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.

Stacking of benzene with metal chelates: calculated CCSD(T)/CBS interaction energies and potential-energy curves.

Accurate values for the energies of stacking interactions of nickel- and copper-based six-membered chelate rings with benzene are calculated at the CCSD(T)/CBS level. The results show that calculations made at the ωB97xD/def2-TZVP level are in excellent agreement with CCSD(T)/CBS values. The energies of [Cu(C3H3O2)(HCO2)] and [Ni(C3H3O2)(HCO2)] chelates stacking with benzene are -6.39 and -4.77 kcal mol(-1), respectively. Understanding these interactions might be important for materials with properties that are dependent on stacking interactions.

Stacking interactions of Ni(acac) chelates with benzene: calculated interaction energies.

Piling 'em up: The stacking energy of the [Ni(acac)2]/benzene system is calculated at local CCSD(T) level and is in good agreement with the values obtained with the SCS-MP2 method. Energies calculated with several DFT-D methods are somewhat overestimated. The calculated stacking energy of the [Ni(acac)2]/benzene system is significantly stronger than that of the benzene dimer.