Hydrosilylation Of Terminal Alkenes Research Articles

Humic Acid: A Promising and Green Bioorganic Catalyst in Organic Syntheses

AbstractThe growing pollution and threat to the environment demand green synthetic methods. Green chemistry mainly focuses on minimizing the waste and utilization of green solvents, energy sources, and catalysts and prefers one‐pot reactions. In this context, humic acid (HA), a natural bioorganic catalyst found in rivers, peat coal and sewage; is a high molecular weight macromolecule containing multifunctional groups, mainly contains quinone, phenolic OH, and COOH groups which make it acidic and activate carbonyl groups by protonation. Owing to its green aspect such as biodegradability, recyclability and reusability, humic acid is considered as sustainable bioorganic catalyst which meets the criteria for industrial requirements. The HA is mild acidic in nature, thus many functional groups tolerate in the HA catalyzed reactions. After few initial reports in 2001 and 2009, the HA catalyzed reactions gained much attention by the organic synthetic community from 2019 in aldol condensation, Knoevenagel condensation, Claisen‐Schmidt reaction, Michael addition, Strecker synthesis, tetrazole synthesis, Hantzsch dihydropyridine synthesis, hydrosilylation of terminal alkenes, hydrogenation, α‐aminophosphonate synthesis, cross coupling reactions such as Heck and Suzuki coupling reactions. Herein we report the comprehensive analysis on the role of HA in organic transformations providing diverse array of molecular scaffolds till date and future perspective.

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.

Anti-Markovnikov terminal and gem-olefin hydrosilylation using a κ4-diimine nickel catalyst: selectivity for alkene hydrosilylation over ether C-O bond cleavage.

The phosphine-substituted α-diimine Ni precursor, (Ph2PPrDI)Ni, has been found to catalyze alkene hydrosilylation in the presence of Ph2SiH2 with turnover frequencies of up to 124 h-1 at 25 °C (990 h-1 at 60 °C). Moreover, the selective hydrosilylation of allylic and vinylic ethers has been demonstrated, even though (Ph2PPrDI)Ni is known to catalyze allyl ester C-O bond hydrosilylation. At 70 °C, this catalyst has been found to mediate the hydrosilylation of ten different gem-olefins, with turnover numbers of up to 740 under neat conditions. Prior and current mechanistic observations suggest that alkene hydrosilylation takes place though a Chalk-Harrod mechanism following phosphine donor dissociation.

Markovnikov Hydrosilylation of Alkenes: How an Oddity Becomes the Goal

Over the years, hydrosilylation of terminal alkenes has emerged as one of the most prominent applications of homogeneous catalysis. While most of the relevant reports concern β-selective hydrosilylation, yielding linear products which are of industrial importance, the opposite selectivity is also gaining increasing interest and sets the scene for the next challenges. Markovnikov hydrosilylation of alkenes, especially in its asymmetric variant, has become the aim of development of new catalytic systems successfully implementing base-metal complexes—one of the most prominent trends in contemporary catalysis. In this Perspective, we present the current state of this topic and the way it has been achieved, with special emphasis put on the issues still unresolved and prospective directions of development based on the trends present in the literature, but without unnecessary attention to some details of only historical significance.

Inexpensive, operationally simple flow reactor for rapid, chromatography free synthesis of siloxane based liquid crystals

We report on the hydrosilylation of terminal alkenes in flow using a “Karstedt-like” platinum-on-silica catalyst to afford liquid-crystalline materials.

Chemoselective Alkene Hydrosilylation Catalyzed by Nickel Pincer Complexes

AbstractChemoselective hydrosilylation of functionalized alkenes is difficult to achieve using base‐metal catalysts. Reported herein is that well‐defined bis(amino)amide nickel pincer complexes are efficient catalysts for anti‐Markovnikov hydrosilylation of terminal alkenes with turnover frequencies of up to 83 000 per hour and turnover numbers of up to 10 000. Alkenes containing amino, ester, amido, ketone, and formyl groups are selectively hydrosilylated. A slight modification of reaction conditions allows tandem isomerization/hydrosilylation reactions of internal alkenes using these nickel catalysts.

Polymeric monolith supported Pt-nanoparticles as ligand-free catalysts for olefinhydrosilylation under batch and continuous conditions

Pt-nanoparticles were generated within the mesopores of polymeric monolithic supports. These monoliths were prepared viaring-opening metathesis polymerization (ROMP) from (Z)-9-oxabicyclo[6.1.0]non-4-ene (OBN) and tris(cyclooct-4-en-1-yloxy)methylsilane (CL) using the 3rd-generation Grubbs-initiator RuCl2(pyridine)2(IMesH2)(CHPh) (1) in the presence of a macro- and microporogen. To generate the Pt nanoparticles inside the porous system, the epoxy-groups of the monolithic supports were hydrolyzed into the corresponding vic-diol with the aid of 0.1 N sulfuric acid. Loading with Pt4+ and reduction with NaBH4 resulted in the formation of Pt nanoparticles <7 nm in diameter that were exclusively located within the mesopores of the support as demonstrated by transmission electron microscopy/EDX spectrometry. The nanoparticles were stabilized by both the vic-diols and the polymeric double bonds as evidenced by control experiments with poly(glycidylmethacrylate)-based monoliths that lack the double bonds. Typical metal loadings of around 1.7 mg g−1 (8.7 μmol g−1) were obtained. Pt(0)-loaded monoliths were used in the hydrosilylation of terminal alkenes, norborn-2-ene and norbornadiene applying both batch and continuous flow conditions. Hydrosilylation of olefins under continuous flow conditions resulted in constant product formation in 98% yield at T = 45 °C applying a linear flow of 12.0 mm min−1. Metal leaching was very low, resulting in Pt-contamination in the addition products of less than 4 ppm throughout.