[RuCl2(η6-p-cymene)] complexes bearing phosphinous acid ligands: preparation, application in C–H bond functionalization and mechanistic investigations

International audience; A series of [RuCl2(η 6 ‐p-cymene)]complexes bearing phosphinous acid (PA) ligands has been straightforwardly prepared from the dimer [RuCl2(p-cymene)]2 and secondary phosphine oxides (SPOs), and fully characterized. The steric parameter quantification of PAs, other L ligands and η 6 ‐p-cymene allowed a better comprehension of the coordinationchemistryof this type of complexes and explained the absence of coordination in the case of bulky SPOs such as Ad2P(O)H. These complexes were tested in theC-H activation/functionalization of 2-phenylpyridine and a good activity was obtained at 80 °C for the complex exhibiting the highest steric bulk. A study on halide effects,either on the ruthenium complex or for the aryl halide partner,has also been carried out and showed drastic differences. Further investigations on halides effects were performed notably using cationic ruthenacycle which was found to be an intermedaite of the reaction. In order to rationalize the role played by the phosphinous acid, a mechanism involving a concerted metallation deprotonation favored by a phosphinito species has been proposed.