A Boron‐Boron One‐Electron π‐Bond

The simplest boron-boron π-bond is to be found in the radical anion (1); from the ESR spectrum of (1b) it follows that each of the two boron atoms and each of the four hydrogen atoms in the two sets are equivalent. (1) has a conformation in which each pair of tert-butyl groups of the trans-neopentyl groups shields both boron atoms from above and below.