A mixed chloride/trifluoromethanesulfonate ligand species in a ruthenium(II) complex

The compound [2‐(aminomethyl)pyridine‐κ²N,N′][chlorido/trifluoromethanesulfonato(0.91/0.09)][(10,11‐η)‐5H‐dibenzo[a,d]cyclohepten‐5‐amine‐κN](triphenylphosphane‐κP)ruthenium(II) trifluoromethanesulfonate dichloromethane 0.91‐solvate, [Ru(CF₃SO₃)_0.09Cl_0.91(C₆H₈N₂)(C₁₅H₁₃N)(C₁₈H₁₅P)]CF₃SO₃·0.91CH₂Cl₂, belongs to a series of Ru^II complexes that had been tested for transfer hydrogenation, hydrogenation of polar bonds and catalytic transfer hydrogenation. The crystal structure determination of this complex revealed disorder in the form of two different anionic ligands sharing the same coordination site, which other spectroscopic methods failed to characterize. The reduced catalytic activity of the title compound was not fully understood until the crystallographic data provided evidence for the mixed ligand species. The crystal structure clearly shows that the majority of the synthesized material has a chloride ligand present. Only a small portion of the material is the expected complex [Ru^II(OTf)(ampy)(η²‐tropNH₂)(PPh₃)]OTf, where OTf is triflate or trifluoromethanesulfonate, ampy is 2‐(aminomethyl)pyridine and tropNH₂ is 5H‐dibenzo[a,d]cyclohepten‐5‐amine.     

Isomerization kinetics of small hydrocarbons in confinement

Chemical reactions are often carried out in nano-structured materials, which can enhance reactions due to their large specific surface area, their interactions with the reacting mixture and confinement effects. In this work, we present a systematic study of the effect that the geometrical restrictions imposed by the pore walls can have on reactions that involve a three dimensional rearrangement of the atoms in a molecule. In particular, we consider the isomerization of three 4-membered hydrocarbons—n-butane, 1-butene and 1,3-butadiene confined in carbon nanopores of slit geometry. Our results illustrate the fact that, in the molecular sieving limit, the reaction rates change as the double exponential of the pore size (Santiso et al., in J. Chem. Phys., 2007a, submitted), and therefore the transition rates in nanopores can be many orders of magnitude different from the corresponding bulk values. These results can be used as a guideline for the molecular-level design of improved catalytic materials.     

A general set of order parameters for molecular crystals

Crystallization is fundamental to many aspects of physics and chemistry in addition to being of technological relevance, for example, in the chemical, food, and pharmaceutical industries. However, the design of crystalline materials and crystallization processes is often challenging due to the many variables that can influence the process. As a part of an effort to gain a molecular-level understanding of the way molecules aggregate and organize themselves into crystal structures, in this work we present a new method to construct order parameters suitable for the study of crystallization and polymorph transformations in molecular systems. Our order parameters can be systematically defined for complex systems using information that can be obtained from simple molecular dynamics simulations of the crystals. We show how to construct the order parameters for the study of three different systems: the formation of α-glycine crystals in solution, the crystallization of benzene from the melt, and the polymorph transformation of terephthalic acid. Finally, we suggest how these order parameters could be used to study order-disorder transitions in molecular systems.     

Nitrous Oxide as a Hydrogen Acceptor for the Dehydrogenative Coupling of Alcohols

The oxidation of alcohols with N₂O as the hydrogen acceptor was achieved with low catalyst loadings of a rhodium complex that features a cooperative bis(olefin)amido ligand under mild conditions. Two different methods enable the formation of either the corresponding carboxylic acid or the ester. N₂ and water are the only by‐products. Mechanistic studies supported by DFT calculations suggest that the oxygen atom of N₂O is transferred to the metal center by insertion into the Rh?H bond of a rhodium amino hydride species, generating a rhodium hydroxy complex as a key intermediate.     

Combinatorial synthesis and hydrogenation of Mg/Al libraries prepared by electron beam physical vapor deposition

We have grown thin film libraries of the Mg-Al system using a high-throughput synthesis methodology that combines the sequential deposition of pure elements (Mg and Al) by an electron-beam (e-beam) evaporation technique and the use of a special set of moving shadow masks. This novel mask has been designed to simultaneously prepare four identical arrays of different compositions that will permit the characterization of the same library after several treatments. Wavelength dispersive spectroscopy (WDS) and micro-X-ray diffraction have been used as high-throughput screening techniques for the determination of the composition and structure of every member of the library in the as-deposited state and after hydrogenation at 1 atm of H2 during 24 h at three different temperatures: 60, 80, and 110 degrees C. We have analyzed the influence of the Mg-Al ratio on the hydrogenation of magnesium, as well as on the appearance of complex hydride phases. We have also found that aluminum can act as a catalyzer for the hydrogenation reaction of magnesium.     

A theoretical investigation of the nonrigid six-coordinate compounds [Mo(R)F5], [W(R)F5], and related compounds

Density functional calculations for [M(CH3)F5], [M(CF3)F5], [M(CH3S)F5], and [M(CF3S)F5] (M=Mo, W) show that they are expected to be nonrigid molecules, with energy barriers for the octahedral-trigonal-prismatic interchange as low as 7.2 kJ mol(-1). The ground state for the CH3- and CF3- compounds is trigonal prismatic, for the CH3S- and CF3S- compounds, (distorted) octahedral. All calculated compounds [M(C6F5)nF(6-n)] (M=Mo, W) have a trigonal-prismatic ground state, whereas the situation for [M(C6H5)nF(6-n)] (M=Mo, W) is more complex.     

Synthesis and Characterization of Terminal [Re(XCO)(CO)2(triphos)] (X=N,P): Isocyanate versus Phosphaethynolate Complexes

The terminal rhenium(I) phosphaethynolate complex [Re(PCO)(CO)₂(triphos)] has been prepared in a salt metathesis reaction from Na(OCP) and [Re(OTf)(CO)₂(triphos)]. The analogous isocyanato complex [Re(NCO)(CO)₂(triphos)] has been likewise prepared for comparison. The structure of both complexes was elucidated by X‐ray diffraction studies. While the isocyanato complex is linear, the phosphaethynolate complex is strongly bent around the pnictogen center. Computations including natural bond orbital (NBO) theory, natural resonance theory (NRT), and natural population analysis (NPA) indicate that the isocyanato complex can be viewed as a classic Werner‐type complex, that is, with an electrostatic interaction between the Re^I and the NCO group. The phosphaethynolate complex [Re(P?C?O)(CO)₂(triphos)] is best described as a metallaphosphaketene with a Re^I–phosphorus bond of highly covalent character.     

Adsorption and catalysis: The effect of confinement on chemical reactions

Confinement within porous materials can affect chemical reactions through a host of different effects, including changes in the thermodynamic state of the system due to interactions with the pore walls, selective adsorption, geometrical constraints that affect the reaction mechanism, electronic perturbation due to the substrate, etc. In this work, we present an overview of some of our recent research on some of these effects, on chemical equilibrium, kinetic rates and reaction mechanisms. We also discuss our current and future directions for research in this area.     

Synthesis of anacardic acids by nucleophilic substitution on 2-aryloxazolines

A new direct synthesis for anacardic acids based in a nucleophilic substitution of a methoxy group in 2-aryloxazolines by long-chained Grignard reagents is reported.