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(p-cymene)Cl₂]₂ is described. The [Ru(p-cymene)Cl₂]₂ precursor reacts with monophosphine ligand (R)-2-diphenylphosphino-2′-methoxy-1,1′-binaphthyl (MOP) to form Ru(p-cymene)(MOP)Cl₂ intermediate (1), 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) (3) and Ru(MOP)(styrene) (4), 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 3 and 4 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 (5, X = I, Br, Cl). The synthetic methodology has been extended to other biaryl phosphines P (CyJohnPhos, MePhos, DavePhos, Cy-vBRIDP) and various stabilizing ligands L (styrene, norbornene, and cyclooctadiene), providing a family of analogous σ-P/η⁶-arene Ru(0) complexes Ru(P)(L) in moderate to good yield.