Two dicarbonylruthenium(II) complexes were prepared with the same framework but different π-conjugation lengths in their supporting ligands. Despite the shared framework, as determined from X-ray structural analysis, they showed significantly different reactivities due to the chemical structures of the supporting ligands. Isolation and characterization of the photoreaction products revealed that the complex with shorter π-conjugation system underwent complete decarbonylation followed by photoisomerization, whereas the other complex with a longer system retained one carbonyl ligand and the original geometry.Keywords: Carbonylruthenium complex with polypyridines | CO-ligand photoreaction | X-ray structural analysis Carbonylruthenium(II) complexes containing polypyridyl supporting ligands like 2,2¤-bipyridine (bpy) can catalyze various useful chemical reactions such as the water-gas shift reaction (WGSR) and multielectron reductions of CO 2 . 1,2Unfortunately, CO ligands in such complexes frequently dissociate under photoirradiation or by reduction. We previously reported an interaction between the CO ligand and a noncoordinated nitrogen atom in the carbonylruthenium complex with the bidentate pyridyl ligand 2-(2-pyridyl)-1,8-naphthyridine (pynp, Chart 1), which inhibits the dissociation of CO caused by the reduction of the complex. 3 There have been few reports on how the chemical structure of the supporting ligand affects the reactivity of the CO ligand, even though the ligands are essential for controlling the reactivity of the complex and its selectivity for various reactions.Herein, we synthesized new dicarbonyl complexes containing pynp or another polypyridyl ligand 3-(pyrid-2¤-yl)-4-azaacridine (paa, Chart 1) 4 that has a more extended π-conjugated system compared to pynp: cis-[Ru(bpy)(pynp)(CO) 2 ] 2+ ( 1 2+ ) and cis-[Ru(bpy)(paa)(CO) 2 ] 2+ (2 2+ ), respectively. We developed a route to selectively synthesize the desired geometrical isomer to eliminate the interligand interactions. We then evaluated the effect of the polypyridyl chemical structure on the CO-ligand reactions for the two complexes.A synthetic strategy for sequentially introducing different bidentate pyridyl ligands in ruthenium complexes was previously reported by Keene and his co-workers. 5 We therefore prepared 1 2+ and 2 2+ according to this method (Scheme 1).Keene et al. mentioned that treating the precursors with trifluoromethanesulfonic acid (TfOH) promotes both the dissociation of Cl ligands and isomerization (trans to cis), and that the products contain triflate-coordinated complexes that facilitate the introduction of the second bidentate pyridyl ligand. Our structural analysis of the intermediate, recrystallized from H 2 O, confirmed that the cis geometry was retained, although two triflate ligands substituted the aqua ones ( Figure S1). 6The second ligand (pynp or paa) was introduced into the diaqua intermediate to obtain the desired dicarbonyl complex (1 2+ or 2 2+ ). Since both pynp and paa are asymmetric with no C 2 axis, ...

The reactivities of transition metal coordination compounds are often controlled by the environment around the coordination sphere. For ruthenium(II) complexes, differences in polypyridyl supporting ligands affect some types of reactivity despite identical coordination geometries. To evaluate the synergistic effects of (i) the supporting ligands, and (ii) the coordination geometry, a series of dicarbonyl–ruthenium(II) complexes that contain both asymmetric and symmetric bidentate polypyridyl ligands were synthesized. Molecular structures of the complexes were determined by X-ray crystallography to distinguish their steric configuration. Structural, computational, and electrochemical analysis revealed some differences between the isomers. Photo- and thermal reactions indicated that the reactivities of the complexes were significantly affected by both their structures and the ligands involved.

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To modulate and evaluate the strength of noncovalent interactions experimentally, mononuclear ruthenium aqua complexes ([Ru(dnp)(OH2)L2]2+: dnp: 2,6-di(1,8-naphthyridin-2-yl)pyridine, L = pyridine or triphenylphosphine) that are capable of forming multiple intramolecular hydrogen bonds have been prepared. In both solution and the solid state, the intramolecular hydrogen-bonding strength in these complexes can be regulated by the axial ligand (L).

The asymmetric unit of the title compound, [Ru(C13H9N3)(C15H11N3)(H2O)](PF6)2·1.5C3H6O, consists of two crystallographically independent RuII complexes. Each complex is approximately octa­hedral with the RuII atom bound by an N,N′-coordinated 2-(2-pyrid­yl)-1,8-naphthyridine (pynp) ligand, a meridional 2,2′:6′,2′′-terpyridine (tpy) ligand and one aqua ligand. The tpy ligand is coordinated in a planar tridentate fashion with the central N atom closest to the RuII atom. The aqua ligand is trans to the pyridine N atom of pynp. The long Ru—O distances [2.150 (5) and 2.138 (5) Å] are typical for aqua ligands in polypyridyl ruthenium complexes. In the crystal, both intra­molecular O—H⋯N and inter­molecular O—H⋯O hydrogen bonds are observed.