Three cobalt complexes bearing tunable,redox-active bipyridyl N-heterocyclic carbene(NHC)-based ligands have been studied for electrocatalytic hydrogen evolution from aqueous solutions.The effect of structural modific...Three cobalt complexes bearing tunable,redox-active bipyridyl N-heterocyclic carbene(NHC)-based ligands have been studied for electrocatalytic hydrogen evolution from aqueous solutions.The effect of structural modifications to the ligand framework is investigated across the catalyst series,which includes a non-macrocyclic derivative(1-Co)and 16-(2-Co)and 15-(3-Co)membered macrocycles.A structure-activity relationship is demonstrated,in which the macrocyclic complexes have greater activity compared to their non-macrocyclic counterpart with the most rigid catalyst,supported by the 15-membered macrocycle,performing best overall.Indeed,3-Co catalyzes H2 evolution from aqueous pH 4 acetate buffer with a Faradaic efficiency of 97%at a low overpotential of 330 mV.Mechanistic studies are consistent with formation of a cobalt-hydride species that is subsequently protonated to evolve H2 via a heterolytic pathway.展开更多
N-heterocyclic carbene （NHC） is both a family of strong o-donor ligands for transition metals and a privileged class of organocatalysts with synthetic potential that rivals popu- lar amine and phosphoric acid cataly...N-heterocyclic carbene （NHC） is both a family of strong o-donor ligands for transition metals and a privileged class of organocatalysts with synthetic potential that rivals popu- lar amine and phosphoric acid catalysts. NHC was found as a key catalytic species in thiamine diphosphate catalyzed biochemical reactions [1]. However, due to their inherent chemical instability, free NHCs had not been isolated until 1991 by Ardungo et al. [2]. Since then, the use of chiral NHC as a versatile organocatalyst has enjoyed tremendous advances and has helped to transform modem synthetic chemistry. There are over 2000 research papers dealing with both ＂N-heterocyclic carbene＂ and ＂Catalysis＂ in the past 15 years [3].展开更多
文摘Three cobalt complexes bearing tunable,redox-active bipyridyl N-heterocyclic carbene(NHC)-based ligands have been studied for electrocatalytic hydrogen evolution from aqueous solutions.The effect of structural modifications to the ligand framework is investigated across the catalyst series,which includes a non-macrocyclic derivative(1-Co)and 16-(2-Co)and 15-(3-Co)membered macrocycles.A structure-activity relationship is demonstrated,in which the macrocyclic complexes have greater activity compared to their non-macrocyclic counterpart with the most rigid catalyst,supported by the 15-membered macrocycle,performing best overall.Indeed,3-Co catalyzes H2 evolution from aqueous pH 4 acetate buffer with a Faradaic efficiency of 97%at a low overpotential of 330 mV.Mechanistic studies are consistent with formation of a cobalt-hydride species that is subsequently protonated to evolve H2 via a heterolytic pathway.
基金the National Natural Science Foundation of China (21372013, 21572004)the Shenzhen Peacock Program (KQTD201103)
文摘N-heterocyclic carbene （NHC） is both a family of strong o-donor ligands for transition metals and a privileged class of organocatalysts with synthetic potential that rivals popu- lar amine and phosphoric acid catalysts. NHC was found as a key catalytic species in thiamine diphosphate catalyzed biochemical reactions [1]. However, due to their inherent chemical instability, free NHCs had not been isolated until 1991 by Ardungo et al. [2]. Since then, the use of chiral NHC as a versatile organocatalyst has enjoyed tremendous advances and has helped to transform modem synthetic chemistry. There are over 2000 research papers dealing with both ＂N-heterocyclic carbene＂ and ＂Catalysis＂ in the past 15 years [3].
