Electron‐Precise Dicationic Tetraboranes: Syntheses, Structures and Rearrangement to an Alkylidene Borate‐Borenium Zwitterion and a 1,3‐Azaborinine

Abstract

AbstractCarbene‐stabilized symmetrical and unsymmetrical dicationic tetraboranes, featuring an electron‐precise tetraborane chain, were synthesized and fully characterized. Reactions of these tetraboranes with reductants/bases give rise to different outcomes according to the conditions employed, including: 1) reduction and rearrangement of the tetraborane chain to give a zwitterionic alkylidene borate–borenium species; 2) cleavage of the tetraborane chain to afford a 1,3‐azaborinine; and 3) reduction of the supporting ligands to provide a diamino dipotassium salt. The zwitterionic alkylidene borate–borenium species can be viewed as an analogue of the base‐stabilized diborenes. NMR spectroscopy and DFT calculations reveal a highly polarized B−B bond in the zwitterionic alkylidene borate–borenium, in which the formal oxidation states of the boron atoms can be considered as −1 and +2. These results suggest the considerable potential of tetraboranes as synthons for low‐valent boron species.