Tracking C–H activation with orbital resolution

Abstract

Transition metal reactivity toward carbon–hydrogen (C–H) bonds hinges on the interplay of electron donation and withdrawal at the metal center. Manipulating this reactivity in a controlled way is difficult because the hypothesized metal-alkane charge-transfer interactions are challenging to access experimentally. Using time-resolved x-ray spectroscopy, we track the charge-transfer interactions during C–H activation of octane by a cyclopentadienyl rhodium carbonyl complex. Changes in oxidation state as well as valence-orbital energies and character emerge in the data on a femtosecond to nanosecond timescale. The x-ray spectroscopic signatures reflect how alkane-to-metal donation determines metal-alkane complex stability and how metal-to-alkane back-donation facilitates C–H bond cleavage by oxidative addition. The ability to dissect charge-transfer interactions on an orbital level provides opportunities for manipulating C–H reactivity at transition metals.

Accessing metal-specific orbital interactions in C–H activation with resonant inelastic X-ray scattering

“…Using time-resolved X-ray absorption spectroscopy at the transition metal L-edge, we were recently able to observe the metal–alkane orbital interactions, which are operative in photoinduced C–H activation. 18 We demonstrated, how with this atom-specific probe we could follow the evolution of orbital interactions and orbital populations as a function of time. 19,20 This enabled us to dissect the C–H σ to metal d charge donation and metal d to C–H σ* (MLCT) charge back-donation in C–H activation.…”

“…19,20 This enabled us to dissect the C–H σ to metal d charge donation and metal d to C–H σ* (MLCT) charge back-donation in C–H activation. 18 For photoinitiated C–H activation with CpRh(CO) 2 (where Cp is cyclopentadienyl) in octane solution, time-resolved X-ray absorption spectroscopy at the Rh L-edge gave access to the two-way charge-transfer interactions between Rh and the C–H group in the essential CpRh(CO)–octane σ-complex reaction intermediate. Metal L-edge X-ray absorption spectroscopy, however, is based on transitions of metal 2p core electrons to unoccupied molecular orbitals.…”

Trendbericht Anorganik 2024: Nebengruppen, Bioanorganik und Koordinationschemie

“…Damit verfolgten sie direkt die Änderungen in den d-Orbitalen des Metalls auf der Femto-und Nanosekundenskala (Abbildung 1A). 1) Die Gruppen um Figueroa und Abram isolierten erstmals 17-Valenz elek tro nen-Komplexe der Grup-pe 7 (Abbildung 1B). Dies gelang mit sterisch anspruchsvollen organischen Isonitrilen.…”

Bimetallic-Derived Catalytic Structures for CO2-Assisted Ethane Activation

“…It remains challenging to control the selective scission of C–H and C–C bonds in alkanes. Analogous to organometallic chemistry, C–H bond activation in alkanes typically proceeds with electrophilic (or radical) activation, oxidative addition (OA), or σ-bond metathesis (σ-MT) mechanisms with the latter two being more common in heterogeneous catalysis. − As shown in Figure b, in a two-step OA mode (I), a metal atom or a low-valence metal ion (d n , n ≠ 0) inserts into the C–H bond to form a three-center transition state (TS) complex, followed by a subsequent elimination of hydride as H 2 (e.g., direct dehydrogenation) to somewhat compensate the energy penalty from the C–H bond dissociation. In the presence of oxidants like CO 2 , oxygen adatoms/ions (O*) or a site pair of metal (ion) and vicinal O* (M–O*) may become surface-prevailing.…”