B.; Mirtschin, S.; Scopelliti, R.; Severin, K. A solvent-
responsive coordination cage. Chem. Sci. 2012, 3 (3), 701−704.
25) Boer, S. A.; Turner, D. R. Self-selecting homochiral quadruple-
1
6+
Homochiral Emissive Λ - and Δ -[Ir Pd ] Supramolecular Cages.
8
8
8
4
(
Chem.-Eur. J. 2017, 23 (57), 14358−14366.
44) Hauke, C. E.; Oldacre, A. N.; Fulong, C. R. P.; Friedman, A. E.;
(
(
Cook, T. R. Coordination-Driven Self-Assembly of Ruthenium
Polypyridyl Nodes Resulting in Emergent Photophysical and
Electrochemical Properties. Inorg. Chem. 2018, 57 (7), 3587−3595.
stranded helicates and control of supramolecular chirality. Chem.
Commun. 2015, 51 (98), 17375−17378.
(
Unique Ruthenium Bimetallic Supramolecular Cages From C4-
Symmetric Tetrapyridyl Metalloligands. Inorg. Chem. 2017, 56 (9),
26) Ryu, J. Y.; Wi, E. H.; Pait, M.; Lee, S.; Stang, P. J.; Lee, J.
(45) Elliott, A. B. S.; Lewis, J. E. M.; van der Salm, H.; McAdam, C.
J.; Crowley, J. D.; Gordon, K. C. Luminescent Cages: Pendant
4
+
Emissive Units on [Pd L ] “Click” Cages. Inorg. Chem. 2016, 55
5
(
471−5477.
27) Jansze, S. M.; Wise, M. D.; Vologzhanina, A. V.; Scopelliti, R.;
2 4
(
7), 3440−3447.
(46) Zhang, Y.; Crawley, M. R.; Hauke, C. E.; Friedman, A. E.;
Cook, T. R. Phosphorescent Decanuclear Bimetallic Pt M (M = Zn,
II
Severin, K. Pd L -type coordination cages up to three nanometers in
size. Chem. Sci. 2017, 8 (3), 1901−1908.
(
B.; Clegg, J. K.; Nitschke, J. R. Reactivity modulation in container
molecules. Chem. Sci. 2011, 2, 51−56.
(
2
4
6
4
Fe) Tetrahedral Cages. Inorg. Chem. 2017, 56 (8), 4258−4262.
47) Rota Martir, D.; Cordes, D. B.; Slawin, A. M. Z.; Escudero, D.;
Jacquemin, D.; Warriner, S. L.; Zysman-Colman, E. A luminescent
28) For reviews of reactions within molecular cages, see: Breiner,
(
2
4+
29) Leenders, S. H. A. M.; Gramage-Doria, R.; de Bruin, B.; Reek, J.
[Pd
4
Ru
8
]
supramolecular cage. Chem. Commun. 2018, 54 (47),
N. H. Transition metal catalysis in confined spaces. Chem. Soc. Rev.
015, 44 (2), 433−448.
30) Otte, M. Size-Selective Molecular Flasks. ACS Catal. 2016, 6
10), 6491−6510.
31) Wang, Z. J.; Brown, C. J.; Bergman, R. G.; Raymond, K. N.;
6016−6019.
2
(
(48) Yan, X.; Cook, T. R.; Wang, P.; Huang, F.; Stang, P. J. Highly
emissive platinum(II) metallacages. Nat. Chem. 2015, 7, 342.
(49) Dalton, D. M.; Ellis, S. R.; Nichols, E. M.; Mathies, R. A.;
Toste, F. D.; Bergman, R. G.; Raymond, K. N. Supramolecular
(
(
1
2‑
Toste, F. D. Hydroalkoxylation Catalyzed by a Gold(I) Complex
Ga
4
L
6
Cage Photosensitizes 1,3-Rearrangement of Encapsulated
Encapsulated in a Supramolecular Host. J. Am. Chem. Soc. 2011, 133
Guest via Photoinduced Electron Transfer. J. Am. Chem. Soc. 2015,
137 (32), 10128−31.
(
19), 7358−7360.
I
DOI: 10.1021/acs.inorgchem.8b01157
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
(
50) Piper, J. R.; Cletheroe, L.; Taylor, C. G. P.; Metherell, A. J.;
(68) Chakraborty, S.; Hong, W.; Endres, K. J.; Xie, T.-Z.; Wojtas, L.;
Moorefield, C. N.; Wesdemiotis, C.; Newkome, G. R. Terpyridine-
Based, Flexible Tripods: From a Highly Symmetric Nanosphere to
Temperature-Dependent, Irreversible, 3D Isomeric Macromolecular
Nanocages. J. Am. Chem. Soc. 2017, 139 (8), 3012−3020.
Weinstein, J. A.; Sazanovich, I. V.; Ward, M. D. Photoinduced energy-
and electron-transfer from a photoactive coordination cage to bound
guests. Chem. Commun. 2017, 53 (2), 408−411.
(
51) Musser, A. J.; Neelakandan, P. P.; Richter, J. M.; Mori, H.;
Friend, R. H.; Nitschke, J. R. Excitation Energy Delocalization and
Transfer to Guests within M L Cage Frameworks. J. Am. Chem. Soc.
(69) Guo, J.; Xu, Y. W.; Li, K.; Xiao, L. M.; Chen, S.; Wu, K.; Chen,
X. D.; Fan, Y. Z.; Liu, J. M.; Su, C. Y. Regio- and Enantioselective
Photodimerization within the Confined Space of a Homochiral
Ruthenium/Palladium Heterometallic Coordination Cage. Angew.
Chem., Int. Ed. 2017, 56 (14), 3852−3856.
II
4
6
2
(
017, 139 (34), 12050−12059.
52) Campagna, S.; Puntoriero, F.; Nastasi, F.; Bergamini, G.;
Balzani, V. Photochemistry and photophysics of coordination
compounds: Ruthenium. In Photochemistry and Photophysics of
Coordination Compounds I; Balzani, V., Campagna, S., Eds.;
Springer-Verlag: Berlin, 2007; Vol. 280, pp 117−214.
(70) Shen, C.; Kennedy, A. D. W.; Donald, W. A.; Torres, A. M.;
Price, W. S.; Beves, J. E. Self-assembled supramolecular cages
containing dinuclear ruthenium(II) polypyridyl complexes. Inorg.
Chim. Acta 2017, 458, 122−128.
(
53) Narayanam, J. M.; Stephenson, C. R. Visible light photoredox
catalysis: applications in organic synthesis. Chem. Soc. Rev. 2011, 40
1), 102−13.
54) Schultz, D. M.; Yoon, T. P. Solar synthesis: prospects in visible
light photocatalysis. Science 2014, 343 (6174), 1239176.
55) Sahoo, B.; Li, J. L.; Glorius, F. Visible-Light Photoredox-
(71) Yang, J.; Bhadbhade, M.; Donald, W. A.; Iranmanesh, H.;
(
Moore, E. G.; Yan, H.; Beves, J. E. Self-assembled supramolecular
cages containing ruthenium(II) polypyridyl complexes. Chem.
Commun. 2015, 51 (21), 4465−8.
(
(
(72) Iranmanesh, H.; Arachchige, K. S. A.; Bhadbhade, M.; Donald,
Catalyzed Semipinacol-Type Rearrangement: Trifluoromethylation/
Ring Expansion by a Radical-Polar Mechanism. Angew. Chem., Int. Ed.
W. A.; Liew, J. Y.; Liu, K. T. C.; Luis, E. T.; Moore, E. G.; Price, J. R.;
Yan, H.; Yang, J.; Beves, J. E. Chiral Ruthenium(II) Complexes as
Supramolecular Building Blocks for Heterometallic Self-Assembly.
Inorg. Chem. 2016, 55 (24), 12737−12751.
2
(
015, 54 (39), 11577−80.
56) Gao, C.; Li, J.; Yu, J.; Yang, H.; Fu, H. Visible-light photoredox
synthesis of internal alkynes containing quaternary carbons. Chem.
Commun. 2016, 52 (45), 7292−7294.
(
73) Glasson, C. R.; Meehan, G. V.; Clegg, J. K.; Lindoy, L. F.;
II
Turner, P.; Duriska, M. B.; Willis, R. A new Fe quaterpyridyl M L
4
6
(
57) Svejstrup, T. D.; Zawodny, W.; Douglas, J. J.; Bidgeli, D.;
tetrahedron exhibiting selective anion binding. Chem. Commun. 2008,
No. 10, 1190−2.
Sheikh, N. S.; Leonori, D. Visible-light-mediated generation of nitrile
oxides for the photoredox synthesis of isoxazolines and isoxazoles.
Chem. Commun. 2016, 52 (83), 12302−12305.
(74) Glasson, C. R. K.; Clegg, J. K.; McMurtrie, J. C.; Meehan, G.
V.; Lindoy, L. F.; Motti, C. A.; Moubaraki, B.; Murray, K. S.; Cashion,
(
58) Amador, A. G.; Sherbrook, E. M.; Yoon, T. P. Enantioselective
III
J. D. Unprecedented encapsulation of a [Fe Cl ]- anion in a cationic
[
4
Photocatalytic [3 + 2] Cycloadditions of Aryl Cyclopropyl Ketones. J.
Am. Chem. Soc. 2016, 138 (14), 4722−5.
(
II
8+
Fe 4L6] tetrahedral cage derived from 5,5‴-dimethyl-
2,2′:5′,5″:2″,2‴-quaterpyridine. Chem. Sci. 2011, 2 (3), 540−543.
75) Glasson, C. R. K.; Meehan, G. V.; Motti, C. A.; Clegg, J. K.;
2
59) Zhang, L.; Hu, X. Room temperature C(sp )−H oxidative
(
chlorination via photoredox catalysis. Chem. Sci. 2017, 8, 7009−7013.
Turner, P.; Jensen, P.; Lindoy, L. F. New nickel(II) and iron(II)
helicates and tetrahedra derived from expanded quaterpyridines.
Dalton Trans. 2011, 40 (40), 10481−10490.
(
60) Wang, C.; Xie, Z.; deKrafft, K. E.; Lin, W. Doping Metal−
Organic Frameworks for Water Oxidation, Carbon Dioxide
Reduction, and Organic Photocatalysis. J. Am. Chem. Soc. 2011, 133
(76) Mal, P.; Schultz, D.; Beyeh, K.; Rissanen, K.; Nitschke, J. R. An
(
34), 13445−13454.
61) Yu, X.; Cohen, S. M. Photocatalytic metal-organic frameworks
for the aerobic oxidation of arylboronic acids. Chem. Commun. 2015,
1 (48), 9880−3.
62) Maza, W. A.; Padilla, R.; Morris, A. J. Concentration
unlockable-relockable iron cage by subcomponent self-assembly.
(
Angew. Chem., Int. Ed. 2008, 47 (43), 8297−301.
(77) Mal, P.; Breiner, B.; Rissanen, K.; Nitschke, J. R. White
5
(
phosphorus is air-stable within a self-assembled tetrahedral capsule.
Science 2009, 324 (5935), 1697−9.
Dependent Dimensionality of Resonance Energy Transfer in a
Postsynthetically Doped Morphologically Homologous Analogue of
UiO-67 MOF with a Ruthenium(II) Polypyridyl Complex. J. Am.
Chem. Soc. 2015, 137 (25), 8161−8168.
(78) Meng, W.; Clegg, J. K.; Thoburn, J. D.; Nitschke, J. R.
Controlling the transmission of stereochemical information through
space in terphenyl-edged Fe L cages. J. Am. Chem. Soc. 2011, 133
4
6
(
34), 13652−60.
(
63) Maza, W. A.; Haring, A. J.; Ahrenholtz, S. R.; Epley, C. C.; Lin,
(
79) Ousaka, N.; Grunder, S.; Castilla, A. M.; Whalley, A. C.;
S. Y.; Morris, A. J. Ruthenium(II)-polypyridyl zirconium(IV) metal-
organic frameworks as a new class of sensitized solar cells. Chem. Sci.
Stoddart, J. F.; Nitschke, J. R. Efficient Long-Range Stereochemical
Communication and Cooperative Effects in Self-Assembled Fe4L
6
2
(
016, 7 (1), 719−727.
64) Li, K.; Zhang, L. Y.; Yan, C.; Wei, S. C.; Pan, M.; Zhang, L.; Su,
C. Y. Stepwise assembly of Pd (RuL ) nanoscale rhombododecahe-
Cages. J. Am. Chem. Soc. 2012, 134 (37), 15528−15537.
(80) Ronson, T. K.; Giri, C.; Kodiah Beyeh, N.; Minkkinen, A.;
6
3 8
Topic, F.; Holstein, J. J.; Rissanen, K.; Nitschke, J. R. Size-Selective
́
Encapsulation of Hydrophobic Guests by Self-Assembled M4L
6
Cobalt and Nickel Cages. Chem.-Eur. J. 2013, 19 (10), 3374−3382.
(81) Zhang, D.; Ronson, T. K.; Mosquera, J.; Martinez, A.; Guy, L.;
dral metal-organic cages via metalloligand strategy for guest trapping
and protection. J. Am. Chem. Soc. 2014, 136 (12), 4456−9.
(
Moorefield, C. N.; Cheng, S. Z. D.; Wesdemiotis, C.; Newkome, G. R.
Towards Molecular Construction Platforms: Synthesis of a Metal-
65) Xie, T.-Z.; Guo, K.; Huang, M.; Lu, X.; Liao, S.-Y.; Sarkar, R.;
Nitschke, J. R. Anion Binding in Water Drives Structural Adaptation
II
II
lotricyclic Spirane Based on Bis(2,2′:6′,2′′-Terpyridine)Ru Con-
in an Azaphosphatrane-Functionalized Fe
4
L
4
Tetrahedron. J. Am.
nectivity. Chem. - Eur. J. 2014, 20 (36), 11291−11294.
Chem. Soc. 2017, 139 (19), 6574−6577.
(
66) Xie, T.-Z.; Liao, S.-Y.; Guo, K.; Lu, X.; Dong, X.; Huang, M.;
(82) Ronson, T. K.; Meng, W.; Nitschke, J. R. Design Principles for
II
Moorefield, C. N.; Cheng, S. Z. D.; Liu, X.; Wesdemiotis, C.;
Newkome, G. R. Construction of a Highly Symmetric Nanosphere via
a One-Pot Reaction of a Tristerpyridine Ligand with Ru(II). J. Am.
Chem. Soc. 2014, 136 (23), 8165−8168.
the Optimization of Guest Binding in Aromatic-Paneled Fe L
4 6
Cages. J. Am. Chem. Soc. 2017, 139 (28), 9698−9707.
(83) Pluth, M. D.; Bergman, R. G.; Raymond, K. N. Acid catalysis in
basic solution: a supramolecular host promotes orthoformate
hydrolysis. Science 2007, 316 (5821), 85−8.
(
67) Wu, K.; Li, K.; Hou, Y. J.; Pan, M.; Zhang, L. Y.; Chen, L.; Su,
C. Y. Homochiral D -symmetric metal-organic cages from stereogenic
Ru(II) metalloligands for effective enantioseparation of atropisomeric
molecules. Nat. Commun. 2016, 7, 10487.
(84) Leung, D. H.; Bergman, R. G.; Raymond, K. N. Highly
Selective Supramolecular Catalyzed Allylic Alcohol Isomerization. J.
Am. Chem. Soc. 2007, 129 (10), 2746−2747.
4
J
DOI: 10.1021/acs.inorgchem.8b01157
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
II
II
II
(
85) Wang, Z. J.; Clary, K. N.; Bergman, R. G.; Raymond, K. N.;
Homo- and Heterotrimetallic Complexes of Fe , Ru , and Os . Chem.
- Eur. J. 2014, 20 (41), 13242−13252.
Toste, F. D. A supramolecular approach to combining enzymatic and
transition metal catalysis. Nat. Chem. 2013, 5 (2), 100−3.
(
(103) Meng, W.; Breiner, B.; Rissanen, K.; Thoburn, J. D.; Clegg, J.
K.; Nitschke, J. R. A self-assembled M L cubic cage that selectively
86) Hong, C. M.; Kaphan, D. M.; Bergman, R. G.; Raymond, K. N.;
8 6
Toste, F. D. Conformational Selection as the Mechanism of Guest
Binding in a Flexible Supramolecular Host. J. Am. Chem. Soc. 2017,
encapsulates large aromatic guests. Angew. Chem., Int. Ed. 2011, 50
(15), 3479−83.
(104) Bilbeisi, R. A.; Clegg, J. K.; Elgrishi, N.; de Hatten, X.;
1
(
39 (23), 8013−8021.
Devillard, M.; Breiner, B.; Mal, P.; Nitschke, J. R. Subcomponent Self-
87) Symmers, P. R.; Burke, M. J.; August, D. P.; Thomson, P. I. T.;
8
+
Nichol, G. S.; Warren, M. R.; Campbell, C. J.; Lusby, P. J. Non-
Assembly and Guest-Binding Properties of Face-Capped Fe4L
4
Capsules. J. Am. Chem. Soc. 2012, 134 (11), 5110−5119.
equilibrium cobalt(III) “click” capsules. Chem. Sci. 2015, 6 (1), 756−
(105) Roberts, D. A.; Pilgrim, B. S.; Cooper, J. D.; Ronson, T. K.;
7
(
60.
Zarra, S.; Nitschke, J. R. Post-assembly Modification of Tetrazine-
88) Burke, M. J.; Nichol, G. S.; Lusby, P. J. Orthogonal Selection
II
4 6
Edged Fe L Tetrahedra. J. Am. Chem. Soc. 2015, 137 (32), 10068−
and Fixing of Coordination Self-Assembly Pathways for Robust
Metallo-organic Ensemble Construction. J. Am. Chem. Soc. 2016, 138
7
(
1.
106) Jansze, S. M.; Cecot, G.; Wise, M. D.; Zhurov, K. O.; Ronson,
(
29), 9308−15.
89) Sanz, S.; O’Connor, H. M.; Pineda, E. M.; Pedersen, K. S.;
Nichol, G. S.; Monsted, O.; Weihe, H.; Piligkos, S.; McInnes, E. J.;
T. K.; Castilla, A. M.; Finelli, A.; Pattison, P.; Solari, E.; Scopelliti, R.;
Zelinskii, G. E.; Vologzhanina, A. V.; Voloshin, Y. Z.; Nitschke, J. R.;
Severin, K. Ligand Aspect Ratio as a Decisive Factor for the Self-
Assembly of Coordination Cages. J. Am. Chem. Soc. 2016, 138 (6),
(
III
II 12+
II
Lusby, P. J.; Brechin, E. K. [Cr M ] Coordination Cubes (M =
8
6
Cu, Co). Angew. Chem., Int. Ed. 2015, 54 (23), 6761−4.
2
(
046−2054.
107) Avram, L.; Cohen, Y. Diffusion NMR of molecular cages and
capsules. Chem. Soc. Rev. 2015, 44 (2), 586−602.
108) Bloch, W. M.; Abe, Y.; Holstein, J. J.; Wandtke, C. M.;
(
90) D’Souza, D. M.; Leigh, D. A.; Papmeyer, M.; Woltering, S. L. A
scalable synthesis of 5,5′-dibromo-2,2′-bipyridine and its stepwise
functionalization via Stille couplings. Nat. Protoc. 2012, 7 (11), 2022−
(
8
(
.
Dittrich, B.; Clever, G. H. Geometric Complementarity in Assembly
91) Ayme, J. F.; Beves, J. E.; Leigh, D. A.; McBurney, R. T.;
A2 B2
and Guest Recognition of a Bent Heteroleptic cis-[Pd L L ]
2
Rissanen, K.; Schultz, D. A synthetic molecular pentafoil knot. Nat.
Chem. 2012, 4 (1), 15−20.
Coordination Cage. J. Am. Chem. Soc. 2016, 138, 13750−13755.
(109) Han, M.; Luo, Y.; Damaschke, B.; Gomez, L.; Ribas, X.; Jose,
́
(
92) Kieffer, M.; Pilgrim, B. S.; Ronson, T. K.; Roberts, D. A.;
A.; Peretzki, P.; Seibt, M.; Clever, G. H. Light-Controlled
Interconversion between a Self-Assembled Triangle and a Rhombi-
cuboctahedral Sphere. Angew. Chem., Int. Ed. 2016, 55 (1), 445−449.
(110) Bloch, W. M.; Holstein, J. J.; Hiller, W.; Clever, G. H.
Morphological Control of Heteroleptic cis- and trans-Pd L L′ Cages.
Aleksanyan, M.; Nitschke, J. R. Perfluorinated Ligands Induce
Meridional Metal Stereochemistry to Generate M L , M L , and
8
12
10 15
M L Prisms. J. Am. Chem. Soc. 2016, 138 (21), 6813−21.
12 18
(
93) Querol, M.; Bozic, B.; Salluce, N.; Belser, P. Synthesis, metal
2
2
2
complex formation, and switching properties of spiropyrans linked to
Angew. Chem., Int. Ed. 2017, 56 (28), 8285−8289.
chelating sites. Polyhedron 2003, 22 (5), 655−664.
(
94) 2,2′:5′,3′′:6′′,2‴-Quaterpyridine has been previously synthe-
sized; see: Das, N.; Bindra, G. S.; Paul, A.; Vos, J. G.; Schulz, M.;
Pryce, M. T. Enhancing Photocatalytic Hydrogen Generation: the
Impact of the Peripheral Ligands in Ru/Pd and Ru/Pt Complexes.
Chem. - Eur. J. 2017, 23 (22), 5330−5337.
(
95) Luis, E. T.; Ball, G. E.; Gilbert, A.; Iranmanesh, H.; Newdick, C.
W.; Beves, J. E. Efficient microwave-assisted synthesis and character-
ization of key ruthenium(II) polypyridyl complexes [Ru(bpy) ]-
3
(
(
1
PF ) , [Ru(phen) ](PF ) , [Ru(bpy) (phen)](PF ) and [Ru-
6 2 3 6 2 2 6 2
phen) (bpy)](PF ) . J. Coord. Chem. 2016, 69 (11−13), 1686−
2
6 2
694.
96) McMurtrie, J.; Dance, I. Engineering grids of metal complexes:
(
development of the 2D M(terpy)2 embrace motif in crystals.
CrystEngComm 2005, 7 (35), 216−229.
(
97) McMurtrie, J.; Dance, I. Crystal packing in metal complexes of
4
1
(
′-phenylterpyridine and related ligands: occurrence of the 2D and
D terpy embrace arrays. CrystEngComm 2009, 11 (6), 1141−1149.
98) McMurtrie, J.; Dance, I. Alternative two-dimensional embrace
nets formed by metal complexes of 4′-phenylterpyridine crystallised
with hydrophilic anions. CrystEngComm 2010, 12 (10), 3207−3217.
(
99) Mulyana, Y.; Weber, D. K.; Buck, D. P.; Motti, C. A.; Collins, J.
G.; Keene, F. R. Oligonuclear polypyridylruthenium(II) complexes
incorporating flexible polar and non-polar bridges: synthesis, DNA-
binding and cytotoxicity. Dalton Trans. 2011, 40 (7), 1510−23.
(
100) Creutz, C.; Chou, M.; Netzel, T. L.; Okumura, M.; Sutin, N.
Lifetimes, spectra, and quenching of the excited states of polypyridine
complexes of iron(II), ruthenium(II), and osmium(II). J. Am. Chem.
Soc. 1980, 102 (4), 1309−1319.
(
101) Lafolet, F.; Chauvin, J.; Collomb, M.-N.; Deronzier, A.;
Laguitton-Pasquier, H.; Lepretre, J.-C.; Vial, J.-C.; Brasme, B.
Photoinduced energy and electron transfer processes in hetero-
polynuclear polypyridyl complexes of Ru(II) and Fe(II). Phys. Chem.
Chem. Phys. 2003, 5 (12), 2520−2527.
(
102) Maity, D.; Bhaumik, C.; Mardanya, S.; Karmakar, S.; Baitalik,
S. Light Harvesting and Directional Energy Transfer in Long-Lived
K
DOI: 10.1021/acs.inorgchem.8b01157
Inorg. Chem. XXXX, XXX, XXX−XXX