Ligands bridging hydroxo

The bridging hydroxo ligand is a weak acid as well as an extremely weak base. The acid properties are by far the best investigated, and acid dissociation constants have been reported for singly and doubly bridged dinuclear complexes containing one or two hydroxo bridges (cf. Tables XV and XVI). 

Observations of triply and doubly bridging hydroxo groups in otherwise low-valent carbonyl clusters is particularly exciting in view of the potentially important role of such ligands in catalytic reductions. Molecules such as Ru4(CO)i<>(C = CHPrl)(OH)(PPh2) are worthy of detailed study. 

Several Ti complexes containing terminal or bridging hydroxo ligands have... 

The hydroxide ion is a well-established bridging ligand, and hydroxo-bridged complexes of iridium(III) have been reviewed. Among the dinuclear iridium(I) complexes that have structures supported by 0H ligands is [Cp Ir(/u.-0H)3lrCp ]+, and closely related to this is (cod)Ir(/u.-OPh)2lr(cod). The presence of the three OH... 

Finally, it is important to note that, while H2O is a relatively poor bridging ligand, both hydroxo and 0x0 ligands readily act as bridges between metal atoms, giving rise to polynuclear species, which are not discussed in detail here see Polyoxometalates). 

Because the metal center is usually chelated by several carboxylate residues that reduce the overall charge of the resulting complex, this might render deprotonation of a metal-bound water molecule less likely. Karlin has proposed that a water molecule or a hydroxo ligand bridging two metals could have a considerably lower pK and might be involved in the nucleophilic attack (306). Such a bridging hydroxo... 

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