Planar chiral (arene)chromiumcarbonyl-substituted propargyl cations -: A spectroscopic and computational study

Planar chiral (arene)Cr(CO)(3)-substituted propargyl cations can be diastereoselectively generated from propargyl acetates with the use of strong Lewis acids, and they have been structurally characterized by UV/Vis and C-13 NMR spectroscopy. At low temperatures (<-65 degrees C) the s-cis isomer is exclusively obtained as a product of a kinetically controlled ionization. DFT studies on the structure of the propargyl cations and on the C-ipso-C-alpha bond rotation to give the thermodynamically favored s-trans isomer reveal that the substitution pattern at the gamma-propargyl position has a stronger impact on the height of the rotational barrier than the substituent on the complexed aryl ring. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).