Spin trapping by bis(benzene)chromium: A density functional study

Abstract

Bis(benzene)chromium [(η⁶–C₆H₆)₂Cr] (BBC) was shown to trap radical species R (R = H, isobutyronitrile (IBN)) to form complex paramagnetic adducts whose structure was characterized in frozen solution by electron nuclear double resonance (ENDOR) spectroscopy. It has been shown that radical attack yields the 17 valence species (η⁶–C₆H₆)(η⁵–C₆H₆R)Cr where R assumes the endo position of the η⁵ ring. To prove the existence of such a mechanism, a density functional study of BBC and corresponding adducts has been carried out. Geometry optimisations of these molecules have been performed at the PBE0 level with an effective core potential for chromium and 6-31G(d) basis sets on carbons and hydrogens. The calculated hyperfine coupling constants of hydrogen nuclei of the obtained structure are in excellent agreement with experimental values, thus proving the formation of the ring-protonated adducts.