Existence of the Halocarbonyl and Trifluoromethyl Cations in the Condensed Phase

Experimental and theoretical studies show that neither CF3+ nor FCO+ can be stabilized in the condensed phase with presently known Lewis acids. In the case of ClCO+, stabilization with SbF6- was also not possible, but Sb3F15 possesses sufficient acidity to abstract a fluoride ion from ClFCO in the formation of ClCO+Sb3F16-. This salt was fully characterized, providing the first well-established proof for the existence of a halocarbonyl cation in the condensed phase. Theoretical calculations and thermochemical cycles were used to corroborate our experimental findings, demonstrating that is possible to predict correctly whether a molecule with three different donor sites, such as ClFCO, will form an oxygen-coordinated donor−acceptor adduct or undergo either F- or Cl- abstraction. Furthermore, a method is described for extending natural bond orbital (NBO) analyses to systems containing two different types of competing, p(π) back-donating ligands.