Time filter

Source Type

Chen C.-F.,CAS Beijing National Laboratory for Molecular
Chemical Communications

The development of new classes of macrocyclic hosts has always been one of the most important topics in supramolecular chemistry. During the past several years, based on the triptycene with unique three-dimensional rigid structure, several different kinds of novel triptycene-derived hosts including triptycene-derived cylindrical macrotricyclic polyether, triptycene-derived tris(crown ether)s, triptycene-derived molecular tweezers, triptycene-derived calixarenes, triptycene-derived heterocalixarenes, triptycene-derived tetralactam macrocycles and molecular cage have been designed and synthesized. Then, by exploring the applications of some of the triptycene derived hosts in molecular recognition and molecular assemblies, a series of new supramolecular systems with specific structures and properties have been developed. This feature article highlights our recent advances in the synthesis of triptycene-derived hosts and their applications in supramolecular chemistry. © 2011 The Royal Society of Chemistry. Source

Liu W.,CAS Beijing National Laboratory for Molecular
Physics Reports

A quantum mechanical equation Hψ=Eψ is composed of three components, viz., Hamiltonian H, wave function ψ, and property E(λ), each of which is confronted with fundamental issues in the relativistic regime, e.g.,(1) What is the most appropriate relativistic many-body Hamiltonian? How to solve the resulting equation? (2) How does the relativistic wave function behave at the coalescence of two electrons? How to do relativistic explicit correlation? (3) How to formulate relativistic properties properly?, to name just a few. It is shown here that the charge-conjugated contraction of Fermion operators, dictated by the charge conjugation symmetry, allows for a bottom-up construction of a relativistic Hamiltonian that is in line with the principles of quantum electrodynamics (QED). Various approximate but accurate forms of the Hamiltonian can be obtained based entirely on physical arguments. In particular, the exact two-component Hamiltonians can be formulated in a general way to cast electric and magnetic fields, as well as electron self-energy and vacuum polarization, into a unified framework. While such algebraic two-component Hamiltonians are incompatible with explicit correlation, four-component relativistic explicitly correlated approaches can indeed be made fully parallel to the nonrelativistic counterparts by virtue of the 'extended no-pair projection' and the coalescence conditions. These findings open up new avenues for future developments of relativistic molecular quantum mechanics. In particular, 'molecular QED' will soon become an active and exciting field. © 2013 Elsevier B.V. Source

A density functional theory study reveals that the dehydrogenation of ethanol catalyzed by an aliphatic PNP pincer ruthenium complex, (PNP)Ru(H)CO {1Ru, PNP = bis[2-(diisopropylphosphino)ethyl]amino}, proceeds via a self-promoted mechanism that features an ethanol molecule acting as a bridge to assist the transfer of a proton from ligand nitrogen to the metal center for the formation of H2. The very different catalytic properties between the aromatic and aliphatic pincer ligand in ruthenium complexes are analyzed. The potential of an iron analogue of 1Ru, (PNP)Fe(H)CO (1Fe), as a catalyst for the dehydrogenation of ethanol was evaluated computationally. The calculated total free energy barrier of ethanol dehydrogenation catalyzed by 1Fe is only 22.1 kcal/mol, which is even 0.7 kcal/mol lower than the calculated total free energy barrier of the reaction catalyzed by 1 Ru. Therefore, the potential of 1Fe as a low-cost and high-efficiency catalyst for the production of hydrogen from ethanol is promising. © 2013 American Chemical Society. Source

A density functional theory study of the reaction mechanism of the production of H2 and CO2 from methanol and water catalyzed by an aliphatic PNP pincer ruthenium complex, (PNP)Ru(H)CO, reveals three interrelated catalytic cycles for the release of three H2 molecules: the dehydrogenation of methanol to formaldehyde, the coupling of formaldehyde and hydroxide for the formation of formic acid, and the dehydrogenation of formic acid. The formation of all three H2 molecules undergoes the same self-promoted mechanism that features a methanol or a water molecule acting as a bridge for the transfer of a ligand proton to the metal hydride in a key intermediate, trans-(HPNP)Ru(H)2CO. © 2014 American Chemical Society. Source

Xi Z.,CAS Beijing National Laboratory for Molecular
Accounts of Chemical Research

The development of organometallic reagents remains one of the most important frontiers in synthetic chemistry. Commonly used organometallic reagents (such as RLi and RMgBr) are typically monometallic compounds, although they aggregate in many cases. When two carbon-metal bonds are in the same molecule in close proximity, however, these two carbon-metal moieties may exhibit novel reactivity. In this Account, we outline our work on new reactions and synthetic applications of the organo-dilithio reagents 1,4-dilithio-1,3- butadienes. The 1,4-dilithio-1,3-butadienes can be accessed readily in high efficiency with a wide variety of substitution patterns on the butadienyl skeleton. The configuration has been predicted and demonstrated to favor a double dilithium bridging structure in both solution and solid states. The two Li atoms are bridged by a butadiene moiety and are in close proximity. By taking advantage of this unique configuration, we have developed useful and interesting synthetic methodologies. Three types of reactions of 1,4-dilithio-1,3-butadienes, termed dilithio reagents here, have been developed and are discussed. An intramolecular reaction is introduced in the first section. The reaction is a result of the intracooperative effect among the two C-Li moieties, the butadienyl bridge, and the substituents. A useful transformation from silylated 1,4-dilithio-1,3-butadienes to α-lithio siloles is described. Second, we discuss an intermolecular reaction that results from the intercooperative effect of the two C-Li moieties toward substrates. As an example of the formation of functionalized cyclic dianions from the linear dianions of the dilithio reagents and organic substrates, we describe the isolation and structural characterization of a novel type of cyclic dianion; that is, fully substituted oxy-cyclopentadienyl dilithium formed via the reaction of dilithio reagents with CO. We also describe diverse reactions of dilithio reagents with nitriles to form substituted pyridines, tricyclic 1-bipyrrolines, and siloles, demonstrating the remarkable effect of substituents on the butadienyl skeleton. Third, we discuss transmetalation of dilithio reagents to generate other organo-dimetallic compounds. This section focuses on organo-dicopper compounds and their reactivity toward the synthesis of strained ring systems, such as semibullvalenes and twisted four-membered rings, with the metal-mediated C-C bond-forming approach. In addition to these three representative reactions, other useful applications are also briefly introduced. The dimetallic 1,4-dilithio-1,3-butadienes and their transmetalated derivatives provide unique synthetic organometallic reagents that are very different from monometallic reagents, both in terms of reactivity and synthetic application. These organo-dimetallic reagents provide access to interesting and useful compounds that are not available by other means. Moreover, given the possibilities afforded, the study of organo-dimetallic and organo-polymetallic compounds should yield further synthetic applications in the near future. © 2010 American Chemical Society. Source

Discover hidden collaborations