Manganese catalyzed hydrogenation of carbamates and urea derivatives

Article abstract of DOI:10.1021/jacs.9b05591

We report the hydrogenation of carbamates and urea derivatives, two of the most challenging carbonyl compounds to be hydrogenated, catalyzed for the first time by a complex of an earth-abundant metal. The hydrogenation reaction of these CO₂-derived compounds, catalyzed by a manganese pincer complex, yields methanol in addition to amine and alcohol, which makes this methodology a sustainable alternative route for the conversion of CO₂ to methanol, involving a base-metal catalyst. Moreover, the hydrogenation proceeds under mild pressure (20 bar). Our observations support a hydrogenation mechanism involving the Mn-H complex. A plausible catalytic cycle is proposed based on informative mechanistic experiments.

Full text of DOI:10.1021/jacs.9b05591

Subscriber access provided by BUFFALO STATE
Communication
Manganese Catalyzed Hydrogenation of Carbamates and Urea Derivatives
Uttam Kumar Das, Amit Kumar, Yehoshoa Ben-David, Mark Iron, and David Milstein
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b05591 • Publication Date (Web): 31 Jul 2019
Downloaded from pubs.acs.org on July 31, 2019
Just Accepted
“Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted
online prior to technical editing, formatting for publication and author proofing. The American Chemical
Society provides “Just Accepted” as a service to the research community to expedite the dissemination
of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in
full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully
peer reviewed, but should not be considered the official version of record. They are citable by the
Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore,
the “Just Accepted” Web site may not include all articles that will be published in the journal. After
a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web
site and published as an ASAP article. Note that technical editing may introduce minor changes
to the manuscript text and/or graphics which could affect content, and all legal disclaimers and
ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or
consequences arising from the use of information contained in these “Just Accepted” manuscripts.
is published by the American Chemical Society. 1155 Sixteenth Street N.W.,
Washington, DC 20036
Published by American Chemical Society. Copyright © American Chemical Society.
However, no copyright claim is made to original U.S. Government works, or works
produced by employees of any Commonwealth realm Crown government in the course
of their duties.

Page 1 of 6
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Manganese Catalyzed Hydrogenation of Carbamates and Urea Deriv-
atives
Uttam Kumar Das,† Amit Kumar,† Yehoshoa Ben-David,† Mark Iron§ and David Milstein*,
†
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
† Department of Organic Chemistry, §Department of Chemical Research Support, The Weizmann Institute of Science,
Rehovot, 76100, Israel
Supporting Information Placeholder
A few years ago we reported the first example of the
ABSTRACT: We report the hydrogenation of carbamates and
direct hydrogenation of carbamate and urea-derivatives to
form methanol using a ruthenium pincer catalyst.6-7 We fur-
ther applied this strategy to demonstrate the conversion of
low-pressure CO2 to methanol by capturing CO2 (1 bar) using
ethanolamine, forming oxazolidinone, followed by its ruthe-
nium catalyzed hydrogenation to methanol, regenerating the
ethanolamine.8 Cascade hydrogenation of CO2 to methanol
was reported by the Sanford group, via formation of formic
acid followed by its esterification and hydrogenation to meth-
anol.9 Cascade CO2 hydrogenation catalysis to form methanol
using amines which capture CO2 as formamides, followed by
their hydrogenation was reported by the Prakash group.10 Re-
cently, we have reported a reversible Liquid Organic Hydro-
gen Carrier (LOHC) based on ruthenium catalyzed dehydro-
genative coupling of ethylene diamine and methanol and its
reverse reaction i.e. hydrogenation of ethylene urea.11 Thus,
hydrogenation of urea derivatives may also have applications
in the development of new chemical hydrogen storage mate-
rials.
urea derivatives, two of the most challenging carbonyl com-
pounds to be hydrogenated, catalyzed for the first time by a
complex of an earth-abundant-metal. The hydrogenation re-
action of these CO2-derived compounds, catalyzed by a man-
ganese pincer complex, yields methanol in addition to amine
and alcohol, which makes this methodology a sustainable al-
ternative route for the conversion of CO2 to methanol, involv-
ing a base- metal catalyst. Moreover, the hydrogenation pro-
ceeds under mild pressure (20 bar). Our observations support
a hydrogenation mechanism involving the Mn-H complex. A
plausible catalytic cycle is proposed based on informative
mechanistic experiments.
Catalytic hydrogenation of polar bonds, in particular
carbonyl groups, offers a green route for the synthesis of useful
organic building blocks such as alcohols and amines.1 The ten-
dency of a carbonyl group to be hydrogenated depends on its
polarizability and follows the trend of aldehyde < ketone < an-
hydride < imide < ester < acid < amide < carbonate < carba-
mate < urea.2 Thus, carbamates and ureas are the most chal-
lenging carbonyl compounds to be hydrogenated. In fact, urea
derivatives were used as solvents for hydrogenation reactions
because of their inert nature towards hydrogenation.3 Thus,
hydrogenation of these carbonic acid derivatives is highly
challenging, and is highly attractive because carbamates and
ureas can be readily prepared by the reaction of CO2 with the
corresponding amines, or with amines and alcohols, and their
direct hydrogenation to methanol can offer a practical, mild
route to convert CO2 to methanol (Scheme 1).4 Although di-
rect hydrogenation of CO2 to methanol has been extensively
studied,5 they involve relatively harsh reaction conditions re-
sulting in a need to develop alternative strategies for the con-
version of CO2 to methanol.
In recent years there has been much interest in the
development of catalysts based on earth-abundant-metals for
a variety of (de)hydrogenation reactions.12 Several groups, in-
cluding ours, have reported on pincer catalysts based on
earth-abundant-manganese for the catalytic hydrogenation of
several carbonyl compounds such as aldehydes, ketones, im-
ides, nitriles, esters and amides.13 Recently, manganese-cata-
lyzed direct hydrogenation of organic carbonates to methanol
and alcohols was reported by us,14 as well as independently by
the groups of Leitner and Rueping.15 Despite such strong in-
terest in using earth-abundant-metal complexes for hydro-
genation reactions, catalytic hydrogenation of carbamate- and
urea- derivatives using an earth-abundant-metal complex is
still unknown. We report here the hydrogenation of carba-
mates and urea derivatives catalyzed by a pincer complex of
the earth-abundant manganese.
Scheme 1. Indirect conversion of CO2 to methanol via hydro-
genation of carbamates or urea derivatives.
Scheme 2. Catalytic hydrogenation of octyl phenylcarbamate
and the manganese complexes (1-4) employed in this study.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 2 of 6
Table 1. Optimization of the catalytic conditions for hydrogenation of octyl phenylcarbamate.a
1
2
3
4
5
6
7
8
entry [Mn]
tBuOK
(mol %)
0
solvent
H2
(bar)
40
Temp
(°C).
110
Time conv.(%)b Yield (%) of Yield (%) of Yield (%) of
(h)
24
methanolc
-
octanolb
-
amineb
-
1
2
1
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
Toluene
THF
-
2
2
3
4
4
4
4
4
4
0
0
0
3
3
3
3
3
3
40
40
40
40
40
25
20
20
20
110
130
110
110
130
130
130
130
110
24
36
24
24
24
36
36
48
36
75
63
68
-
nd
76
nd
3
80
10
72
4
5
-
-
nd
78
75
75
90
81
91
78
nd
9
6
7
90
>99
95
88
85
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
99
95
8
9
10
92
99 (94)d
90
97 (93)d
>99
85
84
81
aReaction conditions: Catalyst [Mn] (0.02 mmol), tBuOK (0-3 mol %), phenyl carbamate (1 mmol), toluene (2 mL), H2 (20-40 bar),
b
130 °C (bath temperature). Conversion of carbamate, yields of alcohol and amine were determined by the GC. Identification of
the products were also confirmed by the GC-MS. cYield of methanol was determined by 1H NMR spectroscopy using mesitylene as
an internal standard. dIsolated yields.
We started our investigation by studying the cata-
lytic hydrogenation of octyl phenylcarbamate employing
manganese pincer complexes (1-4, Scheme 2) developed in our
group for. The Mn-PNP complex 1 (2 mol %), which is the first
manganese pincer complex reported for catalytic dehydro-
genation reactions,16 did not result in any conversion of octyl
phenyl carbamate under 40 bar of H2 at 110 oC for 24 h (Table
1, entry 1). Complex 2 was reported by us as the first complex
of earth-abundant-metal for the dehydrogenative synthesis of
cyclic imides as well as for the hydrogenation of esters and or-
ganic carbonates.17, 14 Interestingly, complex 2 catalyzed the
hydrogenation of octyl phenyl carbamate under the condi-
tions described above in 75% conversion forming methanol in
63% yield as detected by 1H NMR spectroscopy and GC (Table
1, entry 2). At longer reaction time (36 h) and higher tempera-
ture (130oC), the carbamate conversion increased to 80% and
methanol was detected in 68% yield, together with of aniline
(72%) and 1-octanol (76%). Using the Mn-PNN-bipyridyl com-
plex 3 (3 mol %), previously reported to catalyze the dehydro-
genative synthesis of hydrazones, 18 only 10% conversion of the
carbamate was obtained, and no methanol was detected (en-
try 4). We have recently reported the synthesis and catalytic
application of complex 4 for the dehydrogenative cross-cou-
pling of primary alcohols.19 Interestingly, performing the cat-
alytic hydrogenation reaction using complex 4 (3 mol %) and
KOtBu (3 mol %) resulted in 78% conversion of the carbamate
and methanol was detected in 75% yield (Table 1, entry 5).
Moreover, quantitative conversion of the carbamate was ob-
tained using 2 mol % complex 4 even at lower hydrogen pres-
sure (20 bar) upon increasing the reaction temperature (130
oC) and time (48h), forming methanol in 91% yield (entry 9).
Changing the solvent from toluene to THF resulted in a lower
yield of methanol (entry 10).
Table 2. Manganese catalyzed hydrogenation of carbamates.a
After finding the optimized catalytic conditions, we
explored the substrate scope for the manganese catalyzed hy-
drogenation of carbamates. As described in Table 2, a variety
of linear carbamates bearing aliphatic or aromatic substitu-
ents were hydrogenated to methanol in excellent yields. How-
ever, we were not able to hydrogenate the N-methyl benzyl
(methyl) carbamate under these reaction conditions (Table 2,
entry 12).
aReaction conditions: Complex 4 (0.02 mmol), BuOK (0.03 mmol),
carbamate (1 mmol), H2 (20 bar), toluene (2 mL), 130 °C (bath tem-
t
b
perature), reaction time: 48h. Yields of amine and alcohol were de-
termined by GC/GC-MS. cYield of MeOH was determined by 1H NMR
spectroscopy using mesitylene as an internal standard. dIsolated
yields. eComplex 5 was used as catalyst without base (vide infra).
ACS Paragon Plus Environment

Page 3 of 6
Journal of the American Chemical Society
Table 3. Manganese catalyzed hydrogenation of urea deriva-
C=N tautomer of the carbamate or urea derivatives; however
this was excluded, as we have shown by DFT that these tauto-
mers are much less stable (eg by 19.1 kcal/mol in case of methyl
benzylcarbamate). Effect of base on involvement of the C=N
tautomers was also excluded (see SI for detailed discussion
and experiments).
tives.a
1
2
3
4
5
6
7
8
9
Scheme 3. Hydrogenation of 1-benzyl-3-(4-fluorobenzyl)-1-
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
methylurea.
We have recently reported that complex 4 in pres-
ence of KOtBu undergoes deprotonation to form the dearoma-
tized complex 519 that reacts with hydrogen to form the man-
ganese hydride complex 6 (Scheme 4a). We have character-
ized complex 6 by IR and NMR spectroscopy (see SI for de-
tails). Performing the catalytic hydrogenation under the con-
ditions described in Table 2 using complex 5 as catalyst with-
out adding base resulted in almost complete conversion of
methyl benzylcarbamate and 93% of methanol was detected
after 48 h (Table 2 entry 1, second row). A similar result was
obtained when methyl benzyl carbamate was hydrogenated
using complex 6 in absence of added base under the condi-
tions described in Table 2. These experiments suggest that
complexes 5 and 6 are involved in the catalytic cycle. In order
to get further insight into the reaction mechanism we have
studied some stoichiometric reactions. The reaction of com-
plex 6 with an equimolar amount of methyl benzyl carbamate
(2h, 85 oC, THF) resulted in complete consumption of complex
6 with formation of N-benzyl formamide as detected by GC-
MS, as well as unidentified manganese complexes (Scheme
4b). Interestingly reaction between complex 6 and N-benzyl
formamide at room temperature resulted in a new complex,
assigned as complex 9 (Scheme 4c), based on IR and NMR
spectroscopies (see SI for details). Hydrogenation of N-benzyl
formamide and N-methyl-N-benzyl formamide in presence of
complex 4 (2 mol %) and KOtBu (2 mol %) produced methanol
(84% and 81% yield, Scheme 4d).
aReaction condition: Complex 4 (0.03 mmol), tBuOK (0.04 mmol), car-
bamate (1 mmol), H2 (20 bar), THF (2 mL), 130 °C (bath temperature),
reaction time: 48h. bYields of amine were determined by GC/GC-MS.
cYields of MeOH were determined by 1H NMR spectroscopy using me-
sitylene as an internal standard. dIsolated yields. eReaction time 36h.
Following the successful hydrogenation of carba-
mates, we attempted to utilize the manganese complex 4 for
the catalytic hydrogenation of urea derivatives, the most hy-
drogenation-resistant carbonyl compounds. Remarkably, us-
ing complex 4 (3 mol %) in the presence of KOtBu (4 mol %)
o
under H2 (20 bar) at 130 C for 48h in THF, a variety of urea
derivatives were hydrogenated to methanol and amines (Table
3). Linear urea derivatives with aromatic substituents (entries
1-6) gave better yields of methanol than those bearing ali-
phatic substituents (entries 7-9).
Tetra-substituted urea derivatives, bearing two N-
Me groups, did not undergo hydrogenation under these cata-
lytic condition or at elevated hydrogen pressure (60 bar, entry
11). On the other hand, hydrogenation of 1-benzyl-3-(4-fluoro-
benzyl)-1-methylurea, bearing one N-Me group, under the
conditions described in Table 3, resulted in hydrogenation to
form methanol and the corresponding amines, although in
lower yields (Scheme 3). We believe this is a result of the steric
hindrance imposed by the adjacent N-Me group. This might
be also the reason for the lack of hydrogenation of N-methyl
(benzyl)(methyl)carbamate (Table 2, entry 12). We also con-
sidered another potential reason for the lack of hydrogenation
in the absence on an N-H bond, namely involvement of the
Scheme 4. Mechanistic reactions.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 4 of 6
Considering our experimental findings, and previous
pressure CO2 to methanol using a catalyst based on an earth-
abundant metal.
1
2
3
4
5
6
7
8
reports on ruthenium and manganese catalyzed dehydrogena-
tion of organic carbonates,6, 14 and deoxygenation of primary
alcohols catalyzed by 4,19 we propose a catalytic cycle (Scheme
5). Reaction of the pre-catalyst 4 with the base generates the
dearomatized complex 5, which adds H2 by metal-ligand co-
operation (MLC) to give the hydride complex 6. The latter re-
acts with the urea or carbamate derivatives to form complex 7
most probably using the hemilabile properties of the bipyri-
dine moity.20 Elimination of R’XH (X = O, NH), by metal-lig-
and cooperation, from complex 7 yields complex 8, which re-
generates complex 5 by release of N-formamide. Reaction of
N-formamide with complex 6 forms complex 9, which elimi-
nates the amine via MLC to form the formaldehyde complex
10. Complex 10 reacts with hydrogen to form the methoxide
complex 11 via complex 6. Elimination of methanol from 11 re-
generates complex 5. It is worth mentioning that under the
conditions described in Table 2 paraformaldehyde undergoes
hydrogenation to methanol (see SI for the details) which cor-
roborates the possibility of hydrogenation of formaldehyde
complex 10 to the methoxide complex 11.
ASSOCIATED CONTENT
Supporting Information
Experimental details, NMR spectra of crude reactions and
characterization data of complex 6 and complex 9. This mate-
rial is available free of charge via the Internet at
http://pubs.acs.org.
9
AUTHOR INFORMATION
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
Corresponding Author
*E-mail: david.milstein@weizmann.ac.il.
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENT
This research was supported by the European Research Coun-
cil (ERC AdG 692775), and by the Israel Science Foundation.
U. K. D. is thankful to Govt. of India for the DST SERB Over-
seas Postdoctoral Fellowship.
Catalytic hydrogenation of methyl benzylcarbamate
in the presence of 100 equivalents of mercury resulted in very
similar yields as in the absence of mercury, suggesting that the
catalysis does not involve nanoparticles.
REFERENCES
Addition of more substrate (1 mmol) to the com-
(1) (a) Ito, M.; Ikariya, T. Catalytic hydrogenation of polar organic
functionalities based on Ru-mediated heterolytic dihydrogen cleav-
age. Chem. Commun. 2007, 43, 5134–5142. (b) Clapham, S. E.; Had-
zovic, A.; Morris, R. H. Mechanisms of the H2-hydrogenation and
transfer hydrogenation of polar bonds catalyzed by ruthenium hy-
dride complexes. Coord. Chem. Rev. 2004, 248, 2201–2237. (c) O, W.
W. N.; Lough, A. J.; Morris, R. H. The hydrogenation of molecules with
polar bonds catalyzed by a ruthenium (II) complex bearing a chelating
N-heterocyclic carbene with a primary amine donor. Chem. Commun.
2010, 46, 8240–8242 and references therein.
(2) Pritchard, J.; Filonenko, G. A.; van Putten, R.; Hensen, E. J. M.;
Pidko, E. A. Heterogeneous and homogeneous catalysis for the hy-
drogenation of carboxylic acid derivatives: history, advances and fu-
ture directions. Chem. Soc. Rev. 2015, 44, 3808-3833.
(3) (a) Ohgomori, Y.; Mori, S.; Yoshida, S.; Watanabe, Y. The Role
of Amide Solvents in the Formation of Ethylene Glycol from Synthesis
Gas. J. Mol. Cat. 1987, 40, 223–228. (b) Imperato, G.; Hçger, S.; Lenoir,
D.; Kçnig, B. Low melting sugar–urea–salt mixtures as solvents for or-
ganic reactions— estimation of polarity and use in catalysis. Green
Chem. 2006, 8, 1051–1055.
(4) (a) Ion, A.; Van Doorslaer, C.; Parvulescu, V.; Jacobs, P.; De Vos,
D. Green synthesis of carbamates from CO2, amines and alcohols.
Green Chem. 2008, 10, 111–116. (b) Liu, A-H.; Li, Y.-N.; He, L.-N. Or-
ganic synthesis using carbon dioxide as phosgene-free carbonyl rea-
pleted reaction of methylbenzyl carbamate (Table 2, entry 1)
and H2 (20 bar) and performing a second hydrogenation un-
der the same conditions, resulted in a slower reaction (43%
conversion of carbamate), indicating that although the cata-
lyst is present at the end of the first catalytic reaction, it is not
as active as the fresh catalyst.
gent.
Pure
Appl.
Chem.
2012,
84,
581–602.
Scheme 5. Proposed mechanism for the catalytic hydrogena-
tion of carbamate- and urea-derivatives (X = O, NH).
(5) (a) Alberico, E.; Nielsen, M. Towards a methanol economy
based on homogeneous catalysis: methanol to H2 and CO2 to metha-
nol. Chem. Commun. 2015, 51, 6714-6725. (b) Goeppert, A.; Czaun, M.;
Jones, J.-P.; Surya Prakash, G. K.; Olah, G. A. Recycling of carbon di-
oxide to methanol and derived products - closing the loop. Chem. Soc.
Rev. 2014, 43, 7995-8048. (c) Behrens, M.; Studt, F.; Kasatkin, I.; Kühl,
S.; Hävecker, M.; Abild-Pedersen, F.; Zander, S.; Girgsdies, F.; Kurr, P.;
Kniep, B.-L.; Tovar, M.; Fischer, R. W.; Nørskov, J. K.; Schlögl, R. The
Active Site of Methanol Synthesis over Cu/ZnO/Al2O3 Industrial Cat-
alysts. Science 2012, 336, 893-897. (d) Jadhav, S. G.; Vaidya, P. D.;
Bhanage, B. M.; Joshi, J. B. Catalytic Carbon Dioxide Hydrogenation
to Methanol: A Review of Recent Studies. Chem. Eng. Res. Des. 2014,
92, 2557-2567. (e) Kar, S.; Kothandaraman, J.; Goeppert, A.; Prakash,
G. K. S. Advances in catalytic homogeneous hydrogenation of carbon
dioxide to methanol. J. CO2 utilization 2018, 23, 212-218; (f)
Wesselbaum, S.; Moha, V.; Meuresch, M.; Brosinski, S.; Thenert, K. M.;
Kothe, J.; Stein, T. v.; Englert, U.; Holscher, M.; Klankermayer, J.;
In conclusion, the very rare hydrogenation of carba-
mates and urea derivatives was accomplished, for the first
time, using a catalyst based on an earth-abundant-metal, the
manganese complex 4, in the presence of catalytic base. Our
mechanistic investigations suggest that the hydrogenation re-
action proceeds via metal-ligand cooperativity involving, the
dearomatized complex 5, which catalyzes the reaction in ab-
sence of added base, in line with its intermediacy. Addition of
H2 to this complex leads to the Mn-H complex 6, also believed
to be an intermediate in the reaction. Overall, this methodol-
ogy presents an attractive strategy for the conversion of mild-
ACS Paragon Plus Environment

Page 5 of 6
Journal of the American Chemical Society
Leitner, W. Hydrogenation of carbon dioxide to methanol using a ho-
Voisine, A.; Wang, D.; Roisnel, T.; Darcel, C.; Sortais, J.-B. Hydrogena-
tion of Ketones with a Manganese PN3 P Pincer Pre-Catalyst. Catal.
Commun. 2017, 92, 1−4. (g) Glatz, M.; Stꢀger, B.; Himmelbauer, D.;
Veiros, L. F.; Kirchner, K. Chemoselective Hydrogenation of Alde-
hydes under Mild, Base-Free Conditions: Manganese Outperforms
Rhenium. ACS Catal. 2018, 8, 4009−4016. (h) Widegren, M. B.; Hark-
ness, G. J.; Slawin, A. M. Z.; Cordes, D. B.; Clarke, M. L. A Highly Active
Manganese Catalyst for Enantioselective Ketone and Ester Hydro-
genation. Angew. Chem., Int. Ed. 2017, 56, 5825−5828. (i) Garbe, M.;
Junge, K.; Walker, S.; Wei, Z.; Jiao, H.; Spannenberg, A.; Bachmann,
S.; Scalone, M.; Beller, M. Manganese- (I)-Catalyzed Enantioselective
Hydrogenation of Ketones Using a Defined Chiral PNP Pincer Ligand.
Angew. Chem., Int. Ed. 2017, 56, 11237−11241.
mogeneous ruthenium–Triphos catalyst: from mechanistic investiga-
tions to multiphase catalysis. Chem. Sci. 2015, 6, 693-704; (g) Jacob, S.;
Rosa, A.; Wolfgang, B.; Ralf, J.; Beller, M. Low‐Temperature Hydro‐
genation of Carbon Dioxide to Methanol with a Homogeneous Cobalt
Catalyst. Angew. Chem. Int. Ed. 2017, 56, 1890-1893.
(6) Balaraman, E.; Gunanathan, C.; Zhang, J.; Shimon, L. J.; Milstein,
D. Efficient hydrogenation of organic carbonates, carbamates and
formates indicates alternative routes to methanol based on CO2 and
CO. Nat. Chem. 2011, 3, 609-614.
1
2
3
4
5
6
7
8
(7) Balaraman, E.; Ben-David, Y.; Milstein, D. Unprecedented cat-
alytic hydrogenation of urea derivatives to amines and methanol. An-
gew. Chem. Int. Ed. 2011, 50, 11702 –11705.
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
(8) Khusnutdinova, J. R.; Garg, J. A.; Milstein, D. Combining Low-
Pressure CO2 Capture and Hydrogenation to Form Methanol. ACS
Catal. 2015, 5, 2416-2422.
(9) (a) Huff, C. A.; Sanford, M. S. Cascade Catalysis for the Homo-
geneous Hydrogenation of CO2 to Methanol. J. Am. Chem. Soc. 2011,
133, 18122–18125. (b) Rezayee, N. M.; Huff, C. A.; Sanford, M. S. Tandem
Amine and Ruthenium-Catalyzed Hydrogenation of CO2 to Metha-
nol. J. Am. Chem. Soc. 2015, 137, 1028−1031. (c) Huff, C. A.; Sanford, M.
S. Catalytic CO2 Hydrogenation to Formate by a Ruthenium Pincer
Complex. ACS Catal. 2013, 3, 2412−2416.
(14) Kumar, A.; Janes, T.; Espinosa-Jalapa, N. A.; Milstein, D. Man-
ganese catalyzed hydrogenation of organic carbonates to methanol
and alcohols. Angew. Chem. Int. Ed. 2018, 57, 12076-12080.
(15) (a) Kaithal, A.; Hölscher, M.; Leitner, W. Catalytic Hydrogena-
tion of Cyclic Carbonates using Manganese Complexes. Angew. Chem.
2018, 130, 13637–13641. (b) Zubar, V.; Lebedev, Y.; Azofra, L. M.;
Cavallo, L.; El‐Sepelgy, O.; Rueping, M. Hydrogenation of CO2‐
Derived Carbonates and Polycarbonates to Methanol and Diols by
Metal–Ligand Cooperative Manganese Catalysis. Angew. Chem. Int.
Ed. 2018, 57, 13439–13443.
(16) Mukherjee, A.; Nerush, A.; Leitus, G.; Shimon, L. J. W.; Ben-
David, Y.; Espinosa Jalapa, N. A.; Milstein, D. Manganese-Catalyzed
Environmentally Benign Dehydrogenative Coupling of Alcohols and
Amines to Form Aldimines and H2: A Catalytic and Mechanistic Study.
J. Am. Chem. Soc. 2016, 138, 4298-4301.
(17) (a) Kumar, A.; Janes, T.; Espinosa-Jalapa, Milstein, D. Synthesis
of cyclic imides by acceptorless dehydrogenative coupling of diols and
amines catalyzed by a manganese pincer complex. J. Am. Chem.
Soc. 2017, 139, 11722-11725. (b) Espinosa-Jalapa, N. A.; Nerush, A.;
Shimon, L. J. W.; Leitus, G.; Avram, L.; Ben-David, Y.; Milstein. D.
Manganese-Catalyzed Hydrogenation of Esters to Alcohols. Chem.
Eur. J. 2017, 23, 5934-5938.
(10) (a) Kothandaraman, J.; Goeppert, A.; Czaun, M.; Olah, G. A.;
Surya Prakash, G. K. Conversion of CO2 from Air into Methanol Using
a Polyamine and a Homogeneous Ruthenium Catalyst. J. Am. Chem.
Soc. 2016, 138, 778−781. (b) Kar, S.; Goeppert, A.; Jotheeswari Kothan-
daraman, J.; Surya Prakash G. K. Manganese-Catalyzed Sequential
Hydrogenation of CO2 to Methanol via Formamide. ACS Catal. 2017,
7, 6347−6351. (c) Integrative CO2 Capture and Hydrogenation to
Methanol with Reusable Catalyst and Amine: Toward a Carbon Neu-
tral Methanol Economy. J. Am. Chem. Soc. 2018, 140, 1580−1583.
(11) Xie, Y.; Hu, P.; Ben-David, Y.; Milstein. D. A Reversible Liquid
Organic Hydrogen Carrier System Based on Methanol-Ethylenedia-
mine and Ethylene Urea. Angew. Chem. Int. Ed. 2019, 131, 5159-5163.
(12) Reviews on catalysis by base metal complexes: (a) Bullock, R.
M. Abundant Metals Give Precious Hydrogenation Performance. Sci-
ence 2013, 342, 1054-1055. (b) Chirik, P.; Morris, R. Getting Down to
Earth: The Renaissance of Catalysis with Abundant Metals. Acc. Chem.
Res. 2015, 48, 2495-2495. (c) Kallmeier, F.; Kempe, R. Manganese
Complexes for (De) Hydrogenation Catalysis: A Comparison to Cobalt
and Iron Catalysts. Angew. Chem. Int. Ed. 2018, 57, 46-60. (d) Garbe,
M.; Junge, K.; Beller, M. Homogeneous Catalysis by Manganese‐Based
Pincer Complexes. Eur. J. Org. Chem. 2017, 4344-4362. (e) Maji, B.;
Barman, M. K. Recent Developments of Manganese Complexes for
Catalytic Hydrogenation and Dehydrogenation Reactions. Synthesis
2017, 49, 3377–3393. (f) Gorgas, N.; Kirchner, K. Isoelectronic Manga-
nese and Iron Hydrogenation/Dehydrogenation Catalysts: Similarities
and Divergences. Acc. Chem. Res. 2018, 51, 1558−1569. (h) Mukherjee,
A.; Milstein, D. Homogeneous Catalysis by Cobalt and Manganese
Pincer Complexes. ACS Catal. 2018, 8, 11435−11469. (i) Alig, L.; Fritz,
M.; Schneider, S. Chem. Rev., 2019, 119, 2681 –2751.
(13) (a) Kallmeier, F.; Irrgang, T.; Dietel, T.; Kempe, R. Highly Active
and Selective Manganese C=O Bond Hydrogenation Catalysts: The
Importance of the Multidentate Ligand, the Ancillary Ligands, and the
Oxidation State. Angew. Chem. Int. Ed. 2016, 55, 11806-110809. (b)
Elangovan, S.; Topf, C.; Fischer, S.; Jiao, H.; Spannenberg, A.; Bau-
mann, W.; Ludwig, R.; Junge, K.; Beller, M. Selective Catalytic Hydro-
genations of Nitriles, Ketones, and Aldehydes by Well-Defined Man-
ganese Pincer Complexes. J. Am. Chem. Soc. 2016, 138, 8809-8814. (c)
Elangovan, S.; Garbe, M.; Jiao, H.; Spannenberg, A.; Junge, K.; Beller,
M. Hydrogenation of Esters to Alcohols Catalyzed by Defined Manga-
nese Pincer Complexes. Angew. Chem. Int. Ed. 2016, 55, 15364-13368.
(d) Papa, V.; Cabrero-Antonino, J. R.; Alberico, E.; Spanneberg, A.;
Junge, K.; Jungea, H.; Beller, M. Efficient and selective hydrogenation
of amides to alcohols and amines using a well-defined manganese–
PNN pincer complex. Chem. Sci., 2017, 8, 3576-3585. (e) Zou, Y-Q.;
Chakraborty, S.; Nerush, A.; Oren, D.; Diskin-Posner, Y.; Ben-David,
Y.; Milstein, D. Highly selective, efficient deoxygenative hydrogena-
tion of amides catalyzed by a manganese pincer complex via metal-
ligand cooperation. ACS Catal. 2018, 8, 8014-8019. (f) Bruneau-
(18) Das, U. K.; Ben-David, Y.; Diskin-Posner, Y.; Milstein, D. N‐
Substituted Hydrazones by Manganese‐Catalyzed Coupling of Alco‐
hols with Hydrazine: Borrowing Hydrogen and Acceptorless Dehy-
drogenation in One System. Agew. Chem., Int. Ed. 2018, 57, 2179-2182.
(19) Das, U. K.; Ben-David, Y.; Leitus, G.; Diskin-Posner, Y.; Mil-
stein, D. Dehydrogenative Cross-Coupling of Primary Alcohols To
Form Cross-Esters Catalyzed by a Manganese Pincer Complex ACS
Catal. 2019, 9, pp 479–484.
(20) Balaraman, E.; Gnanaprakasam, B.; Shimon, L. J. W.; Milstein,
D. Direct Hydrogenation of Amides to Alcohols and Amines under
Mild Conditions. J. Am. Chem. Soc. 2010, 132, 16756−16758.
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 6 of 6
1
2
Graphics for TOC:
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
ACS Paragon Plus Environment