1400279-89-1Relevant articles and documents
Trifunctional metal ion-catalyzed solvolysis: Cu(II)-promoted methanolysis of N,N-bis(2-picolyl) benzamides involves unusual lewis acid activation of substrate, delivery of coordinated nucleophile, powerful assistance of the leaving group departure
Raycroft, Mark A.R.,Maxwell, Christopher I.,Oldham, Robyn A. A.,Andrea, Areen Saffouri,Neverov, Alexei A.,Brown, R. Stan
, p. 10325 - 10333 (2013/01/15)
The methanolyses of Cu(II) complexes of a series of N,N-bis(2-picolyl) benzamides (4a-g) bearing substituents X on the aromatic ring were studied under s s pHcontrolled conditions at 25 °C. The active form of the complexes at neutral s s pH has a stoichiometry of 4:Cu(II): (-OCH 3)(HOCH3) and decomposes unimolecularly with a rate constant kx. A Hammett plot of log(kx) vs σx values has a ?x of 0.80 ± 0.05. Solvent deuterium kinetic isotope effects of 1.12 and 1.20 were determined for decomposition of the 4-nitro and 4-methoxy derivatives, 4b:Cu(II):( -OCH3)(HOCH3) and 4g:Cu(II):( -OCH3)(HOCH3), in the plateau region of the s s pH/ log(kx) profiles in both CH 3OH and CH3OD. Activation parameters for decomposition of these complexes are ΔH≠ = 19.1 and 21.3 kcal mol -1 respectively and ΔS≠ = -5.1 and -2 cal K-1 mol-1. Density functional theory (DFT) calculations for the reactions of the Cu(II):(-OCH3)(HOCH3) complexes of 4a,b and g (4a, X = 3,5-dinitro) were conducted to probe the relative transition state energies and geometries of the different states. The experimental and computational data support a mechanism where the metal ion is coordinated to the N,N-bis(2-picolyl) amide unit and positioned so that it permits delivery of a coordinated Cu(II):(-OCH3) nucleophile to the C=O in the rate-limiting transition state (TS) of the reaction. This proceeds to a tetrahedral intermediate INT, occupying a shallow minimum on the free energy surface with the Cu(II) coordinated to both the methoxide and the amidic N. Breakdown of INT is a virtually barrierless process, involving a Cu(II)-assisted departure of the bis(2-picolyl)amide anion. The analysis of the data points to a trifunctional role for the metal ion in the solvolysis mechanism where it activates intramolecular nucleophilic attack on the C=O group by coordination to an amidic N in the first step of the reaction and subsequently assists leaving group departure in the second step. The catalysis is very large; compared with the second order rate constant for methoxide attack on 4b, the computed reaction of CH3O- and 4b:Cu(II):(HOCH3)2 is accelerated by roughly 2.0 × 1016 times.
