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Exploring reactivity of four square planar beta-ketoaminato cobalt compounds in the [+1, +2, +3] oxidation states with applications to controlled radical polymerization and lignin degradation

University of British Columbia

Four Schiff-base square planar β‐ketoaminato cobalt(II) compounds and their cobalt(III) ethyl derivatives were synthesized. The relative cobalt-carbon bond strengths of the latter were assessed in order to predict their relative reactivities and potential applicability as organometallic catalysts and as mediators for the radical polymerization of vinyl acetate, methyl acrylate, and acrylonitrile. ¹H NMR, ¹⁹F NMR, UV-vis spectroscopy, and X-ray crystallography were used to characterize all novel Co(III)Et compounds, and previously-synthesized Co(II) compounds not fully characterized. Cyclic voltammetry of all cobalt(II) compounds revealed Co(II/III) redox processes in dichloromethane, and reversible Co(I/II) couplings in donor-solvent acetonitrile. Electronic modifications of the equatorial ligands afforded a series of complexes with varying degrees of reactivity. Relative cobalt-carbon bond strengths of cobalt(III) ethyl compounds were found by monitoring their thermal decompositions in the presence of a radical trap by UV-vis, and by observing equilibrium constants for persistent radical trapping of the ethyl radicals between cobalt(II) compounds by ¹⁹F NMR. Larger bond dissociation energies were found to be largely dependent on stabilization of the Co(III) species by donor ligands; however, solvent stabilization is also thought to play a significant role. Reactions explored included simple oxidation-reductions, Heck-type cross-coupling, lignin model degradation, electrocatalytic evolution of hydrogen, and mediation of radical polymerization of functionalized alkenes. Relative affinities for axial neutral donors and dioxygen were also explored in more detail.

Text

2013-12-15

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/44330

Chemistry

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/