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What makes diborane different from typical compounds with ordinary two-atom bonds?

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A labeled diagram of the periodic table entry for boron shows its atomic number 5, symbol B, electron configuration, atomic weight range, and classification as a solid, weakly acidic, other nonmetal with a rhombohedral crystal structure at room temperature. — boron Properties of boron.

Diborane ( $B_{2} H_{6}$ ) differs from typical compounds because it is an electron-deficient substance that utilizes multicentre bonding rather than relying solely on ordinary two-atom, two-electron covalent bonds.12

In a typical chemical bond, an electron pair is localized between two atoms. In contrast, the structure of diborane features three-centre, two-electron bonds, where a single pair of electrons is delocalized and shared among three atoms—specifically, two boron atoms and one hydrogen atom in a $B -- H -- B$ bridge.123

This unique bonding capability allows boron to form complex polyhedral structures, such as closo-, nido-, and arachno-boranes, which are distinct from the simple chain and ring configurations found in carbon-based compounds. The understanding of these clusters and the delocalized nature of their electrons has been fundamental to rationalizing the chemistry of various inorganic and organometallic compounds.13