Ritsuko Nagahata

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.

Direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol using Pd–Cu based redox catalyst system

A catalyst system was designed for direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol. Besides Pd carbonylation catalyst, inorganic and organic redox cocatalysts were included in the catalyst system for in situ regeneration of active Pd species. Copper(II) acetate was used as inorganic redox cocatalyst and hydroquinone was found to give good results as organic redox cocatalyst. Efficiency of various bases, effect of a drying agent, and optimum reaction conditions for achieving high catalytic activity were also investigated in detail. Using suitable components of catalyst system and under optimum reaction conditions, a Pd turnover number of 250 could be obtained.

Photoisomerization of Stilbene Dendrimers: The Need for a Volume-conserving Isomerization Mechanism¶

Highly branched stilbene dendrimers were synthesized and their photochemical behavior was studied. Even the stilbene dendrimer with molecular weight over 6500 underwent trans–cis isomerization in the excited singlet state within the lifetime of 10 ns. The photoisomerization of C=C double bond of stilbene dendrimers in the excited state may proceed by a volume‐conserving novel mechanism such as hula‐twist rather than conventional 180° rotation around the C=C double bond based on fluorescence and isomerization experiments.

Solid‐phase thermal polymerization of macrocyclic ethylene terephthalate dimer using various transesterification catalysts

Thermal ring-opening polymerization of a uniform macrocyclic ethylene terephthalate dimer with and without catalyst was investigated for the first time. Although polymerization progressed without a catalyst, the reaction was extremely slow and all the products were colored. Various transesterification catalysts were tested for their activity toward this ring-opening polymerization. Among the various catalysts, 1,3-dichloro-1,1,3,3-tetrabutyldistannoxane exhibited the highest catalytic activity, and a colorless polymer with a weight-average molecular weight of 36,100 was obtained in 100% yield by heating for 3 min at 200 °C. It is noteworthy that our method does not need a vacuum because no side products are formed during the process.

Effect of inorganic redox cocatalyst on Pd‐catalyzed oxidative carbonylation of phenol for direct synthesis of diphenyl carbonate

A catalyst system for direct synthesis of diphenyl carbonate by oxidative carbonylation of phenol was investigated with special emphasis on the inorganic redox cocatalyst component. Besides the inorganic redox cocatalyst, the catalyst system was composed of a Pd carbonylation catalyst, an organic redox cocatalyst, a base and a drying agent. Ce(OAc)3·H2O was found to be the most efficient inorganic redox cocatalyst giving DPC in 76% yield with a Pd turnover number of 250 and without producing any major side products.

Direct synthesis of aromatic polycarbonate from polymerization of bisphenol A with CO using a Pd-Cu catalyst system

Abstract Direct polymerization of bisphenol A with CO was carried out using a Pd–Cu-based redox catalyst system. A base for activating the hydroxy group of bisphenol A and a dehydrating agent for removing the water produced during the reaction were other important components of the catalyst system. Synthesized polycarbonate was characterized using IR, NMR, and GPC. MALDI-TOF mass spectroscopy was used for understanding the structure of polymer chain end groups.

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.

Pd catalyzed polycarbonate synthesis from bisphenol A and CO: control of polymer chain—end structure

Abstract Direct polymerization of bisphenol A with CO was carried out using a catalyst system constituted of a Pd carbonylation catalyst, an inorganic redox catalyst, an organic redox cocatalyst, a base and a dehydrating agent. Usage of Cu(OAc)2 as inorganic redox cocatalyst led to the synthesis of polycarbonate of Mw 3600 but the formation of o-phenylene carbonate (o-PC) and salicylic acid type groups at the chain ends was observed. In an attempt to eliminate end group formation and explore the possibility of higher molecular weight polymer synthesis, various modifications were made in the catalyst system. On replacing Cu with Ce, o-PC formation could be eliminated completely. In addition, the usage of bis(triphenylphosphoranylidene) ammonium bromide (PPNBr) instead of tetrabutylammonium bromide [n(Bu)4NBr] resulted in elimination of acid group formation leading to the synthesis of polymer of Mw 3.8×10 3 (determined by GPC), with hydroxy group at both chain terminii. Polymer structure was investigated in detail by IR, NMR, and MALDI-TOF-MS studies.

Novel usage of palladium complexes with P-N-P ligands as catalysts for diphenyl carbonate synthesis

Two palladium complexes with P-N-P ligands [Pd{(sPPh(2))(2)N}(2)]{Pd(S,S)} and [Pd{(SePPh)(2)N}(2)] {PPd(Se,Se)} were prepared and investigated as novel polladium catalysts for oxidative carbonylation of phenol using carbon monoxide and oxygen along with a redox catalyst (for in situ regeneration of palladium) and ammonium halide, The efficiency of these new catalysts was compared with that of a PdCl2-based catalyst system. In order to obtain the maximum efficiency, the effects of various parameters such as concentration of redox catalyst and ammonium halide, the effect of solvent, the influence of a quinone-type redox catalyst in addition to inorganic redox catalyst, and the effect of temperature were studied, Under the reaction conditions employed, the Pd(S,S) catalyst was found to perform better than PdCl2-based catalyst system, whereas the Pd(Se,Se) catalyst had extremely low efficiency.

Rapid synthesis of dendrimers based on calix[4]resorcinarenes

Calix[4]resorcinarenes are phenolic macrocyclic compounds, and readily available from resorcinols and aldehydes. We were interested in calix[4]resorcinarenes as highly functionalized core molecules for the rapid synthesis of dendrimers because of their ease of synthesis and because they are less affected by steric constraints. Calix[4]resorcinarenes having 16 1 and 12 2 reactive hydroxy groups, respectively, were prepared as polyfunctional core molecules. The second-generation dendrimers were synthesized by the divergent method. The first-generation dendrimer 6 was obtained by etherification of 1 with 3,5-bis(allyloxy)benzyl bromide 5. After the deallylation of 6, etherification with 5 afforded the second-generation dendrimer 8. Dendrimers were characterized by 1H- and 13C-NMR, MALDI-TOF mass spectrometry and GPC. The molecular weight of second-generation dendrimers obtained from these calix[4]resorcinarenes and 5 reached 9345 and 7171, respectively.