Transformation of CO and isocyanates mediated by -borane-substituted cyclic phosphine imides (BCPIs) λ-oxazaphosphetanes.

We herein report reliable evidence that λ-oxazaphosphetane species are a key intermediate in the transformation of CO and isocyanates through their reaction with -borane-substituted cyclic phosphine imides (BCPIs). We have isolated and fully characterized several λ-oxazaphosphetane species prepared formal [2 + 2] cycloaddition reactions between BCPIs and CO or isocyanates. The transformation of these λ-oxazaphosphetanes retro-ring opening reaction afforded an isocyanate and a carbodiimide from the CO- and isocyanate-derived λ-oxazaphosphetanes.

In-silico-assisted derivatization of triarylboranes for the catalytic reductive functionalization of aniline-derived amino acids and peptides with H.

Cheminformatics-based machine learning (ML) has been employed to determine optimal reaction conditions, including catalyst structures, in the field of synthetic chemistry. However, such ML-focused strategies have remained largely unexplored in the context of catalytic molecular transformations using Lewis-acidic main-group elements, probably due to the absence of a candidate library and effective guidelines (parameters) for the prediction of the activity of main-group elements. Here, the construction of a triarylborane library and its application to an ML-assisted approach for the catalytic reductive alkylation of aniline-derived amino acids and C-terminal-protected peptides with aldehydes and H is reported.

Electronic Profiling of -Phosphine Oxide-Substituted Imidazolin-2-ylidenes (PoxIms) and Imidazolidin-2-ylidenes (SPoxIms).

A detailed electronic study of the -phosphine oxide functionalized imidazolin-2-ylidenes (PoxIms) and imidazolidin-2-ylidenes (SPoxIms) has been performed experimentally using IR, C, and Se NMR spectroscopies. While the net donor/acceptor properties of the (S)PoxIms could not be differentiated via IR spectroscopy (TEP), NMR spectroscopic methods (HEP, Se) reveal that the (S)PoxIms are slightly weaker σ-donors but stronger π-acceptors compared to common NHCs. Moreover, backbone and substituent-effects could also be resolved by the latter, allowing for a ranking of their electronic properties.

-Heterocyclic Carbenes with Polyfluorinated Groups at the 4- and 5-Positions from [3 + 2] Cycloadditions between Formamidinates and -1,2-Difluoroalkene Derivatives.

We herein report the formation of fluorinated -heterocyclic carbenes (NHCs) that bear fluorine atoms at the 4- and 5-positions of the imidazol-2-ylidene ring. Treatment of sodium ,'-bis(aryl)formamidinates with tetrafluoroethylene followed by the addition of LiBF induced a [3 + 2] cycloaddition to afford 4,5-difluorinated imidazolium salts, which served as the precursors for 4,5-difluorinated NHCs. A key feature of this procedure is its applicability to other perfluorinated compounds, which enabled us to incorporate polyfluorinated functional groups at 4- and 5-positions on the imidazol-2-ylidene skeleton.

Difluoromethylene insertion into fluoroalkyl copper complexes.

Herein, we report the insertion of a difluoromethylene into 1,1,2,2-tetrafluoro-2-arylethyl copper complexes to synthesize extended perfluoroalkyl-bridged compounds that have various functional groups on each edge (ArCFCF(CF)R, R = arenes, halogens, alkyl, alkenyl, and benzyloxycarbonyl). Further, the one-pot syntheses of perfluoroalkyl-bridged compounds from aryl boronic acid esters were carried out.

Reversible Modulation of the Electronic and Spatial Environment around Ni(0) Centers Bearing Multifunctional Carbene Ligands with Triarylaluminum.

Designing and modulating the electronic and spatial environments surrounding metal centers is a crucial issue in a wide range of chemistry fields that use organometallic compounds. Herein, we demonstrate a Lewis-acid-mediated reversible expansion, contraction, and transformation of the spatial environment surrounding nickel(0) centers that bear -phosphine oxide-substituted -heterocyclic carbenes (henceforth referred to as (S)PoxIms). Reaction between tetrahedral (-κ-,-(S)PoxIm)Ni(CO) and Al(CF) smoothly afforded heterobimetallic Ni/Al species such as trigonal-planar {κ--Ni(CO)}(μ--(S)PoxIm){κ--Al(CF)} via a complexation-induced rotation of the -phosphine oxide moieties, while the addition of 4-dimethylaminopyridine resulted in the quantitative regeneration of the former Ni complexes.

Regioselective C-F Bond Transformations of Silyl Difluoroenolates.

Herein, we report the development of a nickel-catalyzed cross-coupling reaction of silyl difluoroenolates with aryl zinc reagents via C-F bond cleavage. Treatment of a stoichiometric amount of Ni(0)/-heterocyclic carbene (NHC) with silyl difluoroenolates in the presence of a lithium salt resulted in C-F bond cleavage to selectively afford the corresponding ()-alkenyl Ni complexes. On the basis of the observations, we developed a catalytic cross-coupling reaction that selectively delivers a single geometric isomer of a fluoroenolate.

Nickel-Catalyzed Exhaustive Hydrodefluorination of Perfluoroalkyl Arenes.

Perfluoroalkyl compounds are persistent environmental pollutants due to their strong C(sp)-F bonds. Hydrodefluorination has emerged as a potential alternative disposal method for perfluoroalkyl compounds. Although the transformation of trifluoromethyl arenes into the corresponding methyl arenes has been studied by several research groups, hydrodefluorination reactions of longer perfluoroalkyl chains remain rare.

Main group catalysis for H purification based on liquid organic hydrogen carriers.

Molecular hydrogen (H) is one of the most important energy carriers. In the midterm future, a huge amount of H will be produced from a variety of hydrocarbon sources through conversion and removal of contaminants such as CO and CO. However, bypassing these purification processes is desirable, given their energy consumption and environmental impact, which ultimately increases the cost of H.

Room-Temperature Reversible Chemisorption of Carbon Monoxide on Nickel(0) Complexes.

Chemisorption on organometallic-based adsorbents is crucial for the controlled separation and long-term storage of gaseous molecules. The formation of covalent bonds between the metal centers in the adsorbents and the targeted gases affects the desorption efficiency, especially when the oxidation state of the metal is low. Herein, we report a pressure-responsive nickel(0)-based system that is able to reversibly chemisorb carbon monoxide (CO) at room temperature.

Overlooked Factors Required for Electrolyte Solvents in Li-O Batteries: Capabilities of Quenching O and Forming Highly-Decomposable Li O.

Although sufficient tolerance against attack by superoxide radicals (O ) has been mainly recognized as an important property for Li-O battery (LOB) electrolytes, recent evidence has revealed that other critical factors also govern the cyclability, prompting a reconsideration of the basic design guidelines of LOB electrolytes. Here, we found that LOBs equipped with a N,N-dimethylacetamide (DMA)-based electrolyte exhibited better cyclability compared with other standard LOB electrolytes. This superior cyclability is attributable to the capabilities of quenching O and forming highly decomposable Li O .

A boron-transfer mechanism mediating the thermally induced revival of frustrated carbene-borane pairs from their shelf-stable adducts.

Chemists have designed strategies that trigger the conformational isomerization of molecules in response to external stimuli, which can be further applied to regulate the complexation between Lewis acids and bases. We have recently developed a system in which frustrated carbene-borane pairs are revived from shelf-stable but external-stimuli-responsive carbene-borane adducts comprised of N-phosphine-oxide-substituted imidazolylidenes (PoxIms) and triarylboranes. Herein, we report the detailed mechanism on this revival process.

Synthesis of Fluoroalkyl Sulfides via Additive-Free Hydrothiolation and Sequential Functionalization Reactions.

A modular synthetic method, involving a hydrothiolation, silylation, and fluoroalkylation, for the construction of highly functionalized fluoroalkyl sulfides has been developed. The use of aprotic polar solvents enables the additive-free chemoselective hydrothiolation of tetrafluoroethylene, trifluorochloroethylene, and hexafluoropropene with various thiols. The stepwise functionalization reactions convert the hydrothiolated intermediates into the tetrafluoroethyl sulfides in high efficiency.

Cleavage of C(sp)-F Bonds in Trifluoromethylarenes Using a Bis(NHC)nickel(0) Complex.

The first example of the oxidative addition of a C(sp)-F bond in trifluoromethylarenes to a nickel(0) complex is described. A nickel(0) complex that bears two -heterocyclic carbene (NHC) ligands of low steric demand is able to cleave C(sp)-F bonds of trifluoromethylarenes to afford the corresponding -difluorobenzyl nickel(II) fluoride complexes. Isolation and characterization studies suggested that the cleavage of the C(sp)-F bond proceeds via an η-arene nickel(0) complex.

Direct Transformation of Tetrafluoroethylene to Trifluorovinylzinc via sp C-F Bond Activation.

Trifluorovinylzinc is a common synthetic intermediate for trifluorovinyl derivatives, including α,β,β-trifluorostyrenes and hexafluorobutadiene. Here, we report a novel synthetic approach for the formation of trifluorovinylzinc chloride via a C-F bond activation of tetrafluoroethylene (TFE), which is an industrially cost-effective bulk feedstock with a negligible GWP. The present system provides a practical synthetic route to various trifluorovinyl derivatives with very low energy consumption.

Halo Structure of the Neutron-Dripline Nucleus ^{19}B.

The heaviest bound isotope of boron ^{19}B has been investigated using exclusive measurements of its Coulomb dissociation, into ^{17}B and two neutrons, in collisions with Pb at 220  MeV/nucleon. Enhanced electric dipole (E1) strength is observed just above the two-neutron decay threshold with an integrated E1 strength of B(E1)=1.64±0.

Axial Chirality around N-P Bonds Induced by Complexation between E(CF) (E = B, Al) and an -Phosphine Oxide-Substituted Imidazolinylidene: A Key Intermediate in the Catalytic Phosphinoylation of CO.

Complexation-induced axial chirality around an N-P bond occurs upon the predominant coordination of the -phosphinoyl group in the -phosphine oxide-substituted imidazolinylidene (SPoxIm) to B(CF). () and () atropisomers of (-SPoxIm)B(CF) were observed independently in the single-crystal lattice and the optimized gas-phase structure. Experimental and theoretical studies confirmed that this axial chirality arises from the restricted rotation around the N-P bond, caused by the steric repulsion between the C5-H atoms of the imidazolinylidene ring and the CF rings on the B(CF) unit.

Enantioselective Synthesis of Polycyclic γ-Lactams with Multiple Chiral Carbon Centers via Ni(0)-Catalyzed Asymmetric Carbonylative Cycloadditions without Stirring.

γ-Lactam derivatives with multiple contiguous stereogenic carbon centers are ubiquitous in physiologically active compounds. The development of straightforward and reliable synthetic routes to such chiral structural motifs in a stereocontrolled manner should thus be of importance. Herein, we report a strategy to construct polycyclic γ-lactam derivatives that contain more than two contiguous stereogenic centers in an enantioselective as well as atom-economic manner.

Nickel-catalyzed decarbonylation of -acylated N-heteroarenes.

Nickel-catalyzed decarbonylation of -acylated N-heteroarenes is developed. This method can be used to produce a variety of -aryl heteroarenes, including pyrroles, indoles, carbazoles and phenoxazines, using benzoic acid derivatives as arylating reagents. Arylnickelamide intermediates that are relevant to the catalytic reaction were characterized by X-ray crystallography.

First Observation of ^{20}B and ^{21}B.

The most neutron-rich boron isotopes ^{20}B and ^{21}B have been observed for the first time following proton removal from ^{22}N and ^{22}C at energies around 230  MeV/nucleon. Both nuclei were found to exist as resonances which were detected through their decay into ^{19}B and one or two neutrons. Two-proton removal from ^{22}N populated a prominent resonancelike structure in ^{20}B at around 2.

Ni(0)-Catalyzed Three-Component Coupling Reaction of Tetrafluoroethylene and N-Sulfonyl-Substituted Imines with Silanes via Aza-Nickelacycles.

A nickel-catalyzed three-component coupling reaction of tetrafluoroethylene (TFE) and N-sulfonyl-substituted imines with silanes that furnishes a variety of fluorine-containing amines is disclosed. Stoichiometric experiments revealed that the aza-nickelacycles generated upon oxidative cyclization of TFE and N-sulfonyl-substituted imines on Ni(0) were identified as the key intermediates in this catalytic reaction. A single-crystal X-ray diffraction analysis of such an aza-nickelacycle revealed that the O atom of the N-sulfonyl group stabilizes the key intermediate via coordination to the nickel center.

Selective Catalytic Formation of Cross-Tetramers from Tetrafluoroethylene, Ethylene, Alkynes, and Aldehydes via Nickelacycles as Key Reaction Intermediates.

In the presence of a catalytic amount of Ni(cod) (cod = 1,5-cyclooctadiene) and PCy (Cy = cyclohexyl), the cross-tetramerization of tetrafluoroethylene (TFE), ethylene, alkynes, and aldehydes leads to a variety of fluorine-containing enone derivatives. This reaction is the first example of a highly selective cross-tetramerization between four different unsaturated compounds. Stoichiometric reactions revealed that the present reaction involves partially fluorinated five- and seven-membered nickelacycles as key reaction intermediates.

Strain-Induced Double Carbon-Carbon Bond Activations of Cycloparaphenylenes by a Platinum Complex: Application to the Synthesis of Cyclic Diketones.

The carbon-carbon (C-C) bond activation of [n]cycloparaphenylenes ([n]CPPs) by a transition-metal complex is herein reported. The Pt complex Pt(PPh ) regioselectively cleaves two C-C σ bonds of [5] CPP and [6]CPP to give cyclic dinuclear platinum complexes in high yields. Theoretical calculations reveal that the relief of ring strain drives the reaction.