Atropisomerism in (±)-7-methyl- and -phenyl-substituted dinaphtho[2,1-b;1′,2′-d]phospholes and dinaphth[2,1-b;1′,2′-d]arsoles

Abstract

The reaction of 2,2′-dilithio-1,1′-binaphthyl with RECl2 (E = P or As; R = Me or Ph) affords the corresponding (±)-7-substituted dinaphtho[2,1-b;1′,2′-d]phospholes and dinaphth[2,1-b:1′,2′-d]arsoles. The molecules are fluxional on the NMR time scale with similar barriers between the conformational isomers (atropisomers) for the four compounds, vis. †G‡ = 56 ± 1 (243 K, ER = PMe), 56 ± 1 (254 K, ER = PPh), 65 ± 1 (287 K, ER = AsMe), 59 ± 1 (259 K, ER = AsPh) kJ mol-1. An X-ray diffraction study of (S)-7-phenyldinaphth[2,1-b;1′,2′-d]arsole which crystallized out by spontaneous resolution reveals appreciable bending of the distorted naphthyl residues away from each other. The asymmetric unidentates (±)-L coordinate to iron(II) in complexes of the type [(η5-C5H5)[1,2-C6H4(PMePh)2]FeL]PF6 with a small degree of enantioselection of one atropisomer of (±)-L. The complexes of the arsines are stable on the NMR time scale in CD2Cl2 at 20°C, but the corresponding phosphine complexes require cooling for observation of diastereomerism. The 7-methyl substituted arsole is demethylated by bromine giving the corresponding 7-bromo compound, which, in turn, is converted by additional bromine into configurationally stable (±)-[2-(2′-bromo-1,1′-binaphthyl)]dibromoarsine. Show more