Synthesis of chiral multidentate tertiary arsines with As4 or As6 donor atoms

Abstract

Reaction of 1,1,1-tris(chloromethyl)ethane with ca. three equivalents of sodium or lithium (2-dimethylarsinophenyl)methylarsenide in thf gave several products including the tetra(tertiary arsine) (R_As*,R_As*)-, (R_As*,S_As*,r*)- and (R_As*,S_As*,s*)-1-(chloromethyl)-1,1-bis{[(2-dimethylarsinophenyl)methylarsino]methyl}ethane and the hexa(tertiary arsine) (R_As*,R_As*,R_As*)-1,1,1-tris{[(2-dimethylarsinophenyl)methylarsino]methyl}ethane. The latter is the first example of a chiral hexa(tertiary arsine). The products from the reaction have been separated by complexation to cobalt(III). The three diastereomers of the tetra(tertiary arsine) each bind to the metal centre in a completely stereoselective manner: the (R_As*,S_As*,r*) and (R_As*,S_As*,s*) forms of the ligand each form a single trans dichloro complex and the (R_As*,R_As*) diastereomer a cis-α complex. The structure of the latter has been confirmed by an X-ray analysis. Three other complexes have also been isolated from this reaction: trans-dichlorobis[1,2-phenylenebis(dimethylarsine)]cobalt(III) chloride, a cis-α complex of the cyclic chiral tetra(tertiary arsine) (R_As*,S_As*,R_As*)-5,6,7,8,9-pentahydro-6-{[(2-dimethylarsinophenyl)methylarsino]methyl}-1,4,6-trimethylbenzo[b][1,4]diarsacycloheptane and a cobalt(III) complex of the chiral hexa(tertiary arsine). The structures of the latter two complexes have been confirmed by X-ray analyses.