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

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. The synthesis of a pyrenetethered TEMPO derivative (TEMPO= 2,2,6,6-tetramethylpiperidinyl- N-oxyl) is described, which undergoes facile in situ noncovalent immobilization onto a carbon cloth electrode. Cyclic voltammetry and controlled potential electrolysis studies demonstrate that the immobilized catalyst exhibits much higher activity relative to 4-acetamido-TEMPO, an electronically similar homogeneous catalyst. In preparative electrolysis experiments with a series of alcohol substrates and the immobilized catalyst, turnover numbers and frequencies approach 2000 and 4000 h(-1), respectively. The synthetic utility of the method is further demonstrated in the oxidation of a sterically hindered hydroxymethylpyrimidine precursor to the blockbuster drug, rosuvastatin.