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

作者：Sommer Michael G; Schweinfurth David; Weisser Fritz; Hohloch Stephan; Sarkar Biprajit^*

来源：Organometallics, 2013, 32(7): 2069-2078.

DOI：10.1021/om300939x

The ligand 2,5-bis[2-(methylthio)anilino]-1,4-benzoquinone (L) was used in its doubly deprotonated form to synthesize the complex [{Cl(eta(6)-Cym)Os}(2){mu-eta(2):eta(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)(3)Os}(2)(mu-eta(3):eta(3)-L-2H)](2+) (2(2+)), 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 2(2+) was confirmed by single-crystal X-ray diffraction data. A structural analysis of 2(2+) reveals localization of double bonds within the %26quot;upper%26quot; and %26quot;lower%26quot; 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- and neutral imine-type N donors. The complexes 1 and 2(2+) were investigated by cyclic voltammetry and UV-vis-near-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 4(2+) (Schweinfurth, D. et al. 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.

• 出版日期2013-4-8