Phenacenes: a family of graphite ribbons. Part 3: Iterative strategies for the synthesis of large phenacenes

Activated Phenacenes from Phenylenes by Nickel‐Catalyzed Alkyne Cycloadditions

“…[17] Both show encumbrance of the phenyl groups in the NMR experiment similar to that of 5, quantified for the relatively faster phenyl rotation at C5 and C8 in 10: DG 6 ¼ 287 = (13.2AE0.1) kcal mol À1 . [7] The [5]phenacene warping is similar to that in 5. As in 6, the atypically [3] short phenacene bond of benzofusion C16bÀC12c in 10 (1.379 ) [7] heralds increased benzocyclobutadienoid character and hence reactivity toward oxygen.…”

“…[1] Functional constraints, such as air-sensitivity, instability, unfavorable band-gap, insolubility, and encumbered processability require tunable synthetic approaches to specific targets. [2] We report the Ni-catalyzed cycloaddition of alkynes to the angular phenylene motif, [3,4] which engenders novel sterically and electronically activated extended phenacenes [5] with extensive selectivity. The potential of phenacenes as components for light-emitting diodes, field-effect transistors, and superconductors has been discovered only recently.…”

“…[12] These effects are even more pronounced in the [a,i] and [a,c] doubly fused and topologically new [13] red phenanthrenes (air sensitive) 6 [l max = 484 nm; cf. [5]phenacene (picene): 376 nm) [12] and 9 (l max = 503 nm; cf. benzo[g]chrysene: 371 nm).…”

“…benzo[g]chrysene: 371 nm). [7,14] Turning to the [5]phenacene structures, colorless derivative 5 (l max = 405 nm) suffers the consequences of severe twisting caused by the 5,6,7,8-tetraphenyl substitution, most dramatically illustrated by the bay region twist C6-C6a-C6b-C7 = 31.18, the associated deplanarization of the internal phenanthrene unit (dihedral angles in the individual benzene rings up to 238), the extreme dihedral angle of the bonds to the attached 6,7-phenyls of 76.28, and bond elongation (relative to [5]phenacene] along the path C4a-C8a. As a consequence, the molecule is chiral and configurationally rigid, as evidenced by the NMR spectra, which reveal dissymmetry of both aryl groups at À60 8C.…”

“…benzo[s] [5]phenacene: 350 nm). [17] Both show encumbrance of the phenyl groups in the NMR experiment similar to that of 5, quantified for the relatively faster phenyl rotation at C5 and C8 in 10: DG 6 ¼ 287 = (13.2AE0.1) kcal mol À1 .…”