Dinickel complexes with anthyridine-based ligands

Article abstract of DOI:10.1039/c6dt00567e

Two new dinickel complexes with anthyridine-based ligands, 5-phenyl-2,8-bis(2-pyridinyl)-1,9,10-anthyridine (L₂) and 5-phenyl-2,8-bis(6′-bipyridinyl)-1,9,10-anthyridine (L₃), are reported. Complexation of Ni(OAc)₂ with L₂ and L₃ in trifluoroacetic acid provided the corresponding dinickel complexes [{Ni₂(L₂)(H₂O)₆(CF₃COO)₂}(CF₃COO)₂] (2) and [Ni₂(L₃)(CF₃COO)₄(H₂O)] (3), respectively. Both complexes were characterized by spectroscopic methods and further confirmed by X-ray crystallography. Structural analyses of 2 and 3 revealed the Ni?Ni distances in the complexes to be 5.4086(6) and 5.0138(7) ?, respectively. The catalytic activities of complexes 2 and 3 toward the reduction of carboxylic acids were evaluated. It appears that complex 3 shows a good catalytic activity toward the reduction of carboxylates into the corresponding alcohols by diphenylsilane.

Full text of DOI:10.1039/c6dt00567e

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Dinickel complexes with anthyridine-based
ligands†
Cite this: DOI: 10.1039/c6dt00567e
Da-Wei Huang, Yi-Hung Liu, Shie-Ming Peng and Shiuh-Tzung Liu*
Two new dinickel complexes with anthyridine-based ligands, 5-phenyl-2,8-bis(2-pyridinyl)-1,9,10-
anthyridine (L
of Ni(OAc) with L
{Ni (L )(H O) (CF COO)
2
) and 5-phenyl-2,8-bis(6’-bipyridinyl)-1,9,10-anthyridine (L
and L in trifluoroacetic acid provided the corresponding dinickel complexes
}(CF COO) ] (2) and [Ni (L )(CF COO) (H O)] (3), respectively. Both complexes
3
), are reported. Complexation
2
2
3
[
2
2
2
6
3
2
3
2
2
3
3
4
2
were characterized by spectroscopic methods and further confirmed by X-ray crystallography. Structural
analyses of 2 and 3 revealed the Ni⋯Ni distances in the complexes to be 5.4086(6) and 5.0138(7) Å,
respectively. The catalytic activities of complexes 2 and 3 toward the reduction of carboxylic acids were
evaluated. It appears that complex 3 shows a good catalytic activity toward the reduction of carboxylates
into the corresponding alcohols by diphenylsilane.
Received 10th February 2016,
Accepted 5th April 2016
DOI: 10.1039/c6dt00567e
www.rsc.org/dalton
Introduction
The use of bimetallic complexes as catalysts in homogeneous
catalysis has received much attention in recent years. A
number of investigations have shown that the bimetallic cata-
lyst is significantly more active than the related monometallic
ones. It is believed that the “cooperative” interaction of the
1
two metal ions might play a key role in increasing the activity.
Among various dinuclear systems, chemists are interested in
dinickel complexes, especially as model compounds for dinuc-
2
lear metallo-enzymes, as catalysts for cross coupling and oxi-
Scheme 1
3
,4
5
dation,
as pre-catalysts for olefin polymerization, and to
understand and control the reactivity of dinuclear metal
6
species.
In our earlier investigations, the distance between Ni⋯Ni
ligands L and L (Scheme 1), in which the metal ions are sep-
2
3
7
(
3.240 Å) in dinickel complexes [(L )(μ-Cl) Ni Cl (CH OH) ] (1)
1
2
2
2
3
2
arated by ca. 5 Å. The resulting complexes were characterized
by both spectroscopic and X-ray crystallographic methods. The
catalytic activities of these complexes toward the reduction of
carboxylic acids were investigated.
is shorter than that in urease, showing no catalytic activity
toward hydrolysis of urea or amides. However, complex 1
appears to be an excellent catalyst for the homo-coupling of
4
b
2
terminal alkynes with the use of O as the oxidant. In an
effort to better understand the inter-metal distances attributed
to the cooperative effect, we report the preparation and charac-
terization of dinickel complexes containing anthyridine-based
Results and discussion
Preparation and characterization of dinickel complexes
The multiple dentates L
2
and L
our earlier work. Heating up a mixture of Ni(OAc)
mixed solvent of methanol and CF COOH gave [{Ni (L )-
3
were prepared according to
7
Department of Chemistry, National Taiwan University, Taipei 106, Taiwan.
E-mail: stliu@ntu.edu.tw
and L in a
2
2
3
2
2
†
Electronic supplementary information (ESI) available: Spectra of complexes 2
(
H
2
O)
ligand (eqn (1)), whereas a reaction of L
similar conditions yielded neutral complex [Ni (L )-
6
(CF
3
COO)
2
}(CF
3
COO)
2
] (2) in 91% yield based on the
and 3; X-ray crystallographic data, structure refinement details, and CIF files for
compounds 2 and 3. CCDC 1450223 and 1450222. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c6dt00567e
3
with Ni(OAc) under
2
a
2
3
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(
3 3 3 2
μ-CF COO)(CF COO) (H O)] (3) in 88% yield (eqn (2)). These Table 1 Selected bond distances (Å) and bond angles (°) for 2
complexes were characterized by both X-ray structural determi-
nation and spectroscopic methods.
Ni(1)–N(1)
Ni(1)–N(2)
Ni(1)–O(1)
Ni(1)–O(3)
Ni(1)–O(4)
Ni(1)–O(5)
2.063(3)
2.137(3)
2.050(3)
2.037(3)
2.043(3)
2.092(3)
Ni(2)–N(4)
Ni(2)–N(5)
Ni(2)–O(6)
Ni(2)–O(8)
Ni(2)–O(9)
Ni(2)–O(10)
2.129(3)
2.058(3)
2.056(3)
2.089(3)
2.020(3)
2.054(3)
N(1)–Ni(1)–N(2)
N(2)–Ni(1)–O(1)
N(1)–Ni(1)–O(4)
O(3)–Ni(1)–O(5)
N(1)–Ni(1)–O(5)
N(2)–Ni(1)–O(5)
77.73(12)
167.56(12)
176.92(13)
174.80(13)
88.25(12)
86.29(12)
N(4)–Ni(2)–N(5)
N(4)–Ni(2)–O(6)
N(5)–Ni(2)–O(9)
O(8)–Ni(2)–O(10)
N(4)–Ni(2)–O(10)
N(5)–Ni(2)–O(10)
78.49(13)
168.18(12)
177.00(12)
175.51(13)
91.87(12)
94.30(13)
ð1Þ
ð2Þ
typical of the bipyridine complexes. It is noticed that two
nickel ions are not seated in the plane defined by the ligand
presumably due to the steric congestion. No significant discre-
pancies in other bond lengths and angles were noticed in
complex 2.
Complex 3 was obtained as a light green crystalline solid.
The molecular structure of complex 3 is shown in Fig. 2 and
the important structural parameters are summarized in
Table 2. The complex has a dinuclear core bridged by a tri-
Light yellow crystals of 2 were grown by vaporization of a
mixed solvent system of acetone and methanol at room temp-
erature. The ORTEP plot of the cationic part of 2 is shown in
Fig. 1 and selected bond distances and bond angles are col-
lected in Table 1. The two nickel(II) centers are embedded in a
distorted octahedral environment in which the coordination
geometry of each metal is completed by the “bipyridine”
moiety, three water molecules and a trifluoroacetate with all
water molecules cis to each other. Two nickel centers are separ-
ated by 5.4086(6) Å. The central nitrogen donor N(3) of anthyri-
dine remains as a free donor site, but this donor shows
hydrogen-bonding interactions with the coordinating water
molecules. The distances of N(3)–O(4) and N(3)–O(9) are 3.096
(4) and 3.058(4) Å, respectively, within the hydrogen bonding
interaction range. The bite angles of N(1)–Ni(1)–N(2) and N(4)–
Ni(2)–N(5) are 77.7(1)° and 78.5(1)°, respectively, which are
Fig. 2 ORTEP plot of the cationic portion of 3 (30% probability level).
Table 2 Selected bond distances (Å) and bond angles (°) for 3
Ni(1)–N(1)
Ni(1)–N(2)
2.097(3)
2.005(3)
Ni(2)–N(5)
Ni(2)–N(6)
2.139(3)
2.002(3)
Ni(1)–N(3)
Ni(1)–O(1)
2.157(3)
2.091(3)
Ni(2)–N(7)
Ni(2)–O(2)
2.114(3)
2.072(3)
Ni(1)–O(3)
Ni(1)–O(5)
2.084(3)
2.047(3)
Ni(2)–O(7)
Ni(2)–O(9)
2.120(3)
2.024(3)
N(1)–Ni(1)–N(2)
N(1)–Ni(1)–N(3)
N(2)–Ni(1)–O(1)
78.08(12)
154.70(12)
172.00(12)
87.72(12)
173.22(10)
N(5)–Ni(2)–N(6)
N(5)–Ni(2)–N(7)
N(6)–Ni(2)–O(2)
N(6)–Ni(2)–O(9)
O(2)–Ni(2)–O(7)
77.10(13)
154.92(13)
95.73(13)
168.61(13)
178.85(11)
Fig. 1 ORTEP plot of the cationic portion of 2 at the 30% probability N(2)–Ni(1)–O(3)
level. Labels of aromatic carbons are omitted for clarity.
O(3)–Ni(1)–O(5)
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2
fluoroacetate group in the μ -1,3-bridging mode, providing a
Ni (L )(μ-CF COO)(CF COO) (H O)] core with a Ni(1)⋯Ni(2)
[
2
3
3
3
3
2
separation of 5.0138(7) Å. The coordination about the Ni(II)
atoms is described as a distorted octahedral geometry. The
coordinating ligands around the two nickel centers are slightly
different. The Ni(1) center is completed by three nitrogen
donors [N(1), N(2) and N(3)] of the “terpyridine” moiety, two
oxygen atoms [O(3) and O(5)] from terminal trifluoroacetates
and one oxygen atom O(1) of the bridging trifluoroacetate,
with two terminal trifluoroacetates occupying apical positions,
while the coordination environment of the Ni(2) center is
different from that of Ni(1). Besides the tridentate of “terpyri-
dine”, a terminal trifluoroacetate, the bridging trifluoroacetate
and a water molecule are surrounded at N(2) by two trifluoro-
acetate oxygen donors [O(2) and O(7)] trans to each other. It is Fig. 3 Plots of χM (□) and μeff (•) vs. T for 3. The solid line corresponds
noticed that the coordination modes of the bridging trifluoro- to the theoretical fit.
acetate toward Ni(1) and Ni(2) are different: O(1) is seated at the
equatorial plane constituted by the ligand in a mer-configur-
ation with Ni(1), whereas O(2) is seated at an apical position
lected on amorphous solids of 3 and the plots of χM and μeff
versus temperature of 3 are presented in Fig. 3. The magnetic
around Ni(2). The average Ni–N distances around Ni(1) and Ni
(2) are 2.086 and 2.085 Å, respectively (Table 2), which
moment is almost constant (3.89μ
decreases below 25 K, reaching 3.61μ
B
) at high temperatures and
at 4 K (for 2, μeff = 3.60
compare well with those observed in the related Ni(II) terpyri-
8
B
dine complexes. The bond lengths of Ni–O are in the range of
at room temperature, 3.07 at 4 K). The experimental magnetic
data have been fitted using eqn (3) with the spin Hamiltonian
2
.024(3)–2.120(3) Å, as expected. The chelation angles of N(1)–
Ni(1)–N(2), N(2)–Ni(1)–N(3), N(5)–Ni(2)–N(6) and N(6)–Ni(2)–
N(7) in the dinickel core are much deviated from 90°, which is
observed in the related terpyridine metal complex due to the
ligand constraint. Although the N(3) donor of anthyridine
remains uncoordinated, it participates in intramolecular
hydrogen bonding with the hydroxylic H atoms on O(9). The
distance between N(3)⋯O(9) is 3.201(4) Å, within the range for
hydrogen-bonding interaction.
1
0
–
JS S (S = S2 = 1). The fitted values are g = 2.14, J =
1 2 1
1
−1
−
0.76 cm− in 3, and g = 1.97, J = −0.59 cm in 2. Both com-
plexes are paramagnetic with a weakly antiferromagnetic coup-
ling between the adjacent metal ions due to the long
separation (>5 Å).
À
Á
Ng2β2 e J=kT þ 5e
3J=kT
2
χ ¼
ð3Þ
J=kT
3J=kT
kTð1 þ 3e
þ 5e
Þ
Electronic absorption spectra for the complexes and free
ligands were recorded in acetonitrile (Table 3). In comparison
with the free ligands, the absorption bands of complexes were
Catalysis–reduction of carboxylic acids
red-shifted, indicating coordination effects. Complexes 2 and 3 The reduction of carboxylic acids to yield the corresponding
show intense ligand to metal charge transfer (LMCT) bands alcohols is a straightforward and useful method to produce
with λmax at 407 and 413 nm, respectively. Each complex exhi- the desired precursors in organic synthesis. Among various
bits a weak absorption at ca. 650 nm, which is assignable to a strategies, the metal-catalyzed hydrosilylation of carboxylate
9
d–d transition arising from the octahedral nickel center.
moieties for this reduction ought to be a safe and operationally
The magnetic properties of both complexes 2 and 3 were simple method. However, only a limited number of homo-
investigated and their properties are quite similar. Variable- geneously catalytic systems have been applied for the hydro-
1
1
12
temperature (4–300 K) magnetic susceptibility data were col- silylation of carboxylates including ruthenium,
boron,
1
3
14
15
indium, iron and main group Lewis acid compounds.
There is no documentation on the use of a nickel complex as
the catalyst for such a reduction. Thus, the activity of com-
plexes 2 and 3 toward the hydrosilylation of carboxylic acids
was investigated. In particular, we hope that dimetallic
systems may assist the reduction through a synergic effect.
Thus, searching for the optimal conditions for the reduction
of benzoic acid leading to benzyl alcohol catalysed by complex
3 was initially examined (Table 4).
A series of screen tests with various reducing agents
suggested that carrying out the reaction by using diphenyl-
silane under refluxing conditions in THF provided the desired
product in 31% yield (Table 4, entry 5). By using varying sol-
a
Table 3 UV-vis absorption data for ligands L
2 3
–L and complexes 2–3
Compound max in nm (ε)
λ
4
4
4
L
L
2
3
2
248 (2.95 × 10 ), 289 (3.29 × 10 ), 377 (1.76 × 10 ),
4
3
94 (2.02 × 10 )
4
4
4
3
204 (2.35 × 10 ), 266 (3.36 × 10 ), 383 (1.92 × 10 ),
4
4
02 (2.33 × 10 )
4
4
4
252 (1.76 × 10 ), 292 (1.53 × 10 ), 407 (1.68 × 10 ),
2
6
53 (1.3 × 10 )
4
4
4
241 (5.34 × 10 ), 279 (4.42 × 10 ), 396 (2.41 × 10 ),
4
2
4
13 (2.66 × 10 ), 650 (1.60 × 10 )
a
In acetonitrile.
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Table 4 Reduction of PhCOOH under various conditions catalysed by
3
In order to demonstrate the unique activity of 3 in the cata-
lysis, the ability of various nickel complexes for this catalytic
reduction was evaluated and the observations are summarized
in Table 6. Quite obviously, complex 3 proved to have the best
activity toward this oxidation. Other nickel complexes were
tested as catalyst precursors and exhibited some activity, but
not as good as complex 3, including the dinickel complexes
a
b
Entry
Reductant
Solvent
Temp.
Yield
1
2
3
4
5
6
7
8
9
H
H
2
(200 psi)
(200 psi)/Zn (0.4 mmol)
THF
THF
THF
THF
THF
THF
THF
MeOH
1,4-Dioxane
DMF
65 °C
65 °C
65 °C
65 °C
65 °C
65 °C
65 °C
65 °C
100 °C
100 °C
110 °C
0
0
2
NaBH
HCOONa (0.8 mmol)/Zn
Ph
Ph
4
(0.8 mmol)
Trace
0
2
SiH
MeSiH (0.8 mmol)
SiH (0.8 mmol)
2
(0.8 mmol)
31%
<10%
12%
Trace
45%
Trace
<10%
associated with ligand L or dpnp (Table 6, entries 8 and 9).
1
2
To our surprise, the catalytic activity of 2 is not as good as that
of 3, presumably due to the slightly longer separation of
Ni⋯Ni ions in 2.
PhMe
2
Ph
Ph
Ph
Ph
2
2
2
2
SiH
SiH
SiH
SiH
2
2
2
2
(0.8 mmol)
(0.8 mmol)
(0.8 mmol)
(0.8 mmol)
1
1
0
1
A comparison of the reaction rates catalyzed by 3, 2 and
other Ni complexes was made and the yields of benzyl alcohol
versus reaction time are summarized in Fig. 4. It appears that
there is an induction period for this catalysis. Based on the
pseudo-first order approximation, the values of kobs for the
pre-catalyst 3, 2, Ni(CF COO) /Terpy, Ni(CF COO) /Bipy and Ni
Toluene
a
Reaction conditions: benzoic acid (0.2 mmol) and complex
3
−
2
b
(1 × 10 mmol) in solvent (0.5 mL) for 16 h. Isolated yields.
3
2
3
2
−
5
−6
(
1
3 2
CF COO) were estimated to be 4.02 × 10 , 8.68 × 10 , 7.77 ×
vents, it was found that the yield of PhCH OH increased up to
2
0
, 5.58 × 10−6 and 1.43 × 10 (s ), respectively. The cata-
−6
−6 −1
4
5% with the use of dioxane as the solvent (Table 4, entry 9).
lytic activity of complex 3 is about 5 times faster than that of
complex 2, and is much better than those of other Ni(II) com-
plexes. Both complexes 2 and 3 are well defined bimetallic
Apparently, these results were not good enough for the syn-
thetic applications. Further modification of the reaction con-
ditions by the addition of bases or auxiliary ligands was
investigated. Table 5 summarizes the results. The addition of
bases into the reactions did not increase the production of the
desired compound (Table 5, entries 3–5). To our delight, carry-
ing out the reduction in the presence of phosphine provided
better results (Table 5, entries 6–8). Particularly, the addition
of 5 mol% of tributylphosphine did assist the reduction
smoothly to render benzoic acid in 82% yield (Table 5, entry
a
Table 6 Catalytic activity of various nickel complexes
b
Entry
Nickel complex
Yield
1
2
3
4
5
6
7
8
9
3 (0.01 mmol, 5 mol%)
2 (0.01 mmol, 5 mol%)
82%
43%
Trace
27%
19%
Trace
14%
29%
40%
Ni(CF
Terpy/Ni(CF
Bipy/Ni(CF COO)
NiCl (0.02 mmol, 10 mol%)
Ni(OAc) (0.02 mmol, 10 mol%)
dpnp /Ni(CF COO) (0.01/0.02 mmol, 10 mol%)
/Ni(CF COO) (0.01/0.02 mmol, 10 mol%)
3
COO)
2
(0.02 mmol, 10 mol%)
COO) (0.02/0.02 mmol, 10 mol%)
(0.02/0.02 mmol, 10 mol%)
7
). It is noticed that the use of bidentate or bulky phosphine
3
2
ligands provided poor results. Under these optimal conditions,
the amount of silane used for the reduction was studied
3
2
2
2
(Table 5, entries 13 and 14). It shows that carrying out the reac-
c
3
2
tion with the use of 4 equimolar amounts of Ph
best choice.
2
SiH
2
is the
L
1
3
2
a
Reaction conditions: benzoic acid (0.2 mmol), Ph SiH
2
2
(0.8 mmol),
P(n-Bu) (0.02 mmol) and Ni(II) complex in dioxane (0.5 mL) at 100 °C
3
b
for 16 h. NMR yields based on the internal standard of mesitylene.
c
dpnp = 2,7-dipyridinyl-1,8-naphthyridine.
a
Table 5 Reduction of PhCOOH catalysed by 3 with various additives
b
Entry
Additives
Yield
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
—
n-Bu
45%
48%
21%
16%
52%
63%
82%
84%
69%
38%
23%
70%
61%
27%
—
4
NBr (0.2 mmol)
(0.2 mmol)
Na CO
Pyridine (0.2 mmol)
DBU (0.2 mmol)
2
3
3
PPh (0.02 mmol)
P(n-Bu)
P(n-Bu)
P(n-Bu)
3
3
3
(0.02 mmol)
(0.04 mmol)
(0.01 mmol)
0
1
2
3
4
5
PCy
Ethylenediamine (0.2 mmol)
Ph PCH CH PPh (0.02 mmol)
P(n-Bu)
P(n-Bu)
P(n-Bu)
3
(0.02 mmol)
2
2
2
2
c
3
3
3
(0.04 mmol)
(0.04 mmol)
(0.04 mmol)
d
e
a
Reaction conditions: benzoic acid (0.2 mmol), complex 3 (5 mol%,
−
2
1
× 10 mmol) and Ph SiH (0.8 mmol) in dioxane (0.5 mL) at 100 °C
2 2
b c d
for 16 h. NMR yields. Ph
2
SiH
2
(0.6 mmol). Ph
2
SiH
2
(0.4 mmol). Fig. 4 Product yields along the reaction time catalysed by nickel
e
No complex 3 in the reaction.
complexes.
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a
Table 7 Reduction carboxylate derivatives catalyzed by 3
Experimental
General information
b
Entry
Substrate
Product
Yield
All the reactions, manipulations and purification steps were
performed under a dry nitrogen atmosphere. Chemicals and
solvents were of analytical grade and were used after a degas-
1
2
3
4
5
6
7
8
9
C
6
H
5
COOH
COOH
COOH
COOH
COOH
C)C COOH
COOMe
p-(OHC)C
C
C
6
H
5
CH
2
OH
OH
CH
CH OH
CH OH
C)C CH
CH OH
p-(HOCH )C
OH
82%
35%
85%
77%
72%
43%
36%
75%
89%
—
C
6
F
5
F
6 5
CH
2
p-MeC
p-ClC
p-(CN)C
p-(MeO
6
H
4
p-MeC
p-ClC
p-(CN)C
p-(MeO
6
H
4
2
OH
6
H
6
4
H
H
6 4
2
sing process. Ligands L
the method reported previously. Nuclear magnetic resonance
spectra were recorded in CDCl on a Bruker AVANCE 400
spectrometer. Chemical shifts are given in parts per million
2 3
and L were prepared according to
4
6
H
4
2
7
2
6
H
4
2
6
H
4
2
OH
C
6
H
5
C
H
6 5
2
3
6
H
4
COOH
2
6 4 2
H CH
OH
C
6
H
5
CHO
C
—
—
C
C
CH
CH
—
H
6 5
CH
2
1
13
10
11
12
13
14
15
16
o-C
6
H
4
(COOH)
2
relative to Me Si for H and C NMR. Molar magnetic suscepti-
4
2-Pyridinecarboxylic acid
—
bility was recorded using a SQUID system with a 2000 G exter-
nal magnetic field.
C
C
6
H
H
5
CHvCHCOOH
CH COOH
6
H
H
5
CHvCHCH
CH CH OH
2
OH
80%
77%
74%
66%
—
6
5
2
6
5
2
2
CH
CH
C H CONH
6 5 2
3
(CH
(CH
2
)
6
COOH
COOH
3
(CH
(CH
2
)
6
CH
CH
2
OH
OH
3
)
2 4
3
2
)
4
2
Preparation of complex 2
A mixture of L
64.7 mg, 0.26 mmol) in a round bottom flask was flashed
with nitrogen for 10 min. A mixture of methanol and
CF COOH (1 : 1, 3 mL) was added. The mixture was heated to
2 2 2
(50 mg, 0.12 mmol) and Ni(OAc) ·4H O
a
Reaction conditions: substrate (0.2 mmol), Ph
2 2
SiH (0.8 mmol),
−2
(
P(n-Bu)
dioxane (0.5 mL) at 100 °C for 16 h. Isolated yields.
3
(0.02 mmol) and complex 3 (5 mol%, 1 × 10 mmol) in
b
3
reflux under nitrogen for 24 h. After the reaction, solvents were
removed under reduced pressure. The residue was dissolved in
systems, but the catalytic activity of 3 is superior to that of 2, methanol and the solution was filtered through Celite. Ether
indicating the important role of ligand L in the reaction.
was slowly added to the filtrate and the desired complex
We next explored the reduction of various carboxylic acids was crystallized from the solution as a light-yellow crystalline
under the optimal conditions (Table 7). Both substituted solid (120 mg, 91%). ESI-HRMS m/z calcd for C33 Ni
benzoic acids and aliphatic carboxylic acids smoothly partici- [M − (CF COO) − (H O) ]: 865.9742; found: 865.9744. IR (KBr)
1679 (CvO), 1445, 1137 cm
Ni 14: C, 38.60; H, 2.68; N, 6.43. Found: C, 38.74;
3
H
17
F
9
N
5
2 6
O
3
2
6
−1
pated in the reduction to afford the corresponding alcohols in
ν
=
. Anal. Calcd for
moderate to good yields except for some functionality present
C
35
H
29
F
12
N
5
2
O
in the molecule. Reduction of benzoic acids was amenable H, 2.81; N, 6.25.
with functional groups such as alkyl (entry 3), halo (entry 4)
Preparation of complex 3
and cyano (entry 5) delivering the corresponding benzyl alco-
hols in 62%–85% yields. However, both ester and aldehyde The procedure is quite similar to that used for the preparation
functionalities were reduced simultaneously (entries 6–8). It is of 2, except for the quantity: L (50 mg, 0.09 mmol) and
noticed that the reduction rate of an ester is slower than that Ni(OAc) ·4H O (47.3 mg, 0.19 mmol). The desired complex
of a carboxylic acid. Thus, we were able to obtain 43% isolated was obtained as a green crystalline solid (93.7 mg, 88%):
yield for the reduction of p-(MeO C)C
COOH. Reduction of ESI-HRMS m/z calcd for C41 Ni [M − (CF COO)
cinnamic acid and aliphatic carboxylic acids gave cinnamyl (OH) + (H O) ]: 990.0873; found: 990.0820. IR (KBr) ν = 1676
alcohol and alkanols in good yields (entries 12–15). However, (CvO), 1451, 1140 cm . Anal. Calcd for C45H F N Ni O :
25 12 7 2 9
3
2
2
2
6
H
4
H
32
F
6
N
7
2
O
9
3
2
+
2
3
−1
the amide functionality remains intact under the catalytic C, 46.87; H, 2.19; N, 8.50. Found: C, 46.68; H, 2.31; N, 8.42.
conditions.
Crystallography
Crystals suitable for X-ray determination were obtained for
·(CH COCH (H O) and 3·(CH COCH )(CH CH OCH CH
by recrystallization. Cell parameters were determined using a
We have prepared two new dinickel complexes 2 and 3 with Siemens SMART CCD diffractometer. The structure was
2
3
3
)
2
2
2
3
3
3
2
2
3
)
Summary
1
6
anthyridine-based ligands L
two nickel centers in complexes 2 and 3 are ca. 5.4086(6) and the SHELXL-97 program by full-matrix least-squares on F
.0138(7) Å, respectively. From the experimental data, we values. Crystal data of these complexes are listed in the ESI.†
believe that both the chelation effect of the terpyridine moiety Other crystallographic data are deposited in the ESI.†
2 3
and L . The distances between solved using the SHELXS-97 program and refined using
1
7
2
5
and the short distance between nickel ions might play a key
Crystal
data 2:
for
yellow
colour,
column,
role for the good catalytic activity of 3 as compared to 2. We
C
41
H
44
F
12
N
5
2 w
Ni O18, F = 1240.23, monoclinic, P2(1)/c, a =
are delighted to learn that the dinickel complex 3 is an 16.6454(7) Å, b = 14.6305(8) Å, c = 21.2591(10) Å, α = 90, β =
3
effective catalyst for the reduction of various carboxylic acids 90.049(4)°, γ = 90, V = 5177.2(4) Å , Z = 4, D
= 1.591
calcd
to give the corresponding alcohols. Further studies of the cata- Mg m− , F(000) = 2532, crystal size: 0.20 × 0.15 × 0.10 mm ,
3
3
lytic activities of both complexes in other reactions are cur- 2.82 to 25.00°, 25 095 reflections collected, 8809 reflections
rently in progress.
[R(int) = 0.0444], final R indices [I > 2sigma(I)]: R = 0.0401,
1
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1
wR
of-fit on F = 1.039.
Crystal data for 3: yellow colour, plate, C52
= 1283.32, monoclinic, P2(1)/c, a = 20.1055(6) Å, b = 18.0229(5)
Å, c = 15.0825(5) Å, α = 90°, β = 90.727(3)°, γ = 90°, V = 5464.8(3)
2
= 0.0893, for all data R
1
= 0.0540, wR
2
= 0.0975, goodness-
1-Hexanol. H NMR (400 MHz, CDCl
3
): δ 3.65 (t, J = 7.2 Hz,
2
2H), 1.55 (m, 2H), 1.33 (m, 6H), 0.87 (t, J = 7.4 Hz, 3H).
C NMR (100 MHz): δ 63.8, 32.9, 31.8, 25.3, 22.7, 14.1.
1
3
H
39
F
12
N
7
Ni
2
O
11
,
F
w
3
−3
Å , Z = 4, Dcalcd = 1.560 Mg m , F(000) = 2608, crystal size:
Acknowledgements
3
0
.25 × 0.15 × 0.10 mm , 2.82 to 25.00°, 27 720 reflections
collected, 9191 reflections [R(int) = 0.0476]. The disordered We thank the Ministry of Science and Technology, Taiwan for
solvent in the crystal was refined by the use of SQUEEZE. The financial support (MOST103-2113-M-002-MY3).
3
total potential volume for solvent molecules is 229.0 Å in the
3
per unit cell volume 5464.9 Å [4.2%]. Final R indices [I >
2
sigma(I)]: R
1 2 1
= 0.0536, wR = 0.1324, for all data R = 0.0828,
References
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wR = 0.1506, goodness-of-fit on F = 1.032.
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Benzyl alcohol. H NMR (400 MHz, CDCl ): δ 7.48–7.32 (m,
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1
3
5
H), 4.63 (s, 2H), 2.51 (s, 1H). C NMR (100 MHz): δ 141.1,
1
28.2, 127.9, 127.3, 64.9.
p-Methylbenzyl alcohol. H NMR (400 MHz, CDCl ): δ 7.30
1
3
(
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3
C NMR (100 MHz): δ 138.2, 137.1, 128.9, 127.4, 65.0, 20.9.
1
p-Chlorobenzyl alcohol.
H NMR (400 MHz, CDCl3):
1
3
δ 7.39–7.25 (m, 4H), 4.61 (s, 2H), 2.18 (s, 1H). C NMR
(100 MHz): δ 139.0, 133.6, 129.1, 128.4, 64.1.
1
p-Cyanobenzyl alcohol. H NMR (400 MHz, CDCl ): δ 7.61
3
1
3
(
(
m, 2H), 7.50 (m, 2H), 4.72 (s, 2H), 2.73 (s, 1H). C NMR
100 MHz): δ 146.2, 132.6, 127.2, 119.1, 111.2, 64.3.
1
p-(Methoxycarbonyl)benzyl alcohol. H NMR (400 MHz,
CDCl
.74 (s, 2H), 3.88 (s, 3H), 2.35 (bs, 1H). C NMR (100 MHz):
δ 166.8, 146.3, 129.4, 129.1, 126.3, 64.6, 51.9.
3
): δ 8.03 (d, J = 8.2 Hz, 2H), 7.45 (d, J = 8.2 Hz, 2H),
1
3
4
1
p-(Methoxymethyl)benzyl alcohol.
CDCl ): δ 7.41 (s, 4H), 4.73 (s, 4H). C NMR (100 MHz):
δ 140.6, 127.4, 65.5.
-Phenylprop-2-en-1-ol. H NMR (400 MHz, CDCl
m, 2H), 7.34 (m, 2H), 7.28 (m, 1H), 6.61 (d, J = 14.7 Hz, 1H),
H NMR (400 MHz,
1
3
3
1
3
3
): δ 7.43
(
6
1
3
.41 (m, 1H), 4.34 (m, 2H). C NMR (100 MHz, CDCl3):
δ 136.9, 131.0, 128.7, 128.5, 127.9, 126.2, 64.0.
1
2
-Phenylethanol. H NMR (400 MHz, CDCl
3
): δ 7.41–7.34 (m,
2
2
1
H), 7.32–7.23 (m, 3H), 3.92–3.83 (m, 2H), 2.89 (t, J = 7.4 Hz,
1
3
H), 2.02 (s, 1H). C NMR (100 MHz): δ 138.8, 129.2, 128.3,
26.6, 63.8, 39.1.
1
1
-Octanol. H NMR (400 MHz, CDCl ): δ 3.63 (t, J = 7.5 Hz,
3
2
H), 1.57 (m, 2H), 1.28 (m, 10H), 0.84 (t, J = 7.1 Hz, 3H).
C NMR (100 MHz): δ 62.9, 33.1, 32.3, 29.6, 29.2, 25.6,
2.1, 14.4.
1
3
2
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Dalton Trans.