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Reactions of the cationic diruthenium carbonyl complex [Ru2(μ-dppm)2(CO)4(μ,η-O2CMe)] with bidentate ligands; intramolecularly assisted stereospecific synthesis via the second-sphere face-to-face π–π stacking interactions |
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| Authors: | Kom-Bei Shiu Shih-Wei Jean Yu Wang and Gene-Hsiang Lee |
| Institution: | a Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan, ROC b Instrument Center, National Taiwan University, Taipei 106, Taiwan, ROC |
| Abstract: | The reactions of the diruthenium carbonyl complexes Ru2(μ-dppm)2(CO)4(μ,η2-O2CMe)]X (X=BF4? (1a) or PF6? (1b)) with neutral or anionic bidentate ligands (L,L) afford a series of the diruthenium bridging carbonyl complexes Ru2(μ-dppm)2(μ-CO)2(η2-(L,L))2]Xn ((L,L)=acetate (O2CMe), 2,2′-bipyridine (bpy), acetylacetonate (acac), 8-quinolinolate (quin); n=0, 1, 2). Apparently with coordination of the bidentate ligands, the bound acetate ligand of Ru2(μ-dppm)2(CO)4(μ,η2-O2CMe)]+ either migrates within the same complex or into a different one, or is simply replaced. The reaction of Ru2(μ-dppm)2(CO)4(μ,η2-O2CMe)]+ (1) with 2,2′-bipyridine produces Ru2(μ-dppm)2(μ-CO)2(η2-O2CMe)2] (2), Ru2(μ-dppm)2(μ-CO)2(η2-O2CMe)(η2-bpy)]+ (3), and Ru2(μ-dppm)2(μ-CO)2(η2-bpy)2]2+ (4). Alternatively compound 2 can be prepared from the reaction of 1a with MeCO2H–Et3N, while compound 4 can be obtained from the reaction of 3 with bpy. The reaction of 1b with acetylacetone–Et3N produces Ru2(μ-dppm)2(μ-CO)2(η2-O2CMe)(η2-acac)] (5) and Ru2(μ-dppm)2(μ-CO)2(η2-acac)2] (6). Compound 2 can also react with acetylacetone–Et3N to produce 6. Surprisingly Ru2(μ-dppm)2(μ-CO)2(η2-quin)2] (7) was obtained stereospecifically as the only one product from the reaction of 1b with 8-quinolinol–Et3N. The structure of 7 has been established by X-ray crystallography and found to adopt a cis geometry. Further, the stereospecific reaction is probably caused by the second-sphere π–π face-to-face stacking interactions between the phenyl rings of dppm and the electron-deficient six-membered ring moiety of the bound quinolinate (i.e. the N-included six-membered ring) in 7. The presence of such interactions is indeed supported by an observed charge-transfer band in a UV–vis spectrum. |
| Keywords: | Ruthenium Carbonyl Acetate 2 2′-Bipyridine Acetylacetonate 8-Quinolinolate |
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