Selective CO 2 Splitting by Doubly Reduced Aryl Boranes to Give CO and [CO 3 ] 2−

Alkali metal salts M 2 [ 1 ] (M=Li, Na) of doubly reduced 9,10‐dimethyl‐9,10‐dihydro‐9,10‐diboraanthracene ( 1 ) instantaneously add the C=O bond of CO 2 across their boron centers to furnish formal [4+2]‐cycloadducts M 2 [ 2 ]. If only 1 equiv of CO 2 is supplied, these products are stable. In the presence of excess CO 2 , however, C−O bond cleavage occurs and an O 2− equivalent is transferred to CO 2 to furnish CO and [CO 3 ] 2− . With M=Li, Li 2 CO 3 precipitates and the neutral 1 is liberated such that it can be reduced again to establish a catalytic cycle. With M=Na, [CO 3 ] 2− remains coordinated to both boron atoms in a bridging mode (Na 2 [ 4 ]). A mechanistic scenario is proposed, based on isolated intermediates and model reactions.