Reduction of dichloro(diaza-phospha)stibanes – isolation of a donor-stabilized distibenium dication

Abstract

A reaction of antimonytrichloride SbCl₃ with potassium bis(terphenylimino)phosphide K[(TerN)₂P] smoothly afforded a novel class of mixed diazadipnictanes, namely dichloro(diaza-phospha)stibane [Ter₂N₂P^(III)Sb^(III)Cl₂], which is considered to exist as open chain-like and cyclic isomers in an equilibrium. [Ter₂N₂PSbCl₂] is a versatile starting material for reduction and halide abstraction experiments. Halide abstraction led to the formation of a cyclic diazastibaphosphenium cation [P(μ-NTer)₂SbCl]⁺. Upon reduction of [Ter₂N₂PSbCl₂], the transient existence of the novel mixed biradicaloid [P(μ-NTer)₂Sb] was proven by a trapping experiment with an alkyne, while reduction in the absence of trapping agents afforded the eight-membered heterocycle [Sb₂-{μ-(TerN)₂P}₂]. This constitutional isomer of a dimerized biradicaloid features a bonding situation that indicates the presence of a donor-stabilized [Sb₂]²⁺ ion.