Carbodiphosphorane-Activated\nDistibene and Dibismuthene\nDications

Low-valent antimony and bismuth have emerged as novel\nplatforms\nfor achieving reversible small-molecule activation at main-group metals.\nAlthough various examples of oxidative addition reactions at monomeric\nSb(I) and Bi(I) have been reported, the chemistry of the heavy group\n15 Sb(I)Sb(I)/Bi(I)Bi(I) double bonds toward small\nmolecules remains largely unexplored. In this study, we present a\nstraightforward synthesis of distibene and dibismuthene dications\ncoordinated with a neutral carbodiphosphorane (CDP) ligand. The nonbonding\ninteractions between the occupied p-orbital at the CDP ligand and\nthe π-bonding orbital of the SbSb/BiBi bonds\nyield compounds with exceptionally small HOMO–LUMO gaps. In\naddition, the reduction of steric hindrance compared to known neutral\nderivatives stabilized with bulky aryl groups allows for better accessibility\nof the double bonds. This high reactivity is demonstrated in the oxidative\naddition of distibene to diphenyldisulfide as well as in [2+2] cycloadditions\nto alkynes. Additionally, the SbSb bond reversibly adds to\n2,3-dimethylbutadiene in a [4+2] cycloaddition reaction.