Olefin Metathesis Catalyzed by a Hoveyda–Grubbs-like Complex Chelated to Bis(2-mercaptoimidazolyl) Methane: A Predictive DFT Study

Abstract

Although highly selective complexes for the cross-metathesis of olefins, particularly oriented toward the productive metathesis of Z -olefins, have been reported in recent years, there is a constant need to design and prepare new and improved catalysts for this challenging reaction. In this work, guided by density functional theory (DFT) calculations, the performance of a Ru-based catalyst chelated to a sulfurated pincer in the olefin metathesis was computationally assessed. The catalyst was designed based on the Hoveyda–Grubbs catalyst (SIMes)Cl 2 Ru(=CH–o–O i PrC 6 H 4 ) through the substitution of chlorides with the chelator bis(2-mercaptoimidazolyl)methane. The obtained thermodynamic and kinetic data of the initiation phase through side- and bottom-bound mechanisms suggest that this system is a versatile catalyst for olefin metathesis, as DFT predicts the highest energy barrier of the catalytic cycle of ca. 20 kcal/mol, which is comparable to those corresponding to the Hoveyda–Grubbs-type catalysts. Moreover, in terms of the stereoselectivity evaluated through the propagation phase in the metathesis of propene–propene to 2-butene, our study reveals that the Z isomer can be formed under a kinetic control. We believe that this is an interesting outcome in the context of future exploration of Ru-based catalysts with sulfurated chelates in the search for high stereoselectivity in selected reactions.

An Anthracene-Thiolate-Ligated Ruthenium Complex: Computational Insights into Z-Stereoselective Cross Metathesis

“…The phenyl group in A can acquire either a contracted or an expanded conformation. Similarly to our previous research findings, it has been demonstrated that the destabilization of OC intermediates is correlated with the destabilization of transition states . Therefore, we investigated the initiation phase exclusively for the most stable conformers.…”

“…Similarly to our previous research findings, it has been demonstrated that the destabilization of OC intermediates is correlated with the destabilization of transition states. 65 Therefore, we investigated the initiation phase exclusively for the most stable conformers. Consequently, we suggest the criterion of ΔG rel < 3 kcal/mol to select the intermediates that undergo a kinetically favored initiation phase, which in this study are all OC A intermediates characterized by the expanded configuration of phenyl in A.…”

H-Bonding leading to latent initiators for olefin metathesis polymerization

“…From Scheme 2, starting with the imine based chelate precatalyst A , and finishing with the ylidene 14e active species F , the mechanism is somewhat analogous with respect to the Hoveyda–Grubbs catalysts, 54 with the replacement of the oxygen atom bonded to ruthenium by nitrogen. 55 Before a detailed structural and electronic analysis of the set of catalysts under analysis, the energetic values for the reaction pathway of the activation are included in Table 1.…”

Electrophilicity of Hoveyda‐Grubbs Olefin Metathesis Catalysts as the Driving Force that Controls Initiation Rates

“…Specifically, the progress of the reactions was monitored by varying the dihedral angle in the case of o-OiPr-benzylidene rotation. [55] Electronic energies were obtained from the single-point M06-D3 calculations [56] including a triple ζ basis set plus polarization and diffuse functions, 6-311G + + (d,p) (standard LACV3P + + ** keyword in Jaguar). Solvent effects were included through the Poisson-Boltzmann self-consistent polarizable continuum model (PB-PCM), with toluene as the solvent.…”

“…Transition states and connecting local minima were searched by means of linear‐transit calculations using the same DFT method. Specifically, the progress of the reactions was monitored by varying the dihedral angle in the case of o ‐O i Pr‐benzylidene rotation [55] . Electronic energies were obtained from the single‐point M06‐D3 calculations [56] including a triple ζ basis set plus polarization and diffuse functions, 6–311G++(d,p) (standard LACV3P++** keyword in Jaguar).…”