Synthesis and Reactivity of Ruthenium(0) Complexes of MOP and Other Biaryl Monophosphine Ligands

A one-pot synthesis of P,arene-chelated ruthenium(0) complexes from readily available [Ru(<i>p</i>-cymene)Cl₂]₂ is described. The [Ru(<i>p</i>-cymene)Cl₂]₂ precursor reacts with monophosphine ligand (<i>R</i>)-2-diphenylphosphino-2'-methoxy-1,1'-binaphthyl (MOP) to form Ru(<i>p</i>-cymene)(MOP)Cl₂ intermediate (<b>1</b>), which then can be reduced under mild conditions by Zn/LiCl in the presence of stabilizing ligands PPh₃ or styrene to give zerovalent ruthenium complexes, Ru(MOP)(PPh₃) (<b>3</b>) and Ru(MOP)(styrene) (<b>4</b>), respectively. NMR and single-crystal X-ray diffraction studies have confirmed a σ-P/η⁶-arene coordination mode of the MOP ligand. Being Ru(0) species, complexes <b>3</b> and <b>4</b> are exceptionally thermally stable, undergoing virtually no decomposition at 100 °C over 48 h. Unlike previously reported Ru(BINAP)(PPh₃), the new Ru-MOP complexes are reluctant to activate C-H and N-H bonds, yet they oxidatively add aryl halides, poorly reactive PhCl included, to give Ru(MOP)(Ph)X (<b>5</b>, X = I, Br, Cl). The synthetic methodology has been extended to other biaryl phosphines <b>P</b> (CyJohnPhos, MePhos, DavePhos, Cy-vBRIDP) and various stabilizing ligands <b>L</b> (styrene, norbornene, and cyclooctadiene), providing a family of analogous σ-P/η⁶-arene Ru(0) complexes Ru(<b>P</b>)(<b>L</b>) in moderate to good yield.