Hiroshi Masai

Synthesis of One-Dimensional Metal-Containing Insulated Molecular Wire with Versatile Properties Directed toward Molecular Electronics Materials

We report, herein, the design, synthesis, and properties of new materials directed toward molecular electronics. A transition metal-containing insulated molecular wire was synthesized through the coordination polymerization of a Ru(II) porphyrin with an insulated bridging ligand of well-defined structure. The wire displayed not only high linearity and rigidity, but also high intramolecular charge mobility. Owing to the unique properties of the coordination bond, the interconversion between the monomer and polymer states was realized under a carbon monoxide atmosphere or UV irradiation. The results demonstrated a high potential of the metal-containing insulated molecular wire for applications in molecular electronics.

Rational Design for Rotaxane Synthesis through Intramolecular Slippage: Control of Activation Energy by Rigid Axle Length

We describe a new concept for rotaxane synthesis through intramolecular slippage using π-conjugated molecules as rigid axles linked with organic soluble and flexible permethylated α-cyclodextrins (PM α-CDs) as macrocycles. Through hydrophilic-hydrophobic interactions and flipping of PM α-CDs, successful quantitative conversion into rotaxanes was achieved without covalent bond formation. The rotaxanes had high activation barrier for their de-threading, so that they were kinetically isolated and derivatized even under conditions unfavorable for maintaining the rotaxane structures. (1) H NMR spectroscopy experiments clearly revealed that the restricted motion of the linked macrocycle with the rigid axle made it possible to control the kinetic stability by adjusting the length of the rigid axle in the precursor structure rather than the steric bulkiness of the stopper unit.

Synthesis of an organic-soluble π-conjugated [3]rotaxane via rotation of glucopyranose units in permethylated β-cyclodextrin

Summary We synthesized symmetrically insulated oligo(para-phenylene) and oligothiophene with a pseudo-linked [3]rotaxane structure by full rotation of glucopyranose units via a flipping (tumbling) mechanism in the π-conjugated guest having two permethylated β-cyclodextrin units at both ends. We also succeeded in the synthesis of an organic-soluble fixed [3]rotaxane by a cross-coupling or complexation reaction of thus formed pseudo linked [3]rotaxane. Oligo(para-phenylene), oligothiophene, and porphyrin derivatives were used as π-conjugated guests with stopper groups.

Regio- and Stereoselective Synthesis of Triarylalkene-Capped Rotaxanes via Palladium-Catalyzed Tandem Sonogashira/Hydroaryl Reaction of Terminal Alkynes

Triarylalkene-capped conjugated rotaxanes were synthesized via a palladium-catalyzed tandem Sonogashira/hydroaryl reaction between aryl halides and terminal alkynes bearing two permethylated α-cyclodextrins (PM α-CDs) with high regioselectivity because of the insulation effect of the PM α-CDs. Moreover, sequential Sonogashira coupling and hydroarylation reactions using different aryl substrates afforded a regio- and stereoselective trisubstituted alkene as a single product. This new class of rotaxane-forming reactions can be used to increase the diversity of rotaxane skeletons, and thereby the material functionalities of rotaxanes.

Programmed Synthesis of Molecular Wires with Fixed Insulation and Defined Length Based on Oligo(phenylene ethynylene) and Permethylated α‐Cyclodextrins

The development of new tuning methods for π-conjugated insulated molecular wires with strictly defined axle lengths as well as positions and degrees of macrocycle coverage would provide unprecedented insight into insulation effects in functionalized materials. Herein, iterative reactions of oligo(phenylene ethynylene) (OPE) linked with permethylated α-cyclodextrins were carried out to fabricate insulated molecular wires with a defined length and insulation in desired areas. Insulated OPEs were elongated in a stepwise manner by performing sequential coupling/deprotection reactions. The insulated areas on the OPE units in each expansion step were selectively controlled by means of programmed solvent conditions (high/low polarity). Moreover, a completely insulated OPE (up to a linked [11]rotaxane) with high structural regularity and high covering ratio was synthesized by appropriate tuning of the Pd catalyst and an extension unit bearing a traceless capping unit based on a tert-butyldimethylsilyl group. This strategy may guide the development of the selective synthesis of fully insulated, partially insulated, and uninsulated molecular wires with well-defined lengths and covered/uncovered areas.

Synthesis of Molecular Wires Strapped by π-Conjugated Side Chains: Integration of Dehydrobenzo[20]annulene Units

In this study, π-conjugated molecular wires strapped by cyclic π-conjugated side chains were efficiently synthesized by the integration of dehydrobenzo[20]annulene units by intramolecular Glaser-type cyclization under high dilution conditions.