| Abstract
| - Bis(4-nitrophenyl) phosphate is hydrolyzed by various mono- and dinuclear lanthanum complexes of a macrocyclic dinucleating ligand. Potentiometry was used to define the various metal-coordinated hydroxide nucleophiles that exist in solution. The dihydroxo dilanthanum complex was found to be the most successful catalyst. The hydrolysis reaction has a highly unusual third-order dependence on the catalyst concentration which is key to understanding the proposed mechanism.
- A series of mono- and dinuclear lanthanum complexes of 15,31-dimethyl-3,11,19,27,33,35-hexaazapentacyclo[27.3.1.15,91.13,17.121,25]hexatriaconta-5,7,9(33),13,15,17(34),21,23,25(35),29,31,1(36)-dodecaene-34,36-diol (24RBPyBC, L) have been defined in solution. Their ability to hydrolyze bis(4-nitrophenyl) phosphate, a phosphatediester, was studied. The various metal-coordinated hydroxide nucleophiles that form in solution attack the substratein the hydrolysis reaction. The dihydroxo dilanthanum complex, L-2La-2(OH), is the most effective catalyst. Itsrate constant is 75 times larger than the rate constant for the monohydroxo dilanthanum complex, L-2La-OH.The mononuclear complexes are not as successful as the dinuclear complexes because they have fewer metalions per complex to act as Lewis acids. They also cannot generate hydroxide nucleophiles at low pH values likethe dinuclear complexes can. The reaction has an unusual third-order dependence on the catalyst concentrationwhich is valid for the dinuclear complexes as well as the mononuclear complexes. This implies a mechanismwhere a metal-coordinated hydroxide nucleophile attacks the phosphorus of the substrate on the side opposite thenegatively charged oxygens.
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