Macrocyclic cyclophanes with two and three alpha,omega-dichalcogena-1,4-diethynylaryl units: syntheses and structural properties

By means of four- and six-component cyclization reaction various cyclophanes were synthesized. The components were the di(lithium) salts of 1,4-di(ethynyl)benzene (11), 4,4'-di(ethynyl)biphenyl (13), 1,4-di(ethynyl)-2,5-di(n-hexyl)benzene (18), and 1,4-di(ethynyl)-2,5-di(n-propyl)benzene (19). These building blocks were reacted with alpha,omega-dithiocyanato-n-alkanes and alpha,omega-diselenocyanato-n-alkanes with n = 3-6. In the case of 10 also 1,1'-di(2-thiocyanatoethyl)cyclohexane (24) was reacted to afford a cyclophane comprising three subunits of 11. From most of the resulting macrocyclic cyclophanes (4(n) (n = 3, 5), 5, 6, 7(n) , 8(n) (n = 3-6), 9(n) (n = 3, 5), and 10), we were able to grow single crystals. The X-ray analysis of 4(3), 7(3), 8(3), 8(4), 6, 7(5), and 8(5) revealed close contacts between the chalcogen atoms. These chalcogen-chalcogen interactions impose a ribbon-shape arrangement of molecules in 4(3) and a mutual crossing of two perdendicular planes built of 8(4) molecules. For 4(3) we found a close contact (3.28 A) between the pi planes of two neighboring C6H4 rings of different molecules, whereas in 8(4) such a close contact (3.74 A) was due to an intermolecular interaction. Tubular stacking of the macrocyclic rings was found for 7(5) and 8(5) caused by a ladder-type intermolecular chalcogen-chalcogen interaction.