Activation of Ene-Diamido Samarium Methoxide with Hydrosilane for Selectively Catalytic Hydrosilylation of Alkenes and Polymerization of Styrene: An Experimental and Theoretical Mechanistic Study

Article abstract of DOI:10.1021/acs.inorgchem.6b01670

Samarium methoxide incorporating the ene-diamido ligand L(DME)Sm(μ-OMe)₂Sm(DME)L (1; L = [DipNC(Me)C(Me)NDip]^2-, Dip = 2,6-iPr₂C₆H₃, and DME = 1,2-dimethoxyethane) has been prepared and structurally c

Full text of DOI:10.1021/acs.inorgchem.6b01670

Article
pubs.acs.org/IC
Activation of Ene-Diamido Samarium Methoxide with Hydrosilane
for Selectively Catalytic Hydrosilylation of Alkenes and
Polymerization of Styrene: an Experimental and Theoretical
Mechanistic Study
Jianfeng Li,† Chaoyue Zhao,† Jinxi Liu,† Hanmin Huang,† Fengxin Wang,† Xiufang Xu,*,†
and Chunming Cui*,†,‡
†State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 300071, P. R. China
‡Collaborative Innovation Center of Chemical Science and Engineering, Tianjin 300071, P. R. China
S
* Supporting Information
ABSTRACT: Samarium methoxide incorporating the ene-
diamido ligand L(DME)Sm(μ-OMe)2Sm(DME)L (1; L =
[DipNC(Me)C(Me)NDip]2−, Dip = 2,6-iPr2C6H3, and DME
= 1,2-dimethoxyethane) has been prepared and structurally
characterized. Complex 1 catalyzed the syndiospecific
polymerization of styrene upon activation with phenylsilane
and regioselective hydrosilylation of styrenes and nonactivated
terminal alkenes. Unprecedented regioselectivity (>99.0%) for
both types of alkenes has been achieved with the formation of
Markovnikov and anti-Markovnikov products in high yields,
respectively, whereas the polymerization of styrene resulted in
the formation of syndiotactic silyl-capped oligostyrenes. The kinetic experiments and density functional theory calculations
strongly support a samarium hydride intermediate generated by σ-bond metathesis of the Sm−OMe bond in 1 with PhSiH3. In
addition, the observed regioselectvity for hydrosilylation and polymerization is consistent with the calculated energy profiles,
which suggests that the bulky ene-diamido ligand and samarium hydride intermediate have important roles for regio- and
stereoselectivity.
hydrosilylation of alkenes are currently not clear. On the other
hand, although a number of rare-earth alkyls and amides have
been reported to catalyze the hydrosilylation reactions, only the
rare-earth amide La[N(SiMe3)2]3 has been reported to exhibit
the relatively satisfactory regioselectivity for both aryl-
substituted (99%) and alkyl-substituted (96%) terminal
alkenes.6e This issue has been complicated by the fact that
both rare-earth hydride and silyl intermediates could be
generated in the catalytic cycle upon the activation of rare-
earth alkyls and hydrides with hydrosilanes, leading to the
insertion of alkenes into either rare-earth hydride or silyl
intermediates.7
Trivalent rare-earth alkoxides/aryloxides are well-known to
be much more resistant to air and moisture and thus much
easier to handle and store for a long time. However, they have
not been reported as hydrosilylation and polymerization
catalysts of alkenes because of the large Ln−O bond enthalpy,8
which impedes the formation of active hydride or silyl
intermediates via σ-bond metathesis with hydrosilane. This
situation is in sharp contrast to that of transition-metal
INTRODUCTION
■
Well-defined rare-earth complexes have emerged as powerful
catalysts for a number of transformations given their unique
selectivity and mechanistic distinctions derived from the high
electrophilicity of rare-earth centers.1 Because both catalytic
hydrosilylation and polymerization of alkenes are important
industrial processes for the production of organosilanes and
polyolefins, the reactions catalyzed by rare-earth and early-
transition-metal complexes have been studied extensively in the
past several decades.2,3 The most distinctive and attractive
features that have been observed for the rare-earth-catalyzed
reactions include the following: (1) hydrosilylation of styrenes
and nonactivated alkenes yielded products with reverse
regioselectivity; (2) polymerization may proceed in the absence
of an expensive cocatalyst, like methylaluminoxane.
The most widely employed catalytic precursors for hydro-
silylation are rare-earth alkyls supported by various ligand
frameworks.4 Some rare-earth hydrides and amides have also
been reported.5,6 However, these catalysts or precatalysts,
especially hydrides and alkyl complexes, suffer from high
sensitivity to air and moisture and thus cannot be stored for a
relatively long time and are not practical. In addition, the
factors that control the regioselectivity of rare-earth-catalyzed
Received: July 19, 2016
© XXXX American Chemical Society
A
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alkoxides, which, in some cases, could be converted to the
corresponding active hydride intermediate by σ-bond meta-
thesis with hydrosilanes.9 Nevertheless, recent studies by the
Marks and Hou groups have shown that the insertion of an
Ln−O bond into CC and CO bonds could occur under
certain conditions.10,11 Inspired by the successes, we are
interested in the investigation of σ-bond metathesis of an Ln−
OR bond supported by suitable ligand frameworks with
hydrosilanes for the development of practical rare-earth
alkoxide catalysts for hydrosilylation reactions.
ion. The structure of 1 features a crystallographic central
symmetry with a Sm1−O4−Sm1*−O4* planar core (Figure
1). The C6−C11 bond length of 1.373(3) Å is lengthened
Herein, we report the selective catalytic hydrosilylation and
polymerization of styrenes with the samarium alkoxide 1
incorporating the bulky ene-diamido ligand (Scheme 1) by
Scheme 1. Synthesis of 1
Figure 1. ORTEP drawing of 1 with 30% probability. Hydrogen atoms
have been omitted for clarity. Selected bond lengths (Å) and angles
(deg): Sm1−N1 2.2816(15), Sm1−N2 2.2783(16), Sm1−O2
2.6011(13), Sm1−O3 2.5768(13), Sm1−O4 2.3104(13), Sm1−O4*
2.3548(12), Sm1−C6 2.8232(18), Sm1−C11 2.8195(19), Sm1−Sm1*
3.8579(6), N1−C6 1.417(2), N2−C11 1.428(2), C6−C11 1.373(3);
N1−Sm1−N2 79.52(5), O4−Sm1−O4* 68.43(5), Sm1−O4−Sm1*
111.57(5), N1−Sm1−O4 89.17(5).
controlling the amount of hydrosilane. Complex 1 appeared to
be the most regioselective catalyst for hydrosilylation of both
styrenes and nonactivated alkenes reported so far. In addition,
polymerization of styrene led to the formation of silyl-capped,
highly syndiotactic polystyrene. The combined experimental
results and density functional theory (DFT) calculations on the
mechanisms disclosed the highly selective formation of the
samarium hydride intermediate by activation of the Sm−OMe
bond, with hydrosilane and the electronic and steric factors of
the ene-diamido ligand being responsible for the high
regioselectivity for hydrosilylation and stereoselective polymer-
ization of styrene.
compared to the corresponding distance [1.339(2) Å] in the
ene-diamine LH2.17 The short distances (av. 2.821 Å) between
the samarium and two olefinic carbon atoms and the folded N−
C−C−N−Sm five-membered ring (the dihedral angle of the
N−Sm−N and N−C−C−N planes = 132.2°) indicated the
σ2,π-coordination mode of the ene-diamido ligand.12b−d,13
The mechanism for the formation of the trivalent samarium
dimer 1 from the divalent precursors is very likely through the
divalent samarium ene-diamido intermediate, which is highly
reactive and cleaved the C−O bonds in DME molecules via an
electron-transfer process. The cleavage of the C−O bond in
ether has precedents with trivalent rare-earth metal alkyl,
hydride, and halide, as well as an in situ generated divalent rare-
earth metal intermediate.15,18,19 In the latter case, an electron-
transfer process has been proposed. The formation of 1
represents a convenient route for the preparation of rare-earth
methoxide.
The isolation of 1 prompted us to investigate its potential for
catalytic hydrosilylation reaction. Thus, the catalytic hydro-
silylation of styrene with phenylsilane using complex 1 as
catalyst has been examined. The results are summarized in
Table 1. The reactions in THF at room temperature with 2.5
mol % loadings of 1 led to the formation of the hydrosilylation
product with low conversions but the very good regioselectivity
(>99.9%, entries 1). It can be seen in Table 1, the catalytic
reaction in toluene is more efficient than those in donor
solvents at room temperature (entries 1, 2 and 3) and the
reaction at 60 °C resulted in a complete conversion in 1 h
(entry 4). On the other hand, the reaction also proceeded with
a good conversion (89%) under solvent-free conditions (entry
5). However, the decrease of the catalyst loading to 1.25 mol %
led to a much low conversion (entry 6). Overall, the catalytic
hydrosilylation of styrene using 1 in toluene at 60 °C is highly
regioselective and efficient.
RESULTS AND DISCUSSION
■
Rare-earth complexes supported by ene-diamido ligands have
been shown to display interesting coordination chemistry and
reactivity.12 Their catalytic applications for the polymerization
of cyclic esters and 4-vinylpyridine have been reported by
Trifonov, Carpentier, and Mashima.13,14 In addition, yttrium
ene-diamido alkyl and hydrido complexes has been reported by
Trifonov to catalyze intermolecular olefin hydrophosphination
and hydroamination.15 More recently, we reported the
synthesis and reactions of yttrium complexes supported by a
bulky ene-diamido ligand.16 In a continuation of our studies on
rare-earth chemistry with redox-active ene-diamido ligands,
rare-earth alkoxides supported by dianionic ligands have been
chosen for this study.
The methoxy-bridged complex [L(DME)Sm(μ-OMe)]2 (1;
L = [DippNC(Me)C(Me)NDipp]2−, Dipp = 2,6-iPr2C6H3, and
DME = 1,2-dimethoxyethane) was easily obtained by the
reaction of LH2 with Sm[N(SiMe3)2]2(THF)2 (THF =
tetrahydrofuran) in DME. Complex 1 was isolated as brown
crystals in ca. 46% yield. Alternatively, complex 1 can also be
prepared by the reaction of the potassium salt LK2 with
1
SmI2(THF)2 and has been characterized by H and 13C NMR
spectroscopy and elemental analysis. The molecular structure of
1 has been determined by single-crystal X-ray analysis.
Complex 1 displays the broad proton resonances in the wide
1
Encouraged by the initial results, various alkenes have been
tested. It can be seen from Table 2 that 1 exhibited high
range from −3.56 to +11.57 ppm in the H NMR spectrum,
indicating the paramagnetic nature of the trivalent samarium
B
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earth catalyst for both styrenes and nonactivated terminal
alkenes reported so far.
Table 1. Optimization of the Hydrosilylation of Styrene with
PhSiH3 Catalyzed by 1
a
It has been reported that hydrosilylation of 1,5-hexadiene
(Scheme 2) catalyzed by rare-earth complexes may yield several
b
c
entry
solvent
T (°C)
convn (%)
regioselectivity (%)
1
2
3
4
5
THF
23
23
23
60
60
60
31
12
>99.9
>99.9
>99.9
>99.9
>99.9
>99.9
DME
Scheme 2. Hydrosilylation of Dienes with PhSiH3 Catalyzed
by 1
toluene
toluene
neat
43
100
89
d
6
toluene
46
a
Reactions were carried out on a scale of 1 mmol of phenylsilane and 1
mmol of styrene, in the presence of 2.5 mol % catalyst, in 1 mL of
b
solvent for 1 h. Conversion was estimated based on integration of the
c
1H NMR spectrum. The regioselectivity was analyzed by GC−MS of
d
the crude reaction mixture. In the presence of 1.25 mol % 1.
products depending on the hydride or silyl intermediates.4b
Hydrosilylation of 2j in C6D6 catalyzed by 1 was monitored in
an NMR tube. The reaction exclusively yielded 1,6-bis-
(phenylsilyl)hexane (3j) and (phenylsilylmethyl)cyclopentane
(3jj; see the SI). The cyclization product 3jj has been proposed
to be formed by the intramolecular alkene coordination−
insertion into the Ln−C bond via a rare-earth hydride
intermediate.4 e , 5 a , d However, the product (3-
methylcyclopentyl)phenylsilane, which was proposed to be
formed via a rare-earth silyl intermediate, was not observed,
indicating that the hydrosilylation reaction is likely to proceed
via a rare-earth hydride intermediate.
Table 2. Results for the Hydrosilylation of Styrene
a
Derivatives and Nonactivated Terminal Alkenes
To provide further evidence for the possible hydride
intermediate, the polymerization of alkenes with 1 activated
by PhSiH3 was investigated. The polymerization of styrene
cannot occur in the absence of PhSiH3. However, the addition
of a small amount of PhSiH3 to the precursor 1 led to the
exclusive formation of polystyrene. 1 exhibited moderate
activity at 60 °C with the formation of highly syndiotactic
(>99%) silyl-capped polystyrene with moderate molecular
weights (Mn = 5100) and narrow molecular weight distribution
(PDI = 1.33) under optimized conditions (Scheme 3). The
Scheme 3. Synthesis of Highly Syndiotactic Silyl-Capped
Polystyrene
a
Reactions were carried out at 60 °C on a scale of 1 mmol of
1
polymer has been characterized by H, 13C, and 29Si NMR, gel
phenylsilane and 1 mmol of the appropriate alkene, in the presence of
2.5 mol % 1, in 1 mL of toluene. Isolated yield. The regioselectivity
was analyzed by GC−MS of the crude reaction mixture.
permeation chromatography (GPC), and IR spectroscopy (see
the SI). Syndiospecific polymerization of styrene has been
realized with the single-component metallocene allyl catalysts
(Flu-CMe2-Cp)Ln(C3H5)(THF) (Flu = fluorenyl; Cp =
cyclopentadienyl; Ln = Y, La, Nd, and Sm) by Carpentier et
al.20 The half-sandwich cationic rare-earth alkyl complexes have
also been reported by the Hou and Chen groups to be highly
syndioselective for styrene polymerization.21 A number of rare-
earth complexes have been reported to give syndio-rich
polystyrenes.22 However, no rare-earth alkoxides have been
reported to be active precursors for polymerization of alkenes
upon activation with hydrosilane.
b
c
regioselectivity (>99%) for both styrene derivatives and
nonactivated terminal alkenes. The styrene derivatives 2a−2c
were exclusively converted to the corresponding Markovnikov
products 3a−3c in 88−99% yield, whereas nonactivated alkenes
2d−2i yielded anti-Markovnikov products 3d−3i in 92−99%
yield. Both the 1H NMR and gas chromatography−mass
spectrometry (GC−MS) spectra of the crude products (see the
Supporting Information, SI) indicated high regioselectivity.
Hydrosilylation of nonconjugated diene 2i led to chemo-
selective silylation of the terminal CC double bond, while the
internal CC bond remained intact with the formation of anti-
Markovnikov product 3i in 95% yield. To the best our
knowledge, complex 1 is the most regioselective (>99.0%) rare-
1
In the H NMR spectrum of the polymer, the characteristic
PhSiH2 resonance at 4.11 ppm indicated that the polymer was
capped with a PhSiH2 group. The intensity ratio of SiH2/CH3
is 2:3, indicating the existence of only one silyl end group in the
polymer chain. The resonance at −21.8 ppm and a strong
C
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absorption at 2130 cm−1 in the 29Si NMR and IR spectra,
respectively, strongly support the silyl-capped polymers.23
These spectroscopic features are consistent with those for the
silyl-capped polystyrenes generated with a cationic Ziegler−
Natta catalyst reported by Koo and Marks.24 The syndiotac-
ticity of the polymers was determined by the characteristic
active samarium species by σ-bond metathesis of the Sm−O
bond. σ-bond metathesis of some transition-metal alkoxides
with hydrosilanes to yield the metal hydride is known.9
However, these types of reactions have not been reported for
rare-earth alkoxides.
Kinetic studies on the hydrosilylation of 1-hexene were
20,21,25
1
1
resonances in the H and 13C NMR spectra.
In the 13C
operated in C6D6 and recorded by H NMR spectroscopy.
NMR spectrum, the phenyl C-1 showed only four signals
assigned to one major rrrrrr (at 145.35 ppm) and three minor
rrmrrr, rmrrrr, and mrrrrr heptads (see the SI). The relative
intensities of these signals are consistent with first-order
Markovian (Bernoullian) statistics of a chain-end stereocontrol
mechanism, giving a probability of racemic linkage between
They indicated that the rate law of hydrosilylation was of first-
order dependence on 1 and 1-hexene but of zero-order on
PhSiH3 (Figures 2 and 3 and Tables S1 and S2 in the SI). The
styrene units Pr of 0.89.26 The Mn value determined by H
1
NMR, based on the relative intensity of the resonances, is close
to that determined by GPC standards (Mn,GPC = 5100 and
M
n,NMR = 4800). To the best of our knowledge, this is the first
example of a silyl-capped syndiotactic oligostyrene prepared
directly by a polymerization process.
Temperatures have significant effects on the polymerization
activity. At low temperatures, only a trace or a small amount of
polymers was obtained (entries 1 and 2 in Table 3). High
Table 3. Catalytic Styrene Polymerization by 1 in the
a
Presence of PhSiH3
T
time
(h)
PhSiH3
(mmol)
yield
(%)
b
b
entry (°C)
solvent
Mn
PDI
1
20
40
60
60
60
60
60
60
60
60
60
6
6
6
2
4
6
6
6
6
6
6
toluene
toluene
toluene
toluene
toluene
THF
0.5
0.5
0.5
0.5
0.5
0.5
0.5
0.1
0.2
0.8
1.0
trace
5
2
5000
5100
4800
5200
2.00
1.33
1.16
1.26
3
71
4
38
5
55
6
trace
61
7
bulk
4900
11200
7800
1.22
1.84
1.61
1.07
1.01
8
toluene
toluene
toluene
toluene
53
9
60
10
11
42
4200
Figure 2. (above) Kinetic plots for the catalytic PhSiH3 hydrosilylation
of 1-hexene as a function of the indicated catalyst concentrations.
Initial [hexene] = 0.5 M and [PhSiH3] = 5 M. (below) Dependence of
the observed rate constants for the hydrosilylation process in the
kinetic plots (above) on the catalyst concentration. The linear
relationship has a slope of 1.02093.
35
3800
a
Polymerization conditions: 1 (0.0125 mmol), styrene (5 mmol, 0.58
b
mL), PhSiH3 (0.5 mmol), toluene (0.5 mL). Determined by GPC in
THF at 25 °C against a polystyrene standard, PDI = Mw/Mn.
activity was achieved at 60 °C (entry 3). The prolonged
polymerization time resulted in an increase of the yields, but
the molecular weights remained in the range of 4800−5200
(entries 3−5). In addition, donor solvents such as THF
significantly suppressed the reaction (entry 6) probably because
of the competition of the coordination of the solvent with that
of styrene. Bulk polymerization of styrene also proceeded with
a good yield (entry 7). The effects of the amount of PhSiH3 on
the catalytic performances have also been studied. With an
increase of [PhSiH3], the molecular weights decreased (entries
3 and 8−11), suggesting that the polymer chain is likely to be
terminated by PhSiH3. This result is consistent with the
proposed samarium hydride intermediate.
The mechanisms for hydrosilylation and stereospecific
polymerization have been investigated experimentally and
theoretically. The addition of 1 to a 15-fold molar excess of
PhSiH3 in C6D6 led to the formation of a small amount (ca. 3%
conversion based on PhSiH3) of Ph2SiH2 and SiH4, indicating
that σ-bond metathesis with the silane occurred to some
extent.7b It is likely that complex 1 reacted with PhSiH3 to form
results suggested that the active catalytic species is a
mononuclear intermediate in the catalytic cycle, and 1-hexene
might be involved in the rate-determining step.
Taking the preliminary mechanistic studies into account, we
propose an insertion/metathesis mechanism involving active
samarium hydride species (Figure 4). Complex 1 may
dissociate in solution and underwent σ-bond metathesis of 1
with PhSiH3 to yield samarium hydride. The subsequent
coordination−insertion of an alkene led to the Sm−C
intermediate, which reacted with PhSiH3 to give the product
and regenerate the samarium hydride intermediate.4−6 The
continuous insertion of styrene into the Sm−C bond resulted
in chain growth to form polymers, which was terminated by σ-
bond metathesis with PhSiH3 to yield the silyl-capped
polystyrenes and samarium hydride intermediate.27
To gain further support for the proposed mechanism, DFT
calculations were performed on the model reaction of the
hydrosilylation of propene with PhSiH3 (Figure 5a,b). In the
initial catalyst activation stage, a samarium hydride intermedi-
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Finally, the release of the hydrosilylation product from B′ by
exchange with DME regenerated the hydride A. The insertion
step has the highest energy barrier and thus is the rate-
determining step, consistent with the kinetic studies.4e
The regioselectivity of hydrosilylation depends on the
coordination−insertion modes. The calculated results are
shown in Figure 5c. The primary 1,2-coordination−insertion
of a propene molecule is favored over the secondary 2,1-
coordination−insertion by 2.6 kcal/mol because of the stronger
steric repulsion between the terminal alkene substituent and the
bulky ene-diamido ligand in R-TS1-B than in R-TS1-L. This is
consistent with the observed regioselectivity for nonactivated
alkenes. With regard to the hydrosilylation of styrene, the 2,1-
coordination−insertion is much favored by 7.8 kcal/mol over
the 1,2 mode because of the stabilizing η3 binding of styrene to
the samarium atom in Ph-TS1-B (Figure 5d), leading to the
Markovnikov products exclusively. Maron and co-workers have
analyzed the energy profiles for the Cp2SmH-catalyzed (Cp =
C5H5) hydrosilylation of propene with SiH4, and their
calculations support the Cp2SmSiH3 mechanism.28 It can be
concluded that both the bulky ene-diamido ligand and the Sm−
OMe bond play important roles for the hydride intermediate
and observed selectivity.
In the chain growth of polymerization, the insertion of
styrene into the LSmCH(Me)Ph intermediate requires an
activation free energy of 23.8 kcal/mol based on calculations
(see Figure S1 in the SI), which suggests that polymerization of
styrene is feasible in the experimental conditions. The solvent
effects observed in the catalytic system are in accordance with
the coordination−insertion mechanism.
We also considered the possible reaction mechanism
involved in the samarium silyl intermediate (see pathway II
in Figure S2 in in the SI). In pathway II, the silyl complex (C)
generated by the reaction of PhSiH3 with 4 requires a total free
energy of 49.0 kcal/mol. Therefore, this mechanism could be
ruled out because of the very high energy barrier.
Figure 3. (above) Kinetic plots for the catalytic PhSiH3 hydrosilylation
of 1-hexene over the indicated range of PhSiH3 concentrations. Initial
[hexene] = 0.5 M and [catalyst] = 0.012 M. (below) Dependence of
the observed rate constants for the hydrosilylation process in the
kinetic plots (above) on the PhSiH3 concentration. The linear
relationship has a slope of 0.03672.
CONCLUSION
■
In summary, we have disclosed the first ene-diamido rare-earth
alkoxide complex that is capable of catalyzing both the
regioselective (>99%) hydrosilylation of terminal alkenes and
the syndiospecific polymerization of styrene with the selective
and clean formation of valuable secondary silanes in high yields
and novel silyl-capped syndiotactic oligostyrenes. The molec-
ular weights of the polymers can be adjusted by variation of the
amount of phenylsilane. It has been observed that hydro-
silylation and polymerization with other silanes such as n-
BuSiH3, Ph2SiH2, and Ph3SiH did not occur under our catalytic
conditions. DFT calculations strongly support the formation of
a samarium hydride intermediate via σ-bond metathesis of the
Sm−O bond in 1 with PhSiH3. The high regioselectivity
observed for the hydrosilylation reaction is due to the unique
steric and electronic factors of the ene-diamido ligand and the
formation of the hydride intermediate. The formation of the
hydride intermediate was also supported by the hydrosilylation
of 1,5-hexadiene and the formation of silyl-capped polystyrene.
The results demonstrated that more stable rare-earth alkoxides
could be used for hydrosilylation and styrene polymerization
reactions. The development of highly active rare-earth alkoxide
precatalysts for the hydroelementation of unsaturated species
are currently underway in our laboratory.
Figure 4. Proposed mechanism of hydrosilylation and polymerization.
ate, LSmH(DME) (A), is formed by σ-bond metathesis of 4
with PhSiH3 via the transition state TS, requiring an activation
free energy of 29.4 kcal/mol. The subsequent primary
coordination of propene to the samarium atom led to the
intermediate A′, which underwent 1,2-insertion via the 4-
centered transition state R-TS1-L with an energy barrier of 25.8
kcal/mol to give the alkyl intermediate B. Subsequently, the
intermediate B underwent σ-bond metathesis with PhSiH3 via
the 4-centered transition state R-TS2-L with an energy barrier
of 19.5 kcal/mol to produce the silane σ intermediate B′.
E
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Figure 5. (a) Mechanism for the formation of the active catalyst A. (b) Gibbs free-energy profile of the 1-catalyzed hydrosilylation of propene.
Energies are calculated using the M06/ECP51MWB-6-311+G(d,p)/SMD(toluene)//B3LYP/ECP51MWB-6-31G(d) method. (c) TS structures
and relative free energies for the regioselectivity-determining insertion of propene. (d) TS structures and relative free energies for the regioselectivity-
determining insertion of styrene.
21421001), Natural Science Foundation of Tianjin (Grant
16JCQNJC05800), and MOE Innovation Teams (IRT-13R30
and IRT13022) of China for financial support.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.6b01670.
■
S
REFERENCES
■
Experimental, crystallographic, and computational details
(PDF)
Crystallographic data for 1 in CIF format (CIF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: xxfang@nankai.edu.cn.
*E-mail: cmcui@nankai.edu.cn.
■
Advances; Marciniec, B., Eds.; Springer: Berlin, Germany, 2009.
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS
We are grateful to the National Natural Science Foundation of
China and 973 program (Grants 2012CB821600, 21390401,
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