Carbocatalytic Acetylene Cyclotrimerization: A Key Role of Unpaired Electron Delocalization

Development
of sustainable catalysts for synthetic transformations
is one of the most challenging and demanding goals. The high prices
of precious metals and the unavoidable leaching of toxic metal species
leading to environmental contamination make the transition metal-free
catalytic systems especially important. Here we demonstrate that carbene
active centers localized on carbon atoms at the zigzag edge of graphene
represent an alternative platform for efficient catalytic carbon–carbon
bond formation in the synthesis of benzene. The studied acetylene
trimerization reaction is an efficient atom-economic route to build
an aromatic ringa step ubiquitously important in organic synthesis
and industrial applications. Computational modeling of the reaction
mechanism reveals a principal role of the reversible spin density
oscillations that govern the overall catalytic cycle, facilitate the
product formation, and regenerate the catalytically active centers.
Dynamic π-electron interactions in 2D carbon systems open new
opportunities in the field of carbocatalysis, unachievable by means
of transition metal-catalyzed transformations. The theoretical findings
are confirmed experimentally by generating key moieties of the carbon
catalyst and performing the acetylene conversion to benzene.