Optically active poly(diphenylacetylene)s showing solvent-dependent helix inversion accompanied by modulation of helix inversion barriers.

Symmetrically substituted poly(diphenylacetylene)s bearing optically active 2-octyloxycarbonyl groups at the para-positions of the pendant phenyl rings not only show a unique solvent-dependent helix inversion to afford diastereomeric right- and left-handed helical polymers but also significant unprecedented solvent-dependent changes in the helix inversion barrier of the polymer backbone resulting in switching between static or dynamic behavior of the helical polymers at approximately room temperature depending on the solvents used.

Synthesis of optically active star polymers consisting of helical poly(phenylacetylene) chains by the living polymerization of phenylacetylenes and their chiroptical properties.

Star polymers consisting of three helical poly(phenylacetylene) chains with a precisely controlled molecular weight (molar mass dispersity < 1.03) were successfully synthesized by the living polymerization of phenylacetylene derivatives with a Rh-based multicomponent catalyst system comprising trifunctional initiators, which have three phenylboronates centered on a benzene ring, the Rh complex [Rh(nbd)Cl]2, diphenylacetylene, triphenylphosphine, and a base. The analysis of chiroptical properties of the optically active star polymers obtained by the living polymerization of optically active phenylacetylene derivatives revealed that the star polymers exhibited chiral amplification properties owing to their unique topology compared with the corresponding linear polymers.

Insight into stability of dithiocarbamate-modified adsorbents: Oxidation of dithiocarbamate.

We previously reported that monoalkyl dithiocarbamate-modified cellulose (DMC) exhibited excellent adsorption performance for arsenite (AsIII), cadmium (CdII), lead (PbII), gold (AuIII), silver (AgI), platinum (PtIV), and palladium (PdII). However, its adsorption capability for AsIII decreased by 96.4% after two weeks of storage at 40 °C under an air atmosphere. This decrease in adsorption ability could occur for other metals that dithiocarbamates can extract. In this study, we investigated the adsorption performance of DMC for various metals before and after storage and proposed a possible mechanism for this decrease. We found significant decreases in the adsorption abilities of PbII (11.4%), AgI (39.5%), PtIV (65.5%), and PdII (69.6%), whereas AuIII and CdII adsorption was largely retained, with decreases of 1.1% and 4.0%, respectively. FTIR analysis of the stored DMC revealed the formation of S-S bonds and the retention of dithiocarbamate peaks, indicating the formation of dithiocarbamate dimers (thiuram disulfides). To further support thiuram disulfide formation, dialkyl thiuram disulfides were tested for the adsorption of the seven employed metals. The metal adsorption behavior of dialkyl thiuram disulfides was almost identical to that of the stored adsorbent, ensuring thiuram disulfide formation. In conclusion, the loss of adsorption capability can be mainly attributable to the formation of thiuram disulfide.

Revisiting the Synthesis of Cellulose Acrylate and Its Modification via Michael Addition Reactions.

The synthesis of cellulose acrylate from cellulose with acryloyl chloride has been problematic due to unexpected gelation of the reaction mixture, but we discovered that the use of bulky amines was crucial for the reproducibility of the synthesis of cellulose acrylate. The solubility of the obtained cellulose acrylate depended on the reaction conditions due to the possible cross-linking oxa-Michael reaction between a remaining hydroxy group and the introduced acrylate group. The synthesized cellulose acrylate worked as a useful precursor of chemically modified cellulose materials because it reacted with various functionalized nucleophiles such as secondary amines and thiols as a Michael donor. This method was applied to the synthesis of N-methyl-d-glucamine-modified cellulose that works as an adsorbent for the removal of B(OH)3 in water.

Facile Synthesis of Linear and Cyclic Poly(diphenylacetylene)s by Molybdenum and Tungsten Catalysis.

Improved methods for the synthesis of linear and cyclic poly(diphenylacetylene)s by polymerization of the corresponding diphenylacetylenes using MoCl5 - and WCl4 -based catalytic systems have been developed. MoCl5 induces migratory insertion polymerization of diphenylacetylenes in the presence of arylation reagents such as Ph4 Sn and ArSnn Bu3 to produce cis-stereoregular linear poly(diphenylacetyelene)s with high molecular weights (number-average molar mass (Mn )=30,000-3,200,000) in good yields (up to 98 %). On the other hand, WCl4 induces ring expansion polymerization of diphenylacetylenes in the presence of Ph4 Sn or reducing reagents to produce cis-stereoregular cyclic poly(diphenylacetylene)s with high molecular weights (Mn =20,000-250,000) in moderate to good yields (up to 90 %). Both catalytic systems are applicable to the polymerization of various diphenylacetylenes having polar functional groups such as esters that are not efficiently polymerized by conventional methods using WCl6 -Ph4 Sn and TaCl5 -n Bu4 Sn systems.

Ultra-fast One-Handed Helix Induction and Its Static Helicity Memory in a Poly(biphenylylacetylene) with a Catalytic Amount of Chiral Ammonium Salts.

We report an ultra-fast helix induction and subsequent static helicity memory in poly(biphenylylacetylene) (PBPA-A) assisted by a catalytic amount of nonracemic ammonium salts comprised of non-coordinating tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (BArF- ) as a counter anion. The remarkable acceleration of the helix-induction rate in PBPA-A accompanied by the significant amplification of the asymmetry relies on the two methoxymethoxy groups of the biphenyl pendants, which can gain access to enfold the chiral ammoniums in a crown-ether manner in specific aromatic solvents, leading to ultra-fast helicity induction, which is completed within 30 s. In aromatic solvents, helicity memory is lost rapidly, but is quite stable in long-chain hydrocarbons. The best use of specific solvents for helicity induction and static helicity memory, respectively, provides a highly sensitive chirality sensing system toward a small amount of chiral amines and amino acids when complexed with BArF- .

Cross-linked dithiocarbamate-modified cellulose with enhanced thermal stability and dispersibility as a sorbent for arsenite removal.

Numerous reports have described dithiocarbamate (DTC)-modified cellulose sorbents that can selectively separate metal ions from water. We have previously synthesized a novel sorbent modified with DTC containing N-heterocycles in the backbone for the selective removal of hazardous metal ions. The sorbent was found to partially dissolve and aggregate in solution, reducing its sorption capacity. In this study, to prepare the sorbent for use as a soli-phase extraction material for the removal of arsenite (AsIII) ions, we attempted to decrease the solubility of the sorbent. The sorbent was cross-linked with epoxy or complexed with iron, and the quantities of the modifiers were varied between 3.0 and 10 mol%. As a result, the iron-complexed sorbents were still partially soluble, and cross-linkage with 6.0 mol% of epoxy made the sorbent almost insoluble and dispersed in solution. This sorbent also exhibited the highest AsIII sorption performance among the sorbents synthesized in this study. Although DTC-modified polymers are reported to lose their sorption capability after storage at 40 °C, the sorbent was found to be thermally stable. The optimum contact time and pH for AsIII removal were 20 min and 3.0, respectively. The maximum sorption capacity of the epoxy-cross-linked sorbent, calculated from the Langmuir isotherm equation, was 600 µmol g-1 (45 mg g-1) at 25 °C. Additionally, the sorbent was highly selective toward AsIII compared with previously reported sorbents and capable of removing approximately 97% of AsIII from environmental water. In conclusion, cross-linking enhances the stability of the sorbents in solutions, which facilitates the removal of AsIII from environmental water.

Well-Controlled Living Polymerization of Phenylacetylenes in Water: Synthesis of Water-Soluble Stereoregular Telechelic Poly(phenylacetylene)s.

Well-controlled living polymerization of water-soluble phenylacetylene derivatives in water was achieved for the first time using a multicomponent catalytic system consisting of [Rh(nbd)Cl]2 , an aryl boronic acid, diphenylacetylene having carboxy groups, a tetraalkylammonium hydroxide, and a water-soluble triphenylphosphine. This catalytic system enables a direct synthesis of various water-soluble cis-stereoregular poly(phenylacetylene)s having a narrow molecular weight distribution, the molecular weight of which can be controlled by the initial feed ratio of the monomer to the catalyst. Moreover, the syntheses of water-soluble telechelic poly(phenylacetylene)s having various functional groups at both chain ends as well as a water-soluble block copolymer were achieved.

Well-Controlled Living Polymerization of N-Propargylamides and Their Derivatives by Rhodium Catalysis.

A substantially improved method for living polymerization of N-propargylamides and their derivatives has been developed. Rhodium(I) complexes bearing an aryl-substituted 1,3,5-hexatriene chain can work as excellent initiators of the polymerization of such non-conjugated terminal alkynes to give the corresponding cis-stereoregular polymers having a narrow molecular weight distribution. The typical living nature has been confirmed by investigating the effects of initial feed ratios of the monomer to the initiator on the molecular weight of the resulting polymers as well as multistage polymerization. Moreover, we demonstrated that the present method enables functionalization of both polymer chain ends and synthesis of novel block copolymers consisting of poly(N-propargylamide) and poly(phenylacetylene) blocks with a narrow molecular weight distribution.

Substituent Effects of Tetracoordinate Boron in Organic Synthesis.

The present review focuses on recent examples of tetracoordinate boryl groups greatly influencing reactions in organic synthesis. Electron-rich tetracoordinate boryl groups stabilize or activate reactive intermediates such as cations, radicals and π-conjugation systems, and interaction of the intermediates with carbon-boron or heteroatom-boron bonds is the origin of such substituent effects. Unique substituent effects of tetracoordinate boryl groups often promote desired reactions and affect results of reactions such as yield and selectivity of products.

Speciation analysis of inorganic selenium in wastewater using a highly selective cellulose-based adsorbent via liquid electrode plasma optical emission spectrometry.

Speciation of selenium (Se) is typically carried out using a sophisticated technique such as ICP-MS after preconcentration using an adsorbent; however, the separation and preconcentration of inorganic Se has not been realized in the solutions containing high concentrations of SO42-. A dithiocarbamate-modified cellulose (DMC) was used in this study for the selective extraction and preconcentration of inorganic Se in wastewater, with a portable liquid electrode plasma-optical emission spectrometry (LEP-OES) being employed for quantification. DMC was found to selectively and quantitatively adsorb selenite (SeIV) over a wide range of pH (1.0-8.0); however, less than 3.0% of selenate (SeVI) was adsorbed in a pH range of 3.0-11. Quantitative extraction of SeIV was achieved even in the presence of 3.5 mol L-1 SO42-. The maximum sample volume from which 10 mg of DMC could quantitatively extract SeIV was found to be 500 mL. KOH (0.60 mL, 1.5 mol L-1) was found to quantitatively desorb SeIV retained on the adsorbent and yielded an enrichment factor of 833. The recovery of Se species from synthetic flue-gas desulfurization wastewater containing SeIV and SeVI at concentrations of 5.0 µmol L-1 was 96.2 ± 1.8% and 105.8 ± 1.8%, respectively.

Understanding the Polymerization of Diphenylacetylenes with Tantalum(V) Chloride and Cocatalysts: Production of Cyclic Poly(diphenylacetylene)s by Low-Valent Tantalum Species Generated in Situ.

A systematic investigation of the polymerization of representative diphenylacetylenes with TaCl5 and cocatalysts suggested that low-valent Ta species, which are formed by in situ reduction of TaCl5 by the cocatalysts, are involved in the polymerization and that the polymerization reaction proceeds by an insertion ring expansion mechanism via the formation of tantalacyclopentadiene intermediates, rather than the previously considered metathesis mechanism. This polymerization mechanism indicates the production of unprecedented cis-stereoregular cyclic poly(diphenylacetylene)s. Indeed, the possibilities of a cyclic structure and high cis-stereoregularity of the resulting polymers were reasonably supported by the results of their detailed atomic force microscopy (AFM) and NMR analyses, respectively.

Rhodium(I) Complexes Bearing an Aryl-Substituted 1,3,5-Hexatriene Chain: Catalysts for Living Polymerization of Phenylacetylene and Potential Helical Chirality of 1,3,5-Hexatrienes.

Unique bench-stable rhodium(I) complexes bearing an aryl-substituted 1,3,5-hexatriene chain have been synthesized by reactions of (bicyclo[2.2.1]hepta-2,5-diene)rhodium(I) chloride dimer ([Rh(nbd)Cl]2 ) with aryl boronic acids and diphenylacetylenes in the presence of a 50 % aqueous solution of KOH. X-ray crystallographic analysis of the isolated complexes indicated a square-planar structure stabilized by a strong interaction with one of the aryl groups on the 1,3,5-hexatriene chain, which has a helical structure. The helical chirality of the isolated rhodium complexes was confirmed to be sufficiently stable to be resolved into enantiomers by HPLC on a chiral stationary phase at room temperature. It was confirmed that the isolated rhodium complexes functioned as initiators for living polymerization of phenylacetylene to give cis-stereoregular poly(phenylacetylene) with a well-controlled molecular weight.

Correction: Advances in chemistry of N-heterocyclic carbene boryl radicals.

Correction for 'Advances in chemistry of N-heterocyclic carbene boryl radicals' by Tsuyoshi Taniguchi, Chem. Soc. Rev., 2021, DOI: .

Advances in chemistry of N-heterocyclic carbene boryl radicals.

Boron-centred radicals (boryl radicals) are potential and attractive species in main group chemistry and synthetic chemistry. Recently, the development of boron compounds ligated by N-heterocyclic carbenes (NHCs) has sparked off advavnces in boryl radical chemistry because NHCs can highly stabilise boryl radicals by electronic and steric factors. This review highlights recent synthesis and reactions of such NHC-boryl radicals. From the standpoint of main group chemistry, examples of isolation or detection of unique NHC-boryl radicals are presented. From the standpoint of synthetic chemistry, on the other hand, the development of reactions of user-friendly NHC-boryl radicals, which has contributed to radical chemistry, organoboron chemistry and polymer science, is comprehensively described.

Comparative evaluation of dithiocarbamate-modified cellulose and commercial resins for recovery of precious metals from aqueous matrices.

Economic and ecological issues motivate the recovery of precious metals (PMs: Ag, Au, Pd, and Pt) from secondary sources. From the viewpoint of eco-friendliness and cost-effectiveness, biomass-based resins are superior to synthetic polymer-based resins for PM recovery. Herein, a detailed comparative study of bio-sorbent dithiocarbamate-modified cellulose (DMC) and synthetic polymer-based commercial resins (Q-10R, Lewatit MonoPlus TP 214, Diaion WA30, and Dowex 1X8) for PM recovery from waste resources was conducted. The performances and applicability of the selected resins were investigated in terms of sorption selectivity, effect of competing anions, sorption isotherms, impact of temperature, and PM extractability from industrial wastes. Although the sorption selectivity toward PMs in acidic solutions by DMC and other resins was comparable, the sorption efficiency of commercial resins was adversely affected by competing anions. The sorption of PMs fitted the Langmuir model for all the studied resins, except Q-10R, which followed the Freundlich model. The maximum sorption capacity of DMC was 2.2-42 times higher than those of the resins. Furthermore, the PM extraction performance of DMC from industrial wastes exceeded that of the commercial resins, with a sorption efficiency ≥99% and a DMC dosage of 5-40 times lower.

Helical springs as a color indicator for determining chirality and enantiomeric excess.

Chirality plays a key role in the physiological system, because molecular functionalities may drastically alter due to a change in chirality. We report herein a unique color indicator with a static helicity memory, which exhibits visible color changes in response to the chirality of chiral amines. A difference of less than 2% in the enantiomeric excess (ee) values causes a change in the absorption that is visible to the naked eyes. This was further quantified by digital photography by converting to RGB values. This system relies on the change in the tunable helical pitch of the π-conjugated polymer backbone in specific solvents and allows rapid on-site monitoring of chirality of nonracemic amines, including drugs, and the simultaneous quantitative determination of their ee values.

Synthesis of Stereoregular Telechelic Poly(phenylacetylene)s: Facile Terminal Chain-End Functionalization of Poly(phenylacetylene)s by Terminative Coupling with Acrylates and Acrylamides in Rhodium-Catalyzed Living Polymerization of Phenylacetylenes.

Various α,ß-unsaturated carbonyl compounds, such as acrylates and acrylamides, were quantitatively introduced to the terminal chain end of poly(phenylacetylene)s by C-C bond formation with terminal organorhodium(I) species formed in the living polymerization of phenylacetylenes with a rhodium-based multicomponent catalytic system that we have recently developed, when these carbonyl compounds were used as terminating reagents. This enables the facile and versatile synthesis of stereoregular telechelic poly(phenylacetylene)s with various functional groups at both the initial and terminal chain ends because the components of aryl boronic acid derivatives used as initiators in our multicomponent catalytic system are quantitatively introduced to the initiating end of the resulting polymer.

Radical trans-Hydroboration of Substituted 1,3-Diynes with an N-Heterocyclic Carbene Borane.

Monohydroboration of substituted 1,3-diynes with an N-heterocyclic carbene borane (NHC-borane) occurs under radical conditions using an azo initiator, such as ACCN and AIBN, and a thiol as a polarity-reversal catalyst. The reaction is highly regio- and stereoselective and provides stable NHC-(E)-alkynylalkenylboranes.

Highly selective and straightforward recovery of gold and platinum from acidic waste effluents using cellulose-based bio-adsorbent.

Recovery of precious metals (PMs: AuIII and PtIV) from waste resources is of high importance due to the environmental concern and imbalance in the supply-demand ratio. A new approach has been explored for the recovery of PM using earlier developed bio-adsorbent, dithiocarbamate-modified cellulose (DMC). The adsorbent exhibits excellent adsorption efficiency (~99%) over a wide range of pH (< 1-6) and high selectivity towards AuIII and PtIV extraction from acidic solutions ([H+]: ≥ 0.2 mol L-1). The adsorption capacity (mmol g-1; AuIII: 5.07, PtIV: 2.41) and rate to reach equilibrium (≤ 30 min) were significantly higher than most of the reported bio-adsorbents. The AuIII or PtIV, after captured in DMC, was subsequently recovered as Au0 and Pt0 (yield > 99%) via incineration. The protocol was verified using real waste samples containing AuIII and PtIV in a mixed matrix of base metal ions, and a quantitative (~100%) and selective extraction of AuIII and PtIV were observed. The proposed technique is more effective and straightforward than the typical adsorption-desorption-reduction based method, because of the advantages like no-use of toxic eluents, and no-addition of any reductants to collect the PMs in elemental form.