Few unexpected results from a Suzuki–Miyaura reaction

In the course of the synthesis of original anti-infectious compounds we focused on the palladium-catalyzed Suzuki–Miyaura aryl–aryl coupling reaction between 2-(3-ethoxy-5-iodo-1H-pyrazol-1-yl)pyridine and phenylboronic acid. A study of the reaction products obtained under different conditions (various ligands and solvents), not only provided us with insights to optimize this reaction but also with few side compounds, resulting from CH activation, along with the unexpected bis(3-ethoxy-1-(pyridin-2-yl)-1H-pyrazol-5-yl)palladium. Stochiometric experiments with this remarkably stable biscyclopalladated reagent and phenylhalides pointed out the occurrence of aryl–aryl coupling, possibly via palladium IV intermediates.