Synthesis, Structure, and Spectroscopic, Photochemical, Redox, and Catalytic Properties of Ruthenium(ll) Isomeric Complexes Containing Dimethyl Sulfoxide, Chloro, and the Dinucleating Bis(2-pyridyl)pyrazole Ligands

Two isomeric Ru(ll) complexes containing the dinucleating Hbpp (3,5-bis(2-pyridyl)pyrazole) ligand together with Cl and dmso ligands have been prepared and their structural, spectroscopic, electrochemical, photochemical, and catalytic properties studied. The crystal structures of trans,cis-(RullCl(2)(Hbpp)(dmso)2], 2a, and cis(out),cis-{RullCl(2)(Hbpp)(dmso)2], 2b, have been solved by means of single-crystal X-ray diffraction analysis showing a distorted octahedral geometry for the metal center where the dmso ligands coordinate through their S atom. 1D and 2D NMR spectroscopy corroborates a similar structure in solution for both isomers. Exposure of either 2a or 2b in acetonitrile solution under UV light produces a substitution of one dmso ligand by a solvent molecule generating the same product namely, cis(out)-[RullCl2(Hbpp)(MeCN)(dmso)], 4. While the 1 e- oxidation of 2b or cis(out),c/s-[Ru"Cl2(bpp)(dmso)2^, 3b, generates a stable product, the same process for2a or ^ans,as-[Ru"Cl2(bpp)(dmso)2^, 3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from Ru-S to Ru-O (Klllo-s- 0.25 ± 0.025, Klllo-s = 0.017 s-1 and Klll s-o = 0.065 s-1; Kll o-s = 6.45 x 10^9 Kll o-s = 0.132 s-1,Kll s-o = 2.1 x 10^-11 s-1). Finally complex 3a presents a relatively high activity as hydrogen transfer catalyst, with regard to its ability to transform acetophenone into 2-phenylethyl alcohol using 2-propanol as the source of hydrogen atoms.