Hikaru Takaya

Homogeneous catalysis in the decomposition of diazo compounds by copper chelates : Asymmetric carbenoid reactions

Abstract Bis9acetylacetonato)copper(II) catalyzes thermal decomposition of diphenyldiazomethane in benzene to afford tetraphenylethylene and benzophenone azine. The absence of 1,1,2,2-tetraphenylethane among the products is explained by assuming a copper carbenoid in which the carbene moiety is attached to the central copper atom as the fifth ligand. The apparently electrophilic nature of this carbenoid is illustrated by isolating cyclopropylamines upon reaction with enamines. Chemical evidence for the postulated coordination has been obtained by observing several instances of asymmetric synthesis, which proceed under influence of a chiral copper chelate, bis[N-( R )-α-phenethylsalicylaldiminato]copper(II), and its enantiomer. Following products have been obtained in partially resolved form from reactions of methyl or ethyl diazoacetate and diazomethane with appropriate optically inactive substrates: ethyl cis - and trans -2-phenylcyclopropanecarboxylate, methyl cis - and trans -3-phenyltetrahydrofuran-2-carboxylate, trans -1-methyl-2-phenylcyclopropane, trans -bicyclo[10.1.0]- cis -4, trans -8-tridecadiene and trans -bicyclo[10.1.0]-tridecane. Intramolecular cyclization of allyl diazoacetate and of 1-diazo-6-phenyl- trans -5-hexene-2-one occurs smoothly in the presence of the same copper chelate to afford 3-oxabicyclo[3.1.0]-hexan-2-one and 6-phenylbicyclo[3.1.0]hexan-2-one both in partially resolved state. The mechanism of these carbenoid reactions is discussed on the basis of further additional observations.

Iron-Catalyzed Suzuki−Miyaura Coupling of Alkyl Halides

In the presence of novel iron(II) chloride-diphosphine complexes and magnesium bromide, lithium arylborates react with primary and secondary alkyl halides to give the corresponding coupling products in good to excellent yields. High functional group compatibility is also demonstrated in the reactions of substrates possessing reactive substituents, such as alkoxycarbonyl, cyano, and carbonyl groups.

Iron-catalysed fluoroaromatic coupling reactions under catalytic modulation with 1,2-bis(diphenylphosphino)benzene

A catalytic amount of 1,2-bis(diphenylphosphino)benzene (DPPBz) achieves selective cleavage of sp(3)-carbon-halogen bond in the iron-catalysed cross-coupling between polyfluorinated arylzinc reagents and alkyl halides, which was unachievable with a stoichiometric modifier such as TMEDA; the selective iron-catalysed fluoroaromatic coupling provides easy and practical access to polyfluorinated aromatic compounds.

Partial Charge Transfer in the Shortest Possible Metallofullerene Peapod, La@C82⊂[11]Cycloparaphenylene

[11]Cycloparaphenylene ([11]CPP) selectively encapsulates La@C82 to form the shortest possible metallofullerene-carbon nanotube (CNT) peapod, La@C82 ⊂[11]CPP, in solution and in the solid state. Complexation in solution was affected by the polarity of the solvent and was 16 times stronger in the polar solvent nitrobenzene than in the nonpolar solvent 1,2-dichlorobenzene. Electrochemical analysis revealed that the redox potentials of La@C82 were negatively shifted upon complexation from free La@C82 . Furthermore, the shifts in the redox potentials increased with polarity of the solvent. These results are consistent with formation of a polar complex, (La@C82 )(δ-) ⊂[11]CPP(δ+) , by partial electron transfer from [11]CPP to La@C82 . This is the first observation of such an electronic interaction between a fullerene pea and CPP pod. Theoretical calculations also supported partial charge transfer (0.07) from [11]CPP to La@C82 . The structure of the complex was unambiguously determined by X-ray crystallographic analysis, which showed the La atom inside the C82 near the periphery of the [11]CPP. The dipole moment of La@C82 was projected toward the CPP pea, nearly perpendicular to the CPP axis. The position of the La atom and the direction of the dipole moment in La@C82 ⊂[11]CPP were significantly different from those observed in La@C82 ⊂CNT, thus indicating a difference in orientation of the fullerene peas between fullerene-CPP and fullerene-CNT peapods. These results highlight the importance of pea-pea interactions in determining the orientation of the metallofullerene in metallofullerene-CNT peapods.

Isolation and Characterization of the Cycloparaphenylene Radical Cation and Dication

Charged nanobelts: The radical cation and the dication of [8]cycloparaphenylene ([8]CPP) were prepared and isolated as hexahaloantimonate salts by the one- or two-electron chemical oxidation of [8]CPP with NOSbF6 or SbCl5 . ESR spectroscopy of CPP(.+) and single-crystal X-ray analysis of CPP(2+) demonstrated that the spin and charge were equally and fully delocalized over the para-phenylene rings.

Synthesis and physical properties of a ball-like three-dimensional π-conjugated molecule

Curved π-conjugated molecules with closed and three-dimensional (3D) structures, such as fullerenes and carbon nanotubes, have been the subject of intensive research due to their potential applications in molecular electronics. However, basic molecular skeletons of 3D molecules are limited because of the lack of a rational and selective synthetic method by organic synthesis. Here we report the synthesis of a 3D π-conjugated molecule based on the platinum-mediated assembly of four molecules of a stannylated trisubstituted benzene derivative forming a hexanuclear platinum complex with an octahedral shape, from which reductive elimination of platinum gave the target molecule. As many supramolecular transition metal-ligand complexes with 3D cages and polyhedral structures have been synthesized by self-assembly of ligands and metals, the current assembly/reductive elimination strategy could provide a variety of new 3D π-conjugated molecules with different structures and topologies, which are challenging to obtain using conventional synthetic methods.

Ruthenium catalysis in organic synthesis

Ruthenium, rhodium, iridium, and rhenium hydride complexes are highly useful redox Lewis acid and base catalysts. Various substrates bearing hetero atoms are activated by these catalysts and undergo reactions with either nucleophiles or electrophiles under neutral conditions. These types of catalytic reactions are described together with their application to the preparation of various biologically active compounds.

Dynamic Vapochromic Behaviors of Organic Crystals Based on the Open–Close Motions of S-Shaped Donor–Acceptor Folding Units

The first vapochromic organic crystals are described with respect to their preparation, color change, adsorption/desorption properties, crystal structures, and color-change mechanism. Non-solvatochromic, 1,4,5,8-naphthalene-tetracarboxylic diimide (NDI) derivatives 1 a bearing two pyrrole imine (PI) tethers have been used as a motif for the crystal packing template. Red-purple vapochromic solid 3 was prepared by evacuation of orange crystals 2 (equivalent to 1 a2 MeOH), obtained by recrystallization of 1 a from MeOH. Solid 3 showed high-adsorption ability and unprecedented vapor-dependent color changes upon exposure to a variety of organic vapors, whereas light brown amorphous solid 1 a, did not show vapo- or solvatochromic behavior toward any organic solvent. The strong adsorption capability of 3 was confirmed by TGA experiments and adsorption/desorption isotherms. Analysis of the solid-state UV/Vis analysis revealed that the vapor-dependent color changes of 3 were owed to the specific interference of solvent vapors with its broad CT absorbance at lambda=450-650 nm. Packing structures of 1 a in orange crystals 2, red-purple solid 3, and regenerated orange solid 2 were unequivocally established by single crystal and synchrotron powder X-ray diffraction, respectively. Molecular structures and arrays of 1 a in these materials indicated that 1) unit 1 a had an S-shaped folded conformation in 2 and 3 by intramolecular donor-acceptor interactions between NDI and two PI units; 2) inclusion of the guest vapor into the S-shaped template decreased the intramolecular PI-NDI interactions, accompanied by increasing intermolecular NDI-NDI and PI-PI interactions; and 3) such flexible, open-close motions of the S-shaped template could be repeated during reversible adsorption/desorption processes without degradation of crystal packing. The adsorption properties and mechanism of molecular shape-dependent vapochromic behavior of 3 are discussed with reference to experimental results, crystallographic data, and theoretical calculations.

Structural alteration of hybrid supramolecular capsule induced by guest encapsulation.

Heterofunctionalized C(2v) symmetrical cavitand 1 with 4-pyridylethynyl and 3-carbamoylphenyl groups in alternating arrangement was designed and synthesized. A 1:1 mixture of the cavitand 1 and a cis-coordinated palladium(II) or platinum(II) complex self-assembled into a hybrid supramolecular capsule via both metal-ligand coordination bonds and hydrogen bonds. Formation of the capsular assembly was confirmed by NMR spectroscopy and mass spectrometry. The hybrid capsule encapsulated the appropriate guest, the molecular sizes of which fit the size of the capsular cavity. Structural alteration of the hybrid capsule was induced by the guest encapsulation. A C(2h) structure for the encapsulation complex was assigned by 2D NMR spectra analysis. Thermodynamic and kinetic properties of the guest encapsulation were investigated. The kinetics of in/out guest exchange was strongly influenced by hydrogen bonding in the hybrid capsule.

Iron-catalyzed aromatic amination for nonsymmetrical triarylamine synthesis.

Novel iron-catalyzed amination reactions of various aryl bromides have been developed for the synthesis of diaryl- and triarylamines. The key to the success of this protocol is the use of in situ generated magnesium amides in the presence of a lithium halide, which dramatically increases the product yield. The present method is simple and free of precious and expensive metals and ligands, thus providing a facile route to triarylamines, a recurrent core unit in organic electronic materials as well as pharmaceuticals.