The phenyl phosphate monoester in (Co$ sb2$(bpmp)($ mu$-PP)(OH)(OH$ sb2$)) (ClO$ sb4) sb2$ is hydrolyzed an unprecedented 10$ sp{11}$ times more rapidly than the corresponding unbound phosphate. Clean conversion of the bidentate monoester ((Co$ sb2$(bpmp)($ mu$-PP)(OH) (OH$ sb2$)) (ClO$ sb4) sb2$) to the tridentate inorganic phosphate ((Co$ sb2$(bpmp)($ mu, mu sp2$-Pi) (OH)) (ClO$ sb4$)), together with the crystal structure of an analog of phenylphosphonate, (Co$ sb2$(bpmp)($ mu$-PPO3)(OH)(OH$ sb2$)) (ClO$ sb4) sb2$ provide detailed mechanistic insight into the hydrolysis reaction. / The structure of (Co$ sb2$(bpmp)($ mu$-DPPO2)($ mu$-O$ sb2$)) (ClO$ sb4) sb2$ contains a diphenylphosphinate and a peroxide bridged between two cobalt(III) centers. Interestingly one of the oxygen atoms of the peroxide is only about 2.8 A away from the phosphorus of the coordinated phosphinate. When the bridging phosphinate is replaced with methyl phenylphosphonate (Co$ sb2$(bpmp)($ mu$-MPPO3)($ mu$-O$ sb2$)) (ClO$ sb4) sb2$, the ester bond is cleaved in aqueous DMSO (2:1 DMSO-d6/D$ sb2$O). The pseudo-first order rate constant for the cleavage of the methyl phenylphosphonate monoester bond in the complex is 5.3 x 10$ sp{-7}$ s$ sp{-1}$ at pH 7 (t$ sb{1/2}$ = 15 days) at 20$ sp circ$C. The estimated rate of base catalysed hydrolysis of the phosphonate is 1.4 $ times$ 10$ sp{-11}$M$ sp{-1}$s$ sp{-1}$ so that ca. 10$ sp{11}$ fold rate enhancement is observed. / The reactivity of dinuclear cobalt(III) complexes for cleaving phosphate diester in (Co$ sb2$(N3)$ sb2( mu$-OH)$ sb2( mu$-PO$ sb4$R$ sb2$)) can be significantly increased by decreasing the O-Co-O bond angle in the intermediate or transition state which forms a four membered ring. This can be achieved by increasing the N-Co-N ligands side bond angle opposite the O-Co-O angle. In (Co$ sb2$( (9) aneN3)$ sb2( mu$-OH)$ sb2( mu$-MPNPP)), the nitrogens are connected by two carbons whereas in (Co$ sb2$(tame)$ sb2( mu$-OH)$ sb2( mu$-MPNPP)), where tame is 1,1,1-tri(aminomethyl)ethane, the nitrogens are connected by three carbons. This results in a 10 fold increase in the reactivity for tame complex over (9) aneN3 complex. / There are three principal modes of activation that metal ions can provide for hydrolyzing phosphate esters. They are Lewis acid activation, nucleophiie activation and leaving group activation. All three modes of activation have been investigated in a three-metal system if the activation is additive. In the system that has a binding site on the leaving group for a third metal ion, double Lewis acid activation, double nucleophile activation and leaving group activation provides an unprecedented 10$ sp{17}$ fold rate enhancement for hydrolyzing a phosphate diester than in the corresponding third metal free system.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.34449 |
| Date | January 1997 |
| Creators | Seo, Jin Seog. |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001564046, proquestno: NQ30381, Theses scanned by UMI/ProQuest. |
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