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The addition of non‐benzenoid quinones, acenapthenequinone or aceanthrenequinone, to the 9‐carbene‐9‐borafluorene monoanion (1) affords the first examples of dianionic 10‐membered bora‐crown ethers (2–5), which are characterized by multi‐nuclear NMR spectroscopy (¹H,¹³C,¹¹B), X‐ray crystallography, elemental analysis, and UV/Vis spectroscopy. These tetraoxadiborecines have distinct absorption profiles based on the positioning of the alkali metal cations. When compound4, which has a vacant C₄B₂O₄cavity, is reacted with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate, a color change from purple to orange serves as a visual indicator of metal binding to the central ring, whereby the Na⁺ion coordinates to four oxygen atoms. A detailed theoretical analysis of the calculated reaction energetics is provided to gain insight into the reaction mechanism for the formation of2–5. These data, and the electronic structures of proposed intermediates, indicate that the reaction proceeds via a boron enolate intermediate.

A combined synthetic and theoretical investigation of N‐heterocyclic carbene (NHC) adducts of magnesium amidoboranes is presented, which involves a rare example of reversible migratory insertion within a normal valents‐block element. The reaction of (NHC)Mg(N(SiMe₃)₂)₂(1) and dimethylamine borane yields the tris(amide) adduct (NHC−BN)Mg(NMe₂BH₃)(N(SiMe₃)₂) (2; NHC−BN = NHC−BH₂NMe₂). In addition to Me₂N=BH₂capture at the^NHCC−Mg bond, mechanistic investigations suggest the likelihood of aminoborane migratory insertion from an RMg(NMe₂BH₂NMe₂BH₃) intermediate. To elucidate these processes, the carbene complexes (NHC)Mg(NMe₂BH₃)₂(8) and (NHC)Mg(NMe₂BH₂NMe₂BH₃)₂(9) were synthesized, and a dynamic migration of Me₂N=BH₂between Mg−N and^NHCC−Mg bonds was observed in9. This unusual reversible migratory insertion is presumably induced by dissimilar charge localization in the⁻{NMe₂BH₂NMe₂BH₃} anion, as well as the capacity of NHCs to reversibly capture Me₂N=BH₂in the presence of Lewis acidic magnesium species.

Abstract Friedel-Crafts Arylation (the Scholl reaction) is the coupling of two aromatic rings with the aid of a strong Lewis or Brønsted acid. This historically significant C–C bond forming reaction normally leads to aromatic products, often as oligomeric mixtures, dictated by the large stabilization gained upon their rearomatization. The coordination of benzene by a tungsten complex disrupts the natural course of this reaction sequence, allowing for Friedel-Crafts Arylation without rearomatization or oligomerization. Subsequent addition of a nucleophile to the coupled intermediate leads to functionalized cyclohexenes. In this work, we show that by coordinating benzene to tungsten through two carbons (dihapto-coordinate), a rarely observed double protonation of the bound benzene is enabled, allowing its subsequent coupling to a second arene without the need of a precious metal or Lewis acid catalyst.

In the face of rising atmospheric carbon dioxide (CO 2 ) emissions from fossil fuel combustion, the hydrogen evolution reaction (HER) continues to attract attention as a method for generating a carbon-neutral energy source for use in fuel cells. Since some of the best-known catalysts use precious metals like platinum, which have low natural abundance and high cost, developing efficient Earth abundant transition metal catalysts for HER is an important objective. Building off previous work with transition metal catalysts bearing 2,2′-bipyridine-based ligand frameworks, this work reports the electrochemical analysis of a molecular nickel( ii ) complex, which can act as an electrocatalyst for the HER with a faradaic efficiency for H 2 of 94 ± 8% and turnover frequencies of 103 ± 6 s −1 when pentafluorophenol is used as a proton donor. Computational studies of the Ni catalyst suggest that non-covalent interactions between the proton donor and ligand heteroatoms are relevant to the mechanism for electrocatalytic HER.