[Pd(4-R3Si-IPr)(allyl)Cl], a Family of Silyl-Substituted Pd-NHC Complexes: Catalytic Systems for the Buchwald-Hartwig Amination

Article abstract of DOI:10.1021/acs.organomet.8b00757

A family of Pd-IPr complexes (1Pd-6Pd) featuring electropositive and bulky R₃Si substituents at the 4-position of the NHC ring was prepared and fully characterized. The catalytic performance of 1Pd (R₃Si = SiMe₃) and 3Pd (R₃Si = Si(allyl)Me₂) in the Buchwald-Hartwig amination was excellent, notably outperforming those of other previously reported catalytic systems by requiring shorter reaction times, lower catalyst loadings, and milder reaction conditions. Furthermore, a systematic evaluation of both the electronic and steric influences of the 4-R₃Si-IPr ligand on the overall catalytic performance of 1Pd-6Pd revealed that electronic rather than steric factors play a dominant role.

Full text of DOI:10.1021/acs.organomet.8b00757

Article
pubs.acs.org/Organometallics
Cite This: Organometallics XXXX, XXX, XXX−XXX
[
Pd(4‑R Si-IPr)(allyl)Cl], a Family of Silyl-Substituted Pd−NHC
3
Complexes: Catalytic Systems for the Buchwald−Hartwig Amination
,
†,‡
§,∥
†,‡
†,‡
§
†,§
Norihisa Fukaya,*
Kazuhiro Matsumoto, Vladimir Ya. Lee, Yukio Takagi, Junpei Kuwabara, Takaki Kanbara,§
Yoong-Kee Choe, and Jun-Chul Choi*
Tomoteru Mizusaki, Kouhei Hatakeyama, Yuto Seo, Yuuya Inaba,
†
⊥
∥
†
,†,§
†National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki
3
05-8565, Japan
‡
Department of Chemistry, Faculty of Science, Ibaraki University, Mito, Ibaraki 310-8512, Japan
§
Tsukuba Research Center for Energy Materials Science (TREMS), Graduate School of Pure and Applied Sciences, University of
Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8573, Japan
∥
N.E. CHEMCAT Corporation, 678 Ipponmatsu, Numazu, Shizuoka 410-0314, Japan
⊥
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba,
Ibaraki 305-8571, Japan
*
S Supporting Information
ABSTRACT: A family of Pd−IPr complexes (1Pd−6Pd) featuring electropositive
and bulky R Si substituents at the 4-position of the NHC ring was prepared and fully
3
characterized. The catalytic performance of 1Pd (R Si = SiMe ) and 3Pd (R Si =
3
3
3
Si(allyl)Me ) in the Buchwald−Hartwig amination was excellent, notably out-
2
performing those of other previously reported catalytic systems by requiring shorter
reaction times, lower catalyst loadings, and milder reaction conditions. Furthermore, a
systematic evaluation of both the electronic and steric influences of the 4-R Si-IPr
3
ligand on the overall catalytic performance of 1Pd−6Pd revealed that electronic
rather than steric factors play a dominant role.
INTRODUCTION
changeably in favor of the oxidative addition and the reductive
elimination processes.
■
Making bonds to carbon is the ultimate goal of organic
chemistry. Among a variety of such bonds, the C−N bond (i.e.,
amine formation) is of paramount importance. The Pd-
catalyzed C−N cross-coupling reaction of amines and aryl
halides, thus forming arylamines that are ubiquitous in natural
products and pharmaceuticals, is one of the numerous
synthetic procedures available for the making of carbon−
nitrogen bonds. This benchmark case is called the Buchwald−
Hartwig amination reaction, named after the milestone reports
of Buchwald and Hartwig published first in 1994, and is an
indispensable tool in the organic chemists’ synthetic arsenal.
Within its commonly recognized catalytic cycle, the palladium
precatalyst first forms LPd , which is the true catalytically
The rates of the two key steps of the overall amination
catalytic cycle, namely oxidative addition and reductive
elimination, are mostly dependent on the electronic and steric
factors of ligand L. As very strong σ-donors manifesting a
remarkably shielding steric pattern, N-heterocyclic carbenes
(
NHC) have emerged as a reasonable alternative and very
prominent alternative of tertiary phosphines, in many aspects
4
outperforming them as ligands of choice. It is well-established
that the very strong σ-electron-donating ability of the NHC
1
0
ligands stabilizes the low-coordinated catalytically active LPd
species, thus accelerating the oxidative addition step,
2
,3
5
,6
whereas the high steric crowding caused by the bulky NHC
ligands facilitates the reductive elimination of the product in
0
6
,7
active species. This then undergoes an oxidative addition of an
aryl halide, followed by an amine coordination at Pd and a
subsequent deprotonation of the resulting intermediate by a
base. The catalytic cycle is finally completed with a reductive
elimination, thereby forming the final product, arylamine, and
the last step of the catalytic cycle.
Recently, Cesar and Lavigne et al. reported their rational
́
synthetic strategy for novel highly effective Buchwald−Hartwig
amination Pd−NHC precatalysts, based on a simple
0
regenerating the LPd intermediate. Notably, the amination
Received: October 17, 2018
rate-determining step is strongly case-sensitive, being inter-
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00757
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Article
modification of a 1,3-bis(2,6-diisopropylphenyl)-2H-imidazol-
derivatives [4-(R Si)-IPr] 1−6 under mild reaction conditions.
3
2
-ylidene (IPr) ligand at the 4- or 4,5-positions of the NHC
Notably, except for [4-(Me Si)-IPr] 1, which has been
3
8
12
11
backbone using Me N-substituents. Notably, the remarkable
previously isolated by Bertrand and Robinson, the isolation
and full characterization of the obtained NHC derivatives have
not been previously reported before.
2
effect of the amino groups enhanced the overall electron-
donating ability of the IPr ligand, thereby improving the
catalytic activity of the Pd−NHC precatalysts. As a result, the
amination of p-chloroanisole with morpholine catalyzed by
Synthesis of the Pd Complexes. As a Pd precatalyst for
the Buchwald−Hartwig amination, we chose a mononuclear π-
allyl palladium complex [(NHC)Pd(allyl)Cl] due to its
{
Pd[4,5-(Me N) -IPr](3-chloropyridine)Cl } proceeded very
2 2 2
1
3
smoothly, reaching full conversion in just 2 h. Such a
remarkable catalytic performance is quite comparable to
those of the best Pd−NHC complexes known for arylamina-
straightforward synthesis and high thermal stability.
Typically, such complexes can be prepared via a simple “free
carbene” synthetic protocol developed by Nolan and co-
8
14
tion, as well as superior phosphine−Pd systems. Furthermore,
workers, which includes the addition of 2 equiv of NHC
{
Pd[4,5-(Me N) -IPr](3-chloropyridine)Cl } can also very
ligand to readily available commercial [Pd(allyl)Cl] . The
2
2
2
2
effectively catalyze amination of aryl tosylates, which is hardly
activation of such a precatalyst resulted in the generation of
9
0
achieved with other catalytic systems. Moreover, by further
transient [(NHC)Pd ], which is a true catalytic species,
increasing the steric bulk of the NHC backbone, the same
thereby promoting a wide range of cross-coupling reactions
authors recently developed novel Pd−IPr precatalyst featuring
(including Buchwald−Hartwig amination) using low catalyst
13
a i-Pr N-substituent at the 4-position of the NHC cycle,
loadings and mild reaction conditions.
2
thereby achieving an excellent catalytic performance in the
Therefore, herein we applied Nolan’s procedure to prepare
our Pd precatalyst complexes by reacting commercial [Pd-
10
arylation of even bulkier primary amines.
Being inspired by the above-mentioned results on the
modification of the NHC backbone of Pd−IPr precatalysts
with electron-donating dialkylamino groups significantly
(
allyl)Cl] with 4-(R Si)-IPr 1−6 at room temperature. When
2
3
performed in THF, the reaction was typically completed within
1
h, forming a series of the corresponding NHC−palladium
8
−10
improving their catalytic activity,
we decided to explore
complexes {[4-(R Si)-IPr]Pd(allyl)Cl} 1Pd−6Pd, in moderate
to good yields (Scheme 2).
3
the catalytic potential of precatalysts having not π- (like NR2)
but σ-electron-donating group at the 4-position of the NHC
ligand. In this regard, the highly electropositive silyl-group R Si
was the substituent of choice, as such a σ-donating group was
anticipated to remarkably enhance the electron-donating
3
Scheme 2. Synthesis of {[4-(R Si)-IPr]Pd(allyl)Cl}
Complexes 1Pd−6Pd
3
ability of the [4-(R Si)-IPr] ligand and accordingly improve
3
the overall catalytic performance of the new palladium
complexes featuring such NHC ligands.
RESULTS AND DISCUSSION
■
Synthesis of the NHC Ligands. A series of novel NHC
ligands, containing a bulky silyl group at the 4-position of the
five-membered ring heterocycle, was readily available by a
straightforward procedure, which included an initial lithiation
of the commercially available precursor IPr with n-BuLi in
hexane, thus forming the corresponding lithium salt, followed
by its reaction with silyl chloride in THF to afford the
corresponding 4-silyl-substituted NHC ligands (Scheme 1).
The synthesis of lithium derivative Li−IPr was performed
according to a straightforward gram-order-scale protocol
The isolation of complexes 1Pd−6Pd was also rather
straightforward: a standard workup procedure and simple
recrystallization from dry hexane were employed to afford the
analytically pure samples. The structures of complexes 1Pd−
6Pd were undoubtedly established by means of spectroscopic
and analytical methods, and two of them, 1Pd and 2Pd, were
crystallographically characterized (Figures 1 and 2, respec-
tively).
11
reported by Robinson, which allowed for its quantitative
isolation and full characterization. Coupling of Li−IPr with
silyl chloride R SiCl resulted in a high-yield formation of NHC
3
Scheme 1. Synthesis of Li−IPr Salt and Its Subsequent
Silylation Forming Target [4-(R Si)-IPr] Ligands 1−6
3
As is diagnostic for such Pd(allyl) complexes, a distorted
square-planar coordination at the palladium center was
observed in both 1Pd and 2Pd. The allyl group was
trihapto-coordinated to the metal center, and the imidazoli-
dene ring of the NHC ligand was practically planar with a
rather negligible folding (N1−C6−C7−N2 torsion angle:
−
0.40° for 1Pd and 1.28° for 2Pd). The bond lengths and
angles in both complexes were unexceptional. More specifi-
cally, the bond between the Pd atom and the NHC ligand,
Pd1−C1, which had a length of 2.040(2) Å for 1Pd and
2.0552(16) Å for 2Pd, was quite typical to the one reported for
other [(NHC)Pd(allyl)Cl] complexes, which is usually in the
narrow range of 2.00−2.04 Å (e.g., 2.040(11) Å for
B
DOI: 10.1021/acs.organomet.8b00757
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Article
rings (on the sterically unhindered site of the IPr ligand) was
still able to rotate freely about the Cipso−N bond. Such an
NMR distinction of 1Pd in different solvents might be ascribed
to the potential complexation of THF, which breaks the
molecular symmetry.
Catalytic Performance of NHC−Pd Complexes 1Pd−
Pd in the Buchwald−Hartwig Amination. Next, we
6
tested the catalytic performance of newly synthesized Pd−
NHC complexes 1Pd−6Pd in the Buchwald−Hartwig
amination. In this respect, we reacted chlorobenzene with di-
n-butylamine and each of the synthesized complexes in 1,2-
dimethoxyethane (DME) at 70 °C and obtained the desired
product, N,N-di-n-butylaniline (Scheme 3, Table 1). Two of
Figure 1. Crystal structure of complex 1Pd, {[4-(Me Si)-IPr]Pd-
3
Scheme 3. Catalytic Performance of Pd−NHC Complexes
(
allyl)Cl}. ORTEP view, thermal ellipsoids are given at 30%
1
Pd−6Pd
probability, H atoms are omitted. The central atom of the allyl
ligand is evenly disordered between the two sites C3 and C4
(
50%:50% occupancy ratio), and only one of them (C3) is shown
here. Selected bond lengths (Å): Pd1−C1 = 2.040(2), Pd1−Cl1 =
2
1
1
.3605(8), C1−N1 = 1.360(3), C1−N2 = 1.359(3), N1−C6 =
.412(3), N2−C7 = 1.388(3), C6−C7 = 1.360(3), C6−Si1 =
.899(2). Selected bond angles (°) C1−N1−C6 = 112.41(16), N1−
C6−C7 = 104.00(17), C6−C7−N2 = 108.64(18), C7−N2−C1 =
1
10.74(16), N2−C1−N1 = 104.20(17).
Table 1. Comparison of the Catalytic Performances of
a
Precatalysts 1Pd−6Pd and parent Pd−IPr
entry
precatalyst
yield (%, by GC)
1
2
3
4
5
6
7
1Pd
2Pd
3Pd
4Pd
5Pd
6Pd
Pd−IPr
64
28
80
34
12
15
31
a
Yields are given after 30 min.
Figure 2. Crystal structure of complex 2Pd, {[4-((EtO) Si)-
3
the tested complexes, namely, 1Pd and 3Pd, showed the
highest catalytic activity giving the target product in 64% for
IPr]Pd(allyl)Cl}. ORTEP view, thermal ellipsoids are given at 30%
probability, H atoms are omitted. The central atom of the allyl ligand
is evenly disordered between the two sites C3 and C4 (50%:50%
occupancy ratio), and only one of them (C3) is shown here. Selected
bond lengths (Å): Pd1−C1 = 2.0552(16), Pd1−Cl1 = 2.3628(4),
C1−N1 = 1.358(2), C1−N2 = 1.3624(19), N1−C6 = 1.413(2), N2−
C7 = 1.388(2), C6−C7 = 1.358(2), C6−Si1 = 1.8606(17). Selected
bond angles (°) C1−N1−C6 = 112.19(12), N1−C6−C7 =
{
(
3
[4-(Me Si)-IPr]Pd(allyl)Cl} 1Pd and 80% for {[4-
3
Me (allyl)Si)-IPr]Pd(allyl)Cl} 3Pd (Table 1, entries 1 and
2
, respectively). Importantly, this remarkable catalytic perform-
ance greatly exceeds that of the commercially available parent
complex Pd−IPr, which yields the product in 31% under the
same catalytic conditions.
1
04.45(14), C6−C7−N2 = 108.22(14), C7−N2−C1 = 110.98(13),
In an effort to shed light on the origin of the difference in
the catalytic activity of palladium catalysts 1Pd−6Pd, we
evaluated the effect of their both electronic and steric factors
on the overall catalytic process. Initially, we estimated of the
importance of electronic factors by using the Tolman
electronic parameter (TEP) as a commonly accepted probe
for the net electron donor/electron acceptor properties of a
N2−C1−N1 = 104.12(13).
14a
[
(IPr)Pd(allyl)Cl]
and 2.0415(14) Å for [(4,5-Me -IPr)-
2
1
4b
Pd(allyl)Cl]).
Interestingly, the resonances of the olefinic protons of the
NHC ligands in all complexes 1Pd−6Pd exhibited a solvent-
dependent behavior, being diagnostically lower-field shifted in
THF-d than in benzene-d . For example, in 1Pd the shift
15
ligand. In this respect, we synthesized rhodium complexes
{[4-(R Si)-IPr]Rh(CO) Cl} 1Rh−6Rh and employed their
8
6
3
2
difference (i.e., Δ[δ(THF-d ) − δ(benzene-d )]) was as large
carbonyl stretching vibrations in the TEP calculations. All
rhodium complexes were readily available by direct complex-
ation of 4-(R Si)-IPr ligands with commercial [Rh(CO) Cl]
8
6
as 0.6 ppm. In addition, the 1Pd aromatic carbons of the IPr-
ligand in THF-d were all nonequivalent, thus causing the
8
3
2
2
maximum number of resonances to total 12, which testifies to
the lack of molecular symmetry in THF (see Figure S60). By
contrast, in benzene the number of aromatic carbon
resonances in 1Pd was reduced due to the higher symmetry
of the molecule. It is likely that in a polar solvent such as THF
the rotation of both flanking aromatic rings in 1Pd was blocked
whereas in a nonpolar solvent like benzene one of the aromatic
in THF (Scheme 4). Notably, the TEPs of complexes 1Rh−
6Rh, which were calculated by applying the general formula
−
1
av/Rh
16
TEP(cm ) = 0.8001ν
+ 420.0, were well-correlated
CO
with the order of observed catalytic activity of 1Pd−6Pd. More
specifically, the two lowest TEP values, 2040.1 and 2037.8
−
1
cm , were obtained for 1Rh and 3Rh, respectively (Table 2),
and were notably smaller than those of the other complexes
C
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Article
Scheme 4. Synthesis of {[4-(R Si)-IPr]Rh(CO) Cl}
Complexes 1Rh−6Rh
SambVca 2 web tool, based on the energy minimum structures
of complexes 1Pd−6Pd. Geometry optimization was per-
formed at the DFT M06-L level of theory using LANL8(f)
basis set for palladium and 6-31G(d) basis set for all other
atoms. The resulting steric map pictures of the complexes
3
2
1
Pd−6Pd are shown in Figure 3.
Analysis of these steric maps clearly revealed that the NHC
ligands in 1Pd−6Pd formed very similar catalytic pockets, in
which the silyl-substituted part was remarkably more sterically
congested (see bottom-right quadrants in the steric maps).
This, in turn, suggests that the approach of the aryl halide
substrate at the oxidative addition step of the catalytic cycle
would be more likely to proceed preferentially from the less
hindered site.
Meanwhile, the reductive elimination might be further
promoted by the presence of these most highly congested
quadrants, which are caused by the presence of voluminous
Table 2. Carbonyl Stretching Frequencies of {[4-(R Si)-
3
a
IPr]Rh(CO) Cl} 1Rh−6Rh and {[IPr]Rh(CO) Cl}
2
2
R Si-substituents. However, the percent buried volume
3
νCORh
νCOav/Rh
TEP
descriptor (%V ) values of the complexes do not indicate
bur
any substantial difference in the steric bulkiness of the NHC
ligands, as they are within the narrow range of 41.0−41.6
1
2
3
4
5
6
Rh
Rh
Rh
Rh
Rh
Rh
2070.2, 1979.6
2071.2, 1996.9
2062.5, 1981.5
2078.9, 1983.4
2075.0, 1986.3
2070.2, 1990.2
2071.2, 1987.3
2024.9
2034.1
2022.0
2031.2
2030.7
2030.2
2029.2
2040.1(−3.5)
2047.4(+3.9)
2037.8(−5.8)
2045.1(+1.5)
2044.7(+1.2)
2044.4(+0.8)
2043.6(0.0)
(
except for 4Pd, which has the bulkiest substituent, giving a
value of 42.2), which is very close to the value of the
unsubstituted parent Pd−IPr complex (40.9). Therefore, the
analysis of the steric maps and buried volumes implies the
minor role of the steric factors in the overall catalytic activity of
the Pd complexes.
Although it is still premature to draw a definite conclusion as
to which is the rate-determining step, it is likely that in our
particular case the oxidative addition (rather than the reductive
elimination) plays a decisive role in the complete catalytic
process.
Having established that 3Pd manifests the best catalytic
activity among all synthesized Pd−NHC complexes, we then
studied its performance in different solvents. As a result, we
found that the model coupling reaction of p-chloroanisole and
the pharmaceutically relevant morpholine tolerates a variety of
different solvents when catalyzed by 3Pd in the presence of t-
BuOK base (Scheme 5, Figure 4). THF and 1,4-dioxane gave
the best results in this case, producing the coupling product
nearly quantitatively (99 and 96%, respectively) in only 10
min. Toluene, which is commonly used in the Buchwald−
Hartwig aminations, also allowed the product in nearly
quantitative yield (96%), although the reaction proceeded
more slowly, requiring 30 min to reach the highest yield
plateau. Although lower that the rest, the yield obtained with
DME was still relatively high (89%), but the reaction rate was
lower.
Rh-IPr
a
Stretching vibrations νCORh, ν av/Rh, and TEP are given in cm−1.
CO
−
1
(
i.e., 2Rh and 4Rh-6Rh, the range of 2044.4−2047.4 cm )
−
1
and for the parent complex Rh−IPr (2043.6 cm ). Moreover,
the lowest TEP value of 2037.8 cm− for 3Rh was also smaller
than those of the structurally similar Rh complexes with IMes-
1
ligands, featuring one or two Me N-substituents at the 4- or
2
−
1
4
,5- positions of the NHC backbone (2048.6 and 2046.6 cm ,
8
respectively). The electronic impact of silyl-substitution is
even more pronounced when comparing the TEP values of
unsubstituted and monosubstituted Rh-NHC complexes: −5.8
(
TEP
TEPRh‑(4‑Me2N‑IMes)).
− TEP ) versus −2.2 (TEP
−
Rh‑IMes
Rh‑IPr
3Rh
Such a decrease in the CO stretching frequencies of 1Rh and
Rh clearly reflects their stronger Rh−CO π-back-donation
and accordingly weaker C−O bonding, which were caused by
the markedly stronger electron-donation from the NHC ligand
to the Rh metal center. This, in turn, implies that from [4-
3
(
[
1
R Si)-IPr] NHC ligands 1−6, 4-(Me Si)-IPr 1 and 4-
3
3
Me (allyl)Si]-IPr 3 were the strongest σ-donors. Accordingly,
2
Pd and 3Pd were the most effective precatalysts for the C−N
coupling reaction. This goes to show that the electronic effects
of the NHC ligands play a crucial role in the catalytic
performance of the respective Pd complexes.
Next, we explored the scope and limitations of applicability
of the precatalyst with the best catalytic activity, namely, 3Pd.
The coupling reaction of aryl chlorides (with both electron-
donating and -withdrawing substituents R) and amines (both
primary and secondary) in THF catalyzed by 3Pd was found to
tolerate a wide range of aromatic substrates and amine
reagents, thereby leading to quantitative formation of the
cross-coupling products, arylamines, in just 5 min at low
catalyst loading (Table 3). Among these, only the carbazole
reaction failed to give the desired product, presumably due to
metalation of the proton of NH group of the starting carbazole
Next, we then turned our attention to the role of steric
factors on the catalytic activity of 1Pd−6Pd. Although there
are various approaches on this topic, some of them would be
inadequate in our case. For example, estimating the Tolman
cone angle is a very popular approach, but this single-value
descriptor can be reliably applied to mostly phosphines. Other
general steric descriptors, including the recently introduced
buried volume parameter, also do not provide a clear picture
of the catalytic pocket of a particular ligand. Therefore, for our
catalytic pocket estimations, we employed one of the most
recently developed approaches in the field, namely, analysis of
1
7
18
20
by the base (t-BuOK) and inhibition of the catalytic process.
The reaction of chlorobenzene with n-butylamine produced a
mixture of phenyl-n-butylamine (27%) and diphenyl-n-butyl-
amine (11%). In the case of the reaction of chlorobenzene with
19
the topographic steric maps. This was done using the
D
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Article
Figure 3. Steric maps of Pd complexes 1Pd−6Pd and parent Pd−IPr.
Scheme 5. Solvent Scope of the Buchwald−Hartwig
Amination Catalyzed by 3Pd Precatalyst
aniline, only diphenylamine was obtained in trace amounts
(
2%), and no formation of triphenylamine was observed.
Compared to other Pd−NHC complexes capable of catalysis
of the C−N cross-coupling reactions, complexes 1Pd and 3Pd
exhibited an excellent catalytic performance. In order to further
examine their catalytic activity, we applied 1Pd and 3Pd with
Figure 4. Solvent effects on the catalytic performance of precatalyst
3
Pd in the reaction of p-chloroanisole and morpholine (yields after 90
2
.0 mol % catalyst loading, using the test reaction depicted on
min are given in parentheses).
Scheme 5. The reaction employed t-BuOK as a base (1.5
mmol) and DME as a solvent, and was performed at room
temperature for 30 min. As a result, both 1Pd and 3Pd
E
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Article
Table 3. Scope and Limitations of the Buchwald−Hartwig
Amination Using Complex 3Pd as a Precatalyst
Figure 5. Catalytic performance of 1Pd and 3Pd. For the sake of
comparison, the conversion data of the previously reported
Buchwald−Hartwig amination precatalysts are given in this graph
(
along with our own data): PEPPSI-(Me N) IPr, PEPPSI-(Me N)-
2 2 2
IPr, and PEPPSI-IPr (see ref 8).
EXPERIMENTAL SECTION
■
General Procedures. All experimental manipulations involving
air-sensitive compounds were performed using high-vacuum line
techniques or in a nitrogen atmosphere of MBRAUN LABmaster Pro
SP glovebox. All solvents were dried and degassed by MBRAUN MB
SPS (solvent purification system) prior to use. NMR spectra were
1
recorded on Bruker AVANCE III HD ( H NMR at 400.1 MHz;
a
Yield after 60 min.
13
1
29
7
C{ H} NMR at 100.6 MHz; Si NMR at 79.5 MHz; Li NMR at
1
55.5 MHz) NMR spectrometer. IR spectra were recorded on a
JASCO ATRS-100-VIR spectrophotometer. High-resolution mass-
spectra were measured on a micrOTOFII ESI-TOF mass
spectrometer (Bruker Daltonics). Elemental analyses were performed
using PerkinElmer 2400 II elemental analyzer. Gas chromatographic
(GC) analysis was performed using Shimadzu GC-2014 instrument.
Gas chromatographic-mass spectrometric (GC-MS) analysis was
performed using Shimadzu QP-2010 spectrometer.
outperformed the recently developed {[4-Me N-IPr]Pd(allyl)-
2
8
Cl} PEPPSI-(Me N)IPr and {[4,5-(Me N) -IPr]Pd(allyl)Cl}
2
2
2
8
PEPPSI-(Me N) IPr complexes (conversion after 30 min: 99
and 95% versus 80 and 33%), also catalyzing the reaction
2
2
8
8
much better than the commercially available PEPPSI-IPr
All computations were performed with the Gaussian 16 suite of
programs. Geometry optimization and frequency calculations were
8
21
(
14%) (Figure 5).
performed using density functional theory (DFT) with M06-L
22
functional. For Pd, core electrons were represented by the Hay-
CONCLUSIONS
23
■
Wadt relativistic effective core potential. For valence electrons of
24
25
In this work, we developed a straightforward gram-order-scale
procedure for the synthesis of a series of novel silyl-substituted
Pd, the LANL8 basis set augmented with f-polarization function
was used, whereas 6-31G(d) basis set was used for all other atoms.
Density fitting approximation was used when we applied auto
keyword in the Gaussian program to automatically generate density
NHC derivatives [4-(R Si)-IPr] from readily available
3
commercial starting materials. On the basis of these NHC
ligands, a family of the palladium complexes with the formula
26
fitting sets.
Synthesis of Li−IPr. n-BuLi (1.6 M hexane solution, 7.8 mmol)
was added dropwise to suspension of 1,3-bis(2,6-
{
[4-(R Si)-IPr]Pd(allyl)Cl}, 1Pd−6Pd, was prepared as
3
a
potential precatalysts for the Buchwald−Hartwig amination
reaction. Two of these complexes, namely, 1Pd and 3Pd,
showed excellent catalytic performance, notably outperforming
that of the previously reported Pd−NHC complexes in terms
of the reaction time, catalyst loading, reaction temperature, and
reaction scope. Investigation of the electronic and steric effects
of the NHC ligands on the catalytic activity of the respective
Pd precatalysts revealed that the overall catalytic performance
was primarily governed by the electronic effects, whereas the
role of the steric factors was less pronounced.
diisopropylphenyl)imidazol-2-ylidene (2.1 g, 1.5 mmol) in hexane
(50 mL) at −30 °C. The mixture was then stirred at room
temperature for 15 h. The precipitated Li−IPr was filtered and
washed with dry hexane (10 mL × 5 times). The resulting Li−IPr was
dried at room temperature under vacuum for 1 h to give the pure
product as colorless solid (2.1 g, 97%).
1
H NMR (THF-d , δ, ppm) 1.14−1.16 (m, 24H), 3.04−3.14 (m,
8
13
1
2
H), 3.17−3.27 (m, 2H), 6.24 (s, 1H), 7.10−7.20 (m, 6H). C{ H}
NMR (THF-d , δ, ppm) 22.7, 23.3, 24.0, 24.4, 27.6, 27.7, 121.6,
122.0, 124.9, 125.9, 126.8, 142.1, 145.9, 146.0, 147.9, 214.3. Li NMR
8
7
(THF-d , δ, ppm) 0.92.
8
F
DOI: 10.1021/acs.organomet.8b00757
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
Typical Procedure for the Synthesis of 4-Silyl-Substituted IPr, 1−
2Rh. H NMR (CDCl , δ, ppm) 1.06 (t, J = 7.0 Hz, 9H), 1.12 (d, J
3
6
. To a solution of Li−IPr (0.6 g, 1.5 mmol) in THF (6 mL) was
= 6.8 Hz, 6H), 1.27 (d, J = 6.8 Hz, 6H), 1.38−1.44 (m, 12H), 2.75
(sept, J = 6.7 Hz, 2H), 3.02 (sept, J = 6.8 Hz, 2H), 3.59 (q, J = 7.0 Hz,
6H), 7.28−7.32 (m, 4H), 7.22 (s, 1H), 7.45−7.50 (m, 2H). C{ H}
NMR (CDCl , δ, ppm) 17.8, 22.9, 25.1, 25.2, 26.3, 28.4, 29.0, 58.8,
124.1, 124.2, 129.4, 129.7, 130.1, 135.0, 135.6, 136.4, 145.7, 146.5,
182.8 (d, JRh−C = 74.2 Hz, CO), 184.8 (d, J
added dropwise the corresponding chlorosilane R SiCl (2.3 mmol) at
3
1
3
1
−
20 °C. The mixture was then stirred at room temperature for 1 h.
The solvent was removed under vacuum, and dry hexane (3 mL) was
added to the residue. Precipitated Li salt was filtered off, and the
solvent was evaporated. The residue was recrystallized from hexane to
3
= 45.6 Hz, NCN),
Rh−C
2
9
give 4-silyl-substituted IPr 1−6 as pale-yellow crystals.
184.9 (d, J
= 54.2 Hz, CO). Si NMR (CDCl , δ, ppm) −69.5.
Rh−C
3
1
1
4
-(Me Si)-IPr (1). Yield 96%. H NMR (THF-d , δ, ppm) 0.02 (s,
3Rh. H NMR (CDCl , δ, ppm) −0.6 (s, 6H), 1.13 (d, J = 6.8 Hz,
3
8
3
9
6
7
2
1
H), 1.18−1.22 (m, 18H), 1.32 (d, J = 6.9 Hz, 6H), 2.70 (sept, J =
6H), 1.25 (d, J = 6.8 Hz, 6H), 1.41−1.44 (m, 12H), 1.59 (d, J = 8.0
Hz, 2H), 2.85 (sept, J = 6.7 Hz, 2H), 3.01 (sept, J = 6.8 Hz, 2H),
4.82−4.90 (m, 2H), 5.63−5.69 (m, 1H), 7.25 (s, 1H), 7.32−7.36 (m,
.8 Hz, 2H), 2.85 (sept, J = 6.9 Hz, 2H), 7.27−7.30 (m, 5H), 7.36−
.42 (m, 2H). 13C{ H} NMR (THF-d , δ, ppm) −1.1, 21.2, 23.2,
1
8
1
3
1
3.8, 25.6, 28.1, 28.6, 122.6, 123.0, 128.1, 128.4, 130.8, 131.3, 138.5,
4H), 7.47−7.54 (m, 2H). C{ H} NMR (CDCl , δ, ppm) −2.8,
3
2
9
39.8, 145.7, 146.1, 222.8. Si NMR (THF-d , δ, ppm) −11.6.
22.8, 25.3, 25.4, 26.3, 28.3, 29.0, 124.1, 124.6, 130.1, 130.3, 134.1,
135.0, 135.1, 136.3, 145.7, 146.2, 182.9 (d, JRh−C = 74.0 Hz, CO),
183.3 (d, JRh−C = 46.4 Hz, NCN), 184.8 (d, JRh−C = 54.3 Hz, CO).
8
1
4
-[(EtO) Si]-IPr (2). Yield 87%. H NMR (THF-d , δ, ppm) 1.09 (t,
3
8
J = 7.0 Hz, 9H), 1.16−1.23 (m, 18H), 1.33 (d, J = 6.9 Hz, 6H), 2.74
sept, J = 6.9 Hz, 2H), 2.86 (sept, J = 6.79 Hz, 2H), 3.62 (q, J = 7.0
2
9
(
Si NMR (CDCl
3
, δ, ppm) −9.2.
4Rh. H NMR (CDCl , δ, ppm) 0.13 (s, 6H), 1.03 (d, J = 6.8 Hz,
3H), 1.13 (d, J = 6.8 Hz, 3H), 1.39 (d, J = 6.7 Hz, 3H), 1.47 (d, J =
1
Hz, 6H), 7.26−7.31 (m, 4H), 7.34−7.42 (m, 2H), 7.45 (s, 1H).
3
13
1
C{ H} NMR (THF-d , δ, ppm) 17.4, 21.7, 23.0, 23.6, 24.8, 28.2,
8
6
7
(
1
1
.7 Hz, 3H), 2.85 (sept, J = 6.7 Hz, 2H), 3.11 (sept, J = 6.8 Hz, 2H),
2
1
8.4, 58.2, 122.5, 123.0, 125.1, 127.8, 128.2, 132.8, 138.3, 139.6,
1
3
1
2
9
.31 (s, 1H), 7.32−7.43 (m, 4H), 7.48−7.54 (m, 2H). C{ H} NMR
45.6, 146.2, 223.3. Si NMR (THF-d , δ, ppm) −65.2.
8
1
CDCl , δ, ppm) −1.8, 22.9, 25.2, 25.4, 26.4, 28.4, 29.0, 124.1, 124.6,
4
-[(allyl)Me Si]-IPr (3). Yield 85%. H NMR (THF-d , δ, ppm)
3
2
8
28.1, 129.7, 130.2, 130.3, 133.5, 134.1, 135.1, 135.2, 136.3, 136.9,
45.7, 146.4, 182.9 (d, JRh−C = 74.1 Hz, CO), 184.0 (d, J = 45.6
−
0.04 (s, 6H), 1.19−1.23 (m, 18H), 1.33 (d, J = 6.9 Hz, 6H), 1.60 (d,
J = 8.0 Hz, 2H), 2.71 (sept, J = 6.8 Hz, 2H), 2.86 (sept, J = 6.9 Hz,
Rh−C
2
9
Hz, NCN), 184.8 (d, JRh−C = 54.1 Hz, CO). Si NMR (CDCl , δ,
2
7
H), 4.80−4.84 (m, 2H), 5.66−5.77 (m, 1H), 7.28−7.31 (m, 4H),
3
1
3
1
ppm) −13.0.
.33 (s, 1H), 7.37−7.43 (m, 2H). C{ H} NMR (THF-d , δ, ppm)
8
1
5
Rh. H NMR (CDCl , δ, ppm) −0.06 (s, 6H), 0.10 (s, 9H), 1.12
−
3.5, 21.2, 23.2, 23.6, 23.7, 25.4, 28.1, 28.5, 113.1, 122.7, 123.0,
3
(
d, J = 6.8 Hz, 6H), 1.24 (d, J = 6.8 Hz, 6H), 1.40−1.44 (m, 12H),
1
28.2, 128.4, 129.5, 131.3, 134.0, 138.4, 139.7, 145.7, 146.1, 222.7.
29
2.85 (sept, J = 6.8 Hz, 2H), 3.02 (sept, J = 6.8 Hz, 2H), 7.14 (s, 1H),
Si NMR (THF-d , δ, ppm) −11.8.
8
1
3
1
1
7.31−7.34 (m, 4H), 7.46−7.54 (m, 2H). C{ H} NMR (CDCl , δ,
3
4
-(PhMe Si)-IPr (4). Yield 93%. H NMR (THF-d , δ, ppm) −0.21
s, 6H), 1.04 (d, J = 6.8 Hz, 6H), 1.15 (d, J = 6.8 Hz, 6H), 1.21 (d, J =
2
8
ppm) −3.0, −1.8, 22.8, 25.2, 25.7, 26.5, 28.4, 28.9, 124.0, 124.5,
(
6
1
30.1, 130.2, 133.2, 135.1, 136.4, 145.7, 146.2, 182.9 (d, J
= 74.2
Rh−C
.9 Hz, 6H), 1.24 (d, J = 7.0 Hz, 6H), 2.89 (sept, J = 6.9 Hz, 2H),
Hz, CO), 183.5 (d, J
= 45.5 Hz, NCN), 184.9 (d, JRh−C = 54.6
Rh−C
7
.22−7.24 (m, 2H), 7.28−7.34 (m, 6H), 7.37−7.44 (m, 4H).
2
9
13
1
Hz, CO). Si NMR (CDCl
3
, δ, ppm) −18.1, 26.2.
C{ H} NMR (THF-d , δ, ppm) −2.7, 20.8, 23.3, 23.7, 25.5, 28.1,
8
1
6
Rh. H NMR (CDCl , δ, ppm) 0.09 (s, 6H), 0.95 (s, 9H), 1.12
3
2
1
−
8.6, 122.6, 123.0, 127.6, 128.2, 128.4,129.0, 129.5, 132.4, 133.7,
37.3, 138.4, 139.6, 145.7, 146.1, 223.0. Si NMR (THF-d , δ, ppm)
(
1
7
−
1
d, J = 6.8 Hz, 6H), 1.27 (d, J = 6.8 Hz, 6H), 1.44 (d, J = 6.6 Hz,
2
9
8
2H), 2.79 (sept, J = 6.7 Hz, 2H), 3.02 (sept, J = 6.8 Hz, 2H), 7.28−
16.4.
13 1
.34 (m, 5H), 7.44−7.54 (m, 2H). C{ H} NMR (CDCl , δ, ppm)
1
3
4
-(Me SiMe Si)-IPr (5). Yield 89%. H NMR (THF-d , δ, ppm)
3
2
8
4.8, 23.0, 25.3, 26.1, 26.5, 26.9, 28.1, 28.9, 124.0, 124.7, 130.0,
30.1, 133.6, 133.7, 135.2, 136.7, 145.7, 146.4, 182.7 (d, JRh−C = 74.2
Hz, CO), 184.5 (d, J
−
6
1
8
1
0.07 (s, 6H), 0.14 (s, 9H), 1.18−1.22 (m, 18H), 1.32 (d, J = 6.9 Hz,
H), 2.72 (sept, J = 6.9 Hz, 2H), 2.87 (sept, J = 6.9 Hz, 2H), 7.21 (s,
= 46.3 Hz, NCN), 184.8 (d, JRh−C = 54.0
Rh−C
1
3
1
H), 7.27−7.30 (m, 4H), 7.37−7.42 (m, 2H). C{ H} NMR (THF-
29
Hz, CO). Si NMR (CDCl , δ, ppm) −1.4.
Typical Procedure for the Synthesis of Pd Complexes with the 4-
Silyl-Substituted IPr Ligand, 1Pd−6Pd. To a solution of 4-silyl-
substituted IPr (1.5 mmol) in THF (2 mL) was added dropwise the
3
d , δ, ppm) −3.6, −3.0, 21.5, 23.2, 23.6, 25.1, 28.1, 28.4, 122.7, 123.0,
28.2, 128.3, 129.0, 130.3, 138.4, 139.8, 145.7, 146.0, 222.4. 29Si
NMR (THF-d , δ, ppm) −29.8, −19.0.
8
1
4
-(t-BuMe Si)-IPr (6). Yield 70%. H NMR (THF-d , δ, ppm)
2
8
THF solution of [Pd(allyl)Cl] (0.28 g, 0.76 mmol) at −20 °C. The
2
−
6
7
−
1
0.13 (s, 6H), 0.98 (s, 9H), 1.19−1.23 (m, 18H), 1.33 (d, J = 6.9 Hz,
mixture was then stirred at room temperature for 2 h. The solvent was
removed under vacuum, and dry hexane was added to the residue.
Precipitated solid was filtered off, and the solvents were evaporated.
The residue was recrystallized from hexane to give Pd complexes with
H), 2.73 (sept, J = 6.8 Hz, 2H), 2.88 (sept, J = 6.9 Hz, 2H), 7.27−
1
3
1
.30 (m, 4H) 7.37−7.41 (m, 3H). C{ H} NMR (THF-d , δ, ppm)
8
5.3, 17.1, 21.3, 23.2, 23.5, 25.3, 26.3, 28.1, 28.4, 122.7, 123.0, 128.2,
28.3, 128.6, 131.0, 138.4, 139.9, 145.7, 146.1, 221.6. Si NMR
2
9
4
-silyl-substituted IPr ligand 1Pd−6Pd as brown crystals.
1
(
THF-d , δ, ppm) −3.0.
1Pd. Mp 167 °C (dec). H NMR (THF-d , δ, ppm) 0.02 (s, 9H),
8
8
Typical Procedure for the Synthesis of Rh Complexes with the 4-
1.03 (d, J = 6.7 Hz, 3H), 1.14−1.24 (m, 9H), 1.27−1.39 (m, 12H),
Silyl-Substituted IPr Ligand, 1Rh−6Rh. To a solution of 4-silyl-
1
1
.55 (d, J = 12.0 Hz, 1H), 2.63 (d, J = 13.4 Hz, 1H), 2.84−2.96 (m,
H), 2.96−3.08 (m, 2H), 3.16−3.32 (m, 2H), 3.60−3.67 (m, 1H),
substituted IPr (0.3 mmol) in THF (1 mL), the THF solution of
[
Rh(CO) Cl] (0.061 g, 0.16 mmol) was added dropwise at −20 °C.
2
2
4.68−4.83 (m, 1H), 7.23−7.33 (m, 4H), 7.33−7.39 (m, 1H), 7.39−
1
3
1
The mixture was then stirred at room temperature for 1 h. The
solvent was removed under vacuum, and dry toluene was added to the
residue. Precipitated solid was filtered off, and the solvents were
evaporated. The residue was recrystallized from toluene to give Rh
complexes with 4-silyl-substituted IPr ligand 1Rh−6Rh as brown
7
2
.45 (m, 1H), 7.60 (s, 1H). C{ H} NMR (THF-d , δ, ppm) 0.04,
8
2.8, 23.5, 24.8, 24.9, 25.4, 25.6, 25.6, 26.3, 28.7, 28.9, 29.2, 29.3,
50.1, 71.5, 114.1, 123.9, 124.4, 124.6, 124.7, 129.9, 130.2, 135.1,
135.9, 137.3, 138.5, 146.5, 146.8, 147.0, 147.3, 189.4. Si NMR
2
9
(THF-d , δ, ppm) −8.3. Anal. Calcd for C H ClN PdSi: C, 61.57;
8
33 49
2
crystals.
H, 7.67. Found: C, 61.56; H, 7.64.
1
1Rh. H NMR (CDCl , δ, ppm) 0.02 (s, 9H), 1.13 (d, J = 6.9 Hz,
The single crystals of 1Pd for X-ray diffraction analysis were grown
from a hexane solution. Diffraction data were collected at 90 K on a
Bruker APEX-II CCD X-ray diffractometer (Mo Kα radiation, λ =
0.71069 Å, 50 kV/90 mA). The structure was solved by the direct
method with the SIR2002 program and refined by the full-matrix
least-squares method with the SHELXL-97 program. Crystal data
3
6
6
4
2
1
=
H), 1.23 (d, J = 6.8 Hz, 6H), 1.40−1.43 (m, 12H), 2.85 (sept, J =
.7 Hz, 2H), 3.01 (sept, J = 6.8 Hz, 2H), 7.22 (s, 1H), 7.32−7.34 (m,
1
3
1
H), 7.47−7.54 (m, 2H). C{ H} NMR (CDCl , δ, ppm) 0.0, 22.9,
3
27
5.3, 25.4, 26.3, 28.4, 29.0, 124.1, 124.6, 130.2, 133.8, 135.2, 136.4,
28
37.1, 145.8, 146.3, 182.8 (d, JRh−C = 45.5 Hz, NCN), 183.0 (d, J
74.2 Hz, CO), 184.9 (d, JRh−C = 54.0 Hz, CO). Si NMR (CDCl3,
Rh−C
2
9
for 1Pd: MF = C H ClN PdSi, MW = 643.70, monoclinic, P2 /c, a
33
49
2
1
δ, ppm) −7.7.
= 10.4846(5), b = 16.0964(8), c = 19.7252(10) Å, β = 93.9940(10)°,
G
DOI: 10.1021/acs.organomet.8b00757
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
3
−3
1
V = 3320.8(3) Å , Z = 4, Dcalcd = 1.287 g cm . The final R factor was
6Pd. Mp 193 °C (dec). H NMR (THF-d , δ, ppm) −0.14 (s, 3H),
8
0
.0312 for 6423 reflections with I > 2σ(I ) (R = 0.0821 for all data),
−0.01 (s, 3H), 0.96 (s, 9H), 1.00−1.46 (m, 24H), 2.46 (s, 1H), 2.65
(d, J = 13.4 Hz, 1H), 2.69−2.85 (m, 2H), 3.05−3.25 (m, 3H), 3.65
(d, J = 7.3 Hz, 1H), 4.62−4.76 (m, 1H), 7.16−7.38 (m, 5H), 7.40−
0
0
w
GOF = 1.071.
The X-ray crystallographic data for 1Pd have been deposited at the
Cambridge Crystallographic Data Centre (CCDC) under deposition
no. CCDC 1859969. These data can be obtained free of charge from
1
3
1
7.46 (m, 1H), 7.60 (s, 1H). C{ H} NMR (THF-d , δ, ppm) −4.9,
8
−4.1, −3.4 18.5, 22.9, 23.6, 25.3, 26.0, 26.1, 26.6, 27.3 (2C), 28.6
(2C), 29.3 (2C), 50.4, 71.3, 114.1, 124.0, 124.4, 124.8, 125.0, 129.7,
130.2, 132.6, 134.8, 137.2, 138.9, 146.4, 146.8, 147.2, 147.5, 190.9.
the CCDC (www.ccdc.cam.ac.uk/data_request/cif).
1
2
Pd. Mp 150 °C (dec). H NMR (THF-d , δ, ppm) 1.03 (t, J = 7.0
8
2
9
Hz, 9H), 1.15 (d, J = 6.8 Hz, 4H), 1.22−1.40 (m, 20H), 1.48 (d, J =
Si NMR (THF-d
PdSi [M − Cl] 649.3177, found: 649.3155.
Typical Procedure for the Buchwald−Hartwig Amination Using
8
, δ, ppm) −1.79. HRMS (ESI): m/z calcd. for
+
1
1.8 Hz, 1H), 2.62 (d, J = 13.4 Hz, 1H), 2.68−2.79 (m, 1H), 2.94 (d,
C H N
36 55 2
J = 5.8 Hz, 1H), 3.04−3.25 (m, 3H), 3.59−3.67 (m, 7H), 4.66−4.78
Complex 3Pd as a Precatalyst. THF solution of complex 3Pd (0.2
mol % relative to aryl chloride) was added to a THF (2 mL) solution
of aryl chloride (1.00 mmol), amine (1.19 mmol), t-BuOK (1.20
mmol), and dodecane (0.075 g, as an internal standard for GC
analysis) at 70 °C. The reaction mixture was then stirred for 5 min.
The conversion of aryl chloride and yield of the coupling product
were determined by GC analysis. All coupling products were
(
m, 1H), 7.20−7.30 (m, 4H), 7.32−7.40 (m, 2H), 7.64 (s, 1H).
1
3
1
C{ H} NMR (THF-d , δ, ppm) 18.0, 22.8, 23.5, 25.0, 25.1, 25.3,
8
2
1
1
5.6, 25.8, 26.5, 28.9 (2C), 29.3, 29.4, 50.4, 59.3, 71.3, 114.1, 124.0,
24.2, 124.5 (2C), 128.4, 129.7, 129.9, 136.6, 137.0, 138.6, 146.4,
2
9
46.8, 147.3, 147.7, 191.6. Si NMR (THF-d , δ, ppm) −68.2. Anal.
8
Calcd for C H ClN O PdSi: C, 58.93; H, 7.56. Found: C, 59.07; H,
36
55
2
3
7.51.
1
13
identified by their GC-MS, H and C NMR spectral data.
The single crystals of 2Pd for X-ray diffraction analysis were grown
from a hexane solution. Diffraction data were collected at 90 K on a
Bruker APEX-II CCD X-ray diffractometer (Mo Kα radiation, λ =
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00757.
■
0
.71069 Å, 50 kV/90 mA). The structure was solved by the direct
*
S
27
method with the SIR2002 program and refined by the full-matrix
least-squares method with the SHELXL-97 program. Crystal data
28
for 2Pd: MF = C H ClN O PdSi, MW = 733.78, monoclinic, P2 /c,
36
55
2
3
1
a = 18.1934(9), b = 13.2031(6), c = 16.3077(8) Å, β =
3
−3
X-ray analysis data and tables of crystallographic data
1
02.4490(10)°, V = 3825.2(4) Å , Z = 4, D
= 1.274 g cm .
calcd
(
including atomic positional and thermal parameters)
The final R factor was 0.0222 for 7781 reflections with I > 2σ(I ) (R
0
0
w
=
0.0614 for all data), GOF = 1.060.
The X-ray crystallographic data for 2Pd have been deposited at the
for 1Pd and 3Pd, as well as computational details
(optimized geometries and total energies for 1Pd−6Pd
and Pd−IPr) (PDF)
Cambridge Crystallographic Data Centre (CCDC) under deposition
no. CCDC 1859968. These data can be obtained free of charge from
the CCDC (www.ccdc.cam.ac.uk/data_request/cif).
Cartesian coordinaes (XYZ)
1
3
Pd. Mp 140 °C (dec). H NMR (THF-d , δ, ppm) −0.06 (d, J =
Accession Codes
8
1
6.0 Hz, 6H), 0.97−1.43 (m, 24H), 1.55 (d, J = 11.0 Hz, 1H), 1.63
CCDC 1859968−1859969 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(
d, J = 7.9 Hz, 1H), 2.64 (d, J = 13.4 Hz, 1H), 2.81−3.11 (m, 4H),
3
4
7
.11−3.32 (m, 2H), 3.64 (d, J = 7.2 Hz, 1H), 4.70−4.79 (m, 1H),
.79−4.83 (m, 1H), 4.83−4.86 (m, 1H), 5.64−5.78 (m, 1H), 7.20−
.33 (m, 4H), 7.33−7.38 (m, 1H), 7.39−7.46 (m, 1H), 7.59 (s, 1H).
13
1
C{ H} NMR (THF-d , δ, ppm) −2.7, 22.8, 23.5, 24.8, 25.0, 25.2,
8
2
1
1
5.3, 25.5, 25.7, 26.5, 28.7, 28.9, 29.3 (2C), 50.3, 71.5, 114.1, 114.6,
24.0, 124.4, 124.7, 124.8, 129.9, 130.3, 134.1, 134.2, 135.3, 137.3,
38.5, 146.5, 146.8, 146.9, 147.3, 190.0. Si NMR (THF-d , δ, ppm)
AUTHOR INFORMATION
Corresponding Authors
E-mail: n.fukaya@aist.go.jp (N.F.).
*E-mail: choi@aist.go.jp (J.-C.C.).
2
9
■
8
+
−
9.54. HRMS (ESI): m/z calcd. for C H N PdSi [M − Cl]
3
5
51
2
*
6
33.2856. Found: 633.2852.
1
4
Pd. Mp 185 °C (dec). H NMR (THF-d , δ, ppm) 0.05 (s, 3H),
8
0
.19 (s, 3H), 0.84−0.96 (m, 3H), 0.99−1.11 (m, 6H), 1.14−1.21 (m,
ORCID
3
H), 1.25−1.46 (m, 12H), 1.60 (d, J = 11.8 Hz, 1H), 2.65 (d, J = 13.4
Norihisa Fukaya: 0000-0001-8319-803X
Kazuhiro Matsumoto: 0000-0003-1580-8822
Vladimir Ya. Lee: 0000-0002-6527-5342
Junpei Kuwabara: 0000-0002-9032-5655
Takaki Kanbara: 0000-0002-6034-1582
Jun-Chul Choi: 0000-0002-7049-5032
Hz, 1H), 2.80−2.94 (m, 1H), 2.97−3.08 (m, 1H), 3.10−3.33 (m,
3
H), 3.66 (d, J = 7.2 Hz, 1H), 4.71−4.85 (m, 1H), 7.23−7.33 (m,
13 1
7
H), 7.34−7.44 (m, 2H), 7.45−7.51 (m, 2H), 7.73 (s, 1H). C{ H}
NMR (THF-d , δ, ppm) −2.0, −1.3, 22.8, 23.6, 24.7, 24.9, 25.5, 25.8,
8
2
1
1
5.9, 26.6, 28.7, 29.0, 29.3, 29.4, 50.3, 71.5, 114.2, 123.9, 124.4, 124.6,
24.9, 128.5, 130.0, 130.0, 130.2, 132.9, 134.4, 136.5, 137.2, 138.3,
2
9
38.4, 146.5, 146.9, 147.0, 147.5, 190.7. Si NMR (THF-d , δ, ppm)
8
Notes
−
13.4. Anal. Calcd for C H ClN PdSi: C, 64.67; H, 7.28. Found: C,
3
8
51
2
The authors declare no competing financial interest.
6
4.66; H, 7.43.
1
5
Pd. Mp 138 °C (dec). H NMR (THF-d , δ, ppm) −0.07 to
8
−
0.01 (m, 6H), 0.11 (s, 9H), 1.03 (d, J = 6.6 Hz, 3H), 1.16 (d, J = 6.6
ACKNOWLEDGMENTS
■
Hz, 3H), 1.22 (d, J = 5.4 Hz, 6H), 1.25−1.41 (m, 12H), 1.50 (d, J =
This work was partially supported by the JSPS KAKENHI
Grant program (No. JP18K05137) from the Ministry of
Education, Science, Sports, and Culture of Japan. The authors
also acknowledge the helpful discussions with Hiroshi Igarashi
and Yasuhiro Seki from the N.E. CHEMCAT Corporation.
1
1
1
7
2.2 Hz, 1H), 2.46 (s, 1H), 2.62 (d, J = 13.4 Hz, 1H), 2.81−2.91 (m,
H), 2.94 (d, J = 6.0 Hz, 1H), 3.13−3.23 (m, 1H), 3.23−3.33 (m,
H), 3.60−3.67 (m, 1H), 4.67−4.80 (m, 1H), 7.18−7.33 (m, 4H),
1
3
1
.33−7.38 (m, 1H), 7.38 (s, 1H), 7.39−7.44 (m, 1H). C{ H} NMR
(THF-d , δ, ppm) −3.0, −2.4, −1.8, 22.8, 23.5, 24.7, 25.4, 25.6, 25.9,
8
2
1
1
6.8, 28.7, 28.9, 29.2, 29.3, 50.2, 71.5, 114.1, 124.0, 124.5, 124.5,
24.8, 129.9, 130.2, 133.8, 134.3, 137.2, 138.6, 146.5, 146.8, 146.9,
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DOI: 10.1021/acs.organomet.8b00757
Organometallics XXXX, XXX, XXX−XXX

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