Insight into Three‐Coordinate Aluminum Species on Ethanol‐to‐Olefin Conversion over ZSM‐5 Zeolites

Commercial bioethanol can be readily converted into ethylene by a dehydration process using solid acids, such as Brønsted acidic H‐ZSM‐5 zeolites, and thus, it is an ideal candidate to replace petroleum and coal for the sustainable production of ethylene. Now, strong Lewis acidic extra‐framework three‐coordinate Al³⁺ species were introduced into H‐ZSM‐5 zeolites to improve their catalytic activity. Remarkably, Al³⁺ species working with Brønsted acid sites can accelerate ethanol dehydration at a much lower reaction temperature and shorten the unsteady‐state period within 1–2 h, compared to >9 h for those without Al³⁺ species, which can significantly enhance the ethanol dehydration efficiency and reduce the cost. The reaction mechanism, studied by solid‐state NMR, shows that strong Lewis acidic EFAl‐Al³⁺ species can collaborate with Brønsted acid sites and promote ethanol dehydration either directly or indirectly via an aromatics‐based cycle to produce ethylene.     

Deprotonation of a Seemingly Hydridic Diborane(6) To Build a B−B Bond

Deprotonation of the doubly arylene‐bridged diborane(6) derivative 1 H₂ with (Me₃Si)₃CLi or (Me₃Si)₂NK gives the B−B σ‐bonded species M[ 1 H] in essentially quantitative yields (THF, room temperature; M=Li, K, arylene=4,4′‐di‐tert‐butyl‐2,2′‐biphenylylene). With nBuLi as the base, the yield of Li[ 1 H] drops to 20 % and the 1,1‐bis(9‐borafluorenyl)butane Li[ 2 H] is formed as a side product (30 %). In addition to the 1,1‐butanediyl fragment, the two boron atoms of Li[ 2 H] are linked by a μ‐H bridge. In the closely related molecule Li[ 3 H], the corresponding μ‐H atom can be abstracted with (Me₃Si)₃CLi to afford the B−B‐bonded conjugated base Li₂[ 3 ] (THF, 150 °C; 15 %). Li[ 1 H] and Li[ 2 H] were characterized by NMR spectroscopy and X‐ray crystallography.     

Acidity and Hydrogen Exchange Dynamics of Iron(II)‐Bound Nitroxyl in Aqueous Solution

Nitroxyl‐iron(II) (HNO‐Fe^II) complexes are often unstable in aqueous solution, thus making them very difficult to study. Consequently, many fundamental chemical properties of Fe^II‐bound HNO have remained unknown. Using a comprehensive multinuclear (¹H, ¹⁵N, ¹⁷O) NMR approach, the acidity of the Fe^II‐bound HNO in [Fe(CN)₅(HNO)]³⁻ was investigated and its pK_a value was determined to be greater than 11. Additionally, HNO undergoes rapid hydrogen exchange with water in aqueous solution and this exchange process is catalyzed by both acid and base. The hydrogen exchange dynamics for the Fe^II‐bound HNO have been characterized and the obtained benchmark values, when combined with the literature data on proteins, reveal that the rate of hydrogen exchange for the Fe^II‐bound HNO in the interior of globin proteins is reduced by a factor of 10⁶.