Stepwise Bi-Bi Bond Formation: From a Bi-centered Radical to Bi₄ Butterfly and Bi₈ Cuneane-Type Clusters

In contrast to their lighter homologues (P, As, Sb), the synthesis of polybismuthane clusters is still restricted to classical solid-state approaches. We herein report on systematic reduction reactions of different bismuth precursors with Ga(I) and Mg(I) complexes. This study not only yielded the first metal-coordinated tetrabismuthane ([{L¹(Cl)Ga}₂-μ,η^1:1-Bi₄] 3, L¹ = HC[C(Me)N(2,6-i-Pr₂C₆H₃)]₂) and realgar-type bismuth cluster ([(L²Mg)₄(μ₄,η^2:2:2:2-Bi₈)] 4, L² = HC[C(Me)N(2,4,6-Me₃C₆H₂)]₂) in addition to the bismuth-centered radical [L¹Ga(Cl)]₂Bi^• 1 and dibismuthene [L¹(Cl)GaBi]₂ 2, but clearly demonstrates the crucial role of the substituents and the oxidation state of the bismuth precursor as well as the specific reduction potential of the main group metal reductants on the product formation. Compounds 3 and 4 were spectroscopically characterized (¹H, ¹³C NMR, IR), and the structures of 1-4 were determined by single-crystal X-ray diffraction. Computational calculations gave deeper insights into the electronic structures of 1', 3', and 4'.