Isolable Dibenzo[]disilapentalene with a Dichotomic Reactivity toward CO.

The first dibenzo[,]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 CO, depending on the reaction conditions. While one product results from fixation of two CO molecules across one Si═C bond, two different products could be isolated from the reaction of three CO molecules with both Si═C bonds. The mechanism has been uncovered by DFT calculations.