A Polar Copper–Boron One-Electron σ‑Bond

Virtually all chemical bonds consist
of one or several pairs of
electrons shared by two atoms. Examples of σ-bonds made of a
single electron delocalized over two neighboring atoms were until
recently found only in gas-phase cations such as H2+ and Li2+ and in highly unstable species
generated in solid matrices. Only in the past decade was bona fide
one-electron bonding observed for molecules in fluid solution. Here
we report the isolation and structural characterization of a thermally
stable compound featuring a Cu–B one-electron bond, as well
as its oxidized (nonbonded) and reduced (two-electrons-bonded) congeners.
This triad provides an excellent opportunity to study the degree of
σ-bonding in a metalloboratrane as a function of electron count.