Multistep oxidation of diethynyl oligophenylamine-bridged diruthenium and diiron complexes

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Zhang, Jing ; Guo, Shen-Zhen ; Don, Yu-Bao ; Rao, Li ; Jin, Yun ; Yu, Guang-Ao ; Hartl, Frantisek ; Liu, Sheng Hua (2017)

Homodinuclear nonlinear complexes [{M(dppe)Cp*}2{μ-(-C≡C)2X}] (X = triphenylamine (TPA), M = Ru (1a) and Fe (1b); X = N,N,N',N',-tetraphenylphenylene-1,4-diamine (TPPD), M = Ru (2a)) were prepared and characterized by 1H, 13C and 31P NMR and single crystal X-ray diffraction (1a, 2a). Attempts to prepare the diiron analogue of 2a were not successful. Experimental data obtained from cyclic voltammetry (CV), square wave voltammetry (SWV), UV-vis-NIR spectroelectrochemistry and very informative IR spectroelectrochemistry in the C≡C-stretching region, combined with density functional theory calculations, afford to make an emphasizing assessment of the close association between the metal‒ethynyl termini and the oligophenylamine bridge core as well as their respective involvement in sequential one-electron oxidations of these complexes. The anodic behavior of the homobimetallic complexes depends strongly both on the metal center and the length of the oligophenylamine bridge core. The poorly separated first two oxidations of diiron complex 1b are localized on the electronically nearly independent Fe termini. In contrast, diruthenium complex 1a exhibits a significantly delocalized character and a marked electronic communication between the ruthenium centers through the diethynyl-TPA bridge. The ruthenium-ethynyl halves in 2a, separated by the doubly extended and more flexible TPPD bridge core, show a lower degree of electronic coupling, resulting in close-lying first two anodic waves and the NIR electronic absorption of [2a]+ with an indistinctive IVCT character. Finally, the third anodic waves in the voltammetric responses of the homobimetallic complexes are associated with the concurrent exclusive oxidation of the TPA or TPPD bridge cores.
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