10.1021/acs.accounts.9b00269.s001
Iago Pozo
Iago
Pozo
Enrique Guitián
Enrique
Guitián
Dolores Pérez
Dolores
Pérez
Diego Peña
Diego
Peña
Synthesis of Nanographenes, Starphenes, and Sterically
Congested Polyarenes by Aryne Cyclotrimerization
American Chemical Society
2019
aryne cycloadditions
Aryne Cyclotrimerization ConspectusIn
Pd-catalyzed aryne cyclotrimerization reaction
Sterically Congested Polyarenes
molecule on-surface characterization
AFM
aryne chemistry
transition metal-catalyzed reactions
scanning tunneling microscopy
UHV
On-surface aryne cyclotrimerization
STM
2019-08-14 19:09:50
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Synthesis_of_Nanographenes_Starphenes_and_Sterically_Congested_Polyarenes_by_Aryne_Cyclotrimerization/9626309
ConspectusIn recent years, synthetic transformations based
on aryne chemistry have become particularly popular, mostly due to
the spread of methods to generate these highly reactive intermediates
in a controlled manner under mild reaction conditions. In fact, aryne
cycloadditions such as the Diels–Alder reaction are nowadays
widely used for the efficient preparation of polycyclic aromatic compounds.In 1998, our group discovered that arynes can undergo transition
metal-catalyzed reactions, a finding that opened new perspectives
in aryne chemistry. In particular, Pd-catalyzed [2 + 2 + 2] cycloaddition
of arynes allowed the straightforward synthesis of triphenylene derivatives
such as starphenes or cloverphenes. We found that this reaction is
compatible with different substituents and sterically demanding arynes
as starting materials. This transformation is especially useful to
increase the molecular complexity in one single step, transforming
molecules formed by <i>n</i> cycles in structures with 3<i>n</i> + 1 cycles. In fact, we took advantage of this protocol
to prepare a large variety of sterically congested polycyclic aromatic
hydrocarbons such as helicenes or twisted polyarenes. Soon after the
discovery of the reaction, the co-cyclotrimerization of arynes with
other reaction partners, such as electron deficient alkynes, significantly
expanded the potential of this transformation. Also the use of catalysts
based on alternative metals besides Pd (e.g., Ni, Cu, Au) or the use
of other strained intermediates such as cycloalkynes or cycloallenes
added value to this reaction.In addition, we realized that
the Pd-catalyzed aryne cyclotrimerization reaction is particularly
useful for the bottom-up preparation of well-defined nanographenes
by chemical methods. Although the extreme insolubility of these planar
nanographenes hampered their manipulation and characterization by
conventional methods, recent advances in single molecule on-surface
characterization by atomic force microscopy (AFM) and scanning tunneling
microscopy (STM) with functionalized tips under ultrahigh vacuum (UHV)
conditions, permitted the impressive visualization of these nanographenes
with submolecular resolution, together with the examination of the
corresponding molecular orbital densities.Moreover, arynes
have been shown to possess a rich on-surface chemistry. In particular,
arynes have been generated and studied on-surface, showing that the
reactivity is preserved even at cryogenic temperatures. On-surface
aryne cyclotrimerization was also demonstrated to obtain large starphene
derivatives. Therefore, it is expected that the combination of aryne
cycloadditions and on-surface synthesis will provide notable findings
in the near future, including the “à la carte”
preparation of graphene materials or the synthesis of elusive molecules
with unique properties.