Hydrosilylation Of Alkenes Research Articles

Cine-Silylative Ring-Opening of α-Methyl Azacycles Enabled by the Silylium-Induced C-N Bond Cleavage.

Described herein is the development of a borane-catalyzed cine-silylative ring-opening of α-methyl azacycles. This transformation involves four-step cascade processes: (i) exo-dehydrogenation of alicyclic amine, (ii) hydrosilylation of the resultant enamine, (iii) silylium-induced cis-β-amino elimination to open the ring skeleton, and (iv) hydrosilylation of the terminal olefin. The present borane catalysis also works efficiently for the C-N bond cleavage of acyclic tertiary amines. On the basis of experimental and computational studies, the silicon atom was elucidated to play a pivotal role in the β-amino elimination step.

Synthesis of Bifunctional Silsesquioxanes and Spherosilicates with Organogermyl Functionalities.

In this paper we present the synthesis of mixed bifunctional compounds of T8 H8 silsesquioxane and spherosilicate (HSiMe2 O)8 Si8 O12 derivatives via platinum-catalyzed hydrosilylation of alkenylgermanes and olefins. To the best of our knowledge, this is the first literature example of bifunctional compounds with organogermyl functionalities. Eleven mixed systems with a variety of substituents (Si-H, alkyl, germyl, epoxy, and hydroxy) were prepared and fully characterized by NMR spectroscopy. Additionally, our research includes a real-time FT-IR study of the synthesis of these bifunctional compounds of the general formula (R)8-m (GeR'3 (CH2 )n+2 R)m Si8 O12 . and (R''(CH2 )2 R)8-m (GeR'3 (CH2 )2 R)m Si8 O12 where m∼4.

Mechanistic Investigations of Nickamine- catalyzed Hydrosilylation of Alkenes: Nickel Nanoparticles Are the Active Species.

Hydrosilylation is an important chemical process for the synthesis of organosilanes and for the production of silicone polymers. The wide variety of catalysts developed for this reaction generally follow a Chalk-Harrod, or a sigma-bond metathesis mechanism. Recently, our group developed a nickel pincer complex, Nickamine, for highly selective hydrosilylation of alkenes. Preliminary mechanistic studies had suggested a pathway that deviates from both Chalk-Harrod and sigma-bond metathesis cycles. Here we used in situ NMR to monitor the hydrosilylation reaction. The observed induction period indicated that the species previously believed to be the resting state is merely a precatalyst. Via a combination of Transmission Electron Microscopy, mercury poisoning test, and competition reactions we show that the true catalyst is not a molecular nickel species, but rather nickel nanoparticles.

Mechanistic Study of Alkene Hydrosilylation Catalyzed by a β-Dialdiminate Cobalt(I) Complex

Alkene hydrosilylation is a large-scale process that typically uses precious-metal catalysts. A new generation of highly selective catalysts is based on inexpensive metals, which may have a high-sp...

CNC]-Pincer Cobalt Hydride Catalyzed Distinct Selective Hydrosilylation of Aryl Alkene and Alkyl Alkene

The reactions of unsymmetrical N-heterocyclic carbene (NHC) [CNC]-pincer preligands with CoMe(PMe3)4 gave rise to NHC [CNC]-pincer cobalt(III) hydrides, [(CcarbeneNaminoCnaphthyl)Co(H)(PMe3)2] (3a) and (3b), via Csp2–H activation and the unexpected trans-bischelate [Ccarbene, Namino] cobalt(II) complexes 4a and 4b via a disproportionation reaction, respectively. It was found that both 3a and 3b are efficient catalysts for hydrosilylation of alkenes. With aryl alkenes as substrates, 3a has high Markovnikov selectivity in excellent yields, while 3a is an efficient anti-Markovnikov catalyst in good yields with alkyl alkenes as substrates. The catalytic process could be promoted with pyridine N-oxide as an initiator. The catalytic mechanisms for the two different selectivities were proposed. Complexes 3a, 3b, 4a, and 4b were characterized by spectroscopic methods, and the molecular structures of 3b, 4a, and 4b were determined by single crystal X-ray diffraction.

Stereospecific Si-C coupling and remote control of axial chirality by enantioselective palladium-catalyzed hydrosilylation of maleimides

Hydrosilylation of unsaturated carbon-carbon bonds with hydrosilanes is a very important process to access organosilicon compounds and ranks as one of the most fundamental reactions in organic chemistry. However, catalytic asymmetric hydrosilylation of activated alkenes and internal alkenes has proven elusive, due to competing reduction of carbon-carbon double bond or isomerization processes. Herein, we report a highly enantioselective Si-C coupling by hydrosilylation of carbonyl-activated alkenes using a palladium catalyst with a chiral TADDOL-derived phosphoramidite ligand, which inhibits O-hydrosilylation/olefin reduction. The stereospecific Si-C coupling/hydrosilylation of maleimides affords a series of silyl succinimides with up to 99% yield, >99:1 diastereoselectivity and >99:1 enantioselectivity. The high degree of stereoselectivity exerts remote control of axial chirality, leading to functionalized, axially chiral succinimides which are versatile building blocks. The product utility is highlighted by the enantioselective construction of N-heterocycles bearing up to three stereocenters.

The effect of Schiff base ligands on the structure and catalytic activity of cobalt complexes in hydrosilylation of olefins

Environmental and economic aspects render the search for new nonprecious metal hydrosilylation catalysts an up-to-date challenge. Cobalt stands as an interesting alternative to the benchmark platinum-based species, nonetheless its relative infancy necessitates further studies, particularly regarding the structure of organic ligands that decorate the catalytically active metallic centre. As a continuation of our previous communication, we synthesized and characterized a series of new cobalt(II) chloride bench-stable precatalysts coordinated to a small library of structurally similar Schiff base ligands. Thus the synthesized species were evaluated for their ability to act as olefin hydrosilylation catalysts in the presence of alkali metal triethylborohydrides. From the crystal engineering point of view, it was observed that the number and arrangement of the Schiff base non-coordinating hydrogen bond donors affects the composition of formed complexes, resulting in predominant formation of either [CoLCl2] ‘open’ or [CoL2]2+ ‘closed’ species or a mixture of these. This affects their catalytic properties, with the benzimidazole/2H-imidazole ‘open’ system being the most efficient in terms of hydrosilylation selectivity and lowest catalyst loading. All in all, our work shows that seemingly similar coordination motifs do not necessarily lead to the isostructural group of catalytically open cobalt(II) coordination compounds, which is an important factor to consider in the design of new catalysts in general.

Bidentate N‐based Ligands for Highly Reusable, Ligand‐coordinated, Supported Pt Hydrosilylation Catalysts

AbstractA significant challenge in designing supported metal‐ligand catalysts for solution‐phase reactions is the stabilization of the metal active sites against leaching into solution. Here, we examine alkene hydrosilylation reactions as model systems to improve the stability of highly dispersed Pt using a metal‐ligand coordination strategy on high surface area oxide supports. By evaluating a series of bidentate N‐based ligands, we demonstrate several design strategies to improve stability of the highly dispersed Pt2+ centers against leaching, while maintaining a high level of catalytic activity, selectivity, and recyclability for alkene hydrosilylation batch reactions under mild conditions. These involve a bi‐functional approach to ligand design, which considers interaction to the support and a well‐defined coordination environment for the metal active site. Three strategies are reported: modifying ligands for stronger interaction with oxide surfaces, mixing ligands, and pre‐depositing an “anchoring ligand” to the support before loading the metal‐ligand catalyst. Each of these is successful in enhancing Pt recyclability. Particularly, two Pt‐phenanthroline catalysts exhibit excellent reusability for multiple batch reaction cycles, due to high stability of the active Pt species. Addressing the active site leaching problem significantly enhances the utility of ligand‐coordinated supported metal catalysts as highly stable and selective catalysts for solution‐phase reactions.

Highly bulky spherosilicates as functional additives for polyethylene processing—Influence on mechanical and thermal properties

AbstractIn this work, a series of cage siloxanes (spherosilicate [SS] type) was tested as functional additives for preparation of polyethylene (PE)‐based nanocomposites. For this purpose, the compounds were prepared by condensation and olefin hydrosilylation reactions. The effect of these products on properties of obtained nanocomposites was analyzed by means of mechanical, microscopic (scanning electron microscopy‐energy dispersive spectroscopy), crystallographic (X‐ray diffraction), thermal (differential scanning calorimetry, thermogravimetry), rheological Melt flow rate (MFR), and thermomechanical (heat deflection temperature) analyses. The results were compared with similar reports on silsesquioxane‐ and SS‐reinforced PE systems. Effects of SS functional group structure on the behavior of the additive and properties of the composite system were discussed. Aspects of thermal decomposition of PE‐containing SS were studied and a probable mechanism of these polymer systems degradation was proposed.

DFT study of trialkylborohydride-catalysed hydrosilylation of alkenes – the mechanism and its implications

A detailed DFT study reveals the mechanism of trialkylborohydride-catalysed Markovnikov hydrosilylation of aromatic alkenes.

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.

Recent Advances on Heterogeneous Metal Catalysts for Hydrosilylation of Olefins

Recent Advances on Heterogeneous Metal Catalysts for Hydrosilylation of Olefins

Partially charged platinum on aminated and carboxylated SBA-15 as a catalyst for alkene hydrosilylation.

In this paper, we report the successful preparation of a novel bifunctional heterogeneous catalyst Ptδ+/SBA-APTE-SA with a partial positively charged Ptδ+ electronic structure via post-synthesis modification of (3-aminopropyl)triethoxysilane (APTE), succinic anhydride (SA) and platinum precursors. The resulting catalyst showed superior catalytic performance for the hydrosilylation of 1,1,1,3,5,5,5-heptamethyltrisiloxane (MDHM) with allyloxy polyethylene glycol (APEG) compared to a heterogeneous platinum catalyst. In addition, our catalyst was suitable for the hydrosilylation of other alkenes. Furthermore, the catalyst displayed sufficient stability after being reused five times without noticeable inactivation. In terms of cycle number and atomic utilization efficiency, it has potential applications as a green hydrosilylation method for industry.

Chemoselective Hydrosilylation of Olefin/Ketone Catalyzed by Iminobipyridine Fe and Co complexes

AbstractThe chemoselective hydrosilylation of olefins and ketones catalyzed by Fe and Co complexes bearing an iminobipyridine derivative ligand was investigated. The reaction of a 1 : 1 mixture of styrene and acetophenone over the Fe catalyst achieved selective hydrosilylation of acetophenone. In contrast, the corresponding Co complex showed the opposite selectivity‐styrene‐selective hydrosilylation. The reaction of 3‐acetylstyrene with both olefin and ketone moieties in the molecule showed that the Co complex catalyzed olefin‐selective hydrosilylation. In contrast, the addition of pyridine to the Co‐catalyzed system showed the opposite chemoselectivity, affording the ketone hydrosilylated product. The chemoselectivity of olefin/ketone hydrosilylation was switched by replacing the central metal of the complex with the iminobipyridine derivative ligand and by changing the simple reaction conditions (absence or presence of pyridine) using an identical Co complex.

Stable Discrete Pt1(0) in Crown Ether with Ultra‐High Hydrosilylation Activity

AbstractObtaining reduced discrete metal atoms that are stable in liquid solvents byin‐situreduction of an ionic metal precursor has been a challenge until recently. A liquid surfactant polydimethylsiloxane‐polyethylene glycol (PDMS‐PEG) enabled the synthesis of stable discrete platinum atoms (Pt1) by reducing Pt(IV) and Pt(II) salts. Here we report the successful preparation of discrete mononuclear platinum atoms (Pt1) in a crown ether, [15]crown‐5, as a structurally much simpler solvent, and the prepared Pt1@[15]crown‐5 was demonstrated for ultra‐high catalytic activity and selectivity in hydrosilylation reactions. A combination of spectroscopic characterizations proves the reduced Pt species is Pt1(0) with partially positive charge.195Pt NMR and DFT calculation indicate the Pt1(0) is stabilized by thepseudooctahedral structure of ([15]crown‐5)PtCl−2H+2involving two adjacent oxygens from the crown ether ring, although the oxygens in the crown ether ring have been known to host and stabilize certain metal cations. The Pt1@[15]crown‐5 shows ultrahigh activity (TOF of 8.3×108 h−1) with excellent terminal adducts selectivity in catalytic olefin hydrosilylation. This catalyst was found to be highly stable under hydrosilylation conditions. For examples, the turnover number (TON) exceeded 1.0×109for hydrosilylation between 1‐octene and (Me3SiO)2MeSiH without showing sign of deactivation; the TON exceeded 2.0×108while the catalyst remained active for a catalytically more demanding reaction between styrene and (Me3SiO)2MeSiH.

Regioselective Hydrosilylation of Olefins Catalyzed by a Molecular Calcium Hydride Cation.

Chemo‐ and regioselectivity are often difficult to control during olefin hydrosilylation catalyzed by d‐ and f‐block metal complexes. The cationic hydride of calcium [CaH]+ stabilized by an NNNN macrocycle was found to catalyze the regioselective hydrosilylation of aliphatic olefins to give anti‐Markovnikov products, while aryl‐substituted olefins were hydrosilyated with Markovnikov regioselectivity. Ethylene was efficiently hydrosilylated by primary and secondary hydrosilanes to give di‐ and monoethylated silanes. Aliphatic hydrosilanes were preferred over other commonly employed hydrosilanes: Arylsilanes such as PhSiH3 underwent scrambling reactions promoted by the nucleophilic hydride, while alkoxy‐ and siloxy‐substituted hydrosilanes gave isolable alkoxy and siloxy calcium derivatives.

Silicon(II) Cation Cp*Si:+ X–: A New Class of Efficient Catalysts in Organosilicon Chemistry

The catalytic activity of the pentamethylcyclopentadienylsilicon(II) cation Cp*Si:+ was investigated. It was shown that Cp*Si:+ efficiently catalyzes reactions of technical relevance in organosilicon chemistry: Cp*Si:+ proved to be a very efficient nonmetallic catalyst for the hydrosilylation of olefins at low catalyst amounts of <0.01 mol % and for the Piers–Rubinsztajn reaction in order to make controlled silicone topologies. The thermal induction of hydrosilylation which is important for the manufacturing of silicone rubber can be achieved by small amounts of alkoxysilanes.

Development of Activator-free Iron Pincer Complexes for Alkene Hydrosilylation and Elucidation of Its Activation Mechanism

Activation of iron dihalide complex for hydrosilylation of alkene was examined along with the disproportionation of hydrosilane. The pre-catalyst prepared in the reaction of activators with iron di...

B(C6F5)3‐Catalyzed sp3 C—Si Bond Forming Consecutive Reactions

Transition metal‐catalyzed hydrosilylation is one of the most widely utilized reduction methods as an alternative to hydrogenation in academia and industry. One feature distinct from hydrogenation would be able to install sp3 C—Si bond(s) onto substrates skeleton via hydrosilylation of alkenes. Recently, B(C6F5)3 with hydrosilanes has been demonstrated to be an efficient, metal‐free catalyst system for the consecutive transformation of heteroatom‐containing substrates accompanied by the formation of sp3 C—Si bond(s), which has not been realized thus far under the transition metal‐catalyzed hydrosilylative conditions. In this review, I outline the B(C6F5)3‐mediated consecutive hydrosilylations of heteroarenes containing quinolines, pyridines, and furans, and of conjugated nitriles/imines to provide a new family of compounds having sp3 C—Si bond(s) with high chemo‐, regio‐ and/or stereoselectivities. The silylative cascade conversion of unactivated N‐aryl piperidines to sila‐N‐heterocycles catalyzed by B(C6F5)3 involving consecutive dehydrogenation, hydrosilylation, and intramolecular C(sp2)—H silylation, is presented in another section. Chemical selectivity and mechanism of the boron catalysis focused on the sp3 C—Si bond formation are highlighted.

Enantioselective Rhodium-Catalyzed Desymmetric Hydrosilylation of Cyclopropenes

Catalytic hydrosilylation of alkenes ranks as one of the most important academic and industrial synthetic reactions in homogeneous catalysis and organosilicon chemistry. In this work, a highly enan...