Sulfur atom-directed metal-ligand synergistic catalysis in zirconium/hafnium-oxo clusters for highly efficient amine oxidation

Interfacial chemical bond accelerating atomic-level charge transfer in step-scheme α-Fe2O3/PbBiO2I for efficient photoconversion of amines to imines

Inadequate contact interface, lack of direct electron-transfer paths and low substrate affinity are considered as the main obstacle inhibiting the heterostructure activity for the sustainable photosynthesis of value-added fine chemicals. Herein, a novel 0D/2D Step-scheme (S-scheme) α-Fe2O3/PbBiO2I (FO/PBOI) composite with abundant interface FeO bonds were initially synthesized via an in-situ growth approach. The created built-in field as a powerful driving force, efficiently steering the migration of photogenerated electrons. The interfacial FeO bonds act as atomic-level transfer highway, lowering charge transfer energy barrier between the interfaces and further accelerating the S-scheme spatial charge separation. Moreover, the FeO bonds bridged FO/PBOI can effectively enhance the activation of O2 and benzylamine, significantly reducing the dehydrogenation barrier for the rate-limiting C6H5CH2NH* intermediate. The optimized FO/PBOI exhibits remarkably improved catalytic activity and general applicability for the dehydrocoupling of primary amines to imines. This work offers an atomic-scale perspective on precise charge flow steering based on interface bond for advanced organic transformations.

Charge-Transport Divergence in Ultrastable Heterometal-Oxo Clusters Exerting Significant Effect on Photoreactivity

The transfer path of photogenerated charges greatly affects the final photocatalytic performance, but this important fact has not been clearly demonstrated experimentally. Here, we construct an ultrastable crystalline catalytic system including three heterometal-oxo clusters, Bi8M7-TBC4A (M = group IVB metal-Ti/Zr/Hf), which include cubic metal-oxo cluster core with eight Bi atoms at the vertices, one M atom at the body center, and six M atoms above the cubic face centers. It is worth noted that the change of group IVB elements in Bi8M7-TBC4A can specifically modulate the LUMO-HOMO orbitals to distribute on different active metal atoms. This allows it to be an excellent model system to verify the effect of the transport paths of photogenerated charges on photoreactivity. In model reaction based on CO2 photoreduction, Bi8Ti7-TBC4A displays superior photocatalytic CO2-to-HCOOH conversion rate of 3580.02 µmol g-1, which is twice that of Bi8Zr7-TBC4A and 4 times that of Bi8Hf7-TBC4A. In situ characterization accompanied by density functional theory (DFT) indicate that the difference in orbital hybridization between Bi and IVB group elements largely affects the orbital distribution of frontier molecular orbital levels in Bi8M7-TBC4A, leading to the transport of photogenerated charges to metal active sites with different reactivities, and thus widely differing photocatalytic performances. This is the first model catalyst system that explores the effect of different photogenerated charge transport pathways on photoreactivity.

Ferrocene-functionalized zirconium-oxo clusters for achieving high-performance thermocatalytic redox reactions

The Zr(IV) ions are easily hydrolyzed to form oxides, which severely limits the discovery of new structures and applications of Zr-based compounds. In this work, three ferrocene (Fc)-functionalized Zr-oxo clusters (ZrOCs), Zr9Fc6, Zr10Fc6 and Zr12Fc8 were synthesized through inhibiting the hydrolysis of Zr(IV) ions, which show increased nuclearity and regular structural variation. More importantly, these Fc-functionalized ZrOCs were used as heterogeneous catalysts for the transfer hydrogenation of levulinic acid (LA) and phenol oxidation reactions for the first time, and displayed outstanding catalytic activity. In particular, Zr12Fc8 with the largest number of Zr active sites and Fc groups can achieve > 95% yield for LA-to-γ-valerolactone within 4 h (130 °C) and > 98% yield for 2,3,6-trimethylphenol-to-2,3,5-trimethyl-p-benzoquinone within 30 min (80 °C), showing the best catalytic performance. Catalytic characterization combined with theory calculations reveal that in the Fc-functionalized ZrOCs, the Zr active sites could serve as substrate adsorption sites, while the Fc groups could act as hydrogen transfer reagent or Fenton reagent, and thus achieve effectively intramolecular metal-ligand synergistic catalysis. This work develops functionalized ZrOCs as catalysts for thermal-triggered redox reactions.

Accurate assembly of thiophene-bridged titanium-oxo clusters with photocatalytic amine oxidation activity

Designing and synthesizing well-defined crystalline catalysts for the photocatalytic oxidative coupling of amines to imines remains a great challenge. In this work, a crystalline dumbbell-shaped titanium oxo cluster, [Ti10O6(Thdc)(Dmg)2(iPrO)22] (Ti10, Thdc = 2,5-thiophenedicarboxylic acid, Dmg = dimethylglyoxime, iPrOH = isopropanol), was constructed through a facile one-pot solvothermal strategy and treated as a catalyst for the photocatalytic oxidative coupling of amines. In this structure, Thdc serves as the horizontal bar, while the {Ti5Dmg} layers on each side act as the weight plates. The molecular structure, light absorption, and photoelectrochemical properties of Ti10 were systematically investigated. Remarkably, the inclusion of the Thdc ligand, with the assistance of the Dmg ligand, broadens the light absorption spectrum of Ti10, extending it into the visible range. Furthermore, the effective enhancement of charge transfer within the Ti10 was achieved with the successful incorporation of the Thdc ligand, as opposed to PTC-211, where terephthalic acid replaces the Thdc ligand, while maintaining consistency in other aspects of Ti10. Building on this foundation, Ti10 was employed as a heterogeneous molecular photocatalyst for the catalytic oxidative coupling reaction of benzylamine (BA), demonstrating very high conversion activity and selectivity. Our study illustrates that the inclusion of ligands derived from Thdc enhances the efficiency of charge transfer in functionalized photocatalysts, significantly influencing the performance of photocatalytic organic conversion.