Helical chiral phosphorus ligand

Figure 4.37 Helical chiral polymeric phosphorus ligand for the Pd-catalyzed asymmetric...

In principle, lanthanide complexes of alkyl- (phosphinates) or alkoxy- (phosphonate esters) DOTP derivatives may give rise to 32 stereoisomers, existing as 16 enantiomeric pairs, which are indistinguishable by NMR spectroscopy. The isomers originate from chiral elements inherent in these complexes, including the R or S configuration at each phosphorus and the helicity defined by the pendant arm orientations (AIA). Various Ln3+ complexes of phosphinate and phosphonate ester ligands derived from 1,4,7,10-tetraazacyclododecane (cyclen) have been described in the literature [104-107]. 

An unusual double-stranded trinuclear structure incorporates one two-coordinate bent Ag and two four-coordinate tetrahedral Ag ions. A double-stranded tetranuclear helicate, [Au4L2]", employs two-coordinate Au. The inner phosphorus atoms of this tetraphosphadecane ligand are chiral, but only three of the four possible stereoisomers were isolated. In each of these structures the two phosphorus atoms binding the same Au ion have the same chirality. Aurophilic interactions are ascribed to the outer Au-Au pairs in each structure. 

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