Pd(acac)2/Xantphos: A highly efficient and readily available catalyst for regioselective hydrosilylation of allenes

Article abstract of DOI:10.1080/10426507.2020.1845683

A convenient and efficient Pd(acac)₂/Xantphos-catalyzed regioselective hydrosilylation of allenes has been developed. This convenient catalyst proved to be suitable for a broad range of allenes, offering a general and efficient route to branche

Full text of DOI:10.1080/10426507.2020.1845683

Phosphorus, Sulfur, and Silicon and the Related Elements
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Pd(acac)2/Xantphos: A highly efficient and readily
available catalyst for regioselective hydrosilylation
of allenes
Xiao-Tao Liu , Guo-Liang Zhang , Jia-Hao Zeng , Jing Hu & Zhuang-Ping Zhan
To cite this article: Xiao-Tao Liu , Guo-Liang Zhang , Jia-Hao Zeng , Jing Hu & Zhuang-Ping
Zhan (2020): Pd(acac)2/Xantphos: A highly efficient and readily available catalyst for regioselective
hydrosilylation of allenes, Phosphorus, Sulfur, and Silicon and the Related Elements, DOI:
10.1080/10426507.2020.1845683
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PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
https://doi.org/10.1080/10426507.2020.1845683
Pd(acac)2/Xantphos: A highly efficient and readily available catalyst for
regioselective hydrosilylation of allenes
Xiao-Tao Liua, Guo-Liang Zhangb, Jia-Hao Zengb, Jing Huc, and Zhuang-Ping Zhanb
b
aWanxiang Technology Co., Ltd., Huaian, Jiangsu, P.R. China; Department of Chemistry, College of Chemistry and Chemical Engineering,
c
Xiamen University, Xiamen, Fujian, P.R. China; Modern Educational Technology and Practice Training Center, Xiamen University, Xiamen,
Fujian, P.R. China
ABSTRACT
ARTICLE HISTORY
Received 12 August 2020
Accepted 30 October 2020
A convenient and efficient Pd(acac)2/Xantphos-catalyzed regioselective hydrosilylation of allenes
has been developed. This convenient catalyst proved to be suitable for a broad range of allenes,
offering a general and efficient route to branched allylsilanes in high yields with exceptional regio-
selectivity. A Pd(0) species involved mechanism is proposed.
KEYWORDS
Hydrosilylation; allenes;
branched allylsilanes
GRAPHICAL ABSTRACT
Catalytic hydrosilylation of C-C multiple bonds is a highly group showed that employing a 3-iminophosphine ligand (L2)
step- and atom-economical route to organosilicon com- produces branched allylsilanes efficiently and regioselective-
pounds,[1] which represent benign synthetic reagents in a wide ly.[9b] More recently, our group designed a bithiophene-alkyne-
variety of subsequent reactions,[2] such as the allylsilanes and based ligand (L3) for the Pd-catalyzed regioselective allene
vinylsilanes are utilized in Hiyama[3] and Sakurai reactions.[4] hydrosilylation. It exhibits high selectivity and catalytic effi-
In contrast to the extensive studies that have been reported on ciency toward the production of branched allylsilanes.[9c] But
the hydrosilylation of alkene and alkyne,[5] the research on there are some inconveniences that they need to use glove box
hydrosilylation of allenes has started relatively late because the or synthesize the ligands (Scheme 1b). All the methods revealed
presence of two continuous orthogonal p bonds makes the that ligands are significant for controlling the regio- and stereo-
hydrosilylation of allene more challenging in controlling the selectivity. Herein, we demonstrate a handy and efficient
regio- and stereoselectivity.[8k,9a] Besides, some side reactions Palladium-catalyzed hydrosilylation of allenes, utilizing a com-
such as hydrogenation[6] and multiaddition[5d,7] of allene can mercially available Xantphos ligand to prepare branched-allylsi-
also complicate the catalytic system. In recent years, consider- lanes with excellent yield and regioselectivity (Scheme 1c).
able efforts have been devoted to developing chemo-, regio-,
In our initial screening experiments, we examined different Pd
and stereoselective hydrosilylation of allenes by transition metal catalysts and phosphorus ligands (Table 1). The 1-octylallene and
catalysts (Scheme 1a).[8,9] For example, in 2017, Ge et al. PhSiH3 were used as model substrates. We first tried the Pd(acac)2
reported a Co-catalyzed hydrosilylation at the terminal C¼ C and PPh3, getting the branched allylsilanes in low yield with poor
bonds of allenes that yielded linear allylsilanes,[8a] and a syn- selectivitiy (Table 1, entry 1). Then, we screened a series of biden-
thetic route to internal vinylsilanes involving the hydrosilyla- tate phosphine ligands. The dppm, dppbz, and dppf were ineffi-
tion of allenes with supported Pd-Au alloy catalysts has been cient for allene hydrosilylation (Table 1, entries 2–4). However,
developed by Shishido group.[8b] In 2013, the Montgomery the reaction afforded the branched allylsilanes in high isolated
group reported a Ni-catalyzed allene hydrosilylation for ter- yield with excellent selectivity when we used the dpephos or
minal vinylsilanes,[9a] and they also first reported the palla- Xantphos as ligand (Table 1, entries 5–6). Decreasing the catalyst
dium-catalyzed hydrosilylation of allene (L1) to access the loading to 1 mol% resulted in obvious reduction of yield (Table 1,
branched allylsilanes (B-Allylsilanes).[9a] Later, the Schmidt entry 7). Other palladium sources, such as Pd(OAc)2, PdCl2, and
CONTACT Xiao-Tao Liu
xiaotao.liu@wxintl.com
Wanxiang Technology Co., Ltd., Huaian 223300, Jiangsu, P.R. China; Zhuang-Ping Zhan
zpzhan@xmu.edu.cn
Department of Chemistry, College of Chemistry and Chemical Engineering, Xiamen University, Xiamen 361005, Fujian, P.R. China.
Supplemental data for this article is available online at https://doi.org/10.1080/10426507.2020.1845683.
ß 2020 Taylor & Francis Group, LLC

2
X.-T. LIU ET AL.
Scheme 2. Scope of allene hydrosilylation with PhSiH3.a,b,c,aReaction conditions:
allenes (1 mmol), PhSiH3 (1.2 mmol), Pd(acac)2 (2 mol%), xantphos (2 mol%),
THF (2 mL), 30 ꢀC, 0.5–3 h, N2 atmosphere. bYields of isolated products. cThe
selectivity of product (r.r. ¼ branched allylsilane product/all other isomers) was
> 15:1, determined by 1H NMR spectroscopy.
Scheme 1. Hydrosilylation of allenes: previous work and our work.
Table 1. Optimization of conditions for hydrosilylation of 1-octylallene
a
and PhSiH3 .
Entry
cat
Ligand
2a/yield%b
r.r.c
1
2
3
4
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(acac)2
Pd(OAc)2
PdCl2
PPh3
Dppm
Dppbz
Dppf
dpephos
xantphos
xantphos
xantphos
xantphos
xantphos
46
25
15
trace
90
96
65
44
trace
trace
1:1
1:2
1:3
–
30:1
32:1
13:1
3:1
–
5
6
7d
8
9
10
Pd(MeCN)2Cl2
–
aReaction conditions: 1-octylallene (0.25 mmol), phenylsilane (0.3 mmol), L (2 mol%), Pd source(2 mol%), THF (1 mL), 30 ꢀC, 1 h, N2 atmosphere. bThe yields of 2a
1
c
1
were determined by H NMR spectroscopy with 1,3,5-trimethoxybenzene as an internal standard. r.r. ¼ 2a/other isomers, determined by H NMR spectroscopy.
dPd(acac)2 (1 mol%), xantphos (1 mol%).
Pd(MeCN)2Cl2, were also tried, but these results were inferior to
Under the identified conditions (Table 1, entry 6), we
that of Pd(acac)2 (Table 1, entries 8–10). So we identified the opti- explored the substrate scope of a variety of allenes with pri-
mum conditions: hydrosilylation of allenes was performed with mary phenylsilane and the results are summarized in
2mol% Pd(acac)2 and Xantphos as the catalyst system at 30 ꢀC.
Scheme 2. In general, a variety of allenes reacted to produce

PHOSPHORUS, SULFUR, AND SILICON AND THE RELATED ELEMENTS
3
mechanistic studies and synthetic applications of the allylsilane
products have been pursued in our lab.
Funding
We are grateful to the National Natural Science Foundation of China
[Nos. 21772166 and 91845101].
References
Scheme 3. Proposed mechanism.
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1General procedure for hydrosilylation of allenes: In a nitrogen-filled Schlenk
tube, Pd(acac)2 (6 mg, 2 mmol%), Xantphos (12 mg, 2 mol%) were added to
THF (1 mL), followed by the addition of allene (1 mmol) and PhSiH3 (130 mg,
1.2 mmol) in THF (1 mL) under nitrogen. The reaction mixture was stirred at
30 ꢀC. When the reaction was completed (0.5–3 h, monitored by TLC), the
solvent was removed in vacuum. The crude product was purified directly by
silica gel column chromatography eluting with petroleum ether and ethyl
acetate to afford the corresponding product. The Supplemental Materials
1
contains sample H and 13C NMR spectra of the products 2 (Figures S1 – S13).

4
X.-T. LIU ET AL.
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