Rational Development of a Metal‐Free Bifunctional System for the C−H Activation of Methane: A Density Functional Theory Investigation

Abstract

The activation or heterolytic splitting of methane, a challenging substrate usually restricted to transition metals, has so far proven elusive in experimental frustrated Lewis pair (FLP) chemistry. In this article, we demonstrate, using density functional theory (DFT), that 1-aza-9-boratriptycene is a conceptually simple intramolecular FLP for the activation of methane. Systematic comparison with other FLP systems allows to gain insight into their reactivity with methane. The thermodynamics and kinetics of methane activation are interpreted by referring to the analysis of the natural charges and by employing the distortion-interaction/activation strain (DIAS) model. These showed that the nature of the Lewis base influences the selectivity over the reaction pathway, with N Lewis bases favoring the deprotonation mechanism and P bases the hydride abstraction one. The lower barrier of activation for 1-aza-9boratriptycene and the higher products stability are due to a better interaction energy than its counterparts, itself due to electrostatic interactions with the methane moiety, favorable orbital overlaps allowed by the side-attack, and space proximity between the B and N atoms.

9-Phosphatriptycene Derivatives: From Their Weak Basicity to Their Application in Frustrated Lewis Pair Chemistry

“…However, with the prediction of 9-phosphatriptycenes p K a ’s, this study has demonstrated that the same result can also be obtained by only changing structural parameters. In our research group, this strategy was already successfully applied to enhance the reactivity of triarylboranes, developing a new family of nonplanar Lewis acids. ,− …”

“…Tight convergence thresholds were used for geometry optimizations, for example, for the residual forces on the atoms, it is 1.5 × 10 –5 Hartree/Bohr or Hartree/radian. This method was shown previously to give satisfactory results in thermochemistry when compared to higher-level methods such as double-hybrid DFT with a more extended and flexible basis set . Calculations were performed at the temperature and pressure of 298.15 K and 1 atm, respectively.…”

“…This method was shown previously to give satisfactory results in thermochemistry when compared to higher-level methods such as double-hybrid DFT with a more extended and flexible basis set. 35 Calculations were performed at the temperature and pressure of 298.15 K and 1 atm, respectively. For ground state equilibrium structures, all vibrational frequencies of the optimized stationary points are real, demonstrating that the structures are minima on the potential energy surface.…”

Hydrogen Activation by Frustrated and Not So Frustrated Lewis Pairs Based on Pyramidal Lewis Acid 9-Boratriptycene: A Computational Study

“…Formal replacement of the CH group in the aromatic ring of B­(C 6 H 4 ) 3 CH by the nitrogen atom results in 1-aza-9-boratriptycene, which may be considered an intramolecular FLP. Its reactivity toward C–H activation was computationally explored …”

“…Its reactivity toward C−H activation was computationally explored. 29 The data on Lewis acidity of 9-boratriptycene vary depending on the used LA scale. The Gutmann acceptor number 30 of 9boratriptycene (76 26 ) is slightly smaller than that of B(C 6 F 5 ) 3 (76−82 31 ), indicating that 9-boratriptycene is a weaker LA than B(C 6 F 5 ) 3 with respect to triethylphosphineoxide.…”