title: Binding to Redox-Inactive Alkali and Alkaline Earth Metal Ions Strongly Deactivates the C-H Bonds of Tertiary Amides toward Hydrogen Atom Transfer to Reactive Oxygen Centered Radicals.
abstract: The effect of alkali and alkaline earth metal ions on the reactions of the cumyloxyl radical (CumO(•)) with N,N-dimethylformamide (DMF) and N,N-dimethylacetamide (DMA) was studied by laser flash photolysis. In acetonitrile, a >2 order of magnitude decrease in the rate constant for hydrogen atom transfer (HAT) from the C-H bonds of these substrates (kH) was measured after addition of Li(+). This behavior was explained in terms of a strong interaction between Li(+) and the oxygen atom of both DMF and DMA that increases the extent of positive charge on the amide, leading to C-H bond deactivation toward HAT to the electrophilic radical CumO(•). Similar effects were observed after addition of Ca(2+), which was shown to strongly bind up to four equivalents of the amide substrates. With Mg(2+), weak C-H deactivation was observed for the first two substrate equivalents followed by stronger deactivation for two additional equivalents. No C-H deactivation was observed in DMSO after addition of Li(+) and Mg(2+). These results point toward the important role played by metal ion Lewis acidity and solvent Lewis basicity, indicating that C-H deactivation can be modulated by varying the nature of the metal cation and solvent and allowing for careful control over the HAT reactivity of amide substrates.
authors: Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata" , Via della Ricerca Scientifica, 1, I-00133 Rome, Italy.
authors: Michela
authors: M
authors: Salamone
authors: Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata" , Via della Ricerca Scientifica, 1, I-00133 Rome, Italy.
authors: Giulia
authors: G
authors: Carboni
authors: Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata" , Via della Ricerca Scientifica, 1, I-00133 Rome, Italy.
authors: Livia
authors: L
authors: Mangiacapra
authors: Dipartimento di Scienze e Tecnologie Chimiche, Università "Tor Vergata" , Via della Ricerca Scientifica, 1, I-00133 Rome, Italy.
authors: Massimo
authors: M
authors: Bietti