A Tricyclic Hexaphosphane

The reaction of the functionalized cyclo‐tetraphosphane [ClP(μ‐PMes*)]₂ (Mes*=2,4,6‐tri‐tert‐butylphenyl) with different Lewis bases led to the formation of an unprecedented tricyclic hexaphosphane, Mes*P₆Mes*. The formation of this compound was investigated by spectroscopic and theoretical methods, revealing an unusual ring expansion reaction. The title compound was fully characterized by experimental and computational methods.     

The Solitary Isomer of C60H18 Is Proven to Have a C3v Crown Shape: Crystal Structure Determination and Synthesis of Its Triruthenium Cluster Complex

Analytically pure C₆₀H₁₈ is obtained by a Ru₃ cluster complexation and decomplexation method. The crystal structure of C₆₀H₁₈ consists of one flattened hemisphere, to which all 18 hydrogen atoms are symmetrically bonded, and one curved hemisphere akin to C₆₀. A benzenoid ring in the flattened hemisphere is isolated from the residual π systems by a belt composed of sp³‐hybridized CH units. The average out‐of‐plane distances for carbon atoms attached to the benzenoid ring (0.14 Å) is substantially larger than that found in C₆₀F₁₈ (0.06 Å). Several long C(sp³)?C(sp³) single bond lengths [1.61(3)–1.65(3) Å] are observed for C₆₀H₁₈. The reaction of [Ru₃(CO)₁₂] and C₆₀H₁₈ produces [Ru₃(CO)₉(μ₃‐η²,η²,η²‐C₆₀H₁₈)] ( 1 ), where the Ru₃ triangle is regiospecifically linked to the hexagon opposite to the benzenoid ring. Compound 1 is the first transition metal complex of a polyhydrofullerene (fullerane). C₆₀H₁₈ and 1 have been characterized by ¹H and ¹³C NMR, UV/Vis, and mass spectroscopies. The HOMO–LUMO gap of C₆₀H₁₈ is evaluated to be 1.51 V by cyclic voltammetry.     

Thermal induced structural properties of silver(I) sulphate (Ag2SO4)

The crystal structures of silver(I) sulphate, Ag₂SO₄, have been investigated as a function of temperature. A main feature is the phase transition from the low‐temperature ordered phase, F ddd, to the high‐temperature disordered phase, . In particular, the high‐temperature structure is solved from single crystal synchrotron X‐ray measurements. In this phase the title compound undergoes a colossal (anisotropic) thermal expansion of . This is presumably owing to a high anisotropic vibration state of one of the two crystallographically independent Ag‐atoms. Simultaneously occurring high ionic conductivity may be associated with silver ions moving along the ‐axis using a “paddle‐wheel” assisted percolative mechanism. Onset of metallic silver in the single crystals is documented, seemingly dependent on thermal pre‐history, mosaic structure and chemical synthesis. Possible mechanisms explaining this effect, comprising disproportionation or photo‐decomposition, are suggested.     

Two 2-(quinonylcarboxamino)benzoates from the lateral roots of Aconitum carmichaelii

Two new 2-(quinonylcarboxamino)benzoates, named aconicarmiquinamides A (1) and B (2), were isolated from an aqueous extract of the lateral roots of Aconitum carmichaelii. Their structures were determined by spectroscopic data analysis, and confirmed by comparison with synthetic methyl 3,6-bis(diethylamino)benzoqunonylcarboxylate (3).     

HyperBIRD: A Sensitivity‐Enhanced Approach to Collecting Homonuclear‐Decoupled Proton NMR Spectra

Samples prepared following dissolution dynamic nuclear polarization (DNP) enable the detection of NMR spectra from low‐γ nuclei with outstanding sensitivity, yet have limited use for the enhancement of abundant species like ¹H nuclei. Small‐ and intermediate‐sized molecules, however, show strong heteronuclear cross‐relaxation effects: spontaneous processes with an inherent isotopic selectivity, whereby only the ¹³C‐bonded protons receive a polarization enhancement. These effects are here combined with a recently developed method that delivers homonuclear‐decoupled ¹H spectra in natural abundance samples based on heteronuclear couplings to these same, ¹³C‐bonded nuclei. This results in the HyperBIRD methodology; a single‐shot combination of these two effects that can simultaneously simplify and resolve complex, congested ¹H NMR spectra with many overlapping spin multiplets, while achieving 50–100 times sensitivity enhancements over conventional thermal counterparts.     

Accelerated NMR Spectroscopy with Low‐Rank Reconstruction

Accelerated multi‐dimensional NMR spectroscopy is a prerequisite for high‐throughput applications, studying short‐lived molecular systems and monitoring chemical reactions in real time. Non‐uniform sampling is a common approach to reduce the measurement time. Here, a new method for high‐quality spectra reconstruction from non‐uniformly sampled data is introduced, which is based on recent developments in the field of signal processing theory and uses the so far unexploited general property of the NMR signal, its low rank. Using experimental and simulated data, we demonstrate that the low‐rank reconstruction is a viable alternative to the current state‐of‐the‐art technique compressed sensing. In particular, the low‐rank approach is good in preserving of low‐intensity broad peaks, and thus increases the effective sensitivity in the reconstructed spectra.     

Synthesis of a Stable Selenoaldehyde by Self‐Catalyzed Thermal Dehydration of a Primary‐Alkyl‐Substituted Selenenic Acid

The unprecedented dehydration of a selenenic acid (RCH₂SeOH) to a selenoaldehyde (RCH?Se) has been demonstrated. A primary‐alkyl‐substituted selenenic acid was synthesized for the first time by taking advantage of a bulky cavity‐shaped substituent. Upon heating in solution, the selenenic acid underwent thermal dehydration to produce a stable selenoaldehyde, which was isolated as stable crystals and crystallographically characterized. Investigation of the reaction mechanism revealed that this β dehydration reaction involves two processes, both of which reflect the characteristics of a selenenic acid: 1) dehydrative condensation of two molecules of selenenic acid to generate a selenoseleninate intermediate [RCH₂SeSe(O)CH₂R], an isomer of a selenenic anhydride, and 2) subsequent β elimination of the selenenic acid from this intermediate to form a C?Se double bond, which establishes the self‐catalyzed β dehydration of the selenenic acid.     

Total Synthesis and Structural Revision of (+)‐Uprolide G Acetate

The first, asymmetric total synthesis of the proposed structure of (+)‐uprolide G acetate (UGA) is reported, and the spectral properties of the synthetic compound clearly differed from those reported for natural UGA. On the basis of comprehensive analysis of the NMR data, two possible structures for the natural UGA were proposed and their total synthesis achieved, thus leading to the identification and confirmation of the correct structure and absolute configuration of the natural UGA. This synthesis was enabled by development of a novel synthetic strategy, which revolved around three key cyclization reactions: an Achmatowicz rearrangement, Sharpless asymmetric dihydroxylation/lactonization, and ring‐closing metathesis. These synthetic studies pave the way for further studies on this class of structurally unusual cytotoxic cembranolides.     

Air‐Stable (CAAC)CuCl and (CAAC)CuBH4 Complexes as Catalysts for the Hydrolytic Dehydrogenation of BH3NH3

The first stable copper borohydride complex [(CAAC)CuBH₄] [CAAC=cyclic(alkyl)(amino)carbene] bearing a single monodentate ligand was prepared by addition of NaBH₄ or BH₃NH₃ to the corresponding [(CAAC)CuCl] complex. Both complexes are air‐stable and promote the catalytic hydrolytic dehydrogenation of ammonia borane. The amount of hydrogen released reaches 2.8 H₂/BH₃NH₃ with a turnover frequency of 8400 mol mol_cat^?1 h^?1 at 25 °C. In a fifteen‐cycle experiment, the catalyst was reused without any loss of efficiency.