Synthesis of Sb-chiral organoantimony compounds having intramolecular Sb⋯N interaction and their separation into optically pure compounds via ortho-palladated benzylamine complexes

A diastereomeric mixture of Sb-chiral triarylstibanes having an amine moiety on an aryl group, Sb(R/S)-(aryl)[2-(S)-(1-dimethylaminoethyl)phenyl](p-tolyl)stibanes (4a–c), has been prepared by stepwise nucleophilic displacement of the ethynyl groups on bis(phenylethynyl)(p-tolyl)stibane (1) with Grignard reagents 2a–c and 2-[(S)-(dimethylamino)ethyl]phenyllithium. Although direct separation of the diastereomeric mixtures of 4 was unsuccessful, they could be separated with ease via their palladium complexes 6 formed from the reactions of the stibanes 4 with di-μ-dichlorobis(2-dimethylaminobenzyl-C1,N)dipalladium(II) (5). The diastereomerically pure Sb-chiral stibanes isolated here were optically stable, and no racemization on the chiral antimony center was observed even when they were heated at 110 °C over 24 h in toluene or pyridine. The single X-ray crystal analysis of Sb(S)–[2-(S)-(1-dimethylaminoethyl)phenyl](1-naphthyl)(p-tolyl)stibane (4b-B) revealed the presence of intramolecular interaction between the antimony and nitrogen atoms.