Redox-active inverse crowns – pockets for heavier chalcogenides

Abstract

The reactivity of the redox-active metal crown complex (BDI*)MgNa₃N′′₂ (VI), formally containing a Mg⁰ centre, with phosphine chalcogenides, R₃PCh (Ch = O, S, Se, Te; R = Me, Et) was investigated (BDI* = HC[tBuCN(DIPeP)]₂ with DIPeP = 2,6-Et₂CH-phenyl). While all R₃PCh reagents could be reduced, only the heavier ones led to clean reduction to S²⁻, Se²⁻ and Te²⁻ anions which were captured in the metalla-cycle. The smaller S²⁻ anion can be stabilized by the tetrametallic MgNa₃-crown but the larger Se²⁻ and Te²⁻ require a pentametallic MgNa₄-crown. Reaction of the sulfide complex with N₂O led to a rare thiohyponitrite cis-SNNO²⁻ anion which is trapped in the pentametallic MgNa₄-crown. Experimental observations and bonding characteristics of all complexes are supported by an additional computational study.