Beyond Continuum Solvent Models in Computational Homogeneous Catalysis

Abstract

In homogeneous catalysis solvent is an inherent part of the catalytic system. As such, it must be considered in the computational modeling. The most common approach to include solvent effects in quantum mechanical calculations is by means of continuum solvent models. When they are properly used, average solvent effects are efficiently captured, mainly those related with solvent polarity. However, neglecting atomistic description of solvent molecules has its limitations, and continuum solvent models all alone cannot be applied to whatever situation. In many cases, inclusion of explicit solvent molecules in the quantum mechanical description of the system is mandatory. The purpose of this article is to highlight through selected examples what are the reasons that urge to go beyond the continuum models to the employment of micro-solvated (cluster-continuum) of fully explicit solvent models, in this way setting the limits of continuum solvent models in computational homogeneous catalysis. These examples showcase that inclusion of solvent molecules in the calculation not only can improve the description of already known mechanisms but can yield new mechanistic views of a reaction. With the aim of systematizing the use of explicit solvent models, after discussing the success and limitations of continuum solvent models, issues related with solvent coordination and solvent dynamics, solvent effects in reactions involving small, charged species, as well as reactions in protic solvents and the role of solvent as reagent itself are successively considered.

Protonated Porphyrins: Bifunctional Catalysts for the Metal‐Free Synthesis of N‐Alkyl‐Oxazolidinones

“…In order to achieve a more accurate value of this barrier, the solvation energy of the different involved species should be considered by using an explicit solvent model. [48,49] In that case, the expected free-energy barrier associated with 21 TS should be higher than the calculated one and more in line with the employed experimental conditions. However, the high number of atoms to be modelled renders calculations very time-consuming and the correction was not introduced.…”

Copper-Catalyzed Homocoupling of Boronic Acids: A Focus on B-to-Cu and Cu-to-Cu Transmetalations

“…Hereafter, energies refer to Gibbs energies (∆ G , kcal mol −1 ) estimated at 298 K and 1 atm upon full geometry optimization. Solvation by methanol has been modeled by means of a micro-solvation approach [ 39 ] that combines an explicit description of the first solvation sphere and an implicit representation of the bulk solvation effects by a polarization continuum model [ 40 ]. The fully detailed computational approach is available in Section 4 , Materials and Methods.…”

“…Figure 5 depicts the most relevant Gibbs energy profile in the case of the di-solvated [Cu II (PhB(OH) 3 )(MeOH) 2 ] + ( 3 +,n = 2 ) heterobimetallic adduct. The influence of solvation on the stabilities of 3 +,n (n = 0, 1 or 2) and on the B-to-Cu transmetalation energy barriers is discussed in the SI ( Figure S15 ) [ 39 ].…”

Copper-Catalyzed Homocoupling of Boronic Acids: A focus on B-to-Cu and Cu-to-Cu Transmetalations

“…[35][36][37][38] Hereafter, energies refer to Gibbs energies (∆G, kcal mol -1 ) estimated at 298 K and 1 atm upon full geometry optimization. Solvation by methanol has been modeled by means of a micro-solvation approach [39] that combines an explicit description of the first solvation sphere and an implicit representation of the bulk solvation effects by a polarization continuum model. [40] The fully detailed computational approach is available in section 4, Materials and Methods.…”

“…The influence of solvation on the stabilities of 3 +,n (n= 0, 1 or 2) and on the B-to-Cu transmetalation energy barriers is discussed in the SI (Figure S15). [39] Complex 3 +,n=2 features two bridging μ-OH groups between Cu(II) and B atoms and the 4-membered ring atoms are nearly co-planar (ΦCu-O-B-O = 1.5°, Figure 6.A.). The formation of such a mixed Cu-(μ-OH)-B dimer as a key pre-transmetalation species mirrors previous reports on Pd [41][42][43] or Ni complexes.…”