(Dicyclopentadiene) platinum(II) dichloride: An efficient catalyst for the hydrosilylation reaction between alkenes and triethoxysilane

(Dicyclopentadiene) platinum(II) dichloride was found to be an efficient hydrosilylation catalyst (homogeneous) upon a wide variety of functionalized alkenes and alkenes terminated with chemical moieties (diphenyl amino-, N-carbazol- and N-isoindoline-1,3-dione-). It is noteworthy that the hydrosilylation of aminated alkenes with triethoxysilane exhibited the yield of over 70% and the selectivity (γ-isomer/β-isomer) of more than 3/1. Due to steric hindrance lowering Markovnikov probability, the alkenes with big terminal moieties (diphenyl amino-, N-carbazol- and N-isoindoline-1,3-dione-) presented the high ratio of anti-Markovnikov isomers. The strategy of the hydrosilylation of the protected diamino chelating alkene was developed.     

Hybrid materials derived from divinylbenzene and cyclic siloxane

In this work, hybrid materials were synthesized as self-supported films from divinylbenzene and cyclic siloxane, in different compositions, by hydrosilylation reaction. These films showed good thermal and mechanical properties. Their glass transition temperatures were higher than those of conventional silicone networks, and dependent on divinylbenzene amounts. Films were homogeneous and no pores were observed by field emission electron scanning microscopy. Relationships between surface roughness and composition of the obtained films were discussed. The nanomorphology of the materials was studied by small angle X-ray scattering, showing polydispersed nano-sized heterogeneities. The gas permeability of the hybrid films was investigated, and the results suggested low permeable behaviour to gases, but high ideal selectivities to some pairs of gases, such as H₂/O₂.     

Selective Zinc-Catalyzed 1,2-hydroboration of N-heteroaromatics via a Non-Hydride Mechanism

A novel bidentate amine-imine ligand precursor LH has been synthesized. This compound was reacted with ZnMe₂ to generate the zinc methyl complex, LZnMe ( 4 ). The latter compound was fully characterized by NMR spectroscopy and single crystal X-ray diffraction. Compound 4 is a catalyst for the hydroboration and hydrosilylation of N-heterocycles, but with moderate catalytic activity. A more active catalyst, the zinc hydride complex LZnH ( 5 ) was synthesized by reacting the lithium salt LLi with ZnCl₂ followed by sequential reaction with tBuOK and PhMeSiH₂. Compound 5 catalyzes the selective 1,2-hydroboration of nitrogen heteroaromatics with decreased catalyst load and under mild conditions. Deuterium-labeling experiments and kinetic studies provided insight into the possible reaction mechanism. It is proposed that hydride transfer to the substrate proceeds directly from the reductant (borane) via a six-membered transition state facilitated by the catalyst, in which it plays an ambiphilic role, activating the substrate via coordination to the Lewis acidic zinc and enhancing the hydricity of the borane through coordination to the zinc hydride.     

Atroposelective Synthesis of Axially Chiral Styrenes by Platinum- Catalyzed Stereoselective Hydrosilylation of Internal Alkynes

Hydrofunctionalization of alkynes is one of the most efficient ways to access axially chiral styrenes with open-chained olefins. While great advances have been achieved for 1-alkynylnaphthalen-2-ols and analogues, atroposelective hydrofunctionalization of unactivated internal alkynes lags. Herein we reported a platinum-catalyzed atroposelective hydrosilylation of unactivated internal alkynes for the first time. With monodentate TADDOL-derived phosphonite L1 used as a chiral ligand, various axially chiral styrenes were achieved in excellent enantioselectivities with high E-selectivities. Control experiments showed that the NH-arylamide groups have significant effects on both the yields and enantioselectivities and could act as directing groups. The potential utilities of the products were shown by the transformations of the amide motifs of the products.     

Dendronized polystyrene supports for new catalytic systems

New catalytic systems based on tris(dimethylvinyl)methyl substituted polystyrene were prepared. Dendronized polystyrenes were obtained by modification of poly(styrene-co-chloromethylstyrene) precursors with LiC(SiMe₂CHCH₂)₃. Platinum was attached to the polymers via coordination to vinyl groups located on carbosilane moieties. Such the catalytic system makes an interesting alternative for heterogenous platinum catalysts (Pt/charcoal, Pt/C_act and Pt/Al₂O₃) and also to Karstedt’s catalyst, when used in hydrosilylation of vinylsilanes.     

Synthesis and hydrosilation of multi-vinyl branched siloxane for self-healing system

In this work, the preparation of α,ω-dichloride-terminated multi-vinyl branched siloxane 1 （yield： 57.1%） used for self-healing polymer composites were synthesized via ring-opening of 1,3,5,7-tetravinyl-1,3,5,7-tetramethyl-cyclotetrasiloxane （D4^vi） in the presence of vinylmethydichlorosilane （VM-32）. 1 was hydrogenated by aluminum lithium hydride （LiAlH4） to get self-healing monomer 2 （yield： 79.8%） which contained both Si-H bonds and Si-vinyl bonds. Then hydrosilation occurred between these two bands and finally silicone 3 was obtained, showing the potential of self-healing.     

Hydrosilylation of olefins over rhodium complex anchored over thioether-functionalized MCM-41

<正>The hydrosilylation of alkenes with triethoxysilane has been achieved at 120 C in the presence of 0.01 mol%of thioetherfunctionalized MCM-41 anchored rhodium complex,affording the corresponding addition products in 68-91%yields.This supported rhodium complex can be reused several times without noticeable loss of activity.Our system not only solves the basic problems of catalyst separation and recovery,but also avoids the use of phosphine ligands.     

Tri(t-butyl)phosphine-assisted selective hydrosilylation of terminal alkynes

<正>A highly efficient and regio-/stereoselective method of hydrosilylating terminal alkynes was developed using Pt(DVDS)-tri(t-butyl) phosphine catalyst system at room temperature.Trans-products or alpha-products were obtained almost exclusively depending on the alkynes and silanes employed.     

Mechanism of ketone hydrosilylation by Cu(I) catalysts: A theoretical study

The plausibility of the catalytic cycle suggested for the hydrosilylation of ketones by Cu(I) hydrides has been investigated by a theoretical DFT study. A model system made up of a CuH(PH₃)₂ catalyst, acetone and SiH₄ gives us the necessary insight into the intrinsic reactivity of the system. This reactivity is confirmed, by introducing the more rigid CuH[C₄H₄(PH₂)₂] catalyst, as well as tetra-coordinated, CuH(PH₃)₃ and CuH(PH₃)[C₄H₄(PH₂)₂] compounds. Computations show the activation of the copper fluoride pre-catalyst, as well as both steps of the catalytic cycle to involve a 4 center metathesis transition state as suggested in literature. These results show the reaction to be favored by the formation of a Van der Waals complex resembling the transition states. The formation of these latter is induced by stabilizing electrostatic interactions between those atoms involved in the bond breaking and bond forming. Both steps of the actual catalytic cycle show a free energy barrier of about 10 kcal/mol with respect to the isolated reactants, hereby confirming the plausibility of the suggested cycle. We have found a substantial overall exothermicity of the catalytic cycle of about 35 kcal/mol.     

Synthesis and characterization ofα-{3-[(2,3-dihydroxy) propoxy]propyl}-ω-butylpolydimethylsiloxanes

Hydrosilylation has been carried out between Si-H terminated polydimethylsiloxanes with narrow molecular weight distribution and protected 3-allyloxy-1,2-propanediol,and after subsequently alcoholyzed,α-{3-[(2,3-dihydroxy)propoxy]propyl}-ω-butyl -polydimethylsiloxanes with varying number of((Si(CH_3)_2-O) unit were obtained.At each step,the produced compounds were carefully characterized.The results showed that each step was successfully carried out and target products were achieved.