Co-Authors:
Poverenov, E., Department of Food Quality and Safety, Agricultural Research Organization, Volcani Center, Bet Dagan, 50250, Israel
Efremenko, I., Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Leitus, G., Unit of Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel
Martin, J.M.L., Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Milstein, D., Department of Organic Chemistry, Weizmann Institute of Science, Rehovot 76100, Israel
Abstract:
Benzyl cations are highly reactive compounds involved as intermediates in various chemical and biochemical processes. In this work metal coordination was utilized to stabilize different coordinated modes of benzyl cations, including methylene arenium (MA), π-benzyl, and σ-benzyl complexes. Two bidentate ligand frameworks, diphenylphosphinoethane (dppe) and di-tert- butylphosphinopropane (dtpp), were studied. η2-Coordination to Pd(II) allows for the characterization and studies of the reactivity of the otherwise unobserved methylene arenium species under ambient conditions. The relative stability and electronic structure of the three forms of the coordinated benzyl molecule, η2-MA, η1-σ- benzylic, and η3- π-benzylic, were investigated experimentally and computationally. The MA and π-benzylic structures are preferred in the absence of counteranions, while the dtpp bulky ligand contributes to stabilization of the methylene arenium form. Counteranions have a significant influence on the relative stability. The triflate anion stabilizes the σ-benzylic form upon coordination to the metal center or the methylene arenium form as a result of compensation of positive charge on the MA ring. Use of the noncoordinating BArF counteranion promotes conversion to the π-benzylic form. © 2013 American Chemical Society.
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