Skip to main content
NCBI home page
iScience logoLink to iScience
. 2020 Jun 15;23(7):101268. doi: 10.1016/j.isci.2020.101268

Catalytic Asymmetric trans-Selective Hydrosilylation of Bisalkynes to Access AIE and CPL-Active Silicon-Stereogenic Benzosiloles

Ren-He Tang 1,3, Zheng Xu 1,3, Yi-Xue Nie 1, Xu-Qiong Xiao 1, Ke-Fang Yang 1, Jia-Le Xie 1, Bin Guo 1, Guan-Wu Yin 1, Xue-Min Yang 1, Li-Wen Xu 1,2,4,∗
PMCID: PMC7326740  PMID: 32599559

Summary

Chirality widely exists in a diverse array of biologically active molecules and life forms, and the catalytic constructions of chiral molecules have triggered a heightened interest in the fields of chemistry and materials and pharmaceutical sciences. However, the synthesis of silicon-stereogenic organosilicon compounds is generally recognized as a much more difficult task than that of carbon-stereogenic centers because of no abundant organosilicon-based chiral sources in nature. Herein, we reported a highly enantioselective rhodium-catalyzed trans-selective hydrosilylation of silicon-tethered bisalkynes to access chiral benzosiloles bearing a silicon-stereogenic center. This protocol featured with chiral Ar-BINMOL-Phos bearing hydrogen-bond donors as a privileged P-ligand for catalytic asymmetric hydrosilylation that is operationally simple and has 100% atom-economy with good functional group tolerability as well as high enantioselectivity (up to >99:1 er). Benefiting from the trans-selective hydrosilylation with the aid of Rh/Ar-BINMOL-Phos-based asymmetric catalysis, the Si-stereogenic benzosiloles exhibited pronounced aggregation-induced emission (AIE) and circularly polarized luminescence (CPL) activity.

Subject Areas: Chemistry, Organic Synthesis, Stereochemistry

Graphical Abstract

graphic file with name fx1.jpg

Open in a new tab

Highlights

  • •

    Precise and facile construction of silicon-stereogenic center by desymmetrization

  • •

    Highly enantioselective Rh-catalyzed hydrosilylation controlled by MFMC P,O,O-ligand

  • •

    Catalytic asymmetric synthesis of AIE- and CPL-active chiral Si-center benzosiloles

  • •

    The proposed mechanism is supported by NMR and kinetic studies

Chemistry; Organic Synthesis; Stereochemistry

Introduction

Silacycles are considered as a new kind of σ∗-π∗ conjugated organic material with low-lying lowest unoccupied molecular orbital (LUMO) energy levels (Chen and Cao, 2007; Fu and Cheng, 2012; Zhao et al., 2015; Pop et al., 2019; Dhbaibi et al., 2019), deriving from the interaction between the σ∗ orbital of two exocyclic silicon-carbon σ-bonds and the π∗ orbital of the butadiene moiety (Yamaguchi and Tamao, 1996). As one of the most important types of silacycles, siloles exhibit unique electronic structure with low-lying LUMO level with intriguing optical and electronic properties due to high electron affinity and fast electron mobility, enabling them to function as luminescent core and electron transporters in optoelectronic devices (Tamao et al., 1996a, 1996b; Uchida et al., 2001, Son et al., 2009), such as organic light-emitting diodes (Chen et al., 2002; Cai et al., 2017 Nie et al., 2018), fluorescent bioprobes (Wu et al., 2010; Zhuang et al., 2017), chemosensors (Toal et al., 2005; Li et al., 2009; Dedeoglu et al., 2014), and circular polarized luminescence (CPL) (Liu et al., 2012; Ng et al., 2014a and 2014b; Li et al., 2016). Therefore, the development of practical methods for the synthesis of silole scaffolds is highly important in both synthetic and materials chemistry, which has attracted increasing attention (Ohmura et al., 2008; Matsuda et al., 2007; Ureshino et al., 2010; Liang et al., 2011; Shimizu et al., 2008; Zhao et al., 2012; Liang et al., 2012; Zhang et al., 2014 and 2015; Ilies et al., 2008; Tobisu et al., 2009; Onoe et al., 2012; Minami et al., 2017; Gimferrer et al., 2018; Yang et al., 2018). Especially, the construction of a stereogenic Si-center of siloles in a catalytic enantioselective manner is an appealing yet challenging task, although there have been some efforts for the catalytic synthesis of chiral Si-centers (Oestreich, 2007; Weickgenannt et al., 2010; Xu et al., 2011; Xu, 2012; Shintani, 2015; Tamao et al., 1996a, 1996b; Igawa et al., 2012; Naganawa et al., 2015; Zhan et al., 2018; Wen et al., 2018; Guo et al., 2019). In this regard, the catalytic enantioselective synthesis of silicon-stereogenic heterocycles have been achieved via Pd-catalyzed C-H arylation (Shintani et al., 2012) or amination (Sato et al., 2017) of prochiral 2-(arylsilyl)aryl triflates or Rh-catalyzed aromatic C-H silylation (Scheme 1A) (Kuninobu et al., 2013; Zhang et al., 2016, 2017). Moreover, the rhodium-catalyzed [2 + 2 + 2] cycloaddition of silicon-containing prochiral triynes with internal alkynes was also a facile approach to the construction of silicon-stereogenic DBS (Shintani et al., 2015). All these methods mentioned above provided complementary processes to the preparation of enantio-enriched chiral DBS bearing a silicon-stereogenic center. However, the construction of Si-chirality on unsymmetrical benzosiloles (BS) via catalytic hydrosilylation is still unknown to date.

Scheme 1.

Scheme 1

Open in a new tab

Catalytic Enantioselective Synthesis of Silicon-Stereogenic Silole Analogues

(A) Previous reports on the catalytic asymmetric synthesis of silicon-stereogenic dibenzosiloles via C-H activation or silylations.

(B) Our strategy with MFMC ligand catalysis via Ar-BINMOL-Phos-controlled Rh-catalyzed intramolecular hydrosilylation to access silicon-stereogenic benzosiloles. MFMC is multi-functional and multi-center.

Very recently, we reported the catalytic asymmetric synthesis of sila-bicyclo[4.1.0]heptanes via palladium-catalyzed [4 + 2] annulation of cyclopropenes with benzosilacyclobutanes (Wang et al., 2020), in which a variety of chiral bicyclic sila-heterocycle derivatives could be achieved with good enantioselectivity (up to 95.5:4.5 er). However, the construction of corresponding silacycles bearing a Si-stereogenic center is not successful in this reaction. Considering the powerful potential of rhodium catalysts for hydrosilylation of alkynes that can provide E- and Z-isomers depending on the precise nature of catalyst systems, substrates, and reaction conditions (Takeuchi and Tanouchi, 1993, 1994; Faller and D'Alliessi, 2002; Sato et al., 2004; Mori et al., 2004; Huckaba et al., 2013; Mancano et al., 2014; Diachenko et al., 2015), we envisioned that the Rh-catalyzed intramolecular and trans-type hydrosilylation might open the door to the enantioselective Si-C bond-forming construction of silicon-stereogenic benzosiloles. Although the desymmetrizative hydrosilylation of alkenes has been achieved to construct silicon-stereogenic center (Naganawa et al., 2015), this reaction suffered limited substrate scope and imperfect enantioselectivity. Comparably, the intramolecular hydrosilylation of Si-tethered bisalkynes is much challenging. This lack of available trans-selective methods with high enantioselectivity is presumably due to the difficulty in the chirality induction during desymmetrization of dihydrosilanes (R1R2SiH2) or silicon-tethered bulky bisalkynes in catalytic asymmetric hydrosilylation. Herein, we reported such a trans-selective intramolecular hydrosilylation reaction with our strategy with Rh/Ar-BINMOL-Phos-based MFMC ligand catalysis (MFMC is multi-functional and multi-center) that can generate silicon-stereogenic siloles with good enantioselectivity (Scheme 1B). This P,O,O-ligand (Ar-BINMOL-Phos) -controlled approach affords a range of alkyne-substituted silicon-stereogenic siloles as potentially useful fluorescent probes from easily available alkynes and hydrosilanes. In addition, it should be noted that the extra alkynyl group on benzosiloles offered a potential functionalization with group transformations.

Results

To construct the silicon-stereogenic BS via catalytic asymmetric hydrosilylation, we are confident that the Rh-catalyzed intramolecular and trans-type hydrosilylation would provide a robust and practical method to the synthesis of this type of alkynyl benzosiloles. Then we began our studies by examining the model hydrosilylation of Si-tethered bisalkyne 1a using Rh catalysts. At 80°C in toluene, various phosphine ligands were evaluated in the [Rh(cod)Cl]2-catalyzed intramolecular hydrosilylation (see Figure 1 and Table S1). Gratifyingly, most of our MFMC Ar-BINMOL-Phos (Song et al., 2014) gave silicon-stereogenic benzosilole 2a in promising conversion (up to >99%) with moderate enantioselectivity (80:20 to 91:9 er in most cases) in the absence of any additives, demonstrating the good feasibility of this Rh-catalyzed hydrosilylation reaction with the aid of chiral P,O,O-ligand; especially, our Tao-Phos (L3) and methyl-substituted Ar-BINMOL-Phos (L8) (Song et al., 2015) gave the desired product 2a with 89.5:10.5 er and 91:9 er, respectively. Notably, other phosphine ligands evaluated in this work, such as BINAP and Segphos, exhibited relatively low enantioselectivity (70:30 er as the best). Then with Tao-Phos in hand, we continued to optimize the reactions by changing rhodium precursors, additives, solvents, and temperature (for representative experimental data, see Tables S2–S4). And finally, the optimized reaction conditions were determined as follows (see Table 1, entry 1): [Rh(cod)Cl]2 (5 mol%), Ar-BINMOL-Phos (o-Me) (12 mol%, simplified as L8 in Supplemental Information), KOtBu (5 mol%), at 70°C. The corresponding product 2a could be obtained in 95.5:4.5 er, albeit the decrease of isolated yield because of low and almost same polarity in comparison with that of starting material 1a. As shown in Table 1, representative reaction results were also important to understand the challenging Rh-catalyzed intramolecular hydrosilylation. The effect of temperature (70°C or 80°C) on enantioselectivity is not obvious as imagined (entry 2). Under the optimized reaction conditions, other rhodium sources did not give better results in term of conversion and enantioselectivity (entry 3). To support the importance of three functional groups (P atom, chiral secondary alcohol, and phenol moiety) on the MFMC P,O,O-ligand (Ar-BINMOL-Phos), we investigated the effect of four representative ligands (CL1-CL4) on the conversion and enantioselectivity (entries 5–9). In sharp contrast, these P-ligands without additional chirality at the carbon of secondary alcohol (CL1 and CL4) gave inferior enantioselectivity (88:12 er for CL1 and 67:33 er for CL4, respectively, entries 6, 9). And more importantly, ligands CL2 and CL4 without secondary alcohol or phenol were not effective in the Rh-catalyzed hydrosilylation because of only moderate conversion (entries 7 and 9). Replacing two OHs (both secondary alcohol and phenol) with MOM and OBn, respectively, deactivated the catalyst (entry 8), probably because of strong hydrogen-bonding interaction between Rh/ligand and substrate. It is easy to understand that Ar-BINMOL without phosphine center is not suitable ligand, which supports the importance of P-atom in the coordination with Rh catalyst. In addition, KOtBu was proved to be an effective additive to promote the intramolecular hydrosilylation. As shown in Table 1 (entries 10–16), the use of other additives, including similar inorganic bases, resulted in inferior results in terms of conversion and enantioselectivity. In fact, we have also investigated the effect of the amount of KOtBu on the Rh-catalyzed intramolecular hydrosilylation of 1a (Table S5). The experimental results showed that the hydrogen-bonding activation from free chiral secondary alcohol is beneficial to the activation of Rh catalyst because large amount of KOtBu could inhibit the hydrosilylation. To our delight, when cobalt and palladium catalysts instead of rhodium catalyst were used in this reaction under the same conditions, only a trace amount of product 2a was detected, and poor enantioselectivity was observed in these experiments (entries 17–19).

Figure 1.

Figure 1

Open in a new tab

Representative Results on Enantioselectivity for Chiral Ligand-Controlled [Rh(cod)Cl]2-Catalyzed Intramolecular Hydrosilylation

(A) The comparable enantioselectivities for various P-ligands (L1-L21) under the same reaction conditions (without any additive and no optimization of reaction conditions).

(B) The chemical structure of various P-ligands (L1-L21) evaluated in this reaction.

Table 1.

Optimization of Reaction Conditions for Rh-catalyzed Desymmetric Hydrosilylation of Bisalkyne 1a

Inline graphic
Entry Variation from Standard Conditionsa T (°C/h) 2a/1ab erc
1 None 70/72 >99:1 (50) 95.5:4.5
2 None 80/34 >99:1 94.5:5.5
3 [Rh(cod)2]BF4 instead of [Rh(cod)Cl]2 80/34 n.r –
4 [Rh(OAc)2]2 instead of [Rh(cod)Cl]2 80/34 n.r –
5 Tao-Phos instead of L8 80/22 80:20 92.5:7.5
6 CL-1 instead of L8 70/72 >99:1 88:12
7 CL-2 instead of L8 70/72 54:46 60:40
8 CL-3 instead of L8 70/72 n.r –
9 CL-4 instead of L8 70/72 34:66 67:33
10 NaHBEt3 instead of KOtBu 80/34 98:2 92.5:7.5
11 NaOtBu instead of KOtBu 80/34 >99:1 90:10
12 NaSbF6 instead of KOtBu 80/34 n.r –
13 CuI instead of KOtBu 80/34 46:54 90:10
14 Ag3PO4 instead of KOtBu 80/34 90:10 92.5:7.5
15 K2CO3 instead of KOtBu 80/34 58:42 90.5:9.5
16 NaOEt instead of KOtBu 80/34 98:2 53.5:46.5
17 OIP Co instead of [Rh]d 80/14 10:90 50:50
18 Pd2(dba)3 80/14 10:90 62.5:37.5
19 (η3-C3H5)2Pd2Cl2 80/14 n.r –
graphic file with name fx3.gif
Open in a new tab
a

Unless otherwise noted, the standard reaction conditions were as follows: 1a (0.2 mmol), and solvent (2.0 mL). The structure of Tao-Phos with o-trimethylsilyl group is different from that of o-methyl substituent on phenyl ring (L8), the conversion is >99% for a family of Ar-BINMOL-Phos.

b

It was difficult to isolate the product 2a from the reaction mixture if the reaction was not completed because of the same polarity of 2a and the starting material 1a. The ratio of 2a/1a was determined by HPLC. n.r = no reaction.

c

The er value of 3a was determined by chiral HPLC analysis.

d

The catalyst OIP Co complex was used instead of [Rh(cod)Cl]2/Ar-BINMOL-Phos catalyst system.

With the optimized reaction conditions in hand, the substrate scope was next explored with respect to the variation of the silicon-tethered bisalkynes (Scheme 2). Si-linked bisalkynes with varied substitution patterns (Me, OMe, F, i-Pr, or t-Bu, etc.) could be smoothly converted to their corresponding hydrosilylation products in moderate to good yields (up to 87%) with high enantioselectivities (up to >99:1 er). Notably, this potassium-assisted Rh-catalyzed hydrosilylation reaction worked well with various types of substrates with electron-neutral, electron-withdrawing or electron-donating groups, having little influence on the Si-centered stereochemistry. When small ring or S-containing heterocycle-substituted bisalkynes were employed, the reaction also worked well under Rh/Ar-BINMOL-Phos catalyst system. For example, the hydrosilylation of 1r proved to be highly enantioselective (93.5:6.5 er) with good yield (75%), and the cyclopropanyl group linked with the terminal position of alkyne on substrate 1q or 1t resulted in the corresponding alkynyl benzosilole 2q or 2t in good yield with high er value, respectively. In addition, the ortho-substituted group did not block the intramolecular hydrosilylation, as evidenced by the reaction of 1n to 2n with 60% yield and 95:5 er. The same level of experimental result was also provided by the intramolecular hydrosilylation reaction of Si-linked bisalkyne 1s, giving the corresponding 2s with 50% yield and 97.5:2.5 er. When the methyl group on silicon atom was replaced by ethyl group, the reaction was also proven to be enantioselective and gave the desired benzosilole 2p in 97.5:2.5 er, albeit with some yield loss in comparison with that of methyl-substituted 2h (80% yield, 94:6 er). Unfortunately, it was found that another bulky group on silicon center, such as t-Bu and phenyl, was not suitable for the construction of their corresponding benzosiloles because of the steric hindrance. Notably, the configuration of the silicon-stereogenic alkynyl benzosiloles (2r) was confirmed by X-ray diffraction pattern (Figure S1). Notably, these compounds were very stable for a long period of time (0.5 year), and its ee value was not changed after reflux in toluene for several days.

Scheme 2.

Scheme 2

Open in a new tab

Scope of MFMC Ar-BINMOL-Phos (L8)-controlled Rh-catalyzed Intramolecular Hydrosilylation of Si-Tethered Bisalkynes

(A) The optimized reaction conditions for the Ar-BINMOL-Phos-based MFMC ligand catalysis based on the experimental results.

(B) Substrate scope for the trans-selective hydrosilylation driven by the MFMC Ar-BINMOL-Phos ligand-controlled desymmetrization of bisalkynes.

Then, the further investigation of such alkynyl benzosiloles as optical material was highly attractive. The fluorescence property of benzosiloles (BS) was subsequently evaluated using 2c, 2g, 2r, 2t, 2q, 2s, and 2l as candidates. As shown in Figure 2, the BS emission was enhanced by the introduction of electron-donating group (-OMe) on the aromatic ring, and p-OMe substituted BS 2g exhibited a very distinctive behavior. The highest occupied molecular orbital (HOMO)-LUMO data might be useful information to distinguish the structural difference. Thus, we then checked the aggregation-induced emission (AIE) property of 2g according to the standard method (Zhou et al., 2019). As expected, the benzosilole 2g showed a blue fluorescence color when the water fraction was above 30% in the THF-water mixture (Figure S7 of Supporting Information). Notably, the relationship of AIE and chirality was also evaluated and it was found that there is no obvious effect for the fluorescence intense.

Figure 2.

Figure 2

Open in a new tab

The Fluorescence Property of Silicon-Stereogenic Benzosiloles

(A) Left: Fluorescence spectra (top) of seven representative and enantioenriched benzosiloles and AIE phenomenon of benzosilole 2g, the fluorescence emission spectra of 2g (5 μM) was achieved in THF/water mixtures (fw = 0% to 90%). λex = 300 nm, λes = 550 nm.

(B) Right: Molecular orbital diagrams of HOMO and LUMO of 2t and 2g, and the energy levels of HOMO and LUMO with their difference (ΔE) of representative benzosiloles shown in this table.

The phenomenon of circularly polarized luminescence (CPL) has attracted considerable attention owing to its wide applications in various research fields (Gao et al., 2019). Therefore, the circular dichroism (CD) and CPL analyses were next performed at 300 nm to evaluate the Si-centered chirality. To our delight, in the test of benzosilole 2g, intensive CPL signs were observed in this case (Figure S8). We anticipated that CPL effect of benzosilole augments its great potential of enantioselective Rh-catalyzed intramolecular hydrosilylation of bisalkynes in the development of a CPL-active material linked with silole backbone.

Discussion

In metal-catalyzed hydrosilylation (Zaranek and Pawluc, 2018; Wen et al., 2019), including the Rh catalysts (Sakaki et al., 2002; Wu et al., 2013 and 2014; Doyle et al., 1991; Sanada et al., 2006; Morales-Ceron et al., 2017) employed for alkyne hydrosilylation, cationic metal complexes usually give predominately (E)-isomer depending on the precise nature of substrates and reaction conditions (Ojima et al., 1990; Trost and Ball, 2005; Ding et al., 2013). In this work, we believed the Rh-catalyzed alkyne trans-hydrosilylation reactions are similar to that of previous reports (Ojima et al., 1990; Matsuda and Ichioka, 2012; Crabtree, 2003) on the isomerization of the M-vinyl complex intermediate to the less sterically congested isomer via an η2-vinyl metal species. In addition, to understand what makes Rh/Ar-BINMOL-Phos (L8) a successful catalyst in the desymmetrization of Si-linked bisalkynes via hydrosilylation, its structure was examined by 31P-NMR and ESI-MS (see Figure 3, and for 31P-NMR analysis, see Figure 3B, and others see Figures S3–S5). And these experimental results indicate that the various types of Rh/L8 complexes might be in situ formed in this reaction, and a dimeric Rh catalyst comprising a dirhodium core is a possible and active species in the pre-activation process (Meiβner et al., 2015a, 2015b; Mannu et al., 2018), which generated through dissociation of cod (1,5-cyclooctadiene) with two coordinating phosphorous centers from Ar-BINMOL-Phos ligands. It is generally accepted that treatment of [Rh(cod)Cl]2 with diphosphine ligands smoothly affords neutral μ2-bridged dimeric/dinuclear rhodium complexes (Meiβner et al., 2015a, 2015b); thus, accordingly, the μ2-bridged dimeric Rh complex is formed probably in the reaction mixtures (the double peaks appeared probably at 33–34 ppm with 1JP-Rh = 204 or 220 Hz in Figure 3B). However, it is difficult to confirm the true structure of dimeric Rh/L8 complex that formed in the pre-activation stage by NMR analysis. Furthermore, the in situ analysis of reaction mixtures with ESI-MS and NLE (Satyanarayana et al., 2009) and kinetic study (Figure 4) showed the mononuclear complex with single Rh(I) catalytic center with one ligand acted probably as majorly active species during the full reaction process. In addition, the stable P/O-coordination of Ar-BINMOL-Phos with [Rh(cod)Cl]2 to give mononuclear Rh complex is supported by 31P-NMR spectra data in which the related 31P signal of such stable mononuclear Rh complex was observed at 41 ppm (Rani et al., 2008).

Figure 3.

Figure 3

Open in a new tab

The Structural Analysis of the Active Rh Species by 31P NMR

(A) The illustrative view of the in situ formed dimeric Rh complex and mononuclear Rh complex from [Rh(cod)Cl]2 and Ar-BINMOL-Phos L8 in CDCl3.

(B) Comparison of 31P NMR of ligand and Rh complex. (a) only L8, a single peak at −14.83 ppm; (b) mixture of [Rh(cod)Cl]2 and L8 (5 min), two double peaks for the Rh/Ar-BINMOL-Phos complex appeared at 22.16 ppm with 1JP-Rh = 183 Hz and 34.40 ppm with 1JP-Rh = 204 Hz, and another single peak appeared at 37.69 ppm, respectively; (c) mixture of L8 and [Rh(cod)Cl]2 (20 min), the double peak at 22.16 ppm disappeared, and another single peak appeared at 45.11 ppm; (d) mixture of substrate 1a, L8 and [Rh(cod)Cl]2 (20 min), a new and single peak appeared at 39.50 ppm; (e) mixture of L8, KOtBu, and [Rh(cod)Cl]2 (5 min); (f) mixture of L8, KOtBu, and [Rh(cod)Cl]2 (20 min); (g) mixture of L8, KOtBu, [Rh(cod)Cl]2, and substrate 1a (20 min), a double peak appeared at 33.72 ppm with 1JP-Rh = 220 Hz and a single peak with 45.27 ppm.

Figure 4.

Figure 4

Open in a new tab

Experimental Results for Relationship of eeprod/eeligand and the Reaction Rate and Enantioselectivity Data with or without KOtBu

(A) The model reaction with intramolecular hydrosilylation of 1a under the optimized reaction conditions.

(B) The NLE result revealed that a mononuclear complex structure with single Rh(I) catalytic center with one ligand acted probably as the true active species.

(C) KOtBu-activated Rh catalysis. There are two stages (before and after 5 h, respectively) for catalytic cycles in the Rh-catalyzed hydrosilylation that detected by ee values and reaction rate under the optimized reaction conditions.

(D) Without KOtBu as additive. When no use of KOtBu for this reaction, the corresponding ee value gradually decreases with reaction time.

It should be noted that the potassium tert-butoxide (KOtBu) played an important role in the in situ formation of the active Rh species to promote the catalytic asymmetric hydrosilylation. As shown in Figure 4, the absence of KOtBu led to decreased enantioselectivity (only 75:25 er), in which the negative result revealed reaction between KOtBu and chiral ligand L8 could form a more stable mononuclear rhodium catalyst that is responsible for the high level of enantioselective induction shown in Figure 4C. When the reaction was performed without KOtBu, enantioselectivity (ee value of 2a) of the same intramolecular hydrosilylation was gradually decreased with time because of irreversible reactions of the active dimeric Rh catalyst with substrate in the catalytic cycle. And notably, excess amount of KOtBu (>24 mol%) decreased the enantioselectivity and much more amount of KOtBu (>36 mol%) inhibited the catalytic activities of all the Rh species reaction to result in almost no reaction. These results provided an indirect evidence for the importance of the chiral secondary alcohol of Ar-BINMOL-Phos (L8) in the enhancement of enantioselectivity and catalytic activity of Rh complex.

Therefore, based on the experimental results and related NMR and ESI-MS analysis, we proposed a reaction mechanism for the asymmetric Rh-catalyzed hydrosilylation (Figure 5). It is expected that the dirhodium core in the chlorine-bridged dimeric rhodium precursor is easily broken by a proton abstraction reaction with ligand L8, releasing HCl with the aid of KOtBu and generating mononuclear precursor complex M0. The cod ligand in the four-coordinated neutral Rh(I) complex will further be replaced by the substrate and leads to an Rh intermediate, in which the alkenyl group and Si-H group of substrate is coordinated to the Rh center in η2 and η1 manner. Then the Rh intermediate underwent Si-H oxidative addition to form a five-coordinated Rh(III) intermediate A. The pre-coordinated alkynyl group is exactly the one to proceed migratory insertion, followed by the Si-H oxidative addition. That is, the two symmetric alkynyl groups in 1a have already been discriminated during the formation of this precursor complex B, in which the reactive alkynyl group and Si-H group linked to the Rh center in enantioselective manner. And then the subsequent process is only related to the Z/E-selectivity but not the enantioselectivity. Similarly to previous Ru catalysis for the trans-selective hydrosilylation of alkynes (Ding et al., 2013), B can be further isomerized to the more stable C (metallacyclohexene intermediate). At this time, the H atom is completely inverted to the trans position, and the alkenyl group is at the trans position of the O-ligand. For the origin of stereoselective induction of such rhodium catalyst, more theoretic studies would be continuously undergoing in our laboratory to gain much more accurate understanding of the hydrosilylation reaction mechanism.

Figure 5.

Figure 5

Open in a new tab

A Proposed Catalytic Cycle for Rh(I)/L8 Complex-Catalyzed Intramolecular Hydrosilylation with Monoalkyne as a Model Substrate

Conclusion

In summary, we accomplished a highly enantioselective Rh-catalyzed intramolecular and trans-type hydrosilylation of silicon-tethered bisalkynes, which provided a practical approach to the construction of AIE and CPL-active benzosiloles bearing silicon-stereogenic center. For this purpose, our chiral Ar-BINMOL-Phos bearing hydrogen-bond donors could be efficiently used as a privileged MFMC P,O,O-ligand in the desymmetrization process of silicon-tethered bisalkynes. The reaction is operationally robust and atom-economic with good functional group tolerability as well as high enantioselectivity (up to >99:1 er) with the aid of Rh/Ar-BINMOL-Phos-based MFMC ligand catalysis. More specially, the use of the basic additive KOtBu is crucial to maintaining of high level of enantioselectivity in this reaction because the catalytic amount KOtBu is responsible for the formation of active Rh/L8 complex. Although the true reaction mechanism for the stereoselective induction of Rh catalyst system is still unclear, the highly enantioselective synthesis of chiral benzosiloles and corresponding construction of silicon-stereogenic center by desymmetric hydrosilylation opens a great opportunity to create the next generation of organosilicon material or possibly better targeted Si-containing biologically active molecules that bring silicon to material and life (Kan et al., 2016). At present, the DFT calculation studies are undergoing in our laboratory to gain a more accurate understanding of the mechanism of trans-selective hydrosilylation and will be reported elsewhere. In addition, the reactive alkyne groups as side chains in the silicon-stereogenic benzosiloles are expected to undergo further functionalization and hold promise for synthesis of conjugate polymers or cross-linked materials.

Limitations of the Study

Terminal alkynes were not applicable in the construction of silicon-stereogenic benzosiloles by the intramolecular hydrosilylation. And the reaction mechanism and the origin of enantioselectivity that is controlled by the Ar-BINMOL-Phos need to be clarified in more reliable manner.

Resource Availability

Lead Contact

Li-Wen Xu, liwenxu@hznu.edu.cn.

Material Availability

No unique reagents or no restrictions to the availability of chemicals.

Data and Code Availability

The related figures and data in this article can be found at the Supplemental Information.

Methods

All methods can be found in the accompanying Transparent Methods supplemental file.

Acknowledgments

This work was supported by the grants of National Natural Science Foundation of China (21773051, 21801056 and 21901056), Zhejiang Provincial Natural Science Foundation of China (LZ18B020001 and LQ19B040001), and the Hangzhou Science and Technology Bureau of China (20170533B08 and 20180432B05). The authors thank Dr. L. Li and Dr. K.Z. Jiang for their assistance on the NMR and MS analysis. L.-W.X. also thanks Prof. Y.X. Zheng (Nanjing University) for his assistance on the CPL analysis, and thanks to Prof. C. Liu (LICP, CAS) and Prof. X.Q. Hu (ZUT) for their help and discussion in this work.

Author Contributions

R.-H.T., Z.X., and Y.-X.N. are co-first authors. L.-W.X. conceived the concept. R.-H.T. carried out experiments, including the preparation of chiral ligands and the rhodium-catalyzed hydrosilylation. Y.-X.N. and Z.X. carried out the experiments for the proposed reaction mechanism. X.-Q.X. carried the X-ray analysis. K.-F.Y. and J.-L.X. carried out partial reactions and the NMR analysis for the products and reaction intermediates. G.-W.Y., B.G., and X.-M.Y. synthesized the substrates and conducted the structural analysis of unknown compounds. L.-W.X wrote the manuscript, and all authors discussed the results and participated in revising the manuscript. L.-W.X. supervised the project.

Declaration of Interests

The authors declare no competing financial interests.

Published: July 24, 2020

Footnotes

Supplemental Information can be found online at https://doi.org/10.1016/j.isci.2020.101268.

Supplemental Information

Document S1. Transparent Methods, Figures S1–S112, and Tables S1–S6
mmc1.pdf (8.1MB, pdf)

References

  1. Cai Y., Qin A., Tang B.Z. Siloles in optoelectronic devices. J. Mater. Chem. C. 2017;5:7375–7389. [Google Scholar]
  2. Chen J., Cao Y. Silole-containing polymers: chemistry and optoelectronic properties. Macromol. Rapid Commun. 2007;28:1714–1742. [Google Scholar]
  3. Chen H.Y., Lam W.Y., Luo J.D., Ho Y.L., Tang B.Z., Zhu D.B., Wong M., Kwok H.S. Highly efficient organic light-emitting diodes with a silole-based compound. Appl. Phys. Lett. 2002;81:574–576. [Google Scholar]
  4. Crabtree R.H. An η 2-vinyl pathway may explain net trans hydrosilylation via transition metal catalysis even in cyclic cases. New J. Chem. 2003;27:771–772. [Google Scholar]
  5. Dedeoglu B., Monari A., Etienne T., Aviyente V., Özen A.S. Detection of nitroaromatic explosives based on fluorescence quenching of silafluorene-and silole-containing polymers: a time-dependent density functional theory study. J. Phys. Chem. C. 2014;118:23946–23953. [Google Scholar]
  6. Dhbaibi K., Favereau L., Crassous J. Enantioenriched helicenes and helicenoids containing main-group elements (B, Si, N, P) Chem. Rev. 2019;119:8846–8953. doi: 10.1021/acs.chemrev.9b00033. [DOI] [PubMed] [Google Scholar]
  7. Diachenko V., Page M.J., Gatus M.R., Bhadbhade M., Messerle B.A. Bimetallic N-heterocyclic carbene Rh (I) complexes: probing the cooperative effect for the catalyzed hydroelementation of alkynes. Organometallics. 2015;34:4543–4552. [Google Scholar]
  8. Ding S., Song L.J., Chung L.W., Zhang X., Sun J., Wu Y.D. Ligand-controlled remarkable regio-and stereodivergence in intermolecular hydrosilylation of internal alkynes: experimental and theoretical studies. J. Am. Chem. Soc. 2013;135:13835–13842. doi: 10.1021/ja405752w. [DOI] [PubMed] [Google Scholar]
  9. Doyle M.P., High K.G., Nesloney C.L., Clayton T.W., Lin J. Rhodium (II) perfluorobutyrate catalyzed hydrosilylation of 1-alkynes. Trans addition and rearrangement to allylsilanes. Organometallics. 1991;10:1225–1226. [Google Scholar]
  10. Faller J.W., D'Alliessi D.G. Tunable stereoselective hydrosilylation of PhC⋮ CH catalyzed by Cp∗ Rh complexes. Organometallics. 2002;21:1743–1746. [Google Scholar]
  11. Fu H., Cheng Y. Electroluminescent and photovoltaic properties of silole-based materials. Curr. Org. Chem. 2012;16:1423–1446. [Google Scholar]
  12. Gao R., Xu L., Hao C., Xu C., Kuang H. Circular polarized light activated chiral satellite nanoprobes for the imaging and analysis of multiple metal ions in living cells. Angew. Chem. Int. Ed. 2019;131:3953–3957. doi: 10.1002/anie.201814282. [DOI] [PubMed] [Google Scholar]
  13. Gimferrer M., Minami Y., Noguchi Y., Hiyama T., Poater A. Monitoring of the phosphine role in the mechanism of palladium-catalyzed benzosilole formation from aryloxyethynyl silanes. Organometallics. 2018;37:1456–1461. [Google Scholar]
  14. Guo J., Wang H., Xing S., Hong X., Lu Z. Cobalt-catalyzed asymmetric synthesis of gem-bis (silyl) alkanes by double hydrosilylation of aliphatic terminal alkynes. Chem. 2019;5:881–895. [Google Scholar]
  15. Huckaba A.J., Hollis T.K., Howell T.O., Valle H.U., Wu Y. Synthesis and characterization of a 1, 3-phenylene-bridged N-alkyl bis (benzimidazole) CCC-NHC pincer ligand precursor: homobimetallic silver and rhodium complexes and the catalytic hydrosilylation of phenylacetylene. Organometallics. 2013;32:63–69. [Google Scholar]
  16. Igawa K., Yoshihiro D., Ichikawa N., Kokan N., Tomooka K. Catalytic enantioselective synthesis of alkenylhydrosilanes. Angew. Chem. Int. Ed. 2012;51:12745–12748. doi: 10.1002/anie.201207361. [DOI] [PubMed] [Google Scholar]
  17. Ilies L., Tsuji H., Sato Y., Nakamura E. Modular synthesis of functionalized benzosiloles by tin-mediated cyclization of (o-alkynylphenyl) silane. J. Am. Chem. Soc. 2008;130:4240–4241. doi: 10.1021/ja800636g. [DOI] [PubMed] [Google Scholar]
  18. Kan S.B.J., Lewis R.D., Chen K., Arnold F.H. Directed evolution of cytochrome c for carbon–silicon bond formation: bringing silicon to life. Science. 2016;354:1048–1051. doi: 10.1126/science.aah6219. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Kuninobu Y., Yamauchi K., Tamura N., Seiki T., Takai K. Rhodium-catalyzed asymmetric synthesis of spirosilabifluorene derivatives. Angew. Chem. Int. Ed. 2013;52:1520–1522. doi: 10.1002/anie.201207723. [DOI] [PubMed] [Google Scholar]
  20. Li Z., Dong Y.Q., Lam J.W.Y., Sun J., Qin A., Häußler M., Dong Y.P., Sung H.H.Y., Williams L.D., Tang B.Z. Functionalized siloles: versatile synthesis, aggregation-induced emission, and sensory and device applications. Adv. Funct. Mater. 2009;19:905–917. [Google Scholar]
  21. Li H., Xue S., Su H., Shen B., Cheng Z., Lam J.W., Wong K.S., Wu H., Li B.S., Tang B.Z. Click synthesis, aggregation-induced emission and chirality, circularly polarized luminescence, and helical self-assembly of a leucine-containing silole. Small. 2016;12:6593–6601. doi: 10.1002/smll.201601542. [DOI] [PubMed] [Google Scholar]
  22. Liang Y., Zhang S., Xi Z. Palladium-catalyzed synthesis of benzosilolo [2, 3-b] indoles via cleavage of a C (sp3)–Si bond and consequent intramolecular C (sp2)–Si coupling. J. Am. Chem. Soc. 2011;133:9204–9207. doi: 10.1021/ja2024959. [DOI] [PubMed] [Google Scholar]
  23. Liang Y., Geng W., Wei J., Xi Z. Palladium-catalyzed intermolecular coupling of 2-silylaryl bromides with alkynes: synthesis of benzosiloles and heteroarene-fused siloles by catalytic cleavage of the C (sp3)-Si bond. Angew. Chem. Int. Ed. 2012;51:1934–1937. doi: 10.1002/anie.201108154. [DOI] [PubMed] [Google Scholar]
  24. Liu J., Su H., Meng L., Zhao Y., Deng C., Ng J.C.Y., Lu P., Faisat M., Lam J.W.Y. What makes efficient circularly polarised luminescence in the condensed phase: aggregation-induced circular dichroism and light emission. Chem. Sci. 2012;3:2737–2747. [Google Scholar]
  25. Mancano G., Page M.J., Bhadbhade M., Messerle B.A. Hemilabile and bimetallic coordination in Rh and Ir complexes of NCN pincer ligands. Inorg. Chem. 2014;53:10159–10170. doi: 10.1021/ic501158x. [DOI] [PubMed] [Google Scholar]
  26. Mannu A., Drexler H.J., Thede R., Ferro M., Baumann W., Rüger J., Heller D. Oxidative addition of CH2Cl2 to neutral dimeric rhodium diphosphine complexes. J. Organomet. Chem. 2018;871:178–184. [Google Scholar]
  27. Matsuda T., Ichioka Y. Rhodium-catalysed intramolecular trans-bis-silylation of alkynes to synthesise 3-silyl-1-benzosiloles. Org. Biomol. Chem. 2012;10:3175–3177. doi: 10.1039/c2ob25242b. Matsuda et al. reported an intramolecular trans-bis-silylation (addition of a Si-Si bond) of alkynes to the preparation of 3-silyl-1-benzosiloles, and they proposed a mechanistic process with η2-vinyl transition metal intermediates featured with with 1,2-silyl shift: [DOI] [PubMed] [Google Scholar]
  28. Matsuda T., Kadowaki S., Goya T., Murakami M. Synthesis of silafluorenes by iridium-catalyzed [2 + 2 + 2] cycloaddition of silicon-bridged diynes with alkynes. Org. Lett. 2007;9:133–136. doi: 10.1021/ol062732n. [DOI] [PubMed] [Google Scholar]
  29. Meißner A., Alberico E., Drexler H.J., Baumann W., Heller D. Rhodium diphosphine complexes: a case study for catalyst activation and deactivation. Cat. Sci. Technol. 2015;4:3409–3425. [Google Scholar]
  30. Meißner A., Preetz A., Drexler H.J., Baumann W., Spannenberg A., König A., Heller D. In situ synthesis of neutral dinuclear rhodium diphosphine complexes [{Rh(diphosphine)(m2-X)}2]: systematic investigations. ChemPlusChem. 2015;80:169–180. [Google Scholar]
  31. Minami Y., Noguchi Y., Hiyama T. Synthesis of benzosiloles by intramolecular anti-hydroarylation via ortho-C–H activation of aryloxyethynyl silanes. J. Am. Chem. Soc. 2017;139:14013–14016. doi: 10.1021/jacs.7b08055. [DOI] [PubMed] [Google Scholar]
  32. Morales-Ceron J.P., Lara P., López-Serrano J., Santos L.L., Salazar V., Alvarez E., Suárez A. Rhodium (I) complexes with ligands based on N-heterocyclic carbene and hemilabile pyridine donors as highly E stereoselective alkyne hydrosilylation catalysts. Organometallics. 2017;36:2460–2469. [Google Scholar]
  33. Mori A., Takahisa E., Yamamura Y., Kato T., Mudalige A.P., Kajiro H., Hirabayashi K., Nishihara Y., Hiyama T. Stereodivergent syntheses of (Z)-and (E)-alkenylsilanes via hydrosilylation of terminal alkynes catalyzed by rhodium (I) iodide complexes and application to silicon-containing polymer syntheses. Organometallics. 2004;23:1755–1765. [Google Scholar]
  34. Naganawa Y., Namba T., Kawagishi M., Nishiyama H. Construction of a chiral silicon center by rhodium-catalyzed enantioselective intramolecular hydrosilylation. Chem. Eur. J. 2015;21:9319–9322. doi: 10.1002/chem.201501568. [DOI] [PubMed] [Google Scholar]
  35. Ng J.C.Y., Li H., Yuan Q., Liu J., Liu C., Fan X., Li B.S., Tang B.Z. Valine-containing silole: synthesis, aggregation-induced chirality, luminescence enhancement, chiral-polarized luminescence and self-assembled structures. J. Mater. Chem. C. 2014;2:4615–4621. [Google Scholar]
  36. Ng J.C.Y., Liu J., Su H., Hong Y., Li H., Lam J.W., Wong K.S., Tang B.Z. Complexation-induced circular dichroism and circularly polarised luminescence of an aggregation-induced emission luminogen. J. Mater. Chem. C. 2014;2:78–83. [Google Scholar]
  37. Nie H., Chen B., Zeng J., Xiong Y., Zhao Z., Tang B.Z. Excellent n-type light emitters based on AIE-active silole derivatives for efficient simplified organic light-emitting diodes. J. Mater. Chem. 2018;6:3690–3698. [Google Scholar]
  38. Oestreich M. Silicon-stereogenic silanes in asymmetric catalysis. Synlett. 2007;2007:1629–1643. doi: 10.1186/1860-5397-3-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Ohmura T., Masuda K., Suginome M. Silylboranes bearing dialkylamino groups on silicon as silylene equivalents: palladium-catalyzed regioselective synthesis of 2, 4-disubstituted siloles. J. Am. Chem. Soc. 2008;130:1526–1527. doi: 10.1021/ja073896h. [DOI] [PubMed] [Google Scholar]
  40. Ojima I., Clos N., Donovan R.J., Ingallina P. Hydrosilylation of 1-hexyne catalyzed by rhodium and cobalt-rhodium mixed-metal complexes. Mechanism of apparent trans addition. Organometallics. 1990;9:3127–3133. [Google Scholar]
  41. Onoe M., Baba K., Kim Y., Kita Y., Tobisu M., Chatani N. Rhodium-catalyzed carbon–silicon bond activation for synthesis of benzosilole derivatives. J. Am. Chem. Soc. 2012;134:19477–19488. doi: 10.1021/ja3096174. [DOI] [PubMed] [Google Scholar]
  42. Pop F., Zigon N., Avarvari N. Main-group-based electro-and photoactive chiral materials. Chem. Rev. 2019;119:8435–8478. doi: 10.1021/acs.chemrev.8b00770. [DOI] [PubMed] [Google Scholar]
  43. Rani P.U., Reddy P.M., Shanker K., Ravinder V. Synthesis, characterization and catalytic applications of rhodium(I) organometallics with substituted tertiary phosphines. Transit. Met. Chem. 2008;33:153–160. [Google Scholar]
  44. Sakaki S., Sumimoto M., Fukuhara M., Sugimoto M., Fujimoto H., Matsuzaki S. Why does the rhodium-catalyzed hydrosilylation of alkenes take place through a modified Chalk− harrod mechanism: a theoretical study. Organometallics. 2002;21:3788–3802. [Google Scholar]
  45. Sanada T., Kato T., Mitani M., Mori A. Rhodium-catalyzed hydrosilylation of internal alkynes with silane reagents bearing heteroatom substituents. Studies on the regio-/stereochemistry and transformation of the produced alkenylsilanes by rhodium-catalyzed conjugate addition. Adv. Synth. Catal. 2006;348:51–54. [Google Scholar]
  46. Sato A., Kinoshita H., Shinokubo H., Oshima K. Hydrosilylation of alkynes with a cationic rhodium species formed in an anionic micellar system. Org. Lett. 2004;6:2217–2220. doi: 10.1021/ol049308b. [DOI] [PubMed] [Google Scholar]
  47. Sato Y., Takagi C., Shintani R., Nozaki K. Palladium-catalyzed asymmetric synthesis of silicon-stereogenic 5, 10-dihydrophenazasilines via enantioselective 1, 5-palladium migration. Angew. Chem. Int. Ed. 2017;56:9211–9216. doi: 10.1002/anie.201705500. [DOI] [PubMed] [Google Scholar]
  48. Satyanarayana T., Abraham S., Kagan H.B. Nonlinear effects in asymmetric catalysis. Angew. Chem. Int. Ed. 2009;48:456–494. doi: 10.1002/anie.200705241. For the importance of nonlinear effect (NLE) in asymmetric catalysis, see: [DOI] [PubMed] [Google Scholar]
  49. Shimizu M., Mochida K., Hiyama T. Modular approach to silicon-bridged biaryls: palladium-catalyzed intramolecular coupling of 2-(arylsilyl)aryl triflates. Angew. Chem. Int. Ed. 2008;47:9760–9764. doi: 10.1002/anie.200804146. [DOI] [PubMed] [Google Scholar]
  50. Shintani R. Recent advances in the transition-metal-catalyzed enantioselective synthesis of silicon-stereogenic organosilanes. Asian J. Org. Chem. 2015;4:510–514. [Google Scholar]
  51. Shintani R., Otomo H., Ota K., Hayashi T. Palladium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles via enantioselective C–H bond functionalization. J. Am. Chem. Soc. 2012;134:7305–7308. doi: 10.1021/ja302278s. [DOI] [PubMed] [Google Scholar]
  52. Shintani R., Takagi C., Ito T., Naito M., Nozaki K. Rhodium-catalyzed asymmetric synthesis of silicon-stereogenic dibenzosiloles by enantioselective [2+ 2+ 2] cycloaddition. Angew. Chem. Int. Ed. 2015;54:1616–1620. doi: 10.1002/anie.201409733. [DOI] [PubMed] [Google Scholar]
  53. Son H.J., Han W.S., Wee K.R., Lee S.H., Hwang A.R., Kwon S., Cho D.W., Suh I.H., Kang S.O. Intermolecular peripheral 2, 5-bipyridyl interactions by cyclization of 1, 1′-silanylene unit of 2, 3, 4, 5-aryl substituted siloles: enhanced thermal stability, high charge carrier mobility, and their application to electron transporting layers for OLEDs. J. Mater. Chem. 2009;19:8964–8973. [Google Scholar]
  54. Song T., Zheng L.S., Ye F., Deng W.H., Wei Y.L., Jiang K.Z., Xu L.W. Modular synthesis of Ar-BINMOL-Phos for catalytic asymmetric alkynylation of aromatic aldehydes with unexpected reversal of enantioselectivity. Adv. Synth. Catal. 2014;356:1708–1718. [Google Scholar]
  55. Song T., Li L., Zhou W., Zheng Z.J., Deng Y., Xu Z., Xu L.W. Enantioselective copper-catalyzed azide–alkyne click cycloaddition to desymmetrization of maleimide-based bis (alkynes) Chem. Eur. J. 2015;21:554–558. doi: 10.1002/chem.201405420. [DOI] [PubMed] [Google Scholar]
  56. Takeuchi R., Tanouchi N. Complete reversal of stereoselectivity in rhodium complex-catalysed hydrosilylation of alk-1-yne. J. Chem. Soc. Chem. Commun. 1993:1319–1320. [Google Scholar]
  57. Takeuchi R., Tanouchi N. Solvent-controlled stereoselectivity in the hydrosilylation of alk-1-ynes catalysed by rhodium complexes. J. Chem. Soc. Perkin Trans. 1994;1:2909–2913. [Google Scholar]
  58. Tamao K., Uchida M., Izumizawa T., Furukawa K., Yamaguchi S. Silole derivatives as efficient electron transporting materials. J. Am. Chem. Soc. 1996;118:11974–11975. [Google Scholar]
  59. Tamao K., Nakamura K., Ishii H., Yamaguchi S., Shiro M. Axially chiral Spirosilanes via catalytic asymmetric intramolecular hydrosilation. J. Am. Chem. Soc. 1996;118:12469–12470. [Google Scholar]
  60. Toal S.J., Jones K.A., Magde D., Trogler W.C. Luminescent silole nanoparticles as chemoselective sensors for Cr (VI) J. Am. Chem. Soc. 2005;127:11661–11665. doi: 10.1021/ja052582w. [DOI] [PubMed] [Google Scholar]
  61. Tobisu M., Onoe M., Kita Y., Chatani N. Rhodium-catalyzed coupling of 2-Silylphenylboronic acids with alkynes leading to benzosiloles: catalytic cleavage of the Carbon− silicon bond in trialkylsilyl groups. J. Am. Chem. Soc. 2009;131:7506–7507. doi: 10.1021/ja9022978. [DOI] [PubMed] [Google Scholar]
  62. Trost B.M., Ball Z.T. Alkyne hydrosilylation catalyzed by a cationic ruthenium complex: efficient and general trans addition. J. Am. Chem. Soc. 2005;127:17644–17655. doi: 10.1021/ja0528580. [DOI] [PMC free article] [PubMed] [Google Scholar]
  63. Uchida M., Izumizawa T., Nakano T., Yamaguchi S., Tamao K., Furukawa K. Structural optimization of 2, 5-diarylsiloles as excellent electron-transporting materials for organic electroluminescent devices. Chem. Mater. 2001;13:2680–2683. [Google Scholar]
  64. Ureshino T., Yoshida T., Kuninobu Y., Takai K. Rhodium-catalyzed synthesis of silafluorene derivatives via cleavage of silicon− hydrogen and carbon− hydrogen bonds. J. Am. Chem. Soc. 2010;132:14324–14326. doi: 10.1021/ja107698p. [DOI] [PubMed] [Google Scholar]
  65. Wang X.B., Zheng Z.J., Xie J.L., Gu X.W., Mu Q.C., Yin G.W., Ye F., Xu Z., Xu L.W. Silicon-mediated catalytic synthesis of chiral acylsilane-substituted pyrrolidines as a Springboard to access structurally diverse amino acid derivatives. Angew. Chem. Int. Ed. 2020;59:790–797. [Google Scholar]
  66. Weickgenannt A., Mewald M., Oestreich M. Asymmetric Si–O coupling of alcohols. Org. Biomol. Chem. 2010;8:1497–1504. doi: 10.1039/b925722e. [DOI] [PubMed] [Google Scholar]
  67. Wen H., Wan X., Huang Z. Asymmetric synthesis of silicon-stereogenic vinylhydrosilanes by cobalt-catalyzed regio-and enantioselective alkyne hydrosilylation with dihydrosilanes. Angew. Chem. Int. Ed. 2018;57:6319–6323. doi: 10.1002/anie.201802806. [DOI] [PubMed] [Google Scholar]
  68. Wen H., Liu G., Huang Z. Recent advances in tridentate iron and cobalt complexes for alkene and alkyne hydrofunctionalizations. Chem. Rev. 2019;386:138–153. [Google Scholar]
  69. Wu W.C., Chen C.Y., Tian Y., Jang S.H., Hong Y., Liu Y., Hu R., Tang B.Z., Lee Y.T., Chen C.T. Enhancement of aggregation-induced emission in dye-encapsulating polymeric micelles for bioimaging. Adv. Funct. Mater. 2010;20:1413–1423. [Google Scholar]
  70. Wu Y., Karttunen V.A., Parker S., Genest A., Rösch N. Olefin hydrosilylation catalyzed by a bis-N-heterocyclic carbene rhodium complex. A density functional theory study. Organometallics. 2013;32:2363–2372. [Google Scholar]
  71. Wu Y., Genest A., Rösch N. Does the preferred mechanism of a catalytic transformation depend on the density functional Ethylene hydrosilylation by a metal complex as a case study. J. Phys. Chem. A. 2014;118:3004–3013. doi: 10.1021/jp5010677. [DOI] [PubMed] [Google Scholar]
  72. Xu L.W. Desymmetrization catalyzed by transition-metal complexes: enantioselective formation of silicon-stereogenic silanes. Angew. Chem. Int. Ed. 2012;51:12932–12934. doi: 10.1002/anie.201207932. [DOI] [PubMed] [Google Scholar]
  73. Xu L.W., Li L., Lai G.Q., Jiang J.X. The recent synthesis and application of silicon-stereogenic silanes: a renewed and significant challenge in asymmetric synthesis. Chem. Soc. Rev. 2011;40:1777–1790. doi: 10.1039/c0cs00037j. [DOI] [PubMed] [Google Scholar]
  74. Yamaguchi S., Tamao K. Theoretical study of the electronic structure of 2, 2′-Bisilole in comparison with 1, 1′-Bi-1, 3-cyclopentadiene: σ∗–π∗ conjugation and a low-lying LUMO as the origin of the unusual optical properties of 3, 3′, 4, 4′-tetraphenyl-2, 2′-bisilole. Bull. Chem. Soc. Jpn. 1996;69:2327–2334. [Google Scholar]
  75. Yang Q., Liu L., Chi Y., Hao W., Zhang W.X., Xi Z. Rhodium-catalyzed intramolecular carbosilylation of alkynes via C (sp 3)–Si bond cleavage. Org. Chem. Front. 2018;5:860–863. [Google Scholar]
  76. Zaranek M., Pawluc P. Markovnikov hydrosilylation of alkenes: how an oddity becomes the goal. ACS Catal. 2018;8:9865–9876. [Google Scholar]
  77. Zhan G., Teng H.L., Luo Y., Lou S.J., Nishiura M., Hou Z. Enantioselective construction of silicon-stereogenic silanes by Scandium-catalyzed intermolecular alkene hydrosilylation. Angew. Chem. 2018;130:12522–12526. doi: 10.1002/anie.201807493. [DOI] [PubMed] [Google Scholar]
  78. Zhang Q.W., An K., He W. Rhodium-catalyzed tandem cyclization/Si-C activation reaction for the synthesis of siloles. Angew. Chem. Int. Ed. 2014;53:5667–5671. doi: 10.1002/anie.201400828. [DOI] [PubMed] [Google Scholar]
  79. Zhang Q.W., An K., Liu L.C., Yue Y., He W. Rhodium-catalyzed enantioselective intramolecular C-H silylation for the syntheses of planar-chiral metallocene siloles. Angew. Chem. Int. Ed. 2015;54:6918–6921. doi: 10.1002/anie.201502548. [DOI] [PubMed] [Google Scholar]
  80. Zhang Q.W., An K., Liu L.C., Guo S., Jiang C., Guo H., He W. Rhodium-catalyzed intramolecular C− H silylation by silacyclobutanes. Angew. Chem. Int. Ed. 2016;55:6319–6323. doi: 10.1002/anie.201602376. [DOI] [PubMed] [Google Scholar]
  81. Zhang Q.W., An K., Liu L.C., Zhang Q., Guo H., He W. Construction of chiral tetraorganosilicons by tandem desymmetrization of silacyclobutanes/intermolecular dehydrogenative silylation. Angew. Chem. Int. Ed. 2017;56:1125–1129. doi: 10.1002/anie.201609022. [DOI] [PubMed] [Google Scholar]
  82. Zhao Z., Guo Y., Jiang T., Chang Z., Lam J.W.Y., Xu L., Qiu H., Tang B. A fully substituted 3-silolene functions as promising building block for hyperbranched poly(silylenevinylene) Macromol. Rapid Commun. 2012;33:1074–1079. doi: 10.1002/marc.201200085. [DOI] [PubMed] [Google Scholar]
  83. Zhao Z., He B., Tang B.Z. Aggregation-induced emission of siloles. Chem. Sci. 2015;6:5347–5365. doi: 10.1039/c5sc01946j. [DOI] [PMC free article] [PubMed] [Google Scholar]
  84. Zhou Z., Xie S., Chen X., Tu Y., Xiang J., Wang J., He Z., Zeng Z., Tang B.Z. Spiro-functionalized diphenylethenes: suppression of a reversible photocyclization contributes to the aggregation-induced emission effect. J. Am. Chem. Soc. 2019;141:9803–9807. doi: 10.1021/jacs.9b04426. [DOI] [PubMed] [Google Scholar]
  85. Zhuang Y., Shang C., Lou X., Xia F. Construction of AIEgens-based bioprobe with two fluorescent signals for enhanced monitor of extracellular and intracellular telomerase activity. Anal. Chem. 2017;89:2073–2079. doi: 10.1021/acs.analchem.6b04696. [DOI] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Document S1. Transparent Methods, Figures S1–S112, and Tables S1–S6
mmc1.pdf (8.1MB, pdf)

Data Availability Statement

The related figures and data in this article can be found at the Supplemental Information.

Articles from iScience are provided here courtesy of Elsevier

RESOURCES