Formation of Acrylates from Ethylene and CO₂ on Ni Complexes: A Mechanistic Viewpoint from a Hybrid DFT Approach

The most challenging step in the production of acrylates from ethylene and CO₂ mediated by transition-metal complexes is the release of the acrylate from the metallalactone intermediate formed by coupling of ethylene and CO₂. Recently, methyl acrylate formation was achieved from nickelalactones by using methyl iodide (MeI) as the electrophile, and the yield was tuned with different amine and phosphine ligands. Modeling organometallic catalysts with such large ligands accurately is a challenge for computational chemistry. A hybrid approach has been designed here by coupling the double hybrid XYG3 and the hybrid B3LYP exchange correlation functionals, using the extended ONIOM scheme. This approach was then applied to explore the role of the MeI electrophile for the formation of methyl acrylate from the initial nickelalactone complex and to rationalize the effect of the ligands on the yield of methyl acrylate. We show that the choice of ligand has little effect on the main productive pathway. However, it has a significant influence on side reactions, which compete with the productive pathway and are detrimental to methyl acrylate formation. Finally, the need for a very large overstoichiometry of MeI for a good yield of methyl acrylate is explained by the lower polarity of MeI, which avoids the stabilization of nonproductive intermediates. The nature of the limiting intermediates has been validated by comparing calculated and experimental vibrational spectra

Ultrafast Spectroscopic Identification of Hole Transfer in All-Polymer Blend Films of Poly(1-{4,8-bis[5-(2-ethylhexyl)thiophen-2-yl]-benzo[1,2‑<i>b</i>:4,5‑<i>b</i>′]dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)‑4<i>H</i>‑thieno[3,4‑<i>c</i>]pyrrole-4,6(5<i>H</i>)‑dione) and Poly[1,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)]

All-polymer solar cells composed of wide-band-gap polymer poly­(1-{4,8-bis­[5-(2-ethylhexyl)­thiophen-2-yl]-benzo­[1,2-<i>b</i>:4,5-<i>b</i>′]­dithiophen-2-yl}-3-methyl-5-(4-octylphenyl)-4<i>H</i>-thieno­[3,4-<i>c</i>]­pyrrole-4,6­(5<i>H</i>)-dione) (PTP8) as the donor and poly­[1,8-bis­(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)] [P­(NDI2OD-T2), also known as Activink N2200] as the acceptor exhibit a broad absorbance in the range 300–900 nm, thanks to complementary absorption of near-infrared light by N2200. Although N2200 shows reasonably high electron mobility, the contribution of the photogenerated excitons in N2200 to the power conversion of the PTP8/N2200 solar cell is insignificant. Here, the hole transfer from N2200 to PTP8 in PTP8/N2200 blend films was investigated by utilizing ultrafast transient absorption spectroscopy. The spectral fingerprints of ground-state bleaching and hole polaron-induced absorption of PTP8 are identified under selective excitation of the N2200 component and unambiguously indicate hole transfer from N2200 to PTP8. The hole transfer is slow (∼100 ps), comparable to the geminate exciton recombination rate, consequently limiting the transfer efficiency and carrier generation. The hole-transfer efficiency depends on the PTP8/N2200 weight ratio, showing a highest value of ∼14.1% in the 3:2 film

Rational Design of Hydrogen-Donor Solvents for Direct Coal Liquefaction

Facing the challenge of processes in direct coal liquefaction (DCL), it is vital to develop optimal hydrogen-donor solvent (H-donor) to dramatically moderate coal liquefaction conditions. Here, we propose an approach for rational design of optimal H-donor candidates based on density functional theory (DFT) calculations combining reverse searching algorithm. First, the mechanism of hydrogen transfer from H-donor to coal radical was investigated by using common model compounds. DFT calculations show that the concerted hydrogen transfer route promoted by coal radicals is the dominant pathway. The C–H bond dissociation enthalpies (BDEs) show strong correlation with intrinsic reaction barriers and rate constants (in log scale), which allow us to define a cheap metric for comparing the hydrogen-donation ability of different H-donors. Then the framework for rational design of H-donor candidates is established to seek molecules with low C–H BDEs based on inverse molecular design strategy. In the searching procedure, the chemical structure of parent molecule is varied by appropriate substituent from a predefined library (15 substituents). To reduce searching space, four empirical rules are proposed to guide the structural modifications. Finally, the H-donor candidates designed are validated by transition state calculations. It is confirmed that the inverse molecular design approach is effective for seeking candidate H-donors with lower reaction barriers and potentially higher rate of hydrogenation, which open a window for the rational design of optimal H-donors to improve the yields of the liquid products from coal under mild conditions

Hunting the Correlation between Fe₅C₂ Surfaces and Their Activities on CO: The Descriptor of Bond Valence

To hunt the correlation between the surfaces of Fe₅C₂ and their corresponding activities, the CO adsorption and dissociation on a series of both low ((010), (001), (110), (111), (111̅)) and high Miller index surfaces of Fe₅C₂((221), (4̅11), and (510)) surfaces are systemically investigated. For the CO adsorption, configurations with bonding to surface Fe sites are much stronger than that on C sites. For the CO dissociation, direct C–O cleavage can take place on the (221), (510), (010), and (111̅) surfaces due to the low activation energy. More importantly, to correlate the surface character and the activity of CO dissociation we proposed a concept of sum bond valence. It is found that the adsorbed CO with more bond valence can dissociate easier, and a linear relationship between the activation energies and the CO bond valence can be established. It can be inferred that the activity of Fe₅C₂ surfaces for CO dissociation strongly relies on the binding characteristics. The relatively stable (100) and (111) surfaces are not active for direct CO dissociation. In this work, the CO bond valence is suggested to be an important descriptor to correlate complicated surfaces and their activities. Furthermore, such a finding can guide the rational design of catalysts with desired activities

Stability and Reactivity of Intermediates of Methanol Related Reactions and C–C Bond Formation over H‑ZSM‑5 Acidic Catalyst: A Computational Analysis

On the basis of density functional theory including dispersion correction [ωB97XD/6-311+G­(2df,2p)//B3LYP/6-311G­(d,p)], the thermodynamics and kinetics of the reactions of CH₃OH and CH₃OCH₃ over H-ZSM-5 have been systematically computed. For the reaction of the methylated surface (CH₃OZ) with CH₃OH, CH₃OCH₃ formation is kinetically controlled and the competitive formation of CH₂O + CH₄ is thermodynamically controlled, in agreement with the observed desorption temperatures of CH₃OH, CH₃OCH₃, and CH₂O under experimental conditions. For the reaction between ZOCH₃ and CH₃OCH₃, the formation of the framework stabilized (CH₃)₃O⁺ is kinetically controlled, consistent with the NMR observation at low temperature, and the competitive formation of surface CH₃OCH₂OZ + CH₄ is thermodynamically controlled. On the basis of the thermodynamically more favored CH₂O and CH₃OCH₂OZ, there are two parallel routes for the first C–C bond formation, from the coupling of CH₃OCH₂OZ with CH₃OH and CH₃OCH₃ as well as from the coupling of CH₂O with CH₃OH and CH₃OCH₃. The most important species is the methylated surface (CH₃OZ), which can react with CH₃OH and CH₃OCH₃ to form the corresponding physisorbed CH₂O and chemisorbed CH₃OCH₂OZ, and they can further couple with additional CH₃OH and CH₃OCH₃ to result in first C–C formation, verifying the proposed formaldehyde (CH₂O) and methoxymethyl (CH₃OCH₂OZ) mechanisms