Antiaromatic Dithieno-1,2-dihydro-1,2-diborin Splits Diatomic Hydrogen

B,B-Dimesityl-substituted dithieno-1,2-dihydro-1,2-diborin was synthesized and its properties and reactivity were studied. Owing to the noticeably electron-deficient and antiaromatic character of the 1,2-dihydro-1,2-diborin ring, this compound was found to homolytically cleave diatomic hydrogen (H2) gas at ambient temperature under 1 atm to afford a hydrogen-bridged bis(borane). This reaction was accompanied by a dramatic color change from dark green to yellow in addition to a turn-on fluorescence response. Induced by its strong electron affinity and antiaromaticity, dithieno-1,2-dihydro-1,2-diborin was found to readily split diatomic hydrogen under mild conditions. The disruption of the antiaromaticity and the fixation of the bithiophene moiety triggers the reaction product, which is a hydrogen-bridged bis(borane), to drastically decolorize and emit bluish purple light.