Secondary hydrosilane

Although a transition metal was not involved, the dehydrocoupling of the secondary hydrosilane, 1,1-dihydrotetraphenylsilole, to polymers with Mw values ranging from 4000 to 6000 (polydispersities ranged between 1.1 and 1.2) in the presence of catalytic quantities of Red-Al, L(N or K)-Selectride or Super-Hydride has been reported.1353 This is the only currently published example of polymeric material produced from a secondary silane. It is interesting that this secondary silane is a heterocyclic system where steric interactions (from substituents at silicon) have been reduced, although the fact that there are phenyl groups on the a-carbon, makes this a rather extraordinary result. 

The most characteristic reaction of butadiene catalyzed by palladium catalysts is the dimerization with incorporation of various nucleophiles [Eq. (11)]. The main product of this telomerization reaction is the 8-substituted 1,6-octadiene, 17. Also, 3-substituted 1,7-octadiene, 18, is formed as a minor product. So far, the following nucleophiles are known to react with butadiene to form corresponding telomers water, carboxylic acids, primary and secondary alcohols, phenols, ammonia, primary and secondary amines, enamines, active methylene compounds activated by two electron-attracting groups, and nitroalkanes. Some of these nucleophiles are known to react oxidatively with simple olefins in the presence of Pd2+ salts. Carbon monoxide and hydrosilanes also take part in the telomerization. The telomerization reactions are surveyed based on the classification by the nucleophiles. 

The Corey group has reported that Cp2TiCl2/nBuLi effectively catalyzes the high yield alcoholysis of primary, secondary, and tertiary silanes with a variety of alcohols under mild reaction conditions.160 All Si-H functionalities are replaced with alkoxy groups in reactions of ethanol and phenol, although increased temperatures and/or reaction times are required for highly substituted hydrosilanes. The system also appears to be influenced... 

Although the silylformylation of aldehydes is catalyzed by [Rh(COD)Cl]2 or [Rh(CO)2Cl]2, no secondary silylformylation of /i-silylenals (316-318) takes place, probably due to the electronic nature of the aldehyde functionality conjugated to olefin moiety (vide supra). Direct comparison of the reactivity of acetylene and aldehyde functionalities is performed using alkynals328. The reactions of 5-hexyn-l-al, 6-heptyn-l-al and 7-octyn-l-al with different hydrosilanes catalyzed by Rh or Rh—Co complexes at... 

Reduction of secondary amides by Ru-catalysis to provide simple secondary amines or tertiary amines is dependent on the hydrosilane used. ... 

Reductions. The InCIj-Bu SnH/PhjP combination (catalytic in indium) reduces acid chlorides to aldehydes." Aryl ketones and secondary benzyl alcohols are deoxygenated with hydrosilanes using InCl, as cataly.st." Deoxygenative allylation of aryl ketones occurs when allyltrimethylsilane is added. ... 

Heating a tertiary alcohol with l-(trimethylsilyl)iniidazole (abbreviated TMSIM. by-product imidazole) at 100 °C accomplishes O-trimethylsilylation even in the presence of a trisubstituled oxirane [Scheme 4.10].Tetrabutylammonium fluoride (TBAP) catalyses the 0-silylation of alcohols with various silazanes, including l-(trimethylsilyI)imidazole, so that silylation takes place at room temperature in DMF [Scheme 4.11]. In the absence of TBAF, no silylation occurs. The use of more hindered silazanes such as the bissilyl derivative of 5,5-dimethyIhy-dantoin allows regioselective TMS or TBS protection of primary hydroxyl groups in the presence of secondary and tertiary ones. Hydrosilanes and disilanes can be used instead of silazanes in TBAF-caialysed protection of primary and secondary alcohols. ... 

Decreasing of the hydrosilane reactivity in the order of primary > secondary > tertiary... 

To illustrate the serious problem, a case in point is the hydrosilation of allyl chloride which produces equimolar quantities of propene and a chlorosilane as the primary byproducts [Eq. (37)]. The propene can undergo hydrosilation itself leading to a secondary byproduct. Some of the best yields of 3-chloropropylsilane lie in the range 70-80% with a few combinations of hydrosilane and catalyst, but for many useful hydrosilanes, the primary byproducts can be 60% or higher. 

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