Redox-Triggered Helicity Inversion in Chiral Cobalt Complexes in Combination with H+ and NO3- Stimuli

Article abstract of DOI:10.1021/acs.inorgchem.5b01902

Three chiral ligands with variable denticity, H₂L2-H₂L4, conjugated by N,N′-ethylenebis[N-methyl-(S)-alanine] and an ortho-heterosubstituted aromatic amine, were newly synthesized as analogues of previously reported H₂L1. Four contracted-Λ_oxo cobalt(III) complexes [Co(L)]⁺ with left-handed helical structure of Λ₄Δ₂ configuration were prepared by one-electron oxidation of the corresponding contracted-Λ_red cobalt(II) complexes [Co(L)], which were generated from chiral ligands and Co(ClO₄)₂·6H₂O or Co(CF₃SO₃)₂·5.2H₂O in the presence of an organic base. Although the prepared cobalt(III) complexes were very inert and kinetically stable against protonation and NO₃^- complexation, cobalt(III) reduction in the presence of CF₃SO₃H and/or Bu₄NNO₃ allowed immediate changing of their three-dimensional structures from the contracted-Λ_oxo form to the extended-Λ [Co(H₂L)Y₂]ⁿ⁺ (Y = solvent and/or anion, n = 0-2) form with left-handed helicity or to the extended-Δ [Co(H₂L)(NO₃)]⁺ form with right-handed helicity via N- to O-amide coordination switching. Both extended forms were contracted to the original Λ_oxo form by oxidation of the cobalt(II) center in the presence of an organic base. Thus, redox reactions triggered dynamic helicity inversion of the chiral cobalt complexes, via multiple molecular motions consisting of relaxation/compression, extension/contraction, and helicity inversion motions in combination with deprotonation/protonation of amide linkages and NO₃^- anion complexation.

Full text of DOI:10.1021/acs.inorgchem.5b01902

Article
pubs.acs.org/IC
Redox-Triggered Helicity Inversion in Chiral Cobalt Complexes
in Combination with H+ and NO3 Stimuli
−
Janusz Gregolinski,†,‡ Masahiro Hikita,† Tatsuya Sakamoto,† Hideki Sugimoto,†,§ Hiroshi Tsukube,†,⊥
́
and Hiroyuki Miyake*,†
⊥
†Department of Chemistry, Graduate School of Science, and JST, CREST, Osaka City University, 3-3-138 Sugimoto,
Sumiyoshi-ku, Osaka 558-8585, Japan
S
* Supporting Information
ABSTRACT: Three chiral ligands with variable denticity,
H2L2−H2L4, conjugated by N,N′-ethylenebis[N-methyl-(S)-
alanine] and an ortho-heterosubstituted aromatic amine, were
newly synthesized as analogues of previously reported H2L1.
Four contracted-Λoxo cobalt(III) complexes [Co(L)]+ with left-
handed helical structure of Λ4Δ2 configuration were prepared
by one-electron oxidation of the corresponding contracted-Λred
cobalt(II) complexes [Co(L)], which were generated from
chiral ligands and Co(ClO4)2·6H2O or Co(CF3SO3)2·5.2H2O
in the presence of an organic base. Although the prepared
cobalt(III) complexes were very inert and kinetically stable
against protonation and NO3− complexation, cobalt(III) reduc-
tion in the presence of CF3SO3H and/or Bu4NNO3 allowed
immediate changing of their three-dimensional structures from the contracted-Λoxo form to the extended-Λ [Co(H2L)Y2]n+
(Y = solvent and/or anion, n = 0−2) form with left-handed helicity or to the extended-Δ [Co(H2L)(NO3)]+ form with right-
handed helicity via N− to O−amide coordination switching. Both extended forms were contracted to the original Λoxo form by
oxidation of the cobalt(II) center in the presence of an organic base. Thus, redox reactions triggered dynamic helicity inversion
of the chiral cobalt complexes, via multiple molecular motions consisting of relaxation/compression, extension/contraction, and
−
helicity inversion motions in combination with deprotonation/protonation of amide linkages and NO3 anion complexation.
Helicity inversion2,8−12 between well-structured stereoisomers
has also attracted recent interest. Right-handed B-DNA changes
INTRODUCTION
■
Many types of molecular motion, such as stretching/contraction,
its helical direction to become left-handed Z-DNA in several cell
winding/unwinding, coiling/uncoiling, rotation, and helicity
processes.1d In addition to synthetic organic systems,9 including
inversion, are involved in dynamic biological processes.1
polymers10 and supramolecular aggregates,11 some helical
Adenosine triphosphate synthase1c and bacterial flagellar
motors1d are representative examples in which external stimuli
metal complexes have been reported to exhibit dynamic helicity
inversion. Canary and co-workers reported that copper complexes
change the conformations of biomolecules to trigger bio-
logical events. Among various structural conversion systems,1−3
with N,N-dialkylmethionine ligands underwent helicity inversion
coupled with a copper(II)/copper(I) redox reaction.8i,j Lisowski
certain metalloproteins dynamically regulate three-dimensional
et al. developed chiral macrocyclic lanthanide complexes for
protein structures by coupling with cis/trans isomerization and
helicity inversion8n,o triggered by thermodynamic changing of
O/N-coordination switching of amide linkages (−CO−NH−).4
the helix axis8p and by anion coordination.8q Akine, Nabeshima,
H+ and metal cations indeed work as effective external stimuli
and co-workers reported helicity inversion systems of multi-
to initiate molecular motion in synthetic metallosystems.
nuclear complexes with chiral oxime ligands; the helicity of one
Lehn et al. reported that switching of protonation/deprotonation
system was controlled by the length of an external diammonium
or metalation/demetalation provided coiled/uncoiled molecular
strands.5a,b Redox reactions of the metal center or organic
guest, while another system was controlled by the subsequent
addition of external metal cations.8s,t Parker et al. presented
residue are also powerful and effective external stimuli, offering
different interactions with a second species.6 Sauvage and
helicity inversion of lanthanide complexes with chiral armed
cyclens via albumin complexation.8u Lin et al. reported pH-
co-workers developed several redox-active metal catenanes
switchable helicity inversion of a ruthenabenzene complex.8v
and rotaxanes exhibiting gliding motions.7a Fabbrizzi et al.
reported a redox-driven transformation of octahedral to
tetrahedral coordination in double-stranded metal helicates.7c
Flood et al. developed redox-active switching in copper(I)-based
pseudorotaxane.7f,g
Ludeke et al. reported solvation-induced helicity inversion of
̈
Received: August 19, 2015
Published: January 5, 2016
© 2016 American Chemical Society
633
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
Scheme 1. Multiple Motions (A ⇄ B ⇄ C ⇄ D ⇄ A, B ⇄ D, and A ⇄ C) in Response to a Combination of External Stimuli
tetrahedral chiral cobalt(II) complexes.8w In these examples,
labile characters of the employed metal centers played important
roles in exhibiting dynamic helicity inversion phenomena.
We previously reported a molecular device based on a chiral
cobalt(II) complex that exhibited dual molecular motions
including helicity inversion and extension/contraction motions.8d
The ligand used, H2L1, includes 2,5-dimethoxybenzene moieties
attached through amide linkages to both terminals of a chiral
bis(S)-alanine and works as a variable polydentate ligand
(tetradentate ⇄ hexadentate). As shown in a part of Scheme 1,
the cobalt(II) complex with H2L1 exhibited the following
molecular motions: (1) the helicity of the [Co(H2L1)Y2]n+
(Y = solvent and/or anion, n = 0−2) complex was dynamically
inverted from the extended-Λ cis-α form to the extended-Δ cis-α
form in response to achiral NO3− anions (type B → type A); (2)
acid and base promoted extension and contraction, respectively,
of the complex structure, in which the coordinating atoms
interconverted between amide oxygen atoms and amide nitrogen
atoms (B ⇄ C); (3) when two different stimuli, i.e., acid/base
and NO3−, were added together, both helicity inversion and
extension/contraction took place (A ⇄ C), which offered the
dual molecular motion. Here, we report “redox-triggered”
multiple molecular motions of chiral cobalt complexes with chiral
ligands, H2L1, H2L2, H2L3, and H2L4 (Scheme 1).
A reversible relaxation/compression motion (C ⇄ D) was
designed using a cobalt(III)/cobalt(II) redox reaction in addition
to helicity inversion (A ⇄ B) and extension/contraction
(B ⇄ C) motions. Because the oxidized cobalt(III) complexes
with deprotonated ligands, [Co(L)]+ with L = L1−L4, are stable
against ligand-exchange reactions, their chiral structures can be
frozen. We demonstrate that reduction of an inert cobalt(III)
complex to a labile cobalt(II) complex switches the ligand sub-
stitution mode, allowing dynamic conversion of stable states in
response to the combination of external stimuli. Although several
methods of freezing or braking molecular motion in organic
molecules have been reported,13 the metal redox system under
discussion easily freezes dynamic molecular motions. The
following molecular motions were investigated using cobalt
complexes with four chiral ligands: helicity inversion (A ⇄ B);
extension/contraction (B ⇄ C); relaxation/compression
(C ⇄ D); redox-triggered extension/contraction (B ⇄ D).
Taking advantage of the reversibility of each process, we success-
fully constructed a cycle of molecular motions (D → C → B →
C → D) and redox-triggered helicity inversion (A ⇄ D).
RESULTS AND DISCUSSION
■
Synthesis of Chiral Ligands and Cobalt Complexes.
Chiral ligands H2L1−H2L4 were derived from N,N′-
ethylenebis[N-methyl-(S)-alanine]8d−g in 35−72% yield,
which included two identical ortho-substituted aromatic rings
via amide linkages at both termini. The chiral ligands were fully
1
characterized by H and 13C NMR, fast-atom-bombardment
mass spectrometry (FAB-MS), elemental analysis, optical
rotation, and IR measurements. Their optical purities were
confirmed as >97% d.e. by 1H NMR spectroscopy. Four types of
cobalt complexes were formed, depending on the oxidation state
of the cobalt center, helical direction, and coordination mode of
the ligand (Scheme 2): type A, extended-Δ [Co(H2L)(NO3)]+;
type B, extended-Λ [Co(H2L)Y2]n+, e.g., [Co(H2L)-
(solvent)2]2+, [Co(H2L)(solvent)(CF3SO3)]+, or [Co(H2L)-
(CF3SO3)2]; type C, contracted-Λred [Co(L)]; type D,
contracted-Λoxo [Co(L)]+.
634
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
a
1
reduction of the corresponding [Co(L4)]+, showed H NMR
signals from about −50 to +160 ppm (see Figure S25b).
[ C o ( L 1 ) ] ( C l O 4 ) · H 2 O , [ C o ( L 1 ) ] ( C F 3 S O 3 ) ·
[(CH3)2CHOH]0.5, [Co(L2)](ClO4)·(H2O)2, [Co(L2)]-
(CF3SO3)·H2O, [Co(L3)](ClO4)·(H2O)1.5, and [Co(L4)]-
Scheme 2. Syntheses of Chiral Cobalt Complexes
1
(ClO4)·H2O, which were of type D, showed H NMR signals
in the diamagnetic region from about 1.3 to 9.1 ppm. These
observations confirmed the formation of low-spin d6 complexes
(see Figures S13−S17).
Crystal Structures of Cobalt Complexes. Figure 1
summarizes the crystal structures of cobalt complexes of
a
[Co(L3)], [Co(H2L4)(solvent)2]2+, and [Co(L4)] were generated
in situ.
Type A [Co(H2L)(NO3)]+ was generated in situ in a CH3CN
or CH3CN/CHCl3 (1:9) solution by mixing equimolar amounts
of ligand (H2L1, H2L2, or H2L3) and Co(NO3)2·6H2O.14
Those electrospray ionization mass spectrometry (ESI-MS)
spectra exhibited the presence of [Co(H2L)(NO3)]+ species
1
(see Figures S1−S3), and H NMR spectra (Figure S4) are
similar to that of the related crystalline complex [Co(H2L5)-
(NO3)](NO3), which was confirmed to be a type A Δ structure
by X-ray crystal structure analysis.8g
Figure 1. Crystal structures of chiral cobalt complexes [Co(H2L2)-
(AcOEt)(H2O)](ClO4)2 (type B), [Co(L2)]·[(C3H7)2(C2H5)NH]-
(ClO4) (type C), and [Co(L2)](ClO4)·CH3OH (type D) and a list of
solved crystal structures. Thermal ellipsoids are drawn at the 50%
probability level. Most of the hydrogen atoms (except amide hydrogen
atoms), noncoordinated solvent molecules, counteranions, and
cocrystallized molecules were omitted for clarity.
[Co(H2L2)(AcOEt)(H2O)](ClO4)2 and [Co(H2L3)-
(H2O)2](ClO4)2, of type B, were isolated as crystals from
a solution of the corresponding ligand and Co(ClO4)2·6H2O
in CH2Cl2/AcOEt for H2L2 and CHCl3/AcOEt for H21L3
(Figures S5 and S6 for FAB-MS spectra and Figure S7 for H
NMR spectra). Although a CH3CN solution of H2L4 and
Co(ClO4)2·6H2O in equimolar amounts gave a complex of
type B (see Figure S7d), it was rapidly oxidized under ambient
atmosphere.
types B−D. No good crystals were obtained for complexes of
type A (see details in Table S1 and Figure S18). [Co(H2L2)-
(AcOEt)(H2O)](ClO4)2, of type B (Figure 1, left), had
an extended-Λ cis-α form, as reported for the complex
[Co(H2L1)(CF3SO3)(H2O)](CF3SO3),8d in which the cobalt(II)
center is coordinated with two amine nitrogen atoms, two
amide oxygen atoms of the ligand, and two donors from solvent
molecules. [Co(L2)]·[(C3H7)2(C2H5)NH](ClO4), of type C
(Figure 1, middle), is characterized by a distorted octahedral
left-handed helical structure (Λ4Δ2 absolute configuration
between the skew chelate pairs),15 as reported for [Co(L1)].8d
The cobalt(II) center is bound with two amine nitrogen atoms,
two deprotonated amide nitrogen atoms, and two methoxy
[CoL2]·[(C3H7)2(C2H5)NH](ClO4), of type C (see Figure S8),
was isolated by the addition of an excess amount of N,N′-
diisopropylethylamine (DIEA) to an in situ generated type B
complex [a C2H5OH solution of H2L2 and Co(ClO4)2·6H2O],
as reported earlier for [Co(L1)].8d The isolated [Co(L1)] and
1
[Co(L2)]·[(C3H7)2(C2H5)NH](ClO4) gave H NMR signals
from −70 to +110 ppm, while the in situ generated [Co(L3)]
exhibited signals from about −50 to +80 ppm (see Figure S9) and
was rapidly oxidized by atmospheric oxygen to give [Co(L3)]+,
of type D. [Co(L4)], which was not able to be generated from
the corresponding type B complex and was generated in situ by
635
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
1
oxygen atoms from the ortho-substituted aromatic moieties.
Cobalt(III) complexes of type D (Figure 1, right), [Co(L1)]-
(CF3SO3)·C3H7OH, [Co(L2)](ClO4)·CH3OH, and [Co(L2)]-
(CF3SO3)·C2H5OH, have the same Λ4Δ2 configuration as the
type C complexes, but the coordination bond lengths in these
complexes are ca. 9% shorter than those in the corresponding
cobalt(II) complexes and adopt strongly twisted structures.
The distances between the first aromatic carbon atoms (C6
and C17) attached to the chiral ligand backbones in cobalt(II)
complexes of types B and C correspond to extended and
contracted structures (Table S2). Typically, the distance in
the extended-Λ complex [Co(H2L2)(AcOEt)(H2O)](ClO4)2
is 9.92 Å, showing that the aromatic moieties lie far away
from each other. In contrast, the equivalent distance in the
contracted-Λred complex [Co(L2)]·[(C3H7)2(C2H5)NH]-
(ClO4) is much shorter (5.68 Å). Because the type D
contracted-Λoxo complexes [Co(L2)]+that is, [Co(L2)]-
(ClO4)·CH3OH and [Co(L2)](CF3SO3)·C2H5OHhave
shorter distances (5.35−5.36 Å) than their reduced analogues
of type C (Table S2), the former type D complexes have
more compressed structures than the latter type C complexes.
The degree of helical twisting is reflected by the torsion angle
formed by the two opposite bonds between the amide carbon
and the α-carbon atoms of the complex (C7−C8−C14−
C16; Table S2). Because the cobalt(III) complex is slightly
more twisted, with a torsion angle of −134° to −137°, than the
cobalt(II) complex (−126°) because of the smaller ionic radius
of the cobalt(III) center, the degree of helical twisting can be
finely tuned by changing the oxidation state of the cobalt center.
Chiroptical Properties and Stepwise Structural Con-
versions of Cobalt Complexes. 1. Helicity Inversion by
to A8f were formed, in which H NMR signals of type B
disappeared and signals around 160, 105, 65, 55, and −50 ppm
of type A newly appeared (Figure S4). Excess NO3 anions
enhanced the intensity of the signals from the type A complex
(see Figure S4) coupled with enhancement of the negative
CD signal (Figure 2), indicating that the equilibrium between
types B and A moved to type A. Although [Co(H2L4)Y2]n+, of
type B, was also generated in situ (see Figure S7d), helicity
−
−
inversion motion was not detected upon the addition of NO3
anions.14
2. Extension/Contraction Motion by Acid−Base Reaction:
Type B ⇄ Type C. The isolated [Co(L1)]8d and [Co(L2)]·
[(C3H7)2(C2H5)NH](ClO4) as well as in situ generated
[Co(L3)] of type C exhibited positive CD signals around
400−450 nm and a negative broad band around 600 nm
(Scheme 3 and Figure S21 and Schemes S1 and S2), while the
in situ generated [Co(L4)] gave similar CD signals with the
opposite sign because of a large blue shift induced by quinoline
coordination (see Scheme S3). These CD spectra changed to
those of the corresponding type B complexes [Co(H2L)Y2]n+
by adding CF3SO3H, as previously reported for the reversible
conversion between [Co(H2L1)(CF3SO3)(H2O)](CF3SO3)
and [Co(L1)].8d These acid/base-triggered extension/contraction
motions of the complexes with H2L1−H2L3 occurred reversibly
but that with H2L4 was not detected because of the rapid oxida-
tion of [Co(L4)] complexes by trace amounts of atmospheric
oxygen.
3. Relaxation/Compression Motion by Redox Reaction:
Type C ⇄ Type D. To choose suitable oxidant and reductant
for the conversion between type C and D complexes, the
redox potentials of isolated type D complexes were measured
by cyclic voltammetry. [Co(L1)](ClO4)·H2O and [Co(L2)]-
(ClO4)·(H2O)2 showed identical cyclic voltammetry behavior
(C ⇄ D) in CH3CN, and their reduction potentials, E1/2, were
measured to be −0.18 V (vs Fc+/Fc) with a cathodic/anodic
peak separation of ca. 200 mV (Figure 3a,b). [Co(L3)](ClO4)·
(H2O)1.5 and [Co(L4)](ClO4)(H2O) exhibited E1/2 values at
−0.58 and −1.00 V (vs Fc+/Fc), respectively, with a peak
separation of 77 mV (see Figure 3c,d), and these E1/2 values are
0.4 and 0.82 V more negative than the values of [Co(L1)]-
(ClO4)·H2O and [Co(L2)](ClO4)·(H2O)2. Ligands H2L3 and
H2L4 have different coordinating atoms at the ortho positions
of their aromatic amide moieties from H2L1 and H2L2 in the
formation of contracted complexes of types C and D. Instead of
two oxygen atoms, H2L3 employs sulfur atoms, which have
softer and larger character, and H2L4 employs quinoline nitrogen
atoms, which have π-acceptor character. These coordination
characters exerted a large influence on the redox properties of the
cobalt complexes.
−
NO3 Coordination: Type B → Type A. The isolated
[Co(H2L1)(CF3SO3)(H2O)](CF3SO3),8d [Co(H2L2)-
(AcOEt)(H2O)](ClO4)2, and [Co(H2L3)(H2O)2](ClO4)2,
of type B, exhibited dynamic helicity inversiontype B →
−
type Aupon the addition of NO3 anions, as we had pre-
viously reported for the cobalt(II) complexes with chiral ligands
of N,N′-ethylenebis[N-methyl-(S)-alanine] amide deriva-
tives.8d−g The helicity inversion around the cobalt(II) center
was characterized by the inversion of the circular dichroism
(CD) signal observed around 530 nm from positive two-
humped signals of type B complexes8d−g to a negative one in a
CH3CN/CHCl3 (1:9) solution of [Co(H2L2)(AcOEt)(H2O)]-
(ClO4)2 or [Co(H2L3)(H2O)2](ClO4)2 (Figures 2 and S20).
The 1H NMR spectrum in CD3CN/CDCl3 (1:9) indicated that
a type A complex and an intermediate in the transition from B
Reversible chemical conversion between types C and D
occurred by sequential treatment with suitable oxidant and
reductant. [Co(L1)]+ and [Co(L2)]+ complexes of type D
were obtained by oxidation of the corresponding [Co(L)] of
type C with AgClO4 or AgCF3SO3,16 while [Co(L3)]+ and
[Co(L4)]+ complexes were prepared from the correspond-
ing in situ generated [Co(L)] complexes with atmospheric
oxygen. For reduction of complex type D, decamethylferrocene
16
FeCp*2 was sufficient for [Co(L1)]+, [Co(L2)]+, and
[Co(L3)]+ complexes, although a stronger reductant, co-
16
baltocene CoCp2 was required for [Co(L4)](ClO4)·H2O
(Figures 4 and S22−S25). [Co(L)]+ gave intense CD signals
due to the strong d−d transition bands (Scheme 3 and
Figure S26 and Schemes S1−S3) compared to [Co(H2L)Y2]n+
Figure 2. CD spectral changes of [Co(H2L2)(AcOEt)(H2O)](ClO4)2
upon the addition of Bu4NNO3 in CH3CN/CHCl3 (1:9) at room
temperature. [complex] = 2.5 × 10−3 mol dm−3.
636
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
a
Scheme 3. Transformation Cycles of Cobalt Complexes with H2L2 in Response to External Stimuli
a
The first cycle begins from the type D contracted-Λoxo [Co(L2)]CF3SO3·H2O complex ([complex] = 2.5 × 10−3 mol dm−3 in CH3CN/CHCl3 =
1/9) reduced by 1 equiv of FeCp*2 to give the type C contracted-Λred [Co(L2)] complex, which provided the type B extended-Λ [Co(H2L2)Y2]n+
complex after the addition of 2 equiv of CF3SO3H. By the addition of 3 equiv of N,N,N′,N′-tetramethyl-1,8-naphthalenediamine (P.S.), the type C
contracted-Λred [Co(L2)] complex was restored. By oxidation with 3.5 equiv of AgCF3SO3, the type D contracted-Λoxo [Co(L2)]+ complex was
reproduced, which then began the second cycle. That cycle was achieved by the successive addition of 3 equiv of FeCp*2, 3 equiv of CF3SO3H,
4 equiv of P.S., and 5 equiv of AgCF3SO3. The third cycle started after the addition of 5 equiv of AgCF3SO3, restoring the type D contracted-Λoxo
[Co(L2)]+ complex. The first, second, and start of the third cycles are shown as green, red, and blue lines, respectively.
Figure 3. Cyclic voltammograms of contracted-Λoxo complexes in
CH3CN at room temperature. [complex] = 1 × 10−3 mol dm−3;
[nBu4NClO4] = 5 × 10−2 mol dm−3. (a) [Co(L1)](ClO4)·H2O;
(b) [Co(L2)](ClO4)·(H2O)2; (c) [Co(L3)](ClO4)·(H2O)1.5; (d)
[Co(L4)](ClO4)·H2O. Scan rate = 50 mV s−1.
(type B) and [Co(L)] (type C), which exhibited particularly
weak CD signals.
4. Stepwise Structural Conversion Cycles of Cobalt
Complexes: Type D → Type C → Type B → Type C →
Type D. By a combination of extension/contraction and
relaxation/compression motions, multiple motion cycles were
efficiently demonstrated in CH3CN/CHCl3 (1:9), as shown
in Schemes 3 and S1−S3, which included the following four
Figure 4. 1H NMR spectra of (a) [Co(L2)](ClO4)·(H2O)2, (b) upon
the addition of 1.1 equiv of FeCp*2, and (c) upon the addition of
2 equiv of CF3SO3H to the solution of part b in CD3CN at room
temperature. [complex] = 2.5 × 10−3 mol dm−3 in CD3CN. *: solvent
and water signals.
637
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
sequential steps: relaxation (D → C); extension (C → B);
contraction (B → C); compression (C → D). This trans-
formation cycle typically started using [Co(L2)](CF3SO3)·
H2O, of type D. Each process could be followed by monitoring
the CD spectral changes. The cobalt(III) complex was first
reduced by 1 equiv of FeCp*2, exhibiting a CD spectrum
identical with that of the isolated [Co(L2)][(C3H7)2(C2H5)-
NH](ClO4) (D → C). The successive addition of 2 equiv
of CF3SO3H gave the extended-Λ [Co(H2L2)Y2]n+, with its
characteristic two-humped CD spectral pattern (C → B). The
addition of 3 equiv of P.S. to the resulting solution provided the
contracted-Λred [Co(L2)] (B → C). By further oxidation with
3.5 equiv of AgCF3SO3, [Co(L2)]+ was reproduced (C → D).
The cycle was repeated again by the addition of 3 equiv of
FeCp*2, 3 equiv of CF3SO3H, 4 equiv of P.S., and 5 equiv of
AgCF3SO3. The regenerated [Co(L2)]+ was demonstrated to
exhibit the same CD signals with an intensity of ca. 90% of
the original [Co(L2)](CF3SO3)·H2O (Scheme 3). The first
half-cycle (D → C → B) starting from [Co(L2)]+ was also
Structural conversion cycles starting from [Co(L3)](ClO4)·
(H2O)1.5 or [Co(L4)](ClO4)·H2O, of type D, were also
demonstrated (D → C → B → C → D), during which CoCp2
and atmospheric oxygen were used as a reductant and an oxidant,
respectively. For the first half of the cycle (D → C → B),
1.5 equiv of CoCp2 and 2 equiv of CF3SO3H were sequentially
added under an argon atmosphere (see Schemes S2 and S3) to
offer the characteristic CD spectra of extended-Λ [Co(H2L)Y2]n+
(L = L3 and L4), which were identical with the CD spectra of
the isolated [Co(H2L3)(H2O)2](ClO4)2 (see Figure S19) and in
situ generated [Co(H2L4)Y2]n+ systems. For the second half-
cycle (B → C → D), the contracted-Λred [Co(L3)] was restored
by the addition of 3 equiv of P.S. to the resulting solution
containing [Co(H2L3)Y2]n+. Subsequent oxidation by atmos-
pheric oxygen provided the blue contracted-Λoxo [Co(L3)]+
complex, the CD spectrum of which overlapped with the
initial [Co(L3)](ClO4)·(H2O)1.5, after 12 h of stirring. When
the extended-Λ [Co(H2L4)Y2]n+ complex was employed, the
presence of contracted-Λred [Co(L4)] was not detected,
probably because of its very high susceptibility to oxidation.
The recorded CD spectrum turned out to have a shape similar
to that of the original contracted-Λoxo [Co(L4)](ClO4)·H2O
solution after 4 h of autooxidation. This means that [Co(L4)]
was oxidized roughly 3 times faster than the corresponding
[Co(L3)]. The D → C → B conversions of [Co(L3)](ClO4)·
(H2O)1.5 and [Co(L4)](ClO4)·H2O were also monitored by
1H NMR spectroscopy in CD3CN (see Figures S24 and S25).
Redox-Triggered One-Step Structural Conversion
Including Multiple Molecular Motions. 1. Redox-Triggered
Extension/Contraction Motion: Type D ⇄ Type B. The
successive addition of 2 equiv of CF3SO3H, followed by a
suitable reductant, to the type D [Co(L)]+ solution gave
[Co(H2L)Y2]n+ of type B, during which [Co(L)] of type C was
skipped (D → B; Figures 5 and S27 and S28). 1H NMR spectra
of [Co(L2)](ClO4)·(H2O)2 in the presence of 2 equiv of
CF3SO3H showed the partial formation of an unknown species
in the diamagnetic region (Figure 5b, left) and [Co(H2L2)Y2]n+
of type B in the paramagnetic region, indicating that the
[Co(L2)]+ complex was partially decomposed, allowing
1
monitored by H NMR (Figure 4) and ESI-MS (Figure S34)
1
spectroscopies. The H NMR spectrum of [Co(L2)]+ changed
to the spectrum identical with the isolated [Co(L2)] of type C
(see Figure S9b) and to the extended-Λ [Co(H2L2)Y2]n+ of
type B (see Figure S7b) by the successive addition of FeCp*2
and CF3SO3H. The ESI-MS peak cluster at m/z 499,
corresponding to [Co(L2)]+, decreased and a new peak cluster
at m/z 500 appeared upon the addition of 1.1 equiv of FeCp*2.
Upon the successive addition of CF3SO3D, new peak clusters
at m/z 650, corresponding to [Co(H2L2) + (CF3SO3)]+, and at
m/z 500, corresponding to [Co(H2L2) − H]+, appeared,
in which a deuterated peak cluster was not clearly observed.
High-resolution ESI-MS strongly supported the D → C → B
transformation. The second half-cycle (B → C → D) is
described in the synthesis of [Co(L2)](ClO4)·(H2O)2 and
[Co(L2)](CF3SO3)(H2O) (see the Supporting Information,
Experimental Section). The transformation cycle of [Co(L1)]-
(ClO4)·(H2O) was similarly carried out (see Scheme S1 and
Figure S22) because [Co(L1)]+ showed the same redox
potential as that of [Co(L2)]+ (Figure 3).
Figure 5. 1H NMR spectra of (a) [Co(L2)](ClO4)·(H2O)2 (left) and [Co(L3)](ClO4)·(H2O)1.5 (right) in CD3CN at room temperature, (b) upon
the addition of 2 equiv of CF3SO3H, and (c) after the addition of 1.2 equiv of FeCp*2 for the former complex and CoCp2 for the latter complex.
[complex] = 1 × 10−2 mol dm−3. *: solvent signals.
638
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
Figure 6. CD (left) and 1H NMR (right) spectra of (a) [Co(L2)](ClO4)·(H2O)2 in CH3CN/CHCl3 (CD3CN/CDCl3) = 1/9 at room temperature
with [complex] = 2.5 × 10−3 (1 × 10−2) mol dm−3, (b) upon the addition of 10 equiv (5 equiv) of Bu4NNO3, 2 equiv of CF3SO3H, and 1.3 equiv of
+
■
FeCp*2, and (c) after the addition of 3 equiv of P.S. (NEt3) and 1.5 equiv of AgClO4 (AgNO3) to part b. : signals of [Co(L2)] ,
[Co(H2L2)(NO3)]+, and [Co(L2)]+, respectively. *: solvent signals.
autoreduction to the extended type B complex. A similar
When Bu4NNO3 (10 equiv in the CD experiment and 5 equiv
for H NMR measurement), CF3SO3H (2 equiv), and the
1
phenomenon was observed for [Co(L1)](ClO4)·H2O. How-
1
reductant FeCp*2 (1.3 equiv) were added to a CH3CN/CHCl3
or CD3CN/CDCl3 (1:9) solution of [Co(L2)](ClO4)·(H2O)2
of type D, the observed CD spectrum changed, becoming
identical with that of in situ generated type A [Co(H2L2)-
ever, the H NMR signals of [Co(L3)](ClO4)·(H2O)1.5 were
shifted slightly in the presence of CF3SO3H, which is pro-
bably due to the interaction of H+ with amide oxygen atoms
(Figure 5b, right). Despite these complexities, the addition of
reductant quantitatively provided type B complexes directly
from the corresponding type D complexes (Figure 5c, right).
When [Co(L4)]+ was employed as a starting complex, the
order of the added external stimuli should be carefully chosen
(CoCp2 and then CF3SO3H) to offer consecutive CD and
1H NMR spectral changes (D → C → B; see Figure S25 vs
Figure S28). The reverse motion (B → D) was demonstrated
in the syntheses of [Co(L3)](ClO4)·(H2O)1.5 and [Co(L4)]-
(ClO4)·H2O, which were obtained directly from the corre-
sponding cobalt(II) extended-Λ complexes of type B (see
Scheme 2 and the Experimental Section).
1
(NO3)]+ (Figure 6b, left, vs Figure 2). The observed H NMR
spectrum was also consistent with that of [Co(H2L2)(NO3)]+
(Figure 6b, right, vs Figure S4(b-2)). The addition of an organic
base and an oxidant to the above-described reaction mixture
achieved the opposite conversion directly (A → D). When
3 equiv of P.S. and 1.5 equiv of AgClO4 were added under an
ambient atmosphere, the recorded CD spectrum was identical
with that of the initial solution of [Co(L2)](ClO4)·(H2O)2
1
(Figure 6c vs Figure 6a). The H NMR spectrum of the
starting [Co(L2)]+ was also reachieved by mixing triethylamine
and AgNO3 into the above reaction solution (Figure 6c vs
Figure 6a). Although the type D [Co(L1)](ClO4)·H2O and
[Co(L3)](ClO4)·(H2O)1.5 complexes similarly exhibited D → A
and A → D direct jumps, the A → D process for the
[Co(L3)](ClO4)·(H2O)1.5 complex was more simple. After
the addition of an organic base, the vial was simply opened
to deliver atmospheric oxygen, resulting in oxidation of the
cobalt(II) center (see Figures S30−S33).
2. Redox-Triggered Helicity Inversion: Type D ⇄ Type A.
After demonstrating redox-triggered extension/contraction
motions, as described in the previous section, we examined
redox-triggered one-step structural conversion from type D
contracted-Λoxo [Co(L)]+ to type A extended-Δ [Co(H2L)-
(NO3)]+, including extension/contraction and helicity inversion,
because the addition of 2 equiv of organic base to solutions of
type A [Co(H2L)(NO3)]+ complexes also produced [Co(L)]
(L = L1−L3), of type C, quantitatively (A → C; see Figures
S10−S12). When 2 equiv of CF3SO3H and excess Bu4NNO3
were added to a CH3CN/CHCl3 (1:9) solution of [Co(L)]+,
the CD spectra did not change significantly (see Figure S29),
indicating that [Co(L)]+ complexes were stable in the presence
CONCLUSIONS
■
Herein, we have successfully demonstrated redox-triggered
dynamic molecular motion systems using chiral cobalt complexes.
The chiral ligands H2L1−H2L4 worked as tetradentate ligands
under neutral conditions to form mononuclear cobalt(II)
complexes with extended-Λ cis-α-helical structures of type B,
which then switched to contracted forms of type C via
coordination isomerism of the amide linkage (O-coordination
−
of both H+ and NO3 anions. A direct jump from D to A and
vice versa, in which the complexes of types C and B were
skipped, could be performed as follows.
639
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
N,N′-Ethylenebis[N-methyl-(S)-alanine 2-methoxyphenylamide]
(H2L2; 1.19 g, 62.2%).
to N-coordination) coupled with coordination of heteroatoms
at ortho-substituted aromatics under basic conditions. The
contracted complexes were further oxidized to the cobalt(III)
state of type D, which were kinetically stable when CF3SO3H
−
and/or NO3 anions were added. The structures of the
contracted cobalt(III) complexes jumped to type C, B, or A
by reduction of the cobalt(III) center in the presence of a
suitable combination of external stimuli. Each cobalt(II)
complex could be switched back to the contracted cobalt(III)
complex by the addition of an organic base and a suitable
oxidant. These redox reactions of the metal center allow
switching between the frozen and thawed states of molecular
structures. In the frozen state [i.e., the cobalt(III) state], the
structure is quite stable, while in the thawed state [i.e., the
cobalt(II) state], the structure is labile and can adopt required
conformations in response to a suitable combination of external
stimuli. This phenomenon is a kind of “AND” logic gate system
consisting of redox and other stimuli as observed in biological
systems.17
A solution of N,N′-ethylenebis[N-methyl-(S)-alanine] (1.00 g, 4.31 mmol)
and 1-hydroxybenzotriazole hydrate (HOBt·H2O; 1.45 g, 9.46 mmol)
in N,N-dimethylformamide (DMF; 60 mL) was cooled to 0 °C
and stirred for 45 min. Next, a precooled solution of 1-ethyl-3-[3-
(dimethylamino)propyl]carbodiimide hydrochloride (WSC·HCl; 1.81 g,
9.46 mmol) in DMF (90 mL) was added. The mixture was stirred for
30 min at 0 °C, and then 2-methoxyaniline (1.165 g, 9.460 mmol) was
added to the solution. The resulting mixture was further stirred
overnight, during which time the temperature of the solution was
allowed to rise to room temperature. DMF was removed under
vacuum, and the residue was dissolved in CHCl3 (30 mL) and washed
with a saturated Na2CO3 aqueous solution (10 mL × 3). The organic
layer was dried over anhydrous Na2SO4. The solvent was removed on a
rotary evaporator, and the crude product was recrystallized from
EXPERIMENTAL SECTION
methanol to give colorless crystals (yield: 1.19 g, 62.2%). H and 13C
■
1
Measurements. NMR spectra were recorded on a JEOL LA-300
or -400 FT-NMR spectrometer at ca. 25 °C. MS spectra were obtained
with a JEOL JMS-700T or a AccuTOF LC-plus 4G spectrometer.
The polarization degrees and melting points were recorded with Jasco
DIP-370 and Yanako MP-J3 devices, respectively. UV−vis and CD
spectra were recorded on Jasco U-670 and Jasco J-820 spectrophoto-
meters, respectively. IR spectra were collected using a Jasco FT/
IR-4100 spectrometer equipped with an ATR Pro450-S with a ZnSe
prism. Cyclic voltammetry was performed with an ALS 611CA
electrochemical analyzer. Cyclic voltammograms were recorded using
a glassy carbon working electrode, a platinum counter electrode, and
a Ag/AgCl reference electrode.
NMR spectra indicated the stereochemical purity to be greater than
98% d.e. Mp: 108−109 °C (from CH3OH). [α]D20 = +100 (c = 0.221
1
in CHCl3). H NMR (400 MHz, CDCl3): δ 9.82 (s, 2H, NH), 8.40
(dd, J = 2.0 and 7.7 Hz, 2H, 3- or 6-Ar), 6.93 (td, J = 1.9 and 7.6 Hz,
2H, 4- or 5-Ar), 6.90 (td, J = 1.5 and 7.8 Hz, 2H, 4- or 5-Ar), 6.66 (dd,
J = 1.6 and 7.7 Hz, 2H, 3- or 6-Ar), 3.68 (s, 6H, OCH3), 3.39 (q, J =
7.0 Hz, 2H, α-H), 2.66 (m, 2H, ethylene), 2.56 (m, 2H, ethylene), 2.29
(s, 6H, NCH3), 1.31 (d, J = 7.0 Hz, 6H, β-CH3). 13C NMR (100 MHz,
CDCl3): δ 171.7 (CO), 148.1 (Ar), 127.4 (Ar), 123.4 (Ar), 120.7
(Ar), 119.2 (Ar), 109.7 (Ar), 64.8 (α-C), 55.4 (ethylene), 39.1
(NCH3), 8.8 (β-CH3). FAB-MS (NBA): m/z 443.2. Calcd for
[C24H35N4O4]+: m/z 443.3. Anal. Calcd (found) for C24H34N4O4:
C, 65.14 (65.18); H, 7.74 (7.80); N, 12.66 (12.66). IR (ATR, cm−1):
νmax 3332 (s, NH), 1693 (s, CO).
Crystallographic Studies. All crystals were mounted in inert
oil and transferred to the cold gas stream of the diffractometer
(−173 °C). Their X-ray diffraction data were collected by a Rigaku/
MSC Mercury CCD diffractometer with graphite-monochromated Mo
Kα radiation (λ = 0.71070 Å) to a 2θ maximum of 55.0°. Data were
processed on a PC using CrystalClear software (Rigaku). The crystal
structures were solved by direct methods (Sir-9718) and refined by full-
matrix least squares on F2 using SHELXL-9719) on Yadokari-GX 2009
software.20 All hydrogen atoms were placed on ideally geometrical
positions. Non-hydrogen atoms were refined anisotropically. The
absolute configuration of the complex was determined by the con-
figuration of the ligand and Flack parameter. Crystals suitable for X-ray
analyses were grown from complex solutions in solvents presented in
Table S1.
N,N′-Ethylenebis[N-methyl-(S)-alanine 2-methylthiophenylamide]
(H2L3; 363 mg, 35%).
A solution of 7-aza-1-hydroxy-1,2,3-benzotriazole (HOAt; 292 mg,
2.15 mmol), O-(7-azabenzotriazol-1-yl)-1,1,3,3-tetramethyluronium
hexafluorophosphate (HATU; 1.64 g, 4.30 mmol), and N,N′-
diisopropylethylamine (DIEA; 1.11 g, 8.60 mmol) in DMF (25 mL)
was added at 0 °C to a suspension of N,N′-ethylenebis[N-methyl-(S)-
alanine] (500 mg, 2.15 mmol) in DMF (25 mL). After the mixture was
stirred at 0 °C for 30 min, 2-methylthioaniline (599 mg, 4.30 mmol)
was added, and the solution was stirred for an additional 72 h. DMF
was removed under vacuum, and the residue was dissolved in CHCl3
(15 mL) and washed with a saturated Na2CO3 aqueous solution
(3 mL × 3). The organic layer was dried over anhydrous Na2SO4. The
solvent was removed on a rotary evaporator, and the crude product
was purified by silica gel column chromatography (50 g of SiO2;
CHCl3/AcOEt/hexane = 50/6/15) to give 124 mg (12% yield) of
a white solid (97% d.e.) and 431 mg (42% yield) of a fraction
contaminated with the meso diastereomer (89% d.e). The chiral ligand
H2L3 in the contaminated fraction (89% d.e.) was isolated by metal
complexation. Crude ligand H2L3 (89% d.e.; 431 mg, 0.908 mmol) in
Synthesis of Chiral Ligands. N,N′-Ethylenebis[N-methyl-(S)-
alanine 2,5-dimethoxyphenylamide] (H2L1).
H2L1 was prepared as described previously.8d
640
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
CH3OH (45 mL) and Co(ClO4)·6H2O (332 mg, 0.908 mmol) in
CH3OH (5 mL) were combined and stirred for 1 h, and then the
pink solution was evaporated to dryness. The crude product was
recrystallized from a mixture of CHCl3 (15 mL)/AcOEt (30 mL) to
give 566 mg of a pink crystalline [Co(H2L3)(H2O)2](ClO4)2·H2O
complex. The complex was destroyed by the addition of a 0.5 M
H2SO4 solution (10 mL). Then the pH was adjusted to ca. 8−9 by the
addition of a saturated Na2CO3 aqueous solution. The released ligand
was extracted with CHCl3 (5 mL × 3). The green CHCl3 solution was
dried over Na2SO4 and evaporated to dryness to give a green glassy
solid, which was purified twice by column chromatography (5 g of
SiO2; CHCl3/CH3OH = 45/1) to give 239 mg (23% yield calculated
from the initial amount of N,N′-ethylenebis[N-methyl-(S)-alanine)])
of H2L3 as a white solid (97% d.e). Mp: 84−85 °C (from CH2Cl2/
[Co(L1)]. This complex was prepared as described previously.8d
[Co(L1)](ClO4)·H2O (69.6 mg 77%). Solid AgClO4 (30.2 mg,
0.146 mmol) was added to a solution of the [Co(L1)] complex
(74.4 mg, 0.133 mmol) in CH2Cl2 (20 mL). The mixture was
vigorously stirred for 24 h. The suspension was evaporated to dryness
and dissolved in CH3CN (10 mL). The silver precipitate was removed
by filtration. The filtrate was evaporated to dryness and dissolved
in a mixture of CH3OH (5 mL)/C2H5OH (10 mL). Fractional
recrystallization resulted in dark-green crystals, which were filtered,
washed with cold C2H5OH, and dried under vacuum. Yield: 69.6 mg
22
(77%). Mp: >270 °C (from C2H5OH). [α]D = +338 (c = 0.214 in
CH3CN). 1H NMR (400 MHz, CD3CN, 298 K): δ 8.74 (d, J = 3.1 Hz,
2H, Ar), 7.04 (d, J = 9.2 Hz, 2H, Ar), 6.67 (dd, J = 3.1 and 9.2 Hz, 2H,
Ar), 3.87 (s, 6H, p-OCH3), 3.41 (q, J = 7.1 Hz, 2H, α-H), 3.35 (s, 6H,
o-OCH3), 2.96 (m, 2H, ethylene), 1.96 (m, 2H, ethylene), 1.66 (s, 6H,
NCH3), 1.36 (d, J = 7.0 Hz, 6H, β-CH3); FAB-MS (NBA): m/z 559.0
{[Co(C26H36N4O6)]+). Anal. Calcd (found) for CoC26H38N4O11Cl:
C, 46.13 (46.23); H, 5.66 (5.57); N, 8.28 (8.20). CD [CH3CN
(2.5 mM), 298 K, λmax/nm (Δε/dm3 mol−1 cm−1)]: 761 (2.56), 621.5
(−14.76), 385 (17.46), 311 (−22.78), 289 (26.20), 255 (−52.19),
236.5 (11.09), 224 (1.87). IR (ATR, cm−1): νmax 1618 (s, CO).
[Co(L1)](CF3SO3)·[(CH3)2CHOH]0.5 (81.5 mg, 84%). Solid
AgCF3SO3 (37.4 mg, 0.146 mmol) was added to a solution of the
[Co(L1)] complex (74.0 mg, 0.132 mmol) in CH2Cl2 (10 mL). The
mixture was vigorously stirred for 48 h. The suspension was
evaporated to dryness and dissolved in CH3CN (10 mL). The silver
precipitate was removed by filtration. The filtrate was evaporated to
dryness and dissolved in a mixture of C2H5OH (4 mL)/2-C3H7OH
(4 mL). Fractional recrystallization resulted in dark-green crystals,
which were filtered, washed with cold 2-C3H7OH, and dried under
21
1
hexane). [α]D = +40.4 (c = 0.208 in CHCl3). H NMR (400 MHz,
CDCl3): δ 10.16 (s, 2H, NH), 8.31 (dd, J = 1.2 and 8.2 Hz, 2H, 3- or
6-Ar), 7.34 (dd, J = 1.4 and 7.8 Hz, 2H, 3- or 6-Ar), 7.22 (ddd, J = 1.4,
7.8, and 8.2 Hz, 2H, 4- or 5-Ar), 7.02 (td, J = 1.2 and 7.6 Hz, 2H, 4- or
5-Ar), 3.45 (q, J = 7.0 Hz, 2H, α-H), 2.80 (m, 4H, ethylene), 2.35 (s,
6H, SCH3 or NCH3), 2.33 (s, 6H, NCH3 or SCH3), 1.32 (d, J =
7.0 Hz, 6H, β-CH3). 13C NMR (100 MHz, CDCl3): δ 172.1 (CO),
137.7 (Ar), 131.3 (Ar), 128.1 (Ar), 125.9 (Ar), 124.1 (Ar), 120.2 (Ar),
64.3 (α-C), 53.7 (ethylene), 38.7 (NCH3), 18.1 (SCH3), 9.4 (β-CH3).
FAB-MS (NBA): m/z 475.2. Calcd for [C24H35N4S2O2]+: m/z
475.2. Anal. Calcd (found) for C24H34N4S2O2: C, 60.73 (61.03);
H, 7.22 (7.31); N, 11.80 (11.55). IR (ATR, cm−1): νmax 3231 (m, NH),
1682 (s, CO).
N,N′-Ethylenebis[N-methyl-(S)-alanine 8-quinolineamide] (H2L4;
704 mg, 68%).
1
vacuum. Yield: 81.5 mg (84%). The H NMR spectrum is identical
with that of [Co(L1)](ClO4)(H2O). FAB-MS (NBA): m/z 559.3
{[Co(C26H36N4O6)]+}. Anal. Calcd (found) for CoC28.5H40N4O9.5F3S:
C, 46.34 (46.44); H, 5.46 (5.71); N, 7.59 (7.28). IR (ATR, cm−1):
νmax 1644 (m, CO).
[Co(H2L2)(AcOEt)(H2O)](ClO4)2 (148 mg, 85.1%). A solution of
ligand H2L2 (95.5 mg, 0.216 mmol) in CH3OH (2 mL) and a solution
of Co(ClO4)2·6H2O (79.0 mg, 0.216 mmol) in CH3OH (in 2 mL)
were combined and stirred for 1 h. Next, the solution was evaporated
to dryness, and the crude product was recrystallized from a mixture of
CH2Cl2 (5 mL)/AcOEt (15 mL) to give pink crystals. Yield: 148 mg
A solution of HOAt (292 mg, 2.15 mmol), HATU (1.64 g,
4.30 mmol), and DIEA (1.11 g, 8.60 mmol) in DMF (25 mL) was
added at 0 °C to a suspension of N,N′-ethylenebis[N-methyl-(S)-
alanine] (500 mg, 2.15 mmol) in DMF (25 mL). The mixture was
stirred at 0 °C for 30 min. Next, 8-aminoquinoline (620 mg, 4.30 mmol)
was added to the solution, which was stirred for an additional 36 h.
DMF was removed under vacuum, and the residue was dissolved in
CHCl3 (15 mL) and washed with a saturated Na2CO3 aqueous solution
(3 mL × 3). The organic layer was dried over anhydrous Na2SO4. The
solvent was removed on a rotary evaporator, and the crude product was
purified by silica gel column chromatography (50 g of SiO2; CHCl3/
AcOEt = 5/1) and then recrystallized from CH3OH to give 704 mg
of yellowish crystals (68% yield). 1H and 13C NMR spectra indicated the
stereochemical purity to be greater than 98% d.e. Mp: 132−133 °C
(from CH2Cl2/hexane). [α]D20 = +178 (c = 0.209 in CHCl3). 1H NMR
(400 MHz, CDCl3): δ 11.30 (s, 2H, NH), 8.61 (dd, J = 1.7 and 4.2 Hz,
2H, 1-Ar), 8.26 (dd, J = 3.5 and 5.5 Hz, 2H, 7-Ar), 7.84 (dd, J = 1.7 and
8.3 Hz, 2H, 4-Ar), 7.26 (dd, J = 4.4 and 8.1 Hz, 2H, 3-Ar), 7.15 (d, J =
5.6 Hz, 2H, 5-Ar), 7.14 (t, J = 2.1 Hz, 2H, 3-Ar), 3.54 (q, J = 7.1 Hz, 2H,
α-H), 3.08 (m, 2H, ethylene), 2.78 (m, 2H, ethylene), 2.43 (s, 6H,
NCH3), 1.40 (d, J = 6.8 Hz, 6H, β-CH3). 13C NMR (100 MHz,
CDCl3): δ 172.3 (CO), 148.2 (Ar), 138.2 (Ar), 135.5 (Ar), 134.0
(Ar), 127.4 (Ar), 126.5 (Ar), 121.3 (Ar) 121.0 (Ar), 115.5 (Ar), 64.8
(α-C), 52.1 (ethylene), 39.7 (NCH3), 8.6 (β-CH3). FAB-MS (NBA):
m/z 485.2. Calcd for [C28H33N6O2]+: m/z 485.3. Anal. Calcd (found)
for C28H32N6O2: C, 69.40 (69.25); H, 6.66 (6.64); N, 17.34 (17.30).
IR (ATR, cm−1): νmax 3278 (m, NH), 1682 (s, CO).
23
(85.1%). Mp: 125−126 °C (from CH2Cl2/AcOEt). [α]D = +30.9
(c = 0.204 in CH3CN). 1H NMR (400 MHz, CD3CN, 298 K): δ 145.1
(2H), 95.0 (2H), 80.2 (2H), 55.2 (2H), 43.3 (6H), 18.4 (2H), 15.5
(2H), 14.8 (2H), 12.8 (6H), 6.7 (6H), −33.7 (2H). FAB-MS (NBA):
m/z 600.1 ({[Co(C24H34N4O4)](ClO4)}+), 500.2 ({[Co-
(C24H34N4O4)]−1H}+). Anal. Calcd (found) for CoC28H44N4O15Cl:
C, 41.91 (41.70); H, 5.48 (5.50); N, 6.94 (6.95). CD [CH3CN
(2.5 mM), 298 K, λmax/nm (Δε/dm3 mol−1 cm−1)]: 1064.5 (−0.35),
539.5 (0.34), 527 (0.30), 512 (0.41), 471 (−0.16), 435.5 (0.02), 290.5
(−5.08), 274 (−4.03), 255 (−8.79), 234 (−3.75). IR (ATR, cm−1):
νmax 3400 (w, NH), 1624 (s, CO).
[Co(L2)]·[(C3H7)2(C2H5)NH](ClO4) (162 mg, 77%). A solution of
ligand H2L2 (128 mg, 0.29 mmol) in C2H5OH (1 mL) and a solution
of Co(ClO4)2·6H2O (117 mg, 0.319 mmol) in C2H5OH (1 mL) were
combined and stirred for 1 h. After that time, a C2H5OH solution of
DIEA (944 μL of a 1.84 mol dm−3 solution, 1.74 mmol) was added.
The solution was left for 24 h to grow green crystals, which were
filtered, washed several times with cold C2H5OH, and dried under
vacuum (90 mg). The filtrate was concentrated twice to deliver
an additional portion of green crystals (71.7 mg). Combined yield:
23
161.7 mg (77%). Mp: 219−220 °C (from C2H5OH). [α]D = +134
(c = 0.234 in CH3CN). 1H NMR (400 MHz, CD3CN, 298 K): δ 100.4
(2H), 82.6 (2H), 50.2 (2H), 42.4 (6H), 11.3 (2H), 0.0 (2H), −15.2
(6H), −23.3 (2H), −31.8 (6H), −67.0 (2H). FAB-MS (NBA):
m/z 500.3 {[Co(C24H33N4O4)]+}. Anal. Calcd (found) for
CoC32H52N5O8Cl: C, 52.71 (52.88); H, 7.19 (7.22); N, 9.60 (9.55).
CD [CH3CN (2.5 mM), 298 K, λmax/nm (Δε/dm3 mol−1 cm−1)]:
926.5 (0.80), 724 (−0.01), 622 (−0.40), 523.5 (0.04), 474 (−0.10),
Synthesis of Chiral Cobalt Complexes. Caution! Perchlorate
salts of transition-metal complexes with organic ligands are potentially
explosive. Only small quantities should be prepared, and the samples
should be handled with great care.
641
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
431.5 (0.54), 348 (0.97), 305 (−2.37), 278 (3.57), 260 (−11.29), 236
(11.73). IR (ATR, cm−1): νmax 1615 (m, CO).
and 8.6 Hz, 2H, Ar), 7.18 (ddd, J = 1.2, 7.1, and 8.1 Hz, 2H, Ar),
4.20 (q, J = 6.7 Hz, 2H, α-H), 3.05 (m, 2H, ethylene), 2.53 (m, 2H,
ethylene), 2.28 (s, 6H, SCH3 or NCH3), 1.98 (s, 6H, SCH3 or NCH3),
1.44 (d, J = 6.8 Hz, 6H, β-CH3). FAB-MS (NBA): m/z
531.1 {[Co(C24H32N4S2O2)]+}. Anal. Calcd (found) for
CoC24H35N4O7.5ClS2: C, 43.80 (43.71); H, 5.36 (5.07); N, 8.51
(8.37). CD [CH3CN (2.5 mM), 298 K, λmax/nm (Δε/dm3 mol−1 cm−1)]:
696 (5.70), 575 (−19.78), 486.5 (−0.37), 407.5 (−9.17), 349.5 (22.68),
313.5 (3.59), 292 (11.05), 267 (−28.74), 248.5 (−1.48), 233 (−48.85).
IR (ATR, cm−1): νmax 1626 (s, CO).
[Co(L2)](ClO4)·(H2O)2 (179.6 mg, 61%). A solution of ligand H2L2
(206.8 mg, 0.4673 mmol) in CH3OH (5 mL) and a solution of
Co(ClO4)2·6H2O (171 mg, 0.467 mmol) in CH3OH (5 mL) were
combined and stirred for 30 min. After that time, a CH3OH solution
of DIEA (2.80 mL of a 1.00 mol dm−3 solution, 2.80 mmol) was
added. The solution was stirred for 2 h and left overnight. Next, it was
evaporated to dryness and dissolved in CH2Cl2 (25 mL). Solid
AgClO4 (107 mg, 0.514 mmol) was added, and the mixture was stirred
for 24 h. The suspension was evaporated to dryness and dissolved in
10 mL of CH3CN. The silver precipitate was removed by filtration.
The filtrate was concentrated to ca. 5, and 5 mL of CH3OH was
added. The solution was concentrated once again to ca. 5 mL, and
the dark-green crystalline precipitate was filtered, washed with cold
CH3OH, and dried under vacuum. Yield: 179.6 mg (61%). Mp:
[Co(L4)](ClO4)·H2O (35.5 mg, 38%). Ligand H2L4 (69.6 mg,
0.144 mmol) and Co(ClO4)2·6H2O (57.8 mg, 0.158 mmol) were
dissolved in CH3CN (5 mL) and stirred for 30 min. A solution of
triethylamine (58.1 mg, 0.576 mmol) in CH3CN (2 mL) was added,
and the mixture was stirred for 24 h. The solution was evaporated
to dryness and recrystallized from EtOH (8 mL). The precipitate
was discarded, and the filtrate was left for 1 day. The needle-shaped
crystals were also discarded, and brown cubic crystals appeared from
the filtrate after 2 days, which were then collected. Yield: 35.5 mg
22
>270 °C (from CH3OH/CH3CN). [α]D = +286 (c = 0.227 in
CH3CN). 1H NMR (400 MHz, CD3CN, 298 K): δ 9.16 (d, J = 8.0 Hz,
2H, Ar), 7.31 (m, 2H, Ar), 7.15 (m, 2H, Ar), 7.14 (m, 2H, Ar), 3.41
(q, J = 7.0 Hz, 2H, α-H), 3.40 (s, 6H, o-OCH3), 2.99 (m, 2H,
ethylene), 1.95 (m, 2H, ethylene), 1.63 (s, 6H, NCH3), 1.36 (d, J =
7.0 Hz, 6H, β-CH3). FAB-MS (NBA): m/z 499.2 {[Co(C24H32N4O4)]+).
Anal. Calcd (found) for CoC24H36N4O10Cl: C, 45.40 (45.50); H,
5.71 (5.43); N, 8.82 (8.57). CD [CH3CN (2.5 mM), 298 K, λmax/nm
(Δε/dm3 mol−1 cm−1)]: 762.5 (1.45), 621.5 (−12.09), 470.5 (3.07),
367 (13.88), 302 (−4.08), 279.5 (19.07), 255 (−63.53), 221 (37.4).
IR (ATR, cm−1): νmax 1625 (s, CO).
23
(38%). Mp: >270 °C (from C2H5OH). [α]D = −56.7 (c = 0.220 in
1
CH3CN). H NMR (400 MHz, CD3CN, 298 K): δ 9.29 (dd, J = 1.0
and 7.8 Hz, 2H, Ar), 8.35 (dd, J = 1.2 and 8.3 Hz, 2H, Ar), 7.83 (t, J =
8.0 Hz, 2H, Ar), 7.73 (d, J = 4.7 Hz, 2H, Ar), 7.62 (dd, J = 1.0 and
8.2 Hz, 2H, Ar), 7.35 (dd, J = 5.3 and 8.4 Hz, 2H, Ar), 3.36 (m, 2H),
3.20 (m, 2H), 2.49 (m, 2H), 2.13 (s, 6H), 1.74 (s, 6H, NCH3),
1.35 (d, J = 7.0 Hz, 6H, β-CH3). FAB-MS (NBA): m/z 541.2
{[Co(C28H30N6O2)]+}. Anal. Calcd (found) for CoC28H32N6O7Cl:
C, 51.31 (51.03); H, 4.84 (4.89); N, 12.66 (12.75). CD [CH3CN
(2.5 mM), 298 K, λmax/nm (Δε/dm3 mol−1 cm−1)]: 616 (1.69),
525 (−6.98), 389.5 (11.18), 333.5 (−1.29), 305 (−9.96), 274 (83.26),
250 (−49.06), 241.5 (−28.78), 233.5 (−58.70). IR (ATR, cm−1):
νmax 1628 (s, CO).
[Co(L2)](CF3SO3)·H2O (95.8 mg, 62%). A solution of ligand H2L2
(102 mg, 0.231 mmol) in CH3OH (3 mL) and a solution of
Co(CF3SO3)2·5.2H2O (104 mg, 0.231 mmol) in CH3OH (2 mL)
were combined and stirred for 30 min. After that time, a CH3OH
solution of DIEA (503 μL, 0.925 mmol) in CH3OH (C = 1.84 mol
dm−3) was added. The solution was stirred for 2 h and left overnight.
Next, the solution was evaporated to dryness and dissolved in CH2Cl2
(15 mL), and solid AgCF3SO3 (71.3 mg, 0.278 mmol) was added.
The mixture was stirred for 24 h. The suspension was evaporated to
dryness and dissolved in 10 mL of C2H5OH. The silver precipitate
was removed by filtration. The filtrate was concentrated to ca. 5 mL,
and the dark-green crystalline precipitate was filtered, washed with
cold C2H5OH, and dried under vacuum. Yield: 95.8 mg (62%). The
1H NMR spectrum was identical with that of the [Co(L2)](ClO4)·
(H2O)2 complex. FAB-MS (NBA): m/z 499.3 {[Co(C24H32N4O4)]+}.
Anal. Calcd (found) for CoC25H34N4O8F3S: C, 45.04 (45.08); H,
5.14 (5.34); N, 8.41 (8.16). IR (ATR, cm−1): νmax 1628 (s, CO).
[Co(H2L3)(H2O)2](ClO4)2 (374 mg, 82%). A solution of ligand
H2L3 (282 mg, 0.594 mmol) in CH3OH (4 mL) and a solution of
Co(ClO4)2·6H2O (217 mg, 0.594 mmol) in CH3OH (6 mL) were
combined and stirred for 1 h. Next, the solution was evaporated
to dryness. The crude product was recrystallized from a mixture of
CHCl3 (10 mL)/C2H5OAc (20 mL) to give pink crystals. Yield: 374
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.inorgchem.5b01902.
■
S
X-ray crystallographic data in CIF format of [Co(H2L2)-
(C4H8O2)(H2O)](ClO4)2 (CCDC 1034665), [Co-
(H2L3)(H2O)2](ClO4)2·H2O (CCDC 1034666), [Co-
(L2)]·[C8H19NH](ClO4) (CCDC 1034668), [Co(L1)]-
( C F 3 S O 3 ) · C 3 H 7 O H ( C C D C 1 0 3 4 6 6 7 ) ,
[Co(L2)](ClO4)·CH3OH (CCDC 1034670), [Co-
(L2)](CF3SO3)·C2H5OH (CCDC 1034669), [Co(L3)]-
(ClO4)·CHCl3 (CCDC 1034671), and [Co(L4)]-
(ClO4)·H2O (CCDC 1034672) (CIF)
1H NMR, CD, and ESI-MS and FAB-MS spectra (PDF)
23
mg (82%). Mp: 159−160 °C (from CHCl3/AcOEt). [α]D = +24.7
AUTHOR INFORMATION
Corresponding Author
*E-mail: miyake@sci.osaka-cu.ac.jp. Fax/Tel: +81 6 6605 3124.
(c = 0.208 in CH3CN). 1H NMR (400 MHz, CD3CN, 298 K): δ 144.8
(2H), 96.0 (2H), 81.2 (2H), 52.3 (2H), 43.3 (6H), 17.5 (2H),
17.1 (2H), 14.4 (2H), 9.6 (6H), 8.4 (6H), −32.5 (2H). FAB-MS
(NBA): m/z 632.0 ({[Co(C24H34N4S2O2)](ClO4)}+), 532.1
({[Co(C24H34N4S2O2)]−1H}+). Anal. Calcd (found) for
CoC24H38N4O12Cl2S2: C, 37.51 (37.40); H, 4.98 (4.91); N, 7.29
(6.98). CD [CH3CN (2.5 mM), 298 K, λmax/nm (Δε/dm3 mol−1
cm−1)]: 1064.5 (−0.33), 539.5 (0.34), 526 (0.31), 512 (0.41), 467
(−0.12), 435.5 (0.02), 247 (−12.28), 234 (−7.47). IR (ATR, cm−1):
νmax 3377, 3289 (w, NH), 1620 (s, CO).
■
Present Addresses
‡J.G.: Faculty of Chemistry, University of Wroclaw, ul. F. Joliot-
Curie 14, 50-383 Wrocław, Poland.
§H.S.: Department of Material and Life Science, Graduate
School of Engineering, Osaka University, 2-1 Yamada-oka,
Suita, Osaka 565-0871, Japan.
[Co(L3)](ClO4)·(H2O)1.5 (55.0 mg, 74.7%). A CH3OH solution of
DIEA (473 μL of a 1.42 mol dm−3 solution, 0.671 mmol) was added
to a solution of the [Co(H2L3)(H2O)2](ClO4)2 complex (86.0 mg,
0.112 mmol) in CH3OH (1 mL). The solution was left overnight to
grow dark-blue crystals, which were filtered, washed twice with cold
CH3OH (0.5 mL), and dried under vacuum. Yield: 55 mg (74.7%).
Mp: >270 °C (from CH3OH). [α]D22 = +33.3 (c = 0.208 in CH3CN).
1H NMR (400 MHz, CD3CN, 298 K): δ 9.17 (dd, J = 1.0 and 8.8 Hz,
2H, Ar), 7.51 (dd, J = 1.3 and 7.9 Hz, 2H, Ar), 7.43 (ddd, J = 1.3, 7.1,
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors are grateful to the Ministry of Education, Culture,
Sports, Science and Technology, Japan, the Japan Society for
the Promotion of Science (Grants-in-Aid for Scientific Research
21·09244 and 26102540 and Postdoctoral Fellowships PE
642
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643

Inorganic Chemistry
Article
R.; Zhang, H.; Li, S.; Chen, L.; Zhang, W.; Wen, T. B.; Zhang, H.; Xia,
08025 and P09244), and the Japan Science and Technology
Agency (Core Research for Evolutional Science and Technol-
ogy program).
H. Chem. - Eur. J. 2011, 17, 2420−2427. (w) Chamayou, A.-C.;
Makhloufi, G.; Nafie, L. A.; Janiak, C.; Ludeke, S. Inorg. Chem. 2015,
̈
54, 2193−2203.
(9) (a) Meudtner, R. M.; Hecht, S. Angew. Chem., Int. Ed. 2008, 47,
4926−4930. (b) Hembury, G. A.; Borovkov, V. V.; Inoue, Y. Chem.
Rev. 2008, 108, 1−73. (c) Hofacker, A. L.; Parquette, J. R. Angew.
Chem., Int. Ed. 2005, 44, 1053−1057. (d) Borovkov, V. V.; Hembury,
G. A.; Inoue, Y. Angew. Chem., Int. Ed. 2003, 42, 5310−5314.
(e) Katoono, R.; Fujiwara, K.; Suzuki, T. Chem. Commun. 2014, 50,
5438−5440.
(10) For examples of controlled helicity inversion in organic
polymeric systems, see: (a) Okoshi, K.; Sakurai, S.-i.; Ohsawa, S.;
Kumaki, J.; Yashima, E. Angew. Chem., Int. Ed. 2006, 45, 8173−8176.
(b) Shimomura, K.; Ikai, T.; Kanoh, S.; Yashima, E.; Maeda, K. Nat.
Chem. 2014, 6, 429−434. (c) Maeda, K.; Mochizuki, H.; Watanabe,
M.; Yashima, E. J. Am. Chem. Soc. 2006, 128, 7639−7650. (d) Tang,
H.-Z.; Novak, B. M.; He, J.; Polavarapu, P. L. Angew. Chem., Int. Ed.
2005, 44, 7298−7301. (e) Tang, H.-Z.; Boyle, P. D.; Novak, B. M. J.
Am. Chem. Soc. 2005, 127, 2136−2142. (f) Tang, K.; Green, M. M.;
Cheon, K. S.; Selinger, J. V.; Garetz, B. A. J. Am. Chem. Soc. 2003, 125,
7313−7323. (g) Brown, R. A.; Diemer, V.; Webb, S. J.; Clayden, J.
Nat. Chem. 2013, 5, 853−860.
REFERENCES
■
(1) (a) Belmont, P.; Constant, J.-F.; Demeunynck, M. Chem. Soc. Rev.
2001, 30, 70−80. (b) Liu, H.; Liu, D. Chem. Commun. 2009, 2625−
2636. (c) Hirono-Hara, Y.; Ishizuka, K.; Kinosita, K., Jr.; Yoshida, M.;
Noji, H. Proc. Natl. Acad. Sci. U. S. A. 2005, 102, 4288−4293.
(d) Sowa, Y.; Rowe, A. D.; Leake, M. C.; Yakushi, T.; Homma, M.;
Ishijima, A.; Berry, R. M. Nature 2005, 437, 916−919. (e) Lubrich, D.;
Lin, J.; Yan, J. Angew. Chem., Int. Ed. 2008, 47, 7026−7028.
(2) Miyake, H.; Tsukube, H. Chem. Soc. Rev. 2012, 41, 6977−6991.
(3) (a) Ferrand, Y.; Kendhale, A. M.; Garric, J.; Kauffmann, B.; Huc,
I. Angew. Chem., Int. Ed. 2010, 49, 1778−1781. (b) Miwa, K.; Furusho,
Y.; Yashima, E. Nat. Chem. 2010, 2, 444−449.
(4) (a) Sigel, H.; Martin, R. B. Chem. Rev. 1982, 82, 385−426.
̋
́ ́ ́
(b) Sovago, I.; Osz, K. Dalton Trans. 2006, 3841−3854. (c) Novokmet,
S.; Heinemann, F. W.; Zahl, A.; Alsfasser, R. Inorg. Chem. 2005, 44,
4796−4805. (d) Novokmet, S.; Alam, M. S.; Dremov, V.; Heinemann,
F. W.; Muller, P.; Alsfasser, R. Angew. Chem., Int. Ed. 2005, 44, 803−
̈
806. (e) Tashiro, S.; Shionoya, M. Chem. Lett. 2013, 42, 456−462.
(5) (a) Kolomiets, E.; Berl, V.; Lehn, J.-M. Chem. - Eur. J. 2007, 13,
5466−5479. (b) Stadler, A.-M.; Kyritsakas, N.; Graff, R.; Lehn, J.-M.
Chem. - Eur. J. 2006, 12, 4503−4522. (c) Barboiu, M.; Lehn, J.-M. Proc.
Natl. Acad. Sci. U. S. A. 2002, 99, 5201−5206.
(11) For examples of controlled helicity inversion in supramolecular
polymeric aggregates, see: (a) Johnson, R. S.; Yamazaki, T.;
Kovalenko, A.; Fenniri, H. J. Am. Chem. Soc. 2007, 129, 5735−5743.
(b) Ajayaghosh, A.; Varghese, R.; George, S. J.; Vijayakumar, C. Angew.
Chem., Int. Ed. 2006, 45, 1141−1144. (c) Lohr, A.; Lysetska, M.;
(6) Boulas, P. L.; Gom
Ed. 1998, 37, 216−247.
́
ez-Kaifer, M.; Echegoyen, L. Angew. Chem., Int.
Wurthner, F. Angew. Chem., Int. Ed. 2005, 44, 5071−5074.
̈
(12) (a) Pijper, D.; Jongejan, M. G. M.; Meetsma, A.; Feringa, B. L. J.
Am. Chem. Soc. 2008, 130, 4541−4552. (b) Eelkema, R.; Pollard, M.
M.; Vicario, J.; Katsonis, N.; Ramon, B. S.; Bastiaansen, C. W. M.;
Broer, D. J.; Feringa, B. L. Nature 2006, 440, 163. (c) ter Wiel, M. K. J;
van Delden, R. A.; Meetsma, A.; Feringa, B. L. J. Am. Chem. Soc. 2003,
125, 15076−15086.
(7) (a) Collin, J.-P.; Heitz, V.; Sauvage, J.-P. Top. Curr. Chem. 2005,
262, 29−62. (b) Periyasamy, G.; Collin, J.-P.; Sauvage, J.-P.; Levine, R.
D.; Remacle, F. Chem. - Eur. J. 2009, 15, 1310−1313. (c) Amendola,
V.; Boiocchi, M.; Brega, V.; Fabbrizzi, L.; Mosca, L. Inorg. Chem. 2010,
49, 997−1007. (d) Amendola, V.; Colasson, B.; Fabbrizzi, L.; Douton,
M.-J. R. Chem. - Eur. J. 2007, 13, 4988−4997. (e) Amendola, V.;
Fabbrizzi, L.; Mangano, C.; Pallavicini, P. Acc. Chem. Res. 2001, 34,
488−493. (f) McNitt, K. A.; Parimal, K.; Share, A. I.; Fahrenbach, A.
C.; Witlicki, E. H.; Pink, M.; Bediako, D. K.; Plaisier, C. L.; Le, N.;
Heeringa, L. P.; Griend, D. A. V.; Flood, A. H. J. Am. Chem. Soc. 2009,
131, 1305−1313. (g) Share, A. I.; Parimal, K.; Flood, A. H. J. Am.
Chem. Soc. 2010, 132, 1665−1675.
(13) (a) Avellini, T.; Li, H.; Coskun, A.; Barin, G.; Trabolsi, A.;
Basuray, A. N.; Dey, S. K.; Credi, A.; Silvi, S.; Stoddart, J. F.; Venturi,
M. Angew. Chem., Int. Ed. 2012, 51, 1611−1615. (b) Wang, Z.-G.;
Elbaz, J.; Remacle, F.; Levine, R. D.; Willner, I. Proc. Natl. Acad. Sci. U.
S. A. 2010, 107, 21996−22001. (c) Yashima, E.; Maeda, K.; Okamoto,
Y. Nature 1999, 399, 449−451. (d) Rasberry, R. D.; Wu, X.; Bullock,
B. N.; Smith, M. D.; Shimizu, K. D. Org. Lett. 2009, 11, 2599−2602.
(e) Helmich, F.; Lee, C. C.; Schenning, A. P. H. J.; Meijer, E. W. J. Am.
Chem. Soc. 2010, 132, 16753−16753. (f) Ohta, E.; Sato, H.; Ando, S.;
Kosaka, A.; Fukushima, T.; Hashizume, D.; Yamasaki, M.; Hasegawa,
K.; Muraoka, A.; Ushiyama, H.; Yamashita, K.; Aida, T. Nat. Chem.
2011, 3, 68−73. (g) Hirose, K. J. Inclusion Phenom. Mol. Recognit.
Chem. 2010, 68, 1−24.
(8) For controlled helicity inversion in inorganic systems, see:
(a) Crassous, J. Chem. Commun. 2012, 48, 9684−9692. (b) Crassous,
J. Chem. Soc. Rev. 2009, 38, 830−845. (c) Canary, J. W.; Mortezaei, S.;
Liang, J. Coord. Chem. Rev. 2010, 254, 2249−2266. (d) Miyake, H.;
Hikita, M.; Itazaki, M.; Nakazawa, H.; Sugimoto, H.; Tsukube, H.
Chem. - Eur. J. 2008, 14, 5393−5396. (e) Miyake, H.; Kamon, H.;
Miyahara, I.; Sugimoto, H.; Tsukube, H. J. Am. Chem. Soc. 2008, 130,
792−793. (f) Miyake, H.; Sugimoto, H.; Tamiaki, H.; Tsukube, H.
Chem. Commun. 2005, 4291−4293. (g) Miyake, H.; Yoshida, K.;
Sugimoto, H.; Tsukube, H. J. Am. Chem. Soc. 2004, 126, 6524−6525.
(h) Hutin, M.; Nitschke, J. Chem. Commun. 2006, 1724−1726.
(i) Zahn, S.; Canary, J. W. Science 2000, 288, 1404−1407. (j) Zahn, S.;
Das, D.; Canary, J. W. Inorg. Chem. 2006, 45, 6056−6063.
(k) Mortezaei, S.; Catarineu, N. R.; Canary, J. W. J. Am. Chem. Soc.
2012, 134, 8054−8057. (l) Biscarini, P.; Kuroda, R. Inorg. Chim. Acta
(14) [Co(H2L4)(NO3)]+ was not generated in situ. Mixing H2L4
and Co(NO3)2·6H2O provided a cobalt(III) complex even under
anaerobic conditions, probably because of oxidation of the cobalt(II)
−
center by a NO3 anion.
(15) Brorson, M.; Damhus, T.; Schaffer, C. E. Inorg. Chem. 1983, 22,
̈
1569−1573.
(16) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877−910.
(17) (a) Katz, E.; Privman, V. Chem. Soc. Rev. 2010, 39, 1835−1857.
(b) Privman, M.; Tam, T. K.; Pita, M.; Katz, E. J. Am. Chem. Soc. 2009,
131, 1314−1321. (c) Szaciłowski, K. Chem. Rev. 2008, 108, 3481−
3548. (d) Won, H.-S.; Low, L. Y.; De Guzman, R.; Martinez-Yamout,
M.; Jakob, U.; Dyson, H. J. J. Mol. Biol. 2004, 341, 893−899.
(18) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.;
Giacovazzo, C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.;
Spagna, R. J. Appl. Crystallogr. 1999, 32, 115−119.
́
1988, 154, 209−214. (m) Gregolin
Inorg. Chem. 2007, 46, 7923−7934. (n) Gregolin
Angew. Chem., Int. Ed. 2006, 45, 6122−6126. (o) Gregolin
Starynowicz, P.; Hua, K. T.; Lunkley, J. L.; Muller, G.; Lisowski, J. J.
Am. Chem. Soc. 2008, 130, 17761−17773. (p) Gregolinski, J.; Lis, T.;
́
́
́
́
Cyganik, M.; Lisowski, J. Inorg. Chem. 2008, 47, 11527−11534.
́
(q) Gerus, A.; Slepokura, K.; Lisowski, J. Inorg. Chem. 2013, 52,
(19) Sheldrick, G. M. SHELXL-97; University of Gottingen:
̈
12450−12460. (r) Miyake, H.; Ueda, M.; Murota, S.; Sugimoto, H.;
Tsukube, H. Chem. Commun. 2012, 48, 3721−3723. (s) Akine, S.;
Hotate, S.; Nabeshima, T. J. Am. Chem. Soc. 2011, 133, 13868−13871.
(t) Akine, S.; Sairenji, S.; Taniguchi, T.; Nabeshima, T. J. Am. Chem.
Soc. 2013, 135, 12948−12951. (u) Montgomery, C. P.; New, E. J.;
Parker, D.; Peacock, R. D. Chem. Commun. 2008, 4261−4263. (v) Lin,
Gottingen, Germany, 1997.
̈
(20) Wakita, K. Yadokari-XG, Software for Crystal Structure Analyses,
2001. Release of Software (Yadokari-XG 2009) for Crystal Structure
Analyses: Kabuto, C.; Akine, S.; Nemoto, T.; Kwon, E. Nippon Kessho
Gakkaishi 2009, 51, 218.
643
DOI: 10.1021/acs.inorgchem.5b01902
Inorg. Chem. 2016, 55, 633−643