The catalysis of the transesterification reaction of 2-hydroxypropyl p-nitrophenyl phosphate HPNP by a series of copper(II) complexes is investigated. Dichloro- ((bis(benzimidazol-2-ylmethyl)amine)copper(II)$ rm rbrack{ cdot}CH sb3OH (Cu(N3))$ and chloro- ((bis(benzimidazol-2ylmethyl)hydroxyethylamine)copper(II)$ rm rbrack chloride{ cdot}3(H sb2O)$ (Cu(N3OH)) are the most reactive mononuclear catalysts for promoting HPNP cleavage. A second order dependence on catalyst and a second order hydroxide dependence is observed for the transesterification reaction of HPNP promoted by Cu(N3). A mechanism is proposed in which a dimerized complex provides double Lewis acid activation followed by nucleophilic attack of the internal alkoxide of HPNP. / A dinuclear copper(II) complex dichloro- ((N,N,N$ sp prime$,N$ sp prime$-tetrakis(2-benzimidazolyl)-2-hydroxy-$1, 3$-di-aminopropane)dicopper(II)) chloride LCu$ sb2$ is also shown to be extremely reactive in promoting the cleavage of HPNP. LCu$ sb2$ (2 mM) cleaves HPNP with an observed psuedo first order rate constant of $ rm 3.9 times 10 sp{-3} s sp{-1}$ at pH 7 and 25$ sp circ$C. The half-life for this reaction is 3 mins. LCu$ sb2$ is as effective as Cu(N3) and Cu(N3OH) for promoting the transesterification reaction of HPNP. A mechanism is proposed which involves double Lewis acid activation and facilitation of nucleophilic attack by the internal alkoxide of HPNP. A value for the rate enhancement expected by a double Lewis acid mechanism $6 times 10 sp6$ in the cleavage reaction of phosphate diesters is reported. The novel compound LCu$ sb2$DMP is synthesized and characterized. The structure of LCu$ sb2$DMP provides supporting evidence for the mechanism proposed. / Two novel and structurally interesting dinuclear cobalt(III) complexes, $ mu$-dimethylphosphato-di-$ mu$-hydroxy-bis ((1,4,7-triazacylononane)cobalt(III)) triperchlorate tacn$ sb2$Co$ sb2$(OH)$ sb2$DMP and $ mu$-(methyl-p-nitro-phenylphosphato)-di-$ mu $-hydroxy-bis ((1,4,7-triazacylononane)cobalt(III)) triperchlorate tacn$ sb2$Co$ sb2$(OH)$ sb2$MPNP are synthesized and characterized. The second order rate constant for the hydroxide caltalyzed hydrolysis of the doubly coordinated methyl (p-nitrophenyl) phosphate MPNP is $ rm 1.1 times 10 sp6 M sp{-1}s sp{-1}$ at 45$ sp circ$C. The proposed mechanism involves double Lewis activation of the phosphate diester and nucleophilic attack by a bridging oxy nucleophile. The breakdown of the species formed by this nucleophilic attack involves Co-O bond cleavage. Oxygen labeling experiments, pH-rate data and the identified reaction products are consistent with the proposed mechanism. A rate acceleration of $6 times 10 sp{11}$ fold is observed for the hydrolysis of the P-O bond in tacn$ sb2$Co$ sb2$OH$ sb2$MPNP over the background hydrolysis rate of MPNP.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.39888 |
| Date | January 1995 |
| Creators | Wahnon, Daphne C. |
| Contributors | Chin, J. (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 | 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: 001475735, proquestno: NN08164, Theses scanned by UMI/ProQuest. |
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