Borazine (${\mathrm{B}}_3{\mathrm{N}}_3{\mathrm{H}}_6$)

Borazine is the alternating six-membered ${\mathrm{B}}_3{\mathrm{N}}_3{\mathrm{H}}_6$ ring. Planar boron and nitrogen centers permit N-to-B pi donation, but unequal orbital energies strongly polarize the bonding. It undergoes addition and hydrolysis much more readily than benzene; the structural analogy does not give benzene-like chemical inertness.

Borazine dearomatization interrupts the planar pi system, for example when a nucleophile makes one boron tetrahedral. In a metal pi complex, this can change ring hapticity and produce a charged ligand with a different donor count.

B-Tribromoborazine is ${\mathrm{B}}_3\mathrm{B}{\mathrm{r}}_3{\mathrm{N}}_3{\mathrm{H}}_3$, retaining all three N–H groups. Ring-retaining bromination replaces B–H groups, whereas simple hydrogen-halide addition also changes ring saturation.

Hexamethylborazine is ${\mathrm{B}}_3{\mathrm{N}}_3\mathrm{M}{\mathrm{e}}_6$, with one methyl on every ring atom. Its nitrogen atoms can form Lewis acid-base adducts, while nucleophiles can attack its boron atoms.