Gold-Ligand-Catalyzed Selective Hydrogenation of Alkynes into cis-Alkenes via H2 Heterolytic Activation by Frustrated Lewis Pairs

Article abstract of DOI:10.1021/acscatal.6b03441

The selective hydrogenation of alkynes to alkenes is an important synthetic process in the chemical industry. It is commonly accomplished using palladium catalysts that contain surface modifiers, such as lead and silver. Here we report that the adsorption of nitrogen-containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates H₂ heterolytically, allowing an unexpectedly high hydrogenation activity. The so-formed tight-ion pair can be selectively transferred to an alkyne, leading to a cis isomer; this behavior is controlled by electrostatic interactions. Activity correlates with H₂ dissociation energy, which depends on the basicity of the ligand and its reorganization on activation of hydrogen. High surface occupation and strong Au atom-ligand interactions might affect the accessibility and stability of the active site, making the activity prediction a multiparameter function. The promotional effect found for nitrogen-containing bases with two heteroatoms was mechanistically described as a strategy to boost gold activity. (Graph Presented).

Full text of DOI:10.1021/acscatal.6b03441

Subscriber access provided by UB + Fachbibliothek Chemie | (FU-Bibliothekssystem)
Article
Gold-ligand catalyzed selective hydrogenation of alkynes into
2
cis-alkenes via H heterolytic activation by frustrated Lewis pairs
Jhonatan Luiz Fiorio, Nuria Lopez, and Liane M. Rossi
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 13 Mar 2017
Downloaded from http://pubs.acs.org on March 13, 2017
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a free service to the research community to expedite the
dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts
appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been
fully peer reviewed, but should not be considered the official version of record. They are accessible to all
readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered
to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published
in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just
Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor
changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers
and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors
or consequences arising from the use of information contained in these “Just Accepted” manuscripts.
ACS Catalysis is published by the American Chemical Society. 1155 Sixteenth Street
N.W., Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
GoldꢀLigand Catalyzed Selective Hydrogenation of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Alkynes into CisꢀAlkenes via H Heterolytic
2
Activation by Frustrated Lewis Pairs
a
b
a
Jhonatan L. Fiorio, Núria López, Liane M. Rossi *.
a
Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Av.
Prof. Lineu Prestes, 748, 05508ꢀ000, São Paulo, SP, Brazil.
b
Institute of Chemical Research of Catalonia, ICIQ, The Barcelona Institute of Science and
Technology, Av. Països Catalans 16, 43007, Tarragona, Spain.
*Correspondence to: lrossi@iq.usp.br.
ABSTRACT. The selective hydrogenation of alkynes to alkenes is an important synthetic
process in the chemical industry. It is commonly accomplished using palladium catalysts that
contain surface modifiers, such as lead or silver. Here we report that the adsorption of nitrogenꢀ
containing bases on gold nanoparticles results in a frustrated Lewis pair interface that activates
H heterolytically allowing an unexpected high hydrogenation activity. The soꢀformed tightꢀion
2
pair can be selectively transferred to an alkyne leading to a cis isomer, this behavior is controlled
by electrostatic interactions. Activity correlates with H dissociation energy, which depends on
2
ACS Paragon Plus Environment
1

ACS Catalysis
Page 2 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
the basicity of the ligand and its reorganization when activating hydrogen. High surface
occupation and strong Au atomꢀligand interactions might affect the accessibility and stability of
the active site making the activity prediction a multiparameter function. The promotional effect
found for nitrogenꢀcontaining bases with two heteroatoms was mechanistically described as a
strategy to boost gold activity.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
KEYWORDS. gold, hydrogenation, alkyne, piperazine, frustrated Lewis pair.
INTRODUCTION
Catalytic hydrogenation is a key process technology in petrochemical industry and has evolved
into an important transformation for the manufacture of pharmaceutical and fine chemicals,
replacing stoichiometric chemical reduction methods that generate large amounts of toxic waste.
Catalytic hydrogenations are usually accomplished by the activation of molecular hydrogen via
1
,2
homolytic H dissociation on metal surfaces, such as Rh, Pt, Pd, Ni. Selective hydrogenations
2
with discrimination between reducible functional groups, such as carbonꢀcarbon triple and
double bonds, are very challenging. Palladium remains the catalyst of choice for many
hydrogenations, but the selective conversion of alkynes into cisꢀalkenes requires the use of a
3
palladium catalyst partially poisoned with metals like lead (Lindlar catalysts). Auxiliary ligands
containing ꢀN, ꢀS, and ꢀO groups have been combined with Pd and a secondary metal (Pb, V) to
improve selectivity. The presence of toxic lead and catalyst deactivation are driving forces for
the search of leadꢀfree Lindlar catalyst replacements for alkyne to cisꢀalkene hydrogenations.
More active and selective palladium catalysts have appeared, but there is still room for the
4
–6
development of catalyst systems based on alternative designs.
ACS Paragon Plus Environment
2

Page 3 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
Gold nanoparticles (Au NPs) have attracted a significant amount of interest as catalysts due to
their exceptional selectivity and surprisingly high activity, which is not replicated by other
7
–10
metals, for some reactions, such as CO oxidation.
Comparatively to the enormous number of
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
studies with Au NP catalysts for oxidations, there are fewer studies in hydrogenations and gold
1
1–16
was often considered only a modest hydrogenation catalyst.
Ultrafine gold particles
supported on alumina were regarded as a unique metal for the selective hydrogenation of
acetylene into ethylene, and gold received attention as a selective catalyst for this gasꢀphase
1
7,18
reaction.
More recently, a new interest emerged for selective hydrogenation of carbonyl or
19–22
nitro groups.
The main virtue was gold’s unique chemoselectivity, which is controlled by
1
8,23
thermodynamics of the adsorption of the organic reactants and products.
In general, the low
2
4,25
activity associated to gold is a consequence of poor H dissociation on gold,
though
2
nanostructuring can improve activity (H dissociation) at structural defects on nanoparticles or
2
1
8
nanoporous materials.
The use of molecular modifiers or auxiliary ligands is a wellꢀknown strategy to enhance
26–28
selectivity in heterogeneous catalysis, mainly as a result of ensemble control,
and similarly
capping ligands (e.g. nitrogenꢀcontaining bases) were found to influence the catalytic properties
2
9–35
of metal nanoparticles.
lead, for the selective hydrogenation of alkynes performed on Pd Lindlar and Pt catalysts.
Nitrogenꢀcontaining bases have also been explored as promoters for hydrogenation reactions by
Quinoline is the most frequently used modifier, either alone or with
3
6,37
38
39
gold via H activation (quinoline and pyridine ) and using other hydrogen sources, such as
2
4
0
41
PhMe SiH and HCOOH, in combination with reaction modifiers. The use of H as the
2
2
hydrogen source is highly desired as it avoids the production of residues, but the channels for
activation of H on gold are not yet fully understood.
2
ACS Paragon Plus Environment
3

ACS Catalysis
Page 4 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Herein, we report the unique promotion effect of nitrogenꢀcontaining bases on the catalytic
activity of gold nanoparticles. The starting inactive gold nanoparticles supported on silica
become highly active for the selective hydrogenation of alkyne into cisꢀalkenes. The
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
hydrogenation proceeded smoothly and fully selective using H as the hydrogen source and
2
under relatively mild conditions (80 °C, 6 bar H ). According to density functional theory
2
calculations, molecular hydrogen dissociation occurs at the ligandꢀgold interface generating a
tightꢀion pair that can be selectively transferred to the adsorbed alkyne in a cis configuration
controlled by electrostatic interactions.
EXPERIMENTAL SECTION
Materials and Methods
All the reagents used for the support and catalyst preparation were of analytical grade, purchased
from SigmaꢀAldrich and used as received. Tetrachloroauric(III) acid was purchased as a 30 wt%
aqueous solution in dilute HCl (SigmaꢀAldrich). Alkynes, alkenes, amines and standards for GC
analysis were purchased from SigmaꢀAldrich having the highest grade available and used as
received. Liquid amines used as additives were purified by standard methods just before use.
Ethanol (99.5%) and DMF (99%) was purchased from Synth (Brazil) and used as received.
Toluene was purchased from Synth (Brazil) and dried before use. The glass reactor was
thoroughly cleaned with aqua regia (HCl:HNO = 3:1 v/v), rinsed with copious pure water, and
3
then dried in an oven prior to use. Gold content in the catalyst was measured by FAAS analysis,
on a Shimadzu AAꢀ6300 spectrophotometer using an Au hollow cathode lamp (Photron). Metal
leaching into the supernatant solution was measured by ICPꢀAES, performed on a Spectro Arcos
ACS Paragon Plus Environment
4

Page 5 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
ICP AES. UVꢀVis spectra were recorded on a Shimadzu UVꢀ1700. TEM analyses were
performed with a JEOL 2100. Xꢀray diffraction (XRD) of the samples was recorded using a
Rigaku miniflex diffractometer with Cu Kα radiation (λ = 1.54 Å) at a 2θ range from 20 to 90°
with a 0.02° step size and measuring time of 5 s per step. GC analyses were carried out with a
Shimadzu GCꢀ2010 equipped with a RTxꢀWax column (30 m x 0.25 mm x 0.25 mm) and a FID
detector. Method: T = 40 °C, T = 200 °C, 25 min, T FID and SPLIT = 200 ºC. Internal standard:
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
i
f
biphenyl. The conversion and selectivity were determined from the total amount of detected
4
2
products and reactant.
Preparation of Au/SiO and Au/Fe O @SiO
2
2
3
4
Silica nanospheres (SiO ) and silicaꢀcoated magnetite nanoparticles (Fe O @SiO ) were
2
3
4
2
obtained by means of a reverse microemulsion process and functionalized with (3ꢀ
4
3
aminopropil)triethoxysilane, as reported elsewhere. Gold nanoparticles were prepared by the
4
4
impregnationꢀreduction method, as reported in literature. Typically, 1.0 g of the aminoꢀ
ꢀ2
ꢀ1
modified support was added to 20 mL of HAuCl aqueous solution (1.3 x 10 mol L ) under
4
continuous stirring. After 30 min, the mixture was filtered and the solid thoroughly washed with
deionized water. The recovered material was dispersed in 10 mL of water and an aqueous NaBH4
ꢀ1
solution (10 mL, 0.2 mol L ) was added dropwise under vigorous stirring. After further stirring
for 20 min, the solid was recovered by filtration and thoroughly washed with water and dried in
vacuum. Both Au/SiO and Au/Fe O @SiO catalysts contain 3.4 wt% of gold as determined by
2
3
4
2
FAAS.
Preparation of Au/Support (TiO ; CeO and Al O )
2
2
2
3
ACS Paragon Plus Environment
5

ACS Catalysis
Page 6 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Au NPs supported on TiO , CeO and Al O were prepared by DP method, as reported in
2
2
2
3
4
5,46
literature.
Typically, 1.0 g of oxide support was added to 100 mL of an aqueous solution of
ꢀ3
ꢀ1
ꢀ1
HAuCl (2.1 × 10 mol L ) and urea (0.42 mol L ). The mixture was heated to 80 °C under
4
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
vigorous stirring for 4 h, centrifuged, washed and dispersed in 10 mL of water. Then, an aqueous
ꢀ1
NaBH solution (10 mL, 0.2 mol L ) was added dropwise under vigorous stirring. After further
4
stirring for 20 min, the solid was recovered by filtration and thoroughly washed with water and
dried in vacuum. The Au loadings were: Au/TiO 3.4 wt%; Au/CeO 3.5 wt%, Au/Al O 2 wt%.
2
2
2
3
General procedure for catalytic hydrogenation of alkynes
A typical procedure for the semihydrogenation of alkynes is as follows: alkyne (1 mmol), Nꢀ
containing base (1 mmol), Au/SiO (1 mol%) and 2 mL of solvent were added to a modified
2
Fischer–Porter 100 mL glass reactor. The reactor was purged five times with H , leaving the
2
vessel at 6 bar. The resulting mixture was vigorously stirred using Teflonꢀcoated magnetic stir
and the temperature was maintained with an oil bath on a hot stirring plate connected to a digital
controller (ETSꢀD5 IKA). After the desired time, the catalyst was removed by centrifugation and
the products were analyzed by GC with an internal standard to determine the conversion of
alkyne and the selectivity for alkene. For kinetic studies, the reaction was performed using 4
times the amount of each component given above and aliquots were collected and analyzed by
GC at different reaction time intervals. To determine the isolated yield of the obtained products,
after the reaction was complete, the crude reaction mixture was transferred to a funnel extraction,
and treated with HCl (20 mL, 10% v/v). The aqueous phase was extracted three times with 5 mL
of dichloromethane. The organic layers were dried with anhydrous MgSO and the solvent was
4
1
removed under reduced pressure, to give the corresponding desired alkene. H NMR confirmed
ACS Paragon Plus Environment
6

Page 7 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
the purity of the isolated products. Details on other catalyst tests (catalyst recycling, scaleꢀup,
isotope H –D exchange, isotopic effect) are given in the Supporting Information.
2
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Computational Details
Density functional theory calculations were performed on slabs representing the gold surface
4
7,48
49
with the VASP code.
The RPBE was the functional of choice and due to the large size of
the molecules dispersion terms were introduced through our modified version of the D2
5
0
51
formulation for the metal. The inner electrons were replaced by PAW and the valence
electrons were expanded in plane waves with a kinetic cutoff energy of 450 eV. The Au(111)
surface was represented by a p(4x4) supercell and four metal layers (>12 Å vacuum) for the
5
2
adsorption and reaction. The kꢀpoint sampling was 3x3x1 in the MonkhorstꢀPack scheme.
Transition states were located through the Climbing Image Nudged Elastic Band (ciꢀNEB)
5
3
method, the nature of the structures was assessed through the vibrational analysis with a 0.02
Å.
RESULTS AND DISCUSSION
Screening of a series of Nꢀcontaining bases (B1-B19) (see Table S1) with a broad range of pKa
values and chemical structures (primary, secondary and tertiary amines, and also heteroaromatic
and cycloaliphatic amines) for the hydrogenation of phenylacetylene 1a over Au NPs, supported
on silica (Au/SiO ) with an average diameter of 2.3 ± 0.6 nm (see Figure S1), provided the
2
results shown in Figure 1. Au/SiO itself performed poorly (conversion < 1%), but it is highly
2
selective and provides exclusively the alkene 1b. The Au/SiO catalyst becomes active in the
2
ACS Paragon Plus Environment
7

ACS Catalysis
Page 8 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
presence of some of the Nꢀcontaining bases studied, but there was no correlation with the amine
pKa values.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ACS Paragon Plus Environment
8

Page 9 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
Figure 1. Screening of nitrogenꢀcontaining bases for phenylacetylene 1a hydrogenation with
Au/SiO catalyst. Reaction conditions: 1 mmol 1a, 0.01 mmol Au (50 mg Au/SiO ), 1 mmol
2
2
amine, 2 mL of ethanol, 100 °C, 6 bar H , 24 h.
2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In general, nitrogenꢀcontaining bases with two heteroatoms (pyrazine B1, 2,2ꢀbipyridine B3,
morpholine B7, 1,4ꢀdiazabicyclo[2.2.2]octane (DABCO) B8, piperazine B10, and imidazole
B17) exhibited a higher promotion effect in the hydrogenation of 1a by gold than the ones with
one nitrogen atom. Morpholine B7 was able to give full conversion of 1a, but the competing
39
hydroamination process occurred and the ketone product was formed in the crude products
(selectivity for acetophenone 1d: 60%). Piperazine B10 provided full conversion of 1a and 100%
selectivity to the alkene 1b, giving the best catalytic result among the amines tested. It is worth
to mention that a blank experiment with B10 and without the catalyst or with the support without
Au NPs showed no conversion of 1a (Table S2). Another experiment carried out in the presence
of catalyst but in the absence of H (reaction performed under nitrogen atmosphere) showed no
2
conversion of 1a (Table S2). A filtration test revealed that the obtained activity is not related to
any leaching of the catalytically active metal (no remaining activity in the supernatant), which
suggests that gold surfaces containing adsorbed auxiliary ligands catalyze the hydrogenation
reaction. In order to further examine the stability of the Au NP catalyst upon recycles, a magnetic
version of the silica support was synthetized to avoid any mass loss during the recycles. The
magnetic catalyst (Au/Fe O @SiO ) was easily recovered by magnetic separation and the
3
4
2
recovered solid remains active for five successive reactions using fresh portions of 1a, piperazine
B10, and solvent (Figure S2). ICP AES analysis of the liquid products isolated after magnetic
separation showed negligible amounts of gold (detection limit: 0.10 ppm). These results
ACS Paragon Plus Environment
9

ACS Catalysis
Page 10 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
corroborate the filtration test, suggesting that the catalytically active metal remains at the support
and does not leach into the solution.
The Au/SiO catalyst was further tested in the hydrogenation of 1a using different solvents and
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
temperatures. The “green” and protic solvent ethanol gave the best catalytic results (full
conversion), while the aprotic solvents such as toluene and DMF were slightly less efficient
(Table S2). Decreasing the reaction temperature to 80 °C did not affect conversion and
selectivity, while further reducing the temperature to 60 °C caused a decreased in conversion to
53% (Table S2). On the basis of the above experiments, we chose ethanol as solvent, piperazine
B10 as the auxiliary ligand and temperature of 80 °C as the optimized conditions for the semiꢀ
hydrogenation reaction. We further examined Au NPs immobilized on different supports, such as
Au/Al O , Au/TiO , and Au/CeO , under the aforementioned conditions (Table S2). TiO
2
2
3
2
2
provided the same activity and selectivity as for SiO , but the CeO support was detrimental to
2
2
activity while the Al O support was detrimental to selectivity. Next, we turned our attention to
2
3
analyze the effect of adding different amounts of piperazine B10 (Figure 2). A very low
conversion of 1a (13%) was obtained using 1a:ligand:Au 100:1:1 (Figure 2a), but full conversion
was achieved with any other concentration of B10 studied (Figure 2 b, c, d). The hydrogenation
of styrene 1b to ethylbenzene 1c was completely suppressed when a large excess of B10 was
used (1a:ligand:Au 100:100:1). It is worth to note that the reaction rate enhances with the
ꢀ1
ꢀ
increase in the concentration of the piperazine (reaction rate = 0.87, 9.0, 15.7, 15.4 mmol gcat
h
1
,
for 1, 10, 50 and 100 equivalents of B10, respectively) suggesting that piperazine plays a very
important role for the activation of Au NPs as hydrogenation catalysts (activity enhancement
effect), but it also works as a selectivity enhancer to avoid the subsequent hydrogenation of the
alkene into alkane. Particularly, in large excess of piperazine (1a:ligand:Au 100:100:1), which
ACS Paragon Plus Environment
10

Page 11 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
would correspond to about 240 ligands per surface Au atom (estimated surface atoms = 42%),
the alkene desorbs without being converted into the alkane.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 2. Time course of hydrogenation of phenylacetylene catalyzed by Au/SiO with
2
increasing amounts of piperazine: a) 0.04 mmol; b) 0.4 mmol; c) 2 mmol and d) 4 mmol.
Reaction conditions: 4 mmol phenylacetylene, 0.04 mmol Au, 0.04 – 4 mmol of amine, 8 mL of
ethanol, 80 °C, 6 bar H2.
Due to the high selectivity of the Au/SiO : piperazine (1Au : 100 B10) catalytic system for the
2
conversion of phenylacetylene 1a into styrene 1b (Table 1, entry 1), it was tested in a
ACS Paragon Plus Environment
11

ACS Catalysis
Page 12 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
competition hydrogenation experiment starting from a mixture of phenylacetylene 1a and styrene
1b (Table 1, entries 2 and 3). These experiments revealed that the reaction selectivity is
maintained even in large excess of the alkene 1b and are relevant to evaluate the application of
our gold catalyst system for purification of styrene, which is an important monomer and usually
contains small quantities of acetylenic compounds, which poison olefin polymerization catalysts
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
5
4
and must be removed via selective hydrogenation before polymerization. Under competitive
conditions, Au/SiO catalyst converted preferentially the alkyne 1a to alkene 1b and less than
2
1% of ethylbenzene 1c was formed.
Finally, the general applicability and limitation of the methodology was evaluated through the
hydrogenation of alkynes under the optimized conditions (100 alkyne: 1Au : 100 B10). A variety
of terminal and internal alkynes were readily hydrogenated to the desired alkene and cisꢀalkene
with moderate to excellent yield and, importantly, hardly any overꢀreduction to alkane (Table 1).
Moreover, both electronꢀdeficient substituents, such as esters (Table 1, entry 25), and electronꢀ
rich groups, for example amino and methoxy (Table 1, entries 15ꢀ16), were tolerated well.
Clearly, the mostꢀchallenging substrates are alkynes with an alkene moiety (Table 1, entries 6, 11
and 19). We were pleased that our Au NP catalyst system was able to reduce only the alkyne unit
without any detectable concurrent reduction of the alkene moieties both in the parent and product
molecules. The results depicted in Table 1 confirmed that a broad range of sensitive and
reducible functional groups, including halide, ether and ester substituents (Table 1, entries 12–
1
6, 25), were tolerated in the alkyne hydrogenation process. The prominent isoprene, which is an
essential building block in the polymer industry, was obtained via hydrogenation of 2ꢀmethylbutꢀ
ꢀenꢀ3ꢀyne 9a (Table 1, entry 11) in 84% isolated yield. (Z)ꢀalkenes were mostly formed from
1
internal alkynes (Table 1, entries 20–25). Notably, the semiꢀhydrogenation of nonꢀpolar internal
ACS Paragon Plus Environment
12

Page 13 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
alkynes such as diphenylacetylene 18a (Table 1, entry 20) and 1ꢀphenylꢀ1ꢀpropyne 19a (Table 1,
entry 21) proceed quite smoothly under mild conditions. The only functional groups that do not
tolerate the reaction conditions are aldehydes, ketones or carboxylic acids (Table S3), which are
known to couple with amines. The catalyst system was also applicable for scaledꢀup conditions,
1a (50 mmol; 5.1 g) and 18a (50 mmol, 8.9 g) were successfully converted into the alkenes 1b
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(4.6 g, 88%) and 19b (7.1 g, 79%), respectively. Considering full conversion, the turnover
number (TON) of 5000 was reached, with an excellent productivity of approximately 200
ꢀ1
ꢀ1
mol.mol .h . These TON and productivity values (not optimized) are remarkably higher than
those reported for other heterogeneous Au catalyst systems for semiꢀhydrogenation of alkynes
3
9,55–58
employing molecular hydrogen or any other hydrogen source.
a
Table 1. Scope of semiꢀhydrogenation of alkynes to alkenes using Au/SiO and piperazine B10.
2
]
b
b
c
Entry
Substrate
t (h)
5
Conv. (%)
>99
Selectivity (%) Z:E
1
>99
ꢀ
1a
2
3
4
1a + 1b (1:1)
1a + 1b (1:100)
24
24
17
>99
>99
>99
>99
99
ꢀ
ꢀ
ꢀ
d
>99
2a
ACS Paragon Plus Environment
13

ACS Catalysis
Page 14 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
5
23
>99
>99
ꢀ
3
a
a
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
e
6
7
45
12
43
>99
>99
ꢀ
ꢀ
4
>99
5a
8
22
>99
>99
ꢀ
6
a
a
9
1
24
24
>99
>99
>99
>99
ꢀ
ꢀ
7
0
8a
f
11
45
91 (84%)
>99
ꢀ
9
1
1
1
a
12
13
14
15
24
24
15
24
>99
>99
>99
35
>99
>99
>99
>99
ꢀ
ꢀ
ꢀ
ꢀ
0a
1a
2a
g
ACS Paragon Plus Environment
14

Page 15 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
13a
14a
1
6
7
16
22
34
>99
79
ꢀ
ꢀ
1
>99
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1
1
5a
6a
18
24
24
6
>99
>99
94
ꢀ
1
9
0
99
ꢀ
17a
18a
2
99 (80%)
>99
97:3
21
24
>99 (79%) >99
100:0
1
9a
0a
22
24
24
60
>99
>99
100:0
100:0
2
23
89 (75%)
2
1a
2a
24
24
24
>99
90
>99
>99
100:0
100:0
2
25
2
3a
ACS Paragon Plus Environment
15

ACS Catalysis
Page 16 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
a
Reaction conditions: 1 mmol alkyne, 0.01 mmol Au, 1 mmol piperazine B10, in 2 mL of
b
ethanol at 80 °C, 6 bar H . Determined by GC using internal standard technique (>99% means
no other product detected); numbers in parenthesis refer to isolated yield. Z/E ratio was
determined by H NMR spectroscopy. 1% of alkane detected by GC. 0.02 mmol Au and
toluene as solvent (2 mL). 0.02 mmol Au. toluene as solvent (2 mL).
2
c
1
d
e
f
g
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Based on the aboveꢀmentioned facts and bearing in mind that primary and secondary amines are
used as ligands in homogeneous catalysis to promote heterolytic cleavage of H to give metalꢀ
2
38,34
hydride species,
we suggest that the key role of piperazine B10 is to facilitate the crucial
heterolytic H activation at the Au NPs. Namely, the nitrogen atom of B10 can serve as a basic
2
ligand to promote the heterolytic H cleavage, providing a favorable situation for hydrogen
2
activation under very mild conditions. The reaction network and the configurations are presented
in Figure 3. Piperazine B10 is adsorbed on the gold surface through one of the Nꢀcenters, due to
the configuration in a boat site the second N is higher on the surface. The adsorption energy is
5
9
sufficiently low (ꢀ0.27 eV) to ensure that no leaching of gold occurs. Upon adsorption, the H
2
molecule can split between the ligand forming a quaternary N center and a second H that goes to
60–63
the surface. Such kind of heterolytic splitting has been proposed for phosphine ligands,
6
4
3,65
nitrogenꢀligands on metals, and single atom catalyst
while the active participation of the
6
6
reactant in the activation of H was also found for Ag catalysts in hydrogenation. The metalꢀ
2
ligand system can be understood as a tight ionꢀpair induced by the frustrated Lewis pair (FLP)
6
7,68
formed by the ligand and the surface.
H dissociation occurs on the Au(111) surface through
2
an energy barrier of 1.45 eV, the reaction is endothermic by 0.69 eV. Instead, if the surface is
decorated with piperazine B10 the dissociation shows a barrier of 0.32 eV (therefore close to
zero if zero point vibrational energies, ZPVE, are taken into account) and the final state is
thermoneutral when compared to reactants (H and the FLP). Then the alkyne can be adsorbed
2
ACS Paragon Plus Environment
16

Page 17 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
on the Au(111). Alkynes are weakly adsorbed on Au but due to the van der Waals contributions
the adsorption energy is ꢀ0.28 eV for 1ꢀphenylꢀ1ꢀpropyne 19a. From the coadsorbed state, the
hydride can be transferred to the alkyne. The reaction is slightly endothermic by 0.28 eV the
barrier being 0.74 eV form the coadsorbed state. Upon the first hydrogenation the moiety is
negatively charged and interacts by electrostatic forces with the protonated piperazine B10, this
is shown in the inset of Figure 2. From this pair, proton transfer occurs, with barriers 0.13 eV and
the total process is exothermic by ꢀ2.39 eV. The alkene requires 0.53 eV for desorption. The
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
particular structures for the transition states are shown in Figure 4. Notice, that even if H is
2
barrierless according to the potential energy surface the introduction of entropies in the gasꢀ
phase molecules implies that there is an entropic barrier on going form the gas to the adsorbed
6
9
+
phase. Finally, an alternative path considering first the transfer of the H and then the hydride
was calculated, however, the intermediate is more than 1.5 eV higher in energy than that of the
ꢀ
+
H , H transfer and thus was discarded.
ACS Paragon Plus Environment
17

ACS Catalysis
Page 18 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 3. Reaction energy profiles with the corresponding configurations for the hydrogenation
of 1ꢀphenylꢀ1ꢀpropyne 19a. The inset corresponds to the charge distribution with respect to the
neutral fragments after the first hydrogenation step. The separation between the yellowꢀblue
colors indicates the electrostatic interactions. Yellow spheres represent Au, blue N, black C and
white H.
ACS Paragon Plus Environment
18

Page 19 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 4. Transition state geometries for the hydrogenation of 1ꢀphenylꢀ1ꢀpropyne 19a. Yellow
spheres represent Au, blue N, black C and white H.
Calculations also highlight the limited basicity window for the Nꢀcontaining bases able to
provide the aforementioned promotion effect for hydrogenation on gold surfaces. Piperazine B10
is unique because it is not strongly bound to the surface, and thus cannot extract the metal, for
instance when compared to pyridine B6. The binding energies for the linear complexes from the
atomic reference is exothermic for pyridine B6 (ꢀ0.1 eV) and very endothermic for piperazine
B10 (> 5 eV). When comparing the Nꢀcontaining bases (Figure 5), the activity (reaction rates
were obtained from the kinetic curves given in Figure S3) is found to correlate with the energy
barrier for H dissociation at the ligand/Au(111) interface for piperazine, DABCO, pyrazine,
2
imidazole, ethyleneamine and diethylenetriamine (Table S4). The barrier is the lowest for B10
thus an indicative of the unique catalytic activity of the piperazineꢀgold interface. The barrier for
the activation is formed by different terms. One stems for the formation of a protonꢀhydride pair,
+
ꢀ
this is a constant going from (H to a H ...H pair separated by a average distance of 2 Å). The
2
second appears as a consequence of the intrinsic basicity of the Nꢀcontaining bases. A third term
appears since at the transition state some of the Nꢀcontaining bases need to rearrange in order to
be an active part in the transition state, this is the case for quinolone B5 that presents a much
ACS Paragon Plus Environment
19

ACS Catalysis
Page 20 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
larger H splitting barrier than would correspond to its thermodynamic (ꢁE) value. The fourth
2
ꢀ
term depends on the adsorption of H to the metal, which is in this case invariant. Notice, that B5
due to its large size can also block too many adsorption sites. Finally, the structures with two
basic Nꢀheteroatoms seem to be more active for hydrogenation purposes. There are two reasons
for that, the first is that two molecules can be dissociated for each ligand, thus being double
active. This is clear with imidazole B17, as only one of the N atoms seems capable of trap H2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(notice that diethylenetriamine B12 converts 23 % while imidazole B17 about 7% even if the
barrier is comparable). The second reason is that having only one Nꢀheteroatom does not ensure
adsorption to the surface for systems, like piperidine B15 that contains one N only. Piperidine
B15, thus easily leaves the surface as in the transition state structure there is no element binding
it to the surface making the configuration unstable.
Figure 5. Reaction rates (experimental) as a function of the computed activation energies for
heterolytic H dissociation at the Nꢀligand/Au(111) interface (without zeroꢀpoint correction). The
2
ACS Paragon Plus Environment
20

Page 21 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
fitting shows that the activity is completely dominated by the H activation. The red points stand
2
for the molecules containing ligands with single N donors and as shown here they do not belong
to the same family for quinoline the adsorption is too strong blocking the reactants on the surface
and while for piperidine the ligand cannot compete with the reactant for adsorption and thus
cannot effectively activate H2.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Finally, to gain a better understanding of the H activation process, we conducted H −D
2
2
2
exchange experiments (Au catalyst, toluene, H :D 1:1, 6 bar, 80 °C, 24 h). The H −D
2
2
2
2
exchange, attested by the formation of HD in the gas phase (detected by mass spectrometry
m/z=3), was much higher over the Au/B10 systems than with pure Au catalyst. These results
suggest that H and D molecules dissociate and recombine to produce HD, and this process is
2
2
significantly enhanced by piperazine. Upon switching H for D in the hydrogenation reaction
2
2
under similar conditions, it is noteworthy that a primary isotope effect (k /k ≈ 2.7, Figure S4)
H
D
7
0
was observed, suggesting hydrogen is involved in the rateꢀdetermining step. To obtain
quantitative information about H dissociation, different amounts of 1a were hydrogenated under
2
limited H conditions (H was pre adsorbed on Au catalysts and B10/Au catalysts system and the
2
2
reaction was conducted under inert atmosphere, see details in supporting information and Table
S5). Within the limits of experimental error, while increasing 1a from 0.01 to 0.05 mmol, a
similar amount of 1b (~0.008 mmol) was obtained, allowing us to estimate that H was the
2
limiting reagent (~0.008 mmol of H activated by B10/Au catalyst). For pure Au catalyst, a low
2
yield of 1b (~0.0001ꢀ0.00045 mmol) was obtained, confirming the very unfavorable hydrogen
dissociation by Au in the absence of B10.
ACS Paragon Plus Environment
21

ACS Catalysis
Page 22 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Based on the experimental and theoretical results described above, we propose the following
mechanism for the hydrogenation of alkynes by Au NPs, which is possible in the presence of
adsorbed piperazine due to the heterolytic activation of H via frustrated Lewis pairs (Figure 6).
2
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Figure 6. A proposed mechanism for goldꢀcatalyzed catalytic hydrogenation of alkynes into cisꢀ
alkenes via a frustratedꢀLewisꢀpair approach.
ACS Paragon Plus Environment
22

Page 23 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
Conclusions
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
In summary, we have described that high conversion of a range of alkynes with excellent
selectivity for cis alkenes was achieved by combining supported Au NPs, Nꢀcontaining bases and
H as hydrogen source. We emphasize the role of the nitrogenꢀcontaining ligand as a means for
2
substantial enhancement of catalytic activity and selectivity, since the auxiliary ligands play a
key role by opening a new channel for the heterolytic dissociation of molecular hydrogen on the
frustrated Lewis pair. This ability to switch on the catalytic activity of Au NPs provides a
promising new method for controlling a reactive system with ligands. The control is such that
stereochemistry of the addition is also achieved due to electrostatic forces. A delicate balance
between (i) the basicity of the ligand, (ii) the reorganization energy of the ligand to activate H2,
(iii) the possibility of site blocking by large ligands and (iv) the metal leaching induced by some
ligands; is the responsible for the activityꢀselectivityꢀstability controls in the catalyst system. We
believe this remarkable promotional effect by Nꢀcontaining ligands may have implications for
gold catalysis while stimulating more applications in the field of selective hydrogenations not
envisaged before. The versatile concept presented can be transferrable to other metal
nanoparticle catalysts.
AUTHOR INFORMATION
Corresponding Author
*lrossi@iq.usp.br
ACS Paragon Plus Environment
23

ACS Catalysis
Page 24 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
Notes
The authors declare no competing financial interests.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
ASSOCIATED CONTENT
Supporting Information. Additional experimental results and details, characterization of
catalysts, procedures and characterization data including NMR spectra. These materials are
available free of charge via the Internet at http://pubs.acs.org.
ACKNOWLEDGEMENTS
The authors are grateful to INCTꢀCatalise and the Brazilian government agencies FAPESP
(Grant 2014/15159ꢀ8), CNPq, and CAPES for financial support. N.L. thanks BSCꢀRES for
providing generous computational resources.
REFERENCES
(1)
Kyriakou, G.; Boucher, M. B.; Jewell, A. D.; Lewis, E. A.; Lawton, T. J.; Baber, A. E.;
Tierney, H. L.; FlytzaniꢀStephanopoulos, M.; Sykes, E. C. H. Science. 2012, 335, 1209–
1212.
(2)
Vilé, G.; Albani, D.; AlmoraꢀBarrios, N.; López, N.; PérezꢀRamírez, J. ChemCatChem
2016, 8, 21–33.
(3)
Vilé, G.; Albani, D.; Nachtegaal, M.; Chen, Z.; Dontsova, D.; Antonietti, M.; López, N.;
PérezꢀRamírez, J. Angew. Chemie Int. Ed. 2015, 54, 11265–11269.
ACS Paragon Plus Environment
24

Page 25 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
(
4)
5)
Jagadeesh, R. V.; Surkus, A.ꢀE.; Junge, H.; Pohl, M.ꢀM.; Radnik, J.; Rabeah, J.; Huan, H.;
Schunemann, V.; Bruckner, A.; Beller, M. Science. 2013, 342, 1073–1076.
Westerhaus, F. A.; Jagadeesh, R. V.; Wienhöfer, G.; Pohl, M.ꢀM.; Radnik, J.; Surkus, A.ꢀ
E.; Rabeah, J.; Junge, K.; Junge, H.; Nielsen, M.; Brückner, A.; Beller, M. Nat. Chem.
2013, 5, 537–543.
(
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(6)
Chen, F.; Kreyenschulte, C.; Radnik, J.; Lund, H.; Surkus, A.; Junge, K.; Beller, M. ACS
Catal. 2017, 7, 1526–1532.
(7)
8)
Hashmi, A. S. K.; Hutchings, G. J. Angew. Chemie Int. Ed. 2006, 45, 7896–7936.
Ciriminna, R.; Falletta, E.; Pina, C. Della; Teles, H.; Pagliaro, M. Angew. Chemie Int. Ed.
(
2016, 55, 14210 –14217.
(9)
Wittstock, A.; Bäumer, M. Acc. Chem. Res. 2014, 47, 731–739.
(
(
(
(
10) Stratakis, M.; Garcia, H. Chem. Rev. 2012, 112, 4469–4506.
11) Bond, G. C.; Sermon, P. A. J. Chem. Soc. Chem. Commun. 1973, 444–445.
12) Bond, G. Gold Bull. 2008, 41, 235–241.
13) CárdenasꢀLizana, F.; Keane, M. A. J. Mater. Sci. 2013, 48, 543–564.
(14) Wang, X.; CárdenasꢀLizana, F.; Keane, M. A. ACS Sustain. Chem. Eng. 2014, 2, 2781–
789.
2
(15) GarcíaꢀMota, M.; Cabello, N.; Maseras, F.; Echavarren, A. M.; PérezꢀRamírez, J.; Lopez,
N. ChemPhysChem 2008, 9, 1624–1629.
(16) Zhang, Y.; Cui, X.; Shi, F.; Deng, Y. Chem. Rev. 2012, 112, 2467–2505.
(17) Zhou, G.; Wang, P.; Jiang, Z.; Ying, P.; Li, C. J. Phys. Chem. B 2000, 104, 11153–11156.
(18) Segura, Y.; López, N.; PérezꢀRamírez, J. J. Catal. 2007, 247, 383–386.
(19) Grirrane, A.; Corma, A.; García, H. Science 2008, 322, 1661–1664.
ACS Paragon Plus Environment
25

ACS Catalysis
Page 26 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
20) Corma, A.; Serna, P.; García, H. J. Am. Chem. Soc. 2007, 129, 6358–6359.
(21) Claus, P.; Brücker, A.; Mohr, C.; Hofmeister, H. J. Am. Chem. Soc. 2000, 122, 11430–
11439.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(22) Corma, A.; Serna, P. Science 2006, 313, 332–334.
(23) Vilé, G.; Albani, D.; AlmoraꢀBarrios, N.; López, N.; PérezꢀRamírez, J. ChemCatChem
016, 8, 21–33.
24) Hammer, B.; Norskov, J. K. Nature. 1995, 238–240.
(25) Fujitani, T.; Nakamura, I.; Akita, T.; Okumura, M.; Haruta, M. Angew. Chemie Int. Ed.
009, 48, 9515–9518.
26) Mallat, T.; Baiker, A. Appl. Catal. A Gen. 2000, 200, 3–22.
(27) Schoenbaum, C. A.; Schwartz, D. K.; Medlin, J. W. Acc. Chem. Res. 2014, 47, 1438–
445.
2
(
2
(
1
(
28) Giesbrecht, P. K.; Herbert, D. E. ACS Energy Lett. 2017, 2, 549–555.
29) Marshall, S. T.; O’Brien, M.; Oetter, B.; Corpuz, A.; Richards, R. M.; Schwartz, D. K.;
Medlin, J. W. Nat. Mater. 2010, 9, 853–858.
(
(30) Chen, G.; Xu, C.; Huang, X.; Ye, J.; Gu, L.; Li, G.; Tang, Z.; Wu, B.; Yang, H.; Zhao, Z.;
Zhou, Z.; Fu, G.; Zheng, N. Nat. Mater. 2016, 15, 564–569.
(31) Kwon, S. G.; Krylova, G.; Sumer, A.; Schwartz, M. M.; Bunel, E. E.; Marshall, C. L.;
Chattopadhyay, S.; Lee, B.; Jellinek, J.; Shevchenko, E. V. Nano Lett. 2012, 12, 5382–
5
388.
32) Moreno, M.; Ibañez, F. J.; Jasinski, J. B.; Zamborini, F. P. J. Am. Chem. Soc. 2011, 133,
389–4397.
(
4
(33) Wu, B.; Huang, H.; Yang, J.; Zheng, N.; Fu, G. Angew. Chemie Int. Ed. 2012, 51, 3440–
ACS Paragon Plus Environment
26

Page 27 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
3
443.
34) Schrader, I.; Warneke, J.; Backenköhler, J.; Kunz, S. J. Am. Chem. Soc. 2015, 137, 905–
12.
35) Kahsar, K. R.; Schwartz, D. K.; Medlin, J. W. J. Am. Chem. Soc. 2014, 134, 520–526.
(
(
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(36) Chinchilla, R.; Nájera, C. Chem. Rev. 2014, 114, 1783–1826.
(37) GarcíaꢀMota, M.; GómezꢀDíaz, J.; NovellꢀLeruth, G.; VargasꢀFuentes, C.; Bellarosa, L.;
Bridier, B.; PérezꢀRamírez, J.; López, N. Theor. Chem. Acc. 2011, 128, 663–673.
(38) Ren, D.; He, L.; Yu, L.; Ding, R. S.; Liu, Y. M.; Cao, Y.; He, H. Y.; Fan, K. N. J. Am.
Chem. Soc. 2012, 134, 17592–17598.
(39) Li, G.; Jin, R. J. Am. Chem. Soc. 2014, 136, 11347–11354.
(40) Yan, M.; Jin, T.; Ishikawa, Y.; Minato, T.; Fujita, T.; Chen, L.ꢀY.; Bao, M.; Asao, N.;
Chen, M.ꢀW.; Yamamoto, Y. J. Am. Chem. Soc. 2012, 134, 17536–17542.
(
41) Li, S.ꢀS.; Tao, L.; Wang, F.ꢀZ.ꢀR.; Liu, Y.ꢀM.; Cao, Y. Adv. Synth. Catal. 2016, 358,
410–1416.
42) Scanlon, J. T.; Willis, D. E. J. Chromatogr. Sci. 1985, 23, 333–340.
1
(
(43) Jacinto, M. J.; Kiyohara, P. K.; Masunaga, S. H.; Jardim, R. F.; Rossi, L. M. Appl. Catal.
A Gen. 2008, 338, 52–57.
(44) Liu, X.; Wang, A.; Yang, X.; Zhang, T.; Mou, C. Y.; Su, D. S.; Li, J. Chem. Mater. 2009,
21, 410–418.
(
(
(
(
45) Dekkers, M. A. P.; Lippits, M. J.; Nieuwenhuys, B. E. Catal. Letters 1998, 56, 195–197.
46) Zanella, R.; Giorgio, S.; Henry, C. R.; Louis, C. J. Phys. Chem. B 2002, 106, 7634–7642.
47) Kresse, G.; Hafner, J. Phys. Rev. B 1993, 47, 558–561.
48) Kresse, G.; Furthmüller, J. Comput. Mater. Sci. 1996, 6, 15–50.
ACS Paragon Plus Environment
27

ACS Catalysis
Page 28 of 37
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
(
49) Hammer, B.; Hansen, L.; Nørskov, J. Phys. Rev. B 1999, 59, 7413–7421.
(50) AlmoraꢀBarrios, N.; Carchini, G.; Błoński, P.; López, N. J. Chem. Theory Comput. 2014,
10, 5002–5009.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
(51) Kresse, G. Phys. Rev. B 1999, 59, 1758–1775.
(52) Monkhorst, H. J.; Pack, J. D. Phys. Rev. B 1976, 13, 5188–5192.
(
53) Henkelman, G.; Uberuaga, B. P.; Jónsson, H. J. Chem. Phys. 2000, 113, 9901.
54) Shao, L.; Huang, X.; Teschner, D.; Zhang, W. ACS Catal. 2014, 4, 2369–2373.
(
(55) Mitsudome, T.; Yamamoto, M.; Maeno, Z.; Mizugaki, T.; Jitsukawa, K.; Kaneda, K. J.
Am. Chem. Soc. 2015, 137, 13452−13455.
(
56) Vasilikogiannaki, E.; Titilas, I.; Vassilikogiannakis, G.; Stratakis, M. Chem. Commun.
2015, 51, 2384–2387.
(57) Li, S.ꢀS.; Liu, X.; Liu, Y.ꢀM.; He, H.ꢀY.; Fan, K.ꢀN.; Cao, Y. Chem. Commun. 2014, 50,
5626–5628.
(
58) Liang, S.; Hammond, G. B.; Xu, B. Chem. Commun. 2016, 52, 6013–6016.
59) Jover, J.; GarcíaꢀRatés, M.; López, N. ACS Catal. 2016, 6, 4135–4143.
(
(60) Cano, I.; Huertos, M. a; Chapman, A. M.; Buntkowsky, G.; Gutmann, T.; Groszewicz, P.
B.; van Leeuwen, P. W. N. M. J. Am. Chem. Soc. 2015, 137, 7718–7727.
(
61) Liu, C.; Abroshan, H.; Yan, C.; Li, G.; Haruta, M. ACS Catal. 2016, 6, 92–99.
(62) Cano, I.; Chapman, A. M.; Urakawa, A.; van Leeuwen, P. W. N. M. J. Am. Chem. Soc.
014, 136, 2520–2528.
2
(
63) LópezꢀSerrano, J.; Duckett, S. B.; Lledós, A. J. Am. Chem. Soc. 2006, 128, 9596–9597.
64) Chen, Z.; Pronkin, S.; Fellinger, T.ꢀP.; Kailasam, K.; Vilé, G.; Albani, D.; Krumeich, F.;
Leary, R.; Barnard, J.; Thomas, J. M.; PérezꢀRamírez, J.; Antonietti, M.; Dontsova, D.
(
ACS Paragon Plus Environment
28

Page 29 of 37
ACS Catalysis
1
2
3
4
5
6
7
8
9
ACS Nano 2016, 10, 3166–3175.
(
(
(
65) Liu, P.; Zhao, Y.; Qin, R.; Mo, S.; Chen, G.; Gu, L.; Chevrier, D. M.; Zhang, P.; Guo, Q.;
Zang, D.; Wu, B.; Fu, G.; Zheng, N. Science. 2016, 352, 797–800.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
66) Vilé, G.; Baudouin, D.; Remediakis, I. N.; Copéret, C.; López, N.; PérezꢀRamírez, J.
ChemCatChem 2013, 5, 3750–3759.
67) Welch, G. C.; Juan, R. R. S.; Masuda, J. D.; Stephan, D. W. Science 2006, 314, 1124–
1
126.
(68) Chernichenko, K.; Madarász, A.; Pápai, I.; Nieger, M.; Leskelä, M.; Repo, T. Nat. Chem.
013, 5, 718–723.
2
(
69) Chorkendorff, I.; Niemantsverdriet, J. W. Concepts of Modern Catalysis and Kinetics;
WileyꢀVCH Verlag GmbH & Co. KGaA: Weinheim, FRG, 2003.
(
70) Carey, F. A.; Sundberg, R. J. Advanced Organic Chemistry Part A: Structure and
Mechanisms; Advanced Organic Chemistry; Springer US: Boston, MA, 2007.
ACS Paragon Plus Environment
29