It is an obscure boron hydride cluster, especially relative to the heavily studied pentaborane(9) (B5H9).

With two more hydrogen atoms than nido-pentaborane(9), pentaborane(11) is classified as an arachno- cluster.

[1] Like many boron hydride clusters, pentaborane(11) was originally obtained from the pyrolysis of diborane.

A more systematic synthesis entails treatment of [B4H9]− with boron tribromide.

The Lewis acid abstracts hydride to give unstable B4H8, the precursor to B5H11:[2]