Hydrosilylation functional alkenes used

The C—Si bond formed by the hydrosilation of alkene is a stable bond. Although it is difficult to convert the C—Si bond to other functional groups, it can be converted to alcohols by oxidation with MCPBA or H2O2. This reaction enhances the usefulness of hydrosilylation of alkenes [219], Combination of intramolecular hydrosilylation of allylic or homoallylic alcohols and the oxidation offers regio- and stereoselective preparation of diols [220], Internal alkenes are difficult to hydrosilylate without isomerization to terminal alkenes. However, intramolecular hydrosilation of internal alkenes can be carried out without isomerization. Intramolecular hydrosilylation of the silyl ether 572 of the homoallylic alcohol 571 afforded 573 regio- and stereoselectively, and the Prelog-Djerassi lactone 574 was prepared by applying this method. 

The catalyst activity decreased with increasing polymer crystallinity. A high regioselectivity of the catalyst in the hydrosilylation of alkenes towards formation of the linear products was achieved due to the favorable microporous structure of the polyamide supports with pore size of 10-20. The stereoselectivity of the reaction can be reversed by a proper choice of donor functions in a polymer support, for example the traditional cis-selectivity of Rh catalysts in hydrosilylation of phen-ylacetylene was changed to trans-selectivity by use of a 2,5-py instead of a 2,6-py moiety. The polyamide-supported catalysts showed high stability through 6-9 synthesis runs [25]. 

We sought to examine the enzymatic dioxygenation of aryl silanes using a number of different aromatic dioxygenases in order to determine if such transformations were possible and to define the substrate-specificity profile. We were also motivated by the rich chemistry of silicon-based materials, which includes the hydrosilylation of alkenes and ketones, the addition of electrophiles to vinyl and allyl silanes, and palladium catalyzed cross-coupling of vinyl silanes with aryl halides (13). As a result, silyl functional cw-diols have potential as chiral intermediates for drug development, as polymer precursors/modifiers and as elements in non-linear optical materials. 

In a manner similar to platinum ones, rhodium—carbene complexes have been recently tested in the hydrosilylation of alkenes and alkynes (3). Especially, rhodium complexes with N-heterocyclic carbene (NHC) ligands have attracted considerable attention. Their performance is comparable with that of phosphine complexes. The following exemplary ligands were used 1,3-imidazoylidene chelate bis(imidazolinum-carbene) phosphine-functionalized NHC alkylammonium-imidazolium chloride salts NHC pincer complexes, pyridine-functionalized N-heterocyclic carbenes (also with iridium), and bis(dichloroimidazolylidene) (also with iridium). 

On the other hand, hydrosilylation of alkenes by hydridosub-stituted POSS (la) proved to be an effective method for the synthesis of monofunctionalized silsesquioxanes (8) (eg, in the presence of Pt-Karstedt catalyst) or their octafunctionalized analogs with the same or different functional groups (9) (eg, in the presence of Rh(l) catalyst) (Scheme 10.3). Due to higher catalytic reactivity, more the commercial availability and ease of handling hydridosubstituted spherosilicates, ie, POSS with —SiOMe2— spacer are mostly used in the hydrosilylation process. 

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. 

Although the hydridorhodacarborane is formally a rhodium (III) derivative, it functions as a facile catalyst in alkenc isomerization, hydrogenation, hydroformylation, and hydrosilylation reactions 80). This catalyst system is extremely stable and may be recovered quantitatively from alkene isomerization and hydrogenation reactions. In addition to these reactions, the hydridorhodacarborane is very effective in the catalysis of deuterium exchange at terminal BH positions 59). These discoveries may soon lead to industrially useful metallocarborane catalysts. 

The ruthenium carbene complex (Grubbs catalyst) which has shown high efficiency in alkene methathesis and related processes, since it displays tolerance toward a wide variety of common functional groups, has also appeared of synthetic utility in the hydrosilylation of ketones to yield silyl ethers-one of the most widely used classes of protecting groups in synthetic chemistry (Eq. 97) [ 151 ]. The reaction requires temperatures above 50 °C, which generate a slightly increased amount of silylated by-products. 

The addition of a silicon compound such as R3SiH to alkene functionality, as shown by reaction 7.25, is used widely in silicone polymer manufacture and is called the hydrosilylation reaction. Although hydrosilylation was discovered in 1947, the first homogeneous catalyst, H2PtCl6 (1-10%), in 2-propanol was reported in 1957 from the laboratories of Dow Coming. 

Catalytic hydrosilylation involves addition of a Si-H bond to an unsaturated substrate (equation 99). Alkene hydrosilation is a useful Si-C bond-forming reaction that has been extensively reviewed8,195,213,261 -263. It may be used to introduce functional groups... 

In recent years hydrosilylation of various organic carbonyl compounds has made considerable progress and became a major tool of synthetic organic and organosilicon chemistry [76-78], in particular with respect to the functionalization of polymers [79]. It could be demonstrated in the previous section that mononitrosyl Re(l) complexes are active in dehydrogenative sUylation reactions of alkenes. In comparison, the hydrosilylation of the polar double bonds of ketones revealed great activities using mononitrosyl Re(l) complexes [80]. 

The ruthenium-catalyzed hydrosilylation/protodesilylation protocol is a useful method for stereoselective internal alkyne (cycloalkyne) reduction to (E)-alkenes [(iJ)-cycloalkenes] and is a complement to the cis selectivity observed in the Lindlar reduction (eqs. (27) and (28)) (184,185). The utility of this reaction sequence is attributed to the fact that many of the knovra methods for transforming ahquies to ( )-alkenes either have poor selectivity or are incompatible with common functional groups. 

Thermal hydrosilylation provides a means to place a wide variety of organic functional groups on a porous Si surface, including carboxylic acid or ester groups that then allow further chemical modification (Buriak 2002). A requirement of the reaction is that the surface contain Si-H species to react with the alkene or alkyne thus it is important to use freshly etched porous Si and to exclude oxygen and water from the reaction. 

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