One way to formulate the electronis structure of B2H6 arises from the realization that B2H6 is isoelectronic with C2H4. we can Imagine the following hypothetical reaction :
B2H42- + 2H+ → B2H6
because B2H42- is isoelectronic with C2H4, we can describe its electronic structure in terms of the bent bond model. we then predict that one proton would attack the bent bond below the B2H42- plane and the other would attack the bent bond above the B2H42- plane
In this model each boron atom uses sp2 hybrid orbitals to bond the two terminal hydrogen atoms. The bridging atoms are involved in three center two electron bonds.
Please refer image attached.