Sawhorse-type diruthenium tetracarbonyl complexes derived from pyrenyl-carboxylic acids

A series of sawhorse-type diruthenium tetracarbonyl complexes containing pyrenyl groups in the equatorial positions of the diruthenium backbone has been synthesized and characterized. The reaction between dodecacarbonyltriruthenium Ru3(CO)12 and pyrene-carboxylic acids, 1-pyrenecarboxylic acid (C16H9COOH), 1-pyreneacetic acid (C16H9CH2COOH) and 1-pyrenebutyric acid (C16H9(CH2)3COOH), followed by addition of axial ligands (L), pyridine (a) and triphenylphosphine (b), affords the stable diruthenium tetracarbonyl complexes, Ru2(CO)4(μ2-η2-OOCC16H9)2(L)2 (1), Ru2(CO)4(μ2-η2-OOCCH2C16H9)2(L)2 (2) and Ru2(CO)4(μ2-η2-OOC(CH2)3C16H9)2(L)2 (3), respectively. The molecular structure of the triphenylphosphine derivatives Ru2(CO)4(μ2-η2-OOCC16H9)2(PPh3)2 (1b), Ru2(CO)4(μ2-η2-OOCCH2C16H9)2(PPh3)2 (2b) and Ru2(CO)4(μ2-η2-OOC(CH2)3C16H9)2(PPh3)2 (3b) was determined by single-crystal X-ray structure analysis and showed a typical diruthenium tetracarbonyl backbone bridged by the pyrene-carboxylato ligands and completed with PPh3 axial ligands. The molecular structure of complexes 2 and 3 reveals that the pyrenyl moieties are adequately positioned to potentially allow these bis-pyrenyl systems to act as molecular tweezers. However, these systems have showed no interaction with fullerene in solution, despite possessing, as suggested by molecular modeling, appropriate structural features.