Custom Hydrosilane Synthesis Based on Monosilane

Article abstract of DOI:10.1016/j.chempr.2018.03.017

The omnipresence of silicon compounds with carbon substituents in synthetic chemistry hides the fact that, except for certain substitution patterns at the silicon atom, their preparation is often far from trivial. The challenge is rooted in the lack of control over nucleophilic substitution with carbon nucleophiles at silicon atoms with three or four leaving groups. For example, SiCl₄ usually converts into intractable mixtures of chlorosilanes, typically requiring several distillation cycles to reach high purity. Accordingly, there is no universal approach to silanes with heteroleptic substitution. Here, using a bench-stable SiH₄ surrogate, we introduce a general strategy for the on-demand synthesis of silicon compounds decorated with different aryl and alkyl substituents. Reliable protocols are the basis of the selective and programmable synthesis of dihydro- and monohydrosilanes; aryl-substituted trihydrosilanes are also accessible in a straightforward fashion. These otherwise difficult-to-access hydrosilanes are only three or fewer easy synthetic operations away from the SiH₄ surrogate. Synthesizing silicon compounds with different carbon substituents from inorganic silicon precursors, i.e., basic silicon chemicals with hydrogen, halogen, or alkoxy substitution, is an intricate and often insoluble task. It is generally difficult to chemoselectively address one of these groups in chemical reactions, particularly when two or more of those are identical. Complicated separation and purification procedures are the result. The challenge of making these silicon compounds containing silicon–carbon bonds, typically hydro- and chlorosilanes, is accentuated considering their high demand in academia and industry. The present approach is a step forward in solving those limitations. It hinges on the stepwise decoration of the silicon atom of a liquid monosilane surrogate. Further development of this strategy and adjusting it to industrial needs could pave the way to easy access of an even more diverse manifold of silicon compounds for synthetic chemistry and material science. Oestreich and colleagues present an approach to the chemoselective stepwise preparation of hydrosilanes with the general formula R_4–nSiH_n where n = 1–3 and R can be different aryl and alkyl groups. The starting point is a bench-stable SiH₄ surrogate with two Si–H bonds masked as cyclohexa-2,5-dien-1-yl substituents. A sequence of palladium-catalyzed Si–H arylation and B(C₆F₅)₃-promoted deprotection and transfer hydrosilylation enables the programmable synthesis of hydrosilanes, even with three different substituents at the silicon atom.

Full text of DOI:10.1016/j.chempr.2018.03.017

Article
Custom Hydrosilane Synthesis Based on
Monosilane
Weiming Yuan, Polina Smirnov,
Martin Oestreich
martin.oestreich@tu-berlin.de
HIGHLIGHTS
Cross-coupling of Si–H bonds and
aryl iodides not interfering with
skipped diene units
Synthetic application of liquid
monosilane surrogate
Straightforward access to a variety
of trihydro-, dihydro-, and
monohydrosilanes
Monohydrosilanes with three
different substituents at the silicon
atom
Oestreich and colleagues present an approach to the chemoselective stepwise
preparation of hydrosilanes with the general formula R4–nSiHn where n = 1–3 and
R can be different aryl and alkyl groups. The starting point is a bench-stable SiH4
surrogate with two Si–H bonds masked as cyclohexa-2,5-dien-1-yl substituents.
A sequence of palladium-catalyzed Si–H arylation and B(C6F5)3-promoted
deprotection and transfer hydrosilylation enables the programmable synthesis of
hydrosilanes, even with three different substituents at the silicon atom.
Yuan et al., Chem 4, 1–8
June 14, 2018 ª 2018 Elsevier Inc.
https://doi.org/10.1016/j.chempr.2018.03.017

Please cite this article in press as: Yuan et al., Custom Hydrosilane Synthesis Based on Monosilane, Chem (2018), https://doi.org/10.1016/
j.chempr.2018.03.017
Article
Custom Hydrosilane Synthesis
Based on Monosilane
Weiming Yuan,1,2 Polina Smirnov,1,2 and Martin Oestreich1,3,
*
The Bigger Picture
SUMMARY
Synthesizing silicon compounds
with different carbon substituents
from inorganic silicon precursors,
i.e., basic silicon chemicals with
hydrogen, halogen, or alkoxy
substitution, is an intricate and
often insoluble task. It is generally
difficult to chemoselectively
The omnipresence of silicon compounds with carbon substituents in synthetic
chemistry hides the fact that, except for certain substitution patterns at the sil-
icon atom, their preparation is often far from trivial. The challenge is rooted in
the lack of control over nucleophilic substitution with carbon nucleophiles at sil-
icon atoms with three or four leaving groups. For example, SiCl4 usually con-
verts into intractable mixtures of chlorosilanes, typically requiring several distil-
lation cycles to reach high purity. Accordingly, there is no universal approach to
silanes with heteroleptic substitution. Here, using a bench-stable SiH4 surro-
gate, we introduce a general strategy for the on-demand synthesis of silicon
compounds decorated with different aryl and alkyl substituents. Reliable proto-
cols are the basis of the selective and programmable synthesis of dihydro- and
monohydrosilanes; aryl-substituted trihydrosilanes are also accessible in a
straightforward fashion. These otherwise difficult-to-access hydrosilanes are
only three or fewer easy synthetic operations away from the SiH4 surrogate.
address one of these groups in
chemical reactions, particularly
when two or more of those are
identical. Complicated separation
and purification procedures are
the result. The challenge of
making these silicon compounds
containing silicon–carbon bonds,
typically hydro- and chlorosilanes,
is accentuated considering their
high demand in academia and
industry. The present approach is
a step forward in solving those
limitations. It hinges on the
INTRODUCTION
The silicon–carbon bond is not found in nature but is relevant to essentially any area
of synthetic chemistry. Although there are numerous ways to reliably form that bond,
methods are largely limited to silicon reagents with either one or more functional
groups of strictly orthogonal reactivity. Selective decoration of the silicon atom
with different carbon substituents in a controllable manner starting from simple
building blocks such as trialkoxysilanes or tetrahalosilanes is one of the remaining
challenges in silicon chemistry. The key problem is that nucleophilic displacements
at either of those silicon electrophiles do not stop at monosubstitution, usually af-
fording difficult-to-separate cocktails of the four possible silicon compounds (Fig-
ure 1A).1 This cannot be fully overcome with an excess of the silicon reagent. One
known controlling factor is steric hindrance, thereby allowing for the selective prep-
aration of di- or trisubstituted alkoxy- and halosilanes in selected cases, respectively.
Another documented solution to the problem is stepwise transition-metal-catalyzed
hydrosilylation of unsaturated hydrocarbons with dichlorosilane, obtainable in bulk
quantities.2–5 The accumulation of salt waste is another penalty often encountered
when converting the aforementioned silanes into the corresponding hydrosilanes
by hydride reduction, typically with LiAlH4 (Figure 1A). What is missing is the custom
synthesis of hydrosilanes R4–nSiHn, where n = 3, 2, and 1, based on the simplest sil-
icon molecule, i.e., monosilane, as a platform.
stepwise decoration of the silicon
atom of a liquid monosilane
surrogate. Further development
of this strategy and adjusting it to
industrial needs could pave the
way to easy access of an even
more diverse manifold of silicon
compounds for synthetic
chemistry and material science.
6
The enormous dangers associated with the handling of gaseous SiH4 have de-
terred synthetic chemists from using it,7–9 and hardly any synthetic chemistry
makes use of it. In an effort to address this limitation, our laboratory recently intro-
duced solid 1 as well as liquid 2 as bench-stable SiH4 surrogates (Figure 1B),10 and
Chem 4, 1–8, June 14, 2018 ª 2018 Elsevier Inc.
1

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j.chempr.2018.03.017
A
RM
(M = MgX or Li)
LiAlH4
SiX4
(X = halo and/or alkoxy)
RSiX3 + R2SiX2 + R3SiX + R4Si
RSiH3 + R2SiH2 + R3SiH
difficult separation
by distillation
difficult separation
by distillation or
chromatography
H
B
Si
H
Ar1
Alkyl
Alkyl
H
Si
Si
H
Alkyl
H
Ar1
Ar1
H
Pd(0)-catalyzed
Si–H arylation
or
Si
Si
Si
H
H
Ar1
H
H
2
1
(from (EtO)2SiCl2)
(from HSiCl3)
Alkyl
Si
Alkyl
bench-stable SiH4 surrogates
Si
H
Alkyl
Ar1
Ar1
Method III
Alkyl
Alkyl'
Method I: B(C6F5)3-catalyzed deprotection
H
Method II: B(C6F5)3-catalyzed transfer hydrosilylation
Method III: B(C6F5)3-catalyzed Si–H arylation
Method IV: Pt(0)-catalyzed hydrosilylation
Si
H
Ar1
Ar2
Figure 1. Silicon–Carbon Bond Formation and Hydrosilane Synthesis
(A) Traditional approach involving nucleophilic-substitution operations at the silicon atom.
(B) Planned on-demand synthesis based on SiH4 surrogates revolving around a single central platform.
tri(cyclohexa-2,5-dien-1-yl)silane (1) is now commercially available. The cyclohexa-
2,5-dien-1-yl substituents in 1 and 2 serve as placeholders for the Si–H bonds, and
these are set free by the action of the strong boron Lewis acid tris(pentafluoro-
phenyl)borane, B(C6F5)3.11 As SiH4 is almost insoluble in any solvent, the buildup
of SiH4 pressure becomes a potential risk. We therefore merged the above deprotec-
tion with the B(C6F5)3-catalyzed hydrosilylation of alkenes12 to directly and safely
consume the in-situ-liberated monosilane.13–15 The net reaction is an ionic transfer
hydrosilylation,16 providing access to alkyl-substituted dihydro- and monohydrosi-
lanes R4–nSiHn, where n = 2 and 1 and R = alkyl.10 We were also able to demonstrate
the compatibility of the cyclohexa-2,5-dien-1-yl units in 2 with platinum catalysis, and
that allowed for the preparation of a small set of alkyl-substituted trihydrosilanes
RSiH3, where R is the primary alkyl after B(C6F5)3-promoted deprotection.17 These
contributions did indeed open the door to SiH4-based synthesis of alkyl-substituted
hydrosilanes, but the installation of aryl groups at the silicon atom was not feasible.
The present work closes this gap by palladium-catalyzed arylation of a SiH4 surrogate
followed by a series of silicon–carbon bond-forming events (Figure 1B). By this, the
selective synthesis of more than 50 different silanes with various substitution patterns
becomes accessible.
1Institut fur Chemie, Technische Universitat
Berlin, Strasse des 17. Juni 115, 10623 Berlin,
Germany
¨
¨
2These authors contributed equally
3Lead Contact
*Correspondence: martin.oestreich@tu-berlin.de
https://doi.org/10.1016/j.chempr.2018.03.017
2
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H
(tBu3P)2Pd (5 mol %)
iPr2NH (3 equiv)
X
X
X
Si
I
B(C6F5)3 (2.5 mol %)
H
H
+
X
H
Si
Si
benzene
RT
24 hr
CD2Cl2
RT
19 hr
H
H
H
5a–5r
3a–3r
2 (1.05 equiv)
4a–4r
Me
6 (selected)
MeO
Me
Me
Me
Me
4a from 3a, 62%
(4a:5a = 95:5)
4b from 3b, 69%
(4b:5b = 100:0)
4c from 3c, 69%
(4c:5c = 94:6)
4d from 3d, 72%
(4d:5d = 92:8)
4e from 3e, 81%
(4e:5e = 96:4)
4f from 3f, 80%
(4f:5f = 97:3)
deprotection failed quant. deprotection quant. deprotection quant. deprotection quant. deprotection quant. deprotection
(decomposition)
Me
to yield 6b
to yield 6c
to yield 6d
to yield 6e
to yield 6f (not pure)
Me(O)C
Me
Cl
NC
4g from 3g, 66%
(4g:5g = 92:8)
4h from 3h, 44%
(4h:5h = 61:39)
4i from 3i, 68%
(4i:5i = 87:13)
4j from 3j, 71%
(4j:5j = 93:7)
4k from 3k, 64%
(4k:5k = 92:8)
4l from 3l, 45%
(4l:5l = 95:5)
deprotection failed
(no reaction)
quant. deprotection quant. deprotection quant. deprotection quant. deprotection deprotection failed
to yield 6g
to yield 6h
to yield 6i
to yield 6j
(no reaction)
S
N
O2N
F3C
H2N
HO
4m from 3m, 65%
(4m:5m = 87:13)
4n from 3n, 76%
(4n:5n = 96:4)
4o from 3o, 47%
(4o:5o = 87:13)
4p from 3p, —
(4p:5p = n.d.)
4q from 3q, 83%
(4q:5q = 100:0)
quant. deprotection
to yield 6q (not pure)
4r from 3r, trace
(4r:5r = n.d.)
deprotection failed quant. deprotection deprotection failed
(no reaction)
to yield 6n
(no reaction)
Figure 2. Palladium-Catalyzed Arylation of SiH4 Surrogate 2 Followed by B(C6F5)3-Catalyzed Deprotection to Arrive at Trihydrosilanes
RESULTS AND DISCUSSION
Si–H Arylation of SiH4 Surrogates
As an entry into the universal synthesis of R4–nSiHn, we chose the transition-metal-
catalyzed cross-coupling of the Si–H bond(s) in surrogates 1 and 2 and aryl halides.
There are several palladium(0)-18–21 and rhodium(I)-catalyzed22,23 methods
20
available, and they rely on either (EtO)3SiH18,19,22 or R2SiH2 and R3SiH21,23 as
the hydrosilane component. The big challenge in these reactions is competing
hydrodehalogenation along with the formation of the corresponding halosilane.24
Yamanoi and co-workers identified (tBu3P)2Pd together with a base as a catalyst
system that would largely suppress that side reaction.20,21 Applying their optimal
setup and variations thereof to the coupling of tri(cyclohexa-2,5-dien-1-yl)silane (1)
and 4-iodoanisole (3a), we always observed full conversion of both reactants to
result in hydrodeiodination exclusively; the iodinated surrogate was also detected
(Table S1). Conversely, less congested di(cyclohexa-2,5-dien-1-yl)silane (2) yielded
the desired hydrosilane 4a with Yamanoi and co-workers’ original procedure for di-
hydrosilanes ((tBu3P)2Pd [5 mol %], Et3N [3 equiv] in tetrahydrofuran at room tem-
perature);21 no 2-fold arylation was obtained, but anisole (5a) was still formed in
substantial amounts. To force back hydrodeiodination, we performed an extensive
optimization study (Table S2), and we were indeed able to minimize competitive
formation of 5a by using iPr2NH as base and benzene as solvent at room temper-
ature (Figure 2). Other coupling partners such as the respective aryl bromide and
triflate showed partial or no conversion (Table S2). The cyclohexa-2,5-dien-1-yl
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3

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substituents in 2 as well as in 1 remained untouched under all of the reaction
conditions tested.
With an optimized setup in hand, we turned our attention toward the scope of the
reaction with aryl iodides (Figure 2). Next to electron-rich 3a, iodobenzene 3b and
several methyl-substituted derivatives 3c–3g reacted selectively in good yields (Fig-
ures S1–S21). However, 2-iodo-1,3-dimethylbenzene was most likely sterically too
hindered, and no reaction happened (not shown). Interestingly, the selectivity was
eroded for both iodonaphthalenes 3h and 3i, particularly for the sterically more hin-
dered a-isomer 3h (Figures S22–S27). A broad range of electron-withdrawing func-
tional groups as in 3j–3n was tolerated (Figures S28–S42). A free aniline as in 3o
engaged in cross-coupling in moderate yield (Figures S43–S45), whereas a free
phenol as in 3p reacted sluggishly. We then tested those heteroaryl groups that
had worked in Yamanoi et al.’s case.21 A thien-2-yl substituent as in 3q was intro-
duced with excellent selectivity in high yield (Figures S46–S48), but the installation
of a pyridin-4-yl group as in 3r failed. Separation of the desired aryl-substituted
di(cyclohexa-2,5-dien-1-yl)silanes 4 from the hydrodeiodinated arene byproducts
5 by flash chromatography on silica gel was generally straightforward.
B(C6F5)3-Catalyzed Deprotection and Transfer Hydrosilylation of the Aryl-
Substituted Surrogates
The two cyclohexa-2,5-dien-1-yl groups attached to the silicon atom in 4 are masked
Si–H bonds, and we anticipated facile release of the aryl-substituted trihydrosilanes
6 by treatment with catalytic B(C6F5)3 (Figure 2). These trihydrosilanes 6 are highly
important precursors, i.e., for the generation of oligo- and polysilanes. The usual
way to prepare 6 is from trialkoxysilanes with LiAlH4 as the hydride source; that
step often furnishes low yields because of significant ligand redistribution.25,26
Conversely, the B(C6F5)3-catalyzed removal of the cyclohexa-2,5-dien-1-yl groups
in 4 in CD2Cl2 at room temperature enabled the rapid release of the trihydrosilanes
6 in quantitative yields (Figures 2 and S49–S75). Substrates containing Lewis-basic
sites that coordinate to the B(C6F5)3 catalyst did not participate, e.g., derivatives
4a (OMe), 4l (CN), or 4o (NH2).
After the successful release of the trihydrosilanes 6 from 4, we decided to directly
subject 4 to the previously reported B(C6F5)3-catalyzed transfer hydrosilylation of
carbon–carbon multiple bonds (Figure 3A).10,13,14,16 To achieve selective 1-fold hy-
drosilylation to arrive at dihydrosilanes 8, we used alkenes 7 as the limiting reagent,
i.e., an excess of 3.0 equiv of 4. With 10 mol % of B(C6F5)3 as catalyst, these transfer
hydrosilylations proceeded smoothly in CH2Cl2 at room temperature, leaving the re-
maining two Si–H bonds intact. Four different types of disubstituted alkenes were
exemplarily used, and isolated yields were good throughout (Figures S76–S93). It
is virtually impossible to prepare dihydrosilanes 8 with one aryl and one alkyl substit-
uent from SiX4 with organometallic reagents. Simply reversing the ratio of the two
reactants, i.e., increasing the amount of the alkene to 2.1 equiv on the basis of the
aryl-substituted surrogate 4, allowed for 2-fold transfer hydrosilylation (Figure 3A).
The monohydrosilanes 9 with one aryl and two identical alkyl groups formed selec-
tively in high yields (Figures S94–S117). The results are in agreement with earlier ob-
servations.10,13 We also attempted the 2-fold transfer hydrosilylation for internal tri-
ple bonds, and hex-3-yne (10a) and 1-phenylprop-1-yne (10b) were converted
quantitatively into the tertiary hydrosilanes 11 in good yields (Figures 3A and
S118–S123); the double bond geometries in 11ca and 11cb were determined to
be Z, and this is in accordance with the assumed intermediacy of carbocations.10,13
For the sake of completeness, we also tried a-olefins 7j and 7k but these always
4
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R2
H
A
R1
R3
B(C6F5)3 (10 mol %)
H
R3
R3
R2
R1
+
or
Si
Si
Si
R3
R2
CH2Cl2
RT
20 hr
R2
H
H
R1
R1
X
X
X
4c (X = Me)
or
4j (X = Cl)
7a–7i (alkenes)
8
9 or 11
w/ surrogates 4
or
w/ alkenes 7
10a and 10b (alkynes)
as the limiting reagent
as the limiting reagent
H
H
R
Ar
Si
Si
H
H
H
H
Ph
Ph
Ph
Me
Si
Ar
Si
Si
Me
Me
Cl
Cl
Ph
H
H
H
Me
Ar
8ca, 84%
8ja, 88%
Me
Ar
Me
R
H
H
X
for X = Me
9cd, 87%
9cg (R = Ph), 85%
(d.r. = 66:34)
9ch (R = C7H15), 55%
(d.r. = 66:34)
Si
Si
9ca (Ar = Ph), 95%
9ce (Ar = 4-MeC6H4), 72%
9cf (Ar = 4-FC6H4), 90%
for X = Cl
9ja (Ar = Ph), 90%
8cb, 71%
8jb, 82%
H
Et
Me
Si
Et
Ph
H
Si
Si
H
H
Si
Si
H
H
Et
Ph
H
Me
Me
Et
11ca, 88%
Me
Me
Me
Me
8cc, 60%
8cd, 45%
9ci, 62%
11cb, 70%
(along with 9cd in ratio of 86:14)
B
R
B(C6F5)3 (10 mol %)
R
+
R
Si
H
Si
CH2Cl2
RT
20 hr
Me
Me
R
4c
7j
7k
12cj
and
(R = Ph), 85%
12ck (R = C6H13), 78%
Figure 3. Selective B(C6F5)3-Catalyzed Transfer Hydrosilylation Using Aryl-Substituted Surrogates 4c and 4j
(A) Preparation of dihydrosilanes (left; 4 [0.3 mmol], 7 [0.1 mmol], B(C6F5)3 [0.01 mmol], CH2Cl2 [0.5 M], room temperature, 20 hr) and monohydrosilanes
(right; 4 [0.10 mmol], 7 or 10 [0.21 mmol], B(C6F5)3 [0.010 mmol], CH2Cl2 [0.5 M], room temperature, 20 hr).
(B) Preparation of silanes (4c [0.10 mmol], 7j or 7k [0.35 mmol], B(C6F5)3 [0.010 mmol], CH2Cl2 [0.5 M], room temperature, 20 hr).
furnished mixtures of dihydro- and monohydrosilanes 8 and 9 as well as fully
substituted silanes 12 under the above-described reaction conditions. Increasing
the amount of these not hindered alkenes to 3.5 equiv afforded the tetraorganosi-
lanes 12 cleanly (Figures 3B and S124–S127).
Further Diversification of the SiH4 Platform
Transfer hydrosilylation cannot bring about the selective installation of linear alkyl
chains. To realize this, we subjected selected aryl-substituted 4 to our platinum-
catalyzed hydrosilylation,17 and surrogates 4c and 4j were converted into 13ck
and 13jk with oct-1-ene (7k) as solvent (Figures 4A and S128–S133). As before,
the masked dihydrosilanes were easily deprotected with B(C6F5)3 to yield 8ck and
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A
H
PtCl2(cod) (10 mol %)
B(C6F5)3 (2.5 mol %)
Si
Si
Si
H
oct-1-ene (7k)
benzene
RT
6 hr
H
RT
24 hr
X
X
X
C6H13
C6H13
4c or 4j
13ck (X = Me), 67%
13jk (X = Cl), 61%
8ck (X = Me), 95%
8jk (X = Cl), 93%
B(C6F5)3 (10 mol %)
7a or 7b (alkenes)
or
10a (alkyne)
(1.5 equiv)
R3
CH2Cl2
RT
20 hr
R1
R2
Ph
H
Et
Ph
Et
Si
Si
Si
H
H
X
Me
Me
C6H13
C6H13
C6H13
9cka (X = Me), 83%
9jka (X = Cl), 86%
9ckb, 78%
14cka, 84%
B
H
Si
H
X
B(C6F5)3 (10 mol %)
+
Si
toluene
120°C
24 hr
Me
N
X
R
H
N
Me
R
Me
Me
4c (3.0 equiv)
15a 15c
16
–
H
H
H
Si
Si
H
Si
Br
16cc, 50%
H
H
Me
Me
Me
Me
Bn
N
Me
N
N
16ca, 60%
16cb, 71%
Me
Me
Me
Figure 4. Further Diversification of the Aryl-Substituted Surrogate
(A) Stepwise installation of two different alkyl groups by platinum-catalyzed hydrosilylation followed by B(C6F5)3-catalyzed transfer hydrosilylation.
(B) B(C6F5)3-catalyzed C–H silylation by electrophilic aromatic substitution combined with deprotection.
8jk (Figures S134–S139), thereby complementing the collection of aryl-/alkyl-
substituted dihydrosilanes 8. To access aryl-substituted hydrosilanes 9 with two
different alkyl groups, e.g., 9cka and 9ckb, we reacted 13ck and 13jk with represen-
tative alkenes 7a and 7b in B(C6F5)3-catalyzed transfer hydrosilylations (Figures
S140–S148); an example of an alkyne was also included (13ck/14cka with 10a; Fig-
ures S149–S151). This sequence offers unprecedented access to hydrosilanes with
three different substituents in a plannable way; selectivities were excellent and yields
satisfactory.
The palladium(0)-catalyzed Si–H bond arylation of SiH4 surrogate 2 did stop at the
monoarylation stage (cf. Figure 2). To install another aryl group at the silicon
6
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atom, we switched to Friedel-Crafts-type C–H silylation of electron-rich arenes
(Figure 4B).27 We as well as Hou and co-workers had recently found that B(C6F5)3 cat-
alyzes the silylation of arene C–H bonds,28,29 and we thought that this methodology
would, in analogy to the transfer hydrosilylation, combine silicon–carbon bond for-
mation and deprotection in a one-pot operation. Building block 4 reacted with an-
ilines 15 in good yield to deliver dihydrosilanes 16 with two different aryl substitu-
ents (Figures S152–S160); indole derivatives were however not compatible (not
shown).
Concluding Remarks
This work demonstrates that the protected version of SiH4, di(cyclohexa-2,5-dien-1-
yl)silane (2), is a highly useful starting point for the on-demand synthesis of hydrosi-
lanes with heteroleptic substitution patterns. The selective arylation of one of the
available Si–H bonds in 2 leads to the central building block 4, the point of
diversification. This is mainly achieved by B(C6F5)3-catalyzed processes, namely
deprotection and hydrosilylation or both (= transfer hydrosilylation) as well as
Friedel-Crafts-type C–H silylation. Diverse sets of tri-, di-, and monohydrosilanes
have been obtained. This approach overcomes the serious issues associated with
traditional methods based on completely unselective nucleophilic substitution of
SiCl4 and related cheap starting materials with carbon nucleophiles.
SUPPLEMENTAL INFORMATION
Supplemental Information includes Supplemental Experimental Procedures, 160
figures, and 2 tables and can be found with this article online at https://doi.org/
10.1016/j.chempr.2018.03.017.
ACKNOWLEDGMENTS
This research was supported by the Minerva Foundation (postdoctoral fellowship to
P.S., 2016–2017) and the Cluster of Excellence Unifying Concepts in Catalysis of the
Deutsche Forschungsgemeinschaft (EXC 314/2). M.O. is indebted to the Einstein
Foundation (Berlin) for an endowed professorship.
AUTHOR CONTRIBUTIONS
M.O. supervised the work. W.Y., P.S., and M.O. conceived and designed the exper-
iments. W.Y. and P.S. conducted the experiments and analyzed the data. W.Y., P.S.,
and M.O. discussed the results, and W.Y. and M.O. co-wrote the paper.
DECLARATION OF INTERESTS
The authors declare no competing interests.
Received: February 3, 2018
Revised: February 28, 2018
Accepted: March 23, 2018
Published: April 26, 2018
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