Pyridyl-based pentadentate ligands: base-catalyzed hydrolysis of asym -[Co(dmptacn)Cl] 2+
Date
2004
Authors
Jackson, William Gregory
Dickie, Alistair J
Bhula, Rajumati
McKeon, Josephine A
Spiccia, Leone
Brudenell, Suzanne
Hockless, David
Willis, Anthony
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American Chemical Society
Abstract
The [Co(dmptacn)Cl]2+ (dmptacn = 1,4-bis(pyridylmethyl)-1,4,7- triazacyclononane) complex has been shown to be the asym isomer through 1D and 2D NMR studies, its optical resolution, and the single-crystal X-ray structure of its perchlorate salt. The kinetics of base-catalyzed hydrolysis establishes the usual [OH-] dependence (KOH = 0.040 M-1 s-1, 25 °C, / = 1.0 M, NaCl), but D-exchange experiments reveal that substantial if not complete reaction proceeds via the new pseudoaminate mechanism, i.e., via deprotonation at an α-CH2 center rather than the NH. The significant kinetic isotope effect (kH/kD = 2.1) is interpreted in terms of rate-limiting deprotonation followed by reprotonation of the conjugate base at a rate competitive with loss of Cl -. NMR and polarimetric studies establish geometric and optical retention for the hydrolysis reaction and exclude even the transient formation of a sym isomer intermediate.
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Keywords: [1,4 bis(pyridylmethyl) 1,4,7 triazacyclononane]cobalt complex; cobalt complex; ligand; perchlorate; pyridine derivative; unclassified drug; article; carbon nuclear magnetic resonance; hydrolysis; isomer; kinetic isotope effect; kinetics; nuclear magnetic
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Inorganic Chemistry
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Journal article
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2037-12-31
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