Biphenylene Dimer. Molecular Fragment of a Two-Dimensional Carbon Net and Double-Stranded Polymer

Abstract

Biphenylene dimers, which may be considered as "macrocyclic" 2 × 2 fragments of net 1 and dimeric fragments of a double-stranded polymer, 5, are prepared. X-ray crystallography on two polymorphs of the dimer 9 reveals that its bond alternation is analogous to that in biphenylene; the tetraphenylene part of 9 has approximately C 2h symmetry with a small dihedral angle (<12°) between the benzene rings in the adjacent biphenylenes. Cyclic voltammetry of 9 gives two reversible waves corresponding to a radical anion and a dianion; the lithium and potassium salts of these anions, 9 •-,M + (M ) Li, K) and 9 2-,2M + (M ) Li, K), were generated and characterized by ESR, NMR, and UV-vis spectroscopies. The spectral data for the dianions are compatible with classical structures; no evidence for "in-plane aromaticity" is found. For polymer 5, a localized band and large density of states near the Fermi level are found, using extended Hu ¨ckel theory calculations.

Electronic structure investigation of biphenylene films

“…Predicted for the first time by Balaban,12 BPC is characterized, theoretically, by an intrinsic band gap and bands with delocalized frontier orbitals. 13,14 Biphenylene sheets, originating from biphenylene dimers, 15 have also been hypothesized and their onedimensional derivatives, like ribbons and tubes, have been theoretically investigated. 16 The most reliable and promising approach to grow this kind of covalently bonded carbon materials is a bottom-up procedure, exploiting the surface-confined self-assembly of functionalized molecular building blocks and their interaction with appropriate surfaces (generally coinage metal substrates).…”

“…Covalently bonded materials show superior thermal and chemical stability with respect to highly ordered hydrogen-bonded porous carbon networks [17][18][19] and to other self-assembled structures given by surface metal coordination 15 or aromatic coupling motifs. 20 In order to investigate the behavior of biphenylene as a precursor of 2D structures like BPC, we have performed a preliminary characterization of biphenylene films deposited on a Cu(111) substrate, through Photoelectron Spectroscopy (PES) and Near-Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy.…”

Heliphenes and Related Structures

“…From this "biphenylene sheet" one cannot obtain bent or kinked [n]phenylenes, because it contains only linear [n]phenylene fragments. The "biphenylene dimer" (strictly speaking a bis-dehydro dimer), which is a fragment of this sheet, was synthesized by Rajca and coworkers, and its nonplanar structure was determined by X-ray crystallography of a tetra-tert-butyl derivative [44]. The parent is also formed by flash-vacuum isomerization of the angular [4] phenylene, as an intermediate in its flash-vacuum conversion into coronene [45].…”

Synthesis of tetraphenylene derivatives and their recent advances

“…Interestingly, Rajca et al synthesized a 'biphenylene dimer' as a nearly planar structure [44]. The synthetic route to this symmetrical biphenylene dimer (64) was based on a Cu-mediated aryl-aryl homocoupling reaction (Scheme 19).…”