First synthesis of a ‘1,2-diquinone-calix[4]arene’. Interaction of its reduced form with Ag+

Electrochemical oxidation of 5,11,17,23-tetra-tert-butyl-25,26-bis(diphenylphosphinoylmethoxy)-27,28-dihydroxycalix[4]arene (3), a calixarene with two phosphoryl units appended on proximal positions, affords the corresponding ‘1,2-diquinone-calix[4]arene’ (4). The formation of 4 results from nucleophilic attack of residual water on anodically generated diphenoxylium cations. Preliminary voltammetric experiments in CH3CN on a platinum electrode showed that 4 is suitable for electrochemical detection of the silver metal cation.