Catalysts For Hydrosilylation Research Articles

Three Reactions, One Catalyst: A Multi‐Purpose Platinum(IV) Complex and its Silica‐Supported Homologue for Environmentally Friendly Processes

Although platinum nanoparticles and complexes ‐especially of Pt(0) and Pt(II)‐ are well known catalysts, siloxane‐based platinum complexes are rarely reported. Herein, a Platinum(IV) complex of 4‐aminopyridinium‐modified disiloxane was prepared and characterized by medium and far infrared spectroscopy, NMR and EDX. The formation of the complex was monitored by UV–Vis spectroscopy, which showed the high affinity and selectivity of this ligand for Pt, with a stability constant of 7.53·103 M−1. The catalytic activity of the siloxane‐based complex was tested in three types of reactions: reduction of p‐nitrophenol, oxidation of glucose and starch, and hydrosilylation. The hydrophobic behavior of the permethylated disiloxane moiety ensures good hydrolytic stability, while the N‐donor ligand stabilizes thein‐situformed Pt nanoparticles. The generation of Pt nanoparticles during p‐nitrophenol reduction was confirmed by TEM and SEM. Contrary to most reports, the aerobic oxidation of mono‐ and polysaccharides occurred without oxidation agents or mediators added, in mild conditions, at room temperature and pH ~9. The same metal complex was found active in hydrosilylation of vinyl‐siloxanes with temperature‐modulated rate, thus being useful in silicone cross‐linking systems without the need of inhibitors. The method was adapted to one‐pot synthesis of silica‐supported Pt(IV) complex, which acted as efficient and reusable heterogeneous hydrosilylation catalyst, limiting the contamination of the product with Pt. This approach is promising for superior valorization of scarcely available and expensive platinum metal. By the same method, multifunctional soluble complexes and mesoporous silica may be obtained, with tunable catalytic performance.

Silica-supported Alkylammonium Formate Catalyst for Hydrosilylation of Carbon Dioxide

An amorphous silica-supported alkylammonium formate catalyst for the reductive transformation of carbon dioxide using silane as a reductant was developed. Alkylammonium iodide was grafted on amorph...

Evaluation of bifunctional chiral phosphine oxide catalysts for the asymmetric hydrosilylation of ketimines

A series of bifunctional phosphine oxides have been prepared and evaluated as catalysts for the trichlorosilane mediated asymmetric hydrosilylation of ketimines. bis-Phosphine oxides, hydroxy-phosphine oxides, and biaryl phosphine oxides all demonstrated good catalytic activity, but poor to moderate enantioselectivity. A bis-P-chiral phosphine oxide displayed the highest enantioselectivity of 60%.

Silica-Supported MnII Sites as Efficient Catalysts for Carbonyl Hydroboration, Hydrosilylation, and Transesterification.

Manganese, the third most abundant transition-metal element after iron and titanium, has recently been demonstrated to be an effective homogeneous catalyst in numerous reactions. Herein, the preparation of silica-supported MnII sites is reported using Surface Organometallic Chemistry (SOMC), combined with tailored thermolytic molecular precursors approach based on Mn2 [OSi(OtBu)3 ]4 and Mn{N(SiMe3 )2 }2 ⋅THF. These supported MnII sites, free of organic ligands, efficiently catalyze numerous reactions: hydroboration and hydrosilylation of ketones and aldehydes as well as the transesterification of industrially relevant substrates.

Carbon Dioxide Hydrosilylation to Methane Catalyzed by Zinc and Other First-Row Transition Metal Salts

Abstract We accomplished zinc catalyzed hydrosilylation of carbon dioxide (CO2) to silyl formate (C+II), bis(silyl)acetal (C0), methoxysilane (C−II), and finally methane (C−IV). Among several zinc salts, we found that Zn(OAc)2 with ligand 1,10-phenanthroline was the best. A turnover number of 815000 was achieved using the zinc catalyst to yield C+II. Unexpectedly, we observed the generation of CO from CO2 and hydrosilane for the first time. In addition to Zn, other first-row transition metals (Mn, Fe, Co, Ni, and Cu) also served as Lewis acid catalysts for CO2 hydrosilylation, regardless of the nature of the metal.

Contra-thermodynamic Olefin Isomerization by Chain-Walking Hydrofunctionalization and Formal Retro-hydrofunctionalization.

We report a contra-thermodynamic isomerization of internal olefins to terminal olefins driven by redox reactions and formation of Si-F bonds. This process involves chain-walking hydrosilylation of internal olefins and subsequent formal retro-hydrosilylation. The process rests upon the high activities of platinum hydrosilylation catalysts for isomerization of metal alkyl intermediates and a new, metal-free process for the conversion of alkylsilanes to alkenes. By this approach, 1,2-disubstituted and trisubstituted olefins are converted to terminal olefins.

Characterization and Synthesis of Functionalized Polysilalkylene Siloxane Monomers by Hydrosilylation Reaction

The synthesis of novel polysilalkylene siloxane monomers is of great interest to industrial chemists owing to their polymeric analogues having extremely useful properties as elastomers, adhesives, fluids, resins, as well as additives to other commercial products. The current industrial process for creating silicone polymers is through hydrosilylation of dienes. This process can produce a wide variety of organosilicon compounds with vast range of uses. The objective of this experiment is to synthesize modified silicone monomers which can be readily hydrolyzed in the presence of water to form their corresponding polymeric analogues. In order to do this, terminal dienes were reacted with either dimethylchlorosilane or methylphenylchlorosilane in the presence of the Karstedt’s catalyst, the most commonly used hydrosilylation catalyst, in order to yield the modified siloxane monomers. We report on the methodologies used to determine the identity of the final products as well as the methods used to determine their properties.

Theoretical prediction of Ni(I)-catalyst for hydrosilylation of pyridine and quinoline.

Catalytic synthesis of dihydropyridine by transition-metal complex is one of the important research targets, recently. Density functional theory calculations here demonstrate that nickel(I) hydride complex (bpy)NiI H (bpy = 2,2'-bipyridine) 1 is a good catalyst for hydrosilylation of both quinoline and pyridine. Two pathways are possible; in path 1, substrate reacts with 1 to form stable intermediate Int1. After that, N3 ─C1 bond of substrate inserts into Ni─H bond of 1 via TS1 to afford N-coordinated 1,2-dihydroquinoline Int2 with the Gibbs activation energy (ΔG°‡ ) of 21.8 kcal mol-1 . Then, Int2 reacts with hydrosilane to form hydrosilane σ-complex Int3; this is named path 1A. In the other route (path 1B), Int1 reacts with phenylsilane in a concerted manner via hydride-shuttle transition state TS2 to afford Int3. In TS2, Si atom takes hypervalent trigonal bipyramidal structure. Formation of hypervalent structure is crucial for stabilization of TS2 (ΔG°‡ = 17.3 kcal mol-1 ). The final step of path 1 is metathesis between Ni─N3 bond of Int3 and Si─H bond of PhSiH3 to afford N-silylated 1,2-dihydroproduct and regenerate 1 (ΔG°‡ = 4.5 kcal mol-1 ). In path 2, 1 reacts with hydrosilane to form Int5, which then forms adduct Int6 with substrate through Si-N interaction between substrate and PhSiH3 . Then, N-silylated 1,2-dihydroproduct is produced via hydride-shuttle transition state TS5 (ΔG°‡ = 18.8 kcal mol-1 ). The absence of N-coordination of substrate to NiI in TS5 is the reason why path 2 is less favorable than path 1B. Quinoline hydrosilylation occurs more easily than pyridine because quinoline has the lowest unoccupied molecular orbital at lower energy than that of pyridine. © 2019 Wiley Periodicals, Inc.

Highly efficient hydrosilylation catalysts based on chloroplatinate “ionic liquids”

The reaction between ionic liquid [Cat]+Cl− (where Cat stands for 1-butyl-3-methylimidazolium, 1-butyl-2,3-dimethylimidazolium or 1-butyl-4-methylpyridinium) and the metal precursor ([PtCl2(cod)], PtCl4, K2[PtCl4] or K2[PtCl6]) yielded two groups of derivatives: [Cat]+[PtCl4]− and [Cat]+[PtCl6]−, which formally are counted among halometallate ionic liquids, however, due to their high melting points they should be classified into anionic platinum complexes rather than into ionic liquids. All the derivatives were isolated and characterized spectroscopically (NMR, ESI-MS) and crystallographic structures were determined for three derivatives: ([BMPy]2[PtCl4], [BMIM]2[PtCl6] and [BMMIM]2[PtCl6]. Moreover, their melting points were measured and thermal stability was assessed. The above derivatives were employed as catalysts for hydrosilylation of olefins with diverse properties. All the studied catalysts showed high activity and their insolubility in the reaction medium made easy their isolation and multiple use in subsequent catalytic runs. The most effective catalysts did not lose their activity even after ten runs, thereby they make a very good alternative to commonly used homogeneous catalysts. Their simple synthesis and stability make them interesting both for economic and ecological reasons.

New Zinc Catalyst for Hydrosilylation of Carbonyl Compounds

A new zinc complex was synthesized and applied in the catalytic hydrosilylation of carbonyl compounds. Optimization of the reaction conditions showed that the presence a substoichiometric amount of methanol accelerates the process significantly. The reaction can proceed at very low catalyst load (down to 0.1 mol%) under mild reaction conditions. The reaction tolerates the presence of C=C bonds, and thus can be useful for the synthesis of allylic alcohols from α,β-unsaturated aldehydes and ketones.

Nickamine and Analogous Nickel Pincer Catalysts for Cross-Coupling of Alkyl Halides and Hydrosilylation of Alkenes.

Ligand development plays an essential role in the advance of homogeneous catalysis. Tridentate, meridionally coordinating ligands, commonly termed pincer ligands, have been established as a privileged class of ligands in catalysis because they confer high stability while maintaining electronic tenability to the resulting metal complexes. Pincer ligands containing "soft" donors such as phosphines are typically used for late transition-metal ions, which are considered "soft" acids. Driven by our interest to develop base-metal catalysis and in view of the "hard" character of base-metal ions, our group explored a pincer ligand containing only "hard" nitrogen donors. A prototypical nickel complex of this ligand, "Nickamine", turned out to be an efficient catalyst in a wide range of organic reactions. Because of its propensity to mediate single-electron redox chemistry, Nickamine is particularly suited to catalyze cross-coupling of nonactivated alkyl halides through radical pathways. These coupling partners have been challenging substrates for traditional, palladium-based catalysts because of difficult oxidative addition and nonproductive β-H elimination. The high activity of Nickamine for cross-coupling leads to high chemoselectivity and functional group tolerance, even when reactive Grignard reagents are employed as nucleophiles. The scope of the catalysis is broad and encompasses sp3-sp3, sp3-sp2, and sp3-sp cross-coupling. The defined nature of Nickamine facilitated the mechanistic study of cross-coupling reactions. Experiments involving radical-probe substrates, presumed intermediates and dormant species, kinetics, and density functional theory computations revealed a bimetallic oxidative addition pathway. In this pathway, two Ni centers each provide one electron to support the two-electron activation of an alkyl halide substrate. The success of Nickamine motivated our systematic structure-activity studies aiming at improved activity in certain reactions through ligand modification. Indeed, better catalysts have been developed for cross-coupling of secondary alkyl halides as well as direct alkynylation of alkyl halides. The improvement is attributed to a more accessible Ni center in the new catalysts than in Nickamine. Surprisingly, the improvement could be obtained simply by replacing a dimethyl amino group in Nickamine with a pyrrolidino group. During the study of the catalytic cycle of Nickamine in cross-coupling reactions, we synthesized the corresponding Ni-H species. Consequently, we explored the catalytic application of Nickamine in Ni-H mediated reactions, such as hydrosilylation. To our delight, Nickamine is a chemoselective catalyst for hydrosilylation of alkenes while tolerating a reactive C=O group. An analogous Ni pincer complex was found to catalyze unusual hydrosilylation reactions using alkoxy hydrosilanes as surrogates of gaseous silanes.

Platinum(II) complexes bearing bulky Schiff base ligands anchored onto mesoporous SBA‐15 supports as efficient catalysts for hydrosilylation

Reported herein is an easy‐to‐prepare novel heterogeneous catalyst of platinum complexes bearing binary ligands of bidentate naphthalenolimine and cyclo‐1,5‐octadiene that are anchored onto mesoporous silica SBA‐15. The presence of the binary ligands not only stabilized the platinum, but also enabled the platinum atoms to form nanoclusters with diameters of ca 1 nm, and led to high platinum loading (8.69 wt%). Moreover, the platinum catalyst exhibited high catalytic activity towards hydrosilylation of terminal alkenes and styrene with silanes under mild and solvent‐free conditions, with excellent regioselectivity.

Rare-earth metal catalysts for alkene hydrosilylation

Rare-earth metal catalyzed hydrosilylation of alkenes has emerged as a powerful and selective strategy for the synthesis of organosilanes. This transformation can offer distinctive catalytic sequences and reaction patterns from other catalysts because of the high electropositivity and lack of oxidative-addition process of rare-earth metal. This review summarizes the rare-earth metal catalysts for hydrosilylation of alkene according to the type of ligands. The synthesis and structure of rare-earth metal catalysts, the substrate scope as well as some preliminary structure-activity relationship and mechanism are discussed.

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.

New anionic rhodium complexes as catalysts for the reduction of acetophenone and its derivatives.

New anionic rhodium(iii) complexes, obtained by a simple reaction of RhCl3 with organic chlorides (derivatives of imidazole and pyridine), have been employed as catalysts for hydrosilylation (reduction) of acetophenone derivatives. The reactions, in which 1,1,1,3,5,5,5-heptamethyltrisiloxane was a reducing agent, proceeded in a biphasic system because the above complexes are insoluble in the reaction medium. Thereby easy isolation of the complexes from post-reaction mixtures was possible after reaction completion. This is the first example of the application of rhodium complexes of this type as catalysts for ketone reduction. The complexes have shown high activity and enabled obtaining the hydrosilylation product in a very short time and in the range of low concentrations (0.1 mol%). By using FT-IR in situ analysis that enables measuring product concentrations in real time, a comparison has been made of the catalytic activity for hydrosilylation of acetophenone and methoxyacetophenone isomers shown by four rhodium complexes ([C+][RhCl4−]) differing in cations and the most effective catalyst for this process has been distinguished.

Air-stable and reusable cobalt ion-doped titanium oxide catalyst for alkene hydrosilylation

Air-stable and highly reusable cobalt ion-doped titanium oxide catalyst was developed for alkene hydrosilylation.

Alkene hydrosilylation catalyzed by easily assembled Ni(ii)-carboxylate MOFs.

We report the first Ni MOF catalysts for anti-Markovnikov hydrosilylation of alkenes. These catalysts are bench-stable and easily-assembled from simple Ni salts and carboxylic acids. The best catalyst gives turnover numbers up to 9500 and is robust even after 10 recycling runs. The catalyst can be applied for the hydrosilylation of a wide range of alkenes, achieving good synthetic utility and functional group tolerance.

Alkene hydrosilylation with supported and unsupported Ni nanoparticles: strong influence of the Ni environment on activity and selectivity

Isolated nickel nanoparticles in suspension or supported on silica are efficient catalysts for inactivated alkene hydrosilylation.

Platinum on 2-aminoethanethiol functionalized MIL-101 as a catalyst for alkene hydrosilylation.

Hydrosilylation is one of the largest-scale applications for homogeneous catalysis and is widely used to enable the commercial manufacture of silicon products. In this paper, a bifunctional heterogeneous catalyst, Ptδ+/AET-MIL-101 (AET = 2-aminoethanethiol) with a partially positively charged Ptδ+ electronic structure is reported, which was successfully prepared using post-synthesis modification with AET and a platinum precursor. The catalysts were characterized using X-ray diffraction (XRD), nitrogen (N2) adsorption–desorption, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) techniques which showed that the synergy of AET-MIL-101 provides a good dispersion of Ptδ+ in the channels, which can efficiently catalyze the hydrosilylation reaction with almost complete conversion and produce a unique adduct. In addition, the synthetic heterogeneous catalyst Ptδ+/AET-MIL-101 achieves reasonable use of Pt in terms of number cycles and atomic utilization efficiency, indicating the potential to achieve a green hydrosilylation industry.

Platinum and rhodium complexes ligated by imidazolium-substituted phosphine as efficient and recyclable catalysts for hydrosilylation

Platinum and rhodium complexes ligated by imidazolium substituted phosphine were obtained with high yields and applied as efficient catalysts.