Chiral bisoxazoline ligands designed to stabilize bimetallic complexes

Article abstract of DOI:10.3762/bjoc.14.175

Chiral bisoxazoline ligands containing naphthyridine, pyridazine, pyrazole, and phenol bridging units were prepared and shown to form bimetallic complexes with various metal salts. X-ray crystal structures of bis-nickel naphthyridine-bridged, bis-zinc pyridazine-bridged, and bis-nickel as well as bis-palladium pyrazole-bridged complexes were obtained.

Full text of DOI:10.3762/bjoc.14.175

Chiral bisoxazoline ligands designed to stabilize
bimetallic complexes
Deepankar Das1, Rudrajit Mal1, Nisha Mittal1, Zhengbo Zhu2, Thomas J. Emge1
and Daniel Seidel*1,2
Full Research Paper
Open Access
Address:
Beilstein J. Org. Chem. 2018, 14, 2002–2011.
1Department of Chemistry and Chemical Biology, Rutgers, The State
doi:10.3762/bjoc.14.175
University of New Jersey, Piscataway, NJ 08854, USA and 2Center
for Heterocyclic Compounds, Department of Chemistry, University of
Florida, Gainesville, Florida 32611, USA
Received: 28 May 2018
Accepted: 12 July 2018
Published: 01 August 2018
Email:
Daniel Seidel* - seidel@chem.ufl.edu
Associate Editor: L. Ackermann
*
Corresponding author
© 2018 Das et al.; licensee Beilstein-Institut.
License and terms: see end of document.
Keywords:
bimetallic complexes; bisoxazolines; chiral ligands; heterocycles
Abstract
Chiral bisoxazoline ligands containing naphthyridine, pyridazine, pyrazole, and phenol bridging units were prepared and shown to
form bimetallic complexes with various metal salts. X-ray crystal structures of bis-nickel naphthyridine-bridged, bis-zinc pyri-
dazine-bridged, and bis-nickel as well as bis-palladium pyrazole-bridged complexes were obtained.
Introduction
Metal-centered asymmetric catalysis most commonly relies on arginase [13], are prominent examples of such bimetallic en-
monometallic complexes of various chiral ligands, among zymes.
which chiral bisoxazolines have been highly successful in facili-
tating various Lewis acid-catalyzed asymmetric transformat- A range of bi- and multi-metallic complexes have been utilized
ions [1-3]. In addition to monometallic catalysis, it has long in asymmetric catalysis (Figure 1) [6]. For instance, Shibasaki
been recognized that catalysts possessing two or more metal and co-workers introduced a number of chiral multi-metallic
centers in close proximity can be uniquely effective in complexes such as the hetero-bimetallic complex 1, in which
catalyzing certain types of reactions [4-6]. Serving as a main the two different metals play distinct roles [14,15]. Jacobsen
source of inspiration in the design of chiral small-molecule and co-workers reported dimeric salen complexes 2 which show
systems, nature utilizes a variety of bimetallic and multi- cooperative reactivity between the two metal centers in the
metallic protein complexes to perform a host of biological func- asymmetric ring opening of meso-epoxides [16]. Trost et al.
tions [7]. Urease [8], hemerythrin [9], methane monooxygenase disclosed the synthesis of dinuclear zinc complexes 3 and their
[
10], ribonucleotide reductase [11], catechol oxidase [12], and application to enantioselective Aldol reactions [17,18] and a
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
host of other asymmetric transformations [18]. Other notable bis-copper complex with two equivalents of CuCl2 (Cu∙∙∙Cu dis-
contributions in this area were provided by the groups of tance = 4.291 Å) [53]. Tetraoxazoline ligand 13 undergoes for-
Martell [19,20], Maruoka [21,22], Wuest [4,23-25], and others mation of dinuclear complexes upon treatment with two equiva-
[
26-46]. In the majority of cases where bimetallic complexes lents of either ZnCl2, Ni(PPh3)2Br2, or Cu(OAc)2 (metal dis-
are used as the catalytically active species, the two metal centers tances: Zn∙∙∙Zn = 8.963 Å; Ni∙∙∙Ni = 11.341 Å; Cu∙∙∙Cu =
perform different functions [47,48]. 9.432 Å) [54].
Efforts toward synthesizing bisoxazoline ligands capable of Results and Discussion
concurrently binding to two metal centers have been rather A number of bisoxazoline ligands with different bridging units
limited. Previous work by Pfaltz, Fahrni, Tsukada, Bellemin- were designed. We rationalized that the presence of three
Laponnaz and our group resulted in the synthesis of bisoxazo- binding sites per metal center would be ideal in order to achieve
line containing ligands 6–13 that can simultaneously bind to the desired 1:2 ligand to metal ratio, and to prevent the poten-
two metals (Figure 2). For instance, treatment of 6 with two tial formation of 2:2 or other higher order complexes. Variation
equivalents of copper perchlorate hexahydrate led to the forma- of the bridging moiety should allow for modulation of the dis-
tion of a bis-copper complex [49,50]. The two Cu(ΙΙ) ions, tance between the metal centers. An important criterion for
which have a Cu∙∙∙Cu distance of 2.947 Å, are coordinated to selecting bridging units was their known ability to engage in
the pentadentate bisoxazoline-imidazole moiety and are bridged metal-binding, along with being readily available. This led to
by the central phenoxy group in addition to a hydroxide ligand. the selection of naphthyridine, pyridazine, pyrazole, and phenol
Ligand 7 forms complex binuclear complexes with ZnCl2 and building blocks. We opted to connect these linkers to oxa-
NiCl2 involving two metal centers and three ligand units. The zolines via amide bonds. The reasoning for this was twofold.
2
:3 ZnCl2/7 complex crystal structure exhibits a Zn∙∙∙Zn dis- Firstly, this should provide ligands with significantly improved
tance of 3.056 Å. Compound 8a forms 2:2 complexes with stabilities over for instance imine linkers. In addition, each
ZnCl2 and NiCl2, whereas 8b was reported to form a bis-palla- amide moiety, upon deprotonation (a requirement for complex
dium complex with one equivalent of [(η3-C3H3)PdCl]2 [51]. formation), would provide a formal negative charge on the
Little is known about the complexing abilities of compounds 9 ligand, thus resulting in increased complex stability while
and 11 [49,52]. The naphthyridine-based ligand 10 forms a reducing the number of spectator anions associated with the two
dinuclear complex with nickel(ΙΙ) acetate (Ni∙∙∙Ni distance = metals. Different combinations of five- and six-membered
3
.132 Å). Compound 12, possessing an urea backbone, forms a chelate rings were considered, as those allow for further modu-
Figure 1: Examples of chiral bimetallic complexes utilized in asymmetric catalysis.
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
Figure 2: Previously reported bisoxazoline ligands capable of stabilizing bimetallic complexes.
lation of metal–metal distances. Convenient synthetic se- line 15 [55] to provide bisoxazoline ligand 16-H2 in 65% yield.
quences were developed for six different ligands.
Upon deprotonation, 16-H2 provides a dianionic ligand with
three nitrogen donor atoms per metal center. Ligand 16-H2 was
Naphthyridine-bridged bisoxazoline ligands. The synthesis of found to undergo complex formation with various copper, zinc,
naphthyridine bridged bisoxazoline ligand 16-H2 is outlined in palladium and nickel salts.
Scheme 1. 1,8-Naphthyridine-2,7-diacyl chloride 14, obtained
via a known procedure from the corresponding diacid [49], was Figure 3 shows the X-ray crystal structure of 16·Ni2(OAc)2, ob-
allowed to react with aminoindanol-derived aminophenyloxazo- tained from ligand 16-H2 and two equivalents of nickel(ΙΙ)
Scheme 1: Synthesis of naphthyridine–bisoxazoline ligand 16-H2.
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
acetate. The asymmetric unit of the crystal 16·Ni2(OAc)2
contains two nickel(ΙΙ) centers held in close proximity by three
donor nitrogen atoms per metal center and two differently
bridged acetate ions inside the coordination sphere. The
nitrogen atoms on the naphthyridine and amide moieties bind to
the nickel(ΙΙ) center to form a five-membered metallacycle,
subtending N(2)–Ni(1)–N(3) and N(5)–Ni(2)–N(6) angles of
8
1.53° and 80.34°, respectively. Additionally, the nitrogen
atoms on the oxazoline and amide moieties form six-membered
rings with the nickel(ΙΙ) center with N(1)–Ni(1)–N(2) and
N(4)–Ni(2)–N(5) angles of 93.03° and 90.24°, respectively. All
of the Ni–N distances are between 2.003 and 2.129 Å, typical
for complexes of this type [56,57]. Interestingly, while one of
the two acetate ions bridge the two nickel(ΙΙ) centers by binding
through the two oxygens, the second acetate unit has a some-
what different binding pattern: one oxygen binds to Ni(1) and
the other oxygen acts as the bridge between Ni(1) and Ni(2).
The Ni(1)∙∙∙Ni(2) distance is 3.448 Å, which is slightly longer
than the corresponding Ni∙∙∙Ni distance in the structurally
related 10. The sixth coordination of Ni(2) is fulfilled by the
amide oxygen of a second molecule of the complex (not shown
in the figure for clarity). Apparently, the coordination environ-
ment involving three O-atoms from acetate groups (the Ni(1)
situation) for one of the two metals is preferred in
1
6·Ni2(OAc)2, presumably for steric reasons, as crystal packing
motivations would likely favor two situations as found for
Ni(2), and possibly favoring formation of the 1D polymeric
chain found here extending along the crystal b-axis. When this
interaction is taken into account, both the nickel(ΙΙ) centers are
in distorted octahedral environment. Overall, the ligand back-
bone of complex 16·Ni2(OAc)2 shows a helical arrangement.
This helicity is facilitated by the innate stereogenic centers of
the oxazoline moieties which is further extended by the flexi-
bility afforded by the amide connections.
Figure 3: Thermal ellipsoid plot (50% probability) of the molecular
structure of 16·Ni2(OAc)2. Hydrogen and solvate atoms have been
omitted for clarity: (A) view normal to the mean molecular plane;
(B) side view nearly perpendicular to (A) to allow better view of the
region of open access to the metal site. The complex 16·Ni2(OAc)2
crystallizes in the orthorhombic space group P212121 with
a = 14.1829(5) Å, b = 14.8645(6) Å, c = 25.2342(10) Å, α = 90°,
β = 90°, γ = 90°, V = 5319.9(4) Å3, Z = 4, Dc = 1.450 mg m−3 and
μ(Mo Kα) = 1.017 mm−1.
Naphthyridine ligand 22-H2 was designed as an analogue of pyrazol-3,5-dicarboxylic acid with thionyl chloride, with
ligand 16-H2 that possesses a shortened amide bridge to allow aminophenyloxazoline 24 [59] provided ligand 25-H3 in 85%
for the formation of bimetallic complexes with all five-mem- yield.
bered chelate rings. Ligand 22-H2 was obtained starting from
glycinol 17 and N-carboxybenzyl glycine (20) via the sequence Treatment of 25-H3 with nickel(II) acetate provided the binu-
of steps outlined in Scheme 2. While X-ray quality crystals clear complex 25·Ni2(OAc), the X-ray structure of which is
have not yet been obtained, preliminary experiments have shown in Figure 4. Each unit of the complex is comprised of
shown that ligand 22-H2 undergoes complex formation with two nickel(II) centers, each bound by three nitrogen atoms from
various nickel and palladium salts [58].
the ligand skeleton and bridged by an acetate anion. The
nitrogen atoms from pyrazole and amide moieties coordinate to
Pyrazole-bridged bisoxazoline ligands. The synthesis of an the two nickel centers to form five-membered metallacycles,
analog of bisoxazoline ligand 16-H2 in which the naphthyridine subtending N(1)–Ni(1)–N(2) and N(4)–Ni(2)–N(5) angles of
bridge is replaced with a pyrazole linker is shown in Scheme 3. 84.0° and 85.0°, respectively. Similarly, the nitrogen atoms on
In addition to the change in geometry, compound 25-H3 is a amide and oxazoline moieties form six-membered metallacyles
potentially trianionic as opposed to a dianionic ligand. A reac- with the two metal centers, with N(2)–Ni(1)–N(3) and
tion of pyrazole-3,5-diacyl chloride 23, obtained by treatment of N(5)–Ni(2)–N(6) angles of 92.63° and 94.33°, respectively. All
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
Scheme 2: Synthesis of naphthyridine–bisoxazoline ligand 22-H2.
Scheme 3: Synthesis of pyrazole–bisoxazoline ligand 25-H3.
the Ni–N distances are between 1.855 and 1.903 Å, typical for Initial experiments have shown that the trianionic ligand 30-H3
Ni–N bonds having this coordination geometry. The two nickel readily forms complexes with various nickel, copper and palla-
centers are bridged by an acetate ion and the pyrazole segment dium salts. Figure 5 shows the X-ray crystal structure of
of the ligand, with a distorted square planar geometry observed 30·Pd2Br, obtained from ligand 30-H3 and two equivalents of
for both metal centers. The resulting Ni(1)∙∙∙Ni(2) distance is palladium(ΙΙ) bromide. Each of the two palladium(ΙΙ) centers of
4
.176 Å.
the complex 30·Pd2Br is confined in a slightly distorted square
planar geometry by three donor nitrogen atoms from the ligand
The synthesis of a pyrazole containing ligand potentially and a bridging bromide ion. Unlike the situation in
capable of forming bimetallic complexes with all five-mem- 16·Ni2(OAc)2, where the Ni–O bond from the carbonyl of an
bered chelate rings is shown in Scheme 4. Trianionic ligand adjacent molecule yields both the five-coordinate Ni and 1D
3
0-H3 was prepared starting from the N-carboxybenzyl amino polymeric chain, there are no Pd–O bonds (not even dative) in
acid 26. Coupling of 26 with phenylglycinol (17) resulted in the 30·Pd2Br and the Pd atoms remain nearly square planar. The
formation of the amide 27. Subsequent treatment with p-tolu- donor nitrogen atoms from pyrazole, amide and oxazoline
enesulfonyl chloride and triethylamine in the presence of a cata- moieties coordinate to the palladium centers, forming five-
lytic amount of DMAP provided oxazoline 28. Following membered chelate rings, with the subtended N–Pd–N angles
deprotection, the resulting amine 29 was allowed to react with ranging from 79.43° to 82.16°. The two palladium centers are
half an equivalent of the pyrazole diacyl chloride 23 to yield the bridged by the bromide ion and the pyrazole segment. All of the
pyrazole-bridged bisoxazoline ligand 30-H3.
Pd–N bond lengths fall within a relatively narrow range of
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
1
.925 to 2.025 Å, and are typical for Pd–N bonds with this
coordination geometry. As expected, the Pd–Br bond lengths
are slightly longer (2.519 and 2.529 Å) than the Pd–N bonds.
The bromide ion bridges the two palladium centers with a
Pd–Br–Pd angle of 98.48°. The two nitrogen donor atoms from
the pyrazole moiety forms the second bridging link between the
two metal centers, thereby restricting the N(1)–Pd(1)–Br(1) and
N(4)–Pd(2)–Br(1) angles to 89.89° and 89.73°, respectively.
The resulting Pd(1)∙∙∙Pd(2) distance was observed to be
3
.824 Å.
Pyridazine-bridged bisoxazoline ligands. Ligand 32-H2 was
synthesized from pyridazine diester 31 [60] and aminopheny-
loxazoline 15 (Scheme 5). Treatment of 15 with LDA, fol-
lowed by addition of 31, resulted in the formation of the pyri-
dazine bridged bisoxazoline ligand 32-H2.
Upon deprotonation, 32-H2 provides a dianionic ligand with
three donor nitrogen atoms per metal center. Ligand 32-H2
forms complexes with different nickel, copper, zinc and palla-
dium salts. Shown in Figure 6 is the molecular structure of
3
2·Zn2Cl2. Each unit of the complex 32·Zn2Cl2 consists of two
zinc(ΙΙ) centers, with each bound by three donor nitrogen atoms
from the ligand skeleton and bridged by a chloride ion. The
nitrogen atoms on the pyridazine and amide moieties form five-
membered chelate rings upon coordination to the zinc centers,
subtending N(2)–Zn(1)–N(1) and N(5)–Zn(2)–N(4) angles of
Figure 4: Thermal ellipsoid plot (50% probability) of the molecular
structure of 25·Ni2(OAc). Hydrogen and solvate atoms have been
omitted for clarity: (A) view normal to the mean molecular plane;
7
4.74° and 77.04°, respectively. The coordination of the
(
B) side view nearly perpendicular to (A) to allow better view of the
nitrogen atoms on oxazoline and amide moieties with the two
zinc centers forms six-membered rings with N(3)–Zn(1)–N(2)
and N(6)–Zn(2)–N(5) angles of 87.05° and 88.55°, respectively.
All of the Zn–N distances are within 2.023–2.177 Å, as ex-
pected for such complexes. Interestingly, the two chloride ions
region of open access to the metal site. The complex 25·Ni2(OAc)
crystallizes in the monoclinic space group P21 with a = 9.0473(9) Å,
b = 17.5433(17) Å, c = 11.7671(11) Å, α = 90°, β = 109.643(2)°,
γ = 90°, V = 1759.0(3) Å3, Z = 2, Dc = 1.614 mg m−3 and
μ(Mo Kα) = 1.281 mm−1.
Scheme 4: Synthesis of pyrazole–bisoxazoline ligand 30-H3.
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
Zn(2)–Cl(2) distance of 2.241 Å. Consistent with having a
bridging chloride atom, the Zn(1)∙∙∙Zn(2) distance of 3.857 Å is
somewhat long, compared to the M∙∙∙M distances in two of the
crystal structures mentioned here, namely, the Ni∙∙∙Ni in
1
6·Ni2(OAc)2 at 3.338 Å, shorter because of the smaller radius
of the bridging μ2-O atom, and the 30·Pd2Br at 3.824 Å, shorter
because of both the Pd coordination geometry and the bridging
μ2-Br atom. The Ni∙∙∙Ni in 25·Ni2(OAc) at 4.176 Å is longer
due to its longer three-atom bridge from OAc. In the Cambridge
Structural Database (CSD), there are ten instances of
Ni–N–N–Ni bond connectivity with sp2 N-atoms that are also
bonded to a C-atom. However, all of those have trans related Ni
atoms unlike the cis related here such that the Ni∙∙∙Ni distances
range from 4.54 to 4.72 Å for those ten compounds. Similarly,
for Pd–N–N–Pd and Zn–N–N–Zn, there are few and only all
trans situations in the CSD with ranges of 4.83 to 4.84 Å and
4
.53 to 4.78 Å, respectively, for the two Pd and three Zn com-
pounds. For M–N–N–M with sp3 bridging N-atoms, only four
instances are found – all with M = Zn and N–N from substi-
tuted aminohydrazido ligands and the distances are longer (4.93
to 5.04 Å) and the trans relationship maintains. Thus, the cis
M–N–N–M geometry observed here is quite rare for M = Ni,
Zn, Pd and is uncommon for M = any transition metal (about 90
instances in CSD). Different coordination environments are
found for Zn(1) and Zn(2) in 32·Zn2Cl2. Zn(1) is found to exist
in a square planar environment that experiences a significant
tetrahedral distortion. In contrast, a distorted square pyramidal
binding mode is observed for Zn(2).
Figure 5: Thermal ellipsoid plot (50% probability) of the molecular
structure of 30·Pd2Br. Hydrogen and solvate atoms have been omitted
for clarity: (A) view normal to the mean molecular plane; (B) side view
nearly perpendicular to (A) to allow a better view of the region of open
access to the metal site. The complex 30·Pd2Br crystallizes in the
monoclinic space group P21 with a = 9.8982(7) Å, b = 10.0139(7) Å,
c = 16.9675(12) Å, α = 90°, β = 101.277(1)°, γ = 90°, V = 1649.3(2) Å3,
Z = 2, Dc = 1.847 mg m−3 and μ(Mo Kα) = 2.510 mm−1.
Phenol-bridged bisoxazoline ligands. Ligands incorporating
naphthyridine, pyridazine and pyrazole linkers discussed thus
far bridge two metal atoms by attachment to two different
nitrogen donor atoms. As a result, metal∙∙∙metal distances tend
to be relatively long. Ligand 34-H3 was designed to explore the
effect of a single atom linker, namely a phenoxy bridge. The
tert-butyl group in the para-position was incorporated as it
bind in discrete manners. While one of them acts as a bridge be- would likely increase the overall solubility of the ligand as well
tween the two zinc centers with a Zn(1)–Cl(1)–Zn(2) angle of as its associated complexes. DCC-mediated coupling of 33 [49]
1
05.97°, the other chloride ion binds to Zn(2) only with a with two equivalents of aminophenyloxazoline 15 led to the for-
Scheme 5: Synthesis of pyridazine–bisoxazoline ligand 32-H2.
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Beilstein J. Org. Chem. 2018, 14, 2002–2011.
Conclusion
We have achieved the synthesis of chiral bisoxazoline ligands
that incorporate naphthyridine, pyrazole, pyridazine and phenol
bridges. These compounds readily form complexes with various
transition metal salts and may provide a platform for the devel-
opment of new catalytic enantioselective transformations.
Supporting Information
Supporting Information File 1
Experimental procedures and characterization data.
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-175-S1.pdf]
Supporting Information File 2
Crystallographic information files of synthesized
complexes (CCDC 1568876–1568879).
[https://www.beilstein-journals.org/bjoc/content/
supplementary/1860-5397-14-175-S2.zip]
Acknowledgements
Acknowledgement is made to the Donors of the American
Chemical Society Petroleum Research Fund for support of this
research (Grant No. 47698-G1). We thank Dr. Jacob M. Janey
(formerly Merck & Co.) for a generous donation of cis-1-
amino-2-indanol.
Figure 6: Thermal ellipsoid plot (50% probability) of the molecular
structure of 32·Zn2Cl2. Hydrogen and solvate atoms have been
omitted for clarity: (A) view normal to the mean molecular plane;
(B) side view nearly perpendicular to (A) to allow better view of the
region of open access to the metal site. The complex 32·Zn2Cl2 crys-
tallizes in the monoclinic space group C2 with a = 40.820(5) Å,
b = 7.4084(9) Å, c = 14.6489(17) Å, α = 90°, β = 108.589(2)°, γ = 90°,
V = 4189.8(9) Å3, Z = 4, Dc = 1.575 mg m−3 and μ(Mo Kα) =
ORCID® iDs
Daniel Seidel - https://orcid.org/0000-0001-6725-111X
1.453 mm−1.
mation of phenol-bridged bisoxazoline ligand 34-H3 in a single References
step and moderate yield (Scheme 6). While X-ray quality crys-
tals have not yet been obtained, preliminary experiments have
shown that ligand 34-H2 forms complexes with nickel, copper
and palladium salts [58].
1. Johnson, J. S.; Evans, D. A. Acc. Chem. Res. 2000, 33, 325.
doi:10.1021/ar960062n
2.
McManus, H. A.; Guiry, P. J. Chem. Rev. 2004, 104, 4151.
doi:10.1021/cr040642v
Scheme 6: Synthesis of phenol–bisoxazoline ligand 34-H3.
2009

Beilstein J. Org. Chem. 2018, 14, 2002–2011.
3
4
5
6
7
8
.
.
.
.
.
.
.
Desimoni, G.; Faita, G.; Jorgensen, K. A. Chem. Rev. 2006, 106, 3561.
doi:10.1021/cr0505324
32.Annamalai, V.; DiMauro, E. F.; Carroll, P. J.; Kozlowski, M. C.
J. Org. Chem. 2003, 68, 1973. doi:10.1021/jo025993t
33.Prokofieva, A.; Dechert, S.; Grosse, C.; Sheldrick, G. M.; Meyer, F.
Chem. – Eur. J. 2009, 15, 4994. doi:10.1002/chem.200900424
34.Oh, T.; Lopez, P.; Reilly, M. Eur. J. Org. Chem. 2000, 2901.
doi:10.1002/1099-0690(200008)2000:16<2901::AID-EJOC2901>3.0.C
O;2-0
Vaugeois, J.; Simard, M.; Wuest, J. D. Coord. Chem. Rev. 1995, 145,
55. doi:10.1016/0010-8545(95)90216-3
Gavrilova, A. L.; Bosnich, B. Chem. Rev. 2004, 104, 349.
doi:10.1021/cr020604g
Shibasaki, M.; Yamamoto, Y., Eds. Multimetallic Catalysts in Organic
Synthesis; Wiley-VCH: Weinheim, 2004.
35.Reilly, M.; Oh, T. Tetrahedron Lett. 1995, 36, 221.
doi:10.1016/0040-4039(94)02227-3
Mitić, N.; Smith, S. J.; Neves, A.; Guddat, L. W.; Gahan, L. R.;
Schenk, G. Chem. Rev. 2006, 106, 3338. doi:10.1021/cr050318f
Karplus, P. A.; Pearson, M. A.; Hausinger, R. P. Acc. Chem. Res.
36.Jammi, S.; Saha, P.; Sanyashi, S.; Sakthivel, S.; Punniyamurthy, T.
Tetrahedron 2008, 64, 11724. doi:10.1016/j.tet.2008.10.009
37.Keller, F.; Rippert, A. J. Helv. Chim. Acta 1999, 82, 125.
doi:10.1002/(SICI)1522-2675(19990113)82:1<125::AID-HLCA125>3.0.
CO;2-W
1997, 30, 330. doi:10.1021/ar960022j
9
1
Stenkamp, R. E. Chem. Rev. 1994, 94, 715. doi:10.1021/cr00027a008
0.Whittington, D. A.; Lippard, S. J. J. Am. Chem. Soc. 2001, 123, 827.
doi:10.1021/ja003240n
38.Takizawa, S.; Katayama, T.; Sasai, H. Chem. Commun. 2008, 4113.
doi:10.1039/b806016a
1
1.Logan, D. T.; Su, X.-D.; Åberg, A.; Regnström, K.; Hajdu, J.;
Eklund, H.; Nordlund, P. Structure 1996, 4, 1053.
doi:10.1016/S0969-2126(96)00112-8
39.Takizawa, S.; Katayama, T.; Somei, H.; Asano, Y.; Yoshida, T.;
Kameyama, C.; Rajesh, D.; Onitsuka, K.; Suzuki, T.; Mikami, M.;
Yamataka, H.; Jayaprakash, D.; Sasai, H. Tetrahedron 2008, 64, 3361.
doi:10.1016/j.tet.2008.01.110
1
1
1
1
1
1
1
1
2
2
2.Gerdemann, C.; Eicken, C.; Krebs, B. Acc. Chem. Res. 2002, 35, 183.
doi:10.1021/ar990019a
3.Kanyo, Z. F.; Scolnick, L. R.; Ash, D. E.; Christianson, D. W. Nature
40.Saito, A.; Yanai, H.; Taguchi, T. Tetrahedron Lett. 2004, 45, 9439.
doi:10.1016/j.tetlet.2004.10.079
1
996, 383, 554. doi:10.1038/383554a0
4.Shibasaki, M.; Sasai, H.; Arai, T. Angew. Chem., Int. Ed. Engl. 1997,
6, 1237. doi:10.1002/anie.199712361
41.Saito, A.; Ito, H.; Taguchi, T. Org. Lett. 2002, 4, 4619.
doi:10.1021/ol026963f
3
5.Shibasaki, M.; Kanai, M.; Matsunaga, S.; Kumagai, N.
42.Kleinbeck, F.; Toste, F. D. J. Am. Chem. Soc. 2009, 131, 9178.
doi:10.1021/ja904055z
Acc. Chem. Res. 2009, 42, 1117. doi:10.1021/ar9000108
6.Konsler, R. G.; Karl, J.; Jacobsen, E. N. J. Am. Chem. Soc. 1998, 120,
43.Zhao, D.; Yuan, Y.; Chan, A. S. C.; Wang, R. Chem. – Eur. J. 2009, 15,
2738. doi:10.1002/chem.200802688
10780. doi:10.1021/ja982683c
7.Trost, B. M.; Ito, H. J. Am. Chem. Soc. 2000, 122, 12003.
doi:10.1021/ja003033n
44.Sun, J.; Yang, M.; Yuan, F.; Jia, X.; Yang, X.; Pan, Y.; Zhu, C.
Adv. Synth. Catal. 2009, 351, 920. doi:10.1002/adsc.200800767
45.Sun, J.; Yuan, F.; Yang, M.; Pan, Y.; Zhu, C. Tetrahedron Lett. 2009,
50, 548. doi:10.1016/j.tetlet.2008.11.060
8.Trost, B. M.; Bartlett, M. J. Acc. Chem. Res. 2015, 48, 688.
doi:10.1021/ar500374r
9.Gao, J.; Reibenspies, J. H.; Martell, A. E. Angew. Chem., Int. Ed. 2003,
46.Sakaguchi, S.; Yoo, K. S.; O'Neil, J.; Lee, J. H.; Stewart, T.;
Jung, K. W. Angew. Chem., Int. Ed. 2008, 47, 9326.
doi:10.1002/anie.200803793
4
2, 6008. doi:10.1002/anie.200351978
0.Gao, J.; Zingaro, R. A.; Reibenspies, J. H.; Martell, A. E. Org. Lett.
004, 6, 2453. doi:10.1021/ol049156k
2
47.Ma, J.-A.; Cahard, D. Angew. Chem., Int. Ed. 2004, 43, 4566.
doi:10.1002/anie.200300635
1.Ooi, T.; Saito, A.; Maruoka, K. Tetrahedron Lett. 1998, 39, 3745.
doi:10.1016/S0040-4039(98)00575-9
48.Park, J.; Hong, S. Chem. Soc. Rev. 2012, 41, 6931.
doi:10.1039/c2cs35129c
2
2.Keiji, M. Bull. Chem. Soc. Jpn. 2009, 82, 917. doi:10.1246/bcsj.82.917
3.Sharma, V.; Simard, M.; Wuest, J. D. J. Am. Chem. Soc. 1992, 114,
2
49.Fahrni, C. J.; Pfaltz, A. Helv. Chim. Acta 1998, 81, 491.
doi:10.1002/hlca.19980810304
7931. doi:10.1021/ja00046a061
2
4.Vaugeois, J.; Wuest, J. D. J. Am. Chem. Soc. 1998, 120, 13016.
doi:10.1021/ja982725x
50.Fahrni, C. J.; Pfaltz, A.; Neuburger, M.; Zehnder, M. Helv. Chim. Acta
1998, 81, 507. doi:10.1002/hlca.19980810305
2
5.Wuest, J. D. Acc. Chem. Res. 1999, 32, 81. doi:10.1021/ar980076o
6.Constable, E. C.; Zhang, G.; Housecroft, C. E.; Neuburger, M.;
Schaffner, S.; Woggon, W.-D. New J. Chem. 2009, 33, 1064.
doi:10.1039/b821995h
51.Tsukada, N.; Sato, T.; Mori, H.; Sugawara, S.; Kabuto, C.; Miyano, S.;
Inoue, Y. J. Organomet. Chem. 2001, 627, 121.
2
doi:10.1016/S0022-328X(01)00729-X
52.Seitz, M.; Kaiser, A.; Tereshchenko, A.; Geiger, C.; Uematsu, Y.;
Reiser, O. Tetrahedron 2006, 62, 9973. doi:10.1016/j.tet.2006.08.003
53.Mal, R.; Mittal, N.; Emge, T. J.; Seidel, D. Chem. Commun. 2009, 7309.
doi:10.1039/b918735a
27.Tschinkl, M.; Schier, A.; Riede, J.; Gabbai, F. P. Organometallics 1999,
18, 1747. doi:10.1021/om990144q
2
8.Guo, Q.-X.; Wu, Z.-J.; Luo, Z.-B.; Liu, Q.-Z.; Ye, J.-L.; Luo, S.-W.;
Cun, L.-F.; Gong, L.-Z. J. Am. Chem. Soc. 2007, 129, 13927.
doi:10.1021/ja074322f
54.Nano, A.; Brelot, L.; Rogez, G.; Maisse-François, A.;
Bellemin-Laponnaz, S. Inorg. Chim. Acta 2011, 376, 285.
doi:10.1016/j.ica.2011.06.029
29.Park, J.; Lang, K.; Abboud, K. A.; Hong, S. J. Am. Chem. Soc. 2008,
1
30, 16484. doi:10.1021/ja807221s
55.Doherty, S.; Knight, J. G.; McRae, A.; Harrington, R. W.; Clegg, W.
Eur. J. Org. Chem. 2008, 1759. doi:10.1002/ejoc.200700922
56.Allen, F. H. Acta Crystallogr., Sect. B: Struct. Sci. 2002, 58, 380.
doi:10.1107/S0108768102003890
3
0.Li, W.; Thakur, S. S.; Chen, S.-W.; Shin, C.-K.; Kawthekar, R. B.;
Kim, G.-J. Tetrahedron Lett. 2006, 47, 3453.
doi:10.1016/j.tetlet.2006.03.042
3
1.Kawthekar, R. B.; Kim, G.-J. Helv. Chim. Acta 2008, 91, 317.
57.Groom, C. R.; Bruno, I. J.; Lightfoot, M. P.; Ward, S. C.
Acta Crystallogr., Sect. B: Struct. Sci., Cryst. Eng. Mater. 2016, 72,
doi:10.1002/hlca.200890037
171. doi:10.1107/S2052520616003954
2010

Beilstein J. Org. Chem. 2018, 14, 2002–2011.
5
8.In preliminary studies regarding complex formation, metal salts were
mixed with the ligand in a 2:1 ratio in dichloromethane. While the metal
salts were essentially insoluble in dichloromethane, nearly
homogeneous solutions resulted after stirring. Following filtration and
removal of solvents, brightly colored solids were obtained as opposed
to white/colorless ligands.
5
9.Wolińska, E. Tetrahedron: Asymmetry 2014, 25, 1478.
doi:10.1016/j.tetasy.2014.10.001
6
0.Bessard, Y.; Crettaz, R.; Brieden, W. Method of producing
pyridazine-3,6-dicarboxylic esters. WO Pat. Appl. WO2001007415A1,
Feb 1, 2001.
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