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1. Insertion of CO ₂ Mediated by a (Xantphos)Ni ^I –Alkyl Species

   https://doi.org/10.1002/anie.201906005  

   Diccianni, Justin B.; Hu, Chunhua T.; Diao, Tianning (August 2019, Angewandte Chemie International Edition)

   Abstract The incorporation of CO₂into organometallic and organic molecules represents a sustainable way to prepare carboxylates. The mechanism of reductive carboxylation of alkyl halides has been proposed to proceed through the reduction of Ni^IIto Ni^Iby either Zn or Mn, followed by CO₂insertion into Ni^I‐alkyl species. No experimental evidence has been previously established to support the two proposed steps. Demonstrated herein is that the direct reduction of (tBu‐Xantphos)Ni^IIBr₂by Zn affords Ni^Ispecies. (tBu‐Xantphos)Ni^I‐Me and (tBu‐Xantphos)Ni^I‐Et complexes undergo fast insertion of CO₂at 22 °C. The substantially faster rate, relative to that of Ni^IIcomplexes, serves as the long‐sought‐after experimental support for the proposed mechanisms of Ni‐catalyzed carboxylation reactions. 

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2. CO ₂ Capture by 2-(Methylamino)pyridine Ligated Aluminum Alkyl Complexes:

   https://doi.org/10.1002/ejic.202000437  

   Yokley, Timothy W.; Tupkar, Hrishikesh; Schley, Nathan D.; DeYonker, Nathan J.; Brewster, Timothy P. (May 2020, European Journal of Inorganic Chemistry)

   A set of novel, easily synthesized aluminum complexes, Al(κ2-N,N-2-(methylamino)pyridine)2R (R = Et, iBu) are reported. When subjected to 1 atm of CO2 pressure, each hemilabile pyridine arm dissociates and facilitates cooperative activation of the CO2 substrate reminiscent of a Frustrated Lewis Pair. This reaction has limited precedent for Al/N based Lewis Pair systems, and this is the first system readily shown to sequester multiple equivalents of CO2 per aluminum center. The ethyl variant then reacts further, inserting a third equivalent of CO2 into the aluminum alkyl to generate an aluminum carboxylate. Examples of this type of reactivity are rare under thermal conditions. A joint experimental/computational study validates the proposed reaction mechanism. 

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3. Ligand and solvent effects on CO ₂ insertion into group 10 metal alkyl bonds

   https://doi.org/10.1039/D1SC06346D  

   Deziel, Anthony P.; Espinosa, Matthew R.; Pavlovic, Ljiljana; Charboneau, David J.; Hazari, Nilay; Hopmann, Kathrin H.; Mercado, Brandon Q. (February 2022, Chemical Science)

   The insertion of carbon dioxide into metal element σ-bonds is an important elementary step in many catalytic reactions for carbon dioxide valorization. Here, the insertion of carbon dioxide into a family of group 10 alkyl complexes of the type ( R PBP)M(CH 3 ) ( R PBP = B(NCH 2 PR 2 ) 2 C 6 H 4 − ; R = Cy or t Bu; M = Ni or Pd) to generate κ 1 -acetate complexes of the form ( R PBP)M{OC(O)CH 3 } is investigated. This involved the preparation and characterization of a number of new complexes supported by the unusual R PBP ligand, which features a central boryl donor that exerts a strong trans -influence, and the identification of a new decomposition pathway that results in C–B bond formation. In contrast to other group 10 methyl complexes supported by pincer ligands, carbon dioxide insertion into ( R PBP)M(CH 3 ) is facile and occurs at room temperature because of the high trans -influence of the boryl donor. Given the mild conditions for carbon dioxide insertion, we perform a rare kinetic study on carbon dioxide insertion into a late-transition metal alkyl species using ( t Bu PBP)Pd(CH 3 ). These studies demonstrate that the Dimroth–Reichardt parameter for a solvent correlates with the rate of carbon dioxide insertion and that Lewis acids do not promote insertion. DFT calculations indicate that insertion into ( t Bu PBP)M(CH 3 ) (M = Ni or Pd) proceeds via an S E 2 mechanism and we compare the reaction pathway for carbon dioxide insertion into group 10 methyl complexes with insertion into group 10 hydrides. Overall, this work provides fundamental insight that will be valuable for the development of improved and new catalysts for carbon dioxide utilization. 

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4. Precise Modulation of CO ₂ Sorption in Ti ₈ Ce ₂ –Oxo Clusters: Elucidating Lewis Acidity of the Ce Metal Sites and Structural Flexibility

   https://doi.org/10.1021/jacs.4c01092  

   Wang, Xingjie; Xie, Haomiao; Sengupta, Debabrata; Sha, Fanrui; Otake, Ken-ichi; Chen, Yongwei; Idrees, Karam B; Kirlikovali, Kent O; Son, Florencia A; Wang, Meng; et al (June 2024, Journal of the American Chemical Society)

   The quest for understanding the structure-property correlation in porous materials has remained a persistent focus across various research domains, particularly within the sorption realm. Molecular metal oxide clusters, owing to their precisely tunable atomic structures and long-range order, exhibit significant potential as versatile platforms for sorption investigations. This study presents a series of isostructural Ti8Ce2-oxo clusters with subtle variations in coordinated linkers and explores their gas sorption behavior. Notably, Ti8Ce2-BA (where BA denotes benzoic acid) manifests a distinctive twostep profile during CO2 adsorption, accompanied by a hysteresis loop. This observation marks a pioneering instance within the metal oxide cluster field. Of particular intrigue, the presence of unsaturated Ce(Ⅳ) sites was found to be correlated with the stepped sorption property. Moreover, the introduction of an electrophilic fluorine atom, positioned ortho or para to the benzoic acid, facilitated precise control over gate pressure and stepped sorption quantities. Advanced in-situ techniques systematically unraveled the underlying mechanism behind this unique sorption behavior. The findings elucidate that robust Lewis base-acid interactions are established between CO2 molecules and Ce ions, consequently altering the conformation of coordinated linkers. Conversely, the F atoms primarily contribute to gate pressure variation by influencing the Lewis acidity of the Ce sites. This research advances the understanding in fabricating geometrically "flexible" metal-oxo clusters and provides profound insights into their host-guest interaction motifs. These insights hold substantial promise across diverse fields, particularly in CO2 gas capture and gas-phase catalysis, and offer valuable guidance for future adsorbent designs grounded in fundamental theories of structure-property relationships. 

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5. Observing Chemical and Morphological Changes in a Cu@TiO _x Core@Shell Catalyst: Impact of Reversible Metal-Oxide Interactions on CO ₂ Activation and Hydrogenation

   https://doi.org/10.1021/acscatal.4c02694  

   Deng, Kaixi; Chen, Xiaobo; Moncada, Jorge; Salvatore, Kenna L; Rui, Ning; Xu, Wenqian; Xiang, Shuting; Marinkovic, Nebojsa; Frenkel, Anatoly I; Zhou, Guangwen; et al (August 2024, ACS Catalysis)

   A combination of several in situ techniques (XRD, XAS, AP-XPS, and E-TEM) was used to explore links between the structural and chemical properties of a Cu@TiOx catalyst under CO2 hydrogenation conditions. The active phase of the catalyst involved an inverse oxide/metal configuration, but the initial core@shell motif was disrupted during the pretreatment in H2. As a consequence of strong metal–support interactions, the titania shell cracked, and Cu particles migrated from the core to on top of the oxide with the simultaneous formation of a Cu–Ti–Ox phase. The generated Cu particles had a diameter of 20–40 nm and were decorated by small clusters of TiOx (<5 nm in size). Results of in situ XAS and XRD and images of E-TEM showed a very dynamic system, where the inverse oxide/metal configuration promoted the reactivity of the system toward CO2 and H2. At room temperature, CO2 oxidized the Cu nanoparticles (CO2,gas → COgas + Ooxide) inducing a redistribution of the TiOx clusters and big modifications in catalyst surface morphology. The generated oxide overlayer disappeared at elevated temperatures (>180 °C) upon exposure to H2, producing a transient surface that was very active for the reverse water–gas shift reaction (CO2 + H2 → CO + H2O) but was not stable at 200–350 °C. When oxidation and reduction occurred at the same time, under a mixture of CO2 and H2, the surface structure evolved toward a dynamic equilibrium that strongly depended on the temperature. Neither CO2 nor H2 can be considered as passive reactants. In the Cu@TiOx system, morphological changes were linked to variations in the composition of metal-oxide interfaces which were reversible with temperature or chemical environment and affected the catalytic activity of the system. The present study illustrates the dynamic nature of phenomena associated with the trapping and conversion of CO2. 

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