An official website of the United States government
Abstract Dual catalysis represents an alternative archetype in carbene chemistry that surpasses traditional single catalyst systems. By employing dual catalyst systems, one can improve the efficiency of existing reactions and enable new chemical transformations. Reactions involving dual synergistic catalysis are increasingly valuable as they offer convenient strategies for synthesizing challenging quaternary carbon centers and bioactive core structures. This review article focuses on trapping diazo‐derived, rhodium (II) zwitterionic intermediates with varying electrophiles such as Michael acceptors, alkynes, π‐allyl Pd(II) complexes, and the Nicholas intermediate.
more »
« less
Pyrolytic Carbon: An Inexpensive, Robust, and Versatile Electrode for Synthetic Organic Electrochemistry
Abstract Synthetic organic electrochemistry is recognized as one of the most sustainable forms of redox chemistry that can enable a wide variety of useful transformations. In this study, readily prepared pyrolytic carbon electrodes are explored in several powerful rAP transformations as well as C−C and C−N bond forming reactions. Pyrolytic carbon provides an alternative to classic amorphous carbon‐based materials that are either expensive or ill‐suited to large‐scale flow reactions.
more »
« less
- Award ID(s):
- 2002158
- PAR ID:
- 10567588
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 64
- Issue:
- 4
- ISSN:
- 1433-7851
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract A transition metal‐free Se‐catalyzed C−H amination protocol for α’‐amination of enol derivatives has been developed. This reaction can be used to functionalize a wide variety of oxygen‐ and halogen‐substituted alkenes spanning a vast range of nucleophilicities, giving α’‐aminated enol derivatives with high regioselectivity. Amination ofE/Zmixtures of alkenes proceeds stereoconvergently to give the (Z)‐enol derivatives exclusively. Mechanistic studies revealed that the relative reactivity and α’‐regioselectivity of these transformations is determined by substantial resonance donation to the heteroatom‐bound carbon in the transition state. These products participate in traditional reactions of enol derivatives, allowing for efficient functionalization of both α‐ and α’‐positions from a single enol derivative with high diastereocontrol.more » « less
-
Abstract Nickel‐catalyzed cross‐electrophile coupling (XEC) is an efficient method to form carbon‐carbon bonds and has become an important tool for building complex molecules. While XEC has most often used stoichiometric metal reductants, these transformations can also be driven electrochemically. Electrochemical XEC (eXEC) is attractive because it can increase the greenness of XEC and this potential has resulted in numerous advances in recent years. The focus of this review is on electrochemical, Ni‐catalyzed carbon‐carbon bond forming reactions reported since 2010 and is categorized by the type of anodic half reaction: sacrificial anode, sacrificial reductant, and convergent paired electrolysis. The key developments are highlighted and the need for more scalable options is discussed.more » « less
-
Abstract Covalent organic frameworks linked by carbon‐carbon double bonds (C=C COFs) are an emerging class of crystalline, porous, and conjugated polymeric materials with potential applications in organic electronics, photocatalysis, and energy storage. Despite the rapidly growing interest in sp2carbon‐conjugated COFs, only a small number of closely related condensation reactions have been successfully employed for their synthesis to date. Herein, we report the first example of a C=C COF, CORN‐COF‐1 (CORN=Cornell University), prepared byN‐heterocyclic carbene (NHC) dimerization. In‐depth characterization reveals that CORN‐COF‐1 possesses a two‐dimensional layered structure and hexagonal guest‐accessible pores decorated with a high density of strongly reducing tetraazafulvalene linkages. Exposure of CORN‐COF‐1 to tetracyanoethylene (TCNE,E1/2=0.13 V and −0.87 V vs. SCE) oxidizes the COF and encapsulates the radical anion TCNE⋅−and the dianion TCNE2−as guest molecules, as confirmed by spectroscopic and magnetic analysis. Notably, the reactive TCNE⋅−radical anion, which generally dimerizes in the solid state, is uniquely stabilized within the pores of CORN‐COF‐1. Overall, our findings broaden the toolbox of reactions available for the synthesis of redox‐active C=C COFs, paving the way for the design of novel materials.more » « less
-
It has been a long-standing challenge in modern material design to create low-density, lightweight materials that are simultaneously robust against defects and can withstand extreme thermomechanical environments, as these properties are often mutually exclusive: The lower the density, the weaker and more fragile the material. Here, we develop a process to create nanoarchitected carbon that can attain specific strength (strength-to-density ratio) up to one to three orders of magnitude above that of existing micro- and nanoarchitected materials. We use two-photon lithography followed by pyrolysis in a vacuum at 900 °C to fabricate pyrolytic carbon in two topologies, octet- and iso-truss, with unit-cell dimensions of ∼2 μm, beam diameters between 261 nm and 679 nm, and densities of 0.24 to 1.0 g/cm3. Experiments and simulations demonstrate that for densities higher than 0.95 g/cm3the nanolattices become insensitive to fabrication-induced defects, allowing them to attain nearly theoretical strength of the constituent material. The combination of high specific strength, low density, and extensive deformability before failure lends such nanoarchitected carbon to being a particularly promising candidate for applications under harsh thermomechanical environments.more » « less
