Yoshiyuki Kuwatani

Dynamic Molecular Tweezers Composed of Dibenzocyclooctatetraene Units: Synthesis, Properties, and Thermochromism in Host–Guest Complexes

Novel dynamic molecular tweezers (DMTs) 3 a, 3 b, 4 a, 4 b, and 5 b, composed of two tub-shaped dibenzocyclooctatetraene (DBCOT) units, were designed and synthesized. The cyclooctatetraene (COT) rings of these DMTs readily invert in solution, and the molecular structure shows rigid syn and anti forms in an equilibrium mixture in solution. The syn and anti conformers can be observed by NMR. The isomerization barriers of 3 a, 3 b, 4 a, 4 b, and 5 b are in the range of 16.5-21.3 kcal mol(-1), depending on steric repulsion between substituents of the COT rings and protons of the central benzene ring. These DMTs form complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and 1,2,4,5-tetracyano-benzene (TCNB) in solution and in the solid state. The binding abilities of these DMTs increase with electron-donating substituents on COT, which increase the electron densities of the cavity of the syn form, as supported by theoretical calculations. In addition, elongation of the terminal alkoxy chains of the DMTs was found to cause the enhancement of van der Waals contact with guest molecules. Therefore, 5 b, which has CH(2)OMe groups on the COT rings and longer ethoxy groups on the terminal benzene rings, showed the highest electron density of the cavity and hence the highest binding ability with the electron-deficient guest molecules. Interestingly, solutions of 3 b, 4 b, and 5 b show thermochromism in the presence of DDQ. A solution of 3 b or 4 b with DDQ in CHCl(3) is green due to charge-transfer interaction at room temperature and the color changes from green to yellow upon heating to 60 degrees C and from green to blue upon cooling to -40 degrees C, whereas the high complexation ability of 5 b with DDQ only shows a change in the shade of blue.

Solvent‐Induced Crystalline‐State Emission and Multichromism of a Bent π‐Surface System Composed of Dibenzocyclooctatetraene Units

All bent out of shape: The solvent of crystallization effectively enhances the emission of flexible, bent, π-conjugated molecules in the crystalline state owing to control of the packing of the molecules in the structure. Multichromism such as thermochromism and vapochromism also arises from the solvent-controlled packing. This crystalline-state emission is attributable to the flexibility of cyclooctatetraene units of the bent π-conjugated molecules in the solid state (see figure).

Synthesis of dithienothiophenes, cyclopentadithiophene and silacyclopentadithiophenes using palladium-catalyzed cyclization

Abstract The intramolecular cyclization of bromothiophene derivatives with hexamethylditin in the presence of tetrakis(triphenylphosphine)palladium(0) gave dithienothiophenes, cyclopentadithiophene, and silacyclopentadithiophenes in moderate to good yields.

Face-to-face fixed ferrocenes. Synthesis and properties of 2,10-diferrocenyl- and 2,5,7,10-tetraferrocenyl-1,6-methano[10]annulenes

Abstract 2,10-Diferrocenyl- and 2,5,7,10-tetraferrocenyl-1,6-methano[10]annulenes, in which the ferrocene nuclei are held proximate and cofacial, have been synthesized by using the palladium-catalyzed cross-coupling reaction of ferrocenylzinc chloride with 2,10-dibromo- and 2,5,7,10-tetrabromo-1,6-methano[10]annulenes. The structures of the face-to-face fixed ferrocene systems were determined by X-ray analysis. Cyclic voltammetric measurements of diferrocenyl- and tetraferrocenyl-1,6-methano[10]annulenes show two and three redox waves, respectively, reflecting the through-space and through-bond interactions of the ferrocene nuclei.

NOVEL SYNTHESIS OF BIPHENYLENE AND ITS DERIVATIVES USING INTRAMOLECULAR COUPLING OF ZINCACYCLOPENTADIENES

Abstract Biphenylene and its derivatives were synthesized using the intramolecular coupling of benzoannelated zincacyclopentadiene intermediates prepared from 2,2′-dilithiobiaryls with ZnCl 2 . The reaction proceeded smoothly and selectively to give the desired biphenylenes in moderate to good yields.

Novel synthesis of hexaaryl[3]radialenes via dibromo[3]dendralenes

Abstract We report here an efficient route to the synthesis of highly fluorescent hexaaryl[3]radialenes using the oligomerization of ate-type copper carbenoids, followed by cyclization with hexamethylditin and Pd(PPh3)4; the structures of the [3]dendralene and hexaaryl[3]radialenes were determined by X-ray crystallographic analysis.

all-Z-Tribenzo[12]-, tetrabenzo[16]- and pentabenzo[20]annulenes

Abstract A new synthetic strategy of all - Z -[ n ]benzo[4 n ]annulenes, which is based on the intramolecular pinacol coupling, followed by the Corey–Winter procedure, has been developed, and three annulenes have been successfully synthesized using this strategy.

Mono- and bis(tetrathiafulvaleno)hexadehydro[12]annulenesElectronic supplementary information (ESI) available: cyclic voltammograms of the annulenes 1 and 2. See http://www.rsc.org/suppdata/cc/b4/b407200f/

Hexadehydro[12]annulenes annelated with one or two TTF units have been synthesized to investigate their pi-amphoteric properties based on the TTF and [12]annulene moieties; these compounds show multi-redox potentials, solvatochromism and the formation of large sandwich complexes.

Synthesis of benzocyclobutadiene trimers and all-Z-tribenzo[12]annulene. A new family of concave π-systems

Abstract Nickel-catalyzed oligomerization of trans-1,2-dibromobenzocyclobutene formed cyclic dimers and trimers. Upon heating, the major anti-cyclic trimer afforded a cage compound, whereas the minor syn-trimer produced all-Z-tribenzo[12]annulene. Dehydrogenation of the anti-trimer with DDQ resulted in the formation of an indenoazulene derivative, and a similar reaction of the syn-trimer yielded a bowl-shaped system. All-Z-tribenzo[12]annulene was also synthesized using a stepwise route starting from o-diiodobenzene and o-ethynylbenzyl alcohol, the overall yield being 22%. All-Z-tribenzo[12]annulene behaved like π-prismand and formed chromium(0) tricarbonyl and silver(I) complexes.

A one-step synthesis of dehydro[12]annulenes using palladium-catalyzed reaction of o-diiodoarenes with acetylene gas

Abstract Hexadehydrotribenzo[12]annulene and its analogues were synthesized in a one-pot procedure by the palladium-catalyzed cross-coupling of o-diiodobenzene and its analogues with acetylene. The reaction proceeded smoothly to give the desired dehydro[12]annulenes in moderate yields.