New Experimental Insight into the Nature of Metal−Metal Bonds in Digallium Compounds: J Coupling between Quadrupolar Nuclei

Multiple bonding between atoms is of ongoing fundamental and applied interest. Here, we report a multinuclear (¹H, ¹³C, and ⁷¹Ga) solid‐state magnetic resonance spectroscopic study of digallium compounds which have been proposed, albeit somewhat controversially, to contain single, double, and triple Ga?Ga bonds. Of particular relevance to the nature of these bonds, we have carried out two‐dimensional ⁷¹Ga J/D‐resolved NMR experiments which provide a direct measurement of J(⁷¹Ga,⁷¹Ga) spin–spin coupling constants across the gallium?gallium bonds. When placed in the context of clear‐cut experimental data for analogous singly, doubly, and triply bonded carbon spin pairs or boron spin pairs, the ⁷¹Ga NMR data clearly support the notion of a different bonding paradigm in the gallium systems. Our findings are consistent with an increasing role across the purported gallane–gallene–gallyne series for classical and/or slipped π‐type bonding orbitals.     

Effect of Headgroups on Small‐Ion Permeability across Archaea‐Inspired Tetraether Lipid Membranes

This paper examines the effects of four different polar headgroups on small‐ion membrane permeability from liposomes comprised of Archaea‐inspired glycerolmonoalkyl glycerol tetraether (GMGT) lipids. We found that the membrane‐leakage rate across GMGT lipid membranes varied by a factor of ≤1.6 as a function of headgroup structure. However, the leakage rates of small ions across membranes comprised of commercial bilayer‐forming 1‐palmitoyl‐2‐oleoyl‐sn‐glycerol (PO) lipids varied by as much as 32‐fold within the same series of headgroups. These results demonstrate that membrane leakage from GMGT lipids is less influenced by headgroup structure, making it possible to tailor the structure of the polar headgroups on GMGT lipids while retaining predictable leakage properties of membranes comprised of these tethered lipids.     

Enantioconvergent Biocatalytic Redox Isomerization

Alcohol dehydrogenases can act as powerful catalysts in the preparation of optically pure γ‐hydroxy‐δ‐lactones by means of an enantioconvergent dynamic redox isomerization of readily available Achmatowicz‐type pyranones. Imitating the traditionally metal‐mediated “borrowing hydrogen” approach to shuffle hydrides across molecular architectures and interconvert functional groups, this chemoinspired and purely biocatalytic interpretation effectively expands the enzymatic toolbox and provides new opportunities in the assembly of multienzyme cascades and tailor‐made cellular factories.     

Homodiselenacalix[4]arenes: Molecules with Unique Channelled Crystal Structures

A synthetic route towards homodiselenacalix[4]arene macrocycles is presented, based on the dynamic covalent chemistry of diselenides. The calixarene inner rim is decorated with either alkoxy or tert‐butyl ester groups. Single‐crystal X‐ray analysis of two THF solvates with methoxy and ethoxy substituents reveals the high similarity of their molecular structures and alterations on the supramolecular level. In both crystal structures, solvent channels are present and differ in both shape and capacity. Furthermore, the methoxy‐substituted macrocycle undergoes a single‐crystal‐to‐single‐crystal transformation during which the molecular structure changes its conformation from 1,3‐alternate (loaded with THF/water) to 1,2‐alternate (apohost form). Molecular modelling techniques were applied to explore the conformational and energetic behaviour of the macrocycles.     

Phosphoryl‐Rich Flame‐Retardant Ions (FRIONs): Towards Safer Lithium‐Ion Batteries

The functionalized catecholate, tetraethyl (2,3‐dihydroxy‐1,4‐phenylene)bis(phosphonate) (H₂‐DPC), has been used to prepare a series of lithium salts Li[B(DPC)(oxalato)], Li[B(DPC)₂], Li[B(DPC)F₂], and Li[P(DPC)₃]. The phosphoryl‐rich character of these anions was designed to impart flame‐retardant properties for their use as potential flame‐retardant ions (FRIONs), additives, or replacements for other lithium salts for safer lithium‐ion batteries. The new materials were fully characterized, and the single‐crystal structures of Li[B(DPC)(oxalato)] and Li[P(DPC)₃] have been determined. Thermogravimetric analysis of the four lithium salts show that they are thermally stable up to around 200 °C. Pyrolysis combustion flow calorimetry reveals that these salts produce high char yields upon combustion.     

Color Bricks: Building Highly Organized and Strongly Absorbing Multicomponent Arrays of Terpyridyl Perylenes on Metal Oxide Surfaces

Terpyridine‐substituted perylenes containing cyclic anhydrides in the peri position were synthesized. The anhydride group served as an anchor for assembly of the terpyridyl‐crowned chromophores as monomolecular layers on metal oxide surfaces. Further coordination with Zn²⁺ ions allowed for layer‐by‐layer formation of supramolecular assemblies of perylene imides on the solid substrates. With properly selected anchor and linker molecules it was possible to build high quality structures of greater than ten successive layers by a simple and straightforward procedure. The prepared films were stable and had a broad spectral coverage and high absorbance. To demonstrate their potential use, the synthesized dyes were employed in solid‐state dye‐sensitized solar cells, and electron injection from the perylene antennas to titanium dioxide was observed.     

Enhancing the Value of Free Metals in the Synthesis of Lanthanoid Formamidinates: Is a Co‐oxidant Needed?

Treatment of N,N′‐bis(aryl)formamidines (ArFormH), N,N′‐bis(2,6‐difluorophenyl)formamidine (DFFormH) or N,N′‐bis(2,6‐diisopropylphenyl)formamidine (DippFormH), with europium metal in CH₃CN is an efficient synthesis of the divalent complexes: [{Eu(DFForm)₂(CH₃CN)₂}₂] ( Eu1 ) or [Eu(DippForm)₂(CH₃CN)₄] ( Eu2 ). The synthetic method was extended to ytterbium, but the metal required activation by addition of Hg⁰. With DFFormH in CH₃CN, [{Yb(DFForm)₂(CH₃CN)}₂] ( Yb1 ) was obtained in good yield, and [Yb(DFForm)₂(thf)₃] ( Yb3 ) was obtained from a synthesis in CH₃CN/THF. Thus, this synthetic method completely circumvents the use of either salt metathesis, or redox transmetallation/protolysis (RTP) protocols to prepare divalent rare‐earth formamidinates. Heating Yb1 in PhMe/C₆D₆ resulted in decomposition to trivalent products, including one from a CH₃CN activation process. For a synthetic comparison, divalent ytterbium DFForm and DippForm complexes were synthesised by RTP reactions between Yb⁰, Hg(R)₂ (R=Ph, C₆F₅), and ArFormH in THF, leading to the isolation of either [Yb(DFForm)₂(thf)₃] ( Yb3 ), or the first five coordinate rare‐earth formamidinate complex [Yb(DippForm)₂(thf)] ( Yb4 b ), and, from adjustment of the stoichiometry, trivalent [Yb(DFForm)₃(thf)] ( Yb6 ). Oxidation of Yb3 with benzophenone (bp), or halogenating agents (TiCl₄(thf)₂, Ph₃CCl, C₂Cl₆) gave [Yb(DFForm)₃(bp)] or [Yb(DFForm)₂Cl(thf)₂], respectively. Furthermore, the structural chemistry of divalent ArForm complexes has been substantially broadened. Not only have the highest and lowest coordination numbers for divalent rare‐earth ArForm complexes been achieved in Eu2 and Yb4 b , respectively, but also dimeric Eu1 and Yb1 have highly unusual ArForm bridging coordination modes, either perpendicular μ‐1κ(N:N′):2κ(N:N′) in Eu1 , or the twisted μ‐1κ(N:N′):2κ(N′:F′) DFForm coordination in Yb1 , both unprecedented in divalent rare‐earth ArForm chemistry and in the wider divalent rare‐earth amidinate field.     

N‐Heterocyclic Silylenes in Boron Chemistry: Facile Formation of Silylboranes and Silaborinines

Reaction of a N‐heterocyclic silylene (NHSi) with PhBX₂ (X=Cl, Br) readily afforded six‐membered silaborinines through an insertion/ring expansion sequence. Increasing the sterics of the borane from phenyl to duryl enabled the selective generation and isolation of the highly colored silylborane intermediates. Theoretical studies on the mechanism and energetics of the silaborinine formation were fully consistent with the experimental observations.     

Bimetallic Gold(I) Complexes with Ethynyl‐Helicene and Bis‐Phosphole Ligands: Understanding the Role of Aurophilic Interactions in their Chiroptical Properties

Monometallic gold(I)‐alkynyl‐helicene complexes ( 1 a , b ) and bimetallic gold(I)‐alkynyl‐helicene architectures featuring the presence ( 2 a , b ) or absence ( 3 a , b ) of aurophilic intramolecular interactions were prepared by using different types of phosphole ligands (mono‐phosphole L1 or bis‐phospholes L2 , 3 ). The influence of the Au^I d¹⁰ metal center(s) on the electronic, photophysical, and chiroptical properties of these unprecedented phosphole‐gold(I)‐alkynyl‐helicene complexes was examined. Experimental and theoretical results highlight the importance of ligand‐to‐ligand‐type charge transfers and the strong effect of the presence or absence of Au^I–Au^I interactions in 2 a , b .