Synthesis of Molybdenum Pincer Complexes and Their Application in the Catalytic Hydrogenation of Nitriles

Article abstract of DOI:10.1002/cctc.202000736

A series of molybdenum(0), (I) and (II) complexes ligated by different PNP and NNN pincer ligands were synthesized and structurally characterized. Along with previously described Mo?PNP complexes Mo-1 and Mo-2, all prepared compounds were tested in the catalytic hydrogenation of aromatic nitriles to primary amines. Among the applied catalysts, Mo-1 is particularly well suited for the hydrogenation of electron-rich benzonitriles. Additionally, two aliphatic nitriles were transformed into the desired products in 80 and 86 percent, respectively. Moreover, catalytic intermediate Mo-1a was isolated and its role in the catalytic cycle was subsequently demonstrated.

Full text of DOI:10.1002/cctc.202000736

The European Society Journal for Catalysis
Supported by
Accepted Article
Title: Synthesis of Molybdenum Pincer Complexes and Their
Application in the Catalytic Hydrogenation of Nitriles
Authors: Thomas Leischner, Anke Spannenberg, Kathrin Junge, and
Matthias Beller
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10.1002/cctc.202000736
ChemCatChem
FULL PAPER
Synthesis of Molybdenum Pincer Complexes and Their
Application in the Catalytic Hydrogenation of Nitriles
Thomas Leischner[a], Anke Spannenberg[a], Kathrin Junge[a], Matthias Beller[a]
Dedicated to Prof. Dr. Uwe Rosenthal on the occasion of his 70th birthday
Abstract: A series of molybdenum(0), (I) and (II) complexes ligated
by different PNP and NNN pincer ligands were synthesized and
structurally characterized. Along with previously described Mo-PNP
complexes Mo-1 and Mo-2, all prepared compounds were tested in
the catalytic hydrogenation of aromatic nitriles to primary amines.
Among the applied catalysts, Mo-1 is particularly well suited for the
hydrogenation of electron-rich benzonitriles. Additionally, two
aliphatic nitriles were transformed into the desired products in 80
and 86%, respectively. Moreover, catalytic intermediate Mo-1a was
isolated and its role in the catalytic cycle subsequently demonstrated.
application in catalytic homogeneous nitrile hydrogenation are
exceptionally scarce. In fact to date, only three examples have
been reported for related reductions (Scheme 2). In 2012,
Nikonov and co-workers described the application of imido-
hydrido Mo(IV) complex I for the catalytic hydroboration of
nitriles in the presence of HBCat (Cat = catechol). However, only
aceto- and benzonitrile were tested as substrates.[11]
Introduction
Reduction of nitriles continues to attract significant attention of
synthetic chemists for the preparation of diverse amines.[1]
Traditionally, these reactions are carried out on laboratory scale
using an excess of stoichiometric reducing agents, resulting in at
least equimolar amounts of waste products.[2,3] On the contrary,
catalytic
homogenous
hydrogenation
using
defined
organometallic complexes provides an environmentally benign
alternative, as it is more atom-economic with less waste
generation.[3b,4]
Nevertheless,
the
selective
catalytic
hydrogenation of nitriles to primary amines remains to be
challenging for certain substrates, due to the underlying reaction
mechanism (see Scheme 1).[5]
Scheme 1. General scheme for the hydrogenation of nitriles.
In general, primary amines are important intermediates for
various applications in organic synthesis as well as in the
production of bulk and fine chemicals.[6] Therefore, the
development of novel (catalytic) protocols for their synthesis
remains of particular interest. Until recently, noble metal-based
catalyst systems prevailed for this purpose in both, industrial
processes and academic research.[7] However, their comparably
high price, limited availability and toxicity issues, set incentives
for their replacement. Yet, in the past two decades significant
progress in this direction has been achieved using for example
Fe, Co and Mn complexes supported by pincer ligands.[8]
In this respect, also molybdenum constitutes an attractive
substitute for precious metals, due to its low costs and
environmentally benign nature.[9] Although the organometallic
chemistry of molybdenum, particularly of its pincer complexes,
has been studied in-depth in recent years[10], reports on its
The group of Berke developed
a molybdenum-catalyzed
homogeneous nitrile hydrogenation, based on molybdenum(I)-
amido pincer catalyst II. However, the developed protocol
operated under relatively harsh conditions (5 mol% catalyst,
140 °C) to yield secondary imines in high selectivity.[5]
In 2020, Wang and co-workers published an efficient transfer
hydrogenation of nitriles using molybdenum-thiolate complex III
in combination with NH3∙BH3 as hydrogen donor. Notably, this
methodology applies particularly mild conditions and is
compatible with aliphatic and aromatic nitriles selectively forming
primary amines. The versatility of the developed system is
highlighted by the successful reduction of both cyano groups of
industrially relevant adiponitrile to corresponding 1,6-diamino-
hexane in 70% yield.[12]
In 2018, we described the synthesis of a series of molecular
defined molybdenum PNP-pincer complexes and subsequently
demonstrated their activity in the catalytic hydrogenation of
acetophenones, styrenes and formamides (Figure 1).[13] Based
on these works, herein we report the synthesis and structural
characterization of a series of previously unknown molybdenum
pincer complexes and their behavior in the hydrogenation of
nitriles to primary amines.
[a]
T. Leischner, Dr. A. Spannenberg, Dr. K. Junge, Prof. Dr. M. Beller
Leibniz Institute for Catalysis
Albert-Einstein-Straße 29a, 18059 Rostock (Germany)
E-mail: Matthias.Beller@catalysis.de
Supporting information for this article is given via a link at the end of
the document.
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Results and Discussion
At the outset of our studies, we investigated whether our
previously developed method for the synthesis of molybdenum
complexes Mo-1 and Mo-2, could be extended to other pincer
ligands (Scheme 3).[13] Thus, PNP ligands (Cy2PCH2CH2)2NH,
(Ph2PCH2CH2)2NH, (Et2PCH2CH2)2NH as well as the NNN
pincer ligand bis-(2-pyridylmethyl)amine were reacted with
Mo(PPh3)2(CH3CN)2(CO)2 in either dichloromethane (DCM) or
tetrahydrofurane (THF). Applying (Cy2PCH2CH2)2NH as ligand in
DCM, resulted in the intended formation of Mo(I) complex Mo-6
in 46% yield. However, when the reaction was carried out in
THF as reaction solvent, the formation of a light green, ill-soluble
powder was observed. Due to the extremely low solubility of this
powder in all common organic solvents, we were not able to
unequivocally confirm its identity by either NMR experiments or
X-ray analysis of suitable single crystals. Nevertheless, EA, IR
and HR/ESI-MS experiments strongly suggest the formation of
the corresponding Mo(0) complex Mo-5.
Next, we subjected (Ph2PCH2CH2)2NH to the reaction with
Mo(PPh3)2(CH3CN)2(CO)2 in THF. Interestingly, we obtained
Mo(0)-complex Mo-3a, featuring a PPh3 ligand coordinated to
the metal center, as the sole reaction product, in 91% yield.
Attempts to transform Mo-3a into the corresponding CH3CN
derivative remained unsuccessful. Surprisingly, when the
reaction was carried out in DCM under otherwise identical
conditions, selective formation of Mo-3a was observed again.
Even after stirring for several days at room temperature, 31P{1H}
NMR analysis revealed Mo-3a as the main species. However,
slow formation of a new resonance at 63 ppm occurred.
Assuming, that Mo-3a is relatively stable towards chlorination,
the reaction mixture was heated to 40 °C for three hours. 31P{1H}
NMR analysis showed complete conversion of Mo-3a into the
new species at 63 ppm. Subsequent isolation and
characterization provided diamagnetic Mo(II) pincer complex
Mo-4a in 56% yield.
Scheme 2. Reported examples of molybdenum-catalyzed homogeneous
nitrile reductions.
Figure 1. Catalytically active molybdenum pincer complexes recently
synthesized by our group.
Scheme 3. Synthesis of new molybdenum PNP pincer complexes.
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When exploring the reactivity of (Et2PCH2CH2)2NH, we observed
a similar reaction behavior as compared to (Ph2PCH2CH2)2NH.
Performing the reaction in THF, we were able to isolate the
corresponding Mo(0) Mo-3b in 82% yield. Nevertheless, carrying
out the reaction in DCM resulted in the formation of complex
product mixtures, even at ‒20 °C.
Finally, the NNN pincer ligand bis-(2-pyridylmethyl)amine was
applied.
The
ligand
reacted
readily
with
Mo(PPh3)2(CH3CN)2(CO)2 in DCM and THF, respectively,
resulting in the formation of Mo-7 in both cases (Scheme 4).
Scheme 4. Synthesis of previously unknown molybdenum NNN pincer
complex Mo-7.
Figure 2. Molecular structures of Mo-3a, Mo-3b, Mo-4a, Mo-6 and Mo-7 in the solid state. Thermal ellipsoids are drawn at 30% probability level. Hydrogen atoms,
except the N-bound are omitted for clarity. For Mo-6, only one molecule of the asymmetric unit is shown.
Complex Mo-7 proved to be remarkably stable towards
chlorination and remained molecularly unchanged even after
refluxing for 24h in DCM and DCE, respectively. All prepared
coordination compounds have been characterized by standard
techniques including 1H, 13C and 31P{1H} NMR (except Mo-6 and
Mo-7, see vide infra) and IR spectroscopy as well as elemental
analysis (for NMR and IR spectra, see supporting information).
Additionally, we were able to determine solid-state structures of
complexes Mo-3a, Mo-3b, Mo-4a, Mo-6 as well as Mo-7 by X-
ray analysis of suitable single crystals. Their structural views are
depicted in Figure 2. However, due to the insolubility of Mo-7 in
all common NMR solvents, including benzene, toluene, THF,
acetonitrile, DMSO and methanol, as well as the paramagnetic
nature of Mo-6, we were unable to obtain meaningful NMR data
of these complexes.
Complexes Mo-3a, Mo-3b and Mo-7 adopt
a distorted
octahedral coordination geometry at the molybdenum center,
with the CO ligands being in a cis orientation. The coordinated
pincer ligands all exhibit a fac arrangement around the central
metal atom. However, in complex Mo-6 the mer coordination
mode of the pincer ligand is observed with the CO ligands being
in a cis arrangement. The described characteristics for Mo-6 are
in agreement with our previously published solid state structure
of Mo-2.[13] The coordination geometry at the Mo atom of the
hepta-coordinated Mo(II)-complex Mo-4a can be best described
as distorted capped octahedral.
The recorded IR spectra of the reported complexes all show
medium to strong carbonyl absorption bands between 1921 cm‒1
and 1679 cm‒1.
Next, we tested the catalytic activity of the newly described
molybdenum pincer complexes Mo-3a, Mo-3b, Mo-4a, Mo-6
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and Mo-7, as well as of the previously reported compounds Mo-
1 and Mo-2, in the catalytic hydrogenation of benzonitrile 1a. It
has to be noted, that in our initial work some activity was
reported in this transformation, using Mo-2 as the catalyst,
without further optimization. However, under the reported
conditions, only modest conversion (42%) and poor product
selectivity (13%) for the desired primary amine were
observed.[13] In order to minimize potential decomposition of the
homogeneous molybdenum catalysts, the initial catalyst
screening was carried out at 100 °C in the presence of 10 mol%
NaBHEt3. Under these conditions full conversion was observed
for Mo-1 and Mo-2, yielding approximately 1:1 mixtures of 2a
and 3a (Table 1, entries 1-2). All other Mo-complexes, however,
provided inferior results (Table 1, entries 3-7). Interestingly, Mo-
4a as well as Mo-7 failed to give any conversion at all.
the optimal setting, we explored several different solvents. In
contrast to previous reports on base metal catalyzed
hydrogenation of nitriles, Mo-1 was found to be completely
inactive in i-PrOH, while toluene as solvent provided the best
results. Applying THF, 1,4-dioxane and Bu2O resulted in
significantly lower activities and predominantly yielded 3a as the
reaction product. Other aliphatic solvents such as n-heptane and
cyclohexane, were not suitable for the attempted transformation
(Fig. 3).
Table 1. Initial screening of Mo-catalysts and reaction parameters[a]
Conversion
[%][b]
Yield 2
[%][b]
Yield 3
[%][b]
Entry
Catalyst
1
2
Mo-1
Mo-2
Mo-3a
Mo-3b
Mo-4a
Mo-6
Mo-7
Mo-1
Mo-2
Mo-1
Mo-1
-
>99
>99
62
70
<1
78
<1
90
81
>99
>99
4
58
52
38
41
<1
41
<1
50
42
55
96
<1
<1
40
42
20
24
<1
35
<1
38
35
41
<1
<1
<1
Figure 3. Study of the solvent effect in the hydrogenation of benzonitrile 1a to
benzylamine 2a and N-benzylidenebenzylamine 3a catalyzed by Mo-1.
3
4
Subsequently, we investigated the influence of dihydrogen
pressure, catalyst loading, the amount of additive used (Table
S1, see supporting information), as well as the substrate
concentration (Table S2, see supporting information) on the
reaction outcome. Reducing the catalyst loading to 2.5 mol%
resulted in a significantly less active system. However, lowering
the amount of additive to 5 mol% led to no loss in reactivity.
Increasing the H2 pressure to 80 bar showed no observable
effect. Albeit, carrying out the reaction at 30 bar of dihydrogen
caused a sharp drop in catalyst activity. A rise of the reaction
temperature to 100 °C eventually resulted in full conversion of
1a in the presence of 5 mol% NaBHEt3 and Mo-1, respectively
(Table 1, entry 10). Next, we evaluated several substrate
concentrations based on 0.5 mmol of 1a, ranging from 0.08M to
0.5M. Notably, using 5 mL of toluene proved to be the optimal
concentration, providing the desired product benzylamine 2a in
96% yield (Table 1, entry 11). Finally, a series of control
experiments were carried out. In the absence of Mo-1, no
catalytic reaction took place (Table 1, entry 12). Similarly, no
product formation could be detected, when the reaction was
performed in the absence of NaBHEt3 (Table 1, entry 13). In
order to confirm, that no heterogeneous catalysis takes place, a
mercury poisoning experiment was conducted, revealing no loss
of activity (Table S2, see supporting information).
5
6
7
8[c]
9[c]
10[d]
11[e]
12[f]
13[g]
Mo-1
7
[a] Reaction conditions: 0.5 mmol substrate, 2 mL toluene, 5 mol% catalyst,
10 mol% NaBHEt3 (1M in THF), 50 bar H2, 100 °C, 24h. [b] Determined by GC
using hexadecane as internal standard. [c] 80 °C. [d] 5 mol% NaBHEt3 (0.5M
in THF). [e] 5 mL toluene, 0.5 mmol substrate. [f] No catalyst was used. [g] No
NaBHEt3 added.
The activity of Mo-1 and Mo-2 was subsequently compared at a
reduced temperature of 80 °C (Table 1, entries 8 and 9). Here,
Mo-1 provided a superior conversion of 90%. Based on this
result and its more convenient synthesis, we focused on Mo-1 in
the due course of the optimization process. Selecting 80 °C
reaction temperature and 5 mol% of Mo-1 (Table 1, entry 8) as
Having optimized conditions in hand, we proceeded to the
application of Mo-1 in the hydrogenation of a variety of different
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benzonitriles to the corresponding benzylamines. As shown in
supported (base) metal catalysts, where basic additives typically
activate the catalyst by deprotonation of the ligand backbone.[14]
Scheme
5 our developed methodology appeared to be
particularly well suited for electron-rich benzonitriles and the
intended primary amines were consistently obtained in high
yields. Substituents in para-, meta- and ortho-position of the
phenyl ring were well tolerated and even sterically hindered
nitriles 1k and 1m were successfully converted, furnishing 2k
and 2m in isolated yields of 68% and 91%, respectively. Notably,
when the steric bulk was further increased, using 2,6-
dimethylbenzonitrile 1n, we were still able to isolate the desired
primary amine 2n in a good yield of 72%. The system proved to
be insensitive towards halides such as fluoride and chloride (2b
and 2c) and no dehalogenation products were observed during
the catalysis. This was additionally the case when 3,5-dichloro
benzonitrile
(1o)
was
employed,
providing
3,5-
dichlorobenzylamine 2o in 60% isolated yield. Moreover, also a
benzylether moiety, often cleaved under hydrogenation
conditions, remained unaffected and no deprotection could be
detected in product (2h). However, some (hetero)benzonitriles
with substituents in either ortho- or para-position, such as H2N-,
CF3-, CO2Me-, carbonyl-, cyano- and nitro groups, either gave
only poor conversions or did not yield the desired primary
amines in sufficient quantities (see Table S3, supporting
information). Clearly, in these cases the observed reactivity of
the catalyst is not an easy function of the electron-donating or
electron-withdrawing character of the respective substituents.
Apparently, there are several factors influencing the observed
reactivity. In Table S3 some of the observed side products are
mentioned.
Interestingly, for 2- and 4-trifluoromethyl-substituted benzonitrile
low conversion and negligible product yields were observed,
while in the case of meta-CF3-substituted nitrile 1l the
corresponding primary amine 2l could be isolated in 61% yield.
Furthermore, we successfully applied two aliphatic nitriles 1p
and 1q to our reported protocol. In both cases, Mo-1 proved to
be a suitable catalyst and we were able to isolate the intended
reaction products 2p and 2q in 80% and 86% yield, respectively.
Scheme 5. Substrate scope for nitrile reduction with molybdenum pincer
complex Mo-1.
Finally, with respect to the mechanism we became interested in
the molecular structure of the organometallic species formed
from the reaction of Mo-1 and NaBHEt3. Hence, we conducted a
control experiment, treating 0.5 mmol of Mo-1 with an excess of
NaBHEt3 in toluene at room temperature (for experimental
details, see Supporting Information). The reaction proceeded
rapidly, resulting in the formation of a clear red solution within
less than one minute. The 31P{1H} NMR analysis of the crude
reaction mixture revealed the formation of a strong singlet
resonance at 74 ppm as the main product alongside some free
ligand. Attempts to characterize the corresponding species by X-
ray analysis of suitable single crystals were successful and
provided the solid-state structure of Mo-1a (Scheme 6). As
expected, the applied additive acts as base and abstracts a
proton from Mo-1. Interestingly, the deprotonation does not
involve the NH moiety of the pincer ligand but takes place at the
CH3-group of the coordinated acetonitrile ligand, resulting in the
formation of a covalent C‒B bond. This observed reactivity is in
sharp contrast to classical reaction patterns observed for pincer
Scheme 6. Synthesis of Mo-1a (top). Molecular structure of Mo-1a in the solid
state (bottom). Thermal ellipsoids are drawn at 30% probability level.
Hydrogen atoms, except the N-bound are omitted for clarity. Disordered parts
of the molecule are only shown in one orientation.
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In order to confirm that Mo-1a indeed plays an active role in the
catalysis, the benchmark reaction was carried out using 5 mol%
Mo-1a in the absence of NaBHEt3 under otherwise identical
conditions. Benzylamine 2a was observed in 92% yield, proofing
the involvement of Mo-1a in in the catalytic hydrogenation of
benzonitrile 1a. Next, we were interested in the reactivity of Mo-
1a towards dihydrogen. Therefore, Mo-1 was activated with two
equivalents of NaBHEt3 in d8-toluene and subsequently stirred
for 3h at 100°C in the presence of 50 bar H2 (for experimental
details see Supporting Information). Analysis of the reaction
mixture by 31P NMR spectroscopy revealed two new main
resonances at 89.1 and 75.9 ppm, thus proving that Mo-1a had
undergone a reaction with H2. However, no hydride signals could
in full conversion of 1a and benzylamine was observed in 72%
yield.
Conclusions
In summary, we reported the synthesis and structural
characterization of a series of previously unknown molybdenum
pincer complexes. Depending on the used pincer ligand and the
reaction solvent, different complex structures are obtained.
Furthermore, the first molybdenum-catalyzed reduction of nitrile
to primary amines using molecular hydrogen is described. In fact,
Mo-pincer complex, Mo-1, can be used as efficient catalyst for
the selective catalytic hydrogenation of selected aromatic and
aliphatic nitriles to give the corresponding primary amines.
Additionally, we isolated and identified catalytic intermediate Mo-
1a and subsequently proved its role in the catalytic process.
1
be detected according to the obtained H NMR spectrum. The
resonance at 75.9 ppm corresponds to the Mo(0) complex fac-
[(iPr2PCH2CH2)2NH]Mo(CO)3[13a], revealing a potential catalyst
deactivation pathway.
Furthermore, to understand the poor catalytic performance of
Mo-1 when electron deficient nitriles are applied, a series of
control experiments were conducted, too (Scheme 7).
Experimental Section
General Procedure for Catalysis Experiments: All hydrogenation
reactions were set up under Ar in a 300 mL autoclave (PARR Instrument
Company). In order to avoid unspecific reductions, all catalytic
experiments were carried out in 8 mL glass vials, which were set up in an
alloy plate and placed inside the autoclave.
In a glove box, an 8 mL glass vial containing a stirring bar was charged
with complex Mo-1 (12.5 mg; 5 mol%). Toluene (5 mL) was added and
the corresponding greenish suspension was treated with NaBHEt3 (0.5 M
in THF; 50 μL; 5 mol%). The reaction mixture was stirred for 20 minutes
and the corresponding substrate was subsequently added. Afterwards,
the vial was capped and transferred into an autoclave. Once sealed, the
autoclave was purged three times with 10 bar of hydrogen, then
pressurized to the desired hydrogen pressure (50 bar) and placed into an
aluminum block that was preheated to the desired temperature (100 ˚C).
After 24 h, the autoclave was cooled in an ice bath and the remaining
gas was released carefully. The solution was subsequently diluted with
50 mL Et2O and filtered through a small pad of silica. The silica was
washed with DCM (10 mL) and the combined filtrates were treated with 2
mL of HCl (2M in Et2O). The obtained precipitate was filtered off, washed
two times with 20 mL ethyl acetate and two times with 20 mL Et2O and
subsequently dried in vacuo. For the characterization of the products of
the catalysis, see Supporting Information.
Scheme 7. Control experiments carried out. [a] Yields determined by GC
using hexadecane as internal standard. 1.) Poisoning experiment using 1
equiv. of 1r. 2.) Poisoning experiment using 10 mol% of 1r. 3.) Poisoning
experiment using 10 mol% of 2r.
Acknowledgements
Adding 0.5 mmol of 4-(trifluoromethyl)benzonitrile 1r to the
benchmark reaction resulted in a complete shut-down of catalyst
activity and no benzylamine 2a could be detected. Interestingly,
also in the presence of only 10 mol% of 1r, no formation of 2a
occurred. We therefore conclude, that 1r acts as a strong
catalyst poison and thus inhibits the catalysis (for experimental
details on the described reactions, see Supporting Information).
Subsequently, we investigated whether the corresponding
primary amine, 4-(trifluomethyl)benzylamine 2r, could act as
catalyst poison too. Interestingly, adding 10 mol% of 2r resulted
This work was supported by the BMBF, the state Mecklenburg-
Western Pomerania and the European Union as part of the
NoNoMeCat (675020) project. We thank the analytic department
of LIKAT for their support and assistance.
Keywords: molybdenum • pincer complexes • hydrogenation •
nitrile • primary amine
References:
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[1]
[2]
a) D. M. Bagal, B. M. Bhanage, Adv. Synth. Catal. 2015, 357, 883-900.
Chakraborty, D. Milstein, ACS Catal. 2017, 7, 3968-3972; h) K. Tokmic,
B. J. Jackson, A. Salazar, T. J. Woods, A. R. Fout, J. Am. Chem. Soc.
2017, 139, 13554-13561; i) R. Adam, C. B. Bheeter, J. R. Cabrero-
Antonino, K. Junge, R. Jackstell, M. Beller, ChemSusChem 2017, 10,
842-846; j) H. Li, A. Al-Dakhil, D. Lupp, S. S. Gholap, Z. Lai, L.-C. Liang.
K. W. Huang, Org. Lett. 2018, 20, 6430-6435; k) H. Dai, H. Guan, ACS
Catal, 2018, 8, 9125-9130; l) J. Schneekönig, J. Tannert, H. Hornke, M.
Beller, K. Junge, Catal. Sci. Technol. 2019, 9, 1779-1783.
For a general book about organic reductions, see: a) J. Seyden-Penne
in Reductions by the Alumino- and Borohydrides in Organic Synthesis,
2nd edition, Wiley-VCH, New Yorck, United States of America, 1997; for
selected examples see: b) S. Zhou, K. Junge, D. Addis, S. Das, M.
Beller, Angew. Chem. Int. Ed. 2009, 48, 9507-9510; c) S. Das, D. Addis,
S. L. Zhou, K. Junge, M. Beller, J. Am. Chem. Soc. 2010, 132, 1770-
1771; d) G. Pelletier, W. S. Bechara, A. B. Charette, J. Am. Chem. Soc.
2010, 132, 12817-12819; e) S. Das, D. Addis, K. Junge, M. Beller,
Chem. Eur. J. 2011, 17, 12186-12192; f) C. Cheng, M. Brookhart, J.
Am. Chem. Soc. 2012, 134, 11304-11307; g) S. Das, B. Wendt, K.
Moller, K. Junge, M. Beller, Angew. Chem. Int. Ed. 2012, 51, 1662-
1666; h) S. Park, M. Brookhart, J. Am. Chem. Soc. 2012, 134, 640-653;
i) T. Dombay, C. Helleu, C. Darcel, J. B. Sortais, Adv. Synth. Catal.
2013, 355, 3358-3362; j) J. T. Reeves, Z. L. Tan, M. A. Marsini, Z. X. S.
Han, Y. B. Xu, D. C. Reeves, H. Lee, B. Z. Lu, C. H. Senanayakea, Adv.
Synth. Catal. 2013, 355, 47-52; k) E. Blondiaux, T. Cantat, Chem.
Commun. 2014, 50, 9349-9352; l) N. L. Lampland, M. Hovey, D.
Mukherjee, A. D. Sadow, ACS Catal. 2015, 5, 4219-4226; m) D.
Mukherjee, S. Shirase, K. Mashima, J. Okuda, Angew. Chem. Int. Ed.
2016, 55, 13326-13329.
[9]
S. Chakraborty, O. Blacque, T. Fox, H. Berke, Chem. Asian J. 2014, 9,
328-337.
[10] a) W. Schirmer, U. Flörke, H. Haupt, Z. anorg. Allg. Chem. 1987, 545,
83-97; b) J. Ellermann, M. Moll, N. Will, J. Organomet. Chem. 1989,
378, 73-79; c) H. F. Lang, P. E. Fanwick, R. A. Dalton, Inorg. Chim.
Acta 2002, 329, 1-8; d) B. Benito-Garagorri, E. Becker, J. Wiedermann,
W. Lackner, M. Pollak, K. Meireiter, J. Kisala, K. Kirchner,
Organometallics 2006, 25, 1900-1913; e) K. Arashiba, Y. Miyake, Y.
Nishibayashi, Nature Chem. 2011, 3, 120-125; f) K. Arashiba, K. Sasaki,
S. Kuriyama, Y. Miyake, Y. Nakanishi, Y. Nishibayashi, Organo-
metallics 2012, 31, 2035-2041; g) E. Kinoshita, K. Arashiba, S.
Kuriyama, Y. Miyake, Y. Shimazaki, H. Nakanishi, Y. Nishibayashi,
Organometallics, 2012, 31, 8437.8443; h) O. Öztopcu, C. Holzhacker,
M. Puchberger, M. Weil, K. Meireiter, L. F. Veiros, K. Kirchner,
Organometallics, 2013, 32, 3042-3052; i) S. R. M. M. de Aguiar, B.
Stöger, B. Pittenauer, M. Puchberger, G. Allmair, L. F. Veiros, K.
Kirchner, J. Organomet. Chem. 2014, 760, 74-83; j) S. R. M. M. de
Aguiar, O. Öztopcu, B. Stöger, K. Meireiter, L. F. Veiros, B. Pittenauer,
G. Allmair, K. Kirchner, Dalton Trans. 2014, 43, 14669-14679; k) S.
Chakraborty, O. Blacque, H. Berke, Dalton Trans. 2015; 44, 6560-6570;
l) R. Castro-Rodrigo, S. Chakraborty, L. Munjanja, W. Brennessel, W. D.
Jones, Organometallics 2016, 35, 3124-3131; m) Y. Zhang, P. G.
Williard, W. H. Bernskoetter, Organometallics 2016, 35, 860-865; n) S.
R. M. M. de Aguiar, B. Stöger, B. Pittenauer, G. Allmaier, L. F. Veiros,
K. Kirchner, Dalton Trans. 2016, 45, 13834-13845; o) G. A. Silantyev,
M. Förster, S. Schluschlaß, J. Abbensetz, C. Würtele, C. Volkmann, M.
C. Holthausen, S. Schneider, Angew. Chem. Int. Ed. 2017, 56, 5872-
5876; p) S. M. M. de Aguiar, O. Öztopcu, A. Troiani, G. de Petris, M.
Weil, B. Stöger, L. F. Veiros, B. Pittenauer, G. Allmair, K. Kirchner, Eur.
J. Inorg. Chem. 2018, 7, 876-884; q) M. V. Joannou, M. J. Bezdek, P. J.
Chirik, ACS Catal. 2018, 8, 5276-5285; r) M. J. Bezdek, P. J. Chirik,
Angew. Chem. Int. Ed. 2018, 8, 2224-2228; s) M. J. Bezdek, P. J.
Chirik, Organometallics 2019, 38, 1682-1687; t) Y. Ashida, S. Kondo, K.
Arashiba, T. Kikuchi, K. Nakajima, S. Kakimoto, Y. Nishibayashi,
Synthesis 2019, 51, 3792-3795; u) M. Alvarez, A. Galindo, P. J. Perez,
E. Carmona, Chem. Sci. 2019, 10, 8541-8546; v) R. Tran, S. M.
Kilyanek, Dalton Trans. 2019, 48, 16304-16311; w) M. Pfeil, T. A.
Engesser, A. Koch, J. Junge, J. Krahmer, C. Näther, F. Tuczek, Eur. J.
Inorg. Chem. 2020, 1437-1448.
[3]
[4]
a) H. C. Brown, S. Narasimhan, Y. M. Choi, Synthesis 1981, 441-442;
b) S. Werkmeister, K. Junge, M. Beller, Org. Process. Res. Dev. 2014,
18, 289-302.
a) P. A. Dub, T. Ikariya, ACS Catal. 2012, 2, 1718-1741; b) A. M. Smith,
R. Whyman, Chem. Rev. 2014, 114, 5477-5510; c) A. M. Smith, R.
Whyman, Chem. Rev. 2014, 114, 5477-5510.
[5]
[6]
[7]
a) S. Chakraborty, H. Berke, ACS Catal. 2014, 4, 2191-2194.
K. Levay, L. Hegedüs, Curr. Org. Chem. 2019, 23, 1881-1900.
For selected examples see on Rh, Ru, Ir and Re-catalyzed nitrile
hydrogenations see: a) T. Yoshida, T. Okano, S. Otsuka, J. Chem.,
Chem. Commun. 1979, 870-871; b) R. A. Grey, G. P. Pez, A. Wall, J.
Corsi, J. Chem. Soc., Chem. Commun. 1980, 783-784; c) R. A. Grey, G.
P. Pez, A. Wallo, J. Am. Chem. Soc. 1981, 103, 7536-7542; d) C. Chin,
B. Lee, Catal. Lett. 1992, 14, 135-140; e) T. Li, I. Bergner, F. N. Haque,
M. Zimmer-De Iuliis, D. Song, R. Morris, Organometallics 2007, 26,
5940-5949; f) S. Enthaler, D. Addis, K. Junge, G. Erre, M. Beller, Chem.
Eur. J. 2008, 14, 9491-9494; g) S. Enthaler, K. Junge. D. Addis, G. Erre,
M. Beller, ChemSusChem 2008, 1, 1006-1010; h) D. Addis, S. Enthaler,
K. Junge, B. Wendt, M. Beller, Tetrahedron Lett. 2009, 50, 3654-3656;
i) R. Reguillo, M. Grellier, N. Vautravers, L. Vendier, S. Sabo-Etienne, J.
Am. Chem. Soc. 2010, 132, 7854-7855; j) C. Gunanathan, M. Hölscher,
W. Leitner, Eur. J. Inorg. Chem. 2011, 3381-3386; k) K. Rajesh, B.
Dudle, O. Blacque, H. Berke, Adv. Synth. Catal. 2011, 353, 1479-1484;
l) S. Werkmeister, K. Junge, B. Wendt, A. Spannenberg, H. Jiao, C.
Bornschein, M. Beller, Chem. Eur. J. 2014, 20, 427-431; m) J.
Neumann, C. Bornschein, H. Jiao, K. Junge, M. Beller, Eur. J. Org.
Chem. 2015, 5944-5948; n) J.-H. Choi, M. H. G. Prechtl,
ChemCatChem 2015, 7, 1023-1028; o) R. Adam, C. B. Bheeter, R.
Jackstell, M. Beller, ChemCatChem 2015, 8, 1329-1334; p) R. Adam, E.
Alberico, W. Baumann, H.-J. Drexler, R. Jackstell, H. Junge, M. Beller,
Chem. Eur. J. 2016, 22, 4991-5002; q) Y. Sato, Y. Kayaki, T. Ikariya,
Organometallics 2016, 35, 1257-1264.
[11] A. Y. Khalimon, P. Farha, L. G. Kuzmina, G. I. Nikonov, Chem.
Commun. 2012, 48, 455-457.
[12] S. F. Hou, J. Y. Chen, M. Xue, M. Jia, X. Zhai, R.-Z. Liao, C.-H. Tung,
W. Wang, ACS Catal. 2020, 10, 380-390.
[13] a) T. Leischner, A. Spannenberg, K. Junge, M. Beller, Organometallics
2018, 37, 4402-4408; b) T. Leischner, L. A. Suarez, A. Spannenberg, K.
Junge, A. Nova, M. Beller, Chem. Sci. 2019, 10, 10566-10576.
[8]
For a general review regarding Co, Fe and Mn catalyzed homogeneous
nitrile hydrogenations see: a) D. M. Sharma, B. Punji, Chem. Asian. J.
2020, 15, 690-708; For selected examples see: b) C. Bornschein, S.
Werkmeister, B. Wendt, H. Jiao, E. Alberico, W. Baumann, H. Junge, K.
Junge, M. Beller, Nat. Commun. 2014, 5, 4111; c) A. Mukherjee, D.
Srimani, S. Chakraborty, Y. Ben-David, D. Milstein, J. Am. Chem. Soc.
2015, 137, 8888-8891; d) S. Lange, S. Elangovan, C. Cordes, A.
Spannenberg, H. Jiao, S. Bachmann, M. Scalone, C. Topf, K. Junge, M.
Beller, Catal. Sci. Technol. 2016, 6, 4768-4772; e) S. Charkraborty, D.
Milstein, Chem. Commun. 2016, 52, 1812-1815; f) S. Elangovan, C.
Topf, S. Fischer, H. Jiao, A. Spannenberg, W. Baumann, R. Ludwig, K.
Junge, M. Belller, J. Am. Chem. Soc. 2016, 138, 8809-8814; g) S.
[14] (a) E. Ben-Ari, G. Leitus, L. J. W. Shimon, D. Milstein, J. Am. Chem.
Soc. 2006, 128, 15390-15391, (b) J. R. Khusnutdinova, D. Milstein,
Angew. Chem. Int. Ed. 2015, 54, 12236-12273.
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