Selective C-H bonds activation reactions catalyzed by N-heterocyclic carbene metal complexes linked to porphyrins – SCARY-NHC

C-H bond activation reactions can have important applications and economic benefits. The most complicated challenge to take up in this field is the selective activation of C-H bonds relative to others within a substrate. Pyridine derivatives are privileged scaffold in medicinal chemistry and selectively activating meta and para C-H bonds can be particularly challenging. Indeed, the activation of ortho C-H bonds is much easier to achieve by homogeneous catalysis with metal complexes. The objective of the “SCARY-NHC” project is to functionalize pyridine derivatives by supramolecular catalysis using molecular systems combining transition metal-based catalysts and recognition sites capable of fixing pyridine substrates. Catalytic sites will be N-heterocyclic carbene metal complexes (NHC-M) catalyzing arylation (M = Pd, Rh), halogenation (M = Pd), borylation (M = Rh) and alkylation/alkenylation (M=Ni) reactions. Recognition sites will be zinc(II) porphyrins (ZnP) which will be able to fix pyridine substrates near the catalytic sites by forming dynamic and reversible Zn-N coordination bonds. Different binding modes between the two NHC-M and ZnP entities will be exploited in order to modify the position, the orientation and the distance of the NHC-M catalytic site with respect to the ZnP recognition site. The various pre-organized molecular systems associating NHC-M and ZnP can therefore make it possible to selectively activate para and meta C-H bonds pyridine substrates, while limiting the activation of the ortho C-H bonds which will be sterically protected by porphyrin core. This pre-organization of the two entities ZnP and NHC-MC can also make it possible to significantly enhance reaction rates.