Isolable Dibenzo[a,e]disilapentalene with a Dichotomic Reactivity toward CO2.

The first dibenzo[a,e]disilapentalene with two Si═C moieties in the heteropentalene core has been prepared. Its solid-state structure and density functional theory (DFT) calculations revealed that the Si═C bonds are involved in an expanded π-conjugated system. The Si═C bonds show a distinguished reactivity toward CO2, depending on the reaction conditions. While one product results from fixation of two CO2 molecules across one Si═C bond, two different products could be isolated from the reaction of three CO2 molecules with both Si═C bonds. The mechanism has been uncovered by DFT calculations.