Noncovalent Immobilization of Molecular Electrocatalysts for Chemical Synthesis: Efficient Electrochemical Alcohol Oxidation with a Pyrene–TEMPO Conjugate

Abstract

Electrocatalytic methods for organic synthesis could offer sustainable alternatives to traditional redox reactions,but strategies are needed to enhance the performance of molecular catalysts designed for this purpose.T he synthesis of ap yrenetethered TEMPO derivative (TEMPO = 2,2,6,6-tetramethylpiperidinyl-N-oxyl) is described, whichu ndergoes facile in situ noncovalent immobilization onto ac arbon cloth electrode. Cyclic voltammetry and controlled potential electrolysis studies demonstrate that the immobilized catalyst exhibits much higher activity relative to 4-acetamido-TEMPO,a ne lectronically similar homogeneous catalyst. In preparative electrolysis experiments with as eries of alcohol substrates and the immobilized catalyst, turnover numbers and frequencies approach 2000 and 4000 h À1 ,respectively.The synthetic utility of the method is further demonstrated in the oxidation of as terically hindered hydroxymethylpyrimidine precursor to the blockbuster drug,r osuvastatin.

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

“…In another notable example, Stahl and co-workers developed a pyrene-tethered TEMPO derivative which undergoes in situ noncovalent immobilization onto a carbon anode. 204 This electrode system was found to demonstrate high catalytic activities in the oxidation of alcohols, exhibiting turnover numbers and frequencies of close to 2000 and 4000 h –1 . Sigman, Minteer, and co-workers reported a method to covalently immobilize TEMPO onto linear poly-(ethylenimine) which is then cross-linked onto the surface of a glassy carbon electrode.…”

2,2,6,6‐Tetramethylpiperidinyloxyl (TEMPO) Radical Mediated Electro‐Oxidation Reactions: A Review

“…These observations provided an extended understanding of the relative activity of TEMPO and bicyclic nitroxyl derivatives towards alcohol oxidation reactions. [113] Another derivative, 4-NH 2 -TEMPO was recognized as a mediator capable of enhancing methodical glycerol electrooxidation in moderately acidic conditions which exhibited increased reactivity. [1141 The improved performance of 4-NH 2 -TEMPO under acidic conditions is attributed to the protonation of the amine functional group which ameliorates the redox potential and reactivity of the corresponding oxoammonium.…”

Electrocatalytic synthesis of heterocycles from biomass-derived furfuryl alcohols

“…To take the advantages of both homogeneous (defined active sites at the molecular level) 38 and heterogeneous (efficient electron transfer between electrode and catalyst without diffusion) electrocatalysts, we immobilized molecular active sites on electrode for the Achmatowicz reaction. Indeed, many elegant approaches, such as ππ stacking 39 , covalent tethering 40 , 41 , and polymerization 42 , have been adopted for catalyst immobilization. However, most of these precedent procedures utilize pre-synthesized molecules and their active sites are usually coordination saturated.…”