Bidentate Rh(I)‐Phosphine Complexes for the C−H Activation of Alkanes: Computational Modelling and Mechanistic Insight

Abstract

The CÀ H activation and subsequent carbonylation mediated by metal complexes, i. e., Rh(I) complexes, has drawn considerable attention in the past. To extend the mechanistic insight from Rh complexes featuring monodentate ligands like P(Me) 3 towards more active bisphosphines (PLP), a computationally derived fully conclusive mechanistic picture of the Rh(I)-catalyzed CÀ H activation and carbonylation is presented here. Depending on the nature of the bisphosphine ligand, the highest lying transition state (TS) is associated either to the initial CÀ H activation in [Rh(PLP)(CO)(Cl)] or to the rearrangement of the chloride in [Rh(PLP)(H)(R)(Cl)]. The chloride rearrangement was found to play a key role in the subsequent carbonylation. A set of 20 complexes of different architectures was studied, in order to fine tune the CÀ H activation in a knowledge-driven approach. The computational analysis suggests that a flexible ligand architecture with aromatic rings can potentially increase the performance of Rh-based catalysts for the CÀ H activation.

Computational Modelling and Mechanistic Insight into Light‐Driven CO Dissociation of Square‐Planar Rhodium(I) Complexes

“…This result is in line with the calculations performed by Margl et al [9] . and also with our previous computational study, [6] which demonstrated that the closed‐shell singlet is the predominant ground state in triply coordinated cis ‐Rh(P−P)(Cl) complexes regardless of the specific choice of bidentate phosphine ligands P−P. The following first and second excited states are triplets.…”

“…Based on the NEVPT2 results, it is evident that the ground state of cis-Rh(PMe 3 ) 2 (Cl) is a closed-shell singlet species. This result is in line with the calculations performed by Margl et al [9] and also with our previous computational study, [6] which demonstrated that the closed-shell singlet is the predominant ground state in triply coordinated cis-Rh(PÀ P)(Cl) complexes regardless of the specific choice of bidentate phosphine ligands PÀ P. The following first and second excited states are triplets. In the MC(T 2 ) at ~1.4 eV, the electron is excited from the d Rh ð Þ z 2 to the d Rh ð Þ x 2 À y 2 orbital; in MC(T 6 ) at an excitation energy of approximately 1.8 eV, the electron is transferred from the d Rh ð Þ yz orbital to the orbital that is represented by the linear…”

“…The triply coordinated species IV.A, characterized by a transconfiguration of both phosphine ligands, is highly unstable and can easily capture the dissociated CO to re-form the original complexes I. Alternatively, it is also possible for IV.A to undergo a structural rearrangement from the trans-to the cis-structure (V.A), which is energetically more favorable and is the chemically active species for the subsequent CÀ H activation. [6] On the other hand, the species III.B are rather stable and thus not catalytically active for CÀ H activation. Therefore, the tetrahedral species is potentially observable using time-resolved spectroscopy.…”

Tailoring Phosphine Ligands for Improved C-H Activation: Insights from Δ-Machine Learning

“…According to the theoretical and experimental mechanistic studies, [26][27][28] the critical 6https://doi.org/10.26434/chemrxiv-2024-d985s ORCID: https://orcid.org/0009-0006-1302-0571 Content not peer-reviewed by ChemRxiv. License: CC BY-NC-ND 4.0 coordinated intermediate can follow one of two pathways: it could proceed with a subsequent C-C formation step in the carbonylation process or undergo a C-H recombination to regenerate the initial 4-coordinated precursor.…”

Tailoring phosphine ligands for improved C–H activation: insights from Δ-machine learning

“…According to the theoretical and experimental mechanistic studies, [29][30][31] the Rh complex undergoes a series of transformations including CO dissociation, C-H activation, CO recombination, C-C coupling and reductive elimination, where C-H activation is identified to be the one of the rate-limiting steps. According to the Bell-Evans-Polanyi principle, the activation energy Δ𝐸 ‡ is highly correlated to the reaction energy.…”