R-allyl nickel(II) complexes with chelating N-heterocyclic carbenes: Synthesis, structural characterization, and catalytic activity

Article abstract of DOI:10.1021/om200937d

The N-heterocyclic carbene (NHC) nickel complexes [(L)Ni(NHC)][BAr ^F₄] (Ar^F = 3,5-bis(trifluoromethyl)phenyl; L = allyl (1), methylallyl (2); NHC = 1-(2-picolyl)-3-methylimidazol-2-ylidene (a), 1-(2-picolyl)-3-isopropylimidazol-2-ylidene (b), 1-(2-picolyl)-3-n- butylimidazol-2-ylidene (c), 1-(2-picolyl)-3-phenylimidazol-2-ylidene (d), 1-(2-picolyl)-3-methylbenzoimidazol-2-ylidene (e), 1-(2-picolyl)-4,5-dichloro-3- methylimidazol-2-ylidene (f)) have been obtained in high yields and characterized by NMR spectroscopy. Furthermore, 1d was unambiguously characterized by single-crystal X-ray crystallography. Complexes 1a-f/2a-f have shown catalytic activity toward dimerization and hydrosilylation of styrenes. In particular, 1a proved to be the most efficient catalyst in the dimerization of styrene derivatives in the absence of cocatalyst. Also, complexes 1a,d showed high selectivity and moderate to good yields in hydrosilylation reactions.

Full text of DOI:10.1021/om200937d

Article
pubs.acs.org/Organometallics
R-Allyl Nickel(II) Complexes with Chelating N-Heterocyclic Carbenes:
Synthesis, Structural Characterization, and Catalytic Activity
́
Lourdes Benıtez Junquera, M. Carmen Puerta,* and Pedro Valerga*
́
́
́
́
Departamento de Ciencia de los Materiales e Ingenierıa Metalurgica y Quımica Inorganica, Facultad de Ciencias, Universidad de
́ ́
Cadiz, 11510 Puerto Real, Cadiz, Espana
̃
S
* Supporting Information
ABSTRACT: The N-heterocyclic carbene (NHC) nickel complexes [(L)Ni(NHC)][BArF ] (ArF = 3,5-bis(trifluoromethyl)-
4
phenyl; L = allyl (1), methylallyl (2); NHC = 1-(2-picolyl)-3-methylimidazol-2-ylidene (a), 1-(2-picolyl)-3-isopropylimidazol-2-
ylidene (b), 1-(2-picolyl)-3-n-butylimidazol-2-ylidene (c), 1-(2-picolyl)-3-phenylimidazol-2-ylidene (d), 1-(2-picolyl)-3-
methylbenzoimidazol-2-ylidene (e), 1-(2-picolyl)-4,5-dichloro-3-methylimidazol-2-ylidene (f)) have been obtained in high
yields and characterized by NMR spectroscopy. Furthermore, 1d was unambiguously characterized by single-crystal X-ray
crystallography. Complexes 1a−f/2a−f have shown catalytic activity toward dimerization and hydrosilylation of styrenes. In
particular, 1a proved to be the most efficient catalyst in the dimerization of styrene derivatives in the absence of cocatalyst. Also,
complexes 1a,d showed high selectivity and moderate to good yields in hydrosilylation reactions.
complexes bearing electron-rich ligands have been synthesized
to avoid the use of cocatalyst, and they have shown activity
in C−C cross-coupling reactions,11,13 polymerization of
styrene,12 amination of aryl halides,14 and Suzuki15,16 and
Kumada reactions.17
INTRODUCTION
■
The synthesis and isolation of the first N-heterocyclic carbene
(NHC) were reported by Wanzlick,1,2 but until 19913 NHCs
did not experience a remarkable development. Since then, NHCs
have became an important class of ligands in organometallic
chemistry and catalysis.4
The first Ni(allyl)−NHC complexes were reported by the
́
groups of Sigman et al.,18 Gomes,19and Campora.20 Complexes
These ligands are often compared to tertiary phosphines
because of the similarities in their bonding with transition
metals, and in many cases, they have successfully replaced them
as auxiliary ligands. However, substantial differences do exist,
especially regarding their electron-donating ability. In general,
NHCs are stronger Lewis bases and have a reduced π-
back-bonding capability in comparison to tertiary phosphines.5
NHCs show superior performances in many aspects, including
higher versatility, easier preparation, thermal, air, and moisture
stability, and lower toxicity. Consequently, complexes that in-
corporate these ligands are more stable toward dissociative and
degradative cleavage. The applications of organometallic com-
plexes bearing NHC ligands in catalysis are now well recognized.3,4
The use of nickel NHC complexes in catalysis has been
eclipsed by the far wider range of applications found for their
palladium and ruthenium analogues.4 However, in the past
decade several NHC−Ni(0) and NHC−Ni(II) systems have
been reported. NHC−Ni(0) complexes have emerged as
efficient catalysts in C−S couplings,6 [2 + 2 + 2] cyclo-
additions,7−9 and amination of aryl chlorides.10 Nevertheless,
they are very air sensitive, and their reactions usually require
the use of a cocatalyst.11,12 On the other hand, NHC−Ni(II)
of the type Ni(allyl)(X)(NHC) (X = Cl, Br) have shown
activity in several C−C coupling reactions.14b,20,21 In particular,
polymerization reactions are very important, considering
the industrial application of the resulting polymers. These reac-
tions have been performed using nickel complexes with MAO
(methylalumoxane) as cocatalyst.22 However, the application of
Ni(allyl)−NHC complexes in polymerization has been quite
limited. Decomposition of the catalyst due to the cleavage of
the Ni−NHC bond, leading to the reductive elimination of the
active species,7a,23 has been proposed to explain the low activity
of such complexes. This behavior has mainly been observed in
cationic complexes.24
Recently, this problem has been avoided by the use of
functionalized NHCs, which may act as bidentate ligands due
to the presence of additional donor atoms (N, S, O) in the
NHC side chains.25 The hemilabile character of these groups
allows additional stabilization of the resulting complexes, whereas
they maintain the catalytic activity due to the possibility of
Received: October 6, 2011
Published: March 5, 2012
© 2012 American Chemical Society
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developing a vacant site. On the other hand, the base-promoted
C−H activation of a labile acetonitrile ligand on a nickel−NHC
center has been recently described.26,27 An appropriate design of
the NHC ligand may also allow tuning of the electronic and
steric properties of the ligand.10,28
form splits and appears as two AB doublets, with typical
coupling constants for these systems (J = 14.0−15.7 Hz),
within the chemical shift range of 6.5−5.5 ppm. However not in
all cases were these two signals unambiguously observed. For
complexes 1b and 2b,e, methylene protons accidentally exhibit
a broad singlet. In the case of complex 1e the two resonances
overlap and only a doublet is observed. Complexes 1f and 2c,f
show two broad singlets. All these assignments of methylene
proton resonances have been confirmed by 2D NMR
experiments. The 13C NMR spectra of 1a−f/2a−f exhibit the
resonances of the carbene carbon atoms in the distinctive
interval 176−153 ppm, already observed for the carbene carbon
signal of Ni−NHC complexes.17a,19,31,32
We have previously reported the synthesis and reactivity of
allyl−Ni(II) complexes bearing phosphines as auxiliary ligands,
and they have shown great activity in alkene polymerization.29
In this paper, we extend previous studies synthesizing a series of
[(L)Ni(NHC)]+ (L = allyl, methylallyl; NHC = 1-(2-picolyl)-
3-(R)-imidazol-2-ylidene (R = Me, iPr, nBu, Ph), 1-(2-picolyl)-
3-methylbenzoimidazol-2-ylidene, 1-(2-picolyl)-4,5-dichloro-3-
methylimidazolylidene) complexes (1a−f/2a−f), reporting the
high-yield synthesis of new NHC−Ni(II) complexes and their
activity toward styrene polymerization. The wide range of
picolyl-NHCs used allowed us to tune the steric and electronic
properties of these new Ni complexes and assess the effect on
the catalytic activity toward polymerization and hydrosilylation
reactions of styrenes. The structure of [(CH2CHCH2)Ni(1-(2-
Crystal Structure of [Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B-
(ArF)4] (1d). After recrystallization from a mixture of diethyl
ether and petroleum ether, complex 1d was further characterized
by single-crystal X-ray diffraction techniques. The ORTEP
drawing of cation complex in 1d is displayed in Figure 1, along
F
picolyl)-3-phenylimidazol-2-ylidene)][BAr4 ] has been deter-
mined by single-crystal X-ray diffraction.
RESULTS AND DISCUSSION
■
Synthesis and Characterization of Ni(II)−NHC Com-
plexes. 2-Picolylimidazolium salts constitute a family of bidentate
NHC ligands easily accessible by coupling of 2-(bromomethyl)-
pyridine with the corresponding imidazole derivative, as described
in the literature.24,30 A series of this type of ligands has been
prepared bearing different substituents at the 3-, 4-, and 5-
positions on the imidazolium ring (see Scheme 1). Several
Scheme 1. Synthesis of R-Allyl−Ni−NHC Complexes
Figure 1. ORTEP view of the cation complex in [Ni(η3-CH2CHCH2)-
(NHC-κ2C,N)][B(ArF)4] (1d; NHC = 1-(2-picolyl)-3-phenylimidazo-
lylidene). Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms have been omitted for clarity. The allyl ligand is
represented only in its major orientation (71%). Selected bond lengths
(Å) and angles (deg): Ni(1)−C(1a) = 2.049(15), Ni(1)−C(2a) =
2.003(8), Ni(1)−C(3a) = 1.95(2), Ni(1)−C(4) = 1.892(5), Ni(1)−
N(3) = 1.946(5), C(1a)−C(2a) = 1.432(17), C(2a)−C(3a) =
1.35(4); C(4)−Ni(1)−N(3) = 92.4(2), C(1a)−C(2a)−C(3a) =
116.9(17). Dihedral angle (deg) between planes C(1a)−C(2a)−
C(3a) and C(4)−Ni(1)−N(3): 68.6(10).
methods can be used to prepare Ni(II)−NHC complexes;28
among them, transmetalation from a silver precursor has
proved to be very efficient. Thus, the Ni(II) complexes [(L)Ni-
(NHC)][B(ArF)4] (L = allyl (1), methylallyl (2); NHC = 1-
(2-picolyl)-3-(R)-imidazol-2-ylidene (R = Me (a), iPr (b), nBu
(c), Ph (d)), 1-(2-picolyl)-3-methylbenzoimidazol-2-ylidene
(e), 1-(2-picolyl)-4,5-dichloro-3-methylimidazol-2-ylidene (f))
have been prepared by transmetalation of the corresponding
silver carbenes. Silver species were generated in situ, by treatment
of the appropriate 2-picolylimidazolium salt in CH2Cl2 with a
slight excess of Ag2O. The mixture was filtered through Celite.
Then [(L)Ni(COD)][BAr4F] (L = allyl, methylallyl) was added
to the previous mixture. After this treatment, complexes 1a−f/
2a−f were obtained in good yields (Scheme 1).
with selected bond lengths and angles. The cation exhibits a
classic pseudo-square-planar geometry characteristic of d8 M(II)
allyl complexes. The allyl ligand coordinates to the metal in a η3
manner. As in other related nickel complexes, the structure
reveals that the allyl ligand is disordered. This disorder has been
modeled in two opposite orientations of this group relative to the
rest of the molecule. Upon refining the occupancy factors, a
population ratio of ca. 71:29 was obtained for the two
orientations. For clarity, only the major position (approximately
71%) has been represented. The ligand 1-(2-picolyl)-3-phenyl-
imidazol-2-ylidene, binding to the central nickel atom in a
bidentate manner, completes the formal tetracoordination. Few
structures of cationic allyl nickel complexes containing a κ1C-
NHC ligand have been reported.18−20,29 None of them contain a
chelating κ2C,E-NHC ligand. The Ni(1)−C(4) distance of
1.892(5) Å is typical for a Ni−NHC distance and compares well
with 1.8780(2) Å for [Ni(η3-allyl)(NHC)(NCCH3]+ (NHC =
1,3,4,5-tetramethylimidazol-2-ylidene) and 1.909(3) Å for [Ni-
(η3-allyl)(NHC)(NCCH3)]+ (NHC = 2,5-bis(2,6-diiso-
propylphenyl)imidazol-2-ylidene).20 Other related neutral Cp,
All of the isolated complexes lack a C2−H imidazolium
proton signal at 10−12 ppm, indicating the coordination of the
1
2-picolylcarbene to the nickel atom. The H NMR spectra of
complexes 1a−f and 2a−f show characteristic signals
corresponding to the diastereotopic methylene protons in the
CH2 bridge of the bidentate ligand, which in its coordinated
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Cp*, or indenyl nickel complexes also show similar parameters:
for instance, in [Ni(Me-NHC)I(η5-C5Me5)], [Ni(Me-NHC)I-
(η5-C5H5)], and [Ni(Mes-NHC)Cl(η5-C5Me5)] the Ni−NHC
distances are 1.887(3), 1.880(4), and 1.906(3) Å, respectively.33
The dihedral angle between planes C(1a)−C(2a)−C(3a) and
C(4)−Ni(1)−N(3) matches with the angles in other [Ni(η3-
allyl)(NHC)]+ systems described in the literature.18−20
Table 1. Dimerization of Styrene: Optimization of Reaction
Conditions
1a
(mol %)
t
yield
(%)
selectivity dimer/
trimer
entry
T (°C)
(h)
a
1
40
40
40
40
40
40
40
40
40
40
40
40
40
60
60
60
60
0.1
0.1
0.1
0.5
0.5
0.5
1
1
2
5
6
100/0
100/0
100/0
98/2
a
a
a
a
a
a
a
b
b
b
b
b
b
b
b
b
2
3
3
8
In neutral complexes [NiBr(η3-CH2CHCH2)(NHC)]
Gomes et al.19 attributed the weakening of the bond between
the metal and the allyl atom placed trans to the NHC to a
stronger donor ability of the imidazol-2-ylidene ring. In our
case, despite the disorder found for the allyl ligand and
consequent greater deviations in bond lengths, the pyridyl ring
seems to show a greater trans influence, as indicated by the
Ni(1)-C(1a) distance (2.049(15) Å) being longer than Ni(1)−
C(3a) (1.95(2) Å). It is necessary to take into account this
indication in relation to the possibilities of hemilability and
chemical reactivity of the chelating ligand.
4
1
7
5
2
30
42
80
91
6
99/1
6
3
90/10
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
100/0
7
1
8
1
4
9
0.5
0.5
0.5
1
1
10
11
12
13
14
15
16
17
18
19
2
25
38
76
89
63
74
89
99
6
3
1
1
4
0.5
0.5
0.5
1
1
Catalytic Oligomerization of Styrenes. Polymerization
of olefins is a very important type of C−C bond coupling
reaction, given the wide range of applications of polymers in
industrial processes.11−13,15,16 Many organometallic com-
pounds, especially those of Ni and Pd, have been used as
catalysts in such processes.25 However, a mixture of oligomers
and polymers is often observed, due to the low selectivity of the
catalysts. Our group has previously reported the oligomeriza-
tion of styrene derivatives using Ni(II) complexes with good
yields.29 However, it has been very difficult to find highly
selective processes for low-molecular-weight oligomers. In
this sense, to the best of our knowledge, the new Ni(II)−
picolyl-NHC complexes have proved to be more active
and selective toward styrene dimer synthesis than any other
reported catalytic system (Scheme 2).
2
3
1
a
a
room temp
room temp
1
24
24
0.5
3
100/0
a
b
Conditions: 10 mmol styrene, 1 mL of dichloroethane. Conditions:
1 mL of dichloroethane.
Table 2. Catalytic Oligomerization of Styrene
a
entry
cat.
yield (%)
dimer (%)
trimer (%)
b
1
1a
1b
1c
1d
1e
1f
99
99
<5
70
<5
60
82
<5
<5
<5
53
<5
100
100
2
3
4
100
5
Scheme 2. Catalytic Dimerization of Styrene
6
66.7
89.4
33.3
10.6
7
2a
2b
2c
2d
2e
2f
8
9
10
11
12
86.2
13.8
a
Conditions: 10 mmol of styrene, 1 mL of 1,2-dichloroethane at
b
60 °C, reaction time 4 h. Reaction time 1 h.
However, inclusion of Cl or a Ph ring in the imidazole
backbone or a phenyl substituent in the imidazole wingtip
significantly decreases the reaction yields (entries 4−6). This
can be rationalized by the weaker donor properties34 of the
substituents on 1d,e and, in the case of 1f, the electron-
withdrawing power of the Cl atoms. In any case, this leads to a
less electron rich Ni(II) center that hinders the release of the
allyl or Me-allyl ligand, which is necessary to complete the
catalytic process according to previously published mechanism
proposals.29 On the other hand, Me-allyl−Ni(II) complexes
2a−f showed less activity and in some cases the absence of
activity in comparison with their allyl−Ni(II) counterparts 1a-f.
A similar behavior has been observed for allyl−Ni and methyl-
allyl−Ni complexes bearing the chelating phosphine ligand
The polymerization of styrene using the catalyst 1a as
catalyst precursor was selected as the representative reaction to
optimize the system conditions. The results, given in Table 1,
show that moderate to high yields were obtained at 60 °C in
short reaction times (entries 14−16), especially when low
catalyst loadings were used. Another result to note is that the
use of a catalytic load of 1 mol % produced the dimer with a
selectivity of 100% and high yield in just 1 h (entry 17), while
most of the systems previously reported require longer reaction
times.29,35,36 Also, a noncoordinating solvent is needed to prevent
solvent coordination to the metal center.29 It is important to note
that, as shown in Table 1, the oligomerization of styrene proceeds
with high selectivity toward dimer in all cases.
The oligomerization of styrene was carried out using
compounds 1a−f and 2a−f to assess the effect of the ligands
in the catalytic activity. As shown in Table 2, compounds 1a,b
showed the best catalytic activity, as evidenced by the high
yields and selectivity of the reaction (entries 1 and 2).
i
i
dippe (dippe = Pr2PCH2CH2 Pr2), as previously reported by
our group.29
In addition, the oligomerization of 4-methylstyrene and α-
methylstyrene was carried out to assess the effect of the methyl
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substituent on the catalytic system. The reaction mechanism
previously proposed for the polymerization of styrene indicates
a strong influence of the methyl substituent, given the nature of
the allyl intermediates that have to be generated to complete
the reaction.29 The results, given in Table 3, show a decreased
produces (4-methylpent-1-ene-2,4-diyl)dibenzene as the only
structure. NMR data suggest that α-methylstyrene dimer is
produced by insertion of one α-methylstyrene into one C−H
bond of another α-methyl substituent.29
Catalytic Hydrosilylation of Styrenes. Catalytic hydro-
silylation of alkenes is one of the most versatile and efficient
methods for the synthesis of alkylsilanes and the preparation of
organosilicon compounds on an industrial scale.35 For this
reason, it has been widely investigated using several catalytic
systems.29,35 The conventionally accepted mechanism for this
reaction includes oxidative addition of substituted silane to a
metal−alkene intermediate complex, followed by migratory
insertion into a M−H bond and reductive elimination by Si−C
bond formation, regenerating the metal−alkene complex. An
alternative pathway goes preferentially through an alkene
insertion into the M−Si bond. In each case a different
metal−hydrido complex is involved.
The addition of Si−H bonds across the CC double bond
can give a mixture of products that follow Markovnikov or anti-
Markovnikov rules. This reaction has been already studied by
our group29 and the Zargarian group35a,b using nickel(II)
complexes bearing phosphine ligands as catalysts. Hence, R-
allyl−Ni−NHC complexes (1a−f/2a−f) have been tested in
the catalytic hydrosilylation of styrenes (Scheme 4).
As previously stated for the polymerization reactions, our aim
has been to study the effect in the catalytic system caused by
several substituents on the NHC and the allyl ligand of the Ni
complexes. Each catalytic run has been carried out at 60 °C
with Ni/R-styrene/PhSiH3 ratios of 1/100/200, using an excess
of PhSiH3 to prevent oligomerization. Under these conditions,
the hydrosilylation product isolated upon purification was
either RC6H4C(R′)(CH3)SiH2C6H5 (A) or RC6H4CH(R′)-
CH2SiH2C6H5 (B). Nevertheless, A was obtained as the major
product in all cases. As shown in Table 4, compounds 1a,d
were highly selective toward product A when styrene and 4-
methylstyrene were used as substrates (entries 1, 3, 10, and 12).
However, 1b showed high selectivity in the styrene reaction but
lost its reactivity when 4-methylstyrene was used (entries 2 and
11). On the other hand, 1e showed an opposite behavior in
comparison with 1b. Compounds 2a−f gave higher yields than
their allyl analogues 1a−f but proved to be less selective in all
cases. Furthermore, only 2d,e showed activity when α-methyl-
styrene was used as substrate, but low yields were obtained.
However, in these cases, B was observed as the only product,
showing an inversion in the selectivity pattern presented by the
other substrates. Also, trisubstituted silanes such as (OEt)3SiH
and PhMe2SiH were tested, but none of them showed activity
in the hydrosilylation of styrene.
Table 3. Catalytic Oligomerization of 4-Methylstyrene and
α-Methylstyrene
a
entry
cat.
olefin
yield (%) dimer (%) trimer (%)
1
2
3
4
5
6
7
8
1a
1b
1d
1f
4-methylstyrene
4-methylstyrene
4-methylstyrene
4-methylstyrene
4-methylstyrene
4-methylstyrene
α-methylstyrene
α-methylstyrene
87
61
35
35
77
35.7
72
60
100
84.1
15.9
9.1
100
100
2a
2e
1a
2a
90.9
100
100
100
a
Conditions: 10 mmol of olefin, 1 mL of 1,2-dichloroethane at 60 °C,
reaction time 4 h.
activity for all the catalysts tested when 4-methylstyrene instead
of styrene was used as substrate (entries 1−5). In addition, the
use of α-methylstyrene diminished significantly the activity of
all Ni(II)−picolyl-NHC complexes; in most cases no activity
was observed. Only 1a and 2a showed catalytic activity toward
oligomerization of α-methylstyrene (entries 7 and 8). These
results are in line with those previously published by our
group,29 indicating that the mechanism should be as depicted
in Scheme 3, implying a very fast β-elimination step that
Scheme 3. Mechanism for Oligomerization Reaction of
Styrenes
explains the high selectivity toward dimer formation. It is
important to note that the structure of the α-methylstyrene
dimer is not homologous with those of the styrene or
4-methylstyrene dimers. Whereas 4-methylstyrene and styrene
dimers have a head-to-tail structure, α-methylstyrene dimer
Furthermore, in order to obtain information regarding the
reaction mechanism, the hydrosilylation of three fluoro-
substituted styrenes (F at the 2-, 3-, or 4-position of the phenyl
ring) was monitored by 19F NMR and 1H NMR. The experiments
Scheme 4. Catalytic Hydrosilylation of Styrenes
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spectrum at −119.7, −121.2, and −121.6 ppm are from
the major reaction product FC6H4CH(CH3)SiH2C6H5 (A),
2-fluorostyrene, and the minor reaction product
FC6H4CH2CH2SiH2C6H5 (B), respectively. However, a fourth
signal in the 19F NMR spectrum at −122.1 ppm is observed
that may correspond to a catalytically active species. In
addition, the 1H NMR of the reaction (Figure 4) clearly
showed distinctive signals in the metal−hydride region
at −29.28 and −29.29 ppm, indicating the presence of Ni−H
intermediates. These experimental data are consistent with the
participation of nickel−silyl and a nickel−hydride intermedi-
ates, as suggested by Zargarian et al.35 However, these data are
insufficient to support a complete mechanistic proposal. They
also illustrate that, as a result of the weakening of the double
bond in the fluorinated styrenes, the hydrosilylation processes
are faster in comparison with those for the non-fluorinated
analogues.
Table 4. Catalytic Hydrosilylation of Styrenes with PhSiH3
A:
B: anti-
Markovnikov
product (%)
yield
(%)
Markovnikov
product (%)
entry cat.
olefin
1a styrene
1b styrene
1
2
40
65
92.5
96
7.5
4
3
1d styrene
1e styrene
60
96.7
65.1
62.8
80.1
85.3
53.8
60.8
96.7
3.3
4
90.6
90
34.9
37.2
19.9
14.7
46.2
39.2
3.3
5
1f
styrene
6
2a styrene
2d styrene
2e styrene
79
7
100
90
8
9
2f
styrene
100
60
10
1a 4-
1b 4-
1d 4-
1e 4-
methylstyrene
methylstyrene
methylstyrene
methylstyrene
11
12
13
14
15
16
17
18
19
20
53
60
71.1
95
28.3
5
60
93.3
57.3
73.1
76.7
76.7
54.4
6.7
CONCLUSION
■
We have reported the synthesis of novel allyl−and methylallyl−
nickel complexes bearing hemilabile picolyl-NHC carbene
ligands using the transmetalation method from silver
precursors. These compounds have proved to be catalytically
active toward dimerization of styrenes without the use of any
cocatalyst, especially 1a. The dimerization reactions were highly
selective toward styrene dimers and occurred with moderate to
good yields. Also, the new nickel compounds showed activity in
hydrosilylation reactions of styrenes. The silylated products
were mainly the Markovnikov addition products when styrene
and 4-methylstyrene were used but anti-Markovnikov products
when α-methylstyrene was the chosen substrate. The use of 19F
1f
4-
90
42.7
26.9
23.3
23.3
45.6
100
100
methylstyrene
methylstyrene
methylstyrene
methylstyrene
2a 4-
2d 4-
2e 4-
88.5
100
100
100
13
2f
4-
methylstyrene
methylstyrene
methylstyrene
2d α-
2e α-
33
1
NMR and H NMR with fluorinated substrates allowed us to
observe some reaction intermediates, and we propose that the
possible reaction mechanism is similar to that previously
reported by Zargarian.35 These catalysts have the potential to
be active in other reactions, and further studies are underway.
were carried out with fluorostyrene (1 mmol) and PhSiH3
(1.3 mmol) using three sets of reaction conditions: (I)
1 mol % of catalyst at 25 °C, (II) 0.5 mol % of catalyst at
60 °C, and (III) 1 mol % of catalyst at 60 °C. Among these
experiments, those including 1e as catalyst and 2-fluorostyrene
and 4-fluorostyrene as substrates were chosen to rationalize the
experimental observations (see the Supporting Information for
more details). As shown in Figure 2, when the different sets of
EXPERIMENTAL SECTION
■
General Procedures. All reactions were performed under a dry
nitrogen or argon atmosphere using standard Schlenk techniques. Dry
and oxygen-free solvents were always used unless otherwise stated.
The starting materials Ni(COD)2,37 [allyl-Ni(COD)][BAr4 ], [Me-
38
F
allyl-Ni(COD)][BAr4 ],38 1-methyl-3-(2-picolyl)imidazolium bromide
F
(a),24 1-isopropyl-3-(2-picolyl)imidazolium bromide (b),30a 1-butyl-3-
(2-picolyl)imidazolium bromide (c),30a 1-phenyl-3-(2-picolyl)-
imidazolium bromide (d),34 1-methyl)-3-(2-picolyl)benzoimidazolium
bromide (e),30b and 1-methyl-3-(2-picolyl)-4,5-dichloroimidazolium
bromide (f)34 were prepared according to the literature methods.
NMR spectra were recorded using Varian INOVA 600 and 400 MHz
spectrometers. Chemical shifts are given in ppm from TMS (1H and
13C{1H}) and J values in Hz; NMR signal assignments were confirmed
by 2D NMR experiments. Microanalysis was performed on a LECO
CHNS-932 elemental analyzer at the Servicio Central de Ciencia y
́
́
Tecnologıa, Universidad de Cadiz. The GC/MS analyses of the
catalytic mixtures were performed using an Agilent 6890N system.
Preparation of Allyl−Nickel Complexes 1a−f. Imidazolium
salts of the ligands a−f (1.0 mmol) and silver oxide (0.12 g, 0.5 mmol)
were stirred in dichloromethane (25 mL) at room temperature for 3 h.
The resulting mixture was then filtered through Celite. [(allyl)Ni(COD)]-
[BAr4F] (0.91 g, 0.85 mmol) was added to the solution, and the mixture
was stirred at room temperature for 3 h. After removal of the formed
silver halide by filtration through Celite, the solvent was evaporated under
vacuum. The residual orange-brown oil was washed with petroleum ether
and dried under vacuum to give an orange-brown solid.
Figure 2. Hydrosilylation of fluorostyrenes with 1 mol % of 1e.
conditions are compared, it is clear that at 60 °C the reaction
occurs within minutes. However, at room temperature a lower
reaction rate was observed and lower conversions were obtained.
The fast conversion of 2-fluorostyrene in 1-(2-fluorophenyl)-
ethyl)diphenylsilane (A) can be observed in Figure 3. Also, it is
important to note that the main signals in the 19F NMR
2179
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Organometallics
Article
Figure 3. 19F NMR spectra (C6D6, 60 °C) with 1 mmol of 2-fluorostyrene, 1.3 mmol of PhSiH3, and 1 mol % of 1e: (1) 0.13 min; (2) 2.28 min; (3)
6.56 min; (4) 12.68 min.
[Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B(ArF)4] (1a). Yield: 0.67 g, 70%.
(m, 2H, CH2 Bu), 13C{1H} NMR (acetone-d6, 298 K): δ 175.87 (CIm),
155.49 (Cpy), 155.44 (Cipso), 140.43 (Cpy), 126.41 (Cpy), 125.28 (Cpy),
123.04 (CIm), 121.76 (CIm), 116.57 (Callyl), 71.14 (Callyl), 54.28
(CH2 bridge), 47.96 (Callyl). Anal. Calcd for C48H34BF24N3Ni: C, 48.93;
H, 2.91; N, 3.57. Found: C, 48.81; H, 3.00; N, 3.49.
3
1H NMR (acetone-d6, 298 K): δ 9.022 (d, 1H, JH−H = 5.28, 1Hpy),
8.091 (vt, 1H, 3JH−H = 5.28, JH−H = 1.46, 1Hpy), 7.875 (d, 1H, 3JH−H
=
F
F
7.62, 1Hpy), 7.804 (s, 8H, BAr4 ), 7.667 (s, 4H, BAr4 ), 7.555 (t, 1H,
3
3JH−H = 7.62, JH−H = 1.46,1Hpy), 7.540 (d, 1H, JH−H = 1.76, 1HIm),
[Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B(ArF)4] (1d). Yield: 0.61 g, 60%.
3
2
7.307 (d, 1H, JH−H = 1.76, 1HIm), 5.798 (d, 1H, JH−H = 14.94,
3
1H NMR (acetone-d6, 298 K): δ 9.167 (d, 1H, JH−H = 4.68, 1Hpy),
2
CH2 bridge), 5.798 (q, 1H, 1Hallyl CH), 5.611 (d, 1H, JH−H = 14.94,
3
3
3
CH2 bridge); 3.882 (s, 3H, CH3), 3.849 (d, 1H, JH−H = 2.34, 1Hallyl),
8.129 (t, 1H, JH−H = 7.03, 1Hpy), 8.004 (d, 1H, JH−H = 7.91, 1Hpy),
3
3
F
3
3.513 (d, 1H, JH−H = 7.04, 1Hallyl), 3.241 (d, 1H, JH−H = 14.35,
overlapped with the BAr4 (2 × 1HIm), 7.574 (vt, 1H, JH−H = 7.61,
1Hallyl), 2.504 (d, 1H, 3JH−H = 13.19, 1Hallyl). 13C{1H} NMR (acetone-
1Hpy), 6.122 (d, 1H, 2JH−H = 14.65, CH2 bridge), 5.885 (d, 1H, 2JH−H
=
F
3
d6, 298 K): δ 176.05 (CIm), 162.54 (BAr4 ), 155.49 (Cpy), 155.29
(Cipso), 140.38 (Cpy), 135.46 (BAr4 ), 129.81 (BAr4 ), 125.69 (Cpy),
124.78 (CIm), 124.45 (Cpy), 122.68 (CIm), 118.28 (BAr4 ), 116.81
14.65, CH2 bridge), 5.656 (q, 1H, 1Hallyl), 3.874 (d, 1H, JH−H = 7.03,
1Hallyl), 3.175 (d, 1H, 3JH−H = 14.36, 1Hallyl), 2.414 (sbroad, 1H, 1Hallyl),
1.933 (d, 1H, 3JH−H = 13.48, 1Hallyl), phenyl group signals are between
7 and 8 ppm. 13C{1H} NMR (acetone-d6, 298 K): δ 176.40 (CIm),
155.05 (Cpy), 154.26 (Cipso), 139.71 (Cpy), 139.64 (Cpy), 124.74 (Cpy),
F
F
F
(C12), 70.93 (Callyl), 54.29 (CCH bridge), 48.32 (Callyl), 37.75 (CCH ).
2
3
Anal. Calcd for C45H28BF24N3Ni: C, 47.57; H, 2.48; N, 3.70. Found:
C, 47.69; H, 2.54; N, 3.58.
F
overlapped with the BAr4 (C4‑Im) and (C5‑Im), 115.52 (Callyl), 69.52
[Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B(ArF)4] (1b). Yield: 0.49 g, 50%.
1H NMR (acetone-d6, 298 K): δ 8.74 (d, 1H, 3JH−H = 5.45, 1Hpy), 7.79
(Callyl), 53.94 (CH2 bridge), 49.22 (Callyl), phenyl group signals are
between 120 and 130 ppm. Anal. Calcd for C50H30BF24N3Ni: C, 50.12;
H, 2.52; N, 3.51. Found: C, 49.98; H, 2.30; N, 3.29.
3
3
(vt, 1H, JH−H = 7.57, 1Hpy), 7.62 (d, 1H, JH−H = 8.03, 1Hpy), 7.36
(vs, 1H, 1HIm), 7.25 (t, 1H, 3JH−H = 7.76, 1Hpy), 7.11 (vs, 1H, 1HIm),
5.45 (sbroad, 2H, CH2 bridge), 5.23 (m, 1H, 1Hallyl), 4.53 (m, 1H, 1HIsp),
1.93 (vs, 1H, 1Hallyl), 1.33 (vs, 1H, 1Hallyl), 1.20 (s, 6H, 2 × CH3 Isp),
0.58 (vs, 1H, 1Hallyl); 0.57 (vs, 1H, 1Hallyl). 13C{1H} NMR (acetone-
d6, 298 K): δ 175.19 (CIm), 154.84 (Cpy), 150.90 (Cipso), 139.74 (Cpy),
128.43 (Callyl), 125.86 (Cpy), 124.72 (Cpy), 124.00 (CIm), 123.11
(CIm), 54.10 (CH2 bridge), 52.50 (CIsp), 27.82 (Callyl), 22.82 (CIsp),
22.08 (Callyl). Anal. Calcd for C47H32BF24N3Ni: C, 48.49; H, 2.77; N,
3.61. Found: C, 48.57; H, 2.65; N, 3.47.
[Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B(ArF)4] (1e). Yield: 0.50 g, 50%.
1H NMR (acetone-d6, 298 K): δ 9.08 (d, 1H, 3JH−H = 5.27, 1Hpy), 8.08
(s, 2H, 2Hbenzo), 7.95 (t, 1H, 3JH−H = 7.62, 1Hpy), 7.67 (d, 1H, 3JH−H
=
3
7.91, 1Hpy), 7.57 (s, 2H, 2Hbenzo), 7.43 (vt, 1H, JH−H = 8.8, 1Hpy),
2
6.097 (d, 2H, JH−H = 15.66, CH2 bridge), 5.954 (q, 1H, 1Hallyl), 4.53
(sbroad, 1H, 1Hallyl), 4.12 (s, 3H, CH3), 2.30 (s, 1H, 1Hallyl), 2.23 (s, 1H,
1Hallyl), 1.46 (s, 1H, 1Hallyl). 13C{1H} NMR (acetone-d6, 298 K): δ
155.03 (Cpy), 154.48 (Cipso), 153.31 (CIm), 139.98 (Cbenzo), 126.09
(Cbenzo), 124.94 (Cpy), 123.87 (Cpy), 123.40 (CIm), 120.67 (CIm),
111.24 (Callyl), 110.60 (Cpy), 50.10 (CH2 bridge), 34.24 (CH3), 32.09
(Callyl), 27.93 (Callyl). Anal. Calcd for C49H30BF24N3Ni: C, 49.61; H,
2.55; N, 3.54. Found: C, 49.78; H, 2.60; N, 3.48.
[Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B(ArF)4] (1c). Yield: 0.40 g, 40%.
1H NMR (acetone-d6, 298 K): δ 9.19 (d, 1H, 3JH−H = 4.4, 1Hpy), 8.25
(vt, 1H, 3JH−H = 7.33, 1Hpy), 8.05 (d, 1H, 3JH−H = 7.33, 1Hpy), 7.74 (s,
[Ni(η3-CH2CHCH2)(NHC-κ2C,N)][B(ArF)4] (1f). Yield: 0.61 g, 60%. 1H
3
1H, 1HIm), 7.72 (t, 1H, JH−H = 6.16, 1Hpy), 7.55 (s, 1H, 1HIm) 6.01
3
(doverlapped, 1H, CH2 bridge), 5.83 (d, 1H, 2JH−H = 14.08, CH2 bridge), 4.35
NMR (acetone-d6, 298 K): δ 8.85 (d, 1H, JH−H = 3.81, 1Hpy), 7.909
(t, 1H, 3JH−H = 7.33, 1Hpy), 7.83 (d, 1H, 3JH−H = 7.04, 1Hpy), 7.39 (t,
1H, 1Hpy), 5.95 (s, 1H, CH2 bridge), 5.80 (sbroad, 1H, CH2 bridge), 5.48
(m, 1H, 1Hallyl), 3.95 (vs, 1H, 1Hallyl), 3.69 (s, 3H, CH3), 3.36 (vs, 1H,
3
3
(t, 2H, JH−H = 7.04, CH2Bu), 4.02 (d, 1H, JH−H = 6.74, 1Hallyl), 3.65
3
(vs, 1H, 1Hallyl), 3.46 (d, 1H, JH−H = 14.08, 1Hallyl), 2.62 (vs, 1H,
1Hallyl), 1.53 (m, 2H, CH2Bu), 1.09 (t, 3H, 3JH−H = 7.23, CH3 Bu), 1.01
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1
Figure 4. H NMR spectrum after reaction of 2-fluorostyrene with PhSiH3 catalyzed by 1e.
1Hallyl), 2.38 (vs, 1H, 1Hallyl), 0.86 (vs, 1H, 1Hallyl). 13C{1H} NMR
(acetone-d6, 298 K): δ 155.36 (Cpy), 155.30 (Cipso), 153.59 (CIm),
139.31 (Cpy), 126.03 (Cpy), 125.32 (Cpy), 124.18 (CIm), 122.30 (CIm),
116.79 (Callyl), 70.48 (Callyl), 51.56 (CH2 bridge), 35.86 (CH3), 28.23
(Callyl). Anal. Calcd for C45H26BCl2F24N3Ni: C, 44.85; H, 2.17; N,
3.49. Found: C, 45.04; H, 2.28; N, 3.38.
[Ni(η3-CH2CCH3CH2)(NHC-κ2C,N)][B(ArF)4] (2b). Yield: 0.45 g, 45%.
1H NMR (acetone-d6, 298 K): δ 9.01 (d, 1H, 3JH−H = 5.28, 1Hpy), 7.84
3
(d, 1H, JH−H = 7.74, 1Hpy), 7.57 (t, 1H, JH−H = 7.62, JH−H = 1.76,
3
3
1Hpy), 7.44 (t, 1H, JH−H = 6.83, 1Hpy), 7.38 (d, 1H, JH−H = 1.75,
1HIm), overlapped with the BAr4F (1HIm), 5.51 (sbroad, 2H, CH2 bridge),
4.84 (m,1H, 1HIsp), 2.07 (s, 1H, 1Hallyl), 1.68 (s, 1H, 1Hallyl), 1.50 (d,
6H, 2 × CH3 Isp), 0.87 (s, 1H, 1Hallyl), 0.84 (s, 1H, 1Hallyl). 13C{1H}
NMR (acetone-d6, 298 K): δ 178.56 (CIm), 154.71 (Cpy), 150.02
(Cipso), 128.47 (Callyl), 126.14 (Cpy), 125.66 (Cpy), 124.64 (Cpy),
123.08 (CIm), 120.72 (CIm), 53.85 (CH2 bridge), 52.61 (CIsp), 28.98
(Callyl), 27.81 (CH3 allyl), 22.73 (CH3 Isp), 21.95 (Callyl). Anal. Calcd for
C48H34BF24N3Ni: C, 48.93; H, 2.91; N, 3.57. Found: C, 49.03; H,
3.09; N, 3.64.
Preparation of Methylallyl−Nickel Complexes 2a−f. Imid-
azolium salts of the ligands a−f (1.0 mmol) and silver oxide (0.12 g,
0.5 mmol) in dichloromethane (25 mL) were stirred at room temperature
for 3 h. The resulting mixture was then filtered through Celite.
F
[Me-(allyl)Ni(COD)][BAr4 ] (0.92 g, 0.85 mmol) was added to the
solution, and the mixture was stirred at room temperature for 3 h.
After removal of the formed silver halide by filtration through Celite,
the solvent was evaporated under vacuum. The residual orange-brown
oil was washed with petroleum ether and dried under vacuum to give
an orange-brown solid.
[Ni(η3-CH2CCH3CH2)(NHC-κ2C,N)][B(ArF)4] (2c). Yield: 0.35 g, 35%.
1H NMR (acetone-d6, 298 K): δ 8.84 (d, 1H, 3JH−H = 5.28, 1Hpy), 7.81
(t, 1H, 3JH−H = 7.69, 1Hpy), 7.72 (d, 1H, 3JH−3H = 7.69, 1Hpy), 7.72 (s,
1H, 1HIm), 7.37 (s, 1H, 1HIm), 7.29 (t, 1H, JH−H = 6.59, 1Hpy), 6.66
[Ni(η3-CH2CCH3CH2)(NHC-κ2C,N)][B(ArF)4] (2a). Yield: 0.64 g, 65%.
3
1H NMR (acetone-d6, 298 K): δ 9.030 (d, 1H, JH−H = 5.12, 1Hpy),
(sbroad, 1H, CH2 bridge), 5.46 (sbroad, 1H, CH2 bridge), 4.03 (t, 2H, JH−H
=
3
7.26, 2Hbutyl), 3.45 (s, 3H, 3HCH3allyl), 3.00 (s, 1H, 1Hallyl), 2.24 (s, 1H,
1Hallyl), 1.58 (s, 1H, 1Hallyl), 1.21 (m, 2H, 2Hbutyl), 0.71 (s, 1H, 1Hallyl),
0.75 (t, 3H, JH−H = 7.25, 3Hbutyl), 0.67 (m, 2H, 2Hbutyl). 13C{1H}
NMR (acetone-d6, 298 K): δ 175.45 (CIm), 154.52 (Cpy), 154.50
(Cipso), 139.47 (Cpy), 128.25 (Callyl), 125.39 (CIm); 124.50 (Cpy),
122.12 (CIm), 121.24 (CIm); 66.61 (CH3 allyl), 53.70 (CH2 bridge), 49.87
(Cbutyl), 47.49 (Callyl), 27.32 (Cbutyl), 21.55 (Callyl), 21.19 (Cbutyl), 12.02
(Cbutyl). Anal. Calcd for C49H36BF24N3Ni: C, 49.36; H, 3.04; N, 3.52.
Found: C, 49.25; H, 3.57; N, 3.40.
8.076 (t, 1H, JH−H = 5.12, JH−H = 1.76, 1Hpy), 7.857 (d, 1H, JH−H
=
3
7.62, 1Hpy), 7.547 (t, 1H, JH−H = 7.62, JH−H = 1.76,1Hpy), 7.527 (d,
1H, 3JH−H = 1.75, 1HIm), 7.303 (d, 1H, 3JH−H = 1.75, 1HIm), 5.757 (d,
1H, 2JH−H = 15.24, CH2 bridge), 5.561 (d, 1H, 2JH−H = 15.24, CH2 bridge),
3.888 (s, 3H, CH3), 3.619 (d, 1H, 3JH−H = 3.23, 1Hallyl); 3.224 (vs, 1H,
1Hallyl), 3.133 (vs, 1H, 1Hallyl), 2.312 (vs, 1H, 1Hallyl), 2.190 (s, 1H,
CH3 allyl). 13C{1H} NMR (acetone-d6, 298 K): δ 176.53 (CIm), 155.68
(Cpy), 155.38 (Cipso), 140.52 (Cpy), 126.72 (Cpy), 125.47 (Cpy), 124.02
(CIm), 123.84 (CIm), 121.31 (Callyl), 70.12 (Callyl), 54.49 (CH2 bridge),
48.78 (Callyl), 37.95 (CH3), 23.49 (CH3 allyl).). Anal. Calcd for
C46H30BF24N3Ni: C, 48.03; H, 2.63; N, 3.65. Found: C, 47.79; H,
2.55; N, 3.72.
[Ni(η3-CH2CCH3CH2)(NHC-κ2C,N)][B(ArF)4] (2d). Yield: 0.62 g, 60%.
3
1H NMR (acetone-d6, 298 K): δ 9.006 (d, 1H, JH−H = 5.56, 1Hpy),
3
3
8.012 (d, 1H, JH−H = 7.62, 1Hpy), 7.993 (t, 1H, JH−H = 7.61, 1Hpy),
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Organometallics
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3
F
7.501 (t, 1H, JH−H = 7.03, 1Hpy), overlapped with the BAr4 (2 ×
Table 5. Summary of Crystallographic Data for 1d
1HIm), 5.897 (d, 1H, 2JH−H = 14.95, CH2 bridge), 5.660 (d, 1H, 2JH−H
=
formula
C54H40BF24N3NiO
1272.41
14.65, CH2 bridge), 3.486 (vs, 1H, 1Hallyl), 2.039 (vs, 1H, 1Hallyl), 1.634
(vs, 1H, 1Hallyl), 1.943 (s, 3H, CH3 allyl), phenyl group signals are
between 7 and 8 ppm. 13C{1H} NMR (acetone-d6, 298 K): δ 177.68
(CIm), 155.93 (Cpy), 155.14 (Cipso), 140.56 (Cpy), 135.62 (Cpy),
fw
T (K)
100
cryst size (mm)
0.59 × 0.54 × 0.27
monoclinic
C2/c
F
131.18 (Cpy), overlapped with the BAr4 (C4‑Im) and (C5‑Im), 121.38
cryst system
(Callyl), 54.92 (CH2 bridge), 31.17 (Callyl), 28.59 (Callyl), 23.28 (CH3 allyl),
phenyl group signals are between 120 and 130 ppm. Anal. Calcd for
C51H32BF24N3Ni: C, 50.53; H, 2.66; N, 3.47. Found: C, 50.70; H,
2.78; N, 3.62.
space group
cell params (Å, deg)
a, Å
b, Å
30.180(6)
12.912(3)
28.568(6)
93.67(3)
11 109(4)
8
[Ni(η3-CH2CCH3CH2)(NHC-κ2C,N)][B(ArF)4] (2e). Yield: 0.51 g, 50%.
1H NMR (acetone-d6, 298 K): δ 8.87 (d, 1H, 3JH−H = 5.11, Hpy), 7.72
c, Å
3
3
β, deg
V (Å3)
Z
ρcalcd (g cm−3
μ(Mo Kα) (mm−1
(t, 1H, JH−H = 7.95, Hpy), 7.45 (d, 1H, JH−H = 7.72, Hpy), 7.34 (m,
1H, Hpy), 7.86 (m, 2H, Hbenzo), 7.21 (d-t, 2H, JH−H = 7.51, Hbenzo),
3
5.89 (sbroad, 2H, CH2 bridge), 3.38 (s, 3H, CH3), 3.92 (s, 3H, CH3 allyl),
2.10 (s, 1H, 1Hallyl), 2.05 (s, 1H, 1Hallyl), 0.65 (s, 1H, 1Hallyl), 0.64 (s,
1H, 1Hallyl). 13C{1H} NMR (acetone-d6, 298 K): δ 155.56 (Cpy),
155.11 (Cipso), 153.58 (CIm), 140.50 (Cbenzo), 129.12 (CIm), 128.08
(CIm), 126.56 (Callyl), 126.28 (Cbenzo), 125.55 (Cpy), 124.46 (Cbenzo),
111.82 (Cpy), 111.18 (Cpy), 67.52 (CH3), 50.83 (CH2 bridge), 34.65
(CH3 allyl); 28.52 (Callyl), 23.46 (Callyl). Anal. Calcd for
C50H32BF24N3Ni: C, 50.03; H, 2.69; N, 3.50. Found: C, 49.91; H,
2.51; N, 3.33.
)
1.522
)
0.472
F(000)
5136
max−min transmissn factors
range for data collection (deg)
index ranges
1.000−0.737
1.43 < θ < 25.14
−35 < h > 34; −15 < k > 14;
−32 < l > 33
no. of rflns collected
36 542
[Ni(η3-CH2CCH3CH2)(NHC-κ2C,N)][B(ArF)4] (2f). Yield: 0.57 g, 55%.
1H NMR (acetone-d6, 298 K): δ 9.05 (d, 1H, 3JH−H = 4.69, 1Hpy), 8.09
(t, 1H, JH−H = 7.92, JH−H = 1.76, 1Hpy), 8.00 (d, 1H, JH−H = 7.92,
1Hpy), 7.58 (t, 1H, JH−H = 5.57, JH−H = 1.47 Hz 1Hpy), 5.83 (sbroad, 1H,
CH2 bridge), 5.00 (sbroad, 1H, CH2 bridge), 3.88 (s, 3H, CH3), 3.87 (vs, 1H,
1Hallyl), 3.66 (vs, 1H, 1Hallyl), 2.31 (vs, 1H, 1Hallyl), 2.21 (s, 3H,
CH3 allyl), 0.83 (vs, 1H, 1Hallyl). 13C{1H} NMR (acetone-d6, 298 K): δ
158.79 (CIm), 155.36 (Cpy), 154.70 (Cipso), 140.70 (Cpy), 129.81
no. of unique rflns
9795
3
no. of obsd rflns (I > 2σI)
no. of params
8795
774
final R1, wR2 values (I > 2σI)
final R1, wR2 values (all data)
residual electron density peaks (e Å−3
0.0982, 0.2305
0.1076, 0.2373
1.681, −0.767
)
F
(BAr4 ), 128.14 (Callyl), 126.81 (Cpy), 125.53 (Cpy), 124.86 (CIm),
petroleum ether (10 mL) and filtered through a silica gel plug. The
silica gel was washed with several small portions of petroleum ether in
order to remove all traces of but-1-ene-1,3-diyldibenzene. The
resulting residue was dried under vacuum to constant weight.
Catalytic Hydrosilylation Studies. A Schlenk tube was loaded
with olefin (10 mmol), PhSiH3 (20 mmol), 1,2- dichloroethane
(1 mL), and the corresponding catalyst (1 mol %) under argon. The
system was heated to 60 °C using a paraffin bath over 4 h. The
reaction time was measured from the moment it was introduced at
60 °C. After this period of time, a dark brown solution was obtained.
The volatiles were pumped off, and the residue was treated with
petroleum ether, which was filtered through a silica gel plug. The silica
gel was washed with several small portions. The resulting residue was
dried under vacuum, and the corresponding hydrosilylation products
were observed in the form of yellowish oils. Their NMR properties
were compared with data in the literature.35a,36
123.59 (CIm), 51.46 (CH2 bridge), 36.16 (CH3), 36.00 (Callyl), 28.27
(Callyl), 23.24 (CH3 allyl). Anal. Calcd for C46H28BCl2F24N3Ni: C,
45.32; H, 2.31; N, 3.45. Found: C, 45.37; H, 2.46; N, 3.63.
Crystal Structure Analysis. A sample of 1d was recrystallized
from a mixture of diethyl ether and petroleum ether (bp 40−60 °C)
at −20 °C. A crystal of 1d suitable for X-ray structural determination was
mounted on a glass fiber and then transferred to the cold nitrogen gas
stream of a Bruker Smart APEX CCD three-circle diffractometer (T =
100 K) with a sealed-tube source and graphite-monochromated Mo
Kα radiation (λ = 0.710 73 Å) at the Servicio Central de Ciencia y
́
́
Tecnologıa de la Universidad de Cadiz. Four sets of frames were
recorded over a hemisphere of the reciprocal space by ω scans with
δ(ω) = 0.30 and an exposure of 10 s per frame. Correction for
absorption was applied by scans of equivalents using the SADABS
program.39 An insignificant crystal decay correction was also applied.
The structure was solved by direct methods and refined on F2 by full-
matrix least squares (SHELX97)40 by using all unique data. All non-
hydrogen atoms were refined anisotropically with hydrogen atoms
included in calculated positions (riding model). The allyl ligand was
refined split in two complementary orientations with site occupation
factors of 0.71 and 0.29, respectively. Also, three disordered CF3
groups in the anion were refined split into two complementary
orientations using displacement parameter restraints. The program
ORTEP-3 was used for plotting.41 Table 5 summarizes the crystal data
and data collection and refinement details for 1d. CCDC 836795
contains 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.
4-Fluorostyrene Hydrosilylation Kinetic Studies. In a NMR
tube was prepared a mixture of 4-fluorostyrene (0.5 mmol), PhSiH3
(1 mmol), 1,2-dichloroethane (300 μL), benzene-d6 (100 μL), and the
corresponding catalyst (1 mol %) under argon in a bath containing
N2(l)/EtOH. This mixture was monitored by NMR at 60 °C: 19F
NMR spectra were measured every 180 s during 1 h. Their NMR
properties were compared with data in the literature and confirmed by
CG-MS.
1H NMR for {1-(4-fluorophenyl)ethyl}phenylsilane (benzene-d6,
298 K): δ 1.19 (d, 3H, JH−H = 6.8, CH3), 2.73 (m, 2H, CH2), 4.15 (vd,
SiH2), aromatic signals 7.6−7.0 ppm.
1H NMR (4-fluorophenylethyl)phenylsilane (benzene-d6, 298 K): δ
1.25 (m, 2H, CH2), δ: 2.63 (m, 2H, CH2), 4.21 (vd, SiH2), aromatic
signals 7.6−7.0 ppm.
Catalytic Oligomerization Studies. A Schlenk tube was loaded
with styrene, 4-methylstyrene, or α-methylstyrene (10 mmol), 1,2-
dichloroethane (1 mL), and the corresponding catalyst (1 mol %)
under argon. The system was heated to 60 °C using a paraffin bath.
The reaction time was measured from the moment the compounds
were introduced at 60 °C. The reaction was quenched by addition of
methanol. The volatiles were pumped off, and the residue was treated
with methanol to yield a white oil of but-1-ene-1,3-diyldibenzene,
which was dried under vacuum. The distyrene was dissolved in
ASSOCIATED CONTENT
■
S
* Supporting Information
Figures, tables, and a CIF file giving catalytic screening results
and crystallographic data for compound 1d. This material is
available free of charge via the Internet at http://pubs.acs.org.
2182
dx.doi.org/10.1021/om200937d | Organometallics 2012, 31, 2175−2183

Organometallics
Article
(17) (a) Liu, A.; Zhang, X.; Chen, W. Organometallics 2009, 28, 4868.
(b) Berding, J.; Lutz, M.; Spek, A. L.; Bouwman, E. Organometallics
2009, 28, 1845. (c) Gu, S.; Chen, W. Organometallics 2009, 28, 909.
(d) Xi, Z.; Liu, B.; Chen, W. J. Org. Chem. 2008, 73, 3954.
(e) Matsubara, K.; Ueno, K.; Shibata, Y. Organometallics 2006, 25,
3422.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: carmen.puerta@uca.es (M.C.P.); pedro.valerga@uca.
es (P.V.).
Notes
(18) Dible, B. R.; Sigman, M. S. Inorg. Chem. 2006, 45, 20.
(19) Silva, L. C.; Gomes, P. T.; Veiros, L. F.; Pascu, S. I.; Duarte,
M. T.; Namorado, S.; Ascenso, J. R.; Dias, A. R. Organometallics 2006,
25, 4391−4403.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
́
(20) Campora, J.; de la Tabla, L. O.; Palma, P.; Alvarez, E.; Lahoz, F.;
We thank the Spanish MICINN (Projects CTQ2007-60137/
BQU and CTQ2010-15390) and “Junta de Andalucia” (PAIDI-
Mereiter, K. Organometallics 2006, 25, 3314−3316.
(21) (a) S, S.; Noh, E. K.; Lee, B. Y.; Han, J. W. J. Organomet. Chem.
2008, 693, 2171. (b) Benson, S.; Payne, B.; Waymouth, R. M. J. Polym.
Sci., Part A 2007, 45, 3637.
́
FQM188 and Project of Excellence P08-FQM-03538) for
financial support. L.B.J. acknowledges fellowship support from
́
“Junta de Andalucia” (ref. 2009-126).
(22) (a) McGuinness, D. S.; Mueller, W.; Wasserscheid, P.; Cavell,
K. J; Skelton, B. W.; White, A. H.; Englert, U. Organometallics 2002,
21, 175. (b) Mackinnon, A. L.; Baird, M. C. J. Organomet. Chem. 2003,
683, 114.
(23) McGuinness, D. S.; Saendig, N.; Yates, B. F.; Cavell, K. J. J. Am.
Chem. Soc. 2001, 123, 4029.
REFERENCES
■
(1) Wanzlick. Angew. Chem., Int. Ed. 1962, 1, 75−80.
(2) Wanzlick. Angew. Chem., Int. Ed. 1968, 7, 141−142.
(3) Arduengo, A. J.; Harlow, R. L.; Kline, M. J. Am. Chem. Soc. 1991,
113, 361.
(24) McGuinness, D. S.; Cavell, K. J. Organometallics 2000, 19, 4918.
(25) Díez-Gonzal
109, 3612−3676.
(26) Oertel, A. M.; Ritleng, V.; Chetcuti, M. J.; Veiros, L. F. J. Am.
Chem. Soc. 2010, 132, 13588−13589.
́
ez, S.; Marion, N.; Nolan, S. P. Chem. Rev. 2009,
(4) Hermann, W. A. Angew. Chem., Int. Ed. 2002, 41, 1290.
(5) (a) Penka, E. F.; Schalapfer, C. W.; Atanasov, M.; Albrecht, M.;
̈
Daul, C. J. Organomet. Chem. 2007, 692, 5709. (b) Díez-Gonzal
́
ez, S.;
Nolan, S. P. Coord. Chem. Rev. 2007, 251, 874.
(27) Oertel, A. M.; Freudenreich, J.; Gein, J.; Ritleng, V.; Veiros,
L. F.; Chetcuti, M. J. Organometallics 2011, 30, 3400−3411.
(28) (a) Poyatos, M.; Mata, J. A.; Peris, E. Chem. Rev. 2009, 109,
3677−3707. (b) Oliver, S.; Yang, L.; Raubenheimer, H. G.; Albrecht,
M. Chem. Rev. 2009, 109, 3445−3478.
(6) Zang, Y.; Ngeow, K. C.; Ying, J. Y. Org. Lett. 2007, 9, 3495.
(7) (a) McCormick, M. M.; Duong, H. A.; Zuo, G.; Louie, J. J. Am.
Chem. Soc. 2005, 127, 5030. (b) Duong, H. A.; Cross, M. J.; Louie, J.
J. Am. Chem. Soc. 2004, 126, 11438. (c) Louie, J.; Gibby, J. E.;
Farnworth, M. V.; Tekavec, T. N. J. Am. Chem. Soc. 2002, 124, 15188.
(d) Tekavec, T. N.; Zuo, G.; Simon, K.; Louie, J. J. Org. Chem. 2006,
71, 5834.
(8) For an example of cycloaddition of unsaturated hydrocarbons,
aldehydes, and ketones, see: Tekavec, T. N.; Louie, J. J. Org. Chem.
2008, 73, 2641.
́
(29) Jimenez-Tenorio, M.; Puerta, M. C.; Salcedo, I.; Valerga, P.;
de los Rios, I.; Mereiter, K. Dalton Trans 2009, 1842−1852.
(30) (a) Grundemann, A.; Kovacevic; Albrecht, M.; Faller, J. W.;
̈
Crabtree, R. H. J. Am. Chem. Soc. 2002, 124, 10473. (b) Jahnke, C. M.;
Pape, T.; Hahn, F. E. Eur. J. Inorg. Chem. 2009, 13, 1960−1969.
(31) (a) Campora, J.; Carmona, E.; Conejo, M. M. ES Patent
2200698, 2004. (b) Campora, J.; Conejo, M. M.; Reyes, M. L.;
Mereiter, K.; Passaglia, E. Chem. Commun. 2003, 78−79.
(32) (a) Ascenso, J. R.; Dias, A. R; Gomes, P. T.; Ramao, C. C.;
Pham, Q.-T.; Neibecker, D; Tkatchenko, I. Macromolecules 1989, 22,
998−1000. (b) Hong, M. S.; Qing, S.; Dong, M. H.; Wan, F. L.; Qi, S.;
Yong, Z. Organometallics 2004, 24, 331−334.
(9) For a recent review about [2 + 2 + 2] cycloaddition reactions,
see: Chopade, P. R.; Louie, J. Adv. Synth. Catal. 2006, 348, 2307.
(10) (a) Omar-Amrani, R.; Thomas, A.; Brenner, E.; Schneider, R.;
Fort, Y. Org. Lett. 2003, 5, 2311. (b) Kuhl, S.; Fort, Y.; Schneider, R.
J. Organomet. Chem. 2005, 690, 6169. (c) Desmarets, C.; Schneider, R.;
Fort, Y. J. Org. Chem. 2002, 67, 3029. (d) Gradel, B.; Brenner, E.;
Schneider, R.; Fort, Y. Tetrahedron Lett. 2001, 42, 5689.
(11) (a) Xi, Z.; Zhang, X.; Chen, W.; Fu, S.; Wang, D.
Organometallics 2007, 26, 6636. (b) Inamoto, K.; Kuroda, J.-i.;
Sakamoto, T.; Hiroya, K. Synthesis 2007, 2853. (c) Inamoto, K.;
Kuroda, J.-i.; Sakamoto, T.; Hiroya, K. Synthesis 2007, 2853.
(12) Buchowicz, W; Koziol, A.; Jerzykiewicz, L. B.; Lis, T.;
Pasynkiewicz, S.; Pecherzewska, A.; Pietrzykowski, A. J. Mol. Catal. A
2006, 257, 118−123.
(33) Ritleng, V.; Barth, C.; Brenner, E.; Milosevic, S.; Chetcuti, M. J.
Organometallics 2008, 27, 4223−4228.
́
(34) Fernandez, F. E.; Puerta, M. C.; Valerga, P. Organometallics
2011, 30, 5793−5802.
(35) (a) Fontaine, F. G.; Neguyen, R. V.; Zargarian, D. Can. J. Chem.
2003, 81, 129. (b) Chen, Y.; Sui-Seng, C.; Boucher, S.; Zargarian, D.
Organometallics 2005, 24, 149.
(36) (a) Fu, P. F.; Brard, Y. L.; Marks, T. J. J. Am. Chem. Soc. 1995,
117, 7157.
(37) Billington, D. C. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon Press: Oxford, U.K., 1991; Vol. 3, p
423.
́
(13) Moreno-Manas, M.; Perez, M.; Pleixats, R. J. Org. Chem. 1996,
̃
61, 2346.
(14) (a) Matsubara, K; Ueno, K.; Koga, Y.; Hara, K. J. Org. Chem.
2007, 72, 5069. (b) Kelly, R. A. III; Scott, N. M.; Díez-Gonzalez, S.;
Stevens, E. D.; Nolan, S. P. Organometallics 2005, 24, 3442.
́
(38) Kesti, M. R.; Coates, G. W.; Waymouth, R. M. J. Am. Chem. Soc.
1992, 114, 9679.
(15) Ritleng, V.; Oerel, A. M.; Chetcuti, M. J. Dalton Trans. 2010, 39,
8153−8160.
(39) Sheldrick, G. M. SADABS 2001 version; University of Gottingen,
̈
(16) (a) Inamoto, K.; Kuroda, J.-i.; Kwon, E.; Hiroya, K.; Doi, T. J.
Organomet. Chem. 2009, 694, 389. (b) Kuroda, J.-i.; Inamoto, K.;
Hiroya, K.; Doi, T. Eur. J. Org. Chem. 2009, 2251. (c) Zhou, Y.; Xi, Z.;
Chen, W.; Wang, D. Organometallics 2008, 27, 5911. (d) Liao, C.-Y.;
Chan, K.-T.; Chang, Y.-C.; Chen, C.-Y.; Tu, C.-Y.; Hu, C.-H.; Lee, H.
M. Organometallics 2007, 26, 5826. (e) Lee, C.-C.; Ke, W.-C; Chan,
K.-T.; Lai, C.-L.; Hu, C.-H.; Lee, H. M. Chem. Eur. J 2007, 13, 582.
(f) Inamoto, K.; Kuroda, J.-i.; Hiroya, K.; Noda, Y.; Watanabe, M.;
Sakamoto, T. Organometallics 2006, 25, 3095. (g) Chiu, P. L.; Lai,
C.-L.; Chang, C.-F.; Hu, C.-H.; Lee, H. M. Organometallics 2005, 24,
6169. (h) McGuinness, D. S.; Cavell, K. J.; Skelton, B. W.; White, A.
H. Organometallics 1999, 18, 1596.
Gottingen, Germany, 2001.
̈
(40) (a) Sheldrick, G. M. SHELXTL version 6.10, Crystal Structure
Analysis Package; Bruker AXS, Madison, WI, 2000. (b) Sheldrick, G.
M. Acta Crystallogr. 2008, A64, 112−122.
(41) Farrugia, L. J. ORTEP-3 for Windows, version 1.076. J. Appl.
Crystallogr. 1997, 30, 565.
2183
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