I’m no chemistry expert, but considering the values of the first ionisation energy, especially as boron is a very small molecule, would mean that the energy required to form a B3+ ion is far too great to occur in standard reaction conditions. Therefore boron does not form ions, and instead forms three covalent bonds as it has three valencd electrons, which require much less energy to create and are more energetically favourable. Boron is an odd one out!