Earth-Abundant Bimetallic Nanoparticle Catalysts for Aerobic Ammoxidation of Alcohols to Nitriles

Article abstract of DOI:10.1021/acs.joc.0c00670

Heterogeneous nitrogen-doped carbon-incarcerated iron/copper bimetallic nanoparticle (NP) catalysts prepared from nitrogen-containing polymers were developed. These catalysts showed activity higher than that of the corresponding monometallic NPs for aerobic ammoxidation of alcohols to nitriles. The important procedure for high activity in the catalyst preparation was found to be a simultaneous reduction of two metal salts.

Full text of DOI:10.1021/acs.joc.0c00670

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Note
Earth-Abundant Bimetallic Nanoparticle Catalysts
for Aerobic Ammoxidation of Alcohols to Nitriles
Tomohiro Yasukawa, Xi Yang, and Shu Kobayashi
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.0c00670 • Publication Date (Web): 28 Apr 2020
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Earth-Abundant Bimetallic Nanoparticle Catalysts for Aerobic
Ammoxidation of Alcohols to Nitriles
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Tomohiro Yasukawa, Xi Yang, and Shu̅
Kobayashi*,a
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a
a
Department of Chemistry, School of Science, The University of Tokyo, Hongo,
Bunkyo-ku, Tokyo 113-0033, Japan
Table of Contents
ABSTRACT: Heterogeneous nitrogen-doped carbon-incarcerated iron/copper
bimetallic nanoparticle (NP) catalysts prepared from nitrogen-containing polymers were
developed. These catalysts showed higher activity than the corresponding monometallic
NPs for aerobic ammoxidation of alcohols to nitriles. The important procedure for high
activity in the catalyst preparation was found to be a simultaneous reduction of two
metal salts.
Supported metal nanoparticle (NP) catalysts have attracted great interest because of the
unique activity of such species, which is derived from their large surface area and
specific interactions with the support. The method of construction of bimetallic NP
structures can additionally tune their physical and chemical properties to improve
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catalytic activity and/or change the selectivity. This strategy is attractive and many
applications have been investigated with respect to numerous organic transformations.1
However, examples have generally been limited to precious metal-based NPs, and
effects of bimetallic structure on earth-abundant metal NPs for organic reactions have
not been well studied, probably because of the limited number of applications for these
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systems. We recently developed a method for the preparation of nitrogen-doped
carbon-incarcerated NP catalysts (NCI metal) from poly-4-vinylpyridine to easily
access multimetallic NP catalysts based on the polymer-incarceration methodology
expecting that metal nanoparticles were encapsulated by nitrogen-doped carbon layers
to be stabilized. Co/Cu bimetallic catalysts were found to show high catalytic
performance comparable to that of noble metal NP catalysts, such as gold for aerobic
3
oxidative esterification of alcohols and aldehydes. These results suggested that the
strategy of using bimetallic structure is effective for nitrogen-doped carbon-supported
earth-abundant metal NP catalysis.4
Nitrile compounds are an important class of organic compounds that are often found
in fine chemicals and are useful intermediates for the synthesis of amines, carboxylic
5
acids, etc. Among several routes to access nitriles, the aerobic ammoxidation of
alcohols is one of the most atom-economical pathways. Heterogeneous catalysis is
desirable because of the ease with which the components of the reaction can be
separated and because of the reusability of the catalysts. While several heterogeneous
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catalysts based on ruthenium, gold, lanthanum, platinum, or silver have been
reported, examples of those based on first-row transition metals as earth-abundant
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metals are limited. In 2014, Beller and coworkers developed cobalt oxide- or iron
oxide-based nanocatalysts supported on nitrogen-doped carbon for aerobic
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ammoxidation of alcohols to nitriles; however, relatively high catalyst loading (>4
mol%) was required.11d Recently, Gao and coworkers reported the use of cobalt11c or
metal-free catalysts11a based on nitrogen-doped carbon with a mesoporous structure for
these reactions. Although they succeeded in preparing highly active catalysts, expensive
polypyridyl ligands and silica gel templates were required. We hypothesized that the use
of bimetallic structures would provide a simpler strategy to construct active catalysts for
these reactions. Herein, we report the use of iron/copper bimetallic NP catalysts
supported on nitrogen-doped carbon for aerobic ammoxidation of alcohols to nitriles.
Considering the previously reported aerobic oxidative esterification, NCI bimetallic
catalysts were examined in nitrile synthesis from alcohols to assess the advantages of
the bimetallic effect in other oxidative reactions. In our methods, two metal salts were
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simultaneously treated with NaBH in the presence of poly-4-vinyl pyridine and carbon
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black prior to pyrolysis. In the nitrile synthesis from benzyl alcohol and ammonia, NCI
NP catalysts were examined with the total metal loading fixed at 2 mol% (Table 1).
NCI-Co 1 and NCI-Cu 2 monometallic catalysts showed moderate yields, whereas the
NCI-Fe 3 monometallic catalyst gave a low yield for the desired nitrile (entries 1–3).
We then examined the use of bimetallic NP catalysts in which the ratio of each metal
was 1:1 (entries 4–6). Among the three combinations, NCI-Co/Cu 4 and NCI-Fe/Cu 6
gave increased yields compared to the corresponding monometallic catalysts (entries 4
and 6). Interestingly, by tuning the metal loading ratio in the bimetallic catalysts (entries
7
–10), NCI-Co/Cu 8 (entry 8) and NCI-Fe/Cu 9 (entry 9) showed significantly higher
catalytic activity in the desired process. This result indicated the importance of
bimetallic NP formation and their structures. To verify this point, combinations of
monometallic NCI catalysts with ratios corresponding to those of metal ratios of
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NCI-Co/Cu 8 and NCI-Fe/Cu 9 were examined (entries 11 and 12). As expected, lower
yields compared to those obtained with bimetallic catalysts were obtained,
demonstrating the superiority of the bimetallic catalysts. We confirmed that the support
itself had no activity to form nitrile (entry 13).
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Table 1. The use of NCI bimetallic catalysts in ammoxidation of benzyl alcohola
Entry Catalyst
x/y
2a 3a
b
b
(
%) (%)
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NCI-Co 1
2:0
2:0
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NCI-Cu 2
NCI-Fe 3
NCI-Co/Cu 4
NCI-Co/Fe 5
NCI-Fe/Cu 6
NCI-Co/Cu 7
NCI-Co/Cu 8
NCI-Fe/Cu 9
NCI-Fe/Cu 10
0.67:1.33 74
0.4:1.6 96
0.67:1.33 >99 N.D.
0.4:1.6 92 <1
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NCI-Co 1 + NCI-Cu 2 0.4:1.6 71
NCI-Fe 3 + NCI-Cu 2 0.67:1.33 60
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N-doped carbonc
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a
Reaction conditions: benzyl alcohol (0.5 mmol), catalyst [weight corresponds to 2
mol% of metal in total (x+y = 2)], NH (100 µL) (28–30% NH ), O (5 bar), t-amyl
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alcohol (1 mL), 130 C, 24 h. Determined by gas chromatography (GC) analysis with
c
anisole as internal standard. The catalyst was prepared without using metal salt.
With the optimized catalyst, NCI-Fe/Cu 9, the substrate scope of the reaction was
examined (Scheme 1). Benzyl alcohols substituted with either electron-donating or
-withdrawing groups, including o-substituted substrates (2b–2h), were converted into
the corresponding nitriles in high yields. 2-Naphthonitrile 2i was obtained in excellent
yield. A diol was successfully converted into the dinitrile 2j in excellent yield with
doubled catalyst loading and ammonia. A variety of heteroaryl alcohols were
compatible with this transformation, giving thiophene- and furan-substituted nitriles 2k
and 2l in good yield. Pyridine substituted nitrile 2m was obtained in moderate yield,
with the reduced yield probably due to competitive adsorption of the hydroxy group of
1m with the pyridinic moiety of both the starting material and the product. We also
tested 3-phenylpropanol as an aliphatic substrate; however, only small amount of the
product (<5%) formed and the starting material was mostly recovered. The reusability
of NCI-Fe/Cu 9 was examined in the reaction with 1a. The catalytic activity gradually
decreased after three runs and the yield of each runs was >99%, 93%, 61%. Therefore,
we treated the catalyst after three runs by heating at 500 ˚C for 2 h under Ar atmosphere
to reactivate it. In the fourth run, the activity was slightly revived to afford the product
in 71% yield.
Scheme 1. Substrate scope
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NCI-Fe/Cu 9 (Fe: 1.34 mol%, Cu: 2.66 mol%) and 200 L of NH was used. 48 h.
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To elucidate the important factors of the catalyst preparation that determine its high
activity, a different method of construction for the bimetallic NP catalysts was
conducted as a control. In an optimized procedure, two metals were reduced with
NaBH simultaneously, expecting alloy NP formation. Revised from the standard
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method of constructing NCI bimetallic NP catalysts, two metal salts were separately
incorporated and sequentially reduced with NaBH with the intention of generating
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nonalloy NPs (Scheme 2). The resulting catalyst is described as NCI-M1-M2, where
M1 refers to one metal being added prior to the other metal M2. NCI-Fe-Cu 11 and
NCI-Cu-Fe 12 were constructed with the same metal ratio as NCI-Fe/Cu 9 by changing
the addition order of metals, and these were also examined in nitrile synthesis (Table 2).
Both catalysts showed significantly decreased yield compared with NCI-Fe/Cu 9
indicating the importance of simultaneous reduction of both metals during the catalyst
preparation. Such positive effects of simultaneous reduction were not observed in the
case of previously reported NCI-Co/Cu 4 catalyzed oxidative esterification of alcohols3
(
Table S3).
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We analyzed these catalysts by scanning transmission electron microscope (STEM)
and energy-dispersive X-ray spectroscopy (EDS) mapping (Figures S2-S4). In spite of
higher activity of NCI-Fe/Cu 9, relatively larger particles were observed in NCI-Fe/Cu
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than those in NCI-Fe-Cu 11 and NCI-Cu-Fe 12 (Figures S10, S13 and S14). The
structure of the NPs was not uniform and both random alloys and nearly monometallic
NPs were observed in all three types of catalysts. XRD analysis of NCI-Fe/Cu 9 was
performed to gain more insights of the catalyst structure (Figure S17). The sharp peaks
derived from metallic copper12 were observed while no iron signals was detected
meaning that there are no large aggregates of iron particles. These results suggested that
at least the number of alloy large aggregates is very limited. We also conducted XPS
analysis of NCI-Fe 3 and NCI-Fe/Cu 9. Although iron oxide species was detected in
NCI-Fe 3 (Figure S19) and copper oxide species was detected in NCI-Fe/Cu 9, no
meaningful peak of iron was detected in NCI-Fe/Cu 9 (Figure S20). It happened
because the concentration of iron on the surface of NCI-Fe/Cu was too low to detect.
Scheme 2. Preparation of bimetallic NP catalysts by sequential reduction of metals
Table 2. Examination of NCI-Fe-Cu 11 and NCI-Cu-Fe 12 in ammoxidation of benzyl
alcohol
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Entry Catalyst
2a (%)a 3a (%)a
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3
NCI-Fe/Cu 9
NCI-Fe-Cu 11
NCI-Cu-Fe 12
>99
79
N.D.
1
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56
a
Determined by GC analysis with anisole as internal standard.
We were then interested in whether larger NPs (>10 nm) influenced the catalytic
activity as the best catalyst, NCI-Fe/Cu 9, contained the largest size distribution (>70
nm). An acid leaching test was conducted for the purpose to discuss whether large NPs
or atomic/subnanometer-sized metals were the active species. Acid can dissolve
unstabilized metal species while metal species that are strongly interacted with nitrogen
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atoms on a support is expected to resist to acid washing. Yu, Zhang, and coworkers
demonstrated that upon acid washing of N-doped carbon-supported Co NP catalysts
with aqueous HCl, the resulting catalyst retained its catalytic activity, indicating that the
active species are highly dispersed on the carbon nanotubes (CNTs) on the atomic or
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subnanometer scale. Inspired by their research, we conducted acid washing of the NCI
NP catalysts with 6 M HCl at room temperature (NCI-M1/M2-H) and at 80 C
(NCI-M1/M2-H-80). The acid washing under room temperature was expected to wash
away large inactive particles, leaving small NPs and single sites; while acid leaching at
higher temperature could possibly remove some active small NPs as well.
When NCI-Fe/Cu 9 was washed with 6 M HCl at room temperature, a significant
amount (ca. 40%) of Fe NPs and almost all (ca. 95%) Cu NPs were washed away (Table
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, entry 2). Ammoxidation of an alcohol was performed using the same mass of these
washed catalysts as the optimized amount of NCI-Fe/Cu 9 regardless of their metal
loading. The nitrile yield catalyzed by NCI-Fe/Cu 9-H was significantly lower than that
with the unwashed catalyst and comparable to that with NCI-Fe 3 (entries 1, 2, and 4).
The catalyst washed at higher temperature (NCI-Fe/Cu 9-H-80) showed a further slight
decrease in both catalytic activity and metal loading (entry 3), indicating that acid
treatment at room temperature is sufficient to wash away the labile species. When
NCI-Fe 3 with a similar total metal loading as NCI-Fe/Cu 9 was washed in acid to give
NCI-Fe 3-H, the metal loading was dramatically decreased (75%) to a similar level to
that of NCI-Fe/Cu 9-H, but only a slight loss of activity was observed (entries 5 and 6).
These results indicated that similar Fe active species might remain in NCI-Fe/Cu 9-H
and NCI-Fe 3-H. STEM analysis of acid-washed catalysts confirmed that most large
NPs were removed and the size distribution of NPs was dramatically changed from ~80
nm in NCI-Fe/Cu 9 to ~3 nm in NCI-Fe/Cu 9-H (Figures S2, S8, S10 and S11). We also
confirmed this phenomenon by X-ray diffraction (XRD) analysis of NCI-Fe/Cu 9 and
NCI-Fe/Cu 9-H (Figures S17 and S18). The sharp peaks corresponding to metallic
copper species in NCI-Fe/Cu 9 disappeared after acid-washing. On the other hands, no
signals corresponding to iron were observed even in NCI-Fe/Cu 9 meaning that there
are no iron species with high crystallinity in this catalyst. XPS analysis of NCI-Fe/Cu
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-H also showed no visible peaks (Figure S21). Moreover, EDS analysis of NCI-Fe/Cu
-H detected metal species in some areas where no visible particles were observed
indicating the existence of atomic/subnanoscale sized species (Figure S8). Similar
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tendency was observed in NCI-Co/Cu catalyzed oxidative esterification of alcohols, for
which most of Cu species were removed after acid-washing and comparable activity
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was observed between acid-washed NCI-Co/Cu 4, NCI-Co 1, and acid-washed NCI-Co
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These observations suggested that the Fe species that were washed out by acid were
mostly inactive and main catalytically active Fe species were atomic/subnanometer
sized species and/or small nanoparticles (~3 nm). In contrast to Fe, Cu species washed
out by acid included those that contributed the catalysis. Therefore, it is difficult to
conclude whether large or small Cu particles contributed the catalysis. The current
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systems were found to be a “cocktail” type catalyst that contains several different
types of active species includes not only monometallic Fe species and Cu species but
also alloy bimetallic species. Considering that dramatic improvement of the activity in
NCI-Fe/Cu catalysts compared with NCI-Fe and NCI-Cu and the effect of simultaneous
reduction of metal salts during the catalyst preparation, the latter bimetallic species
might be a key for high activity. We could not identify which particular steps were
1
6
accelerated by forming bimetallic catalysts at this stage. We also assumed that the
behavior of adsorption of organic compounds on the surface of the NPs might differ and
it would help to prevent undesired adsorption, such as catalytic poisoning from side
products and product inhibition.17
Table 4. Examination of acid-washed NCI-Fe/Cu in nitrile synthesis of benzyl alcohol
Metal loading
2a 3a
Entry Catalyst
b
b
(
% remaining)a (%) (%)
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Fe: 0.100
1c
NCI-Fe/Cu 9
96
41
34
1
2
1
Cu: 0.171
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Fe: 0.060 (60%)
Cu: 0.010 (6%)
Fe: 0.057 (57%)
Cu: 0.009 (5%)
0.256
2c,d
NCI-Fe/Cu 9-H
3c,d
NCI-Fe/Cu 9-H-80
4
NCI-Fe 3
37
29
26
2
2
3
5e
6e
NCI-Fe 3-H
NCI-Fe 3-H-80
0.061 (24%)
0.064 (25%)
a
Determined by inductively coupled plasma mass spectrometry (ICP) analysis
mmol/g). The value in parentheses indicates the ratio of the remaining metal to the
(
loading of metal in the catalyst before washing. b Determined by GC analysis with
anisole as internal standard. c Average of two different batches of catalysts. d Same
e
weight of catalyst was incorporated as that in entry 1. Same weight of catalyst was
incorporated as that in entry 4.
In summary, we developed a bimetallic NP catalyst, NCI-Fe/Cu, for aerobic
ammoxidation of alcohols to nitriles. Bimetallic catalysts showed higher activity than
monometallic catalysts and the ratio of the two metals could be tuned further. The
simultaneous reduction treatment of two metals was crucial for activity, although
relatively large aggregates formed. The acid leaching test revealed that Fe aggregates
that were washed out had almost no activity and the remaining small Fe species could
catalyze the reaction. In contrast to Fe, almost all Cu species was washed out by acid
and it is difficult to distinguish active Cu derived species. The current systems were
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“
cocktail” type catalysts that contain several different types of active species. Further
studies to prepare well-defined bimetallic structure may give more insights of the active
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species and way to improve catalytic activity. These findings will be useful for the
design of highly active metal NP catalysts.
■
EXPERIMENTAL SECTION
General. JEOL JNM-ECA 500 or ECX 600 spectrometers were used for NMR
measurements. Chloroform impurity in CDCl ( = 7.24 ppm) was used as an internal
3
1
13
1
standard for H NMR and CDCl ( = 77.0 ppm) for C NMR ( H broadband
3
decoupled). Structures of known compounds were confirmed by comparison with
commercially available compounds or with reported data. Preparative thin-layer
chromatography was carried out using Wakogel B-5F. ICP analysis was performed with
Shimadzu ICPS-7510 equipment. GC analysis was performed with Shimadzu GC-2010
apparatus (column = GL Science, TCWAX, 0.25 mm ID, 0.25 m, 60.0 m; gas
pressure: 214.2 kPa; total flow: 90.6 mL/min; column flow: 1.86 mL/min; velocity: 30.8
cm/sec; purge flow: 3.0 mL/min; sprit ratio: 46.0; injector: 250 C, FID: 250 C;
column program: starting from 50.0 C, 10 min hold, 10 C/min to 220 C, 5 min hold).
XRD patterns were recorded with a Rigaku MiniFlex 300/600 with a CuK radiation
–
1
source and the measurements were recorded at a scan speed of 1 min . STEM/EDS
images were obtained with a JEOL JEM-2100F instrument operated at 200 kV. All
STEM specimens were prepared by placing a drop of the solution (suspension) on
carbon-coated Cu grids, Ni grids or Mo grids and allowed to dry in air (without
staining). Pyrolysis was conducted with a ceramic tube furnace ARF-40K. The
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temperature was controlled with a YKC-11 thermostat and gradually increased from
room temperature to 800 C over ca. 20 minutes. 4-Vinylpyridine (stabilized with HQ)
was purchased from Sigma Aldrich, and was passed through activated alumina before
use. XPS analysis was performed on JEOL JPS-9010MC. XPS analysis was performed
on JPS-9010MC with an Al Kα X-ray source and the C 1s line at 284.2 eV was used as
reference to correct the binding energies.
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Alumina (activated, for column chromatography, about 75 m) was purchased from
Wako Pure Chemical. Chloroform-d was purchased from Kanto Chemical.
2
,2-Azobis(4-methoxy-2,4-dimethylvaleronitrile) (V-70) was purchased from Wako
Pure Chemical. Co(OAc) ·4H O and Cu(OAc) ·H O were purchased from Wako Pure
2
2
2
2
Chemical. Fe(OAc) was purchased from Sigma Aldrich. NaBH was purchased from
2
4
Wako Pure Chemical and recrystallized from diglyme by heating and stored in a glove
box. Ketjen Black EC300J was purchased from Lion Corporation. Deionized water,
generated with a Millipore MilliQ machine (Gradient A 10), was used as solvent
without further treatment. Nitrile syntheses of benzyl alcohols were conducted with a
HIP-30 type reactor with Personal Organic Synthesizer PPV-3430, ChemiStation.
Ammonia solution (28% in water) was purchased from Tokyo Chemical Industry.
t-Amyl alcohol was purchased from Tokyo Chemical Industry. Aerobic oxidative
esterification reactions were conducted with a Carousel. Aromatic alcohols except for
4-bromobenzyl alcohol, 4-chlorobenzyl alcohol, and 2-thiophenemethanol were
purchased from Tokyo Chemical Industry. 4-bromobenzyl alcohol and 4-chlorobenzyl
alcohol were purchased from Wako Pure Chemical. 2-Thiophenemethanol was prepared
from 2-thiophenecarboxaldehyde purchased from Tokyo Chemical Industry. Methanol
was purchased from Wako Pure Chemical. Methanol was distilled over Mg and dried
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over 3Å molecular sieves. Hydrochloric acid was purchased from Kanto Chemical.
Poly(4-vinylpyridine), NCI-Co/Cu 4 were prepared following previously reported
methods.3,19 Other NCI metal catalysts 1-3 and 5-10 were also prepared by the
procedure based on that of NCI-Co/Cu 43,19 by changing metal species and amounts.
The total amount of metals used for the catalyst preparation was 0.28 mmol per 1 g of
supports that were the 1:1 mixture of poly(4-vinylpyridine) and ketjen black. NCI
catalysts 11-14 were prepared by modifying the standard method to prepare NCI
catalysts.
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Preparation of NCI-M1-M2. To a stirring suspension of poly(4-vinylpyridine) (200
mg) in ethanol (4 mL) and ketjen black (200 mg), a solution of the metal (denoted as a
M1) in ethanol (0.7 mL) was added dropwise under air. The mixture was stirred for 30
min at 50 ˚C using an oil bath under air. To this mixture, a solution of NaBH (7.1 mg,
4
0
.19 mmol) in ethanol (0.7 mL) was slowly added, and the mixture was continued to stir
for 1 h at 50 ˚C using an oil bath under air. To this mixture, a solution of the second
metal (denoted as a M2, M1 + M2 = 0.112 mmol. In the case of NCI-Fe-Cu 11 and
NCI-Cu-Fe 12, the molar ratio of Fe and Cu was 1:2 and in the case of NCI-Co-Cu 13
and NCI-Cu-Co 14 (See Table S3), the molar ratio of Co and Cu was Co : Cu = 1:1) in
ethanol (1.3 mL) was added dropwise. After stirring for 30 min at 50 ˚C using an oil
bath, a solution of NaBH (14.1 mg, 0.37 mmol) in ethanol (1.3 mL) was slowly added,
4
and the mixture was continued to stir for 2 h at 50 ˚C using an oil bath under air. To this
mixture was added ethyl acetate (50 mL) dropwise at room temperature and stirred for 2
h. The catalyst was filtered and washed in water (50 mL). The catalyst was filtered and
washed in acetone (50 mL). After filtration, the catalyst was grinded and dried in vacuo.
The catalyst was treated by pyrolysis at 800 ˚C for 2 h under Ar atmosphere. After
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cooling to room temperature, the catalyst was washed in ethanol (30 mL) under air. The
catalyst was filtered, washed with ethanol, water, THF and acetone and dried in vacuo
to afford NCI-M1-M2. NCI-M1-M2 was heated in a mixture of sulfuric acid and nitric
acid at 200 ˚C using an aluminum heating block, and the mixture was cooled to room
temperature. The amount of metals in the resulting solution was measured by ICP
analysis to determine the loading of metals in the catalyst.
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Nitrile syntheses from alcohols: Typical procedure for nitrile synthesis of alcohols
catalyzed by NCI-Fe/Cu 9. NCI-Fe/Cu 9 (total metal loading = 2 mol%), benzyl
alcohol (54.0 mg, 0.50 mmol), ammonia solution (28% in water, 100 L), and t-amyl
alcohol (1 mL) were added in a pressure-resistant tube under air. The system was closed
and charged with 5 bars of O , and the mixture was stirred for 24 h at 130 °C using
2
EYELA ChemiStation. After the reaction, the reaction mixture was diluted with ethyl
acetate (ca. 5 mL) and anisole (45–50 mg) was added to the mixture as an internal
standard. An aliquot of the reaction mixture (ca. 0.02 mL) was filtered through a
disposable Pasteur pipette packed with silica gel and washed with ethyl acetate for
injection and GC analysis. Ethyl acetate was added to the mixture and the solid catalyst
was removed by filtration. The solvents were then removed in vacuo and the residue
was purified by preparative TLC to afford the corresponding nitriles. To reuse the
catalyst recovered by filtration, it was washed with and dried in vacuo and used for next
run.
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4
6
1
-Chlorobenzonitrile (2b) . Yield: 68.8 mg (quant.), white solid; H NMR (CDCl ,
3
1
3
1
00 MHz):  = 7.45 (d, 2H, J = 8.9 Hz), 7.58 (d, 2 H, 8.9 Hz); C{ H} NMR (CDCl ,
3
50 MHz):  = 110.8, 117.9, 129.7, 133.4, 139.5.
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4
-Bromobenzonitrile (2c) . Yield: 86.5 mg (95%), white solid; H NMR (CDCl , 600
3
1
3
1
MHz):  = 7.50 (d, 2H, J = 8.2 Hz), 7.62 (d, 2H, 8.9 Hz); C{ H} NMR (CDCl , 150
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MHz):  = 111.2, 118.0, 128.0, 132.6, 133.4.
2
1
1
4
6
1
-Nitrobenzonitrile (2d) . Yield: 65.2 mg (88%), pale yellow solid; H NMR (CDCl ,
3
13
1
00 MHz):  = 7.87 (d, 2H, J = 9.1 Hz), 8.33 (d, 2H, 9.1 Hz); C{ H} NMR (CDCl ,
3
50 MHz)  = 116.8, 118.2, 124.2, 133.4, 150.0.
2
0
1
4-Methylbenzonitrile (2e) . Yield: 58.6 mg (quant.), white solid; H NMR (CDCl ,
3
13
1
6
00 MHz):  = 2.38 (s, 3H), 7.23 (d, 2H, J = 7.9 Hz), 7.50 (d, 2H, 7.9 Hz); C{ H}
NMR (CDCl , 150 MHz):  = 21.8, 109.3, 119.1, 129.8, 132.0, 143.7.
3
20
1
4
-Methoxybenzonitrile (2f) . Yield: 63.9 mg (96%), white solid; H NMR (CDCl ,
3
1
3
1
6
00 MHz):  = 3.78 (s, 3H), 6.87 (d, 2H, J = 8.9 Hz), 7.50 (d, 2H, 8.9 Hz); C{ H}
NMR (CDCl , 150 MHz):  = 55.5, 103.8, 114.7, 119.1, 133.9, 162.7.
3
2
1
1
3
-Methoxybenzonitrile (2g) . Yield: 61.2 mg (92%), colorless liquid; H NMR
(
(
CDCl , 500 MHz):  = 3.80 (s, 3H), 7.10–7.09 (m, 2H), 7.21–7.20 (m, 1H), 7.36–7.32
3
13
1
m, 1H); C{ H} NMR (CDCl , 150 MHz):  = 55.4, 113.0, 116.7, 118.6, 119.2, 124.3,
3
1
30.2, 159.5.
2
1
1
2-Methoxybenzonitrile (2h) . Yield: 53.9 mg (81%), white solid; H NMR (CDCl ,
3
13
1
6
00 MHz):  = 3.89 (s, 3H), 6.98–6.94 (m, 2H), 7.52–7.49 (m, 2H); C{ H} NMR
(
CDCl , 150 MHz):  = 55.9, 101.6, 111.2, 116.4, 120.7, 133.6, 134.3, 161.1.
3
2
0
1
2
-Cyanonaphthalene (2i) . Yield: 69.7 mg (91%), white solid; H NMR (CDCl , 600
3
1
3
1
MHz):  = 7.90–7.86 (m, 3H), 7.64–7.57 (m, 3H), 8.21 (s, 1H); C{ H} NMR (CDCl ,
3
150 MHz):  = 109.3, 119.2, 126.3, 127.6, 128.0, 128.4, 129.0, 129.2, 132.2, 134.1,
1
34.6.
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Terephthalonitrile (2j) . Yield: 58.3 mg (91%), white solid; H NMR (CDCl , 600
3
1
3
1
MHz):  = 7.78 (s, 4H); C{ H} NMR (CDCl , 150 MHz):  = 116.7, 117.0, 132.8.
3
1
1
1
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1
Thiophene-2-carbonitrile (2k) . Yield: 44.2 mg (81%), pale yellow solid; H NMR
(
CDCl , 600 MHz):  = 7.12 (dd, 1H, J = 5.2, 3.8 Hz), 7.59 (dd, 1H, J = 2.1, 1.0 Hz),
3
13
1
7
1
.62 (dd, 1H, J = 1.6, 0.8 Hz); C{ H} NMR (CDCl , 150 MHz):  = 109.9, 114.2,
3
27.6, 132.5, 137.4.
2
0
1
Furan-2-carbonitrile (2l) . Yield: 32.6 mg (70%), colorless liquid; H NMR (CDCl ,
3
6
1
00 MHz):  = 6.52 (dd, 1H, J = 1.6, 0.8 Hz), 7.09 (d, 1H, J = 3.4 Hz), 7.57 (d, 1H, J =
13
1
.4 Hz); C{ H} NMR (CDCl , 150 MHz):  = 111.4, 111.4, 122.0, 126.3, 147.3.
3
2
2
1
Nicotinonitrile (2m) . Yield: 30.2 mg (58%), colorless viscos liquid; H NMR (CDCl ,
3
6
00 MHz):  = 7.43 (dd, 1H, J = 7.6, 5.5 Hz), 7.95 (td, 1H, J = 8.0, 1.9 Hz), 8.81 (d, 1H,
1
3
1
J = 4.1 Hz), 8.88 (s, 1H); C{ H} NMR (CDCl , 150 MHz):  = 110.1, 116.5, 123.6,
3
1
39.2, 152.4, 153.0.
Nitrile syntheses from alcohols in large scale. NCI-Fe/Cu 9 (total metal loading = 2
mol%), 4-chlorobenzyl alcohol 1b (285.2 mg, 2.0 mmol), ammonia solution (28% in
water, 400 L), and t-amyl alcohol (4 mL) were added in a pressure-resistant tube under
air. The system was closed and charged with 5 bars of O , and the mixture was stirred
2
for 24 h at 130 °C using EYELA ChemiStation. Ethyl acetate was added to the mixture
and the solid catalyst was removed by filtration. The solvents were then removed in
vacuo and the residue was purified by column chromatography (hexane : ethyl acetate =
9
:1 as an eluent) to afford the corresponding nitrile 2b (274.2 mg, >99% yield).
Acid leaching test: General procedure for acid washing of NCI NP catalysts.
NCI-M1/M2 (100 mg) and 6M HCl solution (10 mL) were added in a round-bottom
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flask under air. The resulting suspension was stirred under air at room temperature for 9
h or at 80 C using an oil bath for 24 h. The catalyst was filtered and washed in water
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(20 mL). After filtration, the catalyst was washed with water, THF, and acetone, and
dried in vacuo to afford NCI-M1/M2-H or NCI-M1/M2-H-80. The resulting catalyst (10
mg) was heated in a mixture of conc. sulfuric acid (1 mL) and conc. nitric acid (several
drops) at 200 °C using an aluminum heating block, and the mixture was cooled to room
temperature. The amount of M1 and M2 in the resulting solution was measured by ICP
analysis to determine the loading of each metal. The amount of acid-washed catalysts
introduced into the reaction system was the same mass as the corresponding unwashed
catalysts.
■ ASSOCIATED CONTENT
The Supporting Information is available free of charge on the ACS Publications
website.
NMR spectra for products, and detailed experimental procedure for the mechanistic
studies
■ AUTHOR INFORMATION
Corresponding Author
*
E-mail: shu_kobayshi@chem.s.u-tokyo.ac.jp
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
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This work was supported in part by a Grant-in-Aid for Scientific Research from JSPS,
the University of Tokyo, and MEXT (Japan), JST. We thank Dr. Tei Maki (The
University of Tokyo) for STEM and EDS analyses.
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exclude the possibility that the hemiacetal/hemiaminal formation step was accelerated
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