Monodentate ligands phosphate

A corresponding reaction of acetate ion with AJP is also catalyzed by a bivalent metal ion. The reaction probably results in the formation of an acyl phosphate, which has not been identified as such but has been identified by trapping of the product with hydroxylamine. The best catalyst is beryllium ion, which catalyzes optimally at molar ratios of 1 to 1 or less. Acetate ion is presumably the reactive species, since the pH optimum of the reaction is 5. It is concluded from the pH effects in this study and in the transphosphorylation reaction that a complex of the metal ion and nucleophile must occur. Since acetate ion is a monodentate ligand, the mechanism postulated for the phosphorylation reaction above cannot be completely applicable to this case (36). 

As substrates and inhibitors, phosphate anions bind as reversibly monodentate ligands to zinc(II) ions in CPA, alkaline phosphatase, phospholipase or alkaline phosphatase A. The... 

Several quite stable complexes can be formed with Cf(iii) (see Table 11.9). Complexes of diketones and aminopolycarboxylic acids are considerably more stable than those of tartrate, lactate, oxalate, etc. In some cases, adduct chelates can be formed with Cf (iii), as with californium thenoyltrifluoroacetone chelate and methyl isobutyl ketone (Cf(TTA)3 + MIBK- Cf(TTA) MIBK or Cf(TTA)3 -2MIBK) [23]. With the monodentate ligand tributyl phosphate, the extractable californium adduct from nitric acid solution has been assigned as the 1 3 species Cf(N03)3 3TBP [227]. Quaternary ammonium bases and alkylpyro-catechols (i.e. 4-(a,a -dioctylethyl)pyrocatechol) can form complexes in alkaline solutions [228]. One recent extraction study has examined the influence of the extractant s structure on the extraction behavior of californium [229]. A large number of materials have been investigated for forming extractable complexes of californium and the reader is referred to reviews on the subject [27, 32, 33]. 

Almost simultaneously, several groups developed efficient procedures for Heck reactions of deactivated chloroarenes 22 involving sterically crowded monodentate phosphines as activating ligand on the palladium (Scheme 11) [31]. Littke and Fu employed commercially available P(t-Bu)3, Hartwig P(t-Bu)3 or bis-t-butyl-ferroce-nylphosphine, and Beller di(l-adamantyl)-n-butylphosphine. The use of biscyclo-hexylmethylamine as the base instead of alkali metal carbonates or phosphates significantly extends the scope of the Fu procedure in respect of the olefin partner. 

Hydrolysis of monodentate phosphate is also very slow and Com-OP03H species (n = 3-0) can be considered inert at room temperature (ka, Table 44). As expected, hydrolysis occurs by substitution at the metal and without exchange into the phosphate (equation 117). Acid catalysis is interpreted in terms of aquation of the acid conjugate of the complexed phosphate (Table 44). [Co OP(OH)3 (NH3)5]3+ (p a — 0.7) hydrolyzes some 102 times slower than [Co OP(OMe)3 (NH3)5]3+, which suggests that protonation at the bound O atom is not important. Base hydrolysis is also very slow (Table 44), occurs via substitution at the metal, and an S lcb process is likely via prior deprotonation of an ammine ligand (equation 118). 

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