synthesis of chiral multidentate tertiary arsines with As_4 or As_6 donor atoms

摘要

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-(hloromethyl)-1,1-bis{[(2-dimethylarsinophenyl)methylarsino]methyl}ethane and the hexa(tertiary arsine) (R_(As),R_(As), R_(As))-1,1,1-bis{[(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 etra(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-#alpha# 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.