Yamamoto Coupling for the Synthesis of Benzophenes and Acene-Based Cyclooctatetraenes.

Two TIPS-ethynylated dibromoacenes were used in a shotgun Yamamoto-reaction with 1,2-dibromobenzene or 4,5-dibromoveratrol. Four soluble benzononaphenes/benzoundecaphenes were isolated in satisfactory yields. Examples of tetracene- and pentacene-fused tetrabenzocyclooctatetraenes also isolated from this reaction are reported. All compounds were characterized by UV/Vis and fluorescence spectroscopy, cyclic voltammetry, X-ray crystallography as well as DFT and NICS calculations.

"Butterfly Wings" Stabilize Heptacene.

The synthesis of bisalkynylated derivatives of tetrabenzo[a,c,p,r]heptacene and tetrabenzo[a,c,l,n]pentacene via two-/fourfold Stille reactions involving a 9-stannafluorene and suitable tetrabromoacenes is reported. These triphenylene-"winged" heptacenes are surprisingly stable and maintain a significant portion of the electronic properties of heptacenes.

A Golden Access to Acenopentalenes.

By employing gold catalysis, starting from dialkynylated acenes a series of novel un-symmetrical aceno-annulated dibenzopentalenes has been prepared. The achieved yields range from 62-68 %. The fused systems contain naphthalene, anthracene, tetracene, and pentacene units. All new compounds are soluble and stable under standard conditions. The optical properties of the systems are dominated by the dibenzopentalene core for the smaller representatives, while for the anthracene-pentacene-based aceno-benzopentalenes the optical properties of the acene group dominates. Preliminary morphology tests on thin films showed a reverse trend between crystal size and molecule size.

Dibenzohexacene: Stabilization Through Additional Clar Sextets.

Triphenylene units stabilize hexacenes as dibenzohexacenes. The hexacenes formed by a statistical Yamamoto coupling of dibromobenzene with dibromo-TIPS-pentacene or, alternatively, Stille coupling with dimethyldibenzostannole. UV/Vis spectroscopy and quantum chemical calculations show that despite the double benzannulation, the species have hexacene-type character, as evidenced by their redshifted absorption characteristics. The charge carrier mobility of dibenzohexacene 1 a was determined up to 0.2 cm2 /(Vs).

Synthesis of Substituted Trinaphthylenes.

A short synthesis of six trinaphthylenes is reported. The cyclotrinaphthylenes carry six alkoxy groups, and derivatives featuring OHex, OBu, OiPr, OPr, OEt, and OMe substituents can be obtained by an ordinary Ni(COD)2-promoted, Yamamoto-type coupling reaction. Cyclotrimerization yields range from 38% to 65%. Dependent upon their structure, the cyclotrinaphthylenes assume different packing patterns, according to single-crystal X-ray structure determination. The crystal structures of such trinaphthylenes were hitherto undescribed.

Synthesis of soluble, alkyne-substituted trideca- and hexadeca-starphenes.

Two literature-known TIPS-ethynyl-dibromoacenes were prepared and employed to synthesize cyclotrimers by using Yamamoto coupling conditions. Two large, well-soluble starphenes were isolated in good yields. Crystallographic characterization verifies the triangular shape and shows significant differences in crystal packing.