Redox-active inverse crowns – pockets for heavier chalcogenides

The reactivity of the redox-active metal crown complex (BDI*)MgNa₃N''₂ (VI), formally containing a Mg⁰ centre, with phosphine chalcogenides, R₃PCh (Ch = O, S, Se, Te; R = Me, Et) was investigated (BDI* = HC[<i>t</i>BuCN(DIPeP)]₂ with DIPeP = 2,6-Et₂CH-phenyl). While all R₃PCh reagents could be reduced, only the heavier ones led to clean reduction to S^2-, Se^2- and Te^2- anions which were captured in the metalla-cycle. The smaller S^2- anion can be stabilized by the tetrametallic MgNa₃-crown but the larger Se^2- and Te^2- require a pentametallic MgNa₄-crown. Reaction of the sulfide complex with N₂O led to a rare thiohyponitrite <i>cis</i>-SNNO^2- anion which is trapped in the pentametallic MgNa₄-crown. Experimental observations and bonding characteristics of all complexes are supported by an additional computational study.