Sensitivity of a Strained C鈥揅 Single Bond to Charge Transfer: Redox Activity in Mononuclear and Dinuclear Ruthenium Complexes of Bis(arylimino)acenaphthene (BIAN) Ligands

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• 作者：Prasenjit Mondal ; Hemlata Agarwala ; Rahul Dev Jana ; Sebastian Plebst ; Anita Grupp ; Fabian Ehret ; Shaikh M. Mobin ; Wolfgang Kaim ; Goutam Kumar Lahiri
• 刊名：Inorganic Chemistry
• 出版年：2014
• 出版时间：July 21, 2014
• 年：2014
• 卷：53
• 期：14
• 页码：7389-7403
• 全文大小：757K
• ISSN：1520-510X

文摘

The new compounds [Ru(acac)₂(BIAN)], BIAN = bis(arylimino)acenaphthene (aryl = Ph (1a), 4-MeC₆H₄ (2a), 4-OMeC₆H₄ (3a), 4-ClC₆H₄ (4a), 4-NO₂C₆H₄ (5a)), were synthesized and structurally, electrochemically, spectroscopically, and computationally characterized. The 伪-diimine sections of the compounds exhibit intrachelate ring bond lengths 1.304 脜 < d(CN) < 1.334 and 1.425 脜 < d(CC) < 1.449 脜, which indicate considerable metal-to-ligand charge transfer in the ground state, approaching a Ru^III(BIAN^{鈥⑩€?/sup>) oxidation state formulation. The particular structural sensitivity of the strained peri-connecting C鈥揅 bond in the BIAN ligands toward metal-to-ligand charge transfer is discussed. Oxidation of [Ru(acac)₂(BIAN)] produces electron paramagnetic resonance (EPR) and UV鈥搗is鈥揘IR (NIR = near infrared) spectroelectrochemically detectable RuIII species, while the reduction yields predominantly BIAN-based spin, in agreement with density functional theory (DFT) spin-density calculations. Variation of the substituents from CH₃ to NO₂ has little effect on the spin distribution but affects the absorption spectra. The dinuclear compounds {(渭-tppz)[Ru(Cl)(BIAN)]₂}(ClO₄)₂, tppz = 2,3,5,6-tetrakis(2-pyridyl)pyrazine; aryl (BIAN) = Ph ([1b](ClO₄)₂), 4-MeC₆H₄ ([2b](ClO₄)₂), 4-OMeC₆H₄ ([3b](ClO₄)₂), 4-ClC₆H₄ ([4b](ClO₄)₂), were also obtained and investigated. The structure determination of [2b](ClO₄)₂ and [3b](ClO₄)₂ reveals trans configuration of the chloride ligands and unreduced BIAN ligands. The DFT and spectroelectrochemical results (UV鈥搗is鈥揘IR, EPR) indicate oxidation to a weakly coupled RuIIIRuII mixed-valent species but reduction to a tppz-centered radical state. The effect of the 蟺 electron-accepting BIAN ancillary ligands is to diminish the metal鈥搈etal interaction due to competition with the acceptor bridge tppz.}