Recent examples for precise synthesis of multi-block, brush, and star polymers by (living) ring-opening metathesis polymerization (ROMP) using Mo, Ru catalysts have been reviewed. Unique characteristics of the living ROMP initiated by the Mo-alkylidene (so-called Schrock type) complexes, which accomplish a precise control of the block segment as well as an exclusive introduction of functionality at the polymer chain end, provide the synthesis of block copolymers varying different backbones by adopting the “grafting to” or the “grafting from” approach. The technique also demonstrated controlled synthesis of soluble star shape polymers containing functionalities on the surface. The “grafting through” approach (polymerization of macromonomers) by the repetitive ROMP technique by the Mo catalysts offers a precise control of the block segments and the end functionalization. The recent progress using so called 3rd generation Grubbs Ru catalyst also demonstrates controlled syntheses of brush/graft copolymers with high degree of (macro) monomer repeating units. These efforts should introduce promising possibilities for evolution of new advanced materials by precise placement of functionalities/segments.
Nickelacycles have been known as a key reaction intermediate. The β-hydrogen transfer reactions from nickelacycles allow us to synthesize acyclic organic compounds. The reductive elimination from nickelacycles allows us to synthesize a variety of cyclic organic compounds. Thus, the generation of a new nickelacycles from a new combination of unsaturated compounds and nickel(0) species is a key to develop nickel-catalyzed new reactions. We report here the new molecular transformations of a variety of unsaturated compounds via nickelacycles in which both acyclic and cyclic compounds were obtained. In addition, the isolation of the reaction intermediates and their reaction mechanisms are discussed as well.
The half-sandwich mono- and dialkyl rare earth metal complexes are prepared either by the alkane elimination reactions or by the metathetical reactions. Half-sandwich scandium alkyl complex bearing the silylene-linked cyclopentadienyl-amido ligand can serve as a unique catalyst for the ortho-selective C-H silylation of various alkoxy-substituted benzene derivatives without requirement for a hydrogen acceptor to achieve high conversion. The reaction of the dialkyl complexes with an equivalent of a borate compound such as [Ph3C][B(C6F5)4] generates easily the corresponding cationic monoalkyl species, which serve as excellent catalysts for the polymerization and copolymerization of a variety of olefins to yield a new family of polymer materials that show novel properties but are difficult to prepare by other catalysts. Mechanistic aspects of these catalytic processes are also described.
In recent years, nanostructured materials such as carbon nanotubes, polymer nanotubes, metal nanotubes, and metal nanoparticles have received a great deal of attention due to their unique physical and chemical properties as well as their enormous potential applications such as catalysts, nanoelectronic devices, magnetic devices, sensors, and biomaterial separation membranes. Although several methods have been developed to functionalize carbon nanotubes with inorganic and organic materials, related works on π-conjugated polymer nanotubes such as polythiophene and metal nanotubes have been reported in only a few cases. In particular, the combination of conducting polymers and metal nanoparticles provides an exciting system to investigate with the possibility of designing nanotube functionality. However, the preparation of nanotube composites consisting of metal nanoparticles and polythiophene as a constituent of nanotubes by electropolymerization of thiophene-modified metal nanoparticles has never been reported. We have developed a new method for the fabrication of metal nanoparticle/polythiophene nanotube composites, i.e., the template-based electrochemical oxidative polymerization of terthiophene-linked-thiol and -phosphine-stabilized gold and palladium nanoparticles in a nanoporous alumina membrane as a template gave the hybrid nanotubes of polythiophene and the metal nanoparticles without aggregation of the metal nanoparticles. This article describes the synthesis and functionalization of metal nanoparticles and polythiophene, and their hybrid nanotubes.
We synthesized the novel electron-poor bidentate ligand (MeO-F12-BIPHEP), which has 3,4,5-trifluorophenyl groups. The large ligand-acceleration effect (LAE) by MeO-F12-BIPHEP was shown in the Rh-catalyzed asymmetric 1,4-addition of arylboronic acid to α,β-unsaturated ketone. The turnover frequency and the turnover number reached 53,000 h-1 and 320,000 cycles, respectively. This large acceleration results from electron-poor nature of MeO-F12-BIPHEP. However, highly electron-poor MeO-F28-BIPHEP showed less catalytic activity for Rh-catalyzed asymmetric 1,4-addition, because of its large cone angle. To avoid steric bulkiness, we developed the MeO-BFPy-BIPHEP. It showed highly electron poor nature as well as MeO-F28-BIPHEP, and had moderate bulkiness as well as MeO-F12-BIPHEP. The MeO-BFPy-BIPHEP accelerated the Rh-catalyzed asymmetric arylation of N-Ts-imine. The turnover frequency was over 10,000 h-1. In the metal-catalyzed reaction, such electron-poor phosphines accelerated transmetalation, migratory insertion, and reductive elimination steps.
The development of biomimetic reactions is one of the major challenges for synthetic chemists, because mimicking these complicated reactions in the laboratory by simple catalytic systems is difficult to achieve in general. Vitamine B6-dependent aminotransferase-catalyzed transamination of α-keto acids from pyridoxamine is an important process to generate α-amino acids in nature. In this review, recent progresses on the biomimetic transamination of α-keto esters are described.