Cobalt complexes phosphate ester hydrolysis

Two different binuclear copperdi) complexes have been prepared recently, one with a bridging phenoxy ligand having two bis-benzi-midazole arms (12, Fig. 14), and the second having a bis-cyclen-naphthalene ligand (13, Fig. 15) (352, 353). Both of them show bimetallic cooperativity for the hydrolysis of phosphate diesters, contrary to studies with the dinuclear cobalt complex (354). The pseudo-first-order rate constants for hydrolysis of the para-nitrophenylphosphate ester of propylene glycol by bis-benzimidazole-based copper complexes... 

Hettich, R., Schneider, H.-J. (1997). Cobalt(III) polyamine complexes as catalysts for the hydrolysis of phosphate esters and of DNA. A measurable million-fold rate increase, /. Am. Chem. Soc., 119 5638. 

A combination of kinetic and labeling studies established a mechanism involving attack by copper-bound hydroxide, followed by PO bond cleavage. Further details of the mechanisms of these reactions has come from a detailed study of the hydrolysis of ci5-[Ir(en)2(0H) 0P(=0)(0R)2 ] (36) complexes (R = ethyl or 4-nitrophenyl). The reaction involves intramolecular attack by coordinated hydroxide, and rate enhancements of 10 are found. The products of the reactions are not the chelated phosphate esters (37) expected from a knowledge of cobalt(III) chemistry, but monodentate phosphate monoesters (38). This is assigned to relative differences in the sizes of the metal ions and the basicity of the coordinated... 

Reactions involving the formation and hydrolysis of phosphate and polyphosphate esters are of vital importance in biological systems in which it is found that magnesium ions are almost invariably implicated. The formation and decomposition of adenosine triphosphate are the fundamental reactions involved in energy storage in living systems. In this context, it is perhaps relevant to note that the hydrolysis of ATP is enhanced, albeit in a very modest manner, by some cobalt(m) complexes. 

Substitutionally inert Co(m) or Ir(m) complexes have been used to measure directly the effect of Lewis acid activation on the hydrolysis of an amide [35-37], a nitrile [38] and a phosphate triester [39] (Figure 6.4). The p/C, of the cobalt-bound water molecule in 5 is 6.6 [40], Thus the upper limit for the rate-acceleration due to Lewis acid activation with this metal in the hydrolysis of esters, amides, nitriles and phosphates should be close to 109-fold. Although the observed rate accelerations for the hydrolysis reac-... 

Recent work has shown that simple nonlabile mono-aqua metal complexes function as general base catalysts in the hydrolysis of neutral phosphate and phosphonate esters in aqueous solution. If general base catalysis operates the reaction of [Co(NH3)50H] with 4-nitrophenyldiethyl phosphate, then (1 = PNPDEP) will give free diethylphosphonic acid in solution, while direct nucleophilic displacement will give the (diethylphosphate)cobalt(III) cation (2). 

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