Separation of light hydrocarbons (C 1 −C 9 ) represents one of the "seven chemical separations to change the world". Boron clusters can potentially play an important role in chemical separation, due to their unique three-dimensional structures and their ability to promote a potentially rich array of weak noncovalent interactions. Herein, we report the rational design of metallacages with carborane functionality and cooperative dihydrogen binding sites for the highly selective capture of cyclohexane molecules. The metallacage 1, bearing the ligand 2,4,6-tris(4-pyridyl)-1,3,5-triazine (TPT), can produce cyclohexane with a purity of 98.5% in a single adsorption−desorption cycle from an equimolar mixture of benzene and cyclohexane. In addition, cyclohexene molecules can be also encapsulated inside the metallacage 1. This selective encapsulation was attributed to spatial confinement effects, C−H•••π interactions, and particularly dihydrogen-bond interactions. This work suggests exciting future applications of carborane cages in supramolecular chemistry for the selective adsorption and separation of alkane molecules and may open up a new research direction in host−guest chemistry.
Non-metal-catalyzed C−H borylation of arenes represents a sustainable and environment-friendly approach for the functionalization of arenes. Despite its promise as an alternative to traditional transition-metal systems, its substrate scope is generally limited to electron-rich arenes, thus hindering its application in organic synthesis. Herein, we report the development of a borenium-ion catalyst which can borylate unactivated arenes under ambient conditions with 4-chlorocatecholborane (HBcat Cl ) as borylation reagent. This metal-free catalytic system is suitable for the borylation of C−H bonds in sterically encumbered positions, which has been a challenging task for transition-metal systems. Additionally, this catalytic system allows para-selective one-pot borylation of phenols, which has not been achieved by using transition-metal systems. Our mechanistic investigations and computational studies support a synergistic activation of the H−Bcat Cl bond by the arene substrate and the borenium-ion catalyst. This generates a Wheland intermediate and a neutral hydroborane species and is followed by deprotonation of the Wheland intermediate with the hydroborane species. The latter step of C−H bond cleavage is likely the rate-limiting step.
The development of biomimetic catalytic systems that can imitate or even surpass natural enzymes remains an ongoing challenge, especially for bioinspired syntheses that can access non-natural reactions. Here, we show how an all-inorganic biomimetic system bearing robust nitrogen-neighbored singlecobalt site/pyridinic-N site (Co−N 4 /Py-N) pairs can act cooperatively as an oxidase mimic, which renders an engaged coupling of oxygen (O 2 ) reduction with synthetically beneficial chemical transformations. By developing this broadly applicable platform, the scalable synthesis of greater than 100 industrially and pharmaceutically appealing O-silylated compounds including silanols, borasiloxanes, and silyl ethers via the unprecedented aerobic oxidation of hydrosilane under ambient conditions is demonstrated. Moreover, this heterogeneous oxidase mimic also offers the potential for expanding the catalytic scope of enzymatic synthesis. We anticipate that the strategy demonstrated here will pave a new avenue for understanding the underlying nature of redox enzymes and open up a new class of material systems for artificial biomimetics.
Catalytic hydrogenolysis of biomass-derived glycerol to 1,3-propanediol (1,3-PDO) represents an important process for the sustainable production of value-added chemicals. However, there is a dearth of understanding of the effect of the polymorph of the support on this reaction. Herein, two Pt–WO x /TiO2 catalysts supported on rutile TiO2 (r-TiO2) and anatase TiO2 (a-TiO2) polymorphs were prepared to investigate the crystal phase effect of TiO2 on the structural property and catalytic performance in glycerol hydrogenolysis. The TiO2 polymorph was identified to impose profound effects on the size of the Pt nanoparticles (NPs) and the dispersion and location of the WO x species, which originated from the discrepancies in the crystal structures between the PtO2 and the TiO2 polymorphs and the discrepancies in the interactions of WO x with different TiO2 polymorphs. In glycerol hydrogenolysis, the Pt–WO x /r-TiO2 catalyst gave a 1,3-PDO selectivity of 51.2% at a glycerol conversion to liquid products of 74.5%, yielding 38.1% of 1,3-PDO. In contrast, the Pt–WO x /a-TiO2 catalyst showed much inferior glycerol conversion and 1,3-PDO selectivity, yielding only 1.0% of 1,3-PDO under identical reaction conditions. The superior catalytic performance of the Pt–WO x /r-TiO2 catalyst is attributed to the r-TiO2 polymorph that facilitates a faster hydrogen spillover than the a-TiO2 polymorph from the Pt NPs to the reaction intermediate on the WO x species, which is substantiated by an even higher 1,3-PDO yield of 44.8% over the physically mixed Pt/r-TiO2 + WO x /r-TiO2 catalyst. This work demonstrates the critical role of the polymorph of the TiO2 support in the design of efficacious Pt–WO x -based catalysts for glycerol hydrogenolysis to 1,3-PDO.
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