Alkenes trichlorosilane

The reagent titanocene dichloride reduces carboxylic esters in a different manner from that of 10-86, 19-36, or 19-38. The products are the alkane RCH3 and the alcohol R OH. The mechanism probably involves an alkene intermediate. Aromatic acids can be reduced to methylbenzenes by a procedure involving refluxing first with trichlorosilane in MeCN, then with tripropylamine added, and finally with KOH and MeOH (after removal of the MeCN). The following sequence has been suggested ... 

The Pd/MOP combination has proved active for the asymmetric hydrosilylation of cyclic alkenes and dienes. Thus treatment of norbornene with HSiCl3 at 0 °C for 24 h in the presence of 0.01 mol.% of M eO-MOIV[Pd(// -C3H5)Cl]2 gave quantitative yield of evo-2-(trichlorosilyl)norbornane oxidation produced the corresponding alcohol in 93% ee (Equation (12)). Lowering the temperature (to — 20 °C) increased this to a 96% ee. Both mono- and difunctionalization of nbd has proved possible, depending upon the quantity of trichlorosilane used (Scheme 22). In both reactions, extremely good enantioselectivities are observed 113... 

The chemistry of silicone halides was recently reviewed by Collins.13 The primary use for SiCU is in the manufacturing of fumed silica, but it is also used in the manufacture of polycrystalline silicon for the semiconductor industry. It is also commonly used in the synthesis of silicate esters. T richlorosilane (another important product of the reaction of silicon or silicon alloys with chlorine) is primarily used in the manufacture of semiconductor-grade silicon, and in the synthesis of organotrichlorosilane by the hydrosilylation reactions. The silicon halohydrides are particularly useful intermediate chemicals because of their ability to add to alkenes, allowing the production of a broad range of alkyl- and functional alkyltrihalosilanes. These alkylsilanes have important commercial value as monomers, and are also used in the production of silicon fluids and resins. On the other hand, trichlorosilane is a basic precursor to the synthesis of functional silsesquioxanes and other highly branched siloxane structures. 

The regioselectivity (branched linear) for the addition of trichlorosilane to 1-alke-nes is in a range of 80 20 93 7 [67], In the case of 1-aryl-1-alkenes such as (2-chlorophenyl)ethene (124), l-pheny)prop-l-ene (125), and indene, the regioselectivity reaches as high as 99 1, although the enantioselectivity for the formation of the correspond-... 

Unlike trichlorosilane, dichlorosilane is very effective in ruthenium-complex-catalyzed addition to 1-alkenes (Eq. 1) [8]. 

Catalyzed addition of trichlorosilane to terminal alkenes and alkynes, followed by the addition of an aqueous solution of potassium fluoride, produces highly reactive organopentafluorosilicates (Scheme 3). 

The hydrosilylation-oxidation of simple unfunctionalized alkenes has not been widely used for the diastereoselective preparation of alcohols, probably because it would not in general be expected to give very different results to hydroboration oxidation. One example which has been reported is the exo-selective hydrosilylation of norbornene (1) with trichlorosilane and hexachloroplatinic acid6, followed by oxidation to c.vo-norbornanol (2)1. 

Early work involving simple alkenes employed the catalyst dichloro (y )-AUV-dimethyl-l-[(S)-2-(diphenylphosphino)ferrocenyl]ethylamine palladium(II), 1 (often abbreviated to Pd-Cl2[(i )-(S)-PPFA]). When applied to the hydrosilylation of norbornene with trichlorosilane, it yielded an adduct which was converted to a pentafluorosilicate and thence to the alcohol 2 in 25% overall yield and with 50% ee26. 

Improved results were achieved when trichlorosilane was treated with alkenes in the presence of a ferrocenyl-palladium catalyst, [(7 )-(5)-PPFA]PdCl2 8a. In the ease of unsymmetrica alkenes, Markovnikov addition products are formed. 

Asymmetric Hydrosilylation of Alkenes. The palladium complex PdCl2[(/ )-(5)-PPFA] catalyzes the asymmetric hydrosilylation of norbornene, styrene, and 1,3-dienes (eq 3). The hydrosilylation of 1-phenyl-1,3-butadiene with Trichlorosilane proceeds regioselectively in a 1,4-fashion to give (Z)-1-phenyl-1-silyl-2-butene of 64% ee. 

The addition reaction of hydrosilanes to alkenes and alkynes is called hydrosilylation, a reaction which was discovered when a mixture of 1-octene and trichlorosilane was heated in the presence of diacetyl peroxide. This reaction is particularly useful for the synthesis of organosilicon compounds. Since then, a variety of catalysts and conditions have been reported. Characteristic features of the reaction are discussed in this chapter. 

Tertiary amines catalyze e addition of trichlorosilane with electron deficient alkenes, e.g. acrylonitrile, and such alkynes as phenylethyne (Scheme 4). The reaction is understood in terms of the nucleophilic addition of a trichiorosilyl anion (17), which is generated by proton abstraction from a zwitterion (18) by tertiary amines. ... 

Hydrosilylation of monosubstituted alkenes with palladium catalysts and trichlorosilane follows a course which favors branched products. By using a chiral phosphine ligand, asymmetric reaction is feasible. Initially, menthyldiphenylphosphine (MDPP, 93) and neomenthyldiphenylphosphine (NMDPP, 94) were employed with little success. Later, (/ )-/VA -dimethyl-l-[(S)-2-diphenylphosphinoferroce-nyl]ethylamine [(R)-(S)-PPFA] (95) and its enantiomer were prepared, and these have proved to be the... 

Trichlorosilanes are readily transformed to the pentafluorosilicate compounds (100) and (101) by reaction with excess potassium fluoride. The C—Si bond of the hexavalent organosilicon species is converted into a C—X (X = halogen or heteroatom like hydroxy and alkoxy) or a C—C bond. Thus, through the hydrosilylation reaction net transformations of alkenes and alkynes to halides, ethers and alcohols, as well as the construction of carbon frameworks, is easily achieved (Scheme 18). ... 

Simple silanes, such as trichlorosilane (5), have been used to reduce the complexes formed by phosphorus pentachloride and alkenes. The products are alkenyl-(dichloro)phosphines (6), although the yields are quite variable. The related chlorophosphines (7) have been prepared from alkyl acetates. ... 

Wagner and Pines [27] carried out the hydrolysis of trichlorosilane on the previously wetted silica surface with a specific surface area of about 300 m /g and obtained samples containing from 7.4 to 16.7 % wt. of HSi03/2. The surface of the silica modified in this way exhibits properties inherent in polyhydrosiloxane, namely hydrophobic nature, ability to evolve hydrogen under the action of an alkali, to reduce silver ions and other ions, and to add alkenes at high temperatures (about 450°C). Thus, in the case of the silica surface with a deposited layer of polyhydrosiloxane the chemisorption of ethylene, pentene, octene, cyclohexene, and butadiene has been carried out. 

In literature there are data on the homogeneous thermal addition of trichlorosilane to aliphatic and cyclic alkenes as well as to alkodienes with isolated and conjugated double bonds which proceeds under high pressures at 280-300°C [161-163]. Voronkov et al. [164] succeeded in carrying out the thermal addition of trichlorosilane to phenylacetylene in a polar solvent at 200°C while without the solvent the reaction proceeds at 500°C. The authors of Refs.[27,165] have performed the addition of ethylene, propylene, butene, butadiene, octene to silica surface at elevated temperatures. These chemical processes may be referred to as reactions of solid-phase thermal hydrosilylation. Unfortunately, these works have not received a large development effort. 

An aminated silica (13 in Scheme 1) was treated with H2PtCI6 and RhCl(PPh3)3 to give the aminated silica-supported platinum (13-Pt) and rhodium (13-Rh) catalysts, respectively. The metal contents in the immobilized catalysts were 0.05 wt% for Pt and 0.35-0.49 wt% for Rh depending on the structure of amine moiety. The hydrosilylation of 1-alkenes, allyl chloride and allyl chloroacetate was studied with trichlorosilane and triethoxysilane. It is noteworthy that 13-Rh (NR2 = morpholino) retains its high catalytic activity even after being used nine times183. 

Semihydrogenation of alkynes The surface of silica gel is covered with hydrosilane groups on reaction with trichlorosilane. The solid-supported silane effects hydrogenation of alkynes to (Z)-alkenes selectively. 

One of the most common methods for the preparation of enantiomerically enriched organosilanes is by palladium-catalysed asymmetric hydrosilylation of alkenes in the presence of trichlorosilane. This area has been dominated by the use of monodentate phosphorus-based ligands and, in particular, Hayashi s MOP ligand/palladium catalyst combination offers a high level of enantioselectivity. The MOP ligands include MeO-MOP (2.139), H-MOP ligands such as (2.140) ... 

Representative alkene hydrosilylation reactions carried out with the MOP ligands are identified in the following schemes. The low catalyst loading in many cases is noteworthy. Norbornene (2.145), dihydrofuran (2.146), styrene (2.147) and cy-clopentadiene (2.148) are all converted into the hydrosilylated derivatives with good to excellent enantioselectivity. In most cases, the trichlorosilanes were deriva-tised into the corresponding alcohols, although the trichloroallylsilane (2.152) was reacted with benzaldehyde to give the addition product (2.156). 

---