Donor arsenic

Based on donor atom type, macrocyclic ligands can be considered to span two extreme types. First there are those systems which chiefly contain nitrogen, sulfur, phosphorus, and/or arsenic donors. These macrocycles tend to have considerable affinity for transition and other heavy metal ions they usually show much less tendency to form stable complexes with ions of the alkali and alkaline earth metals. The present discussion will be restricted to a consideration of a selection of such ligands and their complexes. 

Table 6 Complexes with Phosphorus and Arsenic donors...

A wide range of bidentates containing one or more asymmetric phosphorus or arsenic donor atoms is now available due to the exploitation of a resolution technique involving the fractional crystallization of pairs of diastereomeric complexes formed by the chiral bidentates with pal-ladium(II) complexes containing optically active dimethyl(a-methylbenzyl)amine or dimethyl(l-ethyl-a-naphthyl)amine. Indeed, in recent work the two enantiomer pairs of l-(methylphenyl-arsino)-2-(methylphenylphosphino)benzene, (29a) and (29b), have been separated and isolated as optically pure air-stable crystalline solids with [a]o values of 79° (R, R ) and 15.5° (R, S ). 95... 

The phosphorus macrocycles are made via template condensation of coordinated polyphosphine ligands and a dibromoalkane (equation 8).60 A more recently reported method involves a template-assisted single-stage ring closure (equation 9).61 The arsenic donor macrocycles are synthesized by reacting lithiated polyarsanes with a dichloroalkane (equation 10).62... 

Macrocyclic polyarsanes (43) have been reported by Ennen and Kauffman.62 The complexation tendencies of these ligands are as yet unexplored, although they should, due to the soft arsenic donors, form stable transition metal complexes. 

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