Iron-catalyzed regiodivergent alkyne hydrosilylation

Article abstract of DOI:10.1021/jacs.0c09083

Although tremendous effort has been devoted to the development of methods for iron catalysis, few of the catalysts reported to date exhibit clear superiority to other metal catalysts, and the mechanisms of most iron catalysis remain unclear. Herein, we report that iron complexes bearing 2,9-diaryl-1,10-phenanthroline ligands exhibit not only unprecedented catalytic activity but also unusual ligand-controlled divergent regioselectivity in hydrosilylation reactions of various alkynes. The hydrosilylation protocol described herein provides a highly efficient method for preparing useful di- and trisubstituted olefins on a relatively large scale under mild conditions, and its use markedly improved the synthetic efficiency of a number of bioactive compounds. Mechanistic studies based on control experiments and density functional theory calculations were performed to understand the catalytic pathway and the observed regioselectivity.

Full text of DOI:10.1021/jacs.0c09083

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Iron-Catalyzed Regiodivergent Alkyne Hydrosilylation
Meng-Yang Hu, Peng He, Tian-Zhang Qiao, Wei Sun, Wen-Tao Li, Jie Lian, Jin-Hong Li,
and Shou-Fei Zhu*
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ABSTRACT: Although tremendous effort has been devoted to the development of methods for iron catalysis, few of the catalysts
reported to date exhibit clear superiority to other metal catalysts, and the mechanisms of most iron catalysis remain unclear. Herein,
we report that iron complexes bearing 2,9-diaryl-1,10-phenanthroline ligands exhibit not only unprecedented catalytic activity but
also unusual ligand-controlled divergent regioselectivity in hydrosilylation reactions of various alkynes. The hydrosilylation protocol
described herein provides a highly efficient method for preparing useful di- and trisubstituted olefins on a relatively large scale under
mild conditions, and its use markedly improved the synthetic efficiency of a number of bioactive compounds. Mechanistic studies
based on control experiments and density functional theory calculations were performed to understand the catalytic pathway and the
observed regioselectivity.
unsymmetrical alkynesthat is, alkynes with different
INTRODUCTION
■
substituents at the ends of the triple bondis difficult unless
Because iron, which is abundant in the earth’s crust, is
the two substituents have markedly different electronic or
inexpensive, readily available, and biocompatible, the develop-
steric properties that can be easily identified by the catalyst.
ment of iron-catalyzed reactions has been attracting increasing
Although some catalysts have been shown to give a certain
attention, and considerable progress has been made in recent
regioselectivity, achieving the opposite regioselectivity is
decades.1 However, few of the iron catalysts reported to date
difficult.5 For example, the known catalysts for hydrosilylation
exhibit activity or selectivity superior to those of the well-
of dialkyl acetylenes usually give products with the silyl group
established noble metal catalysts. Moreover, because of the
at the smaller alkyl end of the alkyne,6 but the opposite
magnetism of iron, its numerous oxidation states, and the poor
regioselectivity remains unsuccessful.7
stability of iron catalysts, studying the mechanisms of iron-
Herein, we report that iron complexes bearing 2,9-diaryl-
catalyzed reactions is challenging. Specifically, the effects of
1,10-phenanthroline ligands8 efficiently catalyze the hydro-
spin state on activity and selectivity remain poorly understood,
silylation of terminal and internal alkynes with primary silanes.
and this lack of information has hampered progress in this area.
Specifically, turnover numbers (TONs) up to 35 500 and
The development of iron catalysts for regio- and stereo-
turnover frequencies up to 35.5 s−1 were observed in the
selective synthesis of alkenes would be particularly useful
reactions with terminal alkynes, which are the highest values
because alkenes are widely used in organic chemistry. Although
for such reactions reported to date.3 More interestingly, simply
several powerful methods, including the Wittig reaction and
the alkene metathesis reaction, have been established for this
Received: August 24, 2020
purpose, their utility for stereoselective synthesis of multi-
substituted internal alkenes is unsatisfactory.2 Alkyne hydro-
silylation is an alternative for preparing functionalized or
unfunctionalized alkenes because the silyl groups of alkenyl
silanes readily undergo a diverse array of transformations.3,4
However, achieving regioselectivity in the hydrosilylation of
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a
Table 1. Evaluation of Ligands for Iron-Catalyzed Hydrosilylation of Alkyne 1a with Phenylsilane (2a)
b
b
b
entry
[Fe]
time (min)
conv. (%)
yield (%)
3aa/4aa
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
C1a
C1b
C1c
C1d
C1e
C1f
C1g
C1h
C1i
C1j
C1k
C2
120
10
10
10
10
10
10
10
10
10
10
120
10
20
10
120
<5
38
45
ND
35
43
55
85
86
95
88
89
92
88
ND
74
10
NA
55:45
7:35
62:38
>98:2
>98:2
>98:2
23:77
3:97
<2:98
95:5
NA
58:42
NA
79:21
60
>95
>95
>95
>95
>95
>95
>95
<5
80
15
>95
<5
C3
C4
C5
C6
c
51
ND
NA
a
b
Reaction conditions: 1a (0.35 mmol), 2a (0.4 mmol), iron catalyst (1 mol %), EtMgBr (2.4 mol %) in THF (1 mL) at 30 °C. Conversions,
yields, and product ratios were determined by 1H NMR spectroscopy with 1,3,5-trimethoxybenzene as an internal standard. ND, not detected. NA,
not applicable. Along with (E)-3aa and 4aa, (Z)-3aa was obtained in 39% yield.
c
changing the 2,9-aryl substituents on the ligands completely
reversed the regioselectivity of the reaction even for dialkyl
acetylenes. To our knowledge, this phenomenon has not
previously been observed for other iron catalysts. The
remarkable ligand-induced regiodivergence of this iron-
catalyzed alkyne hydrosilylation enabled us to study its
mechanism by means of control experiments and density
functional theory (DFT) calculations.
obtained (entries 5−7). To our surprise, catalysts with 3,5-
disubstituted phenyl groups (C1h−C1j) gave Markovnikov
addition product α-vinyl silane 4aa as the major product
(entries 8−10). Impressively, catalyst C1j showed >98%
Markovnikov selectivity (entry 10). To the best of our
knowledge, this is the first iron catalyst to show high
Markovnikov selectivity in alkyne hydrosilylation.4
We also evaluated several typical iron catalysts bearing
nitrogen- or phosphine-containing ligands (Table 1, entries
12−16); however, none of these catalysts afforded satisfactory
yields or selectivities. According to the literature, an iron
complex with a pyridine diimine ligand4a gives β-(Z)-vinyl
silane under the similar conditions.4c We found that complexes
prepared in situ from phenanthroline ligand L1g or L1j and
other metals exhibited much lower activity or poor selectivity
compared with those of the corresponding iron catalysts under
our standard conditions (Tables S3−S6). The above-described
results clearly show that the 1,10-phenanthroline skeleton of
the ligands and the iron played important roles in the activity
and selectivity of these catalysts.
RESULTS AND DISCUSSION
■
We initiated our study by exploring conditions for the iron-
catalyzed alkyne hydrosilylation reaction of aliphatic terminal
alkyne (1a) and phenylsilane (2a) using EtMgBr as the
reductant4c in tetrahydrofuran at 30 °C (Table 1). First, we
systematically investigated the effects of various 1,10-
phenanthroline ligands (entries 1−11). The X-ray diffraction
analyses of single crystals of C1g and C1h are included in
Tables S1 and S2). Iron catalysts with bulky 2,4,6-
trialkylsubstituted phenyl groups at the 2- and 9-positions of
the ligands (C1e−C1g) smoothly promoted the hydro-
silylation reaction; conversion was complete within 10 min,
and a single anti-Markovnikov addition product 3aa was
Using the optimal reaction conditions (Table 1, entry 7 or
10), we investigated the substrate scope of this iron-catalyzed
B
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a
Scheme 1. Substrate Scope of Iron-Catalyzed Regiodivergent Hydrosilylation of Terminal Alkynes
a
Condition A (left equation): alkyne/silane/C1g/EtMgBr = 0.5:0.55:0.005:0.012 (mmol). Condition B (right equation): alkyne/silane/C1j
/EtMgBr = 0.5:0.55:0.005:0.012 (mmol), in 1 mL of THF, at 30 °C (for A, C) or 0 °C (for B), 10 min to 1 h. Isolated yields were given. The
1
regioisomeric ratios (r.r.) were determined by H NMR.
alkyne hydrosilylation, starting with alkyl acetylenes and
phenylsilane (Scheme 1A). With C1g and C1j as the catalysts,
all the reactions went to completion in 10 min to afford high
yields (84−95%) of anti-Markovnikov products 3aa−3ar and
C
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a
Scheme 2. Substrate Scope of Iron-Catalyzed Regiodivergent Hydrosilylation of Internal Alkynes
a
Reaction conditions: alkyne/silane/catalyst/EtMgBr = 0.5:0.55:0.005:0.02 (mmol). R1 = n-C12H25, R2 = p-tolylmethyl. For compounds with italic
superscript numbers after, the following catalysts were used: a, 5mol % C1g; b, C1k; c, C1e (with toluene as solvent); d, C1i; e, C1h.
Markovnikov products 4aa−4ar, respectively, with excellent
regioisomeric ratios (r.r. > 98:2 in all cases). The chain length
and steric bulk of the alkylacetylene had little effect on the
yield or regioselectivity (3ab−3af and 4ab−4af). The system
tolerated a variety of functional groups: halogens (3ag−3ai and
4ag−4ai), a thioether (3aj and 4aj), quinoline (3al and 4al),
ethers (3ak−3an and 4ak−4an), alkenes (3am, 3an, 4am, and
4an), and ketals (3ao, 3ap, 4ao, and 4ap). In addition, a
dialkyne and an alkyne derived from structurally complex
natural product were smoothly hydrosilylated in good yields
with high regioselectivities (3aq, 3ar, 4aq, and 4ar).
Our catalytic system was also successfully used for
hydrosilylation of aryl acetylenes and alkenyl acetylenes with
phenylsilane (Scheme 1B). Both anti-Markovnikov and
Markovnikov addition products could be obtained in good
yields (80−94%) with excellent regioselectivities (92−>98%)
by using catalysts C1g and C1j, respectively. Generally, C1g
showed better regioselectivity than C1j. It is worth mentioning
that hydrosilylation reactions of alkenyl acetylenes gave useful
silylated conjugated dienes (3ca, 3cb, 4ca, and 4cb) in high
yields with excellent regio- and stereoselectivities.
primary silanes had a negligible effect on the reaction outcome.
Because secondary and tertiary silanes were less reactive
toward C1g and C1j, these alkyne hydrosilylation reactions
also exhibited excellent chemoselectivity.
To our delight, our iron complexes with 1,10-phenanthroline
ligands catalyzed hydrosilylation of various internal alkynes,
which remains a considerable challenge in literature, with
excellent regioselectivity (Scheme 2). Brief exploration of
reaction conditions revealed that catalyst C1g afforded
hydrosilylation products 3 with the silyl group at the less-
hindered end of the alkynes, whereas C1j catalyzed hydro-
silylation at the more more-hindered end to afford products 4.
Aryl methyl acetylenes generally gave the corresponding
products (3ea−3ee and 4ea−4ee) in high yields (83−98%)
with high regioselectivities (94−>98%). Phenyl ethyl acetylene
was also a suitable substrate: C1g afforded 3ef in good yield
with 78% regioselectivity, whereas C1j gave 4ef in good yield
with excellent regioselectivity. In addition, C1j-catalyzed
hydrosilylation of alkenyl alkyl alkynes with phenylsilane
smoothly afforded vinylsilanes with the silyl group on the
alkenyl side (4eg−4ei), and addition of the silyl group to the
alkyl side to afford 3eg−3ei could be also achieved by varying
the 1,10-phenanthroline ligand or the silane. We were also able
to add a silyl group to either end of dialkyl alkynes with good
to high regioselectivity. Varying the ligands allowed us to
control the regioselectivity even for highly symmetric internal
Hydrosilylation reactions of 1-octyne and various mono-
substituted silanes with catalysis by C1g or C1j also afforded
the corresponding products (3da−3df or 4da−4df, respec-
tively) in high yields (89−95%) with regioselectivities of >98%
(Scheme 1C), and the steric and electronic properties of the
D
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alkynes (3ej and 3ek; 4ej and 4ek) and could force addition of
a large silyl group to the sterically hindered end of
unsymmetrical internal aliphatic alkynes to afford (4el−4en),
which has not previously been achieved with any other catalyst.
The hydrosilylation of 2-methyl-3-octyne having more similar
sized terminal groups (iPr and Bu) afforded modest
regioselectivity under standard reaction conditions (3eo and
4eo).
Scheme 4. Applications of the Hydrosilylation Protocol and
Transformations of the Products
This iron-catalyzed regiodivergent alkyne hydrosilylation
showed a high TON and turnover frequency and was easy to
scale up (Scheme 3). The initial turnover frequency of the
Scheme 3. Efficiency Evaluation of the Iron-Catalyzed
Regiodivergent Alkyne Hydrosilylation
reaction of 1-octyne with phenylsilane in the presence of 0.2
mol % C1g was 35.5 s−1, and TONs as high as 35 500 were
obtained when 0.002 mol % of C1g was used. Moreover, the
Markovnikov hydrosilylation reaction catalyzed by C1j also
showed a satisfactory TON (4 500). The reaction could easily
be scaled up to 100 mmol using a catalyst loading of 0.05 mol
% with full conversion, and high yields of pure products 3ab
(20 g, 92%) and 4ab (19 g, 89%) were obtained by vacuum
distillation.
Because the C−Si bonds of the products can be converted to
C−C bonds by means of a Hiyama−Denmark coupling
reaction,9 the hydrosilylation reaction provides an efficient
route for olefin synthesis. For example, we synthesized a series
of high-value olefins10 in high overall yields with excellent
regio- and stereoselectivities from propyne, a feedstock alkyne,
by means of iron-catalyzed anti-Markovnikov hydrosilylation
(3ac) followed by Hiyama−Denmark cross-coupling (Scheme
4A). Similarly, Markovnikov hydrosilylation product 4ap could
be used to prepare a key intermediate in the synthesis of
posaconazole, a second-generation triazole antifungal drug
(Scheme 4B).11 Deuterated alkynes and deuterated silanes
could be used to synthesize olefins with deuterium labels at
various positions (Scheme 4C), which demonstrates the
potential utility of this reaction for the preparation of
deuterated pharmaceuticals.12 Alkenyl silane 4ab was easily
converted to polyorganicsiloxane 7 by means of a cobalt-
catalyzed hydrosilylation reaction with terephthalaldehyde
(Scheme 4D). This result suggests that the current protocol
may find applications in materials science. In addition, alkenyl
silanes 3ea and 4ea could be converted to α-hydroxy ketones,
versatile synthons,13 by means of two consecutive oxidations in
a single pot (Scheme 4E). Finally, we accomplished the total
synthesis of the natural product asnipyrone B,14 which has a
conjugated multisubstituted polyolefin moiety, starting from
3ea, the product of hydrosilylation of phenyl methyl acetylene
(Scheme 4F); a second iron-catalyzed hydrosilylation, of
alkenyl alkyne 11, was a key step in the synthesis.
E
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The kinetic isotopic effect experiment for parallel reactions
failed to be performed because of the extremely fast reaction
rate.
MECHANISTIC STUDIES
■
This ligand-controlled iron-catalyzed regiodivergent hydro-
silylation provides an ideal model for understanding the
behavior of iron catalysts. To this end, we performed some
control experiments and DFT calculations. We began with
deuterium-labeling experiments (Scheme 5A). When hydro-
To obtain detailed information about this unusual divergent
regioselectivity, we carried out DFT calculations on the
transition-state of ligand to ligand hydrogen transfer (LLHT,
Ts-1a) at all three possible spin states (singlet, triplet, and
quintet) of the iron catalysts (Figure 1a). Gaussian 09 was used
for calculations at the (dispersion-corrected) unrestricted
ωB97XD/6-31G*/TZVP level of theory with CPCM-
UωB97XD/def2-TZVPP single-point energy calculations.
Our calculation revealed that the LLHT at triplet state has
the lowest energy (3Ts-1a, Figure 1a). Next, we calculated the
Scheme 5. Control Experiments
3
energies of Ts-1 with iron catalysts C1e and C1i, which gave
opposite regioselectivities under the identical conditions
(Figure 1b and Table S7). When C1e was used, the energy
of anti-Markovnikov addition transition state Ts-1a was about
3.5 kcal mol−1 lower than that of Markovnikov transition state
Ts-1a′, which is consistent with the experimentally observed
high anti-Markovnikov selectivity. In contrast, the calculations
indicated that anti-Markovnikov addition transition state Ts-
1b was 1.8 kcal mol−1 higher in energy than Markovnikov
addition transition state Ts-1b’ when C1i was used as the
catalyst, which is again consistent with the observed high
Markovnikov selectivity. The calculation results exhibited good
accordance with the experimental outcomes of C1b and C1d
as well (Figure S1).
To gain a better understanding of the parameters
responsible for the regiodivergence of the reaction, we
performed additional calculations by using 1,10-phenanthro-
line-modified iron catalyst C1a as a reference (Figure 1b).
When this catalyst was used, the energy difference between
transition states Ts-1c and Ts-1c′, which lead to anti-
Markovnikov and Markovnikov selectivity, respectively, was
very small (0.13 kcal mol−1), indicating poor regioselectivity.
Because coordination of the triple bond with the iron center
was almost completely unaffected by the ligand, the overlap
between the alkyne and iron center orbitals in this transition
state was larger than that in any of the other transition states.
Because of the directionality of molecular orbitals, addition of
substituents to the 2- and 9-positions of the 1,10-phenanthro-
line ligand resulted in steric hindrance between the
substituents, which decreased the overlap between the alkyne
and iron orbitals and thus increased the transition state energy.
To quantify the degree of orbital overlap, we chose the plane
defined by the iron atom and the nitrogen atoms of the 1,10-
phenanthroline ligand (Fe−N−N) as the reference and the
dihedral angle (θ) between this plane and the plane defined by
the iron atom and the carbon atoms of the alkyne triple bond
(Fe−C−C) as an index to measure the orbital overlap. These
calculations showed that the difference in dihedral angle (Δθ)
between anti-Markovnikov transition state Ts-1a and reference
transition state Ts-1c (Δθ = 76.75° − 77.64° = −0.89°) was
considerably lower than the difference for Markovnikov
transition state Ts-1a′ and Ts-1c′ (Δθ = 78.40° − 80.92° =
−2.52°); these results are consistent with the experimentally
observed anti-Markovnikov selectivity exhibited by C1e. In
contrast, when catalyst C1i, which has 3,5-disubstituted aryl
groups, was used, the difference in dihedral angle between anti-
Markovnikov transition state Ts-1b and reference transition
state Ts-1c (Δθ = 81.51° − 77.64° = 3.87°) is greater than the
difference between Markovnikov transition state Ts-1b′ and
Ts-1c′ (Δθ = 83.10° − 80.92° = 2.18°), which is consistent
silylation reactions of 1-octyne with a 1:1 mixture of PhSiD3
(98% D) and C12H25SiH3 were carried out with catalysis by
C1g (condition A) or C1j (condition B), only homoaddition
products (3ab-d and 3df with C1g; 4ab-d and 4df with C1j)
were obtained; the fact that heteroaddition products 3ab′,
4ab′, 3df′, and 4df′ were not generated indicates that the H/D
atom and the silyl group that added to the 1-octyne came from
a single silane molecule. The results of the mixed-silane
experiments exclude a catalytic cycle that starts from an Fe−H
(Scheme 5, Path a) or Fe−Si (Scheme 5, Path b) species but
support a Chalk−Harrod-type catalytic cycle15 (Scheme 5,
Path c) because the redox-neutral process involving Fe−Si or
Fe−H species would inevitably lead to heteroaddition
products. According to the literature, the precursor of the
iron catalyst can be reduced to active Fe(0) species by
EtMgBr.16 A kinetic isotope effect experiment involving
competitive hydrosilylation reactions between 1-octyne and
phenylsilane/PhSiD3 with catalysis by C1g (condition A) or
C1j (condition B) showed first-order kinetic isotope effects
(kH/kD = 4.0 and 3.8, respectively; Scheme 5B). These data
indicate that hydrogen transfer might be a rate-limiting step.17
F
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Figure 1. (a) Iron-catalyzed LLHT in singlet, triplet, and quintet states; (b) dihedral angles between plane (Fe−N−N) and plane (Fe−C−C) and
energy differences for various possible transitions states in iron-catalyzed LLHT. Although the above calculations are helpful for understanding the
activity and selectivity of iron catalysts, the other mechanisms and regioselective control models cannot be ruled out at the current stage. The
isolation and determination of proposed intermediates are still undergoing in our laboratory.
with Markovnikov selectivity. These results indicate that the
fundamental reason for the selectivity we observed is that the
substituents on the sterically bulky 2,9-aryl groups of the 1,10-
phenanthroline ligand deflected the alkyne during hydrogen
migration and thus decreased the degree of overlap between
the iron and alkyne molecular orbitals, which in turn permitted
regiodifferentiation of the two ends of the alkyne. That is, the
electronic structure of the triplet-state iron catalyst enabled
fine discrimination of the steric differences between the two
ends of the alkynes and thus allowed for the regiodivergent
hydrosilylation.
activity (TONs up to 35 500). This protocol facilitated the
preparation of vinyl silanes containing two Si−H bonds, which
could therefore be used for highly selective synthesis of
disubstituted and trisubstituted olefins, as well as for the
potential of organosilicon materials. Mechanistic studies
suggested that the iron catalysts might promoted the
hydrosilylation by means of 2e− redox cycle and maximization
of the overlap between the iron and alkyne orbitals might be
the driving force for the observed regioselectivity. The above-
described findings have deepened our understanding of iron-
catalyzed reactions and can be expected to facilitate the
development of new iron catalysts and iron-catalyzed reactions.
SUMMARY
■
ASSOCIATED CONTENT
■
In summary, we have developed a protocol for stereospecific,
regiodivergent hydrosilylation reactions of terminal and
internal alkynes with primary silanes catalyzed by iron
complexes bearing 2,9-diaryl-1,10-phenanthroline ligands.
The catalytic system described herein can completely reverse
the regioselectivity of various alkynes by simply changing the
substitution pattern on the ligands and exhibits excellent
sı
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Geometrical parameters for the structure of reagents
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under reference number CCDC 1974110 (CIF)
Crystallographic information file for C1h; this informa-
tion is also available from the Cambridge Crystallo-
graphic Data Centre (https://www.ccdc.cam.ac.uk/)
under reference number CCDC 1960979 (CIF)
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silylation and sequential vinylsilane hydroboration with Markovnikov
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AUTHOR INFORMATION
Corresponding Author
Shou-Fei Zhu − State Key Laboratory and Institute of Elemento-
Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, China; orcid.org/0000-0002-6055-3139;
Email: sfzhu@nankai.edu.cn
■
Authors
Meng-Yang Hu − State Key Laboratory and Institute of
Elemento-Organic Chemistry, College of Chemistry, Nankai
University, Tianjin 300071, China
Peng He − State Key Laboratory and Institute of Elemento-
Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, China
Tian-Zhang Qiao − State Key Laboratory and Institute of
Elemento-Organic Chemistry, College of Chemistry, Nankai
University, Tianjin 300071, China
Wei Sun − State Key Laboratory and Institute of Elemento-
Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, China
Wen-Tao Li − State Key Laboratory and Institute of Elemento-
Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, China
Jie Lian − State Key Laboratory and Institute of Elemento-
Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, China
Jin-Hong Li − State Key Laboratory and Institute of Elemento-
Organic Chemistry, College of Chemistry, Nankai University,
Tianjin 300071, China
Complete contact information is available at:
https://pubs.acs.org/10.1021/jacs.0c09083
Notes
The authors declare no competing financial interest.
(6) (a) Molander, G. A.; Retsch, W. H. Selective hydrosilylation of
alkynes catalyzed by an organoyttrium complex. Organometallics 1995,
14, 4570−4575. (b) Chaulagain, M. R.; Mahandru, G. M.;
Montgomery, J. Alkyne hydrosilylation catalyzed by nickel complexes
of N-heterocyclic carbenes. Tetrahedron 2006, 62, 7560−7566.
(c) Du, X.; Hou, W.; Zhang, Y.; Huang, Z. Pincer cobalt complex-
catalyzed Z-selective hydrosilylation of terminal alkynes. Org. Chem.
Front. 2017, 4, 1517−1521. (d) Wu, G.; Chakraborty, U.; Jacobi von
Wangelin, A. Regiocontrol in the cobalt-catalyzed hydrosilylation of
alkynes. Chem. Commun. 2018, 54, 12322−12325.
(7) Wen, H.; Wan, X.; Huang, Z. Asymmetric synthesis of silicon-
stereogenic vinylhydrosilanes by cobalt-catalyzed regio- and enantio-
selective alkyne hydrosilylation with dihydrosilanes. Angew. Chem., Int.
Ed. 2018, 57, 6319−6323.
(8) (a) Hu, M.-Y.; He, Q.; Fan, S.-J.; Wang, Z.-C.; Liu, L.-Y.; Mu, Y.-
J.; Peng, Q.; Zhu, S.-F. Ligands with 1,10-phenanthroline scaffold for
highly regioselective iron-catalyzed alkene hydrosilylation. Nat.
Commun. 2018, 9, 221. (b) Hu, M.-Y.; Lian, J.; Sun, W.; Qiao, T.-
Z.; Zhu, S.-F. Iron-catalyzed dihydrosilylation of alkynes: efficient
access to geminal bis(silanes). J. Am. Chem. Soc. 2019, 141, 4579−
4583.
ACKNOWLEDGMENTS
■
We thank the National Natural Science Foundation of China
(21625204, 21971119), the “111” project (B06005) of the
Ministry of Education of China, the National Program for
Special Support of Eminent Professionals, Key-Area Research
and Development Program of Guangdong Province
(2020B010188001), and the China Postdoctoral Science
Foundation (2019M660972) for financial support. Generous
help from Prof. Wei Shi (NKU, magnetic moment measure-
ment), Prof. Xiao-Song Xue (helpful discussion on DFT
calculation), Prof. Qian Peng (NKU, helpful discussion on
DFT calculation), and Prof. Hui Chen (ICC, DFT calculation
examination) is highly appreciated. Dedicated to Professor
Eiichi Nakamura on the occasion of his 70th birthday.
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