Hydrosilylation of Terminal Alkynes with Alkylidene Ruthenium Complexes and Silanes

Construction of the Bicyclic Carbon Framework of Euphosalicin

Our studies toward the total synthesis of the natural product euphosalicin (1) are presented. Different approaches targeting key intermediates are described, the synthesis of which includes findings on asymmetric dihydroxylations and ring-closing enyne metatheses (RCEYM). Their connection allowed the isolation of highly advanced precursors for studies on macrocyclizations. Our efforts culminated in the preparation of the unique C11/C12 (Z) isomer of the C13 nor methyl skeleton of euphosalicin (1).

Unconventional Reactivity of a Grubbs Catalyst: Hydroalkylation Overriding Metathesis

Unprecedented reactivity of a Grubbs catalyst has been disclosed in a reaction between vinyl azaarenes and alkenylnitriles under standard metathesis conditions. No metathesis was observed; only hydroalkylation products were obtained in high yields. The practical utility of this method has been demonstrated by the application of the products in useful transformations, e.g., the formation of cyclic iminoesters and highly challenging medium-sized carbocycles.

Hydrosilylation of Terminal Alkynes Catalyzed by an Air-Stable Manganese-NHC Complex

In recent years, catalysis with base metal manganese has received a significant amount of interest. Catalysis with manganese complexes having N-heterocyclic carbenes (NHCs) is relatively underdeveloped in comparison to the extensively investigated manganese catalysts possessing pincer ligands (particularly phosphine-based ligands). Herein, we describe the synthesis of two imidazolium salts decorated with picolyl arms (L₁ and L₂) as NHC precursors. Facile coordination of L₁ and L₂ with MnBr(CO)₅ in the presence of a base resulted in the formation manganese(I)-NHC complexes (1 and 2) as an air-stable solid in good isolated yield. Single-crystal X-ray analysis revealed the structure of the cationic complexes [Mn(CO)₃(NHC)][PF₆] with tridentate N,C,N binding of the NHC ligand in a facile fashion. Along with a few known manganese(I) complexes, these Mn(I)-NHC complexes 1 and 2 were tested for the hydrosilylation of terminal alkynes. Complex 1 was proved to be an effective catalyst for the hydrosilylation of terminal alkynes with good selectivity toward the less thermodynamically stable β-(Z)-vinylsilanes. This method provided good regioselectivity (anti-Markovnikov addition) and stereoselectivity (β-(Z)-product). Experimental evidence suggested that the present hydrosilylation pathway involved an organometallic mechanism with manganese(I)-silyl species as a possible reactive intermediate.

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

Alkyne 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 Introduction

2 Terminal Alkyne Hydrosilylation

2.1 β-E Selectivity

2.2 β-Z Selectivity

2.3 α-selectivity

3 Internal Alkyne Hydrosilylation

3.1 Aryl–Alkyl Acetylenes

3.2 Alkyl–Alkyl Acetylenes

3.3 Internal Alkynes with Polarized Substituents

4 Summary and Outlook

Carbon supported hybrid catalysts for controlled product selectivity in the hydrosilylation of alkynes

A series of Rh- and Ir-hybrid catalysts with varying tether lengths has been prepared by immobilization of Rh^I, Rh^III and Ir^III complexes on carbon black, and applied in the hydrosilylation of alkynes.

Construction of highly sterically hindered 1,1-disilylated terminal alkenes

One direct and efficient procedure for the synthesis of 1,1-disilylated terminal alkenes is demonstrated in this paper. To overcome and rationally utilize the steric hindrance of silyl units, the cationic ruthenium catalyst [CpRu(MeCN)3]+ was found to be effective for Markovnikov hydrosilylation of 1-silyl terminal alkynes with high yields and excellent regioselectivity. Dissimilarities between alkyl and alkoxy silyl units lead to versatile product derivatizations toward a variety of useful building blocks.

An NNN-Pincer-Cobalt Complex Catalyzed Highly Markovnikov-Selective Alkyne Hydrosilylation

A new NNN pincer (amine-pyridine-imine, API) cobalt complex, which is bench-stable and is applicable for the highly efficient and regioselective hydrosilylation of terminal alkynes, is developed. A broad set of α-vinylsilanes was successfully synthesized in good to high yields with up to 98/2 Markovnikov regioselectivity. This protocol can be readily scaled up for gram-scale synthesis and demonstrates the most efficient cobalt-catalyzed hydrosilylation of alkynes with turnover frequencies as high as 126 720 h^-1 to date.

Highly β( Z)-Selective Hydrosilylation of Terminal Alkynes Catalyzed by Thiolate-Bridged Dirhodium Complexes

A series of novel monothiolate-bridged dirhodium complexes, [Cp*Rh(μ-SR)(μ-Cl)₂RhCp*][BF₄] {Cp* = η⁵-C₅Me₅, R = tertiary butyl ( ^tBu), 1a; R = ferrocenyl (Fc), 1b; R = adamantyl (Ad), 1c} were designed and successfully synthesized, which can smoothly facilitate highly regioselective and stereoselective hydrosilylation of terminal alkynes to afford β( Z) vinylsilanes with good functional group compatibility. Furthermore, the hydride bridged dirhodium complex [Cp*Rh(μ-S ^tBu)(μ-Cl)(μ-H)RhCp*][BF₄] (5) as a potential intermediate was obtained by the reaction of 1a with excess HSiEt₃.

Regio-selective and stereo-selective hydrosilylation of internal alkynes catalyzed by ruthenium complexes

In this study, ruthenium(ii)-catalyzed direct hydrosilylation of internal alkynes with high regio-selectivity and stereo-selectivity is reported. This title transformation led to various vinylsilanes in good to excellent yields. This approach features mild reaction conditions, low catalyst loading, air-stability, and good functional group tolerance. Furthermore, gram-scale preparation and some transformations of vinylsilanes were carried out, which further underscored its synthetic utility and applicability.

In this study, ruthenium(ii)-catalyzed direct hydrosilylation of internal alkynes with high regio-selectivity and stereo-selectivity is reported.

Additive-modulated switchable reaction pathway in the addition of alkynes with organosilanes catalyzed by supported Pd nanoparticles: hydrosilylation versus semihydrogenation

A supported Pd nanoparticles on N,O-doped hierarchical porous carbon enabled additive-modulated reaction pathway for alkyne addition with organosilanes between hydrosilylation and semihydrogenation.

Pincer cobalt complex-catalyzed Z-selective hydrosilylation of terminal alkynes

Co-Catalyzed Z-selective hydrosilylation of terminal alkynes produces (Z)-β-vinylsilanes, which are further converted to (Z)-disubstituted alkenes by Pd-catalyzed cross couplings.

Regio- and Stereoselective Dehydrogenative Silylation and Hydrosilylation of Vinylarenes Catalyzed by Ruthenium Alkylidenes

Development of regio- and stereoselective dehydrogenative silylation and hydrosilylation of vinylarenes with alkoxysilanes, catalyzed by ruthenium alkylidenes, is described. Varying L- and X-type ligands on ruthenium alkylidenes permits selective access to either (E)-vinylsilanes or β-alkylsilanes with high regio- and stereocontrol. cis,cis-1,5-Cyclooctadiene was identified as the most effective sacrificial hydrogen acceptor for the dehydrogenative silylation of vinylarenes, which allows use of a nearly equimolar ratio of alkenes and silanes.

Cobalt-Catalyzed Alkyne Hydrosilylation and Sequential Vinylsilane Hydroboration with Markovnikov Selectivity

A pyridinebis(oxazoline) cobalt complex is a very efficient precatalyst for the hydrosilylation of terminal alkynes with Ph2 SiH2 , providing α-vinylsilanes with high (Markovnikov) regioselectivity and broad functional-group tolerance. The vinylsilane products can be further converted into geminal borosilanes through Markovnikov hydroboration with pinacolborane and a bis(imino)pyridine cobalt catalyst.

Ruthenium-catalysed hydrosilylation of carbon–carbon multiple bonds

Recent advances in ruthenium-catalysed hydrosilylation of C–C multiple bonds and its application to organic synthesis are highlighted.

Si–H activation by means of metal ligand cooperation in a methandiide derived carbene complex

Si–H bond activation of a series of silanes by means of metal ligand cooperation is reported.

One-step entry to olefin-tethered N,S-heterocyclic carbene complexes of ruthenium with mixed ligands

A series of Ru(II) mixed-ligand complexes RuBr(2)(PPh(3))(2)(N-AyBzTh) (Ay = prop-2-enyl; BzTh = benzothiazol-2-ylidene) (4), RuBr(OAc)(PPh(3))(N-MeAyBzTh) (5), RuBr(OAc)(PPh(3))(N-MeBnBzTh)(2) (MeBn = 3-methylbut-2-enyl) (6) and RuCl(OAc)(PPh(3))(N-MeBnBzTh) (7) have been synthesized from Ru(OAc)(2)(PPh(3))(2) in one-pot condensation and ligand exchange reactions. X-ray single-crystal diffraction analysis revealed that they are neutral octahedral Ru(II) complexes with one or two N,S-heterocyclic carbene (NSHC) ligands and a coordinated (4, 5 and 7) or dangling (6) olefin arm. The system displays a range of self-selecting structural variations. Entry of the hybrid olefin-NSHC and halide ligands ejects either one (5, 6 and 7) phosphine ligand or keeps both phosphines (4) by replacing the acetate. It is also possible to accommodate two NSHC ligands by keeping the olefin pendant (6). Complexes 5 and 7 are isostructural with all different ligands on the coordination sphere. Complexes 4-6 are active towards transfer hydrosilylation showing good β(Z) selectivity, with the Ru(II) bearing acetate giving higher yields.

Sequential Processes in Palladium-Catalyzed Silicon-Based Cross-Coupling

Although developed somewhat later, silicon-based cross-coupling has become a viable alternative to the more conventional Suzuki-Miyaura, Stille-Kosugi-Migita, and Negishi cross-coupling reactions because of its broad substrate scope, high stability of silicon-containing reagents, and low toxicity of waste streams. An empowering and yet underappreciated feature unique to silicon-based cross-coupling is the wide range of sequential processes available. In these processes, simple precursors are first converted to complex silicon-containing cross-coupling substrates, and the subsequent silicon-based cross-coupling reaction affords an even more highly functionalized product in a stereoselective fashion. In so doing, structurally simple and inexpensive starting materials are quickly transformed into value-added and densely substituted products. Therefore, sequential processes are often useful in constructing the carbon backbones of natural products. In this review, studies of sequential processes involving silicon-based cross-coupling are discussed. Additionally, the total syntheses that utilize these sequential processes are also presented.