RANEY nickel-catalyzed reductive N-methylation of amines with paraformaldehyde: Theoretical and experimental study

Article abstract of DOI:10.1039/c4ra04414b

RANEY Ni-catalyzed reductive N-methylation of amines with paraformaldehyde has been investigated. This reaction proceeds in high yield with water as a byproduct. RANEY Ni can be easily recovered and reused with a slight decrease of the yield. Using density functional theory (DFT), the mechanism of RANEY Ni-catalyzed reductive N-methylation is discussed in detail. The reaction pathway involves the addition of amine with formaldehyde, dehydration to form the imine and hydrogenation. In the transition state of hemiaminal dehydration, the C-O bond cleavage of the aromatic amine is more difficult than that of the aliphatic amine. For the aromatic amine, a higher energy barrier must be overcome, which results in a relatively low yield. After addition of amine with formaldehyde and dehydration, imine is obtained and preferred to adsorb on the bridge site of the Ni(111) surface. The preferential pathways of imine hydrogenation involve the pre-adsorbed hydrogen atom attacking the nitrogen atom of the imine. The energy barrier of hydrogenation is much lower than that of addition and dehydration. Thus, the hydrogenation of imine is a relatively rapid reaction step. In the reductive N-methylation of secondary amine, the possible dehydration pathway is different from the one of the primary amine. In the dehydration of the secondary amine, the intermediate hemiaminal is initially adsorbed on the bridge site of the Ni(111) surface, then undergoes C-O bond cleavage, and eventually the hydroxyl is located in the bridge site. With the final hydrogenation, the product is obtained by adsorption on the top site of the Ni(111) surface.

Full text of DOI:10.1039/c4ra04414b

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PAPER
RANEY® nickel-catalyzed reductive N-methylation
of amines with paraformaldehyde: theoretical and
experimental study†
Cite this: RSC Adv., 2014, 4, 43195
Xin Ge, Chenxi Luo, Chao Qian,* Zhiping Yu and Xinzhi Chen
RANEY® Ni-catalyzed reductive N-methylation of amines with paraformaldehyde has been investigated.
This reaction proceeds in high yield with water as a byproduct. RANEY® Ni can be easily recovered and
reused with a slight decrease of the yield. Using density functional theory (DFT), the mechanism of
RANEY® Ni-catalyzed reductive N-methylation is discussed in detail. The reaction pathway involves the
addition of amine with formaldehyde, dehydration to form the imine and hydrogenation. In the transition
state of hemiaminal dehydration, the C–O bond cleavage of the aromatic amine is more difficult than
that of the aliphatic amine. For the aromatic amine, a higher energy barrier must be overcome, which
results in a relatively low yield. After addition of amine with formaldehyde and dehydration, imine is
obtained and preferred to adsorb on the bridge site of the Ni(111) surface. The preferential pathways of
imine hydrogenation involve the pre-adsorbed hydrogen atom attacking the nitrogen atom of the imine.
The energy barrier of hydrogenation is much lower than that of addition and dehydration. Thus, the
hydrogenation of imine is a relatively rapid reaction step. In the reductive N-methylation of secondary
amine, the possible dehydration pathway is different from the one of the primary amine. In the
dehydration of the secondary amine, the intermediate hemiaminal is initially adsorbed on the bridge site
of the Ni(111) surface, then undergoes C–O bond cleavage, and eventually the hydroxyl is located in the
bridge site. With the final hydrogenation, the product is obtained by adsorption on the top site of the
Ni(111) surface.
Received 12th May 2014
Accepted 29th August 2014
DOI: 10.1039/c4ra04414b
www.rsc.org/advances
7–9
as a reducing agent. As the LW reaction suffers from the high
Introduction
ꢀ
temperature (about 180 C), transition metal such as nickel,
10
N-methyl amines are an important class of compounds, which copper and metal ligand are used to overcome this drawback.
play a major role in the synthesis of dyes, surfactants, preser- Although formic acid is clean and high efficient, the atom
1,2
vatives, pesticides, herbicides and medicinal intermediates.
economy is poor.
N-methyl amine is typically synthesized by conventional alky-
Another attractive protocol is the reductive N-alkylation of
lating agents, such as methyl halide and dimethyl sulfate. amines with aldehydes and ketones catalyzed by the transition
1
1,12
However, it has some problems due to the toxic nature of metal, such as Pd, Ni, Pt and so on.
Moreover, these catalysts
13
conventional alkylating agents, the poor atom economy and the can be recovered and reused. The mechanism of the transition
3
need of a large number of acid-binding agents.
metal catalyzed reductive N-alkylation of amines has long been
For the N-alkylation, the reductive alkylation of amine with known that it proceeded addition of aldehydes or ketones with
1
1
aldehydes and ketones is an attractive and alternative proce- amines, hemiaminal dehydration and imine hydrogenation.
4
dure. It is an efficient protocol to use hydride reducing agents However, the reaction barrier, the mode of adsorption on metal
5
6
such as sodium borohydride, sodium cyanoborohydride etc. surface and hydrogenation pathways involved in the reductive
However, this procedure only applies to the laboratory scale due N-alkylation are still unclear. The density functional theory
to the high cost of hydride reducing agents. Leuckart–Wallach (DFT) calculations can offer a convenient access to study these
(
LW) reaction is well known, which proceeds condensation of issues.
carbonyl with amines to imines and reduction with formic acid
In this paper, we explore RANEY® Ni-catalyzed reductive
N-methylation of amines with paraformaldehyde using
hydrogen as reductant. The addition, dehydration, adsorption
on Ni surface and hydrogenation pathways involved in the
reductive N-methylation are studied. A detailed investigation on
mechanism studies on the Ni surface by using DFT is discussed.
Key Laboratory of Biomass Chemical Engineering of Ministry of Education,
Department of Chemical and Biological Engineering, Zhejiang University, P.R China.
E-mail: qianchao@zju.edu.cn; Fax: +86-571-87951615; Tel: +86-571-87951615
†
Electronic supplementary information (ESI) available. See DOI:
0.1039/c4ra04414b
1
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Results and discussion
As commercial concentrated formaldehyde is a solution of
approximately 37% formaldehyde in water with 10–15%
methanol, it is not accurate and it is difficult for accurate
quantication of formaldehyde. It was reported that the
paraformaldehyde could dissociate to formaldehyde by heat-
1
4
ing. Thus, paraformaldehyde was used to study reductive
N-methylation of amine. Initially, we studied reductive
N-methylation of n-butylamine with paraformaldehyde as the
model reaction for screening the transition metal-based cata-
lysts and reaction parameters (Table 1). To our delight, the
product was obtained in 93% yield and 100% conversion by
Fig. 1 Recycling and reuse of RANEY® Ni.
ꢀ
using RANEY® Ni as catalyst at 115 C under 1.6 MPa hydrogen
gas atmosphere in methanol solvent (Table 1, entry 4).
RANEY® Cu and Co failed to catalyze this reaction in high
yield, affording 61% and 48% yield separately (Table 1, entries
Having identied the RANEY® Ni could catalyze N-methyl-
ation of n-butylamine with paraformaldehyde, the substrate
scope of amines was further explored. In the reductive
N-methylation of primary amines with paraformaldehyde, the
yields were good (85–93%, Table 2, entries 1–4). The yields of
the reductive N-methylation of secondary amines were excellent
2
and 6). When 5 wt% Pd/C and 5 wt% Pt/C were used to
catalyze this N-methylation, the yields were only obtained in
6% and 32% separately (Table 1, entries 3 and 5). Then the
2
catalyst loading and solvent were examined. Firstly, the cata-
lyst loading was investigated (Table 1, entries 4, 7 and 8). As
expected, the lower catalyst loading (2 wt%) resulted in yield
decreasing and the reaction time prolonging. And the higher
catalyst loading (8 wt%) led to the decline of yield. The
appropriate RANEY® Ni loading was 4 wt%. Secondly, the
solvent effect was studied. It was enclosed that methanol was
the best solvent (Table 1, entries 4, 9 and 10). To study whether
RANEY® Ni could be recovered and reused, we carried out a
recycling test of RANEY® Ni to catalyze N-methylation of
n-butylamine with paraformaldehyde (in Fig. 1). When the
reaction completed, RANEY® Ni was easily recovered by
(90–97%, Table 2, entries 5–8). With the steps of N-methylation
increasing, the reaction course was prolonged and the mono
and multi-methyl products couldn't be converted to nal
product completely. Thus the yield was slightly declining. The
aromatic group had adverse effect on the yield (Table 2, entries
9–10). The 80% yield of benzylamine in the reductive N-methyl-
ation is higher than aniline (Table 2, entry 11). Thus, it is
notable that aromatic amine has less activity than aliphatic
amine. The possible reasons will be discussed in the following
section.
The paraformaldehyde can dissociate to formaldehyde by

ltration and methanol washing. Subsequently, recovered
14
heating. Thus, paraformaldehyde rstly dissociated to form-
aldehyde and formaldehyde took place this reductive N-methyl-
ation. The proposed mechanism of RANEY® Ni-catalyzed
RANEY® Ni directly was reused to catalyze this reaction. Aer
four cycles, the slight decline of yield was observed.
a
Table 1 N-methylation of n-butylamine with paraformaldehyde
b
Entry
Catalyst (wt%)
Solvent
Time/h
Cov/%
Yield /%
1
2
3
4
5
6
7
8
9
—
Methanol
Methanol
Methanol
Methanol
Methanol
Methanol
Methanol
Methanol
Water
4
4
4
4
4
4
6
2
4
4
22
80
57
100
64
67
0
61
26
93
32
48
78
82
87
53
RANEY® Cu (4)
Pt/C (5 wt%) (4)
RANEY® Ni (4)
Pd/C (5 wt%) (4)
Co (4)
RANEY® Ni (2)
RANEY® Ni (8)
RANEY® Ni (4)
RANEY® Ni (4)
94
100
100
79
1
0
Hexane
a
Paraformaldehyde (10.496 g, 350 mmol), n-butylamine (11.117 g, 152 mmol) and catalyst were added to solvent (100 ml) in a 250 ml autoclave. The
ꢀ
b
mixture was heated to 115 C. Isolated yield.
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a
Table 2 RANEY® Ni-catalyzed reductive N-methylation of amines with paraformaldehyde
RANEY® n(paraformaldehyde):
b
ꢀ
c
Entry Amine
1
Product
Ni/wt%
n(amine)
Temperature/ C Pressure/MPa Time/h Yield /%
4
2.3
115
115
1.6
1.6
4
4
93
90
2
4
2.3
3
4
5
5
5
5
4.4
4.4
1.2
130
130
125
2.0
2.0
1.4
4.5
4.5
4
89
85
90
6
3
1.05
100
1.3
3
97
7
8
9
4
5
6
2.1
1.2
2.5
105
125
180
1.5
1.4
1.7
3.5
4
95
92
65
7
1
1
0
1
6
6
2.5
2.5
180
180
1.7
1.7
8
4
21
80
a
c
b
Paraformaldehyde, amine and RANEY® Ni were added to methanol (100 ml) in a 250 ml autoclave. This ratio refers to formaldehyde equivalents.
Isolated yield.
reductive N-methylation of n-butylamine with para- formation of imine in the second N-methylation will be studied.
formaldehyde in Fig. 2 is proceeded through twice N-methyl- So we attempt to nd the appropriate reaction pathways of
ation: the addition of n-butylamine with formaldehyde, dehy- RANEY® Ni-catalyzed reductive N-methylation of n-butylamine
dration to form the imine, enamines, or iminium ions and with paraformaldehyde by the computational study.
15–18
hydrogenation.
Paraformaldehyde rstly dissociates to
As Fig. 3 shown, RANEY® Ni catalyst has three diffraction
formaldehyde. In the N-methylation of n-butylamine, the peaks of Ni(111), Ni(200) and Ni(220) and Ni(111) is the main
second N-methylation is slightly different from the rst one. As diffraction peak. At present, the study on Ni(111) for the
19–21
20–23
iminium ions 13 are unstable in the alkaline aqueous, the chemisorption of CO
2
,
formic acid
and aromatic
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Fig. 2 The proposed mechanism of RANEY® Ni-catalyzed reductive N-methylation of n-butylamine with paraformaldehyde.
ꢁ1
ꢁ1
2
63.6 kJ mol is higher than Ts2a with 211.2 kJ mol . Thus, in
transition state Ts2b, the cleavage of the C–O bond is more
difficulty. It can explicate that the yield of aromatic amine in the
reductive N-methylation catalyzed by RANEY® Ni is lower than
that of aliphatic amine.
Adsorption of imine on Ni(111)
As shown in Fig. 5, imine can be adsorbed on Ni(111) surface via
two adsorption sites, bridge and top. The bridge site with
ꢁ1
adsorption enthalpy of ꢁ153.0 kJ mol , forms via the C]N
double bond cleavage and bonding between C, N atoms and the
two neighboring Ni atoms on Ni(111) surface. Two hydrogen
atoms, nitrogen atom and Ni atom separately bond with
C-centered, forming a tetrahedral. The prolongation of C–N
Fig. 3 X-ray diffraction patterns of RANEY® Ni catalyst.
˚
˚
bond from 1.279 A to 1.371 A and the conguration change of
2
4–29
compounds
has gain great achievements. The aromatic
2
imine illustrate that the hybrid orbitals of C, N varied from sp
to sp . It eventually results in the C]N double bond cleavage.
The distances of C–Ni and N–Ni are 2.064 A and 1.841 A,
respectively. For top site with calculated adsorption enthalpy of
111.1 kJ mol , the imine is adsorbed on Ni(111) surface via a
N–Ni bond of 2.001 A. Therefore, the more stable site is the
bridge adsorption site.
ring, formic acid and CO are adsorbed on the Ni(111) surface
3
2
via the p orbitals or lone electron pair. Imine has similar
structure. Moreover, Ni(111) is a well-understanding and
convenient model system. Thus, Ni(111) model is used to illu-
minate the mechanism by the investigation on the formation of
imine, adsorption and hydrogenation.
˚
˚
ꢁ1
ꢁ
˚
Formation of imine
Hydrogenation of imine
Formaldehyde can couple with n-butylamine 1a to form hemi-
aminal 2a (in Fig. 4). The transition state Ts1a with 174.8 kJ As the bridge adsorption site is the preferred site on Ni(111)
ꢁ
1
mol barrier, describes the mechanism of the addition reac- surface, we only study the hydrogenation of imine adsorbed in
tion. With the hydrogen atom of amino group getting close to bridge adsorption site. Hydrogenation of imine on Ni(111)
the carbonyl, the distance between C and H atoms is stretched surface proceeds two reaction pathways. One of them is that the
˚
to 1.313 A. Simultaneously, the electronegative of N atom and N atom of imine is rstly attacked by H atom and the C atom
the electropositive of C atom on the carbonyl are gradually from formaldehyde further bonds with another H atom to form
strengthened, which promotes the C–N bond formation. Then, N-methyl n-butylamine 8 (in Fig. 6, purple curve, hydrogenation
the H atom of amino group is transferred to the carbonyl group. path A). The other reaction pathway is that the C atom from
Finally, the product hemiaminal 2a is formed. As strong protic formaldehyde rstly reacts with H atom and then the H atom
solvent, methanol can improve hydrogen atom transfer capacity attacks the N atom (in Fig. 6, blue curve, hydrogenation path B).
in this reaction. The dehydration of hemiaminal 2a affords the In this reductive N-methylation, the hydrogen molecule is
imine 3a. In the transition state Ts2b, the hydroxyl group is initially dissociated to H atom over the top site of on Ni(111)
30
initially formed by the C–O bond cleavage, and then it localizes surface without barrier, which is consistent with the reported.
the electron density of H atom that the C–H distance is The dissociated H atom has priority for the adsorption on
stretched. The break of the C–H bond leads to the formation of Ni(111) surface via location in the hollow site. In migrate of H
imine. The formation of N-phenylmethanimine 3b is similar to atom from the top site to hollow site, there is no energy barrier
3a. However, the energy barrier of the transition state Ts2b with (see ESI†).
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Fig. 4 Energy profile of the formation of imine.
Hydrogenation path B. Aer overcoming an energy barrier of
ꢁ
1
3
7.3 kJ mol , the C atom from formaldehyde is hydrogenated.
With the C–Ni bond broken, the adsorption site of N atom is
transferred from top site to bridge site. As the steric hindrance
around the N atom, the H atom approaches the N atom with
ꢁ
1
high energy to cross the 140.7 kJ mol barrier. In the second
hydrogenation step, bridge adsorption site is transferred to top
adsorption site again.
In sum, path A is a preferred hydrogenation pathway. It is
initiated by N atom attacked by pre-adsorbed H atom and fol-
lowed by C–H bonding and the C–Ni bond broken. Finally, the
imine is hydrogenated to N-methyl n-butylamine 8 adsorbed on
Ni(111) surface via the top site. By comparing Ts1a, Ts2a, Ts3
and Ts4, the energy barrier of hydrogenation is much lower
than addition and dehydration. Therefore, the hydrogenation of
imine is relatively rapid reaction step. It is consistent with the
reductive N-methylation of benzaldehyde catalyzed by Pd/C that
Fig. 5 The adsorption site of imine on Ni(111) surface.
Hydrogenation path A. On the hydrogen pre-adsorbed
Ni(111) surface, the hydrogenation of imine rstly takes place to
ꢁ
1
the N atom with energy barrier of 66.3 kJ mol . The lone pair
electron of N atom involves in bonding. The hydrogenation of N
atom gives rise to a slight dri of C–N bond. In the following
hydrogenation step, the C atom from formaldehyde reacts with
12
the imine is hydrogenated very rapidly.
ꢁ
1
H atom by overcoming an energy barrier of 66.9 kJ mol . When
H atom approaches C atom from formaldehyde, the C–N bond
is slightly dried again. It stretches the C–Ni distance from
Reductive N-methylation of secondary amine
˚
˚
1
.956 A to 2.193 A. Thus, the C–Ni bond is weakened and it As a secondary amine, N-methyl n-butylamine 8 was obtained.
eventually leads to C–Ni bond break.
Reductive N-methylation of secondary amine is also initiated
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Fig. 6 Reaction pathways of imine hydrogenation on Ni(111) surface.
by addition of amine with formaldehyde. The transition state is initiated by C–O bond cleavage with the energy barrier of
ꢁ1
3
Ts7 is similar to Ts1a (in Fig. 7). When the distance between C 152.6 kJ mol . The new C–Ni bond is formed by sp hybrid
˚
and H atoms is stretched to 1.318 A, the distance between O orbital of C bonding with Ni atom. The adsorption site of the
˚
and H atoms is getting close to 1.543 A, nally, the C–N bond intermediate 11 is still bridge site. The hydroxyl is located in
2
1
is formed. Although methyl group increases steric hindrance, bridge site, which is the preferred adsorption. The following
the electron-donating ability of methyl group is dominant. step is the hydrogenation of intermediate 11. While the H
ꢁ
1
Thus, the 139.3 kJ mol energy barrier of the transition state atom is approaching the C atom, the dri of C atom breaks
Ts7 is lower than Ts1a. Similar to hemiaminal 2, hemiaminal the C–Ni bond. Aer overcoming the energy barrier of 74.7 kJ
ꢁ
1
9
is unstable and can dehydrate. As the iminium ions do not mol , the nal product N,N-dimethyl butylamine adsorbed
exist in the alkaline aqueous, hemiaminal 9 takes place on Ni(111) surface via N–Ni sing bond is obtained. The energy
3
1
dehydration by adsorption on Ni(111) surface (in Fig. 8). barrier of hydrogenation is still much lower than addition and
Firstly, hemiaminal 9 is preferred to adsorb on Ni(111) dehydration.
surface via bridge site. In transition state Ts8, the dehydration
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relatively rapid reaction step. In the reductive N-methylation of
secondary amine, the dehydration is slightly different from the
previous. The intermediate hemiaminal is preferred to adsorb
on the bridge site of Ni(111) surface. The dehydration is initi-
ated by C–O bond cleavage and the hydroxyl is located in bridge
site. With the nal hydrogenation, the product adsorbed on
Ni(111) surface via N–Ni sing bond is obtained.
Experimental section
Nuclear magnetic resonance (NMR) spectra were measured at
1
13
4
00 MHz ( H) or at 100 MHz ( C) on a Bruker Avance DRX-400
spectrometer. GC analyses were performed on GC Agilent 1790F
series and GC-MS analyses were performed on GC-MS Agilent
Fig. 7 Energy profile of N-methyl n-butylamine addition.
5973-6890 series (FID detector, weakly polar capillary column
SE-30, nitrogen as carrier gas). The operating parameters of
chromatography are as follows: nitrogen 0.1 MPa, hydrogen
ꢀ
0
.1 MPa, air 0.03 MPa, vaporizing chamber 260 C and detector
ꢀ
Conclusion
280 C. The column temperature was carried out by program
controlled that initial temperature 60 C, heating rate 20
ꢀ
ꢀ
C
In sum, the reductive N-methylation of amines with para-
formaldehyde catalyzed by RANEY® Ni is described. The
reductive N-methylation proceeds in high yield through the
addition of amine with formaldehyde, and the dehydration to
form the imine and hydrogenation, which is investigated by
DFT. RANEY® Ni can be recovered and reused with the slight
decrease of yield aer four cycles. In the transition state of
hemiaminal dehydration, the energy barrier of aromatic amine
is higher than the one of aliphatic amine. For aromatic amine, it
leads to more difficult cleavage of the C–O bond. Thus,
ꢁ1
ꢀ
min , nal temperature 260 C. XRD analyze was performed
on X'Pert PRO. The RANEY® Ni and RANEY® Cu were
purchased from Zhejiang Metallurgical Research Institute Co.,
Ltd. All reagents and solvents were general reagent grade. All
reactions were carried out in 250 ml autoclave Parr 4576 series.
General procedure for RANEY® Ni-catalyzed reductive
N-methylation of amines with paraformaldehyde by using
hydrogen as reductant
compared with aliphatic amine, the yield of aromatic amine is The synthesis of N,N-dimethyl-n-butyl amine was selected as
lower in the reductive N-methylation catalyzed by RANEY® Ni. model reaction. Paraformaldehyde (10.496 g, 350 mmol),
Aer the condensation of amines with paraformaldehyde, the n-butylamine (11.117 g, 152 mmol) and RANEY® Ni (445 mg)
imine is preferred to adsorb on the bridge site of Ni(111) were added to methanol (100 ml) in a 250 ml autoclave. The
surface. The imine hydrogenation pathways are discussed in autoclave was purged with nitrogen gas three times and then
detail. The results show that the nitrogen atom of imine is was purged with hydrogen gas three times, then maintained 1.6
ꢀ
preferentially attacked by pre-adsorbed hydrogen atom. The MPa pressure. The mixture was heated to 115 C and the pres-
energy barrier of hydrogenation is much lower than that of sure was maintained 2.1 MPa. Then stirring was maintained for
addition and dehydration. The hydrogenation of imine is a 4 h. The pressure was declined to 1.75 MPa. RANEY® Ni was
Fig. 8 Energy profile of hemiaminal dehydration and hydrogenation on Ni(111) surface.
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recovered by ltration and washed by methanol. Then the
reaction mixture was distilled to separate and recover methanol
Computational details
and light component and the product N,N-dimethyl-n-butyl- DFT calculations were carried out by using the CASTEP program
32–34
amine was obtained in 93% yield.
N,N-Dimethyl-n-butylamine. Yield 93%. H NMR (400 MHz, dew, Burke, Erzenhof gradient corrected functional (GGA-PBE)
CDCl
) d 2.31–2.12 (m, 8H), 1.52–1.38 (m, 2H), 1.32 (dq, J ¼ 14.3, is chosen together with plane wave basis functions with spin
package in Materials Studio of Accelrys Inc,
where the Per-
1
3
1
3
35–38
7
5
.1 Hz, 2H), 0.92 (t, J ¼ 7.3 Hz, 3H). C NMR (100 MHz, CDCl
3
) d polarization.
The linear and quadratic synchronous transit
9.62, 45.48, 29.90, 20.61, 14.01. MS (EI, 70 eV), m/z (rel abun- (LST/QST) complete search was chose to search for transition
+
39
dance): 101(M , 8), 86(5), 58(100), 44(13), 39(18), 30(88).
state of the reaction. The simulation of core electron was
1
40
N,N-Dimethyl-2-hydroxyethylamine. Yield 90%. H NMR performed by Ultraso pseudopotential (USP). In order to
(
2
400 MHz, CDCl ) d 4.00 (s, 1H), 3.54 (dd, J ¼ 10.2, 5.0 Hz, 2H), improve computational performance, energy cut-off was set
3
1
3
.38 (dd, J ¼ 10.6, 5.3 Hz, 2H), 2.18 (d, J ¼ 5.3 Hz, 6H). C NMR 400.0 eV.
(100 MHz, CDCl
3
) d 61.16, 58.81, 45.25. MS (EI, 70 eV), m/z (rel
Ni(111) surface was modeled by using a three-layer periodic
slab model with a (5 ꢂ 5) super cell. Then by building a 10 A˚
+
abundance): 89(M , 8), 58(100), 42(31), 30(15).
0
0
1
N,N,N ,N -Tetramethylethylenediamine. Yield 89%. H NMR vacuum slab, the adsorption and reaction occurs in this cell.
1
3
(400 MHz, CDCl
3
) d 2.39 (s, 4H), 2.24 (s, 12H). C NMR (100 The reciprocal space of the (5 ꢂ 5) super cell was sampled using
) d 57.58, 45.78. MS (EI, 70 eV), m/z (rel abundance): the 3 ꢂ 3 ꢂ 1 k-points grid. Larger k-points sets were needed if
more accurate energy value wanted. Study in this work focused
MHz, CDCl
1
3
+
14(M , 99), 99(11), 71(65), 56(32), 43(100), 28(17).
0
0
1
N,N,N ,N -Tetramethylpropanediamine. Yield 85%. H NMR on the relative results of different systems, so the k-points set of
(
400 MHz, CDCl ) d 2.33–2.25 (m, 4H), 2.22 (s, 12H), 1.70–1.57 (3 ꢂ 3 ꢂ 1) should be enough. For the geometry optimization,
3
1
3
3
(m, 2H). C NMR (100 MHz, CDCl ) d 57.80, 45.43, 25.94. MS all Ni atoms were constrained except the uppermost layer, with
+
(
5
EI, 70 eV), m/z (rel abundance): 130(M , 5), 85(79), 70(52), setting the convergence tolerances of energy and displacement
ꢁ
5
ꢁ3
8(100), 42(49), 30(11).
to 2 ꢂ 10 eV per atom and 2 ꢂ 10 A˚ , respectively, and
1
ꢁ6
N,N-Diisopropylmethylamine. Yield 90%. H NMR (400 setting the SCF tolerance to 2 ꢂ 10 eV per atom.
MHz, CDCl
(
2
3
) d 2.91 (dt, J ¼ 12.5, 6.2 Hz, 2H), 2.49 (s, 3H), 1.04
Chemisorption energies were calculated using the following
1
3
d, J ¼ 6.3 Hz, 12H). C NMR (100 MHz, CDCl ) d 59.68, 35.07, formulas:
3
+
3.30. MS (EI, 70 eV), m/z (rel abundance): 115(M , 33), 100(96),
7
2(18), 58(100), 42(22), 30(13).
N-Methylmorpholine. Yield 97%. H NMR (400 MHz, CDCl
DEads ¼ Eadsorbate–Ni ꢁ Eadsorbate ꢁ ENi
1
3
)
1
3
where DEads represented the adsorption energy of the adsorbate
on Ni(111) surface, Eadsorbate was the energy of free adsorbate,
ENi was the energy of clean slab and Eadsorbate–Ni was the energy
of adsorbate–Ni adsorption system.
For a reaction, such as A + B / C + D, the energy barrier was
calculated as follows:
d 3.79–3.59 (m, 4H), 2.41 (s, 4H), 2.29 (s, 3H). C NMR (100
MHz, CDCl ) d 66.87, 55.39, 46.40. MS (EI, 70 eV), m/z (rel
abundance): 101(M , 48), 71(31), 56(6), 43(100), 29(15).
3
+
1
1,4-Dimethylpiperazine. Yield 95%. H NMR (400 MHz,
1
3
CDCl ) d 2.45 (s, 8H), 2.29 (s, 6H). C NMR (100 MHz, CDCl ) d
3
3
+
5
9
5.03, 45.95. MS (EI, 70 eV), m/z (rel abundance): 114(M , 99),
9(11), 71(65), 56(32), 43(100), 28(17).
1
DEReact ¼ ETs ꢁ EA + B ꢁ Ni
N-Methyl-diethanolamine. Yield 92%. H NMR (400 MHz,
3
CDCl ) d 4.50 (s, 2H), 3.76–3.49 (m, 4H), 2.64–2.38 (m, 4H), 2.29
where ETs is the energy of the transition state and EA + B ꢁ Ni is
the energy of A + B ꢁ Ni adsorption system.
1
3
(
3
s, 3H). C NMR (100 MHz, CDCl ) d 59.51, 58.92, 42.09. MS (EI,
+
70 eV), m/z (rel abundance): 119(M , 3), 88(100), 58(12), 44(91),
3
1(20).
1
N,N-Dimethylaniline. Yield 65%. H NMR (400 MHz, CDCl )
3
Acknowledgements
d 7.35–7.14 (m, 2H), 6.72 (dd, J ¼ 13.2, 7.6 Hz, 3H), 2.93 (s, 6H).
1
3
C NMR (100 MHz, CDCl ) d 150.72, 129.09, 116.68, 112.71,
3
The authors are grateful for the nancial support from the
Natural Science Foundation of China (21376213), the Research
Fund for the Doctoral Program of Higher Education of China
+
4
9
0.64. MS (EI, 70 eV), m/z (rel abundance): 120(M , 100), 104(18),
1(7), 77(30), 51(14), 42(9).
1
3
-Dimethylamino-phenol. Yield 21%. H NMR (400 MHz,
(20120101110062) and the Low Carbon Fatty Amine Engi-
CDCl
3
) d 7.07 (t, J ¼ 8.3 Hz, 1H), 6.37–6.29 (m, 1H), 6.24–6.17 (m,
neering Research Center of Zhejiang Province (2012E10033).
Shang Zhicai group is thanked for helping us with calculations.
13
2H), 2.88 (s, 6H). C NMR (100 MHz, CDCl
3
) d 156.67, 152.22,
1
30.01, 105.68, 104.12, 100.17, 40.72. MS (EI, 70 eV), m/z (rel
+
abundance): 136(M , 100), 121(15), 108(9), 94(13), 65(14), 39(7).
1
N,N-Dimethyl-1-phenylmethanamine. Yield 80%. H NMR
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3
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) d 138.88, 129.13,
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