Uptake of One and Two Molecules of 1,3-Butadiene by Platinum Bis(dithiolene): A Theoretical Study

Inspired by Nature-Functional Analogues of Molybdenum and Tungsten-Dependent Oxidoreductases

Throughout the previous ten years many scientists took inspiration from natural molybdenum and tungsten-dependent oxidoreductases to build functional active site analogues. These studies not only led to an ever more detailed mechanistic understanding of the biological template, but also paved the way to atypical selectivity and activity, such as catalytic hydrogen evolution. This review is aimed at representing the last decade’s progress in the research of and with molybdenum and tungsten functional model compounds. The portrayed systems, organized according to their ability to facilitate typical and artificial enzyme reactions, comprise complexes with non-innocent dithiolene ligands, resembling molybdopterin, as well as entirely non-natural nitrogen, oxygen, and/or sulfur bearing chelating donor ligands. All model compounds receive individual attention, highlighting the specific novelty that each provides for our understanding of the enzymatic mechanisms, such as oxygen atom transfer and proton-coupled electron transfer, or that each presents for exploiting new and useful catalytic capability. Overall, a shift in the application of these model compounds towards uncommon reactions is noted, the latter are comprehensively discussed.

Priority of Mixed Diamine Ligands in Cobalt Dithiolene Complex-Catalyzed H2 Evolution: A Theoretical Study

Redox non-innocent metal dithiolene or diamine complexes are potential alternative catalysts in hydrogen evolution reaction and have been incorporated into 2D metal-organic frameworks to obtain unexpected electrocatalytic activity. According to an experimental study, Co-bis(dithiolene), Co-bis(diamine), and Co-dithiolene-diamine portions are considered as active sites where the generation of H₂ occurs and a diamine ligand is necessary for high catalytic efficiency. We are interested in the difference between these catalytic active sites, and mechanistic studies on extracted Co-bis(dithiolene), Co-bis(diamine), and Co-dithiolene-diamine complex-catalyzed hydrogen evolution reactions are carried out by using density functional methods. Our calculated results indicate that the priority of ligand mixed complexes resulted from the readily occurring protonation of diamine ligands and large electron affinity of dithiolene ligands as well as the lowest overall barrier for H₂ evolution.

Computational investigation of cobalt and copper bis (oxothiolene) complexes as an alternative for olefin purification

Considering that olefins present a large volume feedstock, it is reasonable to expect that their purification is industrially critical. After the discovery of the nickel bis (dithiolene) complex Ni(S₂C₂(CF₃)₂)₂ that exhibits electro-catalytic activity with olefins but tends to decompose by a competitive reaction route, related complexes have been explored experimentally and theoretically. In this paper, a computational examination is performed on differently charged cobalt and copper bis (oxothiolene) complexes [M (OSC₂(CN)₂)₂] to test their potential applicability as the catalysts for olefin purification, using the simplest olefin, ethylene. Possible reaction pathways for ethylene addition on these complexes were explored, to determine whether some of these candidates can avoid the reaction route that leads to decomposition, which is distinctive from the nickel complex, and to form stable adducts that can subsequently release ethylene by reduction. Our calculations suggest that the neutral cobalt complex might be an alternative catalyst, because all its forms can bind ethylene to produce stable interligand adducts with moderate to low activation barriers, rather than to form intraligand adducts that lead to decomposition. The calculations also predict that these interligand adducts are capable of releasing ethylene upon reduction. In addition, it can produce the desired interligand adducts following two different reaction pathways, assigned as the direct and the indirect, with no need for anion species as co-catalysts, which is crucial for the nickel complex. Thus, the olefin purification process could be much simpler by using this catalyst.

Influence of chelate ring type on chelate-chelate and chelate-aryl stacking: the case of nickel bis(dithiolene)

Chelate-aryl and chelate-chelate stacking interactions of nickel bis(dithiolene) were studied at the CCSD(T)/CBS and DFT levels. The strongest chelate-aryl stacking interaction between nickel bis(dithiolene) and benzene has a CCSD(T)/CBS stacking energy of -5.60 kcal mol^-1. The strongest chelate-chelate stacking interactions between two nickel bis(dithiolenes) has a CCSD(T)/CBS stacking energy of -10.34 kcal mol^-1. The most stable chelate-aryl stacking has the benzene center above the nickel atom, while the most stable chelate-chelate dithiolene stacking has the chelate center above the nickel atom. Comparison of chelate-aryl stacking interactions of dithiolene and acac-type nickel chelate shows similar strength. However, chelate-chelate stacking is stronger for dithiolene nickel chelate than for acac-type nickel chelate, which has a CCSD(T)/CBS interaction energy of -9.50 kcal mol^-1.

What Happens Without Nickel? Cyclization Reactions of Ethylene with Ethanedithial and Related Molecules

We present a computational study of the mechanism of the formation of 6-member heterocycles through the binding of ethylene to oxaldehyde, ethanedithial, and 2-thioxoacetaldehyde. This process is related to the olefin separation technology by metal dithiolenes and dioxolenes, being the formation of those heterocycles the main decomposition route. We also present a benchmark of 26 density functionals (spanning hybrid, double-hybrid, range-separated, semilocal, and local functionals) related to CCSD(T)/CBS reference values. Both the cyclization reaction and the isomerization of the cyclic product are included in the benchmark. The best functional among those tested for these reactions is ωB97XD, and the effect of the basis set is also investigated for it. © 2017 Wiley Periodicals, Inc.

Nickel Bis(diselenolene) as a Catalyst for Olefin Purification

Nickel bis(dithiolene) reversibly binds olefins via a known interligand binding mechanism, but the complex has limited practical use, due to a competitive intraligand addition which results in decomposition. The present work examines an alternative nickel-based complex that eliminates the decomposition route. Specifically, we have examined the olefin binding processes of nickel bis(diselenolene) complexes using modern density functional theory. Both the inter- and intraligand adducts of the nickel bis(diselenolenes) are thermodynamically more stable than their dithiolene analogues. We have predicted that nickel bis(diselenolene) complexes do not decompose after the intraligand addition, and that the overall activation energies for the kinetically accessible products are quite small. In short, our computational work predicts that nickel bis(diselenolene) complexes are better electrocatalysts for olefin purification than the previous candidates, superior to the previously studied nickel bis(dithiolene) complexes.

Mechanism of Ethylene Addition to Nickel Bis(oxothiolene) and Nickel Bis(dioxolene) Complexes

The electrochemically reversible binding of olefins by nickel bis(dithiolene) has been extensively studied, both theoretically and computationally. To optimize a catalyst for this process, we have investigated all possible reaction pathways of ethylene addition onto the related complex nickel bis(dioxolene), and the two isomers (cis and trans) of nickel bis(oxothiolene). Modern DFT calculations predict that the nickel bis(dioxolene) complex has limited practical use due to high barriers to binding. However, each of the two isomers of the nickel bis(oxothiolene) complexes display enhanced properties versus the original nickel bis(dithiolene) complex. Specifically, in nickel bis(dithiolene), the intraligand binding of olefins leads to decomposition, whereas interligand binding is required for reversibility; the two nickel bis(oxothiolene) complexes have greater selectivity toward the formation of the desired interligand adducts. For the full reaction pathways, the new complexes' binding mechanisms are contrasted with the mechanism of the original catalyst.