Synthesis of N2-Type Superatomic Molecules.

Exploration of multiple bonds between superatoms remains an uncharted territory. In this study, we present the synthesis and characterization of N2-type superatomic molecules featuring triple bonds between two superatoms. The successful synthesis of M2Au17 (M = Pd, Pt) nanoclusters hinged upon the photoinduced fusion of MAu12 superatoms, achieved through sequential electron transfer and detachment of [AuPR3]+ species. Solid-state structures were confirmed via X-ray crystallography, while their electronic structures were elucidated through density functional theory (DFT) calculations. Analysis of electronic absorption properties, coupled with time-dependent DFT calculations, unveiled a symmetry-dependent electron transition nature between superatomic molecular orbitals, akin to that observed in conventional molecules.

Regioselective Propargylic Suzuki-Miyaura Coupling by SciPROP-Iron Catalyst.

The iron-catalyzed Suzuki-Miyaura cross-coupling of secondary propargyl electrophiles with lithium organoborates has been established. A propyl-bridged bulky bisphosphine ligand, SciPROP-TB, cooperated with the bulky TIPS substituent at the alkyne terminal position to achieve the cross-coupling reaction with exclusive propargylic selectivity. The reaction features high functional group compatibility, regioselectivity, and yield with a broad substrate scope. The reaction of an optically active chiral propargyl bromide proceeds with complete racemization, supporting a mechanism involving propargyl radical formation.

Dual Catalysis of Gold Nanoclusters: Photocatalytic Cross-Dehydrogenative Coupling by Cooperation of Superatomic Core and Molecularly Modified Staples.

Thiolate-protected gold nanoclusters (AuNCs) have attracted significant attention as nano-catalysts, revealing a superatomic core and gold-thiolate staples as distinct structural units. Here, we demonstrate the unprecedented dual catalytic activity of thiolate-protected [Au25 (SR)18 ]- nanoclusters, involving both photosensitized 1 O2 generation by the Au13 superatomic core and catalytic carbon-carbon bond formation facilitated by Au2 (SR)3 staples. This synergistic combination of two different catalytic units enables efficient cross-dehydrogenative coupling of terminal alkynes and tertiary aliphatic amines to afford propargylamines in high yields of up to 93 %. Mixed-ligand AuNCs bearing both thiolate and alkynyl ligands revealed the intermediacy of the alkynyl-exchanged AuNCs toward both photosensitization and C-C bond-forming catalytic cycles. Density functional theory calculations also supported the intermediacy of the alkynyl-exchanged AuNCs. Thus, the use of ligand-protected metal nanoclusters has enabled the development of an exceptional multifunctional catalyst, wherein distinct nanocluster components facilitate cooperative photo- and chemo-catalysis.

Laying down of gold nanorods monolayers on solid surfaces for surface enhanced Raman spectroscopy applications.

Laying-down gold nanorods (GNRs) of a monolayer immobilized on a solid substrate was realized with a hybrid method, a combination of three elemental technologies: surface modification, electrophoresis, and solvent evaporation. The self-assembly of CTAB-protected GNRs in the solution was induced by 0.05 mM of EDTA. The assembled GNRs were deposited in a laying-down form on the solid surface during the hybrid method. The final coverage was over 71% on the substrate with an area larger than 0.6 cm2. The spacing between the sides of the GNRs was fixed to be 4.6 ± 0.9 nm by the thermal annealing-promoted crystalline packing of the bilayer of CTAB salt-bridged with EDTA. The obtained laying-down GNRs of a monolayer on the gold substrate show a small shift of the transverse LSPR around 550-570 nm (with a width of around 100 nm) and a large red shift of the longitudinal LSPR to be 900-1050 nm (with a width of 500 nm), because of the strong electromagnetic coupling between the GNRs and gold substrate. Therefore it can be used in a wide range of wavelengths for surface enhanced Raman spectroscopy (SERS) applications. The film has a high enhancement factor with 105 for R6G.

Regio- and stereoselective synthesis of 1,4-enynes by iron-catalysed Suzuki-Miyaura coupling of propargyl electrophiles under ligand-free conditions.

The first iron-catalysed cross coupling of propargyl electrophiles with lithium alkenylborates has been developed. Various propargyl electrophiles can be cross-coupled with lithium (E)- or (Z)-alkenylborates in a stereospecific manner to afford the corresponding 1,4-enynes in good to excellent yields. The reaction features high SN2-type regioselectivity and functional group compatibility.

Synthesis of Aryl C-Glycosides via Iron-Catalyzed Cross Coupling of Halosugars: Stereoselective Anomeric Arylation of Glycosyl Radicals.

We have developed a novel diastereoselective iron-catalyzed cross-coupling reaction of various glycosyl halides with aryl metal reagents for the efficient synthesis of aryl C-glycosides, which are of significant pharmaceutical interest due to their biological activities and resistance toward metabolic degradation. A variety of aryl, heteroaryl, and vinyl metal reagents can be cross-coupled with glycosyl halides in high yields in the presence of a well-defined iron complex, composed of iron(II) chloride and a bulky bisphosphine ligand, TMS-SciOPP. The chemoselective nature of the reaction allows the use of synthetically versatile acetyl-protected glycosyl donors and the incorporation of various functional groups on the aryl moieties, producing a diverse array of aryl C-glycosides, including Canagliflozin, an inhibitor of sodium-glucose cotransporter 2 (SGLT2), and a prevailing diabetes drug. The cross-coupling reaction proceeds via generation and stereoselective trapping of glycosyl radical intermediates, representing a rare example of highly stereoselective carbon-carbon bond formation based on iron catalysis. Radical probe experiments using 3,4,6-tri-O-acetyl-2-O-allyl-α-d-glucopyranosyl bromide (8) and 6-bromo-1-hexene (10) confirm the generation and intermediacy of the corresponding glycosyl radicals. Density functional theory (DFT) calculations reveal that the observed anomeric diastereoselectivity is attributable to the relative stability of the conformers of glycosyl radical intermediates. The present cross-coupling reaction demonstrates the potential of iron-catalyzed stereo- and chemoselective carbon-carbon bond formation in the synthesis of bioactive compounds of certain structural complexity.

ONO-pincer ruthenium complex-bound norvaline for efficient catalytic oxidation of methoxybenzenes with hydrogen peroxide.

The enhanced catalytic activity of ruthenium complex-bound norvaline Boc-l-[Ru]Nva-OMe 1, in which the ONO-pincer ruthenium complex Ru(pydc)(terpy) 2 is tethered to the α-side chain of norvaline, has been demonstrated for the oxidation of methoxybenzenes to p-benzoquinones with a wide scope of substrates and unique chemoselectivity.

Reusable Magnetite Nanoparticle (Fe3O4 NP) Catalyst for Selective Oxidation of Alcohols under Microwave Irradiation.

Iron oxide nanoparticles (NPs) are nontoxic and abundant materials which have long been investigated as reusable catalysts in oxidation reactions, but their use so far has been hampered by a low selectivity. Here, unsupported iron oxide NPs have been found to successfully catalyze the microwave-assisted oxidation of primary and secondary alcohols to their respective aldehydes and ketones with a high selectivity when N-methylmorpholine N-oxide was used as the terminal oxidant. The crystalline phase and size of the iron-based catalyst have a drastic effect on its activity, with small magnetite (Fe3O4) NPs being the optimal catalyst for this reaction. The nanocatalyst could be easily recovered by magnetoseparation and successfully recycled four times without any need for special pretreatment or reactivation step and with a minimal loss of activity. The subsequent loss of activity was attributed to the transition from magnetite (Fe3O4) to maghemite (γ-Fe2O3), as confirmed by X-ray diffraction, Fourier transform infrared, and X-ray absorption near-edge spectroscopy. The nanocatalyst could then be reactivated by the high-temperature microwave treatment and used again for the microwave-assisted oxidation reaction.

Synthesis and self-assembly of NCN-pincer Pd-complex-bound norvalines.

The NCN-pincer Pd-complex-bound norvalines Boc-D/L-[PdCl(dpb)]Nva-OMe (1) were synthesized in multigram quantities. The molecular structure and absolute configuration of 1 were unequivocally determined by single-crystal X-ray structure analysis. The robustness of 1 under acidic/basic conditions provides a wide range of N-/C-terminus convertibility based on the related synthetic transformations. Installation of a variety of functional groups into the N-/C-terminus of 1 was readily carried out through N-Boc- or C-methyl ester deprotection and subsequent condensations with carboxylic acids, R(1)COOH, or amines, R(2)NH2 , to give the corresponding N-/C-functionalized norvalines R(1)-D/L-[PdCl(dpb)]Nva-R(2) 2-9. The dipeptide bearing two Pd units 10 was successfully synthesized through the condensation of C-free 1 with N-free 1. The robustness of these Pd-bound norvalines was adequately demonstrated by the preservation of the optical purity and Pd unit during the synthetic transformations. The lipophilic Pd-bound norvalines L-2, Boc-L-[PdCl(dpb)]Nva-NH-n-C11H23, and L-4, n-C4H9CO-L-[PdCl(dpb)]Nva-NH-n-C11H23, self-assembled in aromatic solvents to afford supramolecular gels. The assembled structures in a thermodynamically stable single crystal of L-2 and kinetically stable supramolecular aggregates of L-2 were precisely elucidated by cryo-TEM, WAX, SAXS, UV/Vis, IR analyses, and single-crystal X-ray crystallography. An antiparallel ß-sheet-type aggregate consisting of an infinite one-dimensional hydrogen-bonding network of amide groups and π-stacking of PdCl(dpb) moieties was observed in the supramolecular gel fiber of L-2, even though discrete dimers are assembled through hydrogen bonding in the thermodynamically stable single crystal of L-2. The disparate DSC profiles of the single crystal and xerogel of L-2 indicate different thermodynamics of the molecular assembly process.

Head-to-tail square-shaped cyclic hydrogen bonds leading to dimeric aggregates: 1,8-dibenzoyl-2,7-dihydroxynaphthalene and a comparison with its analogous benzoylnaphthalene.

The title compound, C24H16O4, crystallized with two independent molecules in the asymmetric unit. Both carbonyl groups in these molecules form intramolecular O-H...O=C hydrogen bonds with neighbouring hydroxy groups, affording six-membered cyclic structures. In the crystal, dimeric aggregates arise from two intermolecular O-H···O=C hydrogen bonds between both independent molecules, forming head-to-tail square-shaped cyclic ···O···H···O···H··· hydrogen bonds. These dimeric aggregates are connected into layers in the bc plane by intermolecular (naphthalene)C-H...O=C interactions. On the other hand, the analogous compound bearing methoxy groups at the 2- and 7-positions of the naphthalene ring, namely 1,8-dibenzoyl-2,7-dimethoxynaphthalene [Nakaema et al. (2008). Acta Cryst. E64, o807], forms a three-dimensional molecular network via C-H···O=C and π-π interactions between the benzoyl groups. These results show that the intramolecular O-HvO=C hydrogen bonds in the title compound control the orientations of the benzoyl groups and thus promote the formation of the cyclic intermolecular O-H···O=C interactions involving the same donor and acceptor groups in pairs of molecules.

[2,7-Dieth-oxy-8-(4-fluoro-benzo-yl)naphthalen-1-yl](4-fluoro-phen-yl)methanone.

In the mol-ecule of the title compound, C28H22F2O4, the benzoyl groups are aligned almost anti-parallel and the fluorobenzene rings form a dihedral angle of 14.12 (7)°. The dihedral angles between the 2,7-dieth-oxy-naphthalene ring system and the benzene rings are 70.00 (4) and 67.28 (4)°. In the crystal, mol-ecules are linked by C-H⋯O and C-H⋯F hydrogen bonds, forming layers parallel to the ab plane. The layers are further connected by π-π inter-actions [centroid-centroid distances of 3.6115 (10) Å] into a three-dimensional structure.

1,8-Bis(4-fluoro-benzo-yl)naphthalen-2,7-diyl dimethane-sulfonate.

The mol-ecule of the title compound, C26H18F2O8S2, lies across a crystallographic twofold rotation axis. The benzene rings of the 4-fluorobenzoyl groups make dihedral angles of 78.93 (12)° with the naphthalene ring system. An intra-molecular C-H⋯π inter-action occurs. In the crystal, a number of C-H⋯O inter-actions link the mol-ecules, forming a three-dimensional structure.

Bis(1-benzoyl-7-meth-oxy-naphthalen-2-yl) terephthalate.

The title molecule, C44H30O8, lies about a crystallographic inversion centre located at the centre of the central benzene ring. The benzene rings in the benzoyl and the terephthalate units make dihedral angles of 67.05 (7)° and 57.57 (7)°, respectively, with the naphthalene ring system. There is an intra-molecular C-H⋯O inter-action between the ketonic carbonyl O atom and an H atom on the naphthalene ring system. In the crystal, C-H⋯O inter-action of the benzene ring in the benzoyl group and weak C=O⋯π inter-action [O⋯centroid = 3.375 (2) Å] of the naphthalene ring with the O atom in the ketonic carbonyl group are observed. These inter-actions form layers parallel to the bc plane.

Iron-catalysed enantioselective carbometalation of azabicycloalkenes.

The first enantioselective carbometalation reaction of azabicycloalkenes has been achieved by iron catalysis to in situ form optically active organozinc intermediates, which are amenable to further synthetic elaborations. The observed chiral induction, along with the DFT and XAS analyses, reveals the direct coordination of the chiral phosphine ligand to the iron centre during the carbon-carbon and carbon-metal bond forming step. This new class of iron-catalysed asymmetric reaction will contribute to the synthesis and production of bioactive molecules.

Racemic (RS(C),SR(S))-(2-{[1-allyl-oxy-carbonyl-3-(methyl-sulfanyl)prop-yl]iminometh-yl}phenyl-κS,N,C)chlorido-platinum(II).

The title compound, [Pt(C(15)H(18)NO(2)S)Cl], was obtained by the cyclo-metallation reaction of cis-bis-(benzonitrile)dichlorido-platinum(II) with N-benzyl-idene-l-methio-nine allyl ester in refluxing toluene. The Pt(II) atom has a square-planar geometry and is tetra-coordinated by the Cl atom and the C, N and S atoms from the benzyl-idene methio-nine ester ligand. In the crystal structure, the S atoms show opposite chiral configurations with respect to the α-carbon of the methio-nine, reducing steric repulsion between the methyl and allyl ester groups.

Robust Surface Plasmon Resonance Chips for Repetitive and Accurate Analysis of Lignin-Peptide Interactions.

We have developed novel surface plasmon resonance (SPR) sensor chips whose surfaces bear newly synthesized functional self-assembled monolayer (SAM) anchoring lignin through covalent chemical bonds. The SPR sensor chips are remarkably robust and suitable for repetitive and accurate measurement of noncovalent lignin-peptide interactions, which is of significant interest in the chemical or biochemical conversion of renewable woody biomass to valuable chemical feedstocks. The lignin-anchored SAMs were prepared for the first time by click chemistry based on an azide-alkyne Huisgen cycloaddition: mixed SAMs are fabricated on gold thin film using a mixture of alkynyl and methyl thioalkyloligo(ethylene oxide) disulfides and then reacted with azidated milled wood lignins to furnish the functional SAMs anchoring lignins covalently. The resulting SAMs were characterized using infrared reflection-absorption, Raman, and X-ray photoelectron spectroscopies to confirm covalent immobilization of the lignins to the SAMs via triazole linkages and also to reveal that the SAM formation induces a helical conformation of the ethylene oxide chains. Further, SPR measurements of the noncovalent lignin-peptide interactions using lignin-binding peptides have demonstrated high reproducibility and durability of the prepared lignin-anchored sensor chips.

Discovery of 12-mer peptides that bind to wood lignin.

Lignin, an abundant terrestrial polymer, is the only large-volume renewable feedstock composed of an aromatic skeleton. Lignin has been used mostly as an energy source during paper production; however, recent interest in replacing fossil fuels with renewable resources has highlighted its potential value in providing aromatic chemicals. Highly selective degradation of lignin is pivotal for industrial production of paper, biofuels, chemicals, and materials. However, few studies have examined natural and synthetic molecular components recognizing the heterogeneous aromatic polymer. Here, we report the first identification of lignin-binding peptides possessing characteristic sequences using a phage display technique. The consensus sequence HFPSP was found in several lignin-binding peptides, and the outer amino acid sequence affected the binding affinity of the peptides. Substitution of phenylalanine7 with Ile in the lignin-binding peptide C416 (HFPSPIFQRHSH) decreased the affinity of the peptide for softwood lignin without changing its affinity for hardwood lignin, indicating that C416 recognised structural differences between the lignins. Circular dichroism spectroscopy demonstrated that this peptide adopted a highly flexible random coil structure, allowing key residues to be appropriately arranged in relation to the binding site in lignin. These results provide a useful platform for designing synthetic and biological catalysts selectively bind to lignin.

Synthesis and Applications of (ONO†Pincer)Ruthenium-Complex-Bound Norvalines.

Two (ONO pincer)ruthenium-complex-bound norvalines, Boc-[Ru(pydc)(terpy)]Nva-OMe (1; Boc=tert-butyloxycarbonyl, terpy=terpyridyl, Nva=norvaline) and Boc-[Ru(pydc)(tBu-terpy)]Nva-OMe (5), were successfully synthesized and their molecular structures and absolute configurations were unequivocally determined by single-crystal X-ray diffraction. The robustness of the pincer Ru complexes and norvaline scaffolds against acidic/basic, oxidizing, and high-temperature conditions enabled us to perform selective transformations of the N-Boc and C-OMe termini into various functional groups, such as alkyl amide, alkyl urea, and polyether groups, without the loss of the Ru center or enantiomeric purity. The resulting dialkylated Ru-bound norvaline, n-C11 H23 CO-l-[Ru(pydc)(terpy)]Nva-NH-n-C11 H23 (l-4) was found to have excellent self-assembly properties in organic solvents, thereby affording the corresponding supramolecular gels. Ru-bound norvaline l-1 exhibited a higher catalytic activity for the oxidation of alcohols by H2 O2 than parent complex [Ru(pydc)(terpy)] (11 a).

Selective Two-Photon-Absorption-Induced Reactions of Anthracene-2-Carboxylic Acid on Tunable Plasmonic Substrate with Incoherent Light Source.

In this research, we report the development, characterization and application of various plasmonic substrates (with localized surface plasmon resonance wavelength tunable by gold nanoparticle size) for two-photon absorption (TPA)-induced photodimerization of an anthracene derivative, anthracene carboxylic acid, in both surface and solution phase under incoherent visible light irradiation. Despite the efficient photoreaction property of anthracene derivatives and the huge number of publications about them, there has never been a report of a multiphoton photoreaction involving an anthracene derivative with the exception of a reverse photoconversion of anthracene photodimer to monomer with three-photon absorption. We examined the progress of the TPA-induced photoreaction by means of surface-enhanced Raman scattering, taking advantage of the ability of our plasmonic substrate to enhance and localize both incident light for photoreaction and Raman scattering signal for analysis of photoreaction products. The TPA-induced photoreaction in the case of anthracene carboxylic acid coated 2D array of gold nanoparticles gave different results according to the properties of the plasmonic substrate, such as the size of the gold nanoparticle and also its resultant optical properties. In particular, a stringent requirement to achieve TPA-induced photodimerization was found to be the matching between irradiation wavelength, localized surface plasmon resonance of the 2D array, and twice the wavelength of the molecular excitation of the target material (in this case, anthracene carboxylic acid). These results will be useful for the future development of efficient plasmonic substrates for TPA-induced photoreactions with various materials.

Hydrogen bonding between aromatic H and F groups leading to a stripe structure with R- and S-columns: the crystal structure of (2,7-dimethoxynaphthalen-1-yl)(3-fluorophenyl)methanone and comparison with its 1-aroylnaphthalene analogues.

In the molecule of (2,7-dimethoxynaphthalen-1-yl)(3-fluorophenyl)methanone, C19H15FO3, (I), the dihedral angle between the plane of the naphthalene ring system and that of the benzene ring is 85.90 (5)°. The molecules exhibit axial chirality, with either an R- or an S-stereogenic axis. In the crystal structure, each enantiomer is stacked into a columnar structure and the columns are arranged alternately to form a stripe structure. A pair of (methoxy)C-H...F hydrogen bonds and π-π interactions between the benzene rings of the aroyl groups link an R- and an S-isomer to form a dimeric pair. These dimeric pairs are piled up in a columnar fashion through (benzene)C-H...O=C and (benzene)C-H...OCH3 hydrogen bonds. The analogous 1-benzoylated compound, namely (2,7-dimethoxynaphthalen-1-yl)(phenyl)methanone [Kato et al. (2010). Acta Cryst. E66, o2659], (II), affords three independent molecules having slightly different dihedral angles between the benzene and naphthalene rings. The three independent molecules form separate columns and the three types of column are connected to each other via two C-H...OCH3 hydrogen bonds and one C-H...O=C hydrogen bond. Two of the three columns are formed by the same enantiomeric isomer, whereas the remaining column consists of the counterpart isomer. In the case of the fluorinated 1-benzoylated naphthalene analogue, namely (2,7-dimethoxynaphthalen-1-yl)(4-fluorophenyl)methanone [Watanabe et al. (2011). Acta Cryst. E67, o1466], (III), the molecular packing is similar to that of (I), i.e. it consists of stripes of R- and S-enantiomeric columns. A pair of C-H...F hydrogen bonds between R- and S-isomers, and C-H...O=C hydrogen bonds between R(or S)-isomers, are also observed. Consequently, the stripe structure is apparently induced by the formation of R...S dimeric pairs stacked in a columnar fashion. The pair of C-H...F hydrogen bonds effectively stabilizes the dimeric pair of R- and S-enantiomers. In addition, the co-existence of C-H...F and C-H...O=C hydrogen bonds makes possible the formation of a structure with just one independent molecule.