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

Abstract 1,2,4,5‐Tetramethyl‐and pentamethylbenzene from stable 1:2 complexes with SbCl 3 of the type (C 6 H 6 ‐Me n ) · 2SbCl 3 ( 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 Sb 4 Cl 12 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 (η 6 ) coordination. The same stoichiometry and the same structural principle are found for the complex (C 6 Me 6 · 2 AsCl 3 ( 4 ), which is obtained from solutions of hexamethylbenzene and AsCl 3 in toluene. In 4 the arsenic atoms are η 6 ‐coordinated to the hexamethylbenzene ring from both sides (X‐ray analysis). Treatment of AsBr 3 with hexamethylbenzene leads to a product of the composition 5 (C 6 Me 6 ) · AsBr 3 . Reaction of hexaethylbenzene with AsCl 3 in petroleum ether leads to the formation of the 1:2 complex (C 6 Et 6 ) · 2 AsCl 3 ( 5 ), built of discrete inverse sandwich units, which are arranged in strings parallel to the crystallographic c axis. From solutions of AsCl 3 (AsBr 3 ), SbCl 3 (SbBr 3 ) 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.