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

Two isomeric Ru(II) 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-[RuIICl2(Hbpp)(dmso)2], 2a, and cis(out),cis-[RuIICl2(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)-[RuIICl2(Hbpp)(MeCN)(dmso)], 4. While the 1 e- oxidation of 2b or cis(out),cis-[RuIICl2(bpp)(dmso)2]+, 3b, generates a stable product, the same process for 2a or trans,cis-[RuIICl2(bpp)(dmso)2]+,
3a, produces the interesting linkage isomerization phenomenon where the dmso ligand switches its bond from
Ru−S to Ru−O (KIIIO→S = 0.25 ± 0.025, kIIIO→S = 0.017 s-1, and kIIIS→O = 0.065 s-1; KIIO→S = 6.45 × 109, kIIO→S
= 0.132 s-1, kIIS→O = 2.1 × 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.