Electron-rich arene-ruthenium metalla-architectures incorporating tetrapyridyl-tetrathiafulvene donor moieties

Article abstract of DOI:10.1021/om401142j

A series of arene ruthenium architectures have been prepared from coordination-driven self-assembly using dinuclear p-cymene ruthenium acceptors and π-donating tetratopic tetrapyridyl-tetrathiafulvalene donor ligands. The synthetic strategy, based on a geometric interaction approach, leads to four electroactive metalla-assemblies, 1-4 (one molecular cube and three metallaplates), that were characterized by NMR, ESI-MS, X-ray diffraction, and cyclic voltammetry. Rationalization of their formation discrepancy was completed by DFT calculations supported by structural features of their constituting TTF and Ru-complex components. Metalla-architectures possessing electron-rich cores (3, cis-4, and trans-4) interact strongly with picric acid (PA) to yield cocrystallized products, PA + metalla-assemblies, confirmed by single-crystal X-ray structure analyses.

Full text of DOI:10.1021/om401142j

Article
pubs.acs.org/Organometallics
Electron-Rich Arene−Ruthenium Metalla-architectures Incorporating
Tetrapyridyl−Tetrathiafulvene Donor Moieties
Vaishali Vajpayee,† Sebastien Bivaud,† Sebastien Goeb,† Vincent Croue,† Magali Allain,† Brian V. Popp,‡
́
́
́
Amine Garci,§ Bruno Therrien,*,§ and Marc Salle*,†
́
†Laboratoire MOLTECH-Anjou, Universite
́
d’Angers, CNRS UMR 6200, , 2 Boulevard Lavoisier, 49045 Angers Cedex, France
‡Eugene Bennett Department of Chemistry, West Virginia University, PO Box 6045, Morgantown, West Virginia, United States
§Institute of Chemistry, Universite
́ ̂ ̂
de Neuchatel, Avenue de Bellevaux 51, CH-2000, Neuchatel, Switzerland
S
* Supporting Information
ABSTRACT: A series of arene ruthenium architectures have
been prepared from coordination-driven self-assembly using
dinuclear p-cymene ruthenium acceptors and π-donating
tetratopic tetrapyridyl−tetrathiafulvalene donor ligands. The
synthetic strategy, based on a geometric interaction approach,
leads to four electroactive metalla-assemblies, 1−4 (one
molecular cube and three metallaplates), that were charac-
terized by NMR, ESI-MS, X-ray diffraction, and cyclic
voltammetry. Rationalization of their formation discrepancy
was completed by DFT calculations supported by structural
features of their constituting TTF and Ru-complex compo-
nents. Metalla-architectures possessing electron-rich cores (3,
cis-4, and trans-4) interact strongly with picric acid (PA) to
yield cocrystallized products, PA + metalla-assemblies, confirmed by single-crystal X-ray structure analyses.
metallacycles and -cages built from side panels incorporating
INTRODUCTION
■
TTF moieties,8,9 namely, bispyrollo(tetrathiafulvalene)
(BPTTF) and the so-called extended-tetrathiafulvalene
(exTTF). It is worth noting that these assemblies were
obtained with square-planar Pt(II) or Pd(II) complexes.
In the last decades, supramolecular coordination-driven
assembly has emerged as a remarkable tool to design intricate
molecular architectures.1 In particular, donor−acceptor coordi-
nation-driven assembly has provided a sophisticated and
efficient way to construct nanosized metalla-architectures with
well-defined shape and size, structures otherwise inaccessible by
conventional routes.2 Metalla-architectures assembled from
arene ruthenium building blocks are particularly attractive due
to their interesting functions and potential applications in
various areas of chemistry, including host−guest chemistry,
catalysis, chemotherapy, and photo- and electrochemical
sensing.3
The electron-donating tetrathiafulvalene moiety (TTF) has
received a great deal of attention and constitutes a major
component of various conducting materials,4 sensors, and
switches.5 The incorporation of TTF in these systems is
rationalized by a well-defined electrochemical behavior of TTF
derivatives, which can be easily and reversibly oxidized into
their corresponding cation radicals (TTF•+) and dications
(TTF2+). On this ground, integrating the TTF backbone within
host structures may favor the recognition of electron-poor
substrates.
Herein, we present the first examples of coordination-driven
self-assembled metalla-architectures involving the parent TTF
core. This has been made possible by the synthesis of the
tetratopic tetrapyridyl-TTF isomeric ligands L1 (tetra(4-
pyridyl)TTF) and L2 (tetra(3-pyridyl)TTF). As already
shown with alternative isomeric compounds bearing 4- and 3-
pyridyl coordinating groups, highly distinctive discrete
structures may be expected from the same metal complex
along the self-assembly process.10 Moreover, in the present
work, the metal complex corresponds to arene ruthenium
acceptors of identical bite angle but involving distinctive
lengths. Therefore, this report addresses the effect of the
crossed influence between the ligand geometry (3- and 4-
pyridyl derivatives) and the length of the dinuclear Ru-based
acceptor, relative to the structure of the resulting assemblies.
These results were supported by DFT calculations. Along with
the synthesis of new metalla-architectures, evidence for the
potential of using these electron-rich metalla-assemblies to
Despite numerous studies dealing with the synthesis of TTF-
based derivatives6 and TTF-based ligands,5,7 the preparation of
discrete self-assembled architectures from a TTF backbone
remains relatively unexplored. Recently, we introduced the first
Received: December 16, 2013
Published: March 27, 2014
© 2014 American Chemical Society
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interact with planar electron-deficient molecules was demon-
strated by X-ray diffraction studies.
Table 1. Frontier Molecular Orbitals of Ligands L1 and L2
(DFT, B3LYP, 6-31G(d,p))
RESULTS AND DISCUSSION
■
Synthesis and Characterization of the Tetratopic
Ligands L1 and L2. The ligand L1, unknown so far, was
prepared by an adaptation of the reported synthesis procedure
for L2.11 The reaction of halo-pyridine (4-iodopyridine for L1
and 3-bromopyridine for L2) with tetrathiafulvalene in the
presence of Pd(OAc)2, tri-tert-butylphosphine tetrafluorobo-
rate, and Cs2CO3 in refluxing dioxane yielded the desired
ligands in good yield (Scheme 1).
from the fact that both optimized geometries of ligands L1 and
L2 reveal a significant rotation of the pyridyl groups around the
TTF−Py bond by 44−49° (Figure 1b). This result strongly
differs from the case of the BPTTF tetrapyridyl ligand,8a for
which the four electron-withdrawing pyridyl units were
conjugated to the coplanar central BPTTF unit, resulting in
an alteration of its π-donating ability. Contrariwise, in the case
of L1 and L2, the pyridyl groups cannot be in the TTF plane
because of the steric contraction brought by their vicinal
positions. Therefore, in L1 and L2, the latter should not
contribute to decrease drastically the π-donating ability of TTF
through conjugation, thus preserving the intrinsic electronic
properties of the redox moiety. This is confirmed by the energy
values of the HOMO orbitals (L1: −5.11 eV; L2: −4.86 eV),
lower than for the parent TTF (−4.52 eV), but still reflecting a
good π-donating ability. It is clear from these calculations that
the electron density of the HOMO orbital is located on the
TTF fragment (see Table 1), while the LUMO is essentially
distributed over the whole molecule including the pyridyl
groups.
Electronic Properties of Ligands L1 and L2. UV−visible
spectra of L1 and L2 exhibit two absorption bands at λ < 350
nm (Figure S22), which are assigned to the local transition in
the TTF moiety. A third broader absorption at a lower energy
and centered at 450 nm is attributed to an intramolecular
charge transfer between the donating unit and the electron-
withdrawing pyridyl groups.14 The experimental HOMO−
LUMO gap measured from these spectra is in good accordance
with the theoretical values obtained from DFT calculations
(Table S1).
Scheme 1. Synthesis of Ligands L1 and L2
X-ray Structure of L1. Single crystals of L1, which
deteriorate rapidly, were obtained by slow diffusion of hexane
in a dichloromethane solution of L1. In the crystal packing, the
pyridyl groups are rotated along the TTF−Py axis by values
ranging from 31° to 77° (Figure 1a). Similar distortions were
found with a tetrapyridyl(vinylenedithio) TTF derivative in the
solid state.12 The four Npyr atoms of L1 define a rectangle of
approximately 6.7 Å × 13.1 Å2. An angle of 73° is found
between vicinal pyridine axes. Such geometric data are
important to consider in order to address the subsequent
self-assembly processes, and additional computational studies
were carried out to answer this issue.
Theoretical Calculations of Ligands L1 and L2. In order
to anticipate the electronic and geometrical behaviors of ligands
L1 and L2, theoretical calculations based on density functional
theory (DFT) methods were performed with the Gaussian 09
program.13 Becke’s three-parameter gradient-corrected func-
tional (B3LYP) with 6-31G(d,p) basis in vacuo was used for
full geometry optimization and to compute the electronic
structure at the minima found. The resulting frontier molecular
orbitals are shown in Table 1. A first striking observation comes
The electrochemical properties of L1 and L2 were further
investigated by cyclic voltammetry (1:1 CH2Cl2/CH3CN,
NBu4PF6) (Figure S21). Two reversible oxidation waves are
observed, located at higher potentials than those of the parent
TTF system (L1: E1ox= 0.22 V, E2ox= 0.55 V; L2: E1ox = 0.12 V,
E2ox = 0.47 V vs Fc/Fc+), in accordance with the electron-
accepting character of the pyridyl groups and as anticipated
from the corresponding HOMO values. The difference in Eox
values between L1 and L2 is in full agreement with the
Figure 1. Ball-and-stick views of L1, showing the main geometrical parameters: (a) top view (X-ray structure); (b) side view (Geometric
optimization).
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Scheme 2. Synthesis of Redox-Active Metalla-assemblies 1−4
respective electronic effects generated by the N-pyridyl atom in
the 4- versus 3-positions.15
and 11.5 Å calculated from the Stokes−Einstein equation (T =
298 K).16
Synthesis and Characterizations of Metalla-architec-
tures 1−4. The reaction of L1 with arene−ruthenium acceptor
A1 in a 1:2 molar ratio in methanol affords the discrete
octanuclear [2+4] cube 1 after stirring for 12 h at room
temperature, whereas the tetranuclear [1+2] plate 2 is obtained
by the reaction (12 h) of a 1:2 mixture of L1 with the arene−
ruthenium acceptor A2 in methanol (Scheme 2). The
formation of two different architectures by varying only the
length of the acceptor can be explained by self-sorting of proper
geometric complementary interactions. As stated above from
the X-ray single-crystal structure analysis of L1, two nitrogen
atoms belonging to two adjacent pyridyl groups in ligand L1
are separated by 6.7 Å. On the other hand, the distance
between two Ru atoms in A1 is approximately 5.5 Å,2c and the
metal−metal distance reaches a value of 7.9 Å in the case of
A2.2d Therefore, whereas a perfect size matching is observed
between L1 and the dimetallic complex A2, thus favoring
formation of the tetranuclear plate structure 2, an octanuclear
cage 1 is observed from the smaller diruthenium acceptor A1.
Cube 1 was isolated by precipitation with diethyl ether and
characterized by 1H NMR spectroscopy in methanol-d4 (Figure
S5). In addition to the expected metal-coordination-induced
upfield shift of the Hpyr resonances as compared to L1,
additional splitting of the pyridyl protons is observed (2:1:1 at
δ = 8.13, 7.46, and 7.09 ppm), suggesting a restricted rotation
of the pyridyl groups upon formation of the metallacubes. Such
splitting of the pyridyl signals is assigned to the steric
The high-resolution ESI-MS data confirm the formation of
the [2+4] octanuclear cube 1 and the [1+2] tetranuclear plate
2. Peaks attributed to the consecutive loss of triflate
counterions [1 − 2CF3SO3]2+, m/z 2078.88, [1 −
3CF3SO3]3+, m/z 1336.28 for 1 and [2 − 3CF3SO3]3+, m/z
1014.99, [2 − 3CF3SO3]3+, m/z 627.01 for 2 are observed.
Experimental isotopic patterns perfectly correlate with the
calculated theoretical isotopic distributions (Figures S17 and
S18) and attest to the different nuclearities of the systems.
Unfortunately, all attempts to grow diffraction quality crystals
of 1 and 2 have failed so far in our hands.
As anticipated from the coordination angles promoted by
ligand L2 as compared to L1, quite different structures are
found upon metal-driven self-assembly. Using the same
experimental conditions as for L1, only [1+2] metalla-
assemblies were obtained from L2 with both A1 and A2
acceptors (Scheme 2). The reaction of L2 with A1 leads to the
exclusive formation of [1+2] trans-metalla-assembly 3, whereas
the reaction with A2 affords a mixture of cis-4 and trans-4
isomeric metallaplates in a 1:1 ratio. The 1H NMR spectra of 3
and 4 show characteristic resonances for the pyridyl protons
with significant metal-coordination-induced upfield shifts as
compared to free ligand L2. The formation of a cis/trans
mixture in the case of 4 is supported by the presence of two sets
1
of signals for the p-cymene units in the H NMR spectrum.
Similar diffusion coefficients (D ≈ 3.48 × 10−10 m2 s−1) are
extracted from the DOSY NMR spectra of 3 and 4 (Figures
S13 and S16), which supports the occurrence of structurally
similar metalla-assemblies in each case. Further ESI-MS analysis
confirmed the formation of [1+2] self-assembled tetranuclear
metalla-assemblies 3 and 4 by the appearance of multiply
charged fragmented ions. Peaks at m/z = 964.97 [3 −
2CF3SO3]2+, 593.66 [3 − 3CF3SO3]3+, 408.01 [3 −
4CF3SO3]4+ and at m/z = 1014.99 [4 − 2CF3SO3]2+, 627.01
[4 − 3CF3SO3]3+ were observed. Their well-resolved isotopic
patterns strongly support the formation of [1+2] metalla-
assemblies in both cases (Figures S19 and S20).
interaction between adjacent coordinated pyridyl groups.9
a
On the other hand, two doublets at δ = 8.10 ppm (Hα) and
7.45 ppm (Hβ) are observed in methanol-d4 for the pyridyl
1
protons of metallaplate 2 (Figure S8). H diffusion-ordered
spectroscopy (DOSY) NMR spectra of 1 and 2 show the
presence of a single alignment of the signals for both metalla-
assemblies, confirming the formation of one discrete species in
both cases. The diffusion coefficients extracted from the DOSY
experiments of 1 (D ≈ 2.14 × 10−10 m2 s−1) and 2 (D ≈ 3.43 ×
10−10 m2 s−1) are significantly different and suggest two
distinctive structures with respective hydrodynamic radii of 18.5
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Figure 2. X-ray structure of 3·PA (a) and packing diagram (b). Solvent molecules and hydrogen atoms are omitted for clarity (color codes: S =
yellow, Ru = green, O = red, N = blue, and C = gray).
Figure 3. DFT-optimized geometry of free ligand L1 illustrating important angles and torsion angles used for the analysis of metalla-assemblies.
The molecular structures of 3, cis-4, and trans-4 as proposed
by the NMR spectroscopy were unambiguously confirmed by
single-crystal X-ray structure analyses. Although we were unable
to get single crystals for the discrete metalla-assemblies, we
could circumvent this difficulty by performing cocrystallization
with an aromatic organic molecule. Indeed, considering the
electron-rich character of the TTF-based metalla-assemblies in
3 and 4, we explored their ability to interact with electron-
deficient derivatives. Two equivalents of picric acid (PA) in
methanol were therefore layered on a CH2Cl2 solution of 3,
and crystals of the picric acid complex 3·PA were grown by
slow diffusion of pentane. Single-crystal X-ray structure analysis
of 3·PA reveals that 3 is present in a trans configuration
(assigned on the relative spatial position of the bimetallic parts
related to the TTF plane). The two ruthenium centers from
one acceptor moiety are separated by 5.521(1) Å, and the
average Ru−N and Ru−O bond distances are 2.153(6) and
2.121(6) Å, respectively (Figure 2a).
The driving force behind the selective formation of the trans
isomer is likely the strain that is associated with the cis isomer,
which is alleviated in the trans derivative. The solid-state
packing diagram of 3 results in a stacked structure involving
π−π interactions between the TTF moiety and the PA unit
(Figure 2b) with interplanar distances of 3.4−3.6 Å.
Interestingly, both isomers of 4 crystallize as their PA
complexes, cis-4·PA and trans-4·PA, respectively, by slow
diffusion of pentane on a solution of picric acid (2 equiv) in
methanol layered on a CH2Cl2 solution of 4. Although poorly
resolved because of the low quality of the crystals, the X-ray
diffraction study on cis-4·PA shows that four picric acid
molecules are trapped between two cis-4 units (Figure S23).
In the cis-4 isomer, the four N-py atoms of L2 are rotated
toward the same face of the TTF plane. Consequently, the four
ruthenium atoms form a rectangle (7.84 Å × 9.46 Å) that is
parallel to the TTF plane (Figure S23). In the case of trans-4·
PA (Figure S23), one Ru-acceptor moiety lies on each side of
the TTF skeleton, and a completely different stacking mode is
observed, with interplanar distances of ∼3.53−3.99 Å between
the planes of the picric acid and the TTF moiety, a standard
value for π−π stacking interactions.
DFT Calculations on Metalla-architectures 1−4. In
order to have a better understanding on the structural
characteristics of the newly designed metalla-assemblies, further
DFT studies were undertaken. Computational models of the
ruthenium coordination complexes were composed of the
complete experimental ligand sphere (i.e., A1 or A2 and L1 or
L2) with the exception of the replacement of the p-cymene
with a benzene ring. The metrical parameters obtained from X-
ray structure determinations of the tetracationic metalla-
assemblies 3 and 4 were used to consider the geometric
accuracy of a selection of DFT functionals and basis sets (see
the Supporting Information). The PBE0 functional, designated
PBE1PBE in Gaussian, was chosen for subsequent full gas-
phase geometry optimization calculations.
Three geometrical parameters related to the TTF ligand, as
defined in Figure 3, proved to be useful in the subsequent
structural analysis of the metalla-assemblies. The bite angle A is
composed by the 4-position of the pyridine rings (i.e., N or C
for L1 and L2, respectively) and the central disulfur-substituted
sp2-carbon. The bite angle B corresponds to the same central
disulfur-substituted sp2-carbon and the position-1 of the
pyridine rings. These two angles are sensitive to the geometric
constraints conferred by different diruthenium acceptor
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Figure 4. DFT-optimized geometry of the octacationic cube 1. Hydrogen atoms have been removed for clarity (color codes: Ru = aquamarine, O =
red, N = blue, C = gray).
Figure 5. DFT-optimized geometry of the tetracationic metallaplate 2 (A2 + L1) (left) and the hypothetical planar complex (A1 + L1) (right).
Hydrogen atoms have been removed for clarity (color codes: Ru = aquamarine, O = red, N = blue, C = gray).
Figure 6. DFT-optimized geometry of the hypothetical octacationic metallacube with acceptor A1 and donor L2. Hydrogen atoms have been
removed for clarity (color codes: Ru = aquamarine, O = red, N = blue, C = gray).
scaffolds. The torsional angle of the TTF ring system also
proved to be useful.
and L1 (Figure 5). Consistent with the expectation, the TTF
ligand of plate 2 is structurally similar to the free TTF ligand
L1. The distance between the pyridine rings has slightly
contracted to accommodate acceptor A2 (bite angle A = 53.1°),
and the TTF ring has moved closer to planarity (TTF torsion =
174.5°).
Accordingly, the hypothetical metallaplate involving acceptor
A1 and L1 shows a significant contraction of the distance
between the pyridyl rings (bite angle A = 41.5°). The increased
strain from this contraction is estimated to cost nearly 8 kcal/
mol in enthalpy. This energetic cost is likely the most
important factor in determining the selectively for the cube
versus the plate for a given combination of donor/acceptor
moieties (Figures 5 and 6).
We were also interested in understanding why the reaction
between the acceptor A1 and the donor L2 yielded the
tetranuclear metallaplate 3, rather than a metallacube similar to
1. Geometry optimization of the hypothetical cube (A1 + L2)
was performed, and a stationary point was identified (Figure 6).
There are two notable features of this cube. First, the TTF
torsion angle is 170° with the acceptor moieties sitting on the
convex face of the ligand. The fact that the tetranuclear cis-
metallaplate 3 is not observed suggests that this conformation
leads to an energetic penalty. Second, the acceptor moieties
Geometry optimization of metallacage 1 yielded a stationary
point (Figure 4). The number of atoms made the normal-mode
analysis computationally inaccessible. Nevertheless, the opti-
mized structure exceeded the default Gaussian convergence
criteria and had a predicted energy change of 0.001 kcal/mol.
We are therefore confident that the identified structure
represents a realistic model for cube 1.
As anticipated, the structural parameters of the cube are quite
similar to those of the corresponding free species. Diruthenium
acceptor A1, constituting the sides of the metalla-assembly,
does not show any perturbation in length from the free species
(i.e., 5.5 Å). The donor TTF moieties (L1), constituting the
floor and ceiling of the cube, show a slight relaxation of the bite
angles A and B (62.0° and 47.4°, respectively) and a nearly
planar TTF torsion angle of 176.5°. The torsion of the pyridyl
rings relative to the TTF plane is 41.2° and 36.1°, respectively.
The donor TTF planes are separated by 6.3 Å, and the volume
of the cavity, based on the ruthenium centers, is estimated to be
870 Å3.
Geometry optimization calculations were also performed on
metallaplate 2 (A2 + L1) and the experimentally unobserved
plate complex resulting from coordination between acceptor A1
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have shifted from the vertices to the sides of the cube. This
structural change results in a significant contraction of two
pyridyl torsional angles (32° and 33°), while the other two
angles slightly relaxed (47° and 48°) relative to L2 (44.9° and
46.6°). Taking these features together, it appears that significant
structural strain is generated in this cubic hypothetical
molecule. The strain is not manifested in the free TTF ligand
though. The compositional isomers L1 and L2 are nearly
isoenergetic (L1 is less stable by −0.5 kcal/mol). However, the
comparison of the total energy of metallacube 1 (A1 + L1) and
the hypothetical one (A1 + L2) shows that the latter is less
stable by 46 kcal/mol, indicating that its formation is highly
unfavorable.
nm for 4. These bands are likely due to the combination of
intra/intermolecular π→π* mixed with metal-to-ligand charge
transitions.
Cyclic voltammetry (CV) studies of 1−4 (5 × 10−4 M) were
performed in CH3CN containing 0.1 M n-Bu4NPF6 as
supporting electrolyte (Figure 7). Metalla-assemblies 2−4
The tetranuclear complexes obtained with 3-pyridyl-TTF
donor L2 were also considered. We sought to rationalize why
selective formation of a trans isomer was observed with A1
(metallaplate 3), while a 1:1 mixture of cis and trans
tetranuclear metalla-assemblies was observed with A2 (metal-
la-assemblies 4) (Tables S3−5). The latter isomers (A2 + L2)
yielded a gas-phase relative enthalpy and free energy of less
than 0.5 kcal/mol, which was anticipated based on the
experimental results. The metrical parameters of the isomers
are also quite similar, with the exception of the TTF torsion
(162° and 176° for cis-4 and trans-4, respectively). When the
former isomers (A1 + L2) were compared, we were surprised
to find a similar energetic result: the isomers were isoenergetic
in terms of both relative enthalpy and free energy (ΔH = 0.13
and ΔG = 0.14 kcal/mol). The metrical parameters of
metallaplate 3 show only small perturbations from those of 4.
Bite angles A and B contract slightly with the smaller acceptor
(5° and 1°, respectively). The acceptor length is largely
accommodated by changes to the pyridyl ring torsion relative to
the TTF backbone. Both isomers of 3 have torsions that are 4°
from orthogonal, while both isomers of 4 have torsions that are
15° from orthogonal. The structural similarities and differences
in the L2 structure for the tetranuclear metalla-assemblies led
us to assess the conformational flexibility of L2 by performing
single-point energy calculations on the isolated L2 ligand
geometries from the four optimized metalla-architectures. Even
though large torsional differences exist in the structures, the
relative energies remain quite similar across all four structures
(ΔE < 0.5 kcal/mol).
Observed DFT calculations suggest, and experimental data
confirm, that the tetranuclear ruthenium complexes are
kinetically nonlabile, so we reasoned that selectivity for the
trans isomer could result from the energetic differentiation of
the dinuclear intermediates (1 + 1 equiv of A1 + L2).
Geometry optimization calculations were performed for two
conformations of the dinuclear intermediate with the free
pyridyl ligands oriented such that they could yield the
corresponding tetranuclear isomers. The predicted relative
enthalpy and free energy changes were again quite small (<0.2
kcal/mol). Our computational studies have not allowed us to
rationalize the selectivity for trans-3. The error associated with
the local minima energies by DFT ( 3 kcal/mol) may provide
the most logical explanation; however, an as yet unidentified
and unexplained noncovalent interaction present during the
reaction (A1 + L2) also cannot be ruled out.
Figure 7. Cyclic voltammograms of metalla-assemblies 1−4 (c = 5 ×
10−4 M, CH3CN, 0.1 M NBu4PF6, 50 mV s−1, Pt, V vs Fc/Fc+).
exhibit the usual two successive one-electron reversible
oxidation behavior that is typical of TTF derivatives (2: E1
ox
=
= 0.28 V, E2ox = 0.58 V; 3: E1ox = 0.34 V, E2ox = 0.66 V; 4: E1
ox
0.23 V, E2ox = 0.52 V vs Fc/Fc+). These values appear at slightly
higher potentials than for their parent ligands L1 and L2, as
anticipated from coordination of the pyridyl groups to metal
centers. The three compounds exhibit a similar ΔE value (E2
ox
− E1ox) of 0.29−0.32 V and present only small differences in
their respective π-donating ability (E1ox), which presumably
accounts for the combined electronic effect generated by the
accepting moiety (A1 vs A2) and the TTF ligand (L1 vs L2).
One can notice that metalla-assembly 4 exhibits a better π-
donating ability than 3 (lower Eox values), synthesized from the
same ligand L2. This observation is ascribed to the higher
delocalization in acceptor A2 than in A1, leading to a lower
electron-withdrawing effect. Nevertheless, in all of these cases
the metalla-assemblies present a high π-donating ability
ascribed to the TTF contribution.
Consistent with the different molecular formulation of 1 as
compared to 2−4, the electrochemical behavior observed for
metallacube 1 is significantly different. A single oxidation wave
is observed for 1, located in the usual oxidation potentials range
of TTF derivatives (E1 = 0.44 V). Such nonclassical
ox
electrochemical behavior, regarding TTF derivatives, was
already observed in the case of a three-dimensional self-
assembled architecture.6a This peculiar behavior is ascribed to
the rigidity of the metal-assembled cube, which may alter the
kinetics of the conformational changes that accompany the
electrochemical processes.
CONCLUSIONS
■
Compounds L1 and L2 are of great interest regarding their dual
redox and coordinating properties. The X-ray structure analysis
of ligand L1 has provided and illustrated the potential of this
new ligand for the construction of metalla-assemblies with
redox-active architectures. On this ground, a set of TTF-based
metalla-assemblies have been prepared from two isomeric
tetrapyridyl-TTF ligands L1 and L2 and two dinuclear arene
Electronic Properties of Metalla-architectures 1−4.
The UV−visible spectroscopic properties of 1−4 (1 × 10−5 M)
were investigated in methanol (Figure S22). The electronic
spectra show peaks at λ = 274 and 379 nm for 1, λ = 278 and
493 nm for 2, λ = 271 and 378 nm for 3, and λ = 285 and 493
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Ligand L2 (ref 11). This was prepared by following experimental
conditions discussed above: from 3-bromopyridine (1.20 g, 7.34
mmol); chromatography eluting from dichloromethane to dichloro-
methane/methanol (97:3 v/v) to give a dark red powder (449 mg,
0.88 mmol, 60%). Melting point: >260 °C. 1H NMR [300 MHz,
CDCl3]: δ (ppm) δ 8.56 (d, 3J = 3.8 Hz, 4H, Hα), 8.49 (d, 3J = 3.8 Hz,
4H, Hβ), 7.57 (m, 4H, Hγ), 7.25 (m, 4H, Hα′). 13C NMR [75 MHz,
CDCl3]: δ (ppm) 149.8, 149.6, 136.3, 128.2, 127.7, 123.5, 108.9. MS
(MALDI-TOF) for C26H16N4S4: calculated 512.69; observed 512.5.
General Procedure for the Synthesis of Metalla-assemblies
1−4. A solution of methanol (2 mL) was added to a solid sample of
the corresponding arene−ruthenium acceptor (A1 and A2) and TTF-
based donor (L1 or L2) in 2:1 molar ratio. The mixture was stirred at
room temperature for 12 h, after which the solution was concentrated
and diethyl ether added to precipitate the pure self-assembled
metallacycles.
ruthenium acceptors. Computational studies have supported
the formation of the different self-assembled architectures from
the various combinations between those species. A TTF-based
redox-active cubic metalla-assembly has been described for the
first time. This result opens promising perspectives in terms of
new electron-rich three-dimensional assemblies designed for
guest transport properties or catalytic purposes. All new redox-
1
active assemblies were characterized by H, 13C, and DOSY-
NMR spectroscopy and HR-ESI-MS. A first illustration of these
electron-rich assemblies to associate electron-deficient species
was provided with picric acid and complexes 3, cis-4, and trans-
4, which showed, by single-crystal X-ray structure analyses,
cocrystalline products.
EXPERIMENTAL DATA
Metalla-assembly 1. Acceptor clip A1 (8.56 mg, 0.01 mmol) and
tetrapyridyl donor L1 (2.56 mg, 0.005 mmol) were stirred in methanol
(2 mL) to obtain 1 as a brown solid, which was isolated by
■
General Details. Arene−ruthenium acceptors (A12c and A22d)
were prepared according to reported methods. Deuterated solvents
were purchased from Cambridge Isotope Laboratory (Andover, MA,
USA). NMR spectra were recorded on a NMR Bruker Avance III 300
spectrometer. 1H NMR chemical shifts were reported relative to
residual solvent signals. MALDI-TOF-MS spectra were recorded on a
MALDI-TOF Bruker Bifle III instrument using a positive-ion mode.
ESI-MS spectra were achieved on a Bruker MicrO-Tof-Q 2
spectrometer in CH2Cl2. Cyclic voltammetry experiments were carried
out on ALS electrochemical analyzer model 660, with the following
conditions: 0.1 M n-Bu4NPF6 in distilled acetonitrile, Ag/Ag+
reference electrode, C-graphite working electrode, and Pt counter
electrode, 50 mV s−1, calibrated using internal ferrocene. UV/visible/
NIR absorption spectra were recorded on a PerkinElmer Lamda19
spectrometer, and spectroscopic grade solvents were used.
1
precipitation with Et2O. Isolated yield: 81%. H NMR [300 MHz,
CD3OD]: δ (ppm) 8.13 (br d, 3J = 6.0 Hz, 16H, Hα), 7.46 (d, 3J, H =
6.0 Hz, 8H, Hβ), 7.09 (m, 8H, Hβ), 6.08−5.77 (m, 32H, Hcym), 2.86
(m, 8H, CH(CH3)2), 2.28 (m, 24, CH3), 1.38 (m, 48H, CH(CH3)2).
13C NMR (75 MHz, CD3OD): δ (ppm) 170.5, 153.1, 141.8, 140.5,
130.6, 125.8, 124.6, 122.6, 118.4, 102.0, 101.5, 98.2, 97.5, 83.5, 82.7,
82.3, 81.8, 81.7, 31.0, 21.3, 21.1, 16.9, 16.7. HRMS (ESI) for
C148H144F24N8O40Ru8S16: calculated 2076.9007 [1 − 2OTf]2+,
1335.2829 [1 − 3OTf]3+; observed 2076.8788 [1 − 2OTf]2+,
1335.2830 [1 − 3OTf]3+. Anal. Calcd for C148H144F24N8O40Ru8S16:
C, 39.93; H, 3.26; N, 2.52. Found: C, 39.78; H, 2.99; N, 2.34.
Metalla-assembly 2. Acceptor clip A2 (9.06 mg, 0.01 mmol) and
tetrapyridyl donor L1 (2.56 mg, 0.005 mmol) were stirred in methanol
(2 mL) to obtain 2 as a dark red solid, which was isolated by
Single-Crystal X-ray Crystallography. X-ray single-crystal
diffraction data were collected at different low temperatures on a
Bruker KappaCCD diffractometer, equipped with a graphite
monochromator utilizing Mo Kα radiation (λ = 0.71073 Å). The
four structures were solved by direct methods, expanded using
difference Fourier map for 3·PA, cis-4·PA, and trans-4·PA and refined
on F2 by full matrix least-squares techniques using the SHELX97 (G.
M. Sheldrick, 1998) package. For all structures, all non-hydrogen
atoms were refined anisotropically, except for cis-4·PA, where C atoms
were refined isotropically. Absorption was corrected by the SADABS
program (Sheldrick, Bruker, 2008). The H atoms were found by
Fourier difference map for L1, and they were included in the
calculation without refinement for 3·PA. No H atoms were added for
cis-4·PA and trans-4·PA because of nonconvergent refinement.
General Procedure for the Synthesis of Ligands L1 and L2.
To a suspension of palladium acetate (82 mg, 0.36 mmol), tri-tert-
butylphosphine tetrafluoroborate (320 mg, 1.10 mmol), and cesium
carbonate (2.40 g, 7.30 mmol) stirred for 10 min at 90 °C under argon
in distilled dioxane (20 mL) was added an argon-degassed solution of
tetrathiafulvalene (300 mg, 1.46 mmol) and the halogenated pyridine
[4-iodopyridine (for L1) and 3-bromopyridine (for L2)] in dioxane
(20 mL). The reaction was stirred under reflux for 24 h. After cooling,
a large excess of dichloromethane and water were added. The aqueous
phase was extracted, and the organic extracts were washed with brine,
dried over magnesium sulfate, filtered, and concentrated. The residue
was purified by chromatography on silica gel (deactivated with
triethylamine 1%).
1
precipitation with Et2O. Isolated yield: 85%. H NMR [300 MHz,
CD3OD]: δ (ppm) 8.14 (d, 3J = 6.0 Hz, 8H, Hα), 7.41 (d, 3J = 6.0 Hz,
3
3
8H, Hβ), 6.09 (d, 8H, J = 6.0 Hz, Hcym), 5.87 (d, 8H, J = 6.0 Hz,
Hcym), 5.63 (s, 4H, Hbq), 2.91 (m, 4H, CH(CH3)2), 2.27 (s, 12H,
3
CH3), 1.37 (d, J = 6.0 Hz, 24H, CH(CH3)2). 13C NMR (75 MHz,
CD3OD): δ (ppm) 184.4, 154.8, 144.5, 130.1, 128.6, 123.1, 120.6,
111.6, 105.3, 102.9, 99.9, 84.6, 83.3, 32.6, 22.6, 18.3. HRMS (ESI) for
C82H76F12N4O20Ru4S8: calculated 1014.4897 [2 − 2OTf]2+, 626.6766
[2 − 3OTf]3+; observed 1014.4880 [2 − 2OTf]2+, 626.6757 [2 −
3OTf]3+. Anal. Calcd for C82H76F12N4O20Ru4S8: C, 42.34; H, 3.29; N,
2.41. Found: C, 41.96; H, 3.04; N, 2.26.
Metalla-assembly 3. Acceptor clip A1 (8.56 mg, 0.01 mmol) and
tetrapyridyl donor L2 (2.56 mg, 0.005 mmol) were stirred in methanol
(2 mL) to obtain 3 as a brown-yellow solid, which was isolated by
1
precipitation with Et2O. Isolated yield: 84%. H NMR [300 MHz,
CD3OD]: δ (ppm) 8.90 (d, 3J = 6.0 Hz, 4H, Hα), 7.92 (d, 3J = 6.0 Hz,
4H, Hβ), 7.50 (s, 4H, Hα′), 7.46 (d, 3J = 6.0 Hz, 4H, Hγ), 6.05 (d, 3J
3
= 6.0 Hz, 8H, Hcym), 5.87 (d, J = 6.0 Hz, 8H, Hcym), 2.87 (m, 4H,
CH(CH3)2), 2.28 (s, 12H, CH3), 1.36 (d, 3J = 6.0 Hz, 24H,
CH(CH3)2). 13C NMR (75 MHz, CD3OD): δ (ppm) 157.2, 151.0,
143.3, 131.8, 130.3, 128.0, 124.0, 119.8, 111.2, 102.7, 99.6, 82.9, 32.5,
22.5, 18.2. HRMS (ESI) for C74H72F12N4O20Ru4S8: calculated
963.9740 [3 − 2OTf]2+, 592.9965 [3 − 3OTf]3+, 407.5108 [3 −
4OTf]4+; observed 963.9702 [3 − 2OTf]2+, 592.9965 [3 − 3OTf]3+,
407.5098 [3 − 4OTf]4+. Anal. Calcd for C74H72F12N4O20Ru4S8: C,
39.93; H, 3.26; N, 2.52. Found: C, 40.29; H, 2.89; N, 2.18.
Metalla-assembly 4. Acceptor clip A2 (9.06 mg, 0.01 mmol) and
tetrapyridyl donor L2 (2.56 mg, 0.005 mmol) were stirred in methanol
(2 mL) to obtain 4 as a dark red solid, which was isolated by
Ligand L1. This was prepared following experimental conditions as
discussed above: from 4-iodopyridine (1.50 g, 7.34 mmol);
chromatography eluting from dichloromethane to dichloromethane/
methanol (97:3 v/v) to give a red powder (530 mg, 1.03 mmol, 71%).
Crystals (dark red needles) were obtained by slow diffusion of hexanes
1
precipitation with Et2O. Isolated yield: 82%. H NMR [300 MHz,
CD3OD]: δ (ppm) 8.83 (d, 3J = 6.0 Hz, 4H, Hα), 8.17 (d, 3J = 6.0 Hz,
4H, Hγ), 7.52 (m, 4H, Hβ), 7.42 (s, 2H, Hα′), 7.37 (s, 2H, Hα′), 6.30
1
in dichloromethane. Melting point: >260 °C. H NMR [300 MHz,
3
CDCl3]: δ (ppm) 8.55 (d, 3J = 6.2 Hz, 4H, Hα), 7.09 (d, 3J = 6.2 Hz,
4H, Hβ). 13C NMR [75 MHz, CDCl3]: δ (ppm) 150.6, 139.4, 129.5,
123.1, 108.9. MS (MALDI-TOF) for [C26H16N4S4]: calculated 512.69;
observed 512.5. Anal. Calcd for C26H16N4S4: C, 60.91; H, 3.15; N,
10.93; S, 25.02. Found: C, 60.70; H, 3.15; N, 10.79, S, 24.94.
(s, 2H, Hbq), 6.21−5.85 (m, 16H, Hcym), 5.29 (d, 2H, J = 6.0 Hz,
Hbq), 2.92 (m, 4H, CH(CH3)2), 2.32 (s, 6H, CH3), 2.29 (s, 6H,
CH3), 1.37 (m, 24H, CH(CH3)2). 13C NMR (75 MHz, CD3OD): δ
(ppm) 185.24, 185.22, 184.09, 184.05, 157.3, 151.7, 151.4, 143.4,
130.9, 129.6, 129.5, 127.6, 127.5, 123.1, 120.6, 110.8, 110.4, 104.4,
1657
dx.doi.org/10.1021/om401142j | Organometallics 2014, 33, 1651−1658

Organometallics
Article
104.3, 104.1, 102.3, 100.9, 99.2, 85.8, 85.7, 83.4, 82.9, 82.7, 82.0, 81.2,
32.68, 32.65, 23.0, 22.9, 22.5, 22.4, 18.4, 18.3. HRMS (ESI) for
C82H76F12N4O20Ru4S8: calculated 1014.4897 [4 − 2OTf]2+, 626.6757
[4 − 3OTf]3+; observed 1014.4882 [4 − 2OTf]2+, 626.6764 [4 −
3OTf]3+. Anal. Calcd for C82H76F12N4O20Ru4S8: C, 42.34; H, 3.29; N,
2.41. Found: C, 42.23; H, 3.10; N, 2.09.
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ASSOCIATED CONTENT
* Supporting Information
■
́
(5) (a) Canevet, D.; Salle, M.; Zhang, G.; Zhang, D.; Zhu, D. Chem.
S
Commun. 2009, 2245−2269. (b) Nielsen, M. B.; Lomholt, C.; Becher,
J. Chem. Soc. Rev. 2000, 29, 153−164. (c) Hardouin-Lerouge, M.;
NMR, MS, UV−vis spectra, cyclic voltammograms, X-ray data,
and computational details. A text file of all computed molecule
Cartesian coordinates in .xyz format for convenient visual-
ization. This material is available free of charge via the Internet
at http://pubs.acs.org. CCDC reference numbers CCDC
951195 (L1), CCDC 951203 (3·PA), CCDC 951207 (cis-4·
PA), and CCDC 951206 (trans-4·PA) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from the Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
́
Hudhomme, P.; Salle, M. Chem. Soc. Rev. 2011, 40, 30−43.
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: bruno.therrien@unine.ch.
*E-mail: marc.salle@univ-angers.fr.
5151−5184. (i) Lorcy, D.; Bellec, N. Chem. Rev. 2004, 104, 5185−
5202. (j) Lincke, K.; Nielsen, M. B. In Organic Synthesis and Molecular
Engineering, Organic Building Blocks for Molecular Engineering; John
Wiley & Sons, Inc.: 2013, pp 4−45.
■
(7) For recent reviews related to TTF-based ligands, see: (a) Lorcy,
Notes
́
D.; Bellec, N.; Fourmigue, M.; Avarvari, N. Coord. Chem. Rev. 2009,
The authors declare no competing financial interest.
253, 1398−1438. (b) Shatruk, M.; Ray, L. Dalton Trans. 2010, 39,
11105−11121.
(8) (a) Bivaud, S.; Balandier, J.-Y.; Chas, M.; Allain, M.; Goeb, S.;
ACKNOWLEDGMENTS
The authors gratefully acknowledge the University of Angers
for a grant (V.V.), and the Reg
■
Salle,
Bivaud, S.; Croue,
2014, 7, 611−622. (c) Goeb, S.; Bivaud, S.; Dron, P. I.; Balandier, J.-
Y.; Chas, M.; Salle, M. Chem. Commun. 2012, 48, 3106−3108.
(d) Balandier, J.-Y.; Chas, M.; Goeb, S.; Dron, P. I.; Rondeau, D.;
Belyasmine, A.; Gallego, N.; Salle, M. New J. Chem. 2011, 35, 165−
168. (e) Bivaud, S.; Goeb, S.; Balandier, J.-Y.; Chas, M.; Allain, M.;
Salle, M. Eur. J. Inorg. Chem., DOI: 10.1002/ejic.201400060.
(9) Bivaud, S.; Goeb, S.; Croue, V.; Dron, P. I.; Allain, M.; Salle,
Am. Chem. Soc. 2013, 135, 10018−10021.
́
M. J. Am. Chem. Soc. 2012, 134, 11968−11970. (b) Goeb, G.;
́
V.; Vajpayee, V.; Allain, M.; Salle, M. Materials
́
́
ion des Pays de la Loire (S.B.).
The PIAM (Univ. Angers) and the CRMPO (Univ. Rennes)
are acknowledged for their assistance in spectroscopic analyses.
The Johnson-Matthey Company is acknowledged for their
generous provision of palladium salts.
́
́
́
́
́
M. J.
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