An Isolable Diborane(4) Compound with Terminal B–H Bonds: Structural Characteristics and Electronic Properties

The first isolable diborane(4) containing terminal B–H bonds, protected by the bulky 1,1,7,7-tetramethyl-3,3,5,5-tetrapropyl-s-hydrindacen-4-yl (MPind) groups, was synthesized as air- and moisture-sensitive colorless crystals. The structure and bonding nature of this H-terminal diborane(4), characterized by X-ray crystallography, NMR studies, and DFT calculations, were compared to those of the previously reported isomer, a doubly H-bridged butterfly-shaped diborane(4) bearing the less bulky 1,1,3,3,5,5,7,7-octaethyl-s-hydrindacen-4-yl (Eind) groups. The two distinct structures of these dihydro-diborane(4) compounds may be primarily attributed to the intramolecular steric effects of the bulky protecting groups.