Enantioenriched Ruthenium-Tris-Bipyridine Complexes Bearing One Helical Bipyridine Ligand: Access to Fused Multihelicenic Systems and Chiroptical Redox Switches

Article abstract of DOI:10.1021/acs.inorgchem.1c01379

The synthesis and photophysical and chiroptical properties of novel aza[n]helicenes (6a-d, 10a,b, n = 4-7) substituted with one or two 2-pyridyl groups are described. The preparation was performed via an adapted Mallory reaction using aromatic imines as p

Full text of DOI:10.1021/acs.inorgchem.1c01379

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Enantioenriched Ruthenium-Tris-Bipyridine Complexes Bearing One
Helical Bipyridine Ligand: Access to Fused Multihelicenic Systems
and Chiroptical Redox Switches
́
̌
Martin Kos, Rafael Rodríguez, Jan Storch, Jan Sykora, Elsa Caytan, Marie Cordier, Ivana Císarová,
Nicolas Vanthuyne, J. A. Gareth Williams,* Jaroslav Zádny,* Vladimír Církva,* and Jeanne Crassous*
̌
́
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ABSTRACT: The synthesis and photophysical and chiroptical proper-
ties of novel aza[n]helicenes (6a−d, 10a,b, n = 4−7) substituted with
one or two 2-pyridyl groups are described. The preparation was
performed via an adapted Mallory reaction using aromatic imines as
precursors. The obtained novel class of helical 2,2′-bipyridine ligands
2+
was then coordinated to Ru(bipy)2 units, thus affording the first
diastereomerically and enantiomerically pure [RuL(bipy)2]2+ (11a,c, L
= 6a,c) or [Ru2L′(bipy)4]4+ (12, L′ = 10b) complexes. The topology
and stereochemistry of these novel metal-based helical architectures
were studied in detail, notably using X-ray crystallography. Interestingly,
the coordination to ruthenium(II) enabled the preparation of fused
multihelical systems incorporating aza- and ruthena-helicenes within the
same scaffold. The photophysical, chiroptical, and redox properties of
these complexes were examined in detail, and efficient redox-triggered chiroptical switching activity was evidenced.
remarkable optical and electronic properties.1,3,7 Interestingly,
appropriate engineering of the helicene ligand framework can
generate multihelicenic systems through metal ion coordina-
INTRODUCTION
■
Helicenes are a unique class of polyaromatic compounds
formed by ortho-fused aromatic rings that adopt an inherently
chiral helical structure.1 Generally, the enantiomers are
tion, making this strategy an alternative to tedious, more
conventional organic syntheses.7c This approach represents an
conformationally stable and separable by chiral HPLC, if the
effective way to obtain materials that display circularly
number of aromatic rings is ≥6 or if the “bay positions” are
substituted with bulky substituents in [5]- or [4]helicenes.2
polarized phosphorescence for application as chiroptical
switches8 or circularly polarized OLEDs (CP-OLEDs).9 In
The extended conjugation over the aromatic rings, together
this context, the ubiquity and versatility of bidentate
2,2′-bipyridine (bipy) in coordination chemistry10 renders
helicenes that incorporate this unit as a particularly appealing
target.
A number of synthetic strategies have been reported for the
preparation of helicene-bipy ligands, leading to products
summarized in Figure 1. The main routes are the Stille-Kelly
reaction of a dibromo derivative (to give A),11 [2+2+2]
cycloaddition of triynes (leading to B),12 C−H activation of an
N-oxide (to generate C),13 and Mallory photocyclization of
stilbenes (in the synthesis of D, E, and F).8,14,15 The
with helical chirality, gives rise to unique chiroptical properties
such as high molar rotation, strong electronic circular
dichroism (ECD), and circularly polarized luminescence
(CPL).3
The introduction of heteroatoms such as nitrogen within the
helical scaffold gives access to azahelicene derivatives with
tuned electronic and optical properties.3b This simple
modification is sufficient to trigger exceptional properties
such as improved charge transport and enhanced photo-
physical and chiroptical properties. Azahelicenes are thus
appealing in diverse applications such as chiral dopants in
organic light-emitting diodes (OLEDs),4 chiral charge trans-
porters in organic field-effect transistors (OFETs),5 and spin
filters for spintronics.6 Moreover, azahelicenes can be applied
as efficient chiral ligands in coordination chemistry.3b,7 In the
past decade, we and others have focused on the development
of new helical architectures bearing bidentate or tridentate
coordinating moieties that, upon coordination to a variety of
metal ions, lead to the formation of unique structures with
Received: May 9, 2021
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Some of the authors of the present work recently reported a
novel method21 to prepare new [n]helicenes with different
numbers of aromatic units (n = 4, 5), on the basis of a
photocyclization similar to Mallory’s reaction but with imines
instead of olefins. Until recently, this method was still very
rare,22 and the preparation of helicenes by this methodology
was limited to a few examples formed in poor yields (2−
10%).23 Superior reaction efficiency has recently been achieved
on corannulene-based imines.24
Here, we report the synthesis of a novel family of helical
ligands (L) bearing either one (6a−d) or two (10a,b) bipy
units via oxidative photocyclization of aromatic imines (Figure
2). In these ligands, the bipy moiety is grafted in a position that
is different from previously reported bipyridine helicenes8,11−15
with a 2-pyridyl pendant at position 6 of the outer groove of a
Figure 1. Examples of helicenes containing 2,2′-bipyridine units that
have been reported in the literature.
5-azahelix. This feature offers enough room for further
2+
coordination of bulky metallic units such as Ru(bipy)2
.
Enantioenriched complexes of the general formula
[RuL(bipy)2]2+ (11a,c, L = 6a,c) and [Ru2L′(bipy)4]4+ (12,
L′ = 10b) with defined stereochemistry have thereby been
prepared in this work. We show that, upon coordination,
unprecedented multihelicenic fused systems25 incorporating
Ru ions are produced. In most cases, their topology and
stereochemistry are dictated by the ruthenium center itself.
Furthermore, taking advantage of their redox properties and
strong ECD response, these complexes were characterized as
redox-triggered chiroptical switches, promising materials for
possible application in molecular electronic or display
technologies.26
coordination chemistry of mono- and bis-helicenic bipyridine
ligands (D and E, respectively) and of helicene-bis-bipyridine
(F) to Pt(II),8 Zn(II),14 Re(I),15 Ru(II),16 and Ln(III)17 has
been studied, giving access to efficient CPL-active chiral
materials, chiroptical switches, and chiral single molecular
magnets (SMMs).
Among the many metal complexes of bipyridines, those of
ruthenium(II) have attracted remarkable attention over the last
five decades. [Ru(bipy)3]2+ and its derivatives have an almost
unique combination of properties that include high chemical
stability, reversible oxidation and reduction, lowest-energy
singlet and triplet excited states of metal-to-ligand charge-
transfer (1,3MLCT) character, excited-state reactivity, and
room-temperature phosphorescence with triplet excited-state
lifetimes of hundreds of nanoseconds.18 They have found
applications in various branches of chemistry such as
photocatalysis, electrochemistry, and electrochemilumines-
cence.18,19 Nevertheless, despite the vast development of
chiral 2,2′-bipyridine ligands in homogeneous catalysis,20 there
are only limited reports on [Ru(bipy)3]2+ derivatives that bear
centrally chiral ligands19b and no report of such a complex
incorporating a ligand with helical chirality.
RESULTS AND DISCUSSION
■
Synthesis of Helical Bipyridine Ligands. The efficient
preparation of phenanthridines/aza[n]helicenes (n = 4, 5)
bearing a pendant phenyl group ortho to the nitrogen atom was
recently described by some of the authors through a
photocyclization reaction of aromatic imines.21 In the current
study, we extend the method to the preparation of 6-(2-
pyridyl)-phenanthridine 2 (Scheme 1) and to helical
polyaromatic hydrocarbons containing a bipy moiety (Figure
Figure 2. Targeted helical ligands incorporating bipyridine-like units (top) and their corresponding heteroleptic Ru(II) complexes with the other
coordination sites occupied by two 2,2′-bipyridines.
B
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and 6d (Figure 2 and Scheme 2a). Lithiation of aryl bromides
3a−d and the reaction with 2-cyanopyridine led to ketones
4a−d in high yields. Their reaction with aniline gave imines
5a−d as mixtures of the E/Z-isomers, which were subsequently
irradiated in the presence of Ti(OiPr)4 and TEMPO under an
inert atmosphere. Compounds 6a,b,d with five ortho-fused
benzene rings were isolated in up to 73% yield while
aza[6]helicene 6c was obtained in 48% yield. To the best of
our knowledge, this is the first preparation of [n]helicene-bipy
by oxidative photocyclization of imines. The product structures
Scheme 1. Optimized Conditions for the Exclusive
Synthesis of Model Compound 2
1
were unambiguously confirmed by HRMS and H and 13C
2 and Scheme 2). The photochemical cyclization of imine 1 in
the presence of HBF4·Et2O and TEMPO proceeded nearly
exclusively at the unsubstituted phenyl ring and gave 2 in
acceptable yield (Scheme 1) with almost no formation of the
alternative isomer 2′. The high selectivity of the photo-
cyclization process is due to the electron-withdrawing nature of
the pyridine, enhanced by protonation under acidic conditions.
The use of TEMPO protected the starting imines from an
undesired reduction, while molecular sieves prevented their
hydrolysis.
NMR spectroscopy and, for 6b and 6c, X-ray crystallography
(Figures 3a and S44, S45 for ORTEP drawings). Both racemic
6b and 6c crystallized in the P1 centrosymmetric space group.
̅
6-(2-Pyridyl)-5-aza[6]helicene 6c exhibits a helical shape with
a helicity (dihedral angle between the terminal rings) of 47°.
There is a mutually anti arrangement of the two N-pyridyl
rings that is typical of 2,2′-bipyridines with a dihedral angle of
51.20°.
The same approach was further examined in the photo-
cyclization of analogous diimines giving rise to 10a,b.27 The
requisite diketones 8a,b were obtained from dibromoarenes
7a,b by lithiation using t-BuLi and subsequent reaction with
2-cyanopyridine (Scheme 2b). Reactions of 8a,b with aniline
gave diimines 9a,b. The irradiation of crude 9a,b in the
presence of Ti(OiPr)4 and TEMPO led to diazahelicenes
10a,b in fair yields. Their C2 symmetry is reflected in simpler
NMR spectra (full characterization is given in the Supporting
Information). The structure of 10b was also confirmed by X-
ray diffraction analysis of a single crystal grown by slow
diffusion of acetonitrile into a chloroform solution (Figures 3b
and S46). Racemic 6,13-bis(2-pyridyl)-5,14-diaza[7]helicene
The synthesis of more extended aromatic systems through
the photocyclization of 5b was then examined on the milligram
scale and monitored by GC-MS analysis (Table 1). Using the
conditions optimized for the preparation of phenanthridines
(Table 1, Entry 121), most of the starting material was
hydrolyzed to ketone 4b, showing the instability of 5b in the
acidic environment under irradiation. In the absence of acid
(Table 1, Entry 2), hydrolysis of the imine was suppressed but
only traces of helicene 6b were detected in the reaction
mixture. Using quartz instead of Pyrex glassware led to an
increased conversion of 5b to 6b, but hydrolysis to ketone 4b
still prevailed (Table 1, Entry 3). The addition of Ti(OiPr)4 as
a water scavenger was finally found to avoid hydrolysis while
promoting almost quantitative conversion of 5b to 6b (Table
1, Entry 4). The reaction on a preparative scale under the same
conditions resulted in the isolation of 6b in 65% yield (Scheme
2a).
̅
10b crystallizes in the P1 space group: it exhibits a helicity of
35.06° and dihedral angles of the two trans-bipy units of
43.01−43.87°.
[n]Helicenes with n ≥ 6 possess a racemization barrier
>150 kJ mol−1, which enables the (M)- and (P)-enantiomers
to be isolated at room temperature.1,28 Ligands 6c, 10a, and
These optimized conditions were utilized for the preparation
of three other helicenes incorporating a bipyridyl unit: 6a, 6c,
a
Scheme 2. Synthesis of (a) Bipyridine Helicenes 6a−d and (b) Diazahelicene-bis-Bipyridines 10a,b
a
(i) n-BuLi, THF, −78° C, then 2-cyanopyridine and then H2O; (ii) PhNH2 (1.5 equiv), toluene, M.S.; (iii) Ti(OiPr)4 (5 or 10 equiv), TEMPO
(2 or 4 equiv), hν, CH2Cl2, quartz glassware.
C
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Table 1. Screening of Reaction Conditions for the Synthesis of 6b
a
composition of the reaction mixture after photolysis [%]
entry
additive, glassware
4b
5b
6b
1
2
3
4
HBF4·Et2O (4 equiv), Pyrex
Pyrex
quartz
81
2
71
1
0
96
0
19
2
29
96
Ti(OiPr)4 (5 equiv), quartz
3
a
2 mg of starting material; 60 min of irradiation.
Figure 3. Single crystal X-ray diffraction structures of (a) 6c and (b)
10b (H atoms have been omitted for clarity).
10b, each formed as racemic mixtures, were separated into
their constituent enantiomers by semipreparative HPLC over a
Chiralpak IE stationary phase (for details, see the Supporting
Information). All enantioenriched samples were obtained with
enantiomeric excesses (ee’s) between 95% and 99.5% (see the
Supporting Information).
Photophysical and Chiroptical Properties of Ligands
6c and 10a,b. The helicene ligands 6c and 10a,b display
broad and intense UV−visible (UV−vis) absorption spectra in
the 200−400 nm range (Figure 4a, bottom). They are
fluorescent in solution at room temperature, as observed for
previously described azahelicenes.8,15 They display slightly
structured emission bands in the blue region of the spectrum
(Figure 4b, bottom). As expected, the emission maxima
increasingly red shift with increasing conjugation with 10b
displaying the lowest energy emission. In CH2Cl2 solution, the
structure is more pronounced with the 0,0 vibrational
component being the most intense (Figures S51−S53).
Under these conditions, the fluorescence quantum yields are
of the order of 2−7% (10% for 6a) and corresponding lifetimes
are of the order of a few nanoseconds (Table S1), values that
are quite typical of aza-aromatics. In a frozen glass at 77 K, the
fluorescence (which is marginally blue-shifted compared to
room temperature) is accompanied by structured phosphor-
escence bands at lower energy (Figures S51−S53). This spin-
forbidden emission from the triplet state is characterized by
very long lifetimes of around 1 s (Table S1).
Figure 4. (a) ECD (up) and UV−vis spectra (bottom) of (P)/(M)-
6c, -10a, and -10b in MeCN (∼10−4 M) at r.t. (b) Emission (bottom)
and CPL (up) spectra of 6c, 10a, and 10b in MeCN (∼10−5 M, λex
360−365 nm) at r.t.
=
The ECD spectra of the three pairs of enantiomers are
displayed in Figure 4a (top part). Ligand (P)-6c shows a
strong negative band at 246 nm (Δε = −260 M−1 cm−1) and a
strong positive one at 330 nm (Δε = +230 M−1 cm−1)
accompanied by a weaker positive band at 284 nm (Δε = +60
M−1 cm−1). Ligand 10a follows a similar pattern with much
weaker signals (Δεmax ∼ 140 M−1 cm−1). Qualitatively, the
helical shape of the molecule is disturbed by the presence of
the additional pyridyl group, which may explain such a
decrease, as a result of the modifications of the magnetic and
electric dipolar moments. The main bands in the ECD
spectrum of 10b are red-shifted by around 20 nm compared to
6c and 10a and of overall higher intensity. This can be
D
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Scheme 3. Synthesis of (a) Racemic and Enantioenriched 11a and (b) Diastereomeric Mixture (P,Δ)/(M,Λ)- and (P,Λ)/
a
(M,Δ)-11c and of Diastereo- and Enantioenriched 11c
a
The colors indicated correspond to those used in Figure 7.
1
classically explained by the more extended π-conjugation and
different helical pitch in heptahelicenes as compared to
hexahelicenes. Thus, (P)-10b displays a strong negative band
at 263 nm (Δε = −220 M−1 cm−1) accompanied by a weaker
negative band at 302 nm (Δε = −90 M−1 cm−1) and a strong
positive one at 349 nm (Δε = +320 M−1 cm−1). The
polarization of the emitted light was studied by CPL
spectroscopy (Figure 4b, top). The (P)- and (M)-enantiomeric
pairs of 6c and 10a,b display mirror-image CPL spectra with
equal but opposite-sign glum values recorded around the
emission maxima [(P)/(M)-6c: +4.0/−3.7 × 10−3; (P)/(M)-
10a: +1.1/−1.2 × 10−3; (P)/(M)-10b: +5.4/−5.4 × 10−3], in
line with CPL data of previously investigated bipyridine
helicenes (glum ∼ 10−3).8,15
chemically inequivalent in the H and 13C NMR spectra (see
the Supporting Information).
The structure of 11a was further confirmed by X-ray
crystallography of a single crystal grown by slow diffusion of
Et2O into a MeCN solution of (rac)-11a. It crystallized in the
̅
centrosymmetric space group in which both enantiomers Δ
and Λ are present (Figures 5a and S47). Remarkably, upon
P1
Synthesis and Characterization of Ruthenium Com-
plexes. The preparation of Ru(II) complexes of the
[RuL(bipy)2]2+ and [Ru2L′(bipy)4]4+] form (11a,c and 12)
was achieved by directly reacting the helicene-bipy ligands L
with Ru(bipy)2Cl2 in a polar solvent.29 Such a reaction of
achiral [4]helicene 6a with racemic Ru(bipy)2Cl2, followed by
metathesis of the chloride anion to hexafluorophosphate,
yielded a racemic mixture of (Δ)- and (Λ)-[Ru(bipy)26a]-
(PF6)2, henceforth referred to as 11a (Scheme 3a).
Enantioenriched (Δ)-11a and (Λ)-11a were obtained by
using chirally resolved precursors (Δ)-[Ru(bipy)2(py)2]((S,S)-
dbt) and (Λ)-[Ru(bipy)2(py)2]((R,R)-dbt) (dbt = O,O′-
dibenzoyl-tartrate)30a,b in place of racemic Ru(bipy)2Cl2,
followed by anion exchange with KPF6. Due to the presence
of the asymmetric bipyridine 6a, complex 11a has C1
symmetry. As a result, all the signals of the atoms are
Figure 5. Single crystal X-ray diffraction structures of (a) 11a and (c)
selected views of the helicenic parts; PF6 anions and H atoms were
−
omitted for the sake of clarity. (b) UV−vis (bottom) and ECD (up)
spectra of (Δ)/(Λ)-11a in MeCN (∼10−4 M) at r.t.
E
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−
Figure 6. Single crystal X-ray diffraction structures and selected views of (a) (M,Λ)-11c and (c) (P,Λ,Λ)-12. PF6 anions and H atoms were
omitted for the sake of clarity. UV−vis (bottom) and ECD (up) spectra of (b) (P,Λ)/(M,Δ)/(P,Δ)/(M,Λ)-11c and (d) (P,Λ,Λ)/(M,Δ,Δ)/
(P,Δ,Δ)/(M,Λ,Λ)-12 in MeCN (∼10−4 M) at r.t.
1
Figure 7. Comparison of H NMR spectra of (P,Δ)- and (P,Λ)-11c at 400 MHz in CD3CN at r.t. See numbering in Scheme 3b.
coordination with Ru(II), the bipy helicene 6a generates a
fused metallic bis-helicenic system, one aza[4]helicene
(displaying a helicity of 26.35°) and one ruthena[4]helicene
(Ru[4]H in Figure 5c) with a helicity of 38.62°. This approach
thus represents a simple yet powerful procedure to generate
metal-based multihelicenic systems. Additionally, the fixed Λ
F
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a
Scheme 4. Synthesis of Diastereo- and Enantioenriched Complexes 12, Either as Mixtures or as Pure Stereoisomers
a
The colors indicated correspond to those used in Figure 6.
configuration at the ruthenium center induces the M helix in
the generated ruthena[4]helicene and the P-handed one in the
fused aza[4]helicene (and vice versa), thus demonstrating
control of the helical stereochemistry by the ruthenium in the
solid. However, these [4]helicenic architectures are most
probably fluxional in solution.
reaction did not proceed with complete stereoselectivity in the
sense of Δ/Λ isomerism.
Finally, the complexation of bis-bipyridine [7]helicene 10b
to the Ru(II) precursor was studied (Scheme 4). The reaction
of (rac)-10b with 2 equiv of (rac)-Ru(bipy)2Cl2 provided two
major products, which were separated by column chromatog-
raphy. Both compounds were unambiguously identified by
mass spectrometry as bis-ruthenium complex 12 and
monoruthenium complex 13. In the case of 12, a single crystal
of the (P,Λ,Λ)/(M,Δ,Δ)-enantiomeric pair was obtained by
slow vapor diffusion of CHCl3 into a MeCN solution of 12
(Figure 6c). Here again, in complex (P,Δ,Δ)-12, two fused
Ru[4]H helicenes are formed. They display helicities of 26.60°
and 33.62° but different (P) and (M) configurations within the
same complex, thus showing no control of their chirality in the
solid. In addition to (M,Δ,Δ)- and (P,Λ,Λ)-isomers, the
diastereomeric mixture also contained the mixed C1 sym-
metrical (Δ,Λ)-isomer (see Figure S35). For 13, a single
crystal containing the (P,Λ)/(M,Δ)-enantiomeric pair was
grown by slow vapor diffusion of Et2O into a MeCN solution
of 13 (see Figure S50). Upon coordination, a fused Ru[4]H
helicene displaying a 35.55° helicity is also formed with its (M)
configuration controlled by the (P)-heptahelicene and vice
versa, thus showing induction of chirality in the solid state.
Diastereo- and enantioenriched complexes 12 were synthe-
sized by the reaction of (M)- or (P)-10b with either (Δ)-
[Ru(bipy)2(Py)2]((S,S)-dbt) or (Λ)-[Ru(bipy)2(Py)2]((R,R)-
dbt) precursors (Scheme 4). Even though an excess of the
ruthenium precursor was employed, the synthesis of the
dinuclear complex 12 was always accompanied by the
formation of a small amount of mono-Ru intermediate 13
(for details, see the Supporting Information). Both ruthenium
ions in the enantioenriched forms of 12 have (Δ,Δ) or (Λ,Λ)
configuration. As a result, all complexes possess an overall C2
symmetry. In (P,Λ,Λ)/(M,Δ,Δ)-12, part of a terminal ring of
The reaction of (rac)-Ru(bipy)2Cl2 with (rac)-6c in place of
achiral 6a, followed by Cl− to PF6 metathesis, should give a
−
diastereomeric mixture of the forms of 11c due to the presence
of two stereogenic elements: helically chiral M/P helix and the
Δ/Λ chirality at the metal (Scheme 3b). Indeed, the
1
complicated H NMR spectrum of 11c after purification by
column chromatography was attributed to two sets of signals
(see Figure S29). To our delight, a single crystal of the
enantiomeric pair (M,Λ)/(P,Δ)-11c suitable for X-ray analysis
was obtained by slow vapor diffusion of Et2O into a MeCN
solution (Figures 6a and S48). A comparison of the NMR
spectra of crystals and mother liquor revealed an almost perfect
separation of the diastereomers and also enabled the
assignment of some signals to the corresponding diastereomers
(see Figures 7 and S29). By this comparison, it was found that
(M,Λ)/(P,Δ)-11c was present in the originally formed mixture
in a small excess of 59:41. It is notable that the coordination to
Ru(II) provokes the formation of a ruthena[4]helicene (with a
helicity of 44.35°) fused to the aza[6]helicene unit (of 54.82°
helicity) in which the (M,Λ) unit imposes the (M)-Ru[4]H
helix, and vice versa, in the solid state. However, no conclusion
can be drawn in the solution state where the ruthena[4]-
helicene unit is expected to be fluxional.
To obtain diastereo- and enantioenriched 11c, the reaction
between (M)/(P)-6c and resolved (Δ)-[Ru(bipy)2(Py)2]-
((S,S)-dbt)/(Λ)-[Ru(bipy)2(Py)2]((R,R)-dbt) precursors was
conducted (see Scheme 3b). In all cases, the minor
diastereomer was present in approximately 10% as revealed
1
by H NMR analysis (see Figure S34), suggesting that the
G
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Figure 8. Absorption spectra (black), emission spectra (red), and excitation spectra (green) in MeCN at 295 K and emission in PrCN at 77 K
(blue) of (a) (M,Δ)-11c and (b) (P,Λ,Λ)-12. The corresponding spectra of other complexes are shown in Figures S54−S56.
a
Table 2. Luminescence Properties of the Ruthenium(II) Complexes
emission at 77 K
emission
Φlum
/
kr/103
Σknr/
c
kQO2/108
d
b
c
complex
absorption λmax/nm (ε/M−1 cm−1
)
λmax/nm
10−2
0.03
τ/ns
s−1
106 s−1
M−1 s−1
λmax/nm
742
τ/ns
(rac)-11a
289 (66 700), 337 (19 250), 405 (10 800),
437 (13 400), 510 (11 400)
239 (44 600), 289 (65 300), 339 (23 600),
446 (7835), 510 (6590)
239 (49 830), 289 (60 930), 337 (26 580),
444 (9020), 515 (7470)
788
779
799
788
786
46 [40]
290 [180]
260 [180]
130 [110]
510 [340]
6.5
3.4
3.5
7.7
4.9
22
17
1800
(P,Δ)-11c
(M,Δ)-11c
0.10
0.09
0.10
0.25
3.4
3.8
7.7
2.0
11
728
761
1300
1400
1000
1800
9.0
7.4
5.2
(M,Λ,Λ)-12 246 (77 300), 288 (139 810), 435sh (21 820),
758, 840sh
522 (16 810)
246 (65 500), 287 (115 850), 344sh (33 200),
444 (18 420), 512 (14 230)
(P,Λ,Λ)-12
761, 837sh
a
b
c
In deoxygenated acetonitrile at 295 1 K and in butyronitrile at 77 K. Values in brackets are for an air-equilibrated solution. Values estimated
assuming that the emitting triplet state is formed with unit efficiency upon excitation into the singlet bands, such that kr = Φ/τ and
d
Σknr = (1−Φ)/τ. Bimolecular rate constants for quenching by O2, estimated on the basis of the lifetimes in a deoxygenated and air-equilibrated
solution.
the helical scaffold is strongly shielded by 2,2′-bipyridine
placed in its vicinity. This is reflected in a significant change in
the chemical shifts of 2-H (5.27 ppm) and 3-H (6.16 ppm),
which are up to 1 ppm lower in comparison to the other
enantiomeric pair (see Figure S35).
and the LUMO on the ligand. The 1,3MLCT energies can thus
be rationalized and controlled according to the nature of the
ligands, often showing good correlation with the oxidation and
reduction potentials.18a,32 In heteroleptic analogs, the LUMO
is typically localized largely on the ligand(s) having the lowest-
energy π* orbitals associated with it. Thus, where one bipy
ligand is replaced by a more conjugated analogue, a reduction
in the 3MLCT and 1MLCT energies can be anticipated;
indeed, numerous such examples have shown the expected red-
shift in the emission and lowest-energy absorption bands,
respectively, as a consequence.18,31,33
Absorption and Emission Properties of Complexes
11a, 11c, and 12. Complexes 11a, 11c, and 12 display broad
and intense UV−vis absorption spectra (Figures 5 and 6,
bottom parts, and Figure 8) with very similar features, notably
a strong absorption band around 290 nm and moderately
intense ones around 250 and 350 nm, likely corresponding to
π−π* transitions of the ligands. These bands are almost 1
order of magnitude stronger in the hexa- and heptahelicenic
complexes 11c and 12 than in 11a.18 They are accompanied by
two bands of weaker intensities around 450 and 520 nm that
are commonly assigned to MLCT-type transitions. Much of
the intense interest in [Ru(bipy)3]2+ and its derivatives over
the past 40 years has been driven by their attractive emission
properties. [Ru(bipy)3]2+ is the archetypal 3MLCT emit-
ter.18,31 The coordination as opposed to the organometallic
nature of the bonding and the relative energies of the orbitals
are such that the HOMO is primarily localized on the metal,
In the present series of heteroleptic complexes, such an
effect is to be expected, since the extended conjugation of the
helicene bipyridine ligand will serve to lower its π* orbitals.
The effect is immediately clear in the absorption spectra
(Figures 5b, 6b,d, and 8 and Table 2), where it can be seen
that the lowest-energy absorption bands are centered around
510−520 nm in each case. These values contrast with that of
around 455 nm for [Ru(bipy)3]2+ under the same conditions,
1
indicating a stabilization of the MLCT state of around 2500
cm−1 as a result of the more extended conjugation associated
with the aza-aromatic. There is, however, little difference
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between 11c/12 and 11a, indicating that the additional
aromatic rings incorporated within the helicene ligands of
11c/12, remote from the quinoline moiety, have little
influence in further stabilizing the LUMO compared to the
parent 11a.
ECD Spectra of Complexes 11a, 11c, and 12. The ECD
spectra of the enantioenriched forms of 11a in MeCN are
mirror images of one another (Figure 5b). Enantiomer (Λ)-
11a shows a positive band at 292 nm (Δε = +60 M−1 cm−1), a
weak positive one at 245 nm (Δε = +24 M−1 cm−1), and two
weak negative bands at 275 nm (Δε = −23 M−1 cm−1) and at
219 nm (Δε = −33 M−1 cm−1). Additionally, two negative
ECD bands of very low intensities (Δε = −2 M−1 cm−1) are
found at 375 and 510 nm, i.e., in the MLCT region. The
absolute stereochemistry can be easily deduced from the
starting enantioenriched Ru precursors and confirmed by
comparison of the ECD fingerprints at 292 nm with known
chiral complexes.30
The ECD spectra of diastereo- and enantioenriched 11c in
MeCN are depicted and compared in Figure 6b. Both
enantiomeric pairs (P,Λ)/(M,Δ)- and (P,Δ)/(M,Λ)-11c
display mirror-image spectra. (P,Λ)-11c exhibits more intense
ECD signals with a strong positive band at 291 nm (Δε =
+120 M−1 cm−1) accompanied by a weaker positive band at
335 nm (Δε = +45 M−1 cm−1), a strong negative band at 251
nm (Δε = −135 M−1 cm−1), and weak bands at 523 nm (Δε =
+8 M−1 cm−1), 451 nm (Δε = −11 M−1 cm−1), and 394 nm
(Δε = +8 M−1 cm−1). (P,Δ)-11c exhibits two strong positive
bands at 344 nm (Δε = +60 M−1 cm−1) and 275 nm (Δε =
+70 M−1 cm−1), two strong negative bands at 294 nm (Δε =
−70 M−1 cm−1) and 236 nm (Δε = −100 M−1 cm−1) and
weak bands at 507 nm (Δε = +17 M−1 cm−1), 443 nm (Δε =
−6 M−1 cm−1), and 314 nm (Δε = +22 M−1 cm−1). Overall,
thanks to the presence of the hexahelix, the enantioenriched
11c derivatives display more intense ECD responses than the
11a ones.
The ECD spectra of diastereo- and enantioenriched 12 in
MeCN are depicted and compared in Figure 6d. Both
enantiomeric pairs (P,Λ,Λ)/(M,Δ,Δ)- and (P,Δ,Δ)/
(M,Λ,Λ)-12 display mirror-image spectra. Overall, the
(P,Λ,Λ)-diastereomer shows less intense ECD signals with
more crossing points than the (P,Δ,Δ) one. (P,Λ,Λ)-12
exhibits three strong bands at 277 nm (Δε = −150 M−1 cm−1),
291 nm (Δε = +105 M−1 cm−1), and 337 nm (Δε = +110 M−1
cm−1), accompanied by several weak bands at 306 nm (Δε =
−23 M−1 cm−1), 435 nm (Δε = −24 M−1 cm−1), 507 nm
(Δε = +16 M−1 cm−1), and 547 nm (Δε = −12 M−1 cm−1).
(P,Δ,Δ)-12 displays one strong negative band at 294 nm
(Δε = −295 M−1 cm−1), one moderate positive band at 367
nm (Δε = +115 M−1 cm−1), three weaker bands at 532 nm
(Δε = +65 M−1 cm−1), 277 nm (Δε = +55 M−1 cm−1), and
266 nm (Δε = −50 M−1 cm−1), and one weak band at 446 nm
(Δε = −10 M−1 cm−1). The heptahelicenic structure thus leads
to a strong chiroptical response, which is further increased
through a synergistic contribution of the two Ru centers. It is
worth noting that mirror-imaged ECD spectra were system-
atically obtained for each enantiomeric pair of 11a, 11c, and
12, which confirms that the reactions proceeded without a loss
of enantiopurity.
All of the new complexes are found to be luminescent in
solution at room temperature (Table 2). The emission and
excitation spectra of (M,Δ)-11c and (P,Λ,Λ)-12 in MeCN at
295 K are shown in Figure 8, together with the emission
spectra in PrCN at 77 K. Corresponding spectra of the other
diastereomers of 11c and 12, and of the parent (rac)-11a, are
given in Figures S54−S56. The onset of the emission is around
700 nm in each case, such that most of the luminescence falls
in the NIR region of the spectrum with a maxima of around
790 nm (Table 2). This is a challenging part of the spectrum
for detection, being at the edge of the range for conventional
visible photomultiplier tubes yet somewhat too short for the
wavelength of the NIR detectors. Optimal results were
obtained using a back-illuminated deep-depletion CCD
detector (the details of the instrumentation are given in the
Supporting Information). As in absorption, there is a large red-
shift in the emission maxima relative to [Ru(bipy)3]2+,
3
reflecting the stabilization of the MLCT associated with the
more extended conjugation on the ligand. Again, there is little
difference between the complexes 11c/12 and 11a. The
emission maxima of around 780 nm compare with values of
700 and 742 nm for quinoline-containing complexes [Ru-
(bipy)2(pq)]2+ and [Ru(bipy)2(biq)]2+, which are perhaps the
closest literature models (pq = 2-pyridylquinoline; biq = 2,2′-
biquinoline).34a A complex featuring an azabenzannulated
perylene diimide could be construed as a related example
featuring the benzannulated phenanthridine moiety of the
em
present complexes for which λmax = 780 nm, though the
nature of the excited state is quite different in that case.34b
The luminescence quantum yields are low, of the order of
0.1% (Table 2). Low values are to be anticipated, given the low
energy of the excited state and the fact that the energy gap law
typically applies well to metal bipyridine-based complexes.34c
However, the luminescence lifetimes of the helicene complexes
remain quite long, of the order of a few hundred nanoseconds
(Table 2), suggesting that the low quantum yields might be
due in part to reduction in the radiative rate rather than to
particularly severe nonradiative decay. Indeed, the estimation
of the radiative and nonradiative rate constants, kr and Σknr,
indicates that the former is around an order of magnitude
lower than for [Ru(bipy)3]2+. Such an effect could be
attributed to reduced metal character in the excited state
with increasingly conjugated ligands35a and/or to changes in
the relative energies of higher singlet and triplet states that
couple through spin−orbit coupling.35b The emission is
modestly quenched by dissolved molecular O2 (as expected
for lifetimes of this order of magnitude) with bimolecular rate
constants of around 109 M−1 s−1.
Although there is little difference between the spectra of the
different diastereoisomers, it is intriguing to note a small but
significant difference between the quantum yields and lifetimes
of the diastereoisomers of 12. The emission of the (P,Λ,Λ)-
isomer is brighter and longer-lived than that of the (M,Λ,Λ),
apparently due largely to an almost 4-fold difference in Σknr.
The difference most likely arises from the different
conformation of the two complex units relative to one another,
influencing the exposure to the solvent and hence the excited-
state deactivation pathways.36
Spectroelectrochemical Properties of Complexes
11a, 11c, and 12. The electrochemical properties of
complexes 11a, 11c, and (M,Δ,Δ)- and (M,Λ,Λ)-12 were
studied by cyclic voltammetry recorded in MeCN under an
inert atmosphere with 0.1 M Bu4NPF6 as the supporting
electrolyte. The half-wave redox potentials were determined
from the average of the anodic and cathodic peak potentials for
the reversible waves. The cyclic voltammograms depicted in
Figure 9 reveal one reversible Ru(II)/Ru(III) oxidation wave
I
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(−1.11 and −1.08 V) corresponding to the two Ru(II)/Ru(I)
processes of the Ru atoms that do not reduce at the same
potential, thus evidencing an electronic interaction between
the two metal centers via the π-helicene bridge.37b,c,d Another
two-electron reduction wave corresponding to the Ru(I)/
Ru(0) reduction of the two Ru centers is also found (−1.50 to
−1.48 V).
Redox-Triggered Chiroptical Switching Activity. On
the basis of these results, it appeared interesting to take
advantage of the reversible oxidation and reduction processes
and to study the electrochromic and chiroptical switching
activity of such complexes. For this purpose, enantioenriched
complexes (Λ)-11a, (P,Δ)-11c, and (P,Δ,Δ)- and (P,Λ,Λ)-12
were examined. The one-electron oxidation process was first
studied by UV−vis and ECD spectroscopies in an optically
transparent thin-layer electrochemical (OTTLE) cell (MeCN/
0.2 M Bu4NPF6) upon applying a potential up to ca. 1.3 V
(Figure 10; see the electrochemical conditions in the
Supporting Information). In all cases, several isosbestic points
were observed in both UV−vis and ECD. Overall, the UV−vis
spectra underwent a strong decrease of intensity of the high
energy band around 290 nm. Oxidation was accompanied by a
15 nm red shift. In the higher energy domain, a disappearance
or a decrease of the broad absorption bands located between
440 and 520 nm was observed. In the ECD spectra, the strong
positive band around 300 nm in (Λ)-11a and (P,Δ)-11c
underwent a significant decrease accompanied by a ca. 15 nm
red shift, while the low-energy bands exhibited intensity
decreases (see Figure 10a,b). Diastereomeric complexes
(P,Δ,Δ)- and (P,Λ,Λ)-12 also evidenced similar changes
(see Figure 10c,d). In contrast to the UV−vis spectra, the
effects in ECD were different for the two diastereomers. The
oxidation of (P,Λ,Λ)-12 resulted in an inversion of the positive
band at 291 nm (Δε value moved from +105 to −70 M−1
cm−1); the broad positive band at 337 nm was split into two
less intense bands, and the two weak bands between 480 and
Figure 9. Cyclic voltammograms of 11a, 11c, and (M,Δ,Δ)- and
(M,Λ,Λ)-12 in degassed MeCN (0.1 M Bu4NPF6) plotted versus the
saturated calomel electrode (SCE), measured using ferrocene as an
internal standard.
at +1.14 and +1.23 vs SCE for complexes 11a and 11c,
respectively. These values are very similar to those found in the
literature for [Ru(bipy)3]2+,19a,37a while for the bis-Ru complex
diastereomers (M,Δ,Δ)- and (M,Λ,Λ)-12, higher values were
obtained (+1.31 and +1.26 V). Monoruthenium complexes
11a and 11c also display three reversible waves in reduction
(−1.10, −1.60, and −1.86 V for 11a; −1.05, −1.51, and −1.75
V for 11c). These reduction potentials correspond to Ru(II)/
Ru(I), Ru(I)/Ru(0), and Ru(0)/Ru(−1) one electron-
reduction steps and are found to be similar to the reduction
potentials of the [Ru(bipy)3]2+ systems.19,23 The bis-
ruthenium complexes (M,Δ,Δ)- and (M,Λ,Λ)-12 appear easier
to reduce and exhibit the first set of two reversible waves
Figure 10. Spectroelectrochemical studies UV−vis (bottom) and ECD (top) studies of the oxidation processes of (a) (Λ)-11a, (b) (P,Δ)-11c, (c)
(P,Λ,Λ)-12, and (d) (P,Δ,Δ)-12 (OTTLE cell, MeCN, 0.2 M Bu4NPF6).
J
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600 nm vanished. Upon the oxidation of (P,Δ,Δ)-12, the
bands at 294 and 367 nm were red-shifted around 24 and 10
nm, respectively, and bands at 266, 277, and 532 nm
disappeared.
fused metallic bis- or tris-helicenic systems. The stereo-
chemistry of these compounds has been examined in detail
through their X-ray crystallographic structures. Spectroelec-
trochemical UV−vis and ECD studies of the prepared
complexes revealed their extensive redox-modulated chirop-
tical properties. Due to the strong reversible changes in the
ECD spectra upon oxidation of the bis-ruthenium complex, the
system may be considered as a redox-triggered chiroptical
switch. The above-described complexes open up new
possibilities in the search for other helicenes with switchable
redox and optical properties and will be further studied in this
regard.
Since the comparison between the ECD spectra of (P,Λ,Λ)-
12 in the Ru(II) and Ru(III) oxidation states shows dramatic
changes in the chiroptical properties, the possibility of using
such a system as a chiroptical switch was explored. For
(P,Λ,Λ)-12, the difference between Δε values at 290 nm is not
only significant (∼170 M−1 cm−1) but also accompanied by a
change in sign. Therefore, it may be considered as a
chiroptical switch. The reversibility of switching was further
proved by several cycles of oxidation and reduction of
(P,Λ,Λ)-12 in MeCN, which were accompanied by a
modulation of the ECD signal upon applying potential steps
between 0.8 and 1.3 V (Figure 11). The helicene-bipy-Ru
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c01379.
General Information on the materials and methods used,
synthetic procedures, chiral separations, and character-
ization data (NMR, X-ray, optical rotation values,
spectroelectrochemical data, and additional spectral
information) (PDF)
Accession Codes
CCDC 2056689−2056691 and 2080927−2080930 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.
AUTHOR INFORMATION
■
Corresponding Authors
J. A. Gareth Williams − Department of Chemistry, Durham
University, Durham DH1 3LE, United Kingdom;
orcid.org/0000-0002-4688-3000; Email: j.a.g.williams@
durham.ac.uk
Figure 11. Redox-triggered chiroptical switching process of (P,Λ,Λ)-
12 following the ECD value at 290 nm (∼10−3 M, Bu4NPF6).
̌
́
Jaroslav Zádny − Institute of Chemical Process Fundamentals
of the Czech Academy of Sciences, 165 02 Prague 6, Czech
Republic; Email: zadny@icpf.cas.cz
complexes described here thus constitute a new class of
helicene-based redox-triggered chiroptical switches.38 Due to
the presence of several simultaneous redox steps, the multiple
electron reduction processes of (Λ)-11a, (P,Δ)-11c, and
(P,Δ,Δ)- and (P,Λ,Λ)-12 resulted in less significant and less
clear changes, as compared to the one-electron oxidation. The
spectroelectrochemical reduction processes are thus more
difficult to interpret (for selected spectra, see Figures S57 and
S58).
Vladimír Církva − Institute of Chemical Process Fundamentals
of the Czech Academy of Sciences, 165 02 Prague 6, Czech
Republic; Email: cirkva@icpf.cas.cz
Jeanne Crassous − Univ Rennes CNRS, , ISCR−UMR 6226
ScanMat−UMS 2001, 35000 Rennes, France; orcid.org/
0000-0002-4037-6067; Email: Jeanne.crassous@univ-
rennes1.fr
Authors
Martin Kos − Institute of Chemical Process Fundamentals of
the Czech Academy of Sciences, 165 02 Prague 6, Czech
Republic
Rafael Rodríguez − Univ Rennes CNRS, , ISCR−UMR 6226
ScanMat−UMS 2001, 35000 Rennes, France
Jan Storch − Institute of Chemical Process Fundamentals of
the Czech Academy of Sciences, 165 02 Prague 6, Czech
Republic
CONCLUSIONS
■
In summary, we have shown that the photocyclization of
aromatic imines is a suitable method for the preparation of
helicenes decorated with one or two bipy-moieties. The
formation of aza[6]- and aza[7]helicenes displaying one or two
complexing bipy units was accessed for the first time by this
methodology. These ligands were used for the preparation of
chiral ruthenium(II) complexes in diastereo- and enantioen-
riched forms, which were subsequently characterized. The
coordination of bipy-helicenes to the ruthenium ion generates
́
Jan Sykora − Institute of Chemical Process Fundamentals of
the Czech Academy of Sciences, 165 02 Prague 6, Czech
Republic
K
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(3) (a) Gingras, M. One Hundred Years of Helicene Chemistry. Part
3: Applications and Properties of Carbohelicenes. Chem. Soc. Rev.
2013, 42 (3), 1051−1095. (b) Dhbaibi, K.; Favereau, L.; Crassous, J.
Enantioenriched Helicenes and Helicenoids Containing Main-Group
Elements (B, Si, N, P). Chem. Rev. 2019, 119 (14), 8846−8953.
(4) (a) Yang, Y.; da Costa, R. C.; Smilgies, D.-M.; Campbell, A. J.;
Fuchter, M. J. Induction of Circularly Polarized Electroluminescence
from an Achiral Light-Emitting Polymer via a Chiral Small-Molecule
Dopant. Adv. Mater. 2013, 25 (18), 2624−2628. (b) Zhao, W.-L.; Li,
M.; Lu, H.-Y.; Chen, C.-F. Advances in Helicene Derivatives with
Circularly Polarized Luminescence. Chem. Commun. 2019, 55 (92),
13793−13803. (c) Crassous, J. In Circularly Polarized Luminescence of
Isolated Small Organic Molecules; Mori, T., Ed.; Springer Singapore:
Singapore, 2020; pp 53−97.
Elsa Caytan − Univ Rennes CNRS, , ISCR−UMR 6226
ScanMat−UMS 2001, 35000 Rennes, France; orcid.org/
0000-0003-0490-3074
Marie Cordier − Univ Rennes CNRS, , ISCR−UMR 6226
ScanMat−UMS 2001, 35000 Rennes, France
̌
Ivana Císarová − Department of Inorganic Chemistry, Faculty
of Science, Charles University in Prague, 128 40 Prague 2,
Czech Republic
Nicolas Vanthuyne − Aix Marseille Université, 7313
Marseille, France; orcid.org/0000-0003-2598-7940
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.1c01379
(5) Yang, Y.; Da Costa, R. C.; Smilgies, D. M.; Campbell, A. J.;
Fuchter, M. J. Induction of Circularly Polarized Electroluminescence
from an Achiral Light-Emitting Polymer via a Chiral Small-Molecule
Dopant. Adv. Mater. 2013, 25 (18), 2624−2628.
Author Contributions
M.K. performed the synthesis of the ligands and complexes.
R.R. performed CD, CPL, and spectroelectochemical studies.
N.V. performed HPLC separation of the ligands. I.C., M.C.,
(6) Kiran, V.; Mathew, S. P.; Cohen, S. R.; Hernández Delgado, I.;
Lacour, J.; Naaman, R. Helicenes-A New Class of Organic Spin Filter.
Adv. Mater. 2016, 28 (10), 1957−1962.
́
E.C., and J. Sykora performed structural analysis (X-ray and
NMR). J.A.G.W. performed nonpolarized luminescence
studies. V.C., J. Storch, and J.Z. designed the synthesis of
helicenes and were involved in the supervision and revision
and editing of the manuscript. J.C. designed the synthesis of
the complexes and wrote/revised together with other authors
the manuscript.
(7) (a) Saleh, N.; Shen, C.; Crassous, J. Helicene-Based Transition
Metal Complexes: Synthesis, Properties and Applications. Chem. Sci.
2014, 5 (10), 3680−3694. (b) OuYang, J.; Crassous, J. Chiral
Multifunctional Molecules Based on Organometallic Helicenes:
Recent Advances. Coord. Chem. Rev. 2018, 376, 533−547.
(c) Gauthier, E. S.; Rodríguez, R.; Crassous, J. Metal-Based
Multihelicenic Architectures. Angew. Chem., Int. Ed. 2020, 59 (51),
22840−22856.
Notes
The authors declare no competing financial interest.
(8) Saleh, N.; Moore, B.; Srebro, M.; Vanthuyne, N.; Toupet, L.;
Williams, J. A. G.; Roussel, C.; Deol, K. K.; Muller, G.; Autschbach, J.;
Crassous, J. Acid/Base-Triggered Switching of Circularly Polarized
Luminescence and Electronic Circular Dichroism in Organic and
Organometallic Helicenes. Chem. - Eur. J. 2015, 21 (4), 1673−1681.
(9) (a) Norel, L.; Rudolph, M.; Vanthuyne, N.; Williams, J. A. G.;
Lescop, C.; Roussel, C.; Autschbach, J.; Crassous, J.; Réau, R.
Metallahelicenes: Easily Accessible Helicene Derivatives with Large
and Tunable Chiroptical Properties. Angew. Chem., Int. Ed. 2010, 49
(1), 99−102. (b) Shen, C.; Anger, E.; Srebro, M.; Vanthuyne, N.;
Deol, K. K.; Jefferson, T. D.; Muller, G.; Williams, J. A. G.; Toupet, L.;
Roussel, C.; Autschbach, J.; Réau, R.; Crassous, J. Straightforward
Access to Mono- and Bis-Cycloplatinated Helicenes Displaying
Circularly Polarized Phosphorescence by Using Crystallization
Resolution Methods. Chem. Sci. 2014, 5 (5), 1915−1927. (c) Brandt,
J. R.; Wang, X.; Yang, Y.; Campbell, A. J.; Fuchter, M. J. Circularly
Polarized Phosphorescent Electroluminescence with a High Dis-
symmetry Factor from PHOLEDs Based on a Platinahelicene. J. Am.
Chem. Soc. 2016, 138 (31), 9743−9746.
ACKNOWLEDGMENTS
■
We thank the Centre National de la Recherche Scientifique
(CNRS) and the University of Rennes. This work was
supported by the Czech Science Foundation (grant no. 20-
19353S). M.K. is grateful to the Ministry of Education, Youth
and Sports of the Czech Republic and EU−European
Structural and Investment FundsOperational Programme
́
Research, Development, and Education for the project UCHP
Mobilita II (CZ.02.2.69/0.0/0.0/18_053/0016920). R.R.
thanks Xunta de Galicia for a Postdoctoral fellowship. The
authors thank Sitthichok Kasemthaveechok from the Uni-
versity of Rennes 1 for help with the electrochemical
measurements. NMR and ECD experiments were performed
on the PRISM core Facility (Biogenouest, UMS Biosit,
Université de Rennes 1).
REFERENCES
(10) Kaes, C.; Katz, A.; Hosseini, M. W. Bipyridine: The Most
Widely Used Ligand. A Review of Molecules Comprising at Least
Two 2,2‘-Bipyridine Units. Chem. Rev. 2000, 100 (10), 3553−3590.
(11) Chen, J.; Captain, B.; Takenaka, N. Helical Chiral 2,2′-
Bipyridine N-Monoxides as Catalysts in the Enantioselective
Propargylation of Aldehydes with Allenyltrichlorosilane. Org. Lett.
2011, 13 (7), 1654−1657.
■
(1) (a) Shen, Y.; Chen, C. F. Helicenes: Synthesis and Applications.
Chem. Rev. 2012, 112 (3), 1463−1535. (b) Chen, C.-F.; Shen, Y.
Helicene Chemistry; Springer Berlin: Heidelberg, 2017; DOI: 10.1007/
978-3-662-53168-6. (c) Gingras, M. One Hundred Years of Helicene
Chemistry. Part 1: Non-Stereoselective Syntheses of Carbohelicenes.
Chem. Soc. Rev. 2013, 42 (3), 968−1006.
̌
̌
̌
(12) Klívar, J.; Sámal, M.; Jancarík, A.; Vacek, J.; Bednárová, L.;
́
(2) Selected examples: (a) Carreno, M. C.; Enríquez, A.; García-
̃
̌
̌
́
́
Budesínsky, M.; Fiedler, P.; Stary, I.; Stará, I. G. Asymmetric Synthesis
of Diastereo- and Enantiopure Bioxahelicene 2,2′-Bipyridines. Eur. J.
Org. Chem. 2018, 2018 (37), 5164−5178.
Cerrada, S.; Sanz-Cuesta, M. J.; Urbano, A.; Maseras, F.; Nonell-
Canals, A. Towards Configurationally Stable [4]Helicenes: Enantio-
selective Synthesis of 12-Substituted 7,8-Dihydro[4]Helicene Qui-
nones. Chem. - Eur. J. 2008, 14 (2), 603−620. (b) Delgado, I. H.;
Pascal, S.; Wallabregue, A.; Duwald, R.; Besnard, C.; Guénée, L.;
(13) Kaneko, E.; Matsumoto, Y.; Kamikawa, K. Synthesis of
Azahelicene N-Oxide by Palladium-Catalyzed Direct C-H Annulation
of a Pendant (Z)-Bromovinyl Side Chain. Chem. - Eur. J. 2013, 19
(36), 11837−11841.
(14) Isla, H.; Saleh, N.; Ou-Yang, J. K.; Dhbaibi, K.; Jean, M.;
Dziurka, M.; Favereau, L.; Vanthuyne, N.; Toupet, L.; Jamoussi, B.;
Srebro-Hooper, M.; Crassous, J. Bis-4-Aza[6]Helicene: A Bis-
Helicenic 2,2′-Bipyridine with Chemically Triggered Chiroptical
Switching Activity. J. Org. Chem. 2019, 84 (9), 5383−5393.
Nanco̧ z, C.; Vauthey, E.; Tovar, R. C.; Lunkley, J. L.; Muller, G.;
Lacour, J. Functionalized Cationic [4]Helicenes with Unique Tuning
of Absorption, Fluorescence and Chiroptical Properties up to the Far-
Red Range. Chem. Sci. 2016, 7 (7), 4685−4693. (c) Hartung, T.;
Machleid, R.; Simon, M.; Golz, C.; Alcarazo, M. Enantioselective
Synthesis of 1,12-Disubstituted [4]Helicenes. Angew. Chem., Int. Ed.
2020, 59 (14), 5660−5664.
L
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Featured Article
(15) (a) Saleh, N.; Srebro, M.; Reynaldo, T.; Vanthuyne, N.;
Toupet, L.; Chang, V. Y.; Muller, G.; Williams, J. A. G.; Roussel, C.;
Autschbach, J.; Crassous, J. Enantio-Enriched CPL-Active Helicene−
Bipyridine−Rhenium Complexes. Chem. Commun. 2015, 51 (18),
3754−3757. (b) Saleh, N.; Kundu, D.; Vanthuyne, N.; Olesiak-
Banska, J.; Pniakowska, A.; Matczyszyn, K.; Chang, V. Y.; Muller, G.;
Williams, J. A. G.; Srebro-Hooper, M.; Autschbach, J.; Crassous, J.
Dinuclear Rhenium Complexes with a Bridging Helicene-bis-
bipyridine Ligand: Synthesis, Structure, and Photophysical and
Chiroptical Properties. ChemPlusChem 2020, 85 (11), 2446−2454.
(16) Saleh, N.; Srebro, M.; Reynaldo, T.; Vanthuyne, N.; Toupet, L.;
Chang, V. Y.; Muller, G.; Williams, J. A. G.; Roussel, C.; Autschbach,
J.; Crassous, J. Enantio-Enriched CPL-Active Helicene−Bipyridine−
Rhenium Complexes. Chem. Commun. 2015, 51 (18), 3754−3757.
(17) (a) Ou-Yang, J.-K.; Saleh, N.; Fernandez Garcia, G.; Norel, L.;
Pointillart, F.; Guizouarn, T.; Cador, O.; Totti, F.; Ouahab, L.;
Crassous, J.; Le Guennic, B. Improved Slow Magnetic Relaxation in
Optically Pure Helicene-Based Dy III Single Molecule Magnets.
Chem. Commun. 2016, 52 (100), 14474−14477. (b) Fernandez-
Garcia, G.; Flores Gonzalez, J.; Ou-Yang, J.-K.; Saleh, N.; Pointillart,
F.; Cador, O.; Guizouarn, T.; Totti, F.; Ouahab, L.; Crassous, J.; Le
Guennic, B. Slow Magnetic Relaxation in Chiral Helicene-Based
Coordination Complex of Dysprosium. Magnetochemistry 2017, 3 (1),
2. (c) Flores Gonzalez, J.; Montigaud, V.; Saleh, N.; Cador, O.;
Crassous, J.; le Guennic, B.; Pointillart, F. Slow Relaxation of the
Magnetization in Bis-Decorated Chiral Helicene-Based Coordination
Complexes of Lanthanides. Magnetochemistry 2018, 4 (3), 39.
(d) Galland, M.; Riobé, F.; Ouyang, J.; Saleh, N.; Pointillart, F.;
Dorcet, V.; Le Guennic, B.; Cador, O.; Crassous, J.; Andraud, C.;
Monnereau, C.; Maury, O. Helicenic Complexes of Lanthanides:
Influence of the f-Element on the Intersystem Crossing Efficiency and
Competition between Luminescence and Oxygen Sensitization. Eur. J.
Inorg. Chem. 2019, 2019 (1), 118−125. (e) Atzori, M.; Dhbaibi, K.;
Douib, H.; Grasser, M.; Dorcet, V.; Breslavetz, I.; Paillot, K.; Cador,
O.; Rikken, G. L. J. A.; Le Guennic, B.; Crassous, J.; Pointillart, F.;
Train, C. Helicene-Based Ligands Enable Strong Magneto-Chiral
Dichroism in a Chiral Ytterbium Complex. J. Am. Chem. Soc. 2021,
143 (7), 2671−2675.
Complexes Δ- and Λ-[Ru(Bpy)2L] (L = o-hpip, m-hpip and p-hpip).
Dalton Trans. 2003, 7, 1352−1359. (g) Shi, S.; Xu, J.-H.; Gao, X.;
Huang, H.-L.; Yao, T.-M. Binding Behaviors for Different Types of
DNA G-Quadruplexes: Enantiomers of [Ru(Bpy)2(L)]2+ (L = dppz,
Dppz-Idzo). Chem. - Eur. J. 2015, 21 (32), 11435−11445.
(20) (a) Chelucci, G.; Thummel, R. P. Chiral 2,2‘-Bipyridines, 1,10-
Phenanthrolines, and 2,2‘:6‘,2‘ ‘-Terpyridines: Syntheses and
Applications in Asymmetric Homogeneous Catalysis. Chem. Rev.
2002, 102 (9), 3129−3170. (b) Fletcher, N. C. Chiral 2,2′-
Bipyridines: Ligands for Asymmetric Induction. J. Chem. Soc., Perkin
Trans. 1 2002, 2 (16), 1831−1842. (c) von Zelewsky, A.
Stereochemistry of Coordination Compounds; J. Wiley & Sons:
Chichester, 1996. (d) Amouri, H.; Gruselle, M. Chirality in Transition
Metal Chemistry; John Wiley & Sons, Ltd.: Chichester, UK, 2008;
DOI: 10.1002/9780470721599.
̌
́
̌
́
(21) Kos, M.; Zádny, J.; Storch, J.; Církva, V.; Curínová, P.; Sykora,
̌
J.; Císarová, I.; Kuriakose, F.; Alabugin, I. V. Oxidative Photo-
cyclization of Aromatic Schiff Bases in Synthesis of Phenanthridines
and Other Aza-PAHs. Int. J. Mol. Sci. 2020, 21 (16), 5868.
(22) (a) Badger, G. M.; Joshua, C. P.; Lewis, G. E. Photocatalysed
Cyclization of Benzalaniline. Tetrahedron Lett. 1964, 5 (49), 3711−
3713. (b) Thompson, C. M.; Docter, S. Lewis Acid Promoted
Photocyclization of Arylimines. Studies Directed towards the
Synthesis of Pentacyclic Natural Products. Tetrahedron Lett. 1988,
29 (41), 5213−5216.
(23) (a) Howarth, J.; Finnegan, J. The Synthesis of 9, 10-
Dimethyl[7]Helicene and 8, 11-Diaza[7]Helicene. Synth. Commun.
1997, 27 (20), 3663−3668. (b) Caronna, T.; Gabbiadini, S.; Mele, A.;
Recupero, F. Approaches to the Azahelicene System: Synthesis and
Spectroscopic Characterization of Some Diazapentahelicenes. Helv.
Chim. Acta 2002, 85 (1), 1−8.
́
(24) Ghosh, A.; Csókás, D.; Budanovic, M.; Webster, R. D.; Pápai,
I.; Stuparu, M. C. Synthesis of Azahelicenes through Mallory Reaction
of Imine Precursors: Corannulene Substrates Provide an Exception to
the Rule in Oxidative Photocyclizations of Diarylethenes. Chem. Sci.
2021, 12, 3977.
(25) (a) Li, C.; Yang, Y.; Miao, Q. Recent Progress in Chemistry of
Multiple Helicenes. Chem. - Asian J. 2018, 13 (8), 884−894. (b) Kato,
K.; Segawa, Y.; Itami, K. Symmetric Multiple Carbohelicenes. Synlett
2019, 30 (04), 370−377. (c) Mori, T. Chiroptical Properties of
Symmetric Double, Triple, and Multiple Helicenes. Chem. Rev. 2021,
121 (4), 2373−2412.
(26) (a) Cortijo, M.; Viala, C.; Reynaldo, T.; Favereau, L.; Fabing,
I.; Srebro-Hooper, M.; Autschbach, J.; Ratel-Ramond, N.; Crassous,
J.; Bonvoisin, J. Synthesis, Spectroelectrochemical Behavior, and
Chiroptical Switching of Tris(β-Diketonato) Complexes of
Ruthenium(III), Chromium(III), and Cobalt(III). Inorg. Chem.
2017, 56 (8), 4555−4567. (b) Li, D.; Wang, Z. Y.; Ma, D.
Electrically-Controlled near-Infrared Chiroptical Switching of Enan-
tiomeric Dinuclear Ruthenium Complexes. Chem. Commun. 2009, 12,
1529. (c) Feringa, B. L.; Browne, W. R. Molecular Switches; Wiley-
VCH Verlag GmbH & Co. KGaA: Weinheim, Germany, 2011; Vol. 1;
DOI: 10.1002/9783527634408. (d) Canary, J. W. Redox-Triggered
Chiroptical Molecular Switches. Chem. Soc. Rev. 2009, 38 (3), 747.
(27) Hoffmann, N. Photochemical Reactions Applied to the
Synthesis of Helicenes and Helicene-like Compounds. J. Photochem.
Photobiol., C 2014, 19 (1), 1−19.
(18) (a) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser,
P.; von Zelewsky, A. Ru(II) Polypyridine Complexes: Photophysics,
Photochemistry, Eletrochemistry, and Chemiluminescence. Coord.
Chem. Rev. 1988, 84 (C), 85−277. (b) Balzani, V.; Credi, A.;
Scandola, F. Transition Metals in Supramolecular Chemistry; Fabbrizzi,
L., Poggi, A., Eds.; Springer Netherlands: Dordrecht, 1994;
DOI: 10.1007/978-94-015-8380-0. (c) Balzani, V.; Juris, A.;
Venturi, M.; Campagna, S.; Serroni, S. Luminescent and Redox-
Active Polynuclear Transition Metal Complexes. Chem. Rev. 1996, 96
(2), 759−834.
(19) Selected examples. Photochemistry: (a) Sato, H.; Yamagishi, A.
Application of the ΔΛ Isomerism of Octahedral Metal Complexes as
a Chiral Source in Photochemistry. J. Photochem. Photobiol., C 2007, 8
(2), 67−84. Photocatalysis: (b) Ohkubo, K.; Hamada, T.; Ishida, H.
Novel Enantioselective Photocatalysis by Chiral, Helical Ruthenium-
(II) Complexes. J. Chem. Soc., Chem. Commun. 1993, 3 (18), 1423.
2+
́
(c) Teply, F. Photoredox Catalysis by [Ru(bpy)3] to Trigger
Transformations of Organic Molecules. Organic Synthesis Using
Visible-Light Photocatalysis and Its 20th Century Roots. Collect.
Czech. Chem. Commun. 2011, 76 (7), 859−917. Electrochromism:
(d) Puodziukynaite, E.; Oberst, J. L.; Dyer, A. L.; Reynolds, J. R.
Establishing Dual Electrogenerated Chemiluminescence and Multi-
color Electrochromism in Functional Ionic Transition-Metal Com-
plexes. J. Am. Chem. Soc. 2012, 134 (2), 968−978. Electro-
chemiluminescence: (e) Voci, S.; Zinna, F.; Arrico, L.; Grass, S.;
Bouffier, L.; Lacour, J.; Di Bari, L.; Sojic, N. Chiroptical Detection of
a Model Ruthenium Dye in Water by Circularly Polarized-
Electrochemiluminescence. Chem. Commun. 2020, 56 (44), 5989−
5992. DNA binding: (f) Mei, W. J.; Liu, J.; Zheng, K. C.; Lin, L. J.;
Chao, H.; Li, A. X.; Yun, F. C.; Ji, L. N. Experimental and Theoretical
Study on DNA-Binding and Photocleavage Properties of Chiral
(28) Martin, R.H.; Marchant, M.J. Thermal Racemisation of Hepta-,
Octa-, and Nonahelicene. Tetrahedron 1974, 30 (2), 347−349.
(29) (a) Ghosh, P.; Spiro, T. G. Photoelectrochemistry of
Tris(Bipyridyl)Ruthenium(II) Covalently Attached to n-Type Tin-
(IV) Oxide. J. Am. Chem. Soc. 1980, 102 (17), 5543−5549.
́
(b) Martínez, M. A.; Carranza, M. P.; Massaguer, A.; Santos, L.;
Organero, J. A.; Aliende, C.; de Llorens, R.; Ng-Choi, I.; Feliu, L.;
Planas, M.; Rodríguez, A. M.; Manzano, B. R.; Espino, G.; Jalón, F. A.
Synthesis and Biological Evaluation of Ru(II) and Pt(II) Complexes
Bearing Carboxyl Groups as Potential Anticancer Targeted Drugs.
Inorg. Chem. 2017, 56 (22), 13679−13696.
M
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Inorganic Chemistry
pubs.acs.org/IC
Featured Article
(30) Tartrate resolving agent: (a) Hua, X.; von Zelewsky, A.
Enantiomerically Pure Chiral RuII(L-L)2 Building Blocks for
Coordination Compounds. Inorg. Chem. 1995, 34 (23), 5791−5797.
(b) Hua, X.; Von Zelewsky, A. First Stereospecific Preparation of a
Polynuclear Coordination Compound. Use of Λ-Bis(o-
Phenanthroline)Ruthenium(II) as a Chiral Building Block. Inorg.
Chem. 1991, 30 (20), 3796−3798. TRISPHAT resolving agent:
(c) Lacour, J.; Torche-Haldimann, S.; Jodry, J. J. Ion Pair
Chromatographic Resolution of Tris(Diimine)Ruthenium(II) Com-
plexes Using TRISPHAT Anions as Resolving Agents. Chem.
Commun. 1998, 16, 1733−1734. Chiral sulfoxide resolving agent:
(d) Hesek, D.; Inoue, Y.; Ishida, H.; Everitt, S. R.; Drew, M. G. The
First Asymmetric Synthesis of Chiral Ruthenium Tris(Bipyridine)
from Racemic Ruthenium Bis(Bipyridine) Complexes. Tetrahedron
Lett. 2000, 41 (15), 2617−2620.
(31) (a) Evans, D. H.; O’Connell, K. M.; Petersen, R. A.; Kelly, M. J.
Cyclic Voltammetry. J. Chem. Educ. 1983, 60 (4), 290. (b) Damrauer,
N. H. Femtosecond Dynamics of Excited-State Evolution in
[Ru(Bpy)3]2+. Science 1997, 275 (5296), 54−57.
(32) Campagna, S.; Puntoriero, F.; Nastasi, F.; Bergami, G.; Balzani,
V. Photochemistry and Photophysics of Coordination Compounds:
Ruthenium. Top. Curr. Chem. 2007, 280, 117−214.
Precursors with Switchable Chiroptical Properties. Chem. - Eur. J.
2013, 19 (39), 13160−13167. (c) Schweinfurth, D.; Zalibera, M.;
Kathan, M.; Shen, C.; Mazzolini, M.; Trapp, N.; Crassous, J.;
Gescheidt, G.; Diederich, F. Helicene Quinones: Redox-Triggered
Chiroptical Switching and Chiral Recognition of the Semiquinone
Radical Anion Lithium Salt by Electron Nuclear Double Resonance
Spectroscopy. J. Am. Chem. Soc. 2014, 136 (37), 13045−13052.
̌
̌
̌
̌
(d) Pospísil, L.; Bednárová, L.; Stepánek, P.; Slavícek, P.; Vávra, J.;
́
Hromadová, M.; Dlouhá, H.; Tarábek, J.; Teply, F. Intense
Chiroptical Switching in a Dicationic Helicene-Like Derivative:
Exploration of a Viologen-Type Redox Manifold of a Non-Racemic
Helquat. J. Am. Chem. Soc. 2014, 136 (31), 10826−10829. (e) Srebro,
M.; Anger, E.; Moore, B., II; Vanthuyne, N.; Roussel, C.; Réau, R.;
Autschbach, J.; Crassous, J. Ruthenium-Grafted Vinylhelicenes:
Chiroptical Properties and Redox Switching. Chem. - Eur. J. 2015,
21 (47), 17100−17115. (f) Shen, C.; Loas, G.; Srebro-Hooper, M.;
Vanthuyne, N.; Toupet, L.; Cador, O.; Paul, F.; López Navarrete, J.
T.; Ramírez, F. J.; Nieto-Ortega, B.; Casado, J.; Autschbach, J.; Vallet,
M.; Crassous, J. Iron Alkynyl Helicenes: Redox-Triggered Chiroptical
Tuning in the IR and Near-IR Spectral Regions and Suitable for
Telecommunications Applications. Angew. Chem., Int. Ed. 2016, 55
(28), 8062−8066. (g) Shen, C.; Srebro-Hooper, M.; Weymuth, T.;
Krausbeck, F.; Navarrete, J. T. L.; Ramírez, F. J.; Nieto-Ortega, B.;
Casado, J.; Reiher, M.; Autschbach, J.; Crassous, J. Redox-Active
Chiroptical Switching in Mono- and Bis-Iron Ethynylcarbo[6]-
Helicenes Studied by Electronic and Vibrational Circular Dichroism
and Resonance Raman Optical Activity. Chem. - Eur. J. 2018, 24 (56),
15067−15079. (h) Shen, C.; He, X.; Toupet, L.; Norel, L.; Rigaut, S.;
Crassous, J. Dual Redox and Optical Control of Chiroptical Activity in
Photochromic Dithienylethenes Decorated with Hexahelicene and
Bis-Ethynyl-Ruthenium Units. Organometallics 2018, 37 (5), 697−
705.
(33) Barigelletti, F.; Juris, A.; Balzani, V.; Belser, P.; Von Zelewsky,
A. Influence of the Ligand Structure on the Electrochemical and
Spectroscopic Properties of Ruthenium(II)-Polypyridine Complexes.
Inorg. Chem. 1987, 26 (24), 4115−4119.
(34) (a) Schulze, M.; Steffen, A.; Wurthner, F. Near-IR
̈
Phosphorescent Ruthenium(II) and Iridium(III) Perylene Bisimide
Metal Complexes. Angew. Chem., Int. Ed. 2015, 54 (5), 1570−1573.
(b) Caspar, J. V.; Meyer, T. J. Photochemistry of Ru(Bpy)32+. Solvent
Effects. J. Am. Chem. Soc. 1983, 105 (17), 5583−5590. (c) Caspar, J.
V.; Meyer, T. J. Application of the Energy Gap Law to Nonradiative,
Excited-State Decay. J. Phys. Chem. 1983, 87 (6), 952−957.
(35) (a) Kozhevnikov, D. N.; Kozhevnikov, V. N.; Shafikov, M. Z.;
Prokhorov, A. M.; Bruce, D. W.; Williams, J. A. G. Phosphorescence
vs Fluorescence in Cyclometalated Platinum(II) and Iridium(III)
Complexes of (Oligo)Thienylpyridines. Inorg. Chem. 2011, 50 (8),
3804−3815. (b) Escudero, D.; Happ, B.; Winter, A.; Hager, M. D.;
Schubert, U. S.; González, L. The Radiative Decay Rates Tune the
Emissive Properties of Ruthenium(II) Polypyridyl Complexes: A
Computational Study. Chem. - Asian J. 2012, 7 (4), 667−671.
(36) Gauthier, E. S.; Abella, L.; Hellou, N.; Darquié, B.; Caytan, E.;
Roisnel, T.; Vanthuyne, N.; Favereau, L.; Srebro-Hooper, M.;
Williams, J. A. G.; Autschbach, J.; Crassous, J. Long-Lived Circularly
Polarized Phosphorescence in Helicene-NHC Rhenium(I) Com-
plexes: The Influence of Helicene, Halogen, and Stereochemistry on
Emission Properties. Angew. Chem., Int. Ed. 2020, 59 (22), 8394−
8400.
(37) (a) Hohloch, S.; Schweinfurth, D.; Sommer, M. G.; Weisser, F.;
Deibel, N.; Ehret, F.; Sarkar, B. The Redox Series [Ru(Bpy)2(L)]n, n
= + 3, + 2, + 1, 0, with L = Bipyridine, “Click” Derived Pyridyl-
Triazole or Bis-Triazole: A Combined Structural, Electrochemical,
Spectroelectrochemical and DFT Investigation. Dalton Trans. 2014,
43 (11), 4437−4450. (b) Connelly, N. G.; Geiger, W. E. Chemical
Redox Agents for Organometallic Chemistry. Chem. Rev. 1996, 96
(2), 877−910. (c) Aguirre-Etcheverry, P.; O’Hare, D. Electronic
Communication through Unsaturated Hydrocarbon Bridges in
Homobimetallic Organometallic Complexes. Chem. Rev. 2010, 110
(8), 4839−4864. (d) Costuas, K.; Rigaut, S. Polynuclear Carbon-Rich
Organometallic Complexes: Clarification of the Role of the Bridging
Ligand in the Redox Properties. Dalton Trans. 2011, 40 (21), 5643−
5658.
(38) (a) Anger, E.; Srebro, M.; Vanthuyne, N.; Toupet, L.; Rigaut,
S.; Roussel, C.; Autschbach, J.; Crassous, J.; Réau, R. Ruthenium-
Vinylhelicenes: Remote Metal-Based Enhancement and Redox
Switching of the Chiroptical Properties of a Helicene Core. J. Am.
Chem. Soc. 2012, 134 (38), 15628−15631. (b) Biet, T.; Fihey, A.;
Cauchy, T.; Vanthuyne, N.; Roussel, C.; Crassous, J.; Avarvari, N.
Ethylenedithio−Tetrathiafulvalene−Helicenes: Electroactive Helical
N
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