Manganese catalyzed dehydrogenative silylation of alkenes: Direct access to allylsilanes

Article abstract of DOI:10.1016/j.tetlet.2020.152053

Dehydrogenative silylation of alkenes with silanes to produce allylsilanes is achieved through manganese catalysis with a wide scope of substrate tolerance. This transformation involves silane radicals initiated by manganese complex without additional oxidant additives. It offers a general, convenient and practical protocol with excellent functional group compatibility and gram-scale capacity for the modular synthesis of allylsilanes.

Full text of DOI:10.1016/j.tetlet.2020.152053

Journal Pre-proofs
Manganese catalyzed dehydrogenative silylation of alkenes: direct access to
allylsilanes
Shang Wu, Ying Zhang, Hongyan Jiang, Ning Ding, Yanbin Wang, Qiong Su,
Hong Zhang, Lan Wu, Quanlu Yang
PII:
S0040-4039(20)30499-8
DOI:
Reference:
https://doi.org/10.1016/j.tetlet.2020.152053
TETL 152053
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
22 April 2020
12 May 2020
15 May 2020
Please cite this article as: Wu, S., Zhang, Y., Jiang, H., Ding, N., Wang, Y., Su, Q., Zhang, H., Wu, L., Yang, Q.,
Manganese catalyzed dehydrogenative silylation of alkenes: direct access to allylsilanes, Tetrahedron Letters
(2020), doi: https://doi.org/10.1016/j.tetlet.2020.152053
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version
will undergo additional copyediting, typesetting and review before it is published in its final form, but we are
providing this version to give early visibility of the article. Please note that, during the production process, errors
may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
© 2020 Published by Elsevier Ltd.

Graphical Abstract
To create your abstract, type over the instructions in the template box below.
Fonts or abstract dimensions should not be changed or altered.
Manganese catalyzed dehydrogenative
silylation of alkenes: direct access to
allylsilanes
Dehydrogenative silylation of alkenes with
silanes to produce allylsilanes is achieved
through manganese catalysis with a wide
a,*
a
a
a
a
a, ***
a
a,
scope of substrate tolerance. This
Shang Wu , Ying Zhang , Hongyan Jiang , Ning Ding , Yanbin Wang , Qiong Su
***, Quanlu Yangb,**
, Hong Zhang , Lan Wu
1. aKey Laboratory for utility of Environment-Friendly Composite Materials and Biomass in university of Gansu
Province, College of Chemical Engineering, Northwest Minzu University, Lanzhou, Gansu 730030, People's
Republic of China.
E-mail: chwush84@163.com
bCollege of Chemical Engineering, Lanzhou University of Arts and Science, Beimiantan 400, Lanzhou, Gansu
730000, People's Republic of China.
E-mail: yangquanlu2002@163.com
Mn2(CO)10 (5 mol%)
R,3SiH
+
SiR,3
R
R
160 oC
Up to 81% yield
R = (Het)aryl-
or aryl-
R' = alkyl-
or aryl-
> 20:1 regioselectivity
Wide tolerance of hydrosilanes

1
Tetrahedron Letters
journal homepage: www.elsevier.com
Manganese catalyzed dehydrogenative silylation of alkenes: direct access to
allylsilanes
Shang Wua, , Ying Zhanga, Hongyan Jianga, Ning Dinga, Yanbin Wanga, Qiong Sua, ***, Hong Zhanga, Lan
Wua, ***, Quanlu Yangb,**
aKey Laboratory for utility of Environment-Friendly Composite Materials and Biomass in university of Gansu Province, College of Chemical Engineering,
Northwest Minzu University, Lanzhou, Gansu 730030, People's Republic of China.
E-mail: chwush84@163.com
bCollege of Chemical Engineering, Lanzhou University of Arts and Science, Beimiantan 400, Lanzhou, Gansu 730000, People's Republic of China.
E-mail: yangquanlu2002@163.com
———
ARTICLE INFO
ABSTRACT
 Corresponding author.
S. Wu, E-mail address: E-mail: chwush84@163.com; Q. Yang, E-mail address: yangquanlu2002@163.com
Article history:
Received
Received in revised form
Accepted
Dehydrogenative silylation of alkenes with silanes to produce allylsilanes is achieved through
manganese catalysis with a wide scope of substrate tolerance. This transformation involves
silane radicals initiated by manganese complex without additional oxidant additives. It offers a
general, convenient and practical protocol with excellent functional group compatibility and
gram-scale capacity for the modular synthesis of allylsilanes.
Available online
2009 Elsevier Ltd. All rights reserved.
Keywords:
Manganese catalysis
Allylsilane synthesis
Dehydrogenative silylation
Allyl arenes
Alkenes
1. Introduction
(a) Silyl-Heck reaction
[Pd]
+
R
TMSI
R
TMS
Allylsilanes are important building blocks as nucleophiles in
organic synthesis1. But for a long time, these compounds are
difficult to prepare. Among those established methods, synthesis
of allylsilanes from easily available materials remains rare. In
recent years, transition metal catalyzed alkene silylation reactions
are found to be important means for organosilane synthesis2.
Silyl-Heck reactions catalyzed by palladium provided new
approaches to vinyl- and allylsilanes3, but the silyl halides used in
these reactions are usually moisture sensitive, toxic and difficult
to prepare (Scheme 1, a).
(b) Chirik, 2014
Me
N
N
Me
Co
Me
N
OSiMe3
Me
Me3SiO
+
H
Me
Si
Si
R
R
OSiMe3
OSiMe3
(c) Faltynek, 1983
H2Si
HMCTS
O
+
[Mn(CO)5SiPh3]
SiH2
O
55%
+
180 o
C
O
HMCTS
O
+
25%
R
HMCTS-H
Untiring efforts were devoted to reformations of the secular
transition metal catalyzed alkene silylations and other
11%
(d) Wang, 2018
SiH
Si
methodologies. In 2014, Chirik et al.4 have reported
a
[Mn2(CO)10
]
+
R
bis(imino)pyridine cobalt methyl complex catalyzed allylsilane
synthesis (Scheme 1, b). Its mechanism involved alkene insertion
into an initially formed cobalt silyl complex and followed by a
selective β-hydrogen elimination to form the allylsilanes. Similar
studies and improvements were thereby reported by Xu5 and
coworkers. But so far, due to the high energy barrier of
dehydrogenation and difficulty of regio-, stereo-selectivity
control, effective approaches to allylsilane synthesis still remain
rare6.
Ph
Ph
-H elimination
Mn(CO)5
Mn(CO)5
radical coupling
[Si]
[Si]
R
R
(e) This work: dehydrogenative silylation of alkenes to produce allylsilanes
Mn2(CO)10 (5 mol%)
+
Ph
R3SiH
Ph
SiR3
Scheme 1. Transition metal catalyzed alkene silylation and
allylsilanes synthesis.

2
Tetrahedron
Studies
on
earth-abundant
manganese
catalyzed
3
Mn2(CO)10
Mn2(CO)10
Mn2(CO)10
Mn2(CO)10
Mn2(CO)10
Mn2(CO)10
Mn2(CO)10
Mn2(CO)10
MnBr(CO)5
Mn2(CO)10
160
120
180
160
160
160
160
160
160
150
-
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
3:1
72%
3%
2%
3%
63%
14%
55%
40%
trace
trace
45%
40%
4%
transformations of silanes have blossomed and harvested many
achievements in recent years. Among these transformations,
studies on manganese catalyzed alkene silylations also obtained
fruitful achievements7, 8 ever since the first example published in
1983 (Scheme 1, c)8a. But so far, most of these reactions mainly
produce hydrosilylation products. Recently, Wang and
coworkers9a reported a manganese catalyzed silylation of alkenes.
In this work, they disclosed a β-hydrogen elimination process of
the manganese radical intermediates, which differentiated from
the hydrosilylation process to produce the dehydrogenative
products (Scheme 1, d).
4
-
4%
29%
trace
14%
trace
trace
15%
8%
5
-
65%
20%
trace
trace
24%
12%
2%
trace
2%
6
hexane
THF
dioxane
decalin
toluene
-
7
trace
trace
3%
8
9
As a key step involved in transition metal catalyzed alkene
dehydrogenative functionalizations, we consider the β-hydrogen
elimination may also induce an olefin migration to produce allyl
groups. Herein, we report an approach of manganese catalyzed
dehydrogenative silylation of allyl benzene derivatives to
produce allylsilanes through a selective β-hydrogen elimination
process (Scheme 1, e).
10
11
12
1%
trace
10%
hexane
19%
2%
6%
38%
a
Reaction conditions: 1a (3.0 mmol), 2a (1.0 mmol), Mn2(CO)10 (5
mol%), neat or with solvent (1 mL).
b Yields are determined by GC-MS, and calculated based on triethylsilane.
2.2. Scope
2. Results and discussion
2.1. Optimizations
With the optimized conditions, a series of allyl benzene and
silanes were tested for an exploration of the substrate scope
(Scheme 2). Various allyl arenes were reacted with triethylsilane
(2a), and they are well tolerated, giving the corresponding allyl
silane products (3a-3l) in good yields and selectivity. Substrates
in allyl benzene weakly affect the yields. Heterocycles (1m, 1n)
are also tolerated. In previous reports, silanes were usually not
widely tolerated. Here in our method, different alkyl and aryl
silanes are well sustained (3o-3r). Above all, this protocol
exhibited wide substrate tolerance to give the allylsilane products
in good selectivity. And all alkene substrates were produced with
the corresponding molecules in trans-configurations only.
At the outset of our studies, the reaction conditions were
optimized with allyl benzene (1a) and triethylsilane (2a) as
starting materials (table 1, and SI for details). To our delight,
with the common manganese catalyst Mn2(CO)10, the desired
allylsilane product (3a) was obtained, along with several
reasonable byproducts: vinyl silane 4a, hydrosilylation product
5a and hydrogenation product 6a. Carefully scan of the
conditions disclosed that temperature, material ratio and solvent
tremendously affect the yields and selectivity among these
products. We therefore further investigated the effects on the
reaction selectivity of the reaction conditions. As the
hydrogenation product, yields of 6a keep in line with the
dehydrosilylaiton products 3a and 4a. Like the previous reports,
material ratio between alkene and silane affect the hydro-
/dehydrosilylaiton selectivity heavily (entry 1-3). Likewise,
higher temperature promotes the dehydrosilylaiton process over
the hidrosilylation, and increase tendency of selective β-hydrogen
elimination to produce 3a than 4a (entry 3 vs. entry 4). But a
temperature too high may induce the deterioration of alkenes and
decrease the yields (entry 5). Solvents (entry 6-10) and additives
(entry 14-17 of table S2) don’t enhance the transformation. And
another common manganese catalyst Mn(CO)5Br performed
poorly in this transformation. Finally, with Wang’s condition9a
(table S1, entry 19), the products were observed in low
conversions. Therefore, an optimized condition of this catalytic
Mn2(CO)10 (5 mol%)a
R3SiH
+
R
SiR3
R
160 oC, 12 h
2
3
1
SiEt3
SiEt3
SiEt3
Me
MeO
SiEt3
3b, 78%
3c, 73%
3a, 72%
3d, 68%
SiEt3
SiEt3
SiEt3
F3C
F
F
3e, 72%
3f, 70%
SiEt3
tBu
SiEt3
Cl
NC
o
regime to produce 3a at 160 C under a solvent free condition
was then concluded with good selectivity and yields of 3a (table
1, entry 3).
3g, 54%
3j, 42%
3h, 76%
3i, 75%
Me
SiEt3
MeS
SiEt3
SiEt3
O2N
S
Table 1. Optimizations of the conditionsa
3l, 79%
3k, 58%
O
SiMe2tBu
Ph
SiEt3
+
Ph
+
SiEt3
Me
SiEt3
SiEt3
Mn2(CO)10 (5 mol%)
conditions
4a
+
3a
Ph
Et3SiH
3m, 66%
3p, 67%
3o, 81%
3r, 71%
3n, 56%
1a
2a
+
Ph
SiEt3
Ph
6a
SinPr3
5a
SiMe2Bn
SiMePh2
3q, 52%b
temp
Yield[b]
5a
en
try
catalyst
.
solvent
1a:2a
(oC)
3a
4a
6a
Scheme 2. Scope (a Conditions: 1a (3.0 mmol), 2a (1.0 mmol),
Mn2(CO)10 (5 mol%), neat, 160 oC, 12 h; b 180 oC)
1
2
Mn2(CO)10
Mn2(CO)10
160
160
-
-
1:3
1:1
16%
32%
trace
1%
55%
18%
20%
30%
In a gram scale test (10 mmol scale), product 3a was obtained
with a stability of yield and selectivity (Scheme 3), which
revealed the potential value of its industrial application.

3
3. Conclusion
Mn2(CO)10 (5 mol%)
+
Ph
Et3SiH
Ph
SiEt3
In conclusion, we have reported an example of
dehydrogenative coupling of allyl arenes with silanes enabled by
a commercially available Mn2(CO)10 complex catalysis. This
manganese catalytic regime can provide an access to extensive
library of allylsilanes from cheap and easily available alkenes and
silanes with effectively selectivity, wide scope tolerance and
good yields. A proposed mechanism is suggested based on
experimental studies and references. This method can provide a
robust path to synthetically relevant allylsilanes. Further
1a (30 mmol)
3a (1.63 g, 70%)
2a (10 mmol)
Scheme 3. Gram scale test
2.3. Mechanism studies
In order to have an insight of the mechanism, a series of
experiments were carried out (Scheme 4). Radical trapping test
supports the inference of its radical process (Scheme 4, a).
Deuterium labeling study (Scheme 4, b) provides evidence for
the existence of the proposed intermediate D (Scheme 4, e),
which can lead to both observed products But the following β-C-
H bond cleavage of D may not be the rate-limiting step as
implied by the KIE test (Scheme 4, c). We also suspect that
preference of selective β-hydrogen might be determined
thermodynamically by the substrate structure, as linear alkene 1o
bias the selectivity toward vinylsilane product (Scheme 4, d).
investigations
on
manganese
catalysis
and
alkene
functionalizations are ongoing in our group.
Acknowledgments
This work is supported by the National Natural Science
Foundation of China (No. 21962017, 21968032 and 51563022),
the Fundamental Research Funds for the Central Universities
(31920190016, 31920200086, 31920200042, 31920200002), and
the Northwest Minzu University’s Double First-class and
Characteristic Development Guide Special Funds-Chemistry Key
Disciplines in Gansu Province (No. 11080316).
(a) Radical trapping
Standard conditions
+ Et3SiH
Ph
SiEt3
+
+
Ph
SiEt3
Ph
TEMPO or BHT
trace
1a
trace
2a
References and notes
(b) Deuterium labeling
Standard conditions
+ Et3SiH
Ph
Ph
Ph
SiEt3
SiEt3
Ph
Ph
SiEt3
SiEt3
1.
For allylsilanes in synthesis: a) T. K. Sakar, Sci. Synth. 2002, 4,
837; b) A. Hosomi, Acc. Chem. Res. 1988, 21, 200; c) Y.
Yamamoto, N. Asao, Chem. Rev. 1993, 93, 2207; d) C. E.Masse, J.
S. Panek, Chem. Rev. 1995, 95, 1293; e) S. E.Denmark, J. Fu,
Chem. Rev. 2003, 103, 2763; f) I. Fleming A. Barbero, D. Walter,
Chem. Rev. 1997, 97, 2063.
72%
52%
1a
2%
D
2a
D
D
D
D
Standard conditions
+
+ Et3SiH
Ph
1a[D]
2a
20%
(c) KIE study
2.
3.
K. M. Korch, D. A. Watson, Chem. Rev. 2019, 119, 8192.
Initial study of palladium catalyzed silyl-Heck reaction: a) H.
Yamashita, T. Kobayashi, T. Hayashi, M. Tanaka, Chem. Lett.
1991, 20, 761; palladium catalyzed silyl-Heck reaction providing
allyl silaines: b) J. R. McAtee, S. E. Martin, D. T. Ahneman, K. A.
Johnson, D. A. Watson, Angew. Chem. Int. Ed. 2012, 51, 3663; c)
J. R. McAtee, G. P. A. Yap, D. A. Watson, J. Am. Chem. Soc.
2014, 136, 10166; d) S. B. Krause, J. R. McAtee, G. P. A. Yap, D.
A. Watson, Org. Lett. 2017, 19, 5641.
C. Atienza, T. Diao, K. Weller, S. Nye, K. Lewis, J. Delis, J.
Boyer, A. Roy, P. J. Chirik, J. Am. Chem. Soc. 2014, 136, 12108.
W. Yu, Y. Luo, L. Yan, D. Liu, Z. Wang, P. Xu, Angew. Chem.
Int. Ed. 2019, 58, 10941.
Other examples: a) C. Cheng, E. M. Simmons, J. F. Hartwig,
Angew. Chem. Int. Ed. 2013, 52, 8984; b) M. P. Doyle, G. A.
Devora, A. O. Nefedov, K. G. high, Organometallics, 1992, 11,
549; c) A. M. LaPointe, F. C.Rix, M. Brookhart, J. Am. Chem.
Soc. 1997, 119, 906; d) Y. Jiang, O. Blacque, T. Fox, C. M. Frech,
H. Berke, Chem. Eur. J. 2009, 15, 2121; e) R. N. Naumov, M.
Itazaki, M. Kamitani, H. Nakazawa, J. Am. Chem. Soc. 2012, 134,
804.
conditions
KH
conditions
KD
1a + 2a
3a ;
1a[D] + 2a
KH/KD = 1.25
3a[D]
(d) Linear alkene performance
Standard
conditions
nPr
SiEt3
3s, 18%
nPr
SiEt3
+ Et3SiH
+
1o
2a
4s, 27%
(e) Proposed mechanism
radical coupling
Ph
SiEt3
Ph
Ph
1a
4.
5.
6.

'

C
Et3Si
SiEt3
B
-H vs. '-H elimination
Mn(CO)5
D
Et3SiH
2a
3a
(CO)5Mn
A
(CO)5MnH
(CO)5MnH
(CO)5Mn
A
E
E
HAT
Me
Ph
Ph
Ph
1a
7.
8.
For a review on Mn-catalyzed hydrosilylations: X. Yang, C.
Wang, Chem. Asian J. 2018, 13, 2307.
Scheme 4. Controlled experiments and proposed mechanism
Examples of Mn-catalyzed hydrosilylations: a) S. L. Pratt, R. A.
Faltynek, J. Organomet. Chem. 1983, 258, C5; b) W. Jondi, A.
Zyoud, W. Mansour, A. Q. Husseinb, H. S. Hilal, J. React. Chem.
Eng. 2016, 1, 194; c) J. S. Price, D. J. H. Emslie, J. F. Britten,
Angew. Chem. Int. Ed. 2017, 56, 6223; e) J. H. Docherty, J. Peng,
A. P. Dominey, S. P. Thomas, Nat. Chem. 2017, 9, 595; f) J. R.
Carney, B. R. Dillon, L. Campbell, S. P. Thomas, Angew. Chem.
Int. Ed. 2018, 57, 10620; g) T. K. Mukhopadhyay, M. Flores, T.
L. Groya, R. J. Trovitch, Chem. Sci. 2018, 9, 7673.
According to the results above and previous literatures9a,10, a
proposed mechanism was suggested (Scheme 4, e). Silyl radical
B is initiated by manganese radical A, and is then added to 1a to
produce intermediate C. Followed by a radical coupling with A,
the resulting intermediate D may undergo a competitive β-
hydrogen elimination to give the product 3a and a manganese
hydride species E. Followed with a hydrogen transfer from E to
another alkene as acceptor, the hydrogenation product 6a is
produced, and the catalyst is regenerated.
9.
a) X. Yang, C. Wang, Chin. J. Chem. 2018, 36, 1047; b) X. Yang,
C. Wang, Angew. Chem. Int. Ed. 2018, 57, 923.
10. For mechanism studies of Mn catalyzed silylations, radical
processes: a) L. Wang, J. M. Lear, S. M. Rafferty, S. C. Fosu, D.
A. Nagib, Science, 2018, 362, 225; b) R. J. Trovitch, Acc. Chem.
Res. 2017, 50, 2842; c) R. S. Herrick, T. R. Herrinton, H. W.
Walker, T. L. Brown, Organometallics, 1985, 4, 42.

4
Tetrahedron
Declaration of interests
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
1. Manganese catalyzed dehydrogenative silylation of
alkenes with silanes
2. Silane radicals initiated by manganese complex
without additional oxidants
3. Convenient and practical protocol for the modular
synthesis of allylsilanes
Graphical Abstract
Mn2(CO)10 (5 mol%)
R,3SiH
+
R
SiR,3
R
160 oC
 Up to 81% yield
R = (Het)aryl-
or aryl-
R' = alkyl-
or aryl-
 > 20:1 regioselectivity
 Wide tolerance of hydrosilanes
Abstract: We have reported an example of
dehydrogenative coupling of allyl arenes with
silanes enabled by a commercial available
Mn2(CO)10 complex catalysis.