Synthesis, characterization and application of nickel(II) complexes modified with N,N′,N″-pincer ligands

Article abstract of DOI:10.1016/j.ica.2014.10.003

Different N,N″-substituted pyridine-2,6-dicarboxamides 1a-d have been synthesized and treated with nickel(II) trifluoromethanesulfonate in the presence of an excess of tetraethylammonium hydroxide to form after double-deprotonation the nickel hydroxido complexes 4a-c. These square planar complexes have been characterized by various techniques, which indicate a tridentate N,N′,N″-coordination mode of the ligands. The other coordination site on the nickel center is occupied by a hydroxido ligand. The reactivity of the complexes was studied in dehalogenation reactions and allows access to square planar nickel chlorido complexes 5a-c. Moreover, by NMR studies it was found that nickel hydroxido complexes as well as chlorido complexes can be converted with diphenylsilane or lithium borohydride to nickel hydrido complexes, which can be seen as a possible catalytic intermediate in reduction chemistry. Based on that, the potential of complexes 4 and 5 were evaluated in the hydrosilylation of ketones to produce alcohols after work-up.

Full text of DOI:10.1016/j.ica.2014.10.003

Inorganica Chimica Acta 425 (2015) 118–123
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Inorganica Chimica Acta
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Synthesis, characterization and application of nickel(II) complexes
0
00
modified with N,N ,N -pincer ligands
a
a
a
b
a,
⇑
Frank Czerny , Peter Döhlert , Maik Weidauer , Elisabeth Irran , Stephan Enthaler
a
Technische Universität Berlin, Department of Chemistry, Cluster of Excellence ‘‘Unifying Concepts in Catalysis’’, Straße des 17. Juni 115/C2, 10623 Berlin, Germany
Institute of Chemistry: Metalorganics and Inorganic Materials, Technische Universität Berlin, Straße des 17. Juni 135/C2, D-10623 Berlin, Germany
b
a r t i c l e i n f o
a b s t r a c t
0
0
Article history:
Different N,N -substituted pyridine-2,6-dicarboxamides 1a–d have been synthesized and treated with
nickel(II) trifluoromethanesulfonate in the presence of an excess of tetraethylammonium hydroxide to
form after double-deprotonation the nickel hydroxido complexes 4a–c. These square planar complexes
Received 14 August 2014
Accepted 3 October 2014
Available online 14 October 2014
0
00
have been characterized by various techniques, which indicate a tridentate N,N ,N -coordination mode
of the ligands. The other coordination site on the nickel center is occupied by a hydroxido ligand. The
reactivity of the complexes was studied in dehalogenation reactions and allows access to square planar
nickel chlorido complexes 5a–c. Moreover, by NMR studies it was found that nickel hydroxido complexes
as well as chlorido complexes can be converted with diphenylsilane or lithium borohydride to nickel
hydrido complexes, which can be seen as a possible catalytic intermediate in reduction chemistry. Based
on that, the potential of complexes 4 and 5 were evaluated in the hydrosilylation of ketones to produce
alcohols after work-up.
Keywords:
Nickel complexes
Pincer complexes
Tridentate ligands
Hydrosilylation
Ó 2014 Elsevier B.V. All rights reserved.
1
. Introduction
Catalysis is one of the key methodologies for the development
demonstrated the usefulness of complexes 2 in cross coupling
reactions of C–H bonds or C–Cl bonds with Grignard reagents to
create new carbon – carbon bonds.
of sustainable, efficient, and selective reactions [1]. In this regard,
metal catalysis has been proven to be an outstanding toolbox for
such requirements [2]. Especially, the addition of ligands to the
metals have a strong influence on the performance of the catalyst;
hence the design of new ligands and the study of their coordination
chemistry is of importance [3,4]. In this regard, in recent times tri-
dentate pincer-type ligands have been established as useful tool
for controlling the catalyst performance [5]. Furthermore, the inex-
pensiveness, great availability, easy synthesis, high tunability, high
flexibility and stability of the ligands should be considered. With
respect to these requirements an attractive ligand motif can be
precursor 1, which is simply accessible from commercially avail-
able chemicals and easily tunable (Fig. 1). Recently, the coordina-
tion chemistry of ligand precursor 1 towards nickel was studied
On the other hand, more recently nickel complexes became
attractive catalyst precursors for hydrosilylation reactions and per-
forming a wide range of reductions, e.g., ketones, aldehydes, imi-
nes, olefins, alkynes in excellent yields and selectivities [8].
However, so far the catalytic activity of pincer complexes 2 was
not evaluated in hydrosilylation reactions. Based on these recent
achievements in hydrosilylation and our interest in nickel pincer
complexes [9] we became interested in the synthesis and charac-
terization of pincer complexes 2 and their application in hydrosily-
lation reactions of ketones.
2. Results and discussion
0
00
revealing a tridentate pincer-type N,N ,N -coordination geometry
and interesting reactivity of the corresponding complexes have
The ligand precursors 1 were synthesized in accordance to liter-
ature protocols [6,10]. In more detail, dipicolinic acid 3 was reacted
with an excess of thionyl chloride (28 equiv.) under refluxing con-
ditions for 12 h (Scheme 1). Subsequently, the volatiles were
removed in vacuum and the residue was dissolved in THF. The
solution was added to a mixture of the corresponding aniline
2
been observed, e.g., activation of small molecules [6]. Moreover,
initial investigations on the catalytic abilities have been carried
out with this complex class [7]. For instance Ghosh and coworkers
(
2.0 equiv.) and triethylamine (2.0 equiv.) in THF and stirred for
⇑
Corresponding author.
E-mail address: stephan.enthaler@tu-berlin.de (S. Enthaler).
16 h at room temperature. The mixture was filtered and the sol-
vent was removed in vacuum. The residue was washed with n-hex-
http://dx.doi.org/10.1016/j.ica.2014.10.003
020-1693/Ó 2014 Elsevier B.V. All rights reserved.
0

F. Czerny et al. / Inorganica Chimica Acta 425 (2015) 118–123
119
Catalysis
Y
O
R
O
R
O
R
O
R
N
N
Ni
X
cross couplings (Ghosh et al.)
hydrosilylation (this work)
NH
HN
N
N
1
2
0
00
Fig. 1. Nickel complexes modified by N,N ,N -ligands and application in catalysis.
SOCl2
RNH , NEt
2 3
O
R
O
R
O
O
O
O
N
N
N
7
5 °C, 12 h
THF, r.t., 16 h
NH
HN
OH
OH
Cl
Cl
3
1a-d
R =
F
1a: 46% yield
1b: 42% yield
1c: 49% yield
1d: 56% yield
Scheme 1. Ligand synthesis.
ane and diethyl ether. The colorless residues were dried in vacuum
and recrystallized from ethanol or THF in yields of 42–56%.
Crystals suitable for single-crystal X-ray diffraction measure-
ments were grown from ethanol or THF. The solid-state structures
of the ligand precursors 1a, 1c and 1d have been characterized by
single-crystal X-ray diffraction analysis. The thermal ellipsoid
plots, selected bond lengths and angles are shown in Figs. 2–4
and Table 1.
Afterwards the ligand precursors were reacted with nickel(II)
trifluoromethanesulfonate (Ni(OTf) ) and tetraethylammonium
2
hydroxide in accordance to literature protocols (Scheme 2) [6].
After 12 h at room temperature the red nickel complexes 4 were
isolated in 81–94% yields. Crystals suitable for single-crystal X-
ray diffraction measurements were grown from diethylether or
ethyl acetate. The solid-state structures of complexes 4a, 4b and
Fig. 3. Molecular structure of ligand precursor 1c. Thermal ellipsoids are drawn at
the 50% probability level. Most hydrogen atoms are omitted for clarify. Selected
bond lengths (Å) and angle (°): C1–O1: 1.2152(17), C4–O2: 1.2185(18), N2–C1:
4
d have been characterized by single-crystal X-ray diffraction anal-
1.3554(19), N2–C2: 1.4141(18), N3–C4: 1.3519(19), N3–C6: 1.4391(18), C3–C1–N2:
ysis. The thermal ellipsoid plots, selected bond lengths and angles
are shown in Figs. 5 and 6, and Table 2. In more detail, the tridentate
dianionic ligand (1-2H) is coordinated in a N,N ,N -mode creating
111.94(12), C5–C4–N3: 113.84(12).
0
00
two five-membered planar ring system and therefore shielding
Fig. 4. Molecular structure of ligand precursor 1d. Thermal ellipsoids are drawn at
the 50% probability level. Selected bond lengths (Å) and angle (°): C1–O1:
1.2254(16), C4–O2: 1.2285(16), N2–C1: 1.3469(18), N2–C2: 1.4109(17), N3–C4:
1.3476(17), N3–C6: 1.4147(16), C3–C1–N2: 120.71(12), C5–C4–N3: 120.69(12).
Fig. 2. Molecular structure of ligand precursor 1a. Thermal ellipsoids are drawn at
the 50% probability level. Most hydrogen atoms and one THF molecule are omitted
for clarify. Selected bond lengths (Å) and angle (°): C1–O1: 1.229(2), N2–C1:
one site of the metal. In case of complexes 4a and 4c the additional
coordination site of the square planar nickel complexes are occu-
pied by a hydroxido ligand. Moreover, both anionic complexes are
1
.3416(18), N2–C2: 1.438(2), C3–C1–N2: 114.69 (12).

1
20
F. Czerny et al. / Inorganica Chimica Acta 425 (2015) 118–123
Table 1
Analytical properties of the ligand precursors 1.
1
a
1b
1c
1.2152(17)
.2185(18)
1.3554(19)
.4141(18)
1.3519(19)
.4391(18)
111.94(12)
13.84(12)
1d
C1(4)–O1(2) (Å)
N2(3)–C1(4) (Å)
N2(3)–C2(6) (Å)
C3(5)–C1(4)–N2(3) (°)
1.229(2)
–
1.2254(16)
1.2285(18)
1.3469(18)
1.3476(17)
1.4109(17)
1.4147(16)
120.71(12)
1
1.3416(18)
1.438(2)
–
–
–
1
1
114.69(12)
1
120.69(12)
1
3
1
a
162.3b
C{ H} NMR (C1) (ppm)
162.6
1666
161.7
1680
162.1
1699
ꢀ
1 c
m
(C@O) (cm
)
1666
a
b
c
In CDCl at r.t.
In THF-d8 at r.t.
In KBr.
3
Fig. 6. Molecular structure of complex 4b. Thermal ellipsoids are drawn at the 50%
probability level. Most hydrogen atoms are omitted for clarify. Selected bond
lengths (Å) and angle (°): C1–O1: 1.229(3), C4–O2: 1.232(3), N2–C1: 1.349(3), N2–
C2: 1.423(3), N3–C4: 1.352(3), N3–C6: 1.418(3), Ni1–O3: 1.825(2), Ni1–N1:
1
1
.822(2), Ni1–N2: 1.923(2), Ni1–N3: 1.903(2), C3–C1–N2: 109.8(2), C5–C4–N3:
09.3(2), O3–Ni1–N1: 176.97(13), O3–Ni1–N3: 97.09(8), N1–Ni1–N3: 82.76(8),
O3–Ni1–N2: 97.41(8), N1–Ni1–N2: 82.87(8), N3–Ni1–N2: 165.35(9).
Table 2
Analytical properties of complexes 4.
4a
4b
4c
Ni1–N1 (Å)
Ni1–N2 (Å)
Ni1–N3 (Å)
Ni1–O3 (Å)
N1–Ni1–N2 (°)
N1–Ni1–O3 (°)
C3(5)–C1(4)–N2(3) (°)
1.820(2)
1.913(2)
1.9086(18)
1.818(2)
83.06(8)
1.822(2)
1.923(2)
1.903(2)
1.825(2)
82.87(8)
176.97(13)
109.8(2)
109.3(2)
–
–
–
–
–
–
–
178.08(8)
110.30(18)
1
09.97(19)
1
a
b
b
H NMR (–OH) (ppm)
C{ H} NMR (C1) (ppm)
ꢀ5.23
ꢀ4.90
ꢀ5.00
13
1
a
168.7b
167.5b
167.2
4.6
c
D
m
D
(C1) (ppm)
7.0
1602
79
5.4
1615
84
(C@O) (cm )d
ꢀ
1
1611
56
(C@O) (cm ) e
ꢀ
1
a
b
c
Fig. 5. Molecular structure of complex 4a-EtOAc. Thermal ellipsoids are drawn at
the 50% probability level. Most hydrogen atoms are omitted for clarify. Selected
bond lengths (Å) and angle (°): C1–O1: 1.240(3), C4–O2: 1.239(3), N2–C1: 1.347(3),
N2–C2: 1.431(3), N3–C4: 1.345(3), N3–C6: 1.429(3), Ni1–O3: 1.8177(16), Ni1–N1:
In THF-d8 at r.t.
In CD Cl2 at r.t.
2
D
(C1) = d (C@O-4) ꢀ d (C@O-1).
In KBr.
(C@O) = m (C@O-1) ꢀ m (C@O-4).
d
e
1
.8199(18), Ni1–N2: 1.9125(17), Ni1–N3: 1.9086(18), C3–C1–N2: 110.30(18), C5–
C4–N3: 109.97(19), O3–Ni1–N1: 178.08(8), O3–Ni1–N3: 95.49(7), N1–Ni1–N3:
2.85(8), O3–Ni1–N2: 98.58(7), N1–Ni1–N2: 83.06(8), N3–Ni1–N2: 165.89(7).
D
8
stabilized by tetraethylammonium cations. Comparing the bond
lengths and angles of the ligand precursor 1a with complex 4a
revealed only minor structural changes. For instances the C@O
bond length is only slightly elongated e.g., 1.229(2) for 1a and
Afterwards the nickel hydroxido complexes 4 were converted to
nickel chlorido complexes 5 (Scheme 3). In more detail, complexes
were dissolved in dichloromethane and stirred for 4 days at room
4
temperature. The complexes 5 were isolated in 68–83% yield. Crys-
tals suitable for single-crystal X-ray diffraction measurements
were grown from dichloromethane. The solid-state structures of
complexes 5a and 5b have been characterized by single-crystal
X-ray diffraction analysis. The thermal ellipsoid plots, selected
bond lengths and angles are shown in Figs. 7 and 8. In more detail,
a similar square planar coordination geometry for complexes 5
with similar bond lengths and angles as found for complexes 4
was observed (Table 3).
1
1
.239(3)–1.240(3) for 4a and the C3–C1–N2 angle is reduced, e.g.,
14.69(12) for 1a and 109.97(19)–110.30(18) for 4a. In contrast
2
to complexes 4a and 4c for the reaction of 1d with Ni(OTf) and tet-
raethylammonium hydroxide as product an octahedral nickel com-
plex was observed by single-crystal X-ray diffraction meas
urements (see Supporting information). In more detail, two ligands
0
00
(
1d-2H) are coordinated to the metal center in a N,N ,N -coordina-
tion mode.
1
The diamagnetic complexes 4a–c were investigated by H NMR
spectroscopy, showing signals in the range of ꢀ4.90 to ꢀ5.23 ppm,
which could be assigned to the hydroxido ligand (–OH). Moreover,
the absence of any signals for the NH function proves the deproto-
nation of 1 and the tridentate coordination mode. In case of C{ H}
NMR measurements a shift of the signal for the C1 to lower field
was noticed. The effect of coordination on the C@O function was
also observed by IR measurements, e.g., the signals were shifted
After having synthesized a set of nickel(II) complexes attempts
were undertaken to convert the nickel(II) hydroxido complexes to
nickel(II) hydrido complexes (Scheme 4). In more detail, the nick-
el(II) hydroxido complex 4b was reacted with diphenylsilane at
low temperature (ꢀ70 °C) in THF-d8 [11]. Interestingly, along to
1
3
1
the signal for the hydroxido complex (–OH) a new signal at
1
ꢀ
22.5 ppm was observed by H NMR measurements, which can
be assigned in accordance to earlier reports as a nickel hydrido
complex [11]. After one hour at room temperature the hydroxido
ꢀ1
by 56–84 cm
.

F. Czerny et al. / Inorganica Chimica Acta 425 (2015) 118–123
121
Et NOH (1M in MeOH)
4
Et N
4
O
R
O
R
O
R
O
R
+
Ni(OTf)
2
N
Ni
OH
N
THF, r.t., 12 h
NH
HN
N
N
1a-d
4a-c
R =
[
(1d-2H) Ni][NEt ]
2
4 2
4
a: 81% yield
4b: 93% yield
4c: 94% yield
4d: 52% yield
Scheme 2. Synthesis of complexes 4.
Et N
Et N
4
O
O
4
O
R
O
R
N
Ni
OH
N
Ni
Cl
CH Cl , r.t., 4 d
N
N
2
2
N
N
R
R
4a-4c
5a-5c
R =
5a: 83% yield
5b: 69% yield
5c: 68% yield
Scheme 3. Synthesis of complexes 5.
Fig. 7. Molecular structure of complex 5a-H
0% probability level. Hydrogen atoms and a water molecule are omitted for clarify.
Selected bond lengths (Å) and angle (°): C1–O1: 1.243(3), C4–O2: 1.244(3), N2–C1:
.341(3), N2–C2: 1.434(3), N3–C4: 1.341(3), N3–C6: 1.430(3), Ni1–Cl1: 2.1839(10),
Ni1–N1: 1.826(2), Ni1–N2: 1.912(2), Ni1–N3: 1.911(2), C3–C1–N2: 110.1(2), C5–
C4–N3: 110.4(2), N1–Ni1–Cl1: 175.97(7), Cl1–Ni1–N3: 97.17(7), N1–Ni1–N3:
2
O. Thermal ellipsoids are drawn at the
5
Fig. 8. Molecular structure of complex 5b. Thermal ellipsoids are drawn at the 50%
probability level. Hydrogen atoms are omitted for clarify. Selected bond lengths (Å)
and angle (°): C1–O1: 1.258(7), C4–O2: 1.226(7), N2–C1: 1.339(8), N2–C2: 1.418(8),
N3–C4: 1.342(8), N3–C6: 1.425(6), Ni1–Cl1: 2.1850(16), Ni1–N1: 1.837(5), Ni1–N2:
1.912(5), Ni1–N3: 1.911(4), C3–C1–N2: 111.1(5), C5–C4–N3: 110.2(5), Cl1–Ni1–
N1: 177.41(16), Cl1–Ni1–N3: 97.07(14), N1–Ni1–N3: 82.4(2), Cl1–Ni1–N2:
1
8
2.77(9), Cl1–Ni1–N2: 97.59(7), N1–Ni1–N2: 82.44(9), N3–Ni1–N2: 165.21(10).
97.97(16), N1–Ni1–N2: 82.6(2), N3–Ni1–N2: 165.0(2).
complex was completely converted to the nickel(II) hydrido com-
plex. Attempts to isolate complex 6b failed so far. In contrast to
that complex 4a was not converted to the corresponding hydrido
complex 6a. Even after heating to 50 °C 6a was not detected. In
case of complex 4c the hydrido complex 6c was observed in lower
yield compared to 6b and two sets of signals were monitored. On
the other hand, the reaction of the chlorido complexes 5 with
diphenylsilane did not lead to the formation of the desired hydrido
complexes 6. However, changing the hydride source to lithium
borohydride allows access to 6 in low yields. Interestingly, the for-
mation of hydrido complexes especially with silanes can be useful
for hydrosilylation catalysis.
Based on that, the catalytic abilities of complex 4b were studied
in the hydrosilylation of ketones (Table 4). In more detail, 2.5 mol%
of 4b were reacted with diphenylsilane and the corresponding

1
22
F. Czerny et al. / Inorganica Chimica Acta 425 (2015) 118–123
Table 3
Table 4
Analytical properties of complexes 5.
Hydrosilylation of ketones.
5
a
5b
5c
Entry
1
Substrate
Yield (%) (4b)
Yield (%) (5b)a
Ni1–N1 (Å)
Ni1–N2 (Å)
Ni1–N3 (Å)
Ni1–Cl1 (Å)
N1–Ni1–N2 (°)
N1–Ni1–Cl1 (°)
C3(5)–C1(4)–N2(3) (°)
1.826(2)
1.912(2)
1.911(2)
2.1839(10)
82.44(9)
175.97(7)
110.1(2)
1.837(5)
1.912(5)
1.911(4)
2.1850(16)
82.6(2)
177.41(16)
111.1(5)
110.2(5)
168.6
–
–
–
–
–
–
–
O
>99
>99
2
3
4
5
O
>99
<1
>99
<1
1
10.4(2)
13
1
a
C{ H} NMR (ppm)
169.5
2.3
4.6
1616
5
50
169.7
2.2
7.0
1632
30
67
b
O
D
D
m
(C1) (ppm)
ꢀ0.1
c
(C1) (ppm)
7.0
(C@O) (cm )d
ꢀ
1
1615
3
65
ꢀ
1 e
m
D
(C@O) (cm
)
(C@O) (cm ) f
ꢀ1
OMe O
10
<1
a
b
c
d
e
f
In CD
2
Cl at r.t.
2
D
D
In KBr.
(C1) = d (C@O-5) ꢀ d (C@O-4).
(C1) = d (C@O-5) ꢀ d (C@O-1).
O
>99
>99
D
D
(C@O) =
(C@O) =
m
m
(C@O-5) ꢀ
(C@O-1) ꢀ
m
m
(C@O-4).
(C@O-4).
F3C
ketone at 70 °C for 24 h in THF. Excellent performance was
observed for different p-substituted acetophenones, while o-sub-
stitution revealed the formation of the products in low yields,
probably due to sterical hindrance. Moreover, no activity was
observed in case of dialkyl ketones. On the other hand, similar
results were observed for complex 5b, which was pre-treated with
LiBH4.
(a)
Et N
Ph SiH2
Et N
4
O
R
O
R
4
2
O
R
O
R
N
Ni
OH
N
Ni
H
THF-d8, -70 °C-r.t.
N
N
N
N
4
a-4c
6a-6c
R =
4
a: <1% conv.
4b: >99% conv. (r.t. 1 h)
4
c: 43% conv. (r.t. 1 h)
(
r.t. 1 h, 50 °C 1 h)
1
6b: H NMR δ = -22.5 ppm
1
6c: H NMR δ = -23.0 ppm,
-23.2 ppm (ratio: 0.25:1)
(b)
LiBH
4
Et N
Et N
4
O
R
O
4
O
O
R
N
Ni
Cl
N
Ni
H
THF-d8, -70 °C-r.t.
N
N
N
N
R
R
5
a-5c
6a-6c
R =
5
a: <1% conv.
5b: 33% conv. (r.t. 1 h)
b: H NMR δ = -23.0 ppm
5
c: 27% conv. (r.t. 1 h)
(
r.t. 1 h, 50 °C 1 h)
1
6
1
6c: H NMR δ = -22.8 ppm
Scheme 4. Synthesis of hydrido complexes 6.

F. Czerny et al. / Inorganica Chimica Acta 425 (2015) 118–123
123
[
4] A selection: (a) R.D. Hancock, A.E. Martell, Chem. Rev. 89 (1989) 1875–1914;
b) A.L. Gavrilova, B. Bosnich, Chem. Rev. 104 (2004) 349–383;
(c) M. Miura, Angew. Chem. 116 (2004) 2251–2253;
Table 4 (continued)
(
Entry
6
Substrate
Yield (%) (4b)
Yield (%) (5b)a
(d) Angew. Chem., Int. Ed., 2004, 43, 2201–2203;
(e) P.J. Steel, Acc. Chem. Res. 38 (2005) 243–250;
(f) A.S. Borovik, Acc. Chem. Res. 38 (2005) 54–61.
O
>99
>99
[
5] K.J. Szabó, O.F. Wendt (Eds.), Pincer Ligands, in Pincer and Pincer-Type
Complexes: Applications in Organic Synthesis and Catalysis, Wiley-VCH Verlag
GmbH & Co. KGaA, Weinheim, 2014.
Me N
2
7
O
<1
<1
[6] (a) O. Troeppner, D. Huang, R.H. Holm, I. Ivanovic-Burmazovic, Dalton Trans. 43
(
(
(
(
(
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Reaction conditions: 2.5 mol% complex 4b or 5b, Ph
ketone (0.5 mmol), THF (2.0 mL), 70 °C, 24 h. Yield determined by H NMR and GC–
MS.
2
SiH
2
(0.75 mmol, 1.5 equiv.),
1
Holm, Inorg. Chem. 50 (2011) 10070;
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(
a
5
b was pre-treated with LiBH4.
(
(
(
(
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3
. Conclusion
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(
(
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63–364 (2012) 322.
00
do complexes 4a–c, which are easily derived from N,N -substituted
pyridine-2,6-dicarboxamides 1a–d, nickel(II) trifluoromethanesul-
fonate and tetraethylammonium hydroxide. In more detail, a
(
(
[
[
0
00
pincer-type tridentate N,N ,N -coordination mode of the ligands
1-2H) was observed after double deprotonation. The other coordi-
5
(
3
nation site on the square planar nickel centre is occupied by a
hydroxido ligand. The reactivity of these complexes was examined
in dehalogenation reactions to allow access to square planar nickel
chlorido complexes 5a–c. Moreover, by NMR studies it was found
that nickel hydroxido complexes as well as chlorido complexes
can be converted with diphenylsilane or lithium borohydride to
nickel hydrido complexes, which can be seen as a possible catalytic
intermediate in reduction chemistry. Indeed, complexes 4 and 5
showed activity in the hydrosilylation of ketones to produce
alcohols after work-up.
8] See the most recent works and references therein: (a) S.N. MacMillan, H.W.
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(
(
(d) T.M. Porter, G.B. Hall, T.L. Groy, R.J. Trovitch, Dalton Trans. 42 (2013)
14689–14692;
(
(
(
c) L. Gonzalez-Sebastian, M. Flores-Alamo, J.J. Garcia, Organometallics 32
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2864;
g) M.L. Lage, S.J. Bader, K. Sa-ei, J. Montgomery, Tetrahedron 69 (2013) 5609–
613;
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(b) C.I. Someya, E. Irran, S. Enthaler, Asian J. Org. Chem. 2 (2013) 322;
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114–118;
(
5
(
2
Acknowledgements
(
Financial support from the Cluster of Excellence ‘‘Unifying Con-
cepts in Catalysis’’ (funded by the Deutsche Forschungsgemeins-
chaft and administered by the Technische Universität Berlin) is
gratefully acknowledged.
[
(
(
(
Appendix A. Supplementary material
(
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.ica.2014.10.003.
(
(
(
g) C.I. Someya, M. Weidauer, S. Enthaler, Catal. Lett. 143 (2013) 424;
h) S. Enthaler, M. Weidauer, E. Irran, J.D. Epping, R. Kretschmer, C.I. Someya, J.
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