Borophenes are atom-thin boron layers that can be grown on coinage metal substrates and have become an important class of synthetic 2D nanomaterials. The interactions between boron and substrates are critical to understand the growth mechanisms of borophenes. Here, we report an investigation of copper-boron interactions in the Cu₂B₈⁻ bimetallic cluster using photoelectron spectroscopy and quantum chemical calculations. Well-resolved photoelectron spectra are obtained at several photon energies and are combined with theoretical calculations to elucidate the structures and bonding of Cu₂B₈⁻. Global minimum searches reveal that Cu₂B₈⁻ consists of a Cu₂ dimer atop a B₈ molecular wheel with a long Cu–Cu bond length close to that in Cu₂⁺. Chemical bonding analyses indicate that there is clear charge transfer from Cu₂ to B₈, and the Cu₂B₈⁻ cluster can be viewed as a [Cu₂⁺]-borozene complex, [Cu₂⁺][B₈^2–]. In the neutral cluster, no Cu–Cu bond exists and Cu₂B₈ consists of two Cu⁺ centers interacting with doubly aromatic B₈²⁻ borozene. The charge transfer interactions between Cu and boron in the Cu₂B₈⁻ cluster are analogous to charge transfer from the copper substrate to the first borophene layer recently reported to be critical in the growth of bilayer borophenes on a Cu(111) substrate.