A DFT study of 76 complexes comprised of 3d transition metals, Ti through Ni, bonded to at least one methyl group was undertaken to compute the Brønsted acidity of methyl C–H bonds. Example complexes were gathered from determined coordinates of experimental crystal structures from the Cambridge Structural Database (CSD). The level of theory was BMK/6-31+G(d), and the SMD solvation model used DMSO as the continuum solvent. Deprotonation of the metal-methyl complex by an equivalent of DMSO resulted in the formation of the conjugate acid of DMSO and the conjugate base (an anionic metal-methylidene complex). From the free energy of this reaction, the pK a(C–H) of the methyl group was calculated to show the effects of metal identity, ligands, oxidation state, spin state, and conjugate base stabilization upon its acidity. In general, the acidity of the C–H bonds of transition metal-methyl complexes decreases from left to right across the 3d row with some anomalies. Factors affecting the range in pK a for each metal are discussed.
Six machine learning models (random forest, neural network, support vector machine, k-nearest neighbors, Bayesian ridge regression, least squares linear regression) were trained on a dataset of 3d transition metal-methyl and -methane complexes to predict p<i>K<sub>a</sub></i>(C–H), a property demonstrated to be important in catalytic activity and selectivity. Results illustrate that the machine learning models are quite promising, with RMSE metrics ranging from 4.6 to 8.8 p<i>K<sub>a</sub></i> units, despite the relatively modest amount of data available to train on. Importantly, the machine learning models agreed that (a) conjugate base properties were more impactful than those of the corresponding conjugate acid, and (b) the energy of the highest occupied molecular orbital conjugate base was the most significant input feature in the prediction of p<i>K<sub>a</sub></i>(C–H). Furthermore, results from additional testing conducted using an external dataset of Sc-methyl complexes demonstrated the robustness of all models, with RMSE metrics ranging from 1.5 to 6.6 p<i>K<sub>a</sub></i> units. In all, this research demonstrates the potential of machine learning models in organometallic catalyst development.
Six machine learning models (random forest, neural network, support vector machine, k-nearest neighbors, Bayesian ridge regression, least squares linear regression) were trained on a dataset of 3d transition metal-methyl and -methane complexes to predict p<i>K<sub>a</sub></i>(C–H), a property demonstrated to be important in catalytic activity and selectivity. Results illustrate that the machine learning models are quite promising, with RMSE metrics ranging from 4.6 to 8.8 p<i>K<sub>a</sub></i> units, despite the relatively modest amount of data available to train on. Importantly, the machine learning models agreed that (a) conjugate base properties were more impactful than those of the corresponding conjugate acid, and (b) the energy of the highest occupied molecular orbital conjugate base was the most significant input feature in the prediction of p<i>K<sub>a</sub></i>(C–H). Furthermore, results from additional testing conducted using an external dataset of Sc-methyl complexes demonstrated the robustness of all models, with RMSE metrics ranging from 1.5 to 6.6 p<i>K<sub>a</sub></i> units. In all, this research demonstrates the potential of machine learning models in organometallic catalyst development.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.