Abstract

Abstract A cationic copper‐stabilized coppoborylene was prepared and structurally characterized via infrared photodissociation spectroscopy and density functional theory calculations. This structure exemplifies a new class of borylenes stabilized by three‐center‐two‐electron metal‐boron‐metal covalent bonding interaction, displaying exceptional σ‐acidity and unparalleled π‐donor capability for CO activation that outperforms all of the known transition metal cations and is comparable or even superior to the documented base‐trapped borylenes. Its neutral form represents a monovalent boron compound with a strongly reactive amphoteric boron center built on transition‐metal‐boron bonds, which inspires the design and synthesis of new members of the borylene family.