Ru(ii)-dmso complexes containing azole-based ligands: synthesis, linkage isomerism and catalytic behaviour

Abstract

The reaction of cis,fac-[RuCl2(dmso-S)3(dmso-O)], 1, with different azole (L) ligands leads to new [RuCl2(L)(dmso-S)3] compounds (L = CH3-pz-H, 2; NO2-pz-H, 3; CF3-pz-H, 4 and Br-Hind, 5). Complexes 2-5 have been characterized by analytical, spectroscopic and electrochemical techniques as well as by monocrystal X-ray diffraction analysis. Upon oxidation to Ru(iii) the complexes undergo linkage isomerization of a S-bound dmso ligand and the corresponding kinetic rates as well as the thermodynamic properties have been determined for compound 2 and also for the previously described [Ru(II)Cl2(pypz-H)(dmso-S)2] (pypz-H = 2-(3-pyrazolyl)pyridine), 6, from cyclic voltammetries performed at different scan rates. The exposure of compound 2 to visible light in acetonitrile produces the substitution of one dmso ligand by a solvent molecule generating a new compound, 2'. The irradiation of solutions of compounds 2 and 6 in chloroform leads in both cases to the substitution of one dmso by a chlorido ligand in parallel to the oxidation of Ru(ii) to Ru(iii) generating complexes 2'' and 6' respectively. The reactivity of compounds 2-6 has been tested with regard to the hydration of nitriles in water as a solvent, displaying in all cases good performance and selectivity for the corresponding amides.

Mono(2,2′‐bipyridyl)RuII Complex with Four Dimethyl Sulfoxide Ligands as Precursor for cis‐Bis‐heteroleptic RuII Complex: Syntheses, Structures, and Substitution Reactions

“…The linkage isomerization between S ‐bonded and O ‐bonded dmso ligands in Ru II ‐dmso complexes commonly occurs by photochemical and electrochemical redox processes, because the electron‐transfer of a Ru II ion induces the linkage isomerization of the dmso ligand . Thus, our case is very unusual from the viewpoint of linkage isomerization.…”

“…This is the first report of thermodynamic data for the linkage isomerization equilibrium between O ‐bonded and S ‐bonded dmso in a Ru II complex using 1 H NMR spectroscopy, as far as we know. On the other hand, many kinetic studies of the linkage isomerization between O ‐bonded and S ‐bonded dmso in Ru III /Ru II complexes have been performed using cyclic voltammetry . The value of K O→S for 1 2+ , 0.099 at 303 K, is similar to that of fac ‐[Ru([9]aneS 3 )(dmso‐ O )(dmso‐ S ) 2 ] 2+ (0.4) and those of Ru III complexes rather than those of Ru II .…”

“…In the aromatic region, the minor four signals (marked with black arrows in Figure ) are observed with the same intensities, and the two pyridyl groups of the bpy are equivalent in the species, which is assigned as the isomer fac ( S )‐[Ru(bpy)(dmso‐ O )(dmso‐ S ) 3 ] 2+ ( 1 iso 2+ , Figure ). The likelihood of the formation of fac (O)‐[Ru(bpy)(dmso‐ O ) 3 (dmso‐ S )] 2+ would be small, because based on HSAB theory one would expect an S ‐bonded dmso ligand to be more favorable relative to an O ‐bonded dmso ligand . The ratio of the two isomers in the 1 H NMR spectrum of 1· (OTf) 2 in [D 6 ]DMSO, [ 1 iso 2+ ]/[ 1 2+ ], is 3:97 at 298 K. At 373 K (Figure b), the minor signals increase in intensity ([ 1 iso 2+ ]/[ 1 2+ ] = 33:67), but after cooling to 298 K, the temperature of sample reached to 298 K for 10 min and the linkage isomerization also achieved the equilibrium; [ 1 iso 2+ ]/[ 1 2+ ] = 3:97, again.…”

“…Furthermore, we report the uncommon linkage isomerization of the dmso ligands in 1 2+ in DMSO. There are many reports on the electrochemical linkage isomerization of Ru III /Ru II complexes with dmso ligands during cyclic voltammetry, and photo‐induced linkage isomerization of dmso ligand on Ru II complex . This is the first report of thermodynamic data for the linkage isomerization of a dmso ligand on a Ru II complex, determined by 1 H NMR spectroscopy, to the best of our knowledge.…”

Ruthenium-Catalyzed Azide Alkyne Cycloaddition Reaction: Scope, Mechanism, and Applications

“…DMF and DMA, while reactions using DMSO have been reported to be problematic, 65 which is most likely related to the ability of DMSO to act as ligand to ruthenium. 66 Protic solvents are not suitable, giving low yields and a high degree of byproduct formation. 27,52 Most reported RuAAC reactions employ either Cp*RuCl(PPh 3 ) 2 or Cp*RuCl(COD) as the catalyst, using between 1 and 5 mol% catalyst, and both these complexes are commercially available.…”