Metal-free Hydrosilylation Research Articles

Organic Photoredox-Catalyzed Hydrosilylation of Vinylboronic Esters for the Synthesis of Geminal and Vicinal Borosilanes.

Geminal and vicinal borosilanes have unique applications in functional materials and synthetic transformations. Herein, a convenient method for the synthesis of geminal and vicinal borosilanes is developed via photoredox metal-free hydrosilylation of vinylboronic esters. This strategy features the advantages of high atom economy, environmental friendliness, and excellent functional group compatibility. The mechanism studies reveal that the catalytic reaction goes through photoredox HAT catalysis and a radical addition pathway.

DIPEA-induced Si-H Activation of Siloxane for Hydrosilylation Polymerization via Metal-Free Photocatalysis

Although metal-free hydrosilylation of siloxanes is essential for the industrial preparation of organosilicon compounds due to its unique advantages, such as the avoidance of the use and residue of precious...

Effect of liquid confinement on regioselectivity in the hydrosilylation of alkynes with cationic Rh(I) N-heterocyclic carbene catalysts.

Polymeric mesoporous monoliths were prepared via ring-opening metathesis polymerization (ROMP) from norbornene (NBE), 1,4,4a,5,8,8a-hexahydro-1,4,5,8-exo,endo-dimethanonaphthalene (DMN-H6), tris(norborn-2-enylmethylenoxy)methylsilane and the 1st-generation Grubbs catalyst [RuCl2(PCy3)2(CHC6H5)] in the presence of 2-propanol and toluene and surface grafted with 1-(2-((norborn-5-ene-2-carbonyl)oxy)ethyl)-3-ethyl-1H-imidazol-3-ium tetrafluoroborate. Subsequently, a supported ionic-liquid-phase (SILP) system was created by immobilizing the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF4] with the cationic catalyst [Rh((1-pyrid-1-yl)-3-mesitylimidazol-2-ylidene)(COD)+BF4-] (Rh-1; COD = 1,4-cyclooctadiene) dissolved therein. The regio- and stereoselectivity of Rh-1 dissolved in the IL and supported on the mesoporous monolith, referred to as Rh@SILPROMP, in the hydrosilylation of 1-alkynes with HSiMe2Ph was studied and compared to that of the homogeneous catalyst Rh-1 under biphasic conditions using methyl tert-butyl ether (MTBE) as a second organic phase. Different amounts of IL were used, which allowed for the creation of SILPs with different layer thicknesses. Rh@SILPROMP provided by far better β-(Z) selectivity for both aromatic and aliphatic 1-alkynes in comparison to Rh-1 used under biphasic conditions. The highest β-(Z) selectivity was obtained with the thinnest IL layer. No leaching of the IL or rhodium from the SILP system into the organic phase was observed, resulting in virtually metal-free hydrosilylation products. The data obtained with Rh@SILPROMP were also compared with those from previous studies with Rh-1 in the same IL supported on polyurethane-derived mesoporous monolithic supports (Rh@SILPPUR) and on mesoporous SBA-15 (Rh@SILPSBA-15). For the first time, the use of a liquid confinement created by both a SILP and the support itself to tune the transition state of an organometallic catalyst by non-covalent interactions and thus stereo- and regioselectivity is outlined.

Asymmetric hydrosilylations of N-sulfonyl ketimines and vicinal diimines with chiral boranes

A metal-free hydrosilylation of N-sulfonyl ketimines under the FLP catalysis has been realized to give optically active amines in high yields with up to 73% ee. Significantly, a chiral borane-catalyzed asymmetric hydrosilylation of vicinal diimines was also achieved, affording the desired cis-1,2-diamines with 12–70% ee’s.

Metal-Free Hydrosilylation Polymerization by Merging Photoredox and Hydrogen Atom Transfer Catalysis.

Organosilicon compounds and polymers have found wide applications as synthetic building blocks and functional materials. Hydrosilylation is a common strategy toward the synthesis of organosilicon compounds and polymers. Although transition-metal-catalyzed hydrosilylation has achieved great advances, the metal-free hydrosilylation polymerization of dienes and bis(silane)s, especially the one suitable for both electron-rich and electron-deficient dienes, is largely lacking. Herein, we report a visible-light-driven metal-free hydrosilylation polymerization of both electron-rich and electron-deficient dienes with bis(silane)s by using the organic photocatalyst and hydrogen atom transfer (HAT) catalyst. We achieved the well-controlled step-growth hydrosilylation polymerizations of the electron-rich diene and bis(silane) monomer due to the selective activation of Si-H bonds by the organic photocatalyst (4CzIPN) and the thiol polarity reversal reagent (HAT 1). For the electron-deficient dienes, hydrosilylation polymerization and self-polymerization occurred simultaneously in the presence of 4CzIPN and aceclidine (HAT 2), providing the opportunity to produce linear, hyperbranched, and network polymers by rationally tuning the concentration of electron-deficient dienes and the ratio of bis(silane)s and dienes to alter the proportion of the two polymerizations. A wide scope of bis(silane)s and dienes furnished polycarbosilanes with high molecular weight, excellent thermal stability, and tunable architectures.

Metal-Free Synthesis of Poly(silyl ether)s under Ambient Conditions

Metal-free hydrosilylation using tris(pentafluorophenyl)borane (B(C6F5)3) as a catalyst enables the rapid polymerization of α-diketone and bis(silane) monomers under ambient conditions to give high molecular weight poly(silyl ether)s (PSEs). A wide selection of commercially available monomers bearing different backbone and side-chain functional groups are shown to be compatible with these metal-free conditions. Significantly, the thermal properties of these poly(silyl ether)s are highly tunable, with novel semicrystalline materials being obtained in a variety of cases. These poly(silyl ether) materials serve as a versatile platform for materials with designed degradation profiles and crystallinity.

Visible Light-Driven Radical trans-Hydrosilylation of Electron-Neutral and -Rich Alkenes with Tertiary and Secondary Hydrosilanes.

A visible light-driven radical hydrosilylation of electron-neutral and -rich alkenes has been investigated on the basis of a newly developed catalytic reaction system composed of eosin Y, thiol, and base additives. A variety of linear and cyclic alkenes with different substitution patterns were found to undergo such metal-free hydrosilylation with tertiary and secondary hydrosilanes in a chemo-, regio-, and stereoselective manner. Comparison of the reactivity of diene compounds and late-stage hydrosilylation of steroid drugs were also explored. Deuterium labeling experiments reveal that a stepwise formation of C-Si and C-H bonds with a trans stereochemistry is preferred, in which the thiol may behave as a hydrogen atom transfer agent.

Recent Advances in Amide Reductions

This short review highlights recent advances in amide reductions. The last two years have witnessed important developments with milestones reached in catalytic hydrogenations and hydrosilylations. While metal-catalyzed processes still focus tremendous efforts from the scientific community, methodologies based on the metal-free hydrosilylation of amides have definitively joined the competition.1 Introduction2 Recent Use of Stoichiometric Reducing Reagents3 Hydrogenations4 Hydrosilylations5 Conclusion and Outlook

Visible-Light-Mediated Metal-Free Hydrosilylation of Alkenes through Selective Hydrogen Atom Transfer for Si-H Activation.

Although there has been significant progress in the development of transition-metal-catalyzed hydrosilylations of alkenes over the past several decades, metal-free hydrosilylation is still rare and highly desirable. Herein, we report a convenient visible-light-driven metal-free hydrosilylation of both electron-deficient and electron-rich alkenes that proceeds through selective hydrogen atom transfer for Si-H activation. The synergistic combination of the organophotoredox catalyst 4CzIPN with quinuclidin-3-yl acetate enabled the hydrosilylation of electron-deficient alkenes by selective Si-H activation while the hydrosilylation of electron-rich alkenes was achieved by merging photoredox and polarity-reversal catalysis.

Mild Metal-Free Hydrosilylation of Secondary Amides to Amines.

The combination of amide activation by Tf2O with B(C6F5)3-catalyzed hydrosilylation with TMDS constitutes a method for the one-pot reduction of secondary amides to amines under mild conditions. The method displays a broad applicability for the reduction of many types of substrates, and shows good compatibility and excellent chemoselectivity for many sensitive functional groups. Reductions of a multifunctionalized α,β-unsaturated amide obtained from another synthetic methodology, and a C-H functionalization product produced the corresponding amines in good to excellent yield. Chemoselective reduction of enantiomeric pure (ee >99%) tetrahydro-5-oxo-2-furaneamides yielded 5-(aminomethyl)dihydrofuran-2(3H)-ones in a racemization-free manner. The latter were converted in one pot to N-protected 5-hydroxypiperidin-2-ones, which are building blocks for the synthesis of many natural products. Further elaboration of an intermediate led to a concise four-step synthesis of (-)-epi-pseudoconhydrine.

Metal-Free Hydrosilylation Polymerization by Borane Catalyst.

The first example of metal-free hydrosilylation polymerization between dienes and disilanes is developed by using a borane catalyst, B(C6F5)3 to replace precious transition-metal-based systems. Under the easy-to-handle and mild conditions, a step-growth polymerization of two readily available diene and disilane units was achieved with high degrees of polymerization. Various combinations of dienes and disilanes produced polycarbosilanes with a broad range of structures and properties.

Bridging Amines with CO2: Organocatalyzed Reduction of CO2 to Aminals

The four-electron reduction of CO2 in the presence of secondary aromatic amines is described for the first time to access aminals. Under metal-free hydrosilylation conditions, the four C–O bonds of CO2 are cleaved, and the organocatalysts are able to balance the reactivity of CO2 to promote the selective formation of two C–N and two C–H bonds. The methodology enables the formation of various symmetrical and unsymmetrical aminals.

Phosphazenes: efficient organocatalysts for the catalytic hydrosilylation of carbon dioxide.

Phosphazene superbases are efficient organocatalysts for the metal-free catalytic hydrosilylation of carbon dioxide. They react with CO2 to form the respective phosphine oxides, but in the presence of hydrosilanes, CO2 can be selectively reduced to silyl formates, which can in turn be reduced to methoxysilanes by addition of an extra loading of silanes. Activities reach a TOF of 32 h(-1) with a TON of 759. It is also shown that unexpectedly, N,N-dimethylformamide can reduce CO2 to a mixture of silyl formates, acetals and methoxides in the absence of any catalyst.

ChemInform Abstract: Efficient Metal‐Free Hydrosilylation of Tertiary, Secondary and Primary Amides to Amines.

ChemInformVolume 46, Issue 1 Preparative Organic Chemistry ChemInform Abstract: Efficient Metal-Free Hydrosilylation of Tertiary, Secondary and Primary Amides to Amines. Enguerrand Blondiaux, Enguerrand Blondiaux Commis. Energ. At., IRAMIS, CNRS, CEA Saclay, F-91191 Gif-sur-Yvette, Fr.Search for more papers by this authorThibault Cantat, Thibault Cantat Commis. Energ. At., IRAMIS, CNRS, CEA Saclay, F-91191 Gif-sur-Yvette, Fr.Search for more papers by this author Enguerrand Blondiaux, Enguerrand Blondiaux Commis. Energ. At., IRAMIS, CNRS, CEA Saclay, F-91191 Gif-sur-Yvette, Fr.Search for more papers by this authorThibault Cantat, Thibault Cantat Commis. Energ. At., IRAMIS, CNRS, CEA Saclay, F-91191 Gif-sur-Yvette, Fr.Search for more papers by this author First published: 11 July 2016 https://doi.org/10.1002/chin.201501046Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume46, Issue1January, 2015 RelatedInformation

Efficient metal-free hydrosilylation of tertiary, secondary and primary amides to amines.

Hydrosilylation of secondary and tertiary amides to amines is described using catalytic amounts of B(C6F5)3. The organic catalyst enables the reduction of amides with cost-efficient, non-toxic and air stable PMHS and TMDS hydrosilanes. The methodology was successfully extended to the more challenging reduction of primary amides.

Experimental and computational studies of borohydride catalyzed hydrosilylation of a variety of CO and CN functionalities including esters, amides and heteroarenes

Sodium borohydride and a series of related borohydrides catalyze a transition metal-free hydrosilylation of a variety of CO and CN functionalities under mild conditions. Importantly, many of these reactions are possible using the cheap and environmentally benign hydrosilane polymethylhydrosiloxane. A mechanism is proposed based on experimental and computational results.

Radical transfer hydrosilylation/cyclization using silylated cyclohexadienes.

[reaction: see text] A new method for mild metal-free hydrosilylation is described. Silylated cyclohexadienes are used as radical transfer hydrosilylating reagents for various double and triple bonds. A trialkylsilane is transferred from a cyclohexadiene moiety to an alkene. The hydrosilylation can be combined with a C-C bond formation as shown for the preparation of silylated cycloalkanes from the corresponding dienes.