π‐Complexes of p‐Block Elements: Synthesis and Structures of Adducts of Arsenic and Antimony Halides with Alkylated Benzenes

1,2,4,5‐Tetramethyl‐and pentamethylbenzene from stable 1:2 complexes with SbCl₃ of the type (C₆H₆‐Me_n) · 2SbCl₃(1,2) with an inverse sandwich structure. The compounds crystallize isotypically and are isostructural to the (hexamethylbenzene)antimony and ‐bismuth complexes.They are thus built of tetrameric chlorine‐bridged Sb₄Cl₁₂ units, which are crosslinked at the metal centers with four other tetramers by double‐sided arene coordination (X‐ray structure analysis of 1). The Sb atoms, which are in a distorted trigonal bipyramidal environment, show a slight deviation from a centric (η⁶) coordination. The same stoichiometry and the same structural principle are found for the complex (C₆Me₆ · 2 AsCl₃ (4), which is obtained from solutions of hexamethylbenzene and AsCl₃ in toluene. In 4 the arsenic atoms are η₆‐coordinated to the hexamethylbenzene ring from both sides (X‐ray analysis). Treatment of AsBr₃ with hexamethylbenzene leads to a product of the composition 5 (C₆Me₆) · AsBr₃. Reaction of hexaethylbenzene with AsCl₃ in petroleum ether leads to the formation of the 1:2 complex (C₆Et₆) · 2 AsCl₃ (5), built of discrete inverse sandwich units, which are arranged in strings parallel to the crystallographic c axis. From solutions of AsCl₃ (AsBr₃), SbCl₃ (SbBr₃) and hexaethylbenzene in petroleum ether ternary compounds are isolated with an As:Sb ratio of 1:5.2 and 1:1.86, respectively. Single crystal X‐ray structure determinations failed as a consequence of severe disorder.