Experimental demonstration of pH-dependent electrostatic catalysis of radical reactions

Abstract

Fluorescence spectroscopy demonstrated pH-dependent electrostatic effects on the kinetics and thermodynamics of hydrogen atom transfer between 1-hydroxy-2,2,6,6-tetramethyl-4-piperidinecarboxylic acid and {2,2,6,6-tetramethyl-4-[(7-nitro-2,1,3-benzoxadiazol-4-yl)amino]-1-piperidinyl}oxidanyl radical in dichloromethane.

Installation of internal electric fields by non-redox active cations in transition metal complexes

“…31 Coote et al have also reported using pH switchable elds that rely on protonationdeprotonation to vary radical stability. 32 Our efforts to generate controllable and directional internal electric elds have focused on installation of non-redox active cations proximal to redox-active reaction sites. We rst reported the cobalt derivatives of the salen-crown complex shown in Chart 1.…”

Electrostatic Switching between SN1 and SN2 Pathways

“…Experiments have shown that this can be achieved at the nanoscale using scanning tunneling microscopy, 4,5 and, at larger scales, using electrodes 6 charged insulators, 7 charged functional groups, [8][9][10] and metal ions. [11][12][13] While catalysis has been the main focus until now, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] perhaps the most interesting applications stem from the ability of electric fields to change outcome of a reaction. For instance, theoretical studies have shown that the regio-and stereoselectivity of a Diels-Alder reaction can be changed with either external oriented fields 16,17 or appropriately placed charged functional groups.…”

Electrostatic Regulation of TEMPO Oxidation by Distal Molecular Charges

“…[16,17] In a subsequent but related study, the same authors used this platform of pointcharges to demonstrate a pH switch to control the rate of hydrogen atom transfer between nitroxides and hydroxylamines. [19] Herein, instead of relying on pH changes to introduce local point-charges in a molecule, we have explored the alternative of creating localized cations using electroactive redox groups and an electron sink/source (i. e., an electrified interface). To this goal we synthesized a molecule containing two separate redox units, ferrocene and TEMPO, linked by a spacer.…”