Principal component analysis of Mn(salen) catalysts

Abstract

The theoretical study of Mn(salen) catalysts has been traditionally performed under the assumption that Mn(acacen') (acacen' = 3,3'-(ethane-1,2-diylbis(azanylylidene))bis(prop-1-en-olate)) is an appropriate surrogate for the larger Mn(salen) complexes. In this work, the geometry and the electronic structure of several Mn(salen) and Mn(acacen') model complexes were studied using Density Functional Theory (DFT) at diverse levels of approximation, with the aim of understanding the effects of truncation, metal oxidation, axial coordination, substitution on the aromatic rings of the salen ligand and chirality of the diimine bridge, as well as the choice of the density functional and basis set. To achieve this goal, geometric and structural data, obtained from these calculations, were subjected to Principal Component Analysis (PCA) and PCA with orthogonal rotation of the components (rPCA). The results show the choice of basis set to be of paramount importance, accounting for up to 30% of the variance in the data, while the differences between salen and acacen' complexes account for about 9% of the variance in the data, and are mostly related to the conformation of the salen/acacen' ligand around the metal centre. Variations in the spin state and oxidation state of the metal centre also account for large fractions of the total variance (up to 10% and 9%, respectively). Other effects, such as the nature of the diimine bridge or the presence of an alkyl substituent in the 3,3 and 5,5 positions of the aldehyde moiety, were found to be less important in terms of explaining the variance within the data set. A matrix of discriminants was compiled using the loadings of the principal and rotated components that best performed in the classification of the entries in the data. The scores obtained from its application to the data set were used as independent variables for devising linear models of different properties, with satisfactory prediction capabilities.

Strengths, Weaknesses, Opportunities and Threats: Computational Studies of Mn- and Fe-Catalyzed Epoxidations

“…They also allow interesting insights into the catalytic cycle, yielding models that are in good accordance with the available experimental data. What is more, some of the most interesting accounts of good accordance between experimental data and theoretical predictions involve the use of rather limited basis sets, in an apparent contradiction to some of the previous studies [35,44]. However, a quantitative comparison between experimental data and theoretical predictions has eluded our bibliographical survey, apart from the comparisons encompassing spectroscopic data [51,90,99] and geometries [60,62,88,89].…”

“…What is more, the cationic model they use had already been considered unfit to give a meaningful representation of either Mn(acacen)Cl or proper Mn(salen) complexes [41,42]. As a result, the calculations by Sears and Sherril [39] Regarding the use of truncated models and smaller basis sets, Teixeira et al [44] recently addressed this problem by testing a number of different models for the Jacobsen catalyst (6), ranging from Mn(acacen) to the full catalyst, in both native and oxo-derived species, as well as using a number of different axial ligands. Their survey took into account geometrical parameters, as well as the charge and distribution of all species under study and used a Principal Component Analysis (PCA) to obtain some insight on the relative importance of each approximation on the overall description of these species.…”

“…These truncations may be in the form of using smaller model transition metal complexes or by using small basis sets, which cannot fully exploit the accuracy of the theoretical framework applied. The consequences of such simplifications have been explored recently [44,135] and should grant the need to re-address the calculations made by previous works. In this regard, it is worth mentioning that a clear trend in newer works is replacing the use of smaller, less flexible basis sets with larger basis sets, usually triple-ζ quality ones, with polarization on all atoms.…”

“…Drzewiecka-Matuszek et al [97] used the RI approximation in their study of the reaction between Mn(porphyrin) and H 2 O 2 , allowing the formulation of a reactivity model, which is in line with the available experimental data. More recently, Teixeira et al [31,44,135] used these linear-scaling strategies in their study of the charge and spin distributions in Mn(salen) and related complexes (including their oxo-derivatives). Here, the results obtained by these authors are in good accordance with those obtained previously without the use of such approximations [17,31,37,82].…”

Combining Internally Contracted States and Matrix Product States To Perform Multireference Perturbation Theory

“…The mechanism of the epoxidation is not clear, with various experiments providing evidence supporting at least three different possibilities 84,85 . To provide further clarification, several theoretical studies [86][87][88][89][90][91][92][93][94][95][96] have tried to understand the electronic structure of these clusters. The chlorine containing neutral oxo-Mn(salen) model cluster studied in this work is shown in Figure 3.…”