Effect of Deprotonation of a Benzimidazolyl Ligand on the Redox Potential and the Structures of Mononuclear Ruthenium(II) Complexes

Abstract

A monoruthenium(II) complex of the benzimidazolyl ligand and its deprotonated counterpart were prepared and structurally characterized. The reversible protonation/deprotonation process of the ancillary ligand switches the redox po-

Liquid-Assisted Solid-State Reaction: Formation of a Three-Dimensional Hydrogen-Bonded Network and Evidence for Proton Induced Electron Transfer

“…The above experiments indicate that H 3 TMA is necessary for the redox reaction. We know that the distal deprotonation of imidazole can reduce the redox potential of metal center. − The more deprotonation of H 2 biim ligands makes the redox potentials of Ru(II) complex shift to a less positive value. Crystal structure of 1 shows that there are 6-fold robust hydrogen bonded interactions between one [Ru(H 2 biim) 3 ] 3+ cation and three TMA anions.…”

“…2 Furthermore, the imidazole-like ligand was widely used as one of the proton carriers because the distal deprotonation of the ligand bearing the imidazole-like component reduces the redox potential of metal center. [13][14][15][16][17] Recently, the strategy of second-sphere coordination has been employed to design ionic receptors based on 2,2 0 -biimidazole (H 2 biim) and 2,2 0 -bibenzimidazole (H 2 bbim) complexes. [18][19][20][21] The most important feature for such a complex is that the chelating coordination enforces the syn conformation, then engages in robust hydrogen bonding via the externally directed pair of N-H groups of the H 2 biim and H 2 bbim ligands to the carboxylate group.…”

“…However, the observation of a redox reaction for coordination compounds by grinding is relatively rare . Furthermore, the imidazole-like ligand was widely used as one of the proton carriers because the distal deprotonation of the ligand bearing the imidazole-like component reduces the redox potential of metal center. − Recently, the strategy of second-sphere coordination has been employed to design ionic receptors based on 2,2′-biimidazole (H 2 biim) and 2,2′-bibenzimidazole (H 2 bbim) complexes. − The most important feature for such a complex is that the chelating coordination enforces the syn conformation, then engages in robust hydrogen bonding via the externally directed pair of N−H groups of the H 2 biim and H 2 bbim ligands to the carboxylate group. − In complexes [Ru(bpy) 2 (L)](PF 6 ) 2 (bpy = 2,2′-bipyridine, L = H 2 biim and H 2 bbim), the formation of dual robust hydrogen bonds between the H 2 biim/H 2 bbim ligand and the carboxylate group triggers the proton transfer from H 2 biim/H 2 bbim to the carboxylate group, and turns the color of the complex from yellow to orange brown and then to violet because of the second sphere donor−acceptor interactions between Ru(II)-H 2 biim/H 2 bbim and anions. Such interaction (deprotonation in H 2 biim/H 2 bbim ligand) greatly increases the electron density at the Ru(II) center and shifts its oxidation potential to a less positive value .…”

Liquid-assisted solid-state reaction: assembly of (6,3) and (10,3) hydrogen-bonded networks based on [M(Hbiim)3] by oxidation of [M(H2biim)3]2+ complexes in the presence of acetate anions

“…We know that the distal deprotonation of imidazole can reduce the redox potential of metal center. [23][24][25][26] Our previous study showed that the addition 1 equiv of acetate to the solution of [Ru(bpy) 2 (H 2biim)] 2+ shifted the absorption band from 485 nm to 507 nm due to the monodeprotonation of the H 2 biim ligand. 27 In this case, each [Ru(H 2 biim) 3 ] 2+ cation can form 6-fold robust hydrogen bonds with three acetate anions, inducing deprotonation at three sites.…”

“…22 It was proved that the increased deprotonation at remote sites of imidazole ligands resulted in a shift in the redox potentials of a metal center to much less positive values. [23][24][25][26] This may afford an effective approach for the preparation of high status metal complexes via modification of the potential. On the other hand, the complex {[Ru(H 2 biim) 3 ](TMA)}$DMF$9H 2 O (H 3 TMA ¼ trimesic acid) which has a three dimensional network was obtained serendipitously during the complexation of [Ru(H 2 biim) 3 ](PF 6 ) 2 and H 3 TMA in a solution of DMF-EtOH at room temperature.…”