Stereodivergent Formation of Alkenylsilanes:syn oranti Hydrosilylation of Alkynes Catalyzed by a Cyclopentadienylcobalt(I) Chelate Bearing a Pendant Phosphane Tether

The stereo-divergent functionalization of alkynes: a comprehensive review

Alkynes are central in crafting pharmaceuticals, agrochemicals, and materials owing to their reactivity and linear geometry. This review unveils cutting-edge advancements in the stereo-divergent functionalization of alkynes, transforming them into invaluable tools for synthesizing stereochemically defined alkenes and alkanes. The review highlights ground-breaking methodologies that achieve exceptional E- and Z-selectivity using innovative catalysts like cobalt, nickel, and palladium through hydrogenation, hydroboration, and hydrosilylation. Recent breakthroughs such as dual-catalytic systems and energy transfer catalysis enable unprecedented stereocontrol. Sustainable strategies including water as a hydrogen source and recyclable catalysts align with green chemistry principles, paving the way for eco-friendly synthesis. This synthesis of cutting-edge techniques and their applications inspire new avenues in synthetic chemistry, offering transformative tools for creating complex molecular architectures with precision and sustainability.

Dirhodium(II)/XantPhos Catalyzed Synthesis of β-(E)-Vinylsilanes via Hydrosilylation and Isomerization from Alkynes

A concise hydrosilylation of alkynes for synthesizing β-(E)-vinylsilanes catalyzed by dirhodium(II)/XantPhos has been developed. In this reaction, β-(E)-vinylsilanes were generated from the isomerization of β-(Z)-vinylsilanes catalyzed by dirhodium(II) hydride species rather than the direct insertion of triple bond into M-H or M-Si bond (traditional Chalk-Harrod mechanism or modified Chalk-Harrod mechanism). The hydrosilylation displayed a broad substrate scope for alkynes and tertiary silanes, tolerating diverse functional groups including halides, nitriles, amines, esters, and heterocycles.

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.

β-(Z)-Selective alkyne hydrosilylation by a N,O-functionalized NHC-based rhodium(I) catalyst

Neutral and cationic cyclooctadiene rhodium(I) complexes with a lutidine-derived polydentate ligand having NHC and methoxy side-donor functions, [RhBr(cod)(κC-tBuImCH2PyCH2OMe)] and [Rh(cod)(κ2C,N-tBuImCH2PyCH2OMe)]PF6, have been prepared. Carbonylation of the cationic compound yields the dicarbonyl complex [Rh(CO)2(κ2C,N-tBuImCH2PyCH2OMe)]PF6 whereas carbonylation of the neutral compound affords a mixture of di- and monocarbonyl neutral complexes [RhBr(CO)2(κC-tBuImCH2PyCH2OMe)] and [RhBr(CO)(κ2C,N-tBuImCH2PyCH2OMe)]. These complexes efficiently catalyze the hydrosilylation of 1-hexyne with HSiMe2Ph with a marked selectivity towards the β-(Z)-vinylsilane product. Catalyst [RhBr(CO)(κ2C,N-tBuImCH2PyCH2OMe)] showed a superior catalytic performance, in terms of both activity and selectivity, and has been applied to the hydrosilylation of a range of 1-alkynes and phenylacetylene derivatives with diverse hydrosilanes, including HSiMe2Ph, HSiMePh2, HSiPh3 and HSiEt3, showing excellent β-(Z) selectivity for the hydrosilylation of linear aliphatic 1-alkynes. Hydrosilylation of internal alkynes, such as diphenylacetylene and 1-phenyl-1-propyne, selectively affords the syn-addition vinylsilane products. The β-(Z) selectivity of these catalysts contrasts with that of related rhodium(I) catalysts based on 2-picolyl-functionalised NHC ligands, which were reported to be β-(E) selective. An energy barrier ΔG‡ of 19.8 ± 2.0 kcal mol-1 (298 K) has been determined from kinetic studies on the hydrosilylation of 1-hexyne with HSiMe2Ph. DFT studies suggest that the methoxy-methyl group is unlikely to be involved in the activation of hydrosilane, and then hydrosilane activation is likely to proceed via a classical Si-H oxidative addition.

Catalytic activation of remote alkenes through silyl-rhodium(III) complexes

The tandem isomerization-hydrosilylation reaction is a highly valuable process able to transform mixtures of internal olefins into linear silanes. Unsaturated and cationic hydrido-silyl-Rh(III) complexes have proven to be effective catalysts for this reaction. Herein, three silicon-based bidentate ligands, 8-(dimethylsilyl)quinoline (L1), 8-(dimethylsilyl)-2-methylquinoline (L2) and 4-(dimethylsilyl)-9-phenylacridine (L3), have been used to synthesize three neutral [RhCl(H)(L)PPh₃] (1-L1, 1-L2 and 1-L3) and three cationic [Rh(H)(L)(PPh₃)₂][BAr^F₄] (2-L1, 2-L2 and 2-L3) Rh(III) complexes. Among the neutral compounds, 1-L2 could be characterized in the solid state by X-ray diffraction showing a distorted trigonal bipyramidal structure. Neutral complexes (1-L1, 1-L2 and 1-L3) failed to catalyze the hydrosilylation of olefins. On the other hand, the cationic compound 2-L2 was also characterized by X-ray diffraction showing a square pyramidal structure. The unsaturated and cationic Rh(III) complexes 2-L1, 2-L2 and 2-L3 showed significant catalytic activity in the hydrosilylation of remote alkenes, with the most sterically hindered (2-L2) being the most active one.

Tunable Aryl Alkyl Ionic Liquid Supported Synthesis of Platinum Nanoparticles and Their Catalytic Activity in the Hydrogen Evolution Reaction and in Hydrosilylation

Tunable aryl alkyl ionic liquids (TAAILs) are ionic liquids (ILs) with a 1-aryl-3-alkylimidazolium cation having differently substituted aryl groups. Herein, nine TAAILs with the bis(trifluoromethylsulfonyl)imide anion are utilized in combination with and without ethylene glycol (EG) as reaction media for the rapid microwave synthesis of platinum nanoparticles (Pt-NPs). TAAILs allow the synthesis of small NPs and are efficient solvents for microwave absorption. Transmission electron microscopy (TEM) shows that small primary NPs with sizes of 2 nm to 5 nm are obtained in TAAILs and EG/TAAIL mixtures. The Pt-NPs feature excellent activity as electrocatalysts in the hydrogen evolution reaction (HER) under acidic conditions, with an overpotential at a current density of 10 mA cm^-2 as low as 32 mV vs the reversible hydrogen electrode (RHE), which is significantly lower than the standard Pt/C 20% with 42 mV. Pt-NPs obtained in TAAILs also achieved quantitative conversion in the hydrosilylation reaction of phenylacetylene with triethylsilane after just 5 min at 200 °C.

Stereoselective Semi-Hydrogenations of Alkynes by First-Row (3d) Transition Metal Catalysts

The chemo- and stereoselective semi-hydrogenation of alkynes to alkenes is a fundamental transformation in synthetic chemistry, for which the use of precious 4d or 5d metal catalysts is well-established. In mankind's unwavering quest for sustainability, research focus has considerably veered towards the 3d metals. Given their high abundancy and availability as well as lower toxicity and noxiousness, they are undoubtedly attractive from both an economic and an environmental perspective. Herein, we wish to present noteworthy and groundbreaking examples for the use of 3d metal catalysts for diastereoselective alkyne semi-hydrogenation as we embark on a journey through the first-row transition metals.

Sweet, Sugar-Coated Hierarchical Platinum Nanostructures for Easy Support, Heterogenization and Separation

Metal nanoparticles are increasingly gaining interest in the field of heterogeneous catalysis. Here, we present a novel strategy for synthesizing sugar-coated platinum nanostructures (SC-Pt-NS) from the carbohydrates sucrose and D(-)-fructose. In the synthesis from a mixture of H2PtCl6·6H2O, the carbohydrate in an ionic liquid (IL) yielded primary particles of a homogeneous average size of ~10 nm, which were aggregated to hierarchical Pt nanostructures of ~40–65 nm and surrounded or supported by the carbohydrate. These sugar-coated platinum nanostructures present a facile way to support and heterogenize nanoparticles, avoid leaching and enable easier separation and handling. The catalytic activity of the SC-Pt-NS was shown in the hydrosilylation test reaction of phenylacetylene with triethylsilane, where very high turnover frequency (TOF) values of up to 87,200 h−1 could be achieved, while the platinum metal leaching into the product was very low.

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.

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

Markovnikov Hydrosilylation of Alkynes with Tertiary Silanes Catalyzed by Dinuclear Cobalt Carbonyl Complexes with NHC Ligation

Metal-catalyzed hydrosilylation of alkynes is an ideal atom-economic method to prepare vinylsilanes that are useful reagents in the organic synthesis and silicone industry. Although great success has been made in the preparation of β-vinylsilanes by metal-catalyzed hydrosilylation reactions of alkynes, reported metal-catalyzed reactions for the synthesis of α-vinylsilanes suffer from narrow substrate scope and/or poor selectivity. Herein, we present selective Markovnikov hydrosilylation reactions of terminal alkynes with tertiary silanes using a dicobalt carbonyl N-heterocyclic carbene (NHC) complex [(IPr)₂Co₂(CO)₆] (IPr = 1,3-di(2,6-diisopropylphenyl)imidazol-2-ylidene) as catalyst. This cobalt catalyst effects the hydrosilylation of both alkyl- and aryl-substituted terminal alkynes with a variety of tertiary silanes with good functional group compatibility, furnishing α-vinylsilanes with high yields and high α/β selectivity. Mechanistic study revealed that the stoichiometric reactions of [(IPr)₂Co₂(CO)₆] with PhC≡CH and HSiEt₃ can furnish the dinuclear cobalt alkyne and mononuclear cobalt silyl complexes [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₃], [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₂(IPr)], and [(IPr)Co(CO)₃(SiEt₃)], respectively. Both dicobalt bridging alkyne complexes can react with HSiEt₃ to yield α-triethylsilyl styrene and effect the catalytic Markovnikov hydrosilylation reaction. However, the mono(NHC) dicobalt complex [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₃] exhibits higher catalytic activity over the di(NHC)-dicobalt complexes. The cobalt silyl complex [(IPr)Co(CO)₃(SiEt₃)] is ineffective in catalyzing the hydrosilylation reaction. Deuterium labeling experiments with PhC≡CD and DSiEt₃ indicates the syn-addition nature of the hydrosilylation reaction. The absence of deuterium scrambling in the hydrosilylation products formed from the catalytic reaction of PhC≡CH with a mixture of DSiEt₃ and HSi(OEt)₃ hints that mononuclear cobalt species are less likely the in-cycle species. These observations, in addition to the evident of nonsymmetric Co₂C₂-butterfly core in the structure of [(IPr)(CO)₂Co(μ-η²:η²-HCCPh)Co(CO)₃], point out that mono(IPr)-dicobalt species are the genuine catalysts for the cobalt-catalyzed hydrosilylation reaction and that the high α selectivity of the catalytic system originates from the joint play of the dicobalt carbonyl species to coordinate alkynes in the Co(μ-η²:η²-HCCR')Co mode and the steric demanding nature of IPr ligand.

Synthesis and structure of thienyl Fischer carbene complexes of PtII for application in alkyne hydrosilylation

Efficient alkyne hydrosilylation mediated by well-defined platinum(ii) bis(ethoxycarbene) complexes of the Fischer-type prepared by facile transmetallation.

Cyclic metal(oid) clusters control platinum-catalysed hydrosilylation reactions: from soluble to zeolite and MOF catalysts

The Pt-catalysed addition of silanes to functional groups such as alkenes, alkynes, carbonyls and alcohols, i.e. the hydrosilylation reaction, is a fundamental transformation in industrial and academic chemistry, often claimed as the most important application of Pt catalysts in solution. However, the exact nature of the Pt active species and its mechanism of action is not well understood yet, particularly regarding regioselectivity. Here, experimental and computational studies together with an ad hoc graphical method show that the hydroaddition of alkynes proceeds through Pt-Si-H clusters of 3-5 atoms (metal(oid) association) in parts per million amounts (ppm), which decrease the energy of the transition state and direct the regioselectivity of the reaction. Based on these findings, new extremely-active (ppm) microporous solid catalysts for the hydrosilylation of alkynes, alkenes and alcohols have been developed, paving the way for more environmentally-benign industrial applications.

Ligand-controlled iridium-catalyzed semihydrogenation of alkynes with ethanol: highly stereoselective synthesis of E- and Z-alkenes

A ligand-controlled iridium-catalyzed semihydrogenation of alkynes to E- and Z-alkenes with ethanol was developed. Effective selectivity control was achieved by ligand regulation. The use of 1,2-bis(diphenylphosphino)ethane (DPPE) and 1,5-cyclooctadiene (COD) was critical for the stereoselective semihydrogenation of alkynes. The general applicability of this procedure was highlighted by the synthesis of more than 40 alkenes, with good stereoselectivities. The value of our approach in practical applications was investigated by studying the effects of pinosylvin and 4,4'-dihydroxystilbene (DHS) on zebrafish as a vertebrate model.

Cobalt(II) and (I) Complexes of Diphosphine-Ketone Ligands: Catalytic Activity in Hydrosilylation Reactions

The hydrosilylation of unsaturated compounds homogeneously catalyzed by cobalt complexes has gained considerable attention in the last years, aiming at substituting precious metal-based catalysts. In this study, the catalytic activity of well-characterized CoII and CoI complexes of the pToldpbp ligand is demonstrated in the hydrosilylation of 1-octene with phenylsilane. The CoI complex is the better precatalyst for the mentioned reaction under mild conditions, at 1 mol-% catalyst, 1 h, room temperature, and without solvent, yielding 84 % of octylphenylsilane. Investigation of the substrate scope shows lower performance of the catalyst in styrene hydrosilylation, but excellent results with allylbenzene (84 %) and acetophenone (> 99 %). This catalytic study contributes to the field of cobalt-catalyzed hydrosilylation reactions and shows the first example of catalysis employing the dpbp ligand in combination with a base metal.

Porous Organic Polymer as a Heterogeneous Ligand for Highly Regio- and Stereoselective Nickel-Catalyzed Hydrosilylation of Alkyne

A porous organic polymer (POL-Xantphos) was synthesized and employed as a heterogeneous ligand for selective hydrosilylation of alkynes. It exhibits high selectivity and catalytic efficiency toward a broad range of alkynes. Owing to the confinement effect of the micropore structure, POL-Xantphos was far superior to the monomeric Xantphos ligands in controlling the selectivity. By performing hydrosilylation in a flow reactor system, separation and regeneration of the Ni/POL-Xantphos catalyst are easily achieved without any loss in selectivity or activity.

Regiocontrol in the cobalt-catalyzed hydrosilylation of alkynes

A highly versatile cobalt-catalyzed hydrosilylations of alkynes is reported. Near-perfect regiocontrol/stereocontrol was induced by the choice of the ligand: bidentate phosphines afforded (E)-β-vinylsilanes; α-vinylsilanes formed with bipyridine ligands.

Hydrofunctionalizations of unsaturated hydrocarbons are key strategies for the synthesis of functionalized building blocks. Here, we report highly versatile cobalt-catalyzed hydrosilylations of alkynes that operate with minute amounts of the inexpensive, bench-stable pre-catalyst Co(OAc)₂·4H₂O under mild conditions (0.1–1 mol%, THF, r.t., 1 h). Near-perfect regiocontrol/stereocontrol was induced by the choice of the ligand: bidentate phosphines afforded (E)-β-vinylsilanes; α-vinylsilanes formed with bipyridine ligands.

Metal Nanoparticles Supported on Biomass-Derived Hierarchical Porous Heteroatom-Doped Carbon from Bamboo Shoots: Design, Synthesis and Applications

Heteroatom-doped porous carbon derived from biomass have recently received increasing attention due to their unique properties such as high electrical conductivity, large specific surface area, high porosity, and easy availability, which are appealing materials for versatile applications in catalysis, energy, separation and adsorption, and life sciences as well. On the basis of our previous work in this field, we summarized in this account our recent progress on design, synthesis of metal (e. g., Pd, Co) nanoparticles supported heteroatom-doped hierarchical porous carbon material derived from bamboo shoots and their applications for important organic transformations, including chemoselective semihydrogenation of alkynes, hydrosilylation of alkynes, cascade synthesis of benzofurans from terminal alkynes and iodophenols, selective hydrogenation of functionalized nitroarenes to form anilines, imines, and formamides. Finally, the current state and future challenges in this field are discussed. We hope this account could shed light on the rational design of novel non-noble metal based heterogeneous catalysts derived from biomass for efficient and sustainable organic transformations.

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.

Solid state 13C NMR spectroscopy provides direct evidence for reaction between ethinyl estradiol and a silicone elastomer vaginal ring drug delivery system

Steroid molecules have a long history of incorporation into silicone elastomer materials for controlled release drug delivery applications. Previously, based on in vitro release testing and drug content analysis, we demonstrated indirectly that the contraceptive progestin levonorgestrel (LNG) chemically and irreversibly binds to addition cure silicone elastomers, presumably via a hydrosilylation reaction between the levonorgestrel ethynyl group and the hydrosilane groups in the poly(dimethylsiloxane-co-methylhydrosiloxane) crosslinker of the silicone elastomer. Here, for the first time, we report that solid state ¹³C nuclear magnetic resonance (NMR) spectroscopy provides direct evidence for the irreversible binding of ethinyl estradiol (EE) - an estrogenic steroid molecule also containing an ethynyl functional group - to an addition cure silicone elastomer. By preparing silicone elastomer samples containing ¹³C-labelled EE, signals in the NMR spectra could readily be assigned to both the free and bound EE. Additional depolymerisation studies, performed on an addition cure silicone elastomer system from which the unbound EE fraction was completely extracted, further confirmed the presence of bound EE through the formation of coloured reaction mixtures resulting from the reaction of bound EE and trifluoroacetic acid (TFA). These methods will be particularly useful in the ongoing development of new steroid-releasing silicone drug delivery devices, including various vaginal ring devices for contraception, HIV prevention and multipurpose prevention technology applications.

Stereodivergent Catalysis

This review covers diastereo- and enantiodivergent catalyzed reactions in acyclic and cyclic systems using metal complexes or organocatalysts. Among them, nucleophilic addition to carbon-carbon and carbon-nitrogen double bonds, α-functionalization of carbonyl compounds, allylic substitutions, and ring opening of oxiranes and aziridines are considered. The diastereodivergent synthesis of alkenes from alkynes is also included. Finally, stereodivergent intramolecular and intermolecular cycloadditions and other cyclizations are also 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.

A Ligand-Free Pt3 Cluster Catalyzes the Markovnikov Hydrosilylation of Alkynes with up to 106 Turnover Frequencies

The Pt-catalyzed hydrosilylation of alkynes is the procedure of choice to obtain vinylsilanes, and is claimed to be the most relevant application of Pt in organic synthesis. More than half a century after its discovery, only β-vinylsilanes (anti-Markovnikov addition) are obtained with simple Pt catalysts, whereas α-vinylsilanes (Markovnikov addition) remain elusive compounds. Here the catalysis of the Markovnikov hydrosilylation of terminal alkynes by Pt₃ clusters, in parts-per-million amounts, to give a wide variety of α-vinylsilanes in reasonable isolated yields and with turnover frequencies that can reach up to one million per hour is reported. Moreover, these α-vinylsilanes are reactive in well-stablished C-C bond-forming cascade reactions, in which the corresponding β-isomers are unreactive. Besides its efficiency and synthetic usefulness, this catalytic system is an excellent example of how the atom-by-atom aggregation of a catalytic metal leads to a different selectivity for a given reaction.

A versatile method for the preparation of carbon-rhodium hybrid catalysts on graphene and carbon black

A direct and rapid access to highly efficient and recyclable carbon–rhodium hybrid catalysts for the hydrosilylation reaction is presented.

Strategies for combining the selectivity and efficiency of homogeneous organometallic catalysts with the versatility of heterogeneous catalysts are urgently needed. Herein a direct and modular methodology is presented that provides rapid access to well-defined carbon–rhodium hybrid catalysts. A pre-synthesized Rh(i) complex containing a carbene-triazole ligand was found to be stable for direct immobilization onto unactivated graphene, carbon black and glassy carbon electrodes. Characterization of the heterogeneous systems using X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), inductively coupled plasma-optical emission spectroscopy/mass spectrometry (ICP-OES/MS), Raman spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the well-defined nature of the hybrid catalysts. The hybrid catalysts show excellent activity, comparable to that of the homogeneous system for the hydrosilylation of diphenylacetylene, with turnover numbers ranging from 5000 to 48 000. These catalysts are the best reported to date for the hydrosilylation of diphenylacetylene. In common with conventional heterogeneous catalysts, high reusability, due to a lack of Rh metal leaching, was also observed for all carbon–rhodium complexes under investigation.

Rapid, Regioconvergent, Solvent-Free Alkene Hydrosilylation with a Cobalt Catalyst

Alkene hydrosilylation is typically performed with Pt catalysts, but inexpensive base-metal catalysts would be preferred. We report a Co catalyst for anti-Markovnikov alkene hydrosilylation that can be used without added solvent at low temperatures with low loadings, and can be generated in situ from an air-stable precursor that is simple to synthesize from low-cost, commercially available materials. In addition, a mixture of Co catalysts performs a tandem catalytic alkene isomerization/hydrosilylation reaction that converts multiple isomers of hexene to the same terminal product. This regioconvergent reaction uses isomerization as a benefit rather than a hindrance.