Ligands hydrolysis

Trimethylphosphate, despite being neutral, is known to form the simple complex [Co(NH3)5(OP(OMe)3)]3+ this reacts with nucleophiles X" S2C)32, I and SCN in that order of reactivity to produce [Co(NH3)5(02P(OMe)2)]3+ and MeX up to 150-fold faster than in the absence of coordination.1008 Both hydroxide and water are ineffective in this reaction, with simple ligand hydrolysis occurring more rapidly than any reaction. 

In any case, the amount of water remaining in the catalyst solution recirculated to the reactor needs to be controlled to avoid undesirable levels of phosphite ligand hydrolysis. 

Figure 1. Schematic of the two iron transport systems of microorganisms. The high affinity system is comprised of specific carriers of ferric ion (siderophores) and their cognate membrane hound receptors. Both components of the system are regulated by iron repression through a mechanism which is still poorly understood. The high affinity system is invoked only when the available iron supply is limiting otherwise iron enters the cell via a nonspecific, low affinity uptake system. Ferri-chrome apparently delivers its iron by simple reduction. In contrasty the tricatechol siderophore enterobactin may require both reduction and ligand hydrolysis for release...

Hay, R. W., Nolan, K. B. (1975). Reactions of co-ordinated ligands. Hydrolysis of tetram-ethyl-ethylenediaminetetra-acetate and its copper(II) complexes, J. Chem. Soc., Dalton Trans., pp. 1348. 

One of the most striking and potentially useful properties of certain (2 + 2) complexes is the inertness of the metal-macrocycle entities with respect to ligand hydrolysis or metal release in solution, associated with a high lability of the exocyclic ligands (anions or solvent molecules). For example, the metal-macrocycle entities of... 

The basic chemical principle behind sol-gel processing of metal alkoxides is the transformation of M—OR groups to M—O—M units via M—OH species. The direct formation of M—O—M units from metal alkoxides by ether cleavage is possible, but is only rarely observed under sol-gel conditions (see Section 7.10.3.3.1). Thus, the alkoxo ligands first have to be converted into hydroxo ligands (hydrolysis reaction), which can then undergo condensation reactions. 

Applying the results of this study, the catalyst prepared fi-om Ga(OTf)3 and chiral semicrown 5 was found to be effective for asymmetric aldol reactions in aqueous media. Interestingly, in the presence of the chiral ligand, hydrolysis of a silyl enol ether was suppressed, while rapid hydrolysis occurred in the absence of the ligand (Scheme 3.20). In addition, water was necessary to give satisfactory yield and enantioselectivity of the aldol adduct. A similar system using pybox-type ligand 6 and Zn(OTf)2 for aqueous asymmetric aldol reactions was also reported (Scheme 3.21). 

Table 12 Kinetic parameters at 298.2 K for chloride ligand hydrolysis and isomeriza tion of some cis- and trms-dichlorochromiumim) complexes (data from ref 118)...

The tris-tiron [tiron (20)] complex of vanadium(IV) is formed slowly, with a half-life of several minutes, from aq, both in acidic and in basic solution. The rate-determining step, here as in the production of the earlier-characterized octahedral tris-catechol-vanadium(IV) complex, is believed to be the removal of the vanadyl-oxygen needed for the addition of the third catecholate ligand. Repeat scan spectra indicate a half-life of about 10 minutes for ligand hydrolysis in the binuclear oxo-bridged complex [ V 0(salamhp) 20], salamhp = (21). ... 

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