Formation of active species from ruthenium alkylidene catalysts\u2014an insight from computational perspective

Paweł Śliwa,Mariusz P Mitoraj,Jarosław Handzlik,Filip Sagan

doi:10.1007/s00894-019-4202-5

Paweł Śliwa, Mariusz P Mitoraj + Show 2 more

Open Access

https://doi.org/10.1007/s00894-019-4202-5

Copy DOI

Abstract

Ruthenium alkylidene complexes are commonly used as olefin metathesis catalysts. Initiation of the catalytic process requires formation of a 14-electron active ruthenium species via dissociation of a respective ligand. In the present work, this initiation step has been computationally studied for the Grubbs-type catalysts (H2IMes)(PCy3)(Cl)2Ru=CHPh, (H2IMes)(PCy3)(Cl)2Ru=CH-CH=CMe2 and (H2IMes)(3-Br-py)2(Cl)2Ru=CHPh, and the Hoveyda-Grubbs-type catalysts (H2IMes)(Cl)2Ru=CH(o-OiPrC6H4), (H2IMes)(Cl)2Ru=CH(5-NO2–2-OiPrC6H3), and (H2IMes)(Cl)2Ru=CH(2-OiPr-3-PhC6H3), using density functional theory (DFT). Additionally, the extended-transition-state combined with the natural orbitals for the chemical valence (ETS-NOCV) and the interacting quantum atoms (IQA) energy decomposition methods were applied. The computationally determined activity order within both families of the catalysts and the activation parameters are in agreement with reported experimental data. The significance of solvent simulation and the basis set superposition error (BSSE) correction is discussed. ETS-NOCV demonstrates that the bond between the dissociating ligand and the Ru-based fragment is largely ionic followed by the charge delocalizations: σ(Ru–P) and π(Ru–P) and the secondary CH…Cl, CH…π, and CH…HC interactions. In the case of transition state structures, the majority of stabilization stems from London dispersion forces exerted by the efficient CH…Cl, CH…π, and CH…HC interactions. Interestingly, the height of the electronic dissociation barriers is, however, directly connected with the prevalent (unfavourable) changes in the electrostatic and orbital interaction contributions despite the favourable relief in Pauli repulsion and geometry reorganization terms during the activation process. According to the IQA results, the isopropoxy group in the Hoveyda-Grubbs-type catalysts is an efficient donor of intra-molecular interactions which are important for the activity of these catalysts.

Highlights

Well-defined ruthenium alkylidene complexes (Fig. 1) are commonly used as highly efficient catalysts for olefin metathesis
A good performance of the M06 functional in predicting energies of reactions involving ruthenium alkylidene complexes [28,29,30,31,32,33], including the dissociation energy for the Grubbs catalysts [28,29,30,31], was proved and it was often used for investigations of real ruthenium systems [28,29,30,31,32,33,34,35,36]
For the phosphine-containing catalysts (1 and 2), rate determining transition states have been localized (Figs. 3 and 4), but the calculated enthalpy profiles (T = 298 K) are monotonic, indicating that these transition states do not affect the enthalpy barriers, which are determined by the reaction, not activation, enthalpies (Table 1)

Summary

Introduction

Well-defined ruthenium alkylidene complexes (Fig. 1) are commonly used as highly efficient catalysts for olefin metathesis. Electron and steric properties of these ligands significantly affect the rate of the catalyst activation [6,7,8, 10,11,12, 14, 15]. In addition to this often postulated dissociative mechanism, where the dissociation/decoordination is the first step, associative and

Methods

Results

Conclusion