Two types of zinc MOF, Zn-X₂Trp and Zn-X₂PET (X=H, F, Cl, Br, I, Me, Et, Pr), with difunctionalized triptycene-hexacarboxylate ligands H₆X₂Trp and H₆X₂PET that differ in size have been synthesized. All of these Zn-MOFs show high thermal stability as well as H₂- and CO₂-adsorption capacities. Moreover, MOFs with smaller pore size showed higher H₂ and CO₂ adsorption. Thus, the introduction of methyl, chloro, and bromo substituents at the bridgehead positions of the triptycene ligands enhances the H₂- and CO₂-adsorption capacities.

Abstract

A series of metal–organic frameworks (MOFs) based on zinc ions and two triptycene ligands of different size have been synthesized under solvothermal conditions. Structural analyses revealed that they are isostructural 3D-network MOFs. The high porosity and thermal stability of these MOFs can be attributed to the highly rigid triptycene-based ligands. Their BET specific surface areas depend on the size of the triptycene ligands. In contrast to these surface-area data, the H₂ and CO₂ adsorption of these MOFs is larger for MOFs with small pores. Consequently, we introduced functional groups to the bridge-head position of the triptycene ligands and investigated their effect on the gas-sorption properties. The results unveiled the role of the functional groups in the specific CO₂ binding via an induced interaction between adsorbates and the functional groups. Excellent H₂ and CO₂ properties in these MOFs were achieved in the absence of open metal sites.

Terminal aluminium and gallium silylimides have been accessed for the first time by exploiting the oxidative reactions of anionic aluminium(I)/gallium(I) (‘aluminyl’/’gallyl’) reagent with silylazides. These compounds feature minimal M=N π-bonding and can be shown to act as sources of the nitride ion, [N]³⁻ in reactions with CO or N₂O.

Abstract

Terminal aluminium and gallium imides of the type K[(NON)M(NR)], bearing heteroatom substituents at R, have been synthesised via reactions of anionic aluminium(I) and gallium(I) reagents with silyl and boryl azides (NON=4,5-bis(2,6-diisopropyl-anilido)-2,7-di-tert-butyl-9,9-dimethyl-xanthene). These systems vary significantly in their lability in solution: the N(SiⁱPr₃) and N(Boryl) complexes are very labile, on account of the high basicity at nitrogen. Phenylsilylimido derivatives provide greater stabilization through the π-acceptor capabilities of the SiR₃ group. K[(NON)AlN(Si^tBuPh₂)] offers a workable compromise between stability and solubility, and has been completely characterized by spectroscopic, analytical and crystallographic methods. The silylimide species examined feature minimal π-bonding between the imide ligand and aluminium/gallium, with the HOMO and HOMO-1 orbitals effectively comprising orthogonal lone pairs centred at N. Reactivity-wise, both aluminium and gallium silylimides can act as viable sources of nitride, [N]³⁻, with systems derived from either metal reacting with CO to afford cyanide complexes. By contrast, only the gallium system K[(NON)Ga{N(SiPh₃)}] is capable of effecting a similar transformation with N₂O to yield azide, N₃ ⁻, via formal oxide/nitride metathesis. The aluminium systems instead generate RN₃ via transfer of the imide fragment [RN]²⁻.

Ring opening of hexamethylcyclotrisoloxane with BeBr₂, BeI₂ and BePh₂ was observed. These reactions yielded previously unknown diorgano bromo and iodo silanolates, [Be₃Br₂(OSiMe₂Br)₄] and [Be₃I₂(OSiMe₂I)₄], respectively, as well as [Be₃Ph₂(OSiMe₂Ph)₄]. Hydrolysis of these beryllium silanolates revealed that dimethyl bromo and iodo silanol are unstable and react to various cyclic cyclosiloxanes.

Abstract

The reactivity of hexamethylcyclotrisiloxane (D₃) towards BeCl₂, BeBr₂, BeI₂ and [Be₃Ph₆]₃ was investigated. While BeCl₂ only showed unselective reactivity, BeBr₂, BeI₂ and [Be₃Ph₆] cleanly react to the trinuclear complexes [Be₃Br₂(OSiMe₂Br)₄], [Be₃I₂(OSiMe₂I)₄] and [Be₃Ph₂(OSiMe₂Ph)₄]. These unprecedented bromide, iodide and phenyl transfer reactions from a group II metal onto silicon offer a versatile access to previously unknown diorgano bromo and iodo silanolates.

Amphiphobic fluoroalkyl chains are exploited for creating robust and diverse self-assembled biomimetic catalysts in aqueous solution. Long terminal perfluoroalkyl chains (CnF2n+1 with n = 6, 8, and 10) yoked with a short perhydroalkyl chains (CmH2m with m = 2 and 3) were used to synthesize several 1,4,7-triazacyclononane (TACN) derivatives, CnF2n+1-CmH2m-TACN. In the presence of an equimolar amount of Zn2+ ions that coordinate the TACN moiety and drive the self-assembly into micelle-like aggregates, the critical aggregation concentration of polyfluorinated CnF2n+1-CmH2mTACN·Zn2+ was lowered by ~1 order of magnitude compared to the traditional perhyroalkyl counterpart with identical carbon number of alkyl chain. When 2’-hydroxypropyl-4-nitrophenyl phosphate was used as the model phosphate substrate, polyfluorinated CnF2n+1CmH2m-TACN·Zn2+ assemblies showed higher affinity and catalytic activity, compared to its perhyroalkyl chain-based counterpart. Coarse-grained molecular dynamic simulations have been introduced to explore the supramolecular assembly of polyfluoroalkyl chains in the presence of Zn2+ ions and to better understand their enhanced catalytic activity.

Homocubane, a highly strained cage hydrocarbon, contains two very different positions for the introduction of a nitrogen atom into the skeleton, e.g., a position 1 exchange results in a tertiary amine whereas position 9 yields a secondary amine. Herein reported is the synthesis of 9-azahomocubane along with associated structural characterization, physical property analysis and chemical reactivity. Not only is 9-azahomocubane readily synthesized, and found to be stable as predicted, the basicity of the secondary amine was observed to be significantly lower than the structurally related azabicyclo[2.2.1]heptane, although similar to 1-azahomocubane.

Oxygen reduction reaction (ORR) is the key reaction in metal air and fuel cells. Among the catalysts towards ORR, carbon-based metal-free catalysts are getting more attention because of their maximum atom utilization, effective active sites and satisfactory catalytic activity and stability. However, the pyrolysis synthesis of these carbons resulted in disordered porosities and uncontrolled catalytic sites, which hindered us to achieve the catalysts’ properties previously, and build the structure–property relationship at molecular level. Covalent organic frameworks (COFs) constructed with designable building blocks have been employed as metal free electrocatalysts towards oxygen reduction reaction (ORR) due to their controlled skeletons, tailored pores size and environments, and well-defined location and kinds of catalytic sites. In this concept article, the development of metal-free COFs for ORR is summarized, and different strategies including skeletons regulation, linkages engineering and edge-sites modulation to improve the catalytic selectivity and activity are discussed. Furthermore, this Concept provides prospective for design and construction high electrocatalysts based on the catalytic COFs.

Allylic alcohols are a privileged motif in natural product synthesis and new methods that access them in a stereoselective fashion are highly sought after. Toward this goal, we found that chiral acetonide-protected polyketide fragments performing the Hoppe–Matteson–Aggarwal rearrangement in the absence of sparteine with high yields and diastereoselectivities rendering this protocol a highly valuable alternative to the Nozaki–Hiyama–Takai–Kishi reaction. Various stereodyads and -triads were investigated to determine their substrate induction. The mostly strong inherent stereoinduction was attributed to a combination of steric and electronic effects.

Reaction of (6-Dipp)CuOtBu (6-Dipp = C{NDippCH2}2CH2, Dipp = 2,6-iPr2C6H3) with B2(OMe)4 provided access to (6-Dipp)CuB(OMe)2 via σ-bond metathesis. (6-Dipp)CuB(OMe)2 was characterised by NMR spectroscopy and X-ray crystallography and shown to be a monomeric acyclic boryl of copper. (6-Dipp)CuB(OMe)2 reacted with ethylene and diphenylacetylene to provide insertion compounds into the Cu-B bond which were characterised by NMR spectroscopy in both cases and X-ray crystallography in the latter. It was also competent in the rapid catalytic deoxygenation of CO2 in the presence of excess B2(OMe)4. Alongside π-insertion, (6-Dipp)CuB(OMe)2 reacted with LiNMe2 to provide a salt metathesis reaction at boron, giving (6-Dipp)CuB(OMe)NMe2, a second monomeric acyclic boryl, which also cuproborated diphenylacetylene. Computational interrogation validated these acyclic boryl species to be electronically similar to (6-Dipp)CuBpin.

Artificial metalloenzymes have emerged as biohybrid catalysts that allow to combine the reactivity of a metal catalyst with the flexibility of protein scaffolds. Here, we report the artificial metalloenzymes based on the β-barrel protein nitrobindin NB4, in which a cofactor [CoIIX(Me3TACD-Mal)]+X- (X = Cl, Br; Me3TACD = N,N´,N´´-trimethyl-1,4,7,10-tetraazacyclododecane, Mal = CH2CH2CH2NC4H2O2) was covalently anchored via a Michael addition reaction. These biohybrid catalysts showed higher efficiency than the free cobalt complexes for the oxidation of benzylic C(sp3)-H bonds in aqueous media. Using commercially available oxone (2KHSO5·KHSO4·K2SO4) as oxidant, a total turnover number of up to 220 and 97% ketone selectivity were achieved for tetralin. As catalytically active intermediate, a mononuclear terminal cobalt(IV)-oxo species [Co(IV)=O]2+ was generated by reacting the cobalt(II) cofactor with oxone in aqueous solution and characterized by ESI-TOF MS.

Worldwide lithium (Li) demand has surged in recent years due to increased production of Li-ion batteries for electric vehicles and stationary storage. Li supply and production will need to increase such that the transition towards increased electrification in the energy sector does not become cost prohibitive. Many countries have taken policy steps such as listing Li as a critical mineral. Current commercial Li mining is mostly from dedicated mine sources, including ores, clays, and brines. The conventional ways to extract Li+ from those resources are through chemical processing. The environmental and economic sustainability of conventional Li processing has recently received increased scrutiny. Routes such as direct Li+ extraction may provide advantages relative to conventional Li+ extraction technologies, and one possible route to direct Li+ extraction includes leveraging of intercalation materials. Intercalation material processing has recently demonstrated high selectivity towards Li+ as opposed to other cations. Reviews and reports of direct Li+extraction with intercalation materials are limited, even as this technology has started to show promise in smaller scale demonstrations. This paper will review selective Li+ extraction via intercalation materials, including both electrochemical and chemical methods to drive Li+ in and out and efforts to characterize the Li+ insertion/deinsertion processes.