New bifunctional bis(Azairidacycle) with axial chirality via double cyclometalation of 2,2′-bis(aminomethyl)-1,1’-binaphthyl

Article abstract of DOI:10.3390/molecules26041165

As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C-N chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is newly designed. An expedient synthesis of chiral 2,2′-bis(aminomethyl)-1,1′-binaphthyl (1) from 1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed cyanation and subsequent reduction with Raney-Ni and KBH₄. The reaction of (S)-1 with an equimolar amount of [IrCl₂Cp*]₂ (Cp^* = η⁵-C₅(CH₃)₅) in the presence of sodium acetate in acetonitrile at 80 ?C gave a diastereomeric mixture of new dinuclear dichloridodiiridium complexes (5) through the double C-H bond cleavage, as confirmed by 1H NMR spectroscopy. A loss of the central chirality on the Ir centers of 5 was demonstrated by treatment with KOC(CH₃)₃ to generate the corresponding 16e amidoiridium complex 6. The following hydrogen transfer from 2-propanol to 6 provided diastereomers of hydrido(amine)iridium retaining the bis(azairidacycle) architecture. The dinuclear chlorido(amine)iridium 5 can serve as a catalyst precursor for the asymmetric transfer hydrogenation of acetophenone with a substrate to a catalyst ratio of 200 in the presence of KOC(CH₃)₃ in 2-propanol, leading to (S)-1-phenylethanol with up to an enantiomeric excess (ee) of 67%.

Full text of DOI:10.3390/molecules26041165

molecules
Article
New Bifunctional Bis(azairidacycle) with Axial Chirality via
0
0
Double Cyclometalation of 2,2 -Bis(aminomethyl)-1,1 -binaphthyl
Yasuhiro Sato 1,2, Yuichi Kawata , Shungo Yasui , Yoshihito Kayaki * and Takao Ikariya 1,†
1
1
1,
1
Department of Chemical Science and Engineering, School of Materials and Chemical Technology,
Tokyo Institute of Technology, 2-12-1-E4-1 O-okayama, Meguro-ku, Tokyo 152-8552, Japan;
satouy@fri.go.jp (Y.S.); step_by_step@dk.pdx.ne.jp (Y.K.); yasui0226@gmail.com (S.Y.)
Hazardous Materials Laboratory, Research and Development Division, National Research Institute of Fire
2
and Disaster, Jindaiji-higashimachi 4-35-3, Chofu, Tokyo 182-8508, Japan
*
†
Correspondence: ykayaki@o.cc.titech.ac.jp; Tel.: +81-3-5734-2881
Deceased on 21 April 2017.
Abstract: As a candidate for bifunctional asymmetric catalysts containing a half-sandwich C–N
chelating Ir(III) framework (azairidacycle), a dinuclear Ir complex with an axially chiral linkage is
0
0
newly designed. An expedient synthesis of chiral 2,2 -bis(aminomethyl)-1,1 -binaphthyl (
1) from
1,1-bi-2-naphthol (BINOL) was accomplished by a three-step process involving nickel-catalyzed
cyanation and subsequent reduction with Raney-Ni and KBH . The reaction of (S)-
1
with an equimo-
4
5
lar amount of [IrCl Cp*] (Cp* =
η
–C (CH ) ) in the presence of sodium acetate in acetonitrile at
2
2
5
3 5
◦
8
0 C gave a diastereomeric mixture of new dinuclear dichloridodiiridium complexes (
5) through
1
the double C–H bond cleavage, as confirmed by H NMR spectroscopy. A loss of the central chirality
on the Ir centers of
16e amidoiridium complex
astereomers of hydrido(amine)iridium retaining the bis(azairidacycle) architecture. The dinuclear
chlorido(amine)iridium can serve as a catalyst precursor for the asymmetric transfer hydrogenation
5 was demonstrated by treatment with KOC(CH ) to generate the corresponding
3 3
ꢀ
ꢁꢂꢀꢃꢄꢅꢆꢇ
ꢀ
ꢁꢂꢃꢄꢅꢆ
6. The following hydrogen transfer from 2-propanol to 6 provided di-
Citation: Sato, Y.; Kawata, Y.; Yasui, S.;
Kayaki, Y.; Ikariya, T. New Bifunctional
Bis(azairidacycle) with Axial Chirality
5
of acetophenone with a substrate to a catalyst ratio of 200 in the presence of KOC(CH ) in 2-propanol,
3 3
0
via Double Cyclometalation of 2,2 -
leading to (S)-1-phenylethanol with up to an enantiomeric excess (ee) of 67%.
0
Bis(aminomethyl)-1,1 -binaphthyl.
Molecules 2021, 26, 1165. https://doi.
Keywords: bifunctional catalyst; metal-ligand cooperation; dinuclear complex; iridacycle; cyclometa-
org/10.3390/molecules26041165
lation; asymmetric transfer hydrogenation; cyanation; 1,1-binaphthyl; axial chirality
Academic Editor: Vincent Ritleng
Received: 31 January 2021
Accepted: 18 February 2021
Published: 22 February 2021
1
. Introduction
The metal/NH bifunctional catalysis has become a pivotal concept for redox trans-
formations based on hydrogen transfer between secondary alcohols and ketones [
From in-depth studies on original (
1
–
5
].
6
η
-arene)Ru catalysts bearing chiral N-sulfonyldiamines
], a fundamental hydrogen
Publisher’s Note: MDPI stays neutral
with regard to jurisdictional claims in
published maps and institutional affil-
iations.
(
N–N chelate complexes) developed by Noyori and Ikariya [
6
,7
delivery process associated with alternating back and forth between 16e amido and 18e
hydrido(amine) complexes has been thoroughly realized. We have systematically inves-
tigated how the interconversion operates in a range of group 8 and 9 metal complexes
with protic amine chelates, and we also investigated how ligand modification, by changing
the chelating atom, significantly influences the catalyst performance [
2
,
8
,
9
]. In particular,
6
half-sandwich (
η
-arene)Ru, Cp*Ir, and Cp*Rh complexes containing a five-membered
Copyright: © 2021 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
bifunctional C–N chelate ring, which were synthesized by the orthometalation of protic
benzylamine derivatives [10 13], have been applied to efficient bifunctional catalysts based
on the amine/amido functionalities (Scheme 1) [14 26]. Compared to the prototype N–N
chelate Ir complex, remarkable enhancement in the transfer hydrogenation of ketones in
-propanol [12] and in the aerobic oxidation of alcohols were observed [13]. The rapid
–
–
2
hydrogen transfer from alcohols to the amidoiridium and from the hydrido(amine)iridium
to ketones also accommodates the dynamic kinetic resolution of racemic secondary alcohols
4
.0/).
Molecules 2021, 26, 1165. https://doi.org/10.3390/molecules26041165
https://www.mdpi.com/journal/molecules

Molecules 2021, 26, 1165
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by combination with enzymatic transesterification using Candida antarctica lipase B [21].
The unique catalytic function could be enhanced by the high basicity of the amido moiety
as well as strong nucleophilicity of the hydrido ligand with the aid of the pronounced
σ-donor nature of the coordinating carbon atom.
Scheme 1. Transfer hydrogenation between alcohols and ketones based on the metal/NH bifunctionality.
The asymmetric versions of amidoiridium have been synthesized by the orthometa-
lation of 1-phenyl-1-aminoalkanes with a chiral center at the benzylic position and have
provided reasonable enantioselectivities in the asymmetric transfer hydrogenation of ace-
tophenone [25]. The structural studies on the isolable catalytic intermediates suggested
that the effective asymmetric induction is intimately bound up with decent diastereomeric
control in the formation of hydrido(amine)iridium possessing central chirality at the metal
by a one-sided approach of the hydrogen donor, 2-propanol, to amidoiridium. Related
cationic Ru, Rh, and Ir complexes bearing cyclometalated C–N chelates were intensively
investigated by Pfeffer and coworkers [14–20] from screening experiments using a vari-
ety of chiral benzylic amine ligands, but catalytically active amido and hydrido(amine)
complexes have not been characterized.
Separately, it has been reported that dinuclear complexes, in which the mononuclear
structure is extended by bridging ligands, exhibit characteristic properties and favorable
catalytic performance compared to the parent mononuclear complexes [27–34]. Thanks to
the cooperative effect, in which the reaction sites on multiple metals play different roles, and
the unique electronic structure of the conjugated bridging ligands, the catalytic activity and
enantioselectivity can be improved by multinuclear assembly. In particular, as beneficial
applications of optically active dinuclear transition metal complexes with axial chirality
introduced into the bridging moiety, Toste et al. have demonstrated the gold-catalyzed
dynamic kinetic resolution of propargylic esters [32] and Sasai et al. have demonstrated
the vanadium-catalyzed asymmetric oxidative coupling of aromatic compounds [33,34].
Encouraged by these works, we focused our interest on a dimetallic compound with a
chiral diamido linkage formed by the double orthometalation of benzylic diamine shown
in Scheme 2. It is expected that inherent intramolecular steric effects arising from the
discrete symmetrical bis(metallacycle) will contribute to enhance the catalytic performance
compared with the mononuclear C–N chelate complexes. We report here a synthetic
0
0
approach toward optically active 2,2 -bis(aminomethyl)-1,1 -binaphthyl (1) and its transfor-
mation into a new chiral dinuclear azairidacycle. Furthermore, catalytic application to the
asymmetric transfer hydrogenation of acetophenone using 2-propanol was also explored.

Molecules 2021, 26, 1165
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H
N
H
Ir
H N
2
Ir
NH2
N
H
H
1
Scheme 2. Retrosynthesis of bis(azairidacycle) with an axially chiral binaphthyl linkage.
2
. Results and Discussion
.1. A Short-Cut Synthesis of 2,2 -Bis(aminomethyl)-1,1 -Binaphthyl
The axially chiral diamine has been synthesized by the reductive transformation of di-
azo or dicarboxamide compounds as reported independently by Shi [35] and Tomioka [36
for each route A and B in Scheme 3); however, these precursors are obtained via multi-
0
0
2
1
]
(
step procedures starting with BINOL. As a simple synthetic strategy enabling C–C bond
0
construction on the 1,1 -binaphthyl scaffold and amine functionalization, we examined a
three-step sequence involving the catalytic dicyanation of easily accessible BINOL ditriflate
(
2; >99% enantiomeric excess (ee)) and the following reduction of the C–N triple bonds to
the aminomethyl group (route C).
HO
Br
N3
OH
Br
N3
2
steps
route A
3
steps H2NC(O)
TfO
CONH2
route B
OTf
2
H N
2
NC
CN
NH2
route C
3
1
.
0
0
Scheme 3. Synthetic routes to 2,2 -bis(aminomethyl)-1,1 -binaphthyl, 1.
The cyanation of aryl halides and pseudo-halides with cyanide salts has been disclosed
by using Ni or Pd catalysts [37 43]. To overcome catalyst deactivation by cyanide anion
due to its strong coordination ability, some Cu and Zn cocatalysts have been reported to
be effective [44 45]. Nevertheless, the employment of as the substrate for dicyanation
shown in Scheme 3 remains far less explored, and there is still room for improvement in
terms of practicality [46 47]. Although it was reported that a limited amount (10%) of the
–
,
2
,

Molecules 2021, 26, 1165
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dinitrile product (
that switching the phosphorus ligand to chelate phosphines resulted in the preferential
formation of the dinitrile rather than the mononitrile ( ) (Scheme 4). Some typical results
are summarized in Table 1. When the reaction of (S)- with KCN (1.1 equiv) was performed
3) was obtained in a Ni/PPh /Zn three-component catalyst, we found
3
4
2
using NiCl (dppe) (10 mol%) with an extra amount (10 mol%) of DPPE (DPPE = 1,2-
2
bis(diphenylphosphino)ethane) in the presence of Zn powder (30 mol %) under reflux
conditions for 24 h, a high boiling point solvent, DMF (N,N-dimethylformamide), was
found to be superior to 1,4-dioxane and acetonitrile (entries 1–3). To our delight, (S)-
3
was obtained in 87% yield without loss of the optical purity (>99% ee). The use of
additional phosphine was advantageous for the cyanation, possibly preventing excessive
coordination of the cyanide anion. Other chelate phosphines (entries 4 and 5) and the Pd
variant (entry 6) resulted in a decrease in the yield of 3. The subsequent reduction of 3 was
achieved by a combined use of Raney-Ni and KBH4 [48], whereas it has been reported that
only trace amounts of the desired diamine were produced in some other approaches [47].
After optimization of the reaction conditions, treatment with excess Raney-Ni (4 equiv)
◦
and KBH (8 equiv) in ethanol at 50 C for 3 h gave (S)-
1
in a good yield of 83% (Scheme 5;
4
Figures S4 and S5, In the Supplementary Materials).
Scheme 4. Catalytic cyanation of ditriflate 2.
Table 1. Catalytic cyanation of 2.
%
Yield 1
Entry
Cat
Ligand
Solvent
Dioxane
3
4
n.d. 2
17
0
1
2
3
4
5
6
NiCl (dppe)
DPPE
DPPE
DPPE
DPPP
DPPF
DPPE
2
2
NiCl (dppe)
CH CN
19
87
57
17
59
2
3
NiCl (dppe)
DMF
DMF
DMF
DMF
2
NiCl (dppp)
5
2
2
NiCl (dppf)
n.d.
2
n.d. 2
PdCl (dppe)
2
1
Isolated yield. 2 Not determined.
H N
2
NC
Raney-Ni 4 equiv
EtOH
NC
+
KBH4
equiv
+
CN
NH2
NH2
8
5
0 °C, 3 h
3
83% yield
<1% yield
Scheme 5. Reduction of 3 with Raney-Ni and KBH4.
.2. Synthesis of Bis(azairidacycle) via Double Cyclometalation
According to our original synthetic procedure for azairidacycles [12], the orthometala-
2
tion of enantiopure was performed by mixing [Cp*IrCl ] with a 2.2 molar amount of
2
2
2
◦
sodium acetate (1.1 equiv/Ir) in acetonitrile at 80 C for 15 h. After the removal of acetic
acid and the remaining salts from the reaction mixture through the work-up process, new
0
dichloridodiiridium (
5
) having an axially chiral 1,1 -binaphthyl linkage was obtained as a

Molecules 2021, 26, 1165
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yellow powder in 69% yield (Scheme 6). Based on the electrospray ionization mass spec-
trum (ESI-MS) displaying characteristic ion peaks at m/z 999.3 and 1001.3 for a fragment of
1
C H N ClIr , a completion of the double cyclometalation was confirmed. The H NMR
42
48
2
2
spectrum of 5 in CD Cl exhibited a singlet signal at 1.73 ppm due to the methyl protons of
2 2
the Cp* ligand along with two minor singlet signals at 1.69 and 1.71 ppm, which suggested
the formation of a diastereomeric mixture caused by the chirality at iridium (Figure S6,
In the Supplementary Materials).
Scheme 6. Synthesis of dichloridodiiridium 5 via double orthometalation.
In fact, the subsequent treatment of
5 with 2 equivalents of KOC(CH ) in CD Cl
3 3 2 2
led to the generation of a coordinatively unsaturated amidoiridium species (
6
) with a
color change from orange to dark red purple (Scheme 7), thereby simplifying the spectrum
owing to a loss of the central chirality at the iridium atoms. As shown in Figure 1, the
signal attributed to the methyl group of Cp* ligand converged to a simple peak at 1.98 ppm.
In analogy with the mononuclear C–N chelate complexes, a marked downfield shift trend
1
relative to the NH signals of amine complexes was observed in the H NMR spectrum
2
of 6 exhibiting the amido signal at 8.20 ppm. These spectroscopic results corroborate that
reactant 5 was comprised of the stereoisomers of chlorido(amine)iridium.
H
N
H H
N
Cl
KOC(CH3)3
2 equiv
Ir
Ir
CD Cl
Ir
2
2
Ir
Cl
N
H H
N
H
5
6
Scheme 7. Formation of coordinatively unsaturated amidoiridium complex by dehydrochlorination
of 5.
The 16-electron amidoiridium complex
drido(amine)iridium quantitatively in 2-propanol at room temperature for 2 h (Scheme 8),
in a similar fashion to the mononuclear complexes [12 25]. After removal of the solvent
6 was convertible into the corresponding hy-
,
from the reaction mixture under reduced pressure, the resulting white solid was dissolved
1
in CD Cl , and the H NMR spectrum was recorded. As shown in Figure 2, four signals in
2
2
the hydride region at –12.81, –12.86,
of three diastereomers involving two homochiral (R R and S S forms) and one here-
−
12.88, and –12.90 ppm are attributable to formation
Ir Ir
Ir Ir
rochiral (an R S form) diiridium centers (Scheme 8). Given the fact that the two signals
Ir Ir
with identical intensity at –12.86 and –12.88 ppm can be assigned to the latter diastereomer
having inequivalent C–N chelating hydridoiridium fragments, the stereoisomers were
1
formed in a ratio of 2:4:5. The H NMR spectrum also showed singlet signals with the simi-
lar intensity ratio at around 1.9 ppm due to the methyl protons of Cp* ligand coordinated
to the C -symmetric bis(azairidacycle)s and the unsymmetrical stereoisomer. The relative
2
ratios were not altered by lowering the measurement temperature.

Molecules 2021, 26, 1165
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1
Figure 1. Selected H NMR spectrum of 6 in CD Cl .
2
2
Scheme 8. Transformation of 6 into hydrido(amine)iridium complexes.
1
Figure 2. Selected H NMR spectrum of a streoisomeric mixture of hydridoiridium generated from
6
with 2-propanol.
2
.3. Catalytic Application to the Asymmetric Transfer Hydrogenation of Acetophenone in
-Propanol
2
Based on the smooth formation of amidoiridium and hydrido(amine)iridium in the
bis(azairidacycle) system, we further explored its catalytic potential for the asymmet-
ric transfer hydrogenation. The reaction of acetophenone in 2-propanol containing the
◦
catalyst precursor
5
with a substrate/iridium ratio of 200 at 30 C proceeded to give (S)-
1
-phenylethanol in 60% yield with a moderate ee of 60% after 1 h (Scheme 9). When the

Molecules 2021, 26, 1165
7 of 12
◦
30 C for 12 h, a slightly higher enantioselectivity (67% ee)
reduction was carried out at
−
was observed, albeit in 46% yield. For the mononuclear C–N chelating ruthenium variants,
it has been argued that precise control of the central chirality at the metal of the catalytically
active hydrido complexes having three-legged piano stool geometry could be vital for the
asymmetric induction through the hydrogen transfer [16]. The above-mentioned formation
of minor diastereomers of hydrido(amine)iridium possibly eroded the ee of the chiral
secondary alcohol product. The catalytic results indicate that the asymmetric dinuclear
complex containing bis(azairidacycle) substructure can behave as a promising bifunctional
catalyst for highly efficient transfer hydrogenation, although a redoubled effort to design
the chiral ligand structure would be required for dramatic improvement in terms of the
discrimination of prochiral face of the ketonic substrates.
O
5 cat, 0.5 mol%
KOC(CH ) , 0.6 mol%
OH
CH3
OH
O
3
3
+
+
CH3
S
2
-propanol
[
ketone] = 0.1 M in 2-propanol
30 °C, 1 h; 60% yield, 60% ee
30 °C, 12 h; 46% yield, 67% ee
–
Scheme 9. Asymmetric transfer hydrogenation of acetophenone in 2-propanol catalyzed by 5.
3. Materials and Methods
3.1. General Information
All manipulations of oxygen and moisture-sensitive materials were performed under
a purified argon atmosphere using standard Schlenk techniques. Solvents were purchased
from Kanto Chemical Co., Inc. (Tokyo, Japan) and dried by refluxing over sodium ben-
zophenone ketyl (THF, 1,4-dioxane, and diethyl ether), P O (CH CN and CH Cl ), or
2
5
3
2
2
CaH (2-propanol, pentane), and distilled under argon before use. Ethyl acetate and
2
chloroform-d was used as delivered. Dichloromethane-d was degassed by three freeze–
1
2
pump–thaw cycles and purified by trap-to-trap distillation after being dried with P O .
2
5
Acetophenone was purchased from Kanto Chemical Co., Ltd. (Tokyo, Japan), degassed,
and stored under argon atmosphere. The other reagents were purchased from Sigma-
Aldrich Co. LLC. (St. Louis, MO, USA), Tokyo Chemical Industry Co., Ltd. (Tokyo, Japan),
Nacalai Tesque Inc. (Kyoto, Japan) and FUJIFILM Wako Pure Chemical Corporation (Osaka,
Japan), and used as delivered. The starting Ir complex, [Cp*IrCl ] [49], and Ni and Pd
2
2
catalysts such as NiCl (dppe) [50] were prepared according to the procedures described
2
1
13
1
in the literature with modifications. H and C{ H} NMR spectra were recorded on a
JEOL JNM-LA300 and JNM-ECX400 spectrometers (JEOL Ltd., Tokyo, Japan) at around
◦
2
5 C unless otherwise noted. The NMR chemical shifts were referenced to an external
tetramethylsilane signal (0.0 ppm) by using the signals of residual proton impurities in
1
13
1
the deuterated solvents for H and C{ H} NMR. ESI-MS was acquired with a JEOL
JMS-T100LC spectrometer (JEOL Ltd., Tokyo, Japan). Analytical gas chromatography was
performed with a Shimadzu GC-17A gas chromatograph equipped with an INNOWAX
capillary column (30 m
×
0.25 mm i.d.) purchased from Agilent Technologies (Santa Clara,
CA, USA). High performance liquid chromatography (HPLC) analysis was performed
using a system comprised of a JASCO column oven: CO-1565, a low-pressure gradient
unit: LG-1580-02, a pump: PU-1580, a degasser: DG 1580-53, and a UV/VIS detector: UV-
1
570. Analytical chiral HPLC was performed on a Chiralcel OD column (4.6 mm
purchased from Daicel Chemical Industries (Osaka, Japan), Ltd. with hexane/2-propanol
95/5) as the eluent where baseline separation was obtained.
×
25 cm)
(

Molecules 2021, 26, 1165
8 of 12
0 0
.2. Synthesis of 2,2 -Bis(aminomethyl)-1,1 -Binaphthyl
3
0
0
3.2.1. Synthesis of (S)-1,1 -Binaphthalene-2,2 -Bis(trifluoromethanesulfonate) (2)
0
To a solution of (S)-1,1 -bi-2-naphthol (2.86 g, 10.0 mmol) in CH Cl (75 mL) was added
2
2
pyridine (3.16 g, 40.0 mmol), which was followed by a dropwise addition of a solution
◦
of (CF SO ) O (6.78 g, 24.0 mmol) in CH Cl (25 mL) at 0 C. After stirring the reaction
3
2 2
2
2
mixture at room temperature for 1 h, an aqueous solution of 3N HCl was added and stirred
for 30 min. The mixture was neutralized by a saturated aqueous solution of NaHCO3,
and the organic layer was separated and washed with water and brine. The organic layer
containing the product was dried over MgSO and concentrated under reduced pressure.
4
Purification by flash chromatography on a silica gel afforded
and S2, In the Supplementary Materials) as a white powder. H NMR (399.8 MHz, CDCl ,
2 (5.43 g, 99%; Figures S1
1
3
3
3
4
RT):
δ
7.26 (d, J
= 9.1 Hz, 2H; C H ), 7.41 (ddd, J
= 7.0 Hz, 7.4 Hz, J
= 1.2 Hz,
HH
10
6
HH
HH
3
4
3
2
9
H; C H ), 7.58 (ddd, J
= 6.9 Hz, 7.2 Hz, J
HH
= 1.2 Hz, 2H; C H ), 7.62 (d, J
=
10
6
HH
HH
10
6
HH
3
3
.2 Hz, 2H; C H ), 8.00 (d, J
= 8.3 Hz, 2H; C H ), 8.14 (d, J
= 9.2 Hz, 2H; C H ).
HH 10 6
1
0
6
10
6
1
3
1
1
C{ H} NMR (100.5 MHz, CDCl , RT): δ 118.2 (q, J = 320 Hz, OSO CF ), 119.4, 123.5,
26.8, 127.4, 128.0, 128.4, 132.1, 132.4, 133.2, 145.5 (C H ). F NMR (376.2 MHz, CDCl3,
3
CF 2 3
19
1
10 6
RT): δ –74.5 (OSO CF ).
2
3
3.2.2. Catalytic Dicyanation of 2
The Schlenk tube containing ditriflate 2 (1.65 g, 3.00 mmol), 1,2-bis(diphenylphosphino)
ethane (DPPE; 120 mg, 0.30 mmol), [1,2-bis(diphenylphosphino)ethane]dichloridonickel
163 mg, 0.30 mmol), zinc powder (58.9 mg, 0.90 mmol), and potassium cyanide (430 mg,
.60 mmol) was flushed with Ar and a deoxygenated DMF (3 mL) was added via syringe.
(
6
The reaction mixture was stirred under reflux conditions for 24 h. Then, the solvent was
removed in vacuo, and ethyl acetate (100 mL) was added to the residue. The resulting
mixture was washed with H O (100 mL
×
2) and brine (10 mL), and then dried over anhy-
2
drous MgSO . After evaporation of the organic layer, the resulting material was dissolved
4
in CH Cl , and the solution was filtered through a Florisil column. Subsequent purification
2
2
0
0
by flash chromatography on a silica gel afforded (S)-1,1 -binaphthalene-2,2 -dicarbonitrile
(799.5 mg, 87%; Figure S3) as white microcrystals. H NMR (399.8 MHz, CDCl , RT):
.16 (dd, J
1.2 Hz, 2H; C H ), 7.66 (ddd, J
1
3
7
δ
3
3
4
3
4
= 8.6 Hz, J
= 0.9 Hz, 2H; C H ), 7.43 (ddd, J
= 7.0 Hz, 8.5 Hz, J
HH
HH
10
6
HH HH
3
4
=
= 6.7 Hz, 8.3 Hz, J
= 0.9 Hz, 2H; C H ), 7.84 (d,
10
6
HH
3
HH 10 6
3
3
JHH = 8.5 Hz, 2H; C H ), 8.03 (d, J
= 8.2 Hz, 2H; C H ), 8.13 (d, J
= 8.3 Hz, 2H;
HH
10
6
HH
10
6
13
1
C H ). C{ H} NMR (100.5 MHz, CDCl , RT): δ 117.5 (ArCN), 111.5, 126.4, 126.8, 128.5,
10
6
3
128.7, 129.2, 130.3, 131.8, 134.8, 140.5 (C H ).
10 6
3.2.3. Reduction of 3
Potassium borohydride (1.73 g, 32 mmol), Raney Ni (470 mg), and 10 mL of dry
ethanol were placed in a 20 mL Schlenk tube; then,
stirring. After stirring vigorously at 50 C for 3 h, the reaction mixture was filtered through
3 (608 mg, 2.00 mmol) was added while
◦
a pad of Celite. The solvent was removed in vacuo, and CH Cl was added to the residue.
2
2
The solution was washed with water. After evaporation of the organic layer, the resulting
material was dissolved in ethyl acetate. The amine product was extracted by 1N HCl into
the aqueous layer, as the HCl salt form. The aqueous layer was neutralized by 1N NaOH
and extracted with diethyl ether. The organic layer was dried over anhydrous Na SO .
2
4
Removal of the solvent under reduced pressure gave the diamine product,
1
2
(518.2 mg,
1
8
3%) as a pale yellow oil. H NMR (399.8 MHz, CDCl , RT): δ 3.48 (d, 2H; CH NH ), 3.54
3
2
3
3
(d, 2H; CH NH ), 7.07 (d, J
= 8.5 Hz, 2H; C H ), 7.20 (dd, J
= 7.0 Hz, 8.0 Hz, 2H;
2
2
HH
10
6
HH
3
3
C H ), 7.41 (dd, J
= 7.3 Hz, 7.7 Hz, 2H; C H ), 7.72 (d, J
= 8.5 Hz, 2H; C H ),
10
6
HH
10
6
HH 10 6
3
3
13
1
7
.91 (d, J
= 8.3 Hz, 2H; C H ), 7.99 (d, J
= 8.5 Hz, 2H; C H ). C{ H} NMR (100.5
HH 10 6
HH
10
6
MHz, CDCl , RT):
δ 44.5 (CH NH ), 125.8, 126.1, 126.5, 126.6, 128.2, 128.7, 132.9, 133.2,
3
2 2
1
33.6, 139.2 (C H ).
10 6

Molecules 2021, 26, 1165
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3.3. Double Cyclometalation of 1
To a solution of [Cp*IrCl ] (798 mg, 1.00 mmol) in CH CN (5 mL) was added a
2
2
3
solution of
1
(1.0 mmol) in CH CN. After stirring for 5 min, NaOAc (197 mg, 2.4 mmol)
3
◦
was added to the reaction mixture. Then, the reaction mixture was stirred at 80 C for
1
5 h. The solvent was removed under reduced pressure. After the reaction mixture was
extracted in toluene (10 mL) and filtered through a filter paper, evaporation of the filtrate to
1
dryness gave the product
5
as a yellow powder (831 mg, 0.80 mmol). H NMR (399.8 MHz,
CDCl , RT, the major isomer):
δ
1.71 (s, 30H; C (CH ) ), 6.95 (m, 2H; C H ), 6.99 (m, 2H;
3
5 3 5 10 5
C H ), 7.28 (dd, 2H; C H ), 7.75 (dd, 2H; C H ), 7.94 (s, 2H; C H ). MS(ESI) calcd for
1
0
5
10
5
10
5
10
5
+
+
[
C H N ClIr ] [M–Cl] 1001.28, found 1001.25.
42 48 2 2
3
.4. Elimination of HCl from 5 by Treatment of KOC(CH3)3
A stereoisomeric mixture of (0.29 g, 0.28 mmol) and dry KOC(CH ) (0.09 g,
.8 mmol) in CH Cl (3 mL) was stirred at room temperature for 30 min. The reaction
5
3
3
0
2
2
mixture was filtered through a pad of Celite under Ar. The solvent was removed under
reduced pressure. After the residue was dissolved in diethyl ether, the solution was filtered
again through Celite under Ar. Evaporation to dryness of the filtrate gave a dark red-purple
1
powder. The product
6
was dissolved in CD Cl and analyzed by H-NMR spectroscopy.
2
2
1
H NMR (399.8 MHz, CD Cl , RT): δ 1.94 (br, 4H; CH ), 1.98 (s, 30H; C (CH ) ), 6.87 (m,
2
2
2 5 3 5
2
H; C H ), 6.95 (m, 2H; C H ), 7.27 (m, 2H; C H ), 7.88 (m, 2H; C H ), 8.22 (br, 4H;
10 5 10 5 10 5 10 5
NH), 8.67 (s, 2H; C H ).
10
5
3.5. H NMR Observation of the Generation of Hydrido(Amine)Iridium Species from 6
Amidoiridium (95.0 mg, 0.1 mmol) was dissolved in 2-propanol (10 mL) and stirred
6
at room temperature for 2 h. After removal of the solvent under reduced pressure, the
resulting solid was washed with pentane and dried under vacuum. The product dissolved
in CD Cl was transferred to an NMR tube equipped with a J-Young valve and analyzed
2
2
1
by H NMR spectroscopy at room temperature.
3.6. Catalytic Asymmetric Transfer Hydrogenation of Acetophenone In 2-Propanol
A 100-mL Schlenk flask was charged with (25.9 mg, 0.025 mmol), KOC(CH3)3
5
(
(
6.7 mg, 0.06 mmol), durene (111.7 g, 0.83 mmol; an internal standard), and 2-propanol
100 mL) under Ar atmosphere. After the addition of acetophenone (1.20 g, 10 mmol),
◦
the reaction mixture was stirred at 30 or –30 C for an appropriate period. The yield of
(S)-1-phenylethanol was determined by GC analysis, and the optical purity was determined
by HPLC analysis.
4
. Conclusions
In summary, we have developed a synthetic route to the bifunctional asymmetric
catalyst based on bis(azairidacycle). The chiral ligand precursor was concisely synthe-
1
sized from (S)-BINOL for a total of 72% yield in three steps including the Ni-catalyzed
dicyanation of BINOL ditriflate and the subsequent primary amine formation by reduction
using Raney-Ni and KBH . The obtained benzylic diamine could be doubly cyclomet-
4
alated to give a diastereomeric mixture of chloridoiridium 5, which was convertible to
the coordinatively unsaturated amidoiridium in common with the well-defined mononu-
clear complexes. The metal–ligand cooperation in the amidoiridium complex allowed
the smooth transformation into the corresponding hydrido(amine)iridium in 2-propanol.
The promotional role of the azairidacycle was also confirmed in the asymmetric transfer
hydrogenation of acetophenone, leading to a reasonable enantioselective.ty. Presumably,
exquisite control of the diastereoselectivity during formation of the catalytically active
hydrido complexes is needed for further improvement of the asymmetric induction ability.
These results will be of assistance in the design of new chiral dinuclear catalyst systems
with the metal/NH bifunctionality.

Molecules 2021, 26, 1165
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1
13
1
Supplementary Materials: The following are available online: copies of H and C{ H} NMR
spectra of 1–3 and selected H NMR spectrum of 5.
1
Author Contributions: Conceptualization, Y.K. (Yoshihito Kayaki); methodology, Y.S., Y.K. (Yuichi
Kawata), S.Y., and Y.K. (Yoshihito Kayaki); validation, Y.S., Y.K. (Yuichi Kawata) S.Y., and Y.K.
(
Yoshihito Kayaki); formal analysis, Y.S., Y.K. (Yuichi Kawata), S.Y., and Y.K. (Yoshihito Kayaki);
investigation, Y.S., Y.K. (Yuichi Kawata), and S.Y.; data curation, Y.S., Y.K. (Yuichi Kawata), S.Y.,
and Y.K. (Yoshihito Kayaki); writing, Y.S. and Y.K. (Yoshihito Kayaki); project administration, Y.K.
(Yoshihito Kayaki); funding acquisition, Y.K. (Yoshihito Kayaki); supervision, T.I. All authors except
T.I. have read and agreed to the published version of the manuscript.
Funding: This study was funded in part by Grant for Basic Science Research Projects from The
Sumitomo Foundation.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Data Availability Statement: The data presented in this study are available in the Supplemen-
tary Materials.
Acknowledgments: We are grateful for the support from the Japan Society of Promotion of Science
(JSPS) and the Sumitomo Foundation.
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are not available from the authors.
References
1.
2.
3.
Ikariya, T.; Blacker, A.J. Asymmetric transfer hydrogenation of ketones with bifunctional transition metal-based molecular
catalysts. Acc. Chem. Res. 2007, 40, 1300–1308. [CrossRef]
Ikariya, T. Chemistry of Concerto Molecular Catalysis Based on the Metal/MH Bifunctionality. Bull. Chem. Soc. Jpn. 2011, 84,
1
–16. [CrossRef]
Zhao, B.; Han, Z.; Ding, K. The N-H Functional Group in Organometallic Catalysis. Angew. Chem. Int. Ed. 2013, 52, 4744–4788.
CrossRef]
[
4
5
.
.
Khusnutdinova, J.R.; Milstein, D. Metal-Ligand Cooperation. Angew. Chem. Int. Ed. 2015, 54, 12236–12273. [CrossRef]
Dub, P.A.; Gordon, J.C. The role of the metal-bound N–H functionality in Noyori-type molecular catalysts. Nat. Rev. Chem. 2018
,
2, 396–408. [CrossRef]
6
7
8
9
1
1
1
1
1
.
.
.
.
Hashiguchi, S.; Fujii, A.; Takehara, J.; Ikariya, T.; Noyori, R. Asymmetric Transfer Hydrogenation of Aromatic Ketones Catalyzed
by Chiral Ruthenium(II) Complexes. J. Am. Chem. Soc. 1995, 117, 7562–7563. [CrossRef]
Haack, K.-J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R. The catalyst precursor, catalyst and intermediate in the Ru -promoted
II
asymmetric hydrogen transfer between alcohols and ketones. Angew. Chem. Int. Ed. Engl. 1997, 36, 285–288. [CrossRef]
Kawano, T.; Watari, R.; Kayaki, Y.; Ikariya, T. Catalytic Hydrogenation of Carboxamides with a Bifunctional Cp*Ru Catalyst
Bearing an Imidazol-2-ylidene with a Protic Aminoethyl Side Chain. Synthesis 2019, 51, 2542–2547. [CrossRef]
Matsunami, A.; Kuwata, S.; Kayaki, Y. Hydrogen Evolution from Formic Acid and Hydrodefluorination of Fluoroarenes by
Bifunctional Iridium Catalysts—Beyond the Transfer Hydrogenation. J. Synth. Org. Chem. Jpn. 2018, 76, 315–324. [CrossRef]
0. Sortais, J.-B.; Pannetier, N.; Holuigue, A.; Barloy, L.; Sirlin, C.; Pfeffer, M.; Kyritsakas, N. Cyclometalation of Primary Benzyl
Amines by Ruthenium(II), Rhodium(III), and Iridium(III) Complexes. Organometallics 2007, 26, 1856–1867. [CrossRef]
1. Sortais, J.-B.; Pannetier, N.; Clément, N.; Barloy, L.; Sirlin, C.; Pfeffer, M.; Kyritsakas, N. Cyclometallation of Secondary Benzyl
Amines by Ruthenium(II) Complexes. Organometallics 2007, 26, 1868–1874. [CrossRef]
2. Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Synthesis and Reactivities of Cp*Ir Amide and Hydride Complexes Bearing C N
−
Chelate Ligands. Organometallics 2008, 27, 2795–2802. [CrossRef]
3. Arita, S.; Koike, T.; Kayaki, Y.; Ikariya, T. Aerobic Oxidation of Alcohols with Bifunctional Transition-Metal Catalysts Bearing
C–N Chelate Ligands. Chem. Asian J. 2008, 3, 1479–1485. [CrossRef]
4. Sortais, J.-B.; Ritleng, V.; Voelklin, A.; Holuigue, A.; Smail, H.; Barloy, L.; Sirlin, C.; Verzijl, G.K.M.; Boogers, J.A.F.; de Vries, A.H.M.;
et al. Cycloruthenated Primary and Secondary Amines as Efficient Catalyst Precursors for Asymmetric Transfer Hydrogenation.
Org. Lett. 2005, 7, 1247–1250. [CrossRef]
1
5. Sortais, J.B.; Barloy, L.; Sirlin, C.; de Vries, A.H.M.; de Vries, J.G.; Pfeffer, M. Cycloruthenated compounds as efficient catalyst for
asymmetric hydride transfer reaction. Pure Appl. Chem. 2006, 78, 457–462. [CrossRef]
1
6. Pannetier, N.; Sortais, J.-B.; Dieng, P.S.; Barloy, L.; Sirlin, C.; Pfeffer, M.; Kyritsakas, N. Kinetics and Mechanism of Ruthenacycle-
Catalyzed Asymmetric Hydrogen Transfer. Organometallics 2008, 27, 5852–5879. [CrossRef]

Molecules 2021, 26, 1165
11 of 12
1
1
1
2
7. Jerphagnon, T.; Haak, R.; Berthiol, F.; Gayet, A.J.A.; Ritleng, V.; Holuigue, A.; Pannetier, N.; Pfeffer, M.; Voelklin, A.; Lefort, L.;
et al. Ruthenacycles and Iridacycles as Catalysts for Asymmetric Transfer Hydrogenation and Racemisation. Top. Catal. 2010, 53,
002–1008. [CrossRef]
8. Barloy, L.; Issenhuth, J.-T.; Weaver, M.G.; Pannetier, N.; Sirlin, C.; Pfeffer, M. Reaction of Chiral Secondary Amines with [(
C Me )MCl ] (M = Rh(III), Ir(III)): Cyclometalation with or without Dehydrogenation. Organometallics 2011, 30, 1168–1174.
1
η
5-
5
5
2 2
[CrossRef]
9. Pannetier, N.; Sortais, J.-B.; Issenhuth, J.-T.; Barloy, L.; Sirlin, C.; Holuigue, A.; Lefort, L.; Panella, L.; de Vries, J.G.; Pfeffer, M.
Cyclometalated Complexes of Ruthenium, Rhodium and Iridium as Catalysts for Transfer Hydrogenation of Ketones and Imines.
Adv. Synth. Catal. 2011, 353, 2844–2852. [CrossRef]
0. Féghali, E.; Barloy, L.; Issenhuth, J.-T.; Karmazin-Brelot, L.; Bailly, C.; Pfeffer, M. Cyclometalation of (2R,5R)-2,5-
Diphenylpyrrolidine and 2- Phenyl-2-imidazoline Ligands with Half-Sandwich Iridium(III) and Rhodium(III) Complexes.
Organometallics 2013, 32, 6186–6194. [CrossRef]
2
2
2
2
2
1. Sato, Y.; Kayaki, Y.; Ikariya, T. Efficient dynamic kinetic resolution of racemic secondary alcohols by a chemoenzymatic system
using bifunctional iridium complexes with C–N chelate amido ligands. Chem. Commun. 2012, 48, 3635–3637. [CrossRef] [PubMed]
2. Ueno, A.; Kayaki, Y.; Ikariya, T. Heterolysis of NH-Indoles by Bifunctional Amido Complexes and Applications to Carboxylation
with Carbon Dioxide. Organometallics 2014, 33, 4479–4485. [CrossRef]
3. Sato, Y.; Kayaki, Y.; Ikariya, T. Cationic Iridium and Rhodium Complexes with C–N Chelating Primary Benzylic Amine Ligands
as Potent Catalysts for Hydrogenation of Unsaturated Carbon–Nitrogen Bonds. Organometallics 2016, 35, 1257–1264. [CrossRef]
4. Matsunami, A.; Kuwata, S.; Kayaki, Y. Hydrodefluorination of Fluoroarenes Using Hydrogen Transfer Catalysts with a Bifunc-
tional Iridium/NH Moiety. ACS Catal. 2016, 6, 5181–5185. [CrossRef]
5. Sato, Y.; Kayaki, Y.; Ikariya, T. Comparative Study of Bifunctional Mononuclear and Dinuclear Amidoiridium Complexes with
Chiral C
−
N Chelating Ligands for the Asymmetric Transfer Hydrogenation of Ketones. Chem. Asian J. 2016, 11, 2924–2931.
[CrossRef]
2
2
2
6. Sato, Y.; Kayaki, Y.; Ikariya, T. Transfer hydrogenation of carbon dioxide via bicarbonate promoted by bifunctional C–N chelating
Cp*Ir(III) complexes. Chem. Commun. 2020, 56, 10762–10765. [CrossRef]
7. Tsuboyama, A.; Takiguchi, T.; Okada, S.; Osawa, M.; Hoshino, M.; Ueno, K. A novel dinuclear cyclometalated iridium complex
bridged with 1,4-bis[pyridine-2-yl]benzene: Its structure and photophysical properties. Dalton Trans. 2004, 1115–1116. [CrossRef]
8. Ho, J.H.H.; Choy, S.W.S.; Macgregor, S.A.; Messerle, B.A. Cooperativity in Bimetallic Dihydroalkoxylation Catalysts Built on
Aromatic Scaffolds: Significant Rate Enhancements with a Rigid Anthracene Scaffold. Organometallics 2011, 30, 5978–5984.
[CrossRef]
2
3
3
9. Choy, S.W.S.; Page, M.J.; Bhadbhade, M.; Messerle, B.A. Cooperative Catalysis: Large Rate Enhancements with Bimetallic
Rhodium Complexes. Organometallics 2013, 32, 4726–4729. [CrossRef]
0. Maity, R.; Hohloch, A.; Su, C.-Y.; Meer, M.; Sarker, B. Cyclometalated Mono- and Dinuclear Ir Complexes with “Click”-Derived
III
Triazoles and Mesoionic Carbenes. Chem. Eur. J. 2014, 20, 9952–9961. [CrossRef] [PubMed]
1. Hull, J.F.; Himeda, Y.; Wang, W.-H.; Hashiguchi, B.; Periana, R.; Szalda, D.J.; Muckerman, J.T.; Fujita, E. Reversible hydrogen
storage using CO and a proton-switchable iridium catalyst in aqueous media under mild temperatures and pressures. Nat.
2
Chem. 2012, 4, 383–388. [CrossRef]
3
3
3
3
3
3
3
2. Wang, Y.; Kuzniewski, C.N.; Rauniyar, V.; Hoong, C.; Toste, F.D. Chiral (Acyclic Diaminocarbene) Gold(I)-Catalyzed Dynamic
Kinetic Asymmetric Transformation of Propargyl Esters. J. Am. Chem. Soc. 2011, 133, 12972–12975. [CrossRef]
3. Takizawa, S.; Katayama, T.; Onitsuka, K.; Suzuki, T.; Yanagida, T.; Kawai, T.; Sasai, H. Chiral dinuclear vanadium(v) catalysts for
oxidative coupling of 2-naphthols. Chem. Commun. 2008, 44, 1810–1812. [CrossRef]
4. Sako, M.; Aoki, T.; Zumbrägel, N.; Schober, L.; Gröger, H.; Takizawa, S.; Sasai, H. Chiral Dinuclear Vanadium Complex-Mediated
Oxidative Coupling of Resorcinols. J. Org. Chem. 2019, 84, 1580–1587. [CrossRef]
5. Shi, M.; Itoh, N.; Masaki, Y. Axially Dissymmetric Chiral (Diamine) copper- and (Diimine)copper-catalysed Asymmetric
Aziridination of Alkenes. J. Chem. Res. (S) 1996, 8, 352–353.
6. Matsumoto, K.; Tomioka, K. An approach to a chiral cycloalkanone-mediated asymmetric epoxidation of stilbene with oxone.
Chem. Pharm. Bull. 2001, 49, 1653–1657. [CrossRef]
7. Takagi, K.; Okamoto, T.; Sakakibara, Y.; Oka, S. PALLADIUM(II) CATALYZED SYNTHESIS OF ARYL CYANIDES FROM ARYL
HALIDES. Chem. Lett. 1973, 2, 471. [CrossRef]
8. Sakakibara, Y.; Okuda, F.; Shimobayashi, A.; Kirino, K.; Sakai, M.; Uchida, N.; Takagi, K. The Cyanation of Aromatic Halides
Catalyzed by Nickel(0) Complexes Generated In Situ. I. General Scope and Limitations. Bull. Chem. Soc. Jpn. 1988, 61, 1985.
[
CrossRef]
9. Takagi, K.; Sakakibara, Y. Nickel(0) or Palladium(0)-catalyzed Cyanation of Aryl Triflates. Chem. Lett. 1989, 18, 1957–1958.
CrossRef]
0. Takagi, K.; Sakai, K.; Sakakibara, Y. Nucleophilic Displacement Catalyzed by Transition Metal. IX. [Pd (dba) ]
Catalyzed Cyanation of Aryl Halides and Ary Triflates. Bull. Chem. Soc. Jpn. 1991, 64, 1118. [CrossRef]
1. Sakakibara, Y.; Sasaki, K.; Okuda, F.; Hokimoto, A.; Ueda, T.; Sakai, M.; Takagi, K. The Cyanation of Aromatic Halides Catalyzed
3
4
4
[
·
CHCl –DPPF
3
2
3
by Nickel(0) Complexes Generated In Situ. III. Kinetic and Mechanistic Aspects. Bull. Chem. Soc. Jpn. 2004, 77, 1013–1019.
[CrossRef]

Molecules 2021, 26, 1165
12 of 12
4
4
4
4
4
4
2. Sundermeier, M.; Zapf, A.; Beller, M. Palladium–Catalyzed Cyanation of Aryl Halides: Recent Developments and Perspectives.
Eur. J. Inorg. Chem. 2003, 3513–3526. [CrossRef]
3. Schareina, T.; Jackstell, R.; Schulz, T.; Zapf, A.; Cotté, A.; Gotta, M.; Beller, M. Increasing the Scope of Palladium–Catalyzed
Cyanations of Aryl Chlorides. Adv. Synth. Catal. 2009, 351, 643–648. [CrossRef]
4. Anderson, B.A.; Bell, E.C.; Ginah, F.O.; Harn, N.K.; Pagh, L.M.; Wepsiec, J.P. Cooperative Catalyst Effects in Palladium-Mediated
Cyanation Reactions of Aryl Halides and Triflates. J. Org. Chem. 1998, 63, 8224–8228. [CrossRef]
5. Buono, F.G.; Chidambaram, R.; Mueller, R.H.; Waltermire, R.E. Insights into palladium-catalyzed cyanation of bromobenzene:
Additive effects on the rate-limiting step. Org. Lett. 2008, 10, 5325–5328. [CrossRef] [PubMed]
6. Kurz, L.; Lee, G.; Morgans, D., Jr.; Waldyke, M.J.; Ward, T. Stereospecific functionalization of (R)-(
0
−
)-1,1 -bi-2-naphthol triflate.
Tetrahedron Lett. 1990, 31, 6321.
0
0
7. Kasak, P.; Putala, M. Stereoconservative cyanation of [1,1 -binaphthalene]-2,2 -dielectrophiles. An alternative approach to
0
0
homochiral C -symmetric [1,1 -binaphthalene]-2,2 -dicarbonitrile and its transformations. Collect. Czech. Chem. Commun. 2000
,
2
6
5, 729–740. [CrossRef]
4
4
5
8. Wu, B.; Zhang, J.; Yang, M.; Ma, L.-J.; Yu, X.-Q. Raney Ni/KBH : An efficient and mild system for the reduction of nitriles to
4
amines. ARKIVOC 2008, 12, 95–102. [CrossRef]
9. White, C.; Yates, A.; Maitlis, P.M.; Heinekey, D.M. (η
5-Pentamethylcyclopentadienyl)rhodium and -iridium compounds. Inorg.
Synth. 1992, 29, 228–234.
0. Booth, G.; Chatt, J. Some Complexes of Ditertiary Phosphines with Nickel(II) and Nickel (III). J. Chem. Soc. 1965, 3238–3241.
CrossRef]
[