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)3Re­(μ-ER)2Re­(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.