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

Reaction of l,l,l-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*,RAi*)-, (RAs*,SAi*,r*)and (R_As*,5 _As*,5*)-l-(chloromethyl)-l,l-bis{[(2- dimethylarsinophenyl)methylarsino]methyl}ethane and the hexa(tertiary arsine) (As*,R _As*,ßAs*)-l,l,l-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(m). The three diastereomers of the tetra(tertiary arsine) each bind to the metal centre in a completely stereoselective manner: the (./?As*As*,r*) and (/?As*,5As*,î*) forms of the ligand each form a single trans dichloro complex and the (AAs*,/?A5*) diastereomer a cis-a complex. The structure of the latter has been confirmed by an X-ray analysis. Three other complexes have also been isolated from this reaction: /ras-dichlorobis[l,2phenylenebis(dimethylarsine)]cobalt(in) chloride, a cis-a complex of the cyclic chiral tetra(tertiary arsine) (A.SAJ./IAR-S.ô.T-pentahydro-ô-f- dimethylarsinophenylJmethylarsinolmethyU-l.ô-trimethylbenzo][ 1,4]diarsacycloheptane and a cobalt(m) complex of the chiral hexa(tertiary arsine). The structures of the latter two complexes have been confirmed by X-ray analyses.