Multi-electron reactivity of a cofacial di-tin(ii) cryptand: partial reduction of sulfur and selenium and reversible generation of S3˙.

Cofacial bimetallic tin(ii) ([Sn2(mBDCA-5t)]2-, 1) and lead(ii) ([Pb2(mBDCA-5t)]2-, 2) complexes have been prepared by hexadeprotonation of hexacarboxamide cryptand mBDCA-5t-H6 together with double Sn(ii) or Pb(ii) insertion. Reaction of 1 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)(mBDCA-5t)]2- (4) indicate that the complex acts reversibly as a source of S3˙- in DMF solution with a Keq = 0.012 ± 0.002. Reductive removal of all six chalcogen atoms is achieved through treatment of [(μ-E5)Sn2(μ-E)(mBDCA-5t)]2- with PR3 (R = t Bu, Ph, OiPr) to produce six equiv. of the corresponding EPR3 compound with regeneration of di-tin(ii) cryptand complex 1.