Selective Formation of a 1,2-Diborane(4) and Alcohol-Driven B─B Bond Cleavage to Generate H2.

Diborane(4) chemistry continues to reveal new aspects of the reactivity of electron-deficient p-block elements. These systems are capable of bond activation and ligand rearrangement-processes once thought to be exclusive to transition metals. Here, we show that reaction of B2Cat2 (Cat = benzene-1,2-diolate) with mesityllithium (MesLi; Mes = 2,4,6-trimethylphenyl) affords an unusual 1,2-disubstituted diborane(4), Mes-B(μ-Cat)-B-Mes. Structural, spectroscopic, and computational data indicate that the catecholate co-ligand favors formation of the 1,2-isomer. Subsequent reaction with alcohols (ROH) cleaves the B─B bond in this compound to form CatBMes and MesB(OR)2 via B(II) → B(III) oxidation, releasing H2. These results expand the reactive landscape of O,O-chelating diborane(4) systems, establish an entry into 1,2-diborane(4) frameworks, and demonstrate that their distinct reactivity toward alcohols can be exploited to differentiate the chemistry of 1,1- and 1,2-diborane(4) isomers.