Water-Assisted H−H Bond Splitting Mediated by [CpRu(PTA)2Cl] (PTA=1,3,5-triaza-7-phosphaadamantane). A DFT Analysis

Beyond Continuum Solvent Models in Computational Homogeneous Catalysis

In homogeneous catalysis solvent is an inherent part of the catalytic system. As such, it must be considered in the computational modeling. The most common approach to include solvent effects in quantum mechanical calculations is by means of continuum solvent models. When they are properly used, average solvent effects are efficiently captured, mainly those related with solvent polarity. However, neglecting atomistic description of solvent molecules has its limitations, and continuum solvent models all alone cannot be applied to whatever situation. In many cases, inclusion of explicit solvent molecules in the quantum mechanical description of the system is mandatory. The purpose of this article is to highlight through selected examples what are the reasons that urge to go beyond the continuum models to the employment of micro-solvated (cluster-continuum) of fully explicit solvent models, in this way setting the limits of continuum solvent models in computational homogeneous catalysis. These examples showcase that inclusion of solvent molecules in the calculation not only can improve the description of already known mechanisms but can yield new mechanistic views of a reaction. With the aim of systematizing the use of explicit solvent models, after discussing the success and limitations of continuum solvent models, issues related with solvent coordination and solvent dynamics, solvent effects in reactions involving small, charged species, as well as reactions in protic solvents and the role of solvent as reagent itself are successively considered.

DFT study on the E-stereoselective reductive A3-coupling reaction of terminal alkynes with aldehydes and 3-pyrroline

The mechanism of the Cu(i)-catalyzed reductive A³-coupling reaction of terminal alkynes with aldehydes and 3-pyrroline for the synthesis of E-allylic amines has been studied by DFT calculations.

Water and catalytic isomerization of linear allylic alcohols by [RuCp(H2O-κO)(PTA)2]+(PTA = 1,3,5-triaza-7-phosphaadamantane)

The water soluble complex [RuCp(H₂O-κO)(PTA)₂]⁺showed to be an excellent catalyst for the isomerization of allylic alcohols from 3-buten-2-ol to 1-octen-3-ol in water, which was mandatory for obtaining the best conversion.

Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides

The dihydrogen bond-an interaction between a transition-metal or main-group hydride (M-H) and a protic hydrogen moiety (H-X)-is arguably the most intriguing type of hydrogen bond. It was discovered in the mid-1990s and has been intensively explored since then. Herein, we collate up-to-date experimental and computational studies of the structural, energetic, and spectroscopic parameters and natures of dihydrogen-bonded complexes of the form M-H···H-X, as such species are now known for a wide variety of hydrido compounds. Being a weak interaction, dihydrogen bonding entails the lengthening of the participating bonds as well as their polarization (repolarization) as a result of electron density redistribution. Thus, the formation of a dihydrogen bond allows for the activation of both the MH and XH bonds in one step, facilitating proton transfer and preparing these bonds for further transformations. The implications of dihydrogen bonding in different stoichiometric and catalytic reactions, such as hydrogen exchange, alcoholysis and aminolysis, hydrogen evolution, hydrogenation, and dehydrogenation, are discussed.

Lower- and upper-rim-modified derivatives of 1,3,5-triaza-7-phosphaadamantane: Coordination chemistry and applications in catalytic reactions in water

In this article, a brief review of the recent functionalizations of the cage-like water-soluble phosphine 1,3,5-triaza-7-phosphaadamantane (PTA), involving N-quaternization (lower rim) and introduction of a side arm in C-6 position (upper rim) will be presented, highlighting selected examples in their use as ligands for ruthenium(II), iridium(I), and rhodium(I) moieties together with applications of the related complexes in homogeneous catalysis.

On the validity of Au-vinylidenes in the gold-catalyzed 1,2-migratory cycloisomerization of skipped propargylpyridines

A mechanism of the Au-catalyzed cycloisomerization of propargylpyridines has been investigated. Both DFT computational and experimental results strongly support generation of a Au-carbene via a cyclization/proton transfer sequence over the previously proposed path involving a Au-vinylidene intermediate. For the β-Si-substituted Au-carbene (G = SiR(3)), a 1,2-Si migration was shown to be kinetically favored over a 1,2-H shift. This study highlights the importance of alternative pathways that could explain reactivities commonly attributed to an alkyne-vinylidene isomerization in Au catalysis.