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A dinuclear approach to phosphate diester hydrolysis

McGill University
Publication Date
  • Chemistry
  • Organic.


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.

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