Multi-electron reactivity of a cofacial di-tin(<scp>ii</scp>) cryptand: partial reduction of sulfur and selenium and reversible generation of S₃˙⁻

Abstract

Cofacial bimetallic tin(ii) ([Sn₂(<i>m</i>BDCA-5t)]^2-, <b>1</b>) and lead(ii) ([Pb₂(<i>m</i>BDCA-5t)]^2-, <b>2</b>) complexes have been prepared by hexadeprotonation of hexacarboxamide cryptand <i>m</i>BDCA-5t-H₆ together with double Sn(ii) or Pb(ii) insertion. Reaction of <b>1</b> with elemental sulfur or selenium generates di-tin polychalcogenide complexes containing μ-E and bridging μ-E₅ ligands where E = S or Se, and the Sn(ii) centers have both been oxidized to Sn(iv). Solution and solid-state UV-Vis spectra of [(μ-S₅)Sn₂(μ-S)(<i>m</i>BDCA-5t)]^2- (<b>4</b>) indicate that the complex acts reversibly as a source of S₃˙^- in DMF solution with a <i>K</i>_eq = 0.012 ± 0.002. Reductive removal of all six chalcogen atoms is achieved through treatment of [(μ-E₅)Sn₂(μ-E)(<i>m</i>BDCA-5t)]^2- with PR₃ (R = ^<i>t</i> Bu, Ph, OⁱPr) to produce six equiv. of the corresponding EPR₃ compound with regeneration of di-tin(ii) cryptand complex <b>1</b>.