A Novel Boron Heterocycle Comprised of an Inner Boronium/Borate Adduct

The
reaction of [MeSCH2Li·(tmeda)] with 9-Cl-9-BBN
led to the formation of the unprecedented boron heterocycle 3, which is an inner salt formally composed of boronium and
borate subunits. This product rearranges upon heating to the thermodynamically
more stable Ci-symmetric
dimer 4, which can also be directly prepared if 9-MeO-9-BBN
is chosen as the starting material instead of 9-Cl-9-BBN. The reasons
for the different outcomes are discussed, and the solid-state structures
of the dimeric products 3 and 4, as well
as of the derived α-functionalized organoboron species 6, 9, and 12, are presented.