Complexes of Bis-ortho-cyclometalated Bisphosphinoaryl Ruthenium(II) Cations with NeutralMeta-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, η 3 - P,C,P ‘ -tridentate-bonded bisphosphinoaryl ligand (R−PCP = [C 6 H 2 (CH 2 PPh 2 ) 2 -2,6-R-4] -; R = H or Br) and one neutral, trans-P,P ‘ -bidentate-bonded bisphosphinoarene ligand (R‘−PCHP = C 6 H 3 (CH 2 PPh 2 ) 2 -3,5-R‘-1). The C−H bond that is ortho to both CH 2 PPh 2 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 1 H NMR spectrum as well as the three-dimensional structure of these complexes in solution was obtained by means of several two-dimensional NMR techniques ( 1 H− 1 H COSY, 31 P− 1 H COSY, 13 C− 1 H COSY, 1 H NOESY, 1 H ROESY, and 31 P 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(OSO 2 CF 3 )(NCN)(PPh 3 )] (NCN = [C 6 H 3 (CH 2 NMe 2 ) 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 PPh 3 .