Reduction of CO2 with silanes

Organic synthesis via transition metal complex-catalyzed electrochemical and photochemical reduction of CO2 has been developed [2,122b, 145-147]. Among transition metal complexes, ruthenium bipyridine complexes show high catalytic activity a typical reaction is shown in Eq. 11.79. [Ru(bpy)2(CO)2] and [Ru(bpy)2(CO)Cl] efficiently catalyze the electrochemical reduction of CO2 to CO and HC02. The nature of the products is dependent upon the pH of the solution. A catalytic cycle involving [Ru(bpy)2(CO)]°, ]Ru(bpy)2(C0)(C02 )] and [Ru(bpy)2(C0)C02H] was proposed (Eq. 11.79) [1461]. 

The electrochemical reduction of CO2 catalyzed by ]Ru(bpy)2(qu)(CO)] (qu = quinoline) in the presence of (CH3)4N or CH3I in dry CH3CN produces CH3COCH3, CH3COCH2CO2 and HCO2 . The fotur-carbon component CH3C0CH2C02 is derived from acetone via a carboxylation reaction by [Ru(bpy)2-(qu)(CO)] [146e,f]. 

Acetone is formed by the double-alkylation of [Ru(bpy)2(L)(CO)] (L= quinoline [146e] or naphthyridine [146d]) with CH3I or (CH3)4N (Eq. 11.81). 

In the photochemical reduction of CO2, mthenium complexes show efficient catalytic activity [148]. Simultaneous photogeneration of CO and H2 takes place by the visible-light irradiation of systems containing the [Ru(bpy)3] complex as a photosensitizer, the Co(II) species as a homogeneous catalyst, which mediates CO2 and H2O reduction via the formation of a Co(I) intermediate, and tertiary amines as electron donors (Eq. 11.82) [148bj. 

In 1986, Sasaki and Dixneuf reported the first example of the Ru3(CO)i2-catalyzed formation of vinyl carbamate from terminal acetylene, CO2 and secondary amines (Eq. 11.83) [149, 150]. 

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