The reactivities of two dinuclear metals complexes with bridging hydroxides for hydrolyzing phosphrite diesters have been examined. / The second-order rate constants ($ rm k sp prime sb{hyd}/M sp{-1} s sp{-1}$) for the hydroxidecatalysed hydrolysis of bridging aryl methyl phosphates in di-$ mu$-hydroxodinuclear cobalt(III) complex ($ rm Co sb2( lbrack 9 rbrack aneN sb3) sb2(OH) sb2(OP(O)(OMe)(OAr) rbrack sp{3+}$ ( (9) aneN$ sb3$ = 1,4,7-triazacyclononane) and the corresponding free aryl methyl phosphates (25$ sp circ$C and 0.1 M ionic strength) obey the following Bronsted equations: eqalign{ rm log k sp prime sb{hyd} (free diester) = -0.70 pK sb{ rm a}-0.66 & quad rm(R = 0.996) cr rm log k sp prime sb{hyd} (bridging diester) = -1.40 pK sb{ rm a} + 14.4 & quad rm (R = 0.999) cr} hese linear free energy relationships suggest that the di-$ mu$-hydroxodinuclear cobalt(III) complex, irrespective of the leaving groups hydrolyzes the bridging phosphate diesters by the same mechanism. They also indicate that the complex provides greater rate-acceleration for hydrolyzing phosphate diesters with good leaving groups than with poor ones. / La(III) cooperates with hydroxide in hydrolyzing bis(4-nitrophenyl) phosphate (BNPP). The close agreement between the titration data and the pH-rate profile indicates that the active core of the catalyst is a dinuclear La(III) complex bridged by five hydroxide ions La$ rm sb2(OH) sb5 sp+.$ The mechanism proposed for $ rm La sb2(OH) sb5 sp+$-promoted hydrolysis of BNPP involves double Lewis acid activation and intramolecular nucleophilic catalysis of the bridging hydroxide.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.23875 |
| Date | January 1996 |
| Creators | Cheung, William M. L. (William Man Lung) |
| Contributors | Chin, Jik (advisor) |
| 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 | Master of Science (Department of Chemistry.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001499612, proquestno: MM12172, Theses scanned by UMI/ProQuest. |
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