Kazuhiko Takeuchi

Oxidative carbonylation of phenol to diphenyl carbonate catalyzed by Pd–carbene complexes

Abstract Various Pd–carbene complexes with bis(heterocyclic carbene) ligands were prepared and was investigated their catalytic activity for oxidative carbonylation of phenol with carbon monoxide to diphenyl carbonate (DPC). The catalyst system was composed of Pd complex, inorganic redox cocatalyst, organic redox cocatalyst, organic salt, and molecular sieve. The Pd–carbene complex systems PdBr 2 (c1- t Bu )/Ce(TMHD) 4 (TMHD: 2,2,6,6-tetramethyl-3,5-heptanedionate)/ n Bu 4 NBr /hydroquinone showed approximately a double activity compared to a conventional PdBr 2 catalytic system without the use of ligands.

Hydrogenation of carbon monoxide over highly dispersed cobalt catalysts derived from cobalt(II) acetate

Abstract Highly dispersed cobalt metal catalysts supported on SiO2 were prepared by using cobalt(II) acetate as a precursor promoted with noble metals such as Ir, Ru, Rh, Re, Pt or Os. The catalysts were active for the formation of oxygenates by CO hydrogenation and the vapor phase hydroformylation of ethene. The selectivity of oxygenates, especially C2-oxygenates, was strongly enhanced by a further modification with basic additives such as alkali and alkaline earth cations. By the characterization of the catalysts using XPS, EXAFS, XRD, FT-IR, etc., it is revealed that highly dispersed Co2+ particles are formed on SiO2 by the decomposition of Co(II) acetate at an elevated temperature in flowing H2. The noble metals promote the reduction of the Co2+ particles to cobalt metals by spilt-over hydrogen activated on the noble metal sites. The effects of the basic additives were discussed.

Oxygenates from syngas over highly dispersed cobalt catalysts

Highly dispersed cobalt metal catalyst has been prepared by the deposition of Co2(CO)8 on silicagel in an oxygen-free condition and has been characterized with EXAFS. This catalyst exhibited high activity for the formation of C2+ oxygenates from syngas without any modification. The formation of hydrocarbons was strongly suppressed and the selectivity of oxygenates, especially C2-oxygenates, was enhanced by the modification with alkali or alkaline earth cations. From the modification effects on CO hydrogenation and by the studies of in situ FT-IR, these basic cations were considered to reduce the hydrogenating ability of the catalyst by controlling the electronic state of the active cobalt site. Noble metals such as iridium and ruthenium have little effect on the catalyst of CO hydrogenation. Similar cobalt catalysts were prepared from C02(CO)8 on other oxide supports and some oxides showed a similar effect on the basic additives. The effect of the cations and the reaction mechanism for the formation of oxygenates were discussed.

An environmentally benign process for aromatic polycarbonate synthesis by efficient oxidative carbonylation catalyzed by Pd-carbene complexes

The direct synthesis of diphenyl carbonate (DPC) and polycarbonate (PC) by oxidative carbonylation was investigated. A palladium catalyst anchored to a resin via a heterocyclic carbene ligand exhibited high performance in DPC synthesis, and the total turnover number (TON) achieved 5100 (mol-DPC/mol-Pd). Bisphenol A was also effectively converted to high molecular weight PC (Mw 22,400) at 95% yield.

A novel catalyst for methanol synthesis

Abstract A novel catalyst for methanol synthesis has been prepared from a solution of copper and zinc nitrates dissolved in ethylene glycol. The highest selectivity for methanol was obtained for a catalyst containing Cu and ZnO with a Cu/Zn ratio of 1/1. By iterative oxidation and reduction of the catalyst, the active sites were concluded to be copper atoms in contact with copper crystallites.

THE PROMOTER FUNCTION OF MOLYBDENUM IN RH/MO/SIO2 CATALYSTS FOR CO HYDROGENATION

A series of Rh/Mo/SiO2 catalysts with fixed Rh and different Mo contents were studied by FT-IR, chemisorption and CO hydrogenation. The FT-IR results at room temperature under CO atmosphere indicate that the addition of Mo to Rh/SiO2 suppresses the linear and bridged CO species and promotes the twin CO species, which is consistent with the chemisorption results. It is suggested that the Mo promoter works via stabilization of Rh1– ions and the coverage of Rh sites. The molybdenum promotes the formation of oxygenates and shifts the selectivity from hydrocarbons to oxygenates.

The synthesis of polyesters with a biphenyl skeleton by palladium catalyzed carbonylation-polycondensation

Abstract For synthesizing heat-resistant polyesters, the one step synthesis of biphenyl-containing polyesters was developed from palladium-catalyzed carbonylation-polycondensation of dihalobiphenyls and bisphenols. Reaction parameters, such as base, solvent, palladium-phosphine catalyst and CO pressure in the reaction of 2,7-dibromo-9,10-dihydrophenanthrene and 4,4′-(1-methylethylidene)bisphenol (bisphenol A), were found to affect the molecular weight of poly[oxy-1,4-phenylene(1-methyethylidene)-1,4-pheny-eneoxycarbonyl-(9,10-dihydro-2,7-phenanthrenediyl)carbonyl] (2). The solution after the reaction was homogeneous when high molecular weight polyester was formed. The use of strong base such as 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) yielded high molecular weight polyesters. Key step for the reaction is considered the alcoholysis step. High nucleophilicity of phenoxide anion formed from the phenol moiety and DBU enhanced the step to increase the rate of the carbonylation-polycondensation. The use of palladium catalyst with PPh 3 gave higher molecular weight polyester than that with Ph 2 P(CH 2 ) 3 PPh 2 in spite of higher catalytic activity of the latter catalyst. This is due to higher termination rate caused by the carbonylation of chlorobenzene for the latter catalyst. Under optimum conditions, polyester 2 was obtained in 95% yield with high molecular weight (polystyrene equivalent M W = 102 600 ). Bisphenols with sufficiently bulkyalkyl spacers, such as 4,4′-cyclohexylidenebisphenol, 4,4′-(s-butylidene)bisphenol, 4,4′-(1-phenylethyl-idene) bisphenol, 4,4′-ethylidenebisphenol, 4,4′-methylidenebis(2,6-dimethylphenol) and 4,4′-(1-methylethylidene)bis(2,6-dimethylphenol) gave polyesters with high to moderately high molecular weight. On the basis of a thermal analysis, 5% weight loss temperature ( T 5 ) and 10% weight loss temperature ( T 10 ) of 2 in air was 394 and 414°C, respectively.

Palladium-catalyzed carbonylation of aryl bromides and iodides with potassium phenoxides

Abstract Palladium-catalyzed aryloxycarbonylation of aryl bromides and iodides show contrastive reactivities with respect to the kind of phenoxides. The carbonylation of bromides with hindered potassium phenoxides in benzene gives ester products in high yields, while that with non-hindred PhOK gives almost no ester product under the same conditions. In contrast, the carbonylation of iodides with hindered potassium phenoxides gives no ester, while that with non-hindered PhOK provides ester products in high yields. Variant reductive elimination steps from aroyl palladium halide species to ester products and Pd(0) species are proposed depending on the steric and electronic properties of the phenoxides and aryl halides. They involve a stepwise ligand exchange path and a concerted path.

Colloidal rhodium catalyzed photo transfer hydrogenation of 1,5-cyclooctadiene

Abstract Colloidal rhodium particles, photochemically generated from Rh 4 CO) 12 , via transfer hydrogenation, photochemically catalyzed the transformation of 1,5-cyclooctadiene (1,5-COD) to cyclooctene (COE) and then to cyclooctane (COA) in the presence of acetone, a triplet sensitizer, and 2-propanol, a hydrogen donor. The hydrogenation rate of 1,5-COD was faster than that of COE by a factor of 4.3. Maximum selectivity of COE was found to be 85%.

Characterization of an oxide semiconductor prepared by microwave sintering

We fabricated a thin-film transistor (TFT) using amorphous indium gallium zinc oxide (a-IGZO), which was formed through annealing of an IGZO precursor film with a single-mode cavity microwave at 2.45 GHz. The transisitor fabricated with the a-IGZO film prepared by microwave annealing for 15 min showed higher device performance, i.e., a field effect mobility of 5.75 × 10−2 cm2·V−1·s−1, an on/off ratio of 106, and a threshold voltage of 20 V, than that prepared by annealing with a conventional oven for 120 min. The Raman spectra confirm that the device improvement originates from the decrease in the number of –OH groups and removal of organic species for 15 min by microwave annealing. These results suggest that the microwave annealing method has an advantage as the annealing process of solution-processed oxide semiconductors to reduce the process time. It can be applied to the fabrication of TFTs.