Munetaka Akita

An M2L4 Molecular Capsule with an Anthracene Shell: Encapsulation of Large Guests up to 1 nm

A new M(2)L(4) molecular capsule with an aromatic shell was prepared using two Pd(II) ions and four bisanthracene ligands. The self-assembled capsule possesses a cavity with a diameter of ~1 nm that can encapsulate medium-sized spherical and planar molecules as well as a very large molecule (C(60)) in quantitative yields. The encapsulated guests are fully segregated and shielded from the external environment by the large anthracene panels.

Combining photoredox-catalyzed trifluoromethylation and oxidation with DMSO: facile synthesis of α-trifluoromethylated ketones from aromatic alkenes.

Trifluoromethylated ketones are useful building blocks for organic compounds with a trifluoromethyl group. A new and facile synthesis of ketones with a trifluoromethyl substituent in the α-position proceeds through a one-pot photoredox-catalyzed trifluoromethylation-oxidation sequence of aromatic alkenes. Dimethyl sulfoxide (DMSO) serves as a key and mild oxidant under these photocatalytic conditions. Furthermore, an iridium photocatalyst, fac[Ir(ppy)3 ] (ppy=2-phenylpyridine), turned out to be crucial for the present photoredox process.

Oxidative cleavage of silicon-carbon bonds in organosilicon fluorides to alcohols

Abstract Certain functional silyi groups have been shown to be synthetically equivalent to the OH group. All of the C-Si bonds in organosilicon fluorides, K 2 (RSiF 5 ] and R n SiF 4-n , (n = 1,2,3) are cleaved by m-chloroperbenzoic acid (MCPBA) in DMF to give the corresponding alcohols in high yields. Although the reaction with RSiF 5 2- and RSiF 3 proceeds without any additive, cleavage of R 2 SiF 2 and R 3 SiF requires, respectively, a catalytic or excess amount of KF. A triorganoethoxysilane also undergoes similar oxidative cleavage reactions in the presence of an excess amount of KF. The MCPBA-oxidation of exo - and endo -2-norbornyl-silicate and -trifluorosilane proceeds stereospecifically with retention of configuration at carbon. A remarkable solvent effect has been observed in the oxidative cleavage of RSiF 3 . A plausable mechanism involves a hexacoordinate silicon species in which the organic group intramolecularly migrates from Si to O of the coordinated MCPBA.

Trifluoromethylation by Visible-Light-Driven Photoredox Catalysis

The trifluoromethyl group widely prevails in pharmaceutical and agrochemical compounds, while accompanying by the development of new methodologies for trifluoromethylation. Recently, the radical trifluoromethylation by photoredox catalysis has emerged. This Article describes several pioneering works and their representative mechanisms via generation of the trifluoromethyl radical based on photoredox processes.

Highly Regio- and Diastereoselective Synthesis of CF3-Substituted Lactones via Photoredox-Catalyzed Carbolactonization of Alkenoic Acids

Trifluoromethylative lactonization of both terminal and internal alkenoic acids by photoredox catalysis has been developed. The use of a Ru photocatalyst and Umemotos reagent as a CF3 source is key in the present carbolactonization. This is the first example of a highly endo- and diastereoselective synthesis of CF3-substituted five-, six-, and seven-membered ring lactones from internal alkenoic acids.

Visible-light radical reaction designed by Ru- and Ir-based photoredox catalysis

Photoredox catalysis by well-known ruthenium(II) polypyridine complexes and the relevant Ir cyclometalated derivatives has become a powerful tool for redox reactions in synthetic organic chemistry, because they can effectively catalyze single-electron-transfer (SET) processes by irradiation with visible light. Remarkably, since 2008, this photocatalytic system has gained importance in radical reactions from the viewpoint of not only a useful and selective protocol but also green chemistry. In this review, we will describe recent developments of radical reactions involving various carbon-centered radicals through photoredox processes mediated by Ru- and Ir-based photocatalysts.

Spin Crossover by Encapsulation

Encapsulation by synthetic hosts can transform the spin states of square planar Ni(II)(acen) and Co(II)(tap) complexes. Upon encapsulation, the red Ni(II) diamagnetic state was converted into a green paramagnetic state, whereas the Co(II) low spin (S = 1/2) state was changed into a coupled (S = 1/2 and S = 3/2) state. The host cages are noninnocent and host-guest interactions within the confined cavity influence the resultant properties of the enclathrated metal complexes.

Selective Host–Guest Interactions of a Transformable Coordination Capsule/Tube with Fullerenes

An M2L4 coordination capsule or an M2L2 coordination tube was selectively formed by the combination of Hg(II) hinges and bent bispyridine ligands. The two structures reversibly interconvert at room temperature in response to modulation of the metal-to-ligand ratio and exhibit different host-guest interaction behavior. The capsule alone encapsulates large spherical molecules, fullerenes C60 and C70, and the bound guests are released upon capsule-to-tube transformation by the simple addition of metal ions.

Facile Catch and Release of Fullerenes Using a Photoresponsive Molecular Tube

A novel M2L2 molecular tube capable of binding fullerene C60 was synthesized from bispyridine ligands with embedded anthracene panels and Ag(I) hinges. Unlike previous molecular cages and capsules, this open-ended tubular host can accommodate a single molecule of various C60 derivatives with large substituents. The fullerene guest can then be released by using the ideal, noninvasive external stimulus, light.

Engineering Double to Quintuple Stacks of a Polarized Aromatic in Confined Cavities

Discrete, well-defined stacks of the polarized aromatic pyrene-4,5-dione (1) were assembled in the cavities of organic-pillared coordination cages (2). The number (n) of stacked guests depends on the pillar length, and up to quintuple stacks (n = 5) were observed when long (16.5 A) organic pillar ligands were incorporated. As previously reported, pyrene-4,5-dione (1) assembles into infinite columnar stacks in the solid state, but the present work demonstrates that the polarized 1 has a strong propensity to stack in layers even in the absence of crystal packing effects. For n = 2 and 3 structures, crystallographic studies revealed that 1 stacks by pi-pi interactions in the cavity in such a way that a net dipole moment is canceled. These results emphasize the important role of dipole-dipole interactions as well as pi-stacking interactions in the formation of columnar stacks of 1.