Nonclassical 1,2‐Diboretanes and 1,2‐Diborolanes

Experiment and theory both indicate that four- and five-membered rings containing two neighboring boron atoms–like the corresponding three-membered ring compounds—favor nonclassical structures with a B-H-B bridge (1 and 2, respectively) when the electron deficiency at boron is not reduced by donor substituents.