Scalable Palladium-Catalyzed Alkoxycarbonylation of Conjugated Dienes.

The Pd(cod)Cl2-catalyzed alkoxycarbonylation of conjugated dienes to ß,γ-unsaturated esters was approached by both intramolecular phosphinesulfonate L1 and intermolecular PPh3/PTSA in this study. However, the poor solubility of the Pd/L1 complex and the labile monodentate Pd/PPh3 structure restricts the system efficiency, especially for the scale-up application. By contrast, the stable and well-soluble bidentate Xantphos system allows for the quantitative formation of 3-pentenoate (96%) on a gram scale within 6 h in weakly alkaline N-methylpyrrolidone (NMP), which also functions as a basic site to promote the rate-limiting alcoholysis step while reducing the dosage of ligand to a theoretical value.

The Difference Se Makes: A Bio-Inspired Dppf-Supported Nickel Selenolate Complex Boosts Dihydrogen Evolution with High Oxygen Tolerance.

Inspired by the metal active sites of [NiFeSe]-hydrogenases, a dppf-supported nickel(II) selenolate complex (dppf=1,1'-bis(diphenylphosphino)ferrocene) shows high catalytic activity for electrochemical proton reduction with a remarkable enzyme-like H2 evolution turnover frequency (TOF) of 7838 s-1 under an Ar atmosphere, which markedly surpasses the activity of a dppf-supported nickel(II) thiolate analogue with a low TOF of 600 s-1 . A combined study of electrochemical experiments and DFT calculations shed light on the catalytic process, suggesting that selenium atom as a bio-inspired proton relay plays a key role in proton exchange and enhancing catalytic activity of H2 production. For the first time, this type of Ni selenolate-containing electrocatalyst displays a high degree of O2 and H2 tolerance. Our results should encourage the development of the design of highly efficient oxygen-tolerant Ni selenolate molecular catalysts.

Observation of a bcc-like framework in polyhydrido copper nanoclusters.

Cu is well-known to adopt a face-centered cubic (fcc) structure in the bulk phase. Ligand-stabilized Cu nanoclusters (NCs) with atomically precise structures are an emerging class of nanomaterials. However, it remains a great challenge to have non-fcc structured Cu NCs. In this contribution, we report the syntheses and total structure determination of six 28-nuclearity polyhydrido Cu NCs: [Cu28H16(dppp)4(RS)4(CF3CO2)8] (dppp = 1,3-bis(diphenylphosphino)propane, RSH = cyclohexylthiol, 1; tert-butylthiol, 3; and 2-thiophenethiol, 4) and [Cu28H16(dppe)4(RS)4(CH3CO2)6Cl2] (dppe = 1,2-bis(diphenylphosphino)ethane, RSH = (4-isopropyl)thiophenol, 2; 4-tert-butylbenzenethiol, 5; and 4-tert-butylbenzylmercaptan, 6). Their well-defined structures solved by X-ray single crystal diffraction reveal that these 28-Cu NCs are isostructural, and the overall metal framework is arranged as a sandwich structure with a core-shell Cu2@Cu16 unit held by two Cu5 fragments. One significant finding is that the organization of 18 Cu atoms in the Cu2@Cu16 could be regarded as an incomplete and distorted version of 3 × 2 × 2 "cutout" of the body-centered cubic (bcc) bulk phase, which was strikingly different to the fcc structure of bulk Cu. The bcc framework came as a surprise, as no bcc structures have been previously observed in Cu NCs. A comparison with the ideal bcc arrangement of 18 Cu atoms in the bcc lattice suggests that the distortion of the bcc structure results from the insertion of interstitial hydrides. The existence, number, and location of hydrides in these polyhydrido Cu NCs are established by combined experimental and DFT results. These results have significant implications for the development of high-nuclearity Cu hydride NCs with a non-fcc architecture.

New protective ligands for atomically precise silver nanoclusters.

Atomically precise silver nanoclusters (NCs) have emerged as a hot topic attracting immense research interest. Protecting ligands are needed for direct capping on cluster surfaces in order to prevent aggregation and to stabilize NCs. It has been demonstrated that protective ligands are critical to determining the sizes, structures and properties of silver NCs. The past decades have witnessed conventionally used organic ligands (thiolates/selenols, phosphines and alkynyls) and inorganic ligands (chalcogens and halogens) being extensively used to passivate NC surfaces. However, only in the most recent years have new-type protecting ligands beyond the conventional ones begun to be introduced in the protecting sphere of new functional silver NCs. The present Frontier article covers the most recent examples of some new protective agents for well-defined silver NCs. We describe four classes of novel silver NCs stabilized by newly-developed surface ligands, namely, nitrogen-donor organic ligands, oxygen-donor inorganic ligands, metalloligands and macrocyclic hosts, paying attention to the synthesis, structures and properties of these silver NCs. This Frontier article will hopefully attract more cluster scientists to explore more freshly ligated atomically precise silver NCs with novel structures and properties in the years ahead. The literature survey in this review is based on publications up to February 2020. Some suggestions for future directions in this field are also given.

Enhanced CO2 capture by reducing cation-anion interactions in hydroxyl-pyridine anion-based ionic liquids.

In this work, an efficient strategy for improving CO2 capture based on anion-functionalized ionic liquids (ILs) by reducing cation-anion interactions in ILs was reported. The influence of the cationic species on CO2 absorption was investigated using 2-hydroxyl pyridium anions ([2-Op]) as a probe. CO2 capture experiments indicated that the CO2 absorption capacity in [2-Op] anion-based ILs varied from 0.94 to 1.69 mol CO2 per mol IL at 30 °C and 1 atm. Spectroscopic analysis and quantum chemical calculations suggested that the increase of the CO2 absorption capacity may be ascribed to the reduction of the strength of cation-anion interactions in ILs, and stronger cation-anion interactions would make one CO2 site in the [2-Op] anion inactive. Furthermore, the effect of the cation unit on the anion was evidenced by FT-IR spectra, implying that strong interactions between ions may lead to the decrease of the IR absorption wavenumber of hydroxy pyridium and work against CO2 capture. Following this strategy, it was finally found that [Ph-C8eim][2-Op] (Ph-C8eim = 1-N-ethyl-3-N-octyl-2-phenylimidazolium) with weaker cation-anion interactions exhibited a significant increase in the CO2 uptake capacity, and extremely high capacities of 1.69 and 1.83 mol CO2 per mol IL could be achieved at 30 and 20 °C, respectively. The study presented here would be helpful for further designing novel and effective ILs for advancing CO2 capturing performance.

Tethered sensitizer-catalyst noble-metal-free molecular devices for solar-driven hydrogen generation.

Inspired by natural photosynthesis in an organized assembly, compact H2-evolving molecular devices, which tether sensitizer and catalyst modules in one single molecule, present an opportunity to overcome the diffusion limit required for multi-component molecular systems, and increase intramolecular electron transfer rates from the photoactivated unit to the catalytic center to improve H2-evolving efficiency. Thereinto absolutely noble-metal free H2-evolving molecular devices are of particular interest because they don't contain precious and scarce noble-metal based components. This Frontier article focuses specifically on the recent advances in the design, synthesis, and photocatalytic properties of all-abundant-element molecular devices for photoinduced H2 generation via intramolecular processes. Some challenges and suggestions for future directions in this field are also illustrated.