Tuning Radical Reactivity in Photocatalytic Transformations of NHC-Activated Substrates
N-Heterocyclic carbenes are known to stabilize adjacent radical centers efficiently. The generation of carbon- or boron-centered unpaired spin-systems however is either happening as a side effect (standard NHC-activation of carbonyls) or if synthetically targeted with the help of stoichiometric oxidants. Here, the generation of the NHC-stabilized open-shell species is intended to be used for broadening the scope of NHC-catalyzed transformations and will be achieved by visible light activation either via direct irradiation or via photo(redox)- catalysis.
The installment of assembly-controlling, reactivity-modulating steps of the in situ generated NHC-stabilized boron-centered radicals via secondary interactions (here: H-bonds, Lewis-acid-base interactions) accompanying the formation of boron-centered radicals will be studied and developed.
The cross-links with projects utilizing H-bond directed assemblies (B6, B7) or analyzing those by sophisticated NMR experiments (R. Gschwind, B3) will path the deduction of generalized concepts of this type of assembly-controlled reactivity.
Likewise, will the characterization of the (ultra)fast photophysical and chemical processes by ps-IR/UV experiments (P. Nürnberger, A5) add to the mechanistic insights that we will elucidate with according computational chemistry and EPR spectroscopy.