Deprotonation/protonation of coordinated secondary thioamide units of pincer ruthenium complexes: modulation of voltammetric and spectroscopic characterization of the pincer complexes

New pincer ruthenium complexes, [Ru(SCS)(tpy)]PF(6) (1) (SCS = 2,6-bis(benzylaminothiocarbonyl)phenyl), tpy = 2,2':6',2'-terpyridyl) and [Ru(SNS)(tpy)]PF(6) (2) (SNS = 2,5-bis(benzylaminothiocarbonyl)pyrrolyl), having κ(3)SCS and κ(3)SNS pincer ligands with two secondary thioamide units were synthesized by the reactions of [RuCl(3)(tpy)] with N,N'-dibenzyl-1,3-benzenedicarbothioamide (L1) and N,N'-dibenzyl-2,5-1H-pyrroledicarbothioamide (L2), respectively, and their chemical and electrochemical properties were elucidated. The structure of 1 was determined by X-ray crystallography. The complexes 1 and 2 showed a two-step deprotonation reaction by treatment with 1,8-diazabicyclo[5,4,0]undec-7-ene (DBU), and the addition of DBU led to a shift of the metal-centered redox couples to a lower potential by 720 and 550 mV, respectively. The di-deprotonated complexes were also studied by (1)H-NMR and UV-vis spectroscopy. The addition of methanesulfonic acid (MSA) to the di-deprotonated complexes enabled the recovery of 1 and 2, indicating that the thioamide moiety underwent a reversible deprotonation-protonation process, which resulted in regulating the redox potentials of the metal center. The Pourbaix diagram of 1 revealed that 1 underwent a one-proton/one-electron transfer process in the pH range of 5.83-10.35, and a two-proton/one-electron process at a pH of over 10.35, indicating that the deprotonation/protonation process of the complexes is related to proton-coupled electron transfer (PCET).     

Versatile bridging ability of secondary thioamide group for constructing metal cluster based on pincer complex

The crystallization of the SCS pincer platinum complex with secondary thioamide groups, [4-methyl-2,6-bis(anilinothiocarbonyl)-κ²S,S’-phenyl-κC¹]chloroplatinum(II), spontaneously forms a trinuclear cluster complex accompanied by liberating HCl in DMSO/EtOH mixture. The crystal structure of the SNS pincer copper complex with secondary thioamide groups, [2,5-bis(benzylaminothiocarbonyl)-κ²S,S’-pyrrolyl-κN¹]chlorocopper(II), exhibits a dimer structure bearing the bridging thioamide group. The thioamide group acts as the bridging ligand of the multimetallic complexes in different anionic and neutral manners.     

Fabrication of arrays of sub-20-nm silica walls via photolithography and solution-based molecular coating

We report herein fabrication of arrays of sub-20-nm silica walls via photolithography and the surface sol-gel process. A photolithographically fabricated line template on a silicon wafer was coated with a silica nanolayer using the surface sol-gel process, and then the topmost portion of the silica layer and the template were successively removed using CHF(3) and oxygen plasma, respectively, leaving the sidewalls of the silica layers remaining on the substrate. These walls were fully self-supporting, and the thicknesses of silica wall were 6, 8, and 12 nm at 20, 30, and 60 cycles, respectively. The height/width ratio of the wall was 38 at the 30-cycle coating. This ratio is surprisingly high when compared to that of the conventional photolithography processes. Successive formation of the silica, polymer, and silica layers yielded a trilayer sidewall, and the spacer polymer layer could be selectively removed to form a doubled sidewall. Size reduction and proliferation of sub-20-nm silica wall was thus achieved. The reported method is simple and cost-efficient and opens a gateway to further miniaturization of nanostructures.     

Linear stability of a two-dimensional uniform fluidized bed

Basic equations in a two-dimensional fluidized bed are constructed for the particle and the fluid phases, and linear stability to two-dimensional disturbances of the volume fractions and the velocities of both phases is analyzed. The diffusion of particles and an effective viscosity in the particle phase are considered. It was found that the inertia term due to the average fluid velocity is responsible for the instability, while the particle diffusion and the effective particle viscosity suppress the growth of disturbances. It was also found that the most unstable state has a vertical wavenumber vector.     

Convenient Synthesis of 2‐Amino‐4H‐chromenes from Photochemically Generated o‐Quinone Methides and Malononitrile

2‐Amino‐4H‐chromenes were synthesized in moderate to good yields by the reaction of o‐quinone methides photochemically generated from o‐(dimethylaminomethyl)phenols with malononitrile. This method was applicable to the synthesis of fluorinated chromenes that were difficult to obtain by other methods. In addition, o‐(hydroxymethyl)phenols could be used for the reaction in the presence of tertiary amine bases.     

Multipoint barrier discharge process for removal of NOxfrom diesel engine exhaust

We investigated the application of the dielectric barrier discharge process to the removal of NO_x from exhaust gas of a 20-kVA diesel engine generator. A multipoint-to-plane geometry was used as an electrode for low-voltage operation. A pyrex glass plate with a 2-mm thickness was put on the plane electrode as the dielectric barrier. The reactor consists of six discharge cells, with each cell consisting of five stacked multipoint-to-plane electrodes where the exhaust gas flows with a high flow rate. The exhaust gas was successfully treated at a flow rate of 1.2 m³/min, In order to produce repetitive high-voltage pulse, we made two switching electronic devices, an insulated gate bipolar transistor (IGBT), and a pulse transformer. This pulse modulator supplied the voltage with peak value of 10 kV and repetition rate of 2.5 kp/s (pulses per second) to the reactor. The energy transfer efficiency of the pulse modulator is 65% at 300 W of the power consumed in the reactor, The NO_x (NO+NO₂) in the exhaust gas was reduced by 35 ppm with an electrical efficiency of 32 g/kWh     

Regioregulated Syntheses of Poly(aminopyridine)s by Pd‐catalyzed Amination Reaction

Regioregulated poly(aminopyridine)s were synthesized by a Pd‐catalyzed C N coupling reaction. The polymerization using Pd(0) and a bulky monodentate phosphine ligand distinctively produced the para‐linked and meta‐linked poly(aminopyridine)s, without the need for a protection process. The regioregularity of the polymer was confirmed by ¹H NMR spectroscopy. Model reactions were studied to evaluate the possibility of crosslinkage in the polymer. A large difference in reactivity was observed between 5‐amino‐2‐bromopyridine and 2‐amino‐5‐bromopyridine, which should have afforded same product. Density functional theory (DFT) calculations indicated that electron densities of the Br‐bound carbon atom and the pyridine‐nitrogen atom determine the reactivity of the monomers.

     

p-Phenylenediamine Epoxy Resin Film for Redox Enzyme Detection

Summary: Phenylenediamine derivatives (PDs) are environmentally hazardous, though very useful for chemical analysis. To minimize release into the environment, a PD-containing epoxy resin film was developed that retained redox enzyme activity. p-Phenylenediamine and 2,2-bis(4-glycidyloxyphenyl)-propane were cured to produce a violet film. This film was reactive against peroxidase, a redox enzyme that oxidizes phenylenediamine to afford an imine. Enzymatic oxidation caused the film to change color from violet to deep green. The film exhibited fluorescence at 394 nm under excitation at 350 nm, and the fluorescent intensity decreased with greater oxidation. Thus, the film could be used to detect redox enzyme activity.