Gold nanoparticles assisted formation of cobalt species for intermolecular hydroaminomethylation and intramolecular cyclocarbonylation of olefins

Article abstract of DOI:10.1039/c3cy00336a

The intermolecular hydroaminomethylation and the intramolecular cyclocarbonylation efficiently proceeded on cobalt oxide supported gold nanoparticles. The intermolecular reaction employing terminal olefins and N-isopropylaniline afforded hydroaminomethylated products as a mixture of regioisomers via a common reaction path consisting of hydroformylation, imine formation, and hydrogenation. In contrast, indolinone derivatives were exclusively obtained in the case of 2-alkenylanilines based on the intramolecular cyclocarbonylation mechanism. Both of these reactions were catalyzed by cobalt species derived from cobalt oxide. The active cobalt species were formed via reduction of the oxide support promoted by deposited gold nanoparticles. Characterization of the catalysts before and after the reaction was also performed.

Full text of DOI:10.1039/c3cy00336a

Catalysis
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Gold nanoparticles assisted formation of cobalt species
for intermolecular hydroaminomethylation and
intramolecular cyclocarbonylation of olefins
Cite this: Catal. Sci. Technol., 2013, 3,
3000
Xiaohao Liu,†ab Akiyuki Hamasaki,ab Yoshihiro Yamane,ab Shohei Aikawa,ab
abd
Tamao Ishida,ab Masatake Harutabc and Makoto Tokunaga
*
The intermolecular hydroaminomethylation and the intramolecular cyclocarbonylation efficiently proceeded on cobalt
oxide supported gold nanoparticles. The intermolecular reaction employing terminal olefins and N-isopropylaniline
afforded hydroaminomethylated products as a mixture of regioisomers via a common reaction path consisting of
hydroformylation, imine formation, and hydrogenation. In contrast, indolinone derivatives were exclusively obtained in
the case of 2-alkenylanilines based on the intramolecular cyclocarbonylation mechanism. Both of these reactions were
catalyzed by cobalt species derived from cobalt oxide. The active cobalt species were formed via reduction of the
oxide support promoted by deposited gold nanoparticles. Characterization of the catalysts before and after the reac-
tion was also performed.
Received 15th May 2013,
Accepted 27th June 2013
DOI: 10.1039/c3cy00336a
www.rsc.org/catalysis
1. Introduction
on cobalt-catalyzed Fischer–Tropsch synthesis.5 The in situ
formed cobalt active species can be used as an alternative to
In recent decades, gold nanoparticles (GNPs) have become
one of the mainstreams in the field of catalysis. As a new era
homogeneous cobalt carbonyl to catalyze hydroformylation,4a,b
amidocarbonylation,4c alkoxycarbonylation,4d Pauson–Khand
reaction,4d and Fischer–Tropsch synthesis.4e,f
of GNPs catalysis was opened by an oxidation reaction,1
a
wide range of reactions can be carried out using GNPs.2 Vari-
ous types of GNP catalysts have been prepared by employing
metal oxides, polymers, and carbon materials as supports.3
Although the choice of support affects the performance and
durability of catalysts, the catalysis is generally recognized as
a function of deposited Au with the supplemental aid of the
support. In contrast, we have recently reported a novel fea-
ture of cobalt oxide supported GNPs (Au/Co3O4) to supply
cobalt active species under a syngas (CO + H2) atmosphere.4
The cobalt oxide is reduced by spillover hydrogen and the
resulting Co(0) subsequently bound with CO to afford the
cobalt carbonyl equivalent. In this process, the deposited
GNPs just promote the reduction step by providing spillover
hydrogen. A similar effect of Au was found in the literature
The hydroaminomethylation reaction is an elegant, atom-
efficient, and clean approach to synthesize amines.6 This tandem
synthesis consists of three consecutive steps: (1) an initial hydro-
formylation of olefins to aldehydes; (2) reaction of resulting
aldehydes with primary or secondary amines to give the corre-
sponding intermediate imines or enamines; and (3) hydrogena-
tion of the intermediates to the desired secondary or tertiary
amine products as shown in Scheme 1. The amine product is
generally obtained as a mixture of linear and branched products.
The ratio of linear and branched products (l/b ratio) of the reac-
tion obviously depends on the product distribution at the stage
of the initial hydroformylation step. Homogeneous Rh-based
catalysts are commonly employed for this reaction because of
their high activity in the initial hydroformylation step and mod-
erate activity in hydrogenation.7,8 In this study, intermolecular
and intramolecular hydroaminomethylation reactions were inves-
tigated to elucidate the compatibility of the Au/Co3O4 catalyst sys-
tem with various amines. In addition, the characterization of
catalysts before and after the reaction was also carried out.
a Department of Chemistry, Graduate School of Sciences, Kyushu University,
6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
E-mail: mtok@chem.kyushu-univ.jp; Fax: +81 92 642 7528; Tel: +81 92 642 7528
b CREST, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi,
Saitama 332-0012, Japan
c Department of Applied Chemistry, Graduate School of Urban Environmental
Sciences, Tokyo Metropolitan University, 1-1 Minami-osawa, Hachioji,
Tokyo 192-0397, Japan
2. Experimental section
2.1 General remarks
1H NMR and 13C NMR spectra were recorded on JEOL AL-400,
JEOL JNM-ECS400, and Bruker DRX-600. 1H assignment
d International Research Center for Molecular Systems (IRCMS), Kyushu University,
Moto-oka 744, Nishi-ku, Fukuoka 819-0395, Japan
† Present address: Low-carbon Energy Conversion Center, Shanghai Advanced
Research Institute, Chinese Academy of Sciences, 100 Haike Road, Shanghai
201210, China.
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2.3 Typical procedure for the intermolecular
hydroaminomethylation of olefins (Table 2)
The 5 atom% Au/Co3O4 catalyst (20 mg, 0.75 mol% Au and
13.8 mol% Co to olefin) and heptane (2 mL) were introduced
into the autoclave reactor and were then purged with hydro-
gen twice. The pressure was adjusted to 2 MPa at room tem-
perature. Then, the temperature was elevated to 100 °C to
pretreat the catalyst for 3 h. After pre-treatment, the catalyst
and solvent were cooled to room temperature and then the
olefin substrate (1.6 mmol) and N-isopropylaniline (2 mL,
14 mmol) were introduced into the autoclave in sequence.
The autoclave was purged with syngas (CO/H2 = 1/1) twice
and then the pressure was adjusted to 4 MPa at room tem-
perature. The temperature was elevated to 120 °C to start the
reaction. After the time indicated in Table 2, the reaction
mixture was analyzed by GC and purified by silica gel column
chromatography to obtain hydroaminomethylation products
as a mixture of regioisomers. Further isolation of the major
isomer was carried out by recycle GPC. Characterization of
the product was performed by GC, GC-MS, 1H NMR, 13C NMR,
and elemental analysis.
Scheme 1 Intermolecular hydroaminomethylation of olefins in the presence of
primary or secondary amines.
abbreviations are the following; singlet (s), doublet (d), triplet
(t), quartet (q), heptet (hept), broad singlet (brs), doublet of
doublets (dd), doublet of triplets (dt), doublet of doublets of
doublets (ddd), doublet of doublets of quartets (ddq), and
multiplet (m). Elemental analysis was performed at the center
of elemental analysis of Kyushu University. Chromatographic
purification was performed on silica gel (Kanto Chemicals,
Silica gel 60N, spherical, neutral). GC analysis was carried out
using an Agilent GC 6850 series II equipped with a HP-1 Col-
umn (length 30 m, 0.32 mm I.D.). The recycle GPC purifica-
tion was performed on a JAI LC-908. All reactions were
conducted in a 50 mL stainless steel autoclave reactor (Toyo
Koatsu Co. Ltd.) with a glass tube equipped inside. All com-
mercial chemicals were used as received unless otherwise
noted. Piperidine, N-methylaniline, and N-isopropylaniline
were distilled under a reduced pressure prior to use. Tempera-
ture programmed reduction (TPR) profiles were measured
with a BEL Japan, BELCAT equipped with a thermal conduc-
tivity detector (TCD). High angle annular dark-field scanning
transmission electron microscopy (HAADF-STEM) was performed
using a JEOL JEM-ARM200F operating at 200 kV at the research
laboratory for high vacuum electron microscopy (HVEM), Kyu-
shu University. X-ray powder diffraction (XRD) measurements
were performed using a Rigaku MultiFlex at a scanning rate of
2° min−1 and a sampling angle interval of 0.02° in the 2θ range
of 10° to 80° with Cu-Kα radiation (λ = 0.151478 nm). The oper-
ating voltage and current were 40 kV and 40 mA. Crystalline
phases were identified by matching the diffraction patterns to
the JCPDS powder diffraction file. The content of metals in the
reaction mixtures was determined using an Agilent 4100 Micro-
wave Plasma-Atomic Emission spectrometer.
N-Heptyl-N-isopropylaniline (4a). 1H NMR (400 MHz,
CDCl3) δ 0.89 (t, J = 6.8 Hz, 3H), 1.17 (d, J = 6.6 Hz, 6H),
1.27–1.36 (m, 8H), 1.52–1.59 (m, 2H), 3.09 (t, J = 8.0 Hz, 2H),
4.03 (hept, J = 6.6 Hz, 1H), 6.65 (t, J = 7.2 Hz, 1H), 6.72 (d, J =
8.3 Hz, 2H), 7.20 (dd, J = 8.3, 7.2 Hz, 2H); 13C NMR (150 MHz,
CDCl3) δ 14.1, 20.0, 22.6, 27.3, 29.1, 29.3, 31.9, 44.0, 48.5, 113.2,
115.9, 129.1, 148.8; elemental analysis calcd (%) for C16H27N:
C 82.34, H 11.66, N 6.00; found: C 82.22, H 11.74, N 5.84.
1
N-Isopropyl-N-nonylaniline (5). H NMR (400 MHz, CDCl3)
δ 0.89 (t, J = 7.8 Hz, 3H), 1.16 (d, J = 6.6 Hz, 6H), 1.24–1.33
(m, 12H), 1.51–1.59 (m, 2H), 3.08 (t, J = 7.9 Hz, 2H), 4.03
(hept, J = 6.6 Hz, 1H), 6.64 (t, J = 7.2 Hz, 1H), 6.72 (d, J =
8.5 Hz, 2H), 7.20 (dd, J = 7.1, 7.1 Hz, 2H); 13C NMR
(150 MHz, CDCl3) δ 14.1, 20.1, 22.7, 27.3, 29.3, 29.4, 29.5,
29.7, 31.9, 44.0, 48.5, 113.2, 115.8, 129.1, 148.8; elemental
analysis calcd (%) for C18H31N: C 82.69, H 11.95, N 5.36;
found: C 82.62, H 11.92, N 5.37.
N-Isopropyl-N-tridecylaniline (6). 1H NMR (400 MHz,
CDCl3) δ 0.88 (t, J = 6.8 Hz, 3H), 1.16 (d, J = 6.6 Hz, 6H),
1.22–1.33 (m, 20H), 1.50–1.60 (m, 2H), 3.09 (t, J = 8.0 Hz,
2H), 4.03 (hept, J = 6.6 Hz, 1H), 6.65 (t, J = 7.2 Hz, 1H),
6.72 (d, J = 8.4 Hz, 2H), 7.20 (dd, J = 8.4, 7.2 Hz, 2H); 13C
NMR (150 MHz, CDCl3) δ 14.1, 20.1, 22.7, 27.3, 29.4, 29.5,
29.62, 29.64, 29.66, 29.68, 29.69, 29.70, 31.9, 44.0, 48.5, 113.2,
115.8, 129.1, 148.8; elemental analysis calcd (%) for C20H35N:
C 83.21, H 12.38, N 4.41; found: C 83.07, H 12.32, N 4.39.
N-(4,4-Dimethylpentyl)-N-isopropylaniline (7). 1H NMR
(400 MHz, CDCl3) δ 0.88 (s, 9H), 1.17 (d, J = 6.6 Hz, 6H),
1.17–1.21 (m, 2H), 1.48–1.57 (m, 2H), 3.05 (t, J = 8.1 Hz, 2H),
4.05 (hept, J = 6.6 Hz, 1H), 6.65 (t, J = 7.2 Hz, 1H), 6.71 (d, J =
8.8 Hz, 2H), 7.21 (dd, J = 8.8, 7.2 Hz, 2H); 13C NMR (150 MHz,
CDCl3) δ 20.0, 24.6, 29.4, 30.2, 41.4, 44.8, 48.2, 112.9, 115.8,
129.2, 148.8; elemental analysis calcd (%) for C16H27N: C 82.34,
H 11.66, N 6.00; found: C 82.21, H 11.77, N 5.92.
2.2 Preparation of catalysts
The 5 and 10 atom% Au/Co3O4 catalysts were prepared by the
coprecipitation method.4 This was performed by adding an
aqueous solution containing Co(NO3)2·6H2O and HAuCl4·4H2O
to an aqueous solution of sodium carbonate at room tempera-
ture. The coprecipitates were washed with water, dried over-
night at 100 °C, and calcined at 400 °C for 4 h. The gold
loading was expressed by atom% = 100 × Au/(Au + Co).
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N-(2-Cyclohexylethyl)-N-isopropylaniline (8). 1H NMR
Catalysis Science & Technology
1-Benzyl-3,3-dimethylindolin-2-one (12c)12. 1H NMR
(400 MHz, CDCl3) δ 1.44 (s, 6H), 4.92 (s, 2H), 6.72 (d, J =
7.8 Hz, 1H), 7.02 (dd, J = 7.6, 7.6 Hz, 1H), 7.13 (dd, J = 7.8,
7.8 Hz, 1H), 7.21 (d, J = 7.8 Hz, 1H), 7.24–7.33 (m, 5H);
13C NMR (100 MHz, CDCl3) δ 24.6 (2C), 43.6, 44.3, 109.2,
122.4, 122.6, 127.3 (2C), 127.6, 127.7, 128.9 (2C), 135.9, 136.2,
141.8, 181.5.
(400 MHz, CDCl3) δ 0.92–1.03 (m, 2H), 1.11–1.37 (m, 4H),
1.16 (d, J = 6.6 Hz, 6H), 1.46 (m, 2H), 1.64–1.78 (m, 5H), 3.14
(t, J = 8.3 Hz, 2H), 4.03 (hept, J = 6.6 Hz, 1H), 6.64 (t, J =
7.2 Hz, 1H), 6.72 (d, J = 8.3 Hz, 2H), 7.20 (dd, J = 7.2, 8.6 Hz,
2H); 13C NMR (150 MHz, CDCl3) δ 20.0, 26.3, 26.6, 33.4, 36.4,
36.7, 41.9, 48.4, 113.1, 115.7, 129.1, 148.8; elemental analysis
calcd (%) for C17H23N: C 83.20, H 11.09, N 5.71; found:
C 83.13, H 11.02, N 5.71.
N-(Bicyclo[2.2.1]heptan-2-ylmethyl)-N-isopropylaniline (9).
1H NMR (400 MHz, CDCl3) δ 1.02–1.13 (m, 4H), 1.10 (d, J =
6.7 Hz, 3H), 1.18 (d, J = 6.7 Hz, 3H), 1.32–1.34 (m, 1H), 1.36–
1.40 (m, 1H), 1.43–1.46 (m, 2H), 1.69–1.76 (m, 1H), 2.12
(brs, 1H), 2.21 (brs, 1H), 2.74 (dd, J = 5.6, 14.5 Hz, 1H), 2.87
(dd, J = 9.0, 14.5 Hz, 1H), 3.97 (hept, J = 6.7 Hz, 1H), 6.72
(d, J = 7.2 Hz, 1H), 6.84 (dd, J = 8.8, 8.8 Hz, 2H), 7.21 (dd, J =
8.8, 7.2 Hz, 2H); 13C NMR (150 MHz, CDCl3) δ 19.8, 20.5,
28.9, 29.8, 35.4, 36.0, 36.3, 39.4, 40.3, 49.0, 51.5, 116.2, 117.2,
128.8, 149.6; elemental analysis calcd (%) for C17H25N: C
83.89, H 10.35, N 5.75; found: C 83.51, H 10.74, N 5.74.
4-Methyl-3,4-dihydroquinolin-2(1H)-one (13a)13. 1H NMR
(400 MHz, CDCl3) δ 1.31 (d, J = 6.9 Hz, 3H), 2.42 (dd, J = 7.2,
16.2 Hz, 1H), 2.74 (dd, J = 5.6, 16.2 Hz, 1H), 3.13 (ddq, J =
6.9, 6.9, 6.9 Hz, 1H), 6.77 (d, J = 7.8 Hz, 1H), 7.03 (dd, J = 7.8,
7.8 Hz, 1H), 7.16–7.21 (m, 2H), 8.07 (brs, 1H); 13C NMR
(100 MHz, CDCl3) δ 19.8, 30.8, 38.4, 115.5, 123.5, 126.7,
127.6, 128.9, 136.4, 171.1; elemental analysis calcd (%) for
C10H11NO: C 74.51, H 6.88, N 8.69; found: C 74.68, H 6.94,
N 8.66.
1
1,4-Dimethyl-3,4-dihydroquinolin-2(1H)-one (13b)14. H NMR
(400 MHz, CDCl3) δ 1.28 (d, J = 7.0 Hz, 3H), 2.45 (dd, J = 7.6,
15.8 Hz, 1H), 2.73 (dd, J = 5.5, 15.8 Hz, 1H), 3.05 (ddq, J = 6.9,
6.9, 6.9 Hz, 1H), 3.36 (s, 3H), 6.99 (d, J = 8.1 Hz, 1H), 7.05
(dd, J = 7.5, 7.5 Hz, 1H), 7.20 (d, J = 7.0 Hz, 1H), 7.23–7.28
(m, 1H); 13C NMR (100 MHz, CDCl3) δ 19.3, 29.5, 30.4, 39.2,
114.9, 123.1, 126.3, 127.5, 131.1, 139.9, 170.0; elemental
analysis calcd (%) for C11H13NO: C 75.40, H 7.48, N 7.99;
found: C 75.22, H 7.52, N 7.80.
2.4 Typical procedure for the intramolecular
cyclocarbonylation of 2-isopropenylanilines (Table 3)
The 10 atom% Au/Co3O4 catalyst (20 mg, 1.4 mol% Au and
12 mol% Co to substrate) and heptane (2 mL) were introduced
into the autoclave reactor and were then purged with hydrogen
twice. The pressure was adjusted to 2 MPa at room temperature.
Then, the temperature was elevated to 100 °C to pretreat the cat-
alyst for 3 h. After pre-treatment, the catalyst and solvent were
cooled to room temperature and then 2-isopropenylaniline
substrate 118a,9 (1.6 mmol) was introduced into the autoclave.
The autoclave was purged with syngas or CO twice and then
the pressure was adjusted to an initial pressure given in
Table 3 at room temperature. The temperature was elevated to
start the reaction. After 24 h, the reaction mixture was ana-
lyzed by GC and purified by silica gel column chromatography
to obtain hydroaminomethylation products as a mixture of
regioisomers. Further isolation of the major isomer was car-
ried out by recycle GPC. Characterization of the products was
3-Benzylindolin-2-one (15)15. 1H NMR (400 MHz, CDCl3) δ 2.93
(dd, J = 13.7, 9.2 Hz, 1H), 3.50 (dd, J = 13.7, 4.6 Hz, 1H), 3.75
(dd, J = 9.2, 4.6 Hz, 1H), 6.73 (d, J = 7.3 Hz, 1H), 6.85–6.91
(m, 2H), 7.14–7.27 (m, 6H), 9.15 (brs, 1H); 13C NMR
(100 MHz, CDCl3) δ 36.7, 47.7, 109.9, 122.1, 124.9, 126.8,
128.1, 128.5, 129.1, 129.5, 137.9, 141.6, 180.1.
1
1-Phenylpyrrolidin-2-one (18)16. H NMR (400 MHz, CDCl3)
δ 2.16 (tt, J = 7.6, 7.6 Hz, 2H), 2.61 (t, J = 8.0 Hz, 2H), 3.86
(t, J = 7.1 Hz, 2H), 7.14 (t, J = 7.3 Hz, 1H), 7.36 (dd, J = 8.0,
8.0 Hz, 2H), 7.60 (d, J = 7.8 Hz, 2H); 13C NMR (100 MHz, CDCl3)
δ 18.2, 32.9, 48.9, 120.1 (2C), 124.6, 128.9 (2C), 139.4, 174.4.
3. Results and discussion
3.1 Intermolecular hydroaminomethylation catalyzed
by Au/Co3O4
1
performed by GC, GC-MS, H NMR, 13C NMR, and elemental
analysis. 1H and 13C NMR spectra of 12a–c and 13a,b were
in agreement with those of the reported one.
The intermolecular hydroaminomethylation of 1-hexene (1)
was investigated by employing piperidine, N-methylaniline,
and N-isopropylaniline (Table 1). Piperidine completely sup-
pressed the initial hydroformylation of 1 to aldehydes probably
due to a strong coordination to the active cobalt site (Table 1,
entry 1). Although all of 1 was converted into corresponding
aldehydes in the presence of N-methylaniline, aldol condensa-
tion of the resulted aldehydes was dominant over the forma-
tion of imine intermediates (Table 1, entry 2). In the case of
N-isopropylaniline, results highly depended on the amount of
amine. With 1.3 equiv. of amine, a significant amount of the
aldehyde intermediate remained (Table 1, entry 3). The yield
of desired tertiary amines reached 89% by using 8.8 equiv. of
N-isopropylaniline (Table 1, entry 4). When the amount of
N-isopropylaniline was further increased from 8.8 equiv., the
3,3-Dimethylindolin-2-one (12a)10. 1H NMR (400 MHz,
CDCl3) δ 1.40 (s, 6H), 6.92 (d, J = 8.2 Hz, 1H), 7.04 (dd, J =
7.5, 7.5 Hz, 1H), 7.18–7.22 (m, 2H), 8.19 (brs, 1H); 13C NMR
(100 MHz, CDCl3) δ 24.4 (2C), 44.7, 109.8, 122.6, 122.8, 127.7,
136.3, 139.7, 183.7; elemental analysis calcd (%) for
C10H11NO: C 74.51, H 6.88, N 8.69; found: C 74.67, H 6.97, N 8.66.
1,3,3-Trimethylindolin-2-one (12b)11. 1H NMR (400 MHz,
CDCl3) δ 1.36 (s, 6H), 3.21 (s, 3H), 6.84 (d, J = 7.8 Hz, 1H),
7.05 (ddd, J = 1.0, 7.5, 7.5 Hz, 1H), 7.20 (ddd, J = 0.5, 1.3,
7.4 Hz, 1H), 7.25 (ddd, J = 1.3, 7.7, 7.7 Hz, 1H); 13C NMR
(100 MHz, CDCl3) δ 24.5 (2C), 26.3, 44.2, 108.1, 122.3, 122.5,
127.7, 135.9, 142.7, 181.4; elemental analysis calcd (%) for
C11H13NO: C 75.40, H 7.48, N 7.99; found: C 75.39, H 7.67,
N 7.99.
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Table 1 Effect of the structure and amount of amines on the intermolecular
both 1-hexene and cis-2-hexene gave 4a as the major product,
the latter took a longer reaction time since isomerization of
olefin was involved in the reaction course (Table 1, entry 4 vs.
Table 2, entry 1). For methylenecyclohexane, the yield of
amine products was slightly lower (71%, Table 2, entry 5). In
the case of styrene, the hydrogenation to ethylbenzene was
much faster, which therefore gave desired amines in very low
yields of 11% (Table 2, entry 7). The dominance of hydroge-
nation over the objective reactions is often observed in
cobalt-catalyzed hydroformylation of styrene derivatives.17
a
hydroaminomethylation of 1-hexene catalyzed by Au/Co3O4
Conv.b
(%)
Yieldb
(%)
Entry Amine (equiv.)
1
Piperidine (8.8)
N-Methylaniline (8.8)
N-Isopropylaniline (1.3)
N-Isopropylaniline (8.8) 100
N-Isopropylaniline (13.1) 84
N-Isopropylaniline (17.5)
0
100
85
0 (2a) 0 (2b)
16 (3a) 17 (3b)
18 (4a) 0 (4b) 0.2 (4c)
61 (4a) 22 (4b)
30 (4a) 11 (4b)
0 (4a) 0 (4b)
0 (2c)
6 (3c)
2c
3d
4
6 (4c)
2 (4c)
0 (4c)
5
6
0
a
Reaction conditions: 5 atom% Au/Co3O4 (20 mg, 0.75 mol% Au
and 13.8 mol% Co to 1), 120 °C, 3.5 h, p(CO) = 2 MPa, p(H2) = 2 MPa,
hetpane + amine = 28 mmol, 1-hexene (1.6 mmol). b Determined by GC.
c
3.2 Intramolecular cyclocarbonylation catalyzed by Au/Co3O4
Heavily branched aldehydes (57%) and heavy amines (4%) were also
d
formed. Remaining unreacted aldehyde intermediate (55%).
As for intramolecular hydroaminomethylation of 2-alkenylaniline
derivatives, which has been demonstrated by rhodium-based
catalysts8a (Scheme 2), the expected reaction did not occur.
Instead, cyclocarbonylation to lactams proceeded in good
yields and regioselectivities (Table 3). Under high H2 partial
pressure, reduction of the C–C double bond was dominant
and a significant amount of 2-isopropylaniline was formed
(Table 3, entry 1). Along with increasing CO partial pressure,
the selectivity of lactam products was improved (Table 3,
entries 2 and 3). However, a minimum amount of H2 seemed
to be essential for the in situ formation of cobalt active species
by the hydrogenation of the cobalt oxide support (Table 3,
entry 4). The product distribution also depended on the sub-
strates. A benzyl compound 11c exclusively gave an indolinone
12c (Table 3, entry 6).
Under the similar conditions, the cyclocarbonylation of
aniline derivatives proceeded with various substrates
(Scheme 3). Due to steric reasons, the substrates having an
internal multiple bond such as 14 and 16 required a longer
reaction time than 11 and gave indolinone products in mod-
erate yields. The same transformations using homogeneous
Pd,18a Rh6(CO)16,19a and Co/Rh bimetallic nanoparticles19b are
reported. N-allylaniline 17 formed the desired lactam 18 only
in 30% yield even after a prolonged reaction time, suggesting
catalytic activity was gradually depressed till completely
deactivated at the amount of 17.5 equiv. (Table 1, entries 5
and 6). After the reaction under the condition shown in entry
4, the contents of Co and Au in the reaction mixture were
determined by MP-AES. Whereas a small amount of leached
Co (2.1%) was found in the solution, leaching of Au was not
practically observed (0.08%).
To generalize this method to the synthesis of tertiary
amines, various olefins have been investigated. As shown in
Table 2, most of selected olefins gave desired tertiary amines
in high yields. The reactivity of olefins and the linear/
branched (l/b) ratio of product amines were similar to that of
the hydroformylation reaction.4a,b This result indicated that
the amine products were afforded via a similar reaction
sequence as shown in Scheme 1. In all cases except styrene,
linear products were obtained as major products. Although
Table 2 Hydroaminomethylation of various olefins with N-isopropylaniline
a
catalyzed by Au/Co3O4
Yield of
Time aminesb Selectivity of normal
Entry Olefin
(h)
(%)
productc (%)
1
2
3
4
5
6
7
cis-2-Hexene
1-Octene
1-Dodecene
3,3-Dimethyl-1-butene
Methylenecyclohexane 21
2-Norbornene
Styrene
17
3.5 89
4.5 94
86
65 (4a)
66 (5)
59 (6)
94 (7)
56 (8)
81 (9)
41 (10)
4
90
71
92
11
18
18
a
Reaction condition: 5 atom% Au/Co3O4 (20 mg, 0.75 mol% Au and
13.8 mol% Co to olefin), 120 °C, p(CO) = 2 MPa, p(H2) = 2 MPa,
heptane (2 mL), N-isopropylaniline (14 mmol), olefin (1.6 mmol).
Determined by GC. Calculated as (100× yield of normal product/
b
c
Scheme
2
Rhodium catalyzed intramolecular hydroaminomethylation of
total yield of products).
2-isopropenylanilines to tetrahydroisoquinolines and indolines.
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Table 3 Au/Co3O4-catalyzed
intramolecular
cyclocarbonylation
of
a
2-isopropenylanilines
Pressure
Entry (CO/H2, MPa) Temp. (°C) Substrate Yieldb (%)
1c
2d
3
4
5
1/1, 4
3/1, 4.5
5/1, 6
CO only, 6
5/1, 6
5/1, 6
120
90
90
90
100
90
11a
11a
11a
11a
11b
11c
39 (12a) 13 (13a)
69 (12a) 14 (13a)
92 (12a)
0 (12a)
2 (13a)
0 (13a)
64 (12b) 17 (13b)
91 (12c) 0 (13c)
Scheme 4 Possible mechanism for the intramolecular cyclocarbonylation of
2-isopropenylaniline to lactams on the Au/Co3O4 catalyst. Co stands for the Co(0)
active sites on the catalyst surface.
6
a
Reaction conditions: 10 atom% Au/Co3O4 (20 mg, 1.4 mol% Au and
12 mol% Co to 11), heptane (2 mL), 11 (1.6 mmol). b Determined by GC.
c
d
48% of 2-isopropylaniline was obtained. 17% of 2-isopropylaniline
was obtained.
by reductive elimination to produce 12 with regeneration of
the Co metal active site. Although CO has a chance of
being inserted into the Co–N bond, the same products will
be eventually obtained. Two impressive characteristics of
Au/Co3O4-catalyzed cyclocarbonylation in Scheme 4 should be
pointed out. The alkenyl group of 11 was not hydroformylated
when catalyzed by Rh catalysts, which is possibly ascribed to –
NHR group coordination to Co metal promoting intramolecu-
lar hydrometallation. The interaction between Co and the –
NHR group may also prevent hydrogenation of the olefin
moiety which was observed in the case of intermolecular
hydroaminomethylation of styrene (Table 2, entry 7). When
styrene is employed for the hydroformylation or hydro-
aminomethylation, the formation of a branched product is gen-
erally dominant. The regioselectivity can be controlled by using
appropriate ligands in Rh-catalyzed intramolecular hydro-
aminomethylation8 and Pd-catalyzed cyclocarbonylation.18 In
the case of Au/Co3O4-catalyzed intramolecular cyclocarbonylation,
exclusive formation of 12c was achieved by modification of
the reaction conditions.
Scheme 3 Cyclocarbonylation of various aniline derivatives catalyzed by
Au/Co3O4.
that a proximity effect was playing an important role in the effi-
cient formation of the lactam ring. The same product 18 can
be obtained from N,N-diallylaniline with Co2(CO)8.20
3.3 Possible mechanism for the intramolecular
cyclocarbonylation of 2-isopropenylanilines catalyzed
by Au/Co3O4
ð1Þ
To obtain information about a reaction mechanism for the
intramolecular cyclocarbonylation, a deuterized substrate 11c
was treated under similar conditions. As the result, the deute-
rium on the nitrogen atom of 11c was incorporated into a
geminal methyl group of 12c (eqn (1)). Based on this result,
the mechanism was presumed as shown in Scheme 4. Oxida-
tive addition of the N–H bond to the Co site, and coordina-
tion of the olefin moiety would form 19. A five-membered
cobaltacycle 20 would be afforded by intramolecular
hydrometallation. Subsequent adsorbed CO insertion into
the Co–C bond forms the six-membered ring 22 followed
3.4 Characterization of catalysts
Temperature programmed reduction (TPR) profiles. In our
previous report, the reduction of Co3O4 was clearly observed
after H2 treatment in X-ray absorption near edge structure
(XANES) spectra4e,f and X-ray diffraction (XRD) patterns.4b Tem-
perature programmed reduction (TPR) profiles of Au/Co3O4
and Co3O4 were obtained under 5% H2/Ar flow (Fig. 1).
Whereas Co3O4 showed two peaks at 234 and 315 °C attrib-
uted to the reduction of Co(II, III) to Co(II) and Co(II) to Co(0),
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Fig. 1 TPR profiles for Au/Co3O4 and Co3O4 under 5% H2/Ar flow (50 mL min−1).
Fig. 3 XRD patterns of Au/Co3O4. (a) after air calcination, (b) after H2 treatment
(2 MPa, 100 °C, 3 h, in heptane), (c) after intermolecular hydroaminomethylation
reaction (1-hexene and N-isopropylaniline, 120 °C, 4 h, CO/H2 = 1 : 1, 4 MPa, in
heptane). The patterns of (d) Co3O4, (e) CoO, (f) Co, and (g) Au are shown based on
JCPDS data.
Thick line, Au/Co3O4; thin line, Co3O4.
a
drastic lowering of the reduction temperatures was
observed by the deposition of GNPs on Co3O4. The H2 pres-
surized conditions for the pretreatment of Au/Co3O4 may
accomplish the reduction of the Co3O4 support even at much
lower temperature.
High angle annular dark field scanning transmission
electron microscopic (HAADF-STEM) images. HAADF-STEM
was performed to obtain structural information of Au/Co3O4.
GNPs having diameters of a few nanometers were well-
dispersed on the surface of Co3O4 after air calcination
(Fig. 2a). Hydrogen treatment resulted in aggregation of GNPs
to some extent (Fig. 2b). After the hydroaminomethylation in
the presence of 1-hexene, N-isopropylaniline, and CO/H2, fur-
ther aggregation of GNPs was observed (Fig. 2c). Whereas the
catalytic activity of GNPs highly depends on the particle
size,1,2 the Au/Co3O4 system is relatively insensitive to the size
of GNPs. Even with 25 atom% Au/Co3O4, which contained
quite larger GNPs than the most effective 5 atom% catalyst,
the hydroformylation of olefins still proceeded in moderate
yield with high selectivity.4b Since the GNPs just participate in
the promotion of the reduction of Co3O4 and are not involved
in the catalysis, the catalytic activity of Au/Co3O4 is probably
insensitive to the size of GNPs. In addition, Co3O4 without
GNPs does not catalyze the hydroformylation around 120 °C
at all because it requires a harsher temperature to be reduced
to Co metal.4b Consequently, the hydroaminomethylation in
this study will not obviously take place without GNPs under
the conditions shown in Tables 1 and 2.
X-ray diffraction (XRD) patterns. The powder XRD patterns
of Au/Co3O4 catalysts are shown in Fig. 3. The catalyst after
calcination in air showed peaks attributable to Co3O4 and Au
(Fig. 3a, d, and g). H2 treatment at 100 °C partially reduced
Co3O4 to CoO and Co metal. As the result, the observed
Fig. 2 HAADF-STEM images of (a) Au/Co3O4, after air calcination, (b) after H2
pattern is
a summation of Co3O4, CoO, Co, and Au
treatment (2 MPa, 100 °C,
3 h, in heptane), (c) after intermolecular
(Fig. 3b and d–g). Since the hydroaminomethylation was
hydroaminomethylation reaction (1-hexene and N-isopropylaniline, 120 °C, 4 h,
CO/H2 = 1 : 1, 4 MPa, in heptane).
conducted in a reducing environment at a slightly higher
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temperature of 120 °C, the remaining Co3O4 and CoO after
H2 treatment were completely reduced to Co metal during
the reaction (Fig. 3c, f, and g). This phenomenon could
account for the necessity of H2 in the case of intramolecular
cyclocarbonylation (Table 3, entry 4).
7 Selected
examples
for
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4. Conclusions
In summary, one-pot intermolecular hydroaminomethylation
and intramolecular cyclocarbonylation of olefins by Au/Co3O4
have been demonstrated. By employing terminal olefins and
N-isopropylanilines as substrates, the intermolecular reactions
proceeded via a common reaction path for hydroamino-
methylation. On the other hand, the intramolecular cyclo-
carbonylation was observed when a C–C double bond and an
amine moiety were located in appropriate positions in the
same molecule under similar conditions.
The characterization of the catalyst was also performed. A
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