Abstract
Abstract The conformational behavior of a series of crown-fused dithia[n.3.3](1,2,6)cyclophanes ( 126-CPs ) and dithia[n.3.3](1,3,5)cyclophanes ( 135-CPs ) was investigated by variable-temperature 1H and 13C NMR spectroscopy, X-ray crystallography and density functional theory (DFT) calculations. Single crystal X-ray structure analysis showed that two thia-bridges in 126-CPs adopted a pseudochair–pseudochair (cc) conformation and the cyclophane decks underwent a ring-tilting motion in the case of [10.3.3](1,2,6)cyclophane ( 1a ). In contrast, the thia-bridges in 135-CPs took both cc and pseudoboat–pseudochair (bc) conformations, and the ring-tilting process was also found in [10.3.3](1,3,5)cyclophane ( 2a ). Variable temperature 1H NMR study revealed that there was no wobbling-motion for two thia-bridges in 126-CPs while thia-bridges in 135-CPs experienced a wobbling-process with a conformational barrier of 9.21 and 8.80 kcal mol−1, respectively, for 2a and [13.3.3](1,3,5)cyclophane ( 2b ). DFT calculations for the two cyclophanes series revealed that 126-CPs preferred a cc conformation which was consistent with the experimental observation; similarly, 135-CPs took a preferential cc conformation, agreeing with 2a having a predominant cc conformer (cc:bc ratio=70:30), but not 2b having a predominant bc conformer (cc:bc ratio=15:85) in the solid state.
Published Version
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