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Thermodynamic and kinetic parameters associated with the fluxional behavior of 2-methyl- and 2,6-dimethyltroponeiron tricarbonyl complexes
Authors:Ambroz Almá  ssy,Andrej Bohá  ?,Marta Sali&scaron  ová  ,Myron Rosenblum
Affiliation:a Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University, Mlynská dolina, 84215 Bratislava, Slovakia
b Chemical Institute, Faculty of Natural Sciences, Comenius University, Mlynská dolina, 84215 Bratislava, Slovakia
c Department of Chemistry, Brandeis University, Waltham, MA 02254-9110, USA
Abstract:The kinetic and thermodynamic parameters for regioisomerisation of 2-methyl- and 2,6-dimethyl-derivatives of tricarbonyl[η4-tropone]iron complexes have been studied by 1H NMR spectrometry over a range of 40 °C. Regioisomerisation of these complexes proceeds by an intramolecular first-order process and results in the almost complete conversion of the less stable complexes (48) to more stable regioisomers (15). The activation energies and half lifes for the conversion (4 → 1) and (8 → 5) were found to be ΔG#=92 kJ mol−1; τ1/2=12.8 h, and ΔG#=107 kJ mol−1; τ1/2=26.8 h, respectively, at 23 °C. Complex 1 reacts with (1R,2S,5R)-menthol in sulphuric acid solution, followed by neutralisation with sodium carbonate to give a separable mixture of diastereomeric tricarbonyl[(2,3,4,5-η)-(1R,2S,5R)-6-menthyloxy-2-methyltropone]iron complexes, 9 and 10. The corresponding dimethylated complex 5 fails to react under these conditions.
Keywords:Troponeiron tricarbonyls   Fluxional behavior   Regioisomerisation   Thermodynamic and kinetic parameters   Dynamic 1H NMR spectroscopy   (1R,2S,5R)-menthol
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