Calix4pyrrole macrocycles (Pacman ligands) were used to incorporate heavy pnictogens (As, Sb, and Bi), yielding halogeno-pnictogen complexes (Pac(EX)2, E = As, Sb, Bi; X = Cl, I). Arsenic(III) chloro complex Pac(AsCl)2 was synthesized in solution and isolated, while arsenic(III), antimony(III), and bismuth(III) complexes (Pac(AsI)2, Pac(SbCl)2, Pac(BiCl)2, Pac(BiI)2) were formed in solution but could not be isolated. The arsenic(III) chloro complex showed temperature- and chloride-dependent dynamics similar to Pac(PCl)2. Hydrolysis of transient iodoarsane and chlorostibane produced oxygen-bridged complexes of the type Pac(E-O-E). In the case of the synthesis of Pac(SbCl)2, an intermediate, PacH2(SbCl2)2, was isolated and fully characterized. Through further HCl elimination, the last two HCl molecules were finally split off, resulting in the formation of Pac(SbCl)2. Bismuth(III) analogues were detected only transiently via 1H NMR spectroscopy. All isolated compounds were characterized spectroscopically, crystallographically, and theoretically. Reducing Pac(EX)2 complexes led to decomposition and not to the desired formation of biradical Pac(E·)2.
Schmidt et al. (Mon,) studied this question.