Zinc and Magnesium Catalysts for the Hydrosilylation of Carbon Dioxide.

The terminal zinc and magnesium hydride compounds, [κ3 -TismPri Benz ]ZnH and [TismPri Benz ]MgH, which feature the tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl ligand, react with B(C6 F5 )3 to afford the ion pairs, {[TismPri Benz ]M}[HB(C6 F5 )3 ] (M = Zn, Mg), which are rare examples of these metals in trigonal monopyramidal coordination environments. Significantly, in combination with B(C6 F5 )3 , {[TismPri Benz ]M}-[HB(C6 F5 )3 ] generates catalytic systems for the hydrosilylation of CO2 by R3 SiH to afford sequentially the bis(silyl)acetal, H2 C(OSiR3 )2 , and CH4 (R3 SiH = PhSiH3 , Et3 SiH, and Ph3 SiH). In contrast to many other catalysts for these transformations, both the zinc and magnesium catalytic systems are active at room temperature, and the latter provides the first example of catalytic hydrosilylation of CO2 involving a magnesium compound. Also of note, the selectivity of the catalytic systems may be controlled by the nature of the silane, with PhSiH3 favoring CH4 , and Ph3 SiH favoring the bis(silyl)acetal, H2 C(OSiPh3 )2 .