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Highlights: The single-atom Cu species with S = 0 spin ground state in CuIII-HHTP have been fabricated. The CuIII-HHTP exhibits remarkable performance with a high urea yield of 7.780 mmol h−1 g−1 with the corresponding Faradaic efficiency of 23.09% at − 0.6 V (vs. RHE). Low spin state and empty ( d x 2 -y 2 0 ) orbitals are favorable to enhance the production urea of C–N coupling process. The catalytic activities are generally believed to be relevant to the electronic states of their active center, but understanding this relationship is usually difficult. Here, we design two types of catalysts for electrocatalytic urea via a coordination strategy in a metal–organic frameworks: CuIII-HHTP and CuII-HHTP. CuIII-HHTP exhibits an improved urea production rate of 7.78 mmol h−1 g−1 and an enhanced Faradaic efficiency of 23.09% at − 0.6 V vs. reversible hydrogen electrode, in sharp contrast to CuII-HHTP. Isolated CuIII species with S = 0 spin ground state are demonstrated as the active center in CuIII-HHTP, different from CuII with S = 1/2 in CuII-HHTP. We further demonstrate that isolated CuIII with an empty d x 2 -y 2 0 orbital in CuIII-HHTP experiences a single-electron migration path with a lower energy barrier in the C–N coupling process, while CuII with a single-spin state ( d x 2 -y 2 1 ) in CuII-HHTP undergoes a two-electron migration pathway. [ABSTRACT FROM AUTHOR]

The mechanisms of the transfer hydroformylation reactions catalyzed by rhodium, cobalt, and iridium complexes were studied by using the density functional theory. There are nine stages in each catalytic cycle: oxidation addition and C−H activation, hydrogen transfer and benzoic acid dissociation, anti-insertion reaction (decarbonylation), β-H elimination, nucleophilic substitution 1 (S N 1) of ligand, C=C insertion, C=O insertion, coordination of benzoic acid and hydrogen transfer, and reductive elimination and aldehyde dissociation for catalyst regeneration. The total free energy barriers of the reactions catalyzed by Rh, Co and Ir complexes are 25.1 ( 3 Rh → TS 11,12-Rh ), 27.3 ( 1 Co → TS 5,6-Co ) and 41.5 ( 14 Ir → TS 14,1-Ir ) kcal/mol, respectively. Such barriers indicate that the newly proposed cobalt complex could be a potential low-cost catalyst for the transfer hydroformylation reaction under mild conditions. The electronic structures of key intermediates and transition states in the reactions were analyzed by using the natural bond orbital theory and the Multiwfn program. [ABSTRACT FROM AUTHOR]