An Organometallic Route to Long Helicenes

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 106; no. 32; pp. 13169 - 13174
• Main Authors: Sehnal, Petr, Stará, Irena G., Šaman, David, Tichý, Miloš, Míšek, Jiří, Cvačka, Josef, Rulíšek, Lubomír, Chocholoušová, Jana, Vacek, Jaroslav, Goryl, Grzegorz, Szymonski, Marek, Císařová, Ivana, Starý, Ivo, Meinwald, Jerrold
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 11.08.2009; National Acad Sciences
• Subjects: Alkynes; Carbon; Catalysis; Chemical compounds; Chemical synthesis; Chirality; Enantiomers; Imaging; Materials; Materials science; Metals; Microscopy, Scanning Tunneling; Models, Molecular; Molecules; Organic chemistry; Organometallic Compounds - chemistry; Physical Sciences; Polycyclic Compounds - chemical synthesis; Polycyclic Compounds - chemistry; Room temperature; Scaffolds; Stereoisomerism; Thermodynamics
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0902612106

Along with the recent progress in the development of advanced synthetic methods, the chemical community has witnessed an increasing interest in promising carbon-rich materials. Among them, helicenes are unique 3D aromatic systems that are inherently chiral and attractive for asymmetric catalysis, chiral recognition and material science. However, there have been only limited attempts at synthesizing long helicenes, which represent challenging targets. Here, we report on an organometallic approach to the derivatives of undecacyclic helicene, which is based on intramolecular [2 + 2 + 2] cycloisomerization of aromatic hexaynes under metal catalysis closing 6 new cycles of a helicene backbone in a single operation. The preparation of nonracemic compounds relied on racemate resolution or diastereoselective synthesis supported by quantum chemical (density functional theory) calculations. The fully aromatic [11] helicene was studied in detail including the measurement and theoretical calculation of its racemization barrier and its organization on the InSb (001) surface by STM. This research provides a strategy for the synthesis of long helical aromatics that inherently comprise 2 possible channels for charge transport: Along a π-conjugated pathway and across an intramolecularly π-π stacked aromatic scaffold.