Chemical Hermaphroditism: The Potential of the Cr(CO)3 Moiety To Stabilize Transition States and Intermediates with Anionic, Cationic, or Radical Character at the Benzylic Position

Abstract

It is known that both benzylic cations and anions are stabilized by Cr(CO)3 complexation. This unusual characteristic of chromium arenes has been the subject of many synthetic, spectroscopic, and physical organic studies over the last four decades. The effect of Cr(CO)3 on benzylic radicals has received comparatively little attention, however. In this report, cyclopropylcarbinyl anions, cations, and radicals substituted with both phenyl and Cr(CO)3-phenyl groups are shown to rearrange via ring-opening to produce, selectively, Cr(CO)3-stabilized benzylic anions, cations, and radicals, implying that the Cr(CO)3 moiety is capable of stabilizing transition states with ionic or radical character at the benzylic position. The highest selectivity (>99:<1) was observed in the anionic reaction, slightly lesser selectivity (95:5) was observed in the cationic reaction, and only modest selectivity (2.5:1) was observed in the radical reaction. A parallel trend in ground-state stabilities of Cr(CO)3-complexed benzyl an...