Formal Cross-Coupling of Diaryl Ethers with Ammonia by Dual C(Ar)-O Bond Cleavages

Article abstract of DOI:10.1021/acscatal.8b02214

The conversion of renewable resources and inexpensive inorganic chemicals directly into higher value-added organic chemicals is becoming more and more important for our society's future sustainable development. Lignin, being the second most abundant organic carbon renewable resource on Earth, has been treated as waste in the pulp and paper industry. The 4-O-5 linkage diaryl ether bond is the strongest among the three types of ether linkages in lignins. Selective cleavage of this linkage can potentially generate smaller processable bio-based aromatic polymeric materials and compounds. Furthermore, there has been a long synthetic interest in coupling reactions with aryl ethers via C(Ar)-O bond cleavage, for example, for polyphenylene oxide (PPO) waste recycling. On the other hand, ammonia is a very inexpensive industrial inorganic chemical. Herein, we report a direct conversion of diaryl ethers and ammonia into aniline derivatives and arenes, providing a model for selective lignin 4-O-5 linkage modification and PPO recycling with inexpensive ammonia. Both symmetrical and unsymmetrical diaryl ethers were successfully cross-coupled with ammonia via dual C(Ar)-O bond cleavages, generating the corresponding cyclohexylanilines and arenes.

Full text of DOI:10.1021/acscatal.8b02214

Research Article
pubs.acs.org/acscatalysis
Cite This: ACS Catal. 2018, 8, 8873−8878
Formal Cross-Coupling of Diaryl Ethers with Ammonia by Dual
C(Ar)−O Bond Cleavages
Dawei Cao,† Huiying Zeng,*,† and Chao-Jun Li*,†,‡
†The State Key Laboratory of Applied Organic Chemistry, Lanzhou University, Lanzhou 730000, People’s Republic of China
‡Department of Chemistry and FQRNT Centre for Green Chemistry and Catalysis, McGill University, 801 Sherbrooke St. West,
Montreal, QC H3A 0B8, Canada
S
* Supporting Information
ABSTRACT: The conversion of renewable resources and inexpensive
inorganic chemicals directly into higher value-added organic chemicals is
becoming more and more important for our society’s future sustainable
development. Lignin, being the second most abundant organic carbon
renewable resource on Earth, has been treated as waste in the pulp and paper
industry. The 4-O-5 linkage diaryl ether bond is the strongest among the three
types of ether linkages in lignins. Selective cleavage of this linkage can
potentially generate smaller processable bio-based aromatic polymeric
materials and compounds. Furthermore, there has been a long synthetic interest in coupling reactions with aryl ethers via
C(Ar)−O bond cleavage, for example, for polyphenylene oxide (PPO) waste recycling. On the other hand, ammonia is a very
inexpensive industrial inorganic chemical. Herein, we report a direct conversion of diaryl ethers and ammonia into aniline
derivatives and arenes, providing a model for selective lignin 4-O-5 linkage modification and PPO recycling with inexpensive
ammonia. Both symmetrical and unsymmetrical diaryl ethers were successfully cross-coupled with ammonia via dual C(Ar)−O
bond cleavages, generating the corresponding cyclohexylanilines and arenes.
KEYWORDS: lignin model, ammonia, PPO, diaryl ether, 4-O-5 linkage, aniline, C(Ar)−O bond cleavage
Scheme 1. Strategies for Converting 4-O-5 Linkage Lignin
or PPO Model Compounds and Ammonia to High Value-
Added Anilines
onverting lower value renewable biomass, e.g., forestry
Cand agricultural wastes, and disused polymers such as
polyphenylene oxide (PPO) into higher value-added chemical
products is becoming increasingly important for social,
economic, and resource sustainability.1 Lignin is a major
renewable biomass waste product in the pulp and paper
industry, with a production of 150−180 million tons per year.2
On the other hand, polyphenylene oxide (PPO) is widely used
as an important engineering plastic. Diaryl ether, which is a
common 4-O-5 linkage lignin model compound and the
building block of PPO, has the highest bond dissociation
energy among the three types of ether linkages (including α-O-
4, β-O-4, and 4-O-5) in lignins,3 and is the most challenging to
cleave. Thus far, success has been achieved to cleave this type
of ether bond to form simple molecules, including hydro-
carbon (benzene, cyclohexane) and oxygen-containing com-
pounds (phenol, cyclohexanol, cyclohexanone, and cyclo-
hexylalkyl ether).4
Converting inexpensive inorganic chemicals into high value-
added organic chemicals has very important economic value
̈
since the report by Wohler nearly two hundred years ago,
which is a milestone work on urea (an organic molecule)
synthesis from the inorganic ammonium cyanate (see Scheme
1a).5 Toward the valorization of lignin and PPO waste to
higher value-added chemicals, we reported a new method of
reacting diaryl ethers with organic amines to form nitrogen-
containing compounds (see Scheme 1b).6
Received: June 6, 2018
Revised: July 29, 2018
© XXXX American Chemical Society
8873
DOI: 10.1021/acscatal.8b02214
ACS Catal. 2018, 8, 8873−8878

ACS Catalysis
Research Article
a
Table 1. Evaluation of Various Conditions
b
b
entry
catalyst
2a
solvent
toluene
toluene
toluene
toluene
[H]
3a (%)
4a (%)
1
2
3
4
5
6
7
8
9
Pd(OH)2/C
Pd/C
Pd/Al2O3
NH4Cl
NH4Cl
NH4Cl
NH4Cl
NH4Cl
NH4Cl
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
HCO2Na
NaBH4
NaH
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
NaBH4
2
trace
n.p.
n.p.
6
n.p.
16
26
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
n.p.
2
n.p.
2
3
2
5
3
5
6
6
Pd(OAc)2
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
Pd(OH)2/C
m-xylene
1,4-dioxane
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
m-xylene
urea
NH4HCO3
NH3·H2O
N2H4·H2O
NH3
30
12
10
11
8
9
c
12
13
14
15
16
17
18
19
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
NH3·H2O
d
43
35
49
25
72
79
48
87 (83)
69
64
87
88
68
e
d
d
df
,
dg
,
dh
,
dgi
,
,
20
21
22
23
24
25
dgj
,
,
dgik
, ,
,
dgil
, ,
,
dgim
, ,
,
NaBH4
NaBH4
dgin
, ,
,
5
a
General conditions: 1a (0.2 mmol), 2a (3 equiv), catalyst (20 mol %), HCO2Na (3 equiv), and solvent (1 mL) at 160 °C for 24 h under an argon
b
c
1
atmosphere. Yields were determined by H NMR with nitromethane as an internal standard; isolated yields given in brackets. NH3·H2O (2
d
e
f
g
h
i
j
equiv). NH3·H2O (5 equiv). NH3·H2O (6 equiv). NaBH4 (1.5 equiv). NaBH4 (1 equiv). NaBH4 (0.5 equiv). At 150 °C. At 140 °C.
k
l
m
n
Pd(OH)2/C (10 mol %). Pd(OH)2/C (30 mol %). For 36 h. For 12 h.
Since ammonia is a very inexpensive and abundant industrial
ammonium bicarbonate, ammonia, hydrazine hydrate, and
ammonia gas, were investigated (Table 1, entries 7−11), with
ammonia providing the highest yield (Table 1, entry 9).
Adjusting the amount of ammonia to 5 equiv gave the optimal
yield (Table 1, entry 13). Increasing or reducing the amount of
ammonia led to lower yields (Table 1, entries 12 and 14).
Using sodium borohydride, which is a strong reducing reagent,
as hydride source resulted in 49% yield of N-cyclohexylaniline,
together with 2% yield of diphenylamine (Table 1, entry 15).
Using sodium hydride as the hydride source, a lower yield was
observed (see Table 1, entry 16). A quantity of 1 equiv of
NaBH4 appeared to be optimal for this reaction (Table 1, entry
18), as either higher or lower amount of NaBH4 resulted in
lower yields (Table 1, entries 17−19). Reducing the reaction
temperature to 150 °C gave 87% yield of the product (Table 1,
entry 20). Further reducing the temperature lowered the
product yield (Table 1, entry 21). The amount of catalyst is
also important for the reaction: a lower yield (64%) was
achieved when 10 mol % catalyst was used in this reaction
system (Table 1, entry 22), and further increasing the amount
of catalyst to 30 mol % did not improve the yield (87%) (Table
1, entry 23). Thus, we chose 20 mol % Pd(OH)2/C as the
optimal amount for subsequent optimizations. Nearly the same
yield (88%) was obtained when prolonging the reaction time
to 36 h (Table 1, entry 24). Reducing the reaction time to 12 h
lowered the product yield (Table 1, entry 25). We also
inorganic chemical, converting lignin or PPO waste with
ammonia directly to high value-added nitrogen-containing
organic chemicals will provide a great economic advantage for
lignin utilizations and PPO recycling. At the same time,
anilines are important building blocks for various organic
molecules and electronic materials, as well as among the most
prevalent structural motifs among pharmaceutical agents.7
Thus, it is highly desirable to explore methods that can directly
react lignin or PPO waste with ammonia to produce higher-
valued products. Herein, we report the direct transformation of
4-O-5 linkage lignin or PPO model diaryl ethers with ammonia
into aniline derivatives, catalyzed by palladium (see Scheme
1c).
We began our initial investigation by screening different
palladium catalysts to couple diphenyl ether with ammonium
chloride (Table 1, entries 1−4). Fortunately, a trace amount
(ca. 2% yield) of N-cyclohexylaniline was detected by 1H NMR
when Pd(OH)2/C was used as a catalyst in toluene at 160 °C
under an argon atmosphere for 24 h, using sodium formate as a
hydride source (Table 1, entry 1). Other palladium catalysts
were also examined without success (Table 1, entries 2−4).
Different solvents were then examined (Table 1, entries 5 and
6), and a 6% yield of N-cyclohexylaniline was obtained when
m-xylene was used as a solvent (Table 1, entry 5). Encouraged
by this result, different nitrogen sources, such as urea,
8874
DOI: 10.1021/acscatal.8b02214
ACS Catal. 2018, 8, 8873−8878

ACS Catalysis
Research Article
examined different phosphine ligands (40 mol %), including
triphenylphosphine, bis(diphenylphosphino)ethane, 1,3-bis-
( d i p h e n y l p h o s p h i n o ) - p r o p a n e , a n d 1 , 4 - b i s -
(diphenylphosphino)butane, under the standard reaction
conditions. These phosphine ligands could not improve the
yield, and only recovered the starting material. We proposed
that Pd(OH)2/C was reduced by NaBH4 to form Pd
nanoparticles at 150 °C in our catalytic system.
With the optimal reaction conditions established, we next
proceeded to explore different symmetrical diaryl ethers to
react with 5.0 equiv of ammonia at 150 °C under argon, using
20 mol % Pd(OH)2/C as the catalyst and 1.0 equiv of sodium
borohydride in m-xylene (1 mL) for 24 h. As shown in Table 2,
moderate to excellent yields were obtained for various
substrates (Table 2, entries 1−7). Diphenyl ether was
transformed to N-cyclohexylaniline in 83% yield, with the
other phenyl group being converted to benzene (82%) and a
small amount of cyclohexane (Table 2, entry 1). Weakly
electron-donating methyl groups at meta- and para-positions
gave the corresponding anilines 3b and 3c in high yields
(Table 2, entries 2 and 3). Similar results were obtained with
longer-chain analogues substituted at the para-position (Table
2, entries 4 and 5). The defluorination product 3a was
obtained with moderate yield (48%) when fluorine-containing
substrate 1f was explored under the standard conditions when
prolonging the reaction time to 36 h and increasing the
amount of NaBH4 to 2 equiv (Table 2, entry 6). The 4,4′-
dimethoxyldiphenyl ether also reacted smoothly, to give the
demethoxylation product 3a (Table 2, entry 7).
We subsequently proceeded to investigate the generality of
our system with a wide range of unsymmetrical diaryl ethers.
Highly regioselective cleavage of C−O bond was obtained
even with only a minute difference between the two aryl
groups (Table 3, entries 1 and 2). Thus, 3- and 4-
methyldiphenyl ethers (1h) and (1i) gave the corresponding
methyl-substituted cyclohexylaniline 3b and 3c with good to
high yields, respectively. The other aryl group of the ethers was
converted to the corresponding benzene (65% and 73% yield,
respectively) (Table 3, entries 1 and 2). It is interesting to note
that the selectivity of C−O bond cleavage was reversed when
the substituent was changed to tert-butyl or phenyl group:
cyclohexylaniline (3a) was obtained selectively in high yields,
with the other aryl group forming the corresponding arene
product tert-butyl benzene (5f) and biphenyl (5g) (Table 3,
entries 3 and 4). It is possible that the solubility might have
reversed the selectivity under heterogeneous conditions. 2-
Phenoxynaphthalene (1l) and 2-(p-tolyloxy)naphthalene (1m)
were also successfully cleaved regioselectively, to give the
corresponding cyclohexylaniline (3a) and 4-methyl-N-(4-
methylcyclohexyl)aniline (3c) in high yields (Table 3, entries
5 and 6). When methyl and phenyl group were substituted on
both phenyl rings, the regioselective cleavage of C−O bond
was achieved (Table 3, entry 7) to give 4-methyl-N-(4-
methylcyclohexyl)-aniline (3c) as a single nitrogen-containing
product in high yield, together with 11% yield of biphenyl and
81% yield of its reduced product, cyclohexylbenzene.
Table 2. Direct Cross-Coupling of Symmetrical Diaryl
a
Ethers with Ammonia
To further investigate the applicability of this catalytic
system, oligomeric phenylene oxides 6 and 7, both containing
four C(Ar)−O bonds as polyphenylene oxide (PPO) model
compounds, were tested under the standard reaction
conditions with increasing sodium borohydride to 2.0 equiv.
N-Cyclohexylaniline (3a) and benzene (5a) were obtained
with high total yields (123% and 112%, respectively) (see
Schemes 2a and 2b), which provides potentials for the
valorization of polyphenylene oxide (PPO) wastes.8
To understand the reaction mechanism, control experiments
were performed. Cyclohexenylphenyl ether (8) was explored as
a possible intermediate under our catalytic system;9 however, it
was proven otherwise (see Scheme 3a). When diphenyl ether
was explored under standard reaction conditions in the
absence of ammonia, oxygen-containing compounds (phenol
and cyclohexanone) and hydrocarbon compounds (benzene
and cyclohexane) were obtained. These results illustrated that
the C−O bond was directly cleaved via palladium-catalyzed
hydrogenolysis of diphenyl ether, which is also consistent with
the observation that the nitrogen-containing products (N-
cyclohexylaniline, N-dicyclohexylamine, and diphenylamine)
and hydrocarbon products (benzene and cyclohexane) were
formed in ca. 1:1 ratio (see Figure 1). On the other hand, both
phenol and cyclohexanone successfully reacted with ammonia
a
Reaction conditions: diaryl ether 1 (0.2 mmol), ammonia (1.0
mmol), Pd(OH)2/C (20 mol %), and NaBH4 (0.2 mmol) in m-xylene
(1 mL). All reactions were carried out at 150 °C in a sealed tube
under an argon atmosphere for 24 h; yields of isolated products were
given. Cis/trans (isomer) ratio was determined by crude H NMR.
cYields of benzene and cyclohexane was determined by GC-MS; a
small peak of cyclohexane was overlapped within the big peak of
benzene. dYield was determined by GC-MS; no corresponding
substituted cyclohexane was detected. Reaction time was prolonged
to 36 h, and NaBH4 was increased to 2 equiv. Reaction time was
prolonged to 36 h.
b
1
e
f
8875
DOI: 10.1021/acscatal.8b02214
ACS Catal. 2018, 8, 8873−8878

ACS Catalysis
Research Article
Table 3. Direct Cross-Coupling of Unsymmetrical Diaryl
Ethers with Ammonia
Scheme 3. Control Experiments
a
Figure 1. Concentration of starting material and products at different
reaction times.
Combining these experimental results, a plausible mecha-
nism for this amination reaction is proposed in Scheme 4. The
Scheme 4. Plausible Mechanism of Amination of Diaryl
Ether
a
Reaction conditions: diaryl ether 1 (0.2 mmol), ammonia (1.0
mmol), Pd(OH)2/C (20 mol %), and NaBH4 (0.2 mmol) in m-xylene
(1 mL). All reactions were conducted at 150 °C in a sealed tube
under an argon atmosphere for 24 h; yields of isolated products were
given. The cis/trans (isomer) ratio was determined by crude 1H
b
NMR. cA trace amount of N-cyclohexylaniline and 8% of toluene were
also obtained. dA trace amount of N-cyclohexylaniline and 9% of
e
f
toluene were also obtained. Isolated yield. Isolated yield; 82% of
cyclohexylbenzene was also obtained. gIsolated yield; in addition, 74%
of 1,2,3,4-tetrahydronaphthalene was obtained. hIsolated yield; in
i
addition, 76% of 1,2,3,4-tetrahydronaphthalene was obtained. Iso-
lated yield; in addition, 81% of cyclohexylbenzene was obtained.
Scheme 2. Conversion of Oligomeric Phenylene Oxides and
Ammonia into Anilines
HPdIIH species is formed by Pd(OH)2/C with sodium
borohydride and water. Then, direct cleavage of the C(Ar)−
O ether bond by the HPdIIH via hydrogenolysis of diphenyl
ether generates benzene and phenol B, which is further
reduced by HPdIIH to form cyclohexanone C.10 Then, C
condenses with ammonia to form imine D, which is further
reduced to form amine E. Condensation of E with cyclo-
hexanone generates imine F (Scheme 4, path a), which is
reduced to dicyclohexylamine G. Amine G then oxidatively
aromatizes to form the product N- cyclohexylaniline H, as well
as regenerates HPdIIH. Alternatively, amine E undergoes
(see Schemes 3b and 3c), suggesting their possible
involvement as intermediates in our catalytic system.
8876
DOI: 10.1021/acscatal.8b02214
ACS Catal. 2018, 8, 8873−8878

ACS Catalysis
Research Article
oxidative aromatization to generate aniline I (path b),11 which
is condensed with cyclohexanone to form imine J. Intermediate
J is reduced to generate the product H and a small amount of J
is oxidized to form byproduct diphenylamine.12
Weckhuysen, B. M. Paving the Way for Lignin Valorisation: Recent
Advances in Bioengineering, Biorefining and Catalysis. Angew. Chem.,
Int. Ed. 2016, 55, 8164−8215. (f) Regalbuto, J. R. Cellulosic
BiofuelsGot Gasoline? Science 2009, 325, 822−824. (g) Ragauskas,
A. J.; Beckham, G. T.; Biddy, M. J.; Chandra, R.; Chen, F.; Davis, M.
F.; Davison, B. H.; Dixon, R. A.; Gilna, P.; Keller, M.; Langan, P.;
Naskar, A. K.; Saddler, J. N.; Tschaplinski, T. J.; Tuskan, G. A.;
Wyman, C. E. Lignin Valorization: Improving Lignin Processing in
the Biorefinery. Science 2014, 344, 1246843.
(2) (a) Sanderson, K. A Chewy Problem. Nature 2011, 474, S12−
S14. (b) Carrier, M.; Loppinet-Serani, A.; Denux, D.; Lasnier, J.-M.;
Ham-Pichavant, F.; Cansell, F.; Aymonier, C. Thermogravimetric
Analysis as a New Method to Determine the Lignocellulosic
Composition of Biomass. Biomass Bioenergy 2011, 35, 298−307.
(3) (a) Luo, Y.-R. Comprehensive Handbook of Chemical Bond
Energies; CRC Press: Boca Raton, FL, 2007. (b) Jarvis, M. W.; Daily,
J. W.; Carstensen, H.-H.; Dean, A. M.; Sharma, S.; Dayton, D. C.;
Robichaud, D. J.; Nimlos, M. R. Direct Detection of Products from
the Pyrolysis of 2-Phenethyl Phenyl Ether. J. Phys. Chem. A 2011, 115,
428−438. (c) Ralph, J.; Brunow, G.; Boerjan, W. Liginin. In
Encyclopedia of Life Sciences; Wiley: New York, 2001.
In conclusion, we have successfully developed a palladium-
catalyzed synthesis of aniline derivatives from 4-O-5 linkage
lignin model compounds and inexpensive industrial inorganic
chemical ammonia via dual C(Ar)−O bond cleavage. Various
symmetrical and unsymmetrical diaryl ethers reacted with
ammonia to form the corresponding aniline derivatives and
arene products. Furthermore, the method can also be extended
to oligomeric phenylene oxide, which provides potential for the
valorization of polyphenylene oxide (PPO) wastes. Further
study on the direct conversion of native lignin, and PPO with
ammonia to nitrogen-contain compounds are proceeding in
our laboratory.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acscatal.8b02214.
■
S
(4) (a) Sergeev, A. G.; Hartwig, J. F. Selective, Nickel-Catalyzed
Hydrogenolysis of Aryl Ethers. Science 2011, 332, 439−443.
(b) Sergeev, A. G.; Webb, J. D.; Hartwig, J. F. A Heterogeneous
Nickel Catalyst for the Hydrogenolysis of Aryl Ethers without Arene
Hydrogenation. J. Am. Chem. Soc. 2012, 134, 20226−20229. (c) He,
J.; Zhao, C.; Lercher, J. A. Ni-Catalyzed Cleavage of Aryl Ethers in the
Aqueous Phase. J. Am. Chem. Soc. 2012, 134, 20768−20775.
(d) Zhao, C.; Lercher, J. A. Selective Hydrodeoxygenation of
Lignin-Derived Phenolic Monomers and Dimers to Cycloalkanes on
Pd/C and HZSM-5 Catalysts. ChemCatChem 2012, 4, 64−68.
(e) Gao, F.; Webb, J. D.; Hartwig, J. F. Chemo- and Regioselective
Hydrogenolysis of Diaryl Ether C−O Bonds by a Robust
Heterogeneous Ni/C Catalyst: Applications to the Cleavage of
Complex Lignin-Related Fragments. Angew. Chem., Int. Ed. 2016, 55,
1474−1478. (f) Meng, Q.; Hou, M.; Liu, H.; Song, J.; Han, B.
Synthesis of Ketones from Biomass-Derived Feedstock. Nat. Commun.
2017, 8, 14190. (g) Wang, M.; Shi, H.; Camaioni, D. M.; Lercher, J.
A. Palladium-Catalyzed Hydrolytic Cleavage of Aromatic C−O
Bonds. Angew. Chem., Int. Ed. 2017, 56, 2110−2114. (h) Ren, Y.-L.;
Tian, M.; Tian, X.-Z.; Wang, Q.; Shang, H.; Wang, J.; Zhang, Z. C.
Highly Selective Reductive Cleavage of Aromatic Carbon−Oxygen
Bonds Catalyzed by a Cobalt Compound. Catal. Commun. 2014, 52,
36−39. (i) Yang, L.; Li, Y.; Savage, P. E. Hydrolytic Cleavage of C−O
Linkages in Lignin Model Compounds Catalyzed by Water-Tolerant
Lewis Acids. Ind. Eng. Chem. Res. 2014, 53, 2633−2639. (j) Ren, Y.;
Yan, M.; Wang, J.; Zhang, Z. C.; Yao, K. Selective Reductive Cleavage
of Inert Aryl C−O Bonds by an Iron Catalyst. Angew. Chem., Int. Ed.
2013, 52, 12674−12678. (k) Wu, W. B.; Huang, J. M. Electro-
chemical Cleavage of Aryl Ethers Promoted by Sodium Borohydride.
J. Org. Chem. 2014, 79, 10189−10195. (l) Stavila, V.; Parthasarathi,
R.; Davis, R. W.; El Gabaly, F.; Sale, K. L.; Simmons, B. A.; Singh, S.;
Allendorf, M. D. MOF-Based Catalysts for Selective Hydrogenolysis
of Carbon−Oxygen Ether Bonds. ACS Catal. 2016, 6, 55−59.
(m) Liu, X.; Xu, L.; Xu, G.; Jia, W.; Ma, Y.; Zhang, Y. Selective
Hydrodeoxygenation of Lignin-Derived Phenols to Cyclohexanols or
Cyclohexanes over Magnetic CoNx@NC Catalysts under Mild
Conditions. ACS Catal. 2016, 6, 7611−7620. (n) Shao, Y.; Xia, Q.;
Liu, X.; Lu, G.; Wang, Y. Pd/Nb2O5/SiO2 Catalyst for the Direct
Hydrodeoxygenation of Biomass-Related Compounds to Liquid
Alkanes under Mild Conditions. ChemSusChem 2015, 8, 1761−
1767. (o) Wang, X.; Rinaldi, R. A Route for Lignin and Bio-Oil
Conversion: Dehydroxylation of Phenols into Arenes by Catalytic
Tandem Reactions. Angew. Chem., Int. Ed. 2013, 52, 11499−11503.
(p) Wu, H. R.; Song, J. L.; Xie, C.; Wu, C. Y.; Chen, C. J.; Han, B. X.
Efficient and Mild Transfer Hydrogenolytic Cleavage of Aromatic
Ether Bonds in Lignin-Derived Compounds over Ru/C. ACS
Sustainable Chem. Eng. 2018, 6, 2872−2877. (q) Wang, M.;
Gutierrez, O. Y.; Camaioni, D.; Lercher, J. Palladium-Catalyzed
General experimental procedures, characterization de-
1
tails, and copies of H and 13C NMR spectra of new
compounds (PDF)
AUTHOR INFORMATION
Corresponding Authors
*E-mail: zenghy@lzu.edu.cn (H. Zeng).
*E-mail: cj.li@mcgill.ca. Home page: http://www.cjlimcgill.
ca/ (C.-J. Li).
■
ORCID
Huiying Zeng: 0000-0002-2535-111X
Chao-Jun Li: 0000-0002-3859-8824
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the Recruitment Program of Global Experts (Short-
Term B) to C.-J.L., the Fundamental Research Funds for the
Central Universities (No. lzujbky-2018-62), the International
Joint Research Centre for Green Catalysis and Synthesis,
Gansu Provincial Sci. & Tech. Department (Nos.
2016B01017, 18JR3RA284) and Lanzhou University for
support of our research. We also thank the Canada Research
Chair (Tier I) foundation, the E.B. Eddy endowment fund, the
CFI, NSERC, and FQRNT to C.-J.L. We thank Mr. Jianjin Yu
in this group for reproducing the results presented in entry 1 in
Table 2 and entry 1 in Table 3.
REFERENCES
■
́
́
(1) (a) Tuck, C. O.; Perez, E.; Horvath, I. T.; Sheldon, R. A.;
Poliakoff, M. Valorization of Biomass: Deriving More Value from
Waste. Science 2012, 337, 695−699. (b) Zakzeski, J.; Bruijnincx, P. C.
A.; Jongerius, A. L.; Weckhuysen, B. M. The Catalytic Valorization of
Lignin for the Production of Renewable Chemicals. Chem. Rev. 2010,
110, 3552−3599. (c) Li, C.; Zhao, X.; Wang, A.; Huber, G. W.;
Zhang, T. Catalytic Transformation of Lignin for the Production of
Chemicals and Fuels. Chem. Rev. 2015, 115, 11559−11624.
(d) Zhang, Z.; Song, J.; Han, B. Catalytic Transformation of
Lignocellulose into Chemicals and Fuel Products in Ionic Liquids.
Chem. Rev. 2017, 117, 6834−6880. (e) Rinaldi, R.; Jastrzebski, R.;
Clough, M. T.; Ralph, J.; Kennema, M.; Bruijnincx, P. C.;
8877
DOI: 10.1021/acscatal.8b02214
ACS Catal. 2018, 8, 8873−8878

ACS Catalysis
Research Article
Reductive Insertion of Alcohols into Aryl Ether Bonds. Angew. Chem.,
Int. Ed. 2018, 57, 3747−3751. (r) Lei, P.; Meng, G.; Shi, S.; Ling, Y.;
An, J.; Szostak, R.; Szostak, M. Suzuki-Miyaura Cross-Coupling of
Amides and Esters at Room Temperature: Correlation with Barriers
to Rotation around C−N and C−O Bonds. Chem. Sci. 2017, 8, 6525−
6530.
̈
̈
(5) Wohler, F. Ueber Kunstliche Bildung des Harnstoffs. Ann. Phys.
1828, 88, 253−256.
(6) Zeng, H.; Cao, D.; Qiu, Z.; Li, C.-J. Palladium-Catalyzed Formal
Cross-Coupling of Diaryl Ethers with Amines: Slicing the 4-O-5
Linkage in Lignin Models. Angew. Chem., Int. Ed. 2018, 57, 3752−
3757.
(7) (a) Lawrence, S. A. Amines Synthesis, Properties and Applications;
Cambridge University Press: New York, 2004. (b) McGrath, N. A.;
Brichacek, M.; Njardarson, J. T. A Graphical Journey of Innovative
Organic Architectures that Have Improved Our Lives. J. Chem. Educ.
2010, 87, 1348−1349.
(8) (a) So, Y. H. Photodegradation Mechanism and Stabilization of
Polyphenylene Oxide and Rigid-Rod Polymers. Polym. Int. 2006, 55,
127−138. (b) Shukla, D.; Negi, Y. S.; Uppadhyaya, J. S.; Kumar, V.
Synthesis and Modification of Poly (Ether Ether Ketone) and Their
Properties: A Review. Polym. Rev. 2012, 52, 189−228.
(9) Cyclohexenylphenyl ether (8) was speculated as a key
intermediate via step-by-step hydrogenation of phenyl group, which
was hydrolyzed by water to cleave the C−O bond under palladium
catalytic system in refs 4f, g, and 4q.
(10) (a) Liu, H.; Jiang, T.; Han, B.; Liang, S.; Zhou, Y. Selective
Phenol Hydrogenation to Cyclohexanone Over a Dual Supported
Pd−Lewis Acid Catalyst. Science 2009, 326, 1250−1252. (b) Chen,
Z.; Zeng, H.; Gong, H.; Wang, H.; Li, C.-J. Palladium-Catalyzed
Reductive Coupling of Phenols with Anilines and Amines: Efficient
Conversion of Phenolic Lignin Model Monomers and Analogues to
Cyclohexylamines. Chem. Sci. 2015, 6, 4174−4178.
(11) (a) Ono, Y.; Ishida, H. Amination of Phenols with Ammonia
over Palladium Supported on Alumina. J. Catal. 1981, 72, 121−128.
(b) Izawa, Y.; Pun, D.; Stahl, S. S. Palladium-Catalyzed Aerobic
Dehydrogenation of Substituted Cyclohexanones to Phenols. Science
2011, 333, 209−213. (c) Izawa, Y.; Zheng, C.; Stahl, S. S. Aerobic
Oxidative Heck/Dehydrogenation Reactions of Cyclohexenones:
Efficient Access to meta-Substituted Phenols. Angew. Chem., Int. Ed.
2013, 52, 3672−3675. (d) Pun, D.; Diao, T.; Stahl, S. S. Aerobic
Dehydrogenation of Cyclohexanone to Phenol Catalyzed by Pd-
(TFA)2/2-Dimethylaminopyridine: Evidence for the Role of Pd-
Nanoparticles. J. Am. Chem. Soc. 2013, 135, 8213−8221. (e) Hong,
W. P.; Iosub, A. V.; Stahl, S. S. Pd-Catalyzed Semmler−Wolff
Reactions for the Conversion of Substituted Cyclohexenone Oximes
to Primary Anilines. J. Am. Chem. Soc. 2013, 135, 13664−13667.
(f) Chen, Z.; Zeng, H.; Girard, S. A.; Wang, F.; Chen, N.; Li, C.-J.
Formal Direct Cross-Coupling of Phenols with Amines. Angew. Chem.,
Int. Ed. 2015, 54, 14487−14491. (g) Zeng, H.; Qiu, Z.; Domínguez-
Huerta, A.; Hearne, Z.; Chen, Z.; Li, C.-J. An Adventure in
Sustainable Cross-Coupling of Phenols and Derivatives via
Carbon−Oxygen Bond Cleavage. ACS Catal. 2017, 7, 510−519.
(h) Iosub, A. V.; Stahl, S. S. Palladium-Catalyzed Aerobic
Dehydrogenation of Cyclic Hydrocarbons for the Synthesis of
Substituted Aromatics and Other Unsaturated Products. ACS Catal.
2016, 6, 8201−8213. (i) Qiu, Z.; Li, J.-S.; Li, C.-J. Formal Aromaticity
Transfer for Palladium-Catalyzed Coupling between Phenols and
Pyrrolidines/Indolines. Chem. Sci. 2017, 8, 6954−6958.
(12) (a) Li, J.-S.; Qiu, Z.; Li, C.-J. Palladium-Catalyzed Synthesis of
N-Cyclohexyl Anilines from Phenols with Hydrazine or Hydroxyl-
amine via N−N/O Cleavage. Adv. Synth. Catal. 2017, 359, 3648−
3653. (b) Koizumi, Y.; Taniguchi, K.; Jin, X.; Yamaguchi, K.; Nozaki,
K.; Mizuno, N. Formal Arylation of NH3 to Produce Diphenylamines
over Supported Pd Catalysts. Chem. Commun. 2017, 53, 10827−
10830.
8878
DOI: 10.1021/acscatal.8b02214
ACS Catal. 2018, 8, 8873−8878