Inverse-Electron-Demand Diels-Alder Reaction of Tropone with Graphene Supported on Cu(111).

An inverse-electron-demand Diels-Alder (IEDDA) reaction between graphene supported on Cu(111) and tropone catalyzed by a Lewis acid is reported. Reaction catalyzed by B(C6F5)3 resulted in a significant change in the Raman G band and the appearance of carbonyl group in the functionalized graphene. Treating the product with a reducing agent NaBH4 or hydrazine led to a near complete disappearance of shoulder peaks in the Raman G band and a decrease in carbonyl intensity. On the other hand, reaction catalyzed by BPh3 resulted in the appearance of C─O group in the functionalized graphene. The findings support [4 + 2] and [8 + 2] cycloaddition for the B(C6F5)3- and BPh3-catalyzed reaction, respectively. Density functional theory (DFT) calculations revealed that favorable cycloaddition reactions with tropone can be achieved through the usage of curved graphene. The origin of the Lewis acid-dependent selectivity inversion is predicted to be based on the requirement for Lewis acid dissociation during the course of the [8 + 2] reaction with B(C6F5)3 dissociation requiring more energy than BPh3 dissociation. This study represents a new strategy in graphene chemistry that combines synergistic activation of graphene via substrate interactions and of tropone via Lewis acid coordination, as well as catalyst selection to modulate reaction pathways.