Download PDF
Synlett 2021; 32(13): 1281-1288
DOI: 10.1055/a-1408-6795
cluster account
Perspectives on Organoheteroatom and Organometallic Chemistry

A Glimpse and Perspective of Current Organosilicon Chemistry from the View of Hydrosilylation and Synthesis of Silicon-Stereogenic Silanes

Fei Ye
,
Li-Wen Xu∗

We thank the National Natural Science Foundation of China (21773051, 21801056, and 22072035) and the Natural Science Foundation of Zhejiang Province (LZ18B020001) for financial support of this work.
› Further Information
 
 PDF Download Permissions and Reprints All articles of this category


Abstract

Silicon and its related organosilicon chemistry has become a mainstay in synthetic chemistry as they can participate in numerous organic transformations. Due to space limitations, this perspective is focused on a glimpse of current organosilicon chemistry from the view of catalytic hydrosilylation and synthesis of silicon-stereogenic silanes. The progress of the two topics fully illustrates that organosilicon chemistry has become a hot research field in recent years and will play a greater role in academic research and industrial applications of silicon element in the future.

1 Introduction

2 Hydrosilylation

3 Catalytic Constructions of Silicon-Stereogenic Centers

4 Conclusion and Perspective


#

Key words

organosilicon - hydrosilylation - silicon-stereogenic center

Biographical Sketches

Zoom Image

Fei Ye was born in Hunan, and he obtained his PhD from the University of Paris VI, France in 2017 under the supervision of Dr. V. Ratovelomanana-Vidal and Prof. Véronique Michelet. He worked with Professor Matthias Beller at the Leibniz Institute for Catalysis (LIKAT), Rostock, Germany as a postdoctoral fellow from 2018 to 2020. Fei’s research transitioned to the synthesis of fluoro-substituted functional molecules. Now, he is an assistant professor at Hangzhou Normal University. His current research focuses on ligand synthesis, organosilicon chemistry, and asymmetric catalysis.

Zoom Image

Li-Wen Xu received his PhD degree from Chinese Academy of Sciences (CAS) in 2004, and from 2004 to 2006 he carried out an independent research career as an associate research professor at Lanzhou Institute of Chemical Physics (CAS). He spent one year (2005–2006) as a postdoctoral fellow at the Université du Maine and CNRS. From 2007 to 2009 he was a research fellow at Department of Chemistry, National University of Singapore and was a JSPS fellow at The University of Tokyo. He was appointed as full professor at Key Laboratory of Organosilicon Chemistry and Material Technology of MOE, Hangzhou Normal University in 2009. Now he is the director of Key Laboratory of Organosilicon Chemistry and Material Technology of MOE. He has authored about more than 150 research publications and ten reviews or book chapters and was awarded the Second Class of Zhejiang Provincial Prize for Natural Sciences and the Thieme Chemistry Journal Awardee in 2014. His current scientific interests are focused on organosilicon chemistry (SiMOS), asymmetric synthesis mediated by homogeneous organometallic and organic catalysts.

1

Introduction

As one of the most abundant elements on the earth, silicon is one of the most potential elements or material resources, thus the conversion of inorganic silicon to organic silicon is one of the most important reactions in synthetic chemistry and material science, which produced a new discipline, namely organosilicon chemistry. Since C. Friedel and J. M. Crafts prepared SiEt4 containing Si–C bonds for the first time in 1863, the academic research of organosilicon chemistry and its industrial application have been developing rapidly, and the research scope has gradually expanded to materials, environment, medicine, and other fields (Figure [1]).[1] Especially, recent developments have also fully demonstrated that organosilicon chemistry has become one of the most attractive hotspots in the current chemical research field.[2] More and more research achievements show its high degree of intersectionality.[2a] In the past two years (2019–2020), chemists have continuously synthesized new organosilicon compounds and conducted in-depth research on their functions,[3] which greatly enriched the chemical properties of silicon,[4] especially in the areas of hydrosilylation (Figure [2]),[5] the synthesis of chiral silanes[6] and silicon-containing polymers[7] from general organic reactions, silicon-mediated organic synthesis,[8] and the chemistry of silicon-based reactive intermediates[9] and silylenes.[10] Each topic of organosilicon chemistry can form a long discussion. Therefore, in this perspective, we will take a glimpse for the recent progress of hydrosilylation and the catalytic construction of silicon-stereogenic centers as two representative examples to show that the research of organosilicon chemistry has entered a booming era.

Zoom Image
Figure 1 The dynamic development of ̒Organosilicon̓ in the past twenty years, data obtained by searching keywords on Web of Science.
Zoom Image
Figure 2 The dynamic development of ̒hydrosilylation̓ and ̒asymmetric hydrosilylation̓ in the past twenty years, data obtained by searching keywords on Web of Science.

# 2

Hydrosilylation

Among the different methods for the construction of organosilicon compounds, catalytic hydrosilylation of alkenes and alkynes is the most powerful and atom-economical approach which allow the straightforward addition of silanes (Si–H) to multiple bonds with the formation of C–Si bonds.[11] Apart from the typical noble metal catalysis (Pt, Rh, Ru, Ir, …), a number of recently disclosed hydrosilylation reactions focused on the development of efficient approaches, in terms of chemo-, regio-, stereo-, and enantio­selectivities, based on earth-abundant transition metals, for example, Fe, Co, Ni, Mn, and metal-free conditions.

The development of a fine catalyst system to furnish the hydrosilylation of alkenes in a green and sustainable manner is always attracting much attention in this field. Designing new ligands to improve the activity and selectivity of the catalyst is undoubtedly the right direction. For example, Deng and co-workers reported a cobalt/N-heterocyclic carbene (NHC) complexes catalyzed hydrosilylation of alkenes with tertiary silanes.[12] Versatile synthetically useful triethoxysilanes have been synthesized in high regioselectivity obviating the use of external activator. In 2018, the Thomas group demonstrated that bench-stable manganese(II) bis(imino)pyridine compounds have also represented high catalytic activity and selectivity in the hydrosilylation of alkenes with tertiary silanes.[13] The alkoxide activation with NaOtBu were found to be uniquely active in addition to assisting operational simplicity.

The hydrosilylation of allenes represents a straightforward and atom-economical approach for the preparation of synthetically useful allylsilanes, vinylsilanes, and its derivatives.[14] However, this transformation is hindered by the generally low regioselectivity and stereoselectivity due to the six possible isomeric organosilanes. To solve this problem, the Ge group examined various methods to control the regio- and stereoisomeric outcomes of the allylsilane in cobalt-catalyzed hydrosilylation of allenes (Scheme [1]). When using BINAP or Xantphos as ligand, the reaction proceeded smoothly to provide linear (Z)-allylsilanes under mild conditions in high yields with excellent stereoselectivities.[14a]

Zoom Image
Scheme 1 Cobalt-catalyzed hydrosilylation of allenes

Normally, the catalytic hydrosilylation of alkynes favorably provide the corresponding vinyl silanes with the silyl group on the side with the smaller alkyl groups. For example, Ge et al. reported an anti-Markovnikov hydrosilylation of terminal alkynes using bench-stable catalyst systems consisting of Co(acac)2 and bidentate phosphine ligands (Scheme [2]).[15] These reactions displayed excellent regioselectivity and stereoselectivity for a wide range of alkynes containing either aromatic or aliphatic substituents to give (E)-vinylsilanes in high isolated yields.

Zoom Image
Scheme 2 Cobalt-catalyzed (E)-selective hydrosilylation of terminal alkynes

Complementary to the synthesis of (E)-β-vinylsilanes, the selective synthesis of (Z)-β-vinylsilanes is considered to be more challenging, and the use of non-noble metal catalyst is rare. In 2017, Ge and co-workers developed a cobalt-catalyzed Z-selective hydrosilylation of terminal alkynes with PhSiH3. A series of sterically diverse pyridine-2,6-diimine (PDI) ligands have been prepared and tested for these reactions, both ethynyl arenes and aliphatic alkynes underwent this reaction to afford a variety of functionalized (Z)-vinylsilanes in high yields with Z/E ratios higher than 91:9 (Scheme [3a]).[16a] The addition of a catalytic amount of phenol was helpful to achieve high Z-selectivity. Later, a similar example was described by Huang and co-workers, providing a wide range of (Z)-β-vinylsilanes through a phosphine-iminopyridine (PCNN) cobalt complex catalyzed hydrosilylation of terminal alkynes with Ph2SiH2 (Scheme [3b]).[16b]

Zoom Image
Scheme 3 Cobalt-catalyzed (Z)-selective hydrosilylation of terminal alkynes

The Huang group has also demonstrated the ­Markovnikov synthesis of α-vinylsilanes with high regioselectivity using a pyridine bis(oxazoline) cobalt complex as precatalyst. The authors also reported that under cobalt-catalyzed Markovnikov hydroboration conditions, the useful vinylsilane can be further converted into borosilanes (Scheme [4]).[17]

Zoom Image
Scheme 4 Cobalt-catalyzed alkyne hydrosilylation and sequential vinylsilane hydroboration

The development of new iron-catalyzed hydrosilylation reactions attracted increasing attention during the past years, owing to the easily available and inexpensive iron catalyst meet the requirements of green and sustainable chemistry applications. Recently, the group of Zhu demonstrated the utility of a series of 1,10-phenanthrolines as efficient ligands for the iron-catalyzed hydrosilylation of multiple carbon–carbon bonds including alkenes, diene, and alkynes. Employing differently substituted 1,10-phenanthrolines, these ligand-controlled transformations underwent either Markovnikov or anti-Markovnikov hydroboration to provide the desired product in high regioselectivity (Scheme [5]).[18a] [b] Notably, recent example revealed that these iron complexes bearing 2,9-diaryl-1,10-phenanthroline ligands exhibited extraordinary ligand-controlled divergent regioselectivity in hydrosilylation reactions of various alkynes.[18c]

Zoom Image
Scheme 5 Iron/1,10-phenanthroline complex catalyzed alkyne hydrosilylations

The copper-catalyzed asymmetric hydrosilylation is a valuable progress in organosilicon chemistry. In 2017, Buchwald reported an elegant example of the asymmetric synthesis of chiral organosilanes, they demonstrated a Cu–H-catalyzed Markovnikov hydrosilylation of styrenes and vinyl heterocycles with Ph2SiH2 proceeded through a high enantioselective manner (Scheme [6]).[19]

Zoom Image
Scheme 6 Cu–H-catalyzed Markovnikov hydrosilylation of vinylarenes

One year later, the Lu group investigated this enantioselective hydrosilylation of olefines utilizing a chiral oxazoline iminopyridine cobalt complex (OIP-Co) and an alkoxide activator. Interestingly, the reaction resulted in high level of regio- and enantioselectivity for both aryl and aliphatic alkenes with excellent functional group tolerability (Scheme [7a]).[20a] Fascinatingly, the combination of chiral oxazolineiminopyridine iron complex (OIP-Fe) with sodium tert-butoxide as activator also represented high reactivity and efficiency for the hydrosilylation of terminal aliphatic alkenes (Scheme [7b]).[20b] These two operationally simple protocols fully demonstrated the power of earth-abundant transition-metal catalyst in the enantioselective synthesis of valuable chiral organosilanes.

Zoom Image
Scheme 7 OIP-Fe- and OIP-Co-catalyzed enantioselective hydrosilylation of alkenes

Although the asymmetric hydrosilylation to make functionalized linear alkylsilanes with good regio- and enantio­selectivities have been generally developed, only few examples focused on the highly enantioselective hydrosilylation of internal alkenes and carbocycles. In 2019, the Xu group explored a straightforward and efficient approach for the construction of structurally diverse and chiral silyl carbocycle compounds, a wide range of optically pure and silyl-functionalized polysubstituted carbocycles and silanol derivatives have been synthesized highly efficient and enantioselective via desymmetric hydrosilylation of 1,1-disubstituted cyclopropenes (Scheme [8]).[21]

Zoom Image
Scheme 8 Rh-catalyzed hydrosilylation of 1,1-disubstituted cyclopropenes

Very recently, the Xu group established the application of carbonyl-activated alkenes for the highly enantioselective Si–C coupling hydrosilylation using a palladium catalyst with a chiral TADDOL-derived phosphoramidite ligand. Notably, when using ortho-substituted N-arylmaleimides, the remote hydrosilylation-controlled construction of C–N axial chirality was achieved ideally (Scheme [9]).[22]

Zoom Image
Scheme 9 Asymmetric hydrosilylation of maleimides

# 3

Catalytic Constructions of Silicon-Stereogenic Centers

Since the early example for the asymmetric synthesis of optically pure organosilanes has been revealed in 1994 by Takaya,[23] limited progress has been reported occasionally in the area of catalytic synthesis of silicon-stereogenic organosilanes in the last two decades (Figure [3]).[24] However, as the vital value of Si-centered chiral organosilanes in materials and organic chemistry has received increasing attention, this situation has improved in the past five years.[25] [26] [27] [28]

Zoom Image
Figure 3 Publications on the construction of silicon-stereogenic organosilicons in the past fifteen years, data obtained by searching key words on Web of Science.

Owing to the versatile reactivity and wide availability, the desymmetrization of dihydrosilanes expresses the most common and straightforward approach for the synthesis of silicon-stereogenic organosilanes (Scheme [10]), especially for the construction of the most valuable chiral monohydrosilanes. Following the first asymmetric palladium-catalyzed desymmetrization of dihydrosilanes with aryl halides,[25a] Xu reported in 2016 an advanced enantioselective synthesis of silicon-stereogenic silanes by palladium-catalyzed Si–C bond-forming silylation of aryl iodides with dihydrosilanes using a modified TADDOL-derived phosphoramidite ligands.[25c] [d] While the transition-metal-catalyzed hydrosilylation of alkenes with dihydrosilanes have been widely explored, an asymmetric version to form chiral vinyl silanes have not been realized until when Tomooka identified a platinum-catalyst system for the hydrosilylation of internal alkynes.[26a] To arise the issue of regioselectivity, Huang developed a cobalt-catalyzed hydrosilylation of unsymmetric internal alkynes with dihydrosilanes, furnishing a broad range of silicon-stereogenic vinylhydrosilanes with high regio- and enantioselectivity.[26b] Later, Hou’s group reported the use of a chiral half-sandwich scandium catalyst for enantioselective hydrosilylation of alkenes with dihydrosilanes,[26c] which fills the gap in this field. Using symmetrical or prochiral diarylcarbene as reactant, a dirhodium(II) carboxylate-catalyzed Si–H insertion reaction was accomplished to produce enantioenriched organosilanes.[26d] Recently, He’s group also reported an intramolecular C(sp 2)–H functionalization in order to desymmetrize dihydrosilanes, achieving a variety of chiral monohydrosilanes in good yields and excellent enantioselectivity.[26e]

Zoom Image
Scheme 10 Asymmetric transition-metal-catalyzed desymmetrization of dihydrosilanes

The silicon-stereogenic monohydrosilane synthesized from dihydrosilane can be further transformed into tetrasubstituted chiral silane via subsequent tandem reactions (Scheme [10]). In He’s recent two reports, rhodium-catalyzed enantioselective silylation of aryl C(sp 2)–H or aliphatic C(sp 3)–H bonds followed by a stereospecific intermolecular alkene hydrosilylation were demonstrated to directly access the asymmetrically tetrasubstituted silanes.[27a] [b] The use of bis(alkenyl)dihydrosilanes in rhodium-catalyzed double hydrosilylation was expanded on by Wang’s group, where a family of enantiopure spirosilabiindane derivatives were prepared in high enantio­selectivity. Notably, this new spirosilabiindane scaffold has been revealed with high potential in asymmetric catalytic reactions.[27c]

In addition to highly reactive dihydrosilanes, the asymmetric synthesis of silicon-stereogenic chiral silanes via metal-catalyzed desymmetrization of prochiral tetraorganosilanes, which did not involve silicon atom in the construction of a new bond, are also accessible (Scheme [11]). In 2016, Nozaki, Shintani, and co-workers reported the catalytic asymmetric synthesis of optical pure arylpyridinones containing a silicon-stereogenic center through a rhodium-catalyzed [2+2+2] cycloaddition of silicon-containing prochiral triynes with isocyanates.[28a] Interestingly, this process has been applied to the synthesis of silicon-stereogenic chiral polymers for the first time. Later, the same group reported a palladium-catalyzed asymmetric synthesis of 5,10-dihydrophenazasilines via an unprecedented enantio­selective 1,5-palladium migration.[28b] The desymmetrization of diaryl-substituted via C–H bond activation process was explored by Xu’s group, the pyridine- and pyrimidine-containing nitrogen serve as powerful chelation-assisted directing groups for C–H functionalization reactions of silicon-tethered arenes.[28c] Recently, Xu’s group developed a rhodium-catalyzed intramolecular hydrosilylation of silicon-tethered bisalkynes. A variety of chiral benzosiloles bearing a silicon-stereogenic center have been proficiently synthesized with good functional group tolerance. Notably, these silicon-stereogenic benzosiloles showed significant aggregation-induced emission (AIE) and circularly polarized luminescence (CPL) activities.[28d] Although fascinating approaches have been established to create silicon-stereogenic centers in the presence of chiral Pt, Ir, Rh, or Pd catalysts, investigations in non-noble metal catalyst were rarely described. Recently, the Xu group reported the first example of copper-catalyzed enantioselective synthesis of silicon-stereogenic silanes. The catalytic esterification of prochiral tetrasubstituted siladiols provides optically active silylmethanols in moderate to good enantiomeric excesses.[28e] The Xiong group demonstrated the potential to incorporate copper-borane with vinyl silanes. In this process, an unprecedented desymmetrizing protoboration of divinyl-substituted silanes with bis(pinacolato)diboron led to a family of enantioenriched boronate-substituted organosilanes bearing contiguous silicon and carbon stereocenters.[28f]

Zoom Image
Scheme 11 Catalytic desymmetrizing the prochiral tetraorganosilanes

The advent of catalytic activation of inert Si–C bonds also represents a powerful and direct route toward chiral silicon-stereogenic from prochiral Si–C precursors. In 2017, He’s group reported a fascinating Rh-catalyzed tandem silacyclobutanes desymmetrization–dehydrogenative silylation in intermolecular fashion (Scheme [12]).[29a] A chiral monohydrosilane was proposed as a key intermediate to furnish the dibenzosilole product. Later, the Song group described a rhodium-catalyzed reaction of silacyclobutanes with unactivated alkynes using a chiral binaphthyl phosphoramidite as ligand to expand the scope of the useful enantioenriched silacyclohexanes.[29b]

Zoom Image
Scheme 12 Desymmetrization of silacyclobutanes

# 4

Conclusion and Perspective

In summary, the above-mentioned studies on catalytic hydrosilylation and the synthesis of silicon-stereogenic organosilicon compounds as miniature aspects of organosilicon chemistry have made significant progress in the past years. In fact, organosilicon chemistry has numerous and good new discoveries in other related fields, especially in synthetic chemistry and material science, which is increasingly showing its unique functions. For example, the silicon-based bulky group with large steric-hindrance function can be used as an indispensable and important structural fragment on the chiral ligands or organocatalysts to play a crucial role with stereoselective synergistic effect in the asymmetric catalysis, silicon can act as a bridging framework to make the reaction easy to occur, and usually plays an important and enhanced role in the development of high-performance optoelectronic materials. We believe that as more and more young scientists join the research team of organosilicon chemistry, more new discoveries in organosilicon chemistry will result. As the late Professor Robert Corriu said, ‘Organosilicon chemistry will be involved at least in part in a new chapter of chemistry. The knowledge already achieved creates new fields of research oriented in terms of properties. In this area, the only limitation for the chemist is mainly his own creativity.’[24a] We look forward to organosilicon chemistry playing a greater role in academic research and industrial applications in the future!


#
#

Conflict of Interest

The authors declare no conflict of interest.

Acknowledgment

The authors thank the support of High-Level Innovation Team of Colleges and Universities in Zhejiang Province and ‘2011’ Collaborative Innovation Center Fluorosilicon-Based Fine Chemicals and Materials Preparation of Zhejiang Province.


Corresponding Author

Li-Wen Xu
Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, and Key Laboratory of Organosilicon Material Technology of Zhejiang Province, Hangzhou Normal University
No. 2318, Yuhangtang Road, 311121 Hangzhou
P. R. of China   

Publication History

Received: 31 January 2021

Accepted after revision: 05 March 2021

Accepted Manuscript online:
05 March 2021

Article published online:
16 March 2021

© 2021. Thieme. All rights reserved

Georg Thieme Verlag KG
Rüdigerstraße 14, 70469 Stuttgart, Germany


   Permissions and Reprints All articles of this category
Zoom Image
Zoom Image
Zoom Image
Figure 1 The dynamic development of ̒Organosilicon̓ in the past twenty years, data obtained by searching keywords on Web of Science.
Zoom Image
Figure 2 The dynamic development of ̒hydrosilylation̓ and ̒asymmetric hydrosilylation̓ in the past twenty years, data obtained by searching keywords on Web of Science.
Zoom Image
Scheme 1 Cobalt-catalyzed hydrosilylation of allenes
Zoom Image
Scheme 2 Cobalt-catalyzed (E)-selective hydrosilylation of terminal alkynes
Zoom Image
Scheme 3 Cobalt-catalyzed (Z)-selective hydrosilylation of terminal alkynes
Zoom Image
Scheme 4 Cobalt-catalyzed alkyne hydrosilylation and sequential vinylsilane hydroboration
Zoom Image
Scheme 5 Iron/1,10-phenanthroline complex catalyzed alkyne hydrosilylations
Zoom Image
Scheme 6 Cu–H-catalyzed Markovnikov hydrosilylation of vinylarenes
Zoom Image
Scheme 7 OIP-Fe- and OIP-Co-catalyzed enantioselective hydrosilylation of alkenes
Zoom Image
Scheme 8 Rh-catalyzed hydrosilylation of 1,1-disubstituted cyclopropenes
Zoom Image
Scheme 9 Asymmetric hydrosilylation of maleimides
Zoom Image
Figure 3 Publications on the construction of silicon-stereogenic organosilicons in the past fifteen years, data obtained by searching key words on Web of Science.
Zoom Image
Scheme 10 Asymmetric transition-metal-catalyzed desymmetrization of dihydrosilanes
Zoom Image
Scheme 11 Catalytic desymmetrizing the prochiral tetraorganosilanes
Zoom Image
Scheme 12 Desymmetrization of silacyclobutanes