Cationic Iridium and Rhodium Complexes with C-N Chelating Primary Benzylic Amine Ligands as Potent Catalysts for Hydrogenation of Unsaturated Carbon-Nitrogen Bonds

Article abstract of DOI:10.1021/acs.organomet.6b00133

Cationic half-sandwich C-N chelating Ir and Rh complexes [Cp?M(NCCH₃){²(N,C)-NH₂CR₂-2-C₆H₄}]⁺SbF₆^- (1a, M = Ir, R = CH₃; 1b, M = Ir, R = C₆H₅; 2a, M = Rh, R = CH₃; 2b, M = Rh, R = C₆H₅) are synthesized by AgSbF₆-mediated halide abstraction from neutral azametallacycles derived from tritylamine or cumylamine and are fully characterized by NMR spectroscopy and X-ray crystallography. The treatment of the cationic complex 1b with H₂ gas under ambient conditions in the presence of triethylamine in THF-d₈ quantitatively yielded hydrido(amine) complex [Cp?Ir(H){²(N,C)-NH₂C(C₆H₅)₂-2-C₆H₄}] (4). The C-N chelating Ir complex shows a higher catalytic activity than an N-N chelating complex, [Cp?Ir(NCCH₃)(Tscydn)]⁺SbF₆^- (3; Tscydn = N-(p-toluenesulfonyl)-1,2-cyclohexanediamime), that has been previously used for the asymmetric hydrogenation of acyclic imines. For example, the cationic Ir complex 1a promoted the hydrogenation of N-(1-phenylethylidene)benzylamine under 30 atm at 30 °C in the presence of excess AgSbF₆ to produce the corresponding amine in 97% yield within 2 h. The cationic Rh complexes 2 serve as efficient catalysts for hydrogenative condensation of nitriles in the presence of AgSbF₆, producing dibenzylamines selectively even at 60 °C.

Full text of DOI:10.1021/acs.organomet.6b00133

Article
pubs.acs.org/Organometallics
Cationic Iridium and Rhodium Complexes with C−N Chelating
Primary Benzylic Amine Ligands as Potent Catalysts for
Hydrogenation of Unsaturated Carbon−Nitrogen Bonds
Yasuhiro Sato, Yoshihito Kayaki,* and Takao Ikariya*
Department of Applied Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology, 2-12-1-E4-1
O-okayama, Meguro-ku, Tokyo 152-8552, Japan
*
S Supporting Information
ABSTRACT: Cationic half-sandwich C−N chelating Ir and Rh
−
2
+
complexes [Cp*M(NCCH ){κ (N,C)-NH CR -2-C H }] SbF
6
3
2
2
6
4
(
1a, M = Ir, R = CH ; 1b, M = Ir, R = C H ; 2a, M = Rh, R =
3 6 5
CH ; 2b, M = Rh, R = C H ) are synthesized by AgSbF -
3
6
5
6
mediated halide abstraction from neutral azametallacycles derived
from tritylamine or cumylamine and are fully characterized by
NMR spectroscopy and X-ray crystallography. The treatment of
the cationic complex 1b with H gas under ambient conditions in
2
the presence of triethylamine in THF-d quantitatively yielded
8
2
hydrido(amine) complex [Cp*Ir(H){κ (N,C)-NH C(C H ) -2-
2
6
5 2
C H }] (4). The C−N chelating Ir complex shows a higher catalytic activity than an N−N chelating complex,
6
4
+
−
[
Cp*Ir(NCCH )(Tscydn)] SbF (3; Tscydn = N-(p-toluenesulfonyl)-1,2-cyclohexanediamime), that has been previously
used for the asymmetric hydrogenation of acyclic imines. For example, the cationic Ir complex 1a promoted the hydrogenation of
3 6
N-(1-phenylethylidene)benzylamine under 30 atm at 30 °C in the presence of excess AgSbF to produce the corresponding
6
amine in 97% yield within 2 h. The cationic Rh complexes 2 serve as efficient catalysts for hydrogenative condensation of nitriles
in the presence of AgSbF , producing dibenzylamines selectively even at 60 °C.
6
4
a,6
INTRODUCTION
the high basicity of the amido moiety as well as the strong
nucleophilicity of the hydrido ligand caused by a pronounced
σ-donor nature of the chelating carbon atom. It should be noted
that these outstanding features accommodate dynamic kinetic
resolution of racemic secondary alcohols through a combina-
tion of the reactions described above with enzymatic trans-
■
Metal/NH bifunctional catalysis has received much attention as a
pivotal concept for redox transformations based on hydrogen
transfer between secondary alcohols and ketones. A funda-
1
mental hydrogen delivery process alternating between 16e amido
and 18e hydrido(amine) complexes has been thoroughly
explored in in-depth studies on the prototype catalyst bearing
chiral N-sulfonyldiamines (N−N chelating ligands) developed
7
formations.
Due to the similarities between the hydrogen transfer and
2
8
by Noyori and Ikariya. We have systematically investigated
H -hydrogenation mechanisms, we anticipated that C−N
chelating complexes can serve as good hydrogenation catalysts
in the case where the hydrido(amine) complexes can be
generated directly from H . In the case of the N−N chelate
system, we and other groups independently reported that direct
hydrogenation is promoted by the protonation of 16e amido
complexes with the help of Brønsted acids or alcoholic media
and by the formation of cationic complexes using silver salts.
This is true even if the original transfer hydrogenation catalysts
2
interconversion operation for a range of group 8 and 9 metal
complexes with protic amine chelates and examined ligand
modification by significantly changing the chelating atom
2
3
influences on the catalyst performance. In particular, bifunc-
tional Cp*Ir and Rh complexes containing a five-membered
C−N chelate ring that were synthesized by cyclometalation of
protic benzylamine derivatives have been successfully designed
9,10
11
4
for use as highly efficient hydrogen transfer catalysts.
Remarkable enhancement of catalytic activity of the amido
complexes derived from the neutral chloro(amine) complexes
was observed in transfer hydrogenation of ketones using
only slightly activate H gas. For the N−N chelating Ir complex
Cp*IrCl{(S,S)-Tscydn}], a combined use of silver salts in
2
[
4
a
4b,c
catalytic asymmetric hydrogenation of acyclic imines proved to
2
-propanol and in aerobic oxidation of alcohols, compared
1
1b
promote the activity and selectivity. As shown in Scheme 1,
mechanistic studies revealed that formation of cationic species
to the results obtained with the original N−N chelating Ir
complex. Pfeffer and co-workers have independently reported
that the related cationic C−N chelating complexes can also be5
utilized for transfer hydrogenation of ketones and imines.
The rapid hydrogen transfer from alcohols to the amidoiridium
and from the hydrido(amine)iridium to ketones is induced by
allows heterolytic bond cleavage of H to generate a hydrido
2
Received: February 17, 2016
©
XXXX American Chemical Society
A
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Scheme 1. Hydrogen Activation Mechanism of Cationic N−N
Chelating Ir Complexes
isolated as yellow crystals in 77% and 72% yields after recrys-
tallization from ether and dichloromethane.
1
The isolated products were fully characterized by H and
13
1
C{ H} NMR, IR spectroscopy, X-ray crystallography, and
elemental analysis. The ORTEP diagrams of the cationic com-
plexes 1 and 2 presented in Figure 1 show a distorted octahedral
intermediate and that the activation of the imine substrates by the
−
silver cation facilitates the subsequent H transfer.
In this paper, we describe the synthesis of new cationic
iridacycles and rhodacycles derived from tritylamine or cumyl-
amine to develop the H -hydrogenation system based on the
2
C−N chelating complexes. The cationic Ir complex exhibited
a higher catalytic activity in the hydrogenation of N-(1-
Figure 1. ORTEP drawings of cationic C−N chelating complexes 1a,
1b, 2a, and 2b. Counter anion and hydrogen atoms other than the amine
protons are omitted for clarity, and the ellipsoids represent 50%
probability.
phenylethylidene)benzylamine in the presence of AgSbF than
6
the previously reported N−N chelating complex. The combina-
tion of the cationic Rh complex with excess AgSbF was also
6
found to catalyze the selective hydrogenative condensation of
nitriles to secondary amines.
geometry with coordination of Cp*, chelating carbon and nitrogen,
and CH CN as observed in the analogous N−N chelating Ir
3
+
−
11b
RESULTS AND DISCUSSION
complex [Cp*Ir(NCCH ){(S,S)-Tscydn}] SbF
The principal bond lengths and angles are summarized in
(3).
■
3
6
Synthesis and Characterization of Cationic C−N
Chelating Ir and Rh Complexes. Prior to the evaluation of
the applicability of the C−N chelating complexes for catalytic
hydrogenation, we first synthesized a series of cationic Ir and Rh
complexes from neutral chloro(amine) complexes that have been
employed as catalytic precursors for redox transformations of
Table 1. The bond distances between the metal center and C−N
Table 1. Selected Bond Lengths and Angles of Cationic Ir and
Rh Complexes 1a, 1b, 2a, and 2b
4
a,c
complex
M−C [Å]
M−N [Å]
M−NCCH
3
[Å] N−M−C [deg]
ketones or alcohols in our previous work. Treatment of the
2
1a
2.056(5)
2.068
2.132(4)
2.135
2.046(4)
2.059
78.27(19)
77.97
chloroiridium complexes [Cp*Ir(Cl){κ (N,C)-NH CR -2-
2
2
a
1
2
2
b
C H }] (R = CH and C H ) with 1−1.5 equiv of AgSbF in a
6
4
3
6
5
6
a
2.045(5)
2.048(5)
2.126(4)
2.118(4)
2.067(5)
2.081(4)
78.51(15)
78.15(15)
mixed solution of CH Cl and CH CN at room temperature
2
2
3
b
gave the corresponding yellow cationic complexes, [Cp*Ir-
2
+
−
a
(
NCCH ){κ (N,C)-NH CR -2-C H }] SbF (1a, R = CH3,;
Mean value.
3
2
2
6
4
6
1
b, R = C H ), in 67% and 47% yields, respectively (Scheme 2).
6 5
chelating ligands are similar to those of the parent neutral
4a,c
complexes.
The cationic Ir complexes 1a and 1b show
Scheme 2. Synthesis of Cationic C−N Chelating Complexes
Ir−NCCH distances of 2.046(5) and 2.059 Å (mean value),
3
which are slightly shorter than that of complex 3 (2.079(2) Å),
reflecting the stronger steric effect of the Tscydn ligand compared
to those of the C−N chelating ligands.
The cationic C−N chelating complexes 1 and 2 are
coordinatively saturated 18e species and are thermally stable in
1
a solid state, yet appear fluxional in solution. The H NMR
spectrum of 1a in CD Cl at room temperature exhibits a singlet
2
2
signal due to the CH CN at 2.42 ppm, and the IR spectrum
3
recorded with a KBr pellet shows a CN stretching band at
−
1
2
331 cm . In contrast to the reported [Cp*Ir(NCCH ){(S,S)-
3
+
−
The cationic C−N chelating Rh analogues, [Cp*Rh(NCCH )-
Tscydn}] SbF6 (3) N−N chelating complex, the NH protons
3
2
2
+
−
{
κ (N,C)-NH CR -2-C H }] SbF (2a, R = CH ; 2b, R =
were detected as a broad singlet signal at 4.20 ppm in the
2
2
6
4
6
3
1
C H ), were also prepared through chloride abstraction from the
H NMR spectroscopy. Furthermore, a broad signal correspond-
6
5
well-defined neutral complexes by using AgSbF and successfully
ing to two methyl substituents on the cumylamine framework
6
B
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Article
was observed at 1.46 ppm, possibly due to the rapid stereo-
chemical inversion of the configuration at the Ir center caused by
Scheme 3. Reactions of Cationic C−N Chelating Complex 1b
or a 16e Amidoiridium Complex under a Hydrogen
Atmosphere
the liberation of the coordinating CH CN ligand.
3
The proposed dynamic behavior was confirmed by variable-
1
temperature H NMR spectroscopy. As shown in Figure 2, the
1
b, only a trace amount of the hydrido complex was generated
from the basic amido complex with H under identical con-
2
ditions, indicating that the amido/metal bifunctional effect will
not operate sufficiently in the H activation step (Scheme 3b).
2
The instantaneous transformation of the hydrido(amine)
complex from the cationic complex 1b and H in the presence
2
of N(C H ) will be attributed to a mechanism involving the
2
5 3
heterolytic cleavage of the H−H bond on the cationic metal
center with the aid of the base, as realized for the N−N chelating
complex shown in Scheme 1.
Comparison of Catalytic Activities of C−N and N−N
Chelating Ir and Rh Complexes for Imine Hydrogenation.
To demonstrate the advantageous catalytic performance of the
newly synthesized C−N chelating complexes, hydrogenation of
N-(1-phenylethylidene)benzylamine was tested following the
11b
procedure described in our previous report (Table 2). For the
Figure 2. Dynamic behavior of 1a in CD Cl observed by variable-
temperature H NMR spectra at 25, 10, 0, −10, and −30 °C.
2
2
Table 2. Catalytic Hydrogenation of N-(1-Phenylethylidene)-
benzylamine
1
1
H NMR spectrum of 1a recorded at −30 °C displayed the two
signals assigned to the diastereotopic methyl protons (red dots)
at 1.16 and 1.64 ppm, indicating that the Ir center is
configurationally stable on the NMR time scale. A set of two
doublets due to the NH protons (blue dots) at 4.08 and
2
4.20 ppm with a geminal coupling constant of 11.9 Hz also
supports the chelating structure of the amine ligand. The
coalescence temperature of these signals is 15 °C. Similar trends
in temperature-dependent spectra were observed for the related
cationic Ir and Rh analogues 1b, 2a, and 2b (see Supporting
Information). Therefore, this confirms that the acetonitrile
ligand easily dissociates from the metal center in solution and
opens a coordination site for the incoming molecular hydrogen.
Stoichiometric Reaction of H2 Gas with the C−N
Chelating Complexes. To confirm the formation of a hydrido
complex from molecular hydrogen, reactivity of the cationic Ir
a
entry
1
catalyst
% yield
1a
1a
2a
3
97
37
29
14
b
2
3
4
complex 1b was investigated under a H atmosphere. Although
2
a
1
1
Yields were determined by H NMR using triphenylmethane as an
H NMR monitoring of a mixture of 1b with atmospheric H in
2
b
internal standard. The reaction without H gas.
2
THF-d at room temperature did not support the formation of
8
2
either the η -hydrogen complex or the corresponding hydrido
complex, addition of an equimolar amount of N(C H ) gave rise
imine hydrogenation using the N−N chelating Ir catalyst, it
2
5 3
to the rapid appearance of a singlet signal at −13.14 ppm ascribed
to the hydrido(amine)-Ir complex 4 (Scheme 3a). The same
complex has been identified in the reaction of the 16e amido
has been demonstrated that an extra amount of AgSbF can
6
participate not only in formation of the cationic species effective
for the facile heterolytic cleavage of H but also in the activation
2
2
4a
complex [Cp*Ir{κ (N,C)-NHC(C H ) -2-C H }] in 2-propanol.
of the substrate imine as a Lewis acid. The imine hydrogenation
6
5 2
6
4
In contrast to the smooth and quantitative formation of 4 from
under 3.0 MPa of H in 2-propanol containing 1a in the presence
2
C
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Article
of AgSbF (substrate/AgSbF /catalyst = 100:3:1) and 4A
system, it was also reported that the transformation from
benzonitrile into benzylamine could be accomplished by using a
dihydrido(dihydrogen)ruthenium complex, [RuH (H )-
6
6
molecular sieves at 30 °C proceeded efficiently to give
the corresponding amine in 97% yield after 2 h (entry 1). The
reaction conducted under an argon atmosphere resulted in
lowering of the yield (37%), suggesting that the imine should be
reduced via the hydrogenation in preference to the transfer
hydrogenation from 2-propanol by using the cationic complex
2
2
17h
(PCyp ) ] (PCyp = tricyclopentylphosphine). Alternatively,
3
2
3
direct and selective synthesis of secondary amines from nitriles is
24,25
also attractive due to its operational simplicity
compared to
other traditional C−N bond formation methods via the
alkylation of primary amines.
(
entry 2). The cationic Rh complex 2a also was used to obtain the
hydrogenated product in yields of 29% (entry 3). The catalytic
activity of 1a was found to be much higher than that of N−N
chelating complex 3 (14% yield) under the same conditions
As a pilot experiment, hydrogenation was carried out with
1.0 mmol of benzonitrile (5a) as a substrate, using Rh or Ir
catalysts for the evaluation of the catalytic potential of the
cationic C−N chelating complexes. THF solutions containing
triethylamine catalyst and 5a in a ratio of 1:5:100 were
(
entry 4). The strong σ-donating ability of the C−N chelating
ligands will affect the smooth hydride transfer from the
nucleophilic hydrido complexes to the imine substrate that
should play a vital role in the catalysis.
pressurized with 10 atm of H
sieves (400 mg) and heated at 60 °C for 21 h. The results are
outlined in Table 3. The addition of AgSbF (Ag/cat = 1)
in the presence of 4A molecular
2
Catalytic Hydrogenation of Nitriles with a Combina-
6
tion of Cationic Rh Complexes and AgSbF . Stimulated by
6
the satisfactory hydrogenation activity of the cationic C−N
Table 3. Catalytic Hydrogenation of Benzonitrile 5a
chelating complexes combined with AgSbF , we set out to
6
explore the catalytic hydrogenation of nitriles, which represents
12
an economical and environmentally benign process for amines.
The nitriles can be generally reduced with stoichiometric
amounts of metal hydrides such as LiAlH or with heterogeneous
4
1
3
catalysts based on Pd, Ni, and Co. With respect to the
homogeneous catalytic nitrile reductions, relatively limited
14
14
15
16
17
18
19
20
examples using Mo, W, Re, Fe, Ru, Co, Rh, Ir,
2
1
22
Ni, and Pd complexes have been reported. In most cases,
somewhat harsh reaction conditions such as high pressure and
elevated temperature are required to activate the unreactive
nitrile substrates and to overcome catalyst poisoning by the
amine products. Moreover, hydrogenation often suffers from the
formation of mixtures of primary, secondary, and tertiary amines
and imine intermediates through a repetitive hydrogenation/
a
entry
catalyst
AgSbF , mol %
solvent
THF
% yield
6
1
2
3
4
5
6
7
8
9
2a
2a
2b
2b
2b
2b
2b
1a
0
1
1
1
1
1
0
1
3
4
0
31
65
44
30
0
THF
THF
CH OH
3
(CH ) CHOH
3
2
23
toluene
THF
THF
THF
THF
THF
condensation sequence as depicted in Scheme 4. In 2007,
b
0
0
Scheme 4. Possible Reaction Pathways for Formation of
Primary, Secondary, and Tertiary Amines in the Catalytic
Hydrogenation of Nitriles
[Cp*RhCl2]2
9
1
1
0
1
0
2b
4
81
a
1
Yields were determined by H NMR using triphenylmethane as an
b
internal standard. One equivalent of t-BuOK was added to 2b as base
instead of N(C H ) .
2
5 3
allowed the hydrogenation to produce dibenzylamine (6a) in
1% yield together with a trace of N-benzylidenebenzylamine,
which agrees with the hydrogenation pathway shown in Scheme 4
entries 1 and 2). Even better catalytic performance (65% yield)
3
(
was obtained with an easily accessible in situ catalyst composed
of 2b and AgSbF (entry 3). Unlike the case of imine hydro-
6
genation, alcoholic solvents slightly reduced the catalytic activity
(
entries 4 and 5). The hydrogenation in toluene was unsuccessful,
possibly due to the limited solubility of the silver salt (entry 6).
Because the use of t-BuOK instead of N(C H ) involves the
2
5 3
preferential formation of an amidoiridium species, 5a remained
intact after the reaction (entry 7). The combination of the Ir
complex 1a with AgSbF did not catalyze the hydrogenation
6
Morris’ group reported that a Ru catalyst with a P−NH−NH−P
under identical conditions (entry 8). The effectiveness of metal/
NH cooperation for the C−N chelating complexes was con-
firmed by a reduced catalytic activity in the hydrogenation using
[Cp*RhCl ] with 3 mol amounts of AgSbF (entry 9). The
tetradentate ligand can catalyze hydrogenation of benzonitrile
17d
to afford benzylamine with complete conversion. Beller and
co-workers developed a Ru catalyst system composed of
2
2
6
[
Ru(cod)(methylallyl) ] with phosphines or N-heterocyclic
amine product 6a was not obtained in a separate experiment
2
carbenes for selective hydrogenation of nitriles to primary
using AgSbF without the Rh catalyst (entry 10). An addition of
6
17e−g
amines in the presence of t-BuOK.
In a study of a base-free
extra AgSbF (Ag/cat = 4) was beneficial for the enhancement of
6
D
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Article
catalytic activity, producing 6a in 81% yield without formation of
primary and tertiary amines (entry 11).
Scheme 5. Reaction Pathway for Hydrogenation of Nitriles
Using C−N Chelating Rh Catalysts
The substrate scope was examined using optimized hydro-
genation conditions with the combined catalyst system of 2b and
AgSbF under 1.0 MPa of H at 60 °C. As shown in Table 4,
6
2
Table 4. Selective Formation of Secondary Amines in the
Catalytic Hydrogenation of Nitriles
dominant formation of the secondary amines will be intimately
associated with the silver-mediated activation of the primary
hydrogenation products (A), which become susceptible to
nucleophilic attack by primary amines, leading to further
hydrogenation. Although the details of the process proceeding
through multiple hydrogenation stages remains unclear, the
further conversion into tertiary amines via condensation of imine
with sterically demanding secondary amines is not favorable
under mild reaction conditions.
CONCLUSIONS
■
We demonstrated that the cationic C−N chelating Ir and Rh
complexes derived from tritylamine and cumylamine are effective
hydrogenation catalysts. The cationic complexes can promote
the heterolytic cleavage of molecular hydrogen in the presence of
base under atmospheric pressure at ambient temperature to
generate the hydrido(amine) complexes; such heterolytic
cleavage is effective for the reduction of polar bonds. Actually,
the Ir complexes serve as highly efficient catalysts for the imine
hydrogenation instead of the complex bearing N-sulfonyldiamine
ligands. Furthermore, the cationic Rh complex 2b was
successfully used for the hydrogenation of nitriles. The combined
use of cationic Rh complex and silver salt efficiently and
selectively converted nitriles into secondary amines under mild
conditions. Silver salts will facilitate the condensation of imines,
with primary amines accompanied by the elimination of
ammonia as well as the subsequent nucleophilic attack to
imine by hydrido-Rh complexes. The powerful reducing nature
of the C−N chelating complexes is highly promising for the
development of catalytic transformations of hardly reducible
substrates, and further research on this is currently in progress in
our laboratory.
a
b
c
Isolated yield. S/C = 50. 69 h.
benzonitrile derivatives with methoxy, fluoro, and acetal groups
5b, 5d−f) and 2-cyanonaphthalene (5g) were substantially
(
converted to obtain the desired secondary amines (6b, 6d−g) in
satisfactory yields after purification, whereas the hydrogenation
of 4-chlorobenzonitrile (5c) was not completed after the same
conditions (entries 1−6). Although the reactivity of aliphatic
nitriles such as benzyl cyanide and cyclohexanecarbonitrile was
slightly lowered, the use of 2 mol % of the catalyst 2a with
elongation of the reaction time to 69 h was effective for increasing
the yield of secondary amine products (6h and 6i; entries 7 and 8).
Analogously to the imine hydrogenation by the combined
EXPERIMENTAL SECTION
■
General Procedures. Reactions requiring air-sensitive manipu-
lations were conducted under an argon atmosphere following standard
Schlenk techniques. Dichloromethane and acetonitrile were distilled
under argon after drying over P O . Diethyl ether and THF were dried
2
5
and deoxygenated by refluxing and distilling from sodium benzophe-
none ketyl under argon. Other reagents were purchased and used as
delivered unless otherwise noted. The starting Ir and Rh complexes
catalyst system of 1 and AgSbF , the mechanism of the nitrile
hydrogenation is considered to involve the heterolytic bond
cleavage of H on a cationic complex to generate a hydrido inter-
mediate with the subsequent H transfer to the nitrile substrates
2
4a
2
6
Cp*IrCl[κ (N,C)-{NH C(CH ) -2-C H }], Cp*IrCl[κ (N,C)-
2
3
2
6
4
4a
2
{
NH C(C H ) -2-C H }], Cp*RhCl[κ (N,C)-{NH C(CH ) -2-
2 6 5 2 6 4 2 3 2
2
4c 4c
2
C H }], Cp*RhCl[κ (N,C)-{NH C(C H ) -2-C H }], and Cp*Ir-
6 4 2 6 5 2 6 4
2
4a
−
[κ (N,C)-{NHC(C H ) -2-C H }] were prepared according to the
6 5 2 6 4
activated by the silver center. As shown in Scheme 5, the
procedures described in the literature with modifications. The N−N
E
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Article
−
1
chelating complex 3 was prepared according to the procedure described
1021, 947, 865, 762, 736, 657 cm . Anal. Calcd for C H F N RhSb:
21 30 6 2
10b
1
13
in a previous work.
H and C NMR spectra were recorded with a
C, 38.86; H, 4.66; N, 4.32. Found: C, 38.59; H, 4.67; N, 4.10.
2
JEOL JNM-ECX400 spectrometer. The NMR chemical shifts were
Synthesis of [Cp*Rh(NCCH ){κ (N,C)-(NH C(C H ) -2-C H )}]-
3
2
6
5 2
6
4
2
referenced to SiMe by using residual protio impurities in the deuterated
(SbF
0.526 mmol), AgSbF
(0.5 mL) were added to a CH
6
) (2b). Cp*RhCl[κ (N,C)-{NH
2
C(C
6
H
5
)
2
-2-C H }] (279.5 mg,
6 4
4
solvent. Elemental analyses were carried out using a PE2400 Series II
CHNS/O analyzer (PerkinElmer). IR spectra were recorded on a
JASCO FT/IR-610 spectrometer. Mass spectra (MS) were obtained
with a JEOL JMS-SX102A instrument. Recyclable preparative high-
performance liquid chromatography was performed on a Japan
Analytical Industry LC-9225 NEXT system equipped with JAIGEL-
6
(193.0 mg, 0.5617 mmol), and acetonitrile
Cl solution (5.0 mL) at room tem-
perature. After the reaction mixture was stirred for 1 h at room
temperature, a yellow suspension was dried under reduced pressure. The
remaining solid was dissolved in CH
pad. Removal of solvents gave the crude product. Recrystallization from
2
2
Cl and filtrated through a Celite
2
2
1
1
1
H and -2H columns using CHCl as an eluent at a flow rate of
CH
(399.8 MHz, CD
CH CN), 4.58−4.74 (br, 2H; NH
14H; NH C(C H ) C H ) ppm. C{ H} NMR (100.5 MHz, CD Cl ,
Cl
2
2
and ether gave orange crystals (293.4 mg, 72% yield). H NMR
Cl , RT): δ 1.41 (s, 15H; C (CH ), 2.33 (s, 3H;
C(C ), 6.27−7.59 (m,
3
−1
4 mL min .
Synthesis of [Cp*Ir(NCCH ){κ (N,C)-(NH C(CH ) -2-C H )}]-
2
2
5
)
3 5
2
H ) C H
6 5 2 6 4
3
2
3 2
6
4
3
2
2
13
1
(SbF ) (1a). The chloride complex Cp*IrCl[κ (N,C)-{NH C(CH ) -
6
2
3
2
2
6
5
2
6
4
2
2
2
-C H }] (359.1 mg, 0.722 mmol), AgSbF (252.5 mg, 0.735 mmol),
−30 °C): δ 4.1 (CH CN), 8.7 (C (CH ) ), 78.1 (NH C(CH ) C H ),
6
4
6
3
5
3
5
2
3
2
6
4
2
and acetonitrile (0.5 mL) were added to a CH Cl solution (5.0 mL) at
97.2 (C (CH ) , J = 5.8 Hz), 123.1 (CH CN, J = 6.7 Hz), 123.7,
5 3 5 CRh 3 CRh
2
2
room temperature. After the reaction mixture was stirred for 1 h at room
temperature, a yellow suspension was dried under reduced pressure. The
remaining solid was dissolved in CH Cl and filtrated through a Celite
127.9 (overlapped), 128.6, 128.7, 128.9, 129.1, 136.3, 144.2, 146.9,
1
154.3, 166.2 (NH C(CH ) C H , J = 28.7 Hz) ppm. IR (KBr) ν:
2
3
2
6
4
CRh
2
2
3351, 3296, 3058, 3035, 2987, 2919, 2318, 2288, 1573, 1514, 1492,
−1
pad. Removal of solvents gave the crude product. Recrystallization from
CH Cl and ether gave pale yellow crystals (360.1 mg, 67% yield).
1444, 1379, 1228, 1132, 1042, 1024, 768, 754, 734, 705, 657 cm . Anal.
Calcd for C H F N RhSb: C, 48.15; H, 4.43; N, 3.62. Found: C, 48.14;
2
2
31 34
6
2
1
H NMR (399.8 MHz, CD Cl , RT): δ 1.46 (br, 6H; NH C-
H, 4.45; N, 3.73.
2
2
2
(
(
CH ) C H ), 1.75 (s, 15H; C (CH ) ), 2.42 (s, 3H; CH CN), 4.20
Formation of Hydrido(amine)iridium Complex 4 by Treat-
3
2
6
4
5
3
5
3
br, 2H; NH C(CH ) C H ), 6.83−7.44 (m, 4H; NH C(CH ) C H )
ment of Cationic Iridium Complex 1b and H . An NMR tube
2
3
2
6
4
2
3
2
6
4
2
13
1
ppm. C{ H} NMR (100.5 MHz, CD Cl , RT): δ 4.1 (CH CN),
equipped with a J-Young valve was loaded with 1b (7.0 mg, 8.1 ×
2
2
3
−
3
−3
9
.1 (C (CH ) ), 31.0 (NH C(CH ) C H ), 67.8 (NH C(CH ) C H ),
10 mmol) and triethylamine (0.8 mg, 7.9 × 10 mmol) in 0.50 mL of
5
3
5
2
3
2
6
4
2
3
2
6
4
9
0.0 (C (CH ) ), 118.7, 122.5, 124.2, 127.6, 136.1, 147.1, 156.7 ppm. IR
THF-d . After the solution was degassed via freeze−pump−thaw cycles,
5
3
5
8
(KBr) ν: 3327, 3282, 3051, 3038, 2969, 2928, 2331, 1592, 1578, 1455,
the system was then filled with H at room temperature for 20 min.
2
The 1H NMR spectrum acquired immediately afterward at room
temperature showed the formation of 4.
1
7
3
429, 1386, 1367, 1284, 1255, 1168, 1118, 1077, 1026, 946, 864, 763,
41, 655 cm . Anal. Calcd for C H F N IrSb: C, 34.16; H, 4.09; N,
.79. Found: C, 34.01; H, 4.06; N, 3.74.
−1
21
30
6
2
NMR Monitoring of a Mixture of Amidoiridium Complex and
2
Synthesis of [Cp*Ir(NCCH ){κ (N,C)-(NH C(C H ) -2-C H )}]-
H . An NMR tube equipped with a J-Young valve was loaded with
2
3
2
6
5 2
6
4
2
2
−3
(
(
SbF ) (1b). The chloride complex Cp*IrCl[κ (N,C)-{NH C-
C H ) -2-C H }] (399.4 mg, 0.643 mmol), AgSbF (262.0 mg,
Cp*Ir[κ (N,C)-{NHC(C H ) -2-C H }] (4.3 mg, 7.3 × 10 mmol) in
6 5 2 6 4
6
2
6
5
2
6
4
6
0.50 mL of THF-d , and the solution was degassed via freeze−pump−
8
0.763 mmol), and acetonitrile (0.6 mL) were added to a CH Cl
thaw cycles with liquid nitrogen. After the NMR tube was then filled
2
2
1
solution (6.0 mL) at room temperature. After the reaction mixture was
stirred for 1 h at room temperature, a yellow suspension was dried under
reduced pressure. The remaining solid was dissolved in CH Cl and
filtrated through a Celite pad. Removal of solvents gave the crude
product. Recrystallization from CH Cl and ether gave pale yellow
with H at room temperature for 20 min, H NMR spectra were
2
recorded.
2
2
General Procedure for Hydrogenation of N-(1-Pheny-
lethylidene)benzylamine. In a typical experiment, a 50 mL stainless
steel autoclave equipped with a pressure gauge and a magnetic
2
2
1
−2
crystals (360.1 mg, 67% yield). H NMR (399.8 MHz, CD Cl , RT): δ
stirrer was loaded with the cationic complex 1a (1.0 × 10 mmol),
2
2
1
.46 (s, 15H; C (CH ) ), 2.51 (s, 3H; CH CN), 5.32 (br, 2H;
N-(1-phenylethylidene)benzylamine (209 mg, 1.00 mmol), and 4A
5
3
5
3
NH C(C H ) C H ), 6.32−7.58 (m, 14H; NH C(C H ) C H ) ppm.
molecular sieves (0.4 g) under an argon atmosphere. After the loading of
2
6
5
2
6
4
2
6
5
2
6
4
1
3
1
−2
C{ H} NMR (100.5 MHz, CD Cl , −30 °C): δ 4.4 (CH CN), 8.4
AgSbF
6
(10.3 mg, 3.0 × 10 mmol) in 2-propanol (2 mL), the autoclave
2
2
3
(
C (CH ) ), 80.6 (NH C(C H ) C H ), 90.0 (C (CH ) ), 119.0,
was flushed with H
2
and then pressurized to 3.0 MPa. The reaction
5
3
5
2
6
5
2
6
4
5
3 5
1
1
2
1
7
3
23.4, 127.5, 127.8, 128.0, 128.2, 128.6, 128.9, 128.97, 129.00, 136.3,
43.7, 146.4, 150.4, 154.2 ppm. IR (KBr) ν: 3340, 3287, 3059, 2991,
920, 2330, 1970, 1909, 1820, 1568, 1494, 1446, 1383, 1293, 1272,
235, 1157, 1082, 1049, 1032, 1001, 980, 917, 862, 848, 768, 754, 738,
mixture was stirred in a water bath at 30 °C for 2 h. After carefully
venting hydrogen, a sample of the reaction mixture was passed through
a small amount of Celite and dried under reduced pressure. The yield
was determined by 1H NMR using triphenylmethane (244.3 mg,
1.00 mmol) as an internal standard.
−1
06, 658 cm . Anal. Calcd for C H F N IrSb: C, 43.16; H, 3.97; N,
31
34
6
2
.25. Found: C, 43.04; H, 3.88; N, 3.20.
General Procedure for Hydrogenation of Nitriles. In a typical
experiment, a 50 mL stainless steel autoclave equipped with a pressure
gauge and a magnetic stirrer was loaded with the cationic complex
2
Synthesis of [Cp*Rh(NCCH ){κ (N,C)-(NH C(CH ) -2-C H )}]-
3
2
3 2
6
4
2
(
(
SbF ) (2a). The chloride complex Cp*RhCl[κ (N,C)-{NH C-
CH ) -2-C H }] (177.6 mg, 0.436 mmol), AgSbF (158.9 mg,
6
2
−2
3
2
6
4
6
(1.0 × 10 mmol), the nitrile substrate 5 (1.00 mmol), and 4A
0.462 mmol), and acetonitrile (0.2 mL) were added to a CH Cl2
molecular sieves (0.4 g) under an argon atmosphere. After the loading of
2
−
2
solution (5.0 mL) at room temperature. After the reaction mixture was
stirred for 1 h at room temperature, a yellow suspension was dried under
reduced pressure. The remaining solid was dissolved in CH Cl and
filtrated through a Celite pad. Removal of solvents gave the crude
product. Recrystallization from CH Cl and ether gave orange crystals
AgSbF (13.7 mg, 4.0 × 10 mmol) in THF (2 mL) and triethylamine
6
−2
(5.1 mg, 5.0 × 10 mmol), the autoclave was flushed with H and then
2
2
2
pressurized to 1.0 MPa. The reaction mixture was stirred in a water bath
at 60 °C. After carefully venting hydrogen, a sample of the reaction
mixture was passed through a small amount of Celite and dried under
2
2
1
1
(
217.5 mg, 77% yield). H NMR (399.8 MHz, CD Cl , RT): δ 1.45 (br,
reduced pressure. The yield of 6a was determined by H NMR using
2
2
6H; NH C(CH ) C H ), 1.70 (s, 15H; C (CH ) ), 2.27 (s, 3H;
triphenylmethane (24.4 mg, 0.100 mmol) as an internal standard. Other
product amines 6b−i were obtained after purification by a recycling
preparative HPLC.
2
3
2
6
4
5
3 5
CH CN), 3.62 (br, 2H; NH C(CH ) C H ), 6.80−7.44 (m, 4H;
NH C(CH ) C H ) ppm. C{ H} NMR (100.5 MHz, CD Cl , RT): δ
3
3
2
3
2
6
4
13
1
2
3
2
6
4
2
2
.9 (CH CN), 9.5 (C (CH ) ), 31.5 (NH C(CH ) C H ), 65.6
Spectroscopic Data of N,N-Bis[{4-(1,1-ethylenedioxy)ethyl}-
3
5
3
5
2
3
2
6
4
1
1
(
NH C(CH ) C H ), 97.3 (C (CH ) , J = 5.7 Hz), 122.8, 122.9,
phenyl]amine (6f). Isolated yield: 67% yield. H NMR (399.8 MHz,
2
3
2
6
4
5
3
5
CRh
1
124.5, 127.7, 136.0, 157.0, 162.8 (NH C(CH ) C H , J = 27.8 Hz)
CDCl , RT): δ 1.64 (s, 6H; CH ), 3.75−3.76 (m, 4H; O CH CH O),
2
3
2
6
4
CRh
3
3
2
2
ppm. IR (KBr) ν: 3336, 3289, 3036, 2969, 2930, 2315, 2286,1590, 1574,
523, 1451,1427, 1385, 1367, 1307, 1281, 1254, 1180,1146, 1110, 1077,
3.80 (s, 4H; CH ), 4.01−4.02 (m, 4H; O CH CH O), 7.31, 7.43 (each d,
2
2
2
3
13
1
1
4H; C H , J = 8.3 Hz). C{ H} NMR (100.5 MHz, CDCl , RT): δ 27.7,
6
4
HH
3
F
DOI: 10.1021/acs.organomet.6b00133
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
5
3
2.8, 64.5, 108.9, 125.5, 128.2, 139.5, 142.2. HR-ESI-MS (ESI+): m/z
(5) (a) 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.; de Vries, J. G.; Pfeffer, M. Org. Lett. 2005, 7, 1247−1250. (b) Sortais,
J.-B.; Pannetier, N.; Holuigue, A.; Barloy, L.; Sirlin, C.; Pfeffer, M.;
Kyritsakas, N. Organometallics 2007, 26, 1856−1868. (c) Sortais, J.-B.;
+
70.2032 [M + H] (m
= 370.2018).
theor
X-ray Structure Determination of 1a, 1b, 2a, and 2b. All
measurements were performed using a Rigaku Saturn CCD area
detector equipped with graphite-monochromated Mo Kα radiation
(
λ = 0.710 70 Å) under a nitrogen stream at 193 K. Indexing was
performed from seven images. The crystal-to-detector distance was
5.05 mm. Data were collected to a maximum 2θ value of 55.0°. A total
́
Pannetier, N.; Clement, N.; Barloy, L.; Sirlin, C.; Pfeffer, M.; Kyritsakas,
N. Organometallics 2007, 26, 1868−1874. (d) Pannetier, N.; Sortais, J.-
B.; Dieng, P. S.; Barloy, L.; Sirlin, C.; Pfeffer, M. Organometallics 2008,
4
of 720 oscillation images were collected. A sweep of the data was carried
out by using ω scans from −110.0° to 70.0° in 0.5° steps at χ = 45.0° and
ϕ = 0.0°. A second sweep was performed by using ω scans from −110.0°
to 70.0° in 0.5° steps at χ = 45.0° and ϕ = 90.0°. Intensity data were
collected for the Lorentz−polarization effects as well as for the
absorption. Structure solution and refinement were performed using
the CrystalStructure program package. The heavy-atom positions were
determined by a direct-program method (SIR2002), and the remaining
non-hydrogen atoms were determined by the subsequent use of Fourier
techniques (DIRDIF99). An empirical absorption correction based on
equivalent reflections was applied to all data. All non-hydrogen atoms
were refined anisotropically by full-matrix least-squared techniques
2
7, 5852−5859. (e) Barloy, L.; Issenhuth, J.-T.; Weaver, M. G.;
Pannetier, N.; Sirlin, C.; Pfeffer, M. Organometallics 2011, 30, 1168−
174. (f) Pannetier, N.; Sortais, J.-B.; Issenhuth, J.-T.; Barloy, L.; Sirlin,
C.; Holiigue, A.; Lefort, L.; Panella, L.; de Vries, J. G.; Pfeffer, M. Adv.
hali, E.; Barloy, L.;
1
Synth. Catal. 2011, 353, 2844−2852. (g) Feg
́
Issenhuth, J.-T.; Karmazin-Brelot, L.; Bailly, C.; Pfeffer, M. Organo-
metallics 2013, 32, 6186−6194.
(
6) Ueno, A.; Kayaki, Y.; Ikariya, T. Organometallics 2014, 33, 4479−
4
(
485.
7) (a) Sato, Y.; Kayaki, Y.; Ikariya, T. Chem. Commun. 2012, 48,
3
635−3637. (b) Haak, R. M.; Berthiol, F.; Jerphagnon, T.; Gayet, A. J.
A.; Tarabiono, C.; Postema, C. P.; Ritleng, V.; Pfeffer, M.; Janssen, D. B.;
Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. J. Am. Chem. Soc. 2008, 130,
1
2
based on F . All hydrogen atoms were constrained to be attached to
their parent atom. The relevant crystallographic data are compiled in
Tables S1 and S2.
3508−13509. (c) Jerphagnon, T.; Gayet, A. J. A.; Berthiol, F.; Ritleng,
V.; Mrsic, N.; Meetsma, A.; Pfeffer, M.; Minnaard, A. J.; Feringa, B. L.; de
̌
́
Vries, J. G. Chem. - Eur. J. 2009, 15, 12780−12790. (d) Jerphagnon, T.;
Haak, R.; Berthiol, F.; Gayet, A. J. A.; Ritleng, V.; Holuigue, A.;
Pannetier, N.; Pfeffer, M.; Voelklin, A.; Lefort, L.; Verzijl, G.; Tarabiono,
C.; Janssen, D. B.; Minnaard, A. J.; Feringa, B. L.; de Vries, J. G. Top.
Catal. 2010, 53, 1002−1008.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the ACS
Publications website at DOI: 10.1021/acs.organomet.6b00133.
■
*
S
(
8) (a) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev.
004, 248, 2201−2237. (b) Samec, J. S.; Backvall, J.-E.; Andersson, P.
G.; Brandt, P. Chem. Soc. Rev. 2006, 35, 237−248.
9) (a) Ohkuma, T.; Utsumi, N.; Tsutsumi, K.; Murata, K.; Sandoval,
Text and figures giving characterization data and NMR
spectra for new compounds (PDF)
Crystallographic data for 1a, 1b, 2a, and 2b (CIF)
2
̈
(
C.; Noyori, R. J. Am. Chem. Soc. 2006, 128, 8724−8725. (b) Sandoval, C.
A.; Ohkuma, T.; Utsumi, N.; Tsutsumi, K.; Murata, K.; Noyori, R. Chem.
- Asian J. 2006, 1−2, 102−110. (c) Ohkuma, T.; Tsutsumi, K.; Utsumi,
N.; Arai, N.; Noyori, R.; Murata, K. Org. Lett. 2007, 9, 255−257. (d) Li,
C.; Wang, C.; Villa-Marcos, B.; Xiao, J. J. Am. Chem. Soc. 2008, 130,
AUTHOR INFORMATION
Corresponding Authors
E-mail: ykayaki@o.cc.titech.ac.jp.
E-mail: tikariya@apc.titech.ac.jp.
■
*
*
1
4450−14451. (e) Zhou, H.; Li, Z.; Wang, Z.; Wang, T.; Xu, L.; He, Y.;
Fan, Q.-H.; Pan, J.; Gu, L.; Chan, A. S. C. Angew. Chem., Int. Ed. 2008, 47,
Notes
8
1
2
464−8467. (f) Heiden, Z. M.; Rauchfuss, T. B. J. Am. Chem. Soc. 2009,
31, 3593−3600. (g) Li, C.; Villa-Marcos, B.; Xiao, J. J. Am. Chem. Soc.
009, 131, 6967−6969.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
(10) (a) Ito, M.; Ikariya, T. Chem. Commun. 2007, 5134−5142. (b) Ito,
M.; Hirakawa, M.; Murata, K.; Ikariya, T. Organometallics 2001, 20,
■
This work was financially supported by JSPS KAKENHI (Grant
Numbers 22225004, 24350079, and 26620143) and partially
supported by the GCOE Program.
3
79−381. (c) Ito, M.; Hirakawa, M.; Osaku, A.; Ikariya, T. Organo-
metallics 2003, 22, 4190−4192. (d) Hedberg, C.; Kallstrom, K.;
Arvidsson, P. I.; Brandt, P.; Andersson, P. G. J. Am. Chem. Soc. 2005, 127,
̈
̈
1
2
5083−15090. (e) Ito, M.; Endo, Y.; Ikariya, T. Organometallics 2008,
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DOI: 10.1021/acs.organomet.6b00133
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DOI: 10.1021/acs.organomet.6b00133
Organometallics XXXX, XXX, XXX−XXX