Control of Product Distribution and Mechanism by Ligation and Electric Field in the Thermal Activation of Methane

Abstract

An unexpected mechanistic switch as well as a change of the product distribution in the thermal gas-phase activation of methane have been identified when diatomic [ZnO] is ligated with acetonitrile. Theoretical studies suggest that a strong metal-carbon attraction in the pristine [ZnO] species plays an important role in the rebound of the incipient CH radical to the metal center, thus permitting the competitive generation of CH , OH , and CH OH. This interaction is drastically weakened by a single CH CN ligand. As a result, upon ligation the proton-coupled single electron transfer that prevails for [ZnO] /CH switches to the classical hydrogen-atom-transfer process, thus giving rise to the exclusive expulsion of CH . This ligand effect can be modeled quite well by an oriented external electric field of a negative point charge.

Electronic Origin of the Competitive Mechanisms in the Thermal Activation of Methane by the Heteronuclear Cluster Oxide [Al2ZnO4].+

“…Herein, we report the thermal reaction of [Al 2 ZnO 4 ]C + with methane.C ompared to the previously investigated [Al 2 O 3 ]C + /CH 4 [4] and [ZnO]C + /CH 4 [6] couples,t he heteronuclear [Al 2 ZnO 4 ]C + cluster exhibits much higher selectivity in the thermal reaction with CH 4 .T he electronic origins of the doping effects on both the increased selectivity as well as on mechanistic aspects are revealed by high-level quantum chemical calculations.…”

“…To facilitate the s-bond metatheses via TS3/9 and TS2/11, however, the plane of the cluster has to be distorted with ad ihedral angle less than 1308 8;t his is rather energydemanding and pushes up these two TSs on the PES. [4] and [ZnO]C + /CH 4 (f = 40 %) [6] couples,[ Al 2 ZnO 4 ]C + /CH 4 exhibits higher selectivity with an intermediate efficiency. Moreover, the mechanisms also vary.F or example,t he PCET pathway mediated by the Al-O pair [14] is thermally unavailable for [Al 2 ZnO 4 ]C + .F urther, in addition to HAT, [ZnO]C + also abstracts one hydrogen from CH 4 via au nique 4-center-3electron TS.However,when the ZnO unit is incorporated as the backbone in [Al 2 ZnO 4 ]C + ,itresults in the well-established 4-center-4-electron PCET.…”

External electric field effects on chemical structure and reactivity

“…In the presence of a Cu + catalyst, CH 4 can react with C to form ethylene. Employing a [ZnO] • + catalyst ligated with an acetonitrile on the other hand affords the transformation of CH 4 exclusively into CH 3 • . In this second strategy, the coordination of a CH 3 CN ligand to the [ZnO] • + catalyst is required in order to impart selectivity on the reaction.…”

TITAN: A Code for Modeling and Generating Electric Fields—Features and Applications to Enzymatic Reactivity

“…Their introduction in the toolbox of synthetic chemists could potentially be a game changer, opening new (and more sustainable) routes toward chemical synthesis . At the same time, an increasing understanding of the role played by electrostatics in (bio)chemistry could offer new fundamental insights into a variety of phenomena associated to chemical reactivity …”

“…[1][2][3][4][5] Their introduction in the toolbox of synthetic chemists could potentially be a game changer, opening new (and more sustainable) routes toward chemical synthesis . [6][7][8][9][10][11] At the same time, an increasing understanding of the role played by electrostatics in (bio)chemistry could offer new fundamental insights into a variety of phenomena associated to chemical reactivity. [12][13][14][15][16][17] The hypothesis that the local electric fields (LEFs), induced by the charged functional groups scattered throughout any (asymmetric) protein matrix, have a profound impact on the catalytic function of enzymes, was originally put forward by Warshel in the 1970s.…”