Boron-based stepwise dioxygen activation with 1,4,2,5-diazadiborinine

Activation of dioxygen (O₂) by 1,4,2,5-diazadiborinine 1 is reported. Two boron centers in 1 undergo a formal [4 + 2] cycloaddition with O₂ at room temperature affording a bicyclo[2.2.2] molecule 2 featuring a B-O-O-B unit. Treatment of 2 with an additional equivalent of 1 leads to the cleavage of the O-O bond in 2 concomitant with the formation of two B-O bonds to yield 4 involving the extremely rare B₄C₂N₂O₂ ten-membered rings. A series of these reactions demonstrate the stepwise scission of the O═O π-bond and the O-O σ-bond of O₂.