Additive-Free Cobalt-Catalyzed Hydrogenation of Esters to Alcohols

Article abstract of DOI:10.1021/acscatal.7b00623

Here, we report an additive-free catalytic system for hydrogenation of carboxylic acid esters to alcohols with a well-defined cobalt pincer catalyst precursor. Various substrates, including methyl, ethyl, and benzyl esters, have been evaluated under hydrogenation conditions; however, methyl esters have low reactivity compared to those of the corresponding ethyl and benzyl esters. The biomass-derived γ-valerolactone successfully formed 1,4-pentanediol with a turnover number of 3890 with this system. Metal-ligand cooperativity is probed with the related [PN(Me)P] derivative of the cobalt catalyst, and the results suggest a nonbifunctional hydrogenation mechanism.

Full text of DOI:10.1021/acscatal.7b00623

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Article
Additive-Free Cobalt-Catalyzed Hydrogenation of Esters to Alcohols
Jing Yuwen, Sumit Chakraborty, William W. Brennessel, and William D. Jones
ACS Catal., Just Accepted Manuscript • Publication Date (Web): 20 Apr 2017
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ACS Catalysis
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Additive-Free Cobalt-Catalyzed Hydrogenation
of Esters to Alcohols
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Jing Yuwen, Sumit Chakraborty, William W. Brennessel and William D. Jones*
Department of Chemistry, University of Rochester, Rochester, New York, 14627
ABSTRACT: Here, we report an additiveꢀfree catalytic system for hydrogenation of carboxylic acid esters to alcohols with a wellꢀ
defined cobalt pincer catalyst precursor. Various substrates including methyl, ethyl and benzyl esters have been evaluated under
hydrogenation conditions, however, methyl esters have low reactivity compared to the corresponding ethyl and benzyl esters. The
biomass derived γꢀvalerolactone (GVL) successfully formed 1,4ꢀpentanediol with a turnover number of 3890 with this system.
Metalꢀligand cooperativity is probed with the related [PN(Me)P] derivative of the cobalt catalyst and the results suggest a nonꢀ
bifunctional hydrogenation mechanism.
Keywords: cobalt, hydrogenation, esters, alcohols, catalysis
43
Introduction
chemistry. However, firstꢀrow transitionꢀmetal complexes
typically react by oneꢀelectron pathways, rather than by the
prevailing twoꢀelectron transformations of precious metals,
resulting in the difficulty of predicting and controlling catalytꢀ
ic reactivity. Recently, remarkable advances have been made
in the application of inexpensive, earthꢀabundant and nontoxic
The reduction of esters to alcohols is an important process for
both laboratory organic synthesis and the chemical industry.
1
Traditionally, stoichiometric amounts of metal hydride reaꢀ
gents (e.g., LiAlH and NaBH ) are applied to hydrogenation
4
4
of esters to alcohols, but stoichiometric amounts of waste are
44ꢀ47
48ꢀ49
2
ironꢀ
and cobaltꢀbased
catalysts for ester hydrogenaꢀ
generated. In contrast, catalytic hydrogenation with molecular
tion. Of particular interest is the first cobalt catalyst, supported
by a PNNꢀpincer ligand, for ester hydrogenation by Milstein et
al. In their system, the cobalt PNNꢀpincer preꢀcatalyst required
hydrogen is environmentally benign, easy to operate, and fully
atom economic. Heterogeneous catalysts are mainly employed
for reduction of esters to alcohols in industry, however, exꢀ
activation by NaHBEt and the amount of the base added to
3
treme pressures (2000ꢀ3000 psi) and temperatures (200ꢀ300
4
8
3ꢀ4
the system has a significant effect on the yield of alcohols.
Recently, Elsevier and de Bruin reported another cobalt sysꢀ
°
C) are required which often leads to side product formation.
Hence, there is a growing demand to develop homogeneous
ester hydrogenation catalysts that could be operate more selecꢀ
tively under mild conditions.
tem of Co(BF ) ꢀ6H O paired with a tridentate phosphine
4
2
2
4
9
ligand to hydrogenate both esters and carboxylic acids.
Cobalt catalysts have been successfully applied in hydrogenaꢀ
tion reactions of various substrates, such as alkynes, alkenes,
In fact, since the 1980s, a variety of homogeneous catalytic
5ꢀ14
systems have been reported for ester hydrogenation. Signifꢀ
50ꢀ57
15
ketones, aldehydes and imines.
the cationic cobalt(II)
(PNHP )Co(CH SiMe )]BAr
In 2012, Hanson reported
alkyl complex
(1) (where PNHP
HN(CH CH PCy ) ) as an efficient catalyst precursor for hyꢀ
icant progress was achieved around 2006 by Milstein et al.
16
and Firmenich SA who developed Ruꢀbased homogeneous
catalysts for hydrogenation of nonactivated esters under relaꢀ
tively mild reaction conditions. Since then, many other cataꢀ
lysts have been prepared to improve the efficiency of ester
cy
F
cy
[
=
2
3
4
2
2
2 2
5
0, 52, 57
drogenation of alkenes, aldehydes, ketones, and imines.
17ꢀ42
Due to its high activity for hydrogenation of carbonyl funcꢀ
tionalities, we became interested to study if the same cobalt
catalyst could also reduce carboxylic acid esters, which have
hydrogenation.
The replacement of preciousꢀmetalꢀbased catalysts by earthꢀ
abundant metal catalysts is a prime goal in current catalytic
1
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inherently less reactivity compared to the corresponding aldeꢀ
Page 2 of 6
(entry 5). Cobalt compound 1 decomposed when the reaction
temperature was raised above 150 °C. A higher yield of benzyl
alcohol was detected when the reaction temperature was lowꢀ
ered to 120°C (97%, entry 8). Only a 52% yield of benzyl
alcohol was observed when the reaction was run at 80 °C (enꢀ
try 9). We assume that cobalt compound 1 partially decomꢀ
poses at 150 °C. The hydrogenation proceeded smoothly at a
shorter reaction time (20 h) and lower catalyst loading (2
mol%, entry 10), but reducing the catalyst loading to 1 mol%
resulted in a significant drop in the yield of benzyl alcohol
1
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hydes and ketones. It is noteworthy that the previously reportꢀ
ed pathway for hydrogenation of aldehydes and ketones inꢀ
5
7
volves a metalꢀligand cooperative mechanism. Here, howevꢀ
er, we find evidence for a nonꢀbifunctional hydrogenation
mechanism for hydrogenation of esters to alcohols using the
5
8
same cobalt catalyst.
Results and Discussion
To determine the optimum conditions for catalysis, we studied
catalytic hydrogenation of benzyl benzoate in the presence of
catalyst precursor 1 (0.01 mmol) under various conditions
(56% entry 11). Almost no benzyl alcohol was detected by GC
0
1
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under the same reaction conditions without cobalt catalyst 1
(entry 12).
(
%
Table 1). Combining benzyl benzoate (0.2 mmol) with 5 mol
of cobalt compound 1 in THF, under 20 bar of H pressure
2
Next, we investigated the scope of the hydrogenation reaction
with a range of ester substrates (Table 2). In the presence of 1
and at 150 °C produced 48% benzyl alcohol after 24 h (Table
, entry 1). Increasing the reaction time to 48 h resulted in a
1
(
2 mol%), 0.5 mmol of benzyl benzoate under 55 bar H at
2
similar yield of benzyl alcohol (45.2%, entry 2), while deꢀ
creasing the reaction time led to a significantly lower yield of
benzyl alcohol (17.4%, entry 3). Methanol has been used as
1
20 °C in THF gave a 97% yield of benzyl alcohol after 20 h
(
Table 2, entry 1). No other side product was observed by gas
chromatography. Under the same reaction conditions, ethyl
benzoate afforded a 90% yield of benzyl alcohol (entry 3).
Methyl benzoate turned out to be a challenging substrate, and
only gave a 15% yield of benzyl alcohol (entry 2). Aliphatic
esters, which
2
9,
solvent in some of the previously reported catalytic systems.
4
9, 59ꢀ60
When MeOH was used in place of THF as reaction
solvent, almost all of the benzyl benzoate was consumed (97%
conversion). However, only 53% of benzyl alcohol was
formed, the remainder of the product being methyl benzoate.
This result suggested that transesterification had occurred and
that the methyl benzoate was not able to be further hydrogenꢀ
ated (entry 4). The hydrogen pressure has a significant impact
on the overall yield of the ester hydrogenation reaction. Inꢀ
creasing the hydrogen pressure to 35 bar did not have any
impact on the yield of benzyl alcohol ꢀ (entry 6), but increasꢀ
ing further to 55 bar increased the yield of benzyl alcohol to
Table 2. Catalytic hydrogenation of esters using the cobalt
a
catalyst 1.
9
0% (entry 7). Decreasing the hydrogen pressure to 10 bar
only slightly decreased the yield of benzyl alcohol to 40%
Table 1. Optimization of the reaction conditions for hyꢀ
drogenation of benzyl benzoate.
(
a)
rxn
cat.
loading
(mol%)
press
temp
(°C)
yield
(%)
entry
time
h)
(b)
(bar)
(
1
2
3
24
48
6
20
20
20
20
10
35
55
55
55
55
55
55
150
150
150
150
150
150
150
120
80
5
5
5
5
5
5
5
5
5
2
1
0
48
45
17
53
40
54
90
97
52
97
56
1
(c)
4
24
24
24
24
24
24
20
20
20
5
6
7
8
9
1
0
120
120
120
11
1
2
(
a) Reaction conditions: catalyst (0.01 mmol), THF (1mL).
b) Determined by GC with respect to benzyl alcohol. (c) MeOH
as solvent.
(a) Reaction conditions: substate (0.5 mmol), catalyst 1 (2
(
mol%), THF (1.0 mL), H (55 bar), 120 °C, 20 hours. (b) Yields
2
were determined by GC. (c) Product yields are ratios at 100%
2
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conversion. Yields of methanol and ethanol are not reported. (d)
Toluene was used as solvent.
was carried out in the presence of one bar of CO (see SI for
details). The cobalt catalyst precursor 1 decomposed under 1
bar of carbon monoxide at room temperature to form the coꢀ
1
2
3
4
5
6
7
8
9
are generally considered to be more challenging substrates
than aromatic esters, could be hydrogenated to afford the corꢀ
responding aliphatic alcohols. Although ethyl butyrate and
ethyl cyclohexanecarboxylate were reduced to the correspondꢀ
ing alcohols in relatively high yields (entry 5, 7), hydrogenaꢀ
tion of methyl butyrate and methyl cyclohexanecarboxylate
proved lowꢀyielding reactions (entry 4, 6).
cy
F
balt(I) complex [(PNHP )Co(CO) ]BAr (2). The Xꢀray
2
4
structure of complex 2 is shown in Figure 1. Also, no catalytic
reaction was observed when complex 2 was used as a catalyst
instead of complex 1.
Neither complex 2 (by NMR or IR) nor CO (by GC) were
observed, however, during hydrogenation of methyl benzoate.
cy
1
Instead,
PhCOO)(κ ꢀPhCOO)]BAr (3) was isolated after the hydroꢀ
4
a
new cobalt(III) complex [(PNHP )Co(κ ꢀ
Cobalt compound 1 has been reported for the hydrogenation of
2
F
52
1
1
1
1
1
1
1
1
1
1
2
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olefins; therefore, we tested it for hydrogenation of methyl
cinnamate and ethyl cinnamate. As we expected, reduction of
methyl cinnamate gave methyl 3ꢀphenylpropanoate as major
product and 3ꢀphenylpropanol as minor product (entry 8),
while for hydrogenation of ethyl cinnamate, almost all of the
ethyl 3ꢀphenylpropanoate was converted to 3ꢀphenylpropanol
under the same reaction conditions (entry 9). Not surprisingly,
a very low methanol yield (7.5%, entry 10) was detected for
hydrogenation of methyl formate. No 6ꢀhydroxyhexanoic acid
was observed upon hydrogenation of adipic acid monoethyl
ester (entry 11), indicating that the compounc 1 is not compatꢀ
ible with carboxylic acid functionalities.
genation reaction. The Xꢀray structure of complex 3 is shown
in Figure 2. The formation of this complex might explain why
methyl esters have low reactivity compared to the correspondꢀ
ing ethyl and benzyl esters. The ester CH –O bond is cleaved
3
by cobalt and consequently the formation of cobalt benzoate
complex 3 inhibits the ester hydrogenation catalytic cycle.
61
Similar results were published by Chirik, when they used a
bis(imino)pyridineiron compound with methyl acetate or meꢀ
thyl benzoate; exclusive ester CH –O bond cleavage was obꢀ
3
served, while phenyl acetate yielded products from selective
acyl C–OPh bond cleavage. Although ethyl benzoate underꢀ
went ester Et–O bond cleavage rather than acyl C–OEt bond
cleavage in their iron system, the cobalt system displayed the
opposite selectivity with the ethyl ester.
Similar to our findings, Chianese et al. observed that methyl
esters showed low activity compared to the corresponding
ethyl and benzyl esters during hydrogenation with a Ruꢀbased
41
In addition to aliphatic and aromatic esters, biomass derived γꢀ
valerolactone was also examined as a substrate for hydrogenaꢀ
tion. The decrease in hydrogen pressure on the reactor gauge
could be used to monitor the reaction (See SI). When 0.1
mol% of catalyst 1 was employed in the reaction, the hydroꢀ
genation process was finished within 5 h and gave a 98% yield
of 1,4ꢀpentanediol. Upon decreasing the catalyst loading to
catalyst system. They observed that methyl esters display an
intrinsically lower reactivity with their catalyst, as demonstratꢀ
ed by observing substantial increases in the rate of hydrogenaꢀ
tion of methyl decanoate upon addition of increasing amounts
of benzyl alcohol to the reaction. However, this is not the case
with cobalt compound 1. An experiment was conducted where
methyl cyclohexanecarboxylate was hydrogenated in the presꢀ
ence of increasing amounts of benzyl alcohol. If methyl esters
are intrinsically less reactive than ethyl esters, we should obꢀ
serve faster hydrogenation when more benzyl alcohol is addꢀ
ed. However, the data in Table 3 indicates that the yields of
cyclohexylmethanol were decreased when more benzyl alcoꢀ
hol was added to the system, and increased amounts of benzyl
cyclohexanecarboxylate was left. This suggests that the cataꢀ
lyst decomposed during the reaction, which could be attributed
to catalyst poisoning by CO generated from the decarbonylaꢀ
tion of MeOH.
0
.01 mol %, the hydrogenation needed 3 d to complete (1 g
scale), and a TON of 3890 for 1,4ꢀpentanediol was obtained
(Table 4).
Table 3. Effect of added benzyl alcohol on the hydrogenaꢀ
a
tion of methyl cyclohexanecarboxylate
equiv BnOH
added
yield
cꢀhexylmethanol
yield benzyl
cꢀhexanecarboxylate
Figure 1. Xꢀray structure of complex 2 (molecular cation shown,
thermal ellipsoid at 50% probability, hydrogen atoms except for
H1 omitted for clarity). Selected bond distances (Å) and angles
(°): Co1ꢀC1 = 1.726(3), Co1ꢀC2 = 1.804(3), Co1ꢀN1 = 2.071(2),
Co1ꢀP1 = 2.2098(7), Co1ꢀP2 = 2.2106(7), C1ꢀCo1ꢀC2 =
115.47(12), C1ꢀCo1ꢀN1 = 143.67(11), C2ꢀCo1ꢀN1 = 100.86(10),
C1ꢀCo1ꢀP1 = 88.20(8), C2ꢀCo1ꢀP1 = 101.89(8), N1ꢀCo1ꢀP1 =
0
1
26%
25%
15%
0
2%
9%
1
0
a
Reaction performed in THF, with a total solution volume of
.0 mL and 0.5 mmol methyl cyclohexanecarboxylate. Yields
were measured by GC.
1
8
5.02(6), C1ꢀCo1ꢀP2 = 90.99(8), C2ꢀCo1ꢀP2 = 94.38(8), N1ꢀCo1ꢀ
Indeed, we observed that the catalytic reaction was inhibited in
the presence of carbon monoxide. Less than 1% benzyl alcoꢀ
hol was produced when the hydrogenation of benzyl benzoate
P2 = 85.22(6), P1ꢀCo1ꢀP2 = 162.34(3).
3
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Table 4. Catalytic hydrogenation of γꢀValerolactone using
Page 4 of 6
(
a)
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
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3
3
3
3
3
4
4
4
4
4
4
4
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4
4
5
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5
5
5
5
5
5
5
6
the cobalt catalyst 1.
entry Pinit H2 Pfinal
H
rxn
cat.
conv. GC
isol.
2
(
b)
(bar) (bar)
time loading (%) yield yield
(
c)
(mol%)
(%) (%)
98 91.6
40.2 38.9 35.7
1
55
55
32
46
5 h
3 d
0.1 99.8
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
2
0.01
(
a) Reaction conditions: γꢀvalerolactone (10 mmol, 1 g), cataꢀ
Figure 2. Xꢀray structure of complex 3 (molecular cation shown,
thermal ellipsoid at 50% probability, hydrogen atoms except for
H1 omitted for clarity). Selected bond distances (Å) and angles
lyst 1, no solvent, H (55 bar), 120 °C. (b) Inside volume of Parr
2
reactor is 22mL, using ideal gas PV = nRT, we can calculate
about 20 mmol hydrogen was consumed for entry 1, and 8 mmol
hydrogen was consumed for entry 2. (c) See SI for details.
(°): Co1ꢀO3 = 1.908(3), Co1ꢀO1 = 1.909(2), Co1ꢀN1 = 1.962(3),
Co1ꢀO2 = 1.998(2), Co1ꢀP1 = 2.2942(11), Co1ꢀP2 = 2.3031(11),
Co1ꢀC1 = 2.319(4), O3ꢀCo1ꢀO1 = 166.14(10), O3ꢀCo1ꢀN1 =
Scheme 1. Comparison of the reactivity of 1 and 4: hydroꢀ
genation of (a) benzyl benzoate and (b) γꢀvalerolactone.
9
7.32(12), O1ꢀCo1ꢀN1 = 96.54(11), O3ꢀCo1ꢀO2 = 99.17(10), O1ꢀ
Co1ꢀO2 = 66.98(9), N1ꢀCo1ꢀO2 = 163.51(11), O3ꢀCo1ꢀP1 =
9.42(8), O1ꢀCo1ꢀP1 = 91.22(7), N1ꢀCo1ꢀP1 = 86.78(9), O2ꢀ
Co1ꢀP1 = 93.54(7), O3ꢀCo1ꢀP2 = 89.18(7), O1ꢀCo1ꢀP2 =
1.83(7), N1ꢀCo1ꢀP2 = 86.38(9), O2ꢀCo1ꢀP2 = 93.68(7), P1ꢀCo1ꢀ
F
BAr4F
BAr
Me
8
H
4
N
N
Co PCy2
Co PCy2
9
CH SiMe
CH SiMe
2
3
2
3
P2 = 172.78(4), O3ꢀCo1ꢀC1 = 132.40(11), O1ꢀCo1ꢀC1 =
33.74(9), N1ꢀCo1ꢀC1 = 130.28(12), O2ꢀCo1ꢀC1 = 33.24(9), P1ꢀ
Co1ꢀC1 = 92.68(8), P2ꢀCo1ꢀC1 = 93.49(8).
1
4
(
a)
O
catalyst
To clarify the potential participation of the NꢀH moiety of the
2
mol%
cy
O
OH
PNHP pincer ligand in catalysis, reactivities of 1 and Nꢀ
+
2H
2
2
5
7
THF
(55 bar)
methyl derivative 4 were compared. Hanson and coꢀworkers
have reported that complex 4 displayed no catalytic activity in
o
1
20 C
with 1: 97%
with 4: 91%
hydrogenation of acetophenone (with 1 atm H pressure, 2
2
mol% catalyst loading), even upon increasing the temperature
to 60 °C (c.f., 98% of 1ꢀphenylethanol was detected by GCꢀ
MS when acetophenone was hydrogenated using 2 mol% of 1
(
b)
catalyst
OH
O
0.1 mol%
within 24 h at 25 °C and under 1 atm H ). Upon increasing the
O
2
+
(
2H2
55 bar)
OH
o
hydrogen pressure to 4 atm and using 10 mol% of 4, ca. 60%
120 C
conversion of acetophenone to 1ꢀphenylethanol was observed
with 1: 98%
with 4: 93%
57
after 4 days at 60 °C. These results point toward a bifuncꢀ
tional hydrogenation mechanism of ketones at 25 °C with low
hydrogen pressures. Since high hydrogen pressure (55 bar)
and high reaction temperature (120 °C) were required for hyꢀ
drogenation of esters with complex 1, the catalytic activity of
complex 4 was tested under the same reaction conditions; simꢀ
ilar hydrogenation performance was observed (Scheme 1). The
results show that 4 performs almost as well as 1, suggesting
that cobalt compound 1 hydrogenates carboxylic acid esters
without the involvement of the NꢀH moiety.
of dihydrogen generates an acidic hydrogen atom that can
protonolyze the hemiacetal, generating one molecule of alcoꢀ
hol plus an Oꢀbound aldehyde. Insertion of the aldehyde C=O
bond into the CoꢀH bond give an alkoxide that can again coorꢀ
dinate dihydrogen leading to protonation and loss of a second
molecule of alcohol. None of these reactions use the N–H
moiety. With methyl esters, it is possible that the Co can unꢀ
dergo an S 2 attack on the methyl group to eject a carboxylate,
leaving an unstable methyl hydride that eliminates methane.
The carboxylate could then trap the metal to produce ultimateꢀ
ly bisꢀcarboxylate 3.
I
N
The mechanism of the ester reduction is complex, in that sevꢀ
eral intermediates must exist on the way to the alcohol prodꢀ
uct. In addition, the mechanism must take into account two
important observations: (1) the NꢀMe complex 4 works almost
as well as NꢀH complex 1, and (2) methyl esters are poor subꢀ
strates, giving reduced yields of products. The isolation of bisꢀ
carboxylate 3 strongly suggests that methyl esters are cleaved
It is also worth pointing out that this system works without
additives – i.e., no base is required. This stands in contrast to
Milstein’s (PNN)Co catalyst that works only with added base.
The base is responsible for formation of an ester enolate that
48
at the O–CH bond to produce the RCO ligands in this prodꢀ
3
2
undergoes subsequent cleavage and hydrogenation.
uct, rendering the catalyst inactive. Scheme 2 shows a mechaꢀ
nism consistent with the above requirements, and is based on
62
the classical Schrock−Osborn (innerꢀsphere) mechanism.
Here, the ester carbonyl undergoes insertion into a cobaltꢀ
hydride bond to give a metalꢀbound hemiacetal. Coordination
4
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(
3) Rieke, R. D.; Thakur, D. S.; Roberts, B. D.; White, G. T., J. Am. Oil
Scheme 2. Proposed mechanism for ester reduction.
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1
1
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1
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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
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6
7
8
9
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(
(
(
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(
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(
Conclusions
(
In summary, we have demonstrated that the inexpensive,
earthꢀabundant molecular cobalt pincer complex 1 is an effiꢀ
cient catalyst precursor for the hydrogenation of carboxylic
acid esters to the corresponding alcohols. In addition to the
aliphatic and aromatic esters, biomass derived γꢀvalerolactone
can be reduced to 1,4ꢀpentanediol in gram scale and with a
TON of 3890. Methyl esters have lower reactivity compared to
T., J. Am. Chem. Soc. 2011, 133, 4240ꢀ4242.
(22) Sun, Y. S.; Koehler, C.; Tan, R. Y.; Annibale, V. T.; Song, D. T.,
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(24) Zhang, J.; Balaraman, E.; Leitus, G.; Milstein, D., Organometallics
2
011, 30, 5716ꢀ5724.
25) Carpenter, I.; Eckelmann, S. C.; Kuntz, M. T.; Fuentes, J. A.;
(
the corresponding ethyl esters, most likely because CH –O
cleavage leads to formation of a bisꢀcarboxylate derivative.
3
France, M. B.; Clarke, M. L., Dalton Trans. 2012, 41, 10136ꢀ10140.
(26) Clarke, M. L., Catal. Sci. Technol. 2012, 2, 2418ꢀ2423.
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(28) Junge, K.; Wendt, B.; Westerhaus, F. A.; Spannenberg, A.; Jiao, H.
ASSOCIATED CONTENT
J.; Beller, M., Chem-Eur. J. 2012, 18, 9011ꢀ9018.
(29) Kuriyama, W.; Matsumoto, T.; Ogata, O.; Ino, Y.; Aoki, K.;
Tanaka, S.; Ishida, K.; Kobayashi, T.; Sayo, N.; Saito, T., Org. Process
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Supporting Information. Crystallographic data for complexes 2
and 3. This material is available free of charge via the Internet at
http://pubs.acs.org. (CCDC# 1533491ꢀ1533492)
(
(
30) Spasyuk, D.; Gusev, D. G., Organometallics 2012, 31, 5239ꢀ5242.
31) Spasyuk, D.; Smith, S.; Gusev, D. G., Angew. Chem., Int. Ed. 2012,
AUTHOR INFORMATION
51, 2772ꢀ2775.
Corresponding Author
(32) Liu, C.; Xie, J. H.; Li, Y. L.; Chen, J. Q.; Zhou, Q. L., Angew.
Chem., Int. Ed. 2013, 52, 593ꢀ596.
*Eꢀmail: jones@chem.rochester.edu
(33) O, W. W. N.; Morris, R. H., Acs. Catal. 2013, 3, 32ꢀ40.
Author Contributions
(34) Spasyuk, D.; Smith, S.; Gusev, D. G., Angew. Chem., Int. Ed. 2013,
2, 2538ꢀ2542.
5
The manuscript was written through contributions of all authors.
All authors have given approval to the final version of the manuꢀ
script.
Notes
(35) Westerhaus, F. A.; Wendt, B.; Dumrath, A.; Wienhofer, G.; Junge,
K.; Beller, M., ChemSusChem 2013, 6, 1001ꢀ1005.
(36) Ziebart, C.; Jackstell, R.; Beller, M., ChemCatChem 2013, 5, 3228ꢀ
3
231.
37) Junge, K.; Wendt, B.; Jiao, H. J.; Beller, M., ChemCatChem 2014,
The authors declare no competing financial interest.
(
6
, 2810ꢀ2814.
ACKNOWLEDGMENT
(38) Filonenko, G. A.; Aguila, M. J. B.; Schulpen, E. N.; van Putten, R.;
Wiecko, J.; Muller, C.; Lefort, L.; Hensen, E. J. M.; Pidko, E. A., J. Am.
Chem. Soc. 2015, 137, 7620ꢀ7623.
Acknowledgment is made to the U.S. Department of Energy Ofꢀ
fice of Science, Basic Energy Sciences Grant #DEꢀFG02ꢀ
86ER13569 for their support of this work.
(39) Tan, X. F.; Wang, Y.; Liu, Y. H.; Wang, F. Y.; Shi, L. Y.; Lee, K.
H.; Lin, Z. Y.; Lv, H.; Zhang, X. M., Org. Lett. 2015, 17, 454ꢀ457.
(40) Brewster, T. P.; Rezayee, N. M.; Culakova, Z.; Sanford, M. S.;
Goldberg, K. I., Acs. Catal. 2016, 6, 3113ꢀ3117.
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