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The photosynthetic oxygen‐evolving center (OEC) is a unique Mn4CaO5 cluster that serves as a blueprint to develop superior water‐splitting catalysts for the generation of solar fuels in artificial photosynthesis. It is a great challenge and long‐standing issue to reveal the synthesizing mechanism of this Mn4CaO5 cluster in both natural and artificial photosynthesis. Herein, efforts were made to reveal the synthesizing mechanism of an artificial Mn4CaO4 cluster, a close mimic of the OEC. Four key intermediates were successfully isolated and structurally characterized for the first time. It was demonstrated that the Mn4CaO4 cluster could be formed through a reaction between a thermodynamically stable Mn3CaO4 cluster and an unusual four‐coordinated MnIII ion, followed by stabilization process through binding an organic base (e.g. pyridine) on the "dangling" Mn ion. These findings shed new light on the synthesizing mechanism of the OEC and rational design of new artificial water‐splitting catalysts. [ABSTRACT FROM AUTHOR]

A palladium-catalyzed multicomponent synthesis of imidazolinium carboxylates and imidazolines is described. The palladium catalyst [Pd(CH(R1)N(R2)COR3)Cl]2, or [Pd(allyl)Cl]2, with P(t-Bu)2(2-biphenyl) can mediate the simultaneous coupling of two imines, acid chloride, and carbon monoxide into substituted imidazolinium carboxylates within hours under mild conditions (45 °C, 4 atm of CO). The reaction proceeds in good yield with aryl-, heteroaryl-, and alkyl-substituted acid chlorides, as well as variously functionalized imines. Imidazolines are formed via the initial generation of Mnchnone intermediates, followed by their cycloaddition with an in situ generated protonated imine. The addition of an amine base can intercept catalysis at Mnchnone formation, which allows the subsequent cycloaddition of a second imine. The latter provides a route for the assembly of complex, polysubstituted imidazolinium carboxylates with independent control of all five substituents. The subsequent removal of the nitrogen substituent(s) provides an overall synthesis of imidazolines. [ABSTRACT FROM AUTHOR]

The oxygen-evolving center (OEC) in photosynthesis is a unique Mn 4 CaO 5 -cluster that catalyzes the water-splitting reaction in nature. Understanding its catalytic mechanism for the O=O bond formation is of great challenge and long-standing issue, which is severely restricted by the lack of precise structure and mechanism mimics of this heterometallic-oxide cluster. Herein, we report two synthetic (Mn 3 XO 4 ) 2 O-clusters (X=Sr 2+ , La 3+ ) that closely mimic the heterometallic-oxide Mn 3 XO 4 cubane and three different types of μ-oxide bridges (μ 2 -O 2- , μ 3 -O 2- , and μ 4 -O 2- ) simultaneously as seen in the OEC. By resolving the crystal structures of both oxidized and reduced forms of the cluster, we have identified significant redox-induced structural changes that take place on the μ 2 -oxide bridge, rather than the μ 4 -oxide or μ 3 -oxide bridges. Our results provide chemical insights into understanding the reactivity of three different types of oxide bridges in the biological Mn 4 CaO 5 -cluster in PSII., (© 2022 Wiley-VCH GmbH.)

The photosynthetic oxygen-evolving center (OEC) is a unique Mn 4 CaO 5 cluster that serves as a blueprint to develop superior water-splitting catalysts for the generation of solar fuels in artificial photosynthesis. It is a great challenge and long-standing issue to reveal the synthesizing mechanism of this Mn 4 CaO 5 cluster in both natural and artificial photosynthesis. Herein, efforts were made to reveal the synthesizing mechanism of an artificial Mn 4 CaO 4 cluster, a close mimic of the OEC. Four key intermediates were successfully isolated and structurally characterized for the first time. It was demonstrated that the Mn 4 CaO 4 cluster could be formed through a reaction between a thermodynamically stable Mn 3 CaO 4 cluster and an unusual four-coordinated Mn III ion, followed by stabilization process through binding an organic base (e.g., pyridine) on the "dangling" Mn ion. These findings shed new light on the synthesizing mechanism of the OEC and rational design of new artificial water-splitting catalysts., (© 2022 Wiley-VCH GmbH.)

The oxygen-evolving center (OEC) in photosynthesis is a unique biological Mn 4 CaO 5 cluster catalyzing the water-splitting reaction. A great current challenge is to achieve a robust and precise mimic of the OEC in the laboratory. Herein, we report synthetic Mn 4 XO 4 clusters (X = calcium, yttrium, gadolinium) that closely resemble the OEC with regard to the main metal-oxide core and peripheral ligands, as well as the oxidation states of the four Mn ions and the redox potential of the cluster. We demonstrate that rare-earth elements can structurally replace the calcium in neutral Mn 4 XO 4 clusters. All three Mn 4 XO 4 clusters with different redox-inactive metal ions display essentially the same redox properties, challenging the conventional view that the Lewis acidity of the redox-inactive metal ions could modulate the redox potential of the heteronuclear-oxide clusters. The new synthetic rare-earth element-containing Mn 4 XO 4 clusters reported here provide robust and structurally well-defined chemical models and shed new light on the design of new water-splitting catalysts in artificial photosynthesis.

Fe 2 TiO 5 was synthesized via the solvothermal method and adopted as co-catalyst to improve the photoelectrochemical (PEC) water splitting performance of BiVO 4 photoanode. After surface modification by Fe 2 TiO 5 , the BiVO 4 /Fe 2 TiO 5 photoanode shows a 300 mV cathodic shift in onset potential and 3 times enhancement in photocurrent, which delivers a photocurrent density of 3.2 mA/cm 2  at 1.23 V vs reverse hydrogen electrode. Systematic optical, electrochemical, and intensity-modulated photocurrent spectroscopy characterizations were performed to explore the role of Fe 2 TiO 5 and reveal that the enhanced PEC performance is mainly caused by the surface passivation effect of Fe 2 TiO 5 .

We describe the use of simple copper-salt catalysts in the selective aerobic oxidation of amines to nitriles or imines. These catalysts are marked by their exceptional efficiency, operate at ambient temperature and pressure, and allow the oxidation of amines without expensive ligands or additives. This study highlights the significant role counterions can play in controlling selectivity in catalytic aerobic oxidations., (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)