TY - JOUR
T1 - Pyridyl-based pentadentate ligands
T2 - Base-catalyzed hydrolysis of asym-[Co(dmptacn)Cl]2+
AU - Jackson, W. Gregory
AU - Dickie, Alistair J.
AU - Bhula, Rajumati
AU - McKeon, Josephine A.
AU - Spiccia, Leone
AU - Brudenell, Suzanne J.
AU - Hockless, David C.R.
AU - Willis, Anthony C.
PY - 2004/10/18
Y1 - 2004/10/18
N2 - 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.
AB - 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.
UR - http://www.scopus.com/inward/record.url?scp=6344250808&partnerID=8YFLogxK
U2 - 10.1021/ic040041m
DO - 10.1021/ic040041m
M3 - Article
SN - 0020-1669
VL - 43
SP - 6549
EP - 6556
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 21
ER -