Alkynes hydrosilylations, triethylsilane

Ruthenium complexes do not have an extensive history as alkyne hydrosilylation catalysts. Oro noted that a ruthenium(n) hydride (Scheme 11, A) will perform stepwise alkyne insertion, and that the resulting vinylruthenium will undergo transmetallation upon treatment with triethylsilane to regenerate the ruthenium(n) hydride and produce the (E)-f3-vinylsilane in a stoichiometric reaction. However, when the same complex is used to catalyze the hydrosilylation reaction, exclusive formation of the (Z)-/3-vinylsilane is observed.55 In the catalytic case, the active ruthenium species is likely not the hydride A but the Ru-Si species B. This leads to a monohydride silylmetallation mechanism (see Scheme 1). More recently, small changes in catalyst structure have been shown to provide remarkable changes in stereoselectivity (Scheme ll).56... 

Among the many available procedures for preparing alkenylsilanes are hydrosilylation of alkynes and partial reduction of alkynylsilanes. Hydrosilylation of 1-alkynes with triethylsilane in the presence of catalytic chloroplatinic acid results in regioselective... 

Additional Hydrosilylations. Hydrosilylations of terminal alkynes with triethylsilane (eq 1) have been improved in terms of their regio- and stereocontrol as well as in other aspects of their operation. Through the employment of Pt(DVDS), Pt-catalyzed hydrosilylations of 1-alkynes can now be performed at room temperature and in water with very high selectivity for the ( )-/3-vinylsilanes (eq 20). It has also been shown that Pt02 catalyzes the internal hydrosilylation of aryl alkynes under orthosubstituent regiocontrol (eq Strong preference for the... 

Lewis acids have also been demonstrated to catalyze terminal and internal alkyne hydrosilylation. Aluminum chloride and EtAlCl2 were found to be very active catalysts for the hydrosilylation with triethylsilane producing the corresponding (Z)-vinylsilane with high regio- and stereoselectivieties as a result of trans addition (4). 

Reductive decomplexation/ Although the common practice for removal of the hexacarbonyldicobalt residue from alkyne complexes involves mild oxidants, it is also possible to convert the complexes to free (Z)-alkenes with BUjSnH. If triethylsilane is used the decomplexation is followed by in situ hydrosilylation. 

The intermediacy of the complex [Os(SiEt3)Cl(H2)(CO)(P Pr3)2] in the catalytic hydrosilylation of phenylacetylene was first observed by Oro and co-workers when the neutral hydride [OsHCl(CO)(P Pr3)2] was reacted with triethylsilane and the alkyne [81]. A theoretical study of silane addition across the C-C triple bond has also been reported [82] and the general scope of this reaction has been amply reviewed [17],... 

Hydrosilylations. Addition of triethylsilane across multiple bonds occurs under the influence of a large number of metal catalysts. Terminal alkynes undergo hydrosilylations easily with triethylsilane in the presence of platinum, rhodium, ruthenium, osmium, or iridium catalysts. For example, phenylacety-lene can form three possible isomeric hydrosilylation products with triethylsilane the (Z)-/3-, the and the a-products... 

To further substantiate the validity of this correlation, we decided to probe the influence of the cr-donating ability of the NHC on the regioselectivity. For this purpose, the hydrosilylation of phenylacetylene by triethylsilane imder the standard conditions was performed with three catalysts possessing the same limited steric hindrance but completely different electronic properties (Figure 5.18) [32]. As can be seen, identical selectivities were obtained, despite the fundamental differences between the catalysts, thereby reinforcing our proposal that the regioselectivity of the hydrosilylation of alkynes is controlled essentially by steric parameters. It is noteworthy that the major isomer obtained in this case is the a-adduct. This is not surprising since arylacetylenes are known to lead... 

Hydrosilylation reactions catalyzed by achiral NHC-Rh complexes were first reported by Lappert and Maskell in 1984, who found 96 and 97 effective for ketones and alkynes (Figure 13.16). In recent studies by Ozdemir and coworkers, different NHC-Rh complexes were applied to the hydrosilylation of acetophenone derivatives with triethylsilane and bimetallic complex 98 was particularly efficient. Also, Rh complexes 99, bearing a hydrophilic tetra-ethylene glycol and/or hydrophobic long-chain alkyl-functionalized NHC, were active catalyst for the hydrosilylation of ketones with Ph2SiH2. ... 

---