π–π Catalysis in Carbon Flatland—Flipping [8]Annulene on Graphene

Abstract

Noncovalent interactions are an integral part of the modern catalysis toolbox. Although stronger noncovalent interactions such as hydrogen bonding are commonly the main driving force of catalysis, π–π interactions typically provide smaller additional stabilizations, for example, to afford selectivity enhancements. Here, it is shown computationally that pristine graphene flakes may efficiently catalyze the skeletal inversions of various benzannulated cyclooctatetraene derivatives, providing an example of a catalytic process driven solely by π–π stacking interactions. Hereby, the catalytic effect results from disproportionate shape complementarity between catalyst and transition structure compared with catalyst and reactant. An energy decomposition analysis reveals electrostatic and, especially with increasing system size, to a larger extent, dispersion interactions as the origin of stabilization.

Graphene‐induced planarization of cyclooctatetraene derivatives

“…It is important to emphasize that both the free and adsorbed planar COT structures are first-order saddle points possessing an imaginary frequency that corresponds to the tub-inversion. 44 In contrast, in the current work we find that the planar structure of para dibenzannulated COT adsorbed on graphene is no longer a first-order saddle point, but a local minimum with all-real frequencies (the optimized structure of the equilibrium complex is depicted in Figure 5). Thus, it seems that in the case of DBCOT, the graphene monolayer reshapes the PES such that the TS for the tub-inversion becomes a local minimum.…”

“…We recently found that adsorption of COT onto a graphene nanoflake catalyst (C 96 H 24 ) reduces its ring inversion barrier height by 20% of the uncatalyzed reaction barrier height. 44 Structural and energetic analyses show that this catalytic activity is driven by shape complementarity between the planar 2D catalyst and planar TS. Namely, the 2D nanomaterial stabilizes the planar TS to a greater extent than the highly nonplanar, tub-shaped reactant.…”

“…The PW6B95 exchange-correlation functional has been extensively benchmarked and found to be robust for both reaction energies and barrier heights involving related systems. 42,44,[60][61][62][63][64][65][66][67] All geometry optimizations, frequency, and SPE calculations were carried out using the Gaussian 16 program suite. 68 Nucleus independent chemical shift (NICS) 69,70 scans were performed by means of the gauge independent atomic orbitals (GIAO) method at the GIAO-B3LYP/6-311+G(d,p) level of theory with the Aroma 1.0 package.…”

“…These results are consistent with previous works, which showed that multiple π-π interactions can collectively provide significant energetic stabilization. [36][37][38][39][40][41][42][43][44] In this context, ref. 44 is of particular relevance since it demonstrates that a graphene sheet can catalyze the tub-totub inversion in COT and its ortho-and meta-benzannulated derivatives.…”

“…[36][37][38][39][40][41][42][43][44] In this context, ref. 44 is of particular relevance since it demonstrates that a graphene sheet can catalyze the tub-totub inversion in COT and its ortho-and meta-benzannulated derivatives. Here we show that para benzannulated COT derivatives (e.g., DBCOT and DNCOT) form planar local minima on a graphene sheet.…”