Hydrosilylation, trichlorosilane bases

Not surprisingly, chiral formamides emerged as prime candidates for the development of an asymmetric variant of this reaction. A selection of the most efficient amide catalysts based on amino acids is shown in Figure 7.4 representative examples of enantioselective hydrosilylation are collected in Tables 7.7 and 7.8. Proline-derived anilide 82a and its naphthyl analogue 82b, introduced by Matsu-mura [3c], produced moderate enantioselectivity in the reduction of aromatic ketimines with trichlorosilane at 10 mol% catalyst loading (Table 7.7, entries 1 and 2). Formamide functionality proved to be crucial for the activation of the silane, as the corresponding acetamides failed to initiate the reaction. 

Seyferth and coworkers 104 prepared a series of Si-based dendrimers up to the fourth generation. Employing the tetravalent nature of silicon, these macromolecules possessed a tetrahedral, four-directional core, as well as 1 — 3 branching centers. The divergent strategy (Scheme 4.52) utilized two repetitive transformations displacement of halide at silicon with vinylmagnesium bromide (vinylation) and Pt-catalyzed alkyl trichlorosilane formation (hydrosilylation). 

Pentacoordinate silicon, in the form of allyltrichlorosilane, in the presence of DMF or HMPA, also undergoes allylation with aldehyde [97,98], The Lewis base-promoted approach has the merit of operational convenience. Stereoselective formation of allylic trichlorosilanes is achieved by copper-catalyzed coupling of allylic chloride and trichlorosilane or by palladium-catalyzed hydrosilylation of 1,3-dienes (Sch. 56) [99],... 

SCHEME 18.25 Synthesis of borazine-based Si-B-C-N-H polymers by hydrosilylation of B-triethynylborazine with trichlorosilane and subsequent hydrogenation with LiAlH4 or aminolysis with methylamine, respectively." - 2 ... 

First attempts to achieve silyl enol ethers ) are known since the late 195O s when hydrosilylation-type procedures were applied to a,d-unsaturated ketones is—i is) based upon the observation by Duffaut and Galas ) that simple ketones are able to add trichlorosilane (2) under UV irradiation. These hydrosilylation reactions were widely expanded and intensively studied ). a,/3-unsaturated ketones react via 1,4-addition ) to silyl enol ethers ) affecting only the conjugated double bonds. It is worth mentioning that the employment of chiral catalysts induces an asymmetrical reaction " ) (Scheme 24). 

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) ... 

Keywords Transfer hydrogenation Organocatalysis Hantzsch ester Trichlorosilane Phosphoric acid Aminocatalysis Thioureas Lewis bases Reduction Hydrosilylation... 

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