Regioselective Hydrosilylation Research Articles

Rare-Earth-Metal-Catalyzed Regioselective Hydrosilylation of Internal Alkenes and Alkynes

AbstractA highly regioselective hydrosilylation reaction of internal alkenes was achieved by using commercially available lanthanum hexamethyldisilazane (La(HMDS)3). Notably, the Z- or E-configuration of internal alkenes has negligible influence on either the reactivity or regioselectivity. Internal alkynes could also be used, affording the mono di-hydrosilylation product in the presence of La(HMDS)3 or mono-hydrosilylation product with Y(HMDS)3 as the promoter.

Regioselective Hydro(deutero)silylation of 1,3-Enynes Enabled by Photoredox/Nickel Dual Catalysis.

In the presence of visible light irradiation, organophoto/nickel dual catalysts, and the mild base K2HPO4, 1,3-enynes react with silanecarboxylic acids to give the corresponding α-silylallenes with high selectivity. In this uniquely decarboxylative hydrosilylation of 1,3-enynes, a silyl radical process is involved and diverse electron-rich and -poor substrates proceed smoothly in moderate to excellent yields. This transformation is particularly synthetically worthwhile when using MeOD as the solvent, which furnishes new access to α-silyldeuteroallenes.

Anti-Markovnikov hydrosilylation and Markovnikov hydroboration of alkenes by a phenanthroline-based tridentate manganese catalyst

The divergent regioselective hydrosilylation and hydroboration of alkenes by a single manganese catalyst are disclosed. Using the Mn catalyst bearing the tridentate phenanthroline scaffold, alkenes were found to undergo anti-Markovnikov hydrosilylation, while the hydroboration of alkenes afforded Markovnikov's products. Both the hydrosilylation and the hydroboration of alkenes proceed under mild conditions (room temperature, neat conditions) with low catalyst loadings (1 mol%) using NaOtBu (3 mol%) as an activator. The reactions are atom-economical, exhibiting a broad substrate scope (46 examples), and excellent functional group tolerance (including aromatic and aliphatic alkenes). Importantly, the presented catalytic systems are suitable for various synthetic applications, and could be extended to the synthesis of bioactive molecules. Mechanistic studies supported that the Mn-H species are crucially important for the catalytic process.

Nickel‐Catalyzed Regioselective Hydrosilylation of Conjugated Dienes†

Comprehensive SummaryWith the increasing demand for homoallylic silanes and allylic silanes, the highly efficient and regioselective hydrosilylations of conjugated dienes are urgently needed. Herein, we developed a Ni‐catalyzed regiodivergent hydrosilylation of aromatic conjugated dienes by adjusting the temperature and ligands. Under low temperature (–30 °C), an eternal‐ligand‐free system (Ni/t‐BuOK) can efficiently facilitate the 3,4‐anti‐Markovnikov hydrosilylation to provide homoallylic silanes via electrophilic activation process; under room temperature (25 °C), a ligand‐controlled system (Ni/t‐BuOK/PPh3) can eventuate the 3,4‐Markovnikov hydrosilylation to produce allylic silanes via Chalk‐Harrod process. Both systems are compatible with various conjugated dienes and primary silanes in excellent yields and regioselectivities.

Experimental and Theoretical Studies on Cobalt-Catalyzed Regioselective Hydrosilylation of Tetrafluorinated Cyclohexa-1,3-dienes.

Cyclohexa-1,3-dienes bearing a tetrafluoroethylene group underwent highly regioselective hydrosilylation in the presence of 1-10 mol % Co2(CO)8 in 1,2-dichloroethane under mild conditions (reflux, 3 h), which led to an abundant yield of homoallylsilanes. Mechanistic studies proved that the reaction proceeds as per the modified Chalk-Harrod mechanism; via DFT calculation, the reason for homoallylsilanes being exclusively obtained was demonstrated. The formal synthesis of a tetrafluorinated negative-type liquid crystal demonstrated the synthetic utility of such hydrosilylation.

Solvent-Dependent Rhodium-Catalyzed Divergent Hydrofunctionalization of Trifluoromethylalkenes.

We report a rhodium-catalyzed anti-Markovnikov regioselective hydrosilylation of trifluoromethylalkenes with substituted silanes giving various α-trifluoromethyl-β-silanes in good to excellent yields. The hydrogenation products were obtained via the same key intermediate treated with methanol as a protic solvent. Both transformations had a broad functional tolerance and were expected to facilitate the construction of complex α-trifluoromethyl compounds.

Photocatalyzed regioselective hydrosilylation for the divergent synthesis of geminal and vicinal borosilanes

Geminal and vicinal borosilanes are useful building blocks in synthetic chemistry and material science. Hydrosilylation/hydroborylation of unsaturated systems offer expedient access to these motifs. In contrast to the well-established transition-metal-catalyzed methods, radical approaches are rarely explored. Herein we report the synthesis of geminal borosilanes from α-selective hydrosilylation of alkenyl boronates via photoinduced hydrogen atom transfer (HAT) catalysis. Mechanistic studies implicate that the α-selectivity originates from a kinetically favored radical addition and an energetically favored HAT process. We further demonstrate selective synthesis of vicinal borosilanes through hydrosilylation of allyl boronates via 1,2-boron radical migration. These strategies exhibit broad scopes across primary, secondary, and tertiary silanes and various boron compounds. The synthetic utility is evidenced by access to multi-borosilanes in a diverse fashion and scaling up by continuous-flow synthesis.

Approaches to the Functionalization of Organosilicon Dendrones Based on Limonene

Previously, we reported the synthesis of carbosilane and carbosilane-siloxane dendrons of various generations based limonene, a natural terpene. Limonene that contains two double bonds, namely cyclohexene and isoprenyl ones, was shown to undergo regioselective hydrosilylation exclusively at its isoprenyl double bond. This finding was used to prepare carbosilane dendrons (CDs) with a limonene moiety at the focal point. In this study, we present variants for the functionalization of the cyclohexene double bond by an epoxidation reaction in order to use the resulting dendrons for the preparation of various macromolecular objects, including Janus dendrimers (JDs), dendronized polymers, and macroinitiators. Moreover, it was shown that dendrons with peripheral azide functions could be obtained. These methods offer both the possibilities of the further growth of branches and the addition of polymers with a different nature by the azide–alkyne cycloaddition reaction.

Nickel-Catalyzed Ring-Opening of Benzofurans for the Divergent Synthesis of ortho-Functionalized Phenol Derivatives

The ring-opening reaction of benzofuran is a highly desirable, yet underdeveloped transformation for the construction of valuable phenol derivatives. Herein, we report a nickel-catalyzed ring-opening transformation of benzofuran with silanes, giving ortho-alkene-, branched/linear alkyl silane-, and alkenyl silane-substituted phenol derivatives selectively. Control experiments and DFT calculations supported Ni–H insertion and β–O elimination to achieve the formal C–O bond activation of benzofuran but not through the direct oxidative addition of nickel (0) into the C–O bond of benzofurans. Further regioselective hydrosilylation or dehydrogenative silylation occurs via Ni(I)–H or Ni(I)–[Si] intermediates to form ortho-branched/linear alkyl silane- or alkenyl silane-substituted phenol derivatives.

Transition-metal- and solvent-free regioselective hydrosilylation of alkenes and allenes enabled by catalytic sodiumtert-butoxide

An efficient and sustainable method involving alkali metal Lewis base NaOtBu as a catalyst and diphenyl silane as a silane reagent for the hydrosilylation of vinylarenes, aliphatic alkenes and allenes with high regioselectivity has been developed.

Synthesis and Catalysis of Anionic Amido Iron(II) Complexes.

Low-coordinate, open-shell 3d metal complexes have attracted great attention due to their critical role in several catalytic transformations but have been notoriously difficult to prepare and study due to their high lability. Here, we report the synthesis of a heteroleptic tri-coordinate amidoferrate that displays high catalytic activity in the regioselective hydrosilylation of alkenes.

Mn2(CO)10 and UV light: a promising combination for regioselective alkene hydrosilylation at low temperature.

The low temperature regioselective hydrosilylation of various alkenes with (1,1,1,3,5,5,5-heptamethyltrisiloxane) MDHM is described using Mn2(CO)10 under UV irradiation with Mn loadings as low as 1 mol%, in the absence of additives and with excellent selectivity and yields. The generation of a manganese radical allowed the anti-Markovnikov hydrosilylation products to be selectively obtained in yields up to 99%.

The two faces of platinum hydrospirophosphorane complexes—Not only relevant catalysts but cytotoxic compounds as well

AbstractPlatinum complexes [PtCl2(L)] L = L1, L2 with symmetrical HP (OCH2CMe2NH)2 (L1) and unsymmetrical HP(OCMe2CMe2O)(OCH2CMe2NH) (L2) hydrospirophosphorane (HSP) ligands were demonstrated to play a dual role of catalysts and cytotoxic compounds as well. The structure of new complex [PtCl2(L2)] was confirmed by physicochemical and spectroscopic methods, as well as single X‐ray diffraction studies for [PtCl2{P (OCMe2CMe2O)(OCH2CMe2NH2)}]. HSP ligand coordinated to the platinum center in bidentate κ2‐P,NH2 chelating mode of fashion. Both complexes were found to exhibit catalytic activity for Heck cross‐coupling reactions of iodobenzene with substituted styrenes, with good conversion and yield of stilbenes. Moreover, complexes have been applied as excellent catalysts for highly regioselective hydrosilylation of aromatic and aliphatic terminal olefins, and acetylenes terminal and internal as well. On the other hand, the preliminary biological studies revealed that in the presence of foretinib, drug candidate in clinical trials for the treatment of cancer, platinum complexes revealed increased synergistic effect and efficiently decreased the number of viable cells of triple negative breast cancer MDA‐MB‐231 cell line.

Transition-Metal-Catalyzed Stereo- and Regioselective Hydrosilylation of Unsymmetrical Alkynes

AbstractAlkyne hydrosilylation is one of the most efficient methods for the synthesis of alkenyl silicon derivatives and has been a hot topic of research for decades. This short review summarizes the progress in transition-metal-catalyzed stereo- and regioselective hydrosilylation of unsymmetrical alkynes. Topics are discussed based on different types of alkynes and the selectivities.1 Introduction2 Terminal Alkyne Hydrosilylation2.1 β-E Selectivity2.2 β-Z Selectivity2.3 α-selectivity3 Internal Alkyne Hydrosilylation3.1 Aryl–Alkyl Acetylenes3.2 Alkyl–Alkyl Acetylenes3.3 Internal Alkynes with Polarized Substituents4 Summary and Outlook

Primary Alcohols via Nickel Pentacarboxycyclopentadienyl Diamide Catalyzed Hydrosilylation of Terminal Epoxides.

The efficient and regioselective hydrosilylation of epoxides co-catalyzed by a pentacarboxycyclopentadienyl (PCCP) diamide nickel complex and Lewis acid is reported. This method allows for the reductive opening of terminal, monosubstituted epoxides to form unbranched, primary alcohols. A range of substrates including both terminal and nonterminal epoxides are shown to work, and a mechanistic rationale is provided. This work represents the first use of a PCCP derivative as a ligand for transition-metal catalysis.

Vacancy engineered polymeric carbon nitride nanosheets for enhanced photoredox catalytic efficiency

Polymeric carbon nitrides (PCNs) have emerged as promising heterogeneous photocatalysts for organic transformations as they are metal-free, inexpensive, and possess tunable bandgaps, with excellent chemical stability and photo-stability. However, current application of PCNs in organic synthesis is rather limited to several well-established materials, which limits the scope of reaction patterns and efficiency. We herein report the synthesis and fabrication of two PCN nanosheets by incorporating nanostructure construction, element doping, and vacancy engineering into one hybrid platform. The heteroatom doped PCN nanosheets with vacancies feature highly porous structures with extremely large substrate-catalyst interface areas and enhanced charge separation. The generated heterogeneous catalysts demonstrate impressive photoredox catalytic performances in a variety of organic transformations (e.g., defluoroborylation; [2+2] cycloaddition; C–N, C–S, C–O cross-couplings; and an unprecedented regioselective hydrosilylation), providing efficiencies comparable to reported optimized homogeneous catalysts and exceeding those with commonly utilized PCNs. Heteroatom doped polymeric carbon nitrides (PCNs) nanosheets with vacancies Notable performance for various photoredox transformations Improved photocatalytic efficiency compared to commonly utilized PCNs Avenue for rational design and development of heterogeneous PCN photocatalysts Polymeric carbon nitrides (PCNs) are promising heterogeneous photocatalysts. Liu et al. synthesize heteroatom doped PCN nanosheets with vacancies that demonstrate competitive photoredox catalytic performances. The efficiencies are comparable to optimized homogeneous photocatalysts and exceed commonly utilized PCNs. This finding may provide new insights for the design of effective heterogeneous PCN photocatalysts.

Regioselective Synthesis of Multifunctional Allylic Amines; Access to Ambiphilic Aziridine Scaffolds.

We describe, for the first time, a highly regioselective hydrosilylation of propargylic amines. The reaction utilizes a PtCl2/XantPhos catalyst system to deliver hydrosilanes across the alkyne to afford multifunctional allylic amines in high yields. The reaction is tolerant to a wide variety of functional groups and provides high value intermediates with two distinct functional handles. The synthetic applicability of the reaction has been shown through the synthesis of diverse ambiphilic aziridines.

Schiff Base Cobalt(II) Complex-Catalyzed Highly Markovnikov-Selective Hydrosilylation of Alkynes.

A bench-stable cobalt(II) complex, with 3N-donor socket-type benzimidazole-imine-2H-imidazole ligand is reported as a precatalyst for regioselective hydrosilylation of terminal alkynes. Both aromatic and aliphatic alkynes could be effectively hydrosilylated with primary, secondary, and tertiary silane to give α-vinylsilanes in high yields with excellent Markovnikov selectivity and extensive functional-group tolerance. Catalyst loading varies within 0.5–0.05 mol %, which is one of the most efficient reported so far in the literature on cobalt-catalyzed alkyne hydrosilylation.

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.

Atomically dispersed gold anchored on carbon nitride nanosheets as effective catalyst for regioselective hydrosilylation of alkynes

The atomically dispersed Au catalysts realize hydrosilylation of alkynes with high activity, selectivity and stability.