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

Abstract

The work establishes the salt of a tetra-cationic distibane, [L2Sb2][CF3SO3]4 = [1]2[OTf]4 (CF3SO3 = OTf), stabilized by a bis(alpha-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]2 4+ 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] 2 [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.