Deeper Insight into the Factors Controlling H₂ Activation by Geminal Aminoborane‐Based Frustrated Lewis Pairs

Abstract

H activation mediated by geminal aminoborane-based frustrated Lewis pairs (FLPs; R N-CH -BR' ) has been computationally explored within the density functional theory framework. It is found that the activation barrier of this process as well as the geometry of the corresponding transition states strongly depend on the nature of the substituents directly attached either to the acidic or the basic centers of the FLPs. The physical factors controlling the whole activation path are quantitatively described in detail by means of the activation strain model of reactivity combined with the energy decomposition analysis method. This methodology suggests a highly orbital-controlled mechanism where the degree of charge transfer cooperativity between the most important donor-acceptor orbital interactions, namely LP(N)→σ*(H ) and σ(H )→p (B), along the reaction coordinate constitutes a suitable indicator of the reaction barrier.

Hydrogenation of Multiple Bonds by Geminal Aminoborane‐Based Frustrated Lewis Pairs

“…On the one hand and as commented above, the hydrogenation of as ubstrate with highly electronegative groups attached to the boron atom of zwitterions 2 leads to lower reaction barriers (DG°increased in the www.chemeurj.org order F < Cl < Br < I). For instance, the activation barrier computed for the H 2 activation by H 2 NCH 2 B(OMe) 2 (1g)w as rather high (DG°= 34.9 kcal mol À1 ), [6] whereas the subsequenth ydrogenationo fO =CH 2 had an activation barrier of only 2.8 kcal mol À1 (which is even lower than that computed for the analogous reaction that involves the fluorine derivative 2b, DG°= 5.4 kcal mol À1 ,T able 1). Strikingly,t his reactivity trend is opposite to that found for the dihydrogen activation by using the same FLPs (the corresponding barriers increased in the order I < Br < Cl < F), [6] which highlights the markedly different nature of both steps of the FLPmediated hydrogenation reaction.…”

“…[6] Therefore, geometry optimizationso ft he molecules were performed without symmetry constraints by using the Gaussian 09 suite of programs [14] and employing the metahybrid M06-2X exchange-correlation functional [15] combined with the triple-z quality def2-TZVPP basis set. [6] Therefore, geometry optimizationso ft he molecules were performed without symmetry constraints by using the Gaussian 09 suite of programs [14] and employing the metahybrid M06-2X exchange-correlation functional [15] combined with the triple-z quality def2-TZVPP basis set.…”

“…[6] By means of the activation strain model( ASM) [7] of reactivity in combination with the energy decomposition analysis (EDA) [8] method,w eg ained ad etailedq uantitative insighti nto the H 2activation reaction and proposed ano rbital-controlled mechanism. [6] By means of the activation strain model( ASM) [7] of reactivity in combination with the energy decomposition analysis (EDA) [8] method,w eg ained ad etailedq uantitative insighti nto the H 2activation reaction and proposed ano rbital-controlled mechanism.…”

Stabilizing a different cyclooctatetraene stereoisomer

“…One of them, t Bu 3 P plus B(p-C 6 F 4 H) 3 , could catalyze reversible hydrogen activation, with a Gibbs energy barrier of 22.6 kcal/mol in solvent, and an exothermicity of 0.3 kcal/mol. In the context of B,N-based FLPs, Yepes et al (48) studied the hydrogen activation by the geminal aminoborane-based frustrated Lewis pairs (R 2 N-CH 2 -BR′ 2 ). The reaction proceeds via a direct H 2 splitting between B and N atoms, without prior H 2 coordination.…”

Influence of the Lewis Acid/Base Pairs on the Reactivity of Geminal E‐CH2‐E′ Frustrated Lewis Pairs

“…The computed reactivity trends will be analyzed in detail by means of the activation strain model (ASM) of reactivity in combination with the energy decomposition analysis (EDA) method . This methodology has been particularly helpful very recently to understand the factors controlling both the H 2 activation and the subsequent dihydrogen release into multiple bonds mediated by geminal B/N FLPs . Indeed, by means of this state‐of‐the‐art approach we have proposed an orbital‐controlled mechanism, complementary to the traditional mechanisms suggested by Pápai et al .…”