Amide-Functionalized Chalcogen-Bridged Flexible Tetranuclear Rhenacycles: Synthesis, Characterization, Solvent Effect on the Structure, and Guest Binding

The synthesis of flexible rhenium(I)-based amide-functionalized chalcogen-bridged tetranuclear metallacycles of general formula [{(CO) 3 Re(μ-ER) 2 Re(CO) 3 } 2 (μ-L) 2 ] ( 1-8 ) was achieved by treating rhenium carbonyl with dialkyl/diaryl chalcogenide (RE-ER; E = S and Se) in the presence of ditopic flexible or semiflexible pyridyl ligand with amide functionality (L = N , N '-bis(4-pyridylcarboxamide)-1,2-ethane (bpce) and N , N '-bis(4-(4-pyridylcarboxamide)phenyl)methane (bpcpm)). Compounds 1-8 were formed by multicomponent self-assembly under one-pot reaction conditions via oxidative addition of dialkyl/diaryl chalcogenide to rhenium carbonyl with pyridyl ligands. The resultant metallacyclophanes were characterized using elemental analyses, infrared, ultraviolet-visible, and NMR spectroscopic techniques. Metallacyclophanes 1-3 and 7 were structurally characterized by single-crystal X-ray diffraction methods. The solvent-induced structural change of flexible tetranuclear metallacyclophane 2 was demonstrated by crystallizing 2 in dichloroethane and dimethylformamide. Molecular recognition capabilities of 2 and 7 were studied with few aromatic compounds containing ethereal linkages.