Metal-free catalytic activation and borylation of the -H bond of 1-methyl pyrrole using adamantane-derived aminoborane frustrated Lewis pairs: A density functional theory study

Frustrated Lewis pair (FLP) chemistry has developed as a novel strategy for catalysis in organic chemistry and opened a new metal-free organic catalysis area for synthesizing various compounds of interest. Adamantane as molecular scaffolds used to design new sets of FLPs (ambiphilic molecules) for the - C-sp2-H activation and subsequent borylation of 1-methyl pyrrole employing DFT (wB97XD/6-31 + G (d,p)) level of theory. The saturated hydrocarbon showed improvement in the energetics of -C-sp2-H activation and subsequent borylation of 1-methyl pyrrole compared with the unsaturated phenylene FLPs employed for such reactions. The Lewis acid and Lewis base characters are augmented with adamantyl-derived FLPs, and the monomers responsible for the catalytic activity are also energetically more stable compared with their corresponding dimers. The H-2 extrusion and the electrophilic borylation steps are energetically comparable on the Gibbs free energy surface in cases of 1-NMe2-2-BH2-C6H4 (I) and 1-Pip-2-BH2-C6H4 (II). The relative free energy barriers of activations of such steps have been significantly lowered with adamantyl scaffold FLPs by similar to 5.5 and similar to 3.7 kcal/mol for 1-NMe2-2-BH2-4-F-C10H13 (B) and similar to 5.6 and similar to 4.9 kcal/mol for 1-Pip-2-BH2-4-F-C10H13 (D), respectively. The enhanced reactivity of adamantyl FLPs has been rationalized with a molecular electrostatic potential (MESP) study. The nucleophilic and electrophilic characters of Lewis base and Lewis acid have been calculated using the conceptual density functional theory (CDFT) that support the results of the MESP study. The saturated scaffold FLPs can be promising candidates to improve the efficiency of catalysts in many reactions.