Observation of Aromatic B₁₃(CO)_n⁺ (n = 1-7) as Boron Carbonyl Analogs of Benzene

CO as a typical σ-donor is one of the most important ligands in chemistry, while planar B₁₃⁺ is experimentally known as the most prominent magic-number boron cluster analogous to benzene. Joint gas-phase mass spectroscopy, collision-induced dissociation, and first-principles theory investigations performed herein indicate that B₁₃⁺ reacts with CO successively under ambient conditions to form a series of boron carbonyl complexes B₁₃(CO)_n⁺ up to n = 7, presenting the largest boron carbonyl complexes observed to date with a quasi-planar B₁₃⁺ core at the center coordinated by nCO ligands around it. Extensive theoretical analyses unveil both the chemisorption pathways and bonding patterns of these aromatic B₁₃(CO)_n⁺ monocations which, with three delocalized π bonds well-retained over the slightly wrinkled B₁₃⁺ moiety, all prove to be boron carbonyl analogs of benzene tentatively named as boron carbonyl aromatics (BCAs). Their π-isovalent B₁₂(CO)_n (n = 1-6) complexes with a quasi-planar B₁₂ coordination center are predicted to be stable neutral BCAs.