Xantphos Doped POPs-PPh3 as Heterogeneous Ligand for Cobalt-Catalyzed Highly Regio- and Stereoselective Hydrosilylation of Alkynes

Article abstract of DOI:10.1002/asia.201801241

A Co(acac)₂/POL-Xantphos@10PPh₃-catalyzed hydrosilylation of unsymmetrical internal alkynes with Ph₂SiH₂ has been developed for the synthesis of highly selective syn-α-vinylsilane products. Furthermore, terminal alkynes were also used and gave the products with excellent regioselectivity and a wide functional group tolerance. Because this porous organic polymer combines the selectivity and activity merits of Xantphos with the stability advantage derived from the high concentration of PPh₃, the Co(acac)₂/POL-Xantphos@10PPh₃ can be recycled multiple times without loss of activity and selectivity. This heterogeneous catalyst is expected to find promising applications in industrial synthesis.

Full text of DOI:10.1002/asia.201801241

CHEMISTRY
AN ASIAN JOURNAL
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Accepted Article
Title: Xantphos Doped POPs-PPh3 as Heterogeneous Ligand
for Cobalt-Catalyzed Highly Regio- and Stereoselective
Hydrosilylation of Alkynes
Authors: Ren-Hao Li, Guo-Liang Zhang, Jia-Xing Dong, Ding-Chang
Li, Ying Yang, Ying-Ming Pan, Hai-Tao Tang, Li Chen, and
Zhuang-Ping Zhan
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10.1002/asia.201801241
Chemistry - An Asian Journal
FULL PAPER
Xantphos Doped POPs-PPh3 as Heterogeneous Ligand for
Cobalt-Catalyzed Highly Regio- and Stereoselective
Hydrosilylation of Alkynes
Ren-Hao Li,[a] Guo-Liang Zhang,[a] Jia-Xing Dong,[a] Ding-Chang Li,[a] Ying Yang,[a] Ying-Ming Pan,[b]
Hai-Tao Tang,*[b] Li Chen[a] and Zhuang-Ping Zhan*[a]
Dedication ((optional))
Abstract: A Co(acac)2/POL-Xantphos@10PPh3-catalyzed hydrosily-
lation of unsymmetrical internal alkynes with Ph2SiH2 have been
firstly developed for the synthesis of highly selectivity syn-α-
vinylsilane products. Furthermore, the terminal alkynes was also
developed with excellent regioselectivity and wide functional group
tolerance. Due to this porous organic polymer combines the
selectivity and activity merits of Xantphos ligands with the stability
advantage derived from the high concentration of PPh3 ligands and
Xantphos firmly coordinated with Co(acac)2, the Co(acac)2/POL-
Xantphos@10PPh3 can recycle multiple times without loss of activity
and selectivity. This heterogeneous catalyst is expected to find
promising applications in industrial synthesis.
catalytic system.
Figure 1. Regio- and stereoselectivity in hydrosilylation of terminal and
internal alkyne
Introduction
In the past decades, a series of noble metal-catalyzed
hydrosilylation reactions have selectively formed (E)-β-
vinylsilanes. Platinum-catalyzed hydrosilylation of alkenes is one
of the most frequently conducted catalytic processes due to its
effectiveness and high selectivity.[2] And a number of other noble
metals, such as rhodium,[3] palladium,[4] iridium,[5] ruthenium,[6]
thorium[7] and gold[8] have also been used for this transformation.
Recently, the field of inexpensive metal catalysts for
hydrosilylation have led to progress.[9] Several groups reported
that non-noble metals cobalt could catalyze the hydrosilylation of
terminal alkynes with (E)-β-selectivity. In 2014, Deng developed
a carbine-coordinate cobalt(I) complex for terminal alkynes
hydrosilylation with high (E)-β-selectivities (Figure 2b).[10]
Thomas’s group described a complex of the MesBIPCoCl2 and
NaOtBu for stereoselective hydrosilylation of 1-octyne to give the
moderate selectivity (E)-β-vinylsilanes.[11] Recently, Ge reported
cobalt complexes of phosphine ligand for the highly (E)-β-
selective hydrosilylation of terminal alkyne.[12]
Vinylsilanes are versatile synthetic intermediates owing to their
stability, non-toxicity and propensity to undergo a variety of
transformations.[1] Alkyne hydrosilylation is the most efficient and
atom-economic method to access such compounds. And for the
preparation
of
vinylsilanes,
transition-metal
catalyzed
hydrosilylation of alkynes is an ideal method. However, control
of stereo- and regioselectivity is a serious issue hampering the
widespread use of this method, since three possible products,
(E)-β-, (Z)-β-, and α-vinylsilanes (Figure 1a), can be generated
at least in terminal alkyne hydrosilylation. Besides, the
hydrosilylation of an internal alkyne can also generate four
possible products, anti-α-, anti-β-, syn-α- and syn-β-vinylsilanes
(Figure 1b). Thus controlling the regio- and stereoselectivity is a
key issue during the H–Si addition process. In addition to the
regioselectivity and stereoselectivity issue, the side reaction of
alkyne oligmerization and hydrogenation could complicate the
As for internal alkynes without directing groups, cobalt-
catalyzed hydrosilylation reactions is not an effective method to
highly selectively generate syn-adducts. Butenschӧn et al. found
that the cyclopentadienylcobalt(I) ethylene complex bearing an
appended phosphine tether is an effective internal alkyne
hydrosilylation catalyst. However, this cobalt(I) complex
catalyzed unsymmetrical internal alkynes hydrosilylation suffers
from poor regioselectivity (Figure 2a).[13] The reaction of an
internal aryl alkyne exclusively provided the syn-addition
products with Deng’s carbine-coordinate cobalt(I) catalysts[10] or
Huang’s (tBuPyBox)CoCl2,[14] but the regioselectivity is poor
[a]
[b]
Li, R. H., Zhang, G. L., Dong, J. X., Li, D. C., Yang, Y., Chen, L.,
Prof. Zhan, Z. P.
Department of Chemistry and Key Laboratory for Chemical Biology
of Fujian Province, College of Chemistry and Chemical Engineering,
Xiamen University, Xiamen 361005, China
E-mail: zpzhan@xmu.edu.cn
Pan, Y. M., Tang, H. T.
State Key Laboratory for the Chemistry and Molecular Engineering
of Medicinal Resources, School of Chemistry and Pharmaceutical
Sciences of Guangxi Normal University, Guilin 541004, People’s
Republic of China
(Figure 2b, 2c). Recetly, Lu’s oxazoline iminopyridine cobalt
E-mail: httang@gxnu.edu.cn
[16]
complex[15] and Huang’s (iPrPCNNiPr)CoCl2
promoted the
Supporting information for this article is given via a link at the end of
the document.((Please delete this text if not appropriate))
hydrosilylation of internal alkynes with moderate regioselectivity
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(Figure 2d, 2e). Petit’s group reported low-valent cobalt(I)
HCo(PMe3)4 catalyzed unsymmetrical internal alkynes
hydrosilylation suffers from good regioselectivity, but a series of
internal alkynes have poor regioselectivity.[17]
tolerance (Figure 3).[20] However, in this system, Cobalt not
catalytic activity with Ph2SiH2 and internal alkynes will be
reduced to alkenes or alkanes. Herein, we develop a highly
regioselective hydrosilylation of terminal internal and terminal
alkynes
with
Ph2SiH2
catalyzed
by
Co(acac)2/POL-
Xantphos@10PPh3 which recycled multiple times without loss of
activity and selectivity (Figure 3). This porous organic polymer
combines the selectivity and activity merits of Xantphos ligands
with the stability advantage derived from the high concentration
of PPh3 ligands and Xantphos firmly coordinated with Co(acac)2.
Results and Discussion
In our initial studies, the electronical unbiased hex-3-yne was
investigated. We examined a variety of cobalt catalysts, ligands,
and additive for this model reaction. The results are summarized
in Table 1. The Co(acac)2/Xantphos complex can catalyze the
reaction of hex-3-yne with 1.1 equiv of Ph2SiH2 at 50 oC to
selectively afford (E)-hex-3-en-3-yldiphenylsilane in 92% yield
(Table 1, entry 1). Under the same reaction condition, Other
cobalt catalysts such as Co(OAc)2 and CoCl2 were inactive for
the hydrosilylation (Table 1, entries 2-3). It’s noted that the
reaction failed to afford the desired product using PPh3 as the
ligand. (Table 1, entry 4). Attempts to enhance the efficiency of
product formation further by screening different kinds of
bidentate phosphine ligands were unsuccessful (Table 1, entries
5-8). Additives were indispensable for promoting the efficacy.
Without NaBHEt3, the reaction did not yield any of the
hydrosilylation product (Table 1, entry 9). And the MeMgBr as
activator led to lower yield in comparison with NaBHEt3 (Table 1,
entry 10). The NaOtBu as activator exhibited no activity in this
reaction (Table 1, entry 11). Excitedly, the use of
Co(acac)2/POL-Xantphos as a heterogeneous catalyst afforded
high yield and excellent selectivity. However, the heterogeneous
catalyst led to lower yield after recycling three times (Table 1,
entry 12). That showed the Cobalt in polymer has been washed
off in recycle process.
Figure 2. Cobalt complexs for catalytic hydrosilylation
Consequently, hydrosilylation of unsaturated hydrocarbon with
homogeneous catalysts finds industrial applications including
fluids, molding products, silicone-based surfactants and release
coatings.[18] However, problems such as competing side
reactions, catalyst activation, catalyst separation and
regeneration have still persisted. Therefore, the development of
heterogeneous ligands supported non-noble metals as
recyclable catalysts capable of promoting highly selective Si-H
additions to alkynes, remains to be greatly challenging and
significant.
Recently, our and Ding’s group jointly reported Xantphos
doped Rh/POPs-PPh3 catalysts appearing high activity,
chemoselectivity and regioselectivity in the hydroformylation of
long-chain olefins.[21] Based on our previous contributions,[22] and
also inspired by the widely explored functional element (such as
N, S, P, etc.) doped carbon materials which was generally
applied in catalysis and electrochemistry,[23] we speculate the
unique location of Co species dispersing on Xantphos doped
POPs-PPh3 materials may integrate the selectivity and activity
merit of the Xantphos ligand with the stability advantages which
contributed to PPh3 matrix. Bearing these knowledge in mind,
heterogeneous ligands with different proportions of Xantphos
and PPh3 were designed and employed in selective
hydrosilylation reaction. Owing to easier synthesis of 2v-
Xantphos than 4v-Xantphos, we used 2v-Xantphos as monomer
to synthesize heterogeneous ligands through free-radical
polymerization with different proportions of 3v-PPh3. For
comparison, the Xantphos doped POPs-DVB ligand was also
Figure 3. Cobalt/POPs complexs for catalytic hydrosilylation
Porous organic polymers (POPs), a class of highly crosslinked
amorphous polymers, consist mainly of carbon, oxygen, nitrogen
and phosphorus that are connected through strong covalent
bonds. More importantly, Porous organic polymers can serve as
a promising platform for incorporating homogeneous catalytic
moieties into the framework.[19] Recently, our group reported a
cobalt/POL-PPh3 catalyzed (E)-selective hydrosilylation of
alkynes with PhSiH3 for the synthesis of (E)-β-vinylsilanes with
high regio- and stereo-selectivity and wide functional group
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Scheme 1. Reuse of porous organic polymers towards hydrosilylation[a]
synthesized (Figure 4). These reusability of porous organic
polymers were examined for the hydrosilylation of hex-3-yne to
Table 1. Optimization of the reaction conditions for hydrosilylation of 1-
[a]
decyne and Ph2SiH2
yield/%[b]
ligand
Xantphos
Xantphos
Xantphos
PPh3
entry
1
cat.
additive
NaBHEt3
NaBHEt3
NaBHEt3
NaBHEt3
NaBHEt3
NaBHEt3
NaBHEt3
NaBHEt3
-
Co(acac)2
Co(OAc)2
CoCl2
92
2
53
3
62
4
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
Co(acac)2
0
BINAP
5
61
dppe
6
43
dppb
7
48
dppf
8
62
Xantphos
Xantphos
Xantphos
POL-Xantphos[c]
9
0
36
[
10
11
12
MeMgBr
NaOtBu
NaBHEt3
a] Reaction condition: hex-3-yne (1.0 mmol), diphenylsilane (1.1 mmol),
NaBHEt3 (4 mol %), THF (2 mL), 50 oC, 12 h, N2 atmosphere, Co(acac)2 (5.1
mg), POL-Xantphos (13.6 mg, synthesized from 13.6 mg 8), POL-
Xantphos@2PPh3 (26.2 mg, synthesized from 0.02 mmol 12 and 0.04 mmol
10), POL-Xantphos@10PPh3 (80.6 mg, synthesized from 0.02 mmol 12 and
0.2 mmol 10), POL-Xantphos@10DVB (38.6 mg, synthesized from 0.02 mmol
12 and 0.2 mmol DVB).
0
89(42)[d]
[a] Reaction condition: hex-3-yne (1.0 mmol), diphenylsilane (1.1 mmol), cat.
(2 mol %), ligand (2 mol %), additive (4 mol %), THF (2 mL), 50 oC, 12 h, N2
atmosphere. [b] The yields were determined by 1H NMR spectroscopy, the
selectivity for 2a (r.r. = syn-α-vinylsilane product / all other isomers) were >
20:1. [c] 13.6 mg POL-Xantphos. [d] recycle three times.
Figure 4. Synthesis of porous organic polymers
obtain 2a (Scheme 1). As can be seen, Co(acac)2/POL-
Xantphos@10PPh3 was recycled seven times without loss of
activity and selectivity, however, other polymers without PPh3 as
stabilizer (POL-Xantphos and POL-Xantphos@10DVB) were
inactive after three times. The polymer synthesized with the 1:2
proportion of Xantphos and PPh3 was also inactive after five
times. Hence, the optimum conditions involved conducting the
reaction in THF at 50 oC with Co(acac)2 as catalyst, POL-
Xantphos@10PPh3 as ligand.
Figure 5. a) N2 adsorption–desorption analysis of POL-Xantphos@10PPh3, b)
N2 adsorption–desorption analysis of POL-Xantphos@10PPh3, c) scanning
electron microscopy of POL-Xantphos@10PPh3, d) transmission electron
microscopy of POL-Xantphos@10PPh3
in strengthening the stability of the catalysts, which can be
attributed to the formation of multi-coordination bonds with
Xantphos and at the same time will not affect Xantphos’ catalytic
activity and selectivity. The advantages of bidentate ligand
(Xantphos) and the monodentate ligand (PPh3) have been
perfectly integrated in POL-Xantphos@10PPh3 catalyst could be
owning to the synergistic effect of the dispersed Co species and
Concluded from the experimental results and our previous
works, the high concentration of PPh3 ligands played a key role
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the synchronous coordination of both of ligands. The Xantphos
ligand takes the role of controlling selectivity and activity while
the PPh3 ligand plays the roles of maintaining high stability
(Figure 3).
To evaluate the scope of the Cobalt/POL-Xantphos@10PPh3
catalyzed alkyne hydrosilylation, reactions with a series of
internal alkynes and a variety of functionalized terminal alkynes
were carried out using Ph2SiH2 as the silicon source. The results
are summarized in Scheme 2 and Scheme 3, respectively. The
hydrosilylation of symmetric dialkyl-substituted alkynes (Scheme
2, products 2a-2c) and diaryl-substituted alkyne (Scheme 2,
product 2d) occurred to form the syn-addition products in good
yields and selectivity. Then, we turned our attention to the more
challenging unsymmetrical internal alkynes.
In an effort to explore the structure–activity relationship, the
POL-Xantphos@10PPh3 was characterized by thermo-
gravimetry (TG), N2 adsorption–desorption analysis, scanning
electron microscopy (SEM) and transmission electron
microscopy (TEM). The TG shows that POL-Xantphos@10PPh3
remains intact at temperatures up to 410 oC, indicating its
superior thermal stability (Supporting Information, Figure S3).
Nitrogen adsorption–desorption analysis (Figure 5a) shows that
As for unsymmetrical internal alkynes without directing groups,
cobalt-catalyzed hydrosilylation reactions generate highly
selective syn-adduct products difficultly.[13-17] Herein, we firstly
POL-Xantphos@10PPh3 gave
a type IV isotherm with a
significant hysteresis loop in the high pressure region. This
result indicates the presence of mesopores in this polymer.
Furthermore, a large number of nitrogen uptake is observed in
the low pressure region (below 0.1 bar), suggesting the
presence of sufficient amount of micropores in POL-
Xantphos@10PPh3. As seen from Figure 5a that POL-
Xantphos@10PPh3 possesses very favorable hierarchical pore
size distributions, which is further confirmed by SEM (Figure 5c)
and TEM (Figure 5d) images. The pore sizes were mainly
distributed at 0.6-1.0 nm and 1.2- 4.0 nm which was calculated
by the method of non-local density functional theory (NLDFT)
(Figure 5b). The BET surface areas and total pore volumes of
POL-PPh3 are up to 880 m2/g and 1.10 cm3/g, respectively. The
hierarchical pore structure, which allows for easy accessibility of
the P coordination sites, is very favorable for the mass transfer.
reported
unsymmetrical
a
highly syn-adducts-selective hydrosilylation of
internal alkynes with Ph2SiH2 using
heterocatalysis system. All reactions were excellently selective
for the formation of the syn-α-vinylsilane products (r.r. > 20:1,
syn-α-vinylsilane product/all other isomers). The reaction of
arylalkyl disubstituted alkynes (Scheme 2, products 2e-h) gave
the products in 65-76% yields. The unsymmetrical disubstituted
alkynes with different steric properties, such as 4,4-
dimethylpent-2-yne and 4-methylpent-2-yne, were suitable for
the selective hydrosilylation, producing the syn-addition products
2i and 2j with the incorporation of the silyl group into the less
sterically demanding sp-hybridised carbon. To our delight, the
reactions of the unsymmetrical internal alkynes that bearing a
trimethylsilyl (TMS) group could give exclusively syn-adducts in
the form of (E)-α,β-disilylalkenes(Scheme 2, products 2k-l).
Scheme 2. Scope of internal alkynes for the Co(acac)2/POL-
Scheme 3. Scope of terminal alkynes for the Co(acac)2/POL-
Xantphos@10PPh3-Catalyzed
anti-Markovnikov
Hydrosilylation
with
Xantphos@10PPh3-Catalyzed
anti-Markovnikov
Hydrosilylation
with
[a,b]
[a,b]
Ph2SiH2
Ph2SiH2
[a] Reaction conditions: internal alkynes (1.0 mmol), Ph2SiH2 (1.1 mmol),
Co(acac)2 (2 mol %), POL-Xantphos@10PPh3 (80.6 mg), NaBHEt3 (4 mol %),
THF (2 mL), 50 oC, N2, 12 h, yields of isolated products. [b] The selectivity for
all products (r.r. = syn-α-vinylsilane product/all other isomers) were > 20:1,
Determined by 1H NMR spectroscopy.
[a] Reaction conditions: terminal alkynes (1.0 mmol), Ph2SiH2 (1.1 mmol),
Co(acac)2 (2 mol %),Xantphos@10PPh3 (80.6 mg), NaBHEt3 (4 mol %), THF
(2 mL), 50 oC, N2, 12 h, yields of isolated products. [b] The selectivity for all
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Co(I) silyl intermediate I play important role in catalytic cycle.
Once intermediate I formed, the alkenyl metal species III will be
produced through migratory insertion of the silyl moiety to the
C≡C triple bond in II. Complex III could further react with Ph2SiH2
to yield the hydrosilylation product vinylsilane and regenerate I.
Other possible pathways cannot be ruled out, such as cobalt
hydride species as important active role.
products (r.r. = (E)-β-vinylsilane product / all other isomers) were > 20:1,
Determined by 1H NMR spectroscopy.
For terminal alkyne substrates, all reactions were highly
selective for the formation of the (E)-β-vinylsilane products (r.r. >
20:1, r.r. = (E)-β-vinylsilane product/all other isomers). The
straight-chain terminal alkynes and branched-chain terminal
alkyne gave the corresponding products 3a-3e in moderate-to-
high isolated yields. Alkynes containing cyclopropyl (Scheme 3,
product 3f) and cyclohexeyl (Scheme 3, product 3g) groups Conclusions
reacted with moderate to good isolated yields. This
In summary, we have developed
a highly regioselective
Co(acac)2/Xantphos-catalyzed hydrosilylation of aliphatic
alkynes shows high functional groups tolerance. A wide range of
functional groups, including hydroxyl (Scheme 3, products 3h,
3i), nitrile(Scheme 3, product 3j), chloride (Scheme 3, product
3k) and tertiary amine (Scheme 3, product 3l), were compatible
with the reaction condition. Aliphatic alkynes containing
protecting groups, such as acetylate (Scheme 3, product 3m)
and silylether (Scheme 3, product 3n), afforded the desired
products in useful yields. Additionally, aryl alkynes also reacted
smoothly with moderate-to-high yields (Scheme 3, product 3o-
3q).
Co(acac)2/POL-Xantphos@10PPh3 catalyzed hydrosilylation of
unsymmetrical internal alkynes method for the synthesis of syn-
α-vinylsilane products in heterocatalysis. Furthermore, an
excellent regioselective cobalt-catalyzed hydrosilylation of
terminal alkynes with Ph2SiH2 to produce vinylsilanes has also
been developed. Various functionalized groups, such as
hydroxyl, nitrile, chloride and tertiary amine, are tolerated to
increase the possibility for future applications and late-stage
derivatizations. The Co(acac)2/POL-Xantphos@10PPh3 recycled
multiple times without loss of activity and selectivity. This porous
organic polymer could integrate the selectivity and activity merits
of Xantphos ligands with the stability advantage derived from the
high concentration of PPh3 ligands and Xantphos firmly
coordinated with Co(acac)2. This heterogeneous catalyst is
expected to find promising applications in industrial synthesis.
The scalability of (E)-dec-1-en-1-yldiphenylsilane (3a)
synthesis was evaluated by performing the hydrosilylation of 1-
decyne on a gram scale. The reaction furnished the desired
product in 83% yields, similar to that obtained on smaller scales
(Scheme 4).
Experimental Section
Scheme 4. Reaction carried out on the gram scale
General procedure for synthesis 2, 3: In a nitrogen filled schlenk tube,
Co(acac)2 (2 mol %), POL-Xantphos@10PPh3 (80.6 mg), NaBHEt3 (4
mol %) and THF (2 mL) were added then stirred at room temperature for
10 minutes, then alkyne (1.0 mmol), diphenylsilane (1.1 mmol) were
added under N2. The reaction mixture was stirred at 50 oC. Upon
completion, the solvent was removed by vacuum and the crude residue
was purified by silica gel column chromatography to afford the
corresponding products 2, 3 (eluent: petroleum ether/EtOAc = 100/1).
A proposed mechanism accounting for the formation of
vinylsilane is presented in Scheme 5. On the basis of the
precedents of previous work,[19] we propose that the low-valent
General procedure for recycling experiment ： In a nitrogen filled
schlenk tube, Co(acac)2 (2 mol %), polymer (POL-Xantphos: 13.6 mg,
POL-Xantphos@2PPh3: 26.2 mg, POL-Xantphos@10PPh3: 80.6 mg or
POL-Xantphos@10DVB: 38.6 mg), NaBHEt3 (4 mol %) and THF (2 mL)
were added and stirred at room temperature for 10 minutes, then alkyne
(1.0 mmol), diphenylsilane (1.1 mmol) were added under N2. The
Scheme 5. Proposed mechanism
o
reaction mixture was stirred at 50 C. Upon completion, the catalyst was
separated through centrifugation, diethyl phthalate was added to the
supernatant liquid as an internal standard, and the mixture was filtered
under vacuum, the yield was determined by NMR and the catalyst was
washed by Et2O, dried, and reused in a next run.
Preparation of POL-Xantphos：9.9-dimethylxanthene (4, 5 g, 24 mmol),
TMEDA (9 mL, 60 mmol) and Et2O (40 mL) was charged in a flask. Then
n-BuLi (24 mL of 2.5 M solution in hexane, 60 mmol) was added
o
dropwise at 0 C, followed by stirring overnight at room temperature. 60
mmol of ClP(NEt2)2 dissolved in 10 mL of Et2O was added dropwise at -
78 oC and the afforded mixture was stirred at room temperature overnight.
After removal of the precipitate and the solvent under vacuum,
compound
6
1,1'-(9,9-dimethyl-9H-xanthene-4,5-diyl)bis(N,N,N',N'-
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tetraethylphosphanedi-amine) (white powder) was afforded. The obtained
white powder 6 was dissolved in 250 mL of dry hexane, dry HCl gas was
passed through the solution at room temperature for 0.5 h. Then the
precipitate was removed, and the solvent was removed under vacuum.
Keywords: hydrosilylation • porous organic polymer • cobalt •
alkynes • heterocatalysis
[1]
a) E. Rꢀmond, C. Martin, J. Martinez, F. Cavelier, Chem. Rev. 2016,
116, 11654-11684. b) S. Bracegirdle, E. A. Anderson, Chem. Soc. Rev.,
2010, 39, 4114-4129. c) E. Langkopf, D. Schinzer, Chem. Rev. 1995,
95, 1375-1408. d) T. A. Blumenkopf, L. E. Overman, Chem. Rev. 1986,
86, 857-873.
Thus
compound
7
(9,9-dimethyl-9H-xanthene-4,5-
diyl)bis(dichlorophosphane) was afforded. 4.03 g of 4-bromostyrene (22
mmol) was dissolved in 40 ml of tetrahydrofuran, n-BuLi (8.8 mL of 2.5 M
solution in hexane, 22 mmol) was added dropwise at -78 oC, followed by
stirring for 2 h at -78 oC. Then compound 7 dissolved in 20 mL of
tetrahydrofuran was added dropwise in the mixture at -78 oC. After
stirring for 2 h, the mixture was quenching with aq. NH4Cl, and extracted
with ethyl acetate. The organic layer was washed with water, dried over
Na2SO4, filtered and concentrated. The residue was purified by silica gel
chromatography (20:1 hexane/EtOAc) to give compound 8 (9,9-dimethyl-
9H-xanthene-4,5-diyl)bis(bis(4-vinylphenyl)phosphane) as the white solid
(1.1 g, 7 % total yield). Under nitrogen, 8 (1.0 g) was dissolved in THF (5
mL), followed by the addition of AIBN (0.1 g) at room temperature. Next,
the mixture was transferred into a sealing tube at 100 oC for 24 h. After
evaporation of THF under vacuum, a white solid POL-Xantphos was
obtained.
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Preparation of tris(4-vinylphenyl)phosphane ： Mg turnings (2.40g,
100 mmol) was added to a round bottom flask under nitrogen, and were
activated by treatment with a grain of I2 in THF (80 mL). p-bromostyrene
(14.64g, 80 mmol) was slowly added to the flask, and the mixture was
stirred for 1 h at room temperature. Next, PCl3 (3.43g, 25 mmol) was
slowly added to the solution in the ice water bath over 30 min followed by
stirring at room temperature for 4 h. The reaction was quenched by
aq.NH4Cl, and the mixture was extracted with ethyl acetate. The organic
layer was washed by H2O twice, dried over Na2SO4, filtered and
concentrated. The residue was purified by silica gel column
chromatography (petroleum ether/ethyl acetate) to afford tris(4-
vinylphenyl)phosphane (10, 5.45 g, 64% yield).
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Preparation of POL-Xantphos@10PPh3：Mg turnings (1.75g, 72 mmol)
was added to a round bottom flask under nitrogen, and were activated by
treatment with a grain of I2 in THF (50 mL). p-bromostyrene (10.98g, 60
mmol) was slowly added to the flask, and the mixture was stirred for 1 h
at room temperature. Next, PhPCl2 (4.83 g，27 mmol) was slowly added
to the solution in -78 oC over 30 min followed by stirring overnight at room
temperature. The compound 11 chloro(phenyl)(4-vinylphenyl)phosphane
was afforded. 9.9-dimethylxanthene (4, 2.52 g, 12 mmol), TMEDA (3.25
g, 28 mmol) and Et2O (20 mL) was charged in a flask. Then n-BuLi (11.2
mL of 2.5 M solution in hexane, 60 mmol) was added dropwise at 0 oC,
followed by stirring overnight at room temperature. Then compound 11
dissolved in 20 mL of tetrahydrofuran was added dropwise in the mixture
at -78 oC. After stirring for 2 h, the mixture was quenching with aq. NH4Cl,
and extracted with ethyl acetate. The organic layer was washed with
water, dried over Na2SO4, filtered and concentrated. The residue was
purified by silica gel chromatography (20:1 hexane/EtOAc) to give
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compound
12
(9,9-dimethyl-9H-xanthene-4,5-diyl)bis(phenyl(4-
vinylphenyl)phosphane) as the white solid (2.19 g, 29 % total yield).
Under nitrogen, 12 (630 mg) and 10 (3.40 g) was dissolved in THF (15
mL), followed by the addition of AIBN (403 mg) at room temperature.
Next, the mixture was transferred into a sealing tube at 100 oC for 24 h.
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After evaporation of THF under vacuum,
Xantphos@10PPh3 was obtained.
a white solid POL-
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Acknowledgements ((optional))
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We are grateful to the National Natural Science Foundation of
China (No. 21772166) and NFFTBS (No. J1310024).
For internal use, please do not delete. Submitted_Manuscript
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Entry for the Table of Contents (Please choose one layout)
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Ren-Hao Li, Guo-Liang Zhang, Jia-Xing
Dong, Ding-Chang Li, Ying Yang, Ying-
Ming Pan, Hai-Tao Tang,* Li Chen and
Zhuang-Ping Zhan*
Page No. – Page No.
Xantphos Doped POPs-PPh3 as
Heterogeneous Ligand for Cobalt-
Catalyzed Highly Regio- and
Stereoselective Hydrosilylation of
Alkynes
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