Ruthenium Complexes of Tripodal Ligands with Pyridine and Triazole Arms: Subtle Tuning of Thermal, Electrochemical, and Photochemical Reactivity

Abstract

Electrochemical and photochemical bond-activation steps are important for a variety of chemical transformations. We present here four new complexes, [Ru(L(n) )(dmso)(Cl)]PF6 (1-4), where L(n) is a tripodal amine ligand with 4-n pyridylmethyl arms and n-1 triazolylmethyl arms. Structural comparisons show that the triazoles bind closer to the Ru center than the pyridines. For L(2) , two isomers (with respect to the position of the triazole arm, equatorial or axial), trans-2sym and trans-2un , could be separated and compared. The increase in the number of the triazole arms in the ligand has almost no effect on the Ru(II) /Ru(III) oxidation potentials, but it increases the stability of the RuSdmso bond. Hence, the oxidation waves become more reversible from trans-1 to trans-4, and whereas the dmso ligand readily dissociates from trans-1 upon heating or irradiation with UV light, the RuS bond of trans-4 remains perfectly stable under the same conditions. The strength of the RuS bond is not only influenced by the number of triazole arms but also by their position, as evidenced by the difference in redox behavior and reactivity of the two isomers, trans-2sym and trans-2un . A mechanistic picture for the electrochemical, thermal, and photochemical bond activation is discussed with data from NMR spectroscopy, cyclic voltammetry, and spectroelectrochemistry.

Synthesis, structure, stability and antimicrobial activity of a ruthenium(II) helicate derived from a bis-bidentate “click” pyridyl-1,2,3-triazole ligand

“…The rutheniumnitrogen (Ru-N py 2.084-2.101 Å and Ru-N tri 2.030-2.066 Å) bond distances and N tri -Ru-N py angles ( Fig. 2) are similar to those previously observed in related monomeric ruthenium(II) pyridyl-1,2,3-triazole complexes [65,66]. The overall structure of the helicate is nearly identical to that observed for the related iron(II) system.…”

Photophysics and photochemistry of 1,2,3-triazole-based complexes

“…Photochemical reactivity in complexes of the form [Ru(L)(DMSO)(Cl)] + (where L is a tripodal amine ligand derived from tris(2-pyridylmethyl)amine with 3-n pyridyl and n triazole arms) can be controlled as a function of triazole content, with a greater number of triazole donors leading to an increase in both the electron density at the metal centre and the strength of the Ru-DMSO bond. [124] Complexes where n = 1 and 2 undergo efficient photoinitiated ligand exchange of DMSO for MeCN when irradiated at 396 nm, whereas the rate of photosubstitution is considerably slower when n = 3, allowing for the detection of bis-solvento DMSO/MeCN and (MeCN)2 photo-product intermediates by 1 H NMR spectroscopy. [125] Photochemical reactivity has also been reported for [Ru(bpy)(L)] 2+ complexes.…”

Ruthenium Tris(2-pyridylmethyl)amine as an Effective Photocaging Group for Nitriles

“…16 A decrease in the absorption peaks at 370 and 365 nm for 1 and 2 , respectively, tentatively assigned as metal-to-ligand charge-transfer bands, 13 is observed within 10–15 min of irradiation with λ > 345 nm in H 2 O solutions (2% acetone), with the concomitant appearance of a new band at 397 and 390 nm, respectively (Figure 3). The quantum yields for decomposition of 1 and 2 are 0.012(1) and 0.011(1), respectively (λ irr = 350 nm).…”