Nature Catalysis - Simple organic molecules that can directly activate carbon–hydrogen bonds when photoexcited are effectively limited to carbonyls. Now, neutral acridines,...

Stony Brook chemistry professor Jeff Lipshultz is exploring how light can transform simple molecules into building blocks of medicine, materials, and products.

Ligand-to-metal charge-transfer (LMCT) excitation has emerged in recent years as a powerful modality in organic synthesis, namely for the generation of heteroatom-centered radicals through formal metal–ligand bond homolysis from the LMCT excited state. However, the exploitation of alternative LMCT excited state processes has been extremely limited. Here, we describe a general strategy for tuning the reaction course from LMCT excited states of titanium alkoxides. This reactivity paradigm has been exploited for tandem β-scission/Giese addition reactions of both scission-amenable and scission-recalcitrant alcohols under divergent reaction pathways of metal–ligand bond homolysis and excited state β-scission through judicious choice of electronically tuned Ti catalysts. Through intramolecular competition studies, catalyst-controlled scission is shown to facilitate a rate enhancement of up to 103-fold over the intrinsic scission of free alkoxyl radicals, highlighting the impact of accessing the excited state scission paradigm. Computations support the relevance of a scission-promoting LMCT excited state with stereoelectronically aligned alkoxyl radical cation character to enable direct, selective β-scission.

[1849-54-3] C6H5NO2 (MW 123.11) InChI = 1S/C6H5NO2/c8-4-5-1-2-7-3-6(5)9/h1-4,9H InChIKey = NVLPDIRQWJSXLZ-UHFFFAOYSA-N (used as a synthon for certain heterocycles, a ligand precur...