From Borapyramidane to Borole Dianion

Nonclassical
pyramidanes with their inverted tetrahedral configuration
of the apical atom are among the most challenging synthetic targets
in cluster chemistry. In this Communication, we report on the synthesis
and structure of the first representative of pyramidal compounds with
the group 13 element at the apex, namely, chloroborapyramidane 2. Reduction of 2 with excess of lithium metal
unexpectedly produced the cage-opening product, borole dianion derivative {32–·[Li­(thf)+]2}, a 6π-electron aromatic system.