Silver nanocluster redox-couple-promoted nonclassical electron transfer:: An efficient electrochemical Wolff rearrangement of α-diazoketones

In this work we report the unique electrocatalytic role of benzoic acid protected silver nanoclusters (Ag-n, mean core diameter 2.5 nm) in the Wolff rearrangement (Scheme 1) of alpha-adiazoketones. More specifically, the presence of a Ag-n(0)/Ag-n(+) redox couple facilitates a nonclassical electron-transfer process, involving chemical reaction(s) interposed between two electron-transfer steps occurring in opposite directions. Consequently, the net electron transfer between the electron mediator (Ag-n) and alpha-diazoketone is zero. In-situ UV-visible studies using pyridine as a nucleophilic probe indicate the participation of alpha-ketocarbene/ketene as important reaction intermediates. Controlled potential coulometry of alpha-diazoketones using Ag-n as the anode results in the formation of Wolff rearranged carboxylic acids in excellent yield, without sacrificing the electrocatalyst.