Monodentate ligands phenols

In their pioneering studies, van Leeuwen and coworkers [3] synthesized monodentate ligands as well as bidentate phosphoramidites by the reaction of Cl2P(NzPr2) with phenols (Figure 2.32). 

From the ligands having oxygen donor atoms the monohydric and poly-hydric phenoles, o-phenolecarboxylic acids, hydroxy-4-pyrones are of particular interest for binding UO in complexes and its spectrophotometric determination in aqueous solution. The monodentate phenolic hydroxyl is already bound giving UO complexes stable against hydrolysis up to pH 5. 

In contrast, the monodentate coordination of catechols to the ferric center in the form of 31 has been shown in the case of 1,2-CTD. Resonance Raman spectroscopy does not readily distinguish between the mono- and bidentate coordination of mode of the catecholate ligand. However, H and H NMR of the model complexes and 1,2-CTD after coordination of catechol and phenols have supported strongly that catechols coordinate to 1,2-CTD in the monodentate manner (see Chapter 2) [88, 89, 91]. The observed data clearly indicate that catechols are coordinated to the ferric center solely through the 0(1) oxygen. 

In the course of these investigations, an interesting dependence on the Pd-ligand was disclosed. In contrast to alcohols such as 310, where the best results were obtained with bisdentate aromatic phosphines, one had to change to monodentate Hgands in the case of the less nucleophilic phenols [99]. 

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