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

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., B2H6 , AI2H6 etc.
These hydrides cannot be represented by conventional Lewis structures. B2H6, for example, contains four regular bonds and two three centered-two electron bond. Its structure can be represented as:



Since these hydrides are electron-deficient, they have a tendency to accept electrons.

Hence, they act as Lewis acids.

B2H6 + 2NMe  2BH3 . NMe3B2H6 + 2CO  2BH3 . CO