Cobalt phosphate esters

The cobalt(III) ion has a small size-to-charge ratio and is therefore a strong Lewis acid which strongly activates coordinated phosphate ester... 

A different application of visible microscopy was pioneered by Gomori. In 1941 he showed that alkaline phosphatase could be specifically located by its hydrolysis of soluble phosphate esters (initially glycerophosphate). If calcium ions were present in the medium in which the sections were incubated, insoluble calcium phosphate precipitated as a result of the action of the hydrolase. The site of the precipitate could be visualized if cobalt or lead salts were subsequently added to replace calcium and the sections exposed to hydrogen sulfide. In principle many hydrolases and other enzymes could be studied using the appropriate substrates and precipitants. It was important to ensure that the products of the enzyme reactions did not diffuse from the sites where the enzymes were located. It was also essential that the reagents could reach the enzyme site. 

Hydrolysis of peptides,84 amides,85 phosphate esters,86 sulfonate esters87 and acetals88 can also be metal catalyzed. The hydrolysis of a phosphate ester coordinated to cobalt(III) also occurs at an increased rate (Scheme 19).89 A rather similar reaction occurs in the amine exchange of coordinated dithiocarbamates (equation 21).90 The conversion of imidates to amidines has been mentioned previously and is a similar type of reaction (see Section 7.4.2.2.1). 

Cobalt-coordinated amide nucleophiles have also been observed to attack coordinated phosphate esters (equation 38),148 disulfides (Scheme 47)149 150 and nitriles (Scheme 48).151>152 Chelated amides can also be formed by intramolecular attack of cobalt hydroxides.153... 

In recent years there has been considerable interest in the hydrolytic activity of cobalt(III) complexes of phosphate esters. This approach has been adopted in order to avoid some of the mechanistic complexities which can arise with kinetically labile metal centres. Some developments in this field have been recently discussed by Dixon and Sargeson.21... 

Donner, R. and Lohs, K., Cobalt chloride in the detection of organic phosphate ester by paper and especially thin-layer chromatography, J. Chromatogr., 17, 349, 1965 Chem. Abs., 62, 13842d, 1965. 

Table 45 Preparations Cobalt Phosphate, Phosphate Ester, Phosphonate and Phosphite 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. 

Jones, D., Lindoy L.F. and Sargeson, A.M. (1983) Hydrolysis of phosphate esters bound to cobalt (III). Kinetics and mechanism of intramolecular attack of hydroxide on coordinated 4-nitro-phenyl phosphate. Journal of the American Chemical Society 1 05, 7327-7336. 

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... 

Phosphoric acid 2-chloro-1-(2,4-dichlorophenyl) ethenyl diethyl ester. See ChlorFenvinphos Phosphoric acid chromium (III) salt. See Chromium phosphate Phosphoric acid, cobalt (2+) salt (2 3). See Cobalt phosphate (ous)... 

Pd(Ph3P)2Cl2(Bu3SnH, benzene) or cobalt carbonyl. The palladium method cleaves allyl esters, propargyl phosphates, and propargyl carbamates as well. 

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