Activation of CS2 and CO2 by Silylium Cations.

The hydride-bridged silylium cation [Et3 Si-H-SiEt3 ]+ , stabilized by the weakly coordinating [Me3 NB12 Cl11 ]- anion, undergoes, in the presence of excess silane, a series of unexpected consecutive reactions with the valence-isoelectronic molecules CS2 and CO2 . The final products of the reaction with CS2 are methane and the previously unknown [(Et3 Si)3 S]+ cation. To gain insight into the entire reaction cascade, numerous experiments with varying conditions were performed, intermediate products were intercepted, and their structures were determined by X-ray crystallography. Besides the [(Et3 Si)3 S]+ cation as the final product, crystal structures of [(Et3 Si)2 SMe]+ , [Et3 SiS(H)Me]+ , and [Et3 SiOC(H)OSiEt3 ]+ were obtained. Experimental results combined with supporting quantum-chemical calculations in the gas phase and solution allow a detailed understanding of the reaction cascade.