Synthesis of the First Heteroaryl-Substituted Boryl Complexes: Strong Stabilizing Effects of Boron–Aryl π‑Conjugation

The
first examples of heteroarylboryl complexes were prepared and have
been found to be unreactive toward a range of strong reductants, strong
Lewis bases, and halide-abstraction reagents. The inertness of the
complexes is attributed to strong π-conjugation between the
π-basic heteroaryl groups and the π-acidic boron atom.
This hypothesis is supported by comparison of the structural and spectroscopic
properties of the heteroarylboryl complexes with analogous previously
reported homoarylboryl complexes, with the former showing greater
coplanarity of the aryl ring with the boron atom and much less facile
reactivity.