A Hybrid Ring‐Opening Metathesis Polymerization Catalyst Based on an Engineered Variant of the β‐Barrel Protein FhuA

A β‐barrel protein hybrid catalyst was prepared by covalently anchoring a Grubbs–Hoveyda type olefin metathesis catalyst at a single accessible cysteine amino acid in the barrel interior of a variant of β‐barrel transmembrane protein ferric hydroxamate uptake protein component A (FhuA). Activity of this hybrid catalyst type was demonstrated by ring‐opening metathesis polymerization of a 7‐oxanorbornene derivative in aqueous solution.     

Dehydrogenation of Amine?Borane Me2NH⋅BH3 Catalyzed by a Lanthanum?Hydride Complex

The rare‐earth‐metal? hydride complexes [{(1,7‐Me₂TACD)LnH}₄] (Ln=La 1 a , Y 1 b ; (1,7‐Me₂TACD)H₂=1,7‐dimethyl‐1,4,7,10‐tetraazacyclododecane, 1,7‐Me₂[12]aneN₄) were synthesized by hydrogenolysis of [{(1,7‐Me₂TACD)Ln(η³‐C₃H₅)}₂] with 1 bar H₂. The tetrameric structures were confirmed by ¹H NMR spectroscopy and single‐crystal X‐ray diffraction of compound 1 a . Both complexes catalyze the dehydrogenation of secondary amine? borane Me₂NH ? BH₃ to afford the cyclic dimer (Me₂NBH₂)₂ and (Me₂N)₂BH under mild conditions. Whilst the complete conversion of Me₂NH ? BH₃ was observed within 2 h with lanthanum? hydride 1 a , the yttrium homologue 1 b required 48 h to reach 95 % conversion. Further reactions of compound 1 a with Me₂NH ? BH₃ in various stoichiometric ratios gave a series of intermediate products, [{(1,7‐Me₂TACD)LaH}₄](Me₂NBH₂)₂ ( 2 a ), [(1,7‐Me₂TACDH)La(Me₂NBH₃)₂] ( 3 a ), [(1,7‐Me₂TACD)(Me₂NBH₂)La(Me₂NBH₃)] ( 4 a ), and [(1,7‐Me₂TACD)(Me₂NBH₂)₂La(Me₂NBH₃)] ( 5 a ). Complexes 2 a , 3 a , and 5 a were isolated and characterized by multinuclear NMR spectroscopy and single‐crystal X‐ray diffraction studies. These intermediates revealed the activation and coordination modes of “Me₂NH ? BH₃” fragments that were trapped within the coordination sphere of a rare‐earth‐metal center.     

Electrochemical Fluorination of Dithiocarbonates Using a Triarylamine Mediator

Electrochemical oxidation of O-(4-chlorobenzyl) S-methyl dithiocarbonate using tris(2,4-dibromophenyl)amine as a redox mediator was studied by cyclic voltammetric measurements. The triarylamine mediated anodic fluorodesulfurization of O-(4-chlorobenzyl) and O-(4-bromobenzyl) S-methyl dithiocarbonates provided 4-chloro- and 4-bromobenzyl fluorides, respectively in moderate yields. On the other hand, similar anodic fluorination of O-(2-phenethyl) S-octyl dithiocarbonate and O-(4-bromophenyl) S-methyl dithiocarbonate afforded 2-phenethyl trifluoromethyl ether and difluoro(methylthio)methyl 4-bromophenyl ether, respectively. Mechanistic aspects are also discussed.     

A Cationic Zinc Hydride Cluster Stabilized by an N‐Heterocyclic Carbene: Synthesis,Reactivity, and Hydrosilylation Catalysis

The trinuclear cationic zinc hydride cluster [(IMes)₃Zn₃H₄(THF)](BPh₄)₂ ( 1 ) was obtained either by protonation of the neutral zinc dihydride [(IMes)ZnH₂]₂ with a Brønsted acid or by addition of the putative zinc dication [(IMes)Zn(THF)]²⁺. A triply bridged thiophenolato complex 2 was formed upon oxidation of 1 with PhS? SPh. Protonolysis of 1 by methanol or water gave the corresponding trinuclear dicationic derivatives. At ambient temperature, 1 catalyzed the hydrosilylation of aldehydes, ketones, and nitriles. Carbon dioxide was also hydrosilylated under forcing conditions when using (EtO)₃SiH, giving silylformate as the main product.     

Reduced Arene Complexes of Scandium

Alkali metal naphthalenide or anthracenide reacted with scandium(III) anilides [Sc(X){N(tBu)Xy}₂(thf)] (X=N(tBu)Xy ( 1 ); X=Cl ( 2 ); Xy=C₆H₃-3,5-Me₂) to give scandium complexes [M(thf)_n][Sc{N(tBu)Xy}₂(RA)] (M=Li–K; n=1–6; RA=C₁₀H₈²⁻ ( 3-Naph-K ) and C₁₄H₁₀²⁻ ( 3-Anth-M )) containing a reduced arene ligand. Single-crystal X-ray diffraction revealed the scandium(III) center bonded to the naphthalene dianion in a σ²:π-coordination mode, whereas the anthracene dianion is symmetrically attached to the scandium(III) center in a σ²-fashion. All compounds have been characterized by multinuclear, including ⁴⁵Sc NMR spectroscopy. Quantum chemical calculations of these intensely colored arene complexes confirm scandium to be in the oxidation state +3. The intense absorptions observed in the UV/Vis spectra are due to ligand-to-metal charge transfers. Whereas nitriles underwent C−C coupling reaction with the reduced arene ligand, the reaction with one equivalent of [NEt₃H][BPh₄] led to the mono-protonation of the reduced arene ligand.     

Alkali Metal Triphenyl- and Trihydridosilanides Stabilized by a Macrocyclic Polyamine Ligand

Potassium silanide [KSiH₃]_∞ contains 4.2 wt % of hydrogen and has been intensely studied as hydrogen storage material. The macrocyclic ligand Me₄TACD (1,4,7,10-tetramethyl-1,4,7,10-tetraaminocyclododecane, L ) stabilizes the full range of triphenylsilyl complexes [( L )MSiPh₃]_n (M=Li–Cs), which react with H₂ or PhSiH₃ to form molecular [( L )MSiH₃]_n that can be isolated in soluble form and fully characterized.     

Onsager coefficients of a Brownian Carnot cycle

We study a Brownian Carnot cycle introduced by Schmiedl and Seifert [Europhys. Lett. 81, 20003 (2008)] from a viewpoint of the linear irreversible thermodynamics. By considering the entropy production rate of this cycle, we can determine thermodynamic forces and fluxes of the cycle and calculate the Onsager coefficients for general protocols, that is, arbitrary schedules to change the potential confining the Brownian particle. We show that these Onsager coefficients contain the information of the protocol shape and they satisfy the tight-coupling condition irrespective of whatever protocol shape we choose. These properties may give an explanation why the Curzon-Ahlborn efficiency often appears in the finite-time heat engines.     

Synthesis of water-soluble C60-porphyrin hybrid compounds

Water-soluble C60-porphyrin hybrid molecules were first synthesized toward their pharmaceutical applications.     

Experimental observation of electrostatic ion cyclotron waves modified by minority ions

Electrostatic ion cyclotron waves in the presence of light minority-species ions are experimentally investigated. The observations reveal that already a small fraction (～1%) of the minority concentratios leads to a new cutoff and resonance near the minority-cyclotron-resonance frequency.