Synthesis and Characterization of Six-Coordinate Ruthenium (II) Complexes That Contain Trans Spanning Diphosphine Ligands

Phosphine-ruthenium(II)-spanned complexes were synthesized and characterized through an in situ trans spanning procedure. The isolated complexes were [(trpy)Ru^II(L)(Cl)](ClO₄) (where trpy = 2,2′,2″-terpyridine and L = diphenyl-P-benzyl-N(Me)- (CH₂)_n-N(Me)-benzyl-P-diphenyl; n = 5 or 6) and [(trpy)Run(L)(Cl)](PF₆)₃ (where L = diphenyl-P-benzyl-N(Me)₂-(CH₂)_n-N(Me)₂-benzyl-P-diphenyl; n = 5 or 6). In these novel complexes, two monodentate phosphine ligands, coordinated in trans positions on an octahedral ruthenium(II) center, are covalently linked. The linkage possesses sufficient length to span over the chloride ligand and thus allows the ruthenium(II) center to remain six-coordinate. Much work has appeared in the literature involving the use of trans spanning ligands on four- and five-coordinate metal species, but this is the first reported case of a trans spanning ligand on an octahedral metal center where the spanning ligand bridges the cis coordinated ligand. The characterization of these complexes involved electrochemistry, UV/vis spectroscopy, NMR spectroscopy, elemental analysis, and conductance experiments. The electrochemical measurements yielded evidence of change in the ruthenium coordination sphere during the multistep synthesis and also demonstrated the effects of an oxidizable amine on the cyclic voltammetry of ruthenium(III)/ruthenium(Il) couples. NMR measurements illustrated the symmetry of the spanned complexes, while conductance measurements determined the charge and the nuclearity of the respective spanned species.