Complexes of bis-ortho-cyclometalated bisphosphinoaryl ruthenium(II) cations with neutral meta-bisphosphinoarene ligands containing an agostic C-H•••Ru interaction

The synthesis, characterization, and reactivity of various ruthenium(II) complexes [Ru(R-PCP)(R'-PCHP)][OTf] are presented. These complexes are highly dissymmetric and show fluxional behavior in solution. They contain one monoanionic, eta (3)-P, C,P'-tridentate-bonded bisphosphinoaryl ligand (R-PCP = [C6H2(CH2PPh2)(2)-2,6-R-4](-); R = H or Br) and one neutral, trans-P,P'-bidentate-bonded bisphosphinoarene ligand (R'-PCHP = C6H3(CH2PPh2)(2)-3,5R'-1). The C-H bond that is ortho to both CH2PPh2 substituents of the bidentate-bonded ligand is interacting with the metal center (i.e., has an agostic contact with the cationic ruthenium center). The location of the agostic proton in the H-1 NMR spectrum as well as the three-dimensional structure of these complexes in solution was obtained by means of several two-dimensional NMR techniques (H-1-H-1 COSY, P-31-H-1 COSY, C-13-H-1 COSY, H-1 NOESY, H-1 ROESY, and P-31 EXSY), The (1)J(HC) Of the agostic contact amounted. to 112 Hz, which represents a reduction of 46 Hz in relation with the same coupling for this C-H bond in the free ligand. Furthermore, the molecular geometry of [Ru(H-PCP)(PCHP)][OTf] in the solid state was established by single-crystal X-ray diffraction techniques, and the structural features corroborate with the observations in solution. In the complex [Ru(H-PCP)(Br-PCHP)[OTf], interconversion of the cyclometalated and neutral bisphosphine ligands via exchange of the agostic hydrogen atom from the neutral to the cyclometalated carbon to yield [Ru(Br-PCP)(H-PCHP)][OTf] was observed, A mechanistic proposal based on an aromatic electrophilic substitution is discussed. Moreover, the reaction of [Ru(OSO2-CF3)(NCN)(PPh3)] (NCN = [C6H3(CH2NMe2)(2)-2,6](-)) with the neutral bisphosphinoarene resulted in the quantitative formation of the new cyclometalated species [Ru(R-PCP)(R-PCHP)[OTf] with the net loss of the neutral bisaminoarene ligand NCHN and PPh3.