Iridium-Catalyzed Hydrosilylation of Unactivated Alkenes: Scope and Application to Late-Stage Functionalization

Hydrosilylation of Arynes with Silanes and Silicon-Based Polymer

Benzyne derived from hexadehydrogenated Diels Alder (HDDA) reactions was found to be an efficient hydrosilylation acceptors. Various silanes can react smoothly with HDDA-derived benzyne to give the arylation products. Lewis acid such as boron trifluoride etherate can accelerate these hydrosilylation reactions. Polyhydromethylsiloxane (PHMS), a widely used organosilicon polymer, was also successfully modified using our method. About 5 % of Si-H bonds in the polymer were inserted by benzynes, giving a functional PHMS with much more solubility in methanol and with a blue-emitting fluorescence behavior. Mechanism research shows that the insertion of benzyne into the Si-H bond probably undergoes a synergistic pathway, which is quite different from the traditional radical-initiated hydrosilylation or transition-metal-catalyzed hydrosilylation.

Unveiling the Reactivity of Part Per Million Levels of Cobalt-Salen Complexes in Hydrosilylation of Ketones

A series of air-stable cobalt(III)salen complexes Co-1 to Co-4 have been synthesized and employed in the hydrosilylation of ketones. Notably, the most intricately tailored Co-3 pre-catalyst exhibited exceptional catalytic activity under mild reaction conditions. The developed catalytic hydrosilylation protocol proceeded with an unusual ppm level (5 ppm) catalyst loading of Co-3 and achieved a maximum turnover number (TON) of 200,000. A wide variety of aromatic, aliphatic, and heterocyclic ketones encompassing both electron-donating and electron-withdrawing substituents were successfully transformed into the desired silyl ethers or secondary alcohols in moderate to excellent yields.

Borane-Protecting Strategy for Hydrosilylation of Phosphorus-Containing Olefins

Ir-catalyzed hydrosilylation of the alkenyl phosphine borane complex 1 was achieved to give the corresponding products 2. Because the phosphino group coordinates with metals and is unstable under aerobic conditions, the formation of the corresponding borane adduct was effective not only to promote the target hydrosilylation but also to keep 1 stable under aerobic conditions. The removal of coordinated borane from 2 was readily performed with the treatment by 1,4-diazabicyclo[2.2.2]octane to apply to further transformations. The immobilization and following deprotection of 2 on the surface of mesoporous silica were also examined.

Asymmetric Total Synthesis of Havellockate

The first total synthesis of the furanobutenolide-derived cembranoid diterpenoid havellockate is disclosed. Our convergent strategy employs a Julia-Kocienski olefination to join two enantioenriched fragments to produce a diene that is subsequently used in a propiolic acid esterification/Diels-Alder cascade. This sequence generates the fused carbocyclic core of the natural product in short order. A challenging Zn-mediated Barbier allylation then forges the final C-C bond and also establishes two vicinal stereogenic centers. Finally, a Cu-catalyzed aerobic oxidation facilitates the formation of the β-hydroxybutanolide to complete the total synthesis.

The Use of the Thiol-Ene Addition Click Reaction in the Chemistry of Organosilicon Compounds: An Alternative or a Supplement to the Classical Hydrosilylation?

This review presents the main achievements in the use of the thiol-ene reaction in the chemistry of silicones. Works are considered, starting from monomers and ending with materials.The main advantages and disadvantages of this reaction are demonstrated using various examples. A critical analysis of the use of this reaction is made in comparison with the hydrosilylation reaction.

Hydroboration and Diboration of Internal Alkynes under Iridium Catalysis

Here we demonstrate the feasibility and efficiency of simple iridium-based catalytic systems in the synthesis of multisubstituted alkenyl boronates from internal alkynes with high selectivities. A variety of alkynes were smoothly decorated with HBpin under a mild [Ir(cod)Cl]₂/dppm/acetone condition to afford trisubstituted alkenyl boronic esters with up to >99:1 regioselectivity. The diboration reaction could effectively occur in the presence of [Ir(cod)Cl]₂/DCM. Plausible mechanisms were provided to illustrate these two catalytic processes, in which the intrinsic functional group of the alkyne was supposed to be important in facilitating these reactions as well as the regioselectivity.

Ga+-catalyzed hydrosilylation? About the surprising system Ga+/HSiR3/olefin, proof of oxidation with subvalent Ga+ and silylium catalysis with perfluoroalkoxyaluminate anions

Already 1 mol% of subvalent [Ga(PhF)2]+[pf]- ([pf]- = [Al(ORF)4]-, RF = C(CF3)3) initiates the hydrosilylation of olefinic double bonds under mild conditions. Reactions with HSiMe3 and HSiEt3 as substrates efficiently yield anti-Markovnikov and anti-addition products, while bulkier substrates such as HSiiPr3 are less reactive. Investigating the underlying mechanism by gas chromatography and STEM analysis, we unexpectedly found that H2 and metallic Ga0 formed. Without the addition of olefins, the formation of R3Si-F-Al(ORF)3 (R = alkyl), a typical degradation product of the [pf]- anion in the presence of a small silylium ion, was observed. Electrochemical analysis revealed a surprisingly high oxidation potential of univalent [Ga(PhF)2]+[pf]- in weakly coordinating, but polar ortho-difluorobenzene of E 1/2(Ga+/Ga0; oDFB) = +0.26-0.37 V vs. Fc+/Fc (depending on the scan rate). Apparently, subvalent Ga+, mainly known as a reductant, initially oxidizes the silane and generates a highly electrophilic, silane-supported, silylium ion representing the actual catalyst. Consequently, the [Ga(PhF)2]+[pf]-/HSiEt3 system also hydrodefluorinates C(sp3)-F bonds in 1-fluoroadamantane, 1-fluorobutane and PhCF3 at room temperature. In addition, both catalytic reactions may be initiated using only 0.2 mol% of [Ph3C]+[pf]- as a silylium ion-generating initiator. These results indicate that silylium ion catalysis is possible with the straightforward accessible weakly coordinating [pf]- anion. Apparently, the kinetics of hydrosilylation and hydrodefluorination are faster than that of anion degradation under ambient conditions. These findings open up new windows for main group catalysis.

Cobalt-catalyzed alkyne hydrosilylation as a new frontier to selectively access silyl-hydrocarbons

The hydrosilylation of alkynes is a chief chemical method for accessing a range of alkenylsilanes, which can be derivatized to obtain value-added hydrocarbons and utilized in diverse applications. While noble metal-based catalytic procedures have shown great success in accessing vinylsilanes within the context of both academia and industry, replacing the noble metals with cheaper and more abundant base metals has recently drawn significant interest due to their catalytic sustainability and competencies including unprecedented reactivity that could expand chemical tools for accessing other types of silicon-containing hydrocarbons. During the past few years, a number of well-defined, robust cobalt-catalyst platforms that broadly operate either the Chalk-Harrod or a modified Chalk-Harrod mechanism have emerged as a new frontier in the field of selective alkyne hydrosilylation. This review describes the main features of cobalt catalyst systems recently documented for the hydrosilylation of alkynes with a strong emphasis on ligand design and reaction pathways involving Co-H and/or Co-silyl species-mediated elementary transformations to achieve Markovnikov/anti-Markovnikov hydrosilylations as well as new migratory transformations.

Iridium-catalyzed regioselective hydrosilylation of internal alkynes facilitated by directing and steric effects

Here we reported the iridium-catalyzed hydrosilylation of internal alkynes under simple and mild conditions. The intrinsic functional groups of alkyne substrates were disclosed to be crucial in facilitating both the hydrosilylation process and related regioselectivity owing to their coordination capability towards the iridium catalyst. Utilization of the steric trimethylsilyl-protected trihydroxysilane proved to be another critical factor in ensuring the efficient proceeding of this process.

Selective hydrosilylation of allyl chloride with trichlorosilane

The transition-metal-catalysed hydrosilylation reaction of alkenes is one of the most important catalytic reactions in the silicon industry. In this field, intensive studies have been thus far performed in the development of base-metal catalysts due to increased emphasis on environmental sustainability. However, one big drawback remains to be overcome in this field: the limited functional group compatibility of the currently available Pt hydrosilylation catalysts in the silicon industry. This is a serious issue in the production of trichloro(3-chloropropyl)silane, which is industrially synthesized on the order of several thousand tons per year as a key intermediate to access various silane coupling agents. In the present study, an efficient hydrosilylation reaction of allyl chloride with trichlorosilane is achieved using the Rh(I) catalyst [RhCl(dppbz^F)]₂ (dppbz^F = 1,2-bis(diphenylphosphino)-3,4,5,6-tetrafluorobenzene) to selectively form trichloro(3-chloropropyl)silane. The catalyst enables drastically improved efficiency (turnover number, TON, 140,000) and selectivity (>99%) to be achieved compared to conventional Pt catalysts.

A library of new bifunctional alkenes obtained by a highly regiodivergent silylation of 1,5-hexadiene

An efficient methodology for the synthesis of two groups of silicon-containing alkenes is reported. It includes a highly regioselective functionalization of 1,5-hexadiene through hydrosilylation and dehydrogenative silylation with organofunctional silanes and siloxanes. The established conditions enable selective monofunctionalization of 1,5-hexadiene regardless of the organosilicon modifier used as well as the type of functional group bonded to the silicon-based compound. All products were isolated and fully characterized by NMR spectroscopy and MS techniques.

An efficient methodology for the synthesis of two groups of silicon-containing alkenes is reported.

Progress on Iridium-Catalyzed Hydrosilylation of Alkenes and Alkynes

Hydrosilylation of multiple carbon–carbon bonds is a well-known process for the construction of organosilicon compounds. Nowadays, precious metal catalysts, especially platinum complexes, still occupy dominant positions in such processes. However, one important member of the precious metal family, iridium, is less used in this field. As early research mainly focused on developing stable and effective iridium catalysts, recent advances have disclosed the specific efficiency of simple iridium catalytic systems in the synthesis of functional organo­silicon compounds. This short review summarizes the utilization of iridium complexes for the hydrosilylation of alkenes and alkynes, with an emphasis on the recent advances published in the last decade.

1 Introduction

2 Iridium-Catalyzed Hydrosilylation of Alkenes

3 Iridium-Catalyzed Hydrosilylation of Alkynes

4 Conclusions and Perspectives

Pt(0)-Catalysed synthesis of new bifunctional silanes

We report herein very efficient syntheses of new functional silanes obtained via olefin hydrosilylation. New bifunctional compounds contain attractive functional groups such as epoxy, fluoroalkyl, trisilylamine, chloropropyl, and methacroiloxy which can play different roles in molecular systems. Moreover, the catalytic system proposed by us exhibits high selectivity and tolerance to a wide range of functional groups. It also permitted obtaining total conversions of the starting reagents in a relatively short time under mild conditions.

One simple Ir/hydrosilane catalytic system for chemoselective isomerization of 2-substituted allylic ethers

Here, we describe one simple Ir/hydrosilane catalytic system for chemoselective isomerization of 2-substituted allylic ethers. This facile strategy shows high efficiency towards a variety of substrates, including derivatives from bioactive molecules. The substituent at the α position of the olefins is supposed to be critical in retarding the alkene hydrosilylation process and leading the reaction to go through the isomerization pathway.

Metal-free catalysis for the Markovnikov hydrosilylation of styrene

Both the directions of the external electric field oriented along the “bond axis” (FX) and the “reaction axis” (FY) influenced the Markovnikov hydrosilylation of styrene, where the negative FY direction induced the largest effect.