Nucleic acids often acquire new functions by forming a variety of complexes with metal ions. Osmium, in an oxidized state, also reacts with C5-methylated pyrimidines in the presence of bipyridine to give a stable ternary complex. We have designed a bipyridine-attached adenine derivative for sequence-specific osmium complexation. Sequence-specific osmium complexation was achieved by hybridization of a short DNA molecule containing this functional nucleotide to a target DNA sequence, and resulted in the formation of a crosslinked structure. The interstrand crosslink clearly distinguished methylated cytosines from unmethylated cytosines, and was used to quantify the degree of methylation at a specific cytosine in the genome.
Porphyrin has been receiving much attention in the wide area of science. Porphyrins generally accommodate a variety of metals in the central cavity. The central metal often plays a critical role to dominate electronic and structural properties of a metalloporphyrin. In contrast, porphyrins which have carbon-metal bond at the porphyrin peripheral remain unexplored. In particular, porphyrins with a peripheral carbon-transition metal σ-bond are very rare. However, we have demonstrated that borylated porphyrins are versatile synthetic intermediates for the creation of novel porphyrin derivatives. Furthermore, porphyrins with a carbon-transition metal bond have exhibited unique structural features and catalytic activity.
The utility of transition metal-catalyzed reactions with organic sulfur compounds, which have been known to act as a “catalyst poison”, has not been well-studied until recently. However, ever since the Pd-catalyzed cis-addition of diaryl disulfides to terminal alkynes was reported in 1991, a variety of regio- and stereoselective metal-catalyzed addition reactions of the compounds with S-G bonds (G; element or group) to unsaturated compounds have been developed. We herein review our achievements: (1) Pd-catalyzed addition of diaryl disulfide to isocyanide, (2) Pd-catalyzed reactions with sulfenamides, carbon monoxide, and terminal alkynes, (3) oxidative additions of S-C bonds of vinyl sulfides and thioesters to Pt(0)-complex and the application to a series of carbothiolations and a unique one-pot cyclization, (4) thermal and photo-promoted insertions of terminal and internal alkynes into S-M (M = Pd, Pt) bonds, “o-halogen effect”, and the application to catalytic reactions, and (5) photo- and -thiol driven trans insertion of phenylacetylene into H-Pt bonds.
The three main parts; i.e., the preparations, structures and reactions of the 1-benzotelluropyrylium salts are described. The synthetic workup has been achieved by transformation from the tellurochromones, which were simply prepared by the reaction of the o-bromophenyl ethynyl ketones with sodium hydrogen telluride (NaHTe). The synthetic method for the preparation of the tellurochromones is based on the intramolecular ring closure of a tellurol moiety into a triple bond. The study shows that these salts, although being stable compounds, are highly reactive with various nucleophiles including OMe-, diethylamine, CN-, an active methylene compound and Grignard reagents, and also hydrogenation and hydrolysis to afford the successful corresponding 2- or 4-substituted tellurochromene derivatives. The chemistry of the 1-benzoselenopyrylium salts is also described. The thermolysis of the 2-azidoselenochromenes, which were easily obtained by the reaction of the selenopyrylium salts with sodium azide, resulted in a ring expansion to produce the novel stable 1,3-benzoselenazepines. X-ray structural analyses of the tert-butyltelluro- and selenopyrylium salts are also reported.
Facile synthesis of ruthenium, palladium and platinum nanoparticles supported on three types of carbon nanofibers (platelet: CNF-P, tubular: CNF-T, herringbone: CNF-H) is accomplished by pyrolysis of ruthenium carbonyl clusters, and pyrolysis and hydrogenolysis of Pd2(dba)3·CHCl3 and Pt(dba)2 [dba: dibenzylideneacetone]. TEM studies of these M/CNFs revealed that size-controlled metal nanoparticles existed on the CNFs, and that of the location was dependent on the surface nanostructures of CNFs: On the edge of the graphite layers (CNF-P), in the tubes and on the surface (CNF-T), and between the layers and on the edge (CNF-H). Among these M/CNFs, the Ru/CNF-P showed excellent catalytic activity towards arene hydrogenation with high reusability and functional group tolerance. The present Ru system is applicable to the production of octahydro-1,1'-binaphthyls by partial hydrogenation of 1,1'-binaphthyls. While the Pt/CNF-P behaves as an efficient catalyst for hydrogenation of substituted nitroarenes to the corresponding aniline derivatives with other functional groups remaining intact.
Nitrogen-containing compounds, such as amines, imines, and enamines, are of importance not only as bulk chemicals but also as fine chemicals and pharmaceuticals. Among the various methods for the synthesis of such compounds, the simple addition of an N-H bond to a C-C double or triple bond, which is referred to as hydroamination, offers an attractive route to the synthesis of highly substituted nitrogen-containing organic molecules without the formation of any side products. Catalytic hydroamination has achieved remarkable development during the last decade. A wide variety of metals, including early- and late-transition metals, lanthanides, and actinides are currently employed in the area of catalytic hydroamination. This review summarizes the transition-metal catalyzed hydroamination of alkenes, alkynes, allenes, and 1,3-dienes. Mechanistic aspects of the reaction, which can be classified into five groups on the basis of C-N bond formation steps in the catalytic cycle, are also described.
Chiral imidazolidinone derivatives are important catalysts for asymmetric syntheses via iminium or enamine intermediates. In this short review, recent reports on catalytic enantioselective α-allylation and α-alkylation of aldehydes via radical species by using the organocatalysts are introduced.