Benzo‐fused Tri[8]annulenes as Molecular Models of Cubic Graphite

Barbara Ejlli,Uwe H F Bunz,Jan Freudenberg,Pascal Nußbaum,Frank Rominger,Klaus Müllen

doi:10.1002/ange.202106233

Barbara Ejlli, Uwe H F Bunz + Show 4 more

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https://doi.org/10.1002/ange.202106233

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Abstract

AbstractCyclotrimerization of 9,10‐dibromo‐9,10‐dihydrodibenzo[3,4:7,8]cycloocta[1,2‐l]phenanthrene with potassium tert‐butoxide in the presence of a transition‐metal catalyst afforded two polycyclic aromatic hydrocarbon stereoisomers consisting of three cyclooctatetraene (COT) moieties connected via a central benzene ring. Both isomeric tri[8]annulenes were obtained selectively through the choice of the catalyst: The α,α,α‐form (Ru catalyst) displayed a threefold symmetrywith the COT subunits forming the side walls of a (chiral) molecular cup. In the thermodynamically more stable α,α,β‐isomer (Pd catalyst), one of the three boat‐shaped COTs was flipped over and faced the opposite molecular hemisphere with respect to the central benzene ring as evidenced by crystal structure analysis. Both title compounds are small segments of “cubic graphite”, an elusive carbon allotrope.

Highlights

Cyclotrimerization of 9,10-dibromo-9,10dihydrodibenzo[3,4:7,8]cycloocta[1,2-l]phenanthrene with potassium tert-butoxide in the presence of a transition-metal catalyst afforded two polycyclic aromatic hydrocarbon stereoisomers consisting of three cyclooctatetraene (COT) moieties connected via a central benzene ring
Cubic graphite can be regarded as a 3D carbon structure[10,11] consisting of hexagons and octagons: Each benzene ring is part of three equivalent polypara-phenylene (PPP) chains while two biphenyl subunits of neighboring PPP strands form eight-membered[6k,12] tetraphenylene rings, rendering all of the sp2 hybridized carbon atoms equivalent
Subunits of cubic graphite were prepared via bottom-up approaches to serve as model compounds.[11b,13] Three-dimensional dendritic oligophenylenes[13b] underline the crowded oligophenylenic nature while the tetraphenylene substructures[14] are lacking entirely

Summary

Introduction

Cyclotrimerization of 9,10-dibromo-9,10dihydrodibenzo[3,4:7,8]cycloocta[1,2-l]phenanthrene with potassium tert-butoxide in the presence of a transition-metal catalyst afforded two polycyclic aromatic hydrocarbon stereoisomers consisting of three cyclooctatetraene (COT) moieties connected via a central benzene ring. Angewandte Chemie International Edition published by Wiley-VCH GmbH. Subunits of cubic graphite were prepared via bottom-up approaches to serve as model compounds.[11b,13] Three-dimensional dendritic oligophenylenes[13b] underline the crowded oligophenylenic nature while the tetraphenylene substructures[14] are lacking entirely.

Results

Conclusion