What characteristics do you expect from an electron-deficient hydride with respect to its structure and chemical reactions?

(N/A) An electron-deficient hydride does not have sufficient electrons to form a regular bond in which two electrons are shared by two atoms,e.g.,$B_{2}H_{6}$,$Al_{2}H_{6}$,etc.
These hydrides cannot be represented by conventional Lewis structures. $B_{2}H_{6}$,for example,contains four regular $2c-2e$ bonds and two $3c-2e$ (three-centered-two-electron) bonds.
Since these hydrides are electron-deficient,they have a strong tendency to accept electrons to complete their octet.
Hence,they act as Lewis acids.
$B_{2}H_{6} + 2 NMe_{3} \longrightarrow 2 BH_{3} \cdot NMe_{3}$
$B_{2}H_{6} + 2 CO \longrightarrow 2 BH_{3} \cdot CO$