Chemoselective semihydrogenation of alkynes catalyzed by manganese(i)-PNP pincer complexes

Article abstract of DOI:10.1039/d0cy00992j

A general manganese catalyzed chemoselective semihydrogenation of alkynes to olefins in the presence of molecular hydrogen is described. The best results are obtained by applying the aliphatic Mn PNP pincer complex Mn-3c which allows the transformation of various substituted internal alkynes to the respective Z-olefins under mild conditions and in high yields. Mechanistic investigations based on experiments and computations indicate the formation of the Z-isomer via an outer-sphere mechanism.

Full text of DOI:10.1039/d0cy00992j

View Article Online
View Journal
Catalysis
Science &
Technology
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: M. Garbe, S.
Budweg, V. Papa, Z. Wei, H. Hornke, S. Bachmann, M. Scalone, A. Spannenberg, H. Jiao, K. Junge and M.
Beller, Catal. Sci. Technol., 2020, DOI: 10.1039/D0CY00992J.
Volume
Number
21 January 2017
Pages 313-534
7
2
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Catalysis
Science &
Technology
rsc.li/catalysis
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 2044-4761
PAPER
Chaoqiu Chen, Yong Qin et al.
Highly dispersed Pt nanoparticles supported on carbon
nanotubes produced by atomic layer deposition for hydrogen
generation from hydrolysis of ammonia borane
rsc.li/catalysis

Please do not adjust margins
Catalysis Science & Technology
Page 1 of 8
View Article Online
DOI: 10.1039/D0CY00992J
ARTICLE
Chemoselective Semihydrogenation of Alkynes catalyzed by
Manganese(I)-PNP Pincer Complexes
Marcel Garbe,a§ Svenja Budweg,a§ Veronica Papa,a Zhihong Wei,a Helen Hornke,a Stephan
Bachmann,b Michelangelo Scalone,b Anke Spannenberg,a Haijun Jiao,a Kathrin Junge,*a and
Matthias Beller*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
A general manganese catalyzed chemoselective semihydrogenation of alkynes to olefins in the presence of molecular
hydrogen is described. Best results are obtained applying the aliphatic Mn PNP pincer complex Mn-3c which allows the
transformation of various substituted internal alkynes to the respective Z-olefins under mild conditions and in high yields.
Mechanistic investigations based on experiments and computations indicate the formation of the Z-isomer via an outer-
sphere mechanism.
Dedicated to Prof. Uwe Rosenthal on the occasion of his 70th birthday
type catalysts have been applied for the (transfer)
semihydrogenation of alkynes to alkenes.
Introduction
The first example of a non-noble metal pincer based
Olefins play an important role as synthetic building blocks for
fine and bulk chemistry as well as in organic synthesis.1
Additionally, alkenes and here especially the Z-isomers can be
found as structural motif in numerous biologically and
pharmaceutically active compounds. Although various
synthetic approaches for these compounds have been
developed in the past, the selective reduction of C-C triple
bonds to alkenes offers a convenient route.2 In general, in this
transformation the control of chemoselectivity (alkenes vs
alkanes) and the stereoselectivity (E- and/or Z-olefins) is
important. A selective preparation of one single isomer
strongly depends on the chosen reaction parameters as well as
on the catalyst. Traditionally, the application of heterogeneous
transition–metal catalysts such as the Lindlar catalyst3a,b (lead-
poisoned Pd on CaCO3) enables the selective
semihydrogenation of alkynes to the Z-olefins. Besides Pd,3
other transition metals, such as Rh,4 Ru,5 Nb,6 Cr,7 and V8 have
been reported for both heterogeneous and homogeneous
catalysis.9
catalyst for the semihydrogenation of alkynes has been
reported by Milstein and co-workers in 2013 (Figure 1).14a
More specifically, the acridine-based PNP iron complex Fe-1
selectively reduced internal alkynes to the E-alkenes, while no
additional base was required to obtain the desired products.
Notably, the corresponding E-isomers were formed in high
yields with E:Z ratios of up to 100:0 via rapid isomerisation of
the originally formed Z-products. Very recently, the Kirchner
group presented a cationic iron pincer complex Fe-2 bearing
an aminoborane ligand, which efficiently reduced internal
alkynes under mild conditions to the respective Z-olefins.14b
Based on the pioneering work of Milstein, Co pincer ligated
catalysts were published for the (transfer) semihydrogenation
of alkynes to the E- or Z-isomers.15 Thus, the Co CCC pincer
complex Co-1 is able to reduce alkynes with high selectivity to
trans-alkenes.15a
+
Me
H
H
Br
Ni
Cl
N
Ph
P
H
N
N
Fe
N
PiPr2
N
Mes
N
PPh2
Cl
PPh2
H
N
Based on the growing significance of sustainability and the
shortage of resources, the development of cheap, more easily
available, non-noble metal catalysts is of increasing
importance. In this respect, catalytic systems derived from first
row transition metals such as Ni,10 Co,11 Fe,12 or Cu,13 were
studied for this reaction. Here, especially homogeneous pincer
Fe
H
N
Co
Me
N
H
B
PPh3
P
P
Ph2
P
iPr2
N2
Ph2
B
H
H
N
Me
N
Mes
Me
Fe-1
Fe-2
Ni-1
Co-1
tBu
Et
N
Ph
tBu
H
N
PR2
Cl
N
N
Si
N
N
N
N
PiPr2
O
N
Co
Co
O
Et
N
Mn
Br
Mn
Cl
Cl
P
Si
tBu
P
iPr2
R2
N
a. Leibniz-Institut für Katalyse e.V., Albert-Einstein-Straße 29a, Rostock, 18059,
Germany. Email: Matthias.Beller@catalysis.de, Kathrin.Junge@catalysis.de
b. F. Hoffmann-La Roche AG, Department of Process Chemistry & Catalysis, Basel,
4070, Switzerland.
Br
Cl
Cl
Cl
N
Ph
tBu
Mn-1
Co-2a
Co-2b
R = tBu
R = iPr
Mn-2
Co-3
§ Both authors contributed equally to this publication.
Fig. 1. Non-noble metal pincer-based catalysts for the (transfer)
semihydrogenation of internal alkynes
Electronic
Supplementary
Information
(ESI)
available:
See
DOI: 10.1039/x0xx00000x
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 2 of 8
ARTICLE
Journal Name
A broad range of substituted diphenylacetylenes was to the corresponding olefin 2a was detected (Entries 2-4),
View Article Online
hydrogenated in high yields and E/Z ratios both with electron- while exclusively the Z-isomer was formeDdO. I: 10.1039/D0CY00992J
Br
Br
Br
Br
donating and –withdrawing groups. Mechanistic studies
showed that the corresponding E-alkenes are produced by
initial cis-hydrogenation followed by cis/trans-isomerisation.
Interestingly, Liu and co-workers developed a stereo-divergent
Co-catalysed transfer hydrogenation of alkynes to Z- and/or E-
alkenes.15b,d They observed that the stereocontrol for the
semihydrogenation of alkynes strongly depends on the ligand
type of the Co-pincer catalyst. Applying the Co PNP pincer
complex Co-2a bearing bulky t-butyl substituents preferentially
the Z-isomers are formed with ammonia borane as hydrogen
source. The E-isomer is usually formed via isomerisation of the
Z-alkene, which occurred on an open coordination site of the
sterically less hindered metal centre of the catalyst. Notably, a
slight change of the PNP-ligand structure from t-butyl (Co-2a)
to i-propyl substituents (Co-2b) of the Co pincer complex
resulted in a completely different stereoselectivity mainly
yielding the E-alkenes. The phosphorous-free Co NNN pincer
pre-catalyst Co-3 also required ammonia borane for activation
transforming internal alkynes to the Z-alkenes.15c Furthermore,
the Ni PPP pincer complex Ni-1 was reported to convert 1,2-
diphenylacetylene quantitatively to E-stilbene.16
Recently, also two manganese derived pincer type
complexes were reported for the transfer semihydrogenation
of internal alkynes.17 Here, the N-heterocyclic silylene–
manganese catalyst Mn-1 produced the respective E-olefins,
while with the manganese pre-catalyst [Mn(II)−PNP][Cl]2 Mn-2
the preferential formation of the Z-alkene was observed. Both
catalytic systems worked at relatively low temperature for
several substrates, but as a drawback equimolar amounts of
borane adducts are required as hydrogen donor and for
catalyst activation.
PEt2
H
N
H
N
H
N
H
N
PiPr2
PCy2
CO
CO
CO
PEt2
CO
Mn
CO
Mn
CO
Mn
Mn
CO
P
P
P
P
CO
iPr2
Cy2
Et2
Et2
CO
Mn-3ck
Mn-3b
Mn-3c
Mn-3a
Br
Br
Br
Br
PiPr2
H
N
Me
N
H
Me
CO
N
CO
N
CO
N
PEt2
CO
N
Mn
CO
Mn
Mn
CO
Mn
Me
CO
CO
N
N
N
CO
N
P
Et2
CO
Mn-5
CO
Mn-6
Mn-7
Mn-4
Fig 2. Selection of manganese pincer based complexes tested in the
semihydrogenation of 1,2-diphenylacetylene (1a).
Notably, the neutral Mn pincer complex Mn-3c produced
between 80-99% of the Z-stilbene in short reaction time
(Entries 8-12) and mild conditions (reaction temperature: 30°C;
Entry 14). The excellent catalytic performance of this system is
also demonstrated using only 0.5 mol% of pre-catalyst Mn-3c
(Entry 17). It is important to mention that in none of these
reactions complete hydrogenation to the corresponding
alkane was observed.
After the identification of the optimal Mn-pincer complex,
the influence of different reaction parameters such as solvent
and bases was further investigated (Table 2).
Table 1. Mn-catalysed hydrogenation of 1,2-diphenylethyne 1a:
Optimization of the reaction conditions[a]
[Mn] (x mol%)
base (5 mol%)
T (°C) , 30 bar H2,
2-16 h, solvent
2b
1a
2a
Although, a reasonable number of non-noble metal pincer-
based catalyst was reported for the semihydrogenation of
internal alkynes in the past years, examples of defined
catalysts operating with molecular hydrogen are still limited.
Herein, we present the development of the first manganese-
based pincer catalyst which allows for the semihydrogenation
of alkynes using inexpensive and atom-efficient H2.
Catalyst
T
(°C)
50
50
50
50
50
50
50
50
50
50
50
50
50
30
30
30
30
30
p
(bar)
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
30
5
conv.
(%)
45
yield
2a (%)
39
93
95
99
---
Entry
h
Z/E
(mol%)
Mn-3a (2)
Mn-3b (2)
Mn-3ck (2)
Mn-3c (2)
Mn-5 (2)
1
2
3
16
16
16
16
16
16
16
5
>99
>99
>99
>99
---
97
>99
>99
2
3
5.5
61
60
>99
61
>99
2
73
4
5
6a
Mn-6 (2)
Mn-7 (2)
---
3
---
n.d.
Results and discussion
Catalytic semihydrogenation of internal alkynes using manganese
pincer complexes
7a
8
9a
Mn-3b (2)
Mn-3ck (2)
Mn-3c (2)
Mn-3b (2)
Mn-3c (2)
Mn-4 (2)
Mn-3c (2)
Mn-3c (1)
Mn-3c (1)
Mn-3c (0.5)
Mn-3c (1)
59
56
99
60
99
---
67
38
99
74
88
97:3
97:3
99:1
>99
>99
---
>99
98:2
>99
>99
>99
5
5
2
2
2
2
2
4
10
11
12
13b
14
15
16a
17a
18a
At the start of our work, various manganese PNP,18 NNP,19 and
NNN20 pincer ligated complexes Mn-3 - Mn-7, which were
developed in our laboratory, were tested for hydrogenation of
the model compound 1,2-diphenylethyne 1a using 2 mol%
catalyst and 5 mol% base loading at 30 bar H2 and 50 °C (Figure
2). Interestingly, the Mn complex Mn-3a with i-Pr2P
substituents in the PNP ligand backbone as well as the NNN
Mn-5 and Mn-6 and NNP ligated Mn species Mn-7 provided
only low or no reactivity (Entries 1, 5-7). In case of Mn pincer
compounds Mn-3b, Mn-3ck, and Mn-3c complete conversion
43
>99
77
4
4
92
General conditions: 0.5 mmol substrate 1a, 2 mol% catalyst Mn-3 - Mn-7, 5 mol%
NaOtBu, 1 mL toluene. [a] 5 mol% KOtBu; 1 mL heptane. [b] 2 mL heptane.
2 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 8
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
Table 2. Influence of solvents and bases for Mn-catalysed
both functionalities are reduced to the respecVtiievweAr(tiZcl)e-1O-n(li4ne-
semihydrogenation of 1,2-diphenylethyne 1aa
DOI: 10.1039/D0CY00992J
styrylphenyl) ethane-1-ol (2j) in 85% isolated yield.
H
H
Mn-3c
KOtBu (2.5-5 mol%)
(1-2 mol%)
Mn-3c
base (5 mol%)
(2 mol%)
R2
R1
R1
R2
30-60°C , 30 bar H2,
16 h, heptane
30 °C , 30 bar H2,
2 h, solvent
1a
1a-1t
2a
conv. (%)
25
2b
2a-2t
Entry
1
Solvent
Base
yield 2a
(%)
21
Z/E
97:3
CH2Cl2
KOtBu
2aa
2ba
F
2cb
Cl
99% (88%), >99:1 Z/E
2
3
4
5
6
Et2O
THF
dioxane
t-AmylOH
EtOH
heptane
heptane
heptane
heptane
heptane
toluene
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
KOtBu
NaOtBu
KOH
53
19
26
5
51
17
23
0
---
>99
98
86
4
99:1
97:3
97:3
---
99% (85%), >99:1 Z/E
99% (85%), >99:1 Z/E
0
---
Br
Br
Br
2dc
CF3
2ec
2fc
7
>99
99
88
8
0
90
>99
>99
>99
n.d.
---
99% (89%), >99:1 Z/E
99% (81%), >99:1 Z/E
99% (79%), >99:1 Z/E
8b
9b
10b
11c
12
---
89
KOtBu
KOtBu
COOMe
MeO
CF3
OMe
2gd
2hd
2id
>99
99% (70%), >99:1 Z/E
99% (95%), >99:1 Z/E
99% (94%), >99:1 Z/E
13d
14d
toluene
toluene
KOtBu
---
85
3
85
2
>99
n.d.
General conditions: a 0.5 mmol substrate, 2 mol% catalyst Mn-3c, 5 mol% KOtBu,
1 mL solvent, 30 bar H2, 30°C, 2 h. 0.5 mmol substrate, 1 mol% Mn-3c, 5 mol%
base, 1 mL heptane. c 0.5 mmol substrate, 5 mol% KOtBu, 1 mL solvent, 30 bar H2,
30°C, 2 h. d 0.5 mmol substrate, 2 mol% catalyst Mn-3ca, 1 mL solvent, 30 bar H2,
30°C, 4 h.
OH
nPr
OMe
Et
Me
2jb
2kb
2ld
99% (74%), >99:1 Z/E
b
Me
99% (85%), >99:1 Z/E
99% (92%), >99:1 Z/E
NH2
SiMe3
nBu
nBu
In dichloromethane or various ethers only moderate yields
of the Z-olefin were observed (Entries 1-4), while the
chemoselective formation of cis-stilbene 2a stayed unaffected.
Also, more polar alcoholic solvents completely failed to give
the desired product (Entries 5-6). In contrast, aprotic nonpolar
solvents such as n-heptane and toluene proved to be suitable
for this transformation producing the cis-alkene in yields
above 90% (Entries 7-10, 12). Notably, apart from KOtBu,
other bases such as NaOtBu and KOH were tested using 1
mol% catalyst loading of Mn-3c (Entries 8-10). Here, again
complete conversion was obtained with KOtBu, while NaOtBu
leads to slightly lower product yield. In case of KOH only poor
reactivity was observed. A blank experiment using 5 mol% of
KOtBu without catalyst shows no conversion (Entry 11).
2od
2mc
2nd
99% (97%), >99:1 Z/E
99% (87%), >99:1 Z/E
99% (68%), >99:1 Z/E
Me
NH2
N
2pd
2qb
2rd
Cl
99% (68%), >99:1 Z/E
99% (68%), >99:1 Z/E
99% (99%), >99:1 Z/E
OH
2uc
0%
2sb
2tc
99% (43%), >99:1 Z/E
95% (90%), >99:1 Z,Z/E,E
R
a
Mn-3c
Mn-3c
Mn-3c
Mn-3c
1 mol%
2 mol%
1 mol%
2 mol%
, 2.5 mol% KOtBu, 5 bar H2, 30°C, 4 h
, 5 mol% KOtBu, 30 bar H2, 60°C, 16 h
, 2.5 mol% KOtBu, 30 bar H2, 60°C, 16 h
, 5 mol% KOtBu, 30 bar H2, 30°C, 16 h
5ab
5db
5cb
b
c
d
R = H
0%
0%
R = Me
R = COOMe 92% (76%)
The general applicability and the functional group
tolerance of pre-catalyst Mn-3c were tested for diverse
substrates (Scheme 1). Here, 20 different internal alkynes
bearing (hetero)aromatic as well as alkyl moieties were
efficiently reduced to the respective alkenes in good to high
isolated yields with excellent Z-selectivities under comparably
mild conditions (30 bar H2, 30-60°C). Alkynes with halide
substituents such as fluorine (2b), chlorine (2c), bromine (2d-e)
or the trifluoromethyl group (2f-g) are quantitatively
transformed to the cis-olefins in 70-89% isolated yields.
Additionally, ester (1i) and amine groups (1o, 1q) on the
alkynes were tolerated by the pincer complex Mn-3c
producing selectively the alkene products. In case of the alkyne
1j bearing a keto group in para-position on the aromatic ring
Scheme 1. Semihydrogenation of alkynes catalysed by Mn-3c.a
Conversions are determined by GC analysis. Isolated yields are given in
parentheses.
Attempts to shift the selectivity for this special substrate
(1j) to the exclusive reduction of the triple bond failed. In fact,
applying 1 mol% Mn-3c at 30°C preferential reduction of the
ketone took place. Furthermore, the heteroaromatic alkyne 1r)
is converted in excellent yield (99%) and selectivity to the cis-
olefin 2r. In addition, the diyne 1t is smoothly reduced on both
triple bonds to the synthetically interesting (Z,Z)-diene 2t.
While the catalyst Mn-3c works efficiently for internal alkynes
bearing at least one aromatic substituent, no conversion was
detected for the related alkyl-substituted internal alkyne 1u.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 4 of 8
ARTICLE
Journal Name
a)
Mn-3c
KOtBu (5 mol%)
(2 mol%)
aliphatic PNP pincer ligand played an active VireowlAerticilne Ontlhinee
hydrogen transfer process.
DOI: 10.1039/D0CY00992J
95 °C , argon, 6 h,
heptane
2b
2a
b)
c)
Mn-3c
KOtBu (2.5 mol%)
(1 mol%)
30 °C: n.r.
80 °C: n.r.
100 °C: 2%
140 °C: 9%
x °C , 30 bar H2,
4 h, heptane
3
2a
Mn-3c
(1 mol%)
30 °C: n.r.
80 °C: n.r.
100 °C: n.r.
140 °C: 4.5%
KOtBu (2.5 mol%)
x °C , 30 bar H2,
4 h, heptane
2b
3
Fig. 3. Molecular structure of Mn-4 in the crystal. Only one molecule of the asymmetric
unit is depicted. Displacement ellipsoids correspond to 30% probability. Hydrogen
atoms and atoms of lower occupancy are omitted for clarity; for further information
see ESI.
Mn-4
KOtBu (5 mol%)
(2 mol%)
d)
50 °C , 30 bar H2,
2 h, heptane
1a
2a
2b
To figure out the possible involvement of the pincer ligand
in the direct hydrogenation of alkynes, a further control
experiment was realised. To prove the ability of metal ligand
cooperation, the NH moiety of the pincer backbone in the
manganese catalyst was blocked with a methyl substituent.
Therefore, the respective N-methylated manganese pincer
complex Mn-4 was synthesised starting from [Mn(CO)5Br] and
pincer ligand MeN(CH2-CH2-PEt2)2 (see SI) and characterised by
spectroscopic methods. The 31P NMR spectra of Mn-4 showed
one signal at 64.6 ppm indicating the formation of only one
isomer. Furthermore, in the IR-spectra two characteristic
bands at 1899 and 1807 cm-1 are found in the carbonyl region
demonstrating the presence of two CO molecules in the
complex Mn-4. Signals at m/z 397 and m/z 415 were detected
in the ESI-spectroscopic analysis referring to [M(Mn-4)-2CO]+
and [M(Mn-4)-Br+ACN]+, respectively. These fragments
indicate the formation of the neutral manganese complex Mn-
4. Additionally, a peak at m/z 402 was observed in trace
amounts which could be assigned to a cationic Mn-species
bearing three CO molecules and the pincer-backbone.
Such a similar coordination behaviour is known for the
related Mn-3c complex, which forms the kinetically stable
cationic Mn-3ck next to the thermodynamically more stable
neutral compound Mn-3c, too.18c Finally, crystals suitable for
X-ray diffraction analysis were grown in methanol solution
stored at 0°C. The molecular structure (Figure 3) exhibited a
distorted octahedral geometry.24 Here, the manganese centre
is surrounded by the PNP donor atoms of the pincer ligand and
one CO molecule placed in an equatorial position and a
bromine atom as well as a second CO molecule arranged in
axial position. Taking all these analytical data into account the
formation of the neutral Mn complex with the structure
[Mn(PMeNPEt)(Br)(CO)2] Mn-4 is confirmed.
Scheme 2. Mechanistic experiments for the semihydrogenation of
alkynes.
However, alkyne 1s with an aromatic and aliphatic moiety
smoothly reacted to the cis-olefin 2s. Finally, three terminal
alkynes 4a-c were tested in the presence of 2 mol% Mn-3c at
30 bar hydrogen, 60°C and 16 hours. Only the activated
terminal alkyne 4c was selectively reduced on the alkyne
moiety giving 4-vinyl methylbenzoate 5c in 76% isolated yield.
Investigation of the reaction mechanism
The reaction mechanism was studied based on both catalytic
experiments and DFT computation. To investigate the
potential isomerisation ability of our optimal catalyst system,
Z-stilbene was heated with 2 mol% Mn-3c at 95°C for 6 hours
in the absence of hydrogen (Scheme 2, a). Interestingly, no
formation of the corresponding E-product was observed. This
finding contrasts with the previous work of Milstein and co-
workers, who reported isomerisation of the initially formed Z-
product to the E-olefin with their acridine-based PNP iron
complex Fe-1.14a
Besides, no isomerisation of 2 or reduction to 1,2-
diphenylethane 3 was observed, when cis- or trans-stilbene
were heated in the presence of 1 mol% of catalyst Mn-3c at 30
bar hydrogen pressure at 30 °C, 80 °C or 100 °C (Scheme 2b, c).
At a temperature of 140 °C only little formation to the alkane
occurred (9% of 1,2-diphenylethane 3) potentially due to the
fact that a major part of heptane and stilbene are in the gas
phase, while the catalyst stays in the liquid phase.
Nevertheless, these findings demonstrate the preference of
Mn-3c for the hydrogenation of the triple bond compared to
olefins and are in good agreement with theory vide infra. Here,
the computations showed a slightly lower energy barrier for
the hydrogenation of cis-stilbene (2a: 21.3 kcal/mol) to 1,2-
diphenylethane than for trans-stilbene (2b: 23.2 kcal/mol).
Moreover, the so-called metal-ligand cooperation (MLC)
was studied, which is often observed in catalytic
hydrogenations with pincer complexes.21 Also, in our previous
works on catalytic reduction of carboxylic acid derivatives with
iron,22 cobalt23 or manganese18a,c pincer complexes, the
Using Mn-4 for the model hydrogenation showed no
conversion (Scheme 2d), which unambiguously proves the
importance of the N-H moiety of the aliphatic ligand backbone.
This experimental result also provides a strong hint for an
outer-sphere hydrogenation mechanism in the catalytic
reaction. This assumption was further explored by DFT
computations. In our previous investigations on the
4 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 8
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
hydrogenation of esters18c as well as nitriles, ketones and
aldehydes18a using the same type of catalysts (Mn-3) (Figure 1)
an outer-sphere hydrogenation mechanism was proposed,
too. In more detail, the Mn-H transfer step with the formation
of an intermediate and a subsequent N-H transfer to the
product could be verified by experiment and theory.
Furthermore, such aliphatic Mn pincer based catalysts have
been successfully used in the isomerisation of allylic alcohols
View Article Online
Ph
Ph
Ph
Ph
DOI: 10.1039/D0CY00992J
2a
1a
TS2
H
H
H
N
H
N
PEt2
CO
PEt2
N
PEt2
CO
- CO
TS1 (- H2)
+ H2
Mn
CO
Mn
CO
Mn
CO
P
P
P
Et2
Et2
Et2
Mn-3cc
Mn-3cb
cis-Mn-3ca
TScis or TStrans
Ph
or
Ph
Ph
to the corresponding carbonyl compounds via
dehydrogenation/hydrogenation pathway, which
a
was
Ph
Ph
Ph
2a
2b
validated by the isolation of an intermediate, deuterium
labelling experiments as well as by comparative DFT
computation.25
Mn-3cc
50.2 kcal/mol
+ CO
2b
)
23.2 kcal/mol
TStrans
(
Furthermore, the hydrogenated complex Mn-3ca, which should
Mn-3ca/Mn-3cb
20.6 kcal/mol
TS1 (
)
be involved in the catalytic cycle, was prepared separately by
treating Mn-3c with 2 equivalents of NaBEt3H (1 M in THF) for 24
hours at room temperature. This complex was isolated from a red
solution giving a brown oil, which was not stable in pure form.
Therefore, Mn-3ca was handled in a stock solution, which was used
2a
)
21.3 kcal/mol
TScis
(
1a
TS2 (
)
17.3 kcal/mol
Mn-3cb
+ H2
1.6 kcal/mol
Mn-3ca
0.0 kcal/mol
1
to confirm the structure by spectroscopic methods. In the H NMR
Scheme 4. Proposed bifunctional outer-sphere mechanism for the Mn-
catalysed hydrogenation of alkyne 1a and alkenes 2 (top) and M06L/6-
311+G(3df,3pd) computed Gibbs free energy in heptane solution
(bottom)
spectrum characteristic peaks for the hydride group were found at -
5.8 and -6.1 ppm. During the MS analysis signals at m/z 360 and 401
were detected, which can be assigned to [M(Mn-3ca)-H]+ and
[M(Mn-3ca)-H+ACN]+ (see SI for further details). Using 2 mol% of
Mn-3ca for the benchmark reaction provided cis-stilbene in 85%
yield (Table 2, entry 13) only in the presence of 5 mol% KOtBu.
Interestingly, the hydride species Mn-3ca is not active without base
(Table 2, entry 14). A possible reason for this catalytic behaviour is
the preferential formation of the thermodynamically more stable
trans-Mn-3ca isomer during the synthesis, which is confirmed by
DFT computation and NMR analysis (see SI).26 As an outer-sphere
mechanism is discussed, in case of a trans-Mn-3ca complex no
concerted hydride transfer from the catalyst to the substrate is
possible. In order to form the active cis-configuration, the base is
needed to generate the amido complex Mn-3cb, which then forms
the cis-Mn-3ca under a hydrogen atmosphere (Scheme 3).
Extensive benchmark calculations including different functional
methods in gas-phase as well as in solution (SMD28) with van der
Waals dispersion correction (GD3BJ29) were carried out on the basis
of the real-size catalysts (ethyl-substituted PNP ligand) and
substrates in order to select the appropriate computational
methods. In the following the data from M06L30 in combination
with the all electron 6-311++G(3df,3pd) basis set31 in heptane
solution are presented (Scheme 4, bottom). Other results are given
in the Supporting Information. For hydrogenation reactions, a
stepwise reaction scheme has been calculated, where the first Mn-
H transfer has a higher barrier than the second N-H transfer.32
Therefore, only the simplified potential free energy surface with
only the highest barriers (the Mn-H transfer step) is discussed. In
agreement with previous results,18 the interconversion from the
hydride Mn-3ca to the amido complex Mn-3cb has a Gibbs free
energy barrier of 20.6 kcal/mol and is slightly endergonic (1.6
kcal/mol) revealing adjustable reversibility and equilibrium under
given conditions. In addition, the CO dissociation to Mn-3cc is highly
endergonic by 50.2 kcal/mol demonstrating an enhanced stability of
complex Mn-3ca.
A similar outer-sphere mechanism has been discussed for the
hydrogenation of quinolines by using well-defined PNP and PNN
pincer manganese complexes.27 Considering all these findings and
the performed experimental work, the hydrogenation of 1,2-
diphenylethyne 1a was computed on the basis of such
a
bifunctional outer-sphere mechanism (Scheme 4, top).
Br
H
N
PEt2
CO
The hydrogenation of 1,2-diphenylethyne (1a) to cis-
stilbene (2a) has a free energy barrier of 17.3 kcal/mol, which
is lower than that (20.6 kcal/mol) of H2 elimination and is
exergonic by 24.4 kcal/mol. Both values indicate that in case of
the hydrogenation reaction the energy barrier is lower. These
findings agree with the experimental results, where the
hydrogenation of 1,2-diphenylethyne (1a) to cis-stilbene (2a) is
accessible at low temperature and low H2 pressure (Table 1,
entries 14-18).
Mn
P
Et2
2 equiv. NaBEt3H,
toluene, rt, 24 h
CO
base, H2
Mn-3ca
R
C
C
R
CO
H
H
H
base, H2
- H2
N
PEt2
N
PEt2
CO
N
PEt2 olefin, H2
Mn
Mn
CO
Mn
- H2
CO
P
P
P
CO
Et2
Et2
Et2
H
CO
Mn-3cb
trans-Mn-3ca
cis-Mn-3ca
Furthermore, the corresponding hydrogenation of cis- (2a)
and trans-stilbene (2b) to 1,2-diphenylethane (Scheme 2b, c)
Scheme 3. Postulated formation of cis- and trans-Mn-3ca.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

Please do not adjust margins
Catalysis Science & Technology
Page 6 of 8
ARTICLE
Journal Name
was computed to have barrier of 21.3 and 23.2 kcal/mol, and olefins. Mechanistic investigations based on experiments and
View Article Online
DOI: 10.1039/D0CY00992J
exergonic reaction free energy by 18.9 and 13.1 kcal/mol, computations reveal a direct involvement of the pincer ligand
respectively. In comparison with the free energy barrier of H2 in the hydrogenation step via an outer sphere pathway.
elimination, the hydrogenation of cis- and trans-stilbene
requires higher temperature and/or higher H2 pressure. Such
high pressure is necessary to keep the stability of complex Mn-
Conflicts of interest
3ca towards H2 elimination, especially in case of trans-stilbene
hydrogenation. The higher barrier of the hydrogenation of cis-
and trans-stilbene compared to the hydrogenation of 1,2-
diphenylethyne explains the observed chemoselectivity as well
as the inactivity of cis- and trans-stilbene up to 110°C (Scheme
2b, c). Under the optimized conditions for the
semihydrogenation of 1,2-diphenylethyne (1a), neither cis-
stilbene nor trans-stilbene can be hydrogenated further on.
However, at elevated temperature of 140°C and 30 bar H2
pressure, slow transformation of cis- and trans-stilbene into
the corresponding alkane was found. As the energy barriers of
the interconversion of the active catalysts between Mn-3ca
and Mn-3cb are close to the hydrogenation barriers of cis- and
trans-stilbene, one could expect that the reaction should occur
at high temperature. The observed low reactivity might be
associated with the reduced solubility of H2 gas in solution at
high temperature,33 as well as with the crossover of the
reaction to the gas phase.
DFT computation is also a helpful tool to understand the
reaction behaviour of different substituted alkynes (Scheme
1): Thus, in substrate 1j the preferential hydrogenation of the
ketone group can be explained by the lower hydrogenation
barrier of benzophenone (15.5 kcal/mol) compared to the
hydrogenation barrier of the alkyne functionality in 1,2-
diphenylacetylene (1a). On the other side, for methyl 4-
(phenylethynyl)benzoate (1i) a barrier of 22.2 kcal/mol was
computed for the first hydrogenation step of methyl benzoate
(Ph-COOCH3), which is higher than that of CC triple bond
hydrogenation of 1a. Therefore, a high chemoselectivity for
the hydrogenation of alkyne moiety was observed in 1i.
Also, the strong influence of the alkyl substitution on the
reactivity of alkynes can be elucidated by DFT computations.
While alkyne 1s with one phenyl and one alkyl substituent can
be smoothly reduced, 4-octyne (1u) bearing two alkyl groups
showed no activity at all. This effect is caused by the high
energy barrier in case of alkyl substitution. Here, a barrier of
26.7 kcal/mol was computed for the hydrogenation of 4-
octyne (1u), which is by 9.4 kcals/mol higher than that of 1a
hydrogenation. All these values clearly explain and support the
experimental results.
There are no conflicts to declare.
Acknowledgements
We thank Dr. C. Fischer, S. Buchholz, S. Schareina (all LIKAT) for
their excellent analytical support. The authors thank Bianca
Tannert for their excellent technical assistance in the
laboratory.
Notes and references
1
a) J. G. de Vries and C. J. Elsevier, in Handbook of
Homogeneous Hydrogenation, Wiley-VCH, Weinheim, 2007.
a) P. N. Rylander, in Catalytic Hydrogenation in Organic
Syntheses, Academic Press: New York, 1979; b) P. G.
Andersson and I. J. Munslow, in Modern Reduction Methods,
Wiley: New York, 2008; c) C. Oger, L. Balas, T. Durand, J.-M.
Galano, Chem. Rev., 2013, 113, 1313–1350.
2
3
a) H. Lindlar, Helv Chim Acta, 1952, 35, 446–450; b) H. Lindlar
and R. Dubuis, Org. Synth., 1966, 46, 89; c) B. M. Trost and R.
Braslau, Tetrahedron Lett., 1989, 30, 4657−4660; d) A.
Bacchi, M. Carcelli, M. Costa, A. Leporati, E. Leporati, P.
Pelagatti, C. Pelizzi and G. Pelizzi, J. Organomet. Chem., 1997,
535, 107−120; e) P. Pelagatti, A. Venturini, A. Leporati, M.
Carcelli, M. Costa, A.; Bacchi, G. Pelizzi and C. Pelizzi, J. Chem.
Soc., Dalton Trans., 1998, 2715−2721; f) C. A. Hamilton, S. D.
Jackson, G. J. Kelly, R. Spence and R. D. de Bruin, Appl. Catal.
A, 2002, 237, 201−209; g) L. L. Wei, L. M. Wei, W. B. Pan, S. P.
Leou and M. J. Wu, Tetrahedron Lett., 2003, 44, 1979−1981.
a) R. R. Schrock and J. A. Osborn, J. Am. Chem. Soc., 1976, 98,
2143−2147; b) C. Kohrt, G. Wienhöfer, C. Pribbenow, M.
Beller and D. Heller, ChemCatChem, 2013, 5, 2818–2821; c)
S. Furukawa, A. Yokoyama and T. Komatsu, ACS Catal., 2014,
4, 3581–3585; d) J. Luo, R. Theron, L. J. Sewell, T. N. Hooper,
A. S. Weller, A. G. Oliver and J. S. McIndoe, Organometallics,
2015, 34, 3021–3028; e) S. A. Jagtap and B. M. Bhanage,
ChemistrySelect, 2018, 3, 713–718; f) S. P Desai, J. Ye, J.
Zheng, M. S. Ferrandon, T. E. Webber, A. E. Platero-Prats, J.
Duan, P. Garcia-Holley, D. Camaioni, K. W. Chapman, M.
Delferro, O. K. Farha, J. L. Fulton, L. Gagliardi, J. A. Lercher, R.
L. Penn, A. Stein and C.C. Lu, J. Am. Chem. Soc., 2018, 140,
15309–15318; g) S. P. Desai, J. Ye, T. Islamoglu, O. K. Farha
and C. C. Lu, Organometallics, 2019, 38, 3466–3473.
a) Y. Shvo, I. Goldberg, D. Czerkie, D. Reshef and Z. Stein,
Organometallics, 1997, 16, 133−138; b) J. Li and R. Hua,
Chem. Eur. J., 2011, 17, 8462−8465; c) Y. Yamamoto, S. Mori
and M. Shibuya, Chem. Eur. J., 2013, 19, 12034−12041; d) K.
Radkowski, B. Sundararaju and A. Fürstner, Angew. Chem.,
Int. Ed., 2013, 52, 355–360; e) M. Leutzsch, L. M. Wolf, P.
Gupta, M. Fuchs, W. Thiel, C. Farès and A. Fürstner, Angew.
Chem., Int. Ed., 2015, 54, 12431–12436; f) S. Musa, A. Ghosh,
L. Vaccaro, L. Ackermann and D. Gelman, Adv. Synth. Catal.,
2015, 357, 2351–2357; g) K. T. Neumann, S. Klimczyk, M. N.
Burhardt, B. Bang-Andersen, T. Skrydstrup and A. T.
Lindhardt, ACS Catal., 2016, 6, 4710–4714; h) R. Kusy and K.
Grela, Org. Lett., 2016, 18, 6196–6199; h) A. Guthertz, M.
Leutzsch, L. M. Wolf, P. Gupta, S. M. Rummelt, R. Goddard,
4
5
Conclusions
For the first time the selective hydrogenation of alkynes using
hydrogen in the presence of molecularly defined manganese
pincer complexes is described. Specifically, the manganese
complex Mn-3c coordinated by an aliphatic PNP pincer ligand
allows
for
highly
chemo-
and
stereoselective
semihydrogenation of internal alkynes under mild conditions.
Moreover, this non-noble metal derived pre-catalyst efficiently
converts various internal alkynes to the corresponding Z-
6 | J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 8
Catalysis Science & Technology
Please do not adjust margins
Journal Name
ARTICLE
C. Fares, W. Thiel and A. Fürstner, J. Am. Chem. Soc., 2018, 16 K. Murugesan, C. Beromeo Bheeter, P. R. Linnebank, A.
View Article Online
140, 3156–3169.
Spannenberg, J. N. H. Reek, R. V. Jagadeesh, and M. Beller,
DOI: 10.1039/D0CY00992J
6
7
8
9
T. L. Gianetti, N. C. Tomson, J. Arnold and R. G. Bergman, J.
Am. Chem. Soc., 2011, 133, 14904−14907.
M. Sodeoka and M. Shibasaki, J. Org. Chem., 1985, 50,
1147−1149.
ChemSusChem, 2019, 12, 3363–3369.
17 a) Y.-P. Zhou, Z. Mo, M.-P. Luecke and M. Driess, Chem. Eur.
J., 2018, 24, 4780 – 4784; b) A. Brzozowska, L. M. l. Azofra, V.
Zubar, I. Atodiresei, L. Cavallo, M. Rueping and O. El-Sepelgy,
ACS Catal., 2018, 8, 4103−4109.
18 a) S. Elangovan, C. Topf, S. Fischer, H. Jiao, A. Spannenberg,
W. Baumann, R. Ludwig, K. Junge and M. Beller, J. Am. Chem.
Soc., 2016, 138, 8809-8814; b) S. Elangovan, J. Neumann, J.-
B. Sortais, K. Junge, C. Darcel, and M. Beller, Nature
Commun. 2016, 7:12641; c) S. Elangovan, M. Garbe, K. Junge,
H. Jiao, A. Spannenberg and M. Beller, Angew. Chem. Int. Ed.,
2016, 56, 15364-15368; d) M. Andérez-Fernández, L. K. Vogt,
S. Fischer, W. Zhou, H. Jiao, M. Garbe, S. Elangovan, K. Junge,
H. Junge, R. Ludwig, and M. Beller, Angew. Chem. Int. Ed.,
2017, 56, 559–562.
H. S. La Pierre, J. Arnold and F. D. Toste, Angew. Chem., Int.
Ed., 2011, 50, 3900−3903.
C. Oger, L. Balas, T. Durand and J. Galano, Chem. Rev., 2013,
113, 1313−1350.
10 a) F. Alonso, M. Osante and M. Yus, Adv. Synth. Catal., 2006,
348, 305−308; b) R. Barrios-Francisco and J. J. Garcia, Inorg.
Chem., 2009, 48, 386–393; c) T. Chen, J. Xiao, Y. Zhou, S. Yin
and L. Han, J. Org. Chem., 2014, 749, 51−54; d) E. Richmond
and J. Moran, J. Org. Chem., 2015, 80, 6922–6929; e) H.
Konnerth and M. H. G. Prechtl, Chem. Commun., 2016, 52,
9129–9132; f) X. Wen, X. Shi, X. Qiao, Z. Wu and G. Bai,
Chem. Commun., 2017, 53, 5372–5375; g) M. D. de los 19 V. Papa, J. R. Cabrero-Antonino, E. Alberico, A. Spannenberg,
Bernardos, S. Pérez-Rodríguez, A. Gual, C. Claver and C.
Godard, Chem. Commun., 2017, 53, 7894–7897; h) K.
H. Junge, K. Junge, and M. Beller, Chem. Sci., 2017, 8, 3576–
3585.
Murugesan, A. S. Alshammari, M. Sohail, M. Beller, and R. V. 20 a) M. Perez, S. Elangovan, H. Jiao, A. Spannenberg, K. Junge,
Jagadeesh, J. Catal., 2019, 370, 372–377.
11 a) C. Chen, Y. Huang, Z. Zhang, X.-Q. Dong and X. Zhang,
Chem. Commun., 2017, 53, 4612–4615; b) F. Chen, C.
and M. Beller, ChemSusChem, 2017, 10, 83–86; b) S. Budweg,
K. Junge, and M. Beller, Chem. Commun., 2019, 55, 14143-
14146.
Kreyenschulte, J. Radnik, H. Lund, A.-E. Surkus, K. Junge and 21 J. R. Khusnutdinova and D. Milstein, Angew. Chem., 2015,
M. Beller, ACS Catal., 2017, 7, 1526–1532.
12 a) C. Bianchini, A. Meli, M. Peruzzini, F. Vizza, F. Zanobini and
127, 12406-12445; Angew. Chem. Int. Ed., 2015, 54, 12236-
12273.
P. Frediani, Organometallics, 1989, 8, 2080−2082; b) C. 22 a) C. Bornschein, S. Werkmeister, B. Wendt, H. Jiao, E.
Bianchini, A. Meli, M. Peruzzini, P. Frediani, C. Bohanna, M.
A. Esteruelas and L. A. Oro, Organometallics, 1992, 11,
138−145; c) S. C. Bart, E. Lobkovsky and P. J. Chirik, J. Am.
Chem. Soc., 2004, 126, 13794–13807; d) G. Wienhöfer, F. A.
Westerhaus, R. V. Jagadeesh, K. Junge, H. Junge and M.
Alberico, W. Baumann, H. Junge, K. Junge and M. Beller,
Nature Commun., 2014, 5:4111; b) S. Lange, S. Elangovan, C.
Cordes, A. Spannenberg, H. Jiao, H. Junge, S. Bachmann, M.
Scalone, C. Topf, K. Junge and M. Beller, Cat. Sci. Technol.,
2016, 6, 4768–4772.
Beller, Chem. Commun., 2012, 48, 4827–4829; e) T. N. 23 a) K. Junge, B. Wendt, A. Cingolani, A. Spannenberg, Z. Wei,
Gieshoff, A. Welther, M. T. Kessler, M. H. G. Prechtl and A.
Jacobi von Wangelin, Chem. Commun., 2014, 50, 2261–2264;
f) L. C. Misal Castro, H. Li, J.-B. Sortais and C. Darcel, Green
H. Jiao and M. Beller, Chem. Eur. J., 2018, 24, 1046−1052; b)
J. Schneekönig, B. Tannert, H. Hornke, M. Beller and K.
Junge, Cat. Sci. Technol., 2019, 9, 1779–1783.
Chem., 2015, 17, 2283–2303; g) D. Wei and C. Darcel, Chem. 24 Deposition Number 1980954 contains the supplementary
Rev., 2019, 119, 2550–2610; h) B. J. Gregori, F.
Schwarzhuber, S. Pöllath, J. Zweck, L. Fritsch, R. Schoch, M.
Bauer and A. Jacobi von Wangelin, ChemSusChem, 2019, 12,
3864–3870; i) W. D. Jones, in Topic in Organometallic
Chemistry, 2019, 63, 141-174.
crystallographic data for this paper. These data are provided
free of charge by the joint Cambridge Crystallographic Data
Centre and Fachinformationszentrum Karlsruhe Access
Structures service www.ccdc.cam.ac.uk/structures.
25 a) K. Singh Rawata and B. Pathak, Catal. Sci. Technol., 2017,
7, 3234–3242, b) T. Xia, B. Spiegelberg, Z. Wei, H. Jiao, S. Tin,
S. Hinze and J. G. de Vries, Catal. Sci. Technol., 2019, 9, 6327-
6334.
13 a) A. M. Whittaker and G. Lalic, Org. Lett., 2013, 15,
1112−1115; b) A. Fedorov, H.-J. Liu, H.-K. Lo and C. Copéret,
J. Am. Chem. Soc., 2016, 138, 16502–16507; c) T.
Wakamatsu, K. Nagao, H. Ohmiya and M. Sawamura, 26 The trans isomer is more stable than the cis isomer by 1.5
Organometallics, 2016, 35, 1354–1357; d) N. Kaeffer, H.-J. kcal/mol, which gives a thermodynamic ratio of 93/7.
Liu, H.-K. Lo, A. Fedorov and C. Copéret, Chem. Sci., 2018, 9, 27 Y. Wang, L. Zhu, Z. Shao, G. Li, Y. Lan and Q. Liu, J. Am. Chem.
5366–5371. Soc., 2019, 141, 17337−17349.
14 a) D. Srimani, Y. Diskin-Posner, Y. Ben-David and D. Milstein, 28 A. V. Marenich, C. J. Cramer and D. G. Truhlar, J. Phys. Chem.
Angew. Chem., 2013, 125, 14131−14134; Angew. Chem., Int. B, 2009, 113, 6378−6396.
Ed., 2013, 52, 14381−14384; b) N. Gorgas, J. Brünig, B. 29 S. Grimme, S. Ehrlich and L. Goerigk, J. Comput. Chem., 2011,
Stöger, S. Vanicek, M. Tilset, L. F. Veiros and K. Kirchner, J.
Am. Chem. Soc., 2019, 141, 17452−14458.
32, 1456−1465.
30 Y. Zhao and D. G. Truhlar, J. Chem. Phys., 2006, 125, 194101.
15 a) K. Tokmic and A. R. Fout, J. Am. Chem. Soc., 2016, 138, 31 M. J. Frisch, J. A. Pople and J. S. Binkley, J. Chem. Phys., 1984,
13700−13705; b) S. Fu, N.-Y. Chen, X. Liu, Z. Shao, S. P. Luo
and Q. Liu, J. Am. Chem. Soc., 2016, 138, 8588−8594; c) V. G. 32 a) Z. Wei, A. de Aguirre, K. Junge, M. Beller and H. Jiao, Eur. J.
80, 3265−3269.
Landge, J. Pitchaimani, S. P. Midya, M. Subaramanian, V.
Madhu and E. Balaraman, Cat. Sci. Technol., 2018, 8,
428−433; d) X. Qi, X. Liu, L.-B. Qu, Q. Liu and Y. Lan, J. Catal.,
2018, 362, 25–34. For hydroboration of alkynes with Co pincer
Inorg. Chem., 2018, 4643−4657; b) Z. Wei, A. de Aguirre, K.
Junge, M. Beller and H. Jiao, Catal. Sci. Technol., 2018, 8,
3649−3665; c) Z. Wei and H. Jiao, Adv. Inorg. Chem., 2019,
73, 323−384.
catalysts, see: e) J. V. Obligacion, J. M. Neely, A. N. Yazdani, I. 33 E. Brunner, J. Chem. Eng. Data, 1985, 30, 269−273.
Pappas and P. J. Chirik, J. Am. Chem. Soc., 2015, 137,
5855−5858; f) J. Guo, B. Cheng, X. Shen and Z. Lu, J. Am.
Chem. Soc., 2017, 139, 15316−15319. For hydrosilylation of
alkynes with Co pincer catalysts, see: g) J. Guo and Z. Lu,
Angew. Chem. Int. Ed., 2016, 55, 10835−103838.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 7
Please do not adjust margins

Catalysis Science & Technology
Page 8 of 8
View Article Online
Chemoselective Semihydrogenation of Alkynes catalyzed by
DOI: 10.1039/D0CY00992J
Manganese(I)-PNP Pincer Complexes
Marcel Garbe,a§ Svenja Budweg,a§ Veronica Papa,a Zhihong Wei,a Helen Hornke,a Stephan Bachmann,b
Michelangelo Scalone,b Anke Spannenberg,a Haijun Jiao,a Kathrin Junge,*a and Matthias Beller*a
A first homogeneous manganese catalyzed chemoselective semihydrogenation of alkynes to Z-olefins
in the presence of molecular hydrogen is described.
H
H
R2
R1
R1
R2
Mn-3c
(1-2 mol%)
KOtBu (2.5-5 mol%)
30-60°C , 30 bar H2,
16 h, heptane
20 examples
up to 99% yield
high selectivity
Mn-3c