Exploring the reactivity of nickel complexes in hydrodecyanation reactions

Article abstract of DOI:10.1016/j.jorganchem.2013.07.068

In the present study, the nickel-catalyzed hydrodecyanation of organic cyanides with lithium borohydride as a cheap hydride source has been examined in detail. As precatalysts straightforward nickel complexes modified by tridentate O,N,O′-ligands and triphenylphosphane as co-ligand have been applied. Noteworthy, excellent yields and chemoselectivities were feasible for a variety of organic cyanides at low catalyst loadings and low temperature (70 C) within short reaction time (3 h).

Full text of DOI:10.1016/j.jorganchem.2013.07.068

Journal of Organometallic Chemistry 745-746 (2013) 262e274
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Exploring the reactivity of nickel complexes in hydrodecyanation
reactions
,
a
b
b
Stephan Enthaler a , Maik Weidauer , Elisabeth Irran , Jan Dirk Epping ,
*
Robert Kretschmer c, Chika I. Someya a
a Technische Universität Berlin, Department of Chemistry, Cluster of Excellence “Unifying Concepts in Catalysis”, Straße des 17. Juni 115/C2,
10623 Berlin, Germany
b Institute of Chemistry: Metalorganics and Inorganic Materials, Technische Universität Berlin, Straße des 17. Juni 135/C2, D-10623 Berlin, Germany
c University of California San Diego, Department of Chemistry and Biochemistry, La Jolla, CA 92093-0343, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
In the present study, the nickel-catalyzed hydrodecyanation of organic cyanides with lithium borohy-
dride as a cheap hydride source has been examined in detail. As precatalysts straightforward nickel
complexes modified by tridentate O,N,O0-ligands and triphenylphosphane as co-ligand have been
applied. Noteworthy, excellent yields and chemoselectivities were feasible for a variety of organic cya-
nides at low catalyst loadings and low temperature (70 ꢀC) within short reaction time (3 h).
Ó 2013 Elsevier B.V. All rights reserved.
Received 17 June 2013
Received in revised form
19 July 2013
Accepted 26 July 2013
Keywords:
Catalysis
Nickel complexes
Hydrodecyanation
Organic cyanides
1. Introduction
and hydrosilanes as hydride source [7,8]. To activate the cyano
group and to facilitate the oxidative addition of the nickel into the
Synthetic transformations supported by the aid of directing
groups are well established methodologies in organic chemistry
[1]. For instance organic cyano functionalities have been proven to
CeCN bond the Lewis acid AlMe3 (up to 3.0 equiv.) was added.
However, high catalyst loadings (nickel source: 15e30 mol%;
ligand: 30e90 mol%) and high reaction temperatures (130 ꢀC) are
required to realize reasonable amounts of product. More recently,
we reported the application of well-defined nickel complexes 4 in
the hydrodecyanation of organic cyanides at lower catalyst loadings
(5.0 mol%) and under mild reaction conditions (70 ꢀC) (Scheme 1b)
[9]. As reductant tert-butylmagnesium chloride was applied. This
be valuable tools, for e.g., a-acidity and ortho-directing effects, to
access a wide range of products [2,3]. In this context, after the
directing groups fulfilled their obligations different subsequent
treatments have been presented, e.g., the unmodified conservation
in the product, the post-functionalization or the removal. Espe-
cially, the removal is of great interest and until now various pro-
tocols have been reported for the hydrodecyanation of organic
cyanides [4]. For instance excellent performances have been real-
ized with the help of metal-based catalysts [5]. Interestingly, the
application of nickel catalysts in hydrodecyanation reactions has
been less investigated so far, which is in contrast to the application
of cyanide functions as leaving groups for CeC and CeP cross
coupling reactions [6]. Recently, the group of Maiti demonstrated
the potential of the nickel-catalyzed decyanation of inert carbone
cyano bonds using in situ generated nickel phosphane complexes
potentially generates via transmetalation and b-hydride elimina-
tion catalytic active nickel-hydride species for the cleavage of the
CeCN bond. However, long reaction times are required to achieve
reasonable amounts of product, e.g., for the model substrate
4-methoxybenzonitrile 48 h are necessary to achieve 74% yield of
anisole. Supposably the formation of the nickel-hydride interme-
diate via transmetalation and b-hydride elimination is slow, hence
the overall rate is low [10]. Based on these initial achievements the
development of more efficient systems is still a challenging task. To
overcome the limitations in activity of our earlier protocol we
wondered if it is possible to apply more reactive hydride sources,
such as metal borohydrides, which have been shown to easily
produce nickel hydride complexes (Scheme 1c) [11]. Advanta-
geously, the nickel hydride should be directly accessible in one step
* Corresponding author. Fax: þ49 3031429732.
E-mail address: stephan.enthaler@tu-berlin.de (S. Enthaler).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.07.068

S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
263
Scheme 1. Cyano functionalities as directing group in organic chemistry and nickel-catalyzed hydrodecyanation protocols.
and as side product borane (BH3) is formed, which can potentially
act as a Lewis acid to activate the CeCN function and increases the
overall activity of the method [6b,12]. Moreover, a cost-saving and
more environmental friendly protocol should be feasible with
lithium or sodium borohydrides compared to earlier approaches
[13,14].
Based on that concept, we report herein our ongoing studies on
the nickel-catalyzed hydrodecyanation of organic cyanides
applying metal borohydrides as hydride source.
corresponding diketone with benzohydrazide, and an excess of
triphenylphosphane (3.0 equiv.) was added to a solution of
Ni(OAc)2$4H2O in methanol at room temperature. After stirring
overnight, all volatiles were removed in vacuum to obtain brown
powders, which were extracted with ethanol and purified by
crystallization to obtain brown crystals in fair to good yields (4a:
59%, 4b: 21%).
Crystals suitable for X-ray measurements were grown from n-
hexane by slow evaporation of the solvent at room temperature.
The solid-state structures of complexes 4a and 4b have been
characterized by single-crystal X-ray diffraction analysis. Thermal
ellipsoid plots, selected bond lengths and angles are shown in
Figs. 1 and 2. In agreement with the work of the Joshi group, and
previous work by our group, square planar arrangements were
observed for the nickelePPh3 complexes 4a and 4b with similar
bond lengths and angles [9,10,15,17,18]. The tridentate ligand
is coordinated in a O,N,O0-mode creating a five-membered and a
six-membered ring system. The triphenylphosphane ligand is
cis-positioned to the oxygen donors, while the nitrogen of the
2. Results and discussion
The precatalysts 4c, 4d, and 5 were synthesized in accordance
with our previously established protocol (Scheme 2a and b)
[9,10,15]. Moreover, complex 7 was obtained by the method re-
ported by Dharmaraj and co-workers with slight modifications
(Scheme 2c) [16]. The new precatalysts 4a and 4b were synthesized
following the reported method (Scheme 2a) [9,10,15]. A methanol
solution of ligands 3, which were accessible by the reaction of the

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S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
Scheme 2. Synthesis of the hydrodecyanation precatalysts.
5-hydroxypyrazoline ligand connected to the nickel is trans-posi-
tioned. Moreover, the molecular structure of 7 is in agreement with
the structure reported by Dharmaraj and co-workers and the bond
lengths and bond angles are comparable to 4a and 4b [16].
revealed the formation of free PPh3. In the 1H NMR (T ¼ ꢁ50 ꢀC) two
broad signals were observed with chemical shifts of ꢁ31.02 ppm
and ꢁ25.44 ppm in a ratio of 1:4.8, which can probably be attrib-
uted to the potential nickel hydride species (4ae2a, 4ae2b), while
After the synthesis and characterization of the nickel complexes
we directed our attention to the formation of nickel-hydride spe-
cies based on those complexes; 4a was chosen as model complex. In
our earlier study we have assumed that for the hydrodecyanation
the hydride source is tert-butylmagnesium chloride and the pro-
cess proceeds via nickel-alkyl intermediates (4ce2a, 4ce2b) that
the signals for LiBH4
¼ 2.74 ppm (br)] [19] or LiH [20] are in a different range. Per-
forming the measurement at 25 ꢀC one broad signal was observed
at ¼ ꢁ21.23 ppm.
¼ ꢁ19.39 ppm besides a minor signal at
Importantly, the signals can also be attributed to nickel borohy-
dride complexes (
1-coordination: 4ae3a, 4ae3b, 2-coordination:
[
d
¼ ꢁ0.53 ppm (m)], BH3 [BH3$THF
d
d
d
h
h
undergo subsequent
b
-hydride elimination leading to nickel-
4ae3c, 4ae3d) and the presence of those complexes cannot be
ruled out [11b,21]. Due to the broadness of the signals no coupling
patterns are visible. The broadness of the signals can arise from
exchange reactions or by paramagnetism of the nickel center (co-
ordination of solvent molecules can form octahedral complexes).
Moreover, in the 7Li NMR two signals were observed with a
chemical shift of ꢁ106.9 ppm and ꢁ79.6 ppm. Along with the two
hydride complexes (4ce3a, 4ce3b) as crucial intermediates
(Scheme 3). However, it was not possible to detect nickel-hydride
intermediates for instance by 1H NMR. One reason can be the
slow formation of the nickel hydride by b-hydride elimination. To
force this formation a higher temperature was required, at which
the nickel hydride decomposes rapidly if no substrate is available.
To overcome the limitations of the
b-hydride elimination, lithium
signals, LiBH4 was detected at
d
¼ ꢁ0.7 ppm.
borohydride was applied as hydride source, which should directly
form the corresponding nickel hydride complex [11]. Indeed, the
reaction of the nickel complex 4a with equimolar amounts of LiBH4
in THF-d8 for 2 min at 70 ꢀC showed a color change from orange to
green. The sample was immediately frozen with liquid nitrogen and
investigated with VT (Variable Temperature) NMR techniques.
Importantly, heating for a longer time resulted in the formation of a
black precipitate, which was also true for standing the solution
for 1 h at room temperature. First, 31P{1H} NMR measurements
To prove the reactivity of the formed species in hydro-
decyanation reactions 4-fluorobenzonitrile (5 equiv.) was added to
the mixture of complex 4a and LiBH4 (10 equiv.) after 2 min at 70 ꢀC
(Scheme 4). The mixture was reacted at 70 ꢀC for 10 min and
subsequent NMR measurements were carried out at room tem-
perature. The formation of the hydrodecyanation product fluo-
robenzene (8a) was detected by 19F NMR showing the appearance
of a new signal at
d
¼ ꢁ116.2(m) ppm, while the peak corre-
sponding to 8 is decreasing (
d
¼ ꢁ106.7(m) ppm). Noteworthy, a

S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
265
Fig. 2. Molecular structures of 6 (a) and 7 (b). Thermal ellipsoids are drawn at the 50%
ꢀ
probability level. 7: Hydrogen atoms are omitted for clarity. Selected bond lengths [A]
and angles [ꢀ] of 6: N(1)eN(2): 1.379(3), 7 [16]: Ni(1)eO(1): 1.8355(11), Ni(1)eO(2):
1.8122(11), Ni(1)eN(1): 1.8668(13), Ni(1)eP(1): 2.2385(5), O(1)eNi(1)eO(2):
175.50(6), N(1)eNi(1)eP(1): 171.92(4).
yield of 66% was observed after 10 min proving the catalytic activity
of the complex. Moreover, in the 1H NMR one broad signal was
observed at
d
¼ ꢁ19.39 ppm and a minor signal at ¼ ꢁ21.23 ppm,
d
which can be attributed to nickel-hydride or nickel-borohydride
species (Scheme 3, 4ae2 and 4ae3).
Moreover, IR measurements were carried out to study a potential
activation of the cyano group. In more detail, a solution of 4-
methoxybenzonitrile (9) in THF was mixed with LiBH4, complex 4a,
or BH3$THF. Only in case of BH3$THF a new band was detected at
2236 cmꢁ1, which indicates the activation of the cyano group by the
Lewis acid BH3$THF, while for all other reagents the band of the cyano
group wasunchanged (2225 cmꢁ1). Theweakeningof the CeCNbond
by BH3 is further indicated by comparing the calculated bond-
dissociation energies (BDEs) of benzonitrile (BDE ¼ 555.6 kJ molꢁ1
)
)
and of the benzonitrile-BH3 adduct complex (BDE ¼ 447.0 kJ molꢁ1
Fig. 1. Molecular structures of 3a (a), 4a (b), and 4b (c). Thermal ellipsoids are drawn at
the 50% probability level. Most hydrogen atoms are omitted for clarity. Selected bond
ꢀ
ꢀ
lengths [A] and angles [ ] of 3a: N(1)eN(2): 1.422(2), N(1)eC(3): 1.486(2), N(2)eC(1):
1.282(2), C(1)eC(2): 1.492(3), C(2)eC(3): 1.533(3), C(3)eC(4): 1.532(3), C(1)eC(5):
1.494(3); 4a (for clarity only one molecule of the unit cell is presented): Ni(1)eO(1):
1.820(2), Ni(1)eO(2): 1.816(2), Ni(1)eN(1): 1.855(3), Ni(1)eP(1): 2.2263(11), N(1)e
N(2): 1.408(3), O(2)eC(3): 1.226(2), O(1)eNieO(2): 179.31(11), N(1)eNieP(1):
172.23(9). 4b (for clarity only one molecule of the unit cell is presented): Ni(1)eO(2):
1.8235(16), Ni(1)eO(1): 1.8389(15), Ni(1)eN(1): 1.8729(16), Ni(1)eP(1): 2.2422(6),
N(1)eN(2): 1.393(2), O(2)eC(3): 1.307(3), O(1)eNi(1)eO(2): 179.14(7), N(1)eNi(1)e
P(1): 172.68(6).

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S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
Scheme 3. Formation of potential nickel-hydride/borohydride species.
Scheme 4. Hydrodecyanation of 4-fluorobenzonitrile (8).

S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
267
[22]. Based on the preliminary investigations we propose a reaction
mechanism as presented in Scheme 5. First the triphenylphosphane
ligand dissociates from complexes 4a to create open coordination
sites, which are temporarily occupied by solvent molecules. The
complex 4ae1 reacts with the lithium borohydride to form the nickel
hydride (4ae2a, 4ae2b) or nickel borohydride intermediates (4ae3a,
4ae3b, 4ae3c, 4ae3d). The organic cyanide or the Lewis acid acti-
vated cyanide approaches the coordination sphere of the nickel and
mediates a single electron transfer (SET) to oxidize the complex and
produce a radical [23]. The one-electron oxidized complex can on the
one hand oxidized at the metal center or on the other hand the
electron can be stored in the ligand (non-innocent ligand). Subse-
quently, lithium cyanide is eliminated and the radical recombines
with the nickel species to form the species B [24]. Finally, an elimi-
nation of AreH occurs to regenerate complex 4ae1.
After isolation, characterization and proving the reactivity of
complex 4a in hydrodecyanation the reaction conditions were
investigated in more detail (Table 1). As model reaction the
hydrodecyanation of 4-methoxybenzonitrile (9) with 2 equiv. LiBH4
was studied. First, the hydrodecyanation was performed in the
presence of 5.0 mol% 4a resulting in an excellent yield of anisole
(9a) of >99% after 24 h at 70 ꢀC (Table 1, entry 2). Noteworthy, the
addition of the nickel complex was necessary to perform the re-
action, while in the absence no product formation was monitored
(Table 1, entry 1). Importantly, an excellent selectivity for the
cleavage of the CeCN bond was observed, while the reduction of
Scheme 5. Proposed catalytic cycle for the nickel-catalyzed hydrodecyanation.

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S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
Table 1
Nickel-catalyzed hydrodecyanation of 4-methoxybenzonitrile (9).
Entrya
Catalyst loading [mol%]
T [ꢀC]
t [h]
Yield [%]b
1
2
3
4
5
6
7
e
70
70
70
70
70
70
40
RT
70
70
70
70
70
70
70
24
24
14
3
14
1
3
14
3
3
24
1
1
1
<1
>99
>99
>99
>99
24
<1
<1
43
<1
<1
<1
<1
<1
<1
5.0
2.5
2.5
1.0
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
8
9c
10d
11e
12d,f
13d,g
14d,h
15d,i
1
a
Reaction conditions: 9 (1.0 mmol), precatalyst 4a (1.0e5.0 mol%), LiBH4 (1.0e2.0 equiv.), THF (5.0 mL), r.t.e70 ꢀC, 1e24 h.
b
c
d
e
f
Determined by GCeMS applying n-dodecane as internal standard.
1.0 equiv. LiBH4.
2.0 equiv. NaBH4.
2.0 equiv. LiBHEt3.
1,4-Dioxane as solvent and complex 4c as precatalyst.
1,2-Dimethoxyethane as solvent and complex 4c as precatalyst.
Diethylene glycol dimethyl ether as solvent and complex 4c as precatalyst.
2.0 equiv. of LiOOCH.
g
h
i
the CeN triple bond by LiBH4 or BH3 did not occur [25]. Decreasing
In addition, changing the square planar geometry to an octahedral
geometry (complex 5) no product was observed. Probably, the
strong coordination of the three dmap ligands and the shielding of
the metal center allow not for an easy creation of free coordination
sites for the substrates. Moreover, the enolate function of the
complex 4a was changed to a phenolate function (complex 7)
showing an improvement of the catalyst activity. Probably the
phenyl substituent allows for a better stabilization of the in-
termediates in the catalytic cycle by delocalization as discussed for
complex 4c.
After investigation of the reaction conditions and the precatalyst-
screening, precatalyst 4c was applied in the hydrodecyanation of
various aryl and alkyl cyanides with LiBH4 as hydride source
(Table 2). Excellent yields (>99%) were observed for methoxy- and
methyl substituted aryl cyanides (Table 2, entries 1e5). For other
functional groups such as amine, ester or thioether in para-position
lower reactivity was observed or an attack of the functional group
(Table 2, entries 6e9). In contrast, 4-fluorobenzonitrile was selec-
tively converted to 4-fluorobenzene in excellent yield and selectivity,
while for 4-bromobenzonitrile the hydrodehalogenation and
hydrodecyanation were monitored (Table 2, entry 11). Moreover, 1,4-
dicyanobenzene was converted with 1.1 equiv. of LiBH4 in excellent
selectivity to benzonitrile (Table 2, entry 13). In contrast to our first
generation hydrodecyanation system most aromatic cyanides were
converted in excellent yields and selectivities in short reaction
times and low catalyst loadings. In addition, heteroaromatic sub-
strates were tested resulting in excellent yield of thiophene, while
3-cyanopyridine was not converted, probably due to the coordina-
tion abilities of the pyridine (Table 2, entries 14 and 15). In case of
cinnamonitrile (24) the reduction of the CeC double bond was
the catalyst loading to 2.5 mol% or 1.0 mol%, respectively, resulted
in an excellent yield after 14 h (Table 1, entries 3e5). With 2.5 mol%
of 4a full conversion was realized after 3 h, while after 1 h 24% yield
of anisole (9a) was detected (Table 1, entries 4 and 6, respectively).
Decreasing the reaction temperature to 40 ꢀC or room temperature
no product formation was noticed (Table 1, entries 7 and 8,
respectively). Reducing the amount of LiBH4 to 1 equiv. showed a
diminished yield of 43% after 3 h (Table 1, entry 9). A change of the
hydride source LiBH4 to NaBH4 resulted in no product formation,
probably due to poor solubility in THF and lower activity of the
NaBH4 (Table 1, entry 10).
Next, the structureeactivity relationship was investigated,
applying complexes 4, 5 and 7 as precatalysts in the hydro-
decyanation of 4-methoxybenzonitrile (9) (Scheme 6). The reaction
conditions are in accordance to Table 1 entry 6. Interestingly, sub-
stitution of the methyl group by a phenyl group (complex 4b)
resulted in an increase of the yield of 9a to 69%. Probably the phenyl
substituent allows for a better stabilization of the intermediates in
the catalytic cycle by delocalization. On the other hand, substitution
of the methyl group by an electron-withdrawing CF3-group (com-
plex 4c) showed an excellent performance with a yield of 89% after
one hour. Significantly, the obtained catalyst activity for the
hydrodecyanation applying LiBH4 as hydride source is superior in
comparison to earlier reports, e.g., the combination of 5.0 mol% of
complex 4c and tert-butylmagnesium chloride as hydride source
requires 48 h to reach 74% of product 9a [9]. Moreover, the sub-
stitution of the phenyl group in 4c by a methyl (complex 4d)
resulted in a decrease of activity, which demonstrated once
more the need for aromatic substituents to realize high activities.

S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
269
Scheme 6. Investigation of the influence of the precatalyst structure on the hydrodecyanation of 9.
observed as major reaction pathway (Table 2, entry 12). In addition,
aliphatic cyanides such as 25 and 26 were not converted to the
desired product, which is in contrast to the first generation hydro-
decyanation protocol. However, the reactions could be of interest for
the selective removal of aromatic cyanides in the presence of
aliphatic cyanides (Table 2, entry 17e18).
cyano group the reactivity is decreased. On the other hand, the side
product 28 was also subjected to hydrodecyanation to obtain
compound 30 in 30% yield. Interestingly, this compound can easily
converted to 29 and in consequence to Nobiletin [26].
3. Conclusion
In addition, the hydrodecyanation protocol was embedded in
the synthesis of pentamethoxybenzene (29), which has been
applied for instance in the total synthesis of Nobiletin a biological
active compound (Scheme 7) [26]. In more detail, multi-step ap-
proaches have been established to access compound 29 [26,27]. For
instance Kan and co-workers reported a 8-step synthesis starting
from 1,2,3-trimethoxybenzene (10a). An alternative approach can
be the application of the commercial available compound 10 and to
make use of the ortho-directing effect of the nitrile functionality in
palladium-catalyzed alkoxylation reactions as recently reported by
Li and Sun [3d]. A subsequent hydrodecyanation reaction should
provide the desired target compound 29 in an overall two-step
synthesis. Hence, the bisalkoxylation of 10 was performed with
10 mol% Pd(OAc)2 and Na2S2O8 (5.0 equiv.) as oxidant in methanol.
After 8 h at room temperature and 16 h at 70 ꢀC the desired product
27 was obtained in 73% yield accompanied by the monoalkoxylated
compound 28. After isolation of the product 27 it was subjected to
the hydrodecyanation protocol applying the optimized conditions.
After 3 h the product 1,2,3,4,5-pentamethoxybenzene (19) was
obtained in moderate yield of 17%. Probably due to sterical and
electronic effects of the methoxy groups in ortho-position to the
In summary, we have set up a methodology for the nickel-
catalyzed hydrodecyanation of organic cyanides with LiBH4 as hy-
dride source under mild reaction conditions, with low catalyst
loadings and within short times. With the well-defined nickel
complex 4c a variety of aryl cyanides were converted. Noteworthy,
in comparison to our earlier work a significant improvement of the
catalyst activity was observed.
4. Experimental section
4.1. General
All compounds were used as received without further purifi-
cation. THF was dried applying standard procedures. 1H, 7Li 19F,
13C and 31P NMR spectra were recorded on a Bruker Avance II 200
spectrometer (1H: 200.13 MHz; 13C: 50.32 MHz; 19F: 188.31 MHz,
31P: 81.01 MHz, 7Li: 77.78 MHz) using the proton signals of the
deuterated solvents as reference. 1H and 7Li Variable Tempera-
ture (VT) NMR measurements were carried out on a Bruker
Avance 400 spectrometer (1H: 400.13 MHz; 7Li: 155.54 MHz).

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S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
Table 2
Scope and limitations of the nickel-catalyzed hydrodecyanation.
Entrya
1
Substrate
Yield [%] [Ref. [9]]b
61
Selectivity [%]c
Yield [%]d
>99
9a: >99 (89)
9
2
63
>99
10a: >99 (94)
10
3
4
57
49
>99
>99
11a: >99
11a: >99
11
12
5
38
>99
11a: >99
13
6
7
8
20
e
>99
e
14a: 17
15a: <1
16a: <1e
14
15
<1
e
16
9
74
80
<1
<1
e
17a: <1
8a: >99
19a: 53f
20a: 68
17
10
11
12
>99
e
8
19
>99
20
13g
e
97
21a: 97h
21
14
15
e
e
22a: <1
22
23
>99
>99
23a: >99

S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
271
Table 2 (continued )
Entrya
Substrate
Yield [%] [Ref. [9]]b
Selectivity [%]c
Yield [%]d
16
17
e
e
24a: 87i
24
25
e
e
e
25a: 7
18
CH3(CH2)8CN 26
64
26a: <1
a
Reaction conditions: substrate (1.0 mmol), precatalyst 4c (2.5 mol%), LiBH4 (2.0 equiv.), THF (5.0 mL), 70 ꢀC, 3 h.
b
c
d
e
f
For comparison the yields of the 1. Generation hydrodecyanation (Ref. [9]) with 5.0 mol% 4c and tert-butylmagnesium chloride after 24 h is stated.
Refers to the hydrodecyanation reaction.
Determined by GCeMS applying n-dodecane as internal standard. In brackets the isolated yield is stated.
Numerous undefined products.
Benzene.
1.1 equiv. LiBH4.
Refers to benzonitrile.
Reduction of the CeC double bond.
g
h
i
Single crystal X-Ray diffraction measurements were recorded on
an Oxford Diffraction Xcalibur S Sapphire spectrometer. GCeMS
measurements were carried out on a Shimadzu GC-2010 gas
chromatograph (30 m Rxi-5 ms column) linked with a Shimadzu
GCMA-QP 2010 Plus mass spectrometer. IR spectra were recorded
on a Perkin Elmer Spectrum 100 FT-IR. Ligands 3c and 3d and
complexes 4c, 4d and 5 were synthesized in accordance to
literature protocols. [10,15].
(s, br, 1H, OH), 3.32e3.04 (m, 2H, CH2), 2.01 (s, 1H, CH3) ppm. 13
{1H} NMR (400 MHz, CDCl3, 25 ꢀC)
¼ 171.1, 154.7, 133.0, 132.1,
130.1, 127.8, 126.3, 92.4, 46.7 (CH2), 15.6 (CH3) ppm. 19F NMR
(188 MHz, CDCl3, 25 ꢀC)
3001 (m), 1661 (s), 1635 (s), 1602 (m), 1579 (m), 1496 (m), 1452 (s),
1435 (s), 1381 (s), 1353 (s), 1334 (s), 1319 (s), 1235 (m),1207 (s), 1180
(vs), 1156 (s), 136 (s), 1121 (s),1100 (m),1049 (m),1029 (m), 997 (m),
969 (m), 892 (m), 841 (m), 825 (m), 791 (m), 755 (m), 736 (m), 717
(m), 696 (m), 671 (m), 654 (m), 620 (m), 494 (m) cmꢁ1. HRMS calcd.
for C12H11F3N2O2 þ H: 273.08454; found 273.08499.
C
d
d
¼ ꢁ81.2 ppm. IR (KBr):
n
¼ 3365 (br),
4.1.1. Synthesis of ligand 3a
A
mixture of benzohydrazide (65.3 mmol) and 1,1,1-
trifluoropenta-2,4-dione (65.3 mmol) was dissolved in ethanol
(50 mL) and stirred for 24 h at 80 ꢀC. Subsequently the solvent was
removed under reduced pressure and the colorless residue was
purified by recrystallization from n-hexane. Crystals suitable for
X-ray diffraction were obtained from a concentrated n-hexane so-
lution. Yield ¼ 40% (colorless crystals). 1H NMR (200 MHz, CDCl3,
4.1.2. Synthesis of complex 4a
A mixture of 3a (7.35 mmol), Ni(OAc)2$4H2O (7.35 mmol) and
triphenylphosphane (14.70 mmol) was dissolved in methanol
(25 mL) and stirred for 24 h at room temperature. After removal of
the volatiles under reduced pressure, a brown solid was obtained.
The residue was purified by recrystallization from n-hexane.
Crystals suitable for X-ray diffraction were obtained from a
25 ꢀC)
d
¼ 7.87e7.84 (m, 2H, AreH), 7.53e7.36 (m, 3H, AreH), 6.55
Scheme 7. Synthetic application of the hydrodecyanation protocol.

272
S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
concentrated n-hexane solution at room temperature. Yield ¼ 59%
(brown crystals). 1H NMR (200 MHz, C6D6, 25 ꢀC)
1091 (w), 1075 (w), 1024 (w), 977 (w), 931 (w), 834 (m), 797 (w),
744 (s), 710 (m), 689 (m), 673 (w), 655 (w), 624 (w), 613 (w) cmꢁ1
.
d
¼ 8.00e7.95 (m,
2H, AreH), 7.84e7.73 (m, 6H, AreH), 7.13e6.99 (m,12H, AreH), 5.76
(s, 1H, CH), 2.35 (s, 3H, CH3) ppm. 13C{1H} NMR (100 MHz, CDCl3,
4.1.6. Synthesis of complex 7 [16]
25 ꢀC)
d
¼ 170.6, 156.1, 134.3, 131.2, 130.4, 129.6, 192.2, 128.4, 128.2,
A mixture of ligand 6 (2.0 mol) and Ni(OAc)2$4H2O (2.0 mmol)
and triphenylphosphane (6.0 mmol) was dissolved in ethanol
(100 mL) and stirred for 20 h at 90 ꢀC. The mixture was filtered and
the volatiles were removed under reduced pressure to obtain a red
solid. The residue was purified by recrystallization from ethanol or
dichloromethane. Crystals suitable for X-ray diffraction were ob-
tained from a concentrated dichloromethane solution at room
temperature. Yield ¼ 64% (red crystals). 1H NMR (200 MHz, DMSO-
97.6, 19.0 ppm (some signals are covert by solvent signals). 19F NMR
(188 MHz, C6D6, 25 ꢀC)
d
¼ ꢁ70.9 ppm. 31P{1H} NMR (81 MHz,
CDCl3, 25 ꢀC)
d
¼ 15.4 ppm. IR (KBr): ¼ 3436 (br), 3058 (w), 1619
n
(s), 1587 (m), 1540 (s), 1520 (s), 1492 (m), 1482 (m), 1437 (s), 1371
(m), 1352 (s), 1313 (vs),1250 (s), 1181 (s), 1143 (s), 1125 (s), 1102 (m),
1070 (m), 1028 (m), 745 (m), 694 (s), 530 (m). 509 (m), 496
(m) cmꢁ1. HRMS calcd. for C30H24F3N2O2NiP þ H: 591.09537; found
591.13079.
d6, 25 ꢀC)
d
¼ 6.47e7.79 (m, 24H, AreH), 3.28 (s, 3H, CH3) ppm. 31
P
{1H} NMR (81 MHz, DMSO-d6, 25 ꢀC)
d
¼ 25.5 ppm. IR (KBr):
4.1.3. Synthesis of ligand 3b
n
¼ 1575 (m), 1529 (s), 1358 (m), 1329 (m), 1098 (m) cmꢁ1. HRMS
A mixture of benzohydrazide (58.8 mmol) and 4,4,4-trifluoro-1-
phenylbutan-1,3-dione (58.8 mmol) was dissolved in ethanol
(50 mL) and stirred for 168 h at room temperature and for 336 h at
40 ꢀC. Subsequently the solvent was removed under reduced
pressure and the colorless residue was purified by recrystallization
from n-hexane. Yield ¼ 29% (colorless crystals). 1H NMR (200 MHz,
calcd. for C33H27N2O2NiP þ H: 573.12364; found 573.12366.
4.2. General procedure for the catalytic hydrodecyanation
A Schlenk flask was charged with an appropriate amount of
complex 4c (0.025 mmol, 2.5 mol%), LiBH4 (2.0 mmol) and the
corresponding organic cyanide (1.0 mmol). The flask was cycled
with nitrogen and vacuum. Afterward THF (5.0 mL) was added. The
flask was sealed and heated at 70 ꢀC for 3 h. After that time, the
mixture was cooled to room temperature, the THF was carefully
removed in vacuum and the residue was dissolved in diethylether
and filtered trough a short plug of silica. The products were
confirmed by GCeMS (n-dodecane was added as internal standard)
and NMR analysis. The analytical properties of the products are in
agreement with literature data.
CDCl3, 25 ꢀC)
d
¼ 8.00e7.96 (m, 2H, AreH), 7.64e7.33 (m, 8H, Are
H), 6.72 (s, 1H, OH), 3.77e3.49 (m, 2H, CH2) ppm. 13C{1H} NMR
(400 MHz, CDCl3, 25 ꢀC)
¼ 171.1, 153.2, 133.0, 132.3, 131.1, 130.4,
129.9, 128.9, 127.9, 126.8, 126.4, 93.1, 43.1 (CH2) ppm. 19F NMR
(188 MHz, CDCl3, 25 ꢀC)
d
d
¼ ꢁ81.0 ppm. IR (KBr):
n
¼ 3372 (br, s),
1644 (s), 1603 (m), 1577 (m), 1450 (s), 1422 (s), 1345 (s), 1309 (m),
1264 (m), 1216 (m), 1179 (s), 1126 (m), 1110 (m), 1039 (m), 1027 (m),
1005 (m), 922 (m), 902 (m), 869 (m), 759 (m), 710 (s), 688 (s), 674
(m), 598 (m), 501 (m) cmꢁ1. HRMS calculated for C17H13F3N2O2 þ H:
335.10019; found 335.09982.
Fluorobenzene (8a): MS (EI) m/z ¼ 96 (61), 70 (20), 50 (11), 44
(11), 40 (100).
4.1.4. Synthesis of complex 4b
Anisole (9a): 1H NMR (CDCl3, 200 MHz)
d
¼ 7.31e7.27 (m, 2H),
A mixture of 3b (2.99 mmol), Ni(OAc)2$4H2O (2.99 mmol) and
triphenylphosphane (5.98 mmol) was dissolved in methanol
(25 mL) and stirred for 24 h at room temperature. After removal of
the volatiles under reduced pressure, a brown solid was obtained.
The residue was purified by recrystallization from n-hexane.
Crystals suitable for X-ray diffraction were obtained from a
concentrated n-hexane solution at room temperature. Yield ¼ 21%
6.96e6.86 (m, 3H), 3.79 (s, 3H) ppm. MS (EI) m/z ¼ 108 (100, Mþ),
93 (23), 78 (96), 65 (99), 51 (33), 40 (75).
1,2,3-Trimethoxybenzene (10a): 1H NMR (CDCl3, 200 MHz)
d
¼ 6.88e7.00 (m, 1H), 6.52e6.58 (m, 2H), 3.82 (s, 9H) ppm. 13C{1H}
NMR (100 MHz, CDCl3, 25 ꢀC)
d
¼ 153.4, 138.1, 123.6, 105.2, 60.7,
56.0 ppm. MS (EI) m/z ¼ 168 (32, Mþ),153 (33),125 (16),110 (21), 95
(15), 40 (100).
(brown crystals). 1H NMR (200 MHz, C3D6O, 25 ꢀC)
d
¼ 7.86e7.08
(m, 25H, AreH), 5.93 (s, 1H, CH) ppm. 13C{1H} NMR (100 MHz,
C3D6O, 25 ꢀC)
¼ 135.7, 134.4, 134.1, 131.0, 130.9, 129.9, 129.2,
Toluene (11a): MS (EI) m/z ¼ 91 (100, Mþ), 89 (9), 65 (28), 63
(20), 51 (19), 40 (98).
d
N,N0-Dimethylaniline (14a): MS (EI) m/z ¼ 121 (14, Mþ), 40 (100).
Benzene (19a): MS (EI) m/z ¼ 78 (64, Mþ), 51 (20), 40 (20).
Trifluoromethylbenzene (20a): MS (EI) m/z ¼ 146 (100, Mþ), 127
(53), 96 (46), 77 (21).
128.8, 128.6, 128.0, 127.8, 127.7, 121.3, 115.7, 99.9, 97.4, 29.2 ppm.
19F NMR (188 MHz, C3D6O, 25 ꢀC)
(81 MHz, C3D6O, 25 ꢀC)
(w), 1598 (s), 1537 (s), 1510 (m), 1485 (m), 1435 (s), 1354 (s), 1325
(s), 1308 (m), 1284 (m), 1255 (m), 1185 (s), 1167 (s), 1132 (s),
1100 (s), 1067 (m), 1027 (m), 747 (m), 693 (s), 529 (m), 509
(m) cmꢁ1. HRMS calcd. for C35H26F3N2O2NiP þ H: 653.11102; found
653.11163.
d
¼ ꢁ71.9 ppm. 31P{1H} NMR
d
¼ 15.1 ppm. IR (KBr): ¼ 3435 (br), 3056
n
Benzonitrile (21a): 1H NMR (CDCl3, 200 MHz)
5H) ppm. 13C{1H} NMR (100 MHz, CDCl3, 25 ꢀC)
d
¼ 7.35e7.66 (m,
d
¼ 133.0, 132.2,
129.2, 118.8, 112.2 ppm. MS (EI) m/z ¼ 103 (100, Mþ), 76 (39).
Thiophene (23a): MS (EI) m/z ¼ 84 (100), 58 (76), 45 (34).
3-Phenylpropionitrile (24a): MS (EI) m/z ¼ 131 (24, Mþ), 91 (100),
65 (15).
4.1.5. Synthesis of ligand 6 [16]
1,2,3,4,5-Pentamethoxybenzene (29): MS (EI) m/z ¼ 228 (100,
Mþ), 213 (99), 185 (24), 170 (36), 155 (22), 127 (15), 99 (13).
1,2,3,4-Tetramethoxybenzene (30): MS (EI) m/z ¼ 198 (100, Mþ),
183 (57), 168 (12), 155 (11), 140 (31), 123 (15), 95 (11), 69 (15).
Single-crystal X-ray structure determination [28]: Crystals were
each mounted on a glass capillary in perfluorinated oil and
measured in a cold N2 flow. The data were collected using an Oxford
A
mixture of benzhydrazide (41.7 mmol) and 2-
hydroxyacetophenone (41.7 mmol) was dissolved in ethanol
(50 mL) and refluxed for 24 h. A white precipitate was formed,
which was filtered, washed with ethanol and dried in vacuum.
Crystals suitable for X-ray diffraction were obtained from a
concentrated ethanol solution at room temperature. Yield ¼ 71%
(colorless crystals). 1H NMR (200 MHz, DMSO-d6, 25 ꢀC)
d
¼ 12.38
Diffraction Xcalibur S Sapphire at 150(2) K (MoK radiation,
a
ꢀ
(s, 1H), 10.35 (s, 1H), 6.92e6.96 (m, 2H), 6.49e6.65 (m, 4H), 6.26e
6.35 (m, 1H), 5.85e5.94 (m 2H), 1.48 (s, 3H, CH3) ppm. IR (KBr):
l
¼ 0.71073 A) or an Agilent Technologies SuperNova (single
ꢀ
source) at 150 K (CuKa radiation,
l
¼ 1.5418 A). The structures were
n
¼ 3204 (m), 3043 (w), 2999 (w), 1650 (s), 1638 (s), 1611 (s), 1577
solved by direct methods and refined on F2 with the SHELX-97
software package. The positions of the hydrogen atoms were
calculated and considered isotropically according to a riding model.
(m), 1526 (m), 1483 (m), 1450 (m), 1398 (w), 1366 (w), 1329 (w),
1304 (w), 1283 (m), 1253 (m), 1238 (s), 1158 (w), 1142 (w), 1125 (w),

S. Enthaler et al. / Journal of Organometallic Chemistry 745-746 (2013) 262e274
273
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Calculations were performed with the Gaussian09 program
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theory [30]. Frequency calculations were performed to verify sta-
tionary points. All energies (given in kJ molꢁ1) were corrected for
(unscaled) zeropoint vibrational energy contributions. The quality
of the computational protocol was proven by comparing the
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Financial support from the Cluster of Excellence “Unifying Con-
cepts in Catalysis” (www.unicat.tu-berlin.de; funded by the Deut-
sche Forschungsgemeinschaft and administered by the Technische
Universität Berlin) is gratefully acknowledged. Chika I. Someya
thanks the Berlin International Graduate School of Natural Sciences
and Engineering (BIG NSE) for ideational support. J. Fuchs and M.
Dettlaff (Technische Universität Berlin) are thanked for technical
support. R.K. thanks the Alexander von Humboldt Foundation for a
Feodor Lynen Research Fellowship. We thank the Institut für Math-
ematik der TU Berlin for the allocation of computer time.
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Appendix A. Supplementary material
CCDC 941131, 941132, 941133, 942994 and 942995 contain the
supplementary crystallographic data for this paper. These data can
be obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
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