Nanoparticle Superlattice Engineering with DNA

This account provides a comprehensive overview of the development of gold and platinum catalysis of the enyne cycloisomerization. The use of these soft, alkynophilic metals enables mild, chemoselective and efficient transformations of a variety of readily available acyclic enynes to a wide range of synthetically useful carbocyclic and heterocyclic products. The review is organized according to diverse structural types of enynes that undergo skeletal cycloisomerizations. The account begins with an overview of transformations of primarily 1,6-enynes to 1-alkenylcyclopentenes, bicyclo[4.1.0]heptenes, methylenecycloalkenes, bicyclo[4.3.0]nonadienes and bicyclo[3.2.0]heptenes. This section is followed by the discussion of cycloisomerizations of 1,5-enynes, which enable a rapid access to a range of other cyclic products, including bicyclo[3.1.0]hexenes, cyclohexadienes, heterobicycloalkenes, methylenecyclopentenes, naphthalenes and methyleneindenes. In addition, the [3,3] rearrangement of 1,5-enynes provides efficient access to the corresponding allenes. The account concludes with an overview of the most recent studies on gold- and platinum-catalyzed cycloisomerizations of 1,4- and 1,3-enynes. Due to the rapidly increasing interest in this area during the past three to five years, we believe that this review provides a timely and comprehensive discussion of the development gold- and platinum-catalyzed cycloisomerization starting from the initial pioneering investigations to the latest advances in the field. A significant emphasis is placed on the mechanistic discussion of the observed manifolds of skeletal reorganizations.

Gold and platinum catalysis of enyne cycloisomerization

Hexagonal boron nitride (h-BN) and semiconducting transition metal dichalcogenides (TMDs) promise greatly improved electrostatic control in future scaled electronic devices. To quantify the prospects of these materials in devices, we calculate the out-of-plane and in-plane dielectric constant from first principles for TMDs in trigonal prismatic and octahedral coordination, as well as for h-BN, with a thickness ranging from monolayer and bilayer to bulk. Both the ionic and electronic contribution to the dielectric response are computed. Our calculations show that the out-of-plane dielectric response for the transition-metal dichalcogenides is dominated by its electronic component and that the dielectric constant increases with increasing chalcogen atomic number. Overall, the out-of-plane dielectric constant of the TMDs and h-BN increases by less than 15% as the number of layers is increased from monolayer to bulk, while the in-plane component remains unchanged. Our computations also reveal that for octahedrally coordinated TMDs the ionic (static) contribution to the dielectric response is very high (4.5 times the electronic contribution) in the in-plane direction. This indicates that semiconducting TMDs in the tetragonal phase will suffer from excessive polar-optical scattering thereby deteriorating their electronic transport properties. The out-of-plane dielectric constant of transition metal dichalcogenides and h-BN is thickness-dependent, unlike their in-plane counterpart. A team led by William Vandenberghe at the University of Texas at Dallas performed calculations of the optical and static relative permittivity of free-standing monolayer, bilayer, and bulk transition metal dichalcogenides, in the in-plane and out-of-plane directions. In h-BN, the in-plane contribution was found to be larger than its out-of-plane counterpart, and independent on the number of h-BN layers. Conversely, the out-of-plane h-BN dielectric constant showed an increase when going from monolayer to bulk. In transition metal dichalcogenides, the dielectric constant components displayed similar trends to those observed in h-BN with regards to their thickness evolution. The calculations also indicated that the electronic component dominates the overall dielectric response for most of the analyzed 2D materials.

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Dielectric properties of hexagonal boron nitride and transition metal dichalcogenides: from monolayer to bulk

Antiferroelectric materials that display double ferroelectric hysteresis loops are receiving increasing attention for their superior energy storage density compared to their ferroelectric counterparts. Despite the good properties obtained in antiferroelectric La-doped Pb(Zr,Ti)O3 -based ceramics, lead-free alternatives are highly desired due to the environmental concerns, and AgNbO3 has been highlighted as a ferrielectric/antiferroelectric perovskite for energy storage applications. Enhanced energy storage performance, with recoverable energy density of 4.2 J cm-3 and high thermal stability of the energy storage density (with minimal variation of ≤±5%) over 20-120 °C, can be achieved in Ta-modified AgNbO3 ceramics. It is revealed that the incorporation of Ta to the Nb site can enhance the antiferroelectricity because of the reduced polarizability of B-site cations, which is confirmed by the polarization hysteresis, dielectric tunability, and selected-area electron diffraction measurements. Additionally, Ta addition in AgNbO3 leads to decreased grain size and increased bulk density, increasing the dielectric breakdown strength, up to 240 kV cm-1 versus 175 kV cm-1 for the pure counterpart, together with the enhanced antiferroelectricity, accounting for the high energy storage density.

Lead-Free Antiferroelectric Silver Niobate Tantalate with High Energy Storage Performance.

For the past dozen years, homogeneous gold catalysis has evolved from a little known topic in organic synthesis to a fully blown research field of significant importance to synthetic practitioners, due to its novel reactivities and reaction modes. Cationic gold(I) complexes are powerful soft Lewis acids that can activate alkynes and allenes toward efficient attack by nucleophiles, leading to the generation of alkenyl gold intermediates. Some of the most versatile aspects of gold catalysis involve the generation of gold carbene intermediates, which occurs through the approach of an electrophile to the distal end of the alkenyl gold moiety, and their diverse transformations thereafter. On the other hand, α-oxo metal carbene/carbenoids are highly versatile intermediates in organic synthesis and can undergo various synthetically challenging yet highly valuable transformations such as C–H insertion, ylide formation, and cyclopropanation reactions. Metal-catalyzed dediazotizations of diazo carbonyl compounds ar...

https://escholarship.org/content/qt0pg244j3/qt0pg244j3.pdf?t=r15td1

K. S. Pitzer

Papers

The Nature of the Chemical Bond and the Structure of Molecules and Crystals: An Introduction to Modern Structural Chemistry.