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Catalytic ethylene oligomerization is important in the petrochemical industry, as it produces valuable products like linear alpha‐olefins (LAOs) for the synthesis of polymers and specialty chemicals. Catalysts, typically transition metal complexes or metal‐containing materials, play a crucial role in selective oligomerization by providing active sites for ethylene activation and controlling product distribution. Recently, defective metal‐organic frameworks (MOFs) with well‐defined structures and unsaturated active sites have emerged as potential catalysts for ethylene oligomerization. In this study, we employ density functional theory calculations to investigate the energetic selectivity of competing pathways (including dimerization, isomerization and trimerization) during ethylene oligomerization on defective HKUST‐1 supported metal hydrides (H−M–DHKUST‐1, M: Co, Ni, Ru, Rh and Pd). On all the five hydrides, ethylene dimerization is found to be more preferential than trimerization and isomerization. In the microenvironment of defective paddlewheel of HKUST‐1, isomerization is highly unfavorable compared with dimerization because of high energy required for chain walk, and 1‐butene is expected to be the major product on all the five hydrides. Analysis of NBO charges reveals a notable reduction in cationic nature at the metal site on H−Ru–DHKUST‐1, which facilitates β‐hydride elimination for dimerization. The microscopic insights from this computational study might facilitate the rational design of new MOFs and other MOF‐supported catalysts for selective ethylene oligomerization. [ABSTRACT FROM AUTHOR]

Metal–organic framework (MOF)-based catalysts have shown enormous potential in CO2 conversion to high-value added chemicals. Herein, we report a density functional theory (DFT) study on CO2 hydrogenation to methanol (CH3OH) on defective UiO-66, in which a frustrated Lewis pair (FLP) is created by removing one organic linker. The hydrogenation is considered a three-stage transformation: (1) CO2 is hydrogenated into formic acid (HCOOH); (2) HCOOH is converted to formaldehyde (HCHO) via hydrogenation and dehydration; (3) HCHO is hydrogenated into CH3OH. The reaction mechanisms are investigated in detail by studying the optimized structures and the corresponding Gibbs energies for the elementary processes involved in the transformation. For CO2 hydrogenation to HCOOH, three pathways are computed comparatively. In Pathway I, adsorbed CO2 reacts with H2 to form HCOOH directly and this step features a high free energy barrier comparable to that in the gas phase. In the other two pathways, adsorbed H2 is first split into a proton (H+) and a hydride (H−) on the FLP, and then CO2 is hydrogenated into HCOOH via a stepwise mechanism (Pathway II) or a concerted mechanism (Pathway III). The DFT calculations reveal that the energy barriers in Pathway II and III are reduced significantly compared to that in Pathway I, and Pathway III is the most favourable for CO2 hydrogenation to HCOOH. Subsequent calculations suggest that the conversion of HCOOH to HCHO and further to CH3OH is also facile via H2 dissociation and the concerted transfer of H+ and H− to HCOOH and HCHO. These results highlight the importance of FLP-assisted heterolytic dissociation of H2 in promoting CO2 hydrogenation. This study suggests that the defective UiO-66 with a FLP might be a potential catalyst for CO2 hydrogenation and it could facilitate the bottom-up design of efficient MOF-based catalysts for CO2 utilization. [ABSTRACT FROM AUTHOR]

The adsorption and dissociation of CO over stepped Ni and Ni3Fe surfaces were systematically studied using density functional theory slab calculations. Both (211)-like surface structure terminations (NiNi step and NiFe step, denoted as Ni3Fe(211)-AA and Ni3Fe(211)-AB) are considered for Ni3Fe. Direct scission of the C–O bond in CO is identified as the least likely one among the three proposed dissociation pathways and CO dissociation via a CHO intermediate appears to be most feasible at low CO coverage on pure and alloyed Ni(211) surfaces. The priority of H-assisted CO dissociation might originate from the more activated C–O bond in COH and CHO. Compared to Ni(211), the Ni3Fe(211)-AB surface could facilitate CO activation especially for the most possible CHO intermediate mechanism, whose rate-limiting step is found to be altered. The d-band center theory and Mulliken charge analysis are also employed to explain the activity difference between Ni3Fe(211)-AB and Ni3Fe(211)-AA. The significant structural sensitivity of CO dissociation highlights the importance of Fe locating in the step edge and the high reactivity of Ni3Fe(211)-AB is largely ascribed to the synergistic effect between Ni and Fe at the step edge. [ABSTRACT FROM AUTHOR]

The reductive coupling of aldehydes to afford pinacolic alcohols using all kinds of reducing agents involving samarium is well known. In this report, however, treatment of aromatic aldehydes with Cu(I)/Sm system produces benoins and/or benzils in good yields. A possible mechanism is proposed where Cu(I) not only activates the Sm metal but also promotes the dehydrogenation of the intermediates, during which a Cu(III) species may be involved. [Supplementary materials are available for this article. Go to the publisher's online edition ofSynthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] [ABSTRACT FROM AUTHOR]

The concurrent conversion of CH 4 and CO 2 into acetic acid is an ideal route to migrate the two greenhouse gases and manufacture a high-value-added C 2 product with an atom economy of 100% but remains challenging due to the chemical inertness of both gases. By leveraging density functional theory (DFT) calculations, we report herein the computational design of metal-alkoxide-functionalized metal-organic framework (MOF) UiO-67 with well-defined dual sites that can activate CH 4 and CO 2 cooperatively to boost acetic acid synthesis. The dual sites are distributed on two adjacent functionalized organic linkers originating from the same node and feature a metal-metal distance of about 6-7 Å. Initially, a total of 13 single-site metal-alkoxide-functionalized UiO-67s (including three alkaline earth metals and 10 transition metals) are examined; then, favorable metal-alkoxides are identified and further used to design dual-site metal-alkoxide-functionalized UiO-67s for converting CH 4 and CO 2 into acetic acid. Detailed mechanistic investigation predicts that the dual-site UiO-67s functionalized with Mn-, Fe-, Co-, Ni-. and Zn-alkoxide are highly promising catalysts for this reaction. Compared to the single-site counterparts, the metal pair-site UiO-67s provide a subtle microenvironment for synergistic dual activation of CH 4 and CO 2 , thus efficiently stabilizing the transition state and substantially reducing the reaction barrier for C-C coupling. The microscopic insights and design strategies in this work might advance the development of efficient MOF-based catalysts with built-in cooperative active sites toward direct acetic acid synthesis from CH 4 and CO 2 .

By synergizing the advantages of homogeneous and heterogeneous catalysis, single-site heterogeneous catalysis represents a highly promising opportunity for many catalytic processes. Particularly, the unprecedented designability and versatility of metal-organic frameworks (MOFs) promote them as salient platforms for designing single-site catalytic materials by introducing isolated, well-defined active sites into the frameworks. Herein, we design new MOF-supported single-site catalysts for CO 2 hydrogenation to methanol (CH 3 OH), a reaction of great significance in CO 2 valorization. Specifically, N-heterocyclic carbene (NHC), a class of excellent modifiers and anchors, is used to anchor coinage metal hydrides M(I)-H (M = Cu, Ag, and Au) onto the organic linker of UiO-68. The strong metal-ligand interactions between NHC and M(I)-H verify the robustness and feasibility of our design strategy. On the tailor-made catalysts, a three-stage sequential transformation is proposed for CH 3 OH synthesis with HCOOH and HCHO as the transit intermediates. A density functional theory-based comparative study suggests that UiO-68 decorated with NHC-Cu(I)-H performs best for CO 2 hydrogenation to HCOOH. This is further rationalized by three linear relationships for the Gibbs energy barrier of CO 2 hydrogenation to HCOO intermediate, the first with the NBO charge of the hydride in NHC-M(I)-H, the second with the electronegativity of M, and the third with the gap between the lowest unoccupied molecular orbital of CO 2 and the highest occupied molecular orbital of the catalyst. It is confirmed that the high efficiency of MOF-supported NHC-Cu(I)-H for CO 2 transformation to CH 3 OH is via the proposed three-stage mechanism, and in each stage, the step involving heterolytic dissociation of H 2 together with product generation is the most energy-intensive. The rate-limiting step in the entire mechanism is identified to be H 2 dissociation accompanying with simultaneous HCHO and H 2 O formation. Altogether, the tailor-made UiO-68 decorated with NHC-Cu(I)-H features well-defined active sites, enables precise manipulation of reaction paths, and demonstrates excellent reactivity for CO 2 hydrogenation to CH 3 OH. It is also predicted to surpass a recently reported MOF-808 catalyst consisting of neighboring Zn 2+ -O-Zr 4+ sites. The designed MOFs as well as the proposed strategy here establish a new paradigm and can be extended to other hydrogenation reactions.

The self-assembly of highly stable zirconium(IV)-based coordination cages with aggregation induced emission (AIE) molecular rotors for in vitro bio-imaging is reported. The two coordination cages, NUS-100 and NUS-101, are assembled from the highly stable trinuclear zirconium vertices and two flexible carboxyl-decorated tetraphenylethylene (TPE) spacers. Extensive experimental and theoretical results show that the emissive intensity of the coordination cages can be controlled by restricting the dynamics of AIE-active molecular rotors though multiple external stimuli. Because the two coordination cages have excellent chemical stability in aqueous solutions (pH stability: 2-10) and impressive AIE characteristics contributed by the molecular rotors, they can be employed as novel biological fluorescent probes for in vitro live-cell imaging., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

In the title compound, C(16)H(12)Cl(2)O(3), the benzene rings form a dihedral angle of 2.0 (3)°. Within the central O=C-CH(2)C(H)OH-C=O unit, the carbonyl groups are coplanar and lie to opposite sides [O-C⋯C-O = -170.1 (6)°]. In the crystal, inter-molecular O-H⋯O hydrogen bonds formed between the hydr-oxy groups lead to a supra-molecular chain along the c axis. In addition, the crystal packing features some very weak C-H⋯π inter-actions.