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.