Journal of the American Chemical Society
DOI: 10.1021/jacs.6b01970
Month: March 2016
Catalyst-controlled selectivity in the C–H borylation of methane and ethane
Catalytic borylation of methane
By
Science25 Mar 2016 : 1424-1427
Metal catalysts in cyclohexane solvent append boron substituents to methane selectively through C–H bond scission at 150°C.
Cationic Noncovalent Interactions: Energetics and Periodic Trends
Chemical Reviews
DOI: 10.1021/acs.chemrev.5b00688
Dirhodium(II)-Catalyzed Annulation of Enoldiazoacetamides with α-Diazoketones: An Efficient and Highly Selective Approach to Fused and Bridged Ring Systems
Abstract
A dirhodium(II)-catalyzed annulation reaction between two structurally different diazocarbonyl compounds furnishes the donor–acceptor cyclopropane-fused benzoxa[3.2.1]octane scaffold with excellent chemo-, regio-, and diastereoselectivity under exceptionally mild conditions. The composite transformation occurs by [3+2]-cycloaddition between donor–acceptor cyclopropenes generated from enoldiazoacetamides and carbonyl ylides formed from intramolecular carbene–carbonyl cyclization in one pot with one catalyst. The annulation products can be readily transformed into benzoxa[3.3.1]nonane and hexahydronaphthofuran derivatives with exact stereocontrol. This method allows the efficient construction of three fused and bridged ring systems, all of which are important skeletons of numerous biologically active natural products.
One, two, three: A dirhodium(II)-catalyzed annulation reaction between two structurally different diazocarbonyl compounds was achieved with excellent chemo-, regio-, and diastereoselectivity under mild conditions. This reaction, along with further one-step transformations, allows the efficient construction of three natural-product-related ring systems from two easily accessible diazo compounds with one commercially available catalyst.
Product-Derived Bimetallic Palladium Complex Catalyzes Direct Carbonylation of Sulfonylazides
Abstract
A novel product-derived bimetallic palladium complex catalyzes a sulfonylazide-transfer reaction with the σ-donor/π-acceptor ligand CO, and is advantageous given its broad substrate scope, high efficiency, and mild reaction conditions (atmospheric pressure of CO at room temperature). This methodology provides a new approach to sulfonylureas, which are present in both pharmaceuticals and agrochemicals. The synthesis of Glibenclamide on a gram scale further revealed the practical utility of this procedure. Mechanistically, the generation of a bridged bimetallic palladium species derived from the product sulfonylurea is disclosed as the crucial step for this catalytic cycle.
Doubling up on Pd: A product-derived bimetallic palladium complex catalyzes a sulfonylazide-transfer reaction with the σ-donor/π-acceptor ligand CO, which is advantageous given its broad substrate scope, high efficiency, and mild reaction conditions under 1 bar of CO at room temperature. Mechanistically, the generation of the sulfonylurea-derived bridged bimetallic palladium species is the crucial step for this catalytic cycle.
Conversion of Dinitrogen into Acetonitrile under Ambient Conditions
Abstract
About 20 % of the ammonia production is used as the chemical feedstock for nitrogen-containing chemicals. However, while synthetic nitrogen fixation at ambient conditions has had some groundbreaking contributions in recent years, progress for the direct conversion of N2 into organic products remains limited and catalytic reactions are unknown. Herein, the rhenium-mediated synthesis of acetonitrile using dinitrogen and ethyl triflate is presented. A synthetic cycle in three reaction steps with high individual isolated yields and recovery of the rhenium pincer starting complex is shown. The cycle comprises alkylation of a nitride that arises from N2 splitting and subsequent imido ligand centered oxidation to nitrile via a 1-azavinylidene (ketimido) intermediate. Different synthetic strategies for intra- and intermolecular imido ligand oxidation and associated metal reduction were evaluated that rely on simple proton, electron, and hydrogen-atom transfer steps.
If it’s broke, fix it: In contrast to synthetic NH3 synthesis, the catalytic conversion of N2 with concomitant C−N bond formation into organic products remains unknown and stoichiometric examples are scarce. Several routes for the rhenium mediated synthesis of acetonitrile at ambient conditions via N2 splitting and alkylation are now possible, leading up to a full synthetic cycle in three steps with more than 50 % overall yield.
Activation of Methane and Ethane as Mediated by the Triatomic Anion HNbN−: Electronic Structure Similarity with Pt Atom
Abstract
Investigations of the intrinsic properties of gas-phase transition metal nitride (TMN) ions represent one approach to gain a fundamental understanding of the active sites of TMN catalysts, the activities and electronic structures of which are known to be comparable to those of noble metal catalysts. Herein, we investigate the structures and reactivities of the triatomic anions HNbN− by means of mass spectrometry and photoelectron imaging spectroscopy, in conjunction with density functional theory calculations. The HNbN− anions are capable of activating CH4 and C2H6 through oxidative addition, exhibiting similar reactivities to free Pt atoms. The similar electronic structures of HNbN− and Pt, especially the active orbitals, are responsible for this resemblance. Compared to the inert NbN−, the coordination of the H atom in HNbN− is indispensable. New insights into how to replace noble metals with TMNs may be derived from this combined experimental/computational study.
A less noble catalyst: The triatomic HNbN− anion was shown to have a reactive electronic structure similar to Pt atom, and displayed similar reactivities toward CH4 and C2H6. Thus, transition metal nitride ions could potentially offer cheaper alternatives to traditional platinum-based catalysts for C−H activation.
A Bio-Inspired, Heavy-Metal-Free, Dual-Electrolyte Liquid Battery towards Sustainable Energy Storage
A Bio-Inspired, Heavy-Metal-Free, Dual-Electrolyte Liquid Battery towards Sustainable Energy Storage
Abstract
Wide-scale exploitation of renewable energy requires low-cost efficient energy storage devices. The use of metal-free, inexpensive redox-active organic materials represents a promising direction for environmental-friendly, cost-effective sustainable energy storage. To this end, a liquid battery is designed using hydroquinone (H2BQ) aqueous solution as catholyte and graphite in aprotic electrolyte as anode. The working potential can reach 3.4 V, with specific capacity of 395 mA h g−1 and stable capacity retention about 99.7 % per cycle. Such high potential and capacity is achieved using only C, H and O atoms as building blocks for redox species, and the replacement of Li metal with graphite anode can circumvent potential safety issues. As H2BQ can be extracted from biomass directly and its redox reaction mimics the bio-electrochemical process of quinones in nature, using such a bio-inspired organic compound in batteries enables access to greener and more sustainable energy-storage technology.
Versatile energy-storage devices: The use of metal-free redox-active organic materials is promising for the development of environmental-friendly, cost-effective, and sustainable energy-storage devices. As hydroquinone can be extracted from biomass directly, using such a bio-inspired organic compound in batteries enables access to green and sustainable energy-storage technology.
Bandgap Engineering of Titanium–Oxo Clusters: Labile Surface Sites Used for Ligand Substitution and Metal Incorporation
Abstract
Through the labile coordination sites of a robust phosphonate-stabilized titanium–oxo cluster, 14 O-donor ligands have been successfully introduced without changing the cluster core. The increasing electron-withdrawing effect of the organic species allows the gradual reduction of the bandgaps of the {Ti6} complexes. Transition-metal ions are then incorporated by the use of bifunctional O/N-donor ligands, organizing these {Ti6} clusters into polymeric structures. The coordination environments of the applied metal ions show significant influence on their visible-light adsorption. Both the above structural functionalizations also tune the photocatalytic H2 production activities of these clusters. This work provides a systematic bandgap engineering study of titanium–oxo clusters, which is important not only for their future photocatalytic applications, also for the better understanding of the structure–property relationships.
Organized titanium clusters: The labile coordination sites of a robust {Ti6} cluster have been used to functionalize the surface of the {Ti6} cluster with organic species and transition-metal ions (see picture). A bandgap engineering study indicates that both the electron-withdrawing effect of the organic ligands and the coordination environments of the incorporated metal ions tune the bandgap structures of the titanium–oxo clusters.
Tomson Group Literature 