Reactions Starting from Insertion into a Rh-Si Bond

4 Design of Reactions Starting from Insertion into a Rh-Si Bond 117 Me 

The aldol-type coupling described in the previous section was completely suppressed under CO (20 atm.). However, Murai and co-workers have reported a new approach to enoxysilanes based on the coupling of an alkene, a hydrosilane, and CO in the presence of Co2(CO)g [14]. This conspicuous difference in catalytic ability between rhodium and cobalt stimulated us to examine the incorporation of CO and a hydrosilane in the presence of rhodium. 

Siiyiformyiation of acetylenic C-C triple bonds was investigated in the first stage of the project. The reaction proceeded smoothly to selectively form y9-silylalkenals by a one-pot operation utilizing a molar equivalent each of an alkyne and hydrosilane with a catalytic amount (0.1-1 mol%) of Rh4(CO)j2 under CO ( 5 atm.) (Eq. 7). This type of CO incorporation is suitable for a variety of hydrosilanes and alkynes, including both terminal and internal types. Some examples are summarized in Tab. 6.3 [15a,bj. 

A moderate pressure ( 5 atm.) of CO in the reaction system leads to the selective formation of 29, while alkynes undergo rhodium-catalyzed hydrosilylation with a hydrosilane to afford vinylsilanes in the absence of CO. The presence of the rhodium complex is crucial for the smooth progression of siiyiformyiation, regardless of the presence of mononuclear or polynuclear complexes. This generalization is supported by the studies of many others [15]. The most important feature of this reaction is the excellent regioselectivity, which favors the formylation of the internal sp-carbon of the acetylenic bond of terminal 

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Design of Reactions Starting from Insertion into a Rh-Si Bond 125 Tab. 6.7 Silylative cyclocarbonylation of 63 catalyzed by Rh4(CO)i2-... 

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