Substituent-Induced Reactivity in Quinonoid-Bridged Dinuclear Complexes: Comparison between the Ruthenium and Osmium Systems

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• 作者：Michael G. Sommer ; David Schweinfurth ; Fritz Weisser ; Stephan Hohloch ; Biprajit Sarkar
• 刊名：Organometallics
• 出版年：2013
• 出版时间：April 8, 2013
• 年：2013
• 卷：32
• 期：7
• 页码：2069-2078
• 全文大小：482K
• 年卷期：v.32,no.7(April 8, 2013)
• ISSN：1520-6041

文摘

The ligand 2,5-bis[2-(methylthio)anilino]-1,4-benzoquinone (L) was used in its doubly deprotonated form to synthesize the complex [{Cl(畏⁶-Cym)Os}₂(渭-畏²:畏²-L_-2H)] (1; Cym = p-cymene = 1-isopropyl-4-methylbenzene). Spectroscopic characterization and elemental analysis confirms the presence of the chloride ligands in 1, which indirectly shows that the bridging ligand L_-2H acts in a bis-bidentate fashion in 1, with the thioether substituents on the bridge remaining uncoordinated. Abstraction of the chloride ligands in 1 by AgBF₄ in CH₃CN leads not only to the release of those chloride ligands but also to a simultaneous substituent-induced release of Cym with the bridging ligand changing its coordination mode to bis-tridentate. In the resulting complex [{(CH₃CN)₃Os}₂(渭-畏³:畏³-L_-2H)]²⁺ (2²⁺), the thioether groups of L_-2H are now coordinated to the osmium centers with the bridging ligand coordinating to the metal center in a bis-meridional form. The coordination mode of L_-2H in 2²⁺ was confirmed by single-crystal X-ray diffraction data. A structural analysis of 2²⁺ reveals localization of double bonds within the 鈥渦pper鈥?and 鈥渓ower鈥?parts of the bridging ligand in comparison to bond distances in the free ligand. Additionally, the binding of the bridge to the osmium centers is seen to occur through O^{鈥?/sup> and neutral imine-type N donors. The complexes 1 and 22+ were investigated by cyclic voltammetry and UV鈥搗is鈥搉ear-IR and EPR spectroelectrochemistry. This combined approach was used to unravel the redox-active nature of the ligand L_-2H, to determine the sites of electron transfer (ligand radical versus mixed valency), and to compare the present systems with their ruthenium analogues 3 and 42+ (Schweinfurth, D. Inorg. Chem. 2011, 50, 1150). The effect of replacing ruthenium by its higher homologue osmium on the reactivity and the electrochemical and spectroscopic properties were explored, and the differences were deciphered by taking into account the intrinsic dissimilarities between the two homologues. The usefulness of incorporating additional donor substituents on potentially bridging quinonoid ligands was probed in this work.}