One-shot K-region-selective annulative π-extension for nanographene synthesis and functionalization

The optoelectronic nature of two-dimensional sheets of sp 2 -hydridized carbons (for example, graphenes and nanographenes) can be dramatically altered and tuned by altering the degree of π -extension, shape, width and edge topology. Among various approaches to synthesize nanographenes with atom-by-atom precision, one-shot annulative π -extension (APEX) reactions of polycyclic aromatic hydrocarbons hold significant potential not only to achieve a ‘growth from template’ synthesis of nanographenes, but also to fine-tune the properties of nanographenes. Here we describe one-shot APEX reactions that occur at the K-region (convex armchair edge) of polycyclic aromatic hydrocarbons by the Pd(CH 3 CN) 4 (SbF 6 ) 2 / o -chloranil catalytic system with silicon-bridged aromatics as π -extending agents. Density functional theory calculations suggest that the complete K-region selectivity stems from the olefinic (decreased aromatic) character of the K-region. The protocol is applicable to multiple APEX and sequential APEX reactions, to construct various nanographene structures in a rapid and programmable manner. Bottom-up synthesis of nanographenes is highly desirable. Here, the authors report one-shot annulative π -extension reactions that occur at the convex armchair edge of polycyclic aromatic hydrocarbons, and show that unfunctionalized precursors can be used for π -component assembly and extension.