Planar-chiral metal complexes comprised of square-planar metal and achiral tetradentate ligands: Design, optical resolution, and thermodynamics

Article abstract of DOI:10.1021/ic2024742

Planar-chiral palladium complexes {[[N,N′-[1,4-butanediylbis(oxy-7,1- naphthalenediyl)]bis(2-pyridinecarboxamidato)](2-)-κN₁, κN₁′,κN₂,κN₂′] palladium (PdL⁴) and [[2,2′-[1,4-butanediylbis[[(oxy-7,1- naphthalenediyl)imino]methyl]]dipyrrolato](2-)-κN₁, κN₁′,κN₂,κN₂′] palladium (PdL⁵)} were synthesized from achiral tetradentate ligands N,N′-[1,4-butanediylbis(oxy-7,1-naphthalenediyl)]bis(2- pyridinecarboxamide) (H₂L⁴) and N,N′-bis[(1H-pyrrol- 2-yl)methylidene]-7,7′-(1,4-butanediyldioxy)bis(1-naphthalenamine) (H ₂L⁵) bearing two dissymmetric bidentate units at both ends and a Pd^II ion, respectively. The palladium complexes were crystallized in the monoclinic space group P2₁/n with the unit cell parameters a = 16.5464(6) A, b = 11.3534(4) A, c = 17.6697(7) A, α = 115.5300(10)°, and Z = 4 for PdL⁴ and a = 17.2271(8) A, b = 10.1016(5) A, c = 17.9361(9) A, α = 105.6310(10)°, and Z = 4 for PdL⁵. The planar-chiral structures of PdL⁴ and PdL⁵ were confirmed by single-crystal X-ray analyses, resulting in the fact that the crystals were racemic mixtures. The racemic mixtures were successfully resolved by using chiral high-performance liquid-chromatography techniques. Racemizations of the complexes were found to be drastically dependent on the arrangement of the charged or uncharged metal-binding N atoms of the ligands.

Full text of DOI:10.1021/ic2024742

Article
pubs.acs.org/IC
Planar-Chiral Metal Complexes Comprised of Square-Planar Metal
and Achiral Tetradentate Ligands: Design, Optical Resolution, and
Thermodynamics
Hidetoshi Goto, Teppei Hayakawa, Kanako Furutachi, Hiroshi Sugimoto,* and Shohei Inoue
Department of Industrial Chemistry, Faculty of Engineering, Tokyo University of Science, 12-1 Ichigaya-funagawara, Shinjuku, Tokyo
162-0826, Japan
*
S Supporting Information
ABSTRACT: Planar-chiral palladium complexes {[[N,N′-[1,4-
b u t a n e d i y l b i s ( o x y - 7 , 1 - n a p h t h a l e n e d i y l ) ] b i s ( 2 -
pyridinecarboxamidato)](2−)-κN ,κN ′,κN ,κN ′]palladium
1
1
2
2
4
(
PdL ) and [[2,2′-[1,4-butanediylbis[[(oxy-7,1-
naphthalenediyl)imino]methyl]]dipyrrolato](2−)-
5
κN ,κN ′,κN ,κN ′]palladium (PdL )} were synthesized from
1
1
2
2
achiral tetradentate ligands N,N′-[1,4-butanediylbis(oxy-7,1-
4
naphthalenediyl)]bis(2-pyridinecarboxamide) (H L ) and N,N′-
2
bis[(1H-pyrrol-2-yl)methylidene]-7,7′-(1,4-butanediyldioxy)bis-
5
II
(
1-naphthalenamine) (H L ) bearing two dissymmetric bidentate units at both ends and a Pd ion, respectively. The palladium
2
complexes were crystallized in the monoclinic space group P2 /n with the unit cell parameters a = 16.5464(6) Å, b = 11.3534(4)
1
4
Å, c = 17.6697(7) Å, β = 115.5300(10)°, and Z = 4 for PdL and a = 17.2271(8) Å, b = 10.1016(5) Å, c = 17.9361(9) Å, β =
5
4
5
1
05.6310(10)°, and Z = 4 for PdL . The planar-chiral structures of PdL and PdL were confirmed by single-crystal X-ray
analyses, resulting in the fact that the crystals were racemic mixtures. The racemic mixtures were successfully resolved by using
chiral high-performance liquid-chromatography techniques. Racemizations of the complexes were found to be drastically
dependent on the arrangement of the charged or uncharged metal-binding N atoms of the ligands.
INTRODUCTION
variety of chiral octahedral complexes having achiral multi-
■
dentate ligands such as bi-, tri-, or hexadentate have been
Chiral metal complexes as represented by metalloporphyrins
vertically coordinated by imidazole, thiol, and phenol residues
assignable to amino acid units (histidine, cysteine, and tyrosine)
in proteins are ubiquitous in nature and play many roles
1
9−21
synthesized
agents
and applied to chiral discrimination re-
1
4,15
8a,c,e
and chiral capsules.
It is known that tetrahedral,
four-coordinate complexes tend to be labile and even
22
stereochemical isomers of the complexes having bi- or
including O activation and utilization (cytochrome P450 and
2
23
tetradentate ligands transform into the other antipodes rather
cytochrome oxidase) and covalent-bond cleavage and for-
mation (hydrolase and lyase). These have prompted chemists
to develop artificial chiral metal complexes from the aspect of
1
quickly. Nevertheless, optical resolutions of chiral tetrahedral
24
complexes with two dissymmetric bidentate or four district
25
2
−5
monodentate ligands were accomplished. Some helicates
composed of tetrahedral complexes as repeating units were
not only unique three-dimensional structures
and their
6
chiroptical properties but also potential applications to
26
7
,8
successfully separated into enantiomerically pure compounds.
catalysts for asymmetric syntheses, catalysts for stereospecific
9
10−12
13−15
Chiral square-planar, four-coordinate complexes were sophisti-
polymerizations, sensors
and selectors
for chiral
16
catedly designed, and those optical resolutions were achieved as
discriminations, and chiral dopants for liquid crystals.
2
7,28
well.
In contrast with the tetra- and octahedral complexes
Optically active compounds having metal-binding functional
groups and asymmetric sources such as asymmetric tetrahedral
C atoms, which are chiral sources of naturally occurring
products (proteins, sugars, and so on), have been widely used
mentioned above, the square-planar complexes needed two
27
kinds of bidentate ligands. We expected to constitute a chiral
square-planar complex from two of the same bidentate ligands
and a four-coordinate metal. as below (Figure 1): (1) two
dissymmetric bidentate ligands are coordinated to metal at
trans positions to each other (trans effect) to generate a
complex having an enantiotopic plane; (2) when a strap unit is
introduced to the trans square-planar complex, the strap unit
covers one face of the enantiotopic plane. Such a complex is
7
,17
for construction of the chiral complexes. On the other hand,
achiral ones such as ethylenediamine, 2,2′-bipyridine, and
acetylacetonate salts have been frequently employed to build
the chiral metal complexes dependent upon coordination
geometries of metals, in particular of four and six coordination
2
,18
numbers.
Since Werner reported syntheses and optical
resolutions of chiral octahedral, six-coordinate cobalt com-
plexes, so-called “Werner complexes”, having three achiral
Received: November 18, 2011
Published: March 21, 2012
19
bidentate ligands (ethylenediamine) about a century ago,
a
©
2012 American Chemical Society
4134
dx.doi.org/10.1021/ic2024742 | Inorg. Chem. 2012, 51, 4134−4142

Inorganic Chemistry
Article
1
spacer bridging two N-phenyl groups of two L at the ortho
positions formed not a planar-chiral complex with a 1:1
stoichiometric ratio, [[2,2′-[1,7-heptanediylbis[[(1,2-
phenylenediyl)imino]methyl]]bis(4,6-di-tert-butylphenolate)]-
2
(
2−)-κN ,κN ′,κO ,κO ′]copper (CuL ), but an achiral (meso)
2
2
1
1
ladder complex with a 2:2 composition {bis[2,2′-[1,7-
heptanediylbis[[(1,2-phenylenediyl)imino]methyl]]bis(4,6-di-
2
tert-butylphenolate)]dicopper complex, Cu L }, confirmed by
2
2
3
1
1
single-crystal X-ray analysis. The flexibility of R was
considered to be one of factors to inhibit the formation of
2
the planar-chiral structure (CuL ). So, [[2,2′-[1,4-butanediylbis-
[
(
(
[
(
[(oxy-7,1-naphthalenediyl)imino]methyl]]bis(phenolate)]
3
2−)-κN ,κN ′,κO ,κO ′]copper (CuL ) comprised of copper-
2
2
1
1
Figure 1. Concept of a planar-chiral metal complex (black sphere,
metal; red and blue spheres, metal-binding site; white tube, coordinate
II) and a newly employed ligand {2,2′-[1,4-butanediylbis-
[(oxy-7,1-naphthalenediyl)imino]methyl]]bis(phenolate)
bond; gray tube, covalent bond). Two C -symmetric bidentate ligands
s
3
2−), L } bearing a more rigid “naphthalene” unit and a shorter
are coordinated to the metal to form a C -symmetric square-planar
2
h
2
29b,c
“
R ” spacer was focused on as an alternative platform.
Such
complex. Cross-linking between two bidentate ligands generates a pair
of enantiomers of the planar-chiral complex.
complexes are reported to form planar-chiral structures in
crystals,
29b,c,f−i,30,31
while the isomerization behaviors of the
planar-chiral. Some research groups have hitherto developed
chiral structures have never been investigated to date. Our
optical resolution of CuL using chiral high-performance liquid
chromatography (HPLC) was unsuccessful (Scheme S1 and
Figure S1 in the Supporting Information). We herein report the
synthesis, optical resolution, and thermodynamic investigation
of novel planar-chiral complexes {[[N,N′-[1,4-butanediylbis-
3
planar-chiral complexes with strap chains called chiral “fly-over”
2
9−31
complexes.
Since the first chiral “fly-over” complex by
29a
Schlesinger in 1927, Martin presented a rational design and
an undoubted structure of chiral-strapped complexes by X-ray
crystallography in 1979.
29b,c
Some chiral “fly-over” complexes
(
(
oxy-7,1-naphthalenediyl)]bis(2-pyridinecarboxamidato)]-
have been reported since then, and a few optical resolutions of
such complexes have been accomplished by Naota and our
4
2−)-κN ,κN ′,κN ,κN ′]palladium (PdL ) and [[2,2′-[1,4-
1
1
2
2
30,31
butanediylbis[[(oxy-7,1-naphthalenediyl)imino]methyl]]-
dipyrrolato](2−)-κN ,κN ′,κN ,κN ′]palladium (PdL ); Chart
1
groups, individually.
5
1
1
2
2
In our and others’ laboratories, metal complexes of planar-
chiral porphyrins obtained by intramolecular cross-linkings of
achiral tetradentate porphyrins having enantiotopic faces (C2h
or C4h symmetry) were found to serve as effective chiral
31
}. Palladium(II) is one of the representative square-planar
coordinate metals and was used for the construction of planar-
27c,d
chiral complexes with two [NN]-bidentate ligands.
The
dissymmetric [NN]-bidentate units [N-phenyl-2-pyridinecar-
3
2,33
catalysts for asymmetric oxidations
selectors for biomolecules.
and as effective
In the beginning of our
research on chiral square-planar complexes different from the
46
47
boxamido and 2-(N-phenylimino)methyl-1H-pyrrolato ] in
N,N′-[1,4-butanediylbis(oxy-7,1-naphthalenediyl)]bis(2-
34−36
4
pyridinecarboxamidato)(2−) (L ) and 2,2′-[1,4-butanediylbis-
37
metalloporphyrins, our platform, based on the design concept
[
(
[(oxy-7,1-naphthalenediyl)imino]methyl]]dipyrrolato(2−)
as described above, was the bis[2-[(N-phenylimino)methyl]-
5
L ) have a monovalent negative charge similar to that of 2-
1
3
phenolate]copper complex (CuL ; Chart 1), of which two N-
2
[(N-phenylimino)methyl]phenolate in L . Although the syn-
thesis and optical resolution of PdL ahead of PdL was
accomplished, racemization of PdL proceeded at ambient
4
5
phenyl groups were roughly orthogonal to the plane of the
4
5
4
copper(II) square-planar geometry. Unfortunately, the
mixture of copper(II) and 2,2′-[1,7-heptanediylbis[[(1,2-
phenylenediyl)imino]methyl]]bis(4,6-di-tert-butylphenolate)-
temperature. Our idea to suppress racemization of the complex
was to exchange the positions of the neutral and negative
2
1
5
(
2−) (L ) having a heptamethylene group (R ) as a flexible
charges. In fact, no racemization of PdL was observed under
Chart 1. Structures of Planar-Chiral Metal Complexes
4
135
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Inorganic Chemistry
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Scheme 1. Synthesis of PdL4
Scheme 2. Synthesis of PdL5
4
4
the same condition as that of PdL . The details will be
described hereinafter.
Table 1. Crystal Data and Structure Refinement for PdL
and PdL
5
PdL4
PdL5
RESULT AND DISCUSSION
■
formula
[C H N O ]Pd [C H N O ]Pd
4
5
36 28
4
4
34 28
4
2
Syntheses and Characterizations of PdL and PdL .
(
CH Cl )
2 2
4
5
Two palladium complexes (PdL and PdL ) were synthesized
according to Schemes 1 and 2. 7,7′-(1,4-Butanediyldioxy)bis(1-
fw
687.02
714.92
cryst syst
space group
T/K
monoclinic
monoclinic
29b
naphthalenamine) as a starting material in both schemes was
P2 /n
P2 /n
1
1
48
reacted with picolinoyl chloride or 1H-pyrrole-2-carbalde-
90
90
4
9
4
hyde to obtain the corresponding compounds H L and
2
a/Å
16.5464(6)
11.3534(4)
17.6697(7)
90
17.2271(8)
10.1016(5)
17.9361(9)
90
5
H L , respectively. The reactions of the compounds with
2
b/Å
5
0
dichloro(1,5-cyclooctadiene)palladium(II) (Pd(cod)Cl )
2
c/Å
1
were followed by H NMR spectroscopy (Figures S2 and S3
α/deg
β/deg
γ/deg
V/Å3
Z
4
in the Supporting Information). Upon the addition of H L or
2
115.5300(10)
90
105.6310(10)
90
5
H L to Pd(cod)Cl , the signals assignable to the amide (NH
2
2
4
5
for H L ) and pyrrole (NH for H L ) at 10−12 ppm became
gradually smaller, as we expected. Furthermore the obtained
2
2
2995.29(19)
4
3005.8(3)
4
4
product from palladium(II) and H L showed signals in the fast
calcd/g cm−3
2
ρ
1.524
1.580
atom bombardment mass spectrometry (FAB-MS) spectrum
that were identical to those of a 1:1 complex of palladium(II)
μ(Mo Kα)/mm−1
0.668
0.836
F(000)
1400
1452
4
2−
and the corresponding anionic ligand ([L ] ). In the case of
cryst size/mm
0.50/0.20/0.20
2.20−27.52
20554
0.50/0.40/0.10
1.92−28.35
21947
5
H L , the signals assignable to the 1:1 complex of palladium(II)
θ range/deg
2
5
2−
and [L ] were observed as well.
reflns collected
indep reflns [Rint]
max, min transmn
data/restraints/param
final R1 [wR2]
final R1 [wR2] (all data)
4
5
The single-crystal X-ray analyses of PdL and PdL also
revealed the planar-chiral formations with the 1:1 stoichio-
metric ratios of tetradentate ligands/palladium(II) (Table 1 and
Figures 2 and S4 and S5 in the Supporting Information). PdL
was crystallized as a racemic mixture in a monoclinic system
6868 [0.0228]
0.8780, 0.7313
6868/0/406
0.0308 [0.0783]
0.0353 [0.0812]
7482 [0.0295]
0.956236, 0.784376
7482/0/397
0.0276 [0.0766]
0.0349 [0.0816]
0.672, −0.554
4
largest diff peak, hole/e Å− 1.805, −0.305
3
with a space group of P2 /n. Two independent molecules,
1
which are pR and pS forms, were found in the dissymmetric
4
unit. Two pyridylamido groups of H L were coordinated to
the two naphthalene rings crossed over one face of the
enantiotopic plane with 1:1 possibility. Each molecule of the
2
II
the Pd ion in a trans geometry: Pd−N distances in the range
of 2.03−2.06 Å, N−N distances in the ranges of 2.61−2.62 and
planar-chiral complex had a C axis perpendicular to the Pd−
2
3
7
.14−3.16 Å, and N−Pd−N angles in the ranges of 79.30−
9.33° and 100.2−100.8° (cis) and 174.7−175.3° (trans),
ONNO plane. These results indicate the formation of the
4
planar-chiral complex from H L and palladium(II) with a 1:1
2
exhibiting that, strictly speaking, the palladium complex formed
slightly distorted square-planar geometries bearing enantiotopic
planes (C2h symmetry). Two naphthalene rings covalently
bonded to the amido N atoms were orthogonally distorted to
the Pd−ONNO planes: dihedral angles in the range of 84.8−
46
5
stoichiometric ratio. PdL was also crystallized as a racemic
mixture in a monoclinic system with a space group of P2 /n
1
4
and formed a planar-chiral structure similar to PdL : Pd−N
distances in the range of 2.01−2.04 Å, N−N distances in the
ranges of 2.61−2.62 and 3.07−3.10 Å, N−Pd−N angles in the
8
7.1°. Furthermore, each 1,4-butylenedioxy group connected to
4
136
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Inorganic Chemistry
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4
Figure 3. Chromatographic resolution of stereoisomers of PdL (A)
5
and PdL (B) on SUMICHIRAL OA-4600. Column: 25 × 0.46 (i.d.)
cm. Eluent: chloroform/ethanol (50:1, v/v) (A); hexane/ethanol
4
5
Figure 2. Ball-and-stick drawings of PdL (A) and PdL (B) with
thermal ellipsoids at 50% probability (carbon, gray; nitrogen, blue;
oxygen, red; palladium, pink). Each one of the independent complexes
is shown here. H atoms (for A and B) and solvent molecules (for B)
are omitted for clarity.
−1
(100:1, v/v) (B). Flow rate: 1 mL min .
ranges of 80.5−80.6° and 99.0−99.8° (cis) and 172.3−178.8°
(
6
trans), and Pd−N−C −C
dihedral angles in the range of
naph
naph
4
7
1.4−71.6°.
4
5
The chiral conformations of PdL and PdL in solutions
1
1
were suggested by H NMR spectroscopy. The H NMR
spectrum of PdL exhibited 10 distinct signals in the aromatic
region, meaning that PdL adopted a single conformation in
4
4
solution. In addition, the signals assignable to the oxymethylene
4
protons (OCH ) of PdL were observed as two signals at 4−4.5
2
ppm, while those attributed to the other methylene protons
(
CH ) near 2 ppm just became slightly broader than those of
2
4
H L . These results indicate that the geminal protons of the
oxymethylene group are diastereotopic, meaning that PdL
2
4
adopts a cyclic structure in solution of which intramolecular
1
rotations are under restriction. The changes between the H
5
5
4
NMR spectra of H L and PdL were similar to those of H L
2
2
4
5
5
and PdL : 4.29 (H L ) to 4.15−4.30 and 4.40−4.50 (PdL )
ppm for oxymethylene protons.
Optical Resolutions and Thermodynamics of PdL
and PdL . The optical resolutions of the planar-chiral
complexes were carried out by using HPLC with SUMICHI-
RAL OA-4600 as a chiral column (Figure 3). A chromatogram
of PdL showed two peaks with comparable peak areas in 3.42
the first fraction) and 3.74 (the second fraction) min. H
2
4
5
Figure 4. CD spectra of fractions of PdL (A) and PdL (B) (red line,
4
(−) isomers; blue line, (+)350 isomers) in 1,2-dichloroethane at
350
4 5
5
room temperature. [Pd complex] = 0.28 (PdL ) and 0.89 (PdL ) mM.
(
+)350-PdL5 (the second fraction, 9.75 min) (Figure 4B).
4
Enantiomeric excesses (ee's) of the enantiomers were estimated
to be more than 99% based on their chiral HPLC analyses
1
(
(
Figure S6 in the Supporting Information).
Finally, we investigated the stability of the planar-chiral
NMR and MS spectra of the component of the first fraction
separated by chiral HPLC were identical with those of the
second fraction. On the other hand, a circular dichroism (CD)
spectrum of the component (the first fraction) exhibited a
complexes toward racemization (Figures 5 and S7 in the
Supporting Information). The ee's of the complexes were
periodically estimated by chiral HPLC after the solutions of
4
negative peak at 350 nm [(−) -PdL ], which has a maximum
3
50
4
5
(
(
−) -PdL and (−) -PdL were kept at room temperature
intensity in the long-wavelength region [“(−)350” denotes the
350
350
ca. 22−24 °C) for a predetermined amount of time. The peak
sign of the peak at 350 nm, vide infra], whereas the second
4
4
of the chromatogram for (−) -PdL gradually became lower
over time, while that for (+)350-PdL became higher. No other
fraction showed a positive peak [(+)350-PdL ]. These CD
350
4
patterns were complete mirror images in the range of 200−500
nm (Figure 4A). These results indicate that the two
peaks were observed during incubation of the solution.
Furthermore, the H NMR spectra of the solutions before
and after incubation were completely identical. These results
indicate that racemization of PdL only proceeded under this
4
1
components [(−) - and (+)350-PdL 's] are a pair of
3
50
4
5
enantiomers of PdL . In a similar fashion, PdL was also
separated successfully to a pair of enantiomers of PdL : one is
−)350-PdL (the first fraction, 9.32 min), and the other is
4
4
5
(
condition. The first-order kinetic constant (k) and the half-life
4
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Inorganic Chemistry
Article
(
imine units), being in the middle of the ligand, were
52
nonconnected. On the basis of these results, the racemization
mechanisms of the planar-chiral metal complexes were
proposed, as shown in Scheme 3. Because the N atoms are
dissociated from the Pd−N bonds in one enantiomer of PdL
and PdL at the first step (a, a′ or d, d′), the cleavages of the
4
5
nonionic Pd−N bonds (a, a′) preferentially proceed because the
binding forces are weaker than those of the ionic Pd−N bonds.
Subsequently, the dissociated N atoms at both ends of the
ligands (b, e′) are rotated faster around the remaining Pd−N
bonds than those in the middle of the ligands. Thereafter, the
dissociated N atoms are associated with the metal to generate
4
the others (c, c′ or f, f′). In other words, PdL is racemized via
the reaction pass of Scheme 3a−c, which proceeds more easily
5
than that of PdL .
4
Figure 5. Racemization behaviors of PdL (full circles) in chloroform/
5
ethanol (50:1, v/v) and PdL (opened circles) in hexane/ethanol
100:1, v/v) at room temperature. The black solid curve is calculated
CONCLUSIONS
■
(
We have designed and synthesized planar-chiral palladium(II)
using the first-order rate equation.
4
5
complexes (PdL and PdL ) consisting of achiral, four-
4
5
−6
coordinate compounds (H2L and H L ) bearing two
period (τ ) of racemization were estimated to be 1.27 × 10
2
1/2
−1
dissymmetric bidentate binding sites at both ends. The
single-crystal X-ray analyses revealed the planar-chiral struc-
tures of the compounds of which crystals were racemic
mixtures. Both enantiomers of the compounds were success-
fully resolved by chiral HPLC. Racemization of the compounds
was found to proceed via cleavage of the Pd−uncharged N
bond and subsequent intramolecular rearrangements. These
optically active, planar-chiral complexes are expected to be
applicable to chiral recognition agents
asymmetric synthesis
phyrins, as was previously reported by our group and others.
This project is now in progress in our laboratory.
s
and 76 h, respectively. In addition, the Gibbs’ free-energy
change (ΔG ) of the rotational barrier around the Pd−N bond
of the complex was calculated as 106 kJ mol using the Eyring
⧧
−1
5
1
5
equation. On the other hand, no racemization of (−)350-PdL
4
was observed under the same condition as that of (−)350-PdL ;
5
assuming that a small amount (1.0 mol %) of (−) -PdL is
350
racemized, the values can be calculated as follows: k < 1.31 ×
−8
−1
‡
−1
10
s , τ1 > 7350 h, and ΔG > 117 kJ mol . Both
32,33
/2
and catalysts for
complexes were built using two kinds of Pd−N bonds: ionic
34−36
such as planar-chiral metallopor-
and nonionic coordination bonds, of which the arrangements
were different from each other. A linear dianion derived from
H L has nonionic pyridyl groups at both ends, while that from
H L has anionic pyrrolato groups at both ends. A dianionic,
linear compound having four metal-binding [N O ] sites was
recently reported to play a role as not a tetradentate but a
bidentate ligand to adopt a metal complex, in which the two
anionic O atoms at both ends of the ligand strand were
coordinated to the metal while the two nonionic N atoms
4
2
5
2
EXPERIMENTAL SECTION
. Materials. 2-Hydroxybenzaldehyde and pyridine-2-carboxylic
acid were purchased from Tokyo Chemical Industry (Japan).
Copper(II) acetate monohydrate was purchased from Kanto
Chemicals (Japan). Triethylamine and benzene were dried with
■
2
2
1
calcium hydride (CaH ) and then distilled over sodium benzophenone
2
Scheme 3. Possible Mechanism of Racemization
4
138
dx.doi.org/10.1021/ic2024742 | Inorg. Chem. 2012, 51, 4134−4142

Inorganic Chemistry
Article
ketyl under nitrogen. Pyridine was dried with CaH and then distilled
the filtrate was purified by silica gel chromatography with chloroform/
2
over CaH under nitrogen. Thionyl chloride was purified by fractional
ethyl acetate (10:1, v/v) and subsequent recrystallization from
2
5
distillation under nitrogen. Copper(II) acetate monohydrate was twice
recrystallized from acetic acid. Pyridine-2-carboxylic acid was recrystal-
lized from benzene. Other reagents were used without purification.
chloroform/hexane to afford H L as a slightly yellow crystal (0.528
2
1
g, 1.00 mmol, 74.4%). H NMR (CDCl ): δ 2.07 (m, 4H, CH ), 4.29
3
2
(m, 4H, OCH ), 5.82 (br, 2H, Ar−H), 6.00 (dd, J = 3.6 and 2.4 Hz,
2
2
9b
7
,7′-(1,4-Butanediyldioxy)bis(1-naphthalenamine),
1H-pyrrole-2-
2H, Ar−H), 6.61 (dd, J = 2.4 and 1.2 Hz, 2H, Ar−H), 7.08 (d, J = 7.2
Hz, 2H, Ar−H), 7.21 (dd, J = 8.8 and 2.4 Hz, 2H, Ar−H), 7.38 (t, J =
7.2 Hz, 2H, Ar−H), 7.70 (d, J = 8.8 Hz, 2H, Ar−H), 7.80 (d, J = 7.2
49
50
carbaldehyde, and Pd(cod)Cl2 were synthesized according to
literatures, respectively.
2
. Synthesis. Synthesis of N,N′-[1,4-Butanediylbis(oxy-7,1-
Hz, 2H, Ar−H), 7.81 (d, J = 2.4 Hz, 2H, Ar−H), 8.28 (s, 2H, C(N)
4
−1
naphthalenediyl)]bis(2-pyridinecarboxamide) (H L ). A solution
H), 11.18 (br, 2H, NH). IR (KBr, cm ): 1620 (ν
), 1250
2
CN
+
of thionyl chloride (2.0 mL, 28 mmol) in benzene (3 mL) was
dropwise added to a suspension of picolinic acid (0.752 g, 6.11
mmol) in benzene (3 mL) at 0 °C over 15 min under nitrogen.
The mixture was stirred for 30 min at room temperature and
subsequently heated under reflux for 60 min. After removal of
excess thionyl chloride and benzene under high vacuum, the
residue was dissolved in benzene (3 mL). The solution was
added to a solution of 7,7′-(1,4-butanediyldioxy)bis(1-naph-
thalenamine) (0.811 g, 2.18 mmol) in pyridine (2.0 mL) at
room temperature. After heating under reflux for 3 h, the
mixture was cooled at room temperature. Chloroform was
added to the mixture, and a chloroform-insoluble fraction was
removed by filtration. After the filtrate was washed with
(νC−O−C). FAB-MS: m/z 527.2 (calcd for C H N O ([M + H] ):
34 31 4 2
m/z 527.2).
Synthesis of [[2,2′-[1,4-Butanediylbis[[(oxy-7,1-naphthalenediyl)-
5
imino]methyl]]dipyrrolato](2−)-κN
,κN
L (263 mg, 499 μmol) in chloroform (25 mL) was
added to a solution of Pd(cod)Cl (142 mg, 497 μmol) in chloroform
′,κN
,κN ′]palladium (PdL ).
1
1
2 2
5
A solution of H
2
2
(50 mL), and the mixture was stirred at room temperature for 26 h.
The crude product obtained by concentration of the mixture was
purified by silica gel chromatography with chloroform and subsequent
5
recrystallization from dichloromethane/hexane to afford PdL as a
1
yellow plate crystal (66.3 mg, 105 μmol, 21.1%). H NMR (CDCl
): δ
), 4.40−4.50 (m,
), 4.68 (br, 2H, Ar−H), 5.74 (dd, J = 3.6 and 2.4 Hz, 2H,
3
1.95−2.15 (m, 4H, CH
2H, OCH
), 4.15−4.30 (m, 2H, OCH
2
2
2
saturated NaHCO (aq), the organic layer was dried with
Ar−H), 6.67 (d, J = 3.6 Hz, 2H, Ar−H), 7.18 (dd, J = 8.8 and 2.4 Hz,
2H, Ar−H), 7.34 (d, J = 7.6 Hz, 2H, Ar−H), 7.40 (t, J = 7.6 Hz, 2H,
Ar−H), 7.47 (s, 2H, C(N)H), 7.83 (d, J = 8.8 Hz, 2H, Ar−H), 7.85
3
Na SO and concentrated under high vacuum. The crude
2
product was purified by silica gel chromatography with
4
chloroform (R = 0.50) and subsequent recrystallization from
2
(d, J = 7.6 Hz, 2H, Ar−H), 8.07 (d, J = 2.4 Hz, 2H, Ar−H). IR (KBr,
f
chloroform/hexane to afford H L as a slightly yellow needle
4
−1
cm ): 1583 (νCN). FAB-MS: m/z 630.0 (calcd for C34
H
N
O
O·-
28
4
2
1
+
crystal (0.640 g, 1.10 mmol, 50.5%). Mp: 143.5−146.0 °C. H
([M] ): m/z 630.1). Calcd for C34
H
28
N
4
O
2
Pd·CH
2
Cl
2
·H
2
NMR (CDCl ): δ 2.12 (m, 4H, CH ), 4.26 (m, 4H, OCH ),
0.4C
6.98.
6
H14: C, 58.46; H, 4.93; N, 7.29. Found: C, 58.62; H, 4.61; N,
3
2
2
7
2
4
7
2
.20 (dd, J = 8.8 and 2.4 Hz, 2H, Ar−H), 7.34 (d, J = 2.4 Hz,
H, Ar−H), 7.40 (t, J = 8.0 Hz, 2H, Ar−H), 7.44 (ddd, J = 7.2,
.8, and 1.2 Hz, 2H, Ar−H), 7.64 (d, J = 8.0 Hz, 2H, Ar−H),
.78 (d, J = 8.8 Hz, 2H, Ar−H), 7.90 (td, J = 7.2 and 1.6 Hz,
H, Ar−H), 8.23 (d, J = 8.0 Hz, 2H, Ar−H), 8.33 (dd, J = 7.2
3. Optical Resolutions. A typical procedure for optical resolutions
4
5
of PdL and PdL is described as follows. A stock solution (1 mg
−1
4
mL ) of PdL in a mixture of chloroform/ethanol (50:1, v/v) was
prepared. A 1.5 mL aliquot of the PdL solution was injected into an
4
and 1.2 Hz, 2H, Ar−H), 8.60 (dd, J = 4.8 and 1.6 Hz, 2H, Ar−
HPLC system [eluent, chloroform/ethanol (50:1, v/v); flow speed, 6.5
−1
−1
mL min ] with a SUMICHIRAL OA-4600 [25 × 2 (i.d.) cm] to
collect fractions. The solvents of the fractions were removed under
reduced pressure at low temperature (less than 20 °C). The same
operations were repeatedly carried out 10 times to give enantiometi-
H), 10.63 (br, 2H, NH). IR (KBr, cm ): 3363 (ν ), 1693
), 1543 (ν
N−H
), 1234 (νC−O−C). FAB-MS: m/z 583.3
(ν
CO
N−CO
+
[calcd for C H N O ([M + H] ): m/z 583.2]. Anal. Calcd for
C H N O : C, 74.21; H, 5.19; N, 9.62. Found: C, 73.85; H,
5
36 31 4 4
3
6
30
.27; N, 9.63.
4
4
4
4
cally pure (−) -PdL (the first eluent) and (+) -PdL (the second
350
350
eluent) as white powders. The optical purities of the collected fractions
were estimated to be more than 99% ee by chiral HPLC analyses.
PdL was also resolved using the same column with a different
Synthesis of [[N,N′-[1,4-Butanediylbis(oxy-7,1-naphthalenediyl)]-
bis(2-pyridinecarboxamidato)](2−)-κN ,κN ′,κN ,κN ′]palladium
1
1
2
2
4
4
5
(
PdL ). A solution of H L (290 mg, 498 μmol) in chloroform (25
2
mL) was added to a solution of Pd(cod)Cl (143 mg, 501 μmol) in
eluent: hexane/ethanol (100:1, v/v).
2
chloroform (50 mL). After the addition of triethylamine (1.4 mL, 10
mmol), the mixture was heated under reflux for 26 h. During heating,
the mixture gradually changed to a reddish-brown suspension. After
filtration of the suspension, the filtrate was concentrated under high
vacuum to leave a crude product. The product was purified by silica gel
chromatography with ethyl acetate and subsequent recrystallization
4. CD Measurements. In order to measure CD spectra of the
isolated stereoisomers of the palladium complexes, each stock solution
of the palladium complexes in 1,2-dichloroethane [1.90 mg/10 mL
−4
4
−4
(2.77 × 10 mM) for PdL and 6.35 mg/10 mL (8.87 × 10 mM)
5
for PdL ] was prepared in measuring flasks. Each stock solution was
transferred to a 0.1 cm quartz cell by a pipet (ca. 0.5 mL). CD spectra
of the stereoisomers of the complexes were measured at the range of
210−500 nm at room temperature (ca. 22−24 °C).
4
from dichloromethane/diethyl ether to afford PdL as an orange
1
needle crystal (68.6 mg, 99.8 μmol, 20.0%). H NMR (CDCl ): δ
3
1
.95−2.15 (m, 4H, CH ), 4.20−4.30 (m, 2H, OCH ), 4.35−4.50 (m,
5. Thermodynamic Investigations. A typical procedure for
investigation of the thermal stabilities of the isolated stereoisomers of
the palladium complexes is described as follows. The solution of
2
2
2
H, OCH ), 6.48 (d, J = 5.6 Hz, 2H, Ar−H), 6.68 (ddd, J = 7.6, 5.6,
2
and 1.6 Hz, 2H, Ar−H), 7.11 (dd, J = 8.8 and 2.4 Hz, 2H, Ar−H), 7.46
t, J = 7.6 Hz, 2H, Ar−H), 7.58 (d, J = 7.6 Hz, 2H, Ar−H), 7.72 (td, J
7.6 and 1.6 Hz, 2H, Ar−H), 7.78 (d, J = 8.8 Hz, 2H, Ar−H), 7.82 (d,
4
(
=
(−)350-PdL in a mixture of hexane/ethanol (9:1, v/v) was prepared
and then kept at 50 °C for a predetermined amount of time. At each
predetermined time, a 100 μL aliquot of the solution was injected into
the chiral HPLC system to estimate an enantiomeric population of
J = 7.6 Hz, 2H, Ar−H), 7.99 (dd, J = 7.6 and 1.6 Hz, 2H, Ar−H), 8.31
−
1
(
d, J = 2.4 Hz, 2H, Ar−H). IR (KBr, cm ): 1628 (ν
), 1250
CO
+
4
(ν
). FAB-MS: m/z 686.0 (calcd for C H N O Pd ([M] ): m/z
PdL . The enantiomer populations were plotted versus time, and then
C−O−C
36 28
4
4
6
86.1). Anal. Calcd for C H N O Pd: C, 62.93; H, 4.11; N, 8.15.
an initial rate constant (k
T
) of isomerization was calculated. Further,
36
28
4
4
‡
4
Found: C, 62.98; H, 4.35; N, 8.01.
Synthesis of N,N′-Bis[(1H-pyrrol-2-yl)methylidene]-7,7′-(1,4-
the isomerization barrier (ΔG ) of PdL was calculated by using k
T
5
1
and the Eyring equation.
5
29b
1
butanediyldioxy)bis(1-naphthalenamine) (H L )..
Na SO was
6. Instruments. NMR measurements (400 MHz for H and 100
2
2
4
MHz for 13C) were performed with CDCl as the solvent at 30 °C on
added to a solution of 1H-pyrrole-2-carbaldehyde (0.51 g, 5.4
mmol) and 7,7′-(1,4-butanediyldioxy)bis(1-naphthalenamine) (0.502
g, 1.35 mmol) in chloroform (20 mL). After the suspension was stirred
at room temperature for 3 weeks, a chloroform-insoluble fraction was
removed by filtration. The crude product obtained by concentration of
3
a Bruker BioSpin DPX-400 spectrometer with respect to tetrame-
thylsilane (TMS; δ 0.00). IR spectra were recorded using a Horiba FT-
720 spectrometer. FAB-MS spectra were measured using a JEOL JMX-
AX505H mass spectrometer. Absorption measurements were
4
139
dx.doi.org/10.1021/ic2024742 | Inorg. Chem. 2012, 51, 4134−4142

Inorganic Chemistry
Article
performed on a JASCO V-550 spectrometer. CD measurements were
carried out with a JASCO J-720 spectropolarimeter. Melting points
were measured using a MEL-TEMP II melting point apparatus
Systems; The Royal Society of Chemistry: Cambridge, U.K., 2000;
Chapter 6, pp 119−184. (c) Albrecht, M. Chem. Rev. 2001, 101,
3457−3497. (d) Albrecht, M. Top. Curr. Chem. 2004, 248, 105−140.
(5) Reviews on helical coordination polymers: (a) Moulton, B.;
Zaworotko, M. J. Chem. Rev. 2001, 101, 1629−1658. (b) Batten, S. R.;
Neville, S. M.; Turner, D. R. Coordination Polymers: Design, Analysis
and Application; The Royal Society of Chemistry: Cambridge, U.K.,
2009. Chapter 11, pp 345−374. (c) Leong, W. L.; Vittal, J. J. Chem.
Rev. 2011, 111, 688−764.
(
Laboratory Devices, MA). Elemental analyses were performed by
using a Yanaco MT-6 CHN analyzer. HPLC experiments for
estimations of enantiomeric excesses were carried out on a Hitachi
instrument (L-7610 degasser, L-6000 pump, L-7400 UV detector, and
D-2500 integrator) with a SUMICHIRAL OA-4600 [25 × 0.46 (i.d.)
cm, 5 μm particle; Sumika Chemical Analysis Service, Osaka, Japan].
HPLC experiments for separations and isolations of stereoisomers
were performed on a Hitachi instrument (L-7110 pump, L-7250
autosampler, L-4000H UV detector, L-5200 fraction collector, and D-
(
6) (a) Autschbach, J.; Nitsch-Velasquez, L.; Rudolph, M. Top. Curr.
Chem. 2011, 298, 1−98. (b) Yang, G.; Xu, Y. Top. Curr. Chem. 2011,
98, 189−236.
7) Reviews on chiral metal complexes for asymmetric reactions: (a)
2
(
2500 integrator) with a SUMICHIRAL OA-4600 [25 × 2 (i.d.) cm, 5
μm particle]. Single-crystal X-ray analyses were conducted using a
Bruker AXS SMART X-ray diffractometer equipped with a CCD area
director and Mo Kα radiation (λ = 0.71073 Å).
Ferrocenes: Homogeneous Catalysis, Organic Synthesis, Materials Science;
Togni, A., Hayashi, T., Eds.; VCH: Weinheim, Germany, 1995. (b)
Comprehensive Asymmetric Catalysis; Jacobsen, E. N., Pfaltz, A.,
Yamamoto, H., Eds.; Springer Verlag: Berlin, 1999. (c) Fu, G. C.
Acc. Chem. Res. 2000, 33, 412−420. (d) Knowles, W. S. Angew. Chem.,
Int. Ed. 2002, 41, 1998−2007. (e) Noyori, R. Angew. Chem., Int. Ed.
ASSOCIATED CONTENT
Supporting Information
X-ray crystallographic data in CIF format, synthesis of CuL ,
single-crystal X-ray data of CuL , PdL , and PdL , and chiral
HPLC profiles on racemization investigations. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
*
S
3
2
002, 41, 2008−2022. (f) Sharpless, K. B. Angew. Chem., Int. Ed. 2002,
3
4
5
41, 2024−2032. (g) Satyanarayana, T.; Abraham, S.; Kagan, H. B.
Angew. Chem., Int. Ed. 2009, 48, 456−494. (h) Catalytic Asymmetric
Synthesis, 3rd ed.; Ojima, I., Ed.; John Wiley & Sons: Hoboken, NJ,
2
(
010.
8) Reviews on chiral supramolecular metal complexes for
AUTHOR INFORMATION
Corresponding Author
E-mail: hrssgmt@rs.kagu.tus.ac.jp.
■
asymmetric reactions: (a) Fiedler, D.; Leung, D. H.; Bergman, R.
G.; Raymond, K. N. Acc. Chem. Res. 2005, 38, 349−358. (b) Lin, W. In
Supramolecular Catalysis; van Leeuwen, P. W. N. M., Ed.; Wiley-VCH-
Verlag: Weinheim, Germany, 2008; Chapter 4, pp 93−111. (c) Pluth,
M. D.; Bergman, R. G.; Raymond, K. N. In Supramolecular Catalysis;
van Leeuwen, P. W. N. M., Ed.; Wiley-VCH-Verlag: Weinheim,
Germany, 2008; Chapter 7, pp 165−197. (d) Takacs, J. M.; Moteki, S.
A.; Reddy, D. S. In Supramolecular Catalysis; van Leeuwen, P. W. N.
M., Ed.; Wiley-VCH-Verlag: Weinheim, Germany, 2008; Chapter 9,
pp 235−253. (e) Pluth, M. D.; Bergman, R. G.; Raymond, K. N. Acc.
Chem. Res. 2009, 42, 1650−1659. (f) Wang, C.; Zheng, M.; Lin, W. J.
Phys. Chem. Lett. 2011, 2, 1701−1709.
*
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank Prof. Y. Nagao, Dr. K. Kozawa, Prof. K.
Miyamura, and K. Ueji of our university for single-crystal X-ray
crystallographic analyses.
REFERENCES
(9) (a) Brintzinger, H. H.; Fischer, D.; Mu
Waymouth, R. M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1143−1170.
b) Kuran, W. Principles of Coordination Polymerization; John Wiley
̈
lhaupt, R.; Rieger, B.;
■
(
1) (a) Lippard, S. J.; Berg, J. M. Principles of Bioinorganic Chemistry;
University Science Books: Mill Valley, CA, 1994. (b) Fraus
(
́
to da Silva,
and Sons: West Sussex, U.K., 2001; Chapter 3, pp 43−245. (c) Suzuki,
J. J. R.; Williams, R. J. P. The Biological Chemistry of the Elements: The
Inorganic Chemistry of Life, 2nd ed.; Oxford University Press: Oxford,
U.K., 2001. (c) Biological Inorganic Chemistry: Structure & Reactivity;
Bertini, I., Gray, H. B., Stiefel, E. I., Valentine, J. S., Eds.; University
Science Books: Sausalito, CA, 2007. (d) Ochiai, E. Bioinorganic
Chemistry: A Survey; Academic Press: Burlington, MA, 2008.
N. Top. Organomet. Chem. 2005, 8, 177−216.
(10) (a) Borovkov, V. V.; Hembury, G. A.; Inoue, Y. Acc. Chem. Res.
2
2
004, 37, 449−459. (b) Borovkov, V. V.; Inoue, Y. Top. Curr. Chem.
006, 265, 89−146. (c) Hembury, G. A.; Borovkov, V. V.; Inoue, Y.
Chem. Rev. 2008, 108, 1−73.
(
11) (a) Shinkai, S.; Ikeda, M.; Sugasaki, A.; Takeuchi, M. Acc. Chem.
(
2) Reviews on stereochemistry of chiral metal complexes: (a)
Rev. 2001, 34, 494−503. (b) Takeuchi, M.; Ikeda, M.; Sugasaki, A.;
Shinkai, S. Acc. Chem. Rev. 2001, 34, 865−873. (c) James, T. D.;
Phillips, M. D.; Shinkai, S. Boronic Acids in Saccharide Recognition; The
Royal Society of Chemistry: Cambridge, U.K., 2006.
Stereochemistry of Optically Active Transition Metal Compounds;
Douglas, B. E., Saito, Y., Eds.; American Chemical Society:
Washington DC, 1980. (b) Amouri, H.; Gruselle, M. Chirality in
Transition Metal Chemistry; John Wiley & Sons: West Sussex, U.K.,
2
008; Chapters 1−3 and 5, pp 1−97 and 121−178. (c) Steed, J. W.;
(12) (a) Tsukube, H.; Shinoda, S. Chem. Rev. 2002, 102, 2389−2403.
(b) Kubo, Y.; Ishii, Y. J. Nanosci. Nanotechnol. 2006, 6, 1489−1509.
(c) Anslyn, E. V. J. Org. Chem. 2007, 72, 687−699. (d) Joyce, L. A.;
Maynor, M. S.; Dragna, J. M.; da Cruz, G. M.; Lynch, V. M.; Canary, J.
W.; Anslyn, E. V. J. Am. Chem. Soc. 2011, 133, 13746−13752.
(13) (a) Wenzel, T. J. Discrimination of Chiral Compounds Using
NMR Spectroscopy; John Wiley & Sons: Hoboken, NJ, 2007; Chapter
9, pp 331−398. (b) Amouri, H.; Gruselle, M. Chirality in Transition
Metal Chemistry; John Wiley & Sons: West Sussex, U.K., 2008;
Chapter 4, pp 99−120.
Atwood, J. L. Supramolecular Chemistry, 2nd ed.; John Wiley & Sons:
West Sussex, U.K., 2009; Chapter 10, pp 591−706.
(
3) Reviews on chiral aggregates of metal complexes: (a) Caulder, D.
L.; Raymond, K. N. Acc. Chem. Res. 1999, 32, 975−982. (b) Leininger,
S.; Olenyuk, B.; Stang, P. J. Chem. Rev. 2000, 100, 853−908.
(
(
c) Swiegers, G. F.; Malefetse, T. J. Chem. Rev. 2000, 100, 3483−3537.
d) Stoddart, J. F.; Lindoy, L. F.; Atkinson, I. M. Self-Assembly in
Supramolecular Systems; The Royal Society of Chemistry: Cambridge,
U.K., 2000; Chapter 7, pp 185−219. (e) Seeber, G.; Tiedemann, B. E.
F.; Raymond, K. N. Top. Curr. Chem. 2006, 265, 147−183. (f) Pluth,
M. D.; Raymond, K. N. Chem. Soc. Rev. 2007, 36, 161−171. (g) Lee, S.
J.; Lin, W. Acc. Chem. Res. 2008, 41, 521−537. (h) Scarso, A.; Borsato,
G. In Chirality at the Nanoscale; Amabilino, D. B., Ed.; Wiley-VCH-
Verlag: Weinheim, Germany, 2009; Chapter 2, pp 29−65.
(14) (a) Lacour, J.; Hebbe-Viton, V. Chem. Soc. Rev. 2003, 32, 373−
382. (b) Constant, S.; Lacour, J. Top. Curr. Chem. 2005, 250, 1−41.
(c) Lacour, J.; Moraleda, D. Chem. Commun. 2009, 7073−7089.
(15) (a) Masuda, Y.; Yamatera, H. Bull. Chem. Soc. Jpn. 1984, 57, 58−
62. (b) Yamagishi, A. J. Coord. Chem. 1987, 16, 131−211. (c) Bergman,
S. D.; Kol, M. Inorg. Chem. 2005, 44, 1647−1654.
(
4) Reviews on helicates: (a) Piguet, C.; Bernardinelli, G.;
Hopfgartner, G. Chem. Rev. 1997, 97, 2005−2062. (b) Stoddart, J.
F.; Lindoy, L. F.; Atkinson, I. M. Self-Assembly in Supramolecular
(16) Amouri, H.; Gruselle, M. Chirality in Transition Metal Chemistry;
John Wiley & Sons: West Sussex, U.K., 2008; Chapter 6, pp 189−204.
4
140
dx.doi.org/10.1021/ic2024742 | Inorg. Chem. 2012, 51, 4134−4142

Inorganic Chemistry
Article
(
3
17) (a) Knof, U.; von Zelewsky, A. Angew. Chem., Int. Ed. 1999, 38,
02−322. (b) von Zelewsky, A.; Mamula, O. J. Chem. Soc., Dalton
Trans. 2000, 219−231.
18) (a) Bailar, J. C. Jr. J. Chem. Educ. 1981, 58, 674−681. (b) Bailar,
J. C. Jr. Coord. Chem. Rev. 1990, 100, 1−27.
19) (a) Werner, A. Z. Anorg. Allg. Chem. 1893, 3, 267−330.
b) Werner, A. Ann. 1912, 386, 1−272. (c) Karrer, P. Helv. Chim. Acta
920, 3, 196−232. (d) Morral, F. R. Adv. Chem. Ser. 1967, 62, 70−77.
20) For chiral octahedral complexes having hexadentate ligands, see:
a) Dwyer, F. P.; Lions, F. J. Am. Chem. Soc. 1947, 69, 2917−2918.
b) Dwyer, F. P.; Gyarfas, E. C.; Mellor, D. P. J. Phys. Chem. 1954, 59,
Adams, M. T.; Dzugan, S. J.; Busch, D. H. Inorg. Chem. 1990, 29,
2945−2947. (g) Liu, Z.-C.; Shao, M.-C.; Tang, Y.-Q. Gaodeng Xuexiao
Huaxue Xuebao 1990, 11, 58−61 (Chinese). (h) Khandar, A. A.;
Cardin, C.; Hosseini-Yazdi, S. A.; McGrady, J.; Abedi, M.; Zarei, S. A.;
Gan, Y. Inorg. Chim. Acta 2010, 363, 4080−4087. (i) Komiya, N.;
Okada, M.; Fukumoto, K.; Jomori, D.; Naota, T. J. Am. Chem. Soc.
2011, 133, 6493−6496.
(30) For examples on optical resolutions of chiral “fly-over”
complexes, see: (a) Naota, T.; Koori, H. J. Am. Chem. Soc. 2005,
127, 9324−9325. (b) Komiya, N.; Muraoka, T.; Iida, M.; Miyanaga,
M.; Takahashi, K.; Naota, T. J. Am. Chem. Soc. 2011, 133, 16054−
16061.
(31) Our researches on this theme have preliminarily been presented
in a presymposium of an international symposium and in an
international symposium. (a) Hayakawa, T.; Sugimoto, H.; Inoue, S.
Poster PA-12 at Symposium on Molecular Chirality, Shizuoka, Japan,
2003. (b) Goto, H.; Hayakawa, T.; Furutachi, K.; Sugimoto, H.; Inoue,
S. Poster PB-89 at the 22nd International Symposium on Chirality
(ISCD-22), Sapporo, Japan, 2010.
(
(
(
1
(
(
(
2
96−297. (c) Chelating Agents and Metal Chelates; Dwyer, F. P.,
Mellor, D. P., Eds.; Academic Press: New York, 1964; references cited
therein. (d) Busch, D. H.; Bailar, J. C. Jr. J. Am. Chem. Soc. 1953, 75,
4
7
8
574−4575. (e) Das Sarma, B.; Bailar, J. C. Jr. J. Am. Chem. Soc. 1955,
7, 5476−5480. (f) Curry, J. D.; Busch, D. H. J. Am. Chem. Soc. 1964,
6, 592−594.
(
21) (a) Hunter, C. A.; Mayers, P. C. Nature 2001, 411, 763.
(
b) Guo, J.; Mayers, P. C.; Breault, G. A.; Hunter, C. A. Nat. Chem.
2
(
010, 2, 218−222.
22) Desvergnes-Breuil, V.; Hebbe, V.; Dietrich-Buchecker, C.;
Sauvage, J.-P.; Lacour, J. Inorg. Chem. 2003, 42, 255−257.
23) For tetrahedral metal complexes having tetradentate ligands,
(32) (a) Chiang, L.-C.; Konishi, K.; Aida, T.; Inoue, S. J. Chem. Soc.,
Chem. Commun. 1992, 254−256. (b) Konishi, K.; Oda, K.; Nishida, K.;
Aida, T.; Inoue, S. J. Am. Chem. Soc. 1992, 114, 1313−1317.
(33) Ito, A.; Konishi, K.; Aida, T. Tetrahedron Lett. 1996, 37, 2585−
2588.
(34) Konishi, K.; Yahara, K.; Toshishige, H.; Aida, T.; Inoue, S. J. Am.
Chem. Soc. 1994, 116, 1337−1344.
(35) (a) Konishi, K.; Kimata, S.; Yoshida, K.; Tanaka, M.; Aida, T.
Angew. Chem., Int. Ed. Engl. 1996, 35, 2823−826. (b) Zheng, J.-Y.;
Konishi, K.; Aida, T. Tetrahedron 1997, 53, 9115−9122. (c) Ishida, Y.;
Konishi, K.; Aida, T.; Nagamume, T. Chem.Eur. J. 1998, 4, 1148−
1153. (d) Shoji, Y.; Tashiro, K.; Aida, T. J. Am. Chem. Soc. 2006, 128,
10690−10691. (e) Shoji, Y.; Tashiro, K.; Aida, T. Chirality 2008, 20,
420−424. (f) Shoji, Y.; Tashiro, K.; Aida, T. J. Am. Chem. Soc. 2010,
132, 5928−5929.
(
see: (a) Graf, E.; Graff, R.; Hosseini, M. W.; Huguenard, C.; Taulelle,
F. Chem. Commun. 1997, 1459−1451. (b) Green, S.; Nelson, A.;
Warriner, S.; Whittaker, B. J. Chem. Soc., Perkin Trans. 1 2000, 4403−
4
(
408.
24) Tetrahedral metal complexes having bidentate ligands. For
beryllium complexes, see: (a) Mills, W. B.; Gotts, R. A. J. Chem. Soc.
1
1
926, 3121−3131. (b) Busch, D. H.; Bailar, J. C. Jr. J. Am. Chem. Soc.
954, 76, 5352−5353. For a zinc complex, see: (c) Liu, J. C. I.;
Bailar, J. C. Jr. J. Am. Chem. Soc. 1951, 73, 5432−5433.
(
25) For tetrahedral metal complexes having four distinct
monodentate ligands, see: (a) Brunner, H.; Schindler, H.-D. J.
Organomet. Chem. 1970, 24, c7−c10. (b) Brunner, H. Angew. Chem.,
Int. Ed. Engl. 1971, 10, 249−260. (c) Jaouen, G.; Meyer, A.;
Simonneaux, G. Tetrahedron 1975, 31, 1889−1895. (d) Flood, T.
C.; DiSanti, F. J.; Miles, D. L. Inorg. Chem. 1976, 15, 1910−1918.
(36) (a) Kuroda, Y.; Kato, Y.; Higashioji, T.; Ogoshi, H. Angew.
Chem., Int. Ed. Engl. 1993, 32, 723−724. (b) Kuroda, Y.; Kato, Y.;
Higashioji, T.; Hasegawa, J.; Kawanami, S.; Takahashi, M.; Shiraishi,
N.; Tanabe, K.; Ogoshi, H. J. Am. Chem. Soc. 1995, 117, 10950−
10958. (c) Mizutani, T.; Kurahashi, T.; Murakami, T.; Matsumi, N.;
Ogoshi, H. J. Am. Chem. Soc. 1997, 119, 8991−9001.
(
e) Leblanc, J. C.; Moise, C.; Tirouflet, J. J. Organomet. Chem. 1978,
1
48, 171−178. (f) Brunner, H. Adv. Organomet. Chem. 1980, 18, 151−
206 and references cited therein..
(37) In our laboratory, metalloporphyrins have frequently been
employed not only as catalysts for precision macromolecular syntheses
(polymethacrylates, polyesters, polyethers, polycarbonates, and so
(
26) For optical resolutions of copper(I) helicates, see: (a) Woods,
C. R.; Benaglia, M.; Cozzi, F.; Siegel, J. S. Angew. Chem., Int. Ed. Engl.
996, 35, 1830−1833. (b) Annunziata, R.; Benaglia, M.; Cinquini, M.;
Cozzi, F.; Woods, C. R.; Siegel, J. S. Eur. J. Org. Chem. 2001, 173−180.
c) Furusho, Y.; Goto, H.; Itomi, K.; Katagiri, H.; Miyagawa, Y.;
Yashima, E. Chem. Commun. 2011, 47, 9795−9797.
27) Square-planar complexes having achiral tetradentate ligands. For
3
8
32,33
1
on) but also as chiral catalysts for asymmetric syntheses
and
3
4−36
chiral selectors for biomolecules.
In addition, a first clear example
(
of an enantiomer-selective polymerization of a racemic epoxide with
chiral initiator systems was reported to afford an optically active
3
9
(
polyether in our former laboratory. Thereafter, Jacobsen and Coates
reported chiral Schiff base/metal complexes as effective catalysts for
enantiomer-selective reactions and polymerizations of racemic
platinum complexes, see: (a) Mills, W. H.; Quibell, T. H. H. J. Chem.
Soc. 1935, 839−846. (b) Habu, T.; Bailar, J. C. Jr. J. Am. Chem. Soc.
1
A. G.; Mills, W. H. J. Chem. Soc. 1939, 1754−1759. (d) Nakamura, K.;
Komorita, T.; Shimura, Y. Bull. Chem. Soc. Jpn. 1981, 54, 1056−1062.
(
4
0
966, 88, 1128−1130. For palladium complexes, see: (c) Lindstone,
epoxides to afford optically active diols and their analogues,
41 42
polyethers, and polycarbonates generated by using alternating
copolymerization with carbon dioxide. In general, chiral metal-
44
4
3
28) Helical conformations of square-planar complexes having achiral
loporphyrins and salen-type [N O ]-Schiff base/metal complexes
2 2
bi- or tetradentate ligands. For an optical resolution using
crystallization, see: (a) Zhang, F.; Bai, S.; Yap, G. P. A; Tarwade,
V.; Fox, J. M. J. Am. Chem. Soc. 2005, 127, 10590−10599. For optical
resolutions using chiral selectors, see: (b) Deuschel-Cornioley, C.;
Stoeckli-Evans, H.; von Zelewsky, A. J. Chem. Soc., Chem. Commun.
utilized as asymmetric catalysts were composed of chiral tetradentate
ligands “porphyrins” or “salen-type Schiff bases” and octahedrally
coordinated metals to preferentially adopt square-planar structures due
to rigidity of the ligands. Other tetradentate compounds such as
porphyrins and salen-type Schiff bases are expected to be effective
ligands for asymmetric syntheses. Because achiral tetradentate
compounds with the aid of four- or six-coordinate metals form chiral
square-planar metal complexes such as chiral metalloporphyrins, the
complexes adopt unique “fly-over” structures, being planar-chiral.
Therefore, in this report, we focus our attention on the chiral
structures of new “strapped” square-planar complexes comprised of
flexible tetradentate ligands and square-planar-coordinated metals.
(38) Aida, T.; Inoue, S. The Porphyrin Handbook Vol. 6: Applications:
Past, Present and Future; Kadish, K. M., Smith, K. M., Guilard, R., Eds.;
Academic Press: San Diego, CA, 2000; Chapter 42, pp 133−156.
1
990, 121−122. (c) O, W. W. N.; Lough, A. J.; Morris, R. H.
Organometallics 2009, 28, 6755−6761.
29) For examples on chiral “fly-over” complexes, see: (a) Schle-
(
singer, N. Ber 1925, 58, 1877−1889. (b) Hendrickson, A. R.; Hope, J.
M.; Martin, R. L. J. Chem. Soc., Dalton Trans. 1979, 1497−1502.
(
c) Baker, A. T.; Martin, R. L.; Taylor, D. J. Chem. Soc., Dalton Trans.
1
979, 1503−1511. (d) Kraihanzel, C. S.; Sinn, E.; Gray, G. M. J. Am.
Chem. Soc. 1981, 103, 960−962. (e) Bailey, N. A.; Barrass, A.; Fenton,
D. E.; Leal Gonzalez, M. S.; Moody, R.; Rodriguez de Barbarin, C. O.
J. Chem. Soc., Dalton Trans. 1984, 2741−2746. (f) Ransohoff, S.;
4
141
dx.doi.org/10.1021/ic2024742 | Inorg. Chem. 2012, 51, 4134−4142

Inorganic Chemistry
Article
(
5
39) (a) Inoue, S.; Tsuruta, T.; Furukawa, J. Makromol. Chem. 1962,
3, 215−218. (b) Tsuruta, T.; Inoue, S.; Yoshida, M.; Furukawa, J.
Makromol. Chem. 1962, 55, 230−231.
40) Tokunaga, M.; Larrow, J. F.; Kakiuchi, F.; Jacobsen, E. N. Science
997, 277, 935−938.
41) Hirahata, W.; Thomas, R. M.; Lobkovsky, E. B.; Coates, G. W. J.
Am. Chem. Soc. 2008, 130, 17658−17659.
42) Qin, Z.-Q.; Thomas, C. M.; Lee, S.; Coates, G. W. Angew.
Chem., Int. Ed. 2003, 42, 5484−5487.
43) Marchon, J.-C.; Ramasseul, R. The Porphyrin Handbook, Vol. 11:
(49) Silverstein, R. M.; Ryskiewicz, E. E.; Chaikin, S. W. J. Am. Chem.
Soc. 1953, 76, 4485−4486.
(50) Drew, D.; Doyle, J. R. Inorg. Synth. 1972, 13, 47−55.
(
1
(
(51) The free activation energy for the racemization process was
⧧
determined according to the Eyring equation: ΔGT = −RT ln(k h/
B
T
−1
−1
κk T), where R is the universal gas constant (=8.31441 J K mol ),
T the absolute temperature (K), k the kinetic rate constant, h Plank’s
T
−34
(
constant (=6.626176 × 10 J s), κ the transition factor (κ = 0.5), and
23
−
−1
kB Boltzmann's constant (=1.380662 × 10 J K ). (a) Trapp, O.;
Trapp, G.; Kong, J.-W.; Hahn, U.; Vo
gtle, F.; Schurig, V. Chem.Eur.
J. 2002, 8, 3629−3634. (b) Osswald, P.; Wurthner, F. J. Am. Chem. Soc.
(
̈
Bioinorganic and Bioorganic Chemistry; Kadish, K. M., Smith, K. M.,
Guilard, R., Eds.; Academic Press: San Diego, CA, 2003; Chapter 64,
pp 75−132.
̈
2007, 129, 14319−14326. (c) Wolf, C. Dynamic Stereochemistry of
Chiral Compounds; The Royal Society of Chemistry: Cambridge, U.K.,
2008; Chapter 4, pp 136−179.
(
44) Jacobsen, E. N. Comprehensive Organometallic Chemistry II; Abel,
E. W., Stone, F. G. A., Wilkinson, G., Eds.; Pergamon, New York,
995; Vol. 12, pp 1097−1135.
45) Wei, L.; Stogsdill, R. M.; Lingafelter, E. C. Acta Crystallogr.
964, 17, 1058−1062.
46) Square-planar metal complexes of N-phenyl-2-pyridinecarbox-
amide derivatives as dissymmetric bidentate ligands. For copper(II):
a) Ray, M.; Mukherjee, R.; Richrdson, J. F.; Mashuta, M. S.;
Buchanan, R. M. J. Chem. Soc., Dalton Trans. 1994, 965−969.
b) Sunatsuki, Y.; Matsumoto, T.; Fukushima, Y.; Mimura, M.;
Hirohata, M.; Matsumoto, N.; Kai, F. Polyhedron 1998, 17, 1943−
952. For platinum(II): (c) Zhang, J.-Y.; Liu, Q.; Duan, C.-Y.; Shao,
Y.; Ding, J.; Miao, Z.-H.; You, X.-Z.; Guo, Z.-J. Dalton Trans. 2002,
(52) For an example of a salen-type [N O ] Schiff base playing a role
2 2
1
(
1
(
as a bidentate ligand binding to a transition metal: (a) Na, S. J.; S, S.;
Cyriac, A.; Kim, B. E.; Yoo, J.; Kang, Y. K.; Han, S. J.; Lee, C.; Lee, B.
Y. Inorg. Chem. 2009, 48, 10455−10465. For examples on complexes
having N atoms noncoordinated to metals, see: (b) Kaye, P. T.;
Nyokong, T.; Watkins, G. M.; Wellington, K. W. Arkivoc 2002, No. ix,
9−18. (c) Wellington, K. W.; Kaye, P. T.; Watkins, G. M. Arkivoc
2009, No. xiv, 301−313. (d) Kose, M.; Mckee, V. Acta Crystallogr.
2011, E67, m149.
(
(
1
4
591−597. Although 1-naphthalenamide subunits of H L essentially
2
possess axial chirality, it is probably difficult that the single subunit is
optically resolved at ambient temperature because of an expectedly low
rotational barrier: (d) Curran, D. P.; Chen, C. H.-T.; Geib, S. J.;
Lapierre, A. J. B. Tetrahedron 2004, 60, 4413−4424. (e) Kessler, H.;
Rieker, A. Liebigs Ann. Chem. 1967, 708, 57−68.
(
47) Square-planar metal complexes of 2-(N-phenylimino)methyl-
1
H-pyrrole derivatives as dissymmetric bidentate ligands. For
copper(II): (a) Castro, J. A.; Romero, J.; Garcia-Vazquez, J. A.;
Castineiras, A.; Duran, D. L.; Sousa, A. Z. Anorg. Allg. Chem. 1992,
6
2
15, 155−160. (b) Grushin, V. V.; Marshall, W. J. Adv. Synth. Catal.
004, 346, 1457−1460. For palladium(II): (c) Yeh, K.-N.; Barker, R.
H. Inorg. Chem. 1967, 6, 830−833. (d) Liang, H.; Liu, J.-G.; Li, X.-F.;
Li, Y.-S. Polyhedron 2004, 23, 1619−1627. Although N-alkylidene-1-
5
naphthalenamine subunits of H L essentially possess axial chirality as
2
well, it is significantly difficult that the single subunit is optically
resolved at ambient temperature because of an expectedly low
rotational barrier: (e) Guerra, A.; Lunazzi, L. J. Org. Chem. 1995, 60,
7959−7965.
(
48) Rowland, J. M.; Thornton, M. L.; Olmstead, M. M.; Mascharak,
P. K. Inorg. Chem. 2001, 40, 1069−1073.
4
142
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