Correlation between the Structure and Catalytic Activity of [Cp*Rh(Substituted Bipyridine)] Complexes for NADH Regeneration

A series of water-soluble half-sandwich [Cp*Rh^III(N^N)­Cl]⁺ (Cp* = pentamethylcyclopentadiene, N^N-substituted 2,2′-bipyridine) complexes containing electron-donating substituents around the 2,2′-bipyridyl ligand were synthesized and fully characterized for the regioselective reduction of nicotinamide coenzyme (NAD⁺). The influence of the positional effect of the substituents on the structural, electrochemical, and catalytic properties of the catalyst was systematically studied in detail. The catalytic efficiency of the substituted bipyridine Cp*Rh^III complexes are inversely correlated with their redox potentials. The 5,5′-substituted bipyridine Cp*Rh^III complex, which had the lowest reduction potential, most effectively regenerated NADH with a turnover frequency of 1100 h^–1. Detailed kinetic studies on the generation of intermediate(s) provide valuable mechanistic insight into this catalytic cycle and help to direct the future design strategy of corresponding catalysts

A Covalent Triazine Framework, Functionalized with Ir/N-Heterocyclic Carbene Sites, for the Efficient Hydrogenation of CO₂ to Formate

Functionalizing the recently developed porous materials such as porous organic frameworks and coordination polymer networks with active homogeneous catalytic sites would offer new opportunities in the field of heterogeneous catalysis. In this regard, a novel covalent triazine framework functionalized with an Ir­(III)-N-heterocyclic carbene complex was synthesized and characterized to have a coordination environment similar to that of its structurally related molecular Ir complex. Because of the strong σ-donating and poor π-accepting characters of the N-heterocyclic carbene (NHC) ligand, the heterogenized Ir-NHC complex efficiently catalyzes the hydrogenation of CO₂ to formate with a turnover frequency of up to 16 000 h^–1 and a turnover number of up to 24 300; these are the highest values reported to date in heterogeneous catalysis for the hydrogenation of CO₂ to formate