Copper-catalyzed asymmetric hydrosilylation of ketones using air and moisture stable precatalyst Cu(OAc)2·H2O

Air and moisture stable copper(II) salts can be used to catalyze the hydrosilylation of aromatic ketones. The combination of catalytic amounts of copper(II) acetate or copper(II) acetate monohydrate (Cu(OAc)₂·H₂O) and BINAP in the presence of organosilanes as the stoichiometric reducing agent generates an active catalyst for the reduction of ketones.     

CROWN FUNCTIONALIZED LINEAR POLYSILOXANE PLATINUM COMPLEX AS HYDROSILYLATION CATALYST

A modified method of preparing crown functionalized linear polysiloxane has been described.4'-allylbenzo-15-crown-5 was subjected to hydrosilylation with methyldichlorosilane,followed bypolycondensation with silanol-terminated polydimethylsiloxane to give the title crownfunctionalized linear polysiloxane. It was found that the polysiloxane could be coordinated withplatinum salt to form platinum complex, which could catalyze the hydrosilylation of olefins withtriethoxysilane efficiently.     

Cationic complexes of dirhodium(II) with 1,8-naphthyridine: Catalysis of reactions involving silanes

The synthesis of cationic dirhodium(II) complexes by partial or total substitution of the acetate groups of [Rh₂(OAc)₄] with different homoleptic neutral bidentate ligands has been attempted. The ligand 1,8-naphthyridine gave the best results: substitution of one as well as of all four acetate ligands is possible, giving rise to mono-, di- and tetra-cationic complexes. One of the resulting tetrasubstituted complexes has been structurally characterised and found to exhibit the expected lantern-shaped structure. All cationic complexes have been investigated as catalysts in different reactions involving silanes: promising results have been obtained, particularly in the silylformylation of alkynes.     

Enhanced mechanical and thermal properties of γ-allyloxymethyl 18-crown-6 and polyimide composites through hydrosilylation crosslinking

Tetrakis-(dimethylsiloxy)-silane (TDSS) was employed to crosslink the complex of γ-allyloxymethyl 18-crown-6 (AC6) and polyimide (PI) (AC6-PI) through hydrosilylation reaction. The crosslinked AC6-PI (SiAC-PI) composites possessed excellent mechanical and thermal properties as well as low dielectric constant.     

Quaternary onium chlorometallates as hydrosilylation catalysts

Sixteen triethylbenzylammonium chlorometallates [Et₃ NCH ₂Ph][MCI_n]^m? (M= transition metal, m= 1–3, n= 3–6) and nine anchored ionic metal complexes [?–CH₂PBu₃][MCI_n]^m? derived from ‘polymer-bound tributylmethylphosphonium chloride’ have been prepared. All the complexes were studied as catalysts in the hydrosilylation of phenylacetylene with triethylsilane. The homogeneous Rh^III, Pt^IV, Ir^III, Cu^II, Zn^II, Fe^III and anchored Pt^IV, Rh^III, Os^IV complexes were found to be active in this reaction. The regio- and stereoselectivity of the following catalyst types is determined by the metal atom involved, being a weak function of the chemical environment; neutral chloride (MCl_n–m); acid (H₂MCl₆); salt containing the lipophilic organic cation ([Et₃NCH₂Ph][MCl_n]^m?); polymer-supported metallate anion ([?–CH₂PBu₃] [MCl_n]^m?).     

SYNTHESIS AND CHARACTERIZATION OF A NOVEL REACTIVE OLIGOMERIC LADDERLIKE COPOLYMETHYL-AMINOPROPYL SILSESQUIOXANE

A novel ordered reactive oligomeric ladderlike copolymethyl-aminopropylsilsesquioxane (Me-AP-T), was successfully synthesized by an efficient hydrosilylation graft reaction of 1,1,1-trimethyl-N-2-propenyl-silanamine with a reactive oligomeric |adderlike copolymethyl-hydrosilsesquioxane (Me-H-T), which was prepared by “supramolecular chemistry-dictated stepwise coupling polymerization” process. FT-IR, ^1H- and ^29Si-NMR spectra show that hydrosilylation reaction proceeds completely. Moreover, ^1H-NMR spectra also indicate that both the molar ratios of ≡SiMe group to Si-H and ≡SiMe group to ≡SiPrNH2 are approximately 1:1 respectively based on the ratio of integrated resonance areas of the different groups. XRD analysis and ^29Si-NMR spectra are used for investigating the ladderlike structure of the polymers. A high Tg (128.38℃) of Me-AP-T shown in DSC measurement implies that the ordered reactive Me-AP-T macromolecules have much stiff chains.     

Neutral hydrophilic coatings for capillary electrophoresis prepared by controlled radical polymerization

In the present study, porous silica particles as well as impervious fused-silica wafers and capillary tubes were modified with hydrophilic polymers (hydroxylated polyacrylamides and polyacrylates), using a surface-confined grafting procedure based on atom transfer radical polymerization (ATRP) which was also surface-initiated from α-bromoisobutyryl groups. Initiator immobilization was achieved by hydrosilylation of allyl alcohol on hydride silica followed by esterification of the resulting propanol-bonded surface with α-bromoisobutyryl bromide. Elemental analysis, IR and NMR spectroscopies on silica micro-particles, atomic force microscopy, ellipsometry and profilometry on fused-silica wafers, as well as CE on fused-silica tubes were used to characterize the chemically modified silica substrate at different stages. We studied the effect of monomer concentration as well as cross-linker on the ability of the polymer film to reduce electroosmosis and to prevent protein adsorption (i. e., its non-fouling capabilities) and found that the former was rather insensitive to both parameters. Surface deactivation towards adsorption was somewhat more susceptible to monomer concentration and appeared also to be favored by a low concentration of the cross-linker. The results show that hydrophilic polyacrylamide and polyacrylate coatings of controlled thickness can be prepared by ATRP under very mild polymerization conditions (aqueous solvent, room temperature and short reaction times) and that the coated capillary tubes exhibit high efficiencies for protein separations (0.3–0.6 million theoretical plates per meter) as well as long-term hydrolytic stability under the inherently harsh conditions of capillary isoelectric focusing. Additionally, there was no adsorption of lysozyme on the coated surface as indicated by a complete recovery of the basic enzyme. Furthermore, since polymerization is confined to the inner capillary surface, simple precautions (e.g., solution filtration) during the surface modification process are sufficient to prevent capillary clogging.     

Xphos ligand and platinum catalysts: A versatile catalyst for the synthesis of functionalized β-(E)-vinylsilanes from terminal alkynes

Hydrosilylation of functionalized terminal arylalkynes with a variety of silanes catalyzed by PtCl₂ or PtO₂ in the presence of the air-stable and bulky Xphos ligand was investigated. Regardless of the electronic nature (electron withdrawing or donating group) and the position (o, m, p) of the substituents on the aromatic ring, a single β-(E)-styrylsilanes was obtained in good to excellent yields. The regioselectivity of the H-Si bond addition was found to be governed by steric effects induced by the bulky Xphos ligand. A dramatic regioselectivity was also observed when functionalized terminal aliphatic alkynes were employed as a substrate and in these cases regioisomeric β-(E)-vinylsilanes were generated with excellent selectivity.     

One-pot hydrosilylation-protodesilylation of functionalized diarylalkynes: a highly selective access to Z-stilbenes. Application to the synthesis of combretastatin A-4

An efficient stereoselective synthesis of Z-stilbenes has been developed from diarylalkynes via a new hydrosilylation-protodesilylation process. The scope and limitation of this method is presented to stereoselectively prepare a wide range of (Z)-stilbenes in a one-pot way is presented. A concise application to the preparation of combretastatin A-4 (CA-4), a vascular targeting agent inhibitor of tubulin polymerisation is described.     

Optimization of Click Chemistry of Ferrocene Derivatives on Acetylene‐Functionalized Silicon(100) Surfaces

The optimization of the reaction conditions for copper‐catalyzed azide‐alkyne ‘click’ cyclo‐addition reactions used to covalently confine substituted ferrocene derivatives on passivated silicon(100) surfaces is reported. Variations in the observed reaction yields and the extent of surface contamination as a function of the source of the copper catalyst and the solvent system used in the ‘click’ procedure were evaluated spectroscopically. The electronic communication between the ferrocene centre and the underlying semiconductor surface was investigated by means of cyclic voltammetry and found to be consistent with that expected for a well‐behaved and robust redox interface.