Ruthenium(II) Pyridylamine Complexes with Diimine Ligands Showing Reversible Photochemical and Thermal Structural Change

Abstract

Ruthenium(II)-TPA-diimine complexes, [Ru(TPA)(diimine)]2+ (TPA=tris(2-pyridylmethyl)amine; diimine=2,2'-bipyridine (bpy), 2,2'-bipyrimidine (bpm), 1,10-phenanthroline (phen)) were synthesized and characterized by spectroscopic and crystallographic methods. Their crystal structures demonstrate severe steric hindrance between the TPA and diimine ligands. They exhibit drastic structural changes on heating and photoirradiation at their MLCT bands, which involve partial dissociation of the tetradentate TPA ligand to exhibit a facially tridentate mode accompanied by structural change and solvent coordination to give [Ru(TPA)(diimine)(solvent)]2+ (solvent=acetonitrile, pyridine). The incoming solvent molecules are required to have pi-acceptor character, since sigma-donating solvent molecules do not coordinate. The thermal process is irreversible dissociation to give the solvent-bound complexes, which takes place by an interchange associative mechanism with large negative activation entropies. The photochemical process is a reversible reaction reaching a photostationary state, probably by a dissociative mechanism involving a five-coordinate intermediate to afford the same product as obtained in the thermal reaction. Quantum yields of the forward reactions to give dissociated products were lower than those of the backward reactions to recover the starting complexes. In the photochemical process, the conversions of the forward and backward reactions depend on the absorption coefficients of the starting materials and those of the products at certain wavelength, as well as the quantum yields of those reactions. The reversibility of the motions can be regulated by heating and by photoirradiation at certain wavelength for the recovery process. In the bpm system, we could achieve about 90 % recovery in thermal/photochemical structural interconversion.

A [4+2] mixed ligand approach to ruthenium DNA metallointercalators [Ru(tpa)(N–N)](PF6)2 using a tris(2-pyridylmethyl)amine (tpa) capping ligand

“…S1-S5 (see Supporting Information). In general, there is very good agreement between the calculated and experimental Ru-N bond lengths and angles with essentially no variation along the series of compounds (Table S1), also with the very recently published structure of 2 [25]. The geometry optimizations correctly reproduce the tilting of the equatorial pyridine ring out of the plane formed by the bidentate N-N ligand and the ruthenium center, as found in the solid state structures of 1 and 2 [24][25][26].…”

“…Ruthenium complexes 1-5 were prepared from [Ru(tpa) (dmso)Cl]PF 6 and the bidentate N-N ligand by the route described in the literature for parent compound [Ru(tpa)(bpy)](PF 6 ) 2 , as shown in Scheme 1 [24][25][26]. After purification by column chromatography on silica with a mixture of methanol/water/sodium chloride (12:6:1) as the eluent and recrystallization from acetone/diethylether, they were obtained as crystalline solids in reasonable yield in a procedure optimized for purity.…”

“…In tpa compounds, the tertiary amine nitrogen atom is forced in plane with the bidentate ligand due to the short methylene linkers of the (2-pyridyl)methyl substituents. Since the two enantiomers possible due to positioning of the equatorial pyridine ring either above or below the plane of the bidentate ligand are known to interconvert in solution, [24,25] an isomer separation step is not required. The ease of modification and functionalization of the N-donor groups in such podant tetradentate ligands will also allow one to fine-tune the electronic and photophysical properties of the metal center [22].…”

Energy‐Level Tailoring in a Series of Redox‐Rich Quinonoid‐Bridged Diruthenium Complexes Containing Tris(2‐pyridylmethyl)amine as a Co‐Ligand

“…[32] Ruthenium complexes of tmpa have recently been studied in a biochemical context, [33] for the oxygenation of C À H bonds, [34] for proton-coupled electron transfer, [35] and for their photophysical properties. [36] Because changing the denticity of co-ligands is known to have dramatic effects on the 2 showed the localization of the double bonds within the quinonoid ring and a twisting of the mesityl substituents with respect to the quinonoid plane. Cyclic voltammetry of the complexes show two reversible oxidation and quinonoid-based reduction processes.…”

A Chemistry of Ruthenium-Tris(2-pyridylmethyl)amine Complexes

“…5b) 30,31) [RuCl((Isob) 2 3 ( Table 3 TPA I a (Interchange-Associative) 82) A Chemistry of Ruthenium-Tris(2-pyridylmethyl)amine Complexes …”