Porous organic materials (polymers and COFs) have shown a number of promising properties; however, the lability of their linkages often limits their robustness and can hamper downstream industrial ...application. Inspired by the outstanding chemical, mechanical, and thermal resistance of the 1D polymer poly(phenylene sulfide) (PPS), we have designed a new family of porous poly(aryl thioether)s, synthesized via a mild Pd-catalyzed C–S/C–S metathesis-based method, that merges the attractive features common to porous polymers and PPS in a single material. In addition, the method is highly modular, allowing to easily introduce application-oriented functionalities in the materials for a series of environmentally relevant applications including metal capture, metal sensing, and heterogeneous catalysis. Moreover, despite their extreme chemical resistance, the polymers can be easily recycled to recover the original monomers, offering an attractive perspective for their sustainable use. In a broader context, these results clearly demonstrate the untapped potential of emerging single-bond metathesis reactions in the preparation of new, recyclable materials.
The assumption that oxidative addition is the key step during the cross-coupling reaction of aryl halides has led to the development of a plethora of increasingly complex metal catalysts, thereby ...obviating in many cases the exact influence of the base, which is a simple, inexpensive, and necessary reagent for this paramount transformation. Here, a combined experimental and computational study shows that the oxidative addition is not the single kinetically relevant step in different cross-coupling reactions catalyzed by sub-nanometer Pt or Pd species, since the reactivity control is shifted toward subtle changes in the base. The exposed metal atoms in the cluster cooperate to enable an extremely easy oxidative addition of the aryl halide, even chlorides, and allow the base to bifurcate the coupling. With sub-nanometer Pd species, amines drive to the Heck reaction, carbonate drives to the Sonogahira reaction, and phosphate drives to the Suzuki reaction, while for Pt clusters and single atoms, good conversion is only achieved using acetate as a base. This base-controlled orthogonal reactivity with ligand-free catalysts opens new avenues in the design of cross-coupling reactions in organic synthesis.
Functional group metathesis is an emerging field in organic chemistry with promising synthetic applications. However, no complete mechanistic studies of these reactions have been reported to date, ...particularly regarding the nature of the key functional group transfer mechanism. Unraveling the mechanism of these transformations would not only allow for their further improvement but would also lead to the design of novel reactions. Herein, we describe our detailed mechanistic studies of the nickel-catalyzed functional group metathesis reaction between aryl methyl sulfides and aryl nitriles, combining experimental and computational results. These studies did not support a mechanism proceeding through reversible migratory insertion of the nitrile into a Ni–Ar bond and provided strong support for an alternative mechanism involving a key transmetalation step between two independently generated oxidative addition complexes. Extensive kinetic analysis, including rate law determination and Eyring analysis, indicated the oxidative addition complex of aryl nitrile as the resting state of the catalytic reaction. Depending on the concentration of aryl methyl sulfide, either the reductive elimination of aryl nitrile or the oxidative addition into the C(sp2)–S bond of aryl methyl sulfide is the turnover-limiting step of the reaction. NMR studies, including an unusual 31P–2H HMBC experiment using deuterium-labeled complexes, unambiguously demonstrated that the sulfide and cyanide groups exchange during the transmetalation step, rather than the two aryl moieties. In addition, Eyring and Hammett analyses of the transmetalation between two Ni(II) complexes revealed that this central step proceeds via an associative mechanism. Organometallic studies involving the synthesis, isolation, and characterization of all putative intermediates and possible deactivation complexes have further shed light on the reaction mechanism, including the identification of a key deactivation pathway, which has led to an improved catalytic protocol.
Carbon–carbon (C–C) bonds are ubiquitous but are among the least reactive bonds in organic chemistry. Recently, catalytic approaches to activate C–C bonds by transition metals have demonstrated the ...synthetic potential of directly reorganizing the skeleton of small molecules. However, these approaches are usually restricted to strained molecules or rely on directing groups, limiting their broader impact. We report a detailed mechanistic study of a rare example of catalytic C–C bond cleavage of unstrained alcohols that enables reversible ketone transfer hydroarylation under Rh-catalysis. Combined insight from kinetic analysis, in situ nuclear magnetic resonance (NMR) monitoring, and density functional theory (DFT) calculations supports a symmetric catalytic cycle, including a key reversible β-carbon elimination event. In addition, we provide evidence regarding the turnover-limiting step, the catalyst resting state, and the role of the sterically encumbered NHC ligand. The study further led to an improved catalytic system with the discovery of two air-stable precatalysts that showed higher activity for the transformation in comparison to the original conditions.
The gram‐scale synthesis, stabilization, and characterization of well‐defined ultrasmall subnanometric catalytic clusters on solids is a challenge. The chemical synthesis and X‐ray snapshots of Pt02 ...clusters, homogenously distributed and densely packaged within the channels of a metal–organic framework, is presented. This hybrid material catalyzes efficiently, and even more importantly from an economic and environmental viewpoint, at low temperature (25 to 140 °C), energetically costly industrial reactions in the gas phase such as HCN production, CO2 methanation, and alkene hydrogenations. These results open the way for the design of precisely defined catalytically active ultrasmall metal clusters in solids for technically easier, cheaper, and dramatically less‐dangerous industrial reactions.
The multigram synthesis of Pt02 clusters within a metal–organic framework (MOF) is presented. The high stability and crystallinity of the selected MOF offers an unprecedented characterization of such ultrasmall entities. This hybrid material catalyzes important industrial reactions efficiently and at low temperature, such as HCN production, CO2 methanation, and alkene hydrogenations.
Carbon dioxide (CO2) impacts every aspect of life, and numerous sensing technologies have been established to detect and monitor this ubiquitous molecule. However, its selective sensing at the ...molecular level remains an unmet challenge, despite the tremendous potential of such an approach for understanding this molecule’s role in complex environments. In this work, we introduce a unique class of selective fluorescent carbon dioxide molecular sensors (CarboSen) that addresses these existing challenges through an activity-based approach. Besides the design, synthesis, and evaluation of these small molecules as CO2 sensors, we demonstrate their utility by tailoring their reactivity and optical properties, allowing their use in a broad spectrum of multidisciplinary applications, including atmospheric sensing, chemical reaction monitoring, enzymology, and live-cell imaging. Collectively, these results showcase the potential of CarboSen sensors as broadly applicable tools to monitor and visualize carbon dioxide across multiple disciplines.
Carbon dioxide (CO
) impacts every aspect of life, and numerous sensing technologies have been established to detect and monitor this ubiquitous molecule. However, its selective sensing at the ...molecular level remains an unmet challenge, despite the tremendous potential of such an approach for understanding this molecule's role in complex environments. In this work, we introduce a unique class of selective fluorescent carbon dioxide molecular sensors (CarboSen) that addresses these existing challenges through an activity-based approach. Besides the design, synthesis, and evaluation of these small molecules as CO
sensors, we demonstrate their utility by tailoring their reactivity and optical properties, allowing their use in a broad spectrum of multidisciplinary applications, including atmospheric sensing, chemical reaction monitoring, enzymology, and live-cell imaging. Collectively, these results showcase the potential of CarboSen sensors as broadly applicable tools to monitor and visualize carbon dioxide across multiple disciplines.
Serpentinite powdered samples from four different regions were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), SBET and porosity measurements, UV-Vis and Infrared ...Spectroscopy of the skeletal region and surface OH groups. SEM micrographs of the samples showed a prismatic morphology when the lizardite was the predominant phase, while if antigorite phase prevailed, the particles had a globular morphology. The few fibrous-shaped particles, only observed by SEM and weakly detected by XRD on MO-9C and MO13 samples, were characteristic of the chrysotile phase. All diffraction XRD patterns showed characteristic peaks of antigorite and lizardite serpentine phases, with crystallite sizes in the range 310–250 Å and with different degrees and types of carbonation processes, one derived from the transformation of the serpentine, generating dolomite, and another by direct precipitation of calcite. The SBET reached values between 38–24 m2∙g−1 for the samples less crystalline, in agreement with the XRD patterns, while those with a higher degree of crystallinity gave values close to 8–9 m2∙g−1. In the UV region all electronic spectra were dominated by the absorption edge due to O2− → Si4+ charge transfer transition, with Si4+ in tetrahedral coordination, corresponding to a band gap energy of ca 4.7 eV. In the visible region, 800–350 nm, the spectra of all samples, except Donai, presented at least two weak and broad absorptions centred in the range 650–800 and 550–360 nm, associated with the presence of Fe3+ ions from the oxidation of structural Fe2+ ions in the serpentinites ((MgxFe2+1−x)3Si2O5(OH)4). The relative intensity of the IR bands corresponding to the stretching modes of the OH’s groups indicated the prevalence of one of the two phases, antigorite or lizardite, in the serpentinites. We proposed that the different relative intensity of these bands could be considered as diagnostic to differentiate the predominance of these phases in serpentinites.
The synthesis and reactivity of single metal atoms in a low‐valence state bound to just water, rather than to organic ligands or surfaces, is a major experimental challenge. Herein, we show a ...gram‐scale wet synthesis of Pt11+ stabilized in a confined space by a crystallographically well‐defined first water sphere, and with a second coordination sphere linked to a metal–organic framework (MOF) through electrostatic and H‐bonding interactions. The role of the water cluster is not only isolating and stabilizing the Pt atoms, but also regulating the charge of the metal and the adsorption of reactants. This is shown for the low‐temperature water–gas shift reaction (WGSR: CO + H2O → CO2 + H2), where both metal coordinated and H‐bonded water molecules trigger a double water attack mechanism to CO and give CO2 with both oxygen atoms coming from water. The stabilized Pt1+ single sites allow performing the WGSR at temperatures as low as 50 °C.
Water do: A catalyst with Pt11+ exclusively coordinated to H2O molecules can be prepared on a gram scale within a metal–organic framework (MOF). It transfers two H2O molecules to CO and gives, very efficiently, CO2 and H2 (water–gas shift reaction) at 50–150 °C.
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