Hexa-carboxylate ligands

A route for designing Gd(HI) complexes whose relaxivity depends on the presence of lactate, is provided by the ability shown by some hexa- or hepta-coordinate chelates to form ternary complexes with a wide array of anionic species (154-161). The interaction between the coordinatively unsatured metal complex and lactate involves the displacement of two water molecules coordinated to Gd(III) ion with the two donor atoms of the substrate, thus leading to a marked decrease in the relaxivity. Lactate is a good ligand for Gd(IH) ion because it can form a stable 5-membered ring by using the hydroxo and carboxylic oxygen donor atoms (Fig. 19). 

The enantioselective deprotonation of 128 and oxidative addition of the carbanion with Cu(II) afforded TangPhos disulfide as a mixture of diaster-eomers where the chiral C2-symmetric product was the major compound (66% de, 95% ee). A single recrystallisation afforded the desired optically pure TangPhos sulfide in 20% yield. The desulfuration was performed with hexa-chlorodisilane to yield the very air-sensitive Tangphos diphosphine in 88% yield. The synthesis of a family of phospholane-oxazoline ligands started with the preparation of carboxylic acid 129 by the proeedure in 40% yield after recrystallisation. The crude product was obtained in relatively low optical... 

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