Supramolecular Stabilization of α,ω-Diphenylpolyynes by Complexation to the Tridentate Lewis Acid [o-C6F4Hg]3

2006-04-24T00:00:00Z (GMT) by Thomas J. Taylor François P. Gabbaï
The interaction of trimeric (perfluoro-o-phenylene)mercury ([o-C6F4Hg]3, 1) with α,ω-diphenylpolyynes containing 4, 6, 8, and 12 sp carbon atoms in CH2Cl2 leads to the formation of (1)2·Ph(C⋮C)2Ph (2), 1·Ph(C⋮C)3Ph (3), (1)2·Ph(C⋮C)4Ph (4), and (1)2·Ph(C⋮C)6Ph·CH2Cl2 (5). Adducts 24 have been characterized by elemental analysis, X-ray crystallography, infrared and fluorescence spectroscopy, differential scanning calorimetry, and thermogravimetric analysis. In the solid state, the α,ω-diphenylpolyynes, which are approximately planar, are associated to molecules of 1 on either side of the molecular plane via secondary Hg−π interactions. The acetylenic stretches of 25 measured by IR spectroscopy are essentially identical with those of the free polyyne. While adducts 35 give rise to only faint emissions upon UV irradiation, the luminescence spectrum of 2 indicates complete quenching of the fluorescence and displays a heavy-atom-induced emission whose energy and vibronic progression are identical with those reported for the phosphorescence of the pure diyne. DSC/TGA studies indicate that adducts 24 are more thermally stable than the respective free α,ω-diphenylpolyynes. For Ph(C⋮C)4Ph, the stability range is increased by almost 120 °C under an oxidizing atmosphere. Similar conclusions are derived by monitoring the acetylenic stretches of Ph(C⋮C)4Ph and 4 as a function of temperature in KBr.