Exceedingly Facile Ph-X Activation (X = Cl, Br, I) with Ruthenium(II): Arresting Kinetics, Autocatalysis, and Mechanisms

Catalytic Method for the Synthesis of Deuterium-Labeled N-Heterocyclic Carbenes Enabled by a Coordinatively Unsaturated Ruthenium N-Heterocyclic Carbene Catalyst

The wide usage of N-heterocyclic carbenes (NHCs) has raised the quest for their deuterated molecules. Effective synthesis method to obtain them, however, has remained elusive. We present here a catalytic method for the preparation of deuterated NHCs, namely, the catalytic hydrogen-deuterium exchange reaction between NHCs and deuterated benzene using a coordinatively unsaturated Ru NHC catalyst. The catalytic system enables selective deuteration of the C(sp³)-H bonds of the alkyl groups on N-substituents, as well as the sterically nonhindered C(sp²)-H bonds of NHCs as demonstrated by the preparation of 16 deuterium-labeled NHCs that have a deuteration ratio on specified sites higher than 90%. The gram-scale synthesis of deuterated IMes indicated the applicability of this catalytic method. Mechanistic studies revealed that the high regio-selectivity toward those C(sp³)-H bonds on NHCs originates from the regio-selectivity of cyclometalation reactions of coordinatively unsaturated Ru NHC species.

Mild, Selective Ru-Catalyzed Deuteration Using D2 O as a Deuterium Source

A method for the selective deuteration of polyfunctional organic molecules using catalytic amounts of [RuCl2 (PPh3 )3 ] and D2 O as a deuterium source is presented. Through variation of additives like CuI, KOH, and various amounts of zinc powder, orthogonal chemoselectivities in the deuteration process are observed. Mechanistic investigation indicates the presence of different, defined Ru-complexes under the given specific conditions.

Chemical Systems Involving Two Competitive Self-Catalytic Reactions

Self-catalytic reactions are chemical phenomena, in which a product catalyzes the reactions of substrates further to yield products. A significant amplification of product concentration occurs during the reactions in a dilute solution, which exhibit notable properties such as sigmoidal kinetics, seeding effects, and thermal hysteresis. Chemical systems involving two competitive self-catalytic reactions can be considered, in which the competitive formation of two products occurs, which is affected by environmental changes, subtle perturbations, and fluctuations, and notable chemical phenomena appear such as formation of different structures in response to slow/fast temperature changes, chiral symmetry breaking, shortcut in reaction time, homogeneous-heterogeneous transitions, and mechanical responses. Studies on such chemical systems provide understanding on biological systems and can also be extended to the development of novel functional materials.

Evaluating Density Functionals by Examining Molecular Structures, Chemical Bonding, and Relative Energies of Mononuclear Ru-Cl-H-PR3 Isomers

In order to define a robust level of theory using density functionals for investigating the reactivity of ruthenium complexes, we used benchmark wave function theory, with saturated basis sets to validate generalized gradient approximation (GGA), meta-GGA, and hyper-GGA functionals in the presence and absence of empirical dispersion and range-separated corrections. We first selected potentially suitable functionals that gave accurate predictions of the relative energetics of coordination isomers. These functionals were further evaluated for the chemical accuracy of their predicted geometric and electronic structures. For the latter, both the ionic and covalent interactions were considered. The reference level of theory for comparison was coupled-cluster perturbation theory using full treatment of singles and doubles (CCSD) with a saturated triple-ζ quality basis set (TZVP) and corresponding small-core, effective core potentials for ruthenium. Several population analysis methods were evaluated to predict the ionic interactions. We found that the atomic charges obtained from fitting the electrostatic potential provided the most reasonable estimates for the ruthenium complexes. The covalent interactions were quantified by considering the atomic compositions of Ru 4d _{x²- y²}- and 4d _z²-based frontier unoccupied orbitals. Comparison of more than two dozen functionals with reference data from high-level wave function calculations revealed trends that allowed for the formulation of an optimal hybrid density functional: PBE exchange and correlation functionals with 50% HF exchange component. This level of theory was found to reproduce the experimental structure of Ru^(II) complexes. These complexes were used to investigate chemical speciation in a simplified model for an ionic liquid environment.

Identification and characterization of intramolecular γ-halo interaction in d0 complexes: a theoretical approach

A mechanistic investigation to detect intramolecular M⋯X-C type interactions in d⁰ neutral and cationic complexes was carried out through a benchmark study employing different density functional methods. As γ-halogen is involved in M⋯X-C type interactions, it is denoted as a γ-halo interaction and the respective conformers are designated as halo-conformers. By analyzing the geometrical parameters of halo-conformers, it was observed that, irrespective of the nature of the metal and the halogen, the C_γ-X bond distance increases compared to the usual C-X bond, which brings the M and X centers close enough to generate a weak interaction. Generation of the M⋯X-C interaction was confirmed by performing NBO, AIM and Wiberg bond index analyses, from which the persistence of γ-halo interaction was seen to be prominent. Moreover, for each neutral and cationic complex, the values of Wiberg bond order are in good agreement with the AIM results. The effect of the metal center, as well as γ-halogen substitution, on γ-halo interaction was also studied in the present work. To justify the practical subsistence of the halo-conformers, we checked the stability of the conformers with respect to their β-conformers by comparing the zero-point-corrected electronic energies. Therefore, the entire study was designed in such a way that it can provide evidence in support of intramolecular M⋯X-C interactions, where, instead of the C-H bond, the C_γ-X bond will interact with the central transition metal.