Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes initiated by water with strong organic base catalysts.

Organocatalytic controlled/living ring-opening polymerization of cyclotrisiloxanes, such as hexamethylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-triphenylcyclotrisiloxane, 1,3,5-trimethyl-1,3,5-trivinylcyclotrisiloxane, and 1,3,5-trimethyl-1,3,5-tris(3,3,3-trifluoropropyl)cyclotrisiloxane, using water as an initiator and strong organic bases, such as amidines, guanidines, phosphazene bases, and proazaphosphatrane, as catalysts produced a variety of polysiloxanes with controlled number-average molecular weights ( = 2.64-102.3 kg mol), narrow polydispersity ( = 1.

Direct Silyl-Heck Reaction of Chlorosilanes.

A nickel complex/Lewis acid combination effectively catalyzed the direct silyl-Heck reaction of chlorosilanes, which are key raw materials in the organosilicon industry, to give synthetically important alkenylsilane products. Trichlorosilanes, dichlorosilanes, and monochlorosilanes underwent the silyl-Heck reaction to afford the corresponding alkenylsilanes in high yields. In the reactions of dichlorosilanes, a single substitution occurred to give monoalkenylsilanes in a highly selective manner.

One-Pot Sequence-Controlled Synthesis of Oligosiloxanes.

Silicones (organopolysiloxanes) have found applications in a wide range of research areas, and their unique and valuable properties have rendered these materials virtually irreplaceable. Despite the fact that silicones have been employed industrially for more than 70 years, synthetic routes to generate silicones remain limited, and the sequence-controlled synthesis of oligo- and polysiloxanes still represents a major challenge in silicone chemistry. Described here is a highly selective sequence-controlled synthesis of linear, branched, and cyclic oligosiloxanes by simple iteration of two reactions, specifically, a B(C F ) -catalyzed dehydrocarbonative cross-coupling of alkoxysilanes with hydrosilanes and a B(C F ) -catalyzed hydrosilylation of carbonyl compounds, in a single flask.

Anti-stress and neuronal cell differentiation induction effects of Rosmarinus officinalis L. essential oil.

Background: Mood disorder accounts for 13 % of global disease burden. And while therapeutic agents are available, usually orally administered, most have unwanted side effects, and thus making the inhalation of essential oils (EOs) an attractive alternative therapy. Rosmarinus officinalis EO (ROEO), Mediterranean ROEO reported to improve cognition, mood, and memory, the effect on stress of which has not yet been determined.

Modulation of Neurogenesis through the Promotion of Energy Production Activity Is behind the Antidepressant-Like Effect of Colonial Green Alga, .

Algae have been recognized as important resources providing functional components due to their capacity to exert beneficial effects on health. Therefore, there is increasing interest in investigating the biological activity of algae. In this study, we evaluated the antidepressant-like effect of the administration of 100 mg/kg/day of the ethanol extract of colonial green alga (EEB) for 14 consecutive days in the forced swimming test (FST)-induced depression in imprinting control region (ICR) mice.

Comment on "Active sites for CO hydrogenation to methanol on Cu/ZnO catalysts".

Kattel (Reports, 24 March 2017, p. 1296) report that a zinc on copper (Zn/Cu) surface undergoes oxidation to zinc oxide/copper (ZnO/Cu) during carbon dioxide (CO) hydrogenation to methanol and conclude that the Cu-ZnO interface is the active site for methanol synthesis. Similar experiments conducted two decades ago by Fujitani and Nakamura demonstrated that Zn is attached to formate rather than being fully oxidized.

Non-aqueous selective synthesis of orthosilicic acid and its oligomers.

Orthosilicic acid (Si(OH)) and its small condensation compounds are among the most important silicon compounds but have never been isolated, due to their instability. These compounds would be highly useful building blocks for advanced materials if they became available at high purity. Here we show a simple procedure to selectively synthesize orthosilicic acid and its dimer, cyclic trimer and tetramer in organic solvents.

Spectroscopic Observation of the Triplet Diradical State of a Cyclobutadiene.

Tetrakis(trimethylsilyl)cyclobuta-1,3-diene (1) was subjected to a temperature-dependent EPR study to allow the first spectroscopic observation of a triplet diradical state of a cyclobutadiene (2). From the temperature dependent EPR absorption area we derive a singlet→triplet (1→2) energy gap, E , of 13.9 kcal mol , in agreement with calculated values.

Visible-Light-Driven Photocatalytic CO Reduction by a Ni(II) Complex Bearing a Bioinspired Tetradentate Ligand for Selective CO Production.

A Ni(II) complex bearing an SN-type tetradentate ligand inspired by the active site of carbon monoxide dehydrogenase was found to selectively catalyze CO reduction to produce CO in a photocatalytic system using [Ru(bpy)] (bpy = 2,2'-bipyridine) as a photosensitizer and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzo[d]imidazole (BIH) as an electron donor. The Ni(II) complex shows a high turnover number over 700 with high CO selectivity of >99% and quantum yield of 1.42% in the photocatalytic system.

By-Product-Free Siloxane-Bond Formation and Programmed One-Pot Oligosiloxane Synthesis.

Siloxane bonds are usually synthesized by condensation reactions, such as hydrolysis/dehydration and cross-coupling reactions, in which the generation of by-products during bond formation can not be avoided. We have developed a one-pot sequence of iridium-catalyzed silyl ester hydrosilylation and boron-catalyzed rearrangement of the resulting disilyl acetals for the construction of siloxane bonds, in principle without the formation of any by-products. Moreover, the programmed synthesis of tri-, tetra-, and pentasiloxanes was possible in a single flask by combining the above sequence of iridium-catalyzed hydrosilylation and boron-catalyzed rearrangement with a boron-catalyzed cross-coupling reaction.

Buttressing Salicylaldehydes: A Multipurpose Directing Group for C(sp )-H Bond Activation.

A palladium-catalyzed reaction of primary amines with iodoarenes produces γ-arylated primary amines. A bulky salicylaldehyde, which is marked as easily available, installable, removable, and recoverable, plays a key role in directing palladium to site-selectively activate the C-H bond located γ to the amino group.

Development of Nickel Hydrosilylation Catalysts.

In this account, our studies on nickel-catalyzed hydrosilylation reactions are described. A series of (salicylaldiminato)methylnickel complexes efficiently catalyze alkene hydrosilylation under ambient reaction conditions. Commercially available Ni(II) salts, Ni(acac) (acac = acetylacetonato) and its derivatives bis(hexafluoroacetylacetonato)nickel(II) and bis (2,2,6,6-tetramethyl-3,5-heptanedionato)nickel(II), also act as versatile hydrosilylation catalyst precursors in the presence of NaBHEt .

PNP-Pincer-Type Phosphaalkene Complexes of Late Transition Metals.

This account summarizes our recent studies on PNP-pincer-type phosphaalkene complexes. Phosphaalkenes with a P=C bond possess an extremely low-lying π* orbital and have a marked tendency to engage in strong π back-bonding with transition metals. This particular ligand property provides PNP-pincer complexes with unique structures and reactivities.

A kinetic model for flavonoid production in tea cell culture.

As one of the strategies for efficient production of a metabolite from cell cultures, a kinetic model is very useful tool to predict productivity under various culture conditions. In this study, we propose a kinetic model for flavonoid production in tea cell culture based on the cell life cycle and expression of PAL, the gene encoding phenylalanine ammonia-lyase (PAL)-the key enzyme in flavonoid biosynthesis. The flavonoid production rate was considered to be related to the amount of active PAL.

Reactions of [Cu(X)(BPEP-Ph)] (X = PF6, SbF6) with silyl compounds. Cooperative bond activation involving non-coordinating anions.

Bond activation of silyl compounds, assisted by the cooperative action of non-coordinating anions, is achieved using Cu(I) complexes coordinated with a PNP-pincer type phosphaalkene ligand, [Cu(X)(BPEP-Ph)] (X = PF6 (1a), SbF6 (1b); BPEP-Ph = 2,6-bis[1-phenyl-2-(2,4,6-tri-tert-butylphenyl)-2-phosphaethenyl]pyridine). Complexes 1a and 1b react with Me3SiCN to form Me3SiF and Cu(i) cyanide complexes of the formula [Cu(CN-EF5)(BPEP-Ph)] (E = P (2a), Sb (2b)), in which the CN ligand is associated with the EF5 group arising from EF6(-). Formation of the intermediary isonitrile complex [Cu(CNSiMe3)(BPEP-Ph)](+)SbF6(-) (3b) is confirmed by its isolation.

Salt-Free Reduction of Nonprecious Transition-Metal Compounds: Generation of Amorphous Ni Nanoparticles for Catalytic C-C Bond Formation.

A salt-free procedure for the generation of a wide variety of metal(0) particles, including Fe, Co, Ni, and Cu, was achieved using 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (1), which reduced the corresponding metal precursors under mild conditions. Notably, Ni particles formed in situ from the treatment of Ni(acac)2 (acac = acetylacetonate) with 1 in toluene exhibited significant catalytic activity for reductive C-C bond-forming reactions of aryl halides in the presence of excess amounts of 1. By examination of high-magnification transmission electron microscopy images and electron diffraction patterns, we concluded that amorphous Ni nanoparticles (Ni aNPs) were essential for the high catalytic activity.

Activation of Homolytic Si-Zn and Si-Hg Bond Cleavage, Mediated by a Pt(0) Complex, via Novel Pt-Zn and Pt-Hg Compounds.

The thermally stable [(tBuMe2 Si)2 M] (M=Zn, Hg) generate R3 Si(.) radicals in the presence of [(dmpe)Pt(PEt3 )2 ] at 60-80 °C. The reaction proceeds via hexacoordinate Pt complexes, (M=Zn (2 a and 2 b), M=Hg (3 a and 3 b)) which were isolated and characterized.