Single‐Site and Cooperative Bond Activation Reactions with Ylide‐Functionalized Tetrylenes: A Computational Study

Abstract

Due to their transition metal‐like behavior divalent group 14 compounds bear huge potential for their application in bond activation reactions and catalysis. Here we report on detailed computational studies on the use of ylide‐substituted tetrylenes in the activation of dihydrogen and phenol. A series of acyclic and cyclic ylidyltetrylenes featuring various α‐substituents with different σ‐ and π‐donating capabilities have been investigated which demonstrate that particularly π‐accepting boryl groups lead to beneficial properties and low barriers for single‐site activation reactions, above all in the case of silylenes. In contrast, for the thermodynamically more stable germylenes and stannylenes an alternative mechanism involving the active participation of the ylide ligand in the E−H bond (E=H or PhO) activation process by addition across the element carbon linkage was found to be energetically favored. Furthermore, the boryl substituted tetrylenes allowed for a further activation pathway involving the active participation of the boron element bond. These cooperative mechanisms are especially attractive for the heavier cyclic ylidyltetrylenes in which the loss of the protonated ylide group is prevented due to the cyclic framework. Overall, the present studies suggest that cyclic ylide‐substituted germylenes and stannylenes bear huge potential for cooperative bond activations at mild conditions which should be experimentally addressed in the future.

Inverting the Electronic Structure of Diylidylgermylenes by Backbone Modification

“…To test this hypothesis, we initially performed density functional theory (DFT) calculations (PW6B95-D3/def2tzvp) on a series of germylenes with different ylide groups to study the impact of the Z substituent on the energy of the molecular orbitals, in particular on the germanium-centered orbitals representing the lone-pair and empty p-orbital (Figure 2, see the Supporting Information for details). [14] Compared to our recently reported sulfonyl-functionalized germylene Da the introduction of a pyridyl or phenyl group leads to an increased HOMO energy and no significant decrease of the LUMO energies, indicating that these germylenes would be even stronger nucleophiles. In contrast, the pentafluorophenyl and especially the cyano-substituted germylene featured lower energies for the orbitals representing the lone pair at germanium and importantly considerably lower LUMO energies, suggesting that they should exhibit a pronounced electrophilic character.…”

“…In the solid‐state, 2 forms a C i symmetrical dimer, in which the two germyl anions are connected via the potassium ions thus forming a K 2 N 2 four‐membered ring as central structural motif (Figure 3). The germanium center is pyramidalized with acute C−Ge−C angles between 94.9(1) and 97.5(1)°, but features no contact to the metal ions, with the shortest Ge⋅⋅⋅K separation being longer than 4.5 Å [14] . The average Ge−C bond length amounts to approx.…”

“…To test this hypothesis, we initially performed density functional theory (DFT) calculations (PW6B95‐D3/def2tzvp) on a series of germylenes with different ylide groups to study the impact of the Z substituent on the energy of the molecular orbitals, in particular on the germanium‐centered orbitals representing the lone‐pair and empty p‐orbital (Figure 2, see the Supporting Information for details) [14] …”

Unravelling the Potential of Ylides in Stabilizing Low-Valent Group 13 Compounds: Theoretical Predictions of Stable, Five-Membered Group 13 (Aluminum and Gallium) Carbenoids Capable of Small-Molecule Activation

“…Compared to the extensive range of carbenes (and their heavier analogues) that are known experimentally in terms of both structure and reactivity, ,,, the number and variety of stable group 13 carbenoids are very limited, and this calls for an in-depth study toward the design and development of novel stable group 13 carbenoids and probing of their potential in stabilizing unusual species as well as in reactions such as small-molecule activation. In this context, it is pertinent to mention the role of ylidic groups in enhancing the singlet state stability and nucleophilicity of divalent group 14 bases. − Recently, we have computationally shown that ylidic groups could be used as building blocks for the stabilization of hitherto unknown boron­(I) carbenoids . Herein, we present the results of our computational studies toward stabilizing monovalent five-membered group 13 carbenoids (Scheme ; E = Al and Ga) by employing strongly electron-donating ylidic moieties.…”

Probing the donor strength of yldiide ligands: synthesis, structure and reactivity of rhodium complexes with a PCylideN pincer ligand

“… 17 For example, bond activation reactions repeatedly proceeded via a bifunctional mechanism with active participation of the ylidic carbon center in the bond cleavage process. 18 Analogous studies with transition metals are yet unknown, but highly desirable for the development of novel catalytic transformations. Previous findings with the main group element compounds have shown that the stability of the metal-ylide bonding would benefit from further coordination sites that prevent elimination of the ylide from the metal sphere after the activation step.…”