Synthesis, Structure, and Catalytic Hydrogenation Activity of [NO]-Chelate Half-Sandwich Iridium Complexes with Schiff Base Ligands

Article abstract of DOI:10.1021/acs.inorgchem.1c00820

A series of N,O-coordinate iridium(III) complexes with a half-sandwich motif bearing Schiff base ligands for catalytic hydrogenation of nitro and carbonyl substrates have been synthesized. All iridium complexes showed efficient catalytic activity for the hydrogenation of ketones, aldehydes, and nitro-containing compounds using clean H2 as reducing reagent. The iridium catalyst displayed the highest TON values of 960 and 950 in the hydrogenation of carbonyl and nitro substrates, respectively. Various types of substrates with different substituted groups afforded corresponding products in excellent yields. All N,O-coordinate iridium(III) complexes 1-4 were well characterized by IR, NMR, HRMS, and elemental analysis. The molecular structure of complex 1 was further characterized by single-crystal X-ray determination.

Full text of DOI:10.1021/acs.inorgchem.1c00820

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Synthesis, Structure, and Catalytic Hydrogenation Activity of [NO]-
Chelate Half-Sandwich Iridium Complexes with Schiff Base Ligands
Wen-Rui Lv, Rong-Jian Li, Zhen-Jiang Liu,* Yan Jin,* and Zi-Jian Yao*
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ABSTRACT: A series of N,O-coordinate iridium(III) complexes
with a half-sandwich motif bearing Schiff base ligands for catalytic
hydrogenation of nitro and carbonyl substrates have been
synthesized. All iridium complexes showed efficient catalytic activity
for the hydrogenation of ketones, aldehydes, and nitro-containing
compounds using clean H2 as reducing reagent. The iridium catalyst
displayed the highest TON values of 960 and 950 in the
hydrogenation of carbonyl and nitro substrates, respectively. Various
types of substrates with different substituted groups afforded corresponding products in excellent yields. All N,O-coordinate
iridium(III) complexes 1−4 were well characterized by IR, NMR, HRMS, and elemental analysis. The molecular structure of
complex 1 was further characterized by single-crystal X-ray determination.
half-sandwich motif often used in the synthesis of organo-
metallic complexes.
INTRODUCTION
■
Catalytic hydrogenation of nitro-containing substrates and
ketones using transition metal catalysts attracted considerable
interest in coordination and organometallic chemistry. A
number of excellent catalytic hydrogenation systems for the
reduction of unsaturated compounds (such as olefins, ketones,
and imines) have been exploited and extensively used in
pharmaceuticals, organic synthesis, and materials science.1
Thus, the development of efficient catalysts plays an important
role for obtaining high yields and selectivity of the
corresponding products. Among different types of reported
catalysts, Group 8 and 9 transition metal complexes have been
paid much attention because of their activity and stability.
Moreover, the good solubility and stability in water of half-
sandwich transition metal complexes give the opportunity of
their catalytic application in aqueous media.2 The physical and
chemical properties of these complexes are facilely altered
through changing the substituted groups in the ligands.
Therefore, a number of transition metal complexes containing
a half-sandwich motif coordinated with various types of ligands
have been prepared and used as hydrogenation precata-
lysts.3−10
Transition metal complexes based on a half-sandwich
structure ([Cp#MCl2]2, Cp# = Cp*, p-cymene; M = Ir, Rh,
Ru) exhibit particular features such as good stability, solubility,
and easy functionalization:11−15 (i) the half-sandwich tran-
sition metal precursors can be prepared smoothly by metal
chlorides through facile routes; (ii) Cp* or cymene ligands
shield the hemisphere of the metal center, so the subsequent
reactions of these precursors would be easily controlled; (iii)
substituted groups bonded to compounds can be readily
changed to tune the physical and chemical properties
conveniently. The advantages mentioned above made the
Amines and alcohols are useful intermediates in fine
chemicals, the flavor industry, drug synthesis, agricultural
sciences, and so on.16−19 Reduction of ketones and nitroarenes
using stochiometric NaBH4 or LiAlH4 is an efficient method to
prepare amines and alcohols; however, a tremendous amount
of waste would be afforded in the meantime. Thus, the
transition metal catalyzed hydrogenation process of such
substrates using clean H2 reduction reagent is a more
environmentally friendly method in this area. During the past
few years, we have concentrated on the synthesis and
application of half-sandwich transition metal complexes with
different ligands because of their prominent catalytic efficiency.
Herein, several N,O-chelated mode half-sandwich iridium
complexes based on Schiff base ligands were prepared.
Experimental results indicated that hydrogenation of both
ketones and nitroarenes occurred smoothly under the catalysis
of these iridium complexes. All iridium complexes were
characterized well, and the influence on the catalytic efficiency
of the iridium complexes was inverstigated.
RESULTS AND DISCUSSION
■
Preparation of Half-Sandwich Iridium(III) Complexes
1−4. Schiff base ligands L1−L4 were obtained through the
Received: March 17, 2021
Published: May 13, 2021
https://doi.org/10.1021/acs.inorgchem.1c00820
© 2021 American Chemical Society
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Scheme 1. Synthesis of N,O-Chelate Half-Sandwich Iridium Complexes 1−4
a
Reaction conditions: (i) 1-tetralone (1.0 equiv), HCOOEt (1.5 equiv), tBuOK (1.5 equiv), 0 °C, 30 min; (ii) aromatic amines (1.1 equiv), HOAc
(3 drops), 4 Å MS (0.1 g), MeOH, reflux, 12 h; (iii) DDQ (1.2 equiv), 1,4-dioxane, reflux, 1 h; (iv) [Cp*IrCl2]2 (0.5 equiv), NaOAc (2.0 equiv),
CH3OH, reflux, 6 h.
modification processes according to the reported method.20
A
β-Diketone intermediate was given through the interaction of
1-tetralone and HCOOEt in the presence of the strong base
tBuOK in anhydrous Et2O. Then the β-enaminoketonato
ligands were obtained through the reactions between
corresponding amines and the β-diketones in MeOH catalyzed
by HOAc. Ligands L1−L4 were finally obtained by an
oxidation reaction of β-enaminoketonato using DDQ as
oxidant (Scheme 1). The broad peak at approximately 3415
cm−1 in the IR spectra of the ligands suggests the existence of
an -OH group. Four new half-sandwich iridium complexes 1−4
containing N,O-chelate mode ligands were obtained with
moderate yields by the interaction of the ligands and iridium
precursor [Cp*IrCl2]2 promoted by NaOAc in boiling
CH3OH for 6 h (Scheme 1). Pure iridium complexes 1−4
were obtained as dark red powders and exhibited good stability
in air for several weeks in the solid state. The iridium
complexes showed good solubility in most polar solvents,
whereas they are almost insoluble in hexane and Et2O.
Elemental analysis data of the iridium complexes confirmed
their expected molecular formula. Good thermal stability of
target complexes 1−4 was confirmed by the TGA analysis (see
Supporting Information); no decomposition was found at 200
°C.
The singlet at approximately 1.40 ppm was assigned to the
protons of the C5Me5 group. The characteristic band at 1410−
1430 cm−1 in the IR spectra of the iridium complexes 1−4 can
be assigned to the signals of the CN groups of the Schiff
base ligand. Compared with the CN bond vibrations at
approximately 1460−1485 cm−1 of the ligands, these signals
shifted to lower wavenumbers (1450−1480 cm−1) possibly
caused by the coordination between the Ir(III) center and the
N donor. The coordination interaction of the iridium
complexes could increase the back bonding ability of Ir(III)
to the imine bond, and consequently, the electron density on
the iridium atom was increased.21 All spectroscopy data of the
iridium complexes 1−4 indicate their structural similarity.
Molecular Structure of Half-Sandwich Iridium Com-
plex. To elaborate the exact structure of the obtained half-
sandwich iridium complex, single-crystal X-ray analysis has
been carried out. Qualified single crystals of complex 1 were
obtained by the liquid diffusion method between n-hexane and
a solution of complex 1 in CH2Cl2. The molecular structure of
complex 1 is shown in Figure 1. Selected geometric data are
given in Table 1, and detailed bond lengths and angles are
summarized in the caption of Figure 1. The iridium complex
exhibited an expected distorted-octahedral environment in
which the metal center was chelated by the N, O, and Cl
Figure 1. Molecular structure of 1 with thermal ellipsoids drawn at
the 30% level. All hydrogen atoms are omitted for clarity. Selected
bond lengths (Å) and angles (deg): Ir(1)−N(1), 2.083(4); Ir(1)−
O(1), 2.074(4); Ir(1)−Cl(1), 2.4255(12); C(11)−N(1), 1.294(6);
C(1)−O(1), 1.299(6); O(1)−Ir(1)−N(1), 87.82(14); O(1)−Ir(1)−
Cl(1), 86.89(11); Cl(1)−Ir(1)−N(1), 84.09(11); Ir(1)−O(1)−
C(1), 128.6(3); Ir(1)−N(1)−C(11), 126.2(3).
atoms. The excellent stability of the iridium complex may be
caused by the formation of the Ir(1)−O(1)−C(1)−C(10)−
C(11)−N(1) six-membered ring. The bond lengths of Ir(1)−
N(1) and Ir(1)−O(1) of 2.083(4) Å and 2.074(4) Å,
respectively, are both located in the normal range of known
values.22 The Ir(1)−Cl(1) distance of 2.4255(12) Å is similar
to that of the analogous complex.22 The crystal stacking
structure of complex 1 does not exhibit any hydrogen bond
between molecules.
Catalytic Hydrogenation of Carbonyl Substrates by
Iridium Complexes. The catalytic hydrogenation activity of
these iridium complexes in the carbonyl compounds’ reduction
with H2 as reductive reagent was investigated. Hydrogenation
of acetophenone was monitored as the sample to screen the
optimal condition. The reaction was carried out at 80 °C with
0.1 mol % catalyst loading in MeOH. The product yields
increased from 22% to 96% over 8 h along with the reaction
pressure (Table 2, entries 1−5). Six atmospheres is proper for
the hydrogenation process, and a further increase of the
pressure showed little influence on the hydrogenation process
(Table 2, entries 4 and 5). The corresponding alcohol was
afforded in good yields at 60 °C for 6 h; however, low
conversion was obtained when the catalytic reaction was
carried out at room temperature (Table 2, entries 6−10). The
reaction gave the best results in MeOH after screening
different solvents such as toluene, DMF, THF, and DMSO
(Table 2, entries 11−14). The hydrogenation process worked
sluggishly in water probably because of the poor solubility of
substrate in water (Table 2, entry 15). The product was
furnished in 68% yield when 0.05 mol % catalyst loading was
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used in the reaction (Table 2, entry 16). All the iridium
complexes were used in the hydrogenation reaction under the
optimal conditions and little differences of catalytic activity
were observed (Table 2, entries 17−19). Little product was
found when the reaction was carried out under the catalysis of
[Cp*IrCl2]2 or in the absence of the catalyst (Table 2, entries
20 and 21).
Table 1. Crystallographic Data and Structure Refinement
Parameters for 1
a
1
Chemical Formula
FW
C27H27ClIrNO
609.14
T/K
173(2)
λ/Å
0.71073
We subsequently investigated the generality of the reaction
after the optimal conditions were obtained. A survey of various
types of ketones and aldehydes was investigated in the
hydrogenation process. Generally, all aromatic substrates
reacted well in such conditions, and the corresponding
aromatic alcohols were furnished in excellent yields (Table 3,
5a−5p). A stereoselectivity study was carried out by employing
ortho-, meta-, and para-methylacetophenone in the reaction
aiming to elaborate the influence of the substituent position on
the catalysis; to our delight, all reactions occurred smoothly
under such conditions (Table 3, 5e−g). High yields of the
alcohols were also observed when bulky substituent bonded
substrates were used in the reaction (Table 3, 5l and 5m).
Additionally, heteroaromatic aldehydes with pyridine and furan
moieties were reduced efficiently under catalysis of iridium
complex 1 (Table 3, 5q and 5r). In comparison with the
aromatic substrates, aliphatic aldehydes and ketones were less
reactive and their hydrogenation process required harsh
conditions such as higher temperature and longer reaction
time to get good results (Table 3, 5s−5u). The catalytic
system showed high efficiency on the hydrogenation of the
carbonyl group, whereas the ester group was intact in the
reaction (Table 3, 5u).
Crystal system
Space group
a/Å
b/Å
c/Å
α/deg
β/deg
γ/deg
V/Å3
Z
ρ/Mg m−3
μ/mm−1
Monoclinic
P2(1)/n
8.1257(3)
12.3595(6)
23.0291(11)
90
92.595(2)
90
2310.43(18)
4
1.751
5.914
1192
2.419−26.817
66015
F(000)
θ range/deg
Reflections collected
Data/restraints/param
Goodness-of-fit on F2
4930/0/285
1.069
R1 = 0.0340
wR2 = 0.0963
1.314/−1.807
a
Final R indices [I > 2σ(I) ]
Largest diff.peak/hole (e Å−3
)
a
R1 = ∑||Fo| − |Fc||/∑|Fo| (based on reflections with Fo2 > 2σF2). wR2
2
2
2
= [∑[w(Fo − Fc2)2]/∑[w(F0 )2]]1/2; w = 1/[σ2(Fo ) + (0.095P)2];
2
2
P = [max(Fo , 0) + 2Fc2]/3 (also with Fo > 2σF2).
The interaction between the iridium catalyst and H2 was
monitored to explore the plausible mechanism of this reaction.
a
Table 2. Catalytic Hydrogenation of Acetophenone under Catalysis of Iridium Complexes 1−4
b
entry
Cat.(mol %)
T/°C
H2/atm
Time/h
Solvent
Yield/%
TON
TOF
1
2
3
4
5
6
7
8
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1(0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.1)
1 (0.05)
2 (0.1)
3 (0.1)
4 (0.1)
80
80
80
80
80
60
40
rt
60
60
60
60
60
60
60
60
60
60
60
60
60
1
2
4
6
8
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
6
8
8
8
8
8
8
8
8
6
3
6
6
6
6
6
6
6
6
6
6
6
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
toluene
DMF
THF
DMSO
H2O
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
22
39
72
96
96
96
61
15
95
69
53
77
38
71
42
68
95
93
93
220
390
720
960
960
960
610
150
950
690
530
770
380
710
420
1360
950
930
930
27.5
48.8
90.0
120.0
120.0
120.0
76.3
18.8
9
158.3
230.0
88.3
128.3
63.3
118.3
70.0
226.7
158.3
155.0
155.0
10
11
12
13
14
15
16
17
18
19
20
21
[Cp*IrCl2]2
trace
a
Reaction conditions: an autoclave was charged with the catalyst and solvent (2.0 mL), followed by acetophenone (1.0 mmol) under Ar. The
b
autoclave was then charged with H2 and heated in an oil bath. Yield was determined by GC analysis.
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a
Table 3. Catalytic Hydrogenation of Carbonyl Substrates
a
Reaction conditions: an autoclave was charged with complex 1 (0.1 mol %) and MeOH (2.0 mL), followed by ketone (1 mmol). The autoclave
was then charged with H2 (6 atm). Six hours at 60 °C in an oil bath. Yield was determined by GC analysis. Isolated yields (%) are provided in
b
parentheses. Reaction conditions: 80 °C, 12 h.
The NMR tube containing a dry C6D6 solution of complex 1
was charged with H2 (6 atm). Then the mixture was reacted at
60 °C and a singlet was observed at very high field, which
suggests the generation of metal hydride intermediates.23 We
speculate that the loss of chloride ligand occurred under high
H2 pressure atmosphere at elevated temperature. A similar
phenomenon was observed in the ruthenium complex
catalyzed hydrogenation process.24 It was concluded from
the condition screening stage that the catalytic hydrogenation
process benefits from higher reaction pressure. Figure 2
indicates a linear correlation between reaction pressure and
conversions, suggesting H2 heterolytic cleavage and the
formation of the metal hydrides are possibly involved in the
rate-determining step of this catalytic reaction.
The plausible catalytic mechanism was proposed based on
the results mentioned above. The heterolytic cleavage of H2
induced by iridium catalyst occurred to give the iridium
hydride intermediate under high pressure and elevated reaction
temperature. The catalytic hydrogenation cycle is composed of
the following steps: (i) reversible coordination of H2 to the
iridium complex; (ii) turnover-limiting heterolytic cleavage of
H2 to give the Ir−H intermediate and the addition of the
proton to the carbonyl group; (iii) transfer of the hydride to
the carbon atom of the oxonium cation (Figure 3).25,26
Catalytic Hydrogenation of Nitro-Containing Com-
pounds. Reduction of nitroarenes represents a direct and
efficient route to synthesize amines in various types of
synthetic methodologies.27 The catalytic efficiency of complex
1 in nitroarenes’ hydrogenation was also investigated.
Fortunately, hydrogenation of nitroarenes occurred smoothly
in the presence of iridium catalyst 1 under the optimal
conditions mentioned above. The electronic effects of the
substituents do not exhibit an obvious influence on the
catalytic efficiency; corresponding amines were all given in
moderate to good yields (Table 4, 6a−6l). However, reduction
of substrates with steric hindrance groups such as 2,6-
diisopropylnitrobenzene was not good and 2,6-diisopropylani-
line was furnished with lower yield (Table 4, 6m). Unsaturated
groups such as -CN, -COOR, and COOH were intact under
such conditions, which indicated the high selectivity of this
reaction (Table 4, 6e, 6k, and 6l). A lower yield of 4-
aminobenzoic acid was probably caused by the instability of
Figure 2. Influence of H2 pressure on the catalytic hydrogenation
process. Reaction conditions: 1.0 mmol of acetonphenone, 0.1 mol %
of iridium catalyst 1, H2, 60 °C for 1 h. The conversion was
determined by GC.
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the effect of the catalytic system on other hydrogenation
processes is currently underway.
EXPERIMENTAL SECTION
General Data. All manipulations were performed under an
atmosphere of nitrogen using standard Schlenk techniques. Chemicals
were used as commercial products without further purification. H
■
1
NMR (500 MHz) spectra were measured with a Bruker DMX-500
spectrometer. Elemental analysis was performed on an Elementar
vario EL III analyzer. IR (KBr) spectra were measured with the
Nicolet FT-IR spectrophotometer. Electrospray ionization mass
spectrometry was carried out on a Waters API Quattro Micro triple
quadrupole mass spectrometer in the positive ion mode.
Synthesis of Schiff Base Ligands L1−L4. tBuOK (6.5 g, 1.5 equiv),
1-tetralone (8.8 g, 40.0 mmol), and ethyl formate (5.8 g, 2.0 equiv)
were stirred at 0 °C in ethyl ether (100 mL) for 30 min. Then the
reaction mixture was warmed to room temperature and stirred for
another 10 h. The precipitate was filtered and washed by Et2O (20
mL); then the crude product was dried under vacuum. HCOOH was
added to the product until pH < 7. Then aromatic amine (1.0 equiv)
was added to the acidic solution, and the mixture was stirred for 24 h
to generate the corresponding β-enaminoketonato as a yellow solid.
The obtained β-enaminoketonato was mixed with DDQ (1.1 equiv),
and the mixture was refluxing in dioxane for 1 h. The reaction was
then monitored by TLC. Column chromatography of the crude
products (PE: EA = 6:1) gave L1−L4 in good yields.
Figure 3. Possible mechanism of the catalytic hydrogenation process.
the iridium catalyst in acidic conditions (Table 4, 6l). Aliphatic
substrate displayed slightly low reactivity in the catalytic
hydrogenation process (Table 4, 6n and 6o). Moreover,
reactions of polynitro compounds gave positive results (Table
4, 6p−6r).
L1. White solid, 63% isolated yield. 1H NMR (500 MHz, CDCl3):
δ 14.89 (s, 1H), 8.47 (d, J = 8.1 Hz, 1H), 8.40 (d, J = 5.4 Hz, 1H),
7.65 (d, J = 7.9 Hz, 1H), 7.59 (t, J = 7.3 Hz, 1H), 7.50−7.42 (m, 3H),
7.34 (d, J = 7.8 Hz, 2H), 7.28 (s, 1H), 7.14 (d, J = 8.7 Hz, 1H), 7.01
(d, J = 8.7 Hz, 1H) ppm. IR (KBr, disk): υ 3423, 1668, 1545, 1530,
1472, 1356, 752 cm−1. Elemental analysis calcd (%) for C17H13NO: C
82.57, H 5.30, N 5.66, found: C 82.65, H 5.38, N 5.60.
CONCLUSIONS
■
In summary, a series of N,O-chelate half-sandwich iridium
complexes based on Schiff-containing Schiff base ligands have
been prepared and characterized. Such air-stable complexes
exhibit good and diverse catalytic hydrogenation activity for
carbonyl and nitro-containing compounds by using clean H2 as
the reduce reagent. Various types of substrates with different
substituted groups afforded corresponding products in
excellent yields under optimal conditions. Experimental results
indicate that metal hydride formation is the rate-determining
step in the catalytic hydrogenation process. Further study of
L2. White solid, 67% isolated yield. 1H NMR (500 MHz, CDCl3):
δ 8.49−8.35 (m, 2H), 7.68 (d, J = 8.0 Hz, 1H), 7.59 (t, J = 7.0 Hz,
1H), 7.49 (t, J = 7.2 Hz, 1H), 7.39 (d, J = 8.7 Hz, 2H), 7.29−7.26 (m,
1H), 7.25 (s, 1H), 7.18 (d, J = 8.7 Hz, 1H), 7.10 (d, J = 8.7 Hz, 1H)
ppm. IR (KBr, disk): υ 3450, 1625, 1575, 1533, 1485, 1302, 755
cm−1. Elemental analysis calcd (%) for C18H15NO: C 82.73, H 5.79,
N 5.36, found: C 82.68, H 5.72, N 5.41.
a
Table 4. Catalytic Hydrogenation of Nitro Substrates
a
Reaction conditions: an autoclave was charged with complex 1 (0.1 mol %) and MeOH (2.0 mL), followed by nitroarenes (1 mmol). The
autoclave was then charged with H2 (6 atm). Six hours at 60 °C in an oil bath. Yield was determined by GC analysis. Isolated yields (%) are
provided in parentheses.
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L3. White solid, 65% isolated yield. 1H NMR (500 MHz, CDCl3):
δ 8.45 (d, J = 8.1 Hz, 2H), 7.69 (d, J = 7.9 Hz, 1H), 7.62−7.54 (m,
3H), 7.50 (t, J = 7.5 Hz, 1H), 7.21 (t, J = 8.7 Hz, 3H), 7.11 (d, J = 8.7
Hz, 1H) ppm. IR (KBr, disk): υ 3425, 1606, 1561, 1513, 1460, 1363,
1271, 759 cm−1. Elemental analysis calcd (%) for C17H12ClNO: C
72.47, H 4.29, N 4.97, found: C 72.55, H 4.32, N 5.03.
General Procedure for Catalytic Hydrogenation of Nitro-
arenes. In a typical run, the substrate (1.0 mmol), iridium complex 1
(0.1 mol %), and MeOH (2 mL) were charged in a 5 mL vial with a
magnetic bar. The vial was then transferred to an autoclave. The
autoclave was purged with H2 (6 atm) via three cycles. The autoclave
was heated to 60 °C. After stirring for 6 h, the autoclave was cooled
and the pressure was slowly released. The resultant mixture was
extracted with diethyl ether (2 × 5 mL) and dried over anhydrous
Na2SO4. Solvent was evaporated under vacuum. The residue was
dissolved in hexane and analyzed by GC-MS.
X-ray Crystallography. Diffraction data of 1 were collected on a
Bruker Smart APEX CCD diffractometer with graphite-monochro-
mated Mo Ka radiation (λ = 0.71073 Å). All the data were collected
at room temperature, and the structures were solved by direct
methods and subsequently refined on F2 by using full-matrix least-
squares techniques (SHELXL).28 SADABS29 absorption corrections
were applied to the data, all non-hydrogen atoms were refined
anisotropically, and hydrogen atoms were located at calculated
positions. All calculations were performed using the Bruker program
Smart.
L4. White solid, 59% isolated yield. 1H NMR (500 MHz, CDCl3):
δ 8.47 (d, J = 8.1 Hz, 1H), 8.39 (s, 1H), 7.65 (d, J = 8.0 Hz, 1H), 7.58
(t, J = 7.5 Hz, 1H), 7.47 (t, J = 7.5 Hz, 1H), 7.24 (s, 4H), 7.14 (d, J =
8.7 Hz, 1H), 7.01 (d, J = 8.7 Hz, 1H), 2.38 (s, 3H) ppm. IR (KBr,
disk): υ 3439, 1630, 1556, 1470, 1308, 1263, 1125, 765 cm−1.
Elemental analysis calcd (%) for C17H12BrNO: C 62.60, H 3.71, N
4.29, found: C 62.65, H 3.73, N 4.25.
Synthesis of Half-Sandwich Iridium Complexes 1−4. A mixture
of [Cp*IrCl2]2 (0.1 mmol), NaOAc (0.4 mmol), and Schiff base
ligands L1−L4 (0.2 mmol) was stirred at 65 °C in 10 mL of methanol
for 6 h. The mixture was filtered and evaporated to give the crude
products which were further purified by silica gel column
chromatography (PE:EA = 4:1) to afford the half-sandwich iridium
complexes.
1
1. Red solid, 57% isolated yield. H NMR (500 MHz, CDCl3): δ
8.64 (d, J = 8.2 Hz, 1H), 8.05 (s, 1H), 7.68 (d, J = 7.7 Hz, 2H), 7.54
(dd, J = 13.4, 6.4 Hz, 2H), 7.42−7.33 (m, 4H), 7.04 (d, J = 8.6 Hz,
1H), 6.82 (d, J = 8.7 Hz, 1H), 1.38 (s, 15H) ppm. 13C NMR (125
MHz, CDCl3): δ 162.5, 159.6, 155.9, 137.8, 130.3, 129.7, 128.8,
128.4, 127.3, 126.9, 125.9, 125.2, 124.7, 114.5, 113.1, 86.0, 8.6 ppm.
IR (KBr, disk): υ 1755, 1636, 1574, 1506, 1422, 1359, 769 cm−1.
Elemental analysis calcd (%) for C27H27NOClIr: C 52.23, H 4.47, N
2.30, found: C 52.28, H 4.49, N 2.23. HRMS calcd for [M−Cl]+: m/z
574.1722; found: 574.1729.
ASSOCIATED CONTENT
■
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.1c00820.
1H NMR spectra of L1−L4; H NMR and 13C NMR
spectra of complexes 1−4; TGA curves of complexes 1−
4 (PDF)
1
1
2. Red solid, 60% isolated yield. H NMR (500 MHz, CDCl3): δ
Accession Codes
8.63 (d, J = 8.3 Hzs, 1H), 7.99 (s, 1H), 7.66 (d, J = 8.6 Hz, 2H), 7.55
(d, J = 6.9 Hz, 2H), 7.37 (t, J = 7.3 Hz, 3H), 7.02 (d, J = 8.7 Hz, 1H),
6.82 (d, J = 8.7 Hz, 1H), 1.40 (s, 15H) ppm. 13C NMR (125 MHz,
CDCl3): δ 162.7, 159.6, 154.4, 137.9, 132.4, 130.2, 129.6, 128.9,
128.4, 127.3, 126.6, 125.9, 124.8, 114.8, 113.1, 86.1, 8.7 ppm. IR
(KBr, disk): υ 1715, 1652, 1563, 1485, 1410, 1358, 856, 763 cm−1.
Elemental analysis calcd (%) for C28H29NOClIr: C 53.96, H 4.69, N
2.25, found: C 54.03, H 4.65, N 2.29. HRMS calcd for [M−Cl]+: m/z
588.1878; found: 588.1870.
CCDC 2058746 contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cam-
bridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
1
AUTHOR INFORMATION
3. Red solids, 61% isolated yield. H NMR (500 MHz, CDCl3): δ
■
8.62 (d, J = 8.2 Hz, 1H), 7.99 (s, 1H), 7.59 (t, J = 7.0 Hz, 3H), 7.53
(dd, J = 10.8, 5.7 Hz, 3H), 7.39 (d, J = 6.3 Hz, 1H), 7.02 (d, J = 8.7
Hz, 1H), 6.82 (d, J = 8.7 Hz, 1H), 1.40 (s, 15H) ppm. 13C NMR (125
MHz, CDCl3): δ 162.8, 159.5, 154.8, 137.9, 131.4, 130.2, 129.6,
128.9, 127.3, 126.9, 125.9, 124.8, 120.3, 114.8, 113.1, 86.0, 8.7 ppm.
IR (KBr, disk): υ 1745, 1634, 1555, 1502, 1419, 1354, 863, 755 cm−1.
Elemental analysis calcd (%) for C27H26Cl2NOIr: C 50.39, H 4.07, N
2.18, found: C 50.33, H 4.11, N 2.25. HRMS calcd for [M−Cl]+: m/z
608.1332; found: 608.1341.
Corresponding Authors
Zi-Jian Yao − School of Chemical and Environmental
Engineering, Shanghai Institute of Technology, Shanghai
201418, China; Key Lab of Synthetic Chemistry of Natural
Substances, Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, Shanghai 200032, China; orcid.org/
0000-0003-1833-1142; Phone: +86-21-60877231;
Email: zjyao@sit.edu.cn; Fax: +86-21-60873335
Zhen-Jiang Liu − School of Chemical and Environmental
Engineering, Shanghai Institute of Technology, Shanghai
201418, China; orcid.org/0000-0001-6850-9485;
Email: zjliu@sit.edu.cn
Yan Jin − College of Sciences, Shanghai Institute of Technology,
Shanghai 201418, China; Key Laboratory of Wireless Sensor
Network&Communication, Shanghai Institute of
Microsystem and Information Technology, Chinese Academy
of Sciences, Shanghai 200050, China; Email: jinyan@
sit.edu.cn
1
4. Red solids, 66% isolated yield. H NMR (500 MHz, CDCl3): δ
8.64 (d, J = 8.2 Hz, 1H), 8.02 (s, 1H), 7.57−7.53 (m, 4H), 7.37 (t, J =
7.1 Hz, 1H), 7.17 (d, J = 8.0 Hz, 2H), 7.04 (d, J = 8.6 Hz, 1H), 6.82
(d, J = 8.6 Hz, 1H), 2.40 (s, 3H), 1.38 (s, 15H) ppm. 13C NMR (125
MHz, CDCl3): δ 162.3, 159.4, 153.7, 137.8, 136.6, 130.4, 129.6,
128.9, 128.7, 127.3, 125.9, 124.9, 124.6, 114.4, 113.1, 86.0, 21.0, 8.6
ppm. IR (KBr, disk): υ 1723, 1600, 1574, 1504, 1430, 1356, 871, 765
cm−1. Elemental analysis calcd (%) for C27H26BrNOClIr: C 47.13, H
3.81, N 2.04, found: C 47.18, H 3.87, N 1.96. HRMS calcd for [M−
Cl]+: m/z 652.0827; found: 652.0833.
General Procedure for Catalytic Hydrogenation of Carbonyl
Substrates. In a typical run, the substrate (1.0 mmol), iridium
complex 1 (0.1 mol %), and MeOH (2 mL) were charged in a 5 mL
vial with a magnetic bar. The vial was then transferred to an autoclave.
The autoclave was purged with H2 (6 atm) via three cycles. The
autoclave was heated to 60 °C. After stirring for 6 h, the autoclave was
cooled and the pressure was slowly released. The resultant mixture
was extracted with diethyl ether (2 × 5 mL) and dried over anhydrous
Na2SO4. Solvent was evaporated under vacuum. The residue was
dissolved in hexane and analyzed by GC-MS.
Authors
Wen-Rui Lv − School of Chemical and Environmental
Engineering, Shanghai Institute of Technology, Shanghai
201418, China; Key Laboratory of Wireless Sensor
Network&Communication, Shanghai Institute of
Microsystem and Information Technology, Chinese Academy
of Sciences, Shanghai 200050, China
8186
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Computational Study of the Mechanism. Chem. - Eur. J. 2015, 21,
16564−16577.
Rong-Jian Li − School of Chemical and Environmental
Engineering, Shanghai Institute of Technology, Shanghai
201418, China
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.1c00820
(6) Liu, J.; Wu, X.; Iggo, J. A.; Xiao, J. Halfsandwich Iridium
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The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the National Natural Science
Foundation of China (No. 21601125), the Chenguang Scholar
of Shanghai Municipal Education Commission (No. 16CG64),
the Shanghai Gaofeng & Gaoyuan Project for University
Academic Program Development, and the research funding of
Shanghai Institute of Technology (ZQ2020-10).
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