Tetra-Cationic Distibane Stabilized by Bis(α-iminopyridine) and Its Reactivity

The work establishes the salt of a tetra-cationic distibane, [L₂Sb₂][CF₃SO₃]₄ = [1]₂[OTf]₄ (CF₃SO₃ = OTf), stabilized by a bis(α-iminopyridine) ligand L, defying the Coulombic repulsion. The synthetic approach involved a dehydrocoupling reaction when a mixture of L and Sb(OTf)₃ in a 1:1 ratio was treated with Et₃SiH/LiBEt₃H as the hydride source. Compound [1]₂[OTf]₄ was also achieved from [LSbCl][OTf]₂ as a precursor and using Et₃SiH. Dissolution of [1]₂[OTf]₄ in polar solvents unveiled the formation of the persistent L-stabilized dicationic Sb(II) radical monomer [1][OTf]₂, while the addition of Me₃SiOTf regenerated the dimer in the salt [1]₂[OTf]₄. The homolytic cleavage of the Sb-Sb bond in [1]₂⁴⁺ has manifested in exchange reactions between [1]₂[OTf]₄ and Ph₂Ch₂ (Ch = S, Se), giving [LSb(SPh)][OTf]₂ = [2][OTf]₂ and [LSb(SePh)][OTf]₂ = [3][OTf]₂, respectively, in acetonitrile. Reaction between [1][OTf]₄ and p-benzoquinone gave [L₂Sb₂(C₆H₄O₂)][OTf]₄ = [4][OTf]₄. An interesting oxygen atom insertion reaction occurred when [1]₂[OTf]₄ was treated with 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) to give [L₂Sb₂O][ OTf]₄ = [5][OTf]₄. The oxo-bridged compound [5][OTf]₄ was also obtained from exposure of [1]₂[OTf]₄ in open air. The strong Mn-Mn bond in [Mn₂(CO)₁₀] could be cleaved by reacting with [1]₂[OTf]₄ in the presence of pyridine to form [LSbMn(CO)₅][ OTf]₂ = [6][OTf]₂. On the other hand, the reaction between [Co₂(CO)₈] and [1]₂[OTf]₄ gave the oxidative addition product [L₂Sb₂Co(CO)₃][OTf]₃ = [7][OTf]₃. The compounds were characterized both in the solid and solution states. Computational studies gave a comprehensive understanding of the experimental findings.