Probing Reaction Mechanism of [1,5]‐Migration in Pyrrolium and Pyrrole Derivatives: Activation of a Stronger Bond in Electropositive Groups Becomes Easier

Abstract

The [1,5]-migration reaction has attractedc onsiderable attention from experimentalists andt heoreticians for decades. Although it has been extensively investigated in various systems, studies on pyrrolium derivatives are underdeveloped. Herein, at heoretical study on the reaction mechanism of [1,5]-migrationi nb oth pyrroliuma nd pyrrole derivatives is presented. The results reveal lower activation barriers in [1,5]-migration of electropositive groups (AuPMe 3 and SnH 3 )i np yrrolium derivatives, although the bond dissociation energies of the AuÀNb ond (98.8 kcal mol À1 )a nd SnÀN bond (81.7 kcal mol À1 )a re larger than that of the NÀFb ond (57.6 kcal mol À1 ). The unexpectedly lower activation barriers (4.5 and 4.9 kcal mol À1 for AuPMe 3 and SnH 3 ,r espectively) for [1,5]-migration of electropositive groups,i nc omparison with the [1,5]-fluorine shift, can be attributed to aromaticity stabilizing the transition states, as revealed by significantly negative nucleus-independent chemical shift (NICS) values. Further studies indicate that charge distribution and frontier molecular orbitals also plays ome roles in [1,5]-migration of pyrrolium derivatives.[a] Q.

Systematic Design of a Frustrated Lewis Pair Containing Methyleneborane and Carbene for Dinitrogen Activation

“…Selected bond lengths, NICS(1) zz values, and ACID plots for the species listed in Figure can be found in Figure and S1. Ring A in all species shows comparable hyperconjugatvie aromaticity due to pseudo six π-electrons in the five-membered ring. Globally clockwise ring current is shown in 4.P , whereas ring C (NICS(1) zz : −2.9 ppm) in 4.P′ is nonaromatic.…”

The application of aromaticity and antiaromaticity to reaction mechanisms

“…The ΔBLs (Å), dihedral angles of the Cp* ring (DA) and NICS(0) values (ppm) were calculated at the level of B3LYP/6–311++G(d,p)(LanL2TZ(f)). (c) Gibbs energy profiles for the [1,5] shift of substituted pyrroliums [53] . Computational method, GD3-M06L/6–311++G(d,p)(ECPnMDF)//TPSS/6–311++G(d,p)(ECPnMDF).…”

Aromaticity‐promoted CO2 Capture by P/N‐Based Frustrated Lewis Pairs: A Theoretical Study

“…Fernández, and Cabrera‐Trujillo proposed aromaticity could promote reactivity of P/B‐FLPs towards a series of small molecules including CO 2 . Our group previously combined FLP chemistry and the concept of aromaticity together and reported aromaticity‐promoted N 2 fixation, C−F bond activation, and [1,5]‐migration in pyrrolium . Now, we are applying this strategy to CO 2 capture by P/N‐based FLPs.…”

“…[17] Our group previously combined FLP [18] chemistry andt he concept of aromaticity [19] togethera nd reported aromaticity-promoted N 2 fixation, [18a] CÀ Fb ond activation, [20] and [1,5]-migrationi np yrrolium. [21] Now, we are applying this strategy to CO 2 captureb yP /N-based FLPs. Based on Stephan's phenyl bridgedP /N-basedF LP (compound d), as eries of FLPs (g,F igure 1) with five-membered rings as al inkagew ere designed.…”