Unsymmetrical, Cyclic Diborenes and Thermal Rearrangement to a Borylborylene.

Cyclic diboranes(4) based on a chelating monoanionic benzylphosphine linker were prepared through boron-silicon exchange between arylsilanes and B Br . Coordination of Lewis bases to the remaining sp boron atom yielded unsymmetrical sp -sp diboranes, which were reduced with KC to their corresponding trans-diborenes. These compounds were studied with a combination of spectroscopic methods, X-ray diffraction, and DFT calculations.