Pentavalent nitrogen and boron

The previous posts have seen how a molecule containing a hypervalent carbon atom can be designed by making a series of logical chemical connections. Another logical step is to investigate whether the adjacent atoms in the periodic table may exhibit similar effects (C²⁺ ≡ B⁺ ≡ N³⁺ ≡ Be ≡ O⁴⁺). So here are reported some results (B3LYP/6-311G(d,p) ) for boron, beryllium and nitrogen, for the general tetramethyl substituted system shown below

The systems H, C and B are stable in the sense that the C_4v-symmetric calculated geometry has only positive calculated force constants (Be has a small negative frequency). All show bond critical points in the  X-C region (although these bonds are clearly  bent) and X-H region, and significant integrations for the X-C disynaptic basins in the  ELF analysis. The boron analogue is also of interest as being a neutral rather than a charged molecule, and therefore may be a worthy target for synthetic effort.