Chromium- and Cobalt-Catalyzed, Regiocontrolled Hydrogenation of Polycyclic Aromatic Hydrocarbons: A Combined Experimental and Theoretical Study

Article abstract of DOI:10.1021/jacs.9b03328

Polycyclic aromatic hydrocarbons are difficult substrates for hydrogenation because of the thermodynamic stability caused by aromaticity. We report here the first chromium- and cobalt-catalyzed, regiocontrolled hydrogenation of polycyclic aromatic hydrocarbons at ambient temperature. These reactions were promoted by low-cost chromium or cobalt salts combined with diimino/carbene ligand and methylmagnesium bromide and are characterized by high regioselectivity and expanded substrate scope that includes tetracene, tetraphene, pentacene, and perylene, which have rarely been reduced. The approach provides a cost-effective catalytic protocol for hydrogenation, is scalable, and can be utilized in the synthesis of tetrabromo- and carboxyl-substituted motifs through functionalization of the hydrogenation product. The systematic theoretical mechanistic modelings suggest that low-valent Cr and Co monohydride species, most likely from zerovalent transition metals, are capable of mediating these hydrogenations of fused PAHs.

Full text of DOI:10.1021/jacs.9b03328

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Article
Chromium- and Cobalt-Catalyzed, Regiocontrolled
Hydrogenation of Polycyclic Aromatic Hydrocarbons:
A Combined Experimental and Theoretical Study
Bo Han, Pengchen Ma, Xuefeng Cong, Hui Chen, and Xiaoming Zeng
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 10 May 2019
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Journal of the American Chemical Society
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Chromium- and Cobalt-Catalyzed, Regiocontrolled Hydrogenation
of Polycyclic Aromatic Hydrocarbons: A Combined Experimental and
Theoretical Study
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Bo Han,†,§,¶ Pengchen Ma, ¶ Xuefeng Cong,ѱ Hui Chen,*, and Xiaoming Zeng
*,†,‡
#,
#
†Frontier Institute of Science and Technology, Xi’an Jiaotong University, Xi’an 710054; ‡College of Chemistry, Sichuan University,
Chengdu 610064, China; #Beijing National Laboratory for Molecular Sciences (BNLMS), CAS Key Laboratory of Photochemistry,
CAS Research/Education Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese Academy of Sciences,
Beijing 100190, China; §Shaanxi Key Laboratory of Chemical Reaction Engineering, College of Chemistry & Chemical Engineering,
Yan'an University, Yan'an 716000, China; ѱDepartment of Chemistry, Northeast Normal University, Changchun 130024, China
ABSTRACT: Polycyclic aromatic hydrocarbons are difficult substrates for hydrogenation because of the thermodynamic stability
caused by aromaticity. We report here the first chromium- and cobalt-catalyzed, regiocontrolled hydrogenation of polycyclic
aromatic hydrocarbons at ambient temperature. These reactions were promoted by low-cost chromium or cobalt salts combined
with diimino/carbene ligand and methylmagnesium bromide, and are characterized by high regioselectivity and expanded
substrate scope that includes tetracene, tetraphene, pentacene and perylene, which have rarely been reduced. The approach
provides a cost-effective catalytic protocol for hydrogenation, is scalable, and can be utilized in the synthesis of tetrabromo- and
carboxyl-substituted motifs through functionalization of the hydrogenation product. The systematic theoretical mechanistic
modelings suggest that low-valent Cr and Co monohydride species, most likely from zero-valent transition metals, are capable of
mediating these hydrogenations of fused PAHs.
1. INTRODUCTION
Scheme 1. Transition-Metal-Catalyzed Regioselective
Hydrogenation of PAHs
Selective hydrogenation is among the most powerful
reactions in modern chemistry because of its central
importance in the creation of pharmaceuticals and
fundamental feedstock chemicals.1,2 Methods that are used
in hydrogenation commonly involve unsaturated compounds
such as alkynes, olefins, imines, ketones, and heterocycles.3–7
Compared with single arenes, polycyclic aromatic
hydrocarbons (PAHs) have extended π-conjugated systems
and the aromaticity of these motifs is usually not completely
destroyed in hydrogenation (Scheme 1a).8 Arenophilic
precious metals such as Ru, Rh, Pd, and Pt nanoparticles
mediated by heterogeneous catalysis dominate the
hydrogenation of PAHs.9 In contrast, homogeneous
transition-metal catalysis has rarely been developed for PAH
hydrogenation.10,11 Given that multiple fused aromatic
carbocycles are present in one PAH molecule, regioselectivity
has long been a prominent issue, and hydrogenation usually
leads to mixed products through the reduction of different
carbocycles (Scheme 1b).9,11a–c Notably, PAHs that contain
four, five, and even six aromatic carbocycles have rarely been
hydrogenated.9d,g,10b,11d Interestingly, these motifs have
generated immense concern because of their negative health
impacts as pervasive environmental pollutants; such
compounds are often produced from the combustion of fossil
fuels, traffic exhaust, and wood smoke.12 Regiocontrolled
hydrogenation of PAHs would help degrade these harmful
compounds and create valuable feedstocks, which are usually
difficult to make by common synthetic protocols.
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Journal of the American Chemical Society
Page 2 of 11
In recent years, the use of earth-abundant, low-cost, first- Based on previous findings that low-valent chromium
1
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3
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5
6
7
8
row metal catalysts to replace precious metal catalysts in
developing cost-effective hydrogenation protocols has
attracted broad interest.13,14 Tremendous advances have
species could be formed in situ by reaction of a Cr or Co salt
with organomagnesium reagent,19–22 we postulated that such
reactive species may chelate with fused aromatic carbocycles
through -coordination (A, Scheme 1c),23 thereby facilitating
a dearomatic hydride-additive reaction. We commenced our
study by choosing anthracene to optimize the hydrogenation
conditions. Using 10 mol % of CrCl3 and phenylmagnesium
bromide, almost no hydrogenation occurred (Table 1, entry
1). The introduction of an N-heterocyclic carbene ligand
bearing IPr or CAAC into the system allowed the
hydrogenation to proceed at room temperature, forming
partial hydrogenation product 2a in more that 30% yield
(entries 3 and 4).24 1,2-Diimino ligand L1, L2, or L3 combined
with methylmagnesium bromide gave the same result,
leading to 2a in 92% yield (entry 7). Notably, the
hydrogenation proceeded with high regioselectivity, with
one of terminal carbocycles of anthracene being reduced to
give 2a as nearly the sole product. The use of 1.0 equiv of
MeMgBr in the hydrogenation led to a decrease in the
conversion of 1a to 74% (see Supporting Information). At
present, we cannot comment definitively regarding the
reason for the use of large amount of MeMgBr for efficient
catalyst activation. In addition to activation of the
precatalyst,25 one possible role of the extra Grignard that
been
achieved
in
cobalt-
and
iron-catalyzed
hydrogenation.15,16 However, hydrogenation of PAHs using
these inexpensive metal catalysts has been rather
limited.10b,17 To our knowledge, there is only one report of a
hydrogenation reaction that was catalyzed by the group 6
metal chromium, appearing at the early of the 1960s.18 Its
reactivity for hydrogenation remains largely unknown.
Herein, we report the first chromium- and cobalt-catalyzed
hydrogenation of PAHs that was enabled by low-cost metal
salts combined with diimino/carbene ligand and
organomagnesium reagent (Scheme 1c). These catalyst
protocols can be used to control the hydrogenation of one or
two terminal aromatic carbocycles of PAHs, thereby
achieving high regioselectivities.
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2. RESULTS AND DISCUSSION
Table 1. The Effect of First-Row Metal Salts and Ligands on
the Hydrogenation of Anthracenea
Scheme 2. Chromium-Catalyzed Hydrogenation of PAHs
by Regioselective Reduction of One Terminal Carbocyclea
entry
1b
metal salt
CrCl3
ligand
R
2a (%)
trace
21
3a (%)
ndc
ndc
ndc
ndc
none
Ph
2b
3b
4b
5b
6b
7d
8d
9d
CrCl3
IPr·HCl
IPr·HCl
CAAC·HCl
2,2-bpy
L1
Ph
CrCl3
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
Me
37
CrCl3
30
ndc
CrCl3
ndc
CrCl3
56
trace
trace
trace
trace
46
CrCl3
L1/L2/L3
L1
92e
91
94 (89)f
CrCl2
Cr(acac)3
CoCl2
L1
10g
11g
12g
13g
14g
15f,g
16g
17g
L1
28
Co(acac)3
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
FeCl2
L1
14
60
L1
6
79
CAAC·HCl
IPr·HCl
IPr·HCl
IPr·HCl
IPr·HCl
19
ndc
43
96 (89)e
13
76
ndc
ndc
ndc
ndc
NiBr2
aConditions: 1a (0.2 mmol), metal salt (0.044 mmol), ligand
(0.044 mmol), RMgBr (0.3 mmol), THF, and H2 (3.5 Mpa), rt,
24 h. 1H NMR yield using 1,3,5-trimethoxybenzene as internal
standard. bCrCl3/ligand (0.02 mmol). cNot detected. dH2 (5
aConditions: 1 (0.2 mmol), CrCl3 (0.044 mmol), L1 (0.044
mmol), MeMgBr (0.3 mL, 1 M in THF), H2 (5 Mpa), and THF,
rt, 24 h. Isolated yield. bYield of compound 3. cL3 (0.044
mmol) was used. dMeMgBr (0.4 mmol), H2 (6 Mpa), 48 h.
f
Mpa). eIsolated yield. Hg(0) (100 equiv) was added. gH2 (8
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Mpa) for 48 h.

Page 3 of 11
Journal of the American Chemical Society
could be envisioned is serving as poison scavenger (e.g. trace retains the phenyl substituents intact (2d–n). Terminal
1
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7
8
amount of moisture and dioxygen that may deactivate metal
catalyst) for keeping the reactivity of the active species
during hydrogenation. CrCl2 and Cr(acac)3 also showed high
aromatic carbocycles without substituents were better
reduced compared with the substituted ones (2o–r).
Strikingly, two terminal carbocycle rings of tetracene were
reduced, allowing the synthesis of 1,2,3,4,7,8,9,10-
octahydrotetracene (2s). In contrast, hydrogenation of
tetraphene formed 8,9,10,11-tetrahydrotetraphene 2t in 89%
yield. Because hydrogenation of the central ring in pentacene
is more exothermic than reduction of the outer ones, the
central ring was hydrogenated to give 6,13-
dihydropentacene (2u).26 Perylene was amenable to the Cr-
catalyzed hydrogenation, whereby two carbocycles (A and D)
were reduced (2v).
reactivity for the hydrogenation (entries
8 and 9).
Interestingly, the replacement by CoCl2 led to two-terminal
ring-reduced octahydroanthracene 3a as the major product
(entry 10). N-Heterocyclic carbene of IPr combined with
Co(acac)2 and MeMgBr increased the hydrogenation rate,
forming 3a as the sole product in excellent yield (entry 14).
However, FeCl2 and NiBr2 did not promote the
hydrogenation (entries 16 and 17).
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The scope of the chromium-catalyzed hydrogenation of
PAHs was then examined (Scheme 2). Introducing methyl
group into the C-9 and C-10 positions of anthracene had no
effect on the hydrogenation; one-terminal carbocycle-
reduced compounds 2b and 2c were obtained in excellent
yields. Noted that using L3 as ligand gave better result than
L2 in the reaction of forming 2c, indicating that the R
substituent in diimino ligand affects the catalytic activity of
chromium in hydrogenation (see Supporting Information). As
expected, reaction with 9-phenyl-containing anthracenes
Inspired by these results, we then probed the efficiency of
the cobalt-catalyzed hydrogenation of PAHs for the buildup
of two-terminal carbocycle-reduced motifs. Hydrogenation
of anthracenes containing aliphatic or aromatic scaffold at
the C-9 position resulted in the products 3b–h in
preparatively useful yields (Scheme 3). In most cases, only
trace amounts of the mono-terminal ring-reduced
compounds were detected. The reaction of sterically
hindered 9,10-dimethyl- or phenyl-substituted anthracenes
occurred smoothly, with forming octahydroanthracenes 3i
and 3j. Two terminal carbocycles in phenanthrene were
hydrogenated at relatively high temperature (3k).
Interestingly, hydrogenation of tetracene led to an
unexpected compound 3l by reducing one central and one
terminal carbocycle together with 2s. The reaction with
tetraphene hydrogenated the carbocycles of A and D to form
3m with high regioselectivity. Furthermore, 4,5,9,10-
tetrahydropyrene can be prepared by reduction of the B and
D carbocycles of pyrene (3n). Importantly, three carbocycles
including A, C, and E in pentacene can be reduced (3o). In
contrast, the reaction with fused perylene hydrogenated the
A and D carbocycles to form 2v. The protocol can be utilized
for the regioselective hydrogenation of bianthracene for the
synthesis of four-terminal carbocycle-reduced compound 3p.
Scheme 3. Cobalt-Catalyzed Hydrogenation of PAHs by
Regiocontrolled Reduction of Two Terminal Carbocyclesa
The kinetic behavior associated with hydrogenation of
anthracene was explored. By using chromium catalysis, the
hydrogenation proceeded rapidly within 2 h to form 2a in
80% yield (Figure 1a). The reaction profile for cobalt catalysis
suggested that hydrogenation of anthracene took place
quickly to initially form 2a in 87% yield within 0.25 h, which
was consumed by continuous hydrogenation of the second
terminal carbocycle to furnish 3a in 66% yield after 1 h
(Figure 1b). Introducing a large amount of Hg(0) into the
system did not inhibit the Cr- or Co-catalyzed hydrogenation
of 1a (Table 1, entries 9 and 15). The chromium- and cobalt-
catalyzed hydrogenations are scalable and can be performed
on 10 mmol scale to give 71% yield of 2a and 85% yield of 3a,
respectively (Scheme 4a). Importantly, the hydrogenation
product 3a can be modified, offering a route to prepare
aConditions: 1 (0.2 mmol), Co(acac)2 (0.044 mmol), IPr·HCl
(0.044 mmol), MeMgBr (0.3 mL, 1 M in THF), H2 (8 Mpa), and
b
c
THF, rt, 48 h. Isolated yields. Yield of compound 2. Trace
amount of 2 was detected. d60 C. The regioisomer ratio
e
was determined by 1H NMR analysis.
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Figure 1. Reaction profile for hydrogenation of anthracene.
(a) Chromium catalysis. (b) Cobalt catalysis.

Journal of the American Chemical Society
Page 4 of 11
tetrabromo and carboxyl-substituted derivatives 4 and 5 via
bromination and oxidation (Scheme 4b).
Scheme 4. Gram-Scale Hydrogenation
Transformation of 3a
pressure of hydrogen (Figures 3b and 3c). The initial reaction
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and
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Figure 3. Kinetic profile for Cr-catalyzed hydrogenation
of 1a. (a) Initial reaction rate against the concentration of
1a. (b) Initial reaction rate against the pressure of
hydrogen. (c) Initial reaction rate against the
concentration of precatalyst of Cr(acac)3/L1. (d) Initial
Because of the difficulty in isolation of catalytically relevant
transition metal intermediates that are responsible for the
hydrogenation of PAHs, alternative strategy by the method
of continuous variation (“Job plots”) was utilized to elucidate
catalyst stoichiometry of Cr or Co with the related ligand of
diketimine L1 or IPr. As shown in Figure 2, conditions C1 and
C2 fixed the stoichiometries of CrCl3 and Co(acac)2 with
MeMgBr, and varied their mole fraction against the ligands of
L1 and IPrHCl, respectively. Both of these conditions gave
maximum conversion to the hydrogenated product 2a or 3a
in mole fraction of 0.5, indicating that a 1:1 stoichiometry of
chromium or cobalt versus the related ligand of L1 or IPr can
be considered for the reactive species in the hydrogenation.
reaction
rate
against
the
concentration
of
rate of showed a positive response to [MeMgBr] at low
concentration (Figure 3d), but exhibiting saturation
a
behavior and reaching a plateau at high concentration (0.17
M). When a similar analysis was carried out with Co catalysis,
the initial reaction rates (Δ[3a]/Δt) against the initial
concentrations of 1a, the precatalyst of Co(acac)2/IPr and
hydrogenation pressure showed clear positive correlations,
indicating that first-order dependence of the initial rates on
the concentration of anthracene, the precatalyst of
Co(acac)2/IPr and hydrogen pressure can be considered
(Figures 4a–c). Similarly, a saturation behavior was observed
for the initial rate of the hydrogenation with MeMgBr when
its concentration became higher than ~0.13 M (Figure 4d).
To gain insight into the mechanistic details associated with
the hydrogenation, we studied the dependence of the initial
reaction rate on the substrate with the precatalyst of
Cr(acac)3/L1 or Co(acac)2/IPr in 1:1 stoichiometric ratio. The
initial rate (Δ[2a]/Δt) against the initial concentration of 1a
ranging from 0.04 to 0.26
M showed a zero-order
In order to get a better mechanistic understanding for the
hydrogenation of fused PAHs reported in this work, density
functional theory (DFT) modelings were carried out. The first
issue to be clarified is the identity of the metal hydride active
species possibly involved in the hydrogenation reactions. The
reductive organomagnesium reagent used in the current
catalytic systems makes it possible to form low-valent metal
dependence of the initial rate on the concentration of 1a
under Cr catalysis, indicating that anthracene may not be
involved in the rate-determining step of the reaction or at
least in the early stage of the hydrogenation (Figure 3a). In
contrast, we observed
a positive response to the
concentration of Cr(acac)3/L1 (0.009–0.026 M) and pressure
of hydrogen (3–7 MPa), indicating a first-order dependence
of the initial rate on the concentration of Cr(acac)3/L1 and
Figure 4. Kinetic profile for Co-catalyzed hydrogenation of
1a in the formation of 3a. (a) Initial reaction rate against
the concentration of 1a. (b) Initial reaction rate against the
pressure of hydrogen. (c) Initial reaction rate against the
concentration of precatalyst of Co(acac)2/IPr·HCl. (d) Initial
reaction rate against the concentration of methyl Grignard
reagent.
ACS Paragon Plus Environment
Figure 2. Job plots for Cr- and Co-catalyzed
hydrogenation of anthracene (1a).

Page 5 of 11
Journal of the American Chemical Society
two-coordinate structure (Scheme 5a, b, c); (b) with one
Scheme 5. Coordination Number Preference of Low-
valent Cr-L1 and Co-IPr Systems Explored by Calculated
Ligand Binding Thermodynamics (in kcal/mol)a
1
2
3
4
bidentate L1 ligand coordinated, both Cr(I) and Cr(0) can
have two more ligands at most to form four-coordinate
structure, which is more favorable in energy than three-
coordinate structure, especially for the Cr(I) system (Scheme
5e).
THF
THF
THF
THF
THF
0
0
Co
0
Co
IPr
THF
(a)
IPr
IPr Co THF
G = 6.8
5
THF
6
7
8
9
With these coordination preference of the low-valent Cr-L1
and Co-IPr systems in hand, we then systematically
investigated the thermodynamics of their hydride formations
from H2. As shown in Scheme 6a (reactions 1a and 3a), for the
Cr system, generating dihydride species via oxidative
addition (OA) of H2 to neither Cr(0) nor Cr(I) is
thermodynamically favorable. On the contrary, as shown in
reactions 2a and 4a of Scheme 6a, transmetalation from
Grignard MeMgBr to Cr to form methyl Cr complex, and then
producing monohydride species via hydrogenolysis of the
methyl Cr complex, either Cr(0) or Cr(I), is
thermodynamically accessible. Therefore, for the low-valent
Cr-L1 system of either Cr(0) or Cr(I), monohydride species
THF
THF
THF
CH3
CH3
THF
0
0
0
(b)
(c)
IPr
IPr
Co
IPr
IPr
Co
THF
THF
IPr Co
CH3
G = 5.0
THF
THF
CH3
10
11
12
13
14
15
16
17
18
19
20
21
CH3
THF
I
I
I
Co
Co
IPr Co CH3
G = 3.9
THF
THF
THF
N
N
THF
CH3
0
Cr
N
N
THF
N
N
0
Cr
Cr0 CH3
(d)
G = – 1.2
N
CH3
THF
N
THF
THF
N
N
THF
CH3
I
N
N
THF
CH3
N
N
I
I
Cr
(e)
Cr
Cr CH3
L1
G = – 12.8
THF
seems
a reasonable candidate for active species in
aRed cross means that ligand (THF) cannot coordinate to the
metal center.
hydrogenation of fused PAHs. Similar to the Cr-L1 system, as
shown in Scheme 6b, the low-valent Co-IPr system also bears
thermodynamically accessible transmetalation from
Grignard MeMgBr, which combined with the following
hydrogenolysis, tends to form monohydride species
(reactions 2b and 4b) for both Co(0) and Co(I).
species in situ from chromium and cobalt salts. Some
previous work supported generation of Cr(0) and Co(0)
species under such reductive condition.19,20,27 The formation
of active Cr or Co species in a different oxidation state after
the addition of methyl Grignard was observed by X-ray
photoelectron spectroscopy (XPS) analysis (see Supporting
Information for details). In addition, here we take Cr(I) and
Co(I) species also into consideration for comparative purpose.
Our experiments of continuous variation for speciation of
catalyst have confirmed that the coordination ratios of the
added ligand (IPr/L1) to the corresponding metal (Co/Cr) are
both 1:1. Based on these results, to know coordination
number preference of the Cr and Co systems, the additional
DFT calculations summarized in Scheme 5 further indicate
that: (a) with one monodentate IPr ligand already
coordinated, both Co(0) and Co(I) can have two more ligands
(Me or THF) at most, but favoring one more only to form
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After obtaining the thermodynamically accessible
candidates of the active low-valent metal hydride species, we
next explored their reactivity towards the hydrogenation of
fused PAHs. For this purpose, anthracene was selected as the
hydrogenation substrate. Extensive calculations were carried
out to search for reaction pathways of hydrogenation of the
first C=C double bond on the terminal aromatic carbocycle of
anthracene, and the corresponding results for the two
chromium monohydride are shown in Figure 5. We can see
(a)
H
N
N
N
C0r
G
(kcal/mol)
H
H
N
H
C
N
N
Cr0
H
H3
H
15.2
H
N
N
L1
H
0
THF
H
5.2
Cr
H2
4.5
CH4
0.0
N
H2
C0r
Scheme 6. Calculated Thermodynamics (in kcal/mol) of
Transmetalation and Metal Hydride Formation from
Reactions of Grignard reagent and H2 with the Low-valent
(a) Cr-L1 System, (b) Co-IPr System
-1.1
H2
TSCD
quintet
N
CH3
TSBC
N
N
THF
0
Cr
-12.3
-15.0
D
C0r
-18.4
CH3
C
B
N
N
H
C0r
H
H
N
N
H
N
0
Cr
H
H
H
H
(a)
N
THF
N
N
H
II
C0r
N
G = 18.2
(1a)
H
H2
THF
Cr
+
N
N
+
MeMgBr
G = -4.3
THFMgBr
N
THF
THF
-
-
N
N
THF
H
N
N
THF
CH3
(b)
C0r
(2a)
G = -19.6
H2
C0r
H
CH4
H
+
+
+
+
N
I
H
L1
Cr
G
(kcal/mol)
H
H
N
N
N
I
+
H
+
H
Cr
C
N
N
H
N
N
THF
THF
III
I
H3
21.3
H
(3a)
(4a)
N
H
G = 48.2
G = -18.4
I
Cr
H
2
THF
CH4
Cr
H
+
MeMgBr
G = -8.1
THFMgBr
Cr
14.0
THF
N
THF
10.1
CH4
H2
5.6
6.5
H2 TSCD(I)
N
N
THF
CH3
N
N
THF
H
I
I
H2
N
N
I
0.0
H2
Cr
Cr
+
Cr
D(I)
TSBC(I)
quartet
CH3
-6.1
H
N
I
H
-11.5
H
N
N
THF
Cr
I
(b)
H
B(I)
H
H
Cr
N
G  -9.8
G = -16.2
G  4.0
C(I)
II
0
(1b)
(2b)
(3b)
(4b)
H
H
CH3
H2
H2
H2
H2
N
THF
CH4
THF
CH4
+
+
+
+
IPr Co
H
I
IPr Co THF
+
+
+
+
MeMgBr
G = -9.7
THFMgBr
N
N
I
Cr
H
Cr
N
-
-
0
0
IPr Co
H
IPr Co CH3
+
+
I
I
IPr
Co H2
IPr Co THF
MeMgBr
G = -17.4
THFMgBr
Figure 5. Calculated reaction profiles for hydrogenation of
anthracene mediated by monohydride intermediate in the low-
valent Cr-L1 system with (a) Cr(0) and (b) Cr(I) center.
I
IPr CoI CH3
G = -17.4
IPr Co
H
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that the Cr(0) and Cr(I) hydrides share similar pathways in
Our extensive calculations indicate that the kinetically most
1
2
3
4
5
6
7
8
favorable mechanism of anthracene hydrogenation is
mediated also by Co(0) monohydride species, as shown in
Figure 6. After generation of the monohydride species E
from hydrogenolysis of methyl Co(0) species, migratory
insertion of C=C of anthracene into Co-H then occur to
produce the semi-hydrogenated intermediate F, which only
needs to overcome a small effective barrier of 7.0 kcal/mol
via TSEF. From F, the second hydrogenolysis process occurs
via TSFG to generate the C=C hydrogenated product, with a
barrier of 5.6 kcal/mol. Thus, similar to the Cr(0) system
H
(a)
H
0
IPr
Co
G
(kcal/mol)
II
0
H3C
Co IPr
Co IPr
16.0
H
H
H
H
H2
H
H
H
CH4
0.0
doublet
H3C C0o
-9.2
-10.6
H2
TSEF
IPr
TSFG
-16.2
E
C0o
-16.2
F
9
0
Co IPr
-31.4
IPr
H
H
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
G
H
0
(Figure 5a), the first incorporation of
H into C=C of
Co IPr
H
anthracene is slightly harder than the second one. Compared
to the calculated pathway of Co(0) hydride species shown in
Figure 6a, our calculations on Co(I) hydride species (Figure 6b)
show that the corresponding pathway is kinetically less
favorable, by bearing higher reaction barriers of 19.4 and
21.9 kcal/mol for the first and second H transfer processes.
Therefore, our calculations suggest that hydrogenation of
fused PAHs by the Co-IPr system is more likely to be
mediated by cobalt(0) hydride species formed from H2
hydrogenolysis with zero-valent cobalt species. Importantly,
the smaller barriers (7.0 and 5.6 kcal/mol) of the most
favorable reaction pathway for the Co-IPr system (Figure 6a)
in comparison with those (17.3 and 16.8 kcal/mol) of the most
favorable reaction pathway for Cr-L1 system (Figure 5a),
suggest that the Co-IPr system is more reactive than the Cr-
L1 system in hydrogenation of fused PAHs. This trend is
consistent with our experimental finding of higher
hydrogenation reactivity of the Co system than the Cr system,
therefore lending more credence to the current theoretical
modelings.
H
H
H
H
H
(b)
H
CoI IPr
I
I
Co IPr
IPr
Co
G
(kcal/mol)
H
H3C
H
H
H
H
H
21.5
H
H2
9.5
TSFG(I)
CH4
2.0
0.0
H2
-12.4
TSEF(I)
triplet
I
IPr
H3C Co
-16.5
-17.4
F(I)
I
Co IPr
G(I)
E(I)
I
I
IPr
Co
H
Co IPr
H
H
H
H
H
H
Figure 6. Calculated reaction profiles for hydrogenation of
anthracene mediated by monohydride intermediate in the
low-valent Co-IPr system with (a) Co(0) and (b) Co(I) center.
anthracene hydrogenation. Taking the Cr(0) system as an
example, hydrogenolysis of methyl Cr complex could readily
render three-coordinate chromium monohydride species B,
with activation barrier of 15.2 kcal/mol in the Cr(0)-L1 system
(note that binding of anthracene to Cr before hydrogenolysis
of methyl group is unfavorable in reaction because H2 would
then dissociate from metal center). Migratory insertion of
C=C of anthracene substrate into Cr-H then occur via TSBC, to
overcome an effective barrier of 17.3 kcal/mol, resulting the
semi-hydrogenated intermediate C. The C=C hydrogenation
is accomplished by the second hydrogenolysis of C, with a
barrier 16.8 kcal/mol via TSCD. Comparing Cr(0) and Cr(I)
reaction pathways depicted in Figure 5a and 5b, it is clear
that Cr(0) is much more reactive than Cr(I), due to the much
higher reaction barrier (25.5 kcal/mol) for the second
hydrogenolysis process in the Cr(I) system. Therefore, our
computational results suggest that hydrogenation of fused
PAHs by the Cr-L1 system is more likely to be mediated by
zero-valent chromium hydride species.
3. CONCLUSIONS
In summary, we have developed efficient chromium and
cobalt catalyst systems for the hydrogenation of fused PAHs
to give partially saturated compounds, by regiocontrolled
reduction of one or two terminal aromatic carbocycles. Low-
cost chromium and cobalt salts combined with
diimino/carbene ligand and methylmagnesium bromide
allowed the hydrogenation to proceed effectively at ambient
temperature. The approach provides a cost-effective method
for catalytic hydrogenation and can be used to address
regioselectivity issues associated with hydrogenation of
PAHs such as substituted anthracenes, tetracene, tetraphene,
pentacene, perylene, and bianthracene. The systematic
theoretical modelings imply that low-valent Cr and Co
monohydride species, most likely from zero-valent transition
metals, are capable of mediating these hydrogenation of
fused PAHs.
Notably, based on the most favorable pathway in Figure 5a,
the experimental regioselectivity can be reproduced. For
example, the barriers of the regioselectivity-determining
steps, i.e., first H transfer in 9,10-addition and second H
transfer in 1,4-addition of anthracene, none of which is
observed in experiments, are higher than the barriers via
TSBC and TSCD by 4.0 and 3.7 kcal/mol, respectively.
4. EXPERIMENTAL SECTION
General
Procedure
for
Chromium-Catalyzed
Regioselective Hydrogenation of PAHs. THF (2 mL) was
added to a dry tube containing PAH (0.2 mmol), CrCl3 (0.044
mmol, 7 mg) and diketimine ligand of L1 or L3 (0.044 mmol)
under nitrogen atmosphere. After stirring at room
temperature for 5 min, MeMgBr (0.3 mL, 1 M in THF) was
added dropwise slowly by using a syringe at 0 oC. The
resulting mixture was stirred for 30 min, and the tube was
For low-valent cobalt system, we explored pathways based
on the two monohydride candidates bearing more favorable
formation thermodynamics (reactions 2b, 4b in Scheme 6b).
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Journal of the American Chemical Society
3029–3070. (c) Wang, D.-S.; Chen, Q.-A.; Lu, S.-M.; Zhou, Y.-
quickly moved to a high-pressure autoclave. The reaction
G. Asymmetric Hydrogenation of Heteroarenes and Arenes.
Chem. Rev. 2012, 112, 2557–2590. (d) He, Y.-M.; Feng, Y.;
Fan, Q.-H. Asymmetric Hydrogenation in the Core of
Dendrimers. Acc. Chem. Res. 2014, 47, 2894–2906. (e) Zhang,
Z.; Butt, N. A.; Zhang, W. Asymmetric Hydrogenation of
Nonaromatic Cyclic Substrates. Chem. Rev. 2016, 116,
14769–14827. (f) Morris, R. H. Exploiting Metal–Ligand
Bifunctional Reactions in the Design of Iron Asymmetric
Hydrogenation Catalysts. Acc. Chem. Res. 2015, 48, 1494–
1502. (g) Zhao, D.; Glorius, F. Enantioselective
Hydrogenation of Isoquinolines. Angew. Chem., Int. Ed. 2013,
52, 9616–9618. (h) Zell, T.; Milstein, D. Hydrogenation and
Dehydrogenation Iron Pincer Catalysts Capable of Metal–
Ligand Cooperation by Aromatization/Dearomatization. Acc.
Chem. Res. 2015, 48, 1979–1994. (i) Zhu, S.-F.; Zhou, Q.-L.
1
2
3
4
5
6
7
8
mixture was stirred under the atmosphere of H2 (5 Mpa) at
room temperature for 24 h. After quenching with saturated
NH4Cl/H2O (2 mL), the crude product was extracted with
EtOAc (3  4 mL). The combined organic phases were dried
over anhydrous Na2SO4 and concentrated under vacuum.
The crude product was purified by silica gel chromatography
to give the desired hydrogenation product.
General Procedure for Cobalt-Catalyzed Hydrogenation
of PAHs by Regiocontrolled Reduction of Two Terminal
Carbocycles. In a dried tube were placed PAH (0.2 mmol),
Co(acac)2 (0.044 mmol, 11 mg), IPr·HCl (0.044 mmol, 19 mg)
and THF (2 mL) under nitrogen atmosphere. After stirring at
room temperature for 5 min, MeMgBr (0.3 mL, 1 M in THF)
was added dropwise by the use of a syringe, and the resulting
mixture was stirred at 0 oC for 30 min. After quickly moving to
a high-pressure autoclave, the reaction mixture was stirred
under the atmosphere of H2 (8 Mpa) at room temperature or
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
Iridium-Catalyzed
Asymmetric
Hydrogenation
of
Unsaturated Carboxylic Acids. Acc. Chem. Res. 2017, 50,
988–1001. (j) Knowles, W. S.; Noyori, R. Pioneering
Perspectives on Asymmetric Hydrogenation. Acc. Chem. Res.
2007, 40, 1238–1239. (k) Kraft, S.; Ryan, K.; Kargbo, R. B.
Recent Advances in Asymmetric Hydrogenation of
Tetrasubstituted Olefins. J. Am. Chem. Soc. 2017, 139,
11630–11641.
o
60 C for 48 h. After quenching with saturated NH4Cl/H2O (2
mL), the crude product was extracted with EtOAc (3  4 mL).
The combined organic layer was dried over anhydrous
Na2SO4 and concentrated under vacuum. The crude product
was purified by silica gel chromatography to give the product.
(3) Selected examples of alkyne hydrogenation: (a)
Karunananda, M. K.; Mankad, N. P. E-Selective Semi-
Hydrogenation of Alkynes by Heterobimetallic Catalysis. J.
Am. Chem. Soc. 2015, 137, 14598–14601. (b) Fu, S.; Chen, N.-
Y.; Liu, X.; Shao, Z.; Luo, S.-P.; Liu, Q. Ligand-Controlled
Cobalt-Catalyzed Transfer Hydrogenation of Alkynes:
Stereodivergent Synthesis of Z- and E-Alkenes. J. Am. Chem.
Soc. 2016, 138, 8588–8594.
ASSOCIATED CONTENT
Supporting Information. Detailed optimization data;
experimental procedures; characterization data of all new
compounds, detailed optimized geometries, and computational
details and results. This material is available free of charge via
the Internet at http://pubs.acs.org.
(4) Selected examples of hydrogenation of olefins: (a) Friedfeld,
M. R.; Shevlin, M.; Hoyt, J. M.; Krska, S. W.; Tudge, M. T.;
Chirik, P. J. Cobalt Precursors for High-Throughput
Discovery of Base Metal Asymmetric Alkene Hydrogenation
Catalysts. Science 2013, 342, 1076–1080. (b) Friedfeld, M. R.;
Shevlin, M.; Margulieux, G. W.; Campeau, L.-C.; Chirik, P. J.ꢀ
Cobalt-Catalyzed Enantioselective Hydrogenation of
Minimally Functionalized Alkenes: Isotopic Labeling
Provides Insight into the Origin of Stereoselectivity and
Alkene Insertion Preferences. J. Am. Chem. Soc. 2016, 138,
3314–3324. (c) Xu, R.; Chakraborty, S.; Bellows, S. M.; Yuan,
H.; Cundari, T. R.; Jones, W. D. Iron-Catalyzed
Homogeneous Hydrogenation of Alkenes under Mild
Conditions by a Stepwise, Bifunctional Mechanism. ACS
Catal. 2016, 6, 2127–2135. (d) Sunada, Y.; Ogushi, H.;
Yamamoto, T.; Uto, S.; Sawano, M.; Tahara, A.; Tanaka, H.;
Shiota, Y.; Yoshizawa, K.; Nagashima, H. Disilaruthena- and
Ferracyclic Complexes Containing Isocyanide Ligands as
Effective Catalysts for Hydrogenation of Unfunctionalized
Sterically Hindered Alkenes. J. Am. Chem. Soc. 2018, 140,
4119–4134. (e) Yang, H.; Wang, E.; Yang, P.; Lv, H.; Zhang, X.
Pyridine-Directed Asymmetric Hydrogenation of 1,1-
Diarylalkenes. Org. Lett. 2017, 19, 5062–5065. (f) Bart, S. C.;
Hawrelak, E. J.; Lobkovsky, E.; Chirik, P. J. Low-Valent α-
Diimine Iron Complexes for Catalytic Olefin Hydrogenation.
Organometallics 2005, 24, 5518–5527.
AUTHOR INFORMATION
Corresponding Author
*E-mails: zengxiaoming@scu.edu.cn (X.Z.)
chenh@iccas.ac.cn (H.C.)
Author Contributions
¶B. Han and P. Ma contributed equally.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
Support for this work by NSFC (21873103, 21833011, 21572175,
21702028), SCU, the Institute of Chemistry, Key Project of
Natural Science of Shaanxi Provincial Education Department
(No. 16JS121), and Industrial Public Relation Project of Science &
Technology Bureau of Yan’an City (No. 2015KG-01) is gratefully
acknowledged. We thank the Reviewers for the valuable
comments and suggestions in the improvement of the quality of
this manuscript.
(5) Selected examples of hydrogenation of imines: (a) Yang, Z.;
Ding, Z.; Chen, F.; He, Y.-M.; Yang, N.; Fan, Q.-H.
Asymmetric Hydrogenation of Cyclic Imines of
Benzoazepines and Benzodiazepines with Chiral, Cationic
Ruthenium–Diamine Catalysts. Eur. J. Org. Chem. 2017,
1973–1977. (b) Chen, M.-W.; Wu, B.; Chen, Z.-P.; Shi, L.;
Zhou, Y.-G. Synthesis of Chiral Fluorinated Propargylamines
via Chemoselective Biomimetic Hydrogenation. Org. Lett.
REFERENCES
(1) de Vries, J. G., Elsevier, C. J., Eds.; The Handbook of
Homogeneous Hydrogenation; Wiley-VCH: Weinheim, 2008.
(2) Selected reviews: (a) Xie, J.-H.; Zhu, S.-F.; Zhou, Q.-L.
Transition Metal-Catalyzed Enantioselective Hydrogenation
of Enamines and Imines. Chem. Rev. 2011, 111, 1713–1760. (b)
Tang, W.; Zhang, X. New Chiral Phosphorus Ligands for
Enantioselective Hydrogenation. Chem. Rev. 2003, 103,
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 8 of 11
2016, 18, 4650–4653. (c) Guo, C.; Sun, D.-W.; Yang, S.; Mao,
hydrogenation of arenes. New J. Chem. 2011, 35, 1649–1660.
S.-J.; Xu, X.-H.; Zhu, S.-F.; Zhou, Q.-L. Iridium-Catalyzed
Asymmetric Hydrogenation of 2-Pyridyl Cyclic Imines: A
Highly Enantioselective Approach to Nicotine Derivatives. J.
Am. Chem. Soc. 2015, 137, 90–93.
(e) Fang, M.; Sánchez-Delgado, R. A. Ruthenium
nanoparticles supported on magnesium oxide: A versatile
and recyclable dual-site catalyst for hydrogenation of mono-
and poly-cyclic arenes, N-heteroaromatics, and S-
heteroaromatics. J. Catal. 2014, 311, 357–368. (f) Bresó-
Femenia, E.; Chaudret, B.; Castillón, S. Selective catalytic
hydrogenation of polycyclic aromatic hydrocarbons
promoted by ruthenium nanoparticles. Catal. Sci. Technol.
2015, 5, 2741–2751. (g) Fang, M.; Machalaba, N.; Sánchez-
Delgado, R. A. Hydrogenation of arenes and N-
heteroaromatic compounds over ruthenium nanoparticles
on poly(4-vinylpyridine): a versatile catalyst operating by a
substrate-dependent dual site mechanism. Dalton Trans.
2011, 40, 10621–10632. (h) Hubert, C.; Bilé, E. G.; Denicourt-
Nowicki, A.; Roucoux, A. Rh(0) colloids supported on TiO2: a
highly active and pertinent tandem in neat water for the
hydrogenation of aromatics. Green Chem. 2011, 13, 1766–
1771. (i) Amer, I.; Amer, H.; Ascher, R.; Blum, J.; Sasson, Y.;
Vollhardt, K. P. C. Hydrogenation of arenes by the RhCl3-
aliquat® 336 catalyst: Part 3. Selective reduction of
polycyclic compounds. J. Mol. Catal. 1987, 39, 185–194. (j) Fu,
P. P.; Lee, H. M.; Harvey, R. G. Regioselective catalytic
hydrogenation of polycyclic aromatic hydrocarbons under
mild conditions. J. Org. Chem. 1980, 45, 2797–2803.
1
2
3
4
5
6
7
8
(6) Selected examples of hydrogenation of ketones: (a) Noyori,
R.; Ohkuma, T. Asymmetric Catalysis by Architectural and
Functional Molecular Engineering: Practical Chemo- and
Stereoselective Hydrogenation of Ketones. Angew. Chem.,
Int. Ed. 2001, 40, 40–73. (b) Xie, J.-H.; Liu, X.-Y.; Xie, J.-B.;
Wang, L.-X.; Zhou, Q.-L. An Additional Coordination Group
Leads to Extremely Efficient Chiral Iridium Catalysts for
Asymmetric Hydrogenation of Ketones. Angew. Chem., Int.
Ed. 2011, 50, 7329–7332. (c) Liang, Y.; Jing, Q.; Li, X.; Shi, L.;
Ding, K. Programmed Assembly of Two Different Ligands
with Metallic Ions:ꢀ Generation of Self-Supported Noyori-
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
type
Catalysts
for
Heterogeneous
Asymmetric
Hydrogenation of Ketones. J. Am. Chem. Soc. 2005, 127,
7694–7695. (d) Lei, A.; Wu, S.; He, M.; Zhang, X. Highly
Enantioselective Asymmetric Hydrogenation of α-
Phthalimide Ketone:ꢀ An Efficient Entry to Enantiomerically
Pure Amino Alcohols. J. Am. Chem. Soc. 2004, 126, 1626–
1627. (e) Xie, J.-H.; Wang, L.-X.; Fu, Y.; Zhu, S.-F.; Fan, B.-M.;
Duan, H.-F.; Zhou, Q.-L. Synthesis of Spiro Diphosphines
and Their Application in Asymmetric Hydrogenation of
Ketones J. Am. Chem. Soc. 2003, 125, 4404–4405. (f)
Ohkuma, T.; Koizumi, M.; Muñiz, K.; Hilt, G.; Kabuto, C.;
(10) Early examples of homogeneous hydrogenation of PAHs: (a)
Yu, J. S.; Ankianiec, B. C.; Nguyen, M. T.; Rothwell, I. P. All-
cis catalytic hydrogenation of polynuclear aromatic
hydrocarbons by Group 5 metal aryl oxide compounds. J. Am.
Chem. Soc. 1992, 114, 1927–1929. (b) Friedman, S.; Metlin, S.;
Svedi, A.; Wender, I. Selective Hydrogenation of Polynuclear
Aromatic Hydrocarbons. J. Org. Chem. 1959, 24, 1287–1289.
(11) (a) Ito, J.-i.; Sugino, K.; Matsushima, S.; Sakaguchi, H.; Iwata,
H.; Ishihara, T.; Nishiyama, H. Synthesis of NHC-Oxazoline
Pincer Complexes of Rh and Ru and Their Catalytic Activity
Noyori, R. trans-RuH(η1-BH4)(binap)(1,2-diamine):ꢀ
A
Catalyst for Asymmetric Hydrogenation of Simple Ketones
under Base-Free Conditions. J. Am. Chem. Soc. 2002, 124,
6508–6509. (g) Ohkuma, T. Asymmetric hydrogenation of
ketones: Tactics to achieve high reactivity, enantioselectivity,
and wide scope. Proc. Jpn. Acad., Ser. B 2010, 86, 202–219.
(h) Matsumura, K.; Arai, N.; Hori, K.; Saito, T.; Sayo, N.;
Ohkuma, T. Chiral Ruthenabicyclic Complexes: Precatalysts
for Rapid, Enantioselective, and Wide-Scope Hydrogenation
of Ketones. J. Am. Chem. Soc. 2011, 133, 10696–10699.
for
Hydrogenation
and
Conjugate
Reduction.
Organometallics 2016, 35, 1885–1894. (b) Borowski, A. F.;
Vendier, L.; Sabo-Etienne, S.; Rozycka-Sokolowska, E.;
Gaudyn, A. V. Catalyzed hydrogenation of condensed three-
ring arenes and their N-heteroaromatic analogues by a
bis(dihydrogen) ruthenium complex. Dalton Trans. 2012, 41,
14117–14125. (c) Borowski, A. F.; Sabo-Etienne, S.; Chaudret,
B. Homogeneous hydrogenation of arenes catalyzed by the
bis(dihydrogen) complex [RuH2(H2)2(PCy3)2]. J. Mol. Catal. A-
Chem. 2001, 174, 69–79. Metal-free catalytic hydrogenation
of PAHs: (d) Segawa, Y.; Stephan, D. W. Metal-free
hydrogenation catalysis of polycyclic aromatic hydrocarbons.
Chem. Commun. 2012, 48, 11963–11965.
(7) Selected examples of hydrogenation of heterocycles: (a)
Wang, J.; Chen, M.-W.; Ji, Y.; Hu, S.-B.; Zhou, Y.-G. Kinetic
Resolution of Axially Chiral 5- or 8-Substituted Quinolines
via Asymmetric Transfer Hydrogenation. J. Am. Chem. Soc.
2016, 138, 10413–10416. (b) Chen, F.; Surkus, A.-E.; He, L.;
Pohl, M.-M.; Radnik, J.; Topf, C.; Junge, K.; Beller, M.
Selective Catalytic Hydrogenation of Heteroarenes with N-
Graphene-Modified
Cobalt
Nanoparticles
(Co3O4–
Co/NGr@α-Al2O3). J. Am. Chem. Soc. 2015, 137, 11718–11724.
(c) Li, W.; Wiesenfeldt, M. P.; Glorius, F. Ruthenium–NHC–
Diamine Catalyzed Enantioselective Hydrogenation of
Isocoumarins. J. Am. Chem. Soc. 2017, 139, 2585–2588.
(12) Shah, A.; Shahzad, S.; Munir, A.; Nadagouda, M. N.; Khan, G.
S.; Shams, D. F.; Dionysiou, D. D.; Rana, U. A. Micelles as
Soil and Water Decontamination Agents. Chem. Rev. 2016,
116, 6042–6074.
(8) Joannou, M. V.; Bezdek, M. J.; Chirik, P. J. Pyridine(diimine)
Molybdenum-Catalyzed Hydrogenation of Arenes and
Hindered Olefins: Insights into Precatalyst Activation and
Deactivation Pathways. ACS Catal. 2018, 8, 5276–5285.
(13) For
a leading reference on cobalt- and iron-catalyzed
(9) Selected reviews of hydrogenation of aromatic carbocycles:
hydrogenation, see: Chirik, P. J. Iron- and Cobalt-Catalyzed
Alkene Hydrogenation: Catalysis with Both Redox-Active
and Strong Field Ligands. Acc. Chem. Res. 2015, 48, 1687–
1695.
(a) Gual, A.; Godard, C.; Castillón, S.; Claver, C. Soluble
transition-metal nanoparticles-catalysed hydrogenation of
arenes. Dalton Trans. 2010, 39, 11499–11512. (b) Qi, S.-C.;
Wei, X.-Y.; Zong, Z.-M. Wang, Y.-K. Application of
supported metallic catalysts in catalytic hydrogenation of
arenes. RSC Adv. 2013, 3, 14219–14232. For selected recent
examples: (c) Yoon, B.; Wai, C. M. Microemulsion-
Templated Synthesis of Carbon Nanotube-Supported Pd
and Rh Nanoparticles for Catalytic Applications. J. Am. Chem.
Soc. 2005, 127, 17174–17175. (d) Pan, H.-B.; Wai, C. M. Facile
sonochemical synthesis of carbon nanotube-supported
bimetallic Pt–Rh nanoparticles for room temperature
(14) (a) Bullock, R. M. Abundant Metals Give Precious
Hydrogenation Performance. Science 2013, 342, 1054–1055.
(b) Crossley, S. W. M.; Obradors, C.; Martinez, R. M.; Shenvi,
R.
A.
Mn-,
Fe-,
and
Co-Catalyzed
Radical
Hydrofunctionalizations of Olefins. Chem. Rev. 2016, 116,
8912−9000. (c) Li, Y.-Y.; Yu, S.-L.; Shen, W.-Y.; Gao, J.-X.
Iron-, Cobalt-, and Nickel-Catalyzed Asymmetric Transfer
Hydrogenation and Asymmetric Hydrogenation of Ketones.
Acc. Chem. Res. 2015, 48, 2587–2598.
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(15) Selected examples of cobalt-catalyzed hydrogenation: (a)
(20) (a) Lee, P.-S.; Fujita, T.; Yoshikai, N. Cobalt-Catalyzed,
Room-Temperature Addition of Aromatic Imines to Alkynes
via Directed C–H Bond Activation. J. Am. Chem. Soc. 2011,
133, 17283–17295. (b) For a review of low-valent cobalt
catalysis, see: Gao, K.; Yoshikai, N. Low-Valent Cobalt
Catalysis: New Opportunities for C–H Functionalization. Acc.
Chem. Res. 2014, 47, 1208–1219.
(21) For report of forming low-valent chromium species by 2e-
reduction of the CrCl2 or CrCl3 complex with Grignard
reagent or Mg, see: (a) Mock, M. T.; Chen, S.; O’Hagan, M.;
Rousseau, R.; Dougherty, W. G.; Kassel, W. S.; Bullock, R. M.
Dinitrogen Reduction by a Chromium(0) Complex Supported
by a 16-Membered Phosphorus Macrocycle. J. Am. Chem.
Soc. 2013, 135, 11493–11496. (b) Albahily, K.; Shaikh, Y.;
Sebastiao, E.; Gambarotta, S.; Korobkov, I.; Gorelsky, S. I.
Friedfeld, M. R.; Shevlin, M.; Margulieux, G. W.; Campeau,
L.-C.; Chirik, P. J. Cobalt-Catalyzed Enantioselective
Hydrogenation of Minimally Functionalized Alkenes:
Isotopic Labeling Provides Insight into the Origin of
Stereoselectivity and Alkene Insertion Preferences. J. Am.
Chem. Soc. 2016, 138, 3314–3324. (b) Adam, R.; Cabrero-
Antonino, J. R.; Spannenberg, A.; Junge, K.; Jackstell, R.;
Beller, M. A General and Highly Selective Cobalt-Catalyzed
Hydrogenation of N-Heteroarenes under Mild Reaction
Conditions. Angew. Chem., Int. Ed. 2017, 56, 3216–3220. (c)
Mukherjee, A.; Srimani, D.; Chakraborty, S.; Ben-David, Y.;
Milstein, D. Selective Hydrogenation of Nitriles to Primary
Amines Catalyzed by a Cobalt Pincer Complex. J. Am. Chem.
Soc. 2015, 137, 8888–8891. (d) Friedfeld, M. R.; Margulieux,
G. W.; Schaefer, B. A.; Chirik, P. J. Bis(phosphine)cobalt
Dialkyl Complexes for Directed Catalytic Alkene
Hydrogenation. J. Am. Chem. Soc. 2014, 136, 13178–13181. (e)
Monfette, S.; Turner, Z. R.; Semproni, S. P.; Chirik, P. J.
Enantiopure C1-Symmetric Bis(imino)pyridine Cobalt
Complexes for Asymmetric Alkene Hydrogenation. J. Am.
Chem. Soc. 2012, 134, 4561–4564. (f) Chen, F.; Topf, C.;
Radnik, J.; Kreyenschulte, C.; Lund, H.; Schneider, M.;
Surkus, A.-E.; He, L.; Junge, K.; Beller, M. Stable and Inert
Cobalt Catalysts for Highly Selective and Practical
Hydrogenation of CN and C=O Bonds. J. Am. Chem. Soc.
2016, 138, 8781–8788. (g) Yu, R. P.; Darmon, J. M.; Milsmann,
C.; Margulieux, G. W.; Stieber, S. C. E.; DeBeer, S.; Chirik, P.
J. Catalytic Hydrogenation Activity and Electronic Structure
Determination of Bis(arylimidazol-2-ylidene)pyridine Cobalt
Alkyl and Hydride Complexes. J. Am. Chem. Soc. 2013, 135,
13168–13184. (h) Tokmic, K.; Markus, C. R.; Zhu, L.; Fout, A.
R. Well-Defined Cobalt(I) Dihydrogen Catalyst: Experimental
1
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3
4
5
6
7
8
9
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38
39
40
41
42
43
44
45
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49
50
51
52
53
54
55
56
57
58
59
60
Vinyl Oxidative Coupling as
a Synthetic Route to
Catalytically Active Monovalent Chromium. J. Am. Chem.
Soc. 2011, 133, 6388−6395.
(22) Selected examples of Cr catalysis using Grignard reagents: (a)
Murakami, K.; Ohmiya, H.; Yorimitsu, H.; Oshima, K.
Chromium-Catalyzed Arylmagnesiation of Alkynes. Org. Lett.
2007, 9, 1569–1571. (b) Steib, A. K.; Kuzmina, O. M.;
Fernandez, S.; Flubacher, D.; Knochel, P. Efficient
Chromium(II)-Catalyzed Cross-Coupling Reactions between
Csp2Centers. J. Am. Chem. Soc. 2013, 135, 15346–15349. (c)
Li, Y.; Deng, G.; Zeng, X. Chromium-Catalyzed
Regioselective
Hydropyridination
of
Styrenes.
Organometallics 2016, 35, 747–750. (d) Steib, A. K.; Kuzmina,
O. M.; Fernandez, S.; Malhotra, S.; Knochel, P.
Chemoselective Chromium(II)–Catalyzed Cross–Coupling
Reactions of Dichlorinated Heteroaromatics with
Functionalized Aryl Grignard Reagents. Chem. Eur. J. 2015,
21, 1961–1965. (e) Kuzmina, O. M.; Knochel, P. Room-
Temperature Chromium(II)-Catalyzed Direct Arylation of
Pyridines, Aryl Oxazolines, and Imines Using Arylmagnesium
Reagents. Org. Lett. 2014, 16, 5208–5211. (f) Yan, J.;
Evidence for
a Co(I)/Co(III) Redox Process in Olefin
Hydrogenation. J. Am. Chem. Soc. 2016, 138, 11907–11913.
(16) Selected examples of iron-catalyzed hydrogenation: (a)
Jagadeesh, R. V.; Surkus, A.-E.; Junge, H.; Pohl, M.-M.;
Radnik, J.; Rabeah, J.; Huan, H.; Schünemann, V.; Brückner,
A.; Beller, M. Nanoscale Fe2O3-Based Catalysts for Selective
Hydrogenation of Nitroarenes to Anilines. Science 2013, 342,
1073–1076. (b) Zuo, W.; Lough, A. J.; Li, Y. F.; Morris, R. H.
Amine(imine)diphosphine Iron Catalysts for Asymmetric
Transfer Hydrogenation of Ketones and Imines. Science 2013,
342, 1080–1083. (c) Trovitch, R. J.; Lobkovsky, E.; Bill, E.;
Chirik, P. J. Functional Group Tolerance and Substrate Scope
in Bis(imino)pyridine Iron Catalyzed Alkene Hydrogenation.
Organometallics 2008, 27, 1470–1478.
(17) (a) Nador, F.; Moglie, Y.; Vitale, C.; Yus, M.; Alonso, F.;
Radivoy, G. Reduction of polycyclic aromatic hydrocarbons
promoted by cobalt or manganese nanoparticles.
Tetrahedron 2010, 66, 4318–4325. (b) Nelkenbaum, E.; Dror,
I.; Berkowitz, B. Reductive hydrogenation of polycyclic
aromatic hydrocarbons catalyzed by metalloporphyrins.
Chemosphere 2007, 68, 210–217.
Yoshikai,
N.
Chromium-catalyzed
migratory
arylmagnesiation of unactivated alkynes. Org. Chem. Front.
2017, 4, 1972–1975. (g) Yan, J.; Yoshikai, N. Phenanthrene
Synthesis via Chromium-Catalyzed Annulation of 2-Biaryl
Grignard Reagents and Alkynes. Org. Lett. 2017, 19, 6630–
6633. (h) Chen, C.; Liu, P.; Luo, M.; Zeng, X. Kumada
Arylation of Secondary Amides Enabled by Chromium
Catalysis for Unsymmetric Ketone Synthesis under Mild
Conditions. ACS Catal. 2018, 8, 5864−5868.
(23) (a) Shuster, V.; Gambarotta, S.; Nikiforov, G. B.; Budzelaar,
P. H. M. Heterometallic Aluminum–Chromium Phenazine
and Thiophenazine Complexes. Formation of a Tetranuclear
Chromium(I) Sandwich Complex. Organometallics 2013, 32,
2329–2335; (b) Miller, J. S.; O'Hare, D. M.; Chakraborty, A.;
Epstein, A. J. Ferromagnetically coupled linear electron-
transfer
complexes.
Structural
and
magnetic
characterization of [Cr(6-C6MexH6-x)2][TCNE] (x = 0, 3, 6)
and S = 0 [TCNE]22-. J. Am. Chem. Soc. 1989, 111, 7853–7860.
(24) Zhao, D.; Candish, L.; Paul, D.; Glorius, F. N-Heterocyclic
Carbenes in Asymmetric Hydrogenation. ACS Catal. 2016, 6,
5978–5988.
(18) Sloan, M. F.; Matlack, A. S.; Breslow, D. S. Soluble Catalysts
for the Hydrogenation of Olefins. J. Am. Chem. Soc. 1963, 85,
4014–4018.
(19) (a) Cong, X.; Tang, H.; Zeng, X. Regio- and Chemoselective
Kumada–Tamao–Corriu Reaction of Aryl Alkyl Ethers
Catalyzed by Chromium Under Mild Conditions. J. Am. Chem.
Soc. 2015, 137, 14367–14372. (b) Cong, X.; Fan, F.; Ma, P.;
Luo, M.; Chen, H.; Zeng, X. Low-Valent, High-Spin
Chromium-Catalyzed Cleavage of Aromatic Carbon–
(25) Selected examples of cobalt catalysis using large amounts of
Grignard reagents: (a) Gao, K.; Lee, P.-S.; Fujita, T.; Yoshikai,
N. Cobalt-Catalyzed Hydroarylation of Alkynes through
Chelation-Assisted C−H Bond Activation. J. Am. Chem. Soc.
2010, 132, 12249–12251. (b) Ohmiya, H.; Wakabayashi, K.;
Yorimitsu, H.; Oshima, K. Cobalt-catalyzed cross-coupling
reactions of alkyl halides with aryl Grignard reagents and
their application to sequential radical cyclization/cross-
coupling reactions. Tetrahedron 2006, 62, 2207–2213. (c)
Nitrogen Bonds at Room Temperature:
A Combined
Experimental and Theoretical Study. J. Am. Chem. Soc. 2017,
139, 15182−15190.
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Wakabayashi, K.; Yorimitsu, H.; Oshima, K. Cobalt-
Catalyzed Tandem Radical Cyclization and Cross-Coupling
Reaction:ꢀ Its Application to Benzyl-Substituted
1
2
Heterocycles. J. Am. Chem. Soc. 2001, 123, 5374–5375. (d)
Czaplik, W. M.; Mayer, M.; Jacobi von Wangelin, A. Direct
Cobalt-Catalyzed Cross-Coupling Between Aryl and Alkyl
Halides. Synlett 2009, 2931–2934. (e) Kauffmann, T.
Nonstabilized Alkyl Complexes and Alkyl–Cyano–Ate
Complexes of Iron(II) and Cobalt(II) as New Reagents in
Organic Synthesis. Angew. Chem., Int. Ed. 1996, 35, 386–403.
(26) Wu, J. I.; Wannere, C. S.; Mo, Y.; Schleyer, P. v. R.; Bunz, U.
3
4
5
6
7
8
9
H.
Dihydrodiazapentacenes. J. Org. Chem. 2009, 74, 4343–4349.
(27) For recent example of low-valent Co-catalyzed
F.
4n
π
Electrons
but
Stable:
N,N-
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45
46
47
48
49
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51
52
53
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55
56
57
58
59
60
a
hydrogenation using zinc as reductant, see: Friedfeld, M. R.;
Zhong, H.; Ruck, R. T.; Shevlin, M.; Chirik, P. J. Cobalt-
Catalyzed Asymmetric Hydrogenation of Enamides Enabled
by Single-Electron Reduction. Science 2018, 360, 888–893.
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