Visible-to-UV upconversion shorter than 340 nm was achieved in organic solvents and the solvent dependent efficiency and photostability were elucidated.

Lignin-based epoxy resins with controlled thermodynamic properties were synthesized.

Acid-catalysed degradation of wood in toluene–MeOH yields the lignin monomers homovanillyl aldehyde dimethyl acetal and homosyringaldehyde dimethyl acetal selectively.

Acid-catalyzed degradation of lignin in toluene containing methanol selectively yields C6-C2 lignin monomers and releases lignin oligomers, a potential raw feedstock for epoxy resins. We herein characterize the structures of the lignin oligomers by focusing on the changes in the interunit linkage types during solvolysis. The oligomeric lignin products were analyzed via thioacidolysis and 2D-HSQC-NMR. The results show that lignin oligomers ranging from monomers to tetramers are released through considerable cleavage of the β-O-4 linkages. The lignin oligomers from Cryptomeria japonica (softwood) mainly comprise β-5, β-1, and tetrahydrofuran β-β linkages, whereas Eucalyptus globulus (hardwood) yields oligomers rich in β-1 and syringaresinol β-β linkages. Both wood samples exhibit selective release of β-β dimers and a relative decrease in 5-5 and 4-O-5 bonds during solvolysis. The method presented for the separation of lignin oligomers without β-O-4 linkages and with linkages unique to each wood species will be useful for the production of lignin-based materials.

Catalytic generation of alkyl radicals from aldehydes via oxidative deformylation was realized using a cobalt-salen complex with H2O2. The deformylation was thought to proceed through homolytic cleavage of peroxohemiacetal intermediates to provide even primary alkyl radicals under mild conditions. Variously substituted and functionalized hydroperoxides were obtained from corresponding aldehydes in good yield.

Reversible insertion of NHC: 1,3‐Di‐tert‐butylimidazol‐2‐ylidene was inserted into a ruthenium–hydride bond of [Cp*Ru(μ‐H)4RuCp*] to form a 4‐imidazoline complex that underwent a dynamic process, namely 1,3‐migratory pendulum motion of the 4‐imidazoline ligand (see scheme). Bimetallic‐system‐assisted NC bond cleavage of the imidazoline ligand proceeded to generate a pseudo‐diazaruthenacycle.

N-Heterocyclic carbenes (NHCs) are strong 2-electron donors and hardly exhibit p-accepting character. [1] NHCs stabilize unsaturated metal centres and have been recently applied as stable spectator ligands in various catalytic transformations of organic molecules in combination with mononuclear transition-metal complexes. [2] However, NHCs can undergo degradation pathways, [3] because they are multifunctional compounds, namely, a lone pair of electrons at C2, which acts as a donor; p-electron lone pairs at N1 and N3; and a C=C double bond between C4 and C5. Because of this multifunctionality, NHCs sometimes undergo a chemical transformation that is possibly related to a deactivation process for catalytically active species.So far, there have been fewer reports on reactions of NHCs with polynuclear complexes than with mononuclear ones, [4] though a variety of patterns are expected to be obtained in the reaction involving a multimetallic system owing to the multifunctional character of NHC molecules. We previously reported the reactions of dinuclear homo-and heterometallic tetrahydrido complexes, [Cp*Ru(m-H) 4 RuCp*] and [Cp*Ru(m-H) 4 OsCp*], with tert-phosphorus ligand that do not contain aryl substituents. [5,6] We examined the reaction of [Cp*Ru(m-H) 4 RuCp*] (1) with 1,3-di-tert-butylimidazol-2-ylidene (ItBu), which is a multifunctional, strong 2-electron donor. We report herein an unprecedented reversible insertion of 1,3-di-tert-butylimidazol-2-ylidene into the ruthenium-hydride bond of 1 and the dynamic process of the resulting dinuclear imidazoline complex. Furthermore, a bimetallic-system-assisted ringopening reaction, that is, the cleavage of the NÀC bond of the imidazoline ligand to generate pseudo-diazaruthenacycle is also reported.The treatment of 1 with 2.3 equivalents of ItBu in tetrahydrofurane at room temperature resulted in the formation of a dinuclear ruthenium m-h 1 :h 2 -4-imidazoline complex 2 as a result of migration of the hydrides from the ruthenium atom to the carbenic carbon (C2) [Eq.(1)]. The yield of the conversion from 1 to 2 reached 56 % under these conditions. The yield inevitably reached a plateau because of the presence of the reverse process, that is, the de-insertion of ItBu. Therefore, a large excess amount of ItBu must be added to carry out the conversion. Time-conversion curves of the reaction of 1 with ItBu are given in the Supporting Information. Complex 2 was efficiently isolated by crystallization from cold pentane (À30 8C).In complex 2, the 4-imidazoline molecule is coordinated as a bridging ligand through a C=C bond and one of the nitrogen atoms. Single crystals of 2 suitable for X-ray diffraction studies were obtained from cold (À30 8C) pentane. The X-ray diffraction data clearly showed the dinuclear structure bridged by 4-imidazoline that was formed by hydride migration to the C2 of the ItBu molecule. The molecular structure of 2 is illustrated in Figure 1 with the relevant bond lengths and angles. [7] The imidazoline molecule is coordinated as 4-electron donor, and...

Recently, dentin bonding systems have been released separately from the resin composites, because the adhesive systems have been quickly improved. Since the merit of each material should be effectively utilized for each clinical case, the bonding systems and resin composites produced by different manufacturers may be combined according to the clinical purpose. The current restorative resins are basically categorized into two groups according to the main resin monomer, bis-GMA or UDMA resins.