Final Report Summary - SYNMICS (Exploiting Synergistic Properties of Mesoionic Carbene Complexes: Teaching Rusty Metals Challenging Catalysis)
The synMICs project has successfully capitalized on so-called mesoionic ligands as dynamic scaffolds for inducing high catalytic activity to Earth-abundant transition metals. The peculiar electronic situation in these ligands presets them for assisting metals in catalytic transformations. The synMICs project has demonstrated the validity of this hypothesis and has disclosed a variety of new redox catalysts based on ‘rusty’ metals that are equally active or even more active than nobel metal catalysts and therefore have the potential to provide more sustainable catalytic processes. Highlights include (i) new, inexpensive nickel complexes for the efficient transformation of CO2 into higher value chemicals for synthesis, (ii) the iron-catalyzed selective reduction of C–C triple bonds to double bonds without the typically observed further reduction of these double bonds to single bonds, and (iii) the direct and mild oxidation of aromatic compounds to phenol-derivatives. This latter reaction is particularly attractive because of its high selectivity and avoids the typically occurring over-oxidation. Moreover, it provides a direct, single-step access at moderate temperatures (50 °C) to a bulk chemical, which is currently produced industrially in a three-step process involving temperatures above 200 °C. In complementary ground-breaking work, synMICs has shown that histidine-containing metalloenzymes may operate through a mechanism that has been overlooked so far, constituting of an isomerization of the metal bound histidine to a carbenic mode. Such a mechanistic proposal provides a new vista on enzyme working modes and may have far reaching consequences, ranging from a better synthetic mimicking of enzymatic catalysts to a revisiting of textbook paradigms. The synMICs project has started to exploit this new bonding scheme by generating miniaturized artificial hydrogenase metalloenzymes.