Imine Nitrogen Bridged Binuclear Nickel Complexes via N-H Bond Activation: Synthesis, Characterization, Unexpected C,N-Coupling Reaction, and Their Catalytic Application in Hydrosilylation of Aldehydes

Article abstract of DOI:10.1021/acs.organomet.5b00734

The reactions of NiMe₂(PMe₃)₃ with 2,6-difluoroarylimines were explored. As a result, a series of binuclear nickel complexes (5-8, 11) were synthesized. Meanwhile, from the reactions of NiMe₂(PMe₃)₃ with [2-CH₃C₆H₄-C(=NH)-2,6-F₂C₆H₃] (9) and [2,6-(CH₃)₂C₆H₃-C(=NH)-2,6-F₂C₆H₃] (10), two unexpected C,N-coupling products (12 and 13) were obtained. It is believed that these coupling reactions underwent activation of the N-H and C-F bonds. The binuclear nickel complexes showed excellent catalytic activity in the hydrosilylation of aldehydes. The mechanism of the reaction was studied through stoichiometric reactions, and the double-(η²-Si-H)-Ni^II intermediate was detected by in situ ¹H NMR spectroscopy, which may be the key point in the catalytic cycle.

Full text of DOI:10.1021/acs.organomet.5b00734

Article
pubs.acs.org/Organometallics
Imine Nitrogen Bridged Binuclear Nickel Complexes via N−H Bond
Activation: Synthesis, Characterization, Unexpected C,N-Coupling
Reaction, and Their Catalytic Application in Hydrosilylation of
Aldehydes
Lin Wang, Hongjian Sun, and Xiaoyan Li*
School of Chemistry and Chemical Engineering, Key Laboratory of Special Functional Aggregated Materials, Ministry of Education,
Shandong University, Shanda Nanlu 27, 250199 Jinan, People’s Republic of China
S
* Supporting Information
ABSTRACT: The reactions of NiMe2(PMe3)3 with 2,6-difluoroar-
ylimines were explored. As a result, a series of binuclear nickel
complexes (5−8, 11) were synthesized. Meanwhile, from the reactions
of NiMe2(PMe3)3 with [2-CH3C6H4-C(NH)-2,6-F2C6H3] (9) and
[2,6-(CH3)2C6H3-C(NH)-2,6-F2C6H3] (10), two unexpected C,N-
coupling products (12 and 13) were obtained. It is believed that these
coupling reactions underwent activation of the N−H and C−F bonds.
The binuclear nickel complexes showed excellent catalytic activity in
the hydrosilylation of aldehydes. The mechanism of the reaction was
studied through stoichiometric reactions, and the double-(η2-Si−H)−
NiII intermediate was detected by in situ 1H NMR spectroscopy, which
may be the key point in the catalytic cycle.
In this work, a series of imine nitrogen bridged binuclear
nickel complexes were synthesized via the selective activation of
N−H bonds from the reactions of NiMe2(PMe3)3 with
fluoroarylimines. These binuclear nickel complexes performed
well in the catalytic hydrosilylation of aromatic aldehydes,
aliphatic aldehydes, and α,β-unsaturated aldehydes. In addition,
two unexpected C,N-coupling products were obtained from the
reactions of NiMe2(PMe3)3 with (2,6-difluorophenyl)(2-
methylphenyl)methanimine and (2,6-difluorophenyl)(2,6-
dimethylphenyl)methanimine. The reaction mechanism was
discussed in this paper.
INTRODUCTION
■
The synthesis and property exploration of binuclear metal
complexes has been a research priority for several years due to
their special catalytic activities.1 Oxidation of alcohols,2
phenols,3,and sulfides,4 olefin epoxidation,5 and polymerization
of olefin6 are the common processes catalyzed by bimetallic
complexes. In the organism, there are various metalloproteins
containing the binuclear metal complexes playing important
roles in the transport of oxygen, catalysis, and photo-
conduction.7 On the basis of this, bimetallic complexes have
been widely utilized in biomimetic catalysis,8 enzymatic
reactions,9 and photocatalysis.10 In addition, C,C-coupling
reactions could also be catalyzed by bimetallic complexes, such
as binuclear palladium and rhodium complexes.11 Even so, the
types of reactions catalyzed by bimetallic complexes are still
limited.
The activation of N−H bonds has been widely used in
building N-bridged binuclear metal complexes: Using bimetallic
complexes bearing oxo-bridging ligands as precursors,12 via the
reactions of diaryl or dialkyl metal complexes with ammonia or
amines13 and with the support of alkyllithium reagents,14 is a
common strategy to obtain binuclear metal complexes.
Moreover, C,N-coupling reaction could be realized through
the N−H bond activation. Palladium, rhodium, copper, and
nickel complexes performed well in cleaving the N−H bonds
and prompting the C,N-coupling reactions.15 However, there
were few precedents reported to obtain the bimetallic
complexes and realize the C,N-coupling reaction via the
activation of N(sp2)−H bonds.
RESULTS AND DISCUSSION
■
Reaction of NiMe2(PMe3)3 with (2,6-Difluorophenyl)-
(aryl)methanimine. Transition-metal complexes, especially
nickel complexes, have often been utilized in the activation of
N−H bonds according to the literature.16 In view of this,
NiMe2(PMe3)3 was used to react with fluoroarylimines. As a
result, a series of imine nitrogen bridged binuclear nickel
complexes were obtained via the activation of N−H bonds
(Scheme 1). A mixture of NiMe2(PMe3)3 with compound 1
was stirred at 20 °C in THF for 2 days. During this period, the
solution turned from pale yellow to red. Complex 5 crystallized
from the diethyl ether solution as red crystals. In the IR
spectrum, the typical ν(CN−H) signal disappeared and the
signals of ν(CN) and ρ1(PCH3) were found at 1612 and 939
Received: August 26, 2015
© XXXX American Chemical Society
A
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Scheme 1. Reaction of NiMe2(PMe3)3 with (2,6-
Difluorophenyl)(aryl)methanimine
cm−1, respectively. In the 1H NMR spectrum of 5, the
resonances of H3C−Ni and P(CH3)3 were recorded at −0.432
and 0.870 ppm, respectively, with a relative integral ratio of 1:3.
3
The coupling constant JP,H was 9 Hz. In the 31P NMR
spectrum of 5, there was only one singlet, appearing at −8.42
ppm. The signals of Ar-F appeared at −110.89 and −110.79
ppm in the 19F NMR spectrum of 5 due to the steric effect of
the imine ligand.
The reactions of NiMe2(PMe3)3 with other imines,
compounds 2−4, were also explored. Although the aryl group
was substituted by either an EDG or EWG, the activation of
N−H bonds could still be realized and binuclear nickel
complexes 6−8 were obtained. The IR and NMR spectroscopic
data of these three complexes were similar to those of complex
5. Red crystals of complexes 6 and 8 suitable for single-crystal
X-ray diffraction were obtained from their diethyl ether
solutions at 10 °C. The molecular structure (Figure 1) of
complex 6 shows the distorted-square-planar coordination
geometry around each nickel center due to the influence of the
bulky imine ligand: The sum of the four bond angles around
the nickel center is 358.7° (N1−Ni1−N1A, 76.9°; N1A−Ni1−
C1, 95.2°; C1−Ni1−P1, 91.5°; P1−Ni1−N1, 95.1°). For the
same reason, the CN double bond is not coplanar with the
two nickel atoms and the sum of the three bond angles around
N1 is 355.5° (Ni1A−N1−Ni1, 84.5°; Ni1−N1−C12, 137.1°;
C12−N1−Ni1A, 133.9°). The N1−Ni1A bond length is 1.897
Å, which is similar to the bond length of N1−Ni1 (1.914 Å.
The molecular structure of complex 8 is comparable with that
of complex 6 in the structural data and configuration
information. In the molecular structure of 8, the sums of the
bond angles around the nickel and N1 atoms are 359.15 and
355.62°, respectively.
Figure 1. Molecular structures of 6 (top), 8 (middle), and 11
(bottom). The hydrogen atoms are omitted for clarity, and thermal
ellipsoids are drawn at the 50% probability level. For selected bond
distances (Å) and angles (deg) see the Supporting Information.
Reactions of NiMe2(PMe3)3 with Compounds 9 and
10. In addition to the binuclear nickel complexes obtained via
N−H bond activation, an unexpected C,N-coupling product,
compound 12, was obtained from the reaction of Ni-
Me2(PMe3)3 with compound 9 in a low yield (Scheme 2).
The binuclear nickel complex 11 was characterized by IR and
NMR spectroscopy and X-ray diffraction analysis (Figure 1).
Meanwhile, MS, IR, and NMR spectroscopy were used to
characterize compound 12. The MS spectrum of 12 indicates
that the molecular weight of 12 is 442. The IR spectrum of 12
A similar result was obtained from the reaction of
NiMe2(PMe3)3 with compound 10. This reaction gave rise to
the C,N-coupling product 13 in a higher yield, 35% (Scheme
1
3). The H, 19F, and 13C NMR spectra of 13 confirm the
structure of compound 13. In the 1H spectrum of 13, there are
three types of aryl-CH3 signals at 2.33, 2.03, and 1.69 ppm with
a relative integral ratio of 2:1:1. As for 12, the 19F NMR
spectrum of 13 shows two singlets at −108.35 and −111.41
ppm in a relative integral ratio of 2:1.
1
shows a strong ν(N−H) signal at 3386 cm−1. In the H NMR
spectrum of 12, two types of Ar-CH3 signals appear at 2.06 and
2.49 ppm with a relative integral radio of 1:1. In the 19F NMR
spectrum of 12, there are two singlets at −106.55 and −109.69
ppm with a relative integral radio of 2:1. These data are
consistent with the structure of compound 12.
In accord with the literature,17 a possible mechanism was
proposed (Scheme 4). The activation of an N−H bond should
B
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Scheme 2. Unexpected C,N-Coupling Reaction of NiMe2(PMe3)3 with 9
This mechanism can also be used to explain why the yields of
12 and 13 are different. In comparison to 9, there are two o-
methyl groups in 10. This makes the electronic effect and steric
hindrance more significant. Therefore, intermediate A prefers
to activate the C−F bond of another imine rather than to form
a binuclear nickel complex. Thus, the yield of 13 is much higher
than that of 12.
Scheme 3. Unexpected C,N-Coupling Reaction of
NiMe2(PMe3)3 with 10
Catalytic Hydrosilylation Reactions of Aldehydes
Catalyzed by Binuclear Nickel Complexes. The nickel
complexes were reported to be applied in the catalytic
hydrosilylation of alkenes, alkynes,19 aldehydes, ketones,20
imines,21 and even CO2.22 However, for binuclear nickel
complexes, there were few reports involving their application in
this reaction type.23 Therefore, the catalytic activities of
complexes 5−8 and 11 for hydrosilylation of aldehydes were
tested (Table 1).
Scheme 4. Possible Mechanism for the C,N-Coupling
Reaction of 10
At first, we chose p-fluorobenzaldehyde as the substrate, an
equal amount of H2SiPh2 as the hydrogen source, and 1 mol %
complex 11 as catalyst. The reaction was completed in 2 h at 70
°C with a conversion of 99% (entry 1). If the other conditions
remained unchanged, the loading of the catalyst could be
Table 1. Hydrosilylation of p-FC6H4CHO Catalyzed by
a
Binuclear Nickel Complexes
amt of cat.
(%)
conversion
b
entry cat.
silane
T (°C) t (h)
(%)
1
11
11
11
11
11
11
11
11
11
11
11
5
H2SiPh2
H2SiPh2
H2SiPh2
H2SiPh2
HSi(OEt)3
HSiPh3
1
70
70
70
70
70
70
70
70
50
45
35
45
45
45
45
60
2
99
99
70
99
65
52
38
25
99
99
99
60
53
55
56
99
be the first step. Due to the steric hindrance of 10, intermediate
A was formed instead of the binuclear nickel complex. The
intermediate B, a nickel(IV) species, could be produced
through the ligand replacement of a PMe3 by 10 and C−F
bond activation. As the electron-donating groups, the methyl
groups on the aryl made the nickel center electron-rich and,
therefore, the C−F bond activation of another imine could be
realized via oxidative addition.17d−g Intermediate B was so
unstable that the reductive elimination would happen
immediately in the presence of PMe3. Therefore, the C,N-
coupling product 13 was obtained with nickel(II) fluoride
([Ni−F]) as a byproduct.
2
0.6
0.5
0.5
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
0.6
2
2
3
2
4
4
5
4
6
4
7
HSiMePh2
HSiEt3
4
8
4
9
H2SiPh2
H2SiPh2
H2SiPh2
H2SiPh2
H2SiPh2
H2SiPh2
H2SiPh2
H2SiPh2
3
10
1
3
7
12
13
14
15
16
3.5
3.5
3.5
3.5
6
In order to find this byproduct, in situ 19F NMR
spectroscopy was used to monitor the reaction process.
Because of the low yield, there was only a weak signal at
−300.0 ppm, which could be regarded as the typical signal of a
Ni−F bond.18 However, when we tried to obtain the
intermediate via shortening the reaction time and lowering
the temperature, we failed due to the instability of the
intermediate.
7
8
5
12
a
Reaction conditions: (1) p-FC6H4CHO (1 mmol); silane (1 mmol),
and binuclear nickel complex in 1 mL of THF at T °C for t h; (2) 3
mL of CH3OH and 5 mL of 10% NaOH added to the mixture at 60
b
°C for 24 h. Determined by GC, with n-dodecane as the standard.
C
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a
reduced to 0.6% (entries 2−4). Different silanes were tested as
hydrogen sources, and H2SiPh2 was found to be the best
(entries 4−8). In the presence of 0.6 mol % of complex 11, the
reaction could be completed under milder conditions (entries 9
and 10). The conversion of aldehyde could still be up to 99% at
35 °C, although a longer reaction time was needed (entry 11).
In addition to complex 11, complexes 5−8 were also able to
catalyze the hydrosilylation reaction of aldehyde (entries 12−
16). However, 11 showed the best activity among them. On the
basis of the above facts, the optimized catalytic conditions for
the hydrosilylation of aldehydes were found to be 0.6 mol %
catalyst loading of 11 and an equimolar amount of H2SiPh2 as
the hydrogen source at a temperature of 45 °C.
Table 2. Hydrosilylation of Aldehydes Catalyzed by 11
Under the optimized conditions, the catalytic hydro-
silylations of aromatic aldehydes with different substituted
groups, aliphatic and α,β-unsaturated aldehydes, were explored
(Table 2).
For most aromatic aldehydes, their corresponding alcohols
could be obtained in good yields in a short time (Table 2,
entries 1, 2, 4, 5, 7, and 8). An EDG on the aryl (entry 3) and
steric hindrance (entry 6) may influence the interaction
between substrate and catalyst thus, the reaction needed a
longer time to be completed. For aliphatic aldehydes, the
loading of the catalyst should be increased to 1 mol % and the
reaction mixture should be heated to 55 °C due to their low
activity (entries 11 and 12). The selective hydrosilylation
reaction of α,β-unsaturated aldehydes was also explored
(entries 13−16). In the presence of 1 mol % of complex 11,
the formyl group was selectively hydrosilylated with retention
of the CC double bond at 60 °C after 7 h. After workup, the
corresponding cinnamyl alcohols were obtained in good yields.
In comparison to most mononuclear nickel catalysts,
complex 11 is more stable and easily prepared. In addition,
this catalytic system is only suitable for the hydrosilylation of
aldehydes. Ketone, ester, and amide could not be reduced
catalytically to the corresponding products with this system.
The catalytic activities of these catalysts are selective.
In order to understand the catalytic transformation, the
stoichiometric reaction of complex 11 with H2SiPh2 was
explored. Two components reacted in C6D6 at 45 °C, just as for
the catalytic conditions. After 24 h, the reaction was monitored
by in situ IR and 1H NMR spectroscopy (Scheme 5a). The 1H
NMR spectrum shows a signal at −6.52 ppm as a quadruplet of
3
doublets which is coupled with methyl protons (q, JH,H = 21
Hz) and with one phosphorus atom (d, JH,P = 9 Hz).
a
2
Reaction conditions unless stated otherwise: (1) aldehyde (1 mmol),
H2SiPh2 (1 mmol), and complex 11 (0.006 mmol) in 1 mL of THF at
45 °C for t h; (2) 3 mL of CH3OH and 5 mL of 10% NaOH added to
the mixture at 60 °C for 24 h. Isolated yield. The temperature of the
According to our early work and the related literature24 this
signal was regarded as the resonance of the H atom of the
coordinated Si−H bond linked to the nickel center. The
absorption at 1976 cm−1 in the IR spectrum can be identified as
the typical ν(Ni−H) signal. Under similar reaction conditions,
the 1H NMR spectrum of the stoichiometric reaction of
complex 7 with H2SiPh2 shows the existence of the [Ni-CH3]
group at −2.26 ppm and the relative integral ratio of this signal
b
c
d
e
reaction was 55 °C. 11 (0.01 mmol); 55 °C. 11 (0.01 mmol); 60 °C.
f
Determined by GC, with n-dodecane as the standard.
At first, the binuclear nickel complex disintegrated in the
presence of silane to form the mononuclear double-(η2-Si−
H)−NiII intermediate C. With the synergy of aldehyde,
cleavage of the Si−H bond and the insertion of the CO
double bond into the Ni−H bond occurred. As a result,
intermediate D was generated. Intermediate D was unstable.
With the assistance of another H2SiPh2, the reductive
elimination at intermediate D took place with the formation
of siloxane. Meanwhile, the nickel−silane intermediate C was
regenerated in the catalytic cycle.
3
to that of (η2-Si−H)−Ni at −5.88 ppm (q, JH,H = 21 Hz) is
about 3:2 (Scheme 5b). These facts confirm the formation of
the double-(η2-Si−H)−NiII intermediate C during the reaction
process (Scheme 6). In addition, after aldehyde was added to
the mixture, the signal of (η2-Si−H)−Ni disappeared
immediately. Moreover, there was no obvious change during
the reaction of nickel complex 7 or 11 with aldehyde under the
same conditions. On the basis of these facts, a possible
mechanism could be proposed (Scheme 6).
D
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Scheme 5. Hydrogen Signals of (η2-Si−H)−NiII in the in Situ 1H NMR Spectra of the Reaction between 11 and H2SiPh2 (a) and
That between 7 and H2SiPh2 (b)
reference at room temperature. Meanwhile, 13C NMR spectra (100
Scheme 6. Possible Mechanism of the Hydrosilylation
Reactions of Aldehydes Catalyzed by a Binuclear Nickel
Complex
MHz) were recorded on a Bruker Avance 400 spectrometer. 13C and
31P NMR resonances were obtained with broad-band proton
decoupling. Elemental analyses were carried out on an Elementar
Vario ELIII instrument. Melting points were measured in capillaries
sealed under nitrogen and are uncorrected. MS were measured on an
Agilent Technologies 6510 QTOF LC/MS instrument.
X-ray Crystal Structure Determinations. Single-crystal X-ray
diffraction data of the complexes were collected on a Bruker SMART
Apex II CCD diffractometer equipped with graphite-monochromated
Mo Kα radiation (λ = 0.71073 Å). During collection of the intensity
data, no significant decay was observed. The intensities were corrected
for Lorentz−polarization effects and empirical absorption with the
SADABS program. The structures were resolved by direct or Patterson
methods with the SHELXS-97 program and were refined on F2 with
SHELXTL. All non-hydrogen atoms were refined anisotropically.
Hydrogen atoms were included in calculated positions and were
refined using a riding model.
A summary of crystal data, data collection parameters, and structure
refinement details is given in the Supporting Information. CCDC
975064 (6), 1400364 (8), and 975063 (11) contain supplementary
crystallographic data for this paper. Copies of the data can be obtained
free of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (+44)1223-336-033; e-mail, deposit@
ccdc.cam.ac.uk).
Synthesis of Complexes. Synthesis of 5. NiMe2(PMe3)3 (0.50 g,
1.58 mmol) dissolved in 20 mL of THF was added to a 30 mL of THF
CONCLUSION
■
In conclusion, we explored the reactions of fluoroarylimine with
NiMe2(PMe3)3 and a series of imine nitrogen bridging
binuclear nickel complexes were obtained via the activation of
N−H bonds. In addition, the reactions of NiMe2(PMe3)3 with
(2,6-difluorophenyl)(2-methylphenyl)methanimine or (2,6-
difluorophenyl)(2,6-dimethylphenyl)methanimine led to un-
expected C,N-coupling products. The binuclear nickel com-
plexes showed good catalytic activity in the hydrosilylation
reaction of aldehyde. From the stoichiometric reaction of the
binuclear nickel complex with H2SiPh2, the formation of a
double-(η2-Si−H)−NiII intermediate was detected. On the
basis of this finding, a possible mechanism was proposed.
solution of (2,6-difluorophenyl)phenylmethanimine (1; 0.34 g, 1.58
mmol) at 20 °C. Then the mixture was stirred at the same temperature
for 48 h. During this period the mixture turned from orange to red.
After removal of the solvent at reduced pressure the solid residue was
extracted with diethyl ether (30 mL × 2). Red crystals of 5 were
obtained from the diethyl ether solution at −20 °C. Yield: 0.36 g, 63%.
Mp: 178 °C dec. Anal. Calcd for C34H40F4N2Ni2P2·C4H10O (804.20 g
mol−1): C, 56.62; H, 6.25; N, 3.47. Found: C,56.72; H,5.28; N, 3.64.
IR (Nujol, cm−1): 1612 ν(CN), 1583, 1563 ν(CC), 940
1
ρ1(PCH3). H NMR (300 MHz, C6D6, 298 K, ppm): δ −0.43 (d,
3JP,H = 8.4 Hz, 6H, Ni−CH3), 0.87 (d, 3JH,P = 8.7 Hz, 18H, P(CH3)3),
6.51−9.01 (m, 16H, Ar-H). 31P NMR (121.5 MHz, C6D6, 298 K,
ppm): δ −8.42 (s, P, P(CH3)3). 19F NMR (282.4 MHz, C6D6, 298 K,
ppm): δ −110.8 (s, 2F, Ar-F), −110.9 (s, 2F, Ar-F). 13C NMR (100
MHz, C6D6, 298 K, ppm): δ −14.1 (d, 2JP,C = 32.0 Hz, H32C-Ni), 13.8
EXPERIMENTAL SECTION
■
1
(d, JP,C = 26.0 Hz, (CH3)3P), 29.9 (Ar-CH3), 110.1 (d, JF,C = 22.0
General Procedures. All operations were conducted utilizing
standard Schlenk techniques under a nitrogen atmosphere. Pentane,
diethyl ether, THF, toluene, and dioxane were dried by distillation
from Na−benzophenone under nitrogen before use. CDCl3 and C6D6
for NMR were degassed and dehydrated. NiMe2(PMe3)3 was prepared
according to the literature method.25 Fluoroimines were obtained by
addition reactions of 2,6-difluorobenzonitrile and arylmagnesium
bromide and subsequent quenching with methanol in diethyl ether
solutions.26 Infrared spectra (4000−400 cm−1), as obtained from
Nujol mulls between KBr disks, were recorded on a Bruker ALPHA
3
Hz, CAr), 111.6 (CAr), 128.4 (CAr), 131.0 (CAr), 142.7 (d, JF,C = 9.0
1
3
Hz, CAr), 155.6 (CAr), 160.2 (dd, JF,C = 249.0 Hz, JF,C = 10.0 Hz, F-
1
3
CAr), 160.8 (dd, JF,C = 240.0 Hz, JF,C = 7.0 Hz, F-CAr).
Synthesis of 6. NiMe2(PMe3)3 (0.50 g, 1.58 mmol) dissolved in 20
mL of THF was added to 30 mL of a THF solution of (2,6-
difluorophenyl)(4-methylphenyl)methanimine (2; 0.36 g, 1.58 mmol)
at 20 °C. Then the mixture was stirred at the same temperature for 48
h. During this period the mixture turned from orange to red. After
removal of the solvent at reduced pressure the solid residue was
extracted with diethyl ether (30 mL × 2). Red crystals of 6 were
obtained from the diethyl ether solution at −20 °C. Yield: 0.35 g, 59%.
Mp: 186 °C dec. Anal. Calcd for C36H44F4N2Ni2P2·2C4H10O (906.31
1
FT-IR instrument. H, 19F, and 31P NMR spectra (300, 282.4, and
121.5 MHz, respectively) were recorded on a Bruker Avance 300
spectrometer with C6D6 or CDCl3 as the solvent without an internal
E
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g mol−1): C, 58.18; H, 7.10; N, 3.08. Found: C,58.81; H, 6.87; N, 3.17.
IR (Nujol, cm−1): 1632 ν(CN), 1615 ν(CN), 1588, 1573 ν(C
C), 948 ρ1(PCH3). 1H NMR (300 MHz, C6D6, 298 K, ppm): δ −0.64
(d, 3JP,H = 9 Hz, 6H, Ni−CH3), 0.70 (d, 3JH,P = 9 Hz, 18H, P(CH3)3),
1.96 (s, 6H, CH3), 6.59−8.74 (m, 14H, Ar-H). 31P NMR (121.5 MHz,
C6D6, 298 K, ppm): δ 5.15 (s, P, P(CH3)3). 19F NMR (282.4 MHz,
K, ppm): δ 4.56 (s, P, P(CH3)3). 19F NMR (282.4 MHz, C6D6, 298 K,
ppm): δ −103.2 (m, 2F, Ar-F), −109.2 (s, 2F, Ar-F).
Synthesis of 12. NiMe2(PMe3)3 (0.50 g, 1.58 mmol) dissolved in
20 mL of THF was added to 30 mL of a THF solution of (2,6-
difluorophenyl)(2-methylphenyl)methanimine (9; 0.36 g, 1.58 mmol)
at 20 °C. Then the mixture was stirred at the same temperature for 48
h. During this period the mixture turned from orange to tan. The
solvent was removed at reduced pressure, and the solid residue was
extracted with diethyl ether (50 mL × 2). After red crystals of 11
crystallized from this solution, the volatile materials were evaporated
under vacuum. The residue was further purified by column
chromatography on silica gel (petroleum ether (60−90 °C)/NEt3
10/1, v/v). After recrystallization in diethyl ether, 12 was obtained as
white crystals. Yield: 0.03 g, 8%. Mp: 187 °C. QTOF LC/MS (m/z):
calcd for C28H21F3N2 [M + H]+, 443.17; found, 443.1801. IR (Nujol,
C6D6, 298 K, ppm): δ −110.8 (s, 2F, Ar-F), −111.0 (s, 2F, Ar-F). 13
C
2
NMR (100 MHz, C6D6, 298 K, ppm): δ −14.2 (d, JP,C = 32.0 Hz,
H3C-Ni), 13.8 (d, 1JP,C = 26.0 Hz, (CH3)3P), 29.9 (Ar-CH3), 110.0 (d,
2JF,C = 23.0 Hz, CAr), 111.5 (CAr), 122.5 (CAr), 138.0 (CAr), 140.3 (d,
1
3
3JF,C = 8.0 Hz, CAr), 155.4 (CAr), 160.3 (dd, JF,C = 250.0 Hz, JF,C
=
1
3
12.0 Hz, F-CAr), 160.8 (dd, JF,C = 242.0 Hz, JF,C = 7.0 Hz, F-CAr).
Synthesis of 7. NiMe2(PMe3)3 (0.50 g, 1.58 mmol) dissolved in 20
mL of THF was added to a 30 mL of a THF solution of (2,6-
difluorophenyl)(4-chlorophenyl)methanimine (3; 0.40 g, 1.58 mmol)
at 20 °C. Then the mixture was stirred at the same temperature for 48
h. During this period the mixture turned from orange to red. After
removal of the solvent at reduced pressure the solid residue was
extracted with diethyl ether (30 mL × 2). Red crystals of 7 were
obtained from the diethyl ether solution at −20 °C. Yield: 0.35 g, 55%.
Mp: 168 °C dec. Anal. Calcd for C36H44F4N2Ni2P2 (906.31 g mol−1):
C, 50.99; H, 4.78; N, 3.50. Found: C,51.36; H, 4.45; N, 3.23. IR
(Nujol, cm−1): 1619 ν(CN), 1606, 1582 ν(CC), 951 ρ1(PCH3).
1
cm−1): 3391 ν(CNH), 1613 ν(CN), 1573 ν(CC). H NMR
(300 MHz, C6D6, 298 K, ppm): δ 2.06 (s, 3H, CH3), 2.49 (s, 3H,
CH3), 6.28−7.20 (m, 15H, Ar-H and CNH). 19F NMR (282.4
MHz, C6D6, 298 K, ppm): δ −106.6 (s, 2F, Ar-F), −109.7 (s, 1F, Ar-
F). 13C NMR (100 MHz, C6D6, 298 K, ppm): δ 19.0 (s, CH3-Ar), 22.3
(s, CH3-Ar), 105.5 (d, 2JF,C = 23.0 Hz, CAr), 110.1 (CAr), 112.0 (d, 2JF,C
2
= 28.0 Hz, CAr), 120.2 (t, JF,C = 13.0 Hz, CAr), 125.5 (CAr), 126.7
3
(CAr3), 128.2 (CAr), 129.7 (t, JF,C = 11.0 Hz, CAr), 133.3 (CAr), 133.9
3
(d, JF,C = 11.0 Hz, CAr), 140.3 (CAr), 146.5 (d, JF,C = 6.0 Hz, CAr),
3
1H NMR (300 MHz, C6D6, 298 K, ppm): δ −0.74 (d, JP,H = 9 Hz,
1
1
160.1 (d, JF,C = 253.0 Hz, F-CAr), 161.0 (d, JF,C = 242.0 Hz).
Synthesis of 13. NiMe2(PMe3)3 (0.50 g, 1.58 mmol) dissolved in
20 mL of THF was added to a 30 mL of a THF solution of (2,6-
difluorophenyl)(2,6-dimethylphenyl)methanimine (10; 0.39 g, 1.58
mmol) at 20 °C. Then the mixture was stirred at the same temperature
for 48 h. After removal of the solvent at reduced pressure the solid
residue was extracted with diethyl ether (50 mL × 2). The extract was
filtered, followed by the evaporation of the volatile materials under
vacuum. The residue was further purified by column chromatography
on silica gel (petroleum ether (60−90 °C)/NEt3 10/1, v/v). After
recrystallization in diethyl ether, 13 was obtained as white crystals.
Yield: 0.13 g, 35%. Mp: 56 °C. QTOF LC/MS: (m/z) calcd for
C30H25F3N2 [M + H]+, 471.197; found, 471.2393. IR (Nujol, cm−1):
3385 ν(CNH), 1620 ν(CN), 1578 ν(CC). 1H NMR (300
MHz, C6D6, 298 K, ppm): δ 1.69 (s, 3H, CH3), 2.03 (s, 3H, CH3),
2.33 (s, 6H, CH3), 6.26−7.27 (m, 13H, Ar-H and CNH). 19F NMR
(282.4 MHz, C6D6, 298 K, ppm): δ −108.4 (s, 2F, Ar-F), −111.4 (s,
1F, Ar-F). 13C NMR (100 MHz, C6D6, 298 K, ppm): δ 18.6 (s, CH3-
Ar), 19.3 (s, CH3-Ar), 23.8 (s, CH3-Ar), 104.9 (d, 2JF,C = 23.0 Hz, CAr),
105.5 (d, 2JF,C = 14.0 Hz, CAr), 110.2 (CAr), 112.6 (d, 2JF,C = 28.0 Hz,
3
6H, Ni−CH3), 0.58 (d, JH,P = 9 Hz, 18H, P(CH3)3), 6.49−8.62 (m,
14H, Ar-H). 31P NMR (121.5 MHz, C6D6, 298 K, ppm): δ 4.81 (s, P,
P(CH3)3). 19F NMR (282.4 MHz, C6D6, 298 K, ppm): δ −111.3 (s,
2F, Ar-F), −111.2 (s, 2F, Ar-F). 13C NMR (100 MHz, C6D6, 298 K,
1
ppm): δ −13.9 (d, 2JP,C = 32.0 Hz, H3C-Ni), 13.7 (d, JP,C = 27.0 Hz,
2
(CH3)3P), 110.2 (d, JF,C = 23.0 Hz, CAr), 111.6 (CAr), 128.8 (CAr),
134.6 (CAr), 140.7 (d, 3JF,C = 8.0 Hz, CAr), 154.4 (CAr), 160.0 (dd, 1JF,C
= 249.0 Hz, 3JF,C = 8.0 Hz, F-CAr), 160.5 (dd, 1JF,C = 244.0 Hz, 3JF,C
6.0 Hz, F-CAr).
=
Synthesis of 8. NiMe2(PMe3)3 (0.50 g, 1.58 mmol) dissolved in 20
mL of THF was added to 30 mL of a THF solution of (2,6-
difluorophenyl)(thiephyl)methanimine (4; 0.35 g, 1.58 mmol) at 20
°C. Then the mixture was stirred at the same temperature for 48 h.
During this period the mixture turned from orange to red. After
removal of the solvent at reduced pressure the solid residue was
extracted with diethyl ether (30 mL × 2). Red crystals of 8 were
obtained from the diethyl ether solution at −20 °C. Yield: 0.34 g, 58%.
Mp: 180 °C dec. Anal. Calcd for C30H36F4N2Ni2P2·C4H10O (816.12 g
mol−1): C, 49.91; H, 5.67; N, 3.42. Found: C,50.32; H, 5.13; N, 3.17.
IR (Nujol, cm−1): 1619 ν(CN), 1607, 1586 ν(CC), 950
CAr), 121.9 (t, 2JF,C = 15.0 Hz, CAr), 127.1 (CAr), 127.5 (d, 2JF,C = 25.0
3
Hz, CAr), 128.9 (t, JF,C = 11.0 Hz, CAr), 131.1 (CAr), 133.8 (d, 3JF,C
=
1
ρ1(PCH3). H NMR (300 MHz, C6D6, 298 K, ppm): δ −0.66 (d,
3
3JP,H = 9 Hz, 6H, Ni−CH3), 0.82 (d, JH,P = 9 Hz, 18H, P(CH3)3),
11.0 Hz, CAr), 134.2 (CAr), 136.1 (CAr), 139.3 (CAr), 142.3 (CAr), 146.7
(d, 3JF,C = 5.0 Hz, CAr), 159.9 (dd, 1JF,C = 249.0 Hz, 3JF,C = 8.0 Hz, F-
6.48−6.96 (m, 12H, Ar-H). 31P NMR (121.5 MHz, C6D6, 298 K,
ppm): δ 4.80 (s, P, P(CH3)3). 19F NMR (282.4 MHz, C6D6, 298 K,
ppm): δ −109.6 (m, 2F, Ar-F), −112.4 (s, 2F, Ar-F). 13C NMR (100
MHz, C6D6, 298 K, ppm): δ −14.3 (d, 2JP2,C = 32.0 Hz, H3C-Ni), 13.8
1
CAr), 160.3 (d, JF,C = 253.0 Hz), 177.4 (s, CN), 185.8 (s, CN).
Representative Experimental Procedure of Catalytic Hydro-
slilylation of Aldehydes. A 25 mL Schlenk tube was charged with a
mixture of PhCHO (1.0 mmol), H2SiPh2 (1.0 mmol), and complex 11
(0.006 mmol) in 2 mL of THF. The contents of the reaction vessel
were stirred at 45 °C for 3 h. The progress of the reaction was
monitored by TLC. After the mixture was cooled to room
temperature, CH3OH (3 mL) and 10% NaOH (5 mL) were placed
in the tube. After this mixture was stirred for 24 h at 60 °C, the
product was extracted with Et2O (30 mL × 2). The combined organic
phases were dried over anhydrous NaSO4 and filtered, and the solvent
was evaporated under reduced pressure. The product was purified by
column chromatography on silica gel (petroleum ether (60−90 °C)/
ethyl acetate 5/1, v/v) to afford PhCH2OH as a colorless liquid (0.10
g, 94%).
1
(d, JP,C = 27.0 Hz, (CH3)3P), 110.0 (d, JF,C = 23.0 Hz, CAr), 111.6
2
(CAr), 125.4 (d, JF,C = 11.0 Hz, CAr), 126.6 (CAr), 149.1 (CAr), 150.4
1
(d, 3JF,C = 8.0 Hz, CAr), 160.0 (dd, JF,C = 249.0 Hz, 3JF,C = 8.0 Hz, F-
1
3
CAr), 160.5 (dd, JF,C = 250.0 Hz, JF,C = 9.0 Hz, F-CAr).
Synthesis of 11. NiMe2(PMe3)3 (0.50 g, 1.58 mmol) dissolved in
20 mL of THF was added to 30 mL of a THF solution of (2,6-
difluorophenyl)(2-methylphenyl)methanimine (9; 0.36 g, 1.58 mmol)
at 20 °C. Then the mixture was stirred at the same temperature for 48
h. During this period the mixture turned from orange to red. After
removal of the solvent at reduced pressure the solid residue was
extracted with diethyl ether (30 mL × 2). Red crystals of 11 were
obtained from the diethyl ether solution at −20 °C. Yield: 0.25 g, 43%.
Mp: 116 °C dec. Anal. Calcd for C36H34F4N2Ni2P2 (758.16 g mol−1):
C, 56.89; H, 5.83; N, 3.69. Found: C, 56.75; H, 5.15; N, 3.47. IR
(Nujol, cm−1): 1616 ν(CN), 1599, 1584 ν(CC), 952 ρ1(PCH3).
Stoichiometric Reaction of Complex 11 with H2SiPh2. A 0.8
mL amount of a C6D6 solution of 11 (0.1 g, 0.13 mmol) and H2SiPh2
(0.048 g, 0.26 mmol) were sealed in a NMR tube. The mixture was
reacted at 45 °C for 24 h. During this period the mixture turned from
red to claret red. The reaction was monitored by 1H NMR
spectroscopy in situ. In the 1H NMR spectrum, the signal of the
Ni−H bond was found at −6.52 ppm as a quadruplet of doublets
3
1H NMR (300 MHz, C6D6, 298 K, ppm): δ −0.63 (d, JP,H = 6 Hz,
3
6H, Ni−CH3), 0.60 (d, JH,P = 6 Hz, 18H, P(CH3)3), 2.46 (s, 6H,
CH3), 6.23−9.06 (m, 14H, Ar-H). 31P NMR (121.5 MHz, C6D6, 298
F
DOI: 10.1021/acs.organomet.5b00734
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(3JH,H = 21 Hz, 2JH,P = 9 Hz). After removal of the solvent at reduced
pressure the solid residue was monitored by IR spectroscopy. In the IR
spectrum, a typical ν(Ni−H) signal was found at 1975.8 cm−1.
Stoichiometric Reaction of Complex 7 with H2SiPh2. A 0.8 mL
portion of a C6D6 solution of 7 (0.1 g, 0.12 mmol) and H2SiPh2 (0.048
g, 0.26 mmol) were sealed in a NMR tube. The mixture was reacted at
70 °C for 48 h. During this period the mixture turned from red to
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1
claret red. The reaction was monitored by H NMR spectroscopy in
1
situ. In the H NMR spectrum, the signal of the Ni−H bond was
found at −5.91 ppm and that of Ni-CH3 was at −2.26 ppm.
ASSOCIATED CONTENT
* Supporting Information
■
Kaluđerovic,
20, 575−583. (b) Daumann, L. J.; Schenk, G.; Ollis, D. L.; Gahan, L.
N. a.;
́
G. N.; Stosic-Grujicic, S. JBIC, J. Biol. Inorg. Chem. 2015,
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.5b00734.
R. Dalton Trans. 2014, 43, 910−928. (c) Schenk, G.; Mitic,
́
Gahan, L. R.; Ollis, D. L.; McGeary, R. P.; Guddat, L. W. Acc. Chem.
Res. 2012, 45, 1593−1603.
Confirmatory experiments to understand the mecha-
nisms of the C,N-coupling reaction and hydrosilylation
reactions of aldehydes and the NMR spectra of
stoichiometric reactions, crystallographic data for 6, 8,
(8) (a) Martin, C. S.; Teixeira, M. F. Inorg. Chim. Acta 2015, 425,
76−82. (b) Jiang, G.; Gu, X.; Jiang, G.; Chen, T.; Zhan, W.; Tian, S.
Sens. Actuators, B 2015, 209, 122−130. (c) Yusubov, M. S.; Celik, C.;
Geraskina, M. R.; Yoshimura, A.; Zhdankin, V. V.; Nemykin, V. N.
Tetrahedron Lett. 2014, 55, 5687−5690. (d) Hammond, C.; Hermans,
I.; Dimitratos, N. ChemCatChem 2015, 7, 434−440.
and 11, and the original IR, 1H NMR, 31P NMR, and 13
NMR spectra of the complexes (PDF)
C
(9) Chalupsky, J.; Rokob, T. A.; Kurashige, Y.; Yanai, T.; Solomon, E.
́
Crystallographic data for 6, 8 and 11 (CIF)
̌
I.; Rulísek, L. r.; Srnec, M. J. Am. Chem. Soc. 2014, 136, 15977−15991.
(10) Zheng, H.-Q.; Rao, H.; Hu, X.-Z.; Li, X.-H.; Fan, Y.-T.; Hou, H.-
W. Sol. Energy 2014, 105, 648−655.
AUTHOR INFORMATION
■
(11) (a) Karami, K.; Abedanzadeh, S.; Yadollahi, F.; Buyukgungor,
O.; Farrokhpour, H.; Rizzoli, C.; Lipkowski, J. J. Organomet. Chem.
2015, 781, 35−46. (b) Wang, G.; Liu, G.; Du, Y.; Li, W.; Yin, S.;
Wang, S.; Shi, Y.; Cao, C. Transition Met. Chem. 2014, 39, 691−698.
(c) Sarkar, M.; Daw, P.; Ghatak, T.; Bera, J. K. Chem. - Eur. J. 2014, 20,
16537−16549.
Corresponding Author
*E-mail for X.L.: xli63@sdu.edu.cn.
Notes
The authors declare no competing financial interest.
(12) (a) Mena, I.; Casado, M. A.; García-Orduna, P.; Polo, V.; Lahoz,
̃
ACKNOWLEDGMENTS
■
F. J.; Fazal, A.; Oro, L. A. Angew. Chem., Int. Ed. 2011, 50, 11735−
11738. (b) Kannan, S.; James, A. J.; Sharp, P. R. Inorg. Chim. Acta
2003, 345, 8−14. (c) Díez, L.; Espinet, P.; Miguel, J. A. J. Chem. Soc.,
We gratefully acknowledge financial support by the NSF of
China (No. 21372143/21172132) and support from Prof. Dr.
Dieter Fenske and Dr. Olaf Fuhr (Karlsruhe Nano-Micro
Facility) on the determination of the crystal structures.
Dalton Trans. 2001, 1189−1195. (d) Ruiz, J.; Rodríguez, V.; Lop
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Casabo,
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J.; Molins, E.; Miravitlles, C. Organometallics 1999, 18, 1177−
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DOI: 10.1021/acs.organomet.5b00734
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