Enzyme-Like Catalysis of Vinyl Copolymer Carrying Boron Directly Connected to Backbone: Catalytic Esterification through Cooperation of Boron with Neighboring Carboxylic Anhydride.

Alternating-rich copolymer of vinylboronic acid pinacol ester (VBpin) and maleic anhydride (MAH) was found to catalyze direct dehydrative esterification of carboxylic acid and alcohol. The key to the catalytic function is the activation of the MAH unit by the neighboring Lewis acidic boron directly connected to the backbone through the formation of five-membered ring. The effects of the side-chain cooperation were clarified through comparisons with the polymers having similar structures and a conventional titanium catalyst as well as the analyses of reactions with carboxylic acid or alcohol. The catalytic activity was enhanced as the molecular weight was higher, which is owing to the structural feature that boron is directly attached to the backbone. The cooperative catalysis is of interest because of its conceptual similarity with enzyme.

Anthranilamide-protected vinylboronic acid: rational monomer design for improved polymerization/transformation ability providing access to conventionally inaccessible copolymers.

We have studied several protecting groups for vinylboronic-acid derivatives as monomers in radical polymerizations with the objective to improve the polymerization ability and C-B bond-cleaving post-transformation performance. Anthranilamide (aam)-protected vinylboronic acid (VBaam) exhibited experimentally a relatively high polymerization activity, which was theoretically corroborated by density functional theory (DFT) calculations that revealed a peculiar effect of the interaction between the aam groups on the polymerization behavior. The VBaam units in the copolymers can subsequently be transformed into vinyl alcohols or into ethylene units through C-B-bond-cleaving side-chain replacement, which affords valuable copolymers such as poly(vinyl alcohol-co-styrene), poly(ethylene-co-styrene), and poly(ethylene-co-acrylate).

Incorporation of a boryl pendant as the trigger in a methacrylate polymer for backbone degradation.

Alkenylboronate units were incorporated into poly(methyl methacrylate) as trigger sites for backbone degradation. The complexation of a fluoride anion to the boron pendant and subsequent activation by a manganese salt triggered the degradation through the generation of a main-chain carbon radical and ß-scission in an adjacent methacrylate unit. The addition of catechol was required, and presumably the chelate coordination to the Mn center was crucial for the degradation.

Orthogonal C-B Bond Transformation as an Approach for Versatile Synthesis of End-Functionalized Polymers.

Conventionally inaccessible end-functionalized vinyl polymers were synthesized via orthogonal side-chain replacement for terminal and repeating units of poly(alkenyl boronate)s. A terminal-defined polymer of isopropenyl boronic acid pinacol ester (IPBpin) was synthesized via RAFT polymerization, and subsequent cobalt (Co)-catalyzed end olefination afforded the polymer carrying the C(sp2)-B bond at the terminal and the C(sp3)-B bond in repeating units. Herein, the terminal C(sp2)-B bond was selectively transformable via palladium (Pd)-catalyzed Suzuki-Miyaura cross coupling, and subsequent transformation of the repeating C(sp3)-B unit gave the poly(α-methyl vinyl alcohol) [poly(MVA)] bearing various functional groups at the terminal. The boron-based stepwise polymer reaction thus overcame the synthetic difficulty of the end-functionalized poly(MVA), which is ascribed to the poor polymerization ability of the corresponding acetate monomer, i.e., isopropenyl acetate.

Vinylboronic acid pinacol ester as a vinyl alcohol-precursor monomer in radical copolymerization with styrene.

The use of vinylboronic acid pinacol ester (VBpin) as a comonomer and post-polymerization oxidation afforded vinyl alcohol (VA)-styrene copolymers, which were difficult to synthesize using a typical VA precursor monomer, vinyl acetate (VAc). The molar mass was controllable by applying RAFT polymerization and the VA composition ratio could be tuned from 11% to 72%. The solubility and glass-transition temperature were also evaluated with the copolymers of different composition ratios.

Correction: Vinylboronic acid pinacol ester as a vinyl alcohol-precursor monomer in radical copolymerization with styrene.

Correction for 'Vinylboronic acid pinacol ester as a vinyl alcohol-precursor monomer in radical copolymerization with styrene' by Hiroshi Makino et al., Chem. Commun., 2021, DOI: 10.1039/D1CC02603H.

Elucidating Monomer Character of an Alkenyl Boronate through Radical Copolymerization Leads to Copolymer Synthesis beyond the Limitation of Copolymerizability by Side-Chain Replacement.

Isopropenyl boronic acid pinacol ester (IPBpin) was used as a comonomer in radical polymerization with a wide range of common vinyl monomers for elucidation of the monomer character and syntheses of conventionally inaccessible copolymers via the replacement of the boron pendant. The study revealed that the boron-containing monomer is categorized into an electron-rich conjugated monomer, which was well consistent with the results of density functional theory (DFT)-based investigation. One of the thus obtained copolymers, the IPBpin-styrene copolymer, was successfully transformed into an α-methyl vinyl alcohol (MVA)-styrene counterpart via oxidation of the boron pendant. The copolymer cannot be synthesized even with the acetyl-protected monomer instead of IPBpin due to poor copolymerization ability based on the nonconjugated character.

Hydrophobicity and CH/π-interaction-driven self-assembly of amphiphilic aromatic hydrocarbons into nanosheets.

The hydrophobicity and CH/π-interaction-driven self-assembly of an amphiphile that contains a biphenylanthracene group furnishes two-dimensional aggregates in dilute aqueous solution. A windmill-shaped molecular packing structure that arises from multiple intermolecular CH/π interactions of the aromatic hydrocarbons is the key motif for the self-assembly into micrometer-scale nanosheets.

An Alkenyl Boronate as a Monomer for Radical Polymerizations: Boron as a Guide for Chain Growth and as a Replaceable Side Chain for Post-Polymerization Transformation.

The ability of isopropenyl boronate pinacol ester to serve as a monomer in radical polymerizations was established and exploited for the synthesis of polymers that are difficult to access using other polymerization techniques. Although the monomer exhibits an α-methyl-substituted unconjugated structure, which is usually unfavorable for radical propagation, both free and controlled radical polymerizations smoothly afford the corresponding polymers. A density-functional-theory-based investigation revealed that the boron atom moderately stabilizes the radical species, which leads to the suppression of the degradative chain transfer to the α-methyl groups, and thus guides the reaction towards the radical polymerization. The boronyl pendants, which are directly attached to the polymer backbone, can be replaced with -OH or -NH2 to yield poly(α-methyl vinyl amine) or poly(α-methyl vinyl alcohol), which has been inaccessible by conventional synthetic methods.

Abnormal sergeants-and-soldiers effects of poly(quinoxaline-2,3-diyl)s enabling discrimination of one-carbon homologous n-alkanes through a highly sensitive solvent-dependent helix inversion.

Poly(quinoxaline-2,3-diyl)s bearing (S)-3-octyloxymethyl and n-propoxymethyl side chains show an abnormal sergeants-and-soldiers effect in n-alkane solvents, which allows the development of a series of PQXs that exhibit an extremely sensitive solvent-dependent helix inversion that permits the discrimination of n-alkane solvents that differ by a single methylene group (e.g. n-heptane and n-octane).

Elucidating the Solvent Effect on the Switch of the Helicity of Poly(quinoxaline-2,3-diyl)s: A Conformational Analysis by Small-Angle Neutron Scattering.

Small-angle neutron scattering (SANS) was used to examine dilute solutions of a poly(quinoxaline-2,3-diyl) (PQX) with (R)-2-octyloxymethyl side chains in deuterated THF or a mixture of deuterated 1,1,2-TCE and THF (8/2, v/v), in which the PQX adopts pure P- and M-helical structures. The structures of the PQX that were obtained based on the SANS experiments in combination with theoretical calculations suggest that in THF, the chiral side chains of the P-helical PQX are extended, whereas in the 1,1,2-TCE/THF mixture, the side chains of the M-helical PQX are folded. Consequently, P-helical structures should be preferred in good solvents such as THF, which solvate the extended side chains, whereas M-helical structures should be preferred in poor solvents such as 1,1,2-TCE, wherein the side chains adopt shrunken conformations with maximized van der Waals interactions between the side chains. This study thus reveals the first example for fully determined nuanced conformations of the side chains of synthetic polymers in solution based on SANS experiments and theoretical calculations.

Synthesis and Catalytic Applications of a Triptycene-Based Monophosphine Ligand for Palladium-Mediated Organic Transformations.

1-Methoxy-8-(diphenylphosphino)triptycene (1), featuring high structural rigidity and steric bulkiness around the phosphine functionality, was synthesized as a new chiral monophosphine ligand for transition metal-catalyzed reactions. In the presence of 5-10 mol ppm (i.e., 0.0005-0.001 mol %) Pd(OAc)2 and 1 (2 equiv for Pd), Suzuki-Miyaura cross-coupling reactions of aryl bromides and arylboronic acids proceeded effectively under mild atmospheric conditions to give the corresponding biaryl compounds in a high yield. The single-crystal X-ray analysis of a Pd(II) complex of 1 revealed its coordination structure, in which two homochiral molecules form a dimer, suggesting that triptycene could provide a chiral environment for asymmetric organic transformations. In fact, optically active 1 obtained by optical resolution showed good enantioselectivity in the palladium-catalyzed asymmetric hydrosilylation of styrene, which represents, for the first time, the asymmetric catalytic activity of triptycene-based monophosphine ligands.

Poly(quinoxaline-2,3-diyl) as a Multifunctional Chiral Scaffold for Circularly Polarized Luminescent Materials: Color Tuning, Energy Transfer, and Switching of the CPL Handedness.

Random poly(quinoxaline-2,3-diyl) copolymers, containing achiral 5,8-diarylquinoxaline units and chiral units bearing (S)-2-butoxymethyl groups, exhibited circularly polarized luminescence (CPL). The emission color was fully tunable by changing the aryl substituents on the 5,8-diarylquinoxaline units. An energy transfer from the quinoxaline main chain to the 5,8-diarylquinoxaline units was observed. The handedness of the CPL was dependent on the helical chirality of the polymer main chain, which could be switched by changing the solvent from CHCl3 to 1,1,2-trichloroethane or n-octane to cyclooctane, depending on the chiral side chain.

Solvent Effect on the Sergeants-and-Soldiers Effect Leading to Bidirectional Induction of Single-Handed Helical Sense of Poly(quinoxaline-2,3-diyl)s Copolymers in Aromatic Solvents.

Random poly(quinoxaline-2,3-diyl) copolymers, containing chiral (S)-3-octyloxymethyl and achiral propoxymethyl side chain units, experience an abnormal sergeants-and-soldiers effect, that is, they adopt, depending on the chiral monomer mole fraction, either P- or M-helical conformations in anisole (PhOCH3) and benzotrifluoride (PhCF3). In benzene (PhH) and toluene (PhCH3), these copolymers exclusively adopt an M-helical conformation, regardless of the chiral monomer mole fraction. For a co-300mer, with a 40% mole fraction of chiral units, the selective induction of an M-helix (>99%) was observed in PhH, while in PhCF3, a P-helical conformation was induced selectively (>99%). This helix inversion of the polymer backbone is thus able to control the chirality of a chiral polymer ligand in aromatic solvents. The incorporation of a small amount of coordinating PPh2 groups into the copolymer resulted in a chiral macromolecular ligand, which allowed the enantioselective synthesis of both enantiomeric products in an asymmetric Suzuki-Miyaura coupling reaction (R-product: 91% ee in PhH; S-product: 95% ee in PhCF3) from a single catalyst.

Exerting control over the helical chirality in the main chain of sergeants-and-soldiers-type poly(quinoxaline-2,3-diyl)s by changing from random to block copolymerization protocols.

Chiral random poly(quinoxaline-2,3-diyl) polymers of the sergeants-and-soldiers-type (sergeant units bearing (S)-3-octyloxymethyl groups) adopt an M- or P-helical conformation in the presence of achiral units bearing propoxymethyl or butoxy groups (soldier units), respectively. Unusual bidirectional induction of the helical sense can be observed for a copolymer with butoxy soldier units upon changing the mole fraction of the sergeant units. In the presence of 16-20% of sergeant units, the selective induction of a P-helix was observed, while the selective induction of an M-helix was observed for a mole fraction of sergeant units of more than 60%. This phenomenon could be successfully employed to control the helical chirality of copolymers by applying either random or block copolymerization protocols. Random or block copolymerization of sergeant and soldier monomers in a 18:82 ratio resulted in the formation of 250mers with almost absolute P- or M-helical conformation, respectively (>99% ee). Incorporation of a small amount of coordination sites into the random and block copolymers resulted in chiral macromolecular ligands, which allowed the enantioselective synthesis of both enantiomers in the Pd-catalyzed asymmetric hydrosilylation of ß-methylstyrene.

Poly(quinoxaline-2,3-diyl)s bearing (S)-3-octyloxymethyl side chains as an efficient amplifier of alkane solvent effect leading to switch of main-chain helical chirality.

Poly(quinoxaline-2,3-diyl) containing (S)-3-octyloxymethyl side chains was synthesized to investigate the induction of a single-handed helical sense to the main chain in various alkane solvents. The polymer showed an efficient solvent dependent helix inversion between n-octane (M-helix) and cyclooctane (P-helix). After a screening of alkane solvents, it was found that linear alkanes having large molecular aspect ratios induced M-helical structure, and branched or cyclic alkanes having small molecular aspect ratios induced P-helical structure. A polymer ligand containing (S)-3-octyloxymethyl side chains and diphenylphosphino pendants also exhibited solvent-dependent helical inversion between n-octane and cyclooctane, leading to the highly enantioselective production of the both enantiomeric product in a palladium-catalyzed asymmetric hydrosilylation reaction of styrene (R-product 94% ee in n-octane and S-product 90% ee in cyclooctane).

Chirality-switchable circularly polarized luminescence in solution based on the solvent-dependent helix inversion of poly(quinoxaline-2,3-diyl)s.

Poly(quinoxaline-2,3-diyl)s containing (S)-2-methylbutoxy side chains were found to exhibit blue circularly polarized luminescence (CPL). The handedness of the CPL could be switched by a solvent-dependent helix inversion of the polymer backbone between chloroform (M-helical structure) and 1,1,1-trichloroethane (P-helical structure).

Solvent-dependent fluorescence and circular dichroism properties of poly(quinoxaline-2,3-diyl)s bearing pyrene pendants.

Poly(quinoxaline-2,3-diyl)s bearing pyrene pendants exhibited solvent-dependent changes of the fluorescence color (blue and green) and the screw-sense selectivity (left-handed and racemic) in chloroform and 1,1,1-trichloroethane, respectively.

Disruption of reverse micelles and release of trapped ribonuclease A photochemically induced by Malachite Green leuconitrile derivative.

Photoinduced disruption of a sodium bis(2-ethylhexyl) sulfosuccinate (AOT) reverse micelle is triggered by a Malachite Green leuconitrile derivative (MGL). UV irradiation of MGL solubilized in an AOT-water-chloroform mixture creates a cationic surfactant that interacts electrostatically with the anionic AOT. We investigated the disruption of the reverse micelle by using proton nuclear magnetic resonance spectroscopy and found that UV irradiation of MGL decreases the number of water molecules solubilized in the interior of the AOT reverse micelles. Furthermore, the photoinduced disruption of the reverse micelle is shown to release ribonuclease A, which is trapped in the water in the interior of the AOT reverse micelle. This photoinduced release may offer a desirable transport system of biopolymers.