Gehinderte Ligandbewegungen in Übergangsmetallkomplexen, XXVIII [1] Photochemische C–H-Aktivierung an 1,3,5-Cycloheptatrien durch Rhenium(O) / Hindered Ligand Movements in Transition Metal Complexes, XXVIII [1] Photochemical C–H-Activation at 1,3,5-Cycloheptatriene by Rhenium(O)

Abstract

Decacarbonyl-dirhenium(O) (1) photochemically cleaves C-H-bonds in 1,3,5-cycloheptatriene (2 ) and forms two isomeric Re2(CO)8(μ-H)(μ-η2:1-cycloheptatrienyl) complexes (3, 4). In addition Re(CO)3(η5-cycloheptatrienyl) (5) and Re(CO)3(η5-cycloheptadienyl) (6) are obtained. The complexes 3 and 4 show temperature dependent 1H NMR spectra due to hindered ligand movements of the cycloheptatrienyl bridges with activation barriers of ⊿G≠ 207 = 39.9±2 kJ mol-1 and ⊿G≠ 255 = 48.0±2 kJ mol-1. 3 and 4 achieve in a thermal reaction an equilibrium with populations of 0.03 and 0.97 at 350 K with ⊿G≠ 350 - 96.5±5 kJ mol-1. The molecular structure of the more stable isomer, Re2(CO)8(μ-H)(μ-η2:1-1 ,3,5-cycloheptatrien-2-yl) (4 ) was determined by X-ray structure analysis.