Hydrosilane Synthesis by Catalytic Hydrogenolysis of Chlorosilanes and Silyl Triflates

Article abstract of DOI:10.1021/acs.inorgchem.8b02336

Hydrogenolysis of the chlorosilanes and silyl triflates (triflate = trifluoromethanesulfonate, OTf^-) Me_3-nSiX_1+n (X = Cl, OTf; n = 0, 1) to hydrosilanes at mild conditions (4 bar of H₂, room temperature) is reported using low loadings (1 mol %) of the bifunctional catalyst [Ru(H)₂CO(HPNP^iPr)] (HPNP^iPr = HN(CH₂CH₂P(iPr)₂)₂). Endergonic chlorosilane hydrogenolysis can be driven by chloride removal, e.g., with NaBAr^F₄ [BAr^F₄^- = B(C₆H₃-3,5-(CF₃)₂)₄^-]. Alternatively, conversion to silyl triflates enables facile hydrogenolysis with NEt₃ as the base, giving Me₃SiH, Me₂SiH₂, and Me₂SiHOTf, respectively, in high yields. An outer-sphere mechanism for silyl triflate hydrogenolysis is supported by density functional theory computations. These protocols provide key steps for synthesis of the valuable hydrochlorosilane Me₂SiClH, which can also be directly obtained in yields of over 50% by hydrogenolysis of chlorosilane/silyl triflate mixtures.

Full text of DOI:10.1021/acs.inorgchem.8b02336

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Hydrosilane Synthesis by Catalytic Hydrogenolysis of Chlorosilanes
and Silyl Triflates
†
‡
‡
†
‡
̈
̈
Arne Gluer, Julia I. Schweizer, Uhut S. Karaca, Christian Wurtele, Martin Diefenbach,
Max C. Holthausen,*,‡ and Sven Schneider*,†
†
̈
̈
Institute for Inorganic Chemistry, University of Gottingen, Tammannstraße 4, 37077 Gottingen, Germany
‡Institut fu
Germany
̈
r Anorganische und Analytische Chemie, Goethe-Universitat, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main,
̈
S
* Supporting Information
ABSTRACT: Hydrogenolysis of the chlorosilanes and silyl triflates
(triflate = trifluoromethanesulfonate, OTf−) Me3−nSiX1+n (X = Cl, OTf;
n = 0, 1) to hydrosilanes at mild conditions (4 bar of H2, room
temperature) is reported using low loadings (1 mol %) of the
bifunctional catalyst [Ru(H)2CO(HPNPiPr)] (HPNPiPr = HN-
(CH2CH2P(iPr)2)2). Endergonic chlorosilane hydrogenolysis can be
driven by chloride removal, e.g., with NaBArF [BArF − = B(C6H3-3,5-
4
4
−
(CF3)2)4 ]. Alternatively, conversion to silyl triflates enables facile
hydrogenolysis with NEt3 as the base, giving Me3SiH, Me2SiH2, and
Me2SiHOTf, respectively, in high yields. An outer-sphere mechanism for
silyl triflate hydrogenolysis is supported by density functional theory
computations. These protocols provide key steps for synthesis of the valuable hydrochlorosilane Me2SiClH, which can also be
directly obtained in yields of over 50% by hydrogenolysis of chlorosilane/silyl triflate mixtures.
Scheme 1. Synthetic Routes to Hydro(chloro)silanes
INTRODUCTION
■
Organohydrosilanes are important reagents for olefin hydro-
silylation1 and other applications such as C−H bond
silylation,2 desulfurization of fuels,3 or dehydrogenative
oligo/polysilane formation.4 (Organo)hydrochlorosilane build-
ing blocks SiHxClyRz enable the orthogonal synthesis of
branched polysiloxanes and self-healing silicones by sequential
polycondensation and cross-linking via hydrosilylation as used,
e.g., for the fabrication of release coatings, moldings, and
adhesives.5
Some of these precursors, like MeSiCl2H, are conveniently
̈
obtained as byproducts of the Muller−Rochow process. In
contrast, Me2SiClH synthesis suffers from low crude yields
(0.01−0.5%, Scheme 1a) and challenging separation proce-
dures, necessitating alternative synthetic routes to hydro-
(chloro)silanes from chlorosilanes.6 Hydrosilanes can be
prepared by salt metathesis from chlorosilanes with LiAlH4
(Scheme 1b). Besides the low atom economy that is associated
with the use of complex hydride reagents, this approach is not
commonly applicable for the synthesis of hydrochlorosilanes
because of overreduction. Alternatively, partial chlorination of
hydrosilanes,7 e.g., selective B(C6F5)3-catalyzed hydrosilane
acidolysis, serves as a versatile route to organohydrochlor-
osilanes (Scheme 1c).8 However, direct organochlorosilane
hydrogenolysis as a source of hydrosilanes remains elusive
because of the unfavorable thermochemistry (Me3SiCl + H2 →
Me3SiH + HCl; ΔG° = +22.2 kcal mol−1).8
iridium catalysts (Scheme 1d,e).10 With relatively high catalyst
loadings (5−10 mol %) and long reaction times (2−7 days),
moderate yields of around 50−60% in Me2SiH2 and Me2SiHCl
could be obtained upon hydrogenolysis of Me2−SiOTf2 [OTf− =
triflate trifluoromethanesulfonate (O3SCF3 )] or in situ
prepared Me2SiI2 and Me2SiICl, respectively. Guided by our
recent work on de/hydrogenation with bifunctional catalysts,11
Very recently, Shimada and co-workers pioneered9 the
hydrogenolysis of silyl triflates and halides R3−nSiXn+1 with
Received: August 17, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b02336
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Inorganic Chemistry
Article
a
we here report ruthenium-catalyzed hydrogenolysis of
chlorosilanes and silyl triflates with low catalyst loadings.
Table 1. Hydrogenolysis of Chlorosilanes with Catalyst 1
RESULTS AND DISCUSSION
■
The considerably higher Si−Cl (∼100 kcal mol−1) versus Si−
H (∼69 kcal mol−1) bond dissociation energy renders hydride
versus chloride metathesis a thermochemically challenging
step.12 Therefore, a transition-metal catalyst with low M−H
hydridicity13,14 was targeted, as indicated, e.g., by its capability
of catalyzing the hydrogenation of CO2 to formate
b
NaBArF
(equiv)4
convn
(%)
product
b
reaction time
(h)
entry substrate
(yield )
c
1
2
3
Me3SiCl
Me2SiCl2
Me2SiCl2
1.1
2.0
1.1
77
Me3SiH
195
(51%)
−
−1
−
100
59
Me2SiH2
(75%)
Me2SiH2
(37%)
24
[ΔG°H (HCO2 ) = 44 kcal mol in MeCN]. Ruthenium
MACHO-type catalysts, i.e., [RuCl(H)CO(HPNPR)] [HPNPR
= HN(CH2CH2PR2)2], show high activities in CO2 hydro-
genation.15 A stoichiometric control experiment confirmed
that the trans-dihydride complex [Ru(H)2(CO)(HPNPiPr)]
(1) readily reacts with Me3SiCl to the corresponding
hydrosilane in almost quantitative spectroscopic yield (Scheme
2). This observation also demonstrates favorable kinetics for
20
a
General conditions: 0.027 mmol of chlorosilane, 0.03 or 0.054 mmol
of NaBArF , 0.26 μmol of 1, 0.36 mmol of NEt3, 0.5 mL of PhF, 4 bar
4
b
of H2, room temperature. Conversions/yields were determined by
1H NMR integration of all signals in the MexSi region around 0 ppm
c
versus an internal standard (1,2,4,5-tetramethylbenzene). The
conversion of [Me3SiNEt3][BArF ] is given.
4
Scheme 2. Stoichiometric Hydride Transfer of 1 with
Me3SiCl
by 2,6-lutidine as the base did not give any hydrogenolysis
product even after several days under otherwise identical
conditions.
Catalytic attempts with other alkaline-metal salts of weakly
coordinating anions (WCAs), such as NaOTf, KPF6, NaBPh4,
NaSbF6, or NaBF4, only gave (sub)stoichiometric hydrosilane
yields with respect to catalyst loading even at high substrate
conversion (see the SI). To clarify the role of the WCAs, the
catalytic reaction with NaBArF was monitored by NMR
hydride transfer to chlorosilanes with this catalyst class.
However, HCl elimination and H2 heterolysis from the
resulting ruthenium chloro complex 2 requires strong bases
like alkaline-metal hydroxides, alkoxides, or amides, which all
proved to be incompatible with chlorosilane substrates.
Accordingly, attempts for the catalytic hydrogenolysis of
Me3SiCl in tetrahydrofuran (THF) with NEt3 as the base
were unsuccessful. Computational evaluation confirmed ender-
gonic hydrogenolysis with the model base NMe3 (Me3SiCl +
H2 + NMe3 → Me3SiH + [HNMe3]Cl; ΔG° = 11.9 kcal
mol−1), suggesting the requirement of an additional driving
force to achieve turnover.
4
spectroscopy. The experiment revealed the presence of an
intermediate with a 29Si resonance of 47.4 ppm, i.e.,
characteristic for base-stabilized silyl cations.18 The same
species was obtained upon mixing Me3SiCl with NaBArF and
4
NEt3 in PhF in the absence of catalyst. Furthermore, NEt3
coordination to silicon is evidenced by a cross peak of the
amine methylene protons with the 29Si resonance in the
1H−29Si HMBC NMR spectrum (Figure 1). These results
suggest that in situ formed [Me3SiNEt3]+ is the actual
substrate, which is sufficiently stabilized by the BArF − anion
4
under catalytic conditions.19
In situ chloride precipitation was therefore evaluated as a
synthetic strategy. The addition of NaBArF [BArF −
=
4
4
−
B(C6H3-3,5-(CF3)2)4 ] to complex 2 in PhF as the solvent
results in the formation of new species by NMR spectroscopy
accompanied by NaCl precipitation (see the Supporting
1
Information, SI). The 31P and H NMR spectroscopic and
mass (MS) spectrometric data closely resemble the reported
values for [Ru(H)CO(HPNPiPr)]BF4.16 Exchange of the
solvent with THF-d8 restores 2, indicating a strong solvent
dependence of the chloride abstraction equilibrium.
Chlorosilane hydrogenolysis (4 bar of H2, room temper-
ature) with 1 (1 mol %) as the catalyst was therefore examined
in the presence of stoichiometric amounts of NaBArF and
1
Figure 1. H−29Si HMBC NMR spectrum of the product from the
4
reaction of Me3SiCl with NaBArF and NEt3.
excess NEt3 as the base in PhF. Trimethylchlorosilane as the
substrate (Table 1, entry 1) requires relatively long reaction
times, giving spectroscopic yields in Me3SiH around 50% after
about 1 week. In contrast, hydrogenolysis of Me2SiCl2 (with 2
4
Alternative hydrogenolysis strategies were examined to avoid
the stoichiometric use of expensive NaBArF as the chloride
4
equiv of NaBArF ) to Me2SiH2 proceeds at a much faster rate
scavenger. Silyl triflates can be easily obtained from organo-
chlorosilanes and HOTf with HCl as the only byproduct,20
possibly providing a better leaving group for catalysis. The
reaction of 1 with Me3SiOTf (1 equiv) in C6D6 selectively
gives Me3SiH and [RuH(OTf)CO(HPNPiPr)] (3) by NMR
spectroscopy. Complex 3 was independently prepared from 1
4
within 1 day in yields up to around 80%17 under otherwise
identical conditions (entry 2), presumably because of the
higher electrophilicity of the substrate. With only 1 equiv of
NaBArF (entry 3), Me2SiH2 remains the preferred product,
4
leaving almost half of the substrate unreacted. Replacing NEt3
B
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Article
with HOTf and fully characterized including single-crystal X-
ray diffraction (Figure 2). Importantly, Me3SiOTf is hydro-
yield with only slighty longer reaction times (entry 3).
Hydrogenolysis of tBuMe2SiOTf was not successful (entry 4)
presumably because of steric shielding.
In comparison, double hydrogenolysis of the bistriflate
substrate Me2SiOTf2 to Me2SiH2 is remarkably facile and far
more rapid than that with the previously reported iridium
catalyst (5 mol % [Ir], 7 days, 53% yield).10 Full conversion
and 82% yield in dihydrosilane is obtained within only 1 h (1
mol % 1, entry 5). Furthermore, highly selective semi-
hydrogenolysis is obtained within the same time (entry 6)
using 1 equiv of base to give Me2SiHOTf in 82% yield.
During the course of catalysis, 3 is the only ruthenium
1
species observed by H and 31P NMR spectroscopy. After
some time, the conjugate acid [HNEt3][OTf] forms a separate
ionic liquid phase, which might be beneficial to driving the
reaction (see below). Importantly, the substrate, base, and
catalyst remain dissolved in the benzene layer.
Density functional theory calculations were performed for
the PMe2-truncated model system 1Me with NMe3 as the
model base to obtain further insight into the hydrogenolysis
mechanism (Scheme 3). Geometry optimizations were
performed at the RI-PBE-D3/def2-SVP level of theory.
Improved energies were obtained from subsequent SMD-
PBE0-D3/def2-TZVP single-point calculations validated
against explicitly correlated coupled-cluster energies.21 The
lowest-energy pathway commences with a barrierless ender-
gonic adduct formation between 1Me and Me3SiOTf to yield
intermediate I1Me. Si−O-bond heterolysis proceeds via ts1Me
as the turnover-limiting transition state of the overall process.
This leads to exergonic formation of I2Me, which is stabilized
by hydrogen bonding of the OTf− anion to the HPNP ligand.
Subsequent displacement of Me3SiH by the triflate anion
exhibits a small activation barrier (10 kcal mol−1 via ts2Me).
The resulting triflate complex 3Me represents the thermody-
namic resting state (ΔG° = −10.4 kcal mol−1), in line with the
experimental observations (see above). Regeneration of 1Me
proceeds without significant barriers and involves H2 binding
to I3Me, followed by base-assisted heterolysis via ts4Me. Overall,
hydrogenolysis of Me3SiOTf and regeneration of the catalyst is
computed to be slightly endergonic. This result suggests that
the reaction is partially driven by the [HNMe3]OTf ionic
liquid phase separation, which was approximated as an isolated
contact ion pair in the computational approach. The effective
activation barrier of 25 kcal mol−1 is therefore estimated from
the energy interval between the resting state 3Me and the rate-
limiting ts1Me. This value is in agreement with a reaction that
proceeds at room temperature.22
Figure 2. Molecular structure of 3 from single-crystal X-ray diffraction
(ellipsoids set at 30% probability; hydrogen atoms, except H111 and
H112, omitted for clarity). Selected bond lengths [Å] and angles
[deg]: Ru1−C17 1.8320(16), Ru1−N1 2.1969(13), Ru1−O2
2.2957(11), Ru1−P1 2.3195(4), Ru1−P2 2.3276(5), Ru1−H112
1.52(2); C17−Ru1−N1 175.11(6), N1−Ru1−O2 90.82(4), P1−
Ru1−P2 164.903(14), O2−Ru1−H112 178.3(8).
genated (1−4 bar of H2, room temperature) to trimethylsilane
in benzene with high yield (>80%) using NEt3 as the base
(Table 2, entries 1−3). Full conversion is obtained overnight
with 4 bar of H2 and 1 mol % catalyst. Almost the same yield is
achieved after 46 h with loadings as low as 0.1 mol % 1 (entry
2). A reduction of the H2 pressure (1.2 bar) gives the same
a
Table 2. Hydrogenolysis of Silyl Triflates with Catalyst 1
b
base
(equiv)
convn
(%)
reaction
time
b
entry
1
substrate
product (yield )
Me3SiOTf
NEt3
(1.1)
NEt3
(1.1)
NEt3
(1.0)
99
92
90
3
Me3SiH (85%)
Me3SiH (82%)
Me3SiH (85%)
<1%
18 h
46 h
26 h
7 days
1 h
The resting state 3Me is stabilized by N−H···OTf hydrogen
bonding, as confirmed by the experimental structure of 3
(Figure 2). The N-methylated catalyst [RuH(OTf)CO-
(MePNPiPr)] [4; MePNPiPr = MeN(CH2CH2PiPr2)2] was
therefore employed to probe for rate acceleration by resting-
state destabilization. The hydrogenolysis rate of Me3SiOTf
with NEt3 as the base is, in fact, slightly increased (91%
conversion after 130 min) with respect to 3 (81% conversion
after 135 min) under identical conditions.
The hydrogenolysis protocols outlined above provide key
precursors for facile organohydrochlorosilane synthesis in high
yield at mild conditions with low catalyst loadings. Chlorosilyl
triflate semihydrogenolysis could be an alternative route for
direct synthesis. Me2SiClOTf can be obtained from Me2SiCl2
with 1 equiv of HOTf as the main product according to in situ
NMR examination. However, isolation attempts by distillation
c
2
Me3SiOTf
Me3SiOTf
d
3
d
4
tBuMe2SiOTf NEt3
(1.1)
Me2SiOTf2
5
6
NEt3
(2.2)
NEt3
(1.0)
100
99
Me2SiH2 (82%)
Me2SiOTf2
Me2SiHOTf
(82%), Me2SiH2
(4%)
1 h
a
General conditions: 0.1 mmol of substrate, 1 μmol of 1, 4 bar of H2,
b
0.5 mL of C6D6, room temperature. Conversions/yields were
determined by 1H NMR integration of all signals in the MexSi region
around 0 ppm versus an internal standard (1,2,4,5-tetramethylben-
c
d
zene). 0.1 μmol of 1 (0.1 mol %). 1.2 bar of H2 was used.
C
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Inorganic Chemistry
Article
Scheme 3. Computed Pathway for Hydrogenolysis of Me3SiOTf Using 1Me [ΔG° in kcal mol−1 (SMD-PBE0-D3/def2-TZVP//
RI-PBE-D3/def2-SVP)]
lead to chloride/triflate dismutation (Scheme 4). At room
temperature, equilibration is slow (ca. 4 days) but considerably
Scheme 5. Hydrogenolysis of a Mixture of Me2SiCl2 and
Me2SiOTf2 with Catalyst 124
Scheme 4. Redistribution of Chlorosilanes and Silyl
Triflates
accelerated upon the addition of amines (e.g., NEt3 or 2,6-
lutidine) or 1 (ca. 1 h).23 Consequently, mixtures of Me2SiCl2
and Me2SiOTf2 might be directly used after equilibration
under catalytic conditions. Rapid (<5 h) full conversion with
respect to triflate is obtained with NEt3 as the base (1 mol %
1). However, Me2SiH2 is the main hydrogenolysis product
(36%).24 The desirable hydrochlorosilane Me2SiClH is
observed only in 5%24 spectroscopic yield, which could be
increased only to 12% using a Me2SiCl2/Me2SiOTf2 ratio of
5:1 to reduce the Me2SiOTf2 equilibrium concentration.
Screening of other ruthenium, iron, and iridium pincer
catalysts (see the SI) gave slightly varying dihydrosilane yields.
We therefore anticipate kinetic control of the selectivity.
Computational evaluation of the Me2SiCl2/Me2SiH2 dismuta-
tion equilibrium, in fact, suggests much higher Me2SiClH
yields under thermodynamic control (Me2SiCl2 + Me2SiH2 →
2Me2SiClH; ΔG° = −0.7 kcal mol−1). In fact, catalytic
R2SiH2/R2SiCl2 dismutation to hydrochlorosilanes has been
reported in the literature, and the experimentally derived
equilibrium constant for R = Me (ΔG°exp ≈ −1.3 kcal mol−1)
is in close agreement with our computational estimate.25
As a strategy to maintain thermodynamic control, weaker
bases than NEt3 (pKa,MeCN = 18.8)26 were screened. With 2,6-
lutidine (pKa,MeCN = 14.1)27 excess base is required for full
conversion (97%). Furthermore, Me2SiClH and 2,6-lutidinium
triflate eliminate H2 under argon, suggesting approximately
thermoneutral hydrogenolysis with the conjugate base. High
selectivities in Me2SiClH versus Me2SiH2 (>10:1) are obtained
for hydrogenolysis of a Me2SiCl2/Me2SiOTf2 (10:1)28 mixture
with 2,6-lutidine (10 equiv) as the base (Scheme 5). Following
the reaction by 1H NMR (Figure 3) reveals that the reaction is
considerably slower than bistriflate hydrogenolysis. Further-
Figure 3. Time-dependent concentration profiles of the reaction
depicted in Scheme 5.
more, the selectivity slightly changes over time in favor of
Me2SiClH. Therefore, high substrate conversion (>90%) and
Me2SiClH yields over 50%24 require about 1 week under these
conditions.
In summary, several catalytic hydrogenolysis routes to
organohydro- and halohydrosilanes are reported. Mild reaction
conditions (1−4 bar of H2, room temperature) at low catalyst
loadings (0.1−1 mol %) and reaction times could be obtained.
Especially, bistriflate (semi)hydrogenolysis rapidly affords the
organohydrosilane building blocks Me2SiH2 and Me2SiHOTf
in excellent yields. Experimental and computational evaluations
support a catalytic cycle via outer-sphere hydride transfer and
H2 heterolysis. Chlorosilane hydrogenolysis is enabled by
chloride precipitation with NaBArF , presumably via base-
4
stabilized silyl cations as key intermediates. In combination,
D
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Synthetic Procedures. Synthesis of Me2SiOTf2. Me2SiCl2 (6.0
mL, 0.05 mol, 1.0 equiv) was stirred at 0 °C and HOTf (12.5 mL,
0.14 mol, 2.8 equiv) added via syringe. The mixture was heated to 60
°C for 2 days with occasional removal of the HCl atmosphere by a
stream of argon. Excess acid was neutralized by the careful addition of
NEt3 (8 mL, 0.07 mol, 1.4 equiv) at 0 °C. The removal of volatiles in
vacuo and distillation (0.3 mbar, 37 °C) gave Me2SiOTf2 as a
the hydrogenolysis of chlorosilane/silyl triflate mixtures can be
optimized to directly give the hydrochlorosilane Me2SiClH in
moderate yields.
EXPERIMENTAL DETAILS
■
General Information. All experiments were carried out under an
argon atmosphere (Linde, 5.0) using Schlenk or glovebox techniques
(O2 and H2O below 0.1 ppm). NMR tubes were silanized with
Me2SiCl2, and all glassware was heated in a vacuum prior to use.
C6H6, Et2O (stabilized with 2,6-di-tert-butyl-4-methylphenol), and
pentane (HPLC-grade; Roth, VWR, or Sigma-Aldrich) were degassed
and dried by passing through columns packed with activated alumina.
Fluorobenzene was degassed and dried over molecular sieves (4 Å).
Deuterated solvents were purchased from Deutero GmbH and dried
over CaH2 (CD2Cl2) or Na/K (THF-d8 and C6D6) and trap-to-trap
transfer in vacuo. NEt3 was dried over KOH, distilled, and stored over
molecular sieves (4 Å). 2,6-Lutidine was dried over AlCl3, distilled,
and stored over molecular sieves (4 Å). Me3SiCl, Me2SiCl2,
Me2SiHCl, Me3SiOTf, tBuMe2SiOTf, and MeOTf were degassed
and distilled prior to use. 1,2,4,5-Tetramethylbenzene and KOtBu
were sublimed prior to use. NaBPh4, NaBF4, NaSbF6, KPF6, and
NaOTf were dried in vacuo prior to use. HOTf (ABCR) was used
without further purification. H2 (Linde, 6.0) was dried by passing
through a spiral cooling system, which was immersed in N2(l).
1
colorless oil (9 mL, 0.04 mol, 79%) in 97% purity according to H
1
and 19F NMR. H NMR (300.13 MHz, C6D6, 300 K): δ −0.01 (s,
CH3). 19F NMR (282.37 MHz, C6D6, 298 K): δ −76.66 (s, CF3). 29Si
1
NMR (59.63 MHz, C6D6, 298 K): δ −14.6 (determined by H−29Si
HMBC).
Synthesis of [RuH(OTf)CO(HPNPiPr)] (3). [Ru(H)2CO(HPNPiPr)]
(1; 100 mg, 0.23 mmol, 1.0 equiv) was dissolved in Et2O (6 mL) in a
J. Young flask, and HOTf (20 μL, 0.23 mmol, 1.0 equiv) was added.
The solution was evaporated to 5 mL in vacuo and the precipitated
product decanted off. After washing with pentane (3 × 3 mL) and
drying in vacuo, crude (99.5% purity) 3 (80 mg, 0.14 mmol, 60%)
was obtained as a white solid. After lyophilization, a suspension in
Et2O (0.5 mL) was stirred overnight, decanted off, and dried in vacuo
to give 3 as a white solid (75 mg, 0.13 mmol, 56%). Crystals suitable
for X-ray crystallography were grown by cooling a saturated Et2O
1
solution to −40 °C. H{31P} NMR (500.25 MHz, C6D6, 298 K): δ
4.52 (t (br), 3JHH = 11.3 Hz, 1H, NH), 2.68 (hept, 3JHH = 7.3 Hz, 2H,
CHsyn), 2.44 (m, 2H, NCH2), 1.88 (m, 2H, PCH2), 1.78 (hept, 3JHH
=
NaBArF ,29 2,6-lutidinium triflate,30 1,31 and 232 were prepared
6.9 Hz, 2H, CH), 1.55 (m, 4H, superposition of PCH2 and NCH2),
4
3
3
1.52 (d, JHH = 7.3 Hz, 6H, CH3), 1.03 (d, JHH = 6.9 Hz, 6H,
following published procedures.
CH3anti), 1.00 (d, JHH = 7.3 Hz, 6H, CH3), 0.73 (d, JHH = 6.9 Hz,
3
3
NMR spectra were recorded on Bruker Avance III HD 300, 400, or
500 (with broadband cryoprobe) spectrometers and calibrated to the
residual proton resonance of the solvent (C6D6, δH = 7.16 ppm, δC =
128.06 ppm; THF-d8, δH = 1.72 ppm/3.58 ppm, δC = 25.31 ppm/
67.21 ppm; CD2Cl2, δH = 5.32 ppm, δC = 53.84 ppm). 31P and 29Si
NMR chemical shifts are reported relative to phosphoric acid (δP =
0.0 ppm) and SiMe4 (δSi = 0.0 ppm), respectively. Signal multiplicities
were abbreviated as s (singlet), d (doublet), t (triplet), q (quartet), p
(pentet), sept (septet), m (multiplet), and br (broad). Liquid
injection field desorption ionization MS (LIFDI-MS) spectra were
measured under inert conditions. Elemental analyses were obtained
with an Elementar Vario EL 3 analyzer. IR spectra were recorded as
powder samples on a Bruker ALPHA FT-IR spectrometer with a
platinum ATR module.
6H, CH3), −20.9 (s, 1H, Ru−H (2JHP = 18.0 Hz by H NMR)).
1
13C{1H} NMR (125.80 MHz, C6D6, 298 K): δ 205.5 (t, JCP = 11.5
2
Hz, CO), 120.2 (obtained by 19F−13C HSQC), 54.0 (vt, N = |1JCP
+
3JCP| = 8.8 Hz, NCH2), 29.6 (vt, N = |2JCP + JCP| = 18.5 Hz, PCH2),
28.1 (vt, N = |1JCP + 3JCP| = 21.6 Hz, CH), 23.9 (vt, N = |1JCP + 3JCP| =
26.1 Hz, CHanti), 20.7 (vt, N = |2JCP + 4JCP| = 6.5 Hz, CH3), 20.1 (vt,
3
N = |2JCP + JCP| = 6.5 Hz, CH3), 18.7 (vt, br, N = |2JCP + 4JCP| = 1.9
4
Hz, CH3), 16.9 (vt, N = |2JCP + JCP| = 3.5 Hz, CH3). Assignments
4
were confirmed by 2D NMR. 31P{1H} NMR (202.52 MHz, C6D6,
298 K): δ 73.8 (s). 19F NMR (470.67 MHz, C6D6, 298 K): δ −77.6
(s). LIFDI-MS: m/z 585.0 (100%; [M]+), 436.1 (80%; [M − OTf]+).
IR: ν (cm−1): 3248 (N−H), 2934, 2871, 2035 (Ru−H), 1920 (C
O), 1879, 1468, 1278, 1231, 1221, 1214, 1188, 1164, 1025, 829, 636,
622. Anal. Calcd for C18H38F3NO4P2RuS: C, 36.98; H, 6.55; N, 2.40.
Found: C, 37.13; H, 6.42; N, 2.34.
Catalytic Protocols. Hydrogenolysis of Silyl Chlorides. NaBArF ,
4
1, and the base were dissolved in PhF in a J. Young NMR tube, and
the solution was frozen in N2(l). Chlorosilane was condensed onto
the mixture in a static vacuum, and the headspace was refilled with H2
(1.2 bar). The sample was thawed and immediately shaken. For
reactions at 4 bar, the NMR tube was nearly completely immersed in
N2(l) for 1 min during the addition of H2 before the tube was closed.
The products were identified by 1H and 1H−29Si HMBC NMR
spectroscopy and quantified by relative integration of the MexSi
signals versus an internal standard (1,2,4,5-tetramethylbenzene).
Hydrogenolysis of Pure Silyl Triflates. Silyl triflate, 1, and the base
were dissolved in C6D6 in a J. Young NMR tube. The mixture was
frozen in N2(l), and the headspace was evacuated, refilled with H2
(1.2 bar), and sealed. For reactions at 4 bar, the NMR tube was nearly
completely immersed in N2(l) for 1 min during the addition of H2
Synthesis of [RuH(OTf)CO(MePNPiPr)] (4). 2 (35.3 mg, 74.3 μmol,
1.0 equiv) and KOtBu (10.1 mg, 90 μmol, 1.2 equiv) were suspended
in Et2O (2 mL) and stirred for 3 h at room temperature. The mixture
was filtered through a fritted funnel and the resulting yellow solution
dried in vacuo. After extraction with pentane (4 × 4 mL total),
MeOTf (8.4 μL, 77 μmol, 1.0 equiv) was added. The precipitated
product was filtered off, washed with pentane (3 × 1.5 mL), and
extracted with benzene (3 × 0.5 mL). Evaporation of the solvent in
vacuo gave 4 as a white powder (33 mg, 74%). Crystals suitable for X-
ray crystallography were grown from a saturated solution of Et2O at
1
−40 °C. H{31P} NMR (500.25 MHz, C6D6, 298 K): δ 2.69 (hept,
3JHH = 7.2 Hz, 2H, CHsyn), 2.06 (s, 3H, NCH3), 1.91−1.82 (m, 4H,
NCHi superposition), 1.79 (hept, 3JHH = 6.9 Hz, 2H, CHanti), 1.60 (d,
3JHH = 7.2 Hz, 6H, CH3), 1.59−1.51 (m, 2H, PCH2syn), 1.43−1.38
1
before the tube was closed. The products were identified by H and
1H−29Si HMBC NMR spectroscopy and quantified by relative
integration of the MexSi signals versus an internal standard (1,2,4,5-
tetramethylbenzene).
(m, 2H, PCH2), 1.06 (d, 3JHH3 = 6.9 Hz, 6H, CH3anti), 0.97 (d, 3JHH
=
7.2 Hz, 6H, CH3), 0.73 (d, JHH = 6.9 Hz, 6H, CH3anti), −20.56 (s,
1
1H, Ru−H (2JHP = 19.0 Hz by H NMR)). 13C{1H} NMR (125.80
Hydrogenolysis of Mixtures of Silyl Triflates and Chlorides.
Me2SiOTf2, Me2SiCl2, and the catalyst were dissolved in C6D6 in a J.
Young NMR tube and shaken for 1.5 h. The base was added, and the
NMR tube was frozen in N2(l). The headspace was evacuated, refilled
with H2 (1.2 bar), and cooled for 1 min. After sealing, the tube was
warmed to room temperature, giving a pressure of about 4 bar. The
products were identified by 1H and 1H−29Si HMBC NMR
spectroscopy and quantified by relative integration of the MexSi
signals versus an internal standard (1,2,4,5-tetramethylbenzene).
MHz, C6D6, 298 K): δ 205.8 (t, 2JCP = 12.1 Hz, CO), 121.0 (q, 1JCF
=
320.1 Hz, CF3), 65.1 (vt, N = |2JCP + 3JCP| = 9.0 Hz, NCH2), 45.6 (s,
3
NCH3), 29.9 (vt, N = |1JCP + JCP| = 20.5 Hz, CHsyn), 28.1 (vt, N =
3
3
|1JCP + JCP| = 18.0 Hz, PCH2), 24.3 (vt, N = |1JCP + JCP| = 26.6 Hz,
C), 20.9 (superposition of two vt), N = |2JCP + JCP| = 6.0 Hz, CH3),
4
19.2 (s, CH3), 17.1 (vt, N = |2JCP + 4JCP| = 3.5 Hz, CH3). Assignments
were confirmed by 2D NMR. 31P{1H} NMR (202.52 MHz, C6D6,
298 K): δ 68.8 (s). 19F NMR (470.67 MHz, C6D6, 298 K): δ −77.5
(s). LIFDI-MS: m/z 599.1 (4%; [M]+), 450.2 (100%; [M − OTf]+).
E
DOI: 10.1021/acs.inorgchem.8b02336
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
IR: ν (cm−1): 2960, 2932, 2873, 2056 (Ru−H), 1917 (CO), 1460,
1295, 1235, 1220, 1155, 1032, 882, 821, 695, 633, 518. Anal. Calcd
for C19H40F3NO4P2RuS: C, 38.12; H, 6.74; N, 2.34. Found: C, 38.05;
H, 6.72; N, 2.33.
Aminocarbene Ligands Work as Catalysts for Hydrosilylation of
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ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b02336.
■
S
Detailed experimental procedures, characterization of
the products, and computational details (PDF)
Accession Codes
CCDC 1855506−1855507 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.
́
̈
Polym. Int. 1999, 48, 491. (c) Cancouet, P.; Daudet, E.; Helary, G.;
Moreau, M.; Sauvet, G. Functional polysiloxanes. I. Microstructure of
poly(hydrogenmethylsiloxane-co-dimethylsiloxane)s obtained by cat-
ionic copolymerization. J. Polym. Sci., Part A: Polym. Chem. 2000, 38,
826. (d) Beckmann, J.; Dakternieks, D.; Duthie, A.; Foitzik, R. C. The
use of Pearlman’s catalyst for the oxidation of Si−H bonds. Synthesis,
structures and acid-catalysed condensation of novel α,ω-oligosilox-
anediols HOSiMe2O(SiPh2O)nSiMe2OH (n = 1−4). Silicon Chem.
2003, 2, 27.
AUTHOR INFORMATION
Corresponding Authors
*E-mail: max.holthausen@chemie.uni-frankfurt.de.
*E-mail: sven.schneider@chemie.uni-goettingen.de.
■
ORCID
(6) Kalchauer, W.; Pachaly, B. In Handbook of Heterogeneous
Max C. Holthausen: 0000-0001-7283-8329
Sven Schneider: 0000-0002-8432-7830
̈
̈
Catalysis; Ertl, G., Knozinger, H., Schuth, F., Weitkamp, J., Eds.;
Wiley-VCH, 2008; p 2635.
Author Contributions
(7) (a) Kunai, A.; Ohshita, J. Selective synthesis of halosilanes from
hydrosilanes and utilization for organic synthesis. J. Organomet. Chem.
2003, 686, 3. (b) Wang, W.; Tan, Y.; Xie, Z.; Zhang, Z. An efficient
method to synthesize chlorosilanes from hydrosilanes. J. Organomet.
Chem. 2014, 769, 29.
A.G. performed all synthetic and spectroscopic work while
supervised by S.S., and J.I.S., U.S.K., and M.D. carried out the
quantum-chemical studies while supervised by M.C.H.
Crystallographic characterization was done by C.W. The
manuscript was written by A.G., J.I.S., M.C.H., and S.S. All
authors commented on the manuscript and approved the final
version.
(8) (a) Chulsky, K.; Dobrovetsky, R. B(C6F5)3-Catalyzed Selective
Chlorination of Hydrosilanes. Angew. Chem., Int. Ed. 2017, 56, 4744.
(b) Sturm, A. G.; Schweizer, J. I.; Meyer, L.; Santowski, T.; Auner, N.;
Holthausen, M. C. Lewis-base catalyzed selective chlorination of
monosilanes. Chem. - Eur. J. 2018, DOI: 10.1002/chem.201803921.
(9) Previously, Hidai and co-workers proposed silyl triflate
hydrogenolysis as one step in catalytic trimethylsilyl enol ether
hydrogenolysis: Nishibayashi, Y.; Takei, I.; Hidai, M.; Takei, I.;
Nishibayashi, Y.; Ishii, Y.; Mizobe, Y.; Uemura, S.; Hidai, M. Novel
Catalytic Hydrogenolysis of Trimethylsilyl Enol Ethers by the Use of
an Acidic Ruthenium Dihydrogen Complex. Angew. Chem., Int. Ed.
1999, 38, 3047. Takei, I.; Nishibayashi, Y.; Ishii, Y.; Mizobe, Y.;
Uemura, S.; Hidai, M. Novel catalytic hydrogenolysis of silyl enol
ethers by the use of acidic ruthenium dihydrogen complexes. J.
Organomet. Chem. 2003, 679, 32.
(10) (a) Tsushima, D.; Igarashi, M.; Sato, K.; Shimada, S. Ir-
Catalyzed Hydrogenolysis Reaction of Silyl Triflates and Halides with
H2. Chem. Lett. 2017, 46, 1532. (b) Beppu, T.; Sakamoto, K.;
Nakajima, Y.; Matsumoto, K.; Sato, K.; Shimada, S. Hydrosilane
Synthesis via Catalytic Hydrogenolysis of Halosilanes Using a Metal-
Ligand Bifunctional Iridium Catalyst. J. Organomet. Chem. 2018, 869,
75.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the European Research Council (Grant
646747) and the Deutsche Forschungsgemeinschaft (CRC
1073, Project C07) for funding and the graduate student
program CaSuS (to A.G.). Quantum-chemical calculations
were performed at the Center for Scientific Computing (CSC),
Frankfurt, Germany, on the FUCHS and LOEWE-CSC high-
performance compute clusters. Dr. C. Volkmann is acknowl-
edged for recording parts of the crystallographic data.
DEDICATION
■
This paper is dedicated to Prof. Dr. Dietmar Stalke on the
occasion of his 60th birthday.
̈
(11) (a) Kaß, M.; Friedrich, A.; Drees, M.; Schneider, S. Ruthenium
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(21) See the SI for full computational details.
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2
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1
1
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G
DOI: 10.1021/acs.inorgchem.8b02336
Inorg. Chem. XXXX, XXX, XXX−XXX