Cp*3Al5I6: An Intermediate in Reactions Leading to Elemental Aluminum and AlIII Species?

A first indication of the reaction mechanism for the disproportionation of an Al^I species to an Al^III compound and metallic aluminum is provided by the isolation of [Cp^*₃Al₅I₆], an intermediate that is formed in the ready disproportionation of [Cp*Al] in the presence of Al₂I₆ (see reaction sequence). This potentially key role of Al^I compounds could be of great significance for large-scale industrial processes. X=I, Cl.     

A dramatic effect of double bond configuration in N-oxy-3-aza Cope rearrangements—a simple synthesis of functionalised allenes

The first examples of low temperature N-oxy-3-aza Cope rearrangements, leading to functionalised allenes are described, where the Z-configuration of the enaminic double bond in the rearranging system proves critical.     

Room-Temperature-Stable Diazoalkenes by Diazo Transfer from Azides: Pyridine-Derived Diazoalkenes

Recently, stable diazoalkenes have received significant attention as a new substance class in organic chemistry. While their previous synthetic access was exclusively limited to the activation of nitrous oxide, we here establish a much more general synthetic approach utilizing a Regitz-type diazo transfer with azides. Importantly, this approach is also applicable to weakly polarized olefins such as 2-pyridine olefins. The new pyridine diazoalkenes are not accessible by the activation of nitrous oxide, allowing for a considerable extension of the scope of this only recently accessed functional group. The new diazoalkene class has properties distinct from the previously reported classes, such as photochemically triggered loss of dinitrogen affording cumulenes and not C−H insertion products. Pyridine-derived diazoalkenes represent the so far least polarized stable diazoalkene class reported.     

Reducing Overpotential of Solid-State Sulfide Conversion in Potassium-Sulfur Batteries

Improving kinetics of solid-state sulfide conversion in sulfur cathodes can enhance sulfur utilization of metal-sulfur batteries. However, fundamental understanding of the solid-state conversion remains to be achieved. Here, taking potassium-sulfur batteries as a model system, we for the first time report the reducing overpotential of solid-state sulfide conversion via the meta-stable S₃²⁻ intermediates on transition metal single-atom sulfur hosts. The catalytic sulfur host containing Cu single atoms demonstrates high capacities of 1595 and 1226 mAh g⁻¹ at current densities of 335 and 1675 mA g⁻¹, respectively, with stable Coulombic efficiency of ≈100 %. Combined spectroscopic characterizations and theoretical computations reveal that the relatively weak Cu-S bonding results in low overpotential of solid-state sulfide conversion and high sulfur utilization. The elucidation of solid-state sulfide conversion mechanism can direct the exploration of highly efficient metal-sulfur batteries.     

[(Ph)2(NMe2)C(OLi)⋅THF]2: Crystal Structure of the Tetrahedral Intermediate Formed in the Reaction of N,N-Dimethylbenzamide and Phenyllithium

Information on the reaction path for the 1,2-eliminiation of LiNMe₂ to form benzophenone is provided by the X-ray crystal structure analysis of the tetrahedral adduct [(Ph)₂(NMe₂)C(OLi)⋅THF]₂ (a portion of the structure is shown schematically), which is prepared from N,N-dimethylbenzamide and phenyllithium. A N1−Li1 interaction, which is not observed, would lead to loss of the anomeric effect (n_N→σ^*_C−O) as well as high conformational strain along the C1−N1 bond.     

Prereactive Complexes of Dihalogens XY with Lewis Bases B in the Gas Phase: A Systematic Case for the Halogen Analogue B⋅⋅⋅XY of the Hydrogen Bond B⋅⋅⋅HX

Similar and yet also notably different are the B⋅⋅⋅XY and B⋅⋅⋅HX complexes in the gas phase, where B is a simple Lewis base, XY is a homo- or heterodihalogen molecule, and HX is a hydrogen halide. This is demonstrated, for example, by the structures of oxirane⋅⋅⋅ClF and oxirane⋅⋅⋅HCl (see picture). Both bonds are dominated by simple electrostatic interactions, but differ in terms of their propensity for nonlinearity.     

An Unprecedented Elimination-Driven Migration: The Reductive Dihalobornane–Camphene Rearrangement

An organometallic counterpart of the Wagner–Meerwein rearrangement, the incarnation of an carbocationic alkyl 1,2-migration, has now been discovered. However, the structural reorganization does not occur through carbanionic intermediates, but can only be brought about by a push–pull process via 1 a (see scheme).     

Remote Participation during Glycosylation Reactions of Galactose Building Blocks: Direct Evidence from Cryogenic Vibrational Spectroscopy

The stereoselective formation of 1,2‐cis‐glycosidic bonds is challenging. However, 1,2‐cis‐selectivity can be induced by remote participation of C4 or C6 ester groups. Reactions involving remote participation are believed to proceed via a key ionic intermediate, the glycosyl cation. Although mechanistic pathways were postulated many years ago, the structure of the reaction intermediates remained elusive owing to their short‐lived nature. Herein, we unravel the structure of glycosyl cations involved in remote participation reactions via cryogenic vibrational spectroscopy and first principles theory. Acetyl groups at C4 ensure α‐selective galactosylations by forming a covalent bond to the anomeric carbon in dioxolenium‐type ions. Unexpectedly, also benzyl ether protecting groups can engage in remote participation and promote the stereoselective formation of 1,2‐cis‐glycosidic bonds.     

Direct Observation by Electrospray Ionization Mass Spectrometry of [Cp*RhMo3O8(OMe)5]−, a Key Intermediate in the Formation of the Double-Bookshelf-Type Oxide Cluster [(Cp*Rh)2Mo6O20(OMe)2]2−

The use of methanol as solvent is essential for the formation of the double-bookshelf-type oxide cluster [(Cp*Rh)₂Mo₆O₂₀(OMe)₂]²⁻ from [{Cp*Rh(μ-Cl)Cl}₂] and four equivalents of [Mo₂O₇]²⁻. The reaction proceeds via [Cp*RhMo₃O₈(OMe)₅]⁻. The proposed structure for this key intermediate (shown schematically) is supported by electrospray ionization mass spectrometry and labeling experiments with CD₃OD as solvent. Cp*=η⁵-C₅Me₅.     

Improving Alkaline Hydrogen Oxidation through Dynamic Lattice Hydrogen Migration in Pd@Pt Core-Shell Electrocatalysts

Tracking the trajectory of hydrogen intermediates during hydrogen electro-catalysis is beneficial for designing synergetic multi-component catalysts with division of chemical labor. Herein, we demonstrate a novel dynamic lattice hydrogen (LH) migration mechanism that leads to two orders of magnitude increase in the alkaline hydrogen oxidation reaction (HOR) activity on Pd@Pt over pure Pd, even ≈31.8 times mass activity enhancement than commercial Pt. Specifically, the polarization-driven electrochemical hydrogenation process from Pd@Pt to PdH_x@Pt by incorporating LH allows more surface vacancy Pt sites to increase the surface H coverage. The inverse dehydrogenation process makes PdH_x as an H reservoir, providing LH migrates to the surface of Pt and participates in the HOR. Meanwhile, the formation of PdH_x induces electronic effect, lowering the energy barrier of rate-determining Volmer step, thus resulting in the HOR kinetics on Pd@Pt being proportional to the LH concentration in the in situ formed PdH_x@Pt. Moreover, this dynamic catalysis mechanism would open up the catalysts scope for hydrogen electro-catalysis.